GB782031A - Improvements in or relating to water-vapour-permeable, composite, leather-like sheets - Google Patents

Abstract

782,031. Laminated materials. DU PONT DE NEMOURS & CO., E. I. May 6, 1955 [May 7, 1954], No. 13239/55. Drawings to Specification. Class 140. A laminated leather substitute comprises a sheet of initially thermoplastic, polymeric binder having an integral porous surface stratum free from fibres, the remaining cross-section of the sheet having uniformly distributed therethrough reinforcing fibres and contiguous channels. It is made by forming an impermeable sheet having a surface stratum of pore-forming fibres embedded in polymeric binder and integral therewith, a base stratum of reinforcing fibres embedded in polymeric binder, treating the sheet to cause the reinforcing fibres to break away from the binder, and dissolving out the pore-forming fibres with a solvent which does not attack the binder or the reinforcing fibres. The reinforcing fibres may be caused to break away from the binder by stretching the sheet in one or more directions or by treating it with a liquid which causes the reinforcing fibres to swell at a temperature above the softening temperature of the binder and drying the sheet to remove the liquid at or below the softening temperature of the binder. The fibres and binder may be associated by hot-pressing an assembly of alternate layers of fibrous webs or mats containing the reinforcing and pore-forming fibres and of sheets or coatings of the binder material. Alternatively, superposed mats of reinforcing fibres may be impregnated with a solution, dispersion, or hot melt of binder material, hotpressed, covered with a layer of pore-forming fibres and again hot-pressed to embed the poreforming fibres in the surface; in this procedure, the pore-forming fibres may be dispersed in a solution of an elastomeric binder which is applied as a coating and hot-pressed after drying to unite the coating with the binder in the sheet. The binder may be in the form of fibres carded with the pore-forming fibres and structural fibres, and later melted in a hot-pressing step. Stretching of the sheet may be effected before soaking in the solvent for the pore-forming fibres to facilitate penetration, and further stretching may be effected later. The solvent may simultaneously dissolve the pore-forming fibres and swell the reinforcing fibres. The binder may be polythene, polyisobutylene, neoprene, a butadiene-styrene copolymer, natural or synthetic polyisoprene, one of a large number of specified vinyl and vinylidene polymers and copolymers and synthetic rubbers, a polyester, a polyamide, a polyurethane, or a reaction product of a diisocyanate with a polyalkylene ether glycol. Plasticizers and cross-linking agents may be added to the binder. The binder polymer in the pore-forming layer may be different from, e.g. harder than, that in the base layer. The reinforcing fibres may be of polyamide, polyester, polyesteramide, cotton, viscose and acetate rayon, wool, polymers and copolymers of acrylonitrile, polyvinyl acetal, or glass. Some pore-forming fibres may be included in the reinforcing fibre layers. The pore-forming fibres may be cellulose acetate, extractable with acetone, polyvinyl alcohol, sodium alginate, potassium metaphosphate polymer glass, and carboxymethyl cellulose, extractable with water. The fibres may be first degraded and then dissolved out. Dyes or pigments may be incorporated in the binder, the reinforcing fibres, or the finished product may be dyed. Specifications 461,236, 535,262, 553,733, [all in Group IV], 711,279, 711,280, [both in Group IV (a)], 751,017 and 763,604 are referred to.