Fremgangsmåde til fremstilling af en mikroporøs plastgenstand

1,183,470. Microporous films. TUDOR A.B. 30 Aug., 1967 [1 Sept., 1966], No. 39686/67. Headings B5A and B5B. [Also in Divisions C3 and H1] A microporous plastics member, e.g. battery separator sheet, is made by forming a coherent dough by mixing a thermoplastic resin with a plasticizing amount of a first solvent and with finely divided particles of a filler which contains a volatilizable constituent releasable therefrom by heating and which shrinks irreversibly on release of this constituent, forming the dough into a shaped member, extracting the first solvent from the member by contacting it with a second solvent at a temperature below the b.p. of any liquid present, the second solvent being one which can dissolve the first solvent without dissolving the resin and filler, thereby deplasticizing the member, and then heating the member without softening the resin contained therein until the filler is shrunk within the member by release of its volatilizable content. The resin may be polyethylene, polypropylene, polystyrene or polyvinyl chloride. The filler may be powdered hydrated silica, silica hydrogel or diatomite with absorbed water. The first solvent may be a ketone, e.g. cyclohexanone and the second solvent may be water. In the examples, the dough was shaped by extrusion into a sheet.