TiO₂–SiO₂ hard coating on polycarbonate substrate by microwave assisted sol–gel technique

To enhance the poor scratch resistance of polycarbonate, a silica (SiO₂) and titania (TiO₂) transparent inorganic coatings was designed and synthesized using a microwave assisted sol–gel heating. Due to the transparency of PC to microwave, the idea was to obtain a localized heating only on the coating film. The obtained films were fully characterized to mainly evaluate the effect of titania content, added both as nanoparticles and from tetraethyl orthotitanate, TEOT, on scratch resistance and surface morphology. Particular attention was paid to preserve the transparency of the final product. The results allowed to define that TEOT addition enhances the adhesion between coating and polycarbonate, even if the optimized quantity have to be defined in order to avoid a decrease of coating mechanical resistance. In this work optimized TEOT level results to be the associated to 5 wt% of TiO₂, which enable the better balancing between adhesion and mechanical resistance performances.