DEVELOPMENT OF AN ABRASION-RESISTANT COATING FROM ORGANIC-INORGANIC POLYMERIC NETWORK BY SOL-GEL PROCESS

The paper describes the evaluation of coating formulations based an 3- methacryloxypropyl trimerhoxysilane, (MEMO) and trimethylolpropane tri acrylate (TMPTA) having reactive monofunctional acrylate diluents (met hyl methacrylate and acrylic acid) as well as difunctional reactive di luents. Simultaneous acid catalysed hydrolysis and condensation of MEM O was used to prepare a transparent condensate (Sol A) which was then utilised in coatings. An optimum coating formulation containing Sal A (33%), TMPTA (33%), acrylic acid (16.5%) and methyl methacrylate prepo lymer syrup (16.5%) gave excellent results. It showed 100% cross-hatch adhesion on PMMA sheet. A deterioration in cross-hatch adhesion was o bserved by addition of difunctional reactive diluents in tile optimal coating formulations. The effect of addition of silica (TS-610) on the hardness and optical properties of the coatings was also studied. Bet ter performance of the coating was observed when silica was added to M EMO before subjecting it to acid hydrolysis and condensation. A mechan ism has been suggested to account for this observation. An Increase in abrasion resistance of the coatings was observed by an increase in si lica content from 1.6 to 6.4% (w/w). The per cent haze after 200 cycle s of Tabers test was reduced to one-fourth in the case of optimum coat ing formulation containing 3.2% silica. These coatings showed a pencil hardness greater than 5H and optical transmittance greater than 90%.