Patent ID: 7691942

Claim:
An aqueous dispersion comprising polymeric particles, the particles comprising: core stage polymer comprising, as polymerized units, from 5 to 100% by weight, based on the weight of the core, of at least one hydrophilic mono-ethylenically unsaturated monomer and from 0 to 95% by weight of at least one nonionic mono-ethylenically unsaturated monomer; from 33% to 58% by weight, based on total polymeric weight of the particles when dry, of a first shell stage polymer having a Tg of 50° C. or greater, the first shell stage polymer comprising when dry, at least one void, the void having a diameter of from 100 to 1200 nanometers, wherein the first shell stage polymer is formed by a polymerization of at least one mono-ethylenically unsaturated monomer and from 0.05 to 50% by weight, based on the total weight of the first shell stage polymer, of at least one multi-ethylenically unsaturated monomer; and from 38% to 67% by weight, based on the weight of the polymeric particles, of at least one second shell stage polymer comprising, as polymerized units, at least one ethylenically unsaturated monomer, the second shell stage polymer substantially encapsulating the first shell stage polymer and having a Tg of from −60° C. to 50° C., wherein the second shell stage polymer is formed by a polymerization of at least one mono-ethylenically unsaturated monomer in the presence of the first shell stage polymer, and further wherein at least 10% of the second shell stage polymer is formed by polymerization at a temperature of from 5° C. to 65° C., the temperature being at least 30° C. below the calculated Tg of the first polymer; wherein the at least one hydrophilic mono-ethylenically unsaturated monomer of the core stage polymer is selected from the group consisting of methacrylic acid, and the at least one non-ionic mono-ethylenically unsaturated monomer of the core stage polymer is selected from the group consisting of methyl methacrylate; the at least one mono-ethylenically unsaturated monomer of the first shell polymer is selected from the group consisting of methyl methacrylate, methacrylic acid, butyl acrylate, styrene and mixtures thereof; and the at least one mono-ethylenically unsaturated monomer of the second shell polymer is selected from the group consisting of methyl methacrylate, methacrylic acid, 2-ethylhexyl acrylate, butyl acrylate, styrene and mixtures thereof; wherein the first shell stage polymer comprises at least two polymers formed in at least two stages wherein the aqueous dispersion has a BCOP biding factor of at least 0.1.