JP2566555B2 - 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, it relates to a method for producing a carbon fiber reinforced carbon composite material having excellent performance by using pitches as a matrix raw material.

(Prior Art) Carbon fiber reinforced carbon composite material (hereinafter abbreviated as "C / C composite material") is light weight, high strength, heat resistance and corrosion resistance, and is utilized for rocket nozzle, nose cone and aircraft. It is used for aerospace materials such as disk brakes, heating elements, hot press molds, other mechanical parts, and reactor components.

In the conventional C / C composite material, carbon fibers are previously impregnated with an organic matrix such as resin or pitch, molded and cured, and then carbonized or graphitized. It is manufactured by the method of filling cracked 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 is C / C
It has the advantage that it is preferable in terms of performance of the composite material, and further that when the carbon fiber used is made of pitch as a raw material, it is well compatible with the fiber and the adhesion between the fiber and the matrix is good. ing. However, on the other hand, pits have a significant expansion during carbonization, and when used as a matrix for C / C composites, they have poor shape retention and dimensional stability when baked into C / C composites. , Or a large number of pores and cracks inside the C / C composite,
There is also a drawback that sufficient performance cannot be achieved unless the densification process of pitch impregnation or resin impregnation-carbonization is repeated many times thereafter.

(Problems to be solved by the invention) Therefore, carbonization after molding is conventionally performed as a method for avoiding such a drawback in the case where pits are used as a matrix material.
At least pits start to carbonize and develop strength
Up to a temperature of 600 to 700 ° C, a method called so-called carbonization under pressure in an autoclave has been adopted. However, even if such a method is adopted, the expansion of pits is not completely suppressed, and there is a problem when the apparatus for carbonization becomes large-scale and complicated.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, impregnated carbon fibers with pits and molding, and after molding, are superior by performing a specific treatment. The present invention has been achieved by finding that a C / C composite material having excellent performance can be obtained.

That is, the object of the present invention is also to provide a method for producing a C / C composite material having a high property in a simple and stable manner.

And, in the method for producing a carbon fiber reinforced carbon composite material using the pitches as a raw material for matrix,
This is achieved by impregnating carbon fibers with pitches and molding, and then subjecting the obtained molded body to heat treatment in an oxidizing atmosphere and then to carbonization treatment.

 The present invention will be described in detail below.

Pits as a matrix raw material used in the present invention are derived from coal tar pitch, petroleum residue pitch or various synthetic pitch by distillation, heat treatment, air blowing or solvent treatment, extraction of a specific component by sedimentation and separation. It may be a carbonaceous bituminous material having a softening temperature suitable for molding, but more specifically, the softening point obtained by the Mettler method is in the range of 200 to 350 ° C. and the distillation at 300 ° C. Use Pitches with a yield of less than 10%.

The carbon fiber is not particularly limited, and polyacrylonitrile-based, pitch-based carbon fiber, carbon fiber obtained by a vapor phase pyrolysis method, or the like can be used. As the form of the carbon fiber to be used, a continuous fiber, a short fiber, a felt-like form or a woven state is used.

Further, the amount of the fiber used cannot be unconditionally specified because it varies depending on the use of the C / C composite material, but it is generally in the range of 20 to 75%, preferably 30 to 60% with respect to the volume of the molded body. Selected from. The carbon fibers are arranged in a molding die after impregnating the melted pitches, or they are arranged by alternately laminating fibers and powders of the pitches in the molding die. The mold filled with carbon fibers and pitches 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,
Until the pits exhibit such a low viscosity that they can sufficiently penetrate between the carbon fibers, that is, the softening point of the pits is usually 50-
It is preferred to heat to a temperature as high as 150 ° C. After the pits are melted, the pressure is applied by a pressure machine, usually 5-100 kg /
A pressure of cm ² is applied and molding into a predetermined shape is performed.
After molding, the mold is cooled, and after sufficiently cooled, the pressure is released to obtain a molded body.

In the method of the present invention, it is important to heat-treat the obtained molded body in an oxidizing atmosphere. The heat treatment conditions are usually
Heat treatment is performed at a temperature in the range of 50 to 450 ° C, preferably 100 to 330 ° C for 1 to 100 hours, preferably 5 to 30 hours.

It is preferable that the treatment temperature is a temperature at which the pitches are not softened or melted at first and then gradually raised in a stepwise or continuous manner.

As the oxidizing atmosphere, for example, an oxidizing gas such as air, oxygen, ozone, chlorine, sulfur, carbon dioxide, nitrogen oxide and sulfur oxide can be used alone or in a mixed state.

It is also possible to appropriately dilute these oxidizing gases with an inert gas such as nitrogen before use. Although the degree of dilution varies depending on the type of oxidizing gas, for example, in the case of oxygen, nitrogen oxides, sulfur oxides, etc., the oxidizing gas is usually 5 to 50 vo
Used in l%. The molded body that has been heat-treated in an oxidizing atmosphere is then carbonized. The carbonization is carried out by a conventional method, for example, the molded body is embedded in packing coke and carbonized. Further, if necessary, it is possible to obtain a more dense C / C composite material by repeating the densification treatment of pitch impregnation or resin impregnation-recarbonization, and if necessary, perform graphitization treatment. Is also good.

(Effect) According to the present invention, the obtained C / C composite material has a small shape collapse and dimensional change due to the carbonization treatment, and has sufficiently few densities of pores and cracks, so that it has a sufficiently high density and is therefore excellent. It shows the characteristics.

Hereinafter, the present invention will be specifically described by way of 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 , same elastic modulus 15 ton in a mold having a thickness of 2 mm, a width of 10 mm and a length of 230 mm).
/ mm ² ) and a powder obtained by heat treatment from coal tar pits and having a softening point of 240 ℃ and a distillate content of less than 10% at 300 ℃ under 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. Pressing was started 15 minutes after the temperature of the mold reached 330 ° C., and the mold was held under a pressure of 50 kg / cm ² for 30 minutes.
After that, the mold was cooled and returned to normal pressure to obtain a molded body. The obtained molded body has a fiber volume content of about 50% and a bulk density of 1.
It was 52 g / cm ³ .

Subsequently, this molded body was placed in a furnace heated to 150 ° C in an air atmosphere, and heated up to a temperature of 320 ° C at a rate of 10 ° C / Hr. After reaching 320 ° C., it was held for 20 hours. The bulk density of the molded product obtained as a result of this heat treatment is
It was 1.48 g / cm ² , and the change in volume of the molded body due to heat treatment was + 5.2%.

Then, this molded body is embedded in packing coke.
Carbonization treatment was carried out by raising the temperature up to 600 ° 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 product due to carbonization was + 7.0%, and the bulk density of the obtained C / C composite material was 1.43 g / cm ² .

Furthermore, the bulk density of the densified C / C composite material is obtained by repeating the process of impregnating this C / C composite material with pitch and re-carbonizing it four times.
It was 1.62 g / cm ² . In addition, there was almost no change in the composite material volume due to the densification treatment.

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 elastic modulus. As a result, the bending strength was 37 kg / mm ² and the elastic modulus was 9.8 tons as an average value of the three test pieces.
It was / mm ² .

Example 2 Under the same conditions as in Example 1, the fiber volume content is about 50%, and the bulk density is
A molded body weighing 1.53 g / cm ³ was obtained. This molded body was placed in a furnace heated to 120 ° C in an oxidizing atmosphere in which 5 vol% of nitrogen oxide gas was mixed with air, and heated up to a temperature of 300 ° C at a rate of 10 ° C / Hr. Further, after reaching 300 ° C., holding was performed for 10 hours. The bulk density of the molded product obtained as a result of this heat treatment is
It was 1.50 g / cm ³ , and the change in volume of the molded body due to heat treatment was + 4.6%.

Next, this molded body was carbonized under the same conditions as in Example 1. The change in volume of the molded product due to carbonization was + 5.8%, and the bulk density of the obtained C / C composite material was 1.46 g / cm ² . Further, the process of impregnating the C / C composite material with pitch and re-carbonizing was repeated 4 times to obtain a densified C / C composite material. The bulk density of this C / C composite material was 1.64 g / cm ³ . In addition, there was almost no change in the composite material volume due to the densification treatment.

The flexural strength and the elastic modulus of this C / C composite material were measured in the same manner as in Example 1. As a result, the average values of the four test pieces were 41 kg / mm ² and 10.4 ton / mm ² , respectively.

Comparative Example Under the same conditions as in Example 1, fiber volume content of about 50%, bulk density
A molded body of 1.52 g / cm ³ was obtained.

Then, this molded body was carbonized in the same manner as in Example 1 except that the heat treatment was not performed in an oxidizing atmosphere, and as a result, a C / C composite material having a bulk density of 1.22 g / cm ³ was obtained. The volume change of the molded body due to the carbonization treatment was + 19.8%. Furthermore, the process of impregnating this C / C composite material with pitch and re-carbonizing it
Repeated times, a densified C / C composite material was obtained. The bulk density of this C / C composite material was 1.39 g / cm ³ . In addition, there was almost no change in the composite material volume due to the densification treatment.

The bending strength and the elastic modulus of this C / C composite material were measured in the same manner as in Example 1, and as a result, the average value of the four test pieces was 26 kg / mm ² ,
It was 6.4 ton / mm ² .

Comparative Example 2 (use of a pitch having a low softening point) As a pitch, a softening point of 140 ° C and a distillate content of 16% at 300 ° C
Molding, heat treatment, and carbonization were performed under the same conditions as in Example 1 of the present specification except that the pitch was used. Foaming occurs at the time of molding, and further heat treatment and carbonization further intensify foaming, causing severe deformation, and subsequent densification treatment,
Both the strength and elastic modulus of the composite thereafter could not be measured.

Comparative Example 3 (Heat Treatment in Oxidizing Atmosphere Performed Before Molding) Similar to Example 1 of the present application, carbon fiber bundles and pitches were alternately laminated. This laminate is placed in a furnace heated to 150 ° C in an air atmosphere, heated up to a temperature of 320 ° C at a rate of 10 ° C / Hr, and held for 20 hours after reaching 320 ° C. Was done.

Next, molding was carried out under the same conditions as in Example 1 by using a pressure machine equipped with a heater to obtain a molded body. The bulk density of the obtained molded body was 1.20 g / cm ³ .

Subsequently, the same carbonization treatment and densification as in Example 1 were performed.
Porosity is generated in the obtained composite material, and the bulk density of the composite material after each of carbonization treatment and densification is 1.24 g / cm ³ , 1.39 g / c.
m is ^3, and the flexural strength of the composite material is 21 kg / mm ^2, a flexural modulus of 6.4ton / mm ^2. It can be seen that this molded body has lower bulk density and bending strength than Example 1.

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Claims (1)

(57) [Claims] 1. A method for producing a carbon fiber reinforced carbon composite material using pitches as a matrix raw material, wherein the carbon fiber has a softening point of 200 ° C. to 350 ° C. and a distillate content at 300 ° C. of less than 10%. A method for producing a carbon fiber-reinforced carbon composite material, comprising impregnating pitches and molding, heat-treating the obtained molded body in an oxidizing atmosphere, and then carbonizing the molded body.