JP4325726B2 - Carbon nanotube aggregate and conductive film - Google Patents

Description

  The present invention relates to an aggregate of carbon nanotubes and a method for producing the same. Further, the present invention relates to a dispersion using a carbon nanotube aggregate, a transparent conductive film, and a field emission material.

  Carbon nanotubes were first widely reported in 1991. The carbon nanotubes have a shape that is substantially formed by winding one surface of graphite into a cylindrical shape. A single-walled carbon nanotube is a single-walled carbon nanotube, and a multi-walled carbon nanotube is a multi-walled carbon nanotube. Among multi-walled carbon nanotubes, those wound in two layers are called double-walled carbon nanotubes. Carbon nanotubes have excellent intrinsic conductivity and are expected to be used as conductive materials.

  Known methods for producing carbon nanotubes include arc discharge, laser evaporation, and chemical vapor deposition. Among these, catalytic chemical vapor deposition is known as a method for producing high-quality carbon nanotubes with few defects in a graphite layer at low cost. In the catalytic chemical vapor deposition method, a method in which a catalyst is supported on a carrier is known.

  In general, it is known that single-walled carbon nanotubes and double-walled carbon nanotubes with a small number of layers have high characteristics such as conductivity and thermal conductivity because they have a high graphite structure. However, since these carbon nanotubes are strong and have a very large bundle structure, the nano effect of each carbon nanotube cannot be exhibited, and it has been difficult to develop various applications. In particular, since it is very difficult to disperse in a resin or a solvent, the development of various uses is limited. In particular, it has been difficult to achieve practical performance using carbon nanotubes for applications such as transparent conductive films, molded products, and membranes.

Among multi-walled carbon nanotubes, 2-5 carbon nanotubes with a relatively small number of layers have both the properties of single-walled carbon nanotubes and the properties of multi-walled carbon nanotubes, and are therefore attracting attention as promising materials in various applications. Collecting. Among them, double-walled carbon nanotubes are considered to have the best characteristics, and several synthesis methods are known. Recently, Endo et al.'S method is known as a method for synthesizing a high-purity double-walled carbon nanotube (Non-Patent Documents 2, 3, 4, and Patent Document 1). In this method, an iron salt is arranged as a main catalyst and a molybdate is arranged as a sub-catalyst, and a carbon source is reacted to synthesize carbon nanotubes. The double-walled carbon nanotube obtained by this method has a high thermal stability with a combustion peak temperature of 717 ° C., and is understood to be a relatively high-quality double-walled carbon nanotube. In addition, as an application, an application as a field emitter used at a high current is described. However, such double-walled carbon nanotubes, like single-walled carbon nanotubes, form strong bundles due to the hydrophobic interaction between tubes and the interaction between π electrons, and the carbon nanotubes are highly dispersed. It was difficult to manufacture, and it was difficult to produce a transparent conductive film excellent in conductivity and transparency.
JP 2005-343726 A Nature, vol. 433, 476 (2005) Chemical Physics Letters, 414 (2005) 444-448. Journal of American Chemical Society, 128 (2006) 12636-12737

  This invention is made | formed in view of the above situations, and makes it a subject to obtain the carbon nanotube aggregate which can give the dispersion | distribution of a high concentration carbon nanotube aggregate by being excellent in a dispersibility. .

That is, this invention consists of the following structures.
1. A carbon nanotube aggregate that satisfies the following conditions (1) to (3).
(1) When observed with a transmission electron microscope, 50 or more of 100 carbon nanotubes
Includes double-walled carbon nanotubes
(2) The height ratio (G / D ratio) of G band and D band by Raman spectroscopic analysis at a wavelength of 532 nm is 30 or more.
(3) A mixture of 10 mg of a carbon nanotube aggregate, 30 mg of sodium polystyrene sulfonate and 10 mL of water was subjected to ultrasonic homogenization, followed by centrifugation at 20000 G, and then 9 mL of the supernatant was sampled. 1. Oxidation treatment was performed until the aggregate content was 0.6 mg / mL or more. 1. A dispersion obtained by dispersing the aggregate of carbon nanotubes in a dispersion medium.
3. A conductive film in which an aggregate of carbon nanotubes is applied on a substrate, the light transmittance is 85% or more, and the surface resistance value is less than 1 × 10 ⁵ Ω / □.
4). A powdery catalyst in which iron is supported on magnesia is present in the entire vertical cross-sectional direction of the reactor in the vertical reactor, and methane is circulated in the vertical direction in the vertical reactor. The manufacturing method of said carbon nanotube aggregate which makes it contact at -1200 degreeC, synthesize | combines a carbon nanotube aggregate, and performs an oxidation process after that.
5). A field emission material using the above carbon nanotube aggregate.

  According to the aggregate of carbon nanotubes of the present invention, it is possible to obtain a highly concentrated dispersion of carbon nanotube aggregates by being extremely excellent in dispersibility. Moreover, by using the dispersion containing the carbon nanotube aggregate of the present invention, a transparent conductive film having extremely excellent transparency and conductivity can be obtained. In particular, when a carbon nanotube aggregate including a double-walled carbon nanotube is used as the carbon nanotube aggregate, a transparent conductive film with higher conductivity and excellent permeability and a field emission material with excellent electron emission characteristics can be obtained. .

  The aggregate of carbon nanotubes of the present invention is very excellent in dispersibility as compared with the conventional aggregate of carbon nanotubes, and the aggregate of carbon nanotubes satisfying such dispersibility is appropriately identified by other methods. Therefore, it is specified by the dispersibility when dispersed under specific conditions.

  That is, in the present invention, a mixture of 10 mg of carbon nanotube aggregates, 30 mg of polystyrene sulfonate sodium and 10 mL of water was subjected to ultrasonic homogenization, followed by centrifugation at 20000 G, and then 9 mL of supernatant was sampled. The content of the carbon nanotube aggregates contained in is 0.6 mg / mL or more as an index of good dispersibility of the carbon nanotube aggregates.

  In the present invention, the aggregate of carbon nanotubes means an aggregate (aggregate) in which a plurality of carbon nanotubes exist, and the form of existence is not particularly limited, and each form is independent, bundled, or entangled Or you may exist in these mixed forms. Also, various layers and diameters may be included. In addition, if a plurality of carbon nanotubes are contained even in a composition in which a dispersion liquid or other components are blended or in a composite composite with other components, the carbon nanotube assembly It is understood that the body is included. Moreover, although the impurity (for example, catalyst) derived from a carbon nanotube manufacturing method may be included, the thing comprised substantially by carbon is shown.

  Sodium polystyrene sulfonate functions as a dispersant for the aggregate of carbon nanotubes. In the case of using an aqueous solution of sodium polystyrene sulfonate, the concentration can be taken into consideration so that the sodium polystyrene sulfonate is added to a solid weight of 30 mg, and the dispersion can be prepared to make a total of 10 mL of water. As a sodium polystyrene sulfonate used for this measurement, a commercially available average molecular weight of 200,000 ± 20,000 can be preferably used. Such sodium polystyrene sulfonate can be purchased from, for example, Aldrich.

  The ultrasonic homogenizer treatment uses an ultrasonic homogenizer and has an output of 25 W, 20 minutes under ice cooling, 10 mg of a carbon nanotube aggregate, 30 mg of sodium polystyrene sulfonate (weight average molecular weight 200,000, manufactured by Aldrich) and 10 mL of water. It shows that the mixture is dispersed. As the ultrasonic homogenizer, a commercially available ultrasonic homogenizer (for example, UH-600S manufactured by SMT Co., Ltd.) can be used. Centrifugation means performing a centrifugation operation at 20000 G for 15 minutes with a centrifuge. As the centrifugal separator, a commercially available centrifugal separator (for example, MX-300 manufactured by TOMY) can be used.

  Sampling of the supernatant is performed 30 minutes after the centrifugation operation. Since the carbon nanotube aggregate of the present invention has good dispersibility, when 9 mL of the supernatant is sampled after the above operation, the content of the carbon nanotube aggregate in the supernatant reaches 0.6 mg / mL or more. In preferred embodiments, 0.6 mg / mL to 1.0 mg / mL can be achieved. At this time, the aggregate amount of carbon nanotubes in the supernatant is measured as follows. That is, 9 mL of the supernatant was sampled and removed, and 1 mL of the liquid containing the remaining carbon nanotube aggregates was filtered, washed with water, and dried using a filter having a mesh with a pore size of 1 μm. Weigh. A value obtained by subtracting the weight of the remaining carbon nanotube aggregate from 10 mg corresponds to the weight of carbon nanotubes contained in 9 mL of the supernatant, and based on this, the content is converted into the content per mL. When the amount of carbon nanotube aggregates in the supernatant at this time is small, the carbon nanotube aggregates have poor dispersibility. If the dispersibility is poor, it is difficult to adjust the surface resistance when applying to a film because the concentration of carbon nanotube aggregates in the dispersion is dilute when the dispersion is subsequently used for various applications. In addition, the cost is a problem because the yield is low.

  The aggregate of carbon nanotubes of the present invention preferably contains multi-walled carbon nanotubes. In terms of transparent conductive properties, double-walled carbon nanotubes are more preferable, and when observed with a transmission electron microscope, it is preferable that 50 or more of 100 carbon nanotubes are double-walled carbon nanotubes. The number of double-walled carbon nanotubes in the aggregate of carbon nanotubes is more preferably 70 or more out of 100, and particularly preferably 75 or more. Although all may be double-walled carbon nanotubes, in reality, the upper limit of the number of double-walled carbon nanotubes is preferably 95 or less out of 100 from the viewpoint of physical properties and production efficiency.

  The number of double-walled carbon nanotubes in the aggregate of carbon nanotubes was observed with a transmission electron microscope at a magnification of 400,000, and 10% or more of the visual field area in the 75 nm square field of view was carbon nanotube aggregates. This can be done by evaluating the number of layers of 100 carbon nanotubes arbitrarily extracted from a certain visual field and confirming the number of double-walled carbon nanotubes. When 100 lines cannot be measured in one field of view, measurement is performed from a plurality of fields until 100 lines are obtained. At this time, one carbon nanotube is counted as one if a part of the carbon nanotube is visible in the field of view, and both ends are not necessarily visible. In addition, even if it is recognized as two in the field of view, it may be connected outside the field of view and become one, but in that case, it is counted as two.

Furthermore, it is preferable that the carbon nanotube aggregate of the present invention has fewer defects in the graphene sheet of carbon nanotubes because the quality is good and the conductivity is improved. The defect of this graphene sheet can be evaluated by Raman spectroscopy. There are various laser wavelengths used in the Raman spectroscopic analysis, but here, wavelengths of 532 nm and 633 nm are used. In the Raman spectrum, the Raman shift seen in the vicinity of 1590 cm ⁻¹ is called the G band derived from graphite, and the Raman shift seen in the vicinity of 1350 cm ⁻¹ is called the D band derived from defects in amorphous carbon or graphite. In order to measure the quality of the carbon nanotube aggregate, the height ratio (G / D ratio) of G band and D band by Raman spectroscopic analysis is used. A carbon nanotube aggregate having a higher G / D ratio has a higher degree of graphitization and higher quality. Here, when evaluating the Raman G / D ratio, a wavelength of 532 nm is used. The higher the G / D ratio, the better. However, if it is 30 or more, it can be said to be a high-quality carbon nanotube aggregate. The G / D ratio is preferably 40 or more and 200 or less, more preferably 50 or more and 150 or less. In addition, solid Raman spectroscopy such as aggregates of carbon nanotubes may vary depending on sampling. Therefore, at least three places and another place are subjected to Raman spectroscopic analysis, and an arithmetic average thereof is taken.

The aggregate of carbon nanotubes used in the present invention preferably further satisfies all the following three conditions.
-Peaks are observed at 140 ± 10 cm ⁻¹ , 160 ± 10 cm ⁻¹ , 180 ± 10 cm ⁻¹ , 270 ± 10 cm ⁻¹ and 320 ± 10 cm ⁻¹ by Raman spectroscopy at a wavelength of 532 nm;
A peak is observed at 220 ± 10 cm ⁻¹ by Raman spectroscopy at a wavelength of 633 nm;
-No peak is observed in the region of more than 190 cm ^{-1 to} less than 260 cm ^{-1 in} Raman spectroscopy at a wavelength of 532 nm.

Since the wave number of Raman spectroscopic analysis may fluctuate depending on the measurement conditions, the wave number specified here is specified in the range of wave number ± 10 cm ⁻¹ . In the above case, for example, when there is a peak at 150 cm ⁻¹ , it falls in both ranges of 140 ± 10 cm ⁻¹ and 160 ± 10 cm ⁻¹ . In such a case, it is considered that peaks exist in both the ranges of 140 ± 10 cm ⁻¹ and 160 ± 10 cm ⁻¹ . In addition, when the attribution of a peak is considered based on the correlation between the peak of the Raman spectrum and the diameter of the carbon nanotube in accordance with the subsequent idea, it may be interpreted as belonging to only one of the ranges in relation to the other peak. For example already 140 ± 10 cm there is a peak in the ^-1, further peak exists in 150 cm ^-1, 160 peak of 150 cm ^-1 if the ± 10 cm ^-1 peak does not exist other than the 150 cm ^-1 is 160 ± 10 cm ^- It can be interpreted as ^one peak. The same applies when there is a peak at 170 cm ⁻¹ .

The region of 150 to 350 cm ⁻¹ of the Raman spectrum is called RBM (radial breathing mode), and the peak observed in this region has the following correlation with the diameter of the carbon nanotube. Therefore, it is possible to estimate the diameter of the carbon nanotube from the peak observed in this region. When the diameter of the carbon nanotube is d (nm) and the Raman shift is υ (cm ⁻¹ ), d = 248 / υ holds. ^140cm -1 in Raman spectroscopic analysis of wavelength 532nm Considering ^{now, 160cm -1, 180cm -1, 270cm} -1, and a peak is observed in the 320 cm ^-1, respectively 1.77nm, 1.55nm, 1. The presence of carbon nanotubes with diameters of 38 nm, 0.92 nm, and 0.78 nm is shown. Similarly, the observation of a peak at 220 cm ⁻¹ by Raman spectroscopy at a wavelength of 633 nm indicates the presence of a carbon nanotube having a diameter of 1.13 nm. In general, the interlayer distance of the graphite of the double-walled carbon nanotube is about 0.34 nm, and the diameter difference between the inner layer and the outer layer of the double-walled carbon nanotube is estimated to be about 0.68 nm. The carbon nanotubes are double-walled carbon nanotubes having outer diameters of 1.77 nm, 1.55 nm, and 1.38 nm, respectively, and the inner layer diameter (ie, inner diameter) is 1.13 nm, 0.92 nm, And is estimated to be 0.78 nm. That is, preferred carbon nanotubes in the present invention are double-walled carbon nanotubes having a certain range in diameter distribution.

Moreover, the fact that no peak is observed from 190 cm ^{−1 to} less than 260 cm ^{−1 in} Raman spectroscopic analysis at a wavelength of 532 nm means that there is little or no single-walled carbon nanotube. Here, a peak from 190 cm ^-1 greater to less than 260 cm ^-1 is not observed, refers to the height of the peaks of more than 10% of the peak height of 270 ± 10 cm ^-1 in the range does not exist. Slight peaks may be observed or noise may be observed.

  One reason for the good dispersibility of the aggregate of carbon nanotubes of the present invention is considered to be that the diameter distribution has a certain width. If the diameters are uniform, the interaction between the carbon nanotubes also becomes strong, and it is presumed that the bundle is firmly formed and held. On the other hand, in the present invention, as shown by Raman spectroscopic analysis, since the carbon nanotubes have a certain diameter distribution, it is estimated that the interaction for forming and holding the bundle is relatively weak. Another reason is presumed that the average diameter of the carbon nanotubes is relatively large. The carbon nanotube of the present invention has a diameter larger than that of the single-walled carbon nanotube, and is relatively thick among the double-walled carbon nanotubes. For this reason, it is considered that the bundle is easily broken and the dispersibility is good.

The aggregate of carbon nanotubes of the present invention is extremely excellent in dispersibility, and can provide a film having both high transparency and high conductivity. That is, a carbon nanotube aggregate is made into a dispersion liquid by a specific method, applied to a substrate by a specific method, and the light transmittance and surface resistance value of the obtained transparent conductive film are measured. The dispersibility of the aggregate can be evaluated. From the carbon nanotube aggregate of the present invention, a transparent conductive film having a light transmittance of 85% or more and a surface resistance value of less than 1 × 10 ⁵ Ω / □ can be obtained. The transmittance of the conductive film is preferably such that the transmittance of the conductive film / the light transmittance of the transparent substrate> 0.85, and 0.99> the transmittance of the conductive film / the light transmittance of the transparent substrate. More preferably,> 0.90. The surface resistance of the conductive film is preferably less than 1 × 10 ⁴ Ω / □, more preferably 1 × 10 ² Ω / □ or more and less than 5 × 10 ³ Ω / □.

  A dispersion of carbon nanotube aggregates used for the measurement of the light transmittance and the surface resistance is prepared as follows. A mixture of 10 mg of a carbon nanotube aggregate, 30 mg of sodium polystyrene sulfonate (weight average molecular weight 200,000, manufactured by Aldrich) and 10 mL of water was dispersed using an ultrasonic homogenizer at an output of 25 W for 20 minutes under ice cooling, followed by After centrifugation at 20000 G for 15 minutes, 9 mL of the supernatant is sampled to prepare a dispersion. After 300 μL of methanol / water (weight ratio 1/1) was added to 300 μL of this dispersion as a wetting agent, polyethylene terephthalate (PET) film (“Lumirror (registered trademark) U36” manufactured by Toray Industries, Inc., 15 cm × 10 cm) After coating with a bar coater (No. 8, coating thickness: 12 μm), air drying, rinsing with distilled water, drying in a 60 ° C. drier for 2 minutes to immobilize the carbon nanotube aggregate on the film .

  The light transmittance of the conductive film is measured using a light source of 550 nm using a spectrophotometer. The conductivity of the conductive film is evaluated by measuring the surface resistance value of the film. The surface resistance value can be measured by, for example, Loresta EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.) using a four-terminal four-probe method according to JIS K7149 (established in December 1994). . In the case of measuring high resistance, for example, measurement can be performed using a Hirestar UP MCP-HT450 (manufactured by Dia Instruments, 10 V, 10 seconds).

  The aggregate of carbon nanotubes of the present invention can be used as a dispersion by being dispersed in a dispersion medium, a resin or the like. When the aggregate of carbon nanotubes is dispersed in a liquid dispersion medium, it may be called a dispersion.

  There is no restriction | limiting in particular in the adjustment method of a carbon nanotube dispersion. For example, when the dispersion medium is a solvent, the aggregate of carbon nanotubes, the dispersant, and the solvent are mixed using a known mixing and dispersing machine (eg, ball mill, bead mill, sand mill, roll mill, homogenizer, attritor, resolver, paint shaker, etc.). Mixing can produce a dispersion.

  The dispersion is preferably centrifuged or filtered before coating. By centrifuging the dispersion, undispersed carbon nanotubes, excess amount of dispersant, metal catalyst that may be mixed during the synthesis of carbon nanotubes, etc. precipitate, so if you collect the supernatant after centrifugation, Undispersed carbon nanotubes and impurities can be removed as precipitates. Thereby, reaggregation of the carbon nanotubes can be prevented, and the stability of the dispersion can be improved. Furthermore, depending on the conditions of centrifugation, fractionation can be performed according to the thickness and length of the carbon nanotubes, and the light transmittance of the resulting conductive film can be improved.

  The centrifugal force at the time of centrifugal separation may be a centrifugal force of 100 G or more, preferably 1000 G or more, more preferably 10,000 G or more. Although there is no restriction | limiting in particular as an upper limit, It is preferable that it is 200,000G or less from the performance of a general purpose ultracentrifuge.

  Moreover, the filter used for filter filtration can be suitably selected between 0.05 micrometer and 0.2 micrometer. Thereby, it is possible to remove undispersed carbon nanotubes and impurities having a relatively large size among impurities that may be mixed during synthesis of the carbon nanotubes.

  In the case of size fractionation, the dispersion is prepared so that the composition of the dispersion after size fractionation falls within the above range in anticipation of the amount of carbon nanotubes to be fractionated. Determination of the blending ratio of each component before size fractionation is a method of drying the precipitate after centrifugation and the fraction remaining on the filter, baking at 400 ° C. for 1 hour, weighing, and calculating the concentration Is done. As a result of such size fractionation, the carbon nanotubes can be separated according to the length, number of layers, other properties, presence or absence of a bundle structure, and the like.

  As the dispersant, a surfactant, various polymer materials, and the like can be used. The dispersant is useful for improving the dispersibility and dispersion stabilization ability of the carbon nanotube aggregate. Surfactants are classified into ionic surfactants and nonionic surfactants. In the present invention, any surfactant can be used. Examples of the surfactant include the following surfactants. Such surfactants can be used alone or in admixture of two or more.

  The ionic surfactant is classified into a cationic surfactant, an amphoteric surfactant and an anionic surfactant. Examples of the cationic surfactant include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkyl betaine surfactants and amine oxide surfactants. Examples of anionic surfactants include alkylbenzene sulfonates such as dodecylbenzene sulfonic acid, aromatic sulfonic acid surfactants such as dodecyl phenyl ether sulfonate, monosoap anionic surfactants, ether sulfate-based interfaces Examples thereof include an activator, a phosphate surfactant, and a carboxylic acid surfactant. Among them, those having an aromatic ring, that is, aromatic ionic surfactants are preferable because they are excellent in dispersibility, dispersion stability, and high concentration, and in particular, aromatics such as alkylbenzene sulfonate and dodecyl phenyl ether sulfonate. Group ionic surfactants are preferred.

  Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters, fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl , Polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, ether surfactants such as polyoxyethylene / polypropylene glycol, polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, poly Oxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl alkyl Aromatic anionic surfactants such as phenyl ether and the like. Of these, aromatic nonionic surfactants are preferred because of their excellent dispersibility, dispersion stability, and high concentration, and polyoxyethylene phenyl ether is particularly preferred.

  Examples of various polymer materials include water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, polystyrene sulfonate ammonium salt, polystyrene sulfonate sodium salt, carboxymethyl cellulose and its salts (sodium salt, ammonium salt, etc.), methyl cellulose, hydroxyethyl cellulose, and the like. Sugar polymers such as amylose, cycloamylose and chitosan. In addition, conductive polymers such as polythiophene, polyethylenedioxythiophene, polyisothianaphthene, polyaniline, polypyrrole, polyacetylene, and derivatives thereof can also be used. Of these, the use of water-soluble polymers such as polystyrene sulfonate ammonium salt and polystyrene sulfonate sodium salt is preferable because the conductive properties of the carbon nanotube aggregate can be efficiently exhibited.

  When water is used as a dispersion medium, it is most preferable to use a compound having a benzene ring and a hydrophilic group, such as polystyrene sulfonate ammonium salt and polystyrene sulfonate sodium salt, as the dispersant. This is because the benzene ring has a strong affinity for carbon nanotubes and the hydrophilic group has a strong affinity for water. As a result, the dispersant works effectively and disperses the carbon nanotubes in water. The hydrophilic group is preferably ionic. This is because the hydrophilic groups repel each other and the carbon nanotubes are separated from each other.

  The dispersion medium of the carbon nanotube aggregate is not particularly limited. An aqueous solvent may be sufficient and a non-aqueous solvent may be sufficient. Non-aqueous solvents include hydrocarbons (toluene, xylene, etc.), chlorine-containing hydrocarbons (methylene chloride, chloroform, chlorobenzene, etc.), ethers (dioxane, tetrahydrofuran, methyl cellosolve, etc.), ether alcohols (ethoxyethanol, methoxy) Ethoxyethanol, etc.), esters (methyl acetate, ethyl acetate, etc.), ketones (cyclohexanone, methyl ethyl ketone, etc.), alcohols (ethanol, isopropanol, phenol, etc.), lower carboxylic acids (acetic acid, etc.), amines (triethylamine, triethylamine, etc.) Methanolamine, etc.), nitrogen-containing polar solvents (N, N-dimethylformamide, nitromethane, N-methylpyrrolidone, etc.), sulfur compounds (dimethyl sulfoxide, etc.) and the like can be used.

  Among these, the dispersion medium is preferably a dispersion medium containing water, alcohol, toluene, acetone, ether, and a solvent obtained by combining them. When an aqueous solvent is required and when a binder is used as will be described later, and the binder is an inorganic polymer binder, polar solvents such as water, alcohols and amines are used. Moreover, when using a liquid thing at normal temperature as a binder so that it may mention later, itself can also be used as a dispersion medium.

  The preferable blending ratio of each component in the dispersion is as follows. The concentration of the carbon nanotube aggregate is preferably 0.01% by weight or more and 20% by weight or less, and more preferably 0.01 to 10% by weight.

  Although content of a dispersing agent is not specifically limited, Preferably, it is 0.01 to 50 weight%, More preferably, it is 0.01 to 30 weight%. The mixing ratio of the dispersant and the carbon nanotube aggregate is not particularly limited, but is preferably 0.1 to 20, more preferably 0.3 to 10 in terms of the weight ratio of the dispersant / carbon nanotube aggregate. In addition, since the aggregate of carbon nanotubes of the present invention is excellent in dispersibility, it is possible to once prepare a dispersion having a concentration higher than the desired carbon nanotube content, dilute with a solvent, and use it at a desired concentration.

  A conductive film can be formed by preparing such a dispersion of carbon nanotube aggregates and then applying the dispersion onto a substrate. The method of applying the carbon nanotube aggregate dispersion liquid is not particularly limited. Known application methods such as spray coating, dip coating, spin coating, knife coating, kiss coating, gravure coating, screen printing, ink jet printing, pad printing, other types of printing, or roll coating can be used. The application may be performed any number of times, and two different application methods may be combined. The most preferred application method is roll coating.

  The coating thickness (wet thickness) of the dispersion liquid also depends on the concentration of the coating liquid. Therefore, if the desired light transmittance and surface resistance value can be obtained, there is no need to define them, but the thickness may be 0.1 μm to 50 μm. preferable. More preferably, it is 1 μm to 20 μm.

  When an aqueous dispersion of carbon nanotube aggregates is applied on a substrate, a wetting agent may be added to the dispersion. In the case of applying to a non-hydrophilic substrate, it is possible to apply the dispersion without repelling the substrate by adding a wetting agent such as a surfactant or alcohol to the dispersion. As the wetting agent, alcohol is preferable, and methanol or ethanol is preferable among alcohols. Since lower alcohols such as methanol and ethanol have high volatility, they can be easily removed when the substrate is dried after coating. In some cases, a mixture of alcohol and water may be used.

  Thus, the conductive film which apply | coated the dispersion liquid of the carbon nanotube aggregate can remove an unnecessary dispersion medium by methods, such as air drying, a heating, and pressure reduction, after apply | coating a dispersion liquid to a base material. Thereby, the carbon nanotube aggregate forms a three-dimensional stitch structure and is fixed to the base material. Thereafter, the dispersant, which is a component in the liquid, is removed using an appropriate solvent. This operation facilitates the dispersion of charges and improves the conductivity of the transparent conductive film.

  The solvent for removing the dispersant is not particularly limited as long as it dissolves the dispersant, and may be an aqueous solvent or a non-aqueous solvent. Specifically, if it is an aqueous solvent, water, alcohols, and acetonitrile can be used, and if it is a non-aqueous solvent, chloroform, toluene and the like can be mentioned.

  It is also preferable to apply a dispersion containing carbon nanotube aggregates to a substrate as described above to form a transparent conductive film, and then overcoat the film with a binder material capable of forming an organic or inorganic transparent film. By overcoating, it is effective for further charge dispersion and movement.

  The transparent conductive film contains a binder material capable of forming an organic or inorganic transparent film in a dispersion containing an aggregate of carbon nanotubes, and is applied to a substrate and then heated as necessary to dry or bake the coating film. It can also be obtained by carrying out (curing). The heating conditions at that time are appropriately set according to the binder type. When the binder is photocurable or radiation curable, the coating film is cured by irradiating the coating film with light or radiation immediately after coating, not by heat curing. As the radiation, ionizing radiation such as electron beam, ultraviolet ray, X-ray and gamma ray can be used, and the irradiation dose is determined according to the binder type.

  The binder material is not particularly limited as long as it is used for conductive paints, and various organic and inorganic binders, that is, transparent organic polymers or precursors thereof (hereinafter sometimes referred to as “organic polymer binders”). Or an inorganic polymer or a precursor thereof (hereinafter sometimes referred to as “inorganic polymer binder”) can be used. The organic polymer binder may be thermoplastic, thermosetting, or radiation curable such as ultraviolet rays or electron beams. Examples of suitable organic binders include polyolefin (polyethylene, polypropylene, etc.), polyamide (nylon 6, nylon 11, nylon 66, nylon 6, 10, etc.), polyester (polyethylene terephthalate, polybutylene terephthalate, etc.), silicone resin, vinyl Resin (polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyacrylate, polystyrene derivatives, polyvinyl acetate, polyvinyl alcohol, etc.), polyketone, polyimide, polycarbonate, polysulfone, polyacetal, fluororesin, phenol resin, urea resin, melamine resin, Organic polymers such as epoxy resins, polyurethane, cellulose polymers, proteins (gelatin, casein, etc.), chitin, polypeptides, polysaccharides, polynucleotides, etc. Chromatography, as well as precursors of these polymers (monomer or oligomer). These can form transparent coatings or matrices simply by evaporation of the solvent, or by thermal curing or curing with light or radiation.

  The organic polymer binder is preferably a compound having an unsaturated bond that can be radically polymerized and cured by radiation or light. This is a monomer, oligomer, or polymer having a vinyl group or a vinylidene group. Examples of this type of monomer include styrene derivatives (such as styrene and methylstyrene), acrylic acid or methacrylic acid or derivatives thereof (such as alkyl acrylate or methacrylate, allyl acrylate or methacrylate), vinyl acetate, acrylonitrile, and itaconic acid. The oligomer or polymer is preferably a compound having a double bond in the main chain or a compound having acryloyl or methacryloyl groups at both ends of the straight chain. This type of radical polymerization curable binder has a high hardness, excellent scratch resistance, and can form a highly transparent film or matrix.

  Examples of inorganic polymer binders include sols of metal oxides such as silica, tin oxide, aluminum oxide and zirconium oxide, or hydrolyzable or thermally decomposable organometallic compounds (organophosphorus compounds, Organic boron compounds, organic silane compounds, organic titanium compounds, organic zirconium compounds, organic lead compounds, organic alkaline earth metal compounds, and the like. Specific examples of hydrolyzable or thermally decomposable organometallic compounds are alkoxides or partial hydrolysates thereof, lower carboxylates such as acetate, and metal complexes such as acetylacetone.

  When these inorganic polymer binders are baked, a glassy inorganic polymer transparent film or matrix made of an oxide or a composite oxide can be formed. The inorganic polymer matrix is generally glassy, has high hardness, excellent scratch resistance, and high transparency.

  The amount of the binder used may be an amount sufficient for overcoating, or an amount sufficient for obtaining a viscosity suitable for coating when mixed in a liquid. If the amount is too small, the coating will not be successful, and if it is too large, the conductivity will be hindered.

  As the dispersion medium used in the present invention, a solvent as described above is generally used. However, in the case of a photocurable or radiation curable organic polymer-based binder, by selecting a liquid binder at room temperature, there is no solvent. A dispersion of As a result, the solvent does not evaporate when the coating is cured and dried, the curing time is greatly shortened, and the solvent recovery operation is not required.

  The carbon nanotube aggregate dispersion of the present invention may contain additives such as a coupling agent, a cross-linking agent, a stabilizer, an anti-settling agent, a colorant, a charge adjusting agent, and a lubricant as necessary. it can.

  Moreover, the dispersion of the carbon nanotube aggregate of the present invention may further include a conductive organic material other than the carbon nanotube aggregate of the present invention, a conductive inorganic material, or a combination of these materials.

  Examples of conductive organic materials include buckyball, carbon black, fullerene, various carbon nanotubes, particles containing them, organic acids such as sulfonic acid, tetracyanoquinodimethane (TCNQ), trinitrofluorenone (TNF), chloranil The organic compound which has acceptor structures, such as, in a molecule | numerator can be used.

  Conductive inorganic materials include aluminum, antimony, beryllium, cadmium, chromium, cobalt, copper, doped metal oxide, iron, gold, lead, manganese, magnesium, mercury, metal oxide, nickel, platinum, silver, steel, Examples include titanium, zinc, and particles containing them. Preferable examples include indium tin oxide, antimony tin oxide, and mixtures thereof.

  Films obtained by containing or overcoating these conductive materials are very advantageous for charge dispersion or migration. Further, a layer containing a conductive material other than these carbon nanotube aggregates and a layer containing carbon nanotube aggregates may be laminated.

  The film used as the base material for the conductive film is not particularly limited. When transparency is required, a transparent film such as a PET film is preferred.

  The conductive film of the present invention can be used while being adhered to the base material, or can be peeled off from the base material and used as a self-supporting film. In order to produce a self-supporting film, for example, an organic polymer binder may be further applied on the transparent conductive film, and then the substrate may be peeled off. Moreover, the base material at the time of preparation can be burnt down or melted by thermal decomposition, and the transparent conductive film can be transferred to another base material. In that case, it is preferable that the thermal decomposition temperature of the base material at the time of preparation is lower than the thermal decomposition temperature of the transfer base material.

  The thickness of the conductive film of the present invention can take various ranges. For example, the conductive film of the present invention can be between about 0.5 nm and about 1000 μm thick. The thickness of the conductive film is preferably about 0.005 to about 1000 μm, more preferably about 0.05 to about 500 μm, more preferably about 1.0 to about 200 μm, and further preferably about 1.0 to about 50 μm. is there.

The conductive film of the present invention thus obtained is a conductive film in which aggregates of carbon nanotubes are laminated on a substrate, the light transmittance is 85% or more, and the surface resistance value is less than 1 × 10 ⁵ Ω / □. .

The transmittance of the conductive film is preferably such that the transmittance of the conductive film / the light transmittance of the transparent substrate> 0.85, and 0.99> the transmittance of the conductive film / the light transmittance of the transparent substrate. More preferably,> 0.90. The surface resistance of the conductive film is more preferably less than 1 × 10 ⁴ Ω / □, and more preferably 1 × 10 ² Ω / □ or more and less than 5 × 10 ³ Ω / □.

  In the present invention, a resin can be used as a dispersion medium, and a carbon nanotube aggregate can be dispersed to form a dispersion. At this time, there is no restriction | limiting in particular in resin to be used, Any of a thermoplastic resin and curable resin can be used. The thermoplastic resin refers to a resin that can be melt-molded by heating. Specific examples thereof include polyethylene resin, polypropylene resin, polystyrene resin, rubber-modified polystyrene resin, acrylonitrile-butadiene-styrene (ABS) resin, acrylonitrile-styrene (AS) resin, polymethyl methacrylate resin, acrylic resin, polyvinyl chloride resin. , Polyvinylidene chloride resin, polyethylene terephthalate resin, ethylene vinyl alcohol resin, cellulose acetate resin, ionomer resin, polyacrylonitrile resin, polyamide resin, polyacetal resin, polybutylene terephthalate resin, polylactic acid resin, polyphenylene ether resin, modified polyphenylene ether resin, Polycarbonate resin, polysulfone resin, polyphenylene sulfide resin, polyetherimide resin, polyethersulfone Resins, polyarylate resins, thermoplastic polyimide resins, polyamideimide resins, polyether ether ketone resin, polyketone resin, liquid crystal polyester resins, fluorine resins, syndiotactic polystyrene resin, cyclic polyolefin resin. These thermoplastic resins can be used alone or in combination of two or more. A curable resin is a resin that has been cured by means such as heating, radiation irradiation, or catalyst addition, and has characteristics that can be substantially insoluble and infusible. Specific examples include phenol resin, urea resin, melamine resin, benzoguanamine resin, alkyd resin, unsaturated polyester resin, vinyl ester resin, diallyl terephthalate resin, epoxy resin, silicone resin, urethane resin, furan resin, ketone resin, xylene. Examples thereof include resins and thermosetting polyimide resins. These curable resins can be used alone or in combination of two or more. In addition, when the main component of the resin is a thermoplastic resin, a small amount of curable resin may be added within a range that does not impair the properties of the thermoplastic resin. Conversely, when the main component is a curable resin, the properties of the curable resin It is also possible to add a small amount of a thermoplastic resin within a range not impairing the above.

  The amount of carbon nanotubes added to the resin is not particularly limited. Usually, it is 0.01 to 50% by weight, preferably 0.01 to 20% by weight, and more preferably 0.1 to 10% by weight. If the amount added is too large, the characteristics of the base resin may be lost, so the smaller the amount added, the better.

  There is no restriction | limiting in particular in the method to disperse | distribute a carbon nanotube in resin. Specific methods include dissolving the resin in a solvent, adding the carbon nanotubes in a resin solution, stirring and mixing and dispersing, then removing the solvent, and heating and melting the thermoplastic resin. A method of adding carbon nanotubes and dispersing them with a melt kneader such as a mixer, kneader, or extruder. In the case of a curable resin, the carbon nanotubes are added to the monomer or prepolymer before curing, and stirred and mixed to disperse. Then, any method may be used, such as a method of curing the resin, a method of adding the carbon nanotubes in the monomer, stirring and mixing and dispersing, and then polymerizing.

  The method for producing a carbon nanotube aggregate is not limited as long as a carbon nanotube aggregate that satisfies the conditions defined in the present invention can be obtained. For example, the following production method is exemplified.

  A powdery catalyst in which iron is supported on magnesia is present in the entire horizontal cross-sectional direction of the reactor in a vertical reactor, methane is circulated in the vertical direction in the reactor, and methane and the catalyst are mixed in 500 to 1200. After making the carbon nanotube aggregates contact at 0 ° C., the carbon nanotube aggregates are oxidized.

  By supporting iron on magnesia, the particle size of iron can be easily controlled, and sintering does not occur at high temperatures even when iron is present at a high density. Therefore, a high quality carbon tube can be efficiently synthesized in large quantities. Furthermore, since magnesia dissolves in an acidic aqueous solution, both the magnesia and iron can be removed simply by treating with an acidic aqueous solution, so that the purification process can be simplified.

As magnesia, a commercially available product may be used, or a synthesized product may be used. As a preferable production method of magnesia, magnesium metal is heated in air, magnesium hydroxide is heated to 850 ° C. or higher, and magnesium carbonate 3MgCO ₃ .Mg (OH) ₂ .3H ₂ O is heated to 950 ° C. or higher. There are methods.

  Among magnesias, light magnesia is preferable. Light magnesia is magnesia with low bulk density. The bulk density of light magnesia is preferably 0.20 g / mL or less, and more preferably 0.05 to 0.16 g / mL from the viewpoint of fluidity of the catalyst. The bulk density of the powder may be affected by the temperature and humidity at the time of measurement. The bulk density referred to here is a value measured at a temperature of 20 ± 10 ° C. and a humidity of 60 ± 10%.

  Iron supported on magnesia is not always in a zero-valent state. Although it can be estimated that the metal is in a zero-valent state during the reaction, it may be a compound containing iron or an iron species. For example, organic salts or inorganic salts such as iron formate, iron acetate, iron trifluoroacetate, iron iron citrate, iron nitrate, iron sulfate, and iron halide, complex salts such as ethylenediaminetetraacetic acid complex and acetylacetonate complex, etc. Used. Iron is preferably fine particles. The particle diameter of the fine particles is preferably 0.5 to 10 nm. When iron is a fine particle, a carbon nanotube with a small outer diameter is likely to be generated.

  The method for supporting iron on magnesia is not particularly limited. For example, magnesia is impregnated in a non-aqueous solution (for example, ethanol solution) or an aqueous solution in which an iron salt to be supported is dissolved, sufficiently dispersed and mixed by stirring, ultrasonic irradiation, or the like, and then dried (impregnation method). Further, iron may be supported on magnesia by heating at a high temperature (300 to 1000 ° C.) in a gas selected from air, oxygen, nitrogen, hydrogen, an inert gas, and a mixed gas thereof or in a vacuum.

  The larger the amount of iron supported, the higher the yield of carbon nanotubes. However, if the amount is too large, the particle diameter of iron increases, and the resulting carbon nanotubes become thick. When the amount of iron supported is small, the particle size of the supported iron becomes small and carbon nanotubes with a thin outer diameter can be obtained, but the yield tends to be low. The optimum iron loading varies depending on the pore volume, outer surface area, and loading method of magnesia, but it is preferable to load 0.1 to 20% by weight of iron with respect to magnesia, particularly 0.2 to 10% by weight. It is preferable that

  Thus obtained magnesia carrying iron is charged into a vertical reactor. The reactor is preferably heat resistant and is preferably made of a heat resistant material such as quartz or alumina.

  Here, the vertical reactor has a reactor installed in a vertical direction (hereinafter sometimes referred to as “longitudinal direction”), and is directed from one end of the reactor toward the other end. Is provided with a mechanism that allows methane to circulate and circulate in such a manner that methane passes through the catalyst layer formed by the catalyst for producing a carbon nanotube aggregate. As the reactor, for example, a reactor having a tube shape can be preferably used. In the above, the vertical direction includes a direction having a slight inclination angle with respect to the vertical direction (for example, 90 ° ± 15 °, preferably 90 ° ± 10 ° with respect to the horizontal plane). The vertical direction is preferable. Note that the methane supply section and the discharge section do not necessarily have to be end portions of the reactor, and methane may flow in the above-described direction and pass through the catalyst layer in the flow process.

  The catalyst is preferably present on the entire surface in the horizontal cross-section direction of the reactor in the vertical reactor. By doing in this way, a catalyst and methane can be made to contact effectively. In the case of a horizontal reactor, in order to obtain such a state, it is necessary to sandwich the catalyst from the left and right because of the gravitational force. However, in the case of the carbon nanotube aggregate formation reaction, the carbon nanotube aggregate is generated on the catalyst as the reaction proceeds, and the volume of the catalyst is increased. Therefore, the method of sandwiching the catalyst from the left and right is not preferable. By placing the reactor vertically and placing a stage through which gas can permeate in the reactor, and placing the catalyst on it, the catalyst exists uniformly in the cross section of the reactor without sandwiching the catalyst from both sides. Can be made. In the case of horizontal reactors such as those described in Non-Patent Documents 2, 3, 4, and Patent Document 1, since the raw material gas contacts only the surface of the catalyst, carbon nanotubes are not generated inside the catalyst. As for each catalyst particle, the portion where the gas contacts is limited, so that the region where the carbon nanotube grows becomes narrow. That is, since carbon nanotubes grow densely, a thick bundle is immediately formed and dispersibility is considered to be poor. Further, since the inside of the catalyst is hardly in contact with the raw material gas, there is a problem that the yield of carbon nanotubes is extremely reduced. In the case of a vertical reactor, since the raw material gas uniformly contacts the entire catalyst, it is considered that the aggregate of carbon nanotubes grows even on the catalyst particles, and the carbon nanotubes having a fine bundle and extremely excellent dispersibility are obtained. Presumed to be obtained. Here, the state where the catalyst is present in the entire horizontal cross-sectional direction of the vertical reactor refers to a state where the catalyst spreads over the entire horizontal cross-sectional direction and the bottom of the catalyst cannot be seen. As a preferable embodiment in such a state, for example, there are the following modes.

  A. A stage (ceramic filter or the like) on which a gas permeable catalyst is placed in the reactor, and the catalyst is filled therewith to a predetermined thickness. The upper and lower sides of the catalyst layer may be slightly uneven (FIG. 1 (a)). FIG. 1A is a conceptual diagram showing a state in which a stand 2 on which a catalyst is placed is installed in a reactor 1 and a catalyst 3 is present on the entire horizontal cross-sectional direction of the reactor.

  B. An object (filler) other than the catalyst and the catalyst are mixed and filled on the table on which the catalyst similar to A is placed. The catalyst layer is preferably uniform, but the upper and lower sides may be somewhat uneven (FIG. 1 (b)). FIG. 1 (b) is a conceptual diagram showing a state in which a platform 2 on which a catalyst is placed is installed in the reactor 1, and a mixture 4 of an object other than the catalyst and the catalyst exists on the entire cross-sectional direction of the reactor. It is.

  C. The catalyst is dropped from the upper part of the reactor by spraying or the like, and the catalyst powder is uniformly present in the horizontal cross-sectional direction of the reactor through the gas (FIG. 1 (c)). FIG. 1C is a conceptual diagram showing a catalyst state in which the catalyst 5 sprayed from the upper part of the reactor 1 spreads over the entire horizontal cross-sectional direction of the reactor.

  The vertical reactor may be a fluidized bed type or a fixed bed type. Examples of the fluidized bed type include a mode in which the catalyst as described above C is dropped from the upper part of the reactor by spraying, and a mode in which a catalyst generally referred to as a boiling bed type flows (method according to the above A and B). Examples of the fixed bed type include the above-described aspects A and B.

  In the fluidized bed type, continuous synthesis is possible by continuously supplying the catalyst and continuously taking out the aggregate containing the catalyst and the aggregate of carbon nanotubes after the reaction. It can be obtained and is preferable. In the present invention, magnesia is used as a catalyst carrier, but magnesia has very good fluidity due to its particle characteristics (specific gravity, bulk density, surface charge, etc.), and in particular, a carbon nanotube aggregate is synthesized in a fluidized bed reactor. Suitable for doing. When a magnesia support is used as a catalyst, when carbon nanotube aggregates are synthesized in a fluidized bed type, long carbon nanotubes are likely to be generated because the fluidized state is good. The long carbon nanotubes defined here are carbon nanotubes having an average length of 1 μm or more. Since fluidity is good in fluidized bed type reaction, carbon nanotube synthesis reaction is performed uniformly so that the raw material methane and catalyst are in uniform and efficient contact, and catalyst covering by impurities such as amorphous carbon is suppressed, and catalytic activity It is considered that such a long carbon nanotube can be obtained because of a long duration.

  By passing methane from the lower part or the upper part of the catalyst layer installed in the reactor, contacting with the catalyst, and reacting, a carbon nanotube aggregate is generated.

  500-1200 degreeC is preferable, as for the temperature which a catalyst and methane are made to contact, 600-950 degreeC is more preferable, More preferably, it is the range of 700 degreeC-900 degreeC. When the temperature is lower than 500 ° C., the yield of the carbon nanotube aggregate is deteriorated. On the other hand, when the temperature is higher than 1200 ° C., the material of the reactor to be used is restricted, and bonding between the carbon nanotubes starts, making it difficult to control the shape of the carbon nanotubes. The reactor may be brought to the reaction temperature while contacting methane, or the supply of methane may be started after the reactor is brought to the reaction temperature after completion of the pretreatment by heat.

  Prior to the reaction for generating the carbon nanotube aggregate, the catalyst may be pretreated with heat. The pretreatment time by heat is not particularly limited. However, if it is too long, metal agglomeration occurs on magnesia, and carbon nanotubes with a large outer diameter may be formed accordingly, and therefore, it is preferably within 120 minutes. The temperature of the pretreatment may be equal to or lower than the reaction temperature as long as the catalytic activity is exhibited, or may be equal to or higher than the reaction temperature. By performing the pretreatment with heat, the catalyst may be brought into a more active state.

  The heat pretreatment and the reaction for generating the carbon nanotube aggregate are preferably performed under reduced pressure or atmospheric pressure.

  When the contact between the catalyst and methane is performed under reduced pressure, the reaction system can be decompressed with a vacuum pump or the like. Moreover, when performing a pretreatment and reaction at atmospheric pressure, you may make it contact with a catalyst as a mixed gas which mixed methane and dilution gas.

  The diluent gas is not particularly limited, but a gas other than oxygen gas is preferably used. Oxygen is not usually used because it may explode, but it may be used if it is outside the explosion range. Nitrogen, argon, hydrogen, helium, etc. are preferably used as the dilution gas. These gases are effective for controlling the linear velocity and concentration of methane and as a carrier gas. Hydrogen is preferable because it is effective in activating the catalytic metal. A gas having a high molecular weight such as argon has a large annealing effect and is preferable for the purpose of annealing. Nitrogen and argon are particularly preferable.

  The aggregate of carbon nanotubes produced by the production process as described above contains impurities such as single-walled carbon nanotubes and amorphous carbon in addition to the double-walled carbon nanotubes. In the production of the carbon nanotube aggregate of the present invention, the carbon nanotube aggregate produced as described above is subjected to an oxidation treatment. The oxidation treatment of the carbon nanotube aggregate is performed by a firing method, a method using an oxidizing agent, or the like. By performing such an oxidation treatment, it is possible to selectively remove impurities such as amorphous carbon and single-walled CNTs having low heat resistance in the product, and the purity of the double-walled carbon nanotube can be improved. .

  When performing the baking treatment as the oxidation treatment, the oxidation temperature is affected by the atmospheric gas. Therefore, the baking treatment is preferably performed at a relatively low temperature when the oxygen concentration is high and at a relatively high temperature when the oxygen concentration is low. When the firing treatment is performed in the air, the firing treatment is preferably performed within the range of the combustion peak temperature of the carbon nanotube aggregate ± 50 ° C. Even if the firing treatment is performed at a combustion peak of less than −50 ° C., impurities and single-walled carbon nanotubes are not removed and the purity of the double-walled carbon nanotubes is not improved. Further, when the baking treatment is performed at the combustion peak temperature + 50 ° C. or higher, even the double-walled carbon nanotube disappears. Therefore, it is preferable to fire near the combustion peak temperature of the carbon nanotube aggregate. More preferably, it is a range of combustion peak temperature ± 15 ° C. When performing a baking process in air | atmosphere, it is preferable to select the temperature of a baking process in the range of 300-1000 degreeC, and 400-600 degreeC is more preferable. When the oxygen concentration is higher than the atmosphere, a lower temperature range is selected, and when the oxygen concentration is lower than the atmosphere, a higher temperature range is selected.

  The combustion peak temperature of the carbon nanotube aggregate can be measured by thermal analysis. About 10 mg of a sample is placed in a differential thermal analyzer (for example, DTG-60 manufactured by Shimadzu Corporation), and the temperature is increased from room temperature to 900 ° C. at a temperature increase rate of 10 ° C./min. At that time, it is possible to determine the exothermic peak temperature during combustion of the sample.

  The reaction conditions can be adjusted by, for example, lengthening the firing time when the firing temperature is low and shortening the firing time when the firing temperature is high. Therefore, the firing time is not particularly limited as long as the carbon nanotube of the present invention is obtained. The firing time is preferably 5 minutes to 24 hours, more preferably 10 minutes to 12 hours, and even more preferably 30 minutes to 5 hours. Firing is preferably performed in the air, but may be performed in an oxygen / inert gas with a controlled oxygen concentration. The oxygen concentration at this time is not particularly limited. Oxygen may be appropriately set in the range of 0.1% to 100%. As the inert gas, helium, nitrogen, argon or the like is used.

  The oxidation treatment can also be performed by a method in which oxygen or a mixed gas containing oxygen is intermittently brought into contact with the carbon nanotubes to perform the firing treatment. When firing is performed by intermittently contacting oxygen or a mixed gas containing oxygen, the treatment can be performed at a relatively high temperature. This is because, since oxygen or a mixed gas containing oxygen is intermittently flowed, even if oxidation occurs, the reaction stops immediately when oxygen is consumed. When the baking treatment is performed in the air, the temperature range is preferably about 500 to 1200 ° C, more preferably about 600 to 950 ° C. As described above, the temperature is about 500 to 1200 ° C. during the production of carbon nanotubes. Therefore, when the firing process is performed immediately after the production of the carbon nanotube, it is preferable to perform such an intermittent firing process.

  As an oxidation treatment of carbon nanotubes, when an oxidizing agent is used, a method of treating with hydrogen peroxide or a mixed acid can be used.

  When carbon nanotubes are treated with hydrogen peroxide, the carbon nanotubes are mixed in, for example, 34.5% hydrogen peroxide water so as to be 0.01 wt% to 10 wt%, and at a temperature of 0 to 100 ° C. The reaction is carried out for 0.5 to 48 hours.

  When the carbon nanotubes are treated with a mixed acid, the carbon nanotubes are mixed in, for example, a concentrated sulfuric acid / concentrated nitric acid (3/1) mixed solution so as to be 0.01% by weight to 10% by weight. The reaction is carried out at temperature for 0.5 to 48 hours. As the mixing ratio of the mixed acid, the ratio of concentrated sulfuric acid / concentrated nitric acid can be set to 1/10 to 10/1 according to the amount of single-walled carbon nanotubes in the produced carbon nanotubes.

  Moreover, you may process with a basic compound after carrying out the said mixed acid process. By treating with a basic compound, the residual mixed acid can be reduced. Furthermore, by treating with a basic compound, it is considered that acidic groups such as carboxyl groups that are considered to be generated in impurities such as amorphous carbon are salified and separation of the impurities and carbon nanotubes is improved. That is, the water solubility of the impurity increases, and the carbon nanotube and the impurity can be easily separated by filtration. The basic compound is not particularly limited, but inorganic alkali salts such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium hydrogen carbonate, methylamine, ethylamine, propylamine, dimethylamine, diethylamine, dipropylamine, Amines such as ammonia and ammonium hydroxide are preferred. Of these, lower amines having 10 or less carbon atoms such as methylamine, ethylamine, propylamine, dimethylamine, diethylamine, and dipropylamine are more preferable, ethylamine or propylamine is more preferable, and propylamine is most preferable.

  These oxidation treatments may be performed immediately after the synthesis of the carbon nanotube aggregate or after another purification treatment. For example, when iron / magnesia is used as a catalyst, after the calcination treatment, a purification treatment for removing the catalyst may be performed with an acid such as hydrochloric acid, or a purification treatment for removing the catalyst with an acid such as hydrochloric acid may be performed first. After performing, you may oxidize.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

  In the examples, various physical properties were evaluated by the following methods.

[Thermal analysis]
About 10 mg of the sample was placed in a differential thermal analyzer (DTG-60 manufactured by Shimadzu Corporation), and the temperature was increased from room temperature to 900 ° C. at a temperature increase rate of 10 ° C./min. The combustion peak temperature due to heat generation was read from the DTA curve at that time.

[Raman spectroscopy]
A powder sample was placed in a resonance Raman spectrometer (INF-300 manufactured by Horiba Joban Yvon), and measurement was performed using a laser wavelength of 532 nm or 633 nm. When measuring the G / D ratio, analysis was performed on three different locations of the sample, and the arithmetic average was obtained.

[High-resolution transmission electron micrograph]
1 mg of the carbon nanotube aggregate was placed in 1 mL of ethanol, and dispersion treatment was performed using an ultrasonic bath for about 15 minutes. A few drops of the dispersed sample were dropped on the grid and dried. The grid thus coated with the sample was placed in a transmission electron microscope (JEM-2100 manufactured by JEOL Ltd.) and measured. The measurement magnification is 50,000 times to 500,000 times. The acceleration voltage is 120 kV.

[Scanning electron micrograph]
1 mg of the carbon nanotube aggregate was placed in 1 mL of ethanol, and dispersion treatment was performed using an ultrasonic bath for about 15 minutes. A few drops of the dispersed sample were dropped on the grid and dried. Thus, the grid with which the sample was apply | coated was installed in the scanning electron microscope (JEOL Co., Ltd. JSM-6301NF), and the measurement was performed. The measurement magnification is 1000 times to 60,000 times. The acceleration voltage is 5 kV.

[Transparent conductive film production]
After adding 300 μL of methanol / water (weight ratio 1/1) as a wetting agent to 300 μL of the carbon nanotube aggregate dispersion liquid, on a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc. (Lumirror (registered trademark) U36)) This was coated using a bar coater (No. 8, coating thickness 12 μm), air-dried, rinsed with distilled water, and dried in a 60 ° C. dryer for 2 minutes to immobilize the carbon nanotube aggregate.

[Light transmittance measurement]
For light transmittance, a carbon nanotube aggregate-coated film was loaded into a spectrophotometer (Hitachi U-2100), and the light transmittance at a wavelength of 550 nm was measured.

[Surface resistance measurement]
The surface resistance value was measured using a 4-terminal 4-probe method according to JIS K7149 (established in December 1994) and Loresta EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.). When measuring high resistance, it was measured using Hiresta UP MCP-HT450 (manufactured by Dia Instruments, 10 V, 10 seconds).

<Example 1>
(Support of metal salt on light magnesia)
5 g of ammonium iron citrate (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 250 mL of methanol (manufactured by Kanto Chemical Co., Inc.). To this solution, 50 g of light magnesia (manufactured by Wako Pure Chemical Industries, Ltd., bulk density was 0.16 g / mL) was added, treated with an ultrasonic cleaner for 60 minutes, and dried with stirring at 40 ° C. to 60 ° C. Then, methanol was removed to obtain a solid catalyst in which a metal salt was supported on light magnesia powder.

(Synthesis of double-walled carbon nanotube)
Carbon nanotubes were synthesized in the vertical reactor shown in FIG.

  The reactor 100 is a cylindrical quartz tube having an inner diameter of 32 mm and a length of 1200 mm. A quartz sintered plate 101 is provided at the center, an inert gas and raw material gas supply line 104 at the lower part of the quartz tube, a waste gas line 105 at the upper part, a sealed catalyst feeder 102 and a catalyst charging line 103. It has. In addition, a heater 106 is provided that surrounds the circumference of the reactor so that the reactor can be maintained at an arbitrary temperature. The heater 106 is provided with an inspection port 107 so that the flow state in the apparatus can be confirmed.

  12 g of the catalyst was taken, and the catalyst was set on the quartz sintered plate 101 through the catalyst charging line 103. Next, supply of nitrogen gas from the source gas supply line 104 was started at 1000 mL / min. After the inside of the reactor was placed in a nitrogen gas atmosphere, the temperature was heated to 900 ° C. (temperature rising time 30 minutes).

  After reaching 900 ° C., the temperature was maintained, the nitrogen flow rate of the raw material gas supply line 104 was increased to 2000 mL / min, and fluidization of the solid catalyst on the quartz sintered plate was started. After confirming fluidization from the heating furnace inspection port 107, supply of methane to the reactor at 95 mL / min (methane concentration 4.5 vol%) was started. After supplying the mixed gas for 30 minutes, the flow was switched to a flow of only nitrogen gas, and the synthesis was terminated.

  The heating was stopped and the mixture was allowed to stand at room temperature. After reaching room temperature, the composition containing the catalyst and the aggregate of carbon nanotubes was taken out from the reactor. The above operation was repeated, and the obtained carbon nanotube aggregate was subjected to the following steps.

  The obtained carbon nanotube aggregate was subjected to thermal analysis by the method described above. The combustion peak temperature was 511 ° C.

(Baking and refining of carbon nanotube aggregates)
30 g of the carbon nanotube aggregate was placed in a magnetic dish (150φ), heated in a muffle furnace (FP41, manufactured by Yamato Kagaku Co., Ltd.) in the atmosphere to 500 ° C. over 1 hour, held for 60 minutes, and then allowed to cool naturally. Furthermore, in order to remove the catalyst from the carbon nanotube, a purification treatment was performed as follows. Carbon nanotubes were added to a 6N hydrochloric acid aqueous solution and stirred in an 80 ° C. water bath for 2 hours. The recovered material obtained by filtration using a filter having a pore size of 1 μm was further added to a 6N hydrochloric acid aqueous solution and stirred in an 80 ° C. water bath for 1 hour. This was filtered using a filter having a pore diameter of 1 μm, washed with water several times, and then the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and metal, and the carbon nanotubes could be purified.

(High-resolution transmission electron microscope analysis of carbon nanotube aggregates)
When the aggregate of carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, as shown in FIG. 3, the carbon nanotubes were composed of clean graphite layers, and the number of the carbon nanotubes was two. Was observed. Two-layer carbon nanotubes accounted for 90% or more (91) of 100 carbon nanotubes.

(Resonance Raman spectroscopic analysis of carbon nanotube aggregates)
The aggregate of carbon nanotubes obtained as described above was subjected to Raman spectroscopic measurement. As a result, as shown in FIG. 4, ^141cm -1 in a Raman spectroscopic analysis of wavelength ^{532nm, 155cm -1, 172cm -1,} 261cm -1, are observed peak 330 cm ^-1, further wavelength 633nm in Raman spectroscopic analysis A peak was observed at 211 cm ⁻¹ . Note that no peak was observed in the region of more than 190 cm ^{−1 to} less than 260 cm ^{−1 in} Raman spectroscopic analysis at a wavelength of 532 nm. Further, the G / D ratio was 75 (532 nm), which was found to be a high-quality double-walled carbon nanotube having a high degree of graphitization.

(Preparation of carbon nanotube aggregate dispersion)
Weigh 10 mg of the carbon nanotube aggregate and 100 mg of polystyrene sulfonate aqueous solution (Aldrich, 30 wt%, weight average molecular weight 200,000) in a 50 mL container, add 9.93 mL of distilled water, and output an ultrasonic homogenizer of 25 W. Then, the dispersion treatment was carried out for 20 minutes under ice cooling to prepare a carbon nanotube aggregate dispersion. Aggregates could not be visually confirmed in the prepared liquid, and the carbon nanotube aggregates were well dispersed. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. 1 mL of the remaining liquid at this time was filtered using a filter having a pore diameter of 1 μm, and then the well-washed filtrate was dried with a 120 ° C. dryer. The weight of the filtrate was measured and found to be 3.9 mg. Therefore, it was found that 6.1 mg (0.68 mg / mL) of carbon nanotube aggregates were dispersed in the supernatant.

Using the carbon nanotube aggregate dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film is 1.7 × 10 ³ Ω / □, and the light transmittance is 85% (transparent conductive film 85% / PET film 90.7% = 0.94). It showed high conductivity and transparency.

<Example 2>
(Support of metal salt on light magnesia)
In the same manner as in Example 1, a solid catalyst was obtained.

(Synthesis of double-walled carbon nanotube)
On a silica / alumina non-woven fabric, 8.0 g of the solid catalyst prepared above was taken and heated to 870 ° C. A quartz tube with an inner diameter of 250 mm installed in the vertical direction in the vertical reactor was installed in the vertical direction of the reactor. The vertical reactor was introduced into the center of the reaction tube. Argon gas was supplied from the bottom of the quartz tube reactor toward the top of the quartz tube reactor at 50 L / min for 5 minutes and circulated so as to pass through the catalyst layer. The mixture was introduced at 0 L / min for 30 minutes and vented so as to pass through the catalyst layer, and both were brought into contact and reacted. After the introduction of methane gas was stopped and argon gas was flowed at 50 L / min for 1 minute, the composition containing the carbon nanotube aggregate was taken out and cooled to room temperature. The above operation was repeated, and the obtained carbon nanotube aggregate was subjected to the following steps.

  The obtained carbon nanotube aggregate was subjected to thermal analysis by the method described above. The combustion peak temperature was 510 ° C.

(Baking and refining of carbon nanotube aggregates)
After taking 30g of carbon nanotube aggregates in a magnetic dish (150φ), heating in a muffle furnace (Yamato Scientific Co., Ltd., FP41) in the air to 500 ° C in 1 hour, holding for 60 minutes, It was allowed to cool naturally. Furthermore, in order to remove the catalyst from the carbon nanotube, a purification treatment was performed as follows. Carbon nanotubes were added to a 6N aqueous hydrochloric acid solution and stirred at room temperature for 1 hour. The recovered product obtained by filtration using a filter having a pore diameter of 1 μm was further added to a 6N aqueous hydrochloric acid solution, and stirred at room temperature for 1 hour. This was filtered using a filter having a pore diameter of 1 μm, washed with water several times, and then the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and metal, and the carbon nanotubes could be purified.

(High-resolution transmission electron microscope analysis of carbon nanotube aggregates)
When the aggregate of carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, as shown in FIG. 5, the carbon nanotubes were composed of a clean graphite layer, and the number of the carbon nanotubes was two. Was observed. Further, 90% or more (90) of 100 carbon nanotubes were occupied by the two-layer carbon nanotubes.

(Resonance Raman spectroscopic analysis of carbon nanotube aggregates)
The aggregate of carbon nanotubes obtained as described above was subjected to Raman spectroscopic measurement. As a result, as shown in FIG. 6, ^146cm -1 in a Raman spectroscopic analysis of wavelength ^{532nm, 165cm -1, 181cm -1,} 263cm -1, is observed peaks 312Cm ^-1, further wavelength 633nm in Raman spectroscopic analysis A peak was observed at 216 cm ⁻¹ . Note that no peak was observed in the region of more than 190 cm ^{−1 to} less than 260 cm ^{−1 in} Raman spectroscopic analysis at a wavelength of 532 nm. In addition, the G / D ratio was 46 (532 nm), which was found to be a high-quality double-walled carbon nanotube having a high degree of graphitization.

(Preparation of carbon nanotube aggregate dispersion)
Weigh 10 mg of the carbon nanotube aggregate and 100 mg of polystyrene sulfonate aqueous solution (Aldrich, 30 wt%, weight average molecular weight 200,000) in a 50 mL container, add 9.93 mL of distilled water, and output an ultrasonic homogenizer of 25 W. Then, the dispersion treatment was carried out for 20 minutes under ice cooling to prepare a carbon nanotube aggregate dispersion. Aggregates could not be visually confirmed in the prepared liquid, and the carbon nanotube aggregates were well dispersed. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. 1 mL of the remaining liquid at this time was filtered using a filter having a pore diameter of 1 μm, and then the well-washed filtrate was dried with a 120 ° C. dryer. The weight of the filtrate was measured and found to be 1.0 mg. Therefore, it was found that 9.0 mg (1.00 mg / mL) of the carbon nanotube aggregate was dispersed in the supernatant.

Using the carbon nanotube aggregate dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film is 1.1 × 10 ³ Ω / □, and the light transmittance is 85% (transparent conductive film 85% / PET film 90.7% = 0.94). It showed high conductivity and transparency.

<Example 3>
(Creation of field electron emission source)
In a 100 mL beaker, 50 mg of carbon nanotubes from which the catalyst obtained in Example 1 had been removed and 100 mL of acetone were added, and ultrasonic waves were applied for 30 minutes to obtain a dispersion. The dispersion was placed in a beaker containing a copper plate, and allowed to stand to spontaneously evaporate acetone, thereby obtaining a copper plate having carbon nanotubes deposited on the surface.

(Evaluation of field electron emission ability)
The obtained copper plate can be used as a cathode of a field emission element. A copper plate having carbon nanotubes deposited on the surface is used as a cathode electrode, and another copper plate is used as an anode electrode, and is arranged to face the cathode electrode. This diode structure can be introduced into an evaluation chamber to evaluate the field electron emission ability. The carbon nanotubes obtained in this example can be expected to show good field electron emission ability.

< Reference Example 1 >
(Support of metal salt on light magnesia)
It carried out like Example 1 and obtained the solid catalyst.

(Synthesis of double-walled carbon nanotube)
Carbon nanotubes were synthesized in the vertical reactor shown in FIG. 12 g of catalyst was set on the quartz sintered plate 101 through the catalyst charging line 103 from the sealed catalyst feeder 102. Subsequently, supply of argon gas from the source gas supply line 104 was started at 1000 mL / min. After the inside of the reactor was placed in an argon gas atmosphere, the temperature was heated to 850 ° C. (temperature rising time 30 minutes).

  After reaching 850 ° C., the temperature was maintained, the argon flow rate of the raw material gas supply line 104 was increased to 2000 mL / min, and fluidization of the solid catalyst on the quartz sintered plate was started. After confirming fluidization from the heating furnace inspection port 107, methane was further supplied to the reactor at 95 mL / min (methane concentration of 4.5 vol%. After supplying the mixed gas for 30 minutes, only argon gas was allowed to flow. Switch and finish the synthesis.

  The heating was stopped and the mixture was allowed to stand at room temperature. After reaching room temperature, the composition containing the catalyst and the aggregate of carbon nanotubes was taken out from the reactor. The above operation was repeated, and the obtained carbon nanotube aggregate was subjected to the following steps.

  The obtained carbon nanotube aggregate was subjected to thermal analysis by the method described above. The combustion peak temperature was 510 ° C.

(Baking and refining of carbon nanotube aggregates)
30 g of the carbon nanotube aggregate was placed in a magnetic dish (150φ), heated in a muffle furnace (FP41, manufactured by Yamato Kagaku Co., Ltd.) in the atmosphere to 500 ° C. over 1 hour, held for 60 minutes, and then allowed to cool naturally. Furthermore, in order to remove the catalyst from the carbon nanotube, a purification treatment was performed as follows. The carbon nanotubes were baked in air at 400 ° C. for 1 hour, then added to a 6N hydrochloric acid aqueous solution, and stirred in a water bath at 80 ° C. for 2 hours. The recovered product obtained by filtration was further added to a 6N hydrochloric acid aqueous solution and stirred in a water bath at 80 ° C. for 1 hour. This was filtered, washed several times with water, and then the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and metal, and the carbon nanotubes could be purified.

(High-resolution transmission electron microscope analysis of carbon nanotube aggregates)
When the aggregate of carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, as shown in FIG. 7, the carbon nanotubes were composed of clean graphite layers, and the number of the carbon nanotubes was two. Was observed. Two-layer carbon nanotubes accounted for 80% or more of the total number of carbon nanotubes.

(Resonance Raman spectroscopic analysis of carbon nanotube aggregates)
The aggregate of carbon nanotubes obtained as described above was subjected to Raman spectroscopic measurement. 211cm Consequently, ^147cm -1 in a Raman spectroscopic analysis of wavelength 532nm, as shown in FIG. ^{8, 170cm -1, 181cm -1,} 271cm -1, the peak was observed at 312cm ^-1, further wavelength 633nm in Raman spectroscopic analysis ^A peak was observed at ^-1 . Note that no peak was observed in the region of more than 190 cm ^{−1 to} less than 260 cm ^{−1 in} Raman spectroscopic analysis at a wavelength of 532 nm. In addition, the G / D ratio was 49 (532 nm) and 49 (633 nm), which were found to be high-quality double-walled carbon nanotubes with a high degree of graphitization.

(Preparation of carbon nanotube dispersion)
In a 50 mL container, weigh 10 mg of the above carbon nanotube and 30 mg of sodium cholate (Aldrich), add 10 mL of distilled water, and disperse under ice cooling with an ultrasonic homogenizer output of 25 W for 20 minutes. Prepared. Aggregates were not visually confirmed in the prepared liquid, and the carbon nanotubes were well dispersed. The obtained liquid was centrifuged at 20000 G for 15 minutes using a high-speed centrifuge, and the supernatant was placed in a 50 ml sample tube and stored. After drying the carbon nanotubes accumulated on the bottom, the organic components were baked at 400 ° C. for 1 hour, and the weight was measured. As a result, the amount of precipitated carbon nanotubes was 13% by weight of the initially added carbon nanotubes. It was.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film is 5.5 × 10 ³ Ω / □, and the light transmittance is 85% (transparent conductive film 85% / PET film 90.7% = 0.94). It showed high conductivity and transparency.

< Reference Example 2 >
(Synthesis of dispersant)
Triethylamine (1.39 mL) was added to a suspension of 2-aminoanisole-4-sulfonic acid (2.0 g) in distilled water (20 mL) to give a solution. Thereafter, a solution of ammonium peroxodisulfate (2.3 g) in distilled water (5 mL) was added dropwise to the previous solution over about 10 minutes. After stirring overnight at room temperature, acetone (200 mL) was added to form a precipitate. The precipitate was filtered through a filter, washed with acetone (300 mL), and then dried in an oven at 120 ° C. overnight. As a result, 2.1 g of poly (2-sulfo-5-methoxy-1,4-iminophenylene) was obtained. .

(Preparation of carbon nanotube dispersion)
Weigh 10 mg of carbon nanotubes and 30 mg of poly (2-sulfo-5-methoxy-1,4-iminophenylene), which were obtained up to the removal of the catalyst in Example 4 above, into a 50 mL container, add 10 mL of distilled water, and apply ultrasonic waves. Dispersion treatment was carried out under ice-cooling at a homogenizer output of 25 W for 20 minutes to prepare a carbon nanotube dispersion. Aggregates were not visually confirmed in the prepared liquid, and the carbon nanotubes were well dispersed. The obtained liquid was centrifuged at 20000 G for 15 minutes using a high-speed centrifuge, and the supernatant was placed in a 50 mL sample tube and stored. After drying the carbon nanotubes accumulated at the bottom, the organic components were baked at 400 ° C. for 1 hour, and the weight was measured. As a result, the amount of precipitated carbon nanotubes was 10% by weight of the initially added amount.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film is 1.0 × 10 ⁴ Ω / □, and the light transmittance is 88% (transparent conductive film 88% / PET film 90.7% = 0.97). It showed high conductivity and transparency. Further, the carbon nanotube dispersion was applied to the film again, followed by air drying, rinsing and drying. As a result, the surface resistance value of the transparent conductive film obtained was 4.0 × 10 ³ Ω / □, and the light transmittance was 86% (transparent conductive film 86% / PET film 90.7% = 0.95). It showed high conductivity and transparency. When the same process was performed again, the obtained transparent conductive film had a surface resistance value of 2.4 × 10 ³ Ω / □ and a light transmittance of 84% (transparent conductive film 84% / PET film 90.7%. = 0.93), indicating high conductivity and transparency.

< Reference Example 3 >
(Hydrogen peroxide treatment of carbon nanotubes)
30 g of the catalyst-attached carbon nanotube aggregate synthesized in Example 4 was placed in a magnetic dish (150φ), heated in a muffle furnace (FP41, manufactured by Yamato Scientific Co., Ltd.) to 400 ° C. in an hour, After holding for a minute, it was allowed to cool naturally. Furthermore, in order to remove the catalyst from the carbon nanotube, a purification treatment was performed as follows. Carbon nanotubes were added to a 6N hydrochloric acid aqueous solution and stirred in an 80 ° C. water bath for 2 hours. The recovered product obtained by filtration was further added to a 6N hydrochloric acid aqueous solution and stirred in a water bath at 80 ° C. for 1 hour. After filtration and washing several times with water, the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and iron, and the carbon nanotubes could be purified. Then, 34.5% hydrogen peroxide water (manufactured by Kanto Chemical Co., Inc.) 50 mL was mixed with 50 mg of carbon nanotubes, and reacted at 80 ° C. for 4 hours. After the reaction, the mixture was filtered and washed with water several times, and then the filtrate was dried in an oven at 120 ° C. overnight.

(Resonance Raman spectroscopic analysis of carbon nanotube aggregates)
The aggregate of carbon nanotubes obtained as described above was subjected to Raman spectroscopic measurement. As a result, ^149cm -1 in a Raman spectroscopic analysis of wavelength ^{532nm, 168cm -1, 181cm -1,} 268cm -1, the peak was observed at 312cm ^-1, further peaks observed at 216 cm ^-1 by Raman spectroscopic analysis of wavelength 633nm It was. Note that no peak was observed in the region of more than 190 cm ^{−1 to} less than 260 cm ^{−1 in} Raman spectroscopic analysis at a wavelength of 532 nm. Further, the G / D ratios were 57 (532 nm) and 57 (633 nm), which were found to be high-quality double-walled carbon nanotubes having a high degree of graphitization.

(Preparation of carbon nanotube dispersion)
Weigh 10 mg of the above carbon nanotube and 20 mg of poly (2-sulfo-5-methoxy-1,4-iminophenylene) in a 50 mL container, add 10 mL of distilled water, and cool with an ultrasonic homogenizer output of 240 W for 30 minutes on ice. Dispersion treatment was performed to prepare a carbon nanotube dispersion. Aggregates were not visually confirmed in the prepared liquid, and the carbon nanotubes were well dispersed. The obtained liquid was centrifuged at 10,000 G for 15 minutes using a high-speed centrifuge, and the supernatant was stored in a 50 ml sample tube. After drying the carbon nanotubes accumulated at the bottom, the organic components were baked at 400 ° C. for 1 hour, and the weight was measured. As a result, the amount of precipitated carbon nanotubes was 5% by weight of the initially added amount. .

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film is 3.0 × 10 ³ Ω / □, and the light transmittance is 88% (transparent conductive film 88% / PET film 92.5% = 0.95). It showed high conductivity and transparency.

< Reference Example 4 >
(Carbon nanotube mixed acid treatment)
30 g of the catalyst-attached carbon nanotube aggregate synthesized in Example 4 was placed in a magnetic dish (150φ), heated in a muffle furnace (FP41, manufactured by Yamato Scientific Co., Ltd.) to 400 ° C. in an hour, After holding for a minute, it was allowed to cool naturally. Furthermore, in order to remove the catalyst from the carbon nanotube, a purification treatment was performed as follows. Carbon nanotubes were added to a 6N hydrochloric acid aqueous solution and stirred in an 80 ° C. water bath for 2 hours. The recovered product obtained by filtration was further added to a 6N hydrochloric acid aqueous solution and stirred in a water bath at 80 ° C. for 1 hour. After filtration and washing several times with water, the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and iron, and the carbon nanotubes could be purified. Thereafter, 30 ml of concentrated sulfuric acid (manufactured by Kanto Chemical Co., Ltd.) and 10 ml of concentrated nitric acid (manufactured by Kanto Chemical Co., Ltd.) were mixed with 200 mg of carbon nanotubes, and reacted at 80 ° C. for 4 hours. After the reaction, the mixture was filtered, washed several times with water, and the filtrate was dried in an oven at 120 ° C. overnight to obtain 140 mg of a recovered product. Thereafter, 14 mL of isopropylamine and 126 mL of distilled water were added to the recovered material, and mixed for about 10 minutes using an ultrasonic bath. After filtration and washing several times with water, the filtrate was dried in an oven at 120 ° C. overnight.

(Resonance Raman spectroscopic analysis of carbon nanotube aggregates)
The aggregate of carbon nanotubes obtained as described above was subjected to Raman spectroscopic measurement. As a result, peaks were observed at 149 cm ⁻¹ , 163 cm ⁻¹ , 181 cm ⁻¹ , 260 cm ⁻¹ , and 310 cm ⁻¹ by Raman spectroscopy at a wavelength of 532 nm, and further at 217 cm ⁻¹ by Raman spectroscopy at a wavelength of 633 nm. It was done. Note that no peak was observed in the region of more than 190 cm ^{−1 to} less than 260 cm ^{−1 in} Raman spectroscopic analysis at a wavelength of 532 nm. Further, the G / D ratio was 62 (532 nm) and 57 (633 nm), and it was found that these were high-quality double-walled carbon nanotubes having a high degree of graphitization.

(Preparation of carbon nanotube dispersion)
Weigh 10 mg of the above carbon nanotube and 20 mg of poly (2-sulfo-5-methoxy-1,4-iminophenylene) in a 50 mL container, add 10 mL of distilled water, and cool with an ultrasonic homogenizer output of 240 W for 30 minutes on ice. Dispersion treatment was performed to prepare a carbon nanotube dispersion. Aggregates were not visually confirmed in the prepared liquid, and the carbon nanotubes were well dispersed. The obtained liquid was centrifuged at 10,000 G for 15 minutes using a high-speed centrifuge, and the supernatant was stored in a 50 ml sample tube. After drying the carbon nanotubes accumulated at the bottom, the organic components were baked at 400 ° C. for 1 hour, and the weight was measured. As a result, the amount of precipitated carbon nanotubes was found to be the detection limit (1% by weight) Below).

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film is 2.5 × 10 ³ Ω / □, and the light transmittance is 87% (transparent conductive film 87% / PET film 92.5% = 0.94). It showed high conductivity and transparency.

<Example 4 >
(Support of metal salt on light magnesia)
2.46 g of ammonium iron citrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 500 mL of methanol (Kanto Chemical Co., Ltd.). To this solution, 100 g of light magnesia (manufactured by Iwatani Corporation) was added, stirred at room temperature for 60 minutes, dried under reduced pressure while stirring at 40 ° C. to 60 ° C. to remove methanol, and a metal salt was supported on the light magnesia powder. A catalyst body was obtained.

(Synthesis of double-walled carbon nanotube)
Carbon nanotubes were synthesized in the same manner as in Example 1 using the catalyst.

  The obtained carbon nanotube aggregate was subjected to thermal analysis by the method described above. The combustion peak temperature was 456 ° C.

(Baking and refining of carbon nanotube aggregates)
30 g of the carbon nanotube aggregate was placed in a magnetic dish (150φ), heated to 446 ° C. in an air in a muffle furnace (FP41, manufactured by Yamato Scientific Co., Ltd.) for 1 hour, held for 60 minutes, and then allowed to cool naturally. Furthermore, in order to remove the catalyst from the carbon nanotube, a purification treatment was performed as follows. Carbon nanotubes were added to a 6N hydrochloric acid aqueous solution and stirred in an 80 ° C. water bath for 2 hours. The recovered material obtained by filtration using a filter having a pore size of 1 μm was further added to a 6N hydrochloric acid aqueous solution and stirred in an 80 ° C. water bath for 1 hour. This was filtered using a filter having a pore diameter of 1 μm, washed with water several times, and then the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and metal, and the carbon nanotubes could be purified.

(High-resolution transmission electron microscope analysis of carbon nanotube aggregates)
When the aggregate of carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, the carbon nanotubes were composed of a clean graphite layer, and carbon nanotubes with two layers were observed. Two-layer carbon nanotubes accounted for 88% (88) of 100 carbon nanotubes.

(Resonance Raman spectroscopic analysis of carbon nanotube aggregates)
The aggregate of carbon nanotubes obtained as described above was subjected to Raman spectroscopic measurement. As a result, ^138cm -1 in a Raman spectroscopic analysis of wavelength ^{532nm, 154cm -1, 183cm -1,} 277cm -1, the peak was observed at 316cm ^-1, further peaks observed at 220 cm ^-1 by Raman spectroscopic analysis of wavelength 633nm It was done. Note that no peak was observed in the region of more than 190 cm ^{−1 to} less than 260 cm ^{−1 in} Raman spectroscopic analysis at a wavelength of 532 nm. Further, the G / D ratio was 84 (532 nm) and 75 (633 nm), and it was found to be a high-quality double-walled carbon nanotube having a high degree of graphitization.

(Preparation of carbon nanotube aggregate dispersion)
Weigh 10 mg of the carbon nanotube aggregate and 100 mg of polystyrene sulfonate aqueous solution (Aldrich, 30 wt%, weight average molecular weight 200,000) in a 50 mL container, add 9.93 mL of distilled water, and output an ultrasonic homogenizer of 25 W. Then, the dispersion treatment was carried out for 20 minutes under ice cooling to prepare a carbon nanotube aggregate dispersion. Aggregates could not be visually confirmed in the prepared liquid, and the carbon nanotube aggregates were well dispersed. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. 1 mL of the remaining liquid at this time was filtered using a filter having a pore diameter of 1 μm, and then the well-washed filtrate was dried with a 120 ° C. dryer. The weight of the filtrate was measured and found to be 3.9 mg. Therefore, it was found that 6.1 mg (0.68 mg / mL) of carbon nanotube aggregates were dispersed in the supernatant.

Using the carbon nanotube aggregate dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film is 1.7 × 10 ³ Ω / □, and the light transmittance is 85% (transparent conductive film 85% / PET film 90.7% = 0.94). It showed high conductivity and transparency.

<Comparative Example 1>
(Analysis of carbon nanotubes)
Raman G / D ratio of Nanotecport double-walled carbon nanotubes (diameter <5 nm, length 5-15 μm, purity ≧ 90%, ash content <2 wt%, specific surface area> 400 m ² / g, amorphous carbon <5%) ( 532 nm) was 14.

(Preparation of carbon nanotube dispersion)
In a 50 mL container, weigh 10 mg of Nanotecport's double-walled carbon nanotubes and 100 mg of polystyrene sulfonate aqueous solution (Aldrich, 30% by weight, weight average molecular weight 200,000), add 9.93 mL of distilled water, Dispersion treatment was performed under homogenizer output 25 W for 20 minutes under ice cooling to prepare a carbon nanotube aggregate dispersion. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. The precipitate in the residual liquid at this time was filtered using a filter having a pore size of 1 μm, washed with water, dried and measured for weight, which was 8.1 mg. That is, it was found that 1.9 mg (0.21 mg / mL) of carbon nanotubes was dispersed in the supernatant.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The obtained transparent conductive film had a surface resistance value of 2.8 × 10 ⁹ Ω / □, and a light transmittance of 90.4% (transparent conductive film 90.4% / PET film 90.7% = 0.99). )Met.

Further, the above coating operation was further repeated twice on the film on which the carbon nanotubes were fixed by the same method as described above. The surface resistance value of the obtained transparent conductive film was 1.0 × 10 ⁷ Ω / □, and the light transmittance was 85% (transparent conductive film 85% / PET film 90.7% = 0.94). .

<Comparative example 2>
(Analysis of carbon nanotubes)
The Raman G / D ratio (532 nm) of Nanosil's double-walled carbon nanotube (Batch No. LDW-P90 / 050517) was 9.

(Preparation of carbon nanotube dispersion)
In a 50 mL container, weigh 10 mg of Nanosil double-walled carbon nanotubes and 100 mg of polystyrene sulfonate aqueous solution (manufactured by Aldrich, 30 wt%, weight average molecular weight 200,000), add 9.93 mL of distilled water, and add an ultrasonic homogenizer. Dispersion treatment was performed with an output of 25 W and ice cooling for 20 minutes to prepare a carbon nanotube aggregate dispersion. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. The precipitate in the residual liquid at this time was filtered using a filter having a pore size of 1 μm, washed with water, dried and measured for weight, and it was 8.3 mg. That is, it was found that 1.7 mg (0.19 mg / mL) of carbon nanotubes were dispersed in the supernatant.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The obtained transparent conductive film film has a surface resistance value of 7.8 × 10 ⁶ Ω / □, and a light transmittance of 90.1% (transparent conductive film 90.1% / PET film 90.7% = 0.0.1). 99).

Further, the above coating operation was further repeated 3 times on the film on which the carbon nanotubes were fixed by the same method as described above. The obtained transparent conductive film film had a surface resistance value of 1.0 × 10 ⁶ Ω / □ and a light transmittance of 85% (transparent conductive film 85% / PET film 90.7% = 0.94). It was.

<Comparative Example 3>
(Analysis of carbon nanotubes)
Single-walled carbon nanotubes (diameter <2 nm, length 0.5-100 μm, purity ≧ 90%, ash content <2%, specific surface area> 600 m ² / g, amorphous carbon <5%) manufactured by Nanotechport, Inc. The ratio (532 nm) was 4.

(Preparation of carbon nanotube dispersion)
In a 50 mL container, weigh 10 mg of Nanotecport single-walled carbon nanotubes and 100 mg of polystyrene sulfonate aqueous solution (Aldrich, 30 wt%, weight average molecular weight 200,000), add 9.93 mL of distilled water, Dispersion treatment was performed under homogenizer output 25 W for 20 minutes under ice cooling to prepare a carbon nanotube aggregate dispersion. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. The precipitate in the residual liquid at this time was filtered using a filter having a pore size of 1 μm, washed with water, dried and measured for weight, which was 8.0 mg. That is, it was found that 2.0 mg (0.22 mg / mL) of carbon nanotubes were dispersed in the supernatant.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. Further, the same operation was repeated to apply the carbon nanotube dispersion liquid three times in total. The obtained transparent conductive film film had a surface resistance value of 1.0 × 10 ⁵ Ω / □ and a light transmittance of 85% (transparent conductive film 85% / PET film 90.7% = 0.94). It was.

<Comparative example 4>
(Analysis of carbon nanotubes)
The Raman G / D ratio (532 nm) of the single-walled carbon nanotube (Batch No. LSW-P90 / 040406) manufactured by Nanosil Corporation was 8.

(Preparation of carbon nanotube dispersion)
In a 50 mL container, weigh 10 mg of Nanosil single-walled carbon nanotubes and 100 mg of polystyrene sulfonate aqueous solution (Aldrich, 30% by weight, 200,000 in weight average molecular weight), add 9.93 mL of distilled water, and add an ultrasonic homogenizer. Dispersion treatment was performed with an output of 25 W and ice cooling for 20 minutes to prepare a carbon nanotube aggregate dispersion. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. The precipitate in the residual liquid at this time was filtered using a filter having a pore size of 1 μm, washed with water, dried and measured for weight, which was 8.1 mg. That is, it was found that 1.9 mg (0.21 mg / mL) of carbon nanotubes was dispersed in the supernatant.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. Further, the same operation was repeated to apply the carbon nanotube dispersion liquid three times in total. The surface resistance value of the obtained transparent conductive film film was 4.7 × 10 ⁷ Ω / □, and the light transmittance was 85% (transparent conductive film 85% / PET film 90.7% = 0.94). It was.

<Comparative Example 5>
(Analysis of carbon nanotubes)
The Raman G / D ratio (532 nm) of the Bayer multi-walled carbon nanotubes (Baytube, MIV-05-182) was 0.7.

(Preparation of carbon nanotube dispersion)
In a 50 mL container, weigh 10 mg of Bayer multi-walled carbon nanotubes (Baytube) and 100 mg of polystyrene sulfonate aqueous solution (Aldrich, 30 wt%, weight average molecular weight 200,000), add 9.93 mL of distilled water, Dispersion treatment was carried out under ice-cooling with a sonic homogenizer output of 25 W for 20 minutes to prepare a carbon nanotube aggregate dispersion. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. The precipitate in the residual liquid at this time was filtered using a filter having a pore size of 1 μm, washed with water, dried and measured for weight, which was 6.3 mg. That is, it was found that 3.7 mg (0.41 mg / mL) of carbon nanotubes were dispersed in the supernatant.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The surface resistance value of the obtained transparent conductive film film is> 1.0 × 10 ¹² Ω / □, and the light transmittance is 85% (transparent conductive film 85% / PET film 90.7% = 0.94). there were.

<Comparative Example 6 >
(Support of metal salt on light magnesia)
0.5 g of ammonium iron citrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 25 mL of methanol (Kanto Chemical Co., Ltd.). 5 g of light magnesia (Wako Pure Chemical Industries, Ltd.) was added to this solution, treated with an ultrasonic cleaner for 60 minutes, dried with stirring at 40 ° C. to 60 ° C. to remove methanol, and light magnesia powder was converted to metal. A solid catalyst carrying a salt was obtained. The bulk density of the obtained catalyst was 0.61 g / mL.

(Synthesis of carbon nanotubes)
1.0 g of the solid catalyst prepared above was placed on the quartz wool at the center of a vertical quartz tube having an inner diameter of 64 mm, and the central temperature was raised to 900 ° C. over 120 minutes. After reaching 900 ° C., methane gas was supplied at 18 mL / min, nitrogen gas was supplied at 376 mL / min (methane concentration 4.7 vol%), and the reaction pressure was 1 × 10 ⁵ Pa (1 atm) for 60 minutes. Then, the temperature was cooled to room temperature under nitrogen flow, and the composition containing the catalyst and the aggregate of carbon nanotubes was taken out. The linear velocity of methane under these reaction conditions is 9.4 × 10 ⁻³ cm / sec. The carbon nanotube aggregate thus obtained was measured with a resonance Raman spectrometer (633 nm). As a result, it was found that the carbon nanotube had a G / D ratio of 20.

(Purification of carbon nanotubes)
Furthermore, in order to remove the catalyst from the carbon nanotube, a purification treatment was performed as follows. The carbon nanotubes were baked in air at 400 ° C. for 1 hour, then added to a 6N hydrochloric acid aqueous solution, and stirred in a water bath at 80 ° C. for 2 hours. The recovered product obtained by filtration was further added to a 6N hydrochloric acid aqueous solution and stirred in a water bath at 80 ° C. for 1 hour. After filtration and washing several times with water, the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and metal, and the carbon nanotubes could be purified.

(Preparation of carbon nanotube dispersion)
Weigh 10 mg of the above carbon nanotube and 100 mg of polystyrene sulfonate aqueous solution (manufactured by Aldrich, 30 wt%, weight average molecular weight 200,000) in a 50 mL container, add 9.93 mL of distilled water, and output an ultrasonic homogenizer of 25 W, 20 Dispersion treatment was performed under ice-cooling for 1 minute to prepare a carbon nanotube aggregate dispersion. The obtained liquid was centrifuged at 20000 G for 15 minutes with a high-speed centrifuge, and 9 mL of the supernatant was sampled. The precipitate in the residual liquid at this time was filtered using a filter with a pore size of 1 μm, washed with water, dried and measured for weight, which was 7.3 mg. That is, it was found that 2.7 mg (0.30 mg / mL) of carbon nanotubes were dispersed in the supernatant.

Using the carbon nanotube dispersion obtained above, a transparent conductive film was obtained by the above method. The obtained transparent conductive film film had a surface resistance value of 6.0 × 10 ⁴ Ω / □, and a light transmittance of 85.0% (transparent conductive film 85.0% / PET film 90.7% = 0. 94).

  The aggregate of carbon nanotubes of the present invention is useful as a field emission material. For example, when the aggregate of carbon nanotubes of the present invention is used as a field emission electron source, the applied voltage can be kept low because the diameter is small and charge concentration is likely to occur. Moreover, since it is a high quality multilayer, especially a double-walled carbon nanotube, it can be estimated that durability is also favorable. Such an aggregate of carbon nanotubes is considered to be a good emission material.

FIG. 1 shows a state in which the catalyst exists uniformly in the cross section of the reaction tube. FIG. 2 is a schematic view of the fluidized bed apparatus used in Example 1. FIG. 3 is a high-resolution transmission electron micrograph of the carbon nanotubes obtained in Example 1. FIG. 4 is a Raman spectroscopic analysis chart of the carbon nanotubes obtained in Example 1. FIG. 5 is a high-resolution transmission electron micrograph of the carbon nanotubes obtained in Example 2. FIG. 6 is a Raman spectroscopic analysis chart of the carbon nanotubes obtained in Example 2. FIG. 7 is a high-resolution transmission electron micrograph of the double-walled carbon nanotube obtained in Reference Example 1 . FIG. 8 is a Raman spectroscopic analysis chart of the double-walled carbon nanotubes obtained in Reference Example 2 . FIG. 9 is a Raman spectroscopic analysis chart of the double-walled carbon nanotubes obtained in Reference Example 3 . FIG. 10 is a Raman spectroscopic analysis chart of the double-walled carbon nanotubes obtained in Reference Example 4 .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reactor 2 Stand which puts catalyst 3 Catalyst 4 Mixture of objects and catalyst other than catalyst 5 Catalyst 100 Reactor 101 Quartz sintered plate 102 Sealed catalyst feeder 103 Catalyst input line 104 Raw gas supply line 105 Waste gas line 106 Heating 107 Inspection port 108 Catalyst

Claims (18)

A carbon nanotube aggregate that satisfies the following conditions (1) to (3).
(1) When observed with a transmission electron microscope, 50 or more double-walled carbon nanotubes are included in 100 carbon nanotubes.
(2) The height ratio (G / D ratio) of G band and D band by Raman spectroscopic analysis at a wavelength of 532 nm is 30 or more.
(3) A mixture of 10 mg of carbon nanotube aggregates, 30 mg of polystyrene sulfonate and 10 mL of water was subjected to an ultrasonic homogenizer treatment, followed by centrifugation at 20000 G, and then 9 mL of the supernatant was sampled. It was obtained by performing an oxidation treatment until the aggregate content was 0.6 mg / mL or more. The film obtained by applying a carbon nanotube aggregate as a dispersion and applying the dispersion to a substrate has a light transmittance of 85% or more, and the surface resistance of the film is 1 × 10 ⁴ Ω / □. The aggregate of carbon nanotubes according to claim 1, which is less than 1. The aggregate of carbon nanotubes according to claim 1 or 2, wherein 70 or more carbon nanotubes out of 100 are double-walled carbon nanotubes when observed with a transmission microscope. A dispersion obtained by dispersing the carbon nanotube aggregate according to any one of claims 1 to 3 in a dispersion medium. The carbon nanotube aggregate dispersion according to claim 4 , further comprising a surfactant or a polymer. The carbon nanotube aggregate dispersion according to claim 4 or 5 , wherein the concentration of the carbon nanotube aggregate is 0.01 wt% to 20 wt%. A film in which a dispersion of carbon nanotube aggregates according to any one of claims 4 to 6 is coated on a substrate, having a light transmittance of 85% or more and a surface resistance value of 1 × 10 ⁵ Ω / A conductive film that is less than □. 8. The conductive film according to claim 7 , wherein the transmittance of the conductive film / the light transmittance of the transparent substrate> 0.85. Conductive film according to claim 7 or 8 surface resistance is 1 × 10 ⁴ Ω / □ below. A powdered catalyst in which iron is supported on magnesia is present in the entire vertical cross-sectional direction of the reactor in a vertical reactor, and methane is circulated in the vertical direction in the vertical reactor, so that methane and the catalyst are mixed in 500 parts. The method for producing a carbon nanotube aggregate according to any one of claims 1 to 3 , wherein the carbon nanotube aggregate is synthesized by contacting at ~ 1200 ° C, and then an oxidation treatment is performed. The method for producing a carbon nanotube aggregate according to claim 10 , wherein the oxidation treatment is performed in a range of a combustion peak temperature of the carbon nanotube aggregate ± 50 ° C. The method for producing a carbon nanotube aggregate according to claim 10 , wherein the oxidation treatment is performed by firing in the atmosphere in a range of a combustion peak temperature of the carbon nanotube aggregate ± 15 ° C. The method for producing a carbon nanotube aggregate according to claim 10 , wherein the oxidation treatment is intermittently contacted with oxygen. The method for producing a carbon nanotube aggregate according to claim 10, wherein the carbon nanotube aggregate generated by the oxidation treatment is treated with hydrogen peroxide. The method for producing a carbon nanotube aggregate according to claim 10, wherein the carbon nanotube aggregate generated by the oxidation treatment is treated with a mixed acid. The method for producing an aggregate of carbon nanotubes according to claim 15 , wherein the treatment with a mixed acid is followed by a further treatment with a basic compound. The method for producing a carbon nanotube aggregate according to claim 16 , wherein the basic compound is an organic amine. A field emission material using the carbon nanotube aggregate according to any one of claims 1 to 3 .

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