GB1352512A - Water vapour permeable sheet material - Google Patents

Abstract

1352512 Smooth, porous films PORVAIR Ltd (Inmount Corp) 19 April 1971 [12 March 1970] 11917/70 Heading B5B [Also in Divisions B2 and C3] A water vapour permeable flexible polymer sheet has a surface zone more dense than the remainder of the structure having a glassy surface having an average glass value (defined) of at least 75 and a glass percentage on the tenminute test (defined) of not more than 25%. The sheet is prepared by treating a surface of the sheet with a solvent in which the polymer is soluble, the solvent being deposited as a discontinuous film over the sheet in amount between 10 and 200 gm. per square metre of the surface, blowing a current of heated air over the solvent treated surface to form a fused vapour permeable surface layer, drying the layer to free it of solvent, overlying the fused surface with a glassy void free film and applying heat and pressure to the film at a temperature within 100‹ C. below the melting point of the polymer sheet material, allowing the material to cool with the film in adherence and stripping off the film. The film is preferably 0À1 to 5 mils. thick and the preferred solvent is dimethylformamide which may be diluted with a less active or inactive liquid which may be more or less volatile, e.g. cyclohexanone and acetone. The solvent may contain dissolved polymer, preferably the same as that being treated. The polymer preferably is in amount less than 10% and a pigment or dye may be present. Preferred polymers are elastomeric polyurethanes and blends of these with up to 49% of polyvinyl chloride, and butadieneacrylonitrile polymers. Other suitable polymers are polyacetal resins, vinyl halide homo- and co-polymers, polyamides, polyesteramides, polyesters, polyvinyl butyral, polyalphamethylstyrene, polyvinylidene chloride, polymers of alkyl esters of acrylic and methacrylic acids, chlorsulphonated polyethylene, butadieneacrylonitrile copolymers, cellulose esters and ethers and polystyrene. The solvent or solvent composition may be applied by spraying, and reverse roller coating. Preferably the materials are microporous throughout their thickness and do not have fibrous reinforcement, although the supports described in Specification 914,713 may be used as well as materials of natural origin such as flank or imperfect hides.