UV curable hard coatings on plastics

Abstract

A photochemically curable transparent hard coating material has been developed to improve the wear resistance of organic polymers. Methacrylate functionalized silanes and nanoscaled boehmite particles were used for the preparation of the UV curable hard coatings by the sol-gel technique. The inorganic network is formed as a result of the controlled hydrolysis and condensation of the methaclyloxysilanes in the presence of nanoparticles (particle size: 15 nm). The hydrolysis and condensation of the methacryloxy silane, for two hours in presence of boehmite nanoparticles (43 wt.%), at 100°C leads to a degree of condensation of 80% of the inorganic network, as determined by Si-29-NMR spectroscopy. The organic network is formed by photoinitiated polymerisation of the methacrylic-functions in only a few minutes, using UV light from a Hg high pressure lamp. Transparent coatings on plastic substrates (PC, PMMA) were produced by spray coating with good optical quality and thicknesses of several micrometers. The transparent coatings show 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 test with haze values of 10% after 1000 cycles (CS 10F rolls, 5,4 N, DIN 52347). The water exposition test (65°C, deionized water) and the Suntest, without using filters, did not result in any crack formation, loss of adhesion or yellowing within the test period of two weeks.