Process for producing porous film and porous film

• US 7,820,281 B2
• Filed: 08/19/2003
• Issued: 10/26/2010
• Est. Priority Date: 11/12/2002
• Status: Expired due to Fees

• Current Assignee: Daicel Chemical Industries Limited
• Original Assignee: Daicel Chemical Industries Limited
• Inventors: Yamato, Yo, Tsuyumoto, Michio
• Primary Examiner(s): Shosho; Callie E
• Assistant Examiner(s): DESAI, ANISH P
• Application Number:
  US10/534,411
• Publication Number:
  US 20060121267A1
• Time in Patent Office: 2,625 Days
• Field of Search: 428/304.4, 428/315.7, 428/315.5
• US Class Current: 428/304.4
• CPC Class Codes: B01D 2325/02 Details relating to pores or porosity of the membranes
• CPC Class Codes: B01D 2325/0283 Pore size
• CPC Class Codes: B01D 2325/04 Characteristic thickness
• CPC Class Codes: B01D 2325/20 Specific permeability or cut-off range
• CPC Class Codes: B01D 67/0009 by phase separation, sol-gel transition, evaporation or solvent quenching
• CPC Class Codes: B01D 67/0013 Casting processes
• CPC Class Codes: B01D 67/0016 Coagulation
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B29C 41/12 Spreading-out the material on a substrate , e.g. on the surface of a liquid
• CPC Class Codes: B29C 41/24 for making articles of indefinite length
• CPC Class Codes: B29D 7/01 Films or sheets
• CPC Class Codes: B29K 2079/085 Thermoplastic polyimides, e.g. polyesterimides, PEI, i.e. polyetherimides, or polyamideimides; Derivatives thereof
• CPC Class Codes: B29K 2105/04 cellular or porous
• CPC Class Codes: B29K 2995/0068 Permeability to liquids; Adsorption
• CPC Class Codes: B29L 2031/755 Membranes, diaphragms
• CPC Class Codes: Y10T 428/249953 Composite having voids in a component [e.g., porous, cellular, etc.]
• CPC Class Codes: Y10T 428/249958 Void-containing component is synthetic resin or natural rubbers
• CPC Class Codes: Y10T 428/249961 With gradual property change within a component
• CPC Class Codes: Y10T 428/249978 Voids specified as micro
• CPC Class Codes: Y10T 428/249979 Specified thickness of void-containing component [absolute or relative] or numerical cell dimension

Abstract

A porous film of the invention is a porous film having a large number of continuous micropores. The film has a thickness of 5 to 200 μm, has an average surface pore size A of 0.01 to 10 μm, an average surface porosity C, and has an average inside pore size B and an average inside porosity D. The ratio A/B of A to B is 0.3 to 3. The porous film is produced by casting a polymer solution containing a polymer onto a substrate to form a film and subjecting the film to phase conversion to thereby form a porous film. In the method, the polymer constituting the porous film has a surface tension Sa [mN/m], the substrate has a surface tension Sb [mN/m], and Sa and Sb satisfy the following condition: Sa−Sb≧−10.

Claims

1. A porous film having a number of continuous micropores, wherein the film has a thickness of 5 to 200 μ

m, has an average surface pore size A of 0.01 to 10 μ

m and an average surface porosity C and has an average inside pore size B and an average inside porosity D,

wherein the ratio A/B of A to B is in the range of 0.3 to 3,

wherein a maximum surface pore size is 15 μ

m or less;

the ratio A¹/A² of an average pore size at one surface A¹ to an average pore size at the other surface A² is from 0.6 to 1.5;

the average surface porosity C has an average porosity C¹ of 48% or more at one surface and an average porosity C² of 48% or more at the other surface;

the average inside porosity D is from 45% to 80%; and

the ratio C/D of C to D is in the range of 0.7 to 1.5,

wherein a polymer component forming the film comprises at least one selected from a group of amide-imide polymers, imide polymers, polyethersulfones, polysulfones, acrylic polymers or cellulose acetate,

wherein a Gurley permeability of the porous film is from 0.2 to 29 seconds per 100 cc, and

wherein the porous film is produced in a method comprising the steps of casting a polymer solution comprising a polymer onto a substrate to form a film; and

subjecting the film to phase conversion to thereby form the porous film, wherein the polymer constituting the porous film has a surface tension Sa [mN/m], wherein the substrate has a surface tension Sb [mN/m], and wherein Sa and Sb satisfy the following condition;

Sa−

Sb≧

−

10.

2. The porous film according to claim 1, wherein the Gurley permeability of the porous film is from 1 to 25 seconds per 100 cc.

3. The porous film according to claim 1, wherein the Gurley permeability of the porous film is from 1 to 18 seconds per 100 cc.

4. The porous film according to claim 1, wherein the film has an average porosity C¹ of from 60% to 80% at one surface and an average porosity C² of from 60% to 80% at the other surface.

5. A method for producing the porous film according to claim 1, comprising the steps of casting a polymer solution comprising a polymer onto a substrate to form a film;

and subjecting the film to phase conversion to thereby form the porous film, wherein the polymer constituting the porous film has a surface tension Sa [mN/m], wherein the substrate has a surface tension Sb [mN/m], and wherein Sa and Sb satisfy the following condition;

Sa−

Sb≧

−

10.

6. The method for producing the porous film according to claim 5, further comprising the steps of casting a solution mixture as the polymer solution onto the substrate to form a cast film, and subjecting the film to phase conversion by bringing the film to a solidifying liquid to thereby form the porous film, the solution mixture comprising 8 to 25 percent by weight of the polymer component for constituting the porous film, 10 to 50 percent by weight of a water-soluble polymer, 0 to 10 percent by weight of water and 30 to 82 percent by weight of a water-soluble polar solvent.

7. The method for producing the porous film according to one of claims 5 and 6, further comprising the steps of holding the cast film in an atmosphere at a relative humidity of 70% to 100% and a temperature of 15°

C. to 90°

C. for 0.2 to 15 minutes, and bringing the film to a solidifying liquid comprising a nonsolvent for the polymer component.

8. A porous film having a number of continuous micropores,

wherein the film has a thickness of 5 to 200 μ

m, has an average pore size A¹ of 0.01 to 10 μ

m at one surface, an average pore size A² of 0.01 to 10 μ

m at the other surface, an average porosity C¹ of 48% or more at one surface, and an average porosity C² of 48% or more at the other surface,

wherein the ratio A¹/A² of A¹ to A² is in the range of 0.6 to 1.5,

wherein the ratio C¹/C² of C¹ to C² is in the range of 0.7 to 1.5,

wherein a maximum surface pore size is 15 μ

m or less;

the average inside porosity D is from 45% to 80%;

the ratio C/D of C to D is in the range of 0.7 to 1.5,

wherein a polymer component forming the film comprises at least one selected from a group of amide-imide polymers, imide polymers, polyethersulfones, polysulfones, acrylic polymers or cellulose acetate,

wherein a Gurley permeability of the porous film is from 0.2 to 29 seconds per 100 cc, and

wherein the porous film is produced in a method comprising the steps of casting a polymer solution comprising a polymer onto a substrate to form a film; and

subjecting the film to phase conversion to thereby form the porous film, wherein the polymer constituting the porous film has a surface tension Sa [mN/m], wherein the substrate has a surface tension Sb [mN/m], and wherein Sa and Sb satisfy the following condition;

Sa−

Sb≧

−

10.

9. The porous film according to claim 8, wherein the Gurley permeability of the porous film is from 1 to 25 seconds per 100 cc.

10. The porous film according to claim 8, wherein the Gurley permeability of the porous film is from 1 to 18 seconds per 100 cc.

11. The porous film according to claim 8, wherein the film has an average porosity C¹ of from 60% to 80% at one surface, and an average porosity C² of from 60% to 80% at the other surface.