JPH0456789B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Fields> This invention can be used in wear-resistant materials such as disc brake materials for aircraft and automobiles, sliding materials such as bearings, abrasion materials such as rocket nozzles, or molds for hot presses. The present invention relates to a method for manufacturing a carbon fiber/carbon composite material that exhibits excellent performance. <Prior art and its problems> Carbon fiber/carbon composites (hereinafter referred to as "C/C composites"), which are lightweight, have high strength, and have excellent wear resistance and lubricity, are now used as spacecraft components. It has become indispensable as an automobile component, medical material, etc., but carbonization of a composite material of carbon fiber and thermosetting resin (CFRP) is generally used to manufacture it. There is. However, when thermosetting resin is carbonized, the carbonization yield is only about 50%, and therefore, simply carbonizing a composite material of carbon fiber and thermosetting resin will cause the matrix after carbonization to have pores and cracks. Since the C/C composite material has a large amount of C/C and cannot secure the desired strength, when manufacturing the C/C composite material according to the above method, densification treatment such as repeating "pitch impregnation-recarbonization" is necessary. It had been. For this reason, the above-mentioned conventional manufacturing method for C/C composite materials has a problem in that the manufacturing process is extremely complicated, resulting in poor production efficiency and, therefore, the product price is extremely high. However, this method could not be said to be an industrially preferable method. Meanwhile, in light of this situation, C/C
Regarding the production of composite materials, there is a possibility of a new method that incorporates the method of ``using pitch and coke powder as a matrix material, mixing it with carbon fiber, and pressurizing and heat forming it at a semi-carbonization temperature of about 500 degrees Celsius.'' The results of the study have also been reported (“Iron and Steel”).
No.5, VOL.72, MAR.1986, page 306). and,
The carbonization yield after pressurizing and heat forming the pitch component is 90%.
It is expected that the above method will yield a matrix with few pores and cracks, and a C/C composite material with relatively good strength will be produced without any special densification treatment. It was expected. However, the C/C composite material obtained by the method reported in this new report can only achieve a strength of 800 kg/cm 2 at most, which is lower than the 1000 to 2000 kg/cm <sup>2</sup> strength of commercially available high-performance C/C composite materials. The reality is that it still falls short of cm <sup>2</sup> . <Means for solving the problem> From the above-mentioned viewpoint, the present inventors have developed a method for bending,
In order to provide a method that can stably produce high-density C/C composite materials on an industrial scale that have excellent tensile, compressive, and shear strengths and other physical properties such as wear resistance, we particularly aim to improve the carbonization yield. Because this method does not use a thermosetting resin with a low carbon content, expectations tend to arise that there may still be room to obtain a sufficiently satisfactory high-density, high-strength C/C composite material through ingenuity. Focusing on the above-mentioned "method for manufacturing C/C composite materials reported in 'Tetsu to Hagane'," we first investigated the reason why C/C composite materials manufactured by this method do not exhibit as high strength as expected. As a result of research aimed at elucidating the issue, we found the following:
This led to the findings shown in (a) to (f).
That is, (a) When a molded material made of a mixture of pitch, aggregate such as coke powder, and carbon fiber is heated under pressure, the pitch becomes molten, but at this time, the molded body melts due to the molding pressure. Since the carbon fibers and coke powder are compacted until they come into contact with each other, excess pitch flows out of the system, and there is no excess or deficiency of pitch.
However, in order to complete the pressurization and heat molding of the molding material, it is necessary to heat it to a higher temperature. However, when such a high-temperature area is heated, pitches generally decompose and generate gas, and the pitches that maintained a quantitative balance due to the gas pressure of this generated gas are further pushed out of the system, and the pitches that flow out are Pores are generated in the molded body by the volume,
This may cause a decrease in the strength of C/C composite products. (b) The amount of decomposition gas generated increases as the volatile content of the pitch increases, so the higher the volatile content of pitch is used, the more porous the molded product becomes, and the C/C composite material obtained accordingly. decrease in strength. (c) However, in 4 above, “Manufacturing method of C/C composite material reported in “Tetsu to Hagane””, the technical paper ““Prototype production of carbon material using bulk mesophase as binder”” by the same reporter is mentioned. (“Carbon” 1985, No.
123, pp. 150-159) states that ``pitch with a volatile content of 30% or more is good'', the use of pitch with a high volatile content is a prerequisite. This is thought to be a major obstacle in obtaining a C/C composite material with the desired strength. (d) Therefore, if a pitch with a low volatile content is used, the C/C strength should be improved. Nevertheless, the technical paper published in the serial "Carbon" states that "the strength decreases when the volatile content in pitch is low." The pituti used contains more than 80% quinoline insoluble matter,
Pitch with this composition has poor meltability (softening properties), so it does not have good adhesion to carbon fibers or coke powder, and it is assumed that this is why it was not possible to achieve sufficient product strength. (e) For this reason, when manufacturing a C/C composite material using a composition consisting of carbon fiber, aggregate such as coke powder, and pitch as a molding material,
We concluded that by using pitch with a low volatile content and good meltability, it is possible to stably manufacture dense C/C composites with sufficient strength without the need for complicated processes. To be done. (f) Pitch with low volatile content and excellent meltability as described above can be easily obtained by heat treating tar or pitch under reduced pressure or while blowing water or gas ( _N2 gas, etc.). thing. This invention was made based on the above knowledge, and uses carbon fiber, finely powdered carbonaceous aggregate, and volatile matter.
By pressurizing and heat-forming a molding material made of binder pitch with a binder pitch of 28% or less and a softening point of 400℃ or less, and then carbonizing or graphitizing it, it is possible to create a molded material with high density and strength without the need for troublesome processing or operations. It is characterized by the ability to stably mass-produce carbon fiber-reinforced carbon materials with excellent wear resistance and wear resistance. The carbon fiber used may be either high-performance grade or general-purpose grade, with high-performance grade products used as structural materials and general-purpose grade products used as wear-resistant materials and sliding materials. It is appropriate to use them in different ways. Further, as the form of the carbon fiber, any of textiles, prepreg-like unidirectional fibers, short fiber-like chops, etc. may be adopted. The carbonaceous aggregate plays the role of suppressing the shrinkage of the matrix and reducing the occurrence of cracks in the matrix during carbonization of the molding material, and is a carbon powder that has been traditionally used in the production of C/C composite materials. Any of carbon black, graphite, etc. can be used. Although the particle size is not particularly limited, if the particle size exceeds 20μ, cracks are likely to occur in the matrix of aggregate and pitch after carbonization of the composite, so it is preferable to use Umizer etc. It is best to use particles with a particle size of 20μ or less (for example, particles with a particle size of 5 to 15μ) that have been finely pulverized in a process. The blending amount thereof is preferably at least 20% by weight based on the total matrix. By the way, as mentioned above, the binder pitch used in this invention must have a volatile content of 28% or less (preferably 10 to 28%) and a softening point of 400°C or less. This is because if the volatile content exceeds 28%, as mentioned above, the amount of decomposed gas generated during pressurization and heat molding increases, causing the matrix to become porous, making it difficult to achieve the desired strength properties of the product. On the other hand, if the softening point exceeds 400°C, it will not show sufficient fluidity during pressure/heat molding and will have poor adhesion to carbon fibers and carbonaceous aggregates. This is because it is not possible to obtain a C/C composite material of Here, the volatile content of the binder pitch is
This value was measured according to JIS8812, and this value indicates the amount of components that volatilize during carbonization. Further, the softening point is measured using a Koka type flow tester, and the measuring method is as follows. That is, fine powder pitch was packed into a cylinder with a cross-sectional area of 1 cm ² and a nozzle of 1 mm diameter at the bottom, and was pressurized from the top with a plunger at a pressure of 10 kg/cm ² .
This method raises the temperature at °C/hr and measures the displacement of the plunger. The softening point here can be defined as "the temperature at which the plunger stops moving after it starts moving due to softening and deformation of the pitch." The physical meaning of the softening point can be said to be "the temperature at which the softened and deformed pitches finish filling the initially existing voids." In this way, pitch that exhibits good melting properties even with a volatile content of 30% or less can be used, for example, for tar or pitch.
It can be easily obtained by heat treatment of heating to a temperature of about 380 to 550°C under reduced pressure of 100 Torr or less and holding it for an appropriate time. In other words, if the atmosphere is reduced in pressure when heat treating tar or pitch, low molecular weight components will be smoothly removed and the raw material composition will become more homogeneous. It shows much better meltability than heat treatment. The degree of pressure reduction at this time must be 100 Torr or less.
A pressure higher than this is not suitable because the effect of improving the pitch's meltability is small. In addition, the heat treatment temperature is 380℃.
If the heat treatment temperature is below 550°C, the reduction in volatile content due to the thermal decomposition reaction of the binder will be slow, which is undesirable. On the other hand, if the heat treatment temperature exceeds 550°C, the thermal decomposition reaction rate will become excessive and difficult to control. When adjusting the heat treatment temperature, the temperature is 380~
It is best to set the temperature to 550℃. In addition to the method of heat treatment under reduced pressure as described above, it is also possible to adopt a method of heat treatment while blowing steam or gas ( _N2 gas, etc.) under atmospheric pressure or reduced pressure to achieve a good result with a low volatile content. Pitch exhibiting melting properties can be obtained. Now, the mixing and dispersion adjustment of the molding materials used in the method of this invention may be carried out as follows. That is, when carbon fibers in the form of fabrics or unidirectional fibers are used, it is preferable to immerse the carbon fibers in a solution in which carbonaceous aggregate powder and binder pitch are dispersed. In this case, the dispersion contains
These solid powders and carbon fibers have good wettability, such as acetone, ethanol, methanol,
A solution of [water + surfactant] or a mixture of these and a resin can be used. By employing such means, the solid component blends well with the carbon fibers and adheres to them with a uniform thickness, making it possible to produce a molded article with a high carbon fiber content. Then, the carbon fibers to which the matrix material is attached as described above are laminated and then pressurized and heat-molded. In addition, when using chop-shaped short fibers as carbon fibers, it is possible to achieve satisfactory results by using a general mixing method in which the fibers and matrix powder are blended and then dry-mixed using a mixer such as a V-type blender. results. The molding materials laminated or mixed as above are
Next, the material is pressurized and heated as it is or after preforming, but it is preferable to use a two-step process as shown below for the pressurized and heated forming means. That is, first, no pressure or low pressure (20Kg/
cm ² or less) at a heating rate of 1 to 50℃/min to a temperature above which the pitch softens and flows, and once this temperature range is reached, increase the pressure to 40Kg/cm ² or more, Furthermore, temperature increase rate: 1 to 20℃/min at 450℃, which is the temperature range in which pitches actively undergo thermal decomposition reactions.
This method involves raising the temperature to around 600°C and pressurizing and holding until the pitch is sufficiently solidified. The pressurized and heated molded product thus obtained is heated in an inert gas atmosphere at a rate of temperature increase:
It is heated at 1 to 100°C/hr to be carbonized or graphitized. According to the method of this invention as described above, it has a high apparent density of 1.5 to 1.7 g/cm ³ even without special densification treatment, which is much higher than that of conventional C/C composite materials. Stable production of C/C composite material with strength (approximately 1000 kg/cm ² when using general-purpose grade carbon fiber, and approximately 2000 kg/cm ² when using high-performance grade carbon fiber) However, the present invention will be specifically explained below with reference to Examples. <Examples> Example 1 4 kg of coal tar was charged into a glass separable flask with an internal volume of 5, and heat treated under the conditions shown in Table 1 to prepare binder pitches with different volatile content ranks. On the other hand, petroleum coke was heated at a temperature of 1000°C to carbonize it, and then finely pulverized using a userizer to prepare coke powder with an average particle size of 11μ. Next, for each of the above binder pitches with different volatile contents, 70 parts of the binder pitches pulverized to 100 mesh or less and 30 parts of coke powder were dispersed in 170 parts of ethanol, and in this dispersion, after washing with acetone, PAN-based carbon fiber fabric (high-strength yarn and filament count: 1000, dried and cut into 9.5 cm x 9.5 cm)
The coke powder and binder pitch were adhered to the coke powder and binder pitch by dipping the plain weave. Next, the matrix material was attached in this way, and then 30 sheets of the dried fabric were layered, and this was placed in a mold with an inner dimension of 10 cm square, and the heating rate:

【table】

【table】

[Table] The temperature was raised to 520°C at 5°C/min. Then, the mixture was kept at this temperature for 30 minutes and then cooled to obtain a molded article having the above dimensions. Next, these compacts are packed into coke powder.
Temperature increase rate: 1000℃ at 15℃/min in _N2 atmosphere
The temperature was raised to 100% to carbonize the material, resulting in a C/C composite material. Table 1 also shows the measurement results of the apparent density and bending strength of the C/C composite material thus obtained. As is clear from the results shown in Table 1, the C/C composite material manufactured according to the conditions of the present invention has a high density and a bending strength of 1500 kg/cm ² or more. I know that there is. Example 2 The same binder pitch and coke powder as in Example 1 were prepared, and general-purpose grade carbon fiber with fiber length: 0.7 mm (thread strength: 70 Kg/cm ² , thread diameter:
18μ) and blending ratio (weight ratio) Binder pitch: Coke powder: Carbon fiber = 25 parts: 25 parts: 50 parts After mixing thoroughly,
100 g was charged into the same mold as in Example 1, molded under the same molding conditions as in Example 1, and then carbonized under the same carbonization conditions as in Example 1. Table 2 shows the measurement results of the apparent density and bending strength of the C/C composite material thus obtained. As is clear from the results shown in Table 2,
It can be seen that the C/C composite material manufactured according to the conditions of the present invention has high density and exhibits high strength even when general-purpose grade chopped carbon fibers are used. Example 3 2 kg of coal tar was charged into a glass separable flask with an internal volume of 5, and the volatile content in the resulting pitch was heated at 450°C and under each pressure shown in Table 3. ]%, the binder pitch was adjusted. The binder pitch obtained in this way,
Using the same coke powder and carbon fiber as in Example 1, C/C was also carried out under the same conditions as in Example 1.
A composite material was manufactured.

[Table] Table 3 shows the measurement results of the apparent density and bending strength of the C/C composite material manufactured in this way, and these results also indicate that the C/C composite material manufactured according to the conditions of the present invention was It can be seen that the C/C composite material has high density and exhibits high strength. Example 4 4 kg of straight asphalt was charged into a glass separable flask with an internal volume of 5, and the temperature was raised to 440°C at a heating rate of 5°C/min. A stainless steel tube with an inner diameter of 3 mmφ was placed in the asphalt liquid. 5g/min of steam preheated to 500℃ through
When heat-treated for 2 hours while blowing in powder, pitch was obtained with a volatile content of 22% and a softening point of 330℃.
The yield upon treatment was 24%. Next, 25 parts of binder pitch obtained by finely pulverizing the above pitch to 60 meshes or less, 35 parts of coke powder similar to that in Example 1, and general-purpose grade carbon with the same fiber length: 0.7 mm as in Example 2. After mixing with 40 parts of fiber (thread strength: 70 Kg/cm ² , thread diameter: 18 μm), the mixture was heated and pressed under the same conditions as in Example 2, and carbonized. When the apparent density and bending strength of the C/C composite material thus produced were measured, it was confirmed that the apparent density was 1.53 g/cm ² and the bending strength was 1020 Kg/cm ² . <Summary of Effects> As explained above, according to the present invention, it is possible to stably produce carbon fiber-reinforced carbon materials on an industrial scale that have high density and are superior in strength and other properties. Therefore, it is expected that the field of application of carbon fiber-reinforced carbon materials will further expand, and extremely useful effects will be brought about industrially.

Claims (1)

[Scope of Claims] 1 A molding material consisting of carbon fibers, finely powdered carbonaceous aggregate, and binder pitch with a volatile content of 28% or less and a softening point of 400°C or less is pressurized and heat-molded,
Characterized by subsequent carbonization or graphitization,
Method for manufacturing carbon fiber reinforced carbon material. 2. The method for producing a carbon fiber-reinforced carbon material according to claim 1, wherein the binder pitch used is obtained by heat-treating tar or pitch under reduced pressure of 100 Torr or less. 3. The binder pitch used is a carbon fiber-reinforced carbon material according to claim 1, which is obtained by heat-treating tar or pitch while blowing water or gas under atmospheric pressure or reduced pressure. Production method.