ELECTROMAGNETIC WAVE ABSORBING MEMBER FOR SUB-TERAHERTZ FREQUENCY BAND OF 100 GHz OR HIGHER

Abstract

An electromagnetic wave absorbing member for a sub-terahertz frequency band according to the present invention contains a polymer material and carbon nanotubes, and is characterized in that: the carbon nanotubes include a single-wall carbon nanotube as the main component; and the electromagnetic wave absorbing member has a conductivity of 0.1-2.0 (S / cm), and an attenuation rate of 5 (dB) or more at a frequency of 300 (GHz).

Description

Electromagnetic wave absorbing material for sub-terahertz frequency bands above 100 GHz

[0001] The present invention relates to an electromagnetic wave absorbing member for use in the sub-terahertz frequency band of 100 GHz or more.

[0002] It has been known that composite materials, which are made by blending an insulating material such as a resin with a conductive material such as carbon nanotubes (hereinafter also referred to as "CNTs"), are used as electromagnetic wave absorbing materials in fields such as electrical and communications. In these fields, the frequencies used vary depending on the application, but in actual usage environments, electromagnetic waves in frequency ranges other than the required frequency range often occur as noise. For this reason, there has been a need for electromagnetic wave absorbing materials that can attenuate electromagnetic waves of unnecessary frequencies while not attenuating electromagnetic waves of required frequencies.

[0003] For example, Patent Document 1 discloses an electromagnetic wave absorbing sheet that includes a sheet-like fibrous substrate and single-walled CNTs located within the sheet-like substrate, and has a conductivity of 0.7 to 20 (S / cm). It is also disclosed that such an electromagnetic wave absorbing sheet has a transmission attenuation rate of 20 dB or more in at least a part of the range of 1 GHz to 10 GHz.

[0004] International Publication No. 2020 / 067203

[0005] In recent years, there has been a demand for electromagnetic wave absorption performance in the 6G band (sub-terahertz frequency band of 100 GHz or more). However, including the above-mentioned Patent Document 1, there has been no sufficient research into CNT-containing electromagnetic wave absorbing sheets that can exhibit electromagnetic wave absorption performance in the sub-terahertz frequency band.

[0006] An object of the present invention is to provide an electromagnetic wave absorbing member that has excellent electromagnetic wave absorbing performance in the sub-terahertz frequency band of 100 GHz or more.

[0007] The present inventors have conducted extensive research with the aim of solving the above problems, and have newly discovered that, in an electromagnetic wave absorbing member containing a polymer material and carbon nanotubes, the attenuation rate in the sub-terahertz frequency band of 100 GHz or more can be increased by configuring the carbon nanotubes to contain single-walled carbon nanotubes as a main component and by setting the electrical conductivity of the electromagnetic wave absorbing member within a predetermined range, and have completed the present invention.

[0008] That is, the present invention aims to advantageously solve the above-mentioned problems, and the electromagnetic wave absorbing member for the sub-terahertz frequency band of the present invention is: [1] An electromagnetic wave absorbing member comprising a polymer material and carbon nanotubes, wherein the carbon nanotubes contain single-walled carbon nanotubes as a main component, and the electromagnetic wave absorbing member is characterized in having a conductivity of 0.1 (S / cm) to 2.0 (S / cm) and an attenuation rate of 5 (dB) or more at a frequency of 300 (GHz). By using single-walled carbon nanotubes as a main component and further controlling the conductivity within the above range, it is possible to exhibit electromagnetic wave absorption performance in the sub-terahertz frequency band of 100 GHz and above. The conductivity and attenuation rate can be measured by the methods described in the examples.

[0009] [2] In the electromagnetic wave absorbing member of [1] above, it is preferable that 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: Index I = C × A (1) If the index I is within the above range, the electromagnetic wave absorption performance in the sub-terahertz frequency band will be even better. Note that in this specification, the "electrical conductivity of carbon nanotubes" means the electrical conductivity measured using buckypaper formed using a predetermined amount of CNTs, as described in the examples.

[0010] [3] In the electromagnetic wave absorbing member of the above [1] or [2], the electromagnetic wave absorbing member is preferably formed as a single-layer sheet. By forming the electromagnetic wave absorbing member as a single-layer sheet, the electromagnetic wave absorbing member can be made thinner and lighter.

[0011] [4] In the electromagnetic wave absorbing members according to [1] to [3] above, the electromagnetic wave absorbing member preferably has a thickness of 300 μm or less. If the thickness of the electromagnetic wave absorbing member is equal to or less than the upper limit, the electromagnetic wave absorbing member can be suitably used in mobile terminals such as smartphones and tablets, automobiles, base stations, medical equipment, and various applications requiring space saving. The thickness of the electromagnetic wave absorbing member can be measured by the method described in the examples.

[0012] [5] In the electromagnetic wave absorbing member according to any one of [1] to [3] above, the electromagnetic wave absorbing member preferably comprises 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, electrical conductivity can be reduced and electromagnetic wave absorption performance can be improved.

[0013] [6] In the electromagnetic wave absorbing member according to any one of the above [1] to [3], the electromagnetic wave absorbing member is preferably a sheet formed from a composition containing the polymer material and the carbon nanotubes.

[0014] [7] In the electromagnetic wave absorbing member of [5] above, the polymer sheet is preferably a nonwoven fabric formed using polymer fibers made of the polymer material. By using a nonwoven fabric made of polymer fibers made of a polymer material, electrical conductivity can be reduced and electromagnetic wave absorption performance can be improved.

[0015] [8] In the electromagnetic wave absorbing members according to any one of [1] to [7] above, the G / D ratio of the carbon nanotubes is preferably 4.0 or less. When the G / D ratio of the carbon nanotubes is equal to or less than the upper limit, it is easy to control the electrical conductivity. The G / D ratio refers to the ratio of the G-band peak intensity to the D-band peak intensity in a Raman spectrum, and the G / D ratio of the carbon nanotubes can be measured by the method described in the Examples.

[0016] [9] In the electromagnetic wave absorbing member according to any one of the above [1] to [8], the BET specific surface area of ​​the carbon nanotubes is 600 (m ２ / g) or more. If the BET specific surface area of ​​the carbon nanotubes is equal to or greater than the above lower limit, the electromagnetic wave absorption performance in the sub-terahertz frequency band will be even better. In this specification, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET (Brunauer-Emmett-Teller) method.

[0017]

[10] In the electromagnetic wave absorbing members according to any one of [1] to [9] above, the effective length of the carbon nanotubes is preferably 40 nm or more and 1000 nm or less. If the effective length of the carbon nanotubes is within this range, the balance between the film properties and the electromagnetic wave absorption ability of the electromagnetic wave absorbing material in the high frequency range can be further improved. The effective length of the carbon nanotubes can be measured by the method described in the Examples.

[0018]

[11] In the electromagnetic wave absorbing member according to any one of [1] to

[10] above, the electromagnetic wave absorbing member preferably has an attenuation rate of 5 dB or more across a frequency band of 200 GHz to 300 GHz inclusive. If the attenuation rate is 5 dB or more across the frequency band, the electromagnetic wave absorbing member has even better electromagnetic wave absorption performance in the sub-terahertz frequency band.

[0019] According to the present invention, it is possible to provide an electromagnetic wave absorbing member that has excellent electromagnetic wave absorbing performance in the sub-terahertz frequency band of 100 GHz or more.

[0020] Hereinafter, embodiments of the present invention will be described in detail.

[0021] (Electromagnetic Wave Absorbing Member) The electromagnetic wave absorbing member of the present invention is an electromagnetic wave absorbing member comprising a polymer material and carbon nanotubes, the carbon nanotubes comprising single-walled carbon nanotubes as a main component, and characterized in that the electromagnetic wave absorbing member has a conductivity of 0.1 (S / cm) or more and 2.0 (S / cm) or less, and an attenuation rate at a frequency of 300 (GHz) of 5 (dB) or more. The electromagnetic wave absorbing member of the present invention may optionally contain other components such as additives used during the production of the electromagnetic wave absorbing member. The electromagnetic wave absorbing member of the present invention can exhibit excellent electromagnetic wave absorption performance in the sub-terahertz frequency band of 100 GHz or more.

[0022] The reason for this is not clear, but is presumed to be as follows. That is, if the conductivity is too high, electromagnetic waves are reflected rather than absorbed by the component. Therefore, by using a polymer material in combination with carbon nanotubes, the conductivity can be appropriately suppressed, and the component can have high absorption performance rather than reflecting electromagnetic waves. Based on the above-mentioned presumed mechanism, it is thought that an electromagnetic wave absorbing component that satisfies the above-mentioned specified properties can exhibit excellent electromagnetic wave absorption performance in the sub-terahertz frequency band.

[0023] The upper limit frequency of the "sub-terahertz frequency band" targeted by the electromagnetic wave absorbing member of the present invention is usually 1 THz. In the examples of this specification, the electromagnetic wave absorbing member was determined to have excellent electromagnetic wave absorption performance in the sub-terahertz frequency band when the attenuation rate of the electromagnetic wave measured in the frequency band of 200 (GHz) to 300 (GHz) inclusive was 5 (dB) or more within the range of 100 GHz to 1 THz, which is the sub-terahertz frequency band.

[0024] <Composition of Electromagnetic Wave Absorbing Member> <<Polymer Material>> The polymer material is not particularly limited, and known resins and insulating fillers can be used depending on the application of the electromagnetic wave absorbing material. Specifically, an insulating material in which an insulating filler is optionally mixed with a resin can be used. In the present invention, rubber and elastomers are considered to be included in the "resin." Furthermore, organic fibers can be suitably used as the polymer material.

[0025] [Resin] Examples of resins include natural rubbers 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, vinylpyridine rubber, butyl rubber, chlorobutyl rubber, polyisoprene rubber), ethylene propylene rubber (EPR, EPDM), acrylic rubber, silicone rubber, epichlorohydrin rubber (CO, ECO), urethane rubber, polysulfide rubber, fluororubber, fluororesin, urea resin, melamine resin, phenolic resin, cellulose-based resins such as cellulose acetate, cellulose nitrate, and cellulose acetate butyrate; casein plastics; soy protein plastics; benzoguanamine resins; epoxy-based resins including bisphenol A-type epoxy resins, novolac-type epoxy resins, polyfunctional epoxy resins, and alicyclic epoxy resins; diallyl phthalate resins; and α-methyl- ... Examples of such resins include vinyl chloride resins, polyvinyl chloride resins, polyethylene resins, polypropylene resins, styrene-based resins such as ABS (acrylonitrile butadiene styrene) resins, AS (acrylonitrile styrene) resins, and polystyrene, acrylic resins, methacrylic resins, organic acid vinyl ester-based resins such as polyvinyl acetate, vinyl ether-based resins, halogen-containing resins, polycycloolefin resins, olefin-based resins, alicyclic olefin-based resins, polycarbonate-based resins, polyester-based resins including unsaturated polyester resins, polyamide-based resins, thermoplastic and thermosetting polyurethane resins, polysulfone-based resins, polyphenylene ether-based resins including modified polyphenylene ether resins, silicone resins, polyacetal resins, polyimide resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polyarylate resins, polyphenylene sulfide resins, and polyether ether ketone resins. These may be used alone or in combination of two or more.

[0026] [Insulating filler] Furthermore, the insulating filler is not particularly limited, and known inorganic or organic fillers having insulating properties can be used. Examples of such insulating fillers include silica, talc, clay, titanium oxide, nylon fiber, vinylon fiber, acrylic fiber, and rayon fiber. These may be used alone or in combination of two or more.

[0027] [Organic Fibers] The organic fibers are not particularly limited, and examples thereof include synthetic fibers made of polymers such as polyvinyl alcohol, vinylon, polyethylene vinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, poly-ε-caprolactone, polyacrylonitrile, polylactic acid, polycarbonate, polyamide, polyimide, polyethylene, polypropylene, polyethylene terephthalate, and modified products thereof; and natural fibers such as cotton, hemp, wool, and silk. Polymers forming synthetic fibers can be used alone or in combination. Carbon nanotubes are not included in the organic fibers described above.

[0028] <<Carbon Nanotubes>> The carbon nanotubes (hereinafter sometimes referred to as CNT) contained in the electromagnetic wave absorbing member of the present invention contain single-walled carbon nanotubes (single-walled CNT) as a main component. Components other than single-walled CNT that may be contained in the CNT include multi-walled carbon nanotubes (multi-walled CNT). Here, the ratio of single-walled CNT to the total mass of the CNT must be more than 50 mass%, preferably 90 mass% or more, more preferably 95 mass% or more, and may even be 100 mass%. When the CNT contains multi-walled CNT, it is preferable that the number of walls of the multi-walled CNT is 5 or less.

[0029] Preferred attributes of CNTs will be explained below, and it is preferable that these attributes apply to both the CNTs used as a material for producing the electromagnetic wave absorbing member of the present invention and the CNTs contained in the electromagnetic wave absorbing member of the present invention.

[0030] [BET specific surface area] The CNT has a BET specific surface area of ​​600 m ２ / g or more, and ２ / g or more is more preferable, and 1000m ２ / g or more, and more preferably 2000m ２ / g or less, and ２ / g or less is more preferable, and 1600m ２ / g or less. If the BET specific surface area is within the above range, the electromagnetic wave absorbing member can exhibit even better electromagnetic wave absorption performance in the sub-terahertz frequency band. In the present invention, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET (Brunauer-Emmett-Teller) method.

[0031] [G / D ratio] The G / D ratio of the CNT is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and is preferably 0.8 or more, more preferably 1.0 or more. If the G / D ratio is not more than the above upper limit, it is easy to control the conductivity, and the electromagnetic wave absorption performance is further improved.

[0032] [Effective Length] The effective length of the CNT is preferably 40 nm or more, more preferably 50 nm or more, and preferably 1000 nm or less, and more preferably 300 nm or less. If the effective length is within the above range, the balance between the film property and the electromagnetic wave absorption ability of the electromagnetic wave absorbing material in the high frequency range can be further improved. Note that in the present invention, the effective length of the CNT refers to the distance between adjacent bent portions in cases where the CNT is not completely straight and there are multiple bent portions (bent portions) along the length.

[0033] [Average diameter and average length] The average diameter of the CNT is preferably 1 nm or more, preferably 60 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. The average length of the 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, preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 450 μm or less. When a dispersion is prepared using CNTs having an average diameter and / or average length within the above ranges, the CNTs are uniformly present in the dispersion, and a homogeneous electromagnetic wave absorbing member having even better electromagnetic wave absorption performance in the sub-terahertz frequency band of 100 GHz or more can be obtained.

[0034] [Purity] The purity of the CNT is preferably 98% by mass or more, and more preferably 99% by mass or more. Such a CNT aggregate contains almost no impurities, and can fully exhibit the inherent properties of the CNT. There is no particular upper limit to the purity of the CNT, but it is difficult to obtain a CNT aggregate of 99.9999% by mass or more in terms of production. The purity of the CNT can be obtained by elemental analysis using fluorescent X-rays, thermogravimetric analysis (TGA), or the like.

[0035] [Aspect Ratio] Furthermore, CNTs typically have an aspect ratio (length / diameter) of greater than 10. 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.

[0036] Furthermore, it is preferable that the t-plot obtained from the adsorption isotherm of the CNTs exhibits an upwardly convex shape.

[0037] Here, in materials with pores on the surface, the growth of a nitrogen gas adsorption layer can be classified into the following processes (1) to (3). The slope of the t-plot changes depending on the following processes (1) to (3): (1) The process of forming a monomolecular adsorption layer of nitrogen molecules on the entire surface; (2) The process of forming a multimolecular adsorption layer and the accompanying capillary condensation filling process within the pores; and (3) The process of forming a multimolecular adsorption layer on an apparently non-porous surface where the pores are filled with nitrogen.

[0038] Furthermore, in a t-plot showing an upward convex shape, the plot is located on a straight line passing through the origin in a region where the average thickness t of the nitrogen gas adsorption layer is small, whereas as t increases, the plot shifts downward from the straight line. CNTs having such a t-plot shape have a large ratio of internal specific surface area to the total specific surface area of ​​the CNT, indicating that many openings are formed in the CNTs. As a result, when a dispersion is prepared using such CNTs, the CNTs are less likely to aggregate in the dispersion, making it possible to obtain an electromagnetic wave absorbing member that is homogeneous and has even better electromagnetic wave absorption performance in the sub-terahertz frequency band.

[0039] The inflection point of the CNT t-plot preferably falls within a range satisfying 0.2≦t (nm)≦1.5, more preferably within a range of 0.45≦t (nm)≦1.5, and even more preferably within a range of 0.55≦t (nm)≦1.0. When a dispersion is prepared using CNTs whose inflection point of the t-plot falls within this range, the CNTs are less likely to aggregate in the dispersion. As a result, an electromagnetic wave absorbing member can be obtained that is more homogeneous and has even better electromagnetic wave absorption performance in the sub-terahertz frequency band. Here, the "position of the inflection point" is the intersection of the approximate line A in the above-mentioned process (1) and the approximate line B in the above-mentioned process (3).

[0040] Furthermore, the CNT preferably have a ratio (S2 / S1) of the internal specific surface area S2 to the total specific surface area S1 obtained from a t-plot of 0.05 or more and 0.30 or less. When a dispersion is prepared using CNTs with an S2 / S1 value within this range, the CNTs are even less likely to aggregate in the dispersion. As a result, an electromagnetic wave absorbing member can be obtained that is more homogeneous and has even better electromagnetic wave absorption performance in the sub-terahertz frequency band.

[0041] Here, the total specific surface area S1 and the internal specific surface area S2 of the CNT can be determined from the t-plot. Specifically, first, the total specific surface area S1 can be determined from the slope of the approximation line in step (1), and the external specific surface area S3 can be determined from the slope of the approximation line in step (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.

[0042] Measurement of the adsorption isotherm of CNT, creation of t-plots, and calculation of the total specific surface area S1 and the internal specific surface area S2 based on analysis of the t-plots can be performed using, for example, a commercially available measuring device, "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Co., Ltd.).

[0043] CNTs can be produced using known CNT synthesis methods, such as arc discharge, laser ablation, and chemical vapor deposition (CVD), without any particular limitation. Specifically, CNTs can be efficiently produced, for example, by supplying raw material compounds and a carrier gas onto a substrate having a catalyst layer for carbon nanotube production on its surface, and synthesizing CNTs by chemical vapor deposition (CVD), by adding a trace amount of oxidizing agent (catalytic activator) to the system, thereby dramatically improving the catalytic activity of the catalyst layer (super-growth method; see International Publication No. 2006 / 011655). Note that, hereinafter, carbon nanotubes obtained by the super-growth method may be referred to as "SGCNT."

[0044] Furthermore, the CNTs contained in the electromagnetic wave absorbing member may be derived from a CNT aggregate (see, for example, WO 2022 / 114237) that satisfies at least one of the following conditions (1) to (3): (1) In a spectrum obtained by Fourier transform infrared spectroscopy of a carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more, at least one peak due to the plasmon resonance of the carbon nanotube dispersion is present in a wavenumber range of more than 300 cm-1 and not more than 2000 cm-1. (2) For the carbon nanotube aggregate, the largest peak in a pore distribution curve showing the relationship between pore size and log differential pore volume, obtained based on the Barrett-Joyner-Halenda method from the adsorption isotherm of liquid nitrogen at 77 K, is in a pore size range of more than 100 nm and less than 400 nm. (3) At least one peak in the two-dimensional spatial frequency spectrum of an electron microscope image of the carbon nanotube aggregate exists in the range of 1 μm −1 or more and 100 μm −1 or less.

[0045] A CNT aggregate that satisfies the above-mentioned predetermined attributes can be produced according to the production method described in WO 2022 / 114237.

[0046] [Content] The content of carbon nanotubes in the electromagnetic wave absorbing member of the present invention depends on the electrical conductivity of the carbon nanotubes, but is preferably 0.1 mg / cm ２ It is preferable that the concentration is 0.2 mg / cm or more. ２ More preferably, it is 2.0 mg / cm or more. ２ Preferably, it is 1.5 mg / cm or less. ２It is more preferable that the CNT content in the electromagnetic wave absorbing member is equal to or greater than the above lower limit. If the CNT content in the electromagnetic wave absorbing member is equal to or greater than the above lower limit, the electromagnetic wave absorbing member can exhibit appropriately high conductivity, and can therefore exhibit even better electromagnetic wave absorbing performance in the sub-terahertz frequency band of 100 GHz or more. On the other hand, if the CNT basis weight in the electromagnetic wave absorbing member is equal to or less than the above upper limit, the electromagnetic wave absorbing member is less likely to reflect electromagnetic waves, and the electromagnetic wave absorbing ability can be further improved. Therefore, the electromagnetic wave absorbing member can exhibit even better electromagnetic wave absorbing performance in the sub-terahertz frequency band. Note that when the electromagnetic wave absorbing member is an electromagnetic wave absorbing sheet described below, the CNT content of the electromagnetic wave absorbing sheet can be measured by the method described in the Examples. The CNT content in the electromagnetic wave absorbing sheet can be adjusted by changing various conditions during the production of the electromagnetic wave absorbing sheet.

[0047] Furthermore, assuming that the amount of carbon nanotubes attached in the electromagnetic wave absorbing member of the present invention is A mg, when 20 mg of the CNTs used to form the electromagnetic wave absorbing member of the present invention are used to create buckypaper with a diameter of 38 mm, the index I obtained according to the following formula (1) for the conductivity C (S / cm) of the buckypaper (this conductivity will be referred to as the "CNT conductivity" in this specification) and A (mg) is preferably 40 to 500, more preferably 70 to 300. If the index I is within the above range, the electromagnetic wave absorption performance in the sub-terahertz frequency band will be even better. I = C (S / cm) × A (mg) (1) Note that the production of buckypaper and the measurement of the conductivity of CNT can be carried out by the method described in the Examples.

[0048] <Shape of Electromagnetic Wave Absorbing Member> The electromagnetic wave absorbing member of the present invention may be in the form of an amorphous composition or powder, or may be a molded product. Examples of the molded electromagnetic wave absorbing member of the present invention include electromagnetic wave absorbing members molded into the shape of a plate, sheet, or film.

[0049] <<Electromagnetic wave absorbing member formed into a sheet>> Hereinafter, the electromagnetic wave absorbing member of the present invention will be described as one formed into a sheet (hereinafter also referred to as an "electromagnetic wave absorbing sheet"). The electromagnetic wave absorbing member formed into a sheet is preferably a single-layer sheet. By forming the electromagnetic wave absorbing member into a single-layer sheet, the electromagnetic wave absorbing member can be made thinner and lighter. Furthermore, the electromagnetic wave absorbing sheet preferably has a thickness of 300 (μm) or less, and more preferably a thickness of 200 (μm) or less. When the thickness of the electromagnetic wave absorbing member is equal to or less than the above upper limit, it can be suitably used in mobile terminals such as smartphones and tablets, automobiles, base stations, medical equipment, and various applications where space saving is required.

[0050] The electromagnetic wave-absorbing sheet of the present invention preferably comprises a polymer sheet containing a polymer material and carbon nanotubes attached to the polymer sheet. Here, "carbon nanotubes attached to" the polymer sheet refers to a state in which the carbon nanotubes are attached to or entangled with the fibers that are the constituent units of the polymer sheet. In the electromagnetic wave-absorbing sheet of the present invention, it is generally preferred that the carbon nanotubes are attached not only to the surface of the polymer sheet but also to the fibers located inside the polymer sheet in the thickness direction. It is believed that the electromagnetic wave-absorbing sheet of the present invention absorbs electromagnetic waves by attenuating incident electromagnetic waves through diffuse reflection within the sheet by the carbon nanotubes attached to the fibers located inside the polymer sheet in the thickness direction.

[0051] [Polymer sheet] In this specification, the term "polymer sheet" refers to a sheet containing a polymer material. Furthermore, the polymer sheet is preferably a nonwoven fabric made of polymer fibers made of a polymer material. By using a nonwoven fabric, electrical conductivity can be reduced and electromagnetic wave absorption performance can be improved.

[0052] [Nonwoven Fabric] In this specification, the term "nonwoven fabric" refers to "a fiber sheet, web, or batt in which the fibers are oriented unidirectionally or randomly and are bonded together by at least one of entanglement, fusion, and adhesion," as defined in JIS L 0222 (however, this does not include paper, woven fabrics, knitted fabrics, tufts, and crepe felt).

[0053] [Polymer Fibers] As the polymer fibers forming the nonwoven fabric, organic fibers can be preferably used. As the organic fibers, the organic fibers described above in the "Organic Fibers" section of the "Polymer Materials" section can be used. Among them, synthetic fibers are preferred as the organic fibers forming the nonwoven fabric, and among them, vinylon, which is an acetalized product of polyvinyl alcohol, is more preferred. Note that carbon nanotubes are not included in the above-mentioned organic fibers.

[0054] The electromagnetic wave absorbing member of the present invention may be a sheet formed from a composition containing a polymeric material and carbon nanotubes. The electromagnetic wave absorbing member of the present invention is not particularly limited, and may have, for example, a structure in which the polymeric material and the carbon nanotubes are uniformly dispersed in the thickness direction of the sheet.

[0055] The sheet formed from the composition containing the polymer material and the carbon nanotubes can be produced by any known sheet-forming method, for example, by pressing a composition obtained by mixing the polymer material, the carbon nanotubes, and any other optional components.

[0056] <Properties of Electromagnetic Wave Absorbing Member> <<Conductivity of Electromagnetic Wave Absorbing Member>> The conductivity of the electromagnetic wave absorbing member of the present invention is 0.05 (S / cm) or more and 2.0 (S / cm) or less. The conductivity of the electromagnetic wave absorbing member of the present invention is preferably 0.1 (S / cm) or more. The conductivity of the electromagnetic wave absorbing member of the present invention is preferably 1.5 (S / cm) or less, and more preferably 1.0 (S / cm) or less. By setting the conductivity of the electromagnetic wave absorbing member within the above range, the electromagnetic wave absorbing member does not reflect electromagnetic waves in the sub-terahertz frequency band of 100 GHz or more, and the absorption ability can be improved. Note that conductivity is the reciprocal of resistivity. The conductivity of the electromagnetic wave absorbing member can be controlled, for example, by changing the CNT content in the electromagnetic wave absorbing member. For example, increasing the CNT content can increase the conductivity of the electromagnetic wave absorbing member. On the other hand, decreasing the CNT content can decrease the conductivity of the electromagnetic wave absorbing member.

[0057] <<Electromagnetic Wave Absorption Performance>> The electromagnetic wave absorbing member of the present invention must have an attenuation rate of 5 dB or more at a frequency of 300 GHz, and preferably 10 dB or more. Furthermore, the attenuation rate is preferably 5 dB or more across the frequency band of 200 GHz or more and 300 GHz or less. If the attenuation rate is 5 dB or more across the above frequency band, the electromagnetic wave absorbing performance in the sub-terahertz frequency band will be even better.

[0058] <Method for manufacturing an electromagnetic wave absorbing member> The electromagnetic wave absorbing sheet of the present invention can be manufactured by carrying out a step of filtering the above-mentioned carbon nanotube dispersion through a polymer sheet (filtration step), or a step of stirring the above-mentioned carbon nanotube dispersion and polymer sheet under reduced pressure conditions (reduced pressure stirring step), etc. According to this method for manufacturing an electromagnetic wave sheet, the above-mentioned electromagnetic wave absorbing sheet can be successfully manufactured.

[0059] <<Method for manufacturing an electromagnetic wave absorbing member including a filtration step>> A method for manufacturing an electromagnetic wave absorbing sheet including a filtration step is characterized by including a filtration step of filtering the above-mentioned dispersion of carbon nanotubes through a polymer sheet. Note that the method for manufacturing the electromagnetic wave absorbing sheet may include other steps in addition to the filtration step.

[0060] [Filtration step] In the filtration step, the above-mentioned dispersion of carbon nanotubes is filtered through a polymer sheet. This makes it possible to produce a primary sheet in which the carbon nanotubes are positioned in the space inside the polymer sheet in the thickness direction. The obtained primary sheet can also be used as the electromagnetic wave absorbing sheet of the present invention as it is.

[0061] 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. Usable single-walled CNTs and other CNTs include the single-walled CNTs, multi-walled CNTs, and CNT aggregates described above. The dispersion medium is not particularly limited, and examples include water, isopropanol, 1-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, toluene, tetrahydrofuran, ethyl acetate, acetonitrile, ethylene glycol, methyl isobutyl ketone, and butyl alcohol. Among these, water is preferably used as the dispersion medium.

[0062] When preparing a CNT dispersion, a dispersant can be added as an additive to improve the dispersibility of CNTs in the CNT dispersion. The dispersant is not particularly limited, and examples thereof include known surfactants such as sodium dodecyl sulfonate, sodium deoxycholate, sodium cholate, and sodium dodecylbenzenesulfonate, as well as synthetic or natural polymers that can function as dispersants. The amount of dispersant added can be within a typical range.

[0063] In preparing a CNT dispersion, CNTs are added to a dispersion medium containing a surfactant as described above to obtain a crude dispersion, and then the crude dispersion is subjected to a dispersion method that provides a cavitation effect and / or a dispersion method that provides a crushing effect, as disclosed in WO 2014 / 115560, thereby obtaining a CNT dispersion with good CNT dispersibility. Note that the dispersion method is not limited to these two methods, and it is of course also possible to apply a method of direct stirring using a stirrer.

[0064] When preparing the CNT dispersion, other components such as carbon materials other than carbon nanotubes and additives may be optionally added to the CNT dispersion. When other components are added, they can be added to the crude CNT dispersion, for example.

[0065] The dispersion time when preparing the CNT dispersion liquid can be, for example, 1 minute or more and 120 minutes or less.

[0066] 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, and more preferably 0.2% by mass or less. If the CNT concentration in the CNT dispersion is within the above range, the CNTs can be efficiently introduced into the inner space in the thickness direction of the polymer sheet in the filtration process described below. As a result, a homogeneous electromagnetic wave absorbing sheet with even better electromagnetic wave absorption performance in the sub-terahertz frequency band can be obtained.

[0067] The obtained CNT dispersion is preferably degassed before being filtered through a polymer sheet. By filtering the degassed CNT dispersion through a polymer sheet, the CNTs can easily enter the spaces inside the polymer sheet in the thickness direction.

[0068] The method for degassing the CNT dispersion is not particularly limited, and any method using a known degassing device can be employed. Among these, a method using a reduced pressure agitator (vacuum agitator) is preferred from the viewpoint of performing good degassing while suppressing aggregation of the CNTs in the CNT dispersion.

[0069] The method for filtering the carbon nanotube dispersion through a polymer sheet is not particularly limited, and known filtration methods such as natural filtration, reduced-pressure filtration (suction filtration), pressure filtration, centrifugal filtration, etc. From the viewpoint of simply and satisfactorily allowing the CNTs to penetrate into the inner space in the thickness direction of the polymer sheet, reduced-pressure filtration (suction filtration) or pressure filtration is preferably used as the filtration method, and reduced-pressure filtration (suction filtration) is more preferably used.

[0070] The conditions such as pressure during reduced pressure filtration (suction filtration) or pressure filtration can be set arbitrarily depending on the desired surface roughness of the main surface of the resulting electromagnetic wave absorbing sheet.

[0071] Furthermore, as the polymer sheet used in the filtering step, for example, the nonwoven fabric made of polymer fibers described above in the section "Electromagnetic wave absorbing member formed into a sheet" can be used.

[0072] The basis weight of the polymer sheet is 4 g / m ２ It is preferable that the content is 8 g / m or more. ２ More preferably, it is 150 g / m or more. ２ Preferably, the weight is 120 g / m or less. ２ It is more preferable that the basis weight of the polymer sheet is equal to or greater than the above lower limit. If the basis weight of the polymer sheet is equal to or greater than the above lower limit, the electromagnetic wave absorbing performance in the sub-terahertz frequency band of the electromagnetic wave absorbing sheet to be produced can be further improved, and the mechanical strength of the electromagnetic wave absorbing sheet can be ensured to be sufficiently high. On the other hand, if the basis weight of the polymer sheet is equal to or less than the above upper limit, the weight of the electromagnetic wave absorbing sheet to be produced can be reduced.

[0073] The thickness of the polymer sheet is preferably 5 μm or more, preferably 500 μm or less, and more preferably 400 μm or less. If the thickness of the polymer sheet is equal to or greater than the above-mentioned lower limit, the electromagnetic wave absorbing performance of the electromagnetic wave absorbing sheet to be manufactured in the sub-terahertz frequency band can be further improved, and the mechanical strength of the electromagnetic wave absorbing sheet can be ensured to be sufficiently high. On the other hand, if the thickness of the polymer sheet is equal to or less than the above-mentioned upper limit, the electromagnetic wave absorbing sheet to be manufactured can be made thinner and lighter.

[0074] [Other Steps] The method for producing an electromagnetic wave-absorbing sheet of the present invention may include other steps in addition to the filtration step described above. The other steps are not particularly limited, and examples thereof include a dispersant removal step and a drying step.

[0075] {Dispersant Removal Step} In the dispersion medium removal step, the dispersion medium in the carbon nanotube dispersion is removed from the polymer sheet to which the dispersion medium is attached by the filtration step described above. By carrying out the dispersion medium removal step, it is possible to produce an electromagnetic wave absorbing sheet in a better condition. The method for removing the dispersion medium in the carbon nanotube dispersion from the polymer sheet to which the dispersion medium is attached is not particularly limited. For example, the dispersion medium can be washed away by pouring isopropyl alcohol onto the polymer sheet after the filtration step and performing a filtration method such as suction filtration described in the "filtration step" section. Conditions such as the substance, amount, and pressure during filtration can be set as desired.

[0076] {Drying Step} In the drying step, the primary sheet is dried to obtain an electromagnetic wave-absorbing sheet. The dispersion medium and solvent used in the above steps may remain in the primary sheet, but by carrying out the dispersant removal step and drying the primary sheet, the amount of the solvent remaining in the resulting electromagnetic wave-absorbing sheet can be reduced. The drying method is not particularly limited, and examples include hot air drying, vacuum drying, heat roll drying, and infrared irradiation. 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 between 1 hour and 48 hours.

[0077] In the method for producing an electromagnetic wave-absorbing sheet of the present invention, the polymer sheet may shrink, for example, due to heating in the drying step. Therefore, the polymer sheet before use in the method for producing an electromagnetic wave-absorbing sheet may differ from the polymer sheet in the electromagnetic wave-absorbing sheet obtained by the method in terms of basis weight, thickness, fineness of the organic fibers, etc.

[0078] <<Method for producing an electromagnetic wave absorbing sheet including a vacuum stirring step>> The method for producing an electromagnetic wave absorbing sheet of the present invention including a vacuum stirring step is characterized by comprising a step of stirring the above-mentioned carbon nanotube dispersion and polymer sheet under reduced pressure. Note that the method for producing an electromagnetic wave absorbing sheet of the present invention may include other steps in addition to the vacuum stirring step.

[0079] [Depressurized Stirring Step] In the reduced pressure stirring step, the above-described carbon nanotube dispersion and polymer sheet are stirred under reduced pressure, thereby obtaining a polymer sheet to which the carbon nanotube dispersion is attached.

[0080] For example, in the reduced pressure stirring step, the above-mentioned carbon nanotube dispersion and polymer sheet can be placed in the same container and stirred under reduced pressure using a known reduced pressure stirring device (vacuum stirring device).

[0081] Here, as the dispersion liquid of carbon nanotubes, for example, the CNT dispersion liquid described above in the section "Filtration step" can be used.

[0082] Furthermore, as the polymer sheet, for example, a nonwoven fabric made of polymer fibers as described above in the section "Electromagnetic wave absorbing member formed into a sheet" can be used.

[0083] The conditions for reducing the pressure during stirring can be appropriately set within a range that allows the desired effects of the present invention to be obtained.

[0084] [Other Steps] The method for producing an electromagnetic wave-absorbing sheet of the present invention may include other steps in addition to the above-mentioned reduced pressure stirring step. The other steps are not particularly limited, and examples thereof include a dispersion medium removal step.

[0085] {Dispersion Medium Removal Step} In the dispersion medium removal step, the dispersion medium in the carbon nanotube dispersion is removed from the polymer sheet to which the dispersion medium is attached by the reduced pressure stirring step described above. By carrying out the dispersion medium removal step, it is possible to produce an electromagnetic wave absorbing sheet in a better condition. The method for removing the dispersion medium in the carbon nanotube dispersion from the polymer sheet to which the dispersion medium is attached is not particularly limited, but the filtration method such as suction filtration described in the "Filtering Step" section, the washing method described in the "Dispersion Medium Removal Step" section, and the drying method described in the "Drying Step" section can be used, and these methods may be used in combination.

[0086] The present invention will be described in detail below 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.

[0087] (Physical Property Measurement) <BET Specific Surface Area of ​​CNT> The nitrogen adsorption specific surface area of ​​the carbon nanotubes used in the examples and comparative examples was measured according to the BET method using "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Co., Ltd.).

[0088] <G / D ratio of CNT> The Raman spectrum of the carbon nanotube was measured using a microscopic laser Raman spectrophotometer (Microscopic Raman Spectroscopy System SENTERRA manufactured by Bruker Corporation). －１ The intensity of the G band peak observed near 1340 cm －１ The intensity of the D band peak observed in the vicinity was determined, and the G / D ratio was calculated.

[0089] <Effective Length of CNT> 100 g of water containing sodium dodecylbenzenesulfonate as a surfactant at a concentration of 1 mass% was added to 10 mg of each CNT prepared in each Example and Comparative Example, and the mixture was stirred at 45 Hz for 1 minute using an ultrasonic bath to obtain 100 ml of a dispersion of each CNT aggregate. Each dispersion prepared as described above was diluted two-fold using a solvent of the same composition, and each was dropped onto a silicon substrate and dried, after which the effective length was measured using a Fourier transform infrared spectrophotometer based on the plasmon far-infrared (FIR) resonance peak.

[0090] <Preparation of Buckypaper (BP) for use in measuring the conductivity of CNT> 20 mg of CNT was added to 20 g of ethanol, and the mixture was dispersed for 1 hour using an ultrasonic disperser to obtain a dispersion. The entire dispersion was dripped and filtered to prepare buckypaper with a diameter of 38 mm.

[0091] <Conductivity of CNT> The conductivity of the CNT was measured by a four-terminal method in accordance with JIS K 7194 using a low-resistivity resistivity meter (Loresta (registered trademark) GX, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) with probes placed on one side of the buckypaper.

[0092] <CNT Content in Electromagnetic Wave Absorbing Sheet> The CNT content in the electromagnetic wave absorbing sheet was calculated by the following method. ２ ) Mass of the test piece obtained by cutting out ｓ (mg) was weighed to obtain the mass W of the polymer sheet used in producing the electromagnetic wave absorbing sheet. ｆ The total CNT adhesion amount W (mg) was obtained by subtracting ＣＮＴ (mg) by the area of ​​the test piece to obtain the weight of 1 cm ２ The CNT content (mg / cm) was calculated as the amount of CNT attached (mg) per ２ ) was calculated.

[0093] <Thickness of Electromagnetic Wave Absorbing Sheet> The thickness of the electromagnetic wave absorbing sheets produced in the examples and comparative examples was measured using a "Digimatic Standard Outside Micrometer" manufactured by Mitutoyo Corporation.

[0094] <Conductivity of Electromagnetic Wave Absorbing Sheet> The conductivity of the electromagnetic wave absorbing sheets produced in the examples and comparative examples was calculated by a four-probe method in which probes were placed on one side of the electromagnetic wave absorbing sheet in accordance with JIS K 7194 using a resistivity meter for low resistance (Loresta (registered trademark) GX, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0095] <Electromagnetic Wave Absorption Performance of Electromagnetic Wave Absorbing Sheet> For the electromagnetic wave absorbing sheets manufactured in the examples and comparative examples, the absorbance was measured using the transmission measurement method of terahertz time-domain spectroscopy (THz-TDS), and the absorption attenuation (dB) at a frequency of 300 GHz was calculated. The measuring equipment and measurement frequency used are as follows: Measuring equipment: "Trea Prospector" terahertz spectrometer manufactured by Nippou Precision Co., Ltd. Measurement frequency: 200 GHz or higher and 3 THz or lower The higher the transmission attenuation rate at a certain frequency, the better the electromagnetic wave absorbing performance of the electromagnetic wave absorbing sheet at that frequency. For the electromagnetic wave absorbing members of the examples of the present application, it was confirmed that the attenuation rate was 5 dB or higher across the frequency band of 200 GHz or higher and 300 GHz or lower according to the above method.

[0096] (Example 1) <Preparation of CNT aggregate> The SGCNT aggregate (hereinafter also referred to as CNT1) used in Example 1 was produced by a method in which a raw material gas was supplied while a particulate catalyst support was continuously transported by screw rotation in a CNT synthesis process.

[0097] <Catalyst Layer Formation Step> Zirconia (zirconium dioxide) beads (ZrO ２The zirconia beads (volume average particle diameter D50: 650 μm) were placed in a rotary drum coater, and while stirring the zirconia beads (20 rpm), an aluminum-containing solution was sprayed with a spray gun (spray rate 3 g / min, spray time 940 seconds, spray air pressure 10 MPa) while drying with compressed air (300 L / min) supplied into the rotary drum, forming 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 with an aluminum oxide layer formed thereon. Furthermore, the primary catalyst particles were placed in another rotary drum coater and while stirring (20 rpm), an iron catalyst solution was sprayed with a spray gun (spray rate 2 g / min, spray time 480 seconds, spray air pressure 5 MPa) while drying with compressed air (300 L / min) supplied into the rotary drum, forming an iron-containing coating film on the primary catalyst particles. Next, a baking treatment was carried out at 220° C. for 20 minutes to prepare a substrate on which an iron oxide layer was further formed.

[0098] <CNT synthesis process> The substrate having a catalyst on its surface produced in this manner was placed in the feeder hopper of a production device, and while being transported by a screw conveyor, it was subjected to the formation process, growth process, and cooling process in this order to produce a CNT aggregate.

[0099] <<Formation Step to Cooling Step>> The conditions for the inlet purge device, formation unit, gas mixing prevention device, growth unit, outlet purge device, and cooling unit of the CNT aggregate manufacturing apparatus were set as follows.

[0100] 3 sLm ・Discharge rate: 47 sLm ・Processing time: 10 minutes Outlet purge device Purge gas: Nitrogen 45 sLm Cooling unit Cooling temperature: Room temperature Discharge rate: 10 sLm (natural exhaust from gap) Inlet purge device Purge gas: Nitrogen 40 sLm Formation unit Furnace temperature: 800°C Reducing gas: Nitrogen 6 sLm, hydrogen 54 sLm Discharge rate: 60 sLm Treatment time: 20 minutes Gas mixing prevention device Purge gas: 20 sLm Discharge rate of exhaust device: 62 sLm ​​Growth unit Furnace temperature: 830°C Raw material gas: Nitrogen 15 sLm, ethylene 5 sLm, carbon dioxide 1 sLm, hydrogen 3 sLm Discharge rate: 47 sLm Treatment time: 10 minutes Outlet purge device Purge gas: Nitrogen 45 sLm Cooling unit Cooling temperature: Room temperature Discharge rate: 10 sLm (natural exhaust from gap) Continuous production was carried out under the above conditions.

[0101] <Separation and Recovery Step> The CNT aggregates synthesized on the substrate were separated using a forced vortex classifier (rotation speed: 2300 rpm, air flow rate: 3.5 Nm ３ Separation and recovery were carried out using a flow rate of 1000 / min. The recovery rate of the CNT aggregate was 96%.

[0102] The properties of the CNT aggregate produced in this example are, as typical values, tap bulk density: 0.02 g / cm ３ , CNT average length: 150 μm, BET specific surface area: 902 m ２ / g, average diameter: 4.0 nm, and carbon purity: 99%.

[0103] <Preparation of CNT Dispersion> A 0.4 mass% SDS aqueous solution was prepared using 80 mg of sodium dodecyl sulfate (SDS) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a dispersant and 19,900 mg of water as a dispersion medium. 20 mg of SGCNT prepared as described above as single-walled CNT was added to this solution to obtain a crude dispersion containing SDS as a dispersant. This crude dispersion containing single-walled CNT was loaded into a disperser (Thinky Corporation, rotating ultrasonic nanodisperser), and the crude dispersion was subjected to ultrasonic dispersion treatment at an output of 150 W for 60 minutes to disperse the CNT, obtaining an SGCNT dispersion with a concentration of 0.1 mass%.

[0104] <Filtration step> A 5 ​​cm x 10 cm polymer sheet of vinylon nonwoven fabric (manufactured by Kuraray Co., Ltd., product number: BFN No. 3, basis weight: 36 g / m) was placed in a suction filter. ２ A sheet (123 μm thick) was set on the tray, and 2 g of the 0.1 mass % SGCNT dispersion liquid obtained as described above was added dropwise. The sheet was subjected to suction filtration until the dispersion liquid was completely removed, and then opened to the atmosphere to obtain a primary sheet.

[0105] <Dispersant Removal Step> 50 mL of isopropyl alcohol (IPA) was poured onto the primary sheet after the filtration step, and suction filtration was performed in the same manner as in the filtration step until the IPA was completely removed, and then the sheet was opened to the atmosphere. Then, 100 mL of water was poured onto the primary sheet, and suction filtration was performed again in the same manner. After suction filtration, the sheet was left for 1 hour, opened to the atmosphere, and then the primary sheet was removed.

[0106] <Drying Step> The primary sheet after the above-mentioned filtration step and dispersant removal step was vacuum dried at a temperature of 150°C for 12 hours to obtain an electromagnetic wave absorbing sheet. The obtained electromagnetic wave absorbing sheet was subjected to various measurements according to the above-mentioned methods. The results are shown in Table 1.

[0107] (Examples 2 to 3) The type of SGCNT was "ZEONANO (registered trademark) SG101" (manufactured by Zeon Corporation, BET specific surface area: 1,250 m ２ / g, average diameter: 3.3 nm, average length: 400 μm, t-plot was changed to be convex upward (position of inflection point: 0.6 nm)), and the amount of CNT dispersion added was changed to 2 g in Example 2, 6 g in Example 3, and 8 g in Example 4. Except for this, various operations and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0108] (Comparative Examples 1 to 3) The type of CNT was changed to "NC7000" (trade name, manufactured by Nanocyl Corporation) in Comparative Example 1, to "eDIPS" (trade name, manufactured by Meijo Nanocarbon Co., Ltd.) in Comparative Example 2, and to "Tuball" (trade name, manufactured by OCSiAl Corporation) in Comparative Example 3, and various operations and measurements were carried out in the same manner as in Example 1, except that the amount of CNT dispersion added was 6 g in Comparative Examples 1 and 2 and 1 g in Comparative Example 3. The results are shown in Table 1.

[0109]

[0110] From the results in Table 1, it can be seen that Examples 1 to 3, which contain a polymer material and carbon nanotubes whose main component is single-walled carbon nanotubes and in which the conductivity of the electromagnetic wave absorbing member is 0.1 (S / cm) or more and 2.0 (S / cm) or less, all have an electromagnetic wave attenuation rate of 5 dB or more at 300 GHz, and have excellent electromagnetic wave absorption performance in the sub-terahertz frequency band.

[0111] According to the present invention, it is possible to provide an electromagnetic wave absorbing member that has excellent electromagnetic wave absorbing performance in the sub-terahertz frequency band of 100 GHz or more.

Claims

1. An electromagnetic wave absorbing material comprising a polymeric material and carbon nanotubes, the carbon nanotubes containing single-walled carbon nanotubes as a main component, the electromagnetic wave absorbing material having 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), for use in the sub-terahertz frequency band of 100 GHz or more.

2. The electromagnetic wave absorbing member according to claim 1, wherein the amount of the carbon nanotubes attached is A (mg), the electrical conductivity of the carbon nanotubes is C (S / cm), and an index I obtained according to the following formula (1) is 40 or more and 500 or less. I=C×A... (1) 3. The electromagnetic wave absorbing member according to claim 1 or 2, wherein the electromagnetic wave absorbing member is formed in the shape of a single-layer sheet.

4. The electromagnetic wave absorbing member according to claim 3, wherein the electromagnetic wave absorbing member has a thickness of 300 (μm) or less.

5. An electromagnetic wave absorbing member according to claim 3, comprising a polymer sheet containing the polymer material, and the carbon nanotubes attached to the polymer sheet.

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

7. An electromagnetic wave absorbing member according to claim 5, wherein the polymer sheet is a nonwoven fabric formed using polymer fibers made of the polymer material.

8. An electromagnetic wave absorbing member according to claim 1 or 2, wherein the G / D ratio of said carbon nanotubes is 4.0 or less.

9. The electromagnetic wave absorbing member according to claim 1 or 2, wherein the BET specific surface area of ​​the carbon nanotubes is 600 (m ２ / g or more.

10. An electromagnetic wave absorbing member according to claim 1 or 2, wherein the effective length of said carbon nanotubes is 40 (nm) or more and 1000 (nm) or less.

11. An electromagnetic wave absorbing member according to claim 1 or 2, wherein the electromagnetic wave absorbing member has an attenuation rate of 5 dB or more over a frequency band of 200 GHz or more and 300 GHz or less.