GB1092673A - Copolymers for use as binders in paper coating compositions - Google Patents

Abstract

Binders for paper-coating compositions comprise a mixture in aqueous dispersion of: (a) 95 to 60% by weight of a copolymer A having a glass temperature of from - 60 DEG to + 20 DEG C. and derived from 40-70% by weight styrene, 30-60% of an acrylate and/or methacrylate ester of a C2-C12 aliphatic alcohol and 0-10% of at least one other ethylenically unsaturated compound, and (b) 5 to 40% by weight of a copolymer B derived from 15-55% by weight of acrylic and/or methacrylic acid, 2-6% of acrylamide and/or methacrylamide and 85-45% of at least one other ethylenically unsaturated compound which forms a water-insoluble homopolymer, of which at least 20% by weight (with reference to these other compounds) is one or more acrylate and/or methacrylate esters of a C1-C4 aliphatic alcohol. The optional monomer components of copolymer A include acrylonitrile, vinyl chloride, vinylidene chloride, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and amides, substituted amides and hemi esters of such acids, vinyl sulphonic acid and p-styrene sulphonic acid. Monomer components (forming water-insoluble homopolymers) which may be incorporated in copolymer B, in addition to the essential (meth)-acrylate esters, include corresponding esters of alcohols with more than 4 carbon atoms, styrene, vinyl chloride, vinylidene chloride, vinyl esters, acrylonitrile and methacrylonitrile. For use as paper-coating compositions, the binders are mixed with fillers or pigments, e.g. clay or titanium dioxide, and other optional components, e.g. sodium polyacrylate, and adjuste to neutral or alkaline pH by treatment with an alkali. In an example, (A) styrene, n-butyl acrylate, acrylic acid and sodium vinyl sulphonate are polymerized in aqueous emulsion using potassium persulphate catalyst, and (B) ethyl acrylate, acrylic acid and acrylamide are polymerized in aqueous emulsion using potassium persulphate catalyst and in the presence of dodecyl mercaptan.ALSO:Neutral or alkaline paper coating compositions comprise a pigment or filler, e.g. clay or titanium dioxide, suspended in a binder comprising an aqueous dispersion of (a) 95 to 60% by weight of a copolymer derived from styrene, an acrylate and/or methacrylate ester of a C2-C12 aliphatic alcohol and optionally at least one other ethylenically unsaturated compound, e.g. acrylic acid, sodium vinyl sulphonate and/or acrylonitrile, and 5 to 40% by weight of a copolymer derived from acrylic and/or methacrylic acid, acrylamide and/or methacrylamide and at least one other ethylenically unsaturated compound which forms a water-insoluble homopolymer, of which at least 20% by weight of these other compounds is one or more acrylate and/or methacrylate esters of C1-C4 aliphatic alcohol (acrylonitrile may also be included, for example, in said other compounds). The coating compositions may include other components, e.g. sodium polyacrylate. Paper can be coated with the compositions by known methods such as roller coating or with a blade coater.