Weakly acidic crosslinked vinyl polymer particles and coating compositions and electrographic elements and developers containing such particles

Claim 1

A plurality of polymeric particles, each particle having a weakly acidic surface and an average diameter less than one micrometer and comprising a crosslinked vinyl addition copolymer obtained by aqueous emulsion polymerization of a mixture of monomers in the presence of a polymerization initiator wherein: 0.5-15 percent by weight of the mixture of monomers comprises vinyl addition-polymerizable monomers capable of forming crosslinking structural units in the copolymer during the aqueous emulsion polymerization and selected from: divinylbenzene, ethylene dimethacrylate, ethylene diacrylate, and N,N'-methylenebisacrylamide; 85-99.5 percent by weight of the mixture of monomers comprises vinyl addition-polymerizable monomers selected such that: A. 0-99.5 percent by weight of the mixture of monomers comprises monomers selected from: alkyl acrylates, alkyl methacrylates, and vinyl alkanecarboxylates, the alkyl and alkane groups of which contain 4 to 7 carbon atoms; and styrenes having one or more alkyl substituents containing a total of 1 to 3 carbon atoms; B. from 0 to less than 98.5 percent by weight of the mixture of monomers comprises monomers selected from: alkyl acrylates, alkyl methacrylates, and vinyl alkanecarboxylates, the alkyl and alkane groups of which contain at least 8 carbon atoms; and styrenes having an alkyl substituent containing at least 4 carbon atoms; and C. 0-60 percent by weight of the mixture of monomers comprises monomers selected from: styrene; styrenes having an electronegative substituent; alkyl acrylates, alkyl methacrylates, and vinyl alkanecarboxylates, the alkyl and alkane groups of which contain less than 4 carbon atoms; nitriles; and acrylic and styrene monomers having a hydroxy, amido, amino, or quaternary ammonium substituent; with the provisos that: I. if more than 0 percent by weight of the mixture of monomers comprises the monomers of part C., above, then more than 0 percent by weight of the mixture of monomers comprises the monomers of part B., above; II. if more than 9 percent by weight of the mixture of monomers comprises the monomers of part C., above, then less than 10 percent by weight of the mixture of monomers comprises the monomers of part A, above; and III. the monomers and amounts thereof and the polymerization initiator are selected such that the weakly acidic surface of each particle is characterized in that an aqueous latex of the particles, having a concentration of about 40 grams of the particles per liter of aqueous medium, after formation by the aqueous emulsion polymerization and removal of any surfactant that may have been present during the aqueous emulsion polymerization, would exhibit a pH greater than 3 at 25° C., and in that the pKa of any acidic moiety bonded to the surface of each particle is at least 4.