WO2022114237A1

WO2022114237A1 - Carbon film

Info

Publication number: WO2022114237A1
Application number: PCT/JP2021/043974
Authority: WO
Inventors: 智子山岸; 貢上島
Original assignee: 日本ゼオン株式会社
Priority date: 2020-11-30
Filing date: 2021-11-30
Publication date: 2022-06-02
Also published as: JPWO2022114237A1

Abstract

Provided is a carbon film comprising carbon nanotube aggregates. The average surface roughness value of the carbon film is 4.0 μm or more.

Description

Carbon film

The present invention relates to a carbon film.

In recent years, carbon nanotubes (hereinafter, may be referred to as "CNT") have been attracting attention as a material having excellent conductivity, thermal conductivity and mechanical properties. However, since CNT is a fine structure having a diameter of nanometer size, it is difficult to handle and process by itself. Therefore, in order to secure handleability and processability and use it for various purposes, it has been conventionally used to form a carbon film by forming an aggregate composed of a plurality of CNTs (hereinafter referred to as "carbon nanotube aggregate"). (See, for example, Patent Document 1).

Patent Document 1 uses a carbon nanotube aggregate having a region of 10 nm or more in which pores having a bore size of 400 nm or more and 1500 nm or less, which are measured by a mercury intrusion method, have a Log differential pore volume of 0.006 cm ³ / g or less. Therefore, a carbon film having excellent mechanical strength is formed.

Japanese Unexamined Patent Publication No. 2018-14502

Here, in recent years, electromagnetic wave shielding has been attracting attention as an application of carbon film. However, there is room for further improvement in the performance of blocking the electromagnetic waves of the conventional carbon film, that is, the electromagnetic wave shielding performance.

Therefore, an object of the present invention is to provide a carbon film having excellent electromagnetic wave shielding performance.

The present inventors have made extensive studies to achieve the above object. Then, the present inventors investigated the microscopic properties of the carbon film formed by using the carbon nanotube aggregate, and the carbon film having an average surface roughness of 4.0 μm or more shields electromagnetic waves well. We have newly found what we can obtain and completed the present invention.

That is, the present invention aims to solve the above problems advantageously, and the carbon film of the present invention is a carbon film made of an aggregate of carbon nanotubes, and the average value of the surface roughness is 4. It is characterized in that it is 0 μm or more. When the average value of the surface roughness of the carbon film is 4.0 μm or more, the carbon film is excellent in electromagnetic wave shielding performance.
Here, the surface roughness of the carbon film can be measured by the method described in the examples of the present specification.

Here, in the carbon film of the present invention, it is preferable that the average value of the surface roughness is 5.0 μm or more. When the average value of the surface roughness of the carbon film is 5.0 μm or more, the electromagnetic wave shielding performance is further excellent.

Here, the carbon film of the present invention is preferably a self-supporting film. The carbon film, which is a self-supporting film, has excellent handleability, and when used as an electromagnetic wave shielding sheet, for example, the degree of freedom in arranging the sheet can be increased. In the present invention, the "self-supporting film" refers to a film that can maintain its film shape by itself without being damaged even in the absence of a support.

Further, in the carbon film of the present invention, it is preferable that the carbon nanotube aggregate satisfies at least one of the following conditions (1) to (3).
(1) The plasmon of the carbon nanotube dispersion in the spectrum obtained by Fourier transform infrared spectroscopic analysis of the carbon nanotube dispersion obtained by dispersing the carbon nanotube aggregate so that the bundle length is 10 μm or more. There is at least one resonance-based peak in the range of wavenumbers above 300 cm ^-1 and above 2000 cm ^-1 .
(2) For the carbon nanotube aggregate, a pore distribution curve showing the relationship between the pore diameter and the Log differential pore volume obtained from the adsorption isotherm of liquid nitrogen at 77K based on the Barrett-Joiner-Halenda method. The largest peak in is in the range of pore diameters greater than 100 nm and less than 400 nm.
(3) At least one peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate exists in the range of 1 μm ^-1 or more and 100 μm ^-1 or less.
A carbon film made of an aggregate of carbon nanotubes satisfying the above-mentioned predetermined conditions is further excellent in electromagnetic wave shielding performance. The sufficiency of the above-mentioned predetermined conditions can be determined according to the method described in the examples.

According to the present invention, it is possible to provide a carbon film having excellent electromagnetic wave shielding performance.

The laser microscope image obtained about the surface of the carbon film produced in Example 1 is shown. The laser microscope image obtained about the surface of the carbon film produced in Example 2 is shown. The laser microscope image obtained about the surface of the carbon film produced in Example 3 is shown. The laser microscope image obtained about the surface of the carbon film prepared in Example 4 is shown. The laser microscope image obtained about the surface of the carbon film prepared in the comparative example 1 is shown. An SEM image of the CNT aggregate according to an example is shown. The FIR resonance chart acquired for the CNT aggregate according to an example is shown. The pore distribution curve of the CNT aggregate according to an example is shown. It is an SEM image of the CNT aggregate according to one example. It is a two-dimensional spatial frequency spectrum of the image of FIG. 8A. It is an SEM image of the CNT aggregate according to another example. 9 is a two-dimensional spatial frequency spectrum of the image of FIG. 9C. The schematic configuration of the CNT manufacturing apparatus is shown. The schematic configuration of the CNT manufacturing apparatus used in Example 4 is shown.

Hereinafter, embodiments of the present invention will be described in detail.
The carbon film of the present invention is composed of an aggregate of a plurality of carbon nanotubes (a carbon nanotube aggregate). The carbon film of the present invention may contain, for example, CNT aggregates and components other than CNTs inevitably mixed in the process of producing the carbon film, but the proportion of CNTs in the carbon film is 95% by mass. The above is preferable, 98% by mass or more is more preferable, 99% by mass or more is further preferable, 99.5% by mass or more is particularly preferable, and 100% by mass (that is,). , The carbon film consists only of CNTs) is most preferable.

Here, the carbon film of the present invention is composed of an aggregate of carbon nanotubes. The carbon film of the present invention is characterized in that the average value of the surface roughness is 4.0 μm or more. The carbon film of the present invention having an average surface roughness of 4.0 μm or more is excellent in electromagnetic wave shielding performance. Therefore, the carbon film of the present invention is not particularly limited, but can be advantageously used, for example, as an electromagnetic wave shielding sheet. Further, the carbon film of the present invention is preferably a self-supporting film. If the carbon film is a self-supporting film, the carbon film is excellent in handleability, and when used as an electromagnetic wave shielding sheet, for example, the degree of freedom in arranging the sheet is high.

In the carbon film of the present invention having an average surface roughness of 4.0 μm or more, there are gaps of an appropriate size or more between the carbon nanotubes as constituents, and therefore, electromagnetic waves are generated in such gaps. It is presumed that the energy of the electromagnetic wave that has entered the carbon film can be attenuated by the diffused reflection. Therefore, according to the carbon film of the present invention, it is considered that excellent electromagnetic wave shielding performance can be exhibited.

(Average value of surface roughness of carbon film)
The average value of the surface roughness of the carbon film needs to be 4.0 μm or more, preferably 5.0 μm or more, more preferably 5.5 μm or more, and 6.5 μm or more. More preferred. When the average value of the surface roughness of the carbon film is at least the above lower limit value, excellent electromagnetic wave shielding can be exhibited. The average value of the surface roughness of the carbon film may be, for example, 30 μm or less.

Note that FIGS. 1 to 5 show, as an example, laser microscope images obtained for carbon film surfaces having various average surface roughness values, which were produced in Examples 1 and Comparative Examples described later. FIG. 1 is one of the laser microscope images of the carbon film surface prepared in Example 1, and the average value of the surface roughness calculated for the carbon film was 10.9 μm. FIG. 2 is one of the laser microscope images of the carbon film surface prepared in Example 2, and the average value of the surface roughness calculated for the carbon film was 6.3 μm. FIG. 3 is one of the laser microscope images of the carbon film surface prepared in Example 3, and the average value of the surface roughness calculated for the carbon film was 5.5 μm. FIG. 4 is one of the laser microscope images of the carbon film surface prepared in Example 4, and the average value of the surface roughness calculated for the carbon film was 4.1 μm. FIG. 5 is one of the laser microscope images of the carbon film surface prepared in Comparative Example 1, and the average value of the surface roughness calculated for the carbon film was 2.5 μm. The shades in FIGS. 1 to 5 correspond to the relative intensities of the reflected light reflected by the surface of the single-layer film and detected by the sensor of the laser microscope when irradiated with the laser light. That is, in FIGS. 1 to 5, when the laser beam is irradiated, the portion having high brightness of the reflected light is displayed on the white side, and the portion having low brightness of the reflected light is displayed on the black side. From FIGS. 1 to 5, the larger the value of the average value of the surface roughness, the lower the brightness of the reflected light when irradiated with the laser light, and the smaller the value of the average value of the surface roughness, the lower the brightness of the reflected light, the more the laser light is irradiated. It can be seen that the brightness of the reflected light is high. When the laser beam is replaced with electromagnetic waves, the amount of electromagnetic waves reflected from the surface of the carbon film is small when the average value of the surface roughness is large, in other words, the electromagnetic wave shielding performance is high and the average value of the surface roughness is small. In some cases, it can be estimated that the amount of electromagnetic waves reflected from the surface of the carbon film tends to be large, in other words, the electromagnetic wave shielding performance tends to be low.

(Manufacturing method of carbon film)
Here, the carbon film of the present invention is used to form a carbon film by forming an aggregate of carbon nanotubes into a carbon film.
As the CNT aggregate, a CNT aggregate satisfying at least any one of (1) to (3) described later is used.
Prior to the film formation of the CNT aggregate, the CNT aggregate is subjected to a dry pulverization treatment.
It can be produced by satisfying at least one of the above.

<CNT aggregate>
Here, as the CNT aggregate used for preparing the carbon film, for example, a known CNT aggregate such as a CNT aggregate obtained by using the super growth method (see International Publication No. 2006/011655) can also be used. However, it is preferable to use a novel CNT aggregate that satisfies at least one of the conditions (1) to (3). A carbon film made of a CNT aggregate satisfying at least one of the following conditions (1) to (3) is excellent in electromagnetic wave shielding performance.

(1) In the spectrum obtained by Fourier transform infrared spectroscopic analysis of the carbon nanotube dispersion obtained by dispersing the carbon nanotube aggregate so that the bundle length is 10 μm or more, the plasmon resonance of the carbon nanotube dispersion is obtained. There is at least one peak based on the wave number in the range of 300 cm ^-1 to 2000 cm ^-1 or less.
(2) In the pore distribution curve showing the relationship between the pore diameter and the Log differential pore volume, which is obtained from the adsorption isotherm of liquid nitrogen at 77K for the carbon nanotube aggregate based on the Barrett-Joiner-Halenda method. The largest peak is in the range of pore diameters greater than 100 nm and less than 400 nm.
(3) At least one peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate exists in the range of 1 μm ^-1 or more and 100 μm ^-1 or less.

The reason why the carbon film composed of CNT aggregates satisfying at least one of the above conditions (1) to (3) is excellent in electromagnetic wave shielding performance is not clear, but it is presumed to be as follows. FIG. 6 shows a scanning electron microscope (SEM) image of an example of a CNT aggregate satisfying at least one of the above (1) to (3). As shown in FIG. 6, the CNTs constituting the CNT aggregate satisfying at least the above conditions (1) to (3) have a wavy structure. Due to such a "wavy structure", it is considered that electromagnetic waves are diffusely reflected between the CNTs constituting the CNT aggregate. It is presumed that the energy of the electromagnetic wave is lost in the process of such diffuse reflection, and the result is reflected in the high electromagnetic wave shielding performance. Hereinafter, the above conditions (1) to (3) that can be satisfied by the CNT aggregate of the present invention will be described in detail.

<< Condition (1) >>
The condition (1) is "a carbon nanotube dispersion in a spectrum obtained by Fourier transform infrared spectroscopic analysis of a carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more. There is at least one peak based on the plasmon resonance in the range of wavenumbers of 300 cm ^-1 to 2000 cm ^-1 or less. " Here, conventionally, strong absorption characteristics in the far infrared region are widely known as optical characteristics of CNTs. It is believed that the strong absorption characteristics in the far infrared region are due to the diameter and length of the CNTs. Regarding the absorption characteristics in the far-infrared region, more specifically, the relationship between the peak based on the plasmon resonance of CNT and the length of CNT, the 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). The present inventors have detected a peak based on the plasmon resonance of CNT in the spectrum obtained by Fourier transform infrared spectroscopic analysis based on the contents of the study as described in the above non-patent document and the original knowledge. It was estimated that the position to be used could be affected by the distance between the defect points in the CNT, and verification was performed. Then, the present inventors have found that the position where the peak based on the plasmon resonance of the CNT is detected can serve as an index corresponding to the distance between the bending points in the CNT having a wavy structure, and the above conditions. (1) was set.

In the condition (1), the wave number is 300 cm ^-1 to 2000 cm ^-1 or less, preferably the wave number 500 cm ^{-1 to 2000 cm -1} ^or less, and more preferably the wave number 650 cm ^{-1 to 2000 cm -1} ^or less. If a peak based on the plasmon resonance of the CNT is present, the CNT can exhibit good electromagnetic wave shielding performance when forming a carbon film.

FIG. 7 shows a spectrum (FIR resonance chart) obtained by Fourier transform infrared spectroscopic analysis of the CNT aggregates used in Examples 1 to 4 and Comparative Example 1 described later. As is clear from FIG. 7, in the obtained spectrum, in addition to the relatively gentle peak based on the plasmon resonance of the CNT dispersion, the wave number is sharp around 840 cm ^-1 and around 1300 cm ^-1 and 1700 cm ^-1 . Can be seen to be confirmed. These sharp peaks do not correspond to "peaks based on plasmon resonance of carbon nanotube dispersion", and each corresponds to infrared absorption derived from a functional group. More specifically, the sharp peak near wave number 840 cm ^-1 is due to the CH out-of-plane angular vibration; the sharp peak near wave number 1300 cm ^-1 is due to the epoxy three-membered ring expansion and contraction vibration; wave number 1700 cm. The sharp peak near ^-1 is due to C = O expansion and contraction vibration. In the region where the wave number exceeds 2000 cm ^-1 , apart from the plasmon resonance, as mentioned in the above-mentioned non-patent document by T. Morimoto et al., A peak similar to the S1 peak is detected. The upper limit of the determination of the presence or absence of a peak based on the plasmon resonance of the CNT dispersion under the condition (1) was set to 2000 ^-1 cm or less.

Here, under the condition (1), in order to acquire the spectrum by Fourier transform infrared spectroscopic analysis, it is necessary to obtain the CNT dispersion by dispersing the CNT aggregate so that the bundle length is 10 μm or more. Here, for example, CNT aggregate, water, and a surfactant (for example, sodium dodecylbenzene sulfonate) are blended in an appropriate ratio and stirred with ultrasonic waves or the like for a predetermined time to be bundled in water. It is possible to obtain a dispersion liquid in which a CNT dispersion having a length of 10 μm or more is dispersed.

The bundle length of the CNT dispersion can be obtained by analyzing with a wet image analysis type particle size measuring device. Such a measuring device calculates the area of each dispersion from an image obtained by photographing the CNT dispersion, and is also referred to as the diameter of a circle having the calculated area (hereinafter, also referred to as ISO circle diameter (ISO area diameter)). There is) can be obtained. Then, in the present specification, the bundle length of each dispersion is defined as the value of the ISO circle diameter thus obtained.

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

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 preferably 2.0 cm ³ / g or more. ..

<< Condition (3) >>
Condition (3) stipulates that "at least one peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate exists in the range of 1 μm ^-1 or more and 100 μm ^-1 or less." Satisfiability of such a condition can be determined as follows. First, the CNT aggregate to be determined is magnified and observed (for example, 10,000 times) using an electron microscope (for example, an electrolytic radiation scanning electron microscope), and a plurality of electron microscope images are obtained in a 1 cm square field (for example). For example, 10 sheets) will be acquired. The obtained plurality of electron microscope images are subjected to a fast Fourier transform (FFT) process to obtain a two-dimensional spatial frequency spectrum. The two-dimensional spatial frequency spectra obtained for each of the plurality of electron microscope images are binarized, and the average value of the peak positions appearing on the highest frequency side is obtained. When the average value of the obtained peak positions was within the range of 1 μm ^-1 or more and 100 μm ^-1 or less, it was determined that the condition (3) was satisfied. Here, as the "peak" used in the above determination, a clear peak obtained by performing an isolated point extraction process (that is, a reverse operation of removing isolated points) is used. Therefore, if a clear peak cannot be obtained within the range of 1 μm ^-1 or more and 100 μm ^-1 or less when the isolated point extraction process is performed, it is determined that the condition (3) is not satisfied.

Here, from the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, it is preferable that the peak of the two-dimensional spatial frequency spectrum exists in the range of 2.6 μm ^-1 or more and 100 μm ^-1 or less.

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 the above (1) to (3). It is more preferable to satisfy all the conditions.

<< Other properties >>
The CNT aggregate that can be used for forming the carbon film of the present invention preferably has the following properties in addition to the above conditions (1) to (3).

For example, the total specific surface area of the CNT aggregate by the BET method is preferably 600 m ² / g or more, more preferably 800 m ² / g or more, preferably 2600 m ² / g or less, and more preferably 1400 m ² / g or less. Is. Further, in the case of the opening-treated one, it 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 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 may contain mainly single-walled CNTs, and may contain two-walled CNTs and multi-walled CNTs to the extent that the functions are not impaired. The total specific surface area of CNTs by the BET method can be measured, for example, by using a BET specific surface area measuring device compliant with JIS Z8830.

Further, the average height of the CNTs constituting the CNT aggregate is preferably 10 μm or more and 10 cm or less, and more preferably 100 μm or more and 2 cm or less. When the average height of the CNTs constituting the CNT aggregate is 10 μm or more, it is possible to prevent aggregation with the adjacent CNT bundle and easily disperse the CNTs. When the average height of the CNTs constituting the CNT aggregate is 10 μm or more, it becomes easy to form a network between the CNTs, and the CNTs can be suitably used in applications requiring conductivity or mechanical strength. When the average height of the CNTs constituting the CNT aggregate is 10 cm or less, the formation can be performed in a short time, so that the adhesion of carbon-based impurities can be suppressed and the specific surface area can be improved. If the average height of the CNTs constituting the CNT aggregate is 2 cm or less, it can be more easily dispersed. The average height of the CNTs can be determined by measuring the height of 100 randomly selected CNTs using a scanning electron microscope (SEM).

The tap bulk density of the CNT aggregate is preferably 0.001 g / cm ³ or more and 0.2 g / cm ³ or less. Since the CNT aggregates in such a density range do not excessively strengthen the bonds between the CNTs, they are excellent in dispersibility and can be molded into various shapes. When the tap bulk density of the CNT aggregate is 0.2 g / cm ³ or less, the bond between the CNTs is weakened, so that when the CNT aggregate is stirred with a solvent or the like, it becomes easy to disperse it uniformly. Further, when the tap bulk density of the CNT aggregate is 0.001 g / cm ³ or more, the integrity of the CNT aggregate is improved and the handling becomes easy. The tap bulk density is the apparent bulk density in a state where the powdery CNT aggregate is filled in a container, the voids between the powder particles are reduced by tapping or vibration, and the containers are tightly packed.

Further, 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, preferably 15.0 nm or less, and 10.0 nm or less. It is more preferably 5.0 nm or less, and further preferably 5.0 nm or less. When the average outer diameter of CNTs is 0.5 nm or more, bundling between CNTs can be reduced and a high specific surface area can be maintained. When the average outer diameter of CNTs is 15.0 nm or less, the ratio of multi-walled CNTs can be reduced and a high specific surface area can be maintained. Here, the average outer diameter of the CNT can be obtained 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 CNTs may be adjusted by changing the manufacturing method and manufacturing conditions of CNTs, or by combining a plurality of types of CNTs obtained by different manufacturing methods. May be good.

The G / D ratio of the CNT aggregate is preferably 1 or more and 50 or less. It is considered that the CNT aggregate having a G / D ratio of less than 1 has low crystallinity of single-walled CNTs, has a lot of stains such as amorphous carbon, and has a high content of multi-walled CNTs. On the other hand, CNT aggregates having a G / D ratio of more than 50 have high linearity, and CNTs tend to form bundles with few gaps, which may reduce the specific surface area. The G / D ratio is an index generally used for evaluating the quality of CNTs. Vibration modes called G band (around 1600 cm ^-1 ) and D band (around 1350 cm ^-1 ) are observed in the Raman spectrum of CNTs measured by a Raman spectroscope. The G band is a vibration mode derived from the hexagonal lattice structure of graphite, which is the cylindrical surface of CNT, and the D band is a vibration mode derived from an amorphous portion. Therefore, the higher the peak intensity ratio (G / D ratio) between the G band and the D band, the higher the crystallinity (linearity) of the CNT.

In order to obtain a high specific surface area, it is desirable that the purity of the CNT aggregate is as high as possible. The term "purity" as used herein is carbon purity, and is a value indicating what percentage of the mass of the CNT aggregate is composed of carbon. Although there is no upper limit to the purity for obtaining a high specific surface area, it is difficult to obtain a CNT aggregate of 99.9999% by mass or more in manufacturing. If the purity is less than 95% by mass, it becomes difficult to obtain a specific surface area of more than 1000 m ² / g in the unopened state. Further, if the carbon purity is less than 95% by mass including the metal impurities, the metal impurities react with oxygen in the opening treatment and hinder the opening of the CNT, and as a result, it becomes difficult to increase the specific surface area. From these points, the purity of the single-walled CNT is preferably 95% by mass or more.
The purity of a predetermined CNT aggregate satisfying at least one of the above-mentioned conditions (1) to (3) is usually 98% by mass or more, preferably 99.9% by mass, even without purification treatment. The above can be done. Almost no impurities are mixed in the CNT aggregate, and various characteristics inherent in CNT can be fully exhibited. The carbon purity of the CNT aggregate can be obtained from elemental analysis using fluorescent X-rays, thermogravimetric analysis (TGA), or the like.

<< Manufacturing method of CNT aggregate >>
The method for producing the CNT aggregate is not particularly limited, and the production conditions can be adjusted according to the desired properties. For example, when producing a CNT aggregate that satisfies at least one of the above-mentioned conditions (1) to (3), the conditions for growth of the CNT aggregate are all of the following (a) to (c). It is necessary to meet.
(A) The growth rate of the CNT aggregate is 5 μm / min or more.
(B) The concentration of the catalyst activator in the growth atmosphere of the CNT aggregate is 4% by volume or more.
(C) When the CNT aggregate grows, an obstacle exists in the growth direction of the CNTs constituting the CNT aggregate.

Then, by the production method satisfying all of the above-mentioned (a) to (c), it is possible to efficiently produce the CNT aggregate satisfying at least one of the above-mentioned conditions (1) to (3). Further, in such a production method, the above conditions (a) to (c) are not particularly limited as long as the above conditions (a) to (c) are satisfied when the CNT aggregate is grown, and known methods such as a fluidized bed method, a mobile layer method and a fixed layer method are used. The CNT synthesis process according to the above can be adopted. Here, the fluidized bed method means a synthesis method for synthesizing CNTs while fluidizing a granular carrier carrying a catalyst for synthesizing CNTs (hereinafter, also referred to as a granular catalyst carrier). Further, the moving layer method and the fixed layer method mean a synthetic method for synthesizing CNTs without flowing a carrier (particulate carrier or plate-like carrier) carrying a catalyst.

In one example, the production method satisfying all of the above-mentioned (a) to (c) uses the catalyst carrier forming step of forming the catalyst carrier and the catalyst carrier obtained in the catalyst carrier forming step. The CNT synthesis step of synthesizing the CNT and the recovery step of recovering the CNT synthesized in the CNT synthesis step are included. Then, the catalyst carrier forming step can be carried out according to a known wet or dry catalyst carrier method. In addition, the recovery step can be carried out using a known separation / recovery device such as a classification device.

[CNT synthesis process]
In the CNT synthesis step, all of the above conditions (a) to (c) are satisfied when the CNT grows. Specifically, the condition (a) that "the growth rate of the carbon nanotube aggregate is 5 μm / min or more" is satisfied by appropriately adjusting the concentration and temperature of the raw material gas as a carbon source in the CNT growth atmosphere. be able to. Here, the raw material gas as a carbon source is not particularly limited, and hydrocarbon gas such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene and acetylene; methanol, ethanol and the like. Gas of lower alcohols; as well as mixtures thereof can also be used. Further, this raw material gas may be diluted with an inert gas. Further, from the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film while further improving the dispersibility of the obtained CNT aggregate, the growth rate of the CNT aggregate is preferably 10 μm / min or more. The temperature can be adjusted, for example, in the range of 400 ° C. or higher and 1100 ° C. or lower.

Under the CNT growth atmosphere, the raw material gas as a carbon source preferably contains ethylene. By heating ethylene in a predetermined temperature range (700 ° C. or higher and 900 ° C. or lower), the decomposition reaction of ethylene is promoted, and when the decomposition gas comes into contact with the catalyst, high-speed growth of CNT is possible. However, if the thermal decomposition time is too long, the decomposition reaction of ethylene proceeds too much, causing deactivation of the catalyst and adhesion of carbon impurities to the CNT aggregate. In the production of the CNT aggregate of the present invention, the thermal decomposition time is preferably 0.5 seconds or more and 10 seconds or less with respect to the ethylene concentration range of 0.1% by volume or more and 40% by volume or less. In less than 0.5 seconds, the thermal decomposition of ethylene is insufficient, and it becomes difficult to grow a CNT aggregate having a high specific surface area at high speed. If it is longer than 10 seconds, the decomposition of ethylene proceeds too much, and a large amount of carbon impurities are generated, which causes catalyst deactivation and deterioration of the quality of CNT aggregates. The pyrolysis time is calculated from the following formula.
(Pyrolysis time) = (Heating flow path volume) / {(Raw material gas flow rate) x (273.15 + T) / 273.15}
Here, the heating flow path volume is the volume of the flow path heated to a predetermined 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 a flow rate at 0 ° C. and 1 atm.

Further, by appropriately adjusting the supply rate of the catalyst activator supplied during CNT growth, the condition (b) that "the concentration of the catalyst activator in the growth atmosphere of the carbon nanotube aggregate is 4% by volume or more" is satisfied. Can be done. From the viewpoint of further improving the electromagnetic wave shielding performance of the carbon film, the concentration of the catalyst activator in the growth atmosphere of the CNT aggregate is preferably 5% by volume or more. The catalyst activator is not particularly limited, and is an oxygen-containing compound having a low carbon number such as water, oxygen, ozone, acidic gas, nitrogen oxide, carbon monoxide and carbon dioxide; alcohols such as ethanol and methanol; tetrahydrofuran. Ethers such as; ketones such as acetone; aldehydes; esters; and mixtures thereof. Of these, carbon dioxide is preferable. A substance containing both carbon and oxygen, such as carbon monoxide and alcohols, may have both functions as a raw material gas and a catalyst activator. For example, carbon monoxide acts as a catalytically activating substance when combined with a more reactive raw material gas such as ethylene, and acts as a raw material gas when combined with a catalytically activating substance that exhibits a large catalytically activating effect even in a trace amount such as water. ..

Furthermore, by selecting the fluidized layer method in the CNT synthesis step or adjusting the arrangement interval of the catalyst carriers in the mobile layer method or the fixed layer method, "when synthesizing the carbon nanotube aggregate, the carbon nanotube aggregate is formed. The condition (c) that "there is an obstacle in the growth direction of the constituent carbon nanotubes" can be satisfied.

Here, when CNT is synthesized by the fluidized bed method, for example, the CNT synthesis step is carried out by supplying the raw material gas while supplying gas from below to flow the particulate catalyst carrier. Alternatively, the raw material gas may be supplied while continuously transporting the particulate catalyst carrier by screw rotation.

The catalyst carrier has a carrier and a catalyst supported on the surface of the carrier, and the carrier is a portion forming a matrix structure for supporting, fixing, forming, or forming a catalyst on the surface of the carrier. be. The structure of the carrier may be only the carrier, or may be a carrier with a base layer provided with an arbitrary base layer for satisfactorily supporting the catalyst on the surface of the carrier. The shape of the carrier is preferably in the form of particles, and the particle size thereof is preferably 1 mm or less, more preferably 0.7 mm or less, and further preferably 0.4 mm or less in terms of volume average particle size. It is preferably 0.05 mm or more. When the particle size is equal to or less than the above upper limit, the growing CNT bundle becomes thin, which is advantageous for forming a wavy structure. The apparent density of the particles is preferably 3.8 g / cm ³ or more, more preferably 5.8 g / cm ³ or more, and preferably 8 g / cm ³ or less. When the particle density is equal to or higher than the above lower limit, the force applied to the growing CNT bundle is increased, which is advantageous for forming a wavy structure. The material of the carrier is preferably a metal oxide containing at least one element of Al and Zr. Among them, zirconia beads containing Zr having a large elemental amount are particularly preferable.

For example, when a particulate carrier is used, as a method of supporting the catalyst on the surface of the particulate carrier, for example, a method of using a rotary drum type coating device provided with a substantially cylindrical rotary drum can be mentioned. .. When the catalyst is supported after arranging the underlayer on the surface of the particulate carrier, the solution containing the components that can form the underlayer is prepared in the form of particles prior to spraying and drying the catalyst solution. The underlayer is placed on the surface of the carrier by spraying and drying on the surface of the carrier. According to such a method, the catalyst layer and the base layer can be formed relatively easily and evenly.

Then, in the CNT synthesis step, a "formation step" for reducing the catalyst carried on the catalyst carrier is carried out prior to the "growth step" carried out so as to satisfy the above conditions (a) to (c). At the same time, after the growth step is completed, a "cooling step" for cooling the catalyst carrier on which the CNT has grown can be carried out. In the "formation step", for example, an atmosphere containing a catalyst carrier is used as a reducing gas atmosphere, and at least one of the reduced gas atmosphere or the catalyst carrier is heated to reduce and atomize the catalyst supported on the catalyst carrier. do. The temperature of the catalyst carrier or the reducing gas atmosphere in the formation step is preferably 400 ° C. or higher and 1100 ° C. or lower. Further, the implementation time of the formation step may be 3 minutes or more and 120 minutes or less. As the reducing gas, for example, hydrogen gas, ammonia gas, water vapor, or a mixed gas thereof can be used. Further, the reducing gas may be a mixed gas obtained by mixing 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 carrier on which the CNT has grown is cooled in an inert gas environment. Here, as the inert gas, an inert gas similar to the inert gas that can be used in the growth step can be used. Further, in the cooling step, the temperature of the catalyst carrier on which the CNTs have grown is preferably lowered to 400 ° C. or lower, more preferably 200 ° C. or lower.

<Drywall crushing process>
In obtaining the carbon film of the present invention, if necessary, the CNT aggregate before film formation can be subjected to a dry pulverization treatment. In the present invention, the "dry crushing treatment" means a crushing treatment in a state where the crushing target substantially does not contain a solvent (for example, a state where the solid content concentration is 95% or more).

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

<Membrane formation>
By filming the CNT aggregate, the carbon film of the present invention can be obtained. Here, the method for forming a film of the CNT aggregate is not particularly limited, but a CNT dispersion liquid is prepared by dispersing the CNT aggregate in a dispersion medium such as water or an organic solvent, and at least the dispersion medium is prepared from the CNT dispersion liquid. A method of removing a part thereof is preferably mentioned.

The method for preparing the CNT dispersion is not particularly limited, but the CNT dispersion is known to be a dispersion method using a stirring blade, a dispersion method using an ultrasonic wave, a dispersion method using a shearing force, and the like. It can be obtained by dispersing in a dispersion medium by the above method. Here, from the viewpoint of further enhancing the electromagnetic wave shielding performance of the obtained carbon film, it is preferable that the CNTs are appropriately dispersed in the CNT dispersion liquid. Preferably, the CNT dispersion liquid does not contain a dispersant. In other words, it is preferable that the CNT dispersion liquid is substantially composed only of CNT and the dispersion medium. In the present specification, "the CNT dispersion liquid is substantially composed of only CNT and the dispersion medium" means that 99.9% by mass or more of the constituents of the CNT dispersion liquid are inevitably attached to CNT and CNT. It means that it consists of impurities and unavoidable impurities associated with the dispersion medium and the dispersion medium.
Examples of the method for removing the dispersion medium from the CNT dispersion liquid include known methods such as filtration and drying.
The filtration method is not particularly limited, and known filtration methods such as natural filtration, vacuum filtration (suction filtration), pressure filtration, and centrifugal filtration can be used.
As the drying method, known drying methods such as a hot air drying method, a vacuum drying method, a hot roll drying method, and an infrared irradiation method 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. Further, the drying can be performed on a known substrate, although the drying is not particularly limited.

Among these, it is preferable to employ at least drying for removing the dispersion medium.
In addition, the above-mentioned filtration and drying can be used in combination. For example, the carbon film of the present invention can be obtained by further drying the film-shaped filter medium (primary sheet) obtained by filtering the CNT dispersion liquid.

(Characteristics of carbon film)
Here, the thickness of the carbon film of the present invention is preferably 5 μm or more, more preferably 10 μm or more, preferably 200 μm or less, and even more preferably 150 μm or less. When 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 200 μm or less, the weight of the carbon film can be reduced.
The "thickness" of the carbon film can be measured by using the method described in Examples.

Hereinafter, the present invention will be specifically described 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.

<Fourier transform infrared spectroscopy (FT-IR)>
To 10 mg of the CNT aggregate, 100 g of water containing sodium dodecylbenzenesulfonate as a surfactant at a concentration of 1% by mass was added, and the mixture was stirred at 45 Hz for 1 minute using an ultrasonic bath, and each CNT aggregate was stirred. 100 ml of the dispersion was obtained.
Each dispersion prepared as described above is diluted 2-fold with a solvent having the same composition, dropped onto a silicon substrate and dried, and then plasmon far infrared using a Fourier transform infrared spectrophotometer. The effective length of the plasmon was measured by the (FIR) resonance peak. The effective length of plasmon is shown in Table 1. The FIR resonance chart of the obtained FIR spectrum is shown in FIG. 7. As shown in FIG. 7, in the curves corresponding to the CNT aggregates used in Examples 1 to 4 and Comparative Example 1, a peak of optical density was observed above 300 cm ^-1 . The plasmon peak top position was obtained from an approximate curve by polynomial fit using drawing software.

<Measurement of CNT bundle length>
For each dispersion prepared by FT-IR measurement, CNT present in the dispersion using a flow-type particle image analyzer (circulation type image analysis particle size distribution meter "CF-3000" manufactured by Jasco International Co., Ltd.). The average ISO circle diameter of the dispersion was measured, and the obtained value was taken as the CNT bundle length. The analysis conditions were as follows.
<Analysis conditions>
-Injection amount: 50 ml (sampling capacity 1.2%)
・ Flow cell spacer: 1000 μm
・ Front lens magnification: 2x ・ Telecentric lens magnification 0.75x ・ Length per pixel: 2.3μm / pixel
Each dispersion was measured four times under the same conditions while being circulated, and their arithmetic mean values were calculated.

<Creation of pore distribution curve (CNT aggregate)>
For 10 mg or more of CNT aggregates, adsorption isotherms were measured using BELSORP-miniII (manufactured by Microtrac Bell) at 77 K using liquid nitrogen (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, the pore distribution curve of each sample was obtained by the BJH method. The results are shown in FIG. As shown in FIG. 8, in the CNT aggregates used in Examples 1 to 4 and Comparative Example 1, the maximum peak of the Log differential pore volume was confirmed in the region having a pore diameter of 100 nm or more.
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.

<Two-dimensional spatial frequency spectrum analysis of electron microscope images>
For the CNT aggregate prepared according to the procedure described later, 0.01 mg was placed on a carbon tape and blown with a blower to remove excess CNTs to prepare a sample, which was observed at 10,000 times with an electrolytic radiation scanning electron microscope. , 10 photographs were taken with a 1 cm square field of view arbitrarily extracted. Fast Fourier transform processing was performed on each of the 10 electron microscope images taken to obtain a two-dimensional spatial frequency spectrum. Each of the obtained two-dimensional spatial frequency spectra was subjected to binarization processing, and the peak position appearing on the outermost side (high frequency side) was obtained to obtain an average value. In the binarization process, the values over 0.75 were set to 1 and the other values were set to zero for the numerical values obtained through the fast Fourier transform process. FIG. 9A is one of the ten images acquired for the prepared CNT aggregate, and FIG. 9B is a two-dimensional spatial frequency spectrum acquired for such images. In FIG. 9B, the component closer to the center means the low frequency component, and the component located more outward from the center corresponds to the higher frequency component. In the figure, the arrow indicates the peak position (3 μm ^-1 ) of the highest wave number among the clear peaks detected in the region of 1 to 100 μm ^-1 . Further, FIG. 9C is one of the 10 images acquired for the CNT aggregate used in Example 4, and FIG. 9D is a two-dimensional spatial frequency spectrum acquired for such an image. In FIG. 9D, the component closer to the center means the low frequency component, and the component located more outward from the center corresponds to the higher frequency component.

<Thickness>
The thickness of the carbon film was measured using a "Digimatic standard outside micrometer" manufactured by Mitutoyo.

<Average value of surface roughness of carbon film>
For the average value of the surface roughness of the carbon film, the surface roughness was measured for four randomly set areas of 5 cm × 7 cm using a one-shot 3D shape measuring machine (“VR-5000” manufactured by KEYENCE CORPORATION). did. Then, the arithmetic mean value of the obtained four surface roughness values was calculated and used as the "average value of the surface roughness of the carbon film".

<Electromagnetic wave shielding performance>
For the carbon film, the reflectance coefficient S11 and the transmission coefficient S21 were measured by the ASTM method (coaxial structure), and the electromagnetic wave shielding effect [dB] was calculated.
Then, the electromagnetic wave shielding effect [dB] at the measurement frequencies of 0.1 MHz, 1 MHz, and 10 MHz was evaluated according to the following criteria. The larger the value of the electromagnetic wave shielding effect [dB] at a certain frequency, the better the electromagnetic wave shielding performance of the carbon film at that frequency.
A: The electromagnetic wave shielding effect is 40 dB or more.
B: The electromagnetic wave shielding effect is 30 dB or more and less than 40 dB.
C: The electromagnetic wave shielding effect is 20 dB or more and less than 30 dB.
D: The electromagnetic wave shielding effect is less than 20 dB.

<Preparation of CNT aggregate>
The CNTs used in Examples 1 to 3 and Comparative Example 1 were synthesized as follows. FIG. 10 shows a schematic configuration of the CNT manufacturing apparatus used at the time of synthesis. The CNT manufacturing apparatus 100 shown in FIG. 10 is composed of a heater 101, a reaction tube 102, a dispersion plate 103, a reducing gas / raw material gas introduction port 104, an exhaust port 105, and a gas heating promotion unit 106. Synthetic quartz was used as the material of the reaction tube 102 and the dispersion plate 103.
<< Catalyst carrier forming step >>
The catalyst carrier forming step will be described below. Zirconia (zirconium dioxide) beads (ZrO ₂ , volume average particle diameter D50: 350 μm) as a carrier are put into a rotary drum type coating device, and the aluminum-containing solution is sprayed with a spray gun while stirring the zirconia beads (20 rpm). While spray spraying (spray amount 3 g / min, spray time 940 seconds, spray air pressure 10 MPa), compressed air (300 L / min) was supplied into the rotating drum and dried to form an aluminum-containing coating film on the zirconia beads. .. Next, firing treatment was performed at 480 ° C. for 45 minutes to prepare primary catalyst particles on which an aluminum oxide layer was formed. Further, while the primary catalyst particles are put into another rotary drum type coating device and stirred (20 rpm), the iron catalyst solution is spray-sprayed with a spray gun (spray amount 2 g / min, spray time 480 seconds, spray air pressure 5 MPa). ), While supplying compressed air (300 L / min) into the rotating drum, the mixture was dried to form an iron-containing coating film on the primary catalyst particles. Next, a firing treatment was carried out at 220 ° C. for 20 minutes to prepare a catalyst carrier on which an iron oxide layer was further formed.
<< CNT synthesis process >>
300 g of the catalyst carrier thus produced is put into the reaction tube 102 of the CNT manufacturing apparatus 100, and the catalyst carrier 107 is fluidized by circulating gas, and the formation step, the growth step, and the cooling step are performed in this order. The treatment was performed to produce a CNT aggregate. The conditions of each step included in the CNT synthesis step were set as follows.
[Formation process]
・ Set temperature: 800 ℃
-Reducing gas: Nitrogen 3sLm, Hydrogen 22sLm
-Processing time: 25 minutes [Growth process]
・ Set temperature: 800 ℃
-Raw material gas: Nitrogen 15sLm, Ethylene 5sLm, Carbon dioxide 2sLm, Hydrogen 3sLm
・ Processing time: 10 minutes ・ Raw material gas pyrolysis time: 0.65 seconds [Cooling process]
・ Cooling temperature: Room temperature ・ Purge gas: Nitrogen 25sLm

The CNT aggregate synthesized on the catalyst carrier was separated and recovered using a forced vortex classification device (rotation speed 3500 rpm, air air volume 3.5 Nm ³ / min). The recovery rate of the CNT aggregate was 99%.
The characteristics of the CNT aggregate produced by this example are tap bulk density: 0.01 g / cm ³ , CNT average height: 200 μm, BET specific surface area: 800 m ² / g, average outer diameter: 4.0 nm, The carbon purity was 99%.

(Example 1)
Add 1000 g of water to 1 g of the CNT aggregate obtained as described above, and stir with an ultra-high-speed emulsification / dispersion device (product name "Lab Solution (registered trademark)", manufactured by Shinky Co., Ltd.) at a rotation speed of 3000 rpm for 10 minutes. Then, a CNT dispersion liquid was obtained.
The obtained CNT dispersion liquid was applied onto the 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 off from the substrate to obtain a carbon film (self-supporting film) having a thickness of 100 μm. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

(Example 2)
In preparing the CNT dispersion liquid, a dispersion treatment was carried out for 10 minutes using an ultrasonic disperser (a desktop ultrasonic cleaner manufactured by Bransonic Co., Ltd.). A carbon film (self-supporting film) having a thickness of 100 μm was obtained in the same manner as in Example 1 except for these points. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

(Example 3)
In preparing the CNT dispersion liquid, a jet mill (manufactured by Yoshida Kikai Kogyo Co., Ltd., NanoVeta) was used to carry out dispersion treatment under the condition of 100 MPa for 15 minutes. A carbon film (self-supporting film) having a thickness of 100 μm was obtained in the same manner as in Example 1 except for these points. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

(Example 4)
<Preparation of CNT aggregate>
The CNT aggregate used in Example 4 was produced by a method of supplying a raw material gas while continuously transporting a particulate catalyst carrier by screw rotation in the CNT synthesis step.
FIG. 11 shows a schematic configuration of the CNT aggregate manufacturing apparatus 200 used. The CNT aggregate manufacturing apparatus 200 shown in FIG. 11 includes a formation unit 202, a growth unit 204, a transfer unit 207 that conveys a base material between the formation unit 202 and the growth unit 204, and the formation unit 202 and the growth unit. A connection unit 208 for spatially connecting the 204 to each other and a gas mixing prevention device 203 for preventing gas from being mixed with each other between the formation unit 202 and the growth unit 204 are provided. Further, the CNT aggregate manufacturing apparatus 200 is arranged in the inlet purge device 201 arranged in the front stage of the formation unit 202, the outlet purge device 205 arranged in the rear stage of the growth unit 204, and further in the rear stage of the outlet purge device 205. It is provided with a component such as a cooling unit 206. The formation unit 202 includes a formation furnace 202a for holding the 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 a gas in the furnace. It is composed of an exhaust device 202d or the like that discharges to the outside of the system. The gas mixing prevention device 203 includes an exhaust device 203a and a purge gas injection device 203b for injecting a purge gas (seal gas). The growth unit 204 includes a growth furnace 204a for maintaining the raw material gas environment, a raw material gas injection device 204b for injecting the raw material gas, a heating device 204c for heating at least one of the catalyst and the raw material gas, and the inside of the furnace. It is equipped with an exhaust device 204d or the like that discharges gas to the outside of the system. The inlet purging device 201 is attached to a connecting portion 209 connecting the front chamber 213, which is a component for introducing the base material 211 into the system via the hopper 212, and the formation furnace 202a. The cooling unit 206 includes a cooling container 206a for holding the inert gas, and a water-cooled cooling device 206b arranged so as to surround the inner space of the cooling container 206a. The transport unit 207 is a unit that continuously transports the base material 211 by screw rotation. It is mounted by a screw blade 207a and a drive device 207b that can rotate the screw blade to exert a substrate transporting 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.

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

<Formation process-cooling process>
The conditions for the inlet purging device, formation unit, gas mixing prevention device, growth unit, outlet purging device, and cooling unit of the CNT aggregate manufacturing device were set as follows.

Feeder hopper ・ Feed speed: 1.25kg / h
・ Displacement: 10sLm (natural exhaust from the gap)
Inlet purge device ・ Purge gas: Nitrogen 40sLm
Formation unit ・ Temperature in the furnace: 800 ℃
-Reducing gas: nitrogen 6sLm, hydrogen 54sLm
・ Displacement: 60sLm
・ Processing time: 20 minutes Gas contamination prevention device ・ Purge gas: 20sLm
・ Displacement of the exhaust device: 62sLm
Growth unit ・ Temperature in the furnace: 830 ℃
-Raw material 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 from gaps)
Continuous production was performed under the above conditions.

<Separation and recovery process>
The CNT aggregate synthesized on the substrate was separated and recovered using a forced vortex classifier (rotation speed 2300 rpm, air air volume 3.5 Nm ³ / min). The recovery rate of the CNT aggregate was 96%.

The characteristics of the CNT aggregate produced by this example are typically tap bulk density: 0.02 g / cm ³ , CNT average length: 150 μm, BET-specific surface area: 900 m ² / g, average outer diameter: It was 4.0 nm and had a carbon purity of 99%.

Add 1000 g of water to 1 g of the CNT aggregate obtained as described above, and stir with an ultra-high-speed emulsification / dispersion device (product name "Lab Solution (registered trademark)", manufactured by Shinky Co., Ltd.) at a rotation speed of 3000 rpm for 10 minutes. Then, a CNT dispersion liquid was obtained.
The obtained CNT dispersion liquid was applied onto the 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 off from the substrate to obtain a carbon film (self-supporting film) having a thickness of 100 μm. The obtained carbon film was evaluated and the electromagnetic wave shielding performance was evaluated. The results are shown in Table 1.

(Comparative Example 1)
In preparing the CNT dispersion liquid, 1 g of sodium dodecyl sulfate as a dispersant was added, and the dispersion treatment was carried out for 15 minutes under the condition of 100 MPa using a jet mill (NanoVeta manufactured by Yoshida Kikai Kogyo Co., Ltd.). A carbon film (self-supporting film) having a thickness of 100 μm was obtained in the same manner as in Example 1 except for these points. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

From Table 1, it can be seen that a carbon film having an average surface roughness of 4.0 μm or more can exhibit excellent electromagnetic wave shielding performance in a wide frequency range.

100 CNT manufacturing equipment 101 Heater 102 Reaction tube 103 Dispersion plate 104 Reducing gas / raw material gas inlet 105 Exhaust port 106 Gas heating promotion unit 107 Catalyst carrier 200 CNT aggregate manufacturing equipment 201 Inlet purge device 202 Formation unit 202a Formation furnace 202b Reduction Gas injection device

202c Heating device

202d Exhaust device 203 Gas mixing prevention device 203a Exhaust device 203b Purge gas injection device 204 Growth unit 204a Growth furnace 204b Raw material gas injection device

204c Heating device

204d Exhaust device 205 Outlet purge device 206 Cooling unit 206a Cooling container 206b Water cooling Cooling device 207 Conveying unit 207a Screw blade 207b Drive device 208-210 Connection part 211 Base material 212 Hopper 214 Heating device

Claims

A carbon film composed of carbon nanotube aggregates,
The average value of the surface roughness is 4.0 μm or more.
Carbon film.
The carbon film according to claim 1, wherein the average value of the surface roughness is 5.0 μm or more.
The carbon film according to claim 1 or 2, which is a self-supporting film.
The carbon film according to any one of claims 1 to 3, wherein the carbon nanotube aggregate satisfies at least one of the following conditions (1) to (3).
(1) The plasmon of the carbon nanotube dispersion in the spectrum obtained by Fourier transform infrared spectroscopic analysis of the carbon nanotube dispersion obtained by dispersing the carbon nanotube aggregate so that the bundle length is 10 μm or more. There is at least one resonance-based peak in the range of wavenumbers above 300 cm -1 and above 2000 cm -1 .
(2) For the carbon nanotube aggregate, a pore distribution curve showing the relationship between the pore diameter and the Log differential pore volume obtained from the adsorption isotherm of liquid nitrogen at 77K based on the Barrett-Joiner-Halenda method. The largest peak in is in the range of pore diameters greater than 100 nm and less than 400 nm.
(3) At least one peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate exists in the range of 1 μm -1 or more and 100 μm -1 or less.