Water-dispersible polyurethane (meth)acrylates for actinic radiation curable coatings

A water-dispersible polyurethane (meth)acrylate U substantially synthesised from at least one multifunctional aromatic or (cyclo)aliphatic isocyanate I, at least one (cyclo)aliphatic diol H2 having a number of carbon atoms of from two to twenty, at least one (cyclo)aliphatic triol H3 having a number of carbon atoms of from three to twenty, an aliphatic hydroxyacid A having at least two carbon atoms, at least one hydroxyl group, and at least one acid group which is selected from the group consisting of a carboxyl group, a sulfonic acid group, or a phosphoric or phosphonic acid group, and at least one component R having at least one isocyanate-reactive group and at least one radically polymerisable olefinically unsaturated group, at least one base B for at least partial neutralisation of the acid groups of component A, and a catalyst C for urethane formation which is a salt or a chelate complex of a metal of any of groups 3 to 15 of the Periodic System of the Elements;

• wherein the at least one component R having at least one isocyanate-reactive group and at least one radically polymerisable olefinically unsaturated group comprises compounds of at least two different classes selected from the group consisting of the classes R1, R2, and R3, wherein the class R1 comprises compounds having on average one olefinic unsaturation per molecule, and one isocyanate reactive group per molecule, the class R2 comprises compounds having on average two olefinic unsaturations per molecule, and one isocyanate reactive group per molecule, and the class R3 comprises compounds having on average three or more olefinic unsaturations per molecule, and one isocyanate reactive group per molecule.