Hydrophobic membrane materials for filter venting applications

• US 6,884,375 B2
• Filed: 01/08/2004
• Issued: 04/26/2005
• Est. Priority Date: 04/12/2002
• Status: Expired due to Term

• Current Assignee: Cytiva (Danaher Corporation)
• Original Assignee: Pall Corporation (Danaher Corporation)
• Inventors: Rudolph, James E. Jr., McDonogh, Richard, Wang, I-fan
• Primary Examiner(s): Fortuna, Ana
• Application Number:
  US10/753,931
• Publication Number:
  US 20040145073A1
• Time in Patent Office: 474 Days
• Field of Search: 264/41, 264/650, 210/500.36, 210/500.27, 210/500.42, 210/500.22, 210/500.23, 96/4
• US Class Current: 264/41
• CPC Class Codes: B01D 19/0031 by filtration
• CPC Class Codes: B01D 2323/12 Specific ratios of components used
• CPC Class Codes: B01D 2323/38 Graft polymerization
• CPC Class Codes: B01D 67/00113 Pretreatment of the casting solutions, e.g. thermal treatment or ageing
• CPC Class Codes: B01D 67/0013 Casting processes
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 71/32 containing fluorine atoms
• CPC Class Codes: B01D 71/36 Polytetrafluoroethene

Abstract

The present invention relates to filtration media having both hydrophobic (water-repellent) properties. The filtration media are produced using a fluorothermoplastic material, such as a terpolymer of tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene. The invention also relates to methods of preparing such filtration media using casting solution phase inversion.

Claims

1. A method for preparing a membrane, the method comprising:

providing a casting dope comprising a solvent and a terpolymer of tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene;

casting the dope to form a thin film;

exposing the film to a humid atmosphere for a period of time sufficient to allow formation of surface pores;

quenching the film in a quenching bath; and

recovering from the quenching bath a flat sheet membrane, the membrane comprising a terpolymer of tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene, the membrane having a first porous face having a first average pore diameter, a second porous face having a second average pore diameter, and a porous supporting structure therebetween wherein the supporting structure comprises a reticulated network of flow channels, and wherein the porous faces and the porous supporting structure comprise a network of structural surfaces capable of contacting a filter stream.

2. The method of claim 1, further comprising:

rinsing the membrane in a rinsing bath, wherein the rinsing step is conducted after the quenching step.

3. The method of claim 2, further comprising:

drying the membrane at an elevated temperature.

4. The method of claim 2, further comprising:

drying the membrane at room temperature.

5. The method of claim 1, wherein the dope comprises a homogeneous solution.

6. The method of claim 1, wherein the dope comprises a dispersion.

7. The method of claim 1, wherein the dope further comprises a nonsolvent.

8. The method of claim 7, wherein the nonsolvent comprises water.

9. The method of claim 7, wherein the dope comprises from about 1 wt. % to about 50 wt. % of nonsolvent.

10. The method of claim 1, wherein the solvent is selected from the group consisting of ketones, esters, ethers, and mixtures thereof.

11. The method of claim 1, wherein the solvent comprises n-butanol.

12. The method of claim 1, wherein the solvent comprises acetone.

13. The method of claim 1, wherein the solvent comprises dimethylformamide.

14. The method of claim 1, wherein the solvent comprises a first solvent having a first vapor pressure and a second solvent having a second vapor pressure, and wherein the first vapor pressure and the second vapor pressure are different.

15. The method of claim 1, wherein the dope comprises from about 15 wt. % to about 95 wt. % of solvent.

16. The method of claim 1, wherein the dope comprises from about 5 wt. % to about 30 wt. % of the terpolymer.

17. The method of claim 1, wherein the quenching bath comprises water.

18. The method of claim 2, wherein the rinsing bath comprises water.