JP2001130963A - Method for producing isotropic high-density carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an isotropic carbon material by which the carbon material having a density higher than that of the conventional one, >=1.85 g/cc bulk density can be produced without causing crack in high yield. SOLUTION: This method for producing an isotropic carbon material is characterized in that a compact obtained by pulverizing carbonic cokes so as to have 4-20 μm size heat-treating the pulverized cokes at >=2,000 deg.C, mixing and kneading the heat-treated cokes with a binder pitch in 100-150% outer percentage, further subjecting the kneaded product to a kneading treatment at 300 deg.C to remove volatile components, repulverizing the treated product to provide fine powder having 10-30 μm average particle diameter, and subjecting the obtained fine powder to a cold isotactic pressing molding is subjected to a heat treatment at 2,000-3,000 deg.C in a nitrogen or reductive atmosphere to fire and graphitize the compact, after once or twice optional densifying treatments, and graphite boards having good thermal conductivity are set on upper and lower surface of the compact in the heat treatment for firing or densifying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an isotropic high-density carbon material, and more particularly, to a step of firing a high-density isotropic carbon material by minimizing the densification treatment by repeated impregnation and refiring.
The present invention relates to a production method capable of suppressing the occurrence of cracks in the graphitization step and achieving good yield and low cost.

[0002]

2. Description of the Related Art Conventionally, isotropic high-density carbon materials have been used in many applications such as crucibles for producing semiconductor single crystals, electrodes for electric discharge machining, dies for hot pressing, and various jig materials.

[0003] In particular, crucibles and heat sinks for producing silicon single crystals.
Although components such as copper are important uses of isotropic carbon materials, erosion by SiO generated by the reaction between raw silicon and quartz crucibles becomes a problem in the production of silicon single crystals.

[0004] Therefore, the isotropic carbon material is made to have a high density and a low porosity in order to suppress the reaction with SiO, and to suppress the reaction with SiO.
Development of materials is being studied in the direction of suppressing the diffusion of gas into the material.

[0005] In general, a method for producing an isotropic carbon material is based on a raw material core.
In general, a method of adding binder-pitch to flour powder, mixing, kneading, and re-grinding, then molding by a cold isostatic pressing method, and calcining and graphitizing the molded body is customary.

In order to increase the density of the isotropic carbon material,
The process of impregnating with a cold pitch or the like after firing and firing is repeated before the graphitization process, but this densification process (densification process) needs to be repeated at least three times. It is.

Therefore, the densification treatment is an expensive method, and if the densification treatment is advanced, defects such as cracks are likely to occur in the carbon material, which is not preferable in terms of the yield.

The isotropic carbon material requires a long firing (carbonization) time, and shortening the firing process is also an issue.

Therefore, a method for producing an isotropic carbon material is described below.
Various methods have been attempted in order to obtain a high-density material at a low cost and with good yield. For example, JP-A-5-229810 describes an invention which provides a method for stably and efficiently producing an isotropic high-density graphite material having excellent material strength and a normal material structure.

The claims of Japanese Patent Application Laid-Open No. 5-229810 disclose that "a pitch-based binder is used in an amount of 70 to 110 parts by weight per 100 parts by weight of an aggregate component mainly composed of non-graphitic carbonaceous material having a maximum particle size of 10 μm or less. Parts are kneaded, and the kneaded material is roughly pulverized and then heat-treated in a temperature range of 250 to 450 ° C so that the toluene-soluble content and the β-resin content are each 5 to 5 parts.
The volatile content is adjusted so as to be within a range of 15% by weight, and is again pulverized, formed into a predetermined shape by a rubber press, and then subjected to calcined carbonization and graphitization treatment. Production method. In the same issue, the β resin content is adjusted to a certain range in combination with the toluene soluble content in the binder, and the volatile content is adjusted to a certain range. It is possible to produce a highly dense graphite material.

Japanese Patent Application Laid-Open No. 6-122552 discloses an invention which provides a manufacturing method for stably and industrially producing a large isotropic high-density graphite material having excellent material strength and uniform tissue properties. Have been.

Claim 1 of the claims of Japanese Patent Application Laid-Open No. 6-122552 discloses a method of kneading an aggregate component mainly composed of non-graphitic carbonaceous material and a pitch binder, and re-grinding the kneaded material. Molding step of rubber press molding raw material powder,
Then, in the production process of isotropic graphite material comprising a carbonization and graphitization step of calcining and graphitizing the compact,
Adjust the kneaded material having a different volatile content in the kneading step,
Production of isotropic graphite material characterized in that raw material powder with low volatility is located in the center of the rubber mold during the molding process and raw material powder with high volatility is interposed outside the rubber powder. Method. When rubber pressing is performed to reduce the volatile content of the central part of the molded body and increase the volatile content of the outer part in the molding process of the raw material powder, the shrinkage during carbonization becomes uniform and the material is damaged. And the like are effectively reduced, homogeneous tissue properties are imparted, and an isotropic graphite material having a high-strength and homogeneous material structure can be stably obtained.

As described above, JP-A-5-229810
And Japanese Patent Application Laid-Open No. 6-122552 are also methods for producing an isotropic high-density carbon material at an excellent rate of a material having excellent quality.
There has been a demand for a method capable of producing a dense material of cc or more inexpensively and with good yield.

Further, there is a demand for a method which can effectively suppress the occurrence of cracks and the like even with a large-sized material, can be manufactured at a high yield, and can reduce the number of steps.

[0015]

In view of the above problems, the present inventor has developed a method for producing an isotropic carbon material by cracking a carbon material having a higher density and a bulk density of 1.85 g / cc or more than before. To provide a method that can prevent the occurrence of odor and can be manufactured with good yield.

[0016]

In order to solve the above problems, the present inventor proposes that carbonaceous coke has an average particle size of 4 to 4.
After pulverized to 20 μm and heat-treated at 2000 ° C. or higher,
The binder-pitch is mixed and kneaded at a ratio of 100 to 150%, and the obtained kneaded material is kneaded at 300 ° C. or less to remove volatile components, and then further pulverized to an average particle size of 10 to 30 μm. The obtained fine powder is cold isostatically pressed at a pressure of 100 kg / cm ² or more to form a molded article, and is heat-treated to 2000 to 3000 ° C. for calcination and graphitization in a nitrogen or reducing atmosphere. The densification treatment is performed once or twice before the graphitization treatment, and in the heat treatment for the sintering or the densification treatment, a graphite plate having good heat conductivity is set on the upper and lower surfaces of the molded product. This is a method for producing an isotropic carbon material.

Hereinafter, the method for producing an isotropic carbon material of the present invention will be described in detail.

In the present invention, graphite powder obtained by pulverizing a graphite material is not used because the aspect ratio is large and a large amount of binder is required, but the obtained graphite material has only a small bulk specific gravity. First, carbonaceous coke is pulverized so that the average particle diameter becomes 4 to 20 μm. If it is 20 μm or more, the bulk specific gravity of the final product is low, and a sufficiently dense material cannot be obtained. If it is 4 μm or less, many cracks occur in the firing step, and both are not preferred.

The coke crushed as described above was
Heat treatment at a temperature of at least ℃. This heat treatment is important for improving the thermal conductivity of the molded article later, uniformizing the carbonization in the firing step, and suppressing the occurrence of cracks. If the temperature of the heat treatment of the pulverized coke is lower than 2000 ° C., the thermal conductivity is poor and the carbonization during firing becomes non-uniform and cracks occur frequently.

Next, the coke that has been heat-treated as described above is mixed and kneaded at a ratio of 100 to 150% of the binder pitch on an external basis. By using a relatively large amount of the binder pitch, the shrinkage in the subsequent firing step is increased, which effectively acts on increasing the density of the material.

If the binder-pitch ratio is less than 100%, the bulk specific gravity of the final product is low, and a sufficiently dense material cannot be obtained. If it exceeds 150%, cracks occur frequently in the firing step, and Is also not preferred.

The kneaded product of coke and binder pitch is kneaded at 300 ° C. or lower by a kneader to remove volatile components. Removal of volatiles allows the use of large amounts of binder pitch as described above. Three
If the temperature is higher than 00 ° C., the surface of the molding powder is oxidized and infused, and molding defects frequently occur.

Next, the obtained kneaded product is subjected to an average particle size of 10 to 30.
Re-grind to μm. When the average particle size exceeds 30 μm, the bulk specific gravity of the final product becomes low, and a sufficiently high-density material cannot be obtained. When the average particle size is less than 10 μm, many cracks occur in the firing step, which is not preferable.

The reground powder obtained in this manner is subjected to a cold isostatic pressing method (rubber press method) to a hydrostatic pressure of 10%.
Mold at 0 kg / cm ² or more. If it is less than 100 kg / cm ² , the bulk specific gravity of the final product is low, and a sufficiently high-density material cannot be obtained.

Next, the obtained molded article is heat-treated at 2000 to 3000 ° C. in a nitrogen or reducing atmosphere to be calcined and graphitized. In this firing step, a graphite plate having good heat conductivity is set on the upper and lower surfaces of the molded product.

By setting such a graphite plate, it is possible to exhibit an excellent effect of improving the heat conduction of the molded product and making the behavior of the firing step uniform.

The fired product is subjected to one or two densification treatments (process of impregnating pitch and refiring). This densification treatment is usually performed repeatedly, and conventionally required at least three times. However, according to the present invention, the densification treatment is minimized to two times. Carbon material can be obtained.

As described above, an isotropic carbon material is obtained by the production method of the present invention. In the method for producing an isotropic carbon material of the present invention, in particular, heat treatment of carbonaceous coke at 2000 ° C. or higher, addition of a relatively large amount of binder pitch, firing and refiring By setting the graphite plate above and below the molded article in the step of, the heat conduction of the molded article is improved, and the behavior of the firing step is made uniform,
An excellent effect of suppressing the generation of cracks is exhibited, and a large-sized material can be obtained with good efficiency.

Further, by specifying the particle size of the raw material and the processing conditions in each step at the same time as the means for suppressing such cracks, it is possible to increase the bulk specific gravity and obtain an excellent high-density carbon material.

The properties of the isotropic carbon material obtained by the production method of the present invention are such that the bulk density is 1.85 g / cc or more, the bending strength is 500 kg / cm ² or more, and the specific resistance is 1500 μΩcm or less.

Further, a good carbon material can be produced without generation of cracks and the like, and the yield is 90% or more. Further, in the present invention, since the heat conductivity of the molded article is good, the time of the firing step is shortened, and it is possible to reduce the firing time by 70%.

[0032]

According to the method for producing an isotropic carbon material of the present invention, a high-density carbon material having a bulk density of 1.85 g / cc or more can be produced. , Is an effective material against erosion by SiO. In addition, the carbon material as described above can be produced stably at a high yield by suppressing the occurrence of cracks and the like, and can be produced at a low cost by minimizing the densification treatment. Furthermore, the process can be shortened by shortening the firing time, and the production can be performed at 70% of the conventional one. The method for producing an isotropic carbon material of the present invention is extremely useful industrially.

[0033]

[Examples and Comparative Examples]

Example 1 Raw material coke was finely pulverized to an average particle diameter of 10 μm and then treated at 2500 ° C.
The mixture was kneaded at a ratio of 130% by weight of binder pitch to 0% by weight, and kneaded at 250 ° C. for 300 minutes using a kneading machine to remove volatile components. The obtained kneaded product is 15 μm
Crushed into rubber and press-molded (hydrostatic pressure 500kg /
cm ² ) to obtain a molded body. Next, when this is fired, a graphite plate having good thermal conductivity is set on the upper and lower surfaces of the molded body, and the density is increased by impregnation of pitch and refiring.
And graphitized to about 3000 ° C. to obtain 20 isotropic high-density carbon materials (size φ800 × 750 m
m). The bulk density of the obtained isotropic high-density carbon material was 1.9.
2 g / cc, flexural strength was 600 kg / cm ² , specific resistance was 1100 μΩcm, cracks and the like did not occur, and the yield of the carbon material having a good appearance was 95%.

[0034]

Comparative Example 1 An isotropic high-density carbon material was obtained in the same manner as in Example 1 except that the coke in Example 1 was not heat-treated. The bulk density of the obtained isotropic high-density carbon material is
The bending strength was 1.87 g / cc, the bending strength was 400 kg / cm ² , and the specific resistance was 1200 μΩcm. The yield of the carbon material having a good appearance was 65%.

[0035]

Comparative Example 2 An isotropic high-density carbon material was obtained in the same manner as in Example 1 except that the amount of the binder pitch was changed to 70% by weight. The bulk density of the isotropic high-density carbon material is 1.75 g / cc, and the bending strength is 450.
kg / cm ² , the specific resistance was 1300 μΩcm, and the yield of the carbon material having good appearance was 85%.

[0036]

Comparative Example 3 An isotropic high-density carbon material was obtained in the same manner as in Example 1 except that the graphite plate was not used during firing. The bulk density of the obtained isotropic high-density carbon material was 1.85 g / cc, the bending strength was 550 kg / cm ² ,
The specific resistance was 1200 μΩcm, and the yield of the carbon material having a good appearance was 75%.

Claims (1)

[Claims] The carbonaceous coke has an average particle size of 4 to 20 μm.
After heat treatment at 2000 ° C. or more, the binder-pitch was mixed and kneaded at a ratio of 100 to 150% on an external basis, and the obtained kneaded product was kneaded at 300 ° C. or less to remove volatile components. Thereafter, the fine powder obtained by re-grinding to an average particle size of 10 to 30 μm is cold isostatically pressed at 100 kg / cm ² or more to form a molded product, which is fired and graphitized in a nitrogen or reducing atmosphere. Heat treatment to 2000 to 3000 ° C., and if necessary, a densification treatment once or twice before the graphitization treatment. A method for producing an isotropic high-density carbon material, comprising setting a graphite plate having good heat conductivity on a lower surface.