JPH0561223B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for manufacturing carbon fiber-reinforced carbon composite materials, and particularly to a method for manufacturing high-density carbon composite materials. <Prior art> A carbon composite material made of carbon as a matrix and reinforced with carbon fibers is called a carbon fiber reinforced carbon composite material (hereinafter referred to as C/C-composite).
This C/C-composite has excellent mechanical properties, heat resistance properties, corrosion resistance, friction, braking properties, etc., and these properties are used to manufacture space products such as rocket nozzles, space shuttle noses and leading edges, and aircraft brake discs. It is put into practical use as an aircraft equipment component. Recently, it has been put to practical use as a first wall material for nuclear reactors and fusion reactors, medical materials for bones, joints, etc., and turbine materials. There are various methods for manufacturing C/C-composites with such excellent properties, but carbon fiber tow, cloth, felt, etc. are impregnated with thermosetting resin such as phenolic resin to create prepreg. A common method is to create a molded body by laminating and curing. Furthermore, carbon fiber itself has extremely strong anisotropy, and the C/C-composite, which is a composite material using carbon fiber as a reinforcing material, has strong anisotropy, so it is necessary to alleviate this anisotropy. A commonly used method is to weave a three-dimensional fabric using tow, then impregnate it with a thermosetting resin such as phenolic resin, and then heat and harden it to obtain a molded article. As the matrix, thermosetting resins such as the above-mentioned phenols, epoxies, and furans, and thermoplastic resins such as coal-based and petroleum-based pitches are generally used. However, when thermosetting resin is used, although it has the advantage of being easy to shape, it is expensive, and furthermore, the process of impregnating carbon fiber with this resin and then heating and curing requires fairly strict temperature control. This process itself is complex and requires a great deal of effort and time. Furthermore, the true specific gravity of the carbide of this thermosetting resin is 1.4 to 1.5, which is smaller than the true specific gravity of the carbide of pitch, which is a thermoplastic resin, of 1.8 to 2.0, and when the thermosetting resin is used as a matrix, C/C. - There is a problem that the bulk density of the composite does not increase very much, resulting in poor mechanical properties. As a matrix, in addition to thermosetting resin,
Thermoplastic resins such as coal tar pitch or petroleum pitch can also be used. Although such pitches have the advantage of being cheaper than thermosetting resins and having a high true specific gravity of carbide, when pitches are heated under normal pressure, the carbonization yield is low, and pitches do not melt. Since carbonization occurs through phases, bubbling occurs during the carbonization process, and the pores generated at that time remain in the C/C-composite.
(Carbon, 1982, No. 109, P46). Conventionally, the bulk density of C/C-composites did not increase due to the presence of these pores (bulk density, 1.3 to 1.5 g/cm ³ );
There was a problem that mechanical strength was not achieved (bending strength of 7 to 10 Kg/mm ² ). Therefore, in order to increase the carbonization yield in carbonization, a pressure carbonization method is used, but in this case the pressure is 100 to 1000.
The pressure is as high as Kg/cm ² , and this equipment itself is special.
- There were problems in manufacturing the composite. In addition, in order to increase the bulk density of conventional C/C-composites, the process of impregnating them with thermosetting resin and mature plastic resin and further carbonizing them is usually repeated 8 to 15 times to increase the bulk density to 1.6 to 1.8 g. / ^cm3 . In this way, the densification treatment of C/C-composites (hereinafter referred to as densification treatment) usually requires repeating the impregnation-carbonization process 8 to 15 times, which requires a great deal of labor and time. and
C/C-composites have become very expensive. <Problems to ^be Solved by the Invention> The purpose of the present invention is to produce high-density C/C-
An object of the present invention is to provide an inexpensive manufacturing method for composites. <Means for Solving the Problems> The present invention impregnates two- or three-dimensionally oriented pitch-based carbon fibers with coal tar pitch and/or petroleum pitch, and then carbonizes the impregnated state. , then 2000 ~
Graphitization treatment is performed at 3000℃, and then densification treatment is performed to soften the graphitized material to a softening point of 150 to 250.
Impregnating coal tar pitch and/or petroleum pitch substantially free of quinoline insoluble matter at ℃,
This is a method for producing a high-density carbon fiber-reinforced carbon composite material, which is characterized by repeating a subsequent carbonization-graphitization process until a desired density is achieved. <Function> Next, the content of the present invention will be explained in more detail. The weaving methods of carbon fibers used in the production of C/C-composites are distinguished by the direction of fiber orientation: (1) two-dimensional orientation of the fibers, such as cross-laminated materials and cross-laminated materials; (2) two-dimensional orientation It can be classified as a three-dimensional orientation in which the vertical threads are oriented in the thickness direction of the laminated material. The present invention uses these two-dimensionally and three-dimensionally oriented carbon fibers as reinforcing fibers. The types of carbon fibers can be broadly divided into polyacrylonitrile-based, rayon-based, and pitch-based carbon fibers, but when made into a C/C-composite, the pitch-based carbon fiber has the highest bulk density. The present inventors found out.
Here, the pitch-based carbon fiber is a so-called high-performance carbon fiber, with a tensile strength of 200 kg/mm ² or more,
It has a tensile modulus of 40t/mm2 or ^more . It is generally known that pitch-based carbon fibers have a higher tensile modulus and true specific gravity than PAN-based carbon fibers. In addition, inexpensive coal tar pitch and/or petroleum pitch is used as the raw material for the carbon material serving as the matrix. Pitch made from high-temperature carbonized coal tar is rich in aromaticity, has a high carbonization rate, and has a high true specific gravity.
Moreover, since it has a characteristic of low viscosity, it is suitable as a matrix raw material for C/C-composites. By the way, coal tar pitch for C/C-based matrices is used as binder pitch, which is normally used as a binder in the production of carbon products such as artificial graphite electrodes and impermeable graphite, and also as impregnating pitch, which is used in the impregnation process of these carbon products. It may be any type of pitch. These coal tar pitches are typical thermoplastic resins, and when the pitch is fluidized at its softening point, it becomes a liquid with a viscosity of 0.5 poise or less when the temperature is increased, and when the temperature is further increased, at a temperature of 500 to 600℃, Due to coking (carbonization), the viscosity increases and eventually solidifies. In order to produce a C/C-composite with a high bulk density, it is necessary for this matrix, coal tar pitch, to sufficiently penetrate between the carbon fiber filaments, but the pitch has a sufficiently low viscosity and has a low surface tension. Since it has a small characteristic of C/C
- Desirable as a matrix for composites. Furthermore, carbonization treatment after impregnating the carbon fiber with the matrix is performed while the carbon fiber is immersed in the pitch that is the matrix. Since coal tar pitch is thermoplastic, it melts during the carbonization process, but the molten pitch penetrates between the carbon fiber filaments and carbonizes, and the surrounding molten pitch fills the pores created by bubbling. After carbonization, large cracks and pores become C/C.
- Not found in the composite. Furthermore, with this method, the carbon fibers are carbonized while being immersed in the pitch, so the pitch during molding or carbonization is different from the conventional method of making prepreg, laminating and molding them, and then carbonizing them. There are no leakage issues at all. Here, coal tar pitch decreases in weight due to thermal decomposition or volatilization of low molecular components during carbonization, and becomes pitch coke after carbonization. Taking this into consideration, the ratio of the two-dimensionally and three-dimensionally oriented carbon fibers to the coal tar pitch may be adjusted so that the C/C-composite is present in the pitch coke after carbonization. More specifically, a required number of planar fabrics such as plain weave, twill weave, and satin weave in which carbon fibers are two-dimensionally oriented may be laminated to form a laminate made of carbon fibers. This laminate is preferably held by a plate made of carbon material, which is tightened from above and below to form a preform. In the case of three-dimensionally oriented carbon fibers, the pitch impregnation treatment may be applied as is. The impregnation treatment of soaking molten coal tar pitch into a laminate made of two-dimensionally oriented planar fabrics and three-dimensionally oriented carbon fibers is performed so that the coal tar pitch has a sufficiently low viscosity, preferably 0.5 poise. It is desirable to process at a temperature exhibiting the following, and the preferred impregnation temperature is usually 150-300°C. Here, the present invention is characterized by the use of pitch-based carbon fibers, but if the matrix is coal tar pitch and/or petroleum pitch, the compatibility between the fibers and the matrix is very good, and the presence of carbon fibers in the carbon fibers is very good. Pitch is easily impregnated into the pores, and the carbon fiber surface is evenly covered with pitch. In the present invention, the carbon fibers are subsequently carbonized at about 600 to 1000°C while immersed in pitch.
At this time, the conditions may be normal pressure, increased pressure, or reduced pressure. In this carbonization treatment, the temperature can be increased at a relatively high rate of 30 to 600° C./hr, and the C/C base material can be produced easily and efficiently. Next, the C/C-base material obtained in this way was
It is necessary to perform graphitization treatment at 2000-3000℃. By the graphitization treatment, closed pores in the C/C-base material change to open pores, and furthermore, cracks are generated. The open pores and cracks are easily and uniformly impregnated with coal tar pitch. If the graphitization temperature is less than 2000°C, the change from closed pores to open pores and the generation of cracks will not be sufficient.
A treatment temperature exceeding 3000°C is undesirable because carbon graphitization progresses too much, large cracks are formed, and lamellar cracks occur. However, the C/C-base material obtained in this way still does not have sufficient bulk density and strength, and has a high density and
In order to obtain a high-strength C/C-composite,
Furthermore, impregnation treatment using a conventional method as a densification treatment,
It is necessary to repeat the carbonization process as appropriate. In the present invention, the impregnating material used for this impregnation treatment does not substantially contain quinoline insoluble matter,
Moreover, it is limited to coal tar pitch and/or petroleum pitch having a softening point in the range of 150 to 250°C. The quinoline insolubles in the pitch are solid particles, and these particles block the pores in the carbon material, thus significantly reducing the permeation rate of the impregnating material during the impregnation operation. It is necessary that it not be substantially contained. Generally, the carbonization yield of coal tar pitch increases as the softening point of the pitch increases. Taking this into consideration, the softening point of pitch, which is the impregnating material in the densification process, is limited to a range of 150 to 250°C. If the softening point is less than 150℃, a considerable amount of low molecular weight components will remain in the pitch, resulting in a low carbonization yield.On the other hand, if the softening point exceeds 250℃,
This is because the viscosity is high at pitch impregnation temperatures and sufficient permeability cannot be obtained. In addition, in order to uniformly impregnate the inside of the C/C base material with pitch, it is necessary to select a temperature at which the pitch exhibits a sufficiently low viscosity (0.5 poise or less, measured by a flow tester). The temperature is 100℃ above the softening point of. That is,
In the present invention, the impregnation temperature is preferably about 250 to 350 DEG C. At this temperature, the pitch is thermally stable and its properties do not change due to heat. Next, the material subjected to this impregnation treatment is again subjected to a carbonization-graphitization treatment, and this treatment may be performed at normal pressure, and the treatment temperature is preferably 2000 to 3000°C. According to the present invention, this impregnation-carbonization-graphitization treatment as a densification treatment is repeated about 3 to 5 times, with a bulk density of 1.85 g/
It is possible to obtain C/C composites with values of cm ³ and higher. Although coal tar pitch has been described above as a matrix, the present invention is not limited to this, and high-density C/C-composites can also be produced using the same method using petroleum pitch. <Example> Example-1 Three-dimensionally oriented carbon fiber with a fiber diameter of 10 μm (thread used: graphitized Pitch yarn, tensile strength: 250 kg/
mm ² , tensile modulus: 45t/mm ² ) into the impregnation tank,
Coal tar pitch melted at 220℃ {softening point = 900℃, benzene insoluble content = 30.7wt%, quinoline insoluble content = 9.0wt% (measurement of properties of these pitches was in accordance with JIS K-2425, the same applies hereinafter) )} to 5mmHg
The carbon fibers were injected into an impregnating bath under vacuum to impregnate the carbon fibers with pitch. Subsequently, the carbon fibers were carbonized to 600°C while immersed in the pitch in a nitrogen gas atmosphere at a temperature increase rate of 200°C/hr under normal pressure, and further held at this temperature for 1 hour. Next, after taking out the molded body from the impregnation tank, in an argon gas atmosphere,
The temperature was raised to 2500°C at a temperature increase rate of 300°C/hr, and this temperature was further maintained for 30 minutes to obtain a C/C-base material. Coal tar pitch {softening point = 208°C (the softening point was measured using a flow tester), benzene insoluble content = 42.0wt%, quinoline insoluble content = trace} was added to this C/C-base material under a vacuum of 3 mmHg. After impregnation at 310°C, this molded body was carbonized at a temperature increase rate of 20°C/hr to 1000°C under normal pressure in a nitrogen gas atmosphere. Next, the temperature was raised to 2500°C in an argon gas atmosphere at a heating rate of 300°C/hr, and this temperature was further maintained for 30 minutes. This impregnation, recarbonization treatment,
After repeating the re-graphitization process a total of 4 times, the bulk density was 1.89.
A high density C/C composite of g/cm ³ was obtained. Example 2 Three-dimensionally oriented carbon fiber with a fiber diameter of 10 μm (thread used: Pitch-based graphitized product, tensile strength: 290 kg/
mm ² , tensile modulus: 65t/mm ² ) into the impregnation tank,
Coal tar pitch melted at 230℃ (softening point = 85.0℃, benzene insoluble content = 18.0wt%, quinoline insoluble content = 3.6wt%) was injected into the impregnation tank under a vacuum of 5mmHg, and the pitch was impregnated into the carbon fiber. I let it happen.
Subsequently, under normal pressure, the temperature was increased at a rate of 200℃/hr.
The carbon fibers were carbonized at 600°C while immersed in the pitch in a nitrogen gas atmosphere, and further held at this temperature for 1 hour. Next, after taking out the molded body from the impregnation tank, the temperature was raised to 2500°C at a rate of 300°C/hr in an argon gas atmosphere, and further maintained at this temperature for 30 minutes to obtain a C/C-base material. Ta. This C/C-base material was impregnated with 4 mmHg of coal tar pitch (softening point = 160°C, benzene insoluble content 37.0wt%, quinoline insoluble content = trace) under vacuum at 290°C, and then the molded body was placed under normal pressure. Carbonization treatment was carried out in a nitrogen gas atmosphere at a heating rate of 20°C/hr to 1000°C. Next, the temperature was raised to 2500°C in an argon gas atmosphere at a heating rate of 300°C/hr, and further maintained at this temperature for 30 minutes. This impregnation, re-carbonization treatment and re-graphitization treatment were repeated five times in total to obtain a high-density C/C-composite with a bulk density of 1.90 g/cm ³ . Example 3 In Example 1, the recarbonization treatment temperature in the densification treatment of the C/C-base material was the same (1000 ° C.),
C/C-composites were produced under exactly the same conditions except that they were regraphitized at the treatment temperatures shown in Table 1.
Bulk density 1.85g/from any graphitization temperature
A high-density C/C-composite with properties greater than cm ³ was obtained. The results are also shown in Table-1. Comparative Example 1 The recarbonization temperature in the densification treatment of the C/C-base material was the same as in Example 1 (1000°C),
C/C-composites were produced under exactly the same conditions except that they were regraphitized at the treatment temperatures shown in Table 1. These graphitization treatment temperatures are outside the scope of the present invention, and the C/C-
The bulk density of the composite was less than 1.85 g/cm ³ .

[Table] Example 4 Two-dimensionally oriented carbon fiber with a fiber diameter of 10 μm (thread used: Pitch-based graphitized product, tensile strength: 270 kg/
mm ² , tensile modulus: 55t/mm ² ) plain weave fabric with 15
The sheets were laminated, and only the outer frame was tightened from above and below with carbon plates to form a preform. This preform was charged into an impregnation tank, and coal tar pitch (softening point = 85.6°C, benzene insoluble content = 18.6 wt%, quinoline insoluble content = trace) melted at 220°C was placed in the impregnation tank under a vacuum of 5 mmHg. The carbon fiber was impregnated with pitch. Subsequently, under normal pressure and at a heating rate of 200°C/hr in a nitrogen gas atmosphere,
The carbon fibers were carbonized to 600°C while immersed in the pitch, and further held at this temperature for 1 hour. Next, after taking out the molded body from the impregnation tank, the temperature was raised to 2500°C at a temperature increase rate of 300°C/hr in an argon gas atmosphere.
This temperature was further maintained for 30 minutes to obtain a C/C-base material. Coal tar pitch (softening point = 250°C, benzene insoluble content = 52.0wt%, quinoline insoluble content = trace) was added to this C/C-base material at 350°C under a vacuum of 3 mmHg.
After being impregnated with water, the molded body was carbonized under normal pressure in a nitrogen gas atmosphere at a heating rate of 20°C/hr to 1000°C. Next, the temperature was raised to 2500°C in an argon gas atmosphere at a heating rate of 300°C/hr, and further maintained at this temperature for 30 minutes. This impregnation, re-carbonization treatment, and re-graphitization treatment were repeated a total of 4 times to achieve a bulk density of 1.88 g/
A high density C/C composite of cm ³ was obtained. Comparative Example 2 Three-dimensionally oriented carbon fiber with a fiber diameter of 7 μm (thread used: PAN-based fired product, tensile strength: 300 Kg/mm ² ,
A C/C-composite was produced under the same conditions as shown in Example 1 using a preform having a tensile modulus of elasticity of 18 t/mm ² ). The bulk density of the obtained C/C-composite was as low as 1.68 g/cm ³ . Comparative Example 3 Three-dimensionally oriented carbon fiber with a fiber diameter of 7 μm (thread used: PAN-based graphitized product, tensile strength 250 Kg/mm ² ,
A C/C-composite was produced under the same conditions as in Example 1 using a preform having a tensile modulus of elasticity of 40 t/mm ² ). The bulk density of the obtained C/C-composite was as low as 1.73 g/cm ³ . Comparative Example 4 A C/C-composite was produced under exactly the same conditions as in Example 1 except that the coal tar pitch used as the impregnating material in the densification treatment was changed. As an impregnating material, softening point = 95℃, benzene insoluble content = 18.0wt
%, quinoline insoluble content=trace coal tar pitch was used. The bulk density of the obtained C/C-composite was as low as 1.75 g/cm ³ . Comparative Example 5 A C/C-composite was produced under exactly the same conditions as in Example 1 except that the coal tar pitch used as the impregnating material in the densification treatment was changed. As an impregnating material, softening point = 300℃, benzene insoluble content =
Coal tar pitch with 68.6 wt% quinoline insoluble content = trace was used. The bulk density of the obtained C/C-composite was as low as 1.60 g/cm ³ . Comparative Example 6 A C/C-composite was produced under exactly the same conditions as in Example 1 except that the coal tar pitch used as the impregnating material in the densification treatment was changed. As an impregnating material, softening point = 158℃, benzene insoluble content =
Coal tar pitch with 32.5 wt% and quinoline insoluble content = 4.8 wt% was used. This pitch contained quinoline insoluble matter and had poor permeability during the impregnation step, and the bulk density of the resulting C/C-composite was as low as 1.63 g/cm ³ . Example 5 In Example 1, petroleum pitch (softening point = 108.0°C,
Benzene insoluble content = 13.0wt%, quinoline insoluble content =
Furthermore, petroleum-based pitch (softening point = 260.0℃, benzene insoluble content = 38.6wt%, quinoline insoluble content = trace) is used as an impregnating agent in the densification treatment.
A C/C-composite was produced under exactly the same conditions except that the following was used. The bulk density of the obtained C/C-composite was as high as 1.89 g/cm ³ . <Effects of the Invention> As described above, according to the present invention, by using pitch-based carbon fiber as a reinforcing material and using inexpensive coal tar pitch as a matrix, it is possible to reduce
Bulk density of 1.85g/cm ³ can be achieved with high productivity and low cost through a simple process by performing high temperature treatment at ℃.
Since the above-mentioned high-density C/C-composite can be easily obtained, the ripple effect of this invention on industry is very large.

Claims (1)

[Claims] 1 Pitch-based carbon fibers oriented in two or three dimensions are impregnated with coal tar pitch and/or petroleum pitch, then carbonized in the impregnated state, and then the treated material is heated at 2000 to 3000°C. Graphitization treatment is performed, and then, as a densification treatment, this graphitized material is impregnated with coal tar pitch and/or petroleum pitch, which has a softening point of 150 to 250°C and does not substantially contain quinoline insoluble matter, and then A method for producing a high-density carbon fiber-reinforced carbon composite material, which comprises repeating the carbonization-graphitization process until a desired density is achieved.