Process for double coating paper and product thereof

Claim 1

A paper coating process comprising: A. applying to the surface of a paper substrate a first coating of a composition comprising an inorganic pigment and a binder; and B. applying onto the surface of said first coating a second coating of a composition comprising an organic pigment and a binder, said organic pigment being water-insoluble graft copolymer particles consisting essentially of the free radical catalyzed graft copolymerization product of (1) at least one ethylenically unsaturated monomer and (2) a water-soluble prepolymer, 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 alpha-chloroacrylate, methyl methacrylate, isopropyl methacrylate, phenyl methacrylate, vinyl chloride, acrylonitrile, methacrylonitrile, and monomers having the formula ##STR11## wherein R is hydrogen or methyl, Y is methyl or chlorine, and n is 0, 1, 2, or 3 and said prepolymer (2) being selected from the group consisting of: a. anionic prepolymers prepared by the addition polymerization of a vinyl monomer or mixtures of vinyl monomers; b. nonionic prepolymers prepared by the addition polymerization of a vinyl monomer or mixtures of vinyl monomers and; c. cationic prepolymers prepared by the addition polymerization of (i) about 5 mole percent to about 95 mole percent of at least one cationic monomer selected from the group consisting of ##STR12## wherein R 1 is hydrogen or methyl, R 2 is hydrogen or a C 1 -C 4 alkyl, R 3 is hydrogen, a C 1 -C 4 alkyl, ##STR13## where Y is hydroxyl or halogen, ##STR14## and (CH 2 CH 2 O) n H where n is an integer 1 or more and X - is an anion, ##STR15## wherein R 1 is hydrogen or a C 1 -C 4 alkyl, R 2 is hydrogen, alkyl or substituted alkyl, and R 3 and X - are as defined in formula (I), ##STR16## wherein R 1 , R 2 , R 3 and X - are as defined in formula (I), ##STR17## wherein R 1 , R 3 and X - are as defined in formula (I), ##STR18## wherein R 1 , R 2 , R 3 and X - are as defined in formula (I), and n is an integer 1, 2 or 3 and ##STR19## wherein R 1 , R 2 , R 3 and X - are as defined in formula (I), and (ii) from about 95 mole percent to about 5 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.