34640218 processing guides isbmbottlepresentation pdf 1

7/31/2019 34640218 Processing Guides Isbmbottlepresentation PDF 1

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Injection Stretch Blow Moldingof NatureWorks PLA


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Blow Molding of PLA


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General PLA vs. PET Properties

1.32Below Tg:

0.26 Above

Tg: 0.48

0.11510-575158-176PET

1.24

Below Tg:

0.29 Above

Tg: 0.51

0.11390-425131-140NatureWorks

PLA (7000D)

Specific

Gravity

(g/cc)

Specific Heat

(BTU/ lb oF)

Thermal

Conductivity

(BTU/ ft-hr-oF)

Process (Barrel)

Temperatures

(oF)

Glass

Transition

Temperature

(oF )


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Permeability Data

Resin OTR WVTR N CO

PLA 38-42 18-22 9.5 201

PET 3-6.1 1-2.8 15-25

Note: Units are ml mil/100 sq. in day for Oxygen and CO2; for water vapor transmission rate are in grams mil/100 sq. in day


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Injection Molding of PLAPreforms


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Trial Preparation

Review MSDS

Review Nature Works ISBM Guide

Ensure proper PPE is being used such as hand and eye protection

Ensure processing equipment is in proper working order.


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Prior to Injection Molding of NatureWorks PLA

PET and PLA are not compatible with each other. They processwithin significantly different temperature ranges.

This means that before running PLA on equipment normally used for

PET, certain items MUST be done beforehand.


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Prior to Injection Molding of NatureWorks PLA

All PET needs to be removed from the drying and conveying

equipment. This includes:

Dryer Hoppers

Vacuum Loaders

Air Filters on Dryers and Vacuum Loaders

Dryer Hoses Conveying Lines.

PET pellets or fines will show up in a PLA preform as un-melted

white particles.

PET contamination can be a difficult, and significant problem if

the cleaning steps are not completed before running PLA.


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Blow Molding of PLA Preforms

PET Contamination


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Drying of NatureWorks PLA

NatureWorks PLA needs to be dry before processing. Failure to do so

may result in significant molecular weight loss due to the combination

of moisture and heat during processing.

Significant reduction in molecular weight can result in preforms that

provide an inconsistent blow molding process, and bottles with poor

physical and mechanical properties.

PLA must be dried using a desiccated drying system that is in good

working order. Dryer should operate with a dew point of -40oF or

lower.


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2.1 hr70C

3.3 hr60C

3.9 hr50C

4.3 hr40C

Drying Half Time (t1/2)Drying Temperature

Required drying time is dependent on the initial moisture level in the resin.Typically, NatureWorks 7000D is dried at 70C for at least 4-6 hrs before injectionmolding.

It is best to make sure that the dryer being used does not have big temperaturespikes during the regeneration process which can result in pellets blocking inthe cone.


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Drying Curve

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5 6 7 8 9

Time (hrs)

MoistureLevel(ppm)

Amorphous 40 C Amorphous 50 C

Crystalline 50 C Crystalline 80 C


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Purging Injection Molder of PET

Since PET melt processes at higher temperatures than PLA, one should

use an intermediate polymer such as a medium melt index PP (4-8MFR), GPPS, or PETG (0.7 IV), to expel the PET from the systembefore adding PLA. PP is the recommended as being the best of the 3resins for purging.

A typical purging compound may also work as a substitute if PS or PP

are not available.

Purging times vary due to machine characteristics.

Injection Molders with shooting pots can take longer to purge thanconventional machines due to more areas available where resin canhang up.


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Purging Injection Molder of PET

1. Introduce a medium melt flow PP (5 - 8 MFR) at normal PET operating temperatures. Purge 10-30 minutes asnecessary. Let system empty as much as possible. Clean our hopper as much as possible.

2. Change to normal PLA operating temperatures.

3. Purge 10-30 minutes as necessary. Let system empty as much as possible.

4. Alternatively, you can purge with a high flow PETG (similar to Eastman copolymer 6763), or GPPS. Thenreduce temperatures to PLA conditions.

5. Stop injection molder and completely clean all hoppers, elbow, slide gates, dryers, hopper loaders bins, hopperloader filters and material conveying lines of residual PET. Load PLA into material handling system.

6. Transition to PLA and purge until melt is clear of any contamination.

7. In order to get PET out of hot-runner, one might have to temporarily increase runner temperatures to 240C or250C until all PET is expelled. Once this is complete you may decrease to normal PLA operating temperatures.

8. At the completion of the run, purge all PLA from the extrusion system, by ramping up temperatures and addingPET back into system.


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Preform Production

Normal PLA injection molding conditions

0.004 in/in +/- 0.001Mold Shrinkage

150-200 psiBack Pressure

50-100 rpmScrew Speed

77 (25)Mold

425 (218)Nozzle Tips

420 (216)Hot Runner

415 (213)Metering Section

410 (210)Compression Section

355 (180)Feed Section

70 (20)Feed throat

Barrel Temperature Setting, F (oC)Zone

(Please note that these are recommended starting parameters and may need to be optimized)


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Injection Molding of NatureWorks PLA

When injection molding PLA for the first time it is usually best to

increase the cooling time by 20-25% over normal PET conditions in

order to find the parameters needed to make a quality part first.

Once these conditions are found, then start decreasing the cooling time

in increments of 5 seconds until the minimum cooling time is reached.

Since the glass transition of PLA is lower than PET, a slightly longer

cooling time might be required in order for the parts to set up properly.

This usually effects the overall cycle time of around 3-6 seconds

depending on the tooling, equipment, mold temperature, and melttemperature being used.


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Injection Molding of NatureWorks PLA

Moldflow Plastics Labs has done an analysis on injection molding of

NatureWorks PLA 7000D.

A report (.pdf) is available on the Moldflow database or by request

from NatureWorks LLC.

This report details some specifics about NatureWorks PLA for

injection molding such as shrinkage, viscosity, and thermal properties.


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Blow Molding of PLA


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NatureWorks PLA can be reheat blow molded using conventionalequipment typically utilized for PET.

PLA typically is blow molded using lower processing temperaturesthan PET. Preform temperatures are usually 85-95C going into theblow mold.

PLA is more temperature sensitive than PET. Smaller temperature

changes can result in changes to material distribution within the bottle.

PLA stretch rod speeds are slightly faster than what is typically usedfor PET, but are also specific to a particular preform, bottle, andprocess equipment.

An adequate oven length will also be required in order to get the innerwall of the preform hot enough for stretching. The use of a reheatadditive might also be desired.


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When Blow Molding PLA preforms for the first time, one of the most

common problems is making a bottle that it too heavy in the base

region.

This can result in a loss to drop impact strength due to less orientation

of the plastic in this region of the bottle.

It can also result in the deformation and the popping out of the base

pushup due to the material still being to hot after leaving the blow

mold.

It is best to adjust oven temperatures, and preblow timing in order to

get the best material distribution possible. A bottle design that has ribs

in the base to help spread material out is also beneficial.


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Deformation of Base Pushup


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Preform Design

Usually, using PLA in a preform initially designed for PETwill work. It is likely, however, that you will need tochange some aspects of the blowing process. If desired,

changes to the design can be made specifically for PLA.

Typical Stretch Ratios Include:

Axial: 2.8-3.2

Radial:3-4

It has also been found that PLA works well in preformswith shorter, uniform, and less abrupt transitions that arefound in some preforms used with PET.


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General Information

On the web, go to natureworksllc.com for more information about

NatureWorks, and NatureWorks PLA.

On the website you can find tech datasheets, latest news, and other

applications where NatureWorks PLA is being used.

Corporate Customer Service:

USA/Canada 1-877-423-7659

Europe +31-(0)35-699-1344 Japan 81-33-285-0824


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General Information

NatureWorks LLC has been working in the area of technical

development with Plastic Technologies Inc. (PTI) as well as Husky

Injection Molding Systems.

Both of these companies have been providing consultation for

NatureWorks customers with specific issues, such as preform and

tooling design, as well as the injection molding and blow molding

processes.

PTI Husky Injection Molding Systems

1440 Timberwolf Dr. 530 Queen Street South

Holland, OH 43528 Bolton, Ontario Canada LE7 5S5

(419) 867-5400 (905) 951-5000


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Thank You

www.natureworkspla.com

34640218 processing guides isbmbottlepresentation pdf 1

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