Polyolefin-based porous film and method for producing the same

• US 9,991,488 B2
• Filed: 10/07/2015
• Issued: 06/05/2018
• Est. Priority Date: 12/28/2010
• Status: Active Grant

• Current Assignee: Asahi Kasei E-materials Corporation (Asahi Kasei Corporation)
• Original Assignee: Asahi Kasei E-materials Corporation (Asahi Kasei Corporation)
• Inventors: Itou, Miyuki
• Primary Examiner(s): ZEMEL, IRINA SOPJIA
• Application Number:
  US14/877,481
• Publication Number:
  US 20160064713A1
• Time in Patent Office: 972 Days
• CPC Class Codes: B29C 55/143 firstly parallel to the direction of feed and then transversely thereto
• CPC Class Codes: C08J 2323/02 not modified by chemical after treatment
• CPC Class Codes: C08J 2433/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: C08J 7/0427 with only one layer of a composition containing a polymer binder with more layers C08J7/042
• CPC Class Codes: C08J 7/123 Treatment by wave energy or particle radiation C08J7/18 takes precedence
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 2220/20 Batteries in motive systems, e.g. vehicle, ship, plane
• CPC Class Codes: H01M 50/403 Manufacturing processes of separators, membranes or diaphragms
• CPC Class Codes: H01M 50/417 Polyolefins
• CPC Class Codes: H01M 50/449 having a layered structure
• CPC Class Codes: H01M 50/489 Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• CPC Class Codes: H01M 50/491 Porosity
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A method for producing a polyolefin-based porous film includes an (A) step: a raw fabric forming step for forming a non-porous raw fabric from a polyolefin-based resin composition, a (B) step: an MD cold stretching step for cold stretching the non-porous raw fabric obtained in the (A) step at a temperature of −20° C. to (Tm−30)° C. (Tm is a melting point (° C.) of the non-porous raw fabric) in an extruding direction (MD) of the raw fabric to make the raw fabric porous; a (D) step: a TD cold stretching step for cold stretching a film processed in the (B) step in a direction (TD) perpendicular to the MD, and an (H) step: a thermal fixing step, in the above order. A thermal fixing temperature T₂ (° C.) in the (H) step satisfies expressions (1) and (2) below; T₂>T₁ (1), (Tm−3)≥T₂≥(Tm−40) (2) (in the expressions, T₁ represents a stretching temperature (° C.) in the (D) step, and Tm represents the melting point (° C.) of the non-porous raw fabric). A polyolefin-based porous film made of a polyolefin-based resin composition has a pore surface area of 35.0 to 42.0 m²/g and birefringence of 2.0×10⁻² to 4.0×10⁻².

Claims

1. A polyolefin-based porous film comprising a polyolefin-based resin composition, where the polyolefin-based porous film has a pore surface area of 35.0 to 42.0 m²/g and birefringence of 2.0×

10<sup>−

2</sup> to 4.0×

10<sup>−

2</sup>, and the polyolefin-based resin composition has a melt flow index of 0.2 to 1 g/10 min.

2. The polyolefin-based porous film according to claim 1, wherein porosity of the porous film is 40 to 80%.

3. The polyolefin-based porous film according to claim 1, wherein the polyolefin resin composition contains a high-density polyethylene having a density of 0.958 to 0.965 g/cm³.

4. A multilayered porous film comprising the polyolefin-based porous film according to claim 1.

5. A multilayered polyolefin-based porous film comprising:

the polyolefin-based porous film according to claim 1; and

a heat resistant layer laminated on at least one surface of the porous film.

6. The multilayered polyolefin-based porous film according to claim 5, wherein the heat resistant layer comprises an inorganic filler having a melting point of 200°

C. or more.

7. A battery separator comprising the porous film according to claim 1.

8. A battery separator comprising the multilayered porous film according to claim 5.