Aggregate of carbon nanotubes

Abstract

To provide an aggregate of carbon nanotubes with excellent dispersibility. 【Solution means】An aggregate of carbon nanotubes (CNTs) containing a plurality of carbon nanotubes. 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), then, with respect to the total of 100% of all the observed CNTs, the total ratio of CNTs with the number of layers being n - 1 to n + 1 exceeds 38% and is less than 65%, the total ratio of CNTs with the number of layers being n - 2 to n + 2 is 45 to 90%, if 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 - 1.8 (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 + 1.8 (nm), and the average value of the outer diameters of all the observed CNTs is X - 3.0 (nm) to X + 3.0 (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, a carbon nanotube film may be used for applications such as a heater (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 an aggregate of carbon nanotubes having excellent dispersibility.

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 having a number of layers of n - 1 to n + 1 exceeds 38% and is less than 65%, and the total ratio of CNTs having a number of layers of n - 2 to n + 2 is 45 to 90%. Further, when the average value of the outer diameter of CNTs having a number of layers of n is X (nm), the average value of the outer diameter of CNTs having a number of layers of n - 1 is X - 1.8 (nm) to X + 0.5 (nm), the average value of the outer diameter of CNTs having a number of layers of n + 1 is X - 0.5 (nm) to X + 1.8 (nm), and the average value of the outer diameter of all the observed CNTs is X - 3.0 (nm) to X + 3.0 (nm). [Advantages of the Invention]

[0006] The aggregate of carbon nanotubes of the present disclosure has excellent dispersibility. [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 "~" indicating the numerical range are the same, the unit of the numerical value described before "~" 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), with respect to 100% of the total number of all CNTs observed, the total ratio of CNTs with the number of layers being n - 1 to n + 1 exceeds 38% and is less than 65%, and the total ratio of CNTs with the number of layers being n - 2 to n + 2 is 45 to 90%. 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 - 1.8 (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 + 1.8 (nm), and the average value of the outer diameter of all CNTs observed is X - 3.0 (nm) to X + 3.0 (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, a CNT forest provided on a substrate or an aggregate obtained from the CNT forest. The 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. 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] 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 so as not to include the CNT from the CNT aggregates. 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 exceeds 38% and is less than 65%, and the total proportion of CNTs with the number of layers from n - 2 to n + 2 is 45 - 90%.

[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 of 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 - 10, still more preferably 4 - 8, and particularly preferably 5 - 7. The total proportion of CNTs with the number of layers from n - 1 to n + 1 is preferably 39 - 60%, more preferably 40 - 55%, and still more preferably 41 - 50%. The total proportion of CNTs with a layer number of n - 2 to n + 2 is preferably 50 to 87%, more preferably 55 to 85%, still more preferably 60 to 83%, and particularly preferably 65 to 82%. When the total proportion of CNTs with a layer number of n - 1 to n + 1 and n - 2 to n + 2 is within the above range, the aggregate of CNTs has excellent dispersibility.

[0020] The proportion of CNTs with a layer number of n is preferably 10 to 40%, more preferably 15 to 35%, and still more preferably 17 to 30%. When the proportion of CNTs with a layer number of n is within the above range, the aggregate of CNTs has excellent dispersibility.

[0021] When the distribution of the layer number of CNTs constituting the aggregate of CNTs is narrow, the total proportion of CNTs with a layer number of n, n - 1 to n + 1, and n - 2 to n + 2 is high.

[0022] The value of n, as well as the total proportion of CNTs with a layer number of n, n - 1 to n + 1, and n - 2 to n + 2, can be adjusted, for example, in the method for producing an aggregate of CNTs described below, by adjusting the type of substrate used for the catalyst substrate, the presence or absence of a 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 observations.

[0023] When observing 110 or more CNTs by TEM, when the average value of the outer diameter of CNTs with a layer number of n is X (nm), the average value of the outer diameter of CNTs with a layer number of n - 1 is X - 1.8 (nm) to X + 0.5 (nm), and the average value of the outer diameter of CNTs with a layer number of n + 1 is X - 0.5 (nm) to X + 1.8 (nm). Also, the average value of the outer diameters of all CNTs (used for calculating n) observed by TEM is X - 3.0 (nm) to X + 3.0 (nm).

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

[0025] From the viewpoint that the aggregate of CNTs has excellent dispersibility, X is preferably 1 to 30 nm, more preferably 3 to 25 nm, still more preferably 5 to 20 nm, and particularly preferably more than 5.1 nm and less than 10.0 nm. The average value of the outer diameter of CNTs with the number of layers being n refers to the arithmetic mean of the outer diameters of CNTs with the number of layers being n. The same applies to the average value of the outer diameter of CNTs with the number of layers being n - 1, the average value of the outer diameter of CNTs with the number of layers being n + 1, and the average value of the outer diameters of all CNTs observed by TEM.

[0026] From the viewpoint that the aggregate of CNTs has excellent dispersibility, the average value of the outer diameter of CNTs with the number of layers being n - 1 is preferably X - 1.7 (nm) to X + 0.4 (nm), more preferably X - 1.6 (nm) to X + 0.3 (nm), and still more preferably X - 1.5 (nm) to X + 0.2 (nm).

[0027] From the viewpoint that the aggregate of CNTs has excellent dispersibility, the average value of the outer diameter of CNTs with the number of layers being n + 1 is preferably X - 0.4 (nm) to X + 1.7 (nm), more preferably X - 0.3 (nm) to X + 1.6 (nm), and still more preferably X - 0.2 (nm) to X + 1.5 (nm).

[0028] From the viewpoint that the aggregate of CNTs has excellent dispersibility, the average value of the outer diameters of all CNTs observed by TEM is preferably X - 2.8 (nm) to X + 2.8 (nm), more preferably X - 2.6 (nm) to X + 2.6 (nm), and still more preferably X - 2.4 (nm) to X + 2.4 (nm).

[0029] The outer diameter of the CNT can be adjusted, for example, in the method for manufacturing an aggregate of CNTs described below, by adjusting the type of substrate used for the catalyst substrate, the presence or absence of a 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 observations.

[0030] From the viewpoint that the aggregate of CNTs has excellent dispersibility, the average value of the inner diameters of all the CNTs observed by TEM (used for calculating n by observing the number of layers) is preferably 1.0 to 6.0 nm, more preferably 3.5 to 6.0 nm, still more preferably 3.6 to 5.9 nm, particularly preferably 3.7 to 5.8 nm, and most preferably 3.8 to 5.7 nm.

[0031] The inner diameter of the CNT refers to the diameter of the innermost layer of the CNT measured using an 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 an aggregate of CNTs described below, by adjusting the type of substrate used for the catalyst substrate, the presence or absence of a 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 observations.

[0033] The average length of the CNTs constituting the aggregate of CNTs 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 acquired using an SEM. For each of the 10 images, 10 measurement points for the length are arbitrarily selected and measured, resulting in a total of 100 length measurements. Then, the average length of the CNTs can be determined by calculating the arithmetic mean of the 100 length measurement values.

[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, % 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 the CNTs can be adjusted respectively, for example, in the method for producing the CNT aggregate described below, 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 an 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. The aggregate obtained from the CNT forest (for example, a powdery aggregate of CNTs) can be obtained, for example, by scraping 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 chemical vapor deposition (CVD method) using a substrate and a catalyst substrate provided with a catalyst layer on the substrate. The CVD method is a method in which the catalyst substrate is placed in a reaction chamber and then a raw material gas is supplied into the reaction chamber to grow CNTs on the surface of the catalyst layer. As the CVD method, 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 substrate cost, 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. 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 to 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 CNTs 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 CNTs to be larger. The thinner the catalyst layer, the narrower the tendency for the distribution of the number of layers of 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 CNTs 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 CNTs tend to be smaller, and when the material is silica (SiO 2 ), the outer diameter and inner diameter of CNTs tend to be larger.

[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 performing sputtering is preferably 0.01 to 10 Pa, more preferably about 0.1 to 1 Pa.

[0046] As the raw material gas, a raw material gas containing carbon can be used. For example, hydrocarbons, sulfur-containing organic gases, phosphorus-containing organic gases, carbon monoxide, and alcohols can be mentioned. 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 raw material gas is preferably a hydrocarbon from the viewpoint of the carbon purity of the obtained CNT.

[0047] The flow rate of the raw material 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 raw material 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 raw material gas, a carrier gas which is a gas for transporting the raw material 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 being 60% of the quartz reaction tube, and the size of the substrate being 2 inches in diameter, the flow rate of the carrier gas is preferably 50 - 2500 sccm, more preferably 200 - 2200 sccm, still more preferably 300 - 2000 sccm, and particularly preferably 400 - 1900 sccm.

[0050] From the viewpoint 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 viewpoint of the growth rate of CNTs and the carbon purity, the pressure in the reaction chamber in the CVD method is preferably normal pressure. Depending on other conditions when implementing the CVD method, the pressure in the reaction chamber may be reduced or increased from normal 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.

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

[0052] [Applications of the carbon nanotube aggregate] 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 has excellent dispersibility due to physical property values such as the number of layers, outer diameter, inner diameter, and length of the CNTs being within the above ranges. Since the aggregate of CNTs has excellent dispersibility, it is suitable as a conductive aid in secondary batteries such as lithium-ion secondary batteries.

[0054] Examples of the dispersion medium for the aggregate of CNTs include water and organic solvents. Examples of the organic solvents include water-soluble organic solvents, specifically, alcohol-based solvents, polyhydric alcohol ether-based solvents, amine-based solvents, amide-based solvents, heterocyclic solvents, sulfoxide-based solvents, sulfone-based solvents, lower ketone-based solvents, urea, and acetonitrile.

[0055] Examples of the alcohol-based 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-based 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.

[0056] Examples of amine solvents include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, and diethylenediamine. Examples of 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.

[0057] Examples of heterocyclic solvents include tetrahydrofuran, cyclohexylpyrrolidone, 2-oxazolidone, and 1,3-dimethyl-2-imidazolidinone. Examples of sulfoxide solvents include dimethyl sulfoxide. Examples of sulfone solvents include hexamethylphosphoramide and sulfolane. Examples of lower ketone solvents include acetone and methyl ethyl ketone.

[0058] This 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 most frequently observed number of layers is n (n is an integer), with respect to 100% in total of all the observed CNTs, The total ratio of CNTs with the number of layers being n - 1 to n + 1 exceeds 38% and is less than 65%, The total ratio of CNTs with the number of layers being n - 2 to n + 2 is 45 to 90%, 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 - 1.8 (nm) to X + 0.5 (nm), The average outer diameter of CNTs with a layer number of n + 1 is X - 0.5 (nm) to X + 1.8 (nm), The average outer diameter of all the observed CNTs is X - 3.0 (nm) to X + 3.0 (nm), An aggregate of carbon nanotubes.

[0059] [2] The average inner diameter of all the observed CNTs is 1.0 to 6.0 nm, and the aggregate of carbon nanotubes according to [1].

[0060] [3] The aggregate of carbon nanotubes according to [1] or [2], wherein n is 3 or more.

[0061] [4] The aggregate of carbon nanotubes according to any one of [1] to [3], wherein the aggregate of CNTs is in powder form.

[0062] [5] 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.

Example

[0063] 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.

[0064] [Example 1] First, by the following procedures (1) to (6), vertically aligned CNTs were grown from a catalyst to fabricate a vertically aligned CNT forest vertically oriented with respect to a wafer. (1) On a titanium metal foil substrate having 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, alumina (Al 2 O 3 ) having a thickness of 40 nm was formed as a buffer layer. (2) On the buffer layer of alumina, 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 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 while maintaining the pressure inside the furnace at 749 torr, the inside of the furnace was set to an atmosphere of carrier gas (nitrogen gas). (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.

[0065] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0066] 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 1.

[0067]

Table 1

[0068] 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%.

[0069] 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 average length per CNT constituting the CNT forest by SEM observation was 250 μm on average.

[0070] In FIG. 1, an example of a TEM image of 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.

[0071] [Example 2] First, vertically aligned CNTs were grown from the catalyst by the following procedures (1) to (6) to fabricate a vertically aligned CNT forest vertically aligned 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 201 sccm of argon and 49 sccm of oxygen and reacting with silicon, a buffer layer of silica (SiO 2 ) with a thickness of 40 nm was formed. (2) A 5-nm-thick iron catalyst layer was uniformly formed on the silica buffer layer by sputtering to obtain a catalyst substrate. (3) The catalyst substrate was placed at the center of the heating zone in the CVD apparatus, and after evacuation, the temperature inside the furnace (reaction chamber) was raised until the furnace temperature 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 in the furnace stabilized at 730 °C, without changing the nitrogen gas introduction amount, 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 stand upright on the substrate) were taken out.

[0072] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0073] 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 later was performed. The observation results are shown in Table 2.

[0074]

Table 2

[0075] 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 being 5 - 7 was 42.2%, and the total ratio of CNTs with the number of layers being 4 - 8 was 65.1%.

[0076] The average outer diameter of CNTs with the number of layers being 6 was 9.3 nm, the average outer diameter of CNTs with the number of layers being 5 was 8.3 nm, and the average outer diameter of CNTs with the number of layers being 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 average length per CNT constituting the CNT forest by SEM observation was 246 μm.

[0077] [Comparative Example 1] First, vertically aligned CNTs were grown from the catalyst according to the following steps (1) to (5), and a vertically aligned CNT forest vertically oriented with respect to the wafer was fabricated. (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 deposited using sputtering with iron as the target to produce 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 the inside of the furnace was set to a carrier gas (nitrogen gas) atmosphere while maintaining the pressure inside the furnace at 751 torr. (4) After the temperature inside the furnace stabilized at 732 °C, without changing the nitrogen gas introduction amount, acetylene gas (C 2 H 2 ) was introduced at 20 sccm and hydrogen gas was introduced at 279 sccm, and the CNTs were grown for 10 minutes. (5) Then, the furnace was cooled, and the catalyst substrate and the CNT forest (where CNTs stand upright on the substrate) were taken out.

[0078] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0079] 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, 115 CNTs were arbitrarily selected from the obtained powdery CNTs, and TEM observation described later was performed. The observation results are shown in Table 3.

[0080]

Table 3

[0081] As a result of observing a total of 115 CNTs, the median number of observed layers was 6, and the most frequently observed number of layers was 6. The total proportion of CNTs with the number of layers being 5 to 7 was 83.5%, and the total proportion of CNTs with the number of layers being 4 to 8 was 95.7%.

[0082] The average outer diameter of CNTs with the number of layers being 6 was 9.2 nm, the average outer diameter of CNTs with the number of layers being 5 was 8.1 nm, and the average outer diameter of CNTs with the number of layers being 7 was 10.6 nm. The average outer diameter of the 115 CNTs observed by TEM was 9.2 nm, and the average inner diameter was 3.9 nm. The length per CNT constituting the CNT forest by SEM observation was on average 247 μm.

[0083] [Comparative Example 2] First, vertically aligned CNTs were grown from the catalyst by the following procedures (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 and reacting with silicon, a buffer layer of silica (SiO 2 ) 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 silica buffer layer 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 the furnace temperature 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 being 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 made into a carrier gas (nitrogen gas) atmosphere. (5) After the temperature in the furnace stabilized at 729 °C, without changing the nitrogen gas introduction amount, 20 sccm of acetylene gas (C 2 H 2 ) and 100 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.

[0084] Next, the CNT forest formed on the catalyst substrate was scraped off from the substrate using a scraper to obtain powdery CNTs.

[0085] 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, 114 CNTs were arbitrarily selected from the obtained powdery CNTs, and TEM observation described later was performed. The observation results are shown in Table 4.

[0086]

Table 4

[0087] 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 - 11 was 32.5%, and the total ratio of CNTs with the number of layers being 8 - 12 was 64.0%.

[0088] The average value of the outer diameter of CNTs with the number of layers being 10 was 10.1 nm, the average value of the outer diameter of CNTs with the number of layers being 9 was 10.4 nm, and the average value of the outer diameter of CNTs with the number of layers being 11 was 12.4 nm. The average value of the outer diameter of the 114 CNTs observed by TEM was 10.3 nm, and the average value of the inner diameter was 4.9 nm. The average length per CNT constituting the CNT forest by SEM observation was 250 μm.

[0089] [TEM Observation] For 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. For 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 thinnest, thickest, and medium-sized locations, were selected as the measurement locations.

[0090] [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 an aggregate of powdered CNTs. Three evaluators who had prepared the CNT dispersion more than 100 times performed the following operations and then evaluated according to the following criteria.

[0091] 0.002 g of the aggregate of powdered CNTs 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 aggregate of powdered CNTs 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 aggregate of CNTs.

[0092] The dispersibility of the CNT aggregates in Example 1 was 3.3, the dispersibility of the CNT aggregates in Example 2 was 3.2, the dispersibility of the CNT aggregates in Comparative Example 1 was 1.4, and the dispersibility of the CNT aggregates in Comparative Example 2 was 2.8. 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 a degree that was not a problem in practical use. 2: Lumps were observed 2 minutes after ultrasonic irradiation, and additional dispersion within 3 minutes was required to disperse it to a degree that was not a problem in practical use. 1: Lumps were observed 2 minutes after ultrasonic irradiation, and additional dispersion exceeding 3 minutes was required to disperse it to a degree that was not a problem in practical use.

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), the total number of layers is 100% of all the CNTs observed. the total percentage of CNTs having wall numbers of n-1 to n+1 is 40 to 50%, the total percentage of CNTs having a number of walls between n-2 and n+2 is between 45% and 90%, If the average outer diameter of a CNT with n walls is X (nm), X is 1 nm or more and less than 10.0 nm; the average outer diameter of the CNTs having n-1 walls is X-1.8 (nm) to X+0.5 (nm); the average outer diameter of the CNTs having n+1 walls is X-0.5 (nm) to X+1.8 (nm); The average outer diameter of all the observed CNTs is X-3.0 (nm) to X+3.0 (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 aggregate of carbon nanotubes according to claim 1 , wherein n is 3 or more.

4. The aggregate of carbon nanotubes according to claim 1 , wherein the aggregate of CNTs is in a powder form.

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

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