Solid polymer fuel cell sealing material

Abstract

The present invention provides a solid polymer fuel cell sealing material which is excellent in hot water resistance and acid resistance, and in which sealing properties do not decrease even if a solid polymer fuel cell is driven for a long time. This solid polymer fuel cell sealing material comprises a carboxyl group-containing acrylonitrile‐butadiene copolymer (a) and an epoxy resin (b). It is preferable that the component (a) is a carboxy-containing acrylonitrile‐butadiene copolymer having an acrylonitrile content of 5-50% and having a carboxyl group equivalent, calculated from the number average molecular weight, of 100-20,000.

Description

Technical Field

[0001] The present invention relates to a solid polymer fuel cell sealing material that is excellent in heat and water resistance and acid resistance, and does not cause a decrease in sealing performance even when the solid polymer fuel cell is driven for a long period of time.

Background Art

[0002] A fuel cell is a power generation system that continuously supplies a fuel and an oxidant and extracts the chemical energy generated by their electrochemical reaction as electric power. A fuel cell using this power generation method based on an electrochemical reaction utilizes the reverse reaction of the electrolysis of water, that is, a mechanism in which hydrogen and oxygen combine to generate electrons and water, and has attracted attention in recent years because of its high efficiency and excellent environmental characteristics.

[0003] Fuel cells are classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, alkaline fuel cells, and solid polymer fuel cells according to the type of electrolyte. In recent years, particular attention has been paid to solid polymer fuel cells, which have advantages such as starting at room temperature and having an extremely short startup time. The basic structure of a single cell constituting this solid polymer fuel cell is such that a gas diffusion electrode having a catalyst layer on both sides of a solid polymer electrolyte membrane is joined (this joined body is hereinafter referred to as MEA), and separators are arranged on both outer surfaces thereof.

[0004] In each separator, in the portion that contacts the MEA, gas flow paths are formed for supplying reaction gases such as fuel gas or oxidant gas to each electrode and carrying away generated water or surplus gas. Supply of reaction gas to the gas flow path formed between each separator and the MEA, reaction gas from the gas flow path, and discharge of generated water are performed by providing through holes called manifold holes at the edges of at least one of the pair of separators, respectively, and connecting the inlets and outlets of each gas flow path to these manifold holes, respectively, and distributing the reaction gas from each manifold hole to each gas flow path.

[0005] Furthermore, to prevent fuel gas or oxidizer gas supplied to the gas flow path from leaking to the outside or the two types of gases from mixing, a polymer electrolyte sealant is placed between a pair of separators, surrounding the outer periphery of the power generation area in the MEA where electrodes and a polymer electrolyte membrane are formed. These polymer electrolyte sealants also seal around each manifold hole. In addition, to protect the solid electrolyte membrane, the periphery of both sides of the polymer electrolyte membrane may be sealed with a two-layer sealant consisting of a base film and an adhesive.

[0006] Since the polymer electrolyte membrane to which the above-mentioned polymer electrolyte fuel cell sealing material is bonded is usually made of a fluororesin with a perfluoroalkyl group as its main chain, conventional polymer electrolyte fuel cell sealing materials have the problem of insufficient adhesion. In response to this, Patent Document 1 discloses a method for achieving good sealing performance by bonding solid polymer electrolyte membranes by thermocompression bonding. Furthermore, Patent Document 2 discloses a method for improving adhesion by ion exchange treatment of the surface of a solid polymer electrolyte membrane. Moreover, Patent Document 3 discloses a method for improving adhesion by incorporating fluorine atom-containing acrylic monomer into the adhesive. However, none of the methods could reliably seal around the polymer electrolyte membrane. In particular, when polymer electrolyte fuel cells are operated for extended periods, the sealing material is exposed to hot water at around 95°C, and it was difficult to maintain high sealing performance to prevent hydrogen leakage in such a hot water environment. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 6-119928 [Patent Document 2] Japanese Patent Application Publication No. 9-199145 [Patent Document 3] Japanese Patent Publication No. 2004-269782 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention has been made in view of the above circumstances, and aims to provide a solid polymer fuel cell sealing material that has excellent resistance to hot water and acid, and whose sealing performance does not deteriorate even when the solid polymer fuel cell is operated for a long period of time. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have discovered that by including a carboxyl group-containing acrylonitrile-butadiene copolymer (a) and an epoxy resin (b), a solid polymer electrolyte membrane made of fluororesin can be made to exhibit high adhesion, and a solid polymer fuel cell sealing material can be obtained that reliably seals and prevents hydrogen leakage even when the solid polymer fuel cell is operated for a long time and exposed to hot water and acidic aqueous solutions at about 95°C, thus completing the present invention.

[0010] The present invention has the following aspects. [1] A solid polymer fuel cell sealant characterized by containing a carboxyl group-containing acrylonitrile-butadiene copolymer (a) and an epoxy resin (b). [2] The solid polymer fuel cell sealing material according to [1], characterized in that component (a) is a carboxyl group-containing acrylonitrile-butadiene copolymer having an acrylonitrile content of 5 to 50% by mass and a carboxyl group equivalent of 100 to 20,000 calculated from the number average molecular weight. [3] The solid polymer fuel cell sealing material according to [1], characterized in that component (b) is an epoxy resin having a number average molecular weight of 400 to 10000 and an epoxy group equivalent of 200 to 5000. [4] The solid polymer fuel cell sealing material according to [1], characterized in that component (b) is 1 to 300 parts by mass with respect to 100 parts by mass of component (a). [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a polymer electrolyte fuel cell sealing material that has excellent resistance to hot water and acid, and whose sealing performance does not deteriorate even when the polymer electrolyte fuel cell is operated for a long period of time. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view showing an example of a solid polymer fuel cell sealing material of the present invention. [Figure 2] This is a perspective view showing an example of a solid polymer fuel cell sealing material of the present invention. [Figure 3] This is a perspective view showing an example of a solid polymer fuel cell sealing material of the present invention. [Figure 4] This is a perspective view showing an example of using the solid polymer fuel cell sealing material of the present invention in a single cell. [Figure 5] This figure illustrates the measurement of the adhesive strength of the solid polymer fuel cell sealing material of the present invention. (a) shows the case when the sealing material is bonded to the substrate of the solid polymer electrolyte membrane on both sides via adhesive members, and (b) shows the case when two sealing materials are bonded to each other via adhesive members of the sealing materials. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below. The carboxyl group-containing acrylonitrile-butadiene copolymer (a) used in the solid polymer fuel cell sealing material (hereinafter referred to as the sealing material) of the present invention plays a role in appropriately maintaining the melt viscosity of the sealing material in the initial stage of heating, and also imparts good flexibility and adhesiveness to the cured sealing material. By containing this, good adhesion to the solid polymer electrolyte membrane, electrode and separator can be achieved, and a sealing material without cracks can be formed. As the carboxyl group-containing acrylonitrile-butadiene copolymer (a), known ones can be used without limitation, but those having an acrylonitrile content of 5 to 50% by mass are preferred, and those having an acrylonitrile content of 10 to 40% by mass are more preferred. When the acrylonitrile content is less than the above range, the solubility in the solvent and the compatibility with other components decrease, so the uniformity of the obtained sealing material tends to deteriorate. On the other hand, when the acrylonitrile content exceeds the above range, the flexibility of the obtained sealing material decreases, and the sealing performance tends to deteriorate. In addition, since the solubility in the solvent decreases, it tends to be difficult to form a paint.

[0014] The carboxyl group equivalent calculated from the number average molecular weight in the carboxyl group-containing acrylonitrile-butadiene copolymer is preferably in the range of 100 to 20,000, and more preferably 200 to 10,000. When the carboxyl group equivalent is less than the above range, the reactivity with other components becomes too high, and the storage stability of the obtained sealing material tends to decrease. On the other hand, when the carboxyl group equivalent exceeds the above range, the reactivity with other components is insufficient, so the obtained sealing material becomes low-viscosity and easy to flow due to heat. As a result, when the sealing material is heated, the sealing material becomes low-viscosity, and it tends to foam or flow out, and the thermal stability deteriorates. The carboxyl group equivalent calculated from the number average molecular weight is the number average molecular weight (Mn) divided by the number of carboxyl groups (functional groups) per molecule, and is represented by the following formula. Carboxyl group equivalent = Mn / Number of functional groups

[0015] The epoxy resin (b) imparts heat and water resistance and acid resistance to the sealing material by reacting with (a) or by the reaction of (b) with a curing agent.

[0016] Examples of the epoxy resin (b) include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol S type epoxy resin, alicyclic epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, glycidyl ether type epoxy resin, etc., and they can be used alone or in admixture of two or more. Further, the epoxy resin (b) preferably has a number average molecular weight of 400 to 10,000. When the number average molecular weight is less than the above range, the reactivity with other components becomes too high, and the storage stability of the resulting sealing material tends to decrease. When it exceeds the above range, the compatibility with other components decreases, and the uniformity of the resulting sealing material tends to deteriorate. Furthermore, the epoxy resin (b) preferably has an epoxy equivalent of 200 to 5,000. When the epoxy equivalent is less than the above range, the reactivity with other components becomes too high, and the storage stability of the resulting sealing material tends to decrease. When it exceeds the above range, the reactivity with other components is insufficient, and the resulting sealing material becomes low-viscosity and easily flows due to heat. As a result, when the sealing material is heated, the sealing material becomes low-viscosity, and it tends to foam or flow out, and the thermal stability tends to decrease.

[0017] The ratio of each component is preferably 1 to 300 parts by mass, more preferably 30 to 200 parts by mass of the component (b) with respect to 100 parts by mass of the component (a). When the component (b) is less than the above range, the reactivity of the sealing material decreases, and insolubilization and crosslinking hardly proceed even by heating, and the thermal stability tends to decrease. On the other hand, when it exceeds the above range, the flexibility of the resulting sealing material decreases, and the sealing performance tends to deteriorate. Here, the carboxyl group content (A) in carboxyl-modified acrylonitrile butadiene rubber can be determined by the ratio of the carboxyl group content (parts by mass) of carboxyl-modified acrylonitrile butadiene rubber to the carboxyl group equivalent (g / eq). Similarly, the epoxy group content (B) of the epoxy resin can be determined by the ratio of the epoxy resin content (parts by mass) to the epoxy equivalent (g / eq) of the epoxy resin. In the present invention, it is preferable that the relationship between the carboxyl group content (A) and the epoxy group content (B) is such that epoxy group content (B) ≥ carboxyl group content (A) × 0.1. If epoxy group content (B) < carboxyl group content (A) × 0.1, the reactivity of the sealing material decreases, insolubility and infusibility do not progress easily even with heating, and thermal stability tends to decrease.

[0018] In addition to the essential components (a) and (b), reaction accelerators such as organic peroxides, imidazoles, and triphenylphosphine may be added to the sealant. These additions can also be used to control the sealant's state at room temperature to a favorable B stage. Furthermore, the resulting sealant's resistance to hot water and acid is improved. Furthermore, fillers with an average particle size of 1 μm or less may be added for purposes such as controlling melt viscosity, improving thermal conductivity, and imparting flame retardancy. Examples of fillers include inorganic fillers such as silica, alumina, magnesia, aluminum nitride, boron nitride, titanium oxide, calcium carbonate, and aluminum hydroxide, and organic fillers such as silicone resins and fluororesins. When using fillers, their content is preferably 1 to 40% by mass in the sealant.

[0019] The present invention will be described below with reference to the figures. Figures 1 to 3 are perspective views showing an example of the solid polymer fuel cell sealing material of the present invention. The solid polymer fuel cell sealing material 10 of the present invention (hereinafter referred to as "sealing material 10") can include a sheet-like adhesive member 1 having a rectangular frame shape, as shown in Figure 1. Furthermore, the shape of the sheet-like adhesive member 1 is not limited to a rectangular frame shape, but can be appropriately selected according to the shape of the fuel cell, such as a circular frame shape. The adhesive member 1 in Figure 1 contains the carboxyl group-containing acrylonitrile-butadiene copolymer (a) and the epoxy resin (b). Furthermore, the sealing material 10 may have a two-layer structure consisting of a base material 2 in contact with the adhesive member 1, as shown in Figure 2. Alternatively, the sealing material 10 may have a three-layer structure in which the adhesive member 1, base material 2, and adhesive layer 3 are laminated, as shown in Figure 3.

[0020] The sealing material of the present invention can be formed, for example, by applying a mixture of the carboxyl group-containing acrylonitrile-butadiene copolymer (a) and the epoxy resin (b) to one side of a peelable protective film to form a sheet, and then cutting it out in a frame shape. When manufacturing such a sealing material, first, a coating is prepared consisting of at least the carboxyl group-containing acrylonitrile-butadiene copolymer (a) and the epoxy resin (b) and a solvent. Then, this coating is applied to one side of a protective film so that the thickness of the sealing material after drying is preferably 1 to 50 μm, more preferably 3 to 20 μm, and then dried. Furthermore, to protect the sealing material, it is preferable to provide another peelable protective film on top of the sealing material formed on the protective film. In this case, the sealing material may be formed by applying the coating to the protective film, drying it, and then providing another protective film on top of it. The protective film is peeled off when the sealing material is used.

[0021] Examples of release-type protective films include plastic films such as polyethylene, polypropylene, vinyl chloride, fluororesins, and silicone, as well as films made by applying a silicone coating or similar method to polyethylene terephthalate, polyethylene naphthalate, paper, etc., to provide release properties.

[0022] Furthermore, one or more solvents from among organic solvents such as hydrocarbons, alcohols, ketones, and ethers, and water can be preferably used as solvents for the paint, and the amount used should be adjusted as appropriate to achieve an appropriate viscosity for the paint. In addition, the properties of the paint may be a solution, emulsion, or suspension, and should be appropriately selected depending on the application equipment and environmental conditions used.

[0023] Furthermore, in the two-layer sealing material 10 shown in Figure 2, a base film serving as the base material 2 can be used instead of the protective film. Examples of the base film include heat-resistant plastic films made of polyimide, polyphenylene sulfide, polyethersulfone, polyetheretherketone, liquid crystal polymer, polyethylene terephthalate, polyethylene naphthalate, etc., and composite heat-resistant films such as epoxy resin-glass cloth. Polyethylene naphthalate is particularly preferred from the viewpoint of hot water resistance, acid resistance, and cost. The thickness of the base film is preferably 12 to 125 μm, and more preferably 12 to 50 μm. If it is less than the above range, the resulting sealing material will be thin and easily broken by external force, which tends to cause problems during processing. If it exceeds the above range, the resulting sealing material will be thick and stiff, which tends to reduce the flexibility of the sealing material and its ability to conform to the adherend, resulting in a deterioration of sealing performance.

[0024] Furthermore, the three-layer sealing material 10 shown in Figure 3 can be obtained by first forming an adhesive member 1 on a base film which serves as the base material 2, consisting of at least the carboxyl group-containing acrylonitrile-butadiene copolymer (a) and the epoxy resin (b) and a solvent, and then applying and drying the paint constituting the adhesive layer 3 on the base film opposite to the surface of the adhesive member 1. The adhesive layer 3 may have the same composition as the adhesive member 1, or it may be a different adhesive.

[0025] Other adhesives include those containing thermoplastic resins and rubber-based resins. Examples of the thermoplastic resins mentioned above include polyolefin resins such as polyethylene (PE), polypropylene (PP), and polybutylene, as well as styrene resins, polyoxymethylene (POM), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene ether (PPE), modified PPE, polysulfone (PSU), polyethersulfone (PESF), polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyethernitrile (PEN), and polyacrylonitrile (PAN). Particularly preferred are ultra-high molecular weight polyethylene, polyphenylene sulfide, polysulfone, polyethernitrile, and polyacrylonitrile. These thermoplastic resins may be used individually or in combination of two or more.

[0026] Examples of rubber-based resins include synthetic rubbers such as methyl methacrylate-butadiene rubber (MBR), ethylene propylene rubber (EPR), acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), chlorosulfonated polyethylene (CSP), chloroprene rubber (CR), isoprene rubber (IR), butyl rubber (IIR), acrylic rubber, fluororubber, silicone rubber, butadiene-based rubber (MBS), polyphenylene sulfide (PPS), and ethylene-propylene dimethyl rubber (EPDM); styrene-based elastomers such as styrene-butadiene-styrene (SBS) copolymer and styrene-isoprene-styrene (SIS) copolymer; olefin-based elastomers; urethane-based elastomers; polyamide-based elastomers; butadiene-based elastomers (MBS); and vinyl chloride-based elastomers (TPVC). These rubber-based resins may be used individually or in combination of two or more.

[0027] The sealing material of the present invention is used in a single cell in a stack of a polymer electrolyte fuel cell, for example, in a single cell as shown in Figure 4. Figure 4 shows a single cell 100, in which sealing material 10 is in contact with both sides of the electrode 20, and a separator 30 is in contact with the side of the sealing material 10 that is not in contact with the electrode 20. Examples of the electrode 20 include a membrane electrode assembly (MEA), a catalyst coated membrane (CCM), and a gas diffusion electrode (GDE). Examples of the separator 30 include a fluororesin with a perfluoroalkyl group as the main chain. [Examples]

[0028] The present invention will be described in detail below with reference to examples. [Examples 1-7 and Comparative Examples 1-4] (Preparation of sealing material) A coating for adhesive members was prepared by mixing component (a), component (b), and other components with the solvent methyl ethyl ketone (MEK) in the mass ratios shown in Table 1. Next, this paint was applied to one side of a 25 μm thick polyethylene naphthalate film so that the thickness after drying would be 20 μm. It was then dried in a hot air circulating oven set to 100°C to obtain a sealing material in which an adhesive member was laminated on one side of the polyethylene naphthalate film. The details of each ingredient used are as follows:

[0029] <Carboxyl group-containing acrylonitrile-butadiene copolymer (a)> • Carboxyl group-containing acrylonitrile-butadiene copolymer: Number average molecular weight 300,000, carboxyl group equivalent calculated from the number average molecular weight 1500 g / eq, acrylonitrile content 27% by mass <Epoxy resin (b)> • Bisphenol A type epoxy resin: Number average molecular weight 900, epoxy group equivalent 450 g / eq • Bisphenol A type epoxy resin: Number average molecular weight 5500, epoxy group equivalent 3000 g / eq ·Trifunctional epoxy resin: Number average molecular weight 630, functional group equivalent 210g / eq <Other ingredients> • Reaction accelerator: Imidazole compound (2-ethyl-4-methylimidazole) • Acrylonitrile-butadiene copolymer: Number average molecular weight 300,000, acrylonitrile content 27% by mass • Carboxyl group-containing polyester resin: Number average molecular weight 20,000, carboxyl group equivalent 18,000 g / eq • Ethylene-methyl acrylate-glycidyl methacrylate copolymer: Number average molecular weight 150,000, functional group equivalent: 2500 g / eq

[0030] [Table 1]

[0031] [evaluation] (1) Adhesion evaluation (I) (1-1) Preparation of test specimens Two sheets were prepared by cutting the sealant obtained in each example to a width of 25 mm and a length of 100 mm. In addition, a solid polymer electrolyte membrane (manufactured by DuPont, trade name: Nafion membrane) was prepared separately and cut to a width of 25 mm and a length of 80 mm. Next, these components were attached as shown in Figure 5(a). As shown in Figure 5(a), a test specimen was prepared by attaching a sealing material 10, in which adhesive members 1 were in contact with both sides of the solid polymer electrolyte membrane 11, using a roll laminator. The lamination conditions were a temperature of 50°C, a pressure of 4 N / cm, and a bonding speed of 1 m / min. The length α in contact between the solid polymer electrolyte membrane 11 and the adhesive member 1 was 80 mm. In Figure 5(a), the portion β of the sealing material 10 that is not attached to the solid polymer electrolyte membrane 11 is the attachment portion for fixing to the universal tensile testing machine described below. A polyimide film (not shown) was attached to the adhesive member 1 at β, and then fixed to the universal tensile testing machine, and the adhesive strength was measured.

[0032] (1-2) Measurement of initial adhesive strength The T-peel strength of the test specimen described in (1-1) above was measured using a universal tensile testing machine without immersion in a 95°C sulfuric acid aqueous solution (pH 2). Specifically, the upper β in Figure 5(a) was pulled upwards while the lower β was pulled downwards. The tensile speed was 50 mm / min. The results of the adhesive strength test are recorded in Table 2, under Adhesion Evaluation (I) - Initial Adhesion Strength. Furthermore, a higher numerical value for adhesive strength indicates superior adhesive strength.

[0033] (1-3) Measurement of acid resistance test at 250H The test specimen described in (1-1) above was immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 250 hours. After that, the moisture on the surface of the test specimen was wiped off, and it was left to stand for 1 hour in an environment of 25°C / 50%RH. Subsequently, the T-peel strength test was performed in the same manner as in (1-2) above. The results are recorded in Adhesion Evaluation (I) - Acid Resistance Test 250H in Table 2. The test results were evaluated as follows: Good (A): After immersion, the test specimen shows no interfacial delamination between the solid electrolyte membrane and the adhesive member. Furthermore, the fracture mode in the T-peel test indicates that fracture occurs within the solid electrolyte membrane layer, but no interfacial delamination occurs between the solid electrolyte membrane and the adhesive member. Defect (X): After immersion, the test specimen shows interfacial delamination between the solid electrolyte membrane and the adhesive member, or the failure mode in the T-peel measurement indicates interfacial delamination between the solid electrolyte membrane and the adhesive member.

[0034] (1-4) Measurement of acid resistance test at 500H The test specimens described in (1-1) above were immersed in a 95°C sulfuric acid aqueous solution (pH 2) for 500 hours. After that, the moisture on the surface of the test specimens was wiped off, and they were left to stand for 1 hour in an environment of 25°C / 50%RH. Subsequently, the T-peel strength test was performed in the same manner as in (1-2) above. The results are recorded in Adhesion Evaluation (I) - Acid Resistance Test 500H in Table 2. The evaluation of the test results was performed in the same manner as in (1-3) above.

[0035] (1-5) Measurement of acid resistance test at 750H The test specimen described in (1-1) above was immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 750 hours. After that, the moisture on the surface of the test specimen was wiped off, and it was left to stand for 1 hour in an environment of 25°C / 50%RH. Subsequently, the T-peel strength test was performed in the same manner as in (1-2) above. The results are recorded in Adhesion Evaluation (I) - Acid Resistance Test 750H in Table 2. The evaluation of the test results was performed in the same manner as in (1-3) above.

[0036] (2) Adhesion evaluation (II) (2-1) Preparation of test specimens Two sheets were prepared by cutting the sealant obtained in each example to a width of 25 mm and a length of 100 mm. Next, these two sheets were attached together as shown in Figure 5(b). As shown in Figure 5(b), the adhesive members 1 of the sealing material 10 were brought into contact with each other and attached using a roll laminator to form the test specimen. The length α over which the adhesive members 1 were in contact with each other was set to 80 mm. The lamination conditions at that time were a temperature of 100°C, a pressure of 4 N / cm, and a bonding speed of 1 m / min. In Figure 5(b), the portion β where the adhesive member 1 of the sealing material 10 is not attached is the attachment portion when fixing it to the universal tensile testing machine described below. A polyimide film (not shown) was attached to the adhesive member 1 at β, and then it was fixed to the universal tensile testing machine, and the adhesive strength was measured.

[0037] (2-2) Measurement of initial adhesive strength The T-peel strength of the test specimen described in (2-1) above was measured using a universal tensile testing machine without immersion in a 95°C sulfuric acid aqueous solution (pH 2). Specifically, the upper β in Figure 5(b) was pulled upwards while the lower β was pulled downwards. The tensile speed was 50 mm / min. The results of the adhesive strength test are recorded in Table 2, under Adhesion Evaluation (II) - Initial Adhesion Strength. Furthermore, a higher numerical value for adhesive strength indicates superior adhesive strength.

[0038] (2-3) Acid resistance test 250H measurement The test specimen described in (2-1) above was immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 250 hours. After that, the moisture on the surface of the test specimen was wiped off, and it was left to stand for 1 hour in an environment of 25°C / 50%RH. Subsequently, the T-peel strength test was performed in the same manner as in (2-2) above. The results are recorded in Adhesion Evaluation (II) - Acid Resistance Test 250H in Table 2. The test results were evaluated as follows: adhesive strength of 0.8 N / cm or higher was rated as good (A), and less than 0.8 N / cm was rated as poor (X).

[0039] (2-4) Acid resistance test 500H measurement The test specimens described in (2-1) above were immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 500 hours, and then the T-peel strength test was performed in the same manner as in (2-2) above. The results are recorded in Adhesion Evaluation B - Acid Resistance Test 500H in Table 2. The test results were evaluated in the same manner as in (2-3) above.

[0040] (2-5) Measurement of acid resistance test at 750H The test specimen described in (2-1) above was immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 750 hours. After that, the moisture on the surface of the test specimen was wiped off, and it was left to stand for 1 hour in an environment of 25°C / 50%RH. Subsequently, the T-peel strength test was performed in the same manner as in (2-2) above. The results are recorded in Table 2, Adhesion Evaluation (II) - Acid Resistance Test 750H. The evaluation of the test results was performed in the same manner as in (2-3) above.

[0041] (3) Mass change rate (3-1) Preparation of test specimens Furthermore, two sheets of the sealant obtained in each example were prepared and laminated together using a roll laminator so that the adhesive layers overlapped. The lamination conditions were a temperature of 100°C, a pressure of 4 N / cm, and a lamination speed of 1 m / min. Then, the above samples were cut to 50 mm x 50 mm and used as test specimens.

[0042] (3-2) Measurement of acid resistance test at 250H The mass of the test specimen described in (3-1) above was measured before and after immersion in a sulfuric acid aqueous solution (pH 2) at 95°C for 250 hours, and the rate of mass change was calculated based on the following formula. Mass change rate = [Mass of test specimen before immersion / Mass of test specimen after immersion] × 100 (%) For the test specimens after immersion, we used specimens that had been immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 250 hours, then the moisture on the surface of the specimens was wiped off, and they were left to stand for 1 hour in an environment of 25°C / 50%RH. The test results were evaluated as follows: a mass change rate of 5% or less was good (A), a mass change rate of 5% or more but less than 10% was acceptable (B), and a mass change rate of 10% or more was poor (X). These results were recorded in Table 2, under Mass Change-Acid Resistance Test 250H.

[0043] (3-3) Measurement of acid resistance test at 500H The test specimen described in (3-1) above was immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 500 hours. After that, the moisture on the surface of the test specimen was wiped off, and it was left to stand for 1 hour in an environment of 25°C / 50%RH. Subsequently, the rate of mass change was determined in the same manner as in (3-2) above. The results are recorded in Table 2, Mass Change - Acid Resistance Test 500H. The evaluation of the test results was carried out in the same manner as in (3-2) above.

[0044] (3-4) Measurement of acid resistance test at 750H The test specimen described in (3-1) above was immersed in a sulfuric acid aqueous solution (pH 2) at 95°C for 750 hours. After that, the moisture on the surface of the test specimen was wiped off, and it was left to stand for 1 hour in an environment of 25°C / 50%RH. Subsequently, the rate of mass change was determined in the same manner as in (3-2) above. The results are recorded in Table 2, Mass Change-Acid Resistance Test 750H. The evaluation of the test results was carried out in the same manner as in (3-2) above.

[0045] [Table 2]

[0046] As is clear from Table 2 above, in the adhesion evaluation (I) - acid resistance test 750H, the sealing materials of Examples 1 to 7 showed that the failure mode in the T-peel measurement was failure within the layer of the solid electrolyte membrane, confirming good adhesion between the solid electrolyte membrane and the adhesive member. Furthermore, in the adhesion evaluation (II) - acid resistance test 750H, the sealing materials of Examples 1 to 7 were confirmed to have an adhesive strength of 0.8 N / cm or higher and excellent heat and acid resistance. On the other hand, in the adhesive evaluation (I) - acid resistance test 750H, the sealing materials of Comparative Examples 1 to 3 showed delamination between the solid electrolyte membrane and the adhesive member, and the failure mode in the T-peel measurement indicated interfacial delamination between the solid electrolyte membrane and the adhesive member. Furthermore, in the adhesive evaluation (II) - acid resistance test 750H, the sealing materials of Comparative Examples 1, 2, and 4 showed an adhesive strength of less than 0.8 N / cm, confirming that they have poor heat and acid resistance and are impractical as sealing materials.

[0047] Furthermore, the sealing materials of Examples 1 to 7 showed a mass change rate of less than 10% in the 750H mass change-acid resistance test, indicating small changes and excellent heat and acid resistance. On the other hand, the sealing materials of Comparative Examples 1 to 4 showed a mass change rate of 10% or more in the 750H mass change-acid resistance test, indicating poor heat and acid resistance and practical problems as sealing materials. [Industrial applicability]

[0048] The solid polymer fuel cell sealing material of the present invention exhibits excellent resistance to hot water and acid, and maintains high sealing performance, enabling it to operate for long periods in a hot water environment. [Explanation of Symbols]

[0049] 1 Adhesive member 2 Base material 3 Adhesive layer 10. Solid polymer fuel cell sealing material

Claims

1. A solid polymer fuel cell sealing material comprising a carboxyl group-containing acrylonitrile-butadiene copolymer (a) and an epoxy resin (b), wherein the carboxyl group-containing acrylonitrile-butadiene copolymer (a) is a carboxyl group-containing acrylonitrile-butadiene copolymer having an acrylonitrile content of 5 to 50% by mass and a carboxyl group equivalent calculated from the number average molecular weight of 100 to 20,000.

2. The solid polymer fuel cell sealing material according to claim 1, characterized in that the epoxy resin (b) has a number average molecular weight of 400 to 10,000 and an epoxy group equivalent of 200 to 5,000.

3. The solid polymer fuel cell sealing material according to claim 1, characterized in that the epoxy resin (b) is 1 to 300 parts by mass per 100 parts by mass of the carboxyl group-containing acrylonitrile-butadiene copolymer (a).

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