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

Abstract

Provided are: an ion exchange membrane capable of lowering the electrolysis voltage during electrolysis of an alkali chloride and increasing current efficiency even under high temperature conditions; an alkali chloride electrolysis device including the ion exchange membrane; and a method for producing an alkali hydroxide.　An ion exchange membrane including a fluorine-containing polymer X having an ion exchange group, a fluorine-containing polymer Y having a group that can be converted into an ion exchange group, and a woven fabric, in which ion exchange membrane the woven fabric is composed of threads A extending in one direction and threads B extending in a direction substantially orthogonal to the threads A. When the ion exchange membrane is cut along the thickness direction, which is the direction parallel to the direction in which the threads A extend in the ion exchange membrane, and at a midpoint between threads A, a region X of the fluorine-containing polymer X and a region Y of the fluorine-containing polymer Y are observed in the cross-section. The average length of region Y in the direction orthogonal to the thickness direction of the ion exchange membrane is shorter than the average length of the threads B in the direction orthogonal to the thickness direction of the ion exchange membrane in the cross-section.

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] On the other hand, in recent years, there has been a demand for further performance improvements in ion exchange membranes, and a further reduction in electrolysis voltage. Furthermore, there has been a demand for further improvement in current efficiency under high-temperature conditions. Conventional ion exchange membranes, such as those described in Patent Document 1, could not achieve both of the above characteristics, and further improvements were needed.

[0005] The present invention aims to provide an ion exchange membrane that can lower the electrolysis voltage during the electrolysis of alkali chloride and achieve high current efficiency even under high-temperature conditions. Furthermore, the present invention aims to provide an alkali chloride electrolysis 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 fluorine-containing polymer X having ion exchange groups, a fluorine-containing polymer Y having groups that can be converted into ion exchange groups, and a woven fabric, wherein 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 in a cross-section obtained by cutting the ion exchange membrane in the thickness direction along yarn A, regions X of fluorine-containing polymer X and regions Y of fluorine-containing polymer Y are observed, and in the cross-section, the average length of region Y in the direction perpendicular to the thickness direction of the ion exchange membrane is shorter than the average length of yarn B in the direction perpendicular to the thickness direction of the ion exchange membrane. (2) The ion exchange membrane according to (1), wherein the ratio of the average length of region Y in the direction perpendicular to the thickness direction of the ion exchange membrane to the average length of yarn B in the direction perpendicular to the thickness direction of the ion exchange membrane is 0.950 or less. (3) The ion exchange membrane according to (2), wherein the above ratio is 0.010 or more. (4) The ion exchange membrane according to (2) or (3), wherein the above ratio is 0.030 or more and 0.900 or less. (5) The ion exchange membrane according to any one of (1) to (4), wherein the fluorine-containing polymer X having an ion exchange group comprises a fluorine-containing polymer having a sulfonic acid type functional group and a fluorine-containing polymer having a carboxylic acid type functional group. (6) The ion exchange membrane according to (5), 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 within layer (S), and layer (S) contains a fluorine-containing polymer Y having a group that can be converted to a sulfonic acid type functional group. (7) The ion exchange membrane according to (6), 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 20 to 140 μm, and the thickness of layer (Sb) is 5 to 100 μm. (8) The ion exchange membrane according to any one of (1) to (7), 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, and yarn made of polypropylene.(9) An ion exchange membrane according to any one of (1) to (8), further having an inorganic particle layer on the outermost surface of at least one of its faces. (10) An ion exchange membrane according to any one of (1) to (9) for use in the electrolysis of an aqueous solution of alkali chloride. (11) 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 (10), wherein the ion exchange membrane is arranged in the electrolytic cell so as to separate the cathode and the anode. (12) A method for producing alkali hydroxide by electrolysis of alkali chloride using the alkali chloride electrolytic apparatus according to (11). (13) A method for producing an ion exchange membrane according to any one of (1) to (10), 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 0.50 to 0.95 times the minimum hydrolysis time.

[0008] According to the present invention, an ion exchange membrane can be provided that allows for a lower electrolysis voltage during the electrolysis of alkali chloride and achieves high current efficiency even under high-temperature conditions. Furthermore, according to the present invention, an alkali chloride electrolysis 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 an enlarged schematic cross-sectional view of the ion exchange membrane to explain regions X and Y. 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 fluorine-containing polymer X having ion exchange groups (hereinafter also referred to as "fluorine-containing polymer (X)"), a fluorine-containing polymer Y having groups that can be converted into ion exchange groups (hereinafter also referred to as "fluorine-containing polymer (Y)"), and a woven fabric, wherein 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 in a cross-section (hereinafter also referred to as "specific cross-section") obtained by cutting the ion exchange membrane along the thickness direction in a direction parallel to the direction in which yarn A extends in the ion exchange membrane and at an intermediate point between the yarns A, a region X of the fluorine-containing polymer (X) and a region Y of the fluorine-containing polymer (Y) can be observed, and in the cross-section, the average length of the region Y in the direction perpendicular to the thickness direction of the ion exchange membrane is shorter than the average length of the yarn B in the direction perpendicular to the thickness direction of the ion exchange membrane.

[0013] The ion exchange membrane of the present invention allows for a lower electrolysis voltage during the electrolysis of alkali chloride and high current efficiency even under high-temperature conditions. The reason for this is thought to be as follows: The ion exchange membrane of the present invention includes a region Y of a fluorine-containing polymer (Y). Groups that can be converted into ion exchange groups in region Y have not been converted into ion exchange groups, and region Y corresponds to a so-called unhydrolyzed region. When such a region Y exists, it is presumed that the ion channel size tends to become a suitable size when the ion exchange membrane swells under high-temperature conditions, resulting in higher current efficiency. Furthermore, because the average length of region Y is shorter than the average length of thread B, the size of the unhydrolyzed region is limited, allowing for a lower electrolysis voltage.

[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 sequentially includes a first inorganic particle layer 10, a layer (C) (hereinafter also referred to as "layer (C)") 12 containing a fluorine-containing polymer having a carboxylic acid-type functional group (hereinafter also referred to as "fluorine-containing polymer (C)"), a layer (S) (hereinafter also referred to as "layer (S)") 14 containing a fluorine-containing polymer having a sulfonic acid-type functional group (hereinafter also referred to as "fluorine-containing polymer (S)"), and a second inorganic particle layer 16. Within layer (S) 14, a woven fabric 18 is arranged between layer (Sa) (hereinafter also referred to as "layer (Sa)") 14A containing fluorine-containing polymer (S) and layer (Sb) (hereinafter also referred to as "layer (Sb)") 14B containing fluorine-containing polymer (S). As described later, the layer (Sa) contains a fluorine-containing polymer (S) and a fluorine-containing polymer having a group that can be converted to a sulfonic acid type functional group corresponding to the fluorine-containing polymer (Y). The ion exchange membrane 1 is arranged in the electrolytic cell 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. Note that 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 A, which are threads 20A to 20E, extending in one direction (up and down direction on the paper), and threads B, which are threads 22A to 22E, extending in a direction approximately perpendicular to thread A (left and right direction on the paper). In Figure 2, there are five threads each of threads A and thread B, but the number is not limited to that shown in the figure.

[0016] In the ion exchange membrane of the present invention, regions X of fluorine-containing polymer (X) and regions Y of fluorine-containing polymer (Y) can be observed in the cross-section. The method for observing the cross-section will be described in detail below. As for the observation method, first, the ion exchange membrane is cut 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 as shown in Figure 3. 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 a position where thread A is present.

[0017] Figure 3 is an enlarged schematic cross-sectional view of the ion exchange membrane 1, and is a cross-sectional view near the intersection of thread A, thread 20C, and thread B, thread 22C. In Figure 3, the first inorganic particle layer 10 and the second inorganic particle layer 16 shown in Figure 1 are omitted. In Figure 3, layer (C) 12 and layer (S) 14 are stacked, and thread A, thread 20C, and thread B, thread 22C are arranged within layer (S) 14. Threads 20C and 22C are arranged between layer (Sa) 14A and layer (Sb) 14B. Layer (Sa) 14A includes a region 24 made of a fluorine-containing polymer (S) corresponding to fluorine-containing polymer (X), and a region Y 26 made of a fluorine-containing polymer having a group that can be converted to a sulfonic acid type functional group, corresponding to fluorine-containing polymer (Y). In other words, layer (Sa) 14A includes a region 24 corresponding to region X of the fluorine-containing polymer (X) and a region 26 corresponding to region Y of the fluorine-containing polymer (Y). Region X of the fluorine-containing polymer (X) is a region containing the fluorine-containing polymer (X), and region Y of the fluorine-containing polymer (Y) is a region containing the fluorine-containing polymer (Y). Region X does not contain the fluorine-containing polymer (Y), and region Y does not contain the fluorine-containing polymer (X). It is preferable that region Y is composed only of the fluorine-containing polymer (Y). As the fluorine-containing polymer having a group that can be converted to the sulfonic acid type functional group, the fluorine-containing polymer (S') described later is preferred. In the embodiment of Figure 3, layer (C) 12 is a layer made of the fluorine-containing polymer (C) corresponding to the fluorine-containing polymer (X), and layer (Sb) 14B is a layer made of the fluorine-containing polymer (S) corresponding to the fluorine-containing polymer (X), and neither contains the fluorine-containing polymer (Y). The ranges of region X and region Y can be determined by observing a cross-section of the ion exchange membrane 1 with an optical microscope (product name "BX-51", manufactured by Olympus Corporation).

[0018] As will be described in detail later, the size of region Y can be controlled by adjusting the conditions when the precursor film, 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 the woven fabric is placed in the precursor layer (S'), is brought into contact with an alkaline aqueous solution. When region Y is produced by this method, as shown in Figure 3, region 26, which is region Y, often occurs in a position that overlaps with the yarn 22C constituting the woven fabric 18 in the in-plane direction of the ion exchange membrane 1. In other words, when the ion exchange membrane 1 is observed from the thickness direction, at least a part of region 26 often overlaps with the yarn 22C constituting the woven fabric 18. In particular, when the ion exchange membrane 1 is observed from the thickness direction, at least a part of region 26 often overlaps with the overlapping portion of the yarn 20C and yarn 22C constituting the woven fabric 18. Furthermore, as shown in Figure 3, region 26 is often located between the surface of layer (C) 12 of the ion exchange membrane 1 and the thread 22C.

[0019] Next, the length L1 of the thread 22C in the cross-section perpendicular to the thickness direction of the ion exchange membrane 1 is measured. Also, the length L2 of the region 26 corresponding to region Y in the cross-section perpendicular to the thickness direction of the ion exchange membrane 1 is measured. The length L1 is the maximum length of the thread 22C in the direction perpendicular to the thickness direction of the ion exchange membrane 1. The length L2 is the maximum length of region 26 in the direction perpendicular to the thickness direction of the ion exchange membrane 1. The above cross-sectional observation is performed at 20 different locations, the length L1 at the 20 locations is determined, and these are arithmetic mean to obtain the average length of the thread. Similarly, the length L2 at the 20 locations is determined, and these are arithmetic mean to obtain the average length of region Y. If region Y does not exist, the length L2 is set to 0. In the ion exchange membrane of the present invention, the average length of region Y is shorter than the average length of the thread. In particular, in terms of achieving a better balance between the electrolysis voltage and current efficiency under high-temperature conditions during the electrolysis of alkali chloride, the ratio of the average length of region Y to the average length of the yarn (average length of region Y / average length of yarn) is preferably 0.950 or less, more preferably 0.900 or less, and even more preferably 0.250 or less. The lower limit of the above ratio is preferably 0.010 or more, more preferably 0.030 or more, even more preferably 0.035 or more, particularly preferably 0.050 or more, even more particularly preferably greater than 0.063, and most preferably 0.100 or more.

[0020] The average length of the above thread (thread B) is preferably 30 to 200 μm, and more preferably 50 to 150 μm, in that it provides a better balance between the electrolysis voltage and the current efficiency under high-temperature conditions during the electrolysis of alkali chloride. The average length of the above region Y is preferably 5 to 100 μm, and more preferably 10 to 80 μm, in that it provides a better balance between the electrolysis voltage and the current efficiency under high-temperature conditions during the electrolysis of alkali chloride.

[0021] In Figure 3, the shape of region 26 was triangular, but its shape is not particularly limited and may be elliptical or amorphous. In Figure 3, region 26 corresponding to region Y is contained only within layer (Sa) 14A, but the present invention is not limited to this embodiment. For example, region Y may be located only within layer (C) 12. In this case, region Y is composed of a fluorine-containing polymer having a group that can be converted to a carboxylic acid-type functional group.

[0022] One preferred embodiment of the ion exchange membrane of the present invention is, as described in Figures 1 to 3 above, an ion exchange membrane comprising a layer (S) containing a fluorine-containing polymer (S) and a layer (C) containing a fluorine-containing polymer (C), wherein a woven fabric is disposed within layer (S), and layer (S) preferably contains a fluorine-containing polymer (Y) having a group that can be converted into an ion exchange group, which is a fluorine-containing polymer having a group that can be converted into a sulfonic acid type functional group. As the fluorine-containing polymer having a group that can be converted into a sulfonic acid type functional group, the fluorine-containing polymer (S') described later is preferred. The layer (S) containing the fluorine-containing polymer (S) preferably has an ion exchange capacity of 1.1 meq / g or more after hydrolysis.

[0023] The following describes in detail each component that makes up the ion exchange membrane 1.

[0024] (Layer (C)) As described above, Layer (C) 12 is a layer made of a fluorine-containing polymer (C), but it may also contain materials other than the fluorine-containing polymer (C). However, from the viewpoint of electrolytic performance, a layer made only of the fluorine-containing polymer (C) and 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 made 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 also 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.

[0025] 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.

[0026] The ion exchange capacity of the fluorine-containing polymer (C) contained in layer (C) 12 is preferably 0.5 to 2.0 mEq / g, more preferably 0.8 to 2.0 mEq / g, and particularly preferably 0.85 to 1.10 mEq / g. If layer (C) 12 is formed from multiple layers, it is preferable that the ion exchange capacity of all fluorine-containing polymers (C) contained in 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.

[0027] The fluorine-containing polymer (C) is preferably obtained by converting groups that can be converted to carboxylic acid-type functional groups of the fluorine-containing polymer described later into carboxylic acid-type functional groups using a method for producing ion-exchange membranes. Specific examples of the fluorine-containing polymer (C) include a fluorine-containing polymer obtained by hydrolyzing a copolymer (hereinafter also referred to as "fluorine-containing polymer (C')") of a monomer having groups that can be converted to carboxylic acid-type functional groups and a fluorine atom (hereinafter also referred to as "fluorine-containing monomer (C')") and a fluorine-containing olefin, thereby converting groups that can be converted to carboxylic acid-type functional groups into carboxylic acid-type functional groups. As a polymer having groups that can be converted to carboxylic acid-type functional groups corresponding to the fluorine-containing polymer (Y), a polymer having constituent units based on the fluorine-containing monomer (C') is preferred, and the above-mentioned fluorine-containing polymer (C') is particularly preferred.

[0028] As the fluorine-containing monomer (C'), any compound having one or more fluorine atoms in the molecule, an ethylenic double bond, and a group convertible to a carboxylic acid type functional group can be used without particular limitation, and conventionally known compounds are used. The fluorine-containing monomer (C') is preferably a monomer represented by the following formula (1) in view of the monomer production cost, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer.

[0029] CF ２ =CF-(O) ｐ -(CF ２ ) ｑ -(CF ２ CFX) ｒ -(O) ｓ -(CF ２ ) ｔ -(CF ２ CFX') ｕ -A １ ・・・(1)

[0030] In formula (1), X and X' are each independently a fluorine atom or a trifluoromethyl group. A １ is a group convertible to a carboxylic acid type 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 [[ID=4)) and R ３ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.). 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. However, 1 ≤ p + s and 1 ≤ r + u.

[0031] Specific examples of the monomer represented by formula (1) include the following compounds. From the viewpoint of easy production, compounds with p = 1, q = 0, r = 1, s = 0 to 1, t = 0 to 3, and u = 0 to 1 are preferred. CF ２ =CF-O-CF ２ CF ２ \n-COOCH ３ 、 CF２ = 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 - COOCH ３ 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 types.

[0032] Examples of the fluorinated olefin include fluoroolefins having 2 to 3 carbon atoms and one or more fluorine atoms in the molecule. 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 resulting fluorinated polymer. The fluorinated olefin may be used alone or in combination of two or more kinds.

[0033] In the production of the fluorinated polymer (C'), in addition to the fluorinated monomer (C') and the fluorinated olefin, other monomers may be further used. Specific examples of the 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.

[0034] The ion exchange capacity of the fluorinated polymer (C) can be adjusted by changing the content of the structural unit derived from the fluorinated monomer (C') in the fluorinated polymer (C'). The content of the carboxylic acid type functional group in the fluorinated polymer (C) is preferably the same as the content of the group that can be converted into the carboxylic acid type functional group in the fluorinated polymer (C').

[0035] The range of the TQ value of the fluorinated polymer (C) is preferably 150 to 350 °C, more preferably 170 to 300 °C, and particularly preferably 200 to 250 °C from the viewpoints of the mechanical strength and film-forming property as an ion exchange membrane.

[0036] (Layer (S)) Layer (S) 14 can be any layer containing a fluorine-containing polymer (S), and as described above, layer (S) 14 contains a fluorine-containing polymer having a group that can be converted to a sulfonic acid type functional group corresponding to the fluorine-containing polymer (Y). As shown in Figure 1, layer (S) 14 contains a woven fabric 18 (described later) to increase the mechanical strength of the ion exchange membrane 1. Of layer (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 each be layers formed from multiple layers. If one or both of layer (Sa) 14A and layer (Sb) 14B are formed from multiple layers, each layer may have a different composition in terms of 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.

[0037] 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 35 to 200 μm, and particularly preferably 40 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.

[0038] The thickness of layer (Sa) 14A (or the total thickness if layer (Sa) 14A) is formed from multiple layers is preferably 20 to 140 μm, more preferably 30 to 140 μm, and particularly preferably 30 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.

[0039] The ion exchange capacity of the fluorine-containing polymer (S) contained in layer (Sa) 14A is preferably 0.6 to 2.5 mEq / g, and particularly preferably 0.9 to 1.5 mEq / g. If layer (Sa) 14A is formed from multiple layers, it is preferable that the ion exchange capacity of all the fluorine-containing polymer (S) contained in 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) contained in 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.

[0040] 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.

[0041] The ion exchange capacity of the fluorine-containing polymer (S) contained in layer (Sb) 14B is preferably 0.5 to 2.5 mEq / g, more preferably 0.6 to 2.5 mEq / g, and particularly preferably 0.9 to 2.0 mEq / g. If layer (Sb) 14B is formed from multiple layers, it is preferable that the ion exchange capacity of the fluorine-containing polymer (S) contained in at least the layer located closest to the anode is within the above range, and it is more preferable that the ion exchange capacity of all the fluorine-containing polymer (S) contained in 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) contained in this layer is within the above range. If the ion exchange capacity of the fluorine-containing polymer (S) contained in 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) contained in layer (Sb) 14B is below the above upper limit, the membrane strength can be maintained and membrane rupture during electrolytic operation or membrane mounting can be suppressed.

[0042] At least a portion of the fluorine-containing polymer having sulfonic acid-type functional groups in layer (Sb) 14B is preferably a polymer having a constituent unit based on monomers having two or more sulfonic acid-type functional groups, and particularly preferably a polymer having a constituent unit based on monomers having two sulfonic acid-type functional groups. This allows for an increase in the concentration of ion exchange groups per unit weight at the same monomer concentration, resulting in a layer (Sb) 14B with higher ion exchange capacity even with a smaller amount of monomer compared to a polymer having a constituent unit with only one sulfonic acid-type functional group.

[0043] 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).

[0044]

[0045] In formula (U1), R ｆ１This 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).

[0046]

[0047] 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.

[0048] Preferably, the fluorine-containing polymer (S) is obtained by converting the groups that can be converted to sulfonic acid-type functional groups of a fluorine-containing polymer having groups that can be converted to sulfonic acid-type functional groups, as described later, into sulfonic acid-type functional groups in the process of obtaining the ion exchange membrane described later. Specific examples of the fluorine-containing polymer (S) include a fluorine-containing polymer obtained by hydrolyzing a copolymer (hereinafter also referred to as "fluorine-containing polymer (S')") of a monomer having groups that can be converted to sulfonic acid-type functional groups and a fluorine atom (hereinafter also referred to as "fluorine-containing monomer (S')") and a fluorine-containing olefin, thereby converting the groups that can be converted to sulfonic acid-type functional groups into sulfonic acid-type functional groups. As a polymer having groups that can be converted to sulfonic acid-type functional groups corresponding to the fluorine-containing polymer (Y), a polymer having constituent units based on the fluorine-containing monomer (S') is preferred, and the above-mentioned fluorine-containing polymer (S') is particularly preferred.

[0049] As the fluorine-containing monomer (S'), any compound can be used without particular limitation as long as it has one or more fluorine atoms in the molecule, has an ethylenic double bond, and has a group that can be converted into a sulfonic acid-type functional group, and conventionally known compounds are used. As the fluorine-containing monomer (S'), a compound represented by the following formula (2) or a compound represented by the following formula (3) is preferable in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer.

[0050] 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 R ｆ１ in formula (U1). A ２ is a group that can be converted into a sulfonic acid-type functional group, and specific examples thereof include -SO ２ F, -SO ２ Cl, -SO ２ Br.

[0051] Specific examples of the compound represented by formula (2) include the following compounds. In the formula, w is an integer from 1 to 8, and x is an integer from 1 to 5. CF ２ =CF - O - (CF ２ ) ｗ -SO ２ F CF ２ =CF - O - CF[[ID=4​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​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.

[0053] 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 ２F, the fluorine-containing monomer (S'), may be used alone or in combination of two or more types.

[0054] 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.

[0055]

[0056] 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.

[0057] The compound represented by formula (m1) is preferably the compound represented by formula (m1-1).

[0058]

[0059] 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.

[0060] Specific examples of compounds represented by formula (m1-1) include the following:

[0061]

[0062] 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 contained in 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.

[0063] 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.

[0064] 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').

[0065] 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').

[0066] 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.

[0067] 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) contained in layer (Sa-1) 14Aa is lower than that of the fluorine-containing polymer (S) contained in layer (Sa-2) 14Ab, more preferably 0.01 to 0.5 mEq / g lower, and particularly preferably 0.03 to 0.4 mEq / g lower. The ion exchange capacity of layer (Sa-1) 14Aa is preferably 0.5 to 2.5 mEq / g, more preferably 0.6 to 2.5 mEq / g, and particularly preferably 0.9 to 1.2 mEq / g. 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.

[0068] (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, which is yarns 20A to 20E, and yarn B, which is yarns 22A to 22E, and yarns A and B are approximately perpendicular. Approximately perpendicular means that the angle between yarns A and B is 90 ± 10 degrees.

[0069] 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).

[0070] 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.

[0071] Threads A20 and B22 may consist of either a monofilament made of one filament or a multifilament made of two or more filaments, with monofilaments being preferred.

[0072] Yarns A and B are preferably selected from the group consisting of yarns made of polytetrafluoroethylene, polyphenylene sulfide, nylon, and polypropylene, in order to provide superior durability.

[0073] 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.

[0074] (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.

[0075] 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 ２ The 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.

[0076] 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.

[0077] 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.

[0078] [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.

[0079] (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').

[0080] 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.

[0081] (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.

[0082] 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.

[0083] Methods for bringing a precursor film (reinforced precursor film) into contact with an alkaline aqueous solution include immersing the precursor film in the alkaline aqueous solution and spraying the alkaline aqueous solution onto the surface of the precursor film. As described above, the size of region Y 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 film 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 film and the alkaline aqueous solution is preferably 0.50 to 0.95 times, and more preferably 0.50 to 0.90 times, the minimum hydrolysis time. By using the above conditions, region Y, which is the so-called unhydrolyzed region, can be included in the ion exchange membrane. 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 film to be hydrolyzed are prepared. Next, under predetermined hydrolysis conditions (temperature of the alkaline aqueous solution, etc.), the precursor film is immersed in the alkaline aqueous solution, washed with pure water, and dried. At this time, films are prepared with immersion times in the alkaline aqueous solution changed every minute. The obtained membrane is observed in cross-section using the following method. First, the ion exchange membrane is cut 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 as shown in Figure 3. That is, 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, regions X of fluorine-containing polymer (X) and Y of fluorine-containing polymer (Y) 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. Using the alkaline aqueous solution and hydrolysis conditions used to calculate the minimum hydrolysis time, an ion exchange membrane containing region Y can be manufactured by multiplying the minimum hydrolysis time by a predetermined factor and using that time as the contact time.

[0084] The temperature of the alkaline aqueous solution is preferably 90°C or lower, and particularly preferably 80°C or lower. From the viewpoint of productivity, the lower limit of the alkaline aqueous solution temperature is preferably 25°C or higher, and particularly preferably 35°C or higher. The contact time between the alkaline aqueous solution and the precursor film is preferably 80 minutes or less, and particularly preferably 60 minutes or less. From the viewpoint of good hydrolysis progression, the lower limit of the above contact time is preferably 3 minutes or more, and more preferably 4 minutes or more.

[0085] 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.

[0086] 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.

[0087] 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).

[0088] 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.

[0089] 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.

[0090] 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').

[0091] [Electrolytic Apparatus] The ion exchange membrane of the present invention can be suitably used for the electrolysis of an alkaline chloride aqueous solution. The alkaline chloride electrolytic apparatus of the present invention comprises an electrolytic cell having a cathode and an anode, and an ion exchange membrane, wherein the ion exchange membrane is arranged in the electrolytic cell so as to separate the cathode and the anode. In particular, when the ion exchange membrane includes the above layer (C) and the above layer (S), the above layer (C) of the ion exchange membrane is arranged on the cathode side, and the above layer (S) of the ion exchange membrane is arranged on the anode side.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] [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).

[0096] 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 12 are examples, and Examples 13 to 16 are comparative examples.

[0097] [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 90°C for 4 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.

[0098] [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.

[0099] [Method for measuring electrolytic voltage and method for measuring current efficiency under high temperature conditions] An ion exchange membrane is placed in a test electrolytic chamber having a rectangular electrolytic surface of 150 mm vertically x 100 mm horizontally, with layer (C) facing the cathode. Sodium hydroxide concentration in the cathode chamber: 32% by mass, sodium chloride concentration in the anode chamber: 200 g / L, temperature: 90°C, current density: 6 kA / m² ２ The electrolysis voltage (V) (referred to as "initial voltage" in the table below) and current efficiency (%) (referred to as "initial CE" in the table below) were measured after electrolysis of an aqueous sodium chloride solution under the specified conditions for three days. Subsequently, the current efficiency (%) (referred to as "high temperature resistance" in the table below) was measured after further operation for seven days at a temperature of 100°C (corresponding to high temperature conditions).

[0100] [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)

[0101] 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)

[0102] 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).

[0103] 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.

[0104] 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).

[0105] 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.

[0106] 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 17 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).

[0107] 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.

[0108] [Examples 2-16] Ion exchange membranes were fabricated following 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. In Examples 11 and 12, unlike the other embodiments, a reinforcing fabric composed of threads A and B with flattened cross-sectional shapes was used.

[0109] In the ion exchange membranes of Examples 1 to 12, region Y was observed in the cross-section of the ion exchange membrane as observed by the method described above. More specifically, as shown in Figure 3, region Y was observed between the surface of layer (C) of the ion exchange membrane and thread B, and when the ion exchange membrane was observed from the thickness direction, a part of region Y overlapped with the part where threads A and B overlapped.

[0110] In Table 1, the "Layer (C)" column shows the composition of Layer (C), the "IEC" column represents the ion exchange capacity (meq / g) 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 (meq / g) 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 (meq / g) after hydrolysis of polymer S2, and the "Thickness" column represents the thickness (μm) of Layer (Sb). In Table 1, the "Reinforcement Fabric" column shows the composition of the reinforcement fabric, "De(A)" represents the denier number of the monofilament PTFE yarn constituting yarn A of the reinforcement fabric, and "De(B)" represents the denier number of the monofilament PTFE yarn constituting yarn B of the reinforcement fabric. In Table 1, the "Composition" column in the "Hydrolysis" column shows 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" column shows the temperature (°C) during hydrolysis, and the "Minutes" column shows the hydrolysis time (minutes). In Table 1, the "Ratio" column in the "Hydrolysis" column shows the ratio of the contact time between the precursor film and the alkaline aqueous solution when using an 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 "Average Length of Thread B" column represents the average length (μm) of thread B in the direction perpendicular to the thickness direction of the ion exchange membrane in the specific cross-section described above. In Table 1, the "Average Length of Region Y" column represents the average length (μm) of region Y in the direction perpendicular to the thickness direction of the ion exchange membrane in the specific cross-section described above. In Table 1, the "Average Length of Region Y / Average Length of Thread B" column represents the ratio of the average length (μm) of region Y to the average length (μm) of thread B. The average length of thread B and the average length of region Y are measured using the method described above.

[0111]

[0112] As shown in Table 1 above, in Examples 1 to 12, which are embodiments, the electrolysis voltage was low (low initial voltage in Table 1) and the current efficiency was high even under high temperature conditions (high high temperature resistance in Table 1), demonstrating excellent effects. In particular, a comparison of Examples 1 to 12 showed that when the "average length of region Y / average length of thread B" was greater than 0.063 and less than or equal to 0.250, a better balance of electrolysis voltage and current efficiency was observed. Furthermore, in Examples 13 and 14, the average length of thread B was shorter than the average length of region Y, and in such cases, the electrolysis voltage was high. Also, in Examples 15 and 16, region Y was absent, and in such cases, the high temperature resistance was poor. The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2025-004928, filed on January 14, 2025, are incorporated herein by reference as disclosure of the present invention.

[0113] 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 20A, 20B, 20C, 20D, 20E Yarn that is yarn A 22A, 22B, 22C, 22D, 22E Yarn that is 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 fluorine-containing polymer X having ion exchange groups, a fluorine-containing polymer Y having groups that can be converted into ion exchange groups, and a woven fabric, wherein 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 in a cross-section obtained by cutting the ion exchange membrane in the thickness direction along yarn A, a region X of the fluorine-containing polymer X and a region Y of the fluorine-containing polymer Y are observed, and in the cross-section, the average length of the region Y in the direction perpendicular to the thickness direction of the ion exchange membrane is shorter than the average length of the yarn B in the direction perpendicular to the thickness direction of the ion exchange membrane.

2. The ion exchange membrane according to claim 1, wherein the ratio of the average length of the region Y in a direction perpendicular to the thickness direction of the ion exchange membrane to the average length of the thread B in a direction perpendicular to the thickness direction of the ion exchange membrane is 0.950 or less.

3. The ion exchange membrane according to claim 2, wherein the ratio is 0.010 or greater.

4. The ion exchange membrane according to claim 2, wherein the ratio is 0.030 or more and 0.900 or less.

5. The ion exchange membrane according to claim 1, wherein the fluorine-containing polymer X having an ion exchange group comprises a fluorine-containing polymer having a sulfonic acid-type functional group and a fluorine-containing polymer having a carboxylic acid-type functional group.

6. The ion exchange membrane according to claim 5, wherein the ion exchange membrane comprises 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, the woven fabric is disposed within the layer (S), and the layer (S) contains a fluorine-containing polymer Y having a group that can be converted to a sulfonic acid-type functional group.

7. The ion exchange membrane according to claim 6, 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 20 to 140 μm, and the thickness of the layer (Sb) is 5 to 100 μm.

8. 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.

9. 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.

10. An ion exchange membrane according to claim 1, for use in the electrolysis of an alkaline chloride aqueous solution.

11. 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 10, wherein the ion exchange membrane is arranged in the electrolytic cell such that it separates the cathode and the anode.

12. A method for producing alkali hydroxide, comprising producing alkali hydroxide by electrolysis of alkali chloride using the alkali chloride electrolytic apparatus described in claim 11.

13. A method for producing an ion exchange membrane according to any one of claims 1 to 10, 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 0.50 to 0.95 times the minimum hydrolysis time.

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