PAPER COATING COMPOSITIONS

1402324 Paper coating compositions BADISCHE ANILIN- & SODA-FABRIK AG 29 Sept 1972 [2 Oct 1971] 44979/72 Heading C3P Aqueous paper coating compositions contain, for every 100 parts by weight of finely divided pigment, from 2 to 25 parts by weight of a synthetic binder comprising (A) a mixture of (a) an emulsion polymer of from 65 to 100% by weight of at least one monovinyl aromatic monomer (e.g. styrene, α-methylstyrene or vinyltoluene), up to 20% by weight of which may be replaced by acrylonitrile, from 0 to 35% by weight of at least one acrylate of C 1-12 non- tertiary alkanol and/or methacrylate of a C 4-12 non-tertiary alkanol, and from 0-10% by weight of at least one olefinically unsaturated monomer containing a carboxylic acid group or a substituted or unsubstituted carboxylic acid amide group, and (b) an emulsion polymer of from 80 to 100% by weight of at least one acrylate and/or methacrylate as defined in (a), from 0 to 20% by weight of at least one monovinyl aromatic monomer and/or acrylonitrile, and from 0 to 10% by weight of at least one acid or amide monomer as defined in (a), said emulsion polymer (b) having been prepared in the absence of special precautions (i.e. in the absence of a significant amount of chain transfer agent) reducing its molecular weight to or below a level corresponding to a K value of 40, and/or (B) a copolymer (c) which has been prepared in two stages, an emulsion polymer (a) or (b) as defined above being prepared in the first stage and the monomer(s) of the other polymer (b) or (a) being emulsion polymerized in the second stage, in an aqueous dispersion of the first stage polymer, in relative proportions within the ranges specified above; the proportions of polymer (a) and polymer (b) and the proportions of the first and second stages of copolymer (c) being such that the total quantities of monomers used are such as would provide a conventionally prepared random copolymer having a glass temperature of from - 20‹ to + 30‹ C. The pigment is generally china clay although in some cases titanium dioxide and synthetic pigments, e.g. those based on finely divided styrene polymers, may be used.