Thermoplastic injection moulding elastomers

Thermo set as well as thermoplastic and elastomer binders are used in compression, injection and calendaring process respectively. Extrusion moulding uses elastomers as well as thermoplastic materials such as PVC. Compression and injection moulding processes make only rigid magnets, calendaring makes flexible magnets and extrusion can lead to both states. 

If the diol chain extender is used in exact molar proportion to the unreacted isocyanate, then a linear polyurethane elastomer is obtained. The resulting thermoplastic elastomer may be extruded or injection-moulded, and the properties arise from the ability of the hard and soft segments to form semi-crystalline domains that act as virtual crosslinks in the polymer and give it elastomeric properties, as shown in Figure 1.17. 

PROCESSING OF TRANSPARENT THERMOPLASTIC POLYURETHANE ELASTOMER BY INJECTION MOULDING... 

Thermoplastic elastomers are materials which possess, at normal temperatures, the characteristic resilience and recovery from extension of cross-linked elastomers but which exhibit plastic flow at elevated temperatures and can be fabricated by the usual techniques applied to thermoplastics, e.g., injection moulding and extrusion. These effects are associated with linear polymers containing segments which give rise to inter-chain secondary valency forces of polar attraction. At normal temperatures, these interactions have the effects of conventional covalent cross-links but at elevated temperatures the secondary bonds dissociate and the polymer exhibits thermoplastic behaviour. 

Pocan is Bayer s trade name for its partially crystalline thermoplastic polyesters based on polybutylene terephthalate. Product offerings include PBT filled injection moulding grades, PBT elastomer modified and PBT standard non-reinforced injection moulding grades. PC/PBT blends, elastomer modified and non-reinforced injection moulding grades, are also available. 

The expanding range of use of two-component hot-crosslinked silicone elastomers is leading to the appearance of injection machines and moulds in which a thermoplastic melt is injected using HR and a hardening plastic from a separate cylinder. 

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