Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-03-24
2002-08-20
Dunn, Tom (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000
Reexamination Certificate
active
06436567
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a separator for fuel cell, particularly a separator for polymer electrolyte fuel cell.
BACKGROUND ART
Fuel cells have various merits. For example, use of fossil fuel (to which resource impoverishment attention must be paid) is not substantially necessary; substantially no noise is made during power generation; and the recovery of energy can be made high as compared with other fuel power-generating systems. Therefore, fuel cells are being developed for use as a relatively small power generator for buildings or factories or as an electric source for pollution-free vehicles.
Of the parts constituting a fuel cell, the separator has functions of securing paths for a reaction gas entering the fuel cell, transferring the electric energy produced in the fuel cell, to outside, and radiating the heat generated in the fuel cell, to outside. To fulfill these functions, the fuel cell separator is required to have high conductivity, high gas impermeability, high strength, etc.
As the material for fuel cell separator, there has been used high-density graphite impregnated with a thermosetting resin, or graphite having a glassy carbon layer thereon.
Of these conventional materials, the graphite impregnated with a thermosetting resin has problems. That is, a step of impregnation and subsequent drying must be repeated a plurality of times in order to obtain a desired gas barrier property; moreover, machining is necessary for forming paths for reaction gas, in the graphite, which incurs a high cost.
The graphite having a glassy carbon layer thereon has problems as well. That is, it is necessary to repeat impregnation and subsequent drying a plurality of times as in the case of the above-mentioned graphite and then conduct firing in a non-oxidizing atmosphere, or to form a glassy carbon layer on graphite by CVD, which makes the production process complicated; machining is necessary for forming paths for reaction gas, in the graphite, which incurs a high cost; moreover, use of graphite results in a large density and makes large the total weight of fuel cell.
Under such a situation, with a view to providing a fuel cell separator of lower cost, there was proposed a process for production of separator, which comprises molding a mixture of a carbon powder (as a conductive powder) and a special thermosetting resin (as a binder) (Japanese Patent Publication No. 57466/1989). This process, however, has problems. That is, as the binder, there is needed a very special phenolic resin having a paraxylene bond in the molecular chain; a long time is required for preheating, making complicated the process; and the separator obtained is inferior in conductivity and gas barrier property.
For improvement in conductivity, there was also proposed a process for production of fuel cell separator, which comprises molding a mixture of a graphite powder having an aspect ratio of 3 or less and a desired particle size, and a thermosetting resin (Japanese Patent Publication No. 340/1989). This process, however, has a problem in that since the graphite powder has a small aspect ratio, the arrangement thereof is bad and the fuel cell separator obtained is inferior in mechanical strengths and gas impermeability.
The present invention has been made to alleviate the above-mentioned problems of the prior art and provide a fuel cell separator which has high conductivity, high gas impermeability and high strength and which can be produced easily.
DISCLOSURE OF THE INVENTION
In order to achieve the above object, the present invention provides a separator for fuel cell, which is a molding comprising a conductive carbon powder and a polymer compound, wherein the conductive carbon powder in the molding has an aspect ratio of 4 to 60, preferably 10 to 30.
That is, in order to achieve the above object, the present inventors made a study. As a result, the present inventors came to an idea that a conductive carbon powder having a given aspect ratio, when mixed with a polymer compound such as thermosetting resin, thermoplastic resin, rubber or the like, might have very high miscibility with the polymer compound and, when the mixture is molded, might be easily arranged in the same direction; as a result, the contact area between conductive carbon powder particles might increase and a fuel cell separator having excellent properties might be obtained by molding the mixture. A further study was made, and the present invention has been completed.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is hereinafter described in detail.
The fuel cell separator of the present invention is the same as conventional fuel cell separators in that it has, as necessary, grooves for feeding an oxidizing agent gas or a fuel gas, at one or both sides.
It is necessary that the fuel cell separator of the present invention is a molding comprising a conductive carbon powder and a polymer compound and that the conductive carbon powder used for production of the molding has an aspect ratio of 4 to 60.
The aspect ratio is a ratio of the major axis and minor axis of particle and is determined, for example, by taking a microphotograph of the conductive carbon powder or the like using a scanning type electron microscope and measuring the major axis and minor axis of each particle constituting the powder.
In the present invention, when the conductive carbon powder has an aspect ratio of 4 or more, the particles of the powder can have sufficient contact with each other and thereby a desired conductivity can be obtained. A conductive carbon powder having an aspect ratio of more than 60 is very costly to produce and therefore is not realistic. The aspect ratio of the carbon powder is preferably 10 to 30 because it can give a separator of higher strength.
The conductive carbon powder used in the present invention can be exemplified by scaly graphite, amorphois graphite and artificial graphite. These conductive carbon powders can be used as they are, as long as they have an aspect ratio falling in the above range. When these conductive carbon powders have an aspect ratio not falling in the above range, they can be made usable in the present invention by allowing them to have the above aspect ratio, by a grinding means such as mixer, jet mill, ball mill, pin mill, freeze-grinding or the like.
The conductive carbon powder ground as above is as necessary subjected to classification by a conventional means such as vibrating screen, Ro-tex screener, sonic screen, microclassifier, forced vortex air classifier or the like to remove the particles having an average particle diameter of smaller than 0.1 &mgr;m or larger than 100 &mgr;m, preferably smaller than 1 &mgr;m or larger than 80 &mgr;m and an aspect ratio of smaller than 4 or larger than 60, whereby a conductive carbon powder usable in the present invention can be obtained.
As the polymer compound usable-in the present invention for production of the molding, there can be mentioned one kind or a mixture of two or more kinds, selected from thermosetting resins, thermoplastic resins and rubbers. Of these, the thermosetting resins can be, for example, polycarbodiimide resin, phenolic resin, furfuryl alcohol resin, epoxy resin, cellulose, urea resin, melamine resin, bismaleimidetriazine resin, unsaturated polyester, silicone resin, diallyl phthalate resin, polyaminobismaleimide resin and aromatic polyimide.
The thermoplastic resins can be, for example, polyethylene, polystyrene, polypropylene, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polycarbonate, polyoxamethylene, polyamide, polyimide, polyamideimide, polyvinyl alcohol, polyvinyl chloride, fluroresin, polyphenylsulfone, polyetheretherketone, polysulfone, polyetherketone, polyarylate, polyetherimide, polymethylpentene, polyoxybenzoyl ester, liquid crystal polyester, aromatic polyester, polyacetal, polyallylsulfone, polybenzimidazole, polyethernitrile, polythioethersulfone and polyphenyl ether.
The rubbers can be, for example, fluororubber, silicone rubber, butyl rub
Hagiwara Atsushi
Hamada Kazutoshi
Okamoto Toshiharu
Saito Kazuo
Tanno Fumio
Dunn Tom
Kubovcik & Kubovcik
Nisshinbo Industries Inc.
Stoner Kiley
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