Patent GB-1132888-A (GB)
Title: Water vapour permeable sheet materials
Inventor: DUNDERDALE KEITH FREDERICK
IPC: D04H1/46
Filed: 1966-07-11
Abstract: 1,132,888. Microporous coatings. IMPERIAL CHEMICAL INDUSTRIES Ltd. 20 June, 1967. [11 July, 1966], No. 30976/66. Heading B2E. A water-vapour permeable sheet material comprises a water-vapour permeable non- woven fabric comprising interlocked and entangled fibres, and a water-vapour permeable coating of flexible polymeric material in superposed adherence with the non-woven fabric, the coating having a microporous structure and having a modulus that varies through its thickness in such a manner that, on moving through the thickness of the coating from the surface adjacent the fabric to the exposed surface of the coating, the modulus increases to a maximum and then decreases in value towards the exposed surface. The term "modulus" is defined as the slope of the load-extension curve at zero extension determined by extending at a rate of 5 cm/min. in an Instron Tester a film 10 cm. by 2 cm. formed by casting a film of the coating composition. The coating may be a multi-layered structure of which neighbouring layers have different moduli, and at least some of the layers of the coating may incorporate a reinforcing filler in particle form. The flexible polymeric material may be a polyurethane elastomer, polyesters, polyethers, polyamides, polyesteramides, polyacetals, polyvinyl derivatives such as vinyl chloride polymer, or a combination thereof. The non-woven fabric may be a needle-punched non-woven fabric containing at least 20% and less than 50% by weight of in-situ retracted organic fibres, the fabric having been shrunk by about 35% of its original planar area and impregnated with an elastomeric or a resinous filling agent, e.g. a butadiene-acrylonitrile copolymer. The non- woven fabric may be formed wholly or partly of synthetic fibres, e.g. polyesters such as polyethylene terephthalate, polyofines such as polypropylene, or polyamides. A thin liquid waterimpermeable top coat may be applied to the microporous coating; which top coat may be embossed, e.g. with a natural leather grain. The material is produced by (a) applying e.g. by doctor knife technique, to the non-woven fabric comprising interlocked and entangled fibres a coating of polymeric material incorporating a filler in particle form in a liquid which is a solvent for the polymeric material and a non- solvent for the filler, (b) removing substantially all of the solvent from the coating, and (c) rendering the coating microporous, the coating being applied in the form of a multi-layered structure of which neighbouring layers have different compositions so that after steps (b) and (c) the microporous coating has the required modulus characteristic. At least part of the filler may be a soluble filler. Some of the coating layers may contain a soluble filler and some contain a mixture of a soluble filler and a reinforcing filler. The coating may be rendered microporous by leaching out the soluble filler; where the filler is a reinforcing filler the coating is rendered microporous by a coagulation technique; or the reinforcing filler is mixed with an agent in particle form which will decompose upon heating into one or more gases to form micropores in the coating; or particles of the gas evolving agent may be used alone. Examples of fillers are given.