Ionizing radiation curable coating composition

The hardness of a coating layer is improved by employing ionizing radiation. In the radiation hardened compositions wherein the main component is an acryl resin containing unsaturated groups, said acryl resin containing unsaturated groups is prepared by polymerizing a mixture which consists of a polymerizable unsaturated monomer containing acid anhydrides and a vinyl monomer which may be of the type to react with said polymerizable unsaturated monomer, until the degree of polymerization reaches 30 to 70%, and thereafter semi-esterifying it by the addition of a polymerizable unsaturated monomer having hydroxyl groups. According to this invention, polymerizable functional groups are introduced into the acryl resin so that the backbone molecules of the acryl resin form a network construction, and the polymerizable unsaturated monomer is easily introduced into the acryl resin in a short time without gelation by semi-esterification, for example, at 1000C for 1 hr. The ionizing radiation may be ionizing electromagnetic radiation such as X-rays and gamma-rays or ionizing particle radiation such as electron or neutron beams. In examples, the coated films formed from the enamelled monomer solution of the modified acryl resin are irradiated with electron beams from a Van de Graaff accelerator with 1.0, 3.0, 5.0 Mrad at 5 mA. The resultant film shows a pencil hardness of 2H to 4H. (Iwakiri, K.)