JP2002201532A - Method for producing coiled carbon fiber and device for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a coiled carbon fiber, by which the coiled carbon fiber capable of absorbing electromagnetic waves in a wide frequency band, can be obtained and to provide a device for producing the same. SOLUTION: This device for producing the coiled carbon fiber is provided with a synthetic resin 13 for thermally decomposing a raw material gas to synthesize the coiled carbon fiber and a plasma-treating region 18 for preliminarily treating a gas (including the raw material gas) introduced in the synthesis region 13 with plasma. At least a part of the gas introduced into the synthesis region 13 is introduced into the synthesis region 13 through the plasma-treating region 18. Therefore, the synthesis of the coiled carbon fibers in the synthesis region 13 is carried out in the presence of the gas in an excited state activated by the plasma treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing coiled carbon fiber used as an electromagnetic wave absorbing material.

[0002]

2. Description of the Related Art In recent years, malfunctions and health problems of electric and electronic devices due to electromagnetic waves generated from mobile phones and the like have become major social problems. Under such circumstances, various electromagnetic wave absorbing materials have been proposed, and one of them is a coiled carbon fiber. When an electromagnetic wave is applied to the coiled carbon fiber from the outside, an induced current due to an induced electromotive force flows in the coil according to Faraday's law to generate Joule heat. That is, the coiled carbon fiber has the ability to convert electromagnetic waves into thermal energy, and this ability enables absorption and attenuation of electromagnetic waves. The production of the coiled carbon fiber is performed by a chemical vapor deposition (CVD) method in which acetylene is thermally decomposed in the presence of a metal catalyst such as nickel and an impurity gas such as hydrogen sulfide.

[0003]

However, in the case of the coiled carbon fiber obtained by the conventional manufacturing method, the electromagnetic wave around 10 GHz is specifically absorbed, but is suitable for absorbing electromagnetic waves in a wide band from low frequency to high frequency. It did not have electromagnetic wave absorption characteristics.

The present invention has been made by focusing on the problems existing in the prior art as described above. An object of the present invention is to provide a method and an apparatus for manufacturing a coiled carbon fiber capable of obtaining a coiled carbon fiber capable of absorbing electromagnetic waves in a wide frequency band.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, at least a part of a mixed gas containing a gas serving as a raw material of a coiled carbon fiber is activated by a plasma treatment. The gist of the present invention is to synthesize a coiled carbon fiber by thermally decomposing a gas serving as a raw material of the coiled carbon fiber in the presence of the gas in the excited state.

According to a second aspect of the present invention, in the method for producing a coiled carbon fiber according to the first aspect, the gas to be excited by the plasma treatment is nitrogen or argon.

According to a third aspect of the present invention, there is provided a method for producing a coiled carbon fiber according to the first or second aspect,
The gist is that the plasma processing is performed by glow discharge plasma.

According to a fourth aspect of the present invention, there is provided a plasma processing region in which at least a part of a mixed gas containing a gas serving as a raw material of coiled carbon fibers is activated by a plasma process to be in an excited state, The present invention has a synthesizing region for synthesizing a coiled carbon fiber by thermally decomposing a gas serving as a raw material of the coiled carbon fiber in the presence of an excited gas.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram schematically illustrating an outline of an apparatus for producing coiled carbon fibers in the present embodiment. The manufacturing apparatus shown in the figure is provided with a tubular reactor 12, and the inside of the reactor 12 is a synthesis area 13 where a coiled carbon fiber is synthesized. A base material 14 is disposed in the synthesis region 13, and when the coiled carbon fiber is synthesized, the coiled carbon fiber grows using the base material 14 as a scaffold. Also, reactor 1
A heater 15 is provided around the area 2, and the temperature of the synthesis area 13 is arbitrarily set by the heater 15.

The reactor 12 is connected to a gas inlet 16 for introducing gas into the synthesis area 13 and a gas outlet 17 for extracting gas in the synthesis area 13 to the outside. The gas introducing section 16 has a plasma processing area 18 for performing a plasma processing on a gas introduced into the synthesis area 13 via the gas introducing section 16 in advance.
The gas introduction unit 16 is provided with a first gas introduction port 16a and a second gas introduction port 16b. The first gas introduction port 16a is located upstream of the plasma processing region 18 at a second gas introduction port. 16 b is provided on the downstream side of the plasma processing region 18. For this reason, the gas introduced from the first gas introduction port 16a passes through the plasma processing area 18 and the synthesis area 13a.
In contrast, the gas introduced from the second gas introduction port 16b is introduced into the synthesis area 13 without passing through the plasma processing area 18.

An internal electrode 19 is provided in the plasma processing region 18.
And an external electrode 20 are provided. The internal electrode 19 is connected to a power supply 21 and the external electrode 20 is grounded. When a voltage is applied between the two electrodes 19 and 20 using the power supply 21, a glow discharge occurs, and the gas introduced into the plasma processing region 18 is turned into a plasma state. The internal electrode 19 is made of a material that functions as a catalyst for synthesizing the coiled carbon fiber. Specifically, nickel, cobalt and the like are preferable.

Further, the reactor 1 is provided at both ends of the reactor 12.
A purge gas introduction port 22 for introducing a purge gas (such as nitrogen) is provided in 2. Further, the reactor 12
In order to measure the temperature of the synthesis area 13, the thermocouple 23
Are arranged.

Next, a method for producing the coiled carbon fiber will be described. When manufacturing the coiled carbon fiber, first, after replacing the inside of the reactor 12 with nitrogen, the temperature of the synthesis region 13 is raised to a predetermined temperature by the heater 15, and further, discharge is started in the plasma processing region 18. I do. Then, in that state, a mixed gas containing a gas (hereinafter, also referred to as a raw material gas) serving as a raw material of the coiled carbon fiber is supplied to the gas introduction unit 1.
6 to the synthesis area 13. Then, the raw material gas in the mixed gas is thermally decomposed, and the carbon fibers are deposited and formed on the base material 14.

Here, at least a part of the mixed gas introduced into the synthesis area 13 is supplied to the first gas introduction port 16a.
Is introduced into the synthesis region 13 through the plasma processing region 18, and the remainder is introduced into the synthesis region 13 from the second gas inlet 16 b without passing through the plasma processing region 18.
Therefore, in the synthesis region 13, the synthesis of the coiled carbon fibers is performed in the presence of the gas activated and excited by the plasma processing (hereinafter, referred to as an excitation gas). The source gas is supplied to the first gas inlet 16a.
When introduced from a source gas, the source gas itself becomes the excitation gas.

Specific examples of the raw material gas introduced into the synthesis zone 13 include acetylene, methane, propane, ethylene, carbon monoxide and the like, among which acetylene is preferable. The mixed gas includes impurity gases such as sulfur, thiophene, methyl mercaptan, hydrogen sulfide, phosphorus, and phosphorus trichloride, and seal gases such as nitrogen, argon, helium, and hydrogen, in addition to the source gas.

The synthetic region 1 during the synthesis of the coiled carbon fiber
The temperature of 3 is preferably set between 600 and 950 ° C. If this temperature is lower than 600 ° C. or higher than 950 ° C., it is not preferable because it becomes difficult to obtain coiled carbon fibers.

The coiled carbon fiber produced by the above method is used, for example, as an electromagnetic wave absorbing material. In that case, it is used as a composite material by dispersing it in various matrices such as synthetic resin, rubber, and elastomer.

According to the above-described embodiment, the following effects are exhibited. Most of the coiled carbon fibers obtained by the conventional method for manufacturing a coiled carbon fiber have a double spiral structure, but in the case of the present embodiment, a coiled carbon fiber having a single spiral structure can be obtained. . The coiled carbon fiber having a single helical structure obtained in the present embodiment has excellent electromagnetic wave absorption characteristics capable of absorbing electromagnetic waves in a wide frequency band, as compared with those having a double helical structure obtained by a conventional manufacturing method.

The electric resistance of the coiled carbon fiber obtained by the conventional method for producing the coiled carbon fiber is approximately 10 to 1
00 Ω / μm, but in the case of this embodiment, approximately 1
A coiled carbon fiber having a large electric resistance of 00 to 2000 Ω / μm can be obtained. For this reason, the coiled carbon fiber of the present embodiment is
It has excellent efficiency in converting electromagnetic waves into heat energy. That is, the coiled carbon fiber of the present embodiment is superior in the electromagnetic wave absorptivity to the conventional coiled carbon fiber.

In the conventional method for producing coiled carbon fibers, the carbon fibers do not grow in a coil shape unless a catalyst such as nickel is supported on the substrate 14. However, in the case of the present embodiment, the internal electrode 19 made of a material that functions as a catalyst for the synthesis of the coiled carbon fiber is connected to the plasma processing
, Carbon fibers can be grown in a coil shape without supporting the catalyst on the substrate 14. For this reason, it is possible to save the trouble of supporting the catalyst on the base material 14 in advance. It is considered that this is because fine particles generated by sputtering the internal electrode 19 in the plasma processing region 18 are carried to the synthesis region 13 and function as a catalyst for coiled carbon fiber synthesis.

Activating nitrogen or argon, which is a seal gas, by plasma treatment to bring it into an excited state,
Coiled carbon fibers having a single helical structure can be obtained with high yield.

By performing the plasma processing with glow discharge plasma, the mixed gas containing the source gas can be effectively activated to be in an excited state. In addition, since a large amount of current is not required (about 1 to 10 mA), there is an advantage that energy consumption in the plasma processing is relatively small.

The yield can be improved by synthesizing the coiled carbon fiber in the presence of the excitation gas. -Since the configuration of the manufacturing apparatus is simple and small, the cost can be reduced and the installation space does not increase.

[0024]

Next, the embodiment will be described more specifically with reference to examples and comparative examples. (Example 1) A coiled carbon fiber was manufactured using the coiled carbon fiber manufacturing apparatus of the embodiment shown in FIG. The manufacturing conditions are as follows. The temperature of the synthesis region 13 is set to 770 ° C., nitrogen as a seal gas is supplied at a flow rate of 100 ml / min from the first gas inlet 16a, and acetylene as a source gas is supplied from the second gas inlet 16b. , Hydrogen sulfide as an impurity gas, and hydrogen as a seal gas at 30 ml / min, 0.1 ml / min, and 100 ml, respectively.
/ Min flow rate. Further, a nickel electrode was used as the internal electrode 19 in the plasma processing region 18 and plasma processing was performed by glow discharge plasma (10 mA × 10 kV).

The obtained coiled carbon fiber has a single helical structure, the fiber diameter is about 1 μm, and the coil pitch is about 2 μm.
0 μm and the coil diameter was about 7 μm. (Examples 2 to 5) The current and voltage during the plasma treatment by glow discharge were changed as shown in Table 2 below, and the other operations were the same as in Example 1. Also in this case, each of the obtained coiled carbon fibers had a single spiral structure.

(Embodiment 6) Argon was replaced by nitrogen instead of nitrogen.
The operation was performed in the same manner as in Example 1 except that the gas was introduced from the gas introduction port 16a. In this case also, a coiled carbon fiber having a single helical structure could be obtained,
The amount was about 1/3 of that in Example 1.

(Comparative Example 1) All the gas was changed to be introduced from the second gas introduction port 16b to omit the plasma treatment, and nickel was supported on the base material 14 as a catalyst. Otherwise, the procedure was the same as in Example 1. As a result, a coiled carbon fiber having a double helical structure was obtained.

Table 1 below shows the results of examining the electromagnetic wave absorption characteristics (reflection attenuation characteristics) of the coiled carbon fibers obtained in Example 1 and Comparative Example 1. Table 2 below shows Example 1
5 shows yields of coiled carbon fibers in Nos. To 5.

[0029]

[Table 1] As shown in Table 1, the coiled carbon fiber (double helix) obtained in Comparative Example 1 has a slightly poor return loss with respect to a low-frequency electromagnetic wave (100 kHz or less), whereas Example 1 has a poor return loss.
In the coiled carbon fiber (single spiral) obtained in (1), the return loss with respect to low-frequency electromagnetic waves was dramatically improved. Further, the return loss with respect to the high-frequency electromagnetic wave was almost the same between the coiled carbon fiber obtained in Example 1 and the coiled carbon fiber obtained in Comparative Example 1. From this, the coiled carbon fiber obtained in Example 1 was 1 kHz.
It has been shown that high electromagnetic wave absorptivity can be exhibited in a broadband from z to 1000 GHz.

[0030]

[Table 2] The results shown in Table 2 show that the yield changes with the change in current and voltage during plasma processing. Also,
Since the yield exceeds 30%, 5 mA × 20 kV to 8 mA
A range of mA × 12.5 kV was shown to be preferred.

The above embodiment can be modified as follows. In the above embodiment, the internal electrode 19 made of a material functioning as a catalyst for coiled carbon fiber synthesis is used, but may be changed to an internal electrode made of a material not functioning as a catalyst for coiled carbon fiber synthesis. However, in this case, it is necessary to previously support nickel or the like as a catalyst on the base material 14.

When the coiled carbon fiber in the present embodiment is dispersed in various matrices and used as an electromagnetic wave absorbing material, a conventional coiled carbon fiber having a double helical structure may be used in combination. With this configuration, the broadband electromagnetic wave absorption characteristics of the coiled carbon fiber (single spiral structure) of the present embodiment and the frequency-specific electromagnetic wave absorption characteristics of the conventional coiled carbon fiber having the double spiral structure are provided. Thus, an electromagnetic wave absorbing material having both functions is obtained. The mixing ratio of the coiled carbon fiber of the present embodiment and the conventional coiled carbon fiber having a double helical structure may be set arbitrarily as needed. For example, when the mixing ratio is set to 1: 1, The result obtained by adding the results obtained when the coiled carbon fibers are used alone is obtained.

Next, the technical ideas that can be grasped from the above embodiment will be described below. The method for producing a coiled carbon fiber according to any one of claims 1 to 3, wherein the electrode used in the plasma treatment is made of a material that functions as a catalyst for the synthesis of the coiled carbon fiber. . With such a configuration, it is not necessary to previously carry the catalyst on the substrate serving as a scaffold during the growth of the coiled carbon fiber, so that the labor can be saved.

The method for producing a coiled carbon fiber according to any one of claims 1 to 3, wherein the mixed gas comprises a gas serving as a raw material for the coiled carbon fiber, an impurity gas, and a seal gas. According to this structure, the coiled carbon fibers can be reliably obtained.

[0035]

Since the present invention is configured as described above, it has the following effects. Claim 1 and Claim 4
According to the invention described in (1), coiled carbon fibers capable of absorbing electromagnetic waves in a wide frequency band can be obtained.

According to the second aspect of the present invention, coiled carbon fibers capable of absorbing electromagnetic waves in a wide frequency band can be obtained with high yield. According to the third aspect of the present invention, it is possible to effectively activate the mixed gas containing the gas serving as the raw material of the coiled carbon fiber by the plasma treatment to bring it into an excited state.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an outline of an apparatus for producing coiled carbon fibers.

[Explanation of symbols]

 13: synthesis area, 18: plasma processing area.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Suji Motojima 1-23-23, Fukumitsuhigashi, Gifu City, Gifu Prefecture (72) Inventor, Kenji Kawabe 4-179, Suecho, Kakamigahara City, Gifu Prefecture Techno Plaza Inn Sea MC Technology Development Co., Ltd. (72) Inventor Yukio Hishikawa 4-179, Sue-cho, Kakamigahara-shi, Gifu Prefecture Techno Plaza CMC Technology Development Co., Ltd. (72) Inventor Fujio Sakamoto Shimoyuzuki, Hachioji-shi, Tokyo 2-10-10 1 Hughes Technonet Co., Ltd. Planet Japan Co., Ltd. F-term (reference) 4L037 CS03 CT05 FA05 PA08 PA26 UA02 5E321 AA24 BB34 BB44 GG05 GG11

Claims (4)

[Claims] At least a part of a mixed gas containing a gas serving as a raw material of a coiled carbon fiber is activated by a plasma treatment to be in an excited state, and the coiled carbon fiber is present in the presence of the excited gas. A method for producing coiled carbon fiber, comprising synthesizing a coiled carbon fiber by thermally decomposing a gas as a raw material for the carbon fiber. 2. The method for producing a coiled carbon fiber according to claim 1, wherein the gas to be excited by the plasma treatment is nitrogen or argon. 3. The method for producing coiled carbon fibers according to claim 1, wherein the plasma treatment is performed by glow discharge plasma. 4. A plasma processing region in which at least a part of a mixed gas containing a gas serving as a raw material of the coiled carbon fiber is activated by plasma processing to be in an excited state, And a synthesis region for synthesizing the coiled carbon fiber by thermally decomposing a gas serving as a raw material of the coiled carbon fiber in the presence of the coiled carbon fiber.