JPWO2005064721A1 - Composition for fuel cell separator and method for producing fuel cell separator - Google Patents

Abstract

The present invention relates to a compound material of graphite and resin which has excellent moldability, shortens the molding cycle, has excellent dimensional accuracy, and can be mass-produced as a separator while satisfying the required characteristics as a fuel cell separator. A compound obtained by mixing graphite powder in an amount of 3 to 7 times by weight with respect to an epoxy resin binder, kneading and crushing the powder, and having a compound viscosity at 150° C. of 200 to 3000 Pa·s, is used as a fuel cell separator. A composition for a fuel cell separator, which comprises an epoxy resin binder having a specific electric resistance of 40 mΩcm or less as a specific resistance and a curing agent, and graphite powder. As the epoxy resin, a crystalline epoxy resin having a viscosity at 150° C. of 1 to 20 mPa·s, a melting point of 45 to 130° C. and a solid at room temperature is suitable.

Description

  The present invention relates to a composition for a fuel cell separator, particularly a polymer electrolyte fuel cell separator, and relates to a separator composition containing graphite and a resin as main components, and a method for producing a fuel cell separator using the composition. It is a thing.

  Fuel cells, which are used for automobiles, household cogeneration, and the like, are receiving attention. This fuel cell directly uses chemical energy as electric energy without converting it into heat energy, and usually refers to a cell that extracts electricity by the reaction of hydrogen and oxygen. There are several types of fuel cells such as phosphoric acid fuel cells, solid oxide fuel cells, and polymer electrolyte fuel cells (PEFC). Among them, PEFC and phosphoric acid fuel cells are electrically conductive. A separator, which is a flexible molded product, is used. The separator constitutes a unit cell together with an electrode and the like, and is used by stacking the unit cells, and it is required to have conductivity while separating gas (hydrogen/oxygen). Therefore, in addition to high electrical conductivity having a specific resistance of 100 mΩcm or less, low gas permeability, mechanical strength, corrosion resistance, and moldability are also required. Materials satisfying the required characteristics are roughly classified into graphite type and metal type. In this case, 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. Further, although metal-based materials are excellent in electrical conductivity and mechanical strength, their corrosion resistance is generally insufficient and surface treatment is required, but recently, stainless-based materials have also been investigated.

Many compound compounds of graphite powder and resin have been studied because the required properties are shared by the graphite and the resin. The following documents are prior art documents related to the present invention.
JP-A-4-214072 JP-A-8-31231 JP, 11-195422, A JP, 11-297338, A JP, 2000-40517, A Japanese Patent Laid-Open No. 2000-21421 JP, 2001-139696, A JP 2001-216976 A JP 2002-83609 A JP, 2002-2012257, A

  For example, in Patent Document 1, graphite having a binder and a carbonaceous powder having a plurality of particle sizes in order to obtain a carbon material that is dense and has high mechanical strength and is excellent in conductivity and suitable as a separator for a fuel cell. Proposed carbonized material. However, this method requires graphitization after molding. In Patent Document 2, in order to obtain a carbon material suitable for a fuel cell separator having a porosity of 5% or less and a ratio of the volume specific resistance in the XY direction of the molded body to the volume specific resistance in the Z direction of 2 or less, heat treatment is performed. We propose a carbon material containing a cured resin, Ketjen Black, and spherical graphite particles. In addition, Patent Document 3 proposes a method of blending a small amount of a binder with a carbon material, performing pressure molding, and then impregnating an impregnating agent in order to reduce the amount of the binder and improve the conductivity. Further, in Patent Document 4, 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 is proposed. Further, Patent Document 5 proposes to use artificial graphite and natural graphite in combination in order to obtain a fuel cell separator having a small anisotropy. Patent Document 6 proposes to use a specific graphite powder in order to obtain a fuel cell separator in which gas impermeability, thermal conductivity, conductivity and the like are well balanced. Patent Documents 7 to 10 describe a conductive epoxy resin molding material containing graphite and an epoxy resin. In Patent Document 7, an ortho-cresol novolac type epoxy resin or a bisphenol type epoxy resin is used as the epoxy resin, but as the bisphenol type epoxy resin, only a bisphenol A type epoxy resin is specifically disclosed. Patent Document 8 merely discloses a bisphenol F type epoxy resin as the epoxy resin. Patent Documents 9 to 10 specifically disclose a cresol novolac type epoxy resin as the epoxy resin.

  However, in a compound material of graphite and a resin, a material having higher moldability while satisfying the required properties as a fuel cell separator, that is, electrical conductivity, mechanical strength, and the like is desired. Therefore, an object of the present invention is to provide a molding material that shortens the molding cycle, has excellent dimensional accuracy, and is suitable for future mass production of separators.

  The present inventors have conducted extensive studies to solve the above problems, and as a resin, by blending an epoxy resin that is a solid at room temperature but exhibits a low viscosity at the time of high temperature melting with a graphite powder in a predetermined ratio, The inventors have found that the problems can be solved and completed the present invention.

According to the present invention, in a composition containing an epoxy resin binder and graphite powder, the graphite powder is mixed with the epoxy resin binder in a weight ratio of 2 to 10 times, preferably 3 to 7 times, to obtain graphite powder. A composition for a fuel cell separator, which has a compound viscosity after kneading with an epoxy resin binder of 200 to 3000 Pa·s and an electrical resistivity of 100 mΩcm or less, preferably 40 mΩcm or less.
In this case, the epoxy resin binder is composed of an epoxy resin and a curing agent, and the epoxy resin has a viscosity at 150° C. of 1 to 20 mPa·s, a melting point of 45° C. to 130° C., preferably 50° C. to 130° C., and is solid at room temperature. It is preferable to contain one or more crystalline epoxy resins.
Further, the present invention provides a composition containing an epoxy resin binder and graphite powder, wherein the graphite powder is blended in an amount of 2 to 10 times, preferably 3 to 7 times the weight ratio of the epoxy resin binder, by weight. The binder is composed of an epoxy resin and a curing agent, the epoxy resin is crystalline, the viscosity at 150° C. is 1 to 20 mPa·s, the melting point is 45° C. to 130° C., preferably 50° C. to 130° C., solid at room temperature. A composition for a fuel cell separator, comprising one or more crystalline epoxy resins.

（但し、Ｇはグリシジル基を示し、Ｒは１価の基を示し、ｎは０〜４の整数を示し、Ｘは２価の基を示す）で表されるエポキシ樹脂が適する。好ましくは、ＸがＯ又はＳであるエーテル型エポキシ樹脂又はチオエーテル型エポキシ樹脂である。
本発明の燃料電池セパレータの製造方法は、かかる組成物を、混練した後、粉砕し、該粉砕物を温度１００〜３５０℃、好ましくは１４０〜２３０℃で成形、硬化することを特徴とする。本発明の燃料電池セパレータはかかる製造方法により得られたものである。The crystalline epoxy resin used for the epoxy resin binder is represented by the following general formula (1)

(However, G shows a glycidyl group, R shows a monovalent group, n shows the integer of 0-4, and X shows a divalent group.) The epoxy resin represented by these is suitable. Preferred is an ether type epoxy resin or a thioether type epoxy resin in which X is O or S.
The method for producing a fuel cell separator of the present invention is characterized in that such a composition is kneaded and then pulverized, and the pulverized product is molded and cured at a temperature of 100 to 350°C, preferably 140 to 230°C. The fuel cell separator of the present invention is obtained by such a manufacturing method.

  A fuel cell separator is a fuel cell that is formed by stacking a plurality of unit cells, is provided between adjacent unit cells, and forms a fuel gas flow path and an oxidizing gas flow path between itself and an electrode. And has a function of separating the gas flow path from each other, and a groove for a gas flow path or the like is formed. The fuel cell separator produced in the present invention is a graphite powder and a thermosetting resin, which are molded into a predetermined shape and are cured, and are used as they are or as a fuel cell separator by grooving or punching if necessary. used. Further, the term “fuel cell separator” is understood to include a molded product for a fuel cell separator before processing.

  The fuel cell separator composition of the present invention contains graphite powder and an epoxy resin binder as essential components. Further, it usually contains a curing accelerator. The blending ratio of the graphite powder and the epoxy resin binder is 2 to 10 parts by weight, preferably 3 to 7 parts by weight, of the graphite powder to 1 part by weight of the epoxy resin binder. If there is too much graphite powder, the fluidity at the time of molding will be poor and a great amount of pressure will be required for molding, which will increase the cost of the molding machine. On the other hand, if there is too little graphite powder, the electrical conductivity will be insufficient.

  The graphite powder used in the present invention is not limited as long as it exhibits high conductivity, and examples thereof include graphitized carbonaceous materials such as mesocarbon microbeads and graphitized coal-based coke and petroleum-based coke. At least one of graphite electrode, processed powder of special carbon material, natural graphite, quiche graphite, and expanded graphite is used.

  In particular, in the present invention, one or more types of coal-based and/or petroleum-based heavy oils are used as raw materials, treated at 600° C. or lower to produce raw coke, and the raw coke is crushed and then the crushed raw It is preferable that the coke is carbonized at 700 to 1500° C. and then graphitized at 2000° C. or higher. In this case, the raw coke is preferably produced by heat treatment using a delayed coker. The average particle size of the crushed raw coke is preferably 1 to 50 μm. Further, after crushing raw coke after carbonization or graphitization, crushing (milling in the present invention means making large particles or agglomerates into powders having a smaller particle size, and there is no limitation on the means. For example, crushing is included) and the average particle size is preferably adjusted to 3 to 50 μm.

Further, it is preferable to add 0.05 to 40% by weight of a graphitization catalyst in any of the treatment steps prior to the graphitization treatment, that is, to the heavy oil, the crushed raw coke or the carbonized carbide. The graphitization catalyst is preferably one or more selected from boron, silicon, iron and compounds thereof. The graphite powder obtained preferably has a BET specific surface area of 10 m ² /g or less.

  Here, the coal-based heavy oil (coal tar-based raw material) removes quinoline insoluble matter (QI content) with coal tar produced during carbonization of coal and high boiling point tar oil and tar pitch separated from coal tar. It is preferable that Tar pitch is preferred. Tar pitches include soft pitches having a softening point of 70° C. or lower, medium pitches having a softening point of 70 to 85° C. and high pitches having a softening point of 85° C. or higher, and any of them can be used. It is advantageous to use. Further, it may be a mixture of two or three kinds of tar pitch, coal tar or high boiling tar oil.

  Examples of the petroleum heavy oil include catalytically cracked oil, atmospheric residual oil, and vacuum residual oil. Particularly, decant oil (FCC-DO), which is a heavy component of fluid catalytic cracking oil of petroleum, is preferable. Further, from the viewpoint of carbonization yield, these heavy oils may be removed from the light components by distillation in advance, or may be heat-treated to be heavy by thermal polymerization. Such petroleum heavy oil contains almost no QI component. The coal-based heavy oil and the petroleum-based heavy oil may be mixed at a mixing ratio of the petroleum-based heavy oil with respect to the coal-based heavy oil at 10 to 80 wt%.

  Raw coke refers to semi-raw coke having a volatile content (weight loss when heated at 950° C. for 7 minutes) of 3% or more, preferably 5% or more. In the production of raw coke with a delayed coker, the coking temperature is 600° C. or lower, usually 400° C. to 600° C., preferably 450° C. to 500° C., but the treatment temperature may be determined depending on the target volatile matter. Raw coke produced in a delayed coker is cut out with jet water, adjusted in water content, and then crushed. The crushing is performed by first crushing with a coarse crusher such as a jaw crusher and then crushing with a fine crusher such as a hammer crusher type to an average particle size of 1 to 50 μm, preferably 15 to 35 μm. If the average particle size exceeds 50 μm, the thickness of the fuel cell separator as a graphite molded body may become larger than that of the thinnest part, so that the specific surface area of the obtained graphite material becomes large, which in turn reduces the physical properties of the separator, especially the bulk density. It leads to decrease, increase in specific resistance, decrease in bending strength, and increase in gas permeability. On the other hand, it is very difficult to pulverize to an average particle size of less than 1 μm, and since the surface area increases, the amount of resin must be increased, which leads to an increase in specific resistance.

  The crusher here is not particularly limited, and any type of crusher may be used as long as it has a desired average particle size. After this pulverization, the raw coke is carbonized. The carbonization temperature is preferably 700°C to 1500°C, more preferably 800°C to 1200°C. For carbonization, a lead hammer type carbonization furnace that puts raw coke into a container and effectively uses waste heat may be used, or a burner type batch type carbonization furnace may be used. Is not particularly limited. It is preferable that the rate of temperature rise is extremely slow at about 10° C./hr at the temperature at which the volatile matter is scattered, because the carbonization yield will be high, but it is not particularly limited.

  Further, when producing raw coke in a delayed coker, coking can be performed after blending the graphitization catalyst with the raw material. The graphitization catalyst is preferably one that forms a carbide with carbon or one that dissolves in carbon. In particular, boron compounds, iron compounds, silicon compounds and their metals are desirable. When these compounds and metals are solid, they can be blended into the raw material after crushing, and those dissolved in a solvent such as alcohols may be blended into the raw material before use. The blending ratio of the graphitization catalyst is preferably in the range of 0.05-40 wt %. By adding a graphitization catalyst, it is possible to further develop the graphite structure of the obtained graphite material, and thus improve the physical properties of the fuel cell separator, that is, improve the bulk density, reduce the specific resistance, improve the bending strength, and reduce the gas permeability. Can be connected.

  When the graphitization catalyst is not added during the production of raw coke, the above-mentioned graphitization catalyst may be blended with the carbide that has been heat-treated at 700 to 1500° C. after crushing the raw coke. In this case, the blending ratio of the graphitization catalyst is in the range of 0.05 to 40 wt% with respect to the carbide.

Graphitization treatment of carbides includes an indirect energization type Acheson furnace in which carbides are put into a graphite container and then graphitized by Joule heat of graphite powder, an LWG type graphitization furnace in which an electric current is applied to the graphite container to heat it, and a high frequency wave. It is better to graphitize in an induction furnace or a continuous graphitization furnace in which the graphitization atmosphere can be adjusted. The graphitization temperature is preferably 2000°C or higher, more preferably 2500°C or higher. The average particle size of the graphitized material is adjusted to 3 to 50 μm, and the specific surface area is preferably 10 m ² /g or less so that the amount used when kneading with the resin is as small as possible, 5 m ² / It is more preferably g or less.

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

  The material obtained by crushing raw coke containing volatile matter, firing, and graphitizing the material is more crushed than graphitized calcinated coke containing no volatile matter. The shape is round, and it is considered that it contributes greatly to the improvement of the molding yield (cracking and cracking during molding, visual inspection of appearance after molding) and physical properties as a fuel cell separator.

  Further, the graphite powder used in the present invention may be a single particle size having an average particle size of 3 to 50 μm in order to facilitate the crushing or crushing of the obtained compound, and it is further unique due to the secondary crushing effect of the graphite particles. When it is desired to reduce the resistance, graphite powder having two types of particle size distribution may be used together. That is, even a mixture of a large particle size graphite powder having an average particle size of 50 to 300 μm, preferably 70 to 150 μm and a small particle size graphite powder having an average particle size of less than 50 μm, preferably 5 to 20 μm. Good. The weight ratio of the large particle size graphite powder and the small particle size graphite powder is 40:60 to 90:10. By using two kinds of graphite powder, large particles can be brought into contact with each other to form a conductive path when crushed after kneading, resulting in a conductive path, while large particles have a small surface area. It is expected that kneading is possible even with a small amount of resin. For small particles, it is expected that the strength of the molded product will be increased while the contact between graphite particles is increased. It is also effective for increasing the bulk density. Further, if desired, it may be a mixture of isotropic graphite powder and anisotropic graphite powder, for example, a mixture of 40:60 to 90:10.

  The epoxy resin binder used in the present invention binds and solidifies graphite powder to a predetermined strength and is composed of an epoxy resin and an epoxy resin curing agent. If desired, a curing accelerator can be added to the composition of the present invention or the epoxy resin binder, but it is not calculated as the epoxy resin binder.

  The epoxy resin compounded in the epoxy resin binder of the present invention has a viscosity of 1 to 20 mPa·s at 150° C., a melting point of 45° C. to 130° C., preferably 50° C. to 130° C., a low viscosity crystalline epoxy that is solid at room temperature. It is desirable to use one or more resins. Accordingly, at room temperature, the composition or compound has excellent storage stability, and at the temperature at the time of molding, good flowability can be exhibited even if a relatively large amount of graphite powder is contained. The epoxy equivalent is about 150 to 300 g/eq, preferably 170 to 250 g/eq.

As such a low-viscosity crystalline epoxy resin, an ether-type or thioether-type epoxy resin represented by the above general formula (1) in which X is O or S is preferable. In the general formula (1), G represents a glycidyl group and R represents a monovalent group, but it may be the same or different halogen atom or a hydrocarbon group having 1 to 6 carbon atoms. It is preferably an alkyl group having 1 to 3 carbon atoms, and the number n of the substituents other than the hydrogen atom contained in one benzene ring is 0 to 4.
As is well known, the epoxy resin often contains an oligomer by polymerization of the epoxy resin represented by the general formula (1). When the degree of polymerization of the epoxy resin represented by the general formula (1) is m=0, it is preferable that the oligomer having m=1 or more is 50 wt% or less, preferably 10 wt% or less.
The low-viscosity crystalline epoxy resin which is solid at room temperature may be contained in the epoxy resin in an amount of 30% by weight or more, preferably 50% by weight or more, and more preferably 80% by weight or more. When another epoxy resin that does not correspond to such a crystalline epoxy resin is used as at least a part of the epoxy resin component, a low-viscosity epoxy resin is preferable, and examples thereof include bisphenol F type epoxy resin and biphenyl type epoxy resin.

  As the curing agent for the epoxy resin, known ones such as phenol type, amine type and carboxylic acid type can be used, but polyphenols are preferable, and phenol or alkylphenol and formalin are more preferable. It is a novolac type curing agent. It is advantageous that the novolac-based curing agent has a softening point of room temperature or higher. 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.

  When the curing accelerator for the epoxy resin is blended, as the curing accelerator, known accelerators such as amines, imidazoles, ureas, organic phosphines and Lewis acids can be used. The compounding amount of the curing accelerator is not particularly limited, but is preferably in the range of 0.01 to 10 parts by weight with respect to 100 parts by weight of the epoxy resin binder. A dimethylurea type accelerator is mentioned as a preferable hardening accelerator.

  The epoxy resin binder comprises an epoxy resin and a curing agent, and the viscosity of the epoxy resin at 150° C. is preferably 1 to 20 mPa·s, preferably 15 mPa·s or less, more preferably 10 mPa·s or less, and at room temperature. (25° C.) An epoxy resin containing at least one solid crystalline epoxy resin. The crystalline epoxy resin has a melting point of 45 to 130°C, preferably 50 to 130°C. The epoxy resin may be composed only of the crystalline epoxy resin or may be a mixture with another epoxy resin, but the epoxy resin as a whole has the above-mentioned viscosity and softening point or melting point. However, it is desirable that it be a solid at room temperature. Further, as an epoxy resin binder, it is desirable that the viscosity at 150° C. is 500 mPa·s or less and the softening point or melting point is 45 to 130° C. This makes it possible to exhibit excellent storage stability and good fluidity during molding. Adjusting to such a viscosity is easy by selecting the softening point and the viscosity of the epoxy resin and the curing agent.

  Further, in the fuel cell separator composition of the present invention, in addition to graphite powder, a resin binder and an epoxy resin curing accelerator, internal release agents such as stearic acid and wax, and other conductive fillers and other additives. It is possible to mix them in a range that does not impair the effects of the present invention, but these are not calculated as a resin binder or graphite powder.

  The graphite powder and the resin binder may be mixed at the same time, or the graphite powder having at least two kinds of particle size distribution may be mixed in advance and then mixed with the resin binder.

  To produce a fuel cell separator using a fuel cell separator composition, a graphite powder and a resin component composed of an epoxy resin binder, a curing accelerator, and additives that are optionally blended are used as a composition. After heating and kneading, the compound as a pulverized product obtained by pulverizing or crushing so that the average particle size is 100 μm or less, preferably 20 to 50 μm is 100° C. to 350° C., preferably 140° C. It is advantageous to mold and cure at 230°C, more preferably 150°C to 200°C.

  In the kneading step, kneading is performed using a kneader. As the kneader, a general-purpose kneader, roll, single-screw extruder, multi-screw extruder, or the like can be used, but the kneader is not limited thereto. The kneading is performed so that the resin and the graphite powder form a composition as uniform as possible. During kneading, heating can be performed for the purpose of lowering the viscosity of the resin, or a low boiling point solvent can be added, but it is necessary that curing is not completed.

  Next, the composition obtained by kneading is crushed or crushed. The crushing can be performed using a known crusher. Examples of the pulverizer used here include a pulverizer for shear pulverization and a disc mill for compression pulverization. When graphite powders with different average particle diameters are used in this crushing process, the large-sized graphite powders are preferentially crushed and a new graphite fracture surface without resin adherence is generated, thus lowering the electrical resistivity. The effect occurs. Therefore, the large particle size graphite powder having an average particle size of 50 to 300 μm used as a raw material is selectively crushed to 50 μm or less, and the small particle size graphite powder having an average particle size of less than 50 μm is preferably not crushed. However, if the resin is crushed more than necessary, the resin may not be sufficiently spread, and the strength of the molded product may be reduced.

  The viscosity of the compound (pulverized product) obtained by pulverizing as described above at 150° C. is 200 to 3000 Pa·s, preferably 2000 Pa·s or less, more preferably 1500 Pa·s or less, and further preferably 200 to 1200 Pa·s. It should be s. The viscosity of such a compound at 150°C varies depending on the type of graphite or epoxy resin binder used, the presence or absence of a curing accelerator, the kneading temperature and the time, etc., but after kneading at 100°C for 10 minutes, crushing at room temperature The value obtained by measuring the obtained compound under the conditions shown in the examples preferably shows the above viscosity. This viscosity is determined mainly by selecting the epoxy resin and the graphite compounding amount. Although the viscosity of the compound rises when it is left for a long period of time, it is sufficient to show the viscosity just before it is used for manufacturing a fuel cell separator.

  By blending graphite powder, an epoxy resin binder, and a small amount of a component such as a curing accelerator that is added as necessary (hereinafter, components other than the graphite material are mainly resin, so are also referred to as resin components), The composition of the present invention. The composition of the present invention comprises a graphite material, a resin component and the like, and the resin component and the like may contain a small amount of components other than the resin. A fuel cell separator is obtained by kneading the composition of the present invention, making the kneaded product 100 μm or less, preferably 3 to 50 μm, more preferably 20 to 50 μm, and then molding. Since this pulverized product is kneaded at a temperature of about 100° C., it is partially cured, but it is an incompletely cured product, and it is pressed and molded at a temperature of about 140° C. or higher, When kept for a time, it becomes a cured product (molded product or separator). The compound preferably has a viscosity at 150° C. of 200 to 3000 Pa·s.

  The method of molding the separator may be press molding, transfer molding, or injection molding using a mold having holes or grooves formed in the separator, depending on the blending ratio of graphite and the resin binder. In the case of press molding, it is suitable when the amount of resin added is low, and when the amount of resin added is relatively large and the compound has fluidity, transfer molding or injection molding is preferable. Further, when a thermoplastic resin is used, continuous molding using a design roll having a groove processed can also be applied.

After crushing, molding is performed using a heating type molding machine using a mold. At this time, in order to cure the epoxy resin binder, which is a thermosetting resin, at the same time as molding, it may be carried out by holding at 100 to 350°C, preferably 140 to 230°C, more preferably 150 to 200°C. Good. The temperature is higher than the curing temperature of the thermosetting resin used and lower than the carbonization temperature. The molding pressure is preferably high in order to reduce the electrical resistivity in the surface direction and increase the bulk density, but increasing the pressure increases the equipment cost, so about ²⁰ to 1000 kg/cm ² , preferably 100 to 800 kg/ cm ² is more suitable, and more preferably about 100 to 500 kg/cm ² .
As a result, a separator having a thickness of 2 mm and an area of 700 cm ² can be molded within a molding time of 20 minutes, particularly 5 minutes, and a dimensional accuracy of 100 μm or less, particularly 50 μm or less.

  If a predetermined fuel cell separator is formed at the time of molding and a predetermined groove and the like are provided at the same time, the fuel cell separator can be formed as it is or by simple processing. However, after being formed into a plate shape or the like, grooves or holes may be added to this to obtain a fuel cell separator.

The fuel cell separator obtained by the process of the present invention has a bulk density of 1.80 g / cm ³ or more, preferably it is possible to 1.85 g / cm ³ or more, gas impermeability, mechanical strength It will be excellent. When the bulk density is less than 1.80 g/cm ³ , not only gas impermeability is poor, but also mechanical strength is poor. Further, the specific resistance is required to be 100 mΩcm or less, preferably 40 mΩcm or less in order to function as a fuel cell, but according to the present manufacturing method, the required characteristics can be sufficiently achieved. This specific resistance can be lowered by making the type of graphite used to have a high degree of crystallinity or by reducing the blending amount of the thermosetting resin, and can also be changed by the molding pressure or the like. In addition, the specific resistance shall follow the measuring method described in the below-mentioned Example.

Further, the fuel cell separator of the present invention desirably has a bending strength of 30 MPa or more and a gas permeability of 1×10 ⁻¹⁴ cm ² or less, or any one or more of the characteristics. If the bending strength is less than 30 MPa, the separator is likely to be broken by vibration or shock, and if the gas permeability exceeds 1 × 10 ^-14 cm ² , hydrogen and oxygen as fuel may be mixed and the power generation efficiency may be increased. Spoil.

  Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited thereto. In this case, the method for measuring the specific resistance, compound viscosity and dimensional accuracy of the molded product is as follows.

Compound viscosity: Measured using a high-down type flow tester (Shimadzu flow tester CFT-500 manufactured by Shimadzu Corporation). The nozzle size used for the measurement was φ1×L1.
In the actual measurement, first, about 2 g of the sample (crushed product) is compression-molded at room temperature into a tablet of size φ10 × L7. Furthermore, after setting the sample in the viscosity measuring device whose temperature has been raised to the measurement temperature (150° C.) in advance and holding it for 10 seconds, the viscosity is measured at a shear rate of 5000 1/s.
Thickness accuracy: The thickness of a predetermined part of the molded body obtained under predetermined molding conditions was measured, and the maximum value-minimum value was defined as the thickness accuracy. In the evaluation of thickness accuracy, ◯ means less than 50 μm, Δ means less than 50 to 100 μm, and x means more than 100 μm.
Specific resistance: The above-mentioned molded product was measured by a 4-terminal voltage drop method. The specific resistance is measured in the thickness direction (press molding pressure direction) and the plane direction (perpendicular to the press molding pressure direction), but the specific resistance shown in this example is regarded as particularly important as a separator characteristic. The value in the thickness direction is shown.

The raw materials used are as follows.
Highly conductive graphite: Bulk coke produced by a delayed coking method using heavy coal-based oil was crushed by a Raymond mill to have an average particle size of 30 μm. This was carbonized at about 800° C. in a lead hammer furnace to obtain a carbide. This carbide added with 5% boron carbide was graphitized at 2800°C.

Orthocresol novolac epoxy resin: Nippon Kayaku Co., Ltd., trade name EOCN-1020, melting point 65°C, 150°C viscosity 0.3 Pa·s
Ether type epoxy resin: manufactured by Tohto Kasei Co., Ltd., trade name YSLV-80DE, melting point 79°C, 150°C viscosity 0.006Pa・s
Thioether type epoxy resin: manufactured by Tohto Kasei Co., Ltd., trade name YSLV-50TE, melting point 50°C, 150°C viscosity 0.006Pa・s
Tetramethylbisphenol F type epoxy resin: manufactured by Nippon Steel Chemical Co., Ltd., trade name YSLV-80XY, melting point 78, 150°C viscosity 0.008Pa・s
Phenol novolac resin: Tamanor 758 manufactured by Arakawa Chemical Industry Co., Ltd., softening point 83°C, 150°C viscosity 0.22-0.35Pa・s
Curing accelerator: dimethyl urea accelerator San-Apro Co., Ltd., trade name U-CAT3502T

Example 1
100 parts by weight of the epoxy resin shown in Table 1 was mixed with 65 parts by weight of phenol novolac resin, 1.6 parts by weight of a curing accelerator, and 495 parts of highly conductive graphite (graphite/resin ratio=3) to obtain a composition. . This composition was kneaded with a roll heated to 100° C. for 10 minutes. The obtained kneaded product was pulverized with a disc mill. This pulverized product was put into a mold, molded under conditions of a temperature of 175° C. and a pressure of 300 kg/cm ² for 3 minutes, and demolded. The physical properties of the obtained molded body were measured.
Table 1 shows the measurement results of the viscosity (compound viscosity) of the pulverized product, the dimensional accuracy of the molded product, and the specific resistance.

Examples 2-6
With the formulation shown in Table 1, a crushed product and a molded product were produced in the same manner as in Example 1, and the physical properties were measured. The results are shown in Table 1.

Comparative Examples 1-3
With the formulation shown in Table 1, a crushed product and a molded product were produced in the same manner as in Example 1, and the physical properties were measured. The results are shown in Table 1.

Experimental example 1
In the same experiment as in Example 1, except that the compounding amount of the highly conductive graphite was 330 parts (graphite/resin ratio=2) or 1650 parts (graphite/resin ratio=10), the pulverized product and A molded body was manufactured.
In the experiment in which the graphite/resin ratio=2, the compound viscosity was 100 Pa·s or less, the thickness accuracy was ◯, and the specific resistance was 48.4 mΩcm.
In an experiment with a graphite/resin ratio of 10, the compound viscosity was 6000 Pa·s or more, the thickness accuracy was Δ, and the specific resistance was 3.2 mΩcm.

  ADVANTAGE OF THE INVENTION According to this invention, the compound material of graphite and resin which can satisfy|fill the required characteristics as a fuel cell separator, ie, electric conductivity, mechanical strength, etc., can provide the material which improved moldability. In particular, the molding cycle is shortened and the dimensional accuracy is excellent, and it is possible to provide a compound material that can be used in future mass production of separators, and this is a great contribution to this field. The fuel cell separator obtained by the production method of the present invention is dense and has high mechanical strength, excellent conductivity, low anisotropy, and low gas permeability. And a long-life fuel cell.

Claims (8)

  In a composition containing an epoxy resin binder composed of an epoxy resin and a curing agent and graphite powder, graphite powder is blended in an amount of 2 to 10 times by weight ratio with respect to the epoxy resin binder, and the composition is kneaded and ground. A composition for a fuel cell separator, characterized in that the viscosity of the resulting compound at 150° C. is 200 to 3000 Pa·s, and the electrical resistivity of a molded article to be a fuel cell separator is 100 mΩcm or less as a specific resistance. ..   The fuel cell separator according to claim 1, wherein the graphite powder is blended in an amount of 3 to 7 times by weight with respect to the epoxy resin binder, and the electrical resistivity of the molded article used as the fuel cell separator is 40 mΩcm or less as a specific resistance. Composition.   The composition for a fuel cell separator according to claim 1, wherein the epoxy resin contains at least one crystalline epoxy resin having a viscosity of 1 to 20 mPa·s at 150°C, a melting point of 45 to 130°C, and a solid at room temperature.   A composition containing graphite powder and an epoxy resin binder in which graphite powder is blended in an amount of 2 to 10 times by weight with respect to an epoxy resin binder composed of an epoxy resin and a curing agent. A composition for a fuel cell separator, comprising at least one crystalline epoxy resin having a solid content at room temperature of 20 mPa·s and a melting point of 45 to 130° C.   The composition for a fuel cell separator according to claim 4, wherein the compounding amount of the graphite powder with respect to the epoxy resin binder is 3 to 7 times by weight. The crystalline epoxy resin has the following general formula (1)

(Wherein 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 1.   A method for producing a fuel cell separator, which comprises kneading and pulverizing the composition according to claim 1 or 4, and then shaping and curing the pulverized material at a temperature of 140 to 230°C.   A fuel cell separator obtained by the method for producing a fuel cell separator according to claim 7.