JP2005285552A - Fuel cell separator and manufacturing method for composite therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a composite for the fuel separator which is compound material shortening a forming cycle and superior in size precision and release property and the manufacturing method for the fuel cell separator using the composite. <P>SOLUTION: The composite for the fuel cell separator contains 65 to 90 wt% graphite powder, 1 to 25 wt% thermosetting resin and/or thermosetting resin composition, and 1 to 30 wt% thermoplastic resin. Boron is contained in the graphite powder according to need. The thermosetting resin and/or thermosetting resin composition contain crystalline epoxide resin with viscosity at 1 to 20 mPa s in 150°C, melting point of 50 to 130°C and being solid in normal temperature. The thermosetting resin contains at least one type of resin from cumarone resin and petroleum resin. Furthermore, a urea-based hardening accelerator is contained as a hardening accelerator. The fuel cell separator is obtained by forming the pulverized composition at 150 to 200°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a composition for a fuel cell separator mainly composed of graphite and a resin, and a method for producing a fuel cell separator using the composition.

Fuel cells that are used in automobile applications and household cogeneration applications are attracting attention. This fuel cell uses chemical energy directly as electric energy without converting it into thermal energy, and usually takes out electricity by reaction of hydrogen and oxygen.
There are several types of fuel cells such as phosphoric acid fuel cells, solid electrolyte fuel cells, and polymer electrolyte fuel cells (PEFC). Among them, in the polymer electrolyte fuel cell and the phosphoric acid fuel cell, a separator which is a conductive molded product is used.

The separator constitutes a unit cell together with an electrode or the like, and is used by laminating unit cells, and requires conductivity while isolating gas (hydrogen / oxygen). Therefore, high electrical conductivity of 100 mΩcm or less is required, gas permeability is low, and mechanical strength, corrosion resistance, moldability, and the like are required.
As materials satisfying these required characteristics, materials roughly classified into graphite and metal are being studied. Examples of the graphite-based material include cutting carbon for cutting a graphite material, special expanded graphite, and a compound material for integrating graphite powder with a resin. In addition, although metal-based materials are excellent in electrical conductivity and mechanical strength, corrosion resistance is generally insufficient and surface treatment is required, but recently stainless-based materials have been studied.

  Graphite powder and resin compound materials share the above required characteristics between graphite and resin, and various studies have been made.

For example, in order to obtain a carbon material suitable as a fuel cell separator with high density, high mechanical strength and excellent electrical conductivity, a graphitized carbon material consisting of a binder and carbonaceous particles having multiple particle sizes is proposed. (See Patent Document 1).
Further, in order to obtain a carbon material suitable as a fuel cell separator having a porosity of 5% or less and a ratio of volume specific resistance in the XY direction and volume specific resistance in the Z direction of 2 or less, A carbon material containing ketjen black and spherical graphite particles has been proposed (see Patent Document 2).
In order to improve the conductivity by reducing the amount of binder, a method has been proposed in which a small amount of binder is blended into a carbon material, pressure-molded, and then impregnated with an impregnating agent (see Patent Document 3). .
Further, in order to obtain a fuel cell separator having a low contact resistance with an electrode portion, a fuel cell separator having a surface roughness within a certain range has been proposed (see Patent Document 4).
Further, in order to obtain a fuel cell separator with little anisotropy, it has been proposed to use artificial graphite and natural graphite in combination (see Patent Document 5).
In addition, it has been proposed to use specific graphite powder in order to obtain a fuel cell separator having a balance of gas impermeability, thermal conductivity, conductivity, and the like (see Patent Document 6).

  On the other hand, various studies have been conducted on conductive epoxy resin molding materials containing graphite and epoxy resins.

For example, it has been proposed to use an ortho cresol novolac type epoxy resin or a bisphenol type epoxy resin as an epoxy resin, and specifically, a bisphenol A type epoxy resin is disclosed as a bisphenol type epoxy resin (see Patent Document 7). .)
Further, it has been proposed to use a bisphenol F type epoxy resin as an epoxy resin (see Patent Document 8).
In addition, it has been proposed to use a cresol novolac type epoxy resin as an epoxy resin (see Patent Documents 9 and 10).
JP-A-4-214072 Japanese Patent Laid-Open No. 8-31231 JP-A-11-195422 Japanese Patent Laid-Open No. 11-297338 Japanese Unexamined Patent Publication No. 2000-40517 JP 2000-21421 A JP 2001-139696 A JP 2001-216976 A JP 2002-83609 A JP 2002-201257 A

  However, a graphite-resin compound material that satisfies the required characteristics as a fuel cell separator, that is, electrical conductivity, mechanical strength, etc., and has improved moldability and is capable of mass production. Yes.

  The present invention has been made in view of the above problems, and a composition for a fuel cell separator, which is a compound material that can shorten a molding cycle and is excellent in dimensional accuracy and releasability, and a composition thereof are used. It aims at providing the manufacturing method of a fuel cell separator.

  In order to achieve the above object, the composition for a fuel cell separator according to the present invention comprises graphite powder 65 to 90 wt%, a thermosetting resin and / or a thermosetting resin composition 1 to 25 wt%, and a thermoplastic resin 1. It is characterized by containing ~ 30 wt%.

  At this time, the graphite powder may contain boron.

At this time, the thermosetting resin and / or the thermosetting resin composition is represented by the following general formula (1), and has a viscosity of 1 to 20 mPa · s at 150 ° C., a melting point of 50 to 130 ° C., and solid at room temperature. It is more preferable to include a crystalline epoxy resin.
(1)

(However, G represents a glycidyl group, R represents a monovalent group, n represents an integer of 0 to 4, and X represents S or O)

  In this case, it is more preferable that the thermoplastic resin contains at least one kind of coumarone resin and petroleum resin.

  At this time, it is more preferable to include a urea-based curing accelerator as the curing accelerator.

  The method for producing a fuel cell separator according to the present invention is characterized in that a pulverized product obtained by pulverizing after molding the above composition for a fuel cell separator is molded at 150 to 200 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, in the compound type | system | group material of graphite and resin, the material which improved the moldability can be provided, satisfy | filling the required characteristic as a fuel cell separator. In particular, since the molding cycle is shortened and the dimensional accuracy and mold release properties are excellent, a compound material that can be used for mass production of separators in the future can be provided.

  Preferred embodiments of a composition for a fuel cell separator and a method for producing a fuel cell separator according to the present invention will be described below.

  The fuel cell separator is provided between adjacent unit cells in a fuel cell configured by stacking a plurality of unit cells, and forms a fuel gas channel and an oxidizing gas channel between the electrodes, and the fuel gas and the oxidizing gas. And a gas channel groove or the like is formed. The fuel cell separator produced by the present invention is obtained by molding and curing graphite powder and a thermosetting resin into a predetermined shape, and as it is or after being subjected to grooving, drilling, etc. as a fuel cell separator. used. Further, the fuel cell separator is understood to include a member of the fuel cell separator before processing.

First, the fuel cell separator composition of the present invention will be described.
The composition for a fuel cell separator of the present invention contains (A) graphite powder, (B) at least one of a thermosetting resin and a thermosetting resin composition, and (C) a thermoplastic resin as an essential component. To do. The blending ratio of these components is (A) 65 to 90 wt%, (B) 1 to 25 wt%, (C) 1 to 30 wt%, and more preferably (A) 75 to 85 wt%, (B) 10 -20 wt%, (C) 5-10 wt%.

Moreover, the composition for fuel cell separators of this invention contains a hardening accelerator as needed.
Hereinafter, each component of the composition for fuel cell separators will be described in detail.

  The blending ratio of the graphite powder in the composition is 65 to 90 wt%, more preferably 75 to 85 wt% as described above. If the graphite powder exceeds 90 wt%, the fluidity at the time of molding is lowered, and a great deal of pressure is required for molding, which may increase the cost of the molding machine. If the graphite powder is less than 65 wt%, the electrical conductivity may be insufficient.

In the present invention, when boron is included in the graphite powder, an effect such as higher electrical conductivity can be obtained.
Hereinafter, the present invention will be described by taking graphite powder containing boron as an example and dividing it into graphite powder and a method of adding boron to graphite powder.

The graphite powder uses one or more of coal-based and / or petroleum-based heavy oil as a raw material, is processed at 600 ° C. or lower to produce raw coke, pulverizes raw coke, and then pulverizes raw coke to 700-1500. Carbonized at 0 ° C and then graphitized at 2000 ° C or higher is preferable.
In this case, the raw coke is preferably generated by heat treatment with a delayed coker.
The average particle size of the crushed raw coke is preferably 1 to 50 μm. Further, after carbonizing or graphitizing the pulverized raw coke, it is preferable to pulverize and pulverize to adjust the particle size to graphite powder having an average particle size of 3 to 50 μm and a BET specific surface area of 10 m ² / g or less.

  Coal heavy oil (coal tar raw material) is coal tar produced when carbonizing coal, high boiling point tar oil and tar pitch separated from coal tar, and quinoline insoluble (QI) content. The removed one is desirable. Preferably tar pitch is used. The tar pitch includes a soft pitch with a softening point of 70 ° C. or lower, a medium pitch with a softening point of 70 to 85 ° C., and a high pitch with a softening point of 85 ° C. or higher. Any of these tar pitches can be used, but it is advantageous to use a soft pitch in terms of handling. Further, the coal-based heavy oil may be a mixture of two or three of tar pitch, coal tar and high boiling point tar oil.

  Examples of the petroleum heavy oil include catalytic cracked oil, normal pressure residual oil, and reduced pressure residual oil. In particular, decant oil (FCC-DO) which is a heavy component of petroleum fluid catalytic cracking oil is preferable. These heavy oils may be those obtained by removing light components by distillation in advance from the viewpoint of carbonization yield or by heat treatment to make them heavy by thermal polymerization. Such petroleum heavy oil contains almost no QI content.

  In addition, you may mix and use these coal-type heavy oil and petroleum-type heavy oil, for example in the ratio of 20-90 wt% of coal-type heavy oil, and 10-80 wt% of petroleum-type heavy oil.

  The raw coke means semi-raw coke having a volatile content (weight reduction when heated at 950 ° C. for 7 minutes) of 3 wt% or more, preferably 5 wt% or more. The coking temperature when producing raw coke with a delayed coker is 600 ° C. or lower, preferably 400 to 600 ° C., more preferably 450 to 500 ° C., but the processing temperature is set according to the volatile content remaining in the raw coke. Just decide.

The raw coke produced in the delayed coker is cut out using jet water, and then the moisture is adjusted and pulverized.
First, raw coke is pulverized by a coarse pulverizer such as a jaw crusher, and further pulverized by a fine pulverizer such as a hammer crusher type to an average particle diameter of 1 to 50 μm, preferably an average particle diameter of 15 to 35 μm.
If the average particle size of the pulverized raw coke exceeds 50 μm, the particle size of the pulverized raw coke may be larger than the thickness of the thinnest portion of the fuel cell separator as the graphite molded body, which is a problem. In this case, the specific surface area of the obtained graphite powder is increased, which may lead to a decrease in physical properties of the separator, particularly a decrease in bulk density, an increase in specific resistance, a decrease in bending strength, an increase in gas permeability, and the like. On the other hand, it is very difficult to pulverize raw coke to an average particle size of less than 1 μm, and the amount of resin must be increased because the surface area of the pulverized raw coke is increased. As a result, a fuel cell as a graphite molded body The specific resistance of the separator increases, which is not preferable.
The grinder to be used is not particularly limited, and any type of grinder may be used as long as the target average particle diameter can be obtained.

The ground raw coke (ground ground coke) is further carbonized to obtain graphite powder.
The carbonization temperature is preferably 700 ° C to 1500 ° C, more preferably 800 ° C to 1200 ° C. Carbonization treatment may be performed using a lead hammer type carbonization furnace in which crushed raw coke is put in a container and waste heat is effectively used, or may be performed using a burner type batch type carbonization furnace. Good. The type of furnace is not particularly limited. The rate of temperature increase is preferably about 10 ° C./hr, which is very slow in the temperature range where volatile components are volatilized, because it can increase the carbonization yield, but is not particularly limited.

As described above, the graphite powder used in the present invention has an average particle size of 3 to 50 μm. The graphite powder having this average particle diameter may be a single type of graphite powder, or may be a mixture of a plurality of types of graphite powder having different particle size distributions.
For example, graphite powder having two types of particle size distribution, that is, a large particle size graphite powder having an average particle size of 50 to 300 μm, preferably an average particle size of 70 to 150 μm, and an average particle size of less than 50 μm, preferably an average particle size of 5 to 20 μm. What blended the small particle size graphite powder of this can be used. The ratio of the large particle size graphite powder and the small particle size graphite powder at this time is 40:60 to 90:10 in mass ratio.
By using two types of graphite powder, large particles are crushed after kneading to produce a new coke surface, so that a conductive path can be made by contact, while large particles have a small surface area. It is expected that kneading is possible even with a small amount of resin. About small particle | grains, while improving the contact property between graphite particles, raising the intensity | strength of a molded article is anticipated. It is also effective for increasing the bulk density.
Further, the graphite powder used in the present invention may be a mixture of isotropic graphite powder and anisotropic graphite powder at, for example, 40:60 to 90:10, if desired.

  The obtained graphite powder preferably has a predetermined particle size distribution. That is, the particle size distribution of graphite powder is expressed by the Rosin-Rammler's distribution formula: R = 100exp (-adn) (where R is the distribution amount accumulated value on the sieve (%), and d is the particle size (μm)). , A represents a constant), the value of n is preferably in the range of 1.2 to 2.0, preferably 1.3 to 1.6.

In order to include boron in the graphite powder, any of the materials in any of the processing steps prior to the graphitization treatment, that is, coal-based and / or petroleum-based heavy oil, crushed raw coke, or carbonized carbide Boron or a boron compound is mixed in any of the materials. At this time, it is preferable to mix 0.05 to 40 parts by mass of boron or a boron compound as boron with respect to 100 parts by mass of the material.
By compounding boron, the graphite structure of the resulting graphite powder can be further developed, so that the physical properties of the fuel cell separator are improved, that is, the bulk density is improved, the specific resistance is reduced, the bending strength is improved, and the gas permeability is reduced. Can do.
Instead of boron or a boron compound (hereinafter collectively referred to as a boron material), carbon or carbides such as silicon, iron and these compounds, or a graphitization catalyst dissolved in carbon may be used. Good.

  A raw coke containing boron can be produced in a delayed coker by adding a boron material to coal-based and / or petroleum-based heavy oil. In this case, when the boron material is solid, it can be blended in heavy oil after the boron material is pulverized in advance. In the case where the boron material is soluble in a solvent, for example, alcohols, the boron material may be blended in the heavy oil as it is. The blending method is not particularly limited.

  When a boron material is not added when producing raw coke, the boron material may be blended with carbides heat treated at 700 to 1500 ° C. after pulverizing the raw coke. The blending method at this time is not particularly limited.

The graphitization treatment of carbides includes indirect energization type atchison furnaces where graphite is graphitized by Joule heat of graphite powder, LWG type graphitization furnaces and high-frequency induction furnaces that heat by supplying current to the graphite container. Or a continuous graphitization furnace in which the graphitizing atmosphere can be adjusted. The graphitization temperature is preferably 2000 ° C. or higher, more preferably 2500 ° C. or higher. Graphite powder containing boron obtained by graphitization treatment, so that the amount of time of the resin and kneaded becomes as small as possible, it is preferable that the specific surface area is less than 10 m ² / g, more preferably less 5 m ² / g .

  The above graphite powder containing boron is at least one of a thermosetting resin and a thermosetting resin composition (hereinafter referred to as a thermosetting resin and / or a thermosetting resin composition). The same applies to the case where this notation is used for other components.), Resin binders made of thermoplastic resins, and minor components such as curing accelerators added if necessary (components other than graphite materials are mainly resins) Therefore, hereinafter, these components may be collectively referred to as a resin component). The resin component in the composition for a fuel cell separator of the present invention (hereinafter sometimes simply referred to as a composition) may further contain a small amount of other components.

The thermosetting resin and / or thermosetting resin composition blended with the above graphite powder containing boron bonds and solidifies the graphite powder to a predetermined strength. As described above, the blending ratio of at least one of the thermosetting resin and the thermosetting resin composition is selected as a balance of functional sharing with the graphite powder containing boron.
The thermosetting resin and / or thermosetting resin composition preferably comprises an epoxy resin and a curing agent. The epoxy resin is preferably a low-viscosity epoxy resin, and examples thereof include bisphenol F-type epoxy resins and direct-bonded biphenyl-type epoxy resins. The blending ratio of the thermosetting resin and / or thermosetting resin composition in the composition is 1 to 25 wt%, and more preferably 10 to 20 wt%.

The epoxy resin preferably contains at least one low-viscosity crystalline epoxy resin having a viscosity of 1 to 20 mPa · s at 150 ° C., a melting point of 50 ° C. to 130 ° C., and a solid at room temperature. The viscosity is preferably 15 mPa · s or less, more preferably 10 mPa · s or less.
Thereby, it is excellent in storage stability as a compound at room temperature, and exhibits good fluidity even when, for example, about 75 to 85 wt% of graphite powder is contained at a molding temperature of about 150 ° C. to 200 ° C. it can. Adjustment to such a viscosity is easy by selecting the softening point and viscosity of the epoxy resin and the curing agent.
The low-viscosity crystalline epoxy resin has an epoxy equivalent of about 150 to 300 g / eq, preferably 170 to 250 g / eq.

The low-viscosity crystalline epoxy resin is preferably an ether type or thioether type epoxy resin represented by the following general formula (1). In the general formula (1), G represents a glycidyl group, and R represents the same or different hydrogen atom, halogen atom or hydrocarbon group having 1 to 6 carbon atoms, preferably a hydrogen atom or carbon It is a C1-C3 alkyl group, and it is good that the substituents other than the hydrogen atom which one benzene ring has are 0-4 pieces.
(1)

As is well known, epoxy resins often contain oligomers. When the epoxy resin represented by the general formula (1) is m (degree of polymerization) = 0, the low-viscosity crystalline epoxy resin may contain 50 wt% or less, preferably 10 wt% or less of oligomers with m = 1 or more. .
As the epoxy resin, one containing 30 wt% or more, preferably 50 wt% or more, more preferably 80 wt% or more of the low-viscosity crystalline epoxy resin that is solid at room temperature is used.

As the curing agent, known ones such as phenols, amines or carboxylic acids such as phthalic acids can be used, preferably polyhydric phenols, more preferably phenol, alkylphenol and formalin. The novolak type obtained from As the novolac-based curing agent, those having a softening point of room temperature or higher are advantageous.
The equivalent ratio of the epoxy resin and the curing agent is not particularly limited, but a range of 0.5 to 1.5 is preferable.

  If desired, a curing accelerator may be added to the thermosetting resin and / or thermosetting resin composition. In this case, the curing accelerator is not calculated as a thermosetting resin and / or a thermosetting resin composition. As the curing accelerator, known accelerators such as amines, imidazoles, ureas, organic phosphines and Lewis acids can be used, and ureas are particularly preferable. Furthermore, a dimethylurea hardening accelerator is particularly preferable among the urea hardening accelerators. Although the compounding quantity of a hardening accelerator is not specifically limited, The range of 0.01-10 mass parts is preferable with respect to 100 mass parts of thermosetting resins and / or thermosetting resin compositions.

The thermoplastic resin blended with the graphite powder containing boron is blended in order to improve the releasability of the molded product from the mold, and various thermoplastic resins can be used, but more preferably. Uses coumarone resin or petroleum resin, or both coumarone resin and petroleum resin.
The compounding ratio in the composition of the thermoplastic resin is 1 to 30 wt%, more preferably 5 to 10 wt%. When the thermoplastic resin exceeds 30 wt%, the electrical conductivity and mechanical strength are insufficient, while when the thermoplastic resin is less than 1 wt%, the releasability during molding is significantly deteriorated.

  Further, an additive such as an internal mold release agent or other conductive filler can be further blended with the above graphite powder containing boron within a range not impeding the effects of the present invention. These are not calculated as resin or graphite powder.

The fuel cell separator composition of the present invention can be obtained by blending graphite powder containing boron with at least one of the above thermosetting resin and thermosetting resin composition, the above thermoplastic resin, and the like.
At this time, the graphite powder containing boron and the thermosetting resin and / or the thermosetting resin composition and the thermoplastic resin may be mixed at the same time, or contain boron having at least two kinds of particle size distributions. After the graphite powder is mixed in advance, the thermosetting resin and / or the thermosetting resin composition and the thermoplastic resin may be mixed.

  Since the composition for a fuel cell separator of the present invention described above contains graphite powder, at least one of a thermosetting resin and a thermosetting resin composition, and a thermoplastic resin, the molding cycle can be shortened. It has excellent dimensional accuracy and releasability. Further, when the graphite powder contains boron, it can contribute to improvement of physical properties of the fuel cell separator such as reduction of specific resistance.

Next, a method for producing the fuel cell separator of the present invention will be described.
The fuel cell separator is obtained by molding the above composition for a fuel cell separator.
At this time, a graphite powder containing boron, a thermosetting resin and / or a thermosetting resin composition, a thermoplastic resin, a curing accelerator, and a resin component made up of additives, etc., blended as necessary are blended. Then, a composition for a fuel cell separator (hereinafter simply referred to as a composition) was heated and kneaded, and then pulverized or crushed so that the average particle size became 20 to 50 μm. It is advantageous to mold and cure at ~ 200 ° C.
Although the molding method depends on the blending ratio of the resin, press molding, transfer molding, or injection molding using a mold in which the holes and grooves of the separator are processed can be used. Press molding is suitable when the amount of resin added is low, and transfer molding and injection molding are suitable when the amount of resin added is relatively large and the compound is fluid. Moreover, since the composition for fuel cell separators contains a thermoplastic resin, continuous molding using a design roll in which hole grooves are processed can also be applied.

  In the kneading step, the composition is kneaded using a kneader. As a kneading machine, general-purpose, for example, a kneader, a roll or the like can be used, but is not limited thereto. The kneading is performed so that the resin and the graphite powder containing boron form as uniform a composition as possible. During kneading, heating can be performed for the purpose of reducing the viscosity of the resin, or a low boiling point solvent can be added, but it is necessary not to complete the curing.

Next, the composition obtained by kneading is pulverized or crushed. The pulverization can be performed using a known pulverizer. Examples of the pulverizer used here include a pulverizer for shear pulverization and a disk mill for compression pulverization. The average particle size of the pulverized product is 50 μm or less, preferably 30 μm or less, or 20 to 50 μm.
In this pulverization process, among the graphite powders with different average particle diameters, it is presumed that the large particle diameter graphite powder is preferentially pulverized, resulting in a surface with no resin attached, resulting in an effect of reducing the electrical resistivity. Is done. Therefore, the large particle size graphite powder having an average particle size of 50 to 300 μm used as a raw material is selectively pulverized to 50 μm or less, and the small particle size graphite powder having an average particle size of less than 50 μm should be crushed as much as possible. It is advantageous, and if it is pulverized more than necessary, the resin will not spread sufficiently and the strength of the molded product may be reduced.

After the composition is pulverized, it is molded using a heating mold molding machine using a mold. At this time, in order to cure the thermosetting resin and / or the thermosetting resin composition simultaneously with the molding, the molding temperature may be kept at 100 to 350 ° C, preferably about 150 to 200 ° C. The molding temperature is set to be not less than the curing temperature and less than the carbonization temperature of the thermosetting resin and / or thermosetting resin composition to be used. The molding pressure is preferably high in order to lower the electrical resistivity in the surface direction and increase the bulk density. However, since the equipment cost increases when the pressure is increased, the pressure is about ²⁰ to 1000 kg / cm ² , preferably 100 to 500 kg / About cm ² is appropriate.
Thus, a separator having a thickness of 2 mm and an area of 300 mm ² can be molded within a molding time of 5 minutes, preferably 3 minutes, and a dimensional accuracy of 100 μm or less, preferably 50 μm or less.

  If the composition is formed into a predetermined fuel cell separator shape and a predetermined groove or the like is provided at the same time, the fuel cell separator can be formed as it is or with simple processing. In addition, after forming the composition into a plate shape or the like, a fuel cell separator can be formed by adding groove processing or hole processing to the composition.

According to the production method of the present invention, the molding cycle can be shortened, and the dimensional accuracy and releasability of the obtained fuel cell separator are excellent. In addition, a fuel cell separator that is dense, has low gas permeability, high mechanical strength, and excellent electrical conductivity can be obtained.
The fuel cell separator, the bulk density of 1.80 g / cm ³ or more, preferably it is possible to 1.85 g / cm ³ or more, gas permeability (gas impermeability) 1 × 10 ^{- 14} or less and the bending strength can be 30 MPa or more. When the bulk density is less than 1.80 g / cm ³ , not only the gas impermeability is inferior, but also the mechanical strength (bending strength) is inferior. If the gas permeability exceeds 1 × 10 ⁻¹⁴ or more, hydrogen and oxygen as fuel may be mixed and power generation efficiency may be impaired. Further, if the bending strength is 30 MPa or less, the separator may be broken by vibration or impact.

  In addition, the specific resistance of the fuel cell separator is preferably low in order to increase the efficiency of the fuel cell, and is required to be 100 mΩcm or less. However, according to this manufacturing method, the required characteristics can be sufficiently achieved. Can do. It is possible to reduce the specific resistance by making the type of graphite used to have a high crystallinity or by reducing the blending amount of the thermosetting resin. Further, the specific resistance can be changed by the molding pressure or the like.

  When the fuel cell separator obtained by the production method of the present invention is used in a fuel cell, it can be a fuel cell with high efficiency and long life.

  Note that the graphite powder obtained by pulverizing raw coke containing volatile components and firing and graphitizing is more than the one obtained by pulverizing and graphitizing calcined cokes not containing volatile components. The rounded shape greatly contributes to improving the yield of molding as a fuel cell separator (non-defective product due to cracks and cracks during molding or non-defective product by visual inspection after molding) and physical properties. It is thought that.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to this. In this case, the measurement methods of the specific resistance, bending strength, dimensional accuracy, and releasability of the molded body are as follows.
○ Bending strength According to JIS K6911.
○ Dimensional accuracy The thickness of a predetermined portion of a molded body obtained under predetermined molding conditions was measured, and the mold surface accuracy was subtracted from the thickness accuracy.
○ Specific Resistance The above molded product was measured by a four-terminal voltage drop method.
○ Releasability A mold release agent was sprayed on the mold, and the number of moldings that could be continuously performed under heat and pressure was measured.

The raw materials used are as follows.
O Highly conductive graphite Coal-based heavy oil was used to grind the bulk raw coke produced by the delayed coking method with a Raymond mill to an average particle size of 30 μm. This was carbonized in a lead hammer furnace at a temperature of about 800 ° C. to obtain a carbide. This carbide added with 5 wt% boron carbide was graphitized at 2800 ° C.
○ Ether type epoxy resin The product name YSLV-80DE (melting point 79 ° C, 150 ° C viscosity 0.006 Pa · s) manufactured by Toto Kasei Co., Ltd. was used.
○ Thioether type epoxy resin The product name YSLV-50TE (melting point 50 ° C., 150 ° C. viscosity 0.006 Pa · s) manufactured by Toto Kasei Co., Ltd. was used.
○ Phenol novolac resin Tamanol 758 (softening point 83 ° C., 150 ° C. viscosity 0.22 to 0.35 Pa · s) manufactured by Arakawa Chemical Industries, Ltd. was used.
○ Coumarone resin The product name N-100S manufactured by Nippon Steel Chemical Co., Ltd. was used.
○ Petroleum resin The product name HRT-100X manufactured by Mitsui Petrochemical was used.
○ Curing accelerator The product name U-CAT3502T manufactured by Sun Apro Co., Ltd. was used as a dimethylurea based curing accelerator.

(Example 1)
11 parts by mass of ether type epoxy resin, 7 parts by mass of phenol novolac resin, 0.2 part by mass of curing accelerator, 7 parts by mass of coumarone resin and 75 parts by mass of highly conductive graphite (graphite / resin ratio = 3) It was set as the composition. This composition was kneaded with a roll heated to 100 ° C. The obtained kneaded material was pulverized by a disk mill. Table 1 shows the measurement results of the viscosity of the pulverized product, the dimensional accuracy of the molded product, and the specific resistance. In Table 1, all the blending ratios of the respective components were also expressed in parts by mass with respect to other examples and comparative examples other than Example 1.
This pulverized product was put into a mold, molded for 3 minutes under conditions of a temperature of 175 ° C. and a pressure of 300 kg / cm ² , and demolded. The physical properties of the obtained molded body were measured.

(Examples 2 to 5)
In the same manner as in Example 1, a pulverized product and a molded product were produced, and their physical properties were measured. The blending ratio and measurement results are shown in Table 1.

(Comparative Examples 1-3)
In the same manner as in Example 1, a pulverized product and a molded product were produced, and their physical properties were measured. The blending ratio and measurement results are shown in Table 1.

Based on the measurement results in Table 1, the excellent characteristics of the composition for a fuel cell separator of the present invention and the method for producing the separator were confirmed.

Claims (6)

A composition for a fuel cell separator, comprising 65 to 90 wt% of graphite powder, 1 to 25 wt% of a thermosetting resin and / or a thermosetting resin composition, and 1 to 30 wt% of a thermoplastic resin. 2. The composition for a fuel cell separator according to claim 1, wherein the graphite powder contains boron. The thermosetting resin and / or the thermosetting resin composition is a crystalline epoxy represented by the following general formula (1), having a viscosity of 1 to 20 mPa · s at 150 ° C., a melting point of 50 to 130 ° C., and a solid at room temperature. 2. The fuel cell separator composition according to claim 1, comprising a resin.
(1)
(However, G represents a glycidyl group, R represents a monovalent group, n represents an integer of 0 to 4, and X represents S or O) The composition for a fuel cell separator according to claim 1, wherein the thermoplastic resin contains at least one resin selected from a coumarone resin and a petroleum resin. 2. The composition for a fuel cell separator according to claim 1, further comprising a urea curing accelerator. A method for producing a fuel cell separator, comprising kneading the composition for a fuel cell separator according to claim 1 and then molding the pulverized product obtained by pulverization at 150 to 200 ° C.