Electrocoating with water-borne coating composition made from epoxy resin, polymeric acid and tertiary amine

In a process of electrocoating an electrically conductive surface serving as an anode which comprises passing electric current between said anode and a cathode in contact with an aqueous electrodepositable composition, the improvement wherein said electrode-positable composition comprises a water-borne coating composition consisting essentially of liquid carrier and the reaction product of:

• (A) not less than 50% by weight, based on the weight of (A) plus (B), of an epoxy resin containing, on the average, two terminal 1,2-epoxy groups per molecule and having an epoxy equivalent weight of 750-5000;
• (B) a carboxyl-functional polymer in an amount sufficient to provide at least 1.25 equivalents of carboxyl groups, when the source of the carboxyl group is a mono-protic acid, and at least 2.0 equivalents of carboxyl groups, when the source of such groups is a diprotic acid, per equivalent of 1,2-epoxy groups in the epoxy resin, said polymer having a weight average molecular weight (determined by light scattering) of about 5000-160,000 and an acid number of 100-500;
• (C) an aqueous solution of at least 1.25 equivalents of a tertiary amine per equivalent of 1,2-epoxy groups in the epoxy resin, said tertiary amine being selected from the group consisting of R.sub.1 R.sub.2 R.sub.3 N, pyridine, N-methylpyrrole, N-methyl piperidine, N-methyl pyrrolidine, N-methyl morpholine, and mixtures thereof and wherein R.sub.1 and R.sub.2 are substituted or unsubstituted monovalent alkyl groups containing one or two carbon atoms in the alkyl portion and R.sub.3 is a substituted or unsubstituted monovalent alkyl weight divided by 1000;
• and
• (E) optionally, 10-90% of the amount required for stoichiometric reaction with the carboxyl-functional polymer of (B) of at least one primary, secondary or tertiary amine or monofunctional quaternary ammonium hydroxide;
• wherein for increasing ratios of carboxyl groups to 1,2-epoxy groups, the amount of amine is increased to keep the carboxyl-functional polymer water dispersible.