Cathodically depositable aqueous electro-dipping lacquer coating composition

Claim 1

A cathodically depositable aqueous electrodipping coating composition comprising a binder dilutable in water by protonization with acids, said binder consisting essentially of: (a) 55 to 95% by weight, based on the total weight of binder being a reaction product of the resin having at least one isocyanate per molecule and a compound selected from the group consisting of polyamines, ketimines containing amino groups, ketimines containing hydroxyl groups and ketimines containing amino and hydroxyl groups and said reaction product having an average molecular weight (Mn) of about 500 to about 10,000, a pk b value of about 3 to about 7, and containing amino groups selected from the group consisting of primary, secondary and tertiary amino groups to an amine value of about 30 to about 150; and (b) 45 to 5% by weight, based on the total weight of the binder, of a cross-linking agent being a reaction product of an hydroxy and/or amino alkyl carboxylic acid ester with a polyisocyanate selected from the group consisting of aliphatic, cycloaliphatic and aromatic polyisocyanates and mixtures thereof, said cross-linking agent having an average molecular weight (Mn) of about 500 to about 5000 and containing terminal carboxyl groups, a sufficient number of which are esterified with monoalcohols containing from 1 to 6 carbon atoms to prevent the cross-linking agent from travelling to the anode during electro-deposition and to provide the cross-linking agent with an ester value of about 30 to about 350, the ester groups being substantially stable in a neutral aqueous medium but being reactive in a basic medium at a temperature above 140° C. with amino groups selected from the group consisting of primary and secondary amino groups which are present in the organic synthetic resin binder.