JPH0788261B2 - Method for producing carbon fiber reinforced carbon composite material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carbon fiber reinforced carbon composite material. More specifically, the present invention relates to a method for producing a carbon fiber reinforced carbon composite material having excellent properties by using pitches as a matrix raw material.

(Prior Art) Carbon fiber reinforced carbon composite materials (hereinafter abbreviated as C / C composite materials) are lightweight, high-strength, and have excellent heat resistance and corrosion resistance, making use of rocket nozzles, nose cones, and aircraft disks. It is used for aerospace materials such as brakes, heating elements, hot press molds, other mechanical parts, and reactor components.

In the conventional C / C composite material, carbon fibers have been impregnated in advance with an organic matrix such as resin or pitch, and they are molded / cured and then carbonized / graphitized, or they are thermally decomposed between carbon fibers by a chemical vapor deposition method. It is manufactured by the method of filling carbon.

Among these methods, the method of using Pitches as a matrix raw material is inexpensive raw material, high carbonization yield,
The carbonaceous material obtained as a result of carbonization is a graphitizable substance, and C /
C has the advantages that it is preferable in terms of performance manifestation, and that the carbon fiber used is made of pitch as the raw material, it has good compatibility with the fiber and good adhesion between the fiber and matrix. is doing. However, on the other hand, pits have a significant expansion during carbonization, and therefore when used as a matrix for C / C composites, the shape retention and dimensional stability when baked into C / C composites are poor. Alternatively, a large number of pores and cracks are generated inside the C / C composite material, and if the densification process of pitch-impregnated or resin-impregnated monocarbonization is not repeated many times, sufficient characteristics will not be expressed, which is a drawback. Atsuta

(Problems to be solved by the invention) Therefore, in the past, as a method of avoiding such a drawback in the case where the pits were used as a matrix raw material, carbonization after molding was started, and at least the pits were carbonized to start developing strength.
A method called so-called carbonization under pressure, which is performed under pressure in an autoclave up to a temperature of 0 to 700 ° C, has been adopted. However, even in such a method, the expansion of pits is not completely suppressed, and there is always a problem when the apparatus for carbonization becomes large-scale and complicated.

(Means for Solving Problems) Therefore, the present inventor has made diligent studies to solve such problems, and after molding by impregnating carbon fibers with pitches,
The inventors have found that the above problems can be solved by performing a specific treatment, and have reached the present invention.

That is, an object of the present invention is to provide a method for producing a C / C composite material which is simple and stable, and has excellent characteristics and has a matrix of pitches. And the purpose is a method for producing a carbon fiber reinforced carbon composite material using pitches as a matrix raw material, in which carbon fibers are impregnated with pitches and heated and pressure molded, and subsequently, in a pressurized state, at a molding temperature. This is easily achieved by a method for producing a carbon fiber-reinforced carbon composite material, which comprises performing carbonization treatment after holding the molded body at a higher temperature of 500 ° C. or less.

The present invention will be described in detail below.

Pits as a matrix raw material used in the present invention are coal tar pitch, petroleum-based residue pitch or various synthetic pitch, and the like, which are obtained by distillation, heat treatment, air blowing or solvent treatment, extraction of specific components by sedimentation separation, etc. A carbonaceous bituminous material having a suitable softening temperature. More specifically, the softening point obtained by the Mettler method is 80 ° C. or higher, preferably in the range of 200 to 350 ° C., and
Pitches having a distillate content of less than 10% at 300 ° C. are preferred.

The carbon fiber used is not particularly limited, but polyacrylonitrile-based, pitch-based, carbon fiber,
Alternatively, it is a carbon fiber or the like obtained by a vapor phase pyrolysis method. Further, as the form of the fibers, continuous fibers, short fibers, and felt-like ones are used.

The carbon fibers are arranged by impregnating the melted pitches and then arranged in a molding die, or by alternately laminating fibers and powders of the pitches in the molding die.

The amount of the fiber used is appropriately determined, but it is usually 20 to 75%, preferably 30 to 60% with respect to the volume of the molded product.

The mold filled with carbon fibers and pitches as a matrix is then placed on a pressurizing machine equipped with a heater, and first, the pitches are heated and melted in a non-pressurized state. The degree of heating varies depending on the softening temperature of the pits used, but it is usually lower than the softening point of the pits until the pits show a low viscosity so that they can sufficiently penetrate between the carbon fibers. It should be heated to 50-150 ° C higher temperature. After the pitches are melted, pressurize to a predetermined pressure, usually 5 to 100k
A pressure of g / cm ² is applied and it is molded into a predetermined shape. In the past, after molding, the mold was cooled and returned to a sufficiently cooled normal pressure to obtain a molded body, but in the present invention, following the above-mentioned molding treatment, holding at a temperature higher than the molding temperature is performed. is important.

That is, after being molded into a predetermined shape, the temperature is usually higher than the molding temperature in a pressurized state, that is, the temperature is higher by 50 ° C. or more, though it is somewhat different depending on the softening point of the pitch used. This temperature may be a temperature at which carbonization does not substantially occur, and is usually a temperature of 300 ° C. or higher and 500 ° C. or lower, preferably 380 ° C. to 500 ° C. A heating temperature of more than 500 ° C. is not preferable because it causes deterioration of the mold depending on the material used and the molded body obtained is difficult to separate from the mold. It is desirable that the heat treatment be gradually raised from the molding temperature stepwise or continuously, but the effect of the present invention is not lost even if the temperature is immediately raised from the molding temperature to a predetermined holding temperature.

As the holding time, it depends on the softening temperature and holding temperature of the Pitches used, but usually 0.5 to 100 hours,
It is preferably in the range of 3 to 20 hours.

The pressure applied while holding the molded body is not particularly limited unless it is completely unpressurized, but maintaining the pressure during molding is in view of pressure operation and the like. preferable.

It should be noted that while holding the molded body, there is a pressure increase due to the expansion of the pitches as a matrix, so it is necessary to operate the pressure maintaining mechanism and the like so that the pressure does not rise dangerously.

After the holding of the predetermined temperature and time is completed in this way, the mold is cooled and returned to normal pressure to obtain a molded body, and carbonized. The carbonization treatment is performed according to a conventional method, for example, a method in which the molded body is embedded in a packing course. If necessary, pitch impregnation or resin impregnation-
It is possible to obtain a C / C composite material by repeating the densification treatment of recarbonization or further performing graphitization treatment.

(Effect) The C / C composite material obtained according to the present invention is small in shape change and dimensional change due to carbonization treatment, and has sufficiently few densities of pores and cracks to have a sufficiently high density, which is excellent. It shows the characteristics.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

Example 1 A carbon fiber bundle of 3000 filaments (tensile strength 200 kg / mm ² , elastic modulus 15 ton / m) in a mold having a thickness of 2 mm, a width of 10 mm and a length of 230 mm.
m ² ) and fine powder obtained by heat treatment from coal tar pits and having a softening point of 240 ° C. under the 60 mesh mesh sieve were alternately laminated. Then, this mold was placed on a pressurizing machine equipped with a heater and heated to 330 ° C. 15 after the mold reaches 330 ℃
After a lapse of minutes, pressurization was started, and the pressure was maintained at 50 kg / cm ² for 30 minutes for molding. Continue to maintain the pressurized state 20
The temperature was raised to 450 ° C at the ratio of ℃ / Hr, and after reaching 450 ° C 1
It was kept as it was for 0 hours. At this time, the pressure holding mechanism of the pressurizer was operated so that the pressure did not exceed 200 kg / cm ² . After that, the mold was cooled and returned to normal pressure to obtain a molded body. The fiber volume content of the obtained molded body is about 50%,
The bulk density was 1.52 g / cm ⁸ .

Then, this molded body was embedded in packing coke 60
Carbonization treatment was performed by raising the temperature up to 0 ° C at a rate of 10 ° C / Hr and then up to 1000 ° C at a rate of 30 ° C / Hr. The change in volume of the molded body due to carbonization was -3.3%, and the bulk density of the obtained C / C composite material was 1.54 g / cm ⁸ .

Further, the process of impregnating the C / C composite material with pitch was repeated four times to obtain a densified C / C composite material. The bulk density of this C / C composite material was 1.72 g / cm ⁸ . In addition, the volume change of the C / C composite material due to the densification treatment was almost nonexistent. This C / C composite material was cut into a test piece having a length of 45 mm, and a three-point bending test was performed at a span distance of 40 mm and a strain rate of 1 mm / min to measure the bending strength and the same elastic modulus. As a result, the bending strength was 55 kg / mm ² and the elastic modulus was 13.5 ton / mm ² as an average value of the four test pieces.

Example 2 Similar to Example 1, carbon fiber bundles of 3000 filaments and Pitch powder having a softening point of 240 ° C. were alternately laminated in a mold having a thickness of 2 mm, a width of 10 mm and a length of 230 mm, and then placed in a press. After placing
Heated to 330 ° C. Pressing was started 15 minutes after the temperature of the mold reached 330 ° C., the pressure was kept at 50 kg / cm ^{2 and} was held for 30 minutes to perform molding. Subsequently, in the pressurized state, the temperature was raised to 380 ° C. and kept for 5 hours. Further raise the temperature to 430 ° C for 3 hours, 4
The temperature was raised to 80 ° C. and kept for 2 hours. At this time, the pressure is 200k
I tried not to exceed g / cm ² . The fiber volume content of the obtained molded product was about 50%, and the bulk density was 1.54 g / cm ⁸ .

Next, as a result of carbonizing this molded body as in Example 1, a C / C composite material having a bulk density of 1.56 g / cm ⁸ was obtained. The volume change of the molded product due to carbonization was -2.7%.

Further, this C / C composite material was impregnated with pitch and recarbonization was repeated 4 times to obtain a densified C / C composite material.
The bulk density of this C / C composite material was 1.73 g / cm ⁸ . In addition, the volume change of the C / C composite material due to the densification treatment was almost nonexistent.

The flexural strength and the elastic modulus of this C / C composite material were measured in the same manner as in Example 1, and the average values of the four test pieces were 59 kg / mm ² and 14.0 ton / mm ² , respectively.

Comparative Example Similar to Example 1, a carbon fiber bundle of 3000 filaments and pitch powder having a softening point of 240 ° C. were alternately laminated in a mold having a thickness of 2 mm, a width of 10 mm and a length of 230 mm, and then placed on a press. After placing
Heated to 330 ° C. Pressing was started 15 minutes after the temperature of the mold reached 330 ° C., the pressure was kept at 50 kg / cm ^{2 and} was held for 30 minutes to perform molding. After that, the mold was cooled and returned to normal pressure to obtain a molded body. The fiber volume content of the obtained molded body is about 50%,
The bulk density was 1.47 g / cm ⁸ .

Next, as a result of carbonizing this molded body in the same manner as in Example 1, a C / C composite material having a bulk density of 1.18 g / cm ⁸ was obtained. The volume change of the molded product due to carbonization was + 22.8%. Further, this C / C composite material was impregnated with pitch and recarbonization was repeated 4 times to obtain a densified C / C composite material. This C
The bulk density of the / C composite material was 1.38 g / cm ⁸ . In addition, the volume change of the C / C composite material due to the densification treatment was almost nonexistent.

The flexural strength and elastic modulus of this C / C composite material were measured in the same manner as in Example 1, and the average values of the four test pieces were 21 kg / mm ² and 5.7 ton / mm ² , respectively.

Claims (1)

[Claims] 1. A method for producing a carbon fiber-reinforced carbon composite material using pitches as a matrix raw material, wherein carbon fibers are impregnated with pitches and heated and pressure-molded, and subsequently, at a molding temperature in a pressurized state. A method for producing a carbon fiber-reinforced carbon composite material, which comprises performing a carbonization treatment after holding a molded body at a temperature higher than or equal to 500 ° C.