Resin composition for sealing material of polymer electrolyte fuel cell, sealing material using said resin composition, and polymer electrolyte fuel cell using said sealing material

Abstract

To provide a resin composition for a solid polymer fuel cell sealing material that has high workability due to low tackiness under room temperature environment, suppresses deterioration of adhesion force under high temperatures and is excellent in durability under high temperature and high humidity and a sealing material using the resin composition, as well as, a solid polymer fuel cell using the sealing material.SOLUTION: A resin composition for a solid polymer fuel cell sealing material formed by containing a copolymer resin having a weight-average molecular weight of 300,000 or more formed by copolymerizing raw material components containing styrene of 5 wt.% or more, methyl methacrylate of 10 mass% or more, and ethyl (meth)acrylate of 60 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition for a sealing material for a polymer electrolyte fuel cell, a sealing material using the resin composition, and a polymer electrolyte fuel cell using the sealing material. [Background technology]

[0002] A polymer electrolyte fuel cell (hereinafter sometimes referred to as a "fuel cell") generates electricity and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen with an oxidant gas containing oxygen. Figure 1 shows a cross-sectional view of a cell 10, which is a constituent unit of a typical fuel cell. A typical fuel cell is constructed by stacking several tens to several hundreds of cells 10, sandwiching the stack between end plates with current collector plates and insulating plates interposed between them, and fastening them together from both ends with fastening bolts. A fuel cell configured in this manner operates under high temperature and humidity conditions, causing a small amount of hydrofluoric acid to leach out from the solid polymer electrolyte membrane (hereinafter sometimes referred to as the "electrolyte membrane"). Therefore, Patent Documents 1 to 3 have proposed means for the sealant 16 to be used under such conditions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-42835 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-56694 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-171667 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 uses urethane resin or liquid silicone rubber as a sealing material. However, urethane resin has the problem of hydrolysis in high-humidity environments. Polyurethane resins are broadly classified into polyester and polyether types, but both are heat-sensitive, with polyester types losing adhesive strength at just under 100°C and polyether types at around 70°C. Liquid silicone rubber has the problem of low mechanical strength and being easily hydrolyzed by acids and alkalis. Patent Document 2 uses an olefin resin or a soft epoxy resin as a sealing material, but there are problems with the olefin resin in that the cohesive strength of the resin decreases in a high-temperature environment, making it impossible to obtain sufficient adhesive strength, and with the soft epoxy resin in that environment, the adhesive strength decreases due to softening. Patent Document 3 discloses a composition containing a styrene-based block polymer elastomer and a tackifier as a sealing material, but the adhesive strength of the composition decreases in a high-temperature environment. Furthermore, the above-mentioned sealing materials tend to have high tackiness in a room temperature atmosphere, making them sticky, which makes it difficult to reapply the sealing materials once they have been applied when assembling a fuel cell.Furthermore, foreign matter is likely to adhere to the sealing materials during the work process, which results in poor workability.

[0005] The present invention aims to provide a resin composition for a sealing material for a polymer electrolyte fuel cell, which has low tackiness at room temperature and therefore high workability, suppresses a decrease in adhesive strength at high temperatures, and has excellent durability at high temperatures and high humidity; a sealing material using the resin composition; and a polymer electrolyte fuel cell using the sealing material.

[0006] In order to solve the above problems, the present invention provides the following [1] to [4]. [1] A resin composition for a sealing material for a polymer electrolyte fuel cell, comprising a copolymer resin having a weight-average molecular weight of 300,000 or more, obtained by copolymerizing raw material components including 5% by mass or more of styrene, 10% by mass or more of methyl methacrylate, and 55% by mass or less of ethyl (meth)acrylate. [2] The resin composition for a sealing material for a polymer electrolyte fuel cell according to [1], wherein the raw material components further contain 0.5 mass% or more of one or more selected from glycidyl acrylate, glycidyl methacrylate, acrylic acid, methacrylic acid, 2-hydroxymethacrylate, acrylamide, and methacrylamide. [3] A sealing material for a polymer electrolyte fuel cell, formed from the resin composition according to [1] or [2]. [4] A polymer electrolyte fuel cell having a sealed portion formed by the sealing material for a polymer electrolyte fuel cell according to [3]. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a resin composition for a sealing material for a polymer electrolyte fuel cell, which has low tackiness in a room temperature atmosphere and therefore high workability, which prevents a decrease in adhesive strength at high temperatures, and which has excellent durability at high temperatures and high humidity, a sealing material using the resin composition, and a polymer electrolyte fuel cell using the sealing material. [Brief explanation of the drawings]

[0008] [Figure 1] This is a cross-sectional view showing an example of a cell that makes up a typical fuel cell. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Resin composition for sealing material of polymer electrolyte fuel cells] The resin composition for a polymer electrolyte fuel cell sealing material of the present invention is characterized by containing a copolymer resin having a weight-average molecular weight of 300,000 or more, which is obtained by copolymerizing raw material components including 5% by mass or more of styrene, 10% by mass or more of methyl methacrylate, and 55% by mass or less of ethyl (meth)acrylate. The resin composition of the present invention has the above characteristics, and therefore it is possible to obtain a sealing material that has low tackiness in a room temperature atmosphere and excellent durability under high temperature and high humidity conditions. In the present invention, the weight average molecular weight is a value measured by gel permeation chromatography (GPC) and converted into polystyrene.

[0010] <Styrene> The copolymer resin in the resin composition of the present invention must contain 5% by mass or more of styrene (styrene monomer) in the raw material components. Styrene is a non-polar component whose constituent element is CH. Therefore, by introducing 5 mass % or more of styrene into the copolymer resin of the present invention, excellent adhesion and bonding properties can be imparted between polar materials (e.g., electrolyte membranes) and non-polar material components. Furthermore, since styrene has a relatively high glass transition temperature (Tg), by introducing styrene into the copolymer resin of the present invention, heat-resistant adhesion can be obtained due to the effect of improving cohesive strength, and further, the tackiness of the sealing material in a room temperature atmosphere can be reduced, thereby suppressing stickiness and improving the workability of the sealing material. A common method for imparting heat-resistant adhesive properties to resin compositions is to add silane coupling agents, tackifiers, etc. to the resin to impart adhesiveness, but the silane coupling agents can bleed out and impair the reliability of the product. However, by incorporating the silane coupling agents into the resin itself as copolymerization components, there is no need to worry about bleed-out. From the above viewpoint, the styrene content in the raw material components is preferably 10% by mass or more, more preferably 12% by mass or more, more preferably 15% by mass or more, and even more preferably 18% by mass or more.

[0011] Furthermore, the copolymer resin in the resin composition of the present invention preferably has a styrene content in the raw material components of 40% by mass or less, more preferably 38% by mass or less, even more preferably 35% by mass or less, and even more preferably 32% by mass or less. By controlling the styrene content in the raw material components to 40% by mass or less, the hardness of the sealing material of the present invention can be easily adjusted to conform to the shape of the adherend. In addition, the ratios of methyl methacrylate and ethyl acrylate described below can be ensured, which further suppresses the decrease in adhesive strength in high-temperature environments and improves acid resistance.

[0012] <Methyl methacrylate> The copolymer resin in the resin composition of the present invention must contain 10% by mass or more of methyl methacrylate (methyl methacrylate monomer) in the raw material components. By using methyl methacrylate together with styrene, it is possible to finely adjust the glass transition temperature (Tg) of the copolymer resin obtained by copolymerizing the raw material components, and also to adjust the weight average molecular weight, which makes it possible to control the adhesion and bonding conditions between materials with different polarities. Furthermore, the copolymer resin containing methyl methacrylate can prevent weight loss due to decomposition by moisture and acid, thereby suppressing a decrease in cohesive strength and adhesive strength of the sealant under high temperature and high humidity conditions. Furthermore, the inclusion of 10% by mass or more of methyl methacrylate can increase the softening point of the copolymer resin, improving handleability when used as a sealant. From the above viewpoints, the content of methyl methacrylate in the raw material components of the copolymer resin is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more.

[0013] Furthermore, the copolymer resin in the resin composition of the present invention preferably has a methyl methacrylate content in the raw material components of 45% by mass or less, more preferably 42% by mass or less, and even more preferably 40% by mass or less. By ensuring that the content of methyl methacrylate in the raw material components is 45 mass % or less, the hardness of the sealing material using the resin composition of the present invention can be easily adjusted to a hardness that easily conforms to the shape of the adherend.

[0014] <Ethyl (meth)acrylate> The copolymer resin in the resin composition of the present invention must contain 55 mass % or less of ethyl (meth)acrylate (ethyl (meth)acrylate monomer) in the raw material components. By including styrene and methyl methacrylate as raw material components, the copolymer resin can suppress deterioration due to moisture and acid and improve adhesion in high-temperature environments, but the softening point of the copolymer resin may become too high. Here, by including ethyl (meth)acrylate as a raw material component, the softening point of the copolymer resin can be lowered, improving workability when heat-sealing a sealant to a sealing portion of a fuel cell. Furthermore, by setting the ethyl (meth)acrylate content to 55% by mass or less, the tackiness of the sealant at room temperature can be reduced, thereby suppressing stickiness and improving workability of the sealant. Furthermore, by ensuring the proportion of methyl methacrylate, adhesion, hot water resistance, and acid resistance in high-temperature environments can be improved. From the above viewpoint, the content of ethyl (meth)acrylate in the raw material components of the copolymer resin is preferably 52% by mass or less, more preferably 50% by mass or less, and even more preferably less than 50% by mass.

[0015] Furthermore, the copolymer resin in the resin composition of the present invention preferably has an ethyl (meth)acrylate content in the raw material components of 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. By ensuring that the content of ethyl (meth)acrylate in the raw material components is 5% by mass or more, the softening point of the copolymer resin can be lowered, facilitating the heat fusion process of the sealing material.

[0016] As the ethyl (meth)acrylate, either ethyl acrylate or ethyl methacrylate can be suitably used, but it is more preferable to use ethyl acrylate from the viewpoints that it is easily copolymerizable, has industrial versatility, and its softening point can be easily adjusted.

[0017] <Other Monomers> In the resin composition for a polymer electrolyte fuel cell sealing material of the present invention, it is preferable that the raw material components of the copolymer resin further contain 0.5 mass% or more of one or more monomers selected from glycidyl acrylate, glycidyl methacrylate, acrylic acid, methacrylic acid, 2-hydroxymethacrylate, acrylamide, and methacrylamide as other monomers. By including 0.5% by mass or more of other monomers in the raw material components of the copolymer resin, it becomes easier to ensure the cohesive strength of the resin while maintaining the adhesive strength in a high-temperature environment. The content of other monomers in the raw material components of the copolymer resin is preferably 0.8% by mass or more, and more preferably 1.0% by mass or more, in order to further improve the cohesive strength of the resin.

[0018] The content of other monomers in the raw material components of the copolymer resin is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less. By making the content of one or more compounds selected from the above compounds in the raw material components 10% by mass or less, gelation of the copolymer resin can be prevented and the proportion of methyl methacrylate can be secured, making it easier to improve hot water resistance and acid resistance.

[0019] As the other monomer in the raw material components of the copolymer resin, any of the above-mentioned compounds can be suitably used, but glycidyl methacrylate is more suitable from the viewpoints of handling such as skin irritation, stability as a compound, and ease of synthesis.

[0020] The copolymer resin is obtained by copolymerizing a raw material composition containing the above-mentioned styrene, methyl methacrylate, and ethyl (meth)acrylate, and other monomers used as needed.

[0021] Examples of copolymerization methods include suspension polymerization, emulsion polymerization, solution polymerization, etc. Among these copolymerization methods, suspension polymerization is preferred because it can give a polymer with a narrow molecular weight distribution and a small amount of residual monomer, it can give a high-molecular-weight polymer, it does not require an emulsifier and therefore contains few impurities, and it can easily give a copolymer resin that is excellent in water resistance and heat resistance even though the polymerization is carried out in water. In the case of suspension polymerization, the polymerization conditions are preferably 50 to 80° C. and 2 to 24 hours. The copolymer may be in any form such as alternating, random, block or graft.

[0022] In the aqueous suspension polymerization for producing granules, one or more suspension stabilizers can be used, such as water-soluble polymers such as polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinylpyrrolidone, (meth)acrylates, polyacrylamide, partially saponified polyacrylamide, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, and inorganic salt powders such as calcium phosphates and calcium carbonate.

[0023] The polymerization initiator preferably generates an oil-soluble polymerization initiating radical species after decomposition. Typical examples of the radical polymerization initiator include an azo-based radical polymerization initiator and a peroxide-based radical polymerization initiator. Examples of azo radical polymerization initiators include 2,2'-azobispropane, 2,2'-dichloro-2,2'-azobispropane, 1,1'-azo(methylethyl) diacetate, 2,2'-azobis(2-amidinopropane) hydrochloride, 2,2'-azobis(2-aminopropane) nitrate, 2,2'-azobisisobutane, 2,2'-azobisisobutylamide, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylmethylpropionate, 2,2' -Dichloro-2,2'-azobisbutane, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobisisobutyric acid dimethyl, 1,1'-azobis(1-methylbutyronitrile-3-sodium sulfonate, 2-(4-methylphenylazo)-2-methylmalonodinitrile, 4,4'-azobis-4-cyanovaleric acid, 3,5-dihydroxymethylphenylazo-2-allylmalonodinitrile, 2,2'-azobis-2-methylvaleronitrile, 4,4'-azobis Dimethyl 2,2'-azobis-4-cyanovalerate, 2,2'-azobis-2,4-dimethylvaleronitrile, 1,1'-azobiscyclohexanenitrile, 2,2'-azobis-2-propylbutyronitrile, 1,1'-azobiscyclohexanenitrile, 2,2'-azobis-2-propylbutyronitrile, 1,1'-azobis-1-chlorophenylethane, 1,1'-azobis-1-cyclohexanecarbonitrile, 1,1'-azobis-1-cycloheptanenitrile, 1 ,1'-azobis-1-phenylethane, 1,1'-azobiscumene, 4-nitrophenylazobenzyl cyanoethyl acetate, phenylazodiphenylmethane, phenylazotriphenylmethane, 4-nitrophenylazotriphenylmethane, 1,1'-azobis-1,2-diphenylethane, poly(bisphenol A-4,4'-azobis-4-cyanopentanoate), poly(tetraethylene glycol-2,2'-azobisisobutyrate), etc. Examples of the peroxide radical polymerization initiator include acetyl peroxide, cumyl peroxide, tert-butyl peroxide, propionyl peroxide, benzoyl peroxide, 2-chlorobenzoyl peroxide, 3-chlorobenzoyl peroxide, 4-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 4-bromomethylbenzoyl peroxide, lauroyl peroxide, potassium persulfate, diisopropyl peroxycarbonate, tetralin hydroperoxide, 1-phenyl-2-methylpropyl-1-hydroperoxide, tert-butyl triphenylperacetate, tert-butyl hydroperoxide, tert-butyl performate, tert-butyl peracetate, tert-butyl benzoate, tert-butyl perphenylacetate, tert-butyl 4-methoxyacetate, and tert-butyl N-(3-toluyl)carbamate. Examples of the polymerization initiator include peroxides such as benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, and methyl ethyl ketone peroxide.

[0024] Furthermore, a mercapto compound can be added as a chain transfer agent. Examples of such chain transfer agents include hydroxyl group-containing chain transfer agents such as mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptopropanediol, mercaptobutanediol, hydroxybenzenethiol and derivatives thereof; 1-butanethiol, butyl-3-mercaptopropionate, methyl-3-mercaptopropionate, 2,2-(ethylenedioxy)diethanethiol, ethanethiol, 4-methylbenzenethiol, dodecyl mercaptan, propanethiol, butanethiol, pentanethiol, 1-octanethiol, cyclopentanethiol, cyclohexanethiol, thioglycerol, and 4,4-thiobisbenzenethiol.

[0025] The copolymer resin has a weight-average molecular weight of 300,000 or more. By setting the weight-average molecular weight to 300,000 or more, it is possible to improve adhesive strength in high-temperature environments. From the viewpoint of suppressing gelation during polymerization and stabilizing quality, the weight-average molecular weight of the copolymer resin is preferably 1,500,000 or less. The weight-average molecular weight of the copolymer resin is preferably 300,000 or more and 1,500,000 or less, more preferably 300,000 or more and 1,000,000 or less, even more preferably 300,000 or more and 800,000 or less, and even more preferably 300,000 or more and 500,000 or less.

[0026] (Other additives) The resin composition of the present invention may contain additives such as pigments, flame retardants, ultraviolet absorbers, antioxidants, antistatic agents, silane coupling agents, and tackifiers, as long as the effects of the present invention are not impaired.

[0027] The resin composition of the present invention preferably has an ammonium ion elution amount of 1 ppm / g or less by mass contained in the total solid content of the resin composition. By keeping the ammonium ion elution amount at 1 ppm / g or less, cations can be prevented from eluting from the sealing material, thereby preventing the performance of the fuel cell from being affected. The ammonium ion elution amount in the copolymer resin is more preferably 1 ppm / g or less, and even more preferably zero. Usually, an amine-based curing agent is used in combination with a resin having a glycidyl group, but in the present invention, it is preferable not to use an amine-based curing agent in order to reduce the amount of nitrogen atoms. The amount of nitrogen atoms in the copolymer resin can be measured, for example, by an ion chromatograph such as HIC-SP manufactured by Shimadzu Corporation.

[0028] [Sealing material for polymer electrolyte fuel cells] The sealing material of the present invention is formed from the resin composition of the present invention described above. The sealing material is preferably in the form of a solid such as particles or a sheet, and more preferably in the form of a sheet from the viewpoint of handling. When forming the sealing material of the present invention into a sheet, from the viewpoint of ease of handling, it is preferable to form the sealing material layer by coating a sealing material layer-forming composition prepared by dissolving the above-mentioned resin composition of the present invention in a solvent onto a substrate film and drying it. In the case of a sheet-like sealing material, the thickness of the sealing material layer is preferably 10 to 500 μm, more preferably 20 to 200 μm, although it cannot be generalized as it differs depending on the separator, electrolyte membrane, etc. of the fuel cell. Note that the sealing material layer may be laminated as necessary.

[0029] The base film of the sealing material is not particularly limited as long as it can form the sealing material into a sheet and has good workability when used as a sealing material for a fuel cell. From the viewpoint of ease of handling, however, it is preferable to use a plastic film such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polystyrene, triacetyl cellulose, poly(meth)acrylate, polyvinyl chloride, polyphenylene sulfide, etc., and polyethylene naphthalate is more preferable.

[0030] Furthermore, when the sealing material is formed into a sheet, it is preferable that a peelable substrate be further laminated onto the sealing material layer of the sheet-like sealing material, which makes it easier to protect the surface of the sealing material from scratches and contamination until it is used as a sealing material for a fuel cell. Suitable peelable substrates include plastic films such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polystyrene, triacetyl cellulose, poly(meth)acrylate, and polyvinyl chloride, as well as paper and the like that have been subjected to a release treatment. From the viewpoint of ease of handling, the thickness of the releasable substrate is preferably 10 to 100 μm, more preferably 25 to 75 μm. The releasable substrate is preferably a substrate treated with a non-silicone release agent to prevent adverse effects caused by migration of silicone components to the electrolyte membrane and the sealing material layer. Examples of non-silicone release agents include polyolefins.

[0031] The sealing material of the present invention can be used in the sealing portion of a fuel cell, more specifically, in the sealing portion of a cell that constitutes a fuel cell. During use, the sealing material is heated and melted to seal the sealing portion of the cell. In addition, when the sealing material layer is sandwiched between peelable substrates, the substrates are peeled off, and then the sealing material layer is heated and melted to seal the sealing portion of the cell.

[0032] [Polymer electrolyte fuel cell] The polymer electrolyte fuel cell of the present invention comprises a sealed portion formed by the sealing material of the present invention. FIG. 1 is a cross-sectional view showing an example of a cell that constitutes a general fuel cell. The cell 10 is composed of a composite (MEA: Membrane and Electrode Assembly) consisting of a solid polymer electrolyte membrane 11 and a pair of electrodes (anode, cathode) 12, 13 arranged on both sides of the membrane, separators (14, 15) arranged on both sides of the composite and having gas flow paths (14a, 15a) for supplying fuel gas and oxidant gas, respectively, and a sealing material 16 that seals between the composite and the separators (14, 15). A typical fuel cell is constructed by stacking several tens to several hundreds of cells 10, sandwiching the stack between end plates via current collector plates and insulating plates, and fastening them together from both ends with fastening bolts. The sealing material of the present invention can be suitably used as a sealing material in such general fuel cells. Note that the position of the sealing material (sealing portion) in Figure 1 is an example, and the position of the sealing material can be changed as appropriate depending on the configuration of the cells that make up the fuel cell. [Example]

[0033] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Each property value was measured and evaluated by the following methods.

[0034] 1. Measurement and Evaluation 1-1. Tackiness A PET film (25 μm thick, 2.5 cm wide, 12.5 cm long) was superimposed on the sealing material layer of the sheet-shaped sealing material obtained in the Examples and Comparative Examples, which had a width of 2.5 cm and a length of 12.5 cm, and the film was laminated using a heated roller at 80°C to prepare a sample for tack evaluation. Next, the tackiness evaluation sample was left at room temperature for 1 minute, and then the PET film was pulled at an angle of 90°, at a speed of 10 mm / min, using a Tensilon tape, at room temperature, to measure the peel strength between the sealant layer and the PET film. The peel strength at this time was used as an index of tackiness. Note that the lower the peel strength at this time, the lower the tackiness and the better the re-application workability. The evaluation results are shown in Table 2.

[0035] 1-2. Heat resistant adhesive strength An electrolyte membrane (Nafion NRE-212, 50 μm thick, manufactured by DuPont) was placed on the sealing material layer of the sheet-shaped sealing material obtained in the Examples and Comparative Examples, which had a width of 5 cm and a length of 10 cm, and press-bonded for 30 seconds under conditions of 2 MPa and 100° C. After press-bonding, the sheet was cut into strips with a width of 1 cm to prepare samples for evaluating heat-resistant adhesive strength. Next, the entire electrolyte membrane side of the sample for evaluating heat-resistant adhesive strength was reinforced with polyimide tape, and the polyimide tape and electrolyte membrane were pulled with a Tensilon at an angle of 180°, a speed of 10 mm / min, and an atmosphere of 120°C to measure the peel strength. The peel strength at this time was used as an index of heat-resistant adhesive strength. Note that the higher the peel strength at this time, the greater and more favorable the heat-resistant adhesive strength. The evaluation results are shown in Table 2.

[0036] 1-3. Heat and humidity durability An electrolyte membrane (Nafion NRE-212, 50 μm thick, manufactured by DuPont) was placed on the sealing material layer of the sheet-shaped sealing material obtained in the Examples and Comparative Examples, which had a width of 5 cm and a length of 10 cm, and press-bonded for 30 seconds under conditions of 2 MPa and 100° C. After press-bonding, the membrane was cut into strips with a width of 1 cm to prepare samples for heat and humidity durability tests. Next, the sample for heat and humidity durability test was left to stand in an atmosphere of a temperature of 110° C. and a humidity of 100% RH for 300 hours to carry out a heat and humidity durability test. After the heat and humidity durability test, the sample was evaluated according to the following procedure. (1) Appearance evaluation After the heat and humidity durability test, the state of the sealing material layer and the electrolyte membrane of the sample was visually inspected to check for peeling, and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2. A: No peeling occurred between the sealing material layer and the electrolyte membrane. B: Peeling was confirmed between the sealing material layer and the electrolyte membrane. (2) Evaluation of adhesive strength after heat and humidity durability test After the heat and humidity durability test, the entire electrolyte membrane side of the sample was reinforced with polyimide tape, and the polyimide tape and electrolyte membrane were pulled with a Tensilon at an angle of 180°, a speed of 10 mm / min, and an atmosphere of 120°C to measure the peel strength. The peel strength at this time was used as an index of adhesive strength after the heat and humidity durability test. Note that the higher the peel strength at this time, the stronger and better the adhesive strength after the heat and humidity durability test. The evaluation results are shown in Table 2.

[0037] 1-4. Theory Tg The theoretical Tg of the copolymer resins obtained in the examples and comparative examples was calculated as the theoretical glass transition temperature (Tg) according to the FOX equation. The results are shown in Table 1. (FOX style) 1 / Tg=W1 / Tg1+W2 / Tg2+…+W i / Tg i +…+W n / Tg n The above FOX formula calculates the glass transition temperature of the homopolymer of each monomer that constitutes a polymer consisting of n types of monomers as Tgi (K), and the mass fraction of each monomer is W i Let (W1+W2+...+W i +…W n =1.

[0038] 1-5. Ion elution 50 g of deionized water was placed in a heat-resistant container, and approximately 2 g of the sealing material layer cut into 1 cm x 5 cm pieces from the sheet-like sealing layers of the Examples and Comparative Examples was placed in the container. The heat-resistant container was then heated in an oven at 95°C for 24 hours. The liquid in the heat-resistant container was then used as a test liquid, and the amount of ions eluted, such as ammonium ions, was measured by ion chromatography to calculate the ion content in the sealing material layer. The thickness of the sealing material layer in Examples 1 to 4 and Comparative Examples 1 to 3 was 50 μm. The results are shown in Table 2.

[0039] 2. Preparation of sealing material Example 1 [Preparation of copolymer resin] A 1-liter separable flask was charged with a homogeneous mixture containing 200 parts by mass of water containing 0.2% by mass of polyvinyl alcohol, 10 parts by mass of styrene monomer (ST), 30 parts by mass of methyl methacrylate monomer (MMA), 1 part by mass of glycidyl methacrylate monomer (GMA), 49 parts by mass of ethyl acrylate monomer (EA), 0.1 parts by mass of benzoyl peroxide as a polymerization initiator, and a chain transfer agent for molecular weight adjustment. The mixture was heated to 70°C under stirring in a nitrogen atmosphere and subjected to suspension polymerization for 4 hours. Next, water was removed from the suspension by decantation. The solid matter was washed with water while suction filtering, and after removing the water, it was vacuum dried at 60°C to obtain the copolymer resin of Example 1. The weight average molecular weight of the copolymer resin of Example 1 was 38.8 × 10 4 The monomer composition and molecular weight are shown in Table 1.

[0040] [Production of sheet-type sealing material] The obtained copolymer resin was melted and stirred in methyl ethyl ketone to prepare a sealant layer-forming composition. The sealant layer-forming composition was applied to a 100 μm-thick PEN (polyethylene naphthalate) film and then dried at 100° C. for 2 minutes to form a 10 μm-thick sealant layer, thereby obtaining a sheet-like sealant of Example 1.

[0041] <Examples 2 to 4, Comparative Examples 1 to 4> Copolymer resins and sheet-like sealing materials of Examples 2 to 4 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the monomer compositions and weight-average molecular weights of the copolymer resins were as shown in Table 1. The weight-average molecular weights of the respective Examples and Comparative Examples were adjusted by the amount of chain transfer agent.

[0042] [Table 1]

[0043] [Table 2]

[0044] From the results in Table 2, it was confirmed that the sealing materials of Examples 1 to 4 having the characteristics of the present invention have good workability due to low tackiness, and also have good heat-resistant adhesive strength and adhesive strength after heat and humidity durability testing, and therefore have excellent durability, especially in harsh environments such as high temperature and high humidity. Furthermore, it was confirmed that the sealing materials of Examples 1 to 4 did not cause ion elution. [Explanation of symbols]

[0045] 10: Cell 11: Electrolyte membrane 12,13 : Electrode 14,15: Separator 14a, 15a: Gas flow path 16: Sealing material

Claims

1. A resin composition for a sealing material for a polymer electrolyte fuel cell, comprising a copolymer resin having a weight average molecular weight of 300,000 or more and 500,000 or less, obtained by copolymerizing raw material components including 5% by mass or more of styrene, 10% by mass or more of methyl methacrylate, 55% by mass or less of ethyl (meth)acrylate, and 0.5% by mass or more and 3% by mass or less of glycidyl methacrylate.

2. A sealing material for a polymer electrolyte fuel cell, formed from the resin composition according to claim 1.

3. A polymer electrolyte fuel cell comprising a sealed portion made of the sealing material for a polymer electrolyte fuel cell according to claim 2.

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