Electromagnetic wave absorbing member for sub-terahertz band of 100 GHz or more

Abstract

This electromagnetic wave absorbing member for a sub-terahertz band is characterized by comprising a polymer material and carbon nanotubes, the carbon nanotubes including single-walled carbon nanotubes as a main component, the electrical conductivity of the electromagnetic wave absorbing member being 0.1 (S / cm) to 2.0 (S / cm), and the attenuation rate at a frequency of 300 (GHz) being 5 (dB) or more.

Description

Technical Field

[0001] This invention relates to an electromagnetic wave absorbing component for the Asia-Pacific Hertz band above 100 GHz. Background Technology

[0002] Previously, composite materials containing conductive materials such as carbon nanotubes (CNTs) in insulating materials like resins were known to be used as electromagnetic wave absorbing materials in electrical and communications fields. In these fields, the operating frequency varies depending on the application, but often, electromagnetic waves in frequencies outside the desired range are generated as noise in actual operating environments. Therefore, there is a need for an electromagnetic wave absorbing material that can attenuate electromagnetic waves of the desired frequency without attenuating them, while attenuating electromagnetic waves of the unwanted frequency.

[0003] For example, Patent Document 1 discloses an electromagnetic wave absorbing sheet comprising a sheet-like fibrous substrate and a single-walled CNT located within the sheet-like substrate, and having an electrical conductivity of 0.7 to 20 (S / cm). The document discloses that the electromagnetic wave absorbing sheet has a transmission attenuation rate of 20 dB or more in at least a portion of the range between 1 GHz and 10 GHz.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent document 1: International Publication No. 2020 / 067203. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In recent years, there has been a need for electromagnetic wave absorption performance in the 6 GHz band (Asia Pacific Hertz band above 100 GHz). However, including the aforementioned Patent Document 1, to date, there has been insufficient research on CNT-containing electromagnetic wave absorbing sheets capable of performing electromagnetic wave absorption in the Asia Pacific Hertz band.

[0009] The purpose of this invention is to provide an electromagnetic wave absorbing component with excellent electromagnetic wave absorption performance in the Asia-Pacific Hertz band above 100 GHz.

[0010] Solution for solving the problem

[0011] To address the aforementioned problems, the inventors conducted in-depth research. They then discovered that by including single-walled carbon nanotubes as the main component in an electromagnetic wave absorbing component comprising polymer materials and carbon nanotubes, and by ensuring the conductivity of the electromagnetic wave absorbing component is within a specified range, the attenuation rate in the Asia-Pacific Hertz band above 100 GHz can be improved, thus completing this invention.

[0012] That is, the object of the present invention is to advantageously solve the above-mentioned problems, and the electromagnetic wave absorbing component for the Asia-Pacific Hertz band of the present invention is as follows.

[0013] [1] An electromagnetic wave absorbing component is characterized in that it comprises a polymer material and carbon nanotubes, wherein the carbon nanotubes comprise single-walled carbon nanotubes as the main component, the electromagnetic wave absorbing component has an electrical conductivity of 0.1 (S / cm) or more and 2.0 (S / cm) or less, and an attenuation rate of 5 (dB) or more at a frequency of 300 (GHz). By using single-walled carbon nanotubes as the main component and ensuring the electrical conductivity is within the above range, electromagnetic wave absorption performance can be achieved in the Asia-Pacific Hertz frequency band above 100 GHz.

[0014] In addition, conductivity and attenuation rate can be measured using the methods described in the examples.

[0015] [2] Preferably, in the electromagnetic wave absorbing component of [1] above, the amount of carbon nanotubes attached is A (mg), the conductivity of the carbon nanotubes is C (S / cm), and the index I obtained according to the following formula (1) is 40 or more and 500 or less.

[0016]

[0017] If the aforementioned index I is within the above range, the electromagnetic wave absorption performance in the Asia-Pacific Hertz band is even better. Furthermore, in this specification, "the electrical conductivity of carbon nanotubes" refers to the electrical conductivity measured using Buck paper formed with a specified amount of CNTs, as described in the examples.

[0018] [3] Preferably, in the electromagnetic wave absorbing member of [1] or [2] above, the electromagnetic wave absorbing member is formed as a single-layer sheet. By making the electromagnetic wave absorbing member a single-layer sheet, the electromagnetic wave absorbing member can be made thinner and lighter.

[0019] [4] Preferably, in the electromagnetic wave absorbing components described in [1] to [3] above, the thickness of the electromagnetic wave absorbing component is 300 (μm) or less. If the thickness of the electromagnetic wave absorbing component is below the above upper limit, it can be suitable for use in mobile terminals such as smartphones and tablets, automobiles, base stations, medical devices, and various applications requiring space saving.

[0020] In addition, the thickness of the electromagnetic wave absorbing component can be measured using the method described in the embodiments.

[0021] [5] Preferably, in the electromagnetic wave absorbing components described in [1] to [3] above, the electromagnetic wave absorbing component is configured to include: a polymer sheet containing the polymer material, and the carbon nanotubes attached to the polymer sheet. By attaching the carbon nanotubes to the polymer sheet, the conductivity can be suppressed and the electromagnetic wave absorption performance can be improved.

[0022] [6] Preferably, in the electromagnetic wave absorbing components of [1] to [3] above, the electromagnetic wave absorbing component is a sheet formed of a composition comprising the above-mentioned polymer material and the above-mentioned carbon nanotubes.

[0023] [7] Preferably, in the electromagnetic wave absorbing component of [5] above, the polymer sheet is a nonwoven fabric made of polymer fibers composed of the aforementioned polymer material. By using a nonwoven fabric made of polymer fibers composed of polymer materials, conductivity can be suppressed and electromagnetic wave absorption performance can be improved.

[0024] [8] Preferably, in the electromagnetic wave absorbing components described in [1] to [7] above, the G / D ratio of the carbon nanotubes is 4.0 or less. If the G / D ratio of the carbon nanotubes is below the above upper limit, the conductivity can be easily controlled.

[0025] In addition, the G / D ratio refers to the ratio of the intensity of the G band peak to the intensity of the D band peak in the Raman spectrum. The G / D ratio of carbon nanotubes can be determined by the method described in the examples.

[0026] [9] Preferably, in the electromagnetic wave absorbing components of [1] to [8] above, the BET specific surface area of ​​the carbon nanotube is 600 (m² / g) or higher. If the BET specific surface area of ​​the carbon nanotube is above the lower limit above, the electromagnetic wave absorption performance in the Asia-Pacific Hertz band is even better.

[0027] Additionally, in this specification, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET (Brunauer-Emmett-Teller) method.

[0028]

[10] Preferably, in the electromagnetic wave absorbing components of [1] to [9] above, the effective length of the carbon nanotube is 40 (nm) or more and 1000 (nm) or less. If the effective length of the carbon nanotube is within the above range, the balance between film-forming properties and the electromagnetic wave absorption capacity of the electromagnetic wave absorbing material in the high-frequency region can be further improved.

[0029] In addition, the effective length of the carbon nanotubes can be determined using the method described in the examples.

[0030]

[11] Preferably, among the electromagnetic wave absorbing components described in [1] to

[10] above, the attenuation rate of the electromagnetic wave absorbing component in the frequency band of 200 (GHz) and above and 300 (GHz) and below is 5 (dB) or above. If the attenuation rate in the above frequency band is 5 (dB) or above, the electromagnetic wave absorption performance in the Asia-Pacific Hertz band is even better.

[0031] Invention Effects

[0032] According to the present invention, an electromagnetic wave absorbing component with excellent electromagnetic wave absorption performance in the Asia-Pacific Hertz band above 100 GHz can be provided. Detailed Implementation

[0033] The embodiments of the present invention will now be described in detail.

[0034] (Electromagnetic wave absorbing component)

[0035] The electromagnetic wave absorbing component of the present invention is characterized by comprising a polymer material and carbon nanotubes, wherein the carbon nanotubes include single-walled carbon nanotubes as the main component, the conductivity of the electromagnetic wave absorbing component is 0.1 (S / cm) or higher and 2.0 (S / cm) or lower, and the attenuation rate at a frequency of 300 (GHz) is 5 (dB) or higher. The electromagnetic wave absorbing component of the present invention may arbitrarily contain other components such as additives used in the manufacture of the electromagnetic wave absorbing component. Furthermore, the electromagnetic wave absorbing component of the present invention can exhibit excellent electromagnetic wave absorption performance in the Asia-Pacific Hertz frequency band above 100 GHz.

[0036] While the exact reason is unclear, it is hypothesized as follows: if the conductivity is too high, electromagnetic waves will not be absorbed by the component but will be reflected. Therefore, by combining polymer materials and carbon nanotubes, the conductivity can be moderately suppressed, so that the component does not reflect electromagnetic waves but has high absorption performance. Based on the above hypothetical mechanism, it can be considered that electromagnetic wave absorbing components that meet the above-mentioned specified properties can exhibit excellent electromagnetic wave absorption performance in the Asia-Pacific Hertz band.

[0037] Furthermore, the upper limit frequency of the "Asia-Pacific Hertz band," which is the target of the electromagnetic wave absorbing member of the present invention, is generally 1 THz. Moreover, in the embodiments of this specification, when the electromagnetic wave attenuation rate measured in the Asia-Pacific Hertz band, i.e., the range of 100 GHz and above to 1 THz, particularly in the band of 200 GHz and above to 300 GHz, is 5 dB or more, the electromagnetic wave absorbing member is determined to have excellent electromagnetic wave absorption performance in the Asia-Pacific Hertz band.

[0038] Composition of Electromagnetic Wave Absorbing Components

[0039] <<Polymer Materials>>

[0040] As a polymer material, there are no particular limitations; known resins and insulating fillers appropriate for the application of electromagnetic wave absorbing materials can be used. Specifically, insulating materials in which insulating fillers are arbitrarily mixed with resin can be used. Furthermore, in this invention, "resin" includes rubber and elastomers. Additionally, organic fibers can be suitable as polymer materials.

[0041] [Resin]

[0042] Examples of resins include: natural rubber including epoxidized natural rubber; diene-based synthetic rubbers (butadiene rubber, epoxidized butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene vinyl acetate rubber, chloroprene rubber, vinyl pyridine rubber, butyl rubber, chlorobutyl rubber, polyisoprene rubber), ethylene propylene rubber (EPR, EPDM), acrylic rubber, silicone rubber, epichlorohydrin rubber (CO, ECO), polyurethane rubber, polysulfide rubber, fluororubber, fluororesins, urea resins, melamine resins, phenolic resins, cellulose acetate, nitrocellulose, cellulose acetate butyrate, and other cellulose-based resins; casein plastics; soybean protein plastics; epoxy resins including benzoguanamine resins; bisphenol A type epoxy resins, phenolic varnish type epoxy resins, multifunctional epoxy resins, and alicyclic epoxy resins. Esters; diallyl phthalate resins; alkyd resins; polyvinyl chloride resins, polyethylene resins; polypropylene resins; ABS (acrylonitrile butadiene styrene) resins, AS (acrylonitrile styrene) resins, polystyrene and other styrene-based resins; acrylic resins; methacrylic resins; vinyl acetate and other organic acid vinyl ester resins; vinyl ether resins; halogenated resins; polycyclic olefin resins; olefin resins; alicyclic olefin resins; polycarbonate resins; polyester resins including unsaturated polyester resins; polyamide resins; thermoplastic and thermosetting polyurethane resins; polysulfone resins; polyphenylene ether resins including modified polyphenylene ether resins; silicone resins; polyacetal resins; polyimide resins; polyethylene terephthalate resins; polybutylene terephthalate resins; polyaryl ester resins; polyphenylene sulfide resins; polyetheretherketone resins, etc. These can be used individually or in combination of two or more.

[0043] [Insulating filler]

[0044] Furthermore, there are no particular limitations on the insulating filler; any known inorganic or organic filler with insulating properties can be used. Examples of such insulating fillers include: silica, talc, clay, titanium dioxide, nylon fiber, vinylon fiber, acrylic fiber, and rayon fiber. These can be used alone or in combination.

[0045] [Organic Fiber]

[0046] As for organic fibers, there are no particular limitations. Examples include: synthetic fibers composed of polymers such as polyvinyl alcohol, vinylon, polyethylene glycol, polyvinylpyrrolidone, polycaprolactone, polyacrylonitrile, polylactic acid, polycarbonate, polyamide, polyimide, polyethylene, polypropylene, polyethylene terephthalate, and their modifiers; natural fibers such as cotton, linen, wool, and silk; etc. One or more polymers can be used alone or in combination as the polymers forming the synthetic fibers.

[0047] In addition, carbon nanotubes are not included in the aforementioned organic fibers.

[0048] <<Carbon Nanotubes>>

[0049] The carbon nanotubes (hereinafter, sometimes referred to as CNTs) contained in the electromagnetic wave absorbing member of the present invention contain single-walled carbon nanotubes (single-walled CNTs) as the main component. Multi-walled carbon nanotubes (multi-walled CNTs) can be included as a component other than single-walled CNTs in the CNTs. Here, the proportion of single-walled CNTs to the total mass of the CNTs needs to be more than 50% by mass, preferably 90% by mass or more, more preferably 95% by mass or more, and may also be 100% by mass. Furthermore, when the CNTs contain multi-walled CNTs, the number of multi-walled CNT layers is preferably 5 or less.

[0050] The preferred properties of CNTs are described below, and these properties are preferably applicable to both CNTs used as materials in manufacturing the electromagnetic wave absorbing component of the present invention and CNTs contained in the electromagnetic wave absorbing component of the present invention.

[0051] [BET specific surface area]

[0052] Furthermore, the BET specific surface area of ​​the CNT is preferably 600 m² / g or more, more preferably 800 m² / g or more, even more preferably 1000 m² / g or more, and preferably 2000 m² / g or less, more preferably 1800 m² / g or less, and even more preferably 1600 m² / g or less. If the BET specific surface area is within the above range, the electromagnetic wave absorbing component can exhibit superior electromagnetic wave absorption performance in the Asia-Pacific Hertz band. In addition, in this invention, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET (Brunauer-Emmett-Teller) method.

[0053] [G / D ratio]

[0054] The G / D ratio of CNTs is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and preferably 0.8 or more, more preferably 1.0 or more. If the G / D ratio is below the above upper limit, conductivity is easier to control, and electromagnetic wave absorption performance is more excellent.

[0055] [Effective Length]

[0056] The effective length of CNTs is preferably 40 nm or more, more preferably 50 nm or more, and more preferably 1000 nm or less, more preferably 300 nm or less. If the effective length is within the above range, the balance between film-forming properties and the electromagnetic wave absorption capacity of the electromagnetic wave absorbing material in the high-frequency region can be further improved.

[0057] Furthermore, in this invention, the effective length of a CNT refers to the distance between adjacent curved sections, since the CNT is not perfectly straight and sometimes has multiple curved sections (bends) in the middle of its length.

[0058] [Average Diameter and Average Length]

[0059] The average diameter of CNTs is preferably 1 nm or more, and more preferably 60 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less.

[0060] In addition, the average length of CNT is preferably 10 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, particularly preferably 200 μm or more, and preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 450 μm or less.

[0061] When CNTs with an average diameter and / or average length within the above range are used to prepare a dispersion, the CNTs are uniformly present in the dispersion, resulting in a homogeneous electromagnetic wave absorbing component with superior electromagnetic wave absorption performance in the Asia-Pacific Hertz band above 100 GHz.

[0062] [purity]

[0063] The purity of CNTs is preferably 98% by mass or higher, more preferably 99% by mass or higher. Such CNT aggregates contain almost no impurities and can fully exhibit the original properties of CNTs. Furthermore, while there is no particular upper limit to the purity of CNTs, it is difficult to obtain CNT aggregates with a purity of 99.9999% by mass or higher in manufacturing. Additionally, the purity of CNTs can be obtained using elemental analysis with X-ray fluorescence or thermogravimetric analysis (TGA).

[0064] Aspect Ratio

[0065] Furthermore, CNTs typically have an aspect ratio (length / diameter) greater than 10.

[0066] In addition, the average diameter, average length, and aspect ratio of CNTs can be determined by measuring the diameter and length of 100 randomly selected CNTs using a scanning electron microscope or a transmission electron microscope.

[0067] In addition, CNTs preferably exhibit an upwardly convex shape in the t-plot obtained from the adsorption isotherm.

[0068] Here, in a material with fine pores on its surface, the growth of the nitrogen adsorption layer is divided into the following processes (1) to (3). Furthermore, through the following processes (1) to (3), the slope of the t-curve changes.

[0069] (1) The process of forming a monolayer of nitrogen molecules on the entire surface

[0070] (2) Formation of a multimolecular adsorption layer and the accompanying capillary condensation filling process within its pores

[0071] (3) The process of forming a multimolecular adsorption layer on the apparent nonporous surface after the micropores are filled with nitrogen.

[0072] Furthermore, in the convex t-curve, in the region where the average thickness t of the nitrogen adsorption layer is small, the curve lies on a straight line passing through the origin, while as t increases, the curve shifts downwards from that straight line. Regarding CNTs with this t-curve shape, the large ratio of internal specific surface area to the total specific surface area of ​​the CNT indicates that the CNT forms multiple openings. As a result, when using this CNT to prepare a dispersion, the CNT is less likely to aggregate in the dispersion, leading to a homogeneous electromagnetic wave absorbing component with superior electromagnetic wave absorption performance in the Asia-Pacific Hertz band.

[0073] Furthermore, the inflection point of the t-curve of CNTs is preferably within the range of 0.2 ≤ t(nm) ≤ 1.5, more preferably within the range of 0.45 ≤ t(nm) ≤ 1.5, and even more preferably within the range of 0.55 ≤ t(nm) ≤ 1.0. CNTs with an inflection point within this range are less likely to aggregate in the dispersion when used to prepare the dispersion. As a result, electromagnetic wave absorbing components with more homogeneity and superior electromagnetic wave absorption performance in the Asia-Pacific Hertz band can be obtained.

[0074] Here, the "inflection point" is the intersection of the approximate straight line A of the aforementioned process (1) and the approximate straight line B of the aforementioned process (3).

[0075] Furthermore, the CNTs preferably have an internal specific surface area S2 to total specific surface area S1 ratio (S2 / S1) of 0.05 or higher and 0.30 or lower, as obtained from the t-curve. CNTs with S2 / S1 values ​​within this range are less prone to aggregation in dispersions. As a result, electromagnetic wave absorbing components with more homogeneity and superior electromagnetic wave absorption performance in the Asia-Pacific Hertz band can be obtained.

[0076] Here, the total specific surface area S1 and the internal specific surface area S2 of the CNT can be obtained from its t-curve. Specifically, firstly, the total specific surface area S1 can be obtained from the slope of the approximate straight line of process (1), and the external specific surface area S3 can be obtained from the slope of the approximate straight line of process (3). Then, the internal specific surface area S2 can be calculated by subtracting the external specific surface area S3 from the total specific surface area S1.

[0077] Furthermore, the determination of the adsorption isotherm of CNTs, the generation of t-curves, and the calculation of the total specific surface area S1 and internal specific surface area S2 based on the analysis of t-curves can be performed, for example, using the commercially available measuring device "BELSORP-mini" (manufactured by Bayer Corporation of Japan).

[0078] CNTs are not particularly limited and can be manufactured using known CNT synthesis methods such as arc discharge, laser ablation, and chemical vapor deposition (CVD). Specifically, for example, CNTs can be efficiently manufactured by supplying a raw material compound and a carrier gas to a substrate having a catalyst layer for carbon nanotube manufacturing on its surface, and then, during the synthesis of CNTs via chemical vapor deposition (CVD), introducing a trace amount of oxidant (catalyst activator) into the system, thereby significantly enhancing the catalyst activity of the catalyst layer (super-growth method; see International Publication No. 2006 / 011655). Hereinafter, carbon nanotubes obtained by the super-growth method are sometimes referred to as "SGCNTs".

[0079] Alternatively, the CNTs contained in the electromagnetic wave absorbing component may be CNTs from a collection of CNTs that satisfy at least one of the conditions (1) to (3) below (e.g., refer to International Publication No. 2022 / 114237).

[0080] (1) Fourier transform infrared spectroscopy analysis was performed on the carbon nanotube dispersion obtained by dispersing the carbon nanotube aggregates in a bundle length of 10 μm or more. In the obtained spectrum, the peak of the carbon nanotube dispersion based on plasmon resonance was found to be above 300 cm⁻¹. -1 And 2000cm -1 At least one of the following ranges exists.

[0081] (2) For carbon nanotube assemblies, the largest peak in the pore distribution curve, which is obtained from the adsorption isotherm of liquid nitrogen at 77 K based on the Barrett-Joyner-Halenda method and represents the relationship between the pore size and the Log differential pore volume, is in the range of pore size greater than 100 nm and less than 400 nm.

[0082] (3) At least one peak exists in the two-dimensional spatial spectrum of the electron microscope image of the carbon nanotube assembly in the range of 1 μm⁻¹ above and 100 μm⁻¹ below.

[0083] CNT assemblies that meet the above-mentioned properties can be manufactured according to the manufacturing method described in International Publication No. 2022 / 114237.

[0084] [content]

[0085] Furthermore, the carbon nanotube content in the electromagnetic wave absorbing component of the present invention depends on the conductivity of the carbon nanotubes, but is preferably 0.1 mg / cm² or more, more preferably 0.2 mg / cm² or more, and preferably 2.0 mg / cm² or less, more preferably 1.5 mg / cm² or less. If the CNT content in the electromagnetic wave absorbing component is above the above-mentioned lower limit, the electromagnetic wave absorbing component can exhibit a moderately high conductivity, and therefore can exhibit superior electromagnetic wave absorption performance in the Asia-Pacific Hertz frequency band above 100 GHz. On the other hand, if the area weight of CNTs in the electromagnetic wave absorbing component is below the above-mentioned upper limit, the electromagnetic wave absorbing component is less likely to reflect electromagnetic waves, and the electromagnetic wave absorption capability can be further improved. Therefore, the electromagnetic wave absorbing component can exhibit superior electromagnetic wave absorption performance in the Asia-Pacific Hertz frequency band.

[0086] In addition, when the electromagnetic wave absorbing component is made into the electromagnetic wave absorbing sheet described later, the CNT content of the electromagnetic wave absorbing sheet can be measured by the method described in the examples.

[0087] In addition, the CNT content in the electromagnetic wave absorbing sheet can be adjusted by changing various conditions during the manufacturing process of the electromagnetic wave absorbing sheet.

[0088] Furthermore, assuming the amount of carbon nanotubes attached to the electromagnetic wave absorbing component of the present invention is A mg, when using 20 mg of CNTs to form the electromagnetic wave absorbing component of the present invention to produce a 38 mm diameter packing paper, the index I obtained according to the following formula (1) regarding the conductivity C (S / cm) of the packing paper (hereinafter referred to as "the conductivity of the CNT") and A (mg) is preferably 40 or more and 500 or less, more preferably 70 or more and 300 or less. If the above index I is within the above range, the electromagnetic wave absorption performance in the Asia-Pacific Hertz band is even better.

[0089]

[0090] Furthermore, the manufacture of Buck paper and the determination of the conductivity of CNTs can be carried out using the methods described in the examples.

[0091] <Shape of electromagnetic wave absorbing component>

[0092] The electromagnetic wave absorbing component of the present invention can be an amorphous material such as a composition or powder, or it can be a molded article. Examples of molded articles of the electromagnetic wave absorbing component of the present invention include electromagnetic wave absorbing components molded into a plate, sheet, or film shape.

[0093] <<Electromagnetic wave absorbing components molded into sheet-like shapes>>

[0094] Hereinafter, the electromagnetic wave absorbing component of the present invention will be described as a component formed into a sheet shape (hereinafter also referred to as "electromagnetic wave absorbing sheet").

[0095] The electromagnetic wave absorbing component, which is formed into a sheet shape, is preferably a single-layer sheet. By making the electromagnetic wave absorbing component a single-layer sheet, it is possible to make the electromagnetic wave absorbing component thinner and lighter.

[0096] Furthermore, the thickness of the electromagnetic wave absorbing sheet is preferably 300 μm or less, and more preferably 200 μm or less. If the thickness of the electromagnetic wave absorbing component is below the above-mentioned upper limit, it can be suitable for use in mobile terminals such as smartphones and tablets, automobiles, base stations, medical devices, and various applications requiring space saving.

[0097] The electromagnetic wave absorbing sheet of the present invention is preferably configured to include: a polymer sheet containing a polymer material and carbon nanotubes attached to the polymer sheet.

[0098] Here, "attached" carbon nanotubes to the polymer sheet refers to the state in which carbon nanotubes are attached to or wrapped around the constituent units of the polymer sheet, namely fibers. Furthermore, in the electromagnetic wave absorbing sheet of the present invention, it is generally preferable that the carbon nanotubes are attached not only to the surface of the polymer sheet but also to the fibers located inside the thickness direction of the polymer sheet. Moreover, it can be considered that the electromagnetic wave absorbing sheet of the present invention absorbs electromagnetic waves by causing diffuse reflection and attenuation of incident electromagnetic waves within the sheet, particularly through the carbon nanotubes attached to the fibers located inside the thickness direction of the polymer sheet.

[0099] [Polymer Tablets]

[0100] In this specification, "polymer sheet" refers to a sheet containing polymer materials.

[0101] Furthermore, the polymer sheet is preferably a nonwoven fabric composed of polymer fibers, which are made of polymer materials. By using nonwoven fabric, electrical conductivity can be suppressed, and electromagnetic wave absorption performance can be improved.

[0102] [Non-woven fabric]

[0103] In this specification, “nonwoven fabric” as defined in JIS L 0222 means “fiber sheet, web or batt, with fibers oriented in one direction or randomly and bonded together by at least one of entanglement, fusion and bonding” (but excluding paper, fabric, knitted fabric, tufted fabric and felt).

[0104] [Polymer Fiber]

[0105] Organic fibers are particularly suitable as polymer fibers for forming nonwoven fabrics. Organic fibers described in the "Organic Fibers" section of "Polymer Materials" can be used as organic fibers. Among these, synthetic fibers are preferred as organic fibers for forming nonwoven fabrics, and vinylon fibers, which are acetalized forms of polyvinyl alcohol, are particularly more preferred.

[0106] In addition, carbon nanotubes are not included in the aforementioned organic fibers.

[0107] The electromagnetic wave absorbing component of the present invention can also be a sheet formed from a composition comprising a polymer material and carbon nanotubes. Furthermore, the electromagnetic wave absorbing component of the present invention is not particularly limited; for example, it can have a structure in which the polymer material and carbon nanotubes are uniformly dispersed in the thickness direction of the sheet.

[0108] Sheets formed from compositions comprising polymeric materials and carbon nanotubes can be manufactured using any known sheet-forming method. Specifically, for example, the aforementioned sheets can be manufactured by pressurizing a composition obtained by mixing polymeric materials, carbon nanotubes, and other arbitrary components.

[0109] Properties of Electromagnetic Wave Absorbing Components

[0110] <<Conductivity of Electromagnetic Wave Absorbing Components>>

[0111] The electromagnetic wave absorbing member of the present invention has a conductivity of 0.05 (S / cm) or more and 2.0 (S / cm) or less. Furthermore, the conductivity of the electromagnetic wave absorbing member of the present invention is preferably 0.1 (S / cm) or more. Additionally, the conductivity of the electromagnetic wave absorbing member of the present invention is preferably 1.5 (S / cm) or less, more preferably 1.0 (S / cm) or less. By ensuring the conductivity of the electromagnetic wave absorbing member is within the above range, the electromagnetic wave absorbing member will not reflect electromagnetic waves in the Asia-Pacific Hertz band above 100 GHz, thereby improving absorption capability.

[0112] Furthermore, conductivity is the reciprocal of resistivity. And the conductivity of an electromagnetic wave absorbing component can be controlled, for example, by changing the CNT content within the component. For instance, increasing the CNT content can increase the conductivity of the electromagnetic wave absorbing component. Conversely, decreasing the CNT content can decrease the conductivity of the electromagnetic wave absorbing component.

[0113] <<Electromagnetic Wave Absorption Performance>>

[0114] The electromagnetic wave absorbing component of the present invention needs to have an attenuation rate of 5 dB or more at a frequency of 300 GHz, preferably 10 dB or more.

[0115] Furthermore, an attenuation rate of 5 dB or higher is preferred in the frequency band above 200 GHz and below 300 GHz. If the attenuation rate is 5 dB or higher in the above frequency band, the electromagnetic wave absorption performance in the Asia-Pacific Hertz band is even better.

[0116] <Manufacturing Method of Electromagnetic Wave Absorbing Components>

[0117] The electromagnetic wave absorbing sheet of the present invention can be manufactured by performing a process of filtering the dispersion of the carbon nanotubes with a polymer sheet (filtration process) or a process of stirring the dispersion of the carbon nanotubes and the polymer sheet under reduced pressure (reduced pressure stirring process). According to this method of manufacturing the electromagnetic wave absorbing sheet, the electromagnetic wave absorbing sheet can be manufactured well.

[0118] <<Manufacturing Method of Electromagnetic Wave Absorbing Components Including Filtering Process>>

[0119] The method for manufacturing an electromagnetic wave absorbing sheet that includes a filtration process is characterized by including a filtration process in which the dispersion of the above-mentioned carbon nanotubes is filtered using a polymer sheet.

[0120] In addition, the manufacturing method of the electromagnetic wave absorbing sheet may include other processes besides the filtration process described above.

[0121] [Filtration Process]

[0122] In the filtration process, the dispersion of carbon nanotubes described above is filtered using a polymer sheet. This allows for the fabrication of a primary sheet in which the carbon nanotubes are positioned within the thickness direction of the polymer sheet. Furthermore, the resulting primary sheet can also be used directly as the electromagnetic wave absorbing sheet of this invention.

[0123] Here, a carbon nanotube dispersion (CNT dispersion) can be prepared by dispersing CNTs containing single-walled CNTs as the main component in a dispersion medium. Single-walled CNTs and other CNTs that can be used include those described above, such as single-walled CNTs, multi-walled CNTs, and CNT aggregates. The dispersion medium is not particularly limited and can include water, isopropanol, 1-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, toluene, tetrahydrofuran, ethyl acetate, acetonitrile, ethylene glycol, methyl isobutyl ketone, and butanol. Water is preferred as the dispersion medium.

[0124] In preparing CNT dispersions, dispersants can be used as additives to improve the dispersibility of CNTs. There are no particular limitations on the type of dispersant; for example, known surfactants such as sodium dodecyl sulfate, sodium deoxycholate, sodium cholate, and sodium dodecylbenzene sulfonate, or synthetic or natural polymers capable of functioning as dispersants, can be used. The amount of dispersant added can be within a general range.

[0125] Furthermore, in preparing the CNT dispersion, CNTs are added to a dispersion medium containing the aforementioned surfactant to obtain a coarse dispersion. This coarse dispersion is then subjected to a dispersion method that achieves cavitation effects and / or a dispersion method that achieves fragmentation effects, as disclosed in International Publication No. 2014 / 115560, thereby obtaining a CNT dispersion with good dispersibility. However, the dispersion method is not limited to these two methods; direct stirring with a stir bar can also be used.

[0126] When preparing CNT dispersions, carbon materials other than carbon nanotubes, as well as other components such as additives, can be added to the CNT dispersions. For example, other components can be added to the coarse dispersion of CNTs.

[0127] In addition, the dispersion time for preparing CNT dispersions can be, for example, more than 1 minute and less than 120 minutes.

[0128] The CNT concentration in the CNT dispersion is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and preferably 0.3% by mass or less, more preferably 0.2% by mass or less. If the CNT concentration in the CNT dispersion is within the above range, then in the subsequent filtration process, CNTs can be efficiently introduced into the thickness-direction inner space of the polymer sheet. As a result, a homogeneous electromagnetic wave absorbing sheet with superior electromagnetic wave absorption performance in the Asia-Pacific Hertz band can be obtained.

[0129] Furthermore, the resulting CNT dispersion is preferably degassed before filtration with a polymer sheet. Filtering the degassed CNT dispersion with a polymer sheet allows the CNTs to easily enter the inward space of the polymer sheet in the thickness direction.

[0130] There are no particular limitations on the method for degassing the CNT dispersion, and any method using a known degassing device can be employed. However, from the viewpoint of effectively degassing while suppressing CNT aggregation in the CNT dispersion, the method of using a vacuum stirring device is preferred.

[0131] Furthermore, there are no particular limitations on the method of filtering the carbon nanotube dispersion using polymer sheets; known filtration methods such as natural filtration, vacuum filtration, pressure filtration, and centrifugal filtration can be used. From the viewpoint of easily and effectively allowing CNTs to enter the inner space of the polymer sheet in the thickness direction, vacuum filtration or pressure filtration is preferred as the filtration method, and vacuum filtration is more preferred.

[0132] In addition, the pressure and other conditions during depressurization filtration (vacuum filtration) or pressurization filtration can be arbitrarily set according to the desired surface roughness of the main surface of the resulting electromagnetic wave absorbing sheet.

[0133] In addition, the polymer sheet used in the filtration process can be, for example, a nonwoven fabric made of polymer fibers as described in the section on "electromagnetic wave absorbing components molded into sheet shape".

[0134] Furthermore, the area weight of the polymer sheet is preferably 4 g / m² or more, more preferably 8 g / m² or more, and preferably 150 g / m² or less, more preferably 120 g / m² or less. If the area weight of the polymer sheet is above the lower limit mentioned above, the electromagnetic wave absorption performance of the manufactured electromagnetic wave absorbing sheet in the Asia-Pacific Hertz band can be further improved, while ensuring that the mechanical strength of the electromagnetic wave absorbing sheet is sufficiently high. On the other hand, if the area weight of the polymer sheet is below the upper limit mentioned above, the manufactured electromagnetic wave absorbing sheet can be made lighter.

[0135] Furthermore, the thickness of the polymer sheet is preferably 5 μm or more, and more preferably 500 μm or less, and even more preferably 400 μm or less. If the thickness of the polymer sheet is above the aforementioned lower limit, the electromagnetic wave absorption performance of the manufactured electromagnetic wave absorbing sheet in the Asia-Pacific Hertz band can be further improved, while ensuring that the mechanical strength of the electromagnetic wave absorbing sheet is sufficiently high. On the other hand, if the thickness of the polymer sheet is below the aforementioned upper limit, the manufactured electromagnetic wave absorbing sheet can be made thinner and lighter.

[0136] [Other processes]

[0137] The method for manufacturing the electromagnetic wave absorbing sheet of the present invention may include other steps besides the filtration step described above. These other steps are not particularly limited; examples include dispersant removal and drying steps.

[0138] {Dispersant Removal Process}

[0139] In the dispersion medium removal process, the dispersant in the dispersion liquid is removed from the polymer sheet to which the carbon nanotube dispersion liquid has adhered after passing through the above-mentioned filtration process. Implementing the dispersion medium removal process allows for the manufacture of electromagnetic wave absorbing sheets with better performance.

[0140] There are no particular limitations on the method for removing the dispersion medium from the polymer sheet with the attached carbon nanotube dispersion. For example, the dispersion medium can be cleaned by injecting isopropanol onto the polymer sheet after the filtration process and performing filtration methods such as vacuum filtration as described in the "Filtration Process" section.

[0141] The substances, quantities, and pressure during filtration can be set arbitrarily.

[0142] {Drying Process}

[0143] In the drying process, an electromagnetic wave absorbing sheet can be obtained by drying the primary sheet. The primary sheet may contain residual dispersion medium and solvent used in the above process, but by performing the above dispersant removal process and drying the primary sheet, the residual amount of solvent in the obtained electromagnetic wave absorbing sheet can be reduced.

[0144] There are no particular limitations on the drying method; examples include hot air drying, vacuum drying, hot roller drying, and infrared irradiation. There are no particular limitations on the drying temperature, which is typically room temperature to 200°C. There are no particular limitations on the drying time, which is typically more than 1 hour and less than 48 hours.

[0145] Furthermore, in the manufacturing method of the electromagnetic wave absorbing sheet of the present invention, the polymer sheet may shrink, for example, due to heating during the drying process described above. Therefore, the polymer sheet used in the manufacturing method of the electromagnetic wave absorbing sheet may sometimes differ from the polymer sheet of the electromagnetic wave absorbing sheet obtained by this manufacturing method in terms of weight per unit area, thickness, and fineness of organic fibers.

[0146] <<Manufacturing Method of Electromagnetic Wave Absorbing Sheets Including Pressure Reduction and Stirring Process>>

[0147] The method for manufacturing the electromagnetic wave absorbing sheet of the present invention, which includes a depressurization stirring step, is characterized by including a step of stirring the dispersion of the carbon nanotubes and the polymer sheet under depressurization conditions.

[0148] In addition, the manufacturing method of the electromagnetic wave absorbing sheet of the present invention may include other steps besides the above-described depressurization stirring step.

[0149] [Reduced pressure stirring process]

[0150] In the reduced-pressure stirring process, the dispersion of carbon nanotubes and the polymer sheet are stirred under reduced-pressure conditions. This yields a polymer sheet coated with the carbon nanotube dispersion.

[0151] For example, in the vacuum stirring process, the above-mentioned carbon nanotube dispersion and polymer sheet can be placed in the same container and stirred under reduced pressure using a known vacuum stirring device.

[0152] Here, as the dispersion liquid of carbon nanotubes, for example, the CNT dispersion liquid described in the "filtration process" section can be used.

[0153] In addition, as the polymer sheet, for example, a non-woven fabric composed of polymer fibers described in the "electromagnetic wave absorbing member formed into a sheet" section can be used.

[0154] In addition, the reduced-pressure conditions during stirring and the like can be appropriately set within the range that can achieve the desired effects of the present invention.

[0155] [Other processes]

[0156] The manufacturing method of the electromagnetic wave absorbing sheet of the present invention described above may include other processes in addition to the above-described reduced-pressure stirring process. As other processes, there is no particular limitation, and for example, a dispersion medium removal process and the like can be cited.

[0157] {Dispersion medium removal process}

[0158] In the dispersion medium removal process, the dispersion medium in the dispersion liquid is removed from the polymer sheet to which the carbon nanotube dispersion liquid is attached by the above-described reduced-pressure stirring process. If the dispersion medium removal process is carried out, the electromagnetic wave absorbing sheet can be manufactured more favorably.

[0159] As a method for removing the dispersion medium in the dispersion liquid from the polymer sheet to which the carbon nanotube dispersion liquid is attached, there is no particular limitation, and filtration methods such as suction filtration described in the "filtration process" section, cleaning methods described in the "dispersion medium removal process" section, drying methods described in the "drying process" section, and the like can be used, and these methods can also be used in combination.

[0160] Examples

[0161] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, various measurements were carried out by the following methods.

[0162] (Physical property measurement)

[0163] <BET specific surface area of CNT>

[0164] Using "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Inc.), the nitrogen adsorption specific surface area of the carbon nanotubes used in the examples and comparative examples was measured according to the BET method.

[0165] <G / D ratio of CNT>

[0166] Using a micro laser Raman spectrometer (the SENTERRA micro Raman spectroscopy system manufactured by Bruker), the Raman spectra of carbon nanotubes were measured. Then, for the obtained Raman spectra, the intensity of the G-band peak observed around 1590 cm⁻¹ and the intensity of the D-band peak observed around 1340 cm⁻¹ were determined, and the G / D ratio was calculated.

[0167] <Effective length of CNT>

[0168] For 10 mg of each CNT prepared in each of the examples and comparative examples as materials, 100 g of water containing sodium dodecylbenzenesulfonate as a surfactant at a concentration of 1% by mass was added, and the mixture was stirred for 1 minute at 45 Hz using an ultrasonic bath to obtain 100 ml of a dispersion of each CNT aggregate. For each of the dispersions prepared as described above, they were diluted 2-fold with a solvent having the same composition, dropped onto a silicon substrate and dried, and then the effective length was measured using a Fourier transform infrared spectrometer based on the surface plasmon far infrared (FIR) resonance peak.

[0169] <Production of buckypaper (BP) for measuring CNT conductivity>

[0170] 20 g of ethanol was added to 20 mg of CNT and dispersed for 1 hour using an ultrasonic disperser to obtain a dispersion. The entire dispersion was dropped and filtered to produce a buckypaper with a diameter of φ38 mm.

[0171] <Conductivity of CNT>

[0172] The conductivity of CNT was measured by the four-terminal method using a resistivity meter for low resistance (manufactured by Mitsubishi Chemical Analytech Co., Ltd., "Loresta (registered trademark) GX") in accordance with JIS K 7194 by arranging the probe on one surface of the buckypaper.

[0173] <CNT content of electromagnetic wave absorbing sheet>

[0174] The CNT content in the electromagnetic wave absorbing sheet was calculated by the following method. That is, the mass W s (mg) of a test piece obtained by cutting out a 5 cm × 5 cm (area: 25 cm²) of the electromagnetic wave absorbing sheet was weighed, and the mass W f (mg) of the polymer sheet used to manufacture the electromagnetic wave absorbing sheet was subtracted to obtain the total CNT adhesion amount W CNT (mg). The total CNT adhesion amount W CNT was divided by the area of the test piece, and thus the CNT content (mg / cm²) as the adhesion amount (mg) per 1 cm² of the test piece was calculated.

[0175] <Thickness of electromagnetic wave absorbing sheet>

[0176] The thickness of the electromagnetic wave absorption sheets produced in the examples and comparative examples was measured using a "Digital Standard External Micrometer" manufactured by Mitutoyo Corporation.

[0177] <Electrical Conductivity of Electromagnetic Wave Absorption Sheet>

[0178] For the electromagnetic wave absorption sheets produced in the examples and comparative examples, a four-probe method was performed in accordance with JIS K 7194 using a resistivity meter for low resistance (manufactured by Mitsubishi Chemical Analytech Co., Ltd., "Loresta (registered trademark) GX") with the probe placed on one surface of the electromagnetic wave absorption sheet, and the electrical conductivity was calculated therefrom.

[0179] <Electromagnetic Wave Absorption Performance of Electromagnetic Wave Absorption Sheet>

[0180] For the electromagnetic wave absorption sheets produced in the examples and comparative examples, the absorbance was measured by the transmission measurement method of terahertz time-domain spectroscopy (THz-TDS), and the absorption attenuation amount (dB) at a frequency of 300 GHz was calculated. In addition, the measurement equipment and measurement frequency used are as follows.

[0181] Measurement Equipment: "Terahertz Spectroscopy System Trea Prospector" manufactured by Nisshinbo Industries, Inc.

[0182] Measurement Frequency: 200 GHz or more and 3 THz or less

[0183] In addition, the greater the transmission attenuation rate at a certain frequency, the more excellent the electromagnetic wave absorption performance of the electromagnetic wave absorption sheet at that frequency.

[0184] For the electromagnetic wave absorption member of the embodiment of the present application, it was confirmed by the above method that the attenuation rate in the frequency band of 200 (GHz) or more and 300 (GHz) or less was 5 (dB) or more.

[0185] (Example 1)

[0186] <Preparation of CNT Aggregate>

[0187] The SGCNT aggregate (hereinafter also referred to as CNT1) used in Example 1 was produced by a method in which while continuously conveying a granular catalyst carrier by screw rotation in the CNT synthesis process, a raw material gas was supplied.

[0188] <Catalyst Layer Formation Process>

[0189] Zirconia (zirconium dioxide) beads (ZrO2, volume average particle size D50: 650 μm) as the substrate were put into a rotary drum coating device. While stirring the zirconia beads (20 rpm), an aluminum-containing solution was sprayed with a spray gun (spray amount 3 g / min, spray time 940 s, spray air pressure 10 MPa). At the same time, compressed air (300 L / min) was supplied into the rotary drum for drying, and an aluminum-containing coating film was formed on the zirconia beads. Then, a firing treatment was carried out at 480 °C for 45 minutes to produce primary catalyst particles with an alumina layer formed thereon. Further, these primary catalyst particles were put into another rotary drum coating device. While stirring (20 rpm), an iron catalyst solution was sprayed with a spray gun (spray amount 2 g / min, spray time 480 s, spray air pressure 5 MPa). At the same time, compressed air (300 L / min) was supplied into the rotary drum for drying, and an iron-containing coating film was formed on the primary catalyst particles. Then, a firing treatment was carried out at 220 °C for 20 minutes to produce a substrate further formed with an iron oxide layer.

[0190] <CNT synthesis process>

[0191] The substrate with a catalyst on the surface thus produced was put into the feed hopper of the manufacturing device, and while being conveyed by a screw conveyor, it was processed in the order of the formation process, the growth process, and the cooling process to produce a CNT aggregate.

[0192] <<Formation process - Cooling process>>

[0193] The conditions of each of the inlet purge device, the formation unit, the gas mixing prevention device, the growth unit, the outlet purge device, and the cooling unit of the CNT aggregate manufacturing device are set as follows.

[0194] Feed hopper

[0195] · Feed rate: 1.25 kg / h

[0196] · Exhaust volume: 10 sLm (natural exhaust from the gap)

[0197] Inlet purge device

[0198] · Purge gas: Nitrogen 40 sLm

[0199] Formation unit

[0200] · Furnace temperature: 800 °C

[0201] · Reduction gas: Nitrogen 6 sLm, Hydrogen 54 sLm

[0202] · Exhaust volume: 60 sLm

[0203] · Processing time: 20 minutes

[0204] Gas mixing prevention device

[0205] · Purge gas: 20 sLm

[0206] · Exhaust volume of the exhaust device: 62 sLm

[0207] Growth unit

[0208] · Furnace temperature: 830 °C

[0209] · Source gas: Nitrogen 15 sLm, ethylene 5 sLm, carbon dioxide 1 sLm, hydrogen 3 sLm

[0210] · Exhaust volume: 47 sLm

[0211] · Processing time: 10 minutes

[0212] Outlet purge device

[0213] · Purge gas: Nitrogen 45 sLm

[0214] Cooling unit

[0215] · Cooling temperature: Room temperature

[0216] · Exhaust volume: 10 sLm (natural exhaust from the gap)

[0217] Continuous manufacturing is carried out under the above conditions.

[0218] <Separation and recovery process>

[0219] The CNT aggregate synthesized on the substrate is separated and recovered using a forced vortex type classifier (rotation speed 2300 rpm, air flow rate 3.5 Nm³ / min). The recovery rate of the CNT aggregate is 96%.

[0220] Regarding the properties of the CNT aggregate manufactured in this embodiment, as typical values, the tapped bulk density: 0.02 g / cm³, the average length of CNT: 150 μm, the BET specific surface area: 902 m² / g, the average diameter: 4.0 nm, and the carbon purity: 99%.

[0221] <Preparation of CNT dispersion liquid>

[0222] A 0.4% by mass SDS aqueous solution was prepared using 80 mg of sodium dodecyl sulfate (SDS) (manufactured by Fujifilm and Kojun Chemical Co., Ltd.) as a dispersant and 19,900 mg of water as a dispersion medium. 20 mg of SGCNTs prepared as described above were added to this solution as single-walled CNTs, resulting in a coarse dispersion containing SDS as a dispersant. This coarse dispersion containing single-walled CNTs was then filled into a disperser (Thinky Corporation, a rotating ultrasonic nanodispersor) and subjected to ultrasonic dispersion treatment at an output power of 150 W for 60 minutes to disperse the CNTs, yielding a 0.1% by mass SGCNT dispersion.

[0223] <Filtration Process>

[0224] A 5cm × 10cm vinylon nonwoven fabric (manufactured by Kuraray, product number: BFN No. 3, unit area weight: 36g / m², thickness: 123μm) was placed in a vacuum filter, and 2g of the 0.1% by mass SGCNT dispersion obtained as described above was added dropwise. Vacuum filtration was performed until the dispersion was completely filtered out, and then the filter was opened to the atmosphere, thereby obtaining a primary sheet.

[0225] <Dispersant Removal Process>

[0226] Add 50 mL of isopropanol (IPA) to the primary tablet after the above filtration process, and perform vacuum filtration in the same manner as the above filtration process until the IPA is completely filtered out, then open to the atmosphere. Then, add 100 mL of water to the primary tablet, and perform vacuum filtration again in the same manner. After filtration, let stand for 1 hour, then open to the atmosphere and remove the primary tablet.

[0227] <Drying Process>

[0228] The first-stage sheet after the above filtration and dispersant removal processes was vacuum-dried at 150°C for 12 hours to obtain the electromagnetic wave absorbing sheet. Various measurements were performed on the obtained electromagnetic wave absorbing sheet according to the above method. The results are shown in Table 1.

[0229] (Examples 2-3)

[0230] The type of SGCNT was changed to "ZEONANO (registered trademark) SG101" (manufactured by Zeon Corporation, Japan, BET specific surface area: 1250 m² / g, average diameter: 3.3 nm, average length: 400 μm, t-curve shows an upward convexity (inflection point: 0.6 nm)). The amount of CNT dispersion added was set to 2 g in Example 2, 6 g in Example 3, and 8 g in Example 4. Otherwise, all operations and measurements were performed in the same manner as in Example 1. The results are shown in Table 1.

[0231] (Comparative Examples 1-3)

[0232] The type of CNTs was changed to "NC7000" (manufactured by Nanocyl Corporation, trade name) in Comparative Example 1, "eDIPS" (manufactured by Meijo Nano Carbon Co., Ltd., trade name) in Comparative Example 2, and "Tuball" (manufactured by OCSiAl Corporation, trade name) in Comparative Example 3. Except that the amount of CNT dispersion added was set to 6 g in Comparative Examples 1 and 2 and 1 g in Comparative Example 3, all operations and measurements were performed in the same manner as in Example 1. The results are shown in Table 1.

[0233] [Table 1]

[0234]

[0235] As shown in Table 1, Examples 1 to 3, which contain polymer materials and carbon nanotubes with single-walled carbon nanotubes as the main component and have an electromagnetic wave absorption component conductivity of 0.1 (S / cm) or higher and 2.0 (S / cm) or lower, all exhibit electromagnetic wave attenuation rates of 5 dB or higher at 300 GHz, demonstrating excellent electromagnetic wave absorption performance in the Asia-Pacific Hertz band.

[0236] Industrial availability

[0237] According to the present invention, an electromagnetic wave absorbing component with excellent electromagnetic wave absorption performance in the Asia-Pacific Hertz band above 100 GHz can be provided.

Claims

1. An electromagnetic wave absorbing component, which is used in the Asia-Pacific Hertz band above 100 GHz. The electromagnetic wave absorbing component comprises polymer materials and carbon nanotubes. The carbon nanotubes contain single-walled carbon nanotubes as the main component. The electromagnetic wave absorbing component has a conductivity of 0.1 (S / cm) or more and 2.0 (S / cm) or less, and an attenuation rate of 5 (dB) or more at a frequency of 300 (GHz).

2. The electromagnetic wave absorbing component according to claim 1, wherein, The amount of carbon nanotubes attached is A (mg). The electrical conductivity of the carbon nanotube is C (S / cm), and the exponent I obtained according to the following formula (1) is above 40 and below 500. 。 3. The electromagnetic wave absorbing component according to claim 1 or 2, wherein, The electromagnetic wave absorbing component is formed as a single-layer sheet.

4. The electromagnetic wave absorbing component according to claim 3, wherein, The thickness of the electromagnetic wave absorbing component is less than 300 μm.

5. The electromagnetic wave absorbing component according to claim 3, wherein, The electromagnetic wave absorbing component comprises: a polymer sheet containing the polymer material, and carbon nanotubes attached to the polymer sheet.

6. The electromagnetic wave absorbing component according to claim 3, wherein, The electromagnetic wave absorbing component is a sheet formed from a composition comprising the polymer material and the carbon nanotubes.

7. The electromagnetic wave absorbing component according to claim 5, wherein, The polymer sheet is a nonwoven fabric formed using polymer fibers made from the polymer material.

8. The electromagnetic wave absorbing component according to claim 1 or 2, wherein, The G / D ratio of the carbon nanotubes is below 4.

0.

9. The electromagnetic wave absorbing component according to claim 1 or 2, wherein, The carbon nanotubes have a BET specific surface area of ​​over 600 (m² / g).

10. The electromagnetic wave absorbing component according to claim 1 or 2, wherein, The effective length of the carbon nanotubes is above 40 (nm) and below 1000 (nm).

11. The electromagnetic wave absorbing component according to claim 1 or 2, wherein, The electromagnetic wave absorbing component has an attenuation rate of 5 dB or more in the frequency band above 200 GHz and below 300 GHz.

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