Water-dispersible binders for cationic electrocoating paints, containing reaction products based on epoxy resins and prepolymers containing both carboxyl and hydroxyl groups

Abstract

The invention relates to water-dispersible binders for cationic electrocoating paints, a process for the preparation of these binders and a process for electrophoretic coating of an electrically conducting substrate, connected as cathode, from an aqueous bath based on this binder. The water-dispersible binders are reaction products of (A) epoxy resins containing low-molecular, preferably aromatic groups, having an epoxide equivalent weight below 750, (B) 10% to 60% by weight, prerferably 20% to 40% by weight, based on the total binder, of a prepolymer having a molecular weight (mass average) of 500 to 5000 and an average content per molecule of 0.1 to 1.9 hydroxyl groups and 0.1 to 1.0 carboxyl groups, the total of the hydroxyl and carboxyl groups being between 1 and 2, with an aromatic groups content of 10% to 45% by weight, calculated as phenylene groups contained in the resin solids in % by weight. In order to achieve water dispersibility, these reaction products are modified with (C) primary, secondary and/or tertiary amines and/or their salts or a sulfide/acid mixture or a phosphine/acid mixture.

Dependencies are inferred from the claim text.