JP2005100757A - Filament made of carbon nanotube and its utilization - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filament having carbon nanotubes as a main component, and to provide its manufacturing method. <P>SOLUTION: The manufacturing method of a filament has a process in which a nanotube assembly made by assembling a plurality of carbon nanotubes in a network state is formed by depositing carbons from gas phase. Then, the method has a process of drawing the nanotube assembly and a process of overlapping the nanotube assembly. The drawing process can be carried out for a plurality of times by having the overlapping process in between. It is desirable that the drawing direction in these plurality of times of drawing processes is kept in a nearly identical direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a filament having a carbon nanotube as a main component and a method for producing the same. The present invention also relates to an electric device such as a vacuum tube and a light bulb using the filament.

  Techniques for applying carbon nanotubes to various products are being studied. However, as is well known, carbon nanotubes are fine structures and generally require expensive equipment to handle them. For example, it is difficult to collect a large number of carbon nanotubes as a whole so as to exhibit a predetermined property (such as an outer shape). This can contribute to an increase in manufacturing cost of a product (or member) using carbon nanotubes.

It would be beneficial if a large number of carbon nanotubes could be collected (formed) in a predetermined shape. Such a molded article can be useful as a filament or the like utilizing its electrical characteristics.
Therefore, an object of the present invention is to provide a method for efficiently producing a filament containing a plurality of carbon nanotubes. Another object of the present invention is to provide a filament produced by such a method. Yet another object is to provide an electrical device (vacuum tube, light bulb, etc.) provided with such a filament.
Another aspect of the present invention is to provide a method for handling carbon nanotubes. In particular, it is to provide a method for forming an aggregate of carbon nanotubes.

In order to solve the above-mentioned problems, according to the present invention, there is provided a method for producing a filament having a carbon nanotube as a main component. The filament manufacturing method includes a step of depositing carbon from a gas phase to form a nanotube aggregate in which a plurality of carbon nanotubes are aggregated in a net shape. Moreover, it has the process of extending | stretching the said nanotube aggregate. Further, the method includes a step of superimposing the nanotube aggregates. Here, the said extending process can be performed in multiple times on both sides of the said superimposition process. For example, it can be performed in the order of a stretching process, a superposition process, and a stretching process. It is preferable that the stretching directions in the plurality of stretching steps are substantially the same direction.
According to such a manufacturing method, the aggregate of nanotubes can be easily formed into a property suitable for the filament by alternately performing the stretching step and the overlapping step.

In the superimposing step, it is preferable to superimpose the nanotube aggregates along the orientation of the carbon nanotubes constituting the nanotube aggregates.
Here, “along the orientation of the carbon nanotubes” means that the aggregates of nanotubes are overlapped so that the direction in which the orientation of the carbon nanotubes is high approximates (preferably, the directions substantially coincide). Thereby, the density and / or orientation of the carbon nanotubes constituting the aggregate of nanotubes can be efficiently increased.

  Examples of the aggregate of nanotubes that can be used in such a filament manufacturing method include those in which the carbon nanotubes constituting the aggregate of nanotubes are mainly single-walled carbon nanotubes. In addition, carbon nanotubes constituting the aggregate of nanotubes are mainly multi-walled carbon nanotubes, or those in which multi-walled carbon nanotubes and single-walled carbon nanotubes are mixed can be used. When the carbon nanotubes constituting the aggregate of nanotubes are mainly single-walled carbon nanotubes, filaments exhibiting unique electrical characteristics can be manufactured, and the quality of the obtained filaments can be easily stabilized (homogenized). It is possible to realize at least one of the effects that the control (design) of the electrical characteristics of the filament is easy.

  In the above production method, a nanotube aggregate in which the purity of carbon nanotubes (atomic ratio of carbon nanotubes in the total aggregate) before performing the stretching step and the overlapping step is 70 at.% Or more can be preferably used. . A treatment for purifying the aggregate of nanotubes can be appropriately performed so as to achieve such a purity of carbon nanotube. By performing the purification treatment prior to the stretching step and the overlapping step, the purity of the aggregate of nanotubes can be improved efficiently. By using such an aggregate of nanotubes, it is possible to produce filaments that exhibit unique electrical characteristics, and to easily stabilize (homogenize) the quality of the resulting filaments. ) Is easy, at least one of the effects can be realized.

The aggregate of nanotubes used in the production method disclosed herein can be suitably formed by, for example, the following method. That is, arc discharge is generated between an anode and a cathode in which a metal catalyst is mixed with graphite. Thereby, carbon can be evaporated from at least the anode. The carbon is deposited to form the nanotube aggregate. According to such a method, the aggregate of nanotubes can be formed efficiently. It is preferable to use Fe alone as the metal catalyst. Further, it is preferable to generate a DC arc discharge in a mixed gas atmosphere of H ₂ and Ar.

The filament manufacturing method disclosed herein is suitable as a method for manufacturing a filament having a relatively large outer shape (for example, a size at least visible to the naked eye). In the production of such a filament, the effect of adopting the method of the present invention can be exhibited particularly well.
Although it does not specifically limit, it will be as follows if the property of the filament which can be suitably manufactured with the said manufacturing method is illustrated. The length (size along the direction in which the orientation of the carbon nanotube is high) is 10 mm or more, typically 10 mm to 300 mm. The width (size along the direction substantially perpendicular to the length) is 0.1 mm or more, typically 0.1 mm to 10 mm. The thickness is 0.005 mm or more, typically 0.005 mm to 0.05 mm. Density 0.3 g / cm ³ or more, typically the density 0.3 to 1.0 g / cm ^3. Further, according to any one of the above-described filament manufacturing methods, a filament having a current with respect to a DC voltage of 40 V, for example, 2 A or more (typically 2 to 4 A) can be manufactured.

According to the present invention, a filament produced by any of the methods described above is provided. Such a filament can withstand a tensile force of 1 N or more with respect to the longitudinal direction (the direction in which the orientation of carbon nanotubes is high).
Moreover, according to this invention, a vacuum tube provided with one of the filaments mentioned above is provided. Furthermore, a light bulb comprising any of the filaments described above is provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that technical matters other than the contents particularly mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the technical contents disclosed in the present specification and drawings and the common general technical knowledge in the field.

  The present invention relates to a filament having a carbon nanotube as a main component. Here, the “filament” refers to a conductive member that can generate heat when energized. Typically, it has a long (string-like, thread-like, belt-like, band-like) or sheet-like outer shape. Such a filament can be used as an electron (particularly thermionic) emission source such as a cathode of a vacuum tube. Moreover, it can be used as a heating element (light source) of a light bulb.

  The nanotube aggregate according to the present invention has a form in which a plurality (typically a large number) of carbon nanotubes are aggregated in a net shape. Here, the “net shape” is a state that can be expressed as a cotton shape, a cotton candy shape, a web shape, etc., and is limited to a state in which individual carbon nanotubes constituting the nanotube aggregate are entangled. It is not a thing. In the preferred one, the whole is linked (linked) to the extent that it can be grabbed and lifted up. Such an aggregate of nanotubes can be handled as an integral body by macroscopic entanglement of a plurality of carbon nanotubes constituting the aggregate. For example, it can be gripped, pulled or bent using a general gripping tool such as tweezers.

  Such an aggregate of nanotubes is subjected to a stretching process (stretching process) and a superposition process to form a predetermined shape. When the nanotube aggregate is stretched, the orientation of the carbon nanotubes constituting the aggregate in the stretching direction tends to be improved. Therefore, in the stretching step, it is preferable to stretch the aggregate along the orientation of the carbon nanotubes constituting the nanotube aggregate (that is, in a direction approximating the direction with high orientation). Thereby, the orientation of the aggregate of nanotubes can be improved efficiently. This stretching process can be performed a plurality of times with the overlapping process interposed therebetween. It is preferable that the stretching direction in these multiple stretching steps is substantially the same direction. Thereby, the density and / or orientation of the carbon nanotubes constituting the aggregate of nanotubes can be efficiently increased.

  The superimposing step may be a step of superimposing a part of one nanotube aggregate and another part, or may be a step of superimposing one nanotube aggregate and another nanotube aggregate. Moreover, you may implement both of these. When a part of one nanotube aggregate is overlapped with another part, the nanotube aggregate may be overlapped by folding, or the nanotube aggregate may be divided into a plurality and overlapped. The overlapping process is performed at least between a plurality of stretching processes. Further, the superposition step can be performed before the first stretching step and / or after the last stretching step. This superposition process is preferably performed along the orientation of the carbon nanotubes. Therefore, when the aggregates of nanotubes are overlapped, they can be folded along a fold line perpendicular to the direction of carbon nanotube orientation (stretching direction) or along a fold line parallel to the direction. preferable. In addition, when the aggregate of nanotubes is divided and overlapped, it is divided along a dividing line perpendicular to the direction in which carbon nanotubes are highly oriented (stretching direction) or along a dividing line parallel to the direction. Are preferably overlapped so that the orientation of the carbon nanotubes in the aggregate of the divided nanotubes is aligned.

  By such a stretching process and a superimposing process, the orientation of the carbon nanotubes constituting the aggregate of nanotubes can be enhanced. That is, the macroscopic orientation of the aggregate of nanotubes is improved. Further, the density of the aggregate of nanotubes (the density of the carbon nanotubes) can be increased by the above process. Therefore, a filament excellent in electrical characteristics can be manufactured. For example, a filament having at least one of the following characteristics can be manufactured: good electron emission characteristics (high emission current can be obtained at a low voltage), high conductivity, low resistance, and the like. Such a filament is suitable for applications such as vacuum tubes and light bulbs. In addition, the filament according to the present invention can be excellent in at least one of physical characteristics such as impact resistance and vibration resistance, thermal stability, and chemical stability.

The following method is mentioned as a preferable method for producing the nanotube aggregate. That is, arc discharge is generated between an anode and a cathode in which a metal catalyst is mixed with graphite. This evaporates carbon from at least the anode. In this method, the aggregate of nanotubes is formed by depositing the carbon.
As the metal catalyst, a Ni-Y catalyst, an S-added Fe-based metal catalyst, an Fe (single) catalyst, or the like can be used. For the purpose of forming a nanotube aggregate containing a relatively large amount of single-walled carbon nanotubes, it is preferable to use an S-added Fe-based metal catalyst or an Fe (single) catalyst, and particularly preferably an Fe (single) catalyst. The ratio of the metal catalyst contained in the anode can be, for example, in the range of Fe 0.5 to 2 at.%, And preferably in the range of Fe 0.5 to 1 at.%.

The arc discharge here may be either normal arc discharge or arc plasma jet. Moreover, the applied voltage for performing arc discharge can be selected, for example in the range of 20-40V (preferably 30-40V). In the case of DC arc discharge using an anode having a diameter of 6 mm, the DC current can be selected in the range of 30 to 70A. The atmospheric pressure during arc discharge can be set to, for example, about 0.3 to 10 × 10 ⁴ Pa (approximately 20 to 750 Torr).
As an atmospheric gas for generating arc discharge, H ₂ gas, a mixed gas of H ₂ and Ar, or the like can be selected. Since it is easy to stabilize the arc discharge, a mixed gas of H ₂ and Ar is preferably used. For example, a mixed gas in which the mixing ratio of H ₂ : Ar is in the range of 1: 4 to 4: 1 (that is, the Ar gas content is 20 to 80% by volume) can be preferably used. A mixed gas in which the mixing ratio of H ₂ : Ar is in the range of 3: 2 to 2: 3 by volume is more preferable. In the case of forming an aggregate of nanotubes containing a large amount of single-walled carbon nanotubes, a combination of a simple substance of Fe as a metal catalyst and a mixed gas of H ₂ and Ar as an atmospheric gas is particularly preferable.

Any of the filament manufacturing methods described above may further include a step of purifying the aggregate of nanotubes. As such a purification step, for example, the following treatment:
(1). A process for removing impurity carbon from the aggregate of nanotubes, for example, a process for heating the aggregate of nanotubes in an oxidizing gas or air (heat treatment); and
(2). Treatment for removing the metal catalyst from the aggregate of nanotubes, for example, treatment for immersing in an acid that dissolves the metal (acid treatment);
It can be performed. It is desirable to carry out both (1) and (2) above, and it is preferable to carry out the treatment (2) after the treatment (1). In particular, when the metal catalyst is covered with carbon, by removing the carbon covering the metal catalyst by the treatment of (1) above and exposing the metal catalyst, the treatment of (2) above is performed. The metal catalyst can be removed more efficiently.

Here, “impurity carbon” refers to a carbon component that can be contained in the aggregate of nanotubes used in the production method of the present invention but is not in the form of a tube. For example, amorphous carbon, fullerene, carbon nanoparticles, a graphite film covering the catalytic metal, and the like can be impurity carbon (removal target).
When the impurity carbon is removed from the aggregate of nanotubes by the heat treatment, it is preferable to select a condition that suppresses damage and disappearance of carbon nanotubes other than the impurity carbon. For example, it may be performed under conditions that satisfy one or more of the following conditions.
(1). Atmospheric gas: An oxidizing atmosphere containing one or more oxidizing gases (O ₂ , CO, NO, etc.) is preferable. An oxidizing atmosphere containing an inert gas such as Ar or N ₂ in addition to the oxidizing gas can be provided.
(2). Atmospheric pressure: 5 × 10 ⁴ to 10 × 10 ⁴ Pa, more preferably 8 × 10 ⁴ to 10 × 10 ⁴ Pa.
(3) Heating temperature: 600-900K, more preferably 670-720K.
(4). Heating time: 20 minutes to 1 hour, more preferably 25 minutes to 35 minutes.
Suitable heat treatment conditions may vary depending on the type and amount of impurity carbon to be removed, the structure of the aggregate of nanotubes, and the like.

  As the acid used for the acid treatment, an appropriate acid can be selected according to the type of the metal catalyst to be removed. For example, one or more acids selected from hydrochloric acid, nitric acid and the like can be used. Hydrochloric acid is mentioned as an acid preferably used for removing the Fe catalyst. For example, hydrochloric acid having a concentration of about 18 to 36% is preferably used.

An example of the structure of a nanotube production apparatus that can be used to form a nanotube aggregate is shown in FIG. In this apparatus 10, an anode 13 can be mounted on a mounting table 12 disposed in a vacuum chamber 11. Further, the cathode 14 can be suspended from the ceiling of the vacuum chamber 11 via the holder 15. The cathode 14 can be moved up and down and rotated by power from a motor 16 connected to the holder 15. Further, the vacuum chamber 11 is provided with an exhaust pipe 23 connected to a vacuum pump 21 such as an oil diffusion pump, whereby the internal pressure of the vacuum chamber 11 can be adjusted. Further, the vacuum chamber 11 is provided with an air supply pipe 22 for introducing a gas G used for atmosphere adjustment or the like.
Connected to the anode 13 and the cathode 14 is a DC power source 31 that can apply a voltage necessary for generating arc discharge. Further, the anode side and the cathode side of the DC power source 31 are connected to an input / output circuit 33 to which a control command from the control mechanism 32 is input.

  As a material constituting the anode 13, graphite mixed with Fe alone as a metal catalyst can be used. As this Fe catalyst, it is preferable to use fine particles (preferably particle size of 1 μm or less) of Fe particles. Such particulate Fe catalyst has particularly good catalytic activity for the synthesis reaction of single-walled carbon nanotubes. For example, the anode 13 can be obtained by blending Fe particles with graphite powder at a ratio of 3 to 40% by mass and compacting the powder into a predetermined shape (for example, a rod shape). In addition, as a material which comprises the cathode 14, the graphite (for example, rod-shaped thing) which does not contain a metal catalyst can be used.

By using the apparatus 10 having such a configuration, for example, a nanotube aggregate can be manufactured as follows. That is, the vacuum pump 21 is operated to depressurize the vacuum chamber 11. When the atmospheric pressure becomes a high vacuum of about 1.3 × 10 ⁻³ Pa, for example, a mixed gas G having a H2: Ar mixing ratio (volume ratio) in the range of 30:70 to 70:30 from the supply pipe 22 Supply. Arc discharge is generated in the H ₂ and Ar mixed gas atmosphere, and carbon is evaporated from the anode 13 by the arc heat. The evaporated carbon is deposited to form a deposit D containing a lot of carbon nanotubes. Typically, a deposit D in which single-walled carbon nanotubes are connected in a net shape (cobweb shape) is generated around the cathode 14. At this time, an arc discharge state is calculated by the control mechanism 32 from the voltage applied between the anode 13 and the cathode 14, and the control for adjusting the elevation and rotation of the cathode 14 according to the growth of the deposit D generated by the arc discharge is performed. The signal s can be output from the input / output circuit 33 to the motor 16.

Note that the arrangement of the anode 13 and the cathode 14 is not limited to a substantially linear arrangement as shown in FIG. 1 (that is, the angle formed by the anode 13 and the cathode 14 is approximately 180 °). For example, it can arrange | position so that the angle which the anode 13 and the cathode 14 make may become an acute angle (namely, 90 degrees or less, typically 5-75 degrees). When such an acute angle arrangement is employed, the angle formed between the anode 13 and the cathode 14 is preferably in the range of about 10 to 60 °, and more preferably in the range of about 20 to 45 °.
Although FIG. 1 shows a device 10 that applies a DC voltage, an AC voltage may be applied between the anode 13 and the cathode 14. In this case, it is preferable to use graphite mixed with a metal catalyst (Fe simple substance) for both the anode 13 and the cathode 14.

  Usually, the deposit D thus obtained contains an Fe catalyst and impurity carbon together with carbon nanotubes. In order to reduce this Fe catalyst and impurity carbon (purify the deposit D), the deposit D is heated (heat treatment) at a temperature of 670 to 720 K for 25 to 35 minutes, and then treated with hydrochloric acid ( Hydrochloric acid treatment). The apparatus for producing the aggregate of nanotubes can be configured such that a part (for example, heat treatment) or all of such purification means can be carried out.

  The filament according to the present invention can be used as a cathode (electron emission source) of various vacuum tubes. For example, the filament can be used as the cathode 32 of the bipolar vacuum tube 30 having the configuration shown in FIG. 2 and the triode vacuum tube 40 having the configuration shown in FIG. In that case, it can be used as either a directly heated cathode or an indirectly heated cathode. 2 and 3, reference numeral 34 represents an anode, and reference numeral 36 in FIG. 3 represents a grid.

  Moreover, the filament according to the present invention can be used as a filament of a light bulb. For example, the filament can be used as the filament 56 of the incandescent lamp 50 having the configuration shown in FIG. In addition, the code | symbol 52 in FIG. 4 has shown the translucent airtight container, such as a glass sphere. The inside of the container 52 may be a vacuum or may be filled with an inert gas (nitrogen, argon, etc.). Reference numeral 54 denotes an introduction line connected to both ends of the filament 56.

Hereinafter, experimental examples relating to the present invention will be described.
<Experimental Example 1: Production of nanotube aggregate and production of filament>
A nanotube aggregate was produced using the apparatus 10 having the configuration shown in FIG. As the anode (lower electrode) 13, a graphite rod (diameter 6 mm, length 75 mm) containing Fe as a metal catalyst (Fe particles having a particle size of 1 μm or less) at a rate of 1 at.% Was used. As the cathode (upper electrode) 14, a graphite rod (diameter 10 mm, length 100 mm) substantially free of a metal catalyst was used. The anode 13 and the cathode 14 were set so that the distance between the two electrodes was about 2 mm.
After evacuating the inside of the vacuum chamber 11, a mixed gas G of H ₂ : Ar = 40: 60 (volume ratio) is introduced into the vacuum chamber 11 from the supply pipe 22, and the atmospheric pressure is about 2.7 × 10 ⁴ Pa ( 200 Torr). A voltage of 30 V was applied between the anode 13 and the cathode 14 to generate arc discharge (DC current: 50 A), and the anode 13 was evaporated. This arc discharge was continued for about 3 minutes. As a result, a spider web-like (web-like, net-like) deposit D having a length of 30 cm or more was generated around the cathode 14 in the vacuum chamber 11. This deposit D (nanotube aggregate) was taken out from the vacuum chamber 11. Its mass was 23 mg. From this result, the production rate of the deposit D is calculated as 7.7 mg / min. Hereinafter, this deposit D, that is, an aggregate of nanotubes that has been generated (unpurified, not subjected to purification treatment) may be referred to as an “as-grown deposit”.

  The as-grown deposit obtained in this way could be easily handled using common tweezers. For example, I was able to grab a part and lift the whole. According to the observation result by a scanning electron microscope (SEM), this as-grown deposit was a collection of a large number of single-walled carbon nanotubes in a net shape. These nanotubes tended to be oriented in the direction of the distance from the tip of the cathode 14 (here, generally coincident with the length direction of the as-grown deposit). According to the evaluation results by SEM and energy dispersive X-ray analyzer (EDX), the proportion of carbon constituting single-walled carbon nanotubes in the as-grown deposit (that is, the purity of single-walled carbon nanotubes) is 70 at. That was all.

Filaments were produced using this as-grown deposit (nanotube aggregate). That is, the aggregate of nanotubes generated as described above was stretched in the direction in which the orientation of the nanotubes constituting the aggregate was high (the length direction of the as-grown deposit). Next, the stretched nanotube aggregate was folded in two so that both ends in the longitudinal direction were matched. Further, the folded nanotube aggregate was stretched in the same direction (highly oriented direction). By repeating the stretching and folding in this way, the aggregate of nanotubes was formed into a strip shape (belt shape) having a length of 22 mm, a width of 4 mm, and a thickness of 0.02 mm. These operations could be performed using general tweezers.
When the electrical characteristics of the obtained filament (molded article) were evaluated by the two-terminal method, a current of about 1.5 A was observed under the condition of a DC voltage of 40V. When the cross-sectional area of the filament was estimated to be about 8 × 10 ⁻⁴ cm ² , the current density was about 2 × 10 ³ A / cm ² and the resistivity was about 1 × 10 ⁻² Ωcm. Furthermore, the temperature dependence of the electrical resistance was evaluated by the four probe method (measurement current: 1 mA). The result is shown in FIG. This filament was able to withstand a tensile force of 1 N or more.

<Experimental Example 2: Production of Filament Using Purified Nanotube Assembly>
Experimental Example 2 is an example in which the as-grown deposit (aggregate of nanotubes) obtained in Experimental Example 1 was subjected to purification treatment and then molded (stretched and folded).
The as-grown sediment was purified as follows. That is, in the first process, the as-grown deposit was heated in air to 693 K for 30 minutes. In the second process, the aggregate of nanotubes obtained through the first process was immersed in 36% hydrochloric acid for 12 hours. Next, the yellow-green liquid (the Fe catalyst was dissolved) was removed from the aggregate of nanotubes by centrifugation. Furthermore, the nanotube aggregate was immersed in distilled water and then centrifuged twice, and the nanotube aggregate was immersed in ethanol and then centrifuged once. Then, ethanol adhering to the aggregate of nanotubes after centrifugation was evaporated on a 473K hot plate.
Filaments thus purified were molded to produce filaments. That is, stretching and folding were performed in the same manner as in Experimental Example 1 to produce (mold) a strip-shaped (belt-shaped, band-shaped) filament having a length of 10 mm, a width of 4 mm, and a thickness of 0.02 mm.

<Experimental Example 3: Characteristic Evaluation (1)>
The electrical characteristics of the filaments produced in Experimental Example 1 and Experimental Example 2 were evaluated.
That is, the filament was cut into an area of 2 to 3 mm ² and the periphery was adhered to a glass plate using an Ag-based conductive paste. A vacuum tube was constructed using this as an emitter (cathode). That is, the glass plate to which the filament was bonded was accommodated in a vacuum chamber, and the anode was disposed at a position of about 400 μm from the filament surface. The inside of the vacuum chamber was depressurized to about 8.8 × 10 ⁻⁸ Pa, and an emission current was measured by applying a voltage between the filament and the anode. The obtained current-voltage characteristics are shown in Table 1 and FIG. In FIG. 6, the characteristic curve labeled “untreated” corresponds to the filament prepared in Experimental Example 1, and the characteristic curve labeled “Purification” corresponds to the filament prepared in Experimental Example 2.

  As shown in Table 1 and FIG. 6, in the filaments according to Experimental Example 1 and Experimental Example 2, the emission current was detected under the condition that the anode voltage was 600 V (corresponding to an electric field strength of 1.5 V / μm) or less. In particular, in the filament according to Experimental Example 2, an emission current was detected under the condition of an anode voltage of 400 V (electric field strength of 1.0 V / μm) or less. In the filaments according to Experimental Example 1 and Experimental Example 2, both are 50 μA or more under the condition of an anode voltage of 800 V (electric field strength 2 V / μm) or less, and 200 μA under the condition of an anode voltage of 1000 V (electric field strength 2.5 V / μm) or less. The above emission current was obtained. In addition, when the state of emission was observed in detail, the filaments according to Experimental Example 1 and Experimental Example 2 both emitted strong electrons from the filament surface.

  Moreover, the voltage change at the time of constant current drive was evaluated about these filaments. That is, the applied voltage was controlled so that an emission current of 200 μA was obtained, and the change with time of the voltage was observed. The results are shown in Table 2 and FIG. In FIG. 7, the characteristic curve marked “untreated” corresponds to the filament produced in Experimental Example 1, and the characteristic curve marked “Purification” corresponds to the filament produced in Experimental Example 2. Compared with the filament according to Experimental Example 1, the filament according to Experimental Example 2 showed less voltage increase over time and exhibited more stable electrical characteristics (emission characteristics).

<Experimental Example 4: Characteristic Evaluation (2)>
Using the filament according to Experimental Example 1, a light bulb 50 having the structure shown in FIG. 4 was produced. The pressure in the container 52 was 1.0 × 10 ⁻⁴ Pa. The bulb 5 emitted strong incandescent light under the conditions of a voltage of 40V and a current of 1.5A. At this time, the temperature of the filament 56 in the brightest part was about 2673K.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

It is a schematic diagram which shows one structural example of the apparatus used for formation of a nanotube aggregate. It is a schematic diagram which illustrates the structure of a bipolar tube. It is a schematic diagram which illustrates the structure of a triode vacuum tube. It is a schematic diagram which illustrates the structure of a light bulb. It is a characteristic view which shows the temperature dependence of the electrical resistance of the filament which concerns on an experiment example. It is a characteristic view which shows the current-voltage characteristic of the filament which concerns on an experiment example. It is a characteristic view which shows the voltage change at the time of the constant current drive of the filament which concerns on an experiment example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Apparatus 11 Vacuum chamber 13 Anode 14 Cathode 30 Bipolar vacuum tube 32 Cathode (filament)
40 Triode vacuum tube 50 Light bulb 56 Filament

Claims (9)

The following steps:
Depositing carbon from the gas phase to form an aggregate of nanotubes in which a plurality of carbon nanotubes are aggregated in a net shape;
Stretching the nanotube aggregate; and
Superimposing the nanotube aggregates;
Wherein the stretching step is performed a plurality of times with the overlapping step interposed therebetween, and the stretching direction in the plurality of stretching steps is substantially the same direction, and the method for producing a filament using carbon nanotubes as a main component .   The method according to claim 1, wherein in the superimposing step, the nanotube aggregates are superimposed along an orientation of carbon nanotubes constituting the nanotube aggregates.   The method according to claim 1 or 2, wherein the carbon nanotubes constituting the nanotube aggregate are mainly single-walled carbon nanotubes.   The method according to any one of claims 1 to 3, wherein the stretching step and the overlapping step are performed on an aggregate of carbon nanotubes having a purity of 70 at.% Or more.   In the step of forming the nanotube aggregate, an arc discharge is generated between an anode and a cathode in which a metal catalyst is mixed with graphite to evaporate at least carbon from the anode, and the carbon is deposited to form the nanotube aggregate. The method according to any one of claims 1 to 4, wherein: The method according to any one of claims 1 to 5, wherein a filament having a length of 10 mm or more, a width of 2 mm or more, a thickness of 0.005 mm or more and a density of 0.3 g / cm ³ or more is formed.   A filament manufactured by the method according to any one of claims 1 to 6.   A vacuum tube comprising the filament according to claim 7.   A light bulb comprising the filament according to claim 7.

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