JPH0269357A - Production of isotropic graphite material having high density and high strength - Google Patents

Abstract

PURPOSE:To easily obtain isotropic graphite material having high density and strength in good productivity by adding tar oil to mesophase microspheres having self-sinterability, thereafter molding, sintering and graphitizing. CONSTITUTION:The mesophase microspheres are produced by heat-treating coal tar pitch, petroleum pitch, etc., and separated by solvent fractionation. Then, the obtd. mesophase microspheres having self-sinterability are added with tar oil (e.g., naphthalene oil, creosote oil). The amt. to be added is suitably 1-5wt.% with respect to the mesophase microspheres. Then, the isotropic graphite material having high density and strength is obtd. by molding, sintering and graphitizing the mesophase microspheres. Thereby, a metal mold can be easily formed with the graphite, because the tar oil is added to mesophase microspheres having inferior formability, and besides, the higher density and strength of the obtd. graphite are attained.

Description

[Detailed Description of the Invention] <Industrial Application Fields> The present invention is used in industrial application fields such as electrodes for electrical discharge machining, semiconductor metallurgy, crucibles, carbon for nuclear power, and carbon for machines such as mechanical seals. carbon material,
In particular, the present invention relates to a method for producing a high-density, high-strength carbon material.

<Conventional technology> 5 pitches of coal tar, 350 to 500 pitches of petroleum pitch, etc.
Heat treatment at a temperature of 0.degree. C. produces mesophase spherules with optical anisotropy in an optically isotropic pitch. These mesophase spherules (hereinafter referred to as spherules) are separated from the pitch matrix by solvent fractionation and serve as a raw material for an isotropic, high-density, and high-strength carbon material.

For example, according to Japanese Patent Publication No. 6G-25364, when small spheres are separated into solvents, solvents such as benzene, pyridine, and oil in tar, which have a weaker extraction power than quinoline for pitch, are used as solvents, and the β components in pitch are separated. A portion of the components of is left with the spherules, and then 2
It has been shown that by calcining at a temperature of 00 to 450°C, a high-density, high-strength raw material for carbon material with excellent self-sintering properties can be obtained. If the raw material obtained by this method is used, the bulk density can be reduced to 1.8 by molding, firing, and graphitizing according to normal methods without using a binder.
A high-density, high-strength, isotropic graphite material with a bending strength of 5 g/cd or more and a bending strength of 800 kg/cd or more can be easily manufactured.

<Problems to be solved by the invention> As mentioned above, mesocarbon spherules with self-sintering properties have extremely excellent characteristics as raw materials for high-density and high-strength carbon materials, but on the other hand, It has the drawbacks of extremely poor slippage and poor moldability as a body.
For example, when performing pressure molding using a mold, there are problems such as poor sliding of the powder, which causes lamination when releasing the mold, or difficulty in improving the bulk density of the molded product despite the molding pressure. There is.

Therefore, the formation of such mesophase spherules is usually C
The IP (cold isostatic pressing) method is often used, however, the CIP method has difficulty in continuous molding and is less economical. In particular, for relatively small carbon materials, continuous molding is often required.

As a means to solve these problems, it is common practice to use natural graphite, silicon stearic acids, etc. as a mold release agent in the film.

However, these measures are not sufficient when targeting the small spheres.

An object of the present invention is to propose a method for producing an isotropic graphite material that is easy to mold with a mold and has high density and high strength using mesophase small spheres having self-sintering properties as a raw material.

Means for Solving the Problems> The present invention provides a method for producing an isotropic graphite material by molding, firing, and graphitizing mesophase spherules having self-sintering properties, in which a tar is added to the mesophase spherules prior to molding. This is a method for producing an isotropic graphite material having high density and high strength, characterized by adding preferably 1 to 5% by weight of oil.

For Kusaku The present invention will be explained in detail below.

The tar-based oil to be added to the small spheres specifically refers to naphthalene oil, creosote oil, cleaning oil, and anthracene oil produced during tar distillation.

The oils have an extremely good affinity with the small spheres, and can be easily and uniformly mixed by stirring with a Henschel mixer or the like at room temperature. The oil uniformly wets the surface of the mesophase spherules and improves the slippage of the surface. The oil-added mesophase microspheres thus obtained have good moldability as a powder, and a good molded product can be obtained without any lamination problems.

What is more important is that the effect of adding the oil is not limited to simply improving formability, but also contributes to increasing the density and strength of the carbon material obtained by firing or graphitizing the compact. . The reason for this can be explained from the following two points. The first point is that the bulk density of the molded product is improved due to its good moldability under the same molding pressure. Second
This is due to the fact that the normal boiling point of the oil is in the range of 100 to 360°C.Normally, most of these low boiling point fractions are scattered as volatile matter during the firing process of the molded product It was thought that it would not contribute to the densification of

However, according to the research conducted by the present inventors, the diffusion of the oil from the inside of the molded body to the outside of the molded body is extremely slow, and the carbonization region of 400 to 600°C, which is an important factor for the densification of mesophase spherules, has been found to be extremely slow. It has been confirmed that the oil remains inside the compact and promotes the carbonization melting reaction, resulting in an increase in volumetric (linear) shrinkage during firing of the compact and promotes densification of the fired compact and even graphite. It was done.

Such a phenomenon cannot occur with commonly used mold release agents such as natural graphite, silicone, and stearic acids.

A sufficient effect can usually be expected if the amount to be added is 1% by weight or more based on the mesophase small spheres. If the amount added is too large, the amount of volatile matter during firing of the molded body will increase, causing cracks and cracks during firing of the molded body. Therefore, although it varies depending on the type of tar oil to be added, the characteristics of the mesophase spherules, and even the firing conditions, it is usually 5% by weight or less, and even if no cracks occur during firing of the molded product, it is 5% by weight or more. The addition of oil does not significantly contribute to the improvement of moldability and densification, and the effect tends to be saturated.

In addition, when it comes to the type of cool oil to be added, heavy oil with a high specific gravity is usually more effective, but on the other hand, as the specific gravity increases, the viscosity also increases, making it difficult to mix uniformly with the mesophase spherules. Therefore, it is desirable to select it appropriately each time.

The present invention will be explained in more detail with reference to specific examples below.

<Example> Example 1 Softening point containing 3% by weight of quinoline solution (R&B method)
Tar pitch at 80″C was heat treated at 450°C to generate mesophase spherules.The heat treated pitch was extracted and filtered twice using 6 times the volume of oil in tar (boiling range 150-230″C). did. Continue filtering residue at 360
Calcination treatment was performed at ℃ for 3 hours in an inert atmosphere to obtain mesophase spherules having self-sintering properties.

For the mesophase spherules, oil in tar (boiling range 1
50~230℃) were added at 1%, 2%, 3%, and 6% by weight, respectively, to obtain mesophase spherules containing four types of oil in tar.Then, they were mixed for 5 minutes in a Henschel mixer at room temperature. .

Four types of mesophase small spheres containing this oil-in-tar were each molded into a size of 120 φ x 40 hm/m using a mold. The molding pressure was 550 kg/C-, and the molded product obtained had no lamination or cracks (
It was in good condition. The molded body was processed for 10 minutes according to the usual method.
After firing at a rate of 00°C for 96 hours, graphitization was further performed at 2500°C.6 Table 1 shows the measurement results of the physical properties of the fired product and the graphitized product.

Example 2 Mesophase spherules were obtained according to the method shown in Example 1. To the mesophase spherules, cleaning oil (boiling point range 240 to 330'C) obtained by tar distillation was added in an amount of 1M, 3%, and 5% by weight, respectively.

7% by weight was added and mixed using a Henschel mixer in the same manner as in Example 1. Shaping the mixture according to Example 1;
Table 1 shows the measurement results of the physical properties of each molded body, fired body, and graphitized product obtained by firing and graphitizing. The molded product had good lamination and no defects.

Comparative Example 1 The mesophase spherules obtained according to the method shown in Example 1 were molded, fired, and subjected to 9wA leading according to Example 1 without adding tar-based oil. In the molded product, lamination was observed in some parts and cracking was observed at the edges.

Only the compacts with relatively good shapes were fired and graphitized, and Table 1 shows the measurement results of the physical properties of the graphitized products obtained.

<Effects of the Invention> According to the present invention, even mesophase small spheres with poor moldability can be easily molded with a mold, and an improvement in productivity can be expected. Furthermore, it has become possible to further increase the density and strength of the resulting carbon material.

Claims (2)

[Claims] 1. A method for producing an isotropic graphite material by molding, firing, and graphitizing mesophase spherules having self-sintering properties, which is characterized by adding tar-based oil to the mesophase spherules prior to molding. A method for producing isotropic graphite material with high density and high strength. 2. 1-5 times tar-based oil for mesophase spherules
2. The method for producing an isotropic graphite material having high density and high strength according to claim 1, wherein the addition is performed in an amount of % by weight.