Patent ID: 6964991

Claim:
A process for preparing a pressure sensitive adhesive having enhanced resistance to water-whitening comprising: (a) forming a polymerizable aqueous pre-emulsion comprising: (i) a hydrophobic monomer mixture of at least one alkyl acrylate or alkyl methacrylate ester of an alcohol wherein the alkyl portion of the alcohol is linear or branched and contains at least 4 carbon atoms, and at least one styrenic monomer, wherein the styrenic monomer is up to about 30 wt. % of the total hydrophobic monomer mixture, (ii) at least about 1 wt. % of at least one hydrophilic monomer, (iii) at least about 5 wt. % of at least one partially hydrophilic monomer selected from alkyl acrylate or alkyl methacrylate esters of an alcohol wherein the alkyl portion of the alcohol has 1 to 2 carbon atoms, N-vinyl-2-pyrrolidone, or mixtures thererof, and (iv) a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salts, or mixtures thereof, wherein the wt. % of monomers (i), (ii) and (iii) are based on the total weight of monomers (i), (ii) and (iii) in said pre-emulsion; (b) contacting water, an effective amount of a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salts, or mixtures thereof, and an initial amount of polymerization initiator to form a mixture; (c) continuously adding said pre-emulsion to said mixture to polymerize said pre-emulsion to form a latex emulsion, wherein additional polymerization initiator is added during the polymerization of said pre-emulsion; and (d) adjusting the pH of said latex emulsion with a suitable base to a pH of about 6.5 to about 9; wherein said effective amount of water-soluble or water-dispersible polymerizable surfactant in said mixture is that amount necessary to produce said pressure sensitive adhesive having an average particle size of less than or equal to 200 nm, and wherein said polymerizable surfactant has a hydrophilic portion selected from a sulfonate allyl amine moiety, a sulfate allyl amine moiety, or a phosphate allyl amine moiety, and a hydrophobic portion selected from —R, or a group having the formula RO—(CH 2 CH 2 O) n —; wherein R is an alkyl group or an alkyl-substituted phenyl group wherein the alkyl group has 1 to 20 carbon atoms, and n is an integer from 2 to 100.