Polytetrafluoroethylene resin porous membrane, separator making use of the porous membrane and methods of producing the porous membrane and the separator

• US 5,286,324 A
• Filed: 07/24/1992
• Issued: 02/15/1994
• Est. Priority Date: 07/30/1987
• Status: Expired due to Fees

• Current Assignee: Toray Industries Incorporated
• Original Assignee: Toray Industries Incorporated
• Inventors: Kawai, Takashi, Yoshioka, Toshio, Katsu, Tomoko
• Primary Examiner(s): AFTERGUT, JEFFRY H
• Application Number:
  US07/918,060
• Time in Patent Office: 571 Days
• Field of Search: 156/155, 156/166, 156/296, 264/49, 264/127, 429/247, 429/249, 210/450, 210/500.23, 210/500.36, 210/321.61, 210/493.2, 210/500.21
• US Class Current: 156/155
• CPC Class Codes: B01D 2323/02 Hydrophilization
• CPC Class Codes: B01D 2323/08 Specific temperatures applied
• CPC Class Codes: B01D 2323/081 Heating
• CPC Class Codes: B01D 63/022 Encapsulating hollow fibres
• CPC Class Codes: B01D 63/0223 by fixing the hollow fibres prior to encapsulation
• CPC Class Codes: B01D 63/0224 Opening the fibre ends after encapsulation
• CPC Class Codes: B01D 63/023 Encapsulating materials
• CPC Class Codes: B01D 67/003 by selective elimination of components, e.g. by leaching
• CPC Class Codes: B01D 69/08 Hollow fibre membranes manufacture of hollow fibres D01D5/24, D01F1/08
• CPC Class Codes: B01D 71/26 Polyalkenes
• CPC Class Codes: B01D 71/32 containing fluorine atoms
• CPC Class Codes: B01D 71/36 Polytetrafluoroethene
• CPC Class Codes: B01D 71/38 Polyalkenylalcohols; Polyalkenylesters; Polyalkenylethers; Polyalkenylaldehydes; Polyalkenylketones; Polyalkenylacetals; Polyalkenylketals
• CPC Class Codes: B01D 71/381 Polyvinylalcohol
• CPC Class Codes: B01D 71/76 Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74 rubbers in general B01D71/24

Abstract

Disclosed are a porous membrane which is made from a material containing, as its main component, a polytetrafluoroethylene resin, and a method of producing a porous membrane comprising forming a hollow or sheet-like film from a mixture of a polytetrafluoroethylene resin dispersion and a fiber-forming polymer, heat-treating the film at a temperature not lower than the melting temperature of the resin, and removing the fiber-forming polymer. Production of polytetrafluoroethylene porous membranes of a variety of pore sizes and porosities is possible by suitably varying the type and amount of additives added to an original liquid. The membrane finds spreading use in the field of separation in high-temperature and strong decomposing or strong dissolving mediums.

Claims

1. A method of producing a porous membrane comprising:

forming a membrane having a hollow fiber construction by coagulation of a dispersion of polytetrafluoroethylene resin in a solution of about 30 to 200% by weight of a film-forming polymer dissolved in said solution based on the weight of the polytetrafluoroethylene resin;

heat-treating said membrane at a temperature not lower than the melting point of said resin; and

removing said film-forming polymer.

2. A method of producing a porous membrane according to claim 1, wherein said polytetrafluoroethylene resin is selected from the group consisting of a tetrafluoroethylene homopolymer, a tetrafluoroethylene-perfluoroalkylvinylether copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-ethylene copolymer, and a mixture of these polymers.

3. A method of producing a porous membrane according to claim 1, wherein the size of the resin particles in said polytetrafluoroethylene resin dispersion is not greater than 1 μ

.

4. A method of producing a porous membrane according to claim 1, wherein said film-forming polymer is selected from a group consisting of a polyvinyl alcohol, a sodium alginate and a mixture thereof.

5. The method of claim 1, wherein the porous membrane resulting from said step of removing said film-forming polymer is in the form of a hollow fiber.

6. The method of claim 1, wherein the amount of film-forming polymer is in the range of from 10 to 200 wt %, based on the polytetrafluorethylene resin.

7. The method of claim 1, wherein the amount of film-forming polymer is in the range of from 30 to 100 wt %, based on the polytetrafluoroethylene resin.

9. A method of producing a porous membrane according to claim 1, wherein said finely dispersible additive is selected from a group consisting of inorganic particles, fine resin particles, heat-resistant organic matters and their mixtures.

8. A method of producing a porous membrane comprising:

forming a membrane having a hollow fiber construction by coagulation of a dispersion of polytetrafluorethylene resin in a solution of a film-forming polymer dissolved in said solution and about 30 to 700% by weight of finely dispersed additives other than said resin,

heat-treating said membrane at a temperature not lower than the melting point of said resin; and

removing said additives and said film-forming polymer.

10. The method of claim 8, wherein the porous membrane resulting from said step of removing said additives and said film-forming polymer is in the form of a hollow fiber.

11. The method of claim 8, wherein the amount of film-forming polymer is in the range of from 10 to 200 wt %, based on the polytetrafluoroethylene resin.

12. The method of claim 8, wherein the amount of film-forming polymer is in the range of from 30 to 100 wt %, based on the polytetrafluoroethylene resin.

13. A method of producing a separator comprising:

forming a membrane having a hollow fiber construction by coagulation of a dispersion of polytetrafluoroethylene resin in a solution of a fiber-forming polymer dissolved in said solution;

heat-treating said membrane at a temperature not lower than the melting point of said resin; and

effecting the following steps (1) and (2) in combination on the heat-treated membrane;

(1) removing said fiber-forming polymer to provide the membrane in the form of a hollow fiber, and

(2) mounting said membrane in a case so as to form independent flow channels in said case and welding and fixing an end of said case with a fluoro-resin.

14. The method of claim 13, wherein the amount of film-forming polymer is in the range of from 10 to 200 wt %, based on the polytetrafluoroethylene resin.

15. The method of claim 13, wherein the amount of film-forming polymer is in the range of from 30 to 100 wt %, based on the polytetrafluoroethylene resin.