Porous film and purification method using same

Abstract

The porous film includes a first polymer that is soluble in N-methyl-2-pyrrolidone and insoluble in water. The first polymer has a cationic group.

Description

Porous membrane and purification method using the same

[0001] The present invention relates to a porous membrane and a purification method using the same.

[0002] Japanese Patent Application Laid-Open No. 2023-013070 (Patent Document 1) discloses a semipermeable membrane for cytokine removal having a high adsorption capacity for both negatively charged cytokines and positively charged cytokines.

[0003] Japanese Patent Application Laid-Open No. 2023-013070

[0004] As an anion exchange membrane that functions for removing substances having a negative charge (hereinafter also referred to as "negatively charged substances"), existing products such as "Mustang Q" sold by Global Life Sciences Technologies Japan Co., Ltd. are known. However, there is a demand for an anion exchange membrane having a larger adsorption capacity of negatively charged substances compared to the above existing products.

[0005] In view of the above circumstances, an object of the present invention is to provide a porous membrane that contributes to the adsorption and removal of negatively charged substances and a purification method using the same.

[0006] The present invention relates to a porous membrane as described below, and a purification method using the same. [1] A porous membrane comprising a first polymer soluble in N-methyl-2-pyrrolidone and insoluble in water, wherein the first polymer has a cationic group. [2] The porous membrane according to [1], wherein the first polymer comprises a constituent unit derived from a monomer having the cationic group and a constituent unit derived from a monomer not having the cationic group, wherein the cationic group is either a tertiary amino group or a quaternary ammonium group. [3] The porous membrane according to [1] or [2], wherein the cationic group is uniformly distributed in a cross section obtained by cutting the porous membrane in a direction normal to the surface. [4] The porous membrane according to any one of [1] to [3], further comprising a hydrophobic polymer and a hydrophilic polymer. [5] The porous membrane according to [4], wherein the hydrophobic polymer is either a polysulfone or a polyethersulfone. [6] The porous membrane according to [4] or [5], wherein the hydrophilic polymer is both or either polyvinylpyrrolidone and a copolymer of vinylpyrrolidone and vinyl acetate. [7] The porous membrane according to any one of [1] to [6], having a hollow fiber membrane shape having a first surface and a second surface, wherein the side with the first surface has a sparse structure, the side with the second surface has a dense structure, and the structure tends to become denser along the direction from the side with the first surface to the side with the second surface. [8] The porous membrane according to [7], wherein the first surface is the inner surface in the hollow fiber membrane shape, and the second surface is the outer surface in the hollow fiber membrane shape. [9] The porous membrane according to [7] or [8], wherein the transmittance of gold colloid having an average particle size of 10 nm from the first surface to the second surface is 20% or more, the transmittance of gold colloid having an average particle size of 30 nm from the first surface to the second surface is 20% or less, and when gold colloid having an average particle size of 20 nm is transmitted from the first surface to the second surface, the ratio of the thickness of the capture layer, which is the layer in which the gold colloid having an average particle size of 20 nm is captured, is 5% or more of the thickness of the porous membrane.

[10] The porous membrane according to any one of [1] to [9], for purification by anion exchange.

[11] A purification method comprising a purification step using a porous membrane as described in any one of items [1] to

[10] .

[0007] The present invention provides a porous membrane that contributes to the adsorption and removal of negatively charged substances, and a purification method using the same.

[0008] Figure 1 is a schematic diagram illustrating filtration using a porous membrane according to this embodiment. Figure 2 is a schematic diagram illustrating the function of the porous membrane according to this embodiment. Figure 3 is a graph showing the results of an albumin adsorption test using the porous membrane according to this embodiment. Figure 4 is a graph showing the results of a DNA adsorption test using the porous membrane according to this embodiment. Figure 5 is a schematic diagram illustrating an example of a method for manufacturing the porous membrane according to this embodiment.

[0009] One embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described below, but the present invention is not limited thereto. In this specification, the notation of the form "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and if no unit is specified for A and only a unit is specified for B, the unit for A and the unit for B are the same.

[0010] [Porous Membrane] The porous membrane according to this embodiment contains a first polymer that is soluble in N-methyl-2-pyrrolidone (hereinafter sometimes simply referred to as "NMP") and insoluble in water. The first polymer has a cationic group. The first polymer may contain a constituent unit (b-1) derived from a monomer having the cationic group and a constituent unit (a-1) derived from a monomer not having the cationic group. The cationic group may be either a tertiary amino group or a quaternary ammonium group. The cationic group may be uniformly distributed in a cross-section of the porous membrane obtained by cutting it in the direction normal to the surface.

[0011] The above-mentioned porous membrane can be manufactured, for example, based on the porous membrane manufacturing method described later, so that the cationic groups are uniformly distributed in the cross-section obtained by cutting in the direction normal to the surface. As a result, the porous membrane can have a larger adsorption capacity for negatively charged substances (for example, anion exchange capacity (AEC)). This effect is difficult to obtain in porous membranes in which cationic groups have been introduced by surface modification or the like.

[0012] In the above cross-section, the statement that the cationic groups are "uniformly distributed" means that after immersing the porous membrane in a 0.1% by mass aqueous solution of bromophenol blue (BPB) (manufactured by Nacalai Tesque) to bond the cationic groups with BPB, when the cross-section of the porous membrane in the film thickness direction (thickness direction) is observed using a digital microscope VHX-X1 (manufactured by Keyence Corporation), the entire surface (total area) of the cross-section is uniformly stained with BPB. On the other hand, in porous membranes in which cationic groups have been introduced by surface modification or the like, color unevenness is observed across the entire surface (total area) of the cross-section in the above observation, which is clearly different from the uniformly stained BPB appearance in this embodiment. Therefore, in porous membranes in which cationic groups have been introduced by surface modification or the like, the cationic groups cannot be said to be "uniformly distributed" in the above cross-section.

[0013] The porous membrane described above may contain hydrophobic polymers and hydrophilic polymers. In particular, the content ratio (mass ratio) of hydrophobic polymer / first polymer / hydrophilic polymer in the porous membrane as a whole may be 60-90 / 7-22 / 3-18.

[0014] In this specification, the first polymer has a cationic group but is insoluble in water because it contains the above-mentioned structural unit (a-1), and is therefore distinguished from the hydrophilic polymer. The first polymer is insoluble in water but has a cationic group, and is therefore distinguished from the hydrophobic polymer. "Insoluble in water" is defined as the elution rate of the target substance in water at 24°C being 5% by mass or less, and "hydrophilic" is defined as the elution rate of the target substance in water at 24°C being 30% by mass or more. "Hydrophobic" is synonymous with "insoluble in water" and is defined as the elution rate of the target substance in water at 24°C being 5% by mass or less.

[0015] The elution rate of the target substance is calculated from the difference in mass of the target substance before and after immersion in water. Specifically, first, the target substance is mixed with 90 parts by mass of deionized water at 24°C so that the amount of the target substance is 10 parts by mass. The mixture obtained is shaken at 24°C for 1 hour and then allowed to stand for 24 hours. Next, the mixture is filtered using a 5 μm syringe filter, and the mass (W1) of the solid obtained by heating the filtrate at 130°C for 1 hour is measured, and the elution rate of the target substance is calculated using the following formula: Elution rate of target substance (mass %) = (W1 / mass of target substance used for measurement) × 100

[0016] The inventors of the present invention have diligently conducted research to solve the above problems and arrived at the present invention. Specifically, they have newly developed a first polymer having a cationic group, soluble in N-methyl-2-pyrrolidone, and insoluble in water, and have arrived at a porous membrane containing this polymer. Furthermore, the inventors of the present invention have found that this porous membrane has a large anion exchange capacity (AEC) and a large adsorption capacity for albumin, DNA, etc., and other properties advantageous for the adsorption and removal of negatively charged substances, thus completing the present invention. In the following, the porous membrane according to this embodiment will be explained by illustrating a porous membrane that further contains a hydrophobic polymer and a hydrophilic polymer in addition to the first polymer.

[0017] <First Polymer> The porous membrane according to this embodiment contains a first polymer that is soluble in N-methyl-2-pyrrolidone and insoluble in water, as described above. The statement that the first polymer is "soluble in N-methyl-2-pyrrolidone" means that the elution rate of the first polymer into N-methyl-2-pyrrolidone at 24°C is 90% by mass or more.

[0018] The elution rate of the first polymer is calculated from the mass difference of the first polymer before and after immersion in N-methyl-2-pyrrolidone. Specifically, first, a mixture is obtained by mixing N-methyl-2-pyrrolidone and the first polymer in a ratio of 90 parts by mass of N-methyl-2-pyrrolidone at 24°C to 10 parts by mass of the first polymer. This mixture is shaken at 24°C for 1 hour and then allowed to stand for 24 hours. Next, the mixture is filtered using a 5 μm syringe filter, and the mass (W2) of the solid obtained by heating the filtrate at 130°C for 1 hour is measured. The elution rate of the first polymer is then calculated using the following formula: Elution rate of the first polymer (mass%) = (W2 / mass of the first polymer used for measurement) × 100

[0019] The first polymer described above has a cationic group. In this specification, "cationic group" means an amino group, ammonium group, sulfonium group, phosphonium group, and other functional group that may exhibit so-called cationic properties (the property of attracting negatively charged substances), regardless of whether the functional group has a positive charge or not, as long as the effects of the present invention are achieved. The cationic group may be an amino group or an ammonium group. In particular, the cationic group may be both or either a tertiary amino group and a quaternary ammonium group. Examples of the cationic group include a dialkylamino group, a trialkylammonium group, and a dialkylarylammonium group.

[0020] The first polymer described above is not particularly limited as long as it is a polymer that exhibits the effects of the present invention. The first polymer may be, for example, an olefin polymer, an aromatic hydrocarbon polymer, a (meth)acrylic polymer, or a urethane polymer. In particular, the first polymer may be a (meth)acrylic polymer. In this specification, "(meth)acrylic polymer" means at least one selected from the group consisting of acrylic polymers and methacrylic polymers. Similarly, in this specification, other terms prefixed with "(meth)acrylic" also mean at least one selected from the group consisting of acrylic and methacrylic.

[0021] (Constituent units derived from monomers that do not have cationic groups) The first polymer may contain the constituent units (a-1) derived from the monomers that do not have cationic groups as described above.

[0022] When the first polymer is a (meth)acrylic polymer, the constituent unit (a-1) of the first polymer may be a constituent unit derived from one or more (meth)acrylic monomers selected from the group consisting of (meth)acrylic monomers having an alkyl group and (meth)acrylic monomers having an aryl group. When the first polymer includes a constituent unit (a-11) derived from a (meth)acrylic monomer having an alkyl group and a constituent unit (a-12) derived from a (meth)acrylic monomer having an aryl group as the constituent unit (a-1), the molar ratio ((a-11) / (a-12)) of the constituent unit (a-11) to the constituent unit (a-12) may be 0.1 to 10, 0.15 to 5, or 0.2 to 1. In this specification, "constituent unit derived from (meth)acrylic monomer" means "a constituent unit in which the radically polymerizable carbon-carbon double bond of the (meth)acrylic monomer polymerizes to form a carbon-carbon single bond."

[0023] Examples of (meth)acrylic monomers having the alkyl group mentioned above include (meth)acrylates having a linear alkyl group, (meth)acrylates having a branched alkyl group, (meth)acrylates having a monocyclic cyclic alkyl group, and cyclic alkyl(meth)acrylates having a polycyclic structure. The cyclic alkyl group may have a chain portion. The number of carbon atoms in the alkyl group may be 1 to 20 or 1 to 12.

[0024] Specific examples of (meth)acrylates having the linear alkyl group mentioned above include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-lauryl (meth)acrylate, and n-stearyl (meth)acrylate. The number of carbon atoms in the linear alkyl group may be 1 to 20 or 1 to 12.

[0025] Specific examples of (meth)acrylates having the above-mentioned branched alkyl group include isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate. The number of carbon atoms in the above-mentioned branched alkyl group may be 3 to 20 or 3 to 12.

[0026] Specific examples of (meth)acrylates having a cyclic alkyl group having the monocyclic structure described above include cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, and cyclododecyl (meth)acrylate. The number of carbon atoms in the cyclic alkyl group having the monocyclic structure may be 6 to 20 or 6 to 12.

[0027] Specific examples of the cyclic alkyl (meth)acrylate having the above polycyclic structure include bornyl (meth)acrylate, isobornyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, norbornyl (meth)acrylate, and the like. The number of carbon atoms in the cyclic alkyl group having the above polycyclic structure may be 6 to 20 or 6 to 12.

[0028] Examples of (meth)acrylic monomers having the aryl group include (meth)acrylates having the aryl group. The aryl group may have a chain-like portion, such as an alkylaryl group, an aralkyl group, or an aryloxyalkyl group. That is, examples of (meth)acrylates having the aryl group include compounds in which an aryl group is directly bonded to a (meth)acryloyloxy group, compounds in which an aralkyl group is directly bonded to a (meth)acryloyloxy group, and compounds in which an aryloxyalkyl group is directly bonded to a (meth)acryloyloxy group. Specific examples of (meth)acrylates having the aryl group include phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate. The number of carbon atoms in the aryl group may be 6 to 12 or 6 to 9.

[0029] The above constituent unit (a-11) may be a constituent unit represented by the following formula (1).

[0030] [In equation (1), R 11 R represents a hydrogen atom or a methyl group. 12 Z represents an alkyl group. 1 This represents O or NH.

[0031] R 12 Examples of alkyl groups represented by include linear alkyl groups, branched alkyl groups, cyclic alkyl groups having a monocyclic structure, and cyclic alkyl groups having a polycyclic structure. The above cyclic alkyl groups may have a chain portion. The number of carbon atoms in the above alkyl group may be 6 to 20 or 6 to 12.

[0032] Specific examples of the linear alkyl group mentioned above include methyl group, ethyl group, n-propyl group, n-butyl group, n-hexyl group, n-octyl group, n-nonyl group, n-decyl group, n-lauryl group, n-stearyl group, and the like. The number of carbon atoms in the linear alkyl group may be 1 to 20 or 1 to 12.

[0033] Specific examples of the branched alkyl group mentioned above include isobutyl group, sec-butyl group, tert-butyl group, isooctyl group, 2-ethylhexyl group, isononyl group, isodecyl group, and the like. The number of carbon atoms in the branched alkyl group may be 3 to 20 or 3 to 12.

[0034] Specific examples of the cyclic alkyl group having the monocyclic structure described above include a cyclohexyl group, a methylcyclohexyl group, and a cyclododecyl group. The number of carbon atoms in the cyclic alkyl group having the monocyclic structure described above may be 6 to 20 or 6 to 12.

[0035] Specific examples of the polycyclic alkyl group described above include bornyl group, isobornyl group, 1-adamantyl group, 2-adamantyl group, 2-methyl-2-adamantyl group, 2-ethyl-2-adamantyl group, norbornyl group, etc. The number of carbon atoms in the polycyclic alkyl group may be 6 to 20 or 6 to 12.

[0036] The above constituent unit (a-12) may be a constituent unit represented by the following formula (2).

[0037] [In equation (2), R 21 R represents a hydrogen atom or a methyl group. 22 This represents an aryl group.

[0038] R 22 The aryl group represented by may have a chain portion. Specific examples of the aryl group include a phenyl group, a benzyl group, and a phenoxyethyl group. The number of carbon atoms in the aryl group may be 6 to 12 or 6 to 9.

[0039] (Constituent units derived from monomers having cationic groups) The first polymer may contain the constituent units (b-1) derived from the monomers having cationic groups as described above.

[0040] When the first polymer is a (meth)acrylic polymer, an example of a constituent unit (b-1) of the first polymer is a constituent unit derived from one or more (meth)acrylic monomers selected from the group consisting of (meth)acrylic monomers having a tertiary amino group and (meth)acrylic monomers having a quaternary ammonium group. When the first polymer includes a constituent unit (b-11) derived from a (meth)acrylic monomer having a tertiary amino group and a constituent unit (b-12) derived from a (meth)acrylic monomer having a quaternary ammonium group, the molar ratio ((b-11) / (b-12)) of the constituent unit (b-11) to the constituent unit (b-12) may be 0.001 to 10, 0.01 to 8, or 0.1 to 5.

[0041] Examples of (meth)acrylic monomers having a tertiary amino group include (meth)acrylates having a tertiary amino group and (meth)acrylamides having a tertiary amino group. Specific examples of (meth)acrylates having a tertiary amino group include dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, dimethylaminobutyl (meth)acrylate, diethylaminoethyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and diethylaminobutyl (meth)acrylate.

[0042] Examples of (meth)acrylamides having the above-mentioned tertiary amino group include dimethylaminoethyl (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, and diethylaminoethyl (meth)acrylamide.

[0043] Examples of (meth)acrylic monomers having a quaternary ammonium group include (meth)acrylates having a quaternary ammonium group and (meth)acrylamides having a quaternary ammonium group.

[0044] As the above (meth)acrylates having a quaternary ammonium group, (meth)acryloyloxyethyltrimethylammonium chloride, (meth)acryloyloxypropyltrimethylammonium chloride, (meth)acryloyloxybutyltrimethylammonium chloride, (meth)acryloyloxyethylbenzyldimethylammonium chloride, (meth)acryloyloxypropylbenzyldimethylammonium chloride, (meth)acryloyloxybutylbenzyldimethylammonium chloride, (meth)acryloyloxyethylbenzyldiethylammonium chloride, (meth)acryloyloxypropylbenzyldiethylammonium chloride, (meth)acryloyloxybutylbenzyldiethylammonium Examples include ammonium chloride, (meth)acryloyloxyethylbenzyldiethylammonium bromide, (meth)acryloyloxypropylbenzyldiethylammonium bromide, (meth)acryloyloxybutylbenzyldiethylammonium bromide, (meth)acryloyloxyethylbenzyldiethylammonium iodide, (meth)acryloyloxypropylbenzyldiethylammonium iodide, (meth)acryloyloxybutylbenzyldiethylammonium iodide, (meth)acryloyloxyethylbenzyldiethylammonium fluoride, (meth)acryloyloxypropylbenzyldiethylammonium fluoride, and (meth)acryloyloxybutylbenzyldiethylammonium fluoride.

[0045] Examples of (meth)acrylamides having the above-mentioned quaternary ammonium group include (meth)acryloylaminoethyltrimethylammonium chloride, (meth)acryloylaminopropyltrimethylammonium chloride, (meth)acryloylaminoethylbenzylmethylammonium chloride, and (meth)acryloylaminopropylbenzyldimethylammonium chloride.

[0046] The above constituent unit (b-11) may be a constituent unit represented by the following formula (3).

[0047] [In equation (3), R 31represents a hydrogen atom or a methyl group. R 32 represents an alkylene group. R 33 and R 34 each independently represent an alkyl group. Z 3 represents O or NH. ]

[0048] R 32 Examples of the alkylene group represented by R 32 include a linear alkylene group, a branched alkylene group, etc. The alkylene group represented by R

[0049] R 33 and R 34 Examples of the alkyl group represented by R 33 and R 34 include a linear alkyl group and a branched alkyl group. The alkyl group represented by R

[0050] The above structural unit (b-12) may be a structural unit represented by the following formula (4).

[0051] [In formula (4), R 41 represents a hydrogen atom or a methyl group. R 42 represents an alkylene group. R 43 and R 44 each independently represent an alkyl group. R 45 represents an alkyl group or an aryl group. X - represents a counter ion. Z 4 represents O or NH. ]

[0052] R 42Examples of alkylene groups represented by include linear alkylene groups and branched alkylene groups. 42 The alkylene group represented by may be a linear alkylene group. Specific examples of the linear alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentamethylene group, a hexamethylene group, a heptamethylene group, and the like. The number of carbon atoms in the alkylene group may be 1 to 10, 1 to 7, or 1 to 5.

[0053] R 43 and R 44 Examples of alkyl groups represented by R include linear alkyl groups and branched alkyl groups. 43 and R 44 The alkyl group represented may be a linear alkyl group. Specific examples of the linear alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-hexyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-lauryl group, and the like. The number of carbon atoms in the alkyl group may be 1 to 10, 1 to 7, or 1 to 5.

[0054] R 45 Examples of alkyl groups represented by R include linear alkyl groups and branched alkyl groups. 45 The alkyl group represented may be a linear alkyl group. Specific examples of the linear alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-hexyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-lauryl group, and the like. The number of carbon atoms in the alkyl group may be 1 to 10, 1 to 7, or 1 to 5.

[0055] R 45 The aryl group represented by may have a chain portion. Specific examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a mesityl group, a benzyl group, and the like. The number of carbon atoms in the aryl group may be 6 to 12 or 6 to 9.

[0056] X -Examples include halogen ions. Specific examples of halogen anions include fluoroanions, chloroanions, bromoanions, and iodoanions.

[0057] When the first polymer contains the constituent unit (a-1), the content of the constituent unit (a-1) in 100 mol% of the constituent units constituting the first polymer may be 10 to 80 mol%, or 15 to 50 mol%. In this case, the insolubility in water is improved.

[0058] When the first polymer contains the constituent unit (b-1), the content of the constituent unit (b-1) in 100 mol% of the constituent units constituting the first polymer may be 20 to 90 mol%, or 50 to 85 mol%. In this case, the adsorption and removal performance of negatively charged substances is improved.

[0059] When the first polymer contains constituent unit (a-1) and constituent unit (b-1), the total content of constituent unit (a-1) and constituent unit (b-1) may be 90 mol% or more out of 100 mol% of the constituent units constituting the first polymer. In this case, the insolubility in water and the adsorption and removal performance of negatively charged substances are improved.

[0060] When the first polymer contains constituent units (a-1) and (b-1), the molar ratio of constituent units (a-1) to (b-1) ((a-1) / (b-1)) may be 0.1 to 5, 0.1 to 3, or 0.2 to 1. In this case, the insolubility in water and the adsorption and removal performance of negatively charged substances are improved.

[0061] (Structure of the first polymer and its manufacturing method) The first polymer may contain a constituent unit (a-1) derived from a monomer that does not have a cationic group and a constituent unit (b-1) derived from a monomer that has a cationic group, as described above. The first polymer may be a random copolymer, a block copolymer, or an alternating copolymer, and may be a block copolymer. In particular, the first polymer may be a block copolymer having an A block containing the above constituent unit (a-1) and a B block containing the above constituent unit (b-1). Because the constituent units of the A block and the B block are localized by forming a block copolymer, the insolubility in water and the adsorption and removal performance of negatively charged substances can be further improved.

[0062] The first polymer described above may be a linear block copolymer. The linear block copolymer may have any structure (arrangement), but from the viewpoint of the physical properties of the linear block copolymer or the physical properties of the composition, when block A is expressed as "A" and block B is expressed as "B", it may be an A-B type diblock copolymer.

[0063] The molar ratio (A block / B block) of A block to B block in the first polymer described above may be 0.1 to 5, 0.1 to 3, or 0.2 to 1. In this case, both insolubility in water and adsorption / removal performance of negatively charged substances are improved.

[0064] Block A may contain other constituent units besides the above constituent unit (a-1), as long as it contains the above constituent unit (a-1). The content of the above constituent unit (a-1) in Block A may be 90 mol% or more out of 100 mol% of the constituent units constituting Block A. In this case, the insolubility in water will be better.

[0065] The various constituent units contained in Block A may be contained in Block A in either a random copolymer or a block copolymer, and may be contained in a random copolymer from the viewpoint of uniformity. For example, Block A may be formed by a copolymer of constituent units consisting of Block a1 and constituent units consisting of Block a2.

[0066] The above-mentioned Block B may contain other constituent units other than the above-mentioned constituent unit (b-1), as long as it contains the above-mentioned constituent unit (b-1). The content of the above-mentioned constituent unit (b-1) in the above-mentioned Block B may be 90 mol% or more out of 100 mol% of the constituent units constituting the above-mentioned Block B. In this case, the adsorption and removal performance of negatively charged substances will be better.

[0067] The various constituent units contained in the above-mentioned Block B may be contained in Block B in either a random copolymer or a block copolymer, and may be contained in a random copolymer from the viewpoint of uniformity. For example, Block B may be formed by a copolymer of constituent units consisting of Block B1 and constituent units consisting of Block B2.

[0068] If the first polymer contains an amino group, the amine value of the first polymer may be 10 to 320 mg KOH / g or 50 to 280 mg KOH / g, from the viewpoint of adsorption and removal performance of negatively charged substances.

[0069] The weight-average molecular weight (Mw) of the first polymer described above may be 5,000 to 500,000, 10,000 to 300,000, or 10,000 to 100,000. In this case, the insolubility in water and durability are better. The weight-average molecular weight of the first polymer described above is measured by gel permeation chromatography (hereinafter also referred to as "GPC").

[0070] The molecular weight distribution (Mw / Mn) of the first polymer may be 3.0 or less, 2.4 or less, or 1.7 or less. In this case, the insolubility in water and durability are better. In this specification, "molecular weight distribution" is determined by (weight-average molecular weight of the first polymer (Mw)) / (number-average molecular weight of the first polymer (Mn)). It is understood that the smaller the molecular weight distribution value of the first polymer, the narrower the molecular weight distribution and the more uniformly molecular weight the polymer is composed of. The molecular weight distribution has the narrowest width when its value is 1.0. That is, the lower limit of the molecular weight distribution is 1.0.

[0071] The above-mentioned first polymer can be produced by polymerizing the above-mentioned various monomers using conventionally known polymerization methods. Examples of such polymerization methods include radical polymerization (also called free radical polymerization), cationic polymerization, anionic polymerization, and living polymerization. The polymerization method may be living polymerization. That is, the above-mentioned first polymer may be polymerized by living polymerization.

[0072] In the above-described living polymerization, among the four elementary reactions in chain polymerization—initiation, growth, termination, and chain transfer—the termination and chain transfer reactions are substantially absent, and the vinyl monomer reacts and the polymer chain grows without deactivation of the reaction sites (polymerization growth ends). Therefore, a polymer with a small molecular weight distribution and a uniform composition can be produced. Known living polymerization methods include living radical polymerization, living anionic polymerization, and living cationic polymerization. From the viewpoint of ease of polymerization, the above-described living polymerization may be living radical polymerization. The above-described living radical polymerization maintains the ease and versatility of free radical polymerization, while allowing for precise control of the molecular weight distribution, thus making it easy to produce polymers with a uniform composition.

[0073] As for the living radical polymerization described above, depending on the method used to stabilize the polymerization growth ends, the following methods may be employed: a method using compounds that can generate nitroxide radicals (nitroxide method; NMP method); a method using metal complexes such as copper and ruthenium, with a halogenated compound as the polymerization initiator, and polymerization carried out in a living manner from that initiator (ATRP method); a method using dithiocarboxylic acid esters or xantate compounds (RAFT method); a method using organotellurium compounds (TERP method); a method using organiodine compounds (ITP method); and a method using an iodine compound as the polymerization initiator and an organic compound such as a phosphorus compound, nitrogen compound, oxygen compound, or hydrocarbon as a catalyst (reversible transfer catalytic polymerization; RTCP method, reversible catalyst-mediated polymerization; RCMP method). Among these methods, the TERP method may be used from the viewpoint of the diversity of monomers that can be used, molecular weight control in the polymer range, uniform composition, and coloration.

[0074] The above-mentioned structural unit (b-12) may be obtained by polymerizing the monomers that form the above-mentioned structural unit (a-1) and the above-mentioned structural unit (b-11), and at least a portion of the tertiary amino groups of the polymer obtained are quaternized.

[0075] <Hydrophobic Polymer> The porous membrane described above may contain a hydrophobic polymer and a hydrophilic polymer. The term "hydrophobic polymer" as used herein does not include the first polymer described above. Examples of the hydrophobic polymer include polysulfone-based polymers such as polysulfone and polyethersulfone, cellulosonic polymers such as cellulose acetate and cellulose derivatives, and polyolefin-based polymers such as polyethylene. The hydrophobic polymer may be both or either polysulfone and polyethersulfone. The hydrophobic polymer may be, for example, polyethersulfone. This polyethersulfone is a compound containing the structural unit shown in the following formula (5).

[0076]

[0077] Specific examples of polyethersulfones include, for example, BASF's Ultrazone® E2020P and E6020P, or Sumitomo Chemical's Sumika Excel® 3600P, 4100P, 4800P, 5200P, and 7600P. The polyethersulfone may be E6020P, 4800P, or 5200P. These may be used individually or in combination.

[0078] <Hydrophilic Polymers> The porous membrane described above may contain hydrophilic polymers. Examples of hydrophilic polymers include polyvinylpyrrolidone, copolymers of vinylpyrrolidone and vinyl acetate (hereinafter also referred to as "vinylpyrrolidone polymers"), polyvinyl alcohol, polyethylene glycol, polyacrylic acid, cellulose, methylcellulose, and chitosan. The hydrophilic polymer may be both or either polyvinylpyrrolidone and copolymers of vinylpyrrolidone and vinyl acetate. The vinylpyrrolidone polymer refers to a polymer of monomers containing at least N-vinylpyrrolidone.

[0079] Vinylpyrrolidone polymers may contain structural units represented by, for example, the following formula (6).

[0080]

[0081] Examples of vinylpyrrolidone polymers include Kollidon® 30, 90, or Luvitec® K30, K80, K85, K90, VA64, all commercially available from BASF, and K-90, K-85, K-30, all commercially available from Nippon Shokubai Co., Ltd.

[0082] <Non-uniform structure in the thickness direction> The above porous membrane may have a non-uniform structure in the thickness direction (hereinafter also referred to as "asymmetric structure"). Examples of porous membranes having the above asymmetric structure include porous membranes in which density, porosity, cross-sectional opening ratio, average pore diameter, etc. differ in the thickness direction. The above porous membrane may be in the shape of a flat membrane or a hollow fiber membrane, but may have a hollow fiber membrane shape from the viewpoint of obtaining excellent effects. In that case, the above hollow fiber membrane shape has a first surface and a second surface.

[0083] When the above porous membrane has a hollow fiber membrane shape having a first surface and a second surface (hereinafter also simply referred to as "hollow fiber membrane"), the side with the first surface may have a sparse structure, the side with the second surface may have a dense structure, and may tend to become denser along the direction from the first surface to the second surface. In particular, the first surface may be the inner surface of the hollow fiber membrane shape, and the second surface may be the outer surface of the hollow fiber membrane shape.

[0084] Specifically, if the porous membrane is a hollow fiber membrane, the first surface side corresponding to the inner surface may have a sparse structure in the cross-section in the thickness direction (hereinafter also referred to as the "cross-section" or "cross-section parallel to the radial direction"), the second surface side corresponding to the outer surface may have a dense structure, and the structure may tend to become denser along the direction from the first surface side to the second surface side. In the hollow fiber membrane, when the liquid to be treated is passed through the side with the sparse structure (the first surface side), the liquid to be treated may be filtered toward the side with the dense structure (the second surface side), and negatively charged substances may be adsorbed and removed (anion exchange). Alternatively, if the porous membrane is a hollow fiber membrane, the first surface side may have a dense structure and the second surface side may have a sparse structure.

[0085] The terms "dense" and "sparse" at specific locations in the hollow fiber membrane (for example, on the first surface side or the second surface side) mean the following, respectively: That is, "dense" at a specific location in the hollow fiber membrane means that the density at that location is high due to a small porosity, as described later. "Sparse" at a specific location in the hollow fiber membrane means that the density at that location is low due to a large porosity, as described later.

[0086] In this specification, "showing a tendency to become denser along the direction from the first surface to the second surface" means that it is sufficient that the region in the direction from the first surface to the second surface includes a portion where the porosity described later decreases. Furthermore, if the vicinity of the first surface is X and the vicinity of the second surface is Y, then measuring the porosity at these locations will always result in a distribution where the porosity of X > the porosity of Y. Therefore, as long as the region in the direction from the first surface to the second surface includes a portion where the porosity described later decreases and the distribution where the porosity of X > the porosity of Y is obtained, there may be locations where the porosity is constant in the direction from the first surface to the second surface. Furthermore, there may be locations where the porosity increases in the direction from the first surface to the second surface.

[0087] The above "porosity" is calculated from the difference between the mass of the porous membrane when water is added to the void portion and the mass of the dried porous membrane. Specifically, the above "porosity" refers to the value obtained by measuring the porous membrane using the following procedure (1) to (5). (1) Remove the portion (sample to be measured) corresponding to the area where the porosity is to be measured from the porous membrane. (2) After thoroughly immersing the sample to be measured in pure water, dewater it by centrifuging at a rotation speed of 900 rpm (gravitational acceleration 116 G) for 5 minutes. (3) Measure the mass (W) of the sample to be measured after dewatering. (4) Measure the mass (P) of the sample to be measured after being completely dried in a dryer. (5) Calculate the porosity (ψ) using the following formula. ψ(%) = W / (W + P / polymer density) × 100 The above "polymer density" refers to the density of the polymer species with the highest content in the above porous membrane (either the first polymer, hydrophobic polymer, or hydrophilic polymer).

[0088] The porosity of the porous membrane described above may be 70% to 95%, 75% to 92%, or 80% to 90%. A porosity of 70% or higher allows the porous membrane to achieve a high recovery rate (pass-through rate) of neutral proteins and the like. On the other hand, if the porosity of the porous membrane is too high, it may lack sufficient strength. When the porosity of the porous membrane falls within the above range, it can achieve both good filtration performance and strength against filtration pressure.

[0089] The density in the thickness direction of the hollow fiber membrane can be confirmed, for example, by observation using the following procedure with an SEM (scanning electron microscope). (1) Lightly wash the hollow fiber membrane as a sample with water, freeze the sample with liquid nitrogen, and cut it. (2) Fix the sample to a sample stage so that the cut surface (fracture surface) can be observed, and stain it with osmium using an osmium coater (Neoc-stb, manufactured by Meiwa Pharmacy). (3) Observe the osmium-stained sample using a scanning electron microscope (Hitachi "S-2500") at an acceleration voltage of 10 kV and acquire an SEM image. By visually determining the size of the porosity (density) in the SEM image, it is possible to confirm that the hollow fiber membrane has density in the thickness direction (asymmetric structure).

[0090] In the porous membrane described above, the transmittance of gold colloid having an average particle size of 10 nm from the first surface to the second surface may be 20% or more. The aforementioned transmittance of gold colloid having an average particle size of 10 nm may be 50% or more, 70% or more, or 80% or more. In the porous membrane described above, the transmittance of gold colloid having an average particle size of 30 nm from the first surface to the second surface may be 20% or less, 15% or less, or 10% or less.

[0091] Furthermore, in the porous membrane described above, when a gold colloid having an average particle size of 20 nm is transmitted from the first surface to the second surface, the ratio of the thickness of the capture layer, which is the layer in which the gold colloid having an average particle size of 20 nm is captured, may be 5% or more of the thickness of the porous membrane (i.e., the shortest distance from the first surface to the second surface). The ratio of the thickness of the capture layer may be 7% or more, or 10% or more. The ratio of the thickness of the capture layer may be 50% or less, 40% or less, or 30% or less. The average particle size of the gold colloid described above refers to the average particle size described in the product instruction manual, etc. A commercially available product (such as BBI Solutions' standard gold colloid product) may be used as the gold colloid.

[0092] If the porous membrane is a hollow fiber membrane, the inner diameter of the circumference of the first surface may be 150 μm or more and 400 μm or less, or 200 μm or more and 350 μm or less. The thickness of the porous membrane may be 30 to 200 μm or 40 to 100 μm. The thickness of the porous membrane is calculated from "(outer diameter - inner diameter) / 2" of the porous membrane (hollow fiber membrane).

[0093] Figure 1 is a schematic diagram illustrating filtration using a porous membrane according to this embodiment. As shown in Figure 1, due to anion exchange by the hollow fiber membrane 3, the first component 5, such as antibodies (IgG) and neutral proteins in the liquid to be treated, permeates the hollow fiber membrane 3 from the side into which the liquid to be treated enters (upper side of Figure 1: first surface (inner surface) side of the hollow fiber membrane 3) and is separated to the second surface (outer surface) side (lower side of Figure 1). At the same time, negatively charged substances such as albumin and DNA are adsorbed onto the hollow fiber membrane 3 based on the cationic groups in the first polymer. On the other hand, the second component 4, such as aggregates of IgG, which is smaller in size than the substances blocked on the first surface (inner surface) side of the hollow fiber membrane 3 but larger in size than the first component 5, may clog the pores of the hollow fiber membrane 3. However, as shown in Figure 1, in the case of filtration using a hollow fiber membrane 3 having the asymmetric structure described above, the second component 4 is dispersed and captured in the thickness direction of the hollow fiber membrane 3 (clogging occurs sequentially in the thickness direction). Therefore, clogging is less likely to occur.

[0094] If the porous membrane is a hollow fiber membrane, its hollowness ratio may be 15-60% or 20-50%. The hollowness ratio is the ratio of the area of ​​the hollow portion in the cross-section (cross-section parallel to the radial direction) of the hollow fiber membrane, and is expressed as "cross-sectional area of ​​hollow portion / (cross-sectional area of ​​membrane portion + cross-sectional area of ​​hollow portion) × 100 (%)". When the hollowness ratio of the hollow fiber membrane is within the above range, it is possible to achieve both filtration performance and strength against filtration pressure.

[0095] <Applications> Figure 2 is a schematic diagram illustrating the function of the porous membrane according to this embodiment. As shown in Figure 2, the porous membrane according to this embodiment (for example, the hollow fiber membrane 3, which is one embodiment) may be used for purification by anion exchange. The hollow fiber membrane 3 shown in Figure 2 is suitably used, for example, in the process of purifying antibodies 2 (IgG, etc.) by removing impurities from cell culture medium during the production of antibody drugs, to adsorb and remove negatively charged substances 1, such as albumin and DNA, contained in the impurities. In such applications, the porous membrane according to this embodiment, in addition to the anion exchange ability described above, has a non-uniform structure in the thickness direction, so that a second component 4, such as aggregates of IgG, is dispersed and captured in the thickness direction of the hollow fiber membrane 3, thereby providing a clogging suppression effect.

[0096] <Performance Evaluation> The above porous membrane exhibits excellent adsorption and removal (anion exchange) performance of negatively charged substances. In this embodiment, the adsorption and removal performance of the negatively charged substances is determined, for example, by the following evaluation method.

[0097] (Anion Exchange Capacity (AEC)) The anion exchange capacity (AEC) per unit mass of the porous membrane described above is measured as follows, for example, when the porous membrane is a hollow fiber membrane. The AEC per unit mass of the porous membrane is an indicator of the amount of positive charge possessed by the porous membrane, and its unit is meq / g. Generally, the larger the AEC value, the better the adsorption and removal performance of negatively charged substances (anion exchange).

[0098] The AEC per unit mass of a hollow fiber membrane is measured by the following procedure (1) to (8). The same procedure can be used to measure the AEC even if the porous membrane is a flat membrane. (1) The mass of the hollow fiber membrane to be used as a sample is weighed by a known method. (2) The sample is immersed in 5 mL of 1 M sodium hydroxide (NaOH) solution. (3) The sample immersed in the NaOH solution in (2) is washed with pure water. (4) The sample washed in (3) is immersed in 5 mL of 0.01 M hydrochloric acid (HCl) solution (hereinafter also referred to as "solution A"). (5) The sample immersed in (4) is removed from solution A, and the solution to be measured is recovered. (6) An appropriate amount of phenolphthalein solution is added to the solution to be measured to prepare the solution for AEC measurement. (7) The AEC measurement solution is titrated with a 0.01 M NaOH solution (hereinafter also referred to as "solution B"). The endpoint is the point at which the AEC measurement solution is colored. (8) Based on the above, the AEC is calculated from the following formula: Anion exchange capacity (AEC) = [(Titration volume of solution A by solution B (mL) - Titration volume of AEC measurement solution by solution B (mL)) × 0.01 M] / [Mass of hollow fiber membrane (g)]

[0099] In the porous membrane according to this embodiment, the AEC may be 0.01 to 2.0 meq / g, 0.05 to 1.2 meq / g, or 0.07 to 0.7 meq / g.

[0100] (Adsorption amount of negatively charged substances (albumin adsorption performance, DNA adsorption performance)) The amount of negatively charged substances adsorbed by the porous membrane described above is measured as follows, depending on whether the porous membrane is a flat membrane or a hollow fiber membrane. The amount of negatively charged substances adsorbed by the porous membrane described above is an indicator of the negatively charged substance removal performance of the porous membrane, and the unit is mg / (g・membrane mass). The higher the value of the adsorption amount of the porous membrane described above, the better the negatively charged substance adsorption and removal performance is considered to be.

[0101] 1) Amount of negatively charged substance adsorbed on a flat membrane: The amount of negatively charged substance adsorbed on a flat membrane in an immersion test is specifically measured by the following steps (1) to (7). (1) The mass of the flat membrane to be used as a sample is measured by a known method. (2) The concentration of the negatively charged substance in the solution of the negatively charged substance to be adsorbed (hereinafter also referred to as the "pre-measurement solution") is measured by a known method. (3) The sample is immersed in the pre-measurement solution to obtain the sample to be measured. (4) The sample to be measured is shaken at 37°C for 2 hours at a shaking rate of 70 rpm. (5) The sample is removed from the sample to be measured after shaking in (4), and the post-shaking solution is recovered. (6) The concentration of negatively charged substance in the post-shaking solution is measured by a known method. (7) The amount of negatively charged substance adsorbed is calculated from the difference in the concentrations of negatively charged substance in the pre-measurement solution and the post-shaking solution using the following formula. Adsorption amount of negatively charged substance (per membrane mass) = [Difference in concentration of negatively charged substance between the pre-measurement solution and the post-shaking solution (mg / g) / Mass of sample (membrane mass: g)]

[0102] 2) Amount of negatively charged substance (albumin) adsorbed in hollow fiber membrane: Dead-end filtration test The amount of negatively charged substance (albumin) adsorbed in the hollow fiber membrane is specifically measured by the following procedure (1) to (10). See also Figure 3. Figure 3 is a graph showing the results of an albumin adsorption test using a porous membrane according to this embodiment. (1) A 0.025 mol / L Tris-HCl buffer is obtained by diluting 1 M Tris-HCl buffer (pH 7.0), commercially available from Fujifilm Wako Pure Chemical Industries, Ltd., 40 times with distilled water to a total volume of 500 mL. Albumin, commercially available from Fujifilm Wako Pure Chemical Industries, Ltd., is added to this buffer so that the concentration is 0.25 mg / mL, and this is used as the measurement solution. (2) A measurement module with 6 hollow fiber membranes is prepared, and a flow rate of 715 mL / m is applied to the hollow part of the measurement module. ２ The above measuring solution is supplied at / min, and dead-end filtration is performed. The filtrate is collected every 10 minutes from the start of filtration, and the filtrate volume Z of each fraction is measured. ｎThe following is measured. Here, n represents the fraction number, which is an ordinal number with the first fraction number being 1. (3) After staining solution (Protein Quantification Kit-Rapid (manufactured by Dojin Chemical Research Institute Co., Ltd.)) is added to the measurement solution and each fraction, the absorbance is measured. A calibration curve prepared separately is referenced to the absorbance to determine the albumin concentration of each fraction and the measurement solution, as well as the ratio Y of the albumin concentration of each fraction to the measurement solution. ｎ Y is required. ｎ = Absorbance of fraction at 595 nm / Absorbance of measurement solution at 595 nm (4) Cumulative filtration volume W from the start of filtration to the end of recovery of each fraction ｎ and the ratio Y of the above albumin concentrations ｎ The relationship is shown in Figure 3. W ｎ = Z １ +Z ２ +...+Z ｎ (5) In the bar graph of Figure 3, the point where the line connecting the centers of the upper ends of adjacent fractions intersects with the line representing the ratio of albumin concentrations = 0.1 is defined as the 10% breakthrough point, and the cumulative filtration amount X up to this point can be calculated. (6) The W closest to the above X. ｎ W ｍ In this case, the total amount of albumin contained in the (m-1)th fraction is A, half the amount of albumin contained in the mth fraction is B, and the cumulative filtration amount is (W ｍ +W ｍ-1 The approximate value of the amount of albumin contained in the filtrate from ) / 2 to X is given as C. In this case, A, B, and C are calculated from the following formulas: A = (Z １ ×Y １ +Z ２ ×Y ２ +...+Z m-1 ×Y m-1 ) × Albumin concentration in the measurement solution B = Z ｍ ×Y ｍ / 2 × Albumin concentration in the measurement solution C = (X - (W) ｍ +W ｍ-1 ) / 2) × (Y ｍ(7) The sum of A, B, and C above is the cumulative leakage amount of albumin up to the cumulative filtration amount X. Cumulative leakage amount = A + B + C (8) The amount of albumin supplied up to the cumulative filtration amount X (cumulative supply amount) is calculated from the following formula. Cumulative supply amount = X × albumin concentration in the measuring solution (9) The amount of albumin adsorbed on the hollow fiber membrane up to the cumulative filtration amount X (cumulative adsorbed amount) is calculated from the following formula. Cumulative adsorbed amount = Cumulative supply amount - Cumulative leakage amount (10) From the above, the amount of albumin adsorbed per unit mass of hollow fiber membrane is measured from the following formula. Amount of albumin adsorbed per unit mass of hollow fiber membrane = Cumulative adsorbed amount / membrane mass

[0103] 3) Adsorption amount of negatively charged substance (DNA) in hollow fiber membrane: Dead-end filtration test The amount of negatively charged substance (DNA) adsorbed in the hollow fiber membrane is specifically measured by the following procedure (1) to (10). See also Figure 4. Figure 4 is a graph showing the results of a DNA adsorption test using a porous membrane according to this embodiment. (1) A 0.025 mol / L Tris-HCl buffer is obtained by diluting 1 M Tris-HCl buffer (pH 7.0), commercially available from Fujifilm Wako Pure Chemical Industries, Ltd., 40 times with distilled water to a total volume of 500 mL. Deoxyribonucleic acid, low molecular weight from salmon sperm (DNA), commercially available from Sigma-Aldrich, is added to this buffer so that the concentration is 70 μg / mL, and this is used as the measurement solution. (2) A measurement module with 6 hollow fiber membranes is prepared, and a flow rate of 715 mL / m is applied to the hollow part of the measurement module. ２ The above measuring solution is supplied at / min, and dead-end filtration is performed. The filtrate is collected every 10 minutes from the start of filtration, and the filtrate volume Z of each fraction is measured. ｎ The following is measured. Here, n represents the fraction number, which is an ordinal number with the first fraction number being 1. (3) The measurement solution and each fraction are subjected to absorbance analysis, and a calibration curve prepared separately is referenced to the analytical values ​​to determine the DNA concentration in the solution of each fraction and the measurement solution, as well as the ratio Y of the DNA concentration of each fraction to the measurement solution. ｎ Y is required. ｎ= Absorbance of fraction at 260 nm / Absorbance of measurement solution at 260 nm (4) Cumulative filtration volume W from the start of filtration to the end of recovery of each fraction ｎ and the ratio Y of the above DNA concentrations ｎ The relationship is shown in Figure 4. W ｎ = Z １ +Z ２ +...+Z ｎ (5) In the bar graph of Figure 4, the point where the line connecting the centers of the upper ends of adjacent fractions intersects with the line representing the ratio of DNA concentrations = 0.2 is defined as the 20% breakthrough point, and the cumulative filtration amount X up to this point can be calculated. (6) The W closest to the above X. ｎ W ｍ In this case, the total amount of DNA contained in the (m-1)th fraction is A, half the amount of DNA contained in the mth fraction is B, and the cumulative filtration amount is (W ｍ +W ｍ-1 The approximate value of the amount of DNA contained in the filtrate from ) / 2 to X is given as C. In this case, A, B, and C are calculated from the following formulas: A = (Z １ ×Y １ +Z ２ ×Y ２ +...+Z m-1 ×Y m-1 ) × DNA concentration in the measurement solution B = Z ｍ ×Y ｍ / 2 × DNA concentration in the measurement solution C = (X - (W) ｍ +W ｍ-1 ) / 2) × (Y ｍ (7) The sum of A, B, and C above is the cumulative amount of DNA leaked up to the cumulative filtration amount X. Cumulative leak = A + B + C (8) The amount of DNA supplied up to the cumulative filtration amount X (cumulative supply) is calculated from the following formula. Cumulative supply = X × DNA concentration in the measurement solution (9) The amount of DNA adsorbed onto the hollow fiber membrane up to the cumulative filtration amount X (cumulative adsorption) is calculated from the following formula. Cumulative adsorption = Cumulative supply - Cumulative leak (10) From the above, the amount of DNA adsorbed per unit mass of hollow fiber membrane is measured from the following formula. DNA adsorbed per unit mass of hollow fiber membrane = Cumulative adsorption / Membrane mass

[0104] In the porous membrane according to this embodiment, the amount of albumin adsorbed as a negatively charged substance may be 1 to 300 mg / g, 3 to 250 mg / g, or 5 to 200 mg / g. In the porous membrane according to this embodiment, the amount of DNA adsorbed as a negatively charged substance may be 10 to 100,000 μg / g, 50 to 70,000 μg / g, or 100 to 50,000 μg / g.

[0105] [Purification Method] The purification method according to this embodiment includes a purification step using the porous membrane described above. Based on the above-described properties of the porous membrane, this purification method can adsorb and remove negatively charged substances from the treatment solution by anion exchange. According to the above purification step, if the porous membrane is a hollow fiber membrane, the treatment solution is first passed through the side having a sparse structure (the first surface side). Furthermore, the treatment solution is filtered toward the side having a dense structure (the second surface side), and negatively charged substances are adsorbed and removed (anion exchange). When the above purification step is applied to the production of antibody drugs, the cell culture medium is passed through the first surface side of the hollow fiber membrane, filtered toward the second surface side, and anion exchange is performed. This removes impurities from the cell culture medium, and antibodies (IgG, etc.) are purified. In this case, negatively charged substances, including albumin and DNA contained in the impurities, are adsorbed and removed by the hollow fiber membrane.

[0106] [Method for Manufacturing a Porous Membrane] The method for manufacturing a porous membrane according to this embodiment is not particularly limited as long as a porous membrane having the above-described characteristics can be obtained. However, according to the following method for manufacturing a porous membrane, a porous membrane having the above-described characteristics may be obtained with good yield. The method for manufacturing a porous membrane according to this embodiment will be explained below by illustrating the method for manufacturing a hollow fiber membrane, which is one form of the above-described porous membrane.

[0107] The above method for producing a hollow fiber membrane includes a spinning step in which a spinning stock and an internal liquid are discharged from a double-tube nozzle through an air-traveling section into a coagulation liquid, the spinning stock is coagulated in the coagulation liquid, and the coagulated product of the spinning stock is drawn out from the coagulation liquid to obtain a hollow fiber membrane. The spinning stock contains a resin raw material including a first polymer, a hydrophobic polymer, and a hydrophilic polymer, a solvent, and a non-solvent. The internal liquid contains water. The total concentration (internal liquid concentration) of components other than water in the internal liquid may be 70 to 90% by mass. The temperature of the coagulation liquid may be 40 to 60°C.

[0108] In the above method for producing hollow fiber membranes, first, a first polymer is prepared by the method described above. A hydrophobic polymer and a hydrophilic polymer are also prepared by obtaining them from the market. The first polymer, the hydrophobic polymer, and the hydrophilic polymer are mixed in predetermined ratios by a known method to prepare a spinning solution. For example, the mixing ratio (mass ratio) of the hydrophobic polymer / first polymer / hydrophilic polymer may be 60-90 / 7-22 / 3-18. A predetermined amount of solvent and non-solvent are also mixed into the spinning solution by a known method.

[0109] <Spinning Process> Figure 5 is a schematic diagram illustrating an example of a method for manufacturing a porous membrane according to this embodiment. As shown in Figure 5, the spinning process 100 may include the following first to third steps, which are carried out in that order. First, in the first step, the spinning dope 10a and the internal liquid 10b are discharged from a double-tube nozzle 11 through an air gap 20 into the solidification liquid 21. In the second step, the spinning dope 10a solidifies in the solidification liquid 21, thereby obtaining a solidified material. In the third step, the solidified material is pulled out from the solidification liquid 21, thereby obtaining a hollow fiber membrane. Pulling out the solidified material (hollow fiber membrane) is performed, for example, by liquid guides 12, 13 and rollers 14, 15, 16. The hollow fiber membrane pulled out from the solidification liquid 21 may be immersed in a water bath 22, for example, and then wound up by a winding machine 23.

[0110] The nozzle 11 is double-tubular and comprises an outer tube and an inner tube provided inside the outer tube. The spinning solution is discharged from the gap (slit) between the outer tube and the inner tube, and the inner solution is discharged from inside the inner tube. The inner diameter of the outer tube may be 500 to 1500 μm, or 600 to 1200 μm. The outer diameter of the inner tube may be 150 to 700 μm, or 150 to 600 μm. The outer diameter of the inner tube may be approximately the same as the inner diameter of the hollow fiber membrane.

[0111] The air gap length (AG length), which is the straight-line distance of the air-traveling section (air gap) 20 (the distance between the tip of the nozzle 11 and the liquid surface of the solidifying liquid 21), may be 10 to 100 mm or 10 to 80 mm.

[0112] The hollow fiber membrane obtained by the above spinning process may be subjected to a further washing process with pure water (washing process). In the washing process, the water flow may be in the opposite direction to the direction of movement of the hollow fiber membrane (countercurrent), or it may be in the same direction as the direction of movement of the hollow fiber membrane (parallel current).

[0113] (Spinning Solution) The spinning solution 10a contains a first polymer, a hydrophobic polymer, and a hydrophilic polymer as described above. Specifically, the spinning solution 10a contains, for example, the above-mentioned structural unit (a-1) and the above-mentioned structural unit (b-1), a first polymer whose cationic group is a dimethylamino group, a hydrophobic polymer such as polyethersulfone, and a hydrophilic polymer such as polyvinylpyrrolidone. The spinning solution 10a further contains a solvent and a non-solvent.

[0114] The temperature of the spinning solution 10a at the nozzle 11 (discharge temperature) may be 40 to 80°C, or 50 to 70°C.

[0115] The concentration of polyethersulfone in the spinning solution 10a may be 10 to 30% by mass, or 10 to 25% by mass. If the concentration of polyethersulfone is too low, the strength of the hollow fiber membrane may be reduced. On the other hand, if the concentration of polyethersulfone is too high, the viscosity of the spinning solution 10a may become too high, making spinning difficult.

[0116] The concentration of polyvinylpyrrolidone in the spinning solution 10a may be 0.5 to 20% by mass, or 1 to 15% by mass. If the concentration of polyvinylpyrrolidone is too low, when the hollow fiber membrane is used for anion exchange, the useful component IgG may be adsorbed to the membrane due to hydrophobic interactions, reducing the recovery rate, or the second component, such as aggregates of IgG in the treated solution, may accumulate and clog the membrane, leading to a rapid deterioration of performance over time. On the other hand, if the concentration of polyvinylpyrrolidone is too high, the viscosity of the spinning solution 10a may become too high, making spinning difficult.

[0117] The concentration of the first polymer in the spinning solution 10a may be 0.2 to 10% by mass, or 0.5 to 6% by mass. If the concentration of the first polymer is too low, when the hollow fiber membrane is used for anion exchange, the adsorption and removal of negatively charged substances in the treated solution may be insufficient, and unwanted components may leak out. On the other hand, if the concentration of the first polymer is too high, the viscosity of the spinning solution 10a may become too high, making spinning difficult.

[0118] The solvent is a liquid capable of dissolving the first polymer and the polyethersulfone. The solvent may be a polar solvent and may be soluble in water. The polar solvent may be an aprotic polar solvent. Examples of the aprotic polar solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), and acetonitrile.

[0119] The non-solvent is a liquid (excluding water) that does not dissolve the first polymer and the polyethersulfone. Examples of the non-solvent include glycol esters, glycerin, and alcohols. The non-solvent may be a glycol ester. Examples of glycol esters include ethylene glycol, triethylene glycol (TEG), polyethylene glycol (polyethylene glycol 200, polyethylene glycol 400, etc.), and propylene glycol.

[0120] In the spinning solution 10a, the ratio of the mass of solvent (S) to non-solvent (NS) (S / NS ratio) may be 15 / 85 to 60 / 40, or 20 / 80 to 55 / 45. If the S / NS ratio in the spinning solution becomes too small, the dissolution of the first polymer and polyethersulfone becomes unstable, which may lead to decreased spinning stability or failure to obtain the asymmetric hollow fiber membrane described above. If the S / NS ratio becomes too large, it may lead to failure to obtain the asymmetric hollow fiber membrane or decreased spinning stability. In addition to the solvent and non-solvent, the spinning solution may also contain water.

[0121] The order of adding materials and the mixing method when mixing the resin raw materials, solvents, and non-solvents that constitute the hollow fiber membrane are not particularly limited, and known orders and methods may be used.

[0122] (Internal liquid) The internal liquid 10b contains water. The water content in the internal liquid 10b may be 5 to 30% by mass, or 10 to 25% by mass.

[0123] The internal liquid 10b may contain solvents, non-solvents, etc., in addition to water. Examples of non-solvents include ethylene glycol, triethylene glycol (TEG), polyethylene glycol 200 or 400, glycerin, and propylene glycol. Examples of solvents include N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide, and dimethyl sulfoxide.

[0124] When the water content of the internal liquid 10b is low and the content of each solvent is high, the solidification rate on the inner surface (first surface) side of the hollow fiber membrane slows down, the phase separation time is extended, and a sparse structure tends to be constructed on the inner surface side. When the water content of the internal liquid 10b is high and the content of each solvent is low, the solidification rate on the inner surface (first surface) side of the hollow fiber membrane speeds up, the phase separation time is shortened, and a dense structure tends to be constructed on the inner surface side. For this reason, in order to obtain a hollow fiber membrane that exhibits a sparse structure on the inner surface (first surface) side, the concentration of components other than water (solvents, non-solvents, etc.) contained in the internal liquid 10b (internal liquid concentration) can be high. In this case, the internal liquid concentration may be 70 to 95% by mass, or 75 to 90% by mass. The ratio of the mass of solvent to non-solvent in the internal liquid (solvent / non-solvent) is, for example, 40 / 60 to 60 / 40.

[0125] When the spinning solution 10a and the internal liquid 10b are discharged from the double-tube nozzle 11, a temperature difference may be provided between the spinning solution 10a and the internal liquid 10b.

[0126] (Coagulation Solution) The coagulation solution 21 may contain a solvent and a non-solvent. The solvent and non-solvent may each be one type or a mixture of multiple types. If the content of each solvent in the coagulation solution 21 is too high, the coagulation rate on the outer surface (second surface) of the hollow fiber membrane will slow down, the phase separation time will be extended, and a sparse structure may be formed on the outer surface. If the water content in the coagulation solution 21 is too high and the content of each solvent is too low, the coagulation rate on the outer surface (second surface) of the hollow fiber membrane will be too fast, the phase separation time will be shortened, and a dense structure may be formed on the outer surface. From the viewpoint of obtaining a hollow fiber membrane with a dense outer surface, the ratio of the total amount of the solvent and non-solvent in the coagulation solution 21 (concentration of the coagulation solution: CB concentration) may be 20 to 60% by mass, or 30 to 45% by mass. The ratio of the mass of the solvent to the non-solvent in the coagulation solution 21 (solvent / non-solvent) is, for example, 30 / 70 to 70 / 30.

[0127] The temperature of the coagulation solution 21 greatly affects the coagulation time of the hollow fiber membrane. If the temperature of the coagulation solution 21 is too high, the coagulation rate on the outer surface (second surface) of the hollow fiber membrane will be slow, the phase separation time will be prolonged, and a sparse structure may be formed on the outer surface. If the temperature of the coagulation solution 21 is too low, the coagulation rate on the outer surface (second surface) of the hollow fiber membrane will be fast, the phase separation time will be shortened, and a dense structure may be formed on the outer surface. From the viewpoint of obtaining a hollow fiber membrane of this embodiment in which the outer surface is dense, the temperature of the coagulation solution 21 may be 30 to 70°C or 40 to 60°C.

[0128] If the solidification rate of the outer surface of the hollow fiber membrane is too fast compared to the inner surface, the outer surface becomes excessively dense, preventing the permeation of useful components such as IgG. Conversely, if the solidification rate of the outer surface is too slow compared to the inner surface, the pore size on the outer surface becomes large, allowing unwanted contaminants to pass through. If the solidification rate is even slower, the inner surface becomes dense and the outer surface becomes sparse, preventing liquid from penetrating from the inner surface into the hollow fiber membrane. Therefore, in order to obtain the hollow fiber membrane of this embodiment, which has a sparse inner surface structure, a dense outer surface structure, and an asymmetric structure that allows useful components to pass through while blocking contaminants, the balance between the internal liquid concentration, the solidification liquid concentration, and the temperature described above is important.

[0129] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0130] [First Example] As the first example, a method for preparing the first polymer (samples 1 to 7) used to produce the porous membranes of samples 11 to 1A and samples 21 to 23, which will be described later, will be explained.

[0131] <Evaluation Method> The weight-average molecular weight, molecular weight distribution, amine value, elution rate in water, and elution rate in NMP of various first polymers (samples 1 to 7) used to prepare the porous membranes of samples 11 to 1A and samples 21 to 23 described later were evaluated according to the evaluation method below. The meanings of the abbreviations are as follows: BTEE: Ethyl-2-methyl-2-n-butylteranyl-propionate DBDT: Dibutylditerlide AIBN: 2,2'-azobis(isobutyronitrile) BzMA: Benzyl methacrylate IBXMA: Isobornyl methacrylate DMAEMA: Dimethylaminoethyl methacrylate DEAEMA: Diethylaminoethyl methacrylate DMAPMAAm: Dimethylaminopropyl methacrylamide BzCl: Benzyl chloride AcOEt: Ethyl acetate

[0132] (Weight-average molecular weight and molecular weight distribution) The weight-average molecular weight and molecular weight distribution of the first polymer of samples 1 to 7 were determined by gel permeation chromatography using a GPCV-2000, manufactured by Waters Corporation of Japan. One SHODEX KF-603 column (φ6 mm × 150 mm) (manufactured by Showa Denko Corporation) was used as the column, a 10 mmol / L lithium bromide / 10 mmol / L acetate / N-methyl-2-pyrrolidone solution was used as the mobile phase, and a differential refractometer was used as the detector. The measurement conditions were a column temperature of 40°C, a sample concentration of 10 mg / mL, a sample injection volume of 10 μm, and a flow rate of 0.2 mL / min. Using polystyrene (molecular weights 1,090,000, 775,000, 427,000, 190,000, 96,400, 37,900, 10,200, 2,630, and 1,150) as standard materials, a calibration curve was created, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were measured. From these measured values, the molecular weight distribution (Mw / Mn) was calculated.

[0133] (Amine Value) The amine value refers to the mass of potassium hydroxide equivalent to the basic component per gram of solid content (first polymer of samples 1 to 7). A potentiometric titrator (product name: "GT-200", manufactured by Mitsubishi Chemical Analytec Co., Ltd.) was used, and the samples to be measured, obtained by dissolving samples 1 to 7 in tetrahydrofuran, were titrated with a 0.1 mol / L hydrochloric acid / 2-propanol solution. The inflection point of the titration pH curve was defined as the titration endpoint, and the amine value was calculated using the following formula: B = 56.11 × Vs × 0.1 × f / w B: Amine value (mg KOH / g) Vs: Amount of 0.1 mol / L hydrochloric acid / 2-propanol solution used for titration (mL) f: Titer of 0.1 mol / L hydrochloric acid / 2-propanol solution w: Mass of the sample (g) (converted to solid content)

[0134] (Water elution rate) Samples 1 to 7 were mixed with 90 parts by mass of deionized water at 24°C so that each sample amounted to 10 parts by mass. The mixture was shaken at 24°C for 1 hour and then allowed to stand for 24 hours. Next, the mixture was filtered using a 5 μm syringe filter (product name: "PTFE Syringe Filter", manufactured by Membrane-Solutions LLC). The filtrate with mass W1 was weighed into an aluminum cup (mass W0) and dried under reduced pressure at 130°C for 1 hour to obtain solids. The mass of the aluminum cup containing the solids (W2) was measured, and the water elution rate of samples 1 to 7 was calculated using the following formula: Water elution rate (mass%) = [(W2 - W0) / (W1 × 0.1)] × 100

[0135] (Elution rate to NMP) Samples 1 to 7 were mixed with 90 parts by mass of NMP at 24°C, with each sample comprising 10 parts by mass. The resulting mixture was shaken at 24°C for 1 hour and then allowed to stand for 24 hours. Next, the mixture was filtered using a 5 μm syringe filter (product name: "PTFE Syringe Filter", manufactured by Membrane-Solutions LLC). The filtrate with mass W3 was weighed into an aluminum cup (mass W0) and dried under reduced pressure at 130°C for 1 hour to obtain solids. The mass of the aluminum cup containing the solids (W4) was measured, and the elution rate of samples 1 to 7 to NMP was calculated using the following formula: NMP elution rate (mass%) = [(W4 - W0) / (W3 × 0.1)] × 100

[0136] <Preparation of the First Polymer> (Samples 1 to 5) A flask equipped with an argon gas inlet tube and a stirrer was used, and a mixed solution of argon-purged vinyl monomers (BzMA and IBXMA), BTEE, DBDT, AIBN, and AcOEt was reacted at 60°C to obtain a first reaction solution in which block A was formed. The vinyl monomers were blended in the proportions shown in Table 1 in order to form block A.

[0137] A mixed solution of vinyl monomer (one selected from the group consisting of DMAEMA, DEAEMA, and DMAPMAAm), AIBN, and AcOEt, which has been pre-substituted with argon, was added to the first reaction solution containing block A, and these reacted at 60°C to obtain a second reaction solution in which block B was formed. The vinyl monomers were blended in the proportions shown in Table 1 in order to form block B.

[0138] The above second reaction solution was poured into stirred heptane, which generated a precipitate. Subsequently, the supernatant containing the heptane was removed, and the precipitate was dried to obtain the first polymers of Samples 1 to 5. The weight-average molecular weight (Mw), molecular weight distribution (Mw / Mn), amine value, elution rate in water, and elution rate in NMP for each of the first polymers of Samples 1 to 5 are shown in Table 1.

[0139] (Samples 6 to 7) Sample 2 was dissolved in NMP to obtain a solution to which DMAEMA and DMAEMA·BzCl were added in the ratios shown in Table 1. These reacted at 60°C to obtain a third reaction solution in which the tertiary amine in Sample 2 was quaternized. Next, the above third reaction solution was poured into stirred heptane to form a precipitate. After that, the supernatant containing the heptane was removed and the precipitate was dried to obtain the first polymers of Samples 6 to 7. The amine values, elution rates in water, and elution rates in NMP for each of the first polymers of Samples 6 to 7 are shown in Table 1. In the first polymer of Sample 6, 52 mol% of the tertiary amine in Sample 2 was quaternized. In the first polymer of Sample 7, 38 mol% of the tertiary amine in Sample 2 was quaternized. The amine values, elution rates in water, and elution rates in NMP for the first polymers of Samples 1 to 7 are shown in Table 1.

[0140]

[0141] In Table 1 above, "A" refers to Block A, and "B" refers to Block B. In Table 1 above, the units for the content of each component constituting Block A, BzMA and IBXMA, and each component constituting Block B, DMAEMA, DEAEMA, DMAPMAAm, and DMAEMA·BzCl, are in mole percent.

[0142] [Second Example] As a second example, the manufacturing method and characteristics of the porous membranes of Samples 11 to 1A and Samples 21 to 23 will be described. The porous membranes of Samples 101, 102, and 201 described in the second example are comparative examples.

[0143] <Production of Porous Membrane> (Sample 11) 1) Preparation of Membrane Stock Solution 16.0% by mass of polyethersulfone (PES, Sumika Excel 4800, Sumitomo Chemical), 4.0% by mass of the first polymer of Sample 1, 3.0% by mass of polyvinylpyrrolidone K-90 (PVP, Nippon Shokubai), 42.35% by mass of N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical Corporation), and 34.65% by mass of triethylene glycol (TEG, Mitsubishi Chemical Corporation) were mixed and heated to dissolve uniformly, thereby preparing the membrane stock solution.

[0144] 2) Manufacturing of a porous membrane The above membrane stock solution was dropped onto a glass plate and spread with a bar coater. The gap between the glass plate and the bar coater was set to 75 μm. The glass plate on which the membrane stock solution was spread was immersed in a solidification solution. The solidification solution was formed by mixing a mixture of NMP (solvent) and TEG (non-solvent) in a mass ratio (S / NS ratio) of NMP / TEG = 55 / 45 with reverse osmosis (RO) water. The total concentration of the solvent and non-solvent in the solidification solution (CB concentration) was 40% by mass, and the RO water was 60% by mass. The glass plate was immersed in the solidification solution for 10 minutes and solidified to obtain a flat membrane. The flat membrane was washed with RO water at 70°C for 1 hour. Subsequently, the flat membrane was dried in a dryer at 60°C. As a result, a porous membrane (flat membrane) of sample 11 was obtained.

[0145] (Sample 12) A porous membrane (flat membrane) of Sample 12 was obtained in the same manner as Sample 11, except that the first polymer of Sample 2 was incorporated in place of Sample 1 in the preparation of the membrane stock solution.

[0146] (Sample 13) A porous membrane (flat membrane) of Sample 13 was obtained in the same manner as Sample 11, except that the first polymer of Sample 3 was incorporated in place of Sample 1 in the preparation of the membrane stock solution.

[0147] (Sample 14) A porous membrane (flat membrane) of Sample 14 was obtained in the same manner as Sample 11, except that the first polymer of Sample 4 was incorporated in place of Sample 1 in the preparation of the membrane stock solution.

[0148] (Sample 15) A porous membrane (flat membrane) of Sample 15 was obtained in the same manner as Sample 11, except that the first polymer of Sample 5 was incorporated in place of Sample 1 in the preparation of the membrane stock solution.

[0149] (Sample 16) A porous membrane (flat membrane) of Sample 16 was obtained in the same manner as Sample 11, except that the first polymer of Sample 6 was incorporated in place of Sample 1 in the preparation of the membrane stock solution.

[0150] (Sample 17) In the preparation of the membrane stock solution, the first polymer of Sample 7 was added instead of Sample 1, except that the porous membrane (flat membrane) of Sample 17 was obtained in the same manner as Sample 11.

[0151] (Sample 18) In the preparation of the film stock solution, the amount of Sample 1 was changed to 0.5% by mass, the amount of N-methyl-2-pyrrolidone (NMP, manufactured by Mitsubishi Chemical Corporation) was changed to 44.28% by mass, and the amount of triethylene glycol (TEG, manufactured by Mitsubishi Chemical Corporation) was changed to 36.22% by mass. A porous film (flat film) of Sample 18 was obtained in the same manner as Sample 11.

[0152] (Sample 19) In the preparation of the membrane stock solution, the porous membrane (flat membrane) of Sample 19 was obtained in the same manner as Sample 11, except that the formulation of Sample 1 was changed to 6% by mass, the amount of N-methyl-2-pyrrolidone was changed to 41.25% by mass, and the amount of triethylene glycol was changed to 33.75% by mass.

[0153] (Sample 1A) In the preparation of the film stock solution, the composition of Sample 1 was changed to 2% by mass, the amount of N-methyl-2-pyrrolidone was changed to 43.45% by mass, and the amount of triethylene glycol was changed to 35.55% by mass. A porous film (flat film) of Sample 1A was obtained in the same manner as Sample 11.

[0154] (Sample 21) Sample 21, a porous membrane (hollow fiber membrane), was manufactured by basically the same method as the method for manufacturing a hollow fiber membrane described in the section [Modes for Carrying Out the Invention] above. In the spinning process, the spinning solution, described later, was discharged together with the internal liquid from a heated tube-in-orifice nozzle, passed through a dry section (air-running section: air gap) that was isolated from the outside air by a spinning tube, and then solidified in a solidification bath to form a hollow fiber membrane. After that, the hollow fiber membrane went through a water washing bath and was wound up at a predetermined spinning speed in a skein winding machine. The specific conditions were as follows.

[0155] 1) Preparation of the spinning stock solution The spinning stock solution was prepared by mixing 16.0% by mass of polyethersulfone (PES, Sumika Excel 4800, manufactured by Sumitomo Chemical), 4.0% by mass of the first polymer of Sample 1, 3.0% by mass of polyvinylpyrrolidone K-90 (PVP, manufactured by Nippon Shokubai), 42.35% by mass of N-methyl-2-pyrrolidone (NMP, manufactured by Mitsubishi Chemical Corporation), and 34.65% by mass of triethylene glycol (TEG, manufactured by Mitsubishi Chemical Corporation), and heating to dissolve uniformly.

[0156] 2) Composition of the internal solution A mixture of NMP (solvent) and TEG (non-solvent) in a mass ratio (S / NS ratio) of NMP / TEG = 55 / 45 was mixed with reverse osmosis (RO) water to form the internal solution. The total concentration of the solvent and non-solvent in the internal solution (internal solution concentration) was 80% by mass, and the RO water was 20% by mass.

[0157] 3) Composition of the coagulation solution A mixture of NMP (solvent) and TEG (non-solvent) in a mass ratio (S / NS ratio) of NMP / TEG = 55 / 45 was mixed with reverse osmosis (RO) water to form the coagulation solution. The total concentration of the solvent and non-solvent in the coagulation solution (CB concentration) was 40% by mass, and the RO water was 60% by mass.

[0158] 4) Conditions for the spinning process Discharge temperature of the spinning solution (set temperature): 60°C Distance of the air-traveling section (air gap length: AG length): 40 mm Drawing speed (spinning speed): 20 m / min

[0159] 5) Conditions for the rinsing process: Flow in the rinsing tank (rinsing bath): Countercurrent; Temperature: 45°C

[0160] The bundles of hollow fiber membranes obtained by the above process were cut to a certain length, wrapped in gauze, and then washed with RO water at 80°C. After that, the bundles of hollow fiber membranes were dried in a hot air dryer at 60°C. Thus, the porous membrane (hollow fiber membrane) of sample 21 was obtained.

[0161] The porous membrane (hollow fiber membrane) of sample 21 had a dense layer on its outer surface, an inner diameter of 265 μm, an outer diameter of 395 μm, and a thickness (film thickness) of 65 μm.

[0162] The method for measuring the inner diameter, outer diameter, and film thickness of the hollow fiber membrane described above was as follows: A predetermined number of hollow fiber membranes were passed through a 3 mm diameter hole in the center of a glass slide, ensuring they did not fall out. A cross-sectional sample was then obtained by cutting the membrane along the top and bottom surfaces of the glass slide with a razor blade. The inner and outer diameters of the cross-sectional sample were measured using a projector (Nikon PROFILE PROJECTOR V-12).

[0163] Specifically, for each cross-sectional sample, the dimensions of the outer surface of the hollow fiber membrane in the X-X and Y-Y directions (two orthogonal directions on the cross-section) were measured, and the arithmetic mean of these values ​​was taken as the outer diameter of the cross-sectional sample. For each cross-sectional sample, the dimensions of the hollow portion in the X-X and Y-Y directions (two orthogonal directions on the cross-section) were measured, and the arithmetic mean of these values ​​was taken as the inner diameter of the cross-sectional sample. The same measurement was performed for 10 cross-sectional samples, and the average values ​​were taken as the inner and outer diameters of the hollow fiber membrane sample. The film thickness (average value) was calculated using the formula "(outer diameter - inner diameter) / 2" based on the measurement results (average values) of the inner and outer diameters of the hollow fiber membrane.

[0164] (Sample 22) The porous membrane of Sample 22 was obtained in the same manner as Sample 21, except that the first polymer of Sample 3 was incorporated in place of Sample 1 during the preparation of the spinning solution.

[0165] The porous membrane (hollow fiber membrane) of sample 22 had a dense layer on its outer surface, an inner diameter of 265 μm, an outer diameter of 395 μm, and a thickness (film thickness) of 65 μm.

[0166] (Sample 23) In the preparation of the spinning solution, the porous membrane of Sample 23 was obtained in the same manner as Sample 22, except that the proportion of Sample 3 was changed to 2% by mass, the amount of N-methyl-2-pyrrolidone was changed to 43.45% by mass, and the amount of triethylene glycol was changed to 35.55% by mass.

[0167] (Sample 101) A porous membrane (flat membrane) of Sample 101 was obtained in the same manner as Sample 11, except that the membrane stock solution was prepared without the first polymer.

[0168] (Sample 102) A porous membrane (flat membrane) of Sample 102 was obtained in the same manner as Sample 11, except that the membrane stock solution was prepared by using polyethyleneimine instead of the first polymer.

[0169] (Sample 201) "Mustang Q" manufactured by Global Life Science Technologies Japan was prepared as the porous membrane (flat membrane) for sample 201.

[0170] <Evaluation Method> The characteristics of the porous membranes of samples 11 to 1A, 21 to 23, 101 to 102, and 201 (anion exchange capacity (AEC), adsorption amount of negatively charged substances (albumin and DNA)) were evaluated according to the evaluation method for anion exchange capacity (AEC) and the evaluation method for adsorption amount of negatively charged substances described above. Furthermore, the amount of neutral protein adsorption in each sample was evaluated in accordance with the evaluation method for adsorption amount of negatively charged substances described above, except that the substance to be adsorbed was changed from a negatively charged substance to a neutral protein.

[0171] Table 2 shows a list of the functional group names and amine grades of the cationic groups in the porous membranes of Samples 11 to 1A, 21 to 23, 101 to 102, and 201, as well as the sample numbers and amounts of the first polymer used in the porous membranes, and their solubility in water and NMP. In Table 2, S indicates solubility and I indicates insolubility for solubility in water and NMP. For the solubility of Sample 201 in water and NMP, the cationic groups are grafted onto the membrane substrate, and the solubility of the polymer with cationic groups alone cannot be evaluated, so it is indicated by "-" in Table 2. Furthermore, the results of the characterization evaluation (anion exchange capacity (AEC), adsorption amount of negatively charged substances (albumin and DNA), and neutral protein adsorption amount) for these samples are shown in Table 3. The albumin adsorption amount and DNA adsorption amount of Sample 102 were not evaluated because the AEC was 0 (zero). Therefore, these adsorption amounts are indicated by "-" in Table 3.

[0172]

[0173]

[0174] <Discussion> From Table 3 above, it is suggested that the porous membranes of Samples 11 to 1A and Samples 21 to 23 have superior anion exchange capacity (AEC) and superior albumin and DNA adsorption performance compared to Samples 101 and 102. Furthermore, it is suggested that the porous membranes of Samples 11 to 1A and Samples 21 to 23 have performance equivalent to or better than that of Sample 201.

[0175] [Third Example] In the third example, the characteristics of the porous membrane (hollow fiber membrane) of sample 22, specifically its porosity and gold colloid transmittance, will be described. Furthermore, the evaluation results are shown in Table 4.

[0176] <Evaluation Method> The porosity of the porous membrane of sample 22 was evaluated according to the evaluation method for porosity described above. Furthermore, the physical property of the gold colloid's transmittance was evaluated according to the following measurement method. The results are shown in Table 4.

[0177] (Gold colloid transmittance) The transmittance of 10 nm gold colloid (gold colloid with an average particle size of 10 nm) and 30 nm gold colloid (gold colloid with an average particle size of 30 nm) was measured as follows.

[0178] 1) Fabrication of Loop-Type Mini-Modules: Bundles of multiple hollow fiber membranes, cut to a length of approximately 40 cm, were bent, their ends overlapped, and these ends were inserted into a pipe (sleeve). After this, the bundles were hardened with hot-melt resin. By cutting a portion of the adhesive fixing portion, a loop-type mini-module was fabricated with an open hollow section of the hollow fiber membrane. The number of hollow fiber membranes was determined as appropriate.

[0179] 2) Preparation of gold colloid dispersion A homogeneous solution of 10 nm and 30 nm gold colloids (standard gold colloid product from BBI Solutions) was mixed with 3 mL of an aqueous solution of 2.0% by mass bovine serum albumin (Albumin, Bovine Serum, F-V, pH 5.2, from Nacalai Tesque). Then, 3 mL of an aqueous solution of 0.4% by mass glutathione (reduced form) (from Nacalai Tesque) was added.

[0180] 3) Gold Colloid Transmission Experiment Using the loop-type minimodule prepared above, (1) the gold colloid dispersion was subjected to dead-end filtration at a pressure of 1000 hPa, and the filtrate was sampled. (2) The transmittance of the gold colloid was calculated from the following absorbance measurement (wavelength 540 nm): Transmittance = Absorbance of gold colloid dispersion / Absorbance of filtrate

[0181] (Results) The absorbances of the 10 nm gold colloid test solution and filtrate at a wavelength of 540 nm were 0.0416 and 0.0348, respectively. Therefore, the transmittance was calculated to be 84%. The absorbances of the 30 nm gold colloid test solution and filtrate at a wavelength of 540 nm were 0.0373 and 0.0019, respectively. Therefore, the transmittance was calculated to be 5%.

[0182] (Thickness of the 20 nm gold colloid capture layer) The thickness of the layer in which the 20 nm gold colloid is captured (capture layer) was measured when the measurement solution (20 nm gold colloid dispersion) was filtered from the inside to the outside of the hollow fiber membrane using the following procedure.

[0183] 1) Preparation of gold colloid dispersion: 6 mL of a 20 nm gold colloid homogeneous solution (Gold Colloid, BBI Solutions) and 3 mL of a 2.0% by mass bovine serum albumin aqueous solution (Albumin, Bovine Serum, F-V, pH 5.2, Nacalai Tesque) were mixed, and then 3 mL of a 0.4% by mass glutathione (reduced form) aqueous solution (Nacalai Tesque) was added.

[0184] 2) Gold Colloid Capture Experiment (1) The measurement solution (20 nm gold colloid dispersion) was subjected to dead-end filtration in the same manner as the measurement of gold colloid transmittance described above, and a cross-section of the hollow fiber membrane (sample 22) after filtration was imaged with a microscope. (2) The image after capture was binarized (WinROOF 2013), and the distance from the primary side (inner surface of the hollow fiber membrane) to the gold colloid capture position was measured. In Table 4 below, the ratio of the thickness of the capture layer to the thickness of the hollow fiber membrane is also shown.

[0185]

[0186] <Discussion> From Table 4 above, the hollow fiber membrane of sample 22 showed that the transmittance of gold colloid with an average particle size of 10 nm from the inner surface (first surface) to the outer surface (second surface) was 20% or more, while the transmittance of gold colloid with an average particle size of 30 nm from the inner surface to the outer surface was 20% or less. When gold colloid with an average particle size of 20 nm was transmitted from the inner surface to the outer surface, the ratio of the thickness of the capture layer, which is the layer in which the gold colloid with an average particle size of 20 nm is captured, was 5% or more of the thickness of the hollow fiber membrane. Considering this, along with the results of the second example, it is suggested that sample 22 has sufficient anion exchange capacity and that a clogging suppression effect can be obtained due to its non-uniform structure in the thickness direction.

[0187] Although embodiments of the present invention have been described above, it is also intended from the outset that the configurations of each of the above embodiments may be combined as appropriate.

[0188] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of equivalents of the claims are intended to be included.

[0189] 1 Negatively charged substance, 2 Antibody, 3 Porous membrane (hollow fiber membrane), 4 Second component, 5 First component, 100 Spinning process, 10a Spinning stock, 10b Internal solution, 11 Nozzle, 12, 13 Guides in liquid, 14, 15, 16 Rollers, 20 Air-running section, 21 Coagulation solution, 22 Water washing bath, 23 Winding machine.

Claims

1. A porous membrane comprising a first polymer soluble in N-methyl-2-pyrrolidone and insoluble in water, wherein the first polymer has cationic groups.

2. The porous membrane according to claim 1, wherein the first polymer comprises a constituent unit derived from a monomer having a cationic group and a constituent unit derived from a monomer not having a cationic group, and the cationic group is both or either a tertiary amino group and a quaternary ammonium group.

3. The porous membrane according to claim 1 or claim 2, wherein the cationic groups are uniformly distributed in a cross-section obtained by cutting the porous membrane in a direction normal to the surface.

4. A porous membrane according to any one of claims 1 to 3, further comprising a hydrophobic polymer and a hydrophilic polymer.

5. The porous membrane according to claim 4, wherein the hydrophobic polymer is both or either polysulfone and polyethersulfone.

6. The porous membrane according to claim 4 or 5, wherein the hydrophilic polymer is both or either polyvinylpyrrolidone and a copolymer of vinylpyrrolidone and vinyl acetate.

7. A porous membrane according to any one of claims 1 to 6, having a hollow fiber membrane shape with a first surface and a second surface, wherein the side with the first surface has a sparse structure, the side with the second surface has a dense structure, and the structure tends to become denser along the direction from the side with the first surface toward the side with the second surface.

8. The porous membrane according to claim 7, wherein the first surface is the inner surface in the hollow fiber membrane shape, and the second surface is the outer surface in the hollow fiber membrane shape.

9. The porous membrane according to claim 7 or claim 8, wherein the transmittance of gold colloid having an average particle size of 10 nm from the first surface to the second surface is 20% or more, the transmittance of gold colloid having an average particle size of 30 nm from the first surface to the second surface is 20% or less, and when gold colloid having an average particle size of 20 nm is transmitted from the first surface to the second surface, the ratio of the thickness of the capture layer, which is the layer in which the gold colloid having an average particle size of 20 nm is captured, is 5% or more of the thickness of the porous membrane.

10. A porous membrane according to any one of claims 1 to 9, for purification by anion exchange.

11. A purification method comprising a purification step using a porous membrane as described in any one of claims 1 to 10.

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