Liquid purification or separation – Filter – Material
Patent
1998-06-18
2000-12-26
Fortuna, Ana
Liquid purification or separation
Filter
Material
21050027, 21050041, 264 41, B01D 6908
Patent
active
061653632
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hollow fiber filter membrane of anisotropic structure which is high in strength and excellent in water permeation performance.
BACKGROUND ART
Hollow fiber membranes are widely employed for industrial uses from microfiltration to ultrafiltration, and polyethylene, cellulose acetate, polysulfone, polyvinylidene fluoride, polycarbonate, polyacrylonitrile, etc. are used as materials for the membranes. Since conventional hollow fiber membranes made of these materials have been developed for the purpose of improving filtration performance, these hollow fiber membranes are low in breaking stress and breaking elongation and are apt to break due to abrupt changes in temperature and changes in pressure at back washing. Various attempts have been made for a solution to these problems, and there is suggested a method of increasing the density of a polymer in the whole hollow fiber membrane by increasing polymer concentration in a membrane-forming solution in the invention disclosed in JP-A-59-228016. However, according to this method, the strength of the membrane is improved, but the pore diameter of the membrane decreases and the water permeability of the membrane greatly decreases. Thus, hollow fiber membranes well-balanced in strength and water permeation performance have not yet been obtained.
On the other hand, a method of increasing the pore diameter of a membrane is generally employed for improving the water permeation performance of a membrane, but an increase in pore diameter generally causes a deterioration in the fractionation performance of the membrane and in the strength of the membrane.
As mentioned above, high-performance hollow fiber membranes well-balanced in strength, water permeation performance and fractionation performance have not been obtained by conventional techniques. For example, JP-A-4-260424 proposes a method for the production of membranes high in strength and excellent in water permeation performance, but membranes produced by this method have a large pore diameter and are not well balanced in water permeation performance and fractionation performance.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a hollow fiber membrane having a high enough strength to withstand abrupt changes in temperature and changes in pressure at back washing and having well-balanced performances in water permeability and fractionation.
Another object of the present invention is to provide a method for producing a hollow fiber membrane high in strength and excellent in fractionation performance and water permeation performance.
The hollow fiber filter membrane of the present invention is characterized in that the inner surface of the membrane comprises a three-dimensional network having thick trunks having a maximum diameter of 10-30 .mu.m, and the average pore diameter in a minimum pore diameter layer is 0.01 .mu.m or more and less than 1 .mu.m.
The method for producing the hollow fiber filter membrane of the present invention comprises discharging a membrane-forming solution comprising a membrane-forming polymer, a solvent for the polymer and specific additives from a double annular nozzle together with an inner solution comprising a high concentration aqueous solution of a good solvent for the polymer, passing the discharged solution through an air gap, and then coagulating the solution in a coagulating bath.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an electron micrograph (350.times.magnification) which shows a cross section of one embodiment of the hollow fiber filter membrane of the present invention.
FIG. 2 is an electron micrograph (1,000.times.magnification) which shows the inner surface of the hollow fiber filter membrane shown in FIG. 1.
FIG. 3 is an electron micrograph (5,000.times.magnification) which shows an enlarged section of the portion of thick trunk seen on the inner surface side of the hollow fiber filter membrane shown in FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
A representative example of the str
REFERENCES:
patent: 4612119 (1986-09-01), Eguchi
patent: 4774039 (1988-09-01), Wrasidlo
patent: 5022990 (1991-06-01), Doi et al.
patent: 5232597 (1993-08-01), Eguchi
patent: 5354470 (1994-10-01), Seita et al.
Ohya Hiroyoshi
Oishi Teruhiko
Asahi Kasei Kogyo Kabushiki Kaisha
Fortuna Ana
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