JP2665957B2 - Carbon fiber / carbon composite - Google Patents

Description

The present invention relates to a carbon fiber / carbon composite. In particular, a carbon fiber / carbon composite material having high specific strength, excellent heat resistance, low thermal expansion properties, etc. by using a vapor-grown carbon fiber and a carbon fiber woven or nonwoven fabric obtained by solid-phase carbonization in combination. About.

[Prior art] Carbon fiber / carbon composite material (hereinafter referred to as CC composite material)
Has excellent specific strength (strength / weight), excellent heat resistance and thermal shock resistance, small thermal expansion coefficient, high elastic modulus, thermal conductivity,
Because of its high electrical conductivity and excellent unique physical properties, it is an indispensable material for components such as aircraft and rockets, exterior materials for flying objects, and mechanical devices that require corrosion resistance and wear resistance. Has a solid position.

In these conventional CC composite materials, in many cases, long fibers obtained by solid-phase carbonization are laminated as a woven fabric, or once cut into short fibers and laminated as a nonwoven fabric. Further, the woven fabric and the non-woven fabric are alternately laminated, shaped with a resin or the like (including pitch, etc .; the same applies hereinafter), and then heated and carbonized in an inert gas, and then further repeated several times. It is obtained by a method of impregnating a resin and repeating carbonization.

In addition, a method of depositing pyrolytic carbon around carbon fibers by a chemical vapor deposition method, or a method in which a carbon fiber is molded using a thermoplastic resin (including a pitch or the like) as a binder is subjected to hot isostatic pressing. There is a proposal of a method of baking under pressure, but since these methods are extremely expensive,
It is only used in special cases.

[Problems to be Solved by the Invention] By the way, the conventional method of producing a C-C composite material (a method of forming carbon fibers with a resin or the like, followed by firing and carbonizing) can be obtained by about one-step firing. There were drawbacks in that the density of the CC composite was low and the strength was low.

Therefore, usually, it is necessary to repeat the operation of sintering several times after impregnating the fired product with the resin (pitch impregnation is also possible). As this operation is repeated and the number of times increases, the process becomes longer, and the cost also increases in proportion to this. However, even if the impregnation and firing are performed a plurality of times in this manner, the density is not sufficiently increased by the above method,
In addition, there is a problem that the strength is not sufficiently high, and it is said that one of the causes is that the carbonization yield of the resin binder is low.

There are several proposals for remedying this drawback. One of them is a method of firing carbon fiber grown by vapor deposition together with a resin (Japanese Patent Application No. 63-168276). Increases the density and the heat resistance (thermal conductivity,
Thermal expansion coefficient, thermal shock resistance, etc.)
The improvement in strength was not sufficient.

[Means for Solving the Problems] The present invention has been studied for the purpose of a carbon material having a short manufacturing process (low cost) and high mechanical strength.
Non-woven fabric of fine vapor grown carbon fiber and woven or non-woven fabric of carbon fiber obtained by solid phase carbonization are alternately laminated,
A carbon fiber obtained by bonding these with a carbide of an organic binder /
It has been found that carbon composites can achieve this purpose.

In other words, when carbon fibers (for example, PAN-based carbon fibers) obtained by solid-phase carbonization having excellent mechanical strength are combined with vapor-grown carbon fibers that can increase the density of the CC composite material, a short manufacturing process is possible. In principle, a C-C composite material having a high density and excellent mechanical strength can be manufactured. However, PAN-based fibers are long fibers, and are vapor-grown carbon fibers which are essentially short fibers. Cannot be blended easily. Even when PAN-based carbon fibers are cut into short fibers, mechanical cutting cannot produce short fibers as large as vapor grown carbon fibers, and there is a large difference not only in fiber thickness but also in fiber length. Therefore, it is difficult to mix them uniformly.

As a result of various studies on the combination of the two, as a result, the respective fibers are once made into a sheet form, laminated, and further bonded by the carbide of the organic binder, whereby an excellent CC composite material is obtained. It turned out to be obtained.

The vapor grown carbon fiber used in this case is a fine one usually obtained, for example, one having a thickness of 0.05 to 1 μm and a length of 1 mm or less, and the filling amount is required for the final CC composite material. Depending on the properties, it is necessary to change the proportion of the carbon fiber obtained by solid-phase carbonization to increase the blending if the density is high and to increase the proportion of the carbon fiber obtained by solid-phase carbonization if the strength is high. A filling of about 1 to 20% by weight is preferred.

A resin such as phenol resin, furan resin, epoxy resin, or polyester resin is added to the fine vapor grown carbon fiber as it is, or 2 to 20% by weight of the carbon fiber is added and mixed. Until it becomes a sheet. The purpose of the sheet in this case is usually
Although it becomes 10-100 g / m ² , even if the basis weight is out of this range, there is no problem in production.

In addition, carbon fibers obtained by solid-phase carbonization include PA
Various carbon fibers such as N-based, pitch-based, and fibrous-based can be used. The carbon fiber may be a woven or non-woven fabric, but the vapor-grown carbon fiber is preferably thin and short, and therefore, the non-woven fabric is preferred in order to take advantage of this combined characteristic. The woven or nonwoven fabric in this case can be used as it is as a commercial product. The amount used is of the order of 1 to 20% by weight of the final composite.

The above fiber sheets are alternately laminated, compressed to a density of about 0.03 to 0.5, impregnated with a resin or the like, and then fired and carbonized at 800 to 1200 ° C. in an inert atmosphere such as nitrogen. In this case, the carbonization rate of the resin and the like varies depending on the type of the resin, but is about 50%. Since the pores cannot be completely filled by only one dipping, the resin is impregnated with the resin, and the carbonization is performed in an inert atmosphere. repeat. When the obtained carbon mass is heat-treated at 2,000 ° C. or more, especially around 2500 ° C., it has a high apparent density CC due to heat shrinkage.
A complex is obtained.

[Operation] The C-C composite material of the present invention can not only achieve a high-density product that could not be achieved by a large number of firings with the conventional technology but also achieve a product of the same density with a small number of firings. Of course, this can be achieved with a smaller number of firings than in the conventional method. When the conventional C-C composite material requires a high-strength product, it has been necessary to obtain a high-density product by firing many times.
The C-composite can obtain a product of the same strength with a lower density product than the conventional method. Therefore, depending on the application of the product, a product of the same quality can be baked very few times, that is, a product of the same quality can be obtained at a very low cost. Will be done.

The advantage of alternately laminating the sheets is not only that a strong and high-density C-C composite material can be obtained by simply utilizing the characteristics of both, but also has the following advantages.

First, it is possible to arbitrarily and accurately control the mixing ratio of PAN-based carbon fiber and vapor grown carbon fiber.

Secondly, PAN-based carbon fibers have a large fiber diameter and many spaces between fibers, but vapor-grown carbon fibers are thin, so that the spaces can be filled and the fiber density can be increased.

[Example] (Example 1) Fibril polyacrylonitrile fiber manufactured by Asahi Kasei Corporation
After crushing 30 g (Cashmilon A104), length 10 mm with a Hensiel mixer for 5 minutes, vapor grown carbon fiber (diameter 0.2 to 0.5)
μm, length about 100μm), and after mixing 170g, 200 ℃, pressure 1kg /
The sheet was pressed into a sheet with a pressure of ² cm ² . The basis weight of this is 30g / m ²
Met.

A PAN-based carbon fiber short fiber in a mat shape (B0-050, manufactured by Toray Industries, Inc., weight: 50 g / m ² ) and the vapor-grown carbon fiber sheet are alternately laminated, and compressed to obtain a vertical density of 0.3. ,
A cube having a width of 10 cm and a height of 10 cm was impregnated with coal tar pitch (IP-90 manufactured by Nippon Steel Corporation) and molded into a plate shape. The molded product was fired at 1000 ° C., and the impregnation and firing of the coal tar pitch were repeated four times, followed by heat treatment at 2500 ° C. to obtain a CC composite material.

(Example 2) A vapor-grown carbon fiber sheet (produced by 50 g / m ² ) and a PAN-based carbon fiber woven fabric (# 6341 manufactured by Toray Industries, Inc.) alternately laminated in the same manner as in Example 1 Was impregnated with a phenolic resin (BRL-120Z, manufactured by Showa Polymer Co., Ltd.) and molded by heating under pressure. The molded product is fired, and the impregnation and firing of coal tar pitch is repeated four times, and then heat-treated at 2500 ° C.
C composite was obtained.

(Comparative Example 1) 2% by weight of a phenol resin was added to a vapor-grown hydrocarbon having a thickness of 0.2 to 0.5 µm and a length of 1 mm or less (10 µm to 1 mm),
Make a block with an apparent density of 0.3, impregnate it with coal tar pitch (IP-90, manufactured by Nippon Steel Chemical Co., Ltd.)
The process was repeated four times including firing at 1000 ° C., pitch impregnation, and firing, and then heat-treated at 2500 ° C. to obtain a CC composite material.

(Comparative Example 2) A PAN-based carbon fiber mat (BO-050, manufactured by Toray Industries, Inc.) was laminated at an apparent density of 0.3, impregnated with coal tar pitch, and molded into a block shape. After firing the molded product, the impregnation and firing of coal tar pitch was repeated a total of 6 times,
Heat treatment was performed at 2500 ° C. to obtain a CC composite material.

Table 1 shows the measurement results of the physical properties of the CC composite materials experimentally manufactured in the above-described Examples and Comparative Examples.

[Effect of the Invention] By combining a high-strength carbon fiber and a vapor-grown carbon fiber, a high-density and high-strength C-C composite material can be obtained in a short process.

Claims (2)

(57) [Claims] 1. A carbon fiber obtained by alternately laminating a nonwoven fabric of fine vapor-grown carbon fibers and a woven or nonwoven fabric of carbon fibers obtained by solidification of carbon, and bonding these with a carbide of an organic binder. / Carbon composite. 2. The method according to claim 1, wherein the fine carbon fibers have a diameter of 0.05-1.
2. The carbon fiber / carbon composite material according to claim 1, wherein the carbon fiber / carbon composite material has a length of 1 μm or less.