| 摘要 |
PROBLEM TO BE SOLVED: To provide a nonflammable separator having shut down property, and to provide a microporous film suitable for the separator. SOLUTION: The polyolefin based microporous film contains a polyolefin of very large molecular weight having a thickness of 0.5 to 75μm, a porosity of 30 to 85%, a permeability blocking temperature of less than 135°C, and a weight average molecular weight of 7×10<SP>5</SP>or larger; a polyolefin of low density; a nonflammability imposing substance containing boron. The separator for a battery is composed of the polyolefin-based microporous film. A borazine compound is preferable as the nonflammability imposing substance. COPYRIGHT: (C)2006,JPO&NCIPI
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