Use in paper coatings of a mixture of a secondary polymeric dispersion and of a primary dispersion of an emulsion polymer

Abstract

The use in paper coatings is described of a mixture of an aqueous secondary dispersion of a polymer selected from polyalkylene carbonates, polyesters and polyethylene and an aqueous primary dispersion of an emulsion polymer having a glass transition temperature of below 50° C.

1 . A process for improving the properties of a paper coating, the process comprising combining a paper composition with a binder comprising a mixture of:
 (a) an aqueous secondary dispersion of at least one polymer selected from the group consisting of a polyalkylene carbonate, a polyester and a polyethylene; and   (b) an aqueous primary dispersion of at least one emulsion polymer having a glass transition temperature of below 50° C.,   to form an improved paper coating.   
     
     
         2 . The process of  claim 1 ,
 wherein the emulsion polymer has a glass transition temperature in the range from −10 to +30° C.   
     
     
         3 . The process of  claim 1 ,
 wherein the at least one polymer of the secondary dispersion has a glass transition temperature in the range from −50 to +50° C.   
     
     
         4 . The process of  claim 1 ,
 wherein the weight ratio of the emulsion polymer to the polymer of the secondary dispersion is in the range from 1:2 to 2:1.   
     
     
         5 . The process of  claim 1 , wherein the emulsion polymer is obtained by a free-radically initiated emulsion polymerization from one or more ethylenically unsaturated, free-radically polymerizable monomers selected from the group consisting of a vinylaromatic compound, a conjugated aliphatic diene, an ethylenically unsaturated acid, an ethylenically unsaturated carboxamide, a ethylenically unsaturated carbonitrile, a vinyl ester of an saturated C 1  to C 20  carboxylic acid, an ester of acrylic acid or methacrylic acid with a monohydric C 1  to C 20  alcohol, an allyl ester of a saturated carboxylic acid, a vinyl ether, a vinyl ketone, a dialkyl ester of an ethylenically unsaturated dicarboxylic acid, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, an N,N-dialkylaminoalkylacrylamide, an N,N-dialkylaminoalkyl acrylate, an N,N-dialkylaminoalkyl methacrylate, a vinyl halide, an aliphatic hydrocarbon having 2 to 8 carbon atoms and one or two double bonds, and a mixture thereof. 
     
     
         6 . The process of  claim 1 , wherein the emulsion polymer is selected from the group consisting of
 (i) a copolymer from 19.8 to 80 parts by weight of at least one vinylaromatic compound, 19.8 to 80 parts by weight of at least one conjugated aliphatic diene, 0.1 to 10 parts by weight of at least one ethylenically unsaturated acid, and 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer, wherein the parts by weight of monomer sum to 100;   (ii) a copolymer from 19.8 to 80 parts by weight of at least one vinylaromatic compound, 19.8 to 80 parts by weight of at least one acrylate monomer selected from C1 to C10 alkyl acrylates and C1 to C10 alkyl methacrylates, or their mixture, 0.1 to 10 parts by weight of at least one ethylenically unsaturated acid, and 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer, wherein the parts by weight of monomer sum to 100;   (iii) a copolymer from vinyl acetate and at least one (meth)acrylate monomer selected from C1 to C10 alkyl acrylates and C1 to C10 alkyl methacrylates, and   (iv) an ethylene-vinyl acetate copolymer.   
     
     
         7 . The process of  claim 1 , wherein the emulsion polymer is constructed from butadiene or mixtures of butadiene and styrene to an extent of at least 60% by weight or from C1 to C20 alkyl (meth)acrylates or mixtures of C1 to C20 alkyl (meth)acrylates and styrene to an extent of at least 60% by weight. 
     
     
         8 . The process of  claim 1 , wherein the emulsion polymer is prepared from
 (A1) 19.8 to 80 parts by weight of at least one vinylaromatic compound,   (B1) 19.8 to 80 parts by weight of at least one conjugated aliphatic diene,   (C1) 0.1 to 15 parts by weight of at least one ethylenically unsaturated acid, and   (D1) 0 to 20 parts by weight of at least one further monoethylenically unsaturated monomer other than said monomers (A1) to (C1);   or   (A2) 19.8 to 80 parts by weight of at least one vinylaromatic compound,   (B2) 19.8 to 80 parts by weight of at least one monomer selected from C1 to C18 alkyl esters of acrylic acid and C1 to C18 alkyl esters of methacrylic acid,   (C2) 0.1 to 15 parts by weight of at least one ethylenically unsaturated acid, and   (D2) 0 to 20 parts by weight of at least one further monoethylenically unsaturated monomer other than said monomers (A2) to (C2),   wherein the parts by weight of monomers (A1) to (D1) or (A2) to (D2) sum to 100 in either case.   
     
     
         9 . The process of  claim 8 , wherein:
 said monomers (D1) and (D2) are included in amounts of 0.1-15 parts by weight;   the vinylaromatic compound is selected from the group consisting of styrene, methylstyrene and their mixture;   the conjugated aliphatic diene is selected from the group consisting of 1,3-butadiene, isoprene and their mixture; and   the ethylenically unsaturated acid is selected from one or more compounds of the group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, vinylacetic acid, vinyllactic acid, vinylsulfonic acid, styrenesulfonic acid, acrylamidomethylpropanesulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate, vinylphosphonic acid and salts thereof.   
     
     
         10 . A paper coating composition, comprising
 (a) an aqueous secondary dispersion of at least one polymer selected from the group consisting of a polyalkylene carbonate, a polyester, and a polyethylene,   (b) an aqueous primary dispersion of at least one emulsion polymer having a glass transition temperature of below 50° C., and preferably in the range from −10 to +30° C., and   (c) inorganic pigments.   
     
     
         11 . The paper coating composition of  claim 10 , wherein the polymeric particles of the emulsion polymer have an average particle size in the range from 80 to 200 nm and the polymeric particles of the polymer of the secondary dispersion have an average particle size in the range from 100 to 400 nm. 
     
     
         12 . The paper coating composition of  claim 10 , wherein the pigments are selected from the group consisting of calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate, calcium carbonate, silicas, aluminas, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin, argillaceous earth, talc and silicon dioxide, and wherein the paper coating slip optionally further comprises at least one additive selected from the group consisting of thickeners, further polymeric binders, co-binders, optical brighteners, fillers, flow control agents, dispersants, surfactants, lubricants, neutralizing agents, defoamers, deaerators, preservatives and dyes. 
     
     
         13 . The paper coating composition according to  claim 10 , wherein:
 the polymers of the emulsion polymer and of the secondary dispersion are present used in total in an amount of 1 to 50 parts by weight, based on the total amount of pigments, and   the pigments are present in an amount of 80 to 95 parts by weight, based on total solids content.   
     
     
         14 . A paper or card coated with a paper coating composition of  claim 10 .