[en] A binder is prepared by reacting isocyanate-functional compound(s) containing uretdione groups; compounds that contain isocyanate-reactive groups and contain groups that react with ethylenically unsaturated compounds; saturated, hydroxyl-containing compound(s); and a catalyst containing ammonium salts or phosphonium salts of aliphatic or cycloaliphatic carboxylic acids. Preparation of a binder containing allophanate groups, groups that react with ethylenically unsaturated compounds with polymerization on exposure to actinic radiation (radiation-curing groups), and optionally isocyanate (NCO)-reactive groups, which comprises reacting at 130[deg]C NCO-functional compound(s) containing uretdione groups; compounds that contain isocyanate-reactive groups and contain groups that react with ethylenically unsaturated compounds with polymerization on exposure to actinic radiation (radiation-curing groups); saturated, hydroxyl-containing compound(s), at least one of these compounds having an OH functionality of 2; and a catalyst containing one or more ammonium salts or phosphonium salts of aliphatic or cycloaliphatic carboxylic acids, the reaction hydroxyl-containing compounds taking place at least proportionally with the formation of allophanate groups. An independent claim is also included for a coating composition comprising: (1) binders; (2) optionally polyisocyanate(s) which contain free or blocked isocyanate groups and optionally contain groups which react with ethylenically unsaturated compounds with polymerization on exposure to actinic radiation; (3) optionally compounds other than the polyisocyanate(s) which contain groups which react with ethylenically unsaturated compounds with polymerization on exposure to actinic radiation and optionally contain NCO-reactive groups; (4) optionally isocyanate-reactive compound(s) which are free from groups which react with ethylenically unsaturated compounds with polymerization on exposure to actinic radiation; and (5) initiators.
