Asahi Kasei Kogyo Kabushiki Kaisha

Yasuhiro Tanabe

Yoshinao Doi

Osamu Fujii

Katsumi Yoshitake

Shigeo Kaneko

Takeo Hanamura

Tetsuhiko Hirata

This invention is directed to a microporous film comprising a 40 to 90 volume percent polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000 and a 10 to 60 volume percent inorganic filler and having a void space rate or porosity of 30 to 75 volume percent based on the volume of the film. The microporous film of such specific composition and structure has a desired wettability and a much reduced electrical resistance. Said resistance being as low as 0.0006 .OMEGA.dm.sup.2 /sheet. Said film has sufficient flexibility and mechanical strength to make it useful in wide variety of applications, especially as separators in batteries or electrolytical apparatuses etc. Such microporous material is prepared by: (a) blending a specified polyolefin, an inorganic filler and an organic liquid in amounts of 10 to 60 volume percent, 6 to 35 volume percent and 30 to 75 volume percent, respectively, based on the total volume of the blend, the amount of the polyolefin being 2/3 to 9 times the amount of the inorganic filler; (b) molding the blend to form a film; and (c) extracting said organic liquid from the molded film.

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Shizuoka, Japan

Yasuhiro Tanabe