INJECTION MOLDING GUIDELINE

PMMA ALTUGLAS granules

Edition 3/ 10.02.2004 / 21 pages

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These suggestions and data are based on information we believe to be reliable. They are offered in good faith,but without guarantee,as conditions and methods of use of our products are beyond our control.Atoglas makes no warranties,either express or implied,as to accuracy of these data. Atoglas expressly disclaims any implied warranty of fitness for a particular purpose.We recommend that the prospective user determine the suitability of our material and suggestions before adopting them on a commercial scale.

Injection moulding processing of Altuglas granules

Influence of the parameters vs. visible defects

Processing parameters Visible defects

1 Pre drying of the granules Silver streaks Little bubbles (high thick item)

2

Handling of the granules Whitening / white and coloured streaks/ inclusion

3 Melt temperature Silver streaks / white bubbles wrong filling/crazing

4 Mould temperature Transparent bubbles/wrong filling

5 Pressure / Hold pressure Wrong filling / transparent bubble breaking / crazing

6 Back pressure and screw speed Black streaks/ irregular dosing/ overheating

7 Injection speed Splash / silver streaks /black streaks /orientation/wrong filling

8 Tool design : runner / gate Wrong filling / jet filling / 9 Tool design: cavity Demoulding / warpage/wrong

filling / item breakiage 10 Tool design: hot runners Splash / overheating / silver

Streaks /wrong filling

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Pre drying of the Altuglas granules Pre drying is an apparently simple process it is in practice the source of operational errors. The main reason being that the degree of moisture in the granule before it is dried and the humidity level finally reached are usually unknown. This problem can be solved ,even without moisture testing equipment, by defining the following parameters: AIR HUMIDITY DRYING TEMPERATURE DRYING TIME PMMA granules must be subjected to very accurate treatment to avoid contamination caused by dust and other polluting agents. Contamination during drying operation is mainly due to polymers tendency to electrostatic charges resulting from friction and to the granules abrading action on the surfaces of contact. The material used in the construction of pre- drying system must be selected carefully. Soft or easily alterable material s must be avoided. Material recommended for ancillaries : iron steel During drying in forced ventilation dryers the air must be purified and filtered to avoid the deposition of impurities on the polymer. Since Altuglas granules have a medium level hygroscopic behaviour, moisture is absorbed within the granules as well as on the surface. The moisture content of an air exposed granule increases constantly until it reaches an equilibrium which depends on the level of relative humidity in the air.

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Pre drying of the Altuglas granules

AIR HUMIDITY The ambient air can be contains some quantity of the water up to saturation, quantity of water increase in function of the ambient temperature.

At 20C 1 kg of air contains 14.7 gr of water

At 30C 1 Kg of air contains 20 gr of water

RELATIVE HUMIDITY OF THE AIR The relative humidity of the air is the real ratio that defines the water quantity into air at defined ambient conditions Relative ambient humidity Ambient temperature Water content into air

100% 20C 14.7 gr 70% 20C 11.7 gr. 50% 20C 7.35 gr.

Using standard drying system for granules the operative conditions are not completely controlled because ambient conditions are variables. It is normal, in fact, that using the same parameters for drying we have not the same results during the various production.

DEW POINT The content of absolute humidity in the air is usually referred to as dew point which is temperature at which humidity begin to condense. This is not an absolute value but must be related to a precise temperature. Lower dew point = greater drying speed and lower the level of residual moisture into granules.

Air temperature Water in 1 Kg of air + 15 C 10 gr

0 C 4.0 gr - 40 C 0.08 gr.

The dew point can be reduced considerably by using the de- humidifying filters, the most efficient filters, i.e. able to reduce the dew point to below 0 C, are silica gel based filters or molecular sieve filters with an air recycling system. The best results, dew point up to 40 C, are obtained when using a silica gel filter with cooler (higher temperature = lower efficiency of the gel) 4/21

Pre drying of the Altuglas granules

OPERATIVE CONDITIONS

DRYING TEMPERATURE / TIME

Altugflas De-humidifying Traditional Time/hours

VM - VML 65 70 C 70 75 C 2 4 V 920 70 75 C 75 80 C 2 4 V 920T 70 75 C 75 80 C 2 4 V 825T- HID 80 85 C 85 90 C 2 4 V044 V045 75 80 C 80 85 C 2 4

MI 2T 80 85 C 85 90 C 2 4 MI 4T 80 85 C 85 90C 2 4 MI 7T 75 80 C 80 85 C 2 4 DRT 75 80 C 80 85 C 2 4 HFI 7 70 75 C 75 80 C 2 4 HFI 10 70 75 C 75 80 C 2 4

HT 121 95 100 C 100 105 C 2 4 327 70 75 C 75 80 C 2 4 VOD 70 75 C 75 80 C 2 - 4

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Pre drying of the Altuglas 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

Technology

Level of criticity

Residual

moisture %

Extrusion with venting Critical level for processing > 0.25 Injection moulding venting Critical level for processing > 0.15 Injection moulding Level to produce normally 0.10 Injection moulding Level to obtaine good performances 0.07 Injection moulding Level to obtaine very good performances 0.05 Extrusion without venting Level to obtaine good performances 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)

% re

sidu

al m

oist

ure

into

gra

nule

s

ABC

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Handling of the Altuglas granules

The excellent clarity of Altuglas resin can be jeopartized with poor material handling. We seal our resins in heavy gauge, moisture resistant , PE lined drums or carton boxes. When loading hoppers, the container lid should be wiped clean to avoid contamination. The container should be kept covered during the run to keep dust and dirt from contaminating the contents of the container. Container should be resealed when not in use Hopper loaders must be disassembled and cleaned before loading if previously used for anything other than acrylic. Similarly, the machine hopper should be should be vacuumed and wiped down before use. A small amount of PS or other plastics resins as PC or SAN can contaminate an entire hopper load. Drying ovens must also be checked to avoid contamination from blowing fines and stray resins. Considering high hardness of the acrylic granules the material used for hopper, tubes for pneumatic transport and generally for all parts in contact with granules, must be iron steel in order to avoid contamination by friction.

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Melt temperature for Altuglas granules In injection moulding process the residence time of the material into cylinder and the thermal profile are the parameter in order to have a real temperature of the material or melt temperature. The melt temperature has a very important rule in processing because permits the control of the other parameters in order to works in very good processability conditions. The residence time evaluation is very important parameter to determine the values of the profile temperatures of the cylinder to obtain a correct melt temperature for each Oroglas type. In fact in some case is necessary to change the cylinder capacity in order to works without degradation problems. Evaluation of residence time The first data at disposal is the real injection capacity (normally for PS) that is function of diameter of the cylinder. Using the data concerning cylinder capacity and the density of melt of the other resins is possible to obtain an accurate data about real injection capacity. Real injection capacity = Real injection volume polymer density (at melt temperature)

Polymer ABS PA PC PE PMMA PP PS SAN

Density gr/cm3

0.88

0.91

0.97

0.71

0.95

0.73

0.91

0.88

Residence time real injection capacity 2 total cycle Item weight 60 Where : real injection capacity /item weight = gr. Total cycle = sec. 8/21

Melt temperature for Altuglas granules The residence time in injection moulding of Altuglas granules has a very important rule in order to obtain item at maximum quality level. Using for example Altuglas V 825T at 245C ( usual melt temperature) we have the following limit: Residence time < 1 minute: not correct plasticating presence on the items of the following defects: flow lines orange skin filling problems -

Residence time > 6 7 minutes : Degradation or depolymerisation presence on the items of bubbles transparent or white silver streaks black streaks The sequence of the defects is usually the following: 1. Silver streaks (1-2 moulded items) for overheating 2. Bubbles and black streaks (2-3 moulded item) for degradation. 3. Bubbles black streaks white bubbles after phases 1-2 principle depolymerisation. Evaluation of real melt temperature To evaluate correctly the real melt temperature is necessary to use the following method: - take the value when the injection machine works in production condition for 1020

moulded items ( about 10 20 minutes) - purge the cylinder and evaluate the melt temperature by thermometer introducing the

sensor into core of molten material. If the sensor is located into nozzle ,the melt temperature will be higher of 5-10 C than real value because friction due to injection.

Ideal melt temperature for Altuglas grades Altuglas VM V 920 V 920T VOD V 825 T V044 V045 HT 121 Melt C 200 225 230 230 240 245 245 Altuglas MI 2T MI4T MI7T DRT HFI7 HFI10 327 Melt C 235 235 240 245 225 235 235 9/21

Mould temperature for Altuglas granules The mould temperature is extremely important since it affects the overall properties of the moulded part (visually and physical) and the filling of the cavity. The effect on the item for not correct mould temperature are : LOW MOULD TEMPERATURE filling problems of the cavity orientation and stress into moulded item bad surface of the item (orange skin flow lines) - reason of the use of the low mould temperature is the total cycle reduction but the final result normally is to decrease the real production because higher reject level of the items HIGH MOULD TEMPERATURE good filling of the mould higher physical properties of the final item very long cooling time before ejection of the item reason of the use of high mould temperature is to increase performances of the photometry, the thermal properties and chemical resistance. MOULD TEMPERATURE for Altuglas grades Use of the oil as fluid for mould cooling system is recommended in order to control very well the temperature.

Altuglas grade Mould temperature C VM - VML 50 60 V 920 60 70 V 920 T VOD 70 80 V 825 T 75 85 V0 44 V0 45 70 80 HT 121 80 90 MI 2T MI 4T 70 80 MI 7T 70 75 DRT 70 80 HF I 7 HFI 10 60 70

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Pressure /hold pressure for Altuglas granules Injection pressure phase

1. Increasing 2. Maximum 3. Holding 4. Residual Filling sprue runner and partially cavity

Complete filling of the cavity.

Complete filling of the item to obtain:

visual aspect physical properties

Residual pressure on the mould wall after Injection phases.

Low influence

1. In this phase pressure have not particular influence on the moulded item because filling of the mould is not completed.

2. This phase is very important as level of pressure and application time because correlated with complete filling of the mould and clamping force on the mould. Low level and /or time Problem to fill the mould cavity High level and /or time Higher level than necessary of clamping force Opening of the mould with presence of the plastic material in parting line.

3. Holding pressure as level and /or application time is the key parameter to obtain the maximum of performances on moulded item from visual and physical point of view. To have a real effect on the moulded part, ensure an extra cushion of polymer after injection. Low level and/or time Surface irregularities Excessive linear shrinkage Transparent irregular bubbles High level and /or time Internal stress of the moulded part (crazing) Demoulding problem (breakage in ejection phase or spontaneous)

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Back pressure and screw speed for Altuglas granules Back pressure Moderate back pressure must be applied during feeding to confer an appropriate level of polymer packing during feeding. This value usually between 10 15% of the pressure available on the machine. Low level Air inclusion during feeding with presence of black streaks on moulded item High level High friction on the granules with possible degradation of the polymer by uncontrolled overheating. Screw rotation speed The number of screw turning varies in relation to its shape and diameter. The rotation speed must be chosen to ensure that feeding is constant. Generally the most commonly used range is between 40 80 RPM Low level Long feeding time with problem to remain in acceptable total cycle High level Big problem on the screw rotation during feeding up to block of the screw due to excessive friction Uncontrolled overheating with presence of bubble and /or silver streaks on moulded item

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Injection speed for Altuglas granules Injection speed varies according to the thickness of the item to be moulded. Generally lower speeds are used for very thick item, higher speeds for thinner items so that the mould is filled before the melted polymer is cooled. Low level Problem to fill correctly the item More evidence welding and flow marks High level Excessive friction into cylinder nozzle gate with presence of : - splash uncontrolled (mostly with hot runners) - bubbles and or burned polymer at the end of path length due to

overheating - black streaks in presence of little quantity of air trapped during feeding

The value of injection speed is usually between 20 50 mm/sec

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Tool design : traditional mould runner /gate /cavity

SPRUE : connects nozzle of cylinder to runner system

RUNNER : channels which transport material from sprue to the parts.Usually quite thick to avoid pressure loss and high shear.

GATE: transition between runner and part. Usually small this freezes first and once frozen the holding pressure is removed

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Tool design : runner / gate for Altuglas granules Runner Circular or trapezoidal rounded edges distribution runner are generally used since these facilitate the flow on the melted polymer, at the same time avoiding narrow curves or sharp changes of direction in the runners. However, it is important, within the limit allocated, as far as the number and position of the cavities is concerned, to use the shortest possible path. This results in maximum flexibility during the filling of the cavity together with the production of good quality items (both aesthetically and physical properties) The size of runner depends on the shape of the item, generally, 2 4 mm. thick items require a primary runner with a 3.5 5 mm. diameter whereas ticker items require a 7 15 mm diameter. The diameter of the secondary runner are usually 1 2 mm lower than primary runner. Gate (injection point) Gate size, shape and placement affect the flow pattern of material entering the mould and may influence the temperature of the melted material, fill time and overall part quality. In parts of variable cross section, the gate should be located in the thickest section to minimize fill problem. Generally, the gate thickness should be 50 60 % of the thickness of item for standard PMMA and 60 70 % for impact PMMA. Concerning centre gate or submarine plug the gate diameter will be between 0.8 2.0 mm. Runner and gate are the feeding system of the cavity, the typical defects with lower dimension in mould project are : Use of high melt temperature to fill the mould with problem of overheating and/or degradation. Use of high injection pressure values to fill the mould with problem of tension into item Bad quality of item aesthetic with presence of welding lines, orange skin, and usually very poor physical properties of the item : (i.e. bad optical performance in captadiotric part)

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TAB gate : avoids jetting and allows area of

highest strain to be removed.

SPRUE gate : provide simplicity for single cavity moulds and simmetry on circular shapes.

Suitable for thick sections.

SIDE gate : simple and can be used

for multicavity moulds.

PIN gate : very small circular gate.

used for thin section

easy to remove

GATES for PMMA

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FLASH gate : provides simultaneous filling over the whole length of the mouldto given even shrinkage along the length

EXTERNAL RING gate : used for multicavity concentric mouldings of ring shape or where a diaphram gate cannot be used.

INTERNAL RING gate : similar to diaphram gate, used for moulds with large internal diameters.

GATES for PMMA

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MULTI - POINT gate : similar to diaphram gate but may produces weld lines

TUNNEL or SUBMARINE gate :

provides automatic de - gating

only suitable for thin section

DIAPHRAM gate : used for single cavity concentric mouldings of ring shape with medium or small internal diameter.

GATES for PMMA

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Tool design: cavity for Altuglas granules When calculating the dimension of the cavity the shrinkage of the polymer during processing must be taken into account. Moreover, the surface of the cavity must be mirror polished to obtain a very good aesthetic aspect of the final item. It is important to avoid , as much as possible, undercut and sharp edges to ensure good demoulding and to avoid breaking the items during use. All the moulds must be fitted with thermostating fluid runners in order to improve filling , aesthetic and physical properties of the items. The setting and shape runners varies according to the item to be moulded and must be designed to ensure even cavity filling and uniform cooling. Air outlets around the cavity must also be included. These outlets must be large enough to ensure fast autflow of air, thus avoiding dead areas or stagnation during cavity filling which could result in surface faults due to localized overheating. Correct cavity and feeding system design permits to work with a large processing window avoiding the problems as : - overheating (silver streaks bubbles) - degradation (white bubbles black streaks) - overpacking (residual stress) - aesthetic of the item (orange skin flow lines ) - physical problems (irregular shrinkage , lower use temperature) - breakage ( during ejection or in use condition)

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Tool design : hot runner system

Mold with hot runners

pneumatic valve

very good for PMMA

free runner

good for PMMA

Torpedo system

NOT GOOD for PMMA

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Tool design: hot runners for Altuglas granules Hot runners system are widely used for acrylic polymers, especially in high productive sectors such as the automotive, household appliance, lighting industrie. The advantages of this technology can be summarized as follows: Eliminating the removal of the feeding system thus recovering polymer Reduce pressure loss during filling as a result of shorter path. Therefore, better control of the filling process and reduced cycles due to lower injected polymer volume are obtained. The disavantages generally are the follows: Changing colour is a longer and more delicate process More care and greater skills are required in handling the equipment The problems which usually arise during moulding are: Streaks as a result of uncontrolled overheating into hot runner Weld lines due to uncontrolled melt temperature into hot runner The problem of overheating is a direct result of friction stress undergone by the polymer in the narrow part of feeding system and is strictly related to both the systems geometry and to processing condition (temperature, injection speed profile) The weld lines are more evident in torpedo system where the polymer must flow into the support spokes. If the melted polymer is not homogeneous, weld lines, which join when the material is relatively cool, are produced on the finished item.

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