Stable aqueous dispersions of mixed resins and process for use as coating compositions

A process for the preparation of a stable aqueous dispersion of mixed resins adapted for application as a thermosetting protective coating for metal surfaces, which process comprises the steps of (1) preparing a solution of an aminoplast component dissolved in a substantially water-miscible organic solvent;

• (2) heating and maintaining the temperature of the solution in the range between about 120.degree. and about 300.degree. F., and adding to the solution at a uniform rate over a period between about 0.5 to about 6 hours a blend of a vinyl polymerization catalyst and monomers comprising (a) between about 20 to about 90 weight percent based on total monomer weight of .alpha.,.beta.-olefinically unsaturated carboxylic acid, and (b) 10 to about 80 weight percent based on total monomer weight of at least one olefinically unsaturated monomer which is copolymerizable with the carboxylic acid monomer, thereby forming a polymerization product solution;
• (3) admixing and interacting at a temperature between about 100.degree. to about 300.degree. F. the polymerization product solution and an epoxy resin component, wherein said epoxy resin is a glycidyl polyether of a polyhydric phenol or hydrogenated phenol and contains an average of more than one epoxide group per molecule and has an epoxy equivalent weight in the range between about 150 to about 8000;
• (4) treating and at least partially neutralizing the admixture reaction product medium with ammonia or an organic amine, thereby forming a substantially homogeneous single phase solution;
• and dispersing the said solution into a sufficient quantity of water to provide a stable aqueous dispersion of mixed resins having a solids content in the range of between about 15 to about 40 weight percent wherein the aminoplast component is present in the amount of about 1 to about 12 weight percent, the monomers are present in the amount of about 20 to about 40 weight percent and the epoxy resin component is present in the amount of about 48 to about 79 weight percent, said weight percents being based on the total weight of aminoplast, monomers and epoxy resin components.

A method for protecting the surface of an article of manufacture which comprises applying to the surface a coating of a stable aqueous dispersion of heat-curable mixed resins, and heat-treating the coating to form an adherent thermoset film on the surface of the article, wherein the said stable aqueous dispersion coating composition is prepared by a process which comprises the steps of (1) preparing a solution of an aminoplast in a substantially water-miscible organic solvent;

• (2) heating the solution and adding thereto a mixture of vinyl polymerization catalyst and .alpha.,.beta.-olefinically unsaturated carboxylic acid monomer and at least one other vinyl polymerizable monomer to form a polymerization product solution wherein the unsaturated monocarboxylic acid monomer is present in the amount of about 20 to about 90 weight percent based on total monomer weight;
• (3) admixing and heating together the polymerization product solution and an epoxy resin;
• (4) at least partially neutralizing the admixture with ammonia or an organic amine;
• and (5) dispersing the admixture into an aqueous medium to provide a stable aqueous dispersion of mixed resin solids having a solids content in the range of between about 15 to about 40 weight percent wherein the aminoplast component is present in the amount of about 1 to about 12 weight percent, the monomers are present in the amount of about 20 to about 40 weight percent and the epoxy resin component is present in the amount of about 48 to about 79 weight percent, said weight percents being based on the total weight of aminoplast, monomers and epoxy resin components.