Patent ID: 7285590

Claim:
An aqueous dispersion, having a minimum film formation temperature no greater than about 50° C., comprising a multi-stage emulsion polymer made by a process that comprises: a first polymerization stage, in which a first monomer mixture having a calculated glass transition temperature of at least about 50° C. is polymerized via free radical emulsion polymerization to obtain a first-stage emulsion polymer, the first monomer mixture comprising: from about 80 to about 99.5% by weight of one or more ethylenically unsaturated non-ionic monomers; from 0 to about 5% by weight of one or more ethylenically unsaturated weak acid monomers; from 0 to about 5% by weight of one or more ethylenically unsaturated strong acid monomers; and from 0 to about 10% by weight of one or more ethylenically unsaturated monomers containing a keto group, wherein the first monomer mixture contains at least about 0.5% by weight of at least one of the ethylenically unsaturated strong acid monomers or the ethylenically unsaturated weak acid monomers, or mixtures thereof; and a second polymerization stage, in which a second monomer mixture having a calculated glass transition temperature from about −30° C. to about 10° C. is polymerized via free radical emulsion polymerization, in the presence of the first-stage emulsion polymer, to obtain the multi-stage emulsion polymer, the second monomer mixture comprising: from about 80 to about 99.5% by weight of one or more ethylenically unsaturated non-ionic monomers; from 0 to about 5% by weight of one or more ethylenically unsaturated weak acid monomers; from about 0.5 to about 10% by weight of one or more ethylenically unsaturated strong acid monomers; and from about 0.5% to about 10% by weight of one or more ethylenically unsaturated monomers containing a keto group.