JP5312813B2 - Highly conductive carbon fiber manufacturing method, power transmission filament manufacturing method, and power transmission cable manufacturing method - Google Patents

Description

The present invention relates to a method for producing a highly conductive carbon fiber, a method for producing a power transmission filament, and a method for producing a power transmission cable .

  Conventionally, as a method for producing carbon fibers, it is known that high strength carbonaceous fibers can be obtained by carbonizing at 1000 to 1500 ° C. in an inert atmosphere using polyacrylonitrile (PAN) or coal tar as a raw material. ing. Moreover, it is known that by performing a graphitization treatment at 2500 to 3000 ° C., a graphite fiber having a high elastic modulus can be obtained although the strength is slightly impaired.

  The carbon fiber thus obtained contains a planar crystal (graphene) composed of a carbon 6-membered ring or graphite in which graphene is layered. These graphenes tend to be oriented with respect to the fiber axis, but are irregular, containing cavities, vacancies, dislocations, grain boundaries, and impurity atoms.

  Graphite crystals have strong electrical conduction anisotropy depending on the crystal axis direction. The in-plane resistance of graphene is as low as one-tenth that of copper, but the C-axis direction has very low electrical conductivity due to the van der Waals coupling, and the thermal conductivity is also low. Carbon fiber forms a fiber structure with this graphene or graphite crystal entangled, but the individual graphene is in a state of being separated from each other, so its electrical conduction is governed by the electrical conduction in the C-axis direction of graphite. Generally, the resistance becomes high.

  As described above, since carbon fiber is a random aggregate of graphite, there is a problem in electric conductivity, and therefore it cannot be used for a power line for the purpose of power transportation.

  On the other hand, the good anisotropic electric conduction and anisotropic heat conduction of graphite are caused by the carbon 6-membered ring. Carbon nanotubes are obtained by rounding this graphene into a tube shape with a nanoscale diameter. For this reason, depending on the graphene rounding method (chirality), specific electrical conductivity characteristics that manifest metal and semiconductor characteristics and mechanical properties such as Young's modulus comparable to diamond are expected to have many applications in the future.

  As a conventional carbon nanotube synthesis technique, Non-Patent Document 1 reports that a super-growth method in which carbon nanotubes are grown in a sheet shape can be obtained with a length of several millimeters. Non-Patent Document 2 reports that a lobe of about 20 centimeters obtained by twisting single-walled carbon nanotubes can be obtained.

  However, with these conventional synthesis techniques, it is possible to selectively synthesize a large amount as a tube-shaped or horn-shaped material, but from a practical point of view, it is not always satisfactory. There is no current situation.

  In addition to the above-mentioned synthesis technique by vapor phase growth, a technique for growing carbon nanotubes in a solid phase has also been reported, and a catalyst growth method using SiC as a base material and not using a source gas is known (non-patent) Reference 3). In this method, SiC, which is a base material, is decomposed by a catalyst while Si evaporates, and the remaining carbon grows as graphite.

  However, while this method can grow a tube-shaped graphite (nanotube in a broad sense) having an arbitrary thickness, it cannot synthesize graphite having an arbitrary shape and structure.

  On the other hand, Non-Patent Document 4 reports a three-dimensional structure growth technique using decomposition reaction by a focused ion beam or electron beam. In this method, a hydrocarbon-based gas such as pyrene or phenanthrene is gasified and sprayed locally at the beam irradiation position. Gas molecules adsorbed on the surface of the substrate are decomposed by secondary electrons emitted from the irradiation position of electrons and ion beams, and the decomposition products grow as amorphous carbon structures.

  It has been reported that nanoscale three-dimensional amorphous carbon structures such as wine glasses, nanocoils, and nanodrills can be synthesized by using such an electronic excitation reaction.

  In addition, as reported in Non-Patent Document 5, an amorphous nano three-dimensional structure formed by a beam application technique is obtained by performing a low-temperature heat treatment at about 700 ° C. using a catalyst such as iron. It is possible to crystallize the graphite while maintaining its shape to stabilize it structurally and chemically, but the graphite obtained here is basically polycrystalline graphite.

  Furthermore, regarding graphite solid phase reaction, Non-Patent Documents 6 and 7 report that nanotubes are generated as a result of solid phase reaction in the process of moving iron fine particles in amorphous carbon heated to about 650 ° C. Has been.

  When the amorphous carbon pillar containing iron is annealed in vacuum, the iron fine particles aggregate inside the pillar and move around in the amorphous carbon. The agglomeration process of iron fine particles starts at about 600 ° C and the particle size grows with the movement of the iron fine particles. In this process, the amorphous carbon base material has already been gradually graphitized. At that time, the moment when the iron fine particles accidentally sink into the ultra-thin nanopillar growing on the side wall is captured by a real-time TEM image. If the direction of movement of the iron fine particles is the head, the head eats amorphous carbon, and a graphite tube is formed at the tail.

  For the synthesis of carbon nanotubes, vapor phase growth using a transition metal catalyst such as iron is mainly used, but it can also be formed by a catalytic reaction using a liquid metal. A new growth mode has been reported in which nanotubes undergo solid phase growth by Ga catalytic action accompanying instantaneous discharge (Non-patent Document 8). In general, Ga is used as an ion source in a focused ion beam apparatus. Therefore, the amorphous carbon pillar manufactured using FIB contains Ga inside. By instantaneously passing a current through the pillar, an instantaneous movement of Ga is observed, and at the same time, a graphite tube structure is formed inside the pillar. The electrical conductivity of as-grown FIV-CVF pillars has strong nonlinearity and exhibits hopping conductivity.

Therefore, when a potential higher than a certain voltage is applied, a current suddenly flows, and an instantaneous solid phase reaction is induced at that time. At the trace of Ga particles moving inside the pillar, a tube-like structure composed of a tubular graphite layer is formed inside the pillar, and it has been found from an electron microscopic image that it is a multilayer graphite tube. On the other hand, the outer layer of the pillar remains covered with amorphous carbon.
Science Magazine 2004 Vol.306 1362–1364 Science 2002 Vol.296 884-886 Japanese Journal of Applied Physics 1998 Vol.37, pages L605-L606 Matsui, Fujita et al. Journal of Vacuum Science and Technology 2000 Vol.6 3181-3184 Fujita, Matsui et al. Journal of Vacuum Science and Technology 2002 Vol.20 pp. 2686-2689 Japanese Journal of Applied Fujis Magazine 2004 VOL.43 3799-3802 Physical Review Letter 2004 VOL.92 21572 Applied Physics Letter magazine Vol.88 093109-093111 2006

  According to the above prior art, a long product can be obtained as carbon fiber. However, this carbon fiber is an aggregate in which graphene and graphite crystals are randomly entangled, and has a problem of high resistivity.

  Also, various methods for synthesizing multi-walled carbon nanotubes have been disclosed, and although it is known that the electric conduction is sufficiently lower than that of copper, no technology for synthesizing long carbon nanotubes has been reported at present. That is, the large electrical conductivity of carbon nanotubes is promising for use in power transmission lines, but it is difficult to synthesize nanotube fibers that are long enough to produce electric wires by general vapor phase growth.

The present invention has been made in view of the circumstances as described above, has a low resistance, and can be used for electric power transportation. A method for producing a long highly conductive carbon fiber, and a method for producing a filament for power transmission It is another object of the present invention to provide a method for manufacturing a power transmission cable .

  The present invention is characterized by the following in order to solve the above problems.

  1st: The manufacturing method of the highly conductive carbon fiber characterized by including the process of supplying and immersing carbon fiber of a raw material continuously in liquid Ga of 600-1500 degreeC.

  Second: The method for producing the first highly conductive carbon fiber according to the first aspect, wherein the raw material carbon fiber contains amorphous carbon.

  Third: The method for producing the first or second highly conductive carbon fiber according to the first or second aspect, wherein the carbon fiber is rolled before the raw material carbon fiber is immersed in the liquid Ga.

  Fourth: A method for manufacturing a power transmission filament, comprising a step of embedding a highly conductive carbon fiber manufactured by the first to third methods in a sheath.

  Fifth: The fourth method for producing a power transmission filament, comprising a step of drawing a highly conductive carbon fiber in a sheath and then drawing.

  Sixth: A method for manufacturing a power transmission cable, comprising a step of bundling power transmission filaments manufactured by the fourth or fifth method to form a power transmission cable.

According to the highly conductive carbon fiber manufactured by the method of manufacturing a highly conductive carbon fiber of the present invention, it has a multilayer graphene structure in which graphenes are joined by a graphitization reaction using liquid Ga as a catalyst. It can be a long one that has low resistance and can also be used for power transportation applications.

The power transmission cable using the highly conductive carbon fiber produced by the method for producing the highly conductive carbon fiber of the present invention has a resistance value of about one-tenth of the weight of a conventional cable mainly composed of copper wire, and the weight. Is about 20%, tension is about 100 times low resistance, light weight and high strength, which not only greatly contributes to energy saving, but also conserves metal resources and is expected to make a great contribution to the global environment It is.

  According to the method for producing highly conductive carbon fiber of the present invention, carbon fiber can be used as a starting material to repair defects on the fiber surface by the catalytic action of liquid Ga, and graphene on the fiber surface can be continuously joined together. Highly conductive carbon fibers that can be used in power lines as low resistance and lightweight wires for power transportation and the like can be obtained at high speed and as long ones.

  In addition, by mixing amorphous carbon into the raw carbon fibers, a graphene reaction using liquid Ga as a catalyst can efficiently form a multilayer graphene structure in which graphenes are joined together, and multilayer graphene formation It is also possible to reduce the amount of other raw materials for the purpose.

Furthermore, before immersing the carbon fiber material in the liquid Ga, by rolling the carbon fibers by a roller or the like, can increase the contact area between the effective Ga catalyst surface increases the surface area of the carbon fibers As a result, the surface graphitization reaction amount can be increased, so that the electrical conductivity of the highly conductive carbon fiber can be further improved.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing a surface structure of a highly conductive carbon fiber produced by the method for producing a highly conductive carbon fiber of the present invention. As shown in the figure, the highly conductive carbon fiber 1 has a multilayer graphene structure 2 including a structure in which graphenes 2a are bonded to each other at least on the surface, and the graphene 2a in the multilayer graphene structure 2 A layered structure with aligned C-planes is formed. The multilayer graphene structure 2 is obtained by joining the graphene 2a separated on the surface of the raw carbon fiber using the catalytic action of liquid Ga, and by forming such a structure on the surface, Electrical conduction can be greatly improved.

As a specific form of the fiber structure of the highly conductive carbon fiber 1 manufactured by the method for manufacturing the highly conductive carbon fiber of the present invention , as shown in FIG. The form in which the entire structure up to the inside is composed of multilayer graphene 2, as shown in FIG. 2 (b), the surface is composed of multilayer graphene 2, and the inside is filled with graphite 3 and amorphous carbon 4, FIG. 2 (c) As shown in FIG. 4, the surface is composed of multilayer graphene 2 and amorphous carbon 4 is filled inside.

  On the other hand, a general carbon fiber has a structure in which fine crystals of graphite 3 having a particle size of several tens of nanometers are entangled with each other as shown in FIGS. 3 (a) and 3 (b). It contains impurities 5 of amorphous carbon and catalytic metals everywhere. Furthermore, although the C-plane spacing of the crystallites of graphite 3 is 0.34 nm, the spacing between the graphenes is much larger than this due to the intertwined structure, and the electrical conductivity in the C-plane direction is extremely poor.

  In the present invention, as shown in FIGS. 1 and 2, the surface structure of such a general carbon fiber is joined to each other by graphene 2a separated on the surface of the carbon fiber by utilizing the catalytic action of liquid Ga. By doing so, the multi-layer graphene 2 is used to greatly improve the surface electrical conduction.

  Also, in the general multi-walled carbon nanotube 6 having the surface structure shown in FIG. 4, the graphene 7 forms a multi-layer structure so that the cross section of the high-quality carbon nanotube 6 is concentric. When the thickness is 10 nm or more, the gap disappears in the semiconducting tube regardless of the chirality, and it becomes metallic conduction. However, while such multi-walled carbon nanotubes 6 exhibit extremely high electrical conductivity and are very promising for power transportation and the like, it has not been realized to grow long nanotubes exceeding several cm at present.

  On the other hand, in the present invention, the graphene 2a on the surface of the carbon fiber is bonded to each other by the catalytic action of Ga, which is a low melting point metal, and defect repair is performed to form the multilayer graphene 2. It is possible to obtain 1.

  Hereinafter, the manufacturing method of the highly conductive carbon fiber which concerns on this invention is demonstrated. In the present invention, as shown in FIG. 5, the raw material carbon fiber 9 is immersed in liquid Ga8 heated to a temperature at which the catalytic reaction is activated. Carbon fiber 1 is synthesized.

  More specifically, as shown in FIG. 6, the raw material carbon fiber 9 is continuously supplied and immersed in the liquid Ga8 heated to a temperature at which the catalytic reaction is activated, whereby graphene on the surface of the carbon fiber 9 is obtained. The highly conductive carbon fibers 1 are continuously synthesized by joining together.

  The temperature of the liquid Ga in which the raw carbon fibers are immersed is preferably 600 to 1500 ° C., more preferably 800 to 1500 ° C., from the viewpoint of efficiently performing the catalytic reaction.

  When amorphous carbon is immersed as a raw material carbon fiber 9 in liquid Ga at 600 to 1500 ° C., the surface of the carbon fiber 9 is graphitized to form the multilayer graphene 2 in FIG. 2A, and its electrical resistance is very low. Become. The graphene 2a of the multilayer graphene 2 does not cover the entire surface as a single graphene, but many graphenes 2a are joined along the Ga liquid surface, and the electrical conductivity is remarkably improved.

  Moreover, when the carbon fiber 9 containing graphite is immersed in the high-temperature liquid Ga, the graphitization reaction with respect to the graphite crystal divided on the surface of the carbon fiber 9 proceeds, and the joining of graphene is realized. In this case, not all the graphenes are regularly arranged on the surface of the carbon fiber 9 as in the case of the multi-walled carbon nanotubes, but are in a nested structure or a wavy structure depending on the location and include a lattice defect in a broad sense. However, the electrical conductivity of the fiber itself is dramatically improved by increasing the number of joints between the C faces.

  Due to the fact that the multilayer graphene 2 in the present invention is formed by the surface graphitization reaction, the graphite layer has a unique multilayer structure different from an ordered layered structure such as a multilayer carbon nanotube. Yes. For example, reflecting the fact that the original random graphite fragments are joined by the graphitization reaction, a graphite layer that existed on the outside in a certain part may be embedded inside the fiber when traced. That is, as shown in FIG. 1, a nested structure may be formed in which a graphite C surface 2a on the outermost surface becomes a lower surface of the third layer in the adjacent structure and another graphite C surface 2a becomes an outermost surface in the adjacent structure. . Further, reflecting the original random fiber structure, a structure having partial irregularities, that is, a wavy structure may be formed on the surface of the graphite layer after the surface graphitization reaction.

In addition, even if it is the highly conductive carbon fiber 1 which performed the surface graphene joining process, the surface graphene from the end of a fiber is not connected, but it joins in the range of several microns-dozens of microns. It is thought that there is. However, it is much longer than the particle size of several tens of nanometers, which is the particle size of graphite in ordinary carbon fibers, and this contributes to the improvement of electrical conductivity. The electrical conductivity between the C plane and the plane of graphite differs by about 10 ^4, but the electrical conductivity is greatly improved by overlapping the graphene surfaces in a sufficiently large area.

Ga as a catalyst metal needs to be in a molten state in order to repair defects by contacting the complicated side walls of the carbon fiber 9 and to obtain high catalytic activity. Ga is a metal with a melting point of 29.78 ° C, boiling point of 2400 ° C, density of 5.91g / cm ³ (25 ° C), 6.10g / cm ³ (30 ° C, liquid), and molten Ga has a surface tension against carbon fibers. Strong and hardly wet. On the other hand, the surface of the amorphous carbon fiber in contact with liquid Ga at 600 ° C. or higher is graphitized.

  At this time, it is considered that the carbon and unreacted amorphous carbon contained in the carbon fiber 9 contribute to the catalytic reaction. In this sense, it is preferable to add amorphous carbon to the carbon fiber 9 before the surface treatment step of the carbon fiber 9 with the liquid Ga.

  It is also effective for joining the surface graphene that the raw material carbon fiber 9 is mixed with the organic polymer resin, that is, the raw material carbon fiber 9 is composited with the organic polymer resin. The carbon fiber raw material for forming can also be reduced.

  When Ga is heated in an inert gas atmosphere, the catalytic reaction of amorphous carbon by liquid Ga starts from about 600 ° C., and graphene microcrystals are generated on the surface of the carbon fiber 9. As the temperature rises, crystal growth on the Ga surface is promoted, and the decomposition and synthesis of graphene proceed in equilibrium from about 800 ° C., and the entire surface of the amorphous carbon fiber (pillar) is covered with the multilayer graphene 2 in FIG. .

  As the amorphous carbon pillar, for example, a material formed by irradiating a focused ion beam in a precursor atmosphere using phenanthrene gas as a raw material and decomposing the raw material gas can be used. For example, it is about 10 microns.

  In this case, it takes more than 30 minutes to raise and lower the sample temperature, but the actual surface reaction proceeds in a very short time, similar to the growth of solid-phase nanotubes from Ga-containing amorphous carbon pillars by instantaneous discharge. It is predicted.

  Then, as shown in FIG. 6, the graphene bonding on the surface of the carbon fiber 9 is continuously advanced by passing the carbon fiber 9 through the high-temperature liquid Ga continuously, so that the surface of the long carbon fiber 9 is The highly conductive carbon fiber 1 having the multilayer graphene 2 in which the graphenes are bonded to each other can be manufactured.

  When the highly conductive carbon fiber 1 is produced by the method shown in FIG. 6, the physical properties such as electrical conductivity in the obtained highly conductive carbon fiber 1 are the moving speed of the raw carbon fiber 9, the degree of polymerization of the surface, and the reaction temperature. Therefore, it is necessary to select an optimum value. Generally, the higher the temperature, the more the carbonization graphitization reaction proceeds, but the fiber becomes brittle. On the other hand, in the low temperature process, the amorphous carbon and the catalytic metal remaining inside the fiber increase, and the electrical conductivity becomes low.

  In a preferred embodiment of the present invention, as shown in FIG. 7, prior to the surface graphitization reaction with the Ga catalyst, the raw carbon fibers 9 are rolled in advance with a roller 10 such as metal to align the direction of graphene, and at the same time, the fiber surface area. , And then, the highly conductive carbon fiber 1 is manufactured by immersing it in the liquid Ga8 to advance the surface graphitization reaction.

  Thus, the electrical conductivity of the highly conductive carbon fiber 1 can be further improved by rolling the raw material carbon fiber 9 in advance with the roller 10 and making it into a flat tape shape. That is, the effective surface graphitization reaction amount can be increased by increasing the surface area of the carbon fiber 9 and effectively increasing the contact area with the Ga catalyst surface, instead of crushing the graphite crystal itself.

  Since the highly conductive carbon fiber 1 of the present invention produced by the above steps is long and low in resistance, it can be used for power transportation as a power transmission cable. In order to improve the mechanical properties as a core for power transportation, the highly conductive carbon fiber 1 is collected and spun simultaneously with filling and embedding in a sheath (metal coating), and then subjected to a drawing process. As shown in FIG. 2, the sheath 11 is processed into a power transmission filament 12 in which the highly conductive carbon fiber 1 is embedded.

  When the highly conductive carbon fibers 1 subjected to the surface graphene bonding treatment are appropriately bundled and embedded in the sheath 11, it is possible to draw a finer filament. In this way, the sheath wire is further drawn, compressed, and twisted together so as to twist a large number of highly conductive carbon fibers 1, thereby reducing the gaps in the graphite and further improving the mechanical strength and the allowable current amount.

  Further, when the highly conductive carbon fiber 1 is manufactured, as shown in FIG. 7, it is compressed by a roller 10 to widen the surface to be graphitized, and the sheath embedded with the highly conductive carbon fiber 1 is drawn to draw the inside of the sheath. Is compressed, the graphene originally in the form of a plate can be relatively easily overlapped with the C-plane to improve electrical conductivity.

  From a practical viewpoint, it is desirable to form a power transmission cable by bundling a large number of power transmission filaments 12 obtained as described above. The cable for power transmission obtained in this way has a resistance value of about 1/10, a weight of about 20%, a tension of about 100 times that of a conventional cable mainly made of copper wire, light weight and high resistance. It is a groundbreaking technology that contributes to the industry as an energy-saving technology and also an environmental countermeasure technology.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.
<Example 1>
A carbon nanotube (CNT) stranded wire having a diameter of about 0.3 mm was rolled into a ribbon shape having a width of about 1 mm. This CNT twisted wire was immersed in liquid Ga in an alumina crucible and heated at 700 ° C. for 10 minutes. After cooling, the CNT twisted wire was taken out of the crucible, and Ga adhering to the surface was removed by washing with dilute hydrochloric acid.

  FIG. 9 shows SEM images (two types) of CNT twisted wire cross sections before treatment with liquid Ga. Thus, it can be seen that a large number of CNT fibers extend from the fiber end face and are stranded. On the other hand, SEM images (three types) of CNT twisted wire gaps after treatment with liquid Ga are shown in FIG. After the treatment with liquid Ga, it was confirmed that fine fibers were dissolved on the surface of the CNT twisted wire and the surface was covered with a graphitized layer. Further, a graphite surface was observed on the surface as shown in the TEM image of FIG.

It was confirmed that the above graphitization reaction occurred remarkably when the temperature of liquid Ga reached about 600 ° C. Moreover, it was confirmed that the resistance value of the fiber after the liquid Ga treatment is clearly lower than that of the CNT twisted wire before the treatment. Moreover, it was confirmed that rolling the CNT twisted wire into a ribbon shape resulted in a greater decrease in resistance value than when not rolling.
<Reference Example 1>
A quartz substrate coated with amorphous carbon was prepared, and liquid Ga was dipped under the same conditions as in Example 1. FIG. 12 shows SEM images (eight types) of the substrate surface after processing. It was clearly observed that the surface area was increased by graphitizing the surface and peeling from the substrate occurred. From this, it was suggested that mixing the amorphous carbon as a raw material for graphitization into the carbon fiber of the raw material is effective for the surface graphitization.

It is sectional drawing which showed typically the surface structure of the highly conductive carbon fiber manufactured by the manufacturing method of the highly conductive carbon fiber of this invention. It is sectional drawing which showed the specific form of the fiber structure of the highly conductive carbon fiber 1 manufactured by the manufacturing method of the highly conductive carbon fiber of this invention. It is the figure which showed the structure of the general carbon fiber. It is sectional drawing which showed the surface structure of the multi-walled carbon nanotube. It is the figure which showed the immersion process in the liquid Ga of the raw material carbon fiber. It is the figure which showed the process of making the carbon fiber of a raw material pass continuously in liquid Ga. It is the figure which showed the process of rolling the carbon fiber of a raw material, and the subsequent immersion process in liquid Ga. It is the figure which showed the structure of the filament for power transmission. It is a SEM image of a CNT twisted wire cross section before processing with liquid Ga. It is a SEM image of a CNT twisted wire gap after processing with liquid Ga. It is a TEM image of the fiber surface after processing with liquid Ga. It is a SEM image of the surface of the quartz substrate coated with amorphous carbon after treatment with liquid Ga.

1 High conductivity carbon fiber 2a Graphene (graphite C surface)
2 Multi-layer graphene structure 3 Graphite 4 Amorphous carbon 5 Impurities of amorphous carbon and catalytic metals 6 Multi-wall carbon nanotubes 7 Graphene 8 Liquid Ga
9 Raw material carbon fiber 10 Roller 11 Sheath 12 Power transmission filament

Claims (6)

  A method for producing a highly conductive carbon fiber, comprising a step of continuously supplying and immersing carbon fiber as a raw material in liquid Ga at 600 to 1500 ° C.   2. The method for producing highly conductive carbon fiber according to claim 1, wherein the raw material carbon fiber contains amorphous carbon.   The method for producing highly conductive carbon fiber according to claim 1 or 2, wherein the carbon fiber is rolled before the raw material carbon fiber is immersed in liquid Ga.   A method for producing a power transmission filament, comprising a step of embedding a highly conductive carbon fiber produced by the method according to claim 1 in a sheath.   The method for manufacturing a power transmission filament according to claim 4, comprising a step of drawing after embedding the highly conductive carbon fiber in the sheath. A method for manufacturing a power transmission cable, comprising a step of bundling power transmission filaments manufactured by the method according to claim 4 or 5 to form a power transmission cable .