Electrolyte membrane manufacturing method and electrolyte membrane

Abstract

A method for producing an electrolyte membrane, comprising: a step of preparing a porous substrate containing a porous membrane and a crosslinking agent retained in the pores of the porous membrane; an impregnation step of impregnating the porous substrate with a solution containing an electrolyte polymer; and a crosslinking step of reacting the electrolyte polymer with the crosslinking agent to form a crosslinked electrolyte polymer.

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing an electrolyte membrane and an electrolyte membrane. [Background technology]

[0002] Fuel cells are attracting attention as a new energy technology with high energy efficiency. Among them, solid polymer fuel cells using electrolyte polymers are attracting particular attention because they have a high maximum current density and operate at low temperatures, making them suitable for use as a mobile power source for automobiles and small-capacity power sources for portable electronic devices.

[0003] The electrolyte membrane used in polymer electrolyte fuel cells can develop cracks on the surface or inside the membrane due to repeated swelling due to wetting and shrinkage due to drying. For this reason, electrolyte membranes with improved mechanical strength, which are reinforced by providing a porous substrate inside the membrane, are being studied.

[0004] For example, Patent Document 1 discloses an electrolyte membrane comprising a porous substrate and a resin composition filled, fixed, and held in the voids and / or pores of the porous substrate, wherein the resin composition comprises an electrolyte polymer crosslinked with a crosslinking agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-117750 Summary of the Invention [Problem to be solved by the invention]

[0006] The electrolyte membrane described in Patent Document 1 was produced by impregnating a porous substrate with a resin composition in which a crosslinker and an electrolyte polymer were mixed in advance. However, resin compositions in which a crosslinker and an electrolyte polymer were mixed in advance tend to increase in viscosity due to their short pot life (usable time). As a result, such resin compositions are difficult to impregnate into the porous substrate, and as a result, the mechanical strength of the electrolyte membrane may not be sufficiently improved.

[0007] An object of the present disclosure is to provide at least one of an electrolyte membrane having high mechanical strength and a method for producing the same. [Means for solving the problem]

[0008] The present disclosure is as set forth in the claims, and the gist of the present disclosure is as follows. [1] providing a porous substrate comprising a porous membrane and a cross-linking agent retained within the pores of the porous membrane; an impregnation step of impregnating the porous substrate with a solution containing an electrolyte polymer; a crosslinking step of reacting the electrolyte polymer with the crosslinking agent to form a crosslinked electrolyte polymer. [2] a drying step of drying the solution filled in the porous substrate in the impregnation step; A step of applying a solution containing the electrolyte polymer to the surface of the porous substrate after the drying step to form a layer made of the solution on the surface of the porous substrate; and drying the layer made of the solution to form a contact layer containing the electrolyte polymer. [3] The method for producing an electrolyte membrane according to [2], wherein the thickness of the contact layer is 1 μm or more and 15 μm or less. [4] The method for producing an electrolyte membrane according to any one of [1] to [3], wherein the number average molecular weight of the electrolyte polymer is 18,000 or more and 60,000 or less. [5] The amount of the crosslinking agent retained in the porous substrate is 3.0 × 10 -8 mol / cm 2 Over 20.0 x 10 -8 mol / cm 2 The method for producing an electrolyte membrane according to any one of [1] to [4], which is as follows: [6] The method for producing an electrolyte membrane according to any one of [1] to [5], wherein the porous substrate further contains, in the pores, a binder that does not react with the crosslinking agent. [7] The method for producing an electrolyte membrane according to [6], wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer. [8] An electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, the reinforcing layer includes a porous membrane and an at least partially cross-linked cross-linked electrolyte polymer contained in the pores of the porous membrane; An electrolyte membrane, wherein the contact layer comprises an uncrosslinked electrolyte polymer. [9] the cross-linked electrolyte polymer is a reaction product of an electrolyte polymer and a cross-linking agent, The electrolyte membrane according to [8], wherein the crosslinked electrolyte polymer has a crosslinking agent-derived portion unevenly distributed in the vicinity of the wall surface of the pores rather than in the center of the pores of the porous membrane.

[10] The electrolyte membrane according to [8] or [9], wherein the number average molecular weight of the crosslinked electrolyte polymer is 50,000 or more and 300,000 or less.

[11] The electrolyte membrane according to any one of [8] to

[10] , wherein the number average molecular weight of the non-crosslinked electrolyte polymer is 18,000 or more and 60,000 or less.

[12] The electrolyte membrane according to any one of [8] to

[11] , wherein the thickness of the contact layer is 1 μm or more and 15 μm or less.

[13] The electrolyte membrane according to any one of [8] to

[12] , wherein the reinforcing layer contains, in the pores of the porous membrane, a binder that does not react with the crosslinking agent.

[14] The electrolyte membrane according to

[13] , wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer.

[15] The electrolyte membrane according to any one of [8] to

[14] , which is an electrolyte membrane for a fuel cell or an electrolyte membrane for water electrolysis. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide at least one of an electrolyte membrane having high mechanical strength and a method for producing the same. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a cross section of an electrolyte membrane according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] An example of an embodiment of the present disclosure will be described below, possibly with reference to the drawings. However, the present disclosure is not limited to the following embodiment. The present disclosure includes any combination of the configurations and parameters disclosed herein, and also includes any combination of the upper and lower limits of the values ​​disclosed herein. Furthermore, "A or B" may include either A or B, or both. Furthermore, unless otherwise specified, the materials exemplified below may be used alone or in combination of two or more. Furthermore, the terms "layer" and "film" encompass not only structures that are formed over the entire surface when observed in a plan view, but also structures that are formed only on a portion of the surface. Furthermore, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0012] <Electrolyte membrane> FIG. 1 is a schematic diagram showing a cross section of an electrolyte membrane of one embodiment. The electrolyte membrane 10 of FIG. 1 has a structure in which a reinforcing layer 4 is sandwiched between contact layers 5. The reinforcing layer 4 includes a porous membrane 1 and an at least partially crosslinked crosslinked electrolyte polymer 3 contained in the pores 2 of the porous membrane 1. The contact layer 5 includes an uncrosslinked electrolyte polymer. The electrolyte membrane 10 of this embodiment may have a structure in which the contact layer 5, the reinforcing layer 4, and the contact layer 5 are laminated in this order and integrated together (i.e., a structure in which the reinforcing layer 4 is sandwiched between two contact layers 5). Note that in FIG. 1, the two contact layers are given the same reference numeral (5), but the two contact layers may be the same or different. Details of the contact layer 5 in the following description apply to both of the two contact layers.

[0013] (reinforcement layer) [Porous membrane] The porous membrane 1 has a plurality of pores 2. The porous membrane 1 may have pores 2 that communicate with each other at least in the thickness direction.

[0014] The porous membrane 1 may be any membrane usable as a reinforcing membrane for a fuel cell, and may be, for example, a membrane formed of a hydrocarbon polymer such as polyethylene or a fluorine-containing polymer such as expanded polytetrafluoroethylene (PTFE). As the porous membrane (for example, a porous membrane formed of the hydrocarbon polymer), one or more sheets selected from the group consisting of nonwoven fabrics, woven fabrics, and porous bodies (sponges, etc.) may be used.

[0015] The average pore diameter of the pores 2 in the porous membrane 1 may be 0.1 nm or more, 1 nm or more, or 5 nm or more, and may be 200 nm or less, 175 nm or less, or 150 nm or less. The average pore diameter of the pores 2 in the porous membrane 1 may be 0.1 nm or more and 200 nm or less, or 1 nm or more and 175 nm or less, or 5 nm or more and 150 nm or less.

[0016] The porosity of the porous membrane 1 may be 50% or more, 60% or more, or 70% or more, from the viewpoint of easily increasing the filling amount of the crosslinked electrolyte polymer. The porosity of the porous membrane 1 may be 98% or less or 95% or less, from the viewpoint of easily maintaining the strength of the porous membrane 1 itself. From the above viewpoint, the porosity of the porous membrane 1 may be 50% or more and 98% or less, 60% or more and 98% or less, or 70% or more and 95% or less.

[0017] The thickness of the porous membrane 1 may be 1 μm or more, 2 μm or more, or 5 μm or more, and may be 50 μm or less, 30 μm or less, or 20 μm or less, from the viewpoint of further increasing the mechanical strength and swelling resistance without impairing the properties as an electrolyte membrane. The thickness of the porous membrane 1 may be 1 μm or more and 50 μm or less, 2 μm or more and 30 μm or less, or 5 μm or more and 20 μm or less.

[0018] [Cross-linked electrolyte polymer] The crosslinked electrolyte polymer 3 is an electrolyte polymer that is at least partially crosslinked and has a crosslinked structure within the molecule. The crosslinked electrolyte polymer 3 may be a reaction product of an electrolyte polymer and a crosslinking agent. That is, the crosslinked electrolyte polymer 3 may be an electrolyte polymer having a plurality of polymer units derived from the electrolyte polymer and sites (crosslinking groups) derived from the crosslinking agent that bond to two or more of the polymer units. In such an electrolyte polymer, the sites derived from the crosslinking agent of the crosslinked electrolyte polymer 3 may be unevenly distributed more in the vicinity of the wall surfaces of the pores 2 of the porous membrane 1 than in the central portions of the pores 2.

[0019] Examples of the electrolyte polymer include hydrocarbon-based or fluorine-based resins having ion-exchange groups. The electrolyte polymer may be a non-crosslinked (uncrosslinked) electrolyte polymer.

[0020] The electrolyte polymer may include an electrolyte polymer having a hydrophilic segment and a hydrophobic segment, and from the viewpoint of increasing the mechanical strength, may include one or more electrolyte polymers selected from the group consisting of electrolyte polymers having structures represented by the following formulas (P1) to (P5). [ka] [In formulas (P1) to (P5), n represents the number of repetitions.]

[0021] The number average molecular weight of the electrolyte polymer may be 18,000 or more and 60,000 or less, 30,000 or more and 55,000 or less, or 40,000 or more and 50,000 or less. The number average molecular weight in the present disclosure is a value measured by gel permeation chromatography (GPC) and calculated as a standard polyethylene glycol / oxide (PEG / PEO).

[0022] The plurality of polymer units derived from the electrolyte polymer may be the same or different from one another.

[0023] The crosslinking agent may be a known crosslinking compound. From the viewpoint of chemical stability, the crosslinking agent may include a crosslinking compound having one or more aromatic rings, or may include a crosslinking compound having one or two aromatic rings. When the crosslinking agent has an aromatic ring, the polymer unit derived from the electrolyte polymer may be directly bonded to the aromatic ring in the crosslinking group, or may be bonded via -O-, -S-, or -SO2-.

[0024] The crosslinkable compound having one or two aromatic rings may include one or more compounds selected from the group consisting of decafluorobiphenyl, 4,4'-dicyano-3,3',5,5'-tetrafluorobiphenyl, 3,3',5,5'-tetrachloro-4,4'-dicyanobiphenyl, and pentachlorobenzonitrile. Among these, decafluorobiphenyl has good reactivity with the electrolyte polymers having the structures represented by formulas (P1) to (P5).

[0025] When a plurality of sites (crosslinking groups) derived from the crosslinking agent are present, they may be the same or different.

[0026] The number average molecular weight (Mn) of the crosslinked electrolyte polymer 3 may be 50,000 or more and 300,000 or less, depending on its molecular structure. When the number average molecular weight of the crosslinked electrolyte polymer 3 is in this range, the mechanical strength tends to be higher and swelling of the electrolyte membrane due to wetting tends to be suppressed. From the same viewpoint, the number average molecular weight of the crosslinked electrolyte polymer 3 may be 60,000 or more and 250,000 or less, 70,000 or more and 250,000 or less, 70,000 or more and 200,000 or less, 80,000 or more and 150,000 or less, or 90,000 or more and 100,000 or less.

[0027] [others] The reinforcing layer 4 may further contain a binder that does not react with the crosslinking agent in the pores 2 of the porous membrane 1. The binder is not particularly limited as long as it is a resin that does not react with the crosslinking agent, and may be a polymer having the same molecular structure as the main chain of the above-mentioned electrolytic polymer (for example, a polymer whose main chain structure of the polymer molecule is the same as the above-mentioned electrolytic polymer). Examples of such a polymer include a polymer having a structure without the ion exchange groups of the above-mentioned electrolytic polymer, and a polymer in which a metal is bonded to the ion exchange group of the above-mentioned electrolytic polymer to form a salt.

[0028] The binder may be one or more polymers selected from the group consisting of polymers having structures represented by the following formulas (P6) to (P10). [ka] [In formulas (P6) to (P10), n represents the number of repetitions.]

[0029] The reinforcing layer 4 may further contain an additive that promotes the reaction between the electrolyte polymer and the crosslinking agent in the pores 2 of the porous membrane 1. The additive may be a known additive used for the above purpose. For example, one or more selected from cesium carbonate and potassium carbonate may be used, or other basic salts may be used.

[0030] The reinforcing layer 4 may contain uncrosslinked electrolyte polymer, unreacted crosslinking agent, other additives, unavoidable impurities, etc. Examples of other additives include water-retentive inorganic substances and radical scavengers, specifically water, silica, cerium oxide, and manganese oxide. These components may be contained in the pores 2 of the porous membrane 1 or may be retained in the pores 2 of the porous membrane 1.

[0031] The thickness of the reinforcing layer 4 may be approximately the same as the thickness of the porous membrane 1. The thickness of the reinforcing layer 4 may be 1 μm or more and 50 μm or less, 2 μm or more and 30 μm or less, or 5 μm or more and 20 μm or less.

[0032] (contact layer) The contact layer 5 contains an uncrosslinked electrolyte polymer and is therefore moderately flexible and easily deformable, which allows the contact layer 5 to absorb the surface irregularities of the electrode catalyst layer and adhere closely to the catalyst particles, tending to expand the proton conduction path.

[0033] [Uncrosslinked electrolyte polymer] Examples of the uncrosslinked electrolyte polymer are the same as the examples of the electrolyte polymer in the (reinforcing layer) described above. The uncrosslinked electrolyte polymer contained in the contact layer 5 and the electrolyte polymer that is the raw material for the crosslinked electrolyte polymer in the (reinforcing layer) described above may be the same or different. One type of uncrosslinked electrolyte polymer may be used alone, or two or more types may be used in combination. The uncrosslinked electrolyte polymers contained in each contact layer 5 may be the same or different.

[0034] An uncrosslinked electrolyte polymer generally has a lower number-average molecular weight than a crosslinked electrolyte polymer (e.g., a crosslinked electrolyte polymer contained in a reinforcing layer). The number-average molecular weight of the uncrosslinked electrolyte polymer may be 18,000 or more and 60,000 or less, depending on its molecular structure. When the number-average molecular weight of the uncrosslinked electrolyte polymer is within this range, swelling of the contact layer 5 is suppressed, preventing a decrease in the mechanical strength of the electrolyte membrane 10, and the flexibility of the contact layer 5 is increased, thereby enhancing the effect of expanding the proton conduction path. From a similar perspective, the number-average molecular weight of the uncrosslinked electrolyte polymer may be 30,000 or more and 55,000 or less, or 40,000 or more and 50,000 or less.

[0035] The contact layer 5 may be a layer essentially consisting of an electrolytic polymer. The electrolytic polymer may be composed only of an uncrosslinked electrolytic polymer and may not contain the crosslinked electrolytic polymer 3. The contact layer 5 may be a layer consisting only of an electrolytic polymer, or may contain other additives, inevitable impurities, etc. Examples of other additives are the same as the examples of other additives in the reinforcing layer 4.

[0036] The contact layer 5 may have a layer containing the crosslinked electrolyte polymer 3 and a layer not containing the crosslinked electrolyte polymer 3. For example, the above-mentioned crosslinked electrolyte polymer 3 may be present so as to cover at least a part of the surface of the porous membrane 1, and form a part of the contact layer 5 (the layer containing the crosslinked electrolyte polymer).

[0037] The thickness of the contact layer 5 may be 1 μm or more and 15 μm or less. Having a thickness of 1 μm or more prevents the porous membrane 1 from being exposed on the surface of the electrolyte membrane 10, and enhances the effect of expanding the proton conduction path. Having a thickness of 15 μm or less suppresses swelling of the contact layer 5, thereby preventing a decrease in the mechanical strength of the electrolyte membrane 10. From the same viewpoint, the thickness of the contact layer 5 may be 1 μm or more and 10 μm or less. When the contact layer 5 has a layer containing a crosslinked electrolyte polymer 3, the thickness of the layer not containing the crosslinked electrolyte polymer 3 may be, for example, 1 μm or more and 10 μm or less. The thicknesses of the contact layers 5 may be the same or different. From the same viewpoint, the total thickness of the contact layers 5 (the sum of the thicknesses of the contact layers 5) may be 2 μm or more and 30 μm or less, or 2 μm or more and 20 μm or less.

[0038] In one embodiment, the number-average molecular weight of the electrolyte polymer in the contact layer 5 may be 18,000 or more and 60,000 or less, and the thickness of the contact layer 5 may be 1 μm or more and 10 μm or less. When the number-average molecular weight of the electrolyte polymer is 18,000 or more and the thickness of the contact layer 5 is 10 μm or less, swelling of the contact layer 5 is further suppressed, and the mechanical strength of the electrolyte membrane 10 tends to be higher. Furthermore, when the thickness of the contact layer 5 is 1 μm or more, exposure of the porous membrane 1 on the surface of the electrolyte membrane 10 can be prevented, and when the electrolyte polymer in the contact layer 5 is 60,000 or less, the effect of expanding the proton conduction path can be further enhanced.

[0039] The thickness of the electrolyte membrane 10 may be, for example, 3 to 70 μm.

[0040] The electrolyte membrane 10 of this embodiment can be used, for example, as an electrolyte membrane for fuel cells such as polymer electrolyte fuel cells, or as an electrolyte membrane for water electrolysis.

[0041] <Method of manufacturing electrolyte membrane> A method for producing an electrolyte membrane according to one embodiment includes the steps of: preparing a porous substrate including a porous membrane and a crosslinking agent held in the pores of the porous membrane (hereinafter also referred to as a "preparation step"); impregnating the porous substrate with a solution containing an electrolyte polymer; and crosslinking reacting the electrolyte polymer with the crosslinking agent to form a crosslinked electrolyte polymer.

[0042] According to the above method, it is not necessary to add a crosslinking agent to the solution containing the electrolyte polymer in the impregnation step. This makes it possible to fill the pores of the porous substrate (porous membrane) with the crosslinked electrolyte polymer without increasing the viscosity due to the reaction between the electrolyte polymer and the crosslinking agent. Furthermore, unlike conventional techniques, there is no restriction on the amount of crosslinking agent required to account for the increase in viscosity, making it possible to increase the crosslink density of the crosslinked electrolyte polymer. Therefore, the above method can produce an electrolyte membrane with high mechanical strength. For the same reasons as above, the above method also tends to produce an electrolyte membrane with excellent swelling resistance. Therefore, it is not necessary to add another resin to suppress swelling, and a decrease in the mechanical strength of the electrolyte membrane due to the swelling suppression method can be suppressed. Furthermore, according to the above method, the electrolyte membrane 10 of the above embodiment can also be obtained by performing the solution layer formation step and contact layer formation step described below. That is, the method for producing the electrolyte membrane of the above embodiment can also be used as a method for producing the electrolyte membrane 10 of the above embodiment.

[0043] (Preparation process) The preparation step may be a step of preparing a pre-prepared porous substrate, or a step of preparing a porous substrate. In the latter case, the preparation step may include a step of retaining a crosslinking agent in the pores of the porous membrane. Examples of the porous membrane and the crosslinking agent are the same as the examples of the porous membrane and the crosslinking agent in the (reinforcing layer) described above.

[0044] A method for retaining a crosslinking agent in the pores of a porous membrane includes impregnating a porous membrane with a solution containing a crosslinking agent and an organic solvent (hereinafter also referred to as a "crosslinking agent solution") and then drying the porous membrane. That is, the preparation step may include a process of impregnating a porous membrane with a crosslinking agent solution and a process of drying the porous membrane impregnated with the crosslinking agent solution. By impregnating a porous membrane with the crosslinking agent solution, the crosslinking agent adheres to the pores of the porous membrane, and by drying the porous membrane after impregnation, the crosslinking agent can be fixed to the porous membrane. Examples of methods for impregnating a porous membrane with a crosslinking agent solution include a method of dropping the crosslinking agent solution onto a porous membrane, a method of applying the crosslinking agent solution to a porous membrane, and a method of immersing a porous membrane in the crosslinking agent solution.

[0045] The amount of crosslinker retained in the porous substrate is 3.0 × 10, depending on the crosslinker and the electrolyte polymer. -8 mol / cm 2 Over 20.0 x 10 -8 mol / cm 2 The amount of crosslinking agent carried on the porous substrate may be 3.0×10 or less. -8 mol / cm 2 When the amount of the crosslinking agent held in the porous substrate is 20.0×10 or more, the crosslink density of the crosslinked electrolyte polymer in the reinforcing layer becomes high, and the mechanical strength of the electrolyte membrane tends to be higher. -8 mol / cm 2 From these viewpoints, the amount of the crosslinking agent held in the porous substrate is set to 5.0×10 or less. -8 mol / cm 2 or more than 10.0 x 10 -8 mol / cm 2 It may be 18.0 x 10 or more. -8 mol / cm 2 or less or 15.0 x 10 -8 mol / cm 2 may be less than 5.0 x 10 -8 mol / cm 2 Over 18.0 x 10 -8 mol / cm 2 or less or 10.0 x 10 -8 mol / cm 2Over 15.0 x 10 -8 mol / cm 2 The amount of crosslinking agent held in the porous substrate means the amount of crosslinking agent fixed per unit surface area of ​​the porous substrate, and is calculated by dividing the total amount of crosslinking agent (unit: mol) by the surface area of ​​the porous membrane (unit: cm 2 The concentration of the crosslinking agent in the crosslinking agent solution may be adjusted appropriately so that the amount of the crosslinking agent retained in the porous substrate falls within the above range.

[0046] The crosslinking agent may be directly attached to the fibers constituting the porous membrane by van der Waals forces or the like, or may be fixed to the porous membrane via a binder that does not react with the crosslinking agent. That is, the porous substrate may further contain a binder that does not react with the crosslinking agent in the pores in order to make it easier to retain the crosslinking agent. When a binder is used, the binder may be contained in the crosslinking agent solution.

[0047] Examples of the binder are the same as the examples of the binder in the (reinforcing layer) described above. Among these, the binder may be a polymer having the same molecular structure as the main chain of the electrolyte polymer, or may be one or more polymers selected from the group consisting of polymers having structures represented by the above formulas (P6) to (P10). By using a polymer having the same molecular structure as the main chain of the electrolyte polymer as the binder, the affinity between the porous substrate and the electrolyte polymer is improved, making it easier to fill the pores of the porous substrate with the electrolyte polymer. Furthermore, because a polymer having the same molecular structure as the main chain of the electrolyte polymer is used, there is no need to prepare a resin different from the electrolyte polymer, and the manufacturing costs of the electrolyte membrane can be reduced.

[0048] The preparation step may further include a step of retaining an additive that promotes the reaction between the electrolyte polymer and the crosslinking agent in the pores of the porous membrane. Examples of the additive are the same as the examples of the additive in the (reinforcing layer) described above.

[0049] Methods for retaining the additive in the pores of the porous membrane include a method in which the additive is contained in a crosslinker solution, and a method in which an aqueous solution containing the additive is impregnated into a porous membrane by coating or the like, and then the porous membrane is dried. When the latter method is adopted, the step of retaining the additive in the pores of the porous membrane may be carried out before or after the step of retaining the crosslinker in the pores of the porous membrane.

[0050] (Impregnation process) In the impregnation step, the porous substrate is impregnated with a solution containing an electrolytic polymer, thereby filling the pores of the porous substrate with the solution containing the electrolytic polymer. As a method for impregnating the porous substrate with the solution containing the electrolytic polymer, for example, a solution casting method such as casting coating may be used.

[0051] Examples of the electrolyte polymer are the same as the examples of the electrolyte polymer in the (reinforcing layer) described above. The range of the number-average molecular weight of the electrolyte polymer may also be the same as above. When the number-average molecular weight of the electrolyte polymer is 18,000 or more, the mechanical strength of the electrolyte membrane tends to be higher. When the number-average molecular weight of the electrolyte polymer is 60,000 or less, the viscosity of the solution containing the electrolyte polymer does not become too high, which makes it easier to fill the pores of the porous substrate with the solution containing the electrolyte polymer and to form a contact layer on the porous substrate. One type of electrolyte polymer may be used alone, or two or more types may be used in combination.

[0052] The solvent used for the solution containing the electrolytic polymer is not particularly limited as long as it is a solvent capable of dissolving the electrolytic polymer, and may be an organic solvent, such as one or more solvents selected from the group consisting of N-methyl-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, and tetramethylurea. The above solvents may be used alone or in combination of two or more.

[0053] The content of the electrolytic polymer in the solution containing the electrolytic polymer may be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more, and 30% by mass or less, 20% by mass or less, or 15% by mass or less, or 1% by mass or more and 30% by mass or less, 3% by mass or more and 20% by mass or less, or 5% by mass or more and 15% by mass or less, based on the total mass of the solution.

[0054] The solution containing the electrolytic polymer may contain components other than the electrolytic polymer and the solvent, but from the viewpoint of making it easier to obtain the effects of the present disclosure, the content of the crosslinking agent may be 0.01 parts by mass or less or 0 parts by mass per 100 parts by mass of the electrolytic polymer.

[0055] (Crosslinking process) In the crosslinking step, the crosslinking agent held in the pores of the porous substrate reacts with the electrolyte polymer filled in the pores to crosslink the electrolyte polymer. This reaction results in the formation of a crosslinked electrolyte polymer in the pores of the porous substrate, with at least a portion of the polymer being crosslinked. The crosslinked electrolyte polymer thus formed is a reaction product of the electrolyte polymer and the crosslinking agent, and has a plurality of polymer units derived from the electrolyte polymer and sites (crosslinking groups) derived from the crosslinking agent that bond to two or more of the polymer units. Because the sites derived from the crosslinking agent in this crosslinked electrolyte polymer are derived from the crosslinking agent held in the pores of the porous substrate, they tend to be more concentrated near the wall surfaces of the pores of the porous membrane than in the center of the pores.

[0056] The reaction between the electrolytic polymer and the crosslinking agent in the crosslinking step can be promoted by heating the porous substrate filled with the electrolytic polymer, although this reaction depends on the combination of the electrolytic polymer and the crosslinking agent. The temperature at which the porous substrate filled with the electrolytic polymer is heated (heating temperature) depends on the type of porous substrate, but if the porous substrate has a melting point, the electrolytic polymer can be crosslinked while preventing deformation or deterioration of the porous substrate if the heating temperature is a temperature below the melting point of the porous substrate.

[0057] The heating temperature may be, for example, 40 to 80° C. from the viewpoint of volatilizing the solvent derived from the solution containing the electrolytic polymer and drying the electrolyte membrane, and from the viewpoint of preventing deformation and deterioration of the porous substrate. The time for which the porous substrate filled with the electrolytic polymer is heated (heating time) may be, for example, 1 to 24 hours.

[0058] According to the method described above, an electrolyte membrane having a reinforcing layer can be obtained, in which the reinforcing layer includes a porous membrane and an at least partially cross-linked cross-linked electrolyte polymer contained in the pores of the porous membrane.

[0059] The method for producing an electrolyte membrane according to the above embodiment may include a drying step of drying the solution containing the electrolyte polymer filled in the porous substrate in the impregnation step, although the drying step is not essential because drying can also be performed in the crosslinking step as described above.

[0060] The drying step may be a step of removing at least a part of the solvent from the solution, for example, a step of drying until the surface of the porous substrate becomes dry to the touch.

[0061] After the drying step, the crosslinking step may be carried out directly, or the impregnation step may be carried out again. That is, the method for producing an electrolyte membrane of the above embodiment may have a first impregnation step and a second impregnation step. In this case, the first impregnation step may be a step of impregnating the pores of the porous substrate from one side of the porous substrate with a solution containing an electrolytic polymer, and the second impregnation step may be a step of impregnating the pores of the porous substrate from the other side of the porous substrate (the side opposite to the first impregnation step) with a solution containing an electrolytic polymer. The second impregnation step may be a solution layer formation step described later.

[0062] When it is desired to use electrolyte polymers with different molecular structures in the reinforcing layer and the contact layer, or when it is desired to prevent the solvent from remaining in the reinforcing layer even if the electrolyte polymers in the reinforcing layer and the contact layer are the same, it is effective to carry out the impregnation process in two stages as described above (for example, after filling the pores of the porous substrate with a solution containing an electrolyte polymer and drying it, further applying the solution containing the electrolyte polymer onto the surface of the porous substrate).

[0063] The method for producing the electrolyte membrane of the above embodiment may include a step of applying a solution containing an electrolyte polymer to the surface of a porous substrate (e.g., one surface, both surfaces, or the entire surface of the porous substrate) to form a layer of the solution (solution layer) on the surface of the porous substrate (hereinafter also referred to as a "solution layer forming step"), and a step of drying the solution layer to form a contact layer containing the electrolyte polymer (hereinafter also referred to as a "contact layer forming step"). These steps may be performed multiple times to form multiple contact layers.

[0064] By carrying out the above-mentioned solution layer forming process and contact layer forming process, a contact layer containing an uncrosslinked electrolyte polymer can be formed on the reinforcing layer, and therefore, for example, the electrolyte membrane 10 of the above-mentioned embodiment can be obtained.

[0065] The solution layer forming step may be performed after the drying step. That is, the porous substrate to which the solution containing the electrolytic polymer is applied may be a porous substrate after the drying step (a porous substrate filled with the electrolytic polymer).

[0066] The solution layer forming step may be a step overlapping with the impregnation step described above. For example, the solution containing the electrolytic polymer may be applied to the surface of the porous substrate, thereby impregnating the porous substrate with the solution containing the electrolytic polymer and forming the solution layer on the surface of the porous substrate.

[0067] In the solution layer forming step, after applying the solution containing the electrolytic polymer, the thickness of the layer made of the solution containing the electrolytic polymer may be adjusted to a desired thickness. For example, the thickness of the solution layer may be adjusted by passing a porous substrate impregnated with the solution containing the electrolytic polymer through a gap adjusted to a desired thickness of the electrolyte membrane (i.e., a thickness obtained by adding the thickness of the porous substrate and the thickness of the desired contact layer).

[0068] The contact layer forming step may be a step overlapping with the drying step or the crosslinking step. For example, after the solution layer forming step, the solution layer may be dried by performing a heat treatment in the drying step or the crosslinking step, thereby forming a contact layer containing the electrolyte polymer.

[0069] In the electrolyte membrane manufacturing method of the above embodiment, the reinforcing layer and the contact layer may be manufactured simultaneously, or the electrolyte membrane may be manufactured by forming the reinforcing layer and then forming the contact layer on the reinforcing layer. It is also possible to manufacture the electrolyte membrane by manufacturing the reinforcing layer and the contact layer separately and then bonding the contact layers to both sides of the reinforcing layer. By manufacturing the reinforcing layer and the contact layer simultaneously, the number of steps required to manufacture the electrolyte membrane can be reduced, and an electrolyte membrane in which the reinforcing layer and the contact layer are continuous can be obtained because no interface is formed between the reinforcing layer and the contact layer.

[0070] When the reinforcing layer and the contact layer are produced simultaneously, for example, as described above, the porous substrate after the solution layer formation step (porous substrate impregnated with a solution containing an electrolyte polymer) may be passed through a gap adjusted to the thickness of the desired electrolyte membrane to adjust the thickness of the solution layer, and the porous substrate may be heated to simultaneously form a crosslinked electrolyte polymer and dry the solution, thereby producing an electrolyte membrane. [Example]

[0071] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0072] <Preparation of electrolyte polymer> (Synthesis of hydrophilic monomer (M1)) A 10 L flask equipped with a dropping funnel, reflux condenser, and mechanical stirrer was purged with nitrogen, and 101 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl and 4 L of dehydrated tetrahydrofuran were added and stirring was initiated. The flask was cooled to -70°C in a methanol-dry ice bath, and 320 mL of a 2.6 mol / L n-butyllithium-hexane solution was added dropwise. The mixture was stirred for 1 hour while still cooled in the bath. 40 mL of sulfur dioxide gas was introduced into the flask using nitrogen gas. The mixture was stirred for 30 minutes while still cooled in the bath. The bath was then removed, and the internal temperature was raised to 0°C.

[0073] The precipitated solid was filtered off by suction filtration and washed with 200 mL of tetrahydrofuran. The collected solid was dissolved in 2 L of pure water, and 260 mL of 35% hydrogen peroxide solution was added and stirred for 18 hours. 600 g of sodium chloride was added to the filtrate collected by suction filtration. The precipitated white solid was collected by suction filtration and purified by recrystallization from water / isopropyl alcohol. The obtained solid was dried under reduced pressure to obtain a hydrophilic monomer represented by the following formula (M1). The yield was 65%. [ka]

[0074] (Synthesis of hydrophobic monomer (M2)) A 200 mL flask equipped with a stirrer, Dean-Stark tube, reflux condenser, and calcium chloride tube was charged with 4.0 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl, 14.8 g of [1,1'-biphenyl]-4,4'-diol, and 13.2 g of potassium carbonate, and 50 mL of N,N-dimethylacetamide (DMAc) and 50 mL of toluene were added. The mixture was heated to 160°C in an oil bath with stirring and continued to be heated and stirred for 4 hours. The toluene was removed from the Dean-Stark tube, and the mixture was heated to 180°C in an oil bath. After heating, the mixture was continued to be heated and stirred for 8 hours. After allowing the reaction mixture to cool to room temperature, it was poured into 200 mL of 10% hydrochloric acid, and the precipitated white solid was filtered off.

[0075] The filtered solid was washed with 300 mL of ethanol and dried. The dried solid was purified by recrystallization from NMP / ethanol. The obtained solid was dried under reduced pressure to obtain a hydrophobic monomer (M2) represented by the following formula (M2). The yield was 50%. [ka]

[0076] (Synthesis of electrolyte polymer (P1)) A 100 mL three-neck flask equipped with a nitrogen inlet tube, stirrer, and Dean-Stark tube was charged with 0.983 g of the hydrophobic monomer (M2), 1.181 g of the hydrophilic monomer (M1), and 0.507 g of potassium carbonate, followed by nitrogen substitution. Then, 10 mL of dimethyl sulfoxide (DMSO) and 10 mL of cyclohexane were added. The mixture was heated to 130 °C and refluxed for 4 hours, after which the cyclohexane was removed from the Dean-Stark tube. Polymerization was continued for 150 hours while heating at 130 °C. After allowing the reaction mixture to cool to room temperature, it was purified by reprecipitation from 300 mL of isopropyl alcohol (IPA), and the solid was collected by suction filtration.

[0077] The obtained solid was immersed in 1M hydrochloric acid for 24 hours to remove metal ions (Na + or K + ) to protons (H + After the protons were substituted, the polymer was thoroughly washed by immersion in pure water and dried under reduced pressure to obtain an electrolyte polymer (P1) (proton-substituted polymer (P1)) having a structure represented by the following formula (P1). The yield was 97%. [ka]

[0078] In formula (P1), n ​​represents a positive number. n in the above formula (P1) was approximately 20.

[0079] [Molecular weight measurement] The number-average molecular weight of the electrolyte polymer (P1) was measured by GPC. The electrolyte polymer (P1) was dissolved at a concentration of 1 mg / mL in the eluent (N,N-dimethylformamide solvent containing 10 mmol / L of lithium bromide) to prepare the sample solution. The Tosoh HLC-8320 GPC was used. Two Tosoh TSKgel SuperAWM-H columns (inner diameter 6.0 mm, length 15 cm) were used. A differential refractometer detector was used. The flow rate was 0.6 mL / min, and the temperature was 40°C. The number-average molecular weight was calculated in terms of standard polyethylene glycol / oxide (PEG / PEO). The number-average molecular weight of the electrolyte polymer (P1) was 50,000.

[0080] <Preparation of porous substrate retaining crosslinking agent> The cross-linking agent (decafluorobiphenyl, purity 98%, manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in isopropyl alcohol to a concentration of 3.0 × 10 -4 A mol / L crosslinker solution was prepared.

[0081] The crosslinking agent solution or its diluted solution obtained above was dropped onto a polyethylene porous substrate (manufactured by Hefei Zhaohui New Material Technology Co., Ltd., product name: CW12L1, porosity 72%, thickness 14 μm nonwoven fabric) and dried at 60°C for 1 hour, resulting in a crosslinking agent retention amount of 3.2 × 10 -8 mol / cm 2 , 6.5×10 -8 mol / cm 2 and 14.9 x 10 -8 mol / cm 2 Three types of porous substrates were prepared. The amount of crosslinking agent retained was adjusted by the concentration and dropwise amount of the crosslinking agent solution.

[0082] <Preparation of electrolyte membrane> Example 1 The electrolyte polymer (P1) was dissolved in dimethyl sulfoxide (DMSO) to obtain a solution containing 10% by mass of the electrolyte polymer (P1) (hereinafter also referred to as "electrolyte polymer (P1) solution"). The solution was diluted to a concentration of 3.2 × 10 -8 mol / cm 2 The solution was cast onto one side of a 20 μm thick porous substrate, and the porous substrate was passed through a gap between glass rods with a thickness gap of 30 μm. After the porous substrate was dried to the touch, the porous substrate was turned over, and the solution was cast onto the side opposite to the side on which the solution was cast, and the porous substrate was passed through a gap between glass rods with a thickness gap of 40 μm. The porous substrate was then heated at 60 ° C for 6 hours to obtain a 40 μm thick electrolyte membrane of Example 1 having a structure in which the reinforcing layer was sandwiched between contact layers. The thickness of the electrolyte membrane in this example is the average thickness of the electrolyte membrane measured at three points in the plane using a micrometer.

[0083] Example 2 The amount of crosslinker retained is 6.5 x 10 -8 mol / cm 2 An electrolyte membrane of Example 2 was obtained in the same manner as in Example 1, except that a porous substrate of

[0084] Example 3 The amount of crosslinker retained was 14.9 × 10 -8 mol / cm 2 An electrolyte membrane of Example 3 was obtained in the same manner as in Example 1, except that a porous substrate of

[0085] Example 4 Before casting the electrolyte polymer (P1) solution onto the porous substrate, a potassium carbonate solution with a pH of 9.5 was applied to the porous substrate at a rate of 0.1 mL / cm. 2 and then dried by heating at 60° C. for 3 hours, in the same manner as in Example 1, to obtain an electrolyte membrane of Example 4.

[0086] (Comparative Example 1) An electrolyte membrane of Comparative Example 1 was obtained in the same manner as in Example 1, except that a porous substrate (porous substrate made of polyethylene) not carrying a crosslinking agent was used.

[0087] (Number average molecular weight of the electrolyte polymer in the reinforcing layer) The number-average molecular weight (Mn) of the electrolyte polymer in the reinforcing layer of the electrolyte membrane of each Example was measured by GPC. The electrolyte polymer in the reinforcing layer was obtained by cutting out the reinforcing layer from the electrolyte membrane of each Example and dissolving it using N,N-dimethylformamide as a solvent. The number-average molecular weight of the obtained electrolyte polymer was measured using the same method as in the above-mentioned [Measurement of molecular weight]. The number-average molecular weights of the electrolyte polymer in the reinforcing layer of the electrolyte membrane of Examples 1 to 4 were 62,000, 78,000, 90,000, and 72,000, respectively. Therefore, it was confirmed that at least a portion of the electrolyte polymer (P1) was crosslinked in the reinforcing layer of the electrolyte membrane of each Example to form a crosslinked electrolyte polymer.

[0088] <Evaluation> (swelling rate) The electrolyte membrane was cut into a 4 cm × 2 cm rectangle using a punching machine, and the size of the electrolyte membrane was measured. The punched electrolyte membrane was sandwiched between 2 mm thick preparation plates and immersed in 100 mL of room temperature pure water for 1 hour. The electrolyte membrane was then taken out, droplets on the surface were removed, and the size was measured. The swelling ratio of the electrolyte membrane in the MD or TD direction was calculated for each of the longitudinal and transverse directions using the following formula (1). Swelling rate [%]=(L2-L1) / L1×100...Formula (1) In formula (1), L1 is the side length of the membrane before swelling, and L2 is the side length of the membrane after swelling.

[0089] (tensile strength) The electrolyte membrane (5 cm x 1 cm) before swelling was cut into a test piece based on JIS K6251, and a tensile test was carried out.

[0090] Under the following measurement conditions, the tensile strain was determined from the parallel length of the test piece and the crosshead displacement, and the tensile strength was calculated from the resulting tensile stress-tensile strain diagram. Equipment name: INSTRON Material Testing Machine 5848 Test speed: 1mm / min Test piece shape: JIS K6251 No. 8 test piece, 40% reduced shape Test room environment: Temperature 23±2℃, humidity 50±5%RH Parallel length: 6.4 mm Chuck distance: 8mm

[0091] [Table 1]

[0092] From the above results, it was confirmed that even an extremely rigid electrolyte polymer, which is a crosslinked rigid electrolyte polymer having a biphenyl skeleton in the main chain, can be filled into fine pores.

[0093] Furthermore, the electrolyte membranes of the Examples, in which the electrolyte polymer in the reinforcing layer has a crosslinked structure, all had lower swelling ratios and improved tensile strengths than the electrolyte membrane of Comparative Example 1, confirming that the electrolyte membranes of the Examples have high mechanical strength and excellent swelling resistance.

[0094] Furthermore, a comparison between Example 1 and Example 2 confirmed that the swelling ratio is improved more significantly when the number average molecular weight of the electrolyte polymer in the reinforcing layer is 78,000 or more (apparent molecular weight 1.56 times that before crosslinking).

[0095] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2024-36172, filed on March 8, 2024, are incorporated herein by reference as the disclosure of the specification of the present disclosure. [Explanation of symbols]

[0096] 1...porous membrane, 2...pore, 3...crosslinked electrolyte polymer, 4...reinforcing layer, 5...contact layer, 10...electrolyte membrane.

Claims

1. providing a porous substrate comprising a porous membrane and a cross-linking agent retained within the pores of the porous membrane; an impregnation step of impregnating the porous substrate with a solution containing an electrolyte polymer; a crosslinking step of reacting the electrolyte polymer with the crosslinking agent to form a crosslinked electrolyte polymer.

2. a drying step of drying the solution filled in the porous substrate in the impregnation step; A step of applying a solution containing the electrolyte polymer to the surface of the porous substrate after the drying step to form a layer made of the solution on the surface of the porous substrate; The method for producing an electrolyte membrane according to claim 1 , further comprising the step of: drying the layer made of the solution to form a contact layer containing the electrolyte polymer.

3. The method for producing an electrolyte membrane according to claim 2 , wherein the thickness of the contact layer is 1 μm or more and 15 μm or less.

4. The method for producing an electrolyte membrane according to claim 1 or 2, wherein the number average molecular weight of the electrolyte polymer is 18,000 or more and 60,000 or less.

5. The amount of the crosslinking agent held in the porous substrate is 3.0 × 10 －８ mol / cm ２ Above 20.0 x 10 －８ mol / cm ２ The method for producing an electrolyte membrane according to claim 1 or 2, wherein:

6. The method for producing an electrolyte membrane according to claim 1 or 2, wherein the porous substrate further contains, in the pores, a binder that does not react with the crosslinking agent.

7. The method for producing an electrolyte membrane according to claim 6 , wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer.

8. An electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, the reinforcing layer includes a porous membrane and an at least partially cross-linked cross-linked electrolyte polymer contained in the pores of the porous membrane; An electrolyte membrane, wherein the contact layer comprises an uncrosslinked electrolyte polymer.

9. the cross-linked electrolyte polymer is a reaction product of an electrolyte polymer and a cross-linking agent, 9. The electrolyte membrane according to claim 8, wherein the crosslinked electrolyte polymer has a crosslinking agent-derived portion that is unevenly distributed in a greater amount near the wall surfaces of the pores than in the center of the pores of the porous membrane.

10. 10. The electrolyte membrane according to claim 8, wherein the number average molecular weight of the crosslinked electrolyte polymer is 50,000 or more and 300,000 or less.

11. 10. The electrolyte membrane according to claim 8, wherein the number average molecular weight of the uncrosslinked electrolyte polymer is 18,000 or more and 60,000 or less.

12. 10. The electrolyte membrane according to claim 8, wherein the thickness of the contact layer is 1 μm or more and 15 μm or less.

13. The electrolyte membrane according to claim 9 , wherein the reinforcing layer contains, in the pores of the porous membrane, a binder that does not react with the crosslinking agent.

14. The electrolyte membrane according to claim 13 , wherein the binder is a polymer having the same molecular structure as the main chain of the electrolyte polymer.

15. The electrolyte membrane according to claim 8 or 9, which is an electrolyte membrane for a fuel cell or an electrolyte membrane for water electrolysis.

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