WO2015045417A1

WO2015045417A1 - Method of producing carbon nanotube dispersion

Info

Publication number: WO2015045417A1
Application number: PCT/JP2014/004980
Authority: WO
Inventors: 克彦藤田; 悟深町; 清茂児島
Original assignee: 日本ゼオン株式会社; 国立大学法人九州大学
Priority date: 2013-09-30
Filing date: 2014-09-29
Publication date: 2015-04-02
Also published as: JPWO2015045417A1

Abstract

The purpose of the present invention is to provide a method which, even without the use of a dispersant, allows efficiently producing a dispersion comprising uniformly dispersed carbon nanotubes. This method of producing a carbon nanotube dispersion is characterized by involving a step for bringing an aligned carbon nanotube aggregate formed on a substrate into contact with a solvent, and a step for separating the aligned carbon nanotube aggregate from the substrate in the solvent, wherein the carbon nanotubes configuring the aligned carbon nanotube aggregate fulfill the relation between the average diameter (Av) and the diameter distribution (3σ) of 0.20 < (3σ / Av) < 0.60, and the average length is greater than or equal to 100μm.

Description

Method for producing carbon nanotube dispersion

The present invention relates to a method for producing a carbon nanotube dispersion.

Conventionally, carbon nanotubes (hereinafter sometimes referred to as “CNT”) are known as substances having excellent conductivity and mechanical properties. And in recent years, the technique which improves the electroconductivity and mechanical characteristic of various products, such as a film and a fiber, by using CNT is proposed. Specifically, by using a carbon nanotube dispersion liquid (hereinafter sometimes referred to as “CNT dispersion liquid”) containing a solvent and CNT as a material and manufacturing a product containing CNT, Techniques for improving the properties and mechanical properties have been proposed.

Here, in order to effectively improve the electrical conductivity and mechanical properties of the product using the above technique, it is useful to use a CNT dispersion in which CNTs are well dispersed. However, in general, CNT is easy to aggregate and difficult to disperse. Therefore, development of a method for producing a CNT dispersion in which CNTs are well dispersed is demanded.

In response to such a request, for example, in Patent Document 1, a substrate in which CNTs are grown on a surface, a solvent, and a dispersant are introduced into a container, and then the CNTs are peeled from the substrate in a solvent containing the dispersant. Has been proposed to produce a CNT dispersion in which CNTs are well dispersed. CNTs grown on a substrate using a chemical vapor deposition method or the like exist in a state in which the distance between adjacent CNTs is relatively long. According to the method described in Patent Document 1, aggregation occurs. Since the CNTs on the substrate kept in a small separated state can be directly dispersed in the solvent in the presence of the dispersant, a CNT dispersion liquid in which CNTs are well dispersed can be obtained.

JP 2008-24523 A

However, since the manufacturing method described in Patent Document 1 uses a solvent containing a dispersant, the dispersant is inevitably mixed into the obtained CNT dispersion. Therefore, when various products such as films and fibers are manufactured using the CNT dispersion, the dispersant may be mixed in the product, and the performance such as conductivity may not be sufficiently improved. On the other hand, when the dispersant is removed from the CNT dispersion or product using means such as washing or heating, the manufacturing process becomes complicated and the cost increases.

Therefore, an object of the present invention is to provide a method for efficiently producing a dispersion in which carbon nanotubes are uniformly dispersed without using a dispersant.

The present inventors have intensively studied for the purpose of solving the above problems. And, when the present inventors manufactured a CNT dispersion by peeling an aligned aggregate of carbon nanotubes having a predetermined property synthesized on a substrate from the substrate in a solvent, surprisingly, a dispersant was used. Even without this, it was found that a CNT dispersion liquid in which CNTs were uniformly dispersed was obtained, and the present invention was completed.

That is, the present invention aims to advantageously solve the above problems, and the method for producing a carbon nanotube dispersion of the present invention comprises an aligned aggregate of carbon nanotubes formed on a substrate, and a solvent. The carbon nanotubes constituting the aligned carbon nanotubes have an average diameter (Av), comprising a step (1) of contacting and a step (2) of separating the aligned carbon nanotubes from the substrate in the solvent. And the diameter distribution (3σ) satisfy the relational expression: 0.20 <(3σ / Av) <0.60, and one of the major features is that the average length is 100 μm or more. As described above, an aligned carbon nanotube assembly composed of carbon nanotubes having a ratio of diameter distribution to average diameter (3σ / Av) of more than 0.20 and less than 0.60 and an average length of 100 μm or more is obtained in a solvent. If the substrate is separated from the substrate, a CNT dispersion in which CNTs are uniformly dispersed in a solvent can be efficiently produced without using a dispersant.
Here, in the present invention, “diameter distribution (3σ)” refers to a value obtained by multiplying the sample standard deviation (σ) of the diameter of the carbon nanotube by 3. In the present invention, “average diameter of carbon nanotube (Av)”, “sample standard deviation of carbon nanotube diameter (σ)”, and “average length of carbon nanotube” are respectively observed with a transmission electron microscope. Below, the diameter (outer diameter) and length of 100 randomly selected carbon nanotubes can be measured and determined.

Here, it is preferable that the method for producing a carbon nanotube dispersion of the present invention further includes a step (3) of dispersing the aligned carbon nanotube aggregate separated from the substrate in the solvent. This is because a CNT dispersion with further improved CNT dispersibility can be obtained by further dispersing the carbon nanotube alignment aggregate after separating it from the substrate.

In the method for producing a carbon nanotube dispersion of the present invention, the carbon nanotube-containing aggregate in contact with the solvent is placed under reduced pressure between the step (1) and the step (2) ( 4) is preferably further included. If the carbon nanotube alignment aggregate is placed in contact with a solvent under a reduced pressure before separating the carbon nanotube alignment aggregate from the substrate, air or the like existing in the gaps between the CNTs constituting the carbon nanotube alignment aggregate Discharged. As a result, it becomes easier for the solvent to be impregnated in the gaps between the CNTs, and the solvent can be uniformly distributed in the aligned CNT aggregate.

In the method for producing a carbon nanotube dispersion of the present invention, it is preferable that the substrate is a plate-like, particle-like or linear substrate. This is because a plate-like, particle-like, or linear substrate is easy to handle, and the aligned carbon nanotube aggregates can be easily separated from the substrate.

According to the method for producing a carbon nanotube dispersion of the present invention, a dispersion in which carbon nanotubes are uniformly dispersed can be efficiently produced without using a dispersant.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the method for producing a carbon nanotube dispersion of the present invention can be used when producing a carbon nanotube dispersion obtained by dispersing CNTs in a solvent.
And the CNT dispersion liquid manufactured according to the manufacturing method of the carbon nanotube dispersion liquid of this invention is not specifically limited, It can use when manufacturing various products, such as a film and a fiber. Specifically, the CNT dispersion liquid is, for example, coated with a CNT dispersion liquid on a substrate and dried to produce a carbon nanotube-containing film, or mixed with a polymer material such as resin or rubber to contain CNT. It can be used when producing a composite material.

(Method for producing carbon nanotube dispersion)
The method for producing a carbon nanotube dispersion according to the present invention includes (1) a step of contacting an aligned aggregate of carbon nanotubes formed on a substrate and a solvent (contact step), and (2) a solvent after the contact step. And a step of separating the aligned carbon nanotube aggregate from the substrate (separation step). In the method for producing a carbon nanotube dispersion according to the present invention, the carbon nanotubes constituting the aligned carbon nanotube aggregate have a predetermined average diameter (Av), diameter distribution (3σ), and average length. One of the features.
And according to the manufacturing method of the carbon nanotube dispersion liquid concerning this invention, even if it does not use a dispersing agent, the dispersion liquid with which the carbon nanotube was disperse | distributed uniformly can be manufactured efficiently.
In the method for producing a carbon nanotube dispersion according to the present invention, after the separation step, (3) a step (dispersion step) of dispersing the carbon nanotube alignment aggregate separated from the substrate in a solvent is performed. May be. Moreover, you may implement (4) the process (pressure reduction process) which puts the carbon nanotube mixing aggregate which is contacting the solvent under reduced pressure arbitrarily between a contact process and a separation process.

Hereinafter, the contact process, the decompression process, the separation process, and the dispersion process of the carbon nanotube dispersion manufacturing method according to the present invention will be described in order.

<Contact process>
In the contacting step, the aligned carbon nanotube aggregate formed on the substrate made of carbon nanotubes having a predetermined property is brought into contact with the solvent.

Here, the contact may be performed by immersing the aligned carbon nanotube aggregate formed on the substrate in a solvent together with the substrate, or the solvent with respect to the substrate on which the carbon nanotube aligned aggregate is formed on the surface. May be performed by adding
In addition, from the viewpoint of smoothly performing the separation step described later after the contact step with the solvent, the aligned carbon nanotube assembly and the solvent may be contacted by immersing the aligned carbon nanotube assembly in the solvent together with the substrate. preferable.

[Aligned carbon nanotube assembly]
The aligned carbon nanotube aggregate formed on the substrate refers to a structure in which a large number of CNTs grown on the substrate are aligned in a specific direction.

[[substrate]]
Here, as the substrate, a base material having a catalyst layer on the surface, which is a catalyst layer for CNT growth, can be used. Specifically, as the substrate, a substrate obtained by forming a catalyst layer made of iron, nickel, cobalt, molybdenum, or a chloride or alloy thereof on a metal or ceramic base material is used. it can.

The shape of the substrate can be any shape, but it may be flat, particulate, or linear from the viewpoint of handleability and ease of separation of the aligned carbon nanotube aggregate from the substrate. preferable.

[[carbon nanotube]]
In the method for producing a carbon nanotube dispersion according to the present invention, the average diameter (Av) and the diameter distribution (3σ) of the CNTs constituting the aligned carbon nanotube aggregate are 0.60> (3σ / Av)> 0. .20 and the average length needs to be 100 μm or more. This is because, when the CNTs have the above properties, the CNTs can be uniformly dispersed in the solvent without using a dispersant when preparing a CNT dispersion by carrying out a separation step described later. In addition, even after making the CNT dispersion, the viewpoint that the CNT can maintain a certain length or more and the performance (for example, conductivity and mechanical properties) of the product manufactured using the CNT dispersion can be satisfactorily exhibited. Therefore, the ratio (3σ / Av) of the diameter distribution (3σ) to the average diameter (Av) is preferably more than 0.50. For the same reason, the average length of the CNT is preferably 300 μm or more, more preferably 500 μm or more. Furthermore, from the viewpoint of enhancing the dispersibility of CNTs and preventing the CNTs from peeling off from the substrate when contacting the aligned carbon nanotube aggregates formed on the substrate with the solvent, the average length of the CNTs Is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 3 mm or less.

The above-mentioned CNT preferably has a normal distribution when plotted by taking the diameter on the horizontal axis and the frequency on the vertical axis and approximating with Gaussian.

Further, the CNT constituting the aligned carbon nanotube assembly may be one having a functional group such as a carboxyl group introduced on the surface. The functional group can be introduced by a known oxidation treatment method using hydrogen peroxide, nitric acid or the like.

Furthermore, the CNTs constituting the aligned carbon nanotube assembly may be single-walled or multi-walled, but the performance (for example, conductivity and mechanical properties) of products manufactured using the CNT dispersion liquid may be used. From the standpoint of improving the optical characteristics, single to five layers are preferable, and single layers are more preferable.
Furthermore, the CNT preferably has a peak of Radial Breathing Mode (RBM) when evaluated using Raman spectroscopy. Note that there is no RBM in the Raman spectrum of multi-walled carbon nanotubes of three or more layers.

CNTs preferably have a G-band peak intensity ratio (G / D ratio) of 1 to 20 in the Raman spectrum. If G / D ratio is 1 or more and 20 or less, the dispersibility with respect to a solvent can be improved.

Here, from the viewpoint of obtaining excellent dispersibility, the average diameter (Av) of the CNT described above is preferably 0.5 nm or more, more preferably 1 nm or more, and preferably 15 nm or less. More preferably, it is 10 nm or less.

Further, the specific surface area of the CNT is preferably 600 m ² / g or more, more preferably 800 m ² / g or more, preferably 2500 m ² / g or less, and 1200 m ² / g or less. Is more preferable. Furthermore, when the CNTs are mainly opened, the specific surface area is preferably 1300 m ² / g or more. In the aligned carbon nanotube aggregate composed of CNTs having a specific surface area of 600 m ² / g or more, it is presumed that there are minute gaps between the CNTs in the vicinity of the surface of the substrate on which the aggregate is formed. In the separation step, CNT can be well dispersed in the solvent. Moreover, if the specific surface area of CNT is 600 m < ² > / g or more, the performance of the product manufactured using CNT dispersion liquid can fully be improved. Moreover, if the specific surface area of CNT is 2500 m < ² > / g or less, a CNT dispersion liquid with favorable dispersibility can be obtained by suppressing aggregation of CNT.
In addition, the specific surface area of a carbon nanotube can be calculated | required as a nitrogen adsorption specific surface area by BET method.

Furthermore, the CNT constituting the aligned carbon nanotube assembly preferably has a plurality of micropores. Among them, the CNT preferably has micropores having a pore diameter smaller than 2 nm, and the abundance of the micropores is a micropore volume determined by the following method, preferably 0.40 mL / g or more, more preferably It is 0.43 mL / g or more, more preferably 0.45 mL / g or more, and the upper limit is usually about 0.65 mL / g. It is preferable that CNT have the above micropores from the viewpoint of improving dispersibility in a solvent. The micropore volume can be adjusted, for example, by appropriately changing the CNT preparation method and preparation conditions.
Here, the “micropore volume (Vp)” is a nitrogen adsorption / desorption isotherm at a liquid nitrogen temperature (77 K) of the carbon nanotube, and V is a nitrogen adsorption amount at a relative pressure P / P0 = 0.19. It can be calculated from the formula (I): Vp = (V / 22414) × (M / ρ). Here, P is a measurement pressure at the time of adsorption equilibrium, P0 is a saturated vapor pressure of liquid nitrogen at the time of measurement, and in formula (I), M is an adsorbate (nitrogen) molecular weight of 28.010, and ρ is an adsorbate (nitrogen). ) At 77K with a density of 0.808 g / cm ³ . The micropore volume can be easily determined using, for example, “BELSORP (registered trademark) -mini” (manufactured by Nippon Bell Co., Ltd.).

Further, the CNT constituting the aligned carbon nanotube assembly preferably has a mass density of 0.002 g / cm ³ or more and 0.2 g / cm ³ or less, more preferably 0.01 g / cm ³ or more and 0.1 g / cm ³ or less. It is. In the aligned carbon nanotube aggregate composed of CNTs having a mass density of 0.2 g / cm ³ or less, the individual CNTs are not excessively strongly bonded to each other and are very loosely bonded. CNT can be well dispersed in the solvent. On the other hand, if the mass density of the CNTs is 0.002 g / cm ³ or more, the carbon nanotube alignment aggregates made of CNTs have some degree of integrity, and the carbon nanotube alignment aggregates and the solvent are brought into contact with each other before contacting them. Can be prevented from peeling off from the substrate.
The mass density can be calculated by dividing the mass of the carbon nanotube alignment aggregate by the volume. The mass of the carbon nanotube alignment aggregate is the mass of the substrate after the carbon nanotube alignment aggregate is formed, and the carbon nanotube. It can be calculated by determining the difference from the mass of the substrate before forming the alignment aggregate. The mass density of the CNTs can be controlled, for example, by adjusting the number density of the catalyst fine particles present on the base material of the substrate.

[[Orientation]]
Here, it is preferable that the CNTs constituting the carbon nanotube alignment aggregate described above have a high degree of orientation and are aligned on the substrate. Specifically, the CNTs preferably have a high degree of orientation that satisfies at least one of the following (i) to (iii).
(I) When the X-ray diffraction intensity is measured by incident X-rays from the first direction parallel to the longitudinal direction of the CNT and the second direction orthogonal to the first direction (θ-2θ method), the second There is a θ angle at which the reflection intensity from the direction is greater than the reflection intensity from the first direction and a reflection azimuth, and the θ angle and the reflection at which the reflection intensity from the first direction is greater than the reflection intensity from the second direction. (Ii) When X-ray diffraction intensity is measured (Laue method) with a two-dimensional diffraction pattern image obtained by entering X-rays from a direction orthogonal to the longitudinal direction of CNT, (Iii) The Herman's orientation coefficient is greater than 0 and less than 1 using the X-ray diffraction intensity obtained by the θ-2θ method or the Laue method.

[[Production of aligned carbon nanotube assemblies]]
The aligned carbon nanotube assembly composed of the above-described carbon nanotubes is used, for example, when a raw material compound and a carrier gas are supplied onto the above-described substrate and the carbon nanotubes are synthesized by chemical vapor deposition (CVD). In addition, in the method of significantly improving the catalytic activity of the catalyst layer for producing CNTs by making a small amount of oxidizing agent present in the system (super growth method; see International Publication No. 2006/011655), The catalyst layer can be formed on the surface by a wet process, and can be efficiently produced by using a raw material gas containing acetylene as a main component (for example, a gas containing 50% by volume or more of acetylene).

[solvent]
The solvent to be brought into contact with the above-mentioned aligned carbon nanotube aggregate is not particularly limited. For example, water, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol , Alcohols such as heptanol, octanol, nonanol, decanol, amyl alcohol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as diethyl ether, dioxane and tetrahydrofuran, N, N -Amide polar organic solvents such as dimethylformamide and N-methylpyrrolidone, aromatic carbonization such as toluene, xylene, chlorobenzene, orthodichlorobenzene and paradichlorobenzene Motorui and the like. These may be used alone or in combination of two or more.
The amount of the solvent to be brought into contact with the aligned carbon nanotube assembly formed on the substrate can be adjusted according to the desired concentration of the carbon nanotube dispersion. Here, from the viewpoint of maintaining good CNT dispersibility in the CNT dispersion, the amount of the solvent used is preferably 20 parts by mass or more per 1 part by mass of the CNTs constituting the aligned carbon nanotube aggregate. On the other hand, from the viewpoint of economy, the amount of the solvent used is preferably 20000 parts by mass or less per 1 part by mass of CNTs constituting the aligned carbon nanotube aggregate.

[Other ingredients]
The carbon nanotube dispersion produced according to the production method of the present invention includes a dispersant, an organic or inorganic binder, a coupling agent, a crosslinking agent, a stabilizer, a colorant, a charge adjusting agent, a lubricant, and the like as necessary. The additive may be contained. Therefore, the solvent may contain the above-described additive.

However, from the viewpoint of enhancing the versatility of the carbon nanotube dispersion liquid produced according to the production method of the present invention, it is preferable that the carbon nanotube dispersion liquid does not substantially contain a dispersant. , Nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants and other surfactants and polymers such as polypeptides, polysaccharides, nucleic acids, conjugated polymers) It is preferably not included. In the present invention, “substantially does not contain a dispersant” means that the concentration of the dispersant described above is less than 0.01% by mass, preferably zero.

<Decompression step>
In the depressurization step, the aligned carbon nanotube assembly in contact with the solvent is placed under reduced pressure after the contacting step and before separating the aligned carbon nanotube assembly from the substrate. By placing the aligned carbon nanotube aggregate in contact with the solvent through the contact step under reduced pressure, air or the like existing in the gaps between the CNTs constituting the aligned carbon nanotube aggregate is discharged from the aligned carbon nanotube aggregate, It becomes easy to impregnate a solvent into the gap. For this reason, it is speculated that in the decompression step, the solvent can be uniformly distributed in the aligned carbon nanotube aggregate before separation from the substrate. As a result, it is considered that the dispersibility of CNTs in the CNT dispersion is further enhanced. And the electrically conductive film etc. which were prepared using the CNT dispersion liquid obtained through the pressure reduction process have higher conductivity than the case where the CNT dispersion liquid which has not been subjected to the pressure reduction process is used.
Here, the depressurization method is not particularly limited as long as the aligned carbon nanotube aggregate after the contacting step is placed under reduced pressure together with the solvent. For example, the carbon nanotube-containing aggregate in contact with the solvent is placed in the desiccator together with the substrate. And a method of degassing the desiccator. The conditions for the depressurization step are not particularly limited, but are usually less than atmospheric pressure (for example, pressure 0.0001 Pa to 5000 Pa) for 1 minute to 600 minutes, more preferably about 5 minutes to 180 minutes. The conditions for the decompression step can be adjusted as appropriate according to the type of the solvent.

<Separation process>
After the contact step, a pressure reduction step is optionally performed, and then a separation step is performed. In the separation step, the aligned carbon nanotube aggregate is separated from the substrate in a solvent. In that case, it is preferable that a solvent does not contain a dispersing agent substantially.

Here, separation of the aligned carbon nanotube aggregate from the substrate can be performed by peeling the aligned carbon nanotube aggregate from the substrate using a physical, chemical or mechanical method. Specifically, as a peeling method, for example, a method of peeling an aligned carbon nanotube aggregate from a substrate using an electric field, a magnetic field, centrifugal force or surface tension, cutting with a thin blade such as a cutter blade, or suction with a vacuum pump is used. For example, a method of mechanically peeling the aligned carbon nanotube aggregate directly from the substrate or a method of peeling the aligned carbon nanotube aggregate from the substrate using pressure or heat can be used.

Then, the CNTs constituting the aligned carbon nanotube aggregate separated from the substrate in the separation step are well dispersed in the solvent. Here, the reason why the CNTs constituting the aligned carbon nanotube aggregate can be favorably dispersed without using a dispersant is not clear, but is presumed to be because the CNTs have the above properties. Is done. That is, the CNTs constituting the aligned carbon nanotube aggregate have an average diameter (Av) and a diameter distribution (3σ) satisfying 0.60> (3σ / Av)> 0.20 and an average length of 100 μm or more. Therefore, it is estimated that a minute gap exists between the CNTs in the vicinity of the surface of the substrate on which the aggregate is formed. Therefore, when the aggregate is brought into contact with the solvent, the solvent penetrates into the gap, and as a result, when the CNT is peeled off from the substrate in the solvent, the CNT is easily released without agglomeration, and the dispersion agent is eliminated. It is estimated that CNTs are uniformly dispersed in the solvent even in the presence.

The substrate after separating the aligned carbon nanotube aggregates can be removed from the solvent using a known method such as decantation, centrifugation, filter filtration, picking using tweezers, a robot arm, or the like. . Among these, since only the substrate can be easily removed mechanically, it is preferable to employ picking as a method for separating the substrate.

<Dispersing process>
In the dispersion step, the aligned carbon nanotube aggregate separated from the substrate in the separation step is dispersed in a solvent, and the CNTs constituting the aligned carbon nanotube assembly are further favorably dispersed in the solvent.
In addition, when performing a dispersion | distribution process, the removal of the board | substrate mentioned above may be implemented before a dispersion | distribution process, and may be implemented after a dispersion | distribution process, but it is a board | substrate from a viewpoint of performing a dispersion process favorably. Is preferably removed before the dispersing step. In addition, from the viewpoint of preventing a decrease in the purity and quality of CNT due to contamination of impurities, the dispersion step is preferably performed separately from the separation step. When the separation step and the dispersion step are performed at the same time, in other words, when the aligned carbon nanotube aggregate is separated from the substrate using the dispersion treatment method described later, collision between the separated CNT and the substrate occurs, and impurities are mixed. And deterioration of CNT is likely to occur.

Here, examples of the dispersion processing method include dispersion processing that can provide a cavitation effect or a crushing effect. Therefore, a description will be given below of distributed processing that provides a cavitation effect or a crushing effect.

[Distributed processing with cavitation effect]
The dispersion treatment that provides a cavitation effect is a dispersion method that uses a shock wave that is generated when a vacuum bubble generated in water bursts when high energy is applied to a liquid. By using this dispersion method, it is possible to further favorably disperse the CNTs constituting the aligned carbon nanotube aggregate.

Here, specific examples of the dispersion treatment that provides a cavitation effect include dispersion treatment using ultrasonic waves, dispersion treatment using a jet mill, and dispersion treatment using high shear stirring. Only one of these distributed processes may be performed, or a plurality of distributed processes may be combined. More specifically, for example, an ultrasonic homogenizer, a jet mill, and a high shear stirring device are preferably used. These devices may be conventionally known devices.

When an ultrasonic homogenizer is used to disperse the CNTs constituting the aligned carbon nanotube aggregate, the ultrasonic homogenizer may be used to irradiate the solvent containing the aligned carbon nanotube aggregate separated from the substrate. The irradiation time may be appropriately set depending on the amount of the aligned carbon nanotube aggregate, and is preferably, for example, 3 minutes or more, more preferably 30 minutes or more, and preferably 5 hours or less, more preferably 2 hours or less. For example, the output is preferably 0.1 W or more and 500 W or less, more preferably 1 W or more and 300 W or less, further preferably 5 W or more and 100 W or less, and the temperature is preferably 15 ° C. or more and 50 ° C. or less.

In the case of using a jet mill, the number of treatments may be appropriately set depending on the amount of aligned carbon nanotube aggregates, etc., for example, preferably 2 times or more, more preferably 5 times or more, preferably 100 times or less, 50 times The following is more preferable. For example, the pressure is preferably 20 MPa or more and 250 MPa or less, and the temperature is preferably 15 ° C. or more and 50 ° C. or less.

Furthermore, when high shear stirring is used, stirring and shearing may be applied to the solvent containing the aligned carbon nanotube aggregate separated from the substrate by a high shear stirring device. The faster the turning speed, the better. For example, the operation time (time during which the machine is rotating) is preferably 3 minutes or more and 4 hours or less, the peripheral speed is preferably 5 m / s or more and 50 m / s or less, and the temperature is preferably 15 ° C. or more and 50 ° C. or less.

In addition, it is more preferable to perform the dispersion treatment for obtaining the above-described cavitation effect at a temperature of 50 ° C. or lower. This is because a change in concentration due to the volatilization of the solvent is suppressed.

[Dispersion treatment that can produce a crushing effect]
The dispersion treatment that provides the crushing effect is not only capable of uniformly dispersing the CNTs constituting the aligned carbon nanotube aggregate in the solvent, but also by the shock wave when the bubbles disappear, compared to the dispersion treatment that provides the cavitation effect described above. This is more advantageous in that damage to CNT can be suppressed.

In the dispersion treatment in which this crushing effect is obtained, a shear force is applied to the solvent containing the aligned carbon nanotube aggregates separated from the substrate to crush and disperse the CNT aggregates, and a back pressure is applied to the solvent containing CNTs. By loading and cooling the solvent containing CNTs as necessary, CNTs can be uniformly dispersed in the solvent while suppressing the generation of bubbles.
In addition, when a back pressure is applied to the solvent containing CNT, the back pressure applied to the solvent containing CNT may be reduced to atmospheric pressure all at once, but it is preferable to reduce the pressure in multiple steps.

Here, in order to further disperse the CNTs in the solvent by applying a shearing force to the solvent containing the CNTs, for example, a dispersion system having a disperser having the following structure may be used.
That is, the disperser includes a disperser orifice having an inner diameter d1, a dispersive space having an inner diameter d2, and a terminal portion having an inner diameter d3 from the inflow side to the outflow side of the solvent containing CNT (where d2> d3 > D1).
In this disperser, the inflowing solvent containing high-pressure (10 to 400 MPa, preferably 50 to 250 MPa) CNT passes through the disperser orifice and becomes a high flow rate fluid with a decrease in pressure. Into the dispersed space. Thereafter, the solvent containing the high flow rate CNTs flowing into the dispersion space flows at high speed in the dispersion space, and receives a shearing force at that time. As a result, the flow rate of the solvent containing CNTs decreases and the CNTs in the solvent are well dispersed. And the fluid of the pressure (back pressure) lower than the pressure of the solvent containing the inflowing CNT flows out from the terminal portion as the CNT dispersion liquid.

In addition, the back pressure of the solvent containing CNT can be applied to the solvent containing CNT by applying a load to the flow of the solvent containing CNT. For example, a multistage step-down pressure device is disposed downstream of the disperser. Thus, a desired back pressure can be applied to the solvent containing CNTs.
And by reducing the back pressure of the solvent containing CNTs in multiple stages with a multistage pressure reducer, it is possible to suppress the generation of bubbles in the CNT dispersion liquid when the CNT dispersion liquid is finally released to atmospheric pressure. .

In addition, the disperser may include a heat exchanger or a coolant supply mechanism for cooling the solvent containing CNTs. This is because the generation of bubbles in the solvent containing CNTs can be further suppressed by cooling the solvent containing CNTs that have been heated to a high temperature by applying a shearing force with a disperser.
In addition, it can suppress that a bubble generate | occur | produces in the solvent containing CNT also by cooling in advance the solvent containing CNT instead of arrangement | positioning of a heat exchanger etc.

As described above, in the dispersion treatment in which this crushing effect is obtained, since the occurrence of cavitation can be suppressed, damage to CNT caused by cavitation that is sometimes a concern, in particular, CNT caused by shock waves when bubbles disappear. Damage can be suppressed. In addition, it is possible to uniformly and efficiently disperse even CNTs having a large specific surface area by suppressing the adhesion of bubbles to the CNTs and energy loss due to the generation of bubbles.
The effect of improving dispersibility by suppressing the adhesion of bubbles to CNTs is very large in CNTs having a large specific surface area, particularly CNTs having a specific surface area of 800 m ² / g or more. This is because the larger the specific surface area of CNTs and the easier the bubbles are attached to the surface, the more easily the dispersibility decreases when bubbles are generated and attached.

As a distributed system having the above-described configuration, for example, there is a distributed system configured by using a product name “BERYU SYSTEM PRO” (manufactured by Migrain Co., Ltd.). And the dispersion | distribution process from which a crushing effect is acquired can be implemented by controlling a dispersion | distribution condition appropriately using such a dispersion | distribution system.

According to the above method for producing a carbon nanotube dispersion of the present invention, a desired CNT dispersion can be efficiently produced. The obtained CNT dispersion is suitably used for the production of, for example, a CNT-containing film or a carbon nanotube-containing composite material. In particular, the CNT-containing film is suitably used as a conductive film.

(Method for producing CNT-containing film)
The production method of the CNT-containing film using the CNT dispersion obtained by the present invention is not particularly limited, and a known film forming method can be used. For example, the CNT-containing film can be produced by using the CNT dispersion and using the following method (i) or (ii).
(I) A method of applying a CNT dispersion onto a substrate film, removing the solvent from the applied CNT dispersion, and obtaining a CNT-containing film laminated on the substrate film.
(Ii) A CNT dispersion liquid is applied on a peeling support, and the solvent is removed from the applied CNT dispersion to form a CNT-containing film with a peeling support, and then optionally obtained CNT with a peeling support. A method of obtaining a CNT-containing film by peeling a peeling support from a containing film.
And the CNT containing film | membrane produced using the method of the above-mentioned (i) or (ii) normally contains CNT and arbitrary additives in the ratio similar to a CNT dispersion liquid.

<Method for producing CNT-containing film (i)>
Here, the substrate film to which the CNT dispersion is applied when the CNT-containing film is produced is not particularly limited, and a known substrate film can be used depending on the application of the produced CNT-containing film. . Specifically, for example, when the obtained CNT-containing film is used as a transparent conductive film, examples of the substrate film include a resin substrate and a glass substrate. Resin base materials include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyimide, polyphenylene sulfide, aramid, polypropylene, polyethylene, polylactic acid, polyvinyl chloride, polycarbonate, polymethyl methacrylate, and alicyclic. The base material which consists of an acrylic resin, a cycloolefin resin, a triacetyl cellulose etc. can be mentioned. Examples of the glass substrate include a substrate made of ordinary soda glass.

And the surface of the base film is treated according to a known method such as treatment by UV irradiation, treatment by corona discharge or treatment by ozone, treatment by application of a silane coupling agent, acrylic resin or urethane resin, etc. It may be. By treating the surface of the base film as described above, it is possible to control the adhesion to the CNT-containing film, the wettability of the CNT dispersion, and the like. Further, for example, a conductive layer (conductive film) other than the hard coat layer, gas barrier layer, pressure-sensitive adhesive layer, and CNT-containing film may be formed on the above-described resin substrate and glass substrate. . The thickness of the base film may be appropriately determined according to the use, but is usually 10 to 10,000 μm.
Moreover, the light transmittance (measurement wavelength: 500 nm) of the base film used when the CNT-containing film is used as a transparent conductive film is preferably 60% or more. The light transmittance (measurement wavelength: 500 nm) of the base film can be measured using, for example, a spectrophotometer (manufactured by JASCO Corporation, V-570).

As a method of applying the CNT dispersion on the base film, a known application method can be adopted. Specifically, the coating method includes dipping method, roll coating method, gravure coating method, knife coating method, air knife coating method, roll knife coating method, die coating method, screen printing method, spray coating method, gravure offset method, etc. Can be used.

As a method for removing the solvent from the CNT dispersion applied on the base film, a known drying method can be employed. Examples of the drying method include a hot air drying method, a vacuum drying method, a hot roll drying method, and an infrared irradiation method. The drying temperature is not particularly limited, but is usually room temperature to 200 ° C., and the drying time is not particularly limited, but is usually 0.1 to 150 minutes.

The thickness of the CNT-containing film obtained after removal of the solvent is not particularly limited, but is usually from 100 nm to 1 mm. Further, the content of carbon nanotubes contained in the CNT-containing film is not particularly limited, but is usually 0.1 × 10 ⁻⁶ to 15 mg / cm ² .

<Method for producing CNT-containing film (ii)>
As a peeling support for applying a CNT dispersion when producing a CNT-containing film, the film formed thereon can be sufficiently fixed, and the formed film can be peeled off using a thin film peeling method. There is no particular limitation as long as it can be peeled off from the support. Examples of the peeling support include synthetic resin sheets such as PTFE (polytetrafluoroethylene) sheet and PET (polyethylene terephthalate) sheet, membrane filters made of nitrocellulose, and the like.
The thickness of the peeling support may be appropriately determined, but is usually 10 to 10,000 μm.

The CNT-containing film formed on the peeling support can be peeled from the peeling support by using a known thin film peeling method. For example, when the peeling support is dissolved in a predetermined solvent, the CNT-containing film is taken out alone by immersing the CNT-containing film with the peeling support in the solvent and dissolving the peeling support. be able to.

The method for applying the CNT dispersion on the peeling support and the method for removing the solvent from the CNT dispersion applied on the peeling support are the same as the method (i) for producing the CNT-containing film described above. Can be adopted.

The CNT-containing film is usually composed of a single layer, but may be a film having a multilayer structure of two or more layers by appropriately repeating the application of the CNT dispersion and the removal of the solvent. Further, after obtaining the CNT-containing film, the dispersant may be appropriately removed from the film according to a known method. Further, the CNT-containing film may be doped with a p-type dopant or an n-type dopant by a known method.

(Conductive film)
The conductive film produced using the CNT dispersion obtained by the present invention has excellent conductivity and reliability.

(Conductive film)
Moreover, an electroconductive film is obtained by laminating | stacking the said electrically conductive film on a base film. Similar to the conductive film, the conductive film has excellent conductivity and reliability. Such a conductive film can be obtained by transferring a conductive film produced on a peeling support to a base film, or by sticking a conductive film that is a self-supporting film on the base film. You can also The conductive film can also be obtained by directly forming a conductive film on the base film, such as by applying the CNT dispersion onto the base film and removing the solvent from the applied CNT dispersion.

The surface resistivity of the conductive film is usually 10 ⁵ Ω / □ or less, preferably 10 ⁴ Ω / □ or less, more preferably 5 × 10 ³ Ω / □ or less, and particularly preferably 2 × 10 ³ Ω / □. The lower limit is not particularly limited, but is usually 0.01Ω / □ or more. In addition, in this invention, the surface resistivity of an electroconductive film can be measured by the method as described in the Example of this specification.

The conductive film obtained by using the CNT dispersion liquid of the present invention and the conductive film including the conductive film are preferably used for, for example, an antistatic film, electronic paper, a light control film, a touch panel and a solar cell, It is suitably used for battery electrodes.
Moreover, since the composite material (CNT containing composite material) of rubber | gum or resin and CNT obtained using the CNT dispersion liquid of this invention is equipped with electroconductivity and intensity | strength, an antistatic sheet | seat, a container, a tire, It is suitably used for hoses, timing belts, rubber packings, tubes, threads and the like. The CNT-containing composite material can be prepared by using a known method such as solidification after mixing the CNT dispersion and rubber or resin latex.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
The substrates with aligned carbon nanotube assemblies used in the examples and comparative examples were prepared by the following methods, respectively. The presence or absence of aggregates in the carbon nanotube dispersion and the dispersibility of the carbon nanotubes were evaluated using the following methods, respectively.

(Preparation of substrate with aligned carbon nanotubes)
<Preparation Example 1>
In accordance with the description in International Publication No. 2006/011655, a substrate A with aligned carbon nanotube aggregates was obtained by the super-growth method.
Specifically, carbon nanotubes were grown on a flat substrate in which a metal catalyst layer made of an iron thin film (thickness 1 nm) was provided on a substrate (1 cm × 1 cm) made of a silicon wafer.
The obtained aligned carbon nanotube assembly was mainly composed of single-walled CNTs. The CNTs constituting the carbon nanotube aligned aggregate have a BET specific surface area of 800 m ² / g, a mass density of 0.03 g / cm ³ , a micropore volume of 0.44 mL / g, and an average diameter. (Av) was 3.3 nm, diameter distribution (3σ) was 1.9 nm, (3σ / Av) was 0.58, and the average length was 500 μm.

<Preparation Example 2>
A substrate B with an aligned carbon nanotube assembly was obtained in the same manner as in Preparation Example 1 except that the thickness of the iron thin film as the metal catalyst layer was changed to 5 nm.
The obtained aligned carbon nanotube assembly was composed of CNTs including double-walled CNTs. The CNTs constituting the aligned carbon nanotube assembly have a BET specific surface area of 620 m ² / g, a mass density of 0.03 g / cm ³ , a micropore volume of 0.41 mL / g, and an average diameter. (Av) was 5.9 nm, the diameter distribution (3σ) was 3.3 nm, (3σ / Av) was 0.56, and the average length was 500 μm.

<Preparation Example 3>
Substrate C with an aligned carbon nanotube assembly was obtained in the same manner as in Preparation Example 1, except that the time for growing carbon nanotubes on the substrate (feeding and heating time for source gas) was doubled.
The obtained aligned carbon nanotube assembly was mainly composed of single-walled CNTs. The CNTs constituting the aligned carbon nanotube aggregate have a BET specific surface area of 820 m ² / g, a mass density of 0.03 g / cm ³ , a micropore volume of 0.42 mL / g, and an average diameter. (Av) was 3.5 nm, the diameter distribution (3σ) was 2.0 nm, (3σ / Av) was 0.57, and the average length was 1000 μm.

(Evaluation methods)
<Presence of aggregates>
The obtained carbon nanotube dispersion was observed with an optical microscope to confirm the presence or absence of aggregates having a diameter of 1 mm or more.
<Dispersibility of carbon nanotubes>
The obtained carbon nanotube dispersion was centrifuged at 1000 G for 15 minutes, the presence or absence of precipitates was visually confirmed, and the dispersibility of the carbon nanotubes was evaluated according to the following criteria.
○: The carbon nanotubes are well dispersed and no precipitate can be confirmed.
X: The carbon nanotube was not disperse | distributed favorably and the deposit was confirmed.
<Surface resistivity>
Using a resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., product name “Loresta (registered trademark) -GP MCP-T610”), it was measured and evaluated by the method in accordance with JIS K7194 as follows.
Specifically, the surface resistivity (sheet resistance) of the laminate was measured using a four-terminal method in an environment of a temperature of 25 ° C. and a humidity of 20% RH, and evaluated according to the following criteria.
A: Less than 6000Ω / □ B: 6000Ω / □ or more and less than 7000Ω / □ C: 7000Ω / □ or more

Example 1
Substrate A with an aligned carbon nanotube assembly produced in Preparation Example 1 was immersed in orthodichlorobenzene as a solvent (contact process). Next, the aligned carbon nanotube aggregate was separated from the substrate using a spatula in a solvent (separation step). Thereafter, the substrate was removed with tweezers, and a dispersion treatment was performed using a ultrasonic homogenizer under the conditions of 20 W and 30 minutes (dispersion step) to obtain a carbon nanotube dispersion.
And the presence or absence of the aggregate and the dispersibility of the carbon nanotube were evaluated about the obtained carbon nanotube dispersion liquid. Further, the above CNT dispersion was applied on a PET film as a base film (Toyobo Co., Ltd., “Cosmo Shine (registered trademark)”, product number A4100, with an easy-adhesion layer) using a spray coating method, The CNT dispersion on the PET film was dried at 80 ° C. to form a CNT-containing film. The surface resistivity of the obtained CNT-containing film and PET film laminate (conductive film formed by laminating a conductive film made of a CNT-containing film on a base film) on the CNT-containing film side was measured. The results are shown in Table 1.

(Example 2)
A carbon nanotube dispersion liquid and a laminate were prepared in the same manner as in Example 1 except that the carbon nanotube dispersion liquid was obtained by performing only the separation process after the contact process without performing the dispersion process.
Then, in the same manner as in Example 1, the presence or absence of aggregates and the dispersibility of the carbon nanotubes were evaluated. Moreover, the surface resistivity of the obtained laminated body was measured. The results are shown in Table 1.

Example 3
A carbon nanotube dispersion and a laminate were prepared in the same manner as in Example 1 except that the substrate B with aligned carbon nanotube assemblies prepared in Preparation Example 2 was used as the substrate with aligned carbon nanotube assemblies.
Then, in the same manner as in Example 1, the presence or absence of aggregates and the dispersibility of the carbon nanotubes were evaluated. Moreover, the surface resistivity of the obtained laminated body was measured. The results are shown in Table 1.

Example 4
The substrate A with an aligned carbon nanotube assembly produced in Preparation Example 1 was immersed in a container (glass petri dish) in orthodichlorobenzene as a solvent (contact process). Next, the substrate A with an aligned CNT aggregate was placed in a desiccator together with the glass petri dish, and the inside of the desiccator was decompressed to less than atmospheric pressure (1000 Pa) with a diaphragm pump (decompression step). Foaming was observed from the aligned CNT aggregate impregnated with orthodichlorobenzene, and foaming continued for about 180 minutes from the start of decompression. Thereafter, the pressure was returned to normal pressure, the glass petri dish was taken out from the desiccator, and the aligned carbon nanotube aggregate was separated from the substrate using a spatula in a solvent (separation step). Thereafter, the substrate was removed with tweezers, and a dispersion treatment was performed using a ultrasonic homogenizer under the conditions of 20 W and 30 minutes (dispersion step) to obtain a carbon nanotube dispersion. In addition, a laminate was prepared in the same manner as in Example 1 using the obtained carbon nanotube dispersion.
Then, in the same manner as in Example 1, the presence or absence of aggregates and the dispersibility of the carbon nanotubes were evaluated. Moreover, the surface resistivity of the obtained laminated body was measured. The results are shown in Table 1.

(Example 5)
Substrate C with an aligned carbon nanotube assembly produced in Preparation Example 3 was immersed in orthodichlorobenzene as a solvent in a glass petri dish (contact process). Next, the substrate C with the aligned CNT aggregate was put into a desiccator together with the glass petri dish, and the inside of the desiccator was decompressed to less than atmospheric pressure (1000 Pa) with a diaphragm pump (decompression step). Foaming was observed from the aligned CNT aggregate impregnated with orthodichlorobenzene, and foaming continued for about 180 minutes from the start of decompression. Thereafter, the pressure was returned to normal pressure, the glass petri dish was taken out from the desiccator, and the aligned carbon nanotube aggregate was separated from the substrate using a spatula in a solvent (separation step). Thereafter, the substrate was removed with tweezers, and a dispersion treatment was performed using a ultrasonic homogenizer under the conditions of 20 W and 30 minutes (dispersion step) to obtain a carbon nanotube dispersion. In addition, a laminate was prepared in the same manner as in Example 1 using the obtained carbon nanotube dispersion.
Then, in the same manner as in Example 1, the presence or absence of aggregates and the dispersibility of the carbon nanotubes were evaluated. Moreover, the surface resistivity of the obtained laminated body was measured. The results are shown in Table 1.

(Comparative Example 1)
The aligned carbon nanotube aggregate was peeled from the substrate A with the aligned carbon nanotube aggregate A using a spatula. Thereafter, the separated aligned carbon nanotubes were put into orthodichlorobenzene as a solvent and stirred to prepare a carbon nanotube dispersion. In addition, a laminate was prepared in the same manner as in Example 1 using the obtained carbon nanotube dispersion.
Then, in the same manner as in Example 1, the presence or absence of aggregates and the dispersibility of the carbon nanotubes were evaluated. Moreover, the surface resistivity of the obtained laminated body was measured. The results are shown in Table 1.

Table 1 shows that in Examples 1 to 5, CNT dispersions in which CNTs are well dispersed can be obtained without using a dispersant. In particular, according to the CNT dispersions obtained in Examples 4 and 5 in which the decompression step was performed, it can be seen that a CNT-containing film (conductive film) having particularly excellent conductivity can be obtained.

Claims

A step (1) of bringing the aligned carbon nanotube assembly formed on the substrate into contact with a solvent;
Separating the aligned aggregate of carbon nanotubes from the substrate in the solvent (2),
The carbon nanotubes constituting the carbon nanotube aligned aggregate satisfy the relational expression: 0.20 <(3σ / Av) <0.60 between the average diameter (Av) and the diameter distribution (3σ), and the average length Is 100 μm or more, A method for producing a carbon nanotube dispersion liquid.
The method for producing a carbon nanotube dispersion liquid according to claim 1, further comprising a step (3) of dispersing the aligned carbon nanotube aggregate separated from the substrate in the solvent.
The method of claim 1, further comprising a step (4) of placing the carbon nanotube-mixed aggregate in contact with the solvent under reduced pressure between the step (1) and the step (2). Or the manufacturing method of the carbon nanotube dispersion liquid of 2.
The method for producing a carbon nanotube dispersion according to any one of claims 1 to 3, wherein the substrate is a plate-like, particle-like or linear substrate.