Study on the design of precious metal based protective films for glass moulding process

Driven by the huge market demand, the glass lenses made of various optical glasses are required to be more diversified in sizes/shapes, to have better form accuracy/surface roughness, to be more environmental durable, and to be more competitive in price. Glass moulding process (GMP) is regarded as a very promising technique for mass producing high precision optical components such as spherical/aspheric glass lenses and free-form optics. However, only a handful of materials can sustain the chemical reaction, mechanical stress and temperature involved in the glass moulding process. Besides, almost all of these mould materials are classified as hard-to-machine materials. This makes the machining of these materials to sub-micrometre form accuracy and nanometre surface finish a rather tough and expensive task. As a result, making service life of mould longer has played a critical part in the GMP industry. The interfacial chemical reaction between optical glass and mould is normally the main reason for pre-matured mould failure. This research aimed to investigate the interfacial chemical reaction between various optical glasses and different precious metal based anti-stick coating designs. The results showed that mould material, coating design, glass composition, moulding temperature and moulding duration could all have profound effects on the interfacial chemical reaction. Based on the results, a design developed specially for certain glasses is more likely to be the viable way of optimizing the effect of the protective coating.