Liquid purification or separation – Filter – Material
Reexamination Certificate
1999-12-16
2001-10-09
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Filter
Material
C210S500420, C264S041000, C264S177140
Reexamination Certificate
active
06299773
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP98/02762 which has an International filing date of Jun. 22, 1998 which designated the United States of America.
TECHNICAL FIELD
The present invention relates to a porous polyvinylidene fluoride resin membrane and a process for preparing the same. The membrane is excellent in chemical resistance, mechanical properties and water permeability and is therefore suitable for treatment of highly viscous liquids.
BACKGROUND ART
Polyvinylidene fluoride resins (PVDF) have been used as materials for porous resin membranes which are excellent in chemical resistance, heat resistance and mechanical properties.
In connection with these porous polyvinylidene fluoride resin membranes, for example, U.S. Pat. No. 5,022,990 discloses a process for producing a porous polyvinylidene fluoride membrane which comprises blending a polyvinylidene fluoride resin with an organic liquid and an inorganic particulate material and subsequently melt molding the resulting blend in the form of a hollow fiber, tubular or flat membrane. The porous membrane prepared with this process has a uniform, three-dimensional, network structure. Particularly, an example of the U.S. patent describes a porous hollow fiber membrane having an inside diameter of 1.10 mm and a wall thickness of 0.45 mm. However, if the inside diameter is increased to larger than this value during the process, the membrane pressure resistance lowers because the membrane wall stretches thin as the inside diameter increases. On the other hand, if both the inside diameter and the wall thickness are increased to larger than these values during the process, then there is the problem that the resulting porous hollow fiber membrane has such a decrease in water flux as to be impractical.
As described above, it has heretofore been impossible for any conventional technique to provide a porous hollow fiber polyvinylidene fluoride resin membrane which has excellent pressure resistance and high water flux despite having a large inside diameter and which is therefore suitable especially for treatment of highly viscous liquids.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a porous hollow fiber polyvinylidene fluoride resin membrane which is excellent in pressure resistance and water permeability despite having a large inside diameter.
It is another object of the present invention to provide a process for producing a porous hollow fiber polyvinylidene fluoride resin membrane which is excellent in pressure resistance and water permeability despite having a large inside diameter.
The porous hollow fiber membrane of the present invention is characterized in that the membrane has a unitary, three-dimensional, network pore structure composed entirely of a polyvinylidene fluoride resin and has an inside diameter of 1.5-5 mm and a wall thickness of 0.5-2 mm and in that the relationship between membrane bubble point (hereinafter referred to as BP) and water flux per unit membrane wall thickness is on or above the curve shown in FIG.
1
.
According to the present invention, the production process of the porous hollow fiber membrane comprises blending a polyvinylidene fluoride resin with an organic liquid and an inorganic particulate material; heat melting the resulting blend at a temperature of 60° C. or more above the melting point of the resin; extruding the resulting molten blend in the form of a hollow fiber; passing the resulting hollow fiber-shaped extrudate through the air; and taking up the extrudate.
REFERENCES:
patent: 3642666 (1972-02-01), Bailey et al.
patent: 3929950 (1975-12-01), Nakamura et al.
patent: 4177228 (1979-12-01), Prolss
patent: 4203848 (1980-05-01), Gradube, II
patent: 4806291 (1989-02-01), Susa
patent: 4810384 (1989-03-01), Fabre
patent: 5022990 (1991-06-01), Doi et al.
patent: A5180686 (1976-07-01), None
patent: A5893734 (1983-06-01), None
patent: A1224005 (1989-09-01), None
patent: A32115535 (1991-09-01), None
Takamura Masakazu
Yoshida Hitoshi
Asahi Kasei Kogyo Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Fortuna Ana
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