Microporous membrane and manufacturing method

1. A microporous membrane comprising (a) from 40 to 60% of a first polyethylene having a weight average molecular weight of from 3×10 5 to 3.5×10 5 and a molecular weight distribution of from 5 to 50, (b) from 20 to 40% of a first polypropylene having a weight average molecular weight of from 0.9×10 6 to 1.1×10 6 , a molecular weight distribution of from 1 to 50, and a heat of fusion of from 80 to 120 J/g, (c) from 10 to 25% of a second polypropylene having a weight average molecular weight of from 5.7×10 5 to 6.6×10 5 , a molecular weight distribution of from 5 to 50, and a heat of fusion of from 80 to 120 J/g, and (d) from 0 to 10% of a second polyethylene having a weight average molecular weight of from 1×10 6 to 3×10 6 and a molecular weight distribution of from 5 to 50, percentages based on the mass of the membrane.

2. The microporous membrane of claim 1 , wherein the microporous membrane has surface roughness of 3×10 2 nm or more when measured as a maximum height difference between two points on the membrane.

3. The microporous membrane of claim 1 , wherein

(a) the first polyethylene is one or more of ethylene homopolymer or ethylene/α-olefin copolymer having a weight average molecular weight of from 2.5×10 5 to 4×10 5 and a molecular weight distribution of from 5 to 100;

(b) the first polypropylene is one or more of propylene homopolymer or propylene/α-olefin copolymer having a weight average molecular weight of from 0.8×10 6 to 1.5×10 6 and a molecular weight distribution of from 1 to 100;

(c) the second polypropylene is one or more of propylene homopolymer or propylene/α-olefin copolymer having a weight average molecular weight of from 4×10 5 to 7×10 5 and a molecular weight distribution of from 5 to 100; and

(d) the second polyethylene is one or more of ethylene homopolymer or ethylene/α-olefin copolymer having a weight average molecular weight of from 1×10 6 to 5×10 6 and a molecular weight distribution of from 5 to 100.

4. The microporous membrane of claim 1 , wherein the membrane further comprises another polymer selected from one or more of polybutene-1, polypentene-1, poly-4-methylpentene-1, polyhexene-1, polyoctene-1, polyvinyl acetate, polymethyl methacrylate, polystyrene, and ethylene/α-olefin copolymer.

5. The microporous membrane of claim 1 , having a melt down temperature of 148° C. or higher and a thermal mechanical analysis maximum shrinkage in the molten state at 140° C. of 30% or less, and one or more properties of (1) an air permeability measured according to JIS P8117 ranging from 100 to 700 seconds/100 cm 3 , (2) a porosity ranging from 25 to 80%, (3) a pin puncture strength of 1,500 mN or more at a membrane thickness of 20 (4) a tensile strength of 40,000 kPa or more, (5) a tensile elongation of 100% or more, (6) a heat shrinkage ratio of 12% or less, (7) a thickness variation ratio of 20% or less after heat compression, (8) an air permeability of 1000 sec/100 cm 3 or less after heat compression, and (9) a surface roughness of 3×10 2 nm or more.

6. A battery separator comprising a microporous membrane comprising (a) from 40 to 60% of a first polyethylene having a weight average molecular weight of from 10 5 and a molecular weight distribution of from 5 to 50, (b) from 20 to 40% of a first polypropylene having a weight average molecular weight of from 0.9×10 6 to 1.1×10 6 , a molecular weight distribution of from 1 to 50, and a heat of fusion of from 80 to 120 J/g, (c) from 10 to 25% of a second polypropylene having a weight average molecular weight of from 5.7 to 10 5 to 6.6×10 5 , a molecular weight distribution of from 5 to 50, and a heat of fusion of from 80 to 120 J/g, and (d) from 0 to 10% of a second polyethylene having a weight average molecular weight of from 1×10 6 to 3×10 6 and a molecular weight distribution of from 5 to 50, percentages based on the mass of the membrane.

7. The battery separator of claim 6 , wherein the microporous membrane has surface roughness of from 3×10 2 nm to 3×10 3 nm when measured as a maximum height difference between two points on the surface of the battery separator.

8. The battery separator of claim 6 , wherein

(a) the first polyethylene is one or more of ethylene homopolymer or ethylene/α-olefin copolymer having a weight average molecular weight of from 2.5×10 5 to 4×10 5 and a molecular weight distribution of from 5 to 100;

(b) the first polypropylene is one or more of propylene homopolymer or propylene/α-olefin copolymer having a weight average molecular weight of from 0.8×10 6 to 1.5×10 6 and a molecular weight distribution of from 1 to 100;

(c) the second polypropylene is one or more of propylene homopolymer or propylene/α-olefin copolymer having a weight average molecular weight of from 4×10 5 to 7×10 5 and a molecular weight distribution of 5 to 100; and

(d) the second polyethylene is one or more of ethylene homopolymer or ethylene/α-olefin copolymer having a weight average molecular weight of from 1×10 6 to 5×10 6 and a molecular weight distribution of from 5 to 100.

9. The battery separator of claim 6 wherein the membrane further comprises another polymer selected from one or more of polybutene-1, polypentene-1, poly-4-methylpentene-1, polyhexene-1, polyoctene-1, polyvinyl acetate, polymethyl methacrylate, polystyrene, and ethylene/α-olefin copolymer.

10. A battery comprising an electrolyte, an anode, a cathode, and a separator situated between the anode and the cathode wherein the separator comprises a microporous membrane comprising (a) from 40 to 60% of a first polyethylene having a weight average molecular weight of from 3×10 5 to 3.5×10 5 and a molecular weight distribution of from 5 to 50, (b) from 20 to 40% of a first polypropylene having a weight average molecular weight of from 0.9×10 6 to 1.1×10 6 , a molecular weight distribution of from 1 to 50, and a heat of fusion of from 80 to 120 J/g, (c) from 10 to 25% of a second polypropylene having a weight average molecular weight of from 5.7 to 10 5 to 6.6×10 5 , a molecular weight distribution of from 5 to 50, and a heat of fusion of from 80 to 120 J/g, and (d) from 0 to 10% of a second polyethylene having a weight average molecular weight of from 1×10 6 to 3×10 6 and a molecular weight distribution of from 5 to 50, percentages based on the mass of the membrane.

11. The battery of claim 10 , wherein the battery is a lithium ion secondary battery, a lithium-polymer secondary battery, a nickel-hydrogen secondary battery, a nickel-cadmium secondary battery, a nickel-zinc secondary battery, or a silver-zinc secondary battery.