Toray Battery Separator Film Co., Ltd.

Yoichi Matsuda

Kotaro Takita

Sadakatsu Suzuki

A method of producing microporous membranes includes stretching a multi-layer layer extrudate having first and second layers, the first layer including a first polyolefin and a first diluent, and the second layer including a second polyolefin and a second diluent, the second polyolefin including polypropylene in an amount of 1.0 wt. % to 40.0 wt. %, the polypropylene having an Mw&#x3e;0.9&#xd7;10and a &#x394;Hm&#x2267;100.0 J/g; removing at least a portion of the diluents to produce a dried membrane having a first length and a first width; stretching the membrane by a first magnification factor of 1.1 to 1.5 and stretching the membrane by a second magnification factor of 1.1 to 1.3; and reducing the width.

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Nasushiobara, Japan

Yoichi Matsuda