this invention provides an acid - hardening resin composition which is activated by exposure to actinic light , wherein the composition is a condensation polymerizable blend of an aminoplast , an alkyd resin ; and a sulfolene catalyst . when the invention coating composition is subjected to ultraviolet light exposure and a subsequent bake cycle , a film is obtained which has good mechanical properties and excellent adherence to substrates . in a further embodiment , a superior substantially 100 % solids coating system is provided which comprises an aminoplast ; an alkyd resin ; a sulfolene catalyst ; a photoinitiator ; and a polymerizable olefinically unsaturated monomer or prepolymer .