Microporous polyolefin film, separator for battery, and production processes therefor

1. A polyolefin microporous membrane having a width of not less than 100 mm, wherein a variation range of an F25 value in a width direction is not greater than 1 MPa, and wherein the F25 value is obtained by dividing a load at 25% elongation of a sample of the polyolefin microporous membrane as measured with a tensile testing machine by a cross-sectional area of the sample.

2. A battery separator comprising:

a polyolefin microporous membrane; and

a porous layer on one or more sides of the polyolefin microporous membrane,

wherein:

the porous layer includes a water-soluble resin or a water-dispersible resin and a heat-resistant particle,

a variation range of an F25 value in a width direction of the polyolefin microporous membrane is not greater than 1 MPa,

an average thickness T(ave) of the porous layer is from 1 μm to 5 μm, and

the F25 value is obtained by dividing a load at 25% elongation of a sample of the polyolefin microporous membrane as measured with a tensile testing machine by a cross-sectional area of the sample.

3. The battery separator according to claim 2 , wherein the polyolefin microporous membrane has a width of not less than 100 mm.

4. The battery separator according to claim 2 , wherein a thickness variation range (R) in a width direction of the porous layer is not greater than 1.0 μm.

5. The battery separator according to claim 2 , wherein the water-soluble resin or the water-dispersible resin includes one or more kinds selected from the group consisting of poly vinyl alcohol, acrylic resin, and polyvinylidene fluoride resin.

6. The battery separator according to claim 3 , wherein a width of the polyolefin microporous membrane is not less than 500 mm.

7. The battery separator according to claim 3 , wherein a width of the polyolefin microporous membrane is not less than 800 mm.