Ion exchange membrane, alkali chloride electrolysis apparatus, and method for producing alkali hydroxide

Abstract

Provided are: an ion exchange membrane which has small variation in current efficiency, and with which it is possible to produce an aqueous alkali hydroxide solution that has excellent caustic quality; an alkali chloride electrolysis apparatus which comprises the ion exchange membrane; and a method for producing an alkali hydroxide.　The ion exchange membrane comprises a layer (S) that contains a fluorine-containing polymer having a sulfonic acid-type functional group and a layer (C) that contains a fluorine-containing polymer having a carboxylic acid-type functional group, wherein: a woven fabric is disposed in the layer S; the woven fabric is configured from yarns A that extend in one direction and yarns B that extend in a direction substantially orthogonal to the yarns A; and the amount of displacement of the ion exchange membrane is 10-20 mm when a pulling operation is performed for 10 minutes, the pulling operation repeatedly performing an operation 1 for pulling the ion exchange membrane for 1 second at a pulling load of 10 N and an operation 2 for pulling the ion exchange membrane for 0.1 second at a pulling load of 0.1 N in a direction that is at an angle of 45 degrees to the direction in which the yarns A extend in the plane of the ion exchange membrane.

Description

Ion exchange membrane, alkali chloride electrolysis apparatus, method for producing alkali hydroxide

[0001] The present invention relates to an ion exchange membrane, an alkali chloride electrolytic apparatus, and a method for producing alkali hydroxide.

[0002] In the alkali chloride electrolysis method, which involves electrolyzing an aqueous solution of alkali chloride such as seawater to produce alkali hydroxide and chlorine, electrolyte membranes made of fluorine-containing polymers having ion exchange groups are known to be used as ion exchange membranes. Patent Document 1 discloses an ion exchange membrane having a layer containing a fluorine-containing polymer having a carboxylic acid-type functional group and a layer containing a fluorine-containing polymer having a sulfonic acid-type functional group.

[0003] Patent No. 4329339

[0004] In recent years, there has been a demand for further improvement in the caustic quality of ion exchange membranes used in alkali chloride electrolysis. Here, "superior caustic quality" means a state in which the concentration of impurities (especially sodium chloride) in the alkali hydroxide aqueous solution (especially sodium hydroxide aqueous solution) obtained by electrolysis of alkali chloride aqueous solution (especially sodium chloride aqueous solution) is low. However, the alkali hydroxide aqueous solution obtained using the ion exchange membrane described in Patent Document 1 does not meet the level of caustic quality required in recent years, and there is room for improvement. Furthermore, when performing alkali chloride electrolysis, it is desirable to have small variations in current efficiency and to be able to perform alkali chloride electrolysis stably.

[0005] The present invention aims to provide an ion exchange membrane capable of producing an aqueous alkali hydroxide solution with low variation in current efficiency and excellent caustic quality. Furthermore, the present invention aims to provide an alkali chloride electrolytic apparatus including the above-mentioned ion exchange membrane, and a method for producing alkali hydroxide.

[0006] The inventors have found that the above problems can be solved by the following configuration.

[0007] (1) An ion exchange membrane comprising a layer (S) containing a fluorine-containing polymer having a sulfonic acid-type functional group, and a layer (C) containing a fluorine-containing polymer having a carboxylic acid-type functional group, wherein a woven fabric is arranged in layer S, and the woven fabric is composed of yarn A extending in one direction and yarn B extending in a direction substantially perpendicular to yarn A, and the displacement of the ion exchange membrane is 10 to 20 mm when a pulling operation is performed for 10 minutes, in which the ion exchange membrane is pulled with a tensile load of 10 N for 1 second and the ion exchange membrane is pulled with a tensile load of 0.1 N for 0.1 seconds, repeatedly in a direction that is 45 degrees to the direction in which yarn A extends within the plane of the ion exchange membrane, and the displacement of the ion exchange membrane is 10 to 20 mm, and the thickness of the ion exchange membrane when dried at 50°C for 16 hours is defined as the DRY thickness, and the thickness of the ion exchange membrane when immersed in pure water at 25°C for 16 hours is defined as the WET thickness, An ion exchange membrane in which the dry film thickness and the wet film thickness satisfy the relationship of formula (Y). Formula (Y) 1.10 ≤ wet film thickness / dry film thickness ≤ 1.40 (2) The ion exchange membrane according to (1), wherein the dry film thickness is 60 to 150 μm. (3) The ion exchange membrane according to (1) or (2), wherein the ion exchange capacity of the fluorine-containing polymer having a sulfonic acid type functional group is 0.5 to 2.5 mm equivalents / g dry resin. (4) The ion exchange membrane according to any one of (1) to (3), wherein the ion exchange capacity of the fluorine-containing polymer having a carboxylic acid type functional group is 0.5 to 2.0 mm equivalents / g dry resin. (5) The ion exchange membrane according to any one of (1) to (4), wherein yarn A and yarn B are at least one selected from the group consisting of yarn made of polytetrafluoroethylene, yarn made of polyphenylene sulfide, yarn made of nylon, yarn made of polypropylene, and yarn made of polyethylene terephthalate. (6) An ion exchange membrane according to any one of (1) to (5), further having an inorganic particle layer on the outermost surface of at least one of its faces. (7) An ion exchange membrane according to any one of (1) to (8) for use in the electrolysis of an alkaline chloride aqueous solution.(8) An ion exchange membrane according to any one of (1) to (7), wherein layer (S) has a layer (Sa) located on the layer (C) side of the woven fabric and a layer (Sb) located on the opposite side from layer (C), the thickness of layer (C) is 1 to 50 μm, the thickness of layer (Sa) is 30 to 140 μm, and the thickness of layer (Sb) is 5 to 100 μm. (9) An alkali chloride electrolytic apparatus comprising an electrolytic cell having a cathode and an anode, and an ion exchange membrane according to any one of (1) to (8), wherein the ion exchange membrane is arranged in the electrolytic cell so as to separate the cathode and the anode, with layer (C) located on the cathode side and layer (S) located on the anode side. (10) A method for producing alkali hydroxide by electrolysis of alkali chloride using the alkali chloride electrolytic apparatus according to (9). (11) A method for producing an ion exchange membrane according to any one of (1) to (8), comprising: laminating a precursor layer (C') containing a fluorine-containing polymer (C') having a group that can be converted to a carboxylic acid-type functional group, and a precursor layer (S') containing a fluorine-containing polymer (S') having a group that can be converted to a sulfonic acid-type functional group, and forming a precursor membrane in which a woven fabric is disposed in the precursor layer (S'); then contacting the precursor membrane with an alkaline aqueous solution to convert the groups in the precursor layer (C') that can be converted to a carboxylic acid-type functional group to form a layer (C) having a carboxylic acid-type functional group, and converting the groups in the precursor layer (S') that can be converted to a sulfonic acid-type functional group to form a layer (S) having a sulfonic acid-type functional group, wherein the contact time between the precursor membrane and the alkaline aqueous solution is 1.1 to 3.0 times the minimum hydrolysis time, and the temperature of the alkaline aqueous solution is 80°C or lower.

[0008] According to the present invention, an ion exchange membrane can be provided that can produce an aqueous alkali hydroxide solution with low variation in current efficiency and excellent caustic quality. Furthermore, according to the present invention, an alkali chloride electrolytic apparatus including the above-mentioned ion exchange membrane and a method for producing alkali hydroxide can be provided.

[0009] This is a schematic cross-sectional view showing an example of an ion exchange membrane in the present invention. This is a schematic plan view showing an example of the structure of a woven fabric when the ion exchange membrane is viewed in the direction of film thickness. This is a diagram for explaining the tensile operation. This is a schematic diagram showing an example of an alkali chloride electrolytic apparatus in the present invention.

[0010] The following definitions of terms apply throughout this specification and the claims unless otherwise specified. “Ion exchange membrane” means a membrane containing a polymer having ion exchange groups. “Ion exchange group” means a group capable of exchanging at least some of the ions it contains for other ions, and examples include carboxylic acid-type functional groups and sulfonic acid-type functional groups. “Carboxylic acid-type functional group” means a carboxylic acid group (-COOH) or a carboxylic acid base (-COOM). １ However, M １ It is an alkali metal or a quaternary ammonium base.) This means "sulfonic acid type functional group" refers to a sulfonic acid group (-SO ３ H), or sulfonic acid base (-SO ３ M ２ However, M ２ This refers to an alkali metal or quaternary ammonium base. The "precursor layer" is a layer (film) containing a polymer that has groups that can be converted into ion exchange groups. "Groups that can be converted into ion exchange groups" refers to groups that can be converted into ion exchange groups by treatments such as hydrolysis and acidification. "Groups that can be converted into carboxylic acid-type functional groups" refers to groups that can be converted into carboxylic acid-type functional groups by treatments such as hydrolysis and acidification. "Groups that can be converted into sulfonic acid-type functional groups" refers to groups that can be converted into sulfonic acid-type functional groups by treatments such as hydrolysis and acidification. The unit of ion exchange capacity, "milliequivalents / gram dry resin," may be abbreviated as "mEq / g."

[0011] "Fluorine-containing polymer" refers to a polymer compound that has fluorine atoms in its molecule. "Monomer" refers to a compound that has a polymerization-reactive carbon-carbon unsaturated double bond. "Fluorine-containing monomer" refers to a monomer that has fluorine atoms in its molecule. "Perfluoroalkylene group" refers to an alkylene group in which all the hydrogen atoms bonded to the carbon atoms in the alkylene group are replaced with fluorine atoms. "Perfluoroalkyl group" refers to an alkyl group in which all the hydrogen atoms bonded to the carbon atoms in the alkyl group are replaced with fluorine atoms. "Constituent unit" refers to a polymerization unit derived from a monomer that exists in the polymer and constitutes the polymer. For example, if a constituent unit is produced by the addition polymerization of a monomer having a carbon-carbon unsaturated double bond, the constituent unit derived from this monomer is a divalent constituent unit produced by the cleavage of this unsaturated double bond. Alternatively, the constituent unit may be a constituent unit obtained by chemically converting, for example, hydrolysis, this constituent unit after forming a polymer having the structure of a certain constituent unit. In some cases, constituent units derived from individual monomers may be described by adding "unit" to the monomer name.

[0012] The ion exchange membrane of the present invention comprises a layer (S) (hereinafter also referred to as "layer (S)") containing a fluorine-containing polymer having a sulfonic acid type functional group (hereinafter also referred to as "fluorine-containing polymer (S)") and a layer (C) (hereinafter also referred to as "layer (C)") containing a fluorine-containing polymer having a carboxylic acid type functional group (hereinafter also referred to as "fluorine-containing polymer (C)"), wherein a woven fabric is arranged in the layer S, and the woven fabric is composed of yarn A extending in one direction and yarn B extending in a direction substantially perpendicular to yarn A, and the displacement of the ion exchange membrane is 10 to 20 mm when a pulling operation (hereinafter also referred to as "specific operation") is performed for 10 minutes, in which the ion exchange membrane is pulled for 1 second with a tensile load of 10 N and the ion exchange membrane is pulled for 0.1 second with a tensile load of 0.1 N, repeatedly in a direction that makes a 45-degree angle with the direction in which yarn A extends within the plane of the ion exchange membrane.

[0013] The ion exchange membrane of the present invention can be used to produce alkali hydroxide aqueous solutions with low variation in current efficiency and excellent caustic quality. The reason for this is thought to be as follows. First, when the displacement of the ion exchange membrane as defined in the present invention is too large, it is thought that the membrane is in a swollen state. In such a swollen state, the distance between the ions passing through the ion exchange membrane and the ion exchange groups of the ion exchange membrane increases. In this state, the interaction between the ions and the ion exchange groups weakens, so anions that would normally not pass through the ion exchange membrane can pass through it. This leads to a decrease in current efficiency, and as a result, it is presumed that variation in current efficiency occurs. Therefore, in the present invention, the displacement of the ion exchange membrane is kept below a predetermined value to make the above phenomenon less likely to occur. In addition, when the ion exchange membrane is attached to the electrolytic cell and filled with liquid, the ion exchange membrane is in contact with a high concentration of caustic, and the phenomenon of the ion exchange membrane shrinking is likely to occur. Normally, membranes that do not stretch easily will stretch when pulled with relatively strong force, but this is prone to causing pinholes and other defects. In this invention, an ion exchange membrane with an excessively small displacement corresponds to the above-mentioned poorly stretchable membrane. In such membranes, pinholes are likely to form when they shrink upon contact with caustic solvent, which is presumed to lead to a decrease in caustic solvent quality. Therefore, in this invention, the displacement of the ion exchange membrane is kept below a predetermined value to reduce the likelihood of the above phenomenon occurring.

[0014] [Ion Exchange Membrane] The ion exchange membrane of the present invention will be described below based on the drawings, but the present invention is not limited to the contents of the drawings. Figure 1 is a schematic cross-sectional view showing an example of the ion exchange membrane of the present invention. The ion exchange membrane 1 has, in order, a first inorganic particle layer 10, a layer (C) 12 containing a fluorine-containing polymer (C), a layer (S) 14 containing a fluorine-containing polymer (S), and a second inorganic particle layer 16. Within layer (S) 14, a woven fabric 18 is arranged between layer (Sa) 14A containing a fluorine-containing polymer (S) and layer (Sb) 14B containing a fluorine-containing polymer (S). In the electrolytic cell, the ion exchange membrane 1 is arranged such that the first inorganic particle layer 10 faces the cathode and the second inorganic particle layer 16 faces the anode. The shape and size of the ion exchange membrane 1 can be appropriately determined according to the electrolytic cell in which the ion exchange membrane 1 is installed. The first inorganic particle layer 10 and the second inorganic particle layer 16 do not necessarily have to be included in the ion exchange membrane of the present invention.

[0015] Figure 2 is a schematic plan view showing an example of the structure of the woven fabric when the ion exchange membrane is viewed in the direction of film thickness. As shown in Figure 2, the woven fabric 18 contained in the ion exchange membrane 1 is composed of threads A20 extending in one direction (up and down direction on the paper) and threads B22 extending in a direction approximately perpendicular to threads A20 (left and right direction on the paper). In Figure 2, there are five threads each of threads A20 and A22, but the number is not limited to that shown in the figure.

[0016] In the ion exchange membrane of the present invention, the amount of displacement when a specific operation is performed is within a predetermined range. Below, the specific operation will be described first. When pulling the ion exchange membrane, a pulling operation is performed by repeatedly performing operation 1, in which the ion exchange membrane is pulled for 1 second with a tensile load of 10 N, and operation 2, in which the ion exchange membrane is pulled for 0.1 seconds with a tensile load of 0.1 N, in a direction that is 45 degrees to the direction in which thread A extends within the plane of the ion exchange membrane (hereinafter also referred to as the "specific direction"). More specifically, as shown in Figure 2, the direction in which the ion exchange membrane 1 is pulled corresponds to the direction indicated by the white arrow in the figure. The direction in which the ion exchange membrane 1 is pulled is the in-plane direction of the ion exchange membrane 1, and also corresponds to the direction midway between the direction in which thread A20 extends and the direction in which thread B22 extends. Furthermore, when stretching the ion exchange membrane 1, as shown in Figure 3, operation 1 is performed by repeatedly stretching the ion exchange membrane with a tensile load of 10 N for 1 second, and operation 2 is performed by repeatedly stretching the ion exchange membrane with a tensile load of 0.1 N for 0.1 seconds. The above stretching operations can be performed using known equipment. For example, the Tensilon universal tester RTI-1225 can be used as equipment. When using the Tensilon universal tester, cycle is selected as the test mode, and the distance between chucks is set to 70.00 mm. Since the loads are different in operation 1 and operation 2, the universal tester stretches the membrane in the direction indicated by the white arrow in Figure 2 during operation 1, but moves in the opposite direction to the white arrow in Figure 2 so that the load is 0.1 N during operation 2. The stretching speed in stretching operation 1 and stretching operation 2 is set to 500 mm / min. Furthermore, the shape of the ion exchange membrane sample used when performing the above pulling operation shall be JIS K6251-1 type.

[0017] The displacement of the ion exchange membrane when a specific operation is performed for 10 minutes is 10 to 20 mm. In particular, 11 to 19 mm is preferred, and 11 to 16 mm is more preferred, as it provides a better balance between the variation in current efficiency and the caustic quality of the alkali hydroxide aqueous solution that can be produced. The above displacement is the difference between the length of the ion exchange membrane in a specific direction after performing the specific operation and the length of the ion exchange membrane in a specific direction before performing the specific operation. In other words, the above displacement corresponds to the amount of elongation of the ion exchange membrane during the specific operation. If the above displacement is less than 10 mm, the caustic quality of the alkali hydroxide aqueous solution that can be produced deteriorates. Also, if the above displacement is greater than 20 mm, the variation in current efficiency is large.

[0018] In the ion exchange membrane of the present invention, it is preferable that the DRY film thickness and the WET film thickness satisfy the following relationship (X). Satisfying the relationship (X) further improves the caustic quality. Equation (X) WET film thickness / DRY film thickness ≥ 1.10 DRY film thickness refers to the film thickness (μm) of the ion exchange membrane when it is dried at 50°C for 16 hours. WET film thickness refers to the film thickness (μm) of the ion exchange membrane when it is immersed in pure water at 25°C for 16 hours. Satisfying the relationship (X) means that the ion exchange membrane is easily stretched and less likely to break. There is no particular upper limit to the ratio expressed as WET film thickness / DRY film thickness, but it is preferable that it is 1.40 or less. When the WET film thickness / DRY film thickness is 1.40 or less, the variation in current efficiency can be further reduced. In other words, it is preferable that the above DRY film thickness and WET film thickness satisfy the relationship (Y). Formula (Y) 1.10 ≤ WET film thickness / DRY film thickness ≤ 1.40 The size of the DRY film thickness is not particularly limited, but is preferably 60 to 150 μm, more preferably 65 to 140 μm, even more preferably 70 to 130 μm, and particularly preferably 90 to 120 μm. The size of the WET film thickness is not particularly limited, but is preferably 70 to 180 μm, more preferably 75 to 175 μm, even more preferably 80 to 170 μm, and particularly preferably 110 to 150 μm. As for the method of measuring the DRY film thickness, one method is to measure the film thickness at the center of the region surrounded by two adjacent yarns A and two adjacent yarns B that constitute the woven fabric contained in the ion exchange membrane dried under the above conditions, and take the arithmetic mean of the obtained film thicknesses to obtain the DRY film thickness. Another method for measuring the wet film thickness involves measuring the film thickness at the center of a region enclosed by two adjacent threads A and two adjacent threads B that constitute the fabric contained in the ion exchange membrane dried under the above conditions, at 10 such regions, and then arithmetically averaging the obtained film thicknesses to obtain the wet film thickness.

[0019] The following describes in detail each component that makes up the ion exchange membrane.

[0020] (Layer (C)) Layer (C) 12 may be any layer containing a fluorine-containing polymer (C), but from the viewpoint of electrolytic performance, a layer consisting only of a fluorine-containing polymer (C) without any materials other than the fluorine-containing polymer (C) is preferred. In other words, it is preferable that layer (C) 12 is a layer consisting of a fluorine-containing polymer having carboxylic acid-type functional groups. In Figure 1, layer (C) 12 is shown as a single layer, but it may be a layer formed from multiple layers. When layer (C) 12 is formed from multiple layers, the types of constituent units that make up the fluorine-containing polymer (C) and the proportion of constituent units having carboxylic acid-type functional groups may be different in each layer.

[0021] The thickness of layer (C) 12 (or the total thickness if layer (C) 12 is formed from multiple layers) is preferably 1 to 50 μm, more preferably 5 to 50 μm, and particularly preferably 8 to 35 μm. If the thickness of layer (C) 12 is greater than or equal to the lower limit, the caustic quality of the alkali hydroxide aqueous solution is better. If the thickness of layer (C) 12 is less than or equal to the upper limit, the increase in electrolysis voltage during alkali chloride electrolysis can be suppressed.

[0022] The ion exchange capacity of the fluorine-containing polymer (C) constituting layer (C) 12 is preferably 0.5 to 2.0 milliequivalents / g dry resin, more preferably 0.8 to 2.0 milliequivalents / g dry resin, and particularly preferably 0.85 to 1.10 milliequivalents / g dry resin. If layer (C) 12 is formed from multiple layers, it is preferable that the ion exchange capacity of all fluorine-containing polymers (C) constituting layer (C) 12 is within the above range. If the ion exchange capacity of the fluorine-containing polymer (C) is above the lower limit, the electrical resistance of the ion exchange membrane 1 when electrolyzing an alkaline chloride aqueous solution will be low, and an ion exchange membrane 1 with a low electrolysis voltage will be obtained. If the ion exchange capacity of the fluorine-containing polymer (C) is below the upper limit, the synthesis of polymers with high molecular weights will be easy, and excessive swelling of the polymer will be suppressed, resulting in an ion exchange membrane 1 that does not easily suffer from a decrease in current efficiency.

[0023] The fluorine-containing polymer (C) is preferably obtained by converting a group capable of being converted into a carboxylic acid functional group of the fluorine-containing polymer described below into a carboxylic acid functional group in the method for producing an ion exchange membrane. Specific examples of the fluorine-containing polymer (C) include a copolymer of a monomer having a group capable of being converted into a carboxylic acid functional group and a fluorine atom (hereinafter also referred to as "fluorine-containing monomer (C')") and a fluorine-containing olefin (hereinafter also referred to as "fluorine-containing polymer (C')"), which is hydrolyzed to convert a group capable of being converted into a carboxylic acid functional group into a carboxylic acid functional group.

[0024] The fluorine-containing monomer (C') is not particularly limited as long as it is a compound having one or more fluorine atoms in the molecule, an ethylenic double bond, and a group capable of being converted into a carboxylic acid functional group, and conventionally known compounds are used. The fluorine-containing monomer (C') is preferably a monomer represented by the following formula (1) in terms of the production cost of the monomer, the reactivity with other monomers, and the excellent properties of the resulting fluorine-containing polymer.

[0025] CF ２ =CF-(O) ｐ -(CF ２ ) ｑ -(CF ２ CFX) ｒ -(O) ｓ -(CF ２ ) ｔ -(CF ２ CFX') ｕ -A １ ・・・(1)

[0026] In formula (1), X and X' are each independently a fluorine atom or a trifluoromethyl group. A １ is a group capable of being converted into a carboxylic acid functional group. Specifically, -CN, -COF, -COOR １ (R １ is an alkyl group having 1 to 10 carbon atoms.), -COONR ２ R ３ (R ２ and R ３Each of these is independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Examples include: p is 0 or 1; q is an integer from 0 to 12; r is an integer from 0 to 3; s is 0 or 1; t is an integer from 0 to 12; u is an integer from 0 to 3; where 1 ≤ p + s and 1 ≤ r + u.

[0027] Specific examples of monomers represented by formula (1) include the following compounds, and compounds with p=1, q=0, r=1, s=0-1, t=0-3, and u=0-1 are preferred because they are easy to manufacture. CF ２ = CF - O - CF ２ CF ２ - COOCH ３ CF ２ = CF - O - CF ２ CF ２ CF ２ - COOCH ３ CF ２ = CF - O - CF ２ CF ２ CF ２ CF ２ - COOCH ３ CF ２ = CF - O - CF ２ CF ２ -O-CF ２ CF ２ - COOCH ３ CF ２ = CF - O - CF ２ CF ２ -O-CF ２ CF ２ CF ２ - COOCH ３ CF ２ = CF - O - CF ２ CF ２ -O-CF ２ CF ２ CF ２ CF ２ - COOCH ３ CF ２ = CF - O - CF ２ CF ２ CF ２ -O-CF ２ CF ２ - COOCH３ , CF ２ =CF - O - CF ２ CF(CF ３ ) - O - CF ２ CF ２ -COOCH ３ , CF ２ =CF - O - CF ２ CF(CF ３ ) - O - CF ２ CF ２ CF ２ -COOCH ３ . The fluorine-containing monomer (C') may be used alone or in combination of two or more.

[0028] As the fluorine-containing olefin, fluorinated olefins having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule can be mentioned. Specific examples thereof include tetrafluoroethylene (TFE), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among them, TFE is particularly preferable in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the obtained fluorine-containing polymer. The fluorine-containing olefin may be used alone or in combination of two or more.

[0029] In the production of the fluorine-containing polymer (C'), in addition to the fluorine-containing monomer (C') and the fluorine-containing olefin, other monomers may be further used. Specific examples of other monomers include CF ２ =CFR ｆ (R ｆ is a perfluoroalkyl group having 2 to 10 carbon atoms.), CF ２ =CF - OR ｆ１ (R ｆ１ is a perfluoroalkyl group having 1 to 10 carbon atoms.), CF ２ =CFO(CF ２ ) ｖ CF = CF ２ (v is an integer of 1 to 3). By copolymerizing other monomers, the flexibility and mechanical strength of the ion exchange membrane 1 can be improved. <0​The ion exchange capacity of the fluorine-containing polymer (C) can be adjusted by changing the content of constituent units derived from the fluorine-containing monomer (C') in the fluorine-containing polymer (C'). Preferably, the content of carboxylic acid-type functional groups in the fluorine-containing polymer (C) is the same as the content of groups that can be converted to carboxylic acid functional groups in the fluorine-containing polymer (C').

[0031] The TQ value range for the fluorine-containing polymer (C) is preferably 150 to 350°C, more preferably 170 to 300°C, and particularly preferably 200 to 250°C, from the viewpoint of mechanical strength and film-forming properties as an ion exchange membrane.

[0032] (Layer (S)) Layer (S) 14 may be any layer containing a fluorine-containing polymer (S), but from the viewpoint of electrolytic performance, a layer consisting only of a fluorine-containing polymer (S) without any materials other than the fluorine-containing polymer (S) is preferred. In other words, it is preferable that layer (S) 14 is a layer consisting of a fluorine-containing polymer having a sulfonic acid type functional group. As shown in Figure 1, a woven fabric 18 (described later) is included in layer (S) 14 to increase the mechanical strength of the ion exchange membrane 1. Of the layers (S) 14, the layer located on the layer (C) 12 side of the woven fabric 18 (the cathode side in the electrolytic device) (i.e., the layer including the surface in contact with layer (C) 12) is layer (Sa) 14A, and the layer located on the opposite side of the woven fabric 18 from the layer (C) 12 side (the anode side in the electrolytic device) (i.e., the layer including the surface opposite to the surface in contact with layer (C) 12) is layer (Sb) 14B. In Figure 1, layer (Sa) 14A and layer (Sb) 14B are shown as single layers, but they may also be layers formed from multiple layers. If one or both of layer (Sa) 14A and layer (Sb) 14B are formed from multiple layers, the types of constituent units that make up the fluorine-containing polymer (S) and the proportion of constituent units having sulfonic acid-type functional groups may be different in each of the layers.

[0033] The thickness of layer (S) 14 (or the total thickness if layer (S) 14 is formed from multiple layers) is preferably 30 to 200 μm, more preferably 45 to 200 μm, and particularly preferably 55 to 120 μm. If the thickness of layer (S) 14 is above the lower limit, the mechanical strength of the ion exchange membrane 1 will be sufficiently high. If the thickness of layer (S) 14 is below the upper limit, the electrical resistance of the ion exchange membrane 1 can be kept low.

[0034] The thickness of layer (Sa) 14A (or the total thickness if layer (Sa) 14A) is formed from multiple layers is preferably 30 to 140 μm, more preferably 35 to 140 μm, and particularly preferably 35 to 90 μm. If the thickness of layer (Sa) 14A when dry is greater than or equal to the lower limit, the mechanical strength of the ion exchange membrane 1 will be sufficiently high. If the thickness of layer (Sa) 14A when dry is less than or equal to the upper limit, the electrical resistance of the ion exchange membrane 1 can be kept low.

[0035] The ion exchange capacity of the fluorine-containing polymer (S) constituting layer (Sa) 14A is preferably 0.5 to 2.5 mm equivalents / g dry resin, and particularly preferably 0.9 to 1.5 mm equivalents / g dry resin. If layer (Sa) 14A is formed from multiple layers, it is preferable that the ion exchange capacity of all fluorine-containing polymers (S) constituting layer (Sa) 14A is within the above range. Furthermore, it is preferable that layer (Sa) 14A consists of multiple layers, and more preferably two layers. In another embodiment, it is preferable that layer (Sa) 14A is a single layer. If the ion exchange capacity of the fluorine-containing polymer (S) constituting layer (Sa) 14A is above the above lower limit, the electrical resistance of the ion exchange membrane 1 becomes low, and the electrolysis voltage when electrolyzing an alkaline chloride aqueous solution can be lowered. Furthermore, for fluorine-containing polymers (S) with an ion exchange capacity below the above upper limit, it becomes easier to increase the molecular weight of the fluorine-containing polymer (S) during polymerization. If a fluorine-containing polymer (S) with a high molecular weight is used in layer (Sa) 14A, the strength of layer (Sa) 14A will be increased.

[0036] The thickness of layer (Sb) 14B (or the total thickness if layer (Sb) 14B is formed from multiple layers) is preferably 5 to 100 μm, more preferably 10 to 50 μm, and particularly preferably 10 to 40 μm. If the thickness of layer (Sb) 14B is greater than or equal to the lower limit, the woven fabric 18 is contained at an appropriate depth from the surface of the ion exchange membrane 1, improving the peel resistance of the woven fabric 18. In addition, cracks are less likely to form on the surface of the ion exchange membrane 1, and as a result, the decrease in mechanical strength is suppressed. If the thickness of layer (Sb) 14B is less than or equal to the upper limit, the electrical resistance of the ion exchange membrane 1 can be kept low, and the increase in electrolysis voltage can be suppressed.

[0037] The ion exchange capacity of the fluorine-containing polymer (S) constituting layer (Sb) 14B is preferably 0.5 to 2.5 milliequivalents / g of dry resin, more preferably 0.6 to 2.5 milliequivalents / g of dry resin, and particularly preferably 0.9 to 2.0 milliequivalents / g of dry resin. If layer (Sb) 14B is formed from multiple layers, it is preferable that the ion exchange capacity of the fluorine-containing polymer (S) constituting at least the layer located furthest to the anode is within the above range, and it is more preferable that the ion exchange capacity of all the fluorine-containing polymers (S) constituting layer (Sb) 14B is within the above range. In another embodiment, layer (Sb) 14B consists of a single layer, and it is preferable that the ion exchange capacity of the fluorine-containing polymer (S) constituting this layer is within the above range. If the ion exchange capacity of the fluorine-containing polymer (S) constituting layer (Sb) 14B is above the lower limit, the electrical resistance of the ion exchange membrane 1 becomes low, and the electrolysis voltage during electrolysis can be lowered. If the ion exchange capacity of the fluorine-containing polymer (S) constituting layer (Sb) 14B is below the above upper limit, the membrane strength can be maintained and membrane rupture can be suppressed during electrolytic operation or membrane mounting.

[0038] At least a portion of the fluorine-containing polymer having sulfonic acid-type functional groups that constitutes layer (Sb) 14B is preferably a polymer having a constituent unit based on a monomer having two or more sulfonic acid-type functional groups, and particularly preferably a polymer having a constituent unit based on a monomer having two sulfonic acid-type functional groups. This allows for an increase in the ion exchange group concentration per unit weight at the same monomer concentration, so that layer (Sb) 14B with higher ion exchange capacity can be obtained with a smaller amount of monomer compared to a polymer having a constituent unit with only one sulfonic acid-type functional group.

[0039] A preferred structural unit based on a monomer having two or more sulfonic acid-type functional groups is the structural unit shown in the following formula (U1).

[0040]

[0041] In formula (U1), R ｆ１ This is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the above perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, preferably 20 or less, and more preferably 10 or less. ｆ２ This is a perfluoroalkylene group which may contain a single bond or an oxygen atom between carbon atoms. The number of carbon atoms in the above perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, preferably 20 or less, and more preferably 10 or less. r is 0 or 1. M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. The unit represented by formula (U1) is preferably the unit represented by formula (U1-1).

[0042]

[0043] R ｆ３ R is a linear perfluoroalkylene group having 1 to 6 carbon atoms, ｆ４ This is a linear perfluoroalkylene group having 1 to 6 carbon atoms, which may contain single bonds or oxygen atoms between carbon atoms. The definitions of r and M are as described above.

[0044] The fluorine-containing polymer (S) is preferably obtained by converting a group capable of being converted into a sulfonic acid-type functional group of a fluorine-containing polymer having a group capable of being converted into a sulfonic acid-type functional group described below in the step of obtaining the ion exchange membrane described below into a sulfonic acid-type functional group. Specific examples of the fluorine-containing polymer (S) include a copolymer of a monomer having a group capable of being converted into a sulfonic acid-type functional group and a fluorine atom (hereinafter also referred to as "fluorine-containing monomer (S')") and a fluorine-containing olefin (hereinafter also referred to as "fluorine-containing polymer (S')"), which is hydrolyzed to convert a group capable of being converted into a sulfonic acid-type functional group into a sulfonic acid-type functional group, thereby obtaining a fluorine-containing polymer.

[0045] The fluorine-containing monomer (S') is not particularly limited as long as it is a compound having one or more fluorine atoms in the molecule, an ethylenic double bond, and a group capable of being converted into a sulfonic acid-type functional group, and conventionally known compounds can be used. From the viewpoints of the production cost of the monomer, the reactivity with other monomers, and the excellent properties of the obtained fluorine-containing polymer, the compound represented by the following formula (2) or the compound represented by the following formula (3) is preferable.

[0046] CF ２ =CF−O−R ｆ１ −A ２ ...(2) CF ２ =CF−R ｆ１ −A ２ ...(3) In formula (2) and formula (3), the definition of R ｆ１ is the same as that of R ｆ１ in formula (U1). A ２ is a group capable of being converted into a sulfonic acid-type functional group, and specific examples thereof include -SO ２ F, -SO ２ Cl, -SO[[ID=X]] ２ Br.

[0047] Specific examples of the compound represented by formula (2) 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 F CF２ = CF - O - CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ F CF ２ =CF - [O - CF ２ CF (CF ３ )] ｘ -SO ２ F

[0048] A specific example of a compound represented by formula (3) is CF ２ = CF - (CF ２ ) ｗ -SO ２ F, CF ２ = CF - CF ２ -O-(CF ２ ) ｗ -SO ２ F is one example. In the formula, w is an integer from 1 to 8.

[0049] As fluorine-containing monomers (S'), the following compounds are preferred due to their ease of industrial synthesis: CF ２ = CF - O - CF ２ CF ２ -SO ２ F CF ２ = CF - O - CF ２ CF ２ CF ２ -SO ２ F CF ２ = CF - O - CF ２ CF ２ CF ２ CF ２ -SO ２ F CF ２ = CF - O - CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F CF ２ = CF - O - CF ２ CF (CF ３ )-O-CF ２ CF ２ CF ２ -SO ２ F CF ２= CF - O - CF ２ CF (CF ３ ) - SO ２ F CF ２ = CF - CF ２ CF ２ -SO ２ F CF ２ = CF - CF ２ CF ２ CF ２ -SO ２ F CF ２ = CF - CF ２ -O-CF ２ CF ２ -SO ２ F, the fluorine-containing monomer (S'), may be used alone or in combination of two or more types.

[0050] When layer (Sb) 14B contains a polymer having a structural unit based on a monomer having two or more sulfonic acid-type functional groups, a monomer having one or more fluorine atoms in the molecule, having an ethylenically active double bond, and having two or more groups that can be converted to a sulfonic acid-type functional group can be used as the fluorine-containing monomer (S'). As such a monomer, a monomer that yields the structural unit of formula (U1) described above is preferred. As a monomer that yields the structural unit of formula (U1), a compound represented by the following formula (m1) is preferred.

[0051]

[0052] In formula (m1), R ｆ１ , R ｆ２ The definitions of r and r are as follows: ｆ１ , R ｆ２ , is the same as r, A ２ The definition of is A in equations (2) and (3). ２ It is the same as this.

[0053] The compound represented by formula (m1) is preferably the compound represented by formula (m1-1).

[0054]

[0055] R in equation (m1-1) ｆ３ , R ｆ４ The definition of r is R in equation (U1-1).ｆ３ , R ｆ４ , is the same as r, A ２ The definition of is A in equations (2) and (3). ２ It is the same as this.

[0056] Specific examples of compounds represented by formula (m1-1) include the following:

[0057]

[0058] By using monomers having two or more sulfonic acid-type functional groups, the concentration of ion exchange groups per unit weight can be increased at the same monomer concentration. This makes it easy to increase the ion exchange capacity of the polymer constituting layer (Sb) 14B without reducing the polymer molecular weight. As a result, a film with high water permeability and low electrolytic voltage can be obtained while maintaining excellent caustic quality.

[0059] Examples of fluorine-containing olefins include the compounds exemplified above, and TFE is particularly preferred due to its excellent monomer production cost, reactivity with other monomers, and the properties of the resulting fluorine-containing polymer. Fluorine-containing olefins may be used individually or in combination of two or more.

[0060] In addition to fluorine-containing monomers (S') and fluorine-containing olefins, other monomers may also be used in the production of the fluorine-containing polymer (S'). Examples of other monomers include the compounds exemplified above. By copolymerizing other monomers, the flexibility and mechanical strength of the ion exchange membrane 1 can be improved. From the viewpoint of maintaining ion exchange performance, the proportion of other monomers is preferably 30 mol% or less of the total constituent units (100 mol%) in the fluorine-containing polymer (S').

[0061] The ion exchange capacity of the fluorine-containing polymer (S) can be adjusted by changing the content of constituent units derived from the fluorine-containing monomer (S') in the fluorine-containing polymer (S'). Preferably, the content of sulfonic acid-type functional groups in the fluorine-containing polymer (S) is the same as the content of groups that can be converted to sulfonic acid-type functional groups in the fluorine-containing polymer (S').

[0062] The TQ value range for the fluorine-containing polymer (S') is preferably 150 to 350°C, more preferably 170 to 300°C, and particularly preferably 200 to 250°C, from the viewpoint of mechanical strength and film-forming properties as an ion exchange membrane.

[0063] When layer (Sa) 14A consists of multiple layers, for example, two layers, the layer in contact with layer (C) 12 is layer (Sa-1) 14Aa, and the layer in contact with layer (Sb) 14B is layer (Sa-2) 14Ab. In this case, from the viewpoint of adhesion to layer (C) 12, it is preferable that the ion exchange capacity of the fluorine-containing polymer (S) constituting layer (Sa-1) 14Aa is lower than that of the fluorine-containing polymer (S) constituting layer (Sa-2) 14Ab, more preferably 0.01 to 0.5 mm equivalents / g dry resin lower, and particularly preferably 0.03 to 0.4 mm equivalents / g dry resin lower. The ion exchange capacity of layer (Sa-1) 14Aa is preferably 0.5 to 2.5 mm equivalents / g dry resin, more preferably 0.6 to 2.5 mm equivalents / g dry resin, and particularly preferably 0.9 to 1.2 mm equivalents / g dry resin. The thickness of layer (Sa-1) 14Aa should be a moderate thickness that contributes to adhesion, preferably 1 to 100 μm, and particularly preferably 10 to 50 μm.

[0064] (Woven Fabric) The woven fabric 18 is contained within layer (S) 14. The woven fabric 18 is a material that reinforces the ion exchange membrane 1. As described above, the woven fabric 18 consists of yarn A 20 and yarn B 22, and yarn A 20 and yarn B 22 are approximately perpendicular to each other. Approximately perpendicular means that the angle between yarn A and yarn B is 90 ± 10 degrees.

[0065] The denier count of yarns A and B constituting the woven fabric 18 is preferably 30 or higher, and particularly preferably 50 or higher. The upper limit of the denier count of yarns A and B constituting the woven fabric 18 is preferably 150 or lower, and particularly preferably 120 or lower, in that it allows for a further reduction in the electrolytic voltage. Note that the denier count is the value obtained by expressing the mass of 9000 m of yarn in grams (g / 9000 m).

[0066] The density of threads A and B is preferably 10 threads / inch or more, and particularly preferably 20 threads / inch or more, in terms of excellent dimensional stability of the ion exchange membrane 1, and preferably 100 threads / inch or less, and particularly preferably 50 threads / inch or less, in terms of further reduction of the electrolytic voltage.

[0067] Threads A20 and B22 may be composed of either a monofilament consisting of one filament or a multifilament consisting of two or more filaments, with monofilaments being preferred.

[0068] Yarns A20 and B22 are preferably selected from the group consisting of yarns made of polytetrafluoroethylene, polyphenylene sulfide, nylon, polypropylene, and polyethylene terephthalate, in order to provide superior durability.

[0069] In the ion exchange membrane 1, sacrificial threads, as described later, may remain. Furthermore, the ion exchange membrane 1 may have elution pores. "Elution pores" refer to pores formed as a result of the sacrificial threads eluting into the alkaline aqueous solution.

[0070] (Inorganic Particle Layer) The ion exchange membrane 1 has a first inorganic particle layer 10 and a second inorganic particle layer 16. Preferably, the first inorganic particle layer 10 and the second inorganic particle layer 16 contain inorganic particles and a binder. In Figure 1, the inorganic particle layer is arranged on the outermost surface of the two main surfaces, but the inorganic particle layer may be arranged on the outermost surface of only one of the main surfaces.

[0071] The inorganic particles preferably have excellent corrosion resistance to alkaline chloride aqueous solutions and are hydrophilic. Specifically, at least one selected from the group consisting of oxides, nitrides, and carbides of Group 4 or Group 14 elements is preferred, and SiO ２ , SiC, ZrO ２ , or ZrC is more preferred, ZrO ２The above is particularly preferable. The average particle size of the inorganic particles is preferably 0.01 to 10 μm, more preferably 0.01 to 1.5 μm, and particularly preferably 0.5 to 1.5 μm. If the average particle size is above the lower limit, a high gas adhesion suppression effect can be obtained. If the average particle size is below the upper limit, the resistance to shedding of inorganic particles is excellent.

[0072] The binder preferably has excellent corrosion resistance to aqueous alkali chloride solutions and is hydrophilic, more preferably a fluorine-containing polymer having a carboxylic acid group or a sulfonic acid group, and particularly preferably a fluorine-containing polymer having a sulfonic acid group. The fluorine-containing polymer may be a homopolymer of monomers having a carboxylic acid group or a sulfonic acid group, or a copolymer of a monomer having a carboxylic acid group or a sulfonic acid group and a monomer copolymerizable with this monomer.

[0073] The ratio of the binder's mass to the total mass of inorganic particles and binder in the first inorganic particle layer 10 and the second inorganic particle layer 16 (hereinafter also referred to as the "binder ratio") is preferably 0.1 to 0.5. If the binder ratio is above the lower limit, the resistance to shedding of inorganic particles is excellent. If the binder ratio is below the upper limit, a high gas adhesion suppression effect can be obtained.

[0074] [Method for Manufacturing an Ion Exchange Membrane] The method for manufacturing an ion exchange membrane of the present invention (hereinafter also referred to as "this manufacturing method") can employ known methods as long as an ion exchange membrane with the above-described characteristics can be obtained. In particular, this manufacturing method is preferable in which a precursor layer (C') containing a fluorine-containing polymer (C') having a group that can be converted to a carboxylic acid-type functional group and a precursor layer (S') containing a fluorine-containing polymer (S') having a group that can be converted to a sulfonic acid-type functional group are laminated, and a woven fabric is arranged in the precursor layer (S') to form a precursor membrane, and then the precursor membrane is brought into contact with an alkaline aqueous solution to convert the group in the precursor layer (C') that can be converted to the carboxylic acid-type functional group to form a layer (C) having the carboxylic acid-type functional group, and the group in the precursor layer (S') that can be converted to a sulfonic acid-type functional group to form a layer (S) having the sulfonic acid-type functional group.

[0075] (Manufacturing of Precursor Film) An example of a method for manufacturing a precursor film in which a precursor layer (C') and a precursor layer (S') are laminated is shown below. First, pellets of fluorine-containing polymer (C') and pellets of fluorine-containing polymer (S') are supplied to a known melt extruder for film manufacturing to obtain molten material of fluorine-containing polymer (C') pellets and molten material of fluorine-containing polymer (S') pellets, respectively. Next, the molten materials of each pellet are extruded from the nozzle (e.g., T-die) of the melt extruder (melt extrusion molding by co-extrusion) to obtain a laminated film having a precursor layer (C') containing fluorine-containing polymer (C') and a precursor layer (S'a) containing fluorine-containing polymer (S'). Separately, a film consisting of a precursor layer (S'b) containing fluorine-containing polymer (S') is obtained by a single-layer extrusion method. Next, the film consisting of the precursor layer (S'b), the woven fabric, and the above laminated film are arranged in this order and laminated using, for example, a lamination roll or a vacuum lamination device. In this case, the laminated film is arranged so that the precursor layer (S'a) is in contact with the woven fabric. In this way, a precursor film (reinforced precursor film) is obtained, which is laminated in the order of precursor layer (S'b), woven fabric, precursor layer (S'a), and precursor layer (C').

[0076] Furthermore, if there are two or more layers (Sa), a film made of a fluorine-containing polymer having a group that can be converted to a sulfonic acid type functional group may be obtained separately, and the layers (Sa) may be laminated between the woven fabric and the laminated film so that there are multiple layers.

[0077] (Contact with alkaline aqueous solution) Next, an example of a method for producing an ion exchange membrane using the above-mentioned precursor membrane (reinforced precursor membrane) is shown. The reinforced precursor membrane is brought into contact with an alkaline aqueous solution to convert the groups in the precursor layer (C') that can be converted to carboxylic acid-type functional groups, thereby forming a layer (C) having carboxylic acid-type functional groups, and convert the groups in the precursor layer (S') that can be converted to sulfonic acid-type functional groups, thereby forming a layer (S) having sulfonic acid-type functional groups, and thus obtaining an ion exchange membrane. At this time, at least a portion of the sacrificial threads contained in the reinforced precursor membrane are eluted by hydrolysis due to the action of the alkaline aqueous solution.

[0078] Upon contact with the alkaline aqueous solution, the precursor layer (C') is converted to layer (C) 12 shown in Figure 1, and the precursor layer (S') is converted to layer (S) 14 shown in Figure 1. Furthermore, as described above, if the precursor layer (S') has a precursor layer (S'a) and a precursor layer (S'b), the precursor layer (S'a) is converted to layer (Sa) 14A in Figure 1, and the precursor layer (S'b) is converted to layer (Sb) 14B in Figure 1.

[0079] Methods for bringing a precursor membrane (reinforced precursor membrane) into contact with an alkaline aqueous solution include immersing the precursor membrane in the alkaline aqueous solution and spraying the alkaline aqueous solution onto the surface of the precursor membrane. As described above, the amount of displacement in a specific operation of an ion exchange membrane can be adjusted by the hydrolysis conditions using the alkaline aqueous solution. The hydrolysis conditions can be adjusted by the temperature of the alkaline aqueous solution, the contact time between the precursor membrane and the alkaline aqueous solution, and the composition of the alkaline aqueous solution. When using an alkaline aqueous solution with a predetermined composition ratio and temperature, the contact time between the precursor membrane and the alkaline aqueous solution is preferably 1.1 to 3.0 times, and more preferably 1.1 to 2.0 times, the minimum hydrolysis time. The method for calculating the minimum hydrolysis time is as follows. First, an alkaline aqueous solution of a predetermined composition to be used for hydrolysis and a precursor membrane to be hydrolyzed are prepared. Next, the precursor membrane is immersed in the alkaline aqueous solution under predetermined hydrolysis conditions (temperature of the alkaline aqueous solution, etc.), washed with pure water, and dried. At this time, membranes are prepared with immersion times in the alkaline aqueous solution changed every minute. The obtained membranes are observed in cross-section using the following method. The observation method involves first cutting the ion exchange membrane in the thickness direction along thread A in the central part of the ion exchange membrane. More specifically, for example, as shown in Figure 2, the ion exchange membrane 1 is cut in the thickness direction along the line A-A' along thread A20C. This exposes the cross-section of the ion exchange membrane 1. In other words, the ion exchange membrane is cut in the thickness direction in a direction parallel to the direction in which thread A extends, and at the location where thread A is present. In the cross-section, a region X of a fluorine-containing polymer (X) having ion exchange groups and a region Y of a fluorine-containing polymer (Y) having groups that can be converted into ion exchange groups are observed. Twenty cross-sections are checked for each immersion time, and the time at which region Y is not observed in all cross-sections is defined as the minimum hydrolysis time. Note that cross-sectional observation with an optical microscope can be performed using the method described above for observing specific cross-sections with an optical microscope. By using the alkaline aqueous solution and hydrolysis conditions used to calculate the minimum hydrolysis time, and setting the time obtained by multiplying the minimum hydrolysis time by a predetermined factor as the contact time, an ion exchange membrane containing region Y can be manufactured.

[0080] The temperature of the alkaline aqueous solution is preferably 80°C or lower, and particularly preferably 70°C or lower. From the viewpoint of productivity, the lower limit of the alkaline aqueous solution temperature is preferably 15°C or higher, and particularly preferably 30°C or higher. The contact time between the alkaline aqueous solution and the precursor film is preferably 1000 minutes or less, and particularly preferably 100 minutes or less. From the viewpoint of good hydrolysis, the lower limit of the above contact time is preferably 5 minutes or more, and more preferably 10 minutes or more.

[0081] The alkaline aqueous solution preferably contains an alkali metal hydroxide, a water-soluble organic solvent, and water. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. In this specification, a water-soluble organic solvent means an organic solvent that dissolves readily in water, and specifically, an organic solvent with a solubility of 0.1 g or more in 1000 ml of water (20°C) is preferred, and an organic solvent with a solubility of 0.5 g or more is particularly preferred. The water-soluble organic solvent preferably contains at least one selected from the group consisting of aprotic organic solvents, alcohols, and amino alcohols, and is particularly preferred to contain an aprotic organic solvent. The water-soluble organic solvent may be used alone or in combination of two or more types.

[0082] Specific examples of aprotic organic solvents include dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), and N-ethyl-2-pyrrolidone, with dimethyl sulfoxide being preferred among these. 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.

[0083] The concentration of alkali metal hydroxide is preferably 1 to 60% by mass, more preferably 3 to 55% by mass, and particularly preferably 5 to 50% by mass, in the alkaline aqueous solution (100% by mass). The content of water-soluble organic solvent is preferably 1 to 60% by mass, more preferably 3 to 55% by mass, and particularly preferably 4 to 50% by mass, in the alkaline aqueous solution (100% by mass). The concentration of water is preferably 39 to 80% by mass, in the alkaline aqueous solution (100% by mass).

[0084] Groups that can be converted to carboxylic acid-type functional groups and groups that can be converted to sulfonic acid-type functional groups by contact with an alkaline aqueous solution are converted to carboxylic acid-type functional groups and sulfonic acid-type functional groups (hereinafter also referred to as "ion exchange groups"), respectively. After this conversion, salt exchange may be performed to exchange the counter cation of the ion exchange group as needed. In salt exchange, for example, the counter cation of the ion exchange group is exchanged from potassium to sodium. Known methods can be used for salt exchange.

[0085] After contact between the precursor film (reinforced precursor film) and the alkaline aqueous solution, a treatment to remove the alkaline aqueous solution may be performed. One method for removing the alkaline aqueous solution is to wash the precursor film that has been in contact with the alkaline aqueous solution with water.

[0086] Furthermore, if an inorganic particle layer is further present, the inorganic particle layer can be formed by applying a coating solution containing inorganic particles, a binder, and a dispersion medium to the surface of layer (C) or layer (S), or the precursor layer (C') or precursor layer (S'), and then removing the dispersion medium by heating or other means and drying. Alternatively, the inorganic particle layer can be formed by applying a paste-like coating solution containing inorganic particles, a binder, and a dispersion medium to a transfer substrate to form an inorganic particle layer, and then transferring this to the surface of layer (C) or layer (S), or the precursor layer (C') or precursor layer (S').

[0087] [Electrolytic Apparatus] The alkali chloride electrolytic apparatus of the present invention comprises an electrolytic cell having a cathode and an anode, and an ion exchange membrane for alkali chloride electrolysis, wherein the ion exchange membrane for alkali chloride electrolysis is arranged in the electrolytic cell so as to separate the cathode and the anode, with layer (C) of the ion exchange membrane for alkali chloride electrolysis being located on the cathode side and layer (S) of the ion exchange membrane for alkali chloride electrolysis being located on the anode side. According to the alkali chloride electrolytic apparatus of the present invention, since it has the above-described ion exchange membrane for alkali chloride electrolysis, alkali hydroxide with excellent caustic quality can be obtained.

[0088] One embodiment of the alkali chloride electrolytic apparatus of the present invention will be described using the schematic diagram in Figure 4 as an example. The alkali chloride electrolytic apparatus 100 includes an electrolytic cell 110 equipped with a cathode 112 and an anode 114, and an ion exchange membrane 1 installed inside the electrolytic cell 110 so as to divide the inside of the electrolytic cell 110 into a cathode chamber 116 on the cathode 112 side and an anode chamber 118 on the anode 114 side. As shown in Figure 1, the ion exchange membrane 1 has a layer (C) 12 and a layer (S) 14, and a woven fabric 18 arranged in layer (S). The ion exchange membrane 1 is installed inside the electrolytic cell 110 so that layer (C) 12 is on the cathode 112 side and layer (S) 14 is on the anode 114 side. The cathode 112 may be placed in contact with the ion exchange membrane 1, or it may be placed with a gap between it and the ion exchange membrane 1.

[0089] The material constituting the cathode chamber 116 is preferably resistant to alkali hydroxide and hydrogen, with stainless steel and nickel being specific examples. The material constituting the anode chamber 118 is preferably resistant to alkali chloride and chlorine, with titanium being a specific example.

[0090] The material constituting the cathode substrate is preferably stainless steel or nickel, from the viewpoint of resistance to alkali hydroxide and hydrogen, and processability. The surface of the cathode substrate is preferably coated with, for example, Raney nickel. The material constituting the anode substrate is preferably titanium, from the viewpoint of resistance to alkali chloride and chlorine, and processability. The surface of the anode substrate is preferably coated with, for example, ruthenium oxide or iridium oxide.

[0091] [Method for Producing Alkali Hydroxide] The method for producing alkali hydroxide of the present invention is carried out by electrolysis of alkali chloride using the alkali chloride electrolytic apparatus of the present invention. Known embodiments can be adopted, except that the method is carried out using the alkali chloride electrolytic apparatus of the present invention. For example, when producing an aqueous sodium hydroxide solution by electrolysis of an aqueous sodium chloride solution, the aqueous sodium chloride solution is supplied to the anode chamber 118 of the alkali chloride electrolytic apparatus 100, the aqueous sodium hydroxide solution is supplied to the cathode chamber 116, and the aqueous sodium chloride solution is electrolyzed while maintaining the concentration of the aqueous sodium hydroxide solution discharged from the cathode chamber 116 at a predetermined concentration (for example, 32% by mass).

[0092] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples. The amounts of each component in the table below are given on a mass basis. Examples 1 to 13 are examples, and Examples 14 to 19 are comparative examples.

[0093] [Layer Thickness] The thickness of each layer in the ion exchange membrane during drying was determined by observing the cross-section of the ion exchange membrane with an optical microscope after drying the membrane at 50°C for 16 hours, and then using image software (Pixs2000 PRO, Innotech). Here, the thickness of each layer is the thickness at a location where there are no reinforcing threads or sacrificial threads constituting the reinforcing material.

[0094] [Calculation of Ion Exchange Capacity] Approximately 0.5 mg of a fluorine-containing polymer having groups that can be converted into ion exchange groups was flat-pressed at a temperature approximately 10°C higher than its TQ value to obtain a film. The obtained film was analyzed using a transmission infrared spectrometer. The obtained spectrum CF ２ Peak, CH ３ Peak, OH peak, CF peak, SO ２The proportion of constituent units having groups that can be converted to carboxylic acid-type functional groups or sulfonic acid-type functional groups was calculated using the peak heights of each F peak. This proportion was defined as the proportion of constituent units having carboxylic acid-type or sulfonic acid-type functional groups in the fluorine-containing polymer obtained after hydrolysis, and the ion exchange capacity was determined using a calibration curve with samples whose ion exchange capacity was known. The above measurement is possible regardless of whether the ion exchange group is acid-type, potassium-type, or sodium-type.

[0095] [Measurement of current efficiency and variation in current efficiency] An ion exchange membrane was installed in the electrolytic cell so as to divide the cell into a cathode chamber on the cathode side and an anode chamber on the anode side, with layer (C) of the ion exchange membrane facing the cathode. The cathode side was pressurized so that the anode and the ion exchange membrane were in contact, and a 290 g / L sodium chloride aqueous solution and water were supplied to the anode chamber and cathode chamber, respectively, while maintaining the sodium chloride concentration discharged from the anode chamber at 200 g / L and the sodium hydroxide concentration discharged from the cathode chamber at 32 mass%, at a temperature of 90°C and a current density of 6 kA / m². ２ Electrolysis was performed for one week under the specified conditions, and the current efficiency (referred to as "current efficiency" in the table below) and electrolysis voltage (referred to as "electrolysis voltage" in the table below) were measured after one week. Furthermore, the variation in current efficiency (referred to as "variation" in the table below) was measured by taking the current efficiency of five ion exchange membranes manufactured under the same conditions, and twice the standard deviation of those values ​​was used as the variation value.

[0096] [Measurement of Caustic Alkali Quality] The caustic alkali quality was determined by the ratio of the mass of alkali chloride to the mass of alkali hydroxide in the alkali hydroxide aqueous solution obtained by electrolysis, using the method described below, and expressed in parts per million (unit: ppm) by the following formula. In the table described below, it will be written as "NaCl / NaOH". (Mass of alkali chloride in alkali hydroxide aqueous solution / Mass of alkali hydroxide in alkali hydroxide aqueous solution) × 1,000,000 To calculate the ratio of the mass of alkali chloride to the mass of alkali hydroxide in the alkali hydroxide aqueous solution (NaCl / NaOH), first, a 1,000 ppm chloride ion standard solution was diluted to prepare standard solutions of 0.005 to 0.5 ppm by mass. Next, these standard solutions were measured using an ion chromatograph, and a calibration curve was created from the peak area. Subsequently, the alkali hydroxide aqueous solution obtained by electrolysis, which was the measurement sample, was diluted 200-fold, and the resulting dilution was measured using an ion chromatograph. The chloride ion concentration was calculated from the calibration curve, and the NaCl / NaOH concentration in the alkali hydroxide aqueous solution before dilution was calculated. The measurement equipment and conditions are as follows: Measurement equipment: Dionex Integrion HPI system Column used: Dionex IonPac AS28-Fast-4μm IC column Column temperature: 35℃ Measurement time: 20 min Eluent: 40 mM KOH aqueous solution flow rate: 1.2 ml / min Sample injection volume: 100 μL Detector: Conductivity detector

[0097] [Example 1] As a fluorine-containing polymer to form the precursor layer (C'), TFE and a fluorine-containing monomer represented by the following formula (X) were copolymerized to synthesize a fluorine-containing polymer having a group that can be converted to a carboxylic acid-type functional group (ion exchange capacity after hydrolysis: 1.06 meq / g, hereinafter referred to as polymer C). CF ２ = CF - O - CF ２ CF ２ CF ２ - COOCH ３ ... (X)

[0098] As a fluorine-containing polymer to form the precursor layer (S'a), TFE and a fluorine-containing monomer represented by the following formula (Y) were copolymerized to synthesize a fluorine-containing polymer having a group that can be converted to a sulfonic acid type functional group (ion exchange capacity after hydrolysis: 1.1 meq / g, hereinafter referred to as polymer S1). CF ２ = CF - O - CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F ... (Y)

[0099] As a fluorine-containing polymer to form the precursor layer (S'b), TFE and a fluorine-containing monomer represented by formula (Y) were copolymerized to synthesize a fluorine-containing polymer having a group that can be converted to a sulfonic acid type functional group (ion exchange capacity after hydrolysis: 1.5 meq / g, hereinafter referred to as polymer S2).

[0100] Polymer C and polymer S1 were molded by melt co-extrusion to obtain a two-layer film A consisting of a precursor layer (C'1) made of polymer C (thickness: 12 μm) and a precursor layer (S'1) made of polymer S1 (thickness: 68 μm). Polymer S2 was molded by melt extrusion to obtain a film B consisting of a precursor layer (S'2) made of polymer S2 (thickness: 30 μm). After rapidly stretching a PTFE film, monofilaments obtained by slitting to a thickness of 100 denier were twisted at 2000 turns / m to produce PTFE yarn, which was used as reinforcing yarn. PET yarn consisting of a 30-denier multifilament made by drawing together six 5-denier PET filaments was used as sacrificial yarn. Reinforcement (density of reinforcing yarn: 27 threads / inch, density of sacrificial yarn: 54 threads / inch) was obtained by plain weaving so that one reinforcing yarn and two sacrificial yarns were arranged alternately.

[0101] Using the films A, B, and reinforcing cloth obtained above, an ion exchange membrane 1 corresponding to the embodiment shown in Figure 1 was manufactured as follows: Film B, reinforcing cloth, film A, and release PET film (thickness: 100 μm) were stacked in that order, with the precursor layer (C'1) of film A facing the release PET film, and laminated using a roll. The release PET film was peeled off to obtain a reinforced precursor membrane. The thicknesses of each layer in the reinforced precursor membrane were 12 μm for the precursor layer (C'), 68 μm for the precursor layer (S'a), and 30 μm for the precursor layer (S'b).

[0102] A paste consisting of 29.0% by mass of zirconium oxide (average particle size (D50: 1 μm)), 1.3% by mass of methylcellulose, 4.6% by mass of cyclohexanol, 1.5% by mass of cyclohexane, and 63.6% by mass of water was transferred to the upper side of the precursor layer (S'2) of the reinforced precursor film by roll pressing to form an inorganic particle layer. The amount of zirconium oxide attached was 20 g / m². ２ That's what I decided.

[0103] A reinforced precursor film with an inorganic particle layer formed on one side was immersed in an aqueous solution of 10% by mass dimethyl sulfoxide and 30% by mass potassium hydroxide at 60°C for 30 minutes. This resulted in the formation of the -COOCH of polymer C. ３ , as well as the -SO of polymer S1 and polymer S2 ２ F was hydrolyzed to convert it into an ion exchange group, and a film was obtained in which the precursor layer (C'1) became layer (C1), layer (S'1) became layer (S1), and layer (S'2) became layer (S2). In Figure 1, layer (C) 12 corresponds to layer (C1), layer (Sa) 14A corresponds to layer (S1), and layer (Sb) 14B corresponds to layer (S2).

[0104] A dispersion was prepared by dispersing zirconium oxide (average particle size: 1 μm) at a concentration of 13% by mass in an ethanol solution containing 2.5% by mass of the acidic polymer S1. This dispersion was sprayed onto the membrane layer (C1) to form an inorganic particle layer, thereby creating an ion exchange membrane. The amount of zirconium oxide deposited was 3 g / m². ２ That's what I decided.

[0105] [Examples 2-19] Ion exchange membranes were prepared in the same procedure as in Example 1, except that various conditions were changed to achieve the configuration shown in Table 1, which will be described later. However, in Example 13, a fluorine-containing monomer represented by the following formula (Z) was used instead of the fluorine-containing monomer represented by formula (Y).

[0106] Fluorine-containing monomers represented by formula (Z)

[0107]

[0108] Furthermore, the displacement (mm) of the ion exchange membranes obtained in Examples 1 to 19 was measured according to the method described above. The results are summarized in Table 1 below.

[0109] In Table 1, the "Layer (C)" column shows the composition of Layer (C), the "IEC" column represents the ion exchange capacity (milliequivalent / g dry resin) after hydrolysis of polymer C, and the "Thickness" column represents the thickness (μm) of Layer (C). In Table 1, the "Layer (Sa)" column shows the composition of Layer (Sa), the "IEC" column represents the ion exchange capacity (milliequivalent / g dry resin) after hydrolysis of polymer S1, and the "Thickness" column represents the thickness (μm) of Layer (Sa). In Table 1, the "Layer (Sb)" column shows the composition of Layer (Sb), the "IEC" column represents the ion exchange capacity (milliequivalent / g dry resin) after hydrolysis of polymer S2, and the "Thickness" column represents the thickness (μm) of Layer (Sb). In Table 1, the "DRY" column in the "Total Thickness" section represents the dry film thickness (μm) of the ion exchange membrane described above, the "WET" column represents the wet film thickness (μm) of the ion exchange membrane described above, and the "Ratio" column represents the ratio of the wet film thickness to the dry film thickness. In Table 1, the "Composition" column in the "Hydrolysis" section represents the concentration (mass%) of dimethyl sulfoxide and the concentration (mass%) of potassium hydroxide in the aqueous solution used for hydrolysis. For example, "10 / 30" represents an aqueous solution of 10 mass% dimethyl sulfoxide and 30 mass% potassium hydroxide. In Table 1, the "Temperature" column in the "Hydrolysis" section represents the temperature (°C) during hydrolysis, and the "Minutes" column represents the hydrolysis time (minutes). In Table 1, the "Ratio" column in the "Hydrolysis" section represents the ratio of the contact time between the precursor membrane and the alkaline aqueous solution when using the alkaline aqueous solution to the minimum hydrolysis time described above. The minimum hydrolysis time in each example is calculated using the method described above. In Table 1, the "Displacement (mm)" column represents the displacement (mm) of the ion exchange membrane described above.

[0110]

[0111] As shown in Table 1 above, the ion exchange membrane of the present invention was confirmed to exhibit the desired effect. Furthermore, it was confirmed that when the displacement is 11 to 16 mm, a smaller NaCl / NaOH ratio is obtained, resulting in a superior effect. In Examples 14 and 16, the displacement is large, and the variation in current efficiency is large. In Examples 15 and 17, the displacement is small, and the caustic quality of the alkali hydroxide aqueous solution is poor. In Example 18, the displacement is small, and the caustic quality of the alkali hydroxide aqueous solution is poor. In Example 19, the displacement is large, and the variation in current efficiency is large. The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2025-004876, filed on January 14, 2025, are incorporated herein by reference as disclosure of the present invention.

[0112] 1 Ion exchange membrane 10 First inorganic particle layer 12 Layer (C) 14 Layer (S) 14A Layer (Sa) 14B Layer (Sb) 16 Second inorganic particle layer 18 Woven fabric 20 Yarn A 22 Yarn B 100 Alkali chloride electrolytic apparatus 110 Electrolytic cell 112 Cathode 114 Anode 116 Cathode chamber 118 Anode chamber

Claims

1. An ion exchange membrane comprising: a layer (S) containing a fluorine-containing polymer having a sulfonic acid-type functional group; and a layer (C) containing a fluorine-containing polymer having a carboxylic acid-type functional group, wherein a woven fabric is disposed in the layer S, and the woven fabric is composed of yarn A extending in one direction and yarn B extending in a direction substantially perpendicular to yarn A, and the displacement of the ion exchange membrane is 10 to 20 mm when a pulling operation is performed for 10 minutes, repeatedly performing operation 1, in a direction at a 45-degree angle to the direction in which yarn A extends within the plane of the ion exchange membrane, with a tensile load of 10 N for 1 second and operation 2, in a tensile load of 0.1 N for 0.1 second, and the displacement of the ion exchange membrane is 10 to 20 mm, and the thickness of the ion exchange membrane after drying the ion exchange membrane at 50°C for 16 hours is defined as the DRY thickness, and the thickness of the ion exchange membrane after immersing the ion exchange membrane in pure water at 25°C for 16 hours is defined as the WET thickness, An ion exchange membrane in which the dry film thickness and the wet film thickness satisfy the relationship given by formula (Y). Formula (Y): 1.10 ≤ wet film thickness / dry film thickness ≤ 1.40 2. The ion exchange membrane according to claim 1, wherein the DRY film thickness is 60 to 150 μm.

3. The ion exchange membrane according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer having the sulfonic acid-type functional group is 0.5 to 2.5 milliequivalents / g dry resin.

4. The ion exchange membrane according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer having the carboxylic acid-type functional group is 0.5 to 2.0 milliequivalents / g dry resin.

5. The ion exchange membrane according to claim 1, wherein yarn A and yarn B are at least one selected from the group consisting of yarn made of polytetrafluoroethylene, yarn made of polyphenylene sulfide, yarn made of nylon, yarn made of polypropylene, and yarn made of polyethylene terephthalate.

6. The ion exchange membrane according to claim 1, further comprising an inorganic particle layer on the outermost surface of at least one of its faces.

7. An ion exchange membrane according to claim 1, used for electrolysis of an alkaline chloride aqueous solution.

8. The ion exchange membrane according to claim 1, wherein the layer (S) has a layer (Sa) located on the layer (C) side of the woven fabric and a layer (Sb) located on the opposite side from the layer (C) side, the thickness of the layer (C) is 1 to 50 μm, the thickness of the layer (Sa) is 30 to 140 μm, and the thickness of the layer (Sb) is 5 to 100 μm.

9. An alkali chloride electrolytic apparatus comprising an electrolytic cell having a cathode and an anode, and an ion exchange membrane according to any one of claims 1 to 8, wherein the ion exchange membrane is arranged in the electrolytic cell so as to separate the cathode and the anode, and the layer (C) is arranged on the cathode side and the layer (S) is arranged on the anode side.

10. A method for producing alkali hydroxide, comprising producing alkali hydroxide by electrolysis of alkali chloride using the alkali chloride electrolytic apparatus described in claim 9.

11. A method for producing an ion exchange membrane according to any one of claims 1 to 8, comprising: laminating a precursor layer (C') containing a fluorine-containing polymer (C') having a group that can be converted to a carboxylic acid-type functional group, and a precursor layer (S') containing a fluorine-containing polymer (S') having a group that can be converted to a sulfonic acid-type functional group, and forming a precursor membrane in which a woven fabric is disposed in the precursor layer (S'); then contacting the precursor membrane with an alkaline aqueous solution to convert the groups in the precursor layer (C') that can be converted to a carboxylic acid-type functional group to form a layer (C) having a carboxylic acid-type functional group, and converting the groups in the precursor layer (S') that can be converted to a sulfonic acid-type functional group to form a layer (S) having a sulfonic acid-type functional group, wherein the contact time between the precursor membrane and the alkaline aqueous solution is 1.1 to 3.0 times the minimum hydrolysis time, and the temperature of the alkaline aqueous solution is 80°C or lower.

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