JPH0352426B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a carbon fiber reinforced carbon material. BACKGROUND ART A carbon fiber reinforced carbon material (hereinafter referred to as a C/C composite) is a composite material in which carbon fiber is used as a reinforcing material and carbon is used as a matrix. Because C/C composites are reinforced with carbon fiber, they have superior mechanical properties at room and high temperatures compared to conventional carbon materials, as well as superior friction and braking properties, thermal and electrical conductivity, and corrosion resistance. For this reason, it has become an indispensable material for spacecraft components such as rocket nozzles and aircraft brake discs. There are currently two main systems of manufacturing methods for C/C composites, which have a wide range of applications. One is to simply mold carbon fiber tow, cloth, felt, etc. obtained by carbonizing polyacrylonitrile, rayon, or pitch fiber.
This is a method in which the fibers are placed in a furnace and heated to 1000 to 1500°C, and hydrocarbon gas is introduced there to cause decomposition and carbonization, and carbon is deposited on the surface of the carbon fibers to form a C/C composite (hereinafter this method is referred to as the CVD method). ).
The CVD method has low productivity and requires a lot of time to obtain a desired density, and requires fairly advanced technology to obtain a uniform carbon material with few pores. The other is carbon fiber tow, cloth, felt, etc. obtained by carbonizing polyacrylonitrile, rayon, or pitch fiber, and prepreg impregnated with thermosetting resin, which is a raw material for carbon materials such as phenolic resin, is laminated. After applying pressure and heating to form a hardened molded body, carbonization treatment is performed in a non-oxidizing atmosphere, and if necessary, impregnation treatment and carbonization treatment are repeated to form a C/C composite. In addition to the two systems broadly classified above, the Pitsui family can also be considered as a matrix. However, since pitches are carbonized once they are in a liquid state, when a molded article in which pitches are laminated with carbon fiber tow, cloth, felt, etc. is carbonized, swelling occurs. In other words, the fibers spread out to form large pores, resulting in a lower density, and as a result, the strength of the C/C composite itself becomes weaker. Therefore, at present, pitches are often used for impregnation. Problems to be Solved by the Invention An object of the present invention is to produce a C/C composite exhibiting good properties by using pitches and carbonaceous powder as constituent raw materials for a matrix. Means for Solving the Problems The method of the present invention includes carbon fibers, pitches and carbonaceous powder are used as constituent raw materials of the matrix, and the ratio of the pitches and carbonaceous powder is 20 to 95% of the pitches.
A carbon material containing 5 to 80% by weight of carbonaceous powder is pre-molded, and the resulting molded body is molded with a fixing material such as a plate-shaped body or a formwork of metal, ceramics, graphite, C/C composite, etc. It is characterized in that it is carbonized by fixing to suppress swelling, and after the fixing material is removed, impregnation, carbonization, and graphitization are carried out as appropriate using conventional methods. Function Next, the content of the present invention will be explained in more detail. The reinforcing carbon fiber used in the present invention may be polyacrylonitrile-based, rayon-based, or pitch-based, and may also be carbonaceous or graphitic. The shape of carbon fiber is 0.05~
Either short fibers of about 50 mm or continuous fibers can be used. It may also be in the form of a sheet, such as cloth, felt, or mat. The carbon fibers may be oriented in completely random directions in the matrix as they are or in a defibrated state, or may be arranged in any specific direction. In addition, the raw material for the carbon material that becomes the matrix is a mixture of pitches such as impregnated pitch and binder pitch, and carbonaceous powder such as raw coke, graphite powder, and carbon black. Preferably, raw coke is used which is carbonized pitch and whose volatile content is adjusted because it is compatible with pitch and has a similar shrinkage rate during carbonization. In addition, the volatile content of the raw coke is preferably 3 to 10% so that the matrix shrinks best during carbonization.
%. A layered or mixed carbon fiber or carbon fiber structure and the matrix,
Press molding or the like is performed to form a molded body. In the molding material, it is desirable that the carbon fiber or carbon fiber structure is contained in an amount of 20 to 90% by weight, preferably 40 to 80% by weight. If the carbon fiber content is less than 20% by weight, the resulting C/C
There are too few reinforcing fibers in the composite, resulting in low strength. On the other hand, if it exceeds 90% by weight, the matrix content is too small, so the shear strength between the layers decreases, and the reinforcing effect of the carbon fibers is not sufficiently exerted. Further, the ratio of pitches and carbonaceous powder constituting the matrix is such that the pitches are 20 to 95% by weight and the carbonaceous powder is 5 to 80% by weight, and the volatile fraction, viscosity, etc. are adjusted. If the amount of piti is less than 20% by weight, the viscosity will increase and molding will be difficult. Moreover, if it exceeds 95% by weight, the viscosity decreases during carbonization and the matrix material flows out, resulting in a very weak interlaminar strength. More preferably, it contains 30 to 70% by weight of pithus. If the molded body is carbonized as it is, the gas produced by thermal decomposition will cause the molded body to swell when the pitches become liquid.
For example, a plate-shaped or mold-shaped fixing material made of a material such as ceramics, graphite, C/C composite, etc. that does not deform even at high temperatures during carbonization is fixed with bolts or the like, and the carbonization treatment is performed as it is. If the entire molded body is surrounded by a fixing material, there will be no place for the gas generated during carbonization to escape, so it is not necessary to completely surround the molded body, and it is recommended to provide at least an opening or an open part for gas to escape. It is essential. In addition, when laminating layers of carbon fibers, pitches, and carbonaceous powder, swelling occurs most noticeably in the direction of pressure during molding. It may be fixed so as to suppress directional swelling. When the molded body is a plate-shaped body or a rectangular parallelepiped, a plate-shaped body fixing material is used, and when the molded body is an odd-shaped body, a mold-shaped fixing material whose shape has been matched in advance is used to fix it. For example, if the molded object is cylindrical, it may be fixed using a frame-shaped fixing material as shown in FIG. After that, the molded body with the fixing material fixed using bolts etc. is placed in a non-oxidizing atmosphere such as nitrogen or argon for 600 minutes.
The desired C/C composite is obtained by carbonization and firing at a temperature of 1000°C or higher and 1500°C or lower. In this case, if the temperature increase rate during carbonization is too fast, the matrix material will shrink due to thermal decomposition and gas generation will be intense, making it easy for large cracks to occur. Therefore, it is desirable that the temperature increase rate is usually 100°C/hr or less, preferably 20°C/hr or less. The C/C composite thus obtained still has a fairly high porosity, and in order to obtain a high density, high strength C/C composite, this C/C composite is further impregnated with a pitch or carbonizable resin. Then, carbonization treatment is carried out again in a non-oxidizing atmosphere such as argon, or graphitization treatment is carried out in a non-oxidizing atmosphere such as argon, usually at a temperature of 1600 to 3000°C, preferably 2000 to 3000°C. This impregnation treatment, carbonization treatment, graphitization treatment is C/C
This can be carried out as appropriate depending on the characteristics of the intended use of the composite. The present invention will be described below with reference to Examples. Examples Example 1 50% by weight of pitch with an average particle size of 10 μm and a softening point of 240°C
and raw coke with an average particle size of 10 μm (volatile content 10%)
Mix 50% by weight at 270℃ using a kneader,
After that, the particle size of this mixture was adjusted to 100μm or less, and carbon fiber bundle cloth (satin weave) 120×120mm
25 layers are alternately stacked in a mold at a temperature of 300℃ and a pressure of
Press molding was performed at 100 Kg/cm ² to obtain a plate-shaped molded product measuring 120×120×9 tmm. Next, this molded body 1 was placed on a stainless steel plate (160×160×
It was sandwiched between fixing materials 2 (10 tmm) and fixed using bolts 3 as shown in Figure 2. This was done at a heating rate of 10℃/hr in a nitrogen atmosphere.
The temperature was raised to 600°C to carbonize the matrix. next,
After removing the fixing material, heat at 3℃/hr in a nitrogen atmosphere.
The temperature was raised to 1100° C. at a heating rate of 1,100° C. to obtain a C/C composite. Furthermore, in this C/C composite,
After the pitch for impregnation was impregnated at 200°C under vacuum, the temperature of this molded body was raised to 850°C at a rate of 10°C/hr in a nitrogen atmosphere to completely carbonize the impregnated pitch. Subsequently, this C/C composite was heated to 2000° C. in an argon atmosphere to graphitize it. Using an impregnating pitch for this graphitized C/C composite, the above carbonization step was further repeated twice and the graphitization step was repeated once to obtain a C/C composite product. Table 1 shows the density and strength test results of the obtained C/C composite product. The density was calculated by measuring the length, width, thickness, and weight.

[Table] Comparative Example 1 A molded body was produced under the same conditions as in Example 1, and then this molded body was carbonized under the same conditions as in Example 1 without being fixed with a fixing material. Determine the density before and after carbonization of Example 1 and Comparative Example 1,
It is shown in Table 2.

[Table] Comparative Example 1, which was not sandwiched, had a very low density after carbonization due to swelling. As in the case of Example 1, it is estimated that dozens of impregnation and carbonization treatments are required to increase the density to 1.67 g/cm ³ . Effects of the Invention As described above, according to the method of the present invention, it has become possible to produce a C/C composite having pitch as a matrix, which is currently not generally produced, without swelling during carbonization. In addition, since pitch has a high carbonization yield, a high-density product can be obtained even with fewer impregnation steps, so it also has the advantage of requiring fewer manufacturing steps. In addition, since a C/C composite product with high strength and excellent heat resistance can be obtained, it can be applied to process applications.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a frame-shaped fixing material for fixing a cylindrical molded body, and 1 is a plan view and 2 is a side view. Figure 2 shows the pre-formed carbon material (120×
120×9tmm) and two stainless steel bodies (160×160
1 is a plan view, and 2 is a side view. 1...Molded body, 2...Fixing material, 3...Bolt.

Claims (1)

[Claims] 1. A carbon material containing carbon fibers and consisting of pitches and carbonaceous powder, in which the ratio of pitches and carbonaceous powder is 20 to 95% by weight of pitches and 5 to 80% by weight of carbonaceous powder is preformed. A carbon fiber-reinforced carbon material characterized in that the obtained molded body is carbonized while being fixed with a fixing material, and then after the fixing material is removed, impregnation treatment, carbonization treatment, and graphitization treatment are performed as appropriate. Manufacturing method.