Supporting base material for polymer electrolyte membrane, polymer electrolyte membrane with supporting base material, and method for producing membrane electrode assembly

Abstract

To provide a support base material capable of suppressing large deformation of a solid polymer electrolyte membrane even when it swells after sticking.SOLUTION: A supporting substrate for a polymer electrolyte membrane, comprising: A first pressure sensitive adhesive layer, a first base material layer, a second pressure sensitive adhesive layer, and a second base material layer in this order. The solid polymer electrolyte membrane with a support substrate includes a solid polymer electrolyte membrane and a support substrate for a solid polymer electrolyte membrane, and a first pressure sensitive adhesive layer is attached to a surface of the solid polymer electrolyte membrane. The method for manufacturing the membrane electrode assembly includes a step of applying an electrode catalyst layer forming ink to a surface of the solid polymer electrolyte membrane with the support base material opposite to a surface on which the support base material for the solid polymer electrolyte membrane is disposed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a supporting substrate for a solid polymer electrolyte membrane, a solid polymer electrolyte membrane with a supporting substrate, and a method for producing a membrane electrode assembly. [Background technology]

[0002] In recent years, there has been an accelerating trend toward using hydrogen as a primary energy source, a CO2-free energy source that can be produced from a variety of resources, in order to achieve carbon neutrality. Water electrolysis using renewable energy is seen as a promising method for producing such hydrogen. Generally, alkaline water electrolysis and polymer electrolyte membrane (PEM) water electrolysis are well-known water electrolysis methods, but PEM water electrolysis in particular has attracted attention as a method that enables the miniaturization of water electrolysis equipment through highly efficient operation.

[0003] A PEM water electrolysis device generally includes a pair of main electrodes and a membrane electrode assembly provided between the pair of main electrodes. The membrane electrode assembly includes a stacked body in which an anode electrode catalyst layer is provided on one surface of a proton-conductive solid polymer electrolyte membrane, and a cathode electrode catalyst layer provided so as to sandwich the solid polymer electrolyte membrane together with the anode electrode catalyst layer.

[0004] When external power is applied to the anode and cathode electrode catalyst layers, a water electrolysis reaction occurs on the catalyst in each electrode catalyst layer. At the anode, protons, electrons, and oxygen are produced from water, and the protons travel through the solid polymer electrolyte membrane and the electrons travel through an external circuit to the cathode, where hydrogen is produced.

[0005] The membrane electrode assembly is obtained by forming an electrode catalyst layer on one side of a solid polymer electrolyte membrane, for example, by a coating method. Because the solid polymer electrolyte membrane absorbs the solvent in the coating material and swells, it is necessary to apply the coating while suppressing membrane deformation due to swelling. In particular, the solid polymer electrolyte membrane used in the water electrolysis device is thick and undergoes significant deformation due to swelling. Therefore, for example, Patent Document 1 uses a support substrate with a thickness of 50 μm or more and 300 μm or less as a base film to be adhered to suppress deformation of the solid polymer electrolyte membrane, and the support substrate has an adhesive layer with an adhesive strength of 0.05 N / cm or more when the adherend is a PET film, as measured according to the JIS Z0237 test method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-104110 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the support substrate disclosed in Patent Document 1 is used, there is a problem with the contact between the solid polymer electrolyte membrane and the support substrate. Generally, solid polymer electrolyte membranes used in water electrolysis devices often have a reinforcing layer formed therein or reinforcing threads woven into them to increase the membrane's mechanical strength. The surface of a solid polymer electrolyte membrane with woven reinforcing threads is not smooth, with irregularities of several tens to several hundred micrometers. When bonding such a solid polymer electrolyte membrane to a support substrate, if a support substrate such as that described in Patent Document 1 is used, the support substrate's flexibility is low, and contact occurs only with the apexes of the protruding portions of the solid polymer electrolyte membrane surface, resulting in fewer effective contact points. This makes it difficult to suppress large deformation of the solid polymer electrolyte membrane due to swelling, and may result in the solid polymer electrolyte membrane peeling off from the support substrate. Large deformation of the solid polymer electrolyte membrane can cause wrinkles and coating defects in the electrode catalyst layer formed by applying ink on top of the membrane, making it difficult to form a uniform electrode catalyst layer.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a support substrate that can suppress large deformation of a solid polymer electrolyte membrane even if the solid polymer electrolyte membrane swells after attachment. [Means for solving the problem]

[0009] Given these challenges, we conducted extensive research and came up with the idea of ​​dividing the substrate layer into two and adding a second adhesive layer between the substrate layers, thereby improving the adhesion between the solid polymer electrolyte membrane and the supporting substrate and suppressing large deformation of the swelling solid polymer electrolyte membrane.

[0010] [1] A supporting substrate for a solid polymer electrolyte membrane comprising a first pressure-sensitive adhesive layer, a first substrate layer, a second pressure-sensitive adhesive layer, and a second substrate layer in this order.

[0011] [2] The supporting substrate according to [1], wherein the thickness of the first substrate layer is smaller than the thickness of the second substrate layer.

[0012] [3] The supporting substrate for a solid polymer electrolyte membrane according to [1] or [2], wherein the adhesive strength based on JIS Z 0237 of the second pressure-sensitive adhesive layer is greater than the adhesive strength based on JIS Z 0237 of the first pressure-sensitive adhesive layer.

[0013] [4] The supporting substrate for a solid polymer electrolyte membrane according to any one of [1] to [3], wherein the adhesive strength of the first pressure-sensitive adhesive layer according to JIS Z 0237 is 0.1 N / cm or more and less than 2 N / cm.

[0014] [5] The supporting substrate for a solid polymer electrolyte membrane according to any one of [1] to [4], wherein the thickness of the first substrate is 10 μm or more and less than 50 μm.

[0015] [6] The supporting substrate for a solid polymer electrolyte membrane according to any one of [1] to [5], wherein the total thickness of the first substrate layer and the second substrate layer is 60 μm or more.

[0016] [7] The supporting substrate for a solid polymer electrolyte membrane according to any one of [1] to [6], wherein the second substrate has a tensile strength of 40 MPa or more.

[0017] [8] A solid polymer electrolyte membrane with a supporting substrate, comprising: a solid polymer electrolyte membrane; and the supporting substrate for a solid polymer electrolyte membrane according to any one of [1] to [7], wherein the first pressure-sensitive adhesive layer is attached to the solid electrolyte membrane.

[0018] [9] A method for producing a membrane-electrode assembly, comprising a step of applying an ink for forming an electrode catalyst layer to a surface of the solid polymer electrolyte membrane with a support substrate according to [7] opposite to the surface on which the support film for the solid polymer electrolyte membrane is disposed. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a support substrate that can suppress large deformation of a solid polymer electrolyte membrane even when the membrane swells after being attached. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 2 is a schematic cross-sectional view illustrating the structure of a supporting substrate according to one embodiment. [Figure 2] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a membrane electrode assembly according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] One embodiment of a support substrate will be described with reference to Figure 1. The figures in the drawings are exaggerated for ease of understanding. Furthermore, the constituent materials and manufacturing method of the present invention are not limited to the configurations and materials described below, but include all materials and configurations that are considered to have similar functions.

[0022] [Supporting base material for solid polymer electrolyte membrane] As shown in FIG. 1, a supporting substrate 100 for a polymer electrolyte membrane according to this embodiment comprises a first pressure-sensitive adhesive layer 10, a first base layer 20, a second pressure-sensitive adhesive layer 30, and a second base layer 40 in this order.

[0023] (first adhesive layer) The first adhesive layer 10 is a layer formed from an adhesive. The adhesive is a pressure-sensitive adhesive layer. There are no particular limitations on the type of adhesive, and examples include acrylic adhesives, silicone adhesives, urethane adhesives, and rubber adhesives. The first adhesive layer 10 is a layer for adhering and fixing the first base layer 20 to the solid polymer electrolyte membrane, which is the adhesion target.

[0024] There are no particular limitations on the adhesive strength of the first pressure-sensitive adhesive layer 10, but it is preferably 0.1 N / cm or more and less than 2 N / cm when measured using the test method specified in JIS Z 0237. When the adhesive strength is 0.1 N / cm or more, good adhesion between the first pressure-sensitive adhesive layer 10 and the solid polymer electrolyte membrane is more likely to be obtained. On the other hand, when the adhesive strength is less than 2 N / cm, it tends to be difficult to peel the support substrate from the solid polymer electrolyte membrane together when peeling the support substrate from the solid polymer electrolyte membrane after forming an electrode catalyst layer on the solid polymer electrolyte membrane with the support substrate.

[0025] There are no particular limitations on the thickness of the first pressure-sensitive adhesive layer 10, and it is set appropriately depending on the adhesiveness and peelability, but it may be, for example, 1 to 20 μm, or may be 2 μm or more, or 10 μm or less.

[0026] [First base layer 20] There are no particular limitations on the material of the first base material layer 20. An example of the first base material layer is a resin film, and examples of the resin film include polyester films such as polyethylene naphthalate (PEN) and polyethylene terephthalate (PET); polyolefin films such as propylene (oriented propylene polypropylene (OPP) and polyethylene); polyvinyl chloride film; polycarbonate film; polyimide film; polystyrene film; polyurethane film; and nylon film. The first base material layer 20 is preferably a layer made of a material that has greater mechanical strength than the solid polymer electrolyte membrane and is less susceptible to deformation due to heat, moisture, etc.

[0027] Although there are no particular limitations on the thickness of the first base material layer 20, it is preferable that the thickness be thinner than the second base material layer 40. This makes it easy to efficiently deform the relatively thin first base material layer 20 to follow the surface shape of the solid polymer electrolyte membrane, while the relatively thick second base material layer 40 firmly supports the laminate of first pressure-sensitive adhesive layer 10 / first base material layer 20 / second pressure-sensitive adhesive layer 30, making it easier to suppress deformation of the solid polymer electrolyte membrane during swelling and further suppressing peeling of the solid polymer electrolyte membrane from the supporting substrate.

[0028] There is no particular limitation on the specific thickness of the first base layer 20, but it can be less than 50 μm, preferably 10 μm or more and less than 50 μm, and may be 40 μm or less.

[0029] As mentioned above, solid polymer electrolyte membranes for water electrolysis often have reinforcing layers or reinforcing threads formed to increase their mechanical strength. When reinforcing threads are formed, the surface of the solid polymer electrolyte membrane is affected by the thickness of the reinforcing threads, resulting in irregularities of up to approximately 100 μm. When a support substrate 100 is bonded to such a solid polymer electrolyte membrane via a first pressure-sensitive adhesive layer 10, if the thickness of the first substrate layer 20 is equal to or less than a predetermined upper limit, the first substrate layer 20 can better conform to the irregularities on the surface of the solid polymer electrolyte membrane. This facilitates surface contact between the support substrate 100 and the solid polymer electrolyte membrane, rather than point contact with only the protruding portions of the irregularities, thereby facilitating better adhesion. If the thickness of the first substrate layer 20 is equal to or greater than a predetermined lower limit, the first substrate layer 20 is easier to handle, and wrinkles and bubbles are less likely to form in the first substrate layer 20 when bonded to the solid polymer electrolyte membrane.

[0030] (Second adhesive layer 30) The second adhesive layer 30 is a layer formed from an adhesive, and fixes the first base material layer 20 and the second base material layer 40. The adhesive is a pressure-sensitive adhesive layer. There are no particular limitations on the type of adhesive, and examples include acrylic adhesives, silicone adhesives, urethane adhesives, and rubber adhesives.

[0031] The adhesive strength of the second pressure-sensitive adhesive layer 30 is not particularly limited as long as it can fix the first base material layer 20 and the second base material layer 40 together.

[0032] The adhesive strength of the second pressure-sensitive adhesive layer 30 is preferably greater than the adhesive strength of the first pressure-sensitive adhesive layer 10 when measured by the test method specified in JIS Z 0237. As a result, after adhering the support substrate 100 to one side of the solid polymer electrolyte membrane and forming an electrode catalyst layer on the other side of the solid polymer electrolyte membrane, when peeling the support substrate 100 from the solid polymer electrolyte membrane on which the electrode catalyst layer has been formed, the adhesive strength between the first substrate layer 20 and the second substrate layer 40 is greater than the adhesive strength between the solid polymer electrolyte membrane and the first substrate layer 20, making it easier to peel the first substrate layer 20 and the second substrate layer 40 together from the solid polymer electrolyte membrane 20. In addition, the second substrate layer 40 more firmly inhibits deformation due to swelling of the solid polymer electrolyte membrane.

[0033] The type of second pressure-sensitive adhesive layer 30 may be the same as that of first pressure-sensitive adhesive layer 10, or may be different from each other.

[0034] The thickness of the second pressure-sensitive adhesive layer 30 may be the same as that of the first pressure-sensitive adhesive layer 10, or may be different from that of the first pressure-sensitive adhesive layer 10.

[0035] There are no particular limitations on the thickness of the second pressure-sensitive adhesive layer 30, but it may be, for example, 1 to 20 μm, or may be 2 μm or more, or 10 μm or less.

[0036] (Second base layer) The second base layer 40 is disposed on the surface of the second pressure-sensitive adhesive layer 30 opposite to the first base layer 20. The main role of the second base layer 40 is to firmly suppress deformation of the solid polymer electrolyte membrane. There are also no particular limitations on the material of the second base layer 40. Examples of the second base layer 40 include polyester films such as polyethylene naphthalate (PEN) and polyethylene terephthalate (PET); polyolefin films such as propylene (oriented propylene polypropylene (OPP)) and polyethylene; polyvinyl chloride films; polycarbonate films; polyimide films; polystyrene films; polyurethane films; and nylon films. The second base layer 40 is preferably made of a material that has greater mechanical strength than the solid polymer electrolyte membrane and is less susceptible to deformation due to heat, moisture, etc.

[0037] The second base material layer 40 may be made of the same material as the first base material layer 20, or may be made of a different material.

[0038] The thickness of the second base layer 40 is not particularly limited, but may be 10 μm or more and less than 100 μm. As described above, it is preferable that the thickness of the second base layer 40 is thicker than that of the first base layer 20.

[0039] The combined thickness of the first substrate layer 20 and the second substrate layer 40 is preferably 60 μm or more. When the combined thickness of the second substrate layer 40 and the first substrate layer 20 is 60 μm or more, the handling properties of the support substrate 100 are good, and after an electrode catalyst layer is formed on the solid polymer electrolyte membrane with the support substrate, the support substrate 100 can be easily peeled off from the solid polymer electrolyte membrane 200.

[0040] The second substrate layer 40 preferably has high mechanical strength. Specifically, the tensile strength of the second substrate layer 40 is preferably 40 MPa or more. When the tensile strength is 40 MPa or more, the effect of suppressing peeling of the solid polymer electrolyte membrane is particularly high. The tensile strength can be measured based on JIS K 7127:1999. The second substrate layer 40 may have a mechanical strength, for example, a tensile strength, greater than that of the first substrate layer 20.

[0041] (Method for manufacturing membrane electrode assembly) A method for manufacturing a membrane electrode assembly will be described with reference to Fig. 2. First, a solid polymer electrolyte membrane 200 is prepared.

[0042] The solid polymer electrolyte membrane 200 is a solid polymer electrolyte membrane and is formed, for example, from a polymer material having proton conductivity.

[0043] Examples of polymeric materials having proton conductivity include fluororesins and hydrocarbon resins, such as Nafion (registered trademark, manufactured by DuPont), Flemion (registered trademark, manufactured by AGC), and Gore-Select (registered trademark, manufactured by Gore).

[0044] Examples of hydrocarbon resins include engineering plastics and engineering plastics into which sulfonic acid groups have been introduced.

[0045] Although there are no particular limitations on the thickness of the solid polymer electrolyte membrane 200, for example, a solid polymer electrolyte membrane used in a water electrolysis device is often relatively thick, at 50 μm or thicker, to ensure separation of hydrogen and oxygen. In addition, a membrane that can deform by 10% or more due to moisture may be used.

[0046] On the other hand, in order to maintain the mechanical strength of these solid polymer electrolyte membranes, reinforcing threads or reinforcing layers are often provided within the solid polymer electrolyte membrane.

[0047] Next, the above-mentioned support substrate 100 is attached to one surface of the solid polymer electrolyte membrane 200 so that the first pressure-sensitive adhesive layer 10 is in contact with the solid polymer electrolyte membrane 200. In this way, a solid polymer electrolyte membrane 400 with a support substrate is obtained.

[0048] There are no particular limitations on the method of attachment. For example, after attaching a laminate of the first pressure-sensitive adhesive layer 10 and the first base layer 20 so that the first pressure-sensitive adhesive layer 10 contacts the solid polymer electrolyte membrane 200, a laminate of the second pressure-sensitive adhesive layer 30 and the second base layer 40 can be attached so that the second pressure-sensitive adhesive layer 30 contacts the first base layer 20. Alternatively, a laminate of the first pressure-sensitive adhesive layer 10, the first base layer 20, the second pressure-sensitive adhesive layer 30, and the second base layer 40 may be prepared first, and the first pressure-sensitive adhesive layer 10 of this laminate may be attached to the solid polymer electrolyte membrane.

[0049] Next, an ink for forming an electrode catalyst layer is applied to the surface of the solid polymer electrolyte membrane 200 opposite the first adhesive layer 10 and dried to form the electrode catalyst layer 300. The ink for forming an electrode catalyst layer can contain, for example, catalyst-supporting carbon particles, a polymer electrolyte, a fibrous material, and a solvent, and its composition is known.

[0050] Thereafter, the support substrate 100 is peeled off from the solid polymer electrolyte membrane 200.

[0051] Next, the ink for forming an electrode catalyst layer is similarly applied to the exposed surface of the solid polymer electrolyte membrane 200 and dried to form the electrode catalyst layer 300. In this way, a membrane electrode assembly can be formed.

[0052] Alternatively, a membrane electrode assembly may be formed by laminating a catalyst layer-equipped electrolyte membrane formed in the same manner to the exposed surface of the solid polymer electrolyte membrane 200 .

[0053] Such a membrane electrode assembly is particularly suitable for a water electrolysis device.

[0054] (Action and effect) In the support substrate 100 according to this embodiment, the substrate layer is divided into two parts, a first substrate layer 20 and a second substrate layer 40. A second pressure-sensitive adhesive layer 30 is provided between the first substrate layer 20 and the second substrate layer 40, separate from the first pressure-sensitive adhesive layer 10 that is attached to the solid polymer electrolyte membrane. This allows the first substrate layer 20, sandwiched between the first pressure-sensitive adhesive layer 10 and the second pressure-sensitive adhesive layer 30, to easily deform in accordance with the surface shape of the solid polymer electrolyte membrane, thereby enhancing adhesion between the support substrate 100 and the solid polymer electrolyte membrane. Furthermore, by utilizing the rigidity of the second substrate layer 40 that is attached to the first substrate layer 20 via the second pressure-sensitive adhesive layer 30, significant deformation of the solid polymer electrolyte membrane can be suppressed even when the membrane swells. This facilitates uniform formation of the electrode catalyst layer. [Example]

[0055] Next, the above embodiment will be described in more detail with reference to examples and comparative examples. Note that the present invention is not limited to the configurations described in the examples section.

[0056] Example 1 〔material〕 The solid polymer electrolyte membrane prepared had a thickness of 200 μm and a surface unevenness (difference in thickness between the thickest and thinnest parts) of about 100 μm due to the reinforcing threads.

[0057] A first laminate having a pressure-sensitive adhesive layer with an adhesive strength of 0.1 N / cm and a PET film with a thickness of 8 μm was prepared as a laminate of the first pressure-sensitive adhesive layer 10 and the first base layer 20. A second laminate having a pressure-sensitive adhesive layer with an adhesive strength of 2 N / cm and a PET film with a thickness of 50 μm and a tensile strength of 40 MPa was prepared as the second pressure-sensitive adhesive layer 30 and the second base layer 40.

[0058] [Laminating a Support Substrate to a Solid Polymer Electrolyte Membrane] A roll laminator was used to bond the first laminate to the solid polymer electrolyte membrane. The lamination conditions were a pressure of 0.4 MPa, a roll temperature of 40°C, and a feed rate of 3 m / min. The second laminate was then bonded to the first laminate under the same conditions to obtain a laminate of solid polymer electrolyte membrane / first pressure-sensitive adhesive layer / first base layer / second pressure-sensitive adhesive layer / second base layer. The supporting substrate had a structure of, in order from the solid polymer electrolyte membrane side, first pressure-sensitive adhesive layer / first base layer / second pressure-sensitive adhesive layer / second base layer.

[0059] [Electrode catalyst layer formation] An electrode catalyst layer was formed by applying an ink for forming an electrode catalyst layer to the side opposite the support substrate of the solid polymer electrolyte membrane to which the support substrate was attached and drying it. The composition of the ink for forming the electrode catalyst layer was a platinum-based catalyst (Tanaka Kikinzoku Kogyo: TEC66E50) as the catalyst material, a Nafion solution (Fujifilm Wako Pure Chemical Industries: DE2020CS) as the ionomer, and a 30:70 (wt%) mixture of pure water and 1-propanol as the solvent. The above materials were prepared using a planetary ball mill to produce the ink for forming the electrode catalyst layer. A variable gap applicator was used to apply the ink to the solid polymer electrolyte membrane, with the platinum loading in the electrode catalyst layer being 0.5 mg / cm. 2 The coating was then dried at 70°C for 10 minutes to form an electrode catalyst layer on the solid polymer electrolyte membrane.

[0060] Example 2 The same procedure as in Example 1 was carried out except that the thickness of the first base material layer was set to 10 μm.

[0061] Example 3 The same procedure as in Example 1 was carried out except that the thickness of the first base material layer was set to 40 μm.

[0062] Example 4 The same procedure as in Example 1 was carried out except that the thickness of the first base material layer was set to 50 μm.

[0063] Example 5 The same procedure as in Example 2 was carried out except that the thickness of the second base layer was set to 40 μm.

[0064] Example 6 The same procedure as in Example 3 was carried out except that the adhesive strength of the first adhesive layer was set to 0.05 N / cm.

[0065] Example 7 The same procedure as in Example 3 was carried out except that the adhesive strength of the first adhesive layer was set to 1 N / cm.

[0066] Example 8 The same procedure as in Example 3 was carried out except that the adhesive strength of the first adhesive was set to 2 N / cm.

[0067] Example 9 The same procedure as in Example 7 was carried out except that the adhesive strength of the second adhesive was set to 0.5 N / cm.

[0068] Example 10 The same procedure as in Example 7 was carried out except that the adhesive strength of the second adhesive was set to 1 N / cm.

[0069] Example 11 The same procedure as in Example 7 was carried out except that the tensile strength of the second base layer was set to 30 MPa.

[0070] (Comparative Example 1) The same procedure as in Example 10 was carried out except that the first laminate was not used and the thickness of the second base material layer in the second laminate was set to 90 μm.

[0071] [Evaluation of the appearance of the solid polymer electrolyte membrane during the formation of the electrode catalyst layer] When forming the electrode catalyst layer, deformation of the swollen solid polymer electrolyte membrane was sufficiently suppressed, and the electrode catalyst layer could be formed without wrinkles or coating voids, as evaluated as "Good." When the swollen solid polymer electrolyte membrane was slightly deformed but the electrode catalyst layer could be formed without major wrinkles or coating voids, as evaluated as "Good." When the swollen solid polymer electrolyte membrane was significantly deformed and peeled off from the support film, causing defects such as serious wrinkles or coating voids in the electrode catalyst layer, as evaluated as "Poor."

[0072] [Evaluation of appearance when bonding to supporting substrate] When bonding the support substrate to the solid polymer electrolyte membrane, if there were no wrinkles or air bubbles in the support substrate or the solid polymer electrolyte membrane and they could be bonded together, the result was evaluated as "Good." If wrinkles occurred in the support substrate or if air bubbles were mixed in between the solid polymer electrolyte membrane and the support substrate or between the first substrate layer and the second substrate layer, the result was evaluated as "Poor."

[0073] [Determination of Support Substrate Peel-Off After Formation of Electrode Catalyst Layer] After the formation of the electrode catalyst layer, when peeling the support substrate from the solid polymer electrolyte membrane, the case where the first substrate layer and the second substrate layer could be peeled off integrally from the solid polymer electrolyte membrane was evaluated as "Good", and the case where only the second substrate layer peeled off leaving the first substrate layer behind, or the case where the support substrate did not peel off from the solid polymer electrolyte membrane was evaluated as "Poor".

[0074] 〔result〕 The results of Examples 1 to 11 are shown in Table 1.

[0075] In Comparative Example 1, when the catalyst layer was applied to the solid polymer electrolyte membrane with supporting substrate, the solid polymer electrolyte membrane was significantly warped due to swelling caused by immersion in the solvent, resulting in large coating voids in the electrode catalyst layer. In Example 7, in which the base material was divided, all items were evaluated as ○. As can be seen from a comparison between Example 7 and Comparative Example 1, it was confirmed that, compared to Comparative Example 1 in which the base material layer was not divided, in the Example in which the base material layer was divided and the second pressure-sensitive adhesive layer was sandwiched, large deformation due to swelling of the solid polymer electrolyte membrane during formation of the electrode catalyst layer could be suppressed, and defective formation of the electrode catalyst layer could be suppressed.

[0076] [Film Thickness of Support Film] With reference to Examples 1 to 5, when the thickness of the first substrate was 10 μm (Example 2) and 40 μm (Example 3), a rating of "Good" was obtained for all items. However, when the thickness of the first substrate was 8 μm (Example 1), wrinkles occurred in the first laminate when the first laminate was bonded to the solid polymer electrolyte membrane, possibly because the first substrate was too thin. On the other hand, when the thickness of the first laminate was 50 μm (Example 4), when the catalyst layer was coated on the solid polymer electrolyte membrane with the support substrate, the solid polymer electrolyte membrane swelled due to solvent immersion, causing some coating defects in the electrode catalyst layer. Furthermore, when the total thickness of the first substrate and the second substrate was 50 μm (Example 5), deformation was well suppressed when the respective laminates were bonded together and when the catalyst layer was formed on the electrolyte membrane with the support substrate, but the support substrate was thin, making it difficult to peel off the support film after the catalyst layer was formed.

[0077] From the above results, it was determined that a thickness of 10 μm or more and less than 50 μm is particularly suitable for the first substrate located on the solid polymer electrolyte membrane side. Furthermore, it was considered that a total thickness of 60 μm or more is suitable for the first substrate and the second substrate from the viewpoint of handling when peeling the support substrate from the solid polymer electrolyte membrane on which the electrode catalyst layer has been formed.

[0078] [Adhesive strength of adhesive layer] With reference to Examples 2, 6 to 10, when the adhesive strength of the first adhesive was 0.1 N / cm (Example 2) and 1 N / cm (Example 7), a rating of "Good" was obtained in all items, but when the adhesive strength of the first adhesive was 0.05 N / cm (Example 6), the support film peeled slightly from the solid polymer electrolyte membrane during catalyst layer formation, resulting in minor coating defects of the catalyst layer. Furthermore, when the adhesive strength of the first adhesive was 2 N / cm (Example 8), there were no problems when bonding each laminate to the solid polymer electrolyte membrane or when coating the catalyst layer on the solid polymer electrolyte membrane, but it was difficult to peel the support substrate after catalyst layer formation.

[0079] On the other hand, when focusing on the difference in adhesive strength between the first adhesive layer and the second adhesive layer, when the adhesive strength of the second adhesive layer was stronger than that of the first adhesive layer (Example 7), the result was rated as "Good" in all processes. However, when the adhesive strength of the first adhesive layer and the second adhesive layer was equal or the adhesive strength of the first adhesive layer was stronger (Examples 9 and 10), only the second substrate layer sometimes peeled off when peeling off the support substrate after forming the catalyst layer.

[0080] From the above results, it was determined that the adhesive strength of the first pressure-sensitive adhesive layer adhered to the solid polymer electrolyte membrane is preferably 0.1 N / cm or more and less than 2 N / cm from the viewpoints of adhesion to the solid polymer electrolyte membrane and peeling the support substrate integrally from the solid polymer electrolyte membrane. Furthermore, if the adhesive strength of the second pressure-sensitive adhesive layer is equal to or less than that of the first pressure-sensitive adhesive layer, when peeling the support substrate from the solid polymer electrolyte membrane, only the second support substrate may peel off and the first support substrate may remain. Therefore, from the viewpoint of simplifying the process, it is preferable that the adhesive strength of the second pressure-sensitive adhesive layer is stronger than that of the first pressure-sensitive adhesive layer.

[0081] [Tensile strength of second base layer] With reference to Examples 7 and 11, when the tensile strength of the second base layer was 40 MPa, a rating of "Good" was obtained in all steps, but when the tensile strength of the second base layer was 30 MPa, slight peeling occurred between the polymer electrolyte membrane and the support film during catalyst formation, resulting in minor defects in the electrode catalyst layer. Therefore, the tensile strength of support film B is preferably 40 MPa or more.

[0082] As explained above, in this embodiment, by using two layers of support film for the solid polymer electrolyte membrane and adding an adhesive layer between them, it is possible to improve the adhesion between the uneven solid polymer electrolyte membrane and the support film, and to impart the effect of suppressing deformation of the polymer electrolyte membrane when it swells. It has been shown that even if a solid polymer electrolyte membrane that deforms significantly due to swelling is used, it is possible to form a good catalyst layer on it.

[0083] [Table 1] [Explanation of symbols]

[0084] 10...first adhesive layer, 20...first substrate layer, 30...second adhesive layer, 40...second substrate layer, 100...support substrate, 200...solid polymer electrolyte membrane, 400...solid polymer electrolyte membrane with support substrate.

Claims

1. A supporting substrate for a solid polymer electrolyte membrane, comprising a first pressure-sensitive adhesive layer, a first substrate layer, a second pressure-sensitive adhesive layer, and a second substrate layer in this order.

2. The support substrate of claim 1 , wherein the thickness of the first substrate layer is less than the thickness of the second substrate layer.

3. The support substrate according to claim 1 or 2, wherein the adhesive strength based on JIS Z 0237 of the second pressure-sensitive adhesive layer is greater than the adhesive strength based on JIS Z 0237 of the first pressure-sensitive adhesive layer.

4. The support substrate according to claim 1 or 2, wherein the adhesive strength of the first pressure-sensitive adhesive layer according to JIS Z 0237 is 0.1 N / cm or more and less than 2 N / cm.

5. The supporting substrate according to claim 1 or 2, wherein the thickness of the first substrate is 10 μm or more and less than 50 μm.

6. The supporting substrate according to claim 1 or 2, wherein the total thickness of the first substrate layer and the second substrate layer is 60 μm or more.

7. The supporting substrate according to claim 1 or 2, wherein the second substrate layer has a tensile strength of 40 MPa or more.

8. 3. A solid polymer electrolyte membrane with a supporting substrate, comprising: a solid polymer electrolyte membrane; and the supporting substrate for a solid polymer electrolyte membrane according to claim 1 or 2, wherein the first pressure-sensitive adhesive layer is attached to a surface of the solid polymer electrolyte membrane.

9. 9. A method for producing a membrane electrode assembly, comprising a step of applying an ink for forming an electrode catalyst layer to a surface of the solid polymer electrolyte membrane with a supporting substrate according to claim 8 opposite to a surface on which the supporting substrate for the solid polymer electrolyte membrane is disposed.

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