JP2013020803A - Fuel cell separator and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell separator exhibiting high corrosion resistance and low impurity eluting property, low in gas impermeability and electrical resistance, and having high strength and durability.SOLUTION: The solid polymer fuel cell separator comprises a material including a graphite powder mixture bound with a thermosetting resin binder, the graphite powder mixture being obtained by mixing first graphite powder having a particle size distribution of 1-150 μm and an average particle size of 30-70 μm and second graphite powder having an average particle size of 1-10 μm and a specific surface area of 30-100 m/g so that a ratio represented as the mass of the first graphite powder/the mass of the second graphite powder is 80/20-60/40.

Description

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

  Fuel cells convert the chemical energy of fuel directly into electrical energy, which has high conversion efficiency to electrical energy and low noise and vibration, so it can be used in various fields such as portable devices, automobiles, railways, and cogeneration. Future development is expected as a power source.

Among fuel cells, a polymer electrolyte fuel cell (PEFC) sandwiches both surfaces of an ion conductive polymer membrane (ion exchange membrane) between an anode electrode plate and a cathode electrode plate carrying a catalyst such as platinum, A single cell in which plate separators are arranged on both outer sides is a basic structural unit, and is composed of a stack in which several tens to several hundreds of single cells are stacked and two current collectors provided on the outside thereof. Typically, a grooved electrode system in which grooves as flow paths for a fuel gas such as hydrogen and an oxidant gas such as air are formed on the separator side surface of each electrode plate, There is a separator system with ribs engraved on the surface (see, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2000-21421)).
Among the PEFCs, in-vehicle PEFCs have hundreds of single cells stacked per stack, so that the number of separators used is several hundred.

  The plate separator requires a high degree of gas impermeability in order to supply the fuel gas and the oxidant gas to the electrode in a completely separated state, and in order to increase power generation efficiency, the internal resistance of the battery Is required to have high conductivity. Furthermore, in order to generate electricity stably over a long period of time, high corrosion resistance and low impurity elution characteristics are required. For separators that require such material characteristics, carbonaceous materials have been conventionally used. A carbon / resin composite mold separator formed by binding a carbon powder such as graphite with a thermosetting resin binder has been used.

When manufacturing the PEFC, it is necessary to strongly tighten the single cells so that the single cells adhere to each other at the time of forming the stack, but in recent years, a thin and lightweight separator has been required as a PEFC separator for vehicles. Individual separators forming a stack are required to have higher strength that can withstand loads during assembly and fastening.
In addition, separators for in-vehicle PEFCs must have high durability (fatigue characteristics) and reliability that can withstand loads caused by repeated thermal expansion and cooling cycles caused by starting and stopping of PEFCs and automobile vibrations. It is supposed to be.

  However, although the above carbon / resin composite mold separator is generally excellent in corrosion resistance and low impurity elution characteristics, it is inferior in mechanical properties such as strength and durability when compared to metal separators. Cracks and cracks are likely to occur depending on the load (load) at the time, and fatigue deterioration or the like is likely to occur due to inferior durability over a long period of time.

  For this reason, in Cited Document 2 (Japanese Patent Laid-Open No. 2007-134225), 24 parts by mass of a thermosetting resin and an internal mold release are used with respect to 100 parts by mass of a porous artificial graphite material having an average particle size of 30 μm or 40 μm. A fuel cell separator made of a composition containing 1 part by weight of carnauba wax as an agent has been proposed, and according to the cited document 2, a fuel cell separator excellent in strength and flexibility can be provided. .

JP 2000-21421 A JP 2007-134225 A

However, according to the studies by the present inventors, the fuel cell separator described in the cited document 2 exhibits high strength at the beginning of use, but is inferior in durability when used for a long period of time, and has resistance to repeated loads. It was found to be low and susceptible to fatigue deterioration.
Under such circumstances, the present invention provides a fuel cell separator that is excellent in corrosion resistance and low impurity elution characteristics, has excellent gas impermeability and electrical characteristics, and exhibits high strength and durability, and a method for producing the same. It is the purpose.

As a result of further investigation by the inventor in order to solve the above technical problem, a first graphite powder having a particle size distribution of 1 to 150 μm and an average particle size of 30 to 70 μm, an average particle size of 1 to 10 μm and a specific surface area There a second graphite powder is 30 to 100 m ² / g, were mixed so mass / second ratio represented by mass of the graphite powder of the first graphite powder is 80 / 20-60 / 40 To find out that the above technical problem can be solved by a separator for a polymer electrolyte fuel cell, characterized in that the graphite powder mixture is made of a material bound by a thermosetting resin binder, and to complete the present invention. It came.

That is, the present invention
(1) A first graphite powder having a particle size distribution of 1 to 150 μm and an average particle diameter of 30 to 70 μm, and a second graphite powder having an average particle diameter of 1 to 10 μm and a specific surface area of 30 to 100 m ² / g Is mixed with a thermosetting resin binder so that the ratio expressed by the mass of the first graphite powder / the mass of the second graphite powder is 80/20 to 60/40. A polymer electrolyte fuel cell separator (hereinafter referred to as a separator of the present invention),
(2) The first graphite powder is artificial graphite powder obtained by pulverizing and classifying isotropic graphite to adjust the particle size, or after graphitizing mosaic coke and then pulverizing and classifying and adjusting the particle size. In addition, the second graphite powder is an artificial graphite powder obtained by pulverizing and classifying isotropic graphite and adjusting the particle size by graphitizing the mosaic coke, and then pulverizing and classifying and adjusting the particle size. A separator for a polymer electrolyte fuel cell according to the above (1),
(3) A method for producing a polymer electrolyte fuel cell separator,
A first graphite powder having a particle size distribution of 1 to 150 μm and an average particle diameter of 30 to 70 μm, and a second graphite powder having an average particle diameter of 1 to 10 μm and a specific surface area of 30 to 100 m ² / g, The graphite powder mixture mixed so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder is 80/20 to 60/40 is dispersed in a thermosetting resin binder solution to form a slurry. Make mixed materials,
A green sheet is produced by the doctor blade method using the slurry-like mixed material,
A method for producing a separator for a polymer electrolyte fuel cell, characterized by laminating the obtained green sheets and hot pressing (hereinafter referred to as the separator production method of the present invention),
(4) The first graphite powder is an artificial graphite powder obtained by pulverizing and classifying isotropic graphite to adjust the particle size, or after graphitizing a mosaic coke, and then pulverizing and classifying and adjusting the particle size. In addition, the second graphite powder is an artificial graphite powder obtained by pulverizing and classifying isotropic graphite and adjusting the particle size by graphitizing the mosaic coke, and then pulverizing and classifying and adjusting the particle size. A method for producing a separator for a polymer electrolyte fuel cell according to the above (3),
Is to provide.

  According to the present invention, the graphite powder contains high corrosion resistance and low impurity elution characteristics, and the graphite powder contains the first graphite powder and the second graphite powder as a gas impermeability. In addition, a polymer electrolyte fuel cell separator having low electrical resistance and high strength and durability can be provided, and a method for producing the polymer electrolyte fuel cell separator can be simply provided.

It is the figure ((a) and (b)) which shows an example of the form of the green sheet used by this invention, and the figure ((c)) which shows an example of the form of the separator obtained. It is a figure explaining the usage pattern of the separator of this invention.

First, the separator of the present invention will be described.
The separator of the present invention has a first graphite powder having a particle size distribution (particle size distribution range) of 1 to 150 μm and an average particle size of 30 to 70 μm, an average particle size of 1 to 10 μm and a specific surface area of 30 to 100 m ^2. A graphite powder mixture obtained by mixing the second graphite powder, which is / g, so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder is 80/20 to 60/40, It is made of a material bound by a thermosetting resin binder.

The separator of the present invention has a first graphite powder having a particle size distribution of 1 to 150 μm and an average particle size of 30 to 70 μm as a separator forming material, an average particle size of 1 to 10 μm and a specific surface area of 30 to 100 m ² /. g of the second graphite powder.

In the separator of the present invention, the first graphite powder has a particle size distribution of 1 to 150 μm, preferably 2 to 120 μm. When the upper limit of the particle size distribution of the first graphite powder is more than 150 μm, gas leakage tends to occur when the separator is thin.
The first graphite powder has an average particle size of 30 to 70 μm, preferably 32 to 60 μm.

  In the separator of the present invention, the particle size distribution of the first graphite powder is 1 to 150 μm, so that the particle size distribution is wide, and the fluidity is high and stable when the separator is manufactured from the slurry-like mixed material as described later. It becomes easy to obtain a slurry. The first graphite powder has a particle size distribution of 1 to 150 μm and an average particle diameter of 30 to 70 μm, so that the separator forming material includes a certain percentage of graphite powder having a particle diameter of several tens of μm or more. As a result, the specific resistance and contact resistance of the separator can be easily reduced.

  In the present application document, the particle size distribution is defined by the upper limit value and the lower limit value of the particle size in the volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution measuring device. The diameter means a particle diameter (average particle diameter D50) of 50% in terms of the accumulated particle size in the volume-based accumulated particle size distribution measured by the above method.

In the separator of the present invention, the second graphite powder has an average particle diameter of 1 to 10 μm, preferably 2 to 8 μm. The particle size distribution of the second graphite powder is preferably 0.3 to 40 μm, and more preferably 0.5 to 20 μm.
The particle size distribution and average particle size of the second graphite powder can be measured by the same method as the particle size distribution and average particle size of the first graphite powder.

In the separator of the present invention, the specific surface area of the second graphite powder is 30 to 100 m ² / g, and preferably 35 to 85 m ² / g.
When the specific surface area of the second graphite powder is smaller than 30 m ² / g, the fatigue properties of the separator are lowered and durability tends to be lowered. When the specific surface area exceeds 100 m ² / g, The fluidity of the molding material decreases during production, and the leak performance (gas impermeability) tends to decrease.

  In the present application documents, the specific surface area of the graphite powder is preliminarily dried at 350 ° C. for 30 minutes under a nitrogen flow with respect to the measurement target using a surface area meter (a fully automatic surface area measuring device manufactured by Shimadzu Corporation). Then, a value measured by a nitrogen adsorption BET 10-point method using a gas flow method using a nitrogen helium mixed gas that is accurately adjusted so that the value of the relative pressure of nitrogen with respect to atmospheric pressure is 0.3 is meant.

The second graphite powder can be produced by pulverizing graphite particles such as artificial graphite to a desired particle size using a pulverizer such as a vibration mill.
In the separator of the present invention, the second graphite powder has an average particle size smaller than that of the first graphite powder, and the graphite powder having such a small average particle size is usually produced by pulverization. The surface becomes chemically active with mechanochemical changes. In addition, by the above pulverization treatment, it is possible to easily obtain a graphite powder having physical irregularities on the surface of the obtained graphite powder and having the above specific surface area, and adhesion to a thermosetting resin binder during the production of the separator. Thus, it is possible to easily obtain a separator having a high breaking strain such as a bending property and a remarkably improved fatigue property (fatigue limit) which is an index of durability.

In the separator of the present invention, as the first graphite powder, an artificial graphite powder obtained by pulverizing and classifying isotropic graphite and adjusting the particle size, or after graphitizing a mosaic coke, and then pulverizing and classifying the artificial graphite powder obtained by adjusting the particle size. A graphite powder is preferred.
In the separator of the present invention, as the second graphite powder, isotropic graphite is pulverized and classified, and the particle size adjusted artificial graphite powder or mosaic coke after graphitization, and then pulverized and classified to adjust the particle size. The artificial graphite powder is preferable.

An artificial graphite powder whose particle size is adjusted by pulverizing and classifying isotropic graphite or an artificial graphite powder whose particle size is adjusted by pulverizing and classifying after mosaic-like coke is graphitized, and the crystal plane spacing d ₀₀₂ of the graphite powder is 0. Since the graphitization degree is low at 3360 nm or more, it has a high affinity with a hard and thermosetting resin binder, an elastic deformation region in a bending characteristic is increased, a fracture strain is increased, and fatigue failure due to repeated load is caused. Since it becomes difficult to occur, a separator having high strength and high mechanical durability can be easily obtained.

  On the other hand, when a needle-shaped artificial graphite powder obtained by graphitizing needle coke or natural graphite is used as a raw material for the first graphite powder or the second graphite powder, graphite crystals develop (graphite The degree of elastic deformation in the bending test becomes smaller, the surface becomes inactive, and the affinity between the graphite powder surface and the thermosetting resin binder becomes weaker. However, since it changes from elastic deformation to plastic deformation, the breaking strain becomes small, and it is easy to generate cracks and the progress of cracks due to repeated loading, resulting in a separator having low fatigue characteristics and low durability.

  In the separator of the present invention, the total content ratio (content ratio of the graphite powder mixture) of the first graphite powder and the second graphite powder in the material constituting the separator (hereinafter, appropriately referred to as separator constituent material) is 65 to 90. It is preferable that it is mass%, It is more preferable that it is 70-85 mass%, It is further more preferable that it is 75-80 mass%.

  In the separator of the present invention, the first graphite powder and the second graphite powder are expressed as “a mass of the first graphite powder / a mass of the second graphite powder” in the separator constituting material as a graphite powder mixture. It is contained so that a ratio may be 80 / 20-60 / 40, and it is contained so that it may become 75 / 25-65 / 35.

When the content ratio of the second graphite powder in the graphite powder mixture is less than 20% by mass (when the content ratio of the first graphite powder exceeds 80% by mass), a green sheet is formed during the production of the separator described later. In the slurry-like mixed material as a material, graphite powder having a large particle size is likely to settle, and the stability of the slurry is lowered.
When the content ratio of the second graphite powder in the graphite powder mixture exceeds 40% by mass (when the content ratio of the first graphite powder becomes less than 60% by mass), the green sheet is hot-pressed as described later. When the separator is manufactured, the fluidity of the green sheet as a molding material is lowered, and a structure defect is easily caused, or gas impermeability is easily lowered.

In the separator of the present invention, the content ratio of the graphite powder having a particle diameter of 30 to 70 μm in the graphite powder mixture is preferably 25 to 55% by mass, and more preferably 30 to 50% by mass.
In the separator of the present invention, the content ratio of the graphite powder having a particle diameter of 1 to 10 μm in the graphite powder mixture is preferably 15 to 45% by mass, and more preferably 20 to 40% by mass.
In the present application documents, the content ratio of the graphite powder can be determined based on the volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution measuring device.

  The separator of the present invention is made of a material in which the graphite powder mixture is bound by a thermosetting resin binder. Specific examples of the thermosetting resin binder are as described later.

  In the separator of the present invention, the content of the thermosetting resin binder in the separator constituting material is preferably 10 to 35% by mass, more preferably 15 to 30% by mass, and 20 to 25% by mass. More preferably it is.

  In the separator of the present invention, the separator constituting material may include a phenol resin curing agent, a curing accelerator, a dispersing agent, and the like. Specific examples of the phenol resin curing agent, the curing accelerator, and the dispersing agent are as described later.

  In the separator of the present invention, the content ratio of the phenol resin curing agent in the separator constituting material is such that when a polyfunctional phenol type epoxy resin is used as the thermosetting resin binder, the phenol resin in the phenol resin with respect to all epoxy groups in the epoxy resin. It is preferable to contain such that the equivalent ratio of total phenolic hydroxyl groups (total phenolic hydroxyl groups in phenol resin / total epoxy groups in epoxy resin) is 0.5 to 1.5, 0.7 to 1.5 More preferably, it is contained so that it may become 0.9-1.1, and it is especially preferable that it is about 1.0. If the equivalent ratio is less than 0.5 or exceeds 1.5, the remaining amount of unreacted thermosetting resin binder or phenol resin curing agent increases, and the efficiency tends to decrease.

  In the separator of the present invention, the content of the curing accelerator in the separator constituting material can be usually added in the range of 0.05 to 3 parts by mass with respect to 100 parts by mass of the thermosetting resin binder.

  In the separator of the present invention, the total amount of the thermosetting resin binder, the phenol resin curing agent and the curing accelerator in the separator constituting material is preferably 10 to 35 parts by mass with respect to 100 parts by mass of the graphite powder mixture. .

  In the separator of the present invention, the content of the dispersant in the separator constituting material is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the graphite powder mixture. When the content ratio of the dispersant is less than 0.1 parts by mass with respect to 100 parts by mass of the graphite powder mixture, the graphite powder is immediately dispersed without being dispersed during the production of the separator. Further, when the content ratio is more than 5 parts by mass with respect to 100 parts by mass of the graphite powder, the resin characteristics are deteriorated, and as a result, mechanical properties of the separator are deteriorated (strength reduction), chemical resistance, In particular, the characteristic deterioration in the sulfuric acid acidic solution is caused.

According to the present invention, the graphite powder contains high corrosion resistance and low impurity elution characteristics, and the graphite powder contains the first graphite powder and the second graphite powder as a gas impermeability. It is possible to provide a separator for a polymer electrolyte fuel cell that has high electrical resistance, low electrical resistance, and high strength and durability.
The separator of the present invention can be produced by the method for producing a separator of the present invention described in detail below.

Next, the manufacturing method of the separator of this invention is demonstrated.
The separator manufacturing method of the present invention includes a first graphite powder having a particle size distribution of 1 to 150 μm and an average particle size of 30 to 70 μm, an average particle size of 1 to 10 μm and a specific surface area of 30 to 100 m ² / g. A graphite powder mixture prepared by mixing a certain second graphite powder so that the ratio expressed by the mass of the first graphite powder / the mass of the second graphite powder is 80/20 to 60/40, is thermosetting. A slurry-like mixed material is prepared by dispersing in a resin binder solution, a green sheet is prepared by a doctor blade method using the slurry-like mixed material, and then the obtained green sheets are laminated and hot-pressed. It is a feature.

  A graphite powder mixture is dispersed in a thermosetting resin binder solution to produce a slurry-like mixed material, and a green sheet is produced using the slurry-like mixed material by a doctor blade method, and then the obtained green sheets are laminated. Then, as a specific aspect of hot pressing, a step of preparing a binder resin solution by dissolving a thermosetting resin binder in an organic solvent together with a phenol resin curing agent and a curing accelerator as necessary (preparation of a binder resin solution) Step), a step of preparing a slurry-like mixed material by dispersing the graphite powder mixture in the binder resin liquid (slurry-like mixed material preparation step), applying the slurry onto the film, drying, and then releasing the mold. A process for producing a green sheet, which is a dense part forming material (green sheet production process), and filling the obtained green sheet in a mold And a method for performing the step (thermal molding process) for molding the heat pressure by.

(1) Binder resin liquid preparation process A binder resin liquid (thermosetting resin binder containing liquid) stirs and mixes a thermosetting resin binder with a phenol resin hardening agent and a hardening accelerator as needed, and also as needed. It can be produced by stirring and dissolving a minimum necessary amount of a dispersant capable of dispersing a graphite powder mixture described later in an appropriate organic solvent at a desired mass ratio.

  The thermosetting resin binder is not particularly limited as long as it has acid resistance to an electrolyte such as sulfonic acid having a pH of about 2 to 3 and heat resistance that can withstand the operating temperature of the fuel cell of about 60 to 100 ° C. For example, resol type phenol resin, phenol resin represented by novolak type phenol resin, furfuryl alcohol resin, furfuryl alcohol furfural resin, furfuryl alcohol phenol resin, furan resin, polyimide resin, polycarbodiimide resin , Polyacrylonitrile resins, pyrene-phenanthrene resins, polyvinyl chloride resins, bifunctional aliphatic alcohol ether type epoxy resins, polyfunctional phenol type epoxy resins and other epoxy resins, urea resins, diallyl phthalate resins, unsaturated polyester resins , Melamine resins. Can be used in combination alone or in combination.

  As a thermosetting resin binder for forming dense parts, a bifunctional aliphatic alcohol ether type epoxy resin, a polyfunctional phenol type epoxy resin, a bifunctional aliphatic alcohol ether type epoxy resin and a polyfunctional phenol type epoxy resin are combined. The mixed resin is preferable.

  The bifunctional aliphatic alcohol ether type epoxy resin has a number average molecular weight of 1500 to 3500 and a number average molecular weight / epoxy equivalent of 2 or more and is represented by the following general formula (I). Ether type epoxy resins are preferred.

G-O- (RO) _k -G (I)
(However, when G is a glycidyl group, O is an oxygen atom, R is an alkylene group having 2 to 10 carbon atoms, k is an integer of 1 or more, and k is an integer of 2 or more, a plurality of R are the same. It may or may not be.)

  In the epoxy resin represented by the general formula (I), when the total number of carbon atoms contained in the k alkylene groups R existing between the two glycidyl groups G and G is more than 120, the flexibility of the resin becomes high. Therefore, the fracture strain of the separator obtained is increased, but the bending strength is reduced to, for example, less than 30 MPa. On the other hand, if the total number of carbon atoms is less than 30, the molecular chain between the two glycidyl groups G and G is too short, so that the flexibility is lowered. Moreover, k is preferably 8-30, and more preferably 15-25.

  Examples of the bifunctional aliphatic alcohol ether type epoxy resin represented by the general formula (I) include a hexanediol type epoxy resin, a polyethylene glycol type epoxy resin, a polypropylene glycol type epoxy resin, and a polyoxytetramethylene glycol type epoxy resin. Among these resins, those having a relatively low proportion of oxygen atoms are preferable, and when the proportion of oxygen atoms is relatively low, water resistance is improved, and the water absorption swelling of the resulting separator Sex can be suppressed.

  Since the bifunctional aliphatic alcohol ether type epoxy resin represented by the general formula (I) has a linear single bond structure, the molecular chain is easy to move, has flexibility, and has a structure that easily exhibits rubber elasticity. Therefore, excellent flexibility, stretchability, and breaking strain characteristics can be imparted to the obtained separator.

  On the other hand, the polyfunctional phenol type epoxy resin is not particularly limited as long as it is a compound having a phenol skeleton in the molecule and having two or more epoxy groups. For example, bisphenol type epoxy resin, novolac type epoxy resin, orthocresol novolak Type epoxy resin, biphenyl type epoxy resin, naphthalene skeleton-containing type epoxy resin, and the like.

  Examples of bisphenol type epoxy resins include bifunctional phenol type epoxy resins.

  The bifunctional phenol type epoxy resin has two epoxy groups in the molecule, and examples of the bifunctional phenol type epoxy resin include a bisphenol A type epoxy resin represented by the general formula (II). it can.

  In the bifunctional phenol type epoxy resin represented by the general formula (II), n is an integer of 1 to 10, preferably an integer of 1 to 5, and more preferably an integer of 2 to 3.

The bisphenol A type epoxy resin represented by the general formula (II) has a planar benzene ring, so that the molecule does not move easily and has low flexibility, but its structure gives the separator high bending strength. Can do.
When the amount of the thermosetting resin binder is small, the strength of the separator obtained is lowered. Conversely, when the amount of the thermosetting resin binder is increased, the electrical resistance is increased.

  The phenol resin curing agent constituting the binder resin liquid is not particularly limited as long as it has a phenol structure in the molecule. Phenol novolak resin, cresol novolac resin, xylene type phenol resin, dicyclopentadiene type phenol resin, bisphenol Type novolac resins such as novolak resins, bisphenols such as bisphenol A, bisphenol F, bisphenol S, tetrabromobisphenol A, and the like. Examples thereof include bisphenol-based resins obtained by reacting the latter in excess.

  When a polyfunctional phenol type epoxy resin is used as the thermosetting resin binder, the content ratio of the phenol resin curing agent is the equivalent ratio of all phenolic hydroxyl groups in the phenol resin to all epoxy groups in the epoxy resin (in the phenol resin). The total phenolic hydroxyl group / total epoxy group in the epoxy resin) is preferably 0.5 to 1.5, more preferably 0.7 to 1.5, and 0.9 to 1.1. More preferably, it is about 1.0. If the equivalent ratio is less than 0.5 or exceeds 1.5, the remaining amount of the unreacted mixed resin or phenol resin curing agent increases, and the efficiency is lowered.

  Examples of the curing accelerator constituting the binder resin liquid include one or more selected from phosphorus compounds, tertiary amines, imidazoles, organic acid metal salts, Lewis acids, amine complex salts, etc., and thermosetting. When a polyfunctional phenol type epoxy resin is used as the conductive resin binder, it can be usually added in an amount of 0.05 to 3 parts by mass with respect to 100 parts by mass of the resin.

  Moreover, it is preferable that the total amount of the thermosetting resin binder contained in the said binder resin liquid, a phenol resin hardening | curing agent, and a hardening accelerator is 10-35 mass parts with respect to 100 mass parts of graphite powder mixtures.

  The organic solvent constituting the binder resin liquid is not particularly limited as long as it is generally available and can dissolve the thermosetting resin binder. For example, alcohols such as ethyl alcohol and isopropyl alcohol, acetone, A lot of ketones such as methyl ethyl ketone are used, and among these organic solvents, when considering the stability and viscosity of the slurry, the drying speed of the sheet, etc. Most preferred is methyl ethyl ketone.

  When the amount of the organic solvent is increased, the precipitation of the graphite powder is accelerated, and there is a case where a difference in structure is generated between the front and back surfaces of the green sheet, which will be described later, to cause warping. Conversely, when the amount of the organic solvent decreases, the viscosity of a slurry described later increases, and the formation of a sheet becomes difficult because the carbonaceous powder in which the blades are aggregated is dragged to form irregularities on the surface.

  Examples of the dispersant constituting the binder resin liquid include a nonionic surfactant, a cationic surfactant, and an anionic surfactant.

  Examples of the nonionic surfactant include aromatic ether type, carboxylic acid ester type, acrylic acid ester type, phosphoric acid ester type, sulfonic acid ester type, fatty acid ester type, urethane type, fluorine type, aminoamide type, The thing which consists of various polymers of an acryl amide type is mentioned.

  Examples of the cationic surfactant include those made of various polymers containing an ammonium group, a sulfonium group, and a phosphonium group.

Examples of the anionic surfactant include those made of various polymers of carboxylic acid type, phosphoric acid type, sulfonic acid type, hydroxy fatty acid type, and fatty acid amide type.
In order to disperse the graphite powder mixture in the organic solvent, the molecular weight of each surfactant is preferably in the range of 2,000 to 100,000 in terms of polystyrene-reduced weight average molecular weight by gel permeation chromatography. . When the weight average molecular weight is less than 2,000, the polymer component cannot form a sufficient steric repulsion layer when the dispersant is adsorbed on the surface of the graphite powder, and reaggregation of the dispersed particles occurs. Absent. On the other hand, if the weight average molecular weight exceeds 100,000, the production reproducibility may be reduced or the flocculant may act.

These surfactants can be used alone or in admixture of two or more.
The dispersant is preferably added in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the graphite powder mixture. If the added amount of the dispersant is less than 0.1 parts by mass with respect to 100 parts by mass of the graphite powder mixture, the graphite powder will settle immediately without being dispersed. Moreover, when the addition amount is more than 5 parts by mass with respect to 100 parts by mass of the graphite powder, the resin characteristics are deteriorated, resulting in deterioration of the mechanical characteristics of the separator (decrease in strength) as well as chemical resistance, In particular, the characteristic deterioration in the sulfuric acid acidic solution is caused.

  In addition to the above dispersant, the binder resin liquid may contain additives such as a wetting penetrating agent, an antiseptic, an antifoaming agent, and a surface conditioner as long as it does not hinder the purpose of the present invention. It can contain suitably. By containing these additives, a stable slurry can be produced and a green sheet with a smooth surface can be obtained.

  The binder resin liquid is prepared by adding a thermosetting resin binder to the organic solvent together with a phenol resin curing agent, a curing accelerator, a dispersing agent, etc., if necessary, and stirring and mixing with a stirrer. be able to. The stirring time is preferably about 1 hour, and the rotation speed of the stirrer is preferably about 100 to 1000 rotations / minute.

(2) Slurry dense part forming material manufacturing process
The binder resin liquid obtained in the step (1) and the graphite powder mixture are mixed to prepare a slurry-like mixed material in which the graphite powder mixture is dispersed.
In the separator production method of the present invention, specific examples of the first graphite powder and the second graphite powder constituting the graphite powder mixture, and the content ratio of the first graphite powder and the second graphite powder in the graphite powder mixture In addition, the content ratio of the graphite powder having a particle diameter of 30 to 70 μm and the content ratio of the graphite particles having a particle diameter of 1 to 10 μm in the graphite powder mixture are as described above.

  In the method for producing a separator of the present invention, by using a graphite powder mixture containing the first graphite powder and the second graphite powder in a specific ratio, even if the amount of the organic solvent is reduced, the fluidity is high. A stable slurry-like mixed material can be obtained, and a green sheet with reduced cracking due to drying shrinkage can be obtained at the time of forming the green sheet in the next step.

  In the separator manufacturing method of the present invention, the graphite powder mixture contains the first graphite powder and the second graphite powder in a specific ratio, so that there is a filling effect that small particles enter the gaps between the large particles. A dense green sheet can be obtained. The first graphite powder contributes to the reduction of electric resistance while improving the filling property of the graphite powder mixture. In addition, the second graphite powder can prevent dry cracking at the time of forming the green sheet, obtain a dense green sheet, improve mechanical properties such as strength and breaking strain of the obtained separator, Furthermore, durability (fatigue characteristics) can be improved.

  In the method for producing a separator of the present invention, it is preferable to prepare a slurry-like mixed material by mixing and dispersing the binder resin liquid and the graphite powder mixture.

  A graphite powder mixture is a mass ratio with respect to the total amount (resin component total amount) of a thermosetting resin binder, a phenol resin hardening agent, and a hardening accelerator, and resin component total amount: Graphite powder mixture = 10: 90-35. : It is preferable to mix with a binder resin liquid so that it may become 65. If the mass proportion of the total amount of the resin components is less than 10% and the mass proportion of the carbonaceous powder is more than 90%, the amount of thermosetting resin binder is reduced, so that the fluidity at the time of molding is lowered and uniform. It becomes difficult to mix and the composition tends to be non-uniform. On the other hand, if the mass proportion of the total amount of the resin components is more than 35% and the mass proportion of the graphite powder mixture is less than 65%, the moldability is improved, but a molded article comprising the graphite powder mixture and a thermosetting resin binder. When the fuel cell is manufactured using the obtained separator, the performance of the fuel cell is likely to be deteriorated.

  The mixing and dispersing treatment of the binder resin liquid and the graphite powder mixture is preferably carried out using a dispersing machine such as a universal stirrer, ultrasonic treatment device, cutter mixer, three rolls, etc., and the graphite powder mixture in the binder resin liquid It is preferable to make a slurry by adjusting the viscosity to 100 to 2000 mPa · s, preferably 100 to 1000 mPa · s by adding an organic solvent as appropriate. When the viscosity of the slurry is less than 100 mPa · s, the slurry flows out from the doctor blade when the green sheet is produced and the sheet spreads, so that it becomes difficult to form a sheet having a uniform thickness. On the other hand, when the viscosity of the slurry exceeds 2000 mPa · s, unevenness is generated on the surface by dragging the carbonaceous powder in which the blades are aggregated during the production of the green sheet, making it difficult to form a sheet.

  In addition, when the green sheet is produced, the air entrained by the mixing and dispersing process may form irregularities on the surface of the green sheet and reduce the homogeneity. Therefore, the slurry may be obtained by a method such as centrifugation or vacuum deaeration. It is desirable to produce a green sheet after degassing the air inside.

(3) Green sheet preparation process The slurry prepared at the said (2) process is apply | coated on films, such as polyester, by the doctor blade method. At this time, after appropriately adjusting the gap between the doctor blade and the film to about 0.2 to 0.8 mm, the slurry which is well stirred with a stirrer is poured into the slurry hopper of the doctor blade, preferably on the film coated with a release agent. Apply to a uniform thickness.

  The thickness of the obtained green sheet can be adjusted by adjusting the gap distance between the doctor blade and the film and the slurry concentration, and can be controlled so that the thickness after drying is 0.1 to 0.5 mm. preferable.

  The obtained green sheet is preferably air-dried or, if desired, cut to a certain length and then blown and dried using a fan or the like, and dried until the solvent content is volatilized visually. In addition, after the solvent has evaporated and the surface is dry, a predetermined size is cut with a cutter knife, or a punching die is used for a predetermined shape and size, followed by drying or cooling for a predetermined time. It is preferable to release the film from the surface after making it easy to release from the film.

  Thus, the doctor blade method is a method in which a slurry-like mixed material composed of raw material powder such as a graphite powder mixture, thermosetting resin binders, a dispersant, an organic solvent, etc. is fixed on a carrier film using a doctor blade device. Is a method of obtaining a green sheet by drying and evaporating and evaporating the organic solvent after continuous coating so that the sheet is formed, dried, wound, punched, etc. Therefore, a green sheet can be produced with high production efficiency.

  Since the green sheet thus obtained is composed of a dense resin film, the gas impermeability of the obtained separator can be improved.

  The green sheet thus obtained is suitably 0.1 to 1.0 mm thick, more suitably 0.15 to 0.8 mm, and 0.2 to 0.6 mm. It is further appropriate that

(4) Hot-pressure forming step A plurality of the green sheets obtained in step (3) above are appropriately laminated according to the thickness of the separator to be obtained, and then hot-pressed to produce a hot-pressure molded product. can do.

  In the hot pressing, for example, the body forming green sheet 31a and the edge forming green sheet 31b having a shape as shown in FIG. 1A are overlapped as shown in FIG. 1B. After being placed in the mold in a heated state, it can be carried out by putting it into a press machine and hot pressing.

  As a shaping | molding die, what consists of a pair of upper mold | type and lower mold | type can be mentioned, What has a shaping | molding surface shape according to the separator shape to obtain can be mentioned. For example, when the separator to be obtained has a corrugated cross-sectional shape as shown in FIG. 1 (c), a molding die in which corrugated grooves are formed on the molding surfaces of the upper die and the lower die. Can be mentioned. A mold release agent may be appropriately applied to the molding surface of the mold.

What is necessary is just to change suitably the number of lamination | stacking of the green sheet 31a for main-body part formation, the green sheet 31b for edge part formation, etc. according to the thickness of the hot-press molding to obtain.
In this way, for example, it is possible to obtain a hot-pressed product having the edge portion 32 having a shape as shown in FIG. 1C and having the main body portion formed into a corrugated shape. The hot-press molded product having the corrugated shape can be produced by introducing a predetermined number of green sheets between an upper mold and a lower mold having a concavo-convex molding surface and performing hot-pressure molding.

  The hot-press molded product is preferably formed by laminating 2 to 6 green sheets. In the case where the hot-press forming part adopts an embodiment as shown in FIG. 1C, 1 to 3 main body forming green sheets 31a and 1 to 3 edge forming green sheets 31b are laminated. It is preferable to be formed by hot pressing.

The irregularities (grooves) provided on the molding surface of the molding die preferably have a width of 0.5 to 3.0 mm, more preferably 0.5 to 2.5 mm, and 0.5 to More preferably, it is 2.0 mm. Moreover, the depth of the irregularities (grooves) is preferably 0.2 to 1.0 mm, more preferably 0.2 to 0.8 mm, and 0.2 to 0.6 mm. Is more preferable.
In the method for producing a separator of the present invention, a gas flow path can be easily imparted to the obtained separator by using a corrugated dense member having the uneven surface as the hot-press molded product.

  Further, the hot-pressed product can take a form other than the form shown in FIG. 1 (c). For example, a green sheet of the same size can be formed by laminating green sheets of the same size in a mold and hot-pressing them. May be produced.

  The pressure at the time of the hot pressing (hot pressing) is preferably 10 to 100 MPa, more preferably 20 to 80 MPa, and further preferably 20 to 60 MPa. Moreover, it is preferable that the temperature at the time of hot press molding is 150-250 degreeC. The pressurization time at the time of hot press molding can be appropriately determined depending on the types of thermosetting resin binder, phenol resin curing agent, and curing accelerator contained in the binder resin liquid. For example, when using a cresol novolak type epoxy resin as a thermosetting resin binder, a novolak type phenol resin as a curing agent, and 2-ethyl-4-methylimidazole as a curing accelerator, the hot press molding pressing time is 1 second to 600 seconds are preferred, 1 second to 300 seconds are more preferred, and 1 second to 30 seconds are even more preferred. Further, at the time of pressurization, the depressurization may be performed by releasing the pressurization state in a timely manner, instead of continuously maintaining the pressurization state. When the pressure at the time of pressurization is within the above range, desired strength and gas impermeability can be imparted to the obtained separator.

The thickness of the hot-pressed product is suitably 0.1 to 0.5 mm, more suitably 0.15 to 0.45 mm, and 0.2 to 0.4 mm. Is more appropriate. In the present specification, when the hot-press molded product takes a form as shown in FIG. 1C, the thickness indicated by t in FIG. 1C corresponds to the thickness of the hot-press molded product. The thickness of the hot-pressed product can be equated with the thickness of the separator obtained.

  Since the hot-press molded product obtained by the separator manufacturing method of the present invention is composed of the green sheet having the above-mentioned dense structure, a separator having a high degree of gas impermeability is produced even when the thickness is thin. Can do.

  The obtained hot-pressed product is preferably subjected to a hydrophilic treatment as appropriate. The hydrophilic treatment can be performed, for example, by treatment with ozone gas. The hydrophilization treatment by ozone gas treatment is preferably performed by exposure to ozone gas having a concentration of 1000 to 50000 ppm (mg / L) in a temperature atmosphere of 0 to 100 ° C. for 0.5 to 10 hours.

The obtained hot-pressed product may be further machined as necessary, and may be appropriately cured at a temperature of about 150 to 250 ° C. as necessary.
Moreover, since the thin film of a thermosetting resin binder exists on the surface of the hot-press molded product, and the contact resistance of the separator is increased by this film, it is preferably removed by blasting. In this case, dry blasting is also possible, but it is desirable to reduce the surface roughness, so it is preferable to perform wet blasting using fine abrasive grains.
According to the present invention, the desired separator can be manufactured in this way.

  According to the present invention, the graphite powder contains high corrosion resistance and low impurity elution characteristics, and the graphite powder contains the first graphite powder and the second graphite powder, thereby reducing the electrical resistance. It is possible to provide a method for easily producing a polymer electrolyte fuel cell separator having high strength and durability.

  As shown in FIG. 2, a single cell 1 of a fuel cell using the separator of the present invention or the separator obtained by the production method of the present invention is, for example, a polymer membrane (ion exchange membrane) 2 having ion conductivity. It can be formed by sandwiching both sides between an anode electrode plate 4 and a cathode electrode plate 5 carrying a catalyst such as platinum, and disposing plate separators 3 and 3 on both outer sides thereof.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited at all by the following examples.

Example 1
Artificial graphite having a particle size distribution of 3 to 98 μm, an average particle size (D50) of 33 μm, and a crystal plane spacing d ₀₀₂ of 0.3366 nm, obtained by pulverizing and classifying isotropic graphite to adjust the particle size. The powder was used as the second graphite powder, and isotropic graphite was pulverized and classified to adjust the particle size. The average particle diameter (D50) was 4 μm, the specific surface area was 39 m ² / g, and the crystal plane distance d ₀₀₂ was 0.00. The graphite powder mixture was obtained by using the artificial graphite powder of 3366 nm and mixing so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder was 75/25.
The content ratio of the graphite powder having a particle diameter of more than 70 μm in the graphite powder mixture is 2% by mass, the content ratio of the graphite powder having a particle diameter of 30 to 70 μm is 35% by mass, and the particle diameter exceeds 10 μm and is 30 μm. The content ratio of the graphite powder having a particle diameter of less than 1 μm was 28 mass%, the content ratio of the graphite powder having a particle diameter of 1 to 10 μm was 34 mass%, and the content ratio of the graphite powder having a particle diameter of less than 1 μm was 1 mass%. It was.
A cresol novolak type epoxy resin (manufactured by Nippon Kayaku Co., Ltd.) as a thermosetting resin binder and a novolac type phenol resin (manufactured by Meiwa Kasei Co., Ltd.) as a curing agent, and a novolak for all epoxy groups in the novolak type epoxy resin The mixed phenol resin is mixed so that the equivalent ratio of all phenolic hydroxyl groups in the phenolic resin (total phenolic hydroxyl groups in the novolak phenol resin / total epoxy groups in the novolak epoxy resin) is 1.0, To the mixed resin, 2-ethyl-4-methylimidazole was mixed as a curing accelerator to obtain a resin component. The said hardening accelerator was mixed so that it might become 1 mass part with respect to 100 mass parts of mixed resin of a cresol novolak type epoxy resin and a novolak type phenol resin.
With respect to 100 parts by mass of the graphite powder mixture, 25 parts by mass of the mixed resin in the resin component and 0.5 parts by mass of the polycarboxylic acid type polymer which is an anionic surfactant as a dispersant for the graphite powder. Then, it was dissolved in methyl ethyl ketone as an organic solvent to prepare a binder resin liquid, and then 100 parts by mass of the graphite powder mixture was put into the binder resin liquid.
The binder resin liquid charged with the graphite powder mixture was mixed with a stirrer for 1 hour to prepare a slurry-like mixed material having a viscosity at 20 ° C. of 1000 mPa · s.

Next, the slurry-like mixed material is injected into a green sheet forming apparatus having a doctor blade, coated on a PET film, a sheet-like material by a doctor blade method is produced, and sufficiently blown and dried. A green sheet having a thickness of about 0.3 mm was produced.
After the green sheet is punched into a predetermined shape with a punching die and peeled off from the film, two main body forming green sheets 31a (external dimensions: 200 mm long, 200 mm wide) each having the form shown in FIG. A green sheet having a form as shown in FIG. 1B, which is adjusted to have a predetermined thickness by laminating two edge forming green sheets 31b (external dimensions: 200 mm in length and 200 mm in width). A laminate was obtained.

  As a forming die, a pair of upper and lower molds having an outer shape of 270 mm in length and 270 mm in width, and a groove shape portion having a width of 1 mm and a single-side groove depth of 0.3 mm is engraved in the range of 200 mm in length and 200 mm in width. The green sheet laminate is placed on the molding surface of the molding die, and pressed for 20 seconds at a pressure of 40 MPa under a temperature condition of 180 ° C., thereby performing hot-pressure molding. c) Hot-press molded product having a shape as shown in c) having a length of 200 mm, a width of 200 mm, a thickness (thickness of the thinnest portion) t of 0.20 mm, and a thickness of the edge 32 of 0.8 mm. Was made.

  After removing the obtained hot-pressed product from the mold, it is further post-cured in a curing furnace at a temperature of 190 ° C. for 5 hours, and then subjected to wet blasting to remove the resin-rich layer on the surface. Thus, a desired separator was obtained.

The obtained separator had a good appearance. Further, the bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) of the obtained separator were measured. The results are shown in Table 1.

<Measurement method of bending strength>
In accordance with JIS R1601, a 4-point bending test was performed at room temperature to measure the bending strength (MPa).
<Measurement method of fracture strain>
In accordance with JIS R1601, a four-point bending test was performed at room temperature, and the fracture strain (%) was measured.
<Specific resistance measurement method>
The specific resistance (mΩ · cm) was measured according to JIS C2525.
<Measurement method of contact resistance>
Cut out the separator to be measured as two 30 mm square test pieces,
While the obtained test pieces were brought into contact with each other at a pressure of 1 MPa, a voltage drop (mV) between the test pieces was measured at an energization amount of 1 A, and a contact resistance (mΩ · cm ² ) was calculated.
<Durability (fatigue characteristics)>
A test piece (5 mm long, 50 mm wide, 0.8 mm thick) is placed on a four-point bending jig with a support side of 40 mm and a load side of 20 mm, and a 0.4% amplitude deflection is repeatedly applied at 5 Hz to break. The number of times was measured.

(Example 2)
As the first graphite powder, mosaic coke (manufactured by Mitsubishi Chemical Corporation) was graphitized at 2500 ° C., and then pulverized and classified to adjust the particle size. The particle size distribution was 2 to 110 μm, and the average particle size (D50) Is artificial graphite powder having a crystal plane distance d ₀₀₂ of 0.3363 nm and, as the second graphite powder, mosaic coke (manufactured by Mitsubishi Chemical Corporation) is graphitized at 2500 ° C., and then pulverized. Using an artificial graphite powder having an average particle diameter (D50) of 5 μm, a specific surface area of 66 m ² / g, and a crystal plane distance d ₀₀₂ of 0.3363 nm, classified and adjusted in particle size, the mass / weight of the first graphite powder / The graphite powder mixture was obtained by mixing so that the ratio represented by the mass of the second graphite powder was 75/25, and the same purpose as in Example 1 was used except that this graphite powder mixture was used. SE Got a parator. The content ratio of the graphite powder having a particle size larger than 70 μm in the graphite powder mixture is 4% by mass, the content rate of the graphite powder having a particle size of 30 to 70 μm is 40% by mass, and the particle size exceeds 10 μm and is 30 μm. The content ratio of graphite powder having a particle diameter of less than 1 μm was 28 mass%, the content ratio of graphite powder having a particle diameter of 1 to 10 μm was 26 mass%, and the content ratio of graphite powder having a particle diameter of less than 1 μm was 2 mass%. It was.
The obtained separator had a good appearance. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

(Example 3)
As the first graphite powder, mosaic coke (manufactured by Mitsubishi Chemical Corporation) was graphitized at 2500 ° C. and then pulverized and classified to adjust the particle size. The particle size distribution was 5 to 120 μm and the average particle size (D50). Is artificial graphite powder having a crystal plane distance d ₀₀₂ of 0.3362 nm, and, as a second graphite powder, a mosaic coke (manufactured by Mitsubishi Chemical Corporation) is graphitized at 2500 ° C., and then pulverized. Using an artificial graphite powder having an average particle diameter (D50) of 2 μm, a specific surface area of 85 m ² / g, and a crystal plane distance d ₀₀₂ of 0.3362 nm, classified and adjusted in particle size, the mass / weight of the first graphite powder / The graphite powder mixture was obtained by mixing so that the ratio represented by the mass of the second graphite powder was 75/25, and the same purpose as in Example 1 was used except that this graphite powder mixture was used. SE Got a parator. The content ratio of the graphite powder having a particle size larger than 70 μm in the graphite powder mixture is 8% by mass, the content rate of the graphite powder having a particle size of 30 to 70 μm is 50% by mass, and the particle size exceeds 10 μm and is 30 μm. The content ratio of the graphite powder having a particle diameter of less than 1 μm was 23 mass%, the content ratio of the graphite powder having a particle diameter of less than 1 μm was 5 mass%. It was.
The obtained separator had a good appearance. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

Example 4
The graphite powder mixture was obtained by mixing so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder was 70/30. Except for using this graphite powder mixture, The target separator was obtained in the same manner as in Example 1. The content ratio of the graphite powder having a particle size larger than 70 μm in the graphite powder mixture is 2% by mass, the content rate of the graphite powder having a particle size of 30 to 70 μm is 32% by mass, and the particle size exceeds 10 μm and is 30 μm. The content ratio of the graphite powder having a particle diameter of less than 1 μm was 26 mass%, the content ratio of the graphite powder having a particle diameter of 1 to 10 μm was 38 mass%, and the content ratio of the graphite powder having a particle diameter of less than 1 μm was 2 mass%. It was.
The obtained separator had a good appearance. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

(Example 5)
Artificial graphite having a particle size distribution of 3 to 98 μm, an average particle size (D50) of 33 μm, and a crystal plane spacing d ₀₀₂ of 0.3366 nm, obtained by pulverizing and classifying isotropic graphite to adjust the particle size. The powder was used as the second graphite powder, and isotropic graphite was pulverized and classified to adjust the particle size. The average particle diameter (D50) was 7 μm, the specific surface area was 35 m ² / g, and the crystal plane distance d ₀₀₂ was 0.00. By using artificial graphite powder of 3366 nm and mixing so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder is 65/35, a graphite powder mixture is obtained. A target separator was obtained in the same manner as in Example 1 except that the powder mixture was used. In the graphite powder mixture, the content ratio of the graphite powder having a particle diameter larger than 70 μm in the graphite powder mixture is 2% by mass, the content ratio of the graphite powder having a particle diameter of 30 to 70 μm is 33% by mass, The content ratio of graphite powder having a diameter of more than 10 μm and less than 30 μm is 27% by mass, the content ratio of graphite powder having a particle diameter of 1 to 10 μm is 35% by mass, and the content ratio of graphite powder having a particle size of less than 1 μm. Was 3% by mass.
The obtained separator had a good appearance. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

(Comparative Example 1)
As the first graphite powder, mosaic coke (manufactured by Mitsubishi Chemical Corporation) was graphitized at 2500 ° C., and then pulverized and classified to adjust the particle size. The particle size distribution was 2 to 110 μm, the average particle size was 35 μm, Artificial graphite powder having a crystal plane distance d ₀₀₂ of 0.3363 nm is used, and mosaic coke (manufactured by Mitsubishi Chemical Corporation) is graphitized at 2500 ° C. as the second graphite powder, and then pulverized and classified. Using an artificial graphite powder having an average particle diameter of 5 μm, a specific surface area of 23 m ² / g, and a crystal plane distance d ₀₀₂ of 0.3363 nm, the particle size of which was adjusted, the mass of the first graphite powder / the second graphite powder A graphite powder mixture was obtained by mixing so that the ratio expressed by mass was 75/25, and a target separator was obtained in the same manner as in Example 1 except that this graphite powder mixture was used. The content ratio of the graphite powder having a particle diameter of more than 70 μm in the graphite powder mixture is 2 mass%, the content ratio of the graphite powder having a particle diameter of 30 to 70 μm is 33 mass%, and the particle diameter exceeds 10 μm and is 30 μm. The content ratio of the graphite powder having a particle diameter of less than 1 μm was 28 mass%, the content ratio of the graphite powder having a particle diameter of 1 to 10 μm was 35 mass%, and the content ratio of the graphite powder having a particle diameter of less than 1 μm was 1 mass%. It was.
The obtained separator had a good appearance. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

(Comparative Example 2)
As the first graphite powder, mosaic coke (manufactured by Mitsubishi Chemical Corporation) was graphitized at 2500 ° C., and then pulverized and classified to adjust the particle size. The particle size distribution was 3 to 98 μm, the average particle size was 33 μm, Artificial graphite powder having a crystal plane spacing d ₀₀₂ of 0.3362 nm is used, and mosaic coke (manufactured by Mitsubishi Chemical Corporation) is graphitized at 2500 ° C. as the second graphite powder, and then pulverized and classified. Using an artificial graphite powder having an average particle diameter of 1 μm, a specific surface area of 110 m ² / g, and a crystal plane distance d ₀₀₂ of 0.3362 nm, adjusted in particle size, the mass of the first graphite powder / the second graphite powder A graphite powder mixture was obtained by mixing so that the ratio expressed by mass was 75/25, and a target separator was obtained in the same manner as in Example 1 except that this graphite powder mixture was used. The content ratio of the graphite powder having a particle diameter larger than 70 μm in the graphite powder mixture is 2 mass%, the content ratio of the graphite powder having a particle diameter of 30 to 70 μm is 30 mass%, and the particle diameter exceeds 10 μm and is 30 μm. The content ratio of the graphite powder having a particle diameter of less than 1 μm was 26 mass%, the content ratio of the graphite powder having a particle diameter of 1 to 10 μm was 35 mass%, and the content ratio of the graphite powder having a particle diameter of less than 1 μm was 7 mass%. It was.
The obtained separator was observed to be defective in structure. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

(Comparative Example 3)
As the first graphite powder, artificial graphite powder having a particle size distribution of 3 to 98 μm, an average particle size of 33 μm, and a crystal plane distance d ₀₀₂ of 0.3366 nm, which is pulverized and classified to adjust the particle size, is used. As the second graphite powder, artificial graphite powder having an average particle diameter of 4 μm, a specific surface area of 39 m ² / g, and a crystal plane distance d ₀₀₂ of 0.3366 nm, obtained by pulverizing and classifying isotropic graphite to adjust the particle size And mixing so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder is 85/15, to obtain a graphite powder mixture, except that this graphite powder mixture was used Obtained the target separator in the same manner as in Example 1. The content ratio of the graphite powder having a particle size larger than 70 μm in the graphite powder mixture is 2% by mass, the content rate of the graphite powder having a particle size of 30 to 70 μm is 34% by mass, and the particle size exceeds 10 μm and is 30 μm. The content ratio of graphite powder having a particle diameter of less than 1 μm was 32% by mass, the content ratio of graphite powder having a particle diameter of 1 to 10 μm was 30% by mass, and the content ratio of graphite powder having a particle diameter of less than 1 μm was 1% by mass. It was.
The obtained separator had a good appearance. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

(Comparative Example 4)
In Comparative Example 4, a graphite powder mixture was obtained by mixing so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder was 50/50, and this graphite powder mixture was used. The target separator was obtained in the same manner as in Comparative Example 4 except that. The content ratio of the graphite powder having a particle size larger than 70 μm in the graphite powder mixture is 2% by mass, the content rate of the graphite powder having a particle size of 30 to 70 μm is 17% by mass, and the particle size exceeds 10 μm and is 30 μm. The content ratio of the graphite powder having a particle diameter of less than 1 μm was 24 mass%, the content ratio of the graphite powder having a particle diameter of 1 to 10 μm was 55 mass%, and the content ratio of the graphite powder having a particle diameter of less than 1 μm was 2 mass%. It was.
The obtained separator was observed to be defective in structure. Further, the obtained separator had the same bending strength (MPa), breaking strain (%), specific resistance (mΩ · cm), contact resistance (mΩ · cm ² ), and durability (fatigue characteristics) as in Example 1. It was measured. The results are shown in Table 1.

(Comparative Example 5)
As the first graphite powder, mosaic coke (manufactured by Mitsubishi Chemical Corporation) was graphitized at 2500 ° C., and then pulverized and classified to adjust the particle size. The particle size distribution was 5 to 200 μm, the average particle size was 80 μm, Artificial graphite powder having a crystal plane distance d ₀₀₂ of 0.3363 nm is used, and mosaic coke (manufactured by Mitsubishi Chemical Corporation) is graphitized at 2500 ° C. as the second graphite powder, and then pulverized and classified. Using an artificial graphite powder having an average particle diameter of 4 μm, a specific surface area of 39 m ² / g, and a crystal plane distance d ₀₀₂ of 0.3363 nm, adjusted in particle size, the mass of the first graphite powder / the second graphite powder A graphite powder mixture was obtained by mixing so that the ratio expressed by mass was 75/25, and a target separator was produced in the same manner as in Example 1 except that this graphite powder mixture was used. It was. The content ratio of the graphite powder having a particle size larger than 70 μm in the graphite powder mixture is 25% by mass, the content rate of the graphite powder having a particle size of 30 to 70 μm is 37% by mass, and the particle size exceeds 10 μm and is 30 μm. The content ratio of graphite powder having a particle diameter of less than 1 μm was 25% by mass, the content ratio of graphite powder having a particle diameter of 1 to 10 μm was 12% by mass, and the content ratio of graphite powder having a particle diameter of less than 1 μm was 1% by mass. It was.

(Comparative Example 6)
As the first graphite powder, needle-shaped coke (manufactured by Nippon Steel Chemical Co., Ltd.) was graphitized at 2800 ° C., and then pulverized and classified to adjust the particle size. The particle size distribution was 3 to 116 μm, the average particle size was 35 μm, Artificial graphite powder having a crystal plane interval d ₀₀₂ of 0.3358 nm is used, and needle-like coke (manufactured by Nippon Steel Chemical Co., Ltd.) is graphitized at 2800 ° C. as the second graphite powder, and then pulverized and classified. Using an artificial graphite powder having an average particle diameter of 7 μm, a specific surface area of 14 m ² / g, and a crystal plane distance d ₀₀₂ of 0.3358 nm, adjusted in particle size, the mass of the first graphite powder / the second graphite powder A graphite powder mixture was obtained by mixing so that the ratio expressed by mass was 75/25, and a target separator was produced in the same manner as in Example 1 except that this graphite powder mixture was used. Tried. The content ratio of the graphite powder having a particle diameter of more than 70 μm in the graphite powder mixture is 6 mass%, the content ratio of the graphite powder having a particle diameter of 30 to 70 μm is 33 mass%, and the particle diameter exceeds 10 μm and is 30 μm. The content ratio of graphite powder having a particle diameter of less than 1 μm was 27% by mass, the content ratio of graphite powder having a particle diameter of 1 to 10 μm was 33% by mass, and the content ratio of graphite powder having a particle diameter of less than 1 μm was 1% by mass. It was.

  The separators obtained in Examples 1 to 5 show high corrosion resistance and low impurity elution characteristics by containing graphite powder. From Table 1, as the graphite powder, the first graphite powder and the second graphite are used. It can be seen that the inclusion of the powder has good appearance, low electrical resistance, high strength and durability, and can be suitably used as a separator for a polymer electrolyte fuel cell.

On the other hand, from Table 2, the separator obtained in Comparative Example 1 has a small fracture strain of 0.65% because the specific surface area of the second graphite powder used as a raw material is as small as 23 m ² / g. In this case, it was broken at 20,000 times and could not exhibit sufficient fatigue properties.

From Table 2, since the separator obtained in Comparative Example 2 has a large specific surface area of 110 m ² / g of the second graphite powder used as a raw material, the fluidity of the green sheet at the time of hot pressing is reduced, and the surface In this case, a structural defect was caused to cause gas leakage, and the electrical resistance was high.

  From Table 2, since the separator obtained in Comparative Example 3 has a small amount of the second graphite powder compared to the amount of the first graphite powder used as a raw material, the breaking strain is as small as 0.67%, In the durability test, it was broken at 37,500 times and could not exhibit sufficient fatigue characteristics.

  From Table 2, since the separator obtained in Comparative Example 4 has a larger amount of the second graphite powder than the amount of the first graphite powder used as a raw material, the fluidity of the green sheet at the time of hot pressing. , The structure of the separator was defective on the surface of the separator, causing gas leakage, and the electrical resistance was high.

  From Table 2, in Comparative Example 5, since the particle size distribution of the first graphite powder used as the raw material is 5 to 200 μm and the average particle size is as large as 80 μm, the graphite powder having a large particle size in the slurry mixture is Sedimentation occurred, and a defective structure was observed in the obtained green sheet. Moreover, in the durability test, it broke at 56,000 times and could not exhibit sufficient fatigue characteristics.

From Table 2, in Comparative Example 6, since the specific surface area of the second graphite powder used as a raw material was as small as 14 m ² / g, the fracture strain was as small as 0.51%, and the fracture was broken at 153 times in the durability test. However, sufficient fatigue properties cannot be exhibited.

  According to the present invention, it is possible to provide a separator for a polymer electrolyte fuel cell that exhibits high corrosion resistance and low impurity elution characteristics, has low gas impermeability and low electrical resistance, and has high strength and durability. A method for easily producing a separator for a polymer electrolyte fuel cell can be provided.

DESCRIPTION OF SYMBOLS 1 Single cell 2 Ion exchange membrane 31a Main part formation green sheet 31b Edge formation green sheet 32 Edge 3 Separator 4 Anode electrode plate 5 Cathode electrode plate

Claims (4)

A first graphite powder having a particle size distribution of 1 to 150 μm and an average particle diameter of 30 to 70 μm, and a second graphite powder having an average particle diameter of 1 to 10 μm and a specific surface area of 30 to 100 m ² / g, From the material in which the graphite powder mixture mixed so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder is 80/20 to 60/40 is bound by the thermosetting resin binder. A separator for a polymer electrolyte fuel cell.   The first graphite powder is an artificial graphite powder obtained by pulverizing, classifying and adjusting the particle size by pulverizing and classifying isotropic graphite, or after graphitizing the mosaic coke, and then pulverizing and classifying the artificial graphite powder obtained by adjusting the particle size. The second graphite powder is also artificial graphite powder obtained by pulverizing and classifying isotropic graphite to adjust the particle size, or artificial graphite powder obtained by subjecting mosaic coke to graphitization and then pulverizing and classifying to adjust particle size. The separator for a polymer electrolyte fuel cell according to 1. A method for producing a polymer electrolyte fuel cell separator comprising:
A first graphite powder having a particle size distribution of 1 to 150 μm and an average particle diameter of 30 to 70 μm, and a second graphite powder having an average particle diameter of 1 to 10 μm and a specific surface area of 30 to 100 m ² / g, The graphite powder mixture mixed so that the ratio represented by the mass of the first graphite powder / the mass of the second graphite powder is 80/20 to 60/40 is dispersed in a thermosetting resin binder solution to form a slurry. Make mixed materials,
A green sheet is produced by the doctor blade method using the slurry-like mixed material,
A method for producing a separator for a polymer electrolyte fuel cell, comprising stacking the obtained green sheets and hot pressing.   The first graphite powder is an artificial graphite powder obtained by pulverizing, classifying and adjusting the particle size by pulverizing and classifying isotropic graphite, or after graphitizing the mosaic coke, and then pulverizing and classifying the artificial graphite powder obtained by adjusting the particle size. The second graphite powder is also artificial graphite powder obtained by pulverizing and classifying isotropic graphite to adjust the particle size, or artificial graphite powder obtained by subjecting mosaic coke to graphitization and then pulverizing and classifying to adjust particle size. 4. A method for producing a polymer electrolyte fuel cell separator as described in 3.