JPH04214072A - Carbonaceous composition, carbon material for fuel cell and its manufacture - Google Patents

Abstract

PURPOSE:To increase the density, mechanical strength and electrical conductivity of a carbon material for a fuel cell. CONSTITUTION:The carbonaceous compsn. is incorporated phenol resin, milled carbon fiber and graphite powder consisting of 100 pts.wt. graphite powder of 25 to 75mum, 10 to 50 pts.wt. that of 75 to 125mum and 100 to 150 pts.wt. granular body of 125 to 175mum in the wt. ratio. The carbonaceous compsn. is formed into a sheet shape and is graphitized to obtain a sheet-shaped carbon material having <=1X10<-2>OMEGA.cm specific resistance and >=1.6g/cm<3> density.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbonaceous composition useful for producing a separator for a fuel cell, particularly a carbon material useful for a fuel cell, and a method for producing the same.

0002

[Prior Art] Fuel cells, unlike other power generation devices,
It is characterized by extremely low generation of pollutants such as Ox, NOx and dust, and low noise sources. In such a fuel cell, a porous cathode normally performs an oxidation reaction of the fuel, a porous anode performs a reduction reaction of an oxidant, and a separator is used between the two electrodes. This separator is required to have high density and high conductivity.

[0003] The separator is usually manufactured by kneading a binder such as a phenolic resin with graphite or the like, compressing the mixture into a sheet, and then curing the binder and firing. In this manufacturing method, gas release during the curing and firing process is poor and foaming occurs, so the resulting carbon plate has pores and has low mechanical strength. That is, the phenol resin is carbonized or graphitized by firing, generating voids, and the porosity of the carbon material reaches 20 to 30%. Therefore, the density and bending strength are reduced. In particular, the obtained carbon plate has low conductivity, particularly in the thickness direction, that is, between the cathode and the anode, so that the conversion efficiency into electrical energy is reduced.

0004

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a carbonaceous composition from which a carbon material that is dense, has high mechanical strength, and has excellent electrical conductivity can be obtained.

Another object of the present invention is to provide a carbon material for fuel cells that exhibits the above-mentioned excellent properties and a method for producing the same.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have made extensive studies and found that when using a specific amount of a plurality of carbonaceous powder particles with different particle sizes, the material is dense and conductive. It was discovered that a carbon material with excellent properties could be obtained, and the present invention was completed. That is, the present invention combines a binder that can be carbonized or graphitized, and fibers that can be made into carbon fibers or carbon fibers (hereinafter referred to as carbon fibers).
Unless otherwise specified, it is simply referred to as fiber); and at least one carbonaceous powder selected from carbonized or graphitizable powder and carbonized or graphitized powder. , the carbonaceous powder has an average particle size of 25 to 75μ
Average particle size 75-12 for 100 parts by weight of powder or granular material
10-50 parts by weight of 5 μm powder, average particle size 125-1
A carbonaceous composition comprising 100 to 150 parts by weight of 75 μm powder or granules is provided.

The present invention also provides a sheet-like carbon material comprising a carbonized or graphitized binder, carbon fibers, and carbonized or graphitized carbonaceous powder, the carbonaceous powder comprising: For 100 parts by weight of powder or granules with an average particle size of 25 to 75 μm, 10 to 50 parts by weight of powder or granules with an average particle size of 75 to 125 μm, 100 to 1 part by weight of powder or granules with an average particle size of 125 to 175 μm
Provided is a carbon material for fuel cells comprising 50 parts by weight.

Furthermore, the present invention provides a method for producing a carbon material for fuel cells, which comprises forming the carbonaceous composition into a sheet shape and carbonizing or graphitizing the carbonaceous composition.

[0009] The definitions of terms used in this specification are as follows.

[0010] Carbonization refers to a component that can be carbonized, for example,
It refers to firing treatment at a temperature of about 450 to 1500°C. Graphitization refers to firing treatment at a temperature of, for example, about 1500 to 3000°C, and is included in the concept of graphitization even when the material does not have the crystal structure of graphite.

[0011] Carbon fiber refers to carbonized or graphitized fiber. Flame-retardant treatment refers to a treatment in which fibers other than pitch-based fibers are heated, for example, at a temperature of about 200 to 450° C. in the presence of oxygen to form a heat-resistant layer on the surface to prevent melting during firing. Infusibility treatment means, for example, that pitch fibers are
This is a process of heating at a temperature of about 200 to 450°C in the presence of oxygen to form a heat-resistant layer on the surface to prevent melting during firing.

The present invention will be explained in more detail below.

Examples of binders that can be carbonized or graphitized include thermosetting resins such as phenolic resins, furan resins, melamine resins, unsaturated polyesters, vinyl ester resins, diallyl phthalate resins, epoxy resins, polyimides, and thermosetting acrylic resins. thermoplastic resins such as polyacrylonitrile; coal or petroleum pitch, etc. Among these binders, thermosetting resins, particularly phenol resins, are preferred, as they can retain their shape when heated, have a large residual carbon content when carbonized or graphitized, and can impart high strength. In addition, the residual carbon percentage of the binder is usually about 50~
It is preferably about 60% by weight or more. At least one of these binders can be used.

[0014] The fibers may be of any type as long as they can reinforce the carbon material obtained by firing. Examples of fibers that can be made into carbon fibers include various fibers that can be used as raw materials for carbon fibers, such as polyacrylonitrile fibers, phenol resin fibers, rayon, cellulose fibers, and pitch fibers. The carbonized or graphitized fibers may be flame-proofed or infusible-treated. Preferred fibers are carbon fibers that can impart high reinforcing properties and conductivity to the carbon material.

[0015] The fibers are milled fibers, for example,
It is preferable that the fibers are short fibers having a fiber length of about 0.01 to 3 mm.

[0016] The carbonaceous powder may be one that imparts high electrical conductivity to the carbon material by itself or by firing. This carbonaceous powder also increases the compressive strength of the carbon material. Examples of the powder that can be carbonized or graphitized include bulk mesophase carbon obtained by infusibleizing crushed pitch, and low-temperature calcined coke obtained by carbonizing coal at a low temperature of about 500° C. and pulverizing it. In addition, examples of carbonized or graphitized powders include carbonaceous small spheres such as mesocarbon microbeads, coke breeze, scaly graphite,
Examples include soil graphite and artificial graphite. At least one of these carbonaceous powders is used. A preferred carbonaceous powder is graphite powder, which can provide high electrical conductivity.

[0017] The ratio of the binder, fibers, and carbonaceous powder is 100 parts by weight of the binder to 1 part by weight of the fibers.
The amount is about 0 to 75 parts by weight, and the carbonaceous powder is about 50 to 150 parts by weight. A preferable composition ratio is 40 to 60 parts by weight of fiber and 75 to 75 parts by weight of carbonaceous powder to 100 parts by weight of binder.
The amount is approximately 125 parts by weight.

[0018] The carbonaceous powder has an average particle size of 2
The proportions are 10 to 50 parts by weight of powder and granules with an average particle diameter of 75 to 125 μm and 100 to 150 parts by weight of powder and granules with an average particle diameter of 125 to 175 μm per 100 parts by weight of powder and granules with an average particle size of 5 to 75 μm. Preferable carbonaceous powder has an average particle size of 35 to
Average particle size: 85% for 100 parts by weight of 65μm powder
15 to 40 parts by weight of powder and granules of ~115 μm, average particle size 13
It consists of 110 to 140 parts by weight of granules having a particle size of 5 to 165 μm. In this way, when multiple carbonaceous powders with different particle sizes are used in combination and fired, the density, mechanical strength, and conductivity of the carbon material decrease, probably because the carbonaceous powders are densely packed between the carbon fibers. sexuality becomes greater. In particular, the electrical resistance in the thickness direction of the carbon material is significantly reduced.

The carbonaceous composition may contain, for example, carbonaceous powder having a particle size other than the above, an organic solvent, a thermoplastic resin, etc., within a range that does not impair the characteristics such as electrical conductivity and mechanical strength of the carbon material. It may also contain additives such as antioxidants, fillers, and plasticizers.

The carbon material for fuel cells of the present invention is in the form of a sheet containing a carbonized or graphitized binder, carbon fibers, and carbonized or graphitized carbonaceous powder. Further, the carbonaceous powder has different particle sizes and is composed of a specific amount of carbonaceous powder, as described above.

[0021] The thickness of the carbon material is, for example, 0.1 to 5 mm.
, preferably about 0.2 to 4 mm. Carbon material has high conductivity, and its specific resistance in the thickness direction is usually 1 x 10-
2Ω・cm or less, e.g. 5×10-3 to 9×10-3Ω
・It is about cm. Further, the carbon material is dense, and its density is usually 1.6 g/cm3 or more, preferably 1.6 g/cm3 or more, and preferably 1.6 g/cm3 or more.
It is about 7 to 2.1 g/cm3. Furthermore, carbon material has excellent mechanical properties, and its bending strength is 6 to 15 kgf.
/mm2 degree, bending elastic modulus 4000-7000Kgf
/mm2.

The carbon material for fuel cells of the present invention can be obtained through a forming step of forming the carbonaceous composition into a sheet, and a firing step of carbonizing or graphitizing the sheet. In addition, prior to the molding process, the carbonaceous composition is usually subjected to a kneading process.

[0023] In the kneading step, a conventional kneader such as a kneader or roll can be used. During kneading, for example, alcohols, hydrocarbons, ketones,
Organic solvents such as esters and ethers may also be used.

[0024] In the molding process, various molds, two rolls, etc. that can be molded into a sheet shape can be used. In addition, when molding into a sheet shape with a molding die, it is preferable to remove the organic solvent prior to the molding step. When a carbon material is used as a thin plate for a fuel cell, it can be formed to a thickness of, for example, about 0.5 to 5 mm, taking into consideration shrinkage due to firing. When molding with a mold, the molding is usually performed by pressurizing and heating. In this pressurization and heating step, the binder made of thermosetting resin is cured. The thermosetting resin is cured by gently increasing the temperature to the resin's curing temperature, e.g.
This can be carried out by maintaining the temperature at about 140 to 220°C, preferably about 140 to 220°C. The molding pressure can be selected depending on the density of the carbon material, for example, 50 to 1000 Kgf.
/cm2.

[0025] By carbonizing or graphitizing in the firing step, the sheet becomes carbonaceous, and a sheet-like carbon material with high density, high mechanical strength, and excellent conductivity can be obtained. In the firing step, the sheet is preferably heated to a temperature of 800° C. or higher, preferably a temperature at which graphitization occurs, for example 2000° C. or higher, in order to improve conductivity. Even in this firing process, the firing should be carried out gently, especially at 10°C/10°C up to about 600°C.
It is preferable to heat at a rate of temperature increase of less than 1 hour. The firing is
It is carried out under vacuum or in an inert gas atmosphere. Nitrogen, helium, argon, etc. can be used as the inert gas.

[0026]

[Effects of the Invention] The carbonaceous composition of the present invention makes it possible to obtain a carbon material that is dense, has high mechanical strength, and has excellent electrical conductivity.

[0027] Furthermore, the carbon material for fuel cells of the present invention exhibits the above-mentioned excellent properties and can improve the conversion efficiency into electrical energy.

Furthermore, according to the manufacturing method of the present invention, a carbon material for fuel cells having the above-mentioned excellent properties can be obtained.

[0029]

EXAMPLES The present invention will be explained in more detail below based on examples.

Example Phenol resin [manufactured by Gunei Chemical Industry Co., Ltd., trade name PL-
3820A] 40 parts by weight, carbon fiber milled fiber [
Manufactured by Donac Co., Ltd., trade name Dona Carbo S-241] 20
Soil graphite powder with an average particle size of 50 μm (manufactured by Nippon Graphite Industries Co., Ltd., trade name GA-2) 16 parts by weight, average particle size 10
0 μm soil graphite powder [manufactured by Nippon Graphite Industries Co., Ltd., product name G
A-3] 4 parts by weight, soil graphite powder with an average particle size of 150 μm [
20 parts by weight of Nippon Graphite Industries Co., Ltd. (trade name: GA-150) and 100 parts by weight of acetone were kneaded in a kneader for 30 minutes, then heated to 60°C to remove acetone. The mixture was ground in a grinder to collect particles finer than 40 mesh.

[0031] Then, the granules were put into a mold and heated at 140°C.
Molded for 30 minutes at a pressure of 300 kgf/cm2,
Demolded sheet (thickness 2mm, 300mm x 300mm
) at 2000°C for 200 hours in a nitrogen gas atmosphere.
The temperature was raised to , and a graphitized carbon material was produced.

The obtained sheet-like carbon material has a density of 1.86
g/cm3, specific resistance in the thickness direction 8×10-3Ω・cm
, bending strength 10.2Kgf/mm2, bending modulus 5
It was 200Kgf/mm2.

Comparative Example 1 Instead of the whole soil graphite powder used in the example, an average particle size of 100
μm soil graphite powder [manufactured by Nippon Graphite Industries Co., Ltd., product name GA
-3] A sheet-like carbon material was produced in the same manner as in the example except that 40 parts by weight was used. The obtained sheet-like carbon material is
Density 1.46g/cm3, specific resistance in the thickness direction 2×10
-2 Ω·cm, bending strength of 4.6 Kgf/mm2, and bending modulus of elasticity of 3200 Kgf/mm2.

Comparative Example 2 The graphite powder of the example was converted into soil graphite powder with an average particle size of 150 μm [
A sheet-like carbon material was produced in the same manner as in the example except that the amount was 40 parts by weight (manufactured by Nippon Graphite Industries Co., Ltd., trade name: GA-150). The obtained sheet-like carbon material has a density of 1.65 g/
cm3, specific resistance in the thickness direction 8×10-2Ω・cm, bending strength 6.2Kgf/mm2, bending modulus 4000
Kgf/mm2.

Claims (6)

[Claims] [Claim 1] A carbonizable or graphitizable binder;
A composition comprising fibers or carbon fibers that can be made into carbon fibers and at least one carbonaceous powder selected from carbonized or graphitized powder and carbonized or graphitized powder, The carbonaceous powder particles have an average particle size of 75 to 125 μm per 100 parts by weight of the powder particles with an average particle size of 25 to 75 μm.
m powder 10 to 50 parts by weight, average particle size 125 to 175
A carbonaceous composition comprising 100 to 150 parts by weight of micrometer powder. 2. The carbonaceous composition according to claim 1, which contains 10 to 75 parts by weight of fibers or carbon fibers that can be made into carbon fibers and 50 to 150 parts by weight of carbonaceous powder per 100 parts by weight of the binder. 3. The carbonaceous composition according to claim 1, wherein the binder is a phenol resin, the fibers that can be made into carbon fibers or carbon fibers are milled carbon fibers, and the carbonaceous powder is graphite powder. 4. A sheet-like carbon material comprising a carbonized or graphitized binder, carbon fibers, and carbonized or graphitized carbonaceous powder, wherein the carbonaceous powder has an average particle size of 25 A fuel cell consisting of 10 to 50 parts by weight of powder and granules with an average particle size of 75 to 125 μm and 100 to 150 parts by weight of powder and granules with an average particle size of 125 to 175 μm to 100 parts by weight of powder and granules with average particle size of ~75 μm. carbon material. [Claim 5] Specific resistance is 1×10-2 Ω·cm or less,
The carbon material for fuel cells according to claim 4, which has a density of 1.6 g/cm3 or more. 6. A method for producing a carbon material for fuel cells, which comprises forming the carbonaceous composition according to claim 1 into a sheet shape and carbonizing or graphitizing the sheet.