JPS59189913A - Preparation of ultrafiltration membrane - Google Patents

Abstract

PURPOSE:To obtain an ultrafiltration membrane excellent in solvent resistance, by treating a fluorine contained high-molecular membrane with fluorine gas. CONSTITUTION:A porous membrane comprising a fluorine contained high-molecular polymer, for example, polyvinylidene fluoride is molded and treated, pref., at about 20-100 deg.C in a reactor filled with fluorine gas, pref., fluorine gas diluted about 100 times with inert gas. After treatment, the internal gas is exhausted and the treated porous membrane is taken out to be directly immersed in an aqueous solution containing alkali metal carbonate, for example, sodium carbonate in order to remove the fluorine gas adhered to the surface thereof to perform washing. Immersion treatment is performed at about 10-100 deg.C, pref., for about 10-15min and, thereafter, washing is performed for about 10-15min before hot air drying.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for producing an ultrafiltration membrane. More specifically, a method for producing a 7-layer ultrafiltration membrane with excellent solvent resistance will be described.

Polymer group′? f: The ultrafiltration membrane used mainly consists of the following two
It is divided into products.

(1) A film obtained by dissolving a high molecular weight polymer in a solvent and casting it. (2) A film obtained by subjecting the thus obtained film to some post-treatment and modification. Generally, the former is In most cases, the solvent resistance of this membrane is determined by that of the high molecular weight polymer forming the membrane. In other words, in order to form a film, it must be soluble in the solvent, but after film formation, we do not want it to dissolve. It is true that Therefore, the latter type of membrane is proposed to improve solvent resistance.

The present inventors selected a fluoropolymer, which generally has good solvent resistance, as a membrane forming material and treated it with fluorine gas to obtain an ultrafiltration membrane with excellent ITl solvent resistance. was completed. Therefore, the present invention relates to a method for manufacturing an ultrafiltration membrane, and in manufacturing method 1 of the ultrafiltration membrane, a fluorine-containing polymer membrane is placed in a fluorine gas, preferably a fluorine gas diluted with an inert gas. This is done by holding.

Because of its good reactivity, fluorine gas can easily carry out a substitution reaction with hydrogen atoms in the fluorine-containing polymer. For example, in the case of polyvinylidene fluoride, F2.

-(-CH3-CF,-+r]→+CF2-CF2+n
It is believed that a fluorine substitution reaction is carried out to at least partially obtain a polytetrafluoroethylene structure such as f). Other than these, fluorine-containing polymers having substitutable hydrogen atoms in their molecules, such as vinyl niborifluoride and polytrifluoroethylene, can be used as the film-forming material.

Film formation using these fluorine-containing polymers is carried out by a dry-wet method, as in the case of conventional ultra-filter membranes. That is, a fluorine-containing high molecular weight polymer is dissolved in a solvent, generally a water-soluble solvent such as dimethylformamide, dimethylacetamide, or dimethyl sulfoxide, and the solution is cast onto a glass substrate and then immersed in water. Displacement of water and solvent occurs9, and the polymer solidifies, forming a membrane with an asymmetric structure.

Fluorine gas is also used as a stand-alone gas, but
Generally, about 100
As a mixed air flow diluted to about twice as much, under normal pressure to pressurization (
~about 20 atm)! or under reduced pressure (C to about 1/loo atmosphere), and is used as a stationary gas or a circulating gas. The treatment temperature is generally about 10 to 150°C, preferably about 20°C.
-100°C is selected.

The fluorine polymer membrane treated with fluorine gas is immediately washed by immersing it in an aqueous solution of alkali metal carbonate to remove the fluorine gas adhering to its surface.

As the alkali metal carbonate, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, etc. are used in the form of an aqueous solution with a concentration of about 5 to 20%. The immersion treatment is carried out at a temperature of about 10 to 100°C and about 5 to 3 Of+m.
j1 It is preferably carried out for about 10 to 15 minutes, and the water is drained and washed thoroughly for about 10 to 15 minutes, followed by drying under warm air.

The fluorine-containing polymer membrane treated with fluorine gas in this way can be used with various solvents without changing its inherent ultrafiltration performance (pure water permeability coefficient, molecular weight fraction, etc.). significantly improves its strong solvent properties. Therefore, this ultrafiltration membrane has excellent solvent resistance, showing insolubility in dimethylformamide, dimethylacetamide, dimethyl sulfoxide, etc. after fluorine gas treatment.
It can be used as a liquid separation membrane, a separation and recovery membrane for colloids and polymeric substances in organic solvents, etc.

Next, the present invention will be explained with reference to examples.

Examples Polyvinylidene fluoride (Kyna manufactured by Benwald Co., Ltd.)
A dimethylacetamide solution containing 2 ozB% of
A porous membrane was formed by casting on a glass plate with a spacer thickness of 02πM and using a wet-dry method using water as a coagulant. The obtained porous membrane with J' has a pure water permeability coefficient (Lp) of 10,
In addition, the molecular weight cutoff (c, M, w,) is 6000 (if<
k, respectively. 'This porous membrane was housed in a cylindrical stainless steel reactor with an inner diameter of BOynm and a length of 300 mm, and the fluorine gas diluted with nitrogen gas to a sufficient concentration was filled therein at a pressure of approximately 1 atm. , then diluted fluorine gas was circulated at a flow rate of about 1204 minutes. After reacting at a predetermined temperature □ and for a predetermined time, the internal gas was discharged, and the porous membrane taken out was washed with an aqueous solution of IJ and running water for 10 minutes each, and then dried.

A swelling test was conducted on this fluorine gas-treated porous membrane to investigate its solvent resistance.

The results obtained are shown in the following table.

Table 1 - - - 1a2 12
0 5a62 13'i' 40 2
82 9.0 34, Ma3 1a9
, tt al ao 3a
3!242, / 3 4.6 revision
22.15 tt 50 //
23 26 235 Note) Swelling degree test: Cut a small piece of the membrane, immerse it in a solvent to swell it, and calculate the volume change from the dimensional change before and after immersion (j area before swelling So, area after filling Sl) When we measured the ultrafiltration performance of the fluorine gas-treated porous membranes of
C, M, W, ) was 6000, the same value as before treatment.

Representative Patent Attorney Toshida Yoshida Continuing Amendment (Spontaneous) June 30, 1988 1. Case description 1988 Patent Application No. 65105 2. Title of invention Process for manufacturing ultra-stomach membrane 3 Amendment Patent applicant 4, agent Address: 5 Ato Building, 1-277 Shiba Daimon, Minato-ku, Tokyo
01 No. 5, Detailed explanation of the invention in the tlif positive subject book J, column 8

Claims (1)

[Claims] A method for producing an ultrafiltration membrane, which comprises maintaining a fluorine-containing polymer membrane in fluorine gas. 2. The fluorine-containing polymer garment is a polyvinylidene fluoride membrane. 3. The method for producing an ultrafiltration membrane according to claim 1. 3. The fluorine-containing polymer membrane is diluted with an inert gas. A method for producing an ultrafiltration membrane according to item 1.