JPH03150266A - Production of carbon/carbon composite material - Google Patents

Abstract

PURPOSE:To obtain carbon/carbon composite material having high density and strength in reduced porosity in carbonization by subjecting finely cut carbon fiber, carbonaceous powder and matrix precursor powder to humid paper making, laminating the these ingredient-mixed paper and heating and forming the laminate under pressure and then subjecting the formed article to carbonization burning. CONSTITUTION:A mixture consisting of (A) 20-80wt.%, preferably 30-60wt.% carbon based fiber (having 5-20mum, preferably 7-13mum diameter and 0.3-20mm, preferably 3-10mm fiber length) such as shortly cut PAN based, pitch based or rayon based carbon fiber, (B) 5-40wt.%, preferably 15-30wt.% carbonaceous powder (having >=90wt.% residual carbon content and 0.1-50mum grain size) and (C) 20-50wt.%, preferably 30-40wt.% matrix precursor powder (e.g. powdery phenol resin or powdery pitch which has 0.1-50mum grain size) is subjected to wet type paper making (paper thickness: 0.2-0.5mm). Then plurality of the mixed papers are laminated, heated, formed and then carbonized and burned in non- oxidizing atmosphere at 800-1000 deg.C to provide the carbon/carbon composite material useful as a rocket nozzle, brake, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a carbon/carbon composite material having high density and high strength.

(Prior art) Charcoal S/carbon composite material (hereinafter referred to as % composite) is
A carbon material reinforced with carbon fiber that has excellent properties such as high mechanical strength, heat resistance, impact resistance, and chemical stability.In recent years, it has been used as rocket nozzle brake material, hot structural material, etc. .

Conventional methods for manufacturing composites include first impregnating a base material made of carbon fiber into cloth, felt, or paper with thermosetting resin such as phenol resin or furan resin, or impregnating it with thermoplastic resin such as pitch. and get prebrag,
This prebrag is laminated to the required thickness, heated and
A molded body is obtained by pressure molding. Afterwards, the molded body is fired at aoo-iooo°C in a non-oxidizing atmosphere to carbonize the matrix portion of the molded body. However, the fired body at this point contains many voids and has low strength, so it is not a practical composite. Therefore, the fired body is re-impregnated with matrix precursor resin and carbonized several times to increase density and strength. Will it become?

Alternatively, carbon obtained by thermally decomposing hydrocarbon gas such as methane or benzene is deposited in the voids of the fired body to achieve high density.

We are increasing the strength.

(Problem to be solved by the invention) However, the densification process of such composites takes a long time and requires advanced technology and equipment, making the resulting composites very expensive. By the way, as an attempt to shorten or omit such densification processing even a little, a method of adding solid carbon powder to the matrix precursor resin in advance is being considered.

The aim of this trial is to achieve a carbonization yield of 50-60% for the matrix precursor resin.

During carbonization, about half of the volume of the resin part becomes voids, so adding carbon increases the carbonization yield of the matrix precursor, thereby reducing the amount of voids during carbonization, resulting in high density and high The point is to try to obtain a composite of strength.

According to this method, carbon powder is dispersed in a matrix precursor resin liquid, and a carbon fiber base material is immersed in the mixed liquid.
If a composite is obtained by impregnating or coating a carbon fiber base material with this mixture to prepare a prepreg and then molding and firing it according to a conventional method, or if a powdered matrix precursor resin is used, Mechanically mixed with carbon powder, inserting this mixed powder between the laminated layers of carbon fiber base material in the form of a sandwich, softening the resin part by heating and pressurizing to obtain a molded body, and then firing it to obtain a composite. It is.

However, with this method, it is difficult to penetrate the carbon powder, which is a filler, between the single fibers of carbon fiber.
Excessive return powder adheres to the surface of the carbon fiber base material. In other words, the returned fiber base material plays the role of a filter.

! This is because a large amount of carbon powder is buried on the surface of the bicomponent fiber base material, but penetration of the carbon powder becomes poor in the center of the base material.

This tendency occurs strongly when resin powder and carbon powder are inserted between carbon fiber base material layers.

When observing the cross section of the molded article thus obtained, it can be seen that carbon fiber-rich layers and matrix precursor-rich layers are alternately laminated.

In addition, when carbonizing this molded body, since the shrinkage rate is different between the carbon fiber-rich area and the matrix precursor-rich area, it becomes strained due to stress caused by the difference in shrinkage between the returned fiber base materials. occurs, and therefore the bonding force between the carbon fiber base materials decreases.

The resulting composite has low interlaminar shear stress, making it unsuitable for practical use.

(Means and effects for solving the problem) In view of the situation of the conventional manufacturing method, the inventors of the present application have infiltrated carbonaceous powder, which is a filler, into the spaces between carbon fiber single fibers, Carbon-based a! By using a prepreg in which carbonaceous powder is uniformly arranged both on the surface and in the center of the II base material, we conducted repeated research and study on a method of obtaining a high-density, high-strength composite, which led to the success of this invention.

According to this invention, carbon fibers cut into short lengths by applying wet papermaking technology and/or organic fibers that are converted into strong carbon fibers by carbonization, carbonaceous powder with a carbon content of 90% by weight or more, and a matrix. Mixed paper obtained by mixing and stirring precursor resin powder in a large amount of water in arbitrary proportions and making paper is laminated, heated and pressure molded, and then carbonized and fired in a non-oxidizing atmosphere to form a high-density paper. This made it possible to obtain a high-strength composite.

This invention will now be explained in more detail.

The reconstituted fibers that can be used in this invention may be any carbon fibers such as PAN, pitch, and rayon fibers, and can be made tough by heat treatment in a non-oxidizing atmosphere at 800 to 1000°C. Organic fibers that can be converted into carbon fibers may be used.Furthermore, these carbon fibers and organic fibers may be mixed in any proportion, and these carbon fibers preferably have a diameter of 5 to 20μ. is 7-13
μ■, and the fiber length is OJ~20μ. If the fiber length is 20 mm or more, the workability during paper making is poor, and the fibers become entangled with each other, making it difficult to make a homogeneous paper.If the fiber length is less than 0.3 mm, there is no entanglement between the fibers, making it possible to make a homogeneous paper. However, the reinforcing effect of the fibers is small, and therefore the strength of the composite obtained is low.More preferably, the strength of the composite obtained is maximum when fibers in the range of 3 to 10 m are used. was confirmed.

Next, it is preferable that the Mls powder has a carbon residue of 9G% by weight or more.

If the powder contains a large amount of volatile components, the powder particles will be significantly deformed or shrunk during firing for back-elementation, which may cause defects as residual stress in the matrix. Further, powder containing a large amount of impurity elements such as Aj, Si, Fe, etc. has a negative effect on the heat resistance, which is a characteristic of the composite. Therefore, a more suitable carbonaceous powder is carbon black, which has less volatile components and higher purity.

Coke, artificial graphite, etc. are suitable. Furthermore, the finer the particle size of the carbonaceous powder, the more uniformly it will be dispersed in the composite structure, but in practice it is preferably 0.1 to 50 μm.

On the other hand, the matrix precursor resin powder is softened by heating during molding after being dispersed in the carbon fiber base material.

It is a resin powder that can be pressurized to make a carbon fiber base material into a strong molded body. In addition, this powder must be in a solid state during papermaking, and it is desirable that it does not dissolve in water, which is a dispersion solvent.If this resin dissolves in water during papermaking, This is because, after papermaking, the liquefied resin may be unevenly arranged in the carbon fiber base material.

In short, if the matrix precursor*a concentration is different in the base material, internal strain will occur due to shrinkage during carbonization firing, which will cause a decrease in the strength of the resulting composite.

The matrix precursor resin that meets these conditions is preferably a powdered phenolic resin or powdered pitch, and its hardness is preferably from 0.1 to 50 mm.

Furthermore, these carbon fibers, carbonaceous powder, matrix fa
The mixing ratio of the W-body resin powder is preferably within the range shown in Table 1 in order to obtain a high-density-high-strength composite.

Table-l (Weight %) 1 l General range 1 Preferred range 11x Qin fiber 120-80130-6011
IR elemental powder 15-40115-3011 Matrix precursor resin 1 20-50130-401 These raw materials are dispersed and mixed in a large amount of water to obtain a uniform mixed solution. Some amount of an organic binder such as polyvinyl alcohol (PVA) can be added to add .

The paper making method may be the same as the conventional method, but the paper thickness of the mixed paper to be produced is preferably 0.1 or more from the viewpoint of workability and efficiency, and preferably 1 or less from the viewpoint of uniformity within the mixed paper. Thickness l
- In the case of above, there is a risk that drying of the dispersion water becomes difficult and non-uniform voids are generated in the mixed paper. Note that a suitable paper thickness range is 0.2 to 0.5-.

The mixed paper can be treated as prepreg by thoroughly draining the water and then slowly heating and drying it with a dryer etc. to completely dehydrate it. In the cross section of the obtained prepreg, the carbonaceous powder and matrix precursor resin powder are uniformly fixed between the carbon fibers, and the compositions at the surface and center of the prepreg are the same.

Next, the prepreg is cut and laminated, and heated and pressure molded in the same manner as conventional methods to obtain a molded body. If phenolic resin powder is selected as the matrix precursor, 150-1
A molded product may be obtained by pressurizing the molded product at 150 to 250 kg/aJ in a mold at 80°C, and then post-curing at about 200°C.

In addition, when selecting the pitch, it is sufficient to pressurize at a temperature near the pitch softening point to obtain a molded body, and perform an infusibility treatment as necessary.

The molded body thus obtained is placed in a non-oxidizing atmosphere.

It can be made into a composite by carbonizing and firing at 800 to 1000°C.

Further, in order to further improve physical property values, densification treatment similar to the conventional method can be performed.

The structure of the composite produced by this invention is more uniform than that of the composite produced by adding carbon powder to the matrix precursor resin by the conventional method, and it can exhibit high density and high strength. can.

〔Example〕

This invention will be specifically described below with reference to Examples.

Example 1 40% by weight of PAN-based carbon fiber (high strength grade manufactured by Toho Veslon II) with a diameter of 6 mm and a fiber length of 6 cm.

Artificial graphite powder, 20% by weight of average particle size 12μ, and phenolic resin powder (manufactured by Kanebo M, Bellbar S890)
) was mixed into paper using a wet paper-making method and heated at 100°C.
It was dried in a dryer for 30 minutes to form a bribregu.

The thickness of this prepreg is 0.445m, and the weight is 140
g/rtl.

This prepreg was cut into 120 x 120 square pieces, 30 sheets were laminated and molded at a pressure of 250 kg/d in a mold heated to 160°C to obtain a molded product, which was then left in an oven at 200°C for 24 hours to post-cure. did. Next, this molded body was
The temperature was raised to 1000° C. at a rate of 20° C./hr in an atmosphere, and the temperature was kept at that temperature for 2 hours for carbonization and firing to obtain a composite. Table 2 shows the physical properties of the composite thus obtained.
I made it.

Comparative Example 1 Wet paper was made using only the same PAN-based carbon fiber as in Example 1,
A paper sheet with a thickness of 0.42 mm and a basis weight of 60 g/m was obtained.

The same artificial graphite powder and phenol resin powder as in Example 1 were mixed into this paper at a weight ratio of 1:2.

Further, a matrix precursor resin mixture solution was coated using N-methyl-2-pyrrolidone as a solvent.

Excess matrix precursor resin mixture was removed by passing through a roller so as to obtain the same blending ratio as in Example 1.

Then, the carbon fiber paper impregnated with the matrix precursor was left in a dryer at 100° C. for 30 minutes.

It was made into Buri Plague, and then subjected to the same process as in Example 1.
I got a composite.

The physical properties of the composite thus obtained are also shown in Table 2.

Example 2 Pitch-based carbon fiber (manufactured by Dainippon Ink Chemical ■, general-purpose grade) with a diameter of 13 mm and fiber length of 6 mm, 30% by weight, novoloid fiber (manufactured by Nippon Kynor ■) with a diameter of 14 μm, and 3 fiber lengths of 30% by weight %, carbon black average particle size 15 mm 2
5% by weight, and bulk mesophase pitch/softening point 18
At 5°C, 35% by weight of the average particle size of 44 mm was mixed into a paper using a wet paper making method, and the paper was left in a dryer at 100°C for 30 minutes.

Obtained Bryplague. The thickness of this bribrae leg is 0.4
8-. The weight was 165 g/durability. This Bribrag was cut into 120×120 square pieces, 30 pieces were laminated, and molded at a pressure of 40 kg/cd in a mold heated to 180° C. to obtain a molded body. Embed this molded body in breeze coke 1
The temperature was raised to 1000°C at a rate of 5°C/hr, and the temperature was maintained for 2 hours for carbonization and firing to obtain a composite. The physical properties of the composite thus obtained are shown in Table 3.

Comparative Example 2 Wet paper was made from the same pitch-based carbon fiber and novoloid fiber as in Example 2, with a thickness of 0.43 mm and a scale fi of 65 g/nf.
A mixed paper was obtained. This mixed paper was cut into 120×12G pieces. On the other hand, the same carbon black and bulk mesophase pitch as in Example 2 were mixed in a ball mill so that the weight ratio was 5 nia, and this mixed powder was sandwiched between the layers of mixed paper so that the mixture ratio was the same as in Example 2. Fill it up,
Thereafter, the same process as in Example 2 was carried out to obtain a composite. The composite thus obtained had some peeling. The physical properties of this composite are shown in Table 3.

Table 2 Example l Comparative example I Bulk Specific gravity 1.45 i 1.28 1 Porosity (%) + 14.0 1 22.6 1
1 Bending strength (kg/aJ) l 1450 1 820
1 Table a 1 1 Example 21 Comparative example 211 Bulk Specific gravity 1.3211.18 J1 Porosity (%) 1 1
6.8 1 28.0 11 Bending strength (kg/cd month)
780 1420 1 (Effects of the Invention) As is clear from the results in Tables 2 and 3, the ¥ composite obtained by the manufacturing method of this invention is.

Compared to the conventional method, the resulting composite has higher density and strength, and the subsequent densification process is shortened, making it possible to produce high-quality composites at low cost and in a short period of time.

Claims (1)

[Claims] 1. A mixed paper is obtained by a wet papermaking method using carbon fibers cut into short lengths, carbonaceous powder, and matrix precursor powder,
A method for producing a carbon/carbon composite material obtained by laminating the mixed paper, heating and press forming, and then carbonizing and firing. 2. A claim characterized in that the carbon-based fibers may be any carbon-based fibers such as PAN-based, pitch-based, rayon-based, etc., and/or are organic fibers that can be made into strong carbon fibers by carbonization. 1. The method for producing a carbon/carbon composite material according to 1. 3 The diameter of the carbon fiber is 5 to 20 μm, and the fiber length is 0.3
3. The method for producing a carbon/carbon composite material according to claim 2, wherein the thickness is 20 mm. 4. The method for producing a carbon/carbon composite material according to claim 1, wherein the carbonaceous powder has a carbon residue of 90% or more and a particle size of 0.1 to 50 μm. 5. The method for producing a carbon/carbon composite material according to claim 1, wherein the matrix precursor powder is a powdered phenolic resin or a powdered pitch.