coextrusion pmma
TRANSCRIPT
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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/
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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.
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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
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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
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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
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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
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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
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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
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EXTRUDER ATTACHMENTS
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
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EXTRUDER ATTACHMENTS
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)
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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
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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
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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.
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EXTRUDED/ COEXTRUDED PROFILES
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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
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Steel,polishing, temperatures
control as die for flat sheet
Steel,polishing as die for flat sheettemperature : 60 -70 °C
Water temperature
40 - 50 °C
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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
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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 »
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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
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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: