Polymer porous membrane and method for manufacturing same

Abstract

One or more embodiments of the present invention relate to a polymer porous membrane including a hydrophobic polymer porous membrane containing a hydrophobic polymer, and a crosslinked membrane of a hydrophilic polymer covering a first surface of the hydrophobic polymer porous membrane, wherein: the hydrophobic polymer contains 35% by mass or more of a constituent unit derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides; the hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymers a containing 50% by mass or more of constituent units derived from monomers containing a hydroxyl group, and hydrophilic polymers b having a polyoxyalkylene structure; and when the crosslinked membrane surface of the hydrophilic polymer is subjected to elemental analysis by SEM-EDS, the atomic composition ratio of oxygen on the first surface is 13.0 atm % or more. As a result, the present invention provides a polymer porous membrane that can be used for membrane filtration, has an improved water permeability after treating water containing impurities, and can reduce operating costs.

Description

Polymer porous membrane and method for producing the same

[0001] The present invention relates to a polymer porous membrane that can be suitably used in water treatment such as wastewater treatment and water purification, and to a method for producing the same.

[0002] Numerous water treatment methods have been developed to remove impurities contained in river water and industrial water, and membrane filtration, one of these methods, is used in many fields, such as cartridges for water purifiers and membrane units for wastewater treatment. As a filter material used in this membrane filtration method, polymer-based porous membranes can be produced in large quantities continuously with stable quality. For example, Patent Document 1 proposes a porous membrane for water treatment using a polymer containing one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides, which has excellent chemical resistance and physical strength.

[0003] International Public Gazette No. 2018 / 230330

[0004] However, the porous membrane described in Patent Document 1, when used for membrane filtration, had the problem of low permeability after treating water containing impurities, which increased operating costs.

[0005] To solve the above-mentioned problems, the present invention provides a polymer porous membrane that can be used in membrane filtration to improve the permeability after treating water containing impurities and reduce operating costs, as well as a method for producing the same.

[0006] One or more embodiments of the present invention relate to a porous polymer membrane comprising a hydrophobic polymer and a crosslinked membrane of a hydrophilic polymer covering the first surface of the hydrophobic polymer porous membrane, wherein the hydrophobic polymer contains 35% by mass or more of constituent units derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides, and the hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymer a, which contains 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b, which has a polyoxyalkylene structure, and the porous polymer membrane relates to such that when the surface of the crosslinked membrane of the hydrophilic polymer is elementally analyzed by SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy), the atomic composition ratio of oxygen on the first surface is 13.0 atm% or more.

[0007] One or more embodiments of the present invention relate to a method for producing a polymer porous membrane, comprising the steps of: obtaining a laminated polymer membrane by immersing a hydrophobic polymer porous membrane containing a hydrophobic polymer in an aqueous solution of a hydrophilic polymer to form a hydrophilic polymer membrane covering a first surface of the hydrophobic polymer porous membrane; and a crosslinking step of immersing the laminated polymer membrane in a crosslinking solution containing a crosslinking agent to form a crosslinked membrane of hydrophilic polymer, wherein the hydrophobic polymer contains 35% by mass or more of constituent units derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides; the hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymer a, which contains 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b, which has a polyoxyalkylene structure; and in the crosslinking step, the temperature of the crosslinking solution is 50°C or higher.

[0008] According to one or more embodiments of the present invention, it is possible to provide a polymer porous membrane that improves the permeability after treating water containing impurities and reduces operating costs. Furthermore, according to the manufacturing method of one or more embodiments of the present invention, it is possible to obtain a polymer porous membrane that improves the permeability after treating water containing impurities and reduces operating costs.

[0009] The inventors of the present invention have diligently studied how to improve the water permeability of a porous polymer membrane when used for membrane filtration, using a hydrophobic polymer containing 35% by mass or more of constituent units derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides. As a result, they found that by coating the surface of a porous polymer membrane containing a hydrophobic polymer containing 35% by mass or more of the halogen-containing monomer constituent units with a crosslinked membrane of one or more hydrophilic polymers selected from the group consisting of hydrophilic polymer a containing 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b having a polyoxyalkylene structure, and by setting the atomic composition ratio of oxygen on the first surface of the crosslinked membrane of the hydrophilic polymer to 13.0 atm% or more, the amount of water that can be treated after processing water containing impurities can be improved, and operating costs can be reduced. By setting the atomic composition ratio of oxygen on the first surface of the hydrophilic polymer crosslinked membrane to 13.0 atm% or higher, the degree of coating of the first surface of the hydrophobic polymer porous membrane by the hydrophilic polymer crosslinked membrane is increased. When the first surface is used as the inflow surface of the polymer porous membrane for membrane filtration, it is expected that impurities such as organic matter and microorganisms will be less likely to adhere to the first surface of the polymer porous membrane, and the permeability after treating water containing impurities such as organic matter and microorganisms will improve. In this specification, the "atomic composition ratio of oxygen" is measured by elemental analysis of the first surface of the hydrophilic polymer crosslinked membrane using SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy), and specifically, it can be measured as described in the examples. In this specification, "first surface" means the surface of the hydrophobic polymer porous membrane or the polymer porous membrane on the inflow side of the filter target.

[0010] Furthermore, the inventors of the present invention have found that by immersing a hydrophobic polymer porous membrane in an aqueous solution of a hydrophilic polymer to form a hydrophilic polymer membrane covering the first surface of the hydrophobic polymer porous membrane, and then immersing the resulting laminated polymer membrane in a crosslinking solution containing a crosslinking agent and crosslinking it by raising the temperature of the crosslinking solution to 50°C or higher to form a crosslinked hydrophilic polymer membrane, a polymer porous membrane can be obtained in which the atomic composition ratio of oxygen on the first surface of the crosslinked hydrophilic polymer membrane is 13.0 atm% or higher.

[0011] In this specification, "hydrophobic polymer" means a polymer whose solubility in water at 25°C is less than 1000 mg / kg, and "hydrophilic polymer" means a polymer whose solubility in water at 25°C is 1000 mg / kg or more. Furthermore, in this specification, "crosslinked membrane of hydrophilic polymer" means a membrane in which the solubility of hydrophilic polymer in water is suppressed by crosslinking, and specifically means that the rate of change in the atomic composition ratio of oxygen on the surface of the membrane, measured by SEM-EDS as defined in the examples, before and after immersion in water at 25°C for 24 hours or more, is 10% or less.

[0012] In this specification, when a numerical range is indicated by "~", the numerical range includes both endpoints (upper and lower limits). For example, the numerical range "X~Y" includes both endpoints, X and Y. Furthermore, when multiple numerical ranges are described in this specification, the range shall include numerical ranges formed by appropriately combining the upper and lower limits of different numerical ranges. Furthermore, when multiple upper and lower limits of a numerical range are described separately in this specification, the range shall include numerical ranges formed by appropriately combining the upper and lower limits.

[0013] In one or more embodiments of the present invention, a "porous membrane" means a membrane having a large number of pores inside, in which these pores are connected, and through which a gas or liquid can pass from one surface to the other. In one or more embodiments of the present invention, the internal structure of the porous membrane can be confirmed by observing a cross-section parallel to the thickness direction of the porous membrane with a scanning electron microscope.

[0014] (Porous polymer membrane) The porous polymer membrane includes a porous polymer membrane containing a hydrophobic polymer, and a crosslinked membrane of a hydrophilic polymer covering the first surface of the porous polymer membrane. The hydrophilic polymer membrane may cover not only the first surface of the porous polymer membrane but also the surface opposite to the first surface of the porous polymer membrane. Furthermore, the porous polymer membrane has a large number of pores inside, and it is desirable that the crosslinked membrane of the hydrophilic polymer covers not only the surface of the porous polymer membrane (the first surface and the surface opposite to the first surface) but also the surface of the pores.

[0015] The hydrophobic polymer porous membrane contains a hydrophobic polymer. In the hydrophobic polymer porous membrane, the content of the hydrophobic polymer is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The hydrophobic polymer porous membrane may consist of 100% by mass of the hydrophobic polymer.

[0016] The hydrophobic polymer may contain 35% by mass or more of constituent unit A derived from one or more halogen-containing monomers (hydrophobic monomers) selected from the group consisting of vinyl halides and vinylidene halides, and is not particularly limited, but for example, from the viewpoint of chemical resistance, it is preferable to contain 40% by mass or more of constituent unit A, and more preferably 45% by mass or more. The hydrophobic polymer may also contain 85% by mass or less, 80% by mass or less, 75% by mass or less, or 70% by mass or less of constituent unit A.

[0017] Examples of the vinyl halogenate include vinyl chloride and vinyl bromide. Examples of the vinylide halogenate include vinylidene chloride and vinylidene bromide.

[0018] The hydrophobic polymer may consist only of constituent unit A, but from the viewpoint of strength, it is preferable to include constituent unit B derived from acrylonitrile (hydrophobic monomer) in addition to constituent unit A. From the viewpoint of fouling resistance, the hydrophobic polymer preferably contains 15% by mass or more of constituent unit B, preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, even more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 45% by mass or more. The hydrophobic polymer may also contain 65% by mass or less, 60% by mass or less, or 55% by mass or less of constituent unit B.

[0019] The hydrophobic polymer preferably contains 35 to 85% by mass of constituent unit A and 15 to 65% by mass of constituent unit B, more preferably 40 to 80% by mass of constituent unit A and 20 to 60% by mass of constituent unit B, even more preferably 45 to 75% by mass of constituent unit A and 25 to 55% by mass of constituent unit B, and still more preferably 45 to 70% by mass of constituent unit A and 30 to 55% by mass of constituent unit B. The hydrophobic polymer preferably contains a total of 50% by mass or more of constituent unit A and constituent unit B, which are constituent units derived from hydrophobic monomers.

[0020] In addition to constituent units A and B, the hydrophobic polymer may also contain constituent unit C derived from a vinyl monomer (hydrophilic monomer) having an ionic substituent, from the viewpoint of fouling resistance. The hydrophobic polymer preferably contains 10% by mass or less of constituent unit C, and may contain 0.1 to 9% by mass, 0.2 to 8% by mass, 0.3 to 7% by mass, 0.4 to 6% by mass, 0.5 to 5% by mass, or 1 to 3% by mass. More specifically, the hydrophobic polymer preferably contains 35 to 85% by mass of constituent unit A, 15 to 65% by mass of constituent unit B, and 0 to 10% by mass of constituent unit C; more preferably contains 39.5 to 80% by mass of constituent unit A, 19.5 to 60% by mass of constituent unit B, and 0.5 to 5% by mass of constituent unit C; even more preferably contains 44 to 75% by mass of constituent unit A, 24 to 55% by mass of constituent unit B, and 1 to 3% by mass of constituent unit C; and still more preferably contains 44 to 70% by mass of constituent unit A, 29 to 55% by mass of constituent unit B, and 1 to 3% by mass of constituent unit C.

[0021] The vinyl monomer having the ionic substituent is not particularly limited, and various vinyl monomers having different ionic substituents can be used. The ionic substituent may be anionic or cationic. Furthermore, the ionic substituent can be of the strongly electrolytic type, which has a degree of ionization of 99% or more in water, or of the weakly electrolytic type, which has a degree of ionization of less than 99% in water. The strongly electrolytic type anionic substituent is not particularly limited, but examples include sulfonic acid groups. The weakly electrolytic type anionic substituent is not particularly limited, but examples include carboxylic acid groups and phosphoric acid groups. The strongly electrolytic type cationic substituent is not particularly limited, but examples include ammonium groups, phosphonium groups, and onium groups such as sulfonium groups. The weakly electrolytic type cationic substituent is not particularly limited, but examples include primary to tertiary amino groups, pyridyl groups, and imino groups.

[0022] The vinyl monomer having the ionic substituent is preferably a vinyl monomer having a strongly electrolytic anionic substituent, and more preferably a vinyl monomer containing a sulfonic acid group. The vinyl monomer containing the sulfonic acid group is not particularly limited, but examples include allyl sulfonic acid, methallyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonic acid, 2-methyl-1,3-butadiene-1-sulfonic acid, and salts thereof (such as sodium salts).

[0023] The vinyl monomer having the ionic substituent may be used individually or in combination of two or more types.

[0024] The hydrophobic polymer may contain, as appropriate, other monomers in addition to constituent units A, B, and C. The other monomers may be hydrophobic monomers or hydrophilic monomers, and are preferably hydrophilic monomers such as unsaturated carboxylic acids such as (meth)acrylic acid and their salts; esters of unsaturated carboxylic acids such as methyl (meth)acrylate and glycidyl (meth)acrylate; and vinyl esters such as vinyl acetate and vinyl butyrate. In the hydrophobic polymer, the content of constituent units derived from other monomers may be 20% by mass or less, 10% by mass or less, or 5% by mass or less.

[0025] The hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymer a, which contains 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b, which has a polyoxyalkylene structure.

[0026] In the hydrophilic polymer a, the monomer containing a hydroxyl group is not particularly limited, but examples include hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and glycerol (meth)acrylate; ε-caprolactone modified forms of hydroxyl group-containing (meth)acrylates such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; (meth)acrylates having polyoxyethylene chains with hydroxyl groups at the molecular termini; hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide; allyl alcohol; and vinyl alcohol (as a precursor, vinyl carboxylate esters such as vinyl acetate). In this specification, (meth)acrylate is a general term for methacrylate and acrylate, and (meth)acrylic is a general term for methacrylic and acrylic.

[0027] The hydrophilic polymer a may contain constituent units derived from other monomers in addition to constituent units derived from monomers containing hydroxyl groups. Other monomers are not particularly limited, as long as they are monomers copolymerizable with monomers containing a hydroxyl group, but examples include α-olefins such as ethylene, propylene, and butylene; (meth)acrylic acid and its salts; (meth)acrylic acid esters such as methyl (meth)acrylate and ethyl (meth)acrylate; (meth)acrylamide compounds such as (meth)acrylamide and N-methyl(meth)acrylamide; N-vinyllactam compounds such as N-vinylpyrrolidone; N-vinylamide compounds such as N-vinylformamide and N-vinylacetamide; vinyl ether compounds such as allyl ethers having polyalkylene oxides in their side chains and methyl vinyl ether; nitrile compounds such as acrylonitrile; and unsaturated carboxylic acids such as (meth)acrylic acid, fumaric acid, crotonic acid, itaconic acid, and (meth)acrylic acid, as well as unsaturated dicarboxylic acid compounds such as their salts, anhydrides, and esters.

[0028] From the viewpoint of hydrophilicity, the hydrophilic polymer a preferably contains 60 to 100% by mass of constituent units derived from monomers containing hydroxyl groups and 0 to 40% by mass of constituent units derived from other monomers, more preferably 70 to 100% by mass of constituent units derived from monomers containing hydroxyl groups and 0 to 30% by mass of constituent units derived from other monomers, even more preferably 80 to 100% by mass of constituent units derived from monomers containing hydroxyl groups and 0 to 20% by mass of constituent units derived from other monomers, even more preferably 90 to 100% by mass of constituent units derived from monomers containing hydroxyl groups and 0 to 10% by mass of constituent units derived from other monomers, and may consist of 100% by mass of constituent units derived from monomers containing hydroxyl groups.

[0029] From the viewpoint of hydrophilicity, the hydrophilic polymer a is preferably a polyvinyl alcohol-based resin containing 50% by mass or more of constituent units derived from vinyl alcohol as constituent units derived from monomers containing hydroxyl groups.

[0030] The polyvinyl alcohol-based resin is not particularly limited as long as it contains 50% by mass or more of constituent units derived from vinyl alcohol, and may also contain constituent units derived from other monomers as described above in addition to the constituent units derived from vinyl alcohol. From the viewpoint of hydrophilicity, the polyvinyl alcohol-based resin preferably contains 60 to 100% by mass of constituent units derived from vinyl alcohol and 0 to 40% by mass of constituent units derived from other monomers, more preferably contains 70 to 100% by mass of constituent units derived from vinyl alcohol and 0 to 30% by mass of constituent units derived from other monomers, even more preferably contains 80 to 100% by mass of constituent units derived from vinyl alcohol and 0 to 20% by mass of constituent units derived from other monomers, and still more preferably contains 90 to 100% by mass of constituent units derived from vinyl alcohol and 0 to 10% by mass of constituent units derived from other monomers, and is particularly preferably polyvinyl alcohol consisting of 100% by mass of constituent units derived from vinyl alcohol.

[0031] The average degree of polymerization of the polyvinyl alcohol-based resin is not particularly limited, but from the viewpoint of uniformity of the crosslinked film of the hydrophilic polymer, it is preferably 500 or more, more preferably 500 to 5000, even more preferably 750 to 4000, and even more preferably 900 to 3000. In this specification, the average degree of polymerization of the polyvinyl alcohol-based resin can be measured in accordance with JIS K 6726.

[0032] From the viewpoint of hydrophilicity, the degree of saponification of the polyvinyl alcohol-based resin is preferably 88 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more. In this specification, the degree of saponification of the polyvinyl alcohol-based resin can be measured in accordance with JIS K 6726.

[0033] The aforementioned polyvinyl alcohol-based resin can also be obtained by saponifying polyvinyl acetate, or by saponifying a copolymer of vinyl acetate and the other monomers mentioned above.

[0034] The hydrophilic polymer b preferably has a polyoxyalkylene structure represented by the following general formula 1: [General formula 1] -(R1-O)n- However, in the general formula 1, R1 is an alkylene group having 1 or more carbon atoms, n is 2 or more, and multiple R1s may be the same alkylene group or alkylene groups with different carbon atoms. In the general formula 1, the number of carbon atoms of R1 is preferably 2 or more, more preferably 2 to 6, even more preferably 2 to 5, even more preferably 2 to 4, and even more preferably 2 to 3. In the general formula 1, n is preferably 3 to 500, and even more preferably 3 to 100. More specifically, the polyoxyalkylene structure may be a polyoxyethylene structure, a polyoxypropylene structure, and a copolymer structure of ethylene oxide and propylene oxide.

[0035] From the viewpoint of hydrophilicity, the hydrophilic polymer b is preferably a polyalkylene glycol, more preferably a polyalkylene glycol having 2 to 6 carbon atoms in the alkylene group, even more preferably one or more selected from the group consisting of polyethylene glycol, polypropylene glycol, and polybutylene glycol, even more preferably one or more selected from the group consisting of polyethylene glycol and polypropylene glycol, and even more preferably polyethylene glycol.

[0036] The hydrophilic polymers described above may be used individually or in combination of two or more. Preferably, the hydrophilic polymers are one or more selected from the group consisting of polyvinyl alcohol-based resins and polyalkylene glycols.

[0037] In the aforementioned porous polymer membrane, the average pore size of the cross-linked membrane surface of the hydrophilic polymer is not particularly limited, but from the viewpoint of excellent water permeability after treating water containing impurities in membrane filtration, the average pore size of the first surface of the cross-linked membrane of the hydrophilic polymer is preferably 3 to 160 nm, more preferably 3 to 100 nm, and even more preferably 3 to 50 nm. Furthermore, in this specification, the average pore size can be measured as described in the examples.

[0038] Although the polymer porous membrane is not particularly limited, for example, from the viewpoint of filtration performance and water permeability, the thickness is preferably 0.01 to 1 mm, more preferably 0.05 to 0.5 mm.

[0039] The shape of the polymer porous membrane is not limited, and any shape can be selected according to specific applications and purposes, for example, hollow fiber shape, flat membrane shape, spiral shape, pleated shape, tubular shape, and the like. Among these, hollow fiber shape and flat membrane shape are preferred from the viewpoints of easy production, low cost, and usability at low pressure.

[0040] From the viewpoint of excellent water permeability after treating water containing impurities in membrane filtration, when an aqueous 50 ppm sodium alginate solution obtained by dissolving sodium alginate in an aqueous 0.5 mM sodium hydrogen carbonate solution is passed through the polymer porous membrane for 30 minutes, the water permeability (hereinafter also referred to as water permeability after fouling) is 1000 L / (m 2 ・atm・h) or more, preferably 1100 L / (m 2 ・atm・h) or more, more preferably 1200 L / (m 2 ・atm・h) or more, still more preferably 1300 L / (m 2 ・atm・h) or more, even more preferably 1400 L / (m 2 ・atm・h) or more. In the present specification, the water permeability after fouling can be specifically measured as described in the Examples.

[0041] From the viewpoint of excellent initial water permeability, the polymer porous membrane has an initial water permeability of 5000 L / (m 2 ・atm・h) or more, preferably 5500 L / (m 2 ・atm・h) or more, more preferably 6000 L / (m 2 ・atm・h) or more, still more preferably 6500 L / (m 2 ・atm・h) or more. In the present specification, the initial water permeability can be specifically measured as described in the Examples.

[0042] (Method for producing a polymer porous membrane) In one or more embodiments of the present invention, the method for producing a polymer porous membrane includes a step of obtaining a laminated polymer membrane (hereinafter also referred to as step A), and a crosslinking step of forming a crosslinked membrane of a hydrophilic polymer (hereinafter also referred to as step B).

[0043] In step A, a laminated polymer film is obtained by immersing a hydrophobic polymer porous film containing a hydrophobic polymer in an aqueous solution of a hydrophilic polymer to form a hydrophilic polymer film that covers the first surface of the hydrophobic polymer porous film. The hydrophilic polymer film may cover not only the first surface of the hydrophobic polymer porous film, but also the surface opposite the first surface (i.e., the surface on which the filtered material flows out) and the surface of the internal pores. The hydrophobic polymer and hydrophilic polymer described above can be used, and redundant explanations are omitted.

[0044] The content (concentration) of the hydrophilic polymer in the aqueous solution of the hydrophilic polymer is not particularly limited, but is preferably 0.01 to 4% by mass, more preferably 0.01 to 2% by mass, and even more preferably 0.05 to 1.5% by mass. If the content of the hydrophilic polymer is too high, the thickness of the coating film becomes a problem and blocks the pores, which reduces the water permeability and is undesirable. On the other hand, if the content of the hydrophilic polymer is too low, sufficient hydrophilicity cannot be obtained, which is also undesirable.

[0045] The amount of aqueous solution of the hydrophilic polymer used is not particularly limited, as long as it is sufficient to immerse the hydrophobic polymer porous membrane. For example, from the viewpoint of forming a uniform coating film, the ratio L1 / W1 of the volume L1 (mL) of the aqueous solution of the hydrophilic polymer to the mass W1 (g) of the hydrophobic polymer porous membrane may be 1 to 1000 mL / g, 2 to 500 mL / g, or 3 to 100 mL / g.

[0046] The immersion time of the hydrophobic polymer porous membrane in the aqueous solution of the hydrophilic polymer is not particularly limited, but for example, from the viewpoint of forming a uniform coating film, it may be 0.5 minutes to 6 hours, 0.5 to 1 hour, or 0.5 minutes to 10 minutes.

[0047] From the viewpoint of obtaining a polymer porous membrane with improved water permeability, the average pore size of the first surface of the hydrophobic polymer porous membrane is preferably 3 to 160 nm, more preferably 3 to 100 nm, and even more preferably 3 to 50 nm.

[0048] In the hydrophobic polymer porous membrane, from the viewpoint of easily obtaining a polymer porous membrane with improved water permeability, the porosity of the first surface is preferably 0.5 to 30%, more preferably 0.5 to 20%, and even more preferably 1 to 20%.

[0049] The hydrophobic polymer porous membrane is not particularly limited, but it is preferably 0.01 to 1 mm thick, and more preferably 0.05 to 0.5 mm thick. A thickness of 0.01 mm or more makes it less prone to defects such as cracking and improves filtration performance, while a thickness of 1 mm or less improves water permeability.

[0050] The shape of the hydrophobic polymer porous membrane is not limited, and any shape can be selected depending on the specific application and purpose, such as hollow fiber, flat film, spiral, pleated, and tubular. Among these, hollow fiber and flat film shapes are preferred from the viewpoint of being easy to manufacture, low cost, and usable at low pressure.

[0051] The hydrophobic polymer porous membrane can be obtained by processing a hydrophobic polymer by any method. Examples of film formation methods include thermally induced phase separation, non-solvent-induced phase separation, and stretching. Among these, the non-solvent-induced phase separation method is preferred from the viewpoint of a simple manufacturing process and low cost.

[0052] In the non-solvent-induced phase separation method, a hydrophobic polymer porous membrane can be obtained by contacting a hydrophobic polymer solution containing a hydrophobic polymer, a porosity-opening agent, and a good solvent with a coagulation solution containing a non-solvent and allowing it to coagulate, similar to known methods.

[0053] The good solvent is not particularly limited as long as it is capable of dissolving the hydrophobic polymer, but examples include dimethyl sulfoxide, dimethylacetamide, dimethylformamide, and acetone.

[0054] Examples of the pore-opening agent include water-soluble metal compounds and hydrophilic polymers. Examples of water-soluble metal compounds include metal halides, acetates, and nitrates of alkali metals and alkaline earth metals, and more specifically, sodium chloride, lithium chloride, sodium acetate, and calcium nitrate. Examples of hydrophilic polymers used as pore-opening agents include polyethylene glycol and polyvinylpyrrolidone. The degree of polymerization of polyethylene glycol is not particularly limited, but for example, a degree of polymerization of about 100 to 5000 can be preferably used.

[0055] As the non-solvent, any solvent that does not dissolve the hydrophobic polymer and is miscible with the good solvent can be used as appropriate. Examples include water, methanol, and ethanol, with water being preferred.

[0056] The hydrophobic polymer solution can be prepared, for example, by mixing the hydrophobic polymer, an aqueous solution of the pore-opening agent (a water-soluble metal compound or a hydrophilic polymer), and the good solvent. In the hydrophobic polymer solution, the concentration of the hydrophobic polymer can be appropriately selected according to the pore size and water permeability of the target hydrophobic polymer porous membrane, and is not limited, but is preferably 5 to 30% by mass, more preferably 8 to 20% by mass. When the concentration of the hydrophobic polymer is within the above range, the processability during film formation and the strength of the resulting hydrophobic polymer porous membrane are improved.

[0057] The temperature of the coagulation solution is not particularly limited and may be, for example, 25 to 75°C. This makes it easier to obtain a polymer porous membrane with improved water permeability by adjusting the average pore size and porosity. The coagulation solution preferably contains 50% by mass or more of water, more preferably 70% by mass or more, and particularly preferably 90% by mass or more. The coagulation solution used during film formation may contain the above-mentioned good solvent in addition to water, but it may also be a water bath consisting of 100% by mass of water.

[0058] After solidification, the hydrophobic polymer porous membrane may be washed with water at 5°C or higher. The water temperature may be 10 to 80°C, or 20 to 70°C. After washing, the hydrophobic polymer porous membrane may be dried as needed. If the hydrophobic polymer porous membrane is dried, it is desirable to thoroughly wet it with water before using it in step A.

[0059] More specifically, the hydrophobic polymer porous membrane can be obtained, for example, by applying the copolymer solution prepared as described above to a support using an applicator, then coagulating and washing it with water as described above. If necessary, drying may be performed after washing with water. As the support, filter paper made of cellulose fibers can be used. In such a hydrophobic polymer porous membrane, the side opposite the support such as filter paper becomes the side into which the material to be filtered flows, and the surfaces of the hydrophobic polymer porous membrane and the polymer porous membrane on the side opposite the support such as filter paper become the first surfaces of the hydrophobic polymer porous membrane and the polymer porous membrane, respectively.

[0060] In step B, the laminated polymer film obtained in step A is immersed in a crosslinking solution containing a crosslinking agent to form a crosslinked film of hydrophilic polymer and obtain a porous polymer film. The laminated polymer film obtained in step A may, if necessary, be immersed in a crosslinking solution containing a crosslinking agent after removing any excess aqueous solution of hydrophilic polymer (used to form the hydrophilic polymer film).

[0061] In step B (crosslinking step), the temperature of the crosslinking solution is 50°C or higher. This results in an oxygen atomic composition ratio of 13.0 atm% or higher on the surface of the resulting hydrophilic polymer crosslinked film. The temperature of the crosslinking solution is preferably 55°C or higher, and more preferably 60°C or higher.

[0062] The crosslinking agent is not particularly limited and can be any agent capable of crosslinking the hydrophilic polymer used for forming the hydrophilic polymer film described above. For example, from the viewpoint of crosslinking properties, one or more selected from the group consisting of aldehyde compounds, methylol compounds, epoxy compounds, carboxylic acid-based crosslinking agents, isocyanate compounds, and metal compounds can be suitably used.

[0063] Examples of aldehyde compounds include monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, and butyraldehyde, as well as dialdehydes such as glyoxal, malondialdehyde, succinidaldehyde, glutaraldehyde, maleidaldehyde, and terephthalaldehyde.

[0064] Examples of methylol compounds include methylol urea, methylol melamine, alkylated methylol urea, and alkylated methylolated melamine.

[0065] Examples of epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diglycidylamine, and bisphenol A diglycidyl ether.

[0066] As carboxylic acid-based crosslinking agents, compounds having two or more carboxyl groups in one molecule can be used as appropriate. Examples include dicarboxylic acids such as succinic acid, glutaric acid, and adipic acid, hydroxyl group-containing dicarboxylic acids such as malic acid, tartaric acid, and citric acid, and polycarboxylic acids such as polyacrylic acid.

[0067] Examples of isocyanate compounds include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and methyl 2,6-diisocyanatohexanoate.

[0068] Examples of metal compounds include divalent or higher metal salts and oxides thereof of magnesium, calcium, aluminum, iron, nickel, titanium, aluminum, zirconium, tin, vanadium, chromium, copper, and cobalt.

[0069] The crosslinking agents described above may be used individually or in combination of two or more. Among these crosslinking agents, dialdehydes such as glutaraldehyde are preferred.

[0070] A crosslinking solution can be obtained by dissolving the crosslinking agent in water. In the crosslinking solution, the content (concentration) of the crosslinking agent is not particularly limited, as long as it is sufficient to crosslink the hydrophilic polymer used to form the hydrophilic polymer film. For example, from the viewpoint of crosslinkability, it may be 0.05 to 20% by mass, 0.1 to 10% by mass, or 0.2 to 10% by mass.

[0071] From the viewpoint of suppressing the elution of hydrophilic polymers used to form hydrophilic polymer films such as polyvinyl alcohol-based resins, the crosslinking liquid preferably further contains one or more inorganic salts selected from the group consisting of sodium sulfate and ammonium sulfate, and more preferably contains sodium sulfate.

[0072] In the crosslinking solution, the content (concentration) of the inorganic salt may be 10 to 35% by mass, 15 to 30% by mass, or 20 to 25% by mass, from the viewpoint of suppressing the elution of hydrophilic polymers.

[0073] The amount of crosslinking solution used is not particularly limited, as long as it is sufficient to immerse the laminated polymer film. However, from the viewpoint of forming a uniform coating film, for example, the ratio L2 / W2 of the volume of the crosslinking solution to the mass W2 (g) of the laminated polymer film may be 1 to 1000 mL / g, 2 to 500 mL / g, or 3 to 100 mL / g.

[0074] In step B (crosslinking step), the time for the crosslinking reaction is not particularly limited, but for example, from the viewpoint of sufficiently completing the crosslinking reaction and increasing industrial productivity, it is preferably 0.5 to 180 minutes, more preferably 0.5 to 60 minutes, and even more preferably 1 to 30 minutes.

[0075] After step B, the resulting polymer porous membrane may be washed with water to remove any remaining crosslinking solution. In the washing step, for example, water at 5°C or higher can be used, and the water temperature may be 10 to 80°C, or 20 to 70°C.

[0076] A drying step may be included after the washing step as needed. Drying may be done, for example, by heating air. The temperature of the heated air may be 30 to 80°C or 40 to 60°C. The drying time may be, for example, 1 minute to 5 hours, 2 minutes to 3 hours, or 5 minutes to 15 minutes.

[0077] The aforementioned porous polymer membrane can be suitably used to remove impurities contained in various treated waters, such as river water and industrial water. For example, it can be used as a filter material in water purifier cartridges or membrane units for wastewater treatment.

[0078] The present invention will be described in detail below based on examples. However, the present invention is not limited to these examples. Unless otherwise specified, the operations are performed at room temperature (20 ± 5°C).

[0079] (Manufacturing Example 1) <Manufacturing of Hydrophilic Polymer Solution: Polyvinyl Alcohol> 5 g of polyvinyl alcohol (vinyl alcohol homopolymer, average degree of polymerization: 1500-1800, degree of saponification: 86-90 mol%) was dissolved in 995 g of pure water to prepare an aqueous solution of polyvinyl alcohol with a concentration of 0.5% by mass (hereinafter also referred to as PVA aqueous solution).

[0080] (Manufacturing Example 2) <Manufacturing of Hydrophilic Polymer Solution: Polyethylene Glycol 200> 5 g of polyethylene glycol 200 (manufactured by Wako Pure Chemical Industries, Ltd., number average molecular weight 180-220) was dissolved in 995 g of pure water to prepare a polyethylene glycol aqueous solution with a concentration of 0.5% by mass (hereinafter also referred to as PEG aqueous solution).

[0081] (Manufacturing Example 3) <Preparation of Crosslinking Solution> 200 g of 25% glutaraldehyde solution and 200 g of sodium sulfate were weighed and placed in a 2 L beaker. Pure water was added while adjusting the pH to 2 with 1 mol / L sulfuric acid, and the total mass was adjusted to 1000 g to prepare a glutaraldehyde crosslinking solution with a concentration of 5% by mass (hereinafter referred to as GA crosslinking solution).

[0082] (Reference Example 1) <Production of Hydrophobic Polymer Porous Membrane> Copolymer 1, comprising 48.0% by mass of constituent units derived from vinyl chloride, 50.5% by mass of constituent units derived from acrylonitrile, and 1.5% by mass of constituent units derived from sodium styrene sulfonate, was synthesized by emulsion polymerization. The solubility of copolymer 1 in water at 25°C was 680 mg / kg. 60 g of copolymer 1, 30 g of an aqueous solution of calcium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (calcium chloride concentration 10% by mass), and 510 g of dimethyl sulfoxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed to obtain a copolymer solution. The obtained copolymer solution was applied to filter paper (Advantec Toyo No. 2 qualitative filter paper) using an applicator with a gap of 200 μm, solidified in a 60°C water bath (coagulation solution), and then washed with 20°C water to obtain a hydrophobic polymer porous membrane.

[0083] (Example 1) 1 g of a hydrophobic polymer porous membrane (10 cm long, 10 cm wide) obtained in the same manner as in Reference Example 1 was immersed for 5 minutes in 100 mL of the PVA aqueous solution obtained in Production Example 1 (concentration: 0.5% by mass, temperature: room temperature (20 ± 5°C)) to allow the PVA aqueous solution to permeate the hydrophobic polymer porous membrane, coating the first surface of the hydrophobic polymer porous membrane (the surface opposite the filter paper side) with PVA to obtain a laminated polymer membrane. At this time, the surface opposite the first surface of the hydrophobic polymer porous membrane (i.e., the surface on the filter paper side) and the surface of the internal pores are also coated with PVA. After that, the laminated polymer membrane was removed and excess PVA aqueous solution adhering to the surface was brushed off. The laminated polymer membrane was then immersed in 100 mL of the GA crosslinking solution (concentration: 5% by mass) obtained in Production Example 3, and a crosslinking reaction was carried out at the temperature and time shown in Table 1 below to form a PVA crosslinked membrane and obtain a polymer porous membrane. Note that the crosslinking temperature shown in Table 1 below is the temperature of the GA crosslinking solution.

[0084] (Examples 2-3, Comparative Examples 1-4) Polymer porous films were obtained in the same manner as in Example 1, except that the temperature and time of the crosslinking reaction were as shown in Table 1 below.

[0085] (Example 4) In the same manner as in Example 1, a hydrophilic polymer (PEG) was coated onto the first surface (the surface opposite the filter paper) of the hydrophobic polymer porous membrane to obtain a laminated polymer membrane. However, the PEG aqueous solution prepared in Production Example 2 (concentration: 0.5% by mass, temperature: 70°C) was used as the hydrophilic polymer aqueous solution, and the immersion time was 5 minutes. After that, a crosslinking reaction was carried out in the same manner as in Example 1 to form a PEG crosslinked membrane and obtain a polymer porous membrane. However, the concentration of the GA crosslinking solution was 1% by mass, the reaction temperature was 70°C, and the reaction time was 10 minutes.

[0086] The initial water permeability and water permeability after fouling of the hydrophobic polymer porous membrane obtained in the reference example, as well as the polymer porous membranes obtained in the examples and comparative examples, were measured and evaluated as follows. Furthermore, the oxygen element concentration on the first surface of the hydrophobic polymer porous membrane obtained in the reference example, as well as the polymer porous membranes obtained in the examples and comparative examples, was measured and evaluated as follows. Additionally, the average pore diameter and porosity of the first surface of the hydrophobic polymer porous membrane obtained in the reference example, as well as the hydrophobic polymer porous membranes obtained in the examples and comparative examples, were measured and calculated as follows. The results are shown in Table 1 below. In the hydrophobic polymer porous membrane obtained in the reference example, as well as the polymer porous membranes obtained in the examples and comparative examples, the surface of the hydrophobic polymer porous membrane or polymer porous membrane on the side opposite the filter paper side is considered the first surface.

[0087] (Initial water permeability) A hydrophobic polymer porous membrane or polymer porous membrane is cut into a 3 cm x 3 cm section to be used as a sample, with the first surface being the side into which the material to be filtered flows, and the effective membrane area being 9 cm². 2 A cross-flow module for flat membranes (3 cm x 3 cm) was used, and ultrapure water was passed through it under conditions of a flow rate of 34 mL / min and a pressure of 0.01 MPa (0.1 atm). The permeability was calculated using Equation 1 below and was defined as the initial permeability. In Equation 1 below, V represents the volume of ultrapure water that permeated the membrane (L), and A represents the effective area of ​​the membrane (m²). 2 The formula shows the rate of water permeability (L / m³), where P represents water pressure (atm) and Δt represents the measurement time (h). [Formula 1] Water permeability (L / m³)2 ・atm・h)=V / (A×P×Δt)

[0088] (Permeability after fouling) Permeability after fouling was measured using a dead-end module following the procedure below. A hydrophobic polymer porous membrane or polymer porous membrane was cut into 3 cm x 3 cm sections to be used as a sample, with an effective membrane area of ​​9 cm². 2 A flat membrane module measuring 3 cm x 3 cm was set with the first surface facing the side into which the material to be filtered flows. A 50 ppm aqueous solution of sodium alginate (test solution), prepared by dissolving sodium alginate in a 0.5 mM sodium bicarbonate aqueous solution, was passed through the membrane at a flow rate of 5 mL / min using a dead-end method for 40 minutes. The pressure P on the membrane was measured over time, and the permeability after 30 minutes was calculated using the above-mentioned formula 1, which was then used as the permeability after fouling.

[0089] (Average pore size and porosity) The hydrophobic polymer porous membrane obtained in the reference example or the polymer porous membrane obtained in the examples and comparative examples was dried in a 40°C forced-air constant-temperature oven for 3 hours, and then the pores on the membrane surface (first surface) were observed using a scanning electron microscope (Hitachi High-Tech S-4800). When observing the pores on the membrane surface (first surface) with the scanning electron microscope (Hitachi High-Tech S-4800), images were acquired at 5,000x and 50,000x magnification. If the estimated pore size was less than 50 nm, the 50,000x image was used to calculate the average pore size and porosity; if it was 50 nm or more, the 5,000x image was used. Image analysis was performed using WinROOF2018 (Mitani Corporation). After setting the image resolution and length per pixel in WinROOF, the analysis range was specified. For the 5,000x magnification image, the analysis range was set to 10 μm square, and for the 50,000x magnification image, to 1 μm square, selecting areas without defects or other abnormalities and with average pore conditions. After checking the luminance histogram in the specified analysis range, the image brightness was adjusted so that the average luminance value of the entire analysis range was between 95 and 105. To enhance the color of the image, the color density distribution of the analysis range was transformed and adjusted so that 99.95% of the range was spread throughout the entire image. The adjusted image was converted to a monochrome image, the brightness was set to +20 and the contrast to +50, and then black and white binarization was performed in the range of 0 to 60. After five morphological processes—(1) degeneracy (1 time), (2) isolated point removal (bright points), (3) exclusive expansion (1 time), (4) closing, and (5) hole filling—the area of ​​each measurement site (black area corresponding to voids) was calculated. After calculating the area, measurement points overlapping the boundary of the analysis range were removed, and the equivalent circle diameter was calculated based on the area of ​​the remaining individual measurement points. In addition, the open area ratio was calculated using the following formula 2. <Method for calculating average hole diameter> The average value of the equivalent circle diameter of each measurement point in the entire analysis range was used as the average hole diameter. <Method for calculating open area ratio> [Formula 2] Open area ratio (%) = {Sum of areas of individual measurement points / Area of ​​analysis range} × 100

[0090] (Oxygen Element Concentration) The hydrophobic polymer porous membrane obtained in the reference example, or the polymer porous membrane obtained in the examples and comparative examples, was dried in a 40°C forced-air constant-temperature oven for 3 hours. Then, the hydrophobic polymer porous membrane or polymer porous membrane was cut into 1 cm x 1 cm sections to make samples. A scanning electron microscope (JCM-6000Plus) was used to acquire 100x magnification images of the first surface of the hydrophobic polymer porous membrane or the first surface of the PVA crosslinked polymer porous membrane. The obtained field of view was irradiated with an electron beam at an accelerating voltage of 15.0 kV, and elemental analysis was performed at five arbitrary locations within the field of view to quantify the atomic composition ratio (atm%) of oxygen at each location. The average value of the five locations was taken as the atomic composition ratio (atm%) of oxygen at the first surface of the sample. The atomic composition ratio (atm%) of oxygen on the first surface of a hydrophobic polymer porous membrane or the first surface of a PVA crosslinked polymer porous membrane is the atomic composition ratio (atm%) relative to the total number of atoms of carbon, nitrogen, oxygen, and chlorine, which is 100 atm%.

[0091]

[0092] As can be seen from the data in Table 1 above, the polymer porous membrane obtained in the examples has a high water permeability after fouling, and therefore, operating costs can be reduced. In the examples, the temperature of the crosslinking solution was 50°C or higher, and the atomic composition ratio of oxygen on the first surface of the hydrophilic polymer crosslinking membrane of the obtained polymer porous membrane was 13.0 atm% or higher.

[0093] On the other hand, the polymer porous membranes obtained in Comparative Examples 1 to 4, where the crosslinking solution temperature was less than 50°C, had an oxygen atomic composition ratio of less than 13.0 atm% on the first surface of the hydrophilic polymer crosslinked membrane, resulting in low water permeability after fouling, and also lower initial water permeability than that of Reference Example 1.

[0094] The present invention is not particularly limited, but preferably includes the following embodiments: [1] A porous polymer membrane comprising a hydrophobic polymer and a crosslinked membrane of a hydrophilic polymer covering the first surface of the hydrophobic polymer porous membrane, wherein the hydrophobic polymer contains 35% by mass or more of constituent units derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides, the hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymer a, which contains 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b, which has a polyoxyalkylene structure, and when the surface of the crosslinked membrane of the hydrophilic polymer is elementally analyzed by SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy), the atomic composition ratio of oxygen on the first surface is 13.0 atm% or more. [2] The polymer porous membrane according to [1], wherein the hydrophobic polymer comprises 35 to 85% by mass of constituent units derived from the halogen-containing monomer and 15 to 65% by mass of constituent units derived from acrylonitrile. [3] The polymer porous membrane according to [1] or [2], wherein the hydrophilic polymer is one or more selected from the group consisting of polyvinyl alcohol-based resins and polyalkylene glycols. [4] The polymer porous membrane has a water permeability of 1000 L / (m³) when a 50 ppm aqueous solution of sodium alginate, obtained by dissolving sodium alginate in a 0.5 mM aqueous solution of sodium bicarbonate, is passed through it for 30 minutes. 2A polymer porous membrane according to any one of [1] to [3], wherein the temperature is 50°C or higher. [5] A method for producing a polymer porous membrane, comprising the steps of: immersing a hydrophobic polymer porous membrane containing a hydrophobic polymer in an aqueous solution of a hydrophilic polymer to form a hydrophilic polymer membrane covering the first surface of the hydrophobic polymer porous membrane to obtain a laminated polymer membrane; and crosslinking, immersing the laminated polymer membrane in a crosslinking solution containing a crosslinking agent to form a crosslinked membrane of a hydrophilic polymer, wherein the hydrophobic polymer contains 35% by mass or more of constituent units derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides; the hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymer a, which contains 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b, which has a polyoxyalkylene structure; and in the crosslinking step, the temperature of the crosslinking solution is 50°C or higher. [6] The method for producing a polymer porous membrane according to [5], wherein the crosslinking agent comprises one or more crosslinking agents selected from the group consisting of aldehyde compounds, methylol compounds, epoxy compounds, carboxylic acid-based crosslinking agents, isocyanate compounds, and metal compounds. [7] The method for producing a polymer porous membrane according to [5] or [6], wherein the crosslinking solution comprises one or more inorganic salts selected from the group consisting of sodium sulfate and ammonium sulfate. [8] The method for producing a polymer porous membrane according to any one of [5] to [7], wherein the hydrophobic polymer comprises 35 to 85% by mass of constituent units derived from the halogen-containing monomer and 15 to 65% by mass of constituent units derived from acrylonitrile. [9] The method for producing a polymer porous membrane according to any one of [5] to [8], wherein the hydrophilic polymer comprises one or more selected from the group consisting of polyvinyl alcohol-based resins and polyalkylene glycols.

Claims

1. A porous polymer membrane comprising a hydrophobic polymer containing a hydrophobic polymer, and a crosslinked membrane of a hydrophilic polymer covering the first surface of the hydrophobic polymer porous membrane, wherein the hydrophobic polymer contains 35% by mass or more of constituent units derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides, and the hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymer a, which contains 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b, which has a polyoxyalkylene structure, and the elemental analysis of the surface of the crosslinked membrane of the hydrophilic polymer by SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy) shows that the atomic composition ratio of oxygen on the first surface is 13.0 atm% or more.

2. The polymer porous membrane according to claim 1, wherein the hydrophobic polymer contains 35 to 85% by mass of constituent units derived from the halogen-containing monomer and 15 to 65% by mass of constituent units derived from acrylonitrile.

3. The polymer porous membrane according to claim 1, wherein the hydrophilic polymer is one or more selected from the group consisting of polyvinyl alcohol-based resins and polyalkylene glycols.

4. The polymer porous membrane has a water permeability of 1000 L / (m³) when a 50 ppm sodium alginate aqueous solution, obtained by dissolving sodium alginate in a 0.5 mM sodium bicarbonate aqueous solution, is passed through it for 30 minutes. 2 A polymer porous membrane according to claim 1, wherein the temperature is ≥ 0.atm·h.

5. A method for producing a polymer porous membrane, comprising the steps of: 1) immersing a hydrophobic polymer porous membrane containing a hydrophobic polymer in an aqueous solution of a hydrophilic polymer to form a hydrophilic polymer membrane covering the first surface of the hydrophobic polymer porous membrane to obtain a laminated polymer membrane; and 2) immersing the laminated polymer membrane in a crosslinking solution containing a crosslinking agent to form a crosslinked membrane of hydrophilic polymer, wherein the hydrophobic polymer contains 35% by mass or more of constituent units derived from one or more halogen-containing monomers selected from the group consisting of vinyl halides and vinylidene halides; 3) the hydrophilic polymer is one or more selected from the group consisting of hydrophilic polymer a, which contains 50% by mass or more of constituent units derived from monomers containing hydroxyl groups, and hydrophilic polymer b, which has a polyoxyalkylene structure; and 4) the temperature of the crosslinking solution is 50°C or higher in the crosslinking step.

6. The method for producing a polymer porous membrane according to claim 5, wherein the crosslinking agent comprises one or more crosslinking agents selected from the group consisting of aldehyde compounds, methylol compounds, epoxy compounds, carboxylic acid-based crosslinking agents, isocyanate compounds, and metal compounds.

7. The method for producing a polymer porous membrane according to claim 5, wherein the crosslinking solution contains one or more inorganic salts selected from the group consisting of sodium sulfate and ammonium sulfate.

8. The method for producing a polymer porous membrane according to claim 5, wherein the hydrophobic polymer contains 35 to 85% by mass of constituent units derived from the halogen-containing monomer and 15 to 65% by mass of constituent units derived from acrylonitrile.

9. The method for producing a polymer porous membrane according to claim 5, wherein the hydrophilic polymer is one or more selected from the group consisting of polyvinyl alcohol-based resins and polyalkylene glycols.

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