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

Waterborne coating composition, comprising:

• a) a dispersion of internally crosslinked polymeric microparticles in an aqueous medium wherein the microparticles are prepared by
• (i) forming a mixture in the aqueous medium of ethylenically unsaturated monomers and a substantially hydrophobic, saturated fatty acid-containing polyester having an acid value of less than 5,
• wherein the ethylenically unsaturated monomers comprise one or more ethylenically unsaturated monomers having more than one site of unsaturation selected from ethylene glycol dimethacrylate, allyl methacrylate, hexanediol diacrylate, methacrylic anhydride, tetraethylene glycol diacrylate, tripropylene glycol diacrylate and mixtures thereof, and
• wherein the amount of saturated 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 containing functional groups which are capable of reacting with a crosslinking agent;
• and
• (ii) particularizing the mixture into microparticles by high stress techniques followed by
• (iii) polymerizing polymerizable species within the microparticles to produce the polymeric microparticles;
• the amount of the fatty acid-containing polyester in the dispersion being at least and up to 70 weight percent based on weight of the ethylenically unsaturated monomers and fatty acid-containing polyester, and
• the amount of the polymeric microparticles in the coating composition being from 20 to 80 weight percent based on total weight of resin solids in the coating composition;
• and
• b) a crosslinking agent.