JPH06263558A - Production of porous carbon plate and porous carbon electrode material - Google Patents

Abstract

PURPOSE:To obtain a porous carbon plate having a prescribed gas permeability and a higher heat conductivity, electric conductivity and mechanical strength than those of a conventional plate by mixing carbon fiber having respective specific values of diameter and aspect ratio with a binder, forming and hardening the resultant mixture and then burning the hardened mixture. CONSTITUTION:A porous carbon plate molding material containing carbon fiber having 15-30mum diameter and preferably 3-30 aspect ratio (L/D) and a binder is formed, hardened and then burned to produce a porous carbon plate. The gas permeability at a constant bulk density is remarkably improved by using the carbon fiber as compared with that of a porous carbon plate using conventional carbon fiber (having 6-14mum diameter). As a result, the porous carbon plate holding higher physical properties such as heat conductivity, electric conductivity or mechanical strength than those of the porous carbon plate having the same gas permeability is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous carbon plate using carbon fibers in a specific range. Used for sex filters.

[0002]

2. Description of the Related Art Among various fuel cells attracting attention as an energy-saving and pollution-free next-generation power generation system, a phosphoric acid fuel cell using phosphoric acid as an electrolyte is most practically used as a first generation fuel cell. The development is being advanced to the stage of conducting a verification test. In a phosphoric acid fuel cell, the cell body is composed of a stack of electrode plates, a separator, a cooling plate, etc., and most of them use carbon materials. In addition to having high mechanical strength and excellent handleability, this is an electrolyte (phosphoric acid) at a reaction temperature of about 200 ° C.
It is characterized by excellent durability against heat, excellent thermal conductivity, and excellent porosity (for electrode plates) and gas impermeability (for separators). Because the carbon material also has.

The inner carbon electrode plate is porous in order to retain phosphoric acid and to permeate gas, is excellent in heat conduction and electric conduction in the thickness direction, and is easy to handle. It is necessary to have strength, and a porous carbon plate having these properties is used.

Conventionally, as a method for producing a porous carbon plate, a method in which a fibrous substance as a main material is formed into a plate shape with a binder such as a resin and then fired is generally used. In this method, organic fibers such as pulp, polyacrylonitrile and phenol resin, or carbon fibers such as carbonaceous fibers and graphite fibers are used alone or in combination as the fibrous substance. . When using organic fibers, in order to prevent shrinkage of the material during the firing process, some infusibilization treatment such as forming an oxide film on the fiber surface is performed, or the composite with carbon fiber that does not shrink during the firing process It is necessary to take measures such as

Therefore, in the production of the porous carbon plate,
The method using carbon fiber as the main material is the easiest method. As the carbon fiber, a general-purpose carbon fiber from an optically isotropic pitch, a high-performance carbon fiber from an optically anisotropic pitch, or a carbon fiber starting from an organic fiber such as polyacrylonitrile or rayon is used. . The fiber diameter of carbon fiber is usually 6 to 8 μm when starting material is organic fiber.
m, high-performance pitch-based carbon fibers of about 10 μm, and general-purpose carbon fibers of 11 to 13 μm are used. These are mainly determined in consideration of increasing physical properties such as mechanical strength as much as possible and not increasing cost.

Among the physical properties generally required for a carbon electrode plate, the physical properties such as porosity (bulk density) and gas permeability, which are based on porosity, and the heat conduction, electric resistance, and dynamics, which are proportional to the compactness. Since physical properties such as strength are contradictory to each other, in manufacturing a carbon electrode plate, it is possible to maintain each physical property in a well-balanced manner without depending on either the porosity or the denseness. It is controlled to have an appropriate degree of porosity (fineness). For example, in the raw material composition, the physical properties of the carbon fiber to be used, the ratio of the carbon fiber and the binder, the mixing ratio of the added graphite powder, etc., and the molding conditions, the molding method, the firing temperature, etc. were examined, and the carbon electrode aimed at a good balance of physical properties. The board is manufactured.

[0007]

In the production of a porous carbon plate, optimization has been hitherto carried out under the condition of balancing the contradictory porosity and denseness as described above.
For example, the performance of a highly efficient phosphoric acid fuel cell is not yet sufficient, and development of a more excellent porous carbon plate other than balancing physical properties is desired. That is, for example, if a predetermined gas permeability can be achieved with a bulk density higher than that of the conventional one, the obtained porous carbon plate has a predetermined gas permeability and high heat conductivity and electric conductivity (because of high density). In addition, it is expected to lead to the development of an excellent porous carbon electrode material because it retains physical properties such as mechanical strength.

[0008]

As a result of intensive studies to solve these problems, the present inventors have used carbon fibers having a diameter of 15 to 30 μm instead of the carbon fibers generally used conventionally. It is preferable that the aspect ratio (L /
By using the carbon fiber having D) of 3 to 30, the gas permeability at a constant bulk density is significantly improved as compared with the conventional one, that is, the bulk density is increased as compared with the conventional one under the condition of keeping the gas permeability constant. The inventors have found that they can do so and have completed the present invention. The porous carbon plate thus obtained has a predetermined gas permeability, and also has heat conduction, electric conduction,
The physical properties proportional to the compactness such as mechanical strength were significantly improved, and they were suitable as an electrode material for fuel cells.

That is, according to the present invention, after curing a molded body made of a material containing a carbon fiber having a diameter of 15 to 30 μm, preferably having an aspect ratio (L / D) of 3 to 30 and a binder, The present invention provides a method for producing a porous carbon plate, which is characterized by firing, and a porous carbon electrode material obtained by this method.

The present invention relates to the control of the physical properties of the porous carbon plate by the porosity (= (1-bulk density / 1.
6)) and the factors governing the relationship between gas permeability and the relationship between these factors are not uniquely determined in the process of detailed examination, and differ greatly depending on the shape factor of the material, that is, carbon plates of the same bulk density. In principle, we found that it is possible to obtain materials with greatly different gas permeability, and develop a material with a prescribed gas permeability and higher thermal conductivity, electrical conductivity, and mechanical strength than before. It is based on what was possible.

FIG. 1 shows the relationship between the bulk density of a porous carbon plate and the gas permeability when the conventionally used carbon fiber is used. This relationship includes one in which the ratio of the carbon fiber and the binder is changed, one in which the compression molding condition is changed, and one in which the kind of carbon fiber having the same diameter is changed. As shown in FIG. 1, in many cases, basically, the gas permeability of a porous carbon plate is determined by the bulk density of the plate, and it is difficult to obtain a gas that largely deviates from the relationship.
However, it can be seen from FIG. 1 that even when the bulk density is constant, the gas permeability is lower when the wood pulp is included in the binder. On the other hand, it was not possible to obtain a material having a higher gas permeability with a constant bulk density from the conventional knowledge and the data of FIG. The present inventors have studied a wide range of additives, binders, and types of carbon fibers, and as shown in FIG.
The present invention has revealed that when carbon fibers having a diameter of 15 to 30 μm are used as shown in FIG. 1, an improved porous carbon plate can be obtained which largely deviates from the conventional data.

The carbon fiber used in the present invention has a diameter of 1
5 to 30 μm, preferably 15 to 30 μm in diameter
It is preferable that the aspect ratio (L / D) is 3 to 30, and there is no particular limitation on the starting material, manufacturing method, or the like. In general, it is preferable to use pitch-based carbon fibers because the carbonization yield is high and that those having a large diameter are easy to produce. When the diameter is less than 15 μm, the value of gas permeability at a constant porosity is the same as that used conventionally. On the other hand, if the diameter is 30 μm or more, it is difficult to produce carbon fibers, and the physical properties such as mechanical strength are low, and the porous carbon plate obtained from them can only have low mechanical strength. If the aspect ratio is less than 3, the production is difficult and the cost is high, and the mechanical strength is poor. If the aspect ratio exceeds 30, in the case of dry molding, uniform dispersion tends to be difficult.

The binder used in the present invention may be an organic binder, an inorganic binder, or a combination thereof, and is preferably a carbonized one at 400 ° C. or higher. Specific examples of these binders include epoxy resins, phenol resins, unsaturated polyester resins, furan resins, polyimide resins and pitches, and among them, phenol resins are preferable from the viewpoint of high residual carbon rate.

In the material containing the carbon fiber and the binder used in the present invention, various fibers such as silicon carbide fiber, inorganic fiber such as silicon nitride fiber, Kevlar, polypropylene, etc. are used for the purpose of price reduction and improvement of physical properties. It is also possible to add organic fibers such as cellulose and polyacrylonitrile, or various powders such as carbon black and graphite. In particular, the addition of graphite powder is effective in improving electrical properties, thermal properties, and mechanical properties.

In the present invention, various methods of forming the material containing the carbon fiber and the binder into various shapes are conceivable, but any method can be used as long as it does not deviate from the purpose, and the method is not particularly limited. For example, in the case of molding into a plate shape, (1) carbon fiber is formed into a sheet shape in advance by a wet papermaking method, then the sheet is impregnated with a binder which is heated and melted, or the sheet is dispersed or dissolved in a solvent. A method of impregnating with a binder and then drying to obtain a so-called prepreg sheet, and then compression molding, (2) a method of uniformly dispersing a powdery binder on the sheet, and then compression molding, (3) a carbon fiber A method of forming a sheet with a powdery binder by a wet papermaking method, and compression-molding the sheet containing the necessary binder in advance. (4) A powder composition in which carbon fibers and a powdery binder are uniformly mixed There are methods such as compression molding of objects, and in any of the methods, when molding to a predetermined thickness from the beginning, or after first molding into a block shape, the block is A method of obtaining a plate-sliced to a constant thickness. Here, the amount of the carbon fiber used is preferably in the range of 50 to 80 parts by weight with respect to 100 parts by weight of the total of the carbon fiber and the binder.

The molded plate thus obtained is
1000 in an inert gas atmosphere such as argon or in a vacuum
The target porous carbon plate can be obtained by firing at a temperature of ℃ or higher.

[0017]

EXAMPLES Next, the present invention will be further described with reference to examples. In the examples,% is based on weight unless otherwise specified.

Examples 1 to 3 and Comparative Examples 1 and 2 isotropic pitch having a softening point of 250 ° C. was melt-spun to have a diameter of 1
1.0 μm, 15.1 μm, 20.2 μm, 25.6 μ
m, 28.8 μm pitch fiber, then 30 in air
After infusibilizing treatment at 0 ° C for 30 minutes, 1 in a nitrogen gas atmosphere
The average diameter is 9.8 each by heating up to 000 ° C and firing.
μm (Comparative example 1), 13.2 μm (Comparative example 2), 18.
0 μm (Example 1), 22.3 μm (Example 2), 2
A general-purpose pitch-based carbon fiber having a size of 7.0 μm (Example 3) was obtained (the variation rate of the diameter is about 15% in each case). Each of the obtained carbon fibers was milled so as to have an average length of 160 μm, and then sieved and used in the following test (variation in length is about 50% in all cases). The aspect ratio (L / D) of each carbon fiber is 1
The values were 6.3, 12.3, 8.9, 7.2 and 5.9.

Each carbon fiber (70%) and binder (30
%) (Novolak phenolic resin (Dainippon Ink and Chemicals
(Ceradic 4331S) manufactured by Sangyo Co., Ltd.)
It is installed in a flat mold and pressed into a plate at 150 ° C for 10 minutes.
After compression molding, further calcination in vacuum at 2000 ℃ for 1 hour
And has a thickness of 2.0 mm and a bulk density of approximately 0.55 g / cm.
³ To obtain a porous carbon plate.

The measurement results of the bulk density and gas permeability of the obtained porous carbon plate are shown in Table 1 and FIG. As shown in Table 1 and FIG. 2, the gas permeability of the porous carbon plate using the carbon fibers having a diameter of 15 to 30 μm was the same as that of the porous carbon plates using the carbon fibers of Comparative Examples 1, 2 and 3 to 5. In comparison, it is significantly improved and has a high value in comparison at a constant bulk density.

[0021]

[Table 1]

Comparative Examples 3 to 5 Anisotropic pitch-based carbon fiber as carbon fiber (Donakabo F manufactured by Dainippon Ink and Chemicals, Inc .: diameter 12.2 μm, L
/ D = 12 (Comparative Example 3) and diameter 8 μm, L / D = 1
8 (Comparative Example 4), PAN-based carbon fiber (Vephite manufactured by Toho Rayon Co., Ltd .: diameter 7 μm, L / D = 25 (Comparative Example 5) A porous carbon plate was produced, and the bulk density and gas permeability of each of the obtained porous carbon plates are shown in Table 2 and FIG.

[0023]

[Table 2]

Example 4 The carbon fiber of Example 2 was used, the ratio of the carbon fiber to the binder was about 80/20, and the porous carbon had a gas permeability value substantially the same as that of Comparative Example 2. Plates were prepared in the same way as in Example 2. The physical properties of the obtained porous carbon plate are shown in Table 3 in comparison with Comparative Example 2. It can be seen that the thermal conductivity in the thickness direction, the electrical resistance, and the flexural modulus are greatly improved in those having the same gas permeability.

[0025]

[Table 3]

Comparative Example 6 A porous carbon plate having a bulk density of 0.55 g / cm ³ was prepared in the same manner as in Example 4, except that isotropic pitch carbon fibers having a fiber diameter of 33 μm prepared in the same manner as in Example 4 were used. Was manufactured. The bending strength of the obtained porous carbon plate was 100 kg / cm ² , which was slightly inferior in handling.

[0027]

The porous carbon plate obtained by the production method of the present invention has a diameter of 15 to 30 μm and an aspect ratio of 3 to 30.
14 μm), the gas permeability at a constant bulk density is significantly improved compared to the porous carbon plate using 14 μm). It is possible to obtain a plate having large properties such as conduction and bending strength.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the bulk density and the gas permeability of conventional carbon plates and porous carbon plates including pulp-containing carbon plates.

FIG. 2 is a graph showing the relationship between the bulk density and the gas permeability of the porous carbon plate containing the carbon plate obtained in the present invention.

Claims (9)

[Claims] 1. A method for producing a porous carbon plate, which comprises molding and curing a porous carbon plate molding material containing a carbon fiber having a diameter of 15 to 30 μm and a binder, and then calcining the material. 2. The aspect ratio (L / D) of carbon fiber is
The method according to claim 1, which is 3 to 30. 3. A diameter of 15 to 30 μm and an aspect ratio (L
The method according to claim 1, wherein the carbon fiber having a diameter of 5 to 14 μm and the aspect ratio (L / D) of 5 to 50 is used in combination. 4. The content ratio of carbon fiber in the porous carbon plate molding material is 50 to 80% by weight.
The manufacturing method described. 5. A material containing carbon fibers having a diameter of 15 to 30 μm and a binder is formed into a plate shape, and after curing,
A porous carbon electrode material characterized by being fired. 6. The aspect ratio (L / D) of carbon fiber is
It is 3-30, The porous carbon electrode material of Claim 5. 7. A diameter of 15 to 30 μm and an aspect ratio (L
The porous carbon electrode material according to claim 5, wherein carbon fibers having a diameter of 5 to 15 μm and an aspect ratio (L / D) of 5 to 50 are used in combination. 8. The content ratio of carbon fiber in the porous carbon plate molding material is 50 to 80% by weight.
The porous carbon electrode material described. 9. The production method according to claim 1, 2, 3 or 4, wherein the binder contains graphite powder, and the porous carbon electrode material according to claim 5, 6, 7 or 8.