Improvements in the physical properties of UV-curable coating by utilizing type II photoinitiator

In our previous studies, we found that the polymerization reaction involving cross-linking occurs in the polymerization of monoacrylate when the photopolymerization reaction is initiated by type II photoinitiator. This means that glassy cross-linked coatings would be obtained without using multiacrylates when a monoacrylate that gives a polymer with high glass transition temperature is employed as a monomer. In this study, we evaluated the physical properties of the UV-cured coatings prepared by the radical photopolymerization reactions using a type I- or type II photoinitiator. The surface hardness and heat resistance of the obtained coatings initiated by type II photoinitiator were higher than those of the coating initiated by type I photoinitiator due to the cross-linked polymer structure. Furthermore, the cross-linked coatings showed higher solvent resistance as well. In general, the coating obtained by UV-curing of the formulation that contains a multiacrylate has a high shrinkage rate, resulting in poor adhesion and a warped substrate. Contrary to the conventional UV-curable coatings using multiacrylates, the cross-linked coatings consisting of monoacrylate and type II photoinitiator achieved high adhesion to a substrate and a warp-free substrate that are comparable with the uncross-linked polymerization system initiated by type I photoinitiator.