GB953456A - Coating cement products - Google Patents

Abstract

Compositions for coating cement products comprise an aqueous dispersion of (a) a polymer of monoethylenically unsaturated monomers which contains 85 to 100 weight per cent. of polymerized methyl methacrylate units and not more than 2 weight per cent., if any, of units imparting hydrophilicity to the polymer and (b) an organic solvent for the polymer which boils in the range 150 to 255 DEG C., which is present in an amount sufficient to result in the formation of a continuous film on drying a coating of said composition and which comprises or consists of an ether which is not subject to hydrolysis under alkaline conditions, a ketone of formula RCOR1 where R and R1 are a saturated hydrocarbon group or an aryl group, or dimethylformamide. The polymers may comprise up to 15% of alkyl acrylates, e.g. methyl, ethyl or butyl acrylate and up to 2% of acrylic, methacrylic or itaconic acid, acrylamide, methacrylamide, b -hydroxyethyl acrylate, b -hydroxyethyl vinyl ether, b -aminoethyl acrylate or b -N,N-dimethylaminoethyl acrylate; and may be prepared by polymerisation in aqueous emulsion in the presence of catalysts, e.g. alkali metal and ammonium persulphates and perborates, hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, t.butyl perbenzoate and redox systems comprising persalts and sodium metabisulphite; and emulsifiers, e.g. sodium lauryl sulphate and t.octyl phenolethylene oxide condensates. Specified solvents are b -phenyloxyethanol, b -butoxyethanol, b -(2-ethylbutoxy)-ethanol and the monomethyl, monoethyl and monobutyl ethers of diethylene glycol, methyl hexyl ketone, amyl hexyl ketone and methyl phenyl ketone. Examples describe aqueous dispersions of copolymers of methyl methacrylate, ethyl acrylate and methacrylic acid containing (1 and 2) b -butoxyethanol, and methyl hexyl ketone, dimethyl formamide and diethylene glycol monomethyl ether. The compositions may be used for coating cement, e.g. asbestos cement, articles such as sheets, tiles and shingles.ALSO:Coated cement products may be prepared by applying to a formed but uncured cement product a coating of a composition comprising (a) an aqueous dispersion of a polymer of monoethylenically unsaturated monomers which contains 85-100 weight per cent of polymerized methyl methacrylate units and not more than 2 weight per cent, if any, of units imparting hydrophilicity to the polymer and (b) an organic solvent boiling in the range 150-255 DEG C. in amount sufficient to result in the formation of a continuous film on drying said coating which solvent is an ether not subject to hydrolysis under alkaline conditions, a ketone of formula RCOR1 where R and R1 are saturated hydrocarbon groups or aryl groups, and drying the applied coating to a non-tacky state at a temperature below 100 DEG C. The polymers may comprise up to 15% of alkyl acrylates, e.g. methyl, ethyl, or butyl acrylate, and up to 2% of acrylic, methacrylic or itaconic acid, acrylamide, methacrylamide, b -hydroxyethyl acrylate, b -hydroxyethyl vinyl ether, b -aminoethyl acrylate or b -N,N-dimethyl-aminoethyl acrylate. Specified solvents are b -phenyloxyethanol, b -butoxyethanol, b -(2-ethylbutoxy)-ethanol, the monomethyl, monoethyl and monobutyl ethers of diethylene glycol, methyl hexyl ketone, amyl hexyl ketone and methyl phenyl ketone. The compositions may be applied by spraying or flooding to cement, e.g. asbestos cement, articles such as sheets, tiles and shingles, the coatings dried and the products then stacked for curing. Examples describe the coating of asbestos cement sheets with aqueous dispersions of copolymers of methyl methacrylate, ethyl acrylate and methacrylic acid containing (1 and 2) b -butoxyethanol, and methyl hexyl ketone, dimethyl formamide and diethylene glycol monomethyl ether.