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

Abstract

Provided is an ion exchange membrane that is less likely to be bent or wrinkled during installation even if it does not have a reinforcing material. An ion exchange membrane that has a base material film formed by molding a base polymer into a film shape, and has a grafted chain having an ion exchange group bonded to the base polymer, the ion exchange membrane having a roughened surface.

Description

Technical Field

[0001] This invention relates to ion exchange membranes, methods for manufacturing ion exchange membranes, and applications of ion exchange membranes. Background Technology

[0002] In the seawater concentration process of ion exchange membrane salt production, an electrodialysis tank utilizing both cation exchange membranes and anion exchange membranes is used.

[0003] Patent documents 1-3 describe the following method: after irradiating a polymer film without ion exchange groups with ionizing radiation to generate free radicals, ion exchange groups are introduced by a method of grafting and polymerizing monomers, thereby manufacturing an ion exchange membrane for salt production.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5120541

[0007] Patent Document 2: Japanese Patent No. 5050284

[0008] Patent Document 3: Japanese Patent No. 5050285 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] According to the methods described in Patent Documents 1 to 3, ion exchange membranes without reinforcing materials such as cloth, porous bodies, or nonwoven fabrics can be manufactured, but because they are very soft membranes, they are sometimes difficult to handle.

[0011] For example, when ion exchange membranes are installed in electrodialysis tanks, diffusion dialysis tanks, or electrochemical cells for electrolysis, bending and wrinkling of the membrane can easily occur at the points where the membrane is fixed (tightened) by the frame. If such bending and wrinkling exist, problems such as leakage of the liquid flowing inside the device and membrane damage during disassembly for maintenance may occur.

[0012] This invention provides an ion exchange membrane that is not prone to bending or wrinkling during installation, even without reinforcing materials.

[0013] Solution for solving the problem

[0014] The present invention has the following features.

[0015] [1] An ion exchange membrane comprising a substrate film formed by molding a base polymer into a thin film, wherein graft chains having ion exchange groups are bonded to the base polymer, and the ion exchange membrane having a roughened surface.

[0016] [2] According to the ion exchange membrane of [1], wherein the base polymer is a copolymer containing ethylene units and tetrafluoroethylene units, or a copolymer containing ethylene units and trifluorochloroethylene units.

[0017] [3] The ion exchange membrane according to [1], wherein the base polymer is a polyolefin.

[0018] [4] According to the ion exchange membrane of [3], wherein the polyolefin comprises one or more selected from the group consisting of polyethylene, polypropylene, poly(4-methyl-1-pentene) and polynorbornene.

[0019] [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.

[0020] [6] The ion exchange membrane according to any one of [1] to [5] has a maximum width of 50 cm or more in its planar shape.

[0021] [7] The ion exchange membrane according to any one of [1] to [6] has a thickness of 10 to 200 μm.

[0022] [8] An ion exchange membrane according to any one of [1] to [7] has a cation exchange group as the ion exchange group and an amino group present on at least one surface.

[0023] [9] A method for concentrating seawater, wherein electrodialysis is performed using an ion exchange membrane as described in any one of [1] to [8].

[0024]

[10] A power generation method, which uses at least one of concentration gradient power generation and reverse electrodialysis power generation using the ion exchange membrane described in any one of [1] to [8] above.

[0025]

[11] A method for manufacturing an ion exchange membrane, wherein a substrate film in which a base polymer is formed into a thin film and has a roughened surface is used, and the base polymer is made to generate free radicals by irradiating the substrate film with ionizing radiation, and a raw material monomer containing a monomer having an ion exchange group is grafted polymerized.

[0026]

[12] A method for manufacturing an ion exchange membrane, wherein a substrate film is formed by molding a base polymer into a thin film and having a roughened surface, the base polymer is irradiated with ionizing radiation to generate free radicals, a raw material monomer containing an ion exchange group introducing monomer is grafted and polymerized, wherein the ion exchange group introducing monomer has a functional group capable of introducing ion exchange groups, and then ion exchange groups are introduced into a unit derived from the ion exchange group introducing monomer.

[0027]

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

[11] or

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

[0028]

[14] The method for manufacturing 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.

[0029] The effects of the invention

[0030] According to the present invention, an ion exchange membrane that is not prone to bending or wrinkling during installation can be obtained even without reinforcing materials. Attached Figure Description

[0031] Figure 1 This is an illustrative diagram schematically representing an example of a process of irradiating ionizing radiation.

[0032] Figure 2 This is a schematic diagram of a simplified structure for measuring membrane resistance. Detailed Implementation

[0033] The following terms are defined in this specification and claims.

[0034] The surface roughness is a value obtained by measuring with a stylus-type surface roughness meter.

[0035] Roughness Rz refers to the "maximum height of the roughness curve" as specified in JIS B0601:2013.

[0036] Roughness Ra refers to the "arithmetic mean height of the roughness curve" as specified in JIS B0601:2013.

[0037] The "~" symbol, which indicates a range of values, refers to the values ​​recorded before and after it as the lower and upper limits.

[0038] Halogen atoms refer to fluorine, chlorine, bromine, and iodine atoms.

[0039] Ion exchange membranes

[0040] The ion exchange membrane of this embodiment comprises a substrate film formed by molding a base polymer into a thin film, on which graft chains having ion exchange groups are bonded, and the ion exchange membrane has a roughened surface.

[0041] The roughened surface of the ion exchange membrane has fine irregularities. Roughening can be performed on only one side of the ion exchange membrane or on both sides. Roughening both sides is preferred.

[0042] For one or both surfaces of an ion exchange membrane, it is preferable to roughen the entire surface.

[0043] In the ion exchange membrane, the roughness Rz of the roughened surface is preferably 1~40 μm, more preferably 5~30 μm, even more preferably 8~25 μm, and particularly preferably 10~20 μm.

[0044] If Rz is above the lower limit of the above range, the effect of suppressing bending and wrinkling of the ion exchange membrane is excellent. If it is below the upper limit of the above range, the reduction in membrane strength caused by roughening is easily suppressed. In addition, it is easy to prevent liquid leakage after installation. For example, when used in a dialysis tank, if the roughness of the membrane surface is too large, the liquid flowing in the device may leak to the outside of the dialysis tank.

[0045] For the same reason, in ion exchange membranes, the roughness Ra of the roughened surface is preferably 0.1 to 10 μm, more preferably 1 to 5 μm, and even more preferably 1.5 to 3.5 μm.

[0046] In ion exchange membranes, the roughness of the roughened surface is preferably at least Rz within the range described above, and more preferably both Rz and Ra are within the range described above.

[0047] The larger the size of the ion exchange membrane, the easier it is to bend and wrinkle during installation.

[0048] Ion exchange membranes are typically 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 region enclosed by the frame.

[0049] Ion exchange membranes can be in various planar shapes, such as polygons, circles, and ellipses. The maximum distance between any two points on the outer perimeter of the planar shape is defined as the "maximum width of the planar shape".

[0050] The greater the maximum width of the planar shape of the ion exchange membrane in 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 the effect is particularly great when the size is 150 cm or more, so it is preferred.

[0051] Reducing the thickness of the ion exchange membrane makes it easier to lower the membrane resistance, but the thinner the membrane, the easier it is to bend and wrinkle during installation. Considering the ease of bending and wrinkling and the maximum effectiveness of this invention, the thickness of the ion exchange membrane is preferably 200 μm or less, more preferably 180 μm or less, even more preferably 150 μm or less, further preferably 100 μm or less, particularly preferably 80 μm or less, and most preferably 60 μm or less.

[0052] On the other hand, if the ion exchange membrane is too thin, pinholes are easily generated 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, further preferably 25 μm or more, and particularly more preferably 30 μm or more.

[0053] <Substrate Film>

[0054] Substrate films are made by molding a base polymer into a thin film. In addition to the base polymer, substrate films may also contain additives as needed.

[0055] Considering the increase in membrane thickness caused by graft polymerization, the thickness of the substrate film is designed to be smaller than the desired thickness of the ion exchange membrane.

[0056] Therefore, the preferred thickness of the substrate film varies depending on the application conditions, for example, preferably 10~200μm, more preferably 15~150μm, even more preferably 20~120μm, and particularly preferably 30~100μm.

[0057] The substrate film may have a roughened surface on one or both sides. As described later, by roughening the surface of the substrate film, the surface state of the substrate film is reflected in the surface state of the ion exchange membrane, thus obtaining a roughened surface for the ion exchange membrane.

[0058] The roughened surface of the substrate film has fine irregularities. Roughening can be performed on only one side of the substrate film or on both sides. Roughening both sides is preferred.

[0059] For one or both surfaces of the substrate film, it is preferable to roughen the entire surface.

[0060] In substrate films with roughened surfaces, the roughening state of the surface can change during the subsequent manufacturing process of ion exchange membranes, without particular limitation.

[0061] For example, in a 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.

[0062] 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.

[0063] In the substrate film, the roughness of the roughened surface is preferably at least Rz within the range described above, and more preferably both Rz and Ra are within the range described above.

[0064] <Basic Polymers>

[0065] The base polymer constituting the substrate film is preferably a fluoropolymer or a polyolefin.

[0066] Examples of fluoropolymers include copolymers comprising ethylene (hereinafter referred to as E) units and tetrafluoroethylene (hereinafter referred to as TFE) units (hereinafter referred to as ETFE), copolymers comprising E units and trifluorochloroethylene (hereinafter referred to as CTFE) units, copolymers comprising 50 mol% or more of trifluoroethylene units, vinylidene fluoride units, or vinyl fluoride units, or homopolymers thereof. A single fluoropolymer may be used alone, or two or more may be used in combination.

[0067] In ETFE, the molar ratio of TFE-based units to E-based units (TFE / E) is preferably 40 / 60 to 80 / 20, more preferably 50 / 50 to 70 / 30. When the molar ratio of TFE-based units is too small, the substrate film tends to have low heat resistance, weather resistance, chemical resistance, gas barrier properties, and fuel barrier properties. When the molar ratio of TFE-based units is too large, the melt-forming properties of ETFE are insufficient, and the substrate film tends to have low mechanical strength. Within the above ranges, ETFE exhibits excellent melt-forming properties, and the substrate film exhibits excellent heat resistance, weather resistance, chemical resistance, gas barrier properties, fuel barrier properties, and mechanical strength.

[0068] In addition to units based on TFE and E, ETFE may also contain units based on other monomers (a) that can copolymerize with TFE and E.

[0069] Other monomers (a) include: vinylidene fluoride, CTFE, hexafluoropropylene (hereinafter referred to as HFP), and CF2=CFR. 1 (where R) 1 (This refers to perfluoroalkyl groups with 2 to 6 carbon atoms, the same applies below), CH2=CHR 2 (where R) 2 (Refers to polyfluoroalkyl groups with 1-8 carbon atoms, the same applies below), CF2=CHR 3 (where R) 3 (This refers to perfluoroalkyl groups with 1 to 6 carbon atoms, the same applies below), CH2=CFR 2 Isofluorinated alkenes (excluding TFE), CF2=CFOR 4 (Here, R) 4 This refers to fluorinated vinyl ethers such as perfluoroalkyl groups (containing 1 to 10 carbon atoms), CF2=CFOR 5 COX 1 (Here, R) 5 X represents a divalent perfluoroalkylene group containing 1 to 10 carbon atoms. 1(representing hydroxyl groups, alkoxy groups with 3 or fewer carbon atoms, or halogen atoms), CF2=CFOR 6 SO2X 2 (R 6 X represents a divalent perfluoroalkylene group containing 1 to 10 carbon atoms. 2 Fluorinated vinyl ethers containing functional groups such as halogen atoms or hydroxyl groups, CF2=CF(CF2) n OCF=CF2 (where n represents 1 or 2), perfluorinated compounds (2-methylene-4-methyl-1,3-dioxane), hydrocarbon alkenes such as propylene and butene (excluding E), aliphatic carboxylic acid vinyl esters such as vinyl acetate and vinyl butyrate, polymerizable unsaturated compounds with anhydride structures such as maleic anhydride, itaconic anhydride, and citraconic anhydride, vinyl ethers such as hydroxybutyl vinyl ether and glycidyl vinyl ether, etc. Other monomers (a) that can copolymerize with TFE and E can be used alone or in combination with two or more.

[0070] As another monomer (a) capable of copolymerizing with TFE and E, CH2=CHR is preferred. 2 HFP, CF2=CFOR 4 Alternatively, it may contain polymeric unsaturated compounds with an anhydride structure. The presence of units based on polymeric unsaturated compounds with an anhydride structure improves the hydrophilicity when forming ion exchange membranes, and is therefore sometimes preferred. Furthermore, the presence of units based on the aforementioned CH2=CHR... 2 The substrate film exhibits excellent mechanical properties due to the presence of such units. As an R... 2 More preferably, it is a perfluoroalkyl group having 1 to 6 carbon atoms, and most preferably, it is a perfluoroalkyl group having 2 to 4 carbon atoms.

[0071] The content of monomer-based units relative to the total amount of TFE units and E units is preferably 7 mol% or less, more preferably 6 mol% or less, and particularly preferably 4 mol% or less. Furthermore, when the base polymer contains monomer-based units, the content of monomer-based units relative to the total amount of TFE units and E units is preferably 1.0 mol% or more, more preferably 1.4 mol% or more, more preferably 1.5 mol% or more, and particularly preferably 2.0 mol% or more. If the content of monomer-based units is at or above the aforementioned lower limit, the polymer has low crystallinity, making it suitable for graft polymerization; if it is below the aforementioned upper limit, the polymer has a high melting point, which can increase the usable temperature when manufacturing ion exchange membranes.

[0072] The copolymer containing E units and CTFE units preferably replaces TFE in the ETFE with CTFE.

[0073] Examples of polyolefins include polyethylene, polypropylene, poly(4-methyl-1-pentene), or polynorbornene. A single polyolefin may be used alone, or two or more may be used in combination. Polyethylene is preferred as a polyolefin, and linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and ultra-high molecular weight polyethylene (UHMWPE), copolymerized from ethylene and α-olefins, are particularly preferred. High-density polyethylene and ultra-high molecular weight polyethylene are especially preferred.

[0074] <Ion exchange groups>

[0075] Examples of anion exchange groups include quaternary ammonium groups, tertiary amino groups, secondary amino groups, primary amino groups, and imidazole groups as shown in formula (1) (wherein, R is selected from R). 11 ~R 15 At least one of them is a linking bond, and the others each independently represent a hydrogen atom, optionally include an ether oxygen atom between carbon-carbon bonds, optionally include an alkyl group with 1 to 8 carbon atoms of -N- between carbon-carbon bonds, or R 11 ~R 15 An alkylene group formed by the bonding of any two of the atoms; wherein R 13 (Indicates groups that are not hydrogen atoms, etc.)

[0076] The imidazole group (hereinafter sometimes referred to as "imidazole group (1)") shown in formula (1) is bonded to the graft chain. The number of bonds connecting the multiple imidazole groups (1) contained in the ion exchange membrane can vary from one another. R 11 ~R 15 The number of linkages in the membrane is not particularly limited, but as the average number of imidazole groups (1) per mole contained in the ion exchange membrane, it is preferably 3 or less, more preferably 2 or less, and particularly preferably 1.5 or less.

[0077]

[0078] <Grafting Chain>

[0079] The grafted chains of an ion exchange membrane are polymeric chains formed by grafting raw material monomers onto a base polymer, and possess ion exchange groups. These ion exchange groups can originate from the raw material monomers, be introduced after graft polymerization, or both.

[0080] When the raw material monomer contains one or more monomers having ion-exchange groups, a graft chain with ion-exchange groups derived from the raw material monomer is formed. The monomer with ion-exchange groups is preferably a compound having one or more polymerizable carbon-carbon double bonds.

[0081] Examples of monomers having cation exchange groups include acrylic acid or its salts, methacrylic acid or its salts, acrylates (e.g., n-butyl acrylate), methacrylates, acrylonitrile and other acrylic acids; maleic anhydride, maleic acid, fumaric acid or their esters; styrene sulfonic acid or its salts; 2-acrylamido-2-methylpropanesulfonic acid or its salts as shown in formula (2); vinyl sulfonic acid or its salts; etc.

[0082] In the case of salts such as acrylates and sulfonates, the base that forms a salt with the acidic group can be a known base such as sodium hydroxide or potassium hydroxide.

[0083]

[0084] Examples of monomers having anion exchange groups include 4-vinylbenzyltrimethylammonium chloride as shown in formula (3); 2-(acryloyloxy)-N,N,N-trimethylethane ammonium chloride as shown in formula (4), (3-acrylamidopropyl)trimethylammonium chloride as shown in formula (5), and other acrylates containing quaternary ammonium salts; acrylamides; allylamines such as allylamine, diallylamine, and diallylmethylamine, and their salts with acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and acetic acid; diallyl dialkyl quaternary ammonium salts such as diallyl dimethylammonium chloride; etc.

[0085]

[0086] When the raw material monomer includes one or more monomers for introducing ion exchange groups that do not have ion exchange groups, a graft chain is formed having units derived from the aforementioned monomers for introducing ion exchange groups. After graft polymerization, by introducing ion exchange groups into the units derived from the aforementioned monomers for introducing ion exchange groups, a graft chain having ion exchange groups can be obtained.

[0087] Examples of monomers that can introduce cation exchange groups include styrene, vinyltoluene, vinylnaphthalene, vinylxylene, α-methylstyrene, acenaphthene, vinylnaphthalene, α-halostyrene, α,β,β'-trihalostyrene, chlorostyrene, glycidyl methacrylate, and other monomers that readily introduce sulfonic acid groups.

[0088] Examples of other examples include acrylates (e.g., n-butyl acrylate), methacrylates (e.g., tert-butyl methacrylate), acrylonitrile, maleate esters, fumarate esters, styrene sulfonates (e.g., methyl styrene sulfonate), vinyl sulfonates, etc.

[0089] Known methods can be used to introduce cation exchange groups onto the units of the grafted chain derived from the monomer used for introducing cation exchange groups. Examples of compounds (sulfonating agents) used for introducing sulfonic acid groups include concentrated sulfuric acid, sulfur trioxide, sodium thiosulfate, chlorosulfonic acid, and trialkylbenzene sulfonic acid, which are particularly suitable for grafted chains containing benzene rings.

[0090] In addition, for substances with epoxy groups or haloalkyl groups in the grafted chain, methods such as (1) reacting sodium sulfite or (2) reacting a thiol compound and then introducing a sulfonic acid group or its salt by oxidation with hydrogen peroxide or hypochlorous acid can also be used. In addition, when the grafted chain is an ester, methods can be used to generate sulfonic acid, carboxylic acid or its salt by hydrolysis with acid or base, but these methods are not limited to.

[0091] As a monomer for introducing anion exchange groups, there are no particular limitations on monomers used in the manufacture of conventionally known anion exchange resins and anion exchange membranes. Specifically, a compound represented by the following formula (6) can be used as an example (where R is a monomer). 18 The following are examples of compounds: alkylene groups (1 to 8 carbon atoms, optionally containing an ether oxygen atom between carbon-carbon bonds, where X is a halogen atom), 4-vinylpyridine, styrene, vinyltoluene, vinylxylene, α-methylstyrene, acenaphthene, vinylnaphthalene, α-halostyrene, α,β,β'-trihalostyrene, chlorostyrene, 2-vinylpyridine, methylvinylpyridine, ethylvinylpyridine, vinylpyrrolidone, vinylcarbazole, vinylimidazole, aminostyrene, alkylaminostyrene, trialkylaminostyrene, acrylamide, oxium, glycidyl methacrylate, vinylimidazole and their derivatives, etc.

[0092] Specifically, from the viewpoint of easily obtaining a film with low resistance, m-chloromethylstyrene, p-chloromethylstyrene, 3-chloropropylstyrene, 4-chlorobutylstyrene, 4-bromobutylstyrene, and 4-vinylpyridine are preferred.

[0093]

[0094] Anion exchange groups can be introduced onto the units of the grafted chain derived from the monomer for introducing anion exchange groups using known methods. Examples of compounds used for introducing anion exchange groups include: ammonia, methylamine, dimethylamine, etc., which can introduce weakly basic ion exchange groups onto halogenated alkyl groups such as chloromethylstyrene and epoxy groups such as glycidyl methacrylate; and trimethylamine, dimethylamine ethanol, triethanolamine, cyclic tertiary amines (e.g., compounds represented by formulas (a1) to (a7) below), or imidazoles (e.g., compounds represented by formula (7) below), which can introduce strongly basic ion exchange groups. From the viewpoint of reducing the resistance of the resulting membrane, trimethylamine is preferred among these compounds. Furthermore, the above compounds can be used alone or in combination of two or more compounds.

[0095] Furthermore, reacting pyridines such as 4-vinylpyridine and imidazoles such as vinylimidazoles with alkyl sulfates, alkyl carbonates, and haloalkanes can generate quaternary ammonium groups as anion exchange groups. The aforementioned alkyl sulfates and other compounds can be used alone or in combination of two or more compounds.

[0096] Alternatively, the following methods can be used: For monomers with aromatic rings that do not have groups capable of introducing anion exchange groups (e.g., styrene), a haloalkyl group can be introduced at the terminal by Friedel-Crafts alkylation with a compound having 1-8 carbon atoms and multiple halogen groups within the molecule, or by chloromethylation using chloromethyl ether, and then anion exchange groups can be introduced using the methods described above. Alternatively, for monomers with halogen atoms bonded to an aromatic ring, a haloalkyl group can be introduced at the terminal by Grignard coupling with a compound having 1-8 carbon atoms and multiple halogen groups within the molecule, and then anion exchange groups can be introduced using the methods described above.

[0097]

[0098] R in equations (a1)~(a7) 21 ~R 26 These can be independently represented as hydrocarbon groups, fluorohydrocarbon groups, or fluorocarbon groups. The term "hydrocarbon group" refers to a group containing CH bonds but not CF bonds within the molecule. The term "fluorohydrocarbon group" refers to a group where some of the hydrogen atoms bonded to the carbon atom of the hydrocarbon group are replaced by fluorine atoms. The term "fluorocarbon group" refers to a group where all the hydrogen atoms bonded to the carbon atom of the hydrocarbon group are replaced by fluorine, i.e., a group containing only CF bonds within the molecule. R 21 ~R 26 Each can independently and optionally contain an ether bond, a sulfonyl bond, and / or a hydroxyl group. Additionally, R 21 ~R 26 In the case of a hydroxyl group, a tertiary alcohol is preferred to prevent oxidation.21 ~R 26 The structure is not particularly limited; it can be a linear chain or a ring structure. Furthermore, R... 21 ~R 26 It can also contain aromatic groups.

[0099]

[0100] In equation (7), R 31 ~R 34 Each is independently a hydrogen atom and a group selected from alkyl groups having 1 to 8 carbon atoms, R 31 and R 32 They can bond together to form a ring. Among them, R... 33 This indicates a group that is not a hydrogen atom.

[0101] Grafted chains may or may not have a cross-linked structure. If the raw monomer contains a cross-linking monomer, graft polymerization forms grafted chains with a cross-linked structure. The cross-linking monomer is preferably a compound having two or more polymerizable carbon-carbon double bonds.

[0102] Examples of crosslinking monomers include divinylbenzene (DVB), trivinylbenzene, divinyltoluene, divinylnaphthalene, styrene derivatives shown in formulas (8) and (9), and ethylene glycol dimethacrylate.

[0103] In equation (9), R 41 It refers to an alkylene group consisting of 1 to 8 carbon atoms, which may contain ether-containing oxygen atoms between carbon-carbon bonds.

[0104]

[0105] When the raw material monomers include crosslinking monomers, the proportion of crosslinking monomers used relative to the total mass of the raw material monomers is not particularly limited. Since it varies depending on the difference in polymerizability with monomers having ion exchange groups and monomers for introducing ion exchange groups, it can be adjusted in a way that results in a membrane resistance suitable for the application. Generally, relative to 100 parts by mass of the monomers having ion exchange groups, monomers for introducing ion exchange groups, and any monomers described later, the crosslinking 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.

[0106] The monomers constituting the graft chain may be any monomer other than monomers with ion exchange groups, monomers for introducing ion exchange groups, and crosslinking monomers. There are no particular limitations on the monomers; examples include vinyl esters such as acrylonitrile, vinyl acetate, and vinyl pivalate; vinyl silanes such as vinyltrimethylsilane, vinyltrimethoxysilane, and vinyldimethoxymethylsilane; acrylamides such as acrylamide, N-methylacrylamide, and N,N-dimethylacrylamide; and so on.

[0107] There is no particular limitation on the amount of any monomer used, but it 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 a total of 100 parts by mass of monomers having ion exchange groups and monomers capable of introducing ion exchange groups. When the amount of any monomer is too large, the ratio of monomers having ion exchange groups to monomers capable of introducing ion exchange groups becomes low, and the ionic conductivity (membrane resistance) of the resulting ion exchange membrane becomes insufficient, which is therefore not preferred.

[0108] An ion exchange membrane can be a cation exchange membrane having cation exchange groups as ion exchange groups and having an amino group on at least one surface. By having an amino group on the surface of the cation exchange membrane, it can exhibit selective permeability to monovalent cations.

[0109] The amino group is preferably derived from an amino-containing compound having at least one, preferably two or more, amino groups in one molecule.

[0110] As a specific example of the above-mentioned amino-containing compounds, R can be cited: 51 -NH2(where R is the formula) 51 Alkylamines are alkylamines represented by alkyl groups having 1 to 30 carbon atoms; NH2-R 52 -NH2(where R is the formula) 52 Diamines (alkylene groups having 1 to 30 carbon atoms); oligomers obtained by polycondensation of epichlorohydrin with one or more of the above-mentioned alkylamines and diamines with ammonia as required; polyethyleneimines; polymers of one or more monomers selected from allylamine hydrochloride, diallylamine hydrochloride, diallyl methylamine hydrochloride, diallyl dimethyl ammonium chloride, acrylamide, N-alkylacrylamide and N,N-dimethylacrylamide; polymers containing amino compounds such as 4-vinylbenzyltrimethylammonium chloride as shown in formula (3), quaternary ammonium salt acrylates as shown in formulas (4) and (5) as shown in formulas (5).

[0111] In addition, examples may include polymers containing alkyl halide monomers as described in the above description of polymers capable of incorporating anion exchange groups, and polymers obtained by reacting the alkyl halide of a polymer incorporating an alkyl halide with ammonia or primary to tertiary amines, but are not limited to these.

[0112] There are no particular limitations on the molecular weight of these amino-containing compounds. However, considering the adhesion of the amino-containing compounds to the membrane surface, a number-average molecular weight of 100 or more is preferred, more preferably 3,000 or more, further preferably 5,000 or more, and particularly preferably 8,000 or more is acceptable. If the molecular weight of the amino-containing compound is too low, there is a problem that it may be difficult to adhere to the cation exchange membrane. In the case of high molecular weight, there are no particular limitations as long as the amino-containing compound has the solubility to be diluted to any proportion with water, alcohol, or other organic solvents. However, considering ease of operation, a number-average molecular weight of 1 million or less is preferred, more preferably 500,000 or less, and particularly preferably 200,000 or less is acceptable.

[0113] As a method for making amino groups present on the surface of a cation exchange membrane (a method for selective treatment of monovalent cations), the following methods (i) to (iii) can be cited.

[0114] (i) A method for contacting a solution containing a specified amino compound or its salt with a cation exchange membrane.

[0115] (ii) A method of treating the surface or the entire ion exchange groups of a cation exchange membrane under acidic conditions to obtain an acidic state such as acrylic acid or sulfonic acid, and then treating it with a solution containing an amino compound.

[0116] (iii) A method of contacting a cation exchange membrane with an aqueous solution of sodium hydroxide, potassium hydroxide, or a mixture of water-soluble organic solvents as needed, stabilizing it under alkaline conditions of pH 8 to 13, and then further treating it by contacting it with a solution containing an amino compound at a specified concentration under the same pH conditions.

[0117] The amino-containing compound used in the method for selective treatment of monovalent cations can be in a neutral state, or in a state of salt formation with acids such as hydrochloric acid, acetic acid, sulfuric acid, and phosphoric acid, or in a partially salt-forming state. Furthermore, as a method for contacting the cation exchange membrane with the solution containing the amino compound under various conditions, methods can include: directly coating the membrane with the solution containing the amino compound under specified conditions; coating the amino-containing compound at a specified concentration onto a release film, drying it as needed, laminating the cation exchange membrane, and then pressing / heating it as needed to fix the compound; or loading the cation exchange membrane into an electrodialysis tank or similar device and contacting it with the solution within that device, etc., but are not limited to these methods.

[0118] By performing this treatment on the cation exchange membrane, an ion exchange membrane with high selective permeability to monovalent cations and low electrical resistance can be obtained. This ion exchange membrane is suitable for electrodialysis applications such as seawater concentration and lithium-ion recovery, as well as reverse electrodialysis power generation, and is particularly expected to improve current efficiency and power generation efficiency.

[0119] <Manufacturing Method>

[0120] The ion exchange membrane of this embodiment can be manufactured, for example, by the following manufacturing methods (1) to (4).

[0121] Manufacturing method (1): A method of grafting monomers containing monomers having ion exchange groups onto a substrate film in which a base polymer is formed into a thin film and has a roughened surface, by irradiating the substrate film with ionizing radiation to generate free radicals in the base polymer.

[0122] Manufacturing method (2): Using a substrate film formed by molding a base polymer into a thin film and having a roughened surface, the base polymer is made to generate free radicals by irradiating the substrate film with ionizing radiation, and a raw material monomer containing an ion exchange group introducing monomer is grafted and polymerized, wherein the ion exchange group introducing monomer has a functional group capable of introducing ion exchange groups, and then ion exchange groups are introduced into the unit derived from the ion exchange group introducing monomer.

[0123] Manufacturing method (3): In manufacturing method (1), a method of roughening the surface of a substrate film that has not been roughened by grafting the raw material monomers.

[0124] Manufacturing method (4): In manufacturing method (2), a method of roughening the surface using an unroughened substrate film, either after graft polymerization of the raw material monomer or after introducing ion exchange groups into a unit of a monomer derived from an ion exchange group.

[0125] In manufacturing methods (3) and (4), the processing temperature required to roughen the grafted polymerized film is often higher than that required to roughen the substrate film. In this respect, manufacturing methods (1) and (2) are preferred over manufacturing methods (3) and (4).

[0126] Furthermore, in manufacturing method (4), the membrane obtained by introducing ion exchange groups is in a wet state. Therefore, if roughening is performed after introducing ion exchange groups, it is difficult to obtain sufficient surface roughness. In addition, if the wet membrane is dried and then roughened, the membrane strength will decrease, and defects such as breakage will easily occur. In this respect, manufacturing methods (1) to (3) are preferred compared to manufacturing method (4).

[0127] As a method for roughening the surface of a film (including substrate films), a transfer printing method can be applied, in which a mold or roller with raised or recessed surfaces is brought into contact with the surface of the film while being heated as needed, with pressure applied or not. Specifically, for example, the raised or recessed surfaces can be transferred to the film by forming raised or recessed surfaces on at least one surface of a pair of rollers and passing the film between the rollers.

[0128] Alternatively, the following method can be used: a film with raised or recessed surfaces on a release film surface can be used instead of the aforementioned mold or roller with raised or recessed surfaces for transfer printing.

[0129] Besides the transfer method, other methods include: roughening the film surface by blowing fine particles (also known as sandblasting); etching using a solution that oxidizes and dissolves the film surface; etc. Considering the ability to eliminate the influence on the film surface properties, the effects of residual treatment agents, and the simplicity of the process, the transfer method using a mold or roller with raised or recessed surfaces is preferred.

[0130] In manufacturing methods (1) to (4), the graft polymerization process can be carried out using known methods. For example, it is preferable to immerse a substrate film irradiated with ionizing radiation in a polymerization solution to carry out the polymerization reaction.

[0131] The polymerization liquid contains raw material monomers that form grafted chains, and may also contain solvents.

[0132] There are no particular limitations on the types of solvents, but examples include hydrocarbons such as benzene, xylene, toluene, and hexane; alcohols such as methanol, ethanol, and isopropanol; 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-pyrrolidone. One solvent may be used, or two or more may be used in combination.

[0133] The graft polymerization of the base polymer from the raw material monomer to the substrate film can be either a so-called pre-irradiation method, in which the substrate film is irradiated with ionizing radiation and then polymerizes with the raw material monomer, or a so-called simultaneous irradiation method, in which the substrate film and the raw material monomer are irradiated simultaneously and polymerize.

[0134] From the viewpoint of minimizing the amount of homopolymer generated that is not grafted onto the substrate film, the pre-irradiation method is preferred. As a method for implementing the pre-irradiation method, it can be either the polymer radical method of irradiating the substrate film in an inert gas or the peroxide method of irradiating the substrate film in the presence of oxygen.

[0135] Specific examples of ionizing radiation include alpha rays, beta rays, gamma rays, electron beams, and ultraviolet rays. From the perspective of being able to homogenize and activate the substrate film, electron beams are preferred.

[0136] A preferred method is to use an electron beam as ionizing radiation, continuously irradiating the substrate film with the electron beam while transporting it. According to this method, even when irradiating a large number of substrate films with ionizing radiation, industrial productivity is excellent in terms of homogeneous activation of the substrate films.

[0137] Figure 1 This is an illustrative diagram schematically representing an example of a process involving the irradiation of ionizing radiation. (Using...) Figure 1 The steps of "continuous electron beam irradiation" described above will be explained in detail. First, the substrate film 10 wound on the roller 12 is unwound in the conveying direction A, and the substrate film 10 is conveyed to the electron beam irradiation position where the electron beam irradiation device 20 is installed. Next, after the substrate film 10 at the electron beam irradiation position is irradiated with an electron beam 22, 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 up by the roller 14. In this way, the substrate film 10 is continuously irradiated with the electron beam 22.

[0138] From the viewpoint of activating the substrate film, the irradiation dose of ionizing radiation on the substrate film is preferably 10 to 1,000 kGy, more preferably 30 to 500 kGy, and even more preferably 40 to 200 kGy.

[0139] Ionizing radiation can be applied in a single irradiation to achieve the desired dose (continuous irradiation) or in multiple irradiations to achieve the desired dose through a total irradiation dose (intermittent irradiation). Especially when an irradiation dose of 80 kGy or higher is required, continuous electron beam irradiation can cause the substrate film to heat up, leading to side reactions such as inactivation or cross-linking of irradiated free radicals, sometimes making it difficult to obtain the target grafted polymer chains. Furthermore, continuous electron beam irradiation of the substrate film can sometimes cause film deformation due to heat (e.g., film elongation). To address these issues, intermittent irradiation allows the substrate film to cool during periods of non-irradiation, thus suppressing thermal modification. Particularly when the substrate film is made of polyethylene, the change in mechanical strength due to heat is significant, therefore intermittent irradiation is preferred.

[0140] Cooling of the substrate film during intermittent irradiation is preferably performed until the temperature drops below the softening point of the material constituting the substrate film.

[0141] use Figure 1A specific example of the intermittent irradiation method will be described. First, after irradiating a specific portion of the substrate film 10 conveyed from roller 12 toward conveying direction A with electron beam 22 (first irradiation), the portion of the substrate film 10 including the specific portion is wound onto roller 14.

[0142] After the specific portion of the substrate film 10 wound on the roller 14 has been sufficiently cooled, the substrate film 10 is wound out in the opposite direction of the conveying direction A. The substrate film 10 is then conveyed to the electron beam irradiation position again. After the specific portion of the substrate film 10 is irradiated by the electron beam 22 (second irradiation), the portion of the substrate film 10 containing the specific portion is wound on the roller 12.

[0143] Alternatively, the substrate film 10 wound on roller 14 can be repositioned on roller 12, wound out again in the direction of conveying direction A, and the substrate film 10 can be conveyed to the electron beam irradiation position again. After irradiating a specific part of the substrate film 10 with electron beam 22 (second irradiation), the portion of the substrate film 10 including the specific part can be wound on roller 14.

[0144] In this way, the substrate film 10 can be irradiated with electron beams twice.

[0145] It should be noted that if more than three irradiations are required, simply perform the above steps to achieve the desired number of irradiations.

[0146] Furthermore, when irradiating more than twice, irradiation can be performed from the same side of the film, or from either side of the surface or the back side, any number of times. When irradiating more than twice, it is sometimes preferable to irradiate the surface and the back side an equal number of times (one more time on one side in the case of an odd number of times).

[0147] The temperature of the substrate film during irradiation is -10 to 50°C, preferably below room temperature. In cases where there is a large spatial or temporal difference between ionizing radiation irradiation and graft polymerization, such as during continuous or intermittent irradiation, the irradiated film can be stored in a dry ice-filled box or freezer (preferably below -30°C) to suppress the modification and disappearance of free radicals before graft polymerization. Next, the irradiated substrate film is removed from the atmosphere, transferred to a glass container, and then filled with a polymerization solution. For the polymerization solution, a solution that has been pre-removed of oxygen through bubbling or freeze degassing with an oxygen-free, inert gas is used. Alternatively, a continuous polymerization apparatus or similar device can be used (e.g., Japanese Patent Application Publication No. 2004-137385, Japanese Patent Application Publication No. 2005-60555, International Publication No. 2018 / 030498). Graft polymerization for introducing graft chains into the irradiated substrate film is typically carried out at room temperature to 80°C, preferably 40 to 70°C.

[0148] The grafting rate (the ratio of the mass of the grafted chain to the mass of the substrate film before polymerization (unit: mass%)) is preferably 10 to 300% by mass, more preferably 20 to 150% by mass. The grafting rate can be adjusted by the irradiation dose, polymerization temperature, polymerization time, etc.

[0149] The process of introducing ion exchange groups after graft polymerization can be carried out using known methods.

[0150] The following is a specific example of introducing sulfonic acid groups as cation exchange groups. The substrate film after graft polymerization is immersed in a 0.2–1.5 mol / L chlorosulfonic acid solution using 1,2-dichloroethane as a solvent at 25–80°C for 1–96 hours to induce a reaction. After the specified reaction time, the film is thoroughly washed. Then, the sulfonation reaction is terminated by immersion in a 1–10% (w / w) sodium hydroxide aqueous solution for 1–24 hours, and the film is thoroughly washed with water.

[0151] Alternatively, the membrane is sulfonated by immersion in concentrated sulfuric acid (concentration 96% or higher, preferably 97% or higher, particularly preferably 98% or higher) and contacted under heating (room temperature to 100°C, preferably 40°C to 70°C, particularly preferably 50°C to 65°C) as needed, then washed thoroughly with water, and then immersed (or contacted) in an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 1 to 10% by mass for 1 to 24 hours to neutralize the membrane.

[0152] For example, the following is a specific example of introducing an amino group as an anion exchange group.

[0153] As the compound used to introduce anion exchange groups, the above-mentioned amine compounds (e.g., the compounds shown in formulas (a1) to (a7) and (7) above) are used.

[0154] When grafted chloromethylstyrene is used as the monomer capable of introducing ion exchange groups, the resulting polymeric membrane is immersed or contacted in a solution prepared with the concentration of the aforementioned amine compound being 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. This causes the chloromethyl group of the chloromethylstyrene to be quaternized, generating anion exchange groups. After the reaction, the membrane is thoroughly washed to obtain an anion exchange membrane. There are no particular limitations on the solvent used in this reaction to prepare the amine compound solution; various solvents can be mixed, but a solvent capable of dissolving the amine compound is preferred. Furthermore, water is particularly preferred for post-reaction washing. Therefore, water-soluble solvents such as (a) water, (b) methanol, ethanol, 1-propanol, 2-propanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and ethylene glycol dimethyl ether are particularly preferred. Two or more of these solvents can be mixed. Furthermore, when using a solvent selected from (a) and (b), it is preferable that the amine compound is uniformly dissolved. Additionally, the preferred reaction temperature varies depending on the solvent used, the boiling point of the compound, and its reactivity. When using compounds with low boiling points such as trimethylamine, methanol, or acetone, the reaction temperature is preferably 60°C or lower, and more preferably 50°C or lower.

[0155] <Applications>

[0156] The ion exchange membrane of the present invention can be used for applications known in the field of ion exchange membranes. In particular, even when the size is large, it is not easy for the membrane to bend or wrinkle during installation, thus making it suitable for applications with a large effective membrane area.

[0157] For example, it can be used as a diaphragm in seawater concentration methods that use electrodialysis to concentrate seawater, power generation methods such as concentration gradient power generation and reverse electrodialysis power generation, water electrolysis, and electrolysis of organic compounds (e.g., methods that replace benzene, toluene, etc. with hexane, methylhexane by electrolytic hydrogenation).

[0158] Seawater concentration methods using ion exchange membranes can include known methods such as those presented in the Journal of the Japan Society for Marine Science, Vol. 34, No. 2 (1980), pp. 121-124.

[0159] Concentration gradient power generation using ion exchange membranes can be employed, for example, by well-known methods such as Bull. Soc. Sea Water Sci., Jpn., 73, 3-8 (2019).

[0160] Reverse electrodialysis power generation using ion exchange membranes can be achieved, for example, by well-known methods such as Bull. Soc. Sea Water Sci., Jpn., 66, 242-247 (2012).

[0161] Example

[0162] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0163] <Determination Method>

[0164] [Membrane resistance]

[0165] The ion exchange membrane was immersed in a 0.5 mol / L sodium chloride aqueous solution and conditioned overnight in a constant temperature bath at 25°C. This membrane was then used as the test object.

[0166] Figure 2 This is a schematic diagram illustrating a simplified structure of the measuring apparatus. Symbol 30 represents a cylindrical half-cell with a circular opening 32 of 15 mm in diameter. Symbol 31 represents the liquid inlet. Symbol 33 represents a platinum wire. Symbol 34 represents the membrane to which the resistance is being measured. The ion exchange membrane 34 of the object being measured is clamped between the left and right sides within the half-cell 30 and secured with constant pressure using spring coils or the like. Next, the interior of the cell 30 is filled with 0.5 equivalents of NaCl. The platinum wire 33 is connected to an AC resistance meter, and the AC resistance (unit: Ω) is measured at 1 kHz. Afterward, the membrane 34 is quickly removed to prevent internal liquid leakage, 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 ).

[0167] The membrane resistance = {(resistance between platinum wires when installing the membrane) - (resistance between platinum wires when removing the membrane)} × 1.77 …(r1)

[0168] It should be noted that the membrane resistance was measured in a constant temperature room at 25°C to determine the resistance at 25°C.

[0169] For the sample to be measured, firstly, 10 cm wide strips of membrane were cut out at 1 m from each end of the ion exchange membrane obtained in each example along its length. Next, the required area was cut from the center of each of the two strips along its width. The membrane resistance of each of the two samples obtained in this way was measured using the method described above, and their average value was taken as the measurement result.

[0170] [Membrane thickness]

[0171] The thickness of the membrane was measured using a micrometer (manufactured by Mitutoyo Corporation, trade name "MDC-25SX").

[0172] For the sample to be measured, 10cm wide strips of membrane were cut at 1m from both ends of the ion exchange membrane obtained in each example along its length. For the two strips of membrane obtained, measurements were taken at 5 random points (10 points in total) along the width direction, and the average value was taken as the measurement result.

[0173] [Surface roughness Ra·Rz]

[0174] The ion exchange membranes obtained in each example, in a moist state, were placed on a glass plate without drying and sealed tightly. The surface (measurement surface) was wiped dry, and the measurement was performed within 5 minutes.

[0175] A stylus with a front-end radius of 2μm and a front-end angle of 60° was installed on a stylus-type surface roughness meter (manufactured by Mitutoyo Corporation, trade name "SURFTEST SJ-310") as a standard testing machine to measure the Ra and Rz of the test surface.

[0176] [Installation test (leakage, bending / wrinkling)]

[0177] Installation tests (installation experiments) were conducted on ion exchange membranes for use in large electrochemical cells. Two types of electrodialysis cells with different membrane sizes were used: (1) DB1 type and (2) CS3 type.

[0178] (1) For the DB1 type electrodialysis cell (effective membrane area 180×550mm) manufactured by AGC Engineering CO., LTD., 200 ion exchange membranes are stacked alternately on a vinyl chloride chamber frame and secured to form the dialysis cell. The pressure at the securing part is 20 kg / cm². 2 .

[0179] (2) For the CS3 type electrodialysis cell (effective membrane area 550×1120mm) manufactured by AGC Engineering CO., LTD., 200 ion exchange membranes were alternately stacked and fastened together in a polypropylene chamber frame to fabricate the dialysis cell. The fastening pressure was 7 kg / cm². 2 .

[0180] It should be noted that cation exchange membranes and anion exchange membranes are usually installed in an alternating stacked state, but in this experiment, only the cation exchange membranes or anion exchange membranes obtained in each example were installed.

[0181] (Leakage test)

[0182] The dialysis tanks prepared in (1) and (2) above were not powered on. Water was circulated from the bottom of the dialysis tank at a speed of 10 cm / s for 24 hours, and the amount of water leaking out of the dialysis tank was measured (leakage amount, unit: mL). It should be noted that a water column with a height of 1 m was erected at the outlet of the dialysis tank to apply water pressure to the inside.

[0183] (The formation of bends / wrinkles)

[0184] Disassemble the dialysis tank prepared in (2) above and visually observe the condition of the fastening parts with the chamber frame. Measure the number of bends and folds of the membrane, and take the total of the two as the measurement result.

[0185] [Seawater Concentration Experiment Using Electrodialysis]

[0186] Using the cation exchange membranes obtained in the examples and a commercially available anion exchange membrane (trade name "ASVN" manufactured by AGC Engineering CO.,LTD.), a small-scale electrodialysis device (effective membrane area 8.0 cm²) was assembled according to the method described in "Bull. Soc. Sea Water Sci., Jpn., 75, 145-152 (2021) Takahashi et al." 2 (2.0×4.0cm)). A 0.5 mol / L NaCl aqueous solution was circulated in the concentration chamber, while a simulated seawater solution prepared with a molar ratio of NaCl / CaCl2 / MgCl2 = 44.3 / 0.9 / 4.7 was circulated in the desalination chamber. The current density was 3 A / dm³. 2 Electrodialysis was performed for at least 3 hours under specific conditions. After the liquid in the concentration chamber was fully replaced and its composition stabilized, the concentrate was sampled.

[0187] The concentrations of Na, Ca, and Mg in the concentrated water were analyzed, and the concentration ratio (molar ratio) expressed as Na / (Na+Ca+Mg) was determined.

[0188] The higher the concentration ratio, the better the selective permeability of the ion exchange membrane to monovalent cations.

[0189] <Ingredients>

[0190] The abbreviation for "table" is shown below.

[0191] St: Styrene, used after pretreatment with activated alumina.

[0192] CMS: Chloromethylstyrene, used after pretreatment with activated alumina of a mixture of isomers (p-body / m-body ratio of approximately 1:1) or 100% p-body raw material.

[0193] DVB: Divinylbenzene (55% purity) is used after pretreatment with activated alumina. BA: n-Butyl acrylate, obtained by pre-permeation with a 5% caustic soda aqueous solution followed by separation.

[0194] [Preparation Example 1: Preparation of Polymerization Solution (1)]

[0195] Prepare a 650L liquid (polymer solution (1)) by mixing 150 parts by mass of styrene, 40 parts by mass of chloromethylstyrene (isomeric mixture), 30 parts by mass of n-butyl acrylate, and 450 parts by mass of n-butyl acetate. The styrene content is approximately 22.4% by mass relative to the total mass of the polymer solution (1).

[0196] [Preparation Example 2: Preparation of Polymerization Solution (2)]

[0197] In Preparation Example 1, the amount of chloromethylstyrene was changed to 15 parts by mass, and the 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 amount of styrene was approximately 24.4% by mass relative to the total mass of polymerization liquid (2).

[0198] [Preparation Example 3: Preparation of Polymerization Solution (3)]

[0199] In Preparation Example 1, the amount of chloromethylstyrene was changed to 25 parts by mass, and the 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 polymerization liquid (3).

[0200] [Preparation Example 4: Preparation of Polymerization Solution (4)]

[0201] Prepare a 650L mixture (polymer solution (4)) of 30 parts by weight of chloromethylstyrene (p body 100%), 1 part by weight of divinylbenzene and 80 parts by weight of n-butyl acetate.

[0202] [Preparation Example 5: Preparation of Polymer Solution (5)]

[0203] In Preparation Example 4, the amount of divinylbenzene was changed to 2 parts by mass. Otherwise, 650 L of polymerization solution (5) was prepared in the same manner as in Preparation Example 4.

[0204] <Substrate Film Manufacturing>

[0205] [Examples 1~9 and Example 11]

[0206] As the base polymer, an ETFE film (substrate film) with embossed surfaces was manufactured using an ethylene-tetrafluoroethylene copolymer (referencing International Publication No. 2021 / 215402, a copolymer with a TFE-based polymer unit / E-based polymer unit / CH2=CH(CF2)4F-based polymer unit ratio of 54 / 46 / 1.4~1.7 (molar ratio), and the mass (g) of polymer flowing out from a nozzle with a diameter of 2 mm and a length of 8 mm per unit time (10 minutes) was measured using a melt index meter (manufactured by Toyo Seiki Co., Ltd.) at a temperature of 297°C and a load of 5 kg, with an MFR in the range of 9~11 g). The film was embossed on both sides using a T-die type extrusion molding method with a pair of surface embossing back rollers. The thickness and surface roughness of the ETFE film are shown in the table (the same applies below).

[0207] The thickness of the ETFE film (substrate film) is adjusted by changing the amount of resin extruded and the speed of the winding roller, while the surface roughness is adjusted by changing the surface roughness of the surface embossing roller.

[0208] [Example 10]

[0209] Using the same ethylene-tetrafluoroethylene copolymer as in Example 1, an ETFE film (substrate film) with only one roughened side and the other smooth side was manufactured by T-die extrusion molding using a pair of rollers consisting of a roughened surface embossed back roller and a smooth surface roller. The data shown in the table are values ​​measured with the roughened side as the object of measurement.

[0210] [Examples 14~17]

[0211] Using the same ethylene-tetrafluoroethylene copolymer as in Example 1, an ETFE film (substrate film) with smooth surfaces on both sides was manufactured by T-die extrusion molding.

[0212] [Example 12]

[0213] An ultra-high molecular weight polyethylene film (trade name "Ultrapolymer", 70 μm thick, manufactured by Yodogawa Hu-Tech Co., Ltd.) obtained by skewing is passed between a pair of surface embossing rollers heated to 100°C to obtain an ultra-high molecular weight polyethylene (UHMWPE) film with roughened surfaces.

[0214] [Example 13]

[0215] A high-density polyethylene film (trade name "HD" manufactured by TAMAPOLY CO., LTD., with a thickness of 70 μm) obtained by blow molding is passed between a pair of surface embossing rollers heated to 80°C to obtain a high-density polyethylene (HDPE) film with roughened surfaces.

[0216] Manufacturing of ion exchange membranes

[0217] Examples 1-13, 18-1-18-2, 19-1-19-2, and 20 are examples, while examples 14-17, 18-3, 19-3, and 21 are comparative examples.

[0218] Examples 1-3, 10, 11 and 14-16 are examples of cation exchange membranes.

[0219] Examples 4-9, 12, 13 and 17, 20, 21 are examples of anion exchange membranes.

[0220] Examples 18-1 to 18-3 and 19-1 to 19-3 are examples of cation exchange membranes that have undergone monovalent ion selective treatment.

[0221] [Example 1]

[0222] (Graft polymerization process: Manufacturing of graft polymerized membrane)

[0223] After the substrate film was subjected to double-sided corona discharge treatment, it was cut into 100m×60cm pieces. Activation was achieved by irradiating one side with an electron beam using a device capable of continuous roll-to-roll irradiation. The electron beam irradiation conditions were set to an accelerating voltage of 200kV and an irradiation dose of 60kGy.

[0224] The electron beam-irradiated substrate film 50m was rolled up together with a 70cm wide mesh so that it could be put into a cylindrical reaction tank (I) with a diameter of 100cm and a height of 80cm.

[0225] The mass of the wound substrate film (denoted as mass A (unit: kg)) is measured and placed into the reaction tank (I), and the reaction tank (I) is sealed.

[0226] Next, the interior of the reaction vessel (I) was degassed to 10 torr (approximately 1333 Pa), and then nitrogen gas was supplied and pressurized to 0.2 MPaG. This operation was repeated several times to achieve a state of 0.05 MPaG under a nitrogen atmosphere. The oxygen concentration in the reaction vessel (I) was below 0.1 ppm.

[0227] Approximately 700 L of polymerization solution (1) was added to a storage tank (II) different from the reaction tank (I), and bubbled with high-purity nitrogen for 30 minutes at room temperature. Then, while continuing to bubble with nitrogen, the internal temperature was adjusted to 40 ± 1 °C, allowing the polymerization solution (1) to circulate within the reaction tank (I) in a manner suitable for impregnating the substrate film. In this way, the substrate film in the reaction tank (I) was impregnated in the polymerization solution (1) for graft polymerization. The impregnation time (polymerization time) was set to 3.5 hours. After 3.5 hours, the liquid in the reaction tank (I) was withdrawn, and acetone, used as a cleaning solvent, was immediately added to the reaction tank (I) to stop the polymerization. Then, the cleaning operation using acetone was repeated 3 times, and then hot air was circulated within the reaction tank (I) to dry the film, resulting in a grafted polymerized film. The mass of the grafted polymerized film was measured (denoted as mass B (unit: kg)).

[0228] The grafting rate (polymerization rate of the grafted polymer film, in %) is calculated using the following formula. The results are shown in Table 1 (the same applies below).

[0229] Grafting rate = (BA) / A × 100

[0230] (Sulfonation process: introduction of cation exchange groups)

[0231] Next, 700L of 98% sulfuric acid was added to reaction tank (II). While maintaining the liquid temperature at 60°C, the sulfuric acid was circulated in reaction tank (I) containing the grafted polymer membrane to impregnate the obtained grafted polymer membrane. This allowed the grafted polymer membrane in reaction tank (I) to react with the sulfuric acid, introducing cation exchange groups (sulfonic acid groups) into the grafted polymer membrane. The impregnation time (circulation time) was set to 24 hours. After 24 hours, the liquid was extracted, and the interior was cleaned with 20% sulfuric acid, followed by ion-exchange water until the pH reached above 3. Then, a 5% NaOH aqueous solution was circulated to treat the sulfonic acid groups into sodium sulfonate groups. Further repeated washing was performed until the pH of the washing water reached below 8, yielding an ion exchange membrane (cation exchange membrane).

[0232] The ion exchange membrane was manufactured in this manner, and its thickness (in μm) and membrane resistance (in Ω·cm) were measured using the method described above. 2 ) and surface roughness (Ra and Rz, unit: μm). Additionally, installation tests were conducted using the methods described above. These results are shown in Table 2. (The same applies below).

[0233] [Examples 2, 3, 10, 11, Examples 14~16]

[0234] (Graft polymerization process: Manufacturing of graft polymerized membrane)

[0235] In Example 1, the manufacturing conditions were changed as shown in Table 1, and the grafted polymer film was obtained in the same manner as in Example 1.

[0236] (Sulfonation process: introduction of cation exchange groups)

[0237] The obtained grafted polymer membrane was subjected to the same sulfonation process as in Example 1 to obtain an ion exchange membrane (cation exchange membrane).

[0238] [Example 4]

[0239] (Graft polymerization process: Manufacturing of graft polymerized membrane)

[0240] In Example 1, the manufacturing conditions were changed as shown in Table 1, and the grafted polymer film was obtained in the same manner as in Example 1.

[0241] (Amination process: introduction of anion exchange groups)

[0242] Next, 700 L of trimethylamine solution (1 mol / L methanol solution) was added to reaction tank (II). While maintaining the liquid temperature at 45°C, the trimethylamine solution was circulated in reaction tank (I) containing the grafted polymer membrane. This allowed the grafted polymer membrane in reaction tank (I) to react with the trimethylamine solution, introducing anion exchange groups (trimethylbenzylammonium chloride groups) into the grafted polymer membrane. The immersion time (circulation time) was set to 20 hours. After 20 hours, the liquid was extracted and repeatedly washed with water until the methanol concentration in the washing water was below 0.1%, yielding anion exchange membrane (anion exchange membrane).

[0243] The thickness, membrane resistance, and surface roughness of the obtained ion exchange membrane were measured, and the results are recorded in Table 2.

[0244] [Examples 5~9, Example 17, Example 20, Example 21]

[0245] (Graft polymerization process: Manufacturing of graft polymerized membrane)

[0246] In Example 1, the manufacturing conditions were changed as shown in Table 1, and the grafted polymer film was obtained in the same manner as in Example 1.

[0247] (Amination process: introduction of anion exchange groups)

[0248] The obtained grafted polymer membrane was subjected to an amination process in the same manner as in Example 4 to obtain an ion exchange membrane (anion exchange membrane).

[0249] [Examples 12, 13]

[0250] In Example 1, the substrate film and manufacturing conditions were changed as shown in Table 1, and otherwise the grafted polymer film was obtained in the same manner as in Example 1.

[0251] (Amination process: introduction of anion exchange groups)

[0252] The obtained grafted polymer membrane was subjected to an amination process in the same manner as in Example 4 to obtain an ion exchange membrane (anion exchange membrane).

[0253] [Example 18-1]

[0254] The cation exchange membrane obtained in Example 1 was cut to a size suitable for insertion into a small electrodialysis device and stabilized by immersion in an aqueous sodium hydroxide solution at room temperature for 24 hours. The pH of the sodium hydroxide solution was adjusted to 9.7. The stabilized cation exchange membrane was then immersed in a solution prepared with sodium hydroxide at 100 ppm of polyallylamine (trade name "PAA-15C", molecular weight 15,000 manufactured by NITTOBO MEDICAL Co., Ltd.) to a pH of 9.7 for 20 hours at room temperature, resulting in a cation exchange membrane with amino groups on its surface. The obtained membrane was washed twice with 3 equivalents of hydrochloric acid aqueous solution, and the membrane resistance was measured to be 2.7 Ω·cm. 2 .

[0255] A seawater concentration experiment using electrodialysis was conducted using this membrane, and the Na / (Na+Ca+Mg) ratio in the resulting concentrate was 0.95.

[0256] [Example 18-2]

[0257] The cation exchange membrane obtained in Example 1 was used directly in a seawater concentration experiment using electrodialysis. The result showed that Na / (Na+Ca+Mg)=0.85, and the membrane obtained in Example 18-1 had high selective permeability to monovalent cations.

[0258] [Example 18-3]

[0259] Using the cation exchange membrane obtained in Example 14, except that a cation exchange membrane with amino groups on its surface was obtained following the same procedure as in Example 18-1, and was similarly washed with hydrochloric acid aqueous solution before testing. The resistivity of the membrane obtained in this example was 4.5 Ω·cm. 2 In the seawater concentration experiment, the Na / (Na+Ca+Mg) ratio in the concentrate was 0.90. Compared with the membrane obtained in Example 18-1, it had higher resistance and poorer selectivity for monovalent cations.

[0260] [Example 19-1]

[0261] The cation exchange membrane obtained in Example 2 was cut to a size suitable for insertion into a small electrodialysis device and stabilized by immersion in an aqueous sodium hydroxide solution at room temperature for 24 hours. The pH of the sodium hydroxide solution was adjusted to 10.5. The stabilized cation exchange membrane was then immersed in a solution prepared with sodium hydroxide at 100 ppm to pH 10.5, containing polyallylamine hydrochloride (trade name "PAA-HCL-10L", molecular weight 100,000, manufactured by NITTOBO MEDICAL Co., Ltd.) for 20 hours at room temperature, resulting in a cation exchange membrane with amino groups on its surface. The obtained membrane was washed twice with a 3-equivalent hydrochloric acid aqueous solution, and the membrane resistance was measured to be 1.7 Ω·cm. 2 .

[0262] A seawater concentration experiment using electrodialysis was conducted using this membrane, and the Na / (Na+Ca+Mg) ratio in the resulting concentrate was 0.96.

[0263] [Example 19-2]

[0264] The cation exchange membrane obtained in Example 2 was used directly in a seawater concentration experiment using electrodialysis. The result showed that Na / (Na+Ca+Mg)=0.85, and the membrane obtained in Example 19-1 had high selective permeability to monovalent cations.

[0265] [Example 19-3]

[0266] Using the cation exchange membrane obtained in Example 15, except that a cation exchange membrane with amino groups on its surface was obtained following the same procedure as in Example 19-1, and was similarly washed with hydrochloric acid aqueous solution before testing. The resistivity of the membrane obtained in this example was 3.5 Ω·cm. 2 In the seawater concentration experiment, the Na / (Na+Ca+Mg) ratio in the concentrate was 0.91. Compared with the membrane obtained in Example 19-1, it had higher resistance and poorer selectivity for monovalent cations.

[0267] [Table 1]

[0268]

[0269] [Table 2]

[0270]

[0271] As shown in Tables 1 and 2, the ion exchange membranes of Examples 1-13 and 20, compared with the ion exchange membranes of Examples 14-17 and 21 whose surfaces were not roughened, showed a significant reduction in the occurrence of bending / wrinkling during installation and a significant reduction in leakage.

[0272] For example, the leakage in Example 1 is 10% (DB1 type) or 10% (CS3 type) of the leakage in Example 14.

[0273] The leakage amount in Example 2 is 15.8% (DB1 type) or 8.6% (CS3 type) of the leakage amount in Example 15.

[0274] The leakage amount in Example 7 is 10% (DB1 type) or 10% (CS3 type) of the leakage amount in Example 17.

[0275] The leakage in Example 10, where only one side was roughened, was 19% (DB1 type) or 24% (CS3 type) of the leakage in Example 16, where no roughening was applied.

[0276] Comparative examples 1, 2, 7, and 10 show that roughening only one side can reduce leakage, and roughening both sides can further reduce leakage.

[0277] Furthermore, as shown in Examples 18-1~3 and 19-1~3, by treating the roughened cation exchange membrane with an amino-containing compound, a membrane with lower resistance and high selective permeability to monovalent cations can be obtained. Such a membrane is best suited for seawater concentration experiments and reverse electrodialysis power generation.

[0278] Explanation of reference numerals in the attached figures

[0279] 10. Substrate film

[0280] 12 and 14 rollers

[0281] 20 Electron Beam Irradiation Device

[0282] 22 electron beams

[0283] 30 batteries (half-cell)

[0284] 31 Input port

[0285] 32. Opening (circular opening)

[0286] 33 Platinum Wire (Platinum Black Platinum Wire)

[0287] 34. Membrane (ion exchange membrane)

[0288] It should be noted that the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2023-215744, filed on December 21, 2023, are incorporated herein as a disclosure of the specification of this invention.

Claims

1. An ion exchange membrane comprising a substrate film formed by molding a base polymer into a thin film, wherein graft chains having ion exchange groups are bonded to the base polymer, and the ion exchange membrane 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 trifluorochloroethylene units.

3. The ion exchange membrane according to claim 1, wherein, The base polymer is a polyolefin.

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

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

7. The ion exchange membrane according to claim 1, wherein the thickness is 10~200μm.

8. The ion exchange membrane according to claim 1, wherein it has a cation exchange group as the ion exchange group and an amino group is present on at least one surface.

9. A method for concentrating seawater, wherein electrodialysis is performed using the ion exchange membrane according to any one of claims 1 to 8.

10. A method for generating electricity, wherein the ion exchange membrane according to any one of claims 1 to 8 is used for at least one of concentration gradient power generation and reverse electrodialysis power generation.

11. A method for manufacturing an ion exchange membrane, wherein, Using a substrate film formed by molding a base polymer into a thin film and having a roughened surface, By irradiating the substrate film with ionizing radiation to generate free radicals in the base polymer, a raw material monomer containing a monomer with ion-exchange groups is grafted and polymerized.

12. A method for manufacturing an ion exchange membrane, wherein, Using a substrate film formed by molding a base polymer into a thin film and having a roughened surface, The base polymer is irradiated with ionizing radiation to generate free radicals, and a raw material monomer containing an ion exchange group introduction monomer is grafted and polymerized, wherein the ion exchange group introduction monomer has functional groups capable of introducing ion exchange groups, and then ion exchange groups are introduced into units derived from the ion exchange group introduction monomer.

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

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

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