JP5082347B2 - Separation membrane manufacturing method and separation membrane for water treatment - Google Patents

Description

  The present invention relates to a method for producing a separation membrane by imparting hydrophilic oil repellency to the surface of a porous membrane.

In recent years, separation membranes using porous membranes have been used in various fields such as water treatment fields such as water purification treatment, waste liquid / drainage treatment, ultrapure water production, medical fields such as hemodialysis and blood filtration, and food industries. It's being used.
In particular, porous membranes used in the field of water treatment such as water purification and wastewater treatment are required to have improved water permeability because of the large amount of treated water. If the water permeation performance is excellent, the amount of treated water per unit area increases, so that the area of the membrane can be reduced. A small membrane area is advantageous in that the membrane replacement cost can be reduced and the apparatus can be miniaturized to save space.

  Moreover, in order to enable the separation membrane to be used continuously for a long period of time, it is desired to improve antifouling properties and easy cleaning properties. In general, in the process of water treatment, substances to be separated in raw water adhere to the separation membrane and membrane contamination (membrane fouling) occurs, so physical cleaning such as back-pressure cleaning and air scrubbing is performed regularly. . Further, when the film fouling progresses and the effect of physical cleaning is reduced, chemical cleaning is performed in which the deposits are chemically decomposed and dissolved and removed. If the antifouling performance of the membrane is high, the interval between the physical cleaning and the chemical cleaning can be increased, so that the filtration efficiency can be improved and the life of the peripheral device can be extended. In addition, the easier the membrane is washed, and the higher the recovery rate of the water permeation performance by physical washing, the shorter the physical washing and chemical washing can be, and the longer the interval.

  In view of other performances required for the separation membrane, such as thermal stability, chemical resistance and mechanical strength, a hydrophobic polymer is often used as the membrane material. When using a porous membrane made of a hydrophobic polymer for water treatment, the water permeability is not sufficient, and it has high affinity with organic molecules such as highly hydrophobic oils and proteins. There is a problem that it is easy. In order to solve this problem, a general method is to improve the water permeability by imparting hydrophilicity to the surface of the porous membrane and suppress the adsorption of hydrophobic organic molecules and mud.

As for the method of hydrophilizing a porous membrane made of a hydrophobic polymer, for example, a method by ozone treatment (Patent Document 1), a method by graft polymerization of a hydrophilic monomer (Patent Document 2), a method of blending a hydrophilic polymer ( A number of reports have been reported, such as Patent Document 3), a method of applying a surfactant to the surface or dipping it inside (Patent Document 4).
Further, from the viewpoint of enhancing the fouling resistance, there is also a method in which a fluorine-based polymer film is formed on the surface to reduce the surface energy of the film and to make it difficult to actively adsorb organic molecules (Patent Document 5). .
Japanese Patent Laid-Open No. 6-343843 Japanese Examined Patent Publication No. 6-104753 Japanese Patent Laid-Open No. 11-156171 JP 2004-202438 A Japanese Patent Laid-Open No. 62-23401

However, the method of hydrophilizing the surface of the porous membrane does not necessarily have sufficient fouling resistance and easy cleaning properties, and further improvements are required.
Moreover, since the fluoropolymer film formed by the method described in Permissible Document 5 exhibits water repellency, there is a problem that water permeability is low.

  This invention is made | formed in view of the said situation, and it aims at providing the method which can manufacture the separation membrane which has the outstanding water permeability, fouling resistance, and easy washing | cleaning property.

The present inventor has intensively studied to solve the above problems, and has found a method capable of imparting surface characteristics having both hydrophilicity and oil repellency, which are usually incompatible characteristics, to the surface of the porous membrane. The present invention is based on the knowledge that a separation membrane having excellent water permeability, fouling resistance and easy washing can be realized by imparting hydrophilic oil repellency to the surface of the porous membrane using the method. It came to be completed.
That is, in the method for producing a separation membrane of the present invention, the surface of the porous membrane comprises (A) perfluorocarbon and (B) an oxygen-containing substance having oxygen atoms and having neither C—H bonds nor halogen atoms. A process for producing a separation membrane having a step of performing a discharge treatment in an atmosphere in which the (A) perfluorocarbon has a polymerizable carbon-carbon double bond, and oxygen atoms present in the atmosphere The ratio of the number of atoms to the number of fluorine atoms (O / F ratio) is 0.05 to 100 .
The abundance ratio (F / C) of fluorine atoms to carbon atoms in the (A) perfluorocarbon is preferably 1.5 or more.
The (B) oxygen-containing substance is preferably at least one selected from the group consisting of oxygen, ozone, carbon dioxide, water, nitric oxide, nitrogen dioxide, sulfur dioxide and sulfur trioxide.
The (A) perfluorocarbon preferably has 2 to 6 carbon atoms.
The (A) perfluorocarbon is preferably tetrafluoroethylene or hexafluoropropylene, and the (B) oxygen-containing substance is preferably oxygen .
The total content of (A) perfluorocarbon and (B) oxygen-containing substance in the atmosphere is preferably 50 mol% or more.
It is preferable that the porous membrane has a pore diameter of 0.01 to 5 μm.
The material of the porous membrane is polyolefin, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyacrylonitrile, polyvinyl alcohol, cellulose acetate, polytetrafluoroethylene, ethylenetetrafluoroethylene copolymer, polychlorotrifluoroethylene, Or it is preferable that it is a polyvinylidene fluoride.
The present invention provides a separation membrane for water treatment produced by the method of the present invention.

  According to the present invention, a separation membrane having excellent water permeability, resistance to fouling and easy cleaning can be obtained.

<Porous membrane>
The porous membrane used as a substrate in the present invention is not particularly limited as long as it can be used as a separation membrane.
The material of the porous membrane may be any material that can be used as a separation membrane, and examples thereof include organic polymers and ceramics. An organic polymer is preferred in that the effect of the present invention is more excellent. This is presumably because, when the porous film is an organic polymer, the adhesion of the coating formed on the treated surface of the porous film by the discharge treatment to the surface of the porous film is excellent.
Specific examples of the organic polymer include polyolefins such as polyethylene and polypropylene; polysulfone; polyethersulfone; polycarbonate; polyamide; polyimide; polyacrylonitrile; polyvinyl alcohol; Polychlorotrifluoroethylene; polyvinylidene fluoride and the like.
The organic polymer may be a hydrophilic polymer or a hydrophobic polymer. Hydrophobic polymers are preferred from the viewpoint of excellent thermal stability, chemical resistance, and mechanical strength. Among the organic polymers listed above, those included in the hydrophobic polymer include polyethylene, polypropylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyacrylonitrile, polytetrafluoroethylene, and ethylenetetrafluoroethylene copolymer. Coalesce, polychlorotrifluoroethylene and polyvinylidene fluoride.
Specific examples of the ceramic include oxide ceramics such as alumina and zirconia; hydroxide ceramics; carbide ceramics such as silicon carbide; carbonate ceramics; nitride ceramics such as silicon nitride; halide ceramics; Examples thereof include phosphate ceramics.
The porous membrane in the present invention is preferably one that can be used as a separation membrane in water treatment, and an ultrafiltration membrane and a microfiltration membrane are preferred. The pore diameter is preferably about 0.01 to 5 μm.
The module form of the porous membrane may be any known form such as a flat membrane shape, a hollow fiber shape, or a cylindrical shape.

<(A) Perfluorocarbon>
The perfluorocarbon used in the present invention is a compound in which all of the hydrogen atoms are substituted with fluorine atoms in hydrocarbons which may contain etheric oxygen atoms (including cyclic ethers). The hydrocarbon is a linear, branched or cyclic, saturated or unsaturated hydrocarbon.
Since perfluorocarbon has high polymerizability and can form a film on the surface of the article to be treated in a short time, it preferably has a polymerizable carbon-carbon double bond.
2-6 are preferable and, as for carbon number of perfluorocarbon, 2-4 are more preferable from the surface of cost.
The greater the abundance ratio (F / C) of fluorine atoms to carbon atoms in perfluorocarbon, the better the oil repellency of the resulting film. In the present invention, in order to obtain good oil repellency, F / C is preferably 1.5 or more, and more preferably 2.0 or more.
Specific examples of the perfluorocarbon include tetrafluoroethylene, hexafluoropropylene, hexafluoropropylene oxide (HFPO), and PPVE, PMVE, AVE, BVE, c-C4F8 and C5F8 represented by the following formula. Of these, tetrafluoroethylene and hexafluoropropylene are particularly preferable from the viewpoints of polymerizability and cost. These have a low global warming potential and are likely to generate CF ₂ carbene that contributes to film growth.
These may be used alone or in combination of two or more.

<(B) Oxygen-containing substance>
As the oxygen-containing substance, a “compound having an oxygen atom, no C—H bond, and no halogen atom” is used. The oxygen-containing substance functions as an oxygen source that liberates oxygen atoms in the plasma. Moreover, since it does not have a C—H bond and a halogen atom, it is preferable in terms of imparting hydrophilicity while suppressing a decrease in oil repellency of a film formed by plasma treatment.
In particular, those selected from the group consisting of oxygen, ozone, carbon dioxide, water, nitrogen monoxide, nitrogen dioxide, sulfur dioxide, and sulfur trioxide are preferred from the viewpoint of ease of handling and cost. One oxygen-containing substance may be used alone, or two or more oxygen-containing substances may be used in combination.

<Method for producing separation membrane>
The method for producing a separation membrane of the present invention includes a step of performing a discharge treatment on the surface of the porous membrane in an atmosphere in which (A) perfluorocarbon and (B) an oxygen-containing substance are present. In the discharge treatment atmosphere, (A) perfluorocarbon and (B) oxygen-containing substance are preferably present in the form of gas.
By this step, a separation membrane having hydrophilic oil repellency provided on the surface of the porous membrane that has been subjected to the discharge treatment (hereinafter also referred to as the treated surface) can be obtained.
The discharge treatment is performed on at least a surface (treated water contact surface) with which the raw water to be treated comes into contact when used as a separation membrane among the surfaces of the porous membrane.

The degree of hydrophilic oil repellency on the treated surface subjected to the discharge treatment is determined by the ratio of the number of oxygen atoms and the number of fluorine atoms present in the atmosphere in which the discharge treatment is performed (number of oxygen atoms / number of fluorine atoms, hereinafter referred to as “O / F ratio "). As the O / F ratio increases, the hydrophilicity of the treated surface increases and the oil repellency decreases, and as the O / F ratio decreases, the oil repellency of the treated surface increases and the hydrophilicity decreases. The O / F ratio can be controlled by adjusting the type and amount of (A) perfluorocarbon supplied to the discharge treatment atmosphere and the type and amount of (B) oxygen-containing substance.
Even if the O / F ratio is constant, the degree of hydrophilic oil repellency on the treated surface can vary depending on the configuration of the apparatus performing the discharge treatment and the discharge conditions.

Therefore, (A) type and supply amount of perfluorocarbon, (B) type and supply amount of oxygen-containing substance, and discharge conditions are set according to the device configuration so that the desired hydrophilic oil repellency can be imparted to the treated surface. It is preferable to do this.
Specifically, a high frequency power source of 13.56 MHz is used as a discharge power source, a discharge device using a capacitively coupled parallel plate is used, (A) hexafluoropropylene as perfluorocarbon, (B) oxygen as oxygen-containing substance. When the surface of the porous membrane made of polyethersulfone is treated with the power during discharge treatment (power per electrode area) in the range of 0.1 to 1.0 W / cm ² , respectively, the treatment surface has good hydrophilicity. In order to impart oil repellency, the O / F ratio is preferably in the range of 0.05 to 100, and particularly preferably in the range of 0.5 to 20.

In the atmosphere during the discharge treatment, in addition to (A) perfluorocarbon and (B) oxygen-containing substance, an inert gas such as argon, helium or neon, or other gas such as nitrogen may be present.
In order to impart good hydrophilic oil repellency to the treated surface, the total content of (A) perfluorocarbon and (B) oxygen-containing substance in the atmosphere is preferably 50 mol% or more, and 100 mol % Is more preferable.

(Discharge conditions)
The discharge treatment method in the present invention is not particularly limited, and for example, corona discharge (spark discharge), glow discharge, and the like can be applied. Glow discharge is more preferable. In either case, the treatment surface is exposed to a gas atmosphere and a discharge treatment is performed by plasma generated by applying a high-frequency voltage between the electrodes. The discharge form can be discharged continuously or in pulses.
The pressure of the discharge treatment atmosphere in the present invention is preferably 10 ⁴ Pa or less, and more preferably 10 ³ Pa or less. When the pressure of the atmosphere is 10 ⁴ Pa or less, the discharge stability is good. The lower limit of the atmospheric pressure of the discharge treatment is not particularly limited as long as it is in a range where good discharge is performed. For example, it is 1 Pa or more.
For example, a high frequency power source of 13.56 MHz is used as a discharge power source, a discharge device using a capacitively coupled parallel plate is used, (A) hexafluoropropylene is used as perfluorocarbon, and (B) oxygen is used as an oxygen-containing substance. Good hydrophilic oil repellency when the surface of the polyethersulfone porous membrane is treated in an atmosphere where the O / F is 3.6 and the power during the discharge treatment is in the range of 0.1 to 1.0 W / cm ^2. In order to form a film having, the pressure of the atmosphere is preferably in the range of 20 to 40 Pa.

According to the production method of the present invention, a separation membrane in which hydrophilic oil repellency is imparted to the surface of the porous membrane can be obtained. This is because (A) a fluorocarbon polymer film composed of monomer units derived from perfluorocarbon is formed on the treated surface of the porous film, thereby providing oil repellency and incorporating oxygen into the film. It is considered that hydrophilicity is obtained and hydrophilic oil repellency is exhibited.
According to the present invention, the process is simple because the treatment surface can be given hydrophilic oil repellency by the discharge treatment in an atmosphere containing (A) perfluorocarbon and (B) an oxygen-containing substance. Moreover, the coating film formed on the treated surface has good adhesion to the porous membrane surface and is excellent in durability. This is because active sites are formed on the surface of the porous film in the course of the discharge treatment, polymer chains are graft-grown starting from the active sites, and a film having a chemical bond with the surface of the porous film is formed. Conceivable.

  The separation membrane obtained according to the present invention has hydrophilic and oil repellency on the treated surface, so that the water permeability is good and the organic molecules and soil mud are hardly attached, and excellent fouling resistance is obtained. Further, dirt attached by physical treatment such as back pressure cleaning is easily removed, and easy cleaning is excellent.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
FIG. 1 is a schematic configuration diagram of an apparatus used in the following examples. The apparatus of this example is generally configured as follows. An upper shower head electrode 7 and a lower electrode 8 (disc shape with a diameter of 100 mm) made of parallel plate electrodes are disposed in the vacuum chamber 5 to face each other. The upper shower head electrode 7 is connected to a high frequency power source 6 of 13.56 MHz, the lower electrode 8 is grounded, and is configured to generate low temperature plasma between the electrodes 7 and 8. A workpiece 10 is detachably fixed on the surface of the lower electrode 8 facing the upper showerhead electrode 7. The upper shower head electrode 7 also serves as a gas supply means. The upper shower head electrode 7 is connected to a perfluorocarbon gas supply means 3 having a flow meter and an oxygen-based gas supply means 4 having a flow meter. Yes. In addition, a number of gas ejection holes are provided on the surface of the upper shower head electrode 7 facing the lower electrode 8 so that gas can be supplied in a shower shape toward the workpiece 10 on the lower electrode 8. It has become. Reference numeral 9 in the drawing denotes an exhaust means provided with a vacuum pump.

(Example 1 and Comparative Examples 1-3)
Using the apparatus shown in FIG. 1, a separation membrane based on a polyethersulfone porous membrane was produced.
First, a commercially available polyethersulfone porous membrane (manufactured by Millipore, product name: Express membrane, pore size: 0.22 μm, diameter: 47 mm) was placed on the lower electrode 8 as the object 10 to be processed, and the vacuum chamber 5 The inside was evacuated with a vacuum pump until the inside became 0.1 Pa or less. Next, after adjusting the distance between the upper showerhead electrode 7 and the lower electrode 8 to 5 cm, a mixed gas containing hexafluoropropylene gas (HFP) and / or oxygen gas from the upper showerhead electrode 7 under the conditions shown in Table 1 The discharge treatment was performed while flowing. Subsequently, after the inside of the vacuum chamber 5 was purged with air, the discharged porous membrane was taken out and used as a separation membrane.
“O / F of mixed gas” in Table 1 represents the ratio of the number of oxygen atoms and the number of fluorine atoms in the mixed gas.

(Comparative Example 4)
The commercially available polyethersulfone porous membrane used in Example 1 was used as it was as a separation membrane without being subjected to a discharge treatment.

<Evaluation test for permeability and fouling resistance>
The respective separation membranes obtained in Example 1 and Comparative Examples 1 to 4 were set in the measurement cell 20 shown in FIG. 2, and the filtration resistance was measured. In FIG. 2, the code | symbol 21 shows the separation membrane of a measuring object. The separation membrane 21 was set so that the treatment surface subjected to the discharge treatment was on the inner side of the measurement cell 20.
First, 500 mL of pure water was put into the cell 20 and pressurized with nitrogen gas to allow the membrane 21 to permeate. The pressurizing pressure was 150 kPa. The elapsed time was measured every time 50 mL permeated, and the permeation flux (unit: m ³ / m ² · day) was calculated. The pure water permeation flux calculated in this way always showed a constant value. The results are shown in Table 1.
Next, 400 mL of model raw water containing organic substances and clay minerals, which are likely to cause fouling in water treatment, is placed in the cell 20 while the membrane 21 is kept as it is, and permeate flow every time 50 mL is filtered as in the case of pure water. The bundle was measured. As the model raw water, 1 L of pure water was used in which 2 mg of sodium humate manufactured by Aldrich and 10 mg of bentonite manufactured by Pure Chemical Co. were dissolved and suspended.
Next, the separation membrane 21 was turned over, that is, set so that the treatment surface subjected to the discharge treatment was on the outside of the cell 20, and 100 mL of pure water was permeated to perform back pressure cleaning. The pressurizing pressure was also 150 kPa.
After the back pressure cleaning is completed, the membrane 21 is turned over once again, that is, set again so that the treated surface is on the inner side of the cell 20, 100 mL of model raw water is filtered, and the permeate flow is the same as above. The bundle was measured.
From the measured value of permeation flux Jv (unit: m ³ / m ² · day) and the value of pressurizing pressure P (unit: kPa) (150 in this example), the filtration resistance R is calculated by the following formula (1). (Unit: m ² · kPa · day / m ³ ) was calculated.
R = P / Jv (1)

As the pure water filtration resistance, the value of the filtration resistance was calculated every time the total pure water permeation amount (total filtered water amount) increased by 50 mL from the time of 50 mL permeation to the time of 500 mL permeation.
As the model raw water filtration resistance, the value of filtration resistance every time the total amount of model raw water filtered (total filtered water volume) increases by 50 mL from the time of 50 mL permeation to the time of 400 mL permeation, and when 50 mL of model raw water is filtered after back pressure washing The value of filtration resistance (total filtered water volume 450 mL) and the value of filtration resistance when 100 mL of model raw water was filtered after total pressure washing (total filtered water volume 500 mL) were obtained.
And the value of "model raw water filtration resistance / pure water filtration resistance" was calculated | required as a "filtration resistance ratio" from the value of the model raw water filtration resistance and the value of pure water filtration resistance in the mutually same total filtered water amount.
The relationship between the value of the filtration resistance ratio thus obtained and the total amount of filtered water (unit: m ³ / m ² ) is shown in the graph of FIG.

Since the membrane obtained in Comparative Example 2 did not permeate water at all, the filtration resistance ratio was not measured.
In Comparative Examples 3 and 4, since water permeability was low, 300 mL of model raw water was filtered, and then back pressure washing was performed. When 50 mL of the model raw water was filtered after the back pressure washing (total filtered water amount 350 mL), Comparative Example 3 recovered only 54 and Comparative Example 4 up to 114.

<Evaluation of water permeability and easy cleaning>
In the above evaluation test, the average permeation flux (unit: m / day) up to the time when 300 mL of model raw water was filtered (initial 300 mL), the average permeation flux (unit: 100 mL of model raw water after back pressure washing) : M / day) and the recovery rate of the model raw water permeation flux by backwashing ([model raw water permeation flux (initial 100 mL)] / [model raw water permeation flux (100 ml after back pressure washing)]) . The evaluation results are shown in Table 1.

As shown in the results of Table 1 and FIG. 3, the separation membrane of Example 1 subjected to discharge treatment in a mixed gas containing a perfluorocarbon gas and an oxygen-based gas has high water permeability and excellent fouling resistance. ing. In addition, the filtration performance is well recovered by back pressure washing, and it is excellent in easy washing.
On the other hand, in Comparative Example 1 in which the discharge treatment was performed in an atmosphere containing only oxygen-based gas, it is estimated that only hydrophilicity was imparted to the treated surface. As shown in Table 1, in Comparative Example 1, the water permeability (pure water permeation flux) of pure water was larger than that in Example 1, but the water permeability of model raw water (initial model water permeation flux of 300 mL) was high. Was inferior to Example 1. Further, as shown in the graph of FIG. 3, the rate of increase in the filtration resistance ratio (model raw water filtration resistance / pure water filtration resistance) before back pressure washing is larger than that in Example 1 and is more resistant to fouling than Example 1. Was inferior. Furthermore, also in the recovery rate of the model raw water permeation flux after back pressure cleaning shown in Table 1 and the model raw water flux by back pressure cleaning, Comparative Example 1 is inferior to Example 1, and easy cleaning properties are inferior. It was.
On the other hand, in Comparative Examples 2 and 3 in which the discharge treatment was performed in an atmosphere containing only perfluorocarbon gas, it is presumed that only the oil repellency was imparted to the treated surface. In Comparative Example 2, no water permeated. Compared with Example 1 and Comparative Example 1, in Comparative Example 3 in which the power during the discharge treatment is lower than that in Comparative Example 2 and the discharge time is short, and in Comparative Example 4 where the discharge treatment is not performed, the water permeability and fouling resistance are increased. And recovery performance of filtration performance by backwashing were significantly inferior.

<Analysis by X-ray photoelectron spectroscopy>
FIG. 4 shows a C1s narrow spectrum obtained by analyzing the treated surfaces of the separation membranes obtained in Example 1 and Comparative Example 4 using X-ray photoelectron spectroscopy (XPS). As shown in FIG. 4, in the separation membrane of Example 1, an increase in C—O bond and C—F bond was observed at 287 to 293 eV. This suggested that both the hydrophilic group containing oxygen and the perfluoroalkyl group having oil repellency were introduced into the treated surface of the separation membrane of Example 1.

It is a schematic block diagram which shows the example of the apparatus used for the discharge process concerning this invention. It is a schematic block diagram which shows the apparatus for measuring a filtration resistance ratio. It is a graph which shows the result of having measured the filtration resistance ratio about the Example and the comparative example. It is a graph which shows the result of having analyzed the processing surface of the separation membrane obtained in Example 1 and Comparative Example 4 by X-ray photoelectron spectroscopy (XPS).

Explanation of symbols

3. Perfluorocarbon supply means,
4 ... oxygen-containing substance supply means,
5 ... Vacuum chamber,
6 ... High frequency power supply,
7 ... Upper showerhead electrode,
8 ... Lower electrode,
9: Exhaust means.

Claims (9)

A step of performing a discharge treatment on the surface of the porous film in an atmosphere in which (A) perfluorocarbon and (B) an oxygen-containing substance having oxygen atoms and neither a C—H bond nor a halogen atom are present. The (A) perfluorocarbon has a polymerizable carbon-carbon double bond, and is a ratio of the number of oxygen atoms and the number of fluorine atoms present in the atmosphere. (O / F ratio) is 0.05-100, The manufacturing method of the separation membrane characterized by the above-mentioned.   The manufacturing method of the separation membrane of Claim 1 whose abundance ratio (F / C) of the fluorine atom and carbon atom in the said (A) perfluorocarbon is 1.5 or more.   3. The oxygen-containing substance (B) is at least one selected from the group consisting of oxygen, ozone, carbon dioxide, water, nitric oxide, nitrogen dioxide, sulfur dioxide, and sulfur trioxide. A method for producing a separation membrane.   The manufacturing method of the separation membrane as described in any one of Claims 1-3 whose carbon number of the said (A) perfluorocarbon is 2-6.   The method for producing a separation membrane according to any one of claims 1 to 4, wherein the (A) perfluorocarbon is tetrafluoroethylene or hexafluoropropylene, and the (B) oxygen-containing substance is oxygen. The manufacturing method of the separation membrane as described in any one of Claims 1-5 whose sum total of the content rate of (A) perfluorocarbon in the said atmosphere and (B) oxygen-containing substance is 50 mol% or more. The method for producing a separation membrane according to any one of claims 1 to 6 , wherein the pore size of the porous membrane is 0.01 to 5 µm. The material of the porous membrane is polyolefin, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyacrylonitrile, polyvinyl alcohol, cellulose acetate, polytetrafluoroethylene, ethylenetetrafluoroethylene copolymer, polychlorotrifluoroethylene, or polyvinylidene fluoride, a manufacturing method of the separation membrane according to any one of claims 1-7. The separation membrane for water treatment manufactured by the method as described in any one of Claims 1-8 .

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