JPH0735251B2 - Graphite fine powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fine graphite powder useful as a lubricant for audio tapes, video tapes, paints, etc., a conductive agent, an additive for various composite materials, and the like.

(Prior Art) Conventionally, fine graphite powder was manufactured by crushing and classifying a graphite block, a graphite plate, a graphite rod, etc. However, crushing is difficult because graphite itself is soft and slippery. there were.

Therefore, for example, when graphite powder having a particle size of 100 to 1000 μm generated when processing an artificial graphite electrode is pulverized by a ball mill etc., submicron particles having a particle size of 1 μm or less are also partially produced. Overall particle size 1 μm
It was impossible to make the following fine powders.

(Problems to be solved by the invention) Generally, graphite processing scraps are pseudospheres or ellipsoids, and therefore, when grinding them as a starting material, it is necessary to reduce the size in any of the three-dimensional directions, but it is originally ground. It is technically difficult to reduce the size of graphite, which is difficult to do in three directions, and it requires an extremely large amount of grinding energy.

As a method for producing graphitized powder, there is also a method of crushing carbonaceous powder that is easy to crush, for example, coke and then graphitizing this, but in this case, the powder re-solidifies during graphitization, which results in It is difficult to obtain fine powder of submicron grade.

(Means for Solving the Problems) In the present invention, as a result of studying the conversion of the starting material in view of the reason that the above-mentioned conventional technology is impossible, carbon fiber is selected as the starting material in order to make the pulverization easier. I thought about it.

Carbon fiber produced by the vapor phase method has a fiber diameter of 0.01 to 0.5μ
It is possible to easily and inexpensively manufacture a product having a length of m and a length of several mm. If this fiber is graphitized and then pulverized, the target graphite powder can be produced significantly more easily and efficiently than in the conventional method. In this case, it is appropriate to say that the crushing of the fibers is substantially rather crushing accompanied by fine cutting of the fibers.

By pre-graphitizing such fibers prior to crushing (cutting), it is possible to prevent re-solidification of the powder particles by the conventional method as described above, and the electric resistance value in the fiber axis direction is extremely high. Since it is low, it has been solved that it efficiently acts for the purpose of imparting conductivity, and it is also known that the sliding property is extremely good.

The present invention resides in pulverized fine powder of graphitized vapor grown carbon fiber having a particle size of 1 μm or less.

The method of producing the vapor grown carbon fiber in the present invention is described in, for example, JP
It is known in Japanese Patent No. 58-180615, Japanese Patent Publication No. 58-22571, etc., but it is specifically as follows.

1000 to 1300 using benzene as a carbon source and organic compounds containing iron etc. as seeds or direct evaporation of Fe etc.
Grow vapor grown carbon fibers in an atmosphere of ° C. At this time, if the growth time is set within 5 minutes, the maximum diameter is 0.5μ.
Fibers of m and length of several mm grow. Take this out of the furnace
Graphitize by heat treatment at 2500 ° C or higher in an atmosphere such as Ar.

Thus, for example, the true specific gravity is 2.15 to 2.20 g / cm ³ and the electrical resistivity is 50.
A carbon fiber of ˜80 / μΩ · cm is obtained, which is then ground.

That is, in the present invention, it is desirable that the graphitization of the carbon fiber is carried out before the pulverization. This is because when pulverized and graphitized, the powder agglomerates into a dumpling and a fine powder having a particle size of 1 μm or less cannot be obtained. The graphite fine powder thus obtained seems to be similar to Khan black in terms of fineness, but carbon black has a large electric resistivity and is non-graphitized hard carbon. The graphite fine powder of the invention is essentially different from carbon black.

Although a wet or dry ball mill can be used for pulverization, it takes a long time for pulverization, and the contamination due to abrasion of the pulverizing balls is serious, so that a removing step is required.

In this respect, the air flow pulverization method is relatively efficient and less polluting, and is effective when applied to the present invention. For example, a commercial jet mill or the like is optimal.

The graphitized fiber can be easily loosened by a coffee mill or the like, supplied to a jet mill, and recycled and pulverized several times to obtain a fine powder having a target particle size.

(Example) A vapor grown carbon fiber was produced from a mixed gas of a hydrocarbon and a carrier gas according to a well-known method, and the carbon fiber was graphitized at 2400 ° C or higher in a non-oxidizing atmosphere and then pulverized by a jet mill. Then, fine graphite powder was obtained.

As a result of SEM measurement, the maximum value of major axis of this fine graphite powder was 0.8μ.
m, and the minor axis was 0.01 to 0.3 μm. In this case, the mechanism of micronization was by crushing and / or partial cutting.

(Sample 1): The above graphite fine powder was mixed in the following formulation, coated on a polyester film and dried, and the coating thickness after drying was set to 3 μm.

Graphite fine powder 5 parts (weight) Toluene 50 parts (〃) MEX 50 parts (〃) Vinyl acetate 25 parts (〃) (Sample 2): Natural graphite powder [Nippon Graphite Co., Ltd. CSSP in Sample 1 instead of graphite fine powder , Average particle size 1 μm] (1)
Was used in the same amount.

(Sample 3): Carbon black [Asahi Thermal Co., Ltd., average particle size 90 μm] was used in the same amount as in (1) instead of the graphite fine powder in Sample 1.

The results shown in the following table were obtained as a result of measuring the light transmittance, the surface electric resistance, and the coefficient of friction of the portion of each sample having a thickness of 3 μm.

However, the measurement method for light transmittance is according to JIS C6290,
The surface electric resistance is obtained by a method according to JIS K6911, and the friction coefficient is obtained from the ratio of load and tensile force.

As is clear from the above results, the graphite fine powder of the present invention (Sample 1)
Is lower in light transmission than natural graphite (Sample 2) and carbon black (Sample 3), and has low surface electric resistance and low friction coefficient. Such properties are particularly suitable for a back coat such as a tape.

(Effect of the invention) As is clear from the above, the graphite fine powder of the present invention starts from vapor grown carbon fiber, so that not only pulverized fine powder having a particle size of 1 μm or less can be easily obtained, but also because the particle size is extremely fine, coating The surface is smooth and has good slidability, and because it has excellent functionality such as light transmission, surface electrical resistance, and friction coefficient, it has a great effect on its performance as a coating agent for audio tapes, video tapes, etc. .

Claims (1)

[Claims] 1. A pulverized fine powder of graphitized vapor grown carbon fiber having a particle size of 1 μm or less.