Composite material

Abstract

A composite material includes a matrix and carbon fibrous structures. The carbon fibrous structure has a three dimensional network of carbon fibers, each having an outside diameter of 15-100 nm, and has a granular part with which two or more carbon fibers are tied together such that the carbon fibers extend therefrom, and the granular part being produced in a growth process of the carbon fibers. The additive amount of the carbon fibers is in the range of 0.1 to 30% by weight of total weight of the composite material.

Description

CROSS REFERENCES TO RELATED APPLICATIONS [0001] This claims the priority of Japanese Patent Application No. 2005-82776, filed on Mar. 22, 2005. This Japanese application is incorporated herein by reference in its entirety. TECHNICAL FIELD [0002] This invention relates to a new composite material. Particularly, this invention relates to a composite material, which comprises minute carbon fibrous structures blended in a matrix. BACKGROUND ART [0003] To date, composite preparations comprising plural materials have been developed in order to attain unique characteristics that are not found in any single material. As an example, glass fiber reinforced plastic has been widely used. The successful development of carbon fibers and reinforced plastic containing carbon fibers (CFRP) has brought such composite materials into general use. [0004] These materials have been widely used in sporting goods and so on, and have also gained much attention as a light weight-, high intensity- and high ela...

AI Technical Summary

Benefits of technology

[0015] Therefore, this invention aims to provide new composite materials capable of solving some or all of above mentioned problems. This invention also aims to provide composite materials having improved physical properties, such as electrical, mechanical and thermal properties, without significantly damaging the innate characteristics of the matrix. These composite materials are prepared by using a small amount of new carbon fibers having unique fibrous structures that have physical properties suitable for use as fillers in composite preparations.

[0016] As a result of our diligent study for solving the above problems, the inventors of the present invention have found that the following approaches are effective in improving various properties of a matrix even at a limited additive amount, and finally accomplished the present invention:

[0032] According to embodiments of the present invention, because the carbon fibrous structures comprise three dimensionally configured carbon fibers having ultrathin diameters and bound together by a granular part produced in a growth process of the carbon fibers such that the carbon fibers elongate (extend) outwardly from the granular part, the carbon fibrous structures can disperse easily into a matrix (such as a resin) upon adding, while maintaining their bulky structure. Even when they are added at a small amount to a matrix, they can be distributed uniformly over the matrix. Therefore, with respect to electrical conductivity, it is possible to obtain good electric conductive paths throughout the matrix even with a small dosage. With respect to mechanical and thermal properties, improvements can be expected in a similar fashion, because the carbon fibrous structures are distributed evenly as fillers in the matrix with only a small dosage. Therefore, by this invention, composite materials can be obtained that are useful as functional materials having good electric conductivity, electric wave shielding ability, heat conductivity, etc., or as structural materials having a high strength, or the like.

Problems solved by technology

As the prevalence of various electronic devices increases, problems such as malfunction of devices caused by static electricity and electromagnetic wave interference caused by noises from certain electronic components are also on the rise, thus creating an increased demand for materials that have excellent functional characteristics such as conductivities and electromagnetic field damping abilities.

However, there are several drawbacks in these types of materials.

For example, when using metallic fibers and metallic powders as the conductive filler, the materials thus obtained have poor corrosion resistance and mechanical strength.

When using carbon fibers as the conductive filler, although a predetermined strength and elastic modulus may be obtained by adding relatively large amounts of the filler, electrical conductivity generally cannot be greatly enhanced by this approach.

If one attempts to attain a predetermined conductivity by adding a large amount of filler, one would invariably degrade the intrinsic properties of the original polymer material.

In such manufacturing processes, the level of material loss during carbonization is high and the carbonization rate is slow.

Therefore, carbon fibers made by these processes tend to be expensive.

On the other hand, however, such fine carbon fibers unfortunately show an aggregate state even just after their synthesis.

When these aggregates are used as-is, the fine carbon fibers would be poorly disperse, and thus the product obtained would not benefit from the desired properties of the nano structures.

Thus, they cannot satisfy the need for ideal additives that are capable of improving various characteristics of a matrix, such as electrical conductivity, at small dosages.

Since the fixing of carbon fibers is performed by such a heat treatment after synthesis of the carbon fibers, the fixing force at the contacting points is weak and do not result in good electrical property of the carbon fibrous structures.

When these carbon fibrous structures are added to a matrix (such as a resin), the carbon fibers fixed at the contacting points are easily detached from each other, and the carbon fiber structures are no longer maintained in the matrix.

Therefore, it is not possible to construct good conductive paths in a matrix such that good electrical properties may be conferred on the matrix by a small additive amount of the carbon fibrous structures.

Furthermore, when a binder is added to promote the fixing and carbonization at the contacting points, fibers in the resultant fibrous structure would have large diameters and inferior surface characteristics because the binder added is attached to the whole surface areas of the fibers rather than to limited areas at the contacting points.

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