Organic pigments

In the method of manufacturing paper wherein an opacifying agent is used to provide opacity in the final paper product, either by means of a coating or by means of internal addition to the paper pulp, the improvement wherein there is employed as at least a portion of the opacifying agent water-insoluble graft copolymer particles consisting essentially of the free radical catalyzed graft copolymerization product of (1) at least one ethylenically unsaturated monomer and 82) a water-soluble cationic prepolymer having an RSV of about 0.1 to about 2.5 (1 M NaCl, 1%, 25.degree. C.), the prepolymer moiety of the graft copolymer particles being present on the surface of the particles,

• said monomer (1) being selected from the group consisting of methyl alpha-chloroacrylate, ethyl alphachloroacrylate, methyl methacrylate, isopropyl methacrylate, phenyl methacrylate, vinyl chloride, acrylonitrile, methacrylonitrile, and monomers having the formula ##STR20## wherein R is hydrogen or methyl, Y is methyl or chlorine, and n is 0, 1, 2, or 3, and said prepolymer (2) being the addition polymerization product of
• (i) about 5 mole percent to 100 mole percent of at least one cationic monomer selected from the group consisting of ##STR21## wherein R.sub.1 is hydrogen or methyl, R.sub.2 is hydrogen or a C.sub.1 -C.sub.4 alkyl, R.sub.3 is hydrogen, a C.sub.1 -C.sub.4 alkyl, ##STR22## where Y is hydroxyl or halogen, ##STR23## where n is an integer 1 or more and X.sup.- is an anion, ##STR24## wherein R.sub.1 is hydrogen or a C.sub.1 -C.sub.4 alkyl, R.sub.2 is hydrogen, alkyl or substituted alkyl, and R.sub.3 and X.sup.- are as defined in formula (I), ##STR25## wherein R.sub.1, R.sub.2, R.sub.3 and X.sup.- are as defined in formula (I), ##STR26## wherein R.sub.1, R.sub.3 and X.sup.- are as defined in formula (I), ##STR27## wherein R.sub.1, R.sub.2, R.sub.3 and X.sup.- are as defined in formula (I), and n is an integer 1, 2 or 3 and ##STR28## wherein R.sub.1, R.sub.2, R.sub.3 and X.sup.- are as defined in formula (I), and
• (ii) from about 95 mole percent to 0 mole percent of at least one ethylenically unsaturated nonionic monomer selected from the group consisting of N-vinyl pyrrolidone, ethylenically unsaturated monomers having amide functionality, and ethylenically unsaturated monomers having hydroxyl functionality,
• the amount of prepolymer (2) employed in preparing the graft copolymer particles being from about 1 part to about 25 parts by weight for each 100 parts by weight of monomer (1) employed.