Method for producing film and method for producing solid polymer electrolyte membrane

Abstract

The present invention provides a method for producing a film, with which it is possible to produce a film in which the occurrence of a pinhole is suppressed and at least one additive that is selected from the group consisting of a platinum-containing material and cerium oxide is contained.　Provided is a method for producing a film, wherein: a fluorine-containing polymer which contains a unit based on tetrafluoroethylene and has a group that can be converted into an ion exchange group is melted and passed through a filter X so as to prepare a first pellet; at least one additive that is selected from the group consisting of a platinum-containing material and cerium oxide and the first pellet are used so as to obtain a melt that contains the additive and the fluorine-containing polymer, and the melt is not allowed to pass through a filter or is allowed to pass through a filter Y which has a mesh diameter larger than 5 times the volume-based 50% cumulative diameter of the additive so as to prepare a second pellet that contains the additive; and melt extrusion molding is performed using the first pellet and the second pellet so as to produce a film that contains the fluorine-containing polymer and the additive.

Description

Film manufacturing method and solid polymer electrolyte membrane manufacturing method

[0001] The present disclosure relates to a method for producing a film and a method for producing a solid polymer electrolyte membrane.

[0002] The use of polymer electrolyte membrane (PEM) water electrolysis devices is being considered for power-to-gas applications, i.e., converting surplus electricity into gas for storage and utilization. In PEM water electrolysis devices, reduction of generated hydrogen crossover is required. Hydrogen crossover refers to the transfer of hydrogen gas generated at the cathode to the anode side through the solid polymer electrolyte membrane in a PEM water electrolysis device. Hydrogen crossover can reduce the hydrogen gas recovery efficiency.

[0003] As a means for reducing such crossover, Patent Document 1 discloses a catalyst-coated membrane having a membrane including a cathode catalyst layer, a membrane including an anode catalyst layer, and a membrane including a recombination catalyst layer. In the catalyst-coated membrane, the membrane including the recombination catalyst layer is disposed between the membrane including the cathode catalyst layer and the membrane including the anode catalyst layer. As the recombination catalyst, for example, a catalytic material including platinum is disclosed.

[0004] Special Publication No. 2020-514528

[0005] Patent Document 1 also describes incorporating a catalyst containing cerium oxide into any of the above membranes as a hydrogen peroxide scavenger catalyst. In order to more efficiently produce a solid polymer electrolyte membrane (film), the present inventors prepared pellets containing at least one additive selected from the group consisting of platinum-containing materials and cerium oxide and a fluorine-containing polymer, and investigated the production of a film using the pellets. However, when attempting to produce a film using the pellets by extrusion molding, there were cases where the film could not be formed, and pinholes were generated in the formed film.

[0006] The present invention has been made in view of the above problems, and an object of one embodiment of the present invention is to provide a method for producing a film that can produce a film that suppresses the generation of pinholes and contains at least one additive selected from the group consisting of a platinum-containing material and cerium oxide. Another object of one embodiment of the present invention is to provide a method for producing a solid polymer electrolyte membrane.

[0007] The present disclosure includes the following aspects: [1] A method for producing a film, comprising: melting a fluoropolymer containing units based on tetrafluoroethylene and having groups convertible to ion-exchange groups, and passing the melt through a filter X to produce first pellets; using at least one additive selected from the group consisting of a platinum-containing material and cerium oxide and the first pellets to obtain a melt containing the additive and the fluoropolymer, and passing the melt through a filter Y having a pore size greater than five times the cumulative 50% diameter on a volume basis of the additive to produce second pellets containing the additive; and melt-extrusion molding the first pellets and the second pellets to produce a film containing the fluoropolymer and the additive. [2] The method for producing a film according to [1], wherein the second pellets contain both the platinum-containing material and the cerium oxide. [3] The method for producing a film according to [1] or [2], wherein two or more types of second pellets are used in the melt extrusion, at least one of the second pellets contains only the platinum-containing material, and at least one of the second pellets contains only the cerium oxide. [4] The method for producing a film according to any of [1] to [3], wherein the platinum-containing material is supported on a carrier. [5] The method for producing a film according to any of [1] to [4], wherein the platinum-containing material has a volume-based cumulative 50% diameter of 500 nm or more. [6] The method for producing a film according to any of [1] to [5], wherein the pore size of the filter Y is 20 times or less the volume-based cumulative 50% diameter of the additive. [7] The method for producing a film according to any of [1] to [6], wherein the group that can be converted into an ion-exchange group is a group that can be converted into a sulfonic acid-type functional group. [8] The method for producing a film according to [7], wherein the fluoropolymer contains at least one unit selected from the group consisting of units based on a compound represented by formula (2-3) and units based on a compound represented by formula (2-4). In formula (2-3) and formula (2-4), R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between the carbon atoms, and Rｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. ｆ３ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. In formula (2-3) and formula (2-4), r is 0 or 1, and each of the multiple A's is independently a group which can be converted into a sulfonic acid functional group. In formula (2-4), m is 0 or 1. [9] A method for producing a solid polymer electrolyte membrane, comprising: producing a film by the film production method according to any one of [1] to [8]; obtaining a precursor membrane by laminating the film and a woven fabric; and converting the groups in the precursor membrane which can be converted into ion exchange groups into ion exchange groups to obtain a solid polymer electrolyte membrane.

[0008] According to one embodiment of the present invention, there is provided a method for producing a film that can suppress the generation of pinholes and that can produce a film containing at least one additive selected from the group consisting of a platinum-containing material and cerium oxide. Also, according to one embodiment of the present invention, there is provided a method for producing a solid polymer electrolyte membrane.

[0009] 1 is a schematic cross-sectional view of an electrolyte membrane for explaining a state in which platinum-containing substances are unevenly distributed. 2 is a cross-sectional view schematically showing an example of a membrane electrode assembly according to the present disclosure. 3 is a cross-sectional view schematically showing an example of a membrane electrode assembly according to the present disclosure.

[0010] The definitions of the following terms apply throughout the present specification and claims unless otherwise specified. An "ion exchange group" is a group that can exchange at least a portion of the ions contained in this group with other ions, and examples thereof include the sulfonic acid functional group and carboxylic acid functional group shown below. A "sulfonic acid functional group" is a sulfonic acid group (-SO ３ Here, the form of the sulfonate group is, for example, (—SO ３ － ) Ma ＋ , (-SO ３ － ) ２ Mb ２＋ , and (-SO ３ － )３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) When there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. "Carboxylic acid type functional group" means a carboxylic acid group (-COOH) or a carboxylic acid salt group. Here, the form of the carboxylic acid salt group can be, for example, (-COO － ) Ma ＋ , (-COO － ) ２ Mb ２＋ , and (-COO － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) Note that when there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. A "precursor membrane" is a membrane containing a polymer having a group that can be converted into an ion exchange group. A "group that can be converted into an ion exchange group" means a group that can be converted into an ion exchange group by 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.

[0011] The term "unit" in a polymer refers to an atomic group based on one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or may be an atomic group in which a part of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction.

[0012] 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.

[0013] [Film Manufacturing Method] The film manufacturing method of the present disclosure is a method for producing a film containing a fluoropolymer and an additive by melt extrusion molding first pellets and second pellets. The first pellets are produced by melting a fluoropolymer containing units based on tetrafluoroethylene and having groups convertible to ion-exchange groups, and passing the melt through filter X. The second pellets are produced by using the first pellets and at least one additive selected from the group consisting of platinum-containing materials and cerium oxide to obtain a melt containing the additive and the fluoropolymer. In this case, the second pellets are produced either without passing through a filter, or by passing through filter Y having a pore size greater than five times the cumulative 50% diameter, based on volume, of the additive.

[0014] The mechanism by which the film production method of the present disclosure (hereinafter also referred to simply as "the present production method") can suppress the occurrence of pinholes and produce a film containing at least one additive selected from the group consisting of a platinum-containing material and cerium oxide is not entirely clear, but the inventors speculate as follows. Hereinafter, the ability to produce a film containing the additive while suppressing the occurrence of pinholes will also be simply referred to as "obtaining a film with suppressed pinhole occurrence." When producing a film containing such an additive, if a molten material containing the additive is passed through a filter, the additive will be removed by the filter, and either a film cannot be formed or the formed film will not contain the additive. Meanwhile, the inventors investigated a method of extruding a molten material without passing it through a filter when producing a film, and found that pinholes sometimes occurred.

[0015] On the other hand, in the present production method, when the first pellets are produced, the fluoropolymer melt is passed through filter X. It is believed that the filter X can remove foreign matter that causes pinholes. Also, in the present production method, when the second pellets containing the additives are produced, either no filter is used or the specified filter Y is used. In this way, the second pellets are produced without the additives being removed by the filter during production. Furthermore, the first pellets used to produce the second pellets have had foreign matter that causes pinholes removed from them, and it is believed that the second pellets do not contain such foreign matter either. Therefore, when the first pellets and the second pellets are used for melt extrusion molding, a film in which pinholes are suppressed is obtained.

[0016] Hereinafter, the step of melting a fluoropolymer containing units based on tetrafluoroethylene and having groups convertible to ion-exchange groups and passing the melt through filter X to prepare first pellets will also be referred to as the "first pellet preparation step." Hereinafter, the step of using at least one additive selected from the group consisting of platinum-containing materials and cerium oxide and the first pellets to obtain a melt containing the additive and the fluoropolymer, and then passing the melt through filter Y having a pore size greater than five times the cumulative 50% diameter of the additive on a volume basis, to prepare second pellets containing the additive, will also be referred to as the "second pellet preparation step." Hereinafter, the step of melt-extrusion molding the first pellets and the second pellets to produce a film containing the fluoropolymer and the additive, will also be referred to as the "melt extrusion molding step." That is, in this production method, first pellets are prepared in the first pellet preparation step, second pellets are prepared using the first pellets in the second pellet preparation step, and a film is produced using the first pellets and the second pellets in the melt extrusion molding step.

[0017] The film manufacturing method of the present disclosure (the present manufacturing method) will be described in detail below.

[0018] <First pellet preparation step> In the first pellet preparation step, first pellets are prepared by the following procedure. First, a fluoropolymer (hereinafter also referred to as "fluoropolymer (I')") containing units based on tetrafluoroethylene and having groups convertible to ion-exchange groups is melted. Next, the molten fluoropolymer (I') is passed through a filter X. Next, first pellets are prepared using the fluoropolymer (I') that has been passed through the filter X.

[0019] The fluoropolymer (I') is preferably a copolymer (hereinafter also referred to as "fluoropolymer (S')") of a fluoromonomer having a group that can be converted into a sulfonic acid functional group (hereinafter also referred to as "fluoromonomer (S')"). The fluoropolymer (S') contains units based on tetrafluoroethylene and units based on the fluoromonomer (S'). That is, the fluoropolymer (S') has a group that can be converted into a sulfonic acid functional group. The fluoropolymer (S') will be described in detail below.

[0020] As the method for copolymerizing the fluoropolymer (S'), known methods such as solution polymerization, suspension polymerization and emulsion polymerization can be adopted.

[0021] 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, more preferably 10 or less.

[0022] L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, more 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.

[0023] A is a group that can be converted into a sulfonic acid functional group. The group that can be converted into a sulfonic acid functional group is preferably a functional group that can be converted into a sulfonic acid functional group by hydrolysis. Specific examples of groups that can be converted into a sulfonic acid functional group include -SO ２ F, -SO ２ Cl, —SO ２ Br. When n=2, two A's may be the same or different.

[0024] 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

[0025]

[0026]

[0027] 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, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0028] R ｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0029] R ｆ３ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0030] r is 0 or 1, and the multiple A's each independently represent a group that can be converted into a sulfonic acid functional group.

[0031] As the compound represented by formula (2-1) and the compound represented by formula (2-2), a compound represented by formula (2-5) is preferred. ２ =CF-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ３ 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 When y=2, the multiple Y's may be the same or different.

[0032] 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

[0033] 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. CF２ =CF-(CF ２ ) ｗ -SO ２ FCF ２ =CF-CF ２ -O-(CF ２ ) ｗ -SO ２ F

[0034] The compound represented by formula (2-3) is preferably a compound represented by formula (2-3-1).

[0035]

[0036] R ｆ４ is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ｆ５ represents a single bond or a linear perfluoroalkylene group having 1 to 6 carbon atoms which may contain an oxygen atom between the carbon atoms. The definitions of r and A are as described above.

[0037] Specific examples of the compound represented by formula (2-3-1) include the following.

[0038]

[0039] The compound represented by formula (2-4) is preferably a compound represented by formula (2-4-1).

[0040]

[0041] R in the formula ｆ１ , R ｆ２ and A are defined as above.

[0042] Specific examples of the compound represented by formula (2-4-1) include the following.

[0043]

[0044] 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 tetrafluoroethylene and the fluorine-containing monomer (S'). 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).

[0045] The ion exchange capacity of the fluoropolymer (I') when the groups convertible to ion exchange groups are converted into ion exchange groups (i.e., the fluoropolymer (I) described below) is preferably 0.9 meq / g resin or more, and from the viewpoint of being able to reduce the electrolysis voltage of a device incorporating an ion exchange membrane, it is more preferably 1.0 meq / g resin or more, even more preferably 1.1 meq / g resin or more, and particularly preferably 1.25 meq / g resin or more. Furthermore, from the viewpoint of obtaining a superior strength of the ion exchange membrane, it is preferably 2.00 meq / g resin or less, more preferably 1.90 meq / g resin or less, and even more preferably 1.40 meq / g resin or less. Here, the fluoropolymer (I) for measuring the ion exchange capacity is obtained as follows. First, the fluoropolymer (I') that has been vacuum heat-treated at 240°C and -0.1 MPaG for 16 hours is 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 that can be converted into ion exchange groups in the fluoropolymer (I') are hydrolyzed to convert them to K-type ion exchange groups, and then washed with water. Thereafter, the polymer is immersed in an aqueous sodium hydroxide solution to convert the terminal groups from K-type to Na-type, thereby obtaining a fluoropolymer (I) for measuring the ion exchange capacity. The method for measuring the ion exchange capacity of the fluoropolymer (I) thus obtained is as described in the Examples section below.

[0046] The fluoropolymer (I') may be used alone or in combination of two or more kinds.

[0047] In the first pellet preparation step, the molten fluoropolymer (I') is passed through a filter X. The pore size of the filter X is preferably 0.010 to 0.87 mm, more preferably 0.020 to 0.32 mm, and particularly preferably 0.026 to 0.132 mm, in order to obtain a film in which the generation of pinholes is further suppressed. In this specification, when the filter X is a mesh filter, the pore size of the filter X refers to the openings of the mesh filter. In order to obtain a film in which the generation of pinholes is further suppressed, the filter X is preferably a mesh filter of 20 to 500 mesh, more preferably a mesh filter of 50 to 500 mesh, and more preferably a mesh filter of 120 to 500 mesh. Here, "mesh" refers to the number of openings of the mesh filter per inch (2.54 cm). The pore size of the filter X is preferably 0.33 mm or less, more preferably 0.14 mm or less. In addition, the pore size of the filter X is often 0.02 mm or more. The material of the filter X is preferably metal from the viewpoint of heat resistance.

[0048] In the first pellet production step, first pellets are produced using the fluoropolymer (I') passed through filter X. The first pellets can be produced by a known method. For example, first, the fluoropolymer (I') passed through filter X is supplied to a known melt extruder to obtain a melt of the fluoropolymer (I'). The obtained melt of the fluoropolymer (I') is extruded from the nozzle of the melt extruder and cooled to obtain strands. The obtained strands are cut to a predetermined size to obtain first pellets. The melting temperature of the fluoropolymer (I') is not particularly limited, but is preferably 150 to 350°C, more preferably 200 to 300°C. The first pellets may be produced by a method other than the above-mentioned method (the so-called strand cutting method), and for example, an underwater cutting method, a hot cutting method, etc. may be applied.

[0049] The above filter X may be placed in the vicinity of the above nozzle in the melt extruder, that is, the procedure of passing the molten fluoropolymer (I') through the filter X may be carried out in the melt extruder.

[0050] The shape of the first pellets is not particularly limited, and may be, for example, any shape such as a sphere (including an ellipsoid), a columnar shape (for example, a cylindrical shape), etc. The size of the first pellets obtained in the first pellet production step is not particularly limited, but for example, when the first pellets are cylindrical, it is preferable that the diameter is 2 to 3 mm and the length is 2 to 3 mm.

[0051] The surfaces of the first pellets obtained by the first pellet production step preferably have a plurality of grooves formed thereon. This can prevent the first pellets from sticking together. The grooves formed on the surfaces of the first pellets may be formed over the entire surfaces of the first pellets, but are typically preferably formed only on the side surfaces of the pellets (surfaces other than the cut surfaces of the strands). The grooves formed on the surfaces of the first pellets preferably extend mainly along a direction intersecting the cut surfaces of the first pellets (the flow direction of the strands).

[0052] In the first pellet production step, after cutting the strands, a surface roughening treatment may be performed to roughen the surfaces of the first pellets. This further roughens the surfaces of the first pellets, thereby further suppressing adhesion between the first pellets. A specific example of a surface roughening treatment method is a method of stirring the first pellets using a mixer (e.g., a V blender).

[0053] The light transmittance of the first pellets is preferably 30 to 60%, more preferably 30 to 50%, and even more preferably 30 to 40%. It is presumed that first pellets with a light transmittance within the above range have roughened surfaces. This reduces the contact area between the first pellets, which is thought to prevent them from sticking together. This reduces pressure fluctuations during film formation in the melt extrusion process described below, resulting in a film with more uniform thickness. The light transmittance of the first pellets refers to the visible light transmittance (measured at a wavelength of 400 to 700 nm) measured using a luminous transmittance meter (manufactured by Asahi Spectroscopy, Model 304, or an equivalent device), and the specific measurement method is as follows.

[0054] First, the luminous transmittance meter is adjusted so that the visible light transmittance is 100% when the sample holder described below is not placed on the sample stage of the luminous transmittance meter. Next, a sample holder with a hole of a predetermined size (e.g., a rectangular hole 2-3 mm long and 2-3 mm wide) for fitting the first pellet is placed on the sample stage, and the light intensity is adjusted so that the visible light transmittance before fitting the first pellet into the hole of the sample holder is 25%. Next, a first pellet of the same size as the hole of the sample holder is fitted into the hole of the sample holder, and the visible light transmittance is measured. Note that the visible light transmittance of the first pellet is measured at multiple locations for each first pellet, and the arithmetic average value is calculated. For example, if the first pellet is cylindrical, the first pellet is fitted into the hole of the sample holder so that light is irradiated onto the side of the first pellet, and the first pellet is rotated 90 degrees in the circumferential direction, and the visible light transmittance is measured at three locations for each first pellet, and the arithmetic average value is calculated. Then, the visible light transmittance of the first pellet is calculated by converting the visible light transmittance (25%) before the first pellet is fitted into the hole of the sample holder to 100% (i.e., multiplying the measured visible light transmittance of the first pellet by 4), and this is the light transmittance (%) of the first pellet.

[0055] <Second Pellets Production Step> In the second pellet production step, second pellets are produced by the following procedure Y1 or Y2. In procedures Y1 and Y2, first, at least one additive selected from the group consisting of platinum-containing materials and cerium oxide and the first pellets are used to obtain a melt containing the additive and the fluoropolymer (fluoropolymer (I')). Next, in procedure Y1, the obtained melt is used to produce second pellets. On the other hand, in procedure Y2, the obtained melt is passed through a filter Y described below, and then second pellets are produced. First, procedure Y1 will be described.

[0056] In step Y1, first, a melt containing the additive and the fluoropolymer is obtained using the first pellets and at least one additive selected from the group consisting of a platinum-containing material and cerium oxide. The additive may be only the platinum-containing material, may be only cerium oxide, or may contain the platinum-containing material and cerium oxide.

[0057] The platinum-containing material may contain platinum atoms. Specific examples of the platinum-containing material include platinum alone, platinum oxide, platinum-containing composite metal oxides, and platinum alloys. Specific examples of platinum-containing composite oxides include M ｘ Pt ３ O ４ (M is at least one metal atom selected from the group consisting of Li, Na, Mg, Ca, Zn, Cd, Co, Ni, Mn, Cu, Ag, Bi, and Ce, and x is greater than 0 and equal to or less than 1.) A specific example of a platinum alloy is an alloy containing platinum and at least one metal selected from the group consisting of transition metals and noble metals other than platinum.

[0058] Specific examples of the shape of the platinum-containing material include particles and sheets. When the platinum-containing material is in the form of particles, the platinum-containing material may be core-shell type particles. An example of a core-shell type particle is a particle in which the core is carbon or contains a metal other than platinum, and the shell contains platinum atoms. The platinum-containing material may also be supported on a carrier. Specific examples of the carrier include carbon carriers such as carbon black powder, graphitized carbon, carbon fiber, and carbon nanotubes. Note that, in terms of heat resistance in high-temperature environments such as during extrusion molding, it is preferable not to include a carbon carrier. When the platinum-containing material is supported on a carrier, the amount of the platinum-containing material supported is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 50% by mass or less, based on the total mass of the platinum-containing material and the carrier.

[0059] When the platinum-containing material is particulate, the average particle diameter (D50 described below) of the platinum-containing material is preferably 1 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, particularly preferably 100 nm or more, and may be 500 nm or more. The average particle diameter (D50 described below) of the platinum-containing material is preferably 50 μm or less, more preferably 30 μm or less, even more preferably 14 μm or less, and particularly preferably 7 μm or less. The average particle diameter of the platinum-containing material is the cumulative 50% diameter (D50) on a volume basis obtained from the particle size distribution measured by the following method. The average particle diameter of the platinum-containing material is obtained by measuring the particle diameters of 40,000 particles in a dry state using an image particle size distribution analyzer (for example, the "Morphologi (registered trademark)" series manufactured by Malvern Panalytic) and determining the cumulative 50% diameter (D50) of the volume-based particle size distribution cumulative curve. When particles smaller than 500 nm are included, the circle-equivalent diameters of 100 particles are measured using a scanning electron microscope (SEM) to determine the cumulative 50% diameter (D50) of the volume-based particle size distribution curve. The platinum-containing material may be composed of monodispersed primary particles or secondary particles formed by aggregation of multiple primary particles. When the platinum-containing material contains secondary particles, the particle size of the secondary particles is measured when measuring the D50.

[0060] Cerium oxide is CeO ２ (cerium (IV) oxide), Ce ２ O ３ (cerium (III) oxide) may be used, but from the viewpoint of stability, CeO ２ Cerium oxide may be doped with polyvalent metal ions such as zirconium and praseodymium.

[0061] The cerium oxide is preferably in particulate form. When the cerium oxide is in particulate form, the average particle size (D50 described below) of the cerium oxide is preferably 10 nm or more, more preferably 100 nm or more, even more preferably 1 μm or more, particularly preferably 3 μm or more, and preferably 30 μm or less, more preferably 14 μm or less, and even more preferably 10 μm or less. When the average particle size of the cerium oxide is 10 nm or more, aggregation of the cerium oxide is suppressed, and it is easy to achieve a stable dispersion state. When the average particle size of the cerium oxide is 30 μm or less, the chemical durability of the ion exchange membrane can be further improved when the obtained film is used as an ion exchange membrane. The method for measuring the average particle size of the cerium oxide is the same as the method for measuring the average particle size (D50) of the platinum-containing material.

[0062] A method for obtaining a melt containing the additives and the fluoropolymer (I') includes, for example, mixing the first pellets with the additives, kneading the mixture while heating, and further heating to melt the mixture. The means for carrying out the method is not particularly limited, and examples include kneading using a mixer and a twin-screw extruder. The content of the additives in the melt is preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, based on the total mass of the melt.

[0063] In step Y1, the obtained melt is used to prepare second pellets. At this time, the melt is not passed through a filter to prepare the second pellets. The method for preparing the second pellets in step Y1 is the same as the method for preparing the first pellets except that the melt is not passed through a filter, so a description thereof will be omitted.

[0064] In step Y2, the resulting melt is passed through filter Y. Filter Y has a pore size greater than 5 times the cumulative 50% diameter (D50) of the additive on a volume basis. The method for measuring the D50 of the additive is as described above. The pore size of filter Y is not particularly limited as long as it is greater than 5 times the D50 of the additive, but is preferably 10 times or greater. Furthermore, the pore size of filter Y is often 1,000 times or less the D50 of the additive. In order to remove foreign matter that may be mixed in during the second pellet production process and obtain a film in which pinholes are further suppressed, filter Y preferably has a pore size of 100 times or less, more preferably 50 times or less, and even more preferably 20 times or less. In particular, when a platinum-containing substance having a D50 of 500 nm or more, or even 5 μm or more, is contained, filter Y preferably has a pore size of 20 times or less, more preferably 15 times or less, in order to obtain a film in which pinholes are further suppressed. When two or more additives are included, the pore size of filter Y is greater than five times the D50 of the additive with the largest D50. When two or more additives are included, the pore size of filter Y is preferably within the above-mentioned preferred range relative to the D50 of the additive with the largest D50. Herein, when filter Y is a mesh filter, the pore size of filter Y refers to the openings of the mesh filter. Filter Y is preferably a 20-300 mesh mesh filter, more preferably a 50-200 mesh filter, and even more preferably a 100-200 mesh filter, in that it removes foreign matter that may be mixed in during the second pellet production process and produces a film with reduced pinhole formation. Here, "mesh" refers to the number of openings in the mesh filter per inch (2.54 cm). The pore size of filter Y is preferably 1.00 mm or less, more preferably 0.33 mm or less, even more preferably 0.30 mm or less, and particularly preferably 0.16 mm or less. The pore size of the filter Y is preferably 0.07 mm or more. The material of the filter Y is preferably metal from the viewpoint of heat resistance.

[0065] In step Y2, the obtained melt is passed through filter Y, and then second pellets are produced. The method for producing the second pellets is the same as that for producing the first pellets, and therefore, description thereof will be omitted. Note that in step Y2, filter Y may be installed near the nozzle of the melt extruder. That is, the step of passing the melt through filter Y may be performed in the melt extruder.

[0066] The preferred aspects of the second pellets obtained in the second pellet preparation step are the same as those of the first pellets except for their transmittance, and therefore, description thereof will be omitted.

[0067] <Melt Extrusion Step> In the melt extrusion step, the first pellets and the second pellets are melt extruded to obtain a film. The obtained film contains the fluoropolymer (I') and the additives. The melt extrusion step is not particularly limited as long as a film can be obtained by melt extrusion. For example, one example of the melt extrusion step is a method in which the first pellets and the second pellets are kneaded to obtain a molten mixture of the first pellets and the second pellets, and the molten mixture is extruded through a mold (die) while being cooled to form a film.

[0068] The molten mixture of the first pellets and the second pellets can be obtained by the same method as that for obtaining the melt in the second pellet production step. When the molten mixture is obtained by the twin-screw extruder, the molten mixture may be continuously fed into a mold and molded into a film.

[0069] The amount of the second pellets supplied in the melt extrusion step may be adjusted appropriately depending on the content of the additives in the second pellets and the desired content of the additives in the film. For example, the amount of the second pellets supplied in the melt extrusion step is preferably 1.0 to 50.0 mass %, more preferably 3.3 to 20.0 mass %, of the total amount of the first pellets and the second pellets supplied.

[0070] The melt extrusion process may also produce a film in which a layer obtained from the first pellets and the second pellets is laminated with another layer. That is, the melt extrusion process may be a co-extrusion process. Examples of the other layer include a layer obtained from the first pellets. Examples of the other layer include a layer obtained from a molten mixture in which the amount of second pellets supplied is different from that of the molten mixture. Furthermore, examples of the other layer include a layer obtained from a molten mixture in which the type of additive contained in the second pellets is different from that of the molten mixture.

[0071] The melt extrusion molding step may use the first pellets, second pellets containing only a platinum-containing material (hereinafter also referred to as "second pellets A" for convenience), and second pellets containing only cerium oxide (hereinafter also referred to as "second pellets B" for convenience). That is, two or more types of second pellets may be used, at least one of which may be second pellets A containing only a platinum-containing material and at least one of which may be second pellets B containing only cerium oxide. The film obtained by the melt extrusion molding step of the above embodiment contains the fluoropolymer (I'), a platinum-containing material, and cerium oxide.

[0072] The thickness of the resulting film can be adjusted as appropriate, but may be, for example, 0.5 to 500 μm. In particular, the thickness of the resulting film is preferably 10 μm or more, more preferably 20 μm or more, and may be 30 μm or more. The thickness of the resulting film is preferably 400 μm or less, more preferably 300 μm or less, and may be 200 μm or less, 90 μm or less, or 60 μm or less. When the resulting film has a multilayer structure, the above-mentioned thickness refers to the total thickness.

[0073] When the obtained film has a monolayer structure and contains a platinum-containing material, the mass ratio of the platinum-containing material to the fluoropolymer (I') in the film (mass of platinum-containing material / mass of fluoropolymer (I')) is preferably 0.0005 or more, more preferably 0.004 or more, even more preferably 0.007 or more, and is preferably 0.024 or less, and preferably 0.014 or less. If the mass ratio is 0.0005 or more, when a solid polymer electrolyte membrane formed using the film is applied to a water electrolysis device, the occurrence of hydrogen crossover can be further suppressed. If the mass ratio is 0.024 or less, when a solid polymer electrolyte membrane formed using the film is applied to a water electrolysis device, the electrolysis voltage can be further reduced. When the resulting film contains a platinum-containing material and the platinum-containing material is supported on a carrier, the mass ratio of the carrier supporting the platinum-containing material to the fluoropolymer (I') (mass of fluoropolymer (I') / mass of carrier) is preferably 10.0 or more, more preferably 30.0 or more, even more preferably 60.0 or more, and preferably 500 or less. Each of the above ratios can be adjusted by the amounts of the first pellets and the second pellets supplied.

[0074] If the resulting film contains platinum, 1 cm of film ２ The mass of platinum content per unit area is 0.005 mg / cm ２ More than 0.010 mg / cm ２ More preferably, 0.015 mg / cm or more ２ More preferably, 0.050 mg / cm ２ Preferably, 0.040 mg / cm or less ２ More preferably, the mass of the platinum-containing material is 0.005 mg / cm ２ When the mass of the platinum-containing material is 0.050 mg / cm or more, the occurrence of hydrogen crossover can be further suppressed when a solid polymer electrolyte membrane formed using the film is applied to a water electrolysis device. ２ If the temperature is below this range, the electrolysis voltage can be further reduced when a solid polymer electrolyte membrane formed using the film is applied to a water electrolysis device.

[0075] If the resulting film contains cerium oxide, 1 cm of film ２The mass of cerium oxide per ２ More than 0.010 mg / cm ２ More preferably, 0.015 mg / cm or more ２ More preferably, 0.020 mg / cm ２ More than 0.030 mg / cm is particularly preferred. ２ More than 0.300 mg / cm is most preferred. ２ Preferably, 0.150 mg / cm or less ２ More preferably, 0.100 mg / cm or less ２ More preferably, the mass of cerium oxide is 0.005 mg / cm ２ If the mass of cerium oxide is 0.300 mg / cm or more, the film will have a whitish color, making it easier to find foreign matter present in the film. As a result, when a solid polymer electrolyte membrane formed using the film is applied to a water electrolysis device, it can be used while avoiding the portion of the electrolyte membrane where foreign matter is present, thereby further suppressing the occurrence of pinholes in the electrolyte membrane due to foreign matter. ２ If it is less than this, the electrolysis voltage can be made lower.

[0076] As described above, the film obtained by this production method is suppressed from generating pinholes, and can be suitably applied to the production of solid polymer electrolyte membranes, which will be described later.

[0077] [Method for Producing a Solid Polymer Electrolyte Membrane] The method for producing a solid polymer electrolyte membrane of the present disclosure is a method for obtaining a precursor membrane by laminating the film obtained by the above-mentioned production method of the present disclosure and a woven fabric, and converting groups in the precursor membrane that can be converted to ion-exchange groups into ion-exchange groups to obtain a solid polymer electrolyte membrane. Hereinafter, the method for producing a solid polymer electrolyte membrane of the present disclosure (hereinafter, the solid polymer electrolyte membrane will also be simply referred to as the "electrolyte membrane," and the method for producing a solid polymer electrolyte membrane of the present disclosure will also be simply referred to as the "method for producing the electrolyte membrane of the present disclosure") will be described.

[0078] In the present electrolyte membrane manufacturing method, a precursor membrane is obtained by laminating the film obtained by the present manufacturing method and a woven fabric. A specific method for obtaining the precursor membrane includes, for example, arranging the film, the woven fabric, and the film in this order and hot-pressing them to obtain the precursor membrane. The hot-pressing method is not particularly limited, and examples thereof include flat plate pressing, roll pressing, and vacuum pressing. To obtain the precursor membrane, one or more films obtained by the present manufacturing method may be used. In the above embodiment, two films obtained by the present manufacturing method are used. However, for example, one of the two films may be replaced with another film formed using the first pellets. Furthermore, the films obtained by the present manufacturing method may include a film containing only a platinum-containing material as an additive and a film containing only cerium oxide as an additive. Furthermore, a precursor membrane may be obtained by arranging another film formed using the first pellets, a woven fabric, another film formed using the first pellets, and the film obtained by the present manufacturing method in this order. By controlling the thickness, stacking order, number of layers, etc. of the film obtained by this production method and other films formed using the first pellets, it is possible to adjust the distribution of additives in the resulting electrolyte membrane.

[0079] The precursor membrane is obtained in a state where the woven fabric is embedded in a film-derived matrix containing the fluoropolymer (I') and the above-mentioned additives.

[0080] Hereinafter, the woven fabric used in the method for producing the electrolyte membrane will be described, and then a method for converting groups that can be converted into ion-exchange groups into ion-exchange groups will be described.

[0081] The woven fabric serves to improve the dimensional stability, strength, and handleability of the resulting electrolyte membrane. 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, in order to further reduce the electrolysis voltage when applied to a water electrolysis device. The upper limit of the aperture ratio of the woven fabric is preferably 90% or less, particularly preferably 80% or less, in order to further improve the strength of a membrane electrode assembly formed using the electrolyte membrane. The aperture ratio of the woven fabric is calculated using the following formula (ε) based on the average diameter R1 of the threads constituting the woven fabric and the average spacing P1 between adjacent threads (hereinafter also referred to as "pitch P1") among the threads constituting the woven fabric. Here, the average diameter R1 of the threads refers to the arithmetic mean value of the diameters of 10 different threads arbitrarily selected based on a magnified image (e.g., 100x magnification) of the woven fabric surface obtained using a microscope. The pitch P1 refers to the arithmetic mean value of 10 different intervals arbitrarily selected based on a magnified image (for example, 100x) of the woven fabric surface obtained using a microscope. Opening ratio of woven fabric (%) = [P1 / (P1+R1)] ２ × 100 (ε)

[0082] The denier number of the yarns constituting the woven fabric is preferably 2 or more, and from the viewpoint of achieving better strength and dimensional stability of a membrane electrode assembly formed using the electrolyte membrane, it is more preferably 10 or more, and particularly preferably 15 or more. The upper limit of the denier number of the yarns constituting the woven fabric is preferably 60 or less, more preferably 50 or less, and particularly preferably 20 or less, from the viewpoint of further reducing the electrolysis voltage when applied to a water electrolysis device. The denier number is the mass of 9,000 m of yarn expressed in grams (g / 9000 m).

[0083] The density of the threads constituting the woven fabric is preferably 50 threads / inch or more, more preferably 70 threads / inch or more, and particularly preferably 90 threads / inch or more, in terms of achieving excellent strength and dimensional stability of a membrane electrode assembly formed using the electrolyte membrane, and is preferably 200 threads / inch or less, more preferably 150 threads / inch or less, and particularly preferably 100 threads / inch or less, in terms of further reducing the electrolysis voltage when applied to a water electrolysis device.

[0084] The yarns constituting the woven fabric may be either monofilaments consisting of one filament or multifilaments consisting of two or more filaments, with monofilaments being preferred.

[0085] The yarns constituting the woven fabric are preferably each independently 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 view of superior yarn durability. The yarns constituting the woven fabric are preferably made of slit yarns in view of superior yarn durability and strength.

[0086] When the material constituting the woven fabric is PTFE, the basis weight of the woven fabric is 20 g / m2, which provides an excellent balance between the strength and handleability of the resulting electrolyte membrane. ２ More than 30 g / m ２ More than 40 g / m ２ When the material constituting the woven fabric is PFA, the weight of the woven fabric is preferably 10 g / m or less, in view of the excellent balance between the strength and the handleability of the resulting electrolyte membrane. ２ More than 30 g / m ２ Preferably, 20 g / m or less ２ When the material constituting the woven fabric is PEEK, the weight per unit area of ​​the woven fabric is preferably 5 g / m2 or less, in view of the excellent balance between the strength and the handleability of the resulting electrolyte membrane. ２ More than 40 g / m ２ Preferably, 30 g / m or less ２ When the material constituting the woven fabric is PPS, the weight per unit area of ​​the woven fabric is preferably 5 g / m2 or less, in view of the excellent balance between the strength and the handleability of the resulting electrolyte membrane. ２ More than 40 g / m ２ More than 30 g / m ２ The following is more preferred:

[0087] The content of the woven fabric is preferably 3 mass% or more, more preferably 5 mass% or more, and is preferably 50 mass% or less, more preferably 40 mass% or less, and even more preferably 30 mass% or less, based on the total mass of the resulting electrolyte membrane.

[0088] Specific examples of methods for converting groups in the precursor membrane that can be converted to ion-exchange groups into ion-exchange groups include methods of subjecting the precursor membrane to hydrolysis treatment, acidification treatment, etc. Among these, a method of contacting the precursor membrane with an alkaline aqueous solution is preferred.

[0089] Specific examples of the method for contacting the precursor film with the 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. The temperature of the alkaline aqueous solution is preferably 30° C. or higher, more preferably 40° C. or higher, and preferably 100° C. or lower. The contact time between the precursor film and the alkaline aqueous solution is preferably 3 minutes or longer, more preferably 5 minutes or longer, and preferably 150 minutes or shorter, more preferably 50 minutes or shorter.

[0090] 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 1000 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 may be used in combination.

[0091] 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.

[0092] The concentration of the alkali metal hydroxide in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less. The content of the water-soluble organic solvent in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less. The concentration of water in the alkaline aqueous solution is preferably 39 to 80% by mass.

[0093] 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.

[0094] 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 the 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.

[0095] When groups in the precursor membrane that can be converted into ion-exchange groups are converted into ion-exchange groups, an electrolyte membrane containing a fluoropolymer having ion-exchange groups (hereinafter also referred to as "fluoropolymer (I)") can be obtained. The fluoropolymer (I) is a fluoropolymer obtained by converting groups in the fluoropolymer (I') contained in the precursor membrane that can be converted into ion-exchange groups into ion-exchange groups. Hereinafter, a fluoropolymer (hereinafter also referred to as "fluoropolymer (S)") obtained by converting groups in the fluoropolymer (S') that can be converted into sulfonic acid type functional groups will be described.

[0096] The fluoropolymer (S) is preferably obtained by converting a group convertible to a sulfonic acid functional group of the above-mentioned fluoropolymer (S') into a sulfonic acid group. The fluoropolymer (S) preferably contains units based on tetrafluoroethylene and units based on a monomer having a sulfonic acid functional group and a fluorine atom.

[0097] As the unit based on a monomer having a sulfonic acid functional group and a fluorine atom, a unit represented by formula (2S) is preferred. Formula (2S): -[CF ２ -CF(-L-(SO ３ M Ｓ ) ｎ )]-

[0098] In formula (2S), the definitions of L and n are the same as those in formula (2). Ｓ is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. When n=2, two M Ｓ may be the same or different.

[0099] The unit represented by formula (2S) is preferably a unit represented by formula (2S-1), a unit represented by formula (2S-2), a unit represented by formula (2S-3), or a unit represented by formula (2S-4). ２ -CF(-O-R ｆ１ -SO ３ M Ｓ )] - Formula (2S-2) - [CF ２ -CF(-R ｆ１ -SO３ M Ｓ )]-

[0100]

[0101]

[0102] In formulas (2S-1) to (2S-4), R ｆ１ , R ｆ２ , R ｆ３ The definitions of r and m are the same as those in the above formulas (2-1) to (2-4). Ｓ The definition of is as described above.

[0103] Specific examples of the unit represented by formula (2S-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. M in the formula Ｓ The definition of -[CF ２ -CF(-O-(CF ２ ) ｗ -SO ３ M Ｓ ) ]- -[CF ２ -CF(-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ３ M Ｓ ) ]- -[CF ２ -CF(-(O-CF ２ CF (CF ３ )) ｘ -SO ３ M Ｓ )]-

[0104] Specific examples of the unit represented by formula (2S-2) include the following units: In the formula, w is an integer of 1 to 8. In the formula, M Ｓ The definition of -[CF ２ -CF(-(CF ２ ) ｗ -SO ３ M Ｓ ) ]- -[CF ２ -CF (-CF ２ -O-(CF ２ ) ｗ -SO ３ MＳ )]-

[0105] As the unit represented by formula (2S-3), a unit represented by formula (2S-3-1) is preferred. Ｓ The definition of is as described above.

[0106]

[0107] In formula (2S-3-1), R ｆ４ , R ｆ５ The definitions of and r are the same as in the above formula (2-3-1). Ｓ The definition of is as described above.

[0108] Specific examples of the unit represented by formula (2S-3) include the following.

[0109]

[0110] As the unit represented by formula (2S-4), a unit represented by formula (2S-4-1) is preferred. ｆ１ , R ｆ２ and M Ｓ The definition of is as described above.

[0111]

[0112] Specific examples of the unit represented by formula (2S-4-1) include the following.

[0113]

[0114] The unit based on a monomer having a sulfonic acid type functional group and a fluorine atom may be contained either alone or in combination of two or more types.

[0115] The fluoropolymer (S) may contain units based on other monomers other than the units based on tetrafluoroethylene and the units based on the monomer having a sulfonic acid functional group and a fluorine atom. Specific examples of the other monomers include those exemplified above. From the viewpoint of maintaining ion exchange performance, the content of the units based on the other monomers is preferably 30 mass% or less based on the total units in the fluoropolymer (S).

[0116] The electrolyte membrane may have a single layer structure or a multilayer structure. Specific examples of the multilayer electrolyte membrane include a laminated structure in which multiple electrolyte layers having different contents of at least one of a platinum-containing material and cerium oxide are stacked, and a laminated structure in which multiple electrolyte layers having different ion exchange capacities are stacked.

[0117] The platinum-containing material and cerium oxide contained in the electrolyte membrane may be dispersed throughout the electrolyte membrane or may be unevenly distributed on one surface side of the electrolyte membrane. It is particularly preferable that at least one of the platinum-containing material and cerium oxide is unevenly distributed on one surface side of the electrolyte membrane, and it is preferable that at least the platinum-containing material, of the platinum-containing material and cerium oxide, is unevenly distributed on one surface side of the electrolyte membrane. Furthermore, the platinum-containing material and cerium oxide (i.e., both the platinum-containing material and cerium oxide) may be unevenly distributed on one surface side of the electrolyte membrane. When the electrolyte membrane is used in a water electrolysis device, it is preferable to position the surface of the electrolyte membrane on which the platinum-containing material is unevenly distributed on the anode side, in order to further suppress the occurrence of hydrogen crossover. In this case, the catalyst contained in the catalyst layer of the anode preferably contains iridium oxide, in order to achieve the above-mentioned effects more effectively.

[0118] In this specification, the phrase "platinum-containing substances are unevenly distributed on one surface side of the electrolyte membrane" means that the concentration of platinum-containing substances in a region from one surface (hereinafter also referred to as "surface A") of the electrolyte membrane to a predetermined depth position (hereinafter also referred to as "depth position B") before reaching the other surface (hereinafter also referred to as "surface C") is higher than the concentration of platinum-containing substances in a region from surface C to depth position B. Furthermore, the phrase "cerium oxide is unevenly distributed on one surface side of the electrolyte membrane" means that the concentration of cerium oxide in a region from surface A to depth position B is higher than the concentration of cerium oxide in a region from surface C to depth position B. Furthermore, the phrase "platinum-containing substances and cerium oxide are unevenly distributed on one surface side of the electrolyte membrane" means that the concentration of platinum-containing substances in a region from surface A to depth position B is higher than the concentration of platinum-containing substances in a region from surface C to depth position B, and the concentration of cerium oxide in a region from surface A to depth position B is higher than the concentration of cerium oxide in a region from surface C to depth position B. Here, in one preferred embodiment in which the platinum-containing substance is unevenly distributed on one surface side of the electrolyte membrane, the platinum-containing substance is unevenly distributed at a depth position B, which is a depth position of 50% of the thickness of the electrolyte membrane from the surface A. ５０ The concentration of platinum-containing substances in the region from the surface C to the depth position B ５０ In one embodiment, the concentration of the platinum-containing material is higher than that in the region up to 10 ...

[0119] The state in which "platinum inclusions are unevenly distributed on one surface side of the electrolyte membrane" will be specifically explained using the example of FIG. 1. FIG. 1 is a cross-sectional schematic diagram of an electrolyte membrane for explaining the state in which platinum inclusions are unevenly distributed. In FIG. 1, the electrolyte membrane 1 has a surface A1, which is one surface, and a surface C1, which is the other surface. The depth position B1 is a distance T from the surface A1 toward the surface C1. Ｘ The distance T １ corresponds to the thickness of the electrolyte membrane 1, and the distance T Ｘ is the distance T １ For example, the length is X% of the distance T Ｘ is the distance T １, the depth position B1 is the thickness of the electrolyte membrane 1 (distance T １ ) corresponds to a position where the thickness is 20% of the surface thickness of the electrolyte membrane. Region X represents the region from surface A1 to depth position B1, and region Y represents the region from surface C1 to depth position B1. If there are irregularities on the surface of the electrolyte membrane 1, the above distances are measured based on the position where the thickness of the electrolyte membrane 1 is minimum. In FIG. 1, if the concentration of the platinum-containing substance in region X is higher than the concentration of the platinum-containing substance in region Y, it can be said that "the platinum-containing substance is unevenly distributed on one surface side of the electrolyte membrane."

[0120] In order to obtain a more excellent effect of the present disclosure, the platinum-containing material contained in the electrolyte membrane is preferably present from one surface of the electrolyte membrane to a position of a thickness equivalent to 25% of the thickness of the electrolyte membrane, more preferably from one surface of the electrolyte membrane to a position of a thickness equivalent to 20% of the thickness of the electrolyte membrane, even more preferably from one surface of the electrolyte membrane to a position of a thickness equivalent to 15% of the thickness of the electrolyte membrane, and even more preferably from one surface of the electrolyte membrane to a position of a thickness equivalent to 10% of the thickness of the electrolyte membrane. Furthermore, it is more preferable that the platinum-containing material contained in the electrolyte membrane is present only up to these thickness positions.

[0121] The positions of the platinum-containing material and cerium oxide in the electrolyte membrane can be identified by element distribution using, for example, an energy dispersive X-ray analyzer (product name "QUANTAX FlatQUAD", manufactured by Bruker). Based on the obtained element distribution, the above-mentioned distance Tx can be calculated.

[0122] The platinum-containing material can be unevenly distributed on one surface of the electrolyte membrane by the methods described above, specifically by adjusting the position of the film obtained by the present production method when obtaining a precursor membrane. Furthermore, the cerium oxide can be unevenly distributed on one surface of the electrolyte membrane by the same method as the platinum-containing material can be unevenly distributed on one surface of the electrolyte membrane.

[0123] The electrolyte membrane preferably does not substantially contain a thickener because the membrane resistance increases. The phrase "the electrolyte membrane is substantially free of a thickener" means that the content of the thickener is 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0% by mass, relative to the total mass of the electrolyte membrane. Specific examples of thickeners will be described later.

[0124] The thickness of the electrolyte membrane is preferably 30 μm or more, and is preferably 400 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, particularly preferably 90 μm or less, and most preferably 60 μm or less. When the electrolyte membrane has a multilayer structure, the thickness of the electrolyte membrane refers to the total thickness of each layer. When the electrolyte membrane has a multilayer structure and includes a first electrolyte layer containing a platinum-containing substance and a second electrolyte layer having a lower concentration of the platinum-containing substance than the first electrolyte layer or not containing the platinum-containing substance, the ratio of the thickness of the first electrolyte layer to the thickness of the second electrolyte layer (thickness of the first electrolyte layer / thickness of the second electrolyte layer) is preferably 0.02 or more, more preferably 0.05 or more, even more preferably 0.12 or more, even more preferably 0.19 or more, and preferably 0.80 or less, more preferably 0.50 or less, and even more preferably 0.30 or less. The thickness of the electrolyte membrane is measured using a magnified image (for example, 100x) of the cross section of the electrolyte membrane taken with an optical microscope (product name "BX-51", manufactured by Olympus Corporation). If the surface of the electrolyte membrane is uneven, the thickness of 10 recessed portions on the electrolyte membrane and the thickness of 10 protruding portions on the electrolyte membrane are measured, and the arithmetic mean value of the thicknesses at a total of 20 points is taken as the thickness of the electrolyte membrane. However, if the protruding portions contain threads that constitute the woven fabric, the thickness of the protruding portions is taken as the value obtained by subtracting the thickness of the threads present in the protruding portions.

[0125] The electrolyte membrane obtained by this electrolyte membrane manufacturing method contains an additive. When a platinum-containing substance is contained as the additive, when the electrolyte membrane is applied to a water electrolysis device, hydrogen generated on the cathode side reacts with oxygen generated on the anode side on the platinum-containing substance contained in the electrolyte membrane to form water, thereby suppressing the movement of hydrogen to the anode side (hydrogen crossover). Furthermore, when cerium oxide is contained as the additive, when the electrolyte membrane is applied to a water electrolysis device, OH radicals generated from hydrogen peroxide generated in the system during operation are quenched by cerium ions dissociated from the cerium oxide contained in the electrolyte membrane, thereby suppressing decomposition of the fluoropolymer (I).

[0126] [Membrane Electrode Assembly] The solid polymer electrolyte membrane (electrolyte membrane) obtained by the method for producing a solid polymer electrolyte membrane of the present disclosure can be suitably applied to a membrane electrode assembly. The membrane electrode assembly includes, for example, the electrolyte membrane, a cathode catalyst layer disposed on one side of the electrolyte membrane, and an anode catalyst layer disposed on the other side of the electrolyte membrane.

[0127] Fig. 2 is a cross-sectional view schematically illustrating an example of a membrane electrode assembly. In the example of Fig. 2, the membrane electrode assembly 20 includes an anode 22 having a catalyst layer 26 and a gas diffusion layer 28, a cathode 24 having the catalyst layer 26 and the gas diffusion layer 28, and an electrolyte membrane 10 disposed between the anode 22 and the cathode 24 in contact with the catalyst layer 26. Note that the woven fabric of the electrolyte membrane 10 shown in Fig. 2 is omitted from the illustration.

[0128] Although the example of FIG. 2 illustrates a case where the electrolyte membrane has a single layer structure, the electrolyte membrane may have a multilayer structure. Specific examples and preferred embodiments of the multilayer electrolyte membrane are as described above. FIG. 3 is a cross-sectional view schematically illustrating an example of a membrane electrode assembly according to the present disclosure, illustrating a case where the electrolyte membrane has a multilayer structure. The structure of the membrane electrode assembly 120 in FIG. 3 is similar to the structure of the membrane electrode assembly 20 in FIG. 2 except that the electrolyte membrane 10 in FIG. 2 has an electrolyte membrane 100 instead of the electrolyte membrane 10 in FIG. 2. The electrolyte membrane 100 in FIG. 3 includes a first electrolyte layer 100A and a second electrolyte layer 100B disposed in this order from the anode 22 side toward the cathode 24 side. Note that the woven fabric is not shown in the electrolyte membrane 100 illustrated in FIG. 3. The first electrolyte layer 100A contains a fluorine-containing polymer (I), a platinum-containing material, and cerium oxide. The second electrolyte layer 100B contains a fluorine-containing polymer (I) and cerium oxide. The second electrolyte layer 100B has a lower concentration of platinum-containing substances than the first electrolyte layer 100A or does not contain platinum-containing substances. At least one of the first electrolyte layer 100A and the second electrolyte layer 100B contains a woven fabric.

[0129] In the example of FIG. 3, the electrolyte membrane has a two-layer structure, but the electrolyte membrane may have a three-layer or more structure.

[0130] In the example of FIG. 3 , only the platinum-containing material is unevenly distributed on one surface side of the electrolyte membrane. However, the electrolyte membrane included in the membrane electrode assembly of the present disclosure may have both the platinum-containing material and cerium oxide unevenly distributed on one surface side.

[0131] <Anode and Cathode> The anode and cathode each have a catalyst layer. In the example of Figure 2, the anode 22 and cathode 24 each have a catalyst layer 26 and a gas diffusion layer 28.

[0132] Specific examples of the catalyst layer include a layer containing a catalyst and a polymer having an ion-exchange group.Specific examples of the catalyst include a supported catalyst in which a catalyst containing platinum, a platinum alloy, or a platinum having a core-shell structure is supported on a carbon support, an iridium oxide catalyst, a composite oxide catalyst containing iridium and other metal elements, an alloy containing iridium oxide, and a catalyst containing iridium oxide having a core-shell structure.An example of the carbon support is carbon black powder.An example of the polymer having an ion-exchange group is a fluorine-containing polymer having an ion-exchange group, and for example, the above-mentioned fluorine-containing polymer (I) can be used.

[0133] Catalyst layer 1cm ２ The mass of the catalytic metal per ２ More than 0.05 mg / cm ２ More preferably, 0.2 mg / cm ２ More preferably, 4 mg / cm ２ Preferably, less than 2 mg / cm ２ More preferably, 1 mg / cm or less ２ The following is more preferred: The mass ratio of the catalyst to the polymer having ion-exchange groups in the catalyst layer (mass of catalyst / mass of polymer having ion-exchange groups) is preferably 2 to 6.

[0134] The catalyst layer preferably contains a thickener from the viewpoint of improving the dispersibility of the catalyst and suppressing aggregation. Specific examples of thickeners include urethane-based thickeners, polyacrylic-based thickeners, polyamide-based thickeners, cellulose-based thickeners, and clay minerals such as bentonite. Zeorora (registered trademark) H (manufactured by Zeon Corporation) can also be used as a thickener. When the catalyst layer contains a thickener, the content of the thickener is preferably 2% by mass or more, more preferably 3% by mass or more, and preferably 7% by mass or less, more preferably 6% by mass or less, relative to the total mass of the coating liquid for forming the catalyst layer described below.

[0135] The gas diffusion layer functions to rapidly diffuse gas generated from the catalyst layer out of the catalyst layer and as a current collector. Specific examples of gas diffusion layers include carbon paper, carbon cloth, carbon felt, sintered titanium oxide fiber, and sintered titanium oxide particles. The anode side has a high potential, and using carbon materials would result in oxidation. Therefore, it is preferable to use sintered titanium oxide fiber or sintered titanium oxide particles. The sintered titanium oxide may be plated with platinum or other metals as needed. The cathode gas diffusion layer may be treated with PTFE or other materials for water repellency. While the membrane electrode assembly in FIG. 2 includes a gas diffusion layer 28, the gas diffusion layer is an optional component and need not be included in the membrane electrode assembly.

[0136] The film thickness of the anode and the cathode is preferably 5 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 15 μm or less, from the viewpoint of achieving superior effects of the present disclosure. The film thickness of the anode and the cathode is measured using an image obtained by measuring a cross section of the membrane electrode assembly cut in the film thickness direction with a laser microscope, and is the arithmetic average value at any 20 points.

[0137] <Method for Manufacturing a Membrane Electrode Assembly> The method for manufacturing a membrane electrode assembly involves forming the cathode catalyst layer on one side of an electrolyte membrane and the anode catalyst layer on the other side of the electrolyte membrane. One example of a method for manufacturing a membrane electrode assembly involves using a laminate having an anode catalyst layer and a releasable substrate (e.g., an ETFE sheet) and another laminate having a cathode catalyst layer and a releasable substrate (e.g., an ETFE sheet), bonding catalyst layers to both sides of the electrolyte membrane, and then peeling off the releasable substrate. The laminate may have a gas diffusion layer between the catalyst layer and the releasable substrate. In this case, the gas diffusion layer can be formed on the catalyst layer opposite the electrolyte membrane. The catalyst layer can be manufactured by applying a catalyst layer-forming coating liquid to a predetermined position (e.g., the surface of the releasable substrate) and drying it as necessary. The catalyst layer-forming coating liquid is a liquid in which a polymer having ion exchange groups and a catalyst are dispersed in a dispersion medium.

[0138] <Applications> The membrane electrode assembly is suitably used in, for example, a polymer electrolyte water electrolysis device.

[0139] [Water Electrolysis Apparatus] The water electrolysis apparatus includes, for example, the membrane electrode assembly described above, a water supply unit that supplies water to the anode catalyst layer side, and a power supply unit that is electrically connected to the anode catalyst layer side and the cathode catalyst layer side. In the water electrolysis apparatus, when the power supply unit applies a DC voltage while water is supplied to the anode catalyst layer side by the water supply unit, oxygen and protons are generated from the water by an electrochemical reaction on the anode catalyst layer side. On the cathode catalyst layer side, the protons that have migrated to the cathode catalyst layer side through the electrolyte membrane obtain electrons, generating hydrogen. The water electrolysis apparatus of the present disclosure may have the same configuration as known water electrolysis apparatuses (e.g., an oxygen recovery member that recovers the generated oxygen and a hydrogen recovery member that recovers the generated hydrogen), except for including the above-described components.

[0140] The present invention will be described in detail below with reference to examples. Examples 1 to 9 are working examples, and Examples 10 to 12 are comparative examples. However, the present invention is not limited to these examples.

[0141] [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 (milli-equivalent / gram dry resin) of the fluoropolymer.

[0142] [First pellet preparation step] First, the following fluoropolymer containing units based on tetrafluoroethylene and having groups convertible to ion-exchange groups was obtained.

[0143] <Production of Fluorine-Containing Polymer (S'-3)> CF ２ =CF ２and a monomer (X1) represented by the following formula (X1) were copolymerized to obtain a fluoropolymer (S'-3) (ion exchange capacity: 1.25 meq / g resin). The blending ratio of each monomer was adjusted so that the ion exchange capacity of the fluoropolymer (S'-3) would be the above-mentioned value. Formula (X1): CF ２ =CF-O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F

[0144] <Production of Fluorine-Containing Polymer (S'-4)> CF ２ =CF ２ and a monomer (X2) represented by the following formula (X2) were copolymerized to obtain a fluoropolymer (S'-4) (ion exchange capacity: 1.90 meq / g resin). The blending ratio of the respective monomers was adjusted so that the ion exchange capacity of the fluoropolymer (S'-4) would be the above-mentioned value.

[0145]

[0146] <First pellets 1> When obtaining the first pellets 1, first, the obtained fluoropolymer (S'-3) was heated to 260°C to melt it, and passed through the following filter X1 (corresponding to the above filter X). Filter X1: metal mesh filter (#500, openings: 0.026 mm) Next, the melt of the fluoropolymer (S'-3) that had passed through the above filter 1 was supplied to a die heated to 260°C and extruded to obtain strands having a diameter of 3.0 mm. The obtained strands were cut to a length of 3.0 mm to obtain the first pellets 1. The above procedure was carried out continuously using a melt extruder.

[0147] <First pellets 2> First pellets 2 were obtained by carrying out the same procedure as for first pellets 1, except that the fluoropolymer used was changed to a fluoropolymer shown in the table below.

[0148] <First Pellets D1> First pellets D1 were obtained by carrying out the same procedure as for first pellets 1, except that the fluoropolymer melt was not passed through a filter.

[0149] [Second Pellets Production Step] Second pellets were obtained using the first pellets obtained by the above procedure. The procedure for obtaining each of the second pellets will be described below.

[0150] <Second pellets 1> A melt containing the first pellets 1 obtained by the above procedure and an additive (platinum-containing material 1 described below) was obtained. Platinum-containing material 1: platinum black ("TEC90300" manufactured by Tanaka Kikinzoku Kogyo K.K., D50: 14 μm) (referred to as "Pt black" in the table). The melt was obtained by supplying the first pellets 1 and the platinum-containing material 1 to a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.) at a heating temperature of 260°C. The platinum-containing material 1 was supplied in an amount of 1.2 parts by mass when the supply amount of the first pellets 1 was taken as 100 parts by mass.

[0151] Next, the obtained melt was used to obtain second pellets 1 in the same procedure as that for obtaining the first pellets 1. When obtaining the second pellets 1, the following filter Y1 was used as the filter. Filter Y1: Metal mesh filter (opening size: 0.150 mm)

[0152] <Second pellets 2 to 6 and E1> Second pellets 2 to 4 and second pellet E1 were obtained in the same manner as second pellet 1, except that the first pellets used, the additives used and their amounts were changed as shown in the table below, and the filter was changed as shown in the table below. Note that when a filter is not specified in the table below, it indicates that the second pellets were obtained without using a filter (without passing the melt through a filter). Note that the following cerium oxide was used to prepare second pellet 4. Cerium oxide: cerium oxide (D50: 7 μm) (in the table, "CeO ２ The second pellets 6 were prepared using the following platinum-containing material 2. Platinum-containing material 2: platinum-supported carbon (D50: 0.1 μm) (referred to as "Pt / C" in the table).

[0153] <Second Pellets E2> Second pellets E2 were obtained in the same manner as in the procedure for obtaining second pellets 1, except that the amounts of additives used were changed as shown in the table below.

[0154] [Melt Extrusion Step] The first pellets and the second pellets obtained by the above procedure were subjected to a melt extrusion step.

[0155] Example 1 First pellets 1 and second pellets 1 were melted to obtain a molten mixture, which was then melt-extruded to obtain a film. Specifically, first pellets 1 and second pellets 1 were supplied to an extruder, a molten mixture was obtained in the heat mixing section of the extruder, and the molten mixture was extruded through a T-die to form a film 1 having a thickness of 30 μm on a substrate. A linear low-density polyethylene (LLDPE) film (melting point: 110-120° C.) was used as the substrate. The amounts of first pellets 1 and second pellets 1 supplied were as shown in the "Amount supplied during film formation" column in the table below.

[0156] Examples 2 to 10 Films 2 to 10 were obtained by melt extrusion molding in the same manner as in Example 1, except that the first pellets and second pellets were used in the combinations shown in the table below. The amounts of the first pellets and second pellets supplied were as shown in the table below.

[0157] Example 11 A melt-extrusion film 8 was obtained in the same manner as in Example 1, except that only the second pellets E2 were used.

[0158] Example 12 An attempt was made to obtain a film by melt extrusion molding the second pellets E2 alone through the filter X1 used in producing the first pellets 1. As a result, clogging occurred in the filter X1, and a film could not be obtained.

[0159] [Evaluation] Each of the obtained films was evaluated for pinholes by the following method. For each of the obtained films, the number of pinholes (holes) was counted using a pinhole inspection device (product name "TRS-70", manufactured by Sanko Electronics Laboratory Co., Ltd.). Whether pinholes were suppressed was evaluated according to the following criteria. Note that, from a practical standpoint, a rating of A or B is preferable. A: No pinholes were found. B: 1 to 2 pinholes were found. C: 3 or more pinholes were found.

[0160] [Results] Table 1 shows the production conditions for the first pellets and second pellets used in each of the above examples, the production conditions for the films, and the evaluation results. Note that examples in which both second pellets A and second pellets B are listed indicate that two types of second pellets were used as the second pellets. For Example 12, the above evaluation was not performed because no film was obtained. In the table, "opening size / D50" indicates how many times the pore size of filter Y is compared to the D50 of the additive listed in the table. Furthermore, "opening size" in the table indicates the pore size of each filter.

[0161]

[0162] As shown in Table 1, a comparison of Examples 10 to 12 with Examples 1 to 9 confirmed that when first pellets were prepared through filter X, second pellets were obtained using the first pellets in a predetermined procedure, and then the first and second pellets were melt-extruded to obtain a film, pinhole formation was suppressed. Furthermore, a comparison of Examples 1 and 4 confirmed that when a platinum-containing substance having a D50 of 500 nm or more was contained, a film in which pinhole formation was further suppressed could be obtained if the pore size of filter Y was 20 times or less than D50. A comparison of Examples 1 and 2 confirmed that a film in which pinhole formation was further suppressed could be obtained if the pore size of filter Y was 0.30 mm or less.

[0163] [Production of Solid Polymer Electrolyte Membrane] A solid polymer electrolyte membrane was produced using the film 1 obtained in Example 1 and the woven fabric A1, which will be described in detail later. Specifically, a film-attached substrate having the film 1, the woven fabric A1, and another film-attached substrate having the film 1 were stacked in this order. The film-attached substrate was positioned so that the film 1 in the film-attached substrate was in contact with the woven fabric A1. The stacked members were then heated at a temperature of 160°C and a surface pressure of 30 MPa / m ２After 10 minutes of heat and pressure bonding using a flat plate press, the substrates on both sides were peeled off at a temperature of 50 ° C. to obtain a precursor membrane. 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 the groups convertible to sulfonic acid functional groups in the precursor membrane were hydrolyzed to K-type sulfonic acid functional groups, and then washed with water. The obtained membrane was then immersed in 1 M sulfuric acid, the terminal groups were converted from K-type to H-type, and then dried to obtain the electrolyte membrane of Example 1 (thickness 90 μm).

[0164] The resulting electrolyte membrane was evaluated for pinholes in the same manner as for the film, and was given a rating of A.

[0165] <Woven Fabric> Woven fabric A1 was obtained by plain weaving 18.6 denier PFA yarns as warp and weft yarns so that the density of the PFA yarns was 100 threads / inch. The weight of the woven fabric A1 was 16.3 g / m ２ The warp and weft were made of slit yarns.

[0166] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-222993 filed on December 28, 2023 are hereby incorporated by reference as the disclosure of the specification of the present invention.

[0167] 1, 10, 100 Electrolyte membrane 20, 120 Membrane electrode assembly 22 Anode 24 Cathode 26 Catalyst layer 28 Gas diffusion layer 100A First electrolyte layer 100B Second electrolyte layer A1, C1 Surface B1 Depth position T １ , T Ｘ Distance X, Y area

Claims

1. A method for producing a film, comprising melting a fluorine-containing polymer containing units based on tetrafluoroethylene and having a group convertible to an ion-exchange group, producing first pellets through a filter X, obtaining a melt containing the additive and the fluorine-containing polymer using at least one additive selected from the group consisting of a platinum-containing substance and cerium oxide and the first pellets, and producing second pellets containing the additive by passing through a filter that does not pass through the filter or has a pore size larger than 5 times the cumulative 50% diameter of the additive based on volume, and melt-extrusion molding using the first pellets and the second pellets to produce a film containing the fluorine-containing polymer and the additive.

2. The method for producing a film according to claim 1, wherein the second pellets contain both the platinum-containing substance and the cerium oxide.

3. In the melt-extrusion molding, two or more kinds of the second pellets are used, at least one kind of the second pellets contains only the platinum-containing substance, and at least one kind of the second pellets contains only the cerium oxide. The method for producing a film according to claim 1.

4. The method for producing a film according to claim 1, wherein the platinum-containing substance is supported on a carrier.

5. The method for producing a film according to claim 1, wherein the cumulative 50% diameter of the platinum-containing substance based on volume is 500 nm or more.

6. The method for producing a film according to claim 1, wherein the pore size of the filter Y is 20 times or less the cumulative 50% diameter of the additive based on volume.

7. The method for producing a film according to claim 1, wherein the group convertible to an ion-exchange group is a group convertible to a sulfonic acid-type functional group.

8. The method for producing a film according to claim 7, wherein the fluorine-containing polymer contains at least one unit selected from the group consisting of a unit based on a compound represented by formula (2-3) and a unit based on a compound represented by formula (2-4). In formula (2-3) and formula (2-4), R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms, and R ｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. In formula (2-4), R ｆ３ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. In formula (2-3) and formula (2-4), r is 0 or 1, and a plurality of A's are each independently a group convertible into a sulfonic acid type functional group. In formula (2-4), m is 0 or 1.

9. A method for producing a solid polymer electrolyte membrane, comprising producing a film by the method for producing a film according to any one of claims 1 to 8, obtaining a precursor membrane by laminating the film and a woven fabric, and converting a group convertible to an ion-exchange group in the precursor membrane to an ion-exchange group to obtain a solid polymer electrolyte membrane.

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