WO2024122588A1 - ABSORBEUR D'ONDES RADIO DE TYPE λ/4 ET FILM POUR ABSORBEUR D'ONDES RADIO DE TYPE λ/4 - Google Patents

ABSORBEUR D'ONDES RADIO DE TYPE λ/4 ET FILM POUR ABSORBEUR D'ONDES RADIO DE TYPE λ/4 Download PDF

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WO2024122588A1
WO2024122588A1 PCT/JP2023/043684 JP2023043684W WO2024122588A1 WO 2024122588 A1 WO2024122588 A1 WO 2024122588A1 JP 2023043684 W JP2023043684 W JP 2023043684W WO 2024122588 A1 WO2024122588 A1 WO 2024122588A1
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layer
radio wave
wave absorber
polymer
dielectric layer
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PCT/JP2023/043684
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English (en)
Japanese (ja)
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博道 加茂
正行 森野
和彦 庭野
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Ａｇｃ株式会社
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Publication of WO2024122588A1 publication Critical patent/WO2024122588A1/fr

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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
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
    • 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

  • This disclosure relates to a ⁇ /4 type radio wave absorber and a film for a ⁇ /4 type radio wave absorber.
  • a ⁇ /4 type radio wave absorber is a radio wave absorber that absorbs radio waves by utilizing the phase difference of the reflected waves, by making the distance between the resistive layer and the reflective layer 1 ⁇ 4 of the wavelength of the radio waves to be absorbed.
  • Patent Document 1 describes a ⁇ /4 type radio wave absorber in which a dielectric layer containing an ethylene-vinyl acetate copolymer is provided between a resistive layer and a reflective layer.
  • Patent Document 2 describes a ⁇ /4 type radio wave absorber in which an acrylic adhesive is used as the dielectric layer.
  • ⁇ /4 type radio wave absorbers are able to absorb radio waves near the target frequency.
  • ⁇ /4 type radio wave absorbers that can provide high radio wave absorption over a wide frequency range.
  • the present disclosure aims to provide a ⁇ /4 type radio wave absorber that has high radio wave absorption properties and a wide frequency range, particularly excellent radio wave absorption properties in the high frequency band, and a film for the ⁇ /4 type radio wave absorber that is used for the ⁇ /4 type radio wave absorber.
  • a ⁇ /4 type radio wave absorber having, in this order, a resistive layer, a dielectric layer containing a tetrafluoroethylene-based polymer, and a reflective layer.
  • the ⁇ /4 type radio wave absorber according to ⁇ 1> comprising, in this order, a support layer, a resistive layer, a dielectric layer containing a tetrafluoroethylene-based polymer, and a reflective layer.
  • ⁇ 4> The ⁇ /4 type radio wave absorber according to ⁇ 3>, wherein the tetrafluoroethylene-based polymer contained in the support layer has a unit based on a perfluoroalkyl vinyl ether.
  • ⁇ 5> The ⁇ /4 type radio wave absorber according to any one of ⁇ 2> to ⁇ 4>, wherein the support layer has a thickness of 5 to 500 ⁇ m.
  • ⁇ 6> The ⁇ /4 type radio wave absorber according to any one of ⁇ 1> to ⁇ 5>, wherein the tetrafluoroethylene-based polymer contained in the dielectric layer has oxygen atoms.
  • ⁇ 7> The ⁇ group according to any one of ⁇ 1> to ⁇ 6>, wherein the tetrafluoroethylene polymer contained in the dielectric layer has at least one selected from the group consisting of a unit based on perfluoroalkyl vinyl ether and a unit based on hexafluoropropylene.
  • /4 type radio wave absorber ⁇ 8> The ⁇ /4 type radio wave absorber according to any one of ⁇ 1> to ⁇ 7>, wherein spherulites of the tetrafluoroethylene-based polymer having a diameter of 10 ⁇ m or less are present on a surface of the dielectric layer.
  • ⁇ 9> The ⁇ /4 type radio wave absorber according to ⁇ 6>, wherein a ratio of a number of oxygen atoms to a total number of carbon atoms, fluorine atoms, and oxygen atoms on a surface of the dielectric layer facing the resistive layer is 2 to 15%.
  • ⁇ 10> The ⁇ /4 type radio wave absorber according to any one of ⁇ 1> to ⁇ 9>, wherein the dielectric layer has a relative dielectric constant of 1.0 to 2.8 at 10 GHz.
  • ⁇ 11> The ⁇ /4 type radio wave absorber according to any one of ⁇ 1> to ⁇ 10>, wherein the dielectric layer has a thickness of 400 to 1500 ⁇ m.
  • a ⁇ /4 type radio wave absorber having, in this order, a support layer containing a tetrafluoroethylene-based polymer having an oxygen-containing polar group, a resistive layer, a dielectric layer, and a reflective layer.
  • a film for a ⁇ /4 type radio wave absorber comprising a resistive layer which is a metal oxide layer, and a dielectric layer which contains a tetrafluoroethylene-based polymer, in this order.
  • ⁇ 15> The film for a ⁇ /4 type radio wave absorber according to ⁇ 13> or ⁇ 14>, wherein the tetrafluoroethylene-based polymer has a unit based on a perfluoroalkyl vinyl ether.
  • ⁇ 16> The ⁇ /4 type radio wave absorber according to ⁇ 12>, wherein the tetrafluoroethylene-based polymer contained in the support layer has a unit based on a perfluoroalkyl vinyl ether.
  • ⁇ 17> The ⁇ /4 type radio wave absorber according to ⁇ 12> or ⁇ 16>, wherein the support layer has a thickness of 5 to 500 ⁇ m.
  • ⁇ 18> The ⁇ /4 type radio wave absorber according to ⁇ 12>, ⁇ 16>, or ⁇ 17>, wherein spherulites of the tetrafluoroethylene-based polymer having a diameter of 10 ⁇ m or less are present on a surface of the support layer.
  • ⁇ 19> The ⁇ /4 type radio wave absorber according to any one of ⁇ 2> to ⁇ 5>, wherein spherulites of the tetrafluoroethylene-based polymer having a diameter of 10 ⁇ m or less are present on a surface of the dielectric layer, and wherein spherulites of the tetrafluoroethylene-based polymer having a diameter of 10 ⁇ m or less are present on a surface of the support layer.
  • the present disclosure provides a ⁇ /4 type radio wave absorber that has high radio wave absorption properties and a wide frequency range, particularly excellent radio wave absorption properties in the high frequency band, and a film for the ⁇ /4 type radio wave absorber that is used for the ⁇ /4 type radio wave absorber.
  • FIG. 1 is a schematic cross-sectional view showing a layer structure of an example of a ⁇ /4 type radio wave absorber according to a first embodiment.
  • each component may contain multiple types of the corresponding substance.
  • the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.
  • the terms “layer” and “film” include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.
  • laminate refers to stacking layers, where two or more layers may be bonded together or two or more layers may be removable.
  • a "polymer” is a compound formed by polymerization of a monomer, i.e., a "polymer” has a plurality of units based on the monomer.
  • a "unit" in a polymer means an atomic group based on a monomer formed by polymerization of the monomer.
  • the unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a part of the unit is converted into a different structure by processing the polymer.
  • the "melting point" of a polymer is the temperature corresponding to the maximum of the melting peak of the polymer as measured by differential scanning calorimetry (DSC) method.
  • the "melt flow rate” of a polymer means the melt mass flow rate of the polymer as defined in JIS K 7210-1:2014 (ISO1133-1:2011).
  • the "glass transition point (Tg)" of a polymer is a value measured by analyzing the polymer using a dynamic mechanical analysis (DMA) method.
  • DMA dynamic mechanical analysis
  • the "dielectric constant” is a value measured by the SPDR (Spirit Post Dielectric Resonator) method in an environment within the range of 23°C ⁇ 2°C and 50 ⁇ 5% RH at a frequency of 10 GHz.
  • the ⁇ /4 type radio wave absorber in the first embodiment has, in this order, a resistive layer, a dielectric layer containing a tetrafluoroethylene-based polymer, and a reflective layer.
  • the ⁇ /4 type radio wave absorber will also be referred to simply as a "radio wave absorber”
  • the tetrafluoroethylene-based polymer will also be referred to as an "F polymer”.
  • resins such as ethylene-vinyl acetate copolymer and acrylic resin are mainly used as materials for forming the dielectric layer, and while using these resins, efforts have been made to improve performance by improving them, such as by making them into foams.
  • the wave absorber of the present embodiment by incorporating the F polymer in the dielectric layer, high wave absorption properties can be obtained in a wide frequency range. Although the reason for this is unclear, it is presumed that the F polymer is easily polarized, which makes it possible to lower the relative dielectric constant of the entire dielectric layer containing the F polymer.
  • the radio wave absorber may further include a support layer on the opposite side of the resistive layer to the dielectric layer.
  • FIG. 1 shows a schematic layer structure of a radio wave absorber further having a support layer, as an example of the radio wave absorber according to the present embodiment.
  • the radio wave absorber 10 shown in FIG. 1 has a support layer 12, a resistive layer 14, a dielectric layer 16, and a reflective layer 18, in this order.
  • the wave absorber 10 shown in Fig. 1 is composed of a support layer 12, a resistive layer 14, a dielectric layer 16, and a reflective layer 18, and the support layer 12 and the resistive layer 14, the resistive layer 14 and the dielectric layer 16, and the dielectric layer and the reflective layer 18 are in contact with each other.
  • the wave absorber of this embodiment is not limited to this, and may have other layers.
  • the other layers include an adhesive layer provided at least one between the support layer 12 and the resistive layer 14, between the resistive layer 14 and the dielectric layer 16, and between the dielectric layer 16 and the reflective layer 18, and a resin layer provided on the reflective layer 18 on the opposite side to the dielectric layer 16.
  • an adhesive layer provided at least one between the support layer 12 and the resistive layer 14, between the resistive layer 14 and the dielectric layer 16, and between the dielectric layer 16 and the reflective layer 18, and a resin layer provided on the reflective layer 18 on the opposite side to the dielectric layer 16.
  • the resistive layer is not particularly limited as long as it functions as a resistive film for the radio wave absorber.
  • the resistive layer include a layer containing a metal oxide such as indium oxide, tin oxide, indium tin oxide (ITO), fluorine-doped tin oxide, or zinc oxide; a layer containing carbon; and the like. From the viewpoint of transmitting the radio waves to be absorbed, a layer containing ITO is preferred.
  • the content of SnO2 relative to the entire ITO is preferably 1 to 40 mass%, more preferably 10 to 35 mass%, from the viewpoints of stability of the amorphous structure and suppression of resistance value fluctuation in a high-temperature and high-humidity environment.
  • the content of ITO in the entire resistance layer is preferably 80 mass % or more, more preferably 90 mass % or more, even more preferably 95 mass % or more, and may be 100 mass %.
  • the sheet resistance of the resistive layer is, for example, 10 to 800 ⁇ / ⁇ , and from the viewpoint of improving the radio wave absorption properties of the radio wave absorber, preferably 15 to 500 ⁇ / ⁇ .
  • the sheet resistance is measured using a surface resistance measuring device (for example, Loresta AP, manufactured by Mitsubishi Petrochemical Co., Ltd.).
  • the thickness of the resistive layer is, for example, from 1 to 200 nm, and preferably from 5 to 50 nm.
  • the method for forming the resistive layer is not particularly limited, and examples thereof include sputtering, ion plating, vacuum deposition, chemical vapor deposition (CVD), pulsed laser deposition (PLD), etc.
  • the method for forming the resistive layer is preferably sputtering from the viewpoint of ease of control of the thickness and sheet resistance of the resistive layer.
  • the resistive layer may be a single layer or a laminate.
  • the dielectric layer is not particularly limited as long as it is a layer containing an F polymer.
  • the dielectric layer may contain only one type of F polymer, or may contain two or more types of F polymer.
  • the F polymer is a polymer containing units based on tetrafluoroethylene (hereinafter also referred to as "TFE").
  • TFE tetrafluoroethylene
  • the F polymer may further have units based on other comonomers.
  • the content of TFE unit in F polymer is preferably 50 mol% or more, more preferably 90 mol% or more, based on the total units in F polymer, from the viewpoint of favorably expressing the characteristics of TFE unit. The content may be 99 mol% or less, or 98 mol% or less.
  • F polymers include polytetrafluoroethylene (PTFE), polymers containing TFE units and units based on ethylene, polymers containing TFE units and units based on propylene, polymers containing TFE units and units based on perfluoroalkyl vinyl ether (PAVE) (PAVE units) (PFA), and polymers containing TFE units and units based on hexafluoropropylene (FEP).
  • PTFE polytetrafluoroethylene
  • PAVE perfluoroalkyl vinyl ether
  • PFA perfluoroalkyl vinyl ether
  • FEP hexafluoropropylene
  • the F polymer is preferably a polymer containing a TFE unit and at least one selected from the group consisting of a PAVE unit and a unit based on hexafluoropropylene, more preferably PFA and FEP, and even more preferably PFA. These polymers may further contain units based on other comonomers.
  • PAVE is preferably CF 2 ⁇ CFOCF 3 (hereinafter also referred to as “PMVE”), CF 2 ⁇ CFOCF 2 CF 3 , or CF 2 ⁇ CFOCF 2 CF 2 CF 3 (hereinafter also referred to as “PPVE”), with PPVE being more preferred.
  • the F polymer is preferably an F polymer having an oxygen atom, more preferably an F polymer having an oxygen-containing polar group, still more preferably an F polymer having at least one of a hydroxyl group-containing group and a carbonyl group-containing group, and particularly preferably an F polymer having a carbonyl group-containing group.
  • the carbonyl group-containing group is a group containing a carbonyl group (>C(O)).
  • the carbonyl group-containing group is preferably a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH 2 ), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.), or a carbonate group (-OC(O)O-), and more preferably an acid anhydride residue.
  • the number of oxygen-containing polar groups in the F polymer is preferably 50 to 5000, more preferably 100 to 2500, per 1 ⁇ 10 6 carbon atoms in the main chain.
  • the number of oxygen-containing polar groups in the F polymer can be quantified by the composition of the polymer or the method described in WO 2020/145133.
  • the oxygen-containing polar group may be contained in a unit based on a monomer in the F polymer, or may be contained in a terminal group of the main chain of the F polymer, the former being preferred.
  • Examples of the latter include an F polymer having an oxygen-containing polar group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc., and an F polymer obtained by subjecting an F polymer to plasma treatment or ionizing radiation treatment.
  • the monomer having a carbonyl group-containing group is preferably itaconic anhydride, citraconic anhydride, or 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH”), and more preferably NAH.
  • the F polymer is preferably an F polymer that contains TFE units and PAVE units and has an oxygen-containing polar group, and is preferably an F polymer that contains TFE units, PAVE units, and units based on a monomer having an oxygen-containing polar group.
  • Specific examples of such F polymers include the polymers described in WO 2018/016644.
  • the F polymer may be either heat-fusible or non-heat-fusible. From the viewpoint of improving the wave absorption properties of the wave absorber and also of forming a dense layer and improving the shape stability, etc., it is preferable that the F polymer be heat-fusible.
  • thermalofusible polymer refers to a polymer that has a temperature at which the melt flow rate is 1 to 1000 g/10 min under a load of 49 N.
  • non-thermofusible polymer refers to a polymer that does not have a temperature at which the melt flow rate is 1 to 1000 g/10 min under a load of 49 N.
  • the melting point of the F polymer which is heat-fusible, is preferably 200° C. or higher, more preferably 260° C. or higher, from the viewpoint of heat resistance of the dielectric layer.
  • the melting point of the F polymer is preferably 325° C. or lower, more preferably 320° C. or lower, from the viewpoint of ease of processing.
  • the F polymer is preferably an F polymer having a melting point of 200 to 325°C, more preferably an F polymer having a melting point of 260 to 320°C.
  • the glass transition point of the F polymer is preferably 50° C. or higher, and more preferably 75° C. or higher. From the viewpoint of ease of processing, the glass transition point of the F polymer is preferably 150° C. or lower, and more preferably 125° C. or lower.
  • the fluorine content of the F polymer is preferably 70% by mass or more, and more preferably 72 to 76% by mass, from the viewpoint of improving the radio wave absorbing properties of the radio wave absorber.
  • the dielectric layer contains at least the F polymer, and may contain other components as necessary, such as resins other than the F polymer, inorganic fillers, and additives such as silane coupling agents, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brightening agents, colorants, conductive agents, release agents, surface treatment agents, and flame retardants.
  • the content of the F polymer in the entire dielectric layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 100% by mass.
  • the dielectric layer does not substantially contain a flame retardant.
  • the content of the flame retardant in the entire dielectric layer is preferably 1 mass % or less, and more preferably 0 mass %.
  • the dielectric layer contains the F polymer, and the F polymer itself has excellent flame retardancy, so that the entire dielectric layer can obtain flame retardancy even if the dielectric layer does not substantially contain a flame retardant.
  • spherulites of the F polymer are present on the surface of the dielectric layer.
  • the diameter of the spherulites present on the surface of the dielectric layer (hereinafter, the diameter of the spherulites is also referred to as the "spherulite diameter") is preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less, even more preferably 2 ⁇ m or less, and particularly preferably 1 ⁇ m or less.
  • the spherulite diameter is preferably 0.01 ⁇ m or more.
  • the size of the step (i.e., unevenness) at the boundary between the crystalline portion (i.e., the spherulite portion) and the amorphous portion becomes sufficiently small, and not only does it improve the adhesion to the layer in contact with the dielectric layer (e.g., the resistive layer or the reflective layer), it also makes it difficult for microscopic voids to form between the layers, which tends to improve the radio wave absorption capacity and light transmittance.
  • the spherulite diameter is measured as follows.
  • the surface of a layer to be measured e.g., a dielectric layer
  • a polymer phase structure analysis system manufactured by Otsuka Chemical Co., Ltd., "PP-1000" that utilizes small-angle light scattering, and the correlation between the scattering vector q ( ⁇ m -1 ) and the scattering intensity (Is) is obtained to measure the spherulite diameter on the surface of the layer to be measured.
  • an F polymer that is likely to form spherulites of the above-mentioned spherulite diameter on the surface of the dielectric layer is an F polymer having the oxygen-containing polar group described above.
  • an example of the F polymer is a mixture of a first F polymer, which is a crystalline F polymer containing TFE units and PPVE units, and an F polymer containing TFE units and PPVE units and having a lower PPVE unit content and molecular weight than the first F polymer, or a second F polymer, which is an F polymer containing TFE units and PMVE units and has a glass transition point of 25°C or less.
  • the ratio of the number of oxygen atoms to the total number of carbon atoms, fluorine atoms, and oxygen atoms on the surface on the resistance layer side is preferably 2 to 15%, and more preferably 5 to 12%.
  • the ratio of the number of oxygen atoms to the total number of carbon atoms, fluorine atoms, and oxygen atoms is also simply referred to as the "ratio of the number of oxygen atoms.”
  • the ratio of oxygen atoms refers to the ratio of the number of oxygen atoms to the total number of carbon atoms, fluorine atoms, and oxygen atoms when the surface of the dielectric layer is measured by XPS (X-ray photoelectron spectroscopy).
  • Examples of the method for controlling the ratio of the number of oxygen atoms within the above range include a method of previously subjecting the surface of the dielectric layer on the resistive layer side to a surface treatment such as plasma treatment, corona treatment, etc.
  • a surface treatment such as plasma treatment, corona treatment, etc.
  • the surface of the dielectric layer is subjected to a plasma treatment, and then the resistive layer is provided in contact with the plasma-treated surface of the dielectric layer, thereby improving the adhesion between the dielectric layer and the resistive layer.
  • the ratio of the number of oxygen atoms can be controlled within the above range by subjecting the surface of the dielectric layer to a surface treatment such as plasma treatment to introduce oxygen atoms. Furthermore, even if the F polymer contained in the dielectric layer has an oxygen-containing polar group, the proportion of the number of oxygen atoms can be increased by subjecting the surface of the dielectric layer to a surface treatment such as plasma treatment, thereby improving adhesion to adjacent layers.
  • plasma treatment refers to a treatment performed by exposing a target surface to a discharge that is initiated and sustained by applying a high DC or AC voltage between electrodes, such as a corona discharge under atmospheric pressure or a glow discharge in a vacuum.
  • plasma irradiation devices used in plasma treatment include devices that employ a high-frequency induction type, a capacitively coupled electrode type, a corona discharge electrode-plasma jet type, a parallel plate type, a remote plasma type, an atmospheric pressure plasma type, an ICP type high density plasma type, and the like.
  • Gases used in the plasma treatment include oxygen, nitrogen, argon, hydrogen, and ammonia.
  • the water contact angle of the plasma-treated dielectric layer surface is preferably 80 to 100°. The smaller the contact angle, the better the adhesion to other materials.
  • the water contact angle is determined, for example, by measuring the contact angle using a Kyowa Interface Science Co., Ltd. DMo-701 measuring device under conditions of a liquid volume of 3 ⁇ L and five repeated measurements, and calculating the average value.
  • the wetting tension of the surface of the plasma-treated dielectric layer is preferably 30 to 70 mN/m, more preferably 40 to 65 mN/m, from the viewpoint of the adhesion of the layer. The wetting tension is measured, for example, using a mixture for wetting tension testing (manufactured by Wako Pure Chemical Industries, Ltd.) according to JIS K 6768:1999 (ISO 8296-1987).
  • the surface of the dielectric layer on the reflective layer side may be subjected to a surface treatment such as plasma treatment.
  • a surface treatment such as plasma treatment.
  • the ratio of the number of oxygen atoms on the surface of the dielectric layer on the reflective layer side, the water contact angle, and the wetting tension may be within the ranges described above as the ratio of the number of oxygen atoms on the surface of the dielectric layer on the resistive layer side, respectively.
  • the transmittance of light having a wavelength of 250 to 400 nm is preferably 75% or more, and more preferably 80% or more, from the viewpoint of improving visibility in the radio wave absorber.
  • the transmittance of light having a wavelength of 250 to 400 nm being 75% or more means that the transmittance is 75% or more over the entire wavelength range of 250 to 400 nm, and that there is no wavelength having a transmittance of less than 75% within the wavelength range of 250 to 400 nm.
  • the upper limit of the transmittance of the dielectric layer for light with wavelengths of 250 to 400 nm is not particularly limited, and may be 99%.
  • the light transmittance is measured, for example, by using a spectrophotometer (eg, "UV-3600" manufactured by Shimadzu Corporation).
  • the dielectric layer is preferably a molten dense layer.
  • the molten dense layer is a layer heated to a temperature equal to or higher than the melting point of the heat-fusible F polymer, and is a dense layer that does not substantially include voids.
  • a method for confirming that the dielectric layer is a molten dense layer includes, for example, observing the cross section of the dielectric layer with a scanning electron microscope (SEM) and confirming that no voids with a minor axis of 0.1 ⁇ m or more exist. For example, when the dielectric layer is a fibrous sintered body, the presence of voids is confirmed when the cross section of the dielectric layer is observed with an SEM.
  • SEM scanning electron microscope
  • the dielectric layer is a foamed body
  • the presence of voids is confirmed when the cross section of the dielectric layer is observed with an SEM.
  • the dielectric layer contains the F polymer, even if the dielectric layer is a molten dense layer rather than a foam, a low dielectric constant can be obtained, and a wide range of frequencies with high radio wave absorption can be achieved in the radio wave absorber.
  • a method for obtaining a dielectric layer which is a molten dense layer for example, a method in which a heat-fusible F polymer is used as the F polymer contained in the dielectric layer and heating is performed at a temperature equal to or higher than the melting point of the F polymer when forming the dielectric layer can be mentioned.
  • the dielectric constant of the dielectric layer at 10 GHz is preferably 2.8 or less, more preferably 2.4 or less, and even more preferably 2.2 or less, from the viewpoint of widening the frequency range of high radio wave absorption in the radio wave absorber.
  • the dielectric constant at 10 GHz is also simply referred to as "dielectric constant.”
  • the dielectric constant of the dielectric layer is preferably 1.0 or more.
  • the thickness of the dielectric layer is not particularly limited and is selected according to the wavelength of the radio waves to be absorbed. Examples of the thickness of the dielectric layer are in the range of 400 to 1500 ⁇ m.
  • the peel strength between the dielectric layer and the reflective layer described later is preferably 5 N/cm or more, and more preferably 10 N/cm or more.
  • the upper limit of the peel strength between the dielectric layer and the reflective layer is not particularly limited, and may be 100 N/cm.
  • the peel strength between the dielectric layer and the reflective layer is measured using a test piece obtained by cutting a laminate to be measured having the dielectric layer and the reflective layer to a size of 100 mm in length and 10 mm in width.
  • the test piece is fixed from one end in the longitudinal direction to a position 50 mm away, and the dielectric layer and the reflective layer are peeled from the other end of the test piece under conditions of a pulling speed of 50 mm/min and a peel angle of 90°, and the maximum load (N/cm) in the peeling is measured and this is defined as the peel strength between the dielectric layer and the reflective layer.
  • the peel strength between the dielectric layer and the resistive layer is preferably 5 N/cm or more, and more preferably 10 N/cm or more.
  • the upper limit of the peel strength between the dielectric layer and the resistive layer is not particularly limited, and may be 100 N/cm.
  • the peel strength between the dielectric layer and the resistive layer can be measured in the same manner as the above-mentioned peel strength.
  • the dielectric layer may be produced by melt extrusion of a composition containing the F polymer, or may be produced using a dispersion containing particles of the F polymer and a liquid dispersion medium.
  • the dielectric layer may be formed by extrusion molding of the composition obtained by melt kneading the F polymer and other components.
  • the composition obtained by the melt kneading may be a pellet-shaped composition.
  • a dispersion containing particles of an F polymer, other components, and a liquid dispersion medium may be used as the dispersion.
  • the dielectric layer may be manufactured by directly applying the above dispersion to the surface of adjacent layers such as a reflective layer described later and heating it, or by applying the above dispersion to the surface of a temporary substrate, heating it, and then removing the temporary substrate. The heating of the dispersion may be performed in two stages: heating to remove the liquid dispersion medium and heating to bake the F polymer.
  • examples of the temporary substrate include metal foil, resin film, etc., and examples of methods for removing the temporary substrate include peeling, etching, etc.
  • the dielectric layer may be a single layer or a laminate.
  • the reflective layer is not particularly limited as long as it functions as a reflective layer of the radio wave absorber and is a layer that reflects the radio waves to be absorbed.
  • Materials contained in the reflective layer include metals and metal oxides, among which metals are preferred.
  • metals include copper, aluminum, nickel, chromium, molybdenum, iron, gold, silver, gallium, zinc, tin, niobium, indium, and alloys thereof.
  • metal oxides include indium oxide, tin oxide, ITO, fluorine-doped tin oxide, and zinc oxide.
  • the reflective layer preferably contains a metal, particularly preferably copper.
  • the metal content in the entire reflective layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass.
  • the sheet resistance of the reflective layer is, for example, 1.0 ⁇ 10 ⁇ 7 to 100 ⁇ / ⁇ , and from the viewpoint of improving the radio wave absorption properties of the radio wave absorber, it is preferably 1.0 ⁇ 10 ⁇ 7 to 20 ⁇ / ⁇ .
  • the sheet resistance is measured by the same method as the sheet resistance of the resistive layer described above.
  • the thickness of the reflective layer is, for example, 1 to 500 ⁇ m, and from the viewpoint of mechanical properties such as the bendability of the radio wave absorber, it is preferably 5 to 100 ⁇ m.
  • the method for forming the reflective layer is not particularly limited. When the reflective layer is a metal foil, the method for forming the reflective layer includes rolling, electrolytic plating, sputtering plating, electroless plating, etc. When the reflective layer is a metal oxide layer, the method for forming the reflective layer includes the same method as the method for forming the resistance layer described above.
  • the reflective layer may be a single layer or a laminate.
  • the support layer is a layer that is provided as necessary, and is not particularly limited as long as it is a layer that transmits at least a part of the radio waves to be absorbed. By having the support layer in the radio wave absorber, the resistive layer is protected. Examples of materials contained in the support layer include resins.
  • resins examples include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate, polyolefin resins such as polyethylene, polypropylene, and polystyrene, vinyl resins such as polyvinyl chloride, polyvinyl acetal resins such as polyvinyl butyral, polycarbonate resins, polyamide resins, polyimide resins, and acrylic resins, in addition to the above-mentioned F polymer.
  • the support layer may contain only one type of these resins, or may contain two or more types. When the support layer contains a resin, the support layer may contain other components other than the resin. Examples of other components include components other than the resin among the other components contained in the dielectric layer as necessary.
  • the content of the resin in the entire support layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass.
  • the support layer preferably contains an F polymer.
  • both the dielectric layer and the support layer contain an F polymer, high radio wave absorption can be obtained in a wider frequency range.
  • the support layer contains an F polymer, which improves the radio wave permeability in the support layer
  • the dielectric layer contains an F polymer, which reduces the relative dielectric constant of the entire dielectric layer, thereby widening the frequency range in which high radio wave absorption can be obtained due to the synergistic effect of these two.
  • the support layer may contain only one type of F polymer, or may contain two or more types.
  • the content of the F polymer in the entire resin contained in the support layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass.
  • the content of the F polymer in the entire support layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass.
  • the F polymer contained in the support layer may be the same as the F polymer contained in the dielectric layer.
  • the F polymer contained in the support layer may be the same type of F polymer as the F polymer contained in the dielectric layer.
  • the F polymer contained in the support layer is preferably a polymer containing TFE units and PAVE units, and more preferably a polymer containing TFE units and units based on PPVE.
  • the F polymer contained in the support layer is preferably an F polymer having an oxygen atom, more preferably an F polymer having an oxygen-containing polar group, and particularly preferably an F polymer having a carbonyl group-containing group, from the viewpoints of expanding the frequency range in which the wave absorber has high wave absorption while improving adhesion to adjacent layers.
  • the support layer contains an F polymer
  • spherulites of the F polymer are present on the surface of the support layer.
  • the support layer contains an F polymer
  • spherulites of the F polymer are present on the surfaces of both the support layer and the dielectric layer.
  • the spherulite diameter of the spherulites present on the surface of the support layer is preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less, even more preferably 2 ⁇ m or less, and particularly preferably 1 ⁇ m or less.
  • the spherulite diameter is preferably 0.01 ⁇ m or more.
  • the support layer contains the F polymer
  • the support layer does not substantially contain a flame retardant, from the viewpoint of widening the frequency range in which the radio wave absorber has high radio wave absorption properties.
  • the surface on the resistance layer side may be subjected to a surface treatment such as plasma treatment from the viewpoint of improving adhesion to the resistance layer.
  • the ratio of the number of oxygen atoms, the contact angle of water, and the wetting tension on the surface on the resistance layer side of the support layer may be within the ranges described above for the ratio of the number of oxygen atoms, the contact angle of water, and the wetting tension on the surface on the resistance layer side of the dielectric layer, respectively.
  • the transmittance of light having a wavelength of 250 to 400 nm is not particularly limited, and from the viewpoint of improving visibility in the radio wave absorber, it is preferably 75% or more, and more preferably 85% or more.
  • the upper limit of the transmittance of light having a wavelength of 250 to 400 nm in the support layer is not particularly limited, and may be 99%.
  • the support layer is preferably a molten dense layer from the viewpoint of mechanical properties such as the bendability of the wave absorber.
  • the method for confirming that the support layer is a molten dense layer is the same as the method for confirming that the dielectric layer is a molten dense layer described above.
  • a method for obtaining a support layer that is a molten dense layer for example, a method of using a thermally fusible F polymer as a resin contained in the support layer and heating the support layer at a temperature equal to or higher than the melting point of the F polymer when forming the support layer can be mentioned.
  • the relative dielectric constant of the support layer at 10 GHz is not particularly limited, and may be from 1.0 to 20. From the viewpoint of the wave absorption characteristics of the wave absorber, it is preferably from 1.0 to 10, more preferably from 1.0 to 5.0, and even more preferably from 1.0 to 2.8.
  • the thickness of the support layer is not particularly limited, and may be in the range of 5 to 500 ⁇ m, and is preferably 25 to 500 ⁇ m from the viewpoint of obtaining the mechanical strength required to support the resistive layer, the dielectric layer, and the reflective layer.
  • the peel strength between the support layer and the resistance layer is preferably 5 N/cm or more, more preferably 10 N/cm or more.
  • the upper limit of the peel strength between the support layer and the resistance layer is 100 N/cm.
  • the peel strength between the support layer and the resistance layer can be measured in the same manner as the above-mentioned peel strength.
  • the method for forming the support layer is not particularly limited and is selected according to the type of resin contained in the support layer.
  • the support layer may be manufactured by the same method as the above-mentioned dielectric layer.
  • the support layer may be a single layer or a laminate.
  • the method for manufacturing the radio wave absorber in this embodiment is not particularly limited.
  • the method for forming each layer is as described above.
  • the method for laminating each layer includes a method in which a dielectric layer and a resistive layer are laminated in this order on a reflective layer.
  • the dielectric layer, resistive layer, and support layer may be laminated in this order on the reflective layer, or the resistive layer, dielectric layer, and reflective layer may be laminated in this order on the support layer.
  • the frequency width of the region in which the absorption amount at the absorption peak near 79 GHz is 20 db or more is preferably 9 GHz or more, and more preferably 11 GHz or more.
  • the upper limit of the frequency width of the region in which the absorption amount at the absorption peak near 79 GHz is 20 db or more is not particularly limited, and may be, for example, 100 GHz.
  • the radio wave absorption spectrum is obtained by measurement using a radio wave absorption rate measuring device (e.g., BD1-26.A manufactured by Keycom Corporation) and a network analyzer (e.g., MS4647B manufactured by Anritsu Corporation).
  • radio waves are incident on each layer of the radio wave absorber in a direction perpendicular to the support layer side of the radio wave absorber, and the amount of radio wave absorption in the 55 to 90 GHz band is measured based on JIS R1679:2007.
  • the wave absorber in the second embodiment has, in this order, a support layer containing an F polymer having an oxygen-containing polar group, a resistive layer, a dielectric layer, and a reflective layer.
  • the F polymer having an oxygen-containing polar group is contained in the support layer, so that high wave absorption is obtained in a wide frequency range, and the durability of the wave absorber is improved.
  • the reason why the frequency range in which high wave absorption is obtained by containing the F polymer having an oxygen-containing polar group in the support layer is expanded is not clear, but it is presumed that the transmittance of the wave in the support layer is improved.
  • the reason why high durability is obtained by containing the F polymer having an oxygen-containing polar group in the support layer is presumed to be because the adhesion between the support layer and the layer in contact with the support layer is improved.
  • the layer structure of the radio wave absorber in this embodiment is similar to the layer structure of the radio wave absorber 10 shown in FIG.
  • the details of the resistive layer and the reflective layer of the radio wave absorber in this embodiment are similar to those of the resistive layer and the reflective layer of the radio wave absorber in the above-described first embodiment.
  • the dielectric layer of the wave absorber in this embodiment is not particularly limited as long as it functions as the dielectric layer of the wave absorber.
  • materials contained in the dielectric layer include resins.
  • resins include synthetic resins such as ethylene-vinyl acetate copolymer, vinyl chloride, urethane, acrylic, acrylic urethane, polyolefin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyester, polystyrene, polyimide, polycarbonate, polyamide, polysulfone, polyethersulfone, epoxy, and fluororesin; and synthetic rubbers such as polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, butyl rubber, acrylic rubber, ethylene-propylene rubber, and silicone rubber.
  • the dielectric layer may contain only one type of these resins, or two or more types.
  • the dielectric layer may contain other components other than the resin.
  • other components include components other than the resin that are contained as necessary in the dielectric layer of the radio wave absorber in the first embodiment described above.
  • the resin content in the entire dielectric layer is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass.
  • the dielectric constant at 10 GHz of the dielectric layer of the wave absorber in this embodiment is, for example, 1.0 to 3. From the viewpoint of broadening the frequency range of high wave absorption properties in the wave absorber, the dielectric constant is preferably 1.0 to 2.8, more preferably 1.0 to 2.4, and even more preferably 1.0 to 2.2.
  • the thickness of the dielectric layer of the wave absorber in this embodiment is not particularly limited and is selected according to the wavelength of the wave to be absorbed.
  • the thickness of the dielectric layer is in the range of 400 to 1500 ⁇ m, may be 400 to 1000 ⁇ m, or may be 400 to 750 ⁇ m.
  • the method for forming the dielectric layer of the wave absorber of this embodiment is not particularly limited, and is selected according to the type of resin contained in the dielectric layer.
  • the support layer of the radio wave absorber in this embodiment is not particularly limited as long as it is a layer containing an F polymer having an oxygen-containing polar group.
  • the support layer may contain only one type of F polymer having an oxygen-containing polar group, or may contain two or more types.
  • the details of the F polymer having an oxygen-containing polar group contained in the support layer of the radio wave absorber in this embodiment are the same as the details of the F polymer having an oxygen-containing polar group described as a component contained in the dielectric layer of the radio wave absorber in the first embodiment.
  • the F polymer having an oxygen-containing polar group contained in the support layer of the radio wave absorber in this embodiment is preferably a polymer containing TFE units and PAVE units (i.e., PFA) from the viewpoint of widening the frequency range of high radio wave absorption in the radio wave absorber.
  • the F polymer having an oxygen-containing polar group contained in the support layer may be an F polymer containing TFE units, PAVE units, and units based on a monomer having an oxygen-containing polar group.
  • the support layer contains at least an F polymer having an oxygen-containing polar group, and may contain other components as necessary.
  • Other components include an F polymer not having an oxygen-containing polar group, a resin other than an F polymer, an inorganic filler, and additives described as other components contained in the dielectric layer of the first embodiment as necessary.
  • the resin other than the F polymer contained in the support layer may include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate; polyolefin resins such as polyethylene, polypropylene, and polystyrene; vinyl resins such as polyvinyl chloride; polyvinyl acetal resins such as polyvinyl butyral; polycarbonate resins; polyamide resins; polyimide resins; acrylic resins, etc.
  • PET polyethylene terephthalate
  • polyethylene naphthalate polyethylene naphthalate
  • polyolefin resins such as polyethylene, polypropylene, and polystyrene
  • vinyl resins such as polyvinyl chloride
  • polyvinyl acetal resins such as polyvinyl butyral
  • polycarbonate resins polyamide resins
  • polyimide resins acrylic resins, etc.
  • the content of the F polymer having an oxygen-containing polar group relative to the entire resin contained in the support layer is preferably 80% by mass or more, and may be 100% by mass.
  • the content of the F polymer having an oxygen-containing polar group relative to the entire support layer is preferably 80% by mass or more, and may be 100% by mass.
  • the content of the F polymer having an oxygen-containing polar group relative to the entire support layer is preferably 80% by mass or more, and may be 100% by mass.
  • the support layer does not substantially contain a flame retardant.
  • the surface of the support layer on the resistive layer side may be subjected to a surface treatment such as plasma treatment, etc.
  • the ratio of the number of oxygen atoms, the contact angle of water, and the wetting tension on the surface of the support layer on the resistive layer side may be within the ranges explained as the ratio of the number of oxygen atoms, the contact angle of water, and the wetting tension on the surface of the dielectric layer on the resistive layer side of the wave absorber in the first embodiment described above, respectively.
  • the transmittance of light having a wavelength of 250 to 400 nm is not particularly limited, and from the viewpoint of improving visibility in the radio wave absorber, it is preferably 75% or more, and more preferably 85% or more.
  • the upper limit of the transmittance of light having a wavelength of 250 to 400 nm in the support layer is not particularly limited, and may be 99%.
  • the support layer is preferably a molten dense layer.
  • a method for confirming that the support layer is a molten dense layer is the same as the method for confirming that the dielectric layer is a molten dense layer in the first embodiment described above.
  • a method for obtaining a support layer that is a molten dense layer is also the same as the first embodiment described above.
  • the details of the relative dielectric constant of the support layer of the wave absorber in this embodiment are similar to the details of the relative dielectric constant of the dielectric layer of the wave absorber in the above-mentioned first embodiment.
  • the thickness of the support layer of the radio wave absorber in this embodiment is similar to that of the support layer of the radio wave absorber in the above-described first embodiment.
  • the method for forming the support layer of the wave absorber in this embodiment is similar to the method for forming the dielectric layer of the wave absorber in the above-described first embodiment.
  • the method for laminating the layers of the radio wave absorber in this embodiment is similar to the method for laminating the layers of the radio wave absorber in the above-described first embodiment.
  • the radio wave absorber in the first and second embodiments is used, for example, for noise suppression of a millimeter wave radar that measures the distance, speed, angle, etc. of an object using radio waves in the millimeter wave band.
  • the frequency of radio waves to be absorbed by the radio wave absorber in the first and second embodiments is, for example, 1 to 100 GHz.
  • the film for a ⁇ /4 type radio wave absorber in the third embodiment has, in this order, a resistive layer which is a metal oxide layer, and a dielectric layer containing an F polymer.
  • the film for a ⁇ /4 type radio wave absorber will also be simply referred to as a "film for a radio wave absorber".
  • the dielectric layer contains the F polymer, by providing a reflective layer on the dielectric layer opposite the resistive layer, a radio wave absorber with high radio wave absorption properties can be obtained over a wide frequency range.
  • the resistive layer of the film for radio wave absorber in this embodiment is a layer containing a metal oxide among the specific examples of the resistive layer of the radio wave absorber in the first embodiment described above, and among these, a layer containing ITO is preferable. Details in the case where the resistive layer contains ITO are the same as those of the resistive layer in the first embodiment described above.
  • the sheet resistance, thickness, and forming method of the resistive layer are also the same as those of the resistive layer in the first embodiment.
  • the wave absorber film of the present embodiment may further include a support layer on the opposite side of the resistance layer to the dielectric layer.
  • the support layer is a layer provided as necessary, and is not particularly limited as long as it is a layer that transmits at least a part of the radio waves to be absorbed.
  • the film for a radio wave absorber in this embodiment has a support layer, the details of the support layer are the same as those of the support layer of the radio wave absorber in the first embodiment described above.
  • a copper foil 1 having a thickness of 32 ⁇ m is used as a reflective layer.
  • a 500 ⁇ m thick F polymer film 1 (a PFA-based polymer film containing 97.9 mol%, 2.0 mol%, and 0.1 mol% of TFE units, PPVE units, and NAH units in this order, melting point: 300° C., molten dense layer) is heat-welded to the copper foil 1 at 10 MPa for 3 minutes while heating to 350° C., and then stopped heating while maintaining 10 MPa for 7 minutes with preheating. Then, a plasma treatment is performed on the surface of the F polymer film 1 opposite to the copper foil 1.
  • the F polymer film 1 obtained by carrying out the above operation is used as a dielectric layer.
  • spherulites with a spherulite diameter of 0.5 ⁇ m are present on the surface of the F polymer film 1.
  • the ratio of the number of oxygen atoms to the total number of carbon atoms, fluorine atoms, and oxygen atoms, the contact angle of water, and the wetting tension are 5.3%, 96°, and 60 mN/m, respectively.
  • An ITO film with a sheet resistance of 400 ⁇ / ⁇ is formed by sputtering on the plasma-treated surface of F polymer film 1.
  • the ITO film is then annealed for 1 hour at 150°C in a vacuum to give it a polycrystalline structure.
  • the ITO film thus obtained, with a sheet resistance of 20 ⁇ / ⁇ , is used as the resistive layer.
  • a PET film with an acrylic adhesive (thickness 75 ⁇ m, manufactured by Nichiei Shinka Co., Ltd., product name: Transparent 75-SN) is peeled off from the release film and attached to the surface of the resistance layer opposite to the F polymer film 1.
  • the PET film obtained by the above operation is used as a support layer.
  • the radio wave absorber thus obtained, having the reflective layer, the dielectric layer, the resistive layer, and the support layer in this order, is designated as the radio wave absorber of Example 1.
  • the support layer is made of a 75 ⁇ m thick F polymer film 2 (a PFA-based polymer film containing 97.9 mol%, 2.0 mol%, and 0.1 mol% of TFE units, PPVE units, and NAH units in this order, melting point: 300° C., molten dense layer) that has been subjected to plasma treatment on its surface. Note that spherulites with a diameter of 0.5 ⁇ m exist on the surface of the F polymer film 2.
  • the ratio of the number of oxygen atoms to the total number of carbon atoms, fluorine atoms, and oxygen atoms, the contact angle of water, and the wetting tension are 6.5%, 98°, and 65 mN/m, respectively.
  • the stack of the reflective layer, the dielectric layer, and the resistive layer is the same as in Example 1.
  • the plasma-treated surface of the support layer, F polymer film 2 is brought into contact with the surface of the resistance layer of the laminate opposite to the F polymer film 1, and they are bonded together at 350° C. for 10 minutes under a pressure of 3 MPa.
  • the radio wave absorber thus obtained, having the reflective layer, the dielectric layer, the resistive layer, and the support layer in this order, is designated as the radio wave absorber of Example 2.
  • Example 3 The surface of F polymer film 2 having a thickness of 75 ⁇ m was subjected to plasma treatment in the same manner as in Example 2 to form a support layer.
  • a 780 ⁇ m thick acrylic double-sided adhesive tape is attached to the same copper foil 1 as in Example 1. This acrylic double-sided adhesive tape is used as a dielectric layer.
  • an ITO film having a sheet resistance of 400 ⁇ / ⁇ is formed by sputtering on the surface of the acrylic double-sided adhesive tape opposite to the copper foil 1 in the same manner as in Example 1, and an annealing treatment is performed in the same manner as in Example 1.
  • the ITO film having a sheet resistance of 20 ⁇ / ⁇ thus obtained is used as a resistive layer.
  • the plasma-treated surface of F polymer film 2 which is the support layer is brought into contact with the surface of the resistance layer opposite the acrylic double-sided adhesive tape, and adhered in the same manner as in Example 2.
  • the radio wave absorber thus obtained having the reflective layer, the dielectric layer, the resistive layer, and the support layer in this order, is designated as the radio wave absorber of Example 3.
  • Example 4 A PET film containing titanium oxide particles (thickness: 125 ⁇ m, titanium oxide particles: 10% by mass) was used as a support layer.
  • a three-layer laminate having a barrier layer 1 (SiO 2 layer, thickness: 10 nm), a metal resistive layer with a surface resistance value of 355 ⁇ / ⁇ , and a barrier layer 2 (SiO 2 layer, thickness: 5 nm) provided in this order on the PET film serving as a support layer is used as a resistive layer (sheet resistance of the laminate: 360 ⁇ / ⁇ ).
  • a 780 ⁇ m-thick double-sided acrylic adhesive tape is laminated on the barrier layer 2. This double-sided acrylic adhesive tape serves as a dielectric layer.
  • radio wave absorber having the reflective layer, the dielectric layer, the resistive layer, and the support layer in this order, is designated as the radio wave absorber of Example 4.
  • Example 1 to 3 are working examples
  • Example 4 is a comparative example. As shown in Table 1, it can be seen that the frequency range in which the amount of radio wave absorption is high is wider in Examples 1 to 3 than in Example 4.
  • the radio wave absorber of Example 5 has a reflective layer, a dielectric layer, a resistive layer, and a support layer in this order, and is obtained in the same manner as in Example 2, except that the F polymer film 1 is changed to an F polymer film 1a having a thickness of 500 ⁇ m (a film of a PFA-based polymer containing 97.5 mol% and 2.5 mol% of TFE units and PPVE units, in that order, melting point: 300° C., molten dense layer, spherulite diameter of spherulites present on the surface: 5 ⁇ m), and the F polymer film 2 is changed to an F polymer film 2a having a thickness of 75 ⁇ m (a film of a PFA-based polymer containing 97.5 mol% and 2.5 mol% of TFE units and PPVE units, in that order, melting point: 300° C., molten dense layer, spherulite diameter of spherulites present on the surface: 5 ⁇
  • the radio wave absorber of Example 6 has a reflective layer, a dielectric layer, a resistive layer, and a support layer in this order, and is obtained in the same manner as in Example 2, except that the F polymer film 1 is changed to an F polymer film 1b having a thickness of 500 ⁇ m (a film of a PFA-based polymer containing 98.7 mol% and 1.3 mol% of TFE units and PPVE units, in that order, melting point: 300° C., molten dense layer, spherulite diameter of spherulites present on the surface: 17 ⁇ m), and the F polymer film 2 is changed to an F polymer film 2b having a thickness of 75 ⁇ m (a film of a PFA-based polymer containing 98.7 mol% and 1.3 mol% of TFE units and PPVE units, in that order, melting point: 300° C., molten dense layer, spherulite diameter of spherulites present on the surface: 17
  • the dielectric layer and the support layer all have a relative dielectric constant of 2.1.
  • the frequency widths of the radio wave absorber of Example 2, the radio wave absorber of Example 5, and the radio wave absorber of Example 6 are 15.0, 13.6, and 13.4, respectively.
  • the peel strength between the dielectric layer and the reflective layer and the peel strength between the dielectric layer and the resistive layer are highest for the radio wave absorber of Example 2, followed by the radio wave absorber of Example 5 and the radio wave absorber of Example 6.
  • the peel strength between the support layer and the resistive layer also shows the same tendency as the peel strength between the dielectric layer and the reflective layer.
  • the light transmittance of 250 to 400 nm in the dielectric layer is highest in the radio wave absorber of Example 2, and tends to decrease in the order of the radio wave absorber of Example 5 and the radio wave absorber of Example 6.
  • the light transmittance of 250 to 400 nm in the support layer also shows the same tendency as the light transmittance of 250 to 400 nm in the dielectric layer.
  • radio wave absorber 12 support layer 14: resistive layer 16: dielectric layer 18: reflective layer

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Abstract

Un absorbeur d'ondes radio de type λ/4 d'un premier mode de réalisation comprend : une couche résistive ; une couche diélectrique contenant un polymère à base de tétrafluoroéthylène ; et une couche réfléchissante, dans cet ordre. Un absorbeur d'ondes radio de type λ/4 d'un deuxième mode de réalisation comprend : une couche de corps de support contenant un polymère à base de tétrafluoroéthylène ayant un groupe polaire contenant de l'oxygène ; une couche résistive ; une couche diélectrique ; et une couche réfléchissante, dans cet ordre. Un film pour absorbeur d'ondes radio de type λ/4 d'un troisième mode de réalisation comprend : une couche résistive qui est une couche d'oxyde métallique ; et une couche diélectrique contenant un polymère à base de tétrafluoroéthylène, dans cet ordre.
PCT/JP2023/043684 2022-12-08 2023-12-06 ABSORBEUR D'ONDES RADIO DE TYPE λ/4 ET FILM POUR ABSORBEUR D'ONDES RADIO DE TYPE λ/4 WO2024122588A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2018098367A (ja) * 2016-12-14 2018-06-21 日東電工株式会社 電磁波吸収体
WO2020196356A1 (fr) * 2019-03-26 2020-10-01 積水化学工業株式会社 ABSORBEUR D'ONDES RADIO DE TYPE λ/4
JP2022165989A (ja) * 2018-03-30 2022-11-01 ダイキン工業株式会社 電波吸収材料および電波吸収シート

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2018098367A (ja) * 2016-12-14 2018-06-21 日東電工株式会社 電磁波吸収体
JP2022165989A (ja) * 2018-03-30 2022-11-01 ダイキン工業株式会社 電波吸収材料および電波吸収シート
WO2020196356A1 (fr) * 2019-03-26 2020-10-01 積水化学工業株式会社 ABSORBEUR D'ONDES RADIO DE TYPE λ/4

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