Water-borne binders for primer-surfacer coating compositions

A water-borne coating binder ABC comprising a mixture of a curing agent C selected from the group consisting of capped isocyanates C1 based on aliphatic isocyanates, and aminoplast curing agents C2, and a reaction product AB made by at least partial esterification of a hydroxyl group-containing polyester A and an acid groups-containing polyurethane B, wherein the polyesters A are made by polyesterification of aliphatic linear branched or cyclic alcohols A1 which are at least difunctional, and of aliphatic linear branched or cyclic carboxylic acids A2 which are at least difunctional, wherein the amounts of A1 and A2 subjected to polyesterification are chosen in a way that the sum n(OH) of the amounts of substance of alcoholic hydroxyl groups in A1 and the sum n(H) of the amounts of substance of acidic hydrogen groups in the acids A2 are in a ratio n(OH):n(H) of from 1.08 to 1.01, and wherein the polyurethane B is made by polyaddition of isocyanate-functional compounds B1 having an average isocyanate functionality of more than one, and of hydroxy functional compounds B2 having an average hydroxyl functionality of more than 1, and wherein at least a mass fraction of 20% of the compounds B2 are such compounds B21 which have at least one acid group that is less reactive towards isocyanate groups than the hydroxyl groups of the said compounds B21, wherein each of A and B comprise not more than 20% of the amount of substance of their educts A1, A2, B1, and B2, of molecules comprising aromatic structures.