Liquid purification or separation – Filter – Material
Patent
1989-06-23
1990-10-09
Sever, Frank
Liquid purification or separation
Filter
Material
264 451, B01D 6700, B01D 6900
Patent
active
049618539
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to porous polyolefin membranes having excellent heat resistance or excellent heat resistance and hydrophilicity, as well as production processes thereof.
2. Background Art
With the recent development of industry, various types of separating membranes have come to be used in such fields as water purification, blood treatment, air cleaning and food industry. For example, microfilters are being utilized to obtain highly pure water or highly clean air. Among others, microfilter formed of a polyolefin such as polyethylene are being widely used because they are cheap, have excellent chemical resistance and exhibit good membrane properties such as strength, elongation and flexibility.
The field of application of microfilter is extending steadily and, at present, it is strongly desired to use them at elevated temperatures, for example, of the order of 80-95.degree. C. Moreover, in certain applications of microfilter, their contamination with microorganisms such as bacteria and molds is not permitted and, therefore, they are sterilized by some means. Useful sterilizing processes include treatment with chemicals such as ethylene oxide, formalin and hydrogen peroxide, exposure to radiation such as gamma rays, and steam heating. Among them, steam heating is most desirable because of its effectiveness and simplicity. Usually, steam heating is done at 121.degree. C. for about 30 minutes.
However, porous membranes formed of polyolefins such as polyethylene and polypropylene are very liable to heat shrinkage. When these porous membranes are heat-treated or used at high temperature, they undergo morphological changes. This causes a sharp reduction in water or air permeability and impairs their function as separating membranes. Moreover, since porous polyolefin membranes are hydrophobic, water cannot permeate therethrough when they are used in an untreated condition.
As a means for improving the heat resistance of porous polyolefin membranes, Japanese Patent Laid-Open No. 33878/'87 proposed a polyolefin hollow fiber membrane in which a heat-resisting polymer film having a crosslinked structure is formed on the surfaces thereof. Moreover, Japanese Patent Laid-Open No. 57836/'81 proposed a porous polyethylene membrane which is rendered hydrophilic by the introduction of sulfonic acid groups.
However, in the heat-resisting polyolefin hollow fiber membrane disclosed in Japanese Patent Laid-Open No. 33878/'87, the heat resistance of the polymer film itself is insufficient. The porous polyethylene membrane disclosed in Japanese Patent Laid-Open No. 57836/'81 is satisfactorily hydrophilic, but its heat resistance is insufficient.
Disclosure of the Invention
The primary object of the present invention is to provide a porous polyethylene or polypropylene membrane which has excellent heat resistance and can hence withstand steam sterilization and other heat treatments, a porous polyolefin membrane which is excellent in both heat resistance and hydrophilicity, and production processes thereof.
In one aspect of the present invention, there is provided a heat-resisting porous membrane comprising a porous polyethylene or polypropylene membrane having a crosslinked polymer held on at least a part of the surfaces thereof, the crosslinked polymer being composed principally of (a) a polymerizable monomer A containing one acid anhydride group or two esterified carboxyl groups and having reactivity ratios r.sub.1 and r.sub.2 of not greater than 0.30 for copolymerization reaction with styrene, (b) divinylbenzene and optionally (c) at least one of styrene and .alpha.-methylstyrene (hereinafter referred to as a styrene monomer).
In another aspect of the present invention, there is provided a process for the production of a heatresisting porous membrane which comprises the steps of holding a monomer mixture composed principally of (a) a polymerizable monomer A as defined above, (b) divinylbenzene and optionally (c) a styrene monomer, on at least a part of the surfaces of a starting porous m
REFERENCES:
patent: 4374232 (1983-02-01), Davis
Aoki Kunihiro
Itoh Hajime
Mitani Kazutami
Ohbori Kouzi
Takahashi Hiroshi
Mitsubishi Rayon Co. Ltd.
Sever Frank
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