Method for the preparation of stable aqueous dispersions of polymer beads and the use of these dispersions in photographic elements

Claim 1

Method for the preparation of stable aqueous dispersions of finely divided solid spherical polymer beads having an average particle size between about 0.5 and about 5 μm and having a glass transition temperature of at least 40° C., comprising the steps of: (A) dissolving in an aqueous solvent mixture of water and at least one water-miscible polar organic solvent chosen from the group consisting of lower alcohol, dioxan, acetone, acetonitrile, and dimethylformamide: (1) at least one alpha,beta-ethylenically unsaturated monomer chosen from the group consisting of styrene, vinyltoluene, substituted vinyltoluene, chlorostyrene, alkyl methacrylate, substituted alkyl methacrylate, butadiene, isobutylene, chlorobutadiene, 2-methylbutadiene, and vinyl pyridine, and capable of forming a polymer that is soluble in the monomer(s) present in said aqueous solvent mixture but which is insoluble in said aqueous solvent mixture, (2) a free radical-forming persulphate polymerization initiator that is soluble in the aqueous solvent mixture, and (3) a graft-polymerizable polymer containing hydrophilic groups, said graft-polymerizable polymer being chosen from the group consisting of polyethylene oxide, low molecular weight polyvinyl alcohol, polyvinyl pyrrolidone, co(vinyl alcohol/vinyl acetate) containing 12 mol % of vinyl acetate units, co(vinyl alcohol/vinyl acetate) containing 40 mol % of vinyl acetate units, sodium or potassium salt of co(acrylic acid/styrene) containing 40 to 60 mol % of acrylic acid, co(vinyl acetate/crotonic acid), a reaction product of copoly(styrene/maleic anhydride) with hydroxyalkyl methacrylate, a reaction product of copoly(styrene/maleic anhydride) with hydroxyalkyl acrylate, a reaction product of copoly(styrene/maleic anhydride) with aminoalkyl methacrylate, a reaction product of copoly(styrene/maleic anhydride) with aminoalkyl acrylate, a reaction product of copoly(vinyl acetate/maleic anhydride) with hydroxyalkyl methacrylate, a reaction product of copoly(vinyl acetate/maleic anhydride) with hydroxyalkyl acrylate, a reaction product of copoly(vinyl acetate/maleic anhydride) with aminoalkyl methacrylate, a reaction product of copoly(vinyl acetate/maleic anhydride) with aminoalkyl acrylate, a reaction product of copoly(ethylene/maleic anhydride) with hydroxyalkyl methacrylate, a reaction product of copoly(ethylene/maleic anhydride) with hydroxyalkyl acrylate, a reaction product of copoly(ethylene/maleic anhydride) with aminoalkyl methacrylate, a reaction product of copoly(ethylene/maleic anhydride) with aminoalkyl acrylate, a reaction product of copoly(N-vinyl pyrrolidone/maleic anhydride) with hydroxyalkyl methacrylate, a reaction product of copoly(N-vinyl pyrrolidone/maleic anhydride) with hydroxyalkyl acrylate, a reaction product of copoly(N-vinyl pyrrolidone/maleic anhydride) with aminoalkyl methacrylate, a reaction product of copoly(N-vinyl pyrrolidone/maleic anhydride) with aminoalkyl acrylate, and co(styrene/maleic acid monosodium salt), and said graft-polymerizable polymer being capable of forming a graft polymer that remains soluble in said aqueous solvent mixture, the weight ratio of said graft-polymerizable polymer to said monomer(s) being in the range from 1.5:100 to 8:100 and the weight ratio of polymerization initiator to monomer(s) from 0.1:100 to 5:100, and (B) heating the solution obtained to a temperature from 50° C. to the reflux temperature thereof with continuous stirring to initiate by polymerization the simultaneous massive formation of homopolymer or copolymer from said monomer and precipitation thereof, and the formation of a small proportion of graft polymer.