The injection-moulding process involves the following procedure: plastic in the form of granulate is placed into a hopper, from which it is removed by a piston worm on the injection-moulding machine and carried to a melting chamber, where the plastic is exposed to friction and heat and transformed into melt. The melt is injected into the mould cavity until it is full, whereby it takes on the cavity’s shape. This is followed by change in dimension and reduction in pressure phase shrinkage. The plastic transfers its heat to the mould, hardening to become the final product through this cooling action. Afterwards, the mould is opened, the product removed and the process repeated.
LDPE, HDPE, PP, PVC, PA and PET films are made by blow moulding. Multi-layer films with various compositions of material are also produced by blow-moulding. Such films can have up to seven layers. The design of extrusion heads for multi-layer films is very complicated and their use in producing film requires strict compliance with the production procedure.