Aggregate of carbon nanotubes

Abstract

To provide a novel aggregate of carbon nanotubes. 【Solution means】An aggregate of carbon nanotubes (CNTs) containing a plurality of CNTs. When observing 110 or more CNTs constituting the aggregate with a transmission electron microscope, if the most frequently observed number of layers is n (n is an integer), for the total 100% of all the observed CNTs, the total ratio of CNTs with the number of layers being n - 1 to n + 1 is 20 to 38%, the total ratio of CNTs with the number of layers being n - 2 to n + 2 is 35 to 80%, when the average value of the outer diameter of CNTs with the number of layers being n is X (nm), the average value of the outer diameter of CNTs with the number of layers being n - 1 is X - 2.8 (nm) to X + 0.5 (nm), the average value of the outer diameter of CNTs with the number of layers being n + 1 is X - 0.5 (nm) to X + 2.8 (nm), and the average value of the outer diameters of all the observed CNTs is X - 1.5 (nm) to X + 1.5 (nm). An aggregate of carbon nanotubes.

Description

Technical Field

[0001] The present disclosure relates to an aggregate of carbon nanotubes.

Background Art

[0002] Carbon nanotubes are used in applications such as electric and electronic devices and transportation machinery. For example, in applications such as heaters, a carbon nanotube film may be used (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide a novel aggregate of carbon nanotubes.

Means for Solving the Problems

[0005] One aspect of the aggregate of carbon nanotubes (CNTs) of the present disclosure includes a plurality of CNTs. When observing 110 or more CNTs constituting the aggregate with a transmission electron microscope (TEM), when the most frequently observed number of layers is n (n is an integer), with respect to 100% of the total number of all the observed CNTs, the total ratio of CNTs with the number of layers being n - 1 to n + 1 is 20 to 38%, and the total ratio of CNTs with the number of layers being n - 2 to n + 2 is 35 to 80%. Further, when the average value of the outer diameter of CNTs with the number of layers being n is X (nm), the average value of the outer diameter of CNTs with the number of layers being n - 1 is X - 2.8 (nm) to X + 0.5 (nm), the average value of the outer diameter of CNTs with the number of layers being n + 1 is X - 0.5 (nm) to X + 2.8 (nm), and the average value of the outer diameter of all the observed CNTs is X - 1.5 (nm) to X + 1.5 (nm). [Advantages of the Invention]

[0006] According to the present disclosure, a novel aggregate of carbon nanotubes can be provided. [Brief Description of the Drawings]

[0007]

Figure 1

[0008] In this specification, the numerical range A to B means A or more and B or less. In this specification, when the units of the numerical values described before and after the "~" indicating the numerical range are the same, the unit of the numerical value described before the "~" may be omitted.

[0009] In this specification, carbon nanotubes are also referred to as "CNT", carbon nanotube forests are also referred to as "CNT forests", carbon nanotube fibers are also referred to as "CNT fibers", and carbon nanotube webs are also referred to as "CNT webs".

[0010] [Aggregate of Carbon Nanotubes] The aggregate of carbon nanotubes (CNT) of the present disclosure contains a plurality of CNTs. When observing 110 or more CNTs constituting the aggregate with a transmission electron microscope (TEM), when the most frequently observed number of layers is n (n is an integer), the total ratio of CNTs with the number of layers being n - 1 to n + 1 is 20 to 38% with respect to 100% of the total of all the observed CNTs, and the total ratio of CNTs with the number of layers being n - 2 to n + 2 is 35 to 80%. Further, when the average value of the outer diameter of CNTs with the number of layers being n is X (nm), the average value of the outer diameter of CNTs with the number of layers being n - 1 is X - 2.8 (nm) to X + 0.5 (nm), the average value of the outer diameter of CNTs with the number of layers being n + 1 is X - 0.5 (nm) to X + 2.8 (nm), and the average value of the outer diameters of all the observed CNTs is X - 1.5 (nm) to X + 1.5 (nm).

[0011] The CNT aggregates of the present disclosure include a plurality of CNTs. The CNTs can be manufactured using methods such as, for example, the thermal chemical vapor deposition (thermal CVD) method, the plasma CVD method, the laser ablation method, the arc discharge method, or the combustion method.

[0012] The CNT aggregates of the present disclosure are, for example, CNT forests provided on a substrate, or aggregates obtained from CNT forests. A CNT forest refers to an aggregate of a plurality of CNTs provided on a substrate and oriented in a direction perpendicular to the surface of the substrate. In the CNT forest, the plurality of CNTs stand upright on the substrate. The aggregate obtained from the CNT forest is, for example, an aggregate of powdery CNTs. Note that the aggregate of powdery CNTs is also simply referred to as powdery CNTs.

[0013] Regarding the number of layers, outer diameter, inner diameter, etc. of the CNTs calculated by observing 110 or more CNTs constituting the CNT aggregates of the present disclosure with a transmission electron microscope (TEM), the following description will be given. Observing CNTs using a transmission electron microscope (TEM) is also referred to as "TEM observation", and an image obtained by TEM observation is also referred to as a "TEM image".

[0014] The 110 or more CNTs for TEM observation can be arbitrarily selected from the CNT aggregates. However, when a CNT with a changing number of layers is observed during TEM observation, 110 or more CNTs are selected from the CNT aggregates so as not to include the CNT. When the CNT aggregate is a CNT forest provided on a substrate, selecting 110 or more CNTs from the CNT aggregate means collecting 110 or more CNTs from the CNT forest. Details of the observation method using TEM are described in the Examples section.

[0015] The CNT aggregate may contain single-walled carbon nanotubes.

[0016] When observing more than 110 CNTs by TEM, when the most frequently observed number of layers is set as n (n is an integer), for 100% of all the observed CNTs, the total proportion of CNTs with the number of layers from n - 1 to n + 1 is 20 - 38%, and the total proportion of CNTs with the number of layers from n - 2 to n + 2 is 35 - 80%.

[0017] The total proportion of CNTs with the number of layers from n - 1 to n + 1 refers to the proportion of the total number (quantity) of CNTs with the number of layers from n - 1 to n + 1 to the total number (quantity) of CNTs observed by TEM. The same applies to the total proportion of CNTs with the number of layers from n - 2 to n + 2 and the proportion of CNTs with the number of layers n. When observing more than 110 CNTs by TEM, if there are two or more most frequently observed numbers of layers, among the most frequently observed numbers of layers, the number of layers closest to the median of all the observed numbers of layers is set as n. The median refers to the median in the distribution of the number of layers of CNTs, specifically, the value (number of layers) at which the cumulative value in the cumulative distribution of the number of layers of CNTs is 50%.

[0018] When n is 1, the total proportion of CNTs with the number of layers from n - 1 to n + 1 means the total proportion of CNTs with the number of layers from 1 to 2, and the total proportion of CNTs with the number of layers from n - 2 to n + 2 means the total proportion of CNTs with the number of layers from 1 to 3. When n is 2, the total proportion of CNTs with the number of layers from n - 1 to n + 1 means the total proportion of CNTs with the number of layers from 1 to 3, and the total proportion of CNTs with the number of layers from n - 2 to n + 2 means the total proportion of CNTs with the number of layers from 1 to 4.

[0019] n is preferably 3 or more, more preferably 3 - 20, still more preferably 4 - 15, even more preferably 5 - 15, and particularly preferably 7 - 13. The total proportion of CNTs with the number of layers from n - 1 to n + 1 is preferably 22 - 36%, more preferably 24 - 35%, and still more preferably 26 - 34%. The total proportion of CNTs with the number of layers from n - 2 to n + 2 is preferably 40 - 76%, more preferably 45 - 73%, and still more preferably 50 - 70%. When the total ratio of CNTs with the number of layers from n - 1 to n + 1 and from n - 2 to n + 2 is within the above range, the aggregate of CNTs, particularly the CNT forest provided on the substrate, is excellent in spinnability, and the aggregate of CNTs is also excellent in dispersibility. In other words, the aggregate of CNTs of the present disclosure is excellent in the balance between spinnability and dispersibility.

[0020] The ratio of CNTs with the number of layers n is preferably 10 to 30%, more preferably 15 to 29%, and still more preferably 17 to 28%. When the ratio of CNTs with the number of layers n is within the above range, the aggregate of CNTs, particularly the CNT forest provided on the substrate, is excellent in spinnability, and the aggregate of CNTs is also excellent in dispersibility. In other words, the aggregate of CNTs of the present disclosure is excellent in the balance between spinnability and dispersibility.

[0021] When the distribution of the number of layers of CNTs constituting the aggregate of CNTs is wide, the total ratio of CNTs with the number of layers n, n - 1 to n + 1, and n - 2 to n + 2 becomes small.

[0022] The value of n, and the total ratio of CNTs with the number of layers n, n - 1 to n + 1, and n - 2 to n + 2 can be adjusted, for example, in the method for manufacturing the aggregate of CNTs described later, by adjusting the type of the substrate used for the catalyst substrate, the presence or absence of the buffer layer, the type and thickness of the buffer layer, the type and thickness of the catalyst layer, the pressure in the reaction chamber in the CVD method, and the flow rates of the raw material gas and the carrier gas. These amounts may be adjusted while sequentially performing TEM observation.

[0023] When observing 110 or more CNTs by TEM, when the average value of the outer diameter of CNTs with the number of layers n is X (nm), the average value of the outer diameter of CNTs with the number of layers n - 1 is X - 2.8 (nm) to X + 0.5 (nm), and the average value of the outer diameter of CNTs with the number of layers n + 1 is X - 0.5 (nm) to X + 2.8 (nm). Also, the average value of the outer diameters of all the CNTs (used for calculating n) observed by TEM is X - 1.5 (nm) to X + 1.5 (nm).

[0024] The outer diameter of the CNT refers to the diameter of the outermost layer of the CNT measured using an image obtained by TEM observation. When amorphous or the like adheres to the outside of the outermost layer, it refers to the diameter including amorphous or the like.

[0025] X is preferably from 1 to 30 nm, more preferably from 3 to 25 nm, still more preferably from 5 to 20 nm, and particularly preferably from 10.0 to 20.0 nm, from the viewpoint that the aggregate of CNTs, particularly the CNT forest provided on the substrate, has excellent spinability and the aggregate of CNTs has excellent dispersibility. The average value of the outer diameter of the CNT with the number of layers being n refers to the arithmetic mean of the outer diameters of the CNTs with the number of layers being n. The same applies to the average value of the outer diameter of the CNT with the number of layers being n - 1, the average value of the outer diameter of the CNT with the number of layers being n + 1, and the average value of the outer diameters of all the CNTs observed by TEM.

[0026] The average value of the outer diameter of the CNT with the number of layers being n - 1 is preferably X - 2.6 (nm) to X + 0.5 (nm), more preferably X - 2.5 (nm) to X + 0.5 (nm), still more preferably X - 2.4 (nm) to X + 0.4 (nm), from the viewpoint that the aggregate of CNTs, particularly the CNT forest provided on the substrate, has excellent spinability and the aggregate of CNTs has excellent dispersibility.

[0027] The average value of the outer diameter of the CNT with the number of layers being n + 1 is preferably X - 0.5 (nm) to X + 2.6 (nm), more preferably X - 0.5 (nm) to X + 2.5 (nm), still more preferably X - 0.4 (nm) to X + 2.4 (nm), from the viewpoint that the aggregate of CNTs, particularly the CNT forest provided on the substrate, has excellent spinability and the aggregate of CNTs has excellent dispersibility.

[0028] The average value of the outer diameters of all the CNTs observed by TEM is preferably X - 1.3 (nm) to X + 1.3 (nm), more preferably X - 1.1 (nm) to X + 1.1 (nm), still more preferably X - 0.9 (nm) to X + 0.9 (nm) from the viewpoints that the aggregate of CNTs, particularly the CNT forest provided on the substrate, is excellent in spinability and the aggregate of CNTs is excellent in dispersibility.

[0029] The outer diameter of the CNT can be adjusted, for example, in the method for manufacturing the aggregate of CNTs described later, by adjusting the type of the substrate used for the catalyst substrate, the presence or absence of the buffer layer, the type and thickness of the buffer layer, the type and thickness of the catalyst layer, the pressure in the reaction chamber in the CVD method, and the flow rates of the source gas and the carrier gas. These amounts may be adjusted while sequentially performing TEM observation.

[0030] The average value of the inner diameters of all the CNTs (the number of layers was observed and used for the calculation of n) observed by TEM is preferably 1.0 to 6.0 nm, more preferably 3.5 to 6.0 nm, still more preferably 3.7 to 5.7 nm, particularly preferably 4.0 to 5.5 nm from the viewpoints that the aggregate of CNTs, particularly the CNT forest provided on the substrate, is excellent in spinability and the aggregate of CNTs is excellent in dispersibility.

[0031] The inner diameter of the CNT refers to the diameter of the innermost layer of the CNT measured using the image obtained by TEM observation. The average value of the inner diameters of all the CNTs observed by TEM refers to the arithmetic mean of the inner diameters of all the CNTs observed by TEM.

[0032] The inner diameter of the CNT can be adjusted, for example, in the method for manufacturing the aggregate of CNTs described later, by adjusting the type of the substrate used for the catalyst substrate, the presence or absence of the buffer layer, the type and thickness of the buffer layer, the type and thickness of the catalyst layer, the pressure in the reaction chamber in the CVD method, and the flow rates of the source gas and the carrier gas. These amounts may be adjusted while sequentially performing TEM observation.

[0033] The average length of the CNTs constituting the CNT aggregate is preferably 10 to 1000 μm, more preferably 30 to 800 μm, and still more preferably 50 to 500 μm. The average length of the CNTs can be adjusted, for example, by adjusting the time for performing the CVD method, that is, the growth time of the CNTs. The average length of the CNTs refers to the arithmetic mean of the lengths of all the CNTs observed using a scanning electron microscope (SEM). Specifically, to obtain the average length of the CNTs, 10 images of the CNTs are obtained using an SEM. For each of the 10 images, 10 measurement points of the length are arbitrarily selected and measured, and the lengths at a total of 100 points are measured. Then, the average length of the CNTs can be obtained by calculating the arithmetic mean of the measured values of the lengths at the 100 points.

[0034] The carbon purity of the CNTs constituting the CNT aggregate is preferably 95.0 to 99.999%. The lower limit value of the carbon purity of the CNTs is preferably 96.0%, more preferably 97.0%, still more preferably 98.0%, even more preferably 99.0%, and particularly preferably 99.8%. The upper limit value of the carbon purity of the CNTs may be, for example, 99.99% or 99.9%. The carbon purity of the CNTs can be determined, for example, by elemental analysis using fluorescent X-rays. In the present disclosure, the % of carbon purity means mass %.

[0035] The crystallinity of the CNTs constituting the CNT aggregate can be evaluated, for example, using Raman spectroscopy. In the evaluation of crystallinity by Raman spectroscopy, the value of the D / G ratio is used as an index. The D / G ratio is the ratio of the peak intensity of the D band appearing near 1360 cm -1 to the peak intensity of the G band appearing near 1580 cm -1 in the Raman spectrum measured by Raman spectroscopy. The smaller the value of the D / G ratio, the higher the crystallinity of the carbon nanotubes. The D / G ratio of the CNTs is preferably 0.5 to 1.0, more preferably 0.6 to 0.8.

[0036] The carbon purity and crystallinity of CNTs can be adjusted respectively, for example, in the method for manufacturing an aggregate of CNTs described later, by adjusting the thickness of the buffer layer on the catalyst substrate, the type of material used for the buffer layer, the thickness of the catalyst layer, the type of catalyst, the type and flow rate of the source gas in the CVD method, and the temperature and pressure in the reaction chamber.

[0037] [Method for Manufacturing Aggregate of Carbon Nanotubes] The aggregate of CNTs of the present disclosure is, for example, a CNT forest provided on a substrate or an aggregate obtained from the CNT forest. The CNT forest can be manufactured, for example, by the method described later. An aggregate obtained from the CNT forest (for example, a powdery aggregate of CNTs) can be obtained, for example, by scraping off CNTs from the substrate using a scraper or the like from the CNT forest.

[0038] The CNT forest can be obtained, for example, by performing a chemical vapor deposition (CVD) method using a catalyst substrate including a substrate and a catalyst layer provided on the substrate. The CVD method is a method in which the above catalyst substrate is placed in a reaction chamber, and then a source gas is supplied into the reaction chamber to grow CNTs on the surface of the catalyst layer. As the CVD method, a thermal CVD method is preferable.

[0039] Examples of the substrate include a silicon substrate, an alumina substrate, a magnesium oxide substrate, a glass substrate, a sapphire substrate, a titanium substrate, and a stainless steel substrate.

[0040] From the viewpoints of handleability and the cost of the substrate, the thickness of the substrate is preferably 0.03 to 2.0 mm, more preferably 0.05 to 1.8 mm, still more preferably 0.07 to 1.6 mm, and particularly preferably 0.09 to 1.4 mm.

[0041] The catalyst layer can be formed, for example, by attaching catalyst particles to the substrate by sputtering. Examples of the catalyst include metals, specifically, iron (Fe), nickel (Ni), cobalt (Co), molybdenum (Mo), gold (Au), and alloys containing at least one metal selected from the group consisting of these metals. Examples of the alloy include iron alloy, nickel alloy, and cobalt alloy. The catalyst may be a metal precursor such as metal oxide and metal compound. Examples of the metal oxide include iron oxide, nickel oxide, and cobalt oxide. Examples of the metal compound include iron chloride. When using a precursor, it is necessary to convert it into a metal before performing the CVD method, such as by heating the precursor. By changing the type of catalyst, the number of layers, outer diameter, and inner diameter of the CNT can be changed.

[0042] The thickness of the catalyst layer is preferably 1 to 20 nm, more preferably 2 to 17 nm, still more preferably 3 to 15 nm, and particularly preferably 4 to 10 nm. The thicker the catalyst layer, the greater the tendency for the number of layers and outer diameter of the CNT to increase. The thinner the catalyst layer, the narrower the tendency for the distribution of the number of layers of the CNTs constituting the CNT aggregate to be.

[0043] The catalyst substrate may further include a buffer layer between the substrate and the catalyst layer. Examples of the material used for the buffer layer include silica (SiO 2 ), alumina (Al 2 O 3 ), silicon nitride (SiN), zinc oxide (ZnO), copper oxide (Cu 2 O), and nickel oxide (NiO). The buffer layer can be formed, for example, by sputtering. By changing the type of material used for the buffer layer, the outer diameter and inner diameter of the CNT can be changed. For example, under certain manufacturing conditions, when the material used for the buffer layer is alumina (Al 2 O 3 ), the outer diameter and inner diameter of the CNT tend to be small, and when the material is silica (SiO 2 ), the outer diameter and inner diameter of the CNT tend to be large.

[0044] The thickness of the buffer layer may be, for example, 10 to 100 nm, may be 20 to 80 nm, or may be 30 to 60 nm.

[0045] Sputtering for forming the catalyst layer and sputtering for forming the buffer layer can be performed using known apparatuses and conditions according to the sputtering target. The pressure condition for sputtering is preferably 0.01 to 10 Pa, more preferably about 0.1 to 1 Pa.

[0046] As the source gas, a source gas containing carbon can be used, and examples thereof include hydrocarbons, sulfur-containing organic gases, phosphorus-containing organic gases, carbon monoxide, and alcohols. Examples of hydrocarbons include alkane compounds such as methane and ethane, alkene compounds such as ethylene and butadiene, alkyne compounds such as acetylene, aryl hydrocarbon compounds such as benzene, toluene, and styrene, aromatic hydrocarbons having condensed rings such as indene, naphthalene, and phenanthrene, cycloalkane compounds such as cyclopropane and cyclohexane, cycloolefin compounds such as cyclopentene, and alicyclic hydrocarbon compounds having condensed rings such as steroids. Examples of alcohols include methanol and ethanol. The source gas is preferably a hydrocarbon from the viewpoint of the carbon purity of the obtained CNT.

[0047] The flow rate of the source gas can be appropriately set according to the size of the reaction chamber in the CVD method, the size of the substrate, etc. For example, as a CVD apparatus, when using an apparatus in which the volume of the quartz reaction tube is 2.0×10 -3 m 3 and the heating zone is 60% of the quartz reaction tube, and the size of the substrate is 2 inches in diameter, the flow rate of the source gas may be 5 to 100 sccm, may be 7 to 80 sccm, may be 10 to 60 sccm, or may be 15 to 40 sccm.

[0048] Together with the source gas, a carrier gas which is a gas for transporting the source gas may be supplied to the reaction chamber. Examples of the carrier gas include helium, neon, argon, nitrogen, and hydrogen. Note that hydrogen is considered to contribute to the productivity and quality of carbon nanotubes and is also called a reactive carrier gas.

[0049] The flow rate of the carrier gas can be appropriately set according to the size of the apparatus used in the CVD method, the size of the substrate, etc. For example, as a CVD apparatus, when using an apparatus with a quartz reaction tube volume of 2.0×10 -3 m 3 and a heating zone of 60% of the quartz reaction tube, and the size of the substrate is 2 inches in diameter, the flow rate of the carrier gas is preferably 50~2500 sccm, more preferably 200~2200 sccm, even more preferably 300~2000 sccm, and particularly preferably 400~1900 sccm.

[0050] From the viewpoints of the growth rate of CNTs and the carbon purity of the obtained CNTs, the temperature in the reaction chamber in the CVD method is preferably 600~850 °C, more preferably 650~800 °C. From the viewpoints of the growth rate of CNTs and the carbon purity, the pressure in the reaction chamber in the CVD method is preferably atmospheric pressure. Depending on other conditions when implementing the CVD method, the pressure in the reaction chamber may be reduced or increased from atmospheric pressure. Under one manufacturing condition, the higher the pressure in the reaction chamber, the narrower the distribution of the number of layers of CNTs constituting the CNT aggregate tends to be. In the production of the CNT aggregate of the present disclosure, the pressure in the reaction chamber is preferably 450~800 torr, more preferably 480~750 torr, even more preferably 510~700 torr, and particularly preferably 540~650 torr.

[0051] The average length of CNTs in the CNT forest is, for example, the same as the average length of CNTs described above.

[0052] [Applications of the Aggregate of Carbon Nanotubes] The aggregate of CNTs of the present disclosure can be used for sports and leisure applications such as shoes, fishing rods, golf shafts, and tennis rackets; electrical and electronic equipment applications such as secondary batteries, heat dissipation materials, electrode sheets, electromagnetic wave shields, electromagnetic wave absorption sheets, antistatic sheets, battery components, electronic components, and the housings of notebook computers, tablets, and smartphones; architectural applications such as building materials; transportation machinery applications such as automobiles, motorcycles, bicycles, railways, drones, rockets, airplanes, and ships; energy applications such as hydraulic generators and wind turbines; and fashion applications such as clothing and bags.

[0053] The aggregate of CNTs of the present disclosure, particularly the CNT forest provided on a substrate, is preferably used for applications using carbon nanotube fibers (CNT fibers) or carbon nanotube webs (CNT webs). Examples of applications using CNT fibers or CNT webs include applications using CNT films. Specifically, in addition to the above-mentioned applications, heaters are also included.

[0054] The CNT web can be manufactured, for example, by pulling out a plurality of CNTs from a CNT forest using an aggregate of CNTs in the state of a CNT forest provided on a substrate, specifically, by pulling out a plurality of CNTs in a sheet shape. More specifically, the CNT web can be manufactured, for example, by pulling out the CNTs located at the ends among the CNTs constituting the CNT forest in a direction away from the CNT forest in a direction parallel to the surface of the substrate on which the CNT forest is provided, using a picking tool such as tweezers. When the CNTs located at the ends of the CNT forest are pulled out, the CNTs adjacent to the pulled-out CNTs are sequentially pulled out by van der Waals forces. The pulled-out CNTs are oriented so that their longitudinal directions are aligned in the pulled-out direction. Therefore, the plurality of CNTs constituting the CNT fiber are oriented in one direction. The plurality of CNTs constituting the CNT fiber are bonded to each other by van der Waals forces. As a result, a CNT web is obtained in which a plurality of CNT fibers extending in the direction in which the CNTs are pulled out are gathered.

[0055] A CNT film containing CNT fibers can be produced, for example, by a method in which a plurality of CNT webs obtained by drawing a plurality of CNTs from a CNT forest are produced in a sheet form and then laminated, or by a method in which a roll is produced by winding a plurality of CNT webs obtained by drawing a plurality of CNTs from a CNT forest around the peripheral surface of a roller or the like a plurality of times, and then the roll is cut along the direction of the rotation axis of the roller.

[0056] The aggregate of CNTs of the present disclosure, particularly the CNT forest provided on a substrate, has excellent spinnability due to physical property values such as the number of CNT layers, outer diameter, inner diameter, and length being within the above ranges, and the aggregate of CNTs has excellent dispersibility. When the aggregate of CNTs has excellent spinnability, when producing CNT fibers and CNT webs using the CNT forest, there is little risk of the CNT fibers and CNT webs breaking during the process of drawing CNTs from the CNT forest. When the aggregate of CNTs has excellent dispersibility, it is suitable, for example, as a conductive aid in secondary batteries such as lithium ion secondary batteries.

[0057] Examples of the dispersion medium for the above aggregate of CNTs include water and organic solvents. Examples of the organic solvents include water-soluble organic solvents, specifically, alcohol solvents, polyhydric alcohol ether solvents, amine solvents, amide solvents, heterocyclic solvents, sulfoxide solvents, sulfone solvents, lower ketone solvents, urea, and acetonitrile.

[0058] Examples of the alcohol solvents include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and polypropylene glycol. Examples of the polyhydric alcohol ether solvents include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether.

[0059] Examples of the amine solvents include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, and diethylenediamine. Examples of the amide solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam.

[0060] Examples of the heterocyclic solvents include tetrahydrofuran, cyclohexylpyrrolidone, 2-oxazolidone, and 1,3-dimethyl-2-imidazolidinone. Examples of the sulfoxide solvents include dimethyl sulfoxide. Examples of the sulfone solvents include hexamethylphosphoramide and sulfolane. Examples of the lower ketone solvents include acetone and methyl ethyl ketone.

[0061] The present disclosure has, for example, the following aspects. [1] An aggregate of carbon nanotubes (CNT) containing a plurality of carbon nanotubes, When observing 110 or more CNTs constituting the aggregate with a transmission electron microscope, When the maximum number of observed layers is n (n is an integer), with respect to 100% in total of all the observed CNTs, The total proportion of CNTs with the number of layers from n - 1 to n + 1 is 20% to 38%, the total proportion of CNTs with the number of layers from n - 2 to n + 2 is 35% to 80%, when the average value of the outer diameter of CNTs with the number of layers n is X (nm), the average value of the outer diameter of CNTs with the number of layers n - 1 is X - 2.8 (nm) to X + 0.5 (nm), the average value of the outer diameter of CNTs with the number of layers n + 1 is X - 0.5 (nm) to X + 2.8 (nm), the average value of the outer diameter of all the observed CNTs is X - 1.5 (nm) to X + 1.5 (nm). An aggregate of carbon nanotubes.

[0062] [2] The aggregate of carbon nanotubes according to [1], wherein the average value of the inner diameter of all the observed CNTs is 1.0 to 6.0 nm.

[0063] [3] The aggregate of carbon nanotubes according to [1] or [2], wherein n is 3 or more.

[0064] [4] The aggregate of carbon nanotubes according to any one of [1] to [3], wherein the aggregate of CNTs is a CNT forest provided on a substrate.

[0065] [5] The aggregate of carbon nanotubes according to any one of [1] to [3], wherein the aggregate of CNTs is an aggregate obtained from a CNT forest.

Example

[0066] Hereinafter, the aggregate of CNTs of the present disclosure will be described more specifically based on examples, but the aggregate of CNTs of the present disclosure is not limited to these examples.

[0067] [Example 1] First, vertically aligned CNTs were grown from the catalyst according to the following steps (1) to (6) to fabricate a vertically aligned CNT forest vertically oriented with respect to the wafer. (1) On a titanium metal foil substrate with a diameter of 2 inches and a thickness of 0.1 mm, using silicon (Si) as a target by reactive sputtering, while introducing 200 sccm of argon and 50 sccm of oxygen to react with silicon, a buffer layer of silica (SiO 2 ) with a thickness of 40 nm was formed. (2) On the buffer layer of silica, an iron catalyst layer with a thickness of 5 nm was uniformly formed by sputtering to obtain a catalyst substrate. (3) The catalyst substrate was placed at the center of the heating zone in the CVD apparatus. After evacuation, the temperature inside the furnace (reaction chamber) was raised until it reached 730 °C to activate the catalyst particles (iron particles). As the CVD apparatus, an apparatus with a volume of the quartz reaction tube of 2.0×10 -3 m 3 and a heating zone of 60% of the quartz reaction tube was used. (4) 1497 sccm of nitrogen gas was introduced, and while maintaining the pressure inside the furnace at 600 torr, the inside of the furnace was set to a carrier gas (nitrogen gas) atmosphere. (5) After the temperature inside the furnace stabilized at 729 °C, without changing the nitrogen gas introduction amount, further, 20 sccm of acetylene gas (C 2 H 2 ) and 100 sccm of hydrogen gas were introduced, and the CNTs were grown for 10 minutes. (6) Then, the furnace was cooled, and the catalyst substrate and the CNT forest (where CNTs stand upright on the substrate) were taken out.

[0068] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0069] The carbon purity of the CNTs constituting the CNT forest was 99.8% or more, and the crystallinity (D / G ratio) was 0.6 to 0.8. Also, 114 CNTs were arbitrarily selected from the obtained powdery CNTs, and TEM observation described later was performed. The observation results are shown in Table 1.

[0070] [Table 1]

[0071] As a result of observing a total of 114 CNTs, the most frequently observed number of layers was 10. The total ratio of CNTs with the number of layers being 9 to 11 was 32.5%, and the total ratio of CNTs with the number of layers being 8 to 12 was 64.0%.

[0072] The average outer diameter of CNTs with the number of layers being 10 was 10.1 nm, the average outer diameter of CNTs with the number of layers being 9 was 10.4 nm, and the average outer diameter of CNTs with the number of layers being 11 was 12.4 nm. The average outer diameter of the 114 CNTs observed by TEM was 10.3 nm, and the average inner diameter was 4.9 nm. The length per CNT constituting the CNT forest by SEM observation was 250 μm on average.

[0073] In Fig. 1, an example of a TEM image of the CNTs obtained in Example 1 is shown. The length D in Fig. 1 is an example of the outer diameter of the CNT, and the length d is an example of the inner diameter.

[0074] [Comparative Example 1] First, vertically aligned CNTs were grown from the catalyst by the following steps (1) to (6) to fabricate a vertically aligned CNT forest vertically oriented with respect to the wafer. (1) On a titanium metal foil substrate with a diameter of 2 inches and a thickness of 0.1 mm, using aluminum (Al) as a target by reactive sputtering, while introducing 98 sccm of argon and 21 sccm of oxygen and reacting with aluminum, a buffer layer of alumina (Al 2 O 3 ) with a thickness of 40 nm was formed. (2) A catalyst layer of iron with a thickness of 5 nm was uniformly formed on the buffer layer of alumina by sputtering to obtain a catalyst substrate. (3) The catalyst substrate was placed at the center of the heating zone in the CVD apparatus. After evacuation, the temperature inside the furnace (reaction chamber) was raised until it reached 730 °C to activate the catalyst particles (iron particles). As the CVD apparatus, an apparatus was used in which the volume of the quartz reaction tube was 2.0×10 -3 m 3 and the heating zone was 60% of the quartz reaction tube. (4) Nitrogen gas was introduced at 1498 sccm, and the inside of the furnace was set to an atmosphere of carrier gas (nitrogen gas) while maintaining the pressure inside the furnace at 749 torr. (5) After the temperature inside the furnace stabilized at 730 °C, without changing the nitrogen gas introduction amount, further, acetylene gas (C 2 H 2 ) was introduced at 21 sccm and hydrogen gas was introduced at 99 sccm, and CNTs were grown for 10 minutes. (6) Then, the furnace was cooled, and the catalyst substrate and the CNT forest (where CNTs stood upright on the substrate) were taken out.

[0075] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0076] The carbon purity of the CNTs constituting the CNT forest was 99.8% or more, and the crystallinity (D / G ratio) was 0.6 to 0.8. Also, 161 CNTs were arbitrarily selected from the obtained powdery CNTs, and TEM observation described later was performed. The observation results are shown in Table 2.

[0077]

Table 2

[0078] As a result of observing a total of 161 CNTs, the most frequently observed number of layers was 6. The total ratio of CNTs with the number of layers of 5 to 7 was 47.8%, and the total ratio of CNTs with the number of layers of 4 to 8 was 80.1%.

[0079] The average outer diameter of CNTs with 6 layers was 7.6 nm, the average outer diameter of CNTs with 5 layers was 7.4 nm, and the average outer diameter of CNTs with 7 layers was 7.5 nm. The average outer diameter of 161 CNTs observed by TEM was 7.5 nm, and the average inner diameter was 4.1 nm. The length per CNT constituting the CNT forest by SEM observation was on average 250 μm.

[0080] [Comparative Example 2] First, vertically aligned CNTs were grown from a catalyst by the following steps (1) to (6) to produce a vertically aligned CNT forest vertically oriented with respect to the wafer. (1) On a titanium metal foil substrate with a diameter of 2 inches and a thickness of 0.1 mm, using silicon (Si) as a target by reactive sputtering, 201 sccm of argon and 49 sccm of oxygen were introduced and reacted with silicon while forming a buffer layer of silica (SiO 2 ) with a thickness of 40 nm. (2) On the buffer layer of silica, a catalyst layer of iron with a thickness of 5 nm was uniformly formed by sputtering to obtain a catalyst substrate. (3) The catalyst substrate was placed at the center of the heating zone in the CVD apparatus. After evacuation, the temperature inside the furnace (reaction chamber) was raised until it reached 730 °C to activate the catalyst particles (iron particles). As the CVD apparatus, an apparatus with a quartz reaction tube volume of 2.0×10 -3 m 3 and a heating zone of 60% of the quartz reaction tube was used. (4) 1502 sccm of nitrogen gas was introduced, and while maintaining the pressure inside the furnace at 751 torr, the inside of the furnace was set to a carrier gas (nitrogen gas) atmosphere. (5) After the temperature inside the furnace stabilized at 730 °C, without changing the nitrogen gas introduction amount, further 20 sccm of acetylene gas (C 2 H 2 ) and 98 sccm of hydrogen gas were introduced, and CNTs were grown for 10 minutes. (6) Then, the furnace was cooled, and the catalyst substrate and the CNT forest (where CNTs stood upright on the substrate) were taken out.

[0081] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0082] The carbon purity of the CNTs constituting the CNT forest was 99.8% or more, and the crystallinity (D / G ratio) was 0.6 - 0.8. Also, 166 CNTs were arbitrarily selected from the obtained powdery CNTs, and TEM observation described below was performed. The observation results are shown in Table 3.

[0083]

Table 3

[0084] As a result of observing a total of 166 CNTs, the most frequently observed number of layers was 6. The total ratio of CNTs with the number of layers of 5 - 7 was 42.2%, and the total ratio of CNTs with the number of layers of 4 - 8 was 65.1%. The average outer diameter of CNTs with the number of layers of 6 was 9.3 nm, the average outer diameter of CNTs with the number of layers of 5 was 8.3 nm, and the average outer diameter of CNTs with the number of layers of 7 was 10.7 nm. The average outer diameter of the 166 CNTs observed by TEM was 11.5 nm, and the average inner diameter was 5.4 nm. The length per CNT constituting the CNT forest by SEM observation was on average 246 μm.

[0085] [Comparative Example 3] First, vertically aligned CNTs were grown from the catalyst by the following procedures (1) - (5) to fabricate a vertically aligned CNT forest vertically aligned with respect to the wafer. (1) On a silicon wafer with a diameter of 2 inches and a thickness of 0.725 mm, an iron (Fe) catalyst layer with a thickness of 3 nm was uniformly formed using iron as a target by sputtering to manufacture a catalyst substrate. (2) The catalyst substrate was placed at the center of the heating zone in the CVD apparatus. After evacuation, the temperature inside the furnace (reaction chamber) was raised until it reached 730 °C to activate the catalyst particles (iron particles). As the CVD apparatus, an apparatus with a quartz reaction tube volume of 2.0×10 -3 m 3 and a heating zone that is 60% of the quartz reaction tube was used. (3) Nitrogen gas was introduced at 1502 sccm, and while maintaining the pressure inside the furnace at 751 torr, the inside of the furnace was set to an atmosphere of carrier gas (nitrogen gas). (4) After the temperature inside the furnace stabilized at 732 °C, without changing the nitrogen gas introduction amount, further, acetylene gas (C 2 H 2 ) was introduced at 20 sccm and hydrogen gas was introduced at 279 sccm, and CNTs were grown for 10 minutes. (5) Thereafter, the furnace was cooled, and the catalyst substrate and the CNT forest (where CNTs stand upright on the substrate) were taken out.

[0086] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0087] The carbon purity of the CNTs constituting the CNT forest was 99.8% or more, and the crystallinity (D / G ratio) was 0.6 - 0.8. Also, 115 CNTs were arbitrarily selected from the obtained powdery CNTs, and TEM observation described later was performed. The observation results are shown in Table 4.

[0088]

Table 4

[0089] As a result of observing a total of 115 CNTs, the median of the observed number of layers was 6, and the most frequently observed number of layers was 6. The total ratio of CNTs with the number of layers being 5 - 7 was 83.5%, and the total ratio of CNTs with the number of layers being 4 - 8 was 95.7%.

[0090] The average outer diameter of CNTs with 6 layers was 9.2 nm, the average outer diameter of CNTs with 5 layers was 8.1 nm, and the average outer diameter of CNTs with 7 layers was 10.6 nm. The average outer diameter of 115 CNTs observed by TEM was 9.2 nm, and the average inner diameter was 3.9 nm. The length per single CNT constituting the CNT forest by SEM observation was on average 247 μm.

[0091] [TEM Observation] Regarding the powdered CNTs produced in the examples and comparative examples, TEM observation and measurement of the number of layers, outer diameter, and inner diameter of the CNTs were performed by the following methods (1) to (3). (1) The obtained powdered CNTs were dispersed in ethanol and dropped onto a microgrid. (2) The dried sample was observed using a FE-TEM (JEM-2100F manufactured by JEOL Ltd.) to obtain a TEM image. At this time, a predetermined number of CNTs were arbitrarily selected. (3) For each TEM image, the number of layers, outer diameter, and inner diameter of the CNTs were measured using ImageJ. Regarding the outer diameter and inner diameter of the CNTs, three measurements were made at three locations each on the CNTs shown in the TEM image, and the average value was used. When the outer diameter or inner diameter of the CNTs shown in the TEM image changed significantly in the middle of the CNTs to the extent that they could be visually distinguished, three locations, namely the thin part, thick part, and medium part of the outer diameter or inner diameter, were selected as the measurement locations.

[0092] [Spinnability Evaluation] Three evaluators who had drawn CNT webs from 100 or more CNT forests evaluated the spinnability by drawing CNT webs from the ends of CNT forests produced under the same conditions as in the examples and comparative examples according to the following criteria. Each evaluator performed the above operation on five CNT forests each, and the average value was taken as the evaluation of each evaluator. The average value of the evaluations of the three evaluators was taken as the spinnability of the CNT aggregate.

[0093] The spinability of the CNT aggregate in Example 1 was 3.8, that of the CNT aggregate in Comparative Example 1 was 1.1, that of the CNT aggregate in Comparative Example 2 was 1.2, and that of the CNT aggregate in Comparative Example 3 was 4.4.

[0094] 5: The CNT web can be drawn out once from one end to the other end of the CNT forest. 4: The CNT web can be drawn out twice from one end to the other end of the CNT forest. 3: The CNT web can be drawn out three times from one end to the other end of the CNT forest. 2: The CNT web can be drawn out 4 to 6 times from one end to the other end of the CNT forest. 1: The CNT web can be drawn out 7 or more times from one end to the other end of the CNT forest, or cannot be drawn out from one end to the other end.

[0095] [Dispersion evaluation] In the CNT forests obtained in the examples and comparative examples, the CNTs were scraped off the wafer using a scraper to obtain a powdery CNT aggregate. Three evaluators who had prepared the CNT dispersion 100 times or more performed the following operations and then evaluated according to the following criteria.

[0096] 0.002 g of the powdery CNT aggregate was weighed into a glass screw tube, 5 ml of ethanol was added, and ultrasonic waves at 40,000 Hz were irradiated for 2 minutes. Visual observation was performed, and the dispersibility was evaluated according to the following criteria. Each evaluator evaluated each powdery CNT aggregate three times, and the average value was taken as the evaluation of each evaluator. The average value of the evaluations of the three evaluators was taken as the evaluation of the dispersibility of the CNT aggregate.

[0097] The dispersibility of the CNT aggregate in Example 1 was 2.8, the dispersibility of the CNT aggregate in Comparative Example 1 was 3.3, the dispersibility of the CNT aggregate in Comparative Example 2 was 3.2, and the dispersibility of the CNT aggregate in Comparative Example 3 was 1.4. 4: It was uniformly dispersed within 2 minutes after ultrasonic irradiation. 3: Although a few lumps were observed within 2 minutes after ultrasonic irradiation, it was dispersed to such an extent that there was no practical problem. 2: Lumps were observed 2 minutes after ultrasonic irradiation, and additional dispersion within 3 minutes was required to disperse it to such an extent that there was no practical problem. 1: Lumps were observed 2 minutes after ultrasonic irradiation, and additional dispersion exceeding 3 minutes was required to disperse it to such an extent that there was no practical problem.

Claims

1. An aggregate of carbon nanotubes (CNTs) including a plurality of CNTs; When the 110 or more CNTs constituting the aggregate were observed with a transmission electron microscope, When the most frequently observed number of layers is n (n is an integer from 3 to 15), the number of layers is 100% of the total number of CNTs observed. the total percentage of CNTs having a number of walls of n-1 to n+1 is 22 to 36%, the total percentage of CNTs having a number of walls of n-2 to n+2 is 50 to 70%, If the average outer diameter of a CNT having n walls is X (nm), the average outer diameter of the CNTs having n-1 walls is X-2.8 (nm) to X+0.5 (nm); the average outer diameter of the CNTs having n+1 walls is X-0.5 (nm) to X+2.8 (nm); The average outer diameter of all the observed CNTs is X-1.5 (nm) to X+1.5 (nm); An aggregate of carbon nanotubes.

2. 2. The aggregate of carbon nanotubes according to claim 1, wherein the average inner diameter of all the observed CNTs is 1.0 to 6.0 nm.

3. The carbon nanotube aggregate of claim 1, wherein the average length of the CNTs constituting the aggregate is 10 to 1000 μm.

4. The carbon nanotube aggregate of claim 1 , wherein the CNT aggregate is a CNT forest disposed on a substrate.

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