JP3867790B2 - Continuous production method of tape-like substance containing carbon nanotube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for continuously producing a tape-like substance containing synthesized high-purity carbon nanotubes.
[0002]
[Prior art]
A carbon nanotube (CNT) is obtained by performing an arc discharge between two carbon materials, and a carbon nanotube (CNT) is obtained by rounding a graphene sheet in which carbon atoms are regularly arranged in a hexagonal shape into a cylindrical shape. The single graphene sheet tube is a single-walled carbon nanotube (SWCNT), and its diameter is 1 to several nm. Further, multi-walled carbon nanotubes (MWCNTs) in which the graphene sheet cylinders are concentrically overlapped with each other have a diameter of several nanometers to several tens of nanometers. The carbon material here is an amorphous or graphitic conductive material containing carbon as a main component (hereinafter the same).
[0003]
In any case, various techniques for synthesizing carbon nanotubes (CNT) by arc discharge between two carbon materials have been proposed.
[0004]
For example, a technique has been proposed in which carbon nanotubes are produced by filling a sealed container with helium or argon and performing a carbon direct current arc discharge with the pressure in the sealed container being 200 Torr or higher (see, for example, Patent Document 1).
[0005]
In addition, arc discharge is performed between opposed electrodes arranged in a horizontal direction in a sealed container filled with an inert gas, and the electrodes are rotated or reciprocated relatively and continuously or intermittently. A technique for manufacturing a nanotube has been proposed (see, for example, Patent Document 2).
[0006]
Furthermore, as a method for continuously synthesizing carbon nanotubes, a step of arc discharge between a carbon anode disposed in a container and a carbon cathode disposed opposite to the anode, and a discharge position on the surface of the cathode are performed. A carbon nanotube manufacturing technique characterized by having a step of discontinuously moving and collecting a generated deposit, and an anode tip flattening step of flattening the tip of the anode before starting arc discharge It has been proposed (see, for example, Patent Document 3).
[0007]
A method of producing a carbon nanotube is characterized in that an arc discharge is generated between a carbon anode and a carbon cathode, the cathode is formed into a disk shape, and the arc discharge is performed while rotating the cathode continuously or intermittently. It has been proposed (see, for example, Patent Document 4).
[0008]
[Patent Document 1]
JP-A-6-280116
[Patent Document 2]
JP-A-7-216660
[Patent Document 3]
JP 2001-192205 A
[Patent Document 4]
JP 2002-88592 A
[0009]
[Problems to be solved by the invention]
By the way, carbon nanotubes are generated in a substance made of carbon atoms deposited on a carbon electrode on the cathode side of a portion where arc discharge is performed, or in a part of soot attached to the arc periphery. However, according to the carbon nanotube production method of the conventional example, it is inevitable that graphite other than carbon nanotubes, amorphous carbon, etc. are mixed in the product, and the ratio of carbon nanotubes itself is low. .
[0010]
In any case, conventionally, in order to increase the stability of the arc and the synthesis rate of carbon nanotubes, an arc discharge device is provided in the sealed container, and the atmospheric gas type and pressure in the sealed container and the temperature in the sealed container are set appropriately. The carbon nanotubes were synthesized only by adjusting the atmospheric gas type and pressure in the sealed container and the temperature in the sealed container, but still a mixture of many impurities and carbon nanotubes. It could be recovered only as a certain cathode deposit or soot-like substance, and it could only be recovered by means of scraping off the cathode deposit (mixed with a large amount of impurities). Therefore, as a result, the yield of carbon nanotubes decreases, and complicated purification work must be performed to increase the purity of the carbon nanotubes, which increases the manufacturing cost of the carbon nanotubes. Furthermore, since the synthesis is performed in an airtight container, it is difficult to realize a continuous manufacturing process, the equipment becomes large, equipment costs increase, and mass synthesis of carbon nanotubes by arc discharge is difficult. It was.
[0011]
The present invention has been made to cope with such problems, and provides a method for continuously producing a tape-like substance composed of high-purity carbon nanotubes.
[0012]
[Means for Solving the Problems]
The present invention has been made to solve the above problems,
From the synthesis step of generating a tape-like material containing carbon nanotubes by arc discharge, the step of recovering the tape-like material containing carbon nanotubes generated, and the regeneration step of polishing the cathode material surface and recovering the surface after recovery A method of repeatedly producing a tape-like substance containing carbon nanotubes, which is again subjected to a synthesis process, a recovery process, and a regeneration process after regeneration of the cathode material surface;
The following steps (1) to (3) depending on the state of the surface of the cathode material after the synthesis step of generating a tape-like material containing carbon nanotubes by arc discharge, the step of recovering the tape-like material containing the generated carbon nanotubes. )
(1) If the clean surface remains on the cathode, use it as it is for the synthesis process.
(2) There is no clean surface enough to synthesize a tape-like material containing carbon nanotubes at the cathode, and soot-like material other than the region after the tape-like material has already been synthesized (amorphous carbon, etc.) ) Is attached and has a rough surface area, it is subjected to a step of polishing the cathode surface, and then subjected to a synthesis step.
(3) When there is no region (1), (2) or when the entire cathode is cracked, it is subjected to a synthesis step through a step of grinding the cathode surface and a step of polishing the cathode surface. ,
This object has been achieved by a method for repeatedly producing a tape-like substance containing carbon nanotubes.
[0013]
In the present invention, the tape-like substance containing carbon nanotubes can be generated by moving an anode or a cathode to be arc-discharged.
[0014]
The produced tape-like substance containing carbon nanotubes can be recovered by peeling off from the surface of the cathode material. The mechanism by which the tape-like substance containing carbon nanotubes peels off in the cooling process after generation is as follows. Thermal stress, because the shrinkage rate of cotton-like material (tape-like material) mainly composed of aggregates of carbon nanotubes differs from the shrinkage rate of the thin and particles of polycrystalline carbon and amorphous carbon adhering to the front and back surfaces. Is considered to occur and separate. In addition, the adhesion between the cathode and the tape-like substance is caused by the burning of the thin and particles of polycrystalline carbon and amorphous carbon adhering to the front and back surfaces of the tape-like substance due to atmospheric oxidation during the formation and cooling process. May be weakened.
[0015]
By the way, in order to continuously synthesize a tape-like substance containing carbon nanotubes, it is sufficient if it can be used again in the synthesis process after recovery. In order to synthesize a tape-like substance containing high-purity carbon nanotubes, It is necessary to make the conditions of various cathodes, such as the surface state of, appropriate. The cathode surface once arc-discharged is different from the initial cathode surface state (hereinafter referred to as “cathode clean surface”). The portion covered with quality carbon etc.) and the cathode clean surface are mixed. When discharge is performed again in a cathode surface state other than the cathode clean surface, a tape-like substance containing carbon nanotubes is synthesized on the surface where impurities such as amorphous carbon are present. It is difficult to form a tape-like substance containing. Moreover, even if it synthesize | combines, peeling of a tape-shaped substance is not performed favorably, but the case where it cannot collect | recover as a tape shape arises.
[0016]
Furthermore, when the surface roughness of the cathode material is rough, the adhesion between the cathode and the tape-like substance is increased, and peeling does not easily occur. It is not easy to mechanically scrape and collect a tape-like substance having a thickness of 10 to 500 μm. Therefore, by smoothing the surface of the cathode carbon material, the adhesive force between the cathode and the tape-like substance is weakened, and the tape-like substance can be easily recovered by being naturally peeled off by thermal stress. That is, in the state of the cathode surface after once synthesizing the tape-like substance containing carbon nanotubes, a smooth surface is not obtained due to impurities or the like, and therefore good tape-like peeling is not performed. Therefore, in order to improve the formability of the tape-like substance containing carbon nanotubes and the releasability as the tape-like substance, it is necessary to polish the cathode surface closer to the cathode clean surface. Through these steps, a tape-like substance containing carbon nanotubes can be continuously produced by repeating the synthesis step, the recovery step, and the cathode surface regeneration step again.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a substance containing carbon nanotubes is formed on a cathode made of a carbon material by arc discharge, and is made into a tape shape by relatively moving between the cathode to be arc-discharged and the anode.
[0018]
The anode is usually rod-shaped, but the cathode is shaped so that a substance containing carbon nanotubes can be formed on the surface. Specific examples of the cathode shape include a columnar shape, a cylindrical shape, a disk shape, a quadrangular shape, and a long shape, but are not limited thereto. In the case of a cylindrical or cylindrical shape, the cathode has a diameter (outer diameter) of about 10 to 100 mm, particularly about 20 to 40 mm.
[0019]
As a typical operation of the electrode, when the cathode is cylindrical or cylindrical, a tape-like substance is spirally formed on the peripheral surface of the cathode by combining an operation of rotating about the axis of the cathode and an operation of moving in the axial direction. Let it form. In the case of a disk shape, the tape-like substance is formed in a spiral shape by combining the operation of rotating about the center of the cathode and the operation of moving the anode in the radial direction. In the case of a quadrangular shape, a tape-like substance is formed in a spiral shape by combining the movement of moving the anode along the side and the movement between the center and the outer edge, or reciprocating in one side direction and the cathode is moved to the side. The tape-like substance is formed in a zigzag shape. In the case of a long shape, the cathode or the anode is moved in the long direction. The above-described operation of the cathode or anode may be performed relatively, and therefore the anode may be moved instead of the cathode or the cathode may be moved instead of the anode, or both electrodes may be moved simultaneously.
[0020]
In the above, one or more anodes may be arranged side by side to form a tape-like substance in parallel lines.
[0021]
In principle, the electrodes are moved at a constant speed.
[0022]
This cathode is normally detachable.
[0023]
Preferred as the cathode material is a carbonaceous carbon material. The reason for using a carbonaceous carbon material as the cathode material is as follows. Carbon materials used for the synthesis of carbon nanotubes by arc discharge are generally manufactured by the following process. Petroleum or coal-based coke powder is used as raw material carbonaceous powder, and various pitches such as coal tar pitch and petroleum-based pitch are mixed and stirred. The organic material thus obtained is formed by a method such as mold molding, extrusion molding or CIP formation, and is generally fired at a temperature of 1500 ° C. or lower. At this point, the raw organic material is almost completely polycondensed and is in a carbonized state. Thereafter, various pitches and the like are impregnated as necessary, and re-heat treatment is performed, and further, if necessary, graphitization heat treatment is performed at a temperature of 3000 ° C. or lower. In this way, a carbon material having the required mechanical performance and physical properties is produced.
[0024]
The carbon material produced in this way varies greatly in structure, structure, mechanical properties, physical properties, etc. depending on the raw material, production method, and heat treatment temperature during production. Using various carbon materials as cathode materials, arc discharge was performed, and the amount of carbon nanotubes synthesized was compared. Carbon materials with a heat treatment temperature during production of 1000 ° C. to 1500 ° C. synthesized the most carbon nanotubes. There was found. A carbon material having a heat treatment temperature of 1000 ° C. to 1500 ° C. at the time of manufacture is a so-called carbonaceous carbon material made of carbon in which carbon graphitization has hardly progressed. Therefore, by selecting and using a carbon material whose material is mainly carbonaceous with a heat treatment temperature of 1000 ° C. to 1500 ° C. as a cathode material, carbon nanotubes can be produced at a higher yield. Can be generated.
[0025]
The carbon material used for the cathode is not limited to carbon, but may be a resin or a mixture with metal as long as it contains 90% or more of carbon. Examples of resins include phenolic resins, thermosetting resins typified by urea resins, polypropylene, thermoplastic resins typified by fluororesins, engineering plastics typified by polycarbonate, polysulfone, and polyamideimide. May include iron, cobalt, nickel, tungsten, and niobium. Furthermore, any of carbonaceous materials having a random carbon crystal structure, graphitized graphite materials, and the like can be used.
[0026]
In order to synthesize carbon nanotubes with high purity and yield, it is advantageous to raise the temperature of the arc cathode spot of the cathode material to some extent. Usually, the electric resistivity (= specific resistance) of a carbon electrode used as an electrode is in the range of about 500 to 2000 μΩ · cm, but 2500 μΩ · cm or more, preferably 3000 μΩ · cm or more, more preferably 4000 μΩ · cm. In particular, when a carbon material having an electrical resistivity of 5000 μΩ · cm or more is used as the cathode material, a high current density is obtained at the arc discharge in the vicinity of the cathode point of the cathode material. Becomes a high temperature. Therefore, the same effect as that obtained by heating the cathode can be obtained, and a tape-like substance containing carbon nanotubes with high yield and purity can be produced. The upper limit of the preferred electrical resistivity is about 20000 μΩ · cm, preferably about 12000 μΩ · cm, from a practical viewpoint.
[0027]
Moreover, the thermal conductivity of the carbon electrode normally used as an electrode is in the range of 50 to 200 W / m · K, and the electrical resistivity and the thermal conductivity in the carbon material have a substantially negative correlation. In other words, a material having a high electrical resistivity has a low thermal conductivity and is difficult to transfer heat, so that the temperature near the cathode spot becomes higher. The thermal conductivity of a carbon material having an electric resistance value of 4000 μΩ · cm or more corresponds to approximately 40 W / m · K or less.
[0028]
Further, in the production of a tape-shaped material containing carbon nanotubes according to the present invention, the arithmetic average roughness (Ra) of the surface of the cathode electrode is less than 4 μm, preferably 3.6 μm or less from the viewpoint of easy peeling of the tape-shaped material. In particular, it is desirable to use a carbon material of 3.2 μm or less.
[0029]
The tape-like substance containing carbon nanotubes peels off during the cooling process after generation. The shrinkage rate of the cotton-like substance mainly composed of aggregates of carbon nanotubes, and the polycrystalline graphite and amorphous materials adhering to the front and back surfaces. It is considered that thermal stress is generated and separated because the shrinkage of carbon skin and particles are different. In addition, the adhesion between the cathode and the tape-like substance is caused by the burning of the thin graphite and amorphous carbon and amorphous carbon particles adhering to the front and back surfaces of the tape-like substance due to atmospheric oxidation during the formation and cooling process. May be weakened.
[0030]
However, when the surface roughness of the cathode material is rough (when the arithmetic average roughness (Ra) is 4.0 μm or more), the adhesion between the cathode and the tape-like substance increases, and peeling does not easily occur. It is not easy to mechanically scrape and collect a tape-like substance having a thickness of 10 to 500 μm. Therefore, by reducing the arithmetic average roughness (Ra) of the surface of the cathode carbon material to less than 4.0 μm, the adhesive force between the cathode and the tape-like material is weakened, and the tape-like material is recovered by spontaneous separation by thermal stress. It can be made easier.
[0031]
The anode is an arc discharge while moving relative to the cathode to generate a tape-like substance containing carbon nanotubes on the cathode, and the shape is usually a rod. However, it is preferable to flow an inert gas from the anode portion toward the cathode in order to induce arc discharge and stabilize its direction. The inert gas may be blown out by attaching an inert gas pipe outside the anode, or accommodating the anode in the pipe and blowing out the inert gas between the anode and the pipe in an annular shape. However, a particularly preferable shape is a structure in which the anode is formed in a cylindrical shape to form a hollow electrode, and an inert gas is blown out from the inside.
[0032]
Thus, when a hollow electrode is used for the anode electrode and an inert gas such as argon gas or a mixed gas containing an inert gas is sprayed from the inside of the hollow electrode toward the cathode electrode, the ionization degree of the gas increases and the gas A condition that an arc is likely to be generated in the ejection path is formed. Moreover, it is considered that the inner surface of the hollow electrode in contact with the inert gas or the mixed gas containing the inert gas forms a stable anode spot. For this reason, the arc generation path is restricted, and irregular movement of the cathode spot of the arc on the cathode electrode is prevented. As a result, carbon nanotubes can be preferentially synthesized at the fixed cathode spot generation position (arc center), and the carbon nanotubes can be synthesized at the fixed cathode spot generation position (arc center). Composites can be produced.
[0033]
The inner diameter of this hollow hole is 1mm ² The gas flow rate is preferably about 10 to 400 ml per unit. The number of hollow holes is not limited to one, and a plurality of hollow holes can be provided.
[0034]
For the arc discharge anode, the same carbon material as the cathode may be used, but a metal electrode can also be used. Examples of metal electrodes include tungsten electrodes, copper electrodes, platinum, molybdenum, hafnium, and the like.
[0035]
The gap between the cathode and the anode is not particularly limited as long as the arc discharge can be stably maintained, but the arc is preferably more stable at 0.5 mm to 5 mm.
[0036]
The atmosphere in which arc discharge is performed in the present invention is N ₂ , CO ₂ Any atmosphere such as an inert gas atmosphere may be used.
[0037]
In order to cause arc discharge, it is necessary to ionize the space between the electrodes. There are various processes for ionization of atoms. In arc discharge, the ionization process by collision with electrons is dominant. In general, except for He and Ne having a small atomic number, inert gases such as Ar, Kr, and Xe have a high ionization efficiency due to collision with electrons and provide a space in which an arc is easily generated. Inert gases such as Ar, Kr, and Xe have a higher ionization efficiency than oxygen, nitrogen, etc., and therefore, these inert gases or a mixture containing an inert gas from the anode electrode to the cathode electrode in the air atmosphere When arc discharge is performed while supplying gas, the arc can be generated in a concentrated manner along the gas flow path. That is, by using an inert gas or a mixed gas containing an inert gas supplied from the anode electrode toward the cathode electrode as the plasma gas, the arc can be concentrated and the cathode spot can be stabilized.
[0038]
In addition, even if the gas delivered from the hole inside the hollow electrode was pure argon or argon gas mixed with about 5% hydrogen gas or helium gas, no significant change was observed in the arc form. In particular, when hydrogen gas was mixed in an inert gas such as argon by several percent to several tens of percent, the yield of carbon nanotubes could be increased without impairing arc stability. This is considered to be because hydrogen gas has an effect of preventing carbon sublimated on the anode electrode from growing as a cluster, and the carbon nanotubes are easily synthesized on the cathode electrode.
[0039]
Further, in the atmosphere, carbon is oxidized and burned because oxygen is involved in the arc discharge part. At this time, the produced carbon nanotubes are also somewhat oxidized, but impurities such as amorphous carbon and polycrystalline graphite powder having a lower combustion temperature are preferentially oxidized and burned, resulting in the purity of the carbon nanotubes in the product. There is an effect to improve.
[0040]
The tape-like substance containing carbon nanotubes according to the present invention has a thickness of 10 to 500 μm, particularly 20 to 100 μm, a width of 1 to 10 mm, particularly 1 to 6 mm, and an arbitrary length, and is mainly a cotton-like aggregate of carbon nanotubes It has a body.
[0041]
The method for recovering the tape-like substance containing the carbon nanotubes formed on the cathode in this way is not limited. For example, the tape-like substance is peeled off from the cathode by blowing a gas to the attached end of the cathode.
[0042]
The gas to be blown may be anything such as air or nitrogen as long as it has a cooling effect other than the flammable gas. That is, since the tape-like substance is formed in a thin film on the surface of the cathode electrode, by blowing gas, the temperature lowers more rapidly than the cathode electrode of the production substrate, and heat is generated between the tape-like substance and the cathode electrode. It is considered that the stress works and peeling is remarkably accelerated.
[0043]
Furthermore, when the gas to be blown contains oxygen, or when synthesis is performed in an air atmosphere without containing oxygen, the air is slightly involved by blowing the gas, so the tape-like substance table is used. It has the effect of promoting the oxidation and combustion of polycrystalline graphite and amorphous carbon skin and particles adhering to the back surface. As a result, the carbon nanotube purity of the tape-like substance increases, and the cathode and the tape-like substance are attached. It is thought that there is also an effect of facilitating the peeling of the tape-like substance because the adhesion is weakened.
[0044]
The spraying is preferably performed using a nozzle, and the spraying direction is between ± 90 ° in the longitudinal direction of the tape-like substance.
[0045]
The nozzle is moved relative to the tape-like substance in order to advance the peeling, but it is also possible to keep the nozzle fixed when the cathode is moved to form the tape-like substance. .
[0046]
After collecting the tape-like substance containing carbon nanotubes, the surface of the cathode material may be polished as it is, and if the cathode material remains on the cathode material, it is discharged and carbon is further discharged. A tape-like material containing nanotubes may be generated.
[0047]
That is, when synthesizing again by arc discharge after synthesizing a tape-like substance containing carbon nanotubes by arc discharge, a step of regenerating the surface state of the cathode to an optimum one as described above is required. Therefore, the most reliable way to shape the cathode surface state is to grind the required amount of the cathode surface layer after every discharge as described above, and then polish it. Using the process is a wasteful process and the yield of the material is also poor. Therefore, selecting the cathode regeneration method according to the state of the cathode surface after discharge can use the cathode material more efficiently and improve the yield.
[0048]
When a tape-like substance containing carbon nanotubes is synthesized by arc discharge, the cathode surface state after synthesis is as follows: (1) a cathode clean surface, (2) a part where adhesion of cage-like substances (amorphous carbon, etc.) (3) It can be classified into four types: near the cathode spot (tape-like substance forming part) and (4) cracking. Therefore, it can be said that performing the cathode surface regeneration treatment according to these four states is an effective means. That is, when the cathode surface is in the state (1), it is sufficient to synthesize it on the clean surface of the cathode. Therefore, the cathode surface may be used as it is without being subjected to special treatment. If there is no state {circle around (1)} sufficient to synthesize the tape-like substance on the cathode and there is a state {circle around (2)} sufficient to synthesize the tape-like substance, the cathode surface is subjected to a step of polishing and used for the synthesis step. When there are no (1) and (2) states sufficient to synthesize a tape-like substance on the cathode ((3) state or (4) state), the steps of grinding the cathode surface and polishing the cathode surface are performed. Then, it will be used for the synthesis process.
[0049]
When grinding is necessary, it occurs as follows. That is, by using a carbonaceous carbon material as the cathode, a tape-like substance containing higher purity carbon nanotubes can be synthesized. However, the portion (cathode spot portion) where the tape-like material is synthesized by arc discharge is the portion exposed to the highest temperature. A tape-like substance is preferentially synthesized at the cathode spot portion, and when exposed to the highest temperature, the surface of the cathode material near the cathode spot is changed from carbonaceous to graphite. As described above, a carbonaceous carbon material is more suitable for synthesizing a tape-like material than a graphitic carbon material. Therefore, in order to stably synthesize a tape-like substance containing high-purity carbon nanotubes by using a carbon material once subjected to synthesis and performing arc discharge again, the altered cathode surface layer (graphitic layer) is scraped off (grinding) Is desirable).
[0050]
Furthermore, when the synthesis is repeated, the portion of the cathode surface where the tape-like substance is synthesized (directly under the arc) increases, and the cathode material surface may crack due to repeated thermal stress. Tape-like material is synthesized at the cathode spot directly under the arc, but this part is the part that is exposed to the hottest arc, and it is difficult to synthesize the tape-like substance when this part is discharged again. Experimental results are obtained. In addition, the stability of the arc (fixation of the cathode spot) and the way heat enters the cathode material are important factors for the synthesis of tape-like materials containing carbon nanotubes. It is difficult to create a discharge state (cathode spot fixation) and heat conduction conditions suitable for tape-like material synthesis. For the above reasons, in such a cathode surface state, a step of grinding (grinding) the cathode surface layer itself before polishing the cathode surface and smoothing the surface is necessary.
[0051]
The amount to be scraped is until there is no rough surface or crack, and is usually 0.5 mm or more, preferably 1 mm or more, more preferably 2 mm or more, and particularly preferably 4 mm or more. The upper limit of the grinding amount is not particularly limited, but is about 10 mm thick from a practical viewpoint.
[0052]
Polishing is performed after grinding or without grinding. Polishing is performed until the surface of the cathode material has an arithmetic average roughness (Ra) of less than 4 μm, preferably 3.6 μm or less, particularly preferably 3.2 μm or less.
[0053]
After the polishing is completed, a tape-like substance containing carbon nanotubes can be continuously produced by repeating the synthesis process, the recovery process, and the cathode surface regeneration process again.
[0054]
FIG. 1 shows a process flow for continuously synthesizing a tape-like substance containing carbon nanotubes. As shown in FIG. 1, a tape-like substance containing carbon nanotubes can be continuously produced by repeatedly performing the steps of synthesis → recovery → cathode regeneration.
[0055]
Next, FIG. 2 shows a flow of changing means to be taken according to the cathode surface state after the tape-like substance containing carbon nanotubes is collected. According to the process flow in the cathode state, if a clean surface remains on the cathode, it can be used as it is in the synthesis process. In other states, the cathode surface regeneration process (grinding and polishing) according to the state. To serve.
[0056]
【Example】
Example 1
An example of a state in which a tape-like substance containing carbon nanotubes is generated in the method of the present invention is shown in FIG.
[0057]
The anode was made of a carbon material, and a cylindrical one having a diameter of 10 mm was used. The cathode was made of a carbon material, and a long plate having a thickness of 15 mm was used. The carbon material of the cathode had an electric resistance value of 4600 μΩ · cm, a thermal conductivity of 31 W / m · K, and an arithmetic average roughness of the surface of 3.2 μm.
[0058]
When arc discharge was performed while moving the anode, a tape-like substance was formed on the cathode electrode through which the center of the arc (cathode spot) passed. Discharge was performed in an open space (under atmospheric pressure and in an atmospheric atmosphere), and argon gas was supplied by a gas supply unit (not shown) toward the arc generation unit in order to stably generate arc discharge. The discharge conditions at this time were 100A-20V, the gas flow rate was 10 liters / minute, and the moving speed of the anode was 40 mm / minute. At this time, a tape-like substance containing carbon nanotubes having a width of about 2 to 3 mm and a thickness of about 100 μm could be synthesized.
[0059]
The phenomenon that the tape-like substance containing the produced carbon nanotubes spontaneously peeled as described above was observed. The generation mechanism (generation mechanism) of this tape-like substance is considered as shown in FIG. In other words, carbon nanotubes are synthesized at the center of the arc (cathode spot), but in the case of a moving arc, amorphous carbon is generated at the periphery of the arc, so the product cross section of the part where the arc has moved is shown in the figure. 4 As shown in the upper part, the aggregate of carbon nanotubes is narrowed by amorphous carbon. However, after the arc has passed, it comes into contact with the atmosphere at a high temperature, so that amorphous carbon having many crystal structure defects is preferentially oxidized and burned, and a part thereof is burned out (middle in FIG. 4). Furthermore, in the subsequent cooling process of the cathode electrode, the phenomenon that the high-purity carbon nanotubes are peeled off in a tape shape is caused by the difference in the thermal expansion coefficient between the amorphous carbon layer and the high-purity carbon nanotube aggregate (Fig. 4 bottom).
[0060]
Next, it is subjected to a step of collecting the peeled tape. It was synthesized in the form of a tape, and since it was peeled off spontaneously, it could be easily recovered. The recovery step may take the form of following the recovery device (for example, a suction device) immediately after synthesis of the tape-like substance, or may be provided with a recovery step after the end of the synthesis. In any case, since the tape-like substance is peeled off, the tape-like substance containing carbon nanotubes can be easily recovered.
[0061]
Next, it is subjected to a step of regenerating the cathode surface after the tape-like material is recovered.
Here, the state of the cathode surface after the synthesis of the tape-like substance containing carbon nanotubes is shown in FIG. The cathode state is the same as the initial cathode surface (cathode clean surface), the surface is rough due to exposure to the arc frame, or the part where the soot-like substance (amorphous carbon) is attached It has been found that it can be classified into four types: a portion immediately below the cathode spot after the tape-like material is synthesized, and a portion where cracks are generated due to repeated thermal stress. As described above, the stable synthesis property and peelability of the tape-like material containing carbon nanotubes differ depending on the surface state of the cathode. In other words, unless proper treatment is performed, carbon nanotubes with high purity and good quality will not be formed even if they are synthesized indiscriminately.
[0062]
Since the polishing of the cathode surface is a polishing of the surface of the carbon material, it is not particularly difficult to ensure smoothness. Therefore, any shape can be used as long as it is polished with a normal paper file. In this example, rough polishing was performed at # 400, and thereafter polishing was performed at # 800 and # 1200 to ensure smoothness.
[0063]
Also, since the grinding process is not a difficult-to-process material, it can be easily scraped off. In this example, the required amount (4 mm thickness) was cut off with a lathe machine.
[0064]
A tape-like substance containing carbon nanotubes could be continuously produced by a process combining the above.
[0065]
Example 2
FIG. 1 shows an example in which a hollow electrode is used for the anode. A hollow carbon electrode having an outer diameter of 10 mm and an inner diameter of 4 mm is used as the anode electrode, and a cylindrical carbon electrode having a diameter of 35 mm is used as the cathode electrode (electric resistivity 5900 μΩ · cm, thermal conductivity 23 W / m · K, arithmetic mean roughness of the surface 4.0 μm) was used. While rotating the cathode electrode, the hollow carbon electrode was linearly moved in the axial direction of the cathode electrode, and the cathode spot was moved in a spiral pattern on the cathode electrode. The rotational speed of the cathode electrode was 1.5 revolutions / minute, and the moving speed of the hollow carbon electrode (anode electrode) was 35 mm / minute. Arc discharge was performed in an open space (under atmospheric pressure and in atmospheric air), pure argon gas was used as the gas fed from the hollow electrode, and the flow rate was 1 liter / min. The discharge conditions were a current of 100 A and a voltage of 20 V (arc length of about 1 mm). After the arc discharge, a tape-like high purity CNT having a width of about 2 to 3 mm and a thickness of about 100 microns was synthesized at a spiral position where the cathode spot moved on the cathode electrode.
[0066]
At the same time, the tape peeling gas feeding device is installed at a position where the gas can be blown when the end of the synthesized and rotated tape-like substance is almost directly below the cathode, and the gas is fed to the end of the tape-like substance. Sprayed on. The gas at this time was air. Gas was blown at 5 liters / minute. This gas supply device was also moved at the same speed as the anode, and was always sprayed onto the tape-like material after synthesis. Then, when a little time has passed from the beginning, the tape-like substance starts to peel spontaneously for the reasons described above, but the peeling was promoted by gas blowing, and smooth peeling was confirmed from the synthesis start part.
[0067]
Furthermore, a tape-like substance recovery bottle was placed immediately below where the tape started to peel. This collection bottle was also moved at the same speed as the anode. As shown in FIG. 7, the tape-like substance peeled from the end part is peeled downward by the rotation of the cathode, and the tape-like substance is recovered well in the collection bottle without being cut off halfway. I was able to confirm.
[0068]
【The invention's effect】
As described above, according to the present invention, the step of synthesizing the tape-like material containing carbon nanotubes, the step of recovering the synthesized tape-like material, the step of regenerating the cathode surface, the synthesis step, the recovery step, the cathode surface Since the regeneration process was repeated, a tape-like substance containing carbon nanotubes could be synthesized continuously.
[0069]
Furthermore, in the cathode regeneration process, since the stable synthesis and releasability of the tape-like material containing carbon nanotubes according to the state of the cathode was clarified, the cathode surface regeneration process suitable for the state at that time was provided, As a result, it was possible to continuously synthesize a tape-like substance containing high-purity carbon nanotubes more reliably and to improve the yield of the cathode material.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a process in one embodiment of the present invention.
FIG. 2 is a diagram illustrating a process in one embodiment of the present invention.
FIG. 3 is a view showing a state in which a tape-like substance containing carbon nanotubes is generated in an embodiment of the present invention.
FIG. 4 is a diagram schematically illustrating a cross-sectional structure of a state where a tape-like substance containing carbon nanotubes is peeled off.
FIG. 5 is a diagram schematically showing the state of the cathode surface after peeling off the tape-like substance containing carbon nanotubes.
FIG. 6 is a view showing a state in which a tape-like substance containing carbon nanotubes is generated in another example of the present invention.
7 is a view showing a state where the tape-like substance containing carbon nanotubes is peeled off by blowing air in FIG. 6. FIG.

Claims (3)

From the synthesis step of generating a tape-like material containing carbon nanotubes by arc discharge, the step of recovering the tape-like material containing carbon nanotubes generated, and the regeneration step of polishing the cathode material surface and recovering the surface after recovery A method of repeatedly producing a tape-like substance containing carbon nanotubes, which is again subjected to a synthesis process, a recovery process, and a regeneration process after regeneration of the cathode material surface A carbonaceous carbon material is used as the cathode material for arc discharge, and the surface polishing in the regeneration process is characterized by scraping off the surface layer of the cathode carbon material that has changed to graphite after synthesizing a tape-like material containing carbon nanotubes by arc discharge. A method for repeatedly producing a tape-like substance containing carbon nanotubes according to claim 1 The following steps (1) to (3) depending on the state of the surface of the cathode material after the synthesis step of generating a tape-like material containing carbon nanotubes by arc discharge, the step of recovering the tape-like material containing the generated carbon nanotubes. )
(1) If the clean surface remains on the cathode, use it as it is for the synthesis process.
(2) There is no clean surface enough to synthesize a tape-like material containing carbon nanotubes at the cathode, and soot-like material other than the region after the tape-like material has already been synthesized (amorphous carbon, etc.) ) Is attached and has a rough surface area, it is subjected to a step of polishing the cathode surface, and then subjected to a synthesis step.
(3) When there is no region (1), (2) or when the entire cathode is cracked, it is subjected to a synthesis step through a step of grinding the cathode surface and a step of polishing the cathode surface. ,
Method for repeatedly producing a tape-like substance containing carbon nanotubes

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