Low temperature cure waterborne coating compositions having improved appearance and humidity resistance and methods for coating substrates

Abstract

A waterborne coating composition having a crosslinking agent and a dispersion of polymeric microparticles in an aqueous medium wherein the microparticles are prepared by first forming a mixture in the aqueous medium of ethylenically unsaturated monomers and a substantially hydrophobic, saturated fatty acid-containing polyester. The amount of fatty acid used to prepare the polyester ranges from about 20 to 80 weight percent of the total weight of the fatty acid-containing polyester. The fatty acid-containing polyester contains functional groups which are capable of reacting with the crosslinking agent. The mixture is particularized into microparticles by high stress techniques, followed by polymerization of polymerizable species within the microparticles to produce the polymeric microparticles. The amount of the fatty acid-containing polyester in the dispersion is at least 10 and up to 70 weight percent based on weight of the ethylenically unsaturated monomers and fatty acid-containing polyester. The amount of the polymeric microparticles in the coating composition is from 20 to 80 weight percent based on total weight of resin solids in the coating composition.