Low viscosity allophanates containing actinically curable groups

PROBLEM TO BE SOLVED: To provide a process for producing a radiation-curing binder containing an allophanate group; and to provide the binder obtained by the process, and a coating composition containing the binder. ; SOLUTION: The process comprises reacting at a temperature of <=130[deg.]C (A) one or more compounds containing uretdione groups with (B) one or more OH-functional compounds which contain groups which react, with polymerization, with ethylenically unsaturated compounds on exposure to actinic radiation (radiation-curing groups), (C) optionally NCO-reactive compounds other than (B) in the presence of (D) a catalyst containing at least one zinc compound to form allophanate groups by opening the uretdione ring.