WO2004070095A1

WO2004070095A1 - Fine carbon fiber with various structures

Info

Publication number: WO2004070095A1
Application number: PCT/JP2004/001400
Authority: WO
Inventors: Takayuki Tukada; Kazuhiro Osato; Kunio Nishimura; Kojuro Takahashi; Morinobu Endo; Fuminori Munekane; Syuji Tsuruoka
Original assignee: Bussan Nanotech Research Institute Inc.
Priority date: 2003-02-10
Filing date: 2004-02-10
Publication date: 2004-08-19

Abstract

Fine carbon fiber having fiber-like substances of such a structure that tubular graphen sheets are radially stacked relative to the axial direction, wherein the sheets forming tubes comprise discontinuous surfaces forming straight lines or curved lines not having continuous curvatures in parts of the cross sections of the tubes perpendicular to the axial direction thereof throughout parts of the axial lengths thereof, the maximum diameters of the cross sections of the tubes are 100 nm or smaller, continuous hollow parts continued to each other in the axial direction are provided at the centers of the cross sections, and an aspect ratio is 105 or less. The fine carbon fiber is formed in a non-graphite multi-layer structure in which the cross section perpendicular to the axis thereof at any axial position shows a contour-like stripe pattern by the observation with an electron microscope and the intervals between the graphen sheets in the cross section vary throughout the fiber.

Description

Fine carbon fiber with various structures

The present invention relates to fine carbon fibers having a variety of structures and formed of a cylindrical laminate of fine carbon sheets. Light

Fine

Background art

Carbon fiber is a well-known fibrous carbon, but in recent years, fine carbon fiber has attracted attention. There are several types of fine carbon fibers depending on the fiber diameter, and are called vapor-grown carbon fibers, carbon nanofibers, and carbon nanotubes. Among them, carbon nanotubes are the finest, with a fiber diameter of less than 100 nm, and their unique physical properties are expected to be widely applied to nanoelectronic materials, composite materials, catalyst support for fuel cells, etc., and gas absorption. Have been.

Carbon nanotubes include a sheet of carbon atoms bonded in a net shape (Dalaphen sheet) Single carbon nanotube (S WNT) with one layer of cylinder 多層 Multilayer force with multiple layers of graphene sheet cylinders nested Monobon nanotubes (MWNT) are known. The geometry of the diameter and the winding of the sheet is determined by the chiral index, which indicates the properties of the metal or semiconductor.

These carbon nanotubes are produced by the arc discharge method using a carbon electrode, the laser-oven method, the method of chemically and thermally decomposing hydrocarbon gas using transition metal fine particles as a catalyst (chemical vapor deposition (CVD) method, It is synthesized by catalytic chemical vapor deposition (CC VD).

As a conventionally known carbon nanotube,

1) Hyperion's patent, U.S. Pat. -There are carbon nanotubes described in 174018, which are fibrils consisting of a continuous multi-layer of carbon atoms having a substantially graphite structure, each of which consists of multiple layers of regularly arranged carbon atoms, The core and the core are arranged substantially concentrically with the cylindrical axis of the fibril, and each layer of carbon atoms is a fibril made of graphite whose C axis is substantially perpendicular to the cylindrical axis of the fibril. Here, "substantially" used by Hyperion refers to "measured along the axis of the structure, in a plane, or by volume," according to the patent application of Hyperion, JP-T-2000-511864. 95% of the value of physical properties at the time should be within V-10% of the average value. "

2) To date, many patent applications related to carbon nanotubes, including Hyperion's patents, have been filed in Japanese Patent Application Laid-open Nos. Hei 05-179514, Hei 06-157016, Heikai Hei 06-280116, Hei Hei 07-150419, Hei 08-150419, Hei 08 — 1003 28, JP 10-273308, JP 11-116218, JP 11-180707, JP 11-263610, JP 2000-95509, JP 2000-203819, JP 2000-319783, JP 2001-80913, JP 2001-115342, JP 2002-154813, U.S. Pat.No. 6,221,330, U.S. Pat. No. 6,333,016 and U.S. Pat. It is defined as having That is, the layers are fixed tightly like graphite. Furthermore, it is assumed that the Graphitization Factor (g) shown in Eq. (1), which is a standard method for expressing physical property values in carbon technology, takes a positive value.

g = (3.44-d ₀₀₂ ) / (3.44— 3.354) (1) 3) Soneda wrote “Oxidation of Hydrogen with Carbon Nanofibers” (NIRE News, National Institute for Resources and Environment Technology, December 1998). We report the results of observing carbon nanotubes deposited on the metal surface from carbon with an electron microscope (SEM, TEM). According to that, one carbon nanotube is called "carbon The quality of the laminated structure develops at a certain angle with respect to the fiber axis, forming a conical structure. " In addition, fibrous carbon in which another graphene sheet grows specifically in the C-axis direction, that is, carbon nanotubes disclosed by Hyperion, etc. has a highly crystalline graphite structure. It is reported.

Here, as a method for determining whether a carbon substance or a fibrous substance composed of carbon is graphite (Gra-phite or Graphitic), a determination method using X-ray electron diffraction (Kerry, BT, Physics of Graphite, Applied Science Publishers (1981)) and a determination method using Magnetoresistance (Dreselhaus, MS, Graphite Fibers and Filaments, Spring-Verlag (1988)).

In the X-ray and Z-electron diffraction methods, a graphite crystal lattice draws points or lines at lattice points determined by black reflection. If the graphite structure is imperfect, these points will be lines, otherwise the lattice points (1 12) will not be clearly visible. Therefore, it is not Graphite if at least the point or line at grid point (1 12) does not appear clearly.

In the method based on the Magnetoresistance value, it is determined whether or not a graphite-like structure is included using the electromagnetic properties of graphite. Specifically, at a certain temperature, the Magnetoresistance is measured with respect to the magnetic flux density. When the specimen contains graphite, the Magnetoresistance value increases as the magnetic flux density increases. When no graphite is included, the value decreases with a negative value. In the case of imperfect graphite, the value temporarily becomes negative and gradually increases to a positive value as the magnetic flux density increases. Also, the higher the measurement temperature, the larger the value.

The above patents and documents disclose methods for producing carbon by evaporating carbon at an extremely high temperature, such as an arc method and a laser ablation method, and a CCVD method in which a catalyst is supported on an inorganic carrier. . In either case, fine carbon fiber Alternatively, carbon nanotubes are reported to have a laminated structure of concentric graphene sheets and a uniform shape in the longitudinal direction, and have a graphite-like structure. However, in the laminated structure of concentric graphene sheets, the fibers are easily deformed, so that the fibers are aggregated by Van der Waals force, and the aggregate of fibers becomes a structure in which fibers are entangled one by one. easy. Therefore, when particles having such an aggregated structure are mixed and dispersed in a matrix material as a filler for a composite material, the entangled aggregated particles are not easily unraveled and are difficult to disperse. Atsuta.

Accordingly, the present invention provides a novel structure characterized by having preferable physical properties as a composite material filler, that is, having high dispersibility in a matrix material in a composite material, and having as small a thickness as possible and relatively linear. The present invention provides fine carbon fibers, preferably having a maximum fiber diameter of 100 nm or less. Disclosure of the invention

The fine carbon fiber of the present invention has a structure in which a discontinuous surface having a non-circular cross section perpendicular to the axial direction of the cylinder is provided over a part of the length in the axial direction. Thereby, the fine carbon fiber of the present invention is hardly bent and can be provided with elasticity, that is, the property of trying to return to the original shape even after being deformed. Can be understood. Therefore, the entangled structure in the aggregated structure is difficult to remove, and can be easily dispersed when mixed with the matrix material.

The structure of the fine carbon fiber of the present invention will be described in detail with reference to FIGS.

A fibrous material with a structure in which cylindrical graph ensheets are laminated in the radial direction with respect to the axial direction, and the sheet constituting the cylinder has a continuous curvature in a part of the cross section perpendicular to the axial direction of the cylinder. There is a discontinuous surface that does not have a straight line or curve over a part of the length in the axial direction, and the maximum diameter of the section of the cylinder is 10 O nm or less, and the center of the section is An aspect ratio having a continuous hollow portion connected in the axial direction is 10 ⁵ or less, and a cross section perpendicular to the axis at an arbitrary position in the axial direction shows a contour-like stripe pattern by observation with an electron microscope. Fine carbon fibers with uneven sheet spacing.

Further, the fine carbon fiber of the present invention has at least one or more refraction points in the axial direction, and the both sides sandwiching the refraction point are linear, and the length of the linear portion is perpendicular to the axis. At the refraction point, the area of the cross section perpendicular to the axis on both sides at the refraction point varies discontinuously, there is a portion where the graph ensheet is discontinuous, and the graph ensheet has a six-membered ring. There are carbocyclic structures that are not.

Further, in the fine carbon fiber of the present invention, a cross section perpendicular to the axis at an arbitrary position in the axial direction shows a contour-like striped pattern when observed by an electron microscope, and the interval of the daraphen sheet in the cross section extends over the entire fiber length. It consists of a non-graphite multilayer structure with adjacent graph ensheet layers that change, and the value of Magnetoresistance takes a negative value with respect to the change in magnetic flux density. Not clearly. Also, it is a fine carbon fiber in which the maximum diameter of the cross section of the hollow part is 10 nm or less, the variation is 2 nm or less, and the difference between the maximum value and the minimum value of the cross section is 1% or more.

In the fine carbon fiber of the present invention, amorphous carbon precipitates on the outermost layer surface of the fiber, the maximum thickness is 10 nm or less, and the specific surface area of the fiber is 20 OmVg or less.

The fine carbon fiber of the present invention is a fine carbon fiber having an outer diameter of 100 nm or less in a cross section perpendicular to an axis as produced by a CVD or CCVD method at a temperature of 1300 ° C. or less, and preferably further comprises It was obtained by processing at 3000 ° C or less.

The present invention further includes an aggregate of fine carbon fibers having a fiber diameter of 100 nm or less containing 0.001% or more of the fine carbon fibers having any one or more of the above structures. When using the fine carbon fiber of the present invention, the form of this aggregate Often used in

Next, the field of use of the fine carbon fiber of the present invention will be described.

The fine carbon fiber of the present invention has the following characteristics.

A) High conductivity

B) High thermal conductivity

C) Good slidability

D) Good chemical stability

Utilizing these properties, it can be used in a wide range as a composite filler.

The method of use is broadly classified into a method using as a single fiber and a method using as a powder. When used as a single fiber, there are fields that utilize characteristics such as electron emission capability, conductivity, and superconductivity, in addition to FEDs, electron microscope elements, semiconductor elements. Depending on the form of use, 1) a 0-dimensional composite material, such as slurry, 2) a linearly processed 1-dimensional composite material, 3) a sheet It can be used for 3D composite materials such as 2D composite materials (fabric, film, paper) processed into a shape, and 4) complex molded objects and blocks. By combining these forms with the desired functions, an extremely wide range of applications is possible. The following is an example of a specific example of this for each function.

1) Use of conductivity

It is suitably used as a conductive resin and a conductive resin molded product by being mixed with a resin, for example, for packaging materials, gaskets, containers, resistors, conductive fibers, electric wires, adhesives, inks, paints, and the like. Similar effects can be expected with composite materials added to inorganic materials, especially ceramics and metals, in addition to composite materials with resins.

2) Using thermal conductivity

The same usage can be performed as in the case of using the conductivity.

3) Devices that use electromagnetic wave shielding

By mixing it with resin, it can be used as an electromagnetic wave shielding paint or molded electromagnetic wave shielding material. It is suitable.

4) Those that use physical characteristics

Used in rolls, brake parts, tires, bearings, gears, pantographs, etc. by mixing with resin and metal to enhance slidability.

Utilizing its light weight and tough properties, it can be used for electric wires, home appliances, vehicles, airplanes, etc. bodies, and machine housings.

In addition, it can also be used as a substitute for conventional carbon fibers and beads. For example, it is applied to battery pole materials, switches, and vibration damping materials.

5) Those utilizing filler characteristics

Fine fibers have excellent strength, are flexible, and have excellent properties of the filter constituting the network structure. By utilizing this characteristic, it is possible to contribute to strengthening the electrodes of energy devices such as lithium-ion secondary batteries, lead-acid batteries, capacitors, and fuel cells and improving the cycle characteristics. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a transmission electron micrograph of the fine carbon fiber of the present invention.

FIG. 2 is a transmission electron micrograph of the fine carbon fiber of the present invention.

FIG. 3 is a transmission electron micrograph of the fine carbon fiber of the present invention.

FIG. 4 is a transmission electron micrograph of the fine carbon fiber of the present invention.

FIG. 5 is a transmission electron micrograph of the fine carbon fiber obtained in Example 1. FIG. 6 is a transmission electron micrograph of the fine carbon fiber obtained in Example 2. FIG. 7 is a diagram schematically illustrating the synthesis apparatus according to the first embodiment.

FIG. 8 is a diagram schematically showing the high-temperature heat treatment apparatuses of Examples 1 and 2.

FIG. 9 is a diagram schematically illustrating the synthesizer according to the second embodiment.

FIG. 10 is a photograph showing an X-ray diffraction grating image of the fine carbon fibers obtained in Example 1. FIG. 11 is a diagram showing Magnetoresistance of the fine carbon fibers obtained in Example 1.

FIG. 12 is a SEM photograph of a composite material using the fine carbon fibers obtained in Example 1.

Figure 13 is a SEM photograph of a composite material using conventional fine carbon fibers. BEST MODE FOR CARRYING OUT THE INVENTION

The fine carbon fiber having a unique structure of the present invention can be produced by the following method. With the extension of the conventional technology for the production of vapor-grown carbon fiber (VGCF), even the CVD method requires a long synthesis time and does not produce fine materials.

Basically, organic compounds such as hydrocarbons are chemically pyrolyzed by CVD method or CCVD method using transition metal ultrafine particles as catalyst, but they are fine carbon fiber nuclei, intermediate products and products in the reactor. Shortening the residence time of the fiber to obtain the fiber and subjecting it to a high-temperature heat treatment is a preferable method for producing a preferable fine carbon fiber.

(1) Synthesis method

It can be synthesized using the usual CVD or CCVD method for hydrocarbons, etc.

A) Reduce the carbon residence time in the furnace calculated from the material balance to 10 seconds or less

B) In order to increase the reaction rate, raise the furnace temperature to 1000 ° C or more.

C) The catalyst and raw material carbon compound are preheated to 300 ° C or more and charged into the furnace in gaseous form.

D) Control the concentration of carbon in the furnace gas to a certain concentration (20% by volume) or less. (2) High temperature heat treatment process

In order to efficiently produce the fine carbon fiber of the present invention, the fiber obtained by the above method is subjected to a high-temperature heat treatment at 3000 ° C or lower by an appropriate method. The As Grown fiber obtained above absorbs many hydrocarbons due to its unique process, and is industrially useful. This hydrocarbon is separated for use. Therefore, for example, heat treatment is performed at a temperature of 1500 ° C. or less to separate the layers. In addition, heat treatment is performed at a processing temperature higher than the synthesis temperature, because the development of crystals is not sufficient with the hydrocarbon separation process alone.

Conventional processes can be applied to the high-temperature heat treatment at 300 ° C. or lower. As the condition,

A) Separate the hydrocarbons from the fibers obtained by the above CVD method or CVCD method at a temperature of 1500 ° C or less.

B) As a next step, high-temperature heat treatment is performed at a temperature of 2000 ° C. or more.

At this time, a reducing gas or a trace amount of carbon monoxide gas may be added to an inert gas atmosphere to protect the crystal. Example

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1

Fine carbon fibers were synthesized using toluene as a raw material by the CVD method.

Figure 7 shows the synthesizer.

The reaction was carried out in a reducing atmosphere of hydrogen gas using a mixture of Fe-mouth sen and thiophene as a catalyst. The toluene and the catalyst were heated to 375 ° C together with hydrogen gas, supplied to the reactor, and reacted at 1200 ° C with a residence time of 8 seconds. Atmospheric gases were separated by separation and reused. The hydrocarbon concentration in the furnace gas was 7% by volume.

The tar content of the synthesized fine carbon fiber of As Grown was 10%. Next, the fiber was heated to 1200, held for 30 minutes to perform a hydrocarbon separation treatment, and further subjected to a high-temperature heat treatment at 280 ° C. Figure 8 shows the equipment for the hydrocarbon separation and high-temperature heat treatment process. Fig. 5 shows an electron micrograph of the obtained fine carbon fiber after the high-temperature heat treatment at 2800 ° C.

From this figure, fine carbon fibers having a unique structure can be confirmed. Observation by SEM showed some variation in the diameter of the formed fiber. The diameter was 10 to 60 ηπιφ, and the specific surface area was 49 m ² / g. Example 2

The synthesis apparatus shown in FIG. 9 and the high-temperature heat treatment apparatus shown in FIG. 8 were used.

Benzene is used as a carbon raw material, and the catalysts, huasen and thiophene, are dissolved, vaporized at 380 ° C, and introduced into the reactor. The temperature of the reactor was 1150 ° (The atmosphere in the furnace was a hydrogen gas atmosphere. The residence time of hydrogen gas and raw material gas in the furnace was 7 seconds. As Gro dragon collected downstream of the furnace The tar content of the carbon fibers was 14%.

Next, after performing a heat treatment of holding the fiber at 1200 ° C. for 35 minutes, the specific surface area of the carbon fiber was measured and found to be 43 m ² / g. FIG. 6 shows an electron micrograph of the fine carbon fibers after the high-temperature heat treatment at 2800 ° C. Example 3

A diffraction grating image of the fine carbon fiber obtained in Example 1 was taken using an X-ray diffractometer. FIG. 10 shows the obtained diffraction grating image.

From this result, the lattice point (1 12) was not observed. Therefore, the fine carbon fiber of the present invention does not have graphite-like physical properties. Example 4

Magnetoresistance measurement

For 1.00 g of the fine carbon fiber obtained in Example 1, a thickener (Susu Co., Ltd.) 19.00 g (5% CNT) and 49.0 g (2.0% CNT) were mixed with 3 pounds of heat-resistant inorganic adhesive made of Ripound and mixed at 2000 rpm for 10 minutes using a centrifugal mixer. The resulting product was linearly adhered in a lmm width on a 125 μπι thick polyimide resin (UPILEX S, manufactured by Ube Industries, Ltd.).

Next, this polyimito. The value of Magnetoresistance when the magnetic flux density and temperature were changed for the resin was measured. The results are shown in Table 1 and FIG. According to FIG. 11, the fine carbon fiber obtained in Example 1 has a negative value of Magnetoresistance as the magnetic flux density increases, and a positive Resistivity Ratio at 77K and 273K (room temperature), that is, the temperature increases. Magnetoresistance also remained negative. Therefore, this fine carbon fiber does not have graphitic properties. table 1

Example 5

The fine carbon fiber obtained in Example 1, methanol, water, and methylcellulose were mixed at a weight ratio of 20: 20: 9: 1, and granulated for 15 minutes by Vertical Granule Yule (manufactured by Parex Co., Ltd.). Thereafter, methanol and water were removed by drying at a temperature of 100 ° C or more by a drier to obtain granules of fine carbon fibers having an average particle diameter of 500 m. Next, 5% by weight of the fine carbon fiber granules were added to the polycarbonate resin, and the mixture was melted and mixed with a vented twin screw extruder (trade name: TEM35, manufactured by Toshiba Machine Co., Ltd.), and the pellets were mixed. Manufactured. Figure 12 shows an SEM photograph of the composite material obtained after melt mixing. Comparative Example 1

Pellets were produced in the same manner as in Example 5 using conventional fine carbon fibers. The SEM photograph of the obtained composite material is shown in FIG.

As shown in Fig. 13, the conventional fine carbon fiber has a cohesive structure that is not easily unraveled and clings to the central part. In contrast, as shown in FIG. 12, it can be seen that the fine carbon fibers of the present invention are hardly entangled in the aggregated structure and are easily dispersed when mixed with the matrix material. Industrial applicability

The fine carbon fiber of the present invention is used for FED, electron microscope element, semiconductor element, conductive fiber, electric wire, electromagnetic wave shielding material, battery electrode, brake part as composite material, and furthermore, home appliance, vehicle, airplane body and machine housing. It can be suitably used.

Claims

The scope of the claims

1. In a fibrous material with a structure in which cylindrical graph ensheets are laminated in the radial direction with respect to the axial direction, the sheet constituting the cylinder has a continuous curvature in a part of the cross section perpendicular to the axial direction of the cylinder. A straight or curved discontinuous surface over a part of the length in the axial direction, the maximum diameter of the cross section of the cylinder is 100 nm or less, and the axis is located at the center of the cross section. § scan Bae transfected ratio 1 0 ⁵ or less of the fine carbon fibers having a continuous hollow portion continuous in the direction.

2. In the fibrous substance, a cross section perpendicular to the axis at an arbitrary position in the axial direction shows a contour-like stripe pattern by observation with an electron microscope, and the intervals of the graph sheets are non-uniform in the cross section. The fine carbon fiber according to item 1.

3. The fibrous substance has at least one or more refraction points in the axial direction, and both sides sandwiching the refraction points are linear, and the length of the linear portion is the maximum of a cross section perpendicular to the axis. 3. The fine carbon fiber according to claim 1, which is not less than a diameter.

4. The fine carbon fiber according to claim 3, wherein, at the refraction point, the area of the cross section perpendicular to the axis on both sides thereof changes discontinuously, and there is a portion where the graph ensheet is discontinuous.

5. The fine carbon fiber according to claim 4, wherein a carbon ring structure other than a 6-membered ring is present in the graph ensheet at the refraction point.

6. The innermost tubular dalaphen sheet of fibrous material has different cross-sectional areas in the axial direction, and the difference between the maximum value and the minimum value of the cross-sectional area is 1% or more. A fine carbon fiber according to any one of No. 5 to No. 5.

7. In the fibrous substance, a cross section perpendicular to the axis at an arbitrary position in the axial direction shows a contour-like stripe pattern when observed with an electron microscope, and the interval between the graph ensheets covers the entire fiber length at the cross section. 2. The fine carbon fiber according to claim 1, which has a non-graphite multilayer structure having adjacent graphene sheet layers that vary.

8. The fine carbon fiber according to claim 7, wherein the fibrous substance has a value of Magnetoresistance that takes a negative value with respect to a change in magnetic flux density.

9. The fine carbon fiber according to claim 7, wherein the fibrous substance does not clearly have a (112) point in a lattice point of X-ray diffraction.

10. The fine carbon fiber according to any one of claims 7 to 9, wherein the maximum diameter of the cross section of the hollow portion changes in the axial direction of the fiber at 10 nm or less, and the change amount is 2 nm or less.

11. The fine carbon fiber according to any one of claims 1 to 10, wherein amorphous carbon is precipitated on the outermost layer surface of the fiber, and has a maximum thickness of 10 nm or less.

12. The fine carbon fiber according to any one of claims 1 to 11, which has a specific surface area of 200 m ² Zg or less.