Bipolar plate for fuel cell and method for manufacturing a bipolar plate for fuel cell

Abstract

To provide a bipolar plate obtained by bonding a cathode separator and an anode separator, which has high bending adhesive strength. [Solution] A bipolar plate for a fuel cell in which a cathode separator and an anode separator provided in a power generation unit cell of a fuel cell are joined together via an adhesive layer, The adhesive layer is a layer made of a cured product of an adhesive containing a thermosetting resin. A bipolar plate for a fuel cell, characterized in that the arithmetic mean roughness Ra of at least the surface of the cathode separator and anode separator in contact with the adhesive layer is 1.61 to 4.05 μm, and the warpage of the cathode separator and anode separator is less than 5 mm.

Description

[Technical Field]

[0001] This invention relates to a bipolar plate for fuel cells and a method for manufacturing a bipolar plate for fuel cells. [Background technology]

[0002] Fuel cells are being developed by various companies as a next-generation clean power source. A fuel cell consists of dozens to hundreds of power-generating units called cells stacked together. A coolant is usually supplied between the stacked cells to cool the system.

[0003] The cell is composed of a membrane electrode assembly (MEA) with a positive electrode and a negative electrode positioned on either side of a polymer electrolyte membrane through which only hydrogen ions can pass, and a separator positioned further outside of the MEA. Hydrogen gas and oxygen gas are supplied to both sides of the MEA, and electricity is generated and water is produced when hydrogen ions that have passed through the polymer electrolyte membrane react with oxygen.

[0004] The outer periphery of the MEA is fitted with O-rings or rubber seals to prevent hydrogen and oxygen gases from leaking out of the system. However, O-rings and rubber seals may not be sufficient to prevent gas leakage, and because precise stacking is required during stacking, the MEA and the separators sandwiching the electrodes, or the MEA and the separators, are sometimes bonded together to form a single unit.

[0005] As a method for bonding separators together and integrating them, for example, Patent Document 1 proposes a method in which the arithmetic mean height Ra of the surfaces of the anode separator and cathode separator is adjusted to 0.4 to 1.6 μm by wet blasting, then washed with deionized water, dried, and the anode separator and cathode separator are bonded together. However, a low surface roughness (Ra) value of the separator resulted in a reduced anchoring effect, making the bonded separator prone to peeling off.

[0006] In Patent Document 2, as a pretreatment before applying adhesive, the surface of the fuel cell separator preform is treated with an average particle size d 50 A method has been proposed for pretreatment using alumina abrasive material with a particle size of 6 μm, performed by wet blasting at a discharge pressure of 0.22 MPa. However, when the separator preform was surface-treated under the wet blasting conditions described above, the surface Ra value of the separator preform was low (less than 0.5 μm), resulting in a low anchoring effect and a problem where the bonded separator preform was prone to peeling off. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-199204 [Patent Document 2] Japanese Patent Publication No. 2019-31646 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention has been made in view of these circumstances, and aims to provide a bipolar plate obtained by bonding a cathode separator and an anode separator, which has high bending adhesive strength. [Means for solving the problem]

[0009] As a result of diligent research to achieve the above objective, the inventors of the present invention discovered that a bipolar plate with high bending adhesive strength can be obtained by bonding a cathode separator and an anode separator whose surface arithmetic mean roughness Ra and warpage are within a predetermined range, thus completing the present invention.

[0010] In other words, the present invention is 1. A bipolar plate for a fuel cell in which a cathode separator and an anode separator, which are provided in a power generation unit cell of a fuel cell, are joined together via an adhesive layer, The adhesive layer is a layer made of a cured product of an adhesive containing a thermosetting resin. A bipolar plate for a fuel cell, characterized in that the arithmetic mean roughness Ra of at least the surface of the cathode separator and anode separator in contact with the adhesive layer is 1.61 to 4.05 μm, and the warpage of the cathode separator and anode separator is less than 5 mm. 2. The bipolar plate for fuel cells described in 1, whose bending adhesive strength by Method A of JIS K6856:1994 Adhesive bending adhesion test method, is 0.50 MPa or higher. 3. Shear rate 10s -1 The bipolar plate for fuel cell according to claim 1, wherein the viscosity of the adhesive, as measured by a rotational rheometer at a measurement temperature of 25°C, is 30 to 500 Pa·s. 4. The gelation point of the adhesive, calculated from the intersection of the storage modulus and the loss modulus in the measurement of the temperature dependence of dynamic viscoelastic properties using a rotational rheometer, is less than 100°C, according to the bipolar plate for fuel cells described in 1. 5. A method for manufacturing a bipolar plate for a fuel cell, in which a cathode separator and an anode separator provided in a power generation unit cell of a fuel cell are joined together via an adhesive layer, (1) A press molding process in which a composition containing graphite powder and epoxy resin components including a main agent, a curing agent and a curing accelerator is heated and pressed in a mold to obtain two molded bodies, (2) A surface roughening step in which each of the two obtained molded bodies is subjected to a surface roughening treatment to obtain a cathode separator and an anode separator in which the arithmetic mean roughness Ra of at least the surface in contact with the adhesive layer is adjusted to 1.61 to 4.05 μm. (3) A coating step of applying an adhesive to the roughened surface of either or both of the cathode separator and the anode separator. (4) A bonding step of bonding the roughened surfaces of the cathode separator and the anode separator together, and (5) A heat curing step of thermally curing the adhesive after bonding the cathode separator and the anode separator together characterized by comprising a method for manufacturing a bipolar plate for a fuel cell, 6. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the roughening treatment is performed by an infrared laser, and both surfaces of the two molded bodies are roughened respectively. 7. The method for manufacturing a bipolar plate for a fuel cell according to claim 6, wherein the beam quality (M 2 ) of the infrared laser is 2.8 or less, and the pulse energy per unit area is 8.0 to 50 mJ / mm 2 . 8. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the application method of the adhesive is by a screen printing method. 9. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the application method of the adhesive is by a dispenser method. 10. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the bipolar plate for a fuel cell has grooves serving as gas flow paths on its surface, and comprises a hydrophilization step of performing a hydrophilization treatment on the entire gas flow path surface having the grooves serving as gas flow paths. 11. The method for manufacturing a bipolar plate for a fuel cell according to claim 10, wherein the hydrophilization treatment is an atmospheric pressure plasma treatment. 12. The method for manufacturing a bipolar plate for a fuel cell according to claim 11, wherein the atmospheric pressure plasma treatment is a remote type atmospheric pressure plasma treatment. 13. The method for manufacturing a bipolar plate for a fuel cell according to claim 11, wherein the treatment gas for the atmospheric pressure plasma treatment is a gas containing nitrogen gas is provided.

Advantages of the Invention

[0011] The bipolar plate for fuel cells of the present invention has high bending adhesive strength because the curvature of the cathode separator and anode separator is within a predetermined range, and the arithmetic mean roughness Ra of the bonding surfaces is within a predetermined range. [Brief explanation of the drawing]

[0012] [Figure 1] The following shows a test specimen for measuring the bending adhesion strength of the bipolar plate for fuel cells of the present invention; (A) is a front view and (B) is a top view. [Modes for carrying out the invention]

[0013] The present invention will be described in more detail below. [Bipolar plate for fuel cell] The bipolar plate of the present invention is a bipolar plate for fuel cells in which a cathode separator and an anode separator provided in a power generation unit cell of a fuel cell are joined together via an adhesive layer, The adhesive layer is a layer made of a cured product of an adhesive containing a thermosetting resin. The cathode separator and anode separator are characterized in that the arithmetic mean roughness Ra of at least the surface in contact with the adhesive layer is 1.61 to 4.05 μm, and the warpage of the cathode separator and anode separator is less than 5 mm.

[0014] (1) Cathode separator and anode separator The cathode separator and anode separator used in this invention are provided in a power generation unit cell in a fuel cell and are not particularly limited as long as they have a predetermined arithmetic mean roughness Ra and warpage. In the cathode separator and anode separator used in the present invention, the arithmetic mean roughness Ra of at least the surface in contact with the adhesive layer is 1.61 to 4.05 μm, but preferably 1.62 to 4.00 μm. If the arithmetic mean roughness Ra is less than 1.61 μm, the specific surface area of ​​the adhesive interface is small, making the bonded separators prone to peeling. On the other hand, if the arithmetic mean roughness Ra is greater than 4.05 μm, the surface energy of the coated surface is high, causing the applied adhesive to seep out, making the bonded separators prone to peeling. If the arithmetic mean roughness Ra is between 1.61 and 4.05 μm, the specific surface area is large and the adhesive is less likely to seep out, thus increasing the adhesive strength between the separators. The method for measuring the arithmetic mean roughness Ra is as described in the examples below.

[0015] The curvature of the cathode separator and anode separator used in this invention is less than 5 mm, but preferably 4.95 mm or less. The method for measuring the warp is also as described in the examples below.

[0016] (2)Adhesive layer The adhesive layer is formed by curing an adhesive containing a thermosetting resin. The thickness of the adhesive layer is preferably 5 to 200 μm, and more preferably 10 to 100 μm.

[0017] The bending adhesive strength of the bipolar plate for fuel cells of the present invention is preferably 0.50 MPa or higher, more preferably 0.55 MPa or higher, and even more preferably 0.6 MPa or higher. The above bending adhesive strength is determined by Method A of the bending adhesive test method for adhesives, as specified in JIS K6856:1994.

[0018] [Manufacturing method for bipolar plates for fuel cells] The present invention provides a method for manufacturing a bipolar plate for fuel cells, characterized by comprising the following steps. (1) A press molding process in which a composition containing graphite powder and epoxy resin components including a main agent, a curing agent and a curing accelerator is heated and pressed in a mold to obtain two molded bodies. (2) A surface roughening process in which each of the two obtained molded bodies is subjected to a surface roughening treatment to obtain a cathode separator and an anode separator in which the arithmetic mean roughness Ra of the surface in contact with the adhesive layer described above is adjusted to 1.61 to 4.05 μm. (3) A coating step of applying adhesive to the roughened surface of either or both of the cathode separator and the anode separator. (4) A bonding process in which the roughened surfaces of the cathode separator and the anode separator are bonded together. (5) A heat curing step in which the adhesive is heat-cured after the cathode separator and anode separator have been bonded together.

[0019] (1) Press forming process This process involves heating and pressing a composition containing graphite powder and epoxy resin components including a main agent, a curing agent, and a curing accelerator in a mold to obtain two molded bodies.

[0020] The graphite powder used in this invention may be appropriately selected from those conventionally used in fuel cell separators, and either natural graphite or artificial graphite may be used. Examples of artificial graphite include artificial graphite produced by calcining needle-shaped coke, artificial graphite produced by calcining lumpy coke, spheroidal artificial graphite, and artificial graphite whose surface has been treated with a pitch coat or the like. Examples of natural graphite include flaky natural graphite, soil graphite, spheroidal natural graphite, and natural graphite whose surface has been treated with pitchcoat or the like. These can be used individually or in combination of two or more types.

[0021] Average particle size of graphite powder d 50While not particularly limited, considering the need to maintain an appropriate gap between graphite particles, increase the contact area between graphite particles, and suppress the generation of irregularities after laser processing to improve conductivity (reduce contact resistance), a particle size of 10 to 200 μm is preferred, and 10 to 100 μm is more preferred. In other words, the average particle size d of graphite powder 50 If the average particle size is 10 μm or larger, when an infrared laser is irradiated onto the molded body, the resin on the surface of the molded body can be removed, improving the conductivity of the separator surface, and the contact area between graphite particles inside the separator can be sufficiently maintained, thereby improving the conductivity in the thickness direction of the separator. 50 If the particle size is 200 μm or less, the voids between graphite particles are adequate. Therefore, even if the resin filling the voids between graphite particles on the separator surface is removed by laser irradiation, large irregularities will not form on the separator surface. As a result, the contact resistance of the separator will be reduced, and the conductivity of the separator itself will not deteriorate. Note that the above average particle size d 50 The measurement method is as described in the examples below.

[0022] The main component constituting the epoxy resin is not particularly limited as long as it has an epoxy group. Examples include orthocresol novolac type epoxy resin, phenol novolac type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, biphenyl aralkyl type epoxy resin, trisphenol type epoxy resin, brominated epoxy resin, dicyclopentadiene type epoxy resin, and biphenyl novolac type epoxy resin. These can be used individually or in combination of two or more. Among these, orthocresol novolac type epoxy resin alone, biphenyl type epoxy resin alone, or mixtures thereof are preferred. The epoxy equivalent of the epoxy resin used in the present invention is not particularly limited, but in the case of orthocresol novolac type epoxy resin, 190 to 215 g / eq is preferred, and in the case of biphenyl type epoxy resin, 180 to 200 g / eq is preferred.

[0023] The hydrolyzable chlorine content of the epoxy resin main component is preferably 450 ppm or less. When the hydrolyzable chlorine content is 450 ppm or less, the crosslinking density of the cured product increases, resulting in improved heat resistance of the resulting separator. On the other hand, there is no particular lower limit, but since epoxy resins with a hydrolyzable chlorine content of less than 370 ppm are very expensive, a lower limit of 370 ppm is preferable from a cost perspective.

[0024] Phenolic resins are preferred as curing agents for epoxy resin components. Specific examples include novolac-type phenolic resins, cresol-novolac-type phenolic resins, resol-type phenolic resins, aralkyl-modified phenolic resins, biphenyl-novolac-type phenolic resins, and trisphenolmethane-type phenolic resins, which may be used individually or in combination of two or more. Among these, novolac-type phenolic resins are preferred. The hydroxyl group equivalent of the phenolic resin used in this invention is not particularly limited, but 100 to 106 g / eq is preferred.

[0025] The curing accelerator that constitutes the epoxy resin component is not particularly limited as long as it promotes the reaction between the epoxy group and the curing agent, and examples include phosphine compounds, amine compounds, and imidazole compounds. Among these, in the present invention, it is preferable to use an imidazole compound having an aryl group at the 2-position. Specific examples of aryl groups include phenyl groups, tolyl groups, and naphthyl groups, but phenyl groups are preferred. Specific examples of imidazole compounds having an aryl group at the 2-position include 2-phenylimidazole and 2-phenyl-4-methylimidazole. Furthermore, using imidazole compounds with short-chain alkyl groups, such as 2-methylimidazole, may result in a curing time that is too fast, making uniform molding impossible. On the other hand, using imidazole compounds with long-chain alkyl groups, such as 2-undecylimidazole, may result in a curing time that is too slow, leading to a longer molding time.

[0026] In addition to the above components, the composition used in the present invention may also contain any other components, such as an internal mold release agent, as appropriate. As the internal release agent, it is acceptable to select from various internal release agents conventionally used for molding separators. Specific examples include stearic acid-based waxes, amide-based waxes, montanic acid-based waxes, carnauba waxes, polyethylene waxes, etc. These can be used individually or in combination of two or more.

[0027] The amounts of graphite powder and epoxy resin components (main agent, curing agent, and curing accelerator) used are not particularly limited, but preferably 22 to 40 parts by mass of epoxy resin component per 100 parts by mass of graphite powder, more preferably 27 to 35 parts by mass, and even more preferably 30 to 33 parts by mass. By using epoxy resin components within this range, the fluidity of the molding material becomes appropriate, resulting in good moldability, and it is possible to prevent a significant decrease in the gas impermeability and conductivity of the resulting bipolar plate for fuel cells.

[0028] The composition can be prepared, for example, by mixing graphite powder, main component, curing agent, and curing accelerator in any order and in predetermined proportions. For this mixing, a planetary mixer, ribbon blender, Reidige mixer, Henschel mixer, rocking mixer, Nauter mixer, etc., can be used. If any optional components, such as an internal release agent, are used, their mixing order is also arbitrary.

[0029] Next, the above composition is placed in a predetermined mold and a molded body is produced by press molding or the like. Preferably, the mold used is one for producing fuel cell separators that can form grooves that serve as gas passages on one or both sides of the surface of the molded body. The press forming conditions are not particularly limited, but typically include a mold temperature of 80-200°C, a forming pressure of 1.0-50 MPa, preferably 5-40 MPa, and a forming time of 10 seconds to 1 hour, preferably 20-180 seconds, more preferably 30-90 seconds. In addition, after press molding, for the purpose of promoting thermosetting, it may be further heated at 150 to 200 °C for about 1 to 600 minutes.

[0030] (2) Roughening process This process is a process of obtaining a cathode separator and an anode separator by subjecting each of the two molded bodies obtained in the press molding process to a roughening treatment and adjusting the arithmetic mean roughness Ra of at least the surface in contact with the above-mentioned adhesive layer to 1.61 to 4.05 μm.

[0031] The roughening treatment is preferably performed on the entire surface of one side or both sides of the molded body, and more preferably on the entire surface of both sides. The method of the roughening treatment is not particularly limited, but it is preferably performed by irradiation with an infrared laser.

[0032] The infrared laser used in the roughening process is not particularly limited, and examples thereof include a YAG laser, a carbon dioxide laser, a dye laser, a semiconductor laser, a fiber laser, etc. A fiber laser is preferred from the viewpoints of depth of focus, light condensing property, and lifetime of the transmitter. The wavelength of the infrared laser is not particularly limited, but 780 to 10600 nm is preferred, 808 to 1095 nm is more preferred, and 920 to 1070 nm is even more preferred.

[0033] The beam quality (M 2 ) of the infrared laser is preferably 2.8 or less, preferably 2.5 or less, more preferably 2 or less, and even more preferably 1.

[0034] The pulse energy per unit area of ​​an infrared laser is 4-50 mJ / mm². 2 Preferably, 8.0 to 50 mJ / mm 2 More preferably, 9-48 mJ / mm 2 A more preferable pulse energy per unit area is 4-50 mJ / mm². 2 As a result, the resin on the separator surface can be completely removed, making it possible to obtain a good bipolar plate for fuel cells with low contact resistance and static contact angle.

[0035] Thus, the beam quality is 2.8 or less, and the pulse energy per unit area is 4-50 mJ / mm². 2 Therefore, even when a laser is irradiated onto a thin-walled molded body, the warping after irradiation is reduced, which can lower the contact resistance of the bipolar plate for fuel cells.

[0036] The spot diameter of the infrared laser is preferably 150 to 300 μm. If the spot diameter is less than 150 μm, it may take a long time to roughen the separator surface, resulting in poor production efficiency. On the other hand, if the spot diameter exceeds 300 μm, the energy within the spot becomes non-uniform, requiring a high overlap rate, which may also result in poor production efficiency.

[0037] The overlap rate of infrared laser spots is preferably 5-30%, and more preferably 10-30%. The above-mentioned overlap rate of infrared lasers refers to the degree of overlap between adjacent laser spots and is calculated from the laser spot diameter and scan pitch. An overlap rate of 5-30% is preferable because it allows the arithmetic mean roughness Ra of the gas flow channel groove bottoms (concave parts) and peaks (convex parts) of the molded body surface to be adjusted to a predetermined range.

[0038] The irradiation time of the infrared laser is not particularly limited, but it is preferable to continue until the arithmetic mean roughness Ra of the surface of the molded body (anode separator and cathode separator) after irradiation falls within the above range.

[0039] Furthermore, blast treatment may be performed on the surface of the molded body before irradiating it with a laser, if necessary. Alternatively, blast treatment may be omitted. Blasting treatments include shot blasting, air blasting, and wet blasting, and any of these can be performed as long as the arithmetic mean roughness Ra of the molded surface after laser irradiation falls within the above range.

[0040] (3) Coating process This step involves applying adhesive to one or both of the roughened surfaces of the cathode separator and anode separator obtained in the roughening step.

[0041] The adhesive is not particularly limited as long as it contains a thermosetting resin. Examples of adhesives containing thermosetting resins include those containing one or more selected resins from phenolic resins, polycarbodiimide resins, polyurethane resins, epoxy resins, polyester resins, silicone resins, and polyimide resins. These can be one-component or two-component types, but one-component epoxy adhesives that do not require the measurement and mixing of the main component and curing agent are preferred. As a one-component epoxy adhesive, one containing, for example, an epoxy resin, a curing agent, and a curing accelerator is preferred.

[0042] As the epoxy resin, epoxy resins commonly used in the field of adhesives can be used. Examples of such epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, glycidylamine type epoxy resin, cresol novolac type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, heterocyclic epoxy resin, spiro ring-containing epoxy resin, halogenated epoxy resin, and the like. Among these, bisphenol A type epoxy resin and bisphenol F type epoxy resin are preferred.

[0043] Furthermore, from the viewpoint of applicability by screen printing and the like, epoxy resins that are liquid at 10°C are preferred. Here, "liquid" means having fluidity, and paste-like substances are included in this category. Some crystalline epoxy resins solidify when left at room temperature for a long period of time, but even such epoxy resins can be used if they are heated to a liquid state and then cooled to a liquid state at 10°C.

[0044] Epoxy resins may be used individually or in combination of two or more types. When using two or more epoxy resins in combination, at least one type must be liquid at 10°C, and the mixture can be used if it is liquid at 10°C. Alternatively, a liquid epoxy resin and a solid epoxy resin can be mixed, for example, under heating, and the mixture can be used if it is liquid when cooled to 10°C.

[0045] To improve heat resistance, epoxy resins with three or more functional properties may be used. Examples of such epoxy resins include YH434L (manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0046] As a curing agent, any commonly used curing agent for epoxy resins can be used, but it is preferable to include at least one amine-based curing agent. In addition, other curing agents that can be used in combination with the amine-based curing agent may be used, and such curing agents include acid anhydride-based curing agents, phenol-based curing agents, Lewis acid-based curing agents, and polymercaptan-based curing agents.

[0047] Examples of amine-based curing agents include aliphatic polyamines such as diethylenetriamine, triethylenetetramine, and metaxylylenediamine; aromatic polyamines such as diaminodiphenylmethane, m-phenylenediamine, and diaminodiphenylsulfone; tertiary amine compounds such as diethylaminopropylamine and 2,4,6-tris(diaminomethyl)phenol; and polyamine compounds such as dicyandiamide, organic acid dihydrazide, amine adduct, and polyamide. Among the amine-based curing agents, dicyandiamide and diaminodiphenylmethane are preferred from the viewpoint of latent properties (storage stability as a one-component adhesive), high adhesion, and improved productivity due to rapid curing.

[0048] Examples of acid anhydride-based curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride, and aromatic acid anhydrides such as trimellitic anhydride, pyromellitic anhydride, and benzophenonetetracarboxylic acid. Examples of phenol-based curing agents include phenolic resins. Examples of Lewis acid-based curing agents include Lewis acids such as boron trifluoride. Examples of polymer captan-based curing agents include polysulfides, thioesters, and thioethers.

[0049] The curing agent may be used alone or in combination of two or more types. When using an amine-based curing agent in combination with other curing agents, it is preferable that the curing agent contains 50% by mass or more of the amine-based curing agent.

[0050] The amount of curing agent in the adhesive is preferably 0.5 to 1.2 equivalents, and more preferably 0.7 to 1.1 equivalents, relative to the epoxy groups in the epoxy resin. Specifically, although it depends to some extent on the epoxy equivalents of the epoxy resin, the amount of curing agent is usually preferably about 3 to 50 parts by mass, and more preferably about 5 to 30 parts by mass, per 100 parts by mass of epoxy resin. If the curing agent content is within the above range, sufficient adhesive properties can be obtained.

[0051] Examples of curing accelerators include amine-based curing accelerators such as imidazole compounds and tertiary amines and their salts, and phosphorus-based curing accelerators.

[0052] The imidazole compounds include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl -s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct Examples include [ru-a]benzimidazole, 1-dodecyl-2-methyl-3-benzyl-1H-imidazole-3-ium chloride, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 2-methylimidazoline, and 2-phenylimidazoline. In addition, adducts of the aforementioned imidazole compounds with epoxy resins can also be used as the imidazole compounds.

[0053] The amount of curing accelerator used is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of epoxy resin. If the amount of curing accelerator used is within the above range, contamination due to bleeding and rapid curing can be achieved.

[0054] The adhesive used in this invention may contain an inorganic filler. The inorganic filler imparts appropriate viscosity and thixotropy to the adhesive, improving its applicability, particularly its screen printing properties, and also improving the mechanical strength of the adhesive.

[0055] From the viewpoint of improving screen printability, the inorganic filler preferably contains at least one type of flake-shaped inorganic filler. Using flake-shaped inorganic fillers imparts appropriate thixotropy to the adhesive, and when screen printing the adhesive, there is no adhesive residue in the screen pores, and deformation of the adhesive applied (printed) on the substrate is suppressed.

[0056] In the aforementioned flake-like inorganic filler, the degree of flake-likeness can be expressed by the aspect ratio. The aspect ratio is one of the particle shape indices expressed as "average particle size / particle thickness," and is measured by a flow-type particle image analyzer or the like. The aspect ratio of the aforementioned flake-like inorganic filler is preferably 5 to 200, more preferably 10 to 100, and even more preferably 20 to 60.

[0057] The average particle size of the flake-like inorganic filler is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and even more preferably 2 to 15 μm. If the average particle size is within the above range, the screen printing characteristics are good. The average particle size is determined by the median diameter (d) measured using a laser diffraction particle size distribution analyzer. 50 This refers to the value of ).

[0058] Examples of materials for the aforementioned flake-shaped filler include talc, silica (fumed silica, precipitated silica, crystalline silica, fused silica, dolomite, anhydrous silicic acid, hydrated silicic acid, etc.), mica, graphite (artificial and natural graphite), heavy calcium carbonate, light calcium carbonate, colloidal calcium carbonate, magnesium carbonate, clay, kaolin, aluminum hydroxide, alumina, aluminum hydroxide, barium sulfate, white carbon, E-glass fine powder, titanium dioxide, zirconia, silicon nitride, barium titanate, barium carbonate diatomaceous earth, carbon black, etc. Of these, talc, silica, mica, and graphite (artificial and natural graphite) are preferred, with mica being particularly preferred. Commercially available products can be used. For example, examples of mica include Micromica MK-100, MK-200, and MK-300 (manufactured by Katakura Coop Agri Co., Ltd.). Examples of silica include Ainaflex (registered trademark) (manufactured by Nippon Sheet Glass Co., Ltd.) and Sunlovely (registered trademark) (manufactured by AGC SI-TEC Inc.). Examples of graphite include CNP-7, CNP-15 (manufactured by Ito Graphite Industry Co., Ltd.), BF-7A, BF-8D, BF-10D, and BF-10A (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0059] Furthermore, the inorganic filler may also include non-flaky inorganic fillers. In this case, the shape of the non-flaky inorganic filler is not particularly limited as long as it is not flaky, but examples include lumps, spheres, needles, irregular shapes, etc. The material of the non-flaky inorganic filler may be the same as that of the flaky filler described above. The average particle size of the non-flaky inorganic filler is not particularly limited as long as it does not impair the effects of the present invention, but it is preferably in the same range as the average particle size of the flake inorganic filler.

[0060] The flake-shaped inorganic filler is preferably present in an amount of 5 to 100% by mass in the inorganic filler.

[0061] The inorganic filler content is preferably 10 to 200 parts by mass per 100 parts by mass of epoxy resin. If the inorganic filler content is less than 10 parts by mass, the adhesive will not have sufficient thixotropy. For example, adhesive may remain in the pores of the screen during screen printing, or the adhesive printed (coated) on the substrate may flow before it can bond with the other substrate, resulting in contamination of areas other than the intended coating area with the flowing adhesive. On the other hand, if the content exceeds 200 parts by mass, the viscosity of the adhesive may become too high, resulting in poor handling, workability, and application. The inorganic filler content is preferably 30 to 150 parts by mass.

[0062] The adhesive used in the present invention may optionally contain a silane coupling agent, a coloring agent (e.g., carbon black, dye, etc.), a flame retardant, an ion trapping agent, an antifoaming agent, a leveling agent, etc. Furthermore, epoxy resins with one epoxy group per molecule and low viscosity, known as reactive diluents, can also be used within a range that does not impair the effects of the present invention. The one-component liquid adhesive used in the present invention may contain a solvent to adjust viscosity, but if a solvent is included, it may volatilize during resin curing and cause gas leakage; therefore, a solvent-free type is preferable.

[0063] The adhesive used in this invention can be prepared by stirring and mixing the aforementioned raw materials in a known manner. Stirring and mixing can be carried out using various mixers such as dissolvers, homogenizers, homodispers, kneaders, roll mills, bead mills, planetary mixers, universal stirrers, orbital stirring devices, or planetary stirring devices. After stirring and mixing, degassing may be performed under vacuum. Furthermore, commercially available products may also be used.

[0064] The adhesive used in this invention is subject to a shear rate of 10s. -1Preferably, the viscosity measured by a rotational rheometer at a measurement temperature of 25°C is 30 to 500 Pa·s, and more preferably 40 to 450 Pa·s. When the viscosity of the adhesive is 30 to 500 Pa·s, it can be applied uniformly without the adhesive overflowing from the bonding area due to "sagging" after application, or the adhesive coming off due to "streaking" during screen printing, and bleeding is less likely to occur during the curing process. This prevents deterioration of conductivity due to contamination of the separator conductive surface by uncured components and contamination of the refrigerant due to the leaching of organic components into the refrigerant, and more reliably suppresses the decrease in adhesive strength.

[0065] Furthermore, the gelation point calculated from the intersection of the storage modulus and loss modulus of the adhesive in the temperature dependence measurement of dynamic viscoelastic properties using a rotational rheometer is preferably less than 100°C. A gelation point below 100°C is preferable because it reduces the likelihood of "bleeding" during the thermal curing process, prevents contamination of the separator conductive surface by uncured components, and more reliably suppresses a decrease in adhesive strength.

[0066] The method of applying the adhesive is not particularly limited and includes screen printing, dispenser, spray gun, inkjet, curtain coater, roll coater, gravure printing, and spray coating, but among these, screen printing and dispenser methods are preferred.

[0067] In the present invention, it is preferable to apply the adhesive to either the cathode separator or the anode separator. Furthermore, it is preferable to apply the adhesive such that the thickness of the adhesive layer after curing falls within the range described above.

[0068] (4) Lamination process This process involves bonding the roughened surfaces of the cathode separator and anode separator together. When adhesive is applied to the roughened surface of either the cathode separator or the anode separator, the surface of the separator with the adhesive applied will bond to the roughened surface of the other separator. When adhesive is applied to both the cathode separator and the anode separator, the adhesive-coated surfaces of the cathode separator and the anode separator will bond to each other.

[0069] (5) Heat curing process This process involves bonding the cathode separator and anode separator together, and then curing the adhesive by heating.

[0070] The heating temperature is preferably around 130 to 220°C, and more preferably around 150 to 200°C. The heating time is preferably around 1 minute to 2 hours, and more preferably around 30 minutes to 1.5 hours.

[0071] The bipolar plates for fuel cells obtained in this way have an arithmetic mean roughness Ra of the surfaces to which the cathode separator and anode separator are bonded adjusted to 1.61 to 4.05 μm. As a result, they have a large specific surface area and the adhesive does not seep out easily, thus providing high bonding strength between the separators.

[0072] (6) Hydrophilization treatment The bipolar plate for fuel cells of the present invention preferably has grooves on its surface that serve as gas channels in order to secure passages for fuel and air (oxygen) supplied to each unit cell of the fuel cell. In the present invention, it is preferable to apply a hydrophilic treatment to the entire gas channel surface having these grooves. Furthermore, when applying a hydrophilic treatment to the bipolar plate for fuel cells, it is preferable to do so after the adhesive has been heat-cured. If the hydrophilic treatment is applied to the bipolar plate for fuel cells before the adhesive has been heat-cured, there is a risk that the hydrophilic groups may be contaminated or attenuated during the heat-curing of the adhesive.

[0073] The hydrophilization treatment should be applied to at least the gas flow path surface that comes into contact with the water generated by power generation, but it may also be applied to the cooling surface if necessary. While there are no particular limitations on the hydrophilization treatment, corona treatment, excimer UV light treatment, and plasma treatment are preferred, with plasma treatment being the most preferred among them.

[0074] Methods for hydrophilization by plasma treatment include, for example, vacuum plasma treatment and atmospheric pressure plasma treatment. Among these, atmospheric pressure plasma treatment is preferred because the equipment is simple and productivity is good, and remote atmospheric pressure plasma treatment is more preferred.

[0075] Examples of gases used to generate plasma include oxygen gas containing oxygen atoms, ozone gas, water, nitrogen gas containing nitrogen atoms, ammonia gas, sulfur dioxide gas containing sulfur atoms, and sulfur trioxide gas. Air can also be used. By performing plasma treatment using these gases, hydrophilic functional groups such as carbonyl groups, hydroxyl groups, amino groups, and sulfo groups can be introduced to the surface of the molded body, thereby imparting hydrophilicity to the surface. Among these, a gas containing 80% or more by volume of nitrogen gas is preferred, and a gas composed of 80% or more by volume of nitrogen gas with the remainder being oxygen gas is more preferred.

[0076] The bipolar plate for fuel cells obtained by the above manufacturing method has high bending adhesion strength and low contact resistance. Furthermore, it exhibits good hydrophilicity after hydrophilic treatment. Generally, a polymer electrolyte fuel cell consists of a large number of unit cells arranged in parallel, each unit cell comprising a pair of electrodes sandwiching a polymer electrolyte membrane and a pair of separators that form gas supply and discharge channels on either side of these electrodes. The bipolar plate of the present invention can be used as some or all of these separators. [Examples]

[0077] The present invention will be described in more detail below with reference to examples, comparative examples, and reference examples, but the present invention is not limited to the following examples. The physical properties in the following examples were measured by the following methods. [Average particle size] The particle size distribution was measured using a particle size analyzer (manufactured by Nikkiso Co., Ltd.). [Measurement of various parameters related to laser irradiation] (1) Beam quality (M 2 ) measurement M 2 The measurements were taken using a beam analyzer (BeamSquared, manufactured by Ophir Optronics Solutions). (2) Measurement of pulse energy per unit area The pulse energy per unit area was calculated using the following formula, after measuring the average laser power output and spot diameter. The repetition frequency is determined by the laser oscillator setting. (i) Measurement of average laser power The power was measured using a power meter (NOVAII, manufactured by Ophir Optronics Solutions). (ii) Measurement of laser spot area The spot diameter was measured using a laser beam profile measurement camera (NOVAII, manufactured by Ophir Optronics Solutions), and the spot area was calculated. Pulse energy (mJ) = Laser average power (W) ÷ Repetition frequency (kHz) Pulse energy per unit area (mJ / mm 2 ) = Pulse energy (mJ) ÷ Spot area (mm²) 2 ) (3) Overlap rate The overlap rate was calculated using the following formula based on the laser spot diameter (irradiation diameter of the laser spot) and scan pitch. Overlap rate (%) = (Laser spot diameter - Scan pitch) / Laser spot diameter [Evaluation of adhesive properties] (1) Measurement of viscosity Using a rotational rheometer (model number Kinexus pro+, manufactured by Netsch), the measurement temperature was 25°C and the shear rate was 10s. -1 Measured at [location / location]. (2) Method for calculating the gelation point The storage modulus and loss modulus were calculated from the intersection of the measurements taken using the same apparatus as described above, under the conditions of a frequency of 1 Hz, a shear stress of 1 Pa, a starting temperature of 25°C, and a heating rate of 2°C / min. [Evaluation of anode separators and cathode separators for fuel cells] (1) Measurement of arithmetic mean roughness Ra The arithmetic mean roughness Ra of the anode separator and cathode separator for fuel cells was measured using a surface roughness meter with a probe tip diameter of 5 μm (model number Surfcom 14000, manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with the method compliant with JIS B0601 2001. (2) Measurement of warping The anode separator and cathode separator for fuel cells were placed on a surface plate, and the maximum and minimum values ​​were measured using a height gauge. The difference between these values ​​was defined as the warp. [Evaluation of bipolar plates for fuel cells] (1) Measurement of bending bond strength (i) Preparation of bending bond strength test specimens (a) Rectangular pieces measuring 100 mm × 25 mm × 1.6 mm were cut by machining from the flat ends of the roughened anode separator and cathode separator. (i) On the side of the anode separator opposite to the side with the gas flow channel groove, the required volume of adhesive was applied to one end portion of 12.5 mm × 25 mm so that the thickness of the adhesive layer after curing would be 50 μm. (c) As shown in Figures 1(A) and (B), the adhesive-coated surface of the anode separator 1 and the corresponding surface of the cathode separator 2 were bonded together so that the length of the overlapping portion was 12.5 mm. (e) The adhesive was heat-cured by heating at 150°C for 1 hour to prepare test specimens. (ii) Measurement of bending bond strength The bending bond strength test specimens prepared by the method described above were measured using a universal material testing machine (Instron 5544A) in accordance with Method A of JIS K6856:1994, Method for testing the bending bond strength of adhesives. (2) Measurement of contact resistance (i) Carbon paper + bipolar plate sample Carbon paper (TGP-H060, manufactured by Toray Industries, Inc.) was placed above and below the fabricated bipolar plate, and copper electrodes were placed above and below that. A surface pressure of 1 MPa was applied in the vertical direction, and the inter-electrode voltage was measured using the four-terminal method. (ii) Carbon paper Copper electrodes were placed above and below a sheet of carbon paper, a surface pressure of 1 MPa was applied in the vertical direction, and the voltage between the electrodes was measured using the four-terminal method. (iii) Contact resistance calculation method The voltage drop between the bipolar plate sample and the carbon paper was determined from the voltage values ​​obtained in (i) and (ii) above, and the contact resistance was calculated using the following formula. Contact resistance (mΩ cm 2 ) = (voltage drop × contact area) / current (3) Evaluation of adhesive bleeding and streaking (i) Evaluation of bleeding The bipolar plate for the fuel cell was disassembled into an anode separator and a cathode separator, and the presence or absence of adhesive seepage was visually evaluated. (ii) Evaluation of faintness Using a screen printing machine (a semi-automatic screen printing machine manufactured by Seria Corporation), a specified adhesive was applied to an anode separator using an 80-mesh screen (mesh opening 210 μm) with a squeegee load of 30 kgf and a squeegee speed of 50 mm / second, and the presence or absence of streaks was evaluated visually.

[0078] [1] Preparation of resin compositions for anode separators and cathode separators for fuel cells and fabrication of molded articles [Manufacturing Example 1] Graphite powder (artificial graphite, average particle size d 50A resin composition was prepared by adding an epoxy resin component consisting of 20.4 parts by mass of epoxy resin (o-cresol novolac type epoxy resin, epoxy equivalent 198 g / eq), 10.7 parts by mass of phenol resin (novolac type phenol resin, hydroxyl group equivalent 103 g / eq), and 0.25 parts by mass of 2-phenylimidazole to 100 parts by mass of (23 μm) in a Henschel mixer and mixing at 800 rpm for 3 minutes. The obtained composition is placed in a mold for manufacturing a fuel cell separator, and the mold temperature is set to 185°C. Compression molding was performed under conditions of a molding pressure of 36.6 MPa and a molding time of 30 seconds to obtain molded bodies of 440 mm × 120 mm × 1.6 mm for fuel cell anode separators and cathode separators having a groove for a gas flow path on one side.

[0079] [2] Preparation of adhesive [Manufacturing Example 2] A pale yellow paste-like one-component epoxy adhesive A was obtained in the same manner as in Example 1 of Japanese Patent Publication No. 2019-31646.

[0080] [Manufacturing Example 3] A pale yellow paste-like one-component epoxy adhesive B was obtained in the same manner as in Comparative Example 2 of Japanese Patent Publication No. 2019-31646.

[0081] [Manufacturing Example 4] A pale yellow paste-like one-component epoxy adhesive C was obtained in the same manner as in Comparative Example 1 of Japanese Patent Publication No. 2019-31646.

[0082] [Manufacturing Example 5] A pale yellow paste-like one-component epoxy adhesive D was obtained in the same manner as in Comparative Example 4 of Japanese Patent Publication No. 2019-31646.

[0083] [Examples 1-5, Comparative Examples 1-4] [3] Surface roughening treatment An infrared laser was irradiated onto both sides of the molded body obtained in Manufacturing Example 1 under the following conditions to obtain an anode separator and a cathode separator for fuel cells. The surface roughness Ra and warpage of the obtained anode separator and cathode separator were measured using the method described above. The results are shown in Table 1. [Infrared laser irradiation conditions] (a) Beam quality 1.6, spot diameter 300 μm, pulse energy 9.9 mJ / mm 2 Overlap rate 20.0% (b) Beam quality 1.6, spot diameter 150 μm, pulse energy 28.3 mJ / mm 2 Overlap rate 20.0% (c) Beam quality 1.6, spot diameter 200 μm, pulse energy 47.8 mJ / mm 2 Overlap rate 20.0% (d) Beam quality 1.6, spot diameter 300 μm, pulse energy 7.9 mJ / mm 2 Overlap rate 20.0% (e) Beam quality 14, spot diameter 150 μm, pulse energy 142 mJ / mm 2 Overlap rate 20.0%

[0084] [4] Application of adhesive On the side of the fuel cell anode separator that was irradiated with an infrared laser, opposite to the side with the gas flow channel groove, a one-component epoxy adhesive A (viscosity 50 Pa·s) obtained in Manufacturing Example 2 was applied using a screen printing machine (semi-automatic screen printing machine manufactured by Seria Corporation) with an 80-mesh screen (mesh opening 210 μm), a squeegee load of 30 kgf, and a squeegee speed of 50 mm / second.

[0085] [5] Bonding and heat curing The surface of a fuel cell anode separator coated with adhesive was bonded to the corresponding surface of a cathode separator, and the adhesive was heat-cured by heating at 150°C for 1 hour.

[0086] [Comparative Example 5] Instead of irradiating with an infrared laser in the surface roughening process, both sides of the molded body obtained in Manufacturing Example 1 were treated with an average particle size d 50Bipolar plates were prepared in the same manner as in Examples 1-5 and Comparative Examples 1-4, except that wet blasting was performed using 6 μm alumina abrasive material under a discharge pressure of 0.22 MPa.

[0087] The bipolar plates obtained in the above examples and comparative examples were measured for bending adhesion strength and contact resistance using the method described above, and the bleeding and smudging of the adhesive were evaluated. The results are shown in Table 1.

[0088] [Table 1]

[0089] The surface roughness Ra of the fuel cell anode separators and cathode separators fabricated under the conditions of Examples 1 to 5 is in the range of 1.61 to 4.05 μm, and the warpage is less than 5 mm, resulting in high adhesive strength and low contact resistance for the fuel cell bipolar plates.

[0090] [Example 6] A bipolar plate was fabricated by bonding a fuel cell anode separator and a cathode separator in the same manner as in Example 1, except that adhesive A in Example 1 was replaced with one-component epoxy adhesive B (viscosity 29 Pa·s) obtained in Manufacturing Example 3.

[0091] [Example 7] A bipolar plate was fabricated by bonding a fuel cell anode separator and a cathode separator in the same manner as in Example 1, except that adhesive A in Example 1 was replaced with a one-component epoxy adhesive C (viscosity 510 Pa·s) obtained in Manufacturing Example 4.

[0092] For the bipolar plates obtained in the above examples, the adhesive seepage and smudging were evaluated using the method described above, and the bending adhesive strength was measured. The results are shown in Table 2. The results for Example 1 are also shown.

[0093] [Table 2]

[0094] In Example 1, in particular, since the viscosity of the adhesive is in the range of 30 to 500 Pa·s, the adhesive strength is high without any bleeding or streaking of the adhesive.

[0095] [Example 8] A bipolar plate was fabricated by bonding a fuel cell anode separator and a cathode separator in the same manner as in Example 1, except that adhesive A in Example 1 was replaced with a one-component epoxy adhesive D (gelling point 101°C) obtained in Manufacturing Example 5. The resulting bipolar plates were evaluated for adhesive seepage and streaking using the method described above, and their bending adhesion strength was measured. The results are shown in Table 3. The results for Example 1 are also included.

[0096] [Table 3]

[0097] In Example 1, in particular, since the gelation point of the adhesive is 79°C, there is no bleeding of the adhesive and the adhesive strength is high.

[0098] [Example 9] A bipolar plate was fabricated by bonding the fuel cell anode separator and cathode separator in the same manner as in Example 1, except that the method of applying the adhesive to the fuel cell anode separator was changed from screen printing to a dispenser. The adhesive was applied using a dispenser under the following conditions: discharge rate of 0.7 mL / min and application speed of 50 mm / second. The resulting bipolar plates were evaluated for adhesive seepage and streaking using the method described above, and their bending adhesion strength was measured. The results are shown in Table 4. The results for Example 1 are also included.

[0099] [Table 4]

[0100] The anode separator and cathode separator of Example 9 have a surface roughness Ra in the range of 1.61 to 4.05 μm, a warpage of less than 5 mm, and an adhesive viscosity in the range of 30 to 500 Pa·s. Therefore, even when the adhesive is applied with a dispenser, there is no bleeding or streaking, and the adhesive strength is high.

[0101] [Reference example 1] A bipolar plate was fabricated by bonding an anode separator and a cathode separator for a fuel cell in the same manner as in Example 1. Then, both sides of the obtained bipolar plate for a fuel cell were subjected to hydrophilization treatment by atmospheric pressure plasma treatment using a remote atmospheric pressure glow discharge plasma generator (AP-T03, manufactured by Sekisui Chemical Co., Ltd.) under the following conditions. [Atmospheric pressure plasma treatment conditions] (1) Frequency 30kHz, pulse width 9μs, plasma electrode 550mm, voltage 420V, current 4.5A (2) Plasma gas: Nitrogen-oxygen mixed gas, nitrogen concentration 99.5% by volume (nitrogen flow rate 330 L / min, oxygen flow rate 1.5 L / min)

[0102] [Reference example 2] An infrared laser was irradiated onto the anode separator and cathode separator for the fuel cell under the same conditions as in Example 1, and then atmospheric pressure plasma treatment was performed on the gas flow path surface in the same manner as in Reference Example 1. Next, an adhesive was applied to the anode separator in the same manner as in Example 1, the anode separator and cathode separator were bonded together in the same manner as in Example 1, and the adhesive was heat-cured to produce a bipolar plate.

[0103] [Measurement of static contact angle] In Example 1 and Reference Examples 1 and 2, 5 μL of deionized water was dropped into the bottom of the gas flow channel groove of the bipolar plates for fuel cells in air, and the static contact angle was measured using a contact angle meter (CA-DT-A type, manufactured by Kyowa Interface Chemical Co., Ltd.). The results are shown in Table 5.

[0104] [Table 5]

[0105] The bipolar plate for fuel cells in Reference Example 1 undergoes atmospheric pressure plasma treatment after the adhesive has been heat-cured, resulting in a low contact angle and excellent hydrophilicity. [Explanation of Symbols]

[0106] 1 Anode separator 2 Cathode Separators

Claims

1. A bipolar plate for a fuel cell in which a cathode separator and an anode separator, which are provided in a power generation unit cell of a fuel cell, are joined together via an adhesive layer, The adhesive layer is a layer made of a cured product of an adhesive containing a thermosetting resin. A bipolar plate for a fuel cell, characterized in that the arithmetic mean roughness Ra of at least the surface of the cathode separator and anode separator in contact with the adhesive layer is 1.61 to 4.05 μm, and the warpage of the cathode separator and anode separator is less than 5 mm.

2. A bipolar plate for a fuel cell according to claim 1, wherein the bending adhesive strength by method A of JIS K6856:1994, a method for testing the bending adhesion of adhesives, is 0.50 MPa or more.

3. shear rate 10s -1 The bipolar plate for a fuel cell according to claim 1, wherein the viscosity of the adhesive, as measured by a rotational rheometer at a measurement temperature of 25°C, is 30 to 500 Pa·s.

4. The bipolar plate for a fuel cell according to claim 1, wherein the gelation point of the adhesive, calculated from the intersection of the storage modulus and the loss modulus in the temperature dependence measurement of dynamic viscoelastic properties using a rotary rheometer, is less than 100°C.

5. A method for manufacturing a bipolar plate for a fuel cell, wherein the cathode separator and anode separator provided in the power generation unit cell of the fuel cell are joined together via an adhesive layer, (1) A press molding process in which a composition containing graphite powder and epoxy resin components including a main agent, a curing agent and a curing accelerator is heated and pressed in a mold to obtain two molded bodies, (2) A surface roughening step to obtain a cathode separator and an anode separator, in which each of the two obtained molded bodies is subjected to a surface roughening treatment to adjust the arithmetic mean roughness Ra of at least the surface in contact with the adhesive layer to 1.61 to 4.05 μm. (3) A coating step of applying an adhesive to the roughened surface of either one or both of the cathode separator and the anode separator. (4) A bonding step of bonding the roughened surfaces of the cathode separator and the anode separator together, (5) A heat curing step in which the adhesive is heat-cured after the cathode separator and anode separator have been bonded together. A method for manufacturing a bipolar plate for a fuel cell, characterized by comprising the following:

6. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the surface roughening treatment is performed by an infrared laser, and both surfaces of the two molded bodies are roughened.

7. The beam quality (M) of the infrared laser 2 ) is 2.8 or less, and the pulse energy per unit area is 8.0 to 50 mJ / mm 2 The method for manufacturing a bipolar plate for a fuel cell according to claim 6.

8. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the method for applying the adhesive is by screen printing.

9. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the method for applying the adhesive is by a dispenser system.

10. The method for manufacturing a bipolar plate for a fuel cell according to claim 5, wherein the bipolar plate for a fuel cell has grooves on its surface that serve as gas channels, and the method further comprises a hydrophilization step of applying a hydrophilization treatment to the entire surface of the gas channel having the grooves that serve as gas channels.

11. The method for manufacturing a bipolar plate for a fuel cell according to claim 10, wherein the hydrophilization treatment is atmospheric pressure plasma treatment.

12. The method for manufacturing a bipolar plate for a fuel cell according to claim 11, wherein the atmospheric pressure plasma treatment is a remote atmospheric pressure plasma treatment.

13. The method for manufacturing a bipolar plate for a fuel cell according to claim 11, wherein the processing gas for the atmospheric pressure plasma treatment is a gas containing nitrogen gas.

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