An improved aqueous cathodic electrocoating composition that contains an
anti-crater agent which is a water-reducible polyester resin having an
acid value less than 40 mg KOH/g. The water-reducible polyester is the
reaction product of (1) a hydroxy cyclic carbonate; (2) a polycarboxylic
acid anhydride; (3) optional monofunctional epoxy resin; (4) a
polyfunctional epoxy resin; and, (5) a polyamine compound containing
tertiary amine and either primary or secondary functionality. The
reaction product is neutralized in the presence of acid and water to
convert the tertiary amine groups to water-dilutable groups. Hydrolyzable
silane groups can also be incorporated into the reaction product to
further enhance its crater resistance property. The electrocoat
composition produces coatings having a smoother appearance with fewer
craters without adversely affecting intercoat adhesion of the cured film
to subsequent coating layers applied thereover.