WO2024018995A1 - Electromagnetic wave absorber - Google Patents

Electromagnetic wave absorber Download PDF

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Publication number
WO2024018995A1
WO2024018995A1 PCT/JP2023/025939 JP2023025939W WO2024018995A1 WO 2024018995 A1 WO2024018995 A1 WO 2024018995A1 JP 2023025939 W JP2023025939 W JP 2023025939W WO 2024018995 A1 WO2024018995 A1 WO 2024018995A1
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Prior art keywords
electromagnetic wave
wave absorber
absorbing layer
wave absorbing
uneven portion
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PCT/JP2023/025939
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French (fr)
Japanese (ja)
Inventor
廣井俊雄
廣瀬健人
川上伸二
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マクセル株式会社
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Publication of WO2024018995A1 publication Critical patent/WO2024018995A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form
    • B32B3/26—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer
    • B32B3/30—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer characterised by a layer formed with recesses or projections, e.g. hollows, grooves, protuberances, ribs
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields

Definitions

  • the present application relates to an electromagnetic wave absorber that absorbs electromagnetic waves in the millimeter wave band.
  • EMC Electromagnetic Compatibility
  • Patent Document 1 a radio wave absorber using a carbon material such as carbon black has been proposed (Patent Document 1).
  • the radio wave absorber proposed in Patent Document 1 has excellent radio wave absorption properties particularly in the X band, which is a frequency band of 8 to 12.5 GHz, it It is not intended to improve radio wave absorption.
  • electromagnetic wave absorbers it may be difficult to attach electromagnetic wave absorbers to all electronic devices, and in that case, electromagnetic waves reflected from the electronic devices attached with electromagnetic wave absorbers may have an unexpected adverse effect on other electronic devices. It is also possible.
  • the present application solves the above problem and provides an electromagnetic wave absorber that can suppress electromagnetic waves reflected on its surface.
  • the electromagnetic wave absorber of the present application includes an electromagnetic wave absorbing layer, the electromagnetic wave absorbing layer includes an electromagnetic wave absorbing material made of a carbon material, and a binder, the electromagnetic wave absorbing layer includes a foam layer, and the electromagnetic wave absorbing layer includes at least one of the electromagnetic wave absorbing layers. It is characterized by having an uneven portion on one main surface.
  • an electromagnetic wave absorber that can suppress the reflection of electromagnetic waves incident from the outside and absorb the incident electromagnetic waves.
  • FIG. 1 is a perspective view showing an example of an electromagnetic wave absorber according to an embodiment.
  • FIG. 2 is a side view of the electromagnetic wave absorber of FIG. 1.
  • FIG. 3 is a side view showing another example of the electromagnetic wave absorber according to the embodiment.
  • FIG. 4 is a schematic diagram for explaining the free space method for measuring the electromagnetic wave return attenuation and electromagnetic wave transmission attenuation of the electromagnetic wave absorber according to the embodiment.
  • FIG. 5 is a schematic diagram for explaining the free space method for measuring the electromagnetic wave return attenuation of the electromagnetic wave absorber according to the embodiment.
  • the electromagnetic wave absorber of the present application includes an electromagnetic wave absorbing layer, the electromagnetic wave absorbing layer includes an electromagnetic wave absorbing material made of a carbon material, and a binder, the electromagnetic wave absorbing layer includes a foam layer, and the electromagnetic wave absorbing layer includes at least one of the electromagnetic wave absorbing layers. It is characterized by having an uneven portion on one main surface.
  • the electromagnetic wave absorbing layer includes an electromagnetic wave absorbing material made of a carbon material, it can absorb higher frequency electromagnetic waves compared to conventional electromagnetic wave absorbing materials made of a magnetic material.
  • the electromagnetic wave absorbing layer includes a foam layer
  • the weight of the electromagnetic wave absorber can be reduced and reflection of electromagnetic waves can be suppressed.
  • the reason why reflection of electromagnetic waves can be suppressed when the electromagnetic wave absorbing layer includes a foam layer is considered to be as follows.
  • the reflectance of an electromagnetic wave absorber increases if the difference between the permittivity of the air layer into which electromagnetic waves are incident and the permittivity of the electromagnetic wave absorber increases.
  • the dielectric constant of the electromagnetic wave absorption layer can be made close to the dielectric constant of air, and the difference between the dielectric constant of the air layer and the dielectric constant of the electromagnetic wave absorption layer becomes small. Therefore, it is considered that reflection of electromagnetic waves incident on the electromagnetic wave absorption layer can be suppressed.
  • the electromagnetic wave absorber of the present application since the electromagnetic wave absorber of the present application has an uneven portion on at least one main surface of the electromagnetic wave absorbing layer, by making the electromagnetic wave incident on the uneven portion side of the electromagnetic wave absorbing layer, the electromagnetic wave is reflected by the uneven portion. However, the reflected electromagnetic waves are repeatedly reflected and absorbed by the surface of the uneven portion, and the ratio of reflected electromagnetic waves being absorbed by the electromagnetic wave absorption layer again increases, so that reflection of electromagnetic waves can be further suppressed. For this reason, when the electromagnetic wave absorber of the present application has an uneven portion only on one side of the electromagnetic wave absorbing layer, it is preferable to arrange the uneven portion side of the electromagnetic wave absorbing layer on the side on which electromagnetic waves are incident.
  • the electromagnetic wave absorbing layer preferably has a foam layer on the surface of the convex portion of the uneven portion, and preferably has a foam layer on the surface of the concave portion of the uneven portion. It is more preferable to have a foam layer on both the surface of the part and the surface of the recess.
  • the foam layer has a sloped structure in which the foaming magnification of the foam layer decreases from the surface to the inside of the uneven portion, the effect of suppressing reflection of electromagnetic waves becomes greater.
  • the cross-sectional shape of the uneven portion is not particularly limited as long as it can improve electromagnetic wave absorption performance, but it is particularly preferably rectangular or trapezoidal. As a result, even if the electromagnetic waves are reflected by the uneven surface, the reflected electromagnetic waves will be repeatedly reflected and absorbed by the rectangular or trapezoidal surface, and the proportion of the reflected electromagnetic waves being absorbed by the electromagnetic wave absorbing layer will increase. reflection can be further suppressed.
  • the cross-sectional shape of the uneven portion is configured in a repeating pattern of substantially the same rectangular or trapezoidal shape.
  • the height of each convex portion and the width of each concave portion in the entire uneven portion become substantially uniform, and the electromagnetic wave absorption characteristics can be made substantially uniform over the entire surface of the electromagnetic wave absorbing layer.
  • substantially the same shape means that each value of the height of each rectangular or trapezoidal convex part and the width of each concave part constituting the above-mentioned uneven part is ⁇ with respect to the arithmetic mean value of each value. This means that it is within 5%.
  • an electromagnetic wave reflective layer made of metal can be further disposed on the side of the electromagnetic wave absorbing layer that does not have the uneven portion, depending on the use thereof. This makes it possible to provide an electromagnetic wave absorber that completely eliminates transmission of electromagnetic waves.
  • FIG. 1 is a perspective view showing an example of an electromagnetic wave absorber according to this embodiment.
  • the electromagnetic wave absorber 10 of this embodiment includes an uneven portion including a concave portion 11 and a convex portion 12 on the incident surface side of the electromagnetic wave 13.
  • the electromagnetic wave absorber 10 can be produced by producing an electromagnetic wave absorbing sheet containing an electromagnetic wave absorbing material made of a carbon material and a binder, and then forming uneven portions on its surface using a molding die.
  • FIG. 2 is a side view of the electromagnetic wave absorber in FIG. 1.
  • A is preferably 6 to 30 mm
  • B is preferably 6 to 30 mm
  • A+B is preferably 12 to 60 mm.
  • A is 0.5 to 5 times the length of the maximum absorption wavelength of electromagnetic waves
  • B is preferably 0.5 to 5 times the length
  • A+B is Preferably, the length is 1 to 10 times longer.
  • the radio wave absorbability in the sub-millimeter wave to millimeter wave band can be further improved.
  • the maximum absorption wavelength of electromagnetic waves can be selected as appropriate depending on the use of the electromagnetic wave absorber, and can usually be selected from the wavelengths of electromagnetic waves in the frequency band of 28 to 80 GHz.
  • the height C of the convex portion is preferably 2.7 to 43 mm. Further, the height C of the convex portion is preferably 0.25 to 4 times the length of the maximum absorption wavelength of electromagnetic waves. Within this range, the rate at which electromagnetic waves reflected from the bottom surface of the uneven portion or the wall surface return to the incident direction decreases, and the rate at which the reflected electromagnetic waves enter the electromagnetic wave absorption layer again while repeating reflection and are absorbed increases.
  • the wall surface refers to a flat surface that connects the convex surface and the concave surface of the concavo-convex portion.
  • the height C of the convex portion is set to be a multiple of 0.25 to 4 for the length of the maximum absorption wavelength of electromagnetic waves as described above, and the thickness D of the substrate portion is set to be the length of the maximum absorption wavelength of electromagnetic waves. It is preferable that the multiple is in the range of 0.1 to 4. Within this range, the effect of suppressing reflection of electromagnetic waves is large, and the strength and flexibility of the electromagnetic wave absorber can be maintained at a practical level.
  • the length from the highest point of the convex part to the lowest point of the concave part is the height C of the convex part
  • the length from the lowest point of the concave part to the lowest point of the concave part is Let the length to the lowest point be the thickness D of the substrate portion.
  • FIG. 3 is a schematic cross-sectional view showing another example of the electromagnetic wave absorber of this embodiment.
  • the electromagnetic wave absorber 20 of this embodiment includes an electromagnetic wave absorbing layer 20a and an electromagnetic wave reflecting layer 20b.
  • the electromagnetic wave absorbing layer 20a has a concavo-convex portion consisting of a concave portion 21 and a convex portion 22 on the side of the electromagnetic wave 23 incident surface.
  • the electromagnetic wave absorbing layer 20a is made by manufacturing an electromagnetic wave absorbing sheet containing an electromagnetic wave absorbing material made of a carbon material and a binder, and then processing it into two sheets with different thicknesses, and each sheet has a width A and a width B.
  • the electromagnetic wave absorbing layer is cut into rectangular pieces, and the rectangular pieces (cut electromagnetic wave absorbing layer) having different heights are alternately arranged on the electromagnetic wave reflecting layer 20b made of metal to form the uneven portion shown in FIG.
  • the electromagnetic wave absorbing layer 20a can be formed.
  • the electromagnetic wave reflecting layer 20b can be formed from a metal plate, metal foil, metal vapor deposition film, or the like.
  • the electromagnetic wave absorbing material constituting the electromagnetic wave absorbing layer is a carbon material that can absorb electromagnetic waves in the frequency band of millimeter waves or higher, and specifically includes graphite; carbon black (acetylene black, Ketjen black, channel black, furnace black). , lamp black, thermal black, etc.); graphene; carbon nanotubes (single-wall carbon nanotubes, multi-wall carbon nanotubes, branched carbon nanotubes, branched multi-wall carbon nanotubes); carbon fibers, and the like.
  • the carbon material contains at least one of carbon nanotubes and carbon black.
  • the electromagnetic wave absorption function of the electromagnetic wave absorption layer can be exhibited.
  • carbon nanotubes carbon nanotubes having branches are preferable, and branched multi-wall carbon nanotubes (carbon nanostructures) are particularly preferable because they can better exhibit the electromagnetic wave absorption function of the electromagnetic wave absorption layer when used in a smaller amount.
  • the content ratio of the carbon material is preferably 0.05 to 0.10 parts by mass based on 100 parts by mass of the binder described below. If the content ratio of the carbon material is too small, the amount of electromagnetic waves absorbed by the electromagnetic wave absorption layer will decrease, and if it is too large, the electromagnetic wave reflection in the electromagnetic wave absorption layer will increase.
  • the binder is used as a matrix material for dispersing and fixing the electromagnetic wave absorbing material described above and forming the foam layer of the electromagnetic wave absorbing layer.
  • the binder constituting the electromagnetic wave absorbing layer thermoplastic resin binders, thermosetting resin binders, rubber binders, etc. can be used, but when a rubber binder is used, flexibility can be imparted to the entire electromagnetic wave absorber, and electromagnetic wave It is preferable to use a rubber-based binder as the binder because it makes it easy to follow the surface shape of the electronic device to which the absorber is attached.
  • the rubber binder examples include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), nitrile rubber (NBR), and ethylene-propylene rubber.
  • EPDM isoprene rubber
  • CR chloroprene rubber
  • ACM acrylic rubber
  • CSR chlorosulfonated polyethylene rubber
  • PUR urethane rubber
  • silicone rubber Q
  • fluororubber FKM
  • EVA ethylene/vinyl acetate rubber
  • At least one selected from the group consisting of , epichlorohydrin rubber (CO), and polysulfide rubber (T) can be used.
  • silicone rubber (Q) and fluororubber (FKM) are particularly preferred among the above rubber binders.
  • silicone rubber any of addition reaction type, condensation reaction type, and peroxide curing type can be used.
  • peroxide-curable silicone rubber is preferable because it can control the crosslink density and obtain any desired hardness.
  • the electromagnetic wave absorber of this embodiment First, the above-mentioned electromagnetic wave absorbing material, binder, and components for forming an electromagnetic wave absorbing layer such as a blowing agent, a thickener, a vulcanizing agent, and a mold release agent are kneaded in a kneader, and then the kneaded product is separated by a calender molding method. , producing an electromagnetic wave absorbing layer precursor. Next, the produced electromagnetic wave absorption layer precursor is subjected to a crosslinking process and a vulcanization process, and then cut into sheets, and passed through a forming roll to form an uneven part on one side surface to produce an electromagnetic wave absorption layer.
  • the electromagnetic wave absorber shown in 2 can be obtained.
  • each of the prepared electromagnetic wave absorbing layer precursors was subjected to a crosslinking process and a vulcanization process to form electromagnetic wave absorbers with different thicknesses.
  • Fabricate the absorbing layer cut each electromagnetic wave absorbing layer into long rectangular electromagnetic wave absorbing layers, and place the long rectangular pieces (cut electromagnetic wave absorbing layers) with different heights on top of the metal electromagnetic wave reflecting layer. If they are arranged alternately, for example, the electromagnetic wave absorber shown in FIG. 3 can be obtained.
  • the electromagnetic wave return attenuation and electromagnetic wave transmission attenuation of the electromagnetic wave absorber of this embodiment can be such that the electromagnetic wave return attenuation is -10 dB or less and the electromagnetic wave transmission attenuation is -10 dB or less in the frequency band of 28 to 80 GHz. .
  • the above-mentioned attenuation amount of -10 dB or less means that 10% or less of the incident electromagnetic wave is reflected or transmitted.
  • the electromagnetic wave return attenuation and electromagnetic wave transmission attenuation of the electromagnetic wave absorber of this embodiment can be measured using the free space method described below.
  • a predetermined input electromagnetic wave (millimeter wave) 34 is irradiated from the antenna 31 connected to the first port 30a to the uneven portion side of the electromagnetic wave absorber 10 via the dielectric lens 33, and the electromagnetic wave is absorbed.
  • Electromagnetic waves 35 reflected by the uneven portions of the layer are measured by an antenna 31 disposed on the uneven portion side of the electromagnetic wave absorber 10.
  • the electromagnetic wave 36 that passes through the electromagnetic wave absorber 10 is measured by an antenna 32 that is arranged on the back side of the electromagnetic wave absorber 10 and connected to the second port 30b.
  • the intensity of the irradiated electromagnetic waves 34, the reflected electromagnetic waves 35, and the transmitted electromagnetic waves 36 are determined as power values, and the electromagnetic wave return attenuation and electromagnetic wave transmission attenuation are determined in dB from the intensity difference.
  • a predetermined input electromagnetic wave (millimeter wave) 34 is irradiated from the antenna 31 connected to the first port 30a to the uneven portion side of the electromagnetic wave absorber 20 through the dielectric lens 33, and the unevenness of the electromagnetic wave absorbing layer is
  • the electromagnetic waves 35 reflected by the electromagnetic wave absorber 20 and the electromagnetic wave reflecting layer 20b are measured by an antenna 31 disposed on the uneven portion side of the electromagnetic wave absorber 20.
  • the intensity of the irradiated electromagnetic wave 34 and the intensity of the reflected electromagnetic wave 35 are determined as power values, and the electromagnetic wave return attenuation is determined in dB from the difference in intensity.
  • Example 1 ⁇ Production of electromagnetic wave absorber> After kneading the following components of the electromagnetic wave absorbing layer in a kneader, the kneaded product was separated by a calender molding method to produce two types of electromagnetic wave absorbing layer precursors with different thicknesses. Through a crosslinking process and a vulcanization process at a crosslinking temperature of 170° C. for 1 hour, electromagnetic wave absorbing layers having different thicknesses were produced. The produced electromagnetic wave absorbing layer is formed of a foamed layer except for the surface portion, but a non-foamed layer (skin layer) is formed on the surface portion.
  • skin layer non-foamed layer
  • each electromagnetic wave absorbing layer having a foam layer on the surface and having different thicknesses was cut into long, square pieces of electromagnetic wave absorbing layer.
  • Long rectangular pieces (cut electromagnetic wave absorbing layers) of different lengths are glued and arranged alternately so that the foam layer side is the top surface, and the electromagnetic wave absorbing layer is made only of the convex and concave surfaces of the uneven parts.
  • An electromagnetic wave absorber (1-1) of Example 1 having a foam layer also on the surface was prepared.
  • the thickness of the electromagnetic wave absorption layer of the produced electromagnetic wave absorber was 20 mm (height of the convex portion: 10 mm, thickness of the substrate portion: 10 mm), and the thickness of the metal plate was 5 mm. Further, in the electromagnetic wave absorber of Example 1, the width A of the uneven portion shown in FIG. 3 was set to 2 mm, and the width B was set to 2 mm.
  • Rubber binder Silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KE-951KU", silica particle content: 10% by mass): 100 parts by mass
  • Colorant powder diiron trioxide ( III) (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KE Color BR-S”): 1 part by mass
  • Foaming agent azobisisobutyronitrile (manufactured by Takehara Rubber Co., Ltd., product name "TR Master AIBN50Q”) ”): 5 parts by mass
  • Thickener benzoyl peroxide (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “C-1A”): 0.2 parts by mass
  • Vulcanizing agent dicumyl peroxide ( Shin-Etsu Chemical Co., Ltd., trade name “C-3”): 2.5 parts by mass (6)
  • Mold release agent Modified organo
  • Example 2 The electromagnetic wave absorber (2-1) consisting of only the electromagnetic wave absorbing layer of Example 2 and the electromagnetic wave absorber (2-1) made of only the electromagnetic wave absorbing layer of Example 2 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 4 mm and the width B was set to 4 mm.
  • Example 3 The electromagnetic wave absorber (3-1) consisting only of the electromagnetic wave absorbing layer of Example 3 and the electromagnetic wave absorber (3-1) made of only the electromagnetic wave absorbing layer of Example 3 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 6 mm and the width B was set to 6 mm.
  • Example 4 The electromagnetic wave absorber (4-1) consisting of only the electromagnetic wave absorbing layer of Example 4 and the electromagnetic wave absorber (4-1) made of only the electromagnetic wave absorbing layer of Example 4 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 10 mm and the width B was set to 10 mm. An electromagnetic wave absorber (4-2) consisting of an absorption layer and a metal plate was produced.
  • Example 5 The electromagnetic wave absorber (5-1) consisting of only the electromagnetic wave absorbing layer of Example 5 and the electromagnetic wave absorber (5-1) made of only the electromagnetic wave absorbing layer of Example 5 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 30 mm and the width B was set to 30 mm.
  • Example 6 The electromagnetic wave of Example 6 was prepared in the same manner as in Example 4, except that it consisted only of an electromagnetic wave absorbing layer, had a foam layer on the surface of the convex part of the uneven part, and did not have a foam layer on the surface of the concave part. An absorber (6-1) was produced.
  • Example 6 it was made of an electromagnetic wave absorbing layer and a metal plate, and had a foam layer on the surface of the convex part of the uneven part, and did not have a foam layer on the surface of the concave part, but in the same manner as in Example 4, An electromagnetic wave absorber (6-2) of Example 6 was produced.
  • Example 7 The electromagnetic wave absorber of Example 7 (7-1 ) was created.
  • Example 7 was prepared in the same manner as in Example 4, except that it consisted of an electromagnetic wave absorbing layer and a metal plate and did not have a foam layer on either the surface of the convex or concave portions of the uneven portion. A body (7-2) was produced.
  • Example 8 An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 8 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.03 parts by mass. (8-1) and an electromagnetic wave absorber (8-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
  • Example 9 An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 9 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.05 part by mass. (9-1) and an electromagnetic wave absorber (9-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
  • Example 10 An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 10 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.10 parts by mass. (10-1) and an electromagnetic wave absorber (10-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
  • Example 11 An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 11 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.13 parts by mass. (11-1) and an electromagnetic wave absorber (11-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
  • Example 12 Same as Example 4 except that the electromagnetic wave absorbing material of the electromagnetic wave absorbing layer component and its content were changed to 1.50 parts by mass of multi-wall carbon nanotubes (manufactured by Hanwha Chemical Corporation, trade name "CM-130").
  • CM-130 multi-wall carbon nanotubes
  • Example 4 was carried out in the same manner as in Example 4, except that the electromagnetic wave absorbing material of the electromagnetic wave absorbing layer component and its content were changed to 6.50 parts by mass of carbon black (manufactured by Lion Specialty Chemicals, trade name "Lionite CB").
  • An electromagnetic wave absorber (13-1) consisting of only the electromagnetic wave absorbing layer of Example 13 and an electromagnetic wave absorber (13-2) consisting of the electromagnetic wave absorbing layer and a metal plate were prepared.
  • Comparative example 1 An electromagnetic wave absorber (1-1) of Comparative Example 1 was produced in the same manner as in Example 1, except that it consisted only of an electromagnetic wave absorbing layer, had no uneven parts, and had a foam layer on the surface.
  • the electromagnetic wave absorber (1-2) of Comparative Example 1 was prepared in the same manner as in Example 1, except that it consisted of an electromagnetic wave absorbing layer and a metal plate, had no uneven parts, and had a foam layer on the surface. Created.
  • An electromagnetic wave absorber (2-1) consisting of only the electromagnetic wave absorbing layer of Comparative Example 2 and an electromagnetic wave absorbing layer and a metal plate were prepared in the same manner as in Example 4, except that the foaming agent was removed from the electromagnetic wave absorbing layer components.
  • An electromagnetic wave absorber (2-2) was produced.
  • the electromagnetic wave absorbing layers of the electromagnetic wave absorbers (2-1) and (2-2) have uneven portions, but do not have a foam layer throughout.
  • Electromagnetic wave return loss and electromagnetic wave transmission loss were measured using the free space method described above. Specifically, an electromagnetic wave absorber is irradiated with electromagnetic waves of a predetermined frequency, and the electromagnetic wave absorber without a metal plate is measured as shown in Figure 4, and the electromagnetic wave absorber with a metal plate is measured as shown in Figure 5. It was measured.
  • Table 1 shows the configuration of each electromagnetic wave absorber
  • Table 2 shows the frequency of the irradiated electromagnetic wave, the multiple of width A and width B with respect to the wavelength of the irradiated electromagnetic wave, the electromagnetic wave return loss, and the electromagnetic wave transmission attenuation. .
  • the electromagnetic wave absorbers of Examples 1 to 13 were able to suppress the electromagnetic wave return loss to ⁇ 10 dB or less.
  • the electromagnetic wave return loss could be suppressed to -14 dB or less.
  • the electromagnetic wave return loss exceeds -10 dB both with and without the metal plate, and the reflection of electromagnetic waves on the surface of the electromagnetic wave absorber is greater than in any of the examples. Ta.
  • the electromagnetic wave absorber of the present application can provide an electromagnetic wave absorber that can absorb electromagnetic waves in a high frequency band higher than the millimeter wave band and can suppress reflection of electromagnetic waves, and can produce electronic components and devices with excellent EMC. It is useful for

Abstract

An electromagnetic wave absorber according to the present application includes an electromagnetic wave absorbing layer, the electromagnetic wave absorbing layer containing an electromagnetic wave absorbing material, which is composed of a carbon material, and a binder. The electromagnetic wave absorbing layer is characterized by including a foaming layer and having an uneven part on at least one of the principal surfaces of the electromagnetic wave absorbing layer. The foaming layer is preferably provided on the surface portion of a convex portion and the surface portion of a concave portion of the uneven part.

Description

電磁波吸収体electromagnetic wave absorber
　本願は、ミリ波帯の電磁波を吸収する電磁波吸収体に関する。 The present application relates to an electromagnetic wave absorber that absorbs electromagnetic waves in the millimeter wave band.
　携帯電話に代表される無線通信技術の発達に伴い、様々な機器やセンサが無線によってネットワークにつながりつつある。また、医療分野でも感染予防の観点から機器のコードレス化が進み、医療機器が無線でつながり始めている。これらの通信は比較的短距離での高速大容量が求められており、利用周波数が高い。この様な高周波数を利用する機器の増加に伴い、機器から発生するノイズによる動作不良・利用電磁波との干渉等によって電子機器や通信に不具合が起こる危険性が増大している。更に、近年、自動車の衝突事故防止を目的としたミリ波レーダの搭載も始まっている。これら医療、自動車分野の機器での不具合は人命に影響を与えるため、誤動作があってはならない。そこで、機器のノイズや干渉による不具合の防止、いわゆるＥＭＣ（Electromagnetic Compatibility：電磁両立性）対策としての電磁波吸収体を、ミリ波帯の電磁波を発受信する回路素子や伝送路に適用する必要性が高まっている。 With the development of wireless communication technology, typified by mobile phones, various devices and sensors are becoming connected to networks wirelessly. Additionally, in the medical field, devices are increasingly becoming cordless to prevent infection, and medical devices are beginning to be connected wirelessly. These communications require high speed and large capacity over relatively short distances, and use high frequencies. With the increase in the number of devices using such high frequencies, there is an increasing risk that electronic devices and communications will malfunction due to malfunction due to noise generated by the devices or interference with the electromagnetic waves being used. Furthermore, in recent years, millimeter wave radars have begun to be installed for the purpose of preventing automobile collisions. Malfunctions in these devices in the medical and automotive fields have an impact on human life, so malfunctions must not occur. Therefore, it is necessary to apply electromagnetic wave absorbers to circuit elements and transmission lines that emit and receive electromagnetic waves in the millimeter wave band as a so-called EMC (Electromagnetic Compatibility) countermeasure to prevent malfunctions caused by equipment noise and interference. It's increasing.
　高い周波数のノイズを抑制するためには、従来用いられてきた磁性材料の磁気損失を利用した電磁波吸収シートでは効果が低い。このため、カーボンブラック等の炭素材料を利用した電波吸収体が提案されている（特許文献１）。しかし、特許文献１に提案されている電波吸収体は、殊に８～１２．５ＧＨｚの周波数帯であるＸバンド帯での電波吸収性には優れてはいるが、３０～３００ＧＨｚのミリ波帯での電波吸収性の向上を図ったものではない。 In order to suppress high frequency noise, conventionally used electromagnetic wave absorbing sheets that utilize the magnetic loss of magnetic materials are not very effective. For this reason, a radio wave absorber using a carbon material such as carbon black has been proposed (Patent Document 1). However, although the radio wave absorber proposed in Patent Document 1 has excellent radio wave absorption properties particularly in the X band, which is a frequency band of 8 to 12.5 GHz, it It is not intended to improve radio wave absorption.
特開２００４－３１１５８６号公報Japanese Patent Application Publication No. 2004-311586
　ところで、シート状の電磁波吸収体をノイズの影響を防ぎたい電子装置に粘着剤等によって貼り合せてノイズを抑制する場合、ノイズの原因となる電磁波の大部分は、電磁波吸収体により吸収され、一定程度のノイズの抑制効果は達成できる。また、電磁波の一部は、電磁波吸収体の表面で反射し、その反射した電磁波が他の電子装置に達するが、他の電子装置にも電磁波吸収体を貼り合わせておけば問題はない。 By the way, when noise is suppressed by attaching a sheet-shaped electromagnetic wave absorber to an electronic device that wants to prevent the effects of noise using an adhesive, most of the electromagnetic waves that cause noise are absorbed by the electromagnetic wave absorber and remain constant. A certain degree of noise suppression effect can be achieved. Further, a part of the electromagnetic waves is reflected by the surface of the electromagnetic wave absorber, and the reflected electromagnetic waves reach other electronic devices, but there is no problem if the electromagnetic wave absorber is bonded to the other electronic devices as well.
　しかし、全ての電子装置に電磁波吸収体を貼り合わせるのは困難な場合があり、その場合には、電磁波吸収体を貼り合わせた電子装置から反射した電磁波が他の思わぬ電子機器に悪影響を及ぼすことも考えられる。 However, it may be difficult to attach electromagnetic wave absorbers to all electronic devices, and in that case, electromagnetic waves reflected from the electronic devices attached with electromagnetic wave absorbers may have an unexpected adverse effect on other electronic devices. It is also possible.
　本願は、上記問題を解決したもので、表面で反射する電磁波を抑制可能な電磁波吸収体を提供するものである。 The present application solves the above problem and provides an electromagnetic wave absorber that can suppress electromagnetic waves reflected on its surface.
　本願の電磁波吸収体は、電磁波吸収層を含み、前記電磁波吸収層は、炭素材料からなる電磁波吸収材料と、バインダとを含み、前記電磁波吸収層は、発泡層を含み、前記電磁波吸収層の少なくとも一方の主面に、凹凸部を有することを特徴とする。 The electromagnetic wave absorber of the present application includes an electromagnetic wave absorbing layer, the electromagnetic wave absorbing layer includes an electromagnetic wave absorbing material made of a carbon material, and a binder, the electromagnetic wave absorbing layer includes a foam layer, and the electromagnetic wave absorbing layer includes at least one of the electromagnetic wave absorbing layers. It is characterized by having an uneven portion on one main surface.
　本願によれば、外部から入射する電磁波の反射を抑制でき、且つ、入射した電磁波を吸収することができる電磁波吸収体を提供できる。 According to the present application, it is possible to provide an electromagnetic wave absorber that can suppress the reflection of electromagnetic waves incident from the outside and absorb the incident electromagnetic waves.
図１は、実施形態の電磁波吸収体の一例を示す斜視図である。FIG. 1 is a perspective view showing an example of an electromagnetic wave absorber according to an embodiment. 図２は、図１の電磁波吸収体の側面図である。FIG. 2 is a side view of the electromagnetic wave absorber of FIG. 1. 図３は、実施形態の電磁波吸収体の他の一例を示す側面図である。FIG. 3 is a side view showing another example of the electromagnetic wave absorber according to the embodiment. 図４は、実施形態の電磁波吸収体の電磁波反射減衰量及び電磁波透過減衰量を測定するフリースペース法を説明するための模式図である。FIG. 4 is a schematic diagram for explaining the free space method for measuring the electromagnetic wave return attenuation and electromagnetic wave transmission attenuation of the electromagnetic wave absorber according to the embodiment. 図５は、実施形態の電磁波吸収体の電磁波反射減衰量を測定するフリースペース法を説明するための模式図である。FIG. 5 is a schematic diagram for explaining the free space method for measuring the electromagnetic wave return attenuation of the electromagnetic wave absorber according to the embodiment.
　本願の電磁波吸収体は、電磁波吸収層を含み、前記電磁波吸収層は、炭素材料からなる電磁波吸収材料と、バインダとを含み、前記電磁波吸収層は、発泡層を含み、前記電磁波吸収層の少なくとも一方の主面に、凹凸部を有することを特徴とする。 The electromagnetic wave absorber of the present application includes an electromagnetic wave absorbing layer, the electromagnetic wave absorbing layer includes an electromagnetic wave absorbing material made of a carbon material, and a binder, the electromagnetic wave absorbing layer includes a foam layer, and the electromagnetic wave absorbing layer includes at least one of the electromagnetic wave absorbing layers. It is characterized by having an uneven portion on one main surface.
　本願の電磁波吸収体では、前記電磁波吸収層が炭素材料からなる電磁波吸収材料を含んでいるので、従来の磁性材料からなる電磁波吸収材料に比べて、より高い周波数の電磁波を吸収できる。 In the electromagnetic wave absorber of the present application, since the electromagnetic wave absorbing layer includes an electromagnetic wave absorbing material made of a carbon material, it can absorb higher frequency electromagnetic waves compared to conventional electromagnetic wave absorbing materials made of a magnetic material.
　また、前記電磁波吸収層は、発泡層を含んでいるので、電磁波吸収体を軽量化できると共に電磁波の反射を抑制できる。前記電磁波吸収層が発泡層を含むと電磁波の反射を抑制できる理由は下記のとおりと考えられる。 Furthermore, since the electromagnetic wave absorbing layer includes a foam layer, the weight of the electromagnetic wave absorber can be reduced and reflection of electromagnetic waves can be suppressed. The reason why reflection of electromagnetic waves can be suppressed when the electromagnetic wave absorbing layer includes a foam layer is considered to be as follows.
　即ち、一般に電磁波吸収体の反射率については、電磁波が入射する空気層の誘電率と、電磁波吸収体の誘電率との差が大きいと、電磁波吸収体の反射率は大きくなることが知られている。ここで、電磁波吸収層が発泡層を含むことにより、電磁波吸収層の誘電率を空気の誘電率に近づけることができ、空気層の誘電率と電磁波吸収層の誘電率との差が小さくなる。このため、電磁波吸収層へ入射する電磁波の反射を抑制できると考えられる。 In other words, it is generally known that the reflectance of an electromagnetic wave absorber increases if the difference between the permittivity of the air layer into which electromagnetic waves are incident and the permittivity of the electromagnetic wave absorber increases. There is. Here, by including the foam layer in the electromagnetic wave absorption layer, the dielectric constant of the electromagnetic wave absorption layer can be made close to the dielectric constant of air, and the difference between the dielectric constant of the air layer and the dielectric constant of the electromagnetic wave absorption layer becomes small. Therefore, it is considered that reflection of electromagnetic waves incident on the electromagnetic wave absorption layer can be suppressed.
　また、本願の電磁波吸収体は、電磁波吸収層の少なくとも一方の主面に凹凸部を有しているので、電磁波を電磁波吸収層の凹凸部側に入射させることにより、電磁波が凹凸部で反射したとしても、反射した電磁波が凹凸部の表面部で反射、吸収を繰り返し、反射した電磁波が再度電磁波吸収層に吸収される割合が増加するため、電磁波の反射をより抑制できる。このため、本願の電磁波吸収体が、電磁波吸収層の片面にのみ凹凸部を有する場合、電磁波吸収層の凹凸部側を電磁波が入射する面側に配置することが好ましい。 In addition, since the electromagnetic wave absorber of the present application has an uneven portion on at least one main surface of the electromagnetic wave absorbing layer, by making the electromagnetic wave incident on the uneven portion side of the electromagnetic wave absorbing layer, the electromagnetic wave is reflected by the uneven portion. However, the reflected electromagnetic waves are repeatedly reflected and absorbed by the surface of the uneven portion, and the ratio of reflected electromagnetic waves being absorbed by the electromagnetic wave absorption layer again increases, so that reflection of electromagnetic waves can be further suppressed. For this reason, when the electromagnetic wave absorber of the present application has an uneven portion only on one side of the electromagnetic wave absorbing layer, it is preferable to arrange the uneven portion side of the electromagnetic wave absorbing layer on the side on which electromagnetic waves are incident.
　前記電磁波吸収層は、前記凹凸部の凸部の表面部に発泡層を有することが好ましく、また、前記凹凸部の凹部の表面部に発泡層を有することが好ましく、更に、前記凹凸部の凸部の表面部及び凹部の表面部のいずれにも発泡層を有することがより好ましい。これにより、電磁波吸収層の凹凸部の表面部の誘電率を空気の誘電率に近づけることでき、空気層の誘電率と電磁波吸収層の表面部の誘電率との差がより小さくなる。このため、電磁波吸収体へ入射する電磁波の反射をより抑制できる。 The electromagnetic wave absorbing layer preferably has a foam layer on the surface of the convex portion of the uneven portion, and preferably has a foam layer on the surface of the concave portion of the uneven portion. It is more preferable to have a foam layer on both the surface of the part and the surface of the recess. Thereby, the dielectric constant of the surface portion of the uneven portion of the electromagnetic wave absorption layer can be brought closer to the dielectric constant of air, and the difference between the dielectric constant of the air layer and the dielectric constant of the surface portion of the electromagnetic wave absorption layer becomes smaller. Therefore, reflection of electromagnetic waves incident on the electromagnetic wave absorber can be further suppressed.
　更に、前記凹凸部の表面から内部に入るほど発泡層の発泡倍率が小さくなる、傾斜構造を有すると、電磁波の反射を抑制する効果がより大きくなる。 Further, if the foam layer has a sloped structure in which the foaming magnification of the foam layer decreases from the surface to the inside of the uneven portion, the effect of suppressing reflection of electromagnetic waves becomes greater.
　前記凹凸部の断面形状は、電磁波吸収性能を向上できれば特に限定されないが、特に矩形又は台形であることが好ましい。これにより、電磁波が凹凸部で反射したとしても、反射した電磁波が矩形又は台形の表面部で反射、吸収を繰り返し、反射した電磁波が再度電磁波吸収層に吸収される割合がより増加するため、電磁波の反射を更に抑制できる。 The cross-sectional shape of the uneven portion is not particularly limited as long as it can improve electromagnetic wave absorption performance, but it is particularly preferably rectangular or trapezoidal. As a result, even if the electromagnetic waves are reflected by the uneven surface, the reflected electromagnetic waves will be repeatedly reflected and absorbed by the rectangular or trapezoidal surface, and the proportion of the reflected electromagnetic waves being absorbed by the electromagnetic wave absorbing layer will increase. reflection can be further suppressed.
　また、前記凹凸部の断面形状は、略同一形状の矩形又は台形の繰り返しパターンで構成されていることが好ましい。これにより、上記凹凸部の全体における各凸部の高さ及び各凹部の幅が略均一となり、電磁波吸収層の全面において電磁波吸収特性を略均一にすることができる。ここで、「略同一形状」とは、上記凹凸部を構成する矩形又は台形の各凸部の高さ及び各凹部の幅の各値が、それぞれの各値の算術平均値に対して、±５％以内の範囲に入っていることを意味する。 Further, it is preferable that the cross-sectional shape of the uneven portion is configured in a repeating pattern of substantially the same rectangular or trapezoidal shape. As a result, the height of each convex portion and the width of each concave portion in the entire uneven portion become substantially uniform, and the electromagnetic wave absorption characteristics can be made substantially uniform over the entire surface of the electromagnetic wave absorbing layer. Here, "substantially the same shape" means that each value of the height of each rectangular or trapezoidal convex part and the width of each concave part constituting the above-mentioned uneven part is ± with respect to the arithmetic mean value of each value. This means that it is within 5%.
　本願の電磁波吸収体は、その用途に応じて、前記電磁波吸収層の、前記凹凸部を有さない面側に、金属からなる電磁波反射層を更に配置することができる。これにより、電磁波の透過を完全に無くした電磁波吸収体を提供できる。 In the electromagnetic wave absorber of the present application, an electromagnetic wave reflective layer made of metal can be further disposed on the side of the electromagnetic wave absorbing layer that does not have the uneven portion, depending on the use thereof. This makes it possible to provide an electromagnetic wave absorber that completely eliminates transmission of electromagnetic waves.
　以下、本願の電磁波吸収体の実施形態を図面に基づき説明する。図１は、本実施形態の電磁波吸収体の一例を示す斜視図である。図１において、本実施形態の電磁波吸収体１０は、凹部１１と凸部１２からなる凹凸部を、電磁波１３の入射面側に備えている。電磁波吸収体１０は、炭素材料からなる電磁波吸収材料と、バインダとを含む電磁波吸収シートを作製した後、成型金型でその表面に凹凸部を形成することができる。 Hereinafter, embodiments of the electromagnetic wave absorber of the present application will be described based on the drawings. FIG. 1 is a perspective view showing an example of an electromagnetic wave absorber according to this embodiment. In FIG. 1, the electromagnetic wave absorber 10 of this embodiment includes an uneven portion including a concave portion 11 and a convex portion 12 on the incident surface side of the electromagnetic wave 13. The electromagnetic wave absorber 10 can be produced by producing an electromagnetic wave absorbing sheet containing an electromagnetic wave absorbing material made of a carbon material and a binder, and then forming uneven portions on its surface using a molding die.
　図２は、図１の電磁波吸収体の側面図である。図２において、凹凸部の凹部１１の幅をＡとし、凸部１２の幅をＢとすると、Ａは６～３０ｍｍが好ましく、Ｂは６～３０ｍｍが好ましく、Ａ＋Ｂは１２～６０ｍｍが好ましい。更に、電磁波の最大吸収波長の長さに対して、Ａは０．５～５倍の長さであることが好ましく、Ｂは０．５～５倍の長さであることが好ましく、Ａ＋Ｂは１～１０倍の長さであることが好ましい。凹凸部の幅Ａと幅Ｂが上記範囲内であれば、準ミリ波からミリ波帯での電波吸収性をより向上できる。ここで、電磁波の最大吸収波長は、電磁波吸収体の用途により適宜選択できるが、通常２８～８０ＧＨｚの周波数帯域における電磁波の波長から適宜選択できる。 FIG. 2 is a side view of the electromagnetic wave absorber in FIG. 1. In FIG. 2, when the width of the concave portion 11 of the uneven portion is A and the width of the convex portion 12 is B, A is preferably 6 to 30 mm, B is preferably 6 to 30 mm, and A+B is preferably 12 to 60 mm. Furthermore, it is preferable that A is 0.5 to 5 times the length of the maximum absorption wavelength of electromagnetic waves, B is preferably 0.5 to 5 times the length, and A+B is Preferably, the length is 1 to 10 times longer. If the width A and the width B of the uneven portion are within the above range, the radio wave absorbability in the sub-millimeter wave to millimeter wave band can be further improved. Here, the maximum absorption wavelength of electromagnetic waves can be selected as appropriate depending on the use of the electromagnetic wave absorber, and can usually be selected from the wavelengths of electromagnetic waves in the frequency band of 28 to 80 GHz.
　また、図２において、凸部の高さをＣとし、基板部の厚さをＤとすると、凸部の高さＣは、２．７～４３ｍｍが好ましい。また、凸部の高さＣは、電磁波の最大吸波長の長さに対して、０．２５～４倍の長さであることが好ましい。この範囲であれば、凹凸部の底部表面や壁部表面で反射した電磁波が入射方向に戻る割合が減少し、反射した電磁波が反射を繰り返しながら再度電磁波吸収層に入射して吸収される割合が増加する。ここで、壁部表面とは、凹凸部の凸部表面と凹部表面とを結ぶ平面部をいう。 Further, in FIG. 2, when the height of the convex portion is C and the thickness of the substrate portion is D, the height C of the convex portion is preferably 2.7 to 43 mm. Further, the height C of the convex portion is preferably 0.25 to 4 times the length of the maximum absorption wavelength of electromagnetic waves. Within this range, the rate at which electromagnetic waves reflected from the bottom surface of the uneven portion or the wall surface return to the incident direction decreases, and the rate at which the reflected electromagnetic waves enter the electromagnetic wave absorption layer again while repeating reflection and are absorbed increases. To increase. Here, the wall surface refers to a flat surface that connects the convex surface and the concave surface of the concavo-convex portion.
　また、凸部の高さＣを上記のように電磁波の最大吸収波長の長さに対する倍数が０．２５から４の範囲とし、更に、基板部の厚さＤを電磁波の最大吸収波長の長さに対する倍数が０．１から４の範囲にすることが好ましい。この範囲であれば、電磁波の反射を抑制する効果が大きく、電磁波吸収体の強度と可撓性を実用レベルに維持できる。 In addition, the height C of the convex portion is set to be a multiple of 0.25 to 4 for the length of the maximum absorption wavelength of electromagnetic waves as described above, and the thickness D of the substrate portion is set to be the length of the maximum absorption wavelength of electromagnetic waves. It is preferable that the multiple is in the range of 0.1 to 4. Within this range, the effect of suppressing reflection of electromagnetic waves is large, and the strength and flexibility of the electromagnetic wave absorber can be maintained at a practical level.
　なお、凹凸部の凸部、凹部が曲面で形成されている場合は、凸部の最高点から凹部の最低点までの長さを凸部の高さＣとし、凹部の最低点から基板部の最低点までの長さを基板部の厚さＤとする。 In addition, when the convex part and the concave part of the uneven part are formed with curved surfaces, the length from the highest point of the convex part to the lowest point of the concave part is the height C of the convex part, and the length from the lowest point of the concave part to the lowest point of the concave part is Let the length to the lowest point be the thickness D of the substrate portion.
　図３は、本実施形態の電磁波吸収体の他の一例を示す模式断面図である。図３において、本実施形態の電磁波吸収体２０は、電磁波吸収層２０ａと、電磁波反射層２０ｂとを備えている。電磁波吸収層２０ａは、凹部２１と凸部２２からなる凹凸部を、電磁波２３の入射面側に備えている。電磁波吸収層２０ａは、炭素材料からなる電磁波吸収材料と、バインダとを含む電磁波吸収シートを作製した後、厚さが異なる２枚のシートに加工し、それぞれのシートを幅Ａと幅Ｂの長尺の角材状の電磁波吸収層に切断し、金属製の電磁波反射層２０ｂの上に、高さが異なる長角材（切断された電磁波吸収層）を交互に配置して、図３に示す凹凸部を有する電磁波吸収層２０ａを形成することができる。 FIG. 3 is a schematic cross-sectional view showing another example of the electromagnetic wave absorber of this embodiment. In FIG. 3, the electromagnetic wave absorber 20 of this embodiment includes an electromagnetic wave absorbing layer 20a and an electromagnetic wave reflecting layer 20b. The electromagnetic wave absorbing layer 20a has a concavo-convex portion consisting of a concave portion 21 and a convex portion 22 on the side of the electromagnetic wave 23 incident surface. The electromagnetic wave absorbing layer 20a is made by manufacturing an electromagnetic wave absorbing sheet containing an electromagnetic wave absorbing material made of a carbon material and a binder, and then processing it into two sheets with different thicknesses, and each sheet has a width A and a width B. The electromagnetic wave absorbing layer is cut into rectangular pieces, and the rectangular pieces (cut electromagnetic wave absorbing layer) having different heights are alternately arranged on the electromagnetic wave reflecting layer 20b made of metal to form the uneven portion shown in FIG. The electromagnetic wave absorbing layer 20a can be formed.
　図３において、凹凸部の凹部２１の幅をＡとし、凸部２２の幅をＢとすると、幅Ａと幅Ｂについては、図２で説明した長さ関係と同じ長さ関係が成立する。 In FIG. 3, if the width of the concave portion 21 of the uneven portion is A, and the width of the convex portion 22 is B, the same length relationship as that explained in FIG. 2 holds true for the widths A and B.
　電磁波反射層２０ｂは、金属板、金属箔、金属蒸着膜等から形成することができる。 The electromagnetic wave reflecting layer 20b can be formed from a metal plate, metal foil, metal vapor deposition film, or the like.
　次に、本実施形態の電磁波吸収体の電磁波吸収層を構成する各成分について説明する。 Next, each component constituting the electromagnetic wave absorbing layer of the electromagnetic wave absorber of this embodiment will be explained.
　＜電磁波吸収材料＞
　電磁波吸収層を構成する電磁波吸収材料は、ミリ波帯域以上の周波数帯域の電磁波を吸収できる炭素材料であり、具体的には、黒鉛；カーボンブラック（アセチレンブラック、ケッチェンブラック、チャンネルブラック、ファーネスブラック、ランプブラック、サーマルブラック等）；グラフェン；カーボンナノチューブ（シングルウォールカーボンナノチューブ、マルチウォールカーボンナノチューブ、分岐型カーボンナノチューブ、分岐型マルチウォールカーボンナノチューブ）；炭素繊維等が挙げられる。 <Electromagnetic wave absorbing material>
The electromagnetic wave absorbing material constituting the electromagnetic wave absorbing layer is a carbon material that can absorb electromagnetic waves in the frequency band of millimeter waves or higher, and specifically includes graphite; carbon black (acetylene black, Ketjen black, channel black, furnace black). , lamp black, thermal black, etc.); graphene; carbon nanotubes (single-wall carbon nanotubes, multi-wall carbon nanotubes, branched carbon nanotubes, branched multi-wall carbon nanotubes); carbon fibers, and the like.
　前記炭素材料は、カーボンナノチューブ及びカーボンブラックの少なくとも１種を含むことが好ましい。これらは少量の使用で、電磁波吸収層の電磁波吸収機能を発揮できる。カーボンナノチューブの中でも分岐を有するものが好ましく、特に、分岐型マルチウォールカーボンナノチューブ（カーボンナノストラクチャー）は、より少量の使用で、電磁波吸収層の電磁波吸収機能をより発揮できるのでより好ましい。 Preferably, the carbon material contains at least one of carbon nanotubes and carbon black. When these are used in small amounts, the electromagnetic wave absorption function of the electromagnetic wave absorption layer can be exhibited. Among carbon nanotubes, carbon nanotubes having branches are preferable, and branched multi-wall carbon nanotubes (carbon nanostructures) are particularly preferable because they can better exhibit the electromagnetic wave absorption function of the electromagnetic wave absorption layer when used in a smaller amount.
　前記炭素材料の含有割合は、後述するバインダ１００質量部に対して、０．０５～０．１０質量部であることが好ましい。前記炭素材料の含有割合が少なすぎると、電磁波吸収層の電磁波の吸収量が減少し、多すぎると電磁波吸収層での電磁波の反射が大きくなる。 The content ratio of the carbon material is preferably 0.05 to 0.10 parts by mass based on 100 parts by mass of the binder described below. If the content ratio of the carbon material is too small, the amount of electromagnetic waves absorbed by the electromagnetic wave absorption layer will decrease, and if it is too large, the electromagnetic wave reflection in the electromagnetic wave absorption layer will increase.
　＜バインダ＞
　前記バインダは、前述の電磁波吸収材料を分散して固定して、電磁波吸収層の発泡層を形成するマトリックス材として使用するものである。その電磁波吸収層を構成するバインダとしては、熱可塑性樹脂バインダ、熱硬化性樹脂バインダ、ゴム系バインダ等が使用できるが、ゴム系バインダを使用すると、電磁波吸収体全体に柔軟性を付与でき、電磁波吸収体を装着させる電子機器の表面形状に追従させることが容易となるため、上記バインダとしては、ゴム系バインダを使用することが好ましい。 <Binder>
The binder is used as a matrix material for dispersing and fixing the electromagnetic wave absorbing material described above and forming the foam layer of the electromagnetic wave absorbing layer. As the binder constituting the electromagnetic wave absorbing layer, thermoplastic resin binders, thermosetting resin binders, rubber binders, etc. can be used, but when a rubber binder is used, flexibility can be imparted to the entire electromagnetic wave absorber, and electromagnetic wave It is preferable to use a rubber-based binder as the binder because it makes it easy to follow the surface shape of the electronic device to which the absorber is attached.
　上記ゴム系バインダとしては、例えば、天然ゴム（ＮＲ）、イソプレンゴム（ＩＲ）、ブタジエンゴム（ＢＲ）、スチレン・ブタジエンゴム（ＳＢＲ）、ブチルゴム（ＩＩＲ）、ニトリルゴム（ＮＢＲ）、エチレン・プロピレンゴム（ＥＰＤＭ）、クロロプレンゴム（ＣＲ）、アクリルゴム（ＡＣＭ）、クロロスルホン化ポリエチレンゴム（ＣＳＲ）、ウレタンゴム（ＰＵＲ）、シリコーンゴム（Ｑ）、フッ素ゴム（ＦＫＭ）、エチレン・酢酸ビニルゴム（ＥＶＡ）、エピクロルヒドリンゴム（ＣＯ）、及び多硫化ゴム（Ｔ）からなる群から選ばれる少なくとも１種を使用できる。 Examples of the rubber binder include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), nitrile rubber (NBR), and ethylene-propylene rubber. (EPDM), chloroprene rubber (CR), acrylic rubber (ACM), chlorosulfonated polyethylene rubber (CSR), urethane rubber (PUR), silicone rubber (Q), fluororubber (FKM), ethylene/vinyl acetate rubber (EVA) At least one selected from the group consisting of , epichlorohydrin rubber (CO), and polysulfide rubber (T) can be used.
　電磁波吸収体の強度を向上させるためには、上記ゴム系バインダの中で、特にシリコーンゴム（Ｑ）及びフッ素ゴム（ＦＫＭ）が好ましい。シリコーンゴムとしては、付加反応型、縮合反応型、過酸化物硬化型のいずれでも用いることができる。しかし、架橋密度を制御し、任意の硬度を得ることができる点で、過酸化物硬化型シリコーンゴムが好ましい。 In order to improve the strength of the electromagnetic wave absorber, silicone rubber (Q) and fluororubber (FKM) are particularly preferred among the above rubber binders. As the silicone rubber, any of addition reaction type, condensation reaction type, and peroxide curing type can be used. However, peroxide-curable silicone rubber is preferable because it can control the crosslink density and obtain any desired hardness.
　次に、本実施形態の電磁波吸収体の製造方法の一例について説明する。先ず、前述の電磁波吸収材料、バインダ、及び発泡剤、増粘剤、加硫剤、離型剤等の電磁波吸収層形成成分をニーダで混練した後、その混練物をカレンダ成形法により分出して、電磁波吸収層前駆体を作製する。次に、作製した電磁波吸収層前駆体を架橋工程及び加硫工程を経て、シートに切断し、成型ロールを通して片側表面に凹凸部を形成して電磁波吸収層を作製し、例えば、図１及び図２に示す電磁波吸収体を得ることができる。 Next, an example of a method for manufacturing the electromagnetic wave absorber of this embodiment will be described. First, the above-mentioned electromagnetic wave absorbing material, binder, and components for forming an electromagnetic wave absorbing layer such as a blowing agent, a thickener, a vulcanizing agent, and a mold release agent are kneaded in a kneader, and then the kneaded product is separated by a calender molding method. , producing an electromagnetic wave absorbing layer precursor. Next, the produced electromagnetic wave absorption layer precursor is subjected to a crosslinking process and a vulcanization process, and then cut into sheets, and passed through a forming roll to form an uneven part on one side surface to produce an electromagnetic wave absorption layer. The electromagnetic wave absorber shown in 2 can be obtained.
　また、上記のようにして、厚さが異なる２種類の電磁波吸収層前駆体を作製し、作製したそれぞれの電磁波吸収層前駆体を架橋工程及び加硫工程を経て、厚さが異なるそれぞれの電磁波吸収層を作製し、それぞれの電磁波吸収層を長尺の角材状の電磁波吸収層に切断し、金属製の電磁波反射層の上に、高さが異なる長角材（切断された電磁波吸収層）を交互に配置すれば、例えば、図３に示す電磁波吸収体を得ることができる。 In addition, two types of electromagnetic wave absorbing layer precursors with different thicknesses were prepared as described above, and each of the prepared electromagnetic wave absorbing layer precursors was subjected to a crosslinking process and a vulcanization process to form electromagnetic wave absorbers with different thicknesses. Fabricate the absorbing layer, cut each electromagnetic wave absorbing layer into long rectangular electromagnetic wave absorbing layers, and place the long rectangular pieces (cut electromagnetic wave absorbing layers) with different heights on top of the metal electromagnetic wave reflecting layer. If they are arranged alternately, for example, the electromagnetic wave absorber shown in FIG. 3 can be obtained.
　次に、本実施形態の電磁波吸収体の特性について説明する。 Next, the characteristics of the electromagnetic wave absorber of this embodiment will be explained.
　＜電磁波反射減衰量及び電磁波透過減衰量＞
　本実施形態の電磁波吸収体の電磁波反射減衰量及び電磁波透過減衰量は、２８～８０ＧＨｚの周波数帯域において、電磁波反射減衰量が－１０ｄＢ以下で、電磁波透過減衰量が－１０ｄＢ以下とすることができる。上記減衰量が－１０ｄＢ以下とは、入射した電磁波の１０％以下が反射又は透過することを意味する。 <Electromagnetic wave return loss and electromagnetic wave transmission loss>
The electromagnetic wave return attenuation and electromagnetic wave transmission attenuation of the electromagnetic wave absorber of this embodiment can be such that the electromagnetic wave return attenuation is -10 dB or less and the electromagnetic wave transmission attenuation is -10 dB or less in the frequency band of 28 to 80 GHz. . The above-mentioned attenuation amount of -10 dB or less means that 10% or less of the incident electromagnetic wave is reflected or transmitted.
　本実施形態の電磁波吸収体の電磁波反射減衰量及び電磁波透過減衰量は、下記のフリースペース法を用いて測定できる。 The electromagnetic wave return attenuation and electromagnetic wave transmission attenuation of the electromagnetic wave absorber of this embodiment can be measured using the free space method described below.
　例えば、図１及び図２に示した電磁波吸収体１０を用いる場合は、図４に示すように、アンリツ株式会社製のベクトルネットワークアナライザ〔“ＭＳ４６５２２Ｂ”（７６．５ＧＨｚ）、“ＭＳ４６１２２Ｂ－０４３”（２８ＧＨｚ）〕３０を用いて、第１のポート３０ａに接続したアンテナ３１から誘電体レンズ３３を介して電磁波吸収体１０の凹凸部側に所定の入力電磁波（ミリ波）３４を照射し、電磁波吸収層の凹凸部で反射する電磁波３５を、電磁波吸収体１０の凹凸部側に配置されたアンテナ３１で計測する。また、電磁波吸収体１０を透過する電磁波３６は、電磁波吸収体１０の裏面側に配置され、第２のポート３０ｂに接続されたアンテナ３２で計測する。照射される電磁波３４の強度と、反射した電磁波３５及び透過した電磁波３６の強度とをそれぞれ電力値として把握し、その強度差から電磁波反射減衰量及び電磁波透過減衰量をｄＢ単位で求める。 For example, when using the electromagnetic wave absorber 10 shown in FIGS. 1 and 2, as shown in FIG. 28 GHz)] 30, a predetermined input electromagnetic wave (millimeter wave) 34 is irradiated from the antenna 31 connected to the first port 30a to the uneven portion side of the electromagnetic wave absorber 10 via the dielectric lens 33, and the electromagnetic wave is absorbed. Electromagnetic waves 35 reflected by the uneven portions of the layer are measured by an antenna 31 disposed on the uneven portion side of the electromagnetic wave absorber 10. Furthermore, the electromagnetic wave 36 that passes through the electromagnetic wave absorber 10 is measured by an antenna 32 that is arranged on the back side of the electromagnetic wave absorber 10 and connected to the second port 30b. The intensity of the irradiated electromagnetic waves 34, the reflected electromagnetic waves 35, and the transmitted electromagnetic waves 36 are determined as power values, and the electromagnetic wave return attenuation and electromagnetic wave transmission attenuation are determined in dB from the intensity difference.
　また、図３に示した電磁波吸収体２０を用いる場合は、図５に示すように、アンリツ株式会社製のベクトルネットワークアナライザ〔“ＭＳ４６５２２Ｂ”（７６．５ＧＨｚ）、“ＭＳ４６１２２Ｂ－０４３”（２８ＧＨｚ）〕３０を用いて、第１のポート３０ａに接続したアンテナ３１から誘電体レンズ３３を介して電磁波吸収体２０の凹凸部側に所定の入力電磁波（ミリ波）３４を照射し、電磁波吸収層の凹凸部及び電磁波反射層２０ｂで反射する電磁波３５を、電磁波吸収体２０の凹凸部側に配置されたアンテナ３１で計測する。照射される電磁波３４の強度と、反射した電磁波３５の強度とをそれぞれ電力値として把握し、その強度差から電磁波反射減衰量をｄＢ単位で求める。 In addition, when using the electromagnetic wave absorber 20 shown in FIG. 3, as shown in FIG. 30, a predetermined input electromagnetic wave (millimeter wave) 34 is irradiated from the antenna 31 connected to the first port 30a to the uneven portion side of the electromagnetic wave absorber 20 through the dielectric lens 33, and the unevenness of the electromagnetic wave absorbing layer is The electromagnetic waves 35 reflected by the electromagnetic wave absorber 20 and the electromagnetic wave reflecting layer 20b are measured by an antenna 31 disposed on the uneven portion side of the electromagnetic wave absorber 20. The intensity of the irradiated electromagnetic wave 34 and the intensity of the reflected electromagnetic wave 35 are determined as power values, and the electromagnetic wave return attenuation is determined in dB from the difference in intensity.
　以下、実施例に基づいて本願を詳細に説明する。但し、本願は以下の実施例に限定されるものではない。 Hereinafter, the present application will be explained in detail based on Examples. However, the present application is not limited to the following examples.
　（実施例１）
　＜電磁波吸収体の作製＞
　下記の電磁波吸収層成分をニーダで混練した後、その混練物をカレンダ成形法により分出し、厚さが異なる２種類の電磁波吸収層前駆体を作製し、作製したそれぞれの電磁波吸収層前駆体を、架橋温度１７０℃で１時間の架橋工程及び加硫工程を経て、厚さが異なるそれぞれの電磁波吸収層を作製した。作製後の電磁波吸収層は、表面部を除いて発泡層で形成されているが、表面部には非発泡層（スキン層）が形成されている。その後、作製した電磁波吸収層の両面に形成したスキン層を除去し、表面部にも発泡層を有する厚さが異なるそれぞれの電磁波吸収層を長尺の角材状の電磁波吸収層に切断し、高さが異なる長角材（切断された電磁波吸収層）を発泡層側が上面となるように交互に接着して配置して、電磁波吸収層のみからなり、凹凸部の凸部の表面部及び凹部の表面部にも発泡層を有する実施例１の電磁波吸収体（１－１）を作製した。 (Example 1)
<Production of electromagnetic wave absorber>
After kneading the following components of the electromagnetic wave absorbing layer in a kneader, the kneaded product was separated by a calender molding method to produce two types of electromagnetic wave absorbing layer precursors with different thicknesses. Through a crosslinking process and a vulcanization process at a crosslinking temperature of 170° C. for 1 hour, electromagnetic wave absorbing layers having different thicknesses were produced. The produced electromagnetic wave absorbing layer is formed of a foamed layer except for the surface portion, but a non-foamed layer (skin layer) is formed on the surface portion. After that, the skin layers formed on both sides of the produced electromagnetic wave absorbing layer were removed, and each electromagnetic wave absorbing layer having a foam layer on the surface and having different thicknesses was cut into long, square pieces of electromagnetic wave absorbing layer. Long rectangular pieces (cut electromagnetic wave absorbing layers) of different lengths are glued and arranged alternately so that the foam layer side is the top surface, and the electromagnetic wave absorbing layer is made only of the convex and concave surfaces of the uneven parts. An electromagnetic wave absorber (1-1) of Example 1 having a foam layer also on the surface was prepared.
　次に、電磁波吸収体（１－１）を更に金属板の上に配置して、図３に示すように、電磁波吸収層と金属板とからなり、凹凸部の凸部の表面及び凹部の表面にも発泡層を有する実施例１の電磁波吸収体（１－２）を作製した。 Next, the electromagnetic wave absorber (1-1) is further placed on the metal plate, and as shown in FIG. An electromagnetic wave absorber (1-2) of Example 1 having a foam layer was also produced.
　作製した電磁波吸収体の電磁波吸収層の厚さは２０ｍｍ（凸部の高さ：１０ｍｍ、基板部の厚さ：１０ｍｍ）、金属板の厚さは５ｍｍとした。また、実施例１の電磁波吸収体において、図３に示す凹凸部の幅Ａを２ｍｍ、幅Ｂを２ｍｍに設定した。 The thickness of the electromagnetic wave absorption layer of the produced electromagnetic wave absorber was 20 mm (height of the convex portion: 10 mm, thickness of the substrate portion: 10 mm), and the thickness of the metal plate was 5 mm. Further, in the electromagnetic wave absorber of Example 1, the width A of the uneven portion shown in FIG. 3 was set to 2 mm, and the width B was set to 2 mm.
　［電磁波吸収層成分］
（１）ゴム系バインダ：シリコーンゴム（信越化学工業株式会社製、商品名“ＫＥ－９５１ＫＵ”、シリカ粒子含有量：１０質量％）：１００質量部
（２）色剤粉：三酸化二鉄（III）（信越化学工業株式会社製、商品名“ＫＥカラーＢＲ－Ｓ”）：１質量部
（３）発泡剤：アゾビスイソブチロニトリル（株式会社竹原ゴム加工製、商品名“ＴＲマスターＡＩＢＮ５０Ｑ”）：５質量部
（４）増粘剤：ベンゾイルパーオキサイド（信越化学工業株式会社製、商品名“Ｃ－１Ａ”）：０．２質量部
（５）加硫剤：ジクミルパーオキサイド（信越化学工業株式会社製、商品名“Ｃ－３”）：２．５質量部
（６）離型剤：変性オルガノポリシロキサン（信越化学工業株式会社製、商品名“ＴＡ－５”）：０．０５質量部
（７）電磁波吸収材料：カーボンナノストラクチャー（キャボットコーポレーション製、商品名“ＡＴＨＬＯＳＳＲ１２００”）：０．０７質量部 [Electromagnetic wave absorption layer component]
(1) Rubber binder: Silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KE-951KU", silica particle content: 10% by mass): 100 parts by mass (2) Colorant powder: diiron trioxide ( III) (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KE Color BR-S"): 1 part by mass (3) Foaming agent: azobisisobutyronitrile (manufactured by Takehara Rubber Co., Ltd., product name "TR Master AIBN50Q") ”): 5 parts by mass (4) Thickener: benzoyl peroxide (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “C-1A”): 0.2 parts by mass (5) Vulcanizing agent: dicumyl peroxide ( Shin-Etsu Chemical Co., Ltd., trade name "C-3"): 2.5 parts by mass (6) Mold release agent: Modified organopolysiloxane (Shin-Etsu Chemical Co., Ltd., trade name "TA-5"): 0 .05 parts by mass (7) Electromagnetic wave absorbing material: Carbon nanostructure (manufactured by Cabot Corporation, trade name "ATHLOSSR1200"): 0.07 parts by mass
　（実施例２）
　電磁波吸収層の凹凸部の幅Ａを４ｍｍ、幅Ｂを４ｍｍに設定した以外は、実施例１と同様にして、実施例２の電磁波吸収層のみからなる電磁波吸収体（２－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（２－２）を作製した。 (Example 2)
The electromagnetic wave absorber (2-1) consisting of only the electromagnetic wave absorbing layer of Example 2 and the electromagnetic wave absorber (2-1) made of only the electromagnetic wave absorbing layer of Example 2 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 4 mm and the width B was set to 4 mm. An electromagnetic wave absorber (2-2) consisting of an absorption layer and a metal plate was produced.
　（実施例３）
　電磁波吸収層の凹凸部の幅Ａを６ｍｍ、幅Ｂを６ｍｍに設定した以外は、実施例１と同様にして、実施例３の電磁波吸収層のみからなる電磁波吸収体（３－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（３－２）を作製した。 (Example 3)
The electromagnetic wave absorber (3-1) consisting only of the electromagnetic wave absorbing layer of Example 3 and the electromagnetic wave absorber (3-1) made of only the electromagnetic wave absorbing layer of Example 3 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 6 mm and the width B was set to 6 mm. An electromagnetic wave absorber (3-2) consisting of an absorption layer and a metal plate was produced.
　（実施例４）
　電磁波吸収層の凹凸部の幅Ａを１０ｍｍ、幅Ｂを１０ｍｍに設定した以外は、実施例１と同様にして、実施例４の電磁波吸収層のみからなる電磁波吸収体（４－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（４－２）を作製した。 (Example 4)
The electromagnetic wave absorber (4-1) consisting of only the electromagnetic wave absorbing layer of Example 4 and the electromagnetic wave absorber (4-1) made of only the electromagnetic wave absorbing layer of Example 4 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 10 mm and the width B was set to 10 mm. An electromagnetic wave absorber (4-2) consisting of an absorption layer and a metal plate was produced.
　（実施例５）
　電磁波吸収層の凹凸部の幅Ａを３０ｍｍ、幅Ｂを３０ｍｍに設定した以外は、実施例１と同様にして、実施例５の電磁波吸収層のみからなる電磁波吸収体（５－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（５－２）を作製した。 (Example 5)
The electromagnetic wave absorber (5-1) consisting of only the electromagnetic wave absorbing layer of Example 5 and the electromagnetic wave absorber (5-1) made of only the electromagnetic wave absorbing layer of Example 5 were prepared in the same manner as in Example 1, except that the width A of the uneven portion of the electromagnetic wave absorbing layer was set to 30 mm and the width B was set to 30 mm. An electromagnetic wave absorber (5-2) consisting of an absorption layer and a metal plate was produced.
　（実施例６）
　電磁波吸収層のみからなり、凹凸部の凸部の表面部に発泡層を有し、凹部の表面部に発泡層を有さないこと以外は、実施例４と同様にして、実施例６の電磁波吸収体（６－１）を作製した。 (Example 6)
The electromagnetic wave of Example 6 was prepared in the same manner as in Example 4, except that it consisted only of an electromagnetic wave absorbing layer, had a foam layer on the surface of the convex part of the uneven part, and did not have a foam layer on the surface of the concave part. An absorber (6-1) was produced.
　また、電磁波吸収層と金属板とからなり、凹凸部の凸部の表面部に発泡層を有し、凹部の表面部に発泡層を有さないこと以外は、実施例４と同様にして、実施例６の電磁波吸収体（６－２）を作製した。 In addition, it was made of an electromagnetic wave absorbing layer and a metal plate, and had a foam layer on the surface of the convex part of the uneven part, and did not have a foam layer on the surface of the concave part, but in the same manner as in Example 4, An electromagnetic wave absorber (6-2) of Example 6 was produced.
　（実施例７）
　電磁波吸収層のみからなり、凹凸部の凸部及び凹部のいずれの表面部にも発泡層を有さないこと以外は、実施例４と同様にして、実施例７の電磁波吸収体（７－１）を作製した。 (Example 7)
The electromagnetic wave absorber of Example 7 (7-1 ) was created.
　また、電磁波吸収層と金属板とからなり、凹凸部の凸部及び凹部のいずれの表面部にも発泡層を有さないこと以外は、実施例４と同様にして、実施例７の電磁波吸収体（７－２）を作製した。 In addition, the electromagnetic wave absorbing layer of Example 7 was prepared in the same manner as in Example 4, except that it consisted of an electromagnetic wave absorbing layer and a metal plate and did not have a foam layer on either the surface of the convex or concave portions of the uneven portion. A body (7-2) was produced.
　（実施例８）
　電磁波吸収層成分の電磁波吸収材料（カーボンナノストラクチャー）の含有量を０．０３質量部に変更したこと以外は、実施例４と同様にして、実施例８の電磁波吸収層のみからなる電磁波吸収体（８－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（８－２）を作製した。 (Example 8)
An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 8 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.03 parts by mass. (8-1) and an electromagnetic wave absorber (8-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
　（実施例９）
　電磁波吸収層成分の電磁波吸収材料（カーボンナノストラクチャー）の含有量を０．０５質量部に変更したこと以外は、実施例４と同様にして、実施例９の電磁波吸収層のみからなる電磁波吸収体（９－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（９－２）を作製した。 (Example 9)
An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 9 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.05 part by mass. (9-1) and an electromagnetic wave absorber (9-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
　（実施例１０）
　電磁波吸収層成分の電磁波吸収材料（カーボンナノストラクチャー）の含有量を０．１０質量部に変更したこと以外は、実施例４と同様にして、実施例１０の電磁波吸収層のみからなる電磁波吸収体（１０－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（１０－２）を作製した。 (Example 10)
An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 10 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.10 parts by mass. (10-1) and an electromagnetic wave absorber (10-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
　（実施例１１）
　電磁波吸収層成分の電磁波吸収材料（カーボンナノストラクチャー）の含有量を０．１３質量部に変更したこと以外は、実施例４と同様にして、実施例１１の電磁波吸収層のみからなる電磁波吸収体（１１－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（１１－２）を作製した。 (Example 11)
An electromagnetic wave absorber consisting only of the electromagnetic wave absorbing layer of Example 11 was prepared in the same manner as in Example 4, except that the content of the electromagnetic wave absorbing material (carbon nanostructure) of the electromagnetic wave absorbing layer component was changed to 0.13 parts by mass. (11-1) and an electromagnetic wave absorber (11-2) consisting of an electromagnetic wave absorbing layer and a metal plate were produced.
　（実施例１２）
　電磁波吸収層成分の電磁波吸収材料及びその含有量を、マルチウォールカーボンナノチューブ（Ｈａｎｗｈａ　Ｃｈｅｍｉｃａｌ　Ｃｏｒｐｏｒａｔｉｏｎ製、商品名“ＣＭ－１３０”）：１．５０質量部に変更したこと以外は、実施例４と同様にして、実施例１２の電磁波吸収層のみからなる電磁波吸収体（１２－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（１２－２）を作製した。 (Example 12)
Same as Example 4 except that the electromagnetic wave absorbing material of the electromagnetic wave absorbing layer component and its content were changed to 1.50 parts by mass of multi-wall carbon nanotubes (manufactured by Hanwha Chemical Corporation, trade name "CM-130"). Thus, an electromagnetic wave absorber (12-1) consisting of only the electromagnetic wave absorbing layer of Example 12 and an electromagnetic wave absorber (12-2) consisting of the electromagnetic wave absorbing layer and a metal plate were produced.
　（実施例１３）
　電磁波吸収層成分の電磁波吸収材料及びその含有量を、カーボンブラック（ライオンスペシャリティケミカルズ製、商品名“ライオナイトＣＢ”）：６．５０質量部に変更したこと以外は、実施例４と同様にして、実施例１３の電磁波吸収層のみからなる電磁波吸収体（１３－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（１３－２）を作製した。 (Example 13)
Example 4 was carried out in the same manner as in Example 4, except that the electromagnetic wave absorbing material of the electromagnetic wave absorbing layer component and its content were changed to 6.50 parts by mass of carbon black (manufactured by Lion Specialty Chemicals, trade name "Lionite CB"). An electromagnetic wave absorber (13-1) consisting of only the electromagnetic wave absorbing layer of Example 13 and an electromagnetic wave absorber (13-2) consisting of the electromagnetic wave absorbing layer and a metal plate were prepared.
　（比較例１）
　電磁波吸収層のみからなり、凹凸部を有さず、表面に発泡層を有すること以外は、実施例１と同様にして、比較例１の電磁波吸収体（１－１）を作製した。 (Comparative example 1)
An electromagnetic wave absorber (1-1) of Comparative Example 1 was produced in the same manner as in Example 1, except that it consisted only of an electromagnetic wave absorbing layer, had no uneven parts, and had a foam layer on the surface.
　また、電磁波吸収層と金属板とからなり、凹凸部を有さず、表面に発泡層を有すること以外は、実施例１と同様にして、比較例１の電磁波吸収体（１－２）を作製した。 Further, the electromagnetic wave absorber (1-2) of Comparative Example 1 was prepared in the same manner as in Example 1, except that it consisted of an electromagnetic wave absorbing layer and a metal plate, had no uneven parts, and had a foam layer on the surface. Created.
　（比較例２）
　電磁波吸収層成分から発泡剤を除いたこと以外は、実施例４と同様にして、比較例２の電磁波吸収層のみからなる電磁波吸収体（２－１）及び電磁波吸収層と金属板とからなる電磁波吸収体（２－２）を作製した。電磁波吸収体（２－１）及び（２－２）の電磁波吸収層は、凹凸部を有するが、全体に発泡層を有しないものである。 (Comparative example 2)
An electromagnetic wave absorber (2-1) consisting of only the electromagnetic wave absorbing layer of Comparative Example 2 and an electromagnetic wave absorbing layer and a metal plate were prepared in the same manner as in Example 4, except that the foaming agent was removed from the electromagnetic wave absorbing layer components. An electromagnetic wave absorber (2-2) was produced. The electromagnetic wave absorbing layers of the electromagnetic wave absorbers (2-1) and (2-2) have uneven portions, but do not have a foam layer throughout.
　次に、実施例１～１３及び比較例１～２で作製した電磁波吸収体の下記特性を測定した。 Next, the following characteristics of the electromagnetic wave absorbers produced in Examples 1 to 13 and Comparative Examples 1 to 2 were measured.
　＜電磁波反射減衰量及び電磁波透過減衰量＞
　電磁波反射減衰量及び電磁波透過減衰量は、前述のフリースペース法を用いて測定した。具体的には、所定の周波数の電磁波を電磁波吸収体に照射し、金属板を有しない電磁波吸収体は図４に示すように測定し、金属板を有する電磁波吸収体は図５に示すように測定した。 <Electromagnetic wave return loss and electromagnetic wave transmission loss>
The electromagnetic wave return loss and electromagnetic wave transmission attenuation were measured using the free space method described above. Specifically, an electromagnetic wave absorber is irradiated with electromagnetic waves of a predetermined frequency, and the electromagnetic wave absorber without a metal plate is measured as shown in Figure 4, and the electromagnetic wave absorber with a metal plate is measured as shown in Figure 5. It was measured.
　表１には、各電磁波吸収体の構成を示し、表２には、照射した電磁波の周波数、照射した電磁波の波長に対する幅Ａ及び幅Ｂの倍数、電磁波反射減衰量及び電磁波透過減衰量を示す。 Table 1 shows the configuration of each electromagnetic wave absorber, and Table 2 shows the frequency of the irradiated electromagnetic wave, the multiple of width A and width B with respect to the wavelength of the irradiated electromagnetic wave, the electromagnetic wave return loss, and the electromagnetic wave transmission attenuation. .
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２から、実施例１～１３の電磁波吸収体では、電磁波反射減衰量を－１０ｄＢ以下に抑えることができた。特に、金属板を備えた電磁波吸収体では、実施例７を除き、電磁波反射減衰量を－１４ｄＢ以下に抑えることができた。一方、比較例１及び２の電磁波吸収体では、金属板無し、金属板有り共に電磁波反射減衰量が－１０ｄＢを上回り、電磁波吸収体の表面での電磁波の反射がいずれの実施例よりも大きくなった。 From Table 2, the electromagnetic wave absorbers of Examples 1 to 13 were able to suppress the electromagnetic wave return loss to −10 dB or less. In particular, in the electromagnetic wave absorbers including metal plates, except for Example 7, the electromagnetic wave return loss could be suppressed to -14 dB or less. On the other hand, in the electromagnetic wave absorbers of Comparative Examples 1 and 2, the electromagnetic wave return loss exceeds -10 dB both with and without the metal plate, and the reflection of electromagnetic waves on the surface of the electromagnetic wave absorber is greater than in any of the examples. Ta.
　本願は、上記以外の形態としても実施が可能である。本願に開示された実施形態は一例であって、これらに限定はされない。本願の範囲は、上述の明細書の記載よりも、添付されている請求の範囲の記載を優先して解釈され、請求の範囲と均等の範囲内での全ての変更は、請求の範囲に含まれるものである。 The present application can be implemented in forms other than those described above. The embodiments disclosed in this application are merely examples, and the present invention is not limited thereto. The scope of this application shall be interpreted with priority given to the description of the attached claims rather than the description of the above-mentioned specification, and all changes within the scope of equivalency to the claims are included within the scope of the claims. It is something that can be done.
　本願の電磁波吸収体は、ミリ波帯域以上の高い周波数帯域の電磁波を吸収できると共に、電磁波の反射を抑制できる電磁波吸収体を提供することができ、ＥＭＣに優れた電子部品及び電子機器を作製するのに有用である。 The electromagnetic wave absorber of the present application can provide an electromagnetic wave absorber that can absorb electromagnetic waves in a high frequency band higher than the millimeter wave band and can suppress reflection of electromagnetic waves, and can produce electronic components and devices with excellent EMC. It is useful for
　１０、２０　電磁波吸収体
　２０ａ　電磁波吸収層
　２０ｂ　電磁波反射層
　１１、２１　凹部
　１２、２２　凸部
　１３、２３　電磁波
　３０　ベクトルネットワークアナライザ
　３０ａ　第１のポート
　３０ｂ　第２のポート
　３１、３２　アンテナ
　３３　誘電体レンズ
　３４　入力電磁波
　３５　反射電磁波
　３６　透過電磁波 10, 20 Electromagnetic wave absorber 20a Electromagnetic wave absorbing layer 20b Electromagnetic wave reflecting layer 11, 21 Concave portion 12, 22 Convex portion 13, 23 Electromagnetic wave 30 Vector network analyzer 30a First port 30b Second port 31, 32 Antenna 33 Dielectric lens 34 Input electromagnetic wave 35 Reflected electromagnetic wave 36 Transmitted electromagnetic wave

Claims (15)

  1. 　電磁波吸収層を含む電磁波吸収体であって、
    　前記電磁波吸収層は、炭素材料からなる電磁波吸収材料と、バインダとを含み、
    　前記電磁波吸収層は、発泡層を含み、
    　前記電磁波吸収層の少なくとも一方の主面に、凹凸部を有することを特徴とする電磁波吸収体。     An electromagnetic wave absorber including an electromagnetic wave absorbing layer,
    The electromagnetic wave absorbing layer includes an electromagnetic wave absorbing material made of a carbon material and a binder,
    The electromagnetic wave absorbing layer includes a foam layer,
    An electromagnetic wave absorber characterized in that the electromagnetic wave absorbing layer has an uneven portion on at least one main surface.
  2. 　前記炭素材料は、カーボンナノチューブ及びカーボンブラックの少なくとも１種を含む請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the carbon material includes at least one of carbon nanotubes and carbon black.
  3. 　前記カーボンナノチューブが、分岐を有する請求項２に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 2, wherein the carbon nanotube has branches.
  4. 　前記炭素材料の含有割合が、前記バインダ１００質量部に対して、０．０５～０．１０質量部である請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the content ratio of the carbon material is 0.05 to 0.10 parts by mass based on 100 parts by mass of the binder.
  5. 　前記電磁波吸収層は、前記凹凸部の凸部の表面部及び凹部の表面部にそれぞれ発泡層を有する請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorbing layer has foam layers on the surface portions of the convex portions and the surface portions of the concave portions of the uneven portion, respectively.
  6. 　前記電磁波吸収層は、前記凹凸部の凸部の表面部に発泡層を有する請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorbing layer has a foam layer on the surface of the convex portion of the uneven portion.
  7. 　前記電磁波吸収層は、前記凹凸部の凹部の表面部に発泡層を有する請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorbing layer has a foam layer on the surface of the concave portion of the uneven portion.
  8. 　前記凹凸部の凸部の高さが、電磁波の最大吸収波長の長さに対して０．２５～４倍の長さである請求項１～７のいずれか１項に記載の電磁波吸収体。 The electromagnetic wave absorber according to any one of claims 1 to 7, wherein the height of the convex portion of the uneven portion is 0.25 to 4 times the length of the maximum absorption wavelength of the electromagnetic wave.
  9. 　前記凹凸部の凸部の高さが、２．７～４３ｍｍである請求項１～７のいずれか１項に記載の電磁波吸収体。 The electromagnetic wave absorber according to any one of claims 1 to 7, wherein the height of the convex portion of the uneven portion is 2.7 to 43 mm.
  10. 　前記凹凸部の凹部の幅が、電磁波の最大吸収波長の長さに対して０．５～５倍の長さであり、前記凹凸部の凸部の幅が、電磁波の最大吸収波長の長さに対して０．５～５倍の長さである請求項１～７のいずれか１項に記載の電磁波吸収体。 The width of the concave portion of the uneven portion is 0.5 to 5 times the length of the maximum absorption wavelength of the electromagnetic wave, and the width of the convex portion of the uneven portion is the length of the maximum absorption wavelength of the electromagnetic wave. The electromagnetic wave absorber according to any one of claims 1 to 7, which has a length of 0.5 to 5 times that of the electromagnetic wave absorber.
  11. 　前記凹凸部の凹部の幅が、６～３０ｍｍであり、前記凹凸部の凸部の幅が、６～３０ｍｍである請求項１～７のいずれか１項に記載の電磁波吸収体。 The electromagnetic wave absorber according to any one of claims 1 to 7, wherein the width of the concave portion of the uneven portion is 6 to 30 mm, and the width of the convex portion of the uneven portion is 6 to 30 mm.
  12. 　前記凹凸部の断面形状が、略同一形状の矩形又は台形の繰り返しパターンで構成されている請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the cross-sectional shape of the uneven portion is comprised of a repeating pattern of substantially the same rectangular or trapezoidal shape.
  13. 　前記バインダが、ゴム系バインダである請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the binder is a rubber-based binder.
  14. 　前記凹凸部の断面形状が、矩形又は台形である請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the cross-sectional shape of the uneven portion is rectangular or trapezoidal.
  15. 　前記電磁波吸収層は、一方の主面にのみ前記凹凸部を有し、前記凹凸部を有さない主面側に、金属からなる電磁波反射層を更に含む請求項１に記載の電磁波吸収体。 The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorbing layer has the uneven portion only on one main surface, and further includes an electromagnetic wave reflecting layer made of metal on the main surface side not having the uneven portion.
PCT/JP2023/025939 2022-07-20 2023-07-13 Electromagnetic wave absorber WO2024018995A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006112001A1 (en) * 2005-04-12 2006-10-26 Ubiquitous Environment Company All-weather radio wave reflector/absorber and its assembling structure
JP2013072786A (en) * 2011-09-28 2013-04-22 Denso Corp Electromagnetic testing apparatus
US20150360427A1 (en) * 2014-06-11 2015-12-17 Applied Nanostructured Solutions, Llc Methods for processing three-dimensional printed objects using microwave radiation

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006112001A1 (en) * 2005-04-12 2006-10-26 Ubiquitous Environment Company All-weather radio wave reflector/absorber and its assembling structure
JP2013072786A (en) * 2011-09-28 2013-04-22 Denso Corp Electromagnetic testing apparatus
US20150360427A1 (en) * 2014-06-11 2015-12-17 Applied Nanostructured Solutions, Llc Methods for processing three-dimensional printed objects using microwave radiation

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