A study on the role of wetting parameters on friction in injection moulding

In the injection moulding of thermoplastics, hot polymer melt wets a cold mould surface during filling. In contrast, ejecting can be considered as de-wetting a solid polymer from a solid mould surface. In ongoing research, we suggest that the interfacial tension gamma(12) predicts the resistance of a solid polymer being separated from a solid mould, i.e. low gamma(12) indicates elevated ejection friction and vice versa. The aim of this study was to validate this assumption for polymer PA6 and the mould surfaces M333_IP, M268_VMR, MoN, and CrC/a-C:H. To calculate gamma(12), we determined the five solids' surface energies at 90 degrees C. Therefore, we conducted contact angle measurements using bromonaphtalene and ethylencarbonate and applied the OWRK method. In succeeding friction experiments, we used a friction-test injection mould to determine the ejection friction of the same material combinations at 90 degrees C. To conclude, the four mould coatings ranked in friction to PA6 as gamma(12) suggested.