Patent GB-1325928-A (GB)
Title: Surface treatment of microporous materials
IPC: D06N3/14
Filed: 1970-07-22
Abstract: 1325928 Microporous coating INMONT CORP 22 July 1970 [22 July 1969 20 Oct 1969] 35445/70 Heading B2E A sheet material has at least a surface zone of micro-porous polymeric material, the micropores of which when viewed in a cross-section perpendicular to the plane of the surface zone being at least one micron across, the surface zone being provided with an adherent layer of coagulated polymeric material which transmits water vapour and has less than 20% of its volume occupied by pores which when viewed in a cross-section perpendicular to the plane of the adherent layer are above 0.3 microns across, the adherent layer bridging and covering micro-pores which pass through the surface of the first zone, the adherent surface layer being up to 30 microns thick. The micropores in the surface zone may be elongated by compression and largely composed of micropores 5-50 microns across. Preferably the sheet material is free. of fibrous reinforcement. The surface zone and the adherent layer may comprise an elastomeric polyurethane containing 0-40% by weight of other high polymer material, the polyurethane materials of the surface zone and the adherent layer having an intrinsic viscosity of at least 0.7. The sheet material may be produced by providing a sheet material having a water vapour transmission of at least about 100 g/m<SP>2</SP>/24 hours and having at least one surface zone of micro-porous elastomeric polyurethane material with micro-pores which are over one micron in diameter passing through the outer surface of the zone, wetting the surface zone with a liquid and applying to the outer surface of the surface zone a solution of elastomeric polyurethane material in a solvent for the elastomeric material of the surface zone, the liquid being a non-solvent for the elastomeric material of the solution and of the surface zone and being a coagulant for the solution. The solution of polyurethane may be pigmented and may be applied by spraying or by rotogravure printing as fine closely spaced spots, or by intaglio printing. The pigmented adherent layer may be oversprayed in an uneven pattern with a second pigmented solution of a polymer in a solvent for the polyurethane of the adherent layer, the second pigmented solution being of a darker colour than the first solution and being deposited in a pattern of discreet small non-uniform areas, the macrodistribution of such areas being also non-uniform. A solvent for the polyurethane of the adherent layer may be applied to form a fused glossy upper surface on the adherent layer. Before or after the gloss producing treatment, the sheet may be subjected to a heat treatment under such conditions that shrinkage occurs. The adherent layer, before or after fusing with solvent, may also be pressed against a heated solid surface at a temperature below the softening temperature of the polyurethane of the adherent layer to impart a grained or a glossy effect, e.g. by applying pressure to a smooth strippable film in contact with the adherent layer, preferably using a heated embossing roll. Polyurethane materials mentioned for the micro-porous sheet are polyurethane per se, blends of polyurethanes and other high polymers such as vinyl chloride-vinyl acetate copolymer, butadieneacrylonitrile copolymer. Examples of other polymers for use in the micro-porous layer and in the coagulated layer are given in U.S.A. Specifications 3481766 and 3501326. The products are useful as substitutes for shoe upper leather.