Cationic electrodeposition using aqueous dispersions of quaternary

Abstract

A method of cationic electrodeposition on an electroconductive substrate is disclosed. The method of the invention employs as the electrocoating vehicle an aqueous dispersion of a quaternary ammonium carbonate-containing resin. Electrodeposition of the resin is accomplished without generating harmful acid from the counter ion. The carbonate counter ion is continuously evolved from the electrodeposition bath at the anode as carbon dioxide. The quaternary ammonium carbonate-containing polymers are also useful as feed resins for controlling the pH of aqueous dispersions of acidified cationic resins used in electrodeposition. Upon electrodeposition, these resins generate acid which can build up to undesirable levels in the electrodeposition bath. The quaternary ammonium carbonate-containing polymers are relatively basic and when fed into the bath react with the acid to form the corresponding quaternary ammonium salt of the acid releasing carbon dioxide. This controls the pH of the bath and provides additional cationic resin for electrodeposition. Utilizing the polymeric quaternary ammonium carbonates in this manner minimizes the need for controlling acid build-up in the electrodeposition bath by conventional techniques such as by treating the bath with ultrafiltration or electrodialysis.