JP3103182B2 - Whisker-like carbon fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a whisker-like carbon fiber.

[0002]

2. Description of the Related Art Carbon whiskers are extremely thin linear crystals of carbon, have extremely high tensile strength, and are attracting attention as reinforcing materials for composite materials. Further, since carbon whiskers are conductive, they are expected to be applied as a conductivity-imparting agent to plastics.

[0003] Such a carbon whisker is manufactured by direct current discharge of a graphite electrode in an Ar atmosphere of 3900 K and 92 atm (R. Bac).
on, J.M. Appl. Phys. 31, 283 (196
0)). It is also produced by growing a hydrocarbon fiber or a natural gas as a carbon source by vapor-phase growth of carbon fibers using iron fine particles or an organometallic compound as a catalyst (Carbo).
n. Vol. 27, No5, P745-747, 198
9).

However, the whiskers obtained by the former method have a high strength and a high elastic modulus, but have a fiber length of about 3 cm, making it difficult to uniformly disperse them in other materials.
For example, when this whisker is used as a plasticity imparting material or as a reinforcing material, it is difficult to uniformly disperse the whisker, and there is a problem that the conductivity of the composite becomes non-uniform. In addition, the whiskers obtained by the latter method are obtained by crystal growth of carbon fibers using iron fine particles or organometallic compounds as nuclei as catalysts. There was a problem that is contained as.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a whisker-like carbon fiber which has a small amount of impurities and can be uniformly dispersed in other materials.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems. As a result, the whisker-like carbon fiber obtained by carbonizing the whisker made of aromatic polyimide has few impurities and other whiskers. The present inventors have found that they can be uniformly dispersed in a material, and based on this finding, have reached the present invention.

That is, the gist of the present invention is that an aromatic polyimide whisker is carbonized and has an average fiber length of 1 mm.
The following whisker-like carbon fibers are shown.

Next, the present invention will be described in more detail. The whisker-like carbon fiber of the present invention is obtained by carbonizing an aromatic polyimide whisker, and the fiber length is 1 mm or less. When the fiber length exceeds 1 mm, the tensile strength decreases. The diameter is preferably set to 10 μm or less. If it exceeds 10 μm, the tensile strength tends to decrease.

Aromatic polyimide whiskers for producing whisker-like carbon fibers are prepared by preparing needle-like crystals of a salt from an aromatic tetracarboxylic acid compound and an aromatic diamine compound as described later, and then preparing the aromatic polyimide whiskers. It is manufactured by heating and dehydrating a salt as a precursor under vacuum.
The aromatic polyimide obtained by this method maintains an acicular crystal state of a salt as a precursor, and is an organic whisker.

The aromatic tetracarboxylic acid is a tetravalent carboxylic acid containing at least one 6-membered carbon ring, of which two divalent pairs form a pair and are bonded to adjacent carbon atoms in the 6-membered ring. Specific examples include the following.

[0011]

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The aromatic diamine compound has 1 to 4 carbon atoms.
It is a diamine containing a member ring, and specific examples thereof include the following.

[0013]

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[0014]

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Among the above aromatic tetracarboxylic acids, the following are particularly preferred.

[0016]

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Among the above aromatic diamines, the following are particularly preferred.

[0018]

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Needle-like crystals of a salt of an aromatic tetracarboxylic acid and an aromatic diamine can be obtained by a method usually called recrystallization. That is, the aromatic tetracarboxylic acid and the aromatic diamine are dissolved in a heated solvent for recrystallization, and if there is any insoluble matter, the insoluble matter is removed by filtration or the like, and the solution is gradually cooled to remove needle-like crystals. obtain. The solvent for recrystallization is not particularly limited as long as the aromatic tetracarboxylic acid and the aromatic diamine can be dissolved at the time of heating, but water is preferable from the viewpoint of operability and economy. The molar ratio of the aromatic tetracarboxylic acid to the aromatic diamine is from 0.5 to
A range of 1.5 is preferred, and a range of 0.9 to 1.1 is more preferred. If it is less than 0.5 or more than 1.5, the organic whisker tends to be easily cut.

When the obtained needle-like crystals of the salt are subjected to a heat treatment,
The ring is closed while maintaining the shape of the salt to obtain an aromatic polyimide whisker. The heat treatment conditions may be the same as those used for producing a normal aromatic polyimide molded body. For example, needle-like crystals of a salt may be formed at 350 to 450 ° C. for 5 to 30 hours under a vacuum of 0.1 to 1 torr. After heating, the mixture is gradually cooled to obtain an aromatic polyimide whisker.

Further, when the aromatic polyimide whisker is heat-treated, it is carbonized while maintaining the shape of the polyimide whisker to form whisker-like carbon fibers. As the heat treatment conditions, ordinary carbonization conditions can be applied.
Under a vacuum of 1 torr or at normal pressure in an atmosphere of an inert gas such as N ₂ or Ar at 500 to 3000 ° C.
After heating for 100 hours, the mixture is gradually cooled to obtain whisker-like carbon fibers.

As described above, since the whisker-like carbon fiber of the present invention is obtained by carbonizing aromatic polyimide whiskers, it can be safely produced in a practical yield and contains no impurities. In addition, since the fiber length is constant at 1 mm or less, it can be uniformly dispersed in other materials when used as a reinforcing material or the like.

[0023]

The present invention will be described below in detail with reference to examples. Examples 1-4 5.1 g of pyromellitic acid and 4.0 g of diaminodiphenyl ether were put into 900 ml of water and heated to boiling.
After filtering off a small amount of insoluble matter, the solution was gradually cooled, and the precipitated needle crystals were collected, washed with cold water, and vacuum dried at 35 ° C. to obtain 7.4 g of needle crystals. The needle-like crystals thus obtained are imidized by maintaining at 400 ° C. for 10 hours under a vacuum of 0.2 torr to obtain an average fiber length of 200 μm and an average fiber diameter of 5 μm.
m of aromatic polyimide whiskers were obtained. The polyimide whisker thus obtained was placed at 0.2 torr.
A heat treatment was carried out at a temperature shown in Table 1 for 10 hours under vacuum to obtain whisker-like carbon fibers having an average fiber length and an average fiber diameter shown in Table 1. 40 parts of the obtained whisker-like carbon fiber and 60 parts of 6 nylon are melt-kneaded at 240 ° C.
Press molding was performed at 0 kg / cm ² to obtain a composite molded body. Table 1 shows the results of measuring the volume resistance value of the obtained composite molded body. In the examples, the volume resistance value is Loreste PA.
Measured with a system (Mitsubishi Yuka).

[0024]

[Table 1]

[0025]

The whisker-like carbon fibers of the present invention are obtained by carbonizing aromatic polyimide whiskers, and therefore do not contain impurities. Furthermore, the average fiber length is 1 mm
Since it is the following, it can be uniformly dispersed in other materials when used as a composite material, and a composite material with uniform performance can be obtained. Further, the aromatic polyimide whisker of the present invention can be used as an electrode material or as a conductivity imparting agent by utilizing its conductivity, and as a reinforcing material by utilizing its strength.

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Claims (1)

(57) [Claims] A whisker-like carbon fiber obtained by carbonizing an aromatic polyimide whisker and having an average fiber length of 1 mm or less.