Effect of hydrolysis groups in fluoro-alkyl silanes on water repellency of transparent two-layer hard-coatings

Transparent two-layer hard-coatings with high water repellency were prepared on transparent resin substrates (polycarbonate: PC) by a dipping method. The top-layer coating was prepared by using the commercial thermally cured hard-coating solution (the main component was polysiloxane) and the underlayer coating was done by using the commercial UV-cured hard-coating solution (the main component was acrylic resin). Two kinds of fluoro-alkyl silanes (FASs), which have the same length of perfluoro-alkyl groups and different hydrolysis groups (trimetoxy and trichloro groups), were added to the thermally cured hard-coating solution to improve the water repellency. The effects of hydrolysis groups on the coating properties like the durability of water repellency in boiling distilled water and the optical transmittance were investigated. The optical transmittance of the two-layer hard-coatings which top layers were prepared with the two different FASs was almost the same. The durability of water repellency in boiling water was, however, different. The chemical states of the surface before and after immersion in boiling water and the effect of heat treatments were investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR).