KR940010099B1 - Process for producing carbon/carbon composite using coaltar-phenol resin - Google Patents

Abstract

The composite comprising a carbon fiber as reinforcing material and mixture of coal tar and phenol resin as matrix, is prepd. by: the mixt. of 30-80 wt.% of coal tar and 70-20 wt.% of phenol resin mixed in organic solvent; after drying the dipped carbon fiber, it is sustained for 2-5 hrs. under 30-300 kg/cm2 at 150-250 deg.C, and then cooling, crosslinking and molding; the obtd. material is heated at 900-1500 deg.C. of 30-300 deg.C/hr of temp. elevating speed for more than 1 hr. under unactive condition, then cooling and carbonizing.

Description

Method for preparing carbon / carbon composites using coal tar-phenol resin mixture

Figure 1a is a microscopic cross-sectional picture of the bright field of the carbon / carbon composite material of the present invention,

1b is a microscopic cross-sectional picture under polarized light.

The present invention relates to a method for producing a carbon fiber reinforced carbon fiber, that is, a carbon / carbon composite material, more specifically using carbon fiber as a reinforcing material, and coal tar and phenol resin as a matrix raw material It relates to a method for producing a carbon / carbon composite material using a mixture of.

Carbon / carbon composite materials are widely used in aircraft brakes, rocket nozzles, and space shuttle structural materials because of their excellent properties such as light weight, high mechanical strength, and excellent heat resistance.

There are many methods for producing a carbon / carbon composite material, but thermosetting resins and thermoplastic resins are used as matrix raw materials on carbon fibers in the form of tows, cloths, felts, mats, and the like. After impregnation, the liquid phase impregnation and carbonization method of laminating and curing the same and then carbonizing at a temperature of 1000 ° C. or more is the most common method.

The carbon / carbon composite material may be manufactured by one impregnation and carbonization process by the above method. Pores are formed in the. Therefore, in order to fill the pores, a method of increasing the density of the carbon / carbon composite material is frequently used by repeating the process of impregnating and carbonizing the matrix raw material several times (for example, Japanese Patent No. 62-212262).

As a raw material of the matrix, thermosetting resins such as epoxy resins, phenol resins, furan resins, and thermoplastic resins such as petroleum or coal-based pitches are generally used. The use of a thermosetting resin has the advantage of being easy to mold, but it is expensive, and the processing process is complicated because rigid temperature control is required when heating and curing after impregnation. In addition, since the specific gravity of the carbide of the thermosetting resin is about 1.4-1.5 g / cm 2 and lower than that of the pitch carbide of 1.8-1.9 g / cm 2, the density of the carbon / carbon composite material using the thermosetting resin does not increase so much. Do not.

Using pitches as the matrix raw material is not only inexpensive, but also through the liquid phase in the carbonization process, thereby improving thermal conductivity with excellent molecular orientation.

Pitches are classified into pitches which are solid at room temperature and tars which are liquid at room temperature. Among them, pitch is mainly used as raw material of matrix because of high carbonization yield because of less content of volatile components than tar. However, in order to form a molded body by impregnating the pitch of carbon fibers in the solid phase, there is a difficulty in processing the pitch while maintaining the molten state. Therefore, the first impregnation and carbonization of the thermosetting resin to form a molded body, and then using the pitch to repeat the re-impregnation and carbonization process (for example, Carbon, vol. 28, p. 125, 1990), or chemical A method of repeating a process of impregnating and carbonizing a pitch by impregnating pyrolytic carbon by vapor deposition and then impregnating with carbon (eg, Fuel, vol. 66, p. 1512, 1987) is used. In this case, however, the mutual compatibility of the thermosetting resin or pyrolytic carbon used in the first impregnation with the pitch used from the second impregnation becomes a problem.

Therefore, when tar is used in the first impregnation, the liquid is impregnated at room temperature, so the impregnation process can be treated at room temperature, and the same pitch as the pitch used since the second impregnation has excellent mutual compatibility. However, the problem of using tar as a matrix raw material for the first impregnation is that the carbonization yield is too low, so that the density of the molded product is low, requiring a large number of times of subsequent impregnation and carbonization processes, and curing in the molding process after impregnation. Or difficult to dissolve.

In order to solve the above problems, the process is carried out by mixing coal tar, a coal-based pitch, capable of expressing anisotropic tissue after carbonization, and a phenol resin, a thermosetting resin having excellent curability and moldability, and then using this as a matrix raw material. Its purpose is to provide a simple and dense carbon / carbon composite material manufacturing method.

According to the present invention, a mixture of coal tar 30-80wt% and phenol resin 20-70wt% is hardened and molded by impregnating and laminating carbon fibers and keeping them in a heated and pressurized state, and the resulting molded body is 30-300 ° C. under an inert atmosphere. Provided is a method for producing a carbon / carbon composite material, characterized in that the carbonization by heating up at 900-1500 ° C. at a heating rate of / hr.

In the present invention, when the coal tar / phenol resin mixture is formed, the coal tar and the phenol resin are not sufficiently uniformly mixed by mechanical mixing, so that they are mixed in an organic solvent such as tetrahydrofuran or toluene to form a uniform mixture. Meanwhile, when the coal tar content is 80% or more or the phenol resin content is 20% or less, they are not completely mixed even in the organic solvent, so that extra coal tar is not cured in the curing process and remains in a liquid state. On the contrary, when the coal tar content is 30% or less or the phenol resin content is 70% or more, the preform swells easily during the curing process. The organic solvent used when mixing coal tar and phenol resin should be removed before the mixture of coal tar and phenol resin hardens the impregnated carbon fibers. The removal method is to leave it in the air at room temperature to volatilize it or to remove it using a freeze dryer.

The curing and molding conditions of carbon fibers impregnated with a mixture of coal tar and phenolic resins may vary depending on the relative content of coal tar and phenolic resins, but are generally about 2-300 kg / cm 2 at a temperature of 150-250 ° C. It is preferable to hold for 5 hours. In general, the curing is not completed at a temperature of less than 150 ℃ and at a temperature of more than 250 ℃ due to a rapid reaction is a poor curing state. In addition, at a pressure of 30 kg / cm 2 or less, the bonding force between the laminated carbon fiber layers is weak, and at a pressure of 300 kg / cm 2 or more, the arrangement state of the carbon fibers is distorted or some fibers are broken. The time required to achieve sufficient curing is generally 2 hours or more, but more than 5 hours is not economically unnecessary since no further curing effect is expected. On the other hand, the curing and molding can be carried out as one step, but the primary curing and molding by holding for 2-5 hours under a pressure of 30-300kg / ㎠ in a temperature range of 150-200 ℃, then at a temperature of 200-250 ℃ More preferred is a two-step treatment of holding for 2-5 hours at a pressure of 30-300kg / cm 2, cooling and then secondary curing and molding. In the case where the two-stage treatment is performed in this way, a very good cured molded body with little swelling of the molded body which may occur during the one-stage treatment can be calculated.

As described above, the cured and molded material is maintained at a temperature of 900-1500 ° C., which is a general carbonization condition, for 1 hour or more, and cooled to yield a carbon / carbon composite material. However, the temperature rising rate to 900-1500 ° C. may be slowed down. If too slow, it is not economical, so it is preferable to use 30-300 ° C / hr.

At an elevated temperature rate of 300 ° C. or more per hour, the physical properties of the final product may be degraded due to thermal expansion. On the other hand, in the prior art, when only the thermosetting resin is used as the matrix raw material, it is common that the physical properties of the carbide are lowered unless the temperature increase rate during carbonization is very slow, such as several degrees per hour. However, in the method of the present invention, even when heated at a temperature increase rate of 30 ° C. or more, the physical properties were satisfactory, and no significant problem was found even at a temperature increase rate of 300 ° C. per hour.

Hereinafter, the present invention will be described in detail through examples.

Example 1

Coal tar used as a matrix raw material was produced by-products during the coke production of steelworks and the results of the component analysis are shown in Table 1. The phenol resin used the resol type. The coal tar and phenol resins were mixed by 50% by weight to make 100 g of a mixture, and 10 cc of tetrahydrofuran was added thereto and stirred for about 5 minutes. The mixture was impregnated evenly on eight cloth-shaped cloths made of polyacrylonitrile-based carbon fibers, and left to dry for 48 hours in the air. Cut the dried cloth into the size of 2cm × 5cm and stack it in 25 layers and put it in the same size metal mold, heat it to 190 ℃ using hot press, hold it under pressure of 100kg / ㎠ and keep it for 3 hours and again 230 ℃ Heated for 3 hours under the same pressure and cooled.

The cooled sample was placed in a carbonization furnace and heated at a temperature rising rate of 120 ° C./hr while flowing nitrogen gas, and maintained at 1200 ° C. for 1 hour, followed by slow cooling at a normal cooling rate.

Density was calculated by measuring the volume and weight of the prepared carbon / carbon composites, and the microstructure was observed through a microscope after the cross section was polished by a conventional method. The prepared carbon / carbon composite material had a density of 1.35 g / cm 2. FIG. 1A is a microstructure under bright field observed through a microscope, and FIG. 1B is a microstructure under polarized light. It can be seen from FIG. 1a that the bonding between the carbon fiber and the carbon matrix is very excellent, and in FIG. 1b, weak anisotropy is shown inside the carbon matrix.

[Table 1] Coal tar component analysis results

Example 2

Heated to 190 ℃ in a hot press and maintained for 3 hours while pressing at a pressure of 200kg / ㎠ and then again heated to 230 ℃ and maintained for 5 hours under the same pressure, and then cooled, the cooled sample is heated at a heating rate of 300 ℃ / hr It was carried out in the same manner as in Example 1 except for maintaining for 1 hour at 1200 ℃.

The density of the prepared carbon / carbon composite material was 1.34 g / cm 2, and the microstructure observed through the microscope was similar to the microstructure of the composite material (FIGS. 1a and b) calculated in Example (1).

Example 3

To prepare a carbon / carbon composite material in the same manner as in Example 1 using a coal tar-phenol resin matrix raw material having a composition as shown in Table 2, the production conditions were carried out as shown in Table 2.

TABLE 2

As shown in Table 2, in the case of Inventive Example (1-4) that satisfies the composition and manufacturing conditions according to the present invention, not only the manufacturing of the molded body was possible but also its microstructure was similar to that of the composite material of Example (1). In the case of Comparative Example (1-2) outside the composition range of the present invention, it was difficult to manufacture a molded article.

In particular, in the case of Inventive Example (3), the curing time was long, and in the case of Inventive Example (4), their microstructure was similar to that of Example (1) except that the curing period was short.

On the contrary, in the case of Comparative Example (1), the content of coal tar was excessive and complete curing was not achieved. In Comparative Example (2), the molded body swelled due to the excessive amount of phenol resin, which made it difficult to maintain the circular shape.

As described above, by using a mixture of coal tar and phenol resin as a matrix raw material, it was possible to cure without complicated temperature and time control, and it was possible to simplify the device by carbonization at atmospheric pressure even during carbonization. The heating time could significantly shorten the carbonization time. In addition, the microstructure of the carbon matrix formed after carbonization showed anisotropic structure.

Claims (2)

In the method for producing a carbon / carbon composite material, a mixture of 30 to 80 wt% of phenol resin and 70 to 20 wt% of phenol resin mixed with an organic solvent is impregnated with carbon fiber, and the impregnated carbon fiber material is dried and then 150 to 250 After curing for 2-5 hours at a temperature of 30-300kg / ㎠ at a temperature of ℃ ℃ hardened and molded, the molded material at a temperature of 900-1500 ℃ at a temperature increase rate of 30-300 ℃ / hr under an inert atmosphere A method for producing a carbon / carbon composite material, characterized in that the temperature is elevated and maintained for at least 1 hour before cooling. According to claim 1, wherein the curing and molding treatment is maintained at a pressure of 30-300kg / ㎠ at a temperature of 150-200 ℃ 2-5 hours the first curing and molding, then 30-300kg at a temperature of 200-250 ℃ The method is characterized in that it is carried out in a two-step process of cooling and secondary curing and molding after holding for 2-5 hours at a pressure / cm 2.