Sol-gel NIR-reflective multilayer coatings on glass through UV-polymerizable ceramic nanoparticles

Abstract

A new preparation route for an dielectric NIR-reflexion filter on glass is described. Coating sols are synthesized from SiO2 and TiO2 nanoparticles with photopolymerizable surface ligands. A 5-layer stack consisting of 2 SiO2 and 3 TiO2 layers was deposited on float glass by angle-dependent dip-coating (ADDC) with a fixed angle of 4° to the vertical and subsequent UV-curing. Finally, the whole stack was densified at 450 °C without cracking or discolouring. UV-vis-NIR transmittance and reflectance spectra show a steep increase of reflectance at 750 nm. In the range between 800 nm and 1200 nm, the reflectance is >80%. The visible transmittance is about 72% due to single reflexion peaks. The bandwidth of the NIR reflection filter prepared by ADDC is about 200 nm larger and its maximum reflectance is only 5% smaller compared to vertical dip-coating. The interference layer stack shows excellent stability in Taber Abraser, rubber, saline and UV tests, indicating a high potential for practical application.