standardization uv flexo manual

1

Success and safetyfor the label printer

Operating manual

StandardizationUV Flexographic ManualOperating instructions 162746 / AI – / 25-August-1998

2

Contents

Introduction 5Standardization

Meaning of standardization ............................... 5Standardization specifications ........................... 5General ................................................................. 5

Amount of ink transferred 6Standardization ink

4-color printing on quality substrateswith closed surface ............................................. 6Solid area printing............................................... 6Lines and types ................................................... 7

Solid area densities 8Standardization ink

Standard densities .............................................. 8Means of measurement ...................................... 8Measured value density solid area .................... 8What can be checked .......................................... 8Standard densities recommended by Gretag,supplemented for label printing ........................ 9

Ink viscosity 10Standardization ink

Means of measurement .................................... 10Inks for high quality 4-color printing ............... 10

Increase of tonal value 11Standardization ink

Formula .............................................................. 11Means of measurement .................................... 11The following parameters influencethe increase in tonal value ............................... 11Printing characteristic curve ............................. 12Preparation of a printing characteristic ........... 13

Speed test 14Standardization ink

Order form 15Standardization ink

Ink order ............................................................. 15Order .................................................................. 15

Goods reception control 16Engraved roller standardization

Visual inspection ............................................... 16Quality test certificate ....................................... 16Control proof print ............................................ 16Sample of an engraved roller data sheet ........ 17

Cell diameter on engraved roller 18Engraved roller standardization

Dot diameter on printing plate 19Engraved roller standardization

The strip engraved roller 20Engraved roller standardization

Sample of a density table ................................. 21

Dialogue with the ink supplier 22Engraved roller standardization

Samples for engraved roller inventory

list / reference list 23Engraved roller standardization

Storage of engraved rollers 24Engraved roller standardization

Order form 25Engraved roller standardization

Ordering engraved rollers ................................ 25Order .................................................................. 25Doctor order ...................................................... 26Order .................................................................. 26

3

Contents

Control circuit for printing

form production 27Standardization film production

Repro specifications for UV flexographic ........ 29Screen dot form................................................. 29Distortion of printing plates in general ........... 32Distortion of printing plates on Arsomaflexographic machines ...................................... 32Calculation of cylinder periphery,incl. attached printing plate .............................. 34Calculation of printing plate distortion ............ 35Distortion factors ............................................... 36

Printing cylinder table 42Standardization printing plate manufacture

Checklist for checking the printing plate copy 48

Goods reception check 49Standardization printing plate manufacture

Optical check ...................................................... 49Measuring checks .............................................. 49Copying check .................................................... 49

Storage of raw printing plates 50Standardization printing plate manufacture

Storage ............................................................... 50

Handling printing plates 50Standardization printing plate manufacture

Handling ............................................................. 50

Testing the wash-out time 51Standardization printing plate manufacture

Definition ........................................................... 51Wash-out test ..................................................... 51Wash-out temperatures .................................... 52

Reverse side exposure 53Standardization printing plate manufacture

Reverse side pre-exposure test ........................ 53Washing out the test ......................................... 53

Main exposure 55Standardization printing plate manufacture

Test for main exposure ..................................... 55

Drying 58Standardization printing plate manufacture

Secondary exposure with UVA light 59Standardization printing plate manufacture

Secondary exposure with UVC light 60Standardization printing plate manufacture

Chemical after-treatment 60Standardization printing plate manufacture

Delivery and storage of copied

printing plates 61Standardization printing plate manufacture

Delivery .............................................................. 61Storage ............................................................... 61

Standardization test formTest printing and demonstration forms .......... 61Outline of composition of a test printing form61Image evaluation ............................................... 62Technical printing parameters .......................... 63Test forms .......................................................... 64

Solid area density 66Standardization test form

Standard densities ............................................ 66Means of measurement .................................... 66Measured value density solid area .................. 66What can be checked ........................................ 66Standard densities recommended by Gretag,supplemented for label printing ...................... 67

4

Contents

Increase of tonal value 68Standardization test form

Formula .............................................................. 68Means of measurement .................................... 68The following parameters influencethe increase in tonal value ............................... 68Printing characteristic curve ............................. 69Preparation of a printing characteristic ........... 70

Determination of suitable printing

plates /adhesive combination 71Standardization

Working sequence for selectionof most suitable materials ................................ 71

Determination of suitable printing ink 72Standardization

Working sequence for selectionof most suitable materials ................................ 72

Plate adhesive foil 73Standardization

Foil summary ..................................................... 73

5

Introduction

Standardization

Meaning of standardization

In the section on standardization we have endeav-oured to provide instructions and help for standard-ization in UV flexographic printing. Of course, italways only represents a general standard for -Gallus/Arsoma machines, which require a furtherfine adaptation depending on customer require-ments or applications.

The findings described here were prepared withinthe scope of a UV flexographic project, in closecollaboration with market partners. Since these re-sults have been prepared closely related to practice,Gallus is able to offer all UV flexographic printerscompetent starting assistance. The user can alsocheck and/or improve his method of working withthese instructions.

Standardization specifications

Since there are still no standardization specificationsfor UV flexographic printing, we have used the offsetstandard as a basis. The offset specifications arecertainly no poor criteria, since UV flexographicresults are often and favourably compared with off-set results. Users will therefore look for an approxi-ma-tion to the offset result with UV flexographicprinting.

In order to achieve a result comparable to offset, thefollowing points for example are important, whichsummarise our basic idea:

• same standard densities

• same ink quantity on substrate

• reproduction of same ink space

• similar increases in tonal values

The optimum must be obtained from all the materi-als available to achieve the ambitious objectives. Theresults should not be laboratory values, but valueswhich can be reliably reproduced in daily practice.

General

As already described in the introduction, we alsofirmly base the standardization of the inks on theoffset data.

Reasons:

• Offset is the best standardized printing process.

• UV flexographic printers want to achieve a print-ing result comparable with offset.

• UV flexographic is often compared with offset.

• UV flexographic machines are superseding offsetmachines.

• Substantial improvements in UV flexographicmaterials in the past few years.

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Amount of ink transferred

Standardization ink

4-color printing on quality substrateswith closed surface

Since it is desired to achieve results by the UVflexographic process which are similar to the offsetprocess (as mentioned above), it is also important totake over specific ink parameters, e.g., ink volume.

It is endeavoured to obtain an ink volume of0.9–1.2 g/m2 on the substrate (with closed surface).

The ink layer thickness is then also approx. 0.9–1.2 µ

With this ink volume the standard values of densityshould also be achieved with the scale colors (cyan,magenta, yellow, black) (see solid area densities).Only then can it be ensured that the same color spaceis also printed in UV flexographic printing.

This also means that the inks must be adapted forquality printing by UV flexographic. This adaptationleads to highly-pigmented inks of somewhat higherviscosity.

The ink volume transferred to the substrate is -approx. 25–30% of the theoretical scoop volume ofan engraved roller.

The disadvantage of these highly pigmented inks isthat:

• They must be brightened with alumina white forsolid area printing, since otherwise the ink nolonger dries if high scoop volumes are used forprinting.

The scoop volumes for the engraved rollers forquality UV flexographic printing are approx.3.0–4.0

cm3/m2 with 60° screen angle

Solid area printing

As already suggested in Part 4, Color Printing, print-ing is performed with higher scoop volumes for solidarea printing.

Reasons:

• Better ink coverage

• More uniform ink dispensing

• More intensive coloring effect

• Less contamination or cleaning

Lower-viscosity, less-pigmented inks are thereforeusually also used in solid area printing to satisfy thepoints mentioned above. With these inks, the cells ofthe engraved rollers can also be drained better.

A standard engraved roller for solid area printing onsubstrate with closed surface is:

140–160 l/cm

7.5 cm3/m2 scoop volume

60° engraved screen angle

For rough writing papers engraved rollers should beused with over

100–140 l/cm

9.0 cm3/m2 scoop volume


7

Amount of ink transferred

Standardization ink

Lines and types

The same engraved rollers can be used as for screenprinting for fine types, printed on material withclosed surface.

For extremely bold types on closed substrate sur-faces and fine types on rough surfaces engravedrollers are necessary with

200–240 l/cm

4.5–5.5 cm3/m2 scoop volume


8

Solid area densities

Standardization ink

Standard densities

Offset values Flexo values

Cyan = DSP 1.40–1.50 = DSP 1.45–1.60

Magenta = DSP 1.35–1.45 = DSP 1.40–1.50

Yellow = DSP 1.30–1.40 = DSP 1.35–1.45

Black = DSP 1.70–1.90 = DSP 1.60–1.80

Values measured on high-gloss substrate (the valuesare some 0.1–0.2 lower on PE with the same plate-ink-adhesive-substrate combination, since the sur-face tension of the substrate is different).

Means of measurement

The solid area density is measured with a densito-meter in the colors cyan, magenta, yellow and black.

Measurement setting: density

Secondary colors should not be measured with adensitometer, since this only has filters for the -above-mentioned, standard colors. If measurementis nevertheless performed, the results are not validand can at best be used as points of reference. Forsecondary colors the filter should be selected for thedensitometer which indicates the highest measuredvalue.

Measured value density solid area

The measured value of a solid area surface is calledthe solid area density (abbreviated to DV). It is deter-mined with the measuring elements or tapes alsoprinted. Measurements can also be performed dur-ing printing in cyan, magenta, yellow or black sur-faces.

It is recommended also to print measuring elementsin all printing forms in all colors. 5 x 5 mm elementsin grid, bridge or at the edge can be printed at thesame time.

What can be checked

• Uniform ink transfer/ink volume over the entireprinting form.

• Ink volume check of engraved rollers, comparisonwith reference printing of engraved rollers, provi-sion of an engraved roller catalogue, determina-tion of soiling and wear of engraved rollers.

• Ink transfer of various printing plates, inks, platebases.

• Ink transfer to various substrates.

9


Standard densities recommended by Gretag, supplemented for label printing

Substrate Color Reference density Density tolerance

Highgloss material Cyan 1,45 +/–0,10

Art paper Magenta 1,40 +/–0,10

Chromo Yellow 1,40 +/-0,10

Black 1,85 +/–0,15

Mat coated paper Cyan 1,35 +/–0,10

PE Magenta 1,30 +/–0,10

Semi-gloss paper Yellow 1,30 +/–0,10

Black 1,75 +/–0,15

Uncoated paper Cyan 1,20 +/–0,10

Vellum Magenta 1,15 +/–0,10

Thermo-paper Yellow 1,20 +/–0,10

Black 1,55 +/–0,15

The densities in yellow are measured with the 47 B filter.

This table is provided to supplement and as an overall review of the foregoing table.

Standardization ink

10

Ink viscosity

Standardization ink

The viscosity of the inks must be considered ex-tremely important.

The following points can be influenced by the vis-cosity:

In the ink tank:

• Circulation of the ink in the tank

• Ink transfer to the fountain roller

On the engraved roller:

• Ink transfer from fountain to engraved roller

• Filling and emptying of the cells

• Ink volume transferred

When wiping:

• Accumulation of ink behind the doctor blade

• Splashing of the ink

• Doctor angle

On the printing plate:

• Filling of fine screen tones with ink

During printing:

• Increase of tonal value

Machine:

• Printing speed


The viscosity of the UV inks cannot be measured witha measuring cup, since the ink is highly viscous.A rotary viscosimeter is required for the purpose.

Unit: dPas

Inks for high quality 4-color printing

The aim is to print all colors for 4-color printingwithin a narrow range of the engraved roller specifi-cations. The entire ink set should therefore have thesame or similar viscosity (pigment-dependent). Thisalso largely ensures that the same ink volume can betransferred for all inks with the same engraved rollerspecification. All color tones therefore also have thesame or similar printing characteristic.

11

Increase of tonal value

Standardization ink

Formula

TWZ (%) = FD-FF

TWZ = tonal value increase

FD = surface coverage in impression

FF = surface coverage in film


The increase in tonal value can be measured with adensitometer.

Measurement setting: increase or surface coverage.

The increase in tonal value TWZ is found from thedifference between the measured screen tonal valuein the impression FD and the screen tonal value in thefilm FF.

The screen tonal value in the film must be known,however, or be measured with a transmitted lightdensitometer in the reproduction.

Only the colors cyan, magenta, yellow and black canbe measured. The measured value for secondarycolors is not valid.

The following parameters influencethe increase in tonal value

Machine:

• Printing stability

• True running

• Printing adjustment

• Printing process

Ink:

• Viscosity

• Pigments

• Ink volume used for printing

• Color density

Engraved roller:

• The screen dots dip in the cells of the engravedroller in the ratio of number of lines of engravedroller to number of lines in the film.

Film:

• Film exposure (also film density)

• Dot form

• Screen width

Printing plate:

• Hardness of printing plate

• Construction of printing plate

• Plate copy

• Resolution of printing plate

• Swelling behaviour with respect to UV ink

• Printing adjustment to engraved roller and sub-strate

• Ink transfer of printing plate (plate surface)

Printing plate base:

• Hardness

• Thickness

• Reset behaviour

• Combination with printing plate

Substrate:

• Surface (closed, rough)

• Absorbency

• Ink receptivity (also surface tension)

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Standardization ink

Printing characteristic curve

The graphical representation of increase in tonalvalue is called the printing characteristic curve. It isone of the basic tools for standardization and pro-vides the specialist with information concerning:

• How the machine is currently printing.

• How materials, i.e., ink, adhesive, printing plate orsubstrate, are used in an optimum way. Materialscan therefore be compared.

• How the repro-specialist must correct the films forthis machine.

The printing characteristic should be prepared forevery machine in operation with the materials mostused. This single additional expense pays for itselfduring the following production by lower reproduc-tion costs. It is also a great advantage to know aboutthe machine and materials. New materials can thenalways be evaluated without prejudice and used inan optimum way.

Various printing characteristics for different material

combinations and machines have already been pro-

duced by Gallus and can be obtained by Gallus

customers.

The Gallus printing department also offers support and

workshops for the preparation of the printing characte-

ristic for customers, including at their own site.


% s

urf

ace

cove

rag

e in

imp

ress

ion

FD

% surface coverage in film FF

0 10 20 30 40 50 60 70 80 90 100

100

90

80

70

60

50

40

30

20

10

0

0 10 20 30 40 50 60 70 80 90 100

50

45

40

35

30

25

20

15

10

05

0


% t

on

al v

alu

e in

crea

se in

imp

ress

ion


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Standardization ink

Preparation of a printing characteristic

A corresponding printing form is also required forthe preparation of a printing characteristic. It is bestto produce a test printing form with the correspond-ing measuring elements. These are above all rowswith screen fields in the tonal values 1–100%. Themeasuring fields should be selected as large aspossible to permit several parallel measurements onthe same field. Measuring wedges in various screenwidths are also an advantage.

Important!

The tonal values of the measuring fields must bemeasured and known in the film, so that the exactincrease in tonal value can be calculated.


% s

urf

ace

cove

rag

e in

imp

ress

ion

FD


0 10 20 30 40 50 60 70 80 90 100

100

90

80

70

60

50

40

30

20

10

0

0 10 20 30 40 50 60 70 80 90 100

50

45

40

35

30

25

20

15

10

05

0


% t

on

al v

alu

e in

crea

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imp

ress

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Speed test

Standardization ink

A speed test must always be performed if new inksare being tested. This is best also done with the testform to permit the following printing parameters ofthe ink to be tested as a function of speed:

• Solid area density

• Tonal value increase

• Behaviour of ink in printing unit and ink tank

The ink series from the various ink manufacturersdiffer considerably in UV flexographic printing. It isalmost impossible to achieve the same printing re-sult with inks from two suppliers. Printers have so fardepended on using inks from only one supplier.Many printers, however, like to keep a stock of inksfrom two suppliers.

Gallus endeavours to adapt and specify standardinks for Gallus/Arsoma machines from the mostimportant ink suppliers.

It is also important for the printer to specify thestandard inks to the ink factory, so that he alwaysobtains the same ink from his supplier at all timesand can therefore better ensure a reproducible print-ing result.

The following reference material is important for

this purpose:

• Ink type

• Ink number

• Ink series

• 1st delivery number

• Color proof print from ink factory with 1 g/m2

• Ink viscosity– viscosity in pot– viscosity when printing

• Color density with 1 g/m2 ink application

• Chromatic aberration of color tone in dE from DINstandard measured with spectrophotometer

• Color position in CIELAB color zone

• Table with ratio of density to ink volume

• Security data sheet

• Declaration of safety

The reference material for inks standardized at -Gallus for Gallus/Arsoma machines can be obtainedby Gallus customers from the Gallus printing depart-ment.

15

Standardization ink

Ink order

Proposal for an ink order form

The following points must be taken into account when ordering ink:

Order form

Order

Ink series:Ink type:Ink no.:Drying process:Pantone no.: PMS –Application:Resistance/fastness required: –

–––

Ink volume: kgContainer:Deadline: Date:Engraved roller: Number of lines: l/cm or l/inch

Scoop volume: cm3/m2

Supplier:Substrate: Supplier:

Substrate type:Pre-treated: yes/noEnclosed: yes/no

Printing specimen: Enclosed: yes/noaffixed overleaf

The following reference materialmust be supplied with the ink: Security data sheet

Proof print

16

Engraved roller standardization

Visual inspection

The following points should be checked:

• Condition of packing

• Condition of roller spigots

• Condition of engraved roller surface– scratching– mechanical damage– surface structure

• Condition of roller edges– blows, detached ceramic

• Are the roller specifications marked on the roller

Quality test certificate

Always request a quality and test certificate with thefollowing data from the engraved roller manufac-turer:

• Order number

• Roller number

• Photograph of roller surface

• Measured roller specifications, including:– lines per cm/inch– scoop volume– cell depth– bridge/cell ratio– engraving angle– true running of rollerCheck whether these data comply with the tole-ranc-es you have specified

• Test date

• Signature of tester

Goods reception control

Control proof print

A control proof should be made from an engravedroller before using for production. This should beperformed with materials and parameters deter-mi-ned by you and which are always the same.

E.g., always with the same

• ink• ink tint (e.g., cyan)• printing plate• plate adhesive tape• printing form• machine speed• printing cylinder• machine

This test proof is used as a reference impression andis therefore like the fingerprint of a roller. This im-pression should be measured by densitometer andpreserved.

An engraved roller data sheet should be openedbased on the data measured, on which later modifi-cations, measurements, cleaning and maintenanceoperations on the engraved roller can be recorded.

The engraved roller is therefore always under con-trol. It is then easier to resolve uncertainties andproblems while printing, e.g., it can very quickly bedecided whether the roller is worn out or only verysoiled.

The reference impression can be reproduced at anytime.

The roller can also be continually assigned toanother application when worn.

An example of an engraved roller data sheet isshown on the next page.

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Sample of an engraved roller data sheet

Roller number: KA 7003

Supplier: Zecher

Roller specifications: lines/cm: 280

scoop volume: 3.5

cell depth: 7

bridge/cell ratio: 1:13

engraving angle: 60°

Printing plate: Cyrel DPH-114

Printing plate adhesive: Rogers R/bak 0.97

Printing ink: Akzo-Nobel, Flexocure, cyan

Solid area density: left centre right

1.55 1.58 1.52

Goods reception control

Date Work Density Signature

1.5.97 Bearing replaced Huber6.7.97 Cleaning with ultrasonics Meier6.7.97 Test proof 1.50 Müller

etc.

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Cell diameter on engraved roller

Engrav-edRollerL/cm

6080

100110120140160170180195200220225255285300315345365385400

The cell diameter of the engraved roller should besmaller for half-tone printing than the smallestscreen dot fixable on the printing plate.

BridgeCell

1:10

µm

151.52113.6490.9182.6572.7564.9456.8153.4750.5046.6145.4541.3140.4035.6531.8930.2928.8626.3524.9023.6122.72

BridgeCell

1:21

µm

159.09119.3295.4486.7779.5468.1859.6556.1553.0248.9547.7243.3842.4137.4333.5031.8030.3027.6726.1424.7923.86

BridgeCell

1:11

µm

152.78114.5891.6683.3376.3865.4857.29539250.9347.0045.8341.6540.7435.9532.1630.5459.0926.5625.1223.8022.92

BridgeCell

1:12

µm

153.85115.3892.3083.9176.9165.9457.6854.2951.2947.3446.1541.9541.0236.2032.3830.7729.3026.7625.2923.9623.07

BridgeCell

1:13

µm

154.77116.0792.8684.4177.3766.3357.8654.8151.5947.6146.4342.2041.2736.4132.5830.9529.4726.9225.4424.1123.20

BridgeCell

1:14

µm

155.56116.6793.3384.8477.7766.6658.3354.9051.8647.8646.6642.4141.4736.6132.7531.1129.6227.0525.5624.2323.32

BridgeCell

1:15

µm

156.25117.1893.7585.2378.1266.9758.5955.1352.0948.0646.8642.6141.6536.7732.9031.2529.7727.1825.6924.3523.44

BridgeCell

1:16

µm

156.87117.6594.1285.5578.4367.2358.8155.3652.2948.2547.0642.7741.8336.9033.0231.3729.8727.2825.9624.4423.53

BridgeCell

1:17

µm

157.41118.0694.4485.8678.6967.4559.0255.5452.4748.4347.2242.9141.9737.0433.1331.4729.9827.3725.8724.5323.61

BridgeCell

1:18

µm

157.80118.4294.7386.1278.9467.6659.2055.7252.6348.5847.3643.0642.0937.1533.2431.5730.0727.4525.9524.6023.68

BridgeCell

1:19

µm

158.34118.7595.0086.3679.1667.8659.3655.8852.7748.7247.5043.1842.2237.2533.3431.6530.1527.5426.0324.6723.75

BridgeCell

1:20

µm

158.78119.0595.4186.5879.3668.0259.5256.0252.9048.8447.6143.2942.3137.3433.4131.7330.2327.6126.1024.7223.80


19

Surfacecoveragein posi-tive film

%

1 2 3 4 5 6 7 8 910

In this table only the 1–10% screen tonal values havebeen taken, since these have the smallest diameterand are more difficult to fix on the plate.

E.g., it is already very difficult with the 60s screen tofix a 1–3% screen dot, depending on the type ofprinting plate.

The table also shows well that if the engraved rolleris to support a 2% screen dot in the 60s screen, anengraved roller with min. 360–380 lines per centime-tre is necessary (see table of cell diameter on en-graved roller).

DotDia-

meter

32 L/cm

µm

35.2549.8661.0870.5178.8486.3793.2999.73105.79111.51

DotDia-

meter

34 L/cm

µm

33.1846.9357.4766.3774.2081.2987.8093.8799.55104.95

DotDia-

meter

36 L/cm

µm

31.3444.3154.2962.6870.0876.7782.9388.6594.0299.12

DotDia-

meter

40 L/cm

µm

28.2039.8848.8656.4163.0869.0974.6379.7984.6289.20

DotDia-

meter

42 L/cm

µm

26.8737.9946.5253.7260.0665.8071.0875.9880.5984.95

DotDia-

meter

44 L/cm

µm

25.6436.2744.4151.2957.3462.8167.8472.5076.9481.09

DotDia-

meter

48 L/cm

µm

23.5133.2540.7247.0252.5657.5862.2066.4870.2574.33

DotDia-

meter

52 L/cm

µm

21.7030.6937.5843.4048.5253.1557.4061.3865.0968.62

DotDia-

meter

54 L/cm

µm

20.8929.5436.1841.7946.7251.1855.2959.0962.6866.08

DotDia-

meter

60 L/cm

µm

18.8026.6032.5637.6142.0446.0649.6653.1856.4159.47

Dot diameter on printing plate


20


A strip engraved roller is an engraved roller providedwith various engravings.

Purpose of a strip engraved roller for the printer

With a roller of this kind it is possible to print a colorwith various engravings in one printing operation. Inother words, various scoop volumes and color den-sities can also be printed. With rollers of this kind, forexample, the optimum engraved roller can bequickly determined for a desired color density.

Density tables for:

• various ink series

• various ink tints

• various substrates

• various printing plate types, etc.

can be prepared from proof prints with strip en-graved rollers.

The interplay of the different materials can veryquickly be determined with rollers of this kind, inorder to obtain a rapid general survey in flexographicprinting.

Application of strip engraved rollers by ink

manufacturers

Some ink manufacturers also have flexographicproof printing machines in their color laboratory. Theapplication of strip engraved rollers by the ink manu-facturer enables extremely accurate proof prints tobe made of ink tints. This would be particularly usefulwith secondary colors.

The strip engraved roller

What strip engraved rollers would be required

Since engraved roller technology is currently under-going continuous improvement, a discussion withthe engraved roller manufacturer is always necess-ary before production or ordering. We at Gallus cancertainly also give a good recommendation.

In principle, however, 2–3 strip engraved rollers witha total of 12–15 engravings are always necessary. Thenumber of rollers always depends on the printingwidth of the printing machine and the strip width.

In general, engravings are necessary for

• half-tone printing

• character/line printing

• printing of solid areas

21

The practical standardization in UV flexographicprinting started with proof printing of these stripengraved rollers with various printing plates, plateadhesive tapes, sleeve cylinders and inks. It wastherefore well possible to test the differences in inktransfer and color densities of the various materialsand hence prepare and specify the initial fittings forengraved rollers.


Sample of a density table

Machine: Arsoma EM-410

Printing speed: 40 m/min.

Printing plate: Du-Pont Cyrel UVB-114

Screen width: 54 l/cm

Ink: Zeller-Gmelin Y

Plate adhesive tape: Rogers R/bak 0.97 mm

Substrate: Jac, Brillant, HGW, SK

Engraved rollers: Praxair, Lightlox

*

The strip engraved roller

L/cm

80100120140160180200260260280300320240240240260260260280280280320320320

µm

453530211714111010 9 7 5 5 912 5 911 4 5 7 5 5 6

cm3/m2

14,012,0 9,0 7,5 6,0 4,5 3,8 3,3 3,2 3,0 2,5 2,0 2,0 3,3 4,1 2,0 2,5 3,4 2,0 2,6 3,0 2,1 2,1 2,7

Angle

606060606060606060606060606060606060606060606060

Cyan

1,991,991,981,921,741,401,671,371,341,301,250,951,021,481,651,121,191,471,051,351,471,171,121,29

Mag.

1,931,921,891,781,691,491,471,231,211,141,130,980,971,291,480,931,111,290,961,181,281,070,991,15

Yellow

1,881,901,901,821,761,541,591,331,381,201,220,980,941,441,651,021,111,460,911,191,371,221,081,24

Black

2,162,142,142,132,111,931,991,771,701,651,661,311,111,792,031,261,271,731,291,601,851,331,331,58

Roller no.

1

2

3

4


22


It is also very important to work in close collabora-tion with the ink supplier in a standardization pro-cess. Only a good collaboration makes the followingpossible:

• constant ink specifications

• exact mixing of inks

which are also reproducible with your engravedrollers in

• ink volume

• color density

• ink tint

What the ink supplier requires from the printer

Provide your ink supplier with a list of your engravedrollers.

Inform the ink supplier how you use your engravedrollers:

• Half-tone printing

• Type/line work

• Solid area printing

• Varnishing

• Substrates

Dialogue with the ink supplier

23

This list can also be used as a reference list for an 8-color UV flexographic machine. The specificationsgenerally correspond to the state-of-the-art in 1998.The data can vary somewhat from one engravedroller manufacturer to the next, since the measuringsystems of the manufacturers differ in their evalua-tion. It is recommended to consult a specialist of theengraved roller manufacturer before ordering.

It is also recommended to work with the same manu-facturer later, so that the same specifications canalways be ordered again and the rollers are thereforemutually adapted in application.

At present, many engraved roller manufacturers areintroducing a new laser technology which permitsthe production of even finer engraved rollers withvery high scoop volumes (e.g., 500 l/cm with approx.4.0 cm3/m2).

Samples for engraved roller inventory list / reference list

L/cm

320320320320300300280280240240160160140100100

m3/m2

URMI

2.7 3 3 3 3.5 3.5 4 4 5.5 5.5 7.5 7.5 91214

°

606060606060606060606060606060

µm Rollerno.

1 2 3 4 5 6 7 8 9101112131415

Paese/Cell

Supplier

Praxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair LightloxPraxair Lightlox

Application

ScreenScreenScreenScreenScreenScreenScreenScreenType/surfaceType/surfaceSurfaceSurfaceSurface/varnishSurface/varnishSurface/varnish


24


The engraved rollers should be stored in a clean anddust-free place.

The rollers must not be in mutual contact.

They should lie on the roller spigots.

The rollers should be covered with a soft cloth orfabric.

The storage place should be accessible.

No dirty rollers should be placed in store.

Engraved rollers not in use should not interfere withwork on the machine or its surroundings. This alsoprevents damage to the rollers outside the machine.

Every roller should be given an internal number andalways be stored in the same place. The numbermust correspond to the inventory list of rollers.

Storage of engraved rollers

25


Ordering engraved rollers

Suggested form for ordering engraved rollers

The following points must be specified in an order:

Order form

Order

Machine manufacturer:

Machine type:

Drawing no.:

Number of rollers: Pcs.:

Deadline: Date:

Roller quality:

Roller coating:

Roller spigots: hardened/unhardened

Roller specifications: Number of lines engraved per cm: l/cm or l/inch

Engraving depth: µ

Engraving angle: °

Scoop volume: cm3/m2

Bridge/cell ratio: 1:

Field of application of roller:

Tolerances: True-running: 0.05 mm

Scoop volume max. +5%

The following data must besupplied with the roller: Quality record with: photo of engraving

measured roller specifications

date/signature

26


Doctor order

Suggestion for a doctor order form

The following points must be observed when ordering:

Order form

Order

Machine:

Number of doctors: Pcs.:

Deadline: Date:

Doctor blade length: mm

Doctor blade width: mm

Lamella thickness: µ

Lamella grinding angle: 60°

Doctor quality: Steel

hardened/unhardened

plastic

Doctor blank: exactly to size specified

Piece goods

60°

Width

Lamella

Length

27

4. Checking of own production for observanceof standardized production procedures

3. Checking of film and proof print receiptsfor observance of reproduction specificationsand if not observed early detection of expectedshortcomings

Control circuit for printing form production

1. Collection and preparation of figures forcopying, printing technology and densitometer

2. Preparation of unmistakable copying andprinting technology specificationsfrom the production sector

Standardization film production

28


Various points should be known before starting reproduction work:

This is a rough checklist. It can be supplemented or modified at will for all requirements.

1. Printing process

2. Screen width

3. Screen dot form

4. Screen positions / screen angle

5. Image processing / UCR / limiting clearance

6. Technical screen

7. Film quality / film type

8. Register cross-line with standard data and number

9. Marks for register control: inks / dies

10. Overlappings

11. Printing characteristic: tonal value increase

12. Number of colors

13. Color sequence

14. Repeat length

15. Repeat area

16. Number of repeats: longitudinal and lateral repeat

17. Bridge widths: longitudinal/lateral

18. Substrate: width, quality, material

19. Proof / proof print / sample / clean drawing

20. Correct data format

21. Printing plate distortion: flat or circular exposure

22. Copying cylinder diameter

23. Printing machines type

etc.


29


Repro specifications for UV flexographic

Film material

Mat film, read-right negative film

Screen angle

Standard flexo angleCyan: 7.5°Magenta: 67.5°Yellow: 82.5°Black: 37.5°

But no film angle must be at 60°.

These are:Cyan: 75°Magenta: 45°Yellow: 90°Black: 105°

Color sequences

1st sequence1. Cyan2. Magenta3. Yellow4. BlackInk receptivity problems can sometimes arisewhen printing magenta and cyan on yellow. Trap-ping problems can be excluded with this se-quence. The black printed at the end provides agood image contrast. A dark color in the 1st print-ing unit is always good as reference color for theregister.

2nd sequence1. Magenta2. Yellow3. Cyan4. BlackThe advantage of this sequence is the somewhatwarmer pictorial effect and a good image contrastby the black printed last.


3rd sequence1. Yellow2. Magenta3. Cyan4. BlackThis is the standard color sequence in convention-al flexographic printing. The advantage of thissequence is that the yellow is printed first, whichis the most covering color in the 4-color set. Thedisadvantage is that the yellow in the first printingunit is not a good reference color for the register.

Screen dot form

A round dot is generally printed in 4-color flexo-graphic printing. A chain dot screen with various dotlayouts can also be tried occasionally for a vignettedscreen.

1. Dot application with approx. 60% tonal value2. Dot application with approx. 80% tonal value

This prevents a considerable increase in tonal valuewhen the dot application is made simultaneously onall sides.

New dot forms will certainly also be used for digitallycomposed printing plates, e.g., round dot combinedwith FM screen and finer screen resolutions. Thistrend is also supported by the multi-lined engravedrollers of the future.

Screen width

High gloss substrate 60 l/cmClosed substrate surfaces 60 l/cmEggshell finish substrates 54 l/cmWriting material (vellum) 44 l/cmLabels 54–60 l/cmLabels on foil 54–60 l/cmFolding cartons 54 l/cmComputer labels 48 l/cmComputer-Etiketten 48 L/cm

30


Tonal value transfer of flexographic plates

High-quality flexographic plates always still haveminor differences in tonal value transfer betweenplate types. Differences can still be seen above all inthe light area (1–5% tonal value) and in the shadows(90–100% tonal value). When plates are assessed, thewhole plate must always be evaluated.

There are plates, for example, which are worse in thelight area (1–3%) than other plates, but have a farsmaller increase in tonal value in the middle tonesand vice-versa.

In general it can be stated:High-gloss materials 2–95%Eggshell finish materials 5–90%Writing materials 7–85%

This also applies to vignetted screens.

Standard densities

Refer to test form section

Printing characteristic

Refer to test form section

Overlappings

0.1 mm should be observed for overlappings ongood, register-stable substrates. More should beallowed for difficult materials.

UCR (Under-Color Reduction)

UCR is increasingly used for 4-color flexographicwork. It is also ensured that no more than 270% coloris superimposed in multi-color printing. Images ofthis kind can also be obtained with less color varia-tion, since black is used intensively as a contrastcolor.


Film density

DV 3.5 in full density, since flexographic plates areexposed very long and the films are therefore sub-ject to the light for a long time.

The negatives must be as transparent as possible atthe unexposed points, max. density log. 0.06. Greyor yellow halos produce errors in printing plateexposure. Halos are caused by:

• darkroom lighting too bright• developing time too long• used developer• developing temperature too high• exposure time too long• inadequate fixing and washing(refer to conversion table on next page).

Film/plate distortion

Fully described later in this section.

Additional characters

Various additional characters are required depend-ing on company, type of machine, register controland plate processing.

• Punching marks• Register marks• Supporting strips• Plate labelling: order

inkdistortion factorplate typeplate thicknessmanufactureroperation, etc.

31

Density(Blackness)

0,000,010,020,030,040,050,060,070,080,090,100,110,120,130,140,150,160,170,180,190,200,220,240,260,280,300,320,34



The screen tonal values can be measured with a transparent densitometer. For units with logarithmic display,conversion can be made with the table below.

This shows the densities and screen tonal value (in %) in the negative film.

Density(Blackness)

0,360,380,400,420,440,460,480,500,540,580,620,660,700,740,780,820,860,900,951,001,101,201,301,401,501,702,00

Tonal value%

100989593918987858381797876747271696866656360585552504846

Tonal value%

44424038363533322926242220181715141311108654321

32


Distortion of printing plates in general

If flexographic printing plates are fixed to a printingcylinder of a rotary printing machine, the platesbecome longer due to bending.

The printing plate dimension is unchanged in print-ing width parallel to the axis of the printing cylinderwhen fixed to the printing cylinder.

It must therefore only be distorted in the printingdirection

Since the flexographic printing plates are usuallyexposed flat (0.76 mm printing plates can also berotary exposed), the film length must be shortenedfor printing plate exposure.

The film must be distorted over the entire repeat orprinting length, so that the image has the right sizeagain when printed.

Example:

If a circular label is not distorted in the film, it willbe oval later in the image, since the surface of theprinting plate is longer on the printing cylinder.

This shortening is called the distortion factor.

The distortion factor can be requested from theprinting plate manufacturer. The following data areusually given:

1.70 mm printing plates = 9.9 mm distortion1.14 mm printing plates = 6.2 mm distortion0.76 mm printing plates = 4.3 mm distortion1.70 mm multi-coated plates = 3.59 mm distortion

The films can be shortened by the same factor for allrepeat lengths to be printed.


Methods for shortening the film

• on the DTP system (computer)

• on the exposure unit

• distortion camera

• corrected repeat setting of distorted and undistort-ed repeat films

• optically-mechanically (distortion unit)

• compensation of distortion factor between print-ed labels

These units must work very accurately.

Distortion of printing plates on Arsomaflexographic machines

Special attention should be paid to the distortionfactor on Arsoma printing machines for the follow-ing reasons:

• The printing cylinder diameter, incl. printing plateand plate adhesive tape, do not correspond withthe pitch of the driving gearwheels (impressionand printing cylinders).

• +0.05 mm compression (pressure adjustment,compression of plate structure) is included for theprinting cylinder.

• The periphery of the printing cylinder (with print-ed plate attached) is longer than the repeat lengthto be printed. The surface speed of the printingplate is higher than that of the substrate.

• The thickness of the foamed plate adhesive tapesis usually thicker than for the given application.

33


Example:

TESA softprint 523800.38 mm application thickness0.46 mm adhesive tape thickness

• Printing of process combinations with screenprinting, hot foil embossing and exact punching.An exact combined printing of the various printingprocesses is indispensable for applications of thiskind and the distortion of the printing plate istherefore extremely important.

• Exact knowledge of the materials used, viz.:

– plate thickness– absolute adhesive tape thickness– printing cylinder diameter

For the reasons stated above, other distortion fac-

tors are also used with Arsoma machines. These are

listed below in special distortion tables.


34


Calculation of cylinder periphery, incl.attached printing plate

Printing cylinder construction

Printing cylinder diameter

+ 2 x printing plate thickness+ 2 x plate adhesive tape thickness

= printing cylinder diameter complete


Example:

117,216 mm (Z-120)

+ 3,400 mm (2 x 1,70 mm)

+ 0,760 mm (2 x 0,38 mm)

= 121,367 mm

Calculation of printing cylinder periphery

Printing cylinder diameter x π = cylinder periphery

Example:

121,367 mm x π (3,1415927 mm) = 381,314 mm

Printing cylinder diameter,incl. printing plate and plateadhesive tape

Printing plate

Printing cylinder

Plate adhesive plate

35



Calculation of printing plate distortion

Compression on segment of printing and impression cylinder.

Distortion factor from manufacturer's data

Repeat length – distortion factor = corrected film lengthExample: 381.000 mm (Z-120) – 9.9 mm (plate 1.70 mm) = 371.100 mm

or distorted film in %: 371.100 mm x 100 : 381.000 mm = 97.402%

This calculation is generally performed on flexographic machines of all makes. It is also used by printing plateproducers. When printing on Arsoma machines, it can only be used subject to reservation for non-high-qualityregister work.

Printing with Arsoma machines

0.38 mm plate adhesive tape and 0.05 mm compression were included in the calculation. The distortion factorwas determined from printing tests.



This calculation is recommended by Gallus for register-accurate flexographic printing. There can still be minorregister differences, however, between flexographic and other printing processes.

Printing with Arsoma machines

0.46 mm TESA softprint 52380 plate adhesive tape and 0.05 mm compression were included in the calculation.



This calculation theoretically includes practically all the factors which can influence the distortion of the printingplates. The effects of printing plates with printing parts of different size have not been considered. Nor can thesebe calculated during film and plate production.

36

Z

58596061626364656667686970717273747576777879808182838485868788899091


Standardization film productionDistortion factors

Cyrel or BASF / 1.70 mm plates / distortion factor 9.9 mm according to manufacturer data

Printing on segment of printing and impression cylinder.

Z

9293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125

Repeat lengthmm

184.150187.325190.500193.675196.850200.025203.200206.375209.550212.725215.900219.075222.350225.425228.600231.775234.950238.125241.300244.475247.650250.825254.000257.175260.350263.525266.700269.875273.050276.225279.400282.575285.750288.925

Repeat lengthmm

292.100295.275298.450301.625304.800307.975311.150314.325317.500320.675323.850327.025330.200333.375336.550339.725342.900346.075349.250352.425355.600358.775361.950365.125368.300371.475374.650377.825381.000384.175387.350390.525393.700396.875

Distortionin %

94.62494.71594.80394.88894.97195.05095.12895.20395.27595.34695.41495.48194.54595.60895.67095.72895.78695.84395.89795.95196.00296.05396.10296.15096.19796.24396.28896.33296.34796.41696.45696.49696.53596.573

Distortionin %

96.61196.64796.68396.71896.75296.78596.81896.85096.88296.91396.94396.97397.00297.03097.05897.08697.11397.13997.16597.19197.21697.34197.26597.28897.31297.33597.35897.38097.40297.42397.44497.46597.48597.505

37

Z

126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159



Cyrel or BASF / 1.70 mm plates / distortion factor 9.9 mm according to manufacturer data

Printing on segment of printing and impression cylinder.

Z

160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192

Repeat lengthmm

400.050403.225406.400409.575412.750415.925419.100422.275425.450428.625431.800434.975438.150441.325444.500447.675450.850454.025457.200460.375463.550466.725469.900473.075476.250479.425482.600485.775488.950492.125495.300498.475501.650504.825

Repeat lengthmm

508.000511.175514.350517.525520.700523.875527.050530.225533.400536.575539.750542.925546.100549.275552.450555.625558.800561.975565.150568.325571.500574.675577.850581.025584.200587.375590.550593.725596.900600.075603.250606.425609.600

Distortionin %

97.52597.54497.56497.58397.60197.62097.63897.65597.67397.69097.70797.72497.74097.75697.77397.78997.80497.82097.83597.85097.86497.87997.89397.90797.92197.93597.94997.96297.97597.98898.00198.01498.02698,039

Distortionin %

98.05198.06398.07598.08798.09998.11098.12298.13398.14498.15598.16698.17698.18798.19798.20898.21898.22898.23898.24898.25898.16898.27798.28798.29698.30598.31598.32398.33398.34198.35098.35998.36798.376

38

Z

58596061626364656667686970717273747576777879808182838485868788899091



Cyrel and BASF / 1.70 mm plates / distortion factor 9.4 mm for Arsoma flexographic machines

0.38 mm plate adhesive tape and 0.05 mm compression were included in the calculation.Z

9293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125

Repeat lengthmm

184.150187.325190.500193.675196.850200.025203.200206.375209.550212.725215.900219.075222.350225.425228.600231.775234.950238.125241.300244.475247.650250.825254.000257.175260.350263.525266.700269.875273.050276.225279.400282.575285.750288.925

Repeat lengthmm

292.100295.275298.450301.625304.800307.975311.150314.325317.500320.675323.850327.025330.200333.375336.550339.725342.900346.075349.250352.425355.600358.775361.950365.125368.300371.475374.650377.825381.000384.175387.350390.525393.700396.875

Distortionin %

94.89594.98295.06595.14695.22595.30095.37495.44595.51495.58195.64695.70995.77195.83095.88895.94495.99996.05296.10496.15596.20496.25296.29996.34596.38996.43396.47596.51796.55796.59796.63696.67396.71096.746

Distortionin %

96.78296.81696.85096.88496.91696.94896.97997.00997.03997.06897.09797.12597.15397.18097.20797.23397.25897.28497.30897.33397.35697.38097.40397.42597.44797.46997.49197.51297.53397.55397.57397.59397.61297.631

39

Z

126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159



Cyrel and BASF / 1.70 mm plates / distortion factor 9.4 mm for Arsoma flexographic machines

0.38 mm plate adhesive tape and 0.05 mm compression were included in the calculation.

Z

160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192

Repeat lengthmm

400.050403.225406.400409.575412.750415.925419.100422.275425.450428.625431.800434.975438.150441.325444.500447.675450.850454.025457.200460.375463.550466.725469.900473.075476.250479.425482.600485.775488.950492.125495.300498.475501.650504.825

Repeat lengthmm

508.000511.175514.350517.525520.700523.875527.050530.225533.400536.575539.750542.925546.100549.275552.450555.625558.800561.975565.150568.325571.500574.675577.850581.025584.200587.375590.550593.725596.900600.075603.250606.425609.600

Distortionin %

97.65097.66997.68797.70597.72297.74097.75797.77497.79197.80797.82397.83997.85497.87097.88597.90097.91597.92997.94497.95897.97297.98697.99999.01398.02698.03998.05298.06598.07898.09098.10298.11498.12698.138

Distortionin %

98.14998.16198.17298.18498.19598.20598.21698.22798.23798.24898.25898.26898.27998.28898.29898.30898.31898.32798.33698.34698.35598.36498.37398.38298.39198.39998.40898.41798.42598.43398.44298.45098.458

40

Z

58596061626364656667686970717273747576777879808182838485868788899091



Cyrel and BASF / 1.14 mm plates / distortion factor 5.7 mm for Arsoma machines


Z

9293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125

Repeat lengthmm

184.150187.325190.500193.675196.850200.025203.200206.375209.550212.725215.900219.075222.350225.425228.600231.775234.950238.125241.300244.475247.650250.825254.000257.175260.350263.525266.700269.875273.050276.225279.400282.575285.750288.925

Repeat lengthmm

292.100295.275298.450301.625304.800307.975311.150314.325317.500320.675323.850327.025330.200333.375336.550339.725342.900346.075349.250352.425355.600358.775361.950365.125368.300371.475374.650377.825381.000384.175387.350390.525393.700396.875

Distortionin %

96.90596.95797.00797.05797.10497.15097.19597.23897.28097.32097.36097.39897.43597.47197.50697.54197.57497.60697.63797.66897.69897.72797.75697.78497.81197.83797.86397.88897.91297.93697.96097.98398.00598.027

Distortionin %

98.04898.07098.09098.11098.13098.14998.16898.18698.20598.22298.24098.25798.27498.29098.30698.32298.33898.35398.36898.38398.39798.41198.42598.43998.45298.46598.47898.49198.50498.51698.52898.54098.55298.564

41

Z

126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159



Cyrel and BASF / 1.14 mm plates / distortion factor 5.7 mm for Arsoma machines


Z

160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192

Repeat lengthmm

400.050403.225406.400409.575412.750415.925419.100422.275425.450428.625431.800434.975438.150441.325444.500447.675450.850454.025457.200460.375463.550466.725469.900473.075476.250479.425482.600485.775488.950492.125495.300498.475501.650504.825

Repeat lengthmm

508.000511.175514.350517.525520.700523.875527.050530.225533.400536.575539.750542.925546.100549.275552.450555.625558.800561.975565.150568.325571.500574.675577.850581.025584.200587.375590.550593.725596.900600.075603.250606.425609.600

Distortionin %

98.57598.58698.59798.60898.61998.63098.64098.65098.66098.67098.68098.69098.69998.70898.71798.72798.73698.74598.75398.76298.77098.77998.78798.79598.80398.81198.81998.82698.83498.84298.94998.85698.86498.871

Distortionin %

98.87898.88598.89298.89998.90598.91298.91998.92598.93198.93898.94498.95098.95698.96298.96898.97498.98098.98698.99198.99799.00399.00899.01499.01999.02499.03099.03599.04099.04599.05099.05599.06099.065

42

Numberof teeth

44454647484950515253545556575859606162636465666768697071727374757677

Printing cylinder table

Standardization printing plate manufacture

Plate thickness: 1.70 Compression: 0.05 mm

Adhesive foil thickness: 0.38 mm all data in mm

Numberof teeth

78798081828384858687888990919293949596979899100101102103104105106107108109110111

Repeat length

139,700142,875146,050149,225152,400155,575158,750161,925165,100168,275171,450174,625177,800180,975184,150187,325190,500193,675196,850200,025203,200206,375209,550212,725215,900219,075222,250225,425228,600231,775234,950238,125241,300244.475

Repeat length

247,650250,825254,000257,175260,350263,525266,700269,875273,050276,225279,400282,575285,750288,925292,100295,275298,450301,625304,800307,975311,150314,325317,500320,675323,850327,025330,200333,375336,550339,725342,900346,075349,250352,425

Diameter

68,70669,71670,72771,73872,74873,579

Diameter

74,77075,78076,79177,80178,81279,82380,83381,84482,85583,86584,87685,88686,89787,90888,91889,92990,94091,95092,96193,97294,98295,99397,00398,01499,025100,035101,046102,057103,067104,078105,089106,099107,110108,120

43

Numberof teeth

112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145





Numberof teeth

146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179

Repeat length

355,600358,775361,950365,125368,300371,475374,650377,825381,000384,175387,350390,525393,700396,875400,050403,225406,400409,575412,750415,925419,100422,275425,450428,625431,800434,975438,150441,325444,500447,675450,850454,025457,200460,375

Repeat length

463,550466,725469,800473,075476,250479,425482,600485,775488,950492,125495,300498,475501,650504,825508,000511,175514,350517,525520,700523,875527,050530,225533,400536,575539,750542,925546,100549,275552,450555,625558,800561,975656,150568,325

Diameter

109.131110,142111,152112,163113,174114,184115,195116,206117,216118,227119,237120,284121,259122,269123,280124,291125,301126,312127,323128,333129,344130,354131,365132,376133,386134,397135,408136,418137,429138,439139,450140,461141,471142,482

Diameter

143,493144,503145,514146,525147,535148,546149,556150,567151,578152,588153,599154,610155,620156,631157,642158,652159,663160,673161,684162,695163,705164,716165,727166,737167,748168,759169,769170,780171,790172,801173,812174,822175,833176,844

44

Numberof teeth

180181182183184185186187188189190191192

1





Repeat length

571,500574,675577,850581,025584,200587,375590,550593,725596,900600,075603,250606,425609,600

3,175

Diameter

177,854178,865179,876180,886181,897182,907183,918184,929185,939186,950187,961188,971189,982

45

Numberof teeth

44454647484950515253545556575859606162636465666768697071727374757677





Numberof teeth

78798081828384858687888990919293949596979899100101102103104105106107108109110111

Repeat length

139,700142,875146,050149,225152,400155,575158,750161,925165,100168,275171,450174,625177,800180,975184,150187,325190,500193,675196,850200,025203,200206,375209,550212,725215,900219,075222,250225,425228,600231,775234,950238,125241,300244.475

Repeat length

247,650250,825254,000257,175260,350263,525266,700269,875273,050276,225279,400282,575285,750288,925292,100295,275298,450301,625304,800307,975311,150314,325317,500320,675323,850327,025330,200333,375336,550339,725342,900346,075349,250352,425

Diameter

68,70669,71670,72771,73872,74873,579

Diameter

74,77075,78076,79177,80178,81279,82380,83381,84482,85583,86584,87685,88686,89787,90888,91889,92990,94091,95092,96193,97294,98295,99397,00398,01499,025100,035101,046102,057103,067104,078105,089106,099107,110108,120

46

Numberof teeth

112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145





Numberof teeth

146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179

Repeat length

355,600358,775361,950365,125368,300371,475374,650377,825381,000384,175387,350390,525393,700396,875400,050403,225406,400409,575412,750415,925419,100422,275425,450428,625431,800434,975438,150441,325444,500447,675450,850454,025457,200460,375

Repeat length

463,550466,725469,800473,075476,250479,425482,600485,775488,950492,125495,300498,475501,650504,825508,000511,175514,350517,525520,700523,875527,050530,225533,400536,575539,750542,925546,100549,275552,450555,625558,800561,975656,150568,325

Diameter

108,791109,802110,812111,823112,834113,844114,855115,866116,876117,887118,897119,908120,919121,929122,940123,951124,961125,972126,983127,993129,004130,014131,025132,036133,046134,057135,068136,078137,089138,099139,110140,121141,131142,142

Diameter

143,153144,163145,174146,185147,195148,206149,216150,227151,238152,248153,259154,270155,280156,291157,302158,312159,323160,333161,344162,355163,365164,376165,387166,397167,408168,419169,429170,440171,450172,461173,472174,482175,493176,504

47

Numberof teeth

180181182183184185186187188189190191192

1





Repeat length

571,500574,675577,850581,025584,200587,375590,550593,725596,900600,075603,250606,425609,600

3,175

Diameter

177,514178,525179,536180,546181,557182,567183,578184,589185,599186,610187,621188,631189,642

48


Checklist for checking the printing plate copy

List of points which can be checked in the printing plate copy

1. Cleanliness and freedom from dust:2. Goods reception control: Plate material

SolventFilms / data

3. Storage of printing plates:4. Plate exposer: Condition of vacuum foil

Type of exposure lampsAge of lamps and their starter

5. Plate exposure: Front or reverse side exposure timeMain exposure time

6. Plate wash-out: Condition of wash-out brushesBrush adjustmentsCondition of wash-out liquid

7. Washing-out plates: Wash-out timeWash-out temperatureRelief depth

8. Plate dryer: Drying temperatureUniformity of temperature in complete dryer

9. Drying plates: Drying time10. Supplementary exposure device: Condition and age of exposure tubes11. Supplementary exposure of plates: Supplementary exposure time12. After-treatment: Condition and age of exposure tubes

Condition of bromine bath13. Plates allowed to rest: Time14. Plate thickness: Measure with measuring unit15. Proof-printing of plate: Proof-print plate if possible16. Plate check: Optical final check17. Plate delivery: Correct packing

Necessary care18. Disposal: Correct disposal and recycling of waste and solvent


49

Standardization printing platemanufacture

Optical check

Check order against delivery note

Check label on packing

Check condition of packing

• Damage

• Tightly sealed

Measuring checks

This includes checking the thickness of the raw platessupplied with a thickness measuring unit.

The differences must not exceed ± 0.02 mm withinthe raw plate format.

Goods reception check

Copying check

Every new plate batch should be retested.

The first quick check is preferable performed with aline job, in which little can normally go wrong and theprinting plate can be used without difficulty follow-ing the test.

The printing plate is copied under the same condi-tions as for the old batch.

A test wedge (e.g., Stouffer wedge) is copied at thesame time.

The relief height is checked.

If nothing has changed compared with the last platebatch, the plate copy is in order.

If major changes are found, the printing platesshould be retested. In extreme cases the plate manu-facturer should be contacted.

Checking printing plate thick-ness with measuring unit

50

Standardizationprinting plate manufacture

Storage

The unexposed plate material is preferably storedflat in a cool, dry room.

Permissible storage temperature: 4–28 °C (Cyrel data)

Ideal storage temperature: 15–20 °C (BASF data)

A check of humidity is also necessary 40–60%

Sufficient conditioning of the plates to room temper-ature is necessary before use.

The printing plates are supplied in airtight, black foilbags impervious to moisture and light. This platepackage in turn is in a stable outer packaging. The rawplates should also be stored in this packing, sincethey are highly sensitive to pressure. This also ap-plies to opened packs.

Plastic foam intermediate layers should be placedbetween the raw plates to protect the sensitive sur-faces of the plates.

Cleanliness must be ensured when placing raw -plates on top of one another.

The raw plates must also not hang over the edges oftables and frames; they must lie flat.

Residual pieces or plate sections must not be placedbetween larger plates. They are best kept in a drawer.

Storage of raw printing plates


Handling

Room light

The raw material (unexposed printing plates) shouldonly be processed in UV-free light, never in daylight.The light sources must be screened from UV light.

It is necessary to cover the windows with suitable,tested UV protective foil. These clear foils are com-mercially available, e.g., from 3M.

Cleanliness

The working rooms must be kept free from dust andclean.

Additional freedom from dust can be achieved in theexposure zone with ionizing systems.

Handling printing plates

51


Definition

The required relief depth for flexographic printingplates results from the shortest possible wash-outtime and the pre-exposure time determined.

Wash-out test

1. Cut out four plate pieces not exposed on thereverse side, approx. 15 x 20 cm.

2. A small cover plate is placed on each piece of rawplate and the whole area exposed for 10 mins. inthe exposure unit. (Image on top)

3. The plate pieces are then washed out with differ-ent processing times in the continuous flow wash-out unit.

Testing the wash-out time

e.g.1st piece 3 mins.2nd piece 6 mins.3rd piece 9 mins.4th piece 12 mins.

Finer gradations of passage times can also beused for a 2nd fine setting.

4. The plate pieces are dried for approx. 15 mins.(this drying time only applies to the test).

5. After drying, the thickness is measured at theplaces washed out.

The wash-out depth is obtained from the differencefrom the reference thickness.

Example:

Reference thickness 1700 µ

washed-out position – 1000 µ

wash-out depth determined 700 µ

52

The optimum wash-out time is correct if the requiredrelief depth is exceeded by 0.2 mm.

Example:

for required relief depth: 0.7 mm

correct wash-out depth: 0.9 mm

Wash-out temperatures

All manufacturers of printing plates supply wash-outagents. They can be used in part for various types ofplate from different plate manufacturers.

PER/n butanol 30 °C

Nylosolv II 30 °C

Optisol 28–30 °C

Flexosol 28–30 °C

Testing the wash-out time

53


Reverse side pre-exposure test

1. Cut out single-coated flexographic plate to format20 x 50 cm.

Place plate on vacuum table of exposer with relieflayer down. The relief coating is where the cover-ing foil is removed. The protective foil must remainon the plate, however, for reverse side exposure.

If the vacuum plate of the exposer is not free fromreflection, a non-reflecting base should be provid-ed for front and reverse side exposure (blackboard or red foil).

2. The printing plate cut out is covered with opaqueplate or pieces of film. The points where the plateslie are the measuring fields.

The first field always remains covered, the stageexposure starts at the 2nd field.

Reverse side exposure

Profile of test plate for variouspre-exposure times

3. The second stage is exposed (e.g., with 5 secs. forplates 1.14 mm thick).

The 2nd cover plate is then removed and a further5 secs exposure performed.

The 3rd cover plate is then removed until all fieldsare uncovered (except the 1st field).

Normally approx. 8 stages/fields are exposed,according to the adjoining exposure diagram.

Washing out the test

The exposed test printing plate is then washed outaccording to the time determined in the wash-outtest depending on the relief depth required.

It is necessary to dry the plates for approx. 15 mins.to measure the different stages.

The relationship between

• the pre-exposure time• the wash-out time• the relief depthcan then be seen.

54

Reverse side exposure

Long pre-exposure + short wash-out time

= flat relief

Short pre-exposure + long wash-out time

= deep relief

The times for reverse side exposure and wash-outmust always be mutually adapted, so that wash-outtakes place down to the polymerized base.

The reason for the recommended additional time for0.2 mm extra relief depth is as follows:

A transition phase in which the material is partlypolymerized takes place between the lower part ofthe coating polymerized by reverse side pre-expo-sure and the non-polymerized upper part. This par-tially polymerized material should be largely washedout, so that the relief platform and base are in a fullypolymerized zone.

Since this material is detached more slowly, how-ever, it is necessary to prolong the wash-out time.

1st exposure

2nd exposure

3rd exposure

4th exposure (etc.)

Criteria for the choice of relief depth:

• Screen or line work

• Substrate conditions

• Machine circumstances

A fine screen and/or vignette should be producedwith a relief depth of 0.7 mm since with a deeperrelief the fine 2–5% screen dots are no longer ancho-red. This is called dot loss.

Rough, dusty substrates require a deeper relief.

55


Test for main exposure

There are various methods for testing the mainexposure.

Stouffer wedge

Many companies copying printing plates use the 21-step Stouffer test wedge. This small test film strip canalso copy during normal plate production withoutproducing waste plates.

The Stouffer wedge is a half-tone test element. Steps16–17 should still be on the plate for screen printing,steps 18–21 should be washed out. In steps 20 and 21the relief flanks should stand firmly.

For solid area printing it is sufficient if steps 15–16

stand on the plate.

Main exposure

Test films from manufacturers of printing plates

The printing plate manufacturers also supply testfilms for testing the main exposure. These are usuallyfilms with various uses of the same test elements.

Main exposure test

1. A plate for the size of the test negative is cut out forthe main exposure test. New plate material shouldbe used and not remnants.

2. The raw plate is pre-exposed from the reverse sideand without film over the entire surface for thetime determined for the reverse side exposure.

3. The raw plate is turned over so that the relief layeris on top and the protective foil removed.

The test film is placed with the coated side (matfilm side) on the printing plate. The film is coveredlaterally with profiled foil covering strips to ensurea good vacuum. This also avoids gluing the vacu-um foil to the cut edges of the plate.

Stouffer test wedge

56

Main exposure

After switching on the vacuum pump, the vacuumfoil is rolled evenly over the printing plate.

The vacuum foil is rubbed on with a roller or anantistatic cloth to prevent the formation of airpockets. This also makes unevenness visible,owing to dust or dirt which must be removedwithout fail to prevent copying errors.

4. The main exposure time is then determined witha multi-stage test like the reverse side exposure(diagram on following page).

Example:

Expose 8 labels for 2 mins.

Expose the 1st label, cover the other 7.

Expose the 2nd label, cover the other 6.

Expose the 3rd label, cover the other 5,

etc.

When all 8 labels have been exposed, the

• 1st label is exposed 16 minutes and the

• 8th label 2 mins.

The times stated here are only rough guides. Whenthe approximate main exposure time has been deter-mined after washing-out the plate, a 2nd test can beexposed with a finer gradation.

5. The exposed printing plate is washed out anddried. It should then be evaluated. The correctexposure time can be recognised from the variedformation of the relief.

1st exposure +2 mins.

2nd exposure +2 mins.

3rd exposure +2 mins.

4th exposure +2 mins.

etc.

plate

plate test film

covering board

57

The following factors can influence the exposuretime:

• Power of fluorescent tubes

• Number of fluorescent tubes

• Transparency of vacuum cloth

Caution:

Only original films should be used for the exposuretest!

The times near the upper exposure limit shouldalways be selected for plate production. This ensuresthat the plate is fully polymerized to obtain thefollowing advantages:

• Optimum plate hardness

• Good elasticity

• Resistance to solvent

• Resistance to cracking

Types of fluorescent tubes

The following tubes can be used:

• Philips TL 10 R

• Sylvania BL 366

Main exposure

58


After washing out, the printing plate is dried in adrying cabinet, on drawers and with a hot air blower.

It is important for the entire drying cabinet to be atthe same temperature, since otherwise the printingplates dry unevenly and the wash-out agent evapo-rates unevenly in the printing plate. Uneven dryingcan also cause differences in thickness of the printingplate, which can lead to displacements of tonal val-ues in the printed image.

The drying times specified by the plate manufactur-ers are always minimum values, but the dryingtemperatures are always maximum values.

If lower temperatures are used, the drying time mustbe increased.

Drying

Checks during drying

Drying of the plate should be checked after approx.15 mins. Residues or smears are rubbed off with afluff-free cloth or chamois leather soaked in freshwash-out agent.

Very important:

After drying, the plate should be left to rest for 12–15hours (e.g., overnight). This rest period is often notincluded or forgotten in the plate production time.

The printing plate should then be measured again.The difference in thickness within a dried plateshould not exceed 10–15 µm. The plate should ingeneral have the thickness of the raw plate again.

59


Secondary exposure is performed with UVC lightbefore after-treatment.

The plate is placed in the exposer unit with the relieflayer on top. No vacuum foil or vacuum is required.

The same time is used for secondary exposure as forthe main exposure.

Secondary exposure ensures that the plate

• is properly hardened/fully polymerized

• obtains optimum elasticity and resistance to sol-vent and cracking.

Secondary exposure with UVA light

60


Irradiation of the printing plate with UVC light elimi-nates the stickiness of the plate surface.

The after-treatment is not evident optically or visually.

The stickiness can be felt by pressing with the ball ofthe hand.

The after-treatment time is determined in stages:stages of 3–5 minutes

The optimum after-treatment time should not beexceeded, since otherwise cracks can form above allat the relief edges (flanks).

The plate should not be after-treated directly in theheat after drying. It must first cool down.

The drying time and rest period of the plate shouldbe observed before after-treatment, since otherwiseswellings left in the plate are fixed, which againcauses tonal value variations when printing.

Cracking can also occur in the plate surface if after-treatment is performed simultaneously with UVAand UVC light. This also applies if the temperature istoo high in the secondary exposure unit.

Caution:

Ozone is produced during after-treatment with lightwhich must be removed.

UVC light is extremely dangerous to the human eye.Only a few seconds eye contact can cause veryserious injury to the eyes.

Secondary exposure with UVC light Chemical after-treatment


Chemical after-treatment is performed as an alterna-tive to after-treatment with light.

The plate is immersed in a 4% bromine solution for

5 mins. The surface of the plate becomes mat and allstickiness is removed.

The temperature of the bath should be 18–22 °C.

A warm bath can accelerate the reaction.

Following the bromine bath the plate is immersed ina neutralizing bath for approx. 10 secs. and thenwashed with water.

Caution:

After-treatment solutions must only be used in unitsdesigned for the purpose, e.g.

• vessels with exhaust hoods

61


Delivery

The printing plates should be supplied as follows:

• Always laid flat

• In a cardboard box larger than the plates

• The soft, white, foamed protective foil of the origi-nal packing should be placed between the plates

• Clean

• Cut ready to size

Storage

The copied printing plates should be stored like rawplates.

The plates should be cleaned and dried before put-ting into store.

The relief layers of the plates should not lie together,but backing foil to backing foil. A soft protective foilshould be placed between the relief layers.

Caution:

Following storage for over 3 months the plate thick-ness decreases by approx. 10–15 µm. Old and newlycopied printing plates should not therefore be usedtogether for a printing job with difficult registers.

Delivery and storage of copied printing plates

Standardization test form

Test printing and demonstration forms

Why use test printing forms?

This is a highly controversial subject. No test formshould actually be required for printing evaluation.Anybody can see that an impression is different fromthe original, assuming they are not absolutely color-blind. When it is a matter of stating the cause of thediscrepancy, however, even experts can disagree.And they are probably all right. Deviations from thereference are not usually due to a single difference,but are generally of complex composition. In orderto tackle this variety of problem sources, controlelements are assembled and tested in test printingforms, from which standards are derived. Thesestandards then in turn serve to classify new testimpressions for quality. The same parameters canalso be used for process comparisons or qualityevaluations in machines.

Outline of composition of a test printingform

A sufficiently instructive test form must consist oftwo main parts:

1. One part for visual evaluation

Deviations from the reference can be determinedhere visually and without auxiliary aids. Imagesare usually selected, which are subject to variousevaluation criteria. One of the images shouldshow the interaction of the 3 Euro-colors withblack (depth). The second image shows grey tonesconsisting of the 3 Euro-colors. Black is subsidiaryhere.

62

Image evaluation

Before starting with the technical measuring para-meters, the image evaluation must first be consid-ered. We are less concerned with the purpose of useor gradation for reproduction, but more with re-cognition of technical printing degrees of difficulty.

The fine, colored images make the biggest impres-sion. These are also gladly shown very often by mostmachine manufacturers. Not only because they arebeautiful, but mainly because they scarcely showcoloring differences. The agreement of original andimpression is or would be the measure of quality.

The eye is unfortunately not very fair when compar-ing performance. Every picture consists of morethan one hue. If the eye looks at more than one huesimultaneously, it is automatically influenced bytheir differences. These differences are called con-trast. There are combinations of contrasts in everypicture:

– light-dark contrast– color contrast– formal contrast

The more complementary colors meet, the greaterthe contrast. Since the eye adjusts to existing con-trasts, it is not objective with respect to color differ-ences. The stronger the contrast, the less are colorvariations detected. But despite all this, we are moresensitive to color balance changes than to the picturegradation or contrast magnitudes.


2. The second part is used for technical evaluation

of measurements

Parts:– Solid area fields– Half-tone fields– Combined screen fields– Balance fields– Line fields– Cross-lines and vernier measuring elements– Screen vignettes– Surfaces– Ghosting and displacement fields

We shall return later to their individual significanceand interaction. Suitable measuring equipment isnaturally also required.

Technical printing quality gradations

This concerns printing quality. This is derived fromthe function of the printed product.

Quality criteria:– Uniformity of optical density in half-tone and solid areas– Tonal value reproduction– Color and detail reproduction– Uniformity of lines and screen– Gloss– Screen frequency– Ink layer thickness– Stencilling– Registers


63


What picture qualities can be distinguished?

Brunner has defined picture contrast classes from 0to 3. The class in which change of color balance is bestperceived is defined as 0.

Class 0Homogenous, three-color areas. Can scarcelybe printed without aberration.

Class 1Pictures with minimum contrasts, mainly com-pris-ing grey and brown hues. These also inclu-de large area skin images.

Class 2Pictures with normal contrasts. These are themajority of pictures.

Class 3Pictures with strong color contrasts.

We should now be able to evaluate pictures orprinting samples for their expressive power.

Technical printing parameters

Dot increase or screen dot widening

The deviation between screen tonal values in thefilm and in the impression is generally termed dotincrease. The dot growth in production of the printingform is usually forgotten. The consequence of this isthat dot increase is specified without any exactpoints of reference. If errors were made in the prelim-inary printing stage, these are continued as far as theprinting machine and thereby lead to an inexactstatement. For every plate behaves slightly different-ly in this respect.

Printing characteristic

The printing characteristic shows the deviation insize of the printed dot from the dot on the film. Formore accurate statements it would have to be deter-mined between the printed dot and the dot on theplate. It is only valid in each case for one machine,one substrate, one plate, one ink type and one blan-ket. This means that the printing characteristic mustbe determined again if a parameter is changed. It isdetermined with the aid of a screen grey scale andcalculated with the Murray-Davis formula. The lessthe dot increase, the greater the detail sharpness.

Resolution

Repro-films and printing plates; reproducibility offinest lines per mm, which represent a light sensitivelayer.

Standardization

Preparation of a reference to which instrumentalmeasurements are related. By standardization,achievement of the expected quality at the first at-tempt and reproduction of an already producedquality.

Register

There is not yet any generally recognised definitionin the technical literature. Various terms are used. Thecoincident position of successively printed elementson the same substrate side is termed the register.


64


Test forms

These consist of measuring and control elements,which were already listed on page 1.

1. Solid area fields

These serve for densitometric control of densitiesand in superimposed printing of ink receptivity. Thisforms the basis for evaluation of other parameters.The screen tonal value, printing contrast and dotwidening can be determined in conjunction with thehalf-tone field.

2. Half-tone fields

These differ in the degrees of surface coverage = Ffilm.Ffilm always refers to the film, i.e., an Ffilm = 40%indicates this in the film. On the printing form thisshows a difference by the copying process.

The half-tone fields can be graded in various ways.They start with light, signifying a low Ffilm and extendto very high shadows. The increase in tonal value andprinting contrast can be determined in conjunctionwith the density. The dot widening, and therefore theprinting characteristic, can be determined from theincrease in tonal value.

3. Combined screen fields

These are used as reference and comparative fields.These are a combination of fine and coarse screens.The tonal values of both fields are equal in optimumconditions.

As soon as increases in tonal value occur outsidetolerance, the fine screen fields are darker than thecoarse screen fields.

4. Balance fields

Half-tone fields for three-color superimposed print-ing are also called color balance or grey balancefields. They are used for visual check of the threeprimary colors. Slight changes in the ink layer thick-ness are shown very clearly.

5. Line fields

These are mainly used for a visual check of the platecopy, whereby the thickness and mutual spacingmust be sensibly graded. The resolution of the print-ing form can also be determined here.

6. Cross-lines and vernier measuring elements

These serve for the determination of register differ-ence. Only one linen tester is necessary for readingthe measured values.

Register differences always result in color change.They are not usually detected in this way, however,in production. It is endeavoured to correct them bychanging the color density.

7. Screen vignettes

The screen vignettes visually reveal disturbances inthe printed image, such as streaking, tonal valuebreakdowns and screen dot deformations.

8. Surfaces

The ink behaviour on the substrate, ink receptivityand drying are assessed with the aid of the solid areaprinting. The speckle behaviour is graded visually byspecifying the cloudiness and surface coverage.


65


9. Ghosting and displacement fields

These include screen or line images, which are dis-played several times and slightly displaced. Theyeach have different causes. With good test fields it isvisible what is concerned. The causes of ghosting canbe the substrate, the blanket or machine. Displace-ment is always a development problem, i.e., thescreen dot is deformed during the printing processby relative motion between blanket and printingplate.

Color variations and chromatic aberration

Chromatic aberration between original and impres-sion can occur if cleanliness and accuracy are notobserved during reproduction until the plate copy.The reason in the machine can be that the inks,rubber blanket, printing plate or substrate do notcomply with the standard. If the problem lies in thereproduction, the printer no longer has any remedialpossibility.

The causes for color variations within a series aredifficult to detect:

– the printer is unsuccessful in keeping the color density constant

– the climate in the machine room is not constant– too large register differences– change in viscosity of ink– change in pigment concentration– machine problems– soiling of engraved rollers

Our demo forms

Customers increasingly ask for test forms for ourmachine demonstrations.

Some want us to print the customer test form. Thismay be due to lack of confidence on the part of thecustomer. The suspicion that work is performed herewith modified values could lead to such a lack ofconfidence. We can vouch for our newly developedtest form. For the BASF form unfortunately only withreservation.

In general, however, only the printing quality isdemonstrated with these forms. The further workingsteps, such as hot foil embossing, blind embossingand punching, are not included. For these applica-tions we have our demo forms, which have mainlybeen on show at trade fairs.

In future an increasing number of machine demon-strations will be performed, so that a demo form isprinted first and then a test form.


66


Standard densities

Offset Flexographicvalues values

Cyan = DSP 1.40–1.50 = DSP 1.45–1.60

Magenta = DSP 1.35–1.45 = DSP 1.40–1.50

Yellow = DSP 1.30–1.40 = DSP 1.35–1.45

Black = DSP 1.70–1.90 = DSP 1.60–1.80

Values measured on high-gloss substrate (the valueson PE are approx. 0.1–0.2 lower with the same com-bination of plate, ink, adhesive and substrate. Rea-son: different surface tension of substrate).


The solid area density is measured with a densito-meter in the colors cyan, magenta, yellow and black.

Measurement setting: density

Secondary colors should not be measured with adensitometer, since this only has filters for the stan-dard colors listed above. If measurement is nev-ertheless made, the results are not valid and can atbest be used as points of reference. For secondarycolors the filter should be selected for the densito-meter which indicates the highest measured value.

Solid area density

Measured value density solid area

The measured value of a solid surface is called thesolid density (abbreviated to DV). It is determinedfrom the measuring elements or tapes printed at thesame time. Measurements can also be performedduring printing in cyan, magenta, yellow or blacksurfaces.

It is recommended also to print measuring elementsin all printing forms in all colors. 5 x 5 mm elementsin grid, bridge or at the edge can be printed at thesame time.

What can be checked

• Uniform ink transfer/ink volume over entire print-ing form.

• Ink volume check of engraved rollers, comparisonwith reference printing of engraved rollers, provi-sion of an engraved roller catalogue, determina-tion of soiling and wear of engraved rollers.

• Ink transfer of various printing plates, inks, platebases.

• Ink transfer to various substrates.

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Standard densities recommended by Gretag, supplemented for label printing

Substrate Color Reference density Density tolerance

High-gloss material Cyan 1.45 +/–0.10Art paper Magenta 1.40 +/–0.10Chromo Yellow 1.40 +/–0.10

Black 1.85 +/–0.15

Mat-coated paper Cyan 1.35 +/–0.10PE Magenta 1.30 +/–0.10Semi-gloss paper Yellow 1.30 +/–0.10

Black 1.75 +/–0.15

Uncoated paper Cyan 1.20 +/–0.10Vellum Magenta 1.15 +/–0.10Thermo-paper Yellow 1.20 +/–0.10

Black 1.55 +/–0.15

The densities in yellow are measured with the 47 B filter.

This table is provided as a supplement to and as an overall review of the foregoing table.

Solid area density

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Formula

TWZ (%) = FD-FF

TWZ = tonal value increase

FD = surface coverage in impression

FF = surface coverage in film


The increase in tonal value can be measured with adensitometer.

Measurement setting: increase or surface coverage

The increase in tonal value TWZ is found from thedifference between the measured half-tone value in theimpression FD and the half-tone value in the film FF.

The half-tone value in the film must be known,however, or measured with a transmitted light den-sitometer in the reproduction.

Only the colors cyan, magenta, yellow and black canbe measured. The measured value for secondarycolors is not valid.

The following parameters influencethe increase in tonal value

Machine:

• Printing stability

• True running

• Printing adjustment

• Printing process

Ink:

• Viscosity


• Pigments

• Ink volume used for printing

• Ink density

Engraved roller:

• The screen dots dip in the cells of the engravedroller in the ratio of number of lines of engravedroller to number of lines in the film.

Film:

• Film exposure (also film density)

• Dot form

• Screen width

Printing plate:

• Hardness of printing plate

• Construction of printing plate

• Plate copy

• Resolution of printing plate

• Swelling behaviour with respect to UV ink

• Printing adjustment to engraved roller and sub-strate

• Ink transfer of printing plate (plate surface)

Printing plate base:

• Hardness

• Thickness

• Reset behaviour

• Combination with printing plate

Substrate:

• Surface (closed, rough)

• Absorbency

• Ink receptivity (also surface tension)

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The graphical representation of increase in tonalvalue is called the printing characteristic curve. It isone of the basic tools for standardization and pro-vides the specialist with information concerning:

• How the machine is currently printing.

• How materials, i.e., ink, adhesive, printing plate orsubstrate, are used in an optimum way. Materialscan therefore be compared.

• How the repro-specialist must correct the films forthis machine.

The printing characteristic should be prepared forevery machine in operation with the materials mostused. This single additional expense pays for itselfduring the following production by lower reproduc-tion costs. It is also a great advantage to know aboutthe machine and materials. New materials can thenalways be evaluated without prejudice and used inan optimum way.


Various printing characteristics for different material

combinations and machines have already been pro-

duced by Gallus and can be obtained by Gallus

customers.

The Gallus printing department also offers support

and workshops for the preparation of the printing

characteristic.


% s

urf

ace

cove

rag

e in

imp

ress

ion

FD


0 10 20 30 40 50 60 70 80 90 100

100

90

80

70

60

50

40

30

20

10

0

0 10 20 30 40 50 60 70 80 90 100

50

45

40

35

30

25

20

15

10

05

0


% t

on

al v

alu

e in

crea

se in

imp

ress

ion


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Preparation of a printing characteristic

A corresponding printing form is also required forthe preparation of a printing characteristic. It is bestto produce a test printing form with the correspon-ding measuring elements. These are above all rowswith screen fields in the tonal values 1–100%. Themeasuring fields should be selected as large aspossible to permit several parallel measurements onthe same field. Measuring wedges in various screenwidths are also always an advantage.

Important!

The tonal values of the measuring fields must bemeasured and known in the film, so that the exactincrease in tonal value can be calculated.



% s

urf

ace

cove

rag

e in

imp

ress

ion

FD


0 10 20 30 40 50 60 70 80 90 100

100

90

80

70

60

50

40

30

20

10

0

0 10 20 30 40 50 60 70 80 90 100

50

45

40

35

30

25

20

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10

05

0


% t

on

al v

alu

e in

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se in

imp

ress

ion


71

Inksdetermined from best

recommendation or from test

Visual evaluation by eye

Determination of suitable printing plates/adhesive combination

Standardization

Working sequence for selectionof most suitable materials

Gallus test formor another suitable,measured test form

Printing plates+ adhesive foils

from various manufacturers

Machine

Proof printingwith specific solid area

densities

Determine printingcharacteristic

with densitometer

Compare and evaluateprinting results

Pass on data to reproand printing form

production

Substratesmost used in operation

Solid area densitiesflexographic printing

Cyan AVT 1,45–1,60 Magenta AVT 1,40–1,50 Yellow AVT 1,35–1,45 Black AVT 1,60–1,80

72

Determination of suitable printing ink

Standardization

Working sequence for selectionof most suitable materials

Printing plates + adhesive foilsdetermined from best recom-

mendation or from test

Visual evaluation by eye

Gallus test formor another suitable,measured test form

Inksfrom various manufacturers

of various ink series

Machine

Proof printingwith specific solid area

densities

Determine printingcharacteristic

with densitometer

Compare and evaluateprinting results

Pass on data to reproand printing form

production

Substratesmost used in operation

Solid area densitiesflexographic printing

Cyan AVT 1,45–1,60 Magenta AVT 1,40–1,50 Yellow AVT 1,35–1,45 Black AVT 1,60–1,80

73

Plate adhesive foil

Standardization

Foil summaryMake Foil type Nr. Foil Printing Applications Advantages Disadventages

thickness platethickness

mm mm

TESA Softprint 52380 0,38 1,70 Labels Half-tone printing Printout in surface printing,usable 1 x

1,14 Folding cartons Half-tone printing Shows unevennessof substrate in image

TESA Softprint 52382 0,38 1,70 Labels All-round foil More tonal value increaseCan be used several timesmixed printing forms

TESA Tesaprint 52338 0,38 1,70 Foil printing Surface printing No half-tone printingUsed with multi-coated with normal flexoprinting plates plates possible

TESA Tesaprint 52916 0,1 1,70 Labels Mounting of printing1,14 Foil printing Plates on sleeve cylinder0,76

3 M 1115 0,38 1,70 Labels Half-tone printing Printout in surface printing,usable 1 x

1,14 Foil printing Half-tone printing Shows unevennessof substrate in image

3 M 1120 0,50 1,70 Labels Half-tone printing Printout in surface printing,usable 1 x


3 M 1015 0,38 1,70 Labels All-round foil Greater increaseFoil printing in tonal valueCan be used several timesmixed printing forms

3 M 1020 0,50 1,70 Folding cartons All-round foil Greater increaseCan be used several times in tonal valuemixed printing forms

Harley green 0,38 1,70 Labels Half-tone printing Printout in surface printing,Can be used several times


Rogers R/back 0,95 1,14 Labels All-round foil Not suitable for all 1.14 mmCan be used several times platesmixed printing forms

standardization uv flexo manual

Documents

screen dots dip

hot foil embossing

reverse side exposure

solid area printing

solid area density

density solid area

uv flexographic printing

determine printing characteristic