Patent GB-1143635-A (GB)
IPC: D06N3/00
Abstract: 1,143,635. Making semi-permeable films. CARL FREUDENBERG. 9 March, 1966 [9 March, 1965], No. 10345/66. Heading B5B. [Also in Divisions B2 and C3] Films permeable to air and water vapour but impermeable to liquid water are produced by preparing a solution of a polymeric material having a torsion modulus, measured according to DIN 53445, of 30 Kg. per sq. cm. in a solvent, incorporating in the solution a polar non-solvent for the polymer, which non-solvent is less volatile than and is miscible with the solvent and which serves as coagulant for the polymer, in an amount less than the critical proportion for coagulation, spraying the solution towards a substrate under such spraying and atmospheric conditions that the solvent evaporates preferentially to such an extent that coagulation starts before the sprayed material strikes the substrate but the sprayed material bonds together to form a film, the critical proportion having been exceeded during travel of the sprayed material. Suitable polymers include polyurethanes, polymers and copolymers of acrylic, methacrylic and ester, e.g. ethyl acrylate-acrylonitrilemethacrylic acid, halongenated sulphonated polyolefins such as chlorosulphonated polyethylene. A polyurethane pre-polymer may be used in the presence of a cross-linking agent, and after coagulation the film is heated to cure the polyurethane. Suitable solvents are water- or lower alcohol-miscible ethers particularly cyclic ethers, and certain non-watermiscible solvents such as ketones, chlorinated hydrocarbons, esters, aromatic hydrocarbons, e.g. tetrahydrofuran, acetone, methyl ethyl ketone, trichloroethylene. The coagulant may be water, a lower aliphatic alcohol, e.g. methanol, ethanol, normal and iso-propanol, butanols, hexanols. The spraying solution preferably has a Brookfield viscosity at 20‹ C. of 10 to 100 centipoise. Suitable substrates are fabrics, woven or non-woven porous materials, the fibres thereof being natural or synthetic, e.g. polyester, polyamide, cellulosic ester, cotton or acrylic or mixtures of these. Other polymers or mixtures of polymers may be combined with the solution of the polymeric material, e.g. polyvinyl chloride. Other additives may be dyes, pigments, fillers, emulsifiers, water repellants, antioxidants, higher boiling solvents, lubricants, plasticizers. In Example (1), a polyurethane is precipitated on to a needled polyamide non-woven web impregnated with a polyurethane to give a 0À3 mm. thick coating, and the coated web is sprayed with a high gloss varnish based on polyurethane, polymethyl methacrylate copolymer and polyamide, in Example (2), a solution of a polyurethane containing polyvinyl chloride, microlith black is treated with a mixture of water and n-propanol and sprayed on to a needled non-woven polyamide fibre fabric impregnated with a 1 : 1 carboxylated butadiene-acrylonitrile copolymer, and thereafter varnished as in (1); in Example (3) a polyether polyurethane is coagulated in the presence of polyvinyl chloride on to a polyurethane impregnated, needled, non-woven polyamide fabric; in Example 4 a copolymer of ethyl acrylateacrylonitrile-methacrylic acid is coagulated in the presence of zinc oxide on to a non- woven polyamide fibre fabric impregnated with a carboxylated butadiene-acrylonitrile-methacrylic acid copolymer; in Example 5 chlorosulphonated polyethylene is coagulated on to the smooth side of a unilaterally roughened cotton twill and the coated fabric varnished.