Organic-Inorganic Hard Coating Layer Formation on Plastic Substrate by UV Curing Process

Efficient methods for making organic-inorganic hard coating layers on a polymethylmethacrylate substrate were developed and optimized to improve the mechanical and optical properties. Colloidal silica was coupled with methacryloxypropyltrimethoxysilane to make Si-O-Si bonds before incorporating them into the organic phase of the monomer and oligomer. A combination of photoinitiators with different absorption bands could utilize the UV light throughout the entire wavelength range to show better curing results than the case of a single photoinitiator with a limited absorption band. The effects of the photoinitiator in terms of the mixing ratio and concentration in the coating solution were examined and optimized. The UV curing reactivity was improved using a mixture of different initiators with different absorption bands, and 4: 1 ratio mixture of Irgacure 184 and Irgacure 907 showed the best hard coating properties, such as hardness and impact strength. The optimum initiator content was determined to be 5 wt% in the hard coating solution. However, too much initiator resulted in excessive primary radical reactions of the monomers, and the competition of primary radicals reduced the conversion and initiator efficiency.