Celgard Inc.

Xiangyun Wei

Charles E Haire

Ronald W Call

Shizuo Ogura

Lie Shi

Zhengming Zhang

Donald K Simmons

Premanand Ramadass

J Robert Dees

A microporous membrane is made by a dry-stretch process and has substantially round shaped pores and a ratio of machine direction tensile strength to transverse direction tensile strength in the range of 0.5 to 5.0. The method of making the foregoing microporous membrane includes the steps of: extruding a polymer into a nonporous precursor, and biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction stretching including a simultaneous controlled machine direction relax.

Biaxially oriented microporous membrane

A microporous membrane is made by a dry-stretch process and has substantially round shaped pores and a ratio of machine direction tensile strength to transverse direction tensile strength in the range of 0.5 to 5.0. The method of making the foregoing microporous membrane includes the steps of: extruding a polymer into a nonporous precursor, and biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction including a simultaneous controlled machine direction relax.

A multi-layer microporous battery separator which comprises: a high molecular weight polypropylene layer having a melt flow index of &#x2266;1.2 measured at layer; a polyethylene layer; and a high molecular weight polypropylene layer having a melt flow index of &#x2266;1.2 measured at layer. The resulting microporous battery separator which is formed by a dry stretch process produces the microporous battery separator which has a porosity of &#x2266;37% while maintaining a gurley from 13-25 seconds and a thickness of &#x2266;25 microns.

Multilayer separator exhibiting improved strength and stability

The present invention is directed to a battery separator. The battery separator comprises a microporous film having a first portion and a second portion. The first portion is bonded to the second portion. The bond has a strength greater than 5 g/in. The film has a thickness less than 1.7 mils, a Gurley of less than 50 sec/10 cc, and a puncture strength of greater than 400 g/mil.

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Charlotte, NC, United States of America

Xiangyun Wei