Multiflex Thermoplastic Elastomers

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Brianna Daniels
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1 Multiflex Thermoplastic Elastomers Molding manual Injection molding Extrusion Overmolding M a t e r i a l s t o w i n

2 INJECTION MOULDING 1. PROCESSING MACHINERY - Can be processed on conventional reciprocating type Injection Moulding machines, which are used for Thermoplastics. These machines provide uniform melt characteristics and high shear rate which is required for fast and uniform injection moulding. - Compression ratio of atleast 2:1 and a L/d ratio of atleast 20:1. - Conventional nozzles are acceptable as these materials do not release any volatile products on heating- thus, drooling at the nozzle is seldom a problem. 2. CLEANING OF MACHINERY The machine should be purged with POLYPROPYLENE before beginning processing of Multiflex. Again when another material is to be used afterwards, machine should be run till empty and then purged with PP. 3. BARREL AND MELT TEMPERATURES - The melt temperature of Multiflex should be between 180C-220C depending on the hardness of the material. The barrel temperatures should be progressively increased by 10-20C starting from the hopper side till the melt temperature is in the range. The nozzle temperature should be the same or 10C lower than the last barrel heating zone. - When processing SBS based Multiflex, the maximum temperatures should not cross 200C. This is because these materials are susceptible to degradations at higher temperatures.

3 INJECTION MOULDING 4. MOULD TEMPERATURE - The mould temperature should be between 25C-40C. - If the parts produced are thin-walled, then it is recommended that the temperatures be between 40C-60C. 5. INJECTION PRESSURE - Can be moulded over a wide range of injection pressures. Best results are however obtained when minimum pressure is required to smoothly fill the mould cavity. 6. INJECTION RATE -SBS based Multiflex compounds are normally moulded at moderate injection rates, wheras SEBS based Multiflex compounds show best results when moulded at relatively fast injection rates. 7. SCREW SPEED AND BACK PRESSURE Typical screw speeds range from 25-75rpm. Usually a back pressure of 20-50bar is recommended. Increase in back pressure results in : - improved colour dispersion - improved melt homogenity

4 INJECTION MOULDING 8. HOLD PRESSURE AND HOLD TIME The mould should be initially filled without any hold pressure. Low hold pressures should then be applied to prevent sink marks and ensuring complete filling. Higher hold pressure will cause: - overfilling of cavities - difficulties in ejection - delamination - deformation around sprue A balance must be obtained between hold time and hold pressure as too low a hold pressure will result in sink marks and reduced adhesion along weld lines.

5 EXTRUSION 1. PROCESSING MACHINERY - Multiflex can be processed on conventional extruders designed for PolyOlefins. Some restrictions may apply to PVC extruders. - Compression ratio of atleast 2.5:1 to 3.5:1 and a L/d ratio of atleast 24:1. Balanced screws of the type used to extrude PolyOlefins are preferred. - A L/d of 20:1 is sufficient to extrude Multiflex-D. Compression ratio also on the lower side is preferred. 2. CLEANING OF MACHINERY The machine should be purged with POLYPROPYLENE before beginning processing of Multiflex. Again when another material is to be used afterwards, machine should be run till empty and then purged with PP. 3. BARREL AND MELT TEMPERATURES Typical processing temperatures are : Feed Compression Metering Extruder Head Die C C C C C In case of SBS based Multiflex compounds, the melt temperatures should never cross 200C.

6 OVERMOULDING 1. GENERAL INFORMATION Overmoulding, also known as 2-component injection moulding, offers great advantages in terms of aesthetics and design. It reduces the need for assembly work and shortens production times. Besides it allows the use of elastomers for soft touch in applications where it cannot be used singly because of load and design constraints. 2. ADVANTAGES OF OVERMOULDING - allows different hardness and flexibility in the same component - more freedom in design - no part assembly - excellent finish - value addition 3. BONDING METHODS In overmoulding, the bonding between the adjacent components is realised by - MECHANICAL ANCHORING or - ADHESION BONDING

7 OVERMOULDING In Mechanical bonding, there is no physical or chemical bonding between the two components. Anchoring is achieved by means of undercuts or openings in the semi-finished substrate. In Adhesion bonding, there is a chemical bonding occurring between the TPE and the Thermoplastic. This bonding is caused by -Intermolecular attraction (Van der Waal s forces) and - Molecular entanglement. When the TPE is injected on the substrate, the heat of the TPE causes the surface layer of the substrate to soften. It is in this hot condition that the above forces are developed and the bonding made. 4. TYPES OF OVERMOULDING MACHINE Co-injection machine Transfer process POSSIBLE MOULDS Index plate or rotary mould Two mould with different cavities PROCESS Substrate material injected followed (2 by the TPE) Semi-finished part is transferred on the (2machines) 2 nd mould on the 2 nd

8 OVERMOULDING 5. PROCESSING INFORMATION -Inject TPE at fast injection rate to facilitate uniform melt distribution. - Melt temperature should be as high as possible to ensure surface melting of the substrate. - Do not use hold pressure as it can cause material displacement at the interface, which may lead to destruction of adhesion immediately achieved. - Do not use demoulding aids like lubricants - The mould surfaces should be rough. In case of transfer process - Surface of the semi-finished substrate should be absolutely free of grease and dust. - The substrate may be required to be pre-heated prior to the second moulding operation. This pre-heating period should last only for a very short time and should heat only the surface of the part. The surface temperature should be upto C. This is especially important where the softening temperature of the substrate is very high. Nylon, ABS, Noryl substrates will require preheating. Normally PP substrates do not require pre-heating.

Lifolit. Soft PVC processing guide

Lifolit. Soft PVC processing guide Lifolit Soft PVC processing guide CONTENTS INTRODUCTION INJECTION MOULDING GENERAL GUIDELINES INJECTION MOULDING - RECOMMENDED TEMPERATURE EXTRUSION GUIDELINES EXTRUSION - RECOMMENDED TEMPERATURES CONTACTS