Polymers for paper and paperboard coatings

A paper or paperboard coating composition comprising

• (a) a substantially water-soluble amphoteric synthetic (co)polymeric 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,
• wherein the primary binder is selected from the group consisting of latex polymers, styrene butadiene, styrene acrylate lattices, starch or modified starch, polyvinyl acetate, hydrolyzed polyvinyl acetate, polyvinyl acetate-acrylate, ethylene vinyl acetate, polyvinyl alcohol and mixtures thereof
• and
• optionally,
• (d) other coating additives,
• wherein the (co)polymeric co-binder is formed from ethylenically unsaturated, monomer(s) or macromer(s) selected from the group consisting of
• i) cationic and anionic or potentially anionic monomer(s) or macromer(s) and optionally nonionic monomer(s) or macromer(s);
• and
• iii) zwitterionic or potentially zwitterionic monomer(s) or macromer(s) and anionic or potentially anionic monomer(s) or macromer(s) and optionally nonionic monomer(s) or macromer(s);
• wherein i,) or iii.) may optionally further comprise a crosslinking agent,
• wherein the cationic monomer(s) 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.