Development of an abrasion resistant coating. from organic-inorganic polymeric network by sol-gel process

Abstract

<span style="font-size:11.0pt;line-height:115%; font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "dejavu="" sans";mso-hansi-theme-font:minor-latin;mso-bidi-font-family:mangal;="" mso-bidi-theme-font:minor-bidi;color:#00000a;mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">The paper describes the evaluation of coating formulations based on 3-methacryloxypropyl trimethoxysilane, (MEMO) and trimethylolpropane triacrylate (TMPTA) having reactive monofunctional acrylate diluents (methyl methacrylate and acrylic acid) as well as difunctional reactive diluents. Simultaneous acid catalysed hydrolysis and condensation of MEMO was used to prepare a transparent condensate (Sol A) which was then utilised in coatings. An optimum coating formulation containing Sol A (33%), TMPTA (33%), acrylic acid (16.5%) and methyl methacrylate prepolymer syrup (16.5%) gave excellent results. Itshowed 100% cross-hatch adhesion on PMMA sheet. A deteriorationin cross-hatch adhesion was observed by addition of difunctional reactive diluents in the optimal coating formulations. The effect of addition of silica (TS-610) on the hardness and optical properties of the coatings was also studied. Better performance of the coating was observed when silica was added to MEMO before subjecting it to acid hydrolysis and condensation. A mechanism has been suggested to account for this observation. An increase in abrasion resistance of the coatings was observed by an increase in silica content from 1.6 to 6.4% (w/w). The percent haze after 200 cycles of Tabers test was reduced to one-fourth in the case of optimum coating formulation containing 3.2% silica. These coatings showed pencil hardness greater than 5H and optical trans-mittance greater than 90%.</span>