received by the International Bureau on 12 July 2019 (12.07.2019)

CLAIMS

1. A separator for an electric storage device, comprising a microporous membrane comprising a polypropylene resin (A) and a thermoplastic elastomer (B), wherein the microporous membrane has the following regions:

(i) a polymeric matrix comprising the polypropylene resin (A) and the thermoplastic elastomer (B);

(ii) fibrils comprising the polypropylene resin (A) and extending in a Machine Direction (MD) of the microporous membrane from the polymeric matrix; and

(iii) pores between the fibrils; and

wherein a Melt Flow Rate (MFR) of the microporous membrane is 1.5g/l0minutes or less.

2. A separator for an electric storage device, comprising a microporous membrane comprising a polypropylene resin (A) and a thermoplastic elastomer (B), wherein the microporous membrane has the following regions:

(i) a polymeric matrix comprising the polypropylene resin (A) and the thermoplastic elastomer (B);

(ii) fibrils comprising the polypropylene resin (A) and extending in a Machine Direction (MD) of the microporous membrane from the polymeric matrix; and

(iii) pores between the fibrils; and

wherein a Melt Flow Rate (MFR) of the polypropylene resin (A) is 1.Og/lOminutes or less.

3. A separator for an electric storage device, comprising a microporous membrane comprising a polypropylene resin (A) and a thermoplastic elastomer (B), wherein the microporous membrane has the following regions:

(i) a polymeric matrix comprising the polypropylene resin (A) and the thermoplastic elastomer (B);

(ii) fibrils comprising the polypropylene resin (A) and extending in a Machine Direction (MD) of the microporous membrane from the polymeric matrix; and

(iii) pores between the fibrils; and

wherein the thermoplastic elastomer (B) forms a region in which a ratio (MD/TD) of a length in the MD to a length in a Transverse Direction (TD) is 1.5 or more.

4. The separator according to claim 3, wherein the region of the thermoplastic elastomer (B) is oriented along the MD of the microporous membrane.

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5. The separator according to claim 3, wherein the ratio (MD/TD) of a length in the MD to a length in a Transverse Direction (TD) is 10.0 or less.

6. The separator according to any one of claims 1 or 2 or 3, wherein the

thermoplastic elastomer (B) is free of propylene.

7. The separator according to any one of claims 1 or 2 or 3, wherein a weight ratio of the polypropylene resin (A) to the thermoplastic elastomer (B) is 99.9:0.1 to 80:20.

8. The separator according to any one of claims 1 or 2 or 3, wherein the

thermoplastic elastomer (B) is present in the polymeric matrix, but is not present in the fibrils.

9. The separator according to any one of claims 1 or 2 or 3, wherein, in the case of a crystalline, thermoplastic elastomer in which a hard segment of the thermoplastic elastomer (B) is crystalline, a crystalline melting point peak of the hard segment is 50 to 1 l0°C, or in the case of an amorphous, thermoplastic elastomer in which a hard segment of the thermoplastic elastomer (B) is amorphous, a glass-transition temperature of the hard segment is 30 to 1 l0°C.

10. The separator according to any one of claims 1 or 2 or 3, wherein a Melt Flow Rate (MFR) of the thermoplastic elastomer (B) is 2.0g/l0minutes or more.

11. The separator according to any one of claims 1 or 2 or 3, wherein the

thermoplastic elastomer (B) is ethylene/a-olefin copolymer.

12. The separator according to any one of claims 1 or 2 or 3, wherein a porosity of the microporous membrane is 30 to 80%.

13. The separator according to any one of claims 1 or 2 or 3, wherein the separator has an air permeability resistance of 100 to 500 seconds/lOO ml, provided that the air permeability resistance is a value obtained by multiplying an actual measured air permeability resistance of the separator by 14mih after dividing the actual measured air permeability resistance by a thickness of the separator.

14. The separator according to any one of claims 1 or 2 or 3, wherein the separator has a puncture strength of 400gf or more, provided that the puncture strength is a value obtained

66 by multiplying an actual measured puncture strength of the separator by 14mhi after dividing the actual measured puncture strength by a thickness of the separator.

15. The separator according to any one of claims 1 or 2 or 3, wherein a Melt Flow Rate (MFR) of the microporous membrane is O. lg/lOminutes or more.

16. The separator according to any one of claims 1 or 2 or 3, wherein a Melt Flow Rate (MFR) of the polypropylene resin (A) is O. lg/lOminutes or more.

17. The separator according to claims 1 or 2 or 3, wherein the separator comprises a microporous multi-layered membrane in which the microporous membrane comprising the polypropylene resin (A) and the thermoplastic elastomer (B) and a microporous membrane comprising polyethylene as a major component are laminated.

18. The separator according to claim 17, wherein a density of the polyethylene for the microporous membrane comprising a polyethylene as a major component is 0.96g/cm 3 or more, and a Melt Flow Rate (MFR) of the microporous membrane comprising a polyethylene as a major component is 0.6g/l0mmutes or less.

19. The separator according to claim 17, wherein the separator comprises not only the microporous membrane comprising the polypropylene resin (A) and the thermoplastic elastomer (B), but also the microporous multi-layered membrane.

20. A method of producing the separator according to any one of claims 1 or 2 or 3, comprising the steps of:

forming a raw film by means of a circular die extrusion method; and annealing the raw film, before heating and stretching the raw film.

21. A separator for an electric storage device, comprising a microporous membrane, wherein the microporous membrane comprises a polyolefin resin as a major component, and wherein the separator has a maximum-stress puncture depth of 4.0mm or more at a maximum puncture strength in a puncture test of the separator.

22. The separator according to claim 21, wherein the maximum-stress puncture depth is from 5.0mm to 20.0mm.

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23. The separator according to claim 21, wherein the maximum puncture strength is 20gf/pm or more.

24. The separator according to claim 21 , wherein a puncture strength of the microporous membrane has at least two maximum values in a depth-strength curve of the puncture test.

25. The separator according to claim 24, wherein the maximum puncture strength is at least one of the at least two maximum values in the depth-strength curve.

26. The separator according to claim 21, wherein the polyolefin resin is a polypropylene resin.

27. The separator according to claim 21, wherein a Melt Flow Rate (MFR) of the microporous membrane is l .4g/l0minutes or less.

28. The separator according to claim 21, wherein a Melt Flow Rate (MFR) of the microporous membrane is O.lg/lOminutes or more.

29. The separator according to claim 21, wherein an average longest pore diameter of the microporous membrane is from lOOnm to 2000nm.

30. The separator according to claim 21, wherein a pore diameter ratio (a/b) of an average longest pore diameter (a) of the microporous membrane to a pore diameter (b) perpendicular to the average longest pore diameter (a) is from 1.5 to 30.

31. The separator according to claim 21 , wherein longest pore diameters of the microporous membrane are arranged in one direction.

32. The separator according to claim 21, wherein the maximum puncture strength is 50gf/pm or less.

33. The separator according to claim 21 , wherein the microporous membrane comprises the polyolefin resin, as well as at least one selected from the group consisting of a thermoplastic elastomer, a copolymer having a branched chain, and a copolymer having a conjugated double bond.

34. The separator according to claim 21, wherein the microporous membrane comprises at least one selected from the group consisting of:

an ethylene/a-olefin copolymer different from the polyolefin resin;

a propylene/a-olefm copolymer different from the polyolefin resin;

a styrene/olefin copolymer different from the polyolefin resin; and a polypropylene elastomer different from the polyolefin resin.

35. The separator according to claim 21 , wherein the microporous membrane has the following regions:

(i) a polymeric matrix comprising the polyolefin resin;

(ii) fibrils comprising the polyolefin resin and extending in a Machine Direction (MD) of the microporous membrane from the polymeric matrix; and

(iii) pores between the fibrils.

36. A separator for an electric storage device, comprising a microporous membrane, wherein the microporous membrane comprises:

(A) a polyolefin resin as a major component; and

(B) at least one selected from the group consisting of an ethylene/a-olefin copolymer different from the polyolefin resin, a propylene/a-olefin copolymer different from the polyolefin resin, a styrene/olefin copolymer different from the polyolefin resin, and a polypropylene elastomer different from the polyolefin resin,

wherein an average longest pore diameter of the microporous membrane is from 1 OOnm to 2000nm, and

wherein a Melt Flow Rate (MFR) of the microporous membrane is 1.4g/l0minutes or less.

37. The separator for an electric storage device according to claim 36, wherein the Melt Flow Rate (MFR) of the microporous membrane is O. lg/lOminuts or more.

38. A separator for an electric storage device, comprising a microporous membrane comprising a polypropylene as a major component, wherein the microporous membrane has the following regions:

(i) a polymeric matrix comprising the polypropylene;

(ii) fibrils comprising the polypropylene and extending in a Machine Direction (MD) of the microporous membrane from the polymeric matrix; and (iii) pores between the fibrils;

wherein a porosity of the microporous membrane is 30 to 80%, and

wherein a puncture strength of the separator is 400gf or more, provided that the puncture strength is a value obtained by multiplying an actual measured puncture strength of the separator by 14mhi after dividing the actual measured puncture strength by a thickness of the separator.

39. The separator according to claim 38, wherein an air permeability resistance of the separator is 100 to 500 seconds/lOO ml, provided that the air permeability resistance is a value obtained by multiplying an actual measured air permeability resistance of the separator by 14pm after dividing the actual measured air permeability resistance by a thickness of the separator.

40. The separator according to claim 38, wherein the puncture strength is 700gf or less.

41. The separator according to claim 38, wherein a Melt Flow Rate (MFR) of the polypropylene is l .Og/lOminutes or less.

42. The separator according to claim 38, wherein a Melt Flow Rate (MFR) of the polypropylene is O. lg/lOminutes or more.

43. The separator according to claim 38, wherein a Melt Flow Rate (MFR) of the microporous membrane is l .5g/l0minutes or less.

44. The separator according to claim 38, wherein a Melt Flow Rate (MFR) of the microporous membrane is O.lg/lOminutes or more.

45. The separator according to claim 38, comprising:

the polypropylene; and

a thermoplastic elastomer being free of propylene.

46. The separator according to claim 38, wherein the separator comprises a microporous multi-layered membrane in which the microporous membrane comprising a polypropylene as a major component and a microporous membrane comprising a polyethylene as a major component are laminated.

47. The separator according to claim 46, wherein a density of the polyethylene for the microporous membrane comprising a polyethylene as a major component is 0.96g/cm or more, and a Melt Flow Rate (MFR) of the microporous membrane comprising a polyethylene as a major component is 0.6g/l0minutes or less.

48. The separator according to claim 46, wherein the separator comprises not only the microporous membrane comprising a polypropylene as a major component, but also the microporous multi-layered membrane. 49. A method of producing the separator according to claim 38, comprising the steps of:

forming a raw film comprising the polypropylene by means of a circular die extrusion method; and

annealing the raw film before heating and stretching the raw film.

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