KR970008693B1 - Process for the preparation of carbon composite material - Google Patents

Abstract

A process for producing a carbon-fiber reinforced carbon composite article with high-density comprises the steps of: adding 2-20% of sulfur and 2-25% cokes (based on the weight of the pitch mixture) to pitch; adding 10-70% of carbon fibers based on the volume of the composite article to the pitch mixture; heating the mixture at 400-600 deg.C for 0.5-8 hr under an inert atmosphere, followed by pressure forming under 30-300kg/cm3; carbonizing at 500-1,000 deg.C under the same pressure.

Description

Manufacturing method of high density carbon fiber reinforced carbon composite material

INDUSTRIAL APPLICABILITY The present invention is used for aerospace materials such as aircraft brake discs, rocket nozzles, heat shields of space shuttles, mechanical materials such as hot press dies for sintering metals and ceramics, and jig for plastic molding of metals. As a method for producing a carbon fiber reinforced carbon composite material, more particularly, a method for producing a high density carbon fiber reinforced carbon composite material using carbon fiber as a reinforcing material and pitch as a main raw material of a matrix.

In general, carbon fiber-reinforced carbon composite materials impregnate carbon fibers with organic materials such as resins and pitches in a liquid phase, and carbonize them after molding and curing them, or filling pyrolytic carbon between carbon fibers by chemical vapor deposition of hydrocarbon gas. Is prepared.

Among the above two methods, in the case of using pitch, in particular, when using pitch, carbon fiber has the advantage of improving the performance of carbon fiber-reinforced carbon composite material, which is low in raw material, excellent in graphitization of carbonaceous carbon obtained after carbonization, and high in thermal conductivity. It is widely used in the production of reinforced carbon composite materials.

However, in the production of carbon fiber-reinforced carbon composite materials using pitch, some of the components contained in the pitch matrix material volatilize when carbonizing after liquid impregnation, so that pores are formed in the composite material after carbonization, so that the resin or pitch is impregnated. And densification by repeating the carbonization process several times. Also, as the number of times of repeated impregnation and carbonization increases, the time and cost used to manufacture the composite increases and the economical efficiency decreases. There is a need for a method for producing a high carbon fiber reinforced carbon composite material.

Conventional techniques for obtaining such a high-density carbon fiber-reinforced carbon composite material include various methods, and the following methods can be mentioned as a representative example.

That is, according to European Patent 323750, European Patent 335736, and Japanese Patent Laid-Open No. 2-258576, the carbonization yield is increased by increasing the carbonization yield by applying a pressure of several tens or hundreds of atmospheric pressure using a carry-on reactor. Tried to try.

However, this method is difficult to manufacture when the size of the composite material to be manufactured is not only difficult, but the pressure reactor is expensive, especially in the case of manufacturing a small composite material, there is a disadvantage that there is no economic.

In addition, a method of adjusting the pitch of the matrix raw material to a component having high carbon yield by heat treatment or solvent extraction treatment, using anisotropic liquid crystal pitch (Carbon No. 123, p. 150, 1985), and using self-sintering coke (Japanese Patent Application Laid-Open No. 60-54974 and Japanese Patent Application Laid-Open No. 61-21973) and how to use pitch microspheres (Japanese Patent Application Laid-Open No. 1-239060), etc., which are difficult to process pitches. Heat treatment step is required.

In particular, the heat treatment product has a problem that the melt viscosity is higher than the original pitch is not easy to impregnate.

In order to solve the above-mentioned problems, the present inventors have performed various modification treatments on the pitch of matrix raw materials having a high carbon yield, and when the heat is added with an appropriate amount of sulfur to the pitch, the heat-treated product is It has been found that the carbonization yield is higher than that of the pitch and has been patented (Patent Application No. 94-26952). The present invention relates to an improved method for producing a high-density carbon fiber reinforced carbon composite material. It has been found that adding a certain amount of coke powder to the added pitch can produce a denser carbon / carbon composite due to the high carbon yield of about 90% by weight of the coke powder itself.

Accordingly, an object of the present invention is to provide a method for producing a high density carbon fiber reinforced carbon composite material more simply by adding sulfur and coke to the pitch and using it as a matrix raw material.

According to the present invention, adding and mixing 2-20% by weight of sulfur and 2-25% by weight of coke on the basis of the weight of the pitch mixture to form a pitch mixture; Adding carbon fiber to the pitch mixture to 10-70% by volume of the total mixture to form a carbon and pitch mixture; Heat treating the carbon and pitch mixture at a temperature of 400-600 ° C. under an inert atmosphere for 0.5-8 hours; Press molding at 30-300 kg / cm ² pressure after the heat treatment; And carbonizing at 500 to 1000 ° C. while maintaining the pressurized state.

Hereinafter, the present invention will be described in detail.

The present invention increases the carbonization yield of the matrix raw material by adding sulfur and coke to the pitch and then mixing it with carbon fiber and heat treatment, and after press molding, the composite material is kept in a pressurized state during the carbonization to sufficiently solidify the matrix raw material. It is characterized by preventing deformation of the composite material.

In the present invention, the pitch used as the matrix raw material can be both a coal pitch made from coal tar or petroleum heavy oil, and a pitch synthesized from petroleum pitch or other organic matter.

In addition, the coke, which is an additive, has a good powder shape, which is advantageous in order to mix as fine as possible and can be evenly distributed among the carbon fibers, and may be powder having a diameter of 100 μm or less in general. The coke may be pulverized using Crucible, a dry method using a Jet Mill, or a wet method using an Atritor. In addition, a method of adding coke to the pitch together with sulfur is preferable because it can be uniformly mixed and finely pulverized powder using a ball mill or the like. In addition, when the amount of sulfur added is 2 wt% or less, it is difficult to increase the carbonization yield of the pitch, and when it is 20 wt% or more, it is preferable to add sulfur at 2-20 wt% because the viscosity of the product is too high to be formed after heat treatment. .

When the amount of coke added is less than 2% by weight, the effect of adding coke is low. When the amount of coke is 25% by weight or more, the coke itself is less sintered, and thus, the cohesion of the coke is weakened. It is preferred to add at 25% by weight.

On the other hand, the carbon fiber polyacrylonitrile or pitch system used as a reinforcing material may be used, and the fiber type may be short fibers such as chopped fibers and milled fibers having a length of 3 cm or less. Iii) It is preferable to use the form because it is easy to mix uniformly with the pitch.

In the present invention, after adding sulfur and coke to the pitch, it may be a conventional method as a method of mixing it with carbon fiber, but when adding sulfur and coke to the pitch, carbon fiber is added and mixed together and heated Impregnation is preferred.

Moreover, although the heating temperature at the time of impregnation changes with the component and kind of pitch used, it is preferable to heat to 50-100 degreeC higher than the softening point of a pitch generally. This is because the pitch generally decreases with increasing temperature and starts to melt at a temperature above 50 ° C above the softening point, and continues to decrease until it reaches 100 ° C above the softening point, after which there is no significant change.

At this time, the amount of carbon fiber mixed in the pitch added with sulfur and coke is typically used in the range of 10-70% by volume. If the amount of reinforcing fibers is too small, the matrix becomes weak, and if the amount is too high, the amount of the matrix is relatively reduced, so that the adhesion Falls.

Thereafter, a mixture of pitch and carbon fiber to which sulfur and coke is added is laminated, arranged or dispersed in a mold according to a desired use, and then heat-treated under an inert atmosphere using a hot press device and then press-molded. . At this time, the heat treatment temperature is preferably a heat treatment to a temperature range of 400 to 600 ℃. When the heat treatment temperature is 400 ° C. or less, the pyrolysis reaction of the pitch or the reaction between the pitch component and sulfur does not occur sufficiently or takes too long. When the heat treatment temperature is 600 ° C. or higher, the reaction occurs rapidly and the viscosity of the pitch becomes too high, making it difficult to mold. do.

In addition, the time for heat treatment requires a relatively long time at low temperatures and even a short time at high temperatures, 0.5 to 8 hours is sufficient within the above temperature range, the important thing is appropriately adjusted according to the type of pitch or the addition ratio of sulfur or coke, etc. It should be.

After the end of the heat treatment, but the pressure molding as it is, it is preferable to press the molding at a molding pressure of 30-300kg / cm ² . If the molding pressure is less than 30kg / cm ² is not sufficiently molded, if the 300kg / cm ² or more is because the coke powder is pressured on the surface of the carbon fiber, the carbon fiber is cut or broken, and as a result the composite is weak.

After the molding is completed, carbon fiber-reinforced carbon composite material is produced by carbonization while maintaining the pressure at 500 ° C. or higher, but at this time, when the carbonization temperature is 500 ° C., the carbonization does not occur sufficiently. The temperature of the hot press may be limited, but the heating capacity of the hot press may be limited according to the material of the mold, and it is usually sufficient to carbonize at 1000 ° C. or lower.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

To a pitch powder having a size of 70-100 mesh prepared by pulverizing coal tar pitch having the characteristics as shown in Table 1, a certain amount of sulfur powder was added, and the coke having the characteristics as shown in Table 2 was crushed into atrita. After a certain amount of coke powder classified into a constant size was added, it was mixed using a ball mill. Subsequently, 30 g of the mixture was mixed with 20 g of chopped fiber made of 10 mm in length by cutting polyacrylonitrile-based carbon fibers, and then dispersed in a mold having a width and length of 5 cm, respectively, and the mold was mounted on an atmosphere-controlled hot press. While flowing the nitrogen gas by heating at a temperature rising rate of 10 ℃ per minute, heat treatment and then pressurized and molded. Subsequently, the temperature was raised to 700 ° C. as it was pressurized in the mold and carbonized for 0.5 hour, followed by cooling to measure the density of the completed carbon fiber reinforced carbon composite material. The addition amount of sulfur and coke, the heat treatment temperature and time, and the molding pressure were adjusted as shown in Table 3 to prepare the carbon fiber-reinforced carbon composite materials of Inventive Example 1-6 and Comparative Example 1-6, and then the density of each Shown in

TABLE 1

TABLE 2

TABLE 3

According to Table 3, in the case of Inventive Examples (1) to (6) using pitches containing an appropriate amount of sulfur and coke as a matrix raw material, Comparative Example (1) prepared by adding only coke without adding sulfur at all Or it can be seen that the density of the carbon composite material is dense as compared to Comparative Example (2) prepared by adding only sulfur without adding coke.

In addition, even when the appropriate amount of sulfur and coke is added as in Comparative Example (3) it can be seen that if the molding pressure is too low, it is difficult to produce a high-density composite.

In addition, as in Comparative Example (4), if the amount of added coke is excessive, it can be seen that the press molding of the composite material is difficult and the density is low.

On the other hand, even if the addition of the appropriate amount of sulfur and coke as in Comparative Example (2), it can be seen that it is difficult to produce a dense composite material because the carbonization yield of the pitch can not be increased if the heat treatment temperature is too low and insufficient heat treatment effect.

In addition, it can be seen that when the size of the coke added as in Comparative Example (6) is too large, the density of the composite material is low because the coke powder is difficult to evenly distribute evenly among the carbon fibers.

As described above, by adding sulfur and coke to the pitch according to the present method, the pitch which is improved in carbonization yield is carbonized while controlling the heat treatment conditions, pressing the mold at an appropriate pressure and maintaining the pressurized state by controlling the heat treatment conditions. In addition, the carbon fiber-reinforced carbon composite material having a high density can be produced. In particular, in the carbon composite material manufacturing process, the densification process can be shortened.

Claims (2)

Adding 2-20 wt% of sulfur and 2-25 wt% of coke to the pitch based on the weight of the pitch mixture to form a pitch mixture; Adding carbon fiber to the pitch mixture so as to be 10-70% based on the volume of the entire mixture to form a carbon fiber and a pitch mixture; Heat treating the carbon fiber and the pitch mixture at a temperature of 400-600 ° C. under an inert atmosphere for 0.5-8 hours; Press-molding at 30-300kg / cm ² pressure after the heat treatment and carbonizing at 500-1000 ° C. while maintaining the pressurized state. The method of claim 1, wherein the coke is a powder having a particle size of 100 μm or less.