JPH03215362A - Production of dense carbon plate - Google Patents

Abstract

PURPOSE:To obtain a dense carbon plate having excellent gas-barrierness and flexural strength by using a specific carbon fiber as a supporting material and a carbon precursor containing graphite particles as a matrix. CONSTITUTION:A slurry is produced by diluting 100 pts.wt. of a composition composed of 10-50 pts.wt. of graphite particles having an average particle diameter of <=40mum and 50-90 pts.wt. of a carbon precursor having a carbonization yield of 50-90wt.% with a dispersing medium or a solvent. The slurry is supported on 2-40 pts.wt. of a supporting member containing semi-carbon fiber baked at >=550 deg.C and <=700 deg.C as a substrate. The obtained green sheet is used singly or plural sheets are laminated and hot-pressed under pressure. The formed product is carbonized and baked to obtain the objective plate.

Description

Detailed Description of the Invention: "Industrial Application Field" The present invention relates to a method for producing carbon plates with low gas permeability and high mechanical strength, particularly for use in sebarators of phosphoric acid fuel cells and high-temperature heat treatment furnaces. The present invention relates to a method of manufacturing a material suitable for internal materials, jigs for sintered materials, etc.

"Background Art" Conventionally, as a method for manufacturing carbon plates with low gas permeability and high mechanical strength, for example, Japanese Patent Application Laid-Open No. 60-239358
number is known. This is a paper-like support that can be carbonized.
A fine mosaic-like or isotropic carbon precursor having an anisotropic structure observed under a polarizing microscope with a particle size of 10 μm or less is supported, heated and hardened under pressure, and then This is a manufacturing method that involves carbonization and firing. The precursor may include graphite powder with an average particle size of 10 μm or less, an example of which is shown in Example 2. Examples of paper-like supports that can be carbonized include paper made from natural fibers, synthetic fibers, or carbon fibers, infusible pitch fiber paper made by papermaking or heat-sealing infusible pitch yarn, and the above-mentioned non-fusible pitch fiber paper. Infusible pitch fiber yarns and the like are shown in which fusible pitch yarns are fired at 600° C. or lower in an inert atmosphere. However, even the example shown in this prior art was still insufficient in gas barrier properties and mechanical strength.

``Problems to be Solved by the Invention'' The purpose of the present invention is to provide a method for manufacturing a dense carbon plate that is superior in gas permeation barrier properties and bending strength compared to the prior art described above.9 ``Means for Solving the Problems'' (Summary) The present invention is based on the discovery that the problems in the prior art can be solved when a special carbon fiber is used as the support and the matrix is a carbon precursor containing graphite particles. Carbon fiber usually refers to fibers fired at about 1000°C, but fibers fired at about 550 to 700°C (hereinafter referred to as "semi-carbon fibers")
It was found that the heat shrinkability matched the matrix and the mechanical strength was high. Furthermore, it has been found that if such carbon fibers are used and graphite particles are dispersed in the matrix at the same time, the stress generated during firing is dispersed and the mechanical strength is further increased. Incidentally, the above-mentioned prior art shows an example in which quasi-carbon fibers fired at 600° C. are used in Example 3, but this example does not contain graphite particles. Further, although graphite particles are included in Example 2, the support is ordinary carbon fiber and does not show the structure of the present invention.

That is, the gist of the present invention is that the average particle size is 40
10 to 50 parts by weight of graphite particles of µm or less and a carbonization yield of 5
A process of diluting 100 parts by weight of a composition consisting of 50 to 90 parts by weight of a carbon precursor of 0 to 90% by weight with a dispersion medium or solvent, using quasi-carbon fibers fired at 550°C or higher and 700°C or lower as a substrate. A step of supporting a diluted solution containing the composition on 2 to 40 parts by weight of a support to form a green sheet, a step of stacking one or more of the green sheets and heat-forming them under pressure, . and a method for producing a dense carbon plate, comprising the steps of carbonizing and firing the molded product.

The present invention will be explained in detail below. (Carbon precursor) When carbonizing and firing a molded plate, if the carbon precursor is pitch-based, it decomposes while melting and causes a polycondensation reaction while releasing low molecular weight molecules as a gaseous substance. It carbonizes when heated. Further, when the carbon precursor is a thermosetting resin, it undergoes a polycondensation reaction and is carbonized in a solid state by increasing temperature while releasing gas. Both of them release gas, but if too much gaseous material is released, bubbles will be generated in the board, and the carbon precursor will shrink more, which will cause the board to break or crack, which is not desirable.
Those with a carbonization yield of 50 to 90% by weight are used.
The carbonization yield here is the carbonization yield at 900°C, and is based on the volatile content determination method of JIS M8812. The carbon precursor used in the present invention is prepared by adding oxygen, sulfur, nitric acid, etc. to tar such as coal tar or petroleum tar, and heat-treating the mixture at a temperature of 150 to 400°C to introduce oxygen, sulfur, or nitrogen. The pitch obtained by the method of obtaining pitches, for example, the method of oxidizing pitches as described in Japanese Patent Publication No. 53-31116, is further
It can be easily obtained by heat treatment at 80° C. or by using a thermosetting resin.

As the thermosetting resin, for example, phenol resin, furan resin, COPNA resin, etc. are suitably employed.

Copner resin mainly consists of a fused polycyclic aromatic compound having two or more rings, a crosslinking agent consisting of an aromatic compound having one or more rings having two or more of at least one of hydroxymethyl group and halomethyl group, It is a thermosetting resin made in combination with an acid catalyst. Examples of the fused polycyclic aromatic compound having two or more rings include naphthalene, anthracene, phenanthrene, birene, etc., and one or more rings having at least two groups of either hydroxymethyl group or halomethyl group. As an aromatic crosslinking agent consisting of aromatics, p-
Examples include xylylene dichloride and p-xylylene glycol. Examples of acid catalysts include Lewis acids such as aluminum chloride and boron fluoride, and protonic acids such as sulfuric acid, phosphoric acid, organic sulfonic acids, and carboxylic acids. Regarding the manufacturing method of Copna resin, for example, Japanese Patent Application Laid-Open No. 62-12735
A known method as disclosed in Japanese Patent No. 0 is employed.

Further, a mixture of carbon precursors as described above may be used. For example, when using a composition of pitches and thermosetting resin produced by the above method as a matrix, if a slurry for the support is prepared using a solvent that dissolves the thermosetting resin, it is possible to The thickening effect of the curable resin stabilizes the slurry, and the resulting green sheet (a material in which a carbon precursor is supported on a support and dried) has strong adhesion to both the Matri-Sox resin and the support. . On the other hand, if the amount of thermosetting resin added is large, the fired product will become hard and difficult to process, so it is usually better to limit the amount of added thermosetting resin to 40% by weight of the entire matrix.

(Graphite particles) The graphite particles used in the present invention have an average particle size of 40 μm.
m or less. If the average particle size is large, the molded product will contain many voids, giving a carbon plate with high gas permeability, so it is preferable that the particle size is as small as possible.

Incidentally, the term "graphite" used in the present invention is used not only to refer to graphite in a narrow sense but also to include graphite in a broad sense.

Note that the average particle size herein is measured according to ASTM C678-75.

(Composition of carbon precursor and graphite particles) The composition ratio of the carbon precursor and graphite particles in the present invention is 5 for the former.
0 to 90 parts by weight, while the latter is 10 to 50 parts by weight. This range is chosen because if the amount of the carbon precursor is less than the above amount, the mechanical strength will decrease, and if the amount is more than the above amount, it will become hard and difficult to process, and the firing shrinkage rate of the carbon precursor will be large. This is due to problems such as easy cracking during firing and high gas permeability. Preferably, the former is 55 to 85 parts by weight and the latter is 15 to 45 parts by weight, and more preferably the former is 60 to 80 parts by weight and the latter is 20 to 45 parts by weight.
A range of 40 parts by weight is adopted. (Support) As the support used in the present invention, quasi-carbon fiber is
A flat aggregate of quasi-carbon fibers fired at a temperature of 0°C or higher and 700°C or lower, preferably 570°C or higher and 670°C or lower, more preferably 590°C or higher and 650°C or lower, is used. It will be done.

The reason why the firing temperature is set in the above range is that if the temperature is higher than the above, the mechanical strength will be lower because the heat shrinkability will not match that of the matrix, and if the temperature is lower than the above, the material will be powdered during handling. Furthermore, both woven and non-woven fabrics can be used as the shape of the above-mentioned flat aggregate. The raw material for the quasi-carbon fiber is not particularly limited, and may be pitch fiber or polyacrylonitrile fiber. Furthermore, it may be an isotropic pitch or an anisotropic pitch, but an isotropic pitch is preferably used.

The method for obtaining a flat support from quasi-carbon fibers is a known method for obtaining a flat support from carbon fibers. for example,
In order to bind so-called chopped fibers, which are short carbon fibers, to each other, for example, those bound with synthetic fibers or those entangled with natural fibers such as bulbs are used. In these cases, it is preferable that at least half of the weight of the support is accounted for by chopped fibers. An example of a method for bonding with organic fibers is a method in which fibers made of a thermoplastic resin such as polyvinyl alcohol or polyacrylonitrile are heat-treated together with quasi-carbon fibers at a temperature of 300° C. or less to thermally fuse the organic fibers. An example of a method for entangling paper with a bulp is normal paper mixing. Further, the woven fabric used in the present invention may be one made by weaving carbon precursor fibers such as pitch fibers or polyacrylic nitrile fibers and then made into quasi-carbon fibers, or one made by weaving quasi-carbon fibers. In particular, twisted so-called yarns are used, and plain weave is preferably used for woven fabrics.

(Method for supporting carbon precursor) In the present invention, the above-mentioned carbon precursor composition is supported on the support. The amount of the composition supported on the support is 2 to 40 parts by weight, preferably 5 to 30 parts by weight per 100 parts by weight of the supported amount.
Parts by weight, more preferably 10 to 20 parts by weight, are employed. The reason for setting this range is that if the amount of support is smaller than the above-mentioned value compared to the amount of support, it will be difficult to support it uniformly and it may cause a decrease in mechanical strength. If the amount is larger than the above, the obtained carbon plate will become a bolus and the gas permeability will increase. The supporting method is not particularly limited, and any known method may be employed. Usually, the following method is preferably employed. First, a carbon precursor is pulverized in advance using a jet mill (dry type) or a ball mill (wet type). Then, since there is no solvent to dissolve the finely powdered graphite particles, a solvent that dissolves a portion of the carbon precursor composition, such as tetrahydrofuran, toluene,
A slurry is prepared using benzene, ethanol, or a dispersion medium that does not even partially dissolve it, such as water. After dipping or applying this slurry, the solvent in this slurry,
Alternatively, there is a method of drying by evaporating the dispersion medium.

In these methods, small amounts of third substances such as thickeners, surfactants, etc. may be added to improve the adhesion of the carbon precursors to each other and to the support, or to improve the stability of the slurry. ．． The evaporation and drying of the dispersion medium or solvent after supporting the carbon precursor by the above method removes the dispersion medium or solvent to the extent that the expansion during pressure and heat molding due to the residual amount can be ignored. It will be a green sheet.
The evaporation drying conditions are, for example, at a temperature of 30 to 70°C, which is such that the composition of the carbon precursor and graphite particles does not separate from the supported part, and under a reduced pressure state, for example, 50 mmHg or less, in a vacuum furnace. A method in which heat treatment is carried out within a chamber is preferably adopted. If the dispersion medium or solvent is not removed, the remaining dispersion medium or solvent will gasify during molding, resulting in insufficient densification of the molded product and a decrease in gas barrier properties.

(Forming) One or more green sheets produced by the method described above are stacked, supplied to a predetermined mold, and heated and press-molded. Ordinary molding conditions are employed as press molding conditions. The limit of the molding temperature is usually 800°C or less, and if the temperature is too high and shrinkage molding distortion occurs due to heating carbonization of the matrix and support, remove the pressure once and mold while removing the molding distortion. Since the green sheet is usually solidified at about 500°C by heating, a temperature of 600°C or lower is preferably used. The lower limit of the molding temperature that is usually adopted is a temperature range below the flow start temperature of the thermosetting resin when the carbon precursor contains a thermosetting resin, and above the softening temperature when the carbon precursor does not contain a thermosetting resin. Ru. Also, the pressure is 100k
gf/am2 or less, a pressure holding time of 1 to 120 minutes is preferably employed, and the process is carried out in an inert atmosphere.

Note that the softening temperature and flow start temperature are determined by the following measurements. Using a Shimadzu high-speed flow tester, 25
1 g of the sample pulverized to 0 microns or less was filled into a cylinder with a cross-sectional area of 1 cm" and a nozzle with a diameter of 1 mm at the bottom, and heated at 6°C/cm2 while applying a load of 10 kgf/cm2.
The temperature increases at a rate of 1 minute. As the temperature rises, the powder particles soften, the filling rate increases, and the volume of the sample powder decreases, but above a certain temperature, the volume stops decreasing. As the temperature continues to rise further, the sample melts and flows out from the nozzle at the bottom of the cylinder. The temperature at which the volume of the sample powder stops decreasing at this time is defined as the softening temperature of the sample, and the temperature at which the sample begins to melt and flow out, that is, the temperature at which the volume of the sample in the cylinder begins to decrease, is defined as the flow start temperature. shall be. For materials with a high softening temperature, melting may not flow out from the nozzle. (Carbonization firing) Next, the pressure is normally removed once, and then the pressure is further increased in an inert gas atmosphere, or carbonization firing is performed at <800° C. or higher, preferably 900° C. or higher without applying pressure, and graphitization is performed if necessary. When high conductivity is required, it is desirable to process at 2000° C. or higher. Firing under pressure is preferable in E because it prevents warping of the plate and produces a denser carbon plate. (Example) Hereinafter, the present invention will be further explained with reference to Examples. The physical properties shown in the examples were measured as follows.

(1) Gas permeability coefficient: Gas permeability measuring device GTR-
10A (manufactured by Ahon Seisakusho) was used, and the measurement method was B method, that is, hydrogen gas, which was a test gas, was applied to the top surface of the film at 2 kg/am to eliminate the time delay in the diffusion coefficient.
The measurement was carried out by continuously evacuation of the lower surface while applying pressure to L (differential pressure: 3 kgf/cm), and after confirming a steady state, hydrogen gas, which is the permeated gas, was stored.

Bending strength: ASTM D790-81 (3-point load) (3) Carbon content: Determined by quantifying combustion gas by gas chromatography. ELEM as a device
ENTAL ANALYZAER HITATCHI
028 Use CHN ANALYZ-ER (manufactured by Hitachi, Ltd.) Bulk density: Measure the dimensions of the carbon plate with calipers and a micrometer to determine the volume, and divide the weight of the carbon plate by the volume. Electrical specific resistance: ASTκD-257-78. (Mercury electrode method) (2) (4) (5) By the method shown in Figure 5B. Example 1 Bitch A was obtained by treating ethylene bottom oil at 370° C. for 3 hours to make it heavier and at the same time remove low boiling point components. Pulverize this bitch A to 100 μm or less for 10'C/hr.
By raising the temperature in air to 190℃ at a rate of was manufactured. Bitch B1 had a softening temperature of 285°C and a carbonization yield of 72% by weight when fired at 900°C.

8112 parts by weight of fine powder pitch obtained by pulverizing Bitch B, so that the particle size of 10 μm or less is 90% by weight or more, particle size 10
A slurry was prepared by uniformly mixing 8 parts by weight of graphite powder of µm or less, 0.5 parts by weight of methyl cellulose, and 80 parts by weight of water.

After uniformly applying the above slurry to carbon paper with a basis weight of 30 g/m2 manufactured by paper-making isotropic pitch-based quasi-carbon fibers fired at 600°C, the slurry was dried to obtain a paper with a basis weight of 230 g/m2.
A green sheet of g/m2 was produced. The carbon precursor and the graphite particles accounted for 60 parts by weight and 40 parts by weight, respectively, and the quasi-carbon fibers accounted for 15 parts by weight in 100 parts by weight of the composition before being diluted with water, which is a dispersion medium. These four green sheets were stacked and filled into a mold, and heated at 300°C/hr.
The temperature was raised to 370°C at a speed of This thin plate was fired at 2000°C in an inert gas atmosphere to produce a carbon plate with a thickness of 0.53+nrn.The properties of the obtained carbon plate are shown in the table.

Comparative Example 1 A carbon plate was manufactured in the same manner as in Example 1, except that carbon fibers made of isotropic infusible pitch yarns were fired at 900°C.Thickness of the carbon plate after firing at 2000°C is 0.57
It was mn+. In 100 parts by weight of the composition before being diluted with water as a dispersion medium, the carbon precursor accounted for 60 parts by weight, the graphite particles accounted for 40 parts by weight, and the carbon fibers accounted for 15 parts by weight. The properties of the obtained carbon plate are shown in the table. Example 2 Bitch A was obtained by treating ethylene bottom oil at 370'C for 3 hours to make it heavier and remove low boiling point components. This pitch A is crushed to 50oμm or less at 10℃/h.
Bitch B2 was produced by raising the temperature in air to 190''C at a heating rate of r.Bitch B2 had a softening temperature of 285°C and a carbonization yield of 72% by weight when fired at 900°C.

Pitch B2 was further heat treated at 420''C in an inert gas for 2 hours to obtain pitch C with a softening temperature of 430'C and a carbonization yield of 84% by weight when fired at 900''C. In addition, the softening temperature of Bitch C is different from the measurement method explained in the main text, and the softening temperature is determined by applying a load of 10
It is set to 0 kgf/cm2. This bitch C 9
A fine powder Bitch C was obtained by pulverizing the powder so that the 0 weight ratio was 30 μm or less.

In addition, Kovner resin has a molar ratio of 7/3 birene/
44.6% by weight of p-xylylene glycol and 5% by weight of valatoluenesulfonic acid were added to 50.4% by weight of phenanthrene, and the mixture was reacted at 120'C for 2 hours. Furthermore, CP (trade name of Oriental Sangyo, average particle size: 12 μm) was used as graphite particles. Next, 30 parts by weight of fine powder Bitch C, 40 parts by weight of Kovner resin, 30 parts by weight of graphite particles, and 20 parts by weight of tetrahydrofuran were uniformly mixed to obtain a slurry.

A carbon paper with a basis weight of 30 g/m" obtained by producing a semi-carbon fiber made by baking isotropic infusible pitch yarn at 60θ℃ is uniformly impregnated with the above slurry, and dried to obtain a fabric weight of 230 g/m". A green sheet of m2 was produced.The carbon precursor accounted for 70 parts by weight, the graphite particles accounted for 30 parts by weight in 100 parts by weight of the composition before diluting with water as a dispersion medium,
The quasi-carbon fibers for this correspond to 15 parts by weight. These four green sheets were stacked and filled into a mold, weighing 15 kg.
The temperature was maintained at 200° C. for 1 hour under a pressure of f/cm 2 , and then the pressure was increased to 1 kgf/cm 2 , and the temperature was raised to 600° C. at a temperature increase rate of 50° C./hr, followed by cooling to obtain a thin plate. This thin plate was fired at 2000°C in nitrogen gas. The characteristics of this carbon plate are shown in the table. Note that no microcracks were observed.

Example 3 Example 2 except that pitch B2 was used instead of Kovner resin
I did the same thing. Its characteristics are shown in the table. No microcracks were observed.

Table 1 Table 2 Comparative Example 2 Same as Example 2 except that a composition of 60 parts by weight of fine pitch (C) and 40 parts by weight of Kovner resin was used as the carbon precursor, and graphite particles were not included in the matrix. I did it. Many cracks were generated on the surface of the obtained carbonaceous plate.

"Effects of the Invention" The carbon plate of the present invention is dense, has few cracks, has low gas permeability, and has high bending strength.

Claims (1)

[Claims] 10 to 50 parts by weight of graphite particles with an average particle size of 40 μm or less and 50 parts by weight of a carbon precursor with a carbonization yield of 50 to 90% by weight
Step of diluting 100 parts by weight of a composition consisting of ~90 parts by weight with a dispersion medium or solvent, 550°C or higher, 700°C
Supports 2 to 40 whose substrate is semi-carbon fiber fired as follows
A step of supporting a diluted solution containing the composition in parts by weight to form a green sheet, a step of laminating one or more of the green sheets and heating and molding them under pressure, and a step of carbonizing and firing the molded product. A method for producing a dense carbon plate.