Cathodic electrocoating compositions having improved appearance, improved edge converage and reduced craters

Abstract

A cathodic electrocoating composition comprises an aqueous carrier, a film forming binder, comprising an epoxy-amine adduct and a blocked polyisocyanate crosslinking agent, dispersed in the carrier, and a novel additive comprising the reaction product of (1) a polyoxy alkylene di or monoamine; (2) a glycidoxy alkyl alkoxy silane; and (3) a glycidyl compound selected from the group consisting of a glycidyl ester of a carboxylic acid and an alkyl glycidyl ether, which reaction product is hydrolyzed in the presence of acid and water to convert alkoxysilane moieties to silanol moieties. The electrocoat composition produces coatings having a smoother appearance with better edge coverage and fewer craters.

Description

Background of the invention

[0001] The invention relates to a cathodic electrocoating composition, in particular to a cathodic electrocoating composition containing an anti-cratering agent which can significantly reduce welding seams and improve the corner covering power of the electrodeposited film of the composition.

[0002] The coating of conductive substrates by electrodeposition, also known as electrocoating, is a well-known and important industrial process. Electrodeposition of primers for automotive substrates is widely used in the automotive industry. In this method, an electrically conductive part, such as an automobile body or an automobile part, is immersed in a bath of a coating composition of an aqueous emulsion of a film-forming polymer and serves as an electrode for an electrodeposition process. Electric current is passed between the opposite electrodes where the part is in electrical contact with the aqueous emulsion until the desired coating is deposited on ...