Fuel cell bipolar plate and method for manufacturing fuel cell bipolar plate

Abstract

Provided is a fuel cell bipolar plate in which a cathode separator and an anode separator provided in a power generation unit cell in a fuel cell are joined via an adhesive layer, wherein: the adhesive layer comprises a cured product of an adhesive containing a thermosetting resin; the arithmetic average roughness Ra of the surfaces of the cathode separator and the anode separator in contact with at least the adhesive layer is 1.61-4.05 μm; and the warpage of the cathode separator and the anode separator is less than 5 mm. Said fuel cell bipolar plate has high flexural bonding strength.

Description

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

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

[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 by the reaction of hydrogen ions and oxygen that have passed through the polymer electrolyte membrane.

[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, may be 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, if the surface roughness Ra value of the separator is low, the anchoring effect is reduced, and there is a problem that the bonded separators tend to peel 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 50A method has been proposed in which alumina abrasive material with a thickness of 6 μm is used for pretreatment by wet blasting at a discharge pressure of 0.22 MPa. However, when the separator preform is surface-treated under the above wet blasting conditions, the surface Ra value of the separator preform is low, less than 0.5 μm, resulting in a low anchoring effect and a problem in that the bonded separator preform tends to peel off.

[0007] Japanese Patent Publication No. 2012-199204 Japanese Patent Publication No. 2019-31646

[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.

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

[0010] In other words, the present invention provides: 1. A bipolar fuel cell plate in which a cathode separator and an anode separator provided in a power generation unit cell of a fuel cell are joined via an adhesive layer, wherein the adhesive layer is a layer made of a cured product of an adhesive containing a thermosetting resin, the arithmetic mean roughness Ra of at least the surface of the cathode separator and anode separator that is 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 fuel cell plate according to 1, wherein the bending adhesive strength by method A of JIS K6856:1994 bending adhesive test method is 0.50 MPa or more; 3. Shear rate 10 s -11. A bipolar fuel cell plate according to claim 1, wherein the viscosity of the adhesive, as measured by a rotating rheometer at a measurement temperature of 25°C, is 30 to 500 Pa·s. 4. A bipolar fuel cell plate 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 measurement of the temperature dependence of dynamic viscoelastic properties using a rotating rheometer, is less than 100°C. 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 via an adhesive layer, comprising: (1) a press molding step of obtaining two molded bodies by heating and pressing a composition containing graphite powder and an epoxy resin component including a main agent, a curing agent and a curing accelerator in a mold; (2) a roughening step of applying a surface roughening treatment to each of the two obtained molded bodies to obtain a cathode separator and an anode separator whose 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 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 method for manufacturing a bipolar plate for a fuel cell, characterized by comprising a thermosetting step of heat-curing the adhesive after bonding the cathode separator and the anode separator together; 6. A method for manufacturing a bipolar plate for a fuel cell according to 5, wherein the roughening treatment is performed by an infrared laser, and both sides 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 2The present invention provides: 6. A method for manufacturing a bipolar plate for a fuel cell; 8. A method for manufacturing a bipolar plate for a fuel cell according to 5, wherein the method for applying the adhesive is by screen printing; 9. A method for manufacturing a bipolar plate for a fuel cell according to 5, wherein the method for applying the adhesive is by dispenser; 10. A method for manufacturing a bipolar plate for a fuel cell according to 5, wherein the bipolar plate for a fuel cell has grooves on its surface that serve as gas channels, and the method comprises a hydrophilization step of applying a hydrophilization treatment to the entire surface of the gas channel having the grooves; 11. A method for manufacturing a bipolar plate for a fuel cell according to 10, wherein the hydrophilization treatment is atmospheric pressure plasma treatment; 12. A method for manufacturing a bipolar plate for a fuel cell according to 11, wherein the atmospheric pressure plasma treatment is remote atmospheric pressure plasma treatment; and 13. A method for manufacturing a bipolar plate for a fuel cell according to 11, wherein the treatment gas for the atmospheric pressure plasma treatment is a gas containing nitrogen gas.

[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.

[0012] The following shows a test specimen for measuring the bending adhesive strength of the bipolar plate for fuel cells of the present invention, where (A) is a front view and (B) is a top view.

[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 cell in which a cathode separator and an anode separator provided in a power generation unit cell of a fuel cell are joined via an adhesive layer, wherein the adhesive layer is a layer made of a cured product of an adhesive containing a thermosetting resin, the arithmetic mean roughness Ra of at least the surface of the cathode separator and anode separator that is 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 the present invention are provided in the power generation unit cell of 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 1.62 to 4.00 μm is preferred. If the above arithmetic mean roughness Ra is less than 1.61 μm, the specific surface area of ​​the adhesive interface is small, making it easy for the bonded separator to peel off. 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 coated adhesive to bleed, making it easy for the bonded separator to peel off. 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 warpage 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 above warpage is 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, JIS K6856:1994.

[0018] [Method for Manufacturing Bipolar Plates for Fuel Cells] The method for manufacturing bipolar plates for fuel cells of the present invention is characterized by comprising the following steps: (1) A press molding step 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 press-molded in a mold to obtain two molded bodies. (2) A roughening step in which each of the two obtained molded bodies is subjected to a 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 described above is adjusted to 1.61 to 4.05 μm. (3) A coating step in which adhesive is applied to the roughened surface of either one or both of the cathode separator and the anode separator. (4) A bonding step in which the roughened surfaces of the cathode separator and the anode separator are bonded together. (5) A thermocuring step in which the adhesive is heat-cured after the cathode separator and the anode separator have been bonded together.

[0019] (1) Press molding 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 lump-shaped coke, spheroidized 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, spheroidized natural graphite, and natural graphite whose surface has been treated with a pitch coat or the like. These can be used individually or in combination of two or more types.

[0021] Average particle size d of graphite powder 50 While not particularly limited, considering the need to maintain an appropriate amount of void space 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. That is, the average particle size d of the graphite powder50 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 average particle size d is 200 μm or less, the voids between graphite particles are appropriate, so even if the resin filling the voids between graphite particles on the separator surface is removed by laser irradiation, large irregularities will not be formed on the separator surface. As a result, the contact resistance of the separator will be low, and the conductivity of the separator itself will not deteriorate. 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 the 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 the phenyl group is preferred. Specific examples of imidazole compounds having an aryl group at the 2-position include 2-phenylimidazole and 2-phenyl-4-methylimidazole. Note that if an imidazole compound having a short-chain alkyl group such as 2-methylimidazole is used, the curing time may be too fast and uniform molding may not be possible, while if an imidazole compound having a long-chain alkyl group such as 2-undecylimidazole is used, the curing time may be too slow and the molding time may be long.

[0026] In addition to the above components, the composition used in the present invention may also contain optional components such as internal release agents. The internal release agent can be appropriately selected from various internal release agents conventionally used for molding separators. Specific examples include stearic acid-based wax, amide-based wax, montanic acid-based wax, carnauba wax, polyethylene wax, 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 molding conditions are not particularly limited, but the mold temperature is 80 to 200°C, the molding pressure is 1.0 to 50 MPa, preferably 5 to 40 MPa, and the molding time is 10 seconds to 1 hour, preferably 20 to 180 seconds, more preferably 30 to 90 seconds. After press molding, the mold may be further heated at 150 to 200°C for about 1 to 600 minutes to promote heat curing.

[0030] (2) Roughening Process This process is a process of subjecting each of the two molded bodies obtained in the press molding process to a roughening treatment and obtaining a cathode separator and an anode separator in which the arithmetic mean roughness Ra of at least the surface in contact with the above-mentioned adhesive layer is adjusted 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 irradiating 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 preferable from the viewpoints of depth of focus, light condensing property, and life of the transmitter. The wavelength of the infrared laser is not particularly limited, but is preferably 780 to 10600 nm, more preferably 808 to 1095 nm, and even more preferably 920 to 1070 nm.

[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 1.8 or less. When the beam quality is 2.8 or less, the light condensing property of the laser is improved, so it is preferable because high energy is not required to disappear the resin in the surface layer part of the molded body. In addition, since high energy is not required for irradiation to the molded body, damage due to heat is small, and even when a thin molded body is irradiated with a laser, the warpage after irradiation is small, so the contact resistance during fuel cell stacking can be lowered. Furthermore, when the beam quality of the laser is 2.8 or less, the depth of focus becomes deeper, so the resin at the bottom of the gas flow path disappears without irradiating high energy to the separator, and the static contact angle after atmospheric pressure plasma treatment can be lowered.

[0034] The pulse energy per unit area of the infrared laser is preferably 4 to 50 mJ / mm 2 and more preferably 8.0 to 50 mJ / mm 2 and even more preferably 9 to 48 mJ / mm 2A more preferable pulse energy per unit area is 4 to 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 to 30%, and more preferably 10 to 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 to 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. Examples of blast 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 body surface after laser irradiation falls within the above range.

[0040] (3) Coating step 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 a thermosetting resin include those containing one selected from phenolic resin, polycarbodiimide resin, polyurethane resin, epoxy resin, polyester resin, silicone resin, and polyimide resin, or mixtures containing two or more such resins. These may 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 for one-component epoxy adhesives, those containing an epoxy resin, curing agent, and curing accelerator are 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 also included in this. 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 must be 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 at 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 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-like 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 Tech Co., Ltd.). 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 lumpy, spherical, needle-shaped, irregularly shaped, etc. The material of the non-flaky inorganic filler is 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 flaky inorganic filler.

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

[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 having one epoxy group per molecule and low viscosity, known as reactive diluents, can also be used to the extent that they do 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, so it is preferable that it be solvent-free.

[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. Furthermore, after stirring and mixing, degassing may be performed under vacuum. In addition, commercially available products may be used.

[0064] The adhesive used in this invention is subject to a shear rate of 10 s. -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) Bonding process This process involves bonding the roughened surfaces of the cathode separator and the anode separator together. If adhesive is applied to the roughened surface of either the cathode separator or the anode separator, the surface of the separator to which the adhesive is applied is bonded to the roughened surface of the other separator. If adhesive is applied to both the cathode separator and the anode separator, the surfaces of the cathode separator and the anode separator to which the adhesive is applied are bonded together.

[0069] (5) Thermosetting process This process involves curing the adhesive by heating after the cathode separator and anode separator have been bonded together.

[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 fuel cell plate obtained in this manner has an arithmetic mean roughness Ra of 1.61 to 4.05 μm on the surfaces to which the cathode separator and anode separator are bonded. As a result, it has 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 flow 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 hydrophilization treatment to the entire gas flow channel surface having these grooves. Furthermore, when applying a hydrophilization treatment to the bipolar plate for fuel cells, it is preferable to do so after the adhesive has been heat-cured. If the hydrophilization treatment to the bipolar plate for fuel cells is performed 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. The hydrophilization treatment is not particularly limited, but corona treatment, excimer UV light treatment, plasma treatment, etc. are preferred, with plasma treatment being more preferred.

[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 plates for fuel cells obtained by the above manufacturing method of the present invention have high bending adhesion strength and low contact resistance. Furthermore, they have good hydrophilicity when subjected to hydrophilic treatment. Generally, polymer electrolyte fuel cells consist 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 sandwich these electrodes and form gas supply and discharge channels. The bipolar plates of the present invention can be used as some or all of these multiple separators.

[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] Measured using a particle size distribution analyzer (manufactured by Nikkiso Co., Ltd.). [Measurement of parameters related to laser irradiation] (1) Beam quality (M 2 ) Measurement M 2The 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 by measuring the average laser power output and spot diameter using the following formula. The repetition frequency is the setting of the laser oscillator. (i) Measurement of average laser power output Measured using a power meter (NOVA II, manufactured by Ophir Optronics Solutions). (ii) Measurement of laser spot area The spot diameter was measured using a laser beam profile measurement camera (NOVA II, manufactured by Ophir Optronics Solutions), and the spot area was calculated. Pulse energy (mJ) = Average laser power output (W) ÷ Repetition frequency (kHz) Pulse energy per unit area (mJ / mm 2 ) = pulse energy (mJ) ÷ spot area (mm) 2 ) (3) Overlap rate The overlap rate was calculated from the following formula using 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) Viscosity measurement A rotational rheometer (model number Kinexus pro+, manufactured by Netsch) was used, with a measurement temperature of 25°C and a shear rate of 10 s. -1Measured at: (2) Method for calculating the gelation point Using the same apparatus as above, the storage modulus and loss modulus were measured under the conditions of frequency 1 Hz, shear stress 1 Pa, measurement start temperature 25°C, and heating rate 2°C / min, and the gelation point was calculated from the intersection of these values. [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 separators and cathode separators 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 warpage The anode separators and cathode separators for fuel cells were placed on a surface plate, and the maximum and minimum values ​​were measured using a height gauge, and the difference between these was defined as warpage. [Evaluation of Bipolar Plates for Fuel Cells] (1) Measurement of Bending Adhesion Strength (i) Preparation of Bending Adhesion 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. (b) The required volume of adhesive was applied to one end portion of the anode separator, 12.5 mm × 25 mm, on the side opposite to the side with the gas flow channel groove, 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 side of the anode separator 1 and the corresponding side of the cathode separator 2 were bonded together so that the length of the overlapping portion was 12.5 mm. (d) The adhesive was heat-cured under heating conditions of 150°C for 1 hour to prepare the test specimens. (ii) Measurement of bending adhesion strength The bending adhesion strength test specimens prepared by the above method were measured using a universal material testing machine (Instron 5544A) in accordance with the method A of JIS K6856:1994 Bending adhesion test method for 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 prepared bipolar plate, and copper electrodes were placed above and below the carbon paper. A surface pressure of 1 MPa was applied in the vertical direction, and the voltage between electrodes was measured using the four-terminal method. (ii) Carbon paper Copper electrodes were placed above and below the carbon paper, and a surface pressure of 1 MPa was applied in the vertical direction, and the voltage between electrodes was measured using the four-terminal method.(iii) Method for Calculating Contact Resistance 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 seepage and streaking (i) Evaluation of seepage The bipolar plate for 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 streaking Using a screen printing machine (semi-automatic screen printing machine manufactured by Seria Corporation), an 80-mesh screen (mesh opening 210 μm) was used, and a predetermined adhesive was applied to the anode separator with a squeegee load of 30 kgf and a squeegee speed of 50 mm / second, and the presence or absence of streaking was visually evaluated.

[0078] [1] Preparation of resin compositions for anode separators and cathode separators for fuel cells and fabrication of molded articles [Production example 1] Graphite powder (artificial graphite, average particle size d 50 A 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) epoxy resin and mixing at 800 rpm for 3 minutes. The obtained composition was placed in a mold for manufacturing fuel cell separators and compression molded under the conditions of a mold temperature of 185°C, a molding pressure of 36.6 MPa, and a molding time of 30 seconds to obtain molded bodies of fuel cell anode separators and cathode separators measuring 440 mm × 120 mm × 1.6 mm, each having a groove on one side that serves as a gas flow path.

[0079] [2] Preparation of adhesive [Production 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 Application 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 Both sides of the molded body obtained in Manufacturing Example 1 were irradiated with an infrared laser 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 (b) Overlap rate 20.0% Beam quality 1.6, spot diameter 150 μm, pulse energy 28.3 mJ / mm 2 (c) Overlap rate 20.0%, Beam quality 1.6, Spot diameter 200 μm, Pulse energy 47.8 mJ / mm 2 (d) Overlap rate 20.0%, beam quality 1.6, spot diameter 300 μm, pulse energy 7.9 mJ / mm 2 (e) Overlap rate 20.0%, Beam quality 14, Spot diameter 150 μm, Pulse energy 142 mJ / mm 2 Overlap rate 20.0%

[0084] [4] Adhesive application On the side of the fuel cell anode separator opposite to the side with the gas flow channel groove that was irradiated with an infrared laser, the one-component epoxy adhesive A (viscosity 50 Pa·s) obtained in Production 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] The surface of the fuel cell anode separator to which the bonding and thermosetting adhesive was applied was bonded to the surface of the cathode separator corresponding to this surface, and the adhesive was thermoset by heating at 150°C for 1 hour.

[0086] [Comparative Example 5] Instead of irradiating with an infrared laser in the surface roughening process, the average particle size d was applied to both sides of the molded body obtained in Manufacturing Example 1. 50 Bipolar 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]

[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 a one-component epoxy adhesive B (viscosity 29 Pa·s) obtained in Manufacturing Example 3.

[0091] [Example 7] 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, 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]

[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 (gel point 101°C) obtained in Manufacturing Example 5. The resulting bipolar plate was evaluated for adhesive seepage and streaking using the method described above, and the bending adhesive strength was measured. The results are shown in Table 3. The results for Example 1 are also shown.

[0096]

[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 a fuel cell anode separator and a 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 at a discharge rate of 0.7 mL / min and an application speed of 50 mm / second. The resulting bipolar plate was evaluated for adhesive bleeding and streaking using the above method, and the bending adhesive strength was measured. The results are shown in Table 4. The results for Example 1 are also shown.

[0099]

[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 warp 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 under the following conditions using a remote atmospheric pressure glow discharge plasma generator (AP-T03 manufactured by Sekisui Chemical Co., Ltd.). [Atmospheric Pressure Plasma Treatment Conditions] (1) Frequency 30 kHz, pulse width 9 μs, plasma electrode 550 mm, voltage 420 V, current 4.5 A (2) Plasma gas: nitrogen-oxygen mixed gas, nitrogen concentration 99.5 vol% (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 a 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] 5 μL of deionized water was dropped into the bottom of the gas flow channel groove of the fuel cell bipolar plates obtained in Example 1 and Reference Examples 1 and 2 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]

[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.

[0106] 1. Anode separator 2. Cathode separator

Claims

1. 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 via an adhesive layer, wherein the adhesive layer is a layer made of a cured product of an adhesive containing a thermosetting resin, the arithmetic mean roughness Ra of at least the surface of the cathode separator and anode separator that is 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 according to claim 1, wherein the bending adhesive strength by method A of JIS K6856:1994 Adhesive bending adhesion test method is 0.50 MPa or more.

3. Shearing rate 10s -1 The bipolar plate for a fuel cell according to claim 1, wherein the viscosity of the adhesive, as measured by a rotating 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 measurement of the temperature dependence 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, in which a cathode separator and an anode separator provided in a power generation unit cell of a fuel cell are joined via an adhesive layer, comprising: (1) a press molding step of obtaining two molded bodies by heating and pressing a composition containing graphite powder and an epoxy resin component including a main agent, a curing agent and a curing accelerator in a mold; (2) a roughening step of applying a surface roughening treatment to each of the two obtained molded bodies to obtain a cathode separator and an anode separator whose 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 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 method for manufacturing a bipolar plate for a fuel cell, characterized by comprising a thermosetting step of heat-curing the adhesive after bonding the cathode separator and the anode separator together.

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. Beam quality of the infrared laser (M 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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