Thermal effects on the behaviour of PET films used in the in-mould-decoration process involved in plastics injection moulding

• Published in: Journal of materials processing technology Vol. 63; no. 1-3; pp. 510 - 513
• Main Authors: Wong, A C-Y, Liang, K Z
• Format: Journal Article
• Language: English
• Published: 12-11-1996
• ISSN: 0924-0136

The decoration of injection moulded plastic products may be carried out by what is known as the in-mould-decoration (IMD) technique. It is neither a pre- nor a post-treatment technique, but actually takes place simultaneously with the injection moulding process. In IMD, a plastic film with the required pre-printed patterns is placed into a mould before the mould is closed. The film is positioned in such a way that its printed surface faces squarely and directly to the flow of melt front. When the hot molten polymer comes into contact with the film, heat is transferred from it to the film, which causes the film to soften and reduce its stiffness. Combining this heat effect with the injection force, the film is made to adhere to the inner walls of the mould cavity. A stronger adhesive force is obtained between the pre-printed patterns and the molten polymer than between the patterns and the carrier plastic film. Upon solidification, the patterns are transferred to the plastic product, the carrier plastic film being peeled off during the mould opening stage. The current study is triggered by the difficulties encountered in the industry which involve IMD, among which has been that, for moulded articles having large curved geometry, the transferred patterns are creased and unacceptable; this is particularly serious for PET films. It is therefore aimed to investigate this behaviour and to establish a "processing window". In view of the mechanism that takes place during the process of IMD, the strain and rate of stretching of the film at different temperatures were chosen to be the variables of this investigation. The results indicate PET film might have undergone some types of phase changes at the four different temperature ranges explored.