Production of Superhydrophobic Surfaces Using a One-Step Variothermal Injection Moulding Process

Polymer parts with superhydrophobic surfaces are currently produced by injection moulding and subsequent surface processing within complex process chains by plasma treatment, etching or special coatings. An innovative approach is to mould the plastics part and create the surface functionality in one single step using a variothermal injection moulding process. For the precise moulding of such microstructured surfaces, elevated mould temperatures are required. A sophisticated injection mould has been designed at the Institute of Plastics Processing (IKV), which allows rapid heating of the cavity wall by an integrated laser. To ensure a well defined and fast changing temperature profile, a diode laser system in combination with a pyrometer-based power control has been implemented. The system was successfully used to heat up the cavity wall with heating rates of up to 300 K/s. Moulding experiments with polypropylene material were performed. The functionality and the moulding accuracy of the polymer surfaces were analysed by scanning electron microscopy and contact angle measurements. It is shown that the combination of a micro-structured mould insert, variothermal process control and a ductile polymer material leads to the creation of unique surface topographies which exhibit excellent superhydrophobic properties.