Twenty Kinds of Plastics and Their Properties—(12) PET
12.PET polybutylene terephthalate
Typical application range:
The automobile industry (structural devices such as mirror box, electrical components such as car headlamp reflector), electrical components (motor shell, electrical connector, relay, switch, microwave internal devices etc.); industrial application (hand pump casing, equipment etc.).
Injection molding process conditions:
Drying process: the drying process before processing is necessary, because the PET has a strong hygroscopicity. It is suggested that the drying condition is 120~165 °C and 4-hour drying. The humidity should be less than 0.02%.
Melting temperature: for non filling type: 265~280 °C; for glass filling type: 275~290 °C.
Mold temperature: 80~120 °C.
Injection pressure: 300~1300bar.
Injection speed: high injection speed can be used on the premise of not causing embrittlement.
Runner and gate: all regular types of gate can be used. The gate size should be 50~100% of the thickness of the plastic part.
Chemical and physical properties:
The glass conversion temperature of PET is about 165 °C, and the temperature range of the material is 120~220. PET has a strong hygroscopicity at high temperature. For glass fiber reinforced PET materials, bending deformation is very easy to occur at high temperature. The crystallinity of the material can be improved by adding a crystalline reinforcing agent. The transparent products made with PET have glossiness and heat distortion temperature. Special additives such as mica can be added to PET to minimize the bending deformation. If lower mold temperature is used, transparent products can be obtained by using non – filled PET materials.