JPH068215B2 - Manufacturing method of carbon fiber reinforced carbon material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a carbon fiber reinforced carbon material (hereinafter referred to as C / C composite) using pitches as a matrix forming raw material.

[Prior Art] C / C composites having high specific strength and excellent heat resistance occupy an important position as materials for aviation and space.

Conventionally, two methods have been known for manufacturing C / C composites.

The first is a product obtained by mixing polyacrylonitrile (PAN) -based, pitch-based or rayon-based carbon fiber with a thermosetting resin such as phenol resin or furan resin, which is a carbon matrix raw material, or pitch, and heat-molding the mixture. Is subjected to carbon treatment in an inert gas atmosphere, and if necessary, the cycle of impregnation of resin, pitch, etc., and carbonization treatment is repeated (for example, Japanese Patent Publication No. 62-212262).

The second is a method of forming a C / C composite by preliminarily shaping the carbon fiber into an approximate shape and then depositing carbon in the gap between the carbon fibers by a chemical vapor deposition method (for example, Carb.
on Vol.6, p397-403, 1968).

Currently, among the above, C / C using pitches as a matrix
To produce a composite, the pitches are mixed with the carbon fibers as powder and put into a mold as it is and press-formed, or the pitches are heated to 250 ° C. or higher and melted, and then the carbon fibers are put therein. There is a method in which pitches are adhered to carbon fibers by passing through them to form a prepreg, which is then put into a mold and press-molded.

[Problems to be Solved by the Invention] However, when producing a C / C composite having pitches as a matrix, if the pitches are mixed as powder, it is difficult to uniformly mix them.
Only short fibers of mm can be used, and it is difficult to use long fibers and woven fabrics. Further, in order to heat and melt the pitches and pass the carbon fibers into the prepreg to form a prepreg, a temperature of 250 ° C. or higher is required, which makes problems such as equipment and safety difficult.

Further, even if the pitches are simply suspended in a solvent and the pitches are attached to the carbon fibers through the carbon fibers, if they are dried and made into a prepreg, the pitches are not completely melted and become non-uniform. And pitches are not flexible,
Pitches fall off from the carbon fiber during post-process work.

Therefore, an object of the present invention is to produce a C / C composite using pitches as a matrix-forming raw material by uniformly adhering the pitches to carbon fibers without using a special device such as heating, thereby effectively producing the C / C composite. To perform.

[Means for Solving the Problems] That is, according to the present invention, in the production of a C / C composite using pitches as a matrix forming raw material, polystyrene and polyvinyl alcohol are dissolved as a pitch adhesive in a solvent to suspend the pitches. The C / C composite in which the solution thus prepared is adhered to the surface of the carbon fiber, the solvent is then removed to form a prepreg, and the prepreg is used for heat molding, followed by carbonization, impregnation, carbonization, and, if necessary, final heat treatment. Is a manufacturing method of.

The present invention, polystyrene as a pitch adhesion in the solution as described above, a solution in which polyvinyl alcohol is dissolved and pitches are suspended is adhered to the surface of the carbon fiber, and then the solvent is removed to obtain a prepreg. The prepreg is characterized in that the pitches are easily and uniformly adhered to the surface of the carbon fiber. Since this prepreg is used, the C / C composite having a desired composition can be obtained without the pitches falling off.

Hereinafter, the present invention will be described in detail.

The reinforcing carbon fiber used in the present invention may be any of polyacrylonitrile (PAN) type, rayon type and pitch type, and may be carbonaceous or graphitic. The form of the carbon fiber may be a short fiber having a length of about 0.05 to 50 mm or a continuous fiber. Further, it may be in a state of a sheet-like carbon fiber structure such as cloth, felt or mat. The carbon fibers may be oriented in a completely random direction as they are in the matrix or in the defibrated state, or may be oriented in any specific direction.

Further, the pitches used as the matrix forming raw material are 30 to 70% by weight of pitches such as impregnated pitch and binder pitch, and 70 to 30% by weight of carbonaceous powder such as raw coke and carbon black are mixed using a kneader or the like. . At this time the pitch is
If it is less than 30% by weight, it is difficult to form a molded product because the amount of the binder is small at the time of molding the C / C composite.
If it exceeds 5% by weight, the pitch will be lost during molding and the intended molding material cannot be obtained.

At this time, the particle size of the pitches is preferably as small as possible, and is preferably 100 μm or less, because if the particle size is large, the carbon particles cannot sufficiently enter into the carbon fiber and a high-strength C / C composite cannot be obtained.

Such pitches are used as a solution by suspending them in a solvent together with polystyrene and polyvinyl alcohol. Polystyrene as a pitch adhesive, polyvinyl alcohol is dissolved in a solvent, and after removing the solvent acts as a binder, and when made into a prepreg, the pitch is less flexible than the surface of the carbon fiber and is not flexible. It is used to prevent falling off. Further, since polystyrene and polyvinyl alcohol as pitch adhesives are gasified at the time of carbonization to form open pores of several μm to several + μm,
In the impregnation and carbonization treatment, a large amount of the impregnating agent enters the open pores and also functions to increase the density. As the solvent, organic solvents such as chloroform and benzene can be used in the case of polystyrene, and water can be used in the case of polyvinyl alcohol. Further, in the method of the present invention, the pitches are mostly insoluble even if a part of the components may be dissolved when an organic solvent is used, and when water is used as the solvent, the pitches are Since they hardly dissolve, they are used in a suspended state.

Immerse carbon fibers or carbon fiber bundles in this solution,
After impregnating the solution into the fiber, the solvent is removed by drying to obtain a prepreg. A mixture obtained by stacking or cutting such prepregs and mixing them is subjected to heat molding or the like to obtain a molded body.

In the molded body, it is desirable that the carbon fiber or the 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 reinforcing fibers of the C / C convoyit obtained will be too small, resulting in low strength. On the other hand, when it exceeds 90% by weight, the content of the matrix is too small, the shear strength between the layers is lowered, and the reinforcing effect of the carbon fiber is not sufficiently exhibited.

The molded body is carbonized in a non-oxidizing gas atmosphere such as nitrogen and argon. At this time, since carbonization of the molded body as it is causes swelling, it is preferable to carry out the carbonization treatment as it is while being fixed using a fixing material made of a material that does not deform even at a high temperature during carbonization.

The temperature during the carbonization treatment is 800 ° C or higher and 1100 ° C or lower. In this case, if the rate of temperature rise during carbonization is too fast, the matrix material (pitch) contracts due to thermal decomposition,
Gas generation becomes more intense and large cracks are more likely to occur. Therefore, the rate of temperature rise is usually 100 ° C./hr or less, preferably 20 ° C./hr or less.

The first intermediate obtained by the carbonization treatment in this way is still high in porosity and further impregnated with a pitch or carbonizable resin to obtain a high density, high strength C / C composite. Then, the carbonization treatment is performed again in a non-oxidizing gas atmosphere such as argon.
The temperature at this time is preferably 800 ° C. or higher and 1100 ° C. or lower, and is kept at a predetermined temperature for about 1 hour.

It is desirable to repeat the impregnation treatment and the carbonization treatment until the pores of the carbon fiber reinforced carbon material are filled and the density becomes almost constant. And, if necessary, the final graphitization treatment is nitrogen,
The final C / C composite is obtained by carrying out at 1200 ° C to 3000 ° C in an atmosphere of non-oxidizing gas such as argon. The graphitization time is 30 minutes or more, preferably 1 hour or more, at a predetermined temperature in order to stabilize the characteristics.

Hereinafter, the present invention will be described according to examples.

[Example] 50% by weight of a pitch having an average particle size of 10 μm and a softening point of 240 ° C. and 50% by weight of raw coke (volatile content of 10%) having an average particle size of 10 μm,
Mix at 270 ° C using a kneader, then mix this mixture 1
The particle size was adjusted to 00 μm or less to obtain a raw material pitch mixture.

Example 1 150 parts by weight of a raw material pitch mixture and 150 parts by weight of polystyrene as a pitch adhesive were put in 1000 parts by weight of chloroform as a solvent and stirred to dissolve polystyrene to prepare a solution in which pitches were suspended.

After dipping a PAN-based carbon fiber bundle cloth (sporeless weave) with 6000 filaments in this solution, it is dried to remove the solvent and made into a prepreg, which is cut into 120 x 120 mm squares and 25 pieces are placed in a mold. The layers were laminated and pressed at a temperature of 300 ° C. and a pressure of 100 kg / cm ² .

Example 2 In Example 1, polyvinyl alcohol was used instead of polystyrene as the pitch adhesive, and water was used instead of chloroform as the solvent, a prepreg was prepared in the same manner as in Example 1, and press-molded under the same conditions.

Comparative Example 1 A prepreg was prepared in the same manner as in Example 1 except that the pitch adhesive polystyrene was not used, and press molding was performed under the same conditions.

Comparative Example 2 Raw material pitch mixture powder and carbon fiber bundle cloth (satin weave) cut into 120 × 120 mm squares similar to those in Example 1 were alternately used so that the ratio of pitch powder and carbon fiber was the same as in Example 1. It was laminated on the mold by hand and press-molded under the same conditions as in Example 1.

Example 3 150 parts by weight of the raw material pitch mixture and 150 parts by weight of polystyrene as a pitch adhesive were put in 1000 parts by weight of chloroform as a solvent and stirred to dissolve polystyrene to prepare a solution in which pitches were suspended.

After immersing 12,000 filaments of PAN-based continuous carbon fiber in this solution, it was dried to remove the solvent and made into prepreg, which was cut into 30 mm short fibers and laminated on a 120 x 120 mm square mold to obtain a temperature of 300 Press molding was carried out at a temperature of 100 ° C. and a pressure of 100 kg / cm ² .

Comparative Example 3 A prepreg was prepared in the same manner as in Example 3 except that the pitch adhesive polystyrene was not used, and press molding was performed under the same conditions.

Comparative Example 4 Raw material pitch mixture and 12,000 filaments of PAN-based continuous carbon fiber cut into 30 mm short fibers were mixed so that the ratio of pitch and carbon fiber was the same as in Example 3,
The mixture was mixed with a dry blender, placed in a mold, and press-molded under the same conditions as in Example 3.

The obtained press molding results are shown in Table 1.

The ones using polystyrene and polyvinyl alcohol (Examples 1, 2 and 3) as pitch adhesives produced clean molded bodies, but those using prepregs without using the pitch adhesives (Comparative Example 1, 3) The pitch fell off and a molded body could not be formed. Further, when the raw material pitch mixture powder was directly mixed with the carbon fiber without making a prepreg (Comparative Examples 2 and 4), a molded product having a non-uniform and low density was obtained.

In this way, a molded product can be easily manufactured by preparing a prepreg using a pitch adhesive such as polystyrene.

Example 4 The molded body of Example 1 was sandwiched between stainless steel plates and fixed with bolts.

This was heated to 600 ° C in a nitrogen atmosphere at a heating rate of 10 ° C / hr to carbonize the matrix. Then, after removing the fixing material, the temperature was raised to 1000 ° C. in a nitrogen atmosphere at a temperature rising rate of 10 ° C./hr, and the temperature was maintained for 1 hour for carbonization. Further, the carbonized first intermediate was impregnated with impregnating pitch at 200 ° C. under vacuum, and then the impregnated body was heated to 1000 ° C. at a heating rate of 10 ° C./hr in a nitrogen atmosphere and impregnated. The pitch was completely carbonized. Subsequently, the impregnation and carbonization steps were repeated three more times to obtain an intermediate.

The obtained intermediate was heated to 2000 ° C. at a temperature rising rate of 10 ° C./min in an argon atmosphere and kept for 1 hour to obtain a C / C composite.

Comparative Example 5 The molded body of Comparative Example 2 was carbonized under the same conditions as in Example 4 to obtain a C / C composite.

The results of the strength test of the obtained C / C composite are shown in Table 2.

The one using polystyrene (Example 4) as the pitch adhesive has excellent bending strength and hardness as compared with Comparative Example 5. As described above, the prepreg prepared by using the pitch adhesive was a C / C composite having excellent strength and the like because the matrix distribution in the carbon fiber was uniform.

[Advantages of the Invention] By using the pitch adhesive of the present invention, when a C / C composite having pitches as a matrix is produced, it is easy and uniform without using a heating device or the like for melting the raw material pitch. It is possible to make a prepreg that does not drop pitches, and in addition to improve the workability of the prepreg, it is possible to make a uniform C / C composite with high strength properties.

C / C composites made from pitch have higher oxidation resistance than those made from resin, and are expected to have wider application fields.

Claims (1)

[Claims] 1. A method for producing a carbon fiber reinforced carbon material using pitches as a matrix forming raw material, wherein a solution of polystyrene and polyvinyl alcohol as a pitch adhering agent in which a pitch is suspended and a pitch is suspended on a surface of the carbon fiber. A method for producing a carbon fiber reinforced carbon material, which comprises: adhering, then removing a solvent to obtain a prepreg, heat-molding using the prepreg, followed by carbonization treatment, impregnation, carbonization treatment and, if necessary, final heat treatment.