carbon film

Abstract

The present invention aims to provide a carbon film having excellent electromagnetic wave shielding performance. The carbon film of the present invention is characterized by being composed of a carbon nanotube aggregate, when at least one surface of the carbon film is subjected to ultra-small-angle X-ray scattering measurement and a scattering pattern obtained is fitted with a Beaucage formula, a fractal dimension in a wave number range of above and below is 2.6 or more and 4 or less, and a porosity of the carbon film is 80% or more and 95% or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a carbon film, and particularly to a carbon film having excellent electromagnetic wave shielding performance. BACKGROUND

[0002] In recent years, carbon nanotubes (hereinafter, sometimes referred to as "CNT") have attracted attention as a material having excellent electrical conductivity, thermal conductivity, and mechanical properties. However, since CNT is a fine structure having a nanometer size in diameter, the handling property and processability of CNT alone are poor. Therefore, in order to ensure the handling property and processability and use for various applications, a carbon film has been formed by film-forming a collection (hereinafter, referred to as "carbon nanotube collection") composed of a plurality of CNTs (for example, refer to Patent Literature 1).

[0003] In Patent Literature 1, a carbon film having excellent mechanical strength has been formed using a carbon nanotube collection having a pore having a pore diameter of 400 nm or more and 1500 nm or less, measured by a mercury intrusion method, in which the Log differential pore volume is 0.006 cm 3 / g or less in a range of 10 nm or more.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2018-145027 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] In recent years, electromagnetic wave shielding has attracted attention as an application of a carbon film. However, the performance of shielding electromagnetic waves (i.e., electromagnetic wave shielding performance) of the above-described conventional carbon film has room for further improvement. Therefore, an object of the present application is to provide a carbon film having excellent electromagnetic wave shielding performance.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] The present inventors have conducted intensive studies in order to achieve the above-described object. Then, the present inventors have studied the microscopic properties of a carbon film formed using a carbon nanotube collection. As a result, the present inventors have newly found that, in the case where a prescribed parameter obtained by a prescribed data processing of a small-angle X-ray scattering curve (graph) of a surface of a carbon film composed of a carbon nanotube collection satisfies a prescribed condition and the porosity of the carbon film is a prescribed value, the carbon film can shield electromagnetic waves well, and thus the present application has been completed.

[0011] That is, the carbon film of the present application is characterized in that it is composed of a carbon nanotube aggregate, when at least one surface of the carbon film is subjected to ultra-small-angle X-ray scattering measurement and the scattering pattern obtained is fitted with the Beaucage equation, The fractal dimension in the wave number range below is 2.6 or more and 4 or less, and the porosity of the carbon film is 80% or more and 95% or less. The carbon film having such a structure can exhibit excellent electromagnetic wave shielding performance. The fractal dimension in the wave number range below is 2.6 or more and 4 or less, and the porosity of the carbon film is 80% or more and 95% or less. The carbon film having such a structure can exhibit excellent electromagnetic wave shielding performance.

[0012] In the present application, the ultra-small-angle X-ray scattering pattern of the surface of the carbon film can be obtained by the method described in the examples. The ultra-small-angle X-ray scattering pattern can be fitted with the Beaucage equation by the method described in the examples of the present specification. Here, the porosity of the carbon film can be obtained by the method described in the examples of the present specification.

[0013] Here, it is preferable that when at least one surface of the above-described carbon film is subjected to ultra-small-angle X-ray scattering measurement and the scattering pattern obtained is fitted with the above-described Beaucage equation, The fractal dimension in the wave number range below is 2.6 or more and 4 or less, and the porosity of the carbon film is 80% or more and 95% or less. The carbon film having such a structure can exhibit excellent electromagnetic wave shielding performance. The size of the carbon nanotube aggregate in the wave number range below is The fractal dimension in the wave number range below is 2.6 or more and 4 or less, and the porosity of the carbon film is 80% or more and 95% or less. The carbon film having such a structure can exhibit excellent electromagnetic wave shielding performance. If the size of the CNT aggregate in the above-described prescribed wave number range is within the above-described prescribed range, the electromagnetic wave shielding performance of the carbon film can be further improved.

[0014] It is preferable that the above-described carbon film be a self-supporting film. The carbon film as a self-supporting film is excellent in handleability, and when used as, for example, an electromagnetic wave shielding sheet, the degree of freedom in arranging the sheet can be improved. In addition, in the present application, the "self-supporting film" refers to a film that can maintain the film shape alone without breaking even in the absence of a support body, and a single-layer carbon film is particularly preferable.

[0015] It is preferable that the thickness of the above-described carbon film be 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 more excellent electromagnetic wave shielding performance. On the other hand, if the thickness is 1000 μm or less, the carbon film can be made lightweight. In addition, in the present application, the "thickness" of the carbon film can be measured by the method described in the examples of the present specification.

[0016] It is preferable that the transmission attenuation rate of the above-described carbon film at at least one frequency in the range of 1 GHz or more and 10 GHz or less be 20 dB or more. The electromagnetic wave shielding performance of the carbon film whose transmission attenuation rate at at least one frequency in the range of 1 GHz or more and 10 GHz or less is 20 dB or more is more excellent. In addition, in the present application, the transmission attenuation rate can be measured by the method described in the examples of the present specification.

[0017] The use of the carbon film is not particularly limited, and for example, it can be favorably used as an electromagnetic wave shielding sheet.

[0018] Effects of Invention

[0019] According to the present application, a carbon film having excellent electromagnetic wave shielding performance can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 An SEM image of the surface of the carbon film of Example 1 is shown.

[0021] Figure 2 A graph obtained by fitting the small-angle X-ray scattering pattern of the surface of the carbon film of Example 1 with the Beaucage equation is shown.

[0022] Figure 3 A graph obtained by fitting the small-angle X-ray scattering pattern of the surface of the carbon film of Comparative Example 2 with the Beaucage equation is shown.

[0023] Figure 4 An SEM image of one example of a CNT aggregate that can be used in the present application is shown.

[0024] Figure 5 An FIR resonance pattern obtained in the CNT aggregate 1 used in each of the embodiments of the present application is shown.

[0025] Figure 6 A pore distribution curve of the above-described CNT aggregate 1 is shown.

[0026] Figure 7A An SEM image of the above-described CNT aggregate 1 is shown.

[0027] Figure 7B An SEM image of Figure 7A is shown.

[0028] Figure 8 A schematic structure of a manufacturing apparatus of the above-described CNT aggregate 1 is shown. DETAILED DESCRIPTION

[0029] Hereinafter, the carbon film of the embodiments of the present application will be described in detail.

[0030] (Carbon film)

[0031] The carbon film of the present application is composed of a carbon nanotube aggregate, and when at least one surface of the carbon film is subjected to small-angle X-ray scattering measurement and the obtained scattering pattern is fitted with the Beaucage equation, The above and The fractal dimension in the following wave number range is 2.6 or more and less than 4, and the porosity of the carbon film is 80% or more and 95% or less.

[0032] The above-described carbon nanotube aggregate is composed of a plurality of carbon nanotubes. In the above-described carbon film, the proportion of CNTs in the carbon film is preferably 95% by mass or more, more preferably 98% by mass or more, further preferably 99% by mass or more, particularly preferably 99.5% by mass or more, and most preferably 100% by mass (i.e., the carbon film is composed only of CNTs). In addition, in the above-described carbon film, various additives (e.g., dispersants and the like) can be contained as components other than the above-described carbon nanotube aggregate, and in addition, components that are inevitably mixed in during the production of the carbon film can also be contained.

[0033] Hereinafter, a method of obtaining the fractal dimension by fitting the small-angle X-ray scattering pattern of the carbon film with the Beaucage equation will be described.

[0034] <Small-angle X-ray scattering measurement>

[0035] First, a small-angle X-ray scattering measurement is performed on the surface of the carbon film, and a scattering pattern is obtained. In the present application, the wave number q is defined as follows: The small-angle X-ray scattering measurement is performed using X-ray energy of 10 keV (0.124 nm), a beam line of SPrimg-8BL24XU, a detector of APD (avalanche photodiode), and a device of Bonse & Hart USAXS. Then, a scattering pattern is obtained with the wave number q as the horizontal axis and the scattering intensity I(q) as the vertical axis.

[0036] <Scattering pattern fitting>

[0037] Next, the obtained scattering pattern is fitted using the Beaucage equation. The fitting of the scattering pattern using the Beaucage equation is known in the art, and can be performed according to the method described in, for example, G. Beaucage, J. Appl. Cryst., 28, 717 (1995). The fitting can be performed by using, for example, Igor Pro 8 (manufactured by WaveMetrics) as an analysis software.

[0038] Specifically, the wave number range is set to The obtained scattering pattern is fitted using the Beaucage equation represented by the following general formula (I).

[0039] [Mathematical Formula 1]

[0040]

[0041] In the above-described general formula (I), q represents the wave number I(q) represents the scattering intensity at wavenumber q, Bkgd represents the background, and G i and B i P represents the proportionality constant. i Represents the fractal dimension of level i, R g，i N represents the length of the structure at level i, and N represents the number of levels.

[0042] As described above, by fitting the scattering map using the general formula (I), the fractal dimension P of each level i can be obtained. i .

[0043] Furthermore, in this invention, if the fractal dimension P1 when i=1 is in the range of 2.6 or higher and 4 or lower, then it is determined that " The above and The fractal dimension of the following wavenumber range is above 2.6 and below 4.

[0044] In the ultrasmall angle X-ray scattering pattern of the carbon film of the present invention, it is possible to observe (1) scattering (R) from the size of the CNT aggregates. g,1 (2) Scattering from the beam diameter of the CNT (R) g,2 (3) Scattering from the relevant length of a CNT (R) g,3 Since three types of scattering are observed, it is preferable to set the number of layers to 3 for fitting. For example, in The above and The following wavenumber range observed (1) size scattering (R) from CNT aggregates g,1 ),exist The above and The following wavenumber range observed (2) scattering from the beam diameter of the CNT, in The above and The following wavenumber range observed (3) scattering (R) from the correlation length of a single CNT g,3 Here, in the scattering diagram, it is possible to determine the scattering pattern based on... The above and The slope of the following wavenumber range resolves the size (R) of the CNT aggregates. g,1 ).

[0045] When ultra-small angle X-ray scattering is measured on at least one surface of the carbon film and the resulting scattering pattern is fitted using the Beaucage formula, The above and The reason why carbon films with a fractal dimension of 2.6 or higher and 4 or lower in the following wavenumber range can exhibit excellent electromagnetic wave shielding performance is not yet clear, but it is speculated as follows: That is, the fractal dimension is an indicator of the size of the aggregates of CNTs forming the carbon film, and it is speculated that... The above and The carbon film in which the fractal dimension in the above wave number range is 2.6 or more and 4 or less has a CNT aggregate well formed. Further, it is presumed that the energy of the electromagnetic wave entering the carbon film is attenuated by making the electromagnetic wave well diffuse and reflect between the gaps of the aggregate, and thus the carbon film of the present application can exhibit excellent electromagnetic wave shielding performance.

[0046] When 2.6 or more and When the fractal dimension in the above wave number range is more than 4, it is presumed that the CNT aggregate is not well formed, and thus the electromagnetic wave is not likely to diffuse and reflect between the gaps of the aggregate, and the electromagnetic wave shielding performance deteriorates. Further, when 2.6 or more and When the fractal dimension in the above wave number range is less than 2.6, it is presumed that the aggregate is not formed, and the electromagnetic wave shielding performance deteriorates.

[0047] Further, in the case where the graph of the ultra-small angle X-ray scattering of the carbon film of the present application is fitted by the above prescribed method, 2.6 or more and The size of the CNT aggregate in the above wave number range is preferably More preferably, Further preferably, Preferably, More preferably, Further, if the size of the CNT aggregate in the above prescribed wave number range is within the above prescribed range, the electromagnetic wave shielding performance of the carbon film can be further improved.

[0048] Here, the wave structure possessed by the above carbon film is described. Figure 1 is an SEM image of the surface of the carbon film of Example 1 described later. As Figure 1 indicated, the surface of the carbon film of Example 1 in which the fractal dimension in the prescribed wave number range is 2.6 or more and 4 or less is formed with a wave structure.

[0049] Further, the fractal dimension P in General Formula (I) i corresponds to the absolute value of the slope of the straight line portion of the coordinate graph obtained by fitting the scattering graph with the Beaucage formula. Figure 2 shows a coordinate graph obtained by fitting the ultra-small angle X-ray scattering graph of the surface of the carbon film of Example 1 described later with the Beaucage formula. Figure 3 shows a coordinate graph obtained by fitting the ultra-small angle X-ray scattering graph of the surface of the carbon film of Comparative Example 2 described later with the Beaucage formula. In Figure 2 , 2.6 or more and The absolute value of the slope of the straight line portion in the above wave number range is more than Figure 3 of The absolute value of the slope of the linear portion in the wave number range of The absolute value of the slope of the linear portion in the wave number range of Figure 2 In the coordinate graph of The absolute value of the slope of the linear portion in the wave number range of The absolute value of the slope of the linear portion in the wave number range of

[0050] From the viewpoint of further improving electromagnetic wave shielding performance, the above-described fractal dimension of the carbon film of the present application is preferably 2.7 or greater, more preferably 2.8 or greater, and furthermore, preferably 3.9 or less, more preferably 3.7 or less. The absolute value of the slope of the linear portion in the wave number range of The absolute value of the slope of the linear portion in the wave number range of The absolute value of the slope of the linear portion in the wave number range of The absolute value of the slope of the linear portion in the wave number range of

[0051] In the carbon film of the present application, the above-described fractal dimension can be controlled by adjusting, for example, the dispersion conditions of the CNTs (dispersion strength, dispersion time, presence or absence of a dispersant, etc.) at the time of preparing the CNT dispersion liquid described later, controlling the CNT bundle length described later, etc. For example, in the case of dispersing the CNTs using a stirring blade, the CNT bundle length can be changed by changing the rotation speed (rpm) and / or the dispersion time and / or the shape of the stirring blade.

[0052] The porosity of the carbon film of the present application is 80% or greater and 95% or less.

[0053] For example, the porosity of the carbon film can be calculated as follows. That is, a 1 cm square of the carbon film produced is cut out to produce a test piece, the mass (g) of the test piece is measured, the density (bulk density) of the carbon film is calculated according to the following formula (1), and next, using the obtained bulk density, the porosity of the carbon film can be calculated according to the following formula (2).

[0054] • Bulk density of carbon film (g / cm 3 ) = mass of test piece (g) / (1 cm 2 × thickness of test piece (cm))... (1)

[0055] • Porosity = (1 - (bulk density of carbon film (g / cm 3 ) / 1.3)) x 100... (2)

[0056] In addition, "1.3" in formula (2) means the true density (g / cm 3 ) of carbon.

[0057] The carbon film has a porosity of 80% or more, which improves the electromagnetic wave absorption properties of the carbon film. Here, the porosity is 95% or less, which sufficiently maintains the self-supporting properties of the carbon film, and provides a carbon film that has good workability and processability.

[0058] <EM SHIELDING PERFORMANCE>

[0059] The carbon film of the present application preferably has a transmission attenuation rate of 25 dB or more at at least one frequency in the range of 1 GHz or more and 10 GHz or less, and more preferably has a transmission attenuation rate of 25 dB or more at all frequencies in the range of 1 GHz or more and 10 GHz or less. The electromagnetic wave shielding performance of the carbon film having a transmission attenuation rate of 25 dB or more at all frequencies in the above range is more excellent, and thus the carbon film can be more advantageously used as an electromagnetic wave shielding sheet.

[0060] <THICKNESS>

[0061] The thickness of the carbon film of the present application is preferably 5 μm or more, more preferably 10 μm or more, and 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 more excellent electromagnetic wave shielding performance. On the other hand, if the thickness is 1000 μm or less, the carbon film can be made lightweight.

[0062] In addition, the thickness of the carbon film of the present application can also be 150 μm or more, 200 μm or more, or 300 μm or more, and in addition, can also be 600 μm or less, 300 μm or less, or 200 μm or less.

[0063] (METHOD FOR PRODUCING CARBON FILM)

[0064] By satisfying at least one of the following (A) and (B) when the carbon film is produced by film-forming a carbon nanotube aggregate, the carbon film of the present application can be produced.

[0065] (A) using a CNT aggregate that satisfies at least one of the following conditions (1) to (3) as the CNT aggregate;

[0066] (B) subjecting the CNT aggregate to dry pulverization treatment before film-forming the CNT aggregate.

[0067] <EM SHIELDING PERFORMANCE>

[0068] Here, it is preferable to use a novel CNT aggregate that satisfies at least one of the conditions (1) to (3) as the CNT aggregate used for producing the carbon film. The 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.

[0069] Condition (1): Carbon nanotube aggregates are dispersed into bundles with a length of 10 μm or more to obtain a carbon nanotube dispersion. In the Fourier transform infrared spectroscopy analysis of the carbon nanotube dispersion, the plasmon resonance-based peak of the carbon nanotube dispersion has a wavenumber greater than 300 cm⁻¹. -1 And it is 2000cm -1 At least one of the following ranges exists.

[0070] Condition (2): For carbon nanotube assemblies, based on the adsorption isotherm of liquid nitrogen at 77 K, the largest peak in the micropore distribution curve obtained by the Barrett-Joyner-Halenda method, which represents the relationship between micropore size and Log differential micropore volume, exists in the range where the micropore size is greater than 100 nm and less than 400 nm.

[0071] Condition (3): The peak of the two-dimensional spatial spectrum of the electron microscope image of the carbon nanotube assembly is at 1 μm. -1 Above and 100μm -1 At least one of the following ranges exists.

[0072] The reason why carbon films composed of CNT assemblies that satisfy at least one of the above conditions (1) to (3) have excellent electromagnetic wave shielding performance is not yet clear, but it is speculated as follows. Figure 4 A scanning electron microscope (SEM) image of an example of a CNT assembly that satisfies at least one of the conditions (1) to (3) above is shown. Figure 4 As shown, the CNTs constituting a CNT assembly that satisfies at least one of the above conditions (1) to (3) have a wavy structure. It is believed that this "wavy structure" causes electromagnetic waves to diffusely reflect between the CNTs constituting the CNT assembly. It is speculated that during this diffuse reflection, the electromagnetic waves lose energy, which is reflected in the higher electromagnetic wave shielding performance. Hereinafter, the above conditions (1) to (3) that the CNT assembly of the present invention can satisfy will be described in detail.

[0073] <<Condition (1)>>

[0074] Condition (1) specifies that "a carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates into bundles with a length of 10 μm or more, wherein in the Fourier transform infrared spectroscopy analysis of the carbon nanotube dispersion, the peak of the carbon nanotube dispersion based on plasmon resonance has a wavenumber greater than 300 cm⁻¹". -1 And 2000cm -1The following range exists a peak based on plasmon resonance of CNT. The following range is preferable, and the following range is more preferable, and the following range is further preferable. The following range exists a peak based on plasmon resonance of CNT, preferably in a wave number of 500 cm -1 or less and 2000 cm -1 or more, more preferably in a wave number of 700 cm -1 or more and 2000 cm -1 or less, and further preferably in a wave number of 800 cm -1 or more and 2000 cm -1 or less. In this case, as an optical property of CNT, a strong absorption property in a far infrared region has been known all along. The strong absorption property in the far infrared region is considered to be caused by the diameter and length of CNT. In addition, the absorption property in the far infrared region, and more specifically the relationship between the peak based on plasmon resonance of CNT and the length of CNT, are studied in detail in a non-patent literature (T. Morimoto et. al., "Length-Dependent Plasmon Resonance in Single-Walled Carbon Nanotubes", pp. 9897-9904, Vol. 8, No. 10, ACS NANO, 2014). The present inventors, based on the research contents and unique insights described in the above non-patent literature, conjectured that the position of the peak based on plasmon resonance of CNT detected in a spectrum obtained by performing Fourier transform infrared spectroscopy is somehow affected by the distance between defect points in CNT, and verified it. Then, the present inventors found that the position of the peak based on plasmon resonance of CNT can function as an index corresponding to the distance between bending points in CNT having a wavy structure, and thus set the above condition (1).

[0075] In condition (1), if a wave number is greater than 300 cm -1 and 2000 cm -1 or less, a peak based on plasmon resonance of CNT exists in the following range. The following range is preferable, and the following range is more preferable, and the following range is further preferable. The following range exists a peak based on plasmon resonance of CNT, preferably in a wave number of 500 cm -1 or more and 2000 cm -1 or less, more preferably in a wave number of 700 cm -1 or more and 2000 cm -1 or less, and further preferably in a wave number of 800 cm -1 or more and 2000 cm -1 or less. In this case, as an optical property of CNT, a strong absorption property in a far infrared region has been known all along. The strong absorption property in the far infrared region is considered to be caused by the diameter and length of CNT. In addition, the absorption property in the far infrared region, and more specifically the relationship between the peak based on plasmon resonance of CNT and the length of CNT, are studied in detail in a non-patent literature (T. Morimoto et. al., "Length-Dependent Plasmon Resonance in Single-Walled Carbon Nanotubes", pp. 9897-9904, Vol. 8, No. 10, ACS NANO, 2014). The present inventors, based on the research contents and unique insights described in the above non-patent literature, conjectured that the position of the peak based on plasmon resonance of CNT detected in a spectrum obtained by performing Fourier transform infrared spectroscopy is somehow affected by the distance between defect points in CNT, and verified it. Then, the present inventors found that the position of the peak based on plasmon resonance of CNT can function as an index corresponding to the distance between bending points in CNT having a wavy structure, and thus set the above condition (1).

[0076] Figure 5 A spectrum (FIR resonance chart) obtained by performing Fourier transform infrared spectroscopy on one example of a CNT aggregate is shown. From the obtained spectrum, it is known that, in addition to a relatively gentle peak based on plasmon resonance of CNT dispersion, sharp peaks are confirmed near a wave number of 840 cm Figure 5 , near a wave number of 1300 cm -1 , and near a wave number of 1700 cm -1 . These sharp peaks do not belong to "a peak based on plasmon resonance of carbon nanotube dispersion", but correspond to infrared absorption from functional groups, respectively. More specifically, the wave number of 840 cm -1 corresponds to a peak based on plasmon resonance of CNT, and the wave numbers of 1300 cm -1The nearby spike is caused by out-of-plane bending vibration of CH; wavenumber 1300 cm⁻¹ -1 The nearby spike is caused by the stretching vibration of the epoxy three-membered ring; wavenumber 1700 cm⁻¹ -1 The nearby spikes are caused by C=O stretching vibrations. Additionally, at wavenumbers exceeding 2000 cm⁻¹... -1 In the region mentioned above by T. Morimoto et al. in non-patent literature, a peak similar to the S1 peak, different from plasmon resonance, was detected. Therefore, the inventors set the upper limit of the judgment on whether the CNT dispersion has a peak based on plasmon resonance in condition (1) to 2000. -1 Less than cm.

[0077] Here, in condition (1), when obtaining the spectrum based on Fourier transform infrared spectroscopy analysis, it is necessary to obtain a CNT dispersion by dispersing the CNT aggregate into bundles with a length of 10 μm or more. Here, for example, by mixing the CNT aggregate, water, and a surfactant (e.g., sodium dodecylbenzenesulfonate) in an appropriate ratio and stirring for a specified time using ultrasonic or other methods, a dispersion of CNTs with a bundle length of 10 μm or more can be obtained by dispersing them in water.

[0078] The bundle length of the CNT dispersion can be obtained by analysis using a wet image analysis particle size analyzer. This analyzer calculates the area of ​​each dispersion based on an image of the CNT dispersion, obtaining the diameter of a circle with the calculated area (hereinafter sometimes referred to as the ISO area diameter). Furthermore, in this specification, the bundle length of each dispersion is defined as the value of the ISO area diameter obtained in this way.

[0079] <<Condition (2)>>

[0080] Condition (2) specifies that "the largest peak in the pore distribution curve exists in the range of pore diameter greater than 100 nm and less than 400 nm". The pore distribution of carbon nanotube aggregates can be determined by the BJH method based on the adsorption isotherm of liquid nitrogen at 77 K. Moreover, the fact that the peak of the pore distribution curve obtained by measuring carbon nanotube aggregates exists in the range of greater than 100 nm means that there are gaps of a certain size between CNTs in the carbon nanotube aggregates, and the CNTs do not form an excessively dense aggregated state. In addition, the upper limit of 400 nm is the measurement limit of the measuring device (BELSORP-mini II) used in the example.

[0081] From the perspective of further improving the electromagnetic wave shielding performance of carbon films, the Log differential pore volume of the largest peak in the pore distribution curve of the CNT assembly is preferably 2.0 cm³. 3 / g or more.

[0082] Condition (3)

[0083] Condition (3) provides that "a peak of a two-dimensional spatial spectrum of an electron microscope image of the carbon nanotube aggregate exists in a range of 1 μm -1 or less and 100 μm -1 or more". The sufficiency of this condition can be judged according to the following points. First, an electron microscope (for example, an electron radiation scanning type electron microscope) is used to magnify and observe (for example, 10,000 times) the CNT aggregate which is the object of judgment, and a plurality of electron microscope images (for example, 10) are obtained in a field of view of 1 cm square. Fast Fourier transform (FFT) processing is performed on the plurality of obtained electron microscope images to obtain two-dimensional spatial spectra. The two-dimensional spatial spectra obtained for the respective plurality of electron microscope images are subjected to binarization processing, and the average of the peak positions appearing on the highest frequency side is calculated. In the case where the average of the obtained peak positions is in a range of 1 μm -1 or less and 100 μm -1 or more, it is judged that Condition (3) is satisfied. Here, as the "peak" used in the above judgment, a clear peak obtained by performing a solitary point extraction process (i.e., a reverse operation of eliminating solitary points) is used. Therefore, in the case where no clear peak is obtained in a range of 1 μm -1 or less and 100 μm -1 or more when the solitary point extraction process is performed, it is judged that Condition (3) is not satisfied.

[0084] Here, from the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, the peak of the two-dimensional spatial spectrum is preferably present in a range of 2.6 μm -1 or less and 100 μm -1 or more.

[0085] Further, from the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, the CNT aggregate preferably satisfies at least two of the above Conditions (1) to (3), and more preferably satisfies all of Conditions (1) to (3).

[0086] Other Properties

[0087] In addition, the CNT aggregate which can be used to form the carbon film of the present application preferably has the following properties in addition to the above Conditions (1) to (3).

[0088] For example, the total specific surface area of the CNT aggregate based on the BET method is preferably 600 m 2 / g or more, more preferably 800 m 2 / g or more, further preferably 900 m 2 / g or more, and preferably 2600 m2 / g or less, more preferably 1400 m 2 / g or less. In the case where the opening treatment is further performed, the total specific surface area is preferably 1300 m 2 / g or more. According to the CNT aggregate having a high specific surface area, the electromagnetic wave can be more favorably diffusely reflected inside the carbon film, and as a result, the electromagnetic wave shielding performance of the carbon film can be further improved. The CNT aggregate is mainly composed of single-walled CNTs, and can also contain double-walled CNTs and multi-walled CNTs to the extent that the function is not impaired. The total specific surface area of the CNTs based on the BET method can be measured, for example, using a BET specific surface area measuring device based on JIS Z8830.

[0089] Further, 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 further 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, the aggregation with the adjacent CNT bundles can be prevented, and dispersion thereof can be facilitated. If the average length of the CNTs constituting the CNT aggregate is 10 μm or more, the network of the CNTs with each other can be easily formed, and the CNT aggregate can be preferably used for applications requiring electrical conductivity or mechanical strength. When the average length of the CNTs constituting the CNT aggregate is 10 cm or less, since the CNT aggregate can be produced in a short time, the attachment of carbon-based impurities can be suppressed, and the specific surface area can be improved. If the average length of the CNTs constituting the CNT aggregate is 2 cm or less, dispersion thereof can be more easily facilitated. In addition, the average length of the CNTs can be measured by measuring the lengths of 100 CNTs selected at random using a scanning electron microscope (SEM).

[0090] The tap density of the CNT aggregate is preferably 0.001 g / cm 3 or more and 0.2 g / cm 3 or less, more preferably 0.02 g / cm 3 or more and 0.2 g / cm 3 or less. The CNT aggregate in such a density range is excellent in dispersibility because the binding of the CNTs with each other is not too strong, and can be formed into various shapes. If the tap density of the CNT aggregate is 0.2 g / cm 3 or less, the binding of the CNTs with each other becomes weak, and thus the CNT aggregate can be uniformly dispersed when the CNT aggregate is stirred in a solvent or the like. Further, if the tap density of the CNT aggregate is 0.001 g / cm 3The above improves the integrity of the CNT aggregate, and facilitates handling. The tap bulk density refers to the apparent bulk density in a tightly packed state after filling a container with a powder-like CNT aggregate, and reducing the interstitial space between the powder particles by tapping or vibration.

[0091] Further, the average outer diameter of the CNTs constituting the CNT aggregate is preferably 0.5 nm or more, further preferably 1.0 nm or more, preferably 15.0 nm or less, more preferably 10.0 nm or less, further preferably 5.0 nm or less, and still further preferably 4.0 nm or less. If the average outer diameter of the CNTs is 0.5 nm or more, the bundling of the CNTs to each other can be reduced, and a high specific surface area can be maintained. If the average outer diameter of the CNTs is 15.0 nm or less, the proportion of multi-walled CNTs can be reduced, and a high specific surface area can be maintained. 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 the standard deviation (σ) of the CNTs can be adjusted by changing the manufacturing method and manufacturing conditions of the CNTs, or by combining a plurality of CNTs obtained by different manufacturing methods.

[0092] The G / D ratio of the CNT aggregate is preferably 1 or more and 50 or less. It is considered that in a CNT aggregate having a G / D ratio of less than 1, the single-walled CNTs have low crystallinity, have much dirt such as amorphous carbon, and have a high content of multi-walled CNTs. On the contrary, in a CNT aggregate having a G / D ratio of more than 50, the linearity is high, the CNTs easily form bundles having few gaps, and it is likely that the specific surface area is reduced. The G / D ratio is an index generally used to evaluate the quality of CNTs. In the Raman spectrum of CNTs measured using a Raman spectrometer, vibration modes called G band (1600 cm -1 and D band (1350 cm -1 are observed. The G band is a vibration mode from the graphite hexagonal lattice structure of the cylindrical face of the CNT, and the D band is a vibration mode from the amorphous portion. Thus, the higher the peak intensity ratio of the G band to the D band (G / D ratio), the higher the crystallinity (linearity) of the CNTs can be evaluated.

[0093] To obtain a high specific surface area, it is desirable that the purity of the CNT aggregate be as high as possible. The purity referred to here is carbon purity, and is a value indicating what percentage of the mass of the CNT aggregate is constituted by carbon. To obtain a high specific surface area, there is no upper limit to the purity, but in terms of manufacturing, it is difficult to obtain a CNT aggregate of 99.9999 mass% or more. When the purity is less than 95 mass%, it is difficult to obtain a specific surface area of more than 1000 m 2The specific surface area is 1,000 m2 / g or more. Further, when the carbon purity is less than 95 mass% including metal impurities, the CNTs are hindered from being opened in the opening treatment due to the reaction of the metal impurities with oxygen, and the like, and as a result, the specific surface area is difficult to expand. From these viewpoints, the purity of the single-walled CNTs is preferably 95 mass% or more.

[0094] The prescribed CNT aggregate satisfying at least one of the above conditions (1) to (3) can have a purity of 98 mass% or more, and preferably 99 mass% or more even without a purification treatment. The CNT aggregate has almost no impurities mixed therein, and can sufficiently exhibit various characteristics of the CNTs as they are. The carbon purity of the CNT aggregate can be obtained by elemental analysis using fluorescent X-rays, thermogravimetric analysis (TGA), or the like.

[0095] <Method for manufacturing CNT aggregate>

[0096] The method for manufacturing the CNT aggregate is not particularly limited, and the manufacturing conditions can be adjusted according to the desired properties. For example, when the CNT aggregate satisfying at least one of the above conditions (1) to (3) is manufactured, the conditions at the time of growth of the CNT aggregate need to satisfy all of the following (a) to (c).

[0097] (a) The growth rate of the CNT aggregate is 5 μm / minute or more.

[0098] (b) The concentration of a catalyst activation substance in the growth environment of the CNT aggregate is 4 vol% or more.

[0099] (c) An obstacle exists in the growth direction of the CNTs constituting the CNT aggregate at the time of growth of the CNT aggregate.

[0100] Further, by the manufacturing method satisfying all of the above (a) to (c), the CNT aggregate satisfying any of the above conditions (1) to (3) can be efficiently manufactured. Further, in the manufacturing method, as long as the above conditions (a) to (c) are satisfied at the time of growth of the CNT aggregate, there is no particular limitation, and a CNT synthesis process according to a known method such as a flow layer method, a moving layer method, and a fixed layer method can be employed. Here, the flow layer method means a method of synthesizing CNTs while fluidizing a particulate support (hereinafter, also referred to as a particulate catalyst support) on which a catalyst for synthesizing CNTs is supported. Here, the moving layer method and the fixed layer method mean synthesis methods of synthesizing CNTs without fluidizing a support (particulate support or plate-shaped support) on which a catalyst is supported.

[0101] In one example, the production method satisfying all of the above (a) to (c) includes the following steps: a catalyst support forming step of forming a catalyst support; a CNT synthesizing step of synthesizing CNT using the catalyst support obtained in the catalyst support forming step; and a recovery step of recovering the CNT synthesized in the CNT synthesizing step. Also, the catalyst support forming step can be performed according to a known catalyst loading method, either wet or dry. Further, the recovery step can be performed using a known separation and recovery device such as a classification device.

[0102] [CNT synthesizing step]

[0103] In the CNT synthesizing step, all of the above conditions (a) to (c) are satisfied when CNT is grown. Specifically, by appropriately adjusting the concentration and temperature of a raw material gas as a carbon source in a CNT growth environment, and the like, the condition (a) that the growth rate of the carbon nanotube aggregate is 5 μm / minute or more can be satisfied. Here, the raw material gas as a carbon source is not particularly limited, and a gas of a hydrocarbon such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene, and acetylene; a gas of a lower alcohol such as methanol, ethanol; and a mixture thereof can be used. Here, the raw material gas can also be diluted with an inert gas. Here, from the viewpoint of further improving the dispersibility of the obtained CNT aggregate and further improving the electromagnetic wave shielding performance of the carbon film, the growth rate of the CNT aggregate is preferably 10 μm / minute or more. In addition, the temperature can be adjusted, for example, in the range of 400°C or more and 1100°C or less.

[0104] It is preferable that the raw material gas as a carbon source contain ethylene under the CNT growth environment. By heating ethylene in a prescribed temperature range (700°C or more and 900°C or less), the decomposition reaction of ethylene is promoted, and when the decomposition gas contacts the catalyst, the CNT can be grown at high speed. However, when the thermal decomposition time is too long, the decomposition reaction of ethylene is excessively performed, causing deactivation of the catalyst and attachment of carbon impurities to the CNT aggregate. In the production of the CNT aggregate of the present application, for an ethylene concentration in the range of 0.1% by volume or more and 40% by volume or less, the thermal decomposition time is preferably in the range of 0.5 seconds or more and 10 seconds or less. If the thermal decomposition time is less than 0.5 seconds, the thermal decomposition of ethylene is insufficient, and it is difficult to grow the CNT aggregate with a high specific surface area at high speed. When it is more than 10 seconds, ethylene is excessively decomposed, a large amount of carbon impurities is generated, and deactivation of the catalyst and a decrease in the quality of the CNT aggregate are caused. The thermal decomposition time is calculated according to the following formula.

[0105] (Thermal decomposition time) = (Heating flow path volume) / {(Raw material gas flow rate) x (273.15 + T) / 273.15}

[0106] Here, the heated flow path volume refers to the volume of the flow path heated to a prescribed temperature T°C through which the raw material gas passes before coming into contact with the catalyst, and the raw material gas flow rate is the flow rate at 0°C, 1 atm.

[0107] Further, by appropriately adjusting the supply rate of the catalyst activation substance supplied when growing the CNT, the condition (b) that the concentration of the catalyst activation substance in the growth environment of the carbon nanotube aggregate is 4% by volume or more can be satisfied. From the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, the concentration of the catalyst activation substance in the growth environment of the CNT aggregate is preferably 5% by volume or more. As the catalyst activation substance, there is no particular limitation, and examples include water, oxygen, ozone, acidic gases, nitrogen oxides, carbon monoxide, carbon dioxide, and other low-carbon-number oxygen-containing compounds; 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. In addition, substances such as carbon monoxide and alcohols that contain both carbon and oxygen sometimes have both the functions of the raw material gas and the catalyst activation substance. For example, carbon monoxide functions as a catalyst activation substance if combined with a raw material gas such as ethylene that has higher reactivity, and functions as a raw material gas if combined with a catalyst activation substance such as water that exhibits a large catalyst activation effect even in a small amount.

[0108] Further, by selecting the flow layer method or by adjusting the arrangement interval of the catalyst support in the moving layer method or the fixed layer method in the CNT synthesis process, the condition (c) that an obstacle exists in the growth direction of the carbon nanotube constituting the carbon nanotube aggregate when synthesizing the carbon nanotube aggregate can be satisfied.

[0109] Here, when synthesizing the CNT by the flow layer method described above, the CNT synthesis process can be performed, for example, while flowing the granular catalyst support by supplying the gas from below and supplying the raw material gas, or can be performed while continuously transporting the granular catalyst support by rotating the screw and supplying the raw material gas.

[0110] The catalyst support has a support and a catalyst supported on the surface of the support, and the support is a portion that forms a basic structure for supporting, fixing, film-forming, or molding the catalyst on the surface of the support. As the structure of the support, it can be only the support, or it can be a support with a base layer provided on the surface of the support for supporting the catalyst well. The shape of the support is preferably granular, and the particle diameter is preferably 1 mm or less, more preferably 0.7 mm or less, further preferably 0.65 mm or less, and preferably 0.05 mm or more, in terms of the volume average particle diameter. If the particle diameter is the above upper limit or less, the CNT bundle grown is thin, and this is advantageous for forming a wavy structure. The particle density is preferably 3.8 g / cm 3More preferably, the above is 5.8 g / cm 3 More preferably, the above is 8 g / cm 3 If the particle density is equal to or higher than the above lower limit, the force applied to the growing CNT bundle increases, which is advantageous for forming a wavy structure. The material of the carrier is preferably a metal oxide containing one or more of Al and Zr. Among them, zirconium oxide beads containing Zr having a large atomic weight are particularly preferable.

[0111] For example, in the case of using a particulate carrier, as a method of loading a catalyst on the surface of the particulate carrier, a method using a drum coater having a substantially cylindrical drum can be given. In the case of loading a catalyst after disposing a base layer on the surface of the particulate carrier, a solution containing a component capable of forming a base layer is sprayed on the surface of the particulate carrier and dried before spraying and drying a catalyst solution, and a base layer is disposed on the surface of the carrier. According to such a method, a catalyst layer and a base layer can be formed relatively simply and uniformly.

[0112] Furthermore, in the CNT synthesis process, before the "growth step" performed in a manner satisfying the above conditions (a) to (c), a "formation step" of reducing the catalyst supported on the catalyst carrier is performed, and after the growth step, a "cooling step" of cooling the catalyst carrier on which CNTs have grown can be performed. In the "formation step", for example, an environment containing the catalyst carrier is set as a reducing gas environment, and at least one of the reducing gas environment or the catalyst carrier is heated to reduce and particulate the catalyst supported on the catalyst carrier. The temperature of the catalyst carrier or the reducing gas environment in the formation step is preferably 400°C or higher and 1100°C or lower. Furthermore, the implementation time of the formation step can be 3 minutes or more and 120 minutes or less. In addition, as the reducing gas, for example, hydrogen, ammonia, water vapor, and a mixed gas thereof can be used. Furthermore, the reducing gas can also be a mixed gas obtained by mixing these gases with an inert gas such as helium, argon, nitrogen, or the like. On the other hand, in the "cooling step", the catalyst carrier on which CNTs have grown is cooled in an inert gas environment. Here, as the inert gas, the same inert gas as that which can be used in the growth step can be used. Furthermore, in the cooling step, the temperature of the catalyst carrier on which CNTs have grown is preferably reduced to 400°C or lower, and further preferably reduced to 200°C or lower.

[0113] Dry pulverization treatment

[0114] In obtaining the carbon film of the present application, dry pulverization treatment can be performed on the CNT aggregate before film formation, as necessary. In the present application, "dry pulverization treatment" means pulverization treatment in a state in which the pulverization target substantially does not contain a solvent (for example, in a state in which the solid content concentration is 95% or more).

[0115] As the pulverization device that can be used for the dry pulverization treatment, there is no particular limitation as long as it is a device that can apply physical load to an aggregate composed of fine structures by stirring or the like. As such a device, a stirrer having a rotating blade can be used.

[0116] Further, the pulverization conditions are not particularly limited. For example, in the case where a stirrer having a rotating blade is used as the pulverization device, the rotation speed is preferably 500 rpm or more and 5000 rpm or less, and the pulverization time is preferably 10 seconds or more and 20 minutes or less.

[0117] < Film formation >

[0118] By film forming the CNT aggregate, the carbon film of the present application can be obtained. In this regard, the method of film forming the CNT aggregate is not particularly limited, and a method of preparing a CNT dispersion liquid by dispersing the CNT aggregate in a dispersion medium such as water or an organic solvent, and removing at least a part of the dispersion medium from the CNT dispersion liquid can be preferably selected.

[0119] The method of preparing the CNT dispersion liquid is not particularly limited, and the CNT dispersion liquid can be obtained by dispersing the CNT aggregate in a dispersion medium by a known method using shear force such as a dispersion method using a stirring blade, a dispersion method using ultrasonic waves, a high-pressure wet jet mill, or the like.

[0120] In this regard, the preferable conditions of each dispersion method for obtaining the carbon film of the present application are as follows.

[0121] In the case where the dispersion method using a stirring blade is used, the dispersion of the CNT in the dispersion medium is preferably performed at a rotation speed of the stirring blade of 1500 rpm or more and 12500 rpm or less, more preferably 2000 rpm or more and 10000 rpm or less, and is preferably performed for 1 minute or more and 120 minutes or less, more preferably for 5 minutes or more and 100 minutes or less. The dispersion using a stirring blade can be performed using a known dispersion device having a stirring blade.

[0122] In the case where the dispersion method using ultrasonic waves is used, the dispersion of the CNT in the dispersion medium is preferably performed at a frequency of 50 kHz or more and 500 kHz or less for 1 minute or more and 120 minutes or less, more preferably for 2 minutes or more and 100 minutes or less. The dispersion using ultrasonic waves can be performed using a known ultrasonic wave disperser.

[0123] In the case of using a dispersion method using a wet jet mill, the dispersion pressure of the CNT in the dispersion medium is preferably 20 to 200 MPa, and the treatment time is preferably 5 to 30 minutes. The dispersion using a wet jet mill can be performed using a publicly known wet jet mill device.

[0124] Further, from the viewpoint of further improving the electromagnetic wave shielding performance of the obtained carbon film, it is preferable that the CNT be moderately dispersed in the CNT dispersion liquid. It is preferable that the CNT dispersion liquid not contain a dispersant. In other words, the CNT dispersion liquid is preferably composed of substantially only the CNT and the dispersion medium. In the present specification, "the CNT dispersion liquid is composed of substantially only the CNT and the dispersion medium" means that 99.9% by mass or more of the constituent components of the CNT dispersion liquid are composed of the CNT and unavoidable impurities accompanying the CNT, and the dispersion medium and unavoidable impurities accompanying the dispersion medium.

[0125] Further, as a method of removing the dispersion medium from the CNT dispersion liquid, known methods such as filtration and drying can be given.

[0126] As the method of filtration, there is no particular limitation, and known filtration methods such as natural filtration, reduced pressure filtration (suction filtration), pressure filtration, centrifugal filtration, and the like can be used.

[0127] As the method of drying, known drying methods such as hot air drying, vacuum drying, heat roll drying, infrared irradiation, and the like can be used. The drying temperature is not particularly limited, and is usually room temperature to 200°C, and the drying time is not particularly limited, and is usually 1 hour or more and 48 hours or less. Further, the drying is not particularly limited, and can be performed on a known substrate.

[0128] Among these, it is preferable to at least use drying in the removal of the dispersion medium.

[0129] Further, the above filtration and drying can be used in combination. For example, a film-shaped filter (primary sheet) obtained by filtering the CNT dispersion liquid can be further dried to obtain the carbon film of the present application.

[0130] Examples

[0131] Hereinafter, the present application will be specifically described by giving examples, but the present application is not limited to these examples.

[0132] Further, in the examples and comparative examples, various measurements and evaluations were performed as follows.

[0133] <Ultra-small-angle X-ray scattering measurement>

[0134] The carbon film produced as described later was cut into a 1.5 cm square to obtain a test piece. Then, the obtained test piece was subjected to ultra-small angle X-ray scattering measurement under the following conditions to obtain a scattering image.

[0135] [Measurement conditions]

[0136] X-ray energy: 10 keV (0.124 nm)

[0137] Beamline: SPrimg-8 BL24XU

[0138] Detector: APD (avalanche photodiode)

[0139] q (wave number) range:

[0140] Apparatus: Bonse & Hart USAXS

[0141] <Utilization of data obtained by ultra-small angle X-ray scattering measurement>

[0142] For the scattering image obtained by the ultra-small angle X-ray scattering measurement as described above, a scattering graph was obtained. Using IgorPro 8 (manufactured by WaveMetrics, Inc.) as analysis software, the wave number range was set to The obtained scattering graph was fitted with the Beaucage formula represented by the above general formula (I) to obtain the fractal dimension P i of each hierarchical level i, and the size of the CNT aggregate In addition, the number of hierarchical levels was N = 3. Here, the fitting indicates the error of the measured scattering graph from the calculated value.

[0143] [Mathematical formula 2]

[0144]

[0145] This was performed in the manner of the above mathematical formula 2 being 10 or less. In the case where this value is 10 or less, it can be considered that the fitting is good. The values of the fractal dimension P1, the size R g，1 of the CNT aggregate, and the size of the CNT aggregate

[0146] <Fourier transform infrared spectroscopy analysis (FT-IR)>

[0147] To 10 mg of the CNT aggregate, 100 g of water containing sodium dodecylbenzenesulfonate as a surfactant at a concentration of 1 mass% was added, and stirring was performed using an ultrasonic bath at 45 Hz for 1 minute to obtain 100 ml of a dispersion liquid of each CNT aggregate. Each of the prepared dispersion liquids was diluted 2-fold using a solvent of the same composition, and after being dropped onto a silicon substrate and dried, a plasmonic far infrared (FIR) resonance spectrum was obtained using a Fourier transform infrared spectrophotometer, and a resonance peak was obtained. In addition, the position of the plasmonic peak top was obtained using a drawing software by a curve approximation of a polynomial.

[0148] <Measurement of CNT bundle length>

[0149] For each of the dispersion liquids prepared in the FT-IR measurement, a flow-type particle imaging analyzer (JASCO International Co., Ltd., circulating image analysis particle size distribution meter "CF-3000") was used to measure the ISO circular diameter average of the CNT dispersion present in the dispersion liquid, and the obtained value was used as the CNT bundle length. The analysis conditions were as follows.

[0150] [Analysis conditions]

[0151] • Injection amount: 50 ml (sampling volume 1.2%)

[0152] • Flow cell gasket: 1000 μm

[0153] • Front lens magnification: 2 times

[0154] • Telecentric lens magnification: 0.75 times

[0155] • Length per pixel: 2.3 μm / pixel

[0156] For each of the dispersion liquids, 4 measurements were performed under the same conditions while circulating, and the arithmetic mean value thereof was obtained.

[0157] <Production of pore distribution curve (CNT aggregate)>

[0158] For 10 mg or more of the CNT aggregate, a BELSORP-mini II (manufactured by BEL Japan Co., Ltd.) was used to measure an adsorption isotherm at 77 K using liquid nitrogen (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, in the production of 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.

[0159] (Two-dimensional spatial frequency spectrum analysis of electron microscope image)

[0160] A 0.01 mg of the CNT aggregate 1 prepared according to the following step was placed on a carbon tape, and the excess CNT was blown off with an air blower to make a test piece, and observation was performed at 10,000 times using an electrolytic radiation scanning electron microscope, and 10 photographs were taken in a 1 cm square field of view extracted at random. The 10 electron microscope images taken were subjected to fast Fourier transform processing to obtain two-dimensional spatial frequency spectra. Each of the obtained two-dimensional spatial frequency spectra was subjected to binarization processing, and the peak position appearing at the outermost side (high frequency side) was found to obtain an average value. In addition, in the binarization processing, values greater than 0.75 were set to 1, and the remaining values were set to 0.

[0161] <Thickness>

[0162] The thickness of the carbon film was measured using a "Digimatic Outside Micrometer" manufactured by Mitutoyo Corporation.

[0163] <Porosity>

[0164] The test piece was cut out to 1 cm square from the carbon film prepared to measure the mass (g) of the test piece, and the density (bulk density) of the carbon film was calculated according to the following formula (1). Next, using the obtained bulk density, the porosity of the carbon film was calculated according to the following formula (2).

[0165] • Bulk density of carbon film (g / cm 3 ) = mass of test piece (g) / (1 cm 2 × thickness of test piece (cm))... (1)

[0166] • Porosity = (1 - (bulk density of carbon film (g / cm 3 ) / 1.3)) x 100... (2)

[0167] In addition, "1.3" in formula (2) refers to the true density (g / cm 3 ) of carbon.

[0168] <Electromagnetic Wave Shielding Performance>

[0169] The reflection coefficient S11 and the transmission coefficient S21 of the carbon film were measured by the microstrip line method based on IEC-62333-2, and the transmission attenuation rate "dB" was calculated as the electromagnetic wave shielding performance.

[0170] Then, the electromagnetic wave shielding performance [dB] at the measurement frequencies of 2.5 MHz, 4.5 MHz, and 7.5 MHz was evaluated according to the following criteria. The greater the value of the transmission attenuation rate [dB] at a certain frequency, the more excellent the electromagnetic wave shielding performance of the carbon film at that frequency.

[0171] A: Transmission attenuation rate is 25 dB or more

[0172] B: Transmission attenuation rate is 20 dB or more and less than 25 dB

[0173] C: Transmission attenuation rate is less than 20 dB

[0174] (Example 1)

[0175] Preparation of CNT aggregate 1

[0176] The CNT aggregate 1 used in Example 1 was produced by the following method, in which a granular catalyst support was continuously fed by screw rotation in a CNT synthesis process while supplying a raw material gas, thereby producing. In Figure 8 The schematic structure of the CNT aggregate production apparatus 200 used is shown in FIG. 1. Figure 8The CNT aggregate manufacturing apparatus 200 shown has a formation unit 202, a growth unit 204, a conveyance unit 207 that conveys a substrate from the formation unit 202 to through the growth unit 204, a connection portion 208 that spatially connects the formation unit 202 and the growth unit 204 to each other, and a gas mixing prevention apparatus 203 that prevents gases from mixing with each other between the formation unit 202 and the growth unit 204. Further, the CNT aggregate manufacturing apparatus 200 has a structure including an inlet purge apparatus 201 disposed at a front stage of the formation unit 202, an outlet purge apparatus 205 disposed at a rear stage of the growth unit 204, and a cooling unit 206 disposed at a rear stage of the outlet purge apparatus 205. The formation unit 202 is composed of a formation furnace 202a for holding a reducing gas, a reducing gas injection apparatus 202b for injecting the reducing gas, a heating apparatus 202c for heating at least one of a catalyst and the reducing gas, and an exhaust apparatus 202d for discharging a gas in the furnace to the outside of the system. The gas mixing prevention apparatus 203 has an exhaust apparatus 203a and a purge gas injection apparatus 203b for injecting a purge gas (sealing gas). The growth unit 204 has a growth furnace 204a for holding a raw material gas environment, a raw material gas injection apparatus 204b for injecting the raw material gas, a heating apparatus 204c for heating at least one of a catalyst and the raw material gas, and an exhaust apparatus 204d for discharging a gas in the furnace to the outside of the system. The inlet purge apparatus 201 is installed in a connection portion 209 that connects a front chamber 213, which is a structure for introducing a substrate 211 into the system via a hopper 212, and the formation furnace 202a. The cooling unit 206 has a cooling container 206a for holding an inert gas, and a water-cooling cooling apparatus 206b disposed so as to surround an inner space of the cooling container 206a. The conveyance unit 207 is a unit that continuously conveys the substrate 211 by screw rotation. The conveyance unit 207 is installed with a screw blade 207a and a driving apparatus 207b that can rotate the screw blade to a state in which the substrate conveying function is exerted. The heating apparatus 214 is configured to be able to heat the inside of the system at a lower temperature than the heating temperature in the formation unit, and to heat a vicinity of the driving apparatus 207b.

[0177]

[0178] ​Zirconia (zirconia) beads (ZrO2, volume average particle size D50: 650 μm) as the substrate were fed into a rotary drum coating apparatus. While stirring (20 rpm), the zirconia beads were sprayed with an aluminum-containing solution using a spray gun (spray rate 3 g / min, spray time 940 s, spray pressure 10 MPa), and compressed air (300 L / min) was supplied to the drum to dry them, forming an aluminum-containing coating film on the zirconia beads. Next, the mixture was sintered at 480°C for 45 minutes to produce primary catalyst particles with an alumina layer. Then, these primary catalyst particles were fed into another rotary drum coating apparatus. While stirring (20 rpm), an iron catalyst solution was sprayed with a spray gun using a spray gun (spray rate 2 g / min, spray time 480 s, spray pressure 5 MPa), and compressed air (300 L / min) was supplied to the drum to dry them, forming an iron-containing coating film on the primary catalyst particles. Next, a sintering process is performed at 220°C for 20 minutes to produce a substrate with an iron oxide layer.

[0179] <<CNT Synthesis Process>>

[0180] The substrate with catalyst on its surface, prepared in this way, is fed into the feed hopper of the CNT aggregate manufacturing apparatus. While being transported by a screw conveyor, it is processed in the order of formation, growth and cooling to manufacture CNT aggregate 1.

[0181] <Forming process ~ Cooling process>

[0182] The conditions for the inlet purging device, forming unit, gas mixing prevention device, growth unit, outlet purging device, and cooling unit of the CNT assembly manufacturing apparatus are set as follows.

[0183] Feed hopper

[0184] • Feeding speed: 1.25 kg / h

[0185] • Exhaust volume: 10sLm (natural exhaust from the gap)

[0186] Inlet purging device

[0187] • Purge gas: Nitrogen 40sLm

[0188] Forming unit

[0189] Furnace temperature: 800℃

[0190] • Reducing gases: Nitrogen 6 s Lm, Hydrogen 5 4 s Lm

[0191] • Displacement: 60Lm

[0192] Processing time: 20 minutes

[0193] Gas mixing prevention device

[0194] • Purge gas: 20 sLm

[0195] • Exhaust amount of the exhaust device: 62 sLm

[0196] Growth unit

[0197] • In-furnace temperature: 830°C

[0198] • Raw material gas: nitrogen 15 sLm, ethylene 5 sLm, carbon dioxide 1 sLm, hydrogen 3 sLm

[0199] • Exhaust amount: 47 sLm

[0200] • Processing time: 10 minutes

[0201] Outlet purge device

[0202] • Purge gas: nitrogen 45 sLm

[0203] Cooling unit

[0204] • Cooling temperature: room temperature

[0205] • Exhaust amount: 10 sLm (naturally exhausted from the gap)

[0206] Continuous production was performed under the above conditions.

[0207] <Separation and recovery process>

[0208] The CNT aggregate 1 synthesized on the substrate was separated and recovered using a forced vortex type classification device (rotation speed 2300 rpm, air flow 3.5 Nm 3 / minute). The recovery rate of the CNT aggregate 1 was 96%.

[0209] As typical values for the properties of the CNT aggregate 1 produced in this example, the tap bulk density was 0.02 g / cm 3 , the average length of the CNTs was 150 μm, the BET specific surface area was 900 m 2 / g, the average outer diameter was 4.0 nm, and the carbon purity was 99%.

[0210] Here, in the CNT aggregate 1, a peak based on plasmon resonance of the CNT dispersion was confirmed. Figure 5 A FIR resonance chart showing the FIR spectrum of the CNT aggregate 1 is shown. As Figure 5 shown, in the CNT aggregate 1, a peak of optical density was observed at 835 cm -1 , satisfying the above condition (1).

[0211] Further, as shown in Figure 6 CNT aggregate 1 confirmed the largest peak of Log differential fine pore volume in the region where the fine pore diameter was 100 nm or more, satisfying the above condition (2).

[0212] Further, in CNT aggregate 1, in the range of 1 μm -1 and 100 μm -1 , it was confirmed that there was at least one peak, satisfying the above condition (3). This can be grasped depending on the following conditions. Figure 7A is one of 10 images obtained for the prepared CNT aggregate 1, Figure 7B is a two-dimensional spatial spectrum obtained for the image. In Figure 7B , the component closer to the center indicates a low frequency component, and the component located further from the center corresponds to a higher frequency component. In the figure, the position of the peak (3 μm -1 ) of the highest wave number in the clear peak detected in the region of 1 to 100 μm -1 is shown with an arrow.

[0213] To 1 g of the CNT aggregate 1 obtained as described above, 1000 g of water was added, and using a super high-speed emulsification dispersing device (product name "LABOLUTION (registered trademark)", New Kikai Seizo Co., Ltd.), stirring was performed at a rotation speed of 3000 rpm for 10 minutes to obtain a CNT dispersion liquid.

[0214] The obtained CNT dispersion liquid was applied to a substrate. The coating film on the substrate was vacuum dried at a temperature of 80°C for 24 hours to form a carbon film on the substrate. Then, the carbon film was peeled from the substrate to obtain a carbon film (self-supporting film) having a thickness of 543 μm. Various measurements and data analysis were performed, and in addition, electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0215] (Example 2)

[0216] In the preparation of the CNT dispersion liquid, using a super high-speed emulsification dispersing device (product name "LABOLUTION (registered trademark)", New Kikai Seizo Co., Ltd.), stirring was performed at a rotation speed of 7500 rpm for 15 minutes, and otherwise, the same as in Example 1 was performed to obtain a carbon film (self-supporting film) having a thickness of 261 μm. The obtained carbon film was evaluated for electromagnetic wave shielding performance. The results are shown in Table 1.

[0217] (Example 3)

[0218] In the preparation of the CNT dispersion liquid, a jet mill (manufactured by YIDAMA KIKAI CO., LTD., NanoVater) was used to disperse the CNTs for 15 minutes at 100 MPa, and a CNT dispersion liquid was obtained. Other than this, the same procedure as in Example 1 was followed to obtain a carbon film (self-supporting film) having a thickness of 190 μm. The obtained carbon film was subjected to various measurements and data analysis, and the electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0219] (Comparative Example 1)

[0220] After 1000 g of an aqueous solution containing 1 mass% of sodium dodecylbenzenesulfonate (SDBS) as a dispersant was mixed with 1 g of the above-described CNT aggregate 1 to obtain a crude dispersion liquid, a jet mill (manufactured by YIDAMA KIKAI CO., LTD., NanoVater) was used to disperse the crude dispersion liquid for 15 minutes at 100 MPa, and a CNT dispersion liquid was obtained. The obtained CNT dispersion liquid was applied to a substrate. The coating film on the substrate was vacuum-dried at 80°C for 24 hours to form a carbon film on the substrate. Then, the carbon film was peeled from the substrate to obtain a carbon film (self-supporting film) having a thickness of 181 μm. Various measurements and data analysis were performed, and the electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0221] (Comparative Example 2)

[0222] As the CNT aggregate, SGCNT (product name "ZEONANO SG101", manufactured by ZEON CORPORATION) as single-walled CNTs was used instead of the above-described CNT aggregate 1, and in the preparation of the CNT dispersion liquid, an ultrahigh-speed emulsifying dispersing device (product name "LABOLUTION (registered trademark)", manufactured by SHINKI CO., LTD.) was used to stir at a rotation speed of 10,000 rpm for 60 minutes, and other than this, the same procedure as in Example 1 was followed to obtain a carbon film (self-supporting film) having a thickness of 159 μm. The obtained carbon film was evaluated for electromagnetic wave shielding performance. The results are shown in Table 1.

[0223] Here, in the above-described SGCNT, a peak of optical density was found at 230 cm -1 in the FIR resonance chart of the FIR spectrum, and the above-described condition (1) was not satisfied. Further, the above-described SGCNT did not have a peak of the largest Log differential pore volume in the range of 100 nm or more in the pore diameter, and the above-described condition (2) was not satisfied. Furthermore, the above-described SGCNT did not have a clear peak in the range of 1 μm -1 or more and 100 μm -1 or less, and the above-described condition (3) was not satisfied.

[0224] (Comparative Example 3)

[0225] As the CNT assembly, the aforementioned SGCNT (product name "ZEONANO SG101", manufactured by Zeon Corporation, Japan) was used instead of CNT assembly 1, and the process was carried out in the same manner as in Example 3, resulting in a carbon film (self-supporting film) with a thickness of 154 μm. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0226] (Comparative Example 4)

[0227] 1 g of the above-mentioned SGCNTs were mixed with 1000 g of an aqueous solution containing 1% by mass of sodium dodecylbenzenesulfonate (SDBS) as a dispersant to obtain a coarse dispersion. This coarse dispersion was then dispersed using a jet mill (manufactured by Yoshida Machinery Co., Ltd., NanoVater) at 100 MPa for 15 minutes to obtain a CNT dispersion. The obtained CNT dispersion was coated onto 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 (self-supporting film). Various measurements and data analysis were performed, and the electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

[0228] [Table 1]

[0229]

[0230] As shown in Table 1, when the carbon films in Examples 1-3 are measured using ultra-small angle X-ray scattering and the resulting scattering patterns are fitted using the Beaucage formula, The above and The fractal dimension in the following wavenumber range is 2.6 or higher and 4 or lower, and the porosity of the carbon film is 80% or higher and 95% or lower. The carbon films of Examples 1 to 3 have a transmission attenuation rate of 25 dB or higher at any measured frequency, and have excellent electromagnetic wave shielding performance.

[0231] In contrast, it can be seen that when the carbon films of Comparative Examples 1-4 are measured by ultra-small angle X-ray scattering and the resulting scattering patterns are fitted using the Beaucage formula, The above and The fractal dimension in the following wavenumber range is not greater than 2.6 and less than 4, or the porosity of the carbon film is not greater than 80% and less than 95%. The carbon films of Comparative Examples 1 to 4 have a transmission attenuation rate of less than 25dB at at least a certain measurement frequency, and their electromagnetic wave shielding performance is poor compared with the carbon films of Examples 1 to 3.

[0232] Industrial availability

[0233] According to the present invention, a carbon film with excellent electromagnetic wave shielding performance can be provided.

[0234] BRIEF DESCRIPTION OF DRAWINGS

[0235] 200: CNT aggregate manufacturing apparatus

[0236] 201: inlet purge device

[0237] 202: formation unit

[0238] 202a: formation furnace

[0239] 202b: reducing gas injection device

[0240] 202c: heating device

[0241] 202d: exhaust device

[0242] 203: gas mixing prevention device

[0243] 203a: exhaust device

[0244] 203b: purge gas injection device

[0245] 204: growth unit

[0246] 204a: growth furnace

[0247] 204b: raw material gas injection device

[0248] 204c: heating device

[0249] 204d: exhaust device

[0250] 205: outlet purge device

[0251] 206: cooling unit

[0252] 206a: cooling container

[0253] 206b: water-cooled cooling device

[0254] 207: conveyance unit

[0255] 207a: screw blade

[0256] 207b: drive device

[0257] 208-209: connection portion

[0258] 211: base material

[0259] 212: hopper

[0260] 213: antechamber

[0261] 214: heating device

Claims

1. A carbon film composed of a carbon nanotube assembly, when at least one surface of the carbon film is subjected to ultra-small angle X-ray scattering measurement and a scattering pattern obtained is fitted with a Beaucage formula, a fractal dimension in a wave number range of 0.0001 1 / A or more and 0.001 1 / A or less is 2.6 or more and 4 or less, and a porosity of the carbon film is 80% or more and 95% or less.

2. The carbon film according to claim 1, wherein, When at least one surface of the carbon film is subjected to ultra-small angle X-ray scattering measurement and the resulting scattering pattern is fitted with the Beaucage equation, the size of the carbon nanotube aggregate in a wave number range of 0.0001 1 / Å or more and 0.001 1 / Å or less is 1.0 x 10 5 Å or more and 4.0 x 10 7 Å or less.

3. The carbon film according to claim 1 or 2, wherein, The carbon film is a self-supporting film.

4. The carbon film according to claim 1 or 2, wherein, A thickness of the carbon film is 5 μm or more and 1000 μm or less.

5. The carbon film according to claim 1 or 2, wherein, A transmission attenuation rate of the carbon film at at least one frequency in a range of 1 GHz or more and 10 GHz or less is 20 dB or more.

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