carbon film

Abstract

The purpose of the present invention is to provide a carbon film having excellent electromagnetic shielding performance. This carbon film is formed from carbon nanotube aggregates, and is characterized in that, when a scattering profile obtained by ultrasmall angle X-ray scattering analysis of at least one surface of the carbon film is fitted to the Beaucage equation, the fractal dimension in the wave number range from 0.0001 (1 / Å) to 0.001 (1 / Å) is 2.6-4, and the porosity is 80-95%.

Description

[Technical Field]

[0001] The present invention relates to a carbon film, and more particularly to a carbon film having excellent electromagnetic wave shielding properties. [Background technology]

[0002] In recent years, carbon nanotubes (hereinafter sometimes referred to as "CNTs") have attracted attention as a material with excellent electrical conductivity, thermal conductivity, and mechanical properties. However, because CNTs are minute structures with diameters on the order of nanometers, they are difficult to handle and process when used alone. Therefore, in order to ensure ease of handling and processability and to use them in various applications, carbon films have traditionally been formed by forming aggregates of multiple CNTs (hereinafter referred to as "carbon nanotube aggregates") into films (see, for example, Patent Document 1).

[0003] In Patent Document 1, pores with a pore size of 400 nm or more and 1500 nm or less measured by mercury intrusion porosimetry have a Log differential pore volume of 0.006 cm 3 A carbon film having excellent mechanical strength is formed by using an aggregate of carbon nanotubes having a region of 10 nm or more where the carbon nanotube density is 10 nm or less / g or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-145027 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, electromagnetic wave shielding has attracted attention as an application of carbon films. However, there is still room for further improvement in the electromagnetic wave blocking performance, i.e., electromagnetic wave shielding performance, of the conventional carbon films. Therefore, an object of the present invention is to provide a carbon film having excellent electromagnetic wave shielding performance. [Means for solving the problem]

[0006] The present inventors have conducted extensive research to achieve the above object. They have investigated the microscopic properties of a carbon film formed using an aggregate of carbon nanotubes. As a result, they have newly discovered that a carbon film can effectively shield electromagnetic waves when predetermined parameters obtained by performing predetermined data processing on an ultra-small angle X-ray scattering curve (profile) of the surface of the carbon film made of an aggregate of carbon nanotubes satisfy predetermined conditions and the porosity is a predetermined value, thereby completing the present invention.

[0007] That is, the present invention has an object to advantageously solve the above-mentioned problems, and the carbon film of the present invention is a carbon film made of an aggregate of carbon nanotubes, characterized in that, when a scattering profile obtained by performing ultra-small angle X-ray scattering measurement on at least one surface of the carbon film is fitted to the Beaucage equation, the fractal dimension is 2.6 or more and 4 or less in the wavenumber range of 0.0001 (1 / Å) or more and 0.04 (1 / Å) or less, and the porosity is 80% or more and 95% or less. A carbon film having such a configuration can exhibit excellent electromagnetic wave shielding performance.

[0008] In the present invention, the ultra-small angle X-ray scattering profile of the surface of the carbon film can be obtained by the method described in the Examples. Fitting of the ultra-small angle X-ray scattering profile using the Beaucage equation can be performed by the method described in the Examples of this specification. Furthermore, the porosity of the carbon film can be measured by the method described in the Examples of this specification.

[0009] Here, when a scattering profile obtained by performing ultra-small angle X-ray scattering measurement on at least one surface of the carbon film is fitted to the Beaucage equation, the size of the carbon nanotube aggregates in the wave number range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less is 1.0 × 10 5 Å or ​​more 4.0×10 7It is preferable that the size of the CNT aggregates in the above-mentioned predetermined wave number range is within the above-mentioned predetermined range, the electromagnetic wave shielding performance of the carbon film can be further improved.

[0010] The carbon film is preferably a self-supporting film. A self-supporting carbon film has excellent handleability and can improve the degree of freedom in arranging the sheet when used, for example, as an electromagnetic wave shielding sheet. In the present invention, the term "self-supporting film" refers to a film that can independently maintain its film shape without being damaged even in the absence of a support, and a single-layer carbon film is particularly preferred.

[0011] The carbon film preferably has a thickness of 5 μm or more and 1000 μm or less. If the thickness is 5 μm or more, the carbon film can have sufficient mechanical strength and can exhibit even better electromagnetic wave shielding performance. On the other hand, if the thickness is 1000 μm or less, the carbon film can be made lighter. In the present invention, the "thickness" of the carbon film can be measured using the method described in the examples of this specification.

[0012] The carbon film preferably has a transmission attenuation rate of 20 dB or more at at least one frequency in the range of 1 GHz to 10 GHz. A carbon film having a transmission attenuation rate of 20 dB or more at at least one frequency in the range of 1 GHz to 10 GHz has even better electromagnetic wave shielding performance. In the present invention, the transmission attenuation rate can be measured by the method described in the examples of this specification.

[0013] The carbon film may be used for any purpose, but may be advantageously used, for example, as an electromagnetic wave shielding sheet. [Effects of the Invention]

[0014] According to the present invention, a carbon film having excellent electromagnetic wave shielding performance can be provided. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows an SEM image of the surface of the carbon film of Example 1. [Figure 2]1 shows a graph obtained by fitting the ultra-small angle X-ray scattering profile of the surface of the carbon film of Example 1 to the Beaucage equation. [Figure 3] 1 shows a graph obtained by fitting the ultra-small angle X-ray scattering profile of the surface of the carbon film of Comparative Example 2 to the Beaucage equation. [Figure 4] 1 shows an SEM image of an example of a CNT aggregate that can be used in the carbon film of the present invention. [Figure 5] 1 shows an FIR resonance chart obtained for the CNT aggregate 1 used in each example of the present invention. [Figure 6] 1 shows a pore distribution curve of the CNT aggregate 1. [Figure 7A] 1 shows an SEM image of the CNT aggregate 1. [Figure 7B] 7B shows the two-dimensional spatial frequency spectrum of the SEM image of FIG. 7A. [Figure 8] 1 shows a schematic configuration of a manufacturing device for the CNT aggregate 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] The carbon film according to the embodiment of the present invention will be described in detail below.

[0017] (carbon film) The carbon film of the present invention is a carbon film composed of an aggregate of carbon nanotubes, and when a scattering profile obtained by performing ultra-small angle X-ray scattering measurement on at least one surface of the carbon film is fitted to the Beaucage equation, the carbon film has a fractal dimension of 2.6 or more and 4 or less in a wavenumber range of 0.0001 (1 / Å) or more and 0.04 (1 / Å) or less, and a porosity of 80% or more and 95% or less.

[0018] The carbon nanotube aggregate is configured to include a plurality of carbon nanotubes. In the carbon film, the proportion of CNTs in the carbon film is preferably 95 mass % or more, more preferably 98 mass % or more, even more preferably 99 mass % or more, particularly preferably 99.5 mass % or more, and most preferably 100 mass % (i.e., the carbon film is composed only of CNTs). Note that the carbon film may contain various additives (for example, dispersants) as components other than the carbon nanotube aggregate, and may also contain components that are inevitably mixed in during the manufacturing process of the carbon film.

[0019] Below, we will explain a method for finding the fractal dimension by fitting the Beaucage equation to the ultra-small angle X-ray scattering profile of a carbon film.

[0020] <Ultra small angle X-ray scattering measurement> First, ultra-small-angle X-ray scattering measurement is performed on the surface of the carbon film to obtain a scattering image. In the present invention, the ultra-small-angle X-ray scattering measurement is performed with a wavenumber q of 0.0001 (1 / Å) to 0.04 (1 / Å), an X-ray energy of 10 keV (0.124 nm), a beamline of SPrimg-8 BL24XU, an APD (avalanche photodiode) detector, and an apparatus of Bonse & Hart USAXS. Then, a scattering profile is obtained with the wavenumber q on the horizontal axis and the scattering intensity I(q) on the vertical axis.

[0021] <Scattering profile fitting> The obtained scattering profile is then fitted using the Beaucage equation. Fitting of a scattering profile using the Beaucage equation is conventionally known and can be performed, for example, according to the method described in G. Beaucage, J. Appl. Cryst., 28, 717 (1995). Fitting can be performed using analysis software such as Igor Pro 8 (WaveMetrics).

[0022] Specifically, the obtained scattering profile is fitted using the Beaucage equation represented by the following general formula (I) within the wavenumber range of 0.0001 (1 / Å) to 0.04 (1 / Å).

number

[0023] In the general formula (I), q is the wave number (1 / Å), I(q) is the scattering intensity at wave number q, Bkgd is the background, and G i and B i is the proportionality constant, P i is the fractal dimension at layer i, R g,i is the length of the structure at layer i, and N is the number of layers.

[0024] As described above, by fitting the scattering profile using the general formula (I), the fractal dimension P i can be obtained. In the present invention, if the fractal dimension P1 for i=1 is within the range of 2.6 or more and 4 or less, it is determined that "the fractal dimension in the wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less is 2.6 or more and 4 or less."

[0025] In the ultra-small angle X-ray scattering profile of the carbon film of the present invention, (1) scattering due to the size of CNT aggregates (R g,1 ), (2) Scattering due to the bundle diameter of CNTs (R g,2 ), and (3) scattering due to the persistence length of a single CNT (R g,3 ) can be observed. Since three scatterings are observed in this way, it is preferable to perform fitting with the number of layers set to 3. For example, in the wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less, (1) scattering due to the size of CNT aggregates (R g,1 ) in the wavenumber range of 0.001 (1 / Å) to 0.01 (1 / Å) is due to (2) scattering from the CNT bundle, and in the wavenumber range of 0.01 (1 / Å) to 0.04 (1 / Å) is due to (3) scattering from the persistence length of a single CNT (R g,3) is observed. In addition, the size of the CNT aggregates (R g,1 ) can be analyzed.

[0026] When a scattering profile obtained by performing ultra-small-angle X-ray scattering measurement on at least one surface of a carbon film is fitted to the Beaucage equation, the reason why a carbon film having a fractal dimension of 2.6 or more and 4 or less in the wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less can exhibit excellent electromagnetic wave shielding performance is not clear, but it is presumed to be as follows. That is, the fractal dimension is an index indicating the size of the CNT aggregates that form the carbon film, and it is presumed that a carbon film having a fractal dimension of 2.6 or more and 4 or less in the wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less has well-formed CNT aggregates. Furthermore, it is presumed that the electromagnetic waves are diffusely reflected well in the gaps between the aggregates, thereby attenuating the energy of the electromagnetic waves that penetrate the carbon film, and that this allows the carbon film of the present invention to exhibit excellent electromagnetic wave shielding performance. If the fractal dimension in the wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less exceeds 4, CNT aggregates are not formed well, making it difficult for diffuse reflection of electromagnetic waves to occur in the gaps between the aggregates, and it is presumed that this will result in a deterioration in electromagnetic wave shielding performance. Also, if the fractal dimension in the wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less is less than 2.6, it is presumed that aggregates will not form and electromagnetic wave shielding performance will deteriorate.

[0027] Furthermore, when the ultra-small angle X-ray scattering profile of the carbon film of the present invention is fitted by the above-mentioned predetermined method, the size of the CNT aggregates in the wave number range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less is 1.0 × 10 5 Å or ​​more, and preferably 1.0×10 6 Å or ​​more is more preferable, and 5.0×10 6 Å or ​​more, and more preferably 4.0×10 7Å or ​​less, and preferably 2.0×10 7 It is preferable that the size of the CNT aggregates in the above-mentioned predetermined wave number range is within the above-mentioned predetermined range, the electromagnetic wave shielding performance of the carbon film can be further improved.

[0028] Here, the wavy structure of the carbon film described above will be explained. Fig. 1 is an SEM image of the surface of the carbon film according to Example 1, which will be described later. As shown in Fig. 1, a wavy structure is formed on the surface of the carbon film of Example 1, which has a fractal dimension of 2.6 or more and 4 or less within a predetermined wave number range.

[0029] In addition, the fractal dimension P in the general formula (I) i corresponds to the absolute value of the slope of the linear portion of the graph obtained by fitting the scattering profile to the Beaucage equation. FIG. 2 shows a graph obtained by fitting the ultra-small-angle X-ray scattering profile of the surface of a carbon film according to Example 1 (described later) to the Beaucage equation. FIG. 3 shows a graph obtained by fitting the ultra-small-angle X-ray scattering profile of the surface of a carbon film according to Comparative Example 2 (described later) to the Beaucage equation. In FIG. 2, the absolute value of the slope of the linear portion in the wavenumber range of 0.0001 (1 / Å) to 0.001 (1 / Å) is greater than the absolute value of the slope of the linear portion in the wavenumber range of 0.0001 (1 / Å) to 0.001 (1 / Å) in FIG. 3. That is, in the graph of FIG. 2, the slope of the linear portion in the wavenumber range of 0.0001 (1 / Å) to 0.001 (1 / Å) is steep, and it can be seen that the fractal dimension is closer to 4, i.e., the aggregates are large.

[0030] From the viewpoint of further improving the electromagnetic wave shielding performance, the carbon film of the present invention preferably has the fractal dimension of 2.7 or more, more preferably 2.8 or more, and preferably 3.9 or less, more preferably 3.7 or less, in a wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less. Furthermore, the carbon film of the present invention preferably has the fractal dimension of 2.6 or more and 4 or less, in a wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less, for both surfaces of the carbon film.

[0031] In the carbon film of the present invention, the fractal dimension can be controlled, for example, by adjusting the CNT dispersion conditions (dispersion strength, dispersion time, presence or absence of a dispersant, etc.) when preparing a CNT dispersion liquid described below, and by controlling the CNT bundle length described below, etc. For example, when CNTs are dispersed using a stirring blade, the CNT bundle length can be changed by changing the rotation speed (rpm) of the stirring blade and / or the dispersion time and / or the shape of the stirring blade.

[0032] The carbon membrane of the present invention has a porosity of 80% or more and 95% or less. For example, the porosity of a carbon membrane can be determined as follows: A test piece is prepared by cutting the produced carbon membrane into a 1 cm square, the mass (g) of the test piece is measured, and the density (bulk density) of the carbon membrane is calculated by the following formula (1). Next, the porosity of the carbon membrane can be calculated by the following formula (2) using the obtained bulk density. Bulk density of carbon film (g / cm 3 ) = mass of test piece (g) / (1cm 2 × thickness of test piece (cm) (1) Porosity = (1 - (bulk density of carbon membrane (g / cm 3 ) / 1.3))×100···(2) The "1.3" in formula (2) is the true density of carbon (g / cm 3 ) refers to

[0033] By making the porosity of the carbon film 80% or more, the electromagnetic wave absorption properties of the carbon film can be improved, and by making the porosity 95% or less, the carbon film can be sufficiently maintained in its self-supporting state, and a carbon film with good handleability and processability can be provided.

[0034] <Electromagnetic wave shielding performance> The carbon film of the present invention preferably has a transmission attenuation rate of 25 dB or more at at least one frequency in the range of 1 GHz to 10 GHz, and more preferably 25 dB or more over the entire range of 1 GHz to 10 GHz. A carbon film having a transmission attenuation rate of 25 dB or more over the entire range has even better electromagnetic wave shielding performance and can therefore be used more advantageously as an electromagnetic wave shielding sheet.

[0035] <Thickness> The thickness of the carbon film of the present invention is preferably 5 μm or more, more preferably 10 μm or more, and is preferably 1000 μm or less, and more preferably 700 μm or less. If the thickness is 5 μm or more, the carbon film can have sufficient mechanical strength and can exhibit even better electromagnetic wave shielding performance. On the other hand, if the thickness is 1000 μm or less, the carbon film can be made lighter. The thickness of the carbon membrane of the present invention may be 150 μm or more, 200 μm or more, or 300 μm or more, or may be 600 μm or less, 300 μm or less, or 200 μm or less.

[0036] (Method of manufacturing carbon film) The carbon film of the present invention can be produced by forming an aggregate of carbon nanotubes into a film, by satisfying at least one of the following (A) and (B). (A) As the CNT aggregate, a CNT aggregate that satisfies at least one of the conditions (1) to (3) described below is used. (B) Prior to forming a film from the CNT aggregate, the CNT aggregate is subjected to a dry pulverization process.

[0037] <CNT aggregate> Here, as the CNT aggregate used for preparing the carbon film, it is preferable to use a novel CNT aggregate that satisfies at least one of the conditions (1) to (3). A carbon film composed of a CNT aggregate that satisfies at least one of the following conditions (1) to (3) has excellent electromagnetic wave shielding performance.

[0038] Condition (1): For a carbon nanotube dispersion obtained by dispersing a carbon nanotube aggregate so that the bundle length is 10 μm or more, in the spectrum obtained by Fourier transform infrared spectroscopic analysis, the peak based on the plasmon resonance of the carbon nanotube dispersion is at a wave number of 300 cm -1 more than 2000 cm -1 There is at least one in the following range. Condition (2): For a carbon nanotube aggregate, in the pore size distribution curve showing the relationship between the pore size and the Log differential pore volume obtained based on the Barrett-Joyner-Halenda method from the adsorption isotherm at 77 K of liquid nitrogen, the maximum peak is in the range where the pore size is more than 100 nm and less than 400 nm. Condition (3): The peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is at 1 μm -1 or more and 100 μm -1 There is at least one in the following range.

[0039] The reason why a carbon film made of a CNT aggregate satisfying at least one of the above conditions (1) to (3) has excellent electromagnetic wave shielding performance is not clear, but it is presumed to be as follows. FIG. 4 shows a scanning electron microscope (SEM) image of an example of a CNT aggregate satisfying at least one of the above conditions (1) to (3). As shown in FIG. 4, the CNTs constituting the CNT aggregate satisfying at least one of the above conditions (1) to (3) have a wave-like structure. It is believed that this "wave-like structure" causes diffuse reflection of electromagnetic waves between the CNTs constituting the CNT aggregate. It is presumed that the energy of the electromagnetic waves is lost in the process of this diffuse reflection, and that this result is reflected in high electromagnetic wave shielding performance. Below, the above conditions (1) to (3) that the CNT aggregate of the present invention can satisfy are each described in detail.

[0040] <<Condition (1)>> Condition (1) is that "in a spectrum obtained by Fourier transform infrared spectroscopy of a carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more, a peak due to the plasmon resonance of the carbon nanotube dispersion is at a wave number of 300 cm -1 Super 2000cm -1The present invention defines that at least one of the following characteristics is present in the following range: "CNTs have long been known to have strong absorption characteristics in the far-infrared region as an optical property. It is believed that this strong absorption characteristic in the far-infrared region is due to the diameter and length of the CNTs. The absorption characteristics in the far-infrared region, more specifically, the relationship between the peak due to the plasmon resonance of CNTs and the length of the CNTs, have been discussed in detail in a non-patent document (T. Morimoto et al., "Length-Dependent Plasmon Resonance in Single-Walled Carbon Nanotubes," pp. 9897-9904, Vol. 8, No. 10, ACS NANO, 2014). Based on the discussions in the non-patent document and our own findings, the present inventors speculated that the position at which the peak due to the plasmon resonance of CNTs is detected in a spectrum obtained by Fourier transform infrared spectroscopy analysis may be affected in some way by the distance between defects in the CNTs, and conducted verification of this assumption. The inventors then discovered that the position at which the peak based on the plasmon resonance of the CNT is detected can serve as an indicator corresponding to the distance between bending points in a CNT having a wavy structure, and set the above-mentioned condition (1).

[0041] Under condition (1), the wave number is 300 cm -1 Super 2000cm -1 Within the following range, preferably within the wavenumber range of 500 cm -1 More than 2000cm -1 In the range below, preferably in the range of 700 cm -1 More than 2000cm -1 If a peak due to the plasmon resonance of CNTs exists within the following range, such CNTs can exhibit good electromagnetic wave shielding performance when a carbon film is formed thereon.

[0042] Fig. 5 shows a spectrum (FIR resonance chart) obtained by Fourier transform infrared spectroscopy of the CNT aggregate according to one example. As is clear from Fig. 5, in the obtained spectrum, in addition to a relatively gentle peak due to the plasmon resonance of the CNT dispersion, there is a peak at a wave number of 840 cm -1 Near 1300cm -1 and around 1700 cm -1 It can be seen that sharp peaks are observed around the wavelength of 840 cm. These sharp peaks do not correspond to "peaks based on plasmon resonance of the carbon nanotube dispersion," but each corresponds to infrared absorption due to functional groups. More specifically, -1 The sharp peak near 1300 cm is due to the CH out-of-plane bending vibration; -1 The sharp peak around 1700 cm is due to the epoxy three-membered ring stretching vibration; -1 The sharp peak around 2000 cm is due to the C=O stretching vibration. -1 In the region above 2000, a peak similar to the S1 peak is detected in addition to the plasmon resonance, as mentioned in the non-patent document by T. Morimoto et al., and therefore the inventors set the upper limit for determining the presence or absence of a peak based on the plasmon resonance of the CNT dispersion under condition (1) to 2000. -1 cm or less.

[0043] Here, in condition (1), when obtaining a spectrum by Fourier transform infrared spectroscopy, it is necessary to obtain a CNT dispersion by dispersing the CNT aggregate so that the bundle length is 10 μm or more. Here, for example, by blending CNT aggregates, water, and a surfactant (e.g., sodium dodecylbenzenesulfonate) in an appropriate ratio and stirring the mixture for a predetermined time using ultrasound or the like, a dispersion liquid in which CNT dispersions with bundle lengths of 10 μm or more are dispersed in water can be obtained.

[0044] The bundle length of a CNT dispersion can be obtained by analysis using a wet image analysis particle size measuring device. This measuring device can calculate the area of ​​each dispersion from an image obtained by photographing the CNT dispersion, and obtain the diameter of a circle having the calculated area (hereinafter, also referred to as the ISO area diameter). In this specification, the bundle length of each dispersion is defined as the ISO area diameter value obtained in this manner.

[0045] <<Condition (2)>> Condition (2) specifies that "the maximum peak in the pore size distribution curve is in the range of pore size greater than 100 nm and less than 400 nm." The pore size distribution of a carbon nanotube aggregate can be determined based on the BJH method from the adsorption isotherm of liquid nitrogen at 77 K. The fact that the peak in the pore size distribution curve obtained by measuring the carbon nanotube aggregate is in the range of greater than 100 nm means that there are voids of a certain size between the CNTs in the carbon nanotube aggregate, and the CNTs are not in an excessively densely aggregated state. The upper limit of 400 nm is the measurement limit of the measurement device (BELSORP-mini II) used in the examples.

[0046] Here, from the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, the value of the Log differential pore volume at the maximum peak of the pore distribution curve of the CNT aggregate is set to 2.0 cm 3 / g or more is preferable.

[0047] <<Condition (3)>> Condition (3) is that the peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is 1 μm -1 More than 100μm -1At least one of the following conditions exists in the range below." Whether or not this condition is satisfied can be determined as follows. First, the CNT aggregate to be determined is observed at a magnification (for example, 10,000 times) using an electron microscope (for example, a field emission scanning electron microscope), and multiple electron microscope images (for example, 10 images) are obtained in a field of view of 1 cm square. A fast Fourier transform (FFT) is performed on the multiple electron microscope images obtained, and a two-dimensional spatial frequency spectrum is obtained. The two-dimensional spatial frequency spectrum obtained for each of the multiple electron microscope images is binarized to find the average value of the peak positions that appear on the highest frequency side. If the average value of the obtained peak positions is less than 1 μm -1 More than 100μm -1 If the value is within the range below, it is determined that the condition (3) is satisfied. Here, the "peak" used in the above determination is a clear peak obtained by performing the extraction process of isolated points (i.e., the reverse operation of the isolated point removal). Therefore, when the extraction process of isolated points is performed, -1 More than 100μm -1 If no clear peak is obtained within the range below, it is determined that condition (3) is not satisfied.

[0048] Here, from the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, the peak of the two-dimensional spatial frequency spectrum is set to 2.6 μm -1 More than 100μm -1 It is preferred that it is in the following range:

[0049] From the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, it is preferable that the CNT aggregate satisfies at least two of the above conditions (1) to (3), and it is more preferable that it satisfies all of the conditions (1) to (3).

[0050] <<Other properties>> In addition to the above conditions (1) to (3), the CNT aggregate that can be used to form the carbon film of the present invention preferably has the following properties.

[0051] For example, the CNT aggregate preferably has a total specific surface area according to the BET method of 600 m 2 / g or more, more preferably 800m 2 / g or more, more preferably 900m 2 / g or more, preferably 2600m 2 / g or less, more preferably 1400m 2 / g or less. Furthermore, in the case of the opening treatment, 2 / g or more is preferable. CNT aggregates with a high specific surface area can more effectively diffusely reflect electromagnetic waves inside the carbon film, thereby further improving the electromagnetic wave shielding performance of the carbon film. The CNT aggregate is primarily single-walled CNTs, and may also contain double-walled CNTs or multi-walled CNTs to the extent that their functionality is not impaired. The total specific surface area of ​​CNTs measured by the BET method can be measured, for example, using a BET specific surface area measurement device in accordance with JIS Z8830.

[0052] Furthermore, the average length of the CNTs constituting the CNT aggregate is preferably 10 μm or more and 10 cm or less, more preferably 100 μm or more and 2 cm or less, and even more preferably 150 μm or more and 2 cm or less. When the average length of the CNTs constituting the CNT aggregate is 10 μm or more, aggregation of adjacent CNT bundles is prevented, enabling easy dispersion. When the average length of the CNTs constituting the CNT aggregate is 10 μm or more, CNTs easily form a network, making the aggregate suitable for applications requiring electrical conductivity or mechanical strength. When the average length of the CNTs constituting the CNT aggregate is 10 cm or less, production can be completed in a short time, suppressing the adhesion of carbon-based impurities and improving the specific surface area. When the average length of the CNTs constituting the CNT aggregate is 2 cm or less, dispersion is easier. The average length of the CNTs can be determined by measuring the length of 100 randomly selected CNTs using a scanning electron microscope (SEM).

[0053] The tapped bulk density of the CNT aggregate is 0.001 g / cm 3 More than 0.2g / cm 3Preferably, it is 0.02 g / cm or less. 3 More than 0.2g / cm 3 It is more preferable that the tap bulk density of the CNT aggregate is 0.2 g / cm or less. CNT aggregates in this density range have excellent dispersibility because the bonds between the CNTs are not excessively strong, and can be molded into various shapes. 3 If the tap bulk density of the CNT aggregate is less than 0.001 g / cm, the bonds between the CNTs will be weak, making it easier to disperse the CNT aggregate homogeneously when stirred in a solvent or the like. 3 If this is the case, the integrity of the CNT aggregate will be improved and handling will be easier. Tapped bulk density is the apparent bulk density when powdered CNT aggregates are filled into a container and then tapped or vibrated to reduce the voids between the powder particles, resulting in a densely packed state.

[0054] Furthermore, the average outer diameter of the CNTs constituting the CNT aggregate is preferably 0.5 nm or more, more preferably 1.0 nm or more, and preferably 15.0 nm or less, more preferably 10.0 nm or less, even more preferably 5.0 nm or less, and even more preferably 4.0 nm or less. If the average outer diameter of the CNTs is 0.5 nm or more, bundling of the CNTs can be reduced, maintaining a high specific surface area. If the average outer diameter of the CNTs is 15.0 nm or less, the proportion of multi-walled CNTs can be reduced, maintaining a high specific surface area. Here, the average outer diameter of the CNTs can be determined by measuring the diameter (outer diameter) of 100 randomly selected CNTs using a transmission electron microscope (TEM). The average diameter (Av) and standard deviation (σ) of the CNTs can be adjusted by changing the CNT manufacturing method and manufacturing conditions, or by combining multiple types of CNTs obtained by different manufacturing methods.

[0055] The G / D ratio of a CNT aggregate is preferably between 1 and 50. A CNT aggregate with a G / D ratio of less than 1 is thought to have low single-walled CNT crystallinity, a lot of contamination such as amorphous carbon, and a high content of multi-walled CNTs. Conversely, a CNT aggregate with a G / D ratio of more than 50 is highly linear, and the CNTs tend to form bundles with few gaps, which may reduce the specific surface area. The G / D ratio is an index commonly used to evaluate the quality of CNTs. The Raman spectrum of CNTs measured with a Raman spectrometer contains the G band (1600 cm -1 around 1350 cm -1 A vibration mode called the G band (near the G band) is observed. The G band is a vibration mode originating from the hexagonal lattice structure of graphite, which is the cylindrical surface of the CNT, and the D band is a vibration mode originating from the amorphous part. Therefore, the higher the peak intensity ratio of the G band to the D band (G / D ratio), the higher the CNT's crystallinity (linearity) can be evaluated.

[0056] To obtain a high specific surface area, it is desirable that the purity of the CNT aggregate be as high as possible. Purity here refers to carbon purity, a value that indicates what percentage of the mass of the CNT aggregate is made up of carbon. There is no upper limit to the purity required to obtain a high specific surface area, but in terms of manufacturing, it is difficult to obtain a CNT aggregate of 99.9999 mass% or more. If the purity is less than 95 mass%, it will be difficult to obtain a CNT aggregate of 1000m without being subjected to aperture treatment. 2 / g。 Furthermore, if the carbon purity is less than 95 mass % due to the inclusion of metal impurities, the metal impurities will react with oxygen during the opening treatment, preventing the opening of the CNTs, making it difficult to increase the specific surface area. From these points of view, it is preferable that the purity of the single-walled CNTs is 95 mass % or more. A predetermined CNT aggregate that satisfies at least one of the above conditions (1) to (3) can have a purity of typically 98% by mass or more, preferably 99% by mass or more, without purification treatment. The CNT aggregate contains almost no impurities and can fully exhibit the inherent properties of CNT. The carbon purity of the CNT aggregate can be determined by elemental analysis using fluorescent X-rays, thermogravimetric analysis (TGA), or the like.

[0057] <<Method for manufacturing CNT aggregate>> The method for manufacturing a CNT aggregate is not particularly limited, and the manufacturing conditions can be adjusted according to the desired properties. For example, when manufacturing a CNT aggregate that satisfies at least any one of the above-mentioned conditions (1) to (3), it is necessary that the conditions during the growth of the CNT aggregate satisfy all of the following (a) to (c). (a) The growth rate of the CNT aggregate is 5 μm / min or more. (b) The concentration of the catalyst activator substance in the growth atmosphere of the CNT aggregate is 4% by volume or more. (c) When the CNT aggregate grows, there are obstacles in the growth direction of the CNTs constituting the CNT aggregate.

[0058] And, by the manufacturing method that satisfies all of the above-mentioned (a) to (c), a CNT aggregate that satisfies at least any one of the above-mentioned conditions (1) to (3) can be efficiently manufactured. Furthermore, in such a manufacturing method, as long as the conditions (a) to (c) are satisfied during the growth of the CNT aggregate, without being particularly limited, a known CNT synthesis process such as a fluidized bed method, a moving bed method, and a fixed bed method can be adopted. Here, the fluidized bed method means a synthesis method for synthesizing CNTs while fluidizing a granular carrier (hereinafter, also referred to as a granular catalyst carrier) carrying a catalyst for synthesizing CNTs. Also, the moving bed method and the fixed bed method mean synthesis methods for synthesizing CNTs without flowing a carrier (particulate carrier or plate-like carrier) carrying a catalyst.

[0059] In one example, the manufacturing method that satisfies all of the above-mentioned (a) to (c) includes a catalyst carrier forming step for forming a catalyst carrier, a CNT synthesis step for synthesizing CNTs using the catalyst carrier obtained in such a catalyst carrier forming step, and a recovery step for recovering the CNTs synthesized in such a CNT synthesis step. And, the catalyst carrier forming step can be carried out according to a known catalyst carrying method, wet or dry. Also, the recovery step can be carried out using a known separation and recovery device such as a classifier.

[0060] [CNT synthesis process] In the CNT synthesis process, all of the above conditions (a) to (c) are satisfied during CNT growth. Specifically, the condition (a) that "the growth rate of carbon nanotube aggregates is 5 μm / min or more" can be satisfied by appropriately adjusting the concentration and temperature of the raw material gas serving as the carbon source in the CNT growth atmosphere. The raw material gas serving as the carbon source is not particularly limited, and hydrocarbon gases such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene, and acetylene; lower alcohol gases such as methanol and ethanol; and mixtures thereof can also be used. The raw material gas may also be diluted with an inert gas. To further enhance the dispersibility of the resulting CNT aggregates and the electromagnetic wave shielding performance of the carbon film, the growth rate of the CNT aggregates is preferably 10 μm / min or more. The temperature can be adjusted, for example, within a range of 400°C to 1100°C.

[0061] The raw material gas serving as the carbon source in the CNT growth atmosphere preferably contains ethylene. Heating ethylene within a specific temperature range (700°C to 900°C) promotes the decomposition reaction of ethylene, enabling rapid CNT growth when the decomposition gas comes into contact with the catalyst. However, if the pyrolysis time is too long, the ethylene decomposition reaction proceeds too quickly, causing catalyst deactivation and carbon impurities to adhere to the CNT aggregate. In the production of CNT aggregates of the present invention, a pyrolysis time of 0.5 seconds to 10 seconds is preferred for an ethylene concentration in the range of 0.1% to 40% by volume. If the pyrolysis time is less than 0.5 seconds, the ethylene pyrolysis is insufficient, making it difficult to rapidly grow a CNT aggregate with a high specific surface area. If the time is longer than 10 seconds, the ethylene decomposition proceeds too quickly, generating a large amount of carbon impurities, which can deactivate the catalyst and reduce the quality of the CNT aggregate. The pyrolysis time is calculated using the following formula: (Pyrolysis time) = (heating flow channel volume) / {(raw material gas flow rate) × (273.15 + T) / 273.15} Here, the heated flow channel volume is the volume of the flow channel heated to a predetermined temperature T°C through which the raw material gas passes before contacting the catalyst, and the raw material gas flow rate is the flow rate at 0°C and 1 atm.

[0062] Furthermore, by appropriately adjusting the supply rate of the catalytic activator supplied during CNT growth, condition (b)—that the concentration of the catalytic activator in the growth atmosphere for the carbon nanotube aggregate is 4% by volume or more—can be satisfied. To further improve the electromagnetic wave shielding performance of the carbon film, the concentration of the catalytic activator in the growth atmosphere for the CNT aggregate is preferably 5% by volume or more. Examples of catalytic activators include, but are not limited to, water, oxygen, ozone, acidic gases, nitrogen oxide, low-carbon oxygen-containing compounds such as carbon monoxide and carbon dioxide; alcohols such as ethanol and methanol; ethers such as tetrahydrofuran; ketones such as acetone; aldehydes; esters; and mixtures thereof. Among these, carbon dioxide is preferred. Substances containing both carbon and oxygen, such as carbon monoxide and alcohols, can function as both a source gas and a catalytic activator. For example, carbon monoxide acts as a catalytic activator when combined with a more reactive source gas such as ethylene, and acts as a source gas when combined with a catalytic activator such as water, which exhibits significant catalytic activation even in trace amounts.

[0063] Furthermore, by selecting a fluidized bed method in the CNT synthesis process or adjusting the spacing between catalyst carriers in a moving bed method or a fixed bed method, the condition (c) that "an obstacle exists in the growth direction of the carbon nanotubes that constitute the carbon nanotube aggregate during synthesis of the carbon nanotube aggregate" can be satisfied.

[0064] Here, when synthesizing CNTs by the fluidized bed method, the CNT synthesis step may be carried out, for example, by supplying a raw material gas while supplying gas from below to fluidize the particulate catalyst support, or by supplying a raw material gas while continuously transporting the particulate catalyst support by screw rotation.

[0065] The catalyst carrier has a carrier and a catalyst supported on the surface of the carrier, and the carrier is a part that forms a matrix structure for supporting the catalyst on the surface of the carrier by adhering, fixing, forming a film, or forming. The carrier structure may consist of the carrier alone, or may be a carrier with an optional underlayer provided on the surface of the carrier for favorably supporting the catalyst. The carrier is preferably in the form of particles, and the particle diameter is preferably 1 mm or less, more preferably 0.7 mm or less, even more preferably 0.65 mm or less, and preferably 0.05 mm or more, in terms of volume average particle diameter. If the particle diameter is less than the upper limit, the growing CNT bundles become thinner, which is advantageous for forming a wave-like structure. The particle density is 3.8 g / cm in apparent density. 3 It is preferable that the concentration is 5.8 g / cm or more. 3 More preferably, it is 8 g / cm or more. 3 It is preferable that the particle density is equal to or less than the lower limit. If the particle density is equal to or greater than the lower limit, the force applied to the growing CNT bundles increases, which is advantageous for forming a wave-like structure. The support material is preferably a metal oxide containing at least one of Al and Zr. Among these, zirconia beads containing a large amount of Zr are particularly preferable.

[0066] For example, when a particulate carrier is used, a method for supporting a catalyst on the surface of the particulate carrier can be, for example, a method using a rotary drum coating device equipped with a substantially cylindrical rotary drum. When a catalyst is supported on the surface of the particulate carrier after a base layer is formed on the surface, a solution containing components that can form the base layer is sprayed onto the surface of the particulate carrier and dried prior to spraying and drying the catalyst solution. This method allows the catalyst layer and base layer to be formed relatively easily and evenly.

[0067] In the CNT synthesis process, a "formation process" for reducing the catalyst supported on the catalyst support can be performed prior to the "growth process" performed so as to satisfy the above conditions (a) to (c). After the growth process is completed, a "cooling process" for cooling the catalyst support on which the CNTs have grown can be performed. In the "formation process," for example, the atmosphere containing the catalyst support is a reducing gas atmosphere, and at least one of the reducing gas atmosphere or the catalyst support is heated to reduce and microparticulate the catalyst supported on the catalyst support. The temperature of the catalyst support or the reducing gas atmosphere in the formation process is preferably 400°C or higher and 1100°C or lower. The formation process can be performed for 3 minutes or longer and 120 minutes or shorter. Examples of the reducing gas include hydrogen gas, ammonia gas, water vapor, and mixtures thereof. The reducing gas may also be a mixture of these gases with an inert gas such as helium gas, argon gas, or nitrogen gas. On the other hand, in the "cooling step," the catalyst support on which CNTs have been grown is cooled in an inert gas environment. Here, the inert gas may be the same as the inert gas that can be used in the growth step. In addition, in the cooling step, the temperature of the catalyst support on which CNTs have been grown is lowered preferably to 400°C or less, more preferably to 200°C or less.

[0068] <Dry grinding process> When obtaining the carbon membrane of the present invention, the CNT aggregate before film formation can be subjected to a dry pulverization treatment, if necessary. Note that, in the present invention, "dry pulverization treatment" refers to a pulverization treatment in a state where the pulverized material does not substantially contain a solvent (for example, a state where the solid content concentration is 95% or more).

[0069] The grinding device that can be used for the dry grinding treatment is not particularly limited as long as it is a device that can apply a physical load to the aggregate of fine structures by stirring, etc. As such a device, a mixer equipped with rotating blades can be used. The grinding conditions are not particularly limited. For example, when a mixer equipped with rotating blades is used as the grinding device, the rotation speed is preferably 500 rpm or more and 5000 rpm or less, and the grinding time is preferably 10 seconds or more and 20 minutes or less.

[0070] <Membrane formation> The carbon film of the present invention can be obtained by forming a film from the CNT aggregate. Although the method for forming a film from the CNT aggregate is not particularly limited, a preferred method is to prepare a CNT dispersion by dispersing the CNT aggregate in a dispersion medium such as water or an organic solvent, and then remove at least a part of the dispersion medium from the CNT dispersion.

[0071] The method for preparing the CNT dispersion is not particularly limited, but the CNT dispersion can be obtained by dispersing CNT aggregates in a dispersion medium using a known method, such as a dispersion method using a stirring blade, a dispersion method using ultrasound, or a dispersion method using shear force such as a high-pressure wet jet mill. Here, the preferred conditions for each dispersion method for obtaining the carbon membrane of the present invention are as follows. When a dispersion method using an agitating blade is used, the CNTs are dispersed in the dispersion medium preferably at a rotation speed of the agitating blade of 1500 rpm to 12500 rpm, more preferably 2000 rpm to 10000 rpm, for 1 minute to 120 minutes, more preferably 5 minutes to 100 minutes. Dispersion using an agitating blade can be carried out using a known dispersion device equipped with an agitating blade. When using a dispersion method using ultrasonic waves, the CNTs are dispersed in the dispersion medium at a frequency of 50 kHz to 500 kHz for 1 minute to 120 minutes, preferably 2 minutes to 100 minutes. Dispersion using ultrasonic waves can be carried out using a known ultrasonic disperser. When a dispersion method using a wet jet mill is used, the pressure for dispersing the CNTs in the dispersion medium is preferably 20 to 200 MPa, and the treatment time is preferably 5 to 30 minutes. Dispersion using a wet jet mill can be carried out using a known wet jet mill device. Furthermore, from the viewpoint of further improving the electromagnetic wave shielding performance of the resulting carbon film, it is preferable that the CNTs are adequately dispersed in the CNT dispersion. Preferably, the CNT dispersion does not contain a dispersant. In other words, it is preferable that the CNT dispersion consists essentially of only CNTs and a dispersion medium. In this specification, "the CNT dispersion consists essentially of only CNTs and a dispersion medium" means that 99.9 mass % or more of the components of the CNT dispersion consist of CNTs, inevitable impurities associated with CNTs, and the dispersion medium and inevitable impurities associated with the dispersion medium. Methods for removing the dispersion medium from the CNT dispersion include known methods such as filtration and drying. The filtration method is not particularly limited, and known filtration methods such as natural filtration, reduced pressure filtration (suction filtration), pressure filtration, and centrifugal filtration can be used. As the drying method, known drying methods such as hot air drying, vacuum drying, heat roll drying, infrared irradiation, etc. can be used. The drying temperature is not particularly limited, but is usually room temperature to 200°C, and the drying time is not particularly limited, but is usually 1 hour or more and 48 hours or less. In addition, drying can be carried out on a known substrate, but is not particularly limited.

[0072] Among these, it is preferable to employ at least drying for removing the dispersion medium. The filtration and drying can also be combined. For example, the carbon membrane of the present invention can be obtained by further drying a membrane-like residue (primary sheet) obtained by filtering the CNT dispersion. [Example]

[0073] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, various measurements and evaluations were carried out as follows.

[0074] <Ultra small angle X-ray scattering measurement> The carbon film prepared as described below was cut into a 1.5 cm square to obtain a test piece. The obtained test piece was subjected to ultra-small angle X-ray scattering measurement under the following conditions to obtain a scattering image. [Measurement conditions] X-ray energy: 10 keV (0.124 nm) Beamline: SPrimg-8 BL24XU Detector: APD (avalanche photodiode) q (wavenumber) range: 0.0001 (1 / Å) to 0.04 (1 / Å) Equipment: Bonse&Hart USAXS

[0075] <Data processing of data obtained by ultra-small angle X-ray scattering measurements> A scattering profile was obtained from the scattering image obtained by the ultra-small angle X-ray scattering measurement as described above. Using Igor Pro 8 (WaveMetrics) as analysis software and setting the wavenumber range to 0.0001 (1 / Å) to 0.04 (1 / Å), the obtained scattering profile was fitted to the Beaucage equation represented by the general formula (I) above, and the fractal dimension P i , and the size of the CNT aggregates R g,i The number of layers was set to N = 3. Here, fitting indicates the error between the measured scattering profile and the calculated value.

number

[0076] <Fourier transform infrared spectroscopy (FT-IR)> 100 g of water containing 1 mass% of sodium dodecylbenzenesulfonate as a surfactant was added to 10 mg of the CNT aggregate, and the mixture was stirred at 45 Hz for 1 minute using an ultrasonic bath to obtain 100 ml of a dispersion of each CNT aggregate. For each of the prepared dispersions, it was diluted 2-fold using a solvent of the same composition, dropped onto a silicon substrate and dried, and then a plasmon far-infrared (FIR) resonance chart was obtained using a Fourier transform infrared spectrophotometer, and the resonance peak was determined. The plasmon peak top position was obtained from an approximate curve by polynomial fitting using drawing software.

[0077] <Measurement of CNT bundle length> For each of the dispersions prepared by FT-IR measurement, the ISO circle diameter average value of the CNT dispersion present in the dispersion was measured using a flow-type particle image analyzer (manufactured by Jasco International Co., Ltd., circulating image analysis particle size distribution meter "CF-3000"), and the obtained value was taken as the CNT bundle length. The analysis conditions were as follows. [Analysis conditions] · Injection volume: 50 ml (sampling volume 1.2%) · Flow cell spacer: 1000 μm · Front lens magnification: 2 times · Telecentric lens magnification 0.75 times · Length per pixel: 2.3 μm / pixel For each of the dispersions, measurements were performed 4 times under the same conditions while circulating, and the arithmetic mean value thereof was determined.

[0078] <Creation of pore distribution curve (CNT aggregate)> For 10 mg or more of the CNT aggregate, the adsorption isotherm was measured at 77 K using liquid nitrogen using BELSORP-miniII (manufactured by MicrotracBEL) (the adsorption equilibrium time was set to 500 seconds). As a pretreatment, vacuum degassing was performed at 100 °C for 12 hours. From the adsorption amount of this adsorption isotherm, a pore distribution curve of each sample was obtained by the BJH method. In addition, when creating the pore distribution curve of the CNT aggregate, the measurement range of the pore diameter was set to 1 nm or more and less than 400 nm.

[0079] (Two-dimensional spatial frequency spectrum analysis of electron microscope images) A sample of 0.01 mg of CNT aggregate 1, prepared according to the procedure described below, was placed on carbon tape and blown with a blower to remove excess CNTs. The sample was then observed at 10,000x magnification using a field emission scanning electron microscope, and 10 photographs were taken of a randomly selected 1 cm square field of view. Each of the 10 electron microscope images was subjected to fast Fourier transform processing to obtain a two-dimensional spatial frequency spectrum. Each of the obtained two-dimensional spatial frequency spectra was then binarized, and the outermost (high-frequency) peak position was determined and the average value was calculated. Note that in the binarization process, values ​​greater than 0.75 obtained through fast Fourier transform processing were assigned a value of 1, and other values ​​were assigned a value of zero.

[0080] <Thickness> The thickness of the carbon film was measured using a "Digimatic Standard Outside Micrometer" manufactured by Mitutoyo Corporation.

[0081] <Porosity> The produced carbon membrane was cut into a 1 cm square to prepare a test piece, and the mass (g) of the test piece was measured to calculate the density (bulk density) of the carbon membrane by the following formula (1). Next, the porosity of the carbon membrane was calculated by the following formula (2) using the obtained bulk density. Bulk density of carbon film (g / cm 3 ) = mass of test piece (g) / (1cm 2 × thickness of test piece (cm) (1) Porosity = (1 - (bulk density of carbon membrane (g / cm 3 ) / 1.3))×100···(2) The "1.3" in formula (2) is the true density of carbon (g / cm 3 ) refers to

[0082] <Electromagnetic wave shielding performance> The reflection coefficient S11 and transmission coefficient S21 of the carbon film were measured using the microstrip line method in accordance with IEC-62333-2, and the transmission attenuation rate "dB" was calculated as the electromagnetic wave shielding performance. Then, the electromagnetic shielding performance [dB] at measurement frequencies of 2.5 MHz, 4.5 MHz, and 7.5 MHz was evaluated according to the following criteria. The larger the value of the transmission attenuation rate [dB] at a certain frequency, the better the carbon film shows the electromagnetic shielding performance at that frequency. A: The transmission attenuation rate is 25 dB or more B: The transmission attenuation rate is 20 dB or more and less than 25 dB C: The transmission attenuation rate is less than 20 dB

[0083] (Example 1) <Preparation of CNT aggregate 1> The CNT aggregate 1 used in Example 1 was produced by a method in which a raw material gas was supplied while a particulate catalyst support was continuously transported by screw rotation in the CNT synthesis process. The schematic configuration of the CNT aggregate production apparatus 200 used is shown in FIG. 8. The CNT aggregate production apparatus 200 shown in FIG. 8 includes a formation unit 202, a growth unit 204, a transport unit 207 that transports the base material from the formation unit 202 until it passes through the growth unit 204, a connection unit 208 that spatially connects the formation unit 202 and the growth unit 204, and a gas mixing prevention device 203 that prevents gases from mixing between the formation unit 202 and the growth unit 204. Furthermore, the CNT aggregate production apparatus 200 includes components such as an inlet purging device 201 arranged in front of the formation unit 202, an outlet purging device 205 arranged in the rear of the growth unit 204, and a cooling unit 206 arranged in the rear of the outlet purging device 205. The formation unit 202 is composed of a formation furnace 202a for holding a reducing gas, a reducing gas injection device 202b for injecting the reducing gas, a heating device 202c for heating at least one of the catalyst and the reducing gas, and an exhaust device 202d for discharging gas in the furnace to the outside of the system. The gas mixing prevention device 203 is equipped with an exhaust device 203a and a purge gas injection device 203b for injecting a purge gas (seal gas). The growth unit 204 is equipped with a growth furnace 204a for maintaining a source gas environment, a source gas injection device 204b for injecting the source gas, a heating device 204c for heating at least one of the catalyst and the source gas, and an exhaust device 204d for discharging gas in the furnace to the outside of the system. An inlet purge device 201 is attached to a connection part 209 that connects the formation furnace 202a to an antechamber 213, which is a component that introduces a substrate 211 into the system via a hopper 212. The cooling unit 206 includes a cooling container 206a for holding an inert gas, and a water-cooling device 206b arranged to surround the interior space of the cooling container 206a. The transport unit 207 is a unit that continuously transports the substrate 211 by screw rotation.It is mounted by a screw blade 207a and a drive device 207b that can rotate the screw blade to exhibit a substrate conveying ability. The heating device 214 is configured to be able to heat the inside of the system at a temperature lower than the heating temperature in the formation unit, and heats the vicinity of the drive device 207b.

[0084] <Catalyst layer formation process> Zirconia (zirconium dioxide) beads (ZrO2, volume average particle diameter D50: 650 μm) as a substrate were put into a rotary drum type coating device, and while stirring the zirconia beads (20 rpm), an aluminum-containing solution was sprayed by a spray gun (spray amount 3 g / min, spray time 940 seconds, spray air pressure 10 MPa), and while supplying compressed air (300 L / min) into the rotary drum, it was dried to form an aluminum-containing coating film on the zirconia beads. Next, a firing treatment was performed at 480 °C for 45 minutes to produce primary catalyst particles on which an aluminum oxide layer was formed. Further, the primary catalyst particles were put into another rotary drum type coating device and stirred (20 rpm), and while spraying an iron catalyst solution by a spray gun (spray amount 2 g / min, spray time 480 seconds, spray air pressure 5 MPa), and while supplying compressed air (300 L / min) into the rotary drum, it was dried to form an iron-containing coating film on the primary catalyst particles. Next, a firing treatment was performed at 220 °C for 20 minutes to produce a substrate on which an iron oxide layer was further formed. <<CNT synthesis process>> The substrate having a catalyst on the surface produced in this way was put into the feeder hopper of the CNT aggregate manufacturing apparatus, and while being conveyed by a screw conveyor, it was processed in the order of the formation process, the growth process, and the cooling process to manufacture the CNT aggregate 1.

[0085] <Formation process to cooling process> The conditions of each of the inlet purge device, the formation unit, the gas mixing prevention device, the growth unit, the outlet purge device, and the cooling unit of the CNT aggregate manufacturing apparatus were set as follows.

[0086] Feeder hopper Feed rate: 1.25kg / h Displacement: 10sLm (natural exhaust through gaps) Inlet purge device Purge gas: Nitrogen 40sLm Formation Unit ·Furnace temperature: 800℃ Reducing gas: Nitrogen 6sLm, Hydrogen 54sLm Displacement: 60sLm Processing time: 20 minutes Gas contamination prevention device Purge gas: 20sLm Exhaust system displacement: 62sLm Growth Unit ·Furnace temperature: 830℃ Feed gas: Nitrogen 15sLm, Ethylene 5sLm, Carbon dioxide 1sLm, Hydrogen 3sLm Displacement: 47sLm Processing time: 10 minutes Outlet Purge Device Purge gas: Nitrogen 45sLm Cooling unit ·Cooling temperature: room temperature Displacement: 10sLm (natural exhaust through gaps) Continuous production was carried out under the above conditions.

[0087] <Separation and recovery process> The CNT aggregate 1 synthesized on the substrate was separated by a forced vortex separator (rotation speed 2300 rpm, air flow rate 3.5 Nm 3 The recovery rate of CNT aggregate 1 was 96%.

[0088] The characteristics of the CNT aggregate 1 produced in this example are, as typical values, tap bulk density: 0.02 g / cm 3 , CNT average length: 150 μm, BET specific surface area: 900 m 2 / g, average outer diameter: 4.0 nm, and carbon purity: 99%.

[0089] Here, a peak due to the plasmon resonance of the CNT dispersion was confirmed in the CNT aggregate 1. Fig. 5 shows an FIR resonance chart of the FIR spectrum of the CNT aggregate 1. As shown in Fig. 5, in the CNT aggregate 1, a peak at 835 cm -1 A peak in optical density was observed at this point, satisfying the above condition (1). Furthermore, as shown in FIG. 6, the maximum peak of the Log differential pore volume was confirmed in the region of pore diameters of 100 nm or more for the CNT aggregate 1, and the condition (2) was satisfied. In addition, in the CNT aggregate 1, 1 μm -1 More than 100μm -1 It was confirmed that at least one exists in the following range, and the condition (3) was satisfied. This can be understood from the following situation. Fig. 7A is one of ten images acquired for the prepared CNT aggregate 1, and Fig. 7B is a two-dimensional spatial frequency spectrum acquired for this image. In Fig. 7B, components closer to the center represent low frequency components, and components located further out from the center correspond to higher frequency components. In the figure, arrows indicate 1 to 100 µm -1 Among the clear peaks detected in the region, the peak position with the highest wavenumber (3 μm -1 ) was shown.

[0090] 1000 g of water was added to 1 g of the CNT aggregate 1 obtained as described above, and the mixture was stirred for 10 minutes at a rotation speed of 3000 rpm using an ultra-high speed emulsifying and dispersing device (product name "Labo-Lution (registered trademark)", manufactured by Thinky Corporation) to obtain a CNT dispersion liquid. The obtained CNT dispersion was applied to a substrate. The coating on the substrate was vacuum dried at 80°C for 24 hours to form a carbon film on the substrate. The carbon film was then peeled off from the substrate to obtain a 543 μm-thick carbon film (freestanding film). Various measurements and data analysis were performed, and the electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0091] Example 2 A carbon film (freestanding film) with a thickness of 261 μm was obtained in the same manner as in Example 1, except that the CNT dispersion was prepared by stirring for 15 minutes at a rotation speed of 7,500 rpm using an ultra-high-speed emulsifying and dispersing device (product name "Labo-Lution (registered trademark)", manufactured by Thinky Corporation). The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0092] Example 3 A carbon film (freestanding film) with a thickness of 190 μm was obtained in the same manner as in Example 1, except that the CNT dispersion was prepared by dispersing the CNTs using a jet mill (NanoVata, manufactured by Yoshida Kikai Kogyo Co., Ltd.) at 100 MPa for 15 minutes. The obtained carbon film was subjected to various measurements and data analysis, and its electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0093] (Comparative Example 1) A crude dispersion was obtained by mixing 1 g of the CNT aggregate 1 with 1000 g of an aqueous solution containing 1% by mass of sodium dodecylbenzenesulfonate (SDBS) as a dispersant. This crude dispersion was then dispersed for 15 minutes at 100 MPa using a jet mill (NanoVeita, manufactured by Yoshida Kikai Kogyo Co., Ltd.) to obtain a CNT dispersion. The resulting CNT dispersion was applied to a substrate. The coating on the substrate was vacuum-dried at 80°C for 24 hours to form a carbon film on the substrate. The carbon film was then peeled off from the substrate to obtain a 181 μm-thick carbon film (freestanding film). Various measurements and data analysis were performed, and the electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0094] (Comparative Example 2) A carbon film (freestanding film) having a thickness of 159 μm was obtained in the same manner as in Example 1, except that SGCNTs (product name "ZEONANO SG101", manufactured by Zeon Corporation) as single-walled CNTs were used as the CNT aggregate instead of the CNT aggregate 1, and the CNT dispersion was prepared by stirring for 60 minutes at a rotation speed of 10,000 rpm using an ultra-high speed emulsifying and dispersing device (product name "LABO-ULTION (registered trademark), manufactured by THINKY CORPORATION). The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0095] Here, in the SGCNT, in the FIR resonance chart of the FIR spectrum, -1 An optical density peak was observed in the region where the pore diameter was 100 nm or more, and the condition (1) was not satisfied. Furthermore, the SGCNT did not have a maximum peak in the Log differential pore volume in the region where the pore diameter was 100 nm or more, and the condition (2) was not satisfied. -1 More than 100μm -1 No clear peak was observed within the range below, and the condition (3) was not satisfied.

[0096] (Comparative Example 3) A carbon film (freestanding film) having a thickness of 154 μm was obtained in the same manner as in Example 3, except that the SGCNTs (product name "ZEONANO SG101", manufactured by Zeon Corporation) were used as the CNT aggregate instead of the CNT aggregate 1. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0097] Comparative Example 4 A crude dispersion was obtained by mixing 1 g of the SGCNTs with 1,000 g of an aqueous solution containing 1% by mass of sodium dodecylbenzenesulfonate (SDBS) as a dispersant. This crude dispersion was then dispersed for 15 minutes at 100 MPa using a jet mill (NanoVeita, manufactured by Yoshida Kikai Kogyo Co., Ltd.) to obtain a CNT dispersion. The resulting CNT dispersion was applied to a substrate. The coating on the substrate was vacuum dried at 80°C for 24 hours to form a carbon film on the substrate. The carbon film was then peeled off from the substrate to obtain a 50 μm-thick carbon film (freestanding film). Various measurements and data analysis were performed, and the electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0098] [Table 1]

[0099] Table 1 shows that when the scattering profiles obtained by performing ultra-small angle X-ray scattering measurements on the surface of the carbon film are fitted to the Beaucage equation, the carbon films of Examples 1 to 3, which have a fractal dimension of 2.6 or more and 4 or less in the wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less and a porosity of 80% or more and 95% or less, have a transmission attenuation rate of 25 dB or more at all measurement frequencies and have excellent electromagnetic wave shielding performance. In contrast, when the scattering profiles obtained by performing ultra-small angle X-ray scattering measurements on the surface of the carbon film are fitted to the Beaucage equation, the carbon films of Comparative Examples 1 to 4, which had a fractal dimension in the wavenumber range of 0.0001 (1 / Å) to 0.001 (1 / Å) that was not between 2.6 and 4, or which had a porosity that was not between 80% and 95%, had a transmission attenuation rate of less than 25 dB at least at any of the measurement frequencies, and were found to have inferior electromagnetic wave shielding performance compared to the carbon films of Examples 1 to 3. [Industrial Applicability]

[0100] According to the present invention, a carbon film having excellent electromagnetic wave shielding performance can be provided. [Explanation of symbols]

[0101] 200 CNT aggregate manufacturing equipment 201 Inlet purge device 202 Formation Unit 202a Formation Furnace 202b Reducing gas injection device 202c heating device 202d Exhaust system 203 Gas contamination prevention device 203a Exhaust system 203b Purge gas injection device 204 Growth Units 204a growth furnace 204b Raw material gas injection device 204c heating device 204d Exhaust system 205 Outlet purge device 206 Cooling Unit 206a Cooling vessel 206b Water-cooled chiller 207 Transport Unit 207a Screw blade 207b Drive unit 208~209 Connection 211 Base material 212 Hopper 213 Front room 214 Heating device

Claims

1. A carbon film made of an aggregate of carbon nanotubes, a carbon film having a fractal dimension of 2.6 or more and 4 or less in a wavenumber range of 0.0001 (1 / Å) or more and 0.001 (1 / Å) or less, when a scattering profile obtained by performing ultra-small angle X-ray scattering measurement on at least one surface of the carbon film is fitted to Beaucage's equation; and a porosity of 80% or more and 95% or less.

2. When a scattering profile obtained by performing ultra-small angle X-ray scattering measurement on at least one surface of the carbon film is fitted to the Beaucage equation, the size of the carbon nanotube aggregates in the wave number range of 0.0001 (1 / Å) to 0.001 (1 / Å) is 1.0 × 10 ５ Å or ​​more 4.0×10 ７ The carbon film according to claim 1 , wherein the surface roughness is 200 nm or less.

3. The carbon membrane according to claim 1 or 2, which is a free-standing membrane.

4. The carbon membrane according to any one of claims 1 to 3, having a thickness of 5 µm or more and 1000 µm or less.

5. 5. The carbon film according to claim 1, wherein the transmission attenuation rate at at least one frequency within the range of 1 GHz to 10 GHz is 20 dB or more.

Images