JP2012155942A - Fuel cell separator, method for producing fuel cell separator, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell separator high in corrosion resistance and suppressed in generation of partial orientation.SOLUTION: A fuel cell separator 20 is formed of a cured product made of a molding material containing a thermosetting resin and graphite. In the fuel cell separator 20, a groove 2 for gas supply/discharge and a manifold 13 are formed. A true density of the graphite is 2.22 g/cmor more, and a content of the graphite is in a range of 70 to 80 mass%. A corrosion current of the fuel cell separator 20 is 10 μA/cmor less. When two small pieces having a dimension of 30 mm×30 mm in plan view are cut out from the fuel cell separator 20, a ratio of contact resistances between the two small pieces falls in a range of 0.9 to 1.1 even if the small pieces are cut out at any positions.

Description

  The present invention relates to a fuel cell separator, a method for producing a fuel cell separator, and a fuel cell.

  Generally, a fuel cell is composed of a cell stack formed by stacking several tens to several hundreds of single cells in series, thereby generating an electromotive force.

  Fuel cells are classified into several types according to the type of electrolyte. Recently, solid polymer fuel cells using a solid polymer electrolyte membrane as an electrolyte have attracted attention as high-power fuel cells.

  FIG. 1 shows an example of a single cell structure of a polymer electrolyte fuel cell. This single cell is configured by stacking separators 20 and 20, gaskets 12 and 12, and membrane-electrode assembly 5. In the separator 20, a fuel manifold 131 and an oxidant manifold 132 are formed in an outer peripheral portion surrounding a region where the gas supply / discharge groove 2 is formed. Two fuel manifolds 131 are formed, and each fuel manifold 131 communicates with both ends of the gas supply / discharge groove 2 on the surface of the separator 20 overlapping the fuel electrode 31. Two oxidant manifolds 132 are also formed, and each oxidant manifold 132 communicates with both ends of the gas supply / discharge groove 2 on the surface of the separator 20 overlapping the oxidant electrode 32. A cooling manifold 133 is also formed on the outer peripheral portion. A gasket 12 for sealing is laminated on the outer peripheral portion of the separator 20.

  In this single cell structure, the fuel manifold 131 of the two separators 20 communicates to form a fuel flow path for supplying and discharging fuel to the fuel electrode. Further, the oxidant manifolds 132 of the two separators 20 communicate with each other to form an oxidant flow path for supplying and discharging the oxidant to the oxidant electrode. In addition, the cooling manifold 133 of the two separators 20 communicates to form a cooling channel through which cooling water or the like flows.

  FIG. 3 shows an example of a fuel cell 40 (cell stack) composed of a plurality of single cells. The fuel cell 40 communicates with a fuel supply port 171 and a discharge port 172 communicating with the fuel flow channel, an oxidant supply port 181 and a discharge port 182 communicating with the oxidant flow channel, and a cooling flow channel. A cooling water supply port 191 and a discharge port 192.

  For the operation of the polymer electrolyte fuel cell, it is necessary to supply and discharge reaction gas, discharge water, and extract current. In addition, a coolant such as water needs to be supplied to the cell stack for reaction control.

That is, the polymer electrolyte fuel cell operates when hydrogen gas, which is a fluid, is supplied from a fuel supply port 171 and oxygen gas, which is a fluid, is supplied from an oxidant supply port 181, and current flows from an external circuit. It is taken out. At this time, a reaction shown in the following formula occurs in each electrode.
Fuel electrode reaction: H ₂ → 2H ⁺ + 2e ⁻ (1)
Oxidant electrode reaction: 2H ⁺ + 2e ⁻ + 1 / 2O ₂ → H ₂ O (2)
Overall reaction: H ₂ + 1 / 2O ₂ → H ₂ O
As described above, hydrogen (H ₂ ) becomes proton (H ⁺ ) on the fuel electrode, and this proton moves through the solid polymer electrolyte membrane to the oxidant electrode, and oxygen (O ₂ ) and oxidant on the oxidant electrode. Reacts to give water (H ₂ O).

In a methanol direct fuel cell (DMFC), which is a type of polymer electrolyte fuel cell, a methanol aqueous solution is supplied instead of hydrogen as a fuel. In this case, the reaction shown in the following formula is performed at each electrode. Has occurred. An oxygen reduction reaction (the same reaction as when hydrogen is used as fuel) occurs at the air electrode.
Fuel electrode reaction: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1 ′)
Air electrode reaction: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2 ′)
Overall reaction: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O
Furthermore, the cooling water is supplied from the cooling water supply port 191 to the fuel cell, whereby the temperature of the fuel cell is adjusted to an appropriate temperature for the reaction.

  Among the components constituting such a fuel cell, the fuel cell separator 20 has a plurality of gas supply / discharge grooves 2 formed on one or both sides of a thin plate-like body as shown in FIG. In addition, the manifold has a unique shape and functions to separate the fuel, oxidant, and cooling water flowing in the fuel cell so that they do not mix, and the electric energy generated by the fuel cell is sent to the outside. It plays an important role in transferring heat and radiating heat generated in the fuel cell to the outside.

  The fuel cell separator 20 is formed of a metal plate, a molding material containing graphite particles and a resin component, or the like. Of these, the fuel cell separator 20 formed of a molding material containing graphite particles and a resin component has been developed in recent years because it is easy to reduce the weight.

  In such a fuel cell, a potential difference is generated between the plurality of fuel cell separators 20 during operation of the fuel cell, and energization is generated between the separators 20 in the cooling flow path of the fuel cell. The vicinity of the 20 cooling manifolds 133 may corrode. If such corrosion progresses, the cooling water may eventually leak from the fuel cell. In order to suppress such energization, pure water is often used as the cooling water, but the metal constituting the piping through which the cooling water circulates, the metal in the fuel cell, the resin, etc. are eluted into the cooling water. It is inevitable that the conductivity of the cooling water will increase.

A technique for improving the corrosion resistance of the fuel cell separator 20 is proposed in Patent Document 1. Patent Document 1 discloses a plate-like molded article composed of 60 to 85% by weight of graphite powder having a particle size distribution with an average particle size of 50 μm or less and a maximum particle size of 100 μm or less and a thermosetting resin of 15 to 40% by weight, or curing thereof. A cured product having a material property having a specific resistance in the plane direction of 300 × 10 ⁻⁴ Ωcm or less, a ratio of specific resistance in the thickness direction / plane direction of 7 or less, and a bending strength of 300 kgf / cm ² or more. It is disclosed that a separator 20 for a polymer electrolyte fuel cell is obtained by performing groove processing or the like. Further, in Patent Document 1, the true specific gravity of graphite powder is 2.15 or more, the average lattice plane distance d002 by X-ray diffraction method is 0.34 nm or less, and the crystallite size Lc (002) is 30 nm or more. It is also disclosed that the corrosion current of the graphite-resin cured molded body is small (1 μA / cm ² or less under the measurement conditions described in Patent Document 1).

JP 2000-21421 A

  However, orientation (anisotropy) tends to occur in a molded body formed from a composition containing highly crystalline graphite. In particular, since the fuel cell separator has a complicated shape in which a gas supply / discharge groove and a manifold are formed, the orientation is particularly remarkable. When the orientation occurs in the fuel cell separator, a partial decrease in strength or conductivity is caused, which adversely affects the durability of the fuel cell separator and the characteristics of the fuel cell including the fuel cell separator. .

  Although Patent Document 1 describes that the ratio of the specific resistance in the thickness direction / plane direction is 7 or less regarding the orientation in the fuel cell separator, graphite having high crystallinity should be used. The orientation is not suppressed in consideration of the above. Furthermore, the technique described in Patent Document 1 merely reduces the ratio of the specific resistance in the thickness direction / plane direction, and suppresses partial orientation caused by the fuel cell separator having a complicated shape. It has not been. Furthermore, in the technique described in Patent Document 1, since the composition is formed into a plate shape and further subjected to grooving or the like, a multi-step process is required, leading to a deterioration in production efficiency.

  The present invention has been made in view of the above-mentioned reasons, and has a high corrosion resistance and a fuel cell separator in which the occurrence of partial orientation is suppressed, a manufacturing method thereof, and a fuel including the fuel cell separator. An object is to provide a battery.

A fuel cell separator according to the present invention is a fuel cell separator formed from a cured product of a molding material containing a thermosetting resin and graphite, and having a gas supply / discharge groove and a manifold. The true density of the graphite is 2.22 g / cm ³ or more, the graphite content is in the range of 70 to 80% by mass, the corrosion current is 10 μA / cm ² or less, and it is a plan view from the fuel cell separator. When two pieces having a size of 30 mm × 30 mm are cut out, the contact resistance ratio between the two pieces is in a range of 0.9 to 1.1 regardless of the position at which the piece is cut out.

The fuel cell separator manufacturing method according to the present invention includes forming a molding material containing a thermosetting resin and graphite, and molding the molding material to form a gas supply / discharge groove and a manifold. The fuel cell separator is manufactured by using graphite having a true density of 2.22 g / cm ³ or more as the graphite when the molding material is prepared, and the total solid content of the molding material. When the molding material is molded by adjusting the disk flow of the molding material to a range of 80 to 100 mm, the content of the graphite is 70 to 80% by mass. Then, the molding material is molded into the shape of the fuel cell separator in which the gas supply / discharge groove and the manifold are formed. Is cured.

  The fuel cell according to the present invention includes the fuel cell separator.

  ADVANTAGE OF THE INVENTION According to this invention, the corrosion resistance is high, and the fuel cell separator provided with this fuel cell separator provided with the separator for fuel cells in which generation | occurrence | production of the partial orientation was suppressed is provided.

It is a disassembled perspective view which shows the single cell structure of the fuel cell in an example of embodiment of this invention. (A) And (b) is sectional drawing which shows the compression molding die for forming the separator for fuel cells in an example of embodiment of this invention. It is a perspective view showing a fuel cell in an example of an embodiment of the invention.

  FIG. 1 shows an example of a polymer electrolyte fuel cell including a separator 20. A membrane-electrode assembly (MEA) 5 comprising an electrolyte 4 such as a solid polymer electrolyte membrane and a gas diffusion electrode (fuel electrode 31 and oxidant electrode 32) is interposed between the two separators 20 and 20. Thus, a unit cell (unit cell) is configured. A gasket 12 is interposed between the separator 20 and the electrolyte 4 of the membrane-electrode assembly 5. A battery body (cell stack) is formed by arranging several tens to several hundreds of unit cells.

  The separator 20 is formed with a gas supply / discharge groove 2 which is a flow path for hydrogen gas or the like as fuel and oxygen gas or the like as an oxidant.

  The separator 20 is composed of an anode side separator having a gas supply / discharge groove 2 only on one surface, and a cathode side separator having a gas supply / discharge groove 2 only on one side opposite to the anode side separator. Also good. By superposing the anode-side separator and the cathode-side separator, a separator 20 having gas supply / discharge grooves 2 on both sides as shown in FIG. 1 is formed. A channel through which cooling water flows may be formed between the anode side separator and the cathode side separator. In this case, a gasket is preferably interposed between the anode side separator and the cathode side separator.

  The outer periphery of the separator 20 surrounding the region where the gas supply / discharge groove 2 is formed has six manifolds 13 (two fuel manifolds 131, two oxidant manifolds 132, and two cooling manifolds). A manifold 133) is formed. Two fuel manifolds 131, 131 are formed, and each fuel manifold 131, 131 communicates with both ends of the gas supply / discharge groove 2 on the surface overlapping the fuel electrode 31 of the separator 20. Two oxidant manifolds 132, 132 are also formed, and each oxidant manifold 132, 132 communicates with both ends of the gas supply / discharge groove 2 on the surface overlapping the oxidant electrode 32 of the separator 20. Two cooling manifolds 133 are also formed on the outer peripheral portion. When the separator 20 is composed of an anode-side separator and a cathode-side separator, the cooling manifold 133 communicates with a flow path through which cooling water between the anode-side separator and the cathode-side separator flows.

  In the present embodiment, as shown in FIG. 1, a straight type gas supply / discharge groove 2 is formed in the separator 20. Generally, the gas supply / discharge groove 2 in the separator 20 includes a serpentine type groove having a bend and a straight type groove having no bend. Of course, in the separator 20 shown in FIG. 1, a serpentine type gas supply / discharge groove 2 may be formed in the separator 20.

The thickness of the separator 20 is formed in the range of 0.5-3.0 mm, for example. The width of the gas supply / discharge groove 2 of the separator 20 is, for example, 1.0 to 1.5 mm, and the depth is, for example, 0.5 to 1.5 mm. The opening area of the manifold 13 is formed in a range of 0.5 to 5.0 cm ² , for example.

  The gasket 12 is laminated on the outer peripheral portion of the separator 20 for sealing. The gasket 12 has an opening 15 for accommodating the fuel electrode 31 and the oxidant electrode 32 in the membrane-electrode assembly 5 at a substantially central portion, and the gas supply / discharge groove 2 of the separator 20 is formed in the opening 15. Exposed. The gasket 12 has a fuel through hole 141 at a position on the outer peripheral side of the opening 15 that matches the fuel manifold 131 of the separator 20, and an oxidant through hole 142 at a position that matches the oxidant manifold 132. Cooling through holes 143 are formed at positions that match the cooling manifold 133.

  The electrolyte 4 in the membrane-electrode assembly 5 also has a fuel through-hole 161 at a position that matches the fuel manifold 131 of the separator 20 on the outer peripheral portion thereof, and an oxidant for the position that matches the oxidant manifold 132. Cooling through holes 163 are formed at positions where the through holes 162 coincide with the cooling manifold 133, respectively.

  In this single cell structure, the fuel manifold 131 of the separator 20, the fuel through hole 141 of the gasket 12, and the fuel through hole 161 of the electrolyte 4 communicate with each other to supply and discharge fuel to the fuel electrode. A fuel flow path is configured. Further, the oxidant manifold 132 of the separator 20, the oxidant through hole 142 of the gasket 12, and the oxidant through hole 162 of the electrolyte 4 communicate with each other to supply and discharge the oxidant to the oxidant electrode. The oxidizing agent flow path is configured. Further, the cooling manifold 133 of the separator 20, the cooling through hole 143 of the gasket 12, and the cooling through hole 163 of the electrolyte 4 communicate with each other, thereby forming a cooling channel through which cooling water or the like flows.

  The fuel electrode 31, the oxidant electrode 32, and the electrolyte 4 are formed of a known material corresponding to the type of fuel cell. In the case of a polymer electrolyte fuel cell, the fuel electrode 31 and the oxidant electrode 32 are configured by supporting a catalyst on a substrate such as carbon cloth, carbon paper, or carbon felt. Examples of the catalyst in the fuel electrode 31 include a platinum catalyst, a platinum / ruthenium catalyst, and a cobalt catalyst. Examples of the catalyst in the oxidant electrode 32 include a platinum catalyst and a silver catalyst. In the case of a solid polymer fuel cell, the electrolyte 4 is formed of, for example, a proton conductive polymer membrane. In particular, in the case of a methanol direct fuel cell, for example, the proton conductivity is high, and the electronic conductivity and methanol permeability are high. It is formed from a fluorine resin or the like that is hardly shown.

  The gasket 12 is, for example, natural rubber, silicone rubber, SIS copolymer, SBS copolymer, SEBS, ethylene-propylene rubber, ethylene-propylene-diene rubber (EPDM), acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber (HNBR). ), A rubber material selected from chloroprene rubber, acrylic rubber, fluorine rubber, and the like. This rubber material may contain a tackifier.

  When laminating the gasket 12 on the separator 20, for example, the gasket 12 formed in a sheet shape or a plate shape in advance is bonded or bonded to the separator 20. The gasket 12 may be laminated on the separator 20 by molding a material for forming the gasket 12 on the surface of the separator 20. For example, an unvulcanized rubber material is applied to a predetermined position on the surface of the separator 20 by screen printing or the like, and a desired shape is formed on the predetermined position on the surface of the separator 20 by vulcanizing the coating film of the rubber material. The gasket 12 is formed. In the vulcanization, heating, irradiation with radiation such as an electron beam, or other appropriate vulcanization methods are employed. In this case, the gasket 12 is easily laminated even on the thin separator 20. Further, the separator 20 is set in a mold, and an unvulcanized rubber material is injected into a predetermined position on the surface of the separator 20 and the rubber material is heated and vulcanized. A gasket 12 having a desired shape may be formed at a predetermined position on the surface of the separator 20. Thus, when the gasket 12 is formed by die molding, a molding method such as transfer molding, compression molding, injection molding or the like can be employed.

Separator 20 is formed from a cured product of a molding material containing a thermosetting resin and graphite particles. The true density of the graphite particles contained in the separator 20 is 2.22 g / cm ³ or more, and the content of the graphite particles with respect to the whole separator 20 is in the range of 70 to 80% by mass. Furthermore, the corrosion current of the separator 20 is 10 μA / cm ² or less. Details of the molding material and the thermosetting resin and graphite particles contained therein will be described later.

  Graphite particles having a high true density have high crystallinity, and when the separator 20 contains such graphite particles, the corrosion current of the separator 20 becomes low. For this reason, the corrosion resistance of the separator 20 is increased. In particular, even when the cooling water flows through the cooling manifold 133 of the separator 20 incorporated in the fuel cell, corrosion hardly occurs on the inner surface of the cooling manifold 133. Become. Details of the graphite particles will be described later.

  When the graphite particle content is in the range of 70 to 80% by mass, the corrosion current of the separator 20 is reduced, the separator 20 is provided with excellent conductivity and mechanical strength, and the separator 20 has high gas permeability. Sex is imparted.

The corrosion current of the separator 20 needs to be 10 μA / cm ² or less as described above. Corrosion current means that a separator 20 as a working electrode and a platinum electrode as a counter electrode are arranged at intervals of 30 mm in an aqueous solution of sodium sulfate adjusted to an electric conductivity of 200 μS / cm, and a liquid temperature of 80 ° C. is 20 V between the electrodes. The value of the current flowing between the electrodes, measured when a voltage is applied for 48 hours. Thus, the corrosion resistance of the separator 20 becomes especially high because the corrosion current of the separator 20 is small. The corrosion current of the separator 20 can be appropriately adjusted by adjusting the content of the graphite particles in the range of 70 to 80% by mass according to the constituent components of the molding material.

  When two small pieces having a size of 30 mm × 30 mm in plan view are cut out from the separator 20, the contact resistance ratio between the two pieces is in the range of 0.9 to 1.1 regardless of the position at which the small pieces are cut out. (If the contact resistance of one small piece is 1, the contact resistance of the other small piece is in the range of 0.9 to 1.1). A small piece is obtained by cutting the separator 20 in the thickness direction, and the plan view means observing the separator 20 in the thickness direction. In this case, variation in contact resistance in the separator 20 is reduced, and in such a separator 20, partial orientation of the graphite particles is suppressed. Thereby, the favorable electrical property of the separator 20 is ensured. Furthermore, the high mechanical strength of the separator 20 is also ensured by suppressing the partial orientation of the graphite particles in the separator 20.

  The contact resistance is determined by placing the carbon paper on the top and bottom of the small piece, further placing the copper plates on the top and bottom, and applying a surface pressure of 1.0 MPa in the up and down direction. It is a value calculated from the result of measuring with a voltmeter and measuring the current flowing between two copper plates with an ammeter.

  The molding material used for manufacturing such a separator 20 contains a resin component and graphite particles.

The molding material preferably does not contain a primary amine and a secondary amine. That is, it is preferable that this molding material does not contain a compound having substituents —NH and —NH ₂ . Furthermore, it is preferable that the molding material does not contain a tertiary amine. Thus, if the molding material does not contain an amine, the separator 20 formed from the molding material does not poison the platinum catalyst in the fuel cell, and the electromotive force when the fuel cell is used for a long time. Reduction is suppressed.

  The resin component contains a thermosetting resin. The thermosetting resin preferably contains at least one of an epoxy resin and a thermosetting phenol resin. Epoxy resins and thermosetting phenol resins are excellent in that they have a good melt viscosity and a small amount of impurities, in particular, a small amount of ionic impurities.

  The content of the epoxy resin and the thermosetting phenol resin with respect to the total amount of the thermosetting resin is preferably in the range of 50 to 100% by mass. It is particularly preferable if the thermosetting resin contains only an epoxy resin, only a thermosetting phenol resin, or only an epoxy resin and a thermosetting phenol resin.

  The epoxy resin is preferably solid, and particularly preferably has a melting point in the range of 70 to 90 ° C. Thereby, the change of material decreases and the handleability of the molding material at the time of shaping | molding improves. When this melting point is less than 70 ° C., aggregation tends to occur in the molding material, and the handleability may be lowered. If a resin having a low melt viscosity is selected as the epoxy resin, the molding material and the separator 20 can be highly filled with graphite particles while maintaining good moldability of the molding material. In addition, a part of epoxy resin may be liquid within the range where the said effect | action is exhibited.

  As the epoxy resin, an ortho cresol novolak type epoxy resin, a bisphenol type epoxy resin, a biphenyl type epoxy resin, a phenol aralkyl type epoxy resin having a biphenylene skeleton, or the like is preferably used. This ortho-cresol novolac type epoxy resin, bisphenol type epoxy resin, and phenol aralkyl type epoxy resin having a biphenylene skeleton are excellent in that they have a good melt viscosity and a small amount of impurities, and in particular, a small amount of ionic impurities.

  In particular, the epoxy resin is composed only of an ortho cresol novolac type epoxy resin, or at least one selected from an ortho cresol novolac type epoxy resin, a bisphenol type epoxy resin, a biphenyl type epoxy resin, and a phenol aralkyl type epoxy resin having a biphenylene skeleton. It is preferable that the component (it is called 1st component) which becomes. When the ortho-cresol novolac type epoxy resin is an essential component, the moldability of the molding material is improved and the heat resistance of the separator 20 is improved. Furthermore, manufacturing costs can be reduced. The proportion of the ortho-cresol novolac type epoxy resin in the first component is preferably in the range of 50 to 100% by mass from the viewpoint of improving the moldability, improving the heat resistance of the separator 20, and reducing the manufacturing cost. In particular, the range is preferably 50 to 70% by mass.

  It is also preferable to use a bisphenol type epoxy resin, a biphenyl type epoxy resin, or a phenol aralkyl type epoxy resin having a biphenylene skeleton together with the orthocresol novolac type epoxy resin. In this case, the melt viscosity of the molding material is further reduced, and the toughness can be improved when a thinner separator 20 is produced.

  In particular, when a bisphenol F type epoxy resin is used, the viscosity of the molding material is reduced, and the moldability of the molding material is particularly improved. In this case, the content of the bisphenol F-type epoxy resin in the first component is preferably in the range of 30 to 50% by mass.

  When a biphenyl type epoxy resin is used, since this biphenyl type resin has a low melt viscosity, the fluidity of the molding material is remarkably improved, and the thin moldability of the molding material is particularly improved. In this case, the content of the biphenyl type epoxy resin in the first component is preferably in the range of 30 to 50% by mass.

  When a phenol aralkyl type epoxy resin having a biphenylene skeleton is used, the strength and toughness of the separator 20 can be improved, and the hygroscopicity of the separator 20 can be further reduced. For this reason, the stability of the mechanical characteristics, electrical conductivity, and characteristics during long-term use of the separator 20 is improved. In this case, the ratio of the phenol aralkyl type epoxy resin having a biphenylene skeleton in the first component is preferably in the range of 30 to 50% by mass.

  The content of the first component with respect to the total amount of the thermosetting resin in the molding material is preferably in the range of 50 to 100% by mass.

  The first component is contained in the molding material as at least a part of the epoxy resin in the thermosetting resin. That is, the thermosetting resin other than the first component is selected from, for example, an epoxy resin other than the first component, a thermosetting phenol resin, a vinyl ester resin, a polyimide resin, an unsaturated polyester resin, a diallyl phthalate resin, and the like. One or more kinds of resins may be used. However, it is desirable not to use a resin containing an ester bond because it may hydrolyze in an acid resistant environment. A polyimide resin is also suitable as the thermosetting resin in that it contributes to improving the heat resistance and acid resistance of the separator 20. As the polyimide resin, it is particularly preferable to use a bismaleimide resin, and it is preferable to use 4,4-diaminodiphenyl bismaleimide, for example. When 4,4-diaminodiphenyl bismaleimide is used, the heat resistance of the separator 20 is further improved.

  When a thermosetting phenol resin is used, it is particularly preferable to use a phenol resin that undergoes a polymerization reaction by ring-opening polymerization. Examples of such phenol resins include benzoxazine resins. In this case, since gas due to dehydration is not generated in the molding process of the molding material, voids are not generated in the molded product, so that a decrease in gas permeability of the separator 20 is suppressed. It is also preferable to use a resol-type phenol resin, for example, a resol-type phenol having a structure of ortho-ortho 25-35%, ortho-para 60-70%, para-para 5-10% by 13C-NMR analysis. A resin is preferably used. The resol resin is usually in a liquid state, but since the softening point of the resol type phenol resin can be easily adjusted, a resol type phenol resin having a melting point of 70 to 90 ° C. can be easily obtained. By using a resol type phenolic resin having a melting point of 70 to 90 ° C., alteration of the molding material is suppressed, and the handleability of the molding material during molding is improved. When this melting point is less than 70 ° C., aggregation tends to occur in the molding material, and the handleability may be lowered.

  Other resins other than the epoxy resin and the thermosetting phenol resin may be used in combination. For example, one or more kinds of resins selected from polyimide resins, unsaturated polyester resins, diallyl phthalate resins, vinyl ester resins, and the like may be used. However, it is desirable not to use a resin containing an ester bond because it may hydrolyze in an acid resistant environment.

  A polyimide resin is also suitable as the thermosetting resin in that it contributes to improving the heat resistance and acid resistance of the separator 20. As such a polyimide resin, a bismaleimide resin and the like are particularly preferable, and specific examples thereof include 4,4-diaminodiphenyl bismaleimide. By using such a resin in combination, the heat resistance of the separator 20 can be further improved.

  When an epoxy resin is used, the resin component preferably contains a curing agent, and this curing agent preferably contains a phenolic compound. Examples of the phenol compound include novolak type phenol resins, cresol novolac type phenol resins, polyfunctional phenol resins, aralkyl-modified phenol resins, and the like.

  The content of the phenolic compound relative to the total amount of the curing agent is determined depending on the amount of the epoxy resin used. Further, it is particularly preferable that the curing agent is only a phenol compound.

  When a curing agent other than a phenol compound is used, a non-amine compound is preferably used as the curing agent. In this case, the electrical conductivity of the separator 20 is maintained at a high level, and poisoning of the fuel cell catalyst is suppressed. It is also preferred that no acid anhydride compound is used as the curing agent. When an acid anhydride compound is used, the cured product is hydrolyzed in an acidic environment such as a sulfuric acid acidic environment, causing a decrease in the electrical conductivity of the separator 20 or elution of impurities from the separator 20. May increase.

  When an epoxy resin is used as the thermosetting resin, the epoxy resin in the thermosetting resin and the phenolic compound in the curing agent have an equivalent ratio of the epoxy resin to the phenolic compound of 0.8 to 1.2. It is preferable to mix | blend so that it may become a range.

The graphite particles improve the electrical conductivity of the separator 20 by reducing the electrical specific resistance of the separator 20. As the graphite particles, graphite particles having a true density of 2.22 g / cm ³ or more are used. Graphite particles with a high true density have high crystallinity, and when the separator 20 contains such graphite particles, the corrosion current of the separator 20 is lowered, and thus the corrosion resistance of the separator 20 is enhanced. The true density of the graphite particles is particularly preferably 2.25 g / cm ³ or more. There is no particular limitation on the upper limit of the true density of the graphite particles, considering the true density of the available graphite particles, it is preferable that the true density of 2.32 g / cm ³ or less, 2.30 g / cm ³ or less More preferably, the true density of the graphite particles is a value measured by a constant volume expansion method. The true density of the graphite particles is, for example, by using a dry automatic density meter (Accuic II 1340) manufactured by Shimadzu Corporation. Helium gas is used for the measurement, the introduction pressure (gauge pressure) is 134.45 kPag, and the number of purges is 10 times. Measured under the conditions of 10 run times and equilibrium determination pressure (gauge pressure) of 0.345 kPag.

  Such high-density graphite particles can be appropriately selected from natural graphite powder. As the graphite particles, artificial graphite powder having high crystallinity (for example, artificial graphite powder subjected to a treatment for improving crystallinity) may be used.

  The graphite particles are preferably purified. In this case, since ash and ionic impurities in the graphite particles are low, elution of impurities from the separator 20 is suppressed. The ash content in the graphite particles is preferably 0.05% by mass or less. If the ash content exceeds 0.05% by mass, the characteristics of the fuel cell produced by using the separator 20 may be deteriorated.

  The average particle size of the graphite particles is preferably in the range of 15 to 100 μm. When the average particle size is 10 μm or more, the moldability of the molding material is improved, and when the average particle size is 100 μm or less, the surface smoothness of the separator 20 is improved. In order to improve the moldability, the average particle size is preferably 30 μm or more, and the surface smoothness of the separator 20 is particularly improved so that the arithmetic average height Ra ( In order for JIS B0601: 2001) to be in the range of 0.4 to 1.6 μm, particularly less than 1.0 μm, the average particle size is preferably 70 μm or less. In particular, the average particle size is preferably in the range of 30 to 70 μm.

  In particular, when the thin separator 20 is produced, the graphite particles preferably have a particle size that passes through a 100 mesh sieve (aperture 150 μm). If the graphite particles contain particles that do not pass through a 100-mesh sieve, graphite particles having a large particle size will be mixed in the molding material, especially when the molding material is molded into a thin sheet. The moldability of the will be reduced.

  The aspect ratio of the graphite particles is preferably 10 or less. In this case, anisotropy is suppressed in the separator 20 and deformation such as warpage is also suppressed.

  Regarding the reduction of the anisotropy of the separator 20, the flow direction of the molding material at the time of molding in the separator 20 (direction perpendicular to the thickness direction of the separator 20) and the direction perpendicular to the flow direction (thickness of the separator 20). The ratio of the contact resistance with respect to (direction) is preferably 2 or less.

  It is also preferable that the entire graphite particles have particularly two or more particle size distributions, that is, the entire graphite particles are a mixture of two or more particle groups having different average particle diameters. In this specification, the particle group means an aggregate of a plurality of particles constituting at least a part of the entire graphite particle. It is preferable that the entire graphite particles are a mixture of a particle group having an average particle diameter of 1 to 50 μm and a particle group having an average particle diameter of 30 to 100 μm. When graphite particles having such a particle size distribution are used, it is expected that particles having a large particle size have a small surface area, so that the molding material can be kneaded even if the resin component content is small. . Further, the contact between the particles is improved by the particles having a small particle size, and the strength of the separator 20 is also expected to be improved. As a result, the density of the separator 20 is improved, the conductivity is improved, the gas impermeability is improved, and the strength is improved. Improvement of performance such as improvement is achieved. The mixing ratio of the particle group having an average particle diameter of 1 to 50 μm and the particle group having an average particle diameter of 30 to 100 μm is appropriately adjusted, and the mixing mass ratio of the former to the latter is particularly 40:60 to 90:10, particularly 65. : It is preferable that it is 35-85: 15.

  The average particle size of the graphite particles is a volume average particle size measured by a laser diffraction / scattering method with a laser diffraction / scattering particle size analyzer (such as Microtrack MT3000II series manufactured by Nikkiso Co., Ltd.).

  The ratio of the graphite particles in the molding material is preferably in the range of 70 to 80% by mass with respect to the entire solid content in the molding material. As described above, when the ratio of the graphite particles is 70% by mass or more, the separator 20 is provided with sufficiently excellent conductivity, and the mechanical strength of the separator 20 is sufficiently improved. Further, when this ratio is 80% by mass or less, sufficiently excellent moldability is imparted to the molding material and sufficiently excellent gas permeability is imparted to the separator 20.

  The molding material may contain additives such as a curing catalyst, a wax (release agent), and a coupling agent as necessary.

  Although it does not restrict | limit especially as a curing catalyst (curing accelerator), In order that a molding material does not contain a primary amine and a secondary amine, it is preferable that a non-amine type compound is used. For example, amine-based diaminodiphenylmethane and the like are not preferable because the residue may poison the fuel cell catalyst. In addition, imidazoles are less preferred because they easily release chlorine ions after curing, and may cause impurity elution.

  However, the weight loss when heated under the conditions of a measurement start temperature of 30 ° C., a heating rate of 10 ° C./min, a holding temperature of 120 ° C., and a holding time of 30 minutes at the holding temperature is 5% or less, and is in the second place. The use of a substituted imidazole having a hydrocarbon group is preferable in that the storage stability of the molding material is improved. Furthermore, particularly when the thin separator 20 is produced, the volatility of the solvent when the sheet-like separator 20 is formed from the molding material prepared in a varnish shape, the smoothness of the separator 20 and the like are good. Become. As this substituted imidazole, a substituted imidazole having 6 to 17 carbon atoms in the hydrocarbon group at the 2-position is particularly preferably used. Specific examples thereof include 2-undecylimidazole, 2-heptadecylimidazole, 2- Examples include phenylimidazole and 1-benzyl-2-phenylimidazole. Of these, 2-undecylimidazole and 2-heptadecylimidazole are preferred. These compounds are used alone or in combination of two or more. The content of such a substituted imidazole can be adjusted as appropriate, whereby the molding curing time can be adjusted. The content of the substituted imidazole is preferably in the range of 0.5 to 3% by mass with respect to the total amount of the thermosetting resin and the curing agent in the molding material.

  Further, a phosphorus compound is preferably used as the curing catalyst. A phosphorus compound and the substituted imidazole may be used in combination. An example of a phosphorus compound is triphenylphosphine. When such a phosphorus compound is used, elution of chlorine ions from the separator 20 is suppressed.

  It is also preferred that the molding material contains a compound represented by the following structural formula (1) as a curing accelerator. In this case, the moisture resistance of the separator 20 is improved. In addition, the compound represented by the structural formula (1) does not cause a decrease in the glass transition temperature of the separator 20, a decrease in rigidity during heat, a deterioration in continuous formability, and the like. Rather, by using the compound represented by the structural formula (1), the glass transition temperature of the separator 20 is increased, the thermal rigidity is improved, and the releasability at the time of molding of the molding composition is improved. Thus, the continuous formability can be improved.

  Furthermore, ionic impurities are not easily eluted from the compound represented by the structural formula (1). For this reason, by using the compound represented by the structural formula (1), elution of ionic impurities from the separator 20 is suppressed, and deterioration of characteristics such as a decrease in starting voltage of the fuel cell due to the elution of impurities is suppressed. . It is assumed that the elution of ionic impurities from the compound represented by the structural formula (1) hardly occurs because the acid dissociation constant (pKa) of this compound is small.

  The ratio of the compound represented by the structural formula (1) to the total amount of the curing accelerator is preferably in the range of 20 to 100% by mass. If this proportion is less than 20% by mass, the glass transition temperature (Tg) of the separator 20 may not be sufficiently increased.

  The content of such a curing catalyst is appropriately adjusted, but is preferably in the range of 0.5 to 3 parts by mass with respect to the epoxy resin in the molding material.

  Although it does not restrict | limit especially as a coupling agent, In order that a molding material does not contain a primary amine and a secondary amine, it is preferable that aminosilane is not used. If aminosilane is used, the fuel cell catalyst may be poisoned, which is not preferable. It is also preferred that mercaptosilane is not used as a coupling agent. Similarly, when this mercaptosilane is used, the fuel cell catalyst may be poisoned.

  Examples of coupling agents include silicon-based silane compounds, titanate-based, and aluminum-based coupling agents. For example, epoxy silane is suitable as a silicon-based coupling agent.

  When the epoxysilane coupling agent is used, the amount used is preferably in the range where the content in the solid content of the molding material is 0.5 to 1.5% by mass. In this range, the coupling agent can be sufficiently suppressed from bleeding on the surface of the separator 20.

  The coupling agent may be previously attached to the surface of the graphite particles by spraying or the like. The addition amount in that case is appropriately set in consideration of the specific surface area of the graphite particles and the coatable area per unit mass of the coupling agent (area that can be coated with the coupling agent). The addition amount of the coupling agent is preferably adjusted so that the total amount of the area that can be coated with the coupling agent is in the range of 0.5 to 2 times the total amount of the surface area of the graphite particles. In this range, the bleeding of the coupling agent on the surface of the separator 20 is sufficiently suppressed, thereby suppressing contamination of the mold surface.

  Although it does not restrict | limit especially as a wax (internal mold release agent), The internal mold release agent which phase-separates without being incompatible with the thermosetting resin and hardening | curing agent in a molding material at 120-190 degreeC may be used. preferable. Examples of such an internal mold release agent include at least one selected from polyethylene wax, carnauba wax, and long-chain fatty acid wax. Such an internal release agent is phase-separated from the thermosetting resin and the curing agent in the molding process of the molding material, so that the release property of the separator 20 is improved.

  The content of the internal mold release agent is appropriately set according to the complexity of the shape of the separator 20, the groove depth, the ease of release from the mold surface such as the draft, etc., but the solid content in the molding material It is preferably in the range of 0.1 to 2.5% by mass with respect to the total amount. When the content is 0.1% by mass or more, the separator 20 exhibits sufficient releasability at the time of molding the mold, and when the content is 2.5% by mass or less, the hydrophilicity of the separator 20 Is kept high enough. The content of the wax is more preferably in the range of 0.1 to 1% by mass, and particularly preferably in the range of 0.1 to 0.5% by mass.

  The content of ionic impurities in the separator 20 is preferably a sodium content of 5 ppm or less and a chlorine content of 5 ppm or less in terms of mass ratio with respect to the total amount of the molding material. For this purpose, it is preferable that the content of ionic impurities in the molding material is a sodium content of 5 ppm or less and a chlorine content of 5 ppm or less by mass ratio with respect to the total amount of the molding material. In this case, the elution of the ionic impurities from the separator 20 is suppressed, and therefore, a decrease in characteristics such as a decrease in starting voltage of the fuel cell due to the elution of impurities is suppressed.

  In order to reduce the content of ionic impurities in the separator 20 and the molding material as described above, each component of each component such as a thermosetting resin, a curing agent, graphite, and other additives constituting the molding material. The content of ionic impurities is preferably a sodium content of 5 ppm or less and a chlorine content of 5 ppm or less by mass ratio with respect to each component.

  The content of the ionic impurities is derived based on the amount of the ionic impurities in the extraction water containing the ionic impurities eluted from the object (molding material, thermosetting resin, etc.). The extraction water is heated in 90 ° C. for 50 hours in a state where the object is put in the ion-exchanged water so that the object has a ratio of 100 ml of ion-exchanged water to 10 g of the object. It can be obtained. Ionic impurities in the extracted water are evaluated by ion chromatography. The amount of ionic impurities in the target is derived by converting the amount of ionic impurities in the extracted water into a mass ratio with respect to the target.

  The molding material is preferably prepared such that the TOC (total organic carbon) of the separator 20 formed from this composition is 100 ppm or less.

TOC is a solution obtained by putting separator 20 in ion-exchanged water at a ratio of 100 ml of ion-exchanged water with respect to 10 g of mass of separator 20, and heating the ion-exchanged water and separator 20 at 90 ° C. for 50 hours. It is a numerical value measured from Such a TOC can be measured by, for example, a total organic carbon analyzer “TOC-50” manufactured by Shimadzu in accordance with JIS K0102. In the measurement, the CO ₂ concentration generated by the combustion of the sample is measured by a non-dispersive infrared gas analysis method, thereby quantifying the carbon concentration in the sample. By measuring the carbon concentration, the organic substance concentration contained in the separator 20 is indirectly measured. When inorganic carbon (IC) and total carbon (TC) in a sample are measured, total organic carbon (TOC) is derived from the difference between total carbon and inorganic carbon (TC-IC).

  When the TOC is 100 ppm or less, deterioration of the characteristics of the fuel cell is further suppressed.

  The value of TOC can be reduced by selecting a high-purity component as each component constituting the molding material, adjusting the equivalent ratio of the resin, or performing a post-curing treatment during molding.

  There is a possibility that a metal component is mixed as an impurity in the raw material component, and a metal component derived from the raw material component or a metal component mixed during manufacture may be mixed as an impurity in the molding material and the separator 20. There is sex. If a metal component is mixed in the separator 20, the corrosion current of the separator 20 increases. Therefore, when the separator 20 is manufactured, it is preferable to perform a treatment for reducing the content of the metal component on at least one of the raw material component, the molding material, and the separator 20. In this case, the content of the metal component of the separator 20 is reduced, thereby further reducing the corrosion current of the separator 20. In particular, at least the molding material is preferably subjected to a treatment for reducing the content of the metal component.

  An example of a process for reducing the content of the metal component relative to the raw material component is a process of attracting the metal component in the raw material component using a magnet. Among the raw material components, the treatment for reducing the content of the metal component, particularly with respect to the graphite particles, includes a treatment for washing the graphite particles with a strongly acidic solution having a pH of 2 or less. As the strongly acidic solution, for example, aqua regia obtained by mixing concentrated nitric acid having a concentration of 69% by mass and concentrated hydrochloric acid having a concentration of 36% by mass in a ratio of 1: 3 by volume ratio, hydrochloric acid having a concentration of 15% by mass or more, At least one selected from sulfuric acid having a concentration of 15% by mass or more and nitric acid having a concentration of 15% by mass or more can be used. In this case, the content of the metal component in the graphite particles is easily reduced. The concentration of the hydrochloric acid water, the sulfuric acid water and the nitric acid water is preferably 30% by mass or less from the viewpoint of operability.

  The treatment for reducing the metal component content for the molding material is similar to the treatment for reducing the metal component content for the raw material component, and the metal component in the molding material is sucked using a magnet. And the like.

  The molding material is prepared by blending the raw material components as described above, and the separator 20 is obtained by molding the molding material. The molding material is formed into an appropriate shape such as a granular shape or a sheet shape.

  When the molding material is granular, the raw material components as described above are stirred and mixed with, for example, a stirrer or the like, or further sized with a granulator or the like, whereby a molding material is obtained.

  The molding material may be in the form of a sheet. In particular, when a thin separator 20 is produced, it is preferable to use a sheet-shaped molding material. When a sheet-shaped molding material is used, for example, a thin separator 20 having a thickness of 0.2 to 1.0 mm can be easily obtained, and the thickness accuracy of the separator 20 is increased.

  In order to prepare the sheet-shaped molding material, first, a liquid composition containing the raw material components as described above is prepared. The liquid composition contains a solvent as necessary. As the solvent, for example, polar solvents such as methyl ethyl ketone, methoxypropanol, N, N-dimethylformamide, dimethyl sulfoxide are preferable. Only 1 type may be used for a solvent, or 2 or more types may be used together. The amount of the solvent used is appropriately set in consideration of moldability and the like, but is preferably adjusted so that the viscosity of the liquid composition is in the range of 1000 to 5000 cps. In addition, as above-mentioned, the solvent should just be used as needed, and when the thermosetting resin in a raw material component is a liquid resin, a solvent does not need to be used.

  By forming this liquid composition into a sheet shape, a sheet-shaped molding material is obtained. The liquid composition is formed into a sheet shape by, for example, casting (progressive) molding, and is dried by heating with casting, or is semi-cured to obtain a sheet-shaped molding material. . This sheet-shaped molding material is formed into an appropriate dimension by cutting (cutting) or punching into a predetermined plane dimension as necessary.

  When a sheet-shaped molding material is formed by a casting method, a plurality of types of film thickness adjusting means can be applied. The casting method using such a plurality of types of film thickness adjusting means is realized by using a multi-coater that has already been put into practical use, for example. As a film thickness adjusting means for casting, it is preferable to use a slit knife and at least one of a doctor knife and a wire bar, that is, either one or both. The thickness of the sheet-shaped molding material is preferably 0.05 mm or more, and more preferably 0.1 mm or more. The thickness is preferably 0.5 mm or less, and more preferably 0.3 mm or less. Thus, when the thickness of the sheet-shaped molding material is 0.5 mm or less, the separator 20 can be made thinner and lighter, and the cost thereof can be reduced. The residual solvent inside the sheet-shaped molding material when using is effectively suppressed. Further, when this thickness is less than 0.05 mm, the advantage in producing the separator 20 is not sufficiently exhibited, and this thickness is preferably 0.1 mm or more in consideration of moldability.

  The separator 20 is obtained by molding the molding material. As a molding method, compression molding is preferably employed.

  FIG. 2 shows an example of a molding die for compression molding. The molding die includes a first template 301 and a second template 302 that face each other. The first template 301 is formed with a recess 303 to which a molding material is supplied, and a protrusion 304 corresponding to the gas supply / discharge groove 2 formed in the separator 20 is formed on the bottom surface of the recess 303. Is formed. Further, the first template 301 is formed with a plurality of through holes 305 that open at the bottom surface of the recess 303.

  The molding die also includes an ejector pin 306 and an ejector plate 307. Ejector pins 306 are inserted into the through holes in the first template 301. The plurality of ejector pins 306 are connected to the ejector plate 307.

  On the second template plate 302, protrusions 304 corresponding to the gas supply / discharge grooves 2 formed in the separator 20 are formed on the surface of the first template plate 301 that faces the recess 303. Furthermore, a plurality of convex portions 308 corresponding to the plurality of manifolds 13 of the separator 20 are formed on the second template 302.

  Thus, when the protrusions 304 are formed on both the first template 301 and the second template 302, the separator 20 in which the gas supply / discharge grooves 2 are formed on both sides by compression molding is obtained. It is done. In the case of obtaining the separator 20 in which the gas supply / discharge groove 2 is formed only on one side, the protrusion 304 is formed on only one of the first template 301 and the second template 302. .

  When the first template plate 301 and the second template plate 302 are clamped, a space (molding) that matches the shape of the separator 20 is formed between the first template plate 301 and the second template plate 302. A space 309) is formed.

  In manufacturing the separator 20 by compression molding, an appropriate amount of molding material is disposed in the recess 303 of the first template 301. When a sheet-shaped molding material is used, one sheet-shaped molding material is used according to the thickness of the separator 20 or the like, or a plurality of sheet-shaped molding materials are formed on the recess 303. Are superimposed.

  The first template 301 and the second template 302 are maintained at a moldable temperature. The molding material is compression-molded by clamping the first template 301 and the second template 302 (FIG. 2A). Thereby, the separator 20 is formed in the molding space 309. The molding conditions are appropriately adjusted according to the composition of the molding material. For example, the molding conditions are adjusted to a molding temperature of 120 to 190 ° C., a molding pressure of 1 to 40 MPa, and a molding time of 1 to 10 minutes.

  When the separator 20 is thus formed in the molding space 309, the first template 301 and the second template 302 are cooled as necessary, and the first template 301 and the second template are further cooled. 302 is opened (FIG. 2B). As a result, the separator 20 remains in the recess 303 of the first template 301. Subsequently, when the ejector plate 307 is driven, the ejector pin 306 protrudes from the bottom surface of the recess 303 toward the recess 303, whereby the separator 20 is taken out from the recess 303.

  When the separator 20 is manufactured by compression molding the molding material, the disk flow of the molding material is preferably 80 to 100 mm. In the disk flow, 3 g of a molding material is densely arranged at one place on a flat surface, and a long diameter (longest length) of a molded body formed when this is compressed for 30 seconds under conditions of a temperature of 170 ° C. and a pressure of 5 MPa. Diameter). The disk flow of the molding material can be adjusted as appropriate by changing the composition of the molding material. For example, if the graphite content in the molding material decreases, the disk flow increases, and if the graphite content increases, the disk flow decreases. If the content of the curing accelerator in the molding material decreases, the disk flow increases. If the content of the curing accelerator in the molding material increases, the disk flow decreases. Furthermore, when the types of components in the molding material are appropriately changed, the disk flow increases or decreases accordingly.

  Thus, when the disk flow of the molding material is 80 to 100 mm, the fluidity of the molding material during compression molding is increased. Therefore, although the molding material contains highly crystalline graphite particles, and the separator 20 having a complicated shape is produced from the molding material by compression molding, the graphite particles are oriented in the separator 20. It becomes difficult to do. As a result, partial orientation in the separator 20 is suppressed, and when two small pieces having a size of 30 mm × 30 mm in plan view are cut out from the separator 20, the contact resistance between the small pieces is cut out from any position. The ratio is in the range of 0.9 to 1.1.

  The separator 20 is preferably subjected to blasting or the like to remove the surface skin layer and adjust the surface roughness of the separator 20.

  The arithmetic average height Ra (JIS B0601: 2001) of the surface of the separator 20 is preferably in the range of 0.4 to 1.6 μm. In this case, the corrosion current of the separator 20 is further reduced, and the corrosion resistance of the separator 20 is further improved. Furthermore, gas leakage at the joint between the separator 20 and the gasket 12 is suppressed. For this reason, it is not necessary to mask the part joined to the gasket 12 in the separator 20 during the wet blasting process, and the production efficiency of the separator 20 is improved. It is difficult for the arithmetic average height Ra to be less than 0.4 μm, and if this value is greater than 1.6 μm, the gas leak may not be sufficiently suppressed. The arithmetic average height Ra of the surface of the separator 20 is particularly preferably 1.2 μm or less. Further, when the arithmetic average height Ra of the surface of the separator 20 is less than 1.0 μm, the gas leak is particularly suppressed, and even when the fastening force at the time of manufacturing the cell stack is lowered as the separator 20 is thinned, Gas leakage is sufficiently suppressed. As described above, the arithmetic average height Ra of the surface of the separator 20 is preferably 0.4 μm or more, and more preferably 0.6 μm or more.

The contact resistance on the surface of the separator 20 is preferably 15 mΩcm ² or less. In this case, the function of the separator 20 for transmitting the electric energy generated by the fuel cell to the outside is maintained at a high level.

  In the blasting process, it is preferable that the separator 20 is subjected to a wet blasting process, and in this process, a metal component is attracted by a magnet from a slurry containing abrasive grains such as alumina particles. There is a possibility that a metal component is mixed as an impurity in the abrasive grains used in the blasting process, and a metal component may be mixed in the slurry containing the abrasive grains during the blasting process. When blasting is performed using a slurry containing such a metal component, the metal component is driven from the abrasive grains onto the surface of the separator 20. However, when the metal component is attracted from the slurry by the magnet as described above and wet blasting is performed with the abrasive grains, the metal component is difficult to adhere to the separator 20 during the blasting. That is, while the skin layer is removed and the surface roughness is adjusted by the wet blasting process, metal components such as metal foreign matters contained in the abrasive grains in the slurry are less likely to be driven into the separator 20 during the wet blasting process. In the wet blasting process, the slurry is repeatedly used while being circulated, and when the metal component is attracted from the slurry by a magnet or the like during the circulation of the slurry, the metal component is attracted by the magnet from the abrasive grains in the slurry. However, wet blasting is performed by the abrasive grains.

  Furthermore, the metal component may be attracted by the magnet from the separator 20 in the same manner as the processing for reducing the content of the metal component of the graphite particles. In this case, for example, the metal component is attracted from the separator 20 by arranging the separator 20 between the pair of magnets. Note that the metal component may be removed from the separator 20 by an appropriate method other than attraction using a magnet. However, the method of washing with a strong acid solution is not preferable because the resin constituting the separator 20 may be dissolved, and the ultrasonic cleaning may cause the graphite particles to be detached from the separator 20.

  In the separator 20 obtained as described above, the degree of adhesion of the metal component was determined by washing the separator 20 with 90 ° C. warm water for 1 hour, and then subjecting the separator 20 to heat drying at 90 ° C. for 1 hour. This is confirmed by observing the surface of the separator 20. If a metal component adheres to the separator 20, a metal oxide (rust) is generated on the surface of the separator 20 by the treatment. Even if the surface of the separator 20 after the treatment is visually observed, it is preferable that the presence of the metal oxide (rust) is not confirmed. In particular, it is preferable that no metal oxide larger than 100 μm in diameter is present on the surface of the separator 20 after the treatment, and it is more preferable if no metal oxide larger than 50 μm in diameter exists. Further, it is particularly preferable if there is no metal oxide having a diameter larger than 30 μm.

The total amount of Fe, Co, and Ni exposed on the surface of the separator 20 is preferably 0.01 μg / cm ² or less. Furthermore, the total amount of Cr, Mn, Fe, Co, Ni, Cu and Zn exposed on the surface of the separator 20 is preferably 0.01 μg / cm ² or less.

  FIG. 3 shows an example of a fuel cell 40 (cell stack) composed of a plurality of single cells. The fuel cell 40 communicates with a fuel supply port 171 and a discharge port 172 communicating with the fuel flow channel, an oxidant supply port 181 and a discharge port 182 communicating with the oxidant flow channel, and a cooling flow channel. A cooling water supply port 191 and a discharge port 192.

  The fuel cell 40 is operated by supplying a fuel such as hydrogen gas from the fuel supply port 171 and an oxidant such as oxygen gas from the oxidant supply port 181. While the fuel cell 40 is operating, cooling water is supplied to the fuel cell from the cooling water supply port 191. For this reason, the temperature of the fuel cell is adjusted to an appropriate temperature for operation. As the cooling water, pure water is preferably used.

  The fuel cell 40 including the separator 20 according to the present embodiment operates stably for a long time because the separator 20 has high corrosion resistance and strength. In particular, the cooling manifold of the separator 20 even if the conductivity of the cooling water rises due to the metal constituting the piping through which the cooling water circulates, the metal in the fuel cell, the resin, etc. are eluted into the cooling water. 133 is less likely to corrode, and accordingly, leakage of cooling water from the fuel cell 40 due to such corrosion is less likely to occur.

  Examples of the present invention will be described below. In addition, this invention is not limited to this Example.

[Examples and Comparative Examples]
For each Example and Comparative Example, the raw material components shown in Table 1 were placed in a stirring mixer (“5XDMV-rr type” manufactured by Dalton) so as to have the composition shown in Table 1, and mixed by stirring. The resulting mixture was prepared. It grind | pulverized to the particle size of 500 micrometers or less with the granulator. Thereby, a molding material was obtained.

  The obtained molding material was compression molded under the conditions of a mold temperature of 170 ° C., a molding pressure of 35.3 MPa, and a molding time of 2 minutes.

By this compression molding, the separator 20 was formed in a size of 200 mm × 250 mm and a thickness of 1.5 mm. In addition, by this compression molding, 57 gas supply / discharge grooves 2 having a length of 250 mm, a width of 1 mm, and a depth of 0.5 mm are formed on one surface of the separator 20, and a length of 250 mm, a width of 0.5 mm, and a depth are formed on the other surface. 58 grooves for gas supply / discharge of 0.5 mm were formed. Further, six manifolds having an opening area of 3.5 cm ² were formed on the outer periphery of the separator 20 by this compression molding.

  The surface of the separator 20 is subjected to a blasting process using a slurry containing alumina particles as abrasive grains using a wet blasting apparatus (model PFE-300T / N) manufactured by Macau Corporation, and then washed with ion-exchanged water. Further, it was dried with warm air. Table 1 shows the results of measuring the arithmetic average height Ra (JIS B0601: 2001) of the surface of the separator 20 after this treatment.

[Disk flow evaluation]
The disk flow of the molding material used in each example and comparative example was measured by the method described above. The results are shown in Table 1.

[Contact resistance evaluation]
By cutting the separator 20 obtained in each example and comparative example, nine small pieces having a size of 30 mm × 30 mm in plan view were cut out from one separator 20.

  Carbon paper was placed above and below these small pieces, copper plates were further placed above and below them, and a surface pressure of 1 MPa was applied in the vertical direction. The voltage between the two carbon papers was measured with a voltmeter, and the current between the two copper plates was measured with an ammeter, and the contact resistance was calculated from the result. The carbon paper used is TGP-HM series (090M: thickness 0.28 mm, 120M: thickness 0.38 mm) manufactured by Toray.

  For each example and comparative example, the average value of the contact resistance of nine pieces was calculated. Furthermore, the ratio (percentage) of the maximum value to the minimum value of the contact resistance was calculated. The results are shown in Table 1.

[Bending strength evaluation]
The three-point bending strength of the outer peripheral portions (two locations on each side, a total of eight locations) along the four sides of the separator 20 obtained in each example and comparative example was measured according to JIS R1601. The distance between fulcrums was 30 mm, and the crosshead speed was 2 mm / min. Table 1 shows the average value of the measurement results and the difference between the maximum value and the minimum value of the measurement results.

[Corrosion current evaluation]
The corrosion current of the separator 20 obtained in each example and comparative example was measured. In the measurement, a separator 20 as a working electrode and a platinum electrode as a counter electrode are arranged at intervals of 30 mm in a sodium sulfate aqueous solution adjusted to have a conductivity of 200 μS / cm, and a voltage of 20 V is applied between the electrodes at a liquid temperature of 80 ° C. At the time of application for 48 hours, the value of current flowing between the electrodes was measured. The results are shown in Table 1.

[Evaluation of corrosion resistance (amount of wear)]
In the corrosion current evaluation, the weight loss rate of the separator 20 after the voltage application relative to the weight of the separator 20 before the voltage application was measured, and this was used as an index of the corrosion resistance of the separator 20. The results are shown in Table 1.

Details of each component in the table are as follows.
Thermosetting resin A: Cresol novolac type epoxy resin (“EOCN-1020-75” manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 199, melting point 75 ° C.)
Curing agent A: Novolac type phenolic resin ("PSM6200" manufactured by Gunei Chemical Co., OH equivalent 105)
Curing agent B: polyfunctional phenol resin (Maywa Kasei Co., Ltd. "MEH-7500", OH equivalent 100)
Curing accelerator A: Triphenylphosphine (“TPP” manufactured by Hokuko Chemical Co., Ltd.)
Curing accelerator B: a compound represented by the structural formula (1).
Graphite particles A: average particle diameter 50 μm, true density 2.28 g / cm ³ , natural graphite.
Graphite particles B: average particle diameter 50 μm, true density 2.25 g / cm ³ , artificial graphite.
Graphite particles C: average particle diameter 50 μm, true density 2.30 g / cm ³ , natural graphite.
Graphite particles D: average particle diameter 5 μm, true density 2.30 g / cm ³ , natural graphite.
Graphite particles E: average particle diameter 50 μm, true density 2.20 g / cm ³ , artificial graphite.
Coupling agent: Epoxy silane (“A187” manufactured by Nihon Unicar)
Wax: Natural carnauba wax ("H1-100" manufactured by Dainichi Chemical Co., Ltd., melting point 83 ° C)
The true density of the graphite particles is a value measured by a constant volume expansion method using a dry automatic densimeter (Acupic II 1340) manufactured by Shimadzu Corporation. In the measurement, helium gas was used, the introduction pressure (gauge pressure) was 134.45 kPag, the number of purges was 10, the number of runs was 10, and the equilibrium judgment pressure (gauge pressure) was 0.345 kPag.

13 Manifold 2 Gas supply / discharge groove 20 Fuel cell separator 40 Fuel cell

Claims (3)

A fuel cell separator formed from a cured product of a molding material containing a thermosetting resin and graphite, and having a gas supply / discharge groove and a manifold,
The true density of the graphite is 2.22 g / cm ³ or more, and the graphite content is in the range of 70 to 80% by mass.
The corrosion current is 10 μA / cm ² or less,
When two small pieces having a size of 30 mm × 30 mm in plan view are cut out from the fuel cell separator, the contact resistance ratio between the two pieces is 0.9 to 1.1 no matter where the small piece is cut out. Fuel cell separator that will be in the range. In this method, a molding material containing a thermosetting resin and graphite is prepared, and the molding material is molded to produce a fuel cell separator in which a groove for supplying and discharging gas and a manifold are formed. And
In preparing the molding material, graphite having a true density of 2.22 g / cm ³ or more is used as the graphite, and the graphite content with respect to the total solid content of the molding material is in the range of 70 to 80% by mass. , Adjusting the disk flow of the molding material to a range of 80 to 100 mm,
In molding the molding material, the molding material is heated and compression-molded to mold the molding material into the shape of the fuel cell separator in which the gas supply / discharge groove and the manifold are formed. A method for producing a separator for a fuel cell in which the molding material is cured.   A fuel cell comprising the fuel cell separator according to claim 1.

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