JPH0456788B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing a carbon fiber reinforced carbon material that exhibits excellent performance when used in rocket nozzles, aircraft disc brakes, carbon heating elements, etc. It is something.

<Prior art and its problems> Carbon fiber-reinforced carbon materials (hereinafter referred to as "C/C composite materials"), which are lightweight, exhibit high strength, and have excellent heat resistance, are now used in spacecraft components, heating elements, Furthermore, it has become indispensable as a medical material, and for its production, ``a method of mixing carbon fiber with a thermosetting resin or pitch and carbonizing the mixture'' is generally adopted. However, when this method is adopted to manufacture C/C composite materials, a large number of pores are likely to be generated in the compact after carbonization. )
The process is extremely complicated, requiring densification treatment such as ``treatment'', and therefore cannot be said to be an industrially preferred method.

On the other hand, if carbon fibers, carbonaceous aggregates, and a mixture of pitch with a high softening point are alternately laminated, then pressurized and heated, and then carbonized, densification treatments such as pitch impregnation and CVD are possible. It has also been reported that a C/C composite material with high density and high strength can be obtained even without the addition of carbonaceous materials. However, even with this method, the strength of the C/C composite material obtained is only about 800 kg/cm ² in terms of bending strength, and the C/C
It could hardly be said that it satisfactorily satisfies current requirements for composite materials.

As described above, although C/C composite materials are attracting attention as lightweight and high-strength materials, there are still strong demands for improvements in their physical properties and manufacturing methods.

For these reasons, the present inventors have established a stable production method for high-density C/C composite materials that have excellent bending, tensile, compression, and shear strength, as well as various physical properties including abrasion resistance. Recognizing that it is an urgent task,
Considering that it is advantageous in terms of density and strength due to its high carbonization yield, we will focus on the method of producing C/C composite materials by pressurizing and heat forming using pitch as a binder, and especially Focusing on the pressure/heat molding pattern, we conducted a basic study on the influence of the pressure/heat molding pattern on product characteristics.

By the way, the following two methods have conventionally been adopted as pressure/heat molding patterns during pressure/heat molding of C/C composite materials using pitch as a binder. Namely, (A) A method in which high pressure is continuously applied from room temperature to the final temperature of molding.

(B) Method of starting pressurization at 550℃, when the pitch becomes highly viscous, and continuing to pressurize until about 650℃.

However, based on the basic study by the present inventors as described above, method (A) tends to cause the product to become porous due to the encapsulation of pyrolysis gas in the molded body, which hinders the improvement of product strength. On the other hand, in method (B) above, the pitch polymerizes excessively at the start of heating and the viscosity becomes too high, reducing the ability to bond carbon fibers and carbonaceous aggregates, so the strength of the product does not improve sufficiently. Each of these facts has been confirmed.

<Means for solving the problem> Therefore, the present inventors developed a high-density C/C composite material that is sufficiently satisfactory in physical properties including strength by using "pressure and heat forming means using pitch as a binder". In order to provide a method for stable production, we conducted repeated research based on the viewpoint that it is essential to devise a pressurization/heating pattern. When producing a C/C composite material by pressurizing and heating the mixed raw materials, forming them, and then carbonizing or graphitizing them,
In the pressure/heat molding process, first, the thermal decomposition of the binder pitch progresses to a certain extent and the amount of gas generated decreases, but the polymerization reaction of the pitch does not progress that much and the viscosity is still low.
Substantial pressurization does not start until the temperature range reaches 480℃, and only after reaching this temperature range does pressure increase above a certain pressure continue and the temperature continues to increase, ensuring that the decomposition and solidification reactions of pitch are efficient By continuing to pressurize to a temperature range of 430 to 550 degrees Celsius, which is higher than the temperature at which pressurization is normally completed, it is possible to stably produce a dense and high-performance C/C composite material. This led to the discovery of new knowledge.

This invention was made based on the above knowledge, and first, a molding raw material consisting of finely powdered carbonaceous aggregate, binder pitch and carbon fiber is heated to a temperature range of 360 to 480°C under a pressure of 20 kg/cm ² or less. The temperature rises at
After being molded under heating at 550°C and under pressure of 30 kg/cm ² or less, it is carbonized or graphitized, resulting in high density, strength in bending, tension, compression, shearing, etc., and wear resistance. C/C with excellent physical properties such as
It is characterized by the ability to stably produce composite materials on an industrial scale.

Here, the carbonaceous aggregate is carbon powder and carbon black, which have been conventionally used in the production of C/C composite materials. Any material such as graphite can be used.
Although the particle size is not particularly limited, if the particle size exceeds 20μ, cracks are likely to occur in the aggregate and pitch matrix after carbonization of the composite, so it is preferable to use a particle size of 20μ or less. It is preferable to use carbonaceous aggregate (for example, one mainly composed of particles with a particle size of 5 to 15 μm).

Furthermore, the method of this invention employs pitch as a binder. This is because pitch is more advantageous than thermosetting resins because it has a higher carbonization yield. There are no particular restrictions on the type of binder pitch, but the lower the volatile content, the higher the carbonization yield and the denser matrix that can be obtained.
% or less of volatile content is preferred. On the other hand, from the viewpoint of adhesion of carbon fibers and carbonaceous aggregates, a material with good softening and fluidity is preferable, and from the viewpoint of such softening and fluidity, a material with a volatile content of 15% or more is suitable.

The binder pitch having a volatile content of 15 to 30% as described above can be obtained, for example, by heat-treating coal tar pitch or petroleum pitch at a temperature of 350° C. or higher under reduced pressure.

The carbon fiber used in this invention may be either a high-performance product or a general-purpose one, and the carbonization temperature of the carbon fiber used does not need to be the usual 1000°C or higher, but a temperature of about 500 to 1000°C is sufficient. Yes (rather,
These materials fired at a relatively low temperature tend to shrink when the compact is carbonized, so the difference in shrinkage with the matrix is eliminated and high strength is often achieved), and these are the target C/C composite materials. It should be selected according to the performance. Furthermore, various forms of carbon fiber can be used, such as chop-like and fiber-like forms.
There are no particular restrictions. However, in the case of woven fabrics, although high properties can be obtained in the direction of fiber orientation, the anisotropy is extremely large, so depending on the application, chop materials that have relatively good isotropy and are easy to mix raw materials are used. In some cases, it may be preferable to use

Further, the fiber diameter is not particularly limited, but it is suitably about 5 to 20 microns. and,
These carbon fibers are usually sized with epoxy resin, etc., but if they are used as they are sized, the sizing agent will harden when heated, making it difficult for the pitch to impregnate into the carbon fiber bundle, and the pitch and carbon Since foreign matter will be present at the interface with the fibers, it is desirable to remove the sizing agent with a solvent before use.

Now, once the carbonaceous aggregate, binder pitch, and carbon fiber are prepared, they can be mixed by normal dry mixing or other means, or the mixture of carbonaceous aggregate, binder pitch, and carbon fiber can be mixed alternately. After the laminated material is laminated, it is subjected to the next pressurization/heat molding process to be formed. Of course, it is a preferable measure to press the mixed molding raw materials at normal pressure and preform them prior to this pressurization and heat molding.

Pressure/heating process is either no pressure or at most 20
Temperature in the range of 360-480℃ under low pressure below Kg/ ^cm2
A first stage of heating up to t _s , followed by
430-550℃ higher than this temperature from said temperature _s
(preferably 430-540℃)
The process consists of a second stage in which the pitch is pressurized at a pressure of 30 Kg/cm ² or more (preferably 40 Kg/cm ² or more) to t _nax and held until the pitch is sufficiently solidified.
Figure 1 is a graph schematically showing an example of a pressure/heat molding pattern in terms of the relationship between temperature, molding pressure, and elapsed time. The reason for limiting the numerical value is as follows.

In other words, at temperatures below 360°C, the pitch is softened, but the thermal decomposition reaction of the pitch does not yet occur, and in the temperature range of 360 to 480°C, thermal decomposition progresses to some extent, but at this point When pressurized at a high pressure exceeding 20Kg/ ^cm2 , the carbon fibers and aggregate of the molded object are brought into close contact with each other, and the gap is compacted until the pitch is filled, and excess pitch flows out from the molded object. . However, as the final temperature of the pressure/heat molding mold needs to be higher, if the temperature of the mold is raised further, the pitch will either undergo a thermal decomposition reaction or increase the degree of the thermal decomposition reaction. Due to the pressure of the generated gas, more pitches flow out of the mold, resulting in a shortage of pitches.
The resulting molded body becomes porous and tends to have reduced strength. In addition, if the pitch is suddenly heated to a temperature range exceeding 480℃, the pyrolysis reaction of the pitch will proceed too much and the viscosity will increase, so even if pressure molding is performed, pyrolysis gas will be trapped, so the pitch and carbon fiber will be separated. There is a concern that sufficient wetting and adhesion may not occur and the strength of the molded product may be adversely affected. However, if the initial process of pressure/heat molding is adjusted to a temperature range of 360 to 480°C with no pressure or at most a pressure of 20 kg/cm ² or less, the high pressure required for molding can be achieved. The pyrolysis progresses to some extent before the pyrolysis occurs, and the amount of gas produced by pyrolysis is reduced, so the outflow phenomenon of the pitch caused by the decomposed gas is reduced.Furthermore, within this range, the viscosity of the pitch is still low, so it is possible to reduce the occurrence of foaming. Problems such as poor contact between aggregates and carbon fibers and pitches are completely eliminated. Following this, the object to be formed is
When the temperature is further increased under pressure of Kg/cm ² or more, preferably 40 Kg/cm ² or more, the molding is completed and carbonized or graphitized, the C/C composite material that fully satisfies the target strength becomes even more stable. can be obtained. In this case, if the maximum temperature reached in the second step, which is higher than the temperature reached in the first step, is less than 430℃, the decomposition and solidification reaction of the pitch will be slow and it will take a long time to form, whereas if it exceeds 560℃ Cracks occur in the molded body due to the "difference in expansion and contraction between the thermally expanding mold surface and the shrinking molded body" caused by the pitch completing solidification and shrinking. Furthermore, if the molding pressure at this time is less than 30 kg/cm ² , there is a possibility that a sufficiently densified molded product cannot be obtained. For this reason, the pressing force and heating temperature in each molding step were limited to the above-mentioned specific ranges. Although the temperature increase rate is not particularly limited, there is a concern that if the temperature increase rate becomes too high, it becomes easier to contain bubbles, resulting in a decrease in density, strength, etc. On the other hand, if the temperature increase rate is low, productivity will not be good. Therefore, the temperature increase rate during pressurization and heat molding is preferably 1 to several +
C/min, more preferably about 1 to 10 C/min.

The molded body formed under pressure and heat as described above is
It has a dense structure in which the fiber filaments are strongly bonded, but by carbonizing or graphitizing this compact using a conventional method, it can be made to have a high bending strength of about 2000 kg/cm ² or more, for example. It also becomes possible to manufacture C/C composite materials with strength.

EXAMPLES The present invention will be specifically described below with reference to Examples.

<Example> 50 parts of GP carbon fiber chops (fiber length: 0.7mm, yarn strength: 70Kg/mm ² , yarn diameter: 18μ), particle size 12μ
Prepare 25 parts of coke powder and 25 parts of coal tar pitch powder with a softening point of 270℃ and a particle size of 100μ,
Mix this thoroughly and then add 60g of it to the inner diameter.
It was placed in a 50φ mold, heated from room temperature to 370℃ at a heating temperature of 10℃/min while being pressurized at 10Kg/ ^cm2 ,
From 370℃, molding pressure: 100Kg/cm ² and heating rate: 4
The temperature was raised to 510°C at a rate of °C/min and held for 1 hour.
Subsequently, the mixture was cooled to 400° C. while being pressurized at 100 Kg/cm ² , and from 400° C. it was cooled to room temperature without applying pressure (pressure: 0 Kg/cm ² ).

Next, the molded body is taken out of the mold, packed in the center of coke powder as usual, heated in _N2 gas at a heating rate of 20°C/min to 1000°C, held for 1 hour, and then cooled. Carbonization treatment was performed.

The C/C composite thus obtained had a bending strength of 1100 kg/cm ² and an apparent density of 1.58 g/cm ² .

<Summary of Effects> As explained above, according to the present invention, it is possible to stably produce, on an industrial scale, a carbon fiber-reinforced carbon material with high density and superior strength and other properties. Therefore, it is expected that the field of application of carbon fiber-reinforced carbon materials will further expand, and extremely useful effects will be brought about industrially.

[Brief explanation of the drawing]

FIG. 1 is a graph schematically showing an example of a pressure/heat molding pattern in relation to temperature, molding pressure, and elapsed time.

Claims (1)

[Claims] 1. A molding raw material consisting of finely powdered carbonaceous aggregate, binder pitch, and carbon fibers is first heated to a temperature range of 360 to 480°C under a pressure of 20 kg/cm ² or less, and then The maximum temperature range higher than the temperature reached is 430
A method for producing a carbon fiber-reinforced carbon material, which comprises shaping the material under heating at ~550°C and applying pressure of 30 kg/cm ² or less, followed by carbonization or graphitization. 2. A method for producing a carbon fiber-reinforced carbon material according to claim 1, which uses chop-shaped carbon fibers. 3. The method for producing a carbon fiber reinforced carbon material according to claim 1 or 2, which uses a binder pitch having a volatile content of 15 to 30%.