COEXTRUSION PMMA

8/9/2019 COEXTRUSION PMMA

1/20

EXTRUSION GUIDELINE

PMMA ALTUGLAS ® granules

Edition4/21.01.2005/ 20pages

PMMA Altuglas ® Training

Return to Advanced Polymers

http://www.advancedpolymers.co.za/http://www.advancedpolymers.co.za/


2/20

EXTRUSION EQUIPMENT

ALTUGLAS ® granules can be processed on any conventional

extrusion equipment as long as the machine has sufficient horse-power to extrude at desidered output rate.

EXTRUDERS

The general specifications for extruders and methods of heating,coolingand controlling are the same for ALTUGLAS ® resins and for most other

plastic.

Nitrided steel barrels and screw should not be used,their tendency to givetrace contamination by abrasion can be objectionable in processing clearand translucent colours.

Xaloy barrels and hard tipped flight lands are recommended.

Chrome plating of the screw is not necessary for satisfactory processing but

s recommended because it makes sleaning the screw easier and providescorrosion and abrasion resistant surface.


3/20

A wide of variety of screw design may be used to process Altuglas® resins.

Only properly designed screw will produce high quality sheet or profileshapes from Altuglas® granules.

Single - stage or two stage- screw may be used.

With two stages screw extrudate temperatures and output rates are moreuniform. Vacuum should be applied at the vent part of the barrel when

processing with two stage screw, otherwise,volatiles streaks may be appear

n the extrudate.

Single stage screw

Feed zone sectionMetering section Transition section

Single stage screw should have a L/D ratio 20 : 1 and medium

compression ratio 2.2 - 2.8

COMPRESSION ratio Ratio of depth of channel in feedsection to depth of channel inmetering section

L / D ratioRatio of length of screw todiameter of screw

With single stage screw it is very important to dry very well the granules.

Level of residual moisture into granules ≤ 0.03%

EXTRUSION EQUIPMENT


4/20

Pre drying of the ALTUGLAS® granules

OPERATIVE CONDITIONS

DRYING TEMPERATURE / TIME

Altuglas®grade De-humidifying Traditional Time/hours

V 920T 70 – 75 °C 75 – 80 °C 2 – 4

V044 – V045

V 04675 – 80 °C 80 – 85 °C 2 – 4

MI 4T 80 – 85 °C 85 – 90°C 2 – 4

MI 7T 75 – 80 °C 80 – 85 °C 2 – 4

DRT 75 – 80 °C 80 – 85 °C 2 – 4

HT 121 95 – 100 °C 100 – 105 °C 2 – 4

327 70 – 75 °C 75 – 80 °C 2 – 4


5/20

Pre drying of theAltuglas® granules

A= air at 70% U.R. B = air at 50% U.R. C = air at dew point – 40°C

Level of residual moisture into granules vs. processability

Extrusion with venting system up to 0.25 %

Extrusion without venting system ≤ 0.03%

Effect of the air humidity vs drying performances

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

1 2 3 4

drying time (hours)

% r

e s i d u a l m o i s t u r e i n t o g r a n u l e

A

B

C


6/20

COMPRESSION ratioRatio of depth of channel in feed

section to depth of channel inmetering section

L / D ratioRatio of length of screw todiameter of screw

Two stage screw

VENT

Feed zone section

Transition

2 nd Metering

Transition

1st Metering

VENT

Vacuum pump

Single stage screw should have a L/D ratio of 24 : 1 to 35:1

and medium compression ratio 2.2 - 2.8

EXTRUSION EQUIPMENT


7/20

TWIN SCREW

IT IS POSSIBLE THE USE ALSO

WITH Altuglas ® grades.

The profile of the screw must bedecided with extruder producer in

order to avoid :

uncontrolled friction,high shear

stress, uncontrolled overheating.

EXTRUSION EQUIPMENT


8/20

EXTRUDER ATTACHMENTS

BREAKER PLATES AND SCREENS

n general,use a breaker plate with nominal screening 20/40 or 20/40/60 meshacks are typical.

Additional screens can be help when the die offers low resistance to flow andhe screw has limited mixing or homogenizing ability

STATIC MIXER

Static mixers are frequently inserted between the extruder and the die toprovide mixing and to promote greater uniformity in the melt temperature ofthe extrudate presented to the die and may conceivably permit higher output

rate without instability.

Whe properly designed,installed and temperature - controlled these unitsproduce only a small drop in pressure.

Typical static - mixer

for extrusion lines


9/20


MELT - PUMPS

Melt pumps are used tro give morestable output to improve yeld and

product quality.

They can also increase increase

output rates.

DIES

Many different commercial sheet or profile dies have been usedsuccessfully to extrudate Altuglas ® granules.

It is essential to provide dies with an effective and properly balancedheating system having adequate sensitive controls, expecially when the

die is divided into heat zones,as in the usual sheet die

DIE FLAT SHEET


10/20


DIES

When an extrudate with minimal die lines must be produced,

the finish of the die lips is very important,particularly in the area

at and just ahead of the point where the melt leaves the lip

surface.

LIPS

Irregularities in the die lip surfaces in this area .whether caused

by mechanical imperfections or corrosion damage,can produce

die lines.

Serious rapid corrosion can occour at the die lip discharge if the

lips are low grade steel and expecially if moisture has not been

effectively removed from the melt and escapes at this point.

A good grade of alloy tool steel is certainly preferable when the

die must produce good results over a prolonged period.

Although chrome plating of the die flow surface is not necessary

but offers some benefits as low polymer adhesion / corrosion.

Disadvantages is the maintenance in case of damageGOOD COMPROMISE :excellent steel polished (mirror surface)


11/20

OPERATING CONDITION IN THE EXTRUDER

Extruder cylinder temperature setting vary with circumstance,

machine and screw design. The table annexed lists range of

temperatures applicable to Altuglas ® grades.

Extrusion line

Altuglas ®

V0 44 – 45 -46

Altuglas ®

MI7T - DRT

Screw zone 1 (feed) 200 – 220 °C 205 –225 °C

Screw zone 2 (feed/ transition) 215 –235 °C 220 –235 °C

Screw zone 3 (metering)

220 –240 °C 225 –240 °C

Screw zone 4 (vent) 225 –245 °C 225 –245 °C

Screw zone 5 (metering) 225 –240 °C 225 –245 °C

Adapter zone220 –240 °C 220 –245 °C

DIE 220 –240°C 220 –245 °C

Melt temperature 230 –245 °C 230 –245 °C

Screw speed 40 – 100 RPM 40 – 100 RPM


12/20

OPERATING CONDITION IN THE EXTRUDER

The most important temperature,and one usyally most difficult toestablish is the rear zone (feed) because this temperature affect the

frictional forces in the feed area,it has a strong influence on the dry

solid conveyng rate and is therefore important in determining the

motor load and process rate.

The temperature of this zone should be given primary attention

particularly in a first run, and should be adjusted to provide apermissible steady motor load and minimum variation of pressure

MELT TEMPERATURE

In operating extruders at relatively low productivity, a direct

correlation can be expected between the melt temperature

developed a the screw discharge and the cylinder profiletemperature,expecially in machine of slow diameter.

Because of the effect of the screw design factor the influence of

the cylinder temperature on melt temperature decrease with

ncreasing poductivity. Other factors,such as screw speed, head

pressure assueme the major role in determining melt temperature

DIE TEMPERATURE

The die temperature can be choiced to provide the best compromise

etween any of the following objective:

. To optimize the flow distribution from the die

. To regulate on influence the head pressure

. To suppress surface defects


13/20

FLAT SHEET / OPERATED SHEET

Roll position Altuglas ®V0 44 – 45 -46

Altuglas ®MI 7T - DRT

1 100 – 110 °C 95 – 100°C

2 95 – 105 °C 85 – 95°C

3 90 – 100 °C 80 – 90 °C

Min. diameter of the roll : 300 mm.


14/20

EXTRUDED/ COEXTRUDED PROFILES


15/20

Equipments for extrusion are generally made up of 3

parts:

a die performing and arranging the profile ’s geometry

a calibrator perfectioning the final product

a cooling system (in thermoregulated water)

CALIBRATOR

COOLING SYSTEM

DIE


16/20

Steel,polishing, temperatures

control as die for flat sheet

Steel,polishing as die for flat sheettemperature : 60 -70 °C

Water temperature

40 - 50 °C


17/20

COEXTRUSION

Coextrusion is the process of extruding one material

on top of another.

Several layers are possible.

Two (or more) extruders required

Two main technologies :

Black box system

Multimanifold die


18/20

COEXTRUSION

Concept of coextrusion is to obtain a final item (flat sheet,profile,tube)

with various layers using different polymers to obtain a final structureusing the specific properties of each polymer.

Example of application : two layers sheet ABS - PMMA to have a very

good mechanical propertiesl (ABS) very high aesthetic aspect level andexcellent wheaterability (PMMA)

Technology is the same of traditional extrusion using modified diegeometry and one extruder for each polymer.

It is possible to obtain final possible structure up to 8 - 10 layers

(experimental level) as example in food packaging sector where arerequested normally some properties as : mechanical,aspect, gas barrier,ambiental humidity barrier….

Normally we have in industrial production item with 2 layers when theadhesion is very good between the polymers, 3 layers when the level of

the adhesion is poor using a polymer in the core of the structure havingexcellent adhesion between basic polymers (glue polymer)

PMMA

ABS

PMMA

HIPS

PMMA

ABS

HIPS

Good adhesion

Poor adhesion

Good adhesion

ABS used as « glue polymer »


19/20

COEXTRUSION

dies

Traditional die flat sheet

Coextrusion 2 layers : BLACK BOX system

ADVANTAGES DISADVANTAGES

Simplicity - low cost

Existing die can be

used( little modification)

High number oflayers possibility

Restricted range of MFR

between the polymers

Not possible individualthickness control of the

layers.

Coextrusion 3 layers : MULTIMANIFOLD DIE

ADVANTAGES DISADVANTAGES

Polymers with large MFR

range can be used

Individual thicknesscontrol for each layer

High degree of layeruniformity

Complex die design

High die cost

Limited number of

layers can be used


20/20

START- UP Conditions

is important to recognize that the « static » temperatures established at thearrel walls,screw surface,adapter,die melt passages during heat up can be

lered substantially by the shearing force and frictional heat developed underdynamic » operation. With the possible exception of the surface temperature

t the front and rear ends of the screw,these temperatures tend to increases

s the machine enter its operating mode. A reduction in motor load andperating stress in the equipment usually occours as the machine aproaches

tressing of the equipment during start up

START - UP Procedures

Before start - up, set the temperatures controls for each zone to give thepredetermined temperatures and throughly heat the extruder and die. At the

end of preheating period,start the screw at low speed whilee making sure tofeed material slowly from the hopper. Never run the screw dry. Continue

running the screw at low speed until an uniform extrusion is obtained at thedie.

f the pressure becomes too great,stop the run,determine the cause of the

difficulty and correct the faulty condition. When the flow of extrudate issatisfactory increase the screw speed gradually and adjust the temperaturesetting to operating conditions. In starting a partially loaded extruder that

has cooled the preheating period should be long enough to soften the

plastic in the barrel and die so that it can flow and permit rotation of thescrew without excessive resistance.

SHUTDOWN Procedure

If the operation is stopped for any lenght of time,shut off the feed and

immediately reduce the screw speed to a minimum. Run the screw at slowspeed until material stops flowing from the die,then turn off the extruder

EXTRUSION GENERAL RECOMMENDATIONS:

COEXTRUSION PMMA

Documents