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 γ12 predicts the resistance of a solid polymer being separated from a solid mould, i.e. low γ12 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 γ12, we determined the five solids surface energies at 90°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°C. To conclude, the four mould coatings ranked in friction to PA6 as γ12 suggested.