JP2002146634A - Fine carbon fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine carbon fiber having good electrical conductivity, having an outer diameter of <400 nm, especially of 2-300 nm, and used as a filler material with good adhesion to a resin or the like, and to provide a method for producing the fine carbon fiber, capable of producing the carbon fiber in a mass production scale, and capable of giving an field electron-emitting material chemically and thermally stable, excellent in electron emission characteristics, and having a long lifetime. SOLUTION: This fine carbon fiber has a multiple-layer structure in which cylindrical carbon sheets overlap each other, a center axis of which has a hollow structure, an outer diameter of 2-30 nm, and an aspect ratio of 10-15,000, wherein at least one layer of the cylindrical carbon sheet is turned at the end of the carbon fiber to be continuous with another cylindrical carbon sheet among the multiple layers, so that the turned and continuous cylindrical carbon sheet forms a cylinder of which the end opens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine carbon fiber having a peculiar structure, a method for producing the same, and its application, particularly, a fine carbon fiber suitable as a filler for a composite material such as resin and rubber, a semiconductor material, a catalyst, or a field electron emission material. The present invention relates to a fiber and a method for producing the fiber.

[0002]

2. Description of the Related Art Carbon fibers are used in various composite materials because of their excellent properties such as high strength, high elastic modulus and high conductivity. Utilizing not only the excellent mechanical properties that have been applied in the past, but also the conductive properties of carbon fiber or carbon materials, with the development of electronics technology in recent years, conductive resins for electromagnetic wave shielding and antistatic materials have been developed. It is expected to be used as a filler or as a filler for electrostatic coating on a resin. In addition, it is expected to be used as a field electron emission material such as a flat display by utilizing the characteristics of chemical stability, thermal stability and microstructure as a carbon material.

Conventional carbon fibers are produced as so-called organic carbon fibers produced by heat-treating and carbonizing fibers such as PAN, pitch, and cellulose. When these are used as fillers of a fiber-reinforced composite material, it is desirable to increase the contact area with the base material, to reduce the diameter, to increase the length, etc., in order to enhance the reinforcing effect. In order to improve the adhesiveness with the base material, it is preferable that the surface of the carbon fiber is not smooth but rough to some extent. For this reason, the carbon fiber is exposed to high temperature in the air to be oxidized, or the surface is coated. Surface treatment such as rubbing is performed.

However, these carbon fibers have a yarn diameter of about 5 to 10 μm of an organic fiber as a raw material, and it has been impossible to produce carbon fibers having a small diameter. Further, there is a limit to the ratio of length to diameter (aspect ratio), and there has been a demand for thin carbon fibers having a large aspect ratio.

[0005] The use of a resin for an automobile body or the use of a resin or rubber for an electronic device is required to have the same conductivity as that of a metal. It has become necessary to increase conductivity in order to satisfy the requirements for conductive paints and conductive resins.
As a means for achieving this, it is necessary to improve these characteristics by graphitization, and for this purpose, a graphitization treatment at a higher temperature is usually performed. However, even this graphitization does not provide the same level of conductivity as metal, and if the blending amount is increased to compensate for this, the workability and mechanical properties will decrease. Improvement,
It has been required to improve the strength by reducing the diameter of the fiber.
As a field emission material, field emission by the Spindt method has been conventionally researched and developed. However, the manufacturing method requires many steps, and the conventional electron emission portion has M
Although the tip is processed into a needle shape using o or the like, when it is used as an electron emission material for a display, it is insufficient chemically and thermally.

[0006] Then, in the late 1980's, a vapor production carbon fiber (Vapor Carbon Carbon Fiber) was used as a completely different production method from these organic fibers.
r; hereinafter abbreviated as VGCF. ) Began to be studied. This VGCF has a diameter of 1 μm by subjecting a gas such as a hydrocarbon to gas phase pyrolysis in the presence of an organic transition metal catalyst.
It is known that carbon fibers of m or less and up to several 100 nm can be obtained. For example, a method in which an organic compound such as benzene is used as a raw material, and an organic transition metal compound such as ferrocene as a catalyst is introduced into a high-temperature reactor together with a carrier gas to form the compound on a substrate (Japanese Patent Laid-Open No. 60-27700). Method of generating VGCF in a floating state
No. 0-54998), or a method of growing on a reactor wall (Japanese Patent No. 2778434).

According to these production methods, carbon fibers suitable for a filler material having a relatively small thickness and excellent conductivity and having a large aspect ratio can be obtained, and have a diameter of about 100 to 200 nm and an aspect ratio of about 10 to 500. Has been mass-produced, and has been used as a conductive filler material in resin fillers and as an additive for lead-acid batteries.

[0008] These VGCFs are characterized in shape and crystal structure, and have a structure in which hexagonal carbon crystals are rolled into a cylindrical shape in a ring shape and stacked in a ring shape, and a fiber having an extremely thin hollow portion at the center. is there. However, as for these VGCFs, those with a smaller diameter of less than 100 nm could not be produced on a mass production scale.

As a carbon fiber finer than the VGCF, multi-walled carbon nanotubes were discovered by Iijima et al. From soot obtained by evaporating a carbon electrode by arc discharge in helium gas. The diameter of this multi-walled carbon nanotube is 1 nm to 30 nm, and like the VGCF, the crystals of the carbon hexagonal plane are superimposed on the axis of the fiber in a number of rings and closed in a cylindrical shape. It is a fine carbon fiber having a hollow diameter.

The method using this arc discharge is not suitable for mass production due to its production method and has not been put to practical use.

On the other hand, the vapor phase method has a large aspect ratio and a high conductivity, and attempts have been made to improve this method to produce finer carbon fibers. U.S. Pat. No. 4,663,230, Japanese Patent Publication No. 3-6460
No. 6 discloses a columnar carbon fibril made of graphite having a diameter of about 3.5 to 70 nm and an aspect ratio of 100 or more. The structure is such that a continuous layer of regularly arranged carbon atoms is arranged concentrically with respect to the cylinder axis over multiple layers, and the C axis of each layer of carbon atoms is substantially orthogonal to the cylinder axis of the fibrils. It does not contain a thermal carbon film deposited by thermal decomposition and has a smooth surface.

Similarly, Japanese Patent Application Laid-Open No. 61-70014 discloses a carbon fiber produced by a gas phase method having an aspect ratio of 2 to 30,000 at a wavelength of 10 to 500 nm. It is stated that:

[0013] The above-mentioned carbon fibers have a smooth surface and thus poor adhesion, wettability and affinity. When used as a composite material, surface treatment such as sufficient oxidation treatment of the surface is required. Come. Further, when it is used as a field electron emission material, it is necessary to make the tip thin.

[0014]

In the present invention, a fine carbon fiber having good adhesion to a resin or the like is obtained on a mass production scale as a filler material having good conductivity of less than 400 nm, particularly 2 to 300 nm. An object of the present invention is to obtain a field emission material which is chemically and thermally stable, has excellent electron emission characteristics, and has a long life.

[0015]

Means for Solving the Problems The present inventors have developed a conventional method for producing VGCF, and have completed a new fine carbon fiber having a structure different from the conventional one and a method for producing the same. That is, (1) a cylindrical carbon sheet overlaps to form a multilayer structure, the central axis of which is a hollow structure, and an outer diameter of 2 to 300 n.
m, a fine carbon fiber having an aspect ratio of 10 to 15000, wherein at least one layer of a cylindrical carbon sheet at the tip of the carbon fiber is folded between the multilayers and is continuous with another cylindrical carbon sheet, A fine carbon fiber characterized in that a folded and continuous cylindrical carbon sheet forms a cylindrical structure open at the tip. (2) The fine carbon fiber according to (1), wherein the folded and continuous cylindrical carbon sheet is present on the outer peripheral portion of the multilayer structure. (3) The fine carbon fiber according to (2), wherein a cylindrical carbon sheet having a closed end is present inside a cylindrical structure formed by folding back and forming a continuous cylindrical carbon sheet. (4) Inside the cylindrical carbon sheet having a closed distal end, there is a cylindrical carbon sheet that is folded back at the distal end and forms a cylindrical shape that is continuous and opens at the distal end of the carbon fiber. Fine carbon fibers according to 3). (5) Outer diameter 2 to 300 nm, aspect ratio 10 to 150
A fine carbon fiber characterized in that the fine carbon fiber according to (1) to (4) accounts for 5% by mass or more of the fine carbon fiber of No. 00. (6) Outer diameter 2 to 300 nm, aspect ratio 10 to 150
The fine carbon fiber according to (5), wherein the fine carbon fiber accounts for 5 to 90% by mass of the fine carbon fiber of No. 00. (7) Outer diameter 2 to 300 nm, aspect ratio 10 to 150
The fine carbon fibers according to (1) to (6), which are observed by a transmission electron microscope in the fine carbon fibers of No. 00, occupy 3 to 80% by volume. (8) The fine carbon fiber according to any one of (1) to (7), wherein the fine carbon fiber is a vapor grown carbon fiber. (9) The fine carbon fiber according to any one of (1) to (8), wherein the boron element is contained in the carbon fiber. (10) The fine carbon fiber according to any one of (1) to (9), wherein the boron element is partially substituted with the carbon element of the carbon fiber. (11) an outer diameter of 2 to 300 nm, in which a cylindrical carbon sheet overlaps to form a multilayer structure, and the central axis of which is a hollow structure;
The method for producing fine carbon fibers according to (1) to (10) by heat-treating fine carbon fibers having an aspect ratio of 10 to 15,000. (12) The method for producing fine carbon fibers according to (11), wherein the heat treatment temperature is 2000 ° C to 3500 ° C. (13) an outer diameter of 2 to 300 nm, in which a cylindrical carbon sheet overlaps to form a multilayer structure, and the central axis thereof is a hollow structure;
It is characterized in that a fine carbon fiber having an aspect ratio of 10 to 15000 and a boron compound are mixed and heat-treated.
The method for producing fine carbon fibers according to 1) or (12).

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present invention has good conductivity, an outer diameter of less than 400 nm,
In order to obtain a fine carbon fiber having good adhesion to a resin or the like as a filler material having a thickness of 2 to 300 nm, more preferably 1 to 80 nm, fine VGCF is subjected to high-temperature heat treatment in the presence of a boron compound. When graphitization was carried out, fine carbon fibers in a conventionally unknown form were obtained, which had high conductivity and excellent adhesiveness to resins, etc. To provide a field electron emission material that is stable and has excellent electron emission characteristics and a long life, and that this new form of fine carbon fiber can be heat-treated not only in the presence of boron compounds. It was found. It is understood that the fine carbon fiber of the present invention is basically one type of carbon fiber obtained in the process of producing a finer and more graphitized carbon fiber. The fine carbon fiber of the present invention will be described. The characteristics of the fine carbon fiber of the present invention will be described with reference to the attached drawings (FIGS. 1 to 4). In these figures, a carbon sheet (a layer of graphite or a crystal close to graphite) is schematically represented by a solid line. First, conventional less than 100 nm, aspect ratio 10-15000
As shown in the schematic cross-sectional view of FIG. 1, there is known a fine carbon fiber having a multilayer structure (annular ring structure) in which cylindrical carbon sheets overlap with each other and having a hollow central axis. In such a known fine carbon fiber, the cylindrical carbon sheet constituting the multilayer structure is all closed at a certain curvature at the tip of the fiber. On the other hand, the fine carbon fiber of the present invention has the following structure. 1) As shown in FIGS. 2 and 4, cylindrical carbon sheets overlap to form a multilayer structure, and the central axis thereof is a hollow structure.
In the fine carbon fiber 10 having an outer diameter of 2 to 300 nm and an aspect ratio of 10 to 15000, at least one layer of the cylindrical carbon sheet 14 (14
a, 14b) is folded between the multilayers and is continuous with another cylindrical carbon sheet 15 (15a, 15b). The cylinder formed by the folded and continuous cylindrical carbon sheets 14, 15 is a tip of carbon fiber. Fine carbon fiber characterized by being open in. Oxidation of conventional fine carbon fibers can forcibly break the ends of the fibers (US Pat.
641,466), but in that case, it is not a condition for forming graphite, so that the carbon sheet does not turn back and continue. 2) Referring to FIG. 2, in the fine carbon fiber of the above 1), the folded and continuous cylindrical carbon sheet 14, 1
5. Fine carbon fibers characterized in that 5 is present in the outer peripheral portion of the multilayer structure. The folded and continuous carbon sheet is generally easily formed on the outer peripheral portion of the multilayer structure. 3) Referring to FIG. 2, in the fine carbon fiber of 2), the folded and continuous cylindrical carbon sheet 14, 1
5. A fine carbon fiber, characterized in that a cylindrical carbon sheet 13 (13a, 13b) having a closed end portion 12A is present inside a cylinder formed by 5. In general, a cylinder formed by a continuous carbon sheet that is folded back tends to be present on the outer peripheral portion of the multilayer structure. However, a cylindrical carbon sheet is further present on the inner side, and the tip portion 12A is closed. There are many. 4) Referring to FIG. 3, in the fine carbon fiber of the above 3), the cylindrical portion is further folded back at the front end inside the cylindrical carbon sheet 13 having the closed front end and opened at the front end of the carbon fiber. A fine carbon fiber characterized by having cylindrical carbon sheets 11 and 12 in a shape. 5) Referring to FIG. 4, the fine carbon fiber may be formed only by a cylinder formed by folding and forming a continuous carbon sheet, and the tip of the carbon fiber may be open. The present invention is not limited to the case of FIG. 4, and the carbon sheet 16 which is not folded may exist somewhere inside the cylinder formed of the continuous carbon sheets 14 and 15 by folding the fine carbon fiber. 6) Outer diameter 2 to 300 nm, aspect ratio 10 to 1500
Fine carbon fibers in which the fine carbon fibers according to any one of 1) to 5) above account for 5% by mass or more of the fine carbon fibers. As described above, the typical form of the fine carbon fiber of the present invention has been described. The cylinder formed by the cylindrical carbon sheet which is continuous with the carbon sheet and is turned back and continuous is characterized by being open at the tip of the carbon fiber, and other changes are optional. For example, the number of layers of the cylindrical carbon sheet that is folded between the multilayers at the tip of the carbon fiber and is continuous with another cylindrical carbon sheet may be at least one layer, and may be two or three or more adjacent cylindrical carbon sheets. The carbon sheet may be folded back to be continuous with another cylindrical carbon sheet. The folded and continuous cylindrical carbon sheets may or may not be adjacent to each other. For example,
In FIG. 4, the cylindrical carbon sheet 14 and the cylindrical carbon sheet 1 are shown.
Although 5 is folded back and continued, the cylindrical carbon sheet 14 and the cylindrical carbon sheet 15 are not adjacent to each other with the cylindrical carbon sheet 16 interposed therebetween. In addition, even if amorphous carbon is present at the tip and surroundings of the carbon fiber constituted by the carbon sheet, the fine carbon fiber of the present invention is not affected.

The fine carbon fiber of the present invention has a multilayer structure in which cylindrical carbon sheets made of carbon atoms are overlapped with each other, and a hollow hollow portion is present on the central axis. When these carbon sheets are viewed from the direction perpendicular to the longitudinal direction of the fiber, or a series of regularly arranged carbon atoms, the carbon sheet is almost linearly overlapped in multiple layers, but the cylindrical sheet is There is a discontinuous part in the longitudinal direction,
The inner diameter of the hollow portion of the central shaft may not be constant. The above-described form of the fine carbon fiber of the present invention has not been reported in conventional carbon fibers produced by various vapor phase methods and is novel.

The fine carbon fiber of the present invention has a different feature at the tip than ever before, and there is a portion having a tip that is narrower than that of the conventional carbon fiber. , The applied electric field can be concentrated, the field electron emission characteristics are improved, and the device is suitable as a field electron emission device. Similarly, since the tip portion is irregularly shaped, when used as a conductive filler or the like, there is an effect that the adhesiveness to a resin or the like is improved. In addition, the present fine carbon fiber is 5% by mass or more and further 5 to 90% by mass, preferably 10% by mass.
When it is contained in an amount of from 70 to 70% by mass, particularly from 10 to 50% by mass, field emission characteristics are improved by its structural characteristics, and when it is used as a conductive filler or the like, the effect of improving the adhesiveness to a resin or the like is obtained. is there. The structure of the fine carbon fiber can be confirmed by observation with a transmission electron microscope. However, when the fine carbon fiber of the present invention is contained in an amount of 3 to 80% by volume, more preferably 5 to 70% by volume, preferably 10 to 50% by volume. Field electron emission characteristics are improved, and when used as a conductive filler or the like, there is an effect that adhesion to a resin or the like is improved.

The fine carbon fiber of the present invention has an outer diameter of 2 to 30.
Since fine and long fibers having an aspect ratio of 10 to 15000 can be obtained at 0 nm, a large amount can be added as a filler material and the reinforcing effect is excellent.

Further, since the carbon sheet having the above-mentioned structure has the end face of the carbon sheet exposed to the outside, when used as an additive for a battery, it has a good ion-capturing property and has a conventional conductivity. Since it is the same as the phase-processed carbon fiber and the surface is not smooth, it has good wettability with the battery electrolyte. Therefore, it has a feature that it is suitable as an additive for batteries. The fine carbon fiber having a peculiar form of the present invention may be produced by a method for producing a fine carbon fiber having a high degree of graphitization. A preferred method for producing fibers will be described. The fine carbon fiber of the present invention is generally obtained by thermally decomposing organic compounds, particularly hydrocarbons, using a transition metal catalyst to obtain coarse and fine carbon fibers.
It is obtained by performing a heat treatment at 3500 ° C., preferably 2500 to 3500 ° C. The reason why the fine carbon fibers have the above-mentioned folded structure is considered to be because the distance between the carbon sheets is reduced.Therefore, by adopting conditions that make the carbon sheet interval as small as possible, the fine carbon fibers of the present invention are more likely to be formed. Obtained easily. Therefore, it is advantageous that a boron compound is present when the coarse and fine carbon fibers are heat-treated. When a boron compound is present, the heat treatment temperature can be lowered by several hundred degrees centigrade as compared with the case where no boron compound is added, and the ratio of the outer peripheral portion to the fiber diameter can be increased at the same heat treatment temperature as compared with the case where no boron compound is added. As the boron compound,
Any substance that generates boron by heating may be used. For example, a solid, liquid, or gas such as boron carbide, boron oxide, or organic boron oxide may be used.

First, an organic compound using a transition metal catalyst,
In particular, coarse and fine carbon fibers are obtained by thermally decomposing hydrocarbons. The organic transition metal compound contains a transition metal serving as a catalyst. As the transition metal, Periodic Table IV
Organic compounds containing metals of groups a, Va, VIa, VIIa and VIII. Among them, compounds such as ferrocene and nickel sen are preferable. The content of the organic transition metal compound as a catalyst is 0.0
1-15.0 mass%, preferably 0.03-10.0 mass%, preferably 0.1-5.0 mass%. In addition, a sulfur compound is used as a co-catalyst, but the form is not particularly limited, and any form may be used as long as it can be dissolved in an organic compound as a carbon source. As the sulfur compound, thiophene, various thiols, inorganic sulfur or the like is used. The use amount thereof is 0.01 to 10.0% by mass, preferably 0.03 to 5.0% by mass, and more preferably 0.1 to 4.0% by mass based on the organic compound.

The organic compounds used as raw materials for carbon fibers include benzene, toluene, xylene, methanol, ethanol,
Naphthalene, phenanthrene, cyclopropane, cyclopentene, cyclohexane organic compounds, volatile oil, kerosene, etc., CO, natural gas, methane, ethane, ethylene,
Gases such as acetylene and mixtures thereof are also possible.
Among them, aromatic compounds such as benzene, toluene and xylene are particularly preferred.

As the carrier gas, a reducing gas such as a hydrogen gas is usually used. It is preferred that the carrier gas be heated to 500 to 1300 ° C. in advance. The reason for heating is to match the generation of the metal of the catalyst and the supply of the carbon source by the thermal decomposition of the carbon compound during the reaction, so that the reaction is instantaneously caused and finer carbon fibers are obtained. . When the heating temperature of the carrier gas is less than 500 ° C. when the carrier gas is mixed with the raw material, thermal decomposition of the carbon compound of the raw material hardly occurs and 13
When the temperature exceeds 00 ° C., the carbon fiber grows in the radial direction, and the diameter tends to increase.

The amount of the carrier gas used is suitably from 1 to 70 mol parts per 1.0 mol part of the organic compound as the carbon source. The diameter of the carbon fiber can be controlled by changing the ratio between the carbon source and the carrier gas. Raw materials are
A transition metal compound and a co-catalyst sulfur compound are dissolved and adjusted in an organic compound as a carbon source. The raw material can be sprayed with a carrier gas in a liquid state and supplied to the reaction furnace. Alternatively, a part of the carrier gas can be vaporized as a purge gas and supplied to the reaction furnace for reaction. When obtaining a carbon fiber having a small fiber diameter, it is preferable that the raw material is vaporized and supplied to the reaction furnace.

As the reaction furnace, a vertical electric furnace is usually used.
The reactor temperature is 800-1300 ° C., preferably 1000
１1300 ° C. To the reaction furnace that has been heated to a predetermined temperature,
A raw material liquid and a carrier gas or a raw material gas obtained by vaporizing the raw material and a carrier gas are supplied and reacted to obtain carbon fibers.

The gas blown into the reaction furnace in this manner is thermally decomposed, the organic compound serves as a carbon source, the organic transition metal compound serves as transition metal particles of the catalyst, and fine carbon fibers having the transition metal particles as nuclei. Generation occurs. The obtained fine carbon fiber is further subjected to a heat treatment at 900 to 1500 ° C. in an atmosphere of an inert gas such as helium or argon,
Further, a heat treatment at 2000 to 3500 ° C. is performed, or
The fine carbon fiber in the state obtained by the reaction is subjected to an inert gas atmosphere, and directly heat-treated at 2000 to 3500 ° C.
It is possible to obtain the unique fine carbon fiber of the present invention.
However, the fine carbon obtained by the reaction or the fine carbon fiber is 900 to 1 under an inert gas atmosphere.
After heat treatment at 500 ° C., boron carbide (B
₄ C), boron oxide _{(B 2 O} 3), elemental boron, boric acid _(H 3 _BO 3), is mixed with a boron compound such as boric acid salts, further heat-treated under 2,000 to 3,500 ° C. inert gas atmosphere By carrying out, the unique fine carbon fiber of the present invention can be obtained more easily. The addition amount of the boron compound is not limited because it depends on the chemical and physical properties of the boron compound used.
_When 4C) is used, 0.1% is used for fine carbon fibers.
The range is from 0.05 to 10% by mass, preferably from 0.1 to 5% by mass. The fact that boron is contained in the fine carbon fiber means that boron is partially dissolved and exists in the surface of the carbon fiber, between layers of the carbon hexagonal mesh plane, in the hollow portion, or partially replaced by carbon atoms and boron atoms. Refers to the state of having done.

[0027]

Embodiments of the present invention will be described below. As shown in FIG. 5 of the schematic diagram, the vertical heating furnace 1 (inside diameter 170 m
(M, 1500 mm in length), a raw material supply pipe 4 for supplying a raw material vaporized through a raw material vaporizer 5 and a carrier gas supply pipe 6 were attached. From the raw material supply pipe 4,
Toluene in which 3% by mass of ferrocene and 1% by mass of thiophene were dissolved was vaporized and supplied at a rate of 20 g / min. Hydrogen was used as a carrier gas and supplied at a rate of 75 L / min to cause a reaction. FIG. 6 shows a transmission electron micrograph of the fine carbon fiber obtained by this reaction. The fine carbon fiber obtained by this reaction was heat-treated at 1300 ° C. in an Ar (argon) atmosphere, and the product treated at 1300 ° C. was further heat-treated at 2800 ° C. in an Ar atmosphere to obtain a fine carbon fiber at a weight recovery of 96%. Further, 4% by mass of B ₄ C was mixed with the heat-treated product of this fine carbon fiber in an Ar atmosphere at 1300 ° C. and heat-treated at 2800 ° C. in an Ar atmosphere to obtain a fine carbon fiber with a weight recovery of 94%. This transmission electron micrograph is shown in FIG. 6 and 7 each have a multilayer structure in which cylindrical carbon sheets made of carbon atoms are overlapped, and the central axis thereof is a hollow structure. However, FIG. 6 corresponds to the schematic diagram of FIG. 1 and the tip is closed, while FIG. 7 shows a multilayer structure having a form roughly corresponding to the schematic diagram of FIG. That is, in FIG. 7, an outer peripheral portion (corresponding to 14 and 15 in FIG. 3) and a middle portion (corresponding to 13 in FIG. 3) having a closed end are formed.
And a cylinder with an open end inside (11,
12). In addition, each of the carbon sheets (14, 15 and 1 in FIG.
(Corresponding to Nos. 1 and 12) are folded back and joined to each other and are continuous. The carbon sheet (corresponding to 13 in FIG. 3), which is located between the folded carbon sheet layers on the outside and inside of the multilayer structure, has a closed end (corresponding to 12A in FIG. 3). In FIG. 7, a carbon sheet can be seen in the cross-sectional direction of the fiber at the tip of the carbon fiber. In this carbon sheet, the folded portion of the carbon sheet in the outer peripheral portion is seen as a carbon sheet, and the axial center of the fiber is There is no carbon sheet in the part. Similarly, at the tip of the carbon fiber, the tip of the carbon sheet at the closed tip of the intermediate carbon sheet appears to be not hollow but some substance is present, but amorphous carbon adheres to this portion. It is not related to the structure of the carbon fiber. It can be seen that amorphous carbon is also present on the circumferential surface of the carbon fiber.

The outer diameter of the fiber at this time is about 10 to 100.
Fibers with an aspect ratio of tens or more in nm were produced. When observed with a transmission electron microscope, more than half of the fibers had the above characteristics.

[0029]

According to the present invention, unlike conventional carbon fibers and vapor grown carbon fibers, the outer diameter is 2 to 300 nm, the aspect ratio is 10 to 15000, and at least the tip of the carbon fiber has One layer of a cylindrical carbon sheet is folded between the multilayers and is continuous with another cylindrical carbon sheet;
The turned back continuous cylindrical carbon sheet forms a cylinder that is open at the tip end, so that it can provide fine carbon fibers, which are useful as field electron emission, gas occlusion, and conductive filler for resin. is there.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view for explaining the structure of a conventional fine carbon fiber.

FIG. 2 is a schematic sectional view for explaining the structure of the fine carbon fiber of the present invention.

FIG. 3 is a schematic sectional view for explaining the structure of the fine carbon fiber of the present invention.

FIG. 4 is a schematic cross-sectional view for explaining the structure of the fine carbon fiber of the present invention.

FIG. 5 is a schematic view of an apparatus for manufacturing shown in an embodiment of the present invention.

FIG. 6 is a transmission electron micrograph (magnification: 20,000 times) of a conventional fine carbon fiber.

FIG. 7 is a transmission electron micrograph (magnification: 20,000 times) of a heat-treated product of a fine carbon fiber according to the present invention which has been heat-treated using a boron compound.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vertical heating furnace 2 ... Heater heater 3 ... Raw material recovery system 4 ... Raw material supply pipe 5 ... Raw material vaporizer 6 ... Carrier gas supply pipe

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yutaka Suhara 5-1 Okawacho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Denko KK Production Technology Center F-term (reference) 4G046 CA02 CB01 CC01 CC03 CC05 CC08 4L037 AT05 CS03 FA02 FA03 FA04 FA05 FA12 PA08 PA13 UA04 UA14 UA20

Claims (13)

[Claims] A cylindrical carbon sheet overlaps to form a multilayer structure, the central axis of which is a hollow structure, and an outer diameter of 2 to 30.
0 nm, a fine carbon fiber having an aspect ratio of 10 to 15000, wherein at least one layer of a cylindrical carbon sheet at the tip of the carbon fiber is folded between the multilayers to be continuous with another cylindrical carbon sheet, A fine carbon fiber characterized in that a folded and continuous cylindrical carbon sheet forms a cylindrical structure open at the tip. 2. The fine carbon fiber according to claim 1, wherein the folded and continuous cylindrical carbon sheet is present on the outer peripheral portion of the multilayer structure. 3. The fine carbon fiber according to claim 2, wherein a cylindrical carbon sheet having a closed end is present inside a cylindrical structure formed by folding and forming a continuous cylindrical carbon sheet. 4. A cylindrical carbon sheet further comprising a cylindrical carbon sheet which is folded back at the distal end and forms a cylindrical shape open at the distal end of the carbon fiber, inside the cylindrical carbon sheet having a closed distal end. The fine carbon fiber according to claim 3, which is used. 5. An outer diameter of 2 to 300 nm and an aspect ratio of 10.
The fine carbon fiber according to any one of claims 1 to 4, wherein the fine carbon fiber occupies 5% by mass or more of the fine carbon fiber. 6. An outer diameter of 2 to 300 nm and an aspect ratio of 10.
15000 fine carbon fibers, 5
The fine carbon fiber according to claim 5, which occupies ~ 90% by mass. 7. An outer diameter of 2 to 300 nm and an aspect ratio of 10.
The fine carbon fiber according to any one of claims 1 to 6, wherein the fine carbon fiber occupies 3 to 80% by volume of the fine carbon fiber observed in a transmission electron microscope. 8. The fine carbon fiber according to claim 1, wherein the fine carbon fiber is a vapor grown carbon fiber. 9. The fine carbon fiber according to claim 1, wherein the boron element is contained in the carbon fiber. 10. The fine carbon fiber according to claim 1, wherein the boron element is partially substituted with the carbon element of the carbon fiber. 11. An outer diameter of 2 to 300, wherein cylindrical carbon sheets overlap to form a multilayer structure, and the central axis thereof is a hollow structure.
The method for producing fine carbon fibers according to claim 1, wherein the fine carbon fibers having an aspect ratio of 10 to 15000 nm are subjected to a heat treatment. 12. A heat treatment temperature of 2000 ° C. to 3500 ° C.
The method for producing fine carbon fibers according to claim 11, wherein: 13. An outer diameter of 2 to 300 wherein cylindrical carbon sheets overlap to form a multilayer structure, and the central axis thereof is a hollow structure.
The method for producing a fine carbon fiber according to claim 11 or 12, wherein a fine carbon fiber having an aspect ratio of 10 to 15000 nm and a boron compound are mixed and heat-treated.