CATHODIC ELECTRODEPOSITION PAINT FORMING FILMS HAVING IMPROVED SURFACE SMOOTHNESS

摘要

A cathodic electrodeposition paint containing a cationically modified epoxy resin and a crosslinker dispersed in an acidic aqueous medium is disclosed. The paint contains an auxiliary resin component capable of improving the surface smoothness of the cured paint films. The auxiliary resin is a reaction product produced by reacting a t-alkylphenol novolac epoxy resin with an active hydrogen compound to open all epoxy rings. When the auxiliary resin has a hydroxyl group introduced by the reaction with the active hydrogen compound, a lactone or alkylene oxide is addition reacted with the hydroxyl group for grafting a soft segment to the auxiliary resin. By grafting a soft segment, the auxiliary resin improves not only the surface smoothness but also the impact strength of the paint films.