Carbon nanotube film, dispersion, and method for producing carbon nanotube film

Abstract

To provide a carbon nanotube membrane which is excellent in uniformity of thickness.SOLUTION: A carbon nanotube membrane comprises a carbon nanotube and has an average thickness of 1 nm to 200 nm. A percentage of an area of an ununiform region having a thickness being at least 10% larger or 10% smaller than the average thickness, to an area of the whole region of the membrane is 15.0% or less. The membrane has 3σ of a reflectance of 15% or less when the reflectance is measured in the following conditions with a reflectance spectroscopic membrane thickness meter while the membrane is disposed on a silicon substrate: [the conditions] a diameter of a measuring point: 20 μm, a reference measured wavelength: 285 nm, a measuring point number: 121 points, and a center point distance between adjacent measuring points: 40 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to carbon nanotube films, dispersions, and methods for producing carbon nanotube films. [Background technology]

[0002] Carbon nanotubes (hereinafter referred to as CNTs), which are composed of carbon atoms, are materials with excellent electrical properties, thermal conductivity, and mechanical properties. CNTs are extremely lightweight and extremely strong, and also have excellent elasticity and resilience. These excellent properties make CNTs an extremely attractive and important industrial material.

[0003] For example, Patent Document 1 discloses that pores having a pore size of 400 nm or more and 1500 nm or less, as measured by mercury intrusion porosimetry, have a log differential pore volume of 0.006 cm 3 The carbon nanotube aggregate has a region of 10 nm or more, in which the densities are 10 nm or less.

[0004] Patent Document 2 also describes a carbon nanotube sintered body having a plurality of mesh-like carbon nanotube bundles each including an aggregate of carbon nanotubes, and a BET specific surface area of ​​600 m2 as determined from a nitrogen adsorption isotherm. 2 / g or more, and the carbon nanotube bundle has pores of a size corresponding to a relative pressure (equilibrium pressure / saturated vapor pressure) of 0.2 to 0.9 in the nitrogen adsorption / desorption isotherm over 400 cm 3 / g(STP) or more. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-145027 [Patent Document 2] Japanese Patent Application Publication No. 2018-024540 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional carbon nanotube (CNT) films sometimes lack uniformity in thickness due to the formation of highly aggregated structures of CNT bundles caused by insufficient opening of the CNT bundles. An uneven surface of the CNT film may reduce the transparency of the CNT film and may cause a decrease in the uniformity of other properties in the plane direction, such as electrical conductivity. Furthermore, the unevenness of the CNT film surface may cause microscopic stress concentrations, which may result in a decrease in the mechanical strength of the CNT film.

[0007] In Patent Documents 1 and 2, the uniformity of the thickness of the CNT film is not sufficiently considered, and there is room for improvement.

[0008] An object of one embodiment of the present disclosure is to provide a carbon nanotube film having excellent thickness uniformity, a dispersion containing the carbon nanotube film, and a method for producing the carbon nanotube film. [Means for solving the problem]

[0009] Specific means for solving the above problems include the following aspects. <1> A carbon nanotube film containing carbon nanotubes, having an average thickness of 1 nm or more and 200 nm or less, in which the ratio of the area of ​​non-uniform regions, which are regions that are 10% or more thicker or 10% or more thinner than the average thickness, to the area of ​​the entire film is 15.0% or less, and when the film is placed on a silicon substrate and the reflectance is measured using a reflection spectroscopic film thickness meter under the following conditions, the 3σ of the reflectance is 15% or less. <Condition> Measurement point diameter: 20 μm Standard measurement wavelength: Wavelength 285nm Number of measurement points: 121 Distance between the centers of adjacent measurement points: 40 μm <2> When the reflectance is measured and the average reflectance is calculated using a reflection spectroscopic film thickness meter at multiple measurement positions placed on a silicon substrate and spaced 2 cm or more apart under the following conditions, the value obtained by subtracting the minimum value of the average reflectance from the maximum value of the average reflectance is 15% or less. <1> The carbon nanotube film according to claim 1. <Condition> Measurement point diameter: 20 μm Standard measurement wavelength: Wavelength 285nm Number of measurement points: 121 Distance between the centers of adjacent measurement points: 40 μm <3> Has a mesh structure <1> or <2> The carbon nanotube film according to claim 1. <4> The carbon nanotubes have a tube diameter of 0.8 nm or more and 6.0 nm or less. <1> ~ <3> 10. The carbon nanotube film according to claim 9, wherein the carbon nanotube film is a film having a thickness of 100 nm or less. <5> The carbon nanotubes have a length of 10 nm or more. <1> ~ <4> 10. The carbon nanotube film according to claim 9, wherein the carbon nanotube film is a film having a thickness of 100 nm or less. <6> The carbon content of the carbon nanotubes is 98% by mass or more based on the total mass of the carbon nanotubes. <1> ~ <5> 10. The carbon nanotube film according to claim 9, wherein the carbon nanotube film is a film having a thickness of 100 nm or less. <7> The G / D ratio measured by resonance Raman scattering is 20 or more. <1> ~ <6> 10. The carbon nanotube film according to claim 9, wherein the carbon nanotube film is a film having a thickness of 100 nm or less. <8> The breaking load measured by nanoindentation testing is 1.0 μN / nm or more. <1> ~ <7> 10. The carbon nanotube film according to claim 9, wherein the carbon nanotube film is a film having a thickness of 100 nm or less. <9> <1> ~ <8> 10. A dispersion liquid used in the production of a carbon nanotube film according to any one of the above. <10> A method for producing a carbon nanotube film, comprising the steps of: preparing crude carbon nanotubes containing aggregates; mixing the crude carbon nanotubes with a solvent to obtain a dispersion; removing the aggregates contained in the dispersion to obtain purified carbon nanotubes; and forming the purified carbon nanotubes into a sheet-like film to produce a carbon nanotube film. [Effects of the Invention]

[0010] According to an embodiment of the present disclosure, it is possible to provide a carbon nanotube film having excellent thickness uniformity, a dispersion containing the carbon nanotube film, and a method for producing the carbon nanotube film. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a CNT film according to an embodiment of the present disclosure. [Figure 2] 1 is a schematic diagram showing a CNT film and a CNT aggregate according to an embodiment of the present disclosure. [Figure 3] 1 is a graph showing the relationship between reflectance and film thickness at wavelengths of 285 nm and 400 nm. [Figure 4] FIG. 1 is a schematic diagram showing the arrangement of measurement positions selected when measuring 3σ of reflectance and average reflectance in the present disclosure. [Figure 5] (a) A schematic diagram showing the arrangement of measurement positions selected when measuring the 3σ of reflectance and the average reflectance in the present disclosure. (b) A schematic diagram showing the arrangement of measurement points at each "measurement position" selected when measuring the 3σ of reflectance and the average reflectance in the present disclosure. [Figure 6] FIG. 1 is a schematic diagram showing a model of an air layer / CNT film layer / silicon substrate. [Figure 7] 1 is a graph plotting the relationship between reflectance and film thickness when the reflectance at a wavelength of 285 nm and film thickness are measured using a conversion method to film thickness according to the present disclosure. [Figure 8] FIG. 2 is a schematic diagram of a method for determining the thickness of a CNT bundle of a CNT aggregate according to an embodiment of the present disclosure. [Figure 9] 1A to 1C are cross-sectional views illustrating a method for manufacturing a CNT film according to an embodiment of the present disclosure. [Figure 10] 1A to 1C are cross-sectional views illustrating a method for manufacturing a CNT film according to an embodiment of the present disclosure. [Figure 11] 1 is an image of the surface of the CNT film according to Example 1, observed using an optical microscope. [Figure 12] 1 is an image of the surface of the CNT film according to Comparative Example 1, observed using an optical microscope. [Figure 13] 1 is an image of the surface of the CNT film according to Example 1, observed using a scanning electron microscope (SEM). [Figure 14] 1 is an image of the surface of the CNT film according to Example 2, observed using a scanning electron microscope (SEM). [Figure 15] 1 is an image of the surface of a CNT film according to Comparative Example 2, observed using a scanning electron microscope (SEM). DETAILED DESCRIPTION OF THE INVENTION

[0012] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified. In the present disclosure, the term "step" includes not only an independent step, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0013] Hereinafter, a carbon nanotube film and a carbon nanotube aggregate according to an embodiment of the present disclosure will be described in detail with reference to the drawings. It should be noted that the present embodiment described below is an example of an embodiment of the present disclosure, and the present disclosure should not be construed as being limited to these embodiments.

[0014] <Carbon nanotube film> The carbon nanotube film of the present disclosure contains carbon nanotubes, has an average thickness of 1 nm or more and 200 nm or less, and the ratio of the area of ​​non-uniform regions, which are regions that are 10% or more thicker or 10% or more thinner than the average thickness, to the area of ​​the entire region of the film is 15.0% or less; When placed on a silicon substrate and the reflectance is measured under the following conditions using a reflection spectroscopic film thickness meter, the 3σ of the reflectance is 15% or less. <Condition> Measurement point diameter: 20 μm Standard measurement wavelength: Wavelength 285nm Number of measurement points: 121 Distance between the centers of adjacent measurement points: 40 μm

[0015] In conventional CNT films, the CNT bundles may not be sufficiently opened, causing the CNT bundles to form a highly aggregated structure, resulting in insufficient thickness uniformity in the CNT film. When observed with an optical microscope, the aggregated structure of the CNT bundles can be observed as regions that are darker in color than other regions (also referred to as aggregates), or as so-called clump-like regions (also simply referred to as clumps).

[0016] CNT membranes are conductive materials with a high specific surface area and excellent chemical stability, and are expected to be used as electrode materials for fuel cells and supercapacitors. There is a demand for the development of technologies to control the pore structure within CNT membranes, as well as for improving their mechanical strength and flexibility to increase their reliability. CNT films are also expected to be used as transparent electrodes to replace ITO. In particular, compared to metal wiring and ITO, they have superior flexibility and mechanical strength, and are therefore expected to be used in applications where severe mechanical loads such as bending, tension, torsion, and repeated fatigue are expected, such as electrodes and wiring for large-screen touch panels and wearable flexible devices. CNT films are also expected to be used in anti-fogging and anti-static films that use heat, filters with low pressure loss, thermophones that convert electrical signals into heat to generate sound, and laser-absorbing materials. Reducing pressure loss due to air or fluids is particularly important in filters and chemical sensors, and films with high mechanical strength are suitable for thinning, making them suitable for reducing pressure loss. Furthermore, thermophones and laser-absorbing materials need to be self-supporting, so high mechanical strength is required.

[0017] The carbon nanotube film of the present disclosure has the above-described configuration, which can suppress the aggregation structure of CNT bundles, and therefore has excellent thickness uniformity.

[0018] The carbon nanotube film of the present disclosure may be a film disposed on a substrate or a frame, or may be a free-standing film (i.e., a free-standing film) that is not disposed on a substrate or a frame.

[0019] (Structure of CNT film) The CNT film 100 will be described below. Fig. 1 is a cross-sectional view of the CNT film 100. Fig. 2 is a schematic diagram of the CNT film 100 and a CNT aggregate 101 formed by an aggregation of CNTs 102. Fig. 2 also shows an enlarged view of a region A1 in the CNT film.

[0020] In FIG. 1, a CNT film 100 is composed of a CNT aggregate 101. As shown in FIG. 2, a CNT aggregate 101 includes many CNTs (or CNT bundles) 102 .

[0021] <Heterogeneous region> In the carbon nanotube film of the present disclosure, the area ratio of non-uniform regions, which are regions that are 10% or more thicker or thinner than the average thickness, is 15.0% or less of the total area of ​​the film. When the area ratio of the non-uniform region is within the above range, a carbon nanotube film with excellent thickness uniformity can be obtained.

[0022] As described above, in conventional CNT films, the CNT bundles may form aggregates or lumps due to reasons such as the CNT bundles not being sufficiently opened. The thickness of the agglomerates and lumps is greater than the thickness of regions other than the agglomerates and lumps in the CNT film. That is, the presence of regions with uneven thickness, such as the agglomerates and lumps, in the CNT film causes unevenness in the entire CNT film, impairing the uniformity of the thickness. In the present disclosure, a non-uniform region refers to a region whose thickness is 10% or more thicker or 10% or more thinner than the average thickness of the entire region.

[0023] The carbon nanotube film of the present disclosure has excellent thickness uniformity when the ratio of the area of ​​the non-uniform regions to the area of ​​the entire region is 15.0% or less.

[0024] From the same viewpoint as above, it is preferable that the area ratio of the non-uniform region is 10.0% or less of the total area of ​​the film, more preferably 5.0% or less, even more preferably 1.0% or less, and particularly preferably 0.3% or less.

[0025] The area ratio of the non-uniform region is measured by the following method. The entire membrane is 200 μm 2 The film thickness is measured in each divided region under the following conditions by the method described below. <Measurement conditions for each area> Measurement point diameter: 20 μm Reference measurement wavelength: 285 nm Measurement points: 100 points

[0026] Using the film thickness obtained above, the average film thickness (Xa) in each region and the average film thickness (Xb) for the entire film are calculated. and, For non-uniform regions where the average film thickness (Xb) of the entire film is 10% or more thicker or 10% or more thinner than the average film thickness (Xa) within the region, the area ratio of the non-uniform region is calculated using the following formula. Area ratio of non-uniform regions = (number of non-uniform regions) / (number of regions in the entire film) × 100 (%)

[0027] <Reflectance> When the CNT film of the present disclosure is disposed on a silicon substrate and the reflectance is measured using a reflection spectroscopic film thickness meter under the following conditions, the 3σ of the reflectance is 15% or less. <Condition> Measurement point diameter: 20 μm Standard measurement wavelength: Wavelength 285nm Number of measurement points: 121 Distance between the centers of adjacent measurement points: 40 μm Here, σ represents the standard deviation.

[0028] By using the above reflectance measurement method, the transmittance uniformity can be evaluated. The measurement wavelength is preferably 285 nm, since this allows for the detection of slight differences in film thickness. For example, when visible light with a wavelength of 400 nm to 800 nm is used, the change in reflectance relative to the film thickness is smaller than in the ultraviolet light region, so it is preferable to use ultraviolet light rather than visible light.

[0029] As shown in Figure 3, in the film thickness range of 1 nm to 20 nm, the reflectance at a wavelength of 400 nm changes by only 4%, from 46% to 42%. However, when using the reflectance of ultraviolet light at a wavelength of 285 nm, a change in thickness from 1 nm to 20 nm can result in a change in reflectance of as much as 32%, from 72% to 40%. If the measurement accuracy of reflectance is 0.5%, the measurement accuracy of film thickness is 0.3 nm, making it possible to detect slight differences in film thickness of 1 nm or less.

[0030] By using a silicon substrate as the substrate on which the CNT film is disposed and ultraviolet light, variations in film thickness of 1 nm to 50 nm can be measured with high sensitivity and precision. Even when using a substrate made of a material other than silicon, it is possible to measure the reflectance of a freestanding film. However, in order to capture slight changes in film thickness and measure reflectance with high precision and reproducibility, it is preferable that (1) the substrate has high reflectance (refractive index and extinction coefficient) in the ultraviolet wavelength range, and (2) the substrate surface has high surface smoothness (for example, a surface roughness Ra of 0.3 nm or less) that allows accurate capture of specularly reflected light from the substrate surface. From these viewpoints, a metal substrate or a silicon substrate is preferred. It is more preferable to use a silicon substrate because it is widely used and there is little variation in the quality of the substrate.

[0031] There are no particular restrictions on the spot size in reflectance measurement, but it is preferably in the range of 10 μm to 1000 μm. The 3σ value, which is an index of film thickness uniformity, is inversely proportional to the measurement area, so by knowing the spot size, it can be converted into a 3σ value in the range of 50 μm to 100 μm. However, since it is preferable that the variation (3σ) due to the measurement accuracy of the measuring device is sufficiently small compared to the true value, the spot size is preferably 10 μm to 1000 μm, and more preferably 20 μm to 500 μm.

[0032] In measuring the reflectance, the method for detecting reflected light is not particularly limited, and a photodiode, a photomultiplier tube, or the like can be used. Alternatively, a multi-channel detector such as a photodiode array or a CCD (Charge Coupled Device) may be used. The reflected light is then detected by a photodiode array, allowing the reflectance at multiple wavelengths to be obtained.The pixel size of the CCD detector may be adjusted to approximately 50 μm to 100 μm to measure the distribution of the reflected light intensity. In evaluating the thickness uniformity, it is preferable that the number of reflectance measurement points is 100 or more.

[0033] When the CNT film has a 3σ reflectance of 15% or less, the film has excellent local uniformity within the region including the above number of measurement points. From the same viewpoint as above, 3σ of the reflectance is preferably 12.0% or less, more preferably 10.0% or less, and even more preferably 8.0% or less.

[0034] [3σ of reflectance and average reflectance] The method for measuring "the 3σ and average reflectance of the reflectance measured by the reflection spectroscopic film thickness meter at the above measurement points, the above reference measurement wavelength, and the above number of measurement points" will be described below. First, a CNT film is placed on a silicon substrate, and the diagonal line of the placed CNT film is taken as the X-axis. When placing a CNT film on a silicon substrate, the silicon substrate and the CNT film are tightly attached without any gaps. By sandwiching a solvent such as water or an organic solvent between the silicon substrate and the CNT film and then drying the solvent, the silicon substrate and the CNT film can be tightly attached without any gaps. For example, a CNT film floating on the water surface can be scooped up with a silicon substrate and then dried; by placing the CNT film on a silicon substrate containing a solvent and drying it, the silicon substrate and the CNT film can be adhered to each other. There is no limitation on the size of the silicon substrate, but from the viewpoint of adhering a CNT film over a wide area, it is preferable to use a silicon wafer of 8 inches or larger. Next, an arbitrary "measurement position" on the CNT film is selected. At the selected "measurement position," 11 measurement points in the X-axis direction are set at intervals where the distance between the centers of adjacent measurement points is 40 μm, and 11 measurement points in the Y-axis direction are set at intervals where the distance between the centers of adjacent measurement points is 40 μm. In other words, 11 vertical points x 11 horizontal points are set, for a total of 121 measurement points. Then, the reference measurement wavelength is set to 285 nm, and the reflectance at each measurement point is measured to calculate the 3σ of the reflectance and the average reflectance. The measurement range of the measurement points is within a diameter of 20 μm. As a specific example of setting measurement points, FIG. 4 shows a schematic diagram showing the arrangement of measurement points at the selected "measurement positions." A microspectrophotometer (e.g., OPTM, model A-1, manufactured by Otsuka Electronics Co., Ltd.) is used as the reflectance measurement device, a 10x reflective lens is used as the lens, and a 200 μm diameter aperture (measurement point diameter: 20 μm) is used as the device for adjusting the diameter of the measurement point. An aluminum substrate is used as a reference for reflection intensity measurement. The reflectance Rs(λ) is calculated by the following formula:

[0035]

number

[0036] where I s (λ) represents the reflection intensity of the CNT film on the silicon substrate at wavelength λ, and I ref (λ) represents the reflection intensity of the reference, and R ref (λ) represents the absolute reflectance of the reference. When aluminum is used as a reference, the optical constants of aluminum are known, so R ref (λ) can be calculated. Note that the gain, exposure time, etc. are the same conditions for the reference and the reflection intensity measurement of the CNT film on the silicon substrate. This allows the absolute reflectance of the CNT film on the silicon substrate to be obtained. The reflectance at a wavelength of 285 nm is calculated using the reflection intensity at a wavelength of 285 nm and the absolute reflectance of the reference according to the following formula.

[0037]

number

[0038] The CNT film of the present disclosure is disposed on a silicon substrate, and when the reflectance is measured and the average reflectance is calculated at each of a plurality of measurement positions that are 2 cm or more apart using a reflection spectroscopic film thickness meter under the following conditions, It is preferable that the value obtained by subtracting the minimum value of the average reflectance from the maximum value of the average reflectance is 15% or less. <Condition> Measurement point diameter: 20 μm Standard measurement wavelength: Wavelength 285nm Number of measurement points: 121 Distance between the centers of adjacent measurement points: 40 μm

[0039] By keeping the difference between the maximum and minimum average reflectances at 15% or less, the difference in average reflectance between the respective average reflectances at multiple measurement points that are 2 cm or more apart can be reduced. As a result, the CNT film of the present disclosure has excellent film uniformity over a wide area. From the same viewpoint as above, the difference between the maximum and minimum values ​​of the average reflectance is more preferably 12% or less, and even more preferably 8% or less.

[0040] [Difference between maximum and minimum average reflectance values] This section explains how to measure the difference between the maximum and minimum average reflectance values ​​when the average reflectance is measured at each of multiple measurement points that are 2 cm or more apart using a reflection spectroscopic film thickness meter. First, the CNT film is placed tightly on a silicon substrate. The diagonal line of the arranged CNT film is taken as the X-axis, and multiple "measurement positions" are selected on the X-axis, spaced at least 2 cm apart from each other. The measurement range at each measurement position is 0.40 mm x 0.40 mm. As a specific example of the selection of "measurement positions," Fig. 5(a) shows a schematic diagram illustrating the arrangement of the selected measurement positions, and Fig. 5(b) shows a schematic diagram illustrating the arrangement of measurement points at each selected "measurement position." At each of the selected "measurement positions," the reflectance at each measurement point is measured and the average reflectance is calculated using the method described above in the section [3σ of reflectance and average reflectance]. From the obtained average reflectance at each "measurement position," the difference between the maximum and minimum values ​​of the average reflectance is calculated.

[0041] ~Conversion method to film thickness (optical thickness)~ For each measurement point, a reflectance spectrum is obtained in the wavelength range of 200 nm to 600 nm at wavelength intervals of 1 nm to 2 nm. Then, using the optical constants (refractive index: n, extinction coefficient: k) shown in Table 1 as the optical constants of the CNT film, and using a model of air layer / CNT film layer / silicon substrate, the reflectance spectrum in the wavelength range of 225 to 500 nm is analyzed by the least squares method to calculate the film thickness at each measurement point. The film thickness at a "measurement position" is the average value of the film thicknesses at each of the 121 measurement points included in the "measurement position." The following describes a method for calculating the film thickness at each measurement point by analyzing the reflectance spectrum in the wavelength range of 225 to 500 nm using the least squares method.

[0042] The film thickness is calculated using a three-layer model of air layer / CNT film layer / silicon substrate, using the following relational expressions (a) to (c). FIG. 6 is a schematic diagram showing a model of an air layer / CNT film layer / silicon substrate.

[0043] The reflectance Rs is the amplitude reflectance r s This is expressed by the following equation (a) using

[0044]

number

[0045] In the above formula, * represents a complex conjugate.

[0046] Amplitude reflectance r from the three layers of air layer / CNT film layer / silicon substrate sis expressed by the following equation (b).

[0047]

number

[0048] In the above formula, r 01 represents the amplitude reflectance from the interface between the air layer and the CNT film layer, and r 12 represents the amplitude reflectance from the interface between the CNT film layer and the silicon substrate layer, and i represents the imaginary unit. In the above formula, δ is the phase difference that occurs when light of wavelength λ makes one round trip within the film, and is expressed by the following formula (c).

[0049]

number

[0050] In the above formula, d represents the film thickness, N represents the complex refractive index (N=n−ik), φ represents the angle of incidence, and i represents the imaginary unit.

[0051] The film thickness can be obtained by calculation using the relationship of the above formulas (a) to (c) by the least squares method, with the film thickness d as a variable for the reflectance Rs in the wavelength range of 225 to 500 nm.

[0052] FIG. 7 is a graph plotting the relationship between reflectance and film thickness when the reflectance at a wavelength of 285 nm and film thickness were measured using the method described above for a sample in which a non-uniform CNT film was transferred onto a silicon substrate. As shown in FIG. 7, the above-described method allows the difference in film thickness to be accurately determined from the reflectance value.

[0053] [Table 1]

[0054] The CNT film of the present disclosure has an average thickness of 1 nm or more and 200 nm or less. The CNT film of the present disclosure can improve mechanical strength by having the area ratio of the non-uniform regions be 15.0% or less of the total area of ​​the film and the 3σ of the reflectance be 15% or less. As a result, the CNT film of the present disclosure can maintain excellent self-supporting properties even when the average thickness is 200 nm or less. The CNT film of the present disclosure can maintain even better self-supporting properties even when the average thickness is 200 nm or less, when the value obtained by subtracting the minimum average reflectance from the maximum average reflectance is 15% or less. From the same viewpoint as above, the CNT film of the present disclosure preferably has an average thickness of 5 nm or more and 200 nm or less, and more preferably 10 nm or more and 200 nm or less.

[0055] The CNT film of the present disclosure has a thickness of 100 μm 2 More than 225cm 2 The CNT film may be disposed on a silicon substrate or frame having the following space so as to cover the space. The CNT film of the present disclosure can maintain excellent self-supporting properties even when arranged as described above.

[0056] The average thickness of the CNT film is measured by the following method. Using the method described above in [Difference between the maximum and minimum average reflectance values], reflectance is measured at each of multiple measurement positions that are 2 cm or more apart using a reflection spectroscopic film thickness meter under the following reflectance measurement conditions: <Condition> Measurement point diameter: 20 μm Measurement wavelength: wavelength 200nm~600nm (wavelength interval: 1.3~1.5nm) Number of measurement points: 121 Distance between the centers of adjacent measurement points: 40 μm

[0057] Then, the film thickness at each measurement point is calculated using the method described above in "Method for converting to film thickness (optical thickness)." The film thickness at each measurement point is also calculated by calculating the average film thickness at each measurement point (121 points) included in each measurement position. The film thickness calculated at each measurement position is then averaged to obtain the average thickness of the CNT film. Similarly, the film thickness σ at each measurement position is calculated from the standard deviation of the film thickness at each measurement point.

[0058] The CNT film 100 can have a mesh structure. That is, in the CNT film 100, a plurality of CNTs 102 can be entangled in a mesh-like manner to form a mesh structure. The CNT film 100 can also have pores. That is, the CNTs 102 can be entangled to form pores.

[0059] From the viewpoint of suppressing the concentration of microscopic stress and improving the mechanical strength of the CNT film, it is preferable that the pore distribution is uniform. That is, the CNT film has a structure with uniform pores, which can increase the mechanical strength of the film. The CNT film has a structure with uniform pores, i.e., a narrow pore distribution in the CNT film, which can increase the tensile strength, for example.

[0060] CNT membranes are composed of entangled CNT bundles, and have a membrane structure similar to that of polymers, paper, nonwoven fabrics, porous materials, etc. If large pores exist in a CNT membrane, the membrane is more likely to break from these large pores. Small pore volumes result in reduced variability in tensile strength measured in tensile tests, for example.

[0061] The CNT aggregate 101 may include single-walled CNTs 102 or double-walled CNTs 102 .

[0062] Furthermore, it is preferable that the CNT aggregate 101 has a relative standard deviation of 30% or less when the distribution of the thickness of the CNT bundles (also referred to as bundle diameter in the present disclosure) is taken. The thickness of the CNT bundle is measured by the following method.

[0063] Figure 8 is a schematic diagram of a method for determining the thickness of a CNT bundle. The method for determining the thickness of a CNT bundle is as follows. (1) Draw a contour line L1. (2) Obtain the bundle thickness by measuring the distance D1 perpendicular to two contour lines belonging to the same CNT bundle. (3) Do not count the area around the nodes where the bundle branches and joins in the bundle thickness. (4) The condition is that the tangents of the two contour lines at the point where the bundle thickness is to be calculated must intersect at an angle of 15° or less or be parallel. (5) Draw a straight line from one edge of the image to the opposite edge, and calculate and count the thickness of the above bundle for each contour line of the CNT bundle that the line crosses. This is to avoid duplicate counts. In this evaluation, the contour lines may also be judged visually.

[0064] <cnt> The CNT film of the present disclosure contains CNTs. The tube diameter of the CNT is preferably 0.8 nm or more and 6.0 nm or less, and more preferably 0.8 nm or more and 3.5 nm or less.

[0065] The CNT preferably has a length of 10 nm or more, more preferably 100 nm or more. When the length of the CNTs is 10 nm or more, the CNTs are well entangled with each other, and a CNT film with excellent mechanical strength can be obtained. There is no particular upper limit to the length of the CNT, but the upper limit may be, for example, 10 cm.

[0066] The tube diameter and length of the CNT are the arithmetic mean values ​​measured for 20 or more carbon materials (primary particles) by electron microscope observation. As the electron microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like can be used.

[0067] The carbon content in the CNT is preferably 98 mass % or more relative to the total mass of the CNT.

[0068] Examples of such CNTs include CNTs synthesized by methods described in known documents such as International Publication No. WO 2006 / 011655.

[0069] The CNT film of the present disclosure preferably has a G / D ratio measured by resonance Raman scattering measurement of 1 or more, more preferably 10 or more, and even more preferably 20 or more. When the G / D ratio is 20 or more, a CNT film containing well-graphitized CNTs can be obtained. Resonance Raman scattering measurement is performed using a laser wavelength of 532 nm, for example, with XploRA manufactured by HORIBA Scientific.

[0070] From the viewpoint of mechanical strength, the CNT film of the present disclosure preferably has a tensile strength measured by a bulge test of 100 MPa or more, more preferably 60 MPa or more, and even more preferably 70 MPa or more. The tensile strength may be, for example, 300 MPa or less.

[0071] From the viewpoint of mechanical strength, the CNT film of the present disclosure preferably has a breaking load measured by a nanoindentation test of 1.0 μN / nm or more, more preferably 2.0 μN / nm or more, and even more preferably 3.0 μN / nm or more. There is no particular upper limit to the breaking load, and it may be, for example, 10.0 μN / nm or less.

[0072] [Nanoindentation test] First, a CNT film is placed on a silicon wafer with a circular hole 30 μm deep or more and 80 μm in diameter, covering the circular hole, to create an evaluation sample with a free-standing CNT film structure. Next, a conical indenter (R = 10 μm) is pressed into the center of the portion of the CNT film covering the circular hole at a speed of 1 μm / s, thereby applying a load to the CNT film. Then, when plastic deformation or fracture occurs in the CNT film, the load at the yield point when plastic deformation or fracture occurs is measured. The obtained load is divided by the film thickness to calculate the breaking load, thereby measuring the film strength. Nanoindentation testing is performed, for example, using an ENT-2100 manufactured by Elionix Co., Ltd.

[0073] The CNT film 100 preferably has an arithmetic mean roughness of the film surface of 100 nm or less, more preferably 20 nm or less, and even more preferably 5 nm or less. The arithmetic mean roughness of the CNT film 100 is measured using a laser microscope.

[0074] Furthermore, in the CNT aggregate 101, it is preferable that the CNT bundles are uniformly dispersed with a fixed distance between them. The fact that the CNT aggregates 101 are dispersed can be confirmed, for example, by performing a fast Fourier transform (FFT) on the SEM image. The closer to the center of the FFT image, the lower the periodic structure in the original image, and the further away from the center, the higher the periodic structure in the original image. Analysis can also be performed by fitting using the pixel distance and brightness of the FFT image. In this case, the following formula (Ornstein-Zernike formula) can be used.

[0075]

number

[0076] In the above formula, I is the intensity, v is the pixel distance, and A, B, and C are fitting constants.

[0077] <Method for manufacturing carbon nanotube film> The method for producing a carbon nanotube film in the present disclosure includes a step of preparing crude carbon nanotubes containing aggregates (preparation step), a step of mixing the crude carbon nanotubes with a solvent to obtain a dispersion (also referred to as a crude carbon nanotube dispersion production step or a crude CNT dispersion production step), a step of removing the aggregates contained in the dispersion to obtain purified carbon nanotubes (also referred to as a purified carbon nanotube production step or a purified CNT production step), and a step of forming the purified carbon nanotubes into a sheet-like film to produce a carbon nanotube film (also referred to as a carbon nanotube film production step or a CNT film production step). A method for manufacturing the CNT film 100 will be described below with reference to FIGS.

[0078] [Preparing the board] First, as shown in FIG. 9, a substrate 110 is prepared. For example, a silicon (Si) wafer is used as the substrate 110. As shown in FIG. 9, an underlayer 120 may be formed on the substrate 110. The underlayer 120 is formed by a sputtering method, a CVD method, a thermal oxidation method, or the like. For example, a silicon nitride (SiN) film formed by a CVD method is used as the underlayer 120. The substrate 110 and the underlayer 120 may be collectively referred to as the substrate 110. A different film may be further provided on the underlayer 120.

[0079] <Preparation process> The preparation step is a step of preparing crude CNTs containing aggregates. The crude CNTs can be used without any particular limitation as long as they are CNTs containing aggregates. For example, commercially available products such as eDIPS manufactured by Meijo Nano Carbon Co., Ltd., ZEONANO manufactured by Zeon Nano Technology Co., Ltd., and TUBALL manufactured by OCSiAl may be obtained, or crude CNT may be synthesized. Examples of methods for synthesizing crude CNTs include the enhanced direct injection pyrolytic synthesis (hereinafter also referred to as the eDIPS method), the super growth method, and the laser ablation method. Among the above, the eDIPS method is preferred as a method for synthesizing crude CNTs.

[0080] The crude CNTs synthesized by the eDIPS method have better diameter distribution, CNT crystallinity, and linearity. As a result, the CNT bundles and their network structures are composed of highly crystalline CNTs, i.e., CNTs with low defect density. The bundle size and network distribution can also be made uniform. As a result, the surface uniformity of the CNT film can be improved, and a strong CNT film can be obtained. Furthermore, the coarse CNTs synthesized by the dry method can suppress the aggregation of CNT bundles, which allows the thickness of the CNT bundles to be reduced, making it possible to further reduce the thickness of the CNT film.

[0081] [eDIPS method] The eDIPS method is a CNT synthesis method that is an improvement over the Direct Injection Pyrolytic Synthesis (hereinafter also referred to as the DIPS method). The DIPS method is a gas-phase flow method in which single-walled carbon nanotubes are synthesized in a flowing gas phase by spraying a hydrocarbon solution containing a catalyst (or catalyst precursor) and a reaction accelerator into a high-temperature heating furnace. The eDIPS method focuses on the particle formation process in which the particle size of ferrocene used as a catalyst varies upstream and downstream in the reactor. Unlike the DIPS method, which uses only an organic solvent as the carbon source, the eDIPS method controls the growth point of single-walled carbon nanotubes by mixing a second carbon source that is relatively easily decomposed, i.e., easily becomes a carbon source, into the carrier gas. For details, the production can be carried out with reference to Saito et al., J. Nanosci. Nanotechnol., 8 (2008) 6153-6157.

[0082] An example of a commercially available carbon nanotube synthesized by the eDIPS method is "MEIJO eDIPS" manufactured by Meijo Nanocarbon Co., Ltd.

[0083] <Crude CNT dispersion manufacturing process> The crude CNT dispersion production step is a step of mixing crude carbon nanotubes with a solvent to obtain a dispersion.

[0084] (dispersion) The dispersion is used to produce the carbon nanotube film of the present disclosure. The dispersion contains crude CNTs obtained in the preparation step. In the dispersion, the crude CNTs exist in a crushed state, forming CNT aggregates. The dispersion may be in the form of a high viscosity paste, if desired.

[0085] The dispersion may further contain a dispersant in addition to crude CNTs. Dispersants are used to disentangle thick bundles of crude CNTs. If the dispersant needs to be removed after film formation, it is preferable to use a dispersant with a low molecular weight.

[0086] Examples of dispersants include flavin derivatives, sodium cholate, sodium deoxycholate, sodium dodecylbenzenesulfonate, and polyacrylic acid. The flavin derivatives include, for example, organic side chain flavins represented by the following formula: Flavins with organic side chains are dispersants that can separate semiconducting CNTs from metallic CNTs and have the effect of unbundling CNTs. From the viewpoint of dispersing CNTs in large quantities as fine aggregate particles in a solvent, flavins with organic side chains are suitable.

[0087] [ka]

[0088] As a dispersant, polyfluorene (poly(9,9-dioctylfluorenyl-2,7-diyl)) may be used as a molecule capable of separating semiconducting CNTs and metallic CNTs. As the dispersant, a known surfactant such as sodium dodecyl sulfate may be used.

[0089] (solvent) The dispersion liquid further contains a solvent in addition to the CNTs. The solvent is not particularly limited. For example, when an organic side chain flavin is used as the dispersant, toluene, xylene, ethylbenzene, or the like can be used as the solvent. When a surfactant is used as the dispersant, water (including heavy water) can be used as the solvent.

[0090] When no dispersant is used, an organic solvent such as n-methylpyrrolidone, N,N-dimethylformamide, propylene glycol, or methyl isobutyl ketone can be used as the solvent.

[0091] Examples of methods for mixing crude carbon nanotubes with a solvent to obtain a dispersion include methods using cavitation (ultrasonic dispersion), methods that mechanically apply shear force (ball mill, roller mill, vibration mill, kneader, homogenizer, etc.), and methods that use turbulence (jet mill, Nanomizer, etc.).

[0092] The above method disperses crude CNTs in a solvent by finely disintegrating them, making it possible to obtain a highly concentrated CNT dispersion even after the purified CNT production process. On the other hand, if the crude CNTs are disintegrated too finely, damage may accumulate in the CNTs, potentially resulting in a decrease in the strength of the CNT film. Therefore, it is preferable to appropriately adjust the treatment time, strength, temperature, etc. so that the strength is not reduced.

[0093] <Purified CNT manufacturing process> The purified CNT production process is a process in which aggregates contained in the dispersion are removed to obtain purified carbon nanotubes. By carrying out the purified CNT production process, it is possible to obtain purified CNTs from which highly agglomerated fibrous nanotubes have been removed. By producing a CNT film using purified CNTs, it is possible to obtain a CNT film with excellent thickness uniformity. Furthermore, by carrying out the purified CNT production process, the thickness of the CNT bundles in the resulting CNT film can be made uniform.

[0094] As a method for removing the aggregates contained in the dispersion, for example, a method for precipitating the aggregates contained in the dispersion can be mentioned. Specific examples include settling, filtration, membrane separation, centrifugation, and ultracentrifugation. Among the above methods, ultracentrifugation is preferred as a method for removing aggregates contained in the dispersion liquid, from the viewpoint of excellent removal of aggregates.

[0095] In ultracentrifugation, it is preferable that the average relative centrifugal force is 3,000 xg or more. When the average relative centrifugal force is 3,000 xg or more, it becomes possible to remove finer aggregates and enhance the uniformity of the pellicle film. From the same viewpoint as above, it is more preferable that the average relative centrifugal force is 5,000 xg or more. Here, the average relative centrifugal force refers to the average centrifugal force generated when extended at a certain rotational speed, and refers to the relative centrifugal force at the midpoint between the maximum radius and the minimum radius.

[0096] In ultracentrifugation, it is preferable that the average relative centrifugal force is 200,000 xg or less. When the average relative centrifugal force is 200,000 xg or less, it is possible to suppress the generation of aggregates and the sedimentation of the CNTs themselves dispersed in the dispersion due to an excessively high relative centrifugal force. From the same viewpoint as above, it is more preferable that the average relative centrifugal force is 150,000 xg or less.

[0097] Also, the centrifugation time is preferably such that the holding time after reaching the target relative centrifugal force is 5 minutes or more and 180 minutes or less.

[0098] <CNT Film Manufacturing Process> The CNT film manufacturing process is a process of forming a purified carbon nanotube into a sheet to produce a carbon nanotube film.

[0099] 〔Film Formation〕 The purified carbon nanotube is formed into a sheet. Thereby, a CNT film can be formed. As shown in FIG. 10, a CNT film 100 is formed on the base layer 120. Specifically, the CNT film 100 is formed by coating a dispersion containing a CNT aggregate on the base layer 120 and removing the solvent by drying or the like. In addition, the dispersant may be removed by washing with a solvent or the like that dissolves the dispersant in the dispersion as necessary.

[0100] The coating method may be selected depending on the viscosity or the concentration of the CNT aggregate. For example, coating methods such as blade coating, slit coating, spin coating, and dip coating may be used. Since the CNT film is formed by coating, the area, thickness, etc. of the resulting CNT film are not limited by the CNT synthesis method but are controlled by the coating method. Therefore, by appropriately selecting and using the above coating methods, CNT films of various thicknesses can be formed over a large area. Among the above methods, spin coating is preferred as the coating method.

[0101] After the CNT film is formed, the drying method for removing the solvent is not particularly limited, and drying may not be necessary depending on the application. For example, when toluene is used as the solvent, the solvent may be dried by leaving it to stand at room temperature. When water or a solvent with a high boiling point is used as the solvent, the solvent may be dried by heating as appropriate. Furthermore, when a solvent with low surface tension is used as the solvent, the shape of the CNT aggregate can be controlled by controlling the temperature, vapor pressure, etc. Examples of solvents with low surface tension include supercritical fluids such as supercritical carbon dioxide.

[0102] The method for removing the dispersant is not particularly limited, and depending on the application, it may not be necessary to remove it. For example, an organic side chain flavin may be included in the CNT film 100. A dispersant is used to prevent aggregation of CNTs, and therefore generally has the property of being adsorbed to the CNT surface. Therefore, by washing with a solvent different from the solvent used during dispersion, the dispersant can be removed in a smaller amount and in a shorter time than when the same solvent is used. For example, when an organic side chain flavin is used as the dispersant, washing may be carried out using chloroform as the washing agent. Examples of the cleaning agent include water, an aqueous solution of an acid or alkali, chloroform, methylene chloride, N,N-dimethylformamide, tetrahydrofuran, acetone, etc. When sodium cholate, sodium deoxycholate, sodium dodecylbenzenesulfonate, etc. are used as dispersants, washing with water or ethanol is preferred.

[0103] In addition to the method using a cleaning agent, other methods for removing the dispersant include a method of cleaning with a supercritical fluid such as supercritical carbon dioxide, a method of heating in oxygen to burn, dissolve, evaporate or sublimate the dispersant, and a method of removing the dispersant by electrochemical oxidation or reduction to change it into a chemical structure that is easier to remove.

[0104] [CNT film peeling] Finally, the CNT film 100 is peeled off from the substrate 110 on which it is formed. The substrate 110 on which the CNT film 100 has been formed is immersed in a solvent and shaken, thereby peeling off the CNT film 100 from the substrate 110. As the solvent, a cleaning agent such as an acid or alkali aqueous solution or an organic solvent may be used. In this way, the CNT film 100 is manufactured. [Example]

[0105] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples. In this example, the measurement of the area ratio of the non-uniform region, the measurement of 3σ of the reflectance and the average reflectance, the conversion into the film thickness (optical thickness), and the measurement of the breaking load were carried out by the methods described above.

[0106] Example 1 [Preparation process] As crude CNTs containing aggregates, single-walled CNTs (crude CNTs, manufactured by Meijo Nano Carbon Co., Ltd., product name: EC1.5-P, tube diameter: 1 nm to 3 nm, tube length: 100 nm or more, carbon content: 99% by mass) synthesized by the improved direct injection pyrolysis synthesis method (eDIPS method) were prepared.

[0107] [Crude CNT dispersion manufacturing process] To 30 mg of single-walled CNTs (crude CNTs, manufactured by Meijo Nanocarbon Co., Ltd., product name: EC1.5-P, tube diameter: 1 nm to 3 nm, tube length: 100 nm or more) synthesized by the improved direct injection pyrolysis synthesis method (eDIPS method), 70 mL of isopropyl alcohol and 30 mL of ethanol were added, and 30 mg of polyacrylic acid was further added as an additive. The mixture was stirred using a magnetic stirrer at 1000 rpm (revolutions per minute) at 40°C for 18 hours to obtain a suspension.

[0108] ~High-speed stirring and dispersion~ The resulting suspension was subjected to high-speed stirring and dispersion at 10,000 rpm at 25° C. for 1 hour using a homogenizer (manufactured by SMT, model: HF93), to obtain a dispersion containing crude CNTs (crude CNT dispersion).

[0109] [Purified CNT manufacturing process] The obtained crude CNT dispersion was centrifuged using a high-speed centrifuge at an average relative centrifugal force of 50,000 xg for 60 minutes at 10°C. After the centrifugation treatment, the supernatant was extracted to obtain a dispersion containing purified CNTs (purified CNT dispersion) from which aggregates or clumps of CNTs had been removed.

[0110] [CNT film manufacturing process] The purified CNT dispersion was spin-coated onto an 8-inch silicon substrate at a rotation speed of 1500 rpm to obtain a thin film of CNT on the silicon substrate. The thin film was washed with water to remove the polyacrylic acid and then dried, after which the silicon substrate was immersed in water.Then, the CNT thin film was left in the water and the silicon substrate was removed from the water, peeling the CNT thin film from the silicon substrate and floating on the water surface to produce a CNT film with a network structure.

[0111] [Placement] The CNT film floating on the water surface was scooped up onto an 8-inch silicon substrate, and the CNT film was placed on the silicon substrate.

[0112] In the CNT film obtained in Example 1, the proportion of the area of ​​the non-uniform regions relative to the total area of ​​the film was 0.3% or less.

[0113] Example 2 A CNT film (pellicle film) was arranged on a silicon substrate in the same manner as in Example 1, except that in the [crude CNT dispersion production process], high-speed stirring and dispersion was not performed, and the resulting suspension was subjected to the following ultrasonic dispersion and then degassed to obtain a dispersion containing crude CNTs (crude CNT dispersion). [Ultrasonic dispersion] The suspension obtained in the crude CNT dispersion production step was subjected to ultrasonic dispersion using a probe-type ultrasonic homogenizer at 40% output for a total of 2 hours, with ice cooling for 5 minutes every 20 minutes.

[0114] In the CNT film obtained in Example 2, the proportion of the area of ​​the non-uniform regions relative to the total area of ​​the film was 0.3% or less.

[0115] (Comparative Example 1) A CNT film having a network structure was arranged on a silicon substrate in the same manner as in Example 1, except that the purified CNT production process was not performed and the crude CNT dispersion obtained in the crude CNT dispersion production process was used to perform the CNT film production process and arrangement.

[0116] In the CNT film obtained in Comparative Example 1, the proportion of the area of ​​the non-uniform regions to the total area of ​​the film was 27%.

[0117] (Comparative Example 2) A CNT film (pellicle film) having a mesh structure was arranged on a silicon substrate in the same manner as in Example 2, except that the [purified CNT production process] was not performed and the crude CNT dispersion obtained in the [crude CNT dispersion production process] was used to perform the [CNT film production process] and [arrangement].

[0118] In the CNT film obtained in Comparative Example 2, the proportion of the area of ​​the non-uniform regions to the total area of ​​the film was 43%.

[0119] (Comparative Example 3) [CNT film production process] and [arrangement] are carried out using the crude CNT dispersion obtained in the [crude CNT dispersion production process] without carrying out the [purified CNT production process], A CNT film having a network structure was disposed on a silicon substrate in the same manner as in Example 2, except that in the crude CNT dispersion production process, 70 mL of isopropyl alcohol and 30 mL of ethanol were changed to 100 mL of toluene, and 50 mg of an organic side-chain flavin was further added as a dispersant.

[0120] In the CNT film obtained in Comparative Example 3, the ratio of the area of ​​the non-uniform regions to the total area of ​​the film was 35%.

[0121] -evaluation- ~Average reflectance and 3σ of reflectance~ In the reflectance measurement, the measurement positions were selected to be X=5 mm, 25 mm, 50 mm, 75 mm, and 95 mm. The average reflectance and 3σ of the reflectance at each selected measurement point were measured, and the results are shown in Table 2.

[0122] ~Average film thickness and 3σ of film thickness~ Using the method described above, the average film thickness and 3σ of the film thickness were measured at each measurement position of X = 5 mm, 25 mm, 50 mm, 75 mm, and 95 mm. The average film thickness values ​​at each measurement position were averaged to obtain the average thickness. The results are shown in Table 2.

[0123] [Table 2]

[0124] ~G / D ratio~ The G / D ratio of the obtained CNT film was measured by resonance Raman scattering measurement, and the results are shown in Table 3.

[0125] ~Breaking Load~ The breaking load of the obtained CNT film was measured by nanoindentation testing, and the results are shown in Table 3.

[0126] [Table 3]

[0127] The CNT film of Example 1, which was produced using the CNT film production method including a preparation step, a crude CNT dispersion production step, a purified CNT production step, and a CNT film production step, had a small area ratio of non-uniform regions and excellent thickness uniformity.

[0128] The CNT film of Example 2, in which the suspension obtained in the crude CNT dispersion liquid production step was subjected to the ultrasonic dispersion described below, had an even smaller area ratio of non-uniform regions and was more uniform in thickness. Furthermore, in the CNT film of Example 2, the 3σ of the reflectance was 15% or less at all measurement positions, and the difference between the maximum and minimum values ​​of the average reflectance was 15% or less. When the CNT film of Example 2 was placed on a silicon substrate and observed with an optical microscope, a slight distribution of light and dark shades was observed, but no lumps or aggregates were observed, and no non-uniform areas were visible. The CNT film of Example 2 had a small average film thickness and little variation in the 3σ of the film thickness. This indicates that the CNT film of Example 2 has little variation in film thickness both in localized regions and in broad regions. In other words, the CNT film of Example 1 was shown to have excellent thickness uniformity.

[0129] The CNT film of Comparative Example 1, which was not subjected to the purified CNT production step, had a large proportion of non-uniform regions and was poor in thickness uniformity.

[0130] The suspension obtained in the crude CNT dispersion production process was subjected to the ultrasonic dispersion described below, but the CNT film of Comparative Example 2, in which the purified CNT production process was not performed, had a large proportion of non-uniform regions and poor thickness uniformity. Furthermore, in the CNT film of Comparative Example 2, the 3σ of the reflectance was 15% or more at all measurement positions, and the difference between the maximum and minimum values ​​of the average reflectance was 10% or more. When the CNT film of Comparative Example 2 placed on a silicon substrate was observed with an optical microscope, a clear distribution of light and dark was observed over the entire surface, lumps or aggregates were observed over the entire surface, and non-uniform areas were visible. The CNT film of Comparative Example 2 had localized variations in thickness, and the thickness uniformity was poor.

[0131] The CNT film of Comparative Example 3, which was not subjected to the purified CNT production step, had a large proportion of non-uniform regions and was inferior in thickness uniformity.

[0132] FIG. 11 shows an image of the surface of the CNT film according to Example 1 observed using an optical microscope. In FIG. 11, a slight light and dark distribution is observed, but lumps or aggregates are hardly observed, and no non-uniform regions are visible.

[0133] FIG. 12 shows an image of the surface of the CNT film according to Comparative Example 1, observed using an optical microscope. In FIG. 12, clumps or aggregates were observed and non-uniform areas were visible.

[0134] FIG. 13 shows an image of the surface of the CNT film according to Example 1, observed using a scanning electron microscope (SEM). In FIG. 13, a structure in which CNT bundles are dispersed in a mesh-like pattern is observed.

[0135] FIG. 14 shows an image of the surface of the CNT film according to Example 2, observed using a scanning electron microscope (SEM). FIG. 15 shows an image of the surface of the CNT film according to Comparative Example 2, observed using a scanning electron microscope (SEM). In Example 2, in which the purified CNT production process was performed, no bundles with a width of 50 nm or more were contained, and the uniformity of the bundle diameter distribution was improved. On the other hand, in Comparative Example 2, in which the purified CNT production process was not performed, bundles with a width of 50 nm or more were contained, and the uniformity of the bundle diameter distribution was poor.

[0136] The CNT film of Example 1, in which the [high-speed stirring process] was performed, had a higher G / D ratio obtained by Raman spectroscopy and superior film strength measured by nanoindentation testing compared to Example 2, in which the [high-speed stirring process] was not performed but the [ultrasonic dispersion process] was performed. [Explanation of symbols]

[0137] 100···CNT (carbon nanotube) film 101...CNT aggregate 102···CNT 110... board 120...base layer< / cnt>

Claims

1. Contains carbon nanotubes, The average thickness is 1 nm or more and 200 nm or less, The ratio of the area of ​​the non-uniform region, which is a region having a thickness 10% or more thicker or 10% or more thinner than the average thickness, to the area of ​​the entire region of the film is 15.0% or less; When the film is placed on a silicon substrate and the reflectance is measured using a reflection spectroscopic film thickness meter under the following conditions, the 3σ of the reflectance is 15% or less, The carbon nanotubes do not include bundles with a width of 50 nm or more; A carbon nanotube film having a breaking load of 1.0 μN / nm or more as measured by a nanoindentation test. <Conditions> Diameter of measurement point: 20 μm Standard measurement wavelength: wavelength 285nm Number of measurement points: 121 Distance between center points of adjacent measurement points: 40 μm

2. The film was placed on a silicon substrate and the reflectance was measured and the average reflectance was calculated at each of a plurality of measurement positions that were 2 cm or more apart using a reflection spectroscopic film thickness meter under the following conditions:

2. The carbon nanotube film according to claim 1, wherein the value obtained by subtracting the minimum value of the average reflectance from the maximum value of the average reflectance is 15% or less. <Conditions> Diameter of measurement point: 20 μm Standard measurement wavelength: wavelength 285nm Number of measurement points: 121 Distance between center points of adjacent measurement points: 40 μm

3. The carbon nanotube film according to claim 1 or 2, which has a network structure.

4. 4. The carbon nanotube film according to claim 1, wherein the carbon nanotubes have a tube diameter of 0.8 nm or more and 6.0 nm or less.

5. 5. The carbon nanotube film according to claim 1, wherein the carbon nanotubes have a length of 10 nm or more.

6. 6. The carbon nanotube film according to claim 1, wherein the carbon content of the carbon nanotubes is 98 mass % or more with respect to the total mass of the carbon nanotubes.

7. 7. The carbon nanotube film according to claim 1, wherein the G / D ratio measured by resonance Raman scattering is 20 or more.

8. A dispersion used in the production of the carbon nanotube film according to any one of claims 1 to 7, comprising carbon nanotubes, a solvent, and a dispersant, and not containing aggregates of carbon nanotubes that are bundles with a width of 50 nm or more.

9. providing crude carbon nanotubes containing aggregates; a step of mixing the crude carbon nanotubes, a solvent, and a dispersant to obtain a dispersion; removing the aggregates contained in the dispersion to obtain purified carbon nanotubes; and forming the purified carbon nanotubes into a sheet-like film to produce a carbon nanotube film, The step of obtaining the dispersion liquid includes a high-speed stirring and dispersing step or an ultrasonic dispersing step, The method for producing a carbon nanotube film includes a step of removing aggregates contained in the dispersion by ultracentrifugation at an average relative centrifugal force of 3,000 x g or more to obtain a dispersion that does not contain aggregates of carbon nanotubes that are bundles with a width of 50 nm or more.

10. 10. The method for producing a carbon nanotube film according to claim 9, wherein the dispersant used in the step of obtaining the dispersion liquid comprises a dispersant selected from the group consisting of a flavin derivative, sodium cholate, sodium deoxycholate, sodium dodecylbenzenesulfonate, and polyacrylic acid.

11. The method for producing a carbon nanotube film according to claim 9 or 10, further comprising the step of removing the dispersant from the obtained carbon nanotube film after the step of producing the carbon nanotube film.

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