Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-06-07
2002-10-08
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S254000, C252S510000, C252S511000, C264S239000
Reexamination Certificate
active
06461755
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electroconductive resin composition, fuel cell separator made of said electroconductive resin composition, process for production of said fuel cell separator, and solid polymer type fuel cell using said fuel cell separator.
2. Description of the Prior Art
In fuel cells, one pair of electrodes are contacted with each other via an electrolyte; a fuel is fed into one of the electrodes and an oxidizing agent is fed to the other electrode; the fuel is oxidized electrochemically; thereby, a chemical energy is converted directly into an electrical energy. Such fuel cells have various types depending upon the kind of the electrolyte used therein. In recent years, attention has been paid to a solid polymer type fuel cell using a solid polymer electrolyte membrane, which is a fuel cell capable of generating a high output.
In such a solid polymer type fuel cell, a hydrogen gas (which is a fluid) is fed to the fuel electrode and an oxygen gas (which is also a fluid) is fed to the oxidizing agent electrode, and an electric current is taken out from an external circuit. In the individual electrodes, the following reactions take place.
Fuel Cell Electrode
H
2
→2H
+
+2e
−
(1)
Oxidizing Agent Electrode
2H
+
+2e
−
+(1/2)O
2
→H
2
O (2)
Hydrogen (H
2
) becomes proton (H
+
) on the fuel cell electrode, and this proton moves onto the oxidizing agent electrode through a solid polymer electrolyte membrane and reacts with oxygen (O
2
) on the oxidizing agent electrode, generating water (H
2
O). Therefore, in operating a solid polymer type fuel cell, it is necessary to feed and discharge reactant gases and take out the electricity generated. Further in the solid polymer type fuel cell, it is necessary to manage and feed water to the fuel electrode and discharge water from the oxidizing agent electrode, because the fuel cell is designed to be operated ordinarily in a wet atmosphere of room temperature to 120° C. and water is inevitably handled in a liquid state.
Of the components constituting a fuel cell, the separator functions so as to prevent a fuel gas, an oxidizing agent gas and cooling water (all flowing in the fuel cell) from mixing with each other, and is required to have gas barrier property, electrical conductivity, corrosion resistance, etc.
As the separator for solid polymer type fuel cell, there have been proposed various types which are advantageous in productivity and cost. They are made of a carbon composite material using, as a binder, a thermoplastic resin or a thermosetting resin. For example, a separator using a thermosetting resin as a binder is described in JP-A-55-019938, and a separator using a thermoplastic resin (e.g. polypropylene or nylon) as a binder is described in JP-A-57-61752 and JP-A-57-617521.
Separators made of a carbon composite material using a thermoplastic or thermosetting resin as a binder, however, as compared with conventional separators produced by machining of graphite sheet, have had problems in high temperature resistance and hydrolysis resistance although they are superior in productivity and cost.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide an electroconductive resin composition which alleviates the above-mentioned problems of the prior art, can be mass-produced, and is superior in high temperature resistance and hydrolysis resistance.
The present inventor made a study on electroconductive resin compositions low in resistivity and high in mechanical strength. As a result, it was found out that by adding, to an electroconductive carbon powder, a binder which is a resin composition comprising a liquid crystal polyester (LCP) and a carbodiimide compound, the resulting electroconductive composite material is improved in water resistance of LCP (the LCP water resistance has been a problem in the prior art), has a low resistivity, and is improved in mechanical strength and gas barrier property. This finding has led to the completion of the present invention.
The present invention provides:
an electroconductive resin composition comprising:
(A) a liquid crystal polyester resin capable of forming an anisotropic melt phase, in an amount of 100 parts by weight,
(B) a carbodiimide compound in an amount of 0.01 to 30 parts by weight,
(C) an electroconductive carbon powder in an amount of 50 to 3,000 parts by weight, and
(D) a filler in an amount of 0 to 10,000 parts by weight;
a fuel cell separator made of the above electroconductive resin composition;
a process for producing the above fuel cell separator; and
a solid polymer type fuel cell using the above fuel cell separator.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The liquid crystal polyester used as the component (A) in the present invention is a polyester called a thermotropic liquid crystal polymer and is capable of forming an anisotropic melt phase. In the present invention, there is used, in particular, a liquid crystal polyester which shows no deformation in the form of a composition when placed in the operating conditions of solid polymer type fuel cell and which has a heat deformation temperature of 80° C. or more, preferably 80 to 400° C., more preferably 120 to 350° C.
As the liquid crystal polyester used in the present invention, there can be specifically mentioned (i) a reaction product of an aromatic dicarboxylic acid and an aromatic hydroxycarboxylic acid, (ii) a reaction product of different aromatic hydroxycarboxylic acids, (iii) a reaction product of an aromatic dicarboxylic acid and an aromatic diol and (iv) a reaction product of a polyester (e.g. polyethylene terephthalate) and an aromatic hydroxycarboxylic acid. Incidentally, the above aromatic dicarboxylic acid or aromatic diol or aromatic hydroxycarboxylic acid may be replaced by an ester-forming derivative thereof.
The repeating structural unit of the liquid crystal polyester can be exemplified by the followings, but is not restricted thereto.
Repeating Structural Units Derived from aromatic hydroxycarboxylic acid
In the above, X is a halogen atom, an allyl group or an alkyl group (the same applies hereinafter).
Repeating Structural Units Derived from aromatic dicarboxylic acid
Repeating Structural Units Derived from aromatic diol
The liquid crystal polyester preferably contains at least 30 mole % of a repeating structural unit derived from aromatic hydroxycarboxylic acid, in view of the balance of heat resistance, mechanical property and processability.
The carbodiimide compound used as the component (B) in the present invention is a compound having at least one carbodiimide group (—N═C═N—) in the molecule, and is a monocarbodiimide compound represented by the following formula:
R—N═C═N—R
or a polycarbodiimide compound represented by the following formula:
(—R—N═C═N—)
n
wherein R has at least one carbon atom and n is an integer of 2 or more.
As the monocarbodiimide compound, there can be used those synthesized by a well known method. It can be synthesized, for example, by subjecting an isocyanate to decarboxylation and condensation at a temperature of about 70° C. or higher in a solvent-free state or in an inert solvent, using, as a carbodiimidization catalyst, 3-methyl-1-phenyl-2-phosphorene-1-oxide.
As specific examples of the monocarbodiimide compound, there can be mentioned dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide and di-&bgr;-naphthylcarbodiimide. Of these, preferred are dicyclohexylcarbodiimide and diisopropylcarbodiimide for their high industrial availability.
The polycarbodiimide can be produced by various methods. Fundamentally, it can be produced by conventional methods for polycarbodiimide production, described in U.S. Pat. No. 2,941,956; JP-B-47-33279; J. Org. Chem., 28, 2069-2075 (1963); and Chemical
Hagiwara Atsushi
Horie Naofumi
Imashiro Yasuo
Saito Kazuo
Tanno Fumio
Kubovcik & Kubovcik
Nisshinbo Industries Inc.
Weiner Laura
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