Effect of plasma pretreatment on adhesion and mechanical properties of sol-gel nanocomposite coatings on polycarbonate

Adhesion of the coatings to the substrate plays a vital role in improving mechanical properties of sol-gel coatings especially when deposited on plastics. In the present study, an attempt was made to study the effect of atmospheric air plasma surface activation on the adhesion of sol-gel nanocomposite coatings on polycarbonate substrate. The sol was synthesized by the hydrolysis and condensation of an epoxy silane (3-Glycidoxypropyl trimethoxy silane) along with titanium tetraisopropoxide. Coatings were deposited on 100 x 100mm substrates by spray coating and subsequently subjected to UV curing followed by thermal curing at 130 degrees C for 1 h. One set of the substrates was subjected to atmospheric air plasma surface pretreatment prior to coating deposition. Coating thickness, adhesion as well as mechanical properties like pencil hardness, scratch resistance and taber abrasion resistance were evaluated for coatings deposited over plasma-treated and -untreated surfaces. It was found that plasma surface pretreatment has improved the pencil hardness from H to 2H and adhesion of coatings from 2B to 4B. Results obtained from the above experiments were discussed on the basis of surface modification using plasma pretreatment.