Ion exchange membrane, method for producing same, and use thereof

Abstract

Provided is an ion exchange membrane in which folding and wrinkles are less likely to occur when implemented without being provided with a reinforcing material.　An ion exchange membrane according to the present invention includes a base material film obtained by molding a base polymer into a film shape, wherein a graft chain having an ion exchange group is bonded to the base polymer, and has a roughened surface.

Description

Ion exchange membrane, its manufacturing method and use

[0001] The present invention relates to an ion exchange membrane, a method for producing an ion exchange membrane, and uses of the ion exchange membrane.

[0002] In the seawater concentration step in the ion exchange membrane salt production method, an electrodialysis cell using a cation exchange membrane and an anion exchange membrane is used. Patent Documents 1 to 3 describe a method for producing an ion exchange membrane for salt production by irradiating a polymer film having no ion exchange groups with ionizing radiation to generate radicals, and then introducing ion exchange groups by graft polymerization of a monomer.

[0003] Patent No. 5120541 Patent No. 5050284 Patent No. 5050285

[0004] According to the methods described in Patent Documents 1 to 3, ion exchange membranes can be produced without reinforcing materials such as cloth, porous fabric, or nonwoven fabric, but they are very flexible and can be difficult to handle. For example, when an ion exchange membrane is mounted in an electrodialysis cell, a diffusion dialysis cell, or an electrochemical cell that performs electrolysis, the membrane is prone to creases and wrinkles at the location where the membrane is fixed (fastened) with a frame. Such creases and wrinkles can lead to problems such as leakage of liquid flowing through the device and damage to the membrane when the device is disassembled for maintenance. The present invention provides an ion exchange membrane that is less likely to crease or wrinkle during mounting, even without reinforcing materials.

[0005] The present invention has the following aspects. [1] An ion exchange membrane comprising a substrate film formed from a base polymer in a film shape, wherein graft chains having ion exchange groups are bonded to the base polymer, and wherein the ion exchange membrane has a roughened surface. [2] The ion exchange membrane according to [1], wherein the base polymer is a copolymer containing ethylene units and tetrafluoroethylene units, or a copolymer containing ethylene units and chlorotrifluoroethylene units. [3] The ion exchange membrane according to [1], wherein the base polymer is a polyolefin. [4] The ion exchange membrane according to [3], wherein the polyolefin comprises one or more selected from the group consisting of polyethylene, polypropylene, poly(4-methyl-1-pentene), and polynorbornene. [5] The ion exchange membrane according to any one of [1] to [4], wherein the roughness Rz of the roughened surface of the ion exchange membrane is 1 to 40 μm. [6] The ion exchange membrane according to any one of [1] to [5], wherein the maximum width of the planar shape is 50 cm or more. [7] The ion exchange membrane according to any one of [1] to [6], wherein the thickness is 10 to 200 μm. [8] The ion exchange membrane according to any one of [1] to [7], which has cation exchange groups as the ion exchange groups and has an amino group on at least one surface. [9] A method for concentrating seawater, which involves electrodialysis using the ion exchange membrane according to any one of [1] to [8].

[10] A method for generating electricity by performing at least one of concentration difference power generation and reverse electrodialysis power generation using the ion exchange membrane according to any one of [1] to [8].

[11] A method for producing an ion exchange membrane, which comprises using a substrate film having a roughened surface formed from a base polymer, irradiating the substrate film with ionizing radiation to generate radicals in the base polymer, and graft polymerizing raw material monomers including a monomer having an ion exchange group.

[12] A method for producing an ion exchange membrane, which comprises using a substrate film having a roughened surface formed from a base polymer, irradiating the substrate film with ionizing radiation to generate radicals in the base polymer, graft polymerizing raw material monomers including a monomer for introducing an ion exchange group having a functional group capable of introducing an ion exchange group, and then introducing an ion exchange group into units derived from the monomer for introducing an ion exchange group.

[13] The method for producing an ion exchange membrane according to

[11] or

[12] , wherein the substrate film has a surface roughened by a transfer method.

[14] The method for producing an ion exchange membrane according to any one of

[11] to

[13] , wherein the roughness Rz of the roughened surface of the substrate film is 3 to 20 μm.

[0006] According to the present invention, an ion exchange membrane that is less likely to break or wrinkle when mounted can be obtained without using a reinforcing material.

[0007] 1 is an explanatory diagram showing an example of a step of irradiating with ionizing radiation. FIG. 2 is a schematic diagram showing a configuration of a device for measuring film resistance.

[0008] The following terms used in this specification and claims are defined as follows: Surface roughness is a value obtained by measurement using a tactile surface roughness measuring instrument. Roughness Rz means the "maximum height of the roughness curve" as defined in JIS B0601:2013. Roughness Ra means the "arithmetic mean height of the roughness curve" as defined in JIS B0601:2013. The symbol "to" indicating a numerical range means that the values ​​before and after it are included as the lower and upper limits. Halogen atoms refer to fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0009] <Ion Exchange Membrane> The ion exchange membrane of the present embodiment includes a substrate film formed by molding a base polymer into a film shape, and graft chains having ion exchange groups are bonded to the base polymer, and the ion exchange membrane has a roughened surface.

[0010] The roughened surface of the ion exchange membrane has fine irregularities. Only one side of the ion exchange membrane may be roughened, or both sides may be roughened. Both sides are preferably roughened. It is preferable that the entire surface of one or both sides of the ion exchange membrane is roughened.

[0011] In the ion exchange membrane, the roughness Rz of the roughened surface is preferably 1 to 40 μm, more preferably 5 to 30 μm, even more preferably 8 to 25 μm, and particularly preferably 10 to 20 μm. When Rz is equal to or greater than the lower limit of the above range, the ion exchange membrane is excellent in preventing folds and wrinkles. When Rz is equal to or less than the upper limit of the above range, it is easy to prevent a decrease in membrane strength due to roughening. In addition, it is easy to prevent liquid leakage after installation. For example, when installed in a dialysis cell and used, if the membrane surface roughness is too high, there is a risk of liquid circulating within the device leaking out of the dialysis cell. For the same reasons, the roughness Ra of the roughened surface of the ion exchange membrane is preferably 0.1 to 10 μm, more preferably 1 to 5 μm, and even more preferably 1.5 to 3.5 μm. In the ion exchange membrane, it is preferable that at least Rz of the roughened surface is within the above range, and it is more preferable that both Rz and Ra are within the above range.

[0012] The larger the size of the ion exchange membrane, the more likely it is to fold or wrinkle during packaging. The ion exchange membrane is usually cut to fit the size of the frame. In this specification, the planar shape of the ion exchange membrane refers to the shape of the area surrounded by the frame. The planar shape of the ion exchange membrane may be any of a variety of shapes, including polygonal, circular, and elliptical. The maximum value of the distance between any two points on the periphery of the planar shape is defined as the "maximum width of the planar shape." The larger the maximum width of the planar shape of the ion exchange membrane of this embodiment, the greater the effect of applying the present invention. In this regard, the planar shape of the ion exchange membrane is preferably 50 cm or more, more preferably 100 cm or more, and is particularly effective and preferred when it is 150 cm or more.

[0013] A thinner ion exchange membrane can easily reduce membrane resistance, but the thinner it is, the more likely it is to fold or wrinkle during implementation. Because folds and wrinkles are more likely to occur and the application of the present invention is more effective, the thickness of the ion exchange membrane is preferably 200 μm or less, more preferably 180 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, particularly preferably 80 μm or less, and most preferably 60 μm or less. On the other hand, if the ion exchange membrane is too thin, pinholes are more likely to occur due to the fine irregularities on the roughened surface. The lower limit of the thickness of the ion exchange membrane is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 25 μm or more, and particularly preferably 30 μm or more.

[0014] <Substrate Film> The substrate film is a film formed from a base polymer. In addition to the base polymer, the substrate film may contain additives, etc., as necessary. The thickness of the substrate film is designed to be smaller than the thickness of the ion exchange membrane to be obtained, taking into account the increase in membrane thickness due to graft polymerization. Therefore, the preferred thickness of the substrate film varies depending on the application conditions, but is, for example, preferably 10 to 200 μm, more preferably 15 to 150 μm, even more preferably 20 to 120 μm, and particularly preferably 30 to 100 μm.

[0015] The substrate film may have a roughened surface on one or both sides. As will be described later, by roughening the surface of the substrate film, the surface condition of the substrate film is reflected in the surface condition of the ion exchange membrane, resulting in a roughened surface in the ion exchange membrane. The roughened surface of the substrate film has fine irregularities. Only one side of the substrate film may be roughened, or both sides may be roughened. Both sides are preferably roughened. It is preferable that the entire surface of one or both sides of the substrate film is roughened.

[0016] In a substrate film having a roughened surface, the state of the roughened surface changes during the subsequent process of forming an ion exchange membrane and is not particularly limited. For example, in the substrate film, the roughness Rz of the roughened surface is preferably 3 to 30 μm, more preferably 5 to 25 μm, and even more preferably 7 to 20 μm. In the substrate film, the roughness Ra of the roughened surface is preferably 0.3 to 10 μm, more preferably 0.5 to 7 μm, and even more preferably 1 to 3 μm. In the substrate film, it is preferable that at least Rz of the roughened surface is within the above range, and it is more preferable that both Rz and Ra are within the above range.

[0017] <Base polymer> The base polymer that constitutes the substrate film is preferably fluororesin or polyolefin.As fluororesin, the copolymer (hereinafter referred to as ETFE) that comprises ethylene (hereinafter referred to as E) unit and tetrafluoroethylene (hereinafter referred to as TFE) unit, the copolymer that comprises E unit and chlorotrifluoroethylene (hereinafter referred to as CTFE) unit, the copolymer that comprises 50 mol% or more of trifluoroethylene unit, vinylidene fluoride unit or vinyl fluoride unit, or these homopolymers can be exemplified.One kind of fluororesin can be used alone, or two or more kinds can be used in combination.

[0018] In ETFE, the molar ratio of the units based on TFE to the units based on E (TFE / E) is preferably 40 / 60 to 80 / 20, more preferably 50 / 50 to 70 / 30. If the molar ratio of the units based on TFE is too small, the heat resistance, weather resistance, chemical resistance, gas barrier property, fuel barrier property, etc. of the base film are low, and if the molar ratio of the units based on TFE is too large, the melt moldability of ETFE is insufficient, and the mechanical strength, etc. of the base film tend to be low. Within the above range, ETFE is excellent in melt moldability, and the base film is excellent in heat resistance, weather resistance, chemical resistance, gas barrier property, fuel barrier property, mechanical strength, etc.

[0019] ETFE may contain, in addition to units based on TFE and E, units based on other monomers (a) copolymerizable with TFE and E. Examples of other monomers (a) include vinylidene fluoride, CTFE, hexafluoropropylene (hereinafter referred to as HFP), CF ２ = CFR １ (However, R １ represents a perfluoroalkyl group having 2 to 6 carbon atoms. The same applies below.), CH ２ = CHR ２ (However, R ２ represents a polyfluoroalkyl group having 1 to 8 carbon atoms. The same applies below.), CF ２ = CHR ３ (However, R ３ represents a perfluoroalkyl group having 1 to 6 carbon atoms. The same applies below.), CH ２ = CFR ２ Fluoroolefins such as (excluding TFE), CF ２ =CFOR ４ (where R ４ represents a perfluoroalkyl group having 1 to 10 carbon atoms which may contain an oxygen atom; ２ =CFOR ５ COX １ (where R ５ represents a divalent perfluoroalkylene group having 1 to 10 carbon atoms which may contain an oxygen atom, X １ represents a hydroxyl group, an alkoxy group having 3 or less carbon atoms, or a halogen atom.), CF ２ =CFOR ６ SO ２ X ２ (R ６ represents a divalent perfluoroalkylene group having 1 to 10 carbon atoms which may contain an oxygen atom, X ２ represents a halogen atom or a hydroxyl group.) ２ =CF(CF ２ ) ｎ OCF = CF ２(where n represents 1 or 2), perfluoro(2-methylene-4-methyl-1,3-dioxolane), hydrocarbon olefins such as propylene and butene (excluding E), aliphatic vinyl carboxylates such as vinyl acetate and vinyl butanoate, polymerizable unsaturated compounds having an acid anhydride structure such as maleic anhydride, itaconic anhydride and citraconic anhydride, and vinyl ethers such as hydroxybutyl vinyl ether and glycidyl vinyl ether. The other monomer (a) copolymerizable with TFE and E may be used alone or in combination of two or more. Examples of the other monomer (a) copolymerizable with TFE and E include CH ２ = CHR ２ , HFP, CF ２ =CFOR ４ or a polymerizable unsaturated compound having an acid anhydride structure is preferred. When a unit based on a polymerizable unsaturated compound having an acid anhydride structure is contained, the hydrophilicity of the ion exchange membrane is improved, which may be preferable. ２ = CHR ２ When the unit based on R is contained, the base film has excellent mechanical properties. ２ As the alkyl group, a perfluoroalkyl group having 1 to 6 carbon atoms is more preferred, and a perfluoroalkyl group having 2 to 4 carbon atoms is most preferred. The content of units based on monomer (a) is preferably 7 mol% or less, more preferably 6 mol% or less, and particularly preferably 4 mol% or less, relative to the total amount of TFE units and E units. Furthermore, when the base polymer contains units based on monomer (a), the content of units based on monomer (a) is preferably 1.0 mol% or more, more preferably 1.4 mol% or more, even more preferably 1.5 mol% or more, and particularly preferably 2.0 mol% or more, relative to the total amount of TFE units and E units. If the content of units based on monomer (a) is above the lower limit, the polymer has low crystallinity and becomes a membrane suitable for graft polymerization; if it is below the upper limit, the melting point of the polymer is high, and the usable temperature when made into an ion exchange membrane can be increased.

[0020] The copolymer containing E units and CTFE units is preferably one in which TFE in the above ETFE is replaced with CTFE.

[0021] Examples of polyolefins include polyethylene, polypropylene, poly(4-methyl-1-pentene), and polynorbornene. One type of polyolefin may be used alone, or two or more types may be used in combination. Polyethylene is preferred as the polyolefin, and among these, linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and ultra-high molecular weight polyethylene (UHMWPE), which are copolymerized with ethylene and an α-olefin, are preferred. High-density polyethylene and ultra-high molecular weight polyethylene are particularly preferred.

[0022] <Ion Exchange Group> Examples of anion exchange groups include quaternary ammonium groups, tertiary amino groups, secondary amino groups, primary amino groups, and imidazole groups such as those represented by the following formula (1) (wherein R １１ ~R １５ At least one selected from the group consisting of R is a bond, and the remaining R are each independently a hydrogen atom, an alkyl group having 1 to 8 carbon atoms which may contain an etheric oxygen atom between the carbon-carbon bonds or which may contain -N- between the carbon-carbon bonds, or R １１ ~R １５ represents an alkylene group in which any two of R １３ represents a group other than a hydrogen atom.) The bond of the imidazole group represented by formula (1) (hereinafter, sometimes referred to as "imidazole group (1)") is bonded to a graft chain. The multiple imidazole groups (1) contained in the ion exchange membrane may have different numbers of bonds. R １１ ~R １５ There is no particular limitation on the number of bonds among them, but the average number per mole of imidazole groups (1) contained in the ion exchange membrane is preferably 3 or less, more preferably 2 or less, and particularly preferably 1.5 or less.

[0023]

[0024] <Graft Chain> The graft chain of the ion exchange membrane is a polymer chain formed by graft polymerization of a raw material monomer onto a base polymer, and has an ion exchange group. The ion exchange group of the graft chain is a group derived from the raw material monomer, a group introduced after graft polymerization, or both.

[0025] When the raw material monomer contains one or more monomers having an ion exchange group, a graft chain having an ion exchange group derived from the raw material monomer is formed. The monomer having an ion exchange group is preferably a compound having one or more polymerizable carbon-carbon double bonds.

[0026] Examples of monomers having a cation exchange group include acrylic acids such as acrylic acid or its salts, methacrylic acid or its salts, acrylic acid esters (for example, normal butyl acrylate), methacrylic acid esters, and acrylonitrile; maleic anhydride, maleic acid, fumaric acid, and esters thereof; styrene sulfonic acid or its salts; 2-acrylamido-2-methylpropanesulfonic acid represented by the following formula (2) or its salts; vinyl sulfonic acid or its salts; etc. In the case of salts such as acrylates and sulfonates, known bases such as sodium hydroxide and potassium hydroxide can be used as the base that forms a salt with the corresponding acidic group.

[0027]

[0028] Examples of monomers having an anion exchange group include 4-vinylbenzyltrimethylammonium chloride represented by the following formula (3); acrylic acid esters containing quaternary ammonium salts, such as 2-(acryloyloxy)-N,N,N-trimethylethanaminium chloride represented by the following formula (4), and (3-acrylamidopropyl)trimethylammonium chloride represented by the following formula (5); acrylamides; allylamines, such as allylamine, diallylamine, and diallylmethylamine, and their salts with acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, and acetic acid; and diallyldialkyl quaternary ammonium salts, such as diallyldimethylammonium chloride.

[0029]

[0030] When the raw material monomer contains one or more ion-exchange group-introducing monomers that do not have ion-exchange groups, graft chains having units derived from the ion-exchange group-introducing monomers are formed. After graft polymerization, ion-exchange groups are introduced into the units derived from the ion-exchange group-introducing monomers, thereby obtaining graft chains having ion-exchange groups.

[0031] Examples of cation-exchange group-introducing monomers that can introduce cation-exchange groups include monomers that are easy to introduce sulfonic acid groups into, such as styrene, vinyltoluene, vinylnaphthalene, vinylxylene, α-methylstyrene, acenaphthylene, vinylnaphthalene, α-halogenated styrene, α,β,β'-trihalogenated styrene, chlorostyrene, and glycidyl methacrylate. Other examples include acrylic acid esters (e.g., n-butyl acrylate), methacrylic acid esters (e.g., tert-butyl methacrylate), acrylonitrile, maleic acid esters, fumaric acid esters, styrene sulfonic acid esters (e.g., methyl styrene sulfonate), and vinyl sulfonic acid esters. Known methods can be used to introduce cation-exchange groups into units derived from the cation-exchange group-introducing monomer of the graft chain. Examples of compounds (sulfonating agents) for introducing sulfonic acid groups include concentrated sulfuric acid, sulfur trioxide, sodium thiosulfate, chlorosulfonic acid, and trialkylbenzenesulfonic acid, and these are particularly suitable for graft chains having a benzene ring. Furthermore, for those in which the graft chain has an epoxy group or a haloalkyl group, (1) a method of reacting with sodium sulfite, or (2) a method of reacting with a thiol compound and then oxidizing with hydrogen peroxide or hypochlorous acid to introduce a sulfonic acid group or a salt thereof, can also be used. Furthermore, when the graft chain has an ester, a method of generating a sulfonic acid, a carboxylic acid, or a salt thereof by hydrolysis with an acid or alkali can be used, but is not limited to these.

[0032] As the monomer for introducing an anion exchange group into which an anion exchange group can be introduced, any monomer that is conventionally known and used in the production of anion exchange resins or anion exchange membranes can be used without any particular limitation. Specifically, a compound represented by the following formula (6) (wherein R １８is an alkylene group having 1 to 8 carbon atoms which may contain an etheric oxygen atom between the carbon-carbon bond, and X is a halogen atom. ), 4-vinylpyridine, styrene, vinyltoluene, vinylxylene, α-methylstyrene, acenaphthylene, vinylnaphthalene, α-halogenated styrene, α,β,β'-trihalogenated styrene, chlorostyrene, 2-vinylpyridine, methylvinylpyridine, ethylvinylpyridine, vinylpyrrolidone, vinylcarbazole, vinylimidazole, aminostyrene, alkylaminostyrene, trialkylaminostyrene, acrylic acid amide, acrylamide, oxime, glycidyl methacrylate, vinylimidazole, and derivatives thereof. Specific examples of the vinyl imidazole include m-chloromethylstyrene, p-chloromethylstyrene, 3-chloropropylstyrene, 4-chlorobutylstyrene, 4-bromobutylstyrene, and 4-vinylpyridine, which are preferred from the viewpoint of easily obtaining a film with low resistance.

[0033]

[0034] Known methods can be used to introduce anion exchange groups into units derived from the anion exchange group-introducing monomer of the graft chain. Examples of compounds for introducing anion exchange groups include ammonia, methylamine, dimethylamine, and the like, which are capable of introducing weakly basic ion exchange groups, for haloalkyl groups such as chloromethylstyrene, and epoxy groups such as glycidyl methacrylate; and trimethylamine, dimethylamineethanol, triethanolamine, cyclic tertiary amines (e.g., compounds represented by the following formulas (a1) to (a7)), and imidazoles (e.g., compounds represented by the following formula (7)), which are capable of introducing strongly basic ion exchange groups. Among these compounds, trimethylamine is preferred because it can reduce the resistance of the resulting membrane. The above compounds may be used alone, or two or more compounds may be mixed and used. Furthermore, pyridines such as 4-vinylpyridine and imidazoles such as vinylimidazole can be reacted with alkyl sulfates, alkyl carbonates, or haloalkanes to produce quaternary ammonium groups, which are anion exchange groups. The above-mentioned alkyl sulfate esters and other compounds may be used alone or in combination. For aromatic monomers (e.g., styrene) that do not have a group capable of introducing an anion-exchange group, a haloalkyl group can be introduced at the end by a Friedel-Crafts alkylation reaction with a compound having 1 to 8 carbon atoms and multiple halogen groups in the molecule, or a chloromethylation reaction using chloromethyl methyl ether, followed by the introduction of an anion-exchange group using the method described above. For monomers with halogen atoms bonded to the aromatic ring, a haloalkyl group can be introduced at the end by Grignard coupling with a compound having 1 to 8 carbon atoms and multiple halogen groups in the molecule, followed by the introduction of an anion-exchange group using the method described above.

[0035]

[0036] In formulas (a1) to (a7), R ２１ ~R ２６each independently represents a hydrocarbon group, a fluorinated hydrocarbon group, or a fluorocarbon group. The "hydrocarbon group" refers to a group that contains a C-H bond but does not contain a C-F bond in the molecule. The "fluorinated hydrocarbon group" refers to a hydrocarbon group in which some of the hydrogen atoms bonded to carbon atoms have been replaced with fluorine atoms. The "fluorocarbon group" refers to a hydrocarbon group in which all of the hydrogen atoms bonded to carbon atoms have been replaced with fluorine, that is, a group that contains only C-F bonds in the molecule. R ２１ ~R ２６ may each independently contain an ether bond, a sulfonyl bond and / or a hydroxy group. ２１ ~R ２６ When R contains a hydroxy group, the hydroxy group is preferably a tertiary alcohol to prevent oxidation. ２１ ~R ２６ The structure of R is not particularly limited, and may be a linear structure or a cyclic structure. ２１ ~R ２６ may contain aromatic groups.

[0037]

[0038] In formula (7), R ３１ ~R ３４ are each independently a group selected from a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, and R ３１ and R ３２ may be bonded to each other to form a ring. ３３ represents a group that is not a hydrogen atom.

[0039] The graft chain may or may not have a crosslinked structure. When the raw material monomer contains a crosslinkable monomer, a graft chain having a crosslinked structure is formed by graft polymerization. The crosslinkable monomer is preferably a compound having two or more polymerizable carbon-carbon double bonds. Examples of the crosslinkable monomer include divinylbenzene (DVB), trivinylbenzene, divinyltoluene, divinylnaphthalene, styrene derivatives represented by the following formulas (8) and (9), ethylene glycol dimethacrylate, etc. In formula (9), R ４１represents an alkylene group having 1 to 8 carbon atoms which may contain an etheric oxygen atom between the carbon-carbon bond.

[0040]

[0041] When the raw material monomers contain a crosslinkable monomer, the proportion of the crosslinkable monomer used is not particularly limited relative to the total mass of the raw material monomers. Since it varies depending on the difference in polymerizability with the monomer having an ion exchange group and the monomer for introducing an ion exchange group, it may be adjusted to obtain a membrane resistance suitable for the application. Generally, the crosslinkable monomer is preferably 20 parts by mass or less, particularly preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to a total of 100 parts by mass of the monomer having an ion exchange group, the monomer for introducing an ion exchange group, and any monomer described below.

[0042] The monomer constituting the graft chain may contain any monomer other than the monomer having an ion exchange group, the monomer for introducing an ion exchange group, and the crosslinkable monomer. The optional monomer is not particularly limited, but examples include vinyl esters such as acrylonitrile, vinyl acetate, and vinyl pivalate; vinyl silanes such as vinyltrimethylsilane, vinyltrimethoxysilane, and vinyldimethoxymethylsilane; and acrylamides such as acrylamide, N-methylacrylamide, and N,N-dimethylacrylamide. The amount of optional monomer used is not particularly limited, but is preferably 200 parts by mass or less, more preferably 100 parts by mass or less, and particularly preferably 50 parts by mass or less, relative to 100 parts by mass of the total of the monomer having an ion exchange group and the monomer capable of introducing an ion exchange group. If the amount of optional monomer is too large, the ratio of the monomer having an ion exchange group and the monomer capable of introducing an ion exchange group decreases, which is undesirable because the ion conductivity (membrane resistance) of the resulting ion exchange membrane becomes insufficient.

[0043] The ion exchange membrane may be a cation exchange membrane having cation exchange groups as ion exchange groups and having amino groups on at least one surface. The presence of amino groups on the surface of the cation exchange membrane can exhibit monovalent cation permselectivity. The amino groups are preferably amino groups derived from an amino group-containing compound having at least one, preferably two or more, amino groups per molecule.

[0044] Specific examples of the amino group-containing compound include R ５１ -NH ２ (In the formula, R ５１ is an alkyl group having 1 to 30 carbon atoms); ２ -R ５２ -NH ２ (In the formula, R ５２ and (C1 to C30 alkylene group) diamines; oligomers obtained by condensation polymerization of one or more selected from the alkylamines and diamines, epichlorohydrin, and, if necessary, ammonia; polyethyleneimines; polymers of one or more selected from monomers such as allylamine hydrochloride, diallylamine hydrochloride, diallylmethylamine hydrochloride, diallyldimethylammonium chloride, acrylamide, N-alkylacrylamide, and N,N-dimethylacrylamide; polymers of amino group-containing compounds such as 4-vinylbenzyltrimethylammonium chloride represented by the formula (3), quaternary ammonium salt-containing acrylic acid esters represented by the formulas (4) and (5), and acrylamides; and the like. Further examples include polymers obtained by reacting the haloalkyl group-containing monomers and polymers obtained by introducing a haloalkyl group into a polymer having an aromatic ring with ammonia and primary to tertiary amines, as described above in the description of the polymer into which an anion exchange group can be introduced, but are not limited to these.

[0045] The molecular weight of these amino group-containing compounds is not particularly limited, but considering the adhesion of the amino group-containing compound to the membrane surface, the number average molecular weight is preferably 100 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and particularly preferably 8,000 or more. If the molecular weight of the amino group-containing compound is too low, there is a problem that it is difficult to adhere to the cation exchange membrane. In the case of a high molecular weight, there is no particular limitation as long as the amino group-containing compound has solubility that allows it to be diluted in any ratio with water, alcohol, or other organic solvents, but considering ease of handling, the number average molecular weight is preferably 1,000,000 or less, more preferably 500,000 or less, and particularly preferably 200,000 or less.

[0046] Methods for causing amino groups to be present on the surface of a cation exchange membrane (monovalent cation selective treatment methods) include the following methods (i) to (iii): (i) A method in which a cation exchange membrane is contacted with a solution containing a predetermined amino group-containing compound or its salt; (ii) A method in which the ion exchange groups on the surface or the entire cation exchange membrane are treated under acidic conditions to create an acidic state with acrylic acid, sulfonic acid, or the like, and then treated with a solution of an amino group-containing compound; (iii) A method in which a cation exchange membrane is contacted with an aqueous solution of sodium hydroxide, potassium hydroxide, or the like, or a mixed solution of a water-soluble organic solvent, if necessary, to stabilize it under basic conditions of pH 8 to 13, and then further contacted with a solution in which an amino group-containing compound is dissolved at a predetermined concentration under the same pH conditions for treatment.

[0047] The amino group-containing compound used in the monovalent cation selective treatment method may be in a neutral state, in the form of a salt with an acid such as hydrochloric acid, acetic acid, sulfuric acid, phosphoric acid, or the like, or may be in the form of a partial salt. Furthermore, as a method for contacting a cation exchange membrane with a solution of the amino group-containing compound under each condition, any method can be employed, including, but not limited to, a method of directly applying a solution of the amino group-containing compound to a membrane under predetermined conditions, a method of applying the amino group-containing compound at a predetermined concentration to a release film, optionally drying, and then laminating the cation exchange membrane and optionally pressing and heating to fix the compound, and a method of incorporating the cation exchange membrane into an electrodialysis cell or the like and contacting the solution within the device.

[0048] By subjecting a cation exchange membrane to such treatment, an ion exchange membrane with high monovalent cation permselectivity and low resistance can be obtained. Such an ion exchange membrane is suitable for electrodialysis applications such as seawater concentration and lithium ion recovery, as well as for reverse electrodialysis power generation, and is expected to have advantages such as high current efficiency and power generation efficiency.

[0049] <Manufacturing Method> The ion exchange membrane of this embodiment can be manufactured by, for example, the following manufacturing methods (1) to (4). Manufacturing method (1): A method in which a substrate film having a roughened surface is used, which is a film obtained by molding a base polymer into a film shape, and the substrate film is irradiated with ionizing radiation to generate radicals in the base polymer, and raw material monomers including a monomer having an ion exchange group are graft-polymerized. Manufacturing method (2): A method in which a substrate film having a roughened surface is used, which is a film obtained by molding a base polymer into a film shape, and the substrate film is irradiated with ionizing radiation to generate radicals in the base polymer, and raw material monomers including an ion-exchange-group-introducing monomer having a functional group capable of introducing an ion exchange group are graft-polymerized, and then the ion exchange group is introduced into the unit derived from the ion-exchange-group-introducing monomer. Manufacturing method (3): A method in which a substrate film that is not roughened in manufacturing method (1) is used, and the surface is roughened after graft-polymerizing the raw material monomers. Production method (4): In production method (2), a substrate film that has not been roughened is used, and the surface is roughened either or both after graft polymerization of raw material monomers and after introduction of ion exchange groups into units derived from monomers for introducing ion exchange groups.

[0050] In production methods (3) and (4), the processing temperature required for roughening the membrane after graft polymerization tends to be higher than that required for roughening the substrate film. In this respect, production methods (1) and (2) are preferred over production methods (3) and (4). In production method (4), the membrane obtained by introducing ion exchange groups is in a wet state, so if roughening is performed after introducing ion exchange groups, it is difficult to obtain sufficient surface roughness. In addition, if a wet membrane is dried and then roughened, the strength of the membrane decreases, making it more susceptible to problems such as breakage. In this respect, production methods (1) to (3) are preferred over production method (4).

[0051] As a method for roughening the surface of a film (including a substrate film), a transfer method can be applied in which a mold or roll with an uneven surface is brought into contact with the surface of the film, heated as needed, with or without pressure, and transferred. Specifically, for example, the unevenness can be transferred to the film by forming an uneven surface on at least one of a pair of rolls, and passing the film between the rolls. Furthermore, instead of the mold or roll with an uneven surface, a transfer method using a releasable film with an uneven surface can also be applied. In addition to the transfer method, methods such as spraying fine particles onto the surface of the film to roughen it (also called a blasting method) and etching using a chemical solution that oxidizes and dissolves the surface of the film are also applicable. A transfer method using a mold or roll with an uneven surface is preferred in terms of the ability to eliminate the influence on the properties of the film surface and the influence of residual treatment agents, and the simplicity of the process.

[0052] In the production methods (1) to (4), known methods can be applied to the graft polymerization step. For example, a method in which a substrate film irradiated with ionizing radiation is immersed in a polymerization solution to cause a polymerization reaction is preferred. The polymerization solution contains raw material monomers that form graft chains and may further contain a solvent. The type of solvent is not particularly limited, but examples include hydrocarbons such as benzene, xylene, toluene, and hexane; alcohols such as methanol, ethanol, and isopropyl alcohol; ketones such as acetone, methyl isopropyl ketone, and cyclohexane; ethers such as dioxane and tetrahydrofuran; esters such as ethyl acetate and butyl acetate; and nitrogen-containing compounds such as isopropylamine, diethanolamine, N-methylformamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidinone. The solvent may be used alone or in combination.

[0053] The graft polymerization of the raw material monomer onto the base polymer of the substrate film may be a so-called pre-irradiation method in which the substrate film is irradiated with ionizing radiation and then polymerized with the raw material monomer, or a so-called simultaneous irradiation method in which the substrate film and the raw material monomer are simultaneously irradiated with ionizing radiation and polymerized. The pre-irradiation method is preferred in that it produces a small amount of homopolymer that is not graft polymerized onto the substrate film. The pre-irradiation method may be implemented by a polymer radical method in which the substrate film is irradiated in an inert gas, or by a peroxide method in which the substrate film is irradiated in an atmosphere containing oxygen.

[0054] Specific examples of ionizing radiation include α-rays, β-rays, γ-rays, electron beams, and ultraviolet rays, with electron beams being preferred because they can uniformly activate the substrate film. A preferred method is to use electron beams as the ionizing radiation and continuously irradiate the substrate film with the electron beam while transporting it. This method is excellent in industrial productivity because it can uniformly activate the substrate film even when irradiating a large amount of substrate film with ionizing radiation.

[0055] FIG. 1 is an explanatory diagram schematically illustrating an example of a process for irradiating ionizing radiation. The above-mentioned procedure for "continuously irradiating with electron beams" will be specifically described with reference to FIG. 1. First, the substrate film 10 wound around a roll 12 is unwound in a conveying direction A, and the substrate film 10 is conveyed to an electron beam irradiation position where an electron beam irradiation device 20 is installed. Next, the substrate film 10 at the electron beam irradiation position is irradiated with an electron beam 22, and then the substrate film 10 is conveyed in the conveying direction A, and the substrate film 10 after being irradiated with the electron beam 22 is wound around a roll 14. In this manner, the substrate film 10 is continuously irradiated with the electron beam 22.

[0056] The dose of ionizing radiation applied to the substrate film is preferably 10 to 1,000 kGy, more preferably 30 to 500 kGy, and even more preferably 40 to 200 kGy, from the viewpoint of activating the substrate film. Ionizing radiation may be applied in a single irradiation to achieve the desired dose (continuous irradiation), or in multiple irradiations to achieve the desired total dose (intermittent irradiation). In particular, when a dose of 80 kGy or more is required, continuous irradiation with electron beams may cause the substrate film to heat up, resulting in side reactions such as deactivation or crosslinking of radicals generated by irradiation, making it difficult to obtain the desired graft polymerization chains. Furthermore, continuous irradiation of the substrate film with electron beams may cause deformation of the film due to heat (e.g., film elongation). To address this problem, intermittent irradiation allows the substrate film to cool during non-irradiation periods, thereby preventing thermal deterioration of the substrate film. Intermittent irradiation is particularly preferred when the substrate film is made of polyethylene, as its mechanical strength is significantly affected by heat. The substrate film is preferably cooled during intermittent irradiation until the temperature falls below the softening point of the material that constitutes the substrate film.

[0057] A specific example of the intermittent irradiation method will be described with reference to Fig. 1 . First, a specific portion of the substrate film 10 transported from the roll 12 in the transport direction A is irradiated with the electron beam 22 (first irradiation), and then the portion of the substrate film 10 including the specific portion is wound onto the roll 14. After the specific portion of the substrate film 10 wound onto the roll 14 has sufficiently cooled, the substrate film 10 is unwound in the direction opposite to the transport direction A and transported again to the electron beam irradiation position. The specific portion of the substrate film 10 is irradiated with the electron beam 22 (second irradiation), and then the portion of the substrate film 10 including the specific portion is wound onto the roll 12. Alternatively, the substrate film 10 wound onto the roll 14 may be placed back at the position of the roll 12, unwound again in the transport direction A, transported again to the electron beam irradiation position, and then irradiated with the electron beam 22 (second irradiation), and then the portion of the substrate film 10 including the specific portion is wound onto the roll 14. In this way, the base film 10 can be irradiated with electron beams twice. If three or more irradiations are required, the above operation can be carried out so that the desired number of irradiations is achieved. When irradiating two or more times, irradiation may be carried out from the same side of the film, or from both the front and back sides any number of times. When irradiating two or more times, it may be preferable to irradiate the front and back sides an equal number of times (in the case of an odd number of irradiations, one side is irradiated one more time).

[0058] The temperature of the substrate film during irradiation is preferably -10 to 50°C, preferably room temperature or below. When there is a large spatial or temporal difference between the time from irradiation with ionizing radiation to graft polymerization, for example, when the above-mentioned continuous or intermittent irradiation is performed, the irradiated film roll can be stored in a dry ice-filled box or a freezer (preferably at -30°C or below) to prevent radical degradation or disappearance during the graft polymerization period. The irradiated substrate film is then removed from the atmosphere and transferred to a glass container, after which the container is filled with a polymerization liquid. The polymerization liquid is prepared by removing oxygen gas in advance by bubbling with an oxygen-free inert gas or by freeze-degassing. Alternatively, a polymerization apparatus such as a continuous polymerization apparatus (e.g., JP 2004-137385 A, JP 2005-60555 A, WO 2018 / 030498 A) may be used. The graft polymerization for introducing graft chains into the irradiated substrate film is usually carried out at room temperature to 80°C, preferably 40 to 70°C.

[0059] The grafting rate (the ratio of the mass of graft chains to the mass of the base film before polymerization (unit: mass %)) is preferably from 10 to 300 mass %, more preferably from 20 to 150 mass %. The grafting rate can be adjusted by the irradiation dose, polymerization temperature, polymerization time, etc.

[0060] A known method can be used for the step of introducing ion exchange groups after graft polymerization. The following is a specific example of introducing sulfonic acid groups as cation exchange groups. The substrate film after the graft polymerization reaction is immersed in a chlorosulfonic acid solution with a concentration of 0.2 to 1.5 mol / L using 1,2-dichloroethane as the solvent at 25 to 80°C for 1 to 96 hours to allow the reaction to occur. After allowing the reaction to occur for a predetermined period of time, the membrane is thoroughly washed. The sulfonation reaction is then terminated by immersion in a sodium hydroxide aqueous solution with a concentration of 1 to 10% by mass for 1 to 24 hours, and the membrane is then thoroughly washed with water. Alternatively, the membrane may be immersed in concentrated sulfuric acid (concentration 96% or more, preferably 97% or more, particularly preferably 98% or more) and contacted with the solution while heating (room temperature to 100°C, preferably 40°C to 70°C, particularly preferably 50°C to 65°C) as necessary to promote sulfonation, followed by rinsing with sufficient water and then immersing (or contacting) the membrane with an aqueous sodium hydroxide or potassium hydroxide solution having a concentration of 1 to 10% by mass for 1 to 24 hours for neutralization to obtain a membrane.

[0061] For example, the following is a specific example of introducing an amino group as an anion exchange group. The above-mentioned amine compounds (e.g., compounds represented by the above formulae (a1) to (a7) and (7)) are used as compounds for introducing anion exchange groups. When chloromethylstyrene is graft polymerized as a monomer capable of introducing ion exchange groups, the resulting polymer membrane is immersed or contacted with a solution prepared so that the amine compound has a concentration of 0.2 to 3.2 mol / L (preferably 0.5 to 1.5 mol / L) at room temperature to 100°C for 1 to 96 hours, whereby the chloromethyl groups of the chloromethylstyrene are quaternized to generate anion exchange groups. After completion of the reaction, the membrane is thoroughly washed to obtain an anion exchange membrane. The solvent used to prepare the amine compound solution in this reaction is not particularly limited, and a mixture of multiple solvents may be used. However, a solvent capable of dissolving the amine compound is preferred. Furthermore, since it is particularly preferable to use water for washing after the reaction, particularly preferred solvents include (a) water and (b) water-soluble solvents such as methanol, ethanol, 1-propanol, 2-propanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and ethylene glycol dimethyl ether. Two or more of these solvents may be mixed and used. Furthermore, even when using a solvent selected from (a) and (b), it is preferable that the amine compound used be homogeneously dissolved in the solvent. Furthermore, the preferred reaction temperature varies depending on the solvent used, the boiling point, and the reactivity of the compound. However, when using a compound with a low boiling point such as trimethylamine, methanol, or acetone, the reaction temperature is preferably 60°C or less, and more preferably 50°C or less.

[0062] <Applications> The ion exchange membrane of the present invention can be used for applications known in the field of ion exchange membranes. Even when the membrane is large in size, it is less likely to fold or wrinkle during implementation, making it suitable for applications with a large effective membrane area. For example, it can be suitably used as a diaphragm used in electrolysis, such as a seawater concentration method for concentrating seawater using electrodialysis, power generation methods such as concentration difference power generation and reverse electrodialysis power generation, water electrolysis, and electrolysis of organic compounds (e.g., a method of replacing benzene, toluene, etc. with hexane or methylhexane by electrolytic hydrogenation). Known methods can be applied to seawater concentration methods using ion exchange membranes, such as those described in Journal of the Society of Sea Water Science of Japan, Vol. 34, No. 2 (1980) pp. 121-124. Known methods can be applied to concentration difference power generation methods using ion exchange membranes, such as those described in Bull. Soc. Sea Water Sci., Jpn., 73, 3-8 (2019). As a reverse electrodialysis power generation method using an ion exchange membrane, known methods such as those described in Bull. Soc. Sea Water Sci., Jpn., 66, 242-247 (2012) can be applied.

[0063] The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

[0064] <Measurement Method> [Membrane Resistance] The ion exchange membrane was immersed in a 0.5 mol / L aqueous sodium chloride solution and conditioned overnight in a thermostatic bath at 25°C. Figure 2 is a schematic diagram showing the measurement device. Reference numeral 30 denotes a cylindrical half cell having a circular opening 32 with a diameter of 15 mm. Reference numeral 31 denotes a liquid inlet. Reference numeral 33 denotes a platinum-black platinum wire. Reference numeral 34 denotes a membrane whose resistance is to be measured. The ion exchange membrane 34 to be measured is sandwiched between the half cell 30 from both sides and fixed at a constant pressure using a spring coil or the like. Next, the inside of the cell 30 is filled with 0.5 N NaCl. The platinum wire 33 is connected to an AC resistance meter, and the AC resistance (unit: Ω) at 1 kHz is measured. The membrane 34 is then quickly removed to prevent leakage of the liquid inside, and the resistance (unit: Ω) is measured again without the membrane. Using these measured values, the membrane resistance (unit: Ω cm) is calculated using the following formula (r1). ２) is calculated. Membrane resistance = {(resistance between platinum wires when membrane is attached) - (resistance between platinum wires when membrane is removed)} x 1.77 ... (r1) The membrane resistance was measured in a thermostatic booth at 25°C and calculated as the resistance at 25°C. To prepare the samples to be measured, first, strip membranes 10 cm wide were cut out from each of the ion exchange membranes obtained in each example, positioned 1 m from both ends in the longitudinal direction. Next, the required area was cut out from the center position in the width direction of each of the two strip membranes obtained. The membrane resistance of each of the two samples thus obtained was measured using the method described above, and the average value was used as the measurement result.

[0065] [Membrane Thickness] The membrane thickness was measured using a micrometer (Mitutoyo Corporation product name "MDC-25SX"). Measurement samples were obtained by cutting out 10 cm wide strip membranes from each of the ion exchange membranes obtained in each example at positions 1 m from both ends in the longitudinal direction. Measurements were made at five arbitrary points (10 points in total) in the width direction for the two obtained strip membranes, and the average value was used as the measurement result.

[0066] [Surface roughness Ra and Rz] The wet ion exchange membrane obtained in each example was placed on a glass plate without drying and pressed tightly against it, and the moisture on the surface (measurement surface) was wiped off and measured within 5 minutes. A tactile surface roughness measuring instrument (Mitutoyo Corporation product name "Surftest SJ-310") was fitted with a stylus with a stylus tip radius of 2 μm and a tip angle of 60° as a standard detector, and the Ra and Rz of the measurement surface were measured.

[0067] [Mounting test (leakage, folds, and wrinkles)] An installation test (mounting test) of an ion exchange membrane to a large electrochemical cell was conducted. Two types of electrodialysis cells with different membrane dimensions were used: (1) DB1 type and (2) CS3 type. (1) For the DB1 type electrodialysis cell (effective membrane area 180 × 550 mm) manufactured by AGC Engineering, 200 ion exchange membranes were fastened together while alternately stacking the vinyl chloride chamber frame and the ion exchange membrane. The fastening pressure was 20 kg / cm. ２(2) For the CS3 type electrodialysis cell (effective membrane area: 550 × 1120 mm) manufactured by AGC Engineering Co., Ltd., 200 ion exchange membranes were assembled by alternately stacking polypropylene chamber frames and ion exchange membranes and fastening them together to prepare a dialysis cell. The pressure at the fastening point was 7 kg / cm. ２ Although cation exchange membranes and anion exchange membranes are typically stacked alternately, in this test, only the cation exchange membrane or anion exchange membrane obtained in each example was used. (Leakage Test) Water was allowed to flow from the bottom of each dialysis cell prepared in (1) and (2) above at a rate of 10 cm / sec for 24 hours without applying electricity, and the amount of water leaking out of the dialysis cell (leakage amount, unit: mL) was measured. A 1-m-high water column was placed at the outlet of the dialysis cell to apply water pressure to the inside. (Occurrence of Folds and Wrinkles) The dialysis cell prepared in (2) above was disassembled, and the condition of the fastening part with the chamber frame was visually observed. The number of folds and wrinkles in the membrane was counted, and the total number of both was used as the measurement result.

[0068] [Seawater concentration test by electrodialysis] Using the cation exchange membrane obtained in each example and a commercially available anion exchange membrane (AGC Engineering product name "ASVN"), a small electrodialysis device (effective membrane area: 8.0 cm) was used in the method described in "Bull. Soc. Sea Water Sci., Jpn., 75, 145-152 (2021) Takahashi et al." ２ The concentration compartment contained 0.5 mol / L of NaCl aqueous solution, and the desalination compartment contained model seawater containing NaCl / CaCl ２ / MgCl ２ Aqueous solutions prepared with a molar ratio of 44.3 / 0.9 / 4.7 were circulated at a current density of 3 A / dm ２ Electrodialysis was carried out for 3 hours or more under the conditions. After the liquid in the concentration compartment was sufficiently replaced and the composition stabilized, the concentrated liquid was sampled. The Na concentration, Ca concentration, and Mg concentration in the concentrated water were analyzed, and the concentration ratio (molar ratio) expressed as Na / (Na + Ca + Mg) was determined. The larger the value of this concentration ratio, the better the monovalent cation selective permeability of the ion exchange membrane.

[0069] <Raw Materials> The abbreviations in the table are as follows: St: styrene, previously treated with activated alumina before use. CMS: chloromethylstyrene, an isomer mixture (p-isomer / m-isomer ratio of approximately 1:1) or 100% p-isomer, previously treated with activated alumina before use. DVB: divinylbenzene (purity 55%) previously treated with activated alumina before use. BA: normal butyl acrylate, previously obtained by impregnation with a 5% aqueous solution of caustic soda followed by liquid separation, was used.

[0070] Preparation Example 1: Preparation of Polymerization Liquid (1) 650 L of a mixture of 150 parts by mass of styrene, 40 parts by mass of chloromethylstyrene (an isomer mixture), 30 parts by mass of n-butyl acrylate, and 450 parts by mass of n-butyl acetate (polymerization liquid (1)) was prepared. The styrene content was approximately 22.4% by mass relative to the total mass of the polymerization liquid (1).

[0071] Preparation Example 2: Preparation of Polymerization Liquid (2) In Preparation Example 1, the blending amount of the chloromethylstyrene was changed to 15 parts by mass, and the blending amount of n-butyl acetate was changed to 420 parts by mass. Otherwise, 650 L of polymerization liquid (2) was prepared in the same manner as in Preparation Example 1. The styrene content was approximately 24.4% by mass relative to the total mass of the polymerization liquid (2).

[0072] Preparation Example 3: Preparation of Polymerization Liquid (3) In Preparation Example 1, the blending amount of the chloromethylstyrene was changed to 25 parts by mass, and the blending amount of n-butyl acetate was changed to 420 parts by mass. Otherwise, 650 L of polymerization liquid (3) was prepared in the same manner as in Preparation Example 1. The amount of styrene was 24% by mass relative to the total mass of the polymerization liquid (3).

[0073] Preparation Example 4: Preparation of polymer solution (4) 650 L of a mixture of 30 parts by mass of chloromethylstyrene (100% p-isomer), 1 part by mass of divinylbenzene, and 80 parts by mass of n-butyl acetate (polymer solution (4)) was prepared.

[0074] Preparation Example 5: Preparation of Polymerization Liquid (5) In Preparation Example 4, the blending amount of divinylbenzene was changed to 2 parts by mass, and otherwise the same procedure as in Preparation Example 4 was repeated to prepare 650 L of polymerization liquid (5).

[0075] <Production of Substrate Film> [Examples 1 to 9 and Example 11] Ethylene-tetrafluoroethylene copolymer (produced with reference to WO 2021 / 215402, polymerized units based on TFE / polymerized units based on E / CH ２ =CH(CF ２ ) ４ A copolymer having a molar ratio of 54 / 46 / 1.4 to 1.7 (based on F) polymerized units, and an MFR of 9 to 11 g (measured by measuring the mass (g) of the polymer flowing out of a nozzle with a diameter of 2 mm and a length of 8 mm per unit time (10 minutes) at a temperature of 297°C under a load of 5 kg using a melt indexer (manufactured by Toyo Seiki Seisakusho), was used to produce an ETFE film (substrate film) embossed on both sides by a T-die extrusion molding method using a pair of surface embossing back rolls. The thickness and surface roughness of the ETFE film are shown in the table (the same applies hereinafter). The thickness of the ETFE film (substrate film) was adjusted by changing the amount of resin extruded and the speed of the winding roll, and the surface roughness was adjusted by changing the surface roughness of the surface embossing roll.

[0076] [Example 10] Use the same ethylene-tetrafluoroethylene copolymer as in example 1, and use a pair of rolls that are made up of the back roll that is roughened and the roll that is smooth, by the T-die extrusion molding method, make the ETFE film (substrate film) that only one side of film is roughened, and the other side is smooth.The data shown in table is the value that rough surface side is measured.

[0077] Examples 14 to 17 Using the same ethylene-tetrafluoroethylene copolymer as in Example 1, ETFE films (substrate films) having smooth surfaces on both sides were produced by a T-die extrusion molding method.

[0078] [Example 12] An ultra-high molecular weight polyethylene film (trade name "Ultra Polymer" manufactured by Yodogawa Hutech Co., Ltd., thickness 70 µm) produced by the skive method was passed between a pair of surface embossing rolls heated to 100°C to obtain an ultra-high molecular weight polyethylene (UHMWPE) film having roughened surfaces on both sides.

[0079] [Example 13] A high-density polyethylene film (trade name "HD" by Tamapoly Co., Ltd., thickness 70 µm) produced by an inflation method was passed between a pair of surface embossing rolls heated to 80°C to obtain a high-density polyethylene (HDPE) film with roughened surfaces on both sides.

[0080] <Production of ion exchange membranes> Examples 1 to 13, 18-1 to 18-2, 19-1 to 19-2, and 20 are working examples, while Examples 14 to 17, 18-3, 19-3, and 21 are comparative examples. Examples 1 to 3, 10, 11, and 14 to 16 are examples of cation exchange membranes. Examples 4 to 9, 12, 13, and 17, 20, and 21 are examples of anion exchange membranes. Examples 18-1 to 18-3 and 19-1 to 19-3 are examples of cation exchange membranes that have been subjected to a monovalent ion selective treatment.

[0081] [Example 1] (Graft Polymerization Step: Production of Graft Polymerized Film) After corona discharge treatment on both sides, the substrate film was cut into a 100 m x 60 cm piece and activated by irradiating one side with an electron beam using a device capable of continuously irradiating electron beams using a roll-to-roll method. The electron beam irradiation conditions were an acceleration voltage of 200 kV and a dose of 60 kGy. 50 m of the substrate film after electron beam irradiation was wound up together with a 70 cm wide net so that it could be placed in a cylindrical reactor (I) with a diameter of 100 cm and a height of 80 cm. The mass of the wound substrate film (referred to as mass A (unit: kg)) was measured, and the reactor (I) was placed in the reactor (I), which was then sealed. Next, the inside of the reactor (I) was degassed to 10 torr (approximately 1333 Pa), and then nitrogen gas was supplied to pressurize it to 0.2 MPaG. This operation was repeated several times to create a state of 0.05 MPaG under a nitrogen atmosphere. The oxygen concentration in the reaction tank (I) was 0.1 ppm or less. Approximately 700 L of polymerization liquid (1) was introduced into a storage tank (II) separate from the reaction tank (I), and high-purity nitrogen gas was bubbled through it at room temperature for 30 minutes. Then, while continuing nitrogen bubbling, the internal temperature was adjusted to 40±1°C, and the polymerization liquid (1) was circulated within the reaction tank (I) so that the substrate film was immersed. Thus, the substrate film within the reaction tank (I) was immersed in the polymerization liquid (1), and graft polymerization was carried out. The immersion time (polymerization time) was 3.5 hours. After 3.5 hours, the liquid within the reaction tank (I) was removed, and acetone was immediately introduced into the reaction tank (I) as a washing solvent to terminate the polymerization. After this, the acetone washing operation was repeated three times, and then warm air was blown into the reaction tank (I) to dry the film, yielding a graft-polymerized membrane. The mass of the graft-polymerized membrane (referred to as mass B (unit: kg)) was measured. The graft ratio (polymerization ratio of the graft-polymerized film, unit: %) was calculated using the following formula. The results are shown in Table 1 (the same applies hereinafter): Graft ratio = (B - A) / A x 100

[0082] (Sulfonation Step: Introduction of Cation Exchange Groups) Next, 700 L of 98% sulfuric acid was placed in the reaction vessel (II), and while maintaining the liquid temperature at 60°C, the sulfuric acid was circulated through the reaction vessel (I) containing the graft polymerized membrane so that the resulting graft polymerized membrane was immersed. In this way, the graft polymerized membrane in the reaction vessel (1) was reacted with sulfuric acid, and cation exchange groups (sulfonic acid groups) were introduced into the graft polymerized membrane. The immersion time (circulation time) was 24 hours. After 24 hours, the liquid was removed, and the interior was washed with 20% sulfuric acid and then with ion-exchanged water until the pH reached 3 or higher. A 5% aqueous NaOH solution was then circulated to convert the sulfonic acid groups to sodium sulfonate groups, and the membrane was repeatedly washed with water until the pH of the wash water reached 8 or lower, yielding an ion-exchange membrane (cation-exchange membrane). The ion-exchange membrane thus produced had a thickness (unit: μm) and a membrane resistance (unit: Ω cm ２ The surface roughness (Ra and Rz, units: μm) was measured by the method described above. A mounting test was also carried out by the method described above. The results are shown in Table 2 (the same applies hereinafter).

[0083] [Examples 2, 3, 10, 11, and 14 to 16] (Graft polymerization step: production of graft-polymerized membrane) Graft-polymerized membranes were obtained in the same manner as in Example 1, except that the production conditions in Example 1 were changed as shown in Table 1. (Sulfonation step: introduction of cation exchange groups) The obtained graft-polymerized membranes were subjected to the sulfonation step in the same manner as in Example 1 to obtain ion-exchange membranes (cation-exchange membranes).

[0084] Example 4 (Graft Polymerization Step: Production of Graft-Polymerized Membrane) A graft-polymerized membrane was obtained in the same manner as in Example 1, except that the production conditions were changed as shown in Table 1. (Amination Step: Introduction of Anion Exchange Groups) Next, 700 L of trimethylamine solution (1 mol / L methanol solution) was placed in the reaction vessel (II), and the trimethylamine solution was circulated through the reaction vessel (I) containing the graft-polymerized membrane while maintaining the liquid temperature at 45°C. In this manner, the graft-polymerized membrane in the reaction vessel (1) reacted with the trimethylamine solution, and anion exchange groups (trimethylbenzylammonium chloride groups) were introduced into the graft-polymerized membrane. The immersion time (circulation time) was 20 hours. After 20 hours, the solution was removed, and the membrane was repeatedly washed with water until the methanol concentration of the wash water was 0.1% or less, yielding an ion exchange membrane (anion exchange membrane). The thickness, membrane resistance, and surface roughness of the resulting ion exchange membrane were measured, and the results are shown in Table 2.

[0085] [Examples 5 to 9, 17, 20, and 21] (Graft polymerization step: production of graft-polymerized membrane) Graft-polymerized membranes were obtained in the same manner as in Example 1, except that the production conditions in Example 1 were changed as shown in Table 1. (Amination step: introduction of anion-exchange groups) The obtained graft-polymerized membrane was subjected to the amination step in the same manner as in Example 4 to obtain an ion-exchange membrane (anion-exchange membrane).

[0086] [Examples 12 and 13] Graft-polymerized membranes were obtained in the same manner as in Example 1, except that the substrate film and production conditions in Example 1 were changed as shown in Table 1. (Amination step: introduction of anion-exchange groups) The obtained graft-polymerized membrane was subjected to the amination step in the same manner as in Example 4 to obtain an ion-exchange membrane (anion-exchange membrane).

[0087] [Example 18-1] The cation exchange membrane obtained in Example 1 was cut into a size suitable for incorporation into a small electrodialysis device and stabilized by immersion in an aqueous sodium hydroxide solution at room temperature for 24 hours. The sodium hydroxide solution was adjusted to a pH of 9.7. The stabilized cation exchange membrane was then placed in a solution prepared by adjusting the pH of a 100 ppm aqueous solution of polyallylamine (Nittobo Medical Co., Ltd. product name "PAA-15C", molecular weight 15,000) to 9.7 with sodium hydroxide, and immersed at room temperature for 20 hours to obtain a cation exchange membrane having amino groups on its surface. The obtained membrane was washed twice with a 3N aqueous hydrochloric acid solution, and the membrane resistance was measured to be 2.7 Ω cm ２ When a seawater concentration test was carried out by electrodialysis using this membrane, the Na / (Na+Ca+Mg) ratio in the obtained concentrate was 0.95.

[0088] [Example 18-2] When a seawater concentration test by electrodialysis was carried out using the cation exchange membrane obtained in Example 1, the Na / (Na + Ca + Mg) ratio was 0.85, and the membrane obtained in Example 18-1 had a higher monovalent cation selective permeability.

[0089] [Example 18-3] A cation exchange membrane having amino groups on its surface was obtained in the same manner as in Example 18-1, except that the cation exchange membrane obtained in Example 14 was used. After washing with an aqueous hydrochloric acid solution in the same manner, a test was carried out. The resistance of the membrane obtained in this example was 4.5 Ω cm ２ The Na / (Na+Ca+Mg) ratio in the concentrate obtained in the seawater concentration test was 0.90. Compared with the membrane obtained in Example 18-1, the resistance was higher and the selectivity for monovalent cations was also inferior.

[0090] [Example 19-1] The cation exchange membrane obtained in Example 2 was cut into a size suitable for incorporation into a small electrodialysis device and stabilized by immersion in an aqueous sodium hydroxide solution at room temperature for 24 hours. The sodium hydroxide solution was adjusted to a pH of 10.5. The stabilized cation exchange membrane was then placed in a solution prepared by adjusting the pH of a 100 ppm aqueous solution of polyallylamine hydrochloride (Nittobo Medical Co., Ltd. product name "PAA-HCL-10L", molecular weight 100,000) with sodium hydroxide, and immersed at room temperature for 20 hours to obtain a cation exchange membrane having amino groups on its surface. The obtained membrane was washed twice with a 3N aqueous hydrochloric acid solution, and the membrane resistance was measured to be 1.7 Ω cm. ２ When a seawater concentration test was carried out using this membrane by electrodialysis, the Na / (Na + Ca + Mg) ratio in the resulting concentrated solution was 0.96.

[0091] [Example 19-2] When a seawater concentration test by electrodialysis was carried out using the cation exchange membrane obtained in Example 2, the Na / (Na + Ca + Mg) ratio was 0.85, and the membrane obtained in Example 19-1 had a higher monovalent cation selective permeability.

[0092] [Example 19-3] A cation exchange membrane having amino groups on its surface was obtained by the same procedure as in Example 19-1, except that the cation exchange membrane obtained in Example 15 was used. After washing with an aqueous hydrochloric acid solution in the same manner, a test was carried out. The resistance of the membrane obtained in this example was 3.5 Ω cm ２ The Na / (Na+Ca+Mg) ratio in the concentrate obtained in the seawater concentration test was 0.91. Compared with the membrane obtained in Example 19-1, the resistance was higher and the selectivity for monovalent cations was also inferior.

[0093]

[0094]

[0095] As shown in the results in Tables 1 and 2, the ion exchange membranes of Examples 1 to 13 and 20 showed significantly less folding and wrinkling when mounted, and also significantly reduced leakage, compared to the ion exchange membranes of Examples 14 to 17 and 21, which had unroughened surfaces. For example, the leakage amount in Example 1 was 10% (DB1 type) or 10% (CS3 type) of the leakage amount in Example 14. The leakage amount in Example 2 was 15.8% (DB1 type) or 8.6% (CS3 type) of the leakage amount in Example 15. The leakage amount in Example 7 was 10% (DB1 type) or 10% (CS3 type) of the leakage amount in Example 17. The leakage amount in Example 10, which had a roughened surface on only one side, was 19% (DB1 type) or 24% (CS3 type) of the leakage amount in Example 16, which had no roughening. Comparing Examples 1, 2, 7, and 10, roughening only one surface reduced leakage, and roughening both surfaces further reduced leakage. Furthermore, as shown in the results of Examples 18-1 to 18-3 and 19-1 to 19-3, treating a roughened cation exchange membrane with an amino group-containing compound resulted in a membrane with lower resistance and higher monovalent cation permselectivity. Such membranes are ideal for seawater concentration tests and reverse electrodialysis power generation.

[0096] REFERENCE SIGNS LIST 10 Base film 12, 14 Roll 20 Electron beam irradiation device 22 Electron beam 30 Cell (half cell) 31 Inlet 32 ​​Opening (circular opening) 33 Platinum wire (platinum black platinum wire) 34 Membrane (ion exchange membrane)

[0097] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-215744, filed on December 21, 2023, are hereby incorporated by reference as the disclosure of the present invention.

Claims

1. An ion exchange membrane comprising a substrate film formed from a base polymer in the form of a film, graft chains having ion exchange groups bonded to the base polymer, and having a roughened surface.

2. The ion exchange membrane according to claim 1, wherein the base polymer is a copolymer containing ethylene units and tetrafluoroethylene units, or a copolymer containing ethylene units and chlorotrifluoroethylene units.

3. The ion exchange membrane of claim 1, wherein the base polymer is a polyolefin.

4. The ion exchange membrane according to claim 3, wherein the polyolefin comprises at least one member selected from the group consisting of polyethylene, polypropylene, poly(4-methyl-1-pentene), and polynorbornene.

5. The ion exchange membrane according to claim 1, wherein the roughness Rz of the roughened surface of the ion exchange membrane is 1 to 40 μm.

6. The ion exchange membrane according to claim 1, wherein the maximum width of the planar shape is 50 cm or more.

7. The ion exchange membrane according to claim 1, which has a thickness of 10 to 200 μm.

8. The ion exchange membrane according to claim 1, which has cation exchange groups as the ion exchange groups and has amino groups on at least one surface.

9. A method for concentrating seawater, comprising electrodialyzing the seawater using the ion exchange membrane according to any one of claims 1 to 8.

10. A method for generating electricity, comprising performing at least one of concentration difference power generation and reverse electrodialysis power generation using the ion exchange membrane according to any one of claims 1 to 8.

11. A method for producing an ion exchange membrane, comprising using a substrate film having a roughened surface, in which a base polymer is formed into a film shape, irradiating the substrate film with ionizing radiation to generate radicals in the base polymer, and graft polymerizing raw material monomers including a monomer having an ion exchange group.

12. A method for producing an ion exchange membrane, comprising using a substrate film having a roughened surface formed by molding a base polymer into a film shape, irradiating the substrate film with ionizing radiation to generate radicals in the base polymer, graft polymerizing raw material monomers including a monomer for introducing an ion exchange group having a functional group capable of introducing an ion exchange group, and then introducing an ion exchange group into a unit derived from the monomer for introducing an ion exchange group.

13. The method for producing an ion exchange membrane according to claim 11 or 12, wherein the substrate film has a surface roughened by a transfer method.

14. The method for producing an ion exchange membrane according to claim 11 or 12, wherein the roughness Rz of the roughened surface of the substrate film is 3 to 20 μm.

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