JP2021172528A - Carbon nanotube membrane, dispersion liquid, and production method of carbon nanotube membrane - Google Patents

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

The present disclosure relates to a carbon nanotube film, a dispersion liquid, and a method for producing a carbon nanotube film.

Carbon nanotubes (hereinafter, also referred to as CNTs) composed of carbon atoms are materials having excellent electrical properties, thermal conductivity, and mechanical properties. CNT is a material that is extremely lightweight, extremely tough, and has excellent elasticity, resilience, and the like. CNT having such excellent properties is an extremely attractive and important substance as an industrial material.

For example, in Patent Document 1, a carbon nanotube set having a region of 10 nm or more in which pores having a pore size of 400 nm or more and 1500 nm or less, which are measured by a mercury intrusion method, have a log differential pore volume of 0.006 cm ^{3 / g or less.} The body is disclosed.

Further, Patent Document 2 is a film structure comprising a plurality of mesh-like carbon nanotube bundles including carbon nanotube aggregates and having a BET specific surface area of 600 m ^{2 / g or more obtained from a nitrogen adsorption isotherm.} The carbon nanotube bundle is provided with pores having a size corresponding to a relative pressure (equilibrium pressure / saturated vapor pressure) of the nitrogen adsorption / desorption isotherm of 0.2 or more and 0.9 or less of 400 cm ³ / g (STP) or more. The characteristic membrane structure is disclosed.

Japanese Unexamined Patent Publication No. 2018-14502 JP-A-2018-024540

In the conventional carbon nanotube (CNT) film, when the CNT bundle forms a high-order aggregated structure due to reasons such as the CNT bundle not being sufficiently opened, the thickness uniformity in the CNT film is insufficient. was there.
The non-uniformity of the surface of the CNT film may reduce the transparency of the CNT film and may cause the non-uniformity of other properties such as conductivity in the plane direction.
In addition, the non-uniformity of the surface of the CNT film may cause microscopic stress concentration and cause a decrease in the mechanical strength of the CNT film.

In Patent Document 1 and Patent Document 2, the uniformity of the thickness of the CNT film has not been sufficiently examined, and there is room for improvement.

An object to be solved in one embodiment of the present disclosure is to provide a carbon nanotube film having excellent thickness uniformity, a dispersion liquid containing the carbon nanotube film, and a method for producing the carbon nanotube film.

Specific means for solving the above problems include the following aspects.
<1> The ratio of the area of the non-uniform region, which contains carbon nanotubes, has an average thickness of 1 nm or more and 200 nm or less, and is a region having a thickness of 10% or more or 10% or more thinner than the average thickness, is a film. It is 15.0% or less of the total area of the area, and when the reflectance is measured under the following conditions by arranging it on a silicon substrate and using a reflection spectroscopic membrane thickness gauge, the reflectance of 3σ is 15. % Or less carbon nanotube membrane.
<Conditions>
Diameter of measurement point: 20 μm
Reference measurement wavelength: Wavelength 285 nm
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm
<2> The reflectance was measured and the average reflectance was calculated under the following conditions using a reflection spectrofilm thickness gauge at each of a plurality of measurement positions separated from each other by 2 cm or more on a silicon substrate. The carbon nanotube film according to <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
Reference measurement wavelength: Wavelength 285 nm
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm
<3> The carbon nanotube film according to <1> or <2>, which has a network structure.
<4> The carbon nanotube film according to any one of <1> to <3>, wherein the carbon nanotube has a tube diameter of 0.8 nm or more and 6.0 nm or less.
<5> The carbon nanotube film according to any one of <1> to <4>, wherein the carbon nanotube has a length of 10 nm or more.
<6> The carbon nanotube film according to any one of <1> to <5>, wherein the content of carbon contained in the carbon nanotubes is 98% by mass or more with respect to the total mass of the carbon nanotubes.
<7> The carbon nanotube film according to any one of <1> to <6>, wherein the G / D ratio measured by the resonance Raman scattering measurement method is 20 or more.
<8> The carbon nanotube film according to any one of <1> to <7>, wherein the breaking load measured by the nanoindentation test is 1.0 μN / nm or more.
<9> The dispersion liquid used for producing the carbon nanotube film according to any one of <1> to <8>.
<10> A step of preparing crude carbon nanotubes containing aggregates, a step of mixing the crude carbon nanotubes with a solvent to obtain a dispersion liquid, and a step of removing the aggregates contained in the dispersion liquid to purify carbon. A method for producing a carbon nanotube film, which comprises a step of obtaining nanotubes and a step of forming the purified carbon nanotubes into a sheet to produce a carbon nanotube film.

According to one embodiment of the present disclosure, it is possible to provide a carbon nanotube film having excellent thickness uniformity, a dispersion liquid containing the carbon nanotube film, and a method for producing the carbon nanotube film.

It is sectional drawing which shows the CNT film which concerns on one Embodiment of this disclosure. It is a schematic diagram which shows the CNT film and the CNT aggregate which concerns on one Embodiment of this disclosure. It is a graph which shows the relationship between the reflectance and the film thickness at wavelengths 285 nm and 400 nm. It is the schematic which shows the arrangement of the measurement position selected at the time of measuring 3σ of the reflectance and the average reflectance in this disclosure. (A) A schematic diagram showing the arrangement of the measurement positions selected when measuring the reflectance of 3σ and the average reflectance in the present disclosure is shown. (B) A schematic diagram showing the arrangement of measurement points at each selected “measurement position” when measuring the reflectance of 3σ and the average reflectance in the present disclosure is shown. It is the schematic which shows the model of the air layer / CNT film layer / silicon substrate. 6 is a graph plotting the relationship between the reflectance and the film thickness when the reflectance and the film thickness at a wavelength of 285 nm are measured by the method of converting to the film thickness in the present disclosure. It is a schematic diagram of the method of determining the thickness of the CNT bundle of the CNT aggregate which concerns on one Embodiment of this disclosure. It is sectional drawing which shows the manufacturing method of the CNT film which concerns on one Embodiment of this disclosure. It is sectional drawing which shows the manufacturing method of the CNT film which concerns on one Embodiment of this disclosure. It is an image of the surface of the CNT film according to Example 1 observed using an optical microscope. It is an image of the surface of the CNT film according to Comparative Example 1 observed using an optical microscope. It is an image of the surface of the CNT film according to Example 1 observed using a scanning electron microscope (SEM). It is an image of the surface of the CNT film according to Example 2 observed using a scanning electron microscope (SEM). It is an image of the surface of the CNT film according to Comparative Example 2 observed using a scanning electron microscope (SEM).

The numerical range indicated by using "~" in the present disclosure means a range including the numerical values before and after "~" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the 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, the amount of each component means the total amount of a plurality of kinds of substances when a plurality of kinds of substances corresponding to each component are present, unless otherwise specified.
In the present disclosure, the term "process" is included in this term not only as an independent process but also as long as the purpose of the process is achieved even if it cannot be clearly distinguished from other processes.

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

≪Carbon nanotube membrane≫
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 has an area of a non-uniform region which is a region where the thickness is 10% or more thicker or 10% or more thinner than the average thickness. Is 15.0% or less of the total area of the membrane.
When the reflectance is measured under the following conditions using a reflection spectroscopic film thickness meter placed on a silicon substrate, the reflectance of 3σ is 15% or less.
<Conditions>
Diameter of measurement point: 20 μm
Reference measurement wavelength: Wavelength 285 nm
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm

In the conventional CNT film, the uniformity of the thickness in the CNT film may be insufficient because the CNT bundle forms a high-order agglutinating structure due to reasons such as the CNT bundle not being sufficiently opened.
When observed with an optical microscope, the aggregated structure of the CNT bundle is observed as a region having a darker color than other regions (also referred to as an aggregate) or a so-called lump-like region (simply also referred to as lump). can.

The CNT film is expected to be applied as an electrode material for fuel cells and supercapacitors as a conductive material having a high specific surface area and exhibiting excellent chemical stability, and development of a technique for controlling the pore structure in the CNT film. In addition, high reliability is required by improving mechanical strength and flexibility.
The CNT film is also expected as a transparent electrode to replace ITO, and is superior in flexibility and mechanical strength to metal wiring and ITO, so that it is subject to severe mechanical loads such as bending, tension, torsion, and repeated fatigue. It is expected to be applied to expected applications such as large screen touch panels and electrodes / wiring for wearable / flexible devices.
The CNT film is also expected to be applied to anti-fog and anti-static films that utilize heat generation, filters with small pressure loss, thermophones that convert electric signals into heat to generate sound, and laser absorbing material members. Especially in filters and chemical sensors, it is important to reduce the pressure loss due to air and fluid, but a film with high mechanical strength is suitable for thinning, so it is suitable for reducing the pressure loss. In addition, since thermophones and laser absorbing materials need to be self-supporting, high mechanical strength is required.

The carbon nanotube film of the present disclosure is excellent in thickness uniformity because the aggregated structure of the CNT bundle can be suppressed by the above configuration.

The carbon nanotube film of the present disclosure may be a film arranged on a base material or a frame, or may be a self-supporting film (that is, a self-supporting film) not arranged on the base material or the frame.

(Construction 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 view of a CNT aggregate 101 formed by assembling the CNT film 100 and the CNT 102. FIG. 2 also shows an enlarged view of the region A1 in the CNT film.

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

<Non-uniform area>
In the carbon nanotube membrane of the present disclosure, the ratio of the area of the non-uniform region, which is a region having a thickness of 10% or more thick or 10% or more thin with respect to the average thickness, is 15. It is 0% or less.
When the ratio of the area of the non-uniform region is within the above range, a carbon nanotube film having excellent thickness uniformity can be obtained.

As described above, in the conventional CNT film, the CNT bundle may form aggregates or lumps due to reasons such as the CNT bundle not being sufficiently opened.
The thickness of the aggregates and lumps is larger than the thickness of the regions other than the aggregates and lumps in the CNT film. That is, the presence of non-uniformly thick regions such as the agglomerates and lumps in the CNT film causes unevenness in the entire CNT film, which causes the thickness uniformity to be impaired.
The non-uniform region in the present disclosure means a region in which the thickness is 10% or more thicker or 10% or more thinner than the average thickness in all regions.

The carbon nanotube film of the present disclosure is excellent in thickness uniformity when the ratio of the area of the non-uniform region is 15.0% or less with respect to the area of the total region.

From the same viewpoint as described above, the ratio of the area of the non-uniform region is preferably 10.0% or less, more preferably 5.0% or less, based on the area of the entire region of the film. It is more preferably 0% or less, and particularly preferably 0.3% or less.

The ratio of the area of the non-uniform region is measured by the following method.
The entire film ^{is divided into 200 μm 2} regions, and the film thickness is measured in each of the divided regions under the following conditions by the method described below.
<Measurement conditions for each area>
Diameter of measurement point: 20 μm
Reference measurement wavelength: 28 nm
Measurement points: 100 points

Using the film thickness obtained as described above, the average value (Xa) of the film thickness in each region and the average value (Xb) of the film thickness in the entire film are obtained.
and,
The following formula is used for a non-uniform region in which the average value (Xb) of the film thickness in the entire film is 10% or more thicker or 10% or more thinner than the average value (Xa) of the film thickness in the region. Then, the ratio of the area of the non-uniform region is calculated.
Area ratio of non-uniform region = (number of non-uniform regions) / (number of regions of the entire film) x 100 (%)

<Reflectance>
The CNT film of the present disclosure is arranged on a silicon substrate, and when the reflectance is measured under the following conditions using a reflection spectroscopic film thickness meter, the reflectance of 3σ is 15% or less.
<Conditions>
Diameter of measurement point: 20 μm
Reference measurement wavelength: Wavelength 285 nm
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm
Note that σ represents the standard deviation.

By using the above-mentioned reflectance measuring method, the transmittance uniformity can be evaluated.
The measurement wavelength is preferably a wavelength of 285 nm because a slight difference in film thickness can be detected.
For example, when visible light having a wavelength of 400 nm to 800 nm is used, the change in reflectance with respect to the film thickness is smaller than that in the ultraviolet light region, so it is preferable to use ultraviolet light rather than the visible light region.

As shown in FIG. 3, in the film thickness range of 1 nm to 20 nm, the reflectance at a wavelength of 400 nm changes from 46% to 42% by only 4%, but the reflectance of ultraviolet light having a wavelength of 285 nm is used. If so, the reflectance can change from 72% to 40%, as much as 32%, as the thickness changes from 1 nm to 20 nm.
Assuming that the reflectance measurement accuracy is 0.5%, the film thickness measurement accuracy is 0.3 nm, and it is possible to detect a slight difference in film thickness of 1 nm or less.

By using a silicon substrate and ultraviolet rays as the substrate on which the CNT film is arranged, variations in film thickness of 1 nm to 50 nm can be measured with high sensitivity and high accuracy.
Even when a substrate made of a material other than silicon is used, the reflectance can be measured in the free-standing film state. However, in order to capture slight changes in film thickness and measure reflectance with high accuracy and reproducibility, (1) a substrate with high reflectance (refractive index and extinction coefficient) in the wavelength region of ultraviolet rays is used. It is preferable that the substrate has (2) specular reflection light from the surface of the substrate and has high surface smoothness of the substrate (for example, surface roughness Ra = 0.3 nm or less).
From these viewpoints, a metal substrate or a silicon substrate is preferable.
It is more preferable to use a silicon substrate because it is used for general purposes and there is little variation in the quality of the substrate.

The spot size in the reflectance measurement is not particularly limited, but is preferably in the range of 10 μm to 1000 μm.
Since the value of 3σ, which is an index of the uniformity of the film thickness, is inversely proportional to the measured area, it can be converted into the value of 3σ in the range of 50 μm to 100 μm by grasping the spot size.
However, the spot size is preferably 10 μm to 1000 μm, more preferably 20 μm to 500 μm, because the variation (3σ) due to the measurement accuracy of the measuring device is preferably sufficiently smaller than the true value.

In the reflectance measurement, the method of detecting the reflected light is not particularly limited, and a photodiode, a photomultiplier tube, or the like can be used.
Further, a multi-channel detector such as a photodiode array or a CCD (Charge Coupled Device) may be used.
By detecting the dispersed reflected light with a photodiode array, it is possible to obtain reflectances at a plurality of wavelengths. Further, the pixel size of the CCD detector may be adjusted to about 50 μm to 100 μm, and the distribution of the reflected light intensity may be measured.
In evaluating the uniformity of the thickness, the number of measurement points of the reflectance is preferably 100 points or more.

Since the reflectance of the CNT film is 3σ of 15% or less, the CNT film is locally excellent in the uniformity of the film in the region including the measurement points of the measurement points.
From the same viewpoint as described above, the reflectance of 3σ is preferably 12.0% or less, more preferably 10.0% or less, and further preferably 8.0% or less.

[Reflectance 3σ and average reflectance]
A method for measuring "3σ of reflectance and average reflectance measured by a reflection spectroscopic membrane thickness meter at the measurement points, the reference measurement wavelength, and the number of measurement points" will be described.
First, the CNT film is arranged on the silicon substrate, and the diagonal line of the arranged CNT film is defined as the X-axis.
When arranging the CNT film on the silicon substrate, the silicon substrate and the CNT film are brought into close contact with each other without any gap. 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 brought into close contact with each other without any gaps.
For example, the CNT film floating on the water surface may be scooped up with a silicon substrate and then dried. By placing the CNT film on the silicon substrate on which the solvent is placed and drying, the silicon substrate and the CNT film are dried. Can be brought into close contact with.
Although the size of the silicon substrate is not limited, it is preferable to use a silicon wafer having a size of 8 inches or more from the viewpoint of adhering a CNT film having a large area.
Next, an arbitrary "measurement position" on the CNT film is selected.
In the selected "measurement position", 11 points at intervals where the distance between the center points at the adjacent measurement points as the measurement points in the X-axis direction is 40 μm, and the distance between the center points at the adjacent measurement points as the measurement points in the Y-axis direction. 11 points are set at intervals of 40 μm. That is, 11 points in the vertical direction x 11 points in the horizontal direction, and a total of 121 measurement points are set.
Then, the reference measurement wavelength is set to a wavelength of 285 nm, the reflectance at each measurement point is measured, and the reflectance of 3σ and the average reflectance are calculated.
The measurement range of the measurement point is a range of 20 μm in diameter.
As a specific example of setting the measurement points, FIG. 4 shows a schematic diagram showing the arrangement of the measurement points at the selected “measurement position”.
A microspectroscopy thickness gauge (for example, OPTM manufactured by Otsuka Electronics Co., Ltd., model: A-1) is used as a reflectance measuring device, and a 10x reflective lens is used as a lens for adjusting the diameter of a measuring point. An aperture with a diameter of 200 μm (measurement point diameter: 20 μm) is used as an apparatus. An aluminum substrate is used as a reference for measuring the reflection intensity.
The reflectance Rs (λ) is calculated by the following formula.

Here, _{I s} (λ) represents the reflection intensity of the CNT film on the silicon substrate at the wavelength _{λ, I ref} (λ) represents the reflection intensity of the _{reference, R ref (λ)} is the absolute reflectance of the reference show.
When aluminum is used as a reference, the optical constant of aluminum is known, so R _ref (λ) can be calculated. In the reference and the measurement of the reflection intensity of the CNT film on the silicon substrate, the gain, the exposure time, and the like are the same conditions. As a result, the absolute reflectance of the CNT film on the silicon substrate can be obtained.
The reflectance at a wavelength of 285 nm is calculated by the following formula using the reflectance intensity at a wavelength of 285 nm and the absolute reflectance of the reference.

The CNT film of the present disclosure is arranged on a silicon substrate, and at each of a plurality of measurement positions separated from each other by 2 cm or more, a reflectance spectrofilm thickness gauge is used to measure the reflectance and the average reflectance under the following conditions. When the calculation is done,
The value obtained by subtracting the minimum value of the average reflectance from the maximum value of the average reflectance is preferably 15% or less.
<Conditions>
Diameter of measurement point: 20 μm
Reference measurement wavelength: Wavelength 285 nm
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm

When the difference between the maximum value and the minimum value of the average reflectance is 15% or less, the difference in the average reflectance between the average reflectances at a plurality of measurement points separated from each other by 2 cm or more is reduced. be able to. As a result, the CNT film of the present disclosure is excellent in film uniformity over a wide area.
From the same viewpoint as described above, the difference between the maximum value and the minimum value of the average reflectance is more preferably 12% or less, and further preferably 8% or less.

[Difference between maximum and minimum average reflectance]
The measuring method of "the difference between the maximum value and the minimum value of the average reflectance when the average reflectance is measured by the reflection spectroscopic membrane thickness meter at each of a plurality of measurement points separated from each other by 2 cm or more" will be described. ..
First, the CNT film is arranged on the silicon substrate without any gaps.
The diagonal line of the arranged CNT film is defined as the X-axis, and a plurality of "measurement positions" separated from each other by 2 cm or more are selected on the X-axis.
The measurement range at each measurement position is a range of 0.40 mm × 0.40 mm.
As a specific example of selection of the "measurement position", FIG. 5A shows a schematic view showing the arrangement of the selected measurement positions. Further, in FIG. 5B, a schematic diagram showing the arrangement of measurement points at each selected “measurement position” is shown.
At each of the selected "measurement positions", the reflectance at each measurement point is measured and the average reflectance is calculated by the method described in the above-mentioned "Reflectance 3σ and average reflectance" section.
From the obtained average reflectance at each "measurement position", the difference between the maximum value and the minimum value of the average reflectance is calculated.

~ Conversion method to film thickness (optical thickness) ~
For each measurement point, a reflectance spectrum in a wavelength range of 200 nm to 600 nm is acquired in a wavelength range of 1 nm to 2 nm.
Then, using the values of the optical constants (refractive index: n, extinction coefficient: k) shown in Table 1 as the optical constants of the CNT film, and using the model of the air layer / CNT film layer / silicon substrate, the wavelength range 225. The film thickness at each measurement point is calculated by analyzing the reflectance spectrum at ~ 500 nm by the minimum square method.
The film thickness of the "measurement position" is the average value of the film thickness of each of the 121 measurement points included in the "measurement position".
A method of calculating the film thickness at each measurement point by analyzing the reflectance spectrum in the wavelength range of 225 to 500 nm by the least squares method will be described below.

The film thickness is calculated using a three-layer model of an air layer / a CNT film layer / a silicon substrate, and using the relational expressions of the following equations (a) to (c).
Note that FIG. 6 is a schematic view showing a model of the air layer / CNT film layer / silicon substrate.

Reflectance Rs is expressed by the following equation using the amplitude reflectance r _s (a).

In the above equation, * represents the complex conjugate.

Amplitude reflectance r _s of the three layers of the layer / silicon substrate of the air layer / CNT film is represented by the following formula (b).

In the above formula, r ₀₁ represents the amplitude reflectance from the interface between the air layer and the CNT film layer, 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. show.
In the above formula, δ is a phase difference that occurs when light having a wavelength λ makes one round trip in the film, and is represented by the following formula (c).

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

The film thickness can be obtained by using the relational expressions according to the above formulas (a) to (c) and calculating by the minimum square method with the film thickness d as a variable with respect to the reflectance Rs in the wavelength range of 225 to 500 nm. ..

FIG. 7 plots the relationship between the reflectance and the film thickness when the reflectance and the film thickness at a wavelength of 285 nm are measured by the method described above for a sample obtained by transferring a non-uniform CNT film onto a silicon substrate. It is a graph.
As shown in FIG. 7, by the above-mentioned method, the difference in film thickness can be accurately obtained from the value of the reflectance.

The CNT film of the present disclosure has an average thickness of 1 nm or more and 200 nm or less.
In the CNT film of the present disclosure, the ratio of the area of the non-uniform region is 15.0% or less with respect to the area of the entire region of the film, and the reflectance of 3σ is 15% or less, thereby improving the mechanical strength. Can be As a result, the CNT film of the present disclosure can maintain excellent independence even if the average thickness is 200 nm or less.
The CNT film of the present disclosure maintains even better independence even if the average thickness is 200 nm or less when the value obtained by subtracting the minimum value of the average reflectance from the maximum value of the average reflectance is 15% or less. can do.
From the same viewpoint as described 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.

The CNT film of the present disclosure may be a CNT film arranged so as to cover the space on a silicon substrate or a frame having a space of ^{100 μm 2} or more and 225 cm ^{2 or less.}
The CNT film of the present disclosure can maintain excellent independence even when it is arranged as described above.

The average thickness of the CNT film is measured by the following method.
By the method described in [Difference between maximum value and minimum value of average reflectance] described above, the reflectance is measured with a reflection spectroscopic membrane thickness meter at each of a plurality of measurement positions separated from each other by 2 cm or more. However, the measurement conditions for reflectance are as follows.
<Conditions>
Diameter of measurement point: 20 μm
Measurement wavelength: Wavelength 200 nm to 600 nm (wavelength interval: 1.3 to 1.5 nm)
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm

Then, the film thickness at each measurement point is calculated by the method described in the above-mentioned "Method for converting to film thickness (optical thickness)". Further, the film thickness at each measurement position is calculated by calculating the average value of the film thickness at each measurement point (121 points) included in each measurement position.
Then, the value obtained by calculating the average value of the calculated film thicknesses at each measurement position is defined as the average thickness of the CNT film.
Similarly, the σ of the film thickness at each measurement position is calculated from the standard deviation of the film thickness at each measurement point.

The CNT film 100 can have a network structure. That is, a plurality of CNTs 102 can be entangled in a mesh pattern in the CNT film 100 to form a network structure.
Moreover, the CNT film 100 can have pores. That is, the CNTs 102 can be entangled to form pores.

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, by providing the CNT film with a structure having uniform pores, the mechanical strength of the film can be increased. The fact that the CNT film has a structure having uniform pores, that is, the narrow pore distribution in the CNT film results in, for example, an increase in tensile strength.

The CNT film has a film structure similar to that of a polymer, paper, non-woven fabric, porous material, etc., in which CNT bundles are entangled with each other. When pores having a large volume are present in the CNT film, the film is easily destroyed starting from the large pores. The small volume of the pores results in, for example, a reduction in the variation in tensile strength measured in tensile tests.

The CNT aggregate 101 may include a single-walled CNT 102 or a two-layer CNT 102.

Further, the CNT aggregate 101 preferably has a relative standard deviation of 30% or less when the thickness of the CNT bundle (also referred to as the bundle diameter in the present disclosure) is distributed.
The thickness of the CNT bundle is measured by the following method.

FIG. 8 is a schematic diagram of a method for determining the thickness of the CNT bundle. How to find the thickness of the CNT bundle is as follows.
(1) Draw a contour line L1. (2) The thickness of the bundle is obtained by measuring the distance D1 in the direction perpendicular to the two contour lines belonging to the same CNT bundle. (3) The area near the turning point where the bundle branches and merges is not counted as the thickness of the bundle. (4) The two contour lines are subject to the condition that the tangents at the point where the thickness of the bundle is obtained intersect or are parallel at 15 ° or less. (5) A straight line is drawn from one end of the image to the opposite end, and the thickness of the above bundle is calculated and counted for each contour line of the CNT bundle crossed by the line. This is to avoid duplication of counts. Further, in this evaluation, the contour line may be judged by the human eye.

<CNT>
The CNT film of the present disclosure contains CNT.
The CNT has a tube diameter of 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.

The length of CNT is preferably 10 nm or more, and more preferably 100 nm or more.
When the length of the CNTs is 10 nm or more, the CNTs are entangled well with each other, and a CNT film having excellent mechanical strength can be obtained.
The upper limit of the length of the CNT is not particularly limited, but the upper limit may be, for example, 10 cm.

The tube diameter and length of the CNT shall be the arithmetic mean value of the 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 (Transmission Electron Microscope: TEM), or the like can be used.

The carbon content in the CNTs is preferably 98% by mass or more with respect to the total mass of the CNTs.

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

In the CNT film of the present disclosure, the G / D ratio measured by the resonance Raman scattering measurement method is preferably 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 CNTs that are well graphitized can be obtained.
The resonance Raman scattering measurement method is performed using 532 nm as the laser wavelength, for example, using XproRA manufactured by HORIBA Scientific.

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

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, and more preferably 2.0 μN / nm or more. , 3.0 μN / nm or more is more preferable.
The upper limit of the breaking load is not particularly limited and may be, for example, 10.0 μN / nm or less.

[Nano indentation test]
First, an evaluation sample having a structure in which the CNT film is self-supporting is prepared by arranging a CNT film so as to cover the circular holes on a silicon wafer having a circular hole having a depth of 30 um or more and a diameter of 80 μm.
Next, a load is applied to the CNT film by pushing a conical indenter (R = 10 μm) at a speed of 1 μm / s with respect to the center of the portion of the CNT film that covers the circular hole. Then, at the stage where the CNT film is plastically deformed or fractured, the load at the yield point when the plastic deformation or fracture occurs is measured. The film strength is measured by calculating the value obtained by dividing the obtained load by the film thickness as the breaking load. The nanoindentation test is performed using, for example, ENT-2100 manufactured by Elionix Inc.

The arithmetic mean roughness of the film surface of the CNT film 100 is preferably 100 nm or less, more preferably 20 nm or less, and further preferably 5 nm or less.
The arithmetic mean roughness of the CNT film 100 is measured using a laser microscope.

Further, it is preferable that the CNT aggregate 101 is uniformly dispersed with the CNT bundles separated by a certain distance.
It can be confirmed that the CNT aggregate 101 is dispersed, for example, by performing a fast Fourier transform (FFT) on the SEM image.
The closer the FFT image is to the center, the lower the frequency is in the original image, and the farther away from the center, the higher the frequency is in the original image. Further, the analysis may be performed by fitting using the pixel distance and the brightness of the FFT image. In this case, the following formula (Ornstein Zernike's formula) may be used.

In the above formula, I is the luminance and v is the pixel distance. A, B, and C are fitting constants.

≪Manufacturing method of 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) and a step of mixing crude carbon nanotubes and a solvent to obtain a dispersion liquid (production of crude carbon nanotube dispersion liquid). A step (also referred to as a crude CNT dispersion manufacturing step), a step of removing aggregates contained in the dispersion to obtain purified carbon nanotubes (also referred to as a purified carbon nanotube manufacturing step or a purified CNT manufacturing step), and a purified carbon nanotube. Is included in a sheet-like film formation to produce a carbon nanotube film (also referred to as a carbon nanotube film manufacturing step or a CNT film manufacturing step).
Hereinafter, a method for producing the CNT film 100 will be described with reference to FIGS. 9 and 10.

[Preparation of board]
First, as shown in FIG. 9, the substrate 110 is prepared. For example, a silicon (Si) wafer is used for the substrate 110. As shown in FIG. 9, the base layer 120 may be formed on the substrate 110. The base layer 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 the CVD method is used for the base layer 120. In addition, the substrate 110 and the base layer 120 may be collectively referred to as a substrate 110. A different film may be further provided on the base layer 120.

<Preparation process>
The preparation step is a step of preparing crude CNTs containing aggregates.
The crude CNT can be used without particular limitation as long as it is a CNT containing agglomerates.
For example, commercially available products such as eDIPS manufactured by Meijo Nanocarbon Co., Ltd., ZEONANO manufactured by Zeon Nanotechnology Co., Ltd., and TUBALL manufactured by OCSiAl Co., Ltd. may be obtained, or crude CNTs may be synthesized.
Examples of the method for synthesizing the crude CNT include an improved direct injection pyrolytic synthesis method (hereinafter, also referred to as an eDIPS method), a super growth method, and a laser ablation method.
Among the above, the eDIPS method is preferable as the method for synthesizing crude CNTs.

The crude CNTs synthesized by the eDIPS method are superior in diameter distribution, CNT crystallinity, and linearity.
Therefore, the CNT bundle and the network structure of the CNT bundle are composed of CNTs having high crystallinity, that is, CNTs having a low defect density. In addition, the size of the bundle and the distribution of the mesh can be made uniform. As a result, the uniformity of the surface of the CNT film can be improved, and a tough CNT film can be obtained.
Further, since the crude CNTs synthesized by the dry method can suppress the aggregation of the CNT bundles, the thickness of the CNT bundles can be reduced and the thickness of the CNT film can be further reduced. It becomes.

[EDIPS method]
The eDIPS method is a CNT synthesis method that is an improvement of the direct injection pyrolysis synthesis method (hereinafter, also referred to as the DIPS method).
The DIPS method is a single-walled carbon in a flowing gas phase by atomizing a hydrocarbon-based solution containing a catalyst (or catalyst precursor) and a reaction accelerator with a spray and introducing it into a high-temperature heating furnace. This is a gas phase flow method for synthesizing nanotubes.
The eDIPS method focuses on the particle formation process in which ferrocene used in the catalyst has different particle sizes on the upstream and downstream sides of the reaction reactor, and is different from the DIPS method in which only an organic solvent is used as a carbon source. This is a method in which the growth point of single-walled carbon nanotubes is controlled by mixing a second carbon source that is relatively easily decomposed, that is, easily becomes a carbon source.
For details, see Saito et al. , J. Nanosci. Nanotechnol. , 8 (2008) 6153-6157.

Examples of commercially available carbon nanotubes synthesized by the eDIPS method include the trade name "MEIJO eDIPS" manufactured by Meijo Nanocarbon Co., Ltd.

<Rough CNT dispersion liquid manufacturing process>
The crude CNT dispersion liquid manufacturing step is a step of mixing crude carbon nanotubes and a solvent to obtain a dispersion liquid.

(Dispersion)
The dispersion is used in the production of the carbon nanotube membranes of the present disclosure.
The dispersion liquid contains crude CNTs obtained in the preparatory step.
In the dispersion liquid, the crude CNTs are present in a small crushed state, and CNT aggregates are formed.
The dispersion may be in the form of a highly viscous paste, if necessary.

The dispersion liquid may further contain a dispersant in addition to the crude CNT.
Dispersants are used to unwind thick bundles of crude CNTs. When it is necessary to remove the dispersant after film formation, it is preferable to use a dispersant having a low molecular weight.

Examples of the dispersant include flavin derivatives, sodium colate, sodium deoxycholate, sodium dodecylbenzenesulfonate, polyacrylic acid and the like.
Examples of the flavin derivative include organic side chain flavin represented by the following formula.
The organic side chain flavin is a dispersant capable of separating semiconducting CNTs and metallic CNTs, and has the effect of unbundle the CNTs. Organic side chain flavins are suitable from the viewpoint of finely dispersing a large amount of agglomerate particles in a solvent.

As the dispersant, polyfluorene (poly (9,9-dioctylfluoreneyl-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.

(solvent)
The dispersion liquid further contains a solvent in addition to CNT.
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.

When a dispersant is not used, an organic solvent such as n-methylpyrrolidone, N, N-dimethylformamide, propylene glycol, or methyl isobutyl ketone can be used as the solvent.

As a method of mixing crude carbon nanotubes and a solvent to obtain a dispersion liquid, for example, a method using cavitation (ultrasonic dispersion method) and a method of mechanically applying a shearing force (ball mill, roller mill, vibration mill, kneader). , Homogenizer, etc.), and methods using turbulent flow (jet mill, nanomizer, etc.).

The above method can be dispersed in a solvent by finely dissolving the crude CNTs. Therefore, it is possible to obtain a high-concentration CNT dispersion liquid even after the purified CNT manufacturing process.
On the other hand, if the crude CNTs are broken down too finely, damage may be accumulated in the CNTs, which may lead to a decrease in the strength of the CNT film. Therefore, it is preferable to appropriately adjust the treatment time, strength, temperature and the like so that the strength does not decrease.

<Purified CNT manufacturing process>
The purified CNT manufacturing step is a step of removing agglomerates contained in the dispersion liquid to obtain purified carbon nanotubes.
By performing the purified CNT manufacturing step, it is possible to obtain a purified CNT from which highly cohesive fibrous nanotubes have been removed. By producing a CNT film using purified CNT, a CNT film having excellent thickness uniformity can be obtained.
Further, by performing the purified CNT manufacturing process, the thickness of the CNT bundle in the obtained CNT film can be made uniform.

Examples of the method for removing the agglomerates contained in the dispersion liquid include a method for precipitating the agglomerates contained in the dispersion liquid.
Specific examples include static, filtration, membrane separation, centrifugation and ultracentrifugation.
Among the above, from the viewpoint of excellent removal of agglomerates, ultracentrifugation is preferable as a method for removing agglomerates contained in the dispersion liquid.

In ultracentrifugal force, the average relative centrifugal force is preferably 3,000 xg or more.
When the average relative centrifugal force is 3,000 xg or more, finer aggregates can be removed and the uniformity of the pellicle membrane can be improved.
From the same viewpoint as described above, it is more preferable that the average relative centrifugal force is 5,000 xg or more.
Here, the average relative centrifugal force is the average centrifugal force generated when stretching at a certain rotation speed, and is the relative centrifugal force at the midpoint between the maximum radius and the minimum radius.

In ultracentrifugal force, the average relative centrifugal force is preferably 200,000 xg or less.
When the average relative centrifugal force is 200,000 xg or less, the relative centrifugal force is excessively high, so that the generation of aggregates and the sedimentation of the CNT itself dispersed in the dispersion liquid can be suppressed.
From the same viewpoint as described above, it is more preferable that the average relative centrifugal force is 150,000 xg or less.

Further, the centrifugal time is preferably 5 minutes or more and 180 minutes or less for the holding time after reaching the target relative centrifugal force.

<CNT film manufacturing process>
The CNT film manufacturing process is a step of forming a sheet of purified carbon nanotubes to manufacture a carbon nanotube film.

[Film film]
The purified carbon nanotubes are formed into a sheet. Thereby, the CNT film can be formed.
As shown in FIG. 10, the CNT film 100 is formed on the base layer 120. Specifically, the CNT film 100 is formed by applying a dispersion liquid containing CNT aggregates on the base layer 120 and removing the solvent by drying or the like. If necessary, the dispersant may be removed by washing with a solvent or the like that dissolves the dispersant in the dispersion liquid.

As the coating method, a method depending on the viscosity or the concentration of the CNT aggregate may be used. For example, a coating method such as a blade coating method, a slit coating method, a spin coating method, or a dip coating method may be used. Since the CNT film is formed by coating, the area, thickness, etc. of the obtained 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 method, CNT films having various thicknesses can be formed over a large area.
Among the above, the spin coating method is preferable as the coating method.

The drying method for removing the solvent after forming the CNT film is not particularly limited. Further, it does not have to be dried depending on the application.
For example, when toluene is used as the solvent, the solvent may be dried by allowing it to stand at room temperature. When water or a solvent having a high boiling point is used as the solvent, the solvent may be dried by heating as appropriate.
When a solvent having a small surface tension is used as the solvent, the shape of the CNT aggregate can be controlled by controlling the temperature, vapor pressure, and the like. Examples of the solvent having a small surface tension include supercritical fluids such as supercritical carbon dioxide.

The method for removing the dispersant is not particularly limited. Further, it may not be removed depending on the application.
For example, the CNT film 100 may contain organic side chain flavins. Since the dispersant is used to prevent agglomeration of CNTs, it generally has a property of adsorbing on the surface of CNTs.
Therefore, by washing with a solvent different from the solvent used for dispersion, the dispersant can be removed in a smaller amount and in a shorter time as compared with the case where the same solvent is used. can.
For example, when organic side chain flavin is used as the dispersant, it may be washed with chloroform as the detergent.
Examples of the cleaning agent include aqueous solutions of water, acid or alkali, chloroform, methylene chloride, N, N-dimethylformamide, tetrahydrofuran, acetone and the like. When sodium cholic acid, sodium deoxycholate, sodium dodecylbenzene sulfonate or the like is used as the dispersant, it is preferable to wash with water or ethanol.

In addition to the method using a cleaning agent, the method for removing the dispersant includes a method of cleaning with a supercritical fluid such as supercritical carbon dioxide, and heating in oxygen to burn, dissolve, evaporate or sublimate the dispersant. Examples thereof include a method, a method of electrochemically oxidizing or reducing the chemical structure to be easily removed, and a method of removing the chemical structure.

[Peeling of CNT film]
Finally, the CNT film 100 is peeled off from the substrate 110 on which the CNT film 100 is formed.
By immersing the substrate 110 on which the CNT film 100 is formed in a solvent and shaking it, the CNT film 100 is peeled off from the substrate 110. As the solvent, a cleaning agent such as an aqueous solution of an acid or an alkali or an organic solvent may be used.
As described above, the CNT film 100 is manufactured.

Hereinafter, the present disclosure will be described in more detail with reference to Examples and the like, but the invention of the present disclosure is not limited to these Examples.
In this example, the measurement of the ratio of the area of the non-uniform region, the measurement of the reflectance of 3σ and the average reflectance, the conversion to the film thickness (optical thickness), and the measurement of the breaking load were performed by the above-mentioned methods.

(Example 1)
[Preparation process]
Single-walled CNTs (crude CNTs, manufactured by Meijo Nanocarbon Co., Ltd., trade name: EC1.5-P, tube diameter: 1 nm) synthesized by the improved direct injection pyrolysis synthesis method (eDIPS method) as crude CNTs containing aggregates. ~ 3 nm, tube length: 100 nm or more, carbon content: 99% by mass) was prepared.

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

~ High speed stirring and dispersion ~
The obtained suspension was subjected to high-speed stirring and dispersion at 10000 rpm at 25 ° C. for 1 hour using a homogenizer (model manufactured by SMT) for 1 hour to carry out a dispersion liquid containing crude CNTs (crude CNT dispersion). Liquid) was obtained.

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

[CNT film manufacturing process]
A purified CNT dispersion was spin-coated on an 8-inch size silicon substrate at a rotation speed of 1500 rpm to obtain a thin film of CNTs on the silicon substrate.
The thin film was washed with water to remove polyacrylic acid in the thin film and dried, and then the silicon substrate was impregnated into water. Next, by leaving only the thin film of CNT in water and taking out only the silicon substrate from water, the thin film of CNT is peeled off from the silicon substrate and has a network structure in a state of floating on the liquid surface of water. A CNT film was manufactured.

[Arrangement]
The CNT film was placed on the silicon substrate by scooping the CNT film floating on the liquid surface of water with an 8-inch size silicon substrate.

In the CNT film obtained in Example 1, the ratio of the area of the non-uniform region was 0.3% or less with respect to the area of the entire region of the film.

(Example 2)
In the [crude CNT dispersion liquid manufacturing step], the obtained suspension is subjected to the following ultrasonic dispersion without high-speed stirring and dispersion, and then defoamed, and the dispersion liquid containing the crude CNT (coarse). The CNT film (pellicle film) was placed on the silicon substrate by the same method as in Example 1 except that the CNT dispersion liquid) was obtained.
[Ultrasonic dispersion]
The suspension obtained in the [crude CNT dispersion liquid production step] was subjected to ultrasonic dispersion at an output of 40% for a total of 2 hours using a probe-type ultrasonic homogenizer. At this time, the ice was cooled every 20 minutes for 5 minutes.

In the CNT film obtained in Example 2, the ratio of the area of the non-uniform region was 0.3% or less with respect to the area of the entire region of the film.

(Comparative Example 1)
Example 1 and Example 1 except that the [CNT film manufacturing step] and the [arrangement] were performed using the crude CNT dispersion obtained in the [crude CNT dispersion manufacturing step] without performing the [purified CNT manufacturing step]. A CNT film having a network structure was placed on the silicon substrate by the same method.

In the CNT film obtained in Comparative Example 1, the ratio of the area of the non-uniform region was 27% with respect to the area of the entire region of the film.

(Comparative Example 2)
Example 2 and Example 2 except that the [CNT film manufacturing step] and the [arrangement] were performed using the crude CNT dispersion obtained in the [crude CNT dispersion manufacturing step] without performing the [purified CNT manufacturing step]. By the same method, a CNT film (pellicle film) having a network structure was placed on the silicon substrate.

In the CNT film obtained in Comparative Example 2, the ratio of the area of the non-uniform region was 43% with respect to the area of the entire region of the film.

(Comparative Example 3)
The [CNT film manufacturing process] and the [arrangement] were performed using the crude CNT dispersion obtained in the [crude CNT dispersion manufacturing step] without performing the [purified CNT manufacturing step].
In the [crude CNT dispersion liquid production step], 70 mL of isopropyl alcohol and 30 mL of ethanol were changed to 100 mL of toluene, and 50 mg of organic side chain flavin was added as a dispersant. A CNT film having a network structure was placed on the top.

In the CNT film obtained in Comparative Example 3, the ratio of the area of the non-uniform region was 35% with respect to the area of the entire region of the film.

-Evaluation-
~ Average reflectance and reflectance of 3σ ~
In the reflectance measurement, the positions of X = 5 mm, 25 mm, 50 mm, 75 mm and 95 mm were selected as the measurement positions.
The average reflectance and reflectance of 3σ at the measurement points at each of the selected positions were measured. The results are shown in Table 2.

~ Average value of film thickness and 3σ of film thickness ~
By the method described above, the average value of the 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. Moreover, the average thickness was obtained by averaging the average value of the film thickness at each measurement position. The results are shown in Table 2.

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

~ Breaking load ~
The breaking load of the obtained CNT film was measured by a nanoindentation test. The results are shown in Table 3.

The CNT film of Example 1 produced by using the CNT film manufacturing method including the preparation step, the crude CNT dispersion liquid manufacturing step, the purified CNT manufacturing step, and the CNT film manufacturing step has an area of a non-uniform region. The ratio was small and the thickness uniformity was excellent.

In the CNT film of Example 2 in which the following ultrasonic dispersion was performed on the suspension obtained in the [crude CNT dispersion liquid production step], the ratio of the area of the non-uniform region was further smaller, and the thickness was uniform. It was excellent.
Further, in the CNT film of Example 2, the reflectance of 3σ was 15% or less at all the measurement positions, and the difference between the maximum value and the minimum value of the average reflectance was 15% or less.
When the CNT film of Example 2 was arranged on the silicon substrate and observed with an optical microscope, a slightly faint light and shade distribution was observed, but lumps or aggregates could not be observed, and non-uniform regions could be visually recognized. There wasn't.
In the CNT film of Example 2, the average value of the film thickness was small, and the variation in the film thickness of 3σ was also small. Therefore, it was shown that the CNT film of Example 2 has little variation in film thickness in both a local region and a wide region. That is, it was shown that the CNT film of Example 1 was excellent in thickness uniformity.

The CNT film of Comparative Example 1 in which the [purified CNT manufacturing process] was not performed had a large proportion of the area of the non-uniform region and was inferior in thickness uniformity.

The CNT film of Comparative Example 2 in which the following ultrasonic dispersion was performed on the suspension obtained in the [crude CNT dispersion liquid production step] but the [purified CNT production step] was not performed has a non-uniform region. The ratio of the area was large, and the uniformity of the thickness was inferior.
Further, in the CNT film of Comparative Example 2, the reflectance of 3σ was 15% or more at all the measurement positions, and the difference between the maximum value and the minimum value of the average reflectance was 10% or more.
As for the CNT film of Comparative Example 2, when the CNT film arranged on the silicon substrate was observed with an optical microscope, a clear shading distribution was observed on the entire surface, lumps or aggregates were observed on the entire surface, and non-uniform regions were observed. I was able to see it.
The CNT film of Comparative Example 2 had variations in film thickness in a local region, and was inferior in thickness uniformity.

The CNT film of Comparative Example 3 in which the [purified CNT manufacturing process] was not performed had a large proportion of the area of the non-uniform region and was inferior in thickness uniformity.

FIG. 11 shows an image of the surface of the CNT film according to Example 1 observed using an optical microscope.
In FIG. 11, although a slightly light shading distribution was observed, lumps or aggregates could hardly be observed, and non-uniform regions could not be visually recognized.

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, lumps or aggregates were observed, and non-uniform regions could be visually recognized.

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 the CNT bundles were dispersed in a mesh pattern was observed.

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 manufacturing process] was performed, bundles having a width of 50 nm or more were not included, and the uniformity of the bundle diameter distribution was improved. On the other hand, in Comparative Example 2 in which the [purified CNT manufacturing process] was not performed, a bundle having a width of 50 nm or more was included, and the uniformity of the bundle diameter distribution was inferior.

The CNT film of Example 1 subjected to the [high-speed stirring step] is G / D obtained from Raman spectroscopy as compared with Example 2 obtained by performing the [ultrasonic dispersion step] without performing the [high-speed stirring step]. The ratio value was higher and was superior to the film strength measured by the nanoindentation test.

100 ... CNT (carbon nanotube) film 101 ... CNT aggregate 102 ... CNT
110 ... Substrate 120 ... Underlayer

Claims (10)

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 of 10% or more thicker or 10% or more thinner than the average thickness, is 15.0% or less with respect to the area of the entire region of the film.
A carbon nanotube film having a reflectance of 3σ of 15% or less when the reflectance is measured under the following conditions using a reflection spectroscopic film thickness meter placed on a silicon substrate.
<Conditions>
Diameter of measurement point: 20 μm
Reference measurement wavelength: Wavelength 285 nm
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm When the reflectance is measured and the average reflectance is calculated under the following conditions using a reflection spectroscopic membrane thickness gauge at each of a plurality of measurement positions separated from each other by 2 cm or more on a silicon substrate.
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
Reference measurement wavelength: Wavelength 285 nm
Number of measurement points: 121 points Distance between center points at adjacent measurement points: 40 μm The carbon nanotube membrane according to claim 1 or 2, which has a network structure. The carbon nanotube film according to any one of claims 1 to 3, wherein the carbon nanotube has a tube diameter of 0.8 nm or more and 6.0 nm or less. The carbon nanotube film according to any one of claims 1 to 4, wherein the carbon nanotube has a length of 10 nm or more. The carbon nanotube film according to any one of claims 1 to 5, wherein the content of carbon contained in the carbon nanotubes is 98% by mass or more with respect to the total mass of the carbon nanotubes. The carbon nanotube film according to any one of claims 1 to 6, wherein the G / D ratio measured by the resonance Raman scattering measurement method is 20 or more. The carbon nanotube membrane according to any one of claims 1 to 7, wherein the breaking load measured by the nanoindentation test is 1.0 μN / nm or more. The dispersion liquid used for producing the carbon nanotube film according to any one of claims 1 to 8. The process of preparing crude carbon nanotubes containing aggregates and
A step of mixing the crude carbon nanotubes and a solvent to obtain a dispersion liquid, and
A step of removing the aggregates contained in the dispersion liquid to obtain purified carbon nanotubes, and
A method for producing a carbon nanotube film, which comprises a step of forming a sheet of the purified carbon nanotube to produce a carbon nanotube film.

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