Interference coatings on glass based on photopolymerizable nanomer material

Abstract

A new sol-gel method for the preparation of optical SiO2 and TiO2 multilayer coatings has been developed. As an example, a 3-layer antireflective (AR-filter) coating and a 5-layer NIR reflective coating on glass are described, For the preparation, a nanoparticulate TiO2 sol was synthesized by hydrolysis and condensation of tetraisopropylorthotitanate and complex formation with methacrylic acid. A SiO2 nanoparticulate sol was synthesized analogeously with tetraethoxysilane (TEOS) as the precursor. By mixing both sols in different ratios, layers with tunable refractive index between 1.46 and 2.2 could be obtained on glass after thermal densification at 450°C for 15 min. Three layers (SiO2-TiO2, TiO2, SiO2) were deposited by dip-coating with subsequent UV-curing, and the layer-stack was thermally densified at 450 C. The so obtained AR-filter shows a reflection of less than or equal to 2% in the wavelength range between 380 and 610 nm, less than or equal to 1% between 450 and 560 nm and 0% at 550 nm. The AR filter shows very good abrasion resistance and scratch hardness, since only 3% haze is obtained after 1000 cycles of Taber test and the AR filter does not show any damage after 300 cycles of rubber test. The high abrasion resistance can be attributed to the surprisingly low surface roughness (about 6 nm) of the filter. The mechanical and optical properties of the AR filter did not change after sun test with 760 W/m(2) for 320 h and after boiling water test for 11 days.