Water reducible epoxy ester using monocarboxylic acid to control molecular weight

Claim 1

An epoxy ester comprising an ester adduct of a polyfunctional 1,2-epoxy resin and an aliphatic monocarboxylic acid having between about 8 carbon atoms and 18 carbon atoms or mixtures thereof and an aliphatic dicarboxylic acid having between about 6 and about 10 carbon atoms, the ratio of dicarboxylic acid to monocarboxylic acid being between about 2 and about 5, based upon the equivalent weight of each acid, the ratio of total aliphatic carboxylic acid equivalents (monocarboxylic acid plus dicarboxylic acid) to epoxide equivalents being between 1.0 and 1.2, and trimellitic anhydride, the ratio of anhydride equivalents in said trimellitic anhydride to equivalents of epoxy being between 0.15 and 0.35; the reaction between said epoxy resin, said monocarboxylic acid, and said dicarboxylic acid being carried out in a solvent under reflux at an elevated temperature until the acid number is 3-22 and the epoxy content is 0.025-0.035 meq./g. to obtain an initial ester and reacting said initial ester with trimellitic anhydride at a lower elevated temperature until the alcoholic acid number and the aqueous acid number are substantially equal.