Process for producing porous film and porous film

• US 20060121267A1
• Filed: 08/19/2003
• Published: 06/08/2006
• Est. Priority Date: 11/12/2002
• Status: Active Grant

• Current Assignee: Daicel Chemical Industries Limited
• Original Assignee: Daicel Chemical Industries Limited
• Inventors: Yamato, Yo, Tsuyumoto, Michio
• Granted Patent: US 7,820,281 B2
• Time in Patent Office: Days
• US Class Current: 428/315.700
• 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 method of the invention produces a porous film 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. This method can produce a porous film having a high rate of hole area at its surfaces and having homogenous micropores from the surfaces to the core thereof. 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 and an average rate of surface hole area C and has an average inside pore size B and an average rate of inside hole area D inside thereof, in which the ratio A/B of A to B is 0.3 to 3, and the ratio C/D of C to D is 0.7 to 1.5.

Claims

1. A method for producing a porous film, 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 a 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 method for producing a porous film according to claim 1, further comprising the steps of casting a solution mixture as the polymer solution onto the substrate to form a film, and subjecting the film to phase conversion by bringing the film to a solidifying liquid to thereby form a porous film, the solution mixture comprising 8 to 25 percent by weight of a 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.

3. The method for producing a porous film according to one of claims 1 and 2, 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.

4. A porous film having a large 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 rate of surface hole area C and has an average inside pore size B and an average rate of inside hole area D, wherein the ratio A/B of A to B is in the range of 0.3 to 3, and wherein the ratio C/D of C to D is in the range of 0.7 to 1.5.

5. A porous film having a large 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 rate of hole area C¹ of 48% or more at one surface, and an average rate of hole area C² of 48% or more at the other surface, wherein the ratio A¹/A² of A¹ to A² is in the range of 0.3 to 3, and wherein the ratio C¹/C² of C¹ to C² is in the range of 0.7 to 1.5.