JPH0542996B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to a pitch film having a fine optically anisotropic structure suitable for the production of isotropic high-density carbon materials, carbon/carbon composite materials (C/C composites), UHP electrodes, etc. This invention relates to a method for producing fine particles. [Prior Art and Problems] Isotropic high-density carbon materials are generally used as electrode materials for electric discharge machining, crucibles for aluminum evaporation, or wall materials for nuclear fusion reactors. When producing this high-density carbon material, petroleum-based coke or coal-based coke is generally pulverized and used as an aggregate. Since aggregate itself does not have caking properties, it cannot be molded by pressure molding as it is, so a binder is used to mold it. This molding is usually performed by cold isostatic pressing in order to achieve isotropic properties. The obtained compact is carbonized at a very slow heating rate of 1 to 10°C/Hr, and then graphitized at a temperature of 2000 to 3000°C. In addition, the above binary system (aggregate and binder pitch)
On the other hand, there is a one-component production method using bulk mesophase or mesocarbon microbeads (hereinafter referred to as MCB). Bulk mesophase is obtained by heat-treating petroleum-based or coal-based pitch in the range of 400 to 450°C, and has a fully developed optically anisotropic structure (liquid crystal), which is highly isotropic. It is used after being finely pulverized as a raw material for density carbon material (Japanese Unexamined Patent Publication No. 164604/1983). Since it maintains self-sintering properties, it fuses itself to each other when molded, so there is no need to add an adhesive such as a binder. Additionally, a method using MCB (Japanese Patent Laid-Open No. 49-2379) has been proposed. MCB
are small anisotropic spherules with a diameter of about 10 μm that are produced during the heat treatment process of various pitches, and are separated and purified by adding a large amount of solvent after the specified heat treatment. The MCB obtained by this method itself has an optically anisotropic structure, but since its shape is spherical, it is randomly oriented during molding, and the molded product has isotropy. Moreover, since MCB itself has self-sintering properties, a carbon material with desired isotropic properties can be obtained without using a binder. In addition, as an improved method, in order to improve the self-sintering property between each particle and to overcome the inhibition of high density due to point contact, when separating from the pitch, the β component consisting of the quinoline-soluble component of the heat-treated pitch is mainly removed. This β
It has been proposed to increase the density of carbon materials and improve their mechanical strength by attaching components such as carbon dioxide to the surface of MCB (Japanese Unexamined Patent Publication No. 62-41707). However, isotropic high-density carbon materials made from the above materials have the following problems. (1) Coke used as a binary filler has a large degree of development of optical anisotropy, so even if it is pulverized, the development of anisotropy will not be lower than the size of the pulverized particles. Therefore, in order to ensure isotropy in properties, it must be pulverized into a very fine powder, which results in an expensive product. Furthermore, the amount of binder required during firing is correspondingly large, making it difficult to achieve high density. Furthermore, in binary systems, there is a large difference in the properties of the filler and matrix.
There are limits to isotropy at the microscopic level. (2) When bulk mesophase is used, it is self-sintering, so there is no need to add a binder, but the anisotropy does not develop below the finely pulverized particle size, and the product charcoal In order to make the material isotropic, it is necessary to pulverize it according to the degree of isotropy. (3) Recently, mesocarbon microbeads (MCB) in particular have been in the spotlight as an excellent raw material with self-sintering properties, but they have an optically anisotropic structure.
Because it is uniformly spread throughout the MCB particles,
Similar to (1) and (2), the isotropic properties of the obtained product cannot be expected if the particle size of the MCB contained in the product is less than (approximately 10 to 20 μm). In the case of MCB, as far as ordinary heat treatment is concerned, the yield is at most about 15% by weight based on the raw material pitch, and in order to isolate MCB, pitch containing MCB is
It has the disadvantage that more than 200 parts by weight of solvent must be used per 100 parts by weight, and it is expensive as a raw material for isotropic high-density carbon material, so it is not a very suitable process from an industrial perspective. . On the other hand, carbon fiber composite materials (hereinafter referred to as
c/c composite) is used.
C/C composites are manufactured using carbon fiber as a filler and resin or binder pitch as a matrix. High-strength, high-elasticity, and regular carbon fibers are used as fillers, and the types of starting materials vary.
The main materials are PAN, pitch, and rayon.
In addition, it is used in the form of tow-like long fibers or felt-like short fibers. The general FRP molding method is used to make molded objects using long fibers, and prepreg is created by impregnating a sheet or fabric with fibers aligned in a uniaxial direction with a binder such as resin. There are a method of laminating and press forming, and a method of winding fibers using a filament winding method and curing them by heating. Further, there is a method of creating a multidimensional interwoven fabric having three or more dimensions, and impregnating and curing the fabric with a resin. When short fibers are used, they are opened and then mixed with a matrix resin by an injection method or a spray method. on the other hand,
As the matrix, thermosetting resins such as phenol resins and furan resins are often used, and epoxy resins such as polyphenylene and polyimide are also being considered. In addition, pitch is often used as a matrix that has a high carbon yield and is inexpensive. After adding the above-mentioned resin and pitch as a matrix, the matrix resin is usually treated at about 1000° C. in an inert atmosphere to carbonize the matrix resin. However, since the carbonization yield of the matrix resin is at most 50 to 60% by weight, this alone results in the c/c composite having a low density of 1.2 to 1.3. Therefore, in order to improve this density, pitch impregnation and carbonization treatment are repeated in the impregnation process. As a result, a product with a density of 1.7 to 1.8 g/cm ³ is finally obtained. As a method to increase this density, impregnation methods such as CVD and high-pressure carbonization methods are being implemented.
In the CVD method, a technology has been developed that effectively impregnates the inside of the sample by creating a temperature and pressure gradient inside the sample (WV Kotlemsky
“Chemistry and Physics of Carbon “9174
(1973)). Furthermore, as part of the effort to improve the carbonization yield, efforts have been made to uniformly disperse carbon fine powder with electrodeposition and self-sintering properties into the carbon fiber base material. However, the c/c composite has the following problems. Commonly used thermosetting resins such as phenolic resins have a carbonization yield of at most 50 to 60% by weight, which alone results in a density of only 1.2 to 1.3. For this reason, the impregnation treatment and carbonization must be repeated 4 to 5 times or more. Furthermore, the matrix obtained by carbonizing the above-mentioned phenolic resin has problems such as very large shrinkage, which makes it easy for fibers to come out and cracks to occur in the matrix. Since such a phenolic resin matrix has high hardness, it has low mechanical impact resistance and is brittle. Furthermore, since the carbonized structure is isotropic, the degree of damage caused by various chemical reactivity or neutron ions is high. Further, there is a method using petroleum-based or coal-based pitch, but this method has the disadvantage that the pitch flows out when hot forming is performed because it is not thermosetting. Furthermore, the carbonized structure exhibits a highly developed optically anisotropic structure. Therefore, there is a drawback that cracks generated when using the manufactured C/C composite propagate along the developed anisotropic structure. Additionally, special carbon raw materials have been developed for use in carbon/graphite electrodes such as UHP electrodes for steelmaking. This special carbon raw material is required to have a high degree of heat resistance and mechanical shock resistance in the extremely severe and high current density of electrodes used in steelmaking arc furnaces among various electrode materials. In particular, with recent advances in electric steel manufacturing technology including UHP operations, the required characteristics for electrode products have become increasingly severe. The manufacturing method for carbon/graphite electrodes is simply explained by mixing a filler such as petroleum coke and a binder such as pitch, forming the mixture into a predetermined shape, and then heat-treating it to carbon/graphitize the product. make.
Unlike CIP, which is used for isotropic high-density carbon materials, molding is performed by extrusion or mold filling. Because approximately 30 to 40% by weight of the binder is volatilized during the firing and carbonization process, and because open pores exist in the filler coke particles, pitch is impregnated and re-fired. However, manufacturing carbon/graphite electrodes has the following problems. That is, the yield of the binder used is at most 60 to 70% by weight, and after carbonization or graphitization, it is necessary to repeat impregnation and carbonization again. Furthermore, since the carbonized structure exhibits a highly developed optically anisotropic structure, there is a drawback that cracks generated when using the manufactured electrode propagate along the anisotropic structure. The present invention has been made in view of these points, and provides a self-sintering raw material for isotropic high-density carbon material, C/
C raw material for composite matrix, or
The present invention provides a method for producing pitch fine particles having a fine anisotropic structure that is extremely useful as a binder raw material for carbon/graphite electrodes such as UHP electrodes. [Means for Solving the Problems] In order to solve the above problems, the present invention provides the first
In this embodiment, the raw material pitch is heat-treated until the optically anisotropic structure becomes 20% by volume or more, and then this is atomized with an inert gas to form fine particles with an average particle size of 1 to 300 μm, and the fine particles are In a second aspect, there is provided a method for producing pitch fine particles having a fine optically anisotropic structure, which is characterized by subjecting Pitch fine particles to an infusible treatment to an extent that does not impair self-sintering properties, and in a second aspect,
The hydrogenated pitch obtained by hydrogenating the raw material pitch is heat-treated until the optically anisotropic structure becomes 20% by volume or more, and then it is sprayed with an inert gas to obtain an average particle size of 1 to 300μ.
Provided is a method for producing pitch fine grains having a fine optically anisotropic structure, characterized in that the fine grains are made into fine grains having a diameter of m, and the fine grains are treated to be infusible to an extent that does not impair self-sintering properties. The pitch fine particles obtained by this invention have a fine optically anisotropic structure in which fine optically anisotropic structures are randomly arranged. This invention will be explained in more detail below. As mentioned above, the pitch fine particles of the present invention have a structure in which fine optically anisotropic structures smaller than the diameter of the pitch fine particles are randomly arranged in the pitch matrix. have. The size of this optically anisotropic structure is
Usually, it is 1 μm or less. The average particle diameter of the fine particles of this invention is generally 1 to 1.
The thickness is 300 μm, preferably 1 to 50 μm. Preferably, the fine particles are substantially spherical. According to the first aspect of the present invention, in order to produce the pitch fine particles, the optically anisotropic structure content is
A raw material pitch prepared to a volume of 20% or more is sprayed in an inert gas. As the pitch, any pitch such as coal tar pitch or petroleum pitch can be used. By heat-treating this pitch at a temperature of about 350° C. to about 500° C. in an inert gas atmosphere or while blowing inert gas, the optically anisotropic structure content can be adjusted to 20% by volume or more. The raw material pitch with the optically anisotropic structure content adjusted as described above is placed in a preheating tank and stirred to uniformly mix the bulk mesophase exhibiting an optically anisotropic structure and the isotropic matrix. After that, it is sprayed using a known two-fluid nozzle or the like. In the method of the second particularly preferred embodiment of the present invention, in producing pitch fine particles, raw pitch made from hydrogenated pitch and having an optically anisotropic structure content of 20% by volume or more is heated with an inert gas. Spray. In order to obtain a high-density, high-strength carbon material, it is preferable to use raw materials with extremely high anisotropy, but if the optically anisotropic structure content is increased too much,
The viscosity of the pitch during spraying becomes high, making it difficult to form fine particles, and in some cases, the particles may not become spherical but have a distorted shape or become fibrous. In particular, when atomizing particles by spraying, it may be difficult to randomly arrange optically anisotropic structural parts and optically isotropic parts. In some cases, the optically anisotropic portion may form fine grains that stand up like floating islands. This is not preferable in producing an isotropic high-density carbon material. In other words, when fine grains in which the fine optically anisotropic structure does not develop randomly and the anisotropic structure stands up like a floating island are used as a raw material for an isotropic high-density carbon material, floating islands with an anisotropic structure Some parts remain in the carbon material molded product, and the micro parts do not show isotropy, impeding uniformity. For example, when considering use as an electrode for electrical discharge machining, uniform discharge does not occur and the machined surface becomes rough. It has a negative impact on the degree. Furthermore, when carbonized and fired, localized isotropic matrix portions may be thermally decomposed and unevenly distributed pores may be generated. Therefore, the obtained isotropic high-density carbon material may not have high strength. In addition, if the shape of the pitch fine particles used is not spherical and contains short fibers, the filling properties will be poor, and when carbonized and fired, each particle may have a different shrinkage rate, making it easier to crack. . On the other hand, as in the method according to the second aspect, if hydrogenated pitch is used as the raw material pitch and the optically anisotropic structure content is 20% or more by volume, the pitch is not hydrogenated. In comparison, a bulk mesophase-containing pitch having a high content of optically anisotropic structure and a low viscosity can be obtained. This bulk mesophase-containing pitch has a low viscosity, so
By stirring in the preheating tank for spraying, the bulk mesophase and the isotropic matrix are sufficiently mixed, and short fibers are not formed by spraying, and a fine optically anisotropic structure is formed. Spherical fine particles randomly spread and arranged are almost completely obtained, and the above-mentioned problems can be solved. The pitch used here before hydrogenation is the same as in the method according to the first embodiment. Hydrogenation may be carried out by either a method using a catalyst or a method using a solvent. In either method, it is desirable to carry out hydrogenation to such an extent that the hydrogen content of the product pitch increases within the range of 0.1 to 0.5% of the hydrogen content of the raw material pitch. In order to adjust the content of the optically anisotropic structure, the hydrogenated pitch is heat treated in the same manner as in the method according to the first aspect, but in this case as well, the content of the optically anisotropic structure is It may be 20% by volume or more. Spraying can be performed in the same manner as in the method according to the first aspect. Pitch fine particles obtained by any of the above methods are subjected to infusibility treatment in order to fix the fine optically anisotropic structure. This infusibility can be achieved by oxidation treatment or solvent extraction treatment. In either case, the infusibility treatment is carried out to the extent that the self-sintering properties of the pitch fine particles are not impaired. The oxidizing agent used in the infusibility treatment may be a gaseous oxidizing agent such as air, or a liquid oxidizing agent such as nitric acid. Further, as the solvent used for the infusibility treatment, quinoline, a mixed solution of quinoline and toluene, a coal-based heavy oil fraction such as anthracene oil, a petroleum-based heavy oil fraction, etc. can be used. The pitch fine particles of this invention obtained in this way are:
Raw materials for isotropic high-density carbon materials used as electrode materials for electrical discharge machining, crucibles for aluminum evaporation, and wall materials for nuclear fusion reactors, and carbon-carbon used as nose cones for spacecraft, rocket nozzles, brake materials, etc. Matrix raw materials for fiber composite materials (C/C composites), and UHP for steel manufacturing
It can be applied to special carbon materials used in carbon/graphite electrodes, etc., and can provide carbon materials that are more homogeneous, dense, high strength, and high density than conventional ones. [Examples] Examples of the present invention will be described below. Example 1 1 kg of pitch with optically anisotropic structure content of 70% by volume
On the other hand, fine particles with a fine optically anisotropic structure were produced by spraying nitrogen gas at a ratio of 2Nm ³ , and then the self-sintering property was controlled by an infusibility treatment. This was molded at 3T/cm ² using a cold isostatic pressure machine, resulting in a density of 1.37/cm ³ , a diameter of 62 mm, and a length of 52 mm.
A cylindrical molded body with a diameter of mm was obtained. This molded body was heated from room temperature to 900°C at a heating rate of 6°C/hour, and allowed to cool naturally. When the obtained molded body was heated from room temperature to 2200°C at a rate of 0.5°C/min and graphitized,
A graphitized product with a density of 1.96 g/cm ³ was obtained. The bending strength of the obtained product is 1000Kg/cm ² and the electrical resistance is
It was 1.7×10 ^-3 Ωcm. Further, when the structure of the product was observed using an optical microscope, it was found that microscopic particles 1 having an anisotropy size of about 1 μm were scattered as shown in FIG. In addition, the isotropic ratio was 1.01 or less when viewed from the electrical resistance value. Example 2 The microparticles obtained in Example 1 were used as a matrix,
It was laminated with PAN-based carbon fiber fabric and molded at high temperature.
When this molded product was impregnated and carbonized 4 times using pitch, the density was 1.98 g/cm ³ and the bending strength was 1500 kg/cm 3 .
A C/C composite of cm ² (CF content 34% by volume) was obtained. Comparative Example 1 A coal-based pitch with a softening point of 120°C was heated to 460°C and held for 20 minutes to form optically anisotropic microspheres (MCBs).
appeared. In order to separate the anisotropic spherules, the resulting heat-treated pitch was diluted with 200 parts by weight of a coal-based solvent (boiling point 370-538°C). A mixture of diluted pitch and solvent was applied to a heated centrifuge to separate MCB. The yield was 5 parts by weight based on 100 weight feed pitches. When this MCB was molded at 3T/cm ² using a cold isostatic pressure device, a cylindrical molded body with a diameter of 64 mm and a length of 56 mm and a density of 1.34 g/cm ³ was obtained. When this molded body was carbonized and graphitized under the same conditions as in Example 1, a product with a density of 1.80 g/cm ³ was obtained. The bending strength of the obtained product is 877Kg/cm ²
The electrical resistance value was 1.42×10 ^-3 Ωcm. In addition, when the structure of the product was observed using an optical microscope, the anisotropy of the scattered fine particles was 20μ as shown in Figure 2.
It was larger than m. Comparative Example 2 In Example 2, instead of fine particles, carbonization yield of 85
%, using a pitch binder with a softening point of 300℃,
Similarly, the density of the C/C composite obtained by performing high-temperature molding and impregnation and carbonization four times was 1.69.
g/cm ³ , and the bending strength was 900 Kg/cm ³ (CF content: 31% by volume). In comparison, Example 2 using microparticles had better shrinkage and substantially higher CF content. Example 3 Coal tar pitch was heat-treated to a softening point of 300°C.
A bulk mesophase-containing pitch (BP) with an optically anisotropic structure content of 70% by volume was prepared. This BP was atomized with nitrogen gas to obtain fine particles with an average particle size of 10 μm. When these fine particles were observed using an optical polarization microscope, it was found that fine optical anisotropic structures of 1 μm or less were randomly developed in each of the fine particles. The fine particles were treated to be infusible in air. In addition, infusible fine particles with a diameter of 100 mm and a length of
It was placed in a 150 mm rubber bag and molded by cold isostatic pressing (CIP) at a pressure of 1 ton/cm ² . The density of the obtained molded product was 1.34 g/cm ³ . This molded product was carbonized by increasing the temperature to 1000℃ at a rate of 6℃/hour, and then to 2000℃ at a rate of 30℃/hour.
Graphitization treatment was performed by raising the temperature to . The obtained graphitized molded body A had a diameter of about 60 mm and a length of 40 mm. The properties of this graphitized compact are shown in Table 1 below. Comparative Example 3 For comparison, needle coke finely pulverized to 10 μm and a binder were mixed at a needle coke:binder = 60:40 (weight ratio), and subjected to CIP molding, carbonization treatment, and graphitization under the same conditions as in Example 3. I processed it. As a result, a graphitized molded body B having a diameter of 50 mm and a length of 30 mm was obtained. Table 1 shows the properties of this molded body B.
Also listed in

[Table] In addition, when graphitized molded products A and B were compared under a microscope, molded product A had almost no voids, with a diameter of 1 μm.
A fine optically anisotropic structure develops in the molded body B, whereas the optically anisotropic structure in the molded body B has the largest size.
It was large at 10 μm and had many pores. Comparative Example 4 Thermal reforming was carried out at 350°C while blowing nitrogen gas into medium pitch (softening point: 87°C) for 3 hours. The resulting heat-treated pitch was optically isotropic. This pitch was atomized with nitrogen gas to obtain fine particles with an average particle size of 10 μm. When this particulate material was observed with an optical polarization microscope, it was not possible to observe a situation in which a fine anisotropic structure was randomly developed as in the particulate material of Example 3, but instead, mesophase spherules were scattered. It was observed that there were. The fine particles were subjected to infusibility treatment in air for 0.2 and 6 hours, respectively. Each infusible fine particle was subjected to CIP molding, carbonization treatment, and graphitization treatment in the same manner as in Example 3 to obtain graphitized molded bodies (C, D, E). The properties of these graphitized molded bodies are shown in Table 2 below.

[Table] Example 4 Catalytically hydrogenated coal tar pitch (softening point
150℃) was heat-treated at a reaction temperature of 440℃ while blowing nitrogen to prepare a bulk mesophase-containing pitch with an optically anisotropic structure content of 70%.This bulk mesophase-containing pitch was preheated, This was sprayed with heated nitrogen gas using a two-fluid nozzle.
In this way, spherical pitch fine particles (average particle size 10 μm) in which a fine optically anisotropic structure was randomly developed were obtained. The pitch fine particles were treated to be infusible using air as an oxidizing agent, and the structure thereof was fixed. The oxidized pitch fine particles were subjected to CIP molding at 3T/cm ² to obtain a molded product with a diameter of 50 mm and a length of 50 mm. The temperature of this molded body was raised to 1000°C at a rate of 6°C/hour, and then the temperature was raised to 2200°C by high-frequency heating to graphitize it. The bending strength of this graphitized compact was 1200 Kg/cm ² . Furthermore, the density was 1.97 g/cm ³ , and a high-strength, high-density isotropic carbon material was obtained. Example 5 Solvent hydrogenated petroleum pitch (softening point 120°C) was heat treated at a reaction temperature of 420°C in a nitrogen gas atmosphere,
A bulk mesophase containing pit with an optically anisotropic structure content of 60% by volume was prepared. This pitch was sprayed and treated to be infusible in the same manner as in Example 4 to obtain fine particles in which a fine optically anisotropic structure was randomly developed. Using this infusible Pitschi fine particles,
CIP molding was performed at 2T/cm ² to obtain a molded product with a diameter of 50 mm and a length of 50 mm. The temperature of this molded body was raised to 1000°C at a rate of 6°C/hour, and then the temperature was raised to 2200°C by high-frequency heating to graphitize it. The bending strength of this graphitized compact was 1000 Kg/cm ² . Furthermore, the density was 1.93 g/cm ³ , and a high-strength, high-density isotropic carbon material was obtained. [Effects of the Invention] According to the invention described above, the following effects are achieved. (1) By applying the fine particles of the present invention as a raw material for isotropic high-density carbon material, it is possible to achieve a high degree of isotropy in the properties of the product, and to expand the range of applications as electrodes for electrical discharge machining. (2) When the fine particles of the present invention are applied to the matrix of a C/C composite, the carbonized structure of the matrix has an optically fine anisotropic structure, so it is possible to suppress the propagation of cracks and increase the A C/C composite with high strength and high toughness can be produced. Furthermore, the carbonization yield is higher than that of ordinary binder pitch and resin, with a carbonization yield of 92% by weight at 1000℃.
It has been confirmed that it can be obtained by heat treatment. (3) By using the fine particles of the present invention as a binder pitch raw material in the manufacturing process of carbon/graphite electrodes such as UHP electrodes, the development of the optically anisotropic structure of the matrix can be made finer. , the mechanical strength of the product electrode can be improved. Furthermore, the carbonization yield can be increased. (4) In particular, according to the method for producing pitchi fine particles of the present invention using hydrogenated pitch as a raw material, pitchi fine particles in which a fine optically anisotropic structure is randomly developed can be made into a substantially spherical shape. It can be manufactured efficiently.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are explanatory diagrams showing the magnitude of anisotropy of microparticles of pitch microparticles. 1, 2...Minute particles.

Claims (1)

[Claims] 1. A raw material pitch is heat-treated until the optically anisotropic structure becomes 20% by volume or more, and then atomized with an inert gas to form fine particles with an average particle size of 1 to 300 μm,
A method for producing pitch fine particles having a fine optically anisotropic structure, which further comprises subjecting the fine particles to an infusible treatment to an extent that does not impair self-sintering properties. 2. Hydrogenated raw material pitch is heat-treated until the optically anisotropic structure becomes 20% by volume or more, and then it is sprayed with an inert gas to reduce the average particle size to 1 to 10% by volume.
A method for producing pitch fine particles having a fine optically anisotropic structure, characterized by forming fine particles with a diameter of 300 μm, and further subjecting the fine particles to an infusible treatment to an extent that does not impair self-sintering properties.