Patent GB-1187040-A (GB)
Title: Improvements relating to Water Vapour Permeable Flexible Sheet Materials.
Inventor: CUNNINGHAM VICTOR RALPH
IPC: C08J9/26
Filed: 1966-03-07
Abstract: 1,187,040. Porous coatings. PORVAIR Ltd. 7 March, 1967 [7 March, 1966; 11 Jan., 1967], Nos. 9974/66 and 1609/67. Heading B2E. Artificial leather sheet material comprises a strength imparting base layer consisting of microporous elastomeric plastics material provided with a microporous appearance modifying surface layer or finish. The base layer may be formed by forming a layer of a mixture comprising the elastomeric material dissolved in a solvent on a temporary support, treating the layer on the support with a coagulating liquid, which is a non-solvent for the elastomeric material, but is at least partially miscible with the solvent so as to coagulate the working material into a microporous sheet, washing the layer with fresh coagulating liquid or continuing the treatment until all the solvent has been removed, and drying the .resultant sheet material. The surface layer may be formed by dispersing a solid removable filler in a thermoplastic plastics material in a plastic or liquid state, removing by evaporation any solvent used, heating the mixture so that the surface layer material is at least rendered plastic and forming the surface layer of the heated mixture directly on the base layer, and exposing the material to a leaching agent to remove the filler to form a porous layer. The surface layer may be formed on the base layer before or after stripping the latter from the temporary support. The temporary support may be porous and sufficiently rough to cause the base layer to adhere to it. The base layer material may be elastomeric polyurethane and the solvent may be N,N-dimethylformamide. The coagulating liquid may be water and may be heated. A removable particulate filler e.g. sodium chloride may also be incorporated in the base layer material. The temporary support may be formed of a sheet of sintered granulated plastics material e.g. high density polyethylene; alternatively by a sintered layer of polymeric plastics material granules on a smooth metal surface. A tie layer may be interposed between the base layer and the surface layer. In example 1 a solution of a thermoplastic polyester based polyurethane in dimethyl formamide is spread onto the smoother surface of a sheet of sintered polyethylene. The material is immersed in and washed with water at 70‹ Centigrade. A tie layer is formed on the base layer by doctor knife coating a solution of a polyester based polyurethane in dimethyl cyclohexanone containing sodium chloride and the layer dried at 100‹ Centigrade. A surface layer is applied to the tie layer by doctor knife coating a solution of a thermoplastic polyester base polyurethane in dimethylformamide containing sodium chloride and pigment. The composite sheet is immersed in water at 20‹ Centigrade washed in water at 80‹ Centigrade and dried at 100‹C. and then stripped from the temporary support. In example 2 hopper 41 feeds a mixture of sodium chloride filler and thermoplastics caprolactone based polyurethane to the nip between the roll 43 and the transfer roll 40 which are heated to temperatures sufficient to cause the surface material to be plastic and the surface layer is transferred onto the base layer 11 of Example 1. The surface of the surface layer is finished by finishing roll 16 to impart a smooth matt or embossed surface and passed over cooling roll 17. The material then passes through leeching tanks 25 containing water and finally through drying oven 30.