Adhesive sheet, adhesive sheet-attached electrolyte film / catalyst layer laminate, fuel battery cell, and fuel battery

Abstract

Provided is an adhesive sheet that is a hot melt adhesive sheet having a base material layer and an adhesive layer. The adhesive layer contains a resin containing a triblock copolymer having a first block, a second block and a third block in the stated order. The glass transition points of the first block and the third block are each independently 90°C or higher. The glass transition point of the second block is 10°C or lower. Relative to all monomer units that constitute the first to third blocks, the total molar ratio of monomer units that constitute the first block and the third block is 5-55 mol% and the molar ratio of monomer units that constitute the second block is 45-95 mol%. Also provided are an adhesive sheet-attached electrolyte film / catalyst layer laminate, a fuel battery cell, and a fuel battery, which are obtained using said adhesive sheet.

Description

Adhesive sheet, electrolyte membrane-catalyst layer laminate with adhesive sheet, fuel cell, and fuel cell

[0001] The present disclosure relates to an adhesive sheet, an electrolyte membrane-catalyst layer laminate with an adhesive sheet, a fuel cell, and a fuel cell.

[0002] Hot melt adhesive compositions are processed into films or sheets and laminated onto the surfaces of components to form adhesive films or sheets, which are used in a variety of industrial fields, including the electrical, automotive, and other industrial fields.

[0003] A fuel cell is a battery that generates electricity by reacting a chemical fuel (usually hydrogen) and an oxidant (usually oxygen) supplied from an external source. Four common types of fuel cells are available: polymer electrolyte fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells. Among these, polymer electrolyte fuel cells have the following advantages: (1) a low operating temperature and (2) lightweight and compact design, making them increasingly popular for automotive and residential applications. A cell, the building block of a polymer electrolyte fuel cell, is constructed with a membrane electrode assembly (MEA) sandwiched between separators. The MEA has a polymer electrolyte membrane sandwiched between a fuel electrode (anode) catalyst layer and an air electrode (cathode) catalyst layer. Each electrode catalyst layer has a porous gas diffusion layer on the side opposite the surface in contact with the polymer electrolyte membrane. By stacking these cells together to form a cell stack, high voltage and power can be generated.

[0004] Known conventional seals for fuel cells are described in Patent Documents 1 and 2. Patent Document 1 discloses a seal using a urethane resin or liquid silicone rubber as an adhesive layer, while Patent Document 2 discloses a seal using an olefin resin or a soft epoxy resin.

[0005] Furthermore, a known conventional resin composition for a sealing material for a polymer electrolyte fuel cell is that described in Patent Document 3. Patent Document 3 discloses a resin composition for a sealing material for a polymer electrolyte fuel cell, which contains an acrylic resin (A) having an acid value of less than 15 mgKOH / g, an acrylic resin (B) having an acid value of 15 mgKOH / g or more, and a crosslinking agent.

[0006] JP 2002-42835 A JP 2008-171667 A JP 2023-17551 A

[0007] When a fuel cell generates electricity, it simultaneously generates water and heat as reaction products. Therefore, fuel cells operate under high temperature and humidity conditions, and the adhesive layer must be water-resistant and heat-resistant.

[0008] The urethane resin disclosed in Patent Document 1 suffers from the problem of hydrolysis occurring in high-humidity environments. Additionally, while polyurethane resins come in polyester and polyether types, both have concerns about heat resistance, with polyester types losing adhesive strength at around 100°C and polyether types losing adhesive strength at around 70°C. Liquid silicone rubber also has low mechanical strength.

[0009] The olefin resin disclosed in Patent Document 2 has the problem that the resin does not easily aggregate in a high-temperature environment, and adhesive strength is not obtained. Soft epoxy resins soften at high temperatures, resulting in a decrease in adhesive strength.

[0010] The acrylic resin disclosed in Patent Document 3 requires epoxy crosslinking, and depending on the polymer mixing ratio, the adhesive strength at high temperatures may decrease.

[0011] The present disclosure has been made in consideration of the above circumstances. An object of the present disclosure is to provide an adhesive sheet that has excellent heat resistance and water resistance in a fuel cell. Another object of the present disclosure is to provide an electrolyte membrane-catalyst layer laminate with an adhesive sheet, a fuel cell, and a fuel cell that use the adhesive sheet.

[0012] Specific means for solving the above problems include the following: <1> A hot melt adhesive sheet having a base layer and an adhesive layer, wherein the adhesive layer contains a resin containing a triblock copolymer having a first block, a second block, and a third block in this order, wherein the first block and the third block each independently have a glass transition point of 90°C or higher, the second block has a glass transition point of 10°C or lower, the total molar ratio of the monomer units constituting the first block and the third block to all the monomer units constituting the first to third blocks is 5 mol% or higher and 55 mol% or lower, and the molar ratio of the monomer units constituting the second block is 45 mol% or higher and 95 mol% or lower. <2> The adhesive sheet according to <1>, wherein the first to third blocks are homopolymers or copolymers of (meth)acrylate compounds. <3> The adhesive sheet according to <1> or <2>, wherein the weight-average molecular weight of the triblock copolymer is 50,000 or higher and 200,000 or lower. <4> The adhesive sheet according to any one of <1> to <3>, wherein the substrate layer has a Young's modulus of 2,000 MPa or more and 8,000 MPa or less. <5> The adhesive sheet according to any one of <1> to <4>, wherein the substrate layer contains at least one resin selected from the group consisting of polyethylene naphthalate, polyphenylene sulfide, polyphenylene sulfone, polycarbonate, polyethyleneimine, polyimide, and polyamide. <6> The adhesive sheet according to any one of <1> to <5>, wherein the substrate is a solid electrolyte membrane. <7> The adhesive sheet according to any one of <1> to <6>, wherein the adhesive sheet is used to seal edges of a solid electrolyte membrane or a laminate thereof from both sides. <8> An electrolyte membrane-catalyst layer laminate with an adhesive sheet, comprising an electrolyte membrane-catalyst layer laminate comprising a solid polymer electrolyte membrane for a fuel cell and a catalyst layer, and an adhesive sheet on at least a portion of both sides of the laminate, wherein the adhesive sheet is the adhesive sheet according to any one of <1> to <7>. <9> A fuel cell having at least the adhesive sheet according to any one of <1> to <7>. <10> A fuel cell having at least the adhesive sheet according to any one of <1> to <7>.

[0013] The present disclosure provides an adhesive sheet that exhibits excellent heat resistance and water resistance in a fuel cell. The present disclosure also provides an electrolyte membrane-catalyst layer laminate with an adhesive sheet, a fuel cell, and a fuel cell that use the adhesive sheet.

[0014] 1 is a schematic diagram showing an example of a fuel cell according to the present disclosure, and is a cross-sectional schematic diagram taken along the line XY in FIG.

[0015] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In the present disclosure, when multiple substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In the numerical ranges described in stages in the present disclosure, the upper or lower limit described in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. In the numerical ranges described in the present disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In the present disclosure, a combination of preferred embodiments is a more preferred embodiment. In the description of a group (atomic group) in the present disclosure, a description that does not specify whether it is substituted or unsubstituted includes both unsubstituted and substituted groups. In the present disclosure, "(meth)acrylate" means at least one of acrylate and methacrylate.

[0016] (Adhesive Sheet) The adhesive sheet according to the present disclosure is a hot melt adhesive sheet having a base layer and an adhesive layer, wherein the adhesive layer comprises a resin containing a triblock copolymer having a first block, a second block, and a third block in this order, wherein the glass transition points of the first block and the third block are each independently 90°C or higher, and the glass transition point of the second block is 10°C or lower, the total molar ratio of the monomer units constituting the first block and the third block to all the monomer units constituting the first to third blocks is 5 mol% or higher and 55 mol% or lower, and the molar ratio of the monomer units constituting the second block is 45 mol% or higher and 95 mol% or lower. The adhesive sheet according to the present disclosure is preferably used in a fuel cell, and more preferably a solid electrolyte membrane for a fuel cell is used as the adherend. Furthermore, the adhesive sheet according to the present disclosure is preferably used to seal the edges of a solid polymer electrolyte membrane or a laminate thereof from both sides.

[0017] Conventional adhesive sheets have the problem of being poor in at least one of heat resistance and water resistance in a fuel cell. The present inventors have discovered that a hot melt adhesive sheet having a base layer and an adhesive layer, wherein the adhesive layer contains a resin containing a triblock copolymer having a first block, a second block, and a third block in this order, wherein the first block and the third block each independently have a glass transition temperature of 90°C or higher and the second block has a glass transition temperature of 10°C or lower, the total molar ratio of the monomer units constituting the first block and the third block to all the monomer units constituting the first to third blocks is 5 mol% to 55 mol%, and the molar ratio of the monomer units constituting the second block is 45 mol% to 95 mol%, can provide excellent heat resistance and water resistance in a fuel cell. The estimated mechanism is shown below.

[0018] In a triblock copolymer, by using a block with a low glass transition point as the internal second block and blocks with a high glass transition point as the end first and third blocks, the second block maintains adhesiveness while the first and third blocks prevent a decrease in adhesiveness due to heat and moisture, resulting in excellent adhesiveness even in a high-temperature, high-humidity environment.

[0019] The adhesive sheet according to the present disclosure will be described in detail below.

[0020] <Adhesive Layer> The adhesive sheet according to the present disclosure is a hot-melt adhesive sheet having a base layer and an adhesive layer. The hot-melt adhesive sheet includes a sheet of so-called hot-melt adhesive, in which the adhesive layer melts, adheres the object, and then is allowed to cool or cooled, and the adhesive function is immediately exhibited. The base layer does not have to be a hot-melt adhesive, but may be a thermoplastic resin or a thermosetting resin. From the perspective of laminating sheets, it is preferable that both the base layer and the adhesive layer are thermoplastic resins. The adhesive sheet according to the present disclosure is in the form of a film (sheet), which allows for great flexibility in shape and easy post-processing. Furthermore, because the adhesive sheet according to the present disclosure is a hot-melt adhesive sheet, it can be bonded by pressing or laminating between rolls, or in some cases, by heat alone, such as with an iron. Since no solvents are used and no drying process is required, the work (processing) time can be shortened. The adhesive layer also contains a resin containing a triblock copolymer having a first block, a second block, and a third block in this order, wherein the glass transition points of the first block and the third block are each independently 90°C or higher, the glass transition point of the second block is 10°C or lower, the total molar ratio of the monomer units constituting the first block and the third block to all the monomer units constituting the first to third blocks is 5 mol% or higher and 55 mol% or lower, and the molar ratio of the monomer units constituting the second block is 45 mol% or higher and 95 mol% or lower.

[0021] <<Triblock Copolymer>> The type of resin for each block of the triblock copolymer is not particularly limited, and examples thereof include acrylic resin, styrene resin, styrene-acrylic resin, etc. Among these, from the viewpoints of heat resistance, water resistance, and ease of adjusting the glass transition temperature, acrylic resin is preferred, and a homopolymer or copolymer of a (meth)acrylate compound is more preferred.

[0022] The glass transition points of the first block and the third block are each independently 90° C. or higher, preferably 100° C. or higher. From the viewpoints of adhesiveness, heat resistance, and water resistance, the glass transition point is preferably 90° C. to 180° C., more preferably 90° C. to 150° C., and particularly preferably 90° C. to 120° C.

[0023] The glass transition point of the second block is 10°C or lower, and from the viewpoints of adhesiveness, heat resistance, and water resistance, it is preferably 0°C or lower, more preferably from -100°C to 0°C, and particularly preferably from -60°C to -20°C.

[0024] In the present disclosure, the glass transition temperatures of the first to third blocks can be calculated from the glass transition temperatures of the homopolymers of the constituent monomers according to the FOX formula. The glass transition temperature is a value measured in accordance with ASTM-D-3418 and can be calculated by the midpoint method.

[0025] Examples of monomers constituting a block having a glass transition temperature of 90° C. or higher include acrylic acid, sodium acrylate, methyl methacrylate, methacrylic acid, acryloylmorpholine, styrene, etc. Among these, from the viewpoints of heat resistance, water resistance, and ease of adjusting the glass transition temperature, at least one monomer selected from the group consisting of acrylic acid, sodium acrylate, methyl methacrylate, methacrylic acid, and acryloylmorpholine is preferred, and methyl methacrylate is more preferred.

[0026] Examples of monomers constituting a block having a glass transition temperature of 10° C. or less include methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, 2-methoxyethyl acrylate, and hydroxypropyl acrylate.

[0027] From the viewpoint of heat resistance, water resistance, and ease of adjusting the glass transition temperature, the monomers constituting the first block, second block, and third block preferably contain a (meth)acrylate compound having an alkyl group of 1 to 10 carbon atoms in the ester moiety, more preferably a (meth)acrylate compound having an alkyl group of 1 to 8 carbon atoms in the ester moiety, and particularly preferably a (meth)acrylate compound having an alkyl group of 1 to 5 carbon atoms in the ester moiety. The monomer of any one of the first block, second block, and third block may contain the above-mentioned (meth)acrylate compound, and it is preferable that the monomers of all of the first block, second block, and third block contain the above-mentioned (meth)acrylate compound, more preferably the above-mentioned (meth)acrylate compound is contained independently in an amount of 70% by weight or more of each block, and it is particularly preferable that all of the monomer units of the first block, second block, and third block consist of the above-mentioned (meth)acrylate compound. The alkyl group may be straight-chain or branched, and may contain a substituent such as --OH or --COOH, or may contain a linking group such as --O-- or --COO--.

[0028] In the triblock copolymer, the total molar ratio of the monomer units constituting the first block and the third block to all the monomer units constituting the first to third blocks is 5 mol% or more and 55 mol% or less, and from the viewpoint of heat resistance and water resistance, it is preferably 10 mol% or more and 50 mol% or less, more preferably 20 mol% or more and 35 mol% or less, and particularly preferably 25 mol% or more and 35 mol% or less.

[0029] In the triblock copolymer, the molar ratio of the monomer units constituting the second block to all the monomer units constituting the first to third blocks is 45 mol% or more and 95 mol% or less, and from the viewpoints of heat resistance and water resistance, it is preferably 50 mol% or more and 90 mol% or less, more preferably 65 mol% or more and 80 mol% or less, and particularly preferably 65 mol% or more and 75 mol% or less.

[0030] In the triblock copolymer, the method for measuring the molar ratio of each monomer unit to all monomer units constituting the first to third blocks is not particularly limited, but may be １ Measurement can be performed using known means such as H-NMR and composition analysis.

[0031] From the viewpoint of heat resistance and water resistance, the weight average molecular weight of the triblock copolymer is preferably 30,000 or more, more preferably 50,000 or more, even more preferably 50,000 or more and 200,000 or less, and particularly preferably 70,000 or more and 180,000 or less.

[0032] The "number average molecular weight" and "weight average molecular weight" of a resin in the present disclosure refer to values ​​obtained by converting the molecular weight measured by gel permeation chromatography (hereinafter also referred to as "GPC") into polystyrene equivalents. Gel permeation chromatography (GPC) measurements can be performed under the measurement conditions described below to obtain the polystyrene-equivalent number average molecular weight (Mn) and weight average molecular weight (Mw). <Measurement conditions> Apparatus: HLC-8320 manufactured by Tosoh Corporation Column: TSKgel-SuperMultipore HZ-M (4.6 mm ID x 15 cm) x 3 columns (for low molecular weights, exclusion limit molecular weight 2 million) manufactured by Tosoh Corporation Column temperature: 40°C Eluent: tetrahydrofuran (0.35 ml / min) Detector: differential refractometer (RI) Sample concentration: 0.1% by mass

[0033] The adhesive layer may contain only one type of triblock copolymer, or may contain two or more types. From the viewpoint of heat resistance and water resistance, the content of the triblock copolymer in the adhesive layer is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total mass of the adhesive layer. It is particularly preferable that the adhesive layer is 100% by mass, i.e., the adhesive layer is made of the triblock copolymer.

[0034] <<Other Components>> The adhesive layer may contain other components in addition to the triblock copolymer, such as known components such as resins, pigments, flame retardants, UV absorbers, antioxidants, antistatic agents, silane coupling agents, tackifiers, and viscosity modifiers.

[0035] The thickness of the adhesive layer may be appropriately selected as desired, but from the viewpoints of adhesiveness, handleability, heat resistance, and water resistance, it is preferably 1 μm to 500 μm, more preferably 5 μm to 200 μm, even more preferably 10 μm to 100 μm, and particularly preferably 15 μm to 50 μm.

[0036] <Substrate Layer> The adhesive sheet according to the present disclosure is a hot melt adhesive sheet having a substrate layer and an adhesive layer. The adhesive sheet according to the present disclosure can be suitably used as a sealing material for cells in a fuel cell system. In addition to adhesion to the MEA, a sealing material for a fuel cell is required to have heat shrinkability, heat resistance, moldability, and the like. By providing the adhesive sheet with a substrate layer, heat shrinkability can be reduced and rigidity can be increased. The rigidity of the adhesive sheet makes it less likely to move even when pressure is applied during molding, etc., thereby improving dimensional accuracy during molding and dimensional stability during use. For these reasons, providing a substrate layer can prevent gas leaks in fuel cells. Furthermore, the presence of a substrate layer can also improve the handling of the adhesive sheet. From the viewpoint of heat resistance and water resistance, the base layer preferably contains at least one resin selected from the group consisting of polyethylene naphthalate, polyphenylene sulfide, polyphenylene sulfone, polycarbonate, polyethyleneimine, polyimide, polyamide, polystyrene, triacetyl cellulose, and polyvinyl chloride, more preferably contains at least one resin selected from the group consisting of polyethylene naphthalate, polyphenylene sulfide, polyphenylene sulfone, polycarbonate, polyethyleneimine, polyimide, and polyamide, and even more preferably contains at least one resin selected from the group consisting of polyethylene naphthalate, polyphenylene sulfide, polyphenylene sulfone, polycarbonate, polyethyleneimine, polyimide, and polyamide. Among these, from the viewpoint of heat resistance and water resistance, polyethylene naphthalate is particularly preferred.

[0037] From the viewpoints of strength, heat resistance, and water resistance, the Young's modulus of the base layer is preferably from 1,000 MPa to 10,000 MPa, more preferably from 2,000 MPa to 5,000 MPa, and particularly preferably from 3,000 MPa to 5,000 MPa. When the Young's modulus of the base layer is within these ranges, an adhesive sheet with better heat shrinkability, heat resistance, and moldability can be obtained.

[0038] The Young's modulus in the present disclosure may be measured by a known method, but specifically, for example, using an Autograph AG-X plus manufactured by Shimadzu Corporation, a test specimen punched into a No. 3 dumbbell is pulled at room temperature (specifically, 25°C, the same applies hereinafter) at a rate of 30 mm / min, and the linear Young's modulus of the tangent to the maximum slope of the SS curve is measured.

[0039] From the viewpoint of strength and ease of handling, the thickness of the substrate layer is preferably 10 μm to 500 μm, more preferably 15 μm to 200 μm, and particularly preferably 20 μm to 100 μm.

[0040] <Primer Layer> The adhesive sheet according to the present disclosure may have a primer layer between the adhesive layer and the substrate layer. Providing a primer layer allows for stronger adhesion between the adhesive layer and the substrate layer. The composition of the primer layer is not particularly limited, but examples include polyolefins such as polyethylene, polypropylene, and polybutene, polystyrene, polyamide, copolymers of the monomers that constitute these, and mixtures thereof. The primer layer may be a cured product obtained by compounding and reacting these main materials with a curing agent. Examples of curing agents include epoxy compounds and isocyanate compounds. From the viewpoint of ensuring adhesive strength between the substrate layer and the adhesive layer, the thickness of the primer layer is preferably 0.5 μm to 50 μm, more preferably 0.5 μm to 10 μm, and particularly preferably 0.5 μm to 5 μm.

[0041] (Electrolyte membrane-catalyst layer laminate with adhesive sheet, fuel cell, and fuel cell) The electrolyte membrane-catalyst layer laminate with adhesive sheet according to the present disclosure has an electrolyte membrane-catalyst layer laminate including a solid polymer electrolyte membrane for a fuel cell and a catalyst layer, and has an adhesive sheet on at least a portion of both sides of the laminate, the adhesive sheet being the adhesive sheet according to the present disclosure. The fuel cell according to the present disclosure has at least the adhesive sheet according to the present disclosure. The fuel cell according to the present disclosure has at least the adhesive sheet according to the present disclosure.

[0042] The present disclosure will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a fuel cell 20 according to the present disclosure. FIG. 1 is a schematic diagram of the fuel cell 20 viewed from above, showing a solid electrolyte membrane-catalyst layer laminate 22 in the center, a gas diffusion layer 24A around the gas diffusion layer 24A, and a separator 26A around the gas diffusion layer 24A. FIG. 2 is a schematic cross-sectional view taken along the X-Y line in FIG. 1. The ends of the solid electrolyte membrane-catalyst layer laminate 22 are sealed by bonding two adhesive sheets 10A and 10B together. The adhesive sheet 10A has an adhesive layer 12A and a substrate layer 14A, and the adhesive sheet 10B has an adhesive layer 12B and a substrate layer 14B. The solid electrolyte membrane-catalyst layer laminate 22 is provided with gas diffusion layers 24A and 24B at the top and bottom in the thickness direction, respectively, and further provided with two separators 26A and 26B, as well as separators 26C and 26D at the top and bottom in the thickness direction, respectively. A rubber gasket 28A is provided between separators 26A and 26B by welding, and a rubber gasket 28B is provided between separators 26C and 26D by welding. Furthermore, the two adhesive sheets 10A and 10B are fixed by being sandwiched between separators 26B and 26D by rubber gaskets 30A and 30B.

[0043] <Solid Electrolyte Membrane> The solid electrolyte membrane constituting the solid electrolyte membrane-catalyst layer laminate is a solid polymer electrolyte membrane that exhibits good proton conductivity in a wet state. Examples of the solid electrolyte membrane include conventional ion exchange resins used in fuel cells (such as solid polymer fuel cells), etc., preferably cation exchange resins such as strong acid cation exchange resins and weak acid cation exchange resins, and examples thereof include ion exchange resins having an acidic group, for example, a sulfonic acid group, a carboxyl group, a phosphoric acid group, a phosphonic acid group, or a salt thereof (more specifically, ion exchange resins into which a sulfonic acid group, a carboxyl group, a phosphoric acid group, a phosphonic acid group, or a salt thereof has been introduced as an electrolyte group having an electrolyte function), and particularly preferably an ion exchange resin having a sulfonic acid group and / or a salt thereof (ion exchange resins into which a sulfonic acid group and / or a salt thereof has been introduced as an electrolyte group).

[0044] The ion exchange resin having a sulfonic acid group and / or a salt thereof can be any of various resins having a sulfonic acid group and / or a salt thereof, such as polyolefins such as polyethylene and polypropylene, acrylic resins, styrene resins, polyacetal resins, polyesters, polycarbonates, polyamides, polyimides (including polyetherimides and polyamideimides), polyether resins, polyether ketones (such as polyether ketones and polyether ether ketones), polysulfone resins (such as polysulfones and polyethersulfones), polyphenylene sulfide resins, and fluororesins.

[0045] The thickness of the solid electrolyte membrane is not particularly limited, but is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 1 μm or more and 50 μm or less.

[0046] <Catalyst Layer> Examples of the catalyst layer include a cathode catalyst layer and an anode catalyst layer. The cathode catalyst layer is a layer containing a catalyst metal supported on a carrier. Examples of the catalyst metal include Pt, Pd, Rh, or alloys containing these. Examples of the support include carbon supports, more specifically carbon particles made of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, etc. Like the cathode catalyst layer, the anode catalyst layer is a layer containing a catalyst metal supported on a carrier. Examples of the catalyst metal include Pt, Pd, Rh, or alloys containing these. Examples of the support include carbon supports, more specifically carbon particles made of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, etc.

[0047] The electrolyte membrane-catalyst layer stack in the present disclosure is preferably a stack of a cathode catalyst layer, a solid electrolyte membrane, and an anode catalyst layer stacked in this order. The electrolyte membrane-catalyst layer stack may further include gas diffusion layers stacked on both sides, i.e., a membrane electrode assembly (MEA) in which a gas diffusion layer, a cathode catalyst layer, a solid electrolyte membrane, an anode catalyst layer, and a gas diffusion layer are stacked in this order. The MEA may further include known components such as sealing.

[0048] <Gas Diffusion Layer> The gas diffusion layer is, for example, a layer composed of a conductive porous material. More specific examples include porous carbon materials (carbon paper, carbon cloth, glassy carbon, etc.), porous metal materials (metal mesh, metal foam), etc. The gas diffusion layer may be provided with an MPL (microporous layer) as needed. The MPL has water repellency or hydrophilicity as needed to regulate moisture. It also serves to prevent fluff generated in the porous carbon material from piercing the electrolyte membrane. Examples of MPL include those primarily composed of a water-repellent resin such as polytetrafluoroethylene (PTFE) and a conductive material such as carbon black. The thickness of the gas diffusion layer is not particularly limited, but is preferably 10 μm to 500 μm, more preferably 50 μm to 250 μm.

[0049] <Separator> The separator is a component that supplies a reactant gas to the gas diffusion layer. For example, the surface facing the gas diffusion layer has multiple grooves, which function as reactant gas flow paths. The shape of the grooves is not particularly limited as long as it can appropriately supply the reactant gas to the gas diffusion layer, and examples include grooves formed by corrugating a plate-like component. The thickness of the separator is not particularly limited, but examples include 0.1 mm to 1 mm, and the height of the irregularities is 0.1 mm to 1 mm. In this case, a groove is formed on the opposite side of the separator between adjacent grooves, which functions as a cooling water flow path. The material constituting the separator may be any material that can be used as a separator for a fuel cell, and may be a gas-impermeable conductive material. Examples of such materials include dense carbon, which is made gas-impermeable by compressing carbon, and press-molded metal plates.

[0050] Furthermore, the fuel cell according to the present disclosure may also include known components other than those described above, such as gaskets (rubber gaskets), welded parts, seals, supports, adhesive parts, and the like.

[0051] A fuel cell according to the present disclosure is a component having a plurality of fuel cell units (e.g., 50 to 400) according to the present disclosure, and collects electricity from the plurality of fuel cell units. The fuel cell may also include other known components, and preferably includes, for example, a stack case, end plates, current collector plates, and a biasing member. The stack case is, for example, a housing that houses a plurality of fuel cell units, current collector plates, and a biasing member. The end plates are plate-shaped components that close the openings of the stack case. For example, the end plates are fixed to the stack case with bolts and nuts, etc., so as to cover the stack case. The current collector plates are components that collect electricity from the fuel cell units. The current collector plates are arranged at one end and the other end of the fuel cell unit assembly, one serving as a positive electrode and the other as a negative electrode. Terminals are connected to the current collector plates, allowing for electrical connection to the outside. The biasing member is housed inside the stack case and applies a pressing force to the fuel cell unit assembly in the stacking direction. The biasing member may be, for example, a disc spring.

[0052] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure. In the following examples, the adhesive layer was evaluated by the following methods.

[0053] ( １ Measurement of H-NMR) The content of monomer units derived from each monomer in the resin was measured by nuclear magnetic resonance (NMR). The resins listed in the examples were dissolved in deuterated chloroform at 5% by mass to prepare samples. １ H-NMR measurement was carried out to obtain the content of monomer units derived from each monomer.

[0054] < １ H-NMR measurement conditions> Apparatus: AVANCE3 (manufactured by Bruker) Measurement temperature: room temperature (approximately 25°C) Number of accumulations: 32

[0055] (Measurement of Molecular Weight) The molecular weight of the resin was measured by gel permeation chromatography (GPC). A solution with a sample concentration (solid content) of 0.1% by mass was prepared using THF containing an internal standard (sulfur), and used as a measurement sample. GPC measurement was performed on the measurement sample under the conditions described below to obtain the weight average molecular weight (Mw) in terms of polystyrene.

[0056] <GPC Measurement Conditions> Apparatus: HLC-8320 (manufactured by Tosoh Corporation) Column: TSKgel-SuperMultipore HZ-M x 3 Eluent: tetrahydrofuran (THF) 0.35 ml / min Detector: differential refractometer (RI)

[0057] (Measurement of Young's Modulus) Using an Autograph AG-X plus manufactured by Shimadzu Corporation, a test piece punched into a No. 3 dumbbell was stretched at room temperature at a rate of 30 mm / min, and the linear Young's modulus of the tangent to the maximum slope of the SS curve was measured.

[0058] (Measurement of Glass Transition Point of Block) The Tg of the multi-component copolymer was calculated based on the Tg of the homopolymer of the monomer unit constituting each block. The Tg of homopolymers 1, 2, ... n was designated as Tg1, Tg2, ... Tgn, and the weight ratios were designated as C1, C2, ... Cn, and the Tg was calculated using the following formula (FOX formula): 1 / Tg = C1 / Tg1 + C2 / Tg2 + C3 / Tg3 + ... + Cn / Tgn

[0059] (Examples 1 to 4 and Comparative Examples 1 to 3) Test pieces were prepared and evaluated as follows. The evaluation results are shown in Table 1.

[0060] <Adhesion Strength (Room Temperature, 75°C)> A 3 cm x 6 cm polyethylene naphthalate (PEN) resin sheet (thickness 0.05 mm, Young's modulus: 4,000 MPa) was coated with the resin shown in Table 1, dissolved in a toluene / methyl ethyl ketone (9 / 1 (mass ratio)) mixed solution to a solid content of 40 mass%, and then dried at 100°C for 2 minutes to obtain a 15 μm thick adhesive layer. The coated sheet was placed on both sides of a solid electrolyte membrane (manufactured by DuPont, Nafion NRE-212, thickness 50 μm) so that the adhesive layer and the solid electrolyte membrane were in contact, and the sheets were press-bonded for 10 seconds under conditions of 1 MPa and 140°C. After press-bonding, a test specimen for evaluation was obtained.

[0061] [1. Initial adhesive strength] The test pieces were cut to a width of 10 mm and left to stand at room temperature (about 25°C) or at 75°C for 3 minutes, and then the resin sheet on one side was pulled with an Instron at an angle of 180° and a speed of 30 mm / min to measure the peel strength. The results are shown in Table 1.

[0062] [2. Adhesion Strength After Hot Water Durability] (Hot Water Durability Treatment) Pure water was poured into a heat-resistant container, and the test piece was immersed in it. It was then placed in a thermostatic chamber (dryer) at 95°C, and after 200 hours, it was removed from the thermostatic chamber (dryer). The moisture on the surface of the sample was then wiped off, and after drying overnight or more, it was cut into 10 mm widths and left at room temperature for 3 minutes. The resin sheet on one side was then pulled with an Instron at an angle of 180° and a speed of 30 mm / min, and the peel strength was measured. The results are shown in Table 1.

[0063] The methods for preparing the resins used in the examples and comparative examples are described below.

[0064] Example 1 For polymerization, a reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. Under a nitrogen atmosphere, 743.3 parts by mass of toluene and 16.0 parts by mass of 1,2-dimethoxyethane were added to the reactor, followed by 32.9 parts by mass of a toluene solution containing 24.2% by mass of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and then 1.2 parts by mass of a cyclohexane solution of sec-butyllithium containing 17.8% by mass of sec-butyllithium. Thereafter, 17.3 parts by mass of methyl methacrylate was added, and the mixture was stirred for 1 hour. The internal temperature of the polymerization solution was cooled to -30°C, and 169.2 parts by mass of a mixed solution of methyl acrylate and n-butyl acrylate (mass ratio 20 / 80) was added dropwise over 2 hours, followed by stirring at -30°C for 5 minutes. Thereafter, 20.0 parts by mass of methyl methacrylate was added, and the mixture was stirred overnight at room temperature. After the polymerization reaction, the resulting reaction solution was poured into methanol with stirring, and the precipitate was collected to obtain a polymer. GPC measurement revealed that Mn was 79,000 and Mw was 90,000.

[0065] Example 2 A reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used for polymerization. Under a nitrogen atmosphere, 711.5 parts by mass of toluene and 16.5 parts by mass of 1,2-dimethoxyethane were added to the reactor, followed by 24.5 parts by mass of a toluene solution containing 24.2% by mass of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and then 12.9 parts by mass of a cyclohexane solution of sec-butyllithium containing 2.2% by mass of sec-butyllithium. 22.0 parts by mass of methyl methacrylate was then added and stirred for 1 hour. The internal temperature of the polymerization solution was cooled to -30°C, and 181.7 parts by mass of n-butyl acrylate was added dropwise over 2 hours, followed by stirring for 5 minutes at -30°C. 31.0 parts by mass of methyl methacrylate was then added and stirred overnight at room temperature. After the polymerization reaction, the resulting reaction solution was poured into methanol with stirring, and the precipitate was collected to obtain a polymer. The Mn and Mw measured by GPC were 65,000 and 78,000, respectively.

[0066] Example 3 For polymerization, a reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. Under a nitrogen atmosphere, 711.2 parts by mass of toluene and 16.5 parts by mass of 1,2-dimethoxyethane were added to the reactor, followed by 24.5 parts by mass of a toluene solution containing 24.2% by mass of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and then 12.0 parts by mass of a cyclohexane solution of sec-butyllithium containing 1.1% by mass of sec-butyllithium. Subsequently, 16.3 parts by mass of methyl methacrylate was added and stirred for 1 hour. The internal temperature of the polymerization solution was cooled to -30°C, and 205.1 parts by mass of n-butyl acrylate was added dropwise over 2 hours, followed by stirring for 5 minutes at -30°C. Subsequently, 22.6 parts by mass of methyl methacrylate was added to the mixture and stirred overnight at room temperature. After the polymerization reaction, the resulting reaction solution was poured into methanol with stirring, and the precipitate was collected to obtain a polymer. The Mn and Mw measured by GPC were 130,000 and 160,000, respectively.

[0067] Example 4 For polymerization, a reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. Under a nitrogen atmosphere, 693.7 parts by mass of toluene and 38.1 parts by mass of 1,2-dimethoxyethane were added to the reactor, followed by 24.4 parts by mass of a toluene solution containing 24.1% by mass of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and then 2.9 parts by mass of a cyclohexane solution of sec-butyllithium containing 7.9% by mass of sec-butyllithium. Then, 39.2 parts by mass of methyl methacrylate was added and stirred for 1 hour. The internal temperature of the polymerization solution was cooled to -30°C, and 167.5 parts by mass of n-butyl acrylate was added dropwise over 2 hours, followed by stirring for 5 minutes at -30°C. Thereafter, 34.1 parts by mass of methyl methacrylate was added and stirred overnight at room temperature. After the polymerization reaction, the resulting reaction solution was poured into methanol with stirring, and the precipitate was collected to obtain a polymer. The Mn and Mw measured by GPC were 76,000 and 83,000, respectively.

[0068] Comparative Example 1: A reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used for polymerization. Under a nitrogen atmosphere, 53.0 parts by mass of ethyl acetate, 70.0 parts by mass of butyl acrylate, and 30.0 parts by mass of methyl methacrylate were placed in the reactor and heated to 75°C. To this solution, 0.16 parts by mass of 2,2'-azobis(2-methylbutyronitrile) (manufactured by Japan Finechem Co., Ltd., trade name "ABN-E"; hereinafter also referred to as "ABN-E") as an initiator and 0.29 parts by mass of S,S-dibenzyl trithiocarbonate (manufactured by Sigma-Aldrich Co., Ltd., hereinafter also referred to as "DBTTC") as a chain transfer agent were added, and the reaction was carried out for 5 hours. Measurement by GPC revealed that the Mn was 58,000 and the Mw was 77,000.

[0069] Comparative Example 2 A reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used for the polymerization. Under a nitrogen atmosphere, 50.0 parts by mass of ethyl acetate, 20.0 parts by mass of methyl acrylate, and 80.0 parts by mass of methyl methacrylate were placed in the reactor for the first-stage reaction, and the mixture was heated to 78°C. 0.31 parts by mass of ABN-E as an initiator and 1.21 parts by mass of DBTTC as a chain transfer agent were added to this solution, and the reaction was carried out for 5 hours. Measurement by GPC revealed that the Mn was 25,000 and the Mw was 44,000. For the second-stage reaction, 30.0 parts by mass of ethyl acetate, 30.0 parts of the first-stage polymer, and 70.0 parts of butyl acrylate were placed in the reactor, and the reaction was carried out for 5 hours. 0.17 parts by mass of ABN-E as an initiator was added to this solution, and the reaction was carried out for 5 hours. The Mn and Mw measured by GPC were 52,000 and 75,000, respectively.

[0070] Comparative Example 3 A reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used for polymerization. Under a nitrogen atmosphere, 634.0 parts by mass of toluene and 34.8 parts by mass of 1,2-dimethoxyethane were added to the reactor, followed by 22.3 parts by mass of a toluene solution containing 24.1% by mass of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and then 7.5 parts by mass of a cyclohexane solution of sec-butyllithium containing 9.4% by mass of sec-butyllithium. Thereafter, 44.0 parts by mass of methyl methacrylate was added and stirred for 1 hour. The internal temperature of the polymerization liquid was cooled to -30°C, and 153.1 parts by mass of n-butyl acrylate was added dropwise over 2 hours, followed by stirring for 5 minutes at -30°C. Thereafter, 109.0 parts by mass of methyl methacrylate was added to the mixture and stirred overnight at room temperature. After the polymerization reaction, the resulting reaction liquid was poured into methanol with stirring, and the precipitate was collected to obtain a polymer. The Mn and Mw measured by GPC were 61,000 and 72,000, respectively.

[0071]

[0072] In Table 1, "x" indicates that spontaneous peeling occurred between the electrolyte membrane and adhesive layer, making measurement impossible. Details of the monomers constituting the copolymers listed in Table 1 are shown below. Note that the following Tg indicates the glass transition temperature of the homopolymer. BA: butyl acrylate (Tg: -54°C) MA: methyl acrylate (Tg: 8°C) MMA: methyl methacrylate (Tg: 105°C)

[0073] As is clear from the results of Examples 1 to 4, the test specimens obtained using the adhesive sheets according to the present disclosure exhibited excellent adhesive strength at room temperature and at high temperatures, as well as excellent adhesive strength after hot water immersion. Among these, the higher the content of the monomer units constituting the second block with a glass transition temperature of 10°C or less (Examples 1, 2, and 3 > Example 4), the better the adhesive strength (heat resistance) at 75°C and the adhesive strength after hot water immersion (water resistance and heat resistance). This is thought to be because the higher the adhesive component content, the softer the adhesive layer becomes, increasing the adhesive surface area to the electrolyte membrane, resulting in stronger adhesion even at high temperatures, and suppressing water penetration into the adhesive layer / electrolyte interface during hot water immersion.

[0074] In contrast, the random copolymer exhibited a significant decrease in adhesive strength at elevated temperatures and peeled from the adherend during hot water immersion (Comparative Example 1). When the glass transition temperatures of the first and third blocks were lower than 100°C, the adhesive strength at room temperature and at elevated temperatures, as well as the adhesive strength after hot water immersion, were significantly decreased (Comparative Example 2). Furthermore, the low content of the monomer units constituting the second block, which had a glass transition temperature of 10°C or lower, significantly decreased the adhesive strength at elevated temperatures and the adhesive strength after hot water immersion (Comparative Example 3).

[0075] (Examples 5 to 13) Test pieces were prepared and evaluated as follows. The evaluation results are shown in Table 2.

[0076] <Adhesion strength (room temperature, 75°C): In the case of polyimide film> A 3 cm x 6 cm polyimide (PI) film (thickness: 25 μm, Young's modulus: 4,500 MPa, Apical 25NPI manufactured by Kaneka Corporation) was used as a substrate layer. A primer (a mixture of hexamethylene diisocyanate in an acid-modified polyolefin solution, solids content 15%) was applied to the polyimide film, and then dried at 100°C for 1 minute to obtain a 3 μm thick primer layer. A solution in which a resin listed in Table 2 was dissolved in methyl ethyl ketone to give a solids content of 30% by mass was applied to the polyimide film coated with the primer layer, and then dried at 100°C for 1 minute to obtain a 12 μm thick adhesive layer (substrate layer / primer layer / adhesive layer = 25 μm / 3 μm / 12 μm, total 40 μm). The coated sheets were placed on both sides of a solid electrolyte membrane (Nafion NRE-212, manufactured by DuPont, thickness: 50 μm) so that the adhesive layers were in contact with the solid electrolyte membrane, and the sheets were press-bonded for 10 seconds under conditions of 1 MPa and 140° C. After press-bonding, a test specimen for evaluation was obtained.

[0077] <Adhesion Strength (Room Temperature, 75°C): For Polyphenylene Sulfide Film> A 3 cm x 6 cm polyphenylene sulfide (PPS) film (thickness: 25 μm, Young's modulus: 4,000 MPa, Toray Industries, Inc.'s TORELINA 3030) was used as a substrate layer. A primer (similar to above) was applied to the polyphenylene sulfide film, and then dried at 100°C for 1 minute to obtain a 3 μm-thick primer layer. A solution in which a resin listed in Table 2 was dissolved in methyl ethyl ketone to give a solids content of 30 mass% was applied to the polyphenylene sulfide film coated with the primer layer, and then dried at 100°C for 1 minute to obtain a 12 μm-thick adhesive layer (substrate layer / primer layer / adhesive layer = 25 μm / 3 μm / 12 μm, total 40 μm). The coated sheets were placed on both sides of a solid electrolyte membrane (Nafion NRE-212, manufactured by DuPont, thickness: 50 μm) so that the adhesive layers were in contact with the solid electrolyte membrane, and the sheets were press-bonded for 10 seconds under conditions of 1 MPa and 140° C. After press-bonding, a test specimen for evaluation was obtained.

[0078] <Adhesion strength (room temperature, 75°C): For polyethylene naphthalate film> A 3 cm x 6 cm polyethylene naphthalate (PEN) film (thickness: 25 μm, Young's modulus: 5600 MPa, Teonex Q51 manufactured by Toyobo Co., Ltd.) was used as a substrate layer. A primer (similar to the above) was applied to the polyethylene naphthalate film, and then dried at 100°C for 1 minute to obtain a 3 μm-thick primer layer. A solution in which a resin listed in Table 2 was dissolved in methyl ethyl ketone to give a solids content of 30 mass% was applied to the polyphenylene sulfide film coated with the primer layer, and then dried at 100°C for 1 minute to obtain a 12 μm-thick adhesive layer (substrate layer / primer layer / adhesive layer = 25 μm / 3 μm / 12 μm, total 40 μm). The coated sheets were placed on both sides of a solid electrolyte membrane (Nafion NRE-212, manufactured by DuPont, thickness: 50 μm) so that the adhesive layers were in contact with the solid electrolyte membrane, and the sheets were press-bonded for 10 seconds under conditions of 1 MPa and 140° C. After press-bonding, a test specimen for evaluation was obtained.

[0079] [Measurement of Peel Strength] The test pieces were cut to a width of 10 mm and left to stand at room temperature (about 25°C) or at 75°C for 3 minutes, and then the resin sheet on one side was peeled off at an angle of 180° and a speed of 30 mm / min using a tensile tester to measure the peel strength. The results are shown in Table 2.

[0080] Details of the resins used in Examples 5 to 13 are shown below. Nanostrength M65: acrylic block copolymer manufactured by Arkema Inc., Mn: 110,000, Mw: 210,000 Nanostrength M65N: acrylic block copolymer manufactured by Arkema Inc., Mn: 98,000, Mw: 240,000 Nanostrength M65A: acrylic block copolymer manufactured by Arkema Inc., Mn: 99,000, Mw: 210,000

[0081]

[0082] Table 3 also shows the monomers that form each block.

[0083]

[0084] In addition, in all of Examples 5 to 13, the evaluation result of adhesive strength after hot water durability was 0.01 or more.

[0085] Details of the monomers constituting the copolymers shown in Table 3 are shown below. Note that the following Tg indicates the glass transition temperature of the homopolymer. MMA: methyl methacrylate (Tg: 105°C) BA: butyl acrylate (Tg: -54°C) MA: methyl acrylate (Tg: 8°C) DMAA: dimethylacrylamide (Tg: 119°C)

[0086] As is clear from the results of Examples 5 to 13, the test pieces obtained using the adhesive sheets according to the present disclosure had excellent adhesive strength at room temperature and at high temperatures.

[0087] The adhesive sheet according to the present disclosure exhibits excellent adhesion to electrolyte membranes, as well as heat resistance and water resistance. Therefore, a fuel cell equipped with an MEA obtained using the adhesive sheet according to the present disclosure is expected to ensure good sealing properties, which is expected to contribute to improving the durability of the fuel cell.

[0088] The disclosure of Japanese Patent Application No. 2024-146843, filed on August 28, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

[0089] 10A, 10B: adhesive sheets, 12A, 12B: adhesive layers, 14A, 14B: substrate layers, 20: fuel cell, 22: solid electrolyte membrane-catalyst layer laminate, 24A, 24B: gas diffusion layers, 26A, 26B, 26C, 26D: separators, 28A, 28B: welded or rubber gaskets, 30A, 30B: rubber gaskets

Claims

1. A hot melt adhesive sheet having a base layer and an adhesive layer, wherein the adhesive layer comprises a resin containing a triblock copolymer having a first block, a second block, and a third block in that order, wherein the glass transition points of the first block and the third block are each independently 90°C or higher, and the glass transition point of the second block is 10°C or lower, and the total molar ratio of the monomer units constituting the first block and the third block to all the monomer units constituting the first to third blocks is 5 mol% or more and 55 mol% or less, and the molar ratio of the monomer units constituting the second block is 45 mol% or more and 95 mol% or less.

2. The adhesive sheet according to claim 1, wherein the first to third blocks are homopolymers or copolymers of a (meth)acrylate compound.

3. The adhesive sheet according to claim 1, wherein the weight average molecular weight of said triblock copolymer is 50,000 or more and 200,000 or less.

4. The adhesive sheet according to claim 1, wherein the Young's modulus of the substrate layer is 2,000 MPa or more and 8,000 MPa or less.

5. The adhesive sheet according to claim 1, wherein the substrate layer contains at least one resin selected from the group consisting of polyethylene naphthalate, polyphenylene sulfide, polyphenylene sulfone, polycarbonate, polyethyleneimine, polyimide, and polyamide.

6. The adhesive sheet according to claim 1, wherein the adherend is a solid electrolyte membrane.

7. The adhesive sheet according to claim 1, which is used to seal the edges of a solid electrolyte membrane or a laminate thereof from both sides.

8. An electrolyte membrane-catalyst layer laminate with adhesive sheet, comprising an electrolyte membrane-catalyst layer laminate comprising a solid polymer electrolyte membrane for a fuel cell and a catalyst layer, and an adhesive sheet provided on at least a portion of both sides of the laminate, wherein the adhesive sheet is the adhesive sheet according to any one of claims 1 to 7.

9. A fuel cell comprising at least the adhesive sheet according to any one of claims 1 to 7.

10. A fuel cell comprising at least the adhesive sheet according to any one of claims 1 to 7.

Images