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Page 1: 44929 Diakon Manuallucitediakon.com/.../2014/08/Lucite-Diakon-Technical-Manual.pdf · TECHNICAL MANUAL. index 1 CONTENTS PAGE ... Moulding Fault Remedies ... index 2 CONTENTS PAGE

T E C H N I C A L M A N U A L

Page 2: 44929 Diakon Manuallucitediakon.com/.../2014/08/Lucite-Diakon-Technical-Manual.pdf · TECHNICAL MANUAL. index 1 CONTENTS PAGE ... Moulding Fault Remedies ... index 2 CONTENTS PAGE

index 1

CONTENTS PAGE

DTM/E/2Ed/Nov01

INTRODUCTION ..............................................................................................01

Chemical Structure ......................................................................................01

General Characteristics of Standard Lucite Diakon Grades ........................01

General Characteristics of Toughened Lucite Diakon ST Grades ................02

The Lucite Diakon Grade Range ..................................................................03

DATA FOR DESIGN ..........................................................................................06

Mechanical Properties ..................................................................................06

Thermal Properties ......................................................................................14

Flammability ..................................................................................................14

Electrical Properties ......................................................................................15

Optical Properties ........................................................................................15

Chemical Resistance ....................................................................................21

Permeability ..................................................................................................23

Melt Flow Behaviour ....................................................................................23

Sound Insulation ..........................................................................................27

Water Absorption ..........................................................................................27

INJECTION MOULDING ..................................................................................29

The Injection Moulding Process....................................................................29

Design of Components for Moulding ............................................................31

Multi-Coloured Mouldings ............................................................................32

Mould Design ................................................................................................33

Moulding Technique ......................................................................................41

Distortion ......................................................................................................48

Mouldflow Simulation ....................................................................................49

Moulding Fault Remedies ............................................................................56

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index 2

CONTENTS PAGE

DTM/E/2Ed/Nov01

EXTRUSION ......................................................................................................58

Extruder ........................................................................................................58

Sheet Extrusion ............................................................................................59

Co-Extrusion ................................................................................................60

Production of Extruded Sheet ......................................................................61

Lighting Diffuser Profile Extrusion ................................................................62

Tube Extrusion ..............................................................................................65

Fabrication of Sheet Extruded from Lucite Diakon ......................................66

Extrusion Fault Remedies ............................................................................67

FINISHING, COLOURING AND DECORATING ..............................................68

Machining......................................................................................................68

Cements and Adhesives ..............................................................................69

Ultrasonic Assembly......................................................................................70

Hot Surface Welding ....................................................................................72

Stresses and Molecular Orientation in Lucite Diakon Components ............72

Cleaning........................................................................................................76

Antistatic Treatment ......................................................................................76

Automotive Signal Lamp Lens Colours ........................................................76

Decoration of Lucite Diakon..........................................................................80

HEALTH, SAFETY AND ENVIRONMENTAL ASPECTS OF LUCITE DIAKON ....82

APPENDICES....................................................................................................83

APPENDIX I ACRYLIC SPECIFICATIONS ..............................................83

APPENDIX II ADDRESSES ......................................................................84

APPENDIX III VOLATILE CHEMICALS EVOLVED DURING

PROCESSING OF LUCITE DIAKON ..................................85

EUROPEAN SALES OFFICES ........................................................................86

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page 1

INTRODUCTION

Lucite Diakon is the trade mark for the range of

acrylic moulding and extrusion polymers made by

Lucite International based on poly methyl

methacrylate (PMMA).

CHEMICAL STRUCTURE

Poly methyl methacrylate is an atactic polymer and

since the methyl and the ester groups are incapable

of being interchanged in a crystal lattice these

polymers are therefore amorphous and transparent.

Since the substituents on the α-carbon atom restrict

chain flexibility, and since the side groups are polar

and relatively small, there is fairly substantial inter-

chain attraction. The polymer is therefore hard and

rigid with a glass transition temperature of 110°C.

The ST grades of Lucite Diakon have properties

modified to give greater toughness and resistance

to environmental stress cracking and crazing

compared with the basic grades. At the same time

the excellent transparency of the basic range has

been largely retained.

Methyl methacrylate monomer is produced by

several manufacturing processes, the most

common of which involves the following stages:

1 Acetone is reacted with hydrogen cyanide to

form acetone cyanhydrin:

GENERAL CHARACTERISTICS OF STANDARD

LUCITE DIAKON GRADES

Clarity

Lucite Diakon mouldings are transparent, crystal

clear and completely colourless even in thick

sections.

As the base polymer is ‘water white’ in colour, a

complete range of colours - transparent, translucent

and opaque - can be produced from Lucite Diakon.

The light transmission is at the theoretical maximum

of 92%, enabling wide use where optical properties

are critical. Indeed acrylics often represent a very

satisfactory replacement for glass, with their

advantages of light weight, ease of shaping into

complicated designs and greater resistance to

breakage.

Resistance To Outdoor Exposure And

Ultra-Violet Light

The weathering properties of acrylics are excellent.

Lighting fittings exposed outdoors in both temperate

and tropical climates for many years show no

changes in colour or physical properties.

Surface Gloss And Hardness

The surface hardness of Lucite Diakon and its

resistance to scratching are exceptionally high for a

plastics material, being approximately the same as

for aluminium. Lighting fittings, after many years’

service in heavily industrialised districts, show no

deterioration in efficiency although they have

inevitably been subjected to abrasion by windborne

dust and by repeated cleaning.

Other Properties

Lucite Diakon components are rigid, dimensionally

stable, odourless, resistant to many common

chemicals, have low water absorption and are easy

to decorate. Lucite Diakon, as with other PMMA

materials, is capable of being fully recycled.

DTM/E/2Ed/Nov01

2 Acetone cyanhydrin is treated with sulphuric acid

and methyl alcohol to give methyl methacrylate

monomer:

Lucite Diakon polymer is produced from

monomer by a free radical vinyl polymerisation

process, ie free radicals are formed and react

with monomer molecules to form long chains

which are substantially unbranched:

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page 2

GENERAL CHARACTERISTICS OF TOUGHENED

LUCITE DIAKON ST GRADES

Clarity

Lucite Diakon ST has a refractive index and

standard transmission comparable with the grades

of Lucite Diakon, while the level of haze is greater.

The haze level increases with temperature,

becoming most apparent during the extrusion

process or when removing hot mouldings from the

mould, and will disappear gradually as the

component cools to ambient temperature.

Resistance To Outdoor Exposure And

Ultra-Violet Light

Although the weathering properties of impact

acrylics are not as good as basic Lucite Diakon, the

ST grades resist yellowing and retain excellent

surface gloss and physical properties.

Impact Strength And Craze Resistance

The higher impact strength, elongation and the

lower flexural modulus of ST grades increase the

range of applications open to acrylic material. The

designer is offered greater freedom and the user

greater flexibility by minimising cracking problems

during processing and subsequent handling,

transportation, assembly and service.

The excellent craze resistance is beneficial where

mouldings or extrudates require a greater craze

resistance than conventional acrylic materials,

especially for articles which come into contact with

aqueous detergents and soap solutions.

By careful examination of component requirements,

namely degree of impact improvement, ease of

processability and flow, and resistance to outdoor

exposure, the designer or user will be able to select

the most appropriate grade of Lucite Diakon ST.

DTM/E/2Ed/Nov01

LUCITE DIAKON ASTM DIN DESCRIPTION

GRADE D788 7745

TYPE % TYPE

CMG302/MG102* 8 108-53 General purpose moulding and extrusion grade with high heat resistance.

Used mainly for optical parts, display items, tube and profile extrusion.

CMG314V 8 116-53 Injection moulding grade with improved heat resistance. Used primarily

for automotive rearlights and dashboard lenses.

CMH454L 8 116-73 High molecular weight grade used for injection moulding with improved heat

and chemical resistance. Used mainly for automotive rearlights.

CMH454/MH254* 8 108-73 High molecular weight grade for extrusion. Used mainly for extruded sheet.

CLG902/LG702* 8 100-53 Injection moulding grade with good melt flow properties and medium heat

resistance. Versatile grade used in many diverse applications such as

telecommunications, copying equipment and lighting diffusers.

CLH952/LH752* 8 108-73 Extrusion grade with improved melt flow and medium heat resistance. Used

mainly for sheet, tube and profile extrusion.

6 92-53 Injection moulding grades with excellent melt flow. Used for large area and thin

wall mouldings or where a long flow length is required.

STANDARD LUCITE DIAKON GRADE RANGE, RELATED TO ACRYLIC MOULDING POWDER SPECIFICATIONS

The Lucite Diakon range of acrylic polymers,

related to acrylic moulding powder specifications, is

shown in the table above.

The standard grades of Lucite Diakon are available

as approximately 2.5 mm cylindrical compound

granules. Certain grades, as indicated above, are

available as free flowing spherical bead polymer

with weight average particle size of 600 microns.

Acrylic materials are hygroscopic but the special

precautions taken during manufacture and

packaging mean that Lucite Diakon polymer does

not normally require drying before processing.

*Denotes grade coding for 600 micron bead polymer

CLG340CLG356/LG156*CLG960

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DTM/E/2Ed/Nov01

page 3

TOUGHENED LUCITE DIAKON ST GRADE RANGE

LUCITE DIAKON ST G8 SERIES

The G8 Series provides the best combination of

impact resistance, rigidity, heat resistance and

surface hardness. They can be processed by

injection moulding or extrusion.

ST15G8 8* Has been developed to minimise cracking

on ejection problems.

ST25G8 8* Has medium impact resistant properties giving

a good balance between heat resistance,

impact strength and processability.

ST35G8 8* Offers high impact strength and good

chemical resistance.

ST45G8 8* Is a very high impact material.

ST15G6 6* Offers very easy melt processing coupled

with adequate impact resistance to overcome

minor cracking problems.

ST25G6 6* Is a medium impact resistant material with

excellent melt flow for large area or

complicated mouldings.

ST35G6 6* Offers high impact resistance with good

chemical resistance and processability.

ST45G6 6* Is a very high impact resistant material while

still processing excellent processing

characteristics.

ST25G7 6* Offers medium impact performance with

good moulding properties.

LUCITE DIAKON ST G6 SERIES

The G6 series is suitable for injection moulding

applications where ease of melt flow is important.

There is some loss in heat resistance compared

with the G8 series.

LUCITE DIAKON ST G7 SERIES

This series offers a balance of properties between

impact strength, heat resistance and surface

hardness and is designed primarily for injection

moulding.

ST25N8 8* Has an excellent combination of impact

resistance and temperature resistance.

LUCITE DIAKON ST N8 SERIES

This series is designed to be used where

temperature resistance coupled with impact

properties are important. The melt characteristics

are also suitable for the extrusion process.

ST25H8 8* Has the best combination of impact

strength, chemical resistance and

heat resistance.

LUCITE DIAKON ST H8 SERIES

The H8 series offers a unique combination of high

impact strength coupled with excellent heat,

chemical, surface scratch resistance and rigidity.

The series is suitable for injection moulding and

extrusion.

*Classification as defined in ASTM D 788 if basic

PMMA materials

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DTM/E/2Ed/Dec02

page 4

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DTM/E/2Ed/Nov01

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DTM/E/2Ed/Nov01

page 6

Figure 1 Creep in tension at 23°C (10 MN/m2)

DATA FOR DESIGN

MECHANICAL PROPERTIES

Many of the standard mechanical tests give

information based on short-term loading at

arbitrarily chosen temperatures and strain rates.

The short-term properties, as measured by ISO,

ASTM or Lucite international standard methods are

given in the preceding section but most of these

results should not be used in the design of load-

bearing articles, because many of the properties of

Lucite Diakon, like those of other thermoplastics,

depend markedly upon temperature and time under

load.

The mechanical properties relevant to design

include the following:

Creep;

Long term strength and fatigue;

Impact strength

Except where otherwise stated, all data have been

obtained from unannealed specimens tested in air,

but some general comments on the effects of

chemical environment are made in a separate

section. If the article is to operate in an environment

other than air, care should always be exercised in

the selection of the appropriate data for design.

Creep

The load-bearing behaviour of an article made from

Lucite Diakon cannot be calculated simply by taking

a value of flexural modulus from a standard test

and applying it to, for example, a standard beam

formula because, in common with all other plastics,

the properties of Lucite Diakon vary appreciably

over a narrow temperature range and, under

constant load, the strain in articles made from

Lucite Diakon increases with time, ie the material

creeps under load.

Hence load-bearing calculations should involve the

use of creep data. Creep is defined as the total

strain, which is time-dependent, resulting from an

applied load, and creep data are often presented in

the form of strain/log time curves at 23°C as shown

in Figures 1 and 2.

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page 7

Figure 2 Creep in tension at 23°C (20 MN/m2)

Figure 3 100-second isochronous stress/strain curves at 23°C

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page 8

Figure 4 100-second apparent flexural modulus vs temperature (°C)

By taking cross-sections of the creep curves at

constant time, it is possible to generate isochronous

stress/strain curves, and Figure 3 represents short-

term data in this form.

Creep behaviour is temperature-dependent: an

increase in temperature decreases the modulus and

increases the strain at constant stress, as shown by

the 100-second apparent flexural modulus data

shown in Figure 4.

The effect of moisture on creep in Lucite Diakon is

comparatively small at constant strains, the total

decrease in stress corresponding to a change in

material from a dry to a wet state is approximately 12%.

Given an appropriate ‘family’ of creep curves of the

kind shown in Figures 1 and 2, it is possible to

calculate the load-bearing behaviour. The design

brief should include details of the function of the

article, the service conditions, estimated lifetime of

the component under load, and the maximum

service temperature. It is then normally assumed

that the component is subjected to a load which is

maintained constant throughout the lifetime at the

maximum service temperature. Working to a

maximum strain of 0.5%, the stress at the maximum

service temperature and lifetime, which cuts the

0.5% strain axis, is multiplied by 200 to give the

appropriate value of creep modulus. This value of

creep modulus may then be used in standard

strength-of-materials formulae, in order to predict

the likely long-term deformation or deflection.

Long Term Strength and Fatigue

The strength of Lucite Diakon also depends upon

time and temperature. Failure data are presented

as curves of stress against log (time to failure) and

typical curves for compression moulded Lucite

Diakon CMG302 tested in air at 23°C under a

constant load, are shown in Figure 5.

Crazing (localised structural breakdown) in standard

Lucite Diakon grades can occur at stresses

considerably below those required to produce

complete failure; the onset of crazing is also shown

in Figure 5. In most articles made from Lucite Diakon

it is necessary to avoid the appearance of crazing for

aesthetic reasons. Thus the crazing data in Figure 5

- normally represent the upper limit to which the

article can be stressed at any given time. A value of

design stress is obtained by dividing the crazing

stress at a given time and temperature by a suitable

safety factor, eg 1.5 to 2.0.

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Figure 5 Static fatigue characteristics at 23°C, 65% rh

The value of design stress should be used in

strength-of-materials formulae to estimate the

minimum part thickness required to avoid mechanical

failure. The failure stress at any time decreases with

increase in temperature.

Failure resulting from a repeatedly applied load is

generally called ‘fatigue’. The failure stress under

dynamic load conditions is generally lower than that

resulting from a static load, at the same time and

temperature. The effect on load-bearing capability

of applying a fully reversed square wave load

pattern at 30 cycles/min to injection moulded Lucite

Diakon CMG302 is shown in Figure 6.

Long term strength also depends on the nature of

the environment. When Lucite Diakon is stressed in

an active environment its strength may decrease as

the result of, for example, solvent stress cracking.

The basic grades of Lucite Diakon are prone to

crazing after repeated immersion in detergent

solutions if the surface of the moulding is stressed

in tension as the result of initial fabrication or

subsequent conditions of use.

One of the significant advantages of ST grades of

Lucite Diakon is much improved resistance to

crazing by solvents and detergent solutions.

Unpolymerised acrylic cements can also be a stress

cracking hazard. When mouldings have to be

cemented together, the risk of cracking and crazing

can be minimised by annealing and by ensuring

that there are no interference fits between mating

surfaces. Wherever possible, holes and slots should

be moulded-in, because any subsequent machining

operations create stresses which in some

applications need to be removed by annealing.

(See page 74 for details of annealing).

Impact Strength

When articles moulded or extruded from standard

grades of Lucite Diakon break in service under

impact conditions, the fractures are almost always

brittle. There are three principle factors which

promote the likelihood of brittle failure:

A decrease in service temperature;

An increase in stress concentration;

Orientation resulting from fabrication.

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Charpy-type specimens of different notch geometry

are tested across the material flow direction over

the range of temperatures of practical importance,

using a pendulum impact machine.

Figure 6 Dynamic fatigue characteristic in flexure at 23°C, 65% rh

Figure 7 Charpy impact strength vs notch tip radius

Impact data at 23°C, presented as energy to break

per unit area, are plotted against notch tip radius in

Figure 7.

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-20 -10 0 10 20 30 40 50 600

4

8

12

16

20

24

Un-notched

2 mm notch tip radius

0.25 mm notch tip radius

CMG302

Test temperature ˚C

Imp

act

stre

ng

th K

J/m

2

Figure 8 Charpy impact strength of CMG302 vs test temperatures

As the notch tip decreases, the stress concentration

increases, the impact energy required to break

specimens decreases. The designer should therefore

conform to the principle of sound design and radius

corners as generously as possible.

Lucite Diakon ST grades show a significant

improvement in impact strength over basic grades. It

should be noted also that Lucite Diakon H grades (eg

CMH) are slightly tougher than G grades (eg CMG).

Figures 8 and 9 present impact strength data on

Lucite Diakon for unnotched, bluntly notched (2mm

notch tip radius) and sharply notched (0.25 mm

notch tip radius) specimens as a function of test

temperature.

As the stress concentration becomes more severe,

i.e. as the notch becomes sharper, the impact

strength at any temperature drops, and the tough-

brittle transition occurs at a higher temperature.

Figure 9 Charpy impact strength of ST45G8 vs test temperatures

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The processing conditions, specifically melt temperature

and factors influencing orientation in the mould can

affect impact behaviour. The effects of different melt

temperatures on the impact strength of the Lucite

Diakon grades are shown in Figures 10 and 11.

Un-notched - along flow

Un - notched - across flow

Notch tip radius - 0.25 mm

220 230 240 250 260 270 2800

2

4

6

8

12

14

16

18

10

Melt temperature ˚C

Imp

act

stre

ng

th K

J/m

2

CMG302

Figure 10 Charpy impact strength of CMG302 vs melt temperature

Figure 11 Charpy impact strength of ST45G8 vs melt temperature

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For standard grades of Lucite Diakon, with a sharp

notch, impact strength is independent of cylinder

temperature and direction of test relative to the flow

direction. In contrast, the behaviour of unnotched

specimens depends on both cylinder temperature

and direction of tests; in the ‘weak’ across-flow

direction the impact strength increases slightly as

the cylinder temperature is increased, whereas it

decreases somewhat in the ‘strong’ along-flow

direction. Melt viscosity decreases with increase in

cylinder temperature and therefore residual

orientation decreases as the cylinder temperature

increases.

Mouldings showing the most severe strains and

highest degree of orientation will have lower impact

strengths - these conditions result from the use of

low melt and low mould temperatures and slow

injection rates. The most robust mouldings are

produced using high mould and melt temperatures,

maximum injection rates and medium injection

pressures.

These general comments apply equally to both

Standard and ST grades of Lucite Diakon.

Figure 12 Force/Time curves on instrumented

fallingweight impact test

Impact Strength of ST Grades

When a specimen of plastic is subjected to an

impact force, two factors in particular influence the

energy required to break the specimen. These are:

The energy required to initiate a crack;

The energy required to propagate the crack.

The energy required to break the specimen is the

sum of these two components.

Standard grades of Lucite Diakon break by a brittle

mechanism which means in effect that once a crack

has been initiated there is no significant resistance

to crack propagation.

Lucite Diakon ST grades on the other hand have

been specially modified to build in resistance to

crack propagation and provide a substantial

increase in toughness.

Most standard impact tests do not distinguish

between the two components of the breaking

energy but an instrumental falling weight impact test

enables the two energies to be separated during a

single impact test.

Using this test force/time curves represented in

Figure 12 for CMG302 and ST45G8 indicate the

process of breaking 3 mm thick injection mould

discs.

In both traces the area under the curve AB

represents the energy required to initiate a crack

and the area under the curve BC represents the

energy required to propagate the crack. The higher

resistance offered by ST45G8 to both crack

initiation and propagation can be clearly seen and

accounts for the fact that ST45G8 is about 10 times

as tough as CMG302 on this test.

The energy required to initiate a crack is dependent

upon the grade chosen and sample thickness. The

crack propagation energy on the other hand is also

influenced by the sample dimensions. If the sample

is too small for the propagation energy to be

absorbed or dissipated then the crack will reach the

sample boundary and complete failure will occur. If

however the sample in question is large, then an

initiated crack will cease to grow before reaching

the sample boundary and although the article may

crack, it will not disintegrate. This is an important

consideration for applications such as vandal-

resistant lighting fittings.

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THERMAL PROPERTIES

Typical values of the thermal properties of Lucite

Diakon relevant to design, such as thermal

expansion coefficient and specific heat, are given in

the tables on pages 4-5. There are slight differences

between the thermal expansion characteristics of

Lucite Diakon grades, as shown in Table 1.

Lucite Diakon Grade cm/cm°C x 10-5

Standard grades 7.1

Medium Impact ST 10.0

High Impact ST 11.5

Table 1 Linear thermal coefficient of expansion -

average results from -10°C to +50°C

The thermal expansion of basic grades over the range

-70°C to +70°C can be represented by the formula: %

expansion = 0.0068t + 0.000015t2, where t is the

temperature rise in degrees C. It is recommended that

designers avoid using moulded-in metal inserts

because the difference in expansion coefficients

between Lucite Diakon and metals can give rise to

stress cracking in the Lucite Diakon. If moulded-in

metal inserts are essential, it is recommended that

Lucite Diakon ST grades are used.

It should be noted that although grades of Lucite

Diakon may be described in terms of their softening

point or deflection temperature under load, these

quantities refer to specific conditions described in

the appropriate test. As a general working guide a

temperature 10°C below the ISO heat deflection

temperature for the grade can be used as the

maximum continuous working temperature for a

well-moulded article which is not under load, as

shown in Table 2.

To assess the maximum service temperature for a

load-bearing application, the designer needs to

assess the load on the article, the environment, the

expected service life and the tolerable maximum

deflection or deformation. In addition, the maximum

service temperature will be affected by the level of

stress during processing or fabrication.

The maximum service temperature range has been

extended by the introduction of the HS (High

Softening) grades of Lucite Diakon for which data is

available on request.

FLAMMABILITY

Although Lucite Diakon is combustible, it burns

slowly without normally producing undue quantities

of smoke, and the main products of combustion are

H20, CO2 and CO; as in the combustion of all

organic materials including paper and wood.

The flammability characteristics of some grades of

Lucite Diakon are shown in Table 3.

Lucite Diakon Grade °C

CLG356,LG156,CLG960,ST25G6,ST45G6 70

CLG340,CLG902,LG702,LH752,CLH952 75

ST25G8,ST45G8 80

MG102,CMG302,MH254,CMH454,CMG314V,CMH454L 85

Table 2 Maximum continuous working

temperatures for the Lucite Diakon

grades

TEST METHOD/ UNITS LUCITE DIAKON LUCITE DIAKON

PROPERTY STANDARD ST GRADES

GRADES

Flammability cm/min 2.8-3.8 4.0-6.5

ASTM D635-96

Burning rate

[Sample Thickness 1.6mm]

BS2752 cm/min 3.5 6.5

Method 508A

Burning rate

DIN 4102 Class B2 B2

Federal Motor Vehicle cm/min 3.1 6.1

Safety Standard

ISO 3795

Burning rate

Underwriters

Laboratories Inc Class HB HB

UL94

Glow Wire Test deg C 650 650

IEC 695-2-1

Smoke density % ‘M’ Grades 5 Medium

Impact ST 7-16

ASTM D2843-93 ‘L’ Grades <5 High

[Sample Thickness 3.2mm] Impact ST 23-30

Table 3 Flammability Characteristics of

Lucite Diakon

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The flammability characteristics of the Lucite Diakon

range have been extended by the introduction of

the MGW grades; data for a grade with an 850 glow

wire rating is available on request.

ELECTRICAL PROPERTIES

The electrical properties of Lucite Diakon depend

on many factors such as the electrical frequency (or

time) and temperature, the quantity of absorbed

moisture, and the grade.

The frequency dependence of permittivity (dielectric

constant) and dissipation factor for some grades of

Lucite Diakon at 23C are shown in detail in Table 4.

An increase in absorbed moisture increases all

these values. In the audio frequency range, the

dielectric properties of the Lucite Diakon grades are

similar. There is, however, some difference between

the values of volume resistivity for the standard

grades of Lucite Diakon at very low frequencies, as

shown in Table 4.

Property Units CMG302 CMG314V CMH454 CLG356 CLG902 CLH952

MG102 MH254 LG156 LG702 LH752

CMH454L

Volume resitivity at

23°C and 60% rh

Polarisation time 60 sec ohm m 7x1015 7x1015 7.5x1015 1x1016 8x1015 7x1015

Polarisation time 1000 sec ohm m 2x1017 3x1017 4x1017 5x1016 3x1016 3x1016

Dissipation factor

23°C and 60% rh 50 Hz 0.050 0.050 0.051 0.064 0.066 0.062

23°C and 60% rh 103 Hz 0.034 0.034 0.034 0.034 0.034 0.035

40°C and 60% rh 103 Hz 0.055 0.055 0.056 0.048 0.052 0.050

60°C and 60% rh 103 Hz 0.075 0.076 0.077 0.064 0.067 0.068

90°C and 60% rh 103 Hz 0.085 0.084 0.083 0.078 0.080 0.081

23°C and 95% rh 103 Hz 0.047 0.050 0.053 0.040 0.044 0.046

Permittivity

23°C 50% rh 50 Hz 3.9 4.0 4.2 3.7 3.8 3.9

23°C 60% rh 103 Hz 3.3 3.4 3.6 3.1 3.4 3.6

23°C 95% rh 103 Hz 3.6 3.5 3.4 3.0 3.3 3.5

Breakdown voltage k V/mm 16 15 15 14 15 16

Table 4 Electrical properties of Lucite Diakon

OPTICAL PROPERTIES

The exceptional clarity of Lucite Diakon has made

the material suitable for many optical applications,

and some of the more important optical properties

are presented below.

Refraction

Values of some primary optical constants at 23°C for

basic Lucite Diakon grades are summarised below.

As the refractive index (nd) depends on the

wavelength of light, the value below is that

measured at 587.6 nm (Sodium line). The critical

angle, Xd is defined by the refractive index

where nf is the refractive index measured at 486.1

nm and nc at 656.3 nm. Also shown in the table is

the variation of refractive index with temperature,

again measured at 587.6 nm.

(sin Xd = 1/n). The variation of refractive index with

wavelength of visible light is shown in Figure 13.

This variation is simplified in the table by the use of

the relative dispersion,

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Figure 13 Refractive index vs wavelength

When carefully compression moulded, Lucite

Diakon is optically isotropic. When Lucite Diakon is

extruded or injection moulded some orientation of

the material occurs causing the moulding to

Figure 14 Dependence of haze level on

temperature for Lucite Diakon ST grades

become optically anisotropic. Different values are

obtained for the refractive index when measured in

different directions, this being related to the extent

and direction of molecular orientation. The

maximum difference between the principal refractive

indices measured parallel with and at right angles to

the main direction of orientation, called the

birefringence, is about 10-3. However, such a large

difference is achieved only by considerable

stretching, and the maximum birefringence in

normal highly oriented mouldings is about 10-4.

See page 72 for further comments on orientation

and stress.

ST grades of Lucite Diakon are toughened by the

inclusion of a specially manufactured impact

modifier which is matched in refractive index to

standard grades of Lucite Diakon at 20°C. The

refractive indices of the modifier and standard

grade Lucite Diakon vary with temperature in

different ways so that as the temperature deviates

from 20°C, the refractive index difference between

the two components becomes great enough to

introduce haze.

The dependence of haze upon temperature is

shown in Figure 14.

Light Transmission

When a parallel beam of light falls normally on to a

polished surface of a material, some light is

reflected as a consequence of the change in

refractive index at the interface with air. In the case

of basic grade Lucite Diakon, about 4% is reflected

at each surface. As the angle of incidence

increases from zero (normal incidence), this

reflection loss increases, slowly at first and then,

beyond 60°, very rapidly as shown in Figure 15.

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Figure 15 Reflection of light at Lucite Diakon/air interface

Thus for a sheet of Lucite Diakon, having two

surfaces, reflections limit the direct transmission

factor to about 92%. If light falls on the sheet

equally from all angles (as from a sky of uniform

brightness), the resultant integrated transmission of

the sheet is reduced to about 85%.

Light may also be absorbed by a material, or

scattered. In the case of basic Lucite Diakon

grades, very little light is scattered from the bulk of

the pure material but scattering may occur at the

surface due to imperfections such as scratches, or

from internal impurities. Such scattering can

adversely affect the resolution of an image seen

through the material (reduce its clarity), and will

cause a deterioration of the contrast in the image

(haziness).

As mentioned above, the two components in Lucite

Diakon ST grades have their refractive indices

matched at 20°C and the greater the deviation from

this temperature, the greater will be the haze level

observed, and the lower light transmission as

shown in Figure 16.

The absorption of light by standard Lucite Diakon

grades in the visible region is extremely low, and is

almost independent of wavelength. Outside this

range of wavelengths significant absorption does

occur and this reduces the transmission factor and

makes it dependent on sheet thickness. The

transmission curve is shown in Figure 17. Whilst the

normal standard Lucite Diakon grades have a high

transmission of UV light some special ultra-violet

(UV) stabilised grades are produced, and their

transmission curves are shown in Figure 18.

The special UV grades of Lucite Diakon are only

recommended for use in particularly critical

applications, for example, with high intensity mercury

vapour lamps having high UV emission characteristics,

or for applications such as camera lenses where UV

transmission similar to glass is required.

Comparative transmissions for Lucite Diakon ST

are given in Figures 19 and 20, pages 19-20.

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Figure 17 Transmission curve for standard Lucite Diakon grades (3.2 mm sample)

Figure 16 Light transmission versus temperature for ST grades

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Figure 18 Comparative transmission curves for normal and uv stabilised Lucite Diakon standard grades

(3.2 mm samples)

Figure 19 Transmission curve for Lucite Diakon ST 45G8 (3.2mm sample)

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Piping of Light

Because of its optical characteristics, and particularly

its low absorption, standard Lucite Diakon grades

lend themselves to the exploitation of the

phenomenon of total internal reflection. In particular, a

beam of light can be efficiently ‘piped’ round bends

and through great lengths of material. The critical

angle for an interface with air is 42°, so that provided

the ‘light-pipe’ end face is perpendicular to its axis,

light incident at any angle on the end face will be

accepted and transmitted, subject to losses due to

reflection from the end face itself. To prevent

excessive loss when light is ‘piped’ around curves, the

radius of curvature should not be less than three

times the diameter of the ‘pipe’. Since optical defects

in a boundary cause scattering of light and reduce the

efficiency of the system, it is important that all

cemented junctions are free from irregularities, and

that all exterior surfaces are highly polished and free

from scratches or other imperfections.

Optical Fibres

The science of fibre optics involves transmittance of

light in a transparent fibre from one end to the other

by total internal reflection, which is made possible

by coating the optical fibre with a material of lower

refractive index.

Acrylic fibre diameters typically range from 0.25 mm

up to 3.0 mm with a fluorinated methacrylate

polymer coating (Refractive Index 1.394) to a

thickness of 8 micrometers. Acrylic fibres have

attenuation losses of 470 decibels/kilometre or

greater compared with 50 dB/Km or lower for silica

optical fibres and are therefore not generally

suitable for distances more than 20 metres.

However acrylic fibres do offer greater flexibility,

toughness and lightness together with lower costs

when compared with silica fibres.

Figure 20 Comparative transmission curves for normal and uv stabilised Lucite Diakon ST45G8 (3.2mm samples)

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CHEMICAL RESISTANCE

All standard grades of Lucite Diakon give mouldings

which are resistant to water and have good

dimensional stability under conditions of changing

humidity. No staining or whitening occurs on

exposure to high temperatures or high humidities.

Articles made from Lucite Diakon are resistant, at

temperatures up to 60°C, to dilute mineral and

organic acids, and dilute and concentrated solutions

of most alkalis. At room temperature, Lucite Diakon

mouldings are unaffected by aqueous solutions of

inorganic salts, aliphatic hydrocarbons, fats and

oils, and most of the common gases. They are

attacked by chlorinated aliphatic hydrocarbons,

aromatic hydrocarbons, ketones, alcohols, ethers

and esters, including those esters which are used

as plasticisers for other plastics. Care should

therefore be taken to ascertain the effect of organic

liquids in prolonged contact with Lucite Diakon.

Table 5 indicates the chemical resistance of Lucite

Diakon grades to a range of common chemicals, as

judged by visual examination of small, unstressed

samples immersed in various liquids at 23°C.

The performance of articles in service will, however,

depend on the presence of internal and external

stresses and orientation in the manufactured article.

It is recommended that appropriate tests be carried

out to simulate the actual conditions of the

application.

In general, Lucite Diakon ST grades are more

resistant to attack than standard grades of Lucite

Diakon upon which they are based, but even they

will be attacked upon prolonged exposure to

chemicals which attack standard grades.

The following symbols are used:

A - Satisfactory

B - Some attack but only slight reduction in

mechanical properties

C - Unsatisfactory

Chemical Concentration Category

Acetaldehyde 100% C

Acetic acid 10% A

100% C

glacial C

Acetic anhydride B

Acetone 100% C

Acetonitrile C

Acetophenone C

Alcohol, allyl C

amyl C

benzyl C

n-butyl C

ethyl 10% A+

50% B

100% C

isopropyl 10% B

50% B

100% B

methyl 10% A

50% B

100% C

Aluminium potassium sulphate Saturated solution A

Ammonia 0.88 relative

density solution A

Liquid C

Ammonium chloride Saturated solution A

Amyl acetate C

Aniline C

Anthracene Solution in paraffin A

Benzaldehyde C

Benzene C

Benzoyl chloride C

Butyl acetate C

Butyl acetyle ricinoleate B

n-Butyle chloride C

Butyl stearate B

Butyraldehyde C

n-Butyric acid Concentrated C

Calcium chloride Saturated solution A

Carbon disulphide C

Carbon tetrachloride C

‘Cetavlon’* 1% aqueous solution A

10% aqueous solution A

1% ‘Cetavlon’ in 5% ethyl A

alcohol/aqueous solution

Chlorine 2% aqueous solution B

Chloroform C

Chromic acid 10% A

Saturated solution C

Citric acid Saturated solution A

Meta-cresol C

Cyclohexane C

Cyclohexanol C

Cyclohexanone C

Cyclohexene C

Decahydronaphthalene C

(Decalin*)

Dialkyl phthalate B

Dibutyl phthalate B

Dinonyl phthalate B

Dioctyl phthalate B

Dialkyl sebacate B

Dibutyl sebacate B

Dioctyl sebacate B

Diethyl ether C

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Chemical Concentration Category

Epichlorhydrin C

Ethylene dibromide C

Ethyl acetate C

Ethylene dichloride C

Ethylene glycol A

Ethylene oxide dry A

moist B

Ferric chloride 10% aq A

Formaldehyde 40% aq A

Formic acid 10% A

90% C

Glycerol A

Hexane A

Hydrochloric acid 10% A

Concentrated A

Hydrocyanic acid C

Hydrofluric acid Concentrated C

Hydrofluoroboric acid B

Hydrogen peroxide 10 vols A

90% C

Iranoline * A

Iron perchloride B

Lactic acid A

Lanoline A

Mercury A

Metol quinone A

Methylamine A

Methyl benzoate C

Methyl cyclohexanol C

Methylene dichloride C

Methyl naphthalene C

Methyl salicylate C

Monochlorobenzene C

Naptha Crystals C

Napthalene Saturated solution B

Naphthalene crystals in paraffin

10% B

Nitic acid A

Nitrobenzene C

n-Octane B

100 octane aviation fuel B

Oils: diesel A

olive A

transformer Saturated solution A

Oxalic acid A

Chemical Concentration Category

Paraffin, medicinal A

Perchloroethylene C

Petroleum ether (100-120°C) A

Phenol C

Phosphoric acid 10% A

95% C

Piperidine C

Potassium chlorate Saturated solution A

Potassium dichromate 10% A

potassium hydroxide Saturated solution A

Potassium permanganate 0.1 N solution A

Polypropylene adipate A

Polypropylene laurate A

Polypropylene sebacate A

Sebacic acid A

Silicones R220 B

F130 B

M441 C

F110 B

Sodium carbonate Saturated solution A

Sodium chlorate Saturated solution A

Sodium hydroxide Saturated solution A

Sodium hypochlorite (105 chlorine) A

Sodium thiosulphate 40% aqueous solution A

Sulphuric acid 10% A

30% A

98% C

Tartaric acid Saturated solution A

Tetrahydrofuran C

Tetrahydronaphthalene

(Tetraline*) C

Toluene C

Trichloroethane C

Trichloroethylene C

Tricresyl phosphate C

Trixylenyl phosphate C

Water A

White spirit A

Xylene C

+ Short term contact is satisfactory, but Lucite Diakon is not

recommended for prolonged contact with alcoholic liquids

*Trade mark

Table 5 Chemical resistance of Lucite Diakon

at 23 C.

The chemical resistance table refers only to the

effects on Lucite Diakon resulting from contact with

the substances listed. Information on compliance

with particular requirements for contact with

foodstuffs, potable water, cosmetics or

pharmaceutical products should be requested from

Lucite international Sales Offices or Agents, giving

details of the application and country for which

regulatory approval is required.

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PERMEABILITY

The permeability of standard grade Lucite Diakon

mouldings to oxygen, nitrogen, and carbon dioxide

is given below.

The values are expressed as the number of cubic

centimetres of gas passing at standard temperature

and pressure per square metre per day per

atmosphere excess pressure through a film 25 μm

thick.

Permeant cm3 (STP)/m2/d/atmosphere

Nitrogen 60

Oxygen 230

Carbon dioxide 1700

For a film 25 μm thick, a temperature of 25°C and a

relative humidity of 75%, the amount of water

vapour transmitted by Lucite Diakon is 68 g/m2/d.

MELT FLOW BEHAVIOUR

Lucite Diakon produces a highly elastic melt whose

flow behaviour differs considerably from that of

‘Newtonian’ fluids.

All the measurements of melt behaviour were

made with a capillary rheometer. The shear rate

η in a circular die of radius R and length

L is related to the volume flow rate of melt Q by

η = 4QπR3 The shear stress τ at the wall of the

die resulting from a pressure drop ΔP is given by

τ = R.ΔP/2L.

The relationship between shear rate and shear

stress is obtained experimentally, and data are

presented in Figures 21 to 23 where apparent shear

viscosity is defined as the ratio of shear stress to

shear rate.

At a given injection rate, an increase in melt

temperature reduces the pressure required to fill a

given cavity. For example, if the shear rate in a

runner is 1000s-1, then for Lucite Diakon CMG302

(Figure 21) the corresponding shear stress at

220°C is 3.6 x 105 Pa, and the pressure drop in the

runner is related to the length of the runner L by the

equation

ΔP = 2L/R

If the temperature is raised to 260°C, then at

1000s-1 the shear stress is only 1.3 x 105 Pa,

ie a 40°C increase in temperature has reduced the

injection pressure by a factor of about 2.8.

However, this factor is underestimated because no

account has been taken of shear heating. Heat

generation during injection moulding is proportional

to the pressure drop in the process. It should be

borne in mind that the heat is dissipated in the

regions of high shear rate, and that under extreme

conditions, excessive local temperature rises can

lead to degradation, for example as the melt passes

through the gate.

Alternatively, a machine developing a given head of

pressure along a runner can deliver a greater

quantity of material at a high temperature than at a

low temperature.

Where fast filling of a cavity is required, it may not be

possible to raise the temperature beyond a certain

value because of the risk of depolymerisation. It may

then be necessary to use an easier-flow grade to

achieve the necessary injection rate.

Figures 22 and 23 present curves of apparent shear

viscosity against shear stress for the Lucite Diakon

grades, at 210°C and 240°C respectively. Referring

to Figure 23, if the pressure developed along the

runner produced a shear stress of 1.6 x 105 Pa, the

shear rate in Lucite Diakon CMG302 would be

about 500 sec-1 compared with about 160 sec-1 for

Lucite Diakon CMH454. Hence the volume flow rate

of Lucite Diakon CMG302 would be approximately

three times that of Lucite Diakon CMH454.

Viscosity depends on the pressure applied to the

melt. A hydrostatic pressure of 100 Pa has the

same effect on viscosity as a drop in temperature of

33°C.

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Figure 21 Variation of melt viscosity with stress for Lucite Diakon’ CMG302 at different temperatures

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Figure 22 Melt viscosity under shear at 210°C by capillary rheometry

(corrected for die entry pressure drop)

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Figure 23 Melt viscosity under shear at 240°C by capillary rheometry

(corrected for die entry pressure drop)

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These figures are averages based on the nature

and intensity of airborne noise. The reduction of

resonance in acrylic glazing as compared with glass

will normally be more than adequate to compensate

for the difference in Sound Reduction Index.

Sheet Weight per unit Sound

area (Kg/m2) Reduction

Index (decibels)

3.2 mm acrylic sheet 3.8 18

6.4 mm acrylic sheet 7.5 23

3.2 mm glass 6.8 22

6.4 mm glass 16.6 27

16 mm twin walled sheet 5.0 25

Figure 24 Water absorption - equilibrium values for

Lucite Diakon standard grades at 1.6

mm thickness

Figure 25 Effect of water absorption on dimensions of Lucite Diakon standard grades at 6.4 mm thickness

(23°C)

WATER ABSORPTION

All grades of ‘Lucite Diakon have a low water

absorption as shown in Figure 24. Although the

equilibrium water content is small, its effect on

dimensions may be considerable, as shown in

Figure 25, and absorbed water may have a slight

effect on mechanical properties, acting to some

extent as a plasticiser. The rate of absorption is

slow, and Figure 26 shows the behaviour of

samples stored at 23°C under conditions of 60%,

80% , 100% relative humidity, and total immersion.

SOUND INSULATION

Insulation against airborne noise may be

represented by the material’s Sound Reduction

Index. The Sound Reduction Index is the ratio of

the sound energy incident on the surface, to that

which is transmitted through and beyond the

material, expressed in decibels. As a general guide

to the meaning of Sound Reduction Index in

decibels, the loudness of the noise will be

approximately halved for every ten decibels

reduction in the index. Comparative figures for

acrylic sheet and glass in a single glazing system

under average conditions would be:

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Figure 26 Amount of water absorbed by Lucite Diakon standard grades at 6.4 mm thickness (23°C)

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INJECTION MOULDING

THE INJECTION MOULDING PROCESS

The injection moulding process comprises three

stages, each of which must be closely regulated to

obtain good quality mouldings:

Feeding material into a heated cylinder, where it

softens and becomes a plasticised melt;

Injecting the correct amount of plasticised

material under controlled rate and pressure into

an enclosed mould;

Maintaining sufficient pressure on the material to

compensate for the shrinkage of the material on

cooling as it cools to a point at which it can be

ejected without deformation taking place.

Figure 27 Screw Profile for Lucite Diakon

A stable and suitable rate of plasticisation is

required to give a uniform and good quality melt for

consistent shot to shot production of mouldings.

See page 44 for moulding conditions.

The melt viscosity of acrylic is relatively high

compared with, for example, polyolefine and

polystyrene moulding materials, see Figure 47.

Therefore the plasticising capability is important and

the screw design in the majority of modern

machines is adequate for processing Lucite Diakon.

Figure 27 illustrates a suitable screw design for

processing Lucite Diakon.

The moulding machine often has interchangeable

cylinders having varying shot capacities and

different injection pressure maxima. The injection

pressure and shot capacity are varied within the

different cylinders by a change of screw diameter.

The cylinders, which are generally coded A, B and

C, change progressively through the range from

smaller shot capacities at higher injection pressures

to larger shot capacities at lower injection

pressures. The most suitable cylinder for Lucite

Diakon is the compromise B type. It is also good

practice not to consider using more than 70% of the

rated capacity of any given cylinder.

With high viscosity the injection pressures needed

are correspondingly high and the mould must be of

robust construction to resist these pressures and so

prevent deformation under load. In addition the

locking force, which keeps the mould closed during

injection, must be adequate to resist the total thrust

over the projected area of the mould cavity and so

prevent the mould from opening. For this a

minimum locking force of 30MPa of projected area

should be available.

The quality of an injection moulded part is

influenced by the temperature and pressure of

material in the mould cavity at the moment when

the material in the gate solidifies. At that instant the

mould is filled with hot material under pressure. As

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the temperature of the material in the mould falls

there are two opposing actions taking place:

Thermal contraction - tending to reduce the

volume of the moulding;

Residual pressure in the melt - tending to

expand the moulding slightly.

The two effects occur at the same time and tend

to counterbalance each other.

The use of programmed injection enables moulds to

be filled at different speeds and pressure during the

injection period. The advantage of being able to fill

the major proportion of a mould quickly whilst at

high pressure and speed and then drop to lower

values maintaining follow-up pressure on the

material helps to reduce the risk of flash and the

degree of moulded-in strain. When using this system

for thick acrylic sections, such as lenses and insignia,

it is possible to inject very slowly at a low pressure

and then, towards the end of the mould filling time, to

increase the pressure to help overcome the

shrinkage.

Control of mould temperature is also important if the

quality of the moulded part is to be kept consistent

throughout production. The use of mould

temperature control units allows the mould

temperature to be raised to its optimum value

before start-up, thus avoiding an initial period of

production of more highly strained parts from a cold

mould, and wastage of material due to short shots.

Figure 28 Nozzles

On most of the screw pre-plasticising machines

various types of nozzle can be fitted. Those nozzles

fall into three basic categories

(see Figure 28).

(1) Mechanical shut-off nozzle

(2) Needle valve shut-off nozzle

(3) Open or straight though nozzle

For Lucite Diakon, nozzles (1) and (3) can be used

quite successfully. However, nozzle (3) is usually

preferred because there are no potential hold-up

points where material can stagnate and

decompose. This is very important when producing

high quality clear mouldings. With this type of

nozzle, however, close temperature control is

required by means of a separate, well-positioned

thermo-couple and temperature controller to

prevent dribble or ‘freeze off’. Type (2) nozzles are

not generally recommended because of the

frictional heating which can occur when using high

injection rates.

Figure 29 Design of components - change of section

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DESIGN OF COMPONENTS FOR MOULDING

Good component design is of great importance in

the injection moulding of Lucite Diakon and the

following points should be considered at the design

stage if later difficulties are to be minimised or

avoided.

If possible, sharp change of section thickness should

be avoided as this creates excessive moulding flow

problems with thicker sections and the possibility of

excessive sinking on cooling if the gating position is

only permissible at the thinner part of the moulding.

To keep the cross-section constant, thick sections

should be cored out wherever possible (Figure 29).

With certain designs, as for example the prismatic

effect in a tap handle, thick and thin sections are

closely alternated. In this instance the rapid change

in section gives attractive optical results, but

differential thicknesses must be kept within certain

limits to avoid problems in moulding or in service.

As a guide, the thickest sections should not exceed

10 mm. Even then, as the mould cavity fills, the melt

will tend to flow into the thick sections first and the

thin ones thereafter, leaving a weld line where the

adjacent flows of melt re-unite. All edges of the core

pin (which forms the hollow in the handle) should be

radiused to ensure that the melt will not drag over

them with consequent formation of flow lines, and to

reduce the possibility of stress cracking by

eliminating sharp corners in the moulding. Different

cooling rates of thick and thin sections can also lead

to stresses in the finished moulding.

To achieve economy, components are often reduced

in section. This practice can be followed provided

the sections are not made so thin as to cause flow

problems during moulding. In addition to the flow

problems, thin sections cool rapidly in the mould and

result in high quenching stresses which make

mouldings more liable to craze and crack. As a

guide, where long flow paths are encountered, wall

sections should not be less than 3 mm.

Problems resulting from uneven filling of the mould

cavity will occur if the component is surrounded by a

rim which is thicker than the internal portion in the

centre (Figure 30). In this instance material will flow

around the rim faster than across the centre and then

give gas entrapment and “Y” weld line problems.

Figure 30 Design of components - thickness of rim

All corners and sections should be radiused as sharp

corners cause stress concentration, brittle moulding

and also pressure drop leading to possible problems in

mould filling. This particularly applies where blind

holes are to be moulded-in to take screw or other

fastening media. Wherever possible all holes and slots

should be moulded-in since post-moulding machining

operations not only increase finished part cost, but

also set up residual stresses which can only be

removed by annealing.

To maintain the benefits arising from increased impact

strength and flexibility with Lucite Diakon ST grades, it

is important, at the initial design stage of components,

to avoid sharp corners and sudden changes in section

thickness, thereby eliminating areas subject to high

tensile stress as with standard grades. All such corners

should have a minimum radius of 1.5-2.0 mm. It is also

important in the design and gating of the components

to pay attention to the avoidance of weld lines as this

effect, common to many impact modified plastics, is

more noticeable than with a similar component in a

standard Lucite Diakon grade.

If inserts are to be moulded-in, sufficient material

should be allowed around the insert to give adequate

keying and to resist stresses which will be set up

during cooling by the differential thermal contraction of

the insert and the Lucite Diakon. High softening point

plastic inserts like glass reinforced nylon are preferable

to metal to minimise the stress. The insert should be

splined on the outside and provided with a

circumferential slot to give a key to the Lucite Diakon

which is moulded over it.

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When numerals or letters are to be moulded into the

component these should not be more than one third of

the depth of the section thickness in order to minimise

division of the melt leading to weld lines and ‘tails’.

To aid ejection, the draft angle on a component should

be as generous as possible. This especially applies to

thick components where long injection times are often

necessary and consequently increases moulding

packing. In general 1° suffices for most thinner sections

but as much as 3-4° may have to be accepted in

extreme circumstances.

The shape of the component often dictates the

positions of the mould parting line, gate and ejection

points, and these should be taken into account at the

design stage in order to facilitate the moulding of

good quality components without objectionable

appearance defects.

With tap handles or control knobs the use of a splined

spigot is recommended.

With splined spigots the torque is distributed very

evenly and a matching hole may therefore be moulded

into the boss of the tap handle. The crests and valleys

of the splining should be radiused to reduce and

distribute any stresses which might be generated by

excessive pressure.

With a square section spigot, the torque applied is

concentrated at the internal angles of the moulded

square hole, and cracking could occur.

MULTI-COLOURED MOULDINGS

The techniques described below have been highly

successful with Lucite Diakon, particularly in the

automotive industry on rear light assemblies.

Edge-to-Edge Insert Moulding

The process involves moulding part of a complete

assembly in one tool, and transferring this part to a

second tool, where further material is moulded

against this insert. The hot melt fuses with the

inserted moulding producing a bond between the

two components. The strength of the bond is further

increased if some form of mechanical key is

designed into the joint area. The design of this key

depends largely on the shape of the component. A

few examples are given in Figure 31.

Figure 31 Forms of key with edge-to-edge moulding

The second tool must be accurately designed to

accept the inserted moulding which must be held and

supported firmly during the moulding cycle. Accuracy

in both component and mould is also required to

prevent flashing between the two components.

The pressures exerted upon the inserted moulding

during the second moulding cycle are often high

and, to avoid cracking, components must be

designed without sharp corners. The gate should be

positioned to minimise the strain on the inserted

moulding. When moulding Lucite Diakon, it has

been found advantageous to use the higher

molecular weight grade CMH454V or low impact

versions of ST for the moulding to be used as the

insert, using their superior mechanical strengths to

help prevent cracking.

Ideally the two moulding operations should be

carried out consecutively on adjacent machines, the

moulded inserts transferred directly from one

machine to the next. Under these conditions the

inserts are still warm and the risk of cracking is

reduced. If direct transfer is not possible then it is

helpful to warm the mouldings prior to placing them

in the second tool.

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Skin Insert Moulding

This process is similar to that described above

except that the insert is a thin component with

smooth surfaces, normally in the region of 1.5 mm

thick. Many of the points mentioned above apply to

skin moulding. The final part is produced by

moulding a second layer skin, which will include the

optics, on to the first in a master tool. It has been

found that when required the use of CMH454V for

the insert skin helps to minimise cracking or colour

bleeding problems. Although, due to component

and tooling considerations, both edge-to-edge and

skin moulding techniques are used, it is considered

skin moulded lenses are more robust than edge to

edge ones.

Multi-Colour Machines

Multi-colour moulding may also be carried out on

special machines with two or more cylinders for

those rearlight assemblies where design, size and

number considerations are suitable. The technique

usually consists of a series of moulds where one

platen is rotated through two or more stations

where injection of the different coloured material

takes place.

MOULD DESIGN

Although many factors have to be considered in the

design of moulds for thermoplastic materials there

are three factors which require special attention for

acrylic materials. Due to the relatively high melt

viscosity and its greater temperature dependence

(see Figure 47) it is usually necessary to use

sprues, runners and gates of generous cross

section compared to those used for material with

low viscosities such as nylon and polystyrene.

Standard grades of Lucite Diakon may be considered

as hard brittle materials and allowance should be

made for this.

• Radius all corners

• Adequate and uniform ejection

• No undercuts

• Minimum 1° taper

• Polish in line of draw

• Uniform mould temperature control

The aesthetic appearance together with high gloss

and clarity obtainable with Lucite Diakon mouldings

requires highly polished moulds.

In general nickel-chrome steels are preferred since in

addition to being tough and hard-wearing they will

take a high polish. For optical quality parts, a steel

like ‘Stavex’* ESR has been found satisfactory.

Sprue Design

The sprue is the channel through which the material

is transferred from the machine nozzle to the

runner(s) and gate(s) and into the mould cavity (ies).

Its design, therefore, is of paramount importance. It

must be of adequate dimensions to prevent freezing

prematurely, but not so large as to extend the cooling

time of the moulding. To fulfil these basic

requirements it is thus important to have a sprue of

adequate diameter but to keep it as short as possible.

A length of approximately 60 mm should be aimed for.

To achieve this mould backing plates or bolsters

should be kept as thin as possible without sacrificing

strength in the mould.

Where it is not possible to provide short sprues due to

component geometry, consideration should be given

to the use of extended machine nozzles (see Figure

32) which can be fitted with suitable heaters and

controlling equipment. An extended nozzle can also

be used to advantage on normal type moulds in order

to obtain better mould filling and to reduce material

wastage.

The size of the sprue necessary for any particular

moulding will vary according to the thickness and the

shape of the parts to be made.

* Trademark of Uddeholm

Figure 32 Extended nozzle

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As a guide the following sprue diameters should be

used:

For thin section moulding, ie 2.5 mm-4 mm, the

machine nozzle should be 4 mm diameter and the

smaller hole in the sprue bush 4.5 mm diameter;

For thick section mouldings, ie 6 mm and upwards,

the machine nozzle should be 7.5 mm diameter

and the sprue accordingly 8.5 mm diameter.

All sprue bushes should have a tapered bore to allow

easy extraction of the sprue. The angle of the taper

should be between 5-7° inclusive. The higher angle is

preferred for thick mouldings because the long

injection times necessary for these mouldings can

cause packing which tends to make the sprue more

difficult to extract. The sprue bush internal surface

should be free from machine and grinding marks and

should preferably be draw-polished. A generous ‘cold

slug-well’ should be positioned opposite the entrance

of the sprue into the mould whenever possible. In

addition to removing the piece of slightly chilled

material left in the nozzle from the previous shot, it

may also be designed with a ‘Z pin or back taper to

aid the removal of the sprue from the sprue-bush.

The cold ‘slug-well’ is ejected with the moulding and

runner system.

Runner Design

To facilitate the production of good quality mouldings,

particular attention should be paid to the design and

layout of the runner system.

Runners, like sprues, should be generous in diameter

and short in length to minimise pressure loss and

permit adequate follow-up pressure in the initial stage

of cooling.

Full-round runners give the best results (see Figure

33) but if these cannot be used trapezoidal runners

can be used satisfactorily. Half-round and flat

runners tend to cause premature freezing of the

melt and should not be used. In multi-cavity moulds

it is necessary to balance the runner layout by

having main and secondary runners to achieve

even pressure transmission into each cavity of the

mould. A cold slug overflow well should be provided

at the end of main runners.

Figure 33 Runners

As a guide to runner design and size the following

should be used:

For thin-section mouldings, ie 2.5 mm-4mm, the

main runner should be 6 to 8 mm in diameter.

For thick-section mouldings, ie 6 mm and

upwards, the main runners should be 10 mm

and above.

The large diameter runners are usually necessary

for items such as lenses, brush backs, insignias,

etc. If secondary runners are to be used they

should not be significantly smaller than the main

runner.

Hot Runner Moulds

The use of the hot-runner technique for feeding

multi-impression and large area mouldings is now

firmly established in the acrylic moulding industry.

The advantages of hot-runner mouldings are:

Melt enters the cavities in a more controlled

condition than with a sprue and runner system,

as temperature control in the hot runner is

adjustable to finer limits;

A possible reduction in post-moulding finishing

operations to remove large sprue gate witness

marks;

The elimination of cold sprues and runners in

multi-impression moulds which would normally

be scrapped or reworked;

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Hot-runners enable single impression, large area

mouldings to be edge-gated, whilst keeping the

moulding in the centre of the machine platen.

Effective increase in the shot capacity of the

machine as, once the hot-runner is filled, the

injection capacity can be fully concentrated into

the cavities.

In designing hot-runner moulds (Figure 34) the

following important points should be observed:

Provide adequate heating for the hot runner

manifold (1.8 watts/cm3 or 30 watts/in3) and

nozzle (approximately 300 watts);

Make provision for closely controlling the

temperature of the manifold and nozzles with

suitable instruments;

Insulate the hot-runner manifold and nozzles

from the machine platen or mould cavities by air

or compressed temperature-resistant sheeting;

Provide adequate runner channels in the heated

manifold, ie minimum 12 mm diameter;

Make the machine nozzle orifice diameter of

similar size to the channels in the hot-runner

manifold;

Ensure that the runner channels are devoid of

any sharp corners or blind spots where melt

could become trapped and consequently

degraded.

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Figure 34 General Assembly of Hot Runner Mould

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Figure 35 General assembly and operation of typical three-plate mould

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Three-Plate Moulds

These are normally used when multi-cavities for small

components are involved and semi- or fully-automatic

working is required. However, as indicated earlier, due

to the brittle nature of acrylic materials, this type of

design has to be used with care.

This type of mould, as it name suggests, has an extra

plate (see Figure 35). This plate (B) usually carries on

one side the gate and the complete runner system,

preferably trapezoidal, and on the opposite side the

plate carries part of the mould form (usually the

female part).

When the mould opens plate (B) is separated by

means of a delayed action mechanism (eg chains or

length bolts), so breaking the restricted gate. The

mouldings are then ejected from one daylight and the

sprue and runner system are ejected from the other.

Successful ejection of mouldings relies on clean

separation of the moulding and gate at the parting line.

With this method of tooling, restricted gates of the

correct design must be used (see Restricted gate,

Figure 37).

Multi-plate moulds are usually more expensive than

two-plate moulds and can be slower in production if

an operator has to remove the sprue and runner

system when the mould is open. This can usually be

avoided by providing automatic ejection of sprue and

runner. Such a mould is shown in Figure 35 where in

addition to plate (B) the runner is stripped out

automatically with a runner stripper plate (C). The

distance travelled by the plates is governed by the

length of the chain or the length of the bolts used to

separate them.

Gate Design

The type and position of the gate is often dictated by

the design of the component and the number of

mouldings to be produced in each cycle. For guidance

the following section provides information on different

gating methods.

Sprue Gate (Figure 36)

This type of gate is the preferred gate and is normally

used for single-impression moulds, especially suitable

when the component is cup shaped and involves a

Restricted Gate (Figure 37)

This type of gating is used for multi-cavity tools.

Finishing operations can often be eliminated

because the small gate is broken off during the

ejection of the moulding. The gate must not be too

small otherwise the filling of the cavity is impaired.

Also, under the effect of high injection pressures

frictional heating of the material passing through the

gate could lead to splash marking and burning on

the finished component. However the gate must not

be made too large otherwise it will not break off

satisfactorily during ejection. As a guide restricted

gates should not be smaller in diameter than 1.0

mm or greater than 1.8 mm. It is also essential to

have a generous runner system to prevent

premature freezing of the melt.

DTM/E/2Ed/Nov01

Figure 36 Sprue Gate

Figure 37 Restricted Gate

To prevent any cracking around the gate during the

ejection of the moulding (particularly where larger

gates are being used) the gate should have a slight

back taper so that it breaks off about 1.5 mm from

the surface of the moulding.

base. Its advantage over a side gate is that the flow

ratio is reduced and the mould will be filled

symmetrically. This system may be extended to multi-

impression moulds in conjunction with a hot-runner

assembly.

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page 39

Owing to the notch effect, restricted gates should

be located at a point in the moulding subject to low

mechanical stresses. Also, where a clean finish is

required, the pronounced orientation of the material

in the gate area often hinders the removal of the

gate-mark by milling, due to small cracks occurring

along the lines of orientation. Hence care should be

taken in the removal of any restricted gates.

Side or Edge Gate (Figure 38)

This is the most common type of gate used to

produce components of a flat or shallow nature.

The size of the gate is dependent upon the shape

and thickness of the moulding. For normal 2 to 4

mm thick mouldings the gate thickness should be

two thirds that of the moulding. For thicker sections

the gate thickness should be approximately 75% of

the component thickness and as wide as the

runner. With multi-cavity moulds where the gates

are arranged in series, it is necessary to balance

the filling of the cavities. This is not always easy to

predict at the design stage of a mould and it may

be necessary to complete the balancing operations

by trial runs. Generally the gates furthest from the

sprue are given the greatest cross-section and

those nearest the sprue the smallest.

Flash Gate (Figure 39)

For long flat components of thin section this type of

gate can be used quite successfully. It enables a

large cavity to be filled quickly and consistently.

The length of the gate is dictated by the length and

width of the article and the flow pattern required. In

some instances it is advantageous to have the gate

the full length of the article, though usually a gate

length which is about 50% of the longer side

dimension is sufficient. However, it is important to

retain adequate thickness of the gate and therefore

more complex finishing operations will be required.

DTM/E/2Ed/Nov01

Figure 38 Side or Edge Gate

Figure 39 Flash Gate

Figure 40 Fan Gate

Fan Gate (Figure 40)

For thick section mouldings such as optical lenses,

this type of gating is used. It enables the runner to

be made of adequate size to aid flow and prevent

the material from chilling off when it is injected

slowly as is necessary when making these

components. It also allows sufficient follow-up

pressure to be maintained on the cavity during the

cooling contraction stage.

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DTM/E/2Ed/Nov01

Spider Gate (Figure 43)

This is a variation of the diaphragm gate. It is

normally used for moulding large diameter

apertures and helps to reduce material wastage. A

disadvantage is that weld lines are created by the

meeting of the separate flow streams and this factor

needs to be considered at the component and

mould design stages.

page 40

Tab Gate (Figure 41)

This type of gating can be used as an alternative to

side gating to produce articles of a flat or shallow

nature. It has certain advantages over normal side

gates in that the design minimises the jetting of

material into the mould cavity which may lead to

weld lines and flow marks.

Tab gates are normally used to produce elongated

articles such as radio scales and rules. The tab in

these instances is located towards one end so that

the mould cavity is filled evenly down the greater

part of its length. The longitudinal orientation of the

material tends to strengthen the article and,

because the gate is remote from the centre point of

maximum stress, it avoids the risk of cracks

developing at the gate area if the moulding is

subsequently flexed.

Figure 41 Tab Gate

Figure 44

Figure 45

Figure 43 Spider Gate

Figure 42 Diaphragm Gate

Diaphragm Gate (Figure 42)

For single-impression moulds which are to be

produced with a central orifice, this type of gating

can be used to obtain uniform radial mould filling.

The diaphragm gate is removed by a subsequent

machining operation.

Ring Gate (Figures 44 and 45)

For single or multi-impression moulds which are to

produce tubular type articles this type of gate

ensures consistent filling of the moulds. It also

helps to ensure that the core pin is central with the

cavity, whereas using an ordinary side gate the

initial pressure would tend to displace the core pin

and so cause the article to have an uneven wall

section.

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page 41

Submarine (Tunnel) Gate (Figure 46)

Although not recommended, this type of gate can

be used on multi-cavity moulds in a similar manner

to the restricted gate. It is normally used for articles

which cannot have a mould mark on the base or for

a tubular type article. The submarine gate differs

from the restricted system in that is below the

parting line of the mould. This means that the gate

will not break off until the moulding is ejected. It is

essential when using submarine gates to have a

sufficient taper on the gating system so that the

portion below the split line of the mould can be

easily removed with the runner system. This system

can be used to advantage with fully automated

moulds.

the material is exposed to the atmosphere for

excessive periods, or if material is kept under damp

storage conditions. Material should not be allowed

to remain in machine hoppers for more than a few

hours. When not in use, bags and containers

should be sealed and re-used as soon as possible.

Stock control should be practised so that material

storage time is kept to a minimum (recommended

maximum 3 months) and the risk of moisture pick-

up, through prolonged storage, reduced.

If material has become wet because of incorrect

storage or handling, splash or mica marks will be

observed on the surface of the moulded article. For

best results wet material should be dried with

dehumidified air driers at a temperature of 80-90°C

for the Lucite Diakon M grades (eg CMG) [type 8]

and 65-75° for the Lucite Diakon L grades (eg CLG)

[type 6] with the residence time in the drier not less

than 4 hours. Temperatures at or below the

minimum will require longer in the drier while

excessive temperature may lead to sintering of the

granules. If the throughput of the moulding

machine is greater than the time capacity of the

drier problems may occur if the moisture is not only

at the surface but has to diffuse from the centre of

the granule.

In those more critical moulding applications it may

be advantageous to pre-dry or pre-heat the material

straight from the bag or container prior to moulding.

Rework Material

There is a tendency for the original water-white

colour of acrylics to deteriorate slightly with

repeated reworking and hence it is recommended

that the amount of added rework material (scrap

moulding, sprues etc ground up for re-use) should

be limited when the moulded colour is critical. For

applications where colour is less critical, a common

addition level is 20%. Up to 100% of good quality

rework may be used with no significant fall-off in

properties but it is not to be recommended.

It is essential to ensure that the grinder is clean and

that dirt contamination is not included during the

grinding process.

DTM/E/2Ed/Nov01

Figure 46

Gating of Thick Sections

To prevent sink marks and voids which must be

absent when moulding lenses and prisms, the

material shrinkage (a few per cent from melt to solid

state) must be compensated by the flow of

additional material into the mould during cooling.

This flow of material can occupy several minutes

depending on the thickness of the moulding.

Hence the cross-section of the runner and gate

must be of adequate size to prevent the gate

freezing-off too soon.

The edges of the components must not be too thin,

as could occur with the edge of a lens, since

insufficient area would be available for the gate. In

producing thick section articles of this type the gate

thickness is more important than the width and

should, in general, be at least three-quarters the

thickness of the edge section. In order to prevent

any flow lines the edge of the gate should be

slightly radiused and the cavity must be filled slowly.

Runner lengths should be kept to a minimum.

MOULDING TECHNIQUE

Care of Raw Material

Lucite Diakon acrylic polymers are normally suitable

for moulding without any preliminary drying

operation. However, moisture will be absorbed if

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page 42

The screen size on the grinder should be 3 mm- 6

mm. Larger screens should not be used since

difficulty could be encountered in feeding, melting

and processing larger particles, particularly if rework

material is being blended with coloured material or

used on shallow-flighted screws.

It is usually necessary to dry rework material prior

to moulding if it has been exposed to the

atmosphere for any length of time. The drying

conditions for rework material are the same as used

for virgin material. It is generally possible, by

grinding sprues and runners soon after they have

been moulded and keeping the material protected

from the atmosphere, to mould it without drying.

Contamination

Lucite Diakon is not compatible with other moulding

materials and strict precautions must be taken to

prevent contamination which is immediately visible

because of the high transparency of the material.

Contamination with other clear materials

(polystyrene and polycarbonate) results in white

cloudy streaks due to differences in refractive index.

Because Lucite Diakon is a good electrical

insulator, it will pick up atmospheric dust by

electrostatic attraction. Care must therefor be taken

when loading machine hoppers to prevent

unnecessary exposure.

Purging

Being a clear material, the changeover from other

materials to Lucite Diakon is more difficult than with

opaque plastics, and many moulders keep a

separate cylinder soley for moulding acrylic. Where

a separate cylinder for acrylic is not available the

most convenient way to clean the cylinder, apart

from a complete strip down, is to purge the machine

using rework Lucite Diakon with the nozzle

removed. The nozzle can be ‘burnt out’ separately.

Where black or heavily filled materials are to be

removed from the cylinder it is useful to use scrap

natural unfilled polypropylene as a purging

compound before changing over to rework Lucite

Diakon.

When purging it is recommended that the cylinder

temperatures be raised during the initial stages of

the operation. This assists removal of material from

cylinder walls. Obviously care must be taken not to

disrupt the carbonised layer on the screw and barrel

or use excessive temperatures which could cause

severe decomposition of the material. After a short

while, temperatures should be reduced and the

machine purged with Lucite Diakon at lower

temperatures to remove remaining traces of

unwanted material. Once the purging operation is

complete a clean nozzle should be fitted.

Temperature Control

The melt viscosity of acrylic is more temperature

dependent than that of many other thermoplastic

materials as can be seen in Figures 47,48 and 49.

It follows, therefore, that the moulding conditions

must be accurately controlled.

DTM/E/2Ed/Nov01

Figure 47 Variation of melt viscosity with

temperature for different thermoplastics

(Shear rate 1000 s-1)

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DTM/E/2Ed/Nov01

page 43

Figure 48 Variation of melt viscosity with temperature for different grades of standard Lucite Diakon

(shear rate 1000s-1)

Figure 49 Variation of melt viscosity with temperature for different grades of Lucite Diakon ST

(Shear rate 1000 s-1)

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DTM/E/2Ed/Nov01

page 44

Position of Thermocouples

Controlling thermocouples should be located as

close as possible to the heaters they control, eg in

a slot directly under the band heaters. This

arrangement eliminates any time lag in the

response of the controllers and minimises cyclic

variations in temperature.

Measurement of cylinder wall temperatures may be

made by a set of deeply recessed thermocouples

connected to a separate recorder. Such facility is not

essential for production purposes but it is a useful

guide for establishing optimum conditions and for

experimental work.

Nozzle Temperature Control

This subject is discussed on page 30 but it is

recommended that wherever possible separate

control of the nozzle temperature should be used.

For long or extended nozzles separate control is

essential to minimise any defects such as matt

patches or splash marking around the sprue which

occur because of the nozzle being too cold or

too hot.

Moulding Conditions

The actual moulding temperatures and pressure

setting required will vary from grade to grade and

from one type of machine to another, depending on

the size of the machine and the shot weight of the

moulding. They will also depend on the design and

section thickness of the component. The material

temperature may be higher or lower than the

indicated cylinder temperature depending on the

amount of frictional heat introduced by the screw. It

is therefore not possible to be specific about the

Figure 50 Variation of melt viscosity with stress for

CMG302 at different temperatures.

exact moulding conditions for Lucite Diakon and

each case must be considered on its own merit and

in the light of experience.

However, remembering that Lucite Diakon has a

high melt viscosity which is very temperature

dependent when compared to many other

thermoplastic materials, the moulding conditions in

table 6 may be used as a guide for all grades, using

the higher end of the melt temperature range for

higher viscosity grades.

Moulding Type

Normal Large Area Thick Section

Melt 230 to 250°C 260 to 270°C As low as 180°C

Mould temperature 60 to 70°C 70°C 70°C

Screw speed Medium Medium Slow

Back pressure Low (to medium) Low (to medium) High (to medium)

Injection speed Medium to fast Medium to fast Slow to very slow

Cycle time 40 seconds 70 seconds > 2 minutes

Table 6 Guide to moulding conditions

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DTM/E/2Ed/Nov01

page 45

Gate Size

The influence of gate size on mouldability or flow

ratio of Lucite Diakon cannot be overstressed.

There is a natural desire to use small gates to

minimise both finishing operations and gate witness

marks. However, the quality and ease of producing

Figure 51 Influence of gate size and melt temperature on the approximate flow ratio for Lucite Diakon

CMG302

mouldings are significantly improved by using large

gates with a balanced sprue and runner system.

Figure 51 shows the influence of gate size and melt

temperature on the approximate flow ratio for Lucite

Diakon CMG302.

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page 46

Cylinder Temperatures

Due to the many factors influencing material or melt

temperature it should be noted that melt and cylinder

temperatures are unlikely to be identical and in fact

may differ by a significant amount.

The approximate range of melt temperature over which

Lucite Diakon may be moulded is 200 to 270°C. For

average size mouldings the easy flow Lucite Diakon

type 6 grades will be in the low to middle range and the

higher viscosity Lucite Diakon Type 8 grades in the

middle to high range. It is common to optimise

temperature settings by applying a small gradient to the

cylinder temperature; 5 to 10°C lower at the nozzle and

10 to 20°C lower at the rear or feed zone.

In the absence of experience or correlation between

melt and cylinder temperatures then initial cylinder

temperature settings of 240°C are recommended.

Mould Temperature

It is essential when moulding Lucite Diakon to have

adequate provision for controlling the mould

temperature. Both halves of the mould should be cored

for circulating water at a controlled temperature. With

some mould designs and component shapes it may

well be necessary to control the mould halves at

different temperatures to achieve an acceptable

product. A separate circuit should be used to control

the sprue bush temperature.

The recommended mould temperature for the Lucite

Diakon type 8 grades is between 60 and 80°C

depending upon section thickness and flow path, and

for Lucite Diakon type 6 grades 55-70°C.

Machine Start-Up

Injection moulding machines should not be allowed to

stand idle for long times while at moulding

temperatures, since this allows heat to conduct

backwards along the screw and could cause material to

melt on to the feed section of the screw and create an

obstruction. Where a delay is involved, rear temperature

should be temporarily reduced. Controlled water should

be circulated around the feed pocket during the heating

up period to prevent this section from becoming too hot

and causing sticking of prematurely melted material.

When in production the feed throat should be

maintained between 40 and 60°C.

If any mould setting is required on the injection unit this

should be done once the cylinder has attained the

moulding temperature. The machine and mould should

never be ‘set’ when cold, otherwise the expansion of

the injection unit when it reaches moulding

temperatures could cause serious damage.

Before commencing to mould, the machine should be

purged briefly to ensure that the material in the barrel is

clean and at the right temperature.

Screw Back Pressure

When the screw unit is plasticising, a regulated forward

hydraulic pressure is applied to the screw in partial

opposition to the back pressure generated by the

plasticised melt. The regulated pressure is known as

the screw back pressure or screw reaction pressure. If

this back pressure is greater than the pressure

generated by the melt in front of the screw then no

screw retraction will take place. However, by

adjustment of the screw back pressure, the screw may

be made to refill under controlled conditions and

produce a uniform melt.

Some back pressure is desirable to help expel air from

between the polymer particles or granules and so

prevent air from being included in the melt. Otherwise

this may lead to burning of the material in the cylinder

and may show as splash marks or bubbles (generally

with white inclusions) in the moulding, or in the extreme

case as black streaks. Screw back pressure is also

useful with blends or dry coloured material to aid

mixing, particularly where lightly tinted materials are

being processed. An increase in screw back pressure

causes more work to be done on the material and so

enhances mixing. However, excessive use of back

pressure can lead to overheating of the material die to

frictional heat, which will show as splash marks and

could eventually lead to screw slip (see below) due to

overheating of material on the rear section of the screw.

Screw Speed

Because acrylic moulding materials have relatively high

melt viscosities, attention must be paid to the screw

speed to avoid excessive frictional heating and

degradation. The screw speeds to be used vary

according to the size of machine (ie screw diameter)

and type of article being moulded, but in general they

should be kept as low as possible consistent with an

acceptable cycle time. For shot weights up to 250g

screw speeds of 80-100 rpm are used satisfactorily; for

machines with large diameter screws it is necessary to

keep screw speeds low in the range of 30-40 rpm.

DTM/E/2Ed/Nov01

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Where temperature controllers indicate a marked

tendency to override the preferred set temperature

due to frictional heating, then adjustment of screw

speed and back pressure should be considered. If

full correction by this means is not possible, but the

developed temperature can be accepted, then the

temperature controller should be re-set to control

the temperature at a higher level.

Screw Slip

This term is applied when the screw turns but does

not refill. It is generally caused by molten or semi-

molten material, in or close to the feed section,

sticking to the screw flights and so impeding the

entry of fresh material into the cylinder. It can also

be caused by too high a screw back pressure.

Screw slip can occasionally occur during start-up.

This arises because the machine has been allowed

to stand at moulding temperature for too long a

time. Under these conditions, heat from the cylinder

conducts along the screw raising the temperature of

the rear section of the screw which then causes

premature melting of material in the feed flights.

This is especially so if the screw flights are full of

material.

To overcome screw slip, ie remove the blockage

caused by molten or semi-molten material, the

temperatures of the rear zone and feed pocket

should be lowered, insuring cooling water is

circulating around the feed throat and the machine

purged with rework material. In extreme instances

the rework material may have to be force-fed on to

the screw. Purging should be continued until the

rear temperature stabilises and the screw refills

consistently.

Where an extended delay is likely to occur it is a

wise precaution to increase cooling to the feed

throat and reduce the rear zone cylinder

temperature to about 150°C.

Injection Speed

There are contradicting requirements on the rate of

filling the mould with acrylic materials. Fast injection

speed decreases cycle time, prevents premature

freezing of the melt before the mould is full and

improves the strength of weld lines. However, with

fast injection speed there is a strong possibility of

frictional heat and splash marking, especially with

small gates, flow lines may be more obvious and

there is a higher risk of flashing the mould.

Programmed injection allows a balanced rate of fill

to be achieved. Fast to medium for the majority of

the shot and medium to slow for the balance.

Shrinkage of Mouldings

Shrinkage of mouldings is caused by the reduction

in volume which the material undergoes when it

changes from the molten to the solid state in the

mould and continues to cool to room temperature.

The shrinkage expressed as a fraction, or as a

percentage, is based on the difference between the

dimensions of the cold moulding and of the cold

mould. The extent of shrinkage of Lucite Diakon,

like that of other thermoplastics, is dependent on

the component design, gate design, moulding

conditions and the manner in which the melt flows

to conform to the shape of the tool.

It is almost impossible to predict accurately the

exact amount of shrinkage which will take place on

a given article but approximate shrinkage figures

which may be used as a guide can be obtained by

measurements made on specific test pieces. If

accurate dimensions are required on the finished

components, it is necessary first to carry out trials

under controlled moulding conditions and then to

make final adjustments to the mould dimensions.

When doing this it is essential to measure the

component sometime after moulding to ensure that

full contraction has occurred. The moulding must be

kept dry during this time and it is important to

measure all critical dimensions both in line with, and

across, the flow path of the material, since

shrinkage can vary with the direction of melt flow.

Shrinkage can be adjusted to some extent by the

moulding conditions, but it must be emphasised that

the amount of shrinkage which may be controlled in

this way is limited and is not always sufficient to

compensate entirely for a mould which has been

made grossly under or over size. This sort of

practice may also lead to the danger of excessive

residual stress in a moulding.

On average the shrinkage of Lucite Diakon is in the

order of 0.3 to 0.7%, the higher shrinkage applying

to a thicker moulding.

DTM/E/2Ed/Nov01

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DTM/E/2Ed/Nov01

page 48

From experiments with various components, the

following conclusions can be drawn:

Shrinkage is inversely proportional to injection

pressure;

Shrinkage is directly proportional to mould

temperature;

Shrinkage is directly proportional to melt

temperature.

It is worth noting that the flow pattern to the

component will tend to determine which is the main

factor in controlling the shrinkage of the moulding.

For example, the shrinkage of long thin mouldings

exhibiting linear flow paths will be dependent more

on changes in injection pressure and speed than on

other variables, while shrinkage of moulding

exhibiting radial flow paths will be more dependent

on changes in melt and/or mould temperature.

DISTORTION

Acrylic materials are amorphous and therefore

significantly less prone to distortion than crystalline

materials. However, distortion or warpage of

mouldings can occur and is the result of differential

cooling rates; the consequence of incorrect

moulding conditions, Figure 52, or component

design, Figure 53.

Figure 52 Influence of mould temperature on

distortion

Figure 53 Influence of Component Design on

Distortion

Strain in Mouldings

Two types of strain can occur in injection mouldings

and these are of consequence in relation to the

subsequent service behaviour of the moulded

component. These strains arise from:

Molecular orientation - introduced during the flow

of the molten polymer in the mould and frozen in

during cooling.

Quenching or cooling stress - resulting from a

differential rate of cooling between the surface

and the interior of the component.

Refer to the section on Stresses and Molecular

Orientation in Lucite Diakon Components on page

72 for information on causes, problems, testing and

remedy.

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MOULDFLOW SIMULATION

Previous sections have described and considered

basic principles on the injection moulding of Lucite

Diakon; including equipment, component design,

mould design and processing conditions. This

information has been gleaned from many years of

practical experience in the injection moulding of

acrylic materials. However significant effort has

been put into the development and use of software

packages to simulate various aspects of the

injection moulding process. Although the initial

component design, method of production and

subsequent mould design still has to be done, these

mouldflow programmes are significant aids to

assessment of component design, tool layout

including feed system, processing conditions and

possible problem areas.

A series of rheology measurements, coefficients

and thermal properties for each specific Lucite

Diakon grade is required as data input for the

software packages. As an illustration, Table 7

provides the information for Lucite Diakon

CMG314V, the standard normal molecular weight

type 8 grade.

DTM/E/2Ed/Nov01

Obs. Shear Rate Exp. Visc. Temp. Calc.Visc. Diff.% Temp. Shift Std Temp

1. 30.00 7116.00 210. 7835.76 -9.19 7.25 218.99

2. 60.00 4864.00 210. 4782.23 1.71 12.06 221.05

3. 100.00 3454.00 210. 3290.69 4.96 14.42 221.75

4. 150.00 2526.00 210. 2437.05 3.65 14.14 221.68

5. 300.00 1465.00 210. 1452.03 .89 13.20 221.41

6. 600.00 880.00 210. 862.40 2.04 14.37 221.74

7. 1000.00 594.00 210. 586.79 1.23 14.23 221.70

8. 1500.00 442.00 210. 432.10 2.29 15.15 221.94

9. 3000.00 259.00 210. 255.98 1.18 14.90 221.88

10. 6000.00 147.50 210. 151.59 -2.70 12.99 221.34

11. 30.00 4157.00 230. 4238.71 -1.93 1.44 231.79

12. 60.00 2826.00 230. 2845.69 -.69 1.68 232.51

13. 100.00 2089.00 230. 2046.82 2.06 2.01 233.37

14. 150.00 1565.00 230. 1552.29 .82 2.06 233.47

15. 300.00 952.00 230. 948.24 .40 2.21 233.80

16 600.00 577.00 230. 570.52 1.14 2.43 234.23

17. 1000.00 395.00 230. 390.25 1.22 2.53 234.41

18. 1500.00 289.00 230. 288.14 .30 2.49 234.35

19. 3000.00 169.00 230. 171.15 -1.26 2.42 234.22

20. 6000.00 93.00 230. 101.49 -8.37 1.82 232.89

21. 30.00 1720.00 250. 1679.00 2.44 .29 243.42

22. 60.00 1377.00 250. 1351.59 1.88 .31 243.75

23. 100.00 1076.00 250. 1087.84 -1.09 .31 243.79

24. 150.00 860.00 250. 885.93 -2.93 .31 243.87

25. 300.00 570.00 250. 589.62 -3.33 .34 244.39

26. 600.00 373.00 250. 372.92 .02 .43 245.62

27. 1000.00 264.00 250. 260.65 1.29 .49 246.27

28. 1500.00 196.00 250. 194.61 .71 .50 246.39

29. 3000.00 120.00 250. 116.93 2.63 .57 247.13

Table 7 Mouldflow rheology measurements for Lucite Diakon CMG314V

CARREAU EQUATION

REFERENCE TEMPERATURE = 230.00

Fitted activation energy = 165714.93108

Fitted E/R = 19931.07581

THE CARREAU EQUATION

COEFF. P1 = 10369.

COEFF. P2 = .75453e-01

COEFF. P3 = .75629

Fit Coeff. = .99928

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DTM/E/2Ed/Nov01

page 50

1st Order 2nd Order

Obs. Shear Rate Exp. Visc. Temp. Calc. Visc. Diff.% Calc.Visc. Diff.%

1. 30.00 7116.00 210. 7111.64 .06 7373.77 -3.50

2. 60.00 4864.00 210. 4394.17 10.69 4760.55 2.17

3. 100.00 3454.00 210. 3081.64 12.08 3390.75 1.87

4. 150.00 2526.00 210. 2325.25 8.63 2563.96 -1.48

5. 300.00 1465.00 210. 1436.74 1.97 1557.21 -5.92

6. 600.00 880.00 210. 887.74 -.87 921.21 -4.47

7. 1000.00 594.00 210. 622.57 -4.59 615.21 -3.45

8. 1500.00 442.00 210. 469.76 -5.91 442.01 .00

9. 3000.00 259.00 210. 290.26 -10.77 245.99 5.29

10. 6000.00 147.50 210. 179.35 -17.76 133.34 10.62

11. 30.00 4157.00 230. 4331.19 -4.02 3923.97 5.94

12. 60.00 2826.00 230. 2676.18 5.60 2648.24 6.71

13. 100.00 2089.00 230. 1876.81 11.31 1948.91 7.19

14. 150.00 1565.00 230. 1416.15 10.51 1512.44 3.48

15. 300.00 952.00 230. 875.01 8.80 960.23 -.86

16 600.00 577.00 230. 540.66 6.72 593.82 -2.83

17. 1000.00 395.00 230. 379.16 4.18 409.75 -3.60

18. 1500.00 289.00 230. 286.10 1.01 302.13 -4.35

19. 3000.00 169.00 230. 176.78 -4.40 175.77 -3.85

20. 6000.00 93.00 230. 109.23 -14.86 99.60 -6.63

21. 30.00 1720.00 250. 2637.82 -34.79 1968.00 -12.60

22. 60.00 1377.00 250. 1629.87 -15.51 1388.42 -.82

23. 100.00 1076.00 250. 1143.03 -5.86 1055.73 1.92

24. 150.00 860.00 250. 862.47 -.29 840.83 2.28

25. 300.00 570.00 250. 532.91 6.96 558.05 2.14

26. 600.00 373.00 250. 329.28 13.28 360.75 3.40

27. 1000.00 264.00 250. 230.92 14.32 257.20 2.64

28. 1500.00 196.00 250. 174.24 12.49 194.63 .70

29. 3000.00 120.00 250. 107.66 11.46 118.37 1.38

1st Order (Power Law) Coeff.A = .13781E+08

Coeff.B = -.69459

Coeff.C = -.24794E-01

Fit Coeff. = .98896

2nd Order (Quadratic) Coeff.A1 = 16.003

Coeff.A2 = -1.0980

Coeff.A3 = -.98320E-02

Coeff.A4 = -.27380E-01

Coeff.A5 = .31997E-02

Coeff.A6 = -.74073E-04

Fit Coeff. = .99827

Specific heat capacity 2300 J/kg deg C

Thermal conductivity 0.2 w/m deg C

Melt density 1100 kg/mx3

No flow temperature 160 deg C

Freeze temperature 120 deg C

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page 51

A joint exercise between Lucite International and

Plastics Design Solutions Ltd (See Appendix II for

full address) was carried out to illustrate how data

for the mouldflow simulation process may be used

to influence the design optimisation and production

of Lucite Diakon mouldings. The simple component

design representing an instrument panel lens

together with cavity, sprue, runner, gate size and

gate position variations is illustrated in Figures 54

and 55. A matrix of mouldflow data obtained from

these variations together with changes in material

and processing conditions is listed in Table 8.

DTM/E/2Ed/Nov01

Table 8 Summary of conditions and results

LUCITE DIAKON® Cavity Gate Gate Sprue Injection Melt Melt Apparent Maximum Maximum Maximum Average Comment

Grade Thickness Size Position and Time Flow Temp. Bulk Melt Pressure Shear Shear Shear Rate

mm mm Runner seconds Rate °C Temp. Bar Stress at Gate at Gate

cm3sec-1 °C KPa sec-1 sec-1

CMG314V 2.2 1 x 5 B Good 2 65 250 - 1,793 776 47,100 - infuence

CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 51,600 - of cavity

CMG314V 2.8 1 x 5 B Good 2 81 250 - 1,321 812 56,800 - thickness

CMG314V 2.5 1 x 5 A Good 2 68 250 - 967 750 48,400 - see fig 56

CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 51,600 -

CMG314V 2.5 1 x 5 C Good 2 81 250 - 1,808 818 56,700 -

CMG314V 2.5 1 x 5 B Good 2 73 250 252 1,505 796 51,600 - see fig 57

CMG314V 2.5 1 x 5 B Poor 2 68 250 283 2,135 746 46,200 -

CMG314V 2.5 1 x 5 B Good 0.5 146 250 - 1,795 1,010 200,900 - see fig 58

CMG314V 2.5 1 x 5 B Good 1.7 86 250 - 1,532 818 60,300 -

CMG314V 2.5 1 x 5 B Good 3 36 250 - 1,725 742 35,800 -

CMG314V 2.5 1 x 5 B Good 2 73 230 - 2,050 994 - - see fig 60

CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 - -

CMG314V 2.5 1 x 5 B Good 2 73 270 - 1,067 661 - -

CMG314V 2.5 1 x 2 B Good 2 73 250 - 1,604 1,010 204,200 169,400 see fig 59

CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 51,600 44,500

CMG314V 2.5 2 x 5 B Good 2 73 250 - 1,423 672 18,100 16,400

CMH454 2.5 1 x 5 B Good 2 73 250 - 1,596 816 - - infuence

CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 - - of Lucite Diakon

CLG356 2.5 1 x 5 B Good 2 73 250 - 502 584 - - grade

Figure 54 Component and mould cavity layout Figure 55 Sprue and runner designs

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DTM/E/2Ed/Nov01

page 52

Figure 56 Influence of gate position on injection pressure,

illustrates that cavity layout has a significant

effect on the required injection pressure and

resultant machine size through locking force

requirement. Similar plots are obtained for

filling pattern and material shear stress. These

may indicate possible distortion, air entrapment

or frictional heating problems

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DTM/E/2Ed/Nov01

page 53

Figure 57 Influence of sprue and runner design on temperature and shear rate profiles. As indicated in other

sections on design and processing, the comparatively high melt viscosity and shear sensitivity of

acrylic materials may lead to overheating, degradation and monomer splashing. Although the

figures produced in a simulation exercise may not be exactly those obtained in practice, the

results in Figure 57 strongly underline the difference between good and bad design in the feed

system. It also illustrates that it is often the feed system and not the mould cavity that controls and

influences the injection moulding process. There are many occasions where mouldflow exercises

are limited to the actual component cavity but for the purpose of production efficiency it is

recommended that consideration is given to modelling the feed system

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DTM/E/2Ed/Nov01

page 54

Figure 58 Influence of injection time on injection

pressure, shows that there is an

optimum fill time to minimise injection

pressure although other factors like

degree of sinking may influence this

Figure 59 Influence of gate size on shear rate at

the gate, aptly illustrates the frictional

shear degradation problems that often

occurs on the injection moulding of

acrylic materials due to the use of small

gates

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DTM/E/2Ed/Nov01

page 55

Figure 60 Influence of melt temperature on injection

pressure. This figure is included to

demonstrate how the mouldflow simulation

may be used to influence processing

conditions

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DTM/E/2Ed/Nov01

page 56

MOULDING FAULT REMEDIES

The following table lists the main moulding faults

likely to be encountered, their causes and the

procedures to be followed in order to correct the

faults.

Moulding Fault Remedy

Splash or mica marks, surface streaks A Too Hot

These are caused by volatiles (moisture, 1 Reduce cylinder temperature

monomer) in the melt. 2 Reduce hot runner temperature

A major source of degradation and 3 Reduce screw speed

splash marks is excess frictional heat. 4 Reduce back pressure

5 Reduce injection speed

6 Increase size of sprue/runner/gate

B Too cold

1 Raise cylinder temperature

2 Raise nozzle temperature

C Moisture

1 Dry the material (70 to 80°C for 6 to 12 hours)

Burning or entrapment of air in cylinder

This usually appears as splash marks and small bubbles with 1 Increase back pressure

white inclusions. In its severest form as black streaks. 2 Decrease screw speed

Burn marks on moulding 1 Reduce injection speed

Usually appear on extremities of the moulding and 2 Reduce injection pressure

are caused by insufficient venting of the cavities. 3 Reduce mould locking pressure

4 Reduce cylinder temperature

5 Improve venting of cavity

Matt patches on moulding surface 1 Check nozzle seating for dribble

These generally occur in the same position on each moulding, usually 2 If using vacuum suck-back check operation

close to the gate area. Often caused by a cold slug from the nozzle. 3 If nozzle has mechanical shut-off check operation

4 Increase nozzle temperature

5 Incorporate cold slug-well opposite sprue or enlarge

existing one

6 Polish runner and gate

‘Orange peel’ and smudge marks 1 Reduce cylinder temperature

Surface imperfections resembling orange peel that occur in the gate area. 2 Reduce mould temperature

3 Reduce injection time

4 Increase injection speed

5 Reduce injection pressure

6 Examine gate area for roughness, and polish

if necessary

Voids and sink marks 1 Check feed setting

These are usually due to insufficient pressure to counterbalance material 2 Increase injection pressure

shrinkage in thick sections or in sections furthermost from the gate. 3 Increase injection time

4 Increase injection speed

5 Reduce mould temperature

6 Reduce cylinder temperature

7 Enlarge gate, sprue or runner to reduce

pressure loss

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DTM/E/2Ed/Nov01

page 57

Moulding Fault Remedy

Short shot (incomplete filling of mould) or rippled surface 1 Check feed setting. Make sure sufficient material available

This usually occurs in an area furthest from the gate. It is usually 2 Increase injection speed

accompanied by a rippled surface in the area surrounding the 3 Increase injection pressure

short, shot. 4 Increase injection forward time

5 Increase mould temperature

6 Increase cylinder temperature

7 Enlarge gate, sprue or runners to reduce pressure loss.

Warping 1 Increase cooling time

Caused by uneven shrinkage in the moulding. Occurs particularly 2 Use even (both sides) mould temperatures for flat mouldings

on flatmouldings or mouldings with long edges. Also found on 3 Use differential mould temperature control over mould

mouldings of uneven section. surfaces, or between mould halves where opposite surface

areas differ.

4 Adjust injection speed.

5 Reduce cylinder temperatures.

6 Use clamping jig in which to cool mouldings.

Weld lines, flow lines 1 Increase injection pressure

These are caused by the melt separating and rejoining in the mould. 2 Reduce injection speed (Occasionally, to eliminate weld

They usually occur around inserts or as tails from raised characters lines, it may be necessary to increase injection speed)

of sections 3 Increase mould temperature

4 Increase cylinder temperature

5 Change location of gate to alter flow pattern

6 Radius corners to improve flow in mould

Jetting or flow line 1 Reduce injection speed

Usually occur in gate area 2 Reduce cylinder temperature

3 Use tab gate

Crazing 1 Clean mould surface

This occurs as minute surface cracks on the moulding, 2 Increase injection speed

usually in line of flow 3 Increase mould temperature

Delamination 1 Check for contamination

This usually occurs in the gate area or as blisters on the moulding

surface

Cracking or breaking of the part on ejection 1 Decrease injection pressure

2 Decrease injection time

3 Mould opening and ejection speed

4 Increase mould temperature

5 Increase draft angle

6 Eliminate sharp corners and undercuts.

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page 58

EXTRUSION

The high molecular weight grades of Lucite Diakon

are normally recommended for extrusion and a

range is available to provide combinations of

properties suited to particular applications.

Where increased toughness is required a range of

Lucite Diakon ST grades is available.

Acrylic materials produce melts which are generally

higher in viscosity than many other thermoplastic

materials under normal processing conditions. The

melt viscosities of the individual grades of Lucite

Diakon are shown in Figures 22 and 23, pages 25-

26.

EXTRUDER

Barrel Design

Single screw vented barrel extruders with bi-metallic

or nitrided barrels are recommended for extruding

Lucite Diakon. (See Appendix III, Volatile Chemicals

Evolved During Processing of Lucite Diakon Acrylic

Polymers.)

Screw Design for Vented Extruders

In the extrusion process a great deal of the power

input to the screw is converted into heat by the

shearing action of the screw on the material. It

follows that screw profile designs need to be

carefully chosen to obtain maximum output per

revolution coupled with adequate homogenisation

without excessive adiabatic heat evolution.

The minimum length/diameter (L/D) ratio for a

vented barrel extruder screw suitable for acrylic

material is about 27:1 but higher L/D ratios of 33:1

are available and these are preferred since they

give higher and extremely steady outputs. Screws

are generally nitrided or chromium plated, or have

‘flame-protected’ flights.

If surging is to be avoided a long feed section is

desirable in the screw since acrylic material is hard

and must have sufficient time to plasticise before it

is compressed. A compression ratio of between

2.2:1 and 3.0:1 is recommended for the first stage

of the screw and a pump ratio (volume of first

metering section to volume of second metering

section) between 1:1.5 an d 1:2.0. A deep

decompression zone in the second stage of the

screw is recommended in order to accommodate

melt swell.

Feed Throat

Feed throats are usually fitted with surrounding

water temperature control to prevent bridging or

premature melting of material. Where Lucite Diakon

bead polymer is used it is essential always to

operate with water cooling on the feed throat.

Breaker Plate

A breaker plate and filter pack are not absolutely

necessary with virgin Lucite Diakon, but can help

pigment dispersion in coloured material and where

rework is being processed, acting as a safety

precaution. Where used, the filter pack would

consist of one fine mesh (aperture 75-150 micron)

supported by a coarser mesh (250-300 micron) and

a breaker plate. Manual or automatic filter changers

are usually incorporated in extruders having barrel

diameters 90 mm and above.

Vacuum Pump

In order to obtain the full benefit of the vented barrel

a vacuum pump should be connected to the vent

port so that all the volatiles can be removed from

the melt as it passes through the decompression

zone. A vacuum pump is absolutely necessary

when operating at high screw speeds if a clear,

glossy extrudate is required.

It is essential to have an efficient water cooled

condenser between the vent port and the vacuum

pump in order to collect the volatiles emitted and

thus prevent the pump from becoming blocked.

All pipes between the vent port and the vacuum

pump should be of at least 50 mm bore and ideally

should be insulated to prevent premature

condensation of the volatiles. Any sharp bends or

restrictions in the pipework should be avoided since

they could be readily blocked if premature

condensation takes place.

DTM/E/2Ed/Nov01

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page 59

SHEET EXTRUSION

Extruder

An adequately powered vented barrel extruder with

suitable screw design is essential since the removal

of volatiles is necessary in order to obtain good

surface finish at high throughputs.

Die

Correct die design is of prime importance. The die

must be:

Robust enough to withstand high internal

pressures;

Capable of easy adjustment to give uniform flow

across the width;

Free of any hold-up areas so that material and

colour changes can rapidly be carried out;

Free from any blemishes, particularly on the die

lips, which could cause die lines.

Various dies have been developed to obtain uniform

flow across the width; the best of these is the

truncated fishtail manifold die sometimes known as

the ‘coathanger’ die as shown in Figure 62.

The finish of the die lips is of great importance

because any imperfection, particularly on the exit

edge, will immediately be transferred to the moving

sheet as it leaves the die causing die lines. Die lips

are usually made of tool steel and are carefully

machined and polished before being hard chromium

finished for protection. The exit edge is normally

radiused very slightly, about 0.25 mm.

If a wide range of sheet thickness is to be

produced, it will be advisable to have three sets of

lips with different parallels in order to maintain

uniform pressure inside the die body.

Recommended die parallels are given in Table 9.

DTM/E/2Ed/Nov01

Figure 61 Sheet extrusion line layout

Sheet thickness (mm) Die parallel (mm)

Up to 2.5 60

2.5 to 5.0 100

5.0 to 10.0 150

Table 9 Recommended die parallels

Three-Roll Polishing Stack

Various methods have been devised to handle and

cool the extruded acrylic sheet as it leaves the die

but the method generally used is that based on a

three-roll polishing stack. The three-roll stack and

ancillary equipment form a versatile unit capable of

handling most thermoplastic sheets and can produce

either a plain or embossed finish. The best system

for acrylic sheet extrusion is the one based on a

separate motor for each roll.

Whilst the sheet is travelling round the rolls it is

cooled uniformly, polished to remove any fine die

lines caused by imperfections in the die lips and

calendered to improve the thickness tolerance

across the width. Sheet produced with a three-roll

stack should have an excellent surface finish, and if

conditions are carefully controlled, will possess low

residual stress and hence exhibit low shrinkage on

reheating before shaping. Thickness tolerances of

±3%, and even less, are possible.

Patterned or embossed sheet can readily be

produced by fitting an embossing roll in the central

position. The operation is then identical to that used

for producing plain sheet.

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page 60

The temperature of embossing rolls must be

accurately controlled and is normally slightly lower

than that required for the production of plain sheet.

The actual roll temperatures depend to some extent

on the pattern and are generally within the range 90-

125°C for three-roll operation. To avoid corrosion and

difficulty in cleaning, it is advisable to have embossing

roll patterns protected by a final flash-chroming.

Surface Protection

In some cases it is desirable to protect the surface

of the sheet with polyethylene film. The film should

be approximately 0.05 mm thick and applied to the

sheet while it is still warm by a separate set of

lightly pressurised rubber-coated rolls positioned

after the thickness monitor and just before the roller

table. The film must be surface treated by electronic

discharge techniques up to 900 W/m2 on the side

which is pressed to the sheet in order to give good

adhesion.

CO-EXTRUSION

With co-extrusion, the advantages of Lucite Diakon

acrylic materials; improved UV resistance and

outdoor weathering, colourability, surface gloss and

surface hardness; are obtained by simultaneously

extruding a thin layer of Lucite Diakon onto the

normal thickness plastic substrate; for example

PVC or ABS. The co-extrusion, commonly referred

to as capping, may be carried out on sheet, profile

and tube.

Selection of the appropriate standard grade of

Lucite Diakon or impact modified grade of Lucite

Diakon ST depends upon the substrate and the

capping properties required. Lucite Diakon ST

grades may also be used to improve the detergent

craze resistance for vanity sinks, work tops and

shower cubicles used in caravans, mobile homes

and hotel bathrooms. To prevent shear degradation

during co-extrusion and promote maximum

adhesion it is important to match the rheology of the

Lucite Diakon grade to that of the substrate

material.

ABS based substrates have similar thermal and

rheological properties to those grades of Lucite

Diakon with medium to high temperature resistance

and melt viscosity. Lucite Diakon CLH952 has been

successfully used but advice should be sought on

the selection of a suitable Lucite Diakon ST grade

depending on the required end use performance.

Rigid PVC is shear sensitive with lower thermal

properties and therefore the lower softening point

easier flow grades of Lucite Diakon are

recommended; for example Lucite Diakon CLG902

or the Lucite Diakon STG6 series.

DTM/E/2Ed/Nov01

Figure 62 Truncated fishtail manifold sheet die

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page 61

PRODUCTION OF EXTRUDED SHEET

Die gap

Before commencing extrusion, the die gap should

be set to a thickness depending upon the thickness

of the sheet to be produced. A guide is given in

Table 10 but it is stressed that this is only a guide

since it depends upon extrusion temperatures,

throughput and melt viscosity of extrudates.

Experience has shown that on non-vented

extruders a moisture level of less than 0.04% is

necessary to achieve acceptable extrudate. Acrylic

can be dried down to these levels but this can be

difficult and time consuming and for this reason

vented extruders are recommended for the majority

of acrylic extrusion processes.

Rework

Rework material can be used satisfactorily. The

levels will depend on the nature of the application

as a slight deterioration in the colour of the rework

may take place during this operation. Material to be

reworked should be processed as quickly as

possible under clean conditions to minimise

moisture absorption and dirt contamination. The

grid size on the grinder should be 3-6 mm.

Shutting Down the Extruder

As standard Lucite Diakon is a relatively thermally

stable material no special precautions are

necessary when shutting down the extruder. The

barrel of the extruder should be emptied, the screw

speed reduced to a minimum and the motor

stopped. However, after running Lucite Diakon ST

grades it is recommended that the extruder is

purged with a high molecular weight grade of

standard Lucite Diakon to avoid possible die build

up and discolouration of material on subsequent

start-up.

Sheet Shrinkage

Extruded acrylic sheet can have the problem of high

shrinkage when heated prior to shaping unless

particular care is paid to extrusion conditions. If the

sheet is clamped during heating and shaping, as in

vacuum forming, some shrinkage can be tolerated,

but if it is heated freely in ovens in a manner similar

to cast sheet then a low shrinkage is desirable.

Extrusion conditions which increase shrinkage are:

Low linear speed through three-roll stack;

Excessive melt build-up in nips of three-roll

stack;

Excessive tension between three-roll stack and

pull rolls;

Die temperatures too low;

Excessive draw-down between the lips and

three-roll stack arising from incorrect relationship

of die and nip gap settings.

DTM/E/2Ed/Nov01

Sheet thickness (mm) Die parallel (mm)

2.0 1.7

2.5 2.3

3.0 2.9

4.0 4.0

5.0 5.5

6.0 7.0

Table 10 Die gap guide

MH254 LH752 ST35G8

CMH454 CLH952

Extruder Barrel

Feed throat cooled cooled cooled

Feed* 200-220 200-210 205-225

Meter 220-250 220-240 220-250

Decompression 220-240 210-230 220-230

Meter 220-240 220-235 225-235

Adaptor 220-240 220-235 225-235

Die 225-245 220-240 220-235

Polishing Rolls

Top 110-120 110-120 110-120

Middle 100-110 100-110 100-110

Bottom 90-100 90-100 90-100

Table 11 Typical temperatures (°C) for Lucite

Diakon sheet extrusion

Temperature Conditions

The temperature conditions for the extrusion of sheet from

the various grades of Lucite Diakon are given in Table 11.

*When using compound versions of Lucite Diakon

such as CMH454 and CLH952, it may be necessary

to raise the temperatures a further 5-10°C on the

feeding zone in order to achieve melt stability. On

larger extruders of 120 mm and above further

increases in feed zone temperatures may be

necessary to achieve melt stability.

Moisture

As acrylic materials are hygroscopic they should not

be left exposed to the atmosphere for any length of

time.

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With 3 mm thick sheet, experience has shown that

the longer the time the sheet takes to go around the

rolls of the three-roll stack the higher the shrinkage.

Figure 63 shows the effect of line speed on

shrinkage of 3 mm extruded acrylic sheet produced

on a three-roll stack with 250 mm diameter rolls.

LIGHTING DIFFUSER PROFILE EXTRUSION

Lighting diffuser profiles can be produced by two

methods depending upon the complexity of the

design. For relatively simple shapes, containing no

corners with a radius smaller than 3 mm, the post-

forming method from a tube die is probably the

most satisfactory. Where sharp corners are required

and there are projections to the periphery or an

embossed base, a profile die must be used.

Post-Forming from Tube Dies

Post-forming from a tube die offers several

advantages over the use of profile dies. Tube dies

can be made accurately at low cost, their symmetry

facilitating uniform flow and, with the usual die

centering arrangements, control of wall thickness is

relatively simple. A wide variety of profiles can be

produced from standard tube dies by the use of

internal and external metal forming plates. These

plates, which can either be steel or brass

approximately 6 mm thick, have the forming

surfaces radiused and polished to reduce friction.

Internal and external perforated copper air cooling

tube rings are used to promote uniform cooling of

the profiles.

A suggested design for a 100 mm die is shown in

Figure 64. The circumference of the die should

allow a minimum of 15% draw-down, ie the

circumference of the die should be at least 15%

greater than the periphery of the required section.

In practice, draw-downs of 20-25% are sometimes

used but this introduces excessive orientation. The

die may be fitted with interchangeables to produce

reeded or plain surface as required.

DTM/E/2Ed/Nov01

Figure 63 Effect of linear speed on shrinkage of

acrylic sheet

Output Capabilities

As shown in Figure 63 when operating with a three-

roll polishing stack the line sheet speed is critical if

excessive shrinkage is to be avoided. Because of

this there is a limit to the maximum sheet width

which it is advisable to produce on a given extruder.

Taking 3 mm thick sheet, a minimum line speed of

0.75 metre/minute and rolls of 250 mm diameter as

standard, the maximum recommended widths for

30:1 L/D ratio extruders are given in Table 12.

Extruder Output Maximum recommended

size (mm) (Kg/h) sheet width (mm)

60 80 500

90 300 1400

120 500 2000

150 800 2200

Table 12 Maximum recommended widths of 3 mm

extruded Lucite Diakon sheet

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Figure 64 Die for 100 mm diameter tube with slitting knife

Figure 65 Die and forming box arrangement

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Operation

When extrusion starts, the emerging tube is slit by

the knife mounted on the die face. The slit tube is

fed through the cooling box containing only the

external formers. Once the extrudate is held by the

haul-off system the internal formers can be inserted,

the positions of the formers adjusted and cooling

regulated until the desired shape is obtained. The

extrudate is cooled by a gentle flow of air from the

cooling rings. To avoid uneven cooling or too rapid

cooling the air should be directed on to the former,

rather than the extrudate.

A suitable arrangement of the die and forming box

is shown in Figure 65.

Units MG102 MH254 LH752 ST35G8

CMG302 CMH454 CLH952

Extruder Barrel

Feed throat °C cooled cooled cooled cooled

Feed °C 190 200 190 200

Metering °C 205 205 205 210

Decompression °C 200 200 200 205

Metering °C 200 205 200 205

Adaptor °C 200 200 195 205

Die body °C 180-200 190-210 190-200 190-205

Table 13 Typical conditions for Lucite Diakon tube and profile extrusion

Typical conditions for producing profiles by this method

for Lucite Diakon grades are given in Table 13.

Profile Dies

No specific recommendations can be given for the

design of profile dies since every shape presents its

own peculiarities. Frictional drag on the material

during its passage through the die must be taken

into consideration and so must the tendency for

preferential flow in the thicker sections. It follows

that the shape of the die orifice often differs

considerably from that of the extrudate obtained

from it.

With complicated profile dies it may be necessary to

incorporate small adjustable restrictor bars in the die

to control the melt flow through certain areas. A

suggested design for a profile die is shown in

Figure 66.

Care is necessary to avoid distortion of the section

and the use of a cooling formers is recommended.

With elaborate profiles, embossing with a light

diffusing pattern may be required on the outer

Figure 66 Profile die for acrylic lighting diffuser.

surface of the base of the profile. This can readily

be done by means of a two-roll system. In order to

move past the embossing mechanism, some

patterns and shapes may require slight outward

displacement of the sides of the profile, while the

material is still hot and pliable near the die. The

sides are then immediately returned to the desired

final position by means of sizing plates.

Two-colour profiles for lighting fittings can also be

produced by using a specially designed die coupled

to two extruders. With this technique, opal and clear

materials are commonly used. Normally a smaller

extruder produces completely opal sides as the

larger machine produces the clear base.

Alternatively the smaller machine can simply lay an

opal film on to the clear sides. Die design is

complicated for two-colour extrusion and it is

advisable that a die be obtained from an

experienced manufacturer of this type of equipment.

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sizing bush submerged in hot water at 70°C to

which a variable vacuum may be applied. In order

to effect a satisfactory seal at the entrance to the

vacuum bath a die diameter 20-25% greater than

the sizing die diameter has been found necessary.

The diameter of the sizing die should equal the

diameter of the required tube size plus an

allowance for shrinkage on cooling. A typical

shrinkage allowance for a wall thickness of 5 mm

would be 1.7% and for a 1 mm wall 1.2%.

Typical line speeds for tubes produced by this

technique would be 1-2 metres/minute.

Suggested processing temperatures for tube are

similar to those given for lighting diffusers in Table 13.

Die Design

A typical die design for acrylic tube is shown in

Figure 67. The die should be fully streamlined and

should be chrome plated to minimise any tendency

to sticking. Alternatively a hard tool steel,highly

polished, may be used.

The high melt viscosity of acrylic can lead to

memory lines from the arms of the torpedo carrier.

To reduce this tendency die land lengths up to 20

times the wall thickness and compression ratios

(areas between arms of torpedo carrier to die

annulus) up to 15:1 are recommended.

TUBE EXTRUSION

In common with other thermoplastics the sizing

methods used for tube production may also be

successfully used with Lucite Diakon. The two most

common methods use either internal air pressure with

external sizing plates or an externally applied vacuum

through a sizing bush fully immersed in water.

Internal Air Pressure

This technique can be used for tube sizes up to 75

mm diameter. The air pressure, which should be

accurately controlled, is quite low (100-150 mm of

water). To maintain the internal air pressure an end

plug or a floating plug is commonly used. The

external diameter is maintained by sizing plates and

cooling in hot water (70°C) for tube sizes up to 30

mm or gentle air cooling for larger diameters up to

75 mm where excessive buoyancy in water could

lead to uneven cooling. Slow cooling is essential to

eliminate residual stresses which otherwise could

lead to failure in service. Line speeds using this

technique tend to be slower than for the water-

cooled vacuum system.

To allow for the melt swell of material as it leaves

the die it is normal for the diameter of the die to be

approximately 5% less than the diameter of the

sizing system.

Water Cooled Vacuum System

This is a widely used method for tube extrusion up

to 150 mm diameter and utilises a perforated brass Figure 67 Die for acrylic tube

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FABRICATION OF SHEET EXTRUDED FROM

LUCITE DIAKON

Sheet extruded from Lucite Diakon can be shaped

by vacuum forming and other conventional shaping

techniques.

Shaping temperatures in the range 150-190°C are

normally used. With vacuum forming it is advisable

to heat the sheet on both sides simultaneously. For

conventional shaping the sheet can be heated in

circulating air or infra-red ovens. Sheet extruded

from MH254 is shaped at the higher end of the

temperature range.

In common with other types of extruded sheet

Lucite Diakon extruded sheet will shrink on heating.

The degree of shrinkage depends upon the

processing conditions, thickness and equipment

used. If the sheet is pre-heated in the unclamped

state in an oven before transferring to a clamping

jig for shaping, allowance must be made for

shrinkage but if the sheet is clamped in a

framework before pre-heating, as in vacuum

forming, no shrinkage allowance is generally

necessary.

Extruded acrylic sheet readily absorbs moisture

from the atmosphere. If pre-heated too rapidly

before shaping, absorbed moisture can produce

small bubbles within the sheet resembling those

formed when the material is overheated. In vacuum

forming, heating rates are generally rapid and

consequently it is essential with this process to use

sheet with a low moisture content. Care should

therefore be taken to minimise moisture uptake

before shaping, either by using the sheet

immediately after extrusion or by storing under

conditions which will reduce moisture absorption.

Packing the sheet in polyethylene film will slow

down the rate of moisture absorption but will not act

as a permanent moisture proof barrier.

If surface bubbling occurs when the sheet is heated

and before it is soft enough to give the required

definition, the moisture content is too high or the

heat too intense. The moisture content can be

reduced by pre-drying the sheets in an air

circulating oven at 70-80°C, and this can

conveniently be done overnight. For effective drying

the sheets should be separated to allow the hot air

to circulate between them.

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Fault Probable cause Remedy

Bubbled extrudate 1 Wet material Dry material in oven/use vented extruder

2 Blocked vent Clean vent and pipework

3 Output too high for extruder Reduce screw speed

4 Overheating Reduce operating temperatures

Surface streaks 1 Wet material Dry material in oven/use vented extruder

2 Blocked vent Clean vent and pipework

3 Output too high Reduce screw speed

4 Contamination in die Clean die or purge

5 Entrapped air Change extrusion conditions or screw design

Die lines 1 Imperfections on die lips Polish or replace die lips

Rough surface 1 Too low die temperature Increase die temperature

2 Too low polishing roll temperatures Increase polishing roll temperature

3 Too low melt temperature Increase melt temperature

4 Poor roll finish Polish rolls

Surface craters 1 Ineffective polishing Increase roll temperature and pressure

Poor colour of extrudate 1 Hold-up in extruder Ensure no dead spots, particularly in vent region

2 Contamination Ensure material and machine are clean

Variation of shape 1 Temperature fluctuation in Check temperature control

extruder or die Modify die design

2 Uneven flow through die Reduce output rate

3 Irregular extruder output Adjust feed zone temperature

Check voltage supply

4 Irregular haul off Check haul off for slip or speed variation

5 Partially blocked screw Purge through with rework

Fold marks (‘chevron’ marks)1 Uneven flow through die Modify die design or adjust flow through die with restrictor bar

Unpolished areas (‘lakes’) 1 Uneven flow through die Adjust flow through die with restrictor bar

Excessive orientation 1 Linear sheet speed too slow Increase output of complete line

2 Polishing pressure too high Reduce polishing pressure

3 Line tension too high Reduce tension between polishing rolls and pull rolls

4 Draw-down too high Reduce draw-down

5 Roll temperature too low Increase roll temperature

Poor embossing 1 Melt too viscous Increase melt temperature

2 Rolls too cold Increase roll temperatures

3 Insufficient polishing pressure Increase pressure on rolls

4 Excessive tension Reduce tension between polishing rolls and pull rolls.

EXTRUSION FAULT REMEDIES

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Standard high speed wood working routers are used

for machining Lucite Diakon. Spindle speeds of

15,000-20,000 rpm are recommended and again,

adequate cooling must be applied to both tool and

work.

Grinding

Parts may be ground with an abrasive disc rotating

at about 3,000 rpm for a 25 cm diameter disc. A

sanding belt may also be used at a speed of about

350 m/min.

These are dry sanding operations and the pressure

must be judged so as to avoid overheating.

It should be noted that the above machining

methods will leave a rough machined edge. If more

exact finishing is required then the roughly

machined edges should be removed by a

subsequent buffing operation.

Buffing

After rough machining, the parts may be polished

using a mechanically driven calico buff. These buffs

are usually 15-35 cm in diameter and are

maintained at a running speed of about 1,400 rpm.

Higher speeds are not recommended since they

may cause overheating of the surface.

The polishing operation requires a compromise

between the speed of the buff and pressure applied

and this must be judged by the operator. It is usual

to apply to the mop a wax dressing containing a

mild abrasive such as Kieselgühr or rouge. A final

cleaning may be given on a swansdown mop with

no wax dressing, but this is not always necessary.

Buffing will cause the acrylic surface to become

stressed and it is therefore essential, in applications

where the parts come into contact with active

solvents, eg decorating or cementing, that the

samples are annealed before further use.

FINISHING, COLOURING AND DECORATING

MACHINING

Components produced from Lucite Diakon may be

finished by simple machining operations such as

sawing and drilling.

Band Saw

Fine-toothed band saws, as used for light metals,

operating at a speed of approximately 1500 m/min

are suitable for cutting Lucite Diakon. For

thicknesses up to 3 mm, blades having 6-8 teeth

per cm should be used. Above 3 mm, up to 12 mm,

blades should have 4-5 teeth per cm. Saw blade

guides should be kept as close together as possible

to prevent blade twisting.

Circular Saw

A Tungsten Carbide tipped circular saw blade with 1 to

2 teeth per cm running at 3000 m/min may be used.

Laser Cutting/De-Gating

Sprue and gates can be effectively removed from

mouldings using Carbon Dioxide laser techniques.

Although expensive, the laser can be accurately

programmed to remove gates and sprues from a

wide range of parts from thick section to

complicated shapes. The main benefit of laser de-

gating is that it leaves no witness mark and no extra

finishing or polishing is required.

To maximise the performance benefit of the laser it

requires accurate location and alignment of

components. This is best achieved using a jig in

combination with a pick and place robot. There are

also certain associated SHE requirements to

consider when working with Carbon Dioxide lasers

which are best covered using automative handling

and appropriate guarding.

Milling and Routing

Milling tools with wide pitch, no front rake and

adequate back clearance are recommended. It is

important to clear away swarf from the work and

cool with copious quantities of soluble oil, coolant

mist or air.

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Drilling

For drilling Lucite Diakon components, it is important

to avoid overheating and it is essential that the swarf

is cleared frequently so that binding does not occur.

Full support must be provided on the underside of

the work which should be clamped or suitably jigged.

Drills should be ground as illustrated in Figure 68.

The important requirements are:

No rake;

A clearance angle of about 15°

The margin between the two cutting faces should

be as small as possible;

The included angle should be obtuse

To produce accurate stress-free holes it is vital to use

an efficient cooling system. Cooling may be of the

soluble cutting-oil type but a strong air jet is equally

effective and avoids the need for a subsequent

cleaning operation. Larger holes can be cut with fly

cutters and trepanning tools with no rake and

adequate back clearance.

Hot Knife

This technique may be used when removing edge or

diaphragm gates from injection mouldings. The

apparatus consists of a knife edge or cutting tool

electrically heated and mounted on a drill-press (see

Figure 69). It is usual to mount the cutting tool on a

block of metal, the temperature of which is

maintained by a band or cartridge heater. The

temperature of the knife should be regulated so that

a clean cut is obtained when the gate is trimmed off.

If the knife is too cold the surface of the moulding will

show a smear mark; if the knife is too hot then the

surface of the moulding will show a bubbled

appearance.

DTM/E/2Ed/Nov01

Figure 68 Design of twist drill

Figure 69 De-gating with a hot knife

CEMENTS AND ADHESIVES

Components made from Lucite Diakon can be

bonded to other acrylics using acrylic cements. A

range of ‘Tensol’ cements and ‘Evo-plas’ adhesives

is produced and supplied by Evode Speciality

Adhesives Ltd, to whom all enquiries should be

directed. These acrylic cements can also be used to

join Lucite Diakon to other materials. However,

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alternative adhesive systems are more suitable in certain

cases, see below. The physical strength, and resultant

appearance of the joint will vary with the type of adhesive

used, and careful consideration should be given to

deciding which adhesive is appropriate for a particular

application.

Preparation of Contact Surfaces

Lucite Diakon should be degreased, if necessary, prior to

application of cements, to ensure a good surface bond.

Antistatic agents should not be used prior to cementing

operations. The best bond strengths are obtained if gloss

surfaces have been lightly abraded with fine emery cloth

before application of cement.

Annealing

It is recommended that components to be cemented are

annealed prior to the application of any cements to

reduce strain induced by moulding, extrusion, machining

or forming operations. Such strain may promote crazing

or cracking in the area of the bond.

Please refer to the section on Stresses and Molecular

Orientation in Lucite Diakon Components on page 72 for

information on causes, problems, testing and remedies.

Bonding

The following text has been reproduced by agreement

with Evode Speciality Adhesives Ltd:

“The correct selection of adhesive is vital in order to

produce bonds with good strength, durability and optical

clarity.

Edge Bonding

Solvent welding is the quickest and easiest way of

forming edge bonds. The best results can be easily and

safely achieved when ‘Etru-Fix’/’Tensol’ 12 are applied

using the appropriate ‘Evo-plas’ application kit. Features

of this system - which is intended for indoor applications -

include high clarity and bubble-free bonds. Filled systems

such as ‘Tensol’ 12 offer slightly better gap filling

properties.

For external applications, a highly durable adhesive such

as ‘Tensol’ 70 is required.

Bonding to Other Substrates (metal, wood, glass etc)

The easiest way to bond Lucite Diakon to other

substrates is by using a cyanoacrylate adhesive. ‘Evo-

Plas’ TC 731, with its low bloom and special adhesion

promoter system is suggested. As well as being useful

for bonding small areas of Lucite Diakon to Lucite

Diakon, this system is also suitable for attaching fittings

to Lucite Diakon.

Where there are high mechanical strength requirements,

then a toughened acrylic adhesive, such as ‘Evo-plas’ TA

431, is to be preferred.

Sealing

Joints in Lucite Diakon and a variety of other materials can

be effectively sealed with a suitable, acrylic compatible

silicone sealant. In order to avoid stress-crazing, the

sealant needs to be neutral cure. A low modulus type,

such as ‘Evo-plas’ Low Modulus Silicone Sealant will best

accommodate any movement in/between the components.

The ‘Evo-Plas’ range of adhesives, cleaning solvents and

Antistatic cleaner is available from most ‘Perspex’

stockists and distributors. Alternatively please contact

Evode Speciality Adhesives Ltd directly” (on +44 (0) 116

232 2922) - see Appendix II for full address.

Before cementing, the user should study the Safety Data

Sheets and ensure that the adhesive is suitable for the

intended application.

ULTRASONIC ASSEMBLY

Ultrasonic welding

This technique offers a quick, clean and efficient method

of joining two components produced from the same

material. Dissimilar materials with a few degrees

difference in melting point is sufficient to allow one

material to melt without allowing the other to achieve its

melting point, preventing a good joint between the parts.

Ultrasonic welding may be divided into two basic types of

operation:

Contact or near field welding where the probe is as

near to the joint area as possible.

Transmission, remote or far-field welding. In this

operation the transmission properties of the rigid

material are used to obtain a weld remote from the

probe.

Both techniques may be used with Lucite Diakon

although contact welding is the better of the two. Contact

welding is the only sure method of producing a water-

tight seal,

DTM/E/2Ed/Nov01

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but here a probe must be used which surrounds the

article so that the complete weld is made at the

same instant. Due to power output limitations, only

small mouldings may be sealed in this manner. For

larger components a ‘spot welding’ principle has to

be adopted and it is not then possible to guarantee

water-tight seals.

It should be noted that during welding there is likely

to be some evidence on the component surface of

the positioning of the probe. Where required the

welding should be carried out on the rear surface of

the component.

Joint Design

Joint design is important with ultrasonic welding.

The main factor to bear in mind is to have a small

contact area which concentrates the applied

vibration energy and permits a rapid development

of melt.

Figures 70 and 71 show the design of joints related

to the strength of the weld.

Figure 70 Joint designs comparing the weld

strengths of different configurations

Figure 72 Ultrasonic staking

Figure 71 Joint designs showing requirements for

improved joint strength.

Figure 73 Ultrasonic insertion

Ultrasonic Staking

Ultrasonic staking or riveting is a technique for either

joining metal plates to a Lucite Diakon component or

a Lucite Diakon component to a metal assembly.

The final shape of the stake head will depend upon

the shape of the horn. Figure 72 illustrates a

conventional stake before and after assembly.

Ultrasonic Insertion

This technique for inserting and encapsulating shaped

metal inserts, commonly brass, into slightly smaller

holes in Lucite Diakon mouldings is an effective

alternative to the conventional method of placing

inserts into the mould before moulding. (Figure 73)

Ultrasonic assembly results in the introduction of

localised stress and it is recommended that

components be annealed if this stress is likely to

have a significant effect on component

performance. Refer to section on Stresses and

Molecular Orientation in Lucite Diakon Components

on page 72.

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HOT SURFACE WELDING

The principle of this method of joining one

component to another is to melt the surfaces to be

mated. It allows dissimilar but melt compatible

materials to be welded. Hot surface welding is

divided into two basic categories:

Hot Plate Welding

Components are placed in tool rests and then

brought into contact with a hot plate which may be

flat or profiled. After a pre-set time the components

withdraw, the plate retracts out of the way and the

components are then brought together under light

pressure and allowed to cool. A typical cycle time is

20 seconds.

Accurate temperature control and time of contact

with the hot plate are important as under or over

heated surfaces will produce poor or untidy welds.

This technique is commonly used for jointing Lucite

Diakon multicoloured rearlight lenses to their ABS

reflector backs where the lens is designed with a

rim to hide the weld.

Hot Punch Welding

The assembled components are positioned under a

heated punch which is lowered on to the top

component. The heat from the punch melts

localised areas of the top component which fuses

itself to the base component. This technique is

commonly used for welding a flange-edged

component and a flat surface together.

Joints made by hot surface welding are usually

highly strained and it is recommended that

components be annealed after welding to improve

component performance. Refer to section following

on Stresses and Molecular Orientation in Lucite

Diakon Components.

STRESSES AND MOLECULAR ORIENTATION IN

LUCITE DIAKON COMPONENTS

Assessment of quenching stress and molecular

orientation in Lucite Diakon articles may be used to

predict their performance in service. Such means of

appraisal give the producer early guidance on

component quality and help to maintain a high

production efficiency of acceptable parts, so as to

avoid problems of crazing or of cracking which

might otherwise arise during subsequent

decoration, or when the parts are in service.

Because of the high transparency of most

components made from Lucite Diakon, a rapid,

visual method of assessing stress can be

conveniently applied to end products. This method

gives a simple, inexpensive technique for a

preliminary assessment of the quality of

components. In addition, immersion testing in an

active liquid can also prove very useful.

During processing a range of molecular

deformations occur. For the sake of simplicity only

two extreme types of deformation, corresponding to

molecular orientation and to quenching stress, are

considered here.

The first, molecular orientation, results from partial

alignment of polymer molecules, when forced, in

the melt state, into the required shape. The regions

where this is chiefly apparent are at the gate on

injection moulding (where melt under pressure

continues to enter the mould while the moulding is

cooling and contracting) and in thin sections.

The second, quenching stress, results from

differential cooling of the polymer melt. Quenching

stress will also result from any subsequent

operation which introduces localised melting as for

example hot plate welding and hot foil stamping.

Quenching stress is also introduced during any

subsequent machining operations due to localised

frictional heating.

Molecular Orientation

Orientation affects the strength of a component.

Components are stronger when flexed

perpendicular to the molecular orientation and

weaker when flexed parallel to this direction. An

unorientated component would be equally strong

when flexed in either direction.

Orientation gives a lower solvent crazing and stress

cracking resistance. This is particularly relevant to

applications involving the cementing, lacquering or

printing of components.

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Quenching Stress

High quenching stresses give rise to cracking when

the component comes into contact with active

liquids, usually solvents in the case of acrylics. The

cracks occur parallel to the principal orientation

direction and perpendicular to the direction of the

stress in the absence of orientation.

In moulding, if the stresses are high enough,

cracking can occur in the absence of solvents either

on, or some time after, removal from the mould.

Although the effects of stress and of orientation are

referred to separately above, they both act

simultaneously in components.

Assessment of Stress by Simple Methods

Stresses and molecular orientation are

simultaneously introduced during the injection

moulding process. Stresses arise due to restricted

volume contraction and differential cooling between

surface and middle layers, or between different

parts of mouldings, as the melt cools and solidifies

in the mould.

Molecular orientation is produced as material flows

through the gate and through other small cross-

sections in the moulding. The long-chain polymer

molecules become orientated (lined-up) in the flow

direction under the influence of shearing forces.

They are ‘frozen’ in position, particularly in the gate

area, as the moulding cools and solidifies.

This uniaxial type of orientation in the gate area

gradually changes to a more biaxial or planar type

of orientation as polymer flows sideways as well as

forward away from the gate. Corresponding types of

uniaxial and biaxial quenching stresses are also

‘moulded-in’.

The levels of ‘moulded-in’ stresses and orientation

are governed by the moulding conditions used. It

has been found that, in general, mouldings with the

lowest stresses and orientation are produced when

high mould and melt temperatures and fast injection

rates are used. To produce consistent quality

mouldings, once the right conditions have been

established, control of mould temperature is

essential.

‘Moulded-in’ quenching stresses can be largely

removed by annealing (see following section on

annealing procedures). Orientation levels are

substantially unaffected by annealing except at

temperatures very near the softening point of the

material, when large shrinkages and distortions

occur.

A rough guide to the levels of stress and orientation

can be obtained by means of two simple tests.

Observation of Mouldings Under the Strain

Viewer

Transparent moulded parts are viewed between a

pair of crossed ‘Polaroid1* filters, preferably

mounted above an opal light-diffusing background.

Localised colour fringe patterns indicate areas of

high stress and orientation. A completely stress and

orientation-free moulding would appear black when

rotated in the plane of the filters and when tilted.

The level of stress and orientation increases in

order of the colours, black, grey, white, yellow, red,

blue to pink and green. The colour seen also

depends on the thickness of the article, the thicker

the section the higher the colour seen for a given

stress and orientation level. It is only safe to judge

the differences between mouldings of a particular

article made under different conditions, although

broad distinctions can be made between different

articles where a ‘good’ moulding has low levels of

stress and orientation, while a ‘bad’ moulding has

high levels of stress and orientation.

Figure 74 is an example of the effect seen in

practice and shows the patterns in a simple side-

gated disc moulding made under a range of

moulding conditions.

Observations of the patterns before and after

annealing can give some idea of the relative

amounts of ‘moulded-in’ stresses and orientation.

A big change in the order of colour, or extent of

pattern on annealing, shows the presence of high

‘moulded-in’ stresses. A small change (or no

change) shows that the colours are largely due to

molecular orientation.

1* Registered trade mark of Polaroid

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Figure 74 The effect of moulding conditions on

‘moulded-in’ stress when viewed through

crossed ‘Polaroid’ filters

Top left: Low cylinder temperature, low mould

temperature

Top right: High cylinder temperature, low mould

temperature

Bottom Low cylinder temperature, high mould

left: temperature

Bottom High cylinder temperature, high mould

right: temperature

Figure 75 Electrical component injection-moulded

from Lucite Diakon and tested by solvent

immersion

Left: Not annealed;

Right: Annealed

Solvent Immersion Test

This is an accelerated crazing test and has the

advantage that coloured and opaque as well as

clear articles can be examined, although the

amount of information obtained is restricted. The

presence of high ‘moulded-in’ stresses is readily

shown by dipping a moulding in a suitable solvent

such as isopropanol and observing any cracking or

crazing which occurs. Immersion in isopropanol for

3 minutes at room temperature followed by draining

and air drying for 60 minutes is a suitable test. An

example is shown in Figure 75. Rapid cracking,

particularly if accompanied by coloured fringes

when viewed through crossed ‘Polaroid’ filters,

should be taken as a warning that improvement in

component quality is desirable in order to ensure

satisfactory, long term performance under normal

use conditions. If the quality of the moulding cannot

be significantly improved by adjustment to moulding

conditions then it is recommended the moulding is

annealed prior to use.

Annealing Procedures

It has been found that annealing temperatures of

82°C for Lucite Diakon type 8 mouldings and 70°C

for Lucite Diakon types 6 and 7 mouldings are

generally sufficient to relax away ‘moulded-in’

stresses without any large changes in orientation or

any significant dimensional changes occurring.

Higher temperatures may be used with shorter

times providing the shape of the article gives

additional dimensional stability and providing that

some shrinkage, particularly in the gate area, can

be permitted in the application. The limits for a

particular article should be found by experiment.

The time required at a particular annealing

temperature will depend on the thickest section

present in the moulding. By setting up an annealed

reference sample for each particular type of

moulding the application of correct annealing

conditions to subsequent mouldings can be

checked.

The annealing process should be carried out in an

oven provided with efficient air circulation and care

must be taken to ensure air circulation around each

part. Mouldings to be annealed should be clean and

dry and should be supported so that they are not

under stress during the annealing process.

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As an initial guide to the conditions required for the

annealing, it is suggested that most sections

moulded from Lucite Diakon type 8 materials can

be annealed by heating for 2 hours at 80-84°C

followed by cooling at a rate of 45°C per hour,

ie 11/2 hours cooling time. Thick sections will require

longer annealing and slower cooling, eg a 5 mm

section will require 4 hours annealing followed by

cooling at a rate of 30°C per hour, ie 2 hours

cooling time. For mouldings made from Lucite

Diakon types 6 and 7 the annealing temperature

should be 68-72°C, and the cooling rate about 35°C

per hour for thin mouldings and 25°C for thicker

mouldings. A controlled rate of cooling is important

as shock cooling, hot oven to cold air, will

reintroduce quenching stress. If the oven cannot be

set to a controlled rate of cooling it is common

practice to switch the oven heating off after the heat

treatment stage and to allow the oven plus contents

to cool to just above room temperature before

removing the mouldings.

Effect of Molecular Weight

Where crazing problems arise in moulding, or

subsequent treatment and handling which cannot

be easily overcome using Lucite Diakon CMG and

CLG, the higher molecular weight Lucite Diakon

CMH and CLH grades are recommended. The

improved mechanical properties of Lucite Diakon

CMH and CLH coupled with superior craze

resistance may be utilised to overcome difficulties

with intermediate cementing and decorating

operations, and for applications where some stress

is applied to the moulding in use.

Influence of Moulding Conditions, Mould and

Component Design

Mouldings with the lowest levels of stress and

orientation are produced using high mould

temperatures, high melt temperatures, maximum

injection rates, and low injection pressures.

Mouldings showing the most severe strains and

highest orientation levels are produced using low

mould and melt temperatures, slow injection rates

and high injection pressures.

The service life of Lucite Diakon components can

be greatly improved if care is taken at the

component and mould design stage.

Sharp corners and sudden changes in section

should be avoided because they give rise to stress

concentrations (notches) which can lead to

premature failure. Flow in long thin sections

requiring the use of high injection pressure should

be avoided. Strength and rigidity is improved by

increasing the thickness in areas of high stress

concentration. Moulded-in metal inserts are not

recommended due to the high stress introduced by

shrinkage around the insert. Care should be taken

with moulded-in holes or slots for the same reason

but a slight taper on highly polished pins can

alleviate the problem. Holes or slots produced by

machining operations create stresses which it may

be necessary to remove by annealing. Weld lines

are areas of weakness and should be avoided in

mouldings subject to high stress concentrations in

service. When mouldings have to be cemented

together the mating halves should not be a tight fit

as this will stress the parts leading to crazing and

cracking when cement is applied.

Moulds for Lucite Diakon should have highly

polished cavities, runners and gates to enable the

material to flow smoothly without interruption into

the cavities. The sprue, runners and gates should

also be kept as short as possible and be of

adequate cross-section to enable the cavities to be

filled without having to apply excessive injection or

hold-on pressures, which cause packing stress. Full

round runners generally give the best results. As

maximum levels of stress and orientation usually

occur round the gate area, the position of the gate

and its size are important. Although design of

components often determines where a gate should

be placed, it is good practice to place the gate at

the thickest portion of the moulding wherever

possible and to make it of as large a cross-section

as possible.

Heating and cooling channels incorporated in the

mould should be placed so that constant controlled

mould temperatures can be maintained.

Intelligent anticipation of possible difficulties and

appropriate attention to component design, gate

position and ease of injection are well repaid by

avoidance of stress-induced problems in

subsequent service.

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CLEANING

Lucite Diakon components may be cleaned by

washing with mild soap or detergent in warm water

using a clean soft cloth or cotton wool. Inaccessible

corners may be cleaned with, or stubborn stains

removed by, the use of a soft brush. Scouring

powders should not be used as they will mar the

surface.

Organic cleaning agents such as acetone and paint

remover must not be used as they attack Lucite

Diakon components.

Light scratches and small surface blemishes may

be removed by hand polishing using proprietary

metal polish with a clean soft cloth or cotton wool.

ANTISTATIC TREATMENT

All grades of Lucite Diakon have good electrical

insulating properties and become electrostatically

charged during fabrication and handling thereby

attracting dust particles to the surface. Normal

dusting with a cloth will only reinforce the charge

and attract more dust.

The solution to this problem is to make the Lucite

Diakon surface conducting so that static electricity

can be discharged. This can be achieved by

washing with water but obviously this dries rapidly

and the effect is not permanent. A surface film of

moisture may however be maintained by the

application to the surface of a substance for which

water has an affinity, ie a suitable antistatic agent.

The most efficient are quaternary ammonium

compounds because they are effective even under

very dry conditions since they are themselves

conducting and can remain effective for some time

if they are undisturbed. However it must be noted

that these compounds and solutions should not be

used in applications involving contact with

foodstuffs.

Lucite Diakon components can be treated with

antistatic solution on removal from the mould, by

dipping in the solution, suspending and allowing to

drain and dry. This can result in runs and tide marks

and where this is unacceptable, for instance with

automotive instrument facia lenses, the antistatic

solution is applied by controlled spraying.

AUTOMOTIVE SIGNAL LAMP LENS COLOURS

The colours of acrylic material used in the production

of automotive signal lamp lenses have to comply with

international colour specifications ie SAE J578. The

various designs and production techniques for signal

lamp lenses has led to the requirement for a range of

amber, red and neutral colours. Table 14 lists the light

transmission (Y) and colour coordinates (x and y) for

the major 3 mm standard Lucite Diakon Amber and

Red colours while figures 76 to 80 give light

transmission and colour co-ordinates against thickness

for the major range of Lucite Diakon amber and red

signal lamp colours. These colours, when used at a

lens thickness falling between the SAE and ECE limits

in relation to each of the colours, are approved in

Lucite Diakon CM grades against SAE J576..

The neutral colours used for styling considerations are

often a mixture of 3 dyes and therefore the range of

colours is quite large. Apart from visual hue acceptance

the main requirement is light transmission. Figure 81

illustrates a series of commonly used neutrals based

on Lucite Diakon Neutral 9321.

DTM/E/2Ed/Nov01

Amber Series Y x y

310 69.2 0.5700 0.4280

311 65.3 0.5795 0.4190

312 63.0 0.5850 0.4135

316 57.8 0.5975 0.4010

319 60.5 0.5910 0.4070

Red 405 Series Y x y

405 22.3 0.6825 0.3165

413 18.2 0.6920 0.3070

415 24.4 0.6780 0.3215

416 18.7 0.6910 0.3085

418 31.1 0.6610 0.3370

419 28.7 0.6675 0.3310

422 20.6 0.6865 0.3130

4088 26.8 0.6720 0.3270

Red 425 Series Y x y

425 22.0 0.6825 0.3165

433 17.7 0.6920 0.3070

435 24.0 0.6780 0.3215

436 18.2 0.6910 0.3085

438 31.1 0.6610 0.3385

439 28.5 0.6675 0.3320

442 20.2 0.6865 0.3130

428 26.6 0.6720 0.3270

Table 14 Light transmission (Y) and colour

coordinates (x,y) for 3 mm standard

Lucite Diakon Amber and Red

Colours. (‘Spectraflash’ 500,

Illuminant A, CIE 1931 2° observer)

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Figure 76 Lucite Diakon Automotive Colours: Amber 1-5mm: Light transmission versus thickness

Figure 77 Lucite Diakon Automotive Colours: Amber 1-5mm: Chromaticity coordinates

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Figure 78 Lucite Diakon Automotive Colours: Red 405 series 1-5mm: Light transmission versus thickness

Figure 79 Lucite Diakon Automotive Colours: Red 425 series 1-5mm: Light transmission versus thickness

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Figure 80 Lucite Diakon Automotive Colours: Red 1-5mm: Chromaticity coordinates

Figure 81 Lucite Diakon neutrals based on Neutral 9321 type formulation

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page 80

DECORATION OF LUCITE DIAKON

The combination of high surface gloss, superb clarity,

good abrasion resistance and excellent weatherability

makes Lucite Diakon an ideally suitable material for

the production of decorated components such as

medallions, insignia, metallised bezels, tap handles

and signs.

It is essential that all the precautions advised are

followed because decoration can be an expensive

operation and the recovery of faulty decorated parts is

difficult or impossible.

Preparation

All the decorating processes mentioned in this section

involve the surface treatment of moulded or extruded

parts. It is therefore essential that the parts are

produced under clean, dry, grease-free conditions.

Moulds must be free from oil contamination, especially

around ejector pins and moving cores. Generous

tapers should be allowed on all surfaces in the line of

draw to reduce the need for mould lubricants.

Silicone-based mould release agents must be avoided

since these cause surface blemishes and loss of

adhesion. When handling components, lint-free cotton

gloves should be worn to avoid fingermarks.

Antistatic agents in the form of aqueous solutions may

be used but care must be taken to ensure that the

film of antistatic agent is dry before decorating or poor

results will be obtained. Although antistatic solutions

prevent dust from being attracted to the component,

they will not prevent gravitational deposition of dust.

When mouldings are to be decorated with more than

one colour it is usually necessary to use one or more

masks. In order to obtain fine definition between

colours, the masks have to be made to fine tolerances.

Consequently the dimensions of the moulding must be

controlled to equally fine limits, and all the principal

moulding variables must therefore be controlled

accurately to ensure dimensional consistency.

Many of the lacquers used for decorating Lucite

Diakon components contain active solvents which will

produce surface crazing or cracking if undue levels of

stress are present. Attention should be paid to the

section on Stresses and Molecular Orientation in

Lucite Diakon Components on page 72.

It is recommended that all components subjected to a

decorating process containing active solvents are

annealed before decorating. All machining, polishing,

hot foil stamping and ultrasonic assembly operations

which are likely to introduce stress should be carried

out before annealing.

Decorating Processes

Either a first (front) or second (back) surface coating

technique may be used for Lucite Diakon. Second

surface decoration is more commonly used because

the high transparency of Lucite Diakon makes it

possible to achieve a wide variety of attractive effects.

The coating is protected by the Lucite Diakon against

deterioration from weathering and abrasion.

Lacquering and Spray Painting

These techniques may be used with Lucite Diakon

and are normally associated with the 3-dimensional

decoration of intricate components where silk-screen

printing cannot be used. Typical examples are

medallions, insignia and thermoformed display signs.

Silk-screen Printing

This is a widely practised technique, ideally suited to

flat acrylic sheet although mouldings with flat surfaces

such as radio scales also lend themselves to this

process. It is particularly adaptable for multi-colour

decorating by successive screening operations with a

series of different screens.

Hot Foil Stamping

This process involves the hot blocking of characters

on to the surface of a component. An electrically

heated metal die of the required design is pressed on

to a stamping foil, the coated side of which is in

contact with the object to be decorated. The hot die

melts the coating, releases it from the foil backing,

and bonds it to the object. Thus, light engraving and

colour filling are achieved in one operation.

Raised lettering on mouldings may be foil stamped by

replacing the metal die with a sheet of aluminium

faced with a sheet of silicone rubber. The flexibility of

the silicone rubber allows for the slight change in

thickness which may occur with some mouldings,

such as rulers, when end gated.

With hot foil stamping it is usually unnecessary to

anneal mouldings as no solvent systems are involved.

DTM/E/2Ed/Nov01

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However localised stress introduced during hot foil

stamping by slight distortion and rapid change in

temperature of the surface may cause cracking or

crazing if any further decoration is carried out by a

solvent-based technique. This can be eliminated by

using the recommended annealing procedure after

the hot foil stamping operation.

Vacuum Metallising

This technique is used to impart a metallic or

mirror-like appearance to the moulded component.

The metal used (commonly aluminium) is deposited

on to the surface by evaporation under high

vacuum using specialised equipment. Gilt and other

coloured metallic effects may be obtained by using

precoloured Lucite Diakon or by spraying the back

of the moulding with a tinted lacquer and then

metallising with aluminium.

Before metallising, it is advisable to spray the

moulding with a base coat. Apart from improving

adhesion between the moulding and the metal

coating, the base coat also acts as a smoothing

coat on those mouldings which do not have a high

surface finish.

First surface coating

The preferred sequence of operation is:

Spraying with base-coat on to the top surface;

Vacuum deposition of the metal coating;

Spraying with a clear top-coat to protect the

metallised coating from damage by abrasion.

Second surface coating

Here the preferred sequence is:

Spraying the reverse side of the moulding with a

clear base coat;

Vacuum deposition of the metal coating;

Spraying with a back-coat to protect the

metallised coating.

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HEALTH, SAFETY AND ENVIRONMENTAL

ASPECTS OF LUCITE DIAKON

It is advisable during the design stage of a

component and certainly before processing any

Lucite Diakon grade, as it is a legal requirement in

the European Union, to obtain the relevant Material

Safety Data Sheet and to be fully conversant with

its contents before proceeding.

Therefore when purchasing any grade of Lucite

Diakon a Material Safety Data Sheet (MSDS) must

be obtained for each Lucite Diakon grade. These

Material Safety Data Sheets will be supplied by the

local Lucite International sales office or by the local

Lucite International appointed distributor or agent.

The Lucite Diakon Material Safety Data Sheets

(MSDS) do not include advice on the suitability of

the Lucite Diakon grades for applications, nor any

precautions that may be necessary during the use

in service of any product made from Lucite Diakon.

However certain individual statements can be made

available upon request regarding the compositional

compliance of various Lucite Diakon grades with

respect to national regulations, for example those

for food contact.

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APPENDICES

APPENDIX I

ACRYLIC SPECIFICATIONS

ASTM D 788-96

Acrylic moulding and extrusion materials are

classified according the heat deflection temperature

(HDT) of the material tested to ASTM D 648-96,

sample annealed to ASTM D 788-96.

HDT Type

79°C and below 5

80-86°C 6

87°C and above 8

LUCITE DIAKON GRADE CLASSIFICATION

Specification CLG340 CLG356 CLG960 CLG902 CMG302 CMG314V CLH952 CMH454 CMH454L

LG156 LG702 MG102 LH752 MH254

ASTM D 788 6 6 6 8 8 8 8 8 8

DIN 7745 92-53 92-53 92-53 100-53 108-53 116-53 108-73 108-73 116-73

Code 1 Vicat Softening Point

VST/B/50 (°C)

84 80-88

92 88-96

100 96-104

108 104-112

116 112-120

Code 2 Viscosity Number

(cm3/g)

53 48-58

63 58-68

73 68-78

83 78-88

93 88-98

103 98-108

DIN 7745

This specification classifies acrylic moulding

materials according to Vicat softening point

(VST/D-50) (code 1) and viscosity number (code 2)

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APPENDIX II

ADDRESSES

Evode Speciality Adhesives Ltd

Anglo House

Scudamore Road

Leicester

LE3 1UQ

Tel: 0116 232 2922

Fax: 0116 232 2933

Plastic Design Solutions Ltd

80 Church Road

Stockton on Tees

TS18 1TW

Tel: 01642 671711

Fax: 01642 671762

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Equipment (RPE) is used to ensure that worker

exposure is maintained below the relevant

Occupational Exposure Levels. In practice respecting

the Occupational Exposure Level(s) for the

predominant acrylic monomer(s) will provide adequate

protection against the lower levels of other

constituents that are evolved. This is not necessarily

the case when processing at temperatures higher than

those recommended, when the likelihood of releasing

toxic, irritant and flammable vapours is increased.

As it is impossible to be precise about which volatiles

will be evolved, and at what levels, it is equally

impossible to be precise about which substances will

be present in the vent port condensate liquor and

their relative levels. It is generally assumed, however,

that acrylic monomers and water will predominate and

will include some residual chemical compounds from

the polymerisation process. In the absence of detailed

compositional information it is prudent to regard this

liquor as hazardous. Appropriate Personal Protective

Equipment (PPE), such as impermeable gloves and

eye/face protection, should be worn on a case by

case basis. Vent port condensation liquor should be

disposed of by burning in an incinerator suitable for

the disposal of methacrylates in accordance with local

regulations.

It is intended that the guidance provided in this

Appendix should be used in conjunction with the

current Material Safety Data Sheets (MSDS) for the

grade(s) of Lucite Diakon being used.

Appropriate Material Safety Data Sheets (MSDS) can

be readily obtained from the local Lucite International

sales office or the officially appointed Lucite

International distributor/ agent. It is a legal requirement

in the European Union that the relevant (MSDS) data

for each Lucite Diakon grade is obtained and its

contents understood before handling and processing

each Lucite Diakon grade involved.

APPENDIX III

VOLATILE CHEMICALS EVOLVED DURING

PROCESSING OF LUCITE DIAKON

During thermal processing of Lucite Diakon acrylic

polymers volatile organic compounds (VOCs) are

evolved. When such processing involves the use of a

‘vented extruder’ these volatiles are present in the

vicinity of the extruder die and the vent port. In the

latter case, volatiles may be condensed to form a

condensate liquor. This technical section addresses the

toxicological hazard and risk associated with the

volatiles and vent port liquor.

It is recommended that the Lucite Diakon acrylic

polymers can be processed safely at melt

temperatures up to 280 degrees centigrade. The more

rapid depolymerisation of the polymer above this

temperature or excessive dwell times can cause

gaseous pressure to build up, with a resultant risk of

spraying low-viscosity polymer from the nozzle or die

without any planned screw movement.

All polymers degrade to some extent at their

processing temperature, an effect which increases

with increasing temperature. It is not possible to be

precise which substances will be evolved under the

specific conditions of use. At the recommended

processing temperatures the volatiles evolved are

likely to be comprised predominantly of residual acrylic

monomers and water. The identity of the acrylic

monomers will be depend upon the composition of the

polymer(s) being processed, reference should

therefore be made to the relevant Material Safety Data

Sheets and technical literature for the grade(s) of

Lucite Diakon being used. In addition to acrylic

monomers, much lower (trace) levels of residual

constituents from the polymerisation process are likely

to be present.

It is generally recommended that Local Exhaust

Ventilation (LEV) and/or Respiratory Protective

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EUROPEAN SALES OFFICE

Lucite International Holland B.V.

Merseyweg 16

3197 KG Botlek Rt.

Postbus 1222

3180 AE Rozenburg

Nederland

Fax +31 (0)181 233243

FRANCE

Tel +31 (0)181 233273

ITALY, PORTUGAL, SPAIN

Tel +31 (0)181 233274

GERMANY, SWITZERLAND, AUSTRIA,

BENELUX, NORDIC REGION

Tel +31 (0)181 233272

UNITED KINGDOM, THE REPUBLIC OF

IRELAND, EASTERN EUROPE, GREECE,

TURKEY, MIDDLE EAST, AFRICA

Tel +31(0)181 233271

LUCITE DIAKON TECHNICAL SERVICE

Lucite International UK Limited

The Wilton Centre

Wilton

Redcar

TS10 4RF

England

Tel +44 (0)1642 447117/447116

Fax +44 (0)1642 447105

DTM/E/2Ed/Dec02

Information contained in this publication (and

otherwise supplied to users) is based on our

general experience and is given in good faith, but

we are unable to guarantee its accuracy or to

accept responsibility in respect of factors outside

our knowledge or control. Freedom under patent,

copyright and registered designs cannot be

assumed.

Lucite Diakon is a registered trademark of the

Lucite International group of companies.

A member of the Lucite International Group. Lucite

International UK Limited.

Registered in England No. 3830161

Registered Office: Queens Gate, 15-17 Queens

Terrace, Southampton SO14 3BP, United Kingdom.

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www.lucitesolutions.com [email protected]

Lucite Diakon and Lucite Elvakon are registered trademarks of the Lucite International group of companies