UV curable hard coatings on plastics

A photochemically curable transparent hard coating material has been develo ped to improve the wear resistance of organic polymers. Methacrylate functi onalized silanes and nanoscaled boehmite particles were used for the prepar ation of the UV curable hard coatings by the sol-gel technique. The inorgan ic network is formed as a result of the controlled hydrolysis and condensat ion of the methaclyloxysilanes in the presence of nanoparticles (particle s ize: 15 nm). The hydrolysis and condensation of the methacryloxy silane, fo r two hours in presence of boehmite nanoparticles (43 wt.%), at 100 degrees C leads to a degree of condensation of 80% of the inorganic network, as de termined by Si-29-NMR spectroscopy. The organic network is formed by photoi nitiated polymerisation of the methacrylic-functions in only a few minutes, using UV light from a Hg high pressure lamp. Transparent coatings on plast ic substrates (PC, PMMA) were produced by spray coating with good optical q uality and thicknesses of several micrometers. The transparent coatings sho w excellent adhesion on PMMA and PC (GT/TT = 0/0, DIN 53151), even without using primers, and also good abrasion resistance after the Taber abraser te st with haze values of 10% after 1000 cycles (CS 10F rolls, 5,4 N, DIN 5234 7). The water exposition test (65 degrees C, deionized water) and the Sunte st, without using filters, did not result in any crack formation, loss of a dhesion or yellowing within the test period of two weeks. (C) 1999 Elsevier Science S.A. All rights reserved.