WO2018043487A1

WO2018043487A1 - Process for producing carbon-nanotube-containing composition, process for producing carbon nanotube dispersion, and carbon-nanotube-containing composition

Info

Publication number: WO2018043487A1
Application number: PCT/JP2017/030939
Authority: WO
Inventors: 平井孝佳; 西野秀和; 今津直樹
Original assignee: 東レ株式会社
Priority date: 2016-08-31
Filing date: 2017-08-29
Publication date: 2018-03-08
Also published as: JP6380687B2; JPWO2018043487A1

Abstract

A process for producing a carbon-nanotube-containing composition, the process including a liquid-phase oxidation step in which an unpurified carbon-nanotube-containing composition in which the intensity ratio between G-band and D-band (G/D ratio), as determined by Raman spectroscopy, is 50 or higher is heated together with nitric acid having a concentration of 1-50 wt%, with refluxing, to thereby conduct liquid-phase oxidation. A higher-quality carbon-nanotube-containing composition which contains no residual catalyst, has high heat resistance, and is reduced in by-product carbon content can be obtained in high yield.

Description

Method for producing carbon nanotube-containing composition, method for producing carbon nanotube dispersion, and carbon nanotube-containing composition

The present invention relates to a carbon nanotube-containing composition and a method for producing the same.

Carbon nanotubes (hereinafter sometimes referred to as CNTs) are chemically highly stable polymer materials that have excellent electrical conductivity, thermal conductivity, and heat resistance, as well as high mechanical properties and biocompatibility. It is a substance that is expected to be used in various applications. In fact, beginning with the composite material field, studies are proceeding in various fields such as the electronics field, energy field, and medical field.

As a method for producing carbon nanotubes, a laser ablation method, an arc discharge method, and a chemical vapor deposition method (CVD method) are known. Above all, the CVD method can synthesize carbon nanotubes in large quantities. A supported catalyst CVD method (hereinafter sometimes abbreviated as “supported catalyst method”) in which carbon nanotubes are grown from a support on which metal catalyst fine particles are supported, or a catalyst (or its precursor) as a carbon source and a CVD method that does not require a support. A gas-phase flow CVD method (hereinafter sometimes abbreviated as “gas-phase flow method”) in which carbon nanotubes are grown by introducing them directly into a reaction tube together with a carrier gas is known. In any production method, carbon by-products and catalyst residues are contained in the CNT composition at the time of production, and some methods for removing these impurities and purifying the CNT composition are also known. For example, since carbon nanotubes immediately after being produced by the supported catalyst method contain a large amount of carbon by-products, a method of purifying with concentrated nitric acid is known (Patent Document 1). On the other hand, high-quality carbon nanotubes with a high Raman G / D ratio can be obtained efficiently and inexpensively using a gas phase flow method, but a small amount of carbon by-products and catalyst residues are contained. (Patent Document 2). As a purification method for removing carbon impurities, heat treatment in an oxidizing gas is known (Patent Document 3).

Depending on the application, the CNTs produced as described above may be used by dispersing them in a dispersion medium. However, it is known that dispersed nanomaterials generally have a high surface area because of their large surface area. Since carbon nanotubes with higher crystallinity and higher purity are more likely to aggregate, various devices have been made to disperse them. For example, in Patent Document 4, when carbon nanotubes are dispersed using an ultrasonic homogenizer, if ultrasonic irradiation is continued until the carbon nanotubes are sufficiently dispersed, defects are introduced into the carbon nanotubes and conductivity is lowered. A method is described in which a carbon nanotube is loosened in a dispersion medium by stirring the medium and the carbon nanotube at a high speed, and then dispersed by an ultrasonic homogenizer.

In Patent Document 5, after purifying single-walled carbon nanotubes produced by the eDIPS method, which is a kind of gas phase flow method, with concentrated nitric acid, the dispersion liquid is obtained by stirring with a thin film swirl type high-speed mixer together with a dispersion medium and a dispersant. It is prepared.

JP 2012-116667 A WO2017 / 010523 Japanese Patent Laid-Open No. 2005-60170 JP 2008-195563 A JP 2016-126847 A

The carbon nanotubes produced by the supported catalyst method in Patent Document 1 have a small Raman G / D ratio and contain a large amount of carbon by-products. In order to remove the catalyst, it is necessary to purify with concentrated nitric acid. However, since concentrated nitric acid also damages carbon nanotubes, the carbon nanotubes after purification are not sufficiently high quality. On the other hand, in order to reduce damage to the carbon nanotubes, in the case of treatment using dilute nitric acid, the removal of the catalyst is insufficient, and the catalyst remains in the carbon nanotube.

Although the carbon nanotubes produced by the gas phase flow method as described in Patent Document 2 are of high quality, a small amount of carbon by-products and catalysts remain, which is insufficient in terms of purity.

In the purification method described in Patent Document 3, carbon impurities can be removed, but catalysts (metals contained in the catalyst source, undecomposed catalyst sources, etc.) cannot be removed. If the catalyst remains in the carbon nanotube, it may cause various properties of the carbon nanotube to be inhibited.

Also, when carbon nanotubes are used in a dispersed manner, it is required to bring out the performance of the carbon nanotube dispersion by devising a dispersion method. In the method described in Patent Document 4, even if the carbon nanotubes are loosened by stirring treatment, which is a relatively mild dispersion method, a dispersion method that requires large energy or force, such as an ultrasonic homogenizer, is finally used. The carbon nanotubes are damaged, and the effect of improving the conductivity cannot be obtained.

In the method of Patent Document 5, single-walled carbon nanotubes with high crystallinity and purity are used, but carbon nanotube defects are increased by the treatment with concentrated nitric acid. As a result, the conductivity is lowered, and the conductivity is reduced. In order to compensate, additional processes such as doping or pressure bonding of carbon nanotubes to the film are required.

An object of the present invention is to obtain a high-quality carbon nanotube-containing composition having no catalyst remaining, high heat resistance, and low carbon by-product in high yield.

Another object of the present invention is to produce a dispersion liquid in which carbon nanotubes are highly dispersed, and to use the dispersion liquid to achieve a transparent conductive film and a transparent conductive laminate that achieve both high conductivity and high transparency. Is to get.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention obtained higher results when liquid phase oxidation was performed with dilute nitric acid on high-quality carbon nanotubes having a Raman G / D ratio of 50 or more. The inventors have found that carbon nanotubes with high quality, no catalyst residue, high heat resistance and few carbon by-products can be obtained, and have led to the following invention.

In addition, carbon nanotubes that are almost free of carbon impurities such as amorphous carbon, have high crystallinity and purity, and are synthesized by vapor phase flow method are subjected to liquid phase oxidation under relatively mild conditions, and then dispersed by stirring. By preparing the liquid, it is possible to produce a dispersion liquid in which carbon nanotubes are highly dispersed, and by using the dispersion liquid, a transparent conductive film and a transparent conductive laminate that achieve both high conductivity and high transparency The inventors have found that the following can be obtained.
[1] A pre-purification carbon nanotube-containing composition having an intensity ratio (G / D ratio) of G band and D band in Raman spectroscopic analysis of 50 or more is used with nitric acid having a concentration of 1 wt% or more and 50 wt% or less. A method for producing a carbon nanotube-containing composition comprising a liquid phase oxidation step of performing liquid phase oxidation by heating to reflux.
[2] A method for producing a carbon nanotube dispersion, comprising a step of dispersing the carbon nanotube-containing composition in the dispersion medium by subjecting the carbon nanotube-containing composition obtained by the above production method to a stirring treatment together with the dispersion medium.
[3] A carbon nanotube-containing composition that satisfies all the following conditions (1) to (5):
(1) The intensity ratio (G / D ratio) of G band and D band in Raman spectroscopic analysis is 90 or more;
(2) The weight loss rate at 200 to 950 ° C. is 95% or more by thermogravimetric analysis when the temperature is raised at 10 ° C./min in air;
(3) In the thermogravimetric analysis when the temperature is raised at 10 ° C./min in air, the combustion peak on the high temperature side is 770 ° C. or higher and lower than 900 ° C .;
(4) In thermogravimetric analysis when the temperature is increased at 10 ° C./min in air, the weight loss on the low temperature side (TG (L)) and the weight loss on the high temperature side (TG (H)) are TG ( H) / (TG (L) + TG (H)) is 0.8 or more;
(5) The ratio of double-walled carbon nanotubes to all carbon nanotubes is 60% or more.

According to the present invention, it is possible to obtain a high-quality carbon nanotube-containing composition with no catalyst remaining, high heat resistance, and low carbon by-product in high yield.

Further, according to the present invention, it is possible to produce a dispersion liquid in which carbon nanotubes are highly dispersed, and by using the dispersion liquid, a transparent conductive film and a transparent conductive laminate that achieve both high conductivity and high transparency. You can get a body.

It is the apparatus schematic for synthesize | combining the carbon nanotube aggregate used in the Example.

The concept of the present invention will be described. The carbon nanotube-containing composition after synthesis and before purification contains carbon impurities such as amorphous carbon and a catalyst. In order to improve the conductivity of the carbon nanotube-containing composition, it is important to remove carbon impurities and the catalyst from the carbon nanotube-containing composition before purification. In the prior art, it has been reported in, for example, Japanese Patent Application Laid-Open No. 2011-148673 that carbon impurities and catalysts can be removed by liquid phase oxidation with concentrated nitric acid (60% by weight). However, this method has the problem that carbon nanotubes such as amorphous carbon increase due to damage and decomposition due to excessive oxidation reaction by acid treatment, resulting in a decrease in the yield of carbon nanotubes. It was. In the present invention, a high-quality carbon nanotube-containing composition having a high degree of graphitization is used as the carbon nanotube-containing composition before purification, and the mixture is heated to reflux under mild conditions where the nitric acid concentration is 1 wt% to 50 wt%. It has been found that by performing liquid phase oxidation, carbon impurities and catalysts can be removed while minimizing damage to the carbon nanotubes, and a high-quality carbon nanotube-containing composition can be obtained in a high yield.

In the present invention, the carbon nanotube-containing composition means a total of a plurality of carbon nanotubes. The existence form of the carbon nanotube is not particularly limited, and may be an independent form, a bundled form, an entangled form, or a mixed form thereof. Further, carbon nanotubes having various numbers of layers and diameters may be included. In addition, impurities derived from the carbon nanotube production method, for example, undecomposed carbon source or tar, carbon impurities generated by decomposition of the carbon source, and metals contained in the catalyst source or undecomposed catalyst source may be included. Good.

In the present invention, the carbon nanotube-containing composition before purification needs to have a G-band to D-band height ratio (G / D ratio) of 50 or more by Raman spectroscopic analysis at a wavelength of 532 nm. More preferably, the G / D ratio is 50 or more and 200 or less. The G / D ratio is a value when the carbon nanotube-containing composition is evaluated by Raman spectroscopy. The laser wavelength used in Raman spectroscopy is 532 nm. The Raman shift observed in the vicinity of 1590 cm ⁻¹ in the Raman spectrum obtained by Raman spectroscopy is called a graphite-derived G band, and the Raman shift observed in the vicinity of 1350 cm ⁻¹ is D derived from defects in amorphous carbon or graphite. Called a band. The ratio of the peak height of the G band and the D band is the G / D ratio. A carbon nanotube-containing composition having a higher G / D ratio has a higher degree of graphitization and higher quality. In addition, solid Raman spectroscopy such as a carbon nanotube-containing composition 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. A G / D ratio of the carbon nanotube-containing composition before purification of 50 or more indicates a considerably high-quality carbon nanotube-containing composition.

The carbon nanotube-containing composition before purification preferably has a weight loss rate of 200 to 950 ° C. of 60% or more, more preferably 80%, in thermogravimetric analysis when the temperature is increased at 10 ° C./min in air. % Or more. In thermogravimetric analysis, a sample of about 1 mg was placed in a thermogravimetric analyzer (eg, Shimadzu Corporation TGA-60), and the temperature was raised from room temperature to 1000 ° C. at a heating rate of 10 ° C./min. The weight loss rate of each sample is measured.

In order to produce a pre-purification carbon nanotube-containing composition having a G / D ratio of 50 or more, it is preferable to use a gas phase flow method. As the gas phase flow method, it is preferable to produce a carbon nanotube-containing composition by introducing a catalyst, a carbon source and a carrier gas into the vertical reaction tube from above. Such a gas phase flow method is disclosed in, for example, Japanese Patent Application Laid-Open No. 2013-18673, but is not limited to this method, and other known gas phase flow methods can also be employed.

The catalyst is not particularly limited, but transition metal compounds or transition metal ultrafine particles are preferably used. Examples of transition metal compounds include organic transition metal compounds and inorganic transition metal compounds. Examples of the organic transition metal compound include ferrocene, cobaltocene, nickelocene, and iron acetylacetonate. Examples of the inorganic transition metal compound include iron chloride.

In addition, when introducing the catalyst into the vertical reaction tube, it is preferable to introduce a co-catalyst that promotes the formation reaction of the carbon nanotube-containing composition by the catalyst. A sulfur compound is preferably used as the cocatalyst, and examples thereof include thiophene, benzothiophene, and thianaphthene.

As the carbon source, a liquid or gaseous one can be used. Examples of the carbon source include aromatic hydrocarbons such as benzene, toluene and xylene; gaseous hydrocarbons such as methane, ethane and ethylene; alcohols such as methanol, ethanol and propanol; and hexane, cyclohexane and decalin. Mention may be made of aliphatic hydrocarbons.

As the carrier gas, an inert gas such as nitrogen, argon or helium, hydrogen, or a mixed gas of inert gas and hydrogen can be used.

In the present invention, liquid phase oxidation is performed by heating and refluxing a carbon nanotube-containing composition before purification having a G / D ratio of 50 or more using nitric acid having a concentration of 1 wt% or more and 50 wt% or less. . The nitric acid concentration is more preferably 1% by weight or more, and further preferably 2% by weight or more. The nitric acid concentration is more preferably less than 30% by weight, and even more preferably less than 20% by weight. When liquid phase oxidation is performed at a concentration of nitric acid higher than 50% by weight, the carbon nanotubes themselves are damaged, which may impair the quality of the carbon nanotubes. Moreover, the problem of the yield reduction of a carbon nanotube arises. When the nitric acid concentration is less than 1% by weight, oxidation of the carbon impurities and the catalyst becomes insufficient, and it becomes difficult to remove the carbon impurities and the catalyst. By performing a purification treatment using a high-quality carbon nanotube-containing composition, carbon impurities and catalysts can be easily removed from the carbon nanotube-containing composition, and a high-quality carbon nanotube-containing composition can be obtained in a high yield. .

In the liquid phase oxidation step, it is preferable to perform heating and refluxing in a temperature range of 100 ° C. or higher and 110 ° C. or lower, and more preferably in a temperature range of 100 ° C. or higher and lower than 106 ° C. When liquid phase oxidation is performed at a temperature exceeding 110 ° C., the carbon nanotubes themselves are damaged, which may impair the quality of the carbon nanotubes. In addition, the yield of carbon nanotubes is reduced. When the temperature is lower than 100 ° C., the oxidation of the carbon impurities and the catalyst becomes low, and the removal of the carbon impurities and the catalyst may be insufficient.

The time for performing the liquid phase oxidation is preferably in the range of 1 hour to 24 hours, more preferably in the range of 1 hour to 12 hours. If liquid phase oxidation is performed for longer than 24 hours, the carbon nanotubes themselves may be damaged, and the quality of the carbon nanotubes may be impaired. In addition, the yield of carbon nanotubes is reduced. If the liquid phase oxidation is less than 1 hour, the oxidation of the carbon impurities and the catalyst will be low, and the removal of the carbon impurities and the catalyst may be insufficient.

The mixing ratio of the oxidizing liquid and the carbon nanotubes during the liquid phase oxidation treatment is not particularly limited as long as the carbon nanotubes can be immersed, but when using a liquid with a specific gravity of about 1 to 1.5, the carbon nanotubes are used. It is preferable to use 100,000 to 150,000 parts by weight of the oxidizing liquid with respect to 100 parts by weight of the composition. If the amount of the oxidizing liquid is too small, the entire carbon nanotube may not be completely immersed in the oxidizing liquid. Therefore, the lower limit of the oxidizing liquid is the above amount. The upper limit of the oxidizing liquid is not particularly limited as long as there is no problem in handling. When the specific gravity of the oxidizing liquid is outside the above range, an amount obtained by multiplying the preferred amount by the specific gravity may be used.

When the crystallinity of the carbon nanotubes before purification is low (G / D ratio is less than 50), even if the concentration of nitric acid in the liquid phase oxidation process is low, excess functional groups are introduced starting from the amorphous part. The carbon nanotubes themselves are easily destroyed. In addition, even if the carbon nanotubes before purification having a G / D ratio of less than 50 are subjected to liquid phase oxidation treatment with nitric acid having a concentration of 50% by weight or less, the conductivity and thermal conductivity are affected by the low crystallinity of the original carbon nanotubes. Only carbon nanotubes with low characteristics such as can be obtained.

After the liquid phase oxidation step, a step of treating with an alkaline aqueous solution may be performed. The alkali is not particularly limited as long as the pH of the alkaline aqueous solution is pH 8 or higher, but ammonia or organic amine is preferably used. The organic amine is preferably an organic compound containing nitrogen such as ethanolamine, ethylamine, n-propylamine, isopropylamine, diethylamine, triethylamine, ethylenediamine, hexamethylenediamine, hydrazine, pyridine, piperidine, hydroxypiperidine. Most preferred among these ammonia and organic amines is ammonia because it volatilizes and has less adverse effects later.

The concentration of the aqueous alkali solution is preferably in the range of 10% by volume or more and less than 30% by volume. The treatment time is not particularly limited and is preferably stirred at room temperature for about 10 minutes to 2 hours. More preferably, it is 30 minutes to 1 hour.

Hereinafter, the carbon nanotube-containing composition of the present invention obtained after purification will be described. The carbon nanotube-containing composition of the present invention has a G-band to D-band height ratio (G / D ratio) of 90 or more by Raman spectroscopy at a wavelength of 532 nm. More preferably, the G / D ratio is 90 or more and 200 or less. A G / D ratio of 90 or more of the carbon nanotube-containing composition after purification indicates a very high quality carbon nanotube-containing composition.

The carbon nanotube-containing composition of the present invention has a weight reduction rate of 200 to 950 ° C. of 95% or more by thermogravimetric analysis when the temperature is increased at 10 ° C./min in air. The weight reduction rate is more preferably 97% or more, and still more preferably 99% or more. When the weight reduction rate is less than 95%, it means that the catalyst was not sufficiently removed and was contained in the carbon nanotube-containing composition. Impairs compatibility.

In thermogravimetric analysis, a sample is heated from room temperature to 1000 ° C. at a rate of temperature increase of 10 ° C./min in air using a thermogravimetric analyzer. The weight loss rate at 200 to 950 ° C. at that time is measured. By differentiating the obtained weight loss curve with time, a differential thermogravimetric curve (DTG) is obtained in which the x-axis is temperature (° C.) and the y-axis is DTG (mg / min). The peak temperature at that time is defined as the combustion peak temperature. The purified carbon nanotube-containing composition often has two combustion peaks on the high temperature side and the low temperature side in the DTG curve.

In the present invention, a combustion peak present at 700 ° C. or higher and lower than 950 ° C. is defined as a high temperature combustion peak. From the viewpoint of heat resistance, the combustion peak temperature on the high temperature side is more preferably 770 ° C. or higher and lower than 900 ° C., further preferably 780 ° C. or higher and lower than 850 ° C. The weight loss in a range corresponding to the peak area of this peak is defined as TG (H). The combustion peak on the low temperature side is a combustion peak existing from 350 ° C. to the inflection point at which the combustion peak changes to the combustion peak on the high temperature side. The weight loss in the range corresponding to the peak area of this peak is defined as TG (L). When there is no inflection point, the weight loss in the range of 350 ° C. to 600 ° C. is defined as TG (L). It is considered that TG (L) has carbon impurities other than carbon nanotubes such as amorphous carbon attached to the carbon nanotubes.

Generally, carbon impurities are combusted at 400 ° C. or lower. However, when adhering to carbon nanotubes, the combustion temperature tends to shift to a high temperature side, so that it is considered that the carbon impurities combust in the temperature range on the low temperature side. On the other hand, in the carbon nanotube to which carbon impurities are attached, the combustion peak temperature shifts to a lower temperature side in comparison with the combustion peak temperature of the original carbon nanotube. This is because the combustion temperature of carbon impurities is low, so the carbon impurities start burning first, and the generated heat energy is transferred to the carbon nanotubes, so the carbon nanotubes burn at a temperature lower than the original combustion temperature. It is. Therefore, since the combustion peak temperature appears on the higher temperature side as the carbon impurity is smaller, the higher the combustion peak temperature, the higher the durability and the higher the purity of the carbon nanotube. The larger the proportion of carbon impurities, the larger TG (L), and the larger the proportion of carbon nanotubes, the larger TG (H). By dividing TG (H) by (TG (H) + TG (L)), it can be expressed as the purity of the carbon nanotube-containing composition. By setting the value of TG (H) / (TG (L) + TG (H)) to 0.8 or more, a carbon nanotube-containing composition having a low carbon impurity ratio and high heat resistance and high conductivity can be obtained. Therefore, it is preferable. When the combustion peak on the low temperature side disappears and only the combustion peak on the high temperature side appears, the value of TG (H) / (TG (L) + TG (H)) is 1.

The number of layers of carbon nanotubes is not particularly limited, but is preferably single-walled or double-walled, with double-walled carbon nanotubes being most preferred. The reason for this is that single-walled carbon nanotubes have only one graphite layer, so when a defect is introduced when treated with an oxidizing liquid or during stirring, the conductive path with only one layer is destroyed, As the number of defects increases, the destruction of the conductive layer proceeds and the conductivity tends to decrease. For this reason, it is necessary to strictly control the temperature and time during the treatment with the oxidizing liquid. When carbon nanotubes are double-walled carbon nanotubes, the layers that carry the conductive path are doubled, so even if the outer layer is damaged or the conductive path is destroyed due to the introduction of functional groups, the inner conductive path is used. Therefore, the conductivity is difficult to decrease. Although the reason is not clear, double-walled carbon nanotubes are preferable to single-walled carbon nanotubes because they are less likely to deteriorate even after oxidation treatment.

The number of layers of carbon nanotubes contained in the carbon nanotube-containing composition of the present invention after purification is preferably such that the ratio of the number of double-walled carbon nanotubes to all carbon nanotubes is 60% or more. More preferably, the ratio of the number of double-walled carbon nanotubes to all carbon nanotubes is 70% or more. The number of carbon nanotube layers is measured, for example, as follows. Observation with a transmission electron microscope at a magnification of 400,000, and the number of layers of 100 carbon nanotubes arbitrarily extracted from the field of view in which 10% or more of the field area is carbon nanotubes in a 75 nm square field of view. taking measurement. When 100 carbon nanotubes cannot be measured in one visual field, measurement is performed from a plurality of visual fields until the number becomes 100. At this time, one carbon nanotube is counted as one if some carbon nanotubes are 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.

The diameter of the carbon nanotube is not particularly limited, but the diameter of the carbon nanotube having the number of layers in the above preferable range is 1 nm to 10 nm, and those having a diameter in the range of 1 to 3 nm are preferably used.

Doping may be performed on the carbon nanotube-containing composition after liquid phase oxidation. The doping technique is not particularly limited, but liquid phase doping is preferred. Examples of the dopant include nitric acid, hydrochloric acid, sulfuric acid and the like, and there are no particular limitations as long as it is an acidic solution.

Further, according to the method for producing a carbon nanotube dispersion of the present invention, the carbon nanotube-containing composition obtained by the production method by the liquid phase oxidation treatment is stirred together with the dispersion medium, whereby the dispersion medium contains carbon nanotubes. A carbon nanotube dispersion liquid can be obtained by dispersing the composition.

The reason why the carbon nanotube-containing composition is dispersed by the stirring treatment is that it is desired to disperse the carbon nanotube-containing composition with a weak force so as not to damage the graphite layer of the carbon nanotube and deteriorate the characteristics. In general, when a carbon nanotube-containing composition is dispersed using a dispersion method that is widely used for dispersing a carbon nanotube-containing composition, such as an ultrasonic homogenizer, a roll mill, or a ball mill, defects may occur in the graphite layer of the carbon nanotube. Since the carbon nanotubes are cut by a strong stress, the characteristics of the carbon nanotubes such as conductivity and thermal conductivity are deteriorated. On the other hand, in the dispersion by stirring, the stress is too weak, and generally, a dispersion in which the carbon nanotube-containing composition is sufficiently dispersed cannot be obtained only by the stirring treatment.

The inventors, using the carbon nanotube-containing composition obtained by the production method of the present invention, by performing a stirring process together with the dispersion medium, the carbon nanotubes without losing characteristics such as conductivity and thermal conductivity, Succeeded in producing highly dispersed dispersion. Here, highly dispersed means that when the dispersion is centrifuged at 10,000 G for 10 minutes and then recovered by 90 vol% as a supernatant, the concentration of the carbon nanotube dispersion in the supernatant is In other words, it means 80% by weight or more of the concentration of the carbon nanotube dispersion before centrifugation.

In the present invention, the reason why a sufficiently dispersed dispersion can be obtained only by stirring treatment is not clear, but is considered as follows. In general, when a carbon nanotube undergoes a liquid phase oxidation treatment step such as nitric acid, a small amount of functional groups such as a carboxyl group, a hydroxyl group, and an epoxy group are introduced on the surface of the carbon nanotube. Since the carbon nanotube-containing composition obtained by the production method of the present invention has moderately functional groups, electrostatic repulsion between the carbon nanotubes due to the functional groups occurs in the solution in the oxidation treatment step, and the bundle is loosened. It becomes easy. As a result, it is presumed that carbon nanotubes that are easy to disperse in the dispersion step, which is the next step, can be obtained.

The reason why carbon nanotubes are less likely to be damaged when dispersed by stirring dispersion is not clear, but in general, dispersion due to stirring and dispersion due to shear stress applied to carbon nanotubes is caused by ultrasonic vibration (and cavitation). It is considered that the dispersion is mild and weak compared to the stress that mechanically crushes.

The stirring process is performed by rotating the stirring blade in the container. The shape of the stirring blade is preferably a solid grinding blade. As the stirrer, a mill for solid grinding by stirring, a juicer mixer, a food processor and the like can be used particularly preferably. More specifically, a trade name “Milcer” series (product of Iwatani Corporation) can be used.

In the stirring treatment, it is preferable to stir the stirring blade at a rotational speed of 3000 revolutions / minute or more. The higher the rotation speed of the stirring blade, the more the carbon nanotubes are strongly sheared and sheared and the like, and the dispersion is quicker. A more preferable rotation speed is 10,000 rotations / minute or more, and further preferably 20,000 rotations / minute or more. However, if the number of revolutions is too high, the heat generation is intense and the dispersion operation cannot be performed practically, so the upper limit is at most 50000 revolutions / minute. In addition, when the rotational speed is too high, the carbon nanotubes are likely to be physically damaged by the stirring blade. The temperature of the stirring and dispersing treatment is preferably performed while cooling in order to suppress the occurrence of extra side reactions due to dispersion. However, if there is no particular reaction with carbon nanotubes, the dispersion medium and other additives, cooling is necessary. Is not necessarily. Although the specific temperature condition varies depending on the dispersion medium, there is no particular limitation as long as the dispersion medium can maintain a liquid form and can be stirred.

The stirring time in the stirring treatment is preferably adjusted so that the graphite structure of the carbon nanotube-containing composition is highly dispersed without being destroyed as much as possible. The specific stirring time is preferably 10 seconds or more and 2 hours or less from the viewpoint of dispersibility and conductivity. More preferably, they are 30 seconds or more and 30 minutes or less, More preferably, they are 1 minute or more and 5 minutes or less. When the time for the stirring treatment is less than 10 seconds, the shearing force is insufficient, and the dispersibility of the resulting dispersion is lowered. On the other hand, when the stirring time exceeds 2 hours, the carbon nanotubes contained in the obtained dispersion liquid are damaged by stirring, and the conductivity may be lowered.

The dispersion medium used for dispersion is not particularly limited, but it is preferable to use a polar solvent having a high affinity for a functional group such as a hydroxyl group, a carboxyl group, or an epoxy group, which is introduced by oxidation treatment. Examples of polar solvents include alcohols such as methanol, ethanol, propanol, isopropanol, butanol, amyl alcohol, terpineol, dihydroterpineol, and menthol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethyl acetate, butyl acetate, and ethyl lactate Esters; ethers such as dioxane, tetrahydrofuran, methyl cellosolve, ethyl cellosolve; ether alcohols such as ethoxyethanol, methoxyethoxyethanol; amide compounds such as dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide; other, water, Examples include morpholine and acetonitrile. Among these, water, alcohol, ether, and a solvent combining them are particularly preferable from the viewpoint of dispersibility of the carbon nanotubes. Among these, use of water is particularly preferable because it is easy to obtain an effect of improving dispersibility by hydrogen bonding with the surface functional group of the carbon nanotube.

During the stirring treatment, it is preferable to add a dispersant and stir with the carbon nanotubes. Since the carbon nanotube-containing composition obtained by the method for producing a carbon nanotube-containing composition of the present invention has only functional groups introduced so as not to deteriorate the characteristics of the carbon nanotube, only the carbon nanotube is stirred with a dispersion medium. If so, the dispersibility is not so high. When the dispersion is applied to the substrate, the dispersion is preferably dispersed so that high conductivity and thermal conductivity can be drawn out.

As the dispersant, when the dispersion medium is a polar organic solvent other than water, a polyvinyl acetal derivative or a cellulose derivative can be preferably used. Specific examples of the polyvinyl acetal derivative include polyvinyl formal and polyvinyl butyral. Examples of the cellulose derivative include methyl cellulose, ethyl cellulose, propyl cellulose, methyl ethyl cellulose, methyl propyl cellulose, and ethyl propyl cellulose when the cellulose derivative is a cellulose ether. When the cellulose derivative is a cellulose ester, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose valerate, cellulose stearate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate valerate, cellulose acetate Examples include proate, cellulose propionate butyrate, and cellulose acetate propionate butyrate. Moreover, when a cellulose derivative is a cellulose ether ester, methyl cellulose acetate, methyl cellulose propionate, ethyl cellulose acetate, ethyl cellulose propionate, propyl cellulose acetate, propyl cellulose propionate, etc. are mentioned, However, it is not limited to these.

When the dispersion medium is water, ionic dispersants can be used. In addition to sodium cholate, sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, etc., carboxylic acid derivatives such as cholic acid, deoxycholic acid, etc. It can be used. Water-soluble cellulose derivatives and polyethylene glycol derivatives can also be used. In particular, the carboxymethyl cellulose derivative is adhered to the carbon nanotubes in the dispersion, and the electrical repulsion of the carboxylate prevents the carbon nanotubes from aggregating. In this case, the conductivity is particularly good. The carboxymethyl cellulose derivative is particularly preferably used when water is used as a dispersion medium, and those having a degree of etherification of 0.4 to 1 are particularly preferable.

The amount of the dispersant contained in the carbon nanotube dispersion liquid is preferably larger than the amount adsorbed on the carbon nanotubes and does not inhibit the conductivity. The carbon nanotube dispersion obtained by the present invention is also characterized in that carbon nanotubes are highly dispersed in a dispersion medium even when a relatively small amount of dispersant is used.

Specifically, the content of the dispersant contained in the carbon nanotube dispersion is preferably 10 parts by weight or more and 500 parts by weight or less with respect to 100 parts by weight of the carbon nanotube-containing composition. The content of the dispersant is more preferably 30 parts by weight or more with respect to 100 parts by weight of the carbon nanotube-containing composition. The content is more preferably 200 parts by weight or less. When the content of the dispersing agent is less than 10 parts by weight, the dispersibility tends to be lowered because the bundle of carbon nanotubes cannot be sufficiently unraveled. If the content is more than 500 parts by weight, the conductive path is hindered by an excessive dispersant, so that the conductivity deteriorates when the dispersion is applied to the substrate. In addition, when a hydrophilic functional group is present in the dispersant, a change in conductivity due to moisture absorption of the dispersant is likely to occur with respect to environmental changes such as high temperature and high humidity.

In addition, the content of the carbon nanotube-containing composition with respect to the entire dispersion is preferably 0.01% by weight or more and 20% by weight or less. The content is more preferably 0.05% by weight or more. Further, the content is more preferably 10% by weight or less. When the content of the carbon nanotube-containing composition is less than 0.01% by mass, it is not preferable because ion repulsion between the dispersants attached to the carbon nanotube and electron repulsion of the carbon nanotube surface functional group cannot be effectively used.

Further, the weight average molecular weight of the dispersant is preferably 10,000 or more and 400,000 or less, more preferably 30,000 or more and 250,000 or less, and further preferably more than 60,000 and 250,000 or less. When the weight average molecular weight of the dispersant is within this range, the dispersant can easily enter the gaps between the carbon nanotubes during dispersion, and the dispersibility of the carbon nanotubes is improved. Furthermore, when the dispersion liquid is applied on the base material, aggregation of the carbon nanotubes on the base material is also suppressed, so that the conductivity and transparency of the obtained conductive molded body can be compatible. The weight average molecular weight in the present invention is determined by gel permeation chromatography (apparatus: LC-10A series manufactured by Shimadzu Corporation), column: GF-7M HQ manufactured by Showa Denko KK, mobile phase: 10 mmol / L lithium bromide aqueous solution, (Flow rate: 1.0 ml / min, column temperature: 25 ° C., detection: differential refractometer), and a value calculated by comparing with a calibration curve using polyethylene glycol.

The dispersant having the weight average molecular weight in the above range may be synthesized so that the range of the weight average molecular weight is in the above range, or by lowering the molecular weight by a method such as hydrolysis of a higher molecular weight dispersant. You may get.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

(Thermogravimetric analysis)
Using a thermogravimetric analyzer (Shimadzu Corporation TGA-60), the temperature of the sample was increased from room temperature to 1000 ° C. at a temperature increase rate of 10 ° C./min. The obtained weight loss curve was differentiated by time to obtain a differential thermogravimetric curve (DTG) in which the x axis is temperature (° C.) and the y axis is DTG (mg / min). The weight loss rate in the temperature range of 200 to 950 ° C. at that time was measured.

(Raman spectroscopy)
A powder sample was placed in a resonance Raman spectrometer (Holiba Joban Yvon INF-300), and measurement was performed using a laser wavelength of 532 nm.

(Observation of outer diameter distribution and wall number distribution of carbon nanotube)
1 mg of the carbon nanotube-containing composition was placed in 1 mL of ethanol, and dispersion treatment was performed using an ultrasonic bath for 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 measurement was performed. Observation of the outer diameter distribution and the wall number distribution of the carbon nanotubes was performed at a magnification of 400,000 times.

(Synthesis and properties of carbon nanotubes)
[Reference Example 1]
A carbon nanotube-containing composition was produced using the vertical production apparatus shown in FIG.

1 includes a vertical reaction tube 22 serving as a reaction vessel for synthesizing a carbon nanotube-containing composition, a heating furnace 21 that is provided on the outer periphery of the vertical reaction tube 22 and heats the inside of the vertical reaction tube 22; A liquid spray nozzle 19 for spraying a catalytic carbon source solution in the vertical reaction tube 22 in the form of a mist, a carrier gas flow meter 14 for liquid spray, a tank 16 for storing a carrier gas for liquid spray, a carrier gas inlet 18, and a carrier gas Carrier gas flow meter 15 for adjusting the flow rate of the liquid, tank 17 for storing the carrier gas, liquid feed pump 13 for introducing the catalytic carbon source solution into the vertical reaction tube 22, and recovery for recovering the synthesized carbon nanotube-containing composition A box 24 and a collection filter 25 installed in the collection box 24 are included. The vertical reaction tube 22 is connected to other members by the upper flange 20 and the lower flange 23 so that gas does not leak from the connection portion.

The syringe 11 stores, as a carbon source, a catalytic carbon source solution 12 in which an aromatic compound in a liquid state at normal temperature and pressure, ferrocene as an organic transition metal compound, and thiophene as an organic sulfur compound are mixed. The introduction amount can be adjusted by the pump 13.

By introducing the catalytic carbon source solution 12 into the vertical reaction tube 22 by spraying from the liquid spray nozzle 19 and performing the gas phase flow CVD method in the vertical reaction tube 22 surrounded by the superheated furnace 21, A carbon nanotube-containing composition before purification was synthesized. The obtained pre-purification carbon nanotube-containing composition was recovered by the filter 25. The carrier gas from which the carbon nanotube-containing composition has been removed by the filter 25 is discharged out of the system through the exhaust port 26.

The collected carbon nanotube-containing composition before purification was placed in an about 1 mg thermogravimetric analyzer, and the temperature was raised from room temperature to 1000 ° C. in air at a rate of 10 ° C./min. The weight loss rate at 200 to 950 ° C. at that time was 89%, and TG (H) / (TG (L) + TG (H)) was 0.81. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 83.

[Reference Example 2]
A carbon nanotube-containing composition was produced and recovered using the method of Example 1 (supported catalyst CVD method) of JP2011-148673A.

The collected carbon nanotube-containing composition before purification was placed in an about 1 mg thermogravimetric analyzer, and the temperature was raised from room temperature to 1000 ° C. in air at a rate of 10 ° C./min. At that time, the weight loss rate from 200 to 950 ° C. was 95%, and TG (H) / (TG (L) + TG (H)) was 0. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 13.

[Example 1]
The purified carbon nanotube-containing composition obtained by subjecting the carbon nanotube-containing composition before purification obtained in Reference Example 1 to liquid phase oxidation in 7.5 wt% nitric acid with stirring at a reflux temperature of 103 ° C. for 2 hours. I got a thing. As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 100%, and TG (H) / (TG (L) + TG (H)) is 0.83. The peak temperature of TG (H) was 835 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 124. The recovery rate was 89% by weight. Here, the recovery rate is a weight ratio of the obtained carbon nanotube-containing composition after purification when the weight of the carbon nanotube-containing composition before purification is 100% by weight.

[Example 2]
The purified carbon nanotube-containing composition obtained by subjecting the carbon nanotube-containing composition before purification obtained in Reference Example 1 to liquid phase oxidation in 7.5 wt% nitric acid with stirring at a reflux temperature of 103 ° C. for 6 hours. Got. As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 100%, and TG (H) / (TG (L) + TG (H)) is 0.81. The peak temperature of TG (H) was 829 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 121. The recovery rate was 89% by weight.

[Example 3]
The purified carbon nanotube-containing composition obtained in Reference Example 1 was subjected to liquid phase oxidation in 15% by weight nitric acid with stirring at a reflux temperature of 105 ° C. for 6 hours to obtain a purified carbon nanotube-containing composition. It was. As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 100%, and TG (H) / (TG (L) + TG (H)) is 0.81. The peak temperature of TG (H) was 784 ° C. Further, as a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 110. The proportion of double-walled carbon nanotubes was 74%. The recovery rate was 88% by weight.

[Example 4]
The purified carbon nanotube-containing composition obtained by subjecting the carbon nanotube-containing composition before purification obtained in Reference Example 1 to liquid phase oxidation in 3.8 wt% nitric acid with stirring at a reflux temperature of 101 ° C. for 2 hours. I got a thing. As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 99%, and TG (H) / (TG (L) + TG (H)) is 0.83. The peak temperature of TG (H) was 832 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 122. The recovery rate was 90% by weight.

[Example 5]
The purified carbon nanotube-containing composition obtained in Reference Example 1 was subjected to liquid phase oxidation in 30 wt% nitric acid with stirring at a reflux temperature of 110 ° C. for 6 hours to obtain a purified carbon nanotube-containing composition. Obtained. As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 99%, and TG (H) / (TG (L) + TG (H)) is 0.8. The peak temperature of TG (H) was 770 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 95. The recovery rate was 85% by weight.

[Comparative Example 1]
The purified carbon nanotube-containing composition obtained in Reference Example 1 was subjected to liquid phase oxidation in 60% by weight nitric acid with stirring at a reflux temperature of 121 ° C. for 2 hours to obtain a purified carbon nanotube-containing composition. It was. As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 100%, and TG (H) / (TG (L) + TG (H)) is 0.79. The peak temperature of TG (H) was 760 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 103. The proportion of double-walled carbon nanotubes was 74%. The recovery rate was 85% by weight.

[Comparative Example 2]
The purified carbon nanotube-containing composition obtained in Reference Example 2 was subjected to liquid phase oxidation in 60 wt% nitric acid with stirring at a reflux temperature of 121 ° C. for 25 hours to obtain a purified carbon nanotube-containing composition. . As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 100%, and TG (H) / (TG (L) + TG (H)) is 0.79. The peak temperature of TG (H) was 725 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 70. The recovery rate was 13% by weight.

[Comparative Example 3]
The purified carbon nanotube-containing composition obtained in Reference Example 2 was subjected to liquid phase oxidation in 50 wt% nitric acid with stirring at a reflux temperature of 117 ° C. for 50 hours to obtain a purified carbon nanotube-containing composition. . As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 100%, and TG (H) / (TG (L) + TG (H)) is 0.84. The peak temperature of TG (H) was 757 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 41. The recovery rate was 10% by weight.

[Comparative Example 4]
The purified carbon nanotube-containing composition obtained in Reference Example 2 was subjected to liquid phase oxidation in 60 wt% nitric acid with stirring at a reflux temperature of 121 ° C. for 5 hours to obtain a purified carbon nanotube-containing composition. . As a result of thermogravimetric analysis of the purified carbon nanotube-containing composition, the weight loss rate at 200 to 950 ° C. is 99%, and TG (H) / (TG (L) + TG (H)) is 0.9. The peak temperature of TG (H) was 725 ° C. As a result of Raman spectroscopic analysis at a wavelength of 532 nm, the G / D ratio was 80. The recovery rate was 80% by weight.

From the above results, 1% by weight or more with respect to the carbon nanotube-containing composition having a G-band to D-band intensity ratio (G / D ratio) of 50 or more in Raman spectroscopic analysis of the carbon nanotube-containing composition before purification. In addition, carbon impurities and the catalyst can be easily removed by performing liquid phase oxidation by heating and refluxing using nitric acid of 50% by weight or less, and a high-quality carbon nanotube-containing composition can be obtained in a high yield.

[Example 6]
56.25 mg of the carbon nanotube-containing composition obtained in Example 3, sodium carboxymethylcellulose (Daiichi Kogyo Seiyaku Co., Ltd., hydrolyzate of serogen 5A, weight average molecular weight 35000) 10 wt% aqueous solution 843.85 mg, and 112.5 mg of ammonium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) was mixed and further distilled water was added to make 37.5 g. Using IMF-800DG (manufactured by Iwatani Corporation) as a stirrer, the rotation speed of the stirring blade was 20000 rpm A carbon nanotube dispersion was prepared by stirring for 3 minutes.

<Evaluation of dispersion>
In order to show that the obtained carbon nanotube dispersion liquid is highly dispersed and maintains the high conductivity that is characteristic of the carbon nanotube, a PET film (U46, thickness 100 μm) manufactured by Toray Industries, Inc. is used. The obtained carbon nanotube dispersion was applied and the transparent conductivity was evaluated.

For the film for measurement, the carbon nanotube dispersion obtained as described above was diluted about 3 times with water, and the coating amount was adjusted within the range of 4 μm to 150 μm using a wire bar coater. After coating, the film was dried to obtain a carbon nanotube-coated film. The transmittance was measured for each substrate in accordance with JIS K7105 using a Nippon Denshoku Industries Co., Ltd. haze meter NDH4000. The surface resistance value was measured using a Loresta (registered trademark) EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.) according to a 4-terminal 4-probe method according to JISK7194 (established in December 1994).

When the evaluation was performed while changing the coating film thickness, it was found that the surface resistance value of the carbon nanotube-coated film at a total light transmittance of 88.5% was 320Ω / □, indicating good transparent conductivity.

In addition, in order to evaluate the dispersibility of the carbon nanotube dispersion, the obtained carbon nanotube dispersion was centrifuged at 10,000 G for 10 minutes, and then 90 vol% was recovered as a supernatant. The concentration of the nanotube dispersion liquid was 90% by weight of the concentration of the carbon nanotube dispersion liquid before the centrifugal treatment. The results are shown in Table 2. The concentration of the carbon nanotube dispersion is such that 10 g of the dispersion is heated to 120 ° C. to evaporate the solvent, and the resulting residue is further dried for 24 hours. The weight of the carbon nanotubes contained in the dispersion was calculated by subtracting the calculated weight of the dispersant from the amount of the above, and the concentration of the carbon nanotube dispersion was calculated.

[Example 7]
Using the carbon nanotube-containing composition obtained in Example 5, a carbon nanotube dispersion was prepared in the same manner as in Example 6. Transparent conductivity and CNT dispersion in the supernatant after centrifugation were performed in the same manner as in Example 6. The concentration of the liquid was measured.

The surface resistance value of the carbon nanotube-coated film at a total light transmittance of 88.5% was 300Ω / □, and it was found that the film had good transparent conductivity.

In addition, in order to evaluate the dispersibility of the carbon nanotube dispersion liquid, the obtained carbon nanotube dispersion liquid was centrifuged at 10,000 G for 10 minutes, and then the carbon in the supernatant when 90 vol% was recovered as the supernatant. The concentration of the nanotube dispersion liquid was 90% by weight of the concentration of the carbon nanotube dispersion liquid before the centrifugal treatment. The results are shown in Table 2.

[Comparative Example 5]
A carbon nanotube dispersion was prepared in the same manner as in Example 6 using the carbon nanotube-containing composition obtained in Comparative Example 4, and the transparent conductive and CNT dispersion in the supernatant after centrifugation as in Example 6. The concentration of was measured.

The surface resistance value of the carbon nanotube-coated film at a total light transmittance of 88.5% was 450Ω / □, and the transparent conductivity was poor as compared with Example 6.

In addition, in order to evaluate the dispersibility of the carbon nanotube dispersion liquid, the obtained carbon nanotube dispersion liquid was centrifuged at 10,000 G for 10 minutes, and then the carbon in the supernatant when 90 vol% was recovered as the supernatant. The concentration of the nanotube dispersion liquid was 75% by weight of the concentration of the carbon nanotube dispersion liquid before the centrifugal treatment. The results are shown in Table 2.

[Comparative Example 6]
A carbon nanotube dispersion was prepared in the same manner as in Example 6 using the carbon nanotube-containing composition (sample not subjected to liquid phase oxidation treatment with nitric acid) shown in Reference Example 1, and evaluated in the same manner as in Example 6. . The results are shown in Table 2. Compared to Example 6, both the transparent conductivity and dispersibility were poor.

[Comparative Example 7]
A carbon nanotube dispersion was prepared in the same manner as in Example 6 except that dispersion by stirring was not performed, and evaluation was performed in the same manner as in Example 6. The results are shown in Table 2. The carbon nanotube-containing composition was not dispersed, and the transparent conductivity could not be evaluated.

[Comparative Example 8]
A carbon nanotube dispersion was prepared in the same manner as in Example 6 except that the carbon nanotube-containing composition was dispersed using an ultrasonic homogenizer instead of stirring, and evaluation was performed in the same manner as in Example 6. The results are shown in Table 2. The dispersibility of the carbon nanotube-containing composition was good, but the surface resistance value was 500Ω / □, which was worse than that of Example 6.

According to the present invention, a dispersion in which carbon nanotubes having high crystallinity and high purity are highly dispersed can be produced. By using such a carbon nanotube dispersion liquid, it is possible to obtain a transparent conductive film or a transparent conductive laminate having both high conductivity and high transparency.

11 Syringe 12 Catalytic carbon source solution 13 Liquid feed pump 14 Carrier gas flow meter for liquid spray 15 Carrier gas flow meter 16 Carrier gas tank for liquid spray 17 Carrier gas tank 18 Carrier gas inlet 19 Liquid spray nozzle 20 Upper flange 21 Heating furnace 22 vertical Type reaction tube 23 lower flange 24 recovery box 25 recovery filter 26 exhaust gas

Claims

Heat-reflux a carbon nanotube-containing composition before purification having a G-band to D-band intensity ratio (G / D ratio) of 50 or more in Raman spectroscopic analysis using nitric acid having a concentration of 1 wt% or more and 50 wt% or less. The manufacturing method of the carbon nanotube containing composition including the liquid phase oxidation process of performing liquid phase oxidation by doing.
The method for producing a carbon nanotube-containing composition according to claim 1, wherein a pre-purification carbon nanotube-containing composition having a G / D ratio of 50 or more is produced by a gas phase flow method, and then the liquid phase oxidation step is performed.
The method for producing a carbon nanotube-containing composition according to claim 2, wherein in the gas phase flow method, a catalyst, a carbon source and a carrier gas are introduced into the vertical reaction tube from above to produce a carbon nanotube-containing composition before purification.
The method for producing a carbon nanotube-containing composition according to any one of claims 1 to 3, wherein the heating reflux temperature is in a temperature range of 100 ° C or higher and 110 ° C or lower.
The method for producing a carbon nanotube-containing composition according to any one of claims 1 to 4, wherein the concentration of nitric acid in the liquid phase oxidation step is 1 wt% or more and less than 20 wt%.
The method for producing a carbon nanotube-containing composition according to any one of claims 1 to 5, wherein the liquid phase oxidation step is performed for 1 hour to 24 hours.
The method for producing a carbon nanotube-containing composition according to any one of claims 1 to 6, wherein in the obtained carbon nanotube-containing composition, the ratio of the number of double-walled carbon nanotubes to all the carbon nanotubes is 60% or more.
A carbon nanotube dispersion liquid comprising a step of dispersing the carbon nanotube-containing composition in the dispersion medium by subjecting the carbon nanotube-containing composition obtained by the production method according to claim 1 to a stirring treatment together with the dispersion medium. Production method.
The method for producing a carbon nanotube dispersion according to claim 8, wherein in the step of performing the stirring treatment, a dispersing agent is further added to perform the stirring treatment.
The method for producing a carbon nanotube dispersion liquid according to claim 8 or 9, wherein the stirring treatment is a treatment of rotating a stirring blade in a container at a rotational speed of 3000 rotations / minute or more and 50000 rotations / minute or less.
Carbon nanotube-containing composition satisfying all of the following conditions (1) to (5):
(1) The intensity ratio (G / D ratio) of G band and D band in Raman spectroscopic analysis is 90 or more;
(2) The weight loss rate at 200 to 950 ° C. is 95% or more by thermogravimetric analysis when the temperature is raised at 10 ° C./min in air;
(3) In the thermogravimetric analysis when the temperature is raised at 10 ° C./min in air, the combustion peak on the high temperature side is 770 ° C. or higher and lower than 900 ° C .;
(4) In thermogravimetric analysis when the temperature is increased at 10 ° C./min in air, the weight loss on the low temperature side (TG (L)) and the weight loss on the high temperature side (TG (H)) are TG ( H) / (TG (L) + TG (H)) is 0.8 or more;
(5) The ratio of the number of double-walled carbon nanotubes to all carbon nanotubes is 60% or more.