Patent ID: 7589158

Claim:
An acrylic latex comprising sequentially polymerized polymer particles formed in at least two polymerization stages so as to form a first phase, which results from a first polymerization stage, and a second phase, which results from a second polymerization stage, wherein: water, a surfactant, a first set of monomers that form the first phase and that comprise at least one polymerizable epoxy-reactive monomer and at least one polymerizable diluent monomer, a second set of monomers that form the second phase and that comprise at least one polymerizable epoxy-reactive monomer and at least one polymerizable diluent monomer, an initiator, optionally an organic solvent, optionally a pH adjustor, optionally a chaser solution, and optionally a preservative are combined under conditions sufficient to form the sequentially polymerized polymer particles; the first set of monomers has a first acid content, the second set of monomers has a second acid content, and the first acid content is lower than the second acid content; both the first set of monomers and the second set of monomers are substantially free from hydroxyl-functional epoxy-reactive monomers; both the first set of monomers and the second set of monomers are substantially free from crosslinking monomers; the glass transition temperatures of the first phase polymer formed by the first set of monomers and of the second phase polymer formed by the second set of monomers are both above 30° C. and less than about 80° C.; the sequentially polymerized polymer particles of the acrylic latex are substantially free from pre-polymerized polymer particles that were not formed during any of the at least two polymerization stages; wherein the second set of monomers comprises an acid monomer content from 6% to about 20% by weight and one or more diluent monomers, and wherein the second set of monomers also comprises an acid monomer content from 2% to about 15% by weight more than the acid monomer content of the first set of monomers; and wherein the latex is suitable for aqueous paint compositions.