JP2003002744A - Carbonaceous thin plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive carbonaceous thin plate having superior mechanical strength, gas impermeability, corrosion resistance and electric conductivity and to provide a separator for a fuel cell using the carbonaceous thin plate. SOLUTION: A mixture prepared by mixing pitch as a matrix raw material with aggregate is molded, fired and carbonized to obtain the objective carbonaceous thin plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbonaceous thin plate obtained by carbonizing and firing a mixture of a matrix raw material pitch and an aggregate, and more specifically, it is useful as a fuel cell separator for mechanical strength and The present invention relates to an inexpensive carbonaceous thin plate having excellent gas impermeability and conductivity.

[0002]

2. Description of the Related Art Carbonaceous thin plates are widely used in the electric and electronic fields because they have excellent heat resistance and corrosion resistance and good conductivity, and are used as, for example, fuel cell separators. At this time, the characteristics required as a separator include gas impermeability, good electrical conductivity, mechanical strength, dimensional accuracy and corrosion resistance, and since a large amount of separators are used in the fuel cell stack,
Productivity, that is, cost reduction is also required.

As a method for manufacturing a carbonaceous thin plate, there is a method in which a composite material in which a thermosetting resin is used as a matrix raw material and a carbonaceous material is an aggregate is carbonized and fired after molding.
For example, there is a carbonaceous thin plate obtained by impregnating a carbonaceous material with a thermosetting resin liquid to cure it and carbonizing it in a non-oxidizing atmosphere.

Further, it can be obtained, for example, by kneading a thermosetting resin and carbonaceous powder as disclosed in JP-A-60-150559, hot pressing or hot roll forming, and then carbonizing. There is a carbon thin plate. Alternatively, the carbonaceous thin plate can be obtained by molding and thermosetting a thermosetting resin itself such as a phenol resin.

However, when a carbonaceous thin plate is obtained by carbonizing and firing a thermosetting resin which is a matrix raw material, the carbonization yield of the thermosetting resin is at most about 75%.
It is not economically satisfactory when many separators are used in a fuel cell stack such as a fuel cell separator.

Further, regarding the carbonaceous thin plate after carbonization and firing,
If the thermosetting resin content is low, the gas impermeability is not sufficient, and if the resin content is high, cracks are likely to occur and the mechanical strength is poor, so problems may occur when holding the separator. Many.

Further, in the case of obtaining a carbonaceous thin plate by impregnating a carbonaceous material with a resin for the purpose of improving gas impermeability, a cavity of the porous carbonaceous thin plate is further impregnated with a thermosetting resin liquid. It has to be fired, and the repeated impregnation and firing have a drawback that cracks due to expansion and contraction of the carbonaceous thin plate increase.

Furthermore, in order to produce a carbonaceous thin plate having excellent denseness, there is a drawback that the time required for heating and cooling during firing in carbonization is long.

[0009]

In view of such circumstances, the present invention provides an inexpensive carbonaceous thin plate having excellent mechanical strength, gas impermeability, corrosion resistance and conductivity.

[0010]

As a result of earnest efforts, the present inventors have found that the above-mentioned problems can be solved by a carbonaceous thin plate as will be described later, and have reached the present invention. That is, the gist of the present invention is, firstly, a carbonaceous thin plate characterized in that a mixture obtained by mixing an aggregate with a pitch, which is a matrix raw material, is carbonized and fired after forming, Secondly, the aggregate is characterized in that it is at least one kind of carbonaceous material selected from graphite powder, carbon black, pitch powder, coal powder, coke powder, carbon fiber powder, Third, the aggregate is
It is characterized in that it is a cured product or a carbide made of a thermosetting resin. Fourthly, the mixture is 50 to 95 mass% of the aggregate with respect to 50 to 95 mass% of the pitch which is the matrix raw material. Fifth, the molding processing means of the mixture is characterized by being injection molding, and sixth, the carbonaceous thin plate is a fuel cell separator It is characterized by being.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The pitch used as the matrix raw material of the carbon thin plate of the present invention is not particularly limited and may be any of coal-based, petroleum-based pitch and synthetic pitch, and isotropic or optically different. The pitch may be any direction. Further, these pitches may be modified by a known method such as filtration or distillation, if necessary. The pitch may be a single kind or a mixture of different kinds of pitches.

The softening point of the pitch is not particularly limited, but in consideration of formability and infusibilization, it is 100 to 3
The temperature is preferably 00 ° C, more preferably 200 to 300 ° C.

The carbonaceous material used as the aggregate of the present invention includes graphite powder, carbon black, pitch powder,
One or more selected from coal powder, coke powder, and carbon fiber powder are listed, and among them, carbon fiber powder is preferable.

The average particle size of these carbonaceous materials is 100 μm.
The thickness is preferably m or less, and more preferably 50 μm or less in order to produce a highly dense carbonaceous thin plate. Particle size is 50
If the thickness exceeds μm, the density of the carbonaceous thin plate may not increase, and gas impermeability and electrical conductivity may not be satisfied.

As the aggregate of the present invention, a hardened material or a carbide made of a thermosetting resin is used. Examples of the thermosetting resin that becomes a cured product or a carbide include phenol resin, furan resin, furfuryl alcohol resin, xylene resin, melamine resin, urea resin, polyimide resin, unsaturated polyester resin, epoxy resin or carbodiimide resin. . The cured product includes not only a cured product but also a cured product that is further heat-treated just before carbonization. Further, the carbide is one which is further heat-treated and carbonized.

The matrix raw material pitch and the aggregate are mixed at a certain ratio. The mixing ratio of these is preferably 50 to 5 mass% of the aggregate with respect to 50 to 95 mass% of the pitch.

The mixing method is not particularly limited, and a conventionally known mixing method such as a wet method or a dry method can be adopted. For example, in the dry method, a method of mixing the matrix raw material as fine powder with the aggregate by a pulverizing mixer such as a ball mill or a Hengel mixer is preferable.

As the molding processing method, a conventional molding processing method such as injection molding, compression molding, transfer molding or the like can be adopted. Of these, injection molding has the advantages that the cycle time is short, there are no grain boundaries caused by the raw material resin, it is homogeneous, it can easily handle complex shapes, and the dimensional accuracy of the product is good. . Although the compression molding has a moderate cycle time, it tends to be non-uniform due to grain boundaries caused by the raw material resin, which makes it difficult to cope with complicated product shapes, and the dimensional accuracy of the products is poor. Transfer molding tends to have a long cycle time and has a complicated mold structure, but grain boundaries due to the raw material resin are unlikely to occur, and therefore the uniformity is moderate. In addition, it is possible to deal with complicated product shapes to some extent, and the dimensional accuracy of the product is moderate. Taking the above points into consideration, injection molding is the most suitable molding method.

At the time of this molding, it is preferable that the pitch raw material is preliminarily processed by injection molding using a die having a size and shape that allows for dimensional shrinkage during firing. For example, when a carbon thin plate after carbonization and firing is used as a fuel cell separator, injection molding is performed using a mold that allows for dimensional shrinkage during firing, and the outer shape of the separator is specified, and reaction on one side or both sides By forming a recess such as a groove that serves as a flow path for a gas or a cooling medium, and carbonizing and firing the obtained molded product, post-processing such as cutting is not necessary or can be omitted, which is good. It is possible to manufacture a fuel cell separator having any shape with high mass productivity.

The molded product after the molding process is dried and infusibilized if necessary. The infusibilizing treatment is a treatment for rendering the pitch infusible by subjecting the pitch showing meltability to heat treatment or the like in an oxidizing atmosphere. This makes it easy to maintain the shape of the molded body during firing.

The infusibilizing treatment method is not particularly limited, but a conventionally known method may be appropriately applied, for example, oxidation of a gas such as air, oxygen, ozone, NO _x or the like or a mixed gas thereof. It is carried out by a method of heat treatment in a neutral atmosphere.

The infusibilizing treatment is carried out at room temperature to 400 ° C.
The heating is preferably performed for about 50 hours, more preferably 300 to 350 ° C. for 30 to 50 hours in order to uniformly infusibilize the molded body.

Carbonization firing is preferably carried out in vacuum or in an inert gas atmosphere, and examples of the inert gas include nitrogen gas, helium gas and argon gas. The carbonization firing temperature is preferably 700 to 1600 ° C., 800 ~ 15
00 ° C is more preferable.

FIG. 1 is a schematic perspective view showing a basic configuration example of a fuel cell (single battery cell). Where 1 is the anode,
2 is an electrolyte membrane, 3 is a cathode, and 4 is a separator. A large number of recesses 5 are formed on both the front and back surfaces of the separator as flow paths for reaction gases such as anode gas and cathode gas.

In the present invention, the separator 4 is a mixture obtained by mixing the aggregate, which is the matrix raw material, with the aggregate, and then carbonizing and firing the mixture.

The recess 5 formed in the separator 4 and serving as a reaction gas flow passage may be provided on at least one surface, and in order to stabilize the operating temperature of the fuel cell, cooling water or the like is provided on one surface. You may provide the recessed part which flows a heat medium.
In addition to the groove shape as shown in the drawing, the recess 5 may have a shape in which a concave flow path is formed by having a large number of projections protruding from the surface of the separator 4 and the like.

The size of the separator is not particularly limited, and various designs can be changed according to the purpose, and the plane shape, the groove shape and the size thereof can be changed according to the purpose.

[0028]

As described above, none of the conventional carbonaceous thin plates has a small carbonization yield after the carbonization and firing, and further sufficiently satisfies the requirements of gas impermeability and mechanical strength. Further, in order to improve gas impermeability and the like, there is a problem that the firing time becomes long and the cost is high. But,
The carbonaceous thin plate of the present invention is a mixture of pitch and aggregate, which is carbonized after molding, so that the carbonization yield is high, and the firing time can be shortened. A carbonaceous thin plate with good mechanical strength and electrical conductivity. In particular, if the method of injection molding is used as a molding method using a mold that allows for firing shrinkage in advance, a molded product with a complicated shape can be easily obtained, and post-processing such as cutting is unnecessary, and mass production is possible. It is excellent and it is possible to reduce the processing cost. Such a carbon thin plate that is excellent in gas impermeability, mechanical strength, and electrical conductivity and is inexpensive is optimal as a fuel cell separator.

[0029]

EXAMPLES Examples of the present invention will be shown below. However, the present invention is not limited to these examples.

Example 1 20% by weight of carbon fiber powder (average particle size 20 μm) was added to 80% by weight of coal-based isotropic pitch (softening point: about 280 ° C.) and mixed uniformly, and then the mixture was put into a mold. It is supplied and hot-press molded under the conditions of a press temperature of 320 ° C., a press pressure of 6 MPa, and a press time of 15 minutes to obtain a thickness of 2.5 mm and a length of 1
A molded body having a groove of 25 mm × width 125 mm was obtained. After heat-treating this molded body at 300 ° C. for 24 hours in the air, it is carbonized and baked at 1000 ° C. for 24 hours in a nitrogen gas atmosphere in a baking furnace to give a length of 120 mm × a width of 120 m.
A carbonaceous thin plate having a thickness of 2 mm and a groove serving as a gas flow path on both front and back surfaces was obtained. The carbonization yield of the obtained carbonaceous thin plate is 8
It was 5%.

Example 2 70% by weight of coal-based isotropic pitch (softening point: about 280 ° C.), 10% by weight of carbon fiber powder (average particle size: 20 μm),
20% by weight of carbon black is blended and mixed uniformly, and under the same conditions as in Example 1, 120 mm in length × 120 m in width.
A carbonaceous thin plate having a thickness of 2 mm and a groove serving as a gas flow path on both front and back surfaces was obtained. The carbonization yield of the obtained carbonaceous thin plate is 8
It was 3%.

Example 3 20% by weight of a thermosetting resin carbide (UNIBEX GCP-30 manufactured by Unitika Ltd., average particle size 30 μm) was mixed with 80% by weight of a coal-based isotropic pitch (softening point: about 280 ° C.). Mix uniformly, and under the same conditions as in Example 1, length 120
A carbon thin plate having a size of mm × width 120 mm, thickness 2 mm and provided with grooves serving as gas channels on both front and back surfaces was obtained. The carbonization yield of the obtained carbonaceous thin plate was 83%.

Example 4 The mixture described in Example 1 was injection-molded using a mold in which firing shrinkage was expected, and the thickness was 2.5 mm and the length was 125 mm.
A molded body having a groove of mm × width 125 mm was obtained. After heat-treating this molded body at 300 ° C. for 24 hours in the air, it is carbonized and baked at 1000 ° C. for 24 hours in a nitrogen gas atmosphere in a baking furnace to form a gas having a length of 120 mm × a width of 120 mm and a thickness of 2 mm on both sides. A carbonaceous thin plate having a groove serving as a flow channel was obtained. The carbonization yield of the obtained carbonaceous thin plate was 85%.

Comparative Example 1 A thermosetting phenolic resin powder was compression-molded by hot pressing at a mold temperature of 150 ° C. using a mold in which firing shrinkage was expected, and then in a baking furnace in a nitrogen gas atmosphere. 100
100 mm in length by carbonizing and firing at 0 ° C for 24 hours
A carbonaceous thin plate having a width of 100 mm and a thickness of 2 mm and having grooves serving as gas flow passages on both sides was obtained. The carbonization yield of the obtained carbonaceous thin plate was 70%.

The carbonaceous thin plates obtained from Examples 1 to 4 were
When used as a fuel cell separator as shown in FIG. 1, it showed sufficient performance as a separator such as gas impermeability, electric conductivity and mechanical strength.

[0036]

The carbon thin sheet of the present invention is inexpensive and exhibits excellent mechanical strength, gas impermeability, corrosion resistance and conductivity, and is injection-molded by using a mold in which firing shrinkage is expected in advance. By doing so, it is possible to provide a carbonaceous thin plate which does not require post-processing such as cutting or can be omitted and which has excellent productivity. Furthermore, since the carbonaceous thin plate of the present invention is inexpensive and exhibits excellent mechanical strength, gas impermeability, corrosion resistance, and conductivity, it can be provided as an inexpensive and excellent fuel cell separator.

[0037]

[Brief description of drawings]

FIG. 1 is a perspective view showing a basic configuration example of a fuel cell.

[Explanation of symbols]

1 anode 2 electrolyte membrane 3 cathode 4 separator 5 grooves

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Claims (6)

[Claims] 1. A carbonaceous thin plate characterized in that a mixture obtained by mixing an aggregate as a matrix raw material with an aggregate is subjected to carbonization and firing after molding. 2. The aggregate is at least one kind of carbonaceous material selected from graphite powder, carbon black, pitch powder, coal powder, coke powder and carbon fiber powder. The carbonaceous thin plate described in. 3. The carbonaceous thin plate according to claim 1, wherein the aggregate is a cured product or a carbide made of a thermosetting resin. 4. An aggregate 5 for a pitch of 50 to 95% by mass.
The carbonaceous thin plate according to any one of claims 1 to 3, which is obtained by mixing 0 to 5 mass% and carbonizing and firing after forming. 5. The carbonaceous thin plate according to claim 1, wherein the molding and processing means of the mixture is injection molding. 6. The carbonaceous thin plate according to claim 1, which is a fuel cell separator.