Cathodic electrocoating process

Claim 1

A process for cathodically electrocoating a metallic substrate to form a cured resinous coating thereon, said process comprising A. establishing simultaneous contact of said metallic substrate and a counter-electrode with a body of liquid aqueous dispersion having dispersed therein a. a cathodically electrodepositable, at least partially cationized binder resin comprising a major proportion by weight of a reaction product of an epoxide-functional resin and a monoamino alcohol or phenol having at least one reactive hydrogen on the amino nitrogen, said reaction product being substantially devoid of reactive epoxide groups and having an average of at least about 2 reactive hydroxyl groups and at least about 0.2 directly or indirectly pendant 5 to 20 carbon atom hydrocarbon radical per molecule, b. from about 0.05 to 1 weight parts, per weight part of said binder resin, of an acid-functional aminoplast resin (i) cathodically co-electrodepositable with said binder resin from said aqueous dispersion to form an intermediate product comprising an intimate mixture of the cathodically electrodeposited forms of said binder resin and said aminoplast resin, (ii) co-reactive in said intermediate product with the cathodically electrodeposited form of said binder resin upon heating, to transform said intermediate product into a cured resinous product, (iii) having at least about 0.0001 equivalent of titratable acid functionality of pK a not greater than about 5 per gram of said aminoplast resin, and (iv) not soluble in the aqueous medium of said dispersion, and c. from about 20 to 150 milliequivalents, per 100 grams of (a) and (b), of an anion of a water-soluble acid to induce and stabilize the cationization of said binder resin, said aqueous dispersion having a pH of from about 2 to about 7 and being substantially free of any water-soluble acid which will be retained in water-soluble form in said cured resinous product and of anions thereof; B. maintaining an electrical potential difference between said metallic substrate and said counter-electrode, while both are in contact with said body of liquid aqueous dispersion, of such polarity that said metallic substrate is charged as a cathode relative to said counter-electrode as an anode and of such magnitude that an uncured coating comprising said intermediate product is cathodically electrodeposited upon said metallic substrate; C. removing said metallic substrate bearing said uncured coating thereon from contact with said body of liquid aqueous dispersion; and D. thereafter heating said uncured coating to transform it into a cured resinous coating comprising said cured resinous product.