Optical application of (pigmented) sol-gel coatings

The performance of the anti-reflection stack antimony-doped tin oxide/SiO2 improves considerably if the refractive index of the SiO2 layer decreases from similar to1.45 to 1.41 by the introduction of porosity. Porosity can be introduced by the addition of high-boiling co-solvents (or templates e. g. sebacates) to the coating liquid. Fine-tuning of the liquid composition allows the formation of a homogeneous, non-scattering SiO2 layer with a refractive index of 1.41 and pencil hardness of H7-H8 on large screens (diagonal >1 meter) if a curing temperature of 160degreesC was used. Another interesting application is the formation of transparent, strongly coloured layers on lamp bulbs. Due to the high operating temperatures, strict requirements are placed on the matrix material and the pigment used. Inorganic pigments have good temperature stability, but their colour saturation is weaker than that of organic pigments, demanding the formation of relatively thick coatings. In order to achieve this, Methyltrimethoxysilane (MTMS) was used as matrix material precursor. Fully transparent, temperature-resistant coatings were developed.