JPS63112463A - Manufacture of carbon fiber/carbon composite material - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention is applicable to wear-resistant materials such as disc brake materials for aircraft and automobiles, sliding materials such as bearings, ablation materials such as rocket nozzles, or hot The present invention relates to a method for manufacturing a carbon fiber/carbon composite material that exhibits excellent performance when used in press molds and the like.

<Prior art and its problems> Carbon fiber/carbon composites (hereinafter referred to as rC/C composites), which are lightweight, have high strength, and have excellent wear resistance and lubricity, are now used in spacecraft components and other materials. It has become indispensable as an automobile component and even a medical material, but its production requires a composite material of carbon fiber and thermosetting resin (CF RP).
) is generally employed.

However, when thermosetting resin is carbonized, the carbonization yield is about 5
Therefore, by simply carbonizing a composite material of carbon fiber and thermosetting resin, the matrix after carbonization becomes a C/C composite material with many pores and cracks, making it impossible to secure the desired strength. Therefore, according to the above method, C
/C When manufacturing composite materials, "pitch impregnation-recarbonization"
Densification processing, such as repeating the process, was required. For this reason, the above-mentioned conventional manufacturing method for C/C composite materials has a problem in that the manufacturing process is extremely complicated, resulting in poor production efficiency and, therefore, the product price is extremely high. It has been pointed out that this method cannot be said to be an industrially preferable method.

On the other hand, in light of this situation, recently, regarding the production of C/C composite materials, ``Pitch and coke powder are used as matrix materials, and carbon fiber is mixed into this, which is then pressurized at a semi-carbonization temperature of about 500℃.'' The results of examining the possibility of a new method that incorporates the method of "heat forming" have also been reported ("Tetsu to Hagane" NO, 5, VOL, 72. MAR, 1
986, p. 306). Since the carbonization yield of the pitch component after pressure and heat molding is as high as about 90%, it is expected that the above method will yield a matrix with few pores and cracks, without the need for a separate densification process. It was expected that a C/C composite material with relatively good strength would be produced even if

However, the C/C composite material obtained by the method reported in this new report currently has a strength of at most 800 K.
The actual situation was that it was only 1,000 to 2,000 kg/cm'' of commercially available high-performance C/C composite materials.

Means for Solving Problems〉 From the above-mentioned viewpoint, the present inventors have discovered that bending, tension,
In order to provide a method that can stably produce high-density C/C composite materials on an industrial scale that have excellent compression and shear strength and other physical properties such as abrasion resistance, we particularly aim to Since thermosetting resins are not used, expectations tend to arise that there may be room to obtain sufficiently satisfactory high-density and high-strength C/C composite materials through ingenuity. ``Manufacturing method of C/C composite material reported in ``And Steel''
Focusing on this, we first conducted research aimed at elucidating the reason why the C/C composite material manufactured by this method does not show as high strength as expected. As a result, we found the following (al to (f)) (a) When a molding material made of a mixture of pitch, aggregate such as coke powder, and carbon fiber is heated under pressure, the pitch becomes molten; At this time, the molded body is consolidated due to the molding pressure until the carbon fibers and coke powder come into contact with each other.
The excess pitch flows out of the system, so that there is no excess or deficiency in the pinch. However, in order to complete the pressurization and heat molding of the molding material, it is necessary to heat it to a higher temperature.

However, when heated to such a high temperature range, bi-sochi generally decomposes and generates gas, and the pitch, which had maintained a quantitative balance, is further pushed out of the system due to the gas pressure of this generated gas, and this outflow Pores are generated in the compact by the volume of the pitch, which causes a decrease in the strength of the C/C composite product.

(b) The amount of decomposed gas generated increases as the volatile content of the pitch increases, so if a pitch with a high volatile content is used, the molded product becomes porous, and the C/C composite obtained accordingly. Decrease in the strength of the material.

(C) Shikaruni, the above-mentioned “C/C reported to “Tetsu to Hagane”
``Manufacturing method for composite materials'' is a technical paper by the same author, ``
゛Prototype production of carbon materials using bulk mesophase as a binder° (“Carbon” 1985. No. 123. No. 15
As is clear from the fact that "pitch with a volatile content of 30% or more is good" on pages 0 to 159, it is assumed that a pinch containing a high volatile content should be used. Therefore, this is thought to be a major obstacle in obtaining a C/C composite material with the desired strength.

(d) From the perspective of C/C, if a pitch with low volatility is used, C/C
Strength should be improved. Nevertheless, the technical paper published in the serial "Carbon" states that "the strength decreases when the volatile content of the pitch is low." The pitch used is 8.
Pitch with this composition has poor meltability (softening properties) and has poor adhesion to carbon fibers and coke powder (thus, sufficient product strength is not achieved). It is assumed that it was not possible.

(e) For these reasons, when producing a C/C composite material using a composition consisting of carbon fiber, aggregate such as coke powder, and pitch as a molding material, it is necessary to It is concluded that by using a pitch with good meltability, it is possible to stably manufacture a dense C/C composite material with sufficiently satisfactory strength without requiring complicated processes.

(f) Pinch with low volatile content and excellent meltability as described above can be easily obtained by heat treating tar or pitch under reduced pressure or while blowing water or gas (Nz gas, etc.). .

This invention was made based on the above findings, and involves pressurizing a molded material consisting of carbon fibers, finely powdered carbonaceous aggregate, and a binder pitch with a volatile content of 28% or less and a softening point of 400°C or less.・By heat forming and then carbonizing or graphitizing, it is possible to stably mass-produce carbon fiber-reinforced carbon materials with high density and excellent physical properties such as strength and abrasion resistance without the need for troublesome processing or operations. It is characterized by the following points.

The carbon fiber used may be either high-performance grade or general-purpose grade, with high-performance grade products used as structural materials and general-purpose grade products used as wear-resistant materials and sliding materials. It is appropriate to use them in the following manner. Furthermore, the form of the carbon fiber may be a woven fabric, a prepreg-like unidirectional fiber, a chopped short fiber, or the like.

The carbonaceous aggregate plays the role of suppressing the shrinkage of the matrix and reducing the occurrence of cracks in the matrix during carbonization of the molded material, and is a carbon powder that has been traditionally used in the production of C/C composite materials. Either carbon blank, graphite, etc. can be used.

Although the particle size is not particularly limited, if the particle size exceeds 20μ, cracks are likely to occur in the matrix of aggregate and pitch after carbonization of the composite, so it is preferable to use Umizer etc. It is preferable to use particles having a particle size of 20 μm or less (for example, particles having a particle size of 5 to 15 μm as a main component) that have been finely pulverized in a process. The blending amount thereof is preferably at least 20% by weight based on the total matrix.

By the way, as mentioned above, the binder Pinochi used in this invention has a volatile content of 28% or less (preferably 10% or less).
~28%) and has a softening point of 400°C or less. This is because if the volatile content exceeds 28%, as mentioned above, the amount of decomposed gas generated during pressurization and heat molding will increase, leading to the matrix becoming porous, and the desired performance such as strength properties of the product will not be achieved. On the other hand, if the softening point exceeds 400°C, it will not show sufficient fluidity during pressure/heat molding and will have poor adhesion to carbon fibers and carbonaceous aggregates. This is because a C/C composite material with high performance cannot be obtained.

Here, the volatile content of the binder pitch is JIS8812
This value was measured according to the method, and this value indicates the amount of components that volatilize during carbonization. Further, the softening point is measured using a Koka type flow tester, and the measuring method is as follows. That is, the cross-sectional area of fine powder pitch is 1 cLll.
In this method, the cylinder is packed in a cylinder with a nozzle of 1 fl φ at the bottom, and the temperature is raised at 6°C/hr while pressurizing with a plunger from the top at a pressure of 10 kg/cm, and the displacement of the plunger is measured. What is the softening point in
It can be defined as the temperature at which the plunger stops moving after it begins to move due to softening and deformation of the pitch. Note that the physical meaning of the softening point can be said to be "the temperature at which the softened and deformed pitch finishes filling the initially existing voids."

In this way, pitch that exhibits good melting properties even with a volatile content of 30% or less can be obtained by, for example, melting tar or pitch at 100 Torr.
It can be easily obtained by the following heat treatment of heating to a temperature of about 380 to 550°C under reduced pressure and holding it for an appropriate time. In other words, if the atmosphere is reduced in pressure when heat treating tar or pitch, low molecular weight components will be smoothly removed and the raw material composition will become more homogeneous. It shows much better meltability than heat treatment. The degree of pressure reduction at this time needs to be 100 Torr or less; a pressure higher than this is not appropriate because the effect of improving pitch meltability is small. Furthermore, if the heat treatment temperature is less than 380°C, the reduction in volatile content due to the thermal decomposition reaction of the pitch will be slow, which is undesirable. On the other hand, if the heat treatment temperature exceeds 550°C, the thermal decomposition reaction rate will become excessive and difficult to control. When adjusting the binder pitch by means of other means, the heat treatment temperature is preferably set at 380 to 550°C.

In addition to the method of simply heat-treating under reduced pressure as described above,
Even if heat treatment is performed under atmospheric pressure or reduced pressure while blowing in water vapor or gas (N2 gas, etc.), it is possible to obtain a pitch that has a low volatile content and exhibits good meltability.

Now, the mixing and dispersion adjustment of the molding materials used in the method of this invention may be carried out as follows.

That is, when using carbon fibers in the form of textiles or unidirectional fibers, it is preferable to immerse the carbon fibers in a solution in which carbonaceous aggregate powder and binder pitch are dispersed. In this case, the dispersion liquid may contain materials such as acetone, ethanol, etc., which have good wettability with both the solid powder and the carbon fibers.
A solution of methanol, [water and surfactant], or a mixture of these and a resin can be used. By employing such means, the solid component blends well with the carbon fibers and adheres to them with a uniform thickness, making it possible to produce a molded article with a high carbon fiber content. Then, the carbon fibers to which the matrix material is attached as described above are laminated and then pressurized and heat-molded.

In addition, when using chopped short fibers as carbon fibers, it is necessary to use the general mixing method of blending the fibers and matrix powder and then dry-mixing them using a mixer such as a type blender. Good results are obtained.

The molding materials laminated or mixed as described above are then
It can be pressurized and heated as it is or after preforming.
If possible, it is desirable to employ a method consisting of the following two-stage process as the pressure/heat forming means. That is, first, under no pressure or low pressure (approximately 20 kg/cm" or less), the temperature is raised to a temperature higher than the temperature at which the pitch softens and flows at a temperature rise rate of 1 to b. Once this temperature range is reached, the temperature is increased. Pressure 40 kg/cm
The heating rate should be 1 to 20℃'c/mi.
In this method, the temperature is raised to about 450 to 600° C., which is the temperature range in which the pitch actively causes a thermal decomposition reaction, and the pitch is pressurized and held until it is sufficiently solidified.

The pressurized and heated molded product obtained in this way is
Next, the temperature is increased at a rate of 1 to b in an inert gas atmosphere.

According to the method of the present invention as described above, it has a high apparent density of 1.5 to 1.7 g/cm3 even without special densification treatment, and has a high apparent density compared to conventional C/C composite materials. to stabilize C/C composite materials with even higher strength (approximately 1000 kg/cm2 when using general-purpose grade carbon fiber, and approximately 2000 kg/cm'' when using high-performance grade carbon fiber). However, the present invention will be specifically explained below with reference to Examples.

<Examples> Example 1 4 kg of coal tar was charged into a glass separable flask with a content rating of 52, and heat treated under the conditions shown in Table 1 to adjust binder pitches with different volatile content ranks.

On the other hand, petroleum coke was heated to a temperature of 1000° C. to carbonize it, and then finely pulverized using a userizer to prepare coke powder with an average particle size of 11 μm.

Next, for each of the above-mentioned binder pitches with different volatile contents, 70 parts of the binder pitches pulverized to 100 mesh or less and 30 parts of coke powder were dispersed in 170 parts of ethanol, and in this dispersion, after washing with acetone, Dry 9.5
A PAN-based carbon fiber fabric (high-strength yarn, number of filaments: 1000, plain weave) cut into a size of 9.5 cm x 9.5 cm was immersed to adhere the coke powder and binder pitch.

Next, the matrix material was attached in this way, and then 30 sheets of the dried fabric were layered, and the inner dimensions were 10.
Temperature rising rate after charging into a cm square mold: Table 1 (Note 1) * indicates that the conditions are outside the conditions of the present invention.

(Note 4) The carbon fiber content in the obtained C/C composite material is 5
It was 0-60%.

Table 2 (Note 1) * indicates that the conditions of the present invention are not met.

The temperature was raised to 520°C at a rate of 5°C/rain. Then, after being maintained at this temperature for 30 minutes, it was cooled to obtain a molded article having the above dimensions.

Subsequently, these molded bodies were packed in coke powder and carbonized by raising the temperature to 1000° C. at a heating rate of 15° C./min in an N2 atmosphere to obtain a C/C composite material.

Table 1 also shows the apparent density and bending strength of the C/C composite material thus obtained.

As is clear from the results shown in Table 1, the C/C composite material manufactured according to the conditions of the present invention has a high density and a high bending strength of 1500 kg/am'' or more. I can see that

Example 2 The same binder pitch and coke powder as in Example 1 were prepared, and general-purpose grade carbon fiber with fiber length: 0.7 mm (thread strength: 70 kg/cm2. thread diameter: 18 μ) was prepared.
and blending ratio (weight ratio) Binder pitch: Coke powder: Carbon fiber - 25 parts: 2
After mixing thoroughly in a ratio of 5 parts: 50 parts, 100 parts of this mixture
Example 1 by charging g into a mold similar to that in Example I.
It was molded under the same molding conditions as in Example 1, and then carbonized under the same carbonization conditions as in Example 1.

Table 2 shows the results of measuring the apparent density and bending strength of the C/C composite material thus obtained.

As is clear from the results shown in Table 2, the C/C composite material produced according to the conditions of the present invention has a high density, which is high even when general-purpose grade chopped carbon fiber is used. It can be seen that it shows strength.

Example 3 2 kg of coal tar was charged into a glass separable flask with an internal volume of 51 cm, and the volatile content in the resulting pitch was heated at a heat treatment temperature of 450°C and under each pressure shown in Table 3.
The binder pitch was adjusted by heat treatment until it became 20±0.5%.

Binder pitch thus obtained and Example 1
A C/C composite material was produced under the same conditions as in Example 1 using the same coke powder and carbon fiber as in Example 1.

The apparent density and bending strength of the C/C composite material manufactured in this way are also shown in Table 3, and from these results, it is clear that the C/C composite material manufactured according to the conditions of the present invention It can be seen that the /C composite material has high density and exhibits high strength.

Example 4 4 kg of straight asphalt was charged into a separable glass flask with an internal volume of 51 cm, and the temperature was increased at a rate of 5°C/w.
After heating the asphalt solution to 440°C, a stainless steel tube with an inner diameter of 311φ was passed through the asphalt solution.
When heat treated for 2 hours while blowing 5 g of steam preheated to ℃ per minute, the volatile content was 22% and the softening point was 330.
A pinch of 0.degree. C. was obtained and the yield on processing was 24%.

Next, 25 parts of the binder pitch obtained by finely pulverizing the above pitch to 60 mS or less, 35 parts of coke powder similar to that in Example 1, and the same fiber length as in Example 2:
0.7mm general-purpose grade carbon fiber (thread strength: 70k)
g/cm2. After mixing 40 parts of yarn diameter: 18μ), the mixture was heated and press-molded under the same conditions as in Example 2, and carbonized.

When the apparent density and bending strength of the C/C composite material manufactured in this way were measured, the apparent density was 1.53 g.
It was confirmed that the bending strength was 1020 kg/cm2.

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. Then,
This will bring about extremely useful effects industrially, such as further expansion of the fields of application of carbon fiber-reinforced carbon materials.

Claims (3)

[Claims] (1) Carbon fiber, finely powdered carbonaceous aggregate, and volatile content of 2
A method for producing a carbon fiber-reinforced carbon material, which comprises pressurizing and heating forming a molding material made of a binder pitch of 8% or less and having a softening point of 400° C. or less, and then carbonizing or graphitizing the material. (2) The method for producing a carbon fiber reinforced carbon material according to claim 1, wherein the binder pitch used is obtained by heat treating tar or pitch under reduced pressure of 100 Torr or less. (3) The binder pitch used is obtained by heat-treating tar or pitch while blowing water or gas under atmospheric pressure or reduced pressure, Claim 1
A method for producing a carbon fiber-reinforced carbon material as described in 2.