Polyolefin-based porous film and method for producing the same

• US 10,693,114 B2
• Filed: 08/09/2017
• Issued: 06/23/2020
• 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 S
• Application Number:
  US15/672,532
• Publication Number:
  US 20170338458A1
• Time in Patent Office: 1,049 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.

Claims

1. A method for producing a polyolefin-based porous film comprising:

an (A) step;

a raw fabric forming step for forming a non-porous raw fabric from a polyolefin-based resin composition; and

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., where 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,

wherein the non-porous raw fabric obtained in the (A) step contains 80 mass % or more of a high-density polyethylene having a density of 0.960 to 0.963 g/cm³ and melt flow index of 0.25 to 1.0 g/10 min, and

wherein a birefringence of the non-porous raw fabric obtained in the (A) step is 3.0×

10<sup>−

2</sup> or more, and a pore surface area of the obtained polyolefin-based porous film is 37.9 to 42.0 m²/g,

wherein in the (A) step, a draft ratio of (draw-off speed of cast roll)/(flow rate of resin from die lip, which is calculated based on density) is 400 to 600 times.

2. The method for producing the polyolefin-based porous film according to claim 1, wherein the birefringence of the non-porous raw fabric obtained in the (A) step is 3.0×

10<sup>−

2</sup> to 4.5×

10<sup>−

2</sup>.

3. The producing method according to claim 1, further comprising:

a (C) step;

an MD heat stretching step for heat stretching a cold stretched porous film obtained in the (B) step at a temperature of (Tm−

40)°

C. to (Tm−

5)°

C. in the MD to obtain a heat stretched porous film.

4. The producing method according to claim 3, further comprising:

a (D) step;

a TD cold stretching step for cold stretching a film processed in the (C) step in a direction (TD) perpendicular to the MD, after the (C) step.

5. The producing method according to claim 4, wherein

a stretching temperature T₁ in the (D) step satisfies a condition below;

(Tg+20)°

C.≤

T₁≤

(Tm−

20)°

C.

(Tg represents a glass-transition temperature (°

C.) of the porous film to be subjected to the TD cold stretching).

6. The producing method according to claim 4, further comprising:

an (H) step;

a thermal fixing step for performing thermal fixation at a temperature equal to or more than the stretching temperature in the (D) step, after the (D) step.