Patent GB-1324063-A (GB)
Title: Synthetic paper
IPC: G03C1/795
Filed: 1971-04-20
Abstract: 1324063 Paper-like polystyrene films SUMITOMO CHEMICAL CO Ltd 20 April 1971 [22 April 1970] 10297/71 Heading B5B [Also in Division G2] A process for preparing a translucent synthetic paper, in which a sheet or film having a heat shrinkage of from 2% to 90% in at least one axial direction and formed from a composition comprising 100 parts by weight of a styrene polymer and from 3 to 40 parts by weight of a white inorganic filler, is treated with a mixed solvent having a shrinkage initiation time of from 40 to 2,000 seconds and comprising (i) a solvent for the sheet or film having a shrinkage initiation time of from 2 to 30 seconds; (ii) a non-solvent for the sheet or film which is homogeneously miscible with and has a lower vaporization rate than the solvent (i), and the treated heat-shrinkable sheet or film is dried in air at a temperature below 90‹ C. The white inorganic filler suitably has an average particle diameter of from 0À01 to 5À0 Á, especially from 0À1 to 2À0 Á, and a refractive index of from 1À50 to 1À70. Specified fillers include calcium carbonate, clay, talc, barium sulphate, and silica. The filler is desirably used in from 5 to 30 parts per 100 parts of styrene polymer, by weight. The styrene polymer may be a styrene homopolymer; copolymers comprising a major portion of styrene units with a minor proportion of units derived from another copolymerizable ethylenically-unsaturated monomer, such as ethylene, acrylonitrile, acrylic and α-alkyl acrylic acids and esters (e.g. acrylic acid, methacrylic acid, ethacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl ethacrylate and ethyl ethacrylate), or α-methylstyrene; polymers obtained by polymerizing styrene, alone or in admixture with an ethylenically-unsaturated monomer as already mentioned, in the presence of an elastomer such as a polybutadiene or a styrene-butadiene copolymer; and mixtures comprising a major proportion of a styrene homopolymer or copolymer and a minor proportion of a polybutadiene, a styrene-butadiene copolymer, an ethylene-vinyl-acetate copolymer or an ethylene-propylene copolymer. The styrene polymer may be an impact-resistant polystyrene, and may have a refractive index of from 1À55 to 1À63, and a melt flow index of from 0À1 to 5 at 230‹ C. under a load of 2,160 grams, as measured by ASTM D-1238. The mixed solvent may comprise a mixture of acetone, cyclohexane and ethyl alcohol; a mixture of methyl ethyl ketone, cyclohexane and n-propyl alcohol; a mixture of ethyl acetate and isopropyl alcohol; a mixture of 1, 4-dioxane and isopropyl alcohol; or a mixture of methyl ethyl ketone and ethyl alcohol. Suitably, the mixed solvent has a shrinkage initiation time of from 100 to 1,500 seconds. The film or sheet formed from the composition suitably has a heat shrinkage of from 10 to 70% in at least one axial direction. The translucent synthetic paper prepared by the process of the invention suitably has an opacity of from 10 to 65%, and especially from 25 to 50%, as measured by the method of JIS P-18128. A photosensitive copying paper may be made by coating a paper so made with a sensitizer, especially a diazonium compound and a coupler. Suitable diazonium compounds and couplers are listed.