Process for the preparation of low-viscosity, water-emulsifiable allophanates with radiation-curable groups

A process for preparing a water-emulsifiable, radiation-curing allophanate having residual monomer contents of less than 0.5 weight % and an NCO content of less than 1 weight %, comprising forming urethanes which contain NCO groups and have radiation-curing groups from

• A) at least one compound containing isocyanate groups,
• B) at least one hydroxy-functional compound which has groups which react, by polymerization, with ethylenically unsaturated compounds under the action of actinic radiation (radiation-curing groups),
• C) at least one polyoxyalkylene mono-ol,
• E) optionally in the presence of a catalyst, and
• a. subsequently reacting said urethanes which contain NCO groups and have radiation-curing groups, without further addition of compounds containing isocyanate groups, in the presence of
• F) an allophanation catalyst, and
• G) optionally a tertiary amine,
• wherein the ratio of NCO groups of the compounds from A) to the OH groups of the compounds from B) and C) is 1.80:1.0 to 1.46:1.0.