| 摘要 |
PROBLEM TO BE SOLVED: To provide a polyolefin microporous film imparting an excellent shut-down function and process passability when combined with a heat-resistant porous layer, and also preventing liquid shortage of an electrolytic solution.SOLUTION: The polyolefin microporous film has the following crystalline structure of polyolefin obtained by X-ray measurement. The structure includes two orientation axes; and when the axes are denoted by an orientation axis 1 and an orientation axis 2, the orientation axis 1 and the orientation axis 2 are inclined by 0 to 20 degrees and 60 to 90 degrees from the machine direction, respectively; the orientation degrees of the orientation axis 1 and of the orientation axis 2 are 65 to 80% and 65 to 80%, respectively; and the proportion of an integral value of the orientation axis 1 with respect to the integral value of the whole orientation is 20 to 40%. |
