| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a polyolefin microporous film that has high MD tensile strength and an excellent balance in the MD tensile strength and TD tensile strength, has high transmissivity, and can be suitably used as a separator for a secondary battery.SOLUTION: In a 10μm-square field of view of an oriented fibril in the polyolefin microporous film, a fibril portion having an orientation direction in an angle range from 0 to 30° with respect to the mechanical direction (MD) is defined as an MD-oriented fibril portion; a fibril portion having an orientation direction in an angle range from 0 to 30° with respect to a direction (TD) perpendicular to the mechanical direction is defined as a TD-oriented fibril portion. A ratio D/Dis 1.2 to 3.0, where Dis a large-side average fibril diameter calculated by selecting 20% of the MD-oriented fibril portion in descending order of diameters, and Dis a large-side average fibril diameter calculated by selecting 20% of the TD-oriented fibril portion in descending order of diameters. The polyolefin microporous film has MD tensile strength of 1000 to 6000 kgf/cmand TD tensile strength of 1000 to 3000 kgf/cm.</p> |
