Polyolefin-based porous film and method for producing the same

• US 9,941,498 B2
• Filed: 11/25/2011
• Issued: 04/10/2018
• 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:
  US13/997,724
• Publication Number:
  US 20130337311A1
• Time in Patent Office: 2,328 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 of forming a non-porous raw fabric from a polyolefin-based resin composition, the polyolefin-based resin composition comprising at least one of a polyethylene and a polypropylene;

a (B) step of 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;

a (D) step of cold stretching a film processed in the (B) step in a direction (TD) perpendicular to the MD, where a stretching ratio in the TD is 1.10 to 1.5 times; and

a (H) step of thermal fixing in the TD by heating the film without substantially stretching the film,

where the steps (A), (B), (D) and (H) are performed in the above order, and

wherein a thermal fixing temperature T₂ (°

C.) in the (H) step satisfies (1) and (2) below;

T₂>

T₁ 

 

(1)

(Tm−

3)≥

T₂≥

(Tm−

40) 

 

(2)

and a stretching temperature T₁ (°

C.) in the (D) step satisfies T₁≤

(Tm−

30),

where Tm represents the melting point (°

C.) of the non-porous raw fabric.

2. The method according to claim 1, wherein the stretching temperature T₁ in the (D) step satisfies (Tg+20)≤

T₁≤

(T₂−

5),

where Tg represents a glass-transition temperature (°

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

3. A polyolefin biaxially-stretched porous film prepared by the method according to claim 1.