Method for producing film containing fluorine-containing polymer

Abstract

Provided is a method for producing a film containing a fluorine-containing polymer, the method being able to produce a film containing a fluorine-containing polymer in which damage is unlikely to occur on a surface of a catalyst layer when the catalyst layer is formed on a surface of the film.　The method for producing a film containing a fluorine-containing polymer, in which a first film containing a fluorine-containing polymer having a group able to be converted into an ion exchange group, a reinforcing material and a second film containing said fluorine-containing polymer are hot pressed by being passed between a pair of rollers to obtain a precursor film, and the group able to be converted into an ion exchange group in the precursor film is hydrolyzed to produce a film containing a fluorine-containing polymer having an ion exchange group. The pair of rollers comprises a first roller that is in contact with the first film and a second roller that is in contact with the second film. The difference between the temperature of the first roller and the temperature of the second roller is 70°C or less. In the hot pressing, a first contact period between the first roller and the first film and a second contact period between the second roller and the second film are both longer than 1 second.

Description

Method for producing a membrane containing a fluoropolymer

[0001] The present disclosure relates to a method for producing a membrane containing a fluoropolymer, and more specifically to a method for producing a membrane containing a fluoropolymer having ion exchange groups.

[0002] Membranes containing fluorine-containing polymers having ion exchange groups have ion exchange ability and exhibit ion conductivity, and are therefore used in a variety of applications. For example, membranes containing fluorine-containing polymers having ion exchange groups are used as electrolyte membranes for polymer electrolyte fuel cells, electrolyte membranes for polymer electrolyte water electrolysis devices, and diaphragms for various electrolysis devices. Such membranes are sometimes reinforced with a reinforcing material to improve their mechanical strength. For example, Patent Document 1 discloses an electrolyte membrane reinforced with a reinforcing material having a predetermined storage modulus.

[0003] International Publication No. 2010 / 098398

[0004] When a membrane containing a fluoropolymer is used for the above-mentioned purposes, a catalyst layer is often formed on at least one side of the membrane containing a fluoropolymer. As a method for forming a catalyst layer, various methods have been studied, and a method in which a composition for forming a catalyst layer is directly applied to a membrane containing a fluoropolymer has been studied because it can be easily formed.

[0005] The present inventors have investigated a method of directly applying a composition for forming a catalyst layer to a membrane containing a fluoropolymer, and have found that scratches may occur on the surface of the catalyst layer that is formed. Since it is desirable that the catalyst layer be formed uniformly, it was necessary to prevent scratches from occurring on the surface of the catalyst layer.

[0006] The present disclosure has been made in view of the above-mentioned circumstances, and an object of one embodiment of the present invention is to provide a method for producing a membrane containing a fluoropolymer, which can produce a membrane containing a fluoropolymer in which scratches are less likely to occur on the surface of a catalyst layer when a catalyst layer is formed on the surface of the membrane.

[0007] The present disclosure includes the following aspects: [1] A method for producing a membrane containing a fluoropolymer, comprising: hot-pressing a first film containing a fluoropolymer having groups convertible to ion-exchange groups, a reinforcing material, and a second film containing a fluoropolymer having groups convertible to ion-exchange groups between a pair of rolls to obtain a precursor membrane containing a fluoropolymer having groups convertible to ion-exchange groups, and hydrolyzing the groups convertible to ion-exchange groups in the precursor membrane to produce a membrane containing a fluoropolymer having ion-exchange groups, wherein the pair of rolls comprises a first roll in contact with the first film and a second roll in contact with the second film, the temperature difference between the first roll and the second roll is 70°C or less, and during the hot pressing, a first contact time between the first roll and the first film and a second contact time between the second roll and the second film are each longer than 1 second. [2] The method for producing a membrane comprising a fluoropolymer according to [1], further comprising: a first substrate disposed on the side of the first film opposite to the reinforcing material side; a second substrate disposed on the side of the second film opposite to the reinforcing material side; and the temperature difference is 1 to 65° C. [3] The method for producing a membrane comprising a fluoropolymer according to [1] or [2], further comprising: a first substrate disposed on the side of the first film opposite to the reinforcing material side; and a second substrate disposed on the side of the second film opposite to the reinforcing material side; and the temperature difference is 5 to 40° C.

[0008] [4] A method for producing a membrane comprising a fluoropolymer according to [2] or [3], wherein the first substrate and the second substrate are peeled off after the heat pressing and before the hydrolysis. [5] A method for producing a membrane comprising a fluoropolymer according to any one of [1] to [4], wherein the first contact time and the second contact time are each 7 seconds or longer. [6] A method for producing a membrane comprising a fluoropolymer according to any one of [1] to [5], wherein the first roll is a metal roll and the second roll is a rubber roll. [7] A method for producing a membrane comprising a fluoropolymer according to any one of [1] to [6], wherein the fluoropolymer having ion exchange groups has an ion exchange capacity of 0.90 to 2.00 milliequivalents / gram dry resin. [8] A method for producing a membrane comprising a fluoropolymer according to any one of [1] to [7], wherein the fluoropolymer having ion exchange groups contains units based on a fluorine-containing olefin and units having a sulfonic acid type functional group and a fluorine atom. [9] A method for producing a membrane containing a fluoropolymer according to [8], wherein the fluorine-containing olefin is a fluoroolefin having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule.

[10] A method for producing a membrane containing a fluoropolymer according to [8] or [9], wherein the unit having a sulfonic acid type functional group and a fluorine atom is a unit represented by formula (1): Formula (1) -[CF ２ -CF(-L-(SO ３ M) ｎ ) )]- L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom, M is a hydrogen atom, an alkali metal or a quaternary ammonium cation, and n is 1 or 2.

[11] A method for producing a membrane comprising a fluoropolymer according to any one of [1] to

[10] , wherein the reinforcing material is a woven fabric.

[12] A method for producing a membrane comprising a fluoropolymer according to any one of [1] to

[11] , wherein the first film and the second film each have a thickness of 15 to 250 μm.

[13] A method for producing a membrane comprising a fluoropolymer according to any one of [1] to

[12] , wherein the temperature of the second roll is higher than the temperature of the first roll.

[0009] According to one embodiment of the present invention, there can be provided a method for producing a membrane containing a fluoropolymer, which can produce a membrane containing a fluoropolymer in which the surface of a catalyst layer is less likely to be damaged when a catalyst layer is formed on the surface.

[0010] FIG. 2 is a cross-sectional view showing a process for obtaining a precursor film by hot pressing.

[0011] The definitions of the following terms apply throughout the present specification and claims unless otherwise specified. An "ion exchange group" is a group that can exchange at least a portion of the ions contained in this group with other ions, and examples thereof include the sulfonic acid functional group and carboxylic acid functional group shown below. A "sulfonic acid functional group" is a sulfonic acid group (-SO ３ H), or sulfonate group (—SO ３ M ２ However, M ２ is an alkali metal or quaternary ammonium cation. The term "carboxylic acid type functional group" refers to a carboxylic acid group (-COOH) or a carboxylic acid salt group (-COOM). １ However, M １ is an alkali metal or a quaternary ammonium cation.) A "precursor membrane" is a membrane containing a polymer having a group that can be converted into an ion exchange group. A "group that can be converted into an ion exchange group" means a group that can be converted into an ion exchange group by treatment such as hydrolysis or acidification. A "group that can be converted into a sulfonic acid functional group" means a group that can be converted into a sulfonic acid functional group by treatment such as hydrolysis or acidification. A "group that can be converted into a carboxylic acid functional group" means a group that can be converted into a carboxylic acid functional group by known treatment such as hydrolysis or acidification.

[0012] The term "unit" in a polymer refers to an atomic group derived from one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or may be an atomic group in which a part of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction.

[0013] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0014] <Method for producing a membrane containing a fluoropolymer> In the method for producing a membrane containing a fluoropolymer of the present disclosure (hereinafter also referred to as the "production method of the present disclosure"), first, a first film containing a fluoropolymer having groups convertible to ion exchange groups (hereinafter also referred to as "fluoropolymer (I')"), a reinforcing material, and a second film containing the fluoropolymer (I') are hot-pressed through a pair of rolls to obtain a precursor membrane containing the fluoropolymer (I'). Next, the groups convertible to ion exchange groups in the obtained precursor membrane are hydrolyzed to produce a membrane containing a fluoropolymer having ion exchange groups (hereinafter also referred to as "fluoropolymer (I)"). Here, the pair of rolls consists of a first roll in contact with the first film and a second roll in contact with the second film, and the temperature difference between the first roll and the second roll is 70°C or less. Furthermore, the first contact time between the first roll and the first film and the second contact time between the second roll and the second film in the hot press are each longer than 1 second.

[0015] When the temperature difference and conveying speed are adjusted within the above ranges, the mechanism by which scratches are less likely to occur on the surface of the resulting membrane containing fluoropolymer (I) when a catalyst layer is formed on the surface of the membrane is not necessarily clear, but the present inventors speculate as follows. The present inventors have investigated the mechanism by which scratches occur on the surface of the catalyst layer and found that when a catalyst layer-forming composition is applied to a membrane containing fluoropolymer (I), the edge of the membrane containing fluoropolymer (I) curls toward the catalyst layer. When curling occurs, the catalyst layer comes into contact with the edge of the membrane, making it easy for scratches to occur on the surface of the catalyst layer. The present inventors have investigated in detail the cause of curling and found that curling can be suppressed by setting the temperature difference between the contacting rolls to a predetermined value or less during the production of the precursor membrane.

[0016] That is, when the temperature difference is equal to or less than a predetermined value, when the first film, the reinforcing material, and the second film are heat-pressed to obtain a precursor membrane, the surface temperature of the precursor membrane on the first film side and the surface temperature of the precursor membrane on the second film side tend to be close. When the surface temperature of the precursor membrane on the first film side and the surface temperature of the precursor membrane on the second film side are close to each other during the production of the precursor membrane, a difference in thermal stress is unlikely to occur. The obtained precursor membrane is subjected to a hydrolysis treatment to obtain a membrane containing the fluoropolymer (I). However, since the hydrolysis treatment involves swelling of the fluoropolymer (I'), the difference in thermal stress is likely to be amplified. Furthermore, when a catalyst layer is formed on the surface of the obtained membrane containing the fluoropolymer (I), the catalyst layer-forming composition is directly applied, and the solvent component contained in the catalyst layer-forming composition penetrates into the membrane containing the fluoropolymer (I), causing swelling of the membrane. Therefore, the difference in thermal stress is likely to be amplified. Therefore, when the temperature difference between the rolls exceeds the predetermined value, it is thought that the difference in thermal stress is likely to be amplified by the above operation, making curling more likely. Therefore, in order to suppress the occurrence of curl, it is considered necessary to reduce the difference in thermal stress caused by the temperature difference between the rolls.

[0017] On the other hand, when the first contact time and the second contact time are less than the predetermined values, the heating time of the first film by the first roll and the heating time of the second film by the second roll are short, which means that the influence of the temperature difference between the rolls is likely to be large and a difference in thermal stress is likely to occur, which is likely to cause curling and, as a result, scratches on the surface of the catalyst layer.

[0018] The heat pressing and hydrolysis treatment carried out in the production method of the present disclosure will be described below. Note that hereinafter, when forming a catalyst layer on the surface of a membrane containing the fluoropolymer (I), the fact that scratches are unlikely to occur on the surface of the catalyst layer will also be simply referred to as "scratches are unlikely to occur on the surface of the catalyst layer."

[0019] [Heat Pressing] In the production method of the present disclosure, first, a first film containing a fluoropolymer (fluoropolymer (I')) having groups convertible to ion-exchange groups, a reinforcing material, and a second film containing the fluoropolymer (I') are heat-pressed through a pair of rolls (first roll and second roll) to obtain a precursor film containing the fluoropolymer (I'). Here, as described above, the temperature difference between the first roll and the second roll is 70°C or less. Furthermore, in the heat press, the first contact time between the first roll and the first film and the contact time between the second roll and the second film each exceed 1 second. The above heat press will be described with reference to the drawings. FIG. 1 is a cross-sectional schematic diagram when a precursor film is obtained by heat pressing. In FIG. 1, a first film 12, a reinforcing material 16, and a second film 14 are transported between a first roll 22 and a second roll 24 so as to be overlapped in this order. The transported first film 12, reinforcing material 16, and second film 14 are heat-pressed by the first roll 22 and the second roll 24, and the components of the first film 12 and the second film 14 penetrate into the reinforcing material 16, forming a precursor film 18. At this time, the temperature difference between the first roll 22 and the second roll 24 is within the above-mentioned range. Furthermore, when being heat-pressed, the first film 12 is wrapped around the first roll 22 at an embrace angle θ １In this specification, the first contact time refers to the time during which the first film 12 is in contact with the first roll 22. Similarly, the second film 14 is heated while being in contact with the second roll 24 at a wrap angle θ ２ In this specification, the second contact time refers to the contact time between the second film 14 and the second roll 24. As described above, in the heat press, the first contact time is longer than 1 second, and the second contact time is longer than 1 second.

[0020] The first contact time is, for example, the wrap angle θ between the first film 12 and the first roll 22. １ and the diameter R of the first roll 22 １ Specifically, the conveying speed of the first film 12, the reinforcing material 16, and the second film 14 is V １ Then, the first contact time t １ It is possible to obtain t １ The unit of is seconds, and R １ The unit of is m, and θ １ The unit of is °, and V １ The unit of is m / sec. １ = (π R １ ・θ １ / 360) / V １ The second contact time can be calculated in the same manner. Specifically, the wrap angle between the second film 14 and the second roll 24 is θ ２ and the diameter of the second roll 24 is R ２ and the conveying speed is V １ Then, the second contact time t ２ is calculated by the following formula: ２ The unit of is seconds, and R ２ The unit of is m, and θ ２ The unit of is °, and V １ The unit of is m / sec. ２ = (π R ２ ・θ ２ / 360) / V １

[0021] The temperature difference between the first roll and the second roll refers to the value obtained by subtracting the lower temperature of the first roll and the second roll from the higher temperature, and is a value of 0°C or higher. The temperatures of the first roll and the second roll refer to the surface temperatures of the roll surfaces of the first roll and the second roll that are in contact with the first film and the second film. The surface temperatures are measured by pressing a contact sensor against the area of ​​the roll surfaces of the first roll and the second roll that are in contact with the film and that are not in contact with the film. Examples of the contact sensor include portable thermometer sensors ST-41, ST-44, ST-36, and ST-37 manufactured by Rika Kogyo Co., Ltd. The temperature difference between the temperature of the first roll and the second roll is preferably 1°C or higher, more preferably 5°C or higher, even more preferably 7°C or higher, and particularly preferably 10°C or higher. In order to prevent scratches on the surface of the catalyst layer, the temperature difference is preferably 65°C or lower, more preferably 50°C or lower, even more preferably 40°C or lower, particularly preferably 30°C or lower, and most preferably 15°C or lower.

[0022] As described above, the first contact time between the first roll and the first film is longer than 1 second, but is preferably 3 seconds or longer, more preferably 5 seconds or longer, and even more preferably 7 seconds or longer, from the viewpoint of preventing scratches on the surface of the catalyst layer. From the viewpoint of more uniform lamination, the first contact time is preferably 60 seconds or shorter, more preferably 50 seconds or shorter, even more preferably 40 seconds or shorter, and particularly preferably 20 seconds or shorter. Furthermore, the second contact time between the second roll and the second film is longer than 1 second, but is preferably 3 seconds or longer, more preferably 5 seconds or longer, and even more preferably 7 seconds or longer, from the viewpoint of preventing scratches on the surface of the catalyst layer. From the viewpoint of more uniform lamination, the second contact time is preferably 60 seconds or shorter, more preferably 50 seconds or shorter, even more preferably 40 seconds or shorter, and particularly preferably 20 seconds or shorter. The first contact time and the second contact time may be different, but are preferably the same.

[0023] The first contact time and the second contact time can be adjusted by the conveying speed, the wrap angle, the diameter of the roll, and the like.

[0024] The conveying speed refers to the distance (m) that a point on the film moves per second when the film-like object is conveyed in the longitudinal direction of the film. The conveying speed of the first film, the reinforcing material, and the second film is, for example, preferably 0.0167 m / s or less, more preferably 0.0116 m / s or less, and even more preferably 0.0083 m / s or less. The conveying speed of the first film, the reinforcing material, and the second film is preferably 0.0002 m / s or more, more preferably 0.0012 m / s or more, and even more preferably 0.0033 m / s or more.

[0025] The linear pressure during the heat pressing is preferably 50 N / cm or more, more preferably 100 N / cm or more, and even more preferably 150 N / cm or more, and is preferably 500 N / cm or less, more preferably 400 N / cm or less, and even more preferably 300 N / cm or less.

[0026] The first film, the reinforcing material, and the second film to be subjected to the heat press will be described below, followed by a description of the first roll and the second roll.

[0027] (First film and second film) The first film and the second film contain a fluoropolymer (I'). As the fluoropolymer (I'), a polymer (hereinafter also referred to as "fluoropolymer (S')") of a fluoromonomer having a group that can be converted into a sulfonic acid type functional group (hereinafter also referred to as "fluoromonomer (S')") is preferred, and a copolymer of a fluorine-containing olefin and a monomer having a fluorine atom and a group that can be converted into a sulfonic acid type functional group is particularly preferred. The fluoropolymer (S') will be described in detail below.

[0028] As the method for copolymerizing the fluoropolymer (S'), known methods such as solution polymerization, suspension polymerization and emulsion polymerization can be adopted.

[0029] Examples of the fluorine-containing olefin include those exemplified above, and TFE is preferred from the viewpoints of the production cost of the monomer, the reactivity with other monomers, and the excellent properties of the resulting fluorine-containing polymer (S). One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0030] The fluorine-containing monomer (S') may be a compound having one or more fluorine atoms in the molecule, an ethylenic double bond, and a group that can be converted into a sulfonic acid functional group. As the fluorine-containing monomer (S'), a compound represented by formula (2) is preferred in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer (S). Formula (2) CF ２ =CF-L-(A) ｎ L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom. The etheric oxygen atom may be located at a terminal of the perfluorohydrocarbon group or between carbon atoms. The (n+1)-valent perfluorohydrocarbon group preferably has 1 or more carbon atoms, more preferably 2 or more carbon atoms, and preferably 20 or less, and more preferably 10 or less carbon atoms.

[0031] L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, and particularly preferably a divalent perfluoroalkylene group which may contain an etheric oxygen atom, where n = 1, or a trivalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, where n = 2. The divalent perfluoroalkylene group may be either linear or branched.

[0032] n is 1 or 2.

[0033] A is a group that can be converted into a sulfonic acid functional group. The group that can be converted into a sulfonic acid functional group is preferably a functional group that can be converted into a sulfonic acid functional group by hydrolysis. Specific examples of groups that can be converted into a sulfonic acid functional group include -SO ２ F, -SO ２ Cl, —SO ２Br. A plurality of A's may be the same or different.

[0034] The compound represented by formula (2) is preferably a compound represented by formula (2-1), a compound represented by formula (2-2), a compound represented by formula (2-3), or a compound represented by formula (2-4). ２ =CF-O-R ｆ１ -A Formula (2-2) CF ２ =CF-R ｆ１ -A

[0035]

[0036]

[0037] R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less.

[0038] R ｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less.

[0039] R ｆ３ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less.

[0040] r is 0 or 1. m is 0 or 1. A is as defined above.

[0041] The compound represented by formula (2-1) is preferably a compound represented by formula (2-5): Formula (2-5) CF ２ =CF-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF２ ) ｚ -SO ２ F x is 0 or 1, y is an integer from 0 to 2, z is an integer from 1 to 4, and Y is F or CF ３ is.

[0042] Specific examples of the compound represented by formula (2-1) include the following compounds. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. CF ２ =CF-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-[O-CF ２ CF (CF ３ )] ｘ -SO ２ F

[0043] Specific examples of the compound represented by formula (2-2) include the following compounds: In the formula, w is an integer of 1 to 8. CF ２ =CF-(CF ２ ) ｗ -SO ２ FCF ２ =CF-CF ２ -O-(CF ２ ) ｗ -SO ２ F

[0044] The compound represented by formula (2-3) is preferably a compound represented by formula (2-3-1).

[0045]

[0046] R in the formula ｆ４ , R ｆ５ , r and A are as defined above.

[0047] Specific examples of the compound represented by formula (2-3-1) include the following.

[0048]

[0049] The compound represented by formula (2-4) is preferably a compound represented by formula (2-4-1).

[0050]

[0051] R in the formula ｆ１ , R ｆ２ and A are defined as above.

[0052] Specific examples of the compound represented by formula (2-4-1) include the following.

[0053]

[0054] The fluorine-containing monomer (S') may be used alone or in combination of two or more. In the production of the fluorine-containing polymer (S'), other monomers may be used in addition to the fluorine-containing olefin and the fluorine-containing monomer (S'). Examples of other monomers include those exemplified above.

[0055] The ion exchange capacity of the fluoropolymer (I') can be adjusted by changing the content of groups convertible to ion exchange groups in the fluoropolymer (I'). The first film and the second film may contain different types of fluoropolymers (I'), but preferably contain the same type of fluoropolymer (I'). The content of the fluoropolymer (I') in each of the first film and the second film is preferably 80 mass% or more, and more preferably 90 mass% or more. It is also preferable that the first film and the second film each consist of the fluoropolymer (I').

[0056] The softening point temperature (temperature at which the polymer begins to flow) of the fluoropolymer (I') is often 100°C or higher, preferably from 100 to 200°C, more preferably from 100 to 150°C.

[0057] The thickness of each of the first film and the second film is preferably 15 to 250 μm, more preferably 20 to 150 μm.

[0058] Examples of methods for producing the first film and the second film include a method in which a solution containing the fluoropolymer (I') is applied to a substrate described below and the solvent component is dried to form the film, and a method in which a film is formed by melt extrusion using pellets containing the fluoropolymer (I').

[0059] (Reinforcing Material) The reinforcing material is not particularly limited as long as it can reinforce the finally obtained membrane containing the fluoropolymer (I), and known reinforcing materials can be used. Preferred examples of the reinforcing material include woven fabric.

[0060] A woven fabric is usually composed of warp yarns and weft yarns. The denier numbers of the warp yarns and weft yarns constituting the woven fabric are each independently preferably 2 or more, more preferably 10 or more, and even more preferably 15 or more, in terms of achieving better strength and dimensional stability of the film containing the fluoropolymer (I). The upper limit values ​​of the denier numbers of the warp yarns and weft yarns constituting the woven fabric are each independently preferably 60, more preferably 50, and particularly preferably 20. The denier number is the value representing the mass of 9,000 m of yarn in grams (g / 9000 m).

[0061] The densities of the warp and weft yarns are each independently preferably at least 50 yarns / inch, more preferably at least 70 yarns / inch, particularly preferably at least 90 yarns / inch, in order to provide a membrane containing the fluoropolymer (I) with excellent strength and dimensional stability. Also, the densities are preferably at most 200 yarns / inch, more preferably at most 150 yarns / inch, particularly preferably at most 100 yarns / inch.

[0062] The warp and weft threads may be made of either monofilaments consisting of one filament or multifilaments consisting of two or more filaments, with monofilaments being preferred.

[0063] The warp and weft yarns are preferably made of a material selected from the group consisting of polytetrafluoroethylene (hereinafter also referred to as "PTFE"), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter also referred to as "PFA"), polyether ether ketone (hereinafter also referred to as "PEEK"), and polyphenylene sulfide (hereinafter also referred to as "PPS"), in order to provide superior durability and strength of the yarns. The warp and weft yarns are preferably made of slit yarns in order to provide superior durability and strength of the yarns.

[0064] In the woven fabric, the warp and weft threads are preferably approximately perpendicular to each other. "Almost perpendicular" means that the angle between the warp and weft threads is 90±10 degrees. The weave of the woven fabric is not particularly limited, and examples thereof include plain weave, twill weave, and satin weave, with plain weave being preferred.

[0065] When the material constituting the woven fabric is PTFE, the basis weight of the woven fabric is 20 to 40 g / m in order to obtain an excellent balance between the strength and handleability of the film containing the fluoropolymer (I). ２ is preferred, and 30 to 40 g / m ２ When the material constituting the woven fabric is PFA, the basis weight of the woven fabric is 10 to 30 g / m from the viewpoint of achieving an excellent balance between the strength and handleability of the film containing the fluoropolymer (I). ２ is preferably 10 to 20 g / m ２ When the material constituting the woven fabric is PEEK, the basis weight of the woven fabric is 5 to 40 g / m from the viewpoint of achieving an excellent balance between the strength and handleability of the film containing the fluoropolymer (I). ２ is preferred, and 5 to 30 g / m ２ When the material constituting the woven fabric is PPS, the basis weight of the woven fabric is preferably 5 to 40 g / m, in view of the excellent balance between the strength and handleability of the film containing the fluoropolymer (I). ２ is preferred, and 5 to 30 g / m ２ is particularly preferred.

[0066] The aperture ratio of the woven fabric is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and particularly preferably 70% or more. The upper limit of the aperture ratio of the woven fabric is preferably 90%, particularly preferably 80%, in that the strength of the membrane containing the fluoropolymer (I) is superior. The aperture ratio of the woven fabric is calculated by the following formula (ε) based on the average thread diameter R1 and the average spacing P1 between adjacent threads (hereinafter also referred to as "pitch P1"). Here, the average thread diameter R1 means the arithmetic mean value of the diameters of 10 different threads arbitrarily selected based on a magnified image (e.g., 100x) of the solid polymer electrolyte membrane obtained using a microscope. The pitch P1 means the arithmetic mean value of the spacing between 10 different points arbitrarily selected based on a magnified image (e.g., 100x) of the surface of the woven fabric obtained using a microscope. Opening ratio of woven fabric (%) = [P1 / (P1+R1)] ２ × 100 (ε)

[0067] The heat pressing may be performed with a first substrate disposed on the opposite side of the first film from the reinforcing material side, and a second substrate disposed on the opposite side of the second film from the reinforcing material side. When the heat pressing is performed in this state, a laminate is obtained in which the first substrate, the precursor film, and the second substrate are laminated in this order. When the heat pressing is performed in the above manner, the temperature difference between the first roll and the second roll is preferably 1°C or more, more preferably 5°C or more, and even more preferably 10°C or more, in order to facilitate peeling of only one of the first substrate or the second substrate. Furthermore, in order to prevent scratches from occurring on the surface of the catalyst layer, the temperature difference is preferably 65°C or less, more preferably 50°C or less, even more preferably 40°C or less, particularly preferably 30°C or less, and most preferably 15°C or less.

[0068] The first substrate and the second substrate are preferably resin substrates. Preferred materials for the resin substrate include polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and tetrafluoroethylene-ethylene copolymer (ETFE). At least one of the first substrate and the second substrate may be a laminated substrate in which two or more substrate films made of the above materials are laminated. When the first substrate or the second substrate is a laminated substrate, the materials of the substrate films contained in the laminated substrate may be the same or different. The thickness of the first substrate and the second substrate is preferably 1 to 500 μm, more preferably 10 to 400 μm, even more preferably 50 to 300 μm, and particularly preferably 100 to 250 μm.

[0069] (First Roll and Second Roll) Conventionally known rolls can be used as the first roll and the second roll. Preferred materials for the roll body include metal, thermoplastic resin, and rubber. The material for the roll surface (the surface in contact with the first film or the second film) is not particularly limited, but metal or rubber is preferred. In this specification, a roll with a metal surface is referred to as a "metal roll," and a roll with a rubber surface is referred to as a "rubber roll." In particular, it is preferred that the first roll is a metal roll and the second roll is a rubber roll.

[0070] When the first roll is a metal roll and the second roll is a rubber roll, it is preferable that the temperature of the second roll is higher than the temperature of the first roll, since this makes it less likely that scratches will occur on the surface of the catalyst layer. When the first roll is a metal roll and the second roll is a rubber roll, the preferable temperature difference is the same as the preferable temperature difference described above.

[0071] The temperatures of the first roll and the second roll are not particularly limited as long as the above-mentioned predetermined temperature difference is achieved, but are preferably equal to or higher than the softening point temperatures of the fluoropolymers contained in the first film and the second film. For example, the temperatures of the first roll and the second roll are preferably equal to or higher than 100°C, preferably equal to or higher than 110°C, and more preferably equal to or higher than 120°C. Furthermore, in order to further reduce the occurrence of scratches on the catalyst layer, the temperatures of the first roll and the second roll are preferably equal to or lower than 220°C, more preferably equal to or lower than 200°C, even more preferably equal to or lower than 170°C, and particularly preferably equal to or lower than 150°C.

[0072] The diameters of the first roll and the second roll are preferably 0.1 to 0.6 m, more preferably 0.2 to 0.5 m, and even more preferably 0.3 to 0.4 m. When hot pressing, a backup roll may be provided on each of the first roll and the second roll, opposite the reinforcing material side. The gap (minimum distance) between the first roll and the second roll when hot pressing can be adjusted appropriately depending on the thickness of the fluoropolymer-containing film to be produced, but is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. The gap may be 0 μm.

[0073] [Hydrolysis Treatment] Groups in the precursor membrane that can be converted into ion exchange groups are hydrolyzed to produce a membrane containing a fluoropolymer having ion exchange groups (fluoropolymer (I)). By the hydrolysis treatment, the groups in the precursor membrane that can be converted into ion exchange groups are converted into ion exchange groups. A specific example of the hydrolysis treatment is preferably a method of contacting the precursor membrane with an alkaline aqueous solution.

[0074] Specific examples of the method for contacting the precursor film with the alkaline aqueous solution include a method of immersing the precursor film in the alkaline aqueous solution and a method of spraying the alkaline aqueous solution onto the surface of the precursor film. The temperature of the alkaline aqueous solution is preferably 30 to 100°C, and more preferably 40 to 100°C. The contact time between the precursor film and the alkaline aqueous solution is preferably 3 to 150 minutes, and more preferably 5 to 50 minutes.

[0075] 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, the water-soluble organic solvent refers to an organic solvent that is easily soluble in water. Specifically, an organic solvent having a solubility of 0.1 g or more in 1,000 ml of water (20°C) is preferred, and an organic solvent having 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 aminoalcohols, and particularly preferably contains an aprotic organic solvent. One water-soluble organic solvent may be used alone, or two or more water-soluble organic solvents may be used in combination.

[0076] Specific examples of aprotic organic solvents include dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone, with dimethyl sulfoxide being preferred. Specific examples of alcohols include methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butylcarbitol, hexyloxyethanol, octanol, 1-methoxy-2-propanol, and ethylene glycol. Specific examples of aminoalcohols 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.

[0077] The concentration of the alkali metal hydroxide in the alkaline aqueous solution is preferably 1 to 60% by mass, and particularly preferably 3 to 55% by mass. The content of the water-soluble organic solvent in the alkaline aqueous solution is preferably 1 to 60% by mass, and particularly preferably 3 to 55% by mass. The concentration of water in the alkaline aqueous solution is preferably 39 to 80% by mass.

[0078] After the precursor film is brought into contact with the alkaline aqueous solution, a treatment for removing the alkaline aqueous solution may be carried out. As a method for removing the alkaline aqueous solution, for example, a method for washing the precursor film that has been brought into contact with the alkaline aqueous solution with water may be mentioned.

[0079] After contacting the precursor membrane with the alkaline aqueous solution, the resulting membrane may be contacted with an acidic aqueous solution to convert the ion exchange groups to an acid form. Specific examples of methods for contacting the precursor membrane with the acidic aqueous solution include immersing the precursor membrane in the acidic aqueous solution and spraying the acidic aqueous solution onto the surface of the precursor membrane. The acidic aqueous solution preferably contains an acid component and water. Specific examples of the acid component include hydrochloric acid and sulfuric acid.

[0080] After the hydrolysis treatment, the resulting membrane containing the fluoropolymer (I) may be subjected to a drying treatment.

[0081] <Membrane containing fluoropolymer> The membrane containing fluoropolymer obtained by the production method of the present disclosure contains a fluoropolymer having ion exchange groups (fluoropolymer (I)), and a reinforcing material. The reinforcing material is as described above. The fluoropolymer will be described below.

[0082] The ion exchange capacity of the fluoropolymer (I) is preferably 0.90 milliequivalents / gram dry resin or more, more preferably greater than 1.10 milliequivalents / gram dry resin, even more preferably 1.15 milliequivalents / gram dry resin or more, particularly preferably 1.20 milliequivalents / gram dry resin or more, and most preferably 1.25 milliequivalents / gram dry resin or more, from the viewpoint of being able to further reduce the electrolysis voltage when applied to a water electrolysis device. The upper limit of the ion exchange capacity of the fluoropolymer (I) is preferably 2.00 milliequivalents / gram dry resin, more preferably 1.50 milliequivalents / gram dry resin, and particularly preferably 1.43 milliequivalents / gram dry resin. The ion exchange capacity of the fluoropolymer (I') can be adjusted by the content of ion exchange groups in the fluoropolymer (I).

[0083] The fluorine-containing polymer (I) may be one type, or two or more types may be laminated or mixed and used. The membrane containing a fluorine-containing polymer may contain a polymer other than the fluorine-containing polymer (I), but it is preferable that the polymer in the membrane containing a fluorine-containing polymer essentially consists of the fluorine-containing polymer (I). "Substantially consisting of the fluorine-containing polymer (I)" means that the content of the fluorine-containing polymer (I) is 95 mass% or more relative to the total mass of the polymers in the membrane containing the fluorine-containing polymer. The upper limit of the content of the fluorine-containing polymer (I) can be 100 mass% relative to the total mass of the polymers in the solid polymer electrolyte membrane. Specific examples of polymers other than the fluorine-containing polymer (I) include one or more polyazole compounds selected from the group consisting of polymers of heterocyclic compounds containing one or more nitrogen atoms in the ring, and polymers of heterocyclic compounds containing one or more nitrogen atoms and an oxygen atom and / or a sulfur atom in the ring. Specific examples of the polyazole compound include polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds, and polybenzothiazole compounds. In addition, from the viewpoint of the oxidation resistance of the film containing the fluorine-containing polymer, examples of other polymers that can be used include polyphenylene sulfide resins and polyphenylene ether resins.

[0084] The fluoropolymer (I) has an ion exchange group. Specific examples of the ion exchange group include a sulfonic acid type functional group and a carboxylic acid type functional group, and the sulfonic acid type functional group is preferred from the viewpoint of being able to further reduce the electrolysis voltage. Below, mainly, embodiments of the fluoropolymer having a sulfonic acid type functional group (hereinafter also referred to as "fluoropolymer (S)") will be described in detail.

[0085] The fluorine-containing polymer (S) preferably contains a unit based on a fluorine-containing olefin and a unit having a sulfonic acid functional group and a fluorine atom. Examples of the fluorine-containing olefin include fluoroolefins having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule. Specific examples of the fluoroolefin include tetrafluoroethylene (hereinafter also referred to as "TFE"), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among these, TFE is preferred from the viewpoints of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer (S). One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0086] As the unit having a sulfonic acid type functional group and a fluorine atom, a unit represented by formula (1) is preferred. ２ -CF(-L-(SO ３ M) ｎ )]-

[0087] L and n are as described above. M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. Multiple Ms may be the same or different.

[0088] The unit represented by formula (1) is preferably a unit represented by formula (1-1), a unit represented by formula (1-2), a unit represented by formula (1-3), or a unit represented by formula (1-4). ２ -CF(-O-R ｆ１ -SO ３ M)] - Formula (1-2) - [CF ２ -CF(-R ｆ１ -SO ３ M) ]-

[0089]

[0090]

[0091] R ｆ１ , R ｆ２ , R ｆ３ , r, m and M are as described above.

[0092] As the unit represented by formula (1-1) and the unit represented by formula (1-2), a unit represented by formula (1-5) is more preferred. ２ -CF(-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ３ M)]—x is 0 or 1, y is an integer from 0 to 2, z is an integer from 1 to 4, and Y is F or CF ３ M is as described above.

[0093] Specific examples of the unit represented by formula (1-1) include the following units. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. The definition of M in the formula is as described above. -[CF ２ -CF(-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-(O-CF ２ CF (CF ３ )) ｘ -SO ３ M) ]-

[0094] Specific examples of the unit represented by formula (1-2) include the following units. In the formula, w is an integer of 1 to 8. The definition of M in the formula is as described above. -[CF ２ -CF(-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF (-CF ２ -O-(CF ２ ) ｗ -SO ３ M) ]-

[0095] The unit represented by formula (1-3) is preferably a unit represented by formula (1-3-1), where M is defined as above.

[0096]

[0097] R ｆ４ is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ｆ５ is a single bond or a linear perfluoroalkylene group having 1 to 6 carbon atoms which may contain an oxygen atom between carbon atoms. The definitions of r and M are as described above.

[0098] Specific examples of the unit represented by formula (1-3-1) include the following.

[0099]

[0100] As the unit represented by formula (1-4), a unit represented by formula (1-4-1) is preferred. ｆ１ , R ｆ２ and M are defined as above.

[0101]

[0102] Specific examples of the unit represented by formula (1-4-1) include the following.

[0103]

[0104] The unit having a sulfonic acid type functional group and a fluorine atom may be used alone or in combination of two or more.

[0105] The fluoropolymer (I) may contain units based on other monomers other than the units based on fluorine-containing olefins and the units having a sulfonic acid functional group and a fluorine atom. Specific examples of other monomers include CF ２ = CFR ｆ６ (However, R ｆ６ is a perfluoroalkyl group having 2 to 10 carbon atoms, CF ２ =CF-OR ｆ７ (However, R ｆ７ is a perfluoroalkyl group having 1 to 10 carbon atoms, CF ２= CFO (CF ２ ) ｖ CF = CF ２ (wherein v is an integer of 1 to 3.) The content of units based on other monomers is preferably at most 30 mass % based on all units in the fluoropolymer (I) from the viewpoint of maintaining ion exchange performance.

[0106] The membrane containing the fluoropolymer obtained by the production method of the present disclosure preferably has a thickness of 20 μm or more, more preferably 40 μm or more, and particularly preferably 70 μm or more. The upper limit of the thickness of the solid polymer electrolyte membrane is preferably 150 μm, more preferably 130 μm, from the viewpoint of further reducing the electrolysis voltage when applied to a water electrolysis device. The thickness of the solid polymer electrolyte membrane is measured using an image obtained by measuring a cross section cut along a plane parallel to the membrane thickness direction with an optical microscope, and is the arithmetic average value at any 20 points.

[0107] <Applications> A membrane containing a fluoropolymer obtained by the production method of the present disclosure is less likely to be damaged when a catalyst layer is formed on the surface of the membrane, and is therefore suitable for applications in which a catalyst layer is to be formed. Examples include various battery applications such as polymer electrolyte fuel cells, direct methanol fuel cells, redox flow batteries, and air batteries, as well as various electrolysis devices such as polymer electrolyte water electrolysis, ozone water electrolysis, organic electrolysis, and chloride or oxide electrolysis.

[0108] The present invention will be described in detail below with reference to examples. Examples 1 to 8 are working examples, and Examples 9 to 11 are comparative examples. However, the present invention is not limited to these examples.

[0109] <Measurement Method> The method for measuring the values ​​in each example will be described below.

[0110] [Ion exchange capacity of fluoropolymer] The fluoropolymer was placed in a glove box filled with dry nitrogen for 24 hours, and the dry mass of the fluoropolymer was measured. Thereafter, the fluoropolymer was immersed in a 2 mol / L aqueous sodium chloride solution at 60°C for 1 hour. The fluoropolymer was washed with ultrapure water and then removed. The solution in which the fluoropolymer had been immersed was titrated with a 0.1 mol / L aqueous sodium hydroxide solution to determine the ion exchange capacity X of the fluoropolymer (milliequivalents / gram of dry resin (also referred to as "meq / g" in the tables below)).

[0111] Example 1 The solid polymer electrolyte membrane used in Example 1 was obtained by the following procedure.

[0112] [Production of Fluorine-Containing Polymer (S'-1)] CF ２ =CF ２ and a monomer (X) represented by the following formula (X) were copolymerized to obtain a fluorine-containing polymer (S'-1) (ion exchange capacity: 1.25 meq / g dry resin): CF ２ =CF-O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F...(X)

[0113] The ion exchange capacity described in the above [Production of Fluoropolymer (S'-1)] represents the ion exchange capacity of the fluoropolymer obtained when the fluoropolymer (S'-1) is hydrolyzed by the procedure described below.

[0114] [Production of film-attached substrate Y1] Next, the fluoropolymer (S'-1) was adhered by melt extrusion onto a substrate made of a linear low-density polyethylene (LLDPE) film (melting point: 110 to 120°C), to obtain a film-attached substrate Y1 in which a film α1 (film thickness: 45 µm) made of the fluoropolymer (S'-1) was formed on the substrate.

[0115] [Production of woven fabric] 18.6 denier PFA yarns were used as warp and weft yarns, and plain weaving was performed so that the density of the PFA yarns was 100 threads / inch to obtain woven fabric A1. The basis weight of woven fabric A1 was 16.3 g / m ２It was.

[0116] [Production of membrane containing fluoropolymer] The components were supplied to a roll press machine so that the film-attached substrate Y1 / woven fabric A1 / film-attached substrate Y1 were stacked in this order. The film-attached substrate Y1 was arranged so that the film α1 in the film-attached substrate Y1 was in contact with the woven fabric A1. The rolls in the roll press machine were such that the upper roll (first roll) was made of metal and the lower roll (second roll) was made of rubber. The temperatures of the first roll and the second roll were as shown in the table below. The contact time between the rolls (first roll and second roll) and the film-attached substrate Y1 (first film and second film) was also as shown in the table below. The contact time between the rolls and the two film-attached substrates Y1 (first film and second film), i.e., the first contact time and the second contact time, were the same. In the roll press machine, the film α1, woven fabric A1, and film α1 were hot-pressed via the substrate of the film-attached substrate Y1 to obtain a precursor membrane sandwiched between the substrates. After the heat pressing, the substrate was peeled off from the precursor film.

[0117] The precursor membrane was immersed in a solution of dimethyl sulfoxide / potassium hydroxide / water = 30 / 5.5 / 64.5 (mass ratio) at 95 ° C. for 30 minutes, and groups in the precursor membrane that can be converted into sulfonic acid type functional groups were hydrolyzed to convert them into K-type sulfonic acid type functional groups, followed by washing with water. Thereafter, the obtained membrane was immersed in 1 M sulfuric acid to convert the terminal groups from K-type to H-type, and then dried to obtain a membrane containing the fluoropolymer of Example 1.

[0118] [Evaluation of Scratches on Catalyst Layer] A catalyst layer-forming composition having the following composition was applied to one surface of the obtained fluoropolymer-containing membrane by die coating, and dried to form a catalyst layer. At this time, the fluoropolymer-containing membrane was cut into a size of 210 × 297 mm, and the coating area was set to 160 × 247 mm so that the edges were equidistant. In addition, during application and drying, the four corners of the fluoropolymer-containing membrane were held with polyimide heat-resistant tape (manufactured by Teraoka Seisakusho, Kapton (registered trademark) adhesive tape). In addition, a catalyst layer was formed on the opposite surface to the one surface in the same manner.

[0119] The surface on which the catalyst layer was formed was observed, and visually checked for the presence of scratches on the surface of the catalyst layer. Based on the observation results, the resistance to scratches on the surface of the catalyst layer was evaluated according to the following criteria. In practice, A, B, C, or D is preferred. The evaluation results for resistance to scratches are shown in the table below. A: No scratches on the surface of the catalyst layer in the coated area B: Less than three scratches on the surface of the catalyst layer in the coated area C: Three scratches on the surface of the catalyst layer in the coated area D: Four scratches on the surface of the catalyst layer in the coated area E: Five or more scratches on the surface of the catalyst layer in the coated area

[0120] [Releasability] In the above procedure, the substrate was peeled from the precursor film after hot pressing, and the releasability of the substrate was evaluated according to the following criteria. When the substrate on the second roll side was peeled off, the adhesion between the substrate on the first roll side and the precursor film was confirmed to evaluate the releasability. Note that, in practice, an A rating or a B rating is preferable. The evaluation results of the releasability are shown in the table below. A: When the substrate on the second roll side was peeled off, no peeling occurred at the interface between the substrate on the first roll side and the precursor film. B: When the substrate on the second roll side was peeled off, a region of peeling was observed at the interface between the substrate on the first roll side and the precursor film, but the substrate on the second roll side could be peeled off without causing wrinkles in the precursor film due to deformation of the peeled region, etc. C: When the substrate on the second roll side was peeled off, a region of peeling was observed at the interface between the substrate on the first roll side and the precursor film, and wrinkles occurred in the precursor film due to deformation of the peeled region, etc.

[0121] Examples 2 to 11 Except for changing the materials and temperatures of the upper roll and the lower roll, and the contact time between the rolls and the film-attached substrate Y1, as shown in the table below, films containing a fluoropolymer were obtained in the same manner as in Example 1. Furthermore, for each of the obtained fluoropolymer-containing films, resistance to scratches when a catalyst layer was formed and peelability were evaluated in the same manner as in Example 1.

[0122] <Results> Table 1 shows the heat pressing conditions for the fluoropolymer-containing membrane and the evaluation results for the resistance to scratches when the catalyst layer was formed.

[0123]

[0124] The results shown in Table 1 indicate that in Examples 9 and 10, where the temperature difference between the first roll and the second roll exceeded 70°C, the occurrence of scratches on the catalyst layer could not be suppressed. Furthermore, in Example 11, where the contact time (first contact time and second contact time) was 1 second or less, the occurrence of scratches on the catalyst layer could not be suppressed. On the other hand, it was confirmed that the occurrence of scratches on the catalyst layer could be suppressed in Examples 1 to 8, where the temperature difference and contact time (first contact time and second contact time) were within the specified range. Comparison of Examples 3, 4, and 6 with other Examples confirmed that when the temperature difference was 1 to 65°C (more preferably 5 to 40°C), the occurrence of scratches on the catalyst layer was further suppressed and excellent releasability was achieved. Comparison of Example 7 with Example 1 confirmed that when the contact time (first contact time and second contact time) was 7 seconds or more, the occurrence of scratches on the catalyst layer was even less likely.

[0125] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-205389 filed on December 5, 2023 are hereby incorporated by reference as the disclosure of the present invention.

[0126] 12 First film 14 Second film 16 Reinforcing material 18 Precursor film 22 First roll 24 Second roll

Claims

1. A method for producing a membrane containing a fluoropolymer, comprising: heat-pressing a first film containing a fluoropolymer having groups convertible to ion-exchange groups, a reinforcing material, and a second film containing a fluoropolymer having groups convertible to ion-exchange groups between a pair of rolls to obtain a precursor membrane containing a fluoropolymer having groups convertible to ion-exchange groups; and hydrolyzing the groups in the precursor membrane that can be converted to ion-exchange groups to produce a membrane containing a fluoropolymer having ion-exchange groups, wherein the pair of rolls comprises a first roll in contact with the first film and a second roll in contact with the second film, the temperature difference between the first roll and the second roll is 70°C or less, and during the heat press, a first contact time between the first roll and the first film and a second contact time between the second roll and the second film are each longer than 1 second.

2. A method for producing a membrane containing a fluoropolymer according to claim 1, further comprising arranging a first substrate on the side of said first film opposite said reinforcing material side, and arranging a second substrate on the side of said second film opposite said reinforcing material, and said temperature difference being 1 to 65°C.

3. A method for producing a membrane containing a fluoropolymer according to claim 1, further comprising: arranging a first substrate on the side of said first film opposite said reinforcing material side; and arranging a second substrate on the side of said second film opposite said reinforcing material side; and said temperature difference being 5 to 40°C.

4. The method for producing a film containing a fluoropolymer according to claim 2 or 3, wherein the first substrate and the second substrate are peeled off after the heat pressing and before the hydrolysis.

5. A method for producing a membrane containing a fluoropolymer according to claim 1, wherein the first contact time and the second contact time are each 7 seconds or longer.

6. The method for producing a film containing a fluoropolymer according to claim 1, wherein the first roll is a metal roll and the second roll is a rubber roll.

7. The method for producing a membrane containing a fluoropolymer according to claim 1, wherein the ion exchange capacity of the fluoropolymer having ion exchange groups is 0.90 to 2.00 milliequivalents / gram of dry resin.

8. A method for producing a membrane containing a fluoropolymer according to claim 1, wherein the fluoropolymer having an ion exchange group contains a unit based on a fluorine-containing olefin and a unit having a sulfonic acid type functional group and a fluorine atom.

9. The method for producing a membrane comprising a fluorine-containing polymer according to claim 8, wherein the fluorine-containing olefin is a fluoroolefin having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule.

10. The method for producing a membrane containing a fluoropolymer according to claim 8, wherein the unit having a sulfonic acid functional group and a fluorine atom is a unit represented by formula (1). ２ -CF(-L-(SO ３ M) ｎ ) )]—L is an (n+1) valent perfluorohydrocarbon group which may contain an etheric oxygen atom; M is a hydrogen atom, an alkali metal or a quaternary ammonium cation; and n is 1 or 2.

11. The method for producing a membrane comprising a fluorine-containing polymer according to claim 1, wherein the reinforcing material is a woven fabric.

12. The method for producing a membrane comprising a fluoropolymer according to claim 1, wherein the first film and the second film each have a thickness of 15 to 250 μm.

13. The method for producing a film containing a fluoropolymer according to claim 1, wherein the temperature of the second roll is higher than the temperature of the first roll.

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