JPH0748182A - Production of porous carbonaceous plate - Google Patents

Abstract

PURPOSE:To provide a production method for a porous carbonaceous plate suppressed in developing abnormalities such as wrinkles, warpages or cracks during its baking process by dividing the baking process for a molded plate into two steps and by specifying baking conditions such as maximum baking temperatures, rates of temperature rise and loads during the respective steps. CONSTITUTION:The baking process for a molded plate obtained by molding and curing a composition comprising carbon fibers and a thermosetting resin binder is divided into two steps. In the 1st step, one carbonaceous plate is inserted as a heat transfer plate every 1 to 15 molded plates and a baking is conducted under the following conditions: (1) maximum baking temperature: 600-850 deg.C, (2) rate of temperature rise between baking temperatures 300-700 deg.C: <=0.5 deg.C/min, and (3) load on the molded plates during baking: <=0.02kg/cm<2>. After baking at the maximum temperature in the 1st step, the molded plate is cooled to room temperature and then baked again in the 2nd step by inserting one carbonaceous plate as a heat transfer plate every 1 to 15 molded plates under the following conditions: (4) maximum baking temperature: >=2000 deg.C (up to ca.2500 deg.C) and (5) load on the molded plates during baking: >=0.02kg/cm<2>.

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, and the obtained porous carbon plate is used for an electrode material such as a phosphoric acid fuel cell, a heat resistant material, a corrosion resistant filter and the like.

[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. Specifically, for example, a thermosetting resin such as a phenol resin as a fibrous substance and a binder to be described later is used, and a paper-like material obtained by wet-paper-making carbon fibers is impregnated with the thermosetting resin. It is obtained by molding and curing to obtain a molded plate for porous carbon plate, and then firing. As the fibrous substance, 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. When using organic fibers, in order to prevent shrinkage of the material in the firing process, some infusibilizing treatment such as forming an oxide film on the fiber surface is performed, or composite with carbon fiber that does not shrink in the firing process Measures such as to be taken. 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. .

For thin porous carbon plates, a paper-like material which is wet-processed as described above is generally used as a starting material, but a thickness of about 1 mm or more is used. It is manufactured by the so-called powder method in which powder such as carbon fiber, graphite and powdered substances such as powdery binder are dry mixed, molded and cured using a mold etc. to obtain a molded plate, and then baked. Often.

Whichever means is adopted, a porous carbon plate is manufactured by first molding and curing the carbon fibers and the binder to form a molded plate and then firing the molded plate in a vacuum or an inert gas atmosphere. . Firing is generally performed continuously from room temperature to the final temperature, but in order to facilitate removal of the tar component by degreasing on the low temperature side, firing at a maximum firing temperature of around 1200 ° C (first stage) and maximum firing Temperature 2000 ° C or higher, usually 2000-2500 ° C (second
In some cases, it may be carried out separately in two steps, i.e. firing in step)). However, these conventional firing methods have a problem in that the obtained porous carbon plate has a shape abnormality such as a warp or a crack. These shape abnormalities are generally observed as wrinkles and cracks when the thickness is thin, and as warps and cracks when the thickness is thick, and are more remarkable especially in large-area porous carbon plates.

[0007]

The porous carbon plate is distorted,
If there is a shape abnormality such as warp, chip, or crack, for example, when trying to incorporate the carbon plate as an electrode plate of a fuel cell,
At the worst, it becomes unusable because of the deviation during installation and the deterioration of performance during use. Among the defects of these porous carbon plates,
Plate distortion, warpage, and cracks often occur during the firing process, and controlling these defects is the most important issue in quality control of the porous carbon plate during the firing process.

[0008]

Means for Solving the Problems The inventors of the present invention have solved these problems, and have conducted diligent research so that a large quantity of good quality products can be stably manufactured at low cost. Particularly, in the firing process, the firing process is performed in two steps, and the maximum firing temperature in the first step is 600 to 8
It is carried out under the condition of 50 ° C., and the baking maximum temperature in the next second step is 2000 ° C. or higher, and preferably, the temperature rising rate during baking is set to a certain value or less under the above conditions. If conditions such as defining the load applied to the sample to a constant value in the first step and the second step and inserting heat transfer plates at fixed intervals between the stacked objects to be fired are taken into consideration, The inventors have found that it is effective in suppressing abnormal shapes such as wrinkles, warpage, and cracks that occur, and have completed the present invention.

In the present invention, the deformation such as warpage, wrinkle, crack, etc., which occurs during firing of the molded plate is mainly related to the firing in the first step when the firing step is performed in two steps.
That is, it is based on the finding that it is caused by thermal expansion / contraction during heating and / or cooling of the formed plate in the first firing step, and temperature distribution in the sample due to poor heat conduction.

FIG. 1 shows a carbon fiber and a phenol resin as main materials, having a thickness of 0.7 mm and a bulk density of 0.9 g /
The thermal expansion / contraction behavior during the temperature rising / cooling process when a cm ³ molded plate is fired at various temperatures up to 1200 ° C. is shown. The molded plate thermally expands up to about 400 ° C. in the temperature rising process, and thereafter exhibits the shrinking behavior as shown in FIG. In the cooling process, all exhibit shrinkage behavior. From FIG. 1, when the firing temperature in the first stage is set to, for example, about 700 ° C., the thermal expansion after cooling is suppressed to the minimum as compared with that before firing, and as a result, generation of wrinkles and cracks generated in the firing process is suppressed. It became clear that it was possible. As a result of continuing such research, the maximum firing temperature of the first stage which is effective in suppressing such shape abnormality is 600 to
It was in the range of 850 ° C. If the temperature is lower than 600 ° C, the original purpose of degreasing is not sufficient and the strength of the fired product is weak. 85
When the temperature exceeds 0 ° C, wrinkles and cracks become remarkable.

As the temperature rising rate in the firing in the first stage, degreasing is performed by increasing the degreasing range of 300 to 700 ° C. at 0.5 ° C./min or less, preferably 0.2 ° C./min or less. It progressed in a balanced manner and was effective in suppressing abnormal shapes.

In the method of the present invention, usually, the temperature is raised to the maximum temperature in the first step and calcined, then cooled to room temperature, and then the maximum calcining temperature from room temperature to the second step is 2000 ° C. or higher. (Usually 2000-25
The temperature is raised to 00 ° C. and baked.

The load applied to the molded plate during firing is not particularly required for the firing in the first stage and the firing in the second stage, but applying a load in the firing in the second stage causes abnormal shape. It was effective in suppressing. Specifically, at the time of firing in the first stage, 0.02 Kg / cm ² or less,
It is preferable to apply a load of 0.02 Kg / cm ² or more during the firing in the second stage.

Improving the heat conduction to the sample at the time of firing also has a great effect on suppressing the shape abnormality. In particular, by inserting a heat transfer plate for every 1 to 15 molded plates that are samples, generation of wrinkles and cracks can be suppressed.

As the molded plate for a porous carbon plate used in the present invention, it is sufficient that a porous carbon plate having the desired physical properties and shape can be finally produced through firing, and its raw material and molded cured product. The manufacturing method and the like are not particularly limited. Specifically, for example, a carbon fiber such as pitch-based carbon fiber is used as the fibrous substance, and a thermosetting resin such as phenol resin is used as the binder. Those obtained by impregnating with a thermosetting resin and then molding and curing, and those obtained by dry-mixing powdery carbon fibers and a binder and then molding and curing with a mold or the like are used.

As the firing conditions for the molded plate used in the present invention, items other than those specified above, for example, types of furnaces such as vacuum furnaces and Addison furnaces, vacuum, firing atmospheres such as inert gas, etc., are particularly preferable. Not limited.

As the heat transfer plate for inter-sample insertion used in the present invention, a homogeneous flat plate having no warp or defect is preferable, and as a material, it has a high thermal conductivity and a strength that does not cause any problem in handling, and is fired. The material is not particularly limited as long as it does not deteriorate in the temperature / atmosphere. Specifically, a C / C (carbon fiber reinforced carbon) composite plate or an isotropic or mold type carbon plate is used. The thickness and shape of the heat transfer plate are preferably the same as or slightly larger than those of the molded plate.

[0018]

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

Reference Example A 10 mm chop of pitch-based carbon fiber (Dunakerbo S manufactured by Donac Co., Ltd.) was used as a binder to prepare a wet paper having a basis weight of 200 g / cm ² . This paper-100
100 parts of phenol resin (Daio Nippon Ink & Chemicals Co., Ltd., Prio-Fen 5900) was wet-impregnated into parts and heat-molded at 150 ° C. for 1 hour to obtain a molded plate.

Examples 1 to 3 and Comparative Examples 1 to 2 Molded plates (1000 mm × 1000) obtained by the reference example.
30 sheets (mm × 0.5 mm ^t ) were placed one on top of another in a vacuum firing furnace capable of heating up to 1200 ° C. with carbonaceous plates having a thickness of 10 mm placed one above the other. 500 at a rate of 2 ° C / min under vacuum
C. (Comparative Example 1), 600.degree. C. (Example 1), 700.degree. C. (Example 2), 850.degree. C. (Example 3), 1000.degree. Stage firing was performed.
After cooling to room temperature, the temperature was raised to 2000 ° C. at a rate of 5 ° C./min under vacuum in a vacuum firing furnace compatible with 2300 ° C., and the temperature was maintained for 1 hour to carry out second stage firing. Appearance of the obtained porous carbon plate
The shape is shown in Table 1. The sample of Comparative Example 1 had a weak bending strength (width 15 mm, L / D = 32, head speed = 2 mm / min) of 60 Kg / cm ² at the time of first-stage firing, and many defects were found in the subsequent handling. Occurred.

COMPARATIVE EXAMPLE 3 Except for the fact that the firing was carried out continuously at a temperature up to 2000 ° C., the appearance shape of the porous carbon plate produced under the same conditions as in Example 2 with respect to the rate of temperature rise and the sample was the same. It shows in Table 1. 1
There was stain on the electrode part of the furnace due to the tar discharged during firing at 000 ° C or lower. It was difficult to sinter several hundred sheets or more by this method because of the influence of these tar components.

Example 4 The appearance shape of the porous carbon plate produced under the same conditions as in Example 2 except that the temperature rising rate in the range of 300 to 700 ° C. was raised at a rate of 0.1 ° C./min. It shows in Table 1.

Example 5 Porous carbon produced under the same conditions as in Example 2 except that a carbon plate having a thickness of 200 mm was placed on the sample so that a load of about 0.03 Kg / cm ² was applied during the second firing. Table 1 shows the external shape of the plate.

Examples 6 and 7 Every 5 sheets of forming plate, every 20 sheets of carbon plate having a thickness of 8 mm (G140A manufactured by Tokai Carbon Co., Ltd., density 1.74, thermal conductivity 130 Kcal / m · hr). Table 1 shows the external shape of the porous carbon plate produced under the same conditions as in Example 2 except that (° C) was inserted.

[0025]

[Table 1]

[0026]

According to the production method of the present invention, it is possible to obtain a porous carbon electrode plate having excellent appearance and no defects in appearance, and to mass-produce the product with stable quality.

[Brief description of drawings]

FIG. 1 shows the thermal expansion / contraction behavior in the temperature rising / cooling process when a molded plate for a porous carbon plate (thickness 0.7 mm, bulk density 0.9 g / cm ³ ) is fired.

Claims (4)

[Claims] 1. When firing a molded body for a porous carbon plate, the firing is performed in two steps, and the firing in the first step is performed at a maximum firing temperature of 600 to 850 ° C., and the firing in the second step. A method for producing a porous carbon plate, characterized in that the maximum firing temperature is 2000 ° C. or higher. 2. The manufacturing method according to claim 1, wherein in the firing in the first step, the temperature rising rate from 300 ° C. to 700 ° C. is 0.5 ° C./min or less. 3. The production method according to claim 1, wherein the firing in the second stage is performed by applying a load of 0.02 Kg / cm ² or more. 4. The porous material according to claim 1, 2 or 3, wherein, when firing the formed body for porous carbon plate, a carbonaceous plate is inserted every 1 to 15 sheets of the formed formed body and fired. Of manufacturing high quality carbon plate.