carbon film

Abstract

This carbon film is formed of a carbon nanotube aggregate. The value of air permeability of the carbon film as measured in accordance with a bubble point method is 0.00010 or more.

Description

[Technical Field]

[0001] The present invention relates to a carbon film. [Background Art]

[0002] In recent years, carbon nanotubes (hereinafter sometimes referred to as "CNTs") have attracted attention as materials excellent in electrical conductivity, thermal conductivity and mechanical properties. However, since CNTs are fine structures with a nanometer-scale diameter, they have poor handleability and processability when used alone. Accordingly, in order to secure handleability and processability for use in various applications, it has been conventionally practiced to form a carbon film by forming an aggregate composed of a plurality of CNTs (hereinafter referred to as "carbon nanotube aggregate") into a film (see, for example, Patent Document 1).

[0003] In Patent Document 1, pores having a bore size of 400 nm or more and 1500 nm or less, measured by mercury porosimetry, have a log differential pore volume of 0.006 cm 3 / g or less, and a carbon film excellent in mechanical strength is formed using a carbon nanotube aggregate having a region of 10 nm or more. [Prior Art Literature] [Patent Literature]

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

[0005] In recent years, electromagnetic wave shielding has attracted attention as an application of carbon films. However, there is still room for further improvement in the electromagnetic wave shielding performance, that is, the performance of blocking electromagnetic waves, of the above-mentioned conventional carbon films.

[0006] Accordingly, an object of the present invention is to provide a carbon film excellent in electromagnetic wave shielding performance. [Means for Solving the Problem]

[0007] The present inventors conducted extensive studies to achieve the above object. Then, the present inventors investigated the microscopic properties of a carbon film formed using a carbon nanotube aggregate, and newly found that a carbon film having an air permeability value of 0.00010 or more measured according to the bubble point method can satisfactorily shield electromagnetic waves, and completed the present invention.

[0008] That is, the present invention aims to advantageously solve the above problem, and the carbon film of the present invention is a carbon film made of a carbon nanotube aggregate, characterized in that the air permeability value measured according to the bubble point method is 0.00010 or more. If the air permeability value of the carbon film measured according to the bubble point method is 0.00010 or more, the carbon film is excellent in electromagnetic shielding performance. Here, the measurement of the air permeability of the carbon film according to the bubble point method can be carried out in accordance with the method described in the Examples of the present specification.

[0009] Here, the carbon film of the present invention is preferably a free-standing film. A carbon film that is a free-standing film is excellent in handleability, and when used, for example, as an electromagnetic wave shielding sheet, the degree of freedom in arranging the sheet can be increased. In the present invention, the term "free-standing film" refers to a film that can maintain its film shape independently without being damaged even when no support is present.

[0010] Here, 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) In a spectrum obtained by Fourier-transform infrared spectroscopy of a carbon nanotube dispersion obtained by dispersing the carbon nanotube aggregate such that the bundle length is 10 µm or more, a peak based on plasmon resonance of the carbon nanotube dispersion is at a wavenumber of 300 cm -1 -1 to 2000 cm -1 -1, there is at least one peak within the following range. (2) For the carbon nanotube aggregate, the largest peak in the pore distribution curve showing the relationship between pore diameter and log differential pore volume, obtained from the adsorption isotherm at 77K of liquid nitrogen using the Barrett-Joyner-Halenda method, is in the range of pore diameters greater than 100 nm and less than 400 nm. (3) The peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is 1 μm -1 More than 100μm -1 At least one exists within the following range. A carbon film made of a carbon nanotube aggregate that satisfies the above-mentioned predetermined conditions exhibits even greater electromagnetic wave shielding performance. The satisfaction of the above-mentioned predetermined conditions can be determined according to the method described in the examples. [Effects of the Invention]

[0011] According to the present invention, a carbon film with excellent electromagnetic wave shielding performance can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] An example of a CNT aggregate is shown in the SEM image. [Figure 2] The FIR resonance chart obtained for one example of a CNT aggregate is shown. [Figure 3] The pore size distribution curve of an example of a CNT aggregate is shown. [Figure 4A] This is an SEM image of a carbon nanotube (CNT) aggregate, one example. [Figure 4B] This is the two-dimensional spatial frequency spectrum of the image in Figure 4A. [Figure 4C] This is a SEM image of a CNT aggregate in another example. [Figure 4D] Figure 4C shows the two-dimensional spatial frequency spectrum of the image. [Figure 5] This shows the general configuration of the CNT manufacturing equipment. [Figure 6] The schematic configuration of the CNT manufacturing apparatus used in Example 4 is shown.

[0013] Embodiments of the present invention will be described in detail below. The carbon film of the present invention is composed of aggregates of multiple carbon nanotubes (carbon nanotube aggregates). The carbon film of the present invention may contain components other than CNTs that are inevitably mixed in during the manufacturing process of CNT aggregates and carbon films, but the proportion of CNTs in the carbon film is preferably 95% by mass or more, more preferably 98% by mass or more, even more 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 consists only of CNTs).

[0014] Here, the carbon film of the present invention is composed of a carbon nanotube aggregate. The carbon film of the present invention is characterized in that its air permeability value, measured according to the bubble point method, is 0.00010 or higher. The carbon film of the present invention, having an air permeability value of 0.00010 or higher measured according to the bubble point method, exhibits excellent electromagnetic wave shielding performance. Therefore, although the carbon film of the present invention is not particularly limited, it can be advantageously used, for example, as an electromagnetic wave shielding sheet.

[0015] The carbon film of the present invention has an air permeability value of 0.00010 or higher, as measured according to the bubble point method. In such a carbon film, there are gaps of an appropriate size between the constituent carbon nanotubes, and it is presumed that the energy of electromagnetic waves that penetrate the carbon film can be attenuated by diffuse reflection in these gaps. Therefore, it is believed that the carbon film of the present invention can exhibit excellent electromagnetic shielding performance. Furthermore, it is preferable that the carbon film of the present invention is a self-supporting film. If the carbon film is self-supporting, it has excellent handling properties, and when used, for example, as an electromagnetic wave shielding sheet, it offers a high degree of freedom in the arrangement of the sheet.

[0016] (Air permeability value according to the bubble point method) The measurement of air permeability of a carbon membrane according to the bubble point method can be carried out in accordance with the method described in the examples of the present specification. The value of air permeability according to the bubble point method needs to be 0.00010 or more, is preferably 0.00020 or more, more preferably 0.00030 or more, and even more preferably 0.00050 or more. When the value of air permeability of the carbon membrane according to the bubble point method is equal to or higher than the above lower limit, excellent electromagnetic wave shielding can be exhibited. Note that the upper limit of the air permeability value according to the bubble point method can be, for example, 10 or less.

[0017] (Method for Producing Carbon Membrane) Here, when the carbon membrane of the present invention is produced by forming a carbon nanotube aggregate into a membrane, as the CNT aggregate, use a CNT aggregate that satisfies at least any one of the following conditions (1) to (3), prior to forming the CNT aggregate into a membrane, subjecting the CNT aggregate to a dry pulverization treatment, can be produced by satisfying at least one of the above.

[0018] <CNT Aggregate> Here, as the CNT aggregate used for preparing the carbon membrane, known CNT aggregates such as a CNT aggregate obtained by the super-growth method (see International Publication No. WO 2006 / 011655) can be used, for example, but it is preferable to use a novel CNT aggregate that satisfies at least one of the conditions (1) to (3). A carbon membrane composed of a CNT aggregate that satisfies at least one of the following conditions (1) to (3) is excellent in electromagnetic wave shielding performance.

[0019] (1) For a carbon nanotube dispersion obtained by dispersing a carbon nanotube aggregate such that the bundle length is 10 µm or more, in a spectrum obtained by Fourier transform infrared spectroscopy, a peak based on plasmon resonance of the carbon nanotube dispersion is at a wavenumber of 300 cm -1 -1 to 2000 cm -1 There is at least one peak in the following range. (2) For a carbon nanotube aggregate, from an adsorption isotherm measured at 77 K using liquid nitrogen, obtained based on the Barrett-Joyner-Halenda method, the maximum peak in a pore distribution curve showing the relationship between pore diameter and Log differential pore volume falls within the range of more than 100 nm and less than 400 nm. (3) A peak in the two-dimensional spatial frequency spectrum of an electron microscope image of the carbon nanotube aggregate is present at 1 μm -1 or more and 100 μm -1 or less in at least one position.

[0020] Although the reason why a carbon film composed of a CNT aggregate that satisfies at least one of the above conditions (1) to (3) is excellent in electromagnetic wave shielding performance is not clear, it is presumed to be as follows. FIG. 1 shows a scanning electron microscope (SEM) image of an example of a CNT aggregate that satisfies at least one of the above (1) to (3). As shown in FIG. 1, the CNTs constituting the CNT aggregate that satisfies at least one of the above conditions (1) to (3) have a wavy structure. It is considered that, due to such a "wavy structure", electromagnetic waves are diffusely reflected between the individual CNTs constituting the CNT aggregate. It is presumed that in the process of such diffuse reflection, the energy of the electromagnetic wave is lost, and the result is reflected in high electromagnetic wave shielding performance. Hereinafter, each of the above conditions (1) to (3) that can be satisfied by the CNT aggregate of the present invention will be described in detail.

[0021] <<Condition (1)>> Condition (1) is: for a carbon nanotube dispersion obtained by dispersing a carbon nanotube aggregate such that the bundle length is 10 μm or more, in a spectrum obtained by Fourier-transform infrared spectroscopy analysis, a peak based on plasmon resonance of the carbon nanotube dispersion is at a wavenumber of 300 cm -1 ‑1 to more than 2000 cm -1The following range contains at least one element: Here, it has been widely known that a strong absorption characteristic in the far-infrared region is a characteristic of CNTs. This strong absorption characteristic in the far-infrared region is thought to be due to the diameter and length of the CNT. The relationship between the absorption characteristics in the far-infrared region, more specifically the peak based on the plasmon resonance of CNTs, and the length of the CNT has been studied in detail in 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). Based on the findings described in the above non-patent literature and our own knowledge, the inventors hypothesized that the position where the peak based on the plasmon resonance of CNTs is detected in the spectrum obtained by Fourier transform infrared spectroscopy may be affected in some way by the distance between defect points in the CNT, and they conducted verification. The inventors then discovered that the location where peaks based on plasmon resonance of CNTs are detected can serve as an indicator corresponding to the path distance between inflection points in CNTs having a wavy structure, and thus established the above condition (1).

[0022] Under condition (1), wavenumber 300cm -1 Super 2000cm -1 Preferably within the following range, with a wavenumber of 500 cm. -1 More than 2000cm -1 For the following range, a more preferable wavenumber is 650 cm. -1 More than 2000cm -1 If peaks based on plasmon resonance of CNTs exist within the following range, such CNTs may exhibit good electromagnetic shielding performance when forming a carbon film.

[0023] Figure 2 shows the spectra (FIR resonance charts) obtained by Fourier transform infrared spectroscopy analysis of the CNT aggregates used in Examples 1-4 and Comparative Example 1, which will be described later. As is clear from Figure 2, in addition to the relatively gentle peak based on the plasmon resonance of the CNT dispersion, the obtained spectra also show a peak at wavenumber 840 cm⁻¹. -1 Nearby, 1300cm -1 Nearby, and 1700cm -1 Sharp peaks can be observed in the vicinity. These sharp peaks do not correspond to "peaks based on plasmon resonance of carbon nanotube dispersions," but rather each corresponds to infrared absorption originating from functional groups. More specifically, at wavenumber 840 cm⁻¹ -1 The sharp peak in the vicinity is due to out-of-plane bending oscillations of CH; wavenumber 1300 cm. -1 The sharp peak in the vicinity is due to epoxy three-membered ring stretching vibrations; wavenumber 1700 cm. -1 The sharp peaks in the vicinity are due to C=O stretching vibrations. Note that the wavenumber is 2000 cm. -1 In the ultra-high region, in addition to plasmon resonance, a peak similar to the S1 peak is detected, as mentioned in the non-patent document by T. Morimoto et al. above. Therefore, the inventors set the upper limit for determining the presence or absence of a peak based on plasmon resonance in the CNT dispersion under condition (1) to 2000. -1 The limit was set to less than 1 cm.

[0024] Here, in condition (1), when obtaining a spectrum by Fourier transform infrared spectroscopy, it is necessary to obtain a CNT dispersion by dispersing the CNT aggregates so that the bundle length is 10 μm or more. For example, by mixing CNT aggregates, water, and a surfactant (e.g., sodium dodecylbenzenesulfonate) in appropriate ratios and stirring them with ultrasound or the like for a predetermined time, a dispersion can be obtained in which CNT dispersions with a bundle length of 10 μm or more are dispersed in water.

[0025] The bundle length of a CNT dispersion can be obtained by analyzing it using a wet-type image analysis particle size analyzer. This analyzer calculates the area of ​​each dispersion from an image obtained by photographing the CNT dispersion, and can obtain the diameter of the circle having the calculated area (hereinafter sometimes referred to as the ISO area diameter). In this specification, the bundle length of each dispersion is defined as the value of the ISO area diameter obtained in this way.

[0026] <<Condition (2)>> Condition (2) specifies that "the largest peak in the pore size distribution curve is in the range of pore size between 100 nm and 400 nm." The pore size distribution of a carbon nanotube aggregate can be determined from the adsorption isotherm at 77 K of liquid nitrogen based on the BJH method. The fact that the peak in the pore size distribution curve obtained from the measurement of the carbon nanotube aggregate is in the range of over 100 nm means that there are voids of a certain size between the CNTs in the carbon nanotube aggregate, and that the CNTs are not excessively densely aggregated. The upper limit of 400 nm is the measurement limit of the measuring device (BELSORP-mini II) used in the example.

[0027] Here, from the viewpoint of further improving the electromagnetic 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 2.0 cm³. 3 It is preferable that the amount is 1 / g or more.

[0028] <<Condition (3)>> Condition (3) is that "the peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is 1 μm -1 More than 100μm -1The condition stipulates that at least one exists within the following range. The satisfaction of this condition can be determined in the following manner. First, the CNT aggregate to be judged is observed under magnification (e.g., 10,000x) using an electron microscope (e.g., electrolytic emission scanning electron microscope), and multiple electron microscope images (e.g., 10 images) are obtained within a 1 cm square field of view. Fast Fourier Transform (FFT) processing is performed on the obtained multiple electron microscope images to obtain a two-dimensional spatial frequency spectrum. The two-dimensional spatial frequency spectrum obtained for each of the multiple electron microscope images is binarized, and the average value of the peak position appearing on the high-frequency side is calculated. -1 More than 100μm -1 If the following range is observed, it is determined that condition (3) is met. Here, the "peak" used in the above determination shall be a clear peak obtained by performing an isolated point extraction process (i.e., the reverse operation of isolated point removal). Therefore, when the isolated point extraction process is performed, 1 μm -1 More than 100μm -1 If a clear peak is not obtained within the following range, it will be determined that condition (3) is not met.

[0029] Here, from the perspective of further improving the electromagnetic shielding performance of the carbon film, the peak of the two-dimensional spatial frequency spectrum is 2.6 μm. -1 More than 100μm -1 It is preferable that it exists within the following range.

[0030] Furthermore, from the viewpoint of further improving the electromagnetic shielding performance of the carbon film, it is preferable that the CNT aggregate satisfies at least two of the above conditions (1) to (3), and it is more preferable that it satisfies all of the above conditions (1) to (3).

[0031] <<Other properties>> Furthermore, the CNT aggregates that can be used to form the carbon film of the present invention preferably have the following properties in addition to the conditions (1) to (3) above.

[0032] For example, the CNT aggregate has a total specific surface area of ​​preferably 600 m² as determined by the BET method. 2 / g or more, more preferably 800m 2 It is 1 / g or more, preferably 2600m 2 / g or less, more preferably 1400m 2 It is less than / g. Furthermore, for those that have undergone opening treatment, it is 1300m 2 It is preferable that the specific surface area is 1 / g or more. A CNT aggregate having a high specific surface area allows for better diffuse reflection of electromagnetic waves within the carbon film, thereby further improving the electromagnetic shielding performance of the carbon film. The CNT aggregate mainly consists of single-walled carbon nanotubes, but may also contain double-walled carbon nanotubes and multi-walled carbon nanotubes to an extent that does not impair its function. The total specific surface area of ​​the CNTs by the BET method can be measured, for example, using a BET specific surface area measuring device in accordance with JIS Z8830.

[0033] Furthermore, 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. If the average height of the CNTs constituting the CNT aggregate is 10 μm or more, aggregation with adjacent CNT bundles is prevented, and dispersion becomes easier. If the average height of the CNTs constituting the CNT aggregate is 10 μm or more, it becomes easier to form a network between CNTs, and it can be suitably used in applications where conductivity or mechanical strength is required. If the average height of the CNTs constituting the CNT aggregate is 10 cm or less, generation can be carried out in a short time, so 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, dispersion becomes easier. The average height of the CNTs can be determined by measuring the height of 100 randomly selected CNTs using a scanning electron microscope (SEM).

[0034] The tap bulk density of the CNT aggregate is 0.001 g / cm³. 3 More than 0.2g / cm 3The following is preferable. CNT aggregates within this density range have excellent dispersibility because the bonds between CNTs are not excessively strong, and can be molded into various shapes. The tap bulk density of the CNT aggregate is 0.2 g / cm³. 3 If the following conditions are met, the bonds between CNTs will be weaker, making it easier to homogeneously disperse the CNT aggregate when stirred in a solvent. Furthermore, if the tap bulk density of the CNT aggregate is 0.001 g / cm³, it will be easier to homogeneously disperse the CNT aggregate. 3 If the above conditions are met, the integrity of the CNT aggregate will be improved and handling will be easier. Tap bulk density refers to the apparent bulk density when powdered CNT aggregate is filled into a container and then the voids between powder particles are reduced by tapping or vibration, resulting in a densely packed state.

[0035] Furthermore, the average outer diameter of the CNTs constituting the CNT aggregate is preferably 0.5 nm or more, more preferably 1.0 nm or more, more preferably 15.0 nm or less, more preferably 10.0 nm or less, and even more preferably 5.0 nm or less. If the average outer diameter of the CNTs is 0.5 nm or more, bundling of CNTs 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 ratio of multilayer 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 standard deviation (σ) of the CNTs may be adjusted by changing the CNT manufacturing method or manufacturing conditions, or by combining multiple types of CNTs obtained by different manufacturing methods.

[0036] The G / D ratio of a CNT aggregate is preferably between 1 and 50. A G / D ratio of less than 1 suggests that the single-walled CNTs have low crystallinity, are heavily contaminated with amorphous carbon, and contain a high amount of multi-walled CNTs. Conversely, a G / D ratio greater than 50 indicates high linearity, making it easier for CNTs to form tightly packed bundles, potentially reducing the specific surface area. The G / D ratio is a commonly used indicator for evaluating the quality of CNTs. The Raman spectrum of CNTs measured by a Raman spectrometer includes the G band (1600 cm⁻¹). -1 (Nearby) and D-band (1350cm) -1 A vibrational mode called the G band is observed. The G band is a vibrational mode originating from the hexagonal lattice structure of graphite, which is the cylindrical surface of the CNT, and the D band is a vibrational mode originating from the amorphous region. Therefore, the higher the peak intensity ratio of the G band to the D band (G / D ratio), the more crystalline (linear) the CNT can be evaluated.

[0037] To obtain a high specific surface area, it is desirable that the purity of the CNT aggregate be as high as possible. Here, purity refers to carbon purity, a value indicating what percentage of the mass of the CNT aggregate is composed of carbon. While there is no upper limit to the purity required to obtain a high specific surface area, it is difficult to obtain CNT aggregates with a purity of 99.9999% or higher in manufacturing. If the purity is less than 95% by mass, the untreated CNT aggregate will have a specific surface area of ​​1000m. 2 It becomes difficult to obtain a specific surface area exceeding / g. Furthermore, if the carbon purity is less than 95% by mass due to the presence of metal impurities, the metal impurities react with oxygen during the opening process, hindering the opening of the CNTs, and as a result, it becomes difficult to increase the specific surface area. For these reasons, it is preferable that the purity of the single-walled carbon nanotubes is 95% by mass or higher. A predetermined CNT aggregate that satisfies at least one of the conditions (1) to (3) described above can have a purity of 98% by mass or higher, preferably 99.9% by mass or higher, without the need for purification treatment. Such a CNT aggregate contains almost no impurities and can fully exhibit the inherent properties of CNTs. The carbon purity of the CNT aggregate can be obtained from elemental analysis using fluorescent X-rays or thermogravimetric analysis (TGA), etc.

[0038] <<Method for producing CNT aggregate>> The method for producing a CNT aggregate is not particularly limited, and production conditions can be adjusted according to desired properties. For example, when producing a CNT aggregate that satisfies at least any one of the above-mentioned conditions (1) to (3), it is necessary that the conditions during growth of the CNT aggregate satisfy all of the following (a) to (c). (a) The growth rate of the CNT aggregate is 5 µm / min or more. (b) The concentration of the catalyst activating substance in the growth atmosphere of the CNT aggregate is 4% by volume or more. (c) During growth of the CNT aggregate, an obstacle is present in the growth direction of the CNTs constituting the CNT aggregate.

[0039] Then, a CNT aggregate that satisfies at least any one of the above-mentioned conditions (1) to (3) can be efficiently produced by the production method that satisfies all of the above (a) to (c). Furthermore, in this production method, there is no particular limitation as long as the above conditions (a) to (c) are satisfied during the growth of the CNT aggregate, and a CNT synthesis step according to known methods such as a fluidized bed method, a moving bed method, and a fixed bed method can be employed. Here, the fluidized bed method means a synthesis method for synthesizing CNTs while fluidizing a granular carrier supporting a catalyst for CNT synthesis (hereinafter also referred to as a granular catalyst support). In addition, the moving bed method and the fixed bed method mean synthesis methods for synthesizing CNTs without fluidizing a catalyst-supporting carrier (particulate carrier or plate-like carrier).

[0040] In one example, the production method that satisfies all of the above (a) to (c) includes: a catalyst support forming step of forming a catalyst support; a CNT synthesis step of synthesizing CNTs using the catalyst support obtained in the catalyst support forming step; and a recovery step of recovering the CNTs synthesized in the CNT synthesis step. The catalyst support forming step can be carried out according to a known wet or dry catalyst supporting method. Further, the recovery step can be carried out using a known separation and recovery apparatus such as a classifier.

[0041] [CNT synthesis process] In the CNT synthesis process, all of the above conditions (a) to (c) are to be satisfied during CNT growth. Specifically, by appropriately adjusting the concentration and temperature of the raw material gas that serves as the carbon source in the CNT growth atmosphere, condition (a), "the growth rate of the carbon nanotube aggregate is 5 μm / min or more," can be satisfied. Here, the raw material gas that serves as the carbon source is not particularly limited and can be hydrocarbon gases such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene, and acetylene; lower alcohol gases such as methanol and ethanol; and mixtures thereof. Furthermore, this raw material gas may be diluted with an inert gas. In addition, from the viewpoint of further improving the electromagnetic shielding performance of the carbon film while further increasing the dispersibility of the resulting CNT aggregate, it is preferable that the growth rate of the CNT aggregate is 10 μm / min or more. The temperature can be adjusted, for example, in the range of 400°C to 1100°C.

[0042] In the CNT growth atmosphere, the raw material gas serving as the carbon source preferably contains ethylene. By heating the ethylene within a predetermined temperature range (700°C to 900°C), the decomposition reaction of ethylene is promoted, and when the decomposition gas comes into contact with the catalyst, rapid growth of CNTs becomes possible. However, if the thermal decomposition time is too long, the ethylene decomposition reaction proceeds too far, causing catalyst deactivation and the adhesion of carbon impurities to the CNT aggregate. In the CNT aggregate production of the present invention, a thermal decomposition time of 0.5 seconds to 10 seconds is preferred for an ethylene concentration of 0.1 volume% to 40 volume%. If the time is less than 0.5 seconds, the thermal decomposition of ethylene is insufficient, making it difficult to rapidly grow CNT aggregates with a high specific surface area. If the time is longer than 10 seconds, the ethylene decomposition proceeds too far, generating a large amount of carbon impurities, causing catalyst deactivation and a decrease in the quality of the CNT aggregate. The thermal decomposition time is calculated using the following formula. (Thermal decomposition time) = (Volume of heated channel) / {(Flow rate of raw material gas) × (273.15 + T) / 273.15} Here, the heated channel volume is the volume of the channel heated to a predetermined temperature T°C through which the raw material gas passes before contacting the catalyst, and the raw material gas flow rate is the flow rate at 0°C and 1 atm.

[0043] Furthermore, by appropriately adjusting the supply rate of the catalyst activating material supplied during CNT growth, condition (b) that "the concentration of the catalyst activating material in the growth atmosphere of the carbon nanotube aggregate is 4% by volume or more" can be satisfied. From the viewpoint of further improving the electromagnetic shielding performance of the carbon film, it is preferable that the concentration of the catalyst activating material in the growth atmosphere of the CNT aggregate is 5% by volume or more. The catalyst activating material is not particularly limited and includes low carbon number oxygen-containing compounds such as water, oxygen, ozone, acidic gases, nitrogen oxides, carbon monoxide and carbon dioxide; alcohols such as ethanol and methanol; ethers such as tetrahydrofuran; ketones such as acetone; aldehydes; esters; and mixtures thereof. Among these, carbon dioxide is preferred. It should be noted that substances containing both carbon and oxygen, such as carbon monoxide and alcohols, may have both the function of a raw material gas and a catalyst activating material. For example, carbon monoxide acts as a catalyst activating material when combined with a more reactive raw material gas such as ethylene, and acts as a raw material gas when combined with a catalyst activating material that shows a large catalytic activation effect even in trace amounts, such as water.

[0044] Furthermore, by selecting the fluidized bed method in the CNT synthesis process, or by adjusting the spacing of the catalyst supports in the mobile bed or stationary bed method, condition (c) that "obstacles exist in the growth direction of the carbon nanotubes constituting the carbon nanotube aggregate during the synthesis of the carbon nanotube aggregate" can be satisfied.

[0045] In the fluidized bed method described above, the CNT synthesis process may be carried out by supplying gas from below to fluidize the particulate catalyst support while supplying the raw material gas, or by continuously conveying the particulate catalyst support by screw rotation while supplying the raw material gas.

[0046] The catalyst support comprises a support and a catalyst supported on the surface of the support. The support is the part that forms the base structure for supporting the catalyst by attaching, fixing, forming a film, or otherwise attaching it to the surface of the support. The structure of the support may be the support alone, or it may be a support with an arbitrary underlayer on the surface of the support to ensure good support of the catalyst. The shape of the support is preferably particulate, and the particle size is preferably 1 mm or less in volume average particle size, more preferably 0.7 mm or less, even more preferably 0.4 mm or less, and preferably 0.05 mm or more. If the particle size is below the above upper limit, the growing CNT bundles become thinner, which is advantageous for forming a wavy structure. The particle density is 3.8 g / cm³ in apparent density. 3 Preferably, it is 5.8 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 8 g / cm³. 3 The following is preferable: If the particle density is above the lower limit, the force applied to the growing CNT bundle increases, which is advantageous for forming a wavy structure. The material of the support is preferably a metal oxide containing one or more elements from Al and Zr. Among these, zirconia beads containing a large amount of Zr are particularly preferred.

[0047] For example, when using a particulate carrier, one method for supporting the catalyst on the surface of the particulate carrier is to use a rotary drum coating apparatus equipped with a substantially cylindrical rotary drum. When a base layer is placed on the surface of the particulate carrier before supporting the catalyst, a solution containing components that can form the base layer is sprayed onto the surface of the particulate carrier and dried before spraying and drying the catalyst solution to form the base layer on the carrier surface. By such a method, the catalyst layer and base layer can be formed relatively easily and uniformly.

[0048] In the CNT synthesis process, prior to the "growth process" which is carried out in accordance with the above conditions (a) to (c), a "formation process" can be performed to reduce the catalyst supported on the catalyst support, and after the growth process is completed, a "cooling process" can be performed to cool the catalyst support on which the CNTs have grown. In the "formation process," for example, the atmosphere containing the catalyst support is used as a reducing gas atmosphere, and at least one of this reducing gas atmosphere or the catalyst support is heated to reduce and atomize the catalyst supported on the catalyst support. The temperature of the catalyst support or the reducing gas atmosphere in the formation process is preferably 400°C to 1100°C. The duration of the formation process may be 3 minutes to 120 minutes. As the reducing gas, for example, hydrogen gas, ammonia gas, water vapor, and mixtures thereof can be used. Alternatively, the reducing gas may be a mixture of these gases with an inert gas such as helium gas, argon gas, or nitrogen gas. On the other hand, in the "cooling process," the catalyst support on which the CNTs have grown is cooled in an inert gas environment. Here, the inert gas can be the same as the inert gas that can be used in the growth process. In the cooling process, the temperature of the catalyst support on which the CNTs have grown is preferably reduced to 400°C or lower, and more preferably to 200°C or lower.

[0049] <Dry grinding process> In obtaining the carbon film of the present invention, the CNT aggregate before film formation may be subjected to dry grinding treatment as needed. In this invention, "dry grinding treatment" means grinding treatment in a state in which the material to be ground does not substantially contain solvent (for example, a state in which the solid content concentration is 95% or higher).

[0050] The grinding device that can be used for dry grinding is not particularly limited as long as it is capable of applying physical load to an aggregate of fine structures by stirring or other means. Such a device can be a mixer equipped with rotating blades. Furthermore, the grinding conditions are not particularly limited. For example, when using a mixer equipped with rotating blades as the grinding device, the rotation speed is preferably 500 rpm or more and 5000 rpm or less, and the grinding time is preferably 10 seconds or more and 20 minutes or less.

[0051] <Membrane formation> The carbon film of the present invention can be obtained by forming a film from a CNT aggregate. Here, the method of forming a film from a CNT aggregate is not particularly limited, but a preferred method is to prepare a CNT dispersion by dispersing the CNT aggregate in a dispersion medium such as water or an organic solvent, and then remove at least a portion of the dispersion medium from the CNT dispersion.

[0052] The method for preparing the CNT dispersion is not particularly limited, but the CNT dispersion can be obtained by dispersing CNT aggregates in a dispersion medium using known methods such as a dispersion method using a stirring blade, a dispersion method using ultrasound, and a dispersion method using shear force. Here, from the viewpoint of further improving the electromagnetic wave shielding performance of the resulting carbon film, it is preferable that the CNTs are appropriately dispersed in the CNT dispersion. Preferably, the CNT dispersion does not contain a dispersant. In other words, it is preferable that the CNT dispersion consists substantially only of CNTs and a dispersion medium. In this specification, "the CNT dispersion consists substantially only of CNTs and a dispersion medium" means that 99.9% by mass or more of the constituent components of the CNT dispersion consist of CNTs and unavoidable impurities associated with CNTs, and a dispersion medium and unavoidable impurities associated with the dispersion medium. Methods for removing the dispersion medium from the CNT dispersion include known methods such as filtration and drying. The filtration method is not particularly limited, and known filtration methods such as natural filtration, reduced pressure filtration (suction filtration), pressure filtration, and centrifugal filtration can be used. As for drying methods, known drying methods such as hot air drying, vacuum drying, hot roll drying, and infrared irradiation can be used. The drying temperature is not particularly limited, but is usually between room temperature and 200°C, and the drying time is not particularly limited, but is usually between 1 hour and 48 hours. Furthermore, drying is not particularly limited, but can be carried out on known substrates.

[0053] Among these methods, it is preferable to employ drying to remove the dispersion medium. Furthermore, the above filtration and drying can also be used in combination. For example, the carbon film of the present invention can be obtained by further drying the film-like filter material (primary sheet) obtained by filtering the CNT dispersion.

[0054] (Properties 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 more preferably 150 μm or less. If the thickness is 5 μm or more, the carbon film can have sufficient mechanical strength and exhibit even better electromagnetic wave shielding performance. On the other hand, if the thickness is 200 μm or less, the carbon film can be made lighter. The "thickness" of the carbon film can be measured using the method described in the examples. [Examples]

[0055] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, various measurements and evaluations were carried out as follows.

[0056] <Fourier Transform Infrared Spectroscopy (FT-IR)> To 10 mg of CNT aggregates, 100 g of water containing 1% by mass of sodium dodecylbenzenesulfonate as a surfactant was added, and the mixture was stirred for 1 minute at 45 Hz using an ultrasonic bath to obtain 100 ml of dispersion of each CNT aggregate. Each dispersion prepared as described above was diluted 2-fold with a solvent of the same composition, dropped onto a silicon substrate respectively and dried, then the effective plasmon length was measured by plasmon far-infrared (FIR) resonance peak using a Fourier transform infrared spectrophotometer. The effective plasmon lengths are shown in Table 1. The FIR resonance chart of the obtained FIR spectrum is shown in Figure 2. As shown in the figure, the curves corresponding to the CNT aggregates used in Examples 1 to 4 and Comparative Example 1 are at 300cm -1 -1 or higher where a peak of optical density was observed. The position of the plasmon peak top was obtained from an approximate curve by polynomial fitting using drawing software.

[0057] <Measurement of CNT bundle length> For each dispersion prepared for FT-IR measurement, the average value of the ISO circular equivalent diameter of CNT dispersions present in the dispersion was measured using a flow-type particle image analyzer (circulation type image analysis particle size distribution analyzer "CF-3000" manufactured by Jasco International), and the obtained value was taken as the CNT bundle length. The analysis conditions were as follows. <Analysis conditions> ·Injection volume: 50 ml (sampling volume 1.2%) ·Flow cell spacer: 1000 μm ·Front lens magnification: 2× ·Telecentric lens magnification: 0.75× ·Length per pixel: 2.3 μm / pixel Each dispersion was measured four times under the same conditions while being circulated, and the arithmetic average value of these measurements was obtained.

[0058] <Preparation of pore distribution curve (CNT aggregate)> For CNT aggregates of 10 mg or more, adsorption isotherms were measured at 77 K using liquid nitrogen with a BELSORP-miniII (Microtrac Bell) (adsorption equilibrium time was set to 500 seconds). As a pretreatment, vacuum degassing was performed at 100°C for 12 hours. Pore distribution curves for each sample were obtained from the adsorption amount of these adsorption isotherms using the BJH method. The results are shown in Figure 3. As shown in Figure 3, the CNT aggregates used in Examples 1-4 and Comparative Example 1 showed the largest peak in the log differential pore volume in the region of pore diameter 100 nm or larger. Furthermore, when creating the pore distribution curve of the CNT aggregate, the measurement range for pore diameter was set to between 1 nm and less than 400 nm.

[0059] <Measurement of air permeability values ​​according to the bubble point method> The air permeability of carbon films according to the bubble point method can be measured in accordance with JIS K 3832 as follows. A 25 mm diameter disc-shaped test piece was cut from the carbon films prepared in the examples and comparative examples and set in a palm porometer (PMI, "CFP-1200-AEXLSPHBB"). Then, under the following conditions, the pressure was gradually increased in the range of 0 to 1000 kPa, and the pressure at the moment when the reagent air was pushed out of the test piece (i.e., the bubble point) and the permeation flow rate were measured. Pressurized gas: Compressed air Pressure gauges: 250 PSIA, 110 PSIA, 5 PSID. Resolution: 1 / 60,000, Accuracy: 0.15% / reading. Flow meter: MFC 10cc / min, MFM 10L / min, MFM 200L / min. Resolution: 1 / 20,000, Accuracy: ±1% of reading / FS Electrical regulator: Resolution is 1 / 4,000. Reagent: Air (Viscosity: 0.019 cP) Measurement temperature: room temperature

[0060] The obtained values ​​of the pressure at the bubble point and the permeation flow rate at that time were substituted into the following formula, along with the conditions shown in the measurement conditions above, to calculate the value of Darcy's permeability constant (Cd; unit: Darcy) as the "value of air permeability according to the bubble point method" in this invention. Cd = 8FTV / [πD] 2 (P 2 -1)] [Here, F is the permeation flow rate at the bubble point (cm 3 ( / second), T represents the thickness of the test specimen (cm), V represents the viscosity of air as a reagent (cP), D represents the diameter of the test specimen (cm), and P represents the pressure at the bubble point (kPa).

[0061] (Two-dimensional spatial frequency spectrum analysis of electron microscope images) For the CNT aggregates 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. This sample was observed at 10,000x magnification using an electrolytic emission scanning electron microscope, and 10 photographs were taken of an arbitrarily selected 1 cm square field of view. Each of the 10 electron microscope images was subjected to a Fast Fourier Transform to obtain a two-dimensional spatial frequency spectrum. Each of the obtained two-dimensional spatial frequency spectra was binarized, and the position of the outermost (highest frequency) peak was determined, and the average value was obtained. In the binarization process, values ​​greater than 0.75 obtained after the Fast Fourier Transform were set to 1, and other values ​​were set to zero. Figure 4A is one of the 10 images obtained for the CNT aggregates used in Examples 1-3 and Comparative Example 1, and Figure 4B is the two-dimensional spatial frequency spectrum obtained for this image. In Figure 4B, components closer to the center represent low-frequency components, and components located further out from the center correspond to higher-frequency components. In the diagram, the arrows indicate 1 to 100 μm. -1 Among the clear peaks detected in the region, the peak position with the highest wavenumber (3μm) -1 Figure 4C shows one of the 10 images obtained of the CNT aggregate used in Example 4, and Figure 4D is the two-dimensional spatial frequency spectrum obtained for that image. In Figure 4D, components closer to the center represent low-frequency components, and components located further out from the center correspond to higher-frequency components.

[0062] <thickness> The thickness of the carbon film was measured using a "Digimatic Standard Outside Micrometer" manufactured by Mitutoyo Corporation.

[0063] <Electromagnetic wave shielding performance> For the carbon film, the reflection 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 measurement frequencies of 0.1 MHz, 1 MHz, and 10 MHz was evaluated according to the following criteria. It should be noted that the larger the value of the electromagnetic wave shielding effect [dB] at a certain frequency, the more excellent 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.

[0064] <Preparation of CNT aggregate> The CNTs used in Examples 1 to 3 and Comparative Example 1 were synthesized as follows. A schematic configuration of the CNT production apparatus used in the synthesis is shown in Fig. 5. The CNT production apparatus 100 shown in Fig. 5 includes a heater 101, a reaction tube 102, a dispersion plate 103, a reducing gas / raw material gas inlet 104, an exhaust port 105, and a gas heating promotion section 106. Synthetic quartz was used as the material for the reaction tube 102 and the dispersion plate 103. <<Catalyst support formation step>> The catalyst support forming step will be described below. Zirconia (zirconium dioxide) beads (ZrO₂, volume-average particle diameter D50: 350 μm) serving as a support are charged into a rotary drum type coating apparatus. While stirring the zirconia beads at 20 rpm, an aluminum-containing solution is sprayed by a spray gun (spray amount: 3 g / min, spraying time: 940 seconds, spray air pressure: 10 MPa), and drying is performed while supplying compressed air (300 L / min) into the rotary drum, thereby forming an aluminum-containing coating film on the zirconia beads. Next, a firing treatment is performed at 480° C. for 45 minutes to produce primary catalyst particles having an aluminum oxide layer formed thereon. Further, the primary catalyst particles are charged into another rotary drum type coating apparatus, and while stirring at 20 rpm, an iron catalyst solution is sprayed by a spray gun (spray amount: 2 g / min, spraying time: 480 seconds, spray air pressure: 5 MPa), and drying is performed while supplying compressed air (300 L / min) into the rotary drum, thereby forming an iron-containing coating film on the primary catalyst particles. Next, a firing treatment is performed at 220° C. for 20 minutes to produce a catalyst support on which an iron oxide layer is further formed. <<CNT Synthesis Step>> 300 g of the catalyst support produced in this manner is charged into a reaction tube 102 of a CNT production apparatus 100, and while fluidizing the catalyst support 107 by circulating a gas, treatment is performed in the order of a formation step, a growth step, and a cooling step to produce a CNT aggregate. The conditions for each step included in the CNT synthesis step were set as follows. [Formation Step] ·Set temperature: 800°C ·Reducing gas: 3 slm nitrogen, 22 slm hydrogen ·Treatment time: 25 minutes [Growth Step] ·Set temperature: 800°C ·Raw material gas: 15 slm nitrogen, 5 slm ethylene, 2 slm carbon dioxide, 3 slm hydrogen ·Treatment time: 10 minutes ·Raw material gas pyrolysis residence time: 0.65 seconds [Cooling Step] ·Cooling temperature: Room temperature ·Purge gas: 25 slm nitrogen

[0065] The CNT aggregate synthesized on the catalyst support was separated using a forced vortex classifier (rotation speed: 3500 rpm, air flow rate: 3.5 Nm 3 / min). The recovery rate of the CNT aggregate was 99%. The characteristics of the CNT aggregate produced according to this example are: tap bulk density: 0.01 g / cm 3 3, average CNT height: 200 μm, BET specific surface area: 800 m 2 2 / g, average outer diameter: 4.0 nm, and carbon purity: 99%.

[0066] (Example 1) 1000 g of water was added to 1 g of the CNT aggregate obtained as described above, and the mixture was stirred for 10 minutes at a rotation speed of 3000 rpm using an ultra-high speed emulsification disperser (product name: "Lab Solution (registered trademark)", manufactured by Sinky Corporation) to obtain a CNT dispersion liquid. The obtained CNT dispersion liquid was applied onto a base material. The coating film on the base material was vacuum-dried at a temperature of 80°C for 24 hours to form a carbon film on the base material. Thereafter, the carbon film was peeled from the base material to obtain a carbon film (free-standing film) with a thickness of 100 μm. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0067] (Example 2) In the preparation of the CNT dispersion liquid, dispersion treatment was performed for 10 minutes using an ultrasonic disperser (tabletop ultrasonic cleaner manufactured by Branson). Except for this point, a carbon film (free-standing film) with a thickness of 100 μm was obtained in the same manner as in Example 1. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0068] (Example 3) In the preparation of the CNT dispersion liquid, dispersion treatment was performed for 15 minutes under a condition of 100 MPa using a jet mill (Nanoveta, manufactured by Yoshida Kikai Kogyo Co., Ltd.). Except for this point, a carbon film (free-standing film) with a thickness of 100 μm was obtained in the same manner as in Example 1. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0069] (Example 4) <Preparation of CNT aggregate> The CNT aggregate used in Example 4 was prepared in a CNT synthesis process by supplying raw material gas while continuously conveying particulate catalyst supporters by screw rotation. Figure 6 shows the schematic configuration of the CNT assembly manufacturing apparatus 200 used. The CNT assembly manufacturing apparatus 200 shown in Figure 6 includes a formation unit 202, a growth unit 204, a transport unit 207 that transports the substrate from the formation unit 202 to the growth unit 204, a connection part 208 that spatially connects the formation unit 202 and the growth unit 204, and a gas contamination prevention device 203 that prevents gases from mixing between the formation unit 202 and the growth unit 204. Furthermore, the CNT assembly manufacturing apparatus 200 includes components such as an inlet purge device 201 located in front of the formation unit 202, an outlet purge device 205 located behind the growth unit 204, and a cooling unit 206 located behind the outlet purge device 205. The formation unit 202 consists of a formation furnace 202a for holding reducing gas, a reducing gas injection device 202b for injecting reducing gas, a heating device 202c for heating at least one of the catalyst and the reducing gas, and an exhaust device 202d for discharging gas from the furnace to the outside of the system. The gas contamination prevention device 203 includes an exhaust device 203a and a purge gas injection device 203b for injecting 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 raw material gas, a heating device 204c for heating at least one of the catalyst and the raw material gas, and an exhaust device 204d for discharging gas from the furnace to the outside of the system. The inlet purge device 201 is attached to a connection part 209 that connects the formation furnace 202a to the pre-chamber 213, which is a component for introducing the substrate 211 into the system via the hopper 212. The cooling unit 206 comprises a cooling container 206a for holding an inert gas, and a water cooling device 206b arranged to surround the space inside the cooling container 206a. The transport unit 207 is a unit that continuously transports the substrate 211 by screw rotation. It is implemented by a screw blade 207a and a drive device 207b that can rotate the screw blade to exert the substrate transport function.The heating device 214 is configured to be capable of heating the inside of the system at a temperature lower than the heating temperature in the formation unit, and heats the vicinity of the driving device 207b.

[0070] <Catalyst Layer Forming Step> Zirconia (zirconium dioxide) beads (ZrO₂, volume average particle diameter D₅₀: 650 μm) serving as a substrate are charged into a rotary drum type coating apparatus. While stirring the zirconia beads at 20 rpm, an aluminum-containing solution is sprayed by a spray gun (spray amount: 3 g / min, spraying time: 940 seconds, spray air pressure: 10 MPa), and dried while supplying compressed air (300 L / min) into the rotary drum, to form an aluminum-containing coating film on the zirconia beads. Next, a firing treatment is performed at 480° C. for 45 minutes to prepare primary catalyst particles having an aluminum oxide layer formed thereon. Further, the primary catalyst particles are charged into another rotary drum type coating apparatus, and while being stirred at 20 rpm, an iron catalyst solution is sprayed by a spray gun (spray amount: 2 g / min, spraying time: 480 seconds, spray air pressure: 5 MPa), and dried while supplying compressed air (300 L / min) into the rotary drum, to form an iron-containing coating film on the primary catalyst particles. Next, a firing treatment is performed at 220° C. for 20 minutes to prepare a substrate on which an iron oxide layer is further formed. <<CNT Synthesis Step>> The substrate having a catalyst on the surface prepared in this manner is charged into a feeder hopper of a manufacturing apparatus, and while being conveyed by a screw conveyor, treatments are performed in the order of a formation step, a growth step, and a cooling step, to manufacture a CNT aggregate.

[0071] <Formation Step to Cooling Step> The respective conditions of the inlet purge device, formation unit, gas mixing prevention device, growth unit, outlet purge device, and cooling unit of the CNT aggregate manufacturing apparatus are set as follows.

[0072] Feeder Hopper · Feed rate: 1.25 kg / h · Exhaust amount: 10 sLm (naturally exhausted through gaps) Inlet Purge Device • Purge gas: Nitrogen 40 sLm Formation Unit ·Furnace temperature: 800℃ • Reducing gases: Nitrogen 6 sLm, Hydrogen 54 sLm • Engine displacement: 60 sLm Processing time: 20 minutes Gas contamination prevention device • Purge gas: 20 sLm • Exhaust system displacement: 62 sLm Growth Unit ·Furnace temperature: 830℃ • Raw material gases: Nitrogen 15 sLm, Ethylene 5 sLm, Carbon dioxide 1 sLm, Hydrogen 3 sLm • Engine displacement: 47 sLm Processing time: 10 minutes Outlet purge device • Purge gas: Nitrogen 45 sLm Cooling unit ·Cooling temperature: room temperature • Displacement: 10 sLm (natural exhaust through gaps) Continuous manufacturing was carried out under the above conditions.

[0073] <Separation and Recovery Process> The CNT aggregate synthesized on the substrate was subjected to forced vortex classification (rotation speed 2300 rpm, airflow 3.5 Nm³). 3 Separation and recovery were performed using ( / min). The recovery rate of CNT aggregates was 96%.

[0074] The properties of the CNT aggregates produced by this embodiment are, as a typical value, tap bulk density: 0.02 g / cm³. 3 CNT average length: 150 μm, BET specific surface area: 900 m² 2 The sample size was / g, with an average outer diameter of 4.0 nm and a carbon purity of 99%.

[0075] 1g of the CNT aggregate obtained as described above was mixed with 1000g of water and stirred for 10 minutes at a rotation speed of 3000 rpm using an ultra-high-speed emulsification and dispersion apparatus (product name "Labo-Solution®", manufactured by Thinky Co., Ltd.) to obtain a CNT dispersion. The obtained CNT dispersion was applied to a substrate. The coating on the substrate was vacuum-dried at 80°C for 24 hours to form a carbon film on the substrate. Subsequently, the carbon film was peeled off the substrate to obtain a 100 μm thick carbon film (self-supporting film). The electromagnetic shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0076] (Comparative Example 1) In preparing the CNT dispersion, 1 g of sodium dodecyl sulfate was added as a dispersant, and the dispersion was treated using a jet mill (NanoVeta, manufactured by Yoshida Machinery Industry Co., Ltd.) at a condition of 100 MPa for 15 minutes. Except for this point, a carbon film (self-supporting film) with a thickness of 100 μm was obtained in the same manner as in Example 1. The electromagnetic wave shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0077] [Table 1]

[0078] Table 1 shows that carbon films with an air permeability value of 0.00010 or higher, measured according to the bubble point method, can exhibit excellent electromagnetic shielding performance over a wide frequency range. [Industrial applicability]

[0079] According to the present invention, a carbon film with excellent electromagnetic wave shielding performance can be provided. [Explanation of Symbols]

[0080] 100 CNT production equipment 101 Heater 102 reaction tube 103 Dispersion plate 104 Reducing gas / raw material gas inlet 105 Exhaust port 106 Gas heating acceleration unit 107 Catalyst support 200 CNT aggregate manufacturing equipment 201 Inlet purge device 202 Formation Unit 202a Formation Furnace 202b Reducing gas injection device 202c heating device 202d Exhaust System 203 Gas contamination prevention device 203a Exhaust system 203b Purge gas injection device 204 Growth Units 204a growth furnace 204b Raw material gas injection device 204c heating device 204d Exhaust System 205 Outlet purge device 206 Cooling Unit 206a Cooling vessel 206b Water-cooled chiller 207 Conveyor Unit 207a Screw blade 207b Drive unit 208~210 Connection section 211 Base material 212 Hopper 214 Heating device

Claims

1. A carbon film made of a carbon nanotube aggregate, The value of Darcy's permeability constant, as measured according to the bubble point method, is 0.00010 or greater. Carbon film.

2. The carbon film according to claim 1, which is a self-supporting film.

3. The carbon film according to claim 1 or 2, wherein the carbon nanotube aggregate satisfies at least one of the following conditions (1) to (3). (1) In the spectrum obtained by Fourier transform infrared spectroscopy analysis of a carbon nanotube dispersion obtained by dispersing the carbon nanotube aggregate such that the bundle length is 10 μm or more, the peak based on plasmon resonance of the carbon nanotube dispersion is at wavenumber 300 cm. －１ Super 2000cm －１ At least one exists within the following range. (2) For the carbon nanotube aggregate, the largest peak in the pore distribution curve showing the relationship between pore size and log differential pore volume, obtained from the adsorption isotherm at 77 K of liquid nitrogen using the Barrett-Joyner-Halenda method, is in the range of pore size greater than 100 nm and less than 400 nm. (3) The peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is 1 μm －１ 100 μm or more －１ There is at least one within the following range.

Images