Method for producing ion exchange membrane

Abstract

To provide a method for producing an ion exchange membrane with which it is possible to produce a water electrolysis apparatus in which the occurrence of liquid leakage is suppressed, the ion exchange membrane also having excellent chemical durability.　A method for producing an ion exchange membrane according to the present disclosure comprises: bringing a precursor film containing a fluorine-containing polymer having a group that can be converted into an ion exchange group into contact with an aqueous alkali solution containing a water-soluble organic solvent and water to hydrolyze the group that can be converted into an ion exchange group to obtain an ion exchange membrane containing a fluorine-containing polymer having an ion exchange group; and then performing a first cleaning treatment for cleaning the ion exchange membrane using water having a conductivity of 3 μS / cm or less and a temperature of 35-60°C.

Description

Method for manufacturing ion exchange membranes

[0001] The present disclosure relates to a method for producing an ion exchange membrane.

[0002] Ion exchange membranes are used in various batteries, electrolysis processes, and processes for separating ions, etc. Patent Document 1 describes a method for separating -SO ２ The precursor film containing the fluorine-containing polymer having F groups was subjected to hydrolysis treatment and acidification treatment, and then washed with ultrapure water at 80°C to form -SO ３ A method for obtaining an ion exchange membrane comprising a fluoropolymer having H groups is disclosed.

[0003] Japanese Patent Application Laid-Open No. 2022-044614

[0004] When an ion exchange membrane is used as a solid polymer electrolyte membrane in a water electrolysis device, hydroxyl radicals generated in the system during operation of the water electrolysis device may decompose the fluoropolymer in the ion exchange membrane. Therefore, an ion exchange membrane with excellent chemical durability is desired. Furthermore, when a membrane electrode assembly is manufactured using the ion exchange membrane and a gasket is attached to the periphery of the membrane electrode assembly, the membrane electrode assembly is installed in a tank of the water electrolysis device, and an electrolyte solution (e.g., water) is supplied into the tank, it is desired that the occurrence of liquid leakage to the outside of the water electrolysis device can be suppressed. The present inventors have found that when a membrane electrode assembly is manufactured using the ion exchange membrane described in Patent Document 1 and the membrane electrode assembly is installed in a tank of the water electrolysis device with a gasket attached to the periphery, liquid leakage to the outside of the water electrolysis device may occur when an electrolyte solution (e.g., water) is supplied into the tank.

[0005] The present disclosure has been made in view of the above-described circumstances, and an object of one embodiment of the present invention is to provide a method for manufacturing an ion exchange membrane that can manufacture a water electrolysis device in which the occurrence of liquid leakage is suppressed and that has excellent chemical durability.

[0006] The present disclosure includes the following aspects. [1] A method for producing an ion exchange membrane, comprising contacting a precursor membrane containing a fluoropolymer having groups convertible to ion exchange groups with an alkaline aqueous solution containing a water-soluble organic solvent and water to hydrolyze the groups convertible to ion exchange groups to obtain an ion exchange membrane containing a fluoropolymer having ion exchange groups, and then performing a first cleaning treatment to wash the ion exchange membrane with water having a conductivity of 3 μS / cm or less and a temperature of 35 to 60°C. [2] The method for producing an ion exchange membrane according to [1], wherein, before the first cleaning treatment, a second cleaning treatment is performed to wash the ion exchange membrane with water having a temperature of 60°C or less. [3] The method for producing an ion exchange membrane according to [2], wherein the temperature of the water in the second cleaning treatment is lower than the temperature of the water in the first cleaning treatment. [4] The method for producing an ion exchange membrane according to [2] or [3], wherein the electrical conductivity of the water in the second cleaning treatment is 0.05 to 100 μS / cm. [5] The method for producing an ion exchange membrane according to any one of [1] to [4], wherein, after the first cleaning treatment, a third cleaning treatment is carried out in which the ion exchange membrane is cleaned with water having a lower conductivity than the water used in the first cleaning treatment and a temperature of 60°C or less. [6] The method for producing an ion exchange membrane according to any one of [1] to [5], wherein the water-soluble organic solvent is at least one selected from the group consisting of aprotic organic solvents, alcohols, and amino alcohols, and the content of the water-soluble organic solvent in the alkaline aqueous solution is 5% by mass or more and 40% by mass or less, based on the total mass of the alkaline aqueous solution. [7] The method for producing an ion exchange membrane according to any one of [1] to [6], wherein, after the first cleaning treatment, an acidification treatment is carried out. [8] The method for producing an ion exchange membrane according to any one of [1] to [7], wherein the fluorine-containing polymer having ion exchange groups has an ion exchange capacity of 0.90 to 2.05 meq / g dry resin. [9] The method for producing an ion exchange membrane according to any one of [1] to [8], wherein the fluorine-containing polymer having ion exchange groups contains a unit represented by formula (2): Formula (2) −[CF ２ -CF(-L-(SO ３ M) ｎ) )]- In formula (2), L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom, M is a hydrogen atom, an alkali metal or a quaternary ammonium cation, and n is 1 or 2.

[10] The method for producing an ion exchange membrane according to any one of [1] to [9], wherein a reinforcing material is contained inside or on a surface of the ion exchange membrane.

[11] The method for producing an ion exchange membrane according to any one of [1] to

[10] , wherein the ion exchange membrane is used as an electrolyte membrane contained in a membrane electrode assembly of a water electrolysis apparatus.

[0007] According to one embodiment of the present invention, it is possible to manufacture a water electrolysis device in which the occurrence of liquid leakage is suppressed, and it is also possible to provide a method for manufacturing an ion exchange membrane that is excellent in chemical durability.

[0008] The definitions of the following terms apply throughout the present specification and claims unless otherwise specified. An "ion exchange group" is a group that can exchange at least a portion of the ions contained in this group with other ions, and examples thereof include the sulfonic acid functional group and carboxylic acid functional group shown below. A "sulfonic acid functional group" is a sulfonic acid group (-SO ３ Here, the form of the sulfonate group is, for example, (—SO ３ － ) Ma ＋ , (-SO ３ － ) ２ Mb ２＋ , and (-SO ３ － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) When there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. "Carboxylic acid type functional group" means a carboxylic acid group (-COOH) or a carboxylic acid salt group. Here, the form of the carboxylic acid salt group can be, for example, (-COO － ) Ma ＋, (-COO － ) ２ Mb ２＋ , and (-COO － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) Note that when there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. A "precursor membrane" is a membrane containing a polymer having a group that can be converted into an ion exchange group. A "group that can be converted into an ion exchange group" means a group that can be converted into an ion exchange group by known treatments such as hydrolysis treatment and acidification treatment. A "group that can be converted into a sulfonic acid functional group" means a group that can be converted into a sulfonic acid functional group by known treatments such as hydrolysis treatment and acidification treatment. A "group that can be converted into a carboxylic acid functional group" means a group that can be converted into a carboxylic acid functional group by known treatments such as hydrolysis treatment and acidification treatment.

[0009] A "unit" in a polymer refers to an atomic group based on one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or may be an atomic group in which part of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction. In the following, units derived from individual monomers may be referred to by the name of the monomer followed by the word "unit."

[0010] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0011] [Method for producing ion exchange membrane] The method for producing an ion exchange membrane according to the present disclosure (hereinafter also referred to as "the present production method") involves bringing a precursor membrane containing a fluoropolymer (hereinafter also referred to as "fluoropolymer (I')") having groups convertible to ion exchange groups (hereinafter also referred to as "precursor groups") into contact with an alkaline aqueous solution containing a water-soluble organic solvent and water to hydrolyze the groups convertible to ion exchange groups to obtain an ion exchange membrane containing a fluoropolymer (hereinafter also referred to as "fluoropolymer (I)") having ion exchange groups, and then carrying out a first washing treatment in which the ion exchange membrane is washed with water having a conductivity of 3 μS / cm or less and a temperature of 35 to 60°C.

[0012] The ion exchange membrane obtained by this production method can be used to produce a water electrolysis device with reduced leakage and excellent chemical durability. Although the details of the reason for this are unclear, it is presumed to be due to the following reasons. After a precursor membrane is hydrolyzed using an alkaline aqueous solution containing a water-soluble organic solvent and water, a cleaning process may be performed to remove the alkaline aqueous solution and other substances contained in the hydrolyzed membrane. If the temperature of the water used in the cleaning process is high, the water content of the ion exchange membrane increases, resulting in significant dimensional change. As a result, wrinkles may occur when the ion exchange membrane is wound into a roll, reducing the surface flatness of the ion exchange membrane. When a membrane electrode assembly is produced using a wrinkled ion exchange membrane and a gasket is attached to the periphery of the membrane electrode assembly, gaps may form between the gasket and the membrane electrode assembly due to the wrinkles in the ion exchange membrane. When a membrane electrode assembly with such a gap is used in a water electrolysis device and the supply of electrolyte is initiated, the electrolyte may leak through the gap. To address these problems, the present production method presumably uses water having a temperature of 60°C or less to obtain an ion exchange membrane that can be used to produce a water electrolysis system in which leakage is suppressed. Furthermore, if the temperature of the water used in the cleaning treatment is low or the conductivity of the water used in the cleaning treatment is high, the water-soluble organic solvent contained in the alkaline aqueous solution may not be sufficiently removed from the membrane after hydrolysis by the cleaning treatment. If the water-soluble organic solvent contained in the alkaline aqueous solution remains in the ion exchange membrane, when the ion exchange membrane is applied to a water electrolysis system, hydroxyl radicals may be generated in the system during operation, and the generated hydroxyl radicals may increase the amount of decomposition of the fluoropolymer in the ion exchange membrane. To address these problems, the present production method presumably uses water having a temperature of 35°C or higher and a conductivity of 3 μS / cm or less in the cleaning treatment to sufficiently remove the water-soluble organic solvent contained in the membrane, thereby obtaining an ion exchange membrane with excellent chemical durability.

[0013] <Precursor Membrane> The precursor membrane used in this production method contains a fluoropolymer (I'). The fluoropolymer (I') is not particularly limited as long as it is a polymer having fluorine atoms and a precursor group, but a copolymer of units based on a fluorine-containing olefin and units based on a fluorine-containing monomer having a precursor group (for example, a group that can be converted into a sulfonic acid functional group, a group that can be converted into a carboxylic acid functional group) is preferred, and from the viewpoint of being able to further reduce the electrolysis voltage when the ion exchange membrane is applied to a water electrolysis device, a copolymer of units based on a fluorine-containing olefin and units based on a fluorine-containing monomer having a group that can be converted into a sulfonic acid functional group (hereinafter also referred to as "fluoropolymer (S')") is more preferred. The fluoropolymer (S') will be described in detail below.

[0014] As the method for copolymerizing the fluoropolymer (S'), known methods such as solution polymerization, suspension polymerization and emulsion polymerization can be adopted.

[0015] Examples of fluorine-containing olefins include fluoroolefins having 2 to 3 carbon atoms and one or more fluorine atoms in the molecule. Specific examples of fluoroolefins include tetrafluoroethylene (hereinafter also referred to as "TFE"), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among these, TFE is preferred in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer. One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0016] The fluorine-containing monomer (S') may be a compound having one or more fluorine atoms in the molecule, an ethylenic double bond, and a group that can be converted into a sulfonic acid functional group. As the fluorine-containing monomer (S'), a compound represented by formula (1) is preferred in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer. Formula (1) CF ２ =CF-L-(A) ｎ

[0017] L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom. The etheric oxygen atom may be located at the terminal of the perfluorohydrocarbon group or between carbon atoms. The number of carbon atoms in the (n+1)-valent perfluorohydrocarbon group is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and is preferably 20 or less, more preferably 10 or less. L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, and more preferably a divalent perfluoroalkylene group which may contain an etheric oxygen atom in the embodiment where n = 1, or a trivalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom in the embodiment where n = 2. The divalent perfluoroalkylene group may be either linear or branched.

[0018] A is a group that can be converted into a sulfonic acid functional group. The group that can be converted into a sulfonic acid functional group is preferably a functional group that can be converted into a sulfonic acid functional group by hydrolysis. Specific examples of groups that can be converted into a sulfonic acid functional group include -SO ２ F, -SO ２ Cl, —SO ２ Br is an example.

[0019] n is 1 or 2. When n is 2, the two As may be the same or different.

[0020] The compound represented by formula (1) is preferably a compound represented by formula (1-1), a compound represented by formula (1-2), a compound represented by formula (1-3), or a compound represented by formula (1-4). ２ =CF-O-R ｆ１ -A Formula (1-2) CF ２ =CF-R ｆ１ -A

[0021]

[0022]

[0023] R ｆ１is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, and is preferably 20 or less, more preferably 10 or less.

[0024] R ｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0025] R ｆ３ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0026] r is 0 or 1. m is 0 or 1.

[0027] The definition of A in the formula is as described above.

[0028] As the compound represented by formula (1-1) and the compound represented by formula (1-2), a compound represented by formula (1-5) is preferred. ２ =CF-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ２ F x is 0 or 1, y is an integer from 0 to 2, z is an integer from 1 to 4, and Y is F or CF ３ is.

[0029] Specific examples of the compound represented by formula (1-1) include the following compounds. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. CF ２ =CF-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-O-CF ２CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-[O-CF ２ CF (CF ３ )] ｘ -SO ２ F

[0030] Specific examples of the compound represented by formula (1-2) include the following compounds: In the formula, w is an integer of 1 to 8. CF ２ =CF-(CF ２ ) ｗ -SO ２ FCF ２ =CF-CF ２ -O-(CF ２ ) ｗ -SO ２ F

[0031] The compound represented by formula (1-3) is preferably a compound represented by formula (1-3-1).

[0032]

[0033] R ｆ４ is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ｆ５ represents a single bond or a linear perfluoroalkylene group having 1 to 6 carbon atoms which may contain an oxygen atom between the carbon atoms. The definitions of r and A are as described above.

[0034] Specific examples of the compound represented by formula (1-3-1) include the following.

[0035]

[0036] The compound represented by formula (1-4) is preferably a compound represented by formula (1-4-1).

[0037]

[0038] R in the formula ｆ１ , R ｆ２ and A are defined as above.

[0039] Specific examples of the compound represented by formula (1-4-1) include the following.

[0040]

[0041] The fluorine-containing monomer (S') may be used alone or in combination of two or more kinds.

[0042] In the production of the fluoropolymer (S'), other monomers may be used in addition to TFE and the fluoromonomer (S'). Specific examples of such other monomers include CF ２ = CFR ｆ６ (However, R ｆ６ is a perfluoroalkyl group having 2 to 10 carbon atoms, CF ２ =CF-OR ｆ７ (However, R ｆ７ is a perfluoroalkyl group having 1 to 10 carbon atoms, CF ２ = CFO (CF ２ ) ｖ CF = CF ２ (wherein v is an integer of 1 to 3.) The content of units based on other monomers is preferably at most 30 mass% based on all units in the fluoropolymer (I') (preferably the fluoropolymer (S')) from the viewpoint of maintaining ion exchange performance.

[0043] The ion exchange capacity of the fluoropolymer (I') can be adjusted by changing the content of groups that can be converted into ion exchange groups in the fluoropolymer (I').

[0044] An example of a method for producing a precursor membrane is the following method. First, a film P1 containing a fluoropolymer (I') is obtained using a fluoropolymer (I'). Next, a laminate obtained by laminating a transfer substrate, a film P1, a reinforcing material (described later), a film P1, and a transfer substrate in this order is heat-pressed, and then the transfer substrates arranged on both sides of the laminate are peeled off to obtain a precursor membrane in which a film P1, a reinforcing material, and a film P1 are laminated in this order. Note that, as a method for producing a precursor membrane, a case in which the precursor membrane contains a reinforcing material has been described as an example, but this is not limited thereto, and a precursor membrane may be produced without using a reinforcing material. Furthermore, although an embodiment in which two films P1 containing a fluoropolymer (I') are laminated has been shown, this is not limited thereto, and only one film P1 may be used, or three or more films P1 may be used. Furthermore, when two or more films P1 are used, the fluoropolymers (I') contained in the films P1 may be the same or different from each other.

[0045] <Ion Exchange Membrane> The ion exchange membrane obtained by the present production method contains a fluoropolymer (I). The fluoropolymer (I) is a polymer in which the precursor groups in the above-mentioned fluoropolymer (I') have been converted into ion exchange groups.

[0046] Specific examples of the ion exchange group possessed by the fluoropolymer (I) include a sulfonic acid type functional group and a carboxylic acid type functional group, and the sulfonic acid type functional group is preferred from the viewpoint of further reducing the electrolysis voltage when the ion exchange membrane is applied to a water electrolysis apparatus. Hereinafter, embodiments of the fluoropolymer having a sulfonic acid type functional group (hereinafter also referred to as "fluoropolymer (S)") will be mainly described in detail.

[0047] The fluoropolymer (S) preferably contains units based on a fluorine-containing olefin and units having a sulfonic acid type functional group and a fluorine atom.

[0048] Examples of the fluorine-containing olefin include those exemplified above, with TFE being preferred. The fluorine-containing olefin may be used alone or in combination of two or more.

[0049] As the unit having a sulfonic acid type functional group and a fluorine atom, a unit represented by formula (2) is preferred. ２ -CF(-L-(SO ３ M) ｎ ) )]--L and n in formula (2) are defined as above. M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. When n is 2, the two Ms may be the same or different.

[0050] The unit represented by formula (2) is preferably a unit represented by formula (2-1), a unit represented by formula (2-2), a unit represented by formula (2-3), or a unit represented by formula (2-4). ２ -CF(-O-R ｆ１ -SO ３ M)] - Formula (2-2) - [CF ２ -CF(-R ｆ１ -SO ３ M) ]-

[0051]

[0052] R in the formula ｆ１ , R ｆ２ , r and M are as defined above.

[0053]

[0054] R in the formula ｆ１ , R ｆ２ , R ｆ３ , r, m and M are as defined above.

[0055] As the unit represented by formula (2-1) and the unit represented by formula (2-2), a unit represented by formula (2-5) is more preferred. ２ -CF(-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ３ M)]—wherein x, y, z, Y and M are as defined above.

[0056] Specific examples of the unit represented by formula (2-1) include the following units. In the formula, w, x, and M are defined as above. -[CF ２ -CF(-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-(O-CF ２ CF (CF ３ )) ｘ -SO ３ M) ]-

[0057] Specific examples of the unit represented by formula (2-2) include the following units. The definitions of w and M in the formula are as described above. -[CF ２ -CF(-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF (-CF ２ -O-(CF ２ ) ｗ -SO ３ M) ]-

[0058] As the unit represented by formula (2-3), a unit represented by formula (2-3-1) is preferred.

[0059]

[0060] R in the formula ｆ４ , R ｆ５ , r and M are as defined above.

[0061] Specific examples of the unit represented by formula (2-3-1) include the following.

[0062]

[0063] As the unit represented by formula (2-4), a unit represented by formula (2-4-1) is preferred.

[0064]

[0065] R in the formula ｆ１ , R ｆ２ and M are defined as above.

[0066] Specific examples of the unit represented by formula (2-4-1) include the following.

[0067]

[0068] The unit having a sulfonic acid type functional group and a fluorine atom may be used alone or in combination of two or more.

[0069] The fluoropolymer (I) (preferably the fluoropolymer (S)) may contain units based on other monomers other than the units based on a fluorine-containing olefin and the units having a sulfonic acid type functional group and a fluorine atom. Specific examples of the other monomers are as described above. From the viewpoint of maintaining ion exchange performance, the content of the units based on other monomers is preferably 30 mass% or less based on the total units in the fluoropolymer (I).

[0070] The content of the fluoropolymer (I) is preferably from 95 to 100% by mass based on the total mass of the ion exchange membrane.

[0071] From the viewpoint of excellent voltage efficiency, the ion exchange capacity of the fluoropolymer (I) is preferably 0.90 milliequivalents / gram dry resin (also referred to as meq / g) or more, more preferably 1.00 meq / g or more, even more preferably more than 1.05 meq / g, and particularly preferably 1.10 meq / g or more. From the viewpoint of the balance between current efficiency and voltage efficiency, the ion exchange capacity of the fluoropolymer (I) is preferably 2.05 meq / g or less, more preferably 1.50 meq / g or less, and particularly preferably 1.25 meq / g or less.

[0072] The ion exchange membrane may contain a reinforcing material inside or on its surface. That is, the ion exchange membrane may be in an embodiment containing the fluorine-containing polymer (I) and a reinforcing material. Examples of the reinforcing material include porous bodies, fibers, woven fabrics, and nonwoven fabrics. Examples of materials for the reinforcing material include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymers, polyethylene, polypropylene, and polyphenylene sulfide.

[0073] The thickness of the ion exchange membrane is preferably 30 μm or more, more preferably 50 μm or more, even more preferably 70 μm or more, particularly preferably 90 μm or more, and preferably 300 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less, and particularly preferably 120 μm or less. When the ion exchange membrane has a multilayer structure, the thickness of the ion exchange membrane refers to the total thickness of each layer. The thickness of the ion exchange membrane is measured using a magnified image (e.g., 100x) of the cross section of the ion exchange membrane taken with an optical microscope (product name "BX-51", manufactured by Olympus Corporation). When the ion exchange membrane has an uneven surface, the thickness of 10 concave portions and the thickness of 10 convex portions are measured, and the arithmetic mean value of the thicknesses at the 20 points is defined as the thickness of the ion exchange membrane. However, when the convex portions contain threads that constitute the woven fabric, the thickness of the convex portions is determined by subtracting the thickness of the threads present in the convex portions.

[0074] <Treatment> The treatments that are performed and that can be performed in this manufacturing method will be described below.

[0075] (Hydrolysis Treatment) This production method includes a hydrolysis treatment in which a precursor membrane is contacted with an alkaline aqueous solution containing a water-soluble organic solvent and water to hydrolyze the precursor group of the fluoropolymer (I'). This results in an ion exchange membrane containing the fluoropolymer (I). For example, when the precursor membrane contains the above-mentioned fluoropolymer (S'), the fluorosulfonyl groups of the fluoropolymer (S') are converted to sulfonate salts by the hydrolysis treatment, thereby obtaining an ion exchange membrane containing a fluoropolymer having a sulfonate salt.

[0076] The alkaline aqueous solution contains a water-soluble organic solvent and water, and preferably further contains a basic compound. The alkaline aqueous solution is alkaline, i.e., has a pH of greater than 7.

[0077] The content of water contained in the alkaline aqueous solution is preferably 50% by mass or more, more preferably 60% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, based on the total mass of the alkaline aqueous solution.

[0078] The water-soluble organic solvent is an organic solvent that dissolves easily in water. Specifically, an organic solvent having a solubility of 0.1 g or more in 1,000 ml of water at 20°C is preferred, and an organic solvent having a solubility of 0.5 g or more is more preferred. The water-soluble organic solvent preferably contains at least one selected from the group consisting of aprotic organic solvents, alcohols, and aminoalcohols, and more preferably contains an aprotic organic solvent. Specific examples of aprotic organic solvents include dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone, with dimethyl sulfoxide being preferred. Specific examples of alcohols include methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butylcarbitol, hexyloxyethanol, octanol, 1-methoxy-2-propanol, and ethylene glycol. Specific examples of amino alcohols include ethanolamine, N-methylethanolamine, N-ethylethanolamine, 1-amino-2-propanol, 1-amino-3-propanol, 2-aminoethoxyethanol, 2-aminothioethoxyethanol, and 2-amino-2-methyl-1-propanol. The water-soluble organic solvents may be used alone or in combination of two or more. The content of the water-soluble organic solvent is preferably 5% by mass or more, and more preferably 10% by mass or more, relative to the total mass of the aqueous alkaline solution, from the viewpoint of improving the reaction rate, and is preferably 40% by mass or less, and more preferably 30% by mass or less, from the viewpoint of suppressing elution of the polymer.

[0079] Specific examples of the basic compound include sodium hydroxide and potassium hydroxide. The content of the basic compound is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, based on the total mass of the alkaline aqueous solution, in order to improve the reaction rate.

[0080] The temperature of the alkaline aqueous solution is preferably 60°C or higher, more preferably 80°C or higher, from the viewpoint of improving the reaction rate, and is preferably 120°C or lower, more preferably 100°C or lower, from the viewpoint of suppressing elution of the polymer.

[0081] The contact time (reaction time) between the precursor film and the alkaline aqueous solution is preferably 5 minutes or more, more preferably 10 minutes or more, from the viewpoint of allowing the reaction to proceed sufficiently, and is preferably 2 hours or less, more preferably 1 hour or less, and even more preferably 30 minutes or less, from the viewpoint of suppressing elution of the polymer.

[0082] The precursor film can be brought into contact with the alkaline aqueous solution by immersing the precursor film in the alkaline aqueous solution or by spraying the alkaline aqueous solution onto the surface of the precursor film, with the immersion method being preferred.

[0083] (First Cleaning Treatment) In this manufacturing method, the first cleaning treatment is carried out, which is a treatment of cleaning the ion exchange membrane using water having a conductivity of 3 μS / cm or less and a temperature of 35 to 60° C.

[0084] The temperature of the water in the first cleaning treatment is 35 to 60°C, and is preferably 40°C or higher, and more preferably 45°C or higher, in order to improve the chemical durability of the ion exchange membrane, and is preferably 55°C or lower, and more preferably 50°C or lower, in order to further suppress the occurrence of liquid leakage from the water electrolysis apparatus.

[0085] The conductivity of the water in the first cleaning treatment is 3 μS / cm or less, and from the viewpoint of improving the chemical durability of the ion exchange membrane, it is preferably 2 μS / cm or less, more preferably 1 μS / cm or less, even more preferably 0.8 μS / cm or less, and particularly preferably 0.5 μS / cm or less. The lower limit of the conductivity of the water in the first cleaning treatment is usually 0.05 μS / cm. As a method for adjusting the water conductivity to the above value, a method of purifying water using an ion exchange resin or the like can be mentioned.

[0086] The conductivity of water in the present disclosure means the electrical conductivity of water at a temperature of 25°C, measured using an electrical conductivity meter according to a method in accordance with JIS K0552-1994.

[0087] The washing time in the first washing treatment is preferably 30 seconds or more, more preferably 1 minute or more, from the viewpoint of improving washing properties, and is usually 30 minutes or less from the viewpoint of improving productivity.

[0088] The cleaning method in the first cleaning treatment may be a method in which the ion exchange membrane is immersed in the water used in the first cleaning treatment.

[0089] (Second Cleaning Treatment) In the present production method, it is preferable to carry out a second cleaning treatment. The second cleaning treatment is a treatment in which the ion exchange membrane is cleaned with water having a temperature of 60° C. or less before the first cleaning treatment. By carrying out the second cleaning treatment, the water used in the first cleaning treatment can more easily penetrate the ion exchange membrane, thereby further improving the cleaning effect of the first cleaning treatment, and therefore further improving the chemical durability of the ion exchange membrane.

[0090] The temperature of the water in the second cleaning treatment is preferably lower than that of the water in the first cleaning treatment. Specifically, the difference between the temperature of the water in the first cleaning treatment and the temperature of the water in the second cleaning treatment ((temperature of the water in the first cleaning treatment) - (temperature of the water in the second cleaning treatment)) is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher, from the viewpoint of efficient cleaning. Furthermore, the temperature of the water in the second cleaning treatment is preferably 40°C or lower, and more preferably 30°C or lower, from the viewpoint of suppressing a sudden dimensional change in the ion exchange membrane and suppressing the occurrence of wrinkles. The temperature of the water in the second cleaning treatment is preferably 10°C or higher, more preferably 20°C or higher, even more preferably 25°C or higher, and particularly preferably 30°C or higher, from the viewpoint of efficient cleaning. Furthermore, the temperature of the water in the second cleaning treatment is preferably 55°C or lower, and more preferably 45°C or lower, from the viewpoint of suppressing a sudden dimensional change in the ion exchange membrane and suppressing the occurrence of wrinkles.

[0091] The temperature of the water in the second washing treatment is preferably 10°C or higher, more preferably 20°C or higher, even more preferably 25°C or higher, and particularly preferably 30°C or higher, from the viewpoint of efficient washing, and is preferably 55°C or lower, more preferably 45°C or lower, from the viewpoint of suppressing a sudden dimensional change in the ion exchange membrane and suppressing the occurrence of wrinkles.

[0092] The conductivity of the water in the second cleaning treatment is preferably 0.05 to 100 μS / cm. The conductivity of the water in the second cleaning treatment is more preferably 50 μS / cm or less, even more preferably 10 μS / cm or less, particularly preferably 5 μS / cm or less, and most preferably 3 μS / cm or less, in order to improve the chemical durability of the ion exchange membrane. The conductivity of the water in the second cleaning treatment is more preferably 0.1 μS / cm or more. The method for adjusting the conductivity of the water used in the second cleaning treatment to the above value is the same as the method described for the first cleaning treatment.

[0093] The water washing time in the second washing treatment is preferably 10 seconds or more, and more preferably 30 seconds or more, from the viewpoint of improving washability, and is usually 30 minutes or less, preferably 10 minutes or less, and more preferably 5 minutes or less, from the viewpoint of improving productivity.

[0094] The cleaning method in the second cleaning process is the same as the method described in the first cleaning process.

[0095] The amount of water used in the second cleaning treatment per unit area of ​​the ion exchange membrane (g / m ２ ) is the amount of water used in the first cleaning treatment per unit area of ​​the ion exchange membrane (g / m ２ ), it is preferably 100% or less, more preferably 80% or less, still more preferably 50% or less, particularly preferably 30% or less, most preferably 10% or less, and is preferably 1% or more, from the viewpoint of improving washability.

[0096] (Third Cleaning Treatment) In the present production method, it is preferable to perform a third cleaning treatment. The third cleaning treatment is a treatment in which, after the first cleaning treatment, the ion exchange membrane is cleaned with water having a lower conductivity than the water used in the first cleaning treatment and a temperature of 60° C. or less. By performing the third cleaning treatment, the water-soluble organic solvent in the ion exchange membrane is further removed, thereby further improving the chemical durability of the ion exchange membrane.

[0097] The temperature of the water in the third cleaning treatment is preferably 40°C or higher, and more preferably 45°C or higher, in order to improve the chemical durability of the ion exchange membrane, and is preferably 55°C or lower, and more preferably 50°C or lower, in order to further suppress the occurrence of liquid leakage from the water electrolysis apparatus.

[0098] The conductivity of the water in the third cleaning treatment is lower than that of the water in the first cleaning treatment. Specifically, the difference between the conductivity of the water in the first cleaning treatment and the conductivity of the water in the third cleaning treatment ((conductivity of the water in the first cleaning treatment) - (conductivity of the water in the third cleaning treatment)) is preferably 0.1 μS / cm or more, more preferably 0.3 μS / cm or more, even more preferably 0.5 μS / cm or more, and preferably 2.9 μS / cm or less, from the viewpoint of further removing the water-soluble organic solvent in the ion exchange membrane. The conductivity of the water in the third cleaning treatment is preferably less than 3 μS / cm, more preferably 2 μS / cm or less, even more preferably 1 μS / cm or less, and particularly preferably 0.5 μS / cm or less, from the viewpoint of more excellent chemical durability of the ion exchange membrane. The lower limit of the conductivity of the water in the third cleaning treatment is usually 0.05 μS / cm. The method for adjusting the conductivity of the water in the third cleaning treatment to the above value is the same as the method described for the first cleaning treatment.

[0099] The water washing time in the third washing treatment is preferably 30 seconds or more, more preferably 1 minute or more, from the viewpoint of improving washability, and is usually 30 minutes or less from the viewpoint of improving productivity.

[0100] The cleaning method in the third cleaning process is the same as the method described in the first cleaning process.

[0101] (Acid Form Conversion Treatment) In the present production method, an acid form conversion treatment may be carried out. The acid form conversion treatment is preferably carried out after the hydrolysis treatment. If the acid form conversion treatment is carried out after the hydrolysis treatment, it may be carried out before the washing treatment or after the washing treatment, and is preferably carried out after the washing treatment. "After the washing treatment" may be after the first washing treatment, the second washing treatment, or the third washing treatment, and it is preferably carried out after all washing treatments have been completed (after the third washing treatment if the third washing treatment is included). The acid form conversion treatment is a treatment in which the ion exchange membrane after the hydrolysis treatment is brought into contact with an acidic aqueous solution containing an acid component and water. For example, when the fluoropolymer contained in the ion exchange membrane obtained by the hydrolysis treatment has a sulfonate, the sulfonate is converted to a sulfonic acid group, and an ion exchange membrane having a sulfonic acid group is obtained.

[0102] The content of water in the acidic aqueous solution is preferably 70% by mass or more, more preferably 75% by mass or more, and is preferably 95% by mass or less, more preferably 92% by mass or less, based on the total mass of the acidic aqueous solution.

[0103] Specific examples of the acid component include sulfuric acid and hydrochloric acid. The content of the acid component is preferably 5% by mass or more, more preferably 8% by mass or more, relative to the total mass of the acidic aqueous solution, from the viewpoint of improving the reaction rate, and is preferably 30% by mass or less, more preferably 25% by mass or less, from the viewpoint of ease of handling the acidic aqueous solution.

[0104] The temperature of the acidic aqueous solution is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher, from the viewpoint of improving the reaction rate, and is preferably 100°C or lower, more preferably 80°C or lower, and even more preferably 60°C or lower, from the viewpoint of suppressing elution of the polymer.

[0105] The contact time (reaction time) between the ion exchange membrane and the acidic aqueous solution after the hydrolysis treatment is preferably 10 minutes or more, more preferably 20 minutes or more, from the viewpoint of allowing the reaction to proceed sufficiently, and is preferably 2 hours or less, more preferably 1 hour or less, from the viewpoint of suppressing elution of the polymer.

[0106] The method for contacting the ion exchange membrane after hydrolysis with the acidic aqueous solution includes immersing the precursor membrane in the acidic aqueous solution and spraying the acidic aqueous solution onto the surface of the precursor membrane, and among these, the immersion method is preferred.

[0107] <Other Treatments> The present production method may include a drying treatment. The drying treatment may be performed multiple times, preferably after a cleaning treatment, for example, after an acid-formation treatment, etc. Furthermore, when the first cleaning treatment and at least one of the second and third cleaning treatments are performed, the drying treatment may be performed after each cleaning treatment, or may be performed only after the final cleaning treatment. Examples of drying methods include natural drying, heated drying, air drying, and a combination thereof. The drying temperature is preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher, from the viewpoint of drying efficiency. Furthermore, the drying temperature is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 105°C or lower, from the viewpoint of further suppressing the occurrence of wrinkles in the ion exchange membrane due to rapid drying. The drying time is preferably 1 minute or longer, more preferably 3 minutes or longer, and even more preferably 5 minutes or longer, from the viewpoint of preventing uneven drying. Furthermore, the drying time is preferably 1 hour or shorter, more preferably 30 minutes or shorter, from the viewpoint of drying efficiency.

[0108] The present production method may be carried out using a precursor membrane in a sheet form (i.e., a batch process) or by roll-to-roll processing. When the present production method is carried out by roll-to-roll processing, a long roll-shaped precursor membrane is unwound, and after each treatment of the present production method is carried out, the ion exchange membrane is wound up into a roll.

[0109] <Applications> The ion exchange membrane obtained by this manufacturing method is suitable for use as an electrolyte membrane included in a membrane electrode assembly of a water electrolysis device (solid polymer water electrolysis device). The membrane electrode assembly includes the ion exchange membrane obtained by this manufacturing method, a cathode catalyst layer disposed on one side of the ion exchange membrane, and an anode catalyst layer disposed on the other side. Each catalyst layer may have a gas diffusion layer on the side facing away from the ion exchange membrane. A method for manufacturing a membrane electrode assembly involves forming a cathode catalyst layer on one side of the ion exchange membrane and an anode catalyst layer on the other side of the electrolyte membrane, and optionally laminating them with a gas diffusion layer. A water electrolysis device includes the above-described membrane electrode assembly, a water supply unit that supplies water to the anode catalyst layer side, and a power supply unit electrically connected to the anode catalyst layer side and the cathode catalyst layer side. Because such a water electrolysis device includes the ion exchange membrane obtained by this manufacturing method, liquid leakage is suppressed when electrolyzing water (electrolyte) to produce hydrogen, and the device has excellent chemical durability.

[0110] The ion exchange membrane obtained by this production method can also be used in applications other than the water electrolysis device described above. Specific examples of applications include various battery applications such as polymer electrolyte fuel cells, direct methanol fuel cells, redox flow batteries, and air batteries, as well as alkaline water electrolysis, ozone water electrolysis, salt electrolysis, organic electrolysis, and various electrolysis devices for chlorides or oxides. In addition to the above applications, the membrane can also be used as a separator or solid electrode in various types of electrochemical cells for selective cation transport at the cell junction. In addition to electrochemical applications, the membrane can also be used in sensor applications such as various gas sensors, biosensors, light-emitting devices, optical devices, and organic sensors, as well as for carbon nanotube solubilization, actuators, and catalysts.

[0111] The present invention will be described in detail below with reference to examples. Examples 1 to 6, 10, and 11 are working examples, and Examples 7 to 9 are comparative examples. However, the present invention is not limited to these examples.

[0112] [Thickness of each film] The thickness of each film was measured using a magnified image (for example, 100x) of the cross section of each film taken with an optical microscope (product name "BX-51", manufactured by Olympus Corporation), and the arithmetic mean value of the thicknesses of 20 arbitrary points on each film was taken as the thickness of each film. If the surface of each film was uneven, the thickness of 10 concave portions on each film and the thickness of 10 convex portions on each film were measured, and the arithmetic mean value of the thicknesses of a total of 20 points was taken as the thickness of each film. However, if the convex portions contained threads that constituted the woven fabric, the thickness of the convex portions was taken as the value obtained by subtracting the thickness of the threads present in the convex portions.

[0113] [Ion exchange capacity of fluoropolymer] The fluoropolymer was placed in a glove box filled with dry nitrogen for 24 hours, and the dry mass of the fluoropolymer was measured. Thereafter, the fluoropolymer was immersed in a 2 mol / L aqueous sodium chloride solution at 60°C for 1 hour. The fluoropolymer was washed with ultrapure water and then taken out, and the solution in which the fluoropolymer had been immersed was titrated with a 0.1 mol / L aqueous sodium hydroxide solution to determine the ion exchange capacity of the fluoropolymer.

[0114] [Softening Point of Fluoropolymer] The softening point of the fluoropolymer was measured using a dynamic viscoelasticity measuring device according to the following procedure. First, dynamic viscoelasticity measurement was carried out using a dynamic viscoelasticity measuring device (DVA-225, manufactured by IT Measurement & Control Co., Ltd.) under the conditions of sample width: 5.0 mm, grip length: 15 mm, measurement frequency: 1 Hz, heating rate: 2°C / min, and tensile mode. Next, tan δ (loss tangent) was calculated from the ratio (E" / E') of loss modulus E" to storage modulus E', and a tan δ-temperature curve was prepared. The peak temperature between -100 and 300°C was read from the prepared tan δ-temperature curve, and this value was taken as the softening point.

[0115] [Water Conductivity] The conductivity (electrical conductivity) of the water used in each washing treatment was measured at 25° C. using an electrical conductivity meter (product name "HE-300C", manufactured by Horiba, Ltd.) according to a method in accordance with JIS K0552-1994.

[0116] [Water Temperature] The temperature of the water used in each cleaning treatment was measured using an electric conductivity meter (product name "HE-300C", manufactured by Horiba, Ltd.).

[0117] [Fluorine release rate] <Production of membrane electrode assembly> CF ２ =CF ２ and a monomer (X) described below were copolymerized, and the resulting polymer (ion exchange capacity: 1.10 meq / g dry resin) was converted to an acid form through hydrolysis and acid treatment. The resulting polymer was dispersed in a water / ethanol solvent of 40 / 60 (mass%) at a solids concentration of 26.0% to obtain a dispersion (hereinafter also referred to as "Dispersion Y"). Ethanol (18.06 g) and Zeorola-H (manufactured by Zeon Corporation) (10.58 g) were added to the resulting dispersion Y (33.0 g), and the mixture was mixed for 5 minutes at 2200 rpm using a planetary centrifugal mixer (Thinky, Awatori Rentaro). Ethanol (46.44 g) and water (75.75 g) were added to the mixed composition (54.06 g), and a mixture having a specific surface area of ​​100 m containing 74.8 mass% iridium was further mixed. ２ 40.0 g of an iridium oxide catalyst (manufactured by Tanaka Kikinzoku Co., Ltd.) was added to the mixture. The resulting mixture was processed in a planetary bead mill (rotational speed: 300 rpm) for 90 minutes to obtain an anode catalyst ink with a solids concentration of 22 mass %. The anode catalyst ink was applied to an ETFE sheet so that the iridium concentration was 1.0 mg / cm. ２ The anode catalyst layer decal was obtained by applying the coating with an applicator so that the coating became smooth, followed by drying at 80° C. for 10 minutes and then heat treating at 150° C. for 15 minutes.

[0118] Water (59.4 g) and ethanol (39.6 g) were added to 11 g of a supported catalyst ("TEC10E50E" manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) in which 46% by mass of platinum was supported on carbon powder, and the mixture was mixed and pulverized using an ultrasonic homogenizer to obtain a catalyst dispersion. To the catalyst dispersion, a mixture (29.2 g) of dispersion Y (20.1 g), ethanol (11 g), and Zeorola-H (manufactured by Zeon Corporation) (6.3 g) was premixed and kneaded. Furthermore, water (3.66 g) and ethanol (7.63 g) were added to the resulting dispersion and mixed for 60 minutes using a paint conditioner to obtain a cathode catalyst ink with a solids concentration of 10.0% by mass. The cathode catalyst ink was applied to an ETFE sheet using a die coater, dried at 80°C, and further heat-treated at 150°C for 15 minutes, resulting in a platinum content of 0.4 mg / cm. ２ As a result, a cathode catalyst layer decal of 1000 nm was obtained.

[0119] The surface of the anode catalyst layer decal on which the catalyst layer was formed was placed opposite one surface of the ion exchange membrane obtained in each example, and the surface of the cathode catalyst layer decal on which the catalyst layer was formed was placed opposite the other surface. The anode catalyst layer, ion exchange membrane, and cathode catalyst layer were bonded together by hot pressing at a pressing temperature of 150°C for 10 minutes under a pressure of 3 MPa. After the temperature was lowered to 70°C, the pressure was released and the membrane was removed. The ETFE sheets of the anode catalyst layer decal and cathode catalyst layer decal were peeled off, and an electrode with an area of ​​16 cm was obtained. ２ As a result, a membrane electrode assembly of 1000 .mu.m was obtained.

[0120] <Evaluation Procedure> A membrane electrode assembly was sandwiched between platinum-plated titanium fiber sintered bodies (manufactured by Bekaert) with a thickness of 0.25 mm and a porosity of 60%, and a platinum-plated titanium plate with a straight flow path was used as a separator. ２ The membrane electrode assembly was incorporated into a single cell of 1.0 μS / cm and was evaluated. The membrane electrode assembly was clamped so that a pressure of 1.5 MPa was applied to the electrode portions when sandwiching the membrane electrode assembly. Next, in order to sufficiently hydrate the ion exchange membrane and both electrode ionomers, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 60°C, and atmospheric pressure was supplied to the anode catalyst layer side and the cathode catalyst layer side at a flow rate of 50 mL / min for 8 hours. Thereafter, pure water with a conductivity of 1.0 μS / cm or less and a temperature of 60°C was supplied to the anode catalyst layer side at a flow rate of 50 mL / min, and while the back pressure was kept at atmospheric pressure for both the anode catalyst layer and the cathode catalyst layer, a current of 16 A (current density 1 A / cm) was applied using a large current potentio / galvanostat HCP-803 (manufactured by Biologic). ２ After that, the water supply rate to the anode catalyst layer was changed to 150 mL / min, the back pressure was changed to 50 kPa for both the anode and cathode, and the current density was changed to 1 A / cm ２Operation at this temperature was continued for 1,000 hours. Between 500 and 1,000 hours after the break-in, wastewater discharged from the cathode catalyst layer side was sampled. The amount of fluoride ions contained in the wastewater was quantified by ion chromatography and averaged to calculate the average amount of fluoride ions per unit electrode area and unit time, and the fluorine release rate was evaluated according to the following criteria. A, B, C, or D rating is preferred. The smaller the value of the fluorine release rate, the more suppressed the decomposition of the fluoropolymer is, and the more excellent the chemical durability of the ion exchange membrane is. A: 1.5×10 －６ mg / (h cm ２ ) Less than B: 1.5 x 10 －６ mg / (h cm ２ ) or more than 3.0 x 10 －６ mg / (h cm ２ ) Less than C: 3.0 x 10 －６ mg / (h cm ２ ) or more than 10.0 x 10 －６ mg / (h cm ２ ) Less than D: 10.0 x 10 －６ mg / (h cm ２ ) or more 20.0 x 10 －６ mg / (h cm ２ ) Less than E: 20.0 x 10 －６ mg / (h cm ２ ) End

[0121] [Evaluation of Leakage from Water Electrolysis Device] A membrane electrode assembly obtained in the same manner as in "<Production of Membrane Electrode Assembly>" in the above "[Fluorine Release Rate]" was heat-treated at 150°C for 15 minutes, and then the peripheral edge of the membrane electrode assembly was sandwiched between a plurality of subgaskets made of PPS (polyphenylene sulfide) and PEN (polyethylene naphthalate) in a stacked state, and the assembly was set in a water electrolysis evaluation jig EH50-25 (manufactured by Greenlight Innovations, Inc.), thereby obtaining a water electrolysis device.

[0122] (Evaluation Method) First, to fully hydrate the solid polymer electrolyte membrane and both electrode ionomers, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode and cathode sides at a flow rate of 50 mL / min for 12 hours. The cathode side was then purged with nitrogen. After the nitrogen purging, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode side at a flow rate of 50 mL / min. While the generated gas pressure on the cathode side was kept at atmospheric pressure, a current density of 2 A / cm was applied using a Kikusui Electronics PWR1600L DC power supply. ２ The battery was operated for 300 hours at 100°C, and the battery was evaluated according to the following criteria. A or B rating was preferable. A: No leakage during 300 hours of operation. B: No leakage during 100 hours of operation, but leakage occurred after 100 hours. C: Leakage occurred during 100 hours of operation.

[0123] [Production of Fluorine-Containing Polymer (S'-1)] CF ２ =CF ２ and a monomer (X) represented by the following formula (X) were copolymerized to obtain a fluoropolymer (S'-1) (ion exchange capacity: 1.25 meq / g): ２ =CF-O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F (X)

[0124] The ion exchange capacity described in the above [Production of Fluoropolymer (S'-1)] represents the ion exchange capacity of the fluoropolymer obtained when the fluoropolymer (S'-1) is hydrolyzed by the procedure described below.

[0125] [Production of Film α1] The fluoropolymer (S'-1) was molded by melt extrusion to obtain a film α1 (thickness: 45 μm) made of the fluoropolymer (S'-1).

[0126] [Production of Woven Fabric 1] 18.6 denier yarns made of PFA (tetrafluoroethylene-perfluoroether copolymer) were used as warp and weft yarns, and plain weaving was performed so that the density of the PFA yarns was 100 threads / inch to obtain Woven Fabric A1. The basis weight of Woven Fabric A1 was 16.3 g / m ２ It was.

[0127] [Example 1] PET film / film α1 / woven fabric 1 / film α1 / PET film were stacked in this order. Each stacked member was heated and pressed using a roll press at a temperature of 200 ° C. and a linear pressure of 40 kg / cm. The transfer substrates (PET films) on both sides were then peeled off at a temperature of 50 ° C. to obtain a precursor film. The precursor film was immersed in a solution of dimethyl sulfoxide / potassium hydroxide / water = 30 / 5.5 / 64.5 (mass ratio) at 95 ° C. for 30 minutes, and groups convertible to sulfonic acid functional groups in the precursor film were hydrolyzed to convert them to K-type sulfonic acid functional groups (hydrolysis treatment). Next, the obtained film was immersed for 10 minutes in a tank filled with water at 40 ° C. with a conductivity of 0.5 μS / cm (first cleaning treatment). Next, the obtained membrane was immersed twice in 1 M sulfuric acid at 40°C for 10 minutes to convert the ends of the sulfonic acid functional groups from K type to H type (acid-form conversion treatment). With the ends of the wet ion exchange membrane thus obtained fixed, it was dried at a temperature (105°C) higher than the softening point of the fluoropolymer (drying treatment) to obtain the ion exchange membrane of Example 1. The wet ion exchange membrane was dried thoroughly until the content of the liquid medium in the ion exchange membrane after drying was 5 mass% or less.

[0128] [Example 2] The ion exchange membrane of Example 2 was obtained in the same manner as in Example 1, except that a second cleaning treatment was performed after the hydrolysis treatment and before the first cleaning treatment, in which the obtained membrane was immersed for 30 seconds in a tank filled with water at 25°C and having a conductivity of 3.0 μS / cm.

[0129] Example 3 An ion exchange membrane of Example 3 was obtained in the same manner as in Example 2, except that water at 40° C. and having a conductivity of 10.0 μS / cm was used in the second washing treatment.

[0130] [Example 4] An ion exchange membrane of Example 4 was obtained in the same manner as in Example 1, except that a third cleaning treatment was performed after the first cleaning treatment and before the acid-formation treatment, in which the obtained membrane was immersed for 10 minutes in a tank filled with water at 40°C and having a conductivity of 0.1 μS / cm.

[0131] Example 5 An ion exchange membrane of Example 5 was obtained in the same manner as in Example 4, except that water at 40° C. and having a conductivity of 0.5 μS / cm was used in the third washing treatment.

[0132] [Example 6] The ion exchange membrane of Example 6 was obtained in the same manner as in Example 1, except that after the hydrolysis treatment and before the first washing treatment, a second washing treatment was performed in which the obtained membrane was immersed for 30 seconds in a tank filled with water at 25°C and having a conductivity of 0.5 μS / cm, and further, after the first washing treatment and before the acid-formation treatment, a third washing treatment was performed in which the obtained membrane was immersed for 10 minutes in a tank filled with water at 40°C and having a conductivity of 0.1 μS / cm.

[0133] Example 7 An ion exchange membrane of Example 7 was obtained in the same manner as in Example 1, except that water at 80° C. and having a conductivity of 0.5 μS / cm was used in the first washing treatment.

[0134] Example 8 An ion exchange membrane of Example 8 was obtained in the same manner as in Example 1, except that water at 25° C. and having a conductivity of 0.5 μS / cm was used in the first washing treatment.

[0135] Example 9 An ion exchange membrane of Example 9 was obtained in the same manner as in Example 1, except that water at 40° C. and having a conductivity of 10.0 μS / cm was used in the first washing treatment.

[0136] Example 10 An ion exchange membrane of Example 10 was obtained in the same manner as in Example 1, except that water at 60° C. and having a conductivity of 0.5 μS / cm was used in the first washing treatment.

[0137] [Example 11] The ion exchange membrane of Example 11 was obtained in the same manner as in Example 1, except that a second cleaning treatment was performed after the hydrolysis treatment and before the first cleaning treatment, in which the obtained membrane was immersed for 30 seconds in a tank filled with water at 25°C and having a conductivity of 100 μS / cm.

[0138] Using the ion exchange membrane obtained in each example, the water electrolysis device was evaluated for liquid leakage and fluorine release rate. The results are shown in Table 1. In Table 1, the water temperature in each cleaning treatment is described as "water temperature."

[0139]

[0140] As shown in Table 1, it was confirmed that when water having a conductivity of 3 μS / cm or less and a temperature of 35 to 60° C. was used in the first cleaning treatment, the occurrence of liquid leakage from the water electrolysis device could be suppressed and an ion exchange membrane having excellent chemical durability could be obtained (Examples 1 to 6, 10, and 11).

[0141] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2023-219197 filed on December 26, 2023 are hereby incorporated by reference as the disclosure of the specification of the present invention.

Claims

1. A method for manufacturing an ion-exchange membrane, comprising: contacting a precursor membrane containing a fluorine-containing polymer having a group convertible to an ion-exchange group with an alkaline aqueous solution containing a water-soluble organic solvent and water to hydrolyze the group convertible to the ion-exchange group to obtain an ion-exchange membrane containing a fluorine-containing polymer having an ion-exchange group; and then performing a first washing treatment of washing the ion-exchange membrane with water having a conductivity of 3 μS / cm or less and a temperature of 35 to 60 °C.

2. The method for manufacturing an ion-exchange membrane according to claim 1, wherein before the first washing treatment, a second washing treatment of washing the ion-exchange membrane with water having a temperature of 60 °C or less is performed.

3. The method for manufacturing an ion-exchange membrane according to claim 2, wherein the temperature of the water in the second washing treatment is lower than the temperature of the water in the first washing treatment.

4. The method for manufacturing an ion-exchange membrane according to claim 2, wherein the conductivity of the water in the second washing treatment is 0.05 to 100 μS / cm.

5. The method for manufacturing an ion-exchange membrane according to claim 1 or 2, wherein after the first washing treatment, a third washing treatment of washing the ion-exchange membrane with water having a lower conductivity and a temperature of 60 °C or less than the water in the first washing treatment is performed.

6. The method for manufacturing an ion-exchange membrane according to claim 1 or 2, wherein the water-soluble organic solvent is at least one selected from the group consisting of an aprotic organic solvent, an alcohol, and an amino alcohol, and the content of the water-soluble organic solvent in the alkaline aqueous solution is 5% by mass or more and 40% by mass or less based on the total mass of the alkaline aqueous solution.

7. The method for manufacturing an ion-exchange membrane according to claim 1 or 2, wherein after the first washing treatment, an acid-form treatment is performed.

8. The method for manufacturing an ion-exchange membrane according to claim 1 or 2, wherein the ion-exchange capacity of the fluorine-containing polymer having an ion-exchange group is 0.90 to 2.05 milliequivalents / gram of dry resin.

9. The method for producing an ion exchange membrane according to claim 1 or 2, wherein the fluorine-containing polymer having an ion exchange group contains a unit represented by the formula (2). Formula (2) -[CF ２ -CF(-L-(SO ３ M) ｎ )]- In the formula (2), L is an (n + 1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom, M is a hydrogen atom, an alkali metal or a quaternary ammonium cation, and n is 1 or 2.

10. The method for manufacturing an ion-exchange membrane according to claim 1 or 2, wherein a reinforcing material is included inside or on the surface of the ion-exchange membrane.

11. The method for manufacturing an ion-exchange membrane according to claim 1 or 2, wherein the ion-exchange membrane is used as an electrolyte membrane included in a membrane electrode assembly of a water electrolysis device.

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