Liquid purification or separation – Filter – Material
Patent
1992-07-02
1994-02-01
Sever, Frank
Liquid purification or separation
Filter
Material
210639, 264 41, 264DIG48, 264DIG62, B01D 7130, B01D 7132, B01D 7134, B01D 7136
Patent
active
052829650
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a membrane filter for liquids which is used in a microfiltration or an ultrafiltration of liquids such as chemicals and water, and to a filtering device using the membrane filter. Specifically, it relates to a membrane filter for liquids which is suitably used to filtrate chemicals for washing silicon wafers in semiconductor industries, and to a filtering device.
BACKGROUND ART
In the microfiltration or ultrafiltration treatment of liquids such as chemicals and water, fine particle-removing performance, permeation flux for liquid, resistance to chemicals, pressure resistance, heat resistance, and the like are important selection factors for membrane filter. For this reason, porous membranes comprising high molecular weight polymers such as fluororesins including polytetrafluoroethylene (hereinafter, abbreviated as "PTFE") and the like, polyethylene, polypropylene, polyolefins, and the like have conventionally been selected.
However, membranes which have been rendered hydrophilic have become more and more necessary in recent years. That is, in the semiconductor industry, for example, washing of silicon wafers is being conducted using nitric acid, hydrofluoric acid, sulfuric acid, or the like, but when replacing the chemicals after circulating and washing, air flows into the cartridge filter for filtration by discharging the chemicals. Because of this, the surface of a hydrophobic membrane such as PTFE membrane or the like in the filter comes into contact with air and the effect that the membrane has been treated with an organic solvent or the like to render the membrane hydrophilic is lost and, hence, introduction of chemicals in the next operation results in a significantly reduced liquid permeation flux.
Therefore, there has been a problem that the membrane should again be rendered hydrophilic with a liquid having a low surface tension.
On the other hand, known methods for rendering a porous polymer membrane hydrophilic include, for example, surface treatment with a plasma or sputtering, exposure to radiation, and the like (Unexamined Published Japanese Patent Applications Nos. 59-186604 and 1-98640, and others). However, such methods have had a problem that the imparted hydrophilicity is insufficient, or if a membrane is to be rendered sufficiently hydrophilic, the membrane surface is modified excessively, causing to change the rejection performance the membrane originally possesses.
DISCLOSURE OF THE INVENTION
The present invention has been completed to solve such problems of the prior art techniques. By treating the surface of a fluorine-containing porous polymer membrane with a low-temperature plasma under specific conditions, the hydrophobic membrane is enabled to retain hydrophilicity without reducing the rejection performance the membrane originally possesses, whereby a membrane filter having a significantly improved permeation flux can be obtained. The present invention provides a membrane filter for liquids which does not show a decrease in permeation flux even if the liquid in the filtering device such as cartridge filter or the like is drained away, and also provides a filtering device in which the membrane filter has been incorporated.
That is, the present invention relates to a membrane filter for liquids which has been rendered hydrophilic, characterized in that the decrease of the pure water permeation flux of the membrane filter after being subjected to wetting treatment with a liquid having a low surface tension (e.g., ethanol, methanol, isopropyl alcohol, or the like), subjected to substitution with pure water, and then exposed to an atmosphere of 25.degree. C. and 60% for 8 hours, to the pure water permeation flux of the membrane filter before the exposure is 20% or less, preferably 10% or less.
The present invention further relates to a membrane filter for liquids, characterized in that the surface of a fluorine-containing porous polymer membrane has been rendered hydrophilic by a low temperature plasma treatment under conditions
REFERENCES:
patent: 4353799 (1982-10-01), Leonard
Matsumoto Kenji
Urairi Masakatsu
Nitto Denko Corporation
Sever Frank
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