Patent GB-1389274-A (GB)
Title: Synthetic paper
IPC: B29C55/00
Filed: 1972-08-25
Abstract: 1389274 Paper-like films SUMITOMO CHEMICAL CO Ltd 25 Aug 1972 [25 Aug 1971] 39811/72 Heading B5B A synthetic paper is made by treating a sheet or film having a heat-shrinkage of from 2 to 90% in at least one axial direction and formed from an elastomer-containing styrene polymer (as defined below), either with a solvent mixture having a shrink initiation time on the styrene polymer of from 5 to 300 seconds and comprising (i) a solvent having a shrink initiation time on the styrene polymer of from 2 to 30 seconds and (ii) a non-solvent for the styrene polymer miscible with said solvent (i) and having a vaporization rate lower than that of said solvent, or first with (i<SP>1</SP>) a solvent having a swelling action on said styrene polymer and subsequently with (ii<SP>1</SP>) a non-solvent for said sheet or film miscible with said solvent (i<SP>1</SP>), and subsequently drying the treated heat-shrinkable sheet or film. Elastomer-containing styrene polymers are defined as styrene polymers containing from 1 to 10% by weight of an elastomer having an average particle diameter of from 0À1 to 5 microns and produced by the suspensionpolymerization or emulsion-polymerization of styrene, or a mixture of styrene and at least one ethylenically unsaturated monomer, in the presence of said elastomer. Such monomers with which the styrene may be copolymerized include acrylonitrile, methyl methacrylate and ethyl methacrylate. Specified elastomers include polybutadiene, a butadiene/styrene copolymer, and an ethylene/propylene/non- conjugated diene terpolymer. Part of the styrene or other ethylenically unsaturated monomer may be grafted on the elastomer. Preferably, the styrene polymer, which may be an impact-resistant polystyrene, or acrylonitrile/ butadiene/styrene copolymer, a methyl methacrylate/styrene/butadiene copolymer or an acrylonitrile/butadiene/styrene/methyl methacrylate copolymer, contains 3 to 7 % by weight of elastomer of average particle size 0À5 to 3 microns, and has a melt flow index of 0À1 to 5, as determined by ASTM D-1238 at 230‹ C. under a load of 2À16 kg. The film may be made by extrusion or calendering and stretched longitudinally and transversely to obtain a heat-shrinkable film. In Example 1, longitudinal stretching is effected using rolls at 115‹ C., and transverse stretching using a tenter at 130‹ C. Preferably, the heat-shrinkage of the film in at least one axial direction is from 10 to 70%: in Example 1, the film has a heat-shrinkage of 65 to 64% in two orthogonal directions. The solvent treatment may be effected by spraying, dipping or coating as a one-step operation or in two or more steps. The solvent (i) or (i<SP>1</SP>) may comprise one or more ethyl acetate, isobutyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, carbon tetrachloride, benzene, toluene, 1,4-dioxane, cyclohexane, isopropyl alcohol, benzyl ether, hexane and pentane, and the non-solvent (ii) or (ii<SP>1</SP>) may comprise an alsohol having 1-4 carbon atoms. Preferably solvent (i) or (i<SP>1</SP>) comprises a mixture of methyl ethyl ketone and cyclohexane, and the non-solvent (ii) or (ii<SP>1</SP>) is methanol. Where a three-step method is used, the film may be first treated with solvent (i<SP>1</SP>), then with one or more other solvents having an intermediate swelling action on the styrene polymer and miscible with said solvent (i<SP>1</SP>) and non-solvent (ii<SP>1</SP>), and finally with said non- solvent (ii<SP>1</SP>), the solvents being used sequentially in order of decreasing swelling action on the styrene polymer. Film so made has a rough surface, giving writability, and a porous surface layer giving receptivity to printing ink, the interior of the film contributing the desired mechanical properties.