carbon film

Abstract

The purpose of the present invention is to provide a carbon film having excellent electromagnetic wave-shielding performance. A carbon film according to the present invention is composed of carbon nanotube aggregates, wherein the pore distribution curve, which shows the relationship between a pore diameter and a Log differential pore volume and is obtained from the adsorption isotherm of liquid nitrogen at 77K, on the basis of the Barrett-Joyner-Halenda method, has a peak at which the Log differential pore volume is maximized within the pore diameter range of 10-100 nm, and the value of the Log differential pore volume at the peak is at least 1.2 cm3 / g.

Description

[Technical Field]

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

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

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

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

[0005] In recent years, attention has been focused on the use of carbon films as sheets that shield electromagnetic waves by absorbing and / or reflecting them (electromagnetic wave shielding sheets). However, even when the above-mentioned conventional carbon films are used as electromagnetic wave shielding sheets, the carbon films have not been able to fully exhibit their electromagnetic wave shielding performance (shielding performance).

[0006] Therefore, an object of the present invention is to provide a carbon film that has excellent electromagnetic wave shielding properties. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to achieve the above object, and have investigated the microscopic properties of a carbon film formed using an aggregate of carbon nanotubes, and have newly found that a carbon film having a pore distribution curve showing the relationship between pore diameter and Log differential pore volume with a predetermined shape can effectively shield electromagnetic waves, thereby completing the present invention.

[0008] That is, the present invention has an object to advantageously solve the above-mentioned problems, and the carbon membrane of the present invention is a carbon membrane made of an aggregate of carbon nanotubes, and a pore distribution curve showing the relationship between pore diameter and Log differential pore volume, obtained from an adsorption isotherm of liquid nitrogen at 77 K based on the Barrett-Joyner-Halenda method, has a peak at which the Log differential pore volume is maximum within a pore diameter range of 10 nm to 100 nm, and the value of the Log differential pore volume at the peak is 1.2 cm 3 A carbon membrane having a pore size distribution curve obtained from the adsorption isotherm of liquid nitrogen at 77 K by the Barrett-Joyner-Halenda method (hereinafter sometimes abbreviated as "BJH method"), in which the maximum peak satisfies the above-mentioned predetermined condition, has excellent shielding performance.

[0009] Here, the carbon film of the present invention is preferably a self-supporting film, which has excellent handleability and allows for greater freedom in the placement of the sheet when used as, for example, an electromagnetic wave shielding sheet. In the present invention, the term "self-supporting film" refers to a film that can independently maintain its shape without being damaged even without a support.

[0010] Furthermore, the carbon membrane of the present invention preferably has a thickness of 5 μm or more and 150 μm or less. If the thickness is within the above range, it is possible to further improve the shielding performance of the carbon membrane while sufficiently achieving a reduction in weight and an improvement in mechanical strength of the carbon membrane.

[0011] The carbon film of the present invention can be advantageously used, for example, as an electromagnetic wave shielding sheet. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a carbon film that has excellent electromagnetic wave shielding properties. [Brief explanation of the drawings]

[0013] [Figure 1] 1 shows an example of a pore distribution curve of a carbon membrane. [Figure 2] An example of a scanning electron microscope (SEM) image of a CNT aggregate is shown. [Figure 3] An example of a spectrum obtained by Fourier transform infrared spectroscopy of a CNT aggregate is shown below. [Figure 4] An example of the pore size distribution curve for a CNT aggregate is shown below. [Figure 5A] 1 shows an example of an SEM image of the CNT aggregate used in Example 1. [Figure 5B] 5B shows the two-dimensional spatial frequency spectrum obtained for the image of FIG. 5A. [Figure 6A] An example of an SEM image of SGCNT is shown. [Figure 6B] 6B shows the two-dimensional spatial frequency spectrum obtained for the image of FIG. 6A. [Figure 7] The schematic configuration of the CNT manufacturing equipment is shown.

[0014] 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 (carbon nanotube aggregate). Note that the carbon film of the present invention may contain, for example, components other than CNTs that are inevitably mixed in during the CNT aggregate and carbon film manufacturing process, but the proportion of CNTs in the carbon film is preferably 95 mass % or more, more preferably 98 mass % or more, even more preferably 99 mass % or more, particularly preferably 99.5 mass % or more, and most preferably 100 mass % (i.e., the carbon film is composed only of CNTs).

[0015] Here, the carbon membrane of the present invention has a pore distribution curve showing the relationship between pore diameter and Log differential pore volume, which is obtained based on the BJH method from the adsorption isotherm of liquid nitrogen at 77 K, and has a peak (maximum peak) at which the Log differential pore volume is maximum within a pore diameter range of 10 nm to 100 nm, and the value of the Log differential pore volume at the maximum peak is 1.2 cm 3 / g or more. The carbon membrane of the present invention, whose pore distribution curve has the above-mentioned predetermined shape, has excellent shielding performance and can therefore be advantageously used, for example, as an electromagnetic wave shielding sheet, although not particularly limited thereto.

[0016] (pore distribution curve) As described above, the pore size distribution curve can be created based on the BJH (Barrett-Joyner-Halenda) method from the adsorption isotherm of liquid nitrogen at 77 K. The BJH method is a measurement method for determining the distribution of pores (pore diameters) assuming that the pores are cylindrical. More specifically, in the present invention, the pore size distribution curve can be created using the method described in the Examples.

[0017] An example of a pore distribution curve for the carbon membrane of the present invention is shown in Figure 1. In Figure 1, the horizontal axis represents the logarithm of the pore diameter (unit: nm) (Log pore diameter), and the horizontal axis represents the Log pore differential volume (dVp / dlogdp, unit: cm 3 / g) on ​​the vertical axis, a pore size distribution curve is drawn for pore sizes in the range of 1 nm to 200 nm. Examples 1 and 2 correspond to the carbon membranes of the present invention. The pore distribution curves for the carbon membranes of Examples 1 and 2 each have a peak (maximum peak) where the Log differential pore volume is maximum within the pore diameter range of 10 nm to 100 nm, and the value of the Log differential pore volume at the maximum peak is 1.2 cm 3 More specifically, the pore size distribution curve of Example 1 shows a pore size distribution of 24 nm and a Log differential pore volume of 3.5 cm 3 / g, and the pore size distribution curve of Example 2 has a pore size of 28 nm and a Log differential pore volume of 2.3 cm 3 / g.

[0018] From the viewpoint of further improving the shielding performance of the carbon membrane, the pore distribution curve preferably has a maximum peak within a pore diameter range of 12 nm or more and 95 nm or less, more preferably within a pore diameter range of 15 nm or more and 90 nm or less, and even more preferably within a pore diameter range of 18 nm or more and 85 nm or less. In addition, from the viewpoint of further improving the shielding performance of the carbon membrane, the pore distribution curve should be such that the value of the Log differential pore volume at the maximum peak is 1.3 cm 3 / g or more is preferable, and 1.4cm 3 / g or more is more preferable, and 1.5cm 3 / g or more is more preferable, and 3 It is particularly preferable that the saturation coefficient is 1 / g or more. The upper limit of the Log differential pore volume at the maximum peak of the pore distribution curve is not particularly limited, but for example, it is 20.0 cm 3 / g or less, 15.0cm 3 / g or less, or 7.0cm 3 / g or less.

[0019] (Method of manufacturing carbon film) Here, the carbon membrane of the present invention capable of drawing the above-mentioned pore distribution curve is obtained by forming an aggregate of carbon nanotubes into a carbon membrane, as follows: As the CNT aggregate, use a CNT aggregate that satisfies at least one of the following conditions (1) to (3) described later. Prior to forming the CNT aggregate into a film, subject the CNT aggregate to dry grinding treatment. It can be produced by satisfying at least one of the following.

[0020] <CNT aggregate> Here, as the CNT aggregate used for the preparation of the carbon film, for example, known CNT aggregates such as a CNT aggregate obtained by using the super growth method (see International Publication No. 2006 / 011655) (which may be referred to as "SGCNT" in this specification) can be used, but it is preferable to use a novel CNT aggregate that satisfies at least one of the conditions (1) to (3). A CNT aggregate that satisfies at least one of the following conditions (1) to (3) has excellent dispersibility.

[0021] (1) Regarding the carbon nanotube dispersion obtained by dispersing the carbon nanotube aggregate so that the bundle length is 10 μm or more, in the spectrum obtained by Fourier transform infrared spectroscopic analysis, the peak based on the plasmon resonance of the carbon nanotube dispersion is at a wavenumber of 300 cm -1 more than 2000 cm -1 There is at least one in the following range. (2) The pore size distribution curve of the carbon nanotube aggregate has a peak where the Log differential pore volume is maximum within the range where the pore diameter is more 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 at 1 μm -1 more than 100 μm -1 There is at least one in the following range.

[0022] The reason why a CNT aggregate satisfying at least one of the above conditions (1) to (3) has excellent dispersibility is unclear, but is presumed to be as follows. FIG. 2 shows a scanning electron microscope (SEM) image of an example of a CNT aggregate satisfying at least one of the above conditions (1) to (3). As shown in FIG. 2, the CNTs constituting a CNT aggregate satisfying at least one of the above conditions (1) to (3) have a wave-like structure. It is presumed that this "wave-like structure" can suppress interactions between the CNTs constituting the CNT aggregate. If interactions between the CNTs are suppressed, the CNTs contained in the CNT aggregate can be suppressed from tightly bundling and agglomerating. This can make it possible to easily disperse the CNT aggregate. Furthermore, if the CNT aggregate is easily dispersible, the CNT aggregate can be easily processed. This effect can result in improved shielding performance when the CNT aggregate is formed into a carbon film, for example. Hereinafter, the above conditions (1) to (3) that can be satisfied by the CNT aggregate of the present invention will be described in detail.

[0023] <<Condition (1)>> Condition (1) is that "in a spectrum obtained by Fourier transform infrared spectroscopy of a carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more, a peak due to the plasmon resonance of the carbon nanotube dispersion is at a wave number of 300 cm -1 Super 2000cm -1The present invention defines that at least one of the following characteristics is present in the following range: "CNTs have a strong absorption characteristic in the far-infrared region, which has been widely known as an optical property of CNTs. This strong absorption characteristic in the far-infrared region is believed to be due to the diameter and length of the CNTs. The absorption characteristics in the far-infrared region, more specifically, the relationship between the peak due to the plasmon resonance of CNTs and the length of the CNTs, have been discussed in detail in a non-patent document (T. Morimoto et al., "Length-Dependent Plasmon Resonance in Single-Walled Carbon Nanotubes," pp. 9897-9904, Vol. 8, No. 10, ACS NANO, 2014). Based on the discussions described in the non-patent document and our own findings, the present inventors speculated that the position at which the peak due to the plasmon resonance of CNTs is detected in a spectrum obtained by Fourier transform infrared spectroscopy analysis may be affected in some way by the distance between defects in the CNTs, and conducted verification. The inventors then discovered that the position at which the peak based on the plasmon resonance of the CNT is detected can serve as an indicator corresponding to the distance between bending points in a CNT having a wavy structure, and set the above condition (1).

[0024] Under condition (1), the wave number is 300 cm -1 Super 2000cm -1 Within the following range, preferably within the wavenumber range of 500 cm -1 More than 2000cm -1 In the range below, preferably in the range of 700 cm -1 More than 2000cm -1 If a peak due to the plasmon resonance of a CNT exists in the following range, the CNT can exhibit good dispersibility.

[0025] As shown in Figure 3, the spectrum obtained by Fourier transform infrared spectroscopy shows a relatively gentle peak due to the plasmon resonance of the CNT dispersion, as well as a peak at a wavenumber of 840 cm -1 Near 1300cm -1 and around 1700cm -1It can be seen that sharp peaks are observed around the wavelength of 840 cm. These sharp peaks do not correspond to "peaks based on plasmon resonance of the carbon nanotube dispersion," but each corresponds to infrared absorption due to functional groups. More specifically, -1 The sharp peak near 1300 cm is due to the CH out-of-plane bending vibration; -1 The sharp peak around 1700 cm is due to the epoxy three-membered ring stretching vibration; -1 The sharp peak around 2000 cm is due to the C=O stretching vibration. -1 In the region above 2000, a peak similar to the S1 peak is detected in addition to the plasmon resonance, as mentioned in the non-patent document by T. Morimoto et al., and therefore the inventors set the upper limit for determining the presence or absence of a peak based on the plasmon resonance of the CNT dispersion under condition (1) to 2000. -1 cm or less.

[0026] Here, in condition (1), when obtaining a spectrum by Fourier transform infrared spectroscopy, it is necessary to obtain a CNT dispersion by dispersing the CNT aggregate so that the bundle length is 10 μm or more. Here, for example, by blending CNT aggregates, water, and a surfactant (e.g., sodium dodecylbenzenesulfonate) in an appropriate ratio and stirring the mixture for a predetermined time using ultrasound or the like, a dispersion liquid in which CNT dispersions with bundle lengths of 10 μm or more are dispersed in water can be obtained.

[0027] The bundle length of a CNT dispersion can be obtained by analysis using a wet image analysis particle size analyzer. This analyzer can calculate the area of ​​each dispersion from an image obtained by photographing the CNT dispersion, and obtain the diameter of a circle having the calculated area (hereinafter, also referred to as the ISO area diameter). In this specification, the bundle length of each dispersion is defined as the ISO area diameter value obtained in this manner.

[0028] <<Condition (2)>> Condition (2) specifies that "the pore distribution curve measured for the carbon nanotube aggregate has a peak where the Log differential pore volume is maximum within the pore diameter range of more than 100 nm and less than 400 nm." Here, the pore distribution curve for the CNT aggregate can be created based on the BJH method from the adsorption isotherm of liquid nitrogen at 77 K, similar to the pore distribution curve for the carbon film described above. The fact that the peak in the pore distribution curve for the carbon nanotube aggregate is in the range of more than 100 nm and less than 400 nm means that there are voids of a certain size between the CNTs in the carbon nanotube aggregate, and the CNTs are not in an excessively densely aggregated state. The upper limit of 400 nm is the measurement limit of the measurement device (BELSORP-mini II) used in the examples.

[0029] Here, from the viewpoint of further improving the shielding performance of the carbon film while further increasing the dispersibility, the value of the Log differential pore volume at the maximum peak of the pore distribution curve of the CNT aggregate is set to 2.0 cm 3 / g or more is preferable.

[0030] <<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 -1 At least one of the following conditions exists in the range below." Whether or not this condition is satisfied can be determined as follows. First, the CNT aggregate to be determined is observed at a magnification (for example, 10,000 times) using an electron microscope (for example, a field emission scanning electron microscope), and multiple electron microscope images (for example, 10 images) are obtained in a field of view of 1 cm square. A fast Fourier transform (FFT) is performed on the multiple electron microscope images obtained, and a two-dimensional spatial frequency spectrum is obtained. The two-dimensional spatial frequency spectrum obtained for each of the multiple electron microscope images is binarized to find the average value of the peak positions that appear on the highest frequency side. If the average value of the obtained peak positions is less than 1 μm -1 More than 100μm -1If the value is within the range below, it is determined that the condition (3) is satisfied. Here, the "peak" used in the above determination is a clear peak obtained by performing the isolated point extraction process (i.e., the reverse operation of the isolated point removal). Therefore, when the isolated point extraction process is performed, -1 More than 100μm -1 If no clear peak is obtained within the range below, it is determined that condition (3) is not satisfied.

[0031] Here, from the viewpoint of further improving the shielding performance of the carbon film while further increasing the dispersibility, the peak of the two-dimensional spatial frequency spectrum is set to 2.6 μm -1 More than 100μm -1 It is preferred that it is in the following range:

[0032] From the viewpoint of further improving the shielding performance of the carbon film while further enhancing dispersibility, it is preferable that the CNT aggregate satisfy at least two of the above conditions (1) to (3), and it is more preferable that it satisfy all of the conditions (1) to (3).

[0033] <<Other properties>> In addition to the above conditions (1) to (3), the CNT aggregate that can be used to form the carbon film of the present invention preferably has the following properties.

[0034] For example, the CNT aggregate preferably has a total specific surface area according to the BET method of 600 m 2 / g or more, more preferably 800m 2 / g or more, preferably 2600m 2 / g or less, more preferably 1400m 2 / g or less. Furthermore, in the case of the opening treatment, 2 / g or more is preferable. In a CNT aggregate with a high specific surface area, there are gaps between the CNTs that make up the aggregate, and the CNTs are not excessively bundled. Therefore, the individual CNTs are loosely bonded to each other, making them easy to disperse. The CNT aggregate is primarily single-walled CNTs, but may also contain double-walled CNTs and multi-walled CNTs to the extent that their functionality is not impaired. The total specific surface area of ​​CNTs measured by the BET method can be measured, for example, using a BET specific surface area measurement device in accordance with JIS Z8830.

[0035] 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. When the average height of the CNTs constituting the CNT aggregate is 10 μm or more, it prevents aggregation of adjacent CNT bundles and allows for easy dispersion. When the average height of the CNTs constituting the CNT aggregate is 10 μm or more, it facilitates the formation of a network between CNTs, making it suitable for use in applications requiring electrical conductivity or mechanical strength. When the average height of the CNTs constituting the CNT aggregate is 10 cm or less, it can be produced in a short time, suppressing the adhesion of carbon-based impurities and improving the specific surface area. When the average height of the CNTs constituting the CNT aggregate is 2 cm or less, it allows for easier dispersion. The average height of the CNTs can be determined by measuring the height of 100 randomly selected CNTs using a scanning electron microscope (SEM).

[0036] The tapped bulk density of the CNT aggregate is 0.001 g / cm 3 More than 0.2g / cm 3 CNT aggregates in this density range have excellent dispersibility because the bonds between CNTs are not excessively strong, and can be molded into various shapes. 3 If the tap bulk density of the CNT aggregate is less than 0.001 g / cm, the bonds between the CNTs will be weak, making it easier to disperse the CNT aggregate homogeneously when stirred in a solvent or the like. 3If this is the case, the integrity of the CNT aggregate will be improved and handling will be easier. Tapped bulk density is the apparent bulk density when powdered CNT aggregates are filled into a container and then tapped or vibrated to reduce the voids between the powder particles, resulting in a densely packed state.

[0037] Furthermore, the average outer diameter of the CNTs constituting the CNT aggregate is preferably 0.5 nm or more, more preferably 1.0 nm or more, and preferably 15.0 nm or less, more preferably 10.0 nm or less, 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 the CNTs can be reduced, allowing a high specific surface area to be maintained. If the average outer diameter of the CNTs is 15.0 nm or less, the proportion of multi-walled CNTs can be reduced, allowing a high specific surface area to 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 can be adjusted by changing the CNT manufacturing method and manufacturing conditions, or by combining multiple types of CNTs obtained by different manufacturing methods.

[0038] The G / D ratio of a CNT aggregate is preferably between 1 and 50. A CNT aggregate with a G / D ratio of less than 1 is thought to have low single-walled CNT crystallinity, a lot of contamination such as amorphous carbon, and a high content of multi-walled CNTs. Conversely, a CNT aggregate with a G / D ratio of more than 50 is highly linear, and the CNTs tend to form bundles with few gaps, which may reduce the specific surface area. The G / D ratio is an index commonly used to evaluate the quality of CNTs. The Raman spectrum of CNTs measured with a Raman spectrometer contains the G band (1600 cm -1 around 1350 cm -1A vibration mode called "vicinity" is observed. The G band is a vibration mode derived from the hexagonal lattice structure of graphite, which is the cylindrical surface of the CNT, and the D band is a vibration mode derived from amorphous regions. Therefore, the higher the peak intensity ratio (G / D ratio) of the G band and the D band, the higher the crystallinity (linearity) of the CNT can be evaluated.

[0039] To obtain a high specific surface area, it is desirable that the purity of the CNT aggregate be as high as possible. The purity referred to here is the carbon purity, which is a value indicating what percentage of the mass of the CNT aggregate is composed of carbon. There is no upper limit to the purity for obtaining a high specific surface area, but it is difficult to obtain a CNT aggregate with a purity of 99.9999 mass% or more in terms of production. If the purity is less than 95 mass%, it is difficult to obtain a specific surface area exceeding 1000 m 2 / g in the unopened state. Furthermore, if it contains metal impurities and the carbon purity is less than 95 mass%, the metal impurities react with oxygen etc. during the opening treatment and prevent the opening of the CNT, resulting in difficulty in expanding the specific surface area. From these points, the purity of the single-walled CNT is preferably 95 mass% or more. The purity of a predetermined CNT aggregate that satisfies at least any one of the above-mentioned conditions (1) to (3) can usually be 98 mass% or more, preferably 99.9 mass% or more, without performing a purification treatment. There are almost no impurities mixed in the CNT aggregate, and various inherent properties of the 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), etc.

[0040] <<Method for Producing CNT Aggregate>> The method for producing a 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 any one of the above-mentioned conditions (1) to (3), it is necessary that the conditions during the growth of the CNT aggregate satisfy all of the following (a) to (c). (a) The growth rate of the CNT aggregate is 5 μm / min or more. (b) The concentration of the catalyst activation material in the growth atmosphere of the CNT aggregate is 4% by volume or more. (c) During the growth of the CNT aggregate, an obstacle exists in the growth direction of the CNTs that make up the CNT aggregate.

[0041] Furthermore, a manufacturing method that satisfies all of the above conditions (a) to (c) can efficiently manufacture a CNT aggregate that satisfies at least one of the above conditions (1) to (3). Furthermore, such a manufacturing method is not particularly limited 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 adopted. Here, the fluidized bed method refers to a synthesis method in which CNTs are synthesized while fluidizing a granular support (hereinafter also referred to as a granular catalyst support) that supports a catalyst for synthesizing CNTs. Furthermore, the moving bed method and the fixed bed method refer to synthesis methods in which CNTs are synthesized without fluidizing a support (a granular support or a plate-like support) that supports a catalyst.

[0042] In one example, a manufacturing method that satisfies all of the above (a) to (c) includes a catalyst support formation step of forming a catalyst support, a CNT synthesis step of synthesizing CNTs using the catalyst support obtained in the catalyst support formation step, and a recovery step of recovering the CNTs synthesized in the CNT synthesis step. The catalyst support formation step can be performed according to a known wet or dry catalyst support method. The recovery step can be performed using a known separation and recovery device such as a classifier.

[0043] [CNT synthesis process] In the CNT synthesis process, all of the above conditions (a) to (c) are satisfied during CNT growth. Specifically, the condition (a) that "the growth rate of the carbon nanotube aggregate is 5 μm / min or more" can be satisfied by appropriately adjusting the concentration and temperature of the raw material gas serving as the carbon source in the CNT growth atmosphere. The raw material gas serving as the carbon source is not particularly limited, and hydrocarbon gases such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene, and acetylene; lower alcohol gases such as methanol and ethanol; and mixtures thereof can also be used. The raw material gas may also be diluted with an inert gas. To further enhance the dispersibility of the resulting CNT aggregate and the shielding performance of the carbon film, the growth rate of the CNT aggregate is preferably 10 μm / min or more. The temperature can be adjusted, for example, within a range of 400°C to 1100°C.

[0044] The raw material gas serving as the carbon source in the CNT growth atmosphere preferably contains ethylene. Heating ethylene within a specific temperature range (700°C to 900°C) promotes the decomposition reaction of ethylene, enabling rapid CNT growth when the decomposition gas comes into contact with the catalyst. However, if the pyrolysis time is too long, the ethylene decomposition reaction proceeds too quickly, causing catalyst deactivation and carbon impurities to adhere to the CNT aggregate. In the production of CNT aggregates of the present invention, a pyrolysis time of 0.5 seconds to 10 seconds is preferred for an ethylene concentration in the range of 0.1% to 40% by volume. If the pyrolysis time is less than 0.5 seconds, the ethylene pyrolysis is insufficient, making it difficult to rapidly grow a CNT aggregate with a high specific surface area. If the time is longer than 10 seconds, the ethylene decomposition proceeds too quickly, generating a large amount of carbon impurities, which can deactivate the catalyst and reduce the quality of the CNT aggregate. The pyrolysis time is calculated using the following formula: (Pyrolysis time) = (heating flow channel volume) / {(raw material gas flow rate) × (273.15 + T) / 273.15} Here, the heated flow channel volume is the volume of the flow channel heated to a predetermined temperature T°C through which the raw material gas passes before contacting the catalyst, and the raw material gas flow rate is the flow rate at 0°C and 1 atm.

[0045] Furthermore, by appropriately adjusting the supply rate of the catalytic activator supplied during CNT growth, the condition (b) that "the concentration of the catalytic activator 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 dispersibility of the resulting CNT aggregate while further improving the shielding performance of the carbon film, the concentration of the catalytic activator in the growth atmosphere of the CNT aggregate is preferably 5% by volume or more. Examples of catalytic activators include, but are not limited to, water, oxygen, ozone, acidic gases, nitrogen oxide, oxygen-containing compounds with low carbon numbers such as carbon monoxide and carbon dioxide; alcohols such as ethanol and methanol; ethers such as tetrahydrofuran; ketones such as acetone; aldehydes; esters; and mixtures thereof. Among these, carbon dioxide is preferred. Substances containing both carbon and oxygen, such as carbon monoxide and alcohols, may function as both a source gas and a catalytic activator. For example, carbon monoxide acts as a catalyst activator when combined with a more reactive raw material gas such as ethylene, and also acts as a raw material gas when combined with a catalyst activator such as water, which exhibits significant catalyst activation even in trace amounts.

[0046] Furthermore, by selecting a fluidized bed method in the CNT synthesis process or adjusting the spacing between catalyst carriers in a moving bed method or a fixed bed method, the condition (c) that "an obstacle exists in the growth direction of the carbon nanotubes that constitute the carbon nanotube aggregate during synthesis of the carbon nanotube aggregate" can be satisfied. Here, when synthesizing CNTs by the above-mentioned fluidized bed method, the CNT synthesis step may be carried out, for example, by supplying a raw material gas while supplying gas from below to fluidize the particulate catalyst support, or by supplying a raw material gas while continuously transporting the particulate catalyst support by screw rotation.

[0047] The catalyst carrier has a carrier and a catalyst supported on the surface of the carrier, and the carrier is a part that forms a matrix structure for supporting the catalyst on the surface of the carrier by adhering, fixing, forming a film, or forming. The carrier structure may consist of the carrier alone, or may be a carrier with an optional underlayer provided on the surface of the carrier for favorably supporting the catalyst. The carrier is preferably in the form of particles, and the particle diameter is preferably 1 mm or less, more preferably 0.7 mm or less, even more preferably 0.4 mm or less, and preferably 0.05 mm or more, in terms of volume average particle diameter. If the particle diameter is less than the above upper limit, the growing CNT bundles will be thinner, which is advantageous for forming a wave-like structure. The particle density is 3.8 g / cm in apparent density. 3 It is preferable that the concentration is 5.8 g / cm or more. 3 More preferably, it is 8 g / cm or more. 3 It is preferable that the particle density is equal to or less than the above lower limit. If the particle density is equal to or greater than the above lower limit, the force applied to the growing CNT bundles increases, which is advantageous for forming a wave-like structure. The support material is preferably a metal oxide containing at least one of Al and Zr. Among these, zirconia beads containing a large amount of Zr are particularly preferable. Here, when a particulate carrier is used, a method for supporting a catalyst on the surface of the particulate carrier can be, for example, a method using a rotary drum coating device equipped with a substantially cylindrical rotary drum. When a base layer is formed on the surface of the particulate carrier and then the catalyst is supported, a solution containing components that can form the base layer is sprayed onto the surface of the particulate carrier and dried prior to spraying and drying the catalyst solution. This method allows the catalyst layer and base layer to be formed relatively easily and evenly.

[0048] In the CNT synthesis process, prior to the "growth process" performed so as to satisfy the above conditions (a) to (c), a "formation process" is performed to reduce the catalyst supported on the catalyst supporter. After the growth process is completed, a "cooling process" can be performed to cool the catalyst supporter on which the CNTs have grown. In the "formation process," for example, the atmosphere containing the catalyst supporter is a reducing gas atmosphere, and at least one of the reducing gas atmosphere or the catalyst supporter is heated to reduce and microparticulate the catalyst supported on the catalyst supporter. The temperature of the catalyst supporter or the reducing gas atmosphere in the formation process is preferably 400°C or higher and 1100°C or lower. The formation process can be performed for 3 minutes or longer and 120 minutes or shorter. Examples of the reducing gas include hydrogen gas, ammonia gas, water vapor, and mixtures thereof. The reducing gas may also be a mixture of these gases with an inert gas such as helium gas, argon gas, or nitrogen gas. On the other hand, in the "cooling step," the catalyst support on which CNTs have been grown is cooled in an inert gas environment. Here, the inert gas may be the same as the inert gas that can be used in the growth step. In addition, in the cooling step, the temperature of the catalyst support on which CNTs have been grown is lowered preferably to 400°C or less, more preferably to 200°C or less.

[0049] <Dry grinding process> When obtaining the carbon film of the present invention, the CNT aggregate before film formation can be subjected to a dry pulverization treatment, if necessary. In the present invention, the term "dry grinding treatment" refers to grinding treatment in a state where the material to be ground does not substantially contain a solvent (for example, a state where the solid content concentration is 95% or more).

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

[0051] <Membrane formation> The carbon film of the present invention can be obtained by forming the CNT aggregate that has been subjected to the above-mentioned dry pulverization treatment into a film as needed. Here, the method for forming a film from the 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, 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, which have been subjected to the above-mentioned dry pulverization treatment as necessary, in a dispersion medium using a known method. Methods for removing the dispersion medium from the CNT dispersion include known methods such as filtration and drying. The filtration method is not particularly limited, and known filtration methods such as natural filtration, reduced pressure filtration (suction filtration), pressure filtration, and centrifugal filtration can be used. As the drying method, known drying methods such as hot air drying, vacuum drying, heat roll drying, infrared irradiation, etc. can be used. The drying temperature is not particularly limited, but is usually room temperature to 200°C, and the drying time is not particularly limited, but is usually 1 hour or more and 48 hours or less. In addition, drying can be carried out on a known substrate, but is not particularly limited.

[0053] Among these, it is preferable to employ at least drying for removing the dispersion medium. The filtration and drying may be combined. For example, the carbon membrane of the present invention can be obtained by further drying a membrane-like residue (primary sheet) obtained by filtering the CNT dispersion.

[0054] (Characteristics of carbon film) Here, the thickness of the carbon membrane of the present invention is preferably 5 μm or more, preferably 150 μm or less, and more preferably 100 μm or less. If the thickness is 5 μm or more, the carbon membrane can have sufficient mechanical strength and can exhibit even better shielding performance. On the other hand, if the thickness is 150 μm or less, the carbon membrane can be made lighter. The "thickness" of the carbon film can be measured using the method described in the Examples. The carbon membrane of the present invention is preferably a self-supporting membrane. Self-supporting carbon membranes have excellent handleability and can increase the degree of freedom in the placement of the sheet when used, for example, as an electromagnetic wave shielding sheet. [Example]

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

[0056] <Fourier transform infrared spectroscopy (FT-IR)> To 10 mg of CNT aggregates (CNT aggregates of Example 1, SGCNTs), 100 g of water containing sodium dodecylbenzenesulfonate as a surfactant at a concentration of 1 mass % was added, and the mixture was stirred at 45 Hz for 1 minute using an ultrasonic bath, thereby obtaining 100 ml of a dispersion liquid of each CNT aggregate. Each dispersion liquid prepared as described above was diluted two-fold using a solvent of the same composition, dropped onto a silicon substrate, and dried. Then, the plasmon effective length was measured using a Fourier transform infrared spectrophotometer based on the plasmon far-infrared (FIR) resonance peak. The plasmon effective length is shown in Table 1. The FIR spectrum obtained is shown in an FIR resonance chart in FIG. 3. The curves shown in FIG. 3 are, from top to bottom, for the CNT aggregate and SGCNT used in Example 1. As shown in the figure, the curve corresponding to the CNT aggregate used in Example 1 has a peak at 300 cm -1There was a peak in the optical density that exceeded it. On the other hand, the peak of the optical density in the curve corresponding to SGCNT was 214 cm -1 It was. The plasmon peak top position was obtained from an approximate curve by polynomial fitting using drawing software.

[0057] <Measurement of CNT bundle length> For each dispersion prepared by FT-IR measurement, using a flow-type particle image analyzer (manufactured by Jasco International Co., Ltd., circulating image analysis particle size distribution meter "CF-3000"), the ISO circle diameter average value of the CNT dispersion present in the dispersion was measured, and the obtained value was taken as the CNT bundle length. The analysis conditions were as follows. <Analysis conditions> · Injection volume: 50 ml (sampling volume 1.2%) · Flow cell spacer: 1000 μm · Front lens magnification: 2 times · Telecentric lens magnification 0.75 times · Length per pixel: 2.3 μm / pixel For each dispersion, measurements were performed 4 times under the same conditions while circulating, and the arithmetic mean value thereof was obtained.

[0058] <Creation of pore size distribution curve (CNT aggregate)> For 10 mg or more of the CNT aggregate (the CNT aggregate of Example 1, SGCNT), the adsorption / desorption isotherm was measured at 77 K using liquid nitrogen with BELSORP-miniII (manufactured by MicrotracBEL) (the adsorption equilibrium time was set to 500 seconds). As a pretreatment, vacuum degassing was performed at 100 °C for 12 hours. From the adsorption amount of this adsorption isotherm, the pore size distribution curve of each sample was obtained by the BJH method. The results are shown in Fig. 4. As shown in Fig. 4, for the CNT aggregate used in Example 1, a peak with the maximum differential pore volume was confirmed in the region where the pore diameter was 100 nm or more, while for SGCNT, a peak with the maximum was confirmed in the region where the pore diameter was less than 100 nm. In addition, when creating the pore size 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. <Creation of pore size distribution curve (carbon film)> Test pieces weighing 10 mg or more were cut from the carbon membranes of Examples 1 and 2 and Comparative Example 1, and adsorption / desorption isotherms were measured using a BELSORP-mini II (manufactured by Microtrack Bell) at 77 K with liquid nitrogen (the adsorption equilibrium time was 500 seconds). As a pretreatment, the membranes were vacuum degassed at 100°C for 12 hours. A pore size distribution curve for each sample was obtained using the BJH method from the adsorption amount in the adsorption isotherm. The results are shown in Figure 1. As shown in Figure 1, Examples 1 and 2 showed the largest peak in differential pore volume in the pore size range of 10 nm to 100 nm, while Comparative Example 1 showed the largest peak in the range of less than 10 nm. In preparing the pore distribution curve of the carbon membrane, the measurement range of the pore diameter was set to 1 nm or more and less than 400 nm.

[0059] (Two-dimensional spatial frequency spectrum analysis of electron microscope images) A sample of 0.01 mg of CNT aggregate (CNT aggregate of Example 1, SGCNT) was prepared by placing it on carbon tape and blowing it with a blower to remove excess CNT. The sample was observed at 10,000x magnification using a field emission scanning electron microscope, and ten photographs were taken of a randomly selected 1 cm square field of view. Each of the ten electron microscope images was subjected to fast Fourier transform processing to obtain a two-dimensional spatial frequency spectrum. Each of the obtained two-dimensional spatial frequency spectra was subjected to binarization processing to determine the outermost (high-frequency) peak position and obtain an average value. Note that in the binarization processing, values ​​greater than 0.75 obtained through fast Fourier transform processing were assigned a value of 1, and other values ​​were assigned a value of zero. Figure 5A shows one of the ten images obtained in Example 1, and Figure 5B shows the two-dimensional spatial frequency spectrum obtained for that image. In Figure 5B, components closer to the center represent low-frequency components, and components located further out from the center correspond to higher-frequency components. In the figure, the arrow indicates 1 to 100 μm -1 Among the clear peaks detected in the region, the peak position with the highest wavenumber (3 μm -1) is shown. Similarly, FIG. 6A is one of the electron microscope images obtained for SGCNT, and FIG. 6B is the two-dimensional spatial frequency spectrum obtained for such an image. For all the images obtained with SGCNT, including the data shown in FIGS. 6A and 6B, an outlier extraction process was performed and an attempt was made to detect distinct peaks, but no distinct peaks were detected in the region of 1 to 100 μm -1 No distinct peaks were detected in the region of. Therefore, it was confirmed that SGCNT does not satisfy the above-described condition (3).

[0060] <Thickness> The thickness of the carbon film was measured using a "Digital Micrometer for External Measurement" manufactured by Mitutoyo Corporation.

[0061] <Shielding Performance> For the carbon film, the reflection coefficient S11 and the transmission coefficient S21 were measured by the microstrip line method conforming to IEC-62333-2, and the transmission attenuation rate Rtp was calculated. The measuring instruments and measuring frequencies used are as follows. Network Analyzer: "Vector Network Analyzer 37 169A" manufactured by Anritsu Corporation Measuring Instrument: "TF-3B" manufactured by Keycom Corporation (0.1 to 3 GHz), "TF-18C" manufactured by Keycom Corporation (2.0 GHz to 18 GHz) Then, the transmission attenuation rate Rtp at measuring frequencies of 2.5 GHz, 4.5 GHz, and 7.5 GHz was evaluated according to the following criteria. Note that the larger the transmission attenuation rate at a certain frequency, the better the shielding performance of the carbon film at that frequency. A: The transmission attenuation rate is 20 dB or more. B: The transmission attenuation rate is less than 20 dB.

[0062] (Example 1) <Preparation of CNT Aggregate> In this embodiment, CNTs were synthesized by adopting the fluidized bed method in the CNT synthesis process. The schematic configuration of the used CNT manufacturing apparatus is shown in FIG. 7. The CNT manufacturing apparatus 100 shown in FIG. 7 is composed of a heater 101, a reaction tube 102, a dispersion plate 103, a reduction gas / raw material gas inlet 104, an exhaust port 105, and a gas heating promotion unit 106. The materials of the reaction tube 102 and the dispersion plate 103 were synthetic quartz. [<Catalyst carrier formation process>] The catalyst carrier formation process will be described below. Zirconia (zirconium dioxide) beads (ZrO2, volume average particle diameter D50: 350 μm) as the carrier were put into a rotary drum type coating apparatus, and while stirring the zirconia beads (20 rpm), an aluminum-containing solution was spray-sprayed (spraying amount 3 g / min, spraying time 940 seconds, spray air pressure 10 MPa) with a spray gun, and while supplying compressed air (300 L / min) into the rotary drum, it was dried to form an aluminum-containing coating film on the zirconia beads. Next, a calcination treatment was performed at 480 °C for 45 minutes to produce primary catalyst particles on which an aluminum oxide layer was formed. Further, the primary catalyst particles were put into another rotary drum type coating apparatus and stirred (20 rpm), and while spray-spraying an iron catalyst solution with a spray gun (spraying amount 2 g / min, spraying time 480 seconds, spray air pressure 5 MPa), and while supplying compressed air (300 L / min) into the rotary drum, it was dried to form an iron-containing coating film on the primary catalyst particles. Next, a calcination treatment was performed at 220 °C for 20 minutes to produce a catalyst carrier on which an iron oxide layer was further formed. [<CNT synthesis process>] 300 g of the catalyst carrier thus produced was put into the reaction tube 102 of the CNT manufacturing apparatus 100, and while fluidizing the catalyst carrier 107 by flowing gas, the processes were carried out in the order of the formation process, the growth process, and the cooling process to manufacture a CNT aggregate. The conditions of each process included in the CNT synthesis process were set as follows. [Formation process] ·Set temperature: 800 °C ·Reduction gas: Nitrogen 3 sLm, hydrogen 22 sLm ·Treatment time: 25 minutes [Growth process] ·Set temperature: 800 °C ·Raw material gas: Nitrogen 15 sLm, ethylene 5 sLm, carbon dioxide 2 sLm, hydrogen 3 sLm ·Treatment time: 10 minutes ·Raw material gas pyrolysis time: 0.65 seconds [Cooling process] ·Cooling temperature: Room temperature ·Purge gas: Nitrogen 25 sLm

[0063] The CNT aggregate synthesized on the catalyst support was separated and recovered 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 properties of the CNT aggregate produced by this example were 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, carbon purity 99%.

[0064] [Production of carbon film] 1000 g of water was added to 1 g of the CNT aggregate obtained as described above, and the mixture was stirred at a rotation speed of 3000 rpm for 5 minutes using an ultra-high-speed emulsification and dispersion device (product name "Lab Revolution (registered trademark)", manufactured by Shinky Co., Ltd.) to obtain a CNT dispersion liquid. The obtained CNT dispersion liquid was applied onto a substrate. The coating film on the substrate was vacuum dried at a temperature of 80 °C for 24 hours to form a carbon film on the substrate. Then, the carbon film was peeled off from the substrate to obtain a carbon film (self-supporting film) with a thickness of 100 μm. The shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0065] (Example 2) [Preparation of CNT aggregate] SGCNT (product name "SG101", manufactured by Nippon Zeon Co., Ltd.) was prepared as the CNT aggregate. [Dry grinding treatment] The SGCNTs were subjected to a dry pulverization process using a mixer equipped with rotating blades (product name "Magic Bread", model number MGTXH-AM, manufactured by Shop Japan Co., Ltd.) at a rotation speed of 1000 rpm for 6 minutes. <Manufacturing carbon films> A carbon film (freestanding film) having a thickness of 100 μm was obtained in the same manner as in Example 1, except that the SGCNTs after the above-mentioned dry pulverization treatment were used. The shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0066] (Comparative Example 1) A carbon film (freestanding film) having a thickness of 100 μm was obtained in the same manner as in Example 2, except that the dry pulverization treatment was not performed. The shielding performance of the obtained carbon film was evaluated. The results are shown in Table 1.

[0067] [Table 1]

[0068] From Table 1, it can be seen that the peak where the Log differential pore volume is maximum is in the pore diameter range of 10 nm to 100 nm, and the value of the Log differential pore volume at this peak is 1.2 cm 3 It can be seen that the carbon films of Examples 1 and 2, which have a shielding coefficient of 1 / g or more, can exhibit excellent shielding performance over a wide frequency range. [Industrial Applicability]

[0069] According to the present invention, it is possible to provide a carbon film that has excellent electromagnetic wave shielding properties. [Explanation of symbols]

[0070] 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 promotion section 107 Catalyst support

Claims

1. A carbon film made of an aggregate of carbon nanotubes, The pore size distribution curve showing the relationship between pore size and log differential pore volume, obtained from the liquid nitrogen adsorption isotherm at 77 K based on the Barrett-Joyner-Halenda method, is: The log differential pore volume has a maximum peak within a pore diameter range of 24 nm to 28 nm, A carbon membrane in which the value of the log differential pore volume at the peak is 2.3 cm 3 / g or more and 3.5 cm 3 / g or less.

2. The carbon membrane of claim 1 which is a free-standing membrane.

3. The carbon membrane according to claim 1 or 2, which has a thickness of 5 μm or more and 150 μm or less.

4. The carbon film according to any one of claims 1 to 3, which is an electromagnetic wave shielding sheet.

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