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

Abstract

To provide a bipolar plate obtained by bonding a cathode separator and an anode separator together and having high bending adhesive strength. A bipolar plate for a fuel cell is provided in which a cathode separator and an anode separator provided in a power generation unit cell of the fuel cell are joined 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 surfaces of the cathode separator and anode separator that are 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] The present invention relates to a bipolar plate for a fuel cell and a method for manufacturing a bipolar plate for a fuel cell. [Background technology]

[0002] Fuel cells are being developed by various companies as a next-generation clean power source. Fuel cells are made up of tens to hundreds of power generating units called cells stacked together. A refrigerant is usually supplied between the cells in the stack to cool the system.

[0003] The cell is composed of a membrane electrode assembly (MEA) with a positive electrode and a negative electrode on either side of a polymer electrolyte membrane that only allows hydrogen ions to pass through, and a separator placed on the outside of that. 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 the hydrogen ions that have passed through the polymer electrolyte membrane with the oxygen.

[0004] O-rings or rubber seals are placed around the periphery of the MEA to prevent hydrogen gas and oxygen gas from leaking out of the system. However, since O-rings and rubber seals are sometimes insufficient to prevent gas leakage and precise stacking is required when stacking, the MEA and the separators sandwiching the electrodes, or the MEA and the separator, may be bonded together to form a single unit.

[0005] As a method for bonding and integrating separators together, 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, followed by rinsing with ion-exchanged water and drying to bond the anode separator and cathode separator together. However, if the surface roughness Ra of the separator is low, the anchoring effect is reduced, and the bonded separator is prone to peeling off.

[0006] In Patent Document 2, as a pretreatment before applying an adhesive, the surface of a fuel cell separator preform is coated with an average particle size d 50 A pretreatment method using wet blasting with an alumina abrasive grain size of 6 μm at a discharge pressure of 0.22 MPa has been proposed. However, when the separator preform is surface-treated under the above-mentioned wet blasting conditions, the surface Ra value of the separator preform is low, less than 0.5 μm, which reduces the anchoring effect and causes the adhered separator preform to easily peel off. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-199204 [Patent Document 2] Japanese Patent Application Publication No. 2019-31646 Summary of the Invention [Problem to be solved by the invention]

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

[0009] As a result of extensive research into achieving the above object, the inventors discovered that a bipolar plate with high bending adhesive strength can be obtained by bonding together a cathode separator and an anode separator whose surfaces have an arithmetic mean roughness Ra and warpage within a predetermined range, and thus completed the present invention.

[0010] That is, the present invention is 1. A bipolar plate for a fuel cell, in which a cathode separator and an anode separator provided in a power generation unit cell in the fuel cell are bonded 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, wherein the arithmetic mean roughness Ra of at least the surfaces of the cathode separator and the anode separator that are in contact with the adhesive layer is 1.61 to 4.05 μm, and the warpage of the cathode separator and the anode separator is less than 5 mm; 2. A bipolar plate for a fuel cell according to 1, having a bending adhesive strength of 0.50 MPa or more according to JIS K6856:1994 Bending Adhesion Test Method for Adhesives, Method A. 3. Shear rate 10s -1 2. The bipolar plate for a fuel cell according to 1, wherein the viscosity of the adhesive measured with a rotational rheometer at a measurement temperature of 25°C is 30 to 500 Pa s. 4. A bipolar plate for a fuel cell according to 1, wherein the gel point of the adhesive calculated from the intersection of the storage modulus and loss modulus in temperature dependence measurement of dynamic viscoelastic properties using a rotational 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 the fuel cell are bonded via an adhesive layer, comprising: (1) a press molding step in which a composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator is hot-press molded 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 having an arithmetic mean roughness Ra of at least the surface in contact with the adhesive layer 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 lamination step of laminating the roughened surfaces of the cathode separator and the anode separator together; and (5) a thermal curing step of thermally curing the adhesive after bonding the cathode separator and the anode separator together. A method for manufacturing a bipolar plate for a fuel cell, comprising: 6. The method for producing a bipolar plate for a fuel cell according to 5, wherein the surface roughening treatment is performed using an infrared laser to roughen both surfaces of the two molded bodies. 7. Beam quality (M 2 ) is 2.8 or less, and the pulse energy per unit area is 8.0 to 50 mJ / mm 2 7. The method for producing a bipolar plate for a fuel cell according to 6, 8. The method for producing a bipolar plate for a fuel cell according to 5, wherein the adhesive is applied by screen printing. 9. The method for producing a bipolar plate for a fuel cell according to 5, wherein the adhesive is applied by a dispenser method. 10. The method for producing a bipolar plate for a fuel cell according to 5, wherein the bipolar plate for a fuel cell has grooves on its surface that become gas flow paths, and the method further comprises a hydrophilization step of subjecting the entire gas flow path surface having the grooves that become the gas flow paths to hydrophilization. 11. The method for producing a bipolar plate for a fuel cell according to 10, wherein the hydrophilization treatment is atmospheric pressure plasma treatment. 12. The method for producing a bipolar plate for a fuel cell according to 11, wherein the atmospheric pressure plasma treatment is a remote atmospheric pressure plasma treatment. 13. The method for producing 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. to provide. [Effects of the Invention]

[0011] The bipolar plate for a fuel cell of the present invention has high bending adhesive strength because the warpage 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 drawings]

[0012] [Figure 1] 1A and 1B show a test piece for measuring the bending adhesive strength of a bipolar plate for a fuel cell according to the present invention, in which (A) is a front view and (B) is a plan view. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in more detail below. [Bipolar plates for fuel cells] The bipolar plate of the present invention is a bipolar plate for a fuel cell, in which a cathode separator and an anode separator provided in a power generation unit cell of the fuel cell are bonded 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 the anode separator are characterized in that at least the surfaces in contact with the adhesive layer have an arithmetic mean roughness Ra of 1.61 to 4.05 μm, and the cathode separator and the anode separator have a warp of 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 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, 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 more likely to peel off. On the other hand, if the arithmetic mean roughness Ra is greater than 4.05 μm, the surface energy of the coating surface is high, causing the applied adhesive to bleed, making the bonded separators more likely to peel off. If the arithmetic mean roughness Ra is 1.61 to 4.05 μm, the specific surface area is large and the adhesive is less likely to bleed out, thereby 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 the present invention is less than 5 mm, and preferably 4.95 mm or less. The method for measuring the warpage 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, more preferably 10 to 100 μm.

[0017] The flexural bond strength of the bipolar plate for a fuel cell of the present invention is preferably 0.50 MPa or more, more preferably 0.55 MPa or more, and even more preferably 0.6 MPa or more. The flexural bond strength is measured according to Method A of JIS K6856:1994, flexural bond test method for adhesives.

[0018] [Manufacturing method of bipolar plates for fuel cells] The method for manufacturing a bipolar plate for a fuel cell of the present invention is characterized by comprising the following steps. (1) A press molding step in which a composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator is heated and press-molded in a mold to obtain two molded bodies. (2) A surface roughening process in which the two obtained molded bodies are each subjected to a surface roughening treatment to obtain a cathode separator and an anode separator having an arithmetic mean roughness Ra of at least the surface in contact with the adhesive layer 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. (5) a thermal curing step of thermally curing the adhesive after bonding the cathode separator and the anode separator together.

[0019] (1) Press molding process In this step, a composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator is hot-press molded in a mold to obtain two molded bodies.

[0020] The graphite powder used in the present 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 obtained by burning needle coke, artificial graphite obtained by burning lump coke, spheroidized artificial graphite, and artificial graphite whose surface has been treated with pitch coating or the like. Examples of natural graphite include flake 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 alone or in combination of two or more.

[0021] Average particle size of graphite powder d 50is not particularly limited, but is preferably 10 to 200 μm, more preferably 10 to 100 μm, in order to maintain an appropriate amount of voids between graphite particles, increase the contact area between graphite particles, and suppress the occurrence of irregularities particularly after laser treatment to increase conductivity (reduce contact resistance). That is, the average particle size of the graphite powder d 50 If the average particle diameter d is 10 μm or more, when the molded body is irradiated with an infrared laser, the resin on the surface of the molded body is removed, improving the conductivity of the separator surface, and the contact area between the graphite particles inside the separator can be sufficiently maintained, thereby improving the conductivity in the thickness direction of the separator. 50 When the particle size is 200 μm or less, the gaps between the graphite particles are appropriate, so that even if the resin that filled the gaps between the graphite particles on the separator surface is removed by laser irradiation, large irregularities are not formed on the separator surface. As a result, the contact resistance of the separator is reduced, and the conductivity of the separator itself is not deteriorated. In addition, the above average particle size d 50 The measurement method is as described in the Examples below.

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

[0023] The hydrolyzable chlorine content of the epoxy resin base is preferably 450 ppm or less. When the hydrolyzable chlorine content is 450 ppm or less, the crosslink density of the cured product increases, resulting in improved heat resistance of the resulting separator. On the other hand, the lower limit is not particularly limited, but since epoxy resins with a hydrolyzable chlorine content of less than 370 ppm are very expensive, a lower limit of 370 ppm is preferred from the standpoint of cost.

[0024] The curing agent constituting the epoxy resin component is preferably a phenolic resin. Specific examples thereof include novolac phenolic resin, cresol novolac phenolic resin, resol phenolic resin, aralkyl-modified phenolic resin, biphenyl novolac phenolic resin, and trisphenolmethane phenolic resin. These may be used alone or in combination of two or more. Among these, novolac phenolic resin is preferred. The hydroxyl group equivalent of the phenolic resin used in the present invention is not particularly limited, but is preferably 100 to 106 g / eq.

[0025] The curing accelerator constituting the epoxy resin component is not particularly limited as long as it accelerates the reaction between the epoxy group and the curing agent, and examples thereof 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 the aryl group include a phenyl group, a tolyl group, and a naphthyl group, with a phenyl group being preferred. Specific examples of the imidazole compound having an aryl group at the 2-position include 2-phenylimidazole and 2-phenyl-4-methylimidazole. When an imidazole compound having a short-chain alkyl group such as 2-methylimidazole is used, the curing time may be too fast to achieve uniform molding, while when an imidazole compound having a long-chain alkyl group such as 2-undecylimidazole is used, the curing time may be too slow, resulting in a long molding time.

[0026] In addition to the above components, the composition used in the present invention may also contain optional components such as an internal mold release agent. The internal mold release agent may be appropriately selected from various internal mold release agents that have conventionally been used in molding separators. Specific examples include stearic acid wax, amide wax, montanic acid wax, carnauba wax, and polyethylene wax. These may be used alone 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 are preferably 22 to 40 parts by mass, more preferably 27 to 35 parts by mass, and even more preferably 30 to 33 parts by mass of the epoxy resin components per 100 parts by mass of graphite powder. By using an amount of the epoxy resin components within this range, the fluidity of the molding material becomes appropriate, improving moldability, and preventing a significant decrease in the gas impermeability and electrical conductivity of the resulting bipolar plate for a fuel cell.

[0028] The composition may be prepared, for example, by mixing the graphite powder, base material, curing agent, and curing accelerator in any order in predetermined proportions. For this purpose, a mixer such as a planetary mixer, ribbon blender, Loedige mixer, Henschel mixer, rocking mixer, or Nauta mixer can be used. When an optional component such as an internal mold release agent is used, the order of mixing the components may also be arbitrary.

[0029] Next, the composition is placed in a predetermined mold and a molded article is produced by press molding, etc. The mold used is preferably a mold for producing fuel cell separators, which is capable of forming grooves that serve as gas flow paths on one or both surfaces of the surface of the molded article. The press molding conditions are not particularly limited, but are preferably a mold temperature of 80 to 200°C, a molding pressure of 1.0 to 50 MPa, preferably 5 to 40 MPa, and a molding time of 10 seconds to 1 hour, preferably 20 to 180 seconds, more preferably 30 to 90 seconds. After press molding, the composition may be further heated at 150 to 200° C. for 1 to 600 minutes to promote thermal curing.

[0030] (2) Roughening process In this step, the two molded bodies obtained in the press molding step are each 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 surfaces in contact with the adhesive layer described above is adjusted to 1.61 to 4.05 μm.

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

[0032] The infrared laser used in the roughening step 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 in terms of focal depth, light-gathering ability, and transmitter life. 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] Infrared laser beam quality (M 2 ) is preferably 2.8 or less, preferably 2.5 or less, more preferably 2 or less, and even more preferably 1.8 or less. A beam quality of 2.8 or less is preferable because the laser has good focusing properties and does not require high energy to remove the resin from the surface layer of the molded body. Furthermore, because high energy is not required for irradiating the molded body, heat damage is minimal. Even when a thin-walled molded body is irradiated with a laser, warping after irradiation is reduced, thereby reducing contact resistance in a fuel cell stack. Furthermore, when the laser beam quality is 2.8 or less, the focal depth is deep, so the resin at the bottom of the gas flow path is removed without irradiating the separator with high energy, thereby reducing the static contact angle after atmospheric pressure plasma treatment.

[0034] The pulse energy per unit area of ​​an infrared laser is 4 to 50 mJ / mm 2 is preferable, and 8.0 to 50 mJ / mm 2 More preferably, 9 to 48 mJ / mm 2 More preferably, the pulse energy per unit area is 4 to 50 mJ / mm 2 In this case, the resin on the surface layer of the separator can be completely removed, and therefore a good bipolar plate for a fuel cell having low contact resistance and static contact angle can be obtained.

[0035] In this way, the beam quality is 2.8 or less, and the pulse energy per unit area is 4 to 50 mJ / mm 2 In this case, even when a thin molded body is irradiated with a laser, warping after irradiation is small, and therefore the contact resistance of the bipolar plate for a fuel cell can be reduced.

[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, 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 ratio, which may result in poor production efficiency.

[0037] The overlap rate of the infrared laser spots is preferably 5 to 30%, more preferably 10 to 30%. The overlap rate of the infrared laser 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 surfaces of the bottoms (concave portions) and peaks (convex portions) of the gas flow channel grooves on the surface of the molded article to be adjusted within a predetermined range.

[0038] The irradiation time of the infrared laser is not particularly limited, and 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] Before irradiating the surface of the molded body with the laser, a blasting treatment may be carried out as necessary, or the blasting treatment may not be carried out. Examples of blasting include shot blasting, air blasting, and wet blasting, and any of these can be carried out as long as the arithmetic mean roughness Ra of the surface of the molded article after laser irradiation falls within the above range.

[0040] (3) Coating process This step involves applying an adhesive to the roughened surface of either or both of the cathode separator and the anode separator obtained in the surface 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 a mixture of two or more selected from phenolic resin, polycarbodiimide resin, polyurethane resin, epoxy resin, polyester resin, silicone resin, and polyimide resin. These may be either one-component or two-component types, but one-component epoxy adhesives that do not require the steps of measuring and mixing the base resin and curing agent are preferred. The one-component epoxy adhesive preferably contains, for example, an epoxy resin, a curing agent, and a curing accelerator.

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

[0043] Furthermore, from the viewpoint of application properties by screen printing or the like, it is preferable that the epoxy resin is liquid at 10°C. Here, "liquid" means having fluidity, and this includes paste. Some crystalline epoxy resins solidify if 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, and remain liquid at 10°C.

[0044] The epoxy resin may be used alone or in combination of two or more. When two or more epoxy resins are used in combination, at least one of them is liquid at 10°C, and the mixture is liquid at 10°C. Alternatively, a liquid epoxy resin and a solid epoxy resin may be mixed under heating, and the mixture may be liquid when cooled to 10°C.

[0045] In order to improve heat resistance, an epoxy resin having three or more functional groups may be used. Examples of such an epoxy resin include YH434L (manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0046] The curing agent may be any commonly used curing agent for epoxy resins, but preferably contains at least one amine-based curing agent. Other curing agents that can be used in combination with the amine-based curing agent may also be used, and examples of 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 dihydrazides, amine adducts, and polyamides. As the amine-based curing agent, dicyandiamide, diaminodiphenylmethane, and the like are preferred from the viewpoints of latency (storage stability as a one-component adhesive), high adhesion, and improved productivity due to fast curing properties.

[0048] Examples of acid anhydride 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 phenolic curing agents include phenolic resins. Examples of Lewis acid curing agents include Lewis acids such as boron trifluoride. Examples of polymercaptan curing agents include polysulfides, thioesters, thioethers, etc.

[0049] The curing agent may be used alone or in combination of two or more. When an amine-based curing agent is used in combination with another curing agent, the amine-based curing agent preferably accounts for 50 mass% or more of the curing agent.

[0050] The content of the curing agent in the adhesive is preferably an amount that corresponds to 0.5 to 1.2 equivalents relative to the epoxy groups in the epoxy resin, and more preferably an amount that corresponds to 0.7 to 1.1 equivalents. Specifically, although this depends on the epoxy equivalent of the epoxy resin, the content of the 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 content of the curing agent is within the above range, sufficient adhesive properties can be obtained.

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

[0052] Examples of the imidazole compound 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-undecylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 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 of imidazole compounds include 1-dodecyl-2-methyl-3-benzyl-1H-imidazol-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. Adducts of the aforementioned imidazole compounds and epoxy resins can also be used as the imidazole compounds.

[0053] The amount of the curing accelerator used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the epoxy resin. When the amount of the curing accelerator used is within the above range, it is possible to prevent staining due to bleeding and achieve rapid curing.

[0054] The adhesive used in the present invention may contain an inorganic filler. The inorganic filler imparts appropriate viscosity and thixotropy to the adhesive, improving the applicability, particularly the 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 scaly inorganic filler. The use of a scaly inorganic filler imparts appropriate thixotropy to the adhesive, and has the effects of preventing adhesive residue in the screen holes when the adhesive is screen-printed and suppressing deformation of the adhesive applied (printed) to the adherend.

[0056] The degree of scaly shape of the scaly inorganic filler can be expressed by the aspect ratio. The aspect ratio is one of the particle shape indexes expressed as "average particle diameter / particle thickness" and is measured using a flow particle image analyzer or the like. The aspect ratio of the scaly 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 scaly inorganic filler is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and even more preferably 2 to 15 μm. When the average particle size is within the above range, the screen printing properties are good. The average particle size is determined by measuring the median diameter (d 50 ) value.

[0058] Examples of materials for the scaly filler include talc, silica (fumed silica, precipitated silica, crystalline silica, fused silica, dolomite, silicic anhydride, 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 oxide, zirconia, silicon nitride, barium titanate, barium carbonate diatomaceous earth, and carbon black. Among these, talc, silica, mica, and graphite (artificial and natural graphite) are preferred, with mica being particularly preferred. Commercially available products can be used. Examples of mica include Micromica MK-100, MK-200, and MK-300 (manufactured by Katakura Co-op Agri Co., Ltd.). Examples of silica include Inaflex (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 Industries Co., Ltd.), BF-7A, BF-8D, BF-10D, and BF-10A (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0059] The inorganic filler may also contain a non-scale inorganic filler. In this case, the shape of the non-scale inorganic filler is not particularly limited as long as it is not scaly, and examples thereof include block, spherical, needle-like, and irregular shapes. In addition, examples of the material of the non-scale inorganic filler include the same materials as those described above as the material of the scaly filler. The average particle size of the non-scale-like 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 scale-like inorganic filler.

[0060] The scaly inorganic filler is preferably contained in an amount of 5 to 100 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 screen holes during screen printing, or the adhesive printed (applied) on an adherend may flow before being bonded to another adherend, resulting in contamination of areas other than the intended application site with the flowed adhesive. On the other hand, if the content exceeds 200 parts by mass, the adhesive may become too viscous, resulting in poor handling, workability, and applicability. The inorganic filler content is preferably 30 to 150 parts by mass.

[0062] The adhesive used in the present invention may contain, as necessary, a silane coupling agent, a colorant (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, known as reactive diluents, and having low viscosity can also be used as long as the effects of the present invention are not impaired. The one-component liquid adhesive used in the present invention may contain a solvent to adjust the viscosity, but if a solvent is contained, it may volatilize during curing of the resin, causing gas leakage, so a solvent-free type is preferred.

[0063] The adhesive used in the present invention can be prepared by stirring and mixing the above-mentioned raw materials by a known method. Stirring and mixing can be performed using, for example, various mixers such as a dissolver, homogenizer, or homodisper, as well as kneaders, roll mills, bead mills, planetary mixers, universal mixers, planetary mixers, and the like. After stirring and mixing, the mixture may be degassed under vacuum. Furthermore, commercially available products may also be used.

[0064] The adhesive used in the present invention is applied at a shear rate of 10 s -1The viscosity of the adhesive measured with a rotational rheometer at a measurement temperature of 25°C is preferably 30 to 500 Pa·s, and more preferably 40 to 450 Pa·s. When the adhesive has a viscosity of 30 to 500 Pa·s, it can be applied evenly without problems such as the adhesive spilling out of the bonded area due to "drooping" after application or the adhesive coming off due to "smearing" during screen printing, and bleeding is less likely to occur during the curing process, preventing deterioration of conductivity due to contamination of the separator's conductive surface by uncured components and refrigerant contamination due to elution of organic components into the refrigerant, and more reliably preventing a decrease in adhesive strength.

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

[0066] The method for applying the adhesive is not particularly limited, and examples thereof include screen printing, dispenser, spray gun, inkjet, curtain coater, roll coater, gravure printing, and spray application. Of 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 so that the thickness of the adhesive layer after curing falls within the above-mentioned range.

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

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

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

[0071] The bipolar plate for fuel cells obtained in this manner has an arithmetic mean roughness Ra of the bonding surfaces of the cathode separator and anode separator adjusted to 1.61 to 4.05 μm, which results in a large specific surface area and less adhesive seepage, resulting in high adhesive strength between the separators.

[0072] (6) Hydrophilic treatment The bipolar plate for a fuel cell of the present invention preferably has grooves on its surface that serve as gas channels to ensure passage of fuel and air (oxygen) to each unit cell of the fuel cell. In the present invention, it is preferable to subject the entire gas channel surface having the grooves that serve as gas channels to a hydrophilic treatment. Furthermore, when subjecting the bipolar plate for a fuel cell to a hydrophilic treatment, it is preferable to perform the treatment after thermally curing the adhesive. If the bipolar plate for a fuel cell is hydrophilized before thermally curing the adhesive, the hydrophilic groups may be contaminated or weakened during thermal curing of the adhesive.

[0073] The hydrophilization treatment should be performed at least on the gas flow path surface that comes into contact with water generated by power generation, but may also be performed on the cooling surface as needed. The hydrophilization treatment is not particularly limited, but corona treatment, excimer UV light treatment, plasma treatment, etc. are preferred, and among these, plasma treatment is more preferred.

[0074] Examples of methods for hydrophilizing by plasma treatment include vacuum plasma treatment, atmospheric pressure plasma treatment, etc. Among these, atmospheric pressure plasma treatment is preferred because it requires a simple device and has good productivity, and remote atmospheric pressure plasma treatment is particularly preferred.

[0075] Gases used to generate plasma include oxygen gas containing oxygen atoms, ozone gas, water, nitrogen gas containing nitrogen atoms, ammonia gas, sulfur dioxide gas and sulfur trioxide gas containing sulfur atoms, etc. Air can also be used. Plasma treatment using these gases can introduce hydrophilic functional groups such as carbonyl groups, hydroxyl groups, amino groups, and sulfo groups into the surface of a molded article, thereby making the surface hydrophilic. Among these, gases containing 80% by volume or more of nitrogen gas are preferred, and gases consisting of 80% by volume or more of nitrogen gas and the remainder oxygen gas are more preferred.

[0076] The bipolar plate for a fuel cell according to the present invention obtained by the above-described method has high bending adhesive strength and low contact resistance, and also has good hydrophilicity when subjected to hydrophilization treatment. Generally, a polymer electrolyte fuel cell is made up of a large number of unit cells arranged side by side, each of which is composed of a pair of electrodes sandwiching a polymer electrolyte membrane and a pair of separators sandwiching these electrodes to form a gas supply / exhaust flow path. The bipolar plate of the present invention can be used as some or all of these separators. [Example]

[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] Measurement was performed using a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd.). [Measurement of various parameters related to laser irradiation] (1) Beam quality (M 2 ) measurement M 2 Measurement was performed 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 output and spot diameter using the following formula: The repetition frequency was set by the laser oscillator. (i) Measurement of the average laser power Measurement was performed using a power meter (NOVAII manufactured by Ophir Optronics Solutions). (ii) Measurement of the laser spot area The spot diameter was measured using a laser beam profile measuring camera (NOVAII manufactured by Ophir Optronics Solutions), and the spot area was calculated. Pulse energy (mJ) = average laser power (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 using the following formula based on the laser spot diameter (irradiation diameter of the laser spot) and the scan pitch. Overlap rate (%) = (laser spot diameter - scan pitch) / Laser spot diameter [Evaluation of adhesive properties] (1) Viscosity measurement Using a rotational rheometer (model number Kinexus pro+, manufactured by Netsch), the measurement temperature was 25°C and the shear rate was 10 s -1 Measurement was carried out at. (2) Calculation method of gel point Using the same equipment as above, the storage modulus and loss modulus were measured under the conditions of a frequency of 1 Hz, a shear stress of 1 Pa, a measurement starting temperature of 25°C, and a temperature rise rate of 2°C / min. The value 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 separator and cathode separator for the fuel cell was measured according to JIS B0601 2001 using a surface roughness meter with a probe tip diameter of 5 μm (model Surfcom 14000, manufactured by Tokyo Seimitsu Co., Ltd.). (2) Measurement of warpage The anode separator and cathode separator for the fuel cell were placed on a surface plate, and the maximum and minimum values ​​were measured using a height gauge, and the difference between these values ​​was taken as the warpage. [Evaluation of bipolar plates for fuel cells] (1) Measurement of bending adhesive strength (i) Preparation of bending adhesive strength test specimens (a) Rectangular pieces measuring 100 mm x 25 mm x 1.6 mm were machined from the flat ends of the roughened anode separator and cathode separator. (a) A required volume of adhesive was applied to a 12.5 mm x 25 mm area at one end of the surface of the anode separator opposite to the surface having the gas flow channel grooves so that the thickness of the adhesive layer after curing would be 50 μm. (c) As shown in Figures 1(A) and 1(B), the adhesive-coated surface of the anode separator 1 and the corresponding surface of the cathode separator 2 were attached together so that the overlapping length was 12.5 mm. (d) The adhesive was thermally cured by heating at 150°C for 1 hour to prepare a test specimen. (ii) Measurement of bending adhesive strength The bending adhesive strength test pieces prepared by the above method were measured using a universal testing machine (Instron 5544A) in accordance with JIS K6856:1994 bending adhesive test method for adhesives, Method A. (2) Contact resistance measurement (i) Carbon paper + bipolar plate sample Carbon paper (TGP-H060, manufactured by Toray Industries, Inc.) was placed on the top and bottom of the prepared bipolar plate, and copper electrodes were placed on the top and bottom of that. 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. (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 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 ​​determined in (i) and (ii) above, and the contact resistance was calculated using the following formula. Contact resistance (mΩ cm 2 ) = (voltage drop x contact area) / current (3) Evaluation of adhesive bleeding and smearing (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 bleeding of the adhesive was visually evaluated. (ii) Evaluation of cassoulet Using a screen printer (a semi-automatic screen printer manufactured by Seria Corporation) and an 80 mesh (opening size 210 μm) screen, a predetermined adhesive was applied to the anode separator at a squeegee load of 30 kgf and a squeegee speed of 50 mm / sec, and the presence or absence of smearing was evaluated visually.

[0078] [1] Preparation of resin compositions for fuel cell anode separators and cathode separators and fabrication of molded articles [Manufacturing Example 1] Graphite powder (artificial graphite, average particle size d 50An epoxy resin component consisting of 100 parts by mass of a cellulose acylate copolymer (cellulose acetate ester copolymer, 23 μm), 20.4 parts by mass of an epoxy resin (o-cresol novolac epoxy resin, epoxy equivalent 198 g / eq), 10.7 parts by mass of a phenolic resin (novolac phenolic resin, hydroxyl group equivalent 103 g / eq), and 0.25 parts by mass of 2-phenylimidazole was placed in a Henschel mixer and mixed at 800 rpm for 3 minutes to prepare a resin composition. The obtained composition was poured into a mold for producing a fuel cell separator, and the mold temperature was 185°C. Compression molding was carried out under conditions of a molding pressure of 36.6 MPa and a molding time of 30 seconds to obtain a 440 mm x 120 mm x 1.6 mm molded anode separator and cathode separator for fuel cells having grooves on one side to serve as gas flow paths.

[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 JP 2019-31646 A.

[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 JP 2019-31646 A.

[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 JP 2019-31646 A.

[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 JP 2019-31646 A.

[0083] [Examples 1 to 5, Comparative Examples 1 to 4] [3] Surface roughening treatment Both sides of the molded article obtained in Production Example 1 were irradiated with an infrared laser under the following conditions to obtain an anode separator and a cathode separator for a fuel cell. The surface roughness Ra and warpage of the resulting anode separator and cathode separator were measured using the methods 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] Applying adhesive The one-component epoxy adhesive A (viscosity 50 Pa s) obtained in Production Example 2 was applied to the surface of the fuel cell anode separator irradiated with the infrared laser opposite to the surface having the gas flow channel grooves using a screen printer (semi-automatic screen printer manufactured by Ceria Corporation) with an 80 mesh (opening size 210 μm) screen at a squeegee load of 30 kgf and a squeegee speed of 50 mm / sec.

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

[0086] Comparative Example 5 Instead of irradiating an infrared laser in the roughening step, both sides of the molded body obtained in Production Example 1 were irradiated with an average particle diameter d 50Bipolar plates were produced in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 4, except that wet blasting was carried out using an alumina abrasive material with a particle size of 6 μm at a discharge pressure of 0.22 MPa.

[0087] The bipolar plates obtained in the above Examples and Comparative Examples were measured for bending adhesive strength and contact resistance by the above methods, and evaluated for adhesive bleeding and smearing. The results are shown in Table 1.

[0088] [Table 1]

[0089] The surface roughness Ra of the anode separators and cathode separators for fuel cells produced under the conditions of Examples 1 to 5 was in the range of 1.61 to 4.05 μm and the warpage was less than 5 mm, so the adhesion strength of the bipolar plates for fuel cells was high and the contact resistance was low.

[0090] [Example 6] A bipolar plate was produced 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 changed to the one-component epoxy adhesive B (viscosity 29 Pa s) obtained in Production Example 3.

[0091] [Example 7] A bipolar plate was produced 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 changed to the one-component epoxy adhesive C (viscosity 510 Pa s) obtained in Production Example 4.

[0092] The bipolar plates obtained in the above examples were evaluated for adhesive bleeding and smearing using the above methods, and the bending adhesive strength was measured. The results are shown in Table 2. The results of Example 1 are also shown.

[0093] [Table 2]

[0094] In Example 1, the viscosity of the adhesive is particularly in the range of 30 to 500 Pa·s, so the adhesive does not bleed or fade, and the adhesive strength is high.

[0095] [Example 8] A bipolar plate was produced 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 changed to one-component epoxy adhesive D (gel point 101°C) obtained in Production Example 5. The resulting bipolar plate was evaluated for adhesive bleeding and smearing using the methods described above, and the bending adhesive strength was measured. The results are shown in Table 3. The results of Example 1 are also shown.

[0096] [Table 3]

[0097] In Example 1, in particular, the gel point of the adhesive is 79°C, so the adhesive does not bleed and the adhesive strength is high.

[0098] [Example 9] A bipolar plate was produced by bonding an anode separator and a cathode separator for a fuel cell in the same manner as in Example 1, except that the method of applying the adhesive to the anode separator for a fuel cell in Example 1 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 / sec. The resulting bipolar plate was evaluated for adhesive bleeding and smearing using the methods described above, and the bending adhesive strength was measured. The results are shown in Table 4. The results of Example 1 are also shown.

[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, it does not bleed or fade, and the adhesive strength is high.

[0101] [Reference example 1] A bipolar plate was produced by bonding an anode separator and a cathode separator for a fuel cell in the same manner as in Example 1, and then both sides of the obtained bipolar plate for a fuel cell were subjected to a 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 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 channel 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, and the anode separator and cathode separator were bonded together in the same manner as in Example 1, and the adhesive was thermally cured to produce a bipolar plate.

[0103] [Static Contact Angle Measurement] Five microliters of ion-exchanged water was dropped in the air onto the bottom of the gas flow channel grooves of the bipolar plates for fuel cells obtained in Example 1 and Reference Examples 1 and 2, and the static contact angle was measured using a contact angle meter (Model CA-DT·A, manufactured by Kyowa Interface Science Co., Ltd.). The results are shown in Table 5.

[0104] [Table 5]

[0105] The bipolar plate for a fuel cell of Reference Example 1 is subjected to atmospheric pressure plasma treatment after the adhesive is thermally cured, and therefore has a low contact angle and excellent hydrophilicity. [Explanation of symbols]

[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 the 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 the anode separator are formed by molding a composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator; a cathode separator and an anode separator, the surfaces of which at least come into contact with the adhesive layer have an arithmetic mean roughness Ra of 1.61 to 4.05 μm, and the cathode separator and the anode separator have a warpage of less than 5 mm.

2. 2. The bipolar plate for a fuel cell according to claim 1, wherein the bending adhesive strength measured by Method A of JIS K6856:1994, Bending Adhesion Test Method for Adhesives, is 0.50 MPa or more.

3. shear rate 10s -1 2. The bipolar plate for a fuel cell according to claim 1, wherein the viscosity of the adhesive measured by a rotational rheometer at a measurement temperature of 25° C. is 30 to 500 Pa·s.

4. 2. The bipolar plate for a fuel cell according to claim 1, wherein the gel point of the adhesive calculated from the intersection of the storage modulus and loss modulus in temperature dependence measurement of dynamic viscoelastic properties using a rotational 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 the fuel cell are bonded via an adhesive layer, comprising: (1) a press molding step in which a composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator is hot-press molded in a mold to obtain two molded bodies; (2) a surface roughening step of subjecting each of the two resulting molded bodies to a surface roughening treatment to obtain a cathode separator and an anode separator having an arithmetic mean roughness Ra of at least the surface in contact with the adhesive layer adjusted to 1.61 to 4.05 μm; (3) a coating step of coating an adhesive on the roughened surface of either or both of the cathode separator and the anode separator; (4) a lamination step of laminating the roughened surfaces of the cathode separator and the anode separator together; and (5) A thermal curing step of thermally curing the adhesive after bonding the cathode separator and the anode separator together. A method for manufacturing a bipolar plate for a fuel cell, comprising:

6. 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 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 7. The method for producing a bipolar plate for a fuel cell according to claim 6, wherein

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

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

10. 6. A 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 flow paths, and further comprising a hydrophilization step of subjecting the entire gas flow path surface having the grooves that serve as gas flow paths to a hydrophilization treatment.

11. 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. 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. 12. 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.

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