Radiation hardening process for coatings

A radiation hardening process is provided, comprising a first step of applying a vinyl copolymer as the primer (hereafter called ''A'') having 0.1 to 4.0 hydroxyl or carboxyl groups for 1,000 units of molecular weight on its side chain, and preliminary hardening, if necessary, by heating or irradiating with a low dose of radiation (0.5-3 Mrad); and a second step of applying a reactive polymer as a top coat (hereafter called ''B'') on to the coating of the copolymer ''A'', and completely hardening with a dose of radiation of 0.5 to 10 Mrad; whereby a superior adhesion and solvent proof coating is obtained. In embodiments, the vinyl copolymer ''A'' may be produced by the polymerization of 50 to 100 parts of solvents, 0.1 to 5 parts of an initiator for 100 parts of the total vinyl monomer at 400 to 1500C, preferably 600 to 1200C. To 100 parts of the monomer may be added 0.5 to 10 parts, preferably 2 to 5, of polyfunctional long chain cross-linking agents. The preferred ionizing radiation is accelerated electron beams at an energy level of 0.1 to 2 MeV, preferably 0.2 to 0.5 MeV. In one of the examples, a primer was prepared by mixing 100 parts of the copolymer ''A'' with 3 parts of zinc chromate, applied to a galvanized sheet and air-dried. Next, an urethane-modified vinyl copolymer solution was applied on to the primer and irradiated with accelerated electron beams of 0.3 MeV and 5 Mrad. The copolymer was composed of methyl methacrylate, butyl acrylate, acrylic acid, azobis-isobutyl nitrile, lauryl mercaptane and methyl isobutyl ketone. The urethane-modified copolymer included an unsaturated isocyanate. (Iwakiri, K.)