Patent GB-1186975-A (GB)
Title: Man-Made Suede and Method of Making Same.
IPC: D06N3/00
Filed: 1968-06-20
Abstract: 1,186,975. Porous sheet material. E.I. DU PONT DE NEMOURS & CO. 20 June, 1968 [3 July, 1967], No. 29564/68. Heading B2E. [Also in Division C3] . A sheet material having a suede-like upper surface comprises (A) a porous fibrous substrate, (B) a predominantly fine-pore layer of porous polymeric material in superposed adherence with (A), from 75 to 100% of the pores therein having an average cross-section diameter of less than 20 microns, and (C) a predominantly coarse-pore cellular layer of polymeric material in superposed adherence with layer (B) and having from 75 to 100% of its volume composed of contiguous elongated cells having (i) an average cross-section diameter of from 20 to 200 microns, (ii) a substantially perpendicular orientation of their longest dimension in relation to the plane of the surface of the sheet, and (iii) thin microporous cell walls which, by virtue of their microporosity, render the cells intercommunicating. The sheet material and layers (A), (B) and (C) may be moisture-permeable and flexible, e.g. having a permeability value defined of at least 750. Substantially all the cells which form the upper surface of layer (C) may have an open uppermost portion having an average cross-section diameter of from 20 to 200 microns. Layer (A) may be a fabric e.g. a non-woven fabric; layer (B) may have a thickness from 0.5 to 15 mils and in which layer the pores communicate with one another, and layer (c) may have a thickness of from 5 to 40 mils. The polymeric material of layers (B) and (C) may have a secant tensile modulus (defined) at 5% elongation of over 600 psi and may contain from 51 to 100% by weight of a polyurethane polymer and from 0 to 49% by weight of a vinyl chloride polymer, based on the weight of polymer in said material. From 50 to 100% of said elongated cells in layer (C) have a tapered shape such that their diameters become progressively smaller from the bottom to the top of the layer. The sheet material may be produced by (1) wetting at least one surface of a porous fibrous substrate with a wetting liquid which is coagulant for the polymer solution described in step (2), (2) applying to the upper surface of the .substrate, a layer of a solution of a polymeric material in a liquid which is a solvent for the polymeric material, (3) bathing the layer of polymer solution with a bathing liquid adapted to coagulate the layer and to extract at least part of the solvent from the layer until the layer is coagulated and solidified in situ into a composite cellular layer containing a fine-pore layer beneath a coarsepore layer as described in (B) and (C) of Claim 1, and until at least part of the solvent is extracted from the layer, (4) removing from the layer substantially all of any solvent remaining therein, and (5) drying the resulting composite sheet material and (6) before or after step (5), .  subjecting the upper surface of the sheet material to treatment whereby a nap is produced thereon e.g. by rubbing with an abrasive member until a nap is formed or enough of the uppermost portion of said composite cellular layer is removed so that substantially all the cells which form the upper surface of the sheet material have an open uppermost portion having an average crosssection diameter of from 20 to 200 microns. The substrate may be a fabric and the polymer solution applied in step (2) has a polymer solids content of from 10 to 30% by weight and a viscosity of from 10 to 500 poises at 24C. The polymeric material used in step (2) may have a secant tensile modulus at 5% elongation of over 600 psi and the layer of polymer solution applied in step (2) contains one or more pigments, fillers or thixotropic agents. The layer of polymer solution applied in step (2) may be thick enough so that the coarse-pore layer formed in step (3) has a thickness of from 6 to 40 mils. Step (1) may be carried out prior to step (2). Step (1) may be carried out by immersing the substrate in the wetting liquid and then removing any excess wetting liquid from the substrate. The wetting liquid may be applied to the substrate by means of a roller having an absorbent surface containing the wetting liquid. The wetting liquid used in step (1) and the bathing liquid used in step (3) may be both water or a mixture of water with a minor amount of water-miscible organic liquid. The substrate just prior to step (2), may have a wetting liquid content of from 0.5 to 70% based on the combined weight of substrate and wetting liquid. The liquid component of the polymer solution used in step (2) may consist essentially of from 98 to 100% by weight of a water-miscible organic solvent and from 0 to 2% by weight of water. The organic solvent may be dimethylformamide or a mixture thereof with a minor proportion of methyl ethyl ketone: The polymeric material used in step (2) may contain from 51 to 100% by weight of a polyurethane polymer and from 0 to 49% by weight of a vinyl chloride polymer, based on the weight of polymer in the material.