Improvements in or relating to the production of microporous sheet material

摘要

A method of producing microporous sheet material comprises the steps of (a) depositing a layer of thermoplastic synthetic resinous particles upon a substantially horizontal, steadily moving, metal band; (b) carrying the layer on the band past first gauging means which compresses it to a desired thickness; (c) carrying the layer on the band past heating means while not subjecting it to pressure, and heating the layer to a temperature sufficient to cause the particles to soften and cohere together; (d) carrying the layer on the band past second gauging means where it is further compressed with the application of heat; and (e) cooling the layer. A laminate comprising microporous sheet material is obtained by following step (c), above, by the steps of (d) leading a sheet of backing material into contact with the layer's upper surface, under the application of heat and pressure, thus to provide a laminate comprising a desired thickness of microporous sheet material bonded to said sheet of backing material and (e) cooling the laminate. A suitable composition obtainable in particle form comprises vinyl chloride-vinyl acetate copolymer; a plasticizer (dimethoxy ethyl phthalate, alkyl aryl phosphate and dioctyl phthalate; colour and filler; wetting agent (to aid transpiration through the sheet) and an epoxy resin heat stabilizer for polyvinyl chloride. In forming microporous sheet the layer of resin particles are deposited from the hopper 6 on to the moving surface 4 and the layer passes through the first gauging means 10, comprising a plate 24 with its surface inclined to the band 14, then through the electrically heated oven 26 and through the second gauging means 12 comprising three sets of two opposed rollers, a continuous band 40 passing round the top rollers. Electrically heated plates 42 and 44 are fitted, in contact with bands 14 and 40 and arranged at a tapering angle. From the gauging means the layer passes (between bands 40 and 14) through cooling plates 48 and 50, in contact with the bands. A process and an apparatus for forming a laminate comprising the microporous material are also described (see Group VIII). Specifications 679,549 and 781,983 are referred to.