Environmentally friendly aqueous coating composition

A coating composition comprising an aqueous emulsion of a hydrophobic polymer made from at least one free-radically polymerizable monomer and 0.1 to 20 wt. %, based on the weight of free-radically polymerizable monomer(s), of at least one di- or higher-functional chain-extending monomer(s), the hydrophobic polymer having been emulsion polymerized in the presence of an aqueous solution of an oligomer made from a mixture of free-radically polymerizable monomers in aqueous solution, the mixture including 1 to 45 wt. % acid-functional free-radically polymerizable comonomer(s), 0.5 to 20 wt. % adhesion-promoting free-radically polymerizable comonomer(s), and 98.5 to 50 wt. % other free-radically polymerizable comonomer(s), the acid-functional comonomer(s) rendering the oligomer water-soluble per se or by neutralization and the adhesion-promoting comonomer(s) imparting improved adhesion to a wood, plastic, metal or cementitious substrate when the coating composition is applied and dried on such a substrate, the oligomer having an Mn of 500 to 50,000 and a Tg of at least 70° C., and the hydrophobic polymer having a Tg at least 40° C. lower than the Tg of the oligomer, wherein the weight of oligomer is 5 to 50 wt. % of the weight of oligomer plus hydrophobic polymer, and the aqueous emulsion is substantially free of adipic dihydrazide and other hydrolyzable crosslinkers, has a minimum film forming temperature≤55° C. and on drying has a Koenig hardness of at least 40 sec.

A coated article comprising a substrate having thereon a layer of a coating composition comprising an aqueous emulsion of a hydrophobic polymer made from at least one free-radically polymerizable monomer and 0.1 to 20 wt. %, based on the weight of free-radically polymerizable monomer(s), of at least one di- or higher-functional chain-extending monomer(s), the hydrophobic polymer having been emulsion polymerized in the presence of an aqueous solution of an oligomer made from a mixture of free-radically polymerizable monomers in aqueous solution, the mixture including 1 to 45 wt. % acid-functional free-radically polymerizable comonomer(s), 0.5 to 20 wt. % adhesion-promoting free-radically polymerizable comonomer(s), and 98.5 to 50 wt. % other free-radically polymerizable comonomer(s), the acid-functional comonomer(s) rendering the oligomer water-soluble per se or by neutralization and the adhesion-promoting comonomer(s) imparting improved adhesion to the substrate when the coating composition is dried, the oligomer having a number average molecular weight Mn of 500 to 50,000 and a glass transition temperature Tg of at least 70° C., and the hydrophobic polymer having a Tg at least 40° C. lower than the Tg of the oligomer, wherein the weight of oligomer is 5 to 50 wt. % of the weight of oligomer plus hydrophobic polymer, and the aqueous emulsion is substantially free of adipic dihydrazide, and other hydrolyzable crosslinkers and has a minimum film forming temperature≤55° C. and on drying has a Koenig hardness of at least 40 sec.