Influence of interlayer thickness of a thin noble metal MSIP-PVD coating on compound and system properties for glass lens moulding

The replicative production of complex optical lenses made of glass has become very important over the last decades. The technology precision glass moulding has a great potential to fulfil the optical demands on high surface quality, small tolerances and high uniformity of glass lenses at high production volumes. A noble metal MSIP-PVD coating is used to increase lifetime of the precision moulds. Beside the chemical resistance and protection of the moulds against the hot glass, prevention of glass sticking and oxidation adhesion between coating and substrate is of great importance. As state-of-the-art a noble metal coating based on platinum and iridium is used with a nickel interlayer. As a result of previously presented research replacement of the nickel interlayer by a chromium interlayer has increased adhesion between coating and substrate significantly. The present research work shows an increase of this adhesion as a function of interlayer thickness. Application oriented heating tests show an influence of the interlayer on the glass behaviour during the heating cycle due to a diffusion process between interlayer and toplayer. A coating system of 20 nm Cr interlayer and 300 nm Pt₄₀Ir₆₀ function layer exhibits a good combination between good compound adhesion and little influence on the glass behaviour.