Polyolefin microporous membrane and production method thereof

Patent metadata

Field	Value
Publication number	US-10079378-B2
Application number	US-201515312558-A
Country	US
Kind code	B2
Filing date	May 28, 2015
Priority date	May 28, 2014
Publication date	Sep 18, 2018
Grant date	Sep 18, 2018

Abstract

A polyolefin microporous membrane is disclosed. The membrane includes at least one microporous membrane layer, where the microporous membrane layer has an air permeability between about 100 sec/100 cc and about 220 sec/100 cc, a pin puncture strength of at least 550 gf, and a crystallization half time t 1/2 of from 10 to 35 minutes when subjected to isothermal crystallization at 117° C. The air permeability and the pin puncture strength are normalized to a thickness of 16 μm.

First claim

The invention claimed is:

1. A polyolefin microporous membrane, comprising:
at least one microporous membrane layer,
wherein the microporous membrane layer has an air permeability between 100 sec/100 cc and 220 sec/100 cc, a pin puncture strength of at least 550 gf, and a crystallization half time t 1/2 of from 10 to 35 minutes when subjected to isothermal crystallization at 117° C., wherein the air permeability and the pin puncture strength are normalized to a thickness of 16 μm, and
wherein the microporous membrane layer comprises an ultra-high molecular weight polyethylene concentration of at least 30 wt. %, and wherein the ultra-high molecular weight polyethylene has an average molecular weight of at least 1.0×10 6 and less than 2.0×10 6 .

2. The polyolefin microporous membrane according to claim 1 , wherein a curl of a 18.5 mm×95 mm section of the microporous membrane layer is less than 2 mm.

3. The polyolefin microporous membrane according to claim 1 , wherein a thickness of the microporous membrane layer is between 5 μm and 30 μm.

4. The polyolefin microporous membrane according to claim 1 , wherein the microporous membrane layer has a shrinkage in a transverse direction at 105° C. which is less than 6%, and a shrinkage in a longitudinal direction at 105° C. which is between 1.1 and 2.0 times the shrinkage in the transverse direction.

5. A separator for a non-aqueous electrolyte secondary battery comprising a polyolefin microporous membrane comprising:
at least one microporous membrane layer,
wherein the microporous membrane layer has an air permeability between 100 sec/100 cc and 220 sec/100 cc, a pin puncture strength of at least 550 gf, and a crystallization half time t 1/2 of from 10 to 35 minutes when subjected to isothermal crystallization at 117° C., wherein the air permeability and the pin puncture strength are normalized to a thickness of 16 μm, and
wherein the microporous membrane layer comprises an ultra-high molecular weight polyethylene concentration of at least 30 wt. %, and wherein the ultra-high molecular weight polyethylene has an average molecular weight of at least 1.0×10 6 and less than 2.0×10 6 .

6. A non-aqueous electrolyte secondary battery comprising the separator according to claim 5 .

7. The separator according to claim 5 , wherein a curl of a 18.5 mm×95 mm section of the microporous membrane layer is less than 2 mm.

8. The separator according to claim 5 wherein a thickness of the microporous membrane layer is between 5 μm and 30 μm.

9. The separator according to claim 5 , wherein the microporous membrane layer has a shrinkage in a transverse direction at 105° C. which is less than 6%, and a shrinkage in a longitudinal direction at 105° C. which is between 1.1 and 2.0 times the shrinkage in the transverse direction.

10. A method of producing a polyolefin microporous membrane, the method comprising:
(a) preparing a polyolefin solution by melt-kneading:
(i) a polyolefin resin containing an ultra-high molecular weight polyethylene having a concentration of at least 30 wt. % and an average molecular weight of at least 1.0×10 6 and less than 2.0×10 6 , and
(ii) a membrane-forming solvent;

(b) molding a sheet by extruding the polyolefin solution from an extruder to form an extrudate and subsequently cooling the extrudate, wherein a crystallization half time t 1/2 of the gel-like sheet between 10 and 35 minutes when subjected to isothermal crystallization at 117° C.;
(c) stretching the sheet in a longitudinal direction;
(d) stretching the sheet in a transverse direction;
(e) extracting a membrane-forming solvent from the stretched sheet; and
(f) drying the stretched sheet.

Assignees

• Toray Industries

Inventors

• Matsumoto Tomiko
• Sugata Masami
• Kono Koichi

Classifications

• C08J9/28 Primary

  by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum · CPC title

• B01D69/02

  characterised by their properties · CPC title

• C08J5/18

  Manufacture of films or sheets · CPC title

• B29C48/625

  characterised by the ratio of the threaded length of the screw to its outside diameter [L/D ratio] · CPC title

• C08J2423/06

  Polyethene · CPC title