POROUS MEMBRANE OF VINYLIDENE FLUORIDE RESIN AND PROCESS FOR PRODUCING THE SAME

• US 20090148659A1
• Filed: 02/09/2009
• Published: 06/11/2009
• Est. Priority Date: 08/10/2006
• Status: Active Grant

• Current Assignee: Kuraray Company Limited
• Original Assignee: Kuraray Company Limited
• Inventors: YAMADA, Koji, ISHIODORI, Arata, KOMATSU, Kensaku
• Granted Patent: US 7,909,178 B2
• Time in Patent Office: Days
• US Class Current: 428/131
• CPC Class Codes: B01D 2325/021 Pore shapes
• CPC Class Codes: B01D 2325/36 Hydrophilic membranes
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/08 Hollow fibre membranes manufacture of hollow fibres D01D5/24, D01F1/08
• CPC Class Codes: B01D 71/34 Polyvinylidene fluoride
• CPC Class Codes: C02F 1/444 by ultrafiltration or microfiltration
• CPC Class Codes: C08J 2201/0522 the liquid phase being organic
• CPC Class Codes: C08J 2327/16 Homopolymers or copolymers of vinylidene fluoride
• CPC Class Codes: C08J 2439/06 Homopolymers or copolymers of N-vinyl-pyrrolidones
• CPC Class Codes: C08J 9/283 a discontinuous liquid phase emulsified in a continuous macromolecular phase
• CPC Class Codes: D01F 6/12 from polymers of fluorinated hydrocarbons
• CPC Class Codes: Y10T 428/24273 including aperture

Abstract

A porous membrane, made of polyvinylidene fluoride which is excellent in fractionating capability, permeating capability and physical strength and suitable for use in water treatment such as water purification, preparation of drinking water, preparation of water for industrial use and wastewater treatment, and which can be manufactured inexpensively and easily. The porous membrane has one surface formed with round or oval micropores and the opposite surface formed with substantially slit shaped micropores. The round or oval micropores have an average ratio between the major axis and the minor axis, which is within the range of 1:1 to 5:1, and the substantially slit shaped micropores have an average ratio between the major axis and the minor axis, which is not smaller than 5:1 and the particle cutoff of the membrane is not smaller than 0.2 μm.

Claims

1. A porous membrane made of a vinylidene fluoride resin of a particle cutoff not smaller than 0.2 μ

m, including a first surface and a second surface opposite to each other, the first surface having micropores of a round or oval shape of average ratio, between the major axis and the minor axis, within the range of 1;

1 to 5;

1 and the second surface having micropores of substantially slit shape of average ratio, between the major axis and the minor axis, not smaller than 5;

1.

2. The porous membrane made of the vinylidene fluoride resin as claimed in claim 1, which is made of a blended polymer including the vinylidene fluoride resin in a quantity within the range of 90 to 99 wt % and a hydrophilic resin in a quantity within the range of 1 to 10 wt %.

3. The porous membrane made of the vinylidene fluoride resin ac claimed in claim 2, wherein the hydrophilic resin is a vinylpyrrolidone resin.

4. The porous membrane made of the vinylidene fluoride resin as claimed in claim 1, which is a hollow fiber membrane.

5. The porous membrane made of the vinylidene fluoride resin as claimed in claim 4, wherein the first surface, having the micropores of round or oval shape of the average ratio, between the major axis and the minor axis, within the range of 1:

1 to 5;

1 is an outer surface of the hollow fiber membrane and the second surface having micropores of substantially slit shape of average ratio, between the major axis and the minor axis, not smaller than 5;

1 is an inner surface of the hollow fiber membrane.

6. A method of preparing a porous membrane made of a vinylidene fluoride resin, which comprises:

cooling a porous membrane preparing stock solution, containing a vinylidene fluoride resin, a solvent, inorganic particles and an aggregating agent, in which the inorganic particles and the aggregating agent have an affinity and the solvent and the coagulant are not compatible to each other or have an upper critical solution temperature, to induce a phase separation to thereby solidify; and

drawing the porous membrane before the solvent, the inorganic particles and the aggregating agent are extracted completely.

7. The method of preparing the porous membrane made of the vinylidene fluoride resin as claimed in claim 6, wherein the solvent is a water soluble solvent.

8. The method of preparing the porous membrane made of the vinylidene fluoride resin as claimed in claim 6, wherein the porous membrane is made of a blended polymer including the vinylidene fluoride resin in a quantity within the range of 90 to 99 wt % and a hydrophilic resin in a quantity within the range of 1 to 10 wt %.

9. The method of preparing the porous membrane made of the vinylidene fluoride resin as claimed in claim 8, wherein the hydrophilic resin is a vinyl pyrrolidone resin.

10. The method of preparing the porous membrane made of the vinylidene fluoride resin as claimed in claim 6, wherein the porous membrane is a hollow fiber membrane.

11. The method of preparing the porous membrane made of the vinylidene fluoride resin as claimed in claim 10, wherein the first surface having the micropores of round or oval shape of the average ratio, between the major axis and the minor axis, within the range of 1:

1 to 5;

1 is an outer surface of the hollow fiber membrane and the second surface having micropores of substantially slit shape of average ratio, between the major axis and the minor axis, not smaller than 5;

1 is an inner surface of the hollow fiber membrane.