Cathodic electrocoating process for forming resinous coating using an aqueous dispersion of polyamino polyhydroxy polyether resinous adduct and acid-functional aminoplast

Claim 1

A process for forming a cured resinous coating on a conductive substrate, comprising: (A) forming a liquid aqueous dispersion comprising: (i) an aqueous medium having pH from about 3 to 9 and containing an acid with a pK a not greater than about 5; (ii) a substantially oxirane-free, non-gelled, resinous adduct of (a) a substantially oxirane-free precursor adduct of a polyether diepoxide having molecular weight from about 300 to 10,000 and a polyamine having molecular weight from about 60 to 600 and (b) a mono-epoxide having molecular weight from about 100 to 500 and having a normal alkyl group of at least about 4 carbon atoms pendant through only hydrolysis-resistant linkages from the epoxy group of said mono-epoxide, the mole ratio of residues of said mono-epoxide to residues of said diepoxide in said resinous adduct being from about 0.2:1 to 2:1, the mole ratio of residues of said polyamine to residues of said diepoxide in said resinous adduct being from about 1.25:1 to 2:1, and said polyamine having from 2 to 5 amine groups per molecule and at least sufficient amino hydrogens to react with substantially all of the epoxy groups of both said diepoxide and said mono-epoxide; and (iii) from about 0.05 to 0.4 weight parts, per weight part of said resinous adduct, of an aminoplast resin having at least about 1 gram-equivalent, per 1,000 grams of said aminoplast resin, of carboxylic acid groups with pK a from about 2 to 6 for catalyzing the heat-induced cure of said resinous adduct with said aminoplast resin; (B) establishing concurrent contact of said conductive substrate and of another electrode with a common body of liquid aqueous dispersion; (C) maintaining a net unidirectional electrical current through said body of aqueous dispersion between said conductive substrate as cathode and said other electrode as anode to electrodeposit upon accessible portions of said conductive substrate a film comprising an intimate mixture of said polyamino polyhydroxy polyether resin and said aminoplast resin; (D) removing said conductive substrate coated with said film from contact with said body of aqueous dispersion; (E) thereafter heating said film on said substrate to cure said film by the acid-catalyzed reaction of said aminoplast resin with said polyamino polyhydroxy polyether resin.