JP2005056642A - Graphite material powder for fuel cell separator, and fuel cell separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide graphite material powder for a fuel cell separator which is superior in molding workability, and provide the fuel cell separator which uses the graphite material powder, of which the specific resistance is low, and which is superior in gas blocking ability. <P>SOLUTION: By using the graphite material powder containing graphite powder, monovalent alcohols of which boiling point is 160°C or more, polyvalent alcohols, carboxylic acid or one or two kinds or more of organic compounds among their dehydrated condensation products, the fuel cell separator is manufactured by a molding method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a graphite powder used as a material for a fuel cell separator and a fuel cell separator using the same.

  Fuel cells generate electricity by reacting hydrogen and oxygen, so they have excellent characteristics such as high power generation efficiency and low generation of harmful gases and pollutants. Large-scale power generation, cogeneration systems, automotive power supplies The future is expected as a power supply device in a wide range of fields. In this fuel cell, two separators for supplying hydrogen and oxygen, two electrodes (combustion electrode and air electrode), and an electrolyte membrane (ion exchange membrane) are laminated like a sandwich to form one single cell. In general, a single cell is connected to several tens to several hundreds in series via a separator to form a fuel cell stack.

  Fuel cells are classified into alkaline types, phosphoric acid types, molten carbonate types, solid electrolyte types, solid polymer types, and the like, depending on the type of electrolyte, and developments utilizing the respective characteristics are being promoted. Among these fuel cells, the polymer electrolyte fuel cell has a low power generation temperature of 80 to 100 ° C., the cell body can be made smaller and lighter, the start-up is quick, the fuel efficiency and the output density are high, etc. Therefore, it attracts attention as a power source for mounting an electric vehicle, a small-scale power generator for home use, a portable power generator, and a portable power generator.

  In a polymer electrolyte fuel cell, a perfluorocarbon sulfonic acid (PFSA) ion exchange membrane or the like is mainly used as an electrolyte. On the other hand, since the separator 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 the unit cells, the separator has excellent gas barrier properties and high thermal conductivity. In addition, the specific resistance is required to be low and to have excellent heat resistance and mechanical strength at the operating temperature. Therefore, conventionally, as a separator, those obtained by machining artificial graphite or those obtained by machining metal materials such as titanium and stainless steel have been studied.

However, a separator obtained by machining artificial graphite has a problem that it has a low specific resistance but has insufficient gas barrier properties and is very expensive. In addition, a metal material machined separator is exposed to an oxidizing atmosphere at a high temperature, so that it may be oxidized by long-term use, and is expensive as artificial graphite. There was a problem. For this reason, technology development for solving these problems is being carried out in each field. For example, in a technique using graphite as a separator, Patent Document 1 discloses a polymer electrolyte fuel cell separator formed by blending an artificial graphite or natural graphite powder with a thermosetting resin, and Patent Document 2 discloses a mesophase. A phosphoric acid fuel cell separator comprising powder and a thermosetting resin is disclosed.
JP-A-10-334927 Japanese Patent Publication No. 6-92269

  However, the separator disclosed in Patent Document 1 has a problem that the specific resistance is high, although the problems of gas barrier properties and oxidation are improved to some extent. The reason is that the blend of graphite powder and thermosetting resin has high viscosity, low fluidity during separator molding, and poor molding processability, so the ratio of thermosetting resin is 20-60 volumes. This is because it needs to be as high as%. Then, in order to reduce a specific resistance, although metal powder is not mix | blended, another problem that oxidation is inevitable by this has generate | occur | produced. On the other hand, the technique disclosed in Patent Document 2 uses a resin-rich compound consisting of mesophase powder: 5 to 70% by weight and thermosetting resin: 30 to 95% by weight. Although the fluidity is high and there is no problem in molding processability, there is a problem that the specific resistance is high. In order to reduce the specific resistance, it is necessary to perform firing and graphitization of the molded product. However, the heat treatment of the molded product has problems that the dimensional accuracy is deteriorated due to shrinkage and the heat treatment itself is extremely inefficient and expensive.

  An object of the present invention is to provide a fuel cell separator having excellent molding processability, a low specific resistance and an excellent gas barrier property, and a fuel obtained from the graphite powder for a fuel cell separator. The object is to provide a battery separator.

  In order to solve the above-described problems of the prior art, the inventors used various graphite powders as a material for a fuel cell separator, and mixed a mixture obtained by mixing a thermosetting resin as a binder (binder) with the separator. And then intensively investigated the moldability and separator characteristics. As a result, when graphite powder containing a certain organic compound is used as the separator material, the fluidity of the mixture with the thermosetting resin is improved, and the molding processability is greatly improved. I found it. In addition, it was confirmed that the separator formed using the powder satisfied the performance of excellent gas barrier properties and low specific resistance, and the present invention was completed.

  The present invention developed based on the above knowledge contains graphite powder and an organic compound, and the organic compound is a monohydric alcohol, a polyhydric alcohol, a carboxylic acid, or a dehydration condensate thereof. A graphite powder for a fuel cell separator, characterized by being one or more of the above.

  The organic compound of the present invention preferably has a boiling point of 160 ° C. or higher.

  In the present invention, the organic compound is preferably contained in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the graphite powder.

  The present invention also provides a fuel cell separator obtained by molding a mixture of the above-described graphite powder and a binder by a molding method.

  According to the present invention having the above-described configuration, a graphite powder having a high fluidity of a mixture with a binder and excellent moldability can be obtained by containing an appropriate organic compound. Therefore, the amount of the binder to be mixed can be reduced, and the fuel cell separator obtained by using this graphite powder has characteristics of high bulk density, low specific resistance, and excellent gas barrier properties. In addition, according to the present invention, since a heat treatment such as graphitization after forming the separator is unnecessary, a fuel cell separator having excellent performance can be provided with high productivity with simple equipment.

  In the present invention, the graphite powder as a material used for the fuel cell separator is not particularly limited, and natural graphite powder, artificial graphite powder, mesophase carbon graphitized powder, or a mixed powder thereof can be used. Natural graphite powder is a naturally occurring graphite powder and is a scaly powder that is more graphitized than artificial graphite powder. There are Austria, Switzerland, China, and the like as production areas of natural graphite, but the production area of natural graphite is not particularly limited in the present invention. The artificial graphite powder is, for example, graphite powder obtained by heat-treating coke at 2500 to 4000 ° C., and is a lump before pulverization, but becomes a scaly powder by pulverization or cutting. In the present invention, the method for producing artificial graphite is not particularly limited. Also, mesophase carbon graphitized material is a small amount of optical anisotropy generated in a bulk carbonized product produced by heat treatment of coal-based pitch or petroleum-based pitch, or in a pitch matrix before becoming bulky. A spherical carbonized material obtained by extracting, filtering, or centrifuging spheres is obtained by carbonization, graphitization, pulverization / classification, or the like. There is no particular limitation on the method for producing mesophase carbon graphitized material, and the pulverization / classification treatment may be performed before or after carbonization or before or after graphitization.

  The graphite powder of the present invention contains the above graphite powder and an organic compound described below. The reason for containing the organic compound is that when the fuel cell separator is molded, the miscibility with the thermosetting resin added as a binder is improved, and as a result, the graphite powder of the present invention and the binder are mixed. The fluidity of the mixture is improved. As a result, molding processability is improved, and molding can be easily performed even if the amount of the binder is small. Further, the generation of pores inside the molded body is suppressed and the bulk density is increased. As a result, the contact frequency between graphite powders is increased, the electrical conductivity is improved, and a low specific resistance is obtained.

  Here, the organic compound contained in the graphite powder is one or more of monohydric alcohols, polyhydric alcohols, carboxylic acids, or dehydration condensates thereof. Since these organic compounds have a hydrophilic or lipophilic functional group, the wettability with the thermosetting resin added as a binder is improved, and the miscibility is improved. Therefore, in order to improve the miscibility with the binder of the graphite powder of the present invention, these organic compounds must be contained. Among the above organic compounds, monohydric alcohols having 5 or more carbon atoms, polyhydric alcohols having 2 or more carbon atoms, carboxylic acids having 2 or more carbon atoms, or dehydration condensates thereof can be suitably used. Specifically, as monohydric alcohols, pentyl alcohol, hexyl alcohol, cetyl alcohol, stearyl alcohol, etc., as polyhydric alcohols, glycol, glycerin, polyvinyl alcohol, etc., as carboxylic acids, acetic acid, Examples include higher fatty acids such as butyric acid, acrylic acid, stearic acid, and oleic acid. Examples of these dehydration condensates include esters of the above compounds, such as acetylates and acetals. In particular, polyvinyl alcohol or a butyral resin obtained by acetalizing polyvinyl alcohol can be suitably used because of its strong binding force and good miscibility with graphite powder.

  In addition, the graphite powder containing the graphite powder and the organic compound is then made into a mixture mixed with a binder and molded by a molding method such as press molding. In this case, in order to improve the fluidity of the mixture In addition, it is generally heated to about 70 to 160 ° C. and mixed or preformed. Therefore, when the boiling point of the organic compound to be contained is low, the organic compound volatilizes and the above effect may be lost. Therefore, the organic compound to be contained is preferably selected according to the processing temperature. Any organic compound having a boiling point of 160 ° C. or higher can be suitably used.

Next, a method for producing the fuel cell separator according to the present invention will be described.
As the material for the fuel cell separator, the above-mentioned natural graphite powder, artificial graphite powder, graphite powder such as mesophase carbon, and graphite powder containing the above organic compound are used. The content of the organic compound is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of natural graphite powder, artificial graphite powder, mesophase carbon graphitized powder, or a mixed powder thereof. If the amount is less than 0.1 part by mass, the effect of improving the miscibility with the binder is insufficient. On the other hand, if the amount exceeds 10 parts by mass, the electrical conductivity is hindered due to a decrease in the contact frequency between the graphite powders. The more preferable organic compound content is 0.2 to 5 parts by mass.

  It is preferable that the graphite powder containing the organic compound and the graphite powder at such a ratio is further uniformly mixed. As a mixing method, either a dry method or a wet method may be used. Moreover, as an apparatus used for mixing, generally used mixing, granulating, and surface modifying apparatuses such as a stirring blade type and a spraying type can be used.

  Next, the binder is mixed with the graphite powder obtained by mixing the graphite powder and the organic compound as described above. As the binder, it is preferable to use a thermosetting resin. For example, it is 1 type or 2 or more types chosen from a phenol resin, a furfural resin, a furan resin, an epoxy resin, an unsaturated polyester resin, a polyimide resin etc., and a phenol resin is especially suitable. This is because the phenol resin is easy to handle and inexpensive, and the resulting separator has excellent dimensional accuracy and mechanical strength.

  The mixing amount of the binder is preferably 3 to 30 parts by mass with respect to 100 parts by mass of the graphite powder, that is, the graphite powder of the present invention in which the graphite powder and the organic compound are mixed. When the mixing amount of the binder is less than 3 parts by mass, the fluidity of the mixture is insufficient, so that pores are easily generated inside the molded body, and a fuel cell separator with excellent gas barrier properties cannot be obtained. There is a fear. Moreover, since the binding force is insufficient, the molded product has a low strength. On the other hand, when the amount exceeds 30 parts by mass, the ratio of the resin increases, so that the specific resistance tends to increase. A more preferable mixing amount is 5 to 20 parts by mass.

For example, a molding method such as a press molding method or an injection molding method is advantageously suited as a molding method for the fuel cell separator. When the press molding method is used, a fuel cell separator is manufactured by supplying a mixture obtained by mixing one or more of the above-described binders to the graphite powder according to the present invention to a press molding machine. In addition, at the time of the above-mentioned mixing, in order to add a solvent as needed, or to improve moldability, it is preferable to adjust the fluidity by heating and pre-curing the mixture before supplying it to the mold. The conditions for press molding differ depending on the thermosetting resin used as the binder, but it is preferable that the heating temperature of the mold during pressure molding is 130 to 220 ° C. and the press pressure is 200 N / cm ² or more.

  When the injection molding method is used, a fuel cell separator is manufactured by supplying a mixture obtained by mixing one or more binders with the graphite powder according to the present invention to an injection molding machine. As conditions for injection molding, it is preferable to mix at a temperature of 100 to 140 ° C. and then injection mold into a mold. In this case, the mold is heated to 40 to 200 ° C. in order to cure the resin. It is preferable to keep it.

  In addition, since the separator obtained as described above has excellent electrical conductivity (low specific resistance) even as it is in press molding or injection molding, it can be fired after molding as performed in the prior art. There is no need to perform graphitization. Incidentally, in the present invention, excellent electrical conductivity means a specific resistance of 10 mΩ · cm or less, and the present invention aims to develop a separator having the above value or less.

  50 parts by mass of methylene chloride solution in which 0.5 part by mass of butyral resin (6000EP manufactured by Denka) was added to 100 parts by mass of graphite powder of mesocarbon spherules with an average particle size of 15 μm. A kneading process was performed using a granule apparatus to obtain a graphite powder A for a fuel cell separator. Similarly, 50 parts by mass of an aqueous solution containing 0.5 parts by mass of a polyvinyl alcohol resin (PA-05GP manufactured by Shin-Etsu Chemical Co., Ltd.) is added to 100 parts by mass of graphite powder of mesocarbon spherules having an average particle size of 15 μm and stirred. A kneading process was performed using a rolling granulator to obtain a graphite powder B for a fuel cell separator. After mixing 80 parts by mass of each of these graphite powders A and B with 20 parts by mass of a liquid resol phenolic resin having a viscosity coefficient of 0.7 Pa · s (20 ° C.), it is coated on release paper and left overnight. The powder obtained by drying and crushing was measured for viscosity coefficient at 80 ° C. with a flow tester (FT-500, manufactured by Shimadzu Corporation).

Next, 20 parts by mass of phenol resin is mixed with 80 parts by mass of each of the above graphite powders A and B, and then coated on a release paper and left to dry overnight. After pre-curing by heating for 90 minutes, the powder is crushed, and the resulting powder is supplied to a mold, press-molded under conditions of a mold temperature of 160 ° C. and a press pressure of 700 N / cm ² , and the thickness: A molded body of 2 mm, width: 200 m, and length: 200 mm was produced. About the obtained molded object, the bulk density, the specific resistance, and the gas permeation amount were measured by the following methods. As a comparative example, mesocarbon spherule graphite powder having an average particle size of 15 μm was used as it was as the graphite powder C for fuel cell separator, and the same measurement as the graphite powders A and B was performed.
-Average particle size: The particle size distribution measured by the laser diffraction method was a particle size at which the cumulative frequency was 50% by volume.
Bulk specific gravity: Determined by dividing the weight (mass) of the graphite molded body by the volume of the graphite molded body.
Specific resistance: Measured using an electrical specific resistance measuring device according to the method of JIS-K7194-1994.
-Gas permeation amount: Using a gas permeation amount measuring device, supply nitrogen at a pressure of 0.098 MPa (gauge pressure) (= 1 kgf / cm ² · G) from one side of the graphite compact (thin plate). The amount of permeation was measured.

  The measurement results are shown in Table 1. Graphite powders A and B obtained according to the present invention have a low viscosity coefficient, good fluidity, and excellent moldability. Furthermore, it can be seen that molded bodies using these have a high bulk density, a specific resistance as small as 10 mΩ · cm or less, a small amount of gas permeation, and excellent gas barrier properties. On the other hand, the graphite powder C of the comparative example has an extremely high viscosity coefficient, cannot be measured, and has poor moldability. In addition, the compact using the graphite powder has a low bulk density and a specific resistance of 10 mΩ · cm or less cannot be achieved.

  50 parts by weight of a methylene chloride solution in which 0.5 parts by weight of a butyral resin (6000 EP made by Denka) was added to 100 parts by weight of artificial graphite powder having an average particle size of 10 μm (SP-10 made by Nippon Graphite Co., Ltd.) and stirred. A kneading process was performed using a rolling granulator to obtain a graphite powder D for a fuel cell separator. Using this graphite powder D, the viscosity coefficient of the powder was measured in the same manner as in Example 1. Moreover, it carried out similarly to Example 1, and manufactured the molded object, and measured the bulk density, the specific resistance, and the gas permeation amount. As a comparative example, the same measurement was performed when artificial graphite powder having an average particle size of 10 μm (SP-10 manufactured by Nippon Graphite Co., Ltd.) was used as it was as graphite powder E for fuel cell separators.

  The measurement results are shown in Table 2. Graphite powder D produced according to the present invention has a low viscosity coefficient and excellent moldability. Further, a molded body using the powder has a high bulk density, a specific resistance as small as 10 mΩ · cm, a small gas permeation amount, and an excellent gas barrier property. On the other hand, the graphite powder E of the comparative example has poor fluidity and poor moldability. Furthermore, a molded body using this powder has a low bulk density and a specific resistance of 10 mΩ · cm or less cannot be achieved.

  The present invention is not limited to the fuel cell separator, and can be suitably used as a raw material for conductive resin materials, conductive paints, and the like.

Claims (4)

  It contains graphite powder and an organic compound, and the organic compound is a monohydric alcohol, a polyhydric alcohol, a carboxylic acid, or one or more of these dehydration condensates. A graphite powder for fuel cell separators.   The graphite powder for a fuel cell separator according to claim 1, wherein the organic compound has a boiling point of 160 ° C. or higher.   The graphite powder for a fuel cell separator according to claim 1 or 2, wherein the organic compound is contained in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the graphite powder. A fuel cell separator obtained by molding a mixture of the graphite powder according to any one of claims 1 to 3 and a binder by a molding method.