JP2002100378A - Separator for fuel cell and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for fuel cells excellent in dimension accuracy, and in both of conductivity and gas impermeability, and the fuel cell excellent in power generating efficiency. SOLUTION: The separator for fuel cells is a molded thing that contains a harden thing of a heat-hardening resin: 3 to 20 weight parts to a coarse grain powder of small sphere of meso-carbon made to graphite: 100 weight parts, the above coarse grain powder of the thing made to graphite is the powder of the thing made to graphite having 50 μm < grain size <=300 μm, a specific surface area <=1.5 m2/g, and an average aspect ratio of the powder grains <=3. Further the separator for fuel cells has the above molded thing which contains one sort, or two or more sorts chosen from the granule powder of the small sphere of meso-carbon made to graphite, the granule powder of the small sphere of bulk meso-phase pitch made to graphite, a graphite powder, a carbon black, and fine detailed carbon fibers, and the fuel cell uses these separators for fuel cells.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel cell separator and a fuel cell, and more particularly to a fuel cell separator excellent in dimensional accuracy, conductivity and gas impermeability, and power generation efficiency using the fuel cell separator. To an excellent fuel cell.

[0002]

2. Description of the Related Art The future of fuel cells is expected as a power generator having high power generation efficiency and low generation of pollutants. Depending on the type of electrolyte, the type of fuel cell includes an alkaline type, a phosphoric acid type, a molten carbonate type, a solid electrolyte type, a solid polymer type, and the like. Because the temperature is as low as 80-100 ° C,
It is attracting attention as a small-scale power generator for home use and a portable power generator for electric vehicles.

FIG. 1 is a perspective view showing the structure of a polymer electrolyte fuel cell. In FIG. 1, 1 indicates a solid polymer electrolyte plate, 2 indicates an air electrode, 3 indicates a fuel electrode, 4 indicates a separator, and 5 indicates a groove for a gas flow path. As shown in FIG. 1, the polymer electrolyte fuel cell has a structure in which an air electrode 2 and a fuel electrode 3 are provided on both sides of a solid polymer electrolyte plate 1 to form a unit cell, and the unit cells are stacked with a separator 4 interposed therebetween.

As the solid polymer electrolyte, a perfluorocarbonsulfonic acid (PFSA) ion exchange membrane or the like is mainly used. On the other hand, since the separator 4 is required to have a function as a boundary for separating the fuel gas and the oxidizing gas and a function as an electric conductor between unit cells, excellent gas impermeability, heat conductivity, With high strength, low electrical resistivity,
It is required to have low volume resistivity and heat resistance at operating temperatures.

Hitherto, as this kind of separator, a separator machined from artificial graphite or a separator machined from a metal material such as titanium or stainless steel has been studied. However, a separator obtained by machining artificial graphite has a problem in that although it has excellent electric conductivity, it has insufficient gas impermeability and is very expensive. Further, in the case of a separator formed by machining a metal material, there has been a problem that the separator is oxidized due to long-term use, and is expensive similarly to the above.

As a separator for solving the above-mentioned problems, a separator for a polymer electrolyte fuel cell formed by mixing a thermosetting resin with artificial graphite powder and forming the same has been disclosed (JP-A-10-334927). And JP-A-11-297337). Although the above-described separator has the problems of gas impermeability and oxidation, it has problems in dimensional accuracy, and it is difficult to obtain a separator having excellent dimensional accuracy in the thickness direction.

That is, as shown in FIG. 1, the fuel cell normally has a gas flow channel groove 5 for supplying a fuel gas such as hydrogen and an oxidizing gas such as air on the separator side, that is, in the fuel cell. Formed on both sides of the separator. In this case, if the depth of the groove 5 for the gas flow path is not uniform, the gas flow resistance differs for each groove and the distribution of the gas flow rate in the fuel cell is generated, thereby producing a fuel cell with excellent power generation efficiency. It will be difficult to do.

[0008] Important characteristics required for a fuel cell separator include low electrical resistivity and low volume resistivity. That is, in recent years, there has been an increasing demand for reducing the electrical resistivity and volume resistivity to improve the conductivity and increase the power generation efficiency in order to reduce the size of the fuel cell. For this reason, in JP-A-62-260709, the particle size is 50 μm.
A phosphoric acid type fuel cell separator is disclosed in which a graphitized mesocarbon spheroid having a particle size of m or less is used as an aggregate, and 10 to 30% by weight of a thermosetting resin is used as a binder.

Since the electrical resistivity and the volume resistivity depend on the content of the mesocarbon spheroidal graphite, which is a conductive substance, the electrical resistivity is further reduced by reducing the amount of the binder to less than 10% by weight. It is possible. However, because the particle size of the mesocarbon small sphere graphitized material is as small as 50 μm or less, if the amount of the binder is less than 10% by weight,
It becomes difficult to fill the voids between the particles with the binder, the gas permeability increases, and the mechanical strength decreases, so that it cannot be used as a separator.

On the other hand, if the amount of the binder is less than 10% by weight, the moldability decreases, and it becomes difficult to obtain a separator having excellent dimensional accuracy in the thickness direction. Decrease. In addition, Japanese Unexamined Patent Publication No.
Japanese Patent No. 214072 discloses a fuel cell separator obtained by curing and firing a composition of carbonaceous powder such as graphitized mesocarbon spheres or graphite powder, a carbon fiber, and a phenol resin.

However, the above-mentioned separator is characterized in that phenol resin is added to 50 to 150 parts by weight of carbonaceous powder.
It is contained in an amount of 00 parts by weight and contains a large amount of resin components. As described later, it is difficult to obtain sufficient conductivity only by curing. As a result, in the separator described above, the cured product is fired,
It needs to be graphitized, but typically 2000-3000
High temperature treatment in a non-oxidizing atmosphere of ℃ is required,
There is a problem in industrially adopting equipment, operation and energy.

[0012]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a fuel cell separator excellent in dimensional accuracy, conductivity and gas impermeability, which is industrially advantageous. It is an object of the present invention to provide a fuel cell separator obtainable by the method, and a fuel cell excellent in power generation efficiency using the fuel cell separator.

[0013]

Means for Solving the Problems The first invention is a molded article containing 3 to 20 parts by weight of a cured product of a thermosetting resin with respect to 100 parts by weight of coarse particles of graphitized mesocarbon spheres. Wherein the coarse graphitized powder has a particle size of 50 μm <particle diameter ≦ 300.
A fuel cell separator characterized in that it is a graphitized powder having a μm, specific surface area ≦ 1.5 m ² / g and an average aspect ratio of powder particles ≦ 3.

In the first aspect of the present invention, the molded article may be a mesocarbon small sphere graphitized fine particle satisfying the following formula (1) with respect to 100 parts by weight of the graphitized coarse powder: Powder: preferably not more than 100 parts by weight,
It is more preferable to contain the graphitized fine powder in an amount of 1 to 100 parts by weight (first preferred embodiment of the first invention). Particle size of graphitized fine powder ≦ 50 μm (1) Further, in the first invention and the first preferred embodiment of the first invention, the molded article is the graphitized coarse powder:
It is preferable to contain 100 parts by weight or less of one or more selected from graphite powder, graphite powder, carbon black, and fine carbon fiber of the bulk mesophase pitch in a total amount of 100 parts by weight with respect to 100 parts by weight. More preferably, the content is 1 to 100 parts by weight (the second preferred embodiment and the third preferred embodiment of the first invention).

In the second and third preferred embodiments of the first invention, the average particle size of the graphite powder of the bulk mesophase pitch is 50 μm or less, and the average particle size of the graphite powder is 50 μm. Hereinafter, the average particle diameter of carbon black is 100 nm or less, and the average fiber diameter of fine carbon fibers is 2 μm.
Hereinafter, the average fiber length is preferably 500 μm or less (fourth preferred embodiment and fifth preferred embodiment of the first invention).

According to a second aspect of the present invention, there is provided the first aspect of the present invention,
A fuel cell using the fuel cell separator according to any one of the first to fifth preferred embodiments of the present invention. Further, in the fuel cell according to the preferred embodiment of the second invention, an air electrode is provided on one side of the solid polymer electrolyte plate,
A unit cell formed by providing a fuel electrode on the other one side of the fuel cell according to any one of the first to fifth preferred embodiments of the first invention and the first invention described above. It is a polymer electrolyte fuel cell stacked with a separator interposed therebetween.

In the present invention, the weight in parts by weight means mass. For example, 100 parts by weight of graphitized mesocarbon spheroidized powder: 100 parts by weight of cured product of thermosetting resin: 3 to 20 parts By weight, the cured product of the thermosetting resin:
3 to 20 parts by mass.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have found the following findings [I] to [III], and have reached the present invention. [I] Improvement of gas impermeability (gas barrier property) and dimensional accuracy of fuel cell separator by using mesocarbon small sphere graphitized powder with specified particle characteristics: [I-1] Mesocarbon small sphere graphitized powder Of the gas impermeability (gas barrier property) of the fuel cell separator by defining the particle size and specific surface area of the fuel cell: The present inventors reduce the gas barrier property even with a small amount of binder (resin). As a result of intensive studies on a method of firmly bonding aggregates without any problem, it was considered that the specific surface area of the aggregate powder had a great effect.

That is, when the separator is manufactured, the binder bonds the aggregate particles to each other. However, when the particle size of the aggregate is small, the total surface area of the aggregate becomes very large, and most of the added binder becomes large. It is used to coat the surface of the aggregate and the amount of binder required to fill the voids between the aggregate particles is insufficient. As a result, it was considered that when the amount of the binder (resin) was small, the obtained separator had a structure with many gaps, and the gas barrier property was reduced.

For this reason, in the present invention, a graphitized powder of mesocarbon small spheres having a large particle diameter exceeding 50 μm (: a graphitized coarse powder) is used as an aggregate, and the specific surface area is 1.5 m ² / g. g or less. As a result, the amount of the binder covering the aggregate surface becomes smaller, the amount of the binder necessary to fill the gap between the aggregate particles can be secured, and the obtained separator has a structure without gaps, Gas barrier properties are improved.

[I-2] Improvement of dimensional accuracy of fuel cell separator by using mesocarbon small sphere graphitized powder having a small aspect ratio: As a part of the raw material of the fuel cell separator, the average aspect ratio of the powder particles is as follows. By using 3 or less mesocarbon small sphere graphitized coarse powder (hereinafter also referred to as mesocarbon small sphere graphitized coarse powder), a fuel cell separator excellent in dimensional accuracy can be obtained.

This is because the particles of the mesocarbon small sphere graphitized coarse powder have an average aspect ratio of 3 or less, have a substantially spherical shape, and have excellent fluidity during molding of a fuel cell separator. It is considered that this is likely to be an isotropic molded body. [II] Improvement of conductivity of fuel cell separator by regulation of resin content: As described above, by defining the particle size and specific surface area of mesocarbon small sphere graphitized coarse powder, the binder (resin) Since the amount of addition can be reduced, by regulating the resin compounding amount, it is possible to obtain sufficient conductivity (low electric resistivity, low volume resistivity) without firing and graphitizing the separator molded product as in the past. it can.

[III] Improvement of conductivity of fuel cell separator by use of fine carbon powder and fine carbon fiber: In addition to the mesocarbon fine-grained powder of mesocarbon small spheres, By incorporating fine-grained graphitized powder of microspheres, graphitized powder of bulk mesophase pitch, graphite powder, fine carbon powder that is carbon black, and fine carbon fiber, particles of graphitized coarse powder of mesocarbon small spheres And the electrical conductivity of the fuel cell separator (low electric resistivity, low volume resistivity) can be further improved.

In the following, [I] use of mesocarbon spheroidized graphitized coarse powder having specified particle characteristics, [II] regulation of resin blending amount, [III] use of fine carbon powder and fine carbon fiber, And [IV] a method for producing a fuel cell separator, [V]
The description will be made in the order of the fuel cells. [I] Use of Mesocarbon Spheroid Graphitized Coarse-Grained Powder with Defined Particle Properties: As shown in FIG. 1 above, a fuel cell separator such as a polymer electrolyte fuel cell separator is formed on both sides of the separator during molding. Are often provided, and the width and depth of the groove are required to be extremely high in dimensional accuracy in view of uniformity of the reaction in the cell.

The present inventors considered that the problem of the dimensional accuracy of the separator when the artificial graphite powder was used in the prior art described above was due to the shape of the particles of the artificial graphite powder. That is, when the artificial graphite powder is used as a main material of the carbonaceous material, that is, the aggregate, the artificial graphite powder usually has a flaky powder particle shape. It is easy to line up, and the mean square error with respect to the average value of the groove depth shown in the examples described later is ± 5 × 10 ⁻²
It is difficult to obtain a fuel cell separator with grooves within mm.

On the other hand, in the case of a separator using the coarse powder of graphitized mesocarbon spheres having the specified particle characteristics of the present invention as an aggregate, the flowability of the aggregate particles during separator molding is excellent. Because of its excellent fillability, the average square error with respect to the average groove depth is within ± 5 × 10 ^-2 mm. It has excellent dimensional accuracy and low electrical resistivity and low volume resistivity. Is obtained.

That is, a first feature of the present invention is that in order to obtain a fuel cell separator having excellent dimensional accuracy, a mesocarbon small sphere graphitized coarse powder having a specific particle size range and a specific particle shape is obtained. This is the point that was used. The graphitized coarse powder of mesocarbon small spheres used in the present invention can be obtained by the following method.

That is, the self-sintering property obtained by filtering the mesocarbon small spheres having optical anisotropy generated in the pitch matrix when the coal-based pitch and / or the petroleum-based pitch is heat-treated is evaluated. Filtration residue and / or
Alternatively, the mesocarbon small spheres exhibiting the optical anisotropy are extracted using an organic solvent such as oil in tar, and the self-sinterable mesocarbon small spheres obtained by separation and carbonization are graphitized to form a mass. Become

Next, the obtained massive graphitized material is pulverized and classified to obtain a mesocarbon small sphere graphitized coarse powder. When crushing general artificial graphite lump,
As shown in the electron micrograph of FIG. 2, only a plate-like powder having a large aspect ratio of the powder particles can be obtained.

On the other hand, when the massive graphitized mesocarbon spheroids are pulverized and classified, as shown in the electron micrograph shown in FIG. 3, the particles have a small aspect ratio and a small specific surface area. A coarse powder having a nearly spherical shape is obtained. In the present invention, a mesocarbon small sphere graphitized coarse powder obtained by carbonizing and graphitizing a mesocarbon small sphere preferably at a temperature of 2500 to 3000 ° C. is used.

Further, in order to obtain a separator which is dense and excellent in gas impermeability and excellent in conductivity, the particle size of the graphitized coarse powder of mesocarbon small spheres is more than 50 μm and not more than 300 μm, The specific surface area of the granular powder is 1.5 m ² / g or less, and the average aspect ratio of the powder particles of the graphitized coarse powder is 3 or less. If the particle size of the graphitized coarse powder is 50 μm or less, or if the specific surface area of the powder exceeds 1.5 m ² / g, the gas impermeability of the resulting separator will be poor.

When the particle size of the graphitized coarse powder exceeds 300 μm, the dimensional accuracy of the obtained separator is difficult to obtain, and the average aspect ratio of the powder particles is 3%.
If it exceeds, the filling property of the powder particles decreases, and the conductivity and dimensional accuracy of the obtained separator deteriorate. The average aspect ratio of the powder particles in the present invention indicates the average value of the ratio of the maximum length to the minimum length of each particle in the projection view of each particle in an electron micrograph.

In addition, the lower limit of the average aspect ratio of the powder particles of the graphitized coarse powder is the aspect ratio [= 1] of the spherical powder particles. In the present invention, the particle size, average aspect ratio and graphitized material coarse particles of the graphitized coarse particles are controlled by controlling the extraction conditions during the production of the above-mentioned mesocarbon small spheres, the pulverizing conditions of the massive graphitized material, and the like. The specific surface area of the powder can be controlled.

[II] Regulation of resin blending amount: In the present invention, separator molding which is a resin molded product (hereinafter also referred to as a carbonaceous molded product) containing the above-mentioned mesocarbon microsphere graphitized coarse powder or the like is used. One major goal was to obtain a fuel cell separator having sufficient conductivity (low electrical resistivity and low volume resistivity) without graphitizing the product.

For this reason, in the present invention, the mesocarbon small spherical graphitized material powder is used by improving the packing density and reducing the resin content by using coarse powder of mesocarbon small spherical particles. Increase the probability of contact between the particles of the coarse powder. As a result, according to the present invention, sufficient conductivity can be obtained without firing and graphitizing the molded separator.

In the present invention, as the thermosetting resin, one or more selected from phenol resins, furan resins, epoxy resins, unsaturated polyester resins, polyimide resins and the like are preferably used. In the present invention, it is more preferable to use a phenol resin as the thermosetting resin.

This is because when a phenol resin is used, the properties of the obtained separator are excellent, and the phenol resin is easy to handle and inexpensive. The content of the thermosetting resin is in the range of 3 to 100 parts by weight of the mesocarbon small sphere graphitized coarse powder and the thermosetting resin:
The amount is 20 parts by weight, more preferably 5 to 15 parts by weight.

When the content of the cured product of the thermosetting resin is less than 3 parts by weight, many pores are generated inside the separator,
When a fuel cell separator having excellent gas impermeability is not obtained and exceeds 20 parts by weight, the electrical resistivity and the volume resistivity are increased. In addition, the above-mentioned weight part in the present invention is:
In each case, each part by weight after molding is shown.

According to the present invention, by regulating the content of the thermosetting resin to the above-mentioned range, the separator molded product is excellent in gas impermeability without firing and graphitization,
A fuel cell separator having a low electric resistivity and a low volume resistivity can be obtained. [III] Use of fine carbon powder and fine carbon fiber: In the present invention, in addition to the above-mentioned coarse mesocarbon sphere graphitized powder in the molded separator, further, the fine mesocarbon sphere graphitized fine powder is used. By incorporating granular powder, graphite powder of bulk mesophase pitch, graphite powder, fine carbon powder that is carbon black, and fine carbon fiber, electrical conduction between particles of mesocarbon small sphere graphitized coarse powder is ensured. Can be

That is, the fine carbon powder and the fine carbon fibers are interposed between the particles of the graphitized coarse powder of mesocarbon small spheres, whereby the conductivity (low electric resistivity, low volume) of the fuel cell separator is obtained. Resistivity) can be further improved. Hereinafter, the fine carbon powder and the fine carbon fiber in the present invention will be described. [Mesocarbon Spheroid Graphitized Fine Powder:] In the fuel cell separator of the present invention, the particle size exceeds 50 μm,
Mesocarbon small sphere graphitized coarse powder having a particle size of 300 μm or less: Mesocarbon small sphere graphitized fine powder having a particle size satisfying the following formula (1) per 100 parts by weight: 100 parts by weight or less It is preferable to contain the above-mentioned graphitized fine powder: 1 to 100 parts by weight.

Particle size of graphitized fine powder ≦ 50 μm (1) When the content of the graphitized fine powder is less than 1 part by weight, the effect of lowering the electrical resistivity and volume resistivity is small. On the other hand, if it exceeds 100 parts by weight, the moldability decreases, and it becomes difficult to obtain a separator having a mean square error of ± 5 × 10 ⁻² mm or less with respect to the average value of the groove depth of the fuel cell separator described above. .

If the content of the graphitized fine powder exceeds 100 parts by weight, their dispersibility in the separator becomes uneven, which is not preferable from the viewpoint of conductivity. The mesocarbon small sphere graphitized fine powder used in the present invention is selected from the following:
It is preferable to use one or more species.

A pulverized product of the above described mesocarbon small sphere graphitized coarse powder having a particle size of 50 μm or less. Filtration residue obtained by filtering small spheres showing optical anisotropy generated when heat treatment is performed on coal-based pitch and / or petroleum-based pitch is washed with tar oil, etc., and self-sintered. After firing, baking and graphitizing the binder component that imparts the particle size of 50 μm or less.

The spheres having the above-mentioned optical anisotropy separated by specific gravity separation such as a precipitation method are washed with a tar oil or the like, and a binder component for imparting self-sintering properties is washed away. Graphite, particle size 50μm
The following: FIG. 4 shows an example of an electron micrograph of the finely divided graphitized powder of mesocarbon small spheres.

According to the present invention, the above-mentioned fine carbon powder, which is the fine-grained powder of mesocarbon small spheres, is interposed between the particles of the coarse-grained powder of mesocarbon small spheres, whereby the separator for a fuel cell is obtained. (Low electric resistivity, low volume resistivity) can be further improved. [Graphite powder of bulk mesophase pitch, graphite powder, carbon black and fine carbon fiber:]
In the fuel cell separator of the present invention, the particle size is 50μ.
Graphite coarse powder of mesocarbon small spheres having a particle size exceeding 300 m and not more than 300 µm: one or more selected from graphitized powder of bulk mesophase pitch, graphite powder, carbon black and fine carbon fiber per 100 parts by weight In a total amount of 100 parts by weight or less, more preferably the total amount is 1 to 100 parts by weight, and even more preferably the total amount is 2 to 30 parts by weight.

When the total amount is less than 1 part by weight, the effect of lowering the electrical resistivity and volume resistivity is small, and
If the amount is more than 0 parts by weight, the moldability decreases, and it becomes difficult to obtain a separator having a mean square error of ± 5 × 10 ⁻² mm or less with respect to the average groove depth of the fuel cell separator described above. If the total amount exceeds 100 parts by weight, their dispersibility in the separator becomes uneven, which is not preferable from the viewpoint of conductivity.

As the graphitized powder, graphite powder, carbon black and fine carbon fiber of the bulk mesophase pitch in the present invention, the following graphitized powder, graphite powder, carbon black and fine carbon fiber are preferably used. (Graphite Powder of Bulk Mesophase Pitch :) As the graphitized powder of bulk mesophase pitch in the present invention, it is preferable to use the graphitized powder described below.

That is, when a petroleum-based or coal-based heavy oil or a petroleum-based or coal-based pitch is heated at 350 to 500 ° C., an optically anisotropic sphere called a mesocarbon sphere is formed in the initial stage of heating. When generated in the mother liquor and further heated, the mesocarbon small spheres unite and grow repeatedly, and the whole mother liquor becomes an optically anisotropic substance (bulk mesophase pitch).

After the bulk mesophase pitch obtained as described above is pulverized and classified, it is preferably graphitized at 2000 to 3000 ° C. to obtain a graphitized powder of bulk mesophase pitch. The above-mentioned graphitized powder can also be produced by graphitizing a bulk mesophase pitch, followed by pulverization and classification. The quinoline insoluble content (: QI) in the coal pitch and / or the petroleum pitch for producing the bulk mesophase pitch is preferably 5% by mass or less.

This is because when a graphitized powder produced using a pitch having a quinoline insoluble content (: QI) of more than 5% by mass as a raw material is used, the electrical resistivity and volume resistivity of the finally obtained separator are obtained. This is because The average particle size of the graphitized powder of bulk mesophase pitch is 50
μm or less, and more preferably the average particle size is 30 μm or less.

This is because the fine carbon powder, which is the graphitized powder of the bulk mesophase pitch, is interposed between the particles of the graphitized coarse powder of the mesocarbon spheroids, whereby the conductivity (low conductivity) of the fuel cell separator is reduced. This is because it is possible to further improve the electrical resistivity and the low volume resistivity. (Graphite powder) As the graphite powder in the present invention, artificial graphite powder and / or natural graphite powder are preferable, and those having a purity of 95% or more and an average particle size of 50 μm or less are preferable, and more preferably the average particle size is 50% or less. The diameter is 10 μm or less.

When the purity is less than 95%, the metal salt contained as an impurity tends to impair the stability of the characteristics of the fuel cell. On the other hand, when the average particle size exceeds 50 μm, the uniform mixing of the mesocarbon small spheres with the coarse powder of the graphitized material is deteriorated, and the effect of improving the conductivity of the fuel cell separator is likely to be reduced.

The lower limit of the average particle size of the graphite powder is not particularly limited. The artificial graphite powder is, for example, a graphite powder obtained by heat-treating amorphous carbon at 2500 to 4000 ° C., and is usually a flaky powder. Natural graphite powder is
It is a naturally occurring graphite powder, usually a flaky powder that has been graphitized more than artificial graphite powder.

(Carbon Black :) Carbon black having a purity of 95% or more and an average particle diameter of 100 nm
The following are preferred. When the purity is less than 95%, as in the case of artificial graphite powder and natural graphite powder, the metal salt contained as an impurity tends to impair the stability of the characteristics of the fuel cell.

When the average particle size exceeds 100 nm, the effect of improving conductivity tends to decrease. The lower limit of the average particle size of the carbon black is not particularly limited. In addition, the particle size of the graphitized coarse powder of mesocarbon small spheres and the fine powder of graphitized mesocarbon small spheres in the present invention,
The average particle size of the graphitized powder, the graphite powder, and the carbon black of the bulk mesophase pitch can be determined by the measurement method described in Examples described later.

(Fine Carbon Fiber :) The fine carbon fiber in the present invention is preferably a carbon fiber having an average fiber diameter (diameter) of 2 μm or less, and more preferably an average fiber diameter (diameter).
Carbon fibers having a diameter of 500 nm or less are more preferred. The lower limit of the average fiber diameter of the fine carbon fibers is not particularly limited.

In the present invention, the average fiber diameter of the fine carbon fibers means an average value obtained by dividing the total diameter of the cross sections of the individual fibers by the number thereof when the fine carbon fibers have a circular fiber cross-sectional shape. When the fiber cross-sectional shape is not circular, the average value is obtained by dividing the total circle equivalent diameter obtained from the cross-sectional area of each fiber by the number of fibers. The average fiber length of the fine carbon fiber is 500
It is preferably less than μm.

The lower limit of the average fiber length of the fine carbon fibers is not particularly limited. In addition, the average fiber length of the fine carbon fibers in the present invention indicates an average value obtained by dividing the total fiber length of individual fibers by the number of fibers. If the average fiber diameter of the above fine carbon fibers exceeds 2 μm or the average fiber length exceeds 500 μm, the dispersibility of the mesocarbon small spheres in the graphitized coarse powder becomes poor, and pores are formed in the molded body. , Gas impermeability tends to decrease.

The purity of the fine carbon fibers is preferably 95% or more. When the purity is less than 95%, the effect of improving conductivity is likely to be reduced. Further, the above-mentioned fine carbon fiber in the present invention is a carbon fiber (vapor-grown carbon fiber) produced by a vapor growth method and having an extremely small fiber diameter and fiber length as compared with a general carbon fiber. Preferably, nanofibers are used.

The degree of graphitization of fine carbon fibers such as carbon nanofibers is changed by high-temperature treatment.
In the present invention, in order to increase conductivity, it is preferable to use fine carbon fibers which have been subjected to a high-temperature treatment to increase the degree of graphitization. Incidentally, the fuel cell separator of the present invention,
In order to improve heat resistance, durability, and the like, an additive such as an antioxidant may be contained.

As the antioxidant, for example, an antioxidant used as an auxiliary material for plastics can be used. [IV] Manufacturing method of fuel cell separator: Next, the manufacturing method of the fuel cell separator of the present invention will be described. The method for molding the fuel cell separator of the present invention is not particularly limited, and for example, a press molding method or an injection molding method can be used.

When the press molding method is used, a mixture of a mesocarbon small sphere graphitized coarse powder and a thermosetting resin, or a mixture of a mesocarbon small sphere graphitized fine powder, a bulk mesophase pitch, One or more selected from graphite powder, graphite powder, carbon black and fine carbon fiber are added and mixed, and the mixture is supplied to a mold, heated under pressure to cure the thermosetting resin, and the fuel is cured. Manufacture battery separators.

In addition, during the above-mentioned mixing, in order to add a solvent as necessary or to improve moldability, it is necessary to carry out preliminary curing for heating the mixture to adjust the fluidity before supplying the mixture to the mold. Is preferred. The conditions for press molding differ depending on the resin used, but it is preferable that the heating temperature during pressurization and heating in the mold: 130 to 220 ° C. and the press pressure: 200 N / cm ² or more.

When the injection molding method is used, a mixture of a mesocarbon small sphere graphitized coarse powder and a thermosetting resin,
Or, they further include mesocarbon small sphere graphitized fine powder, bulk mesophase pitch graphitized powder,
One or more selected from graphite powder, carbon black and fine carbon fiber are added and mixed, and the mixture is supplied to an injection molding machine and injection molded to produce a fuel cell separator.

In the injection molding method, it is preferable that the mixture is mixed at a temperature of 100 to 140 ° C. and then injected into a mold. In order to cure the resin, the mold is preferably 40 to 140 ° C.
It must be heated to 200 ° C. [V] Fuel Cell: Next, the fuel cell of the present invention will be described.

The fuel cell of the present invention comprises a unit cell formed by providing an air electrode on one side of a solid polymer electrolyte plate and a fuel electrode on the other side of the solid polymer electrolyte plate. It is preferable that the fuel cell is a polymer electrolyte fuel cell laminated via a fuel cell. That is, a preferred fuel cell of the present invention is obtained by laminating unit cells each composed of an air electrode, an electrolyte, and a fuel electrode with the fuel cell separator of the present invention interposed therebetween.

In the present invention, the solid polymer of the solid polymer electrolyte plate is not particularly limited as long as hydrogen ions (protons) can selectively move through the solid polymer. Instead, a perfluorocarbonsulfonic acid (PFSA) ion exchange membrane is exemplified. Although the fuel cell separator and the fuel cell of the present invention have been described above, the fuel cell separator of the present invention has excellent gas impermeability, low electric resistivity, low volume resistivity, and gas flow. Since the dimensional accuracy of the road groove is very excellent, the use of the fuel cell separator of the present invention makes it possible to obtain a uniform fuel gas flow distribution in the fuel cell and obtain a fuel cell with excellent power generation efficiency. It has become possible.

Further, since the fuel cell separator of the present invention does not require graphitization, the fuel cell separator and the fuel having the above-mentioned excellent performance can be obtained with a simple facility using a method excellent in energy and productivity. It has become possible to provide batteries.

[0069]

EXAMPLES The present invention will be described below more specifically based on examples. First, (1) compounding raw materials, (2) test method and measurement method used in the following examples will be described. (1) Ingredients: Coarse pitch (coal tar pitch) having a quinoline insoluble content (QI) of 3% and a softening point of 100 ° C for 1 hour at 250 ° C After filtration of the mesocarbon small spheres generated by the heat treatment, the filtration residue is filtered.
A coarse-grained powder obtained by pulverizing and classifying a massive graphitized material obtained by heating and heating to 3000 ° C. (: graphitized coarse-grained powder a,
b, c, d).

Table 1 shows the properties (particle characteristics) of the graphitized coarse powders a, b, c and d of the mesocarbon small spheres obtained above. (Thermosetting resin) Phenol resins A and B shown in Table 2 were used. (Mesocarbon small sphere graphitized fine powder :) Particle size: 2
4040 μm (graphitized powder of bulk mesophase pitch :) Quinoline insoluble matter (QI): 3%, softening point: 100 ° C coal-based pitch (coal tar pitch) heat-treated at 650 ° C for 5 hours to form bulk Graphitized powder having an average particle size of 10 μm obtained by pulverizing and classifying a graphitized product obtained by heating and heating a mesophase pitch to 3000 ° C.

(Artificial graphite powder :) Average particle size: 10 μm (trade name: SP-10, manufactured by Nippon Graphite Co., Ltd.) (Natural graphite powder :) Average particle size: 6 μm (trade name: ACP-10)
00, manufactured by Nippon Graphite Co., Ltd.) (Carbon black :) Average particle size: 25 nm (Fine carbon fiber :)
Carbon nanofiber) was used.

Glass car GWH (manufactured by Nikkiso Co., Ltd.) (carbon fiber produced by vapor phase growth method, average fiber diameter (average diameter): 300 nm, average fiber length: 10 μm, heat-treated at 2900 ° C.)

[0073]

[Table 1]

[0074]

[Table 2]

(2) Test method and measurement method: (2-1) Particle size range of graphitized coarse powder and fine graphite powder of mesocarbon small spheres: Using a laser diffraction / scattering type particle size distribution analyzer. Measured value (2-2) Average particle size of graphitized powder, graphite powder, and carbon black of bulk mesophase pitch: 50% by volume measured using a laser diffraction / scattering type particle size distribution analyzer (2-3) Specific surface area of graphitized coarse powder of mesocarbon small spheres: Measured by BET method (nitrogen adsorption). (2-4) Average aspect ratio of powder particles of coarse graphitized mesocarbon spheres: each in electron micrograph The average value of the ratio of the maximum length to the minimum length of each particle in the projection of the particle (2-5) The characteristics of the carbonaceous compact (thin plate) [bulk density, electrical resistivity, volume resistivity, gas permeation, Flexural strength]: (Bulk density :) The weight (mass) of the carbonaceous molded body It was determined by dividing by body volume.

(Electric resistivity :) Using an electric resistivity measuring device (trade name: Loresta, manufactured by Mitsubishi Chemical Corporation), JISK 7
Measured according to the method shown in 197. (Volume resistivity :) The volume resistivity was measured using the measuring device shown in FIG. 5, and the volume resistivity was calculated based on the following equation (2).

Volume resistivity = (volume resistance / plate thickness of sample) × surface area of sample (2) [in the above formula (2), surface area of sample = 25 cm ² ] In FIG. 11a and 11b are insulation materials (PTFE (polytetrafluoroethylene)), 12a and 12b
Is a copper plate, P is a pressure (9.8 × 1000N), S is a sample (50 mm
Corner).

(Gas permeation amount :) Using a gas permeation amount measuring device, pressure: 0.098 MPa from one side of the carbonaceous molded body (thin plate)
(Gauge pressure) (1 kgf / cm ² · G) of nitrogen was supplied, and the amount of permeated nitrogen was measured. (Bending strength :) Autograph (manufactured by Shimadzu Corporation)
Was measured by a three-point bending test method.

(2-6) Mean square error ε with respect to the average value of the groove depth of the grooved carbonaceous molded article (: fuel cell separator with grooves): using a surface roughness measuring device, Measure the groove depth of the fuel cell separator at 20 points.
Mean square error with respect to the average value of groove depth based on (3): ε
I asked.

Specification of grooved fuel cell separator: thickness: 2 mm, width: 200 mm, length: 200 mm, groove width: 1 mm,
Groove depth: 0.8mm

[0081]

(Equation 1)

[Examples 1 to 3 and Comparative Examples 1 to 6] A coarse powder of mesocarbon spheroids and a phenol resin were uniformly mixed in a mixing ratio shown in Table 3 using methanol as a solvent and then separated. It was applied on a pattern paper and left to dry overnight.
Next, the obtained dried product was pre-cured by heating at 100 ° C. for 90 minutes.

Next, after the obtained bulk mixture was pulverized with a pulverizer, the powder was supplied to a mold and subjected to molding conditions shown in Table 2.
Hot-press molding by press molding, thickness: 2mm, width: 200mm
A carbonaceous molded product (thin plate) having a length of 200 mm was manufactured (Examples 1 to 3 and Comparative Examples 1 to 4). In addition, carbonaceous compacts (thin plates) were produced in the same manner as above using only artificial graphite powder or mesocarbon small sphere graphitized fine powder as a carbon material (Comparative Examples 5 and 6).

Next, the obtained carbonaceous molded body was measured for bulk density, electric resistivity, volume resistivity, gas permeation amount, and bending strength. Table 4 shows the obtained measurement results. Next, using a mold having continuous projections corresponding to the grooves of the separator, in the same manner as described above, thickness: 2 mm, width: 200 m
A grooved carbonaceous molded article having a length of 200 mm and a length of 200 mm (a grooved fuel cell separator, a grooved separator) was produced.

The width of the groove (the groove for the gas flow path) is 1 m.
m and the depth were 0.8 mm. Next, the mean square error ε with respect to the average value of the groove depth of the obtained grooved separator was measured. Table 4 shows the obtained measurement results. [Examples 4 to 11 and Comparative Examples 7 to 9] Mesocarbon small sphere graphitized coarse powder and phenolic resin, mesocarbon small sphere graphitized fine powder, bulk mesophase pitch graphitized powder, graphite powder, Fine carbon powders and fine carbon fibers selected from carbon black and carbon nanofibers were uniformly mixed in a mixing ratio shown in Table 5 using methanol as a solvent, then applied on release paper and left to dry overnight. .

Next, the obtained dried product was subjected to the conditions of 100 ° C.
Precured by heating for 90 minutes. Next, after the obtained bulk mixture was crushed by a crusher, the powder was supplied to a mold and pressed under the molding conditions shown in Table 2, and the thickness was 2 mm and the width was 200 mm.
A carbonaceous molded body (thin plate) having a length of 200 mm was produced.
Next, the bulk density, electric resistivity, volume resistivity, gas permeation amount, and bending strength of the obtained carbonaceous molded body were measured.

Table 6 shows the measurement results obtained. next,
Using a mold having continuous projections corresponding to the grooves of the separator, in the same manner as described above, thickness: 2 mm, width: 20
A grooved carbonaceous molded article having a length of 0 mm and a length of 200 mm (: a grooved fuel cell separator, a grooved separator) was produced.
The width of the groove (the groove for the gas flow path) is 1 mm and the depth is 0.8 m
m.

Next, the mean square error ε with respect to the average value of the groove depth of the obtained grooved separator was measured. In Table 6,
The obtained measurement results are shown. As shown in Tables 4 and 6, the fuel cell separator of the present invention has excellent gas impermeability, low electric resistivity, low volume resistivity, and high dimensional accuracy of the gas flow channel groove. It turned out to be excellent.

Further, since the fuel cell separator of the present invention does not require graphitization, the fuel cell separator having the above-mentioned excellent performance can be provided with a simple facility and with a method excellent in energy and productivity. It turned out that it was possible. In the present example, further, a unit cell was formed by providing an air electrode on one side of a solid polymer electrolyte plate comprising a perfluorocarbon sulfonate ion exchange membrane and a fuel electrode on the other side. The unit cells were stacked via the grooved separator obtained in any of Examples 1 to 11 described above, and a solid polymer fuel cell was prototyped.

Next, as a result of evaluating the performance of the obtained polymer electrolyte fuel cell, the gas flow distribution was uniform in all of the grooved separators obtained in Examples 1 to 11, and the power generation efficiency was improved. An excellent fuel cell was obtained.

[0091]

[Table 3]

[0092]

[Table 4]

[0093]

[Table 5]

[0094]

[Table 6]

[0095]

According to the present invention, gas impermeability is excellent,
It is possible to provide a fuel cell separator with low electric resistivity, low volume resistivity, and excellent dimensional accuracy,
It has become possible to provide a fuel cell with excellent power generation efficiency. Furthermore, according to the present invention, since the graphitization of the separator molded product is not required, the separator for a fuel cell and the fuel cell having the above-mentioned excellent performance can be obtained with a simple facility and with a method excellent in energy and productivity. It became possible to provide.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a polymer electrolyte fuel cell.

FIG. 2 is an electron micrograph showing the particle structure of artificial graphite powder.

FIG. 3 is an electron micrograph showing the particle structure of coarse powder of graphitized mesocarbon spheres.

FIG. 4 is an electron micrograph showing the particle structure of mesocarbon small sphere graphitized fine powder.

FIG. 5 is an explanatory diagram showing a method of measuring volume resistivity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte board 2 Air electrode 3 Fuel electrode 4 Separator 5 Groove for gas flow path 10 Resistance meter 11a, 11b Insulation material 12a, 12b Copper plate P Pressure S Sample

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noboru Shinohara 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Pref. Kawasaki Steel Research Institute Co., Ltd. (72) Inventor Yasunobu Iizuka 2-3-2 Uchisaiwaicho, Chiyoda-ku, Tokyo F-term (reference) in Kawasaki Steel Corporation 5H026 AA06 CC03 CX02 EE05 EE06 EE18 HH01 HH02 HH05

Claims (5)

[Claims] 1. Mesocarbon small sphere graphitized coarse powder: 100 to 100 parts by weight of cured thermosetting resin: 3 to 20
A molded article containing parts by weight, wherein the graphitized coarse powder contains 50 μm <particle diameter ≦ 300 μm, specific surface area ≦ 1.5 m ² / g,
A separator for a fuel cell, wherein the separator is a graphitized powder having an average aspect ratio of powder particles ≦ 3. 2. Mesocarbon small sphere graphitized fine powder having a particle size satisfying the following formula (1) per 100 parts by weight of the graphitized coarse powder: 100 parts by weight or less. The fuel cell separator according to claim 1, wherein Note: Graphite fine powder particle size ≦ 50μm ............ (1) 3. A mass of one or more selected from graphite powder, graphite powder, carbon black and fine carbon fiber of bulk mesophase pitch in a total amount of 100 parts by weight with respect to 100 parts by weight of said graphitized coarse powder. The fuel cell separator according to claim 1, wherein the content of the fuel cell is not more than 3 parts by weight. 4. An average particle size of the graphitized powder of the bulk mesophase pitch is 50 μm or less, and an average particle size of the graphite powder is
4. The fuel cell separator according to claim 3, wherein the carbon black has an average particle diameter of 100 nm or less, the fine carbon fibers have an average fiber diameter of 2 μm or less, and the average fiber length is 500 μm or less. 5. A fuel cell using the fuel cell separator according to claim 1.