Manufacturing method of precursor for regenerated fuel cell separator

Abstract

A manufacturing method of a precursor for a regenerated fuel cell separator includes: a step of preparing a slurry by mixing a precursor for a fuel cell separator containing graphite particles and a water-soluble resin with an aqueous solvent; and a step of drying the slurry. The manufacturing method uses a reusable material as precursor for the fuel cell separator, for example defective articles obtained during manufacturing and waste material generated during processing.

Description

Method for producing precursor for regenerative fuel cell separator

[0001] The present invention relates to a method for producing a precursor for a regenerative fuel cell separator.

[0002] Fuel cell separators provide electrical conductivity to each unit cell, ensure passage for fuel and air (oxygen) to be supplied to the unit cells, and serve as a boundary wall separating them. Generally, fuel cell separators are required to have properties such as gas (hydrogen and oxygen) impermeability, electrical conductivity, mechanical strength, durability (heat resistance, water resistance, acid resistance), thin and lightweight, and formability.

[0003] A conventional method for producing such fuel cell separators involves heat-compression molding a sheet-shaped separator precursor. For example, Patent Document 1 discloses a fuel cell separator obtained by compression molding a fuel cell separator precursor sheet, the fuel cell separator precursor sheet including a conductive substrate sheet, a dense layer containing first graphite particles having a predetermined bulk density and volume resistivity (conductivity), and a conductive layer containing second graphite particles having a predetermined bulk density and volume resistivity, the dense layer and the conductive layer comprising a resin. Patent Document 2 discloses a fuel cell separator obtained by heat-molding a stampable sheet containing a conductive filler and a polymer material in a molding machine equipped with a pair of molds engraved with the shape of the fuel cell separator.

[0004] Thus, although there have been many separator manufacturing techniques using sheet-shaped precursors, no method has been known to easily reuse the sheet-shaped precursor (by forming a slurry) in an aqueous solvent. For example, Patent Document 1 discloses that the conductive layer can be produced using a conductive layer-forming composition containing a water-soluble resin binder, graphite, and a resin. However, because the conductive layer is impregnated with a water-insoluble resin solution dissolved in a solvent, the water-insoluble resin solution coats the graphite, causing it to fuse. This makes it difficult to redissolve or reslurry the precursor in an aqueous solvent for reuse. Patent Document 2 also uses a stampable sheet produced by a papermaking process from a suspension containing a conductive filler and a polymer material. However, the sheet is dried at a high temperature and then compressed by a press. This causes the polymer particles to fuse together and the polymer material to the conductive filler, making it difficult to redissolve or reslurry the precursor in an aqueous solvent for reuse. Furthermore, neither document mentions the reuse of the sheet-shaped precursor. Furthermore, separators obtained from conventional sheet-shaped precursors have the problem of poor electrical conductivity because insulating layers of water-insoluble resins tend to form between the graphite particles on the surface and on the surface of the graphite particles.

[0005] Furthermore, Patent Document 3 discloses a coating composition for use in a current collector plate with a coating layer for a fuel cell, which contains a carbon material, a water-soluble resin binder, a water-dispersible resin particulate binder, and an aqueous liquid medium. Patent Document 4 discloses a coating composition for use in a separator with a coating layer for a fuel cell, which contains a carbon material, a water-soluble resin binder, a water-dispersible resin particulate binder, and an aqueous liquid medium. However, the compositions of Patent Documents 3 and 4 are coating compositions for coating the surface of a current collector plate or separator, but are not precursor sheets for fuel cell separators. Furthermore, the above coating compositions are not formed into a sheet for use as separator precursors, and because they form a water-resistant coating film after application and drying, they cannot be redissolved in an aqueous solvent or reslurried for reuse.

[0006] Japanese Patent No. 7056796 Japanese Patent Application Laid-Open No. 2006-269313 Japanese Patent Application Laid-Open No. 2016-183325 Japanese Patent Application Laid-Open No. 2016-81717

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing a precursor for a regenerated fuel cell separator, which converts, for example, defective products generated during manufacturing or scrap materials generated during processing into reusable materials as precursors for fuel cell separators.

[0008] As a result of extensive research to achieve the above-mentioned object, the inventors discovered that a precursor for a fuel cell separator containing graphite particles and a water-soluble resin can be reslurried in an aqueous solvent, making it possible to easily reuse defective products generated during manufacturing and scrap materials generated during processing, and thus completed the present invention.

[0009] That is, the present invention provides: 1. a method for producing a precursor for a regenerated fuel cell separator, comprising the steps of mixing a precursor for a fuel cell separator containing graphite particles and a water-soluble resin with an aqueous solvent to prepare a slurry, and drying the slurry; 2. a method for producing a precursor for a regenerated fuel cell separator according to 1, wherein the precursor for a fuel cell separator contains a particulate or fibrous water-insoluble resin; 3. a method for producing a fuel cell separator, comprising the step of molding the precursor for a regenerated fuel cell separator obtained by the method for producing a precursor for a regenerated fuel cell separator according to 1 or 2; and 4. a method for producing a fuel cell separator according to 3, wherein the molding step is a step of heat compression molding.

[0010] According to the present invention, defective products generated during the production of precursors for fuel cell separators and scrap materials generated during processing can be reslurried and reprocessed into precursors for fuel cell separators, thereby reducing losses during production.

[0011] The present invention will be described in more detail below. A method for producing a precursor for a regenerated fuel cell separator (hereinafter abbreviated as "regenerated precursor") according to the present invention is characterized by comprising the steps of: mixing a precursor for a fuel cell separator (hereinafter abbreviated as "precursor") containing graphite particles and a water-soluble resin with an aqueous solvent to prepare a slurry; and drying the prepared slurry.

[0012] [1] Graphite Particles The graphite particles constituting the precursor used in the present invention are not particularly limited, and either natural graphite or artificial graphite may be used. The artificial graphite particles may be appropriately selected from those conventionally used in fuel cell separators. Specific examples thereof include artificial graphite obtained by calcining needle coke and artificial graphite obtained by calcining lump coke. Meanwhile, the natural graphite particles may also be appropriately selected from those conventionally used in fuel cell separators. Specific examples thereof include lump natural graphite and flake natural graphite. These graphite particles may be used alone or in combination of two or more.

[0013] The shape of the graphite particles is not particularly limited, but is preferably spherical or flaky from the viewpoint of electrical conductivity. The average particle size of the graphite particles is not particularly limited, but in consideration of increasing electrical conductivity, it is preferably 5 to 200 μm, more preferably 10 to 200 μm, even more preferably 10 to 100 μm, and even more preferably 10 to 50 μm. In the present invention, the average particle size is the median diameter (d 50 ) (same below).

[0014] [2] Water-Soluble Resin The water-soluble resin preferably has dispersibility, thickening properties, and adhesive properties from the viewpoint of uniformly dispersing graphite particles and optionally used particulate or fibrous water-insoluble resins and further converting them into precursors. In the present invention, "water-soluble" means that the resin is completely soluble in water at 25°C at a concentration of at least 1% by mass. Specific examples of water-soluble resins include aqueous resins such as acrylic resins, polyvinyl resins, polyether resins, polyurethane resins, polyester resins, polyolefin resins, polyamide resins, polyimide resins, polyallylamine resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, formaldehyde resins, silicone resins, fluororesins, and polysaccharides such as carboxymethyl cellulose. These resins may be used alone or in combination of two or more. Among these, acrylic resins, polyvinyl resins, polyether resins, and polysaccharides such as carboxymethyl cellulose are preferred from the viewpoint of uniformly dispersing graphite particles and optionally used particulate or fibrous water-insoluble resins and further converting them into precursors with particularly small addition amounts. These water-soluble resins are commercially available.

[0015] The content of the water-soluble resin in the precursor used in the present invention is not particularly limited as long as the precursor can be reslurried, but from the viewpoints of ease of reslurrying the precursor and dispersibility of the slurry, the content is preferably 0.1 to 30.0 parts by mass, and more preferably 0.5 to 25.0 parts by mass, relative to 100 parts by mass of graphite particles, and furthermore from the viewpoint of increasing the strength of the recycled precursor, 1.0 to 25.0 parts by mass is even more preferable.

[0016] [3] Particulate or fibrous water-insoluble resin The precursor used in the present invention preferably contains a particulate or fibrous water-insoluble resin. This water-insoluble resin is not particularly limited as long as it is particulate or fibrous and does not dissolve in water, and may be a thermoplastic resin or a thermosetting resin. As the thermoplastic resin, a resin with a melting point or glass transition point of 100°C or higher is preferred, as it has heat resistance that allows it to maintain its particulate or fibrous form during drying when preparing the precursor. Specific examples thereof include polyethylene, polypropylene, polyphenylene sulfide, polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymer, polychlorotrifluoroethylene, polyamide, polyetherketoneetherketoneketone, polyetherketone, liquid crystal polymer, polyimide, polyamideimide, polyphenylsulfone, polyetherimide and polysulfone, polybutylene terephthalate, polyethylene naphthalate, ABS resin, polycycloolefin and polyethersulfone, and derivatives thereof having a melting point of 100°C or higher, polycarbonate, polystyrene and polyphenylene oxide, and derivatives thereof having a glass transition point of 100°C or higher, and these may be used alone or in combination of two or more. The upper limit of the melting point or glass transition point is not particularly limited, but from the viewpoint of productivity of precursors and fuel cell separators, a value of 300°C or lower is preferred.

[0017] The thermosetting resin can be appropriately selected from those commonly used as binder resins for carbon separators, etc. Specific examples include phenolic resins, epoxy resins, furan resins, unsaturated polyester resins, urea resins, melamine resins, diallyl phthalate resins, bismaleimide resins, polycarbodiimide resins, silicone resins, vinyl ester resins, and benzoxazine resins. These resins may be used alone or in combination. Among these, epoxy resins and phenolic resins are preferred because of their excellent heat resistance and mechanical strength. These water-insoluble resins are commercially available.

[0018] The particle shape of the water-insoluble resin is not particularly limited and may be any shape such as spherical, scale-like, block-like, foil-like, plate-like, needle-like, or amorphous, but spherical is preferred from the viewpoint of particle packing. The average particle size of the water-insoluble resin is also not particularly limited, but is preferably 1 to 150 μm from the viewpoints of improving particle packing and reducing the resistance of the resulting fuel cell separator.

[0019] When the precursor used in the present invention contains a particulate or fibrous water-insoluble resin, the content thereof is not particularly limited as long as the precursor can be reslurried. From the viewpoint of ease of reslurrying, however, the content is preferably 10.0 to 70.0 parts by mass, and more preferably 15.0 to 65.0 parts by mass, per 100 parts by mass of the graphite particles.

[0020] [4] Other Components In addition to the components described above, the precursor used in the present invention may contain other components commonly used in fuel cell separators. Examples of other components include internal release agents such as stearic acid wax, amide wax, montanic acid wax, carnauba wax, and polyethylene wax; conductive additives such as carbon black; and reinforcing materials such as carbon fiber. In particular, carbon fiber is preferably included from the viewpoint of further improving the strength of the recycled precursor and the separator obtained therefrom. The content of the other components is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.1 to 3 parts by mass, per 100 parts by mass of graphite particles, from the viewpoint of improving the reslurrying of the precursor.

[0021] [5] Method for Producing Precursor The precursor used in the present invention can be obtained by, for example, dispersing a composition containing graphite particles, a particulate or fibrous water-insoluble resin used as needed, and a water-soluble resin in water to prepare a precursor-producing slurry, molding the slurry by coating or casting, and then drying and removing the water. By uniformly dispersing the slurry by wet kneading and then molding the slurry, it is possible to suppress the generation of voids due to unfilled resin during heat compression molding, and to further improve gas impermeability.

[0022] Examples of the method for preparing a precursor by coating include coating a slurry onto a resin film such as a PET film, drying the slurry, and then peeling the slurry from the resin film. The coating method is not particularly limited and may be appropriately selected from known methods such as spin coating, dipping, flow coating, inkjet coating, jet dispenser coating, spray coating, bar coating, gravure coating, roll coating, transfer printing, brush coating, blade coating, air knife coating, die coating, and screen printing.

[0023] An example of a method for producing a precursor by casting is to pour the slurry into a box-shaped mold, dry it, and then remove it from the mold. If a mold with a shape that reflects the irregularities of the separator is used, it is possible to produce a precursor with locally varying thicknesses, which is difficult to achieve by a coating method. The material of the mold is not particularly limited, and may be appropriately selected from known materials such as a metal mold with a release treatment, or a plastic mold made of silicone, fluororesin, or the like.

[0024] When a particulate or fibrous water-insoluble resin is used, the drying temperature of the slurry is not particularly limited as long as it is equal to or lower than the melting point or glass transition point of the resin. However, the drying temperature is preferably 100°C or lower, more preferably from room temperature to 100°C, and even more preferably from 50 to 100°C.

[0025] The precursor used in the present invention may have any shape, such as a sheet, a plate, etc. Furthermore, defective products generated during the production of a precursor by the above-described method or scraps produced during processing can also be used as the precursor.

[0026] The form of the precursor used in the present invention is not particularly limited, but it is preferable that at least a portion of it has a structure in which graphite particles and a particulate or fibrous water-insoluble resin used as needed are fixed by a water-soluble resin.

[0027] [5] Method for Producing Regenerated Precursor The above-described precursor and an aqueous solvent are mixed to prepare a slurry, and the resulting slurry is dried to obtain a regenerated precursor. The aqueous solvent can be water or a mixed solvent of water and an organic solvent, with water being preferred. The organic solvent is not particularly limited as long as it is soluble in water and does not dissolve the particulate or fibrous water-insoluble resin. Examples of the organic solvent include alcohols such as methanol and ethanol, and polyhydric alcohols such as diethylene glycol and glycerin. When an organic solvent is used, its amount in the aqueous solvent is preferably less than 50% by mass, more preferably less than 30% by mass, and even more preferably less than 15% by mass.

[0028] The method for mixing the precursor and the aqueous solvent is arbitrary, and the aqueous solvent may be added to the precursor, or the precursor may be added to the aqueous solvent. The amount of aqueous solvent used is not particularly limited as long as it can be used to form a slurry, but an amount that results in a solids content of approximately 1 to 80 mass %, more preferably 10 to 75 mass %, and even more preferably 30 to 70 mass % in the slurry, is preferred. The precursor used in the present invention has the characteristic that the water-soluble resin redissolves upon contact with water, allowing for easy formation of a slurry. Therefore, the slurry can be prepared at room temperature (approximately 15 to 30°C), but may be heated, if necessary, to a temperature that does not melt the particulate or fibrous water-insoluble resin. The heating temperature can be, for example, approximately 50 to 80°C.

[0029] To obtain a recycled precursor from the slurry, the slurry can be formed using the coating or casting method described above for precursor production, and then dried at the same temperature as during precursor production. The recycled precursor of the present invention can be formed into a sheet simply by drying and removing the aqueous solvent from the slurry. Therefore, it is easy to form a sheet with an uneven shape of varying thickness, in addition to the simple flat shape used in the past. The thickness of the recycled precursor is not particularly limited, but is preferably 100 μm to 1 mm, and more preferably 200 to 800 μm.

[0030] Furthermore, the recycled precursor of the present invention is retained in shape by the dried water-soluble resin and has the strength to be handled in sheet form. However, since the water-soluble resin dissolves again when it comes into contact with water, it can be made into a slurry multiple times, and defective products generated during precursor production and scraps during processing can be used without loss.

[0031] [6] Fuel Cell Separator The recycled precursor obtained above can be heated and molded to produce a fuel cell separator. The molding method is not particularly limited, but compression molding is preferred. The temperature during compression molding is not particularly limited as long as it exceeds the melting point or glass transition point of the particulate or fibrous water-insoluble resin, but a mold temperature of 150 to 250°C is preferred. The molding pressure is preferably 1 to 100 MPa, more preferably 1 to 60 MPa. The compression molding time is not particularly limited, but can be set appropriately from about 3 seconds to 1 hour.

[0032] If the recycled precursor contains a particulate or fibrous water-insoluble resin, the water-insoluble resin can be melted by heat compression molding to fill the voids and bond the graphite particles, resulting in a separator of the desired shape. Unlike conventional methods, the graphite particles in this recycled precursor are not pre-coated with a water-insoluble resin, which prevents a resin layer from forming on the separator surface during compression molding. This reduces contact resistance and penetration resistance, resulting in a separator with high electrical conductivity and gas impermeability. In particular, the prevention of resin layer formation on the separator surface eliminates the need for a resin layer removal process to improve electrical conductivity. The increased surface exposure of the graphite particles results in the formation of fine irregularities, improving the adhesiveness of gaskets and other components, and further improving mold releasability during heat compression molding.

[0033] Generally, a solid polymer 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 solid polymer membrane and a pair of separators sandwiching these electrodes to form a gas supply / exhaust flow path. The fuel cell separator of the present invention can be used as some or all of these multiple separators.

[0034] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0035] [1] Preparation of Recycled Precursor Sheet [Example 1-1] 100 parts by weight of flake graphite (particle size 20 μm, same below), 7.1 parts by weight of a water-soluble resin, polyacrylic acid (molecular weight 150,000, solids concentration 25% by weight aqueous solution, same below), 35.7 parts by weight of a particulate phenolic resin (particle size 25 μm, molecular weight 10,000, same below), a particulate water-insoluble resin, and water were mixed to prepare a precursor sheet slurry with a final solids concentration of 50% by weight. This slurry was applied to a release-treated PET film using a bar coater, dried in a blower dryer at 80 °C, and peeled from the PET film after drying to obtain a precursor sheet. The thickness of the resulting precursor sheet was 480 μm. The resulting precursor sheet was mixed with water to prepare a slurry for producing a recycled precursor sheet with a final solids concentration of 50% by mass. This slurry was applied to a release-treated PET film using a bar coater, dried in a blower dryer at 80°C, and peeled off from the PET film to obtain a recycled precursor sheet with a thickness of 480 μm.

[0036] Example 1-2 A recycled precursor sheet having a thickness of 480 μm was obtained in the same manner as in Example 1-1, except that the particulate water-insoluble resin was changed from particulate phenolic resin to powdered polypropylene (particle size 15 μm).

[0037] Example 1-3 A recycled precursor sheet having a thickness of 480 μm was obtained in the same manner as in Example 1-1, except that the amount of polyacrylic acid used was changed to 1.4 parts by mass and the amount of particulate phenolic resin used was changed to 33.8 parts by mass.

[0038] Example 1-4 A recycled precursor sheet having a thickness of 480 μm was obtained in the same manner as in Example 1-1, except that the amount of polyacrylic acid used was changed to 15.4 parts by mass and the amount of particulate phenolic resin used was changed to 38.5 parts by mass.

[0039] Example 1-5 A recycled precursor sheet having a thickness of 480 μm was obtained in the same manner as in Example 1-1, except that the amount of polyacrylic acid used was changed to 6.4 parts by mass and the amount of particulate phenolic resin used was changed to 21.8 parts by mass.

[0040] Example 1-6 A recycled precursor sheet having a thickness of 480 μm was obtained in the same manner as in Example 1-1, except that the amount of polyacrylic acid used was changed to 8.3 parts by mass and the amount of particulate phenolic resin used was changed to 58.3 parts by mass.

[0041] [Example 1-7] A recycled precursor sheet having a thickness of 480 μm was obtained in the same manner as in Example 1-1, except that the amount of polyacrylic acid used was changed to 7.2 parts by mass, the amount of particulate phenolic resin used was changed to 36.1 parts by mass, and 1 part by mass of carbon fiber (φ7 μm, fiber length 6 mm) was further added.

[0042] Comparative Example 1-1 A slurry was prepared in the same manner as in Example 1-1, except that the amount of particulate phenolic resin used was changed to 33.3 parts by mass and polyacrylic acid was not added, but a precursor sheet could not be obtained.

[0043] [Comparative Example 1-2] A precursor sheet having a thickness of 480 μm obtained in the same manner as in Example 1-1 was pulverized in a mill mixer (manufactured by Yamazen Corporation, YMH400-W) for 10 seconds x 5 times, and the pulverized powder was spread in a metal mold and pressed at 130°C and 30 MPa for 1 minute to obtain a recycled precursor sheet.

[0044] Table 1 shows a summary of the above examples and comparative examples.

[0045]

[0046] The slurry dispersibility and reslurry in Table 1 were evaluated by the following methods. [Slurry dispersibility] The presence or absence of streaks or defects when the precursor sheet-making slurry was applied to a PET film was visually confirmed, the thickness was measured at six random points, and the evaluation was based on the following criteria: ⊚: No streaks or defects, and the thickness variation of the obtained precursor sheet was less than 3%. ◯: No streaks or defects, and the thickness variation of the obtained precursor sheet was 3% or more but less than 5%. Δ: Irregularities due to streaks or defects were observed, and the thickness variation of the obtained precursor sheet was 5% or more. ×: Obvious streaks or defects prevented the preparation of a precursor sheet. [Reslurry] 30 g of precursor sheet pieces were added to 30 mL of water and stirred to reslurry, and the presence or absence of streaks or defects when the PET film was applied was visually confirmed, and the evaluation was based on the same criteria as for the slurry dispersibility described above. ◎: No streaks or defects, and the thickness variation of the obtained recycled precursor sheet is less than 3%. ○: No streaks or defects, and the thickness variation of the obtained recycled precursor sheet is 3% or more but less than 5%. △: Irregularities are observed due to streaks and defects, and the thickness variation of the obtained recycled precursor sheet is 5% or more. ×: There are obvious streaks and defects, and a recycled precursor sheet cannot be obtained.

[0047] [2] Fabrication of fuel cell separator [Example 2-1] The recycled precursor sheet obtained in Example 1-1 was compression molded using a flat mold at 180°C and 60 MPa for 5 minutes to obtain a fuel cell separator. The thickness of the flat molded separator was 250 μm.

[0048] [Example 2-2] The recycled precursor sheet obtained in Example 1-2 was heated at 180°C for 10 minutes, and then compressed at 60 MPa using a flat mold while cooling for 20 minutes to obtain a fuel cell separator. The thickness of the flat molded separator was 250 µm.

[0049] Examples 2-3 to 2-7, Comparative Example 2-1 Fuel cell separators were obtained in the same manner as in Example 2-1, except that the recycled precursor sheets were changed to those prepared in Examples 1-3 to 1-7 and Comparative Example 1-2.

[0050] The conductivity of the obtained fuel cell separator was measured by the following method and evaluated according to the following criteria. The results are shown in Table 2. [Conductivity] A flat separator was molded, sandwiched between gold-plated copper electrodes with a side length of 2 cm, pressurized at 2.5 MPa for 10 seconds, then reduced to 1.0 MPa, and a current of 1 A / cm was applied between the gold-plated copper electrodes. 2 The interelectrode voltage was measured when a constant current of 1000 kJ / cm was applied. The obtained interelectrode voltage was converted into resistance, which was used as the separator penetration resistance (unit: mΩ cm). 2 ) and the conductivity was evaluated according to the following criteria: ⊚: Penetration resistance was 8 mΩ cm 2 Less than ○: Penetration resistance is 8 mΩ cm 2 10 mΩ・cm or more 2 Less than △: Penetration resistance is 10 mΩ cm 2 15 mΩ・cm or more 2 Less than ×: Penetration resistance is 15 mΩ cm 2 In the above cases

[0051]

[0052] As shown in Table 2, the fuel cell separators produced in Examples 2-1 to 2-7 have good electrical conductivity, whereas the fuel cell separator produced in Comparative Example 2-1 has poor electrical conductivity.

Claims

1. A method for producing a precursor for a regenerated fuel cell separator, comprising the steps of mixing a precursor for a fuel cell separator containing graphite particles and a water-soluble resin with an aqueous solvent to prepare a slurry, and drying the slurry.

2. The method for producing a precursor for a regenerated fuel cell separator according to claim 1, wherein the precursor for a fuel cell separator contains a particulate or fibrous water-insoluble resin.

3. A method for producing a fuel cell separator, comprising a step of molding a precursor for a regenerated fuel cell separator obtained by the method for producing a precursor for a regenerated fuel cell separator according to claim 1 or 2.

4. The method for producing a fuel cell separator according to claim 3, wherein the molding step is a step of heat compression molding.

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