Celanese Gmbh

Irving Brazinsky

William M Cooper

Arnold S Gould

A process for the preparation of an open-celled microporous, polymer film. The improved process comprises the heat relaxing of a microporous polymer film which is formed from a non-porous, crystalline, elastic polymer film which has been uniaxially cold stretched at a temperature in the range of between about -20.degree. C. and a temperature 25.degree. C. below the crystalline melting temperature of the polymer film, followed by hot stretching, in the same direction, the cold-stretched film at a temperature in the range of between about 25.degree. C. below the crystalline melting temperature of the polymer film and 5.degree. C. below the crystalline melting temperature of the polymer film. The heat relaxing step comprises exposing the film under tension to a temperature in the range of between about 40.degree. C. below the crystalline melting temperature of the polymer film and 5.degree. C. below the crystalline melting temperature of the polymer film, such that the maximum dimension in the direction of stretch, of the cold and hot stretched microporous film is reduced.

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Matawan, NJ, United States of America

Irving Brazinsky