Plastic polymer materials used for plastic injection moulding are called thermoplastics because they become molten when heated but harden again when cooled. The mould design, properties required for the finished component and its function will determine thermoplastic selection.
Polymers commonly used for plastic injection moulding:
Commodity Polymers – such as PP, PE and ABS are low cost and readily available. Many of these grades are ISO 10993 compliant for Biocompatibility.
Examples of Commodity Polymers:
- Polyvinyl Chloride (PVC)
- Polypropylene (PP)
- Polyethylene (PE)
- Polystyrene (PS)
- Acrylonitrile Butadiene Styrene (ABS)
Engineering Polymers – such as Copolyester, PBT and PET, PC, PC-ABS, Nylon and PPO. These are more expensive than commodity polymers, but provide improved thermal properties, electrical, wear and solvent resistance. Most have a higher melting point and require more expertise and knowledge for processing.
High Performance Polymers – such as polyketones, polysulfones (PPSU), polyarylates, polyamides, and liquid crystal polymers (LCP) such as PEEK are characterised by a combination of high modulus, melting points (greater than 250°C), biocompatibility, electrical insulation and low-friction surfaces.
In addition to the Thermoplastic polymers listed, there is also a wide range of Thermoplastic Elastomers (TPE) and Thermoplastic Urethanes (TPU) as well as more unusual materials such as PCU (Polycarbonate Urethane) which passes USP XXII Class VI Biological Reaction. These are generally soft, rubber compounds, used for seals, cushioning features and soft touch surfaces. These materials can be moulded in on their own as components or bonded to polymers with matching chemistry, for a chemical bond, as opposed to a mechanical bond using either overmoulding or 2-shot moulding technology.
Selecting the right material for plastic injection moulding is a crucial step that requires careful consideration. To make an informed decision, it is essential to evaluate several aspects.