UV CURABLE HARD TRANSPARENT HYBRID COATING MATERIALS ON POLYCARBONATEPREPARED BY THE SOL-GEL METHOD

UV curable, hard, transparent inorganic/organic composites with covale nt links between the inorganic and the organic networks were prepared by the sol-gel method. These hybrid coating materials were synthesized using a commercially available, acrylate end-capped polyester or poly urethane oligomeric resin (EBC80, EBC284), hexanedioldiacrylate (HDDA) as a reactive solvent, 3-(trimethoxysilyl)propoxymethacrylate (TMSPM) as a coupling agent between the organic and inorganic phase, and a me tal alkoxide, tetraethylorthosilicate (TEOS). The materials were appli ed on primer or oxygen plasma pretreated polycarbonate sheets and UV c ured, followed by a thermal treatment to give a transparent coating wi th a good adhesion and abrasion resistance. The high transmission and the thermogravimetric behavior indicate the presence of a nanoscale hy brid composite, as is confirmed by SAXS and TEM measurements. In a Tab er Abrasion Test, uncoated polycarbonate sheets exhibit a 48% decrease in light transmittance at 600 nm after 300 wear cycles, whereas the E BC80 hybrid coating system containing 9 wt% SiO2 (EBC80/25Si) shows on ly 28% decrease in light transmittance. A maximal improvement of the a brasion resistance is achieved when 23 wt% SiO2 is incorporated (EBC80 /60Si, EBC284/60Si) with only 20% decrease in light transmittance. The abrasion resistance of glass is not yet encountered. For optimal resu lts, it is essential that the rate of condensation of the silanol grou ps is sufficiently high to form a dense three-dimensional network.