Porous membrane and method for manufacturing a porous membrane

Abstract

To provide a porous film having excellent antifouling property.SOLUTION: This porous film contains a film forming polymer (A) and an amphiphatic copolymer (B). On the surface of the porous film, the composition ratio of the film forming polymer (A) to the amphiphatic copolymer (B) is 100:10-100:50, and the contact angle of hexadecane in water is 100°-180°.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a porous membrane and a method for producing a porous membrane. [Background technology]

[0002] Porous membranes are used in various fields, including water treatment such as drinking water production, water purification, and wastewater treatment. Porous membranes are sometimes required to have antifouling properties. For example, in the membrane bioreactor (MBR) method, a contaminated water treatment technology that separates treated water using a separation membrane, separation membranes made of hydrophobic polymers such as polyvinylidene fluoride are commonly used. However, due to their high hydrophobicity, these separation membranes are prone to contamination from activated sludge, such as sugars and proteins, which are metabolites of activated sludge. This necessitates periodic chemical cleaning and membrane replacement due to fouling and pore blockage, making improved antifouling a challenge.

[0003] One known method for imparting antifouling properties to porous membranes involves using polymers containing zwitterionic structures, such as phosphorylcholine structures (zwitterionic polymers), to impart hydrophilicity to the surface of the porous membrane. Patent Document 1 proposes a method in which a porous polyvinylidene fluoride membrane is brought into contact with a solution in which a random copolymer of 2-methacryloyloxyethyl phosphorylcholine and butyl methacrylate is dissolved in a solvent. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-55870 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] When a porous membrane is brought into contact with the above-mentioned random copolymer solution, the surface of the porous membrane becomes coated with the random copolymer, making it hydrophilic. When the porous membrane surface becomes hydrophilic, hydrophobic dirt such as dirt derived from activated sludge becomes less likely to adhere, improving its antifouling properties. However, according to the inventors' research, in the method described in Patent Document 1, when attempting to thinly coat the porous membrane surface with a random copolymer, uncoated areas remain, and dirt derived from activated sludge adheres to these areas. Therefore, there is a concern that sufficient antifouling properties cannot be obtained. Furthermore, if sufficient coverage is sought, the pores of the porous membrane may become blocked, raising concerns about reduced water permeability. The object of the present invention is to provide a porous membrane with excellent antifouling properties and a method for producing the same. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A porous membrane comprising a film-forming polymer (A) and an amphiphilic copolymer (B), The surface of the porous membrane is a porous membrane in which the composition ratio of the film-forming polymer (A) and the amphiphilic copolymer (B), as determined by X-ray photoelectron spectroscopy, is 100:10 to 100:50, and the contact angle of hexadecane in water is 100° or more and 180° or less. [2] A porous membrane of [1] in which the amphiphilic copolymer (B) comprises a constituent unit having a zwitterionic structure. [3] A porous membrane of the amphiphilic copolymer (B) being a block copolymer or a graft copolymer [1] or [2]. [4] A porous membrane of any of [1] to [3] wherein the film-forming polymer (A) is a fluorine-containing polymer. [5] The porous membrane of [4], wherein the surface of the porous membrane has a ratio of 1.0:0.75 to 1.0:5.0 between the peak area at 292 eV corresponding to the film-forming polymer (A) and the peak area at 287 eV corresponding to the amphiphilic copolymer (B), as determined by X-ray photoelectron spectroscopy. [6]A method for manufacturing a porous membrane, comprising the step of bringing a first porous membrane containing a film-forming polymer (A) into contact with a liquid composition containing an amphiphilic copolymer (B) and a liquid medium (C). [7]The method for manufacturing a porous membrane according to [6], wherein the amphiphilic copolymer (B) contains a structural unit containing a zwitterionic structure. [8]The method for manufacturing a porous membrane according to [6] or [7], wherein the amphiphilic copolymer (B) is a block copolymer or a graft copolymer. [9]The method for manufacturing a porous membrane according to any one of [6] to [8], wherein the film-forming polymer (A) is a fluorine-containing polymer. [Effect of the Invention]

[0007] According to the present invention, it is possible to provide a porous membrane excellent in antifouling property and a method for manufacturing the same. [Brief Description of the Drawings]

[0008] [Figure 1] IR spectrum of PBMA-b-PSBMA. [Figure 2] XPS C1s spectrum of the porous membrane of Comparative Example 1 (PVDF thin film before the contact step). [Figure 3] XPS C1s spectrum of PMMA thin film. [Figure 4] XPS C1s spectrum of the porous membrane of Comparative Example 2 (PVDF porous membrane coated with PSBMA). [Figure 5] XPS C1s spectrum of the porous membrane of Comparative Example 3 (PVDF porous membrane coated with PSBMA). [Figure 6] XPS C1s spectrum of the porous membrane of Example 1 (second porous membrane 1-1). [Figure 7] XPS C1s spectrum of the porous membrane of Example 2 (second porous membrane 1-2). [Figure 8] XPS C1s spectrum of the porous membrane of Example 3 (second porous membrane 2-1). [Figure 9]XPS C1s spectrum of the porous membrane (second porous membrane 3-1) of Example 5. [Modes for carrying out the invention]

[0009] The following definitions of terms apply throughout this specification and the claims. "(Meth)acrylate" is a general term for acrylates and methacrylates. "(Meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. The "~" symbol indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0010] [Porous membrane] A porous membrane according to one aspect of the present invention (hereinafter also referred to as "the porous membrane") comprises a film-forming polymer (A) and an amphiphilic copolymer (B). Furthermore, the surface of the porous membrane has a composition ratio of film-forming polymer (A) to amphiphilic copolymer (B) of 100:10 to 100:50 as determined by X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS"), and the contact angle of hexadecane in water is 100° to 180°.

[0011] <Membrane-forming polymer (A)> The film-forming polymer (A) is one of the components of this porous membrane. The film-forming polymer (A) may be used alone or in combination of two or more types. The film-forming polymer (A) is used to maintain the structure of the porous membrane. The composition of the film-forming polymer (A) can be selected according to the properties required for the porous membrane.

[0012] When chemical resistance, oxidative degradation resistance, and heat resistance are required for this porous membrane, examples of film-forming polymers (A) include fluorine-containing polymers, polyvinyl chloride, polyethylene, polypropylene, polystyrene, polystyrene derivatives, polyamide, polyurethane, polycarbonate, polysulfone, polyethersulfone, and cellulose acetate.

[0013] A hydrophobic polymer is preferred as the film-forming polymer (A). If the film-forming polymer (A) is a hydrophobic polymer, the porous membrane will not dissolve easily in pure water, and the structure of the porous membrane will be easily maintained. In this invention, hydrophobicity means that the contact angle of the polymer bulk with respect to pure water is 60° or more. The bulk contact angle refers to the contact angle when a water droplet is attached to the surface of a smooth film formed by dissolving the polymer in a solvent (S) described later, letting the dissolved solution flow, and then evaporating the solvent (S).

[0014] As a hydrophobic polymer, fluorine-containing polymers are particularly preferred because they can impart chemical resistance and oxidative degradation resistance to porous membranes. Examples of fluorine-containing polymers include polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene-chlorotrifluoroethylene copolymer, polyvinyl fluoride, and polytetrafluoroethylene. Polyvinylidene fluoride is preferred as the fluorine-containing polymer because it can impart oxidation resistance and mechanical durability to porous membranes.

[0015] As the film-forming polymer (A), a polymer that is soluble in the solvent (S) described later and poorly soluble in pure water is preferred. Polyvinylidene fluoride is particularly preferred as the film-forming polymer (A) because it has good solubility in the solvent (S), and the porous film has good chemical resistance and heat resistance.

[0016] The weight-average molecular weight (Mw) of the film-forming polymer (A) is preferably 100,000 to 2,000,000, and more preferably 300,000 to 1,500,000. If the weight-average molecular weight of the film-forming polymer (A) is above the lower limit, the mechanical strength of the porous film tends to be good, and if it is below the upper limit, the solubility in the solvent (S) tends to be good. When using a film-forming polymer (A) having a weight-average molecular weight within the aforementioned range, a film-forming polymer (A) having a predetermined weight-average molecular weight can be obtained by mixing polymers with different weight-average molecular weights. The weight-average molecular weight of the film-forming polymer (A) is determined by gel permeation chromatography (GPC) using polystyrene or polymethyl methacrylate as a standard sample.

[0017] <Amphiphilic copolymer (B)> An "amphiphilic copolymer" refers to a copolymer that contains both a hydrophilic and a hydrophobic part within its molecule. The "hydrophilic part" refers to the part (polymer chain) that is easily soluble in water or easily swells in water. The "hydrophobic part" refers to the part (polymer chain) that is poorly soluble in water or poorly swells in water. The amphiphilic copolymer (B) may be, for example, a block copolymer in which one or more hydrophilic parts and one or more hydrophobic parts are bonded, a graft copolymer in which one or more hydrophilic parts and one or more hydrophobic parts are bonded, or a random copolymer in which hydrophilic parts and hydrophobic parts are randomly bonded, or a mixture thereof. In terms of improving the hydrophilicity of the porous membrane surface, using a block copolymer or a graft copolymer is preferable to using a random copolymer, which has an averaged composition, because it allows the hydrophobic and hydrophilic parts to exhibit higher performance.

[0018] The amphiphilic copolymer (B) preferably contains a constituent unit that includes a zwitterionic structure (hereinafter also referred to as "unit (b1)"). When the amphiphilic copolymer (B) contains unit (b1), it exhibits excellent inhibitory effects on the adhesion of oils, proteins, microorganisms, etc., to the porous membrane. Examples of zwitterionic structures include sulfobetaine structures, carboxybetaine structures, and phosphobetaine structures. If the hydrophilic copolymer (B) contains unit (b1), typically unit (b1) is contained in the hydrophilic portion of the amphiphilic copolymer (B).

[0019] From the viewpoint of suppressing the nucleophilic acyl substitution reaction of ester groups in the polymerization reaction during the production of amphiphilic copolymer (B) and the hydrolysis of ester bonds in the contact step, it is preferable that unit (b1) does not contain ester bonds.

[0020] Examples of the unit (b1) include a unit represented by the following formula (1-1) and a unit represented by the following formula (1-2). Among these, the unit represented by the formula (1-1) is preferred in that it does not contain an ester bond.

[0021]

Chemical formula

[0022] However, R a represents a hydrogen atom or a methyl group, R b and R c each independently represent an alkylene group having 1 to 5 carbon atoms, R d and R e each independently represent an alkyl group having 1 to 5 carbon atoms, and R f represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. R b and R c The alkylene groups in may be linear or branched. Examples of the alkylene group include an ethylene group and a propylene group. R d , R e and R f The alkyl groups in may be linear or branched. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an n-butyl group, and a t-butyl group.

[0023] In addition to the unit (b1), the amphiphilic copolymer (B) may contain a structural unit that does not contain a zwitterionic structure (hereinafter, also referred to as "unit (b2)"). Examples of the unit (b2) include structural units based on the following monomers. Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, isoamyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, dodecyl methacrylate, stearyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate, 2 methacrylates -Ethylhexyl, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, n-butoxyethyl (meth)acrylate, isobutoxyethyl (meth)acrylate, t-butoxyethyl (meth)acrylate ,(meth)acrylate phenoxyethyl,(meth)acrylate nonylphenoxyethyl,(meth)acrylate 3-methoxybutyl, Praxel FM (trade name, manufactured by Daicel Chemicals, Ltd., unsaturated fatty acid hydroxyalkyl ester modified ε-caprolactone), Bremmer® PME-100 (trade name, manufactured by NOF Corporation, methoxypolyethylene glycol methacrylate (ethylene glycol with 2 chains)), Bremmer® PME-200 (trade name, manufactured by NOF Corporation, methoxypolyethylene glycol methacrylate ( (Ethylene glycol chain has 4 links), Bremmer® PME-400 (product name, manufactured by NOF Corporation, methoxy polyethylene glycol methacrylate (ethylene glycol chain has 9 links)), Bremmer® 50POEP-800B (product name, manufactured by NOF Corporation, octoxy polyethylene glycol-polypropylene glycol-methacrylate (ethylene glycol chain has 8 links and propylene glycol chain has 6 links)), Bremmer® 20ANEP-600 (product name, manufactured by NOF Corporation,Nonylphenoxy(ethylene glycol-polypropylene glycol) monoacrylate), Bremmer® AME-100 (product name, manufactured by NOF Corporation), Bremmer® AME-200 (product name, manufactured by NOF Corporation), Bremmer® 50AOEP-800B (product name, manufactured by NOF Corporation), etc.

[0024] An example of an amphiphilic copolymer (B) is a copolymer (hereinafter also referred to as "copolymer (B1)") comprising a first polymer chain containing unit (b1) and a second polymer chain consisting of unit (b2). The first polymer chain may further contain unit (b2). Copolymer (B1) may be a block copolymer, a graft copolymer, a random copolymer, or a mixture thereof.

[0025] Preferably, at least a portion of the units (b2) constituting the second polymer chain are units having a hydrophobic alkyl group or aryl group. If at least a portion of the units (b2) constituting the second polymer chain are units having a hydrophobic group, the affinity between the second polymer chain and the film-forming polymer (A) tends to be good. The content of units having hydrophobic groups in the second polymer chain is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass, based on the total amount of all constituent units that make up the second polymer chain.

[0026] The number-average molecular weight (Mn) of the amphiphilic copolymer (B) is preferably 5,000 to 10,000, more preferably 10,000 to 75,000, and even more preferably 15,000 to 50,000. If the number-average molecular weight of the amphiphilic copolymer (B) is above the lower limit, the proportion of amphiphilic copolymer (B) on the porous membrane surface improves, and the antifouling properties tend to be better. If it is below the upper limit, the amphiphilic copolymer (B) tends to dissolve more easily in the liquid medium (C). The molecular weight distribution (Mw / Mn: weight-average molecular weight / number-average molecular weight) of the amphiphilic copolymer (B) is preferably 1.0 to 3.0, as this allows for easy and uniform solubility in the liquid composition. When using an amphiphilic copolymer (B) having a number-average molecular weight or molecular weight distribution within the aforementioned range, an amphiphilic copolymer (B) having a predetermined number-average molecular weight or molecular weight distribution can be obtained by mixing materials having different number-average molecular weights or molecular weight distributions. The quantity-average molecular weight and weight-average molecular weight of the amphiphilic copolymer (B) are determined by gel permeation chromatography (GPC) using polystyrene as a standard sample.

[0027] The amphiphilic copolymer (B) can be produced by known methods. For example, if the amphiphilic copolymer (B) is a block copolymer or a graft copolymer, it can be produced by general methods for producing block copolymers or graft copolymers. As a method for producing the amphiphilic copolymer (B), living radical polymerization (sometimes called controlled radical polymerization) is preferred in terms of the ease of controlling the molecular weight and primary structure. Examples of living radical polymerization include reversible addition-cleavage chain transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP), and nitroxide-mediated polymerization (NMP).

[0028] The method for producing the amphiphilic copolymer (B) will be described below, using the example of producing a diblock copolymer (B1), in which one first polymer chain and one second polymer chain are linked, by RAFT polymerization. However, the method for producing the amphiphilic copolymer (B) is not limited to this example.

[0029] In this example of a manufacturing method, first, monomers that form the second polymer chain are polymerized in the presence of a RAFT agent and a radical polymerization initiator (first polymerization step). Next, monomers that form the first polymer chain are polymerized in the presence of the second polymer chain obtained in the first polymerization step and a radical polymerization initiator (second polymerization step). This yields the desired diblock copolymer. Alternatively, monomers that form the first polymer chain may be polymerized in the first polymerization step, and monomers that form the second polymer chain may be polymerized in the second polymerization step.

[0030] In this example, the monomer forming the first polymer chain includes a (meth)acrylic acid ester corresponding to the aforementioned unit (b1). The (meth)acrylic acid ester corresponding to unit (b1) is the (meth)acrylic acid ester corresponding to the unit represented by formula (1-1) above, i.e., CH2=C(R a )-C(=O)-N(R f )-R b -N + (R d )(R e )-R c -SO3 - Compounds represented by are preferred.

[0031] RAFT polymerization enables reversible chain transfer during polymerization by using a RAFT agent in combination with conventional radical polymerization. Known RAFT agents can be used. Specific examples of RAFT agents include thiocarbonylthio compounds such as 4-cyano-4-(thiobenzoylthio)pentanoic acid (CPADB).

[0032] Various compounds can be used as radical polymerization initiators, but organic peroxides and / or azo compounds that can generate radicals under polymerization temperature conditions are preferred. Examples of organic peroxides include diacyl peroxides such as benzoyl peroxide; dialkyl peroxides such as dicumyl peroxide; and alkyl peresters such as diisopropyl peroxydicarbonate and t-butyl peroxybenzoate. Among these, benzoyl peroxide is preferred. Examples of azo compounds include azobisisobutyronitrile (AIBN) and 2,2'-azobis(2,4-dimethylvaleronitrile). The amount of radical polymerization initiator used is, for example, 0.1 to 10 moles per mole of RAFT agent.

[0033] In the first polymerization step and the second polymerization step, polymerization may be carried out in a solvent-free environment (bulk polymerization) or in various solvents. Suitable solvents include, for example, hydrocarbon solvents such as toluene; ketone solvents such as acetone; alcohol solvents such as propanol and trifluoroethanol; nitrile solvents such as acetonitrile; ester solvents such as ethyl acetate; carbonate solvents such as ethylene carbonate; and aqueous solutions. These solvents may be used individually or in combination of two or more. Polymerization can be carried out at room temperature to 200°C, preferably in the range of 50 to 150°C. After polymerization, purification, drying, etc., may be performed as needed.

[0034] <Polymer (D)> The porous membrane may further contain a polymer (D) having units based on vinylpyrrolidone, to the extent that it does not depart from the purpose of the present invention. Polymer (D) can be used as one of the components of the film-forming stock solution in the production of porous membranes. Polymer (D) is added as a pore-opening aid to control the phase separation between the film-forming polymer (A) and the solvent (S) described later.

[0035] Examples of polymer (D) include polyvinylpyrrolidone, as well as copolymers having units based on vinylpyrrolidone and units based on other monomers. Other monomers are not particularly limited as long as they can copolymerize with vinyl pyrrolides, for example, hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, (meth)acrylate, n-butyl acrylate, isobutyl methacrylate, t-butyl methacrylate, isoamyl methacrylate, hexyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate, 2-ethylhexyl methacrylate , Praxel FM (product name, manufactured by Daicel Corporation, caprolactone addition monomer), methoxyethyl methacrylate, ethoxyethyl (meth)acrylate, n-butoxyethyl (meth)acrylate, isobutoxyethyl (meth)acrylate, t-butoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, nonylphenoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, Bremmer (registered trademark) PME-100 (product name, manufactured by NOF Corporation, methoxypolyethylene glycol methacrylate (ethylene glycol compound) (Those with 2 chains), Bremmer (registered trademark) PME-200 (product name, manufactured by NOF Corporation, methoxypolyethylene glycol methacrylate (ethylene glycol with 4 chains)), 2-methacryloyloxyethyl phosphorylcholine, dimethylaminoethyl methacrylate, dimethylaminoethyl methyl chloride salt of methacrylate, dimethylaminoethyl methyl sulfate of methacrylate, 3-(methacrylamide)propyltrimethylammonium chloride, 3-(methacrylamide)propyltrimethylammonium methyl sulfate,Dimethylaminoethyl quaternary methacrylate is an example. Other monomers may be used individually or in combination of two or more. Polymer (D) may be used alone or in combination of two or more types.

[0036] As for polymer (D), considering the physical properties of the porous membrane, the weight-average molecular weight is 1 × 10⁻¹⁰ 6 A polymer having a molecular weight distribution with peak area values ​​of 10% or less is preferred. By using a polymer (D) having such a molecular weight distribution, it exhibits good cleaning (removal) properties as a phase separation control agent, and fine cracks tend to occur easily in the structure of the porous membrane, thus improving the filtration performance of the porous membrane.

[0037] Polymer (D) has a weight-average molecular weight of 1 × 10 6 The lower limit of the polymer content described above is preferably 5% by mass, more preferably 8% by mass, and even more preferably 10% by mass, considering that polymer (D) can be easily removed from the porous membrane precursor described later, and that the presence of polymer (D) in the porous membrane prevents the porous membrane from swelling with water and clogging of pores, thus allowing the porous membrane to have good water permeability. 6 The upper limit for the content of the polymer is preferably 25% by mass, and more preferably 20% by mass. 6 By setting the content of the above-mentioned high-molecular-weight polymers to above the lower limit percentage, it tends to be possible to improve filtration characteristics, especially when used as a filtration membrane for wastewater.

[0038] <Other ingredients> The porous membrane may further contain other components besides the film-forming polymer (A), the amphiphilic copolymer (B), and the polymer (D), without departing from the objectives of the present invention. Other components include, for example, fibrous materials such as cellulose nanofibers, glass fibers, carbon fibers, and acrylic fibers; resin powders such as polyvinyl acetate, cellulose derivatives, and acrylic resins; inorganic particles such as silica particles, titanium dioxide particles, and activated carbon; inorganic salts such as sodium chloride, lithium chloride, and lithium bromide; and various additives such as surfactants like polyvinyl alcohol, polyethylene glycol, polypropylene glycol, ethylene glycol, and glycerin.

[0039] In this porous membrane, the content of the film-forming polymer (A) is preferably 83% by mass or more, more preferably 90% by mass or more, even more preferably 93% by mass or more, and particularly preferably 95% by mass or more, based on the total mass of the porous membrane. If the content of the film-forming polymer (A) is above the lower limit, the mechanical properties of the porous membrane tend to be better. Furthermore, the content of the film-forming polymer (A) is preferably 99.99% by mass or less, and more preferably 99.9% by mass or less, relative to the total mass of the porous membrane. If the porous membrane contains polymer (D), it may be 99.98% by mass or less, or 99.8% by mass or less. If the content of the film-forming polymer (A) is below the above upper limit, the antifouling properties of the porous membrane are better. The above lower and upper limits can be combined as appropriate. For example, the content of the film-forming polymer (A) may be 93-99.99% by mass, 95-99.9% by mass, 83-99.98% by mass, or 90-99.8% by mass, based on the total mass of the porous membrane.

[0040] The content of the amphiphilic copolymer (B) is preferably 0.01 to 7% by mass, and more preferably 0.1 to 5% by mass, relative to the total mass of the porous membrane. If the content of amphiphilic copolymer (B) is above the lower limit, the antifouling properties of the porous membrane tend to be better, and if it is below the upper limit, the membrane performance such as mechanical properties and water permeability tends to be better. The amphiphilic polymer (B) is typically coated as an extremely thin film (e.g., about 5-10 nm) on the first porous film described later. In this case, the amphiphilic copolymer (B) is present in a substantially very small amount, although it is observable by XPS.

[0041] When the porous membrane contains polymer (D), the polymer (D) content is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and even more preferably 0.5 to 3% by mass, relative to the total mass of the porous membrane. If the polymer (D) content is above the lower limit, it tends not to impair the fouling resistance and water permeability of the porous membrane, and if it is below the upper limit, pore blockage by polymer (D) is reduced. Furthermore, since polymer (D) is soluble in water, keeping the polymer (D) content below the upper limit reduces the risk of water quality being impaired by polymer (D) dissolving into the treated water.

[0042] This porous membrane may be a porous membrane having multiple porous layers. If the porous membrane has multiple porous layers, a support may be provided between the multiple porous layers. By providing a support, the multiple porous layers are reinforced by the support, and physical properties such as burst pressure and tensile strength can be improved. Support materials include woven fabrics, nonwoven fabrics, braided cords, knitted cords, and nets. Support material materials include synthetic fibers, semi-synthetic fibers, regenerated fibers, and natural fibers.

[0043] Examples of synthetic fibers include polyamide fibers such as nylon 6, nylon 66, and aromatic polyamides; polyester fibers such as polyethylene terephthalate, polybutylene terephthalate, polylactic acid, and polyglycolic acid; acrylic fibers such as polyacrylonitrile; polyolefin fibers such as polyethylene and polypropylene; polyvinyl alcohol fibers; polyvinylidene chloride fibers; polyvinyl chloride fibers; polyurethane fibers; phenolic resin fibers; fluorine fibers such as polyvinylidene fluoride and polytetrafluoroethylene; and polyalkylene parahydroxybenzoate fibers. Examples of semi-synthetic fibers include cellulose derivative fibers made from raw materials such as cellulose diacetate, cellulose triacetate, chitin, and chitosan, as well as protein-based fibers called Promix. Examples of regenerated fibers include cellulose-based regenerated fibers (rayon, cupro, polynosic, etc.) obtained by methods such as the viscose method, copper-ammonia method, and organic solvent method. Examples of natural fibers include flax and jute.

[0044] A preferred embodiment of this porous membrane is a porous membrane (hereinafter also referred to as the "second porous membrane") in which a part or all of the surface of a porous membrane containing a film-forming polymer (A) (hereinafter also referred to as the "first porous membrane") is covered with a layer containing an amphiphilic copolymer (B) (hereinafter also referred to as the "coating layer").

[0045] The first porous membrane may further contain a polymer (D) having units based on vinylpyrrolidone, without departing from the objectives of the present invention. The first porous membrane may further contain other components besides the film-forming polymer (A) and polymer (D), without departing from the objectives of the present invention. Other components in the first porous membrane include, for example, the aforementioned fibrous material, resin powder, inorganic particles, surfactants, and various other additives.

[0046] In the first porous membrane, the content of the film-forming polymer (A) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass, based on the total mass of the first porous membrane. If the content of the film-forming polymer (A) is above the lower limit, the mechanical properties of the porous membrane tend to be better.

[0047] When the first porous membrane contains polymer (D), the polymer (D) content is preferably 0.01 to 30% by mass, more preferably 0.1 to 20% by mass, and even more preferably 0.5 to 15% by mass, relative to the total mass of the first porous membrane. If the polymer (D) content is above the lower limit, it tends not to impair the fouling resistance and water permeability of the porous membrane, and if it is below the upper limit, pore blockage by polymer (D) is reduced. Furthermore, since polymer (D) is soluble in water, keeping the polymer (D) content below the upper limit reduces the risk of water quality being impaired by polymer (D) dissolving into the treated water. Furthermore, the total content of film-forming polymer (A) and polymer (D) shall not exceed 100% by mass relative to the total mass of the first porous membrane.

[0048] The average pore size of the first porous membrane is preferably 1 to 1200 nm, considering that the second porous membrane can be used for removing bacteria and viruses, purifying proteins and enzymes, or for tap water applications. If the average pore size is 1 nm or larger, high water pressure tends not to be required when treating water. If the average pore size is 1200 nm or smaller, bacteria, viruses, and suspended solids in tap water tend to be easily removed. The average pore size of the first porous membrane is more preferably 500 nm or less, even more preferably 300 nm or less, and particularly preferably 100 nm or less. The average pore diameter is a value obtained by taking cross-sectional images of a porous membrane using a scanning electron microscope and performing image analysis. For example, the outer surface of a porous membrane is observed using a scanning electron microscope, 30 pores are randomly selected, the longest diameter of each pore is measured, and the average of the longest diameters of the 30 pores is calculated.

[0049] The first porous membrane may be a porous membrane having a plurality of porous layers containing a membrane-forming polymer (A). At least a portion of the plurality of porous layers may further contain polymer (D). At least a portion of the plurality of porous layers may further contain other components. The content of the film-forming polymer (A) in each of the multiple porous layers may be the same or different. If the first porous membrane has multiple porous layers, a support may be provided between the multiple porous layers.

[0050] The coating layer may further contain other components besides the amphiphilic copolymer (B) without departing from the objectives of the present invention. Other components in the coating layer include, for example, polymers other than the amphiphilic copolymer (B), ethylene glycol, and the aforementioned inorganic salts. The coating layer preferably does not contain film-forming polymer (A).

[0051] In the coating layer, the content of the amphiphilic copolymer (B) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass, based on the total mass of the coating layer. If the content of the amphiphilic copolymer (B) is above the lower limit, the antifouling properties of the second porous membrane are further improved.

[0052] Examples of the form of this porous membrane (or the first porous membrane) include hollow fiber membranes and flat membranes, but hollow fiber membranes are preferred because they are easy to process to any length and can fill membrane modules with a high packing efficiency. The first porous membrane may have macrovoids or spherulite structures within the membrane.

[0053] When the porous membrane takes the form of a hollow fiber membrane, a hollow braided or woven cord can be used as a support. By providing a porous layer on the inner or outer surface of the cord, a reinforced hollow fiber membrane is created.

[0054] When the porous membrane is a hollow fiber membrane, the outer diameter of the hollow fiber membrane is preferably 20 to 3,000 μm, more preferably 30 to 2,800 μm, and even more preferably 40 to 2,700 μm. If the outer diameter of the hollow fiber membrane is above the lower limit, it tends to be less prone to fiber breakage during film formation. If the outer diameter of the hollow fiber membrane is below the upper limit, it is easier to maintain its hollow shape, and it tends to be less prone to flattening, especially when external pressure is applied.

[0055] When the porous membrane is a hollow fiber membrane, the film thickness of the hollow fiber membrane (however, if a support is included, this means the film thickness excluding the support) is preferably 5 to 250 μm, more preferably 30 to 200 μm, and even more preferably 50 to 180 μm. If the film thickness of the hollow fiber membrane is above the lower limit, there is a tendency for the fibers to break less easily during film formation. If the film thickness of the hollow fiber membrane is below the upper limit, there is a tendency for it to have high water permeability.

[0056] <Characteristics of porous membranes> The composition ratio of the XPS-formed film-forming polymer (A) and the amphiphilic copolymer (B) on the surface of this porous membrane (hereinafter also referred to as "(A):(B)") is 100:10 to 100:50, preferably 100:12 to 100:40, and more preferably 100:15 to 100:30. If (A):(B) is within the above range, the film-forming polymer (A) is either absent or present in small amounts on the porous membrane surface, resulting in excellent antifouling properties. For the measurement of (A):(B), the Take-off Angle in XPS is set to 45°. (A):(B) will change depending on the XPS measurement conditions. This is because the detection depth differs when the Take-off Angle is different. When the Take-off Angle is 45°, it is thought that the information obtained is approximately 10 nm from the outermost surface of the porous membrane. Detailed XPS measurement conditions are as described in the examples below. (A):(B) can be adjusted, for example, in the manufacturing method described later, by the content of the amphiphilic copolymer (B) in the liquid composition and the contact time of the liquid composition in the contact step.

[0057] When the film-forming polymer (A) is a fluorine-containing polymer, the surface of this porous membrane shows a C1s peak at 292 eV corresponding to CF2 of the fluorine-containing polymer in XPS. Additionally, a C1s peak corresponding to the amphiphilic copolymer (B) is observed at 287 eV. Since a peak corresponding to film-forming polymer (A) is also observed at 287 eV, the peak area at 287 eV corresponding to amphiphilic copolymer (B) can be obtained by subtracting the peak area corresponding to film-forming polymer (A), calculated from the 292 eV peak, from the peak area at 287 eV. When the film-forming polymer (A) is polyvinylidene fluoride, which accounts for the majority of water treatment membranes, especially wastewater treatment membranes, the peak areas at 287 eV and 292 eV corresponding to film-forming polymer (A) can be obtained in approximately a 1:1 ratio based on their chemical structure. On the surface of the porous membrane, the ratio of the 292 eV peak area corresponding to the film-forming polymer (A) to the 287 eV peak area corresponding to the amphiphilic copolymer (B) (hereinafter also referred to as "peak area ratio (A):(B)") is preferably 1.0:0.75 to 1.0:5.0. If the peak area ratio (A):(B) is within the above range, the contact angle of hexadecane in water tends to be between 100° and 180°. In addition, because a very thin layer of amphiphilic copolymer (B) is present on the surface of the porous membrane, blockage of the pores of the porous membrane can be reduced. From the viewpoint of achieving both hydrophilicity and water permeability, the peak area ratio (A):(B) is more preferably 1.0:1.0 to 1.0:4.0, and even more preferably 1.0:0.75 to 1.2:3.0.

[0058] The contact angle of hexadecane in water on the surface of this porous membrane is 100° to 180°, preferably 110° to 180°, and more preferably 120° to 180°. If the contact angle of hexadecane in water is above the lower limit, excellent hydrophilicity and excellent antifouling properties are obtained. It is practically inconceivable that the contact angle of hexadecane in water will exceed 180°. The contact angle of hexadecane in water is measured under the conditions of a hexadecane droplet volume of 6.0 μL and a temperature of 25°C. The detailed measurement method is described in the examples below.

[0059] The average pore size of this porous membrane is preferably 1 to 1200 nm, given its suitability for use in removing bacteria and viruses, purifying proteins and enzymes, and for applications in tap water. If the average pore size is 1 nm or larger, high water pressure is generally not required when treating water, and if the average pore size is 1200 nm or smaller, bacteria, viruses, and suspended solids in tap water tend to be easily removed. The average pore size of this porous membrane is more preferably 500 nm or less, even more preferably 300 nm or less, and particularly preferably 100 nm or less.

[0060] This porous membrane can be manufactured, for example, by the manufacturing method shown below. However, the manufacturing method for this porous membrane is not limited to this.

[0061] [Method for manufacturing porous membranes] A method for producing a porous membrane according to one aspect of the present invention (hereinafter also referred to as "this production method") includes a step of contacting a first porous membrane containing a membrane-forming polymer (A) with a liquid composition containing an amphiphilic copolymer (B) and a liquid medium (C) (hereinafter also referred to as "contact step"). The contact step yields the second porous membrane described above. This manufacturing method may further include a step of manufacturing a first porous membrane before the contact step, if necessary. This manufacturing method may further include a step of preparing a liquid composition before the contact step, if necessary.

[0062] <Method for manufacturing the first porous membrane> The first porous membrane can be manufactured by known methods. An example of a method for manufacturing the first porous membrane is described below.

[0063] A film-forming polymer (A) and, if necessary, a polymer (D) are mixed with a solvent (S) to prepare a film-forming stock solution (a solution for preparing porous films) (preparation step). The obtained film-forming stock solution is brought into contact with a coagulation solution to coagulate it and obtain a porous film precursor (coagulation step). The remaining solvent (S) and polymer (D) in the obtained porous membrane precursor are washed away by a washing process. The washed porous membrane precursor is dried to obtain a porous membrane (drying step).

[0064] "Preparation process" The film-forming stock solution is obtained by mixing film-forming polymer (A) and polymer (D) with solvent (S). Other components may be mixed in as needed. In the film-forming stock solution, it is preferable that the film-forming polymer (A), polymer (D), and, if other components are present, some or all of the other components are dissolved in the solvent (S), but they do not necessarily need to be dissolved as long as they are uniformly dispersed.

[0065] When adding other components to the film-forming stock solution, they may be added directly to the solvent (S), dissolved in the solvent (S), or pre-compounded with the film-forming polymer (A) and polymer (D).

[0066] Furthermore, when preparing the film-forming stock solution, the film-forming polymer (A) and polymer (D) may be dissolved while heating the solvent (S) as long as the temperature is below the boiling point of the solvent (S), and the solvent (S) may be cooled as needed.

[0067] The concentration of the film-forming polymer (A) in the film-forming stock solution (100% by mass) is preferably 10 to 30% by mass, more preferably 12 to 28% by mass, and even more preferably 15 to 25% by mass. If the concentration of the film-forming polymer (A) is above the lower limit, it tends to be easily formed into a porous film, and if it is below the upper limit, it tends to be easily dissolved in the solvent (S).

[0068] The concentration of polymer (D) in the film-forming stock solution (100% by mass) is preferably 0 to 30% by mass, more preferably 5 to 28% by mass, and even more preferably 10 to 25% by mass. If the concentration of polymer (D) is above the lower limit, a porous film tends to be easily formed, and if it is below the upper limit, the solubility of the film-forming polymer (A) in the solvent (S) tends to increase.

[0069] The concentration of solvent (S) in the film-forming stock solution (100% by mass) is preferably 40 to 90% by mass, more preferably 50 to 85% by mass, and even more preferably 60 to 80% by mass. If the concentration of solvent (S) is above the lower limit, a high permeation flux tends to be obtained, and if it is below the upper limit, a porous film can be easily formed.

[0070] "Coagulation process" As the coagulation solution, an aqueous solution containing 50% by mass or less of solvent (S) is preferred from the viewpoint of controlling the pore size of the membrane. The solvent (S) contained in the coagulation solution and the solvent (S) contained in the film-forming stock solution may be of the same type or different types, but it is preferable that they be of the same type.

[0071] The temperature of the coagulation solution is preferably 10 to 90°C. If the temperature of the coagulation solution is above the lower limit, the water permeability of the porous membrane tends to improve, and if it is below the upper limit, the mechanical strength of the porous membrane tends to be maintained well.

[0072] "Washing process" It is preferable to wash away some or all of the solvent (S) and polymer (D) remaining in the porous membrane precursor by contacting it with either water or an aqueous solution such as a sodium hypochlorite aqueous solution at 40 to 100°C. The step of contacting the polymer (D) with water and / or an aqueous solution such as sodium hypochlorite solution can be repeated multiple times to remove the polymer (D).

[0073] "Drying process" The washed porous membrane precursor is preferably dried at 60-120°C for 1 minute to 24 hours. If the drying temperature is above the lower limit, the drying time is shortened and production costs can be reduced, which is preferable for industrial production. If the temperature is below the upper limit, excessive shrinkage of the porous membrane precursor during the drying process can be suppressed, and minute cracks tend to be less likely to occur on the outer surface of the porous membrane.

[0074] If the first porous membrane is a porous membrane having multiple porous layers containing a membrane-forming polymer (A), it can be manufactured, for example, by a method including the following steps.

[0075] Step (a): A step of preparing multiple film-forming stock solutions containing film-forming polymer (A) and polymer (D). Step (b): A step of forming a porous membrane precursor having multiple porous precursor layers corresponding to each of the multiple film-forming stock solutions, using multiple film-forming stock solutions. Step (c): A step of removing part or all of the polymer (D) from the porous membrane precursor to obtain a porous membrane having multiple porous layers containing a membrane-forming polymer (A).

[0076] "Process (a)" In step (a), for example, film-forming polymers (A) and polymers (D), and other components as needed, are dissolved in a solvent (S) to prepare several film-forming stock solutions. Step (a) can be carried out in accordance with the preparation step described above.

[0077] "Process (b)" In step (b), for example, multiple film-forming stock solutions are arranged in layers and brought into contact with a coagulation solution to coagulate, thereby forming a porous film precursor having multiple porous precursor layers corresponding to each of the multiple film-forming stock solutions. Step (b) can be carried out in accordance with the solidification step described above.

[0078] "Process (c)" Step (c) can be carried out in accordance with the washing and drying steps described above.

[0079] <Liquid composition> The liquid composition comprises an amphiphilic copolymer (B) and a liquid medium (C). The liquid medium (C) typically contains water. The liquid medium containing water may be water alone, or a mixture of water and a water-soluble organic solvent. Examples of water-soluble organic solvents include alcohols such as methanol and ethanol, aprotic amides such as dimethylacetamide and dimethylformamide, and acetone. These water-soluble organic solvents may be used individually or in combination of two or more. Water is preferred as the liquid medium (C) from the standpoint of cost and environmental impact.

[0080] The liquid composition may further contain other components besides the amphiphilic copolymer (B) and the liquid medium (C), without departing from the objectives of the present invention. Other components in the liquid composition include, for example, polymers other than the amphiphilic copolymer (B), ethylene glycol, and the inorganic salts mentioned above. The liquid composition preferably does not contain film-forming polymer (A).

[0081] In the liquid composition, the content of the amphiphilic copolymer (B) is preferably 0.0001 to 1.0% by mass, more preferably 0.001 to 0.5% by mass, and even more preferably 0.01 to 0.1% by mass, based on the total mass of the liquid composition. If the content of the amphiphilic copolymer (B) is above the lower limit, the antifouling properties of the second porous membrane are better, and if it is below the upper limit, the pores of the second porous membrane can be sufficiently secured, resulting in better membrane performance such as water permeability.

[0082] The content of other components is, for example, 0 to 10% by mass relative to the total mass of the liquid composition.

[0083] The liquid composition can be prepared, for example, by mixing an amphiphilic copolymer (B) and a liquid medium (C), and other components as needed.

[0084] <Contact process> In the contact step, the first porous membrane is brought into contact with the liquid composition. This results in the acquisition of a second porous membrane. One possible contact method is to immerse the first porous membrane in a liquid composition. When the first porous membrane is brought into contact with the liquid composition, it is preferable that the amphiphilic copolymer (B) in the liquid composition is dissolved in the liquid medium (C).

[0085] When the liquid composition comes into contact with the first porous membrane, the amphiphilic copolymer (B) comes into even contact with the surface of the first porous membrane, and the hydrophobic portion of the amphiphilic copolymer (B) is adsorbed and / or compatible with the film-forming polymer (A) of the first porous membrane, causing the amphiphilic copolymer (B) to spontaneously accumulate at the solid-liquid interface. As a result, the surface of the first porous membrane is evenly coated with the amphiphilic copolymer (B). Furthermore, it is conceivable that thermal energy activates the molecular motion of the film-forming polymer (A) and the amphiphilic copolymer (B), causing the film-forming polymer (A) and the hydrophobic portion of the amphiphilic copolymer (B) to become compatible, thereby fixing the amphiphilic copolymer (B) to the surface of the first porous membrane. Since the hydrophilic portion of the amphiphilic copolymer (B) is predominantly located on the liquid medium (C) side, the hydrophilic portion of the amphiphilic copolymer (B) accumulates highly at the interface between the resulting second porous membrane and the liquid medium (C). Therefore, it is thought that the resulting second porous membrane may have a structure in which a layer of miscible material between the film-forming polymer (A) and the hydrophobic portion of the amphiphilic copolymer (B), and a layer of the hydrophilic portion of the amphiphilic copolymer (B) are sequentially stacked on top of the first porous membrane. Because the film-forming polymer (A) is absent or present in small amounts on the surface of the second porous membrane, it is thought that excellent antifouling properties are exhibited.

[0086] After the contact step, the obtained second porous film is removed from the liquid composition and dried. Drying can be carried out by known methods such as air drying or heat drying. The drying temperature is, for example, 50 to 100°C. [Examples]

[0087] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass" respectively, unless otherwise specified.

[0088] [Materials used] (1) Methyl methacrylate (MMA): A commercially available product (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 98.0%) was separated with an aqueous sodium hydroxide solution, and the organic phase was dried with magnesium sulfate. It was then distilled under reduced pressure in the presence of calcium hydride and stored in a refrigerator. (2) 2,2'-Azobis(isobutyronitrile) (AIBN): A commercially available product (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 98.0%) was recrystallized with methanol. The precipitated crystals were filtered off by suction filtration and stored in a refrigerator. (3) N-(3-dimethylaminopropyl)methacrylamide: A commercially available product (manufactured by Tokyo Chemical Industry Co., Ltd., purity 98.0%) was distilled under reduced pressure and stored in a refrigerator. (4) The following items were used as commercially available products. 4-Cyano-4-(thiobenzoylthio)pentanoic acid (CPADB): Manufactured by Aldrich. Sodium hydroxide: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 85.0%. Calcium hydride: Manufactured by Fujifilm Wako Pure Chemical Industries. Magnesium sulfate: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 95.0%. Dichloromethane: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Hexane: Manufactured by Fujifilm Wako Pure Chemical Industries. 1,3-Propanesultone: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 97.0%. Methanol: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.8% purity. Toluene: Manufactured by Fujifilm Wako Pure Chemical Industries, 99.0% purity. Acetone: Manufactured by Fujifilm Wako Pure Chemical Industries. Ethanol: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. N,N-dimethylacetamide (DMAc): Manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.0%. 2,2,2-Trifluoroethanol: Manufactured by Tokyo Chemical Industry Co., Ltd., 99.0% purity. Polyvinylidene fluoride (PVDF): Arkema Corporation, trade name: Kynar 761A, weight-average molecular weight (Mw) 550,000.

[0089] [Synthesis Example 1.3: Synthesis of 3-(methacrylicamino)propyl-N,N-dimethyl)ammonatopropanesulfonate (SBMA)] 3.0 mL (17 mmol) of N-(3-dimethylaminopropyl)methacrylamide and 20 mL of acetone were added to a 200 mL round-bottom flask. A solution of 1.5 mL (17 mmol) of 1,3-propanesultone dissolved in 5 mL of acetone was added dropwise to the ice-cooled flask and stirred at room temperature for 5 hours. The precipitate was collected by vacuum filtration, dissolved in a small amount of methanol, and reprecipitated by adding dropwise to acetone. The powder was filtered off by vacuum filtration and dried under reduced pressure (yield 4.1 g, yield 81.6%). 1 The molecular structure was confirmed by 1H-NMR measurement. 1 Based on the chemical shift, coupling state, and integral value of the H-NMR signal, a signal attributable to SBMA was observed, and the product was identified as SBMA. Furthermore, no signals from impurities were observed, indicating that the SBMA was of sufficiently high purity. 1 H-NMR (0.1M NaCl heavy aqueous solution): / ppm 1.8(s,3H,CH2CH(CH3)CO-),1.9-2.0(m,2H,-CH2CH2SO3),2.0-2.1(m,4H,-CH2CH2N(CH3)2CH2CH2CH2-),2.8-2.9(t,2H,-CH2N(CH3)2-),3.0(s ,6H,-CH2N(CH3)2-),3.2-3.3(m,2H,-CONHCH2-),3.3-3.4(m,2H,-N(CH3)2CH2-),5.3-5.4(s,1H,CH2C(CH3)2CO-),5.6(s,1H,CH2C(CH3)2CO-)

[0090] [ka]

[0091] [Synthesis Example 2. Synthesis of PMMA by RAFT polymerization] 10.65 mL (100 mmol) of MMA, 65.7 mg (0.4 mmol) of AIBN, 58.7 mg (2.0 mmol) of CPADB, and 5.0 mL of toluene were added to a polymerization tube. Ar gas was bubbling for 20 minutes, the polymerization tube was sealed, and the mixture was stirred at 75°C for 16 hours. The product was diluted with dichloromethane and reprecipitation with hexane. The precipitate was filtered off by vacuum filtration and dried under reduced pressure (yield 11.0 g, yield 73.6%). 1 The molecular structure was confirmed by 1H-NMR measurement. 1 The monomer conversion rate calculated from the 1H-NMR spectrum was 97.6%. Furthermore, the Mn value determined by GPC measurement was 5000, and the Mw / Mn ratio was 1.14.

[0092] [ka]

[0093] [Synthesis Example 3. Synthesis of Block Copolymer (PMMA-b-PSBMA) by RAFT Polymerization] In a polymerization tube, 697 mg (0.14 mmol) of PMMA obtained in Synthesis Example 2, 3.00 g (10 mmol) of SBMA obtained in Synthesis Example 1, 16.4 mg (0.10 mmol) of AIBN, and 10.0 mL of trifluoroethanol were added. Ar gas was bubbling for 20 minutes, the polymerization tube was sealed, and the mixture was stirred at 65°C for 20 hours. The product was reprecipitated by adding methanol dropwise, the powder was filtered off by vacuum filtration, and the mixture was dried under reduced pressure (yield 2.8818 g, yield 77.6%). 1 The molecular structure was confirmed by 1H-NMR and IR measurements. 1 While a signal originating from PSBMA was observed in the 1H-NMR spectrum, no NMR signal was observed from the PMMA chain due to aggregation. 1 The monomer conversion rate calculated from the 1H-NMR spectrum was 66.1%. Based on the molar ratio of PMMA to SBMA (PMMA / SBMA = 1 / 70) and the monomer conversion rate, the Mn content of the PSBMA portion of PMMA-b-PSBMA was estimated to be 13500.

[0094] [ka]

[0095] [Synthesis Example 4. Synthesis of PSBMA by RAFT polymerization] SBMA 200 mg (0.6 mmol), initiator VA-044 (2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride) 1.3 mg (0.004 mmol), CPADB 5.6 mg (0.02 mmol), and 4.0 mL of a mixed solvent of methanol / 0.1 M NaCl aqueous solution = 3 / 1 (mass ratio) were added to a polymerization tube. Ar gas was bubbling for 20 minutes, the polymerization tube was sealed, and stirred at 45°C for 15 hours. Dialysis was performed for 2 days, and the polymer was obtained by freeze-drying (yield 72.5 mg, yield 36.3%). Regarding the obtained polymer, 1 The molecular structure was confirmed by 1H-NMR and IR measurements. Furthermore, the Mn value determined by GPC was 8700, and the Mw / Mn ratio was 1.06.

[0096] [ka]

[0097] [Synthesis Example 5. Synthesis of PBMA by RAFT polymerization] 5.56 mL (35.2 mmol) of n-butyl methacrylate (BMA), 72.8 mg (0.98 mmol) of CPADB, 64.1 mg (0.39 mmol) of AIBN, and 3.3 mL of toluene were added to a polymerization tube. The mixture was bubbled with Ar gas for 20 minutes, the polymerization tube was sealed, and the mixture was stirred at 75°C for 6 hours to stop the polymerization reaction. The mixture was reprecipitated and purified with methanol / hexane, dissolved in dichloromethane, and the dichloromethane was removed under reduced pressure to obtain a dried polymer (PBMA). 1 The structure was confirmed by 1H-NMR measurement. 1 H-NMR (deuterated solvent: CDCl3). The molecular weight calculated from the molar ratio of monomer to chain transfer agent (monomer / CPADB = 36 / 1) and monomer conversion rate is Mn_ NMR The concentration was 5280 g / mol.

[0098] [ka]

[0099] [Synthesis Example 6. Synthesis of Block Copolymer (PBMA-b-PSBMA) by RAFT Polymerization] 500 mg (0.046 mmol) of PBMA obtained in Synthesis Example 5, 947.6 mg (3.24 mmol) of SBMA obtained in Synthesis Example 1, 15.2 mg (0.09 mmol) of AIBN, and 6.5 mL of trifluoroethanol were added to a polymerization tube. The mixture was bubbled with Ar gas for 20 minutes, the polymerization tube was sealed, and the mixture was stirred at 65°C for 16 hours to stop the polymerization reaction. The mixture was reprecipitated and purified with a methanol:water = 1:1 mixed solvent and centrifuged. The polymer (PBMA-b-PSBMA) obtained by suction filtration was subjected to IR measurement to confirm its structure. Figure 1 shows the IR spectrum of PBMA-b-PSBMA. From the IR spectrum of PBMA-b-PSBMA, the value at 1040 cm⁻¹ was obtained. -1 Symmetrical stretching vibration of the sulfonic acid group, 1730 cm -1 Carbonyl stretching vibration of ester group, 1645 cm -1 A signal attributable to the carbonyl stretching vibration of the amide group was observed. From this result, the synthesis of PBMA-b-PSBMA by chain extension via RAFT polymerization using PBMA-CTA as a polymer chain transfer agent was confirmed. Assuming that the IR absorption intensities of the carbonyl stretching vibration of the ester group and the carbonyl stretching vibration of the amide group correspond to the degree of polymerization of PBMA and PSBMA, these peaks were separated by Igor, the integral ratio was determined, and the molecular weight of the PSBMA chain was calculated, resulting in Mn_ PSBMA The value was 18300g / mol.

[0100] [ka]

[0101] The measurement conditions used in synthesis examples 1 to 6 are shown below. <Nuclear Magnetic Resonance Spectrum ( 1 H-NMR) measurement> Measurements were performed using an AVANCE III 400 MHz (Bruker) analyzer. PMMA was tested with chloroform-d1 as the deuterated solvent, while SBMA and PMMA-b-PSBMA were tested with a 0.1 M NaCl deuterated aqueous solution as the deuterated solvent. Measurements were taken at 25°C.

[0102] <Gel Permeation Chromatography (GPC)> A GPC system equipped with a RID-10A (Shimadzu Corporation) RI detector, an LC-20AD (Shimadzu Corporation) pump, and a CTO-10ASVP (Shimadzu Corporation) column oven was used to analyze TSKgel a-4000 (exclusion limit molecular weight: 1.0 × 10⁶). 6 Measurements were taken using separation columns (manufactured by Tosoh Corporation and Shimadzu Corporation) and TSKguardcolumn PWXL guard columns at 40°C and a flow rate of 0.8 mL / min. Tetrahydrofuran (THF) was used as the eluent, and the number-average molecular weight (Mn) and molecular weight distribution (Mw / Mn) were calculated by creating a calibration curve using polystyrene (M=133,000, 55,100, 19,600, 7,210, 3,070) as standard samples. A PMMA THF solution with a high molecular weight concentration of 2.0 mg / mL was filtered through a 0.2 μm pore size hydrophilic PTFE filter ADVANTEC, HP020AN and measured.

[0103] <Infrared absorption spectroscopy (IR) measurement> An IRAffinity-1 (manufactured by Shimadzu Corporation) was used. A TGS detector was employed. • PSBMA Using a CaF2 optical crystal, the thin-film method was performed with 64 integration cycles and a resolution of 2.0 cm. -1 It was measured using [this method]. • PMMA-b-PSBMA, PBMA-b-PSBMA KBr tablets were prepared and measured using the transcatheter method with a cumulative count of 64 times and a resolution of 2.0 cm. -1 It was measured using [this method].

[0104] [Example 1] <Preparation of liquid composition> Water was added to PMMA-b-PSBMA to prepare a liquid composition such that the final concentration of PMMA-b-PSBMA was 0.1%. In these liquid compositions, PMMA-b-PSBMA did not completely dissolve in water at room temperature and showed a turbid dispersion state.

[0105] <Preparation of PVDF thin film> PVDF and DMAc were placed in a beaker and stirred to prepare a PVDF DMAc solution with a PVDF concentration of 2%. A silicon wafer (10 mm × 20 mm × 0.5 mm thick) was brought into contact with ethanol and ultrasonicated for 10 minutes for cleaning. The cleaned silicon wafer was immersed in an aqueous ethanol solution containing 2% by volume of a silane compound (3-Aminopropyl trimethoxysilane) for 5 minutes, then washed with an excess amount of ethanol, and allowed to stand at room temperature for 24 hours to perform silane coupling agent treatment. The silicon wafer treated with this silane coupling agent was placed on the sample stage of a spin coater (K-359S1 simple type, Kyowa Riken Co., Ltd.). A PVDF DMAc solution filtered through a regenerated cellulose filter with a pore size of 0.2 μm (Sartorius RC 0.20 mm) was dropped thereon, and spin-coated at 3000 rpm for 30 seconds at room temperature to form a thin film of PVDF (the first porous membrane).

[0106] <Contact process> The formed thin film was dried under reduced pressure and immersed in the prepared liquid composition (PMMA-b-PSBMA concentration 0.1%) at room temperature for 1 hour. After immersion, the thin film was taken out from the liquid composition, thoroughly washed with pure water, and left at room temperature to dry, thereby obtaining the second porous membrane 1-1.

[0107] [Example 2] In the contact process of Example 1, the second porous membrane 1-2 was obtained in the same manner except that the liquid composition (PMMA-b-PSBMA concentration 0.1%) was heated to 80 °C and the thin film was immersed therein.

[0108] [Example 3] The second porous membrane 2-1 was obtained in the same manner as in Example 1, except that a 0.1 M NaCl aqueous solution was added instead of water to prepare the liquid composition so that the final PMMA-b-PSBMA concentration was 0.1%.

[0109] [Example 4] In preparing the liquid composition of Example 2, a second porous membrane 2-2 was obtained using the same method, except that a 0.1 M NaCl aqueous solution was added instead of water so that the final PMMA-b-PSBMA concentration was 0.1%.

[0110] [Example 5] The second porous membrane 3-1 was obtained by the same method as in Example 1, except that in the contact step, the liquid composition (PMMA-b-PSBMA concentration 0.1%) was obtained in Synthesis Example 6 (PBMA-b-PSBMA concentration 0.1%).

[0111] [Example 6] The second porous membrane 3-2 was obtained by the same method as in Example 2, except that in the contact step, the liquid composition (PMMA-b-PSBMA concentration 0.1%) was obtained in Synthesis Example 6 (PBMA-b-PSBMA concentration 0.1%).

[0112] [Example 7] The second porous membrane 4-1 was obtained by the same method as in Example 3, except that in the contact step, the liquid composition (PMMA-b-PSBMA concentration 0.1%) was obtained in Synthesis Example 6 (PBMA-b-PSBMA concentration 0.1%).

[0113] [Example 8] The second porous membrane 4-2 was obtained by the same method as in Example 4, except that in the contact step, the liquid composition (PMMA-b-PSBMA concentration 0.1%) was obtained in Synthesis Example 6 (PBMA-b-PSBMA concentration 0.1%).

[0114] [Comparative Example 1] A PVDF thin film was fabricated in the same manner as in Example 1. Subsequently, without performing a contact step, the fabricated PVDF thin film was used as the porous film of Comparative Example 1.

[0115] [Comparative Example 2] A PVDF thin film was fabricated in the same manner as in Example 1. Then, an aqueous solution of 1.0 mg of PSBMA obtained in Synthesis Example 4 dissolved in 10 mL of water was filtered through a hydrophilic PTFE filter with a pore size of 0.2 m (ADVANTEC, HP020AN). The resulting filtrate was dropped onto the PVDF thin film and dried under reduced pressure to obtain the porous film of Comparative Example 2 coated with PSBMA.

[0116] [Comparative Example 3] A PVDF thin film was fabricated in the same manner as in Example 1. Then, an aqueous solution of 10 mg of PSBMA obtained in Synthesis Example 4 dissolved in 10 mL of water was filtered through a 0.2 m pore size hydrophilic PTFE filter (ADVANTEC, HP020AN). The resulting filtrate was dropped onto the PVDF thin film and dried under reduced pressure to obtain the porous film of Comparative Example 3 coated with PSBMA.

[0117] 〔evaluation〕 <Surface composition of thin films (XPS)> For each example of porous membrane, the XPS C1s spectrum was measured under the conditions described below. Furthermore, a PMMA thin film was fabricated by spin coating in the same manner as described above, except that PMMA obtained in Synthesis Example 2 was used instead of PVDF. The XPS C1s spectrum of this PMMA thin film was also measured in the same manner. Figure 2 shows the XPS C1s spectrum of the porous membrane of Comparative Example 1 (PVDF thin film before the contact process). Figure 3 shows the XPS C1s spectrum of the PMMA thin film. Figures 4-5 show the XPS C1s spectra of the porous membranes of Comparative Examples 2-3 (PVDF porous membranes coated with PSBMA). Figures 6-9 show the XPS C1s spectra of the second porous membranes 1-1, 1-2, 2-1, and 3-1.

[0118] "XPS measurement conditions" Equipment: K-Alpha Thermo Fisher Scientific Detector: 180° dual-focus hemispherical analyzer, 128-channel detector Take-off Angle: 45° X-ray source: AlK, X-ray spot size: 400mm Survey scan:Energy step size:1.00eV,1351 Energy Channels,Pass Energy:200eV,Number of scan:3,Dwell Time:10msec Narrow scan:Energy step size:0.100eV,191 Energy Channels,Pass Energy:50 eV,Number of scan:10,Dwell Time:50 msec

[0119] As shown in Figure 2, the XPS C1s spectrum of the porous film of Comparative Example 1 (PVDF thin film before the contact process) clearly showed signals originating from CH2 and CF2 of the PVDF. As shown in Figure 3, the XPS C1s spectrum of the PMMA thin film showed signals from the carbonyl carbon, signals from the CH2 in the main chain and the methyl group attached to the main chain, and signals from the esterified methyl group. As shown in Figure 4, the XPS C1s spectrum of the porous membrane of Comparative Example 2 clearly showed signals originating from PSBMA and PVDF, indicating that in the porous membrane of Comparative Example 2, a very thin layer of PSBMA was coated on top of the PVDF. As shown in Figure 5, the XPS C1s spectrum of the porous membrane of Comparative Example 3 clearly showed signals originating from PSBMA, while no signals originating from CH2 and CF2 of PVDF were observed. This indicates that the porous membrane of Comparative Example 3 was coated with a very thick layer of PSBMA on top of the PVDF. As shown in Figure 6, the XPS C1s spectrum of the second porous membrane 1-1 (PVDF thin film after the contact process) clearly showed signals originating from PMMA-b-PSBMA and PVDF, indicating that the second porous membrane 1-1 is coated with a very thin layer of PMMA-b-PSBMA on top of the PVDF. As shown in Figure 7, the XPS C1s spectrum of the second porous membrane 1-2 (PVDF thin film after the contact process) clearly showed signals originating from PMMA-b-PSBMA and PVDF, indicating that the second porous membrane 1-2 is coated with a very thin layer of PMMA-b-PSBMA on top of the PVDF. As shown in Figure 8, the XPS C1s spectrum of the second porous membrane 2-1 (PVDF thin film after the contact process) clearly showed signals originating from PMMA-b-PSBMA and PVDF, indicating that the second porous membrane 2-1 is coated with a very thin layer of PMMA-b-PSBMA on top of the PVDF. As shown in Figure 9, the XPS C1s spectrum of the second porous membrane 3-1 (PVDF thin film after the contact process) clearly showed signals originating from PBMA-b-PSBMA and PVDF, indicating that the second porous membrane 3-1 is coated with a very thin layer of PBMA-b-PSBMA on top of the PVDF.

[0120] The integral value of the peak originating from CF2 of PVDF around 291 eV was set to 1. The integral value of the peak originating from CF2 of PVDF was subtracted from the integral value of the CH2 of PVDF and the carbon of PMMA-b-PSBMA around 286 eV by 1, and the remaining value was taken as the total amount of carbon in PMMA-b-PSBMA. From this total amount, the composition ratio of MMA and PSBMA in PMMA-b-PSBMA was calculated from the number-average molecular weight of the PMMA-b-PSBMA skeleton and the molecular weight of the constituent monomers. Based on this composition ratio, the relative abundance (theoretical abundance) of PVDF and PMMA-b-PSBMA on the surface of the second porous membrane was calculated from the total amount of carbon in PMMA-b-PSBMA. The theoretical abundance was similarly calculated for other porous membranes. The results are shown in Tables 1-2.

[0121] <Contact angle of hexadecan in water> The contact angle of hexadecane in water on the surface of the porous membrane in each example (hereinafter also referred to as the "oil droplet in water contact angle") was measured under the conditions shown below. The results are shown in Table 3. If hexadecane oil droplets did not adhere to the porous membrane in water and the oil droplet in water contact angle could not be measured, the oil droplet in water contact angle was set to 180°. A larger oil droplet in water contact angle indicates higher hydrophilicity and superior antifouling properties.

[0122] "Contact angle measurement conditions for oil droplets in water" Water temperature: 25℃ Hexadecane oil drop volume: 6.0 μL Oil droplet: Hexadecane; Surface tension: 27.6 mN / m (25.0℃) Interfacial tension between water and hexadecane: 53.7 mN / m (25.0℃)

[0123] [Table 1]

[0124] [Table 2]

[0125] [Table 3]

[0126] The second porous membranes, 1-1, 1-1, 2-1, 2-2, 3-1, 3-2, 4-1, and 4-2, either did not allow hexadecane oil droplets to adhere in water, or had a water contact angle of 110° or more, indicating excellent hydrophilicity. The excellent hydrophilicity is thought to have been achieved by contacting the PVDF film with a liquid composition containing PMMA-b-PSBMA, which caused the PMMA chains of PMMA-b-PSBMA to adsorb onto the PVDF film, thus immobilizing the PMMA-b-PSBMA on the PVDF film. This adsorption behavior is spontaneous and forms a uniform surface, which is thought to have resulted in hydrophilicity so high that hexadecane oil droplets do not adhere to it. By bringing a PVDF film into contact with a liquid composition containing PBMA-b-PSBMA, the PVDF film can be made hydrophilic in the same way as with PMMA-b-PSBMA. When a solution containing PSBMA, a simple hydrophilic material, was coated onto a PVDF film, the hydrophilicity did not increase significantly if the coating thickness was insufficient. While a thicker coating could impart hydrophilicity, it required a large amount of PSBMA, raising concerns about clogging the pores of the porous film. Therefore, it is thought that the above phenomenon is specific to cases where block copolymers such as PMMA-b-PSBMA are used. Furthermore, if a liquid composition of PMMA-b-PSBMA is used for coating without an immersion process, the concentration of the coating solution must be high, which is economically disadvantageous. On the other hand, attempting to coat thinly results in unevenness, making it difficult to impart hydrophilicity. [Industrial applicability]

[0127] The porous membrane of the present invention is suitable as a porous membrane used in water treatment fields such as drinking water production, water purification, and wastewater treatment. In particular, hollow porous membranes and hollow fiber membrane modules using the porous membrane of the present invention are suitable for use in water treatment equipment of the membrane bioreactor (MBR) method.

Claims

1. A porous membrane comprising a film-forming polymer (A) and an amphiphilic copolymer (B), The surface of the porous membrane has a composition ratio of the film-forming polymer (A) to the amphiphilic copolymer (B) of 100:10 to 100:50, determined by X-ray photoelectron spectroscopy, and the contact angle of hexadecane in water is 100° to 180°. The aforementioned amphiphilic copolymer (B) is a block copolymer, The amphiphilic copolymer (B) comprises a constituent unit including a zwitterionic structure, The aforementioned zwitterionic structure is 3-(methacrylamino)propyl-N,N-dimethyl)ammonatopropanesulfonate (SBMA), and the membrane is porous.

2. The porous membrane according to claim 1, wherein the film-forming polymer (A) is a fluorine-containing polymer.

3. The porous membrane according to claim 1 or 2, wherein the film-forming polymer (A) is polyvinylidene fluoride.

4. The porous membrane according to claim 3, wherein the surface of the porous membrane has a ratio of 1.0:0.75 to 1.0:5.0 between the peak area at 292 eV corresponding to the film-forming polymer (A) and the peak area at 287 eV corresponding to the amphiphilic copolymer (B), as determined by X-ray photoelectron spectroscopy analysis.

5. The porous membrane according to claim 1, wherein the number-average molecular weight (Mn) of the amphiphilic copolymer (B) is 10,000 to 15,000.

6. The porous membrane according to claim 1, wherein the molecular weight distribution (Mw / Mn: weight-average molecular weight / number-average molecular weight) of the amphiphilic copolymer (B) is 1.0 to 3.

0.

7. The porous membrane according to claim 1, wherein the block copolymer is a block copolymer of methyl methacrylate and SBMA (PMMA-b-PSBMA) or a block copolymer of n-butyl methacrylate and SBMA (PBMA-b-PSBMA).

8. A method for producing a porous membrane according to any one of claims 1 to 7, A method for producing a porous membrane, comprising the step of contacting a first porous membrane containing the film-forming polymer (A) with a liquid composition containing the amphiphilic copolymer (B) and a liquid medium (C).

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