Patent ID: 7807271

Claim:
A process for coating paper or paperboard comprising mixing a coating composition comprising (a) a substantially water-soluble amphoteric synthetic (co)polymer co-binder, having an overall anionic charge, and a weight average molecular weight of about 40,000 to about 2,000,000 Daltons, (b) a pigment, wherein the pigment makes up about 50 to about 90 percent by weight of the total solids weight of the coating composition, (c) a primary binder selected from the group consisting of latex polymers, styrene butadiene, styrene acrylate lattices, starch or modified starch, polyvinylacetate, hydrolyzed polyvinyl acetate, polyvinyl acetate-acrylate, ethylene vinyl acetate, polyvinyl alcohol and mixtures thereof and optionally (d) other coating additives, wherein the polymeric co-binder is formed from ethylenically unsaturated monomers or macromers selected from the group consisting of i.) cationic and anionic or potentially anionic monomers or macromers and optionally nonionic monomers or macromers and ii) zwitterionic or potentially zwitterionic monomers or macromers and anionic or potentially anionic monomers or macromers and optionally nonionic monomers or macromers; and i.) or ii.) may optionally further comprise a crosslinking agent, and the cationic monomers are selected from the group consisting of dialkylaminoalkyl(meth)acrylates quaternary salts, dialkylaminoalkyl(meth)acrylamides quaternary salts, N,N-diallyldialkyl ammonium halides, acid addition salts or quaternary ammonium salts of allyl amines, acid addition salts or quaternary ammonium salts of diallyl amines and cationic vinylpyridines, and applying said coating composition to the paper or paperboard.