WO2019235539A1

WO2019235539A1 - Electromagnetic wave absorber and electromagnetic wave absorber composition

Info

Publication number: WO2019235539A1
Application number: PCT/JP2019/022395
Authority: WO
Inventors: 藤田真男; 廣井俊雄
Original assignee: マクセルホールディングス株式会社
Priority date: 2018-06-08
Filing date: 2019-06-05
Publication date: 2019-12-12
Also published as: JPWO2019235539A1; TWI787517B; TW202000461A

Abstract

Provided are an electromagnetic wave absorber and an electromagnetic wave absorber composition capable of satisfactorily absorbing electromagnetic waves of a predetermined wide bandwidth in a high frequency band over the millimeter wave band. The electromagnetic wave absorber is formed of an electromagnetic wave absorption layer 1 including a magnetic iron oxide 1a that magnetically resonates at a high frequency over the millimeter wave band, and a resin binder 1b. The electromagnetic wave absorber comprises two or more kinds of magnetic iron oxides 1a₁, 1a₂ having different values of anisotropic magnetic field H_A. A differential curve obtained by differentiating a hysteresis loop with a magnetic characteristic between the applied magnetic field intensities of 16kOe and -16kOe has one extreme value.

Description

Electromagnetic wave absorber and electromagnetic wave absorber composition

The present disclosure relates to an electromagnetic wave absorber that absorbs electromagnetic waves, and in particular, a frequency band of several tens of gigahertz (GHz) to several hundred gigahertz (GHz), which is referred to as a millimeter wave band, and even a high frequency up to 3 terahertz (THz). The present invention relates to an electromagnetic wave absorber having a predetermined bandwidth at the frequency of electromagnetic waves to be absorbed and a composition for electromagnetic wave absorbers.

In mobile communications such as mobile phones, wireless LANs, automatic toll collection systems (ETC), etc., electromagnetic waves called centimeter waves having a frequency band of several gigahertz (GHz) are used.

As an electromagnetic wave absorbing sheet that absorbs such a centimeter wave, a laminated sheet in which a rubbery electromagnetic wave absorbing sheet and a paper sheet material such as cardboard are laminated has been proposed (see Patent Document 1). Further, an electromagnetic wave absorbing sheet has been proposed in which electromagnetic wave absorption characteristics are stabilized regardless of the electromagnetic wave incident direction by alternately laminating thin sheets containing anisotropic graphite and a binder and adjusting the thickness thereof ( Patent Document 2).

Furthermore, for the purpose of enabling absorption of electromagnetic waves in a higher frequency band, electromagnetic waves in a frequency band of 20 gigahertz or more can be absorbed by aligning the longitudinal direction of the flat soft magnetic particles with the surface direction of the sheet. An electromagnetic wave absorbing sheet has been proposed (see Patent Document 3).

Further, it is known that an electromagnetic wave absorber having a particle-filled structure having epsilon magnetic iron oxide (ε-Fe ₂ O ₃ ) crystals as a magnetic phase exhibits electromagnetic wave absorbing performance in the range of 25 to 100 gigahertz. (See Patent Document 4).

JP 2011-233834 A JP 2006-80352 A Japanese Patent Laid-Open No. 2015-198163 JP 2008-60484 A

In recent years, in order to further increase the capacity of data to be transmitted, wireless communication using a frequency of 60 gigahertz has been planned, and a so-called in-vehicle radar device utilizing extremely narrow directivity is a so-called tens of gigahertz or more. The use of a millimeter wave laser having a frequency in the millimeter wave band (30 to 300 gigahertz) is being promoted. In addition, research on technology using electromagnetic waves having a frequency on the order of terahertz (THz) as electromagnetic waves in a high frequency band exceeding the millimeter wave band is also progressing.

However, an electromagnetic wave absorber that absorbs an electromagnetic wave having a specific frequency in a so-called millimeter wave band around 60 GHz has been proposed as an electromagnetic wave absorber that is one of electromagnetic wave utilization technologies and is indispensable for preventing leaked electromagnetic waves. However, an electromagnetic wave absorber that absorbs an electromagnetic wave having a predetermined wide bandwidth in a frequency band higher than the millimeter wave band has not been realized.

The present disclosure solves the above-described conventional problems and realizes an electromagnetic wave absorber capable of satisfactorily absorbing an electromagnetic wave having a predetermined wide bandwidth and a composition for the electromagnetic wave absorber in a high frequency band of a millimeter wave band or higher. The purpose is to do.

In order to solve the above problems, an electromagnetic wave absorber disclosed in the present application is an electromagnetic wave absorber formed by an electromagnetic wave absorption layer including magnetic iron oxide magnetically resonating at a high frequency of a millimeter wave band or higher, and a resin binder, _A differential curve obtained by differentiating the hysteresis loop of the magnetic characteristics including two or more kinds of magnetic iron oxides having different values of the anisotropic magnetic field _HA and having an applied magnetic field strength between 16 kOe and -16 kOe has one extreme value. It is characterized by having.

Further, the electromagnetic wave absorber composition disclosed in the present application is a composition for an electromagnetic wave absorber formed by magnetic iron oxide that magnetically resonates at a high frequency of a millimeter wave band or higher, and a resinous binder. includes a magnetic field H and the magnetic iron oxide values two or more different of _a, the magnetic field strength applied is to have a differential curve is one extreme hysteresis loop obtained by differentiating the magnetic properties between -16kOe from 16kOe Features.

Each of the electromagnetic wave absorber and the electromagnetic wave absorber composition disclosed in the present application is an electromagnetic wave absorbing material, and as an electromagnetic wave absorbing material, two or more kinds of anisotropic magnetic fields _HA that magnetically resonate at a high frequency of the millimeter wave band or higher are different. A differential curve obtained by differentiating a hysteresis loop of magnetic characteristics having magnetic iron oxide and an applied magnetic field strength between 16 kOe and −16 kOe has one extreme value. For this reason, electromagnetic waves in a high frequency band of several tens of gigahertz or more can be favorably absorbed over a predetermined wide bandwidth.

It is a section lineblock diagram explaining composition of an electromagnetic wave absorption sheet which is a sheet-like electromagnetic wave absorber concerning this embodiment. It is a figure explaining the electromagnetic wave absorption characteristic of the epsilon magnetic iron oxide which substituted a part of Fe site. It is a figure which shows the relationship between the coercive force of epsilon magnetic iron oxide, and the frequency of the electromagnetic wave absorbed. It is a figure which shows the relationship between the coercive force of strontium ferrite magnetic iron oxide magnetic iron oxide, and the frequency of the electromagnetic wave absorbed. It is a figure which shows the hysteresis loop of a magnetic characteristic in the 1st structural example of the electromagnetic wave absorption layer which comprises the electromagnetic wave absorption sheet concerning this embodiment, and the differential curve which differentiated this. It is a figure which shows the hysteresis loop of a magnetic characteristic in the 2nd structural example of the electromagnetic wave absorption layer which comprises the electromagnetic wave absorption sheet concerning this embodiment, and the differential curve which differentiated this. It is a figure which shows the hysteresis loop of a magnetic characteristic in the 3rd structural example of the electromagnetic wave absorption layer which comprises the electromagnetic wave absorption sheet concerning this embodiment, and the differential curve which differentiated this. It is a figure which shows the hysteresis loop of a magnetic characteristic in the 4th structural example of the electromagnetic wave absorption layer which comprises the electromagnetic wave absorption sheet concerning this embodiment, and the differential curve which differentiated this. It is a figure which shows the hysteresis loop of a magnetic characteristic in the 5th structural example of the electromagnetic wave absorption layer which comprises the electromagnetic wave absorption sheet concerning this embodiment, and the differential curve which differentiated this. It is a figure which shows the hysteresis loop of a magnetic characteristic in the 6th structural example of the electromagnetic wave absorption layer which comprises the electromagnetic wave absorption sheet concerning this embodiment, and the differential curve which differentiated this. It is a figure which shows the absorption frequency and the transmission attenuation amount in the 6th structural example of the electromagnetic wave absorption layer which comprises the electromagnetic wave absorption sheet concerning this embodiment.

The electromagnetic wave absorber disclosed in the present application is an electromagnetic wave absorber formed by an electromagnetic wave absorption layer including magnetic iron oxide that magnetically resonates at a high frequency of a millimeter wave band or higher and a resin binder, and an anisotropic magnetic field _HA A differential curve obtained by differentiating the hysteresis loop of the magnetic characteristics in which the magnetic field strength applied is between 16 kOe and −16 kOe has two extreme values.

By doing so, the electromagnetic wave absorber disclosed in the present application is an anisotropic magnetic field H in which the resonance frequency of magnetic iron oxide, which is a member that absorbs electromagnetic waves, that is, the frequency of electromagnetic waves absorbed by the magnetic iron oxide is determined. _{By including} two or more kinds of magnetic iron oxides having different values of _A, a plurality of peak frequencies of electromagnetic waves absorbed by the respective magnetic iron oxides exist. On the other hand, since the differential curve obtained by differentiating the hysteresis loop of the magnetic characteristics between 16 kOe and −16 kOe has one extreme value, the frequency characteristic of the electromagnetic wave absorbed as a whole of the electromagnetic wave absorber has a shape having one peak. . For this reason, it is possible to obtain an electromagnetic wave absorber having high electromagnetic wave absorption characteristics and at the same time having a wider width in the frequency band of electromagnetic waves absorbed than when only one type of magnetic iron oxide is used.

In the invention disclosed in the present application, “the differential curve obtained by differentiating the hysteresis loop has one extreme value” means that the differential curve has an extreme value, that is, only one inflection point. It is not included when there are two or more values (inflection points).

In the electromagnetic wave absorber disclosed in the present application, it is preferable that two or more kinds of the magnetic iron oxides included in the electromagnetic wave absorption layer have the same main element configuration and different substitute elements. In this way, an electromagnetic wave absorber having more uniform characteristics with excellent dispersibility can be obtained by using an electromagnetic wave absorbing material having similar characteristics such as particle size and shape although the frequency of electromagnetic waves to be absorbed is different. Even when two or more kinds of magnetic iron oxides are used, the differential curve obtained by differentiating the hysteresis loop of the magnetic characteristics can easily have one extreme value.

The magnetic iron oxide is preferably strontium ferrite magnetic iron oxide or epsilon magnetic iron oxide.

Furthermore, it is preferable that the electromagnetic wave absorbing layer is formed to be thin with respect to the size of the electromagnetic wave absorbing layer when viewed in plan, and is formed into a sheet shape as a whole. By doing in this way, the electromagnetic wave absorber disclosed by this application can be utilized as an electromagnetic wave absorption sheet with easy handling.

Further, the electromagnetic wave absorber composition disclosed in the present application is a composition for an electromagnetic wave absorber formed by magnetic iron oxide that magnetically resonates at a high frequency of a millimeter wave band or higher, and a resinous binder. _A differential curve obtained by differentiating the hysteresis loop of the magnetic characteristics including two or more kinds of the magnetic iron oxides having different values of the magnetic field _HA and having an applied magnetic field strength between 16 kOe and −16 kOe has one extreme value.

By doing in this way, the composition for electromagnetic wave absorbers disclosed in the present application forms an electromagnetic wave absorber that has high electromagnetic wave absorption characteristics and at the same time the frequency band of the absorbed electromagnetic waves has a predetermined wide width. Can do.

In the composition for an electromagnetic wave absorber disclosed in the present application, it is preferable that two or more kinds of the magnetic iron oxides included in the electromagnetic wave absorption layer have the same main element configuration and different substitution elements. By doing so, a composition for an electromagnetic wave absorber with more uniform characteristics can be obtained, and a differential curve obtained by easily differentiating the hysteresis loop of the magnetic characteristics even when two or more kinds of magnetic iron oxides are used. Can have one extreme value.

The magnetic iron oxide is preferably either strontium ferrite magnetic iron oxide or epsilon magnetic iron oxide.

Furthermore, the building member and the electronic device formed using the electromagnetic wave absorber composition disclosed in the present application are both high in the above-described electromagnetic wave absorber composition and have a wide frequency band to be absorbed. It can be set as the building member and electronic device provided with the outstanding electromagnetic wave absorption characteristic.

Hereinafter, the electromagnetic wave absorber and the electromagnetic wave absorber composition disclosed in the present application will be described with reference to the drawings.

(First embodiment)
As a first embodiment of the electromagnetic wave absorber disclosed in the present application, an electromagnetic wave absorption layer containing particulate magnetic iron oxide and a resin binder is formed with a thickness smaller than that when viewed in plan. An example of a so-called transmission-type electromagnetic wave absorbing sheet configured as a sheet as a whole will be described.

[Sheet configuration]
FIG. 1 is a cross-sectional view showing a configuration of an electromagnetic wave absorbing sheet as an electromagnetic wave absorber described in the present embodiment.

FIG. 1 shows a state in which an electromagnetic wave absorbing sheet 1 is molded by applying and drying an electromagnetic wave absorbing composition on a resin sheet 2 as a base material.

In addition, FIG. 1 is a figure described in order to make it easy to understand the configuration of the electromagnetic wave absorbing sheet according to the present embodiment, and the size and thickness of the members shown in the figure are represented in actuality. It is not a thing.

The electromagnetic wave absorbing sheet exemplified in this embodiment is formed as an electromagnetic wave absorbing layer 1 including two types of

magnetic iron oxides

1a ₁ and 1a ₂ having different anisotropic magnetic field values _HA and a resin binder 1b. Yes.

In the electromagnetic wave absorbing sheet according to the present embodiment shown in FIG. 1, the two

magnetic iron oxides

1a ₁ and 1a ₂ included in the electromagnetic wave absorbing layer 1 have different anisotropic magnetic field _HA values, and the magnetic iron oxide 1a ₁ is magnetic. The coercive force of iron oxide 1a ₂ is different. Since the frequency of electromagnetic waves absorbed by magnetic iron oxide by magnetic resonance varies depending on the coercive force value, in the electromagnetic wave absorbing sheet of this embodiment, each

magnetic iron oxide

1a ₁ , 1a ₂ absorbs electromagnetic waves having different frequencies. . On the other hand, the electromagnetic wave absorption characteristic of the entire electromagnetic wave absorbing sheet has one extreme value as a differential curve obtained by differentiating a hysteresis loop which is a magnetic characteristic with respect to a magnetic field applied from the outside. This means that the absorption characteristic with respect to the frequency of the electromagnetic wave appears as one mountain shape having a peak at a predetermined frequency.

In the electromagnetic wave absorbing sheet according to the present embodiment, magnetic iron oxides having different values of the anisotropic magnetic field _HA contained as the electromagnetic wave absorbing material thus absorb electromagnetic waves having different frequencies, so that only one type of magnetic iron oxide is used. The frequency band of electromagnetic waves to be absorbed is wider than that of an electromagnetic wave absorbing sheet containing. On the other hand, the differential curve obtained by differentiating the hysteresis loop indicating the magnetic characteristics of the entire electromagnetic wave absorbing sheet has one extreme value, and the frequency characteristics of the absorbed electromagnetic waves are expressed as one mountain shape. In the case of having two peaks, that is, compared to the case where the frequency of the electromagnetic wave absorbed by each magnetic iron oxide is separated and the differential curve obtained by differentiating the hysteresis loop has two maximum values and one minimum value, The peak of electromagnetic wave absorption characteristics can be kept high. For this reason, the electromagnetic wave absorbing sheet according to the present embodiment can achieve both high electromagnetic wave absorption characteristics and a wide absorption frequency band.

In addition, in FIG. 1, although the case where the magnetic iron oxide contained in the electromagnetic wave absorption layer 1 is two types is illustrated, in the electromagnetic wave absorption sheet concerning this embodiment, it is contained in the electromagnetic wave absorption layer 1 so that it may mention later. There may be three or more kinds of magnetic iron oxides.

Further, in the electromagnetic wave absorbing sheet according to the present embodiment, the value of the anisotropic magnetic field _HA of the magnetic iron oxide contained in the electromagnetic wave absorbing layer 1 is different, and the differential curve obtained by differentiating the hysteresis loop of the magnetic characteristics has one extreme value. The state of having will be described later with a specific example.

[Magnetic iron oxide]
In the electromagnetic wave absorbing sheet according to the present embodiment, epsilon magnetic iron oxide is used as the particulate magnetic iron oxide.

Epsilon magnetic iron oxide (ε-Fe ₂ O ₃ ) is an intermediate between the alpha phase (α-Fe ₂ O ₃ ) and the gamma phase (γ-Fe ₂ O ₃ ) in ferric oxide (Fe ₂ O ₃ ). It is a magnetic material that can be obtained in a single-phase state by a nanoparticle synthesis method combining a reverse micelle method and a sol-gel method.

Epsilon magnetic iron oxide has a maximum coercive force as a metal oxide of about 20 kOe at room temperature while being a fine particle of several nm to several tens of nm, and further has a natural resonance due to a gyromagnetic effect based on precession. Since it occurs in the so-called millimeter wave band frequency band above gigahertz, it can be used as an electromagnetic wave absorbing material that absorbs electromagnetic waves in the millimeter wave band.

Further, epsilon magnetic iron oxide is a crystal in which part of the Fe site of the crystal is replaced with a trivalent metal element such as aluminum (Al), gallium (Ga), rhodium (Rh), indium (In), or the like. Thus, the magnetic resonance frequency, that is, the frequency of the electromagnetic wave absorbed when used as an electromagnetic wave absorbing material can be varied.

FIG. 2 shows the relationship between the coercive force Hc of epsilon magnetic iron oxide and the natural resonance frequency f when the metal element substituted for the Fe site is different. Note that the natural resonance frequency f matches the frequency of the electromagnetic wave to be absorbed.

FIG. 2 shows that the natural resonance frequency of epsilon magnetic iron oxide in which a part of the Fe site is substituted differs depending on the type of the substituted metal element and the amount of substitution. Moreover, it turns out that the coercive force of the said epsilon magnetic iron oxide becomes large, so that the value of the natural resonance frequency becomes high.

More specifically, in the case of gallium-substituted epsilon magnetic iron oxide, that is, ε-Ga _x Fe _2-x O ₃ , the frequency band from about 30 GHz to about 150 GHz by adjusting the substitution amount “x”. In the case of aluminum-substituted epsilon magnetic iron oxide, that is, ε-Al _x Fe _2-x O ₃ , a frequency of about 100 GHz to 190 GHz by adjusting the substitution amount “x”. It has an absorption peak in the band. For this reason, the type of element to be replaced with the Fe site of epsilon magnetic iron oxide is determined so as to obtain the natural resonance frequency of the frequency to be absorbed by the electromagnetic wave absorbing sheet, and the electromagnetic wave absorbed by adjusting the amount of substitution with Fe is adjusted. Can be set to a desired value. Furthermore, in the case of epsilon magnetic iron oxide in which the metal to be replaced is rhodium, that is, ε-Rh _x Fe _2-x O ₃ , the frequency band of the electromagnetic wave to be absorbed is shifted in a higher direction from 180 gigahertz to more. It is possible.

Epsilon magnetic iron oxide can be obtained including those in which some Fe sites are metal-substituted. Epsilon magnetic iron oxide can be obtained as particles having an approximately spherical shape or a short rod shape (rod shape) with an average particle size of about 30 nm.

In addition, as magnetic iron oxide used for the electromagnetic wave absorbing sheet according to the present embodiment, strontium ferrite magnetic iron oxide or M-type ferrite can be used in addition to the above-described epsilon magnetic iron oxide.

Strontium ferrite magnetic iron oxide is a system in which Al is added to SrFe ₁₂ O ₁₉ in order to design an electromagnetic wave absorber corresponding to a 60 GHz band wireless LAN. The frequency indicating absorption shifts to the high frequency side. This is considered to correspond to an increase in the value of the anisotropic magnetic field _HA .

M type ferrite pays attention to the fact that the imaginary part (μr ″) of the complex permeability related to electromagnetic wave absorption becomes higher at the frequency at which resonance occurs when the magnetic material is magnetized at a high frequency. because of the anisotropic magnetic field H _a having a material proportional value of the natural resonant frequency f higher the anisotropy field H _a material becomes higher. Natural resonant frequency f of BaFe ₁₂ O ₁₉ is a M-type ferrite, the value of the H _A is calculated as 48GHz from 1.35 mA / m, it is possible to absorb electromagnetic waves of high GHz band. In addition, by substituting part of Fe ³⁺ with (TiMn) ³⁺ or Al ³⁺ , the value of the anisotropic magnetic field _HA is controlled to control the natural resonance frequency f in the range of 5 to 150 GHz. can do.

Thus, by using epsilon magnetic iron oxide, M-type ferrite, and strontium ferrite magnetic iron oxide as magnetic iron oxide, the value of anisotropic magnetic field (H _A ) of each magnetic iron oxide can be controlled. As a result, the frequency of electromagnetic waves absorbed by the electromagnetic wave absorbing sheet containing these magnetic iron oxides in the electromagnetic wave absorbing layer 1 can be changed.

Here, for the epsilon magnetic iron oxide and the strontium ferrite magnetic iron oxide used as the electromagnetic wave absorbing material in the electromagnetic wave absorbing sheet according to the present embodiment, the results of measuring the relationship between the coercive force of each and the frequency of the electromagnetic wave to be absorbed are shown. explain.

FIG. 3 is a diagram showing the relationship between the coercive force of epsilon magnetic iron oxide and the frequency of electromagnetic waves absorbed.

In FIG. 3, for epsilon magnetic iron oxides with different types of substitution elements and substitution amounts, the coercivity (Hc) value (Oe) measured for each and the peak value (GHz) of the frequency of the absorbed electromagnetic wave are shown. Plotting. As shown in FIG. 3, a clear linear relationship is recognized between the coercive force and the absorption frequency of various epsilon magnetic iron oxides as indicated by reference numeral 31 in FIG.

FIG. 4 shows the relationship between the coercive force of strontium ferrite magnetic iron oxide and the frequency of electromagnetic waves absorbed.

In FIG. 4, for the strontium ferrite magnetic iron oxide having different aluminum (Al) substitution amounts, the coercive force (Hc) value (Oe) measured for each and the peak value (GHz) of the frequency of the absorbed electromagnetic wave Is plotted. Although the number of samples is small, even in strontium ferrite magnetic iron oxide, a linear relationship as indicated by reference numeral 41 in FIG. 4 is recognized between the coercive force and the absorption frequency of various strontium ferrite magnetic iron oxides.

From these facts, there is a strong correlation between the coercive force of magnetic iron oxide and the frequency of electromagnetic waves absorbed by the magnetic iron oxide. By changing the coercive force of magnetic iron oxide used as an electromagnetic wave absorbing material, It can be seen that the frequency of the electromagnetic wave to be absorbed can be controlled.

In comparison between FIG. 3 and FIG. 4, for example, when the frequency of the absorbed electromagnetic wave is 75 GHz, the coercive force of epsilon magnetic iron oxide is about 7500 Oe, whereas the coercive force of strontium ferrite magnetic iron oxide is As small as about 2500 Oe. This difference in coercivity is related to the electromagnetic wave absorption characteristics of each member, and epsilon magnetic iron oxide has a higher ability to absorb electromagnetic waves than strontium ferrite magnetic iron oxide.

[Electromagnetic wave absorption layer]
In the electromagnetic wave absorbing sheet according to the present embodiment, in the electromagnetic wave absorbing layer 1, magnetic

iron oxide particles

1a ₁ and 1a ₂ are dispersed by a resin binder 1b, thereby providing flexibility as a sheet.

As the resin-made binder used for the electromagnetic wave absorption layer 1, resin materials such as epoxy resins, polyester resins, polyurethane resins, acrylic resins, phenol resins, melamine resins, rubber resins, and the like can be used. .

More specifically, a compound obtained by epoxidizing hydroxyl groups at both ends of bisphenol A can be used as the epoxy resin. As the polyurethane resin, a polyester urethane resin, a polyether urethane resin, a polycarbonate urethane resin, an epoxy urethane resin, or the like can be used. Acrylic resins include methacrylic resins, alkyl acrylates and / or methacrylic acid alkyl esters in which the alkyl group has 2 to 18 carbon atoms, functional group-containing monomers, and if necessary, these A functional group-containing methacrylic polymer or the like obtained by copolymerizing with another modifying monomer that can be copolymerized with the monomer can be used.

In addition, SIS (styrene-isobrene block copolymer) and SBS (styrene-butadiene block copolymer), which are styrene thermoplastic elastomers, and EPDM (ethylene propylene Diene / rubber) and other rubber materials such as acrylic rubber and silicone rubber can be used as a binder.

In addition, when using a heat-resistant high melting point thermoplastic resin as the thermoplastic resin for forming the electromagnetic wave absorber as a molded body, 6T nylon (6TPA), 9T nylon (9TPA), 10T nylon (10TPA), 12T Aromatic polyamides such as nylon (12TPA), MXD6 nylon (MXDPA) and their alloy materials, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyetheretherketone (PEEK), polyetherimide (PEI), polyphenyl Sulfone (PPSU) or the like can be used.

Also, from the viewpoint of environmental considerations, it is preferable to use a halogen-free resin that does not contain halogen as the resin used as the binder. Since these resin materials are common as binder materials for resin sheets, they can be easily obtained.

In this specification, the term “flexible” means that the electromagnetic wave absorbing layer can be bent to a certain extent, that is, it is flat without causing plastic deformation such as breakage when the sheet is rolled and returned to its original state. The state which returns to a sheet-like sheet is shown.

The electromagnetic wave absorbing layer of the electromagnetic wave absorbing sheet according to the present embodiment uses epsilon magnetic iron oxide as an electromagnetic wave absorbing material. Epsilon magnetic iron oxide is a fine nanoparticle having a particle size of several nm to several tens of nm as described above. For this reason, it is important to disperse well in the binder when forming the electromagnetic wave absorbing layer. For this reason, in the electromagnetic wave absorbing layer, aryl sulfonic acid such as phenylphosphonic acid and phenylphosphonic dichloride, alkylphosphonic acid such as methylphosphonic acid, ethylphosphonic acid, octylphosphonic acid and propylphosphonic acid, or hydroxyethane diphosphonic acid, It contains phosphate compounds such as polyfunctional phosphonic acids such as nitrotrismethylene phosphonic acid. Since these phosphoric acid compounds have flame retardancy and function as a fine magnetic iron oxide powder dispersant, the epsilon magnetic iron oxide particles in the binder can be well dispersed.

More specifically, examples of the dispersant include phenylphosphonic acid (PPA) manufactured by Wako Pure Chemical Industries, Ltd. or Nissan Chemical Industries, Ltd., and phosphoric acid ester “JP-502” manufactured by Johoku Chemical Industries, Ltd. (Product name) can be used.

As an example of the composition of the electromagnetic wave absorbing layer, the resin binder is 2 to 50 parts and the phosphoric acid compound content is 0.1 to 15 parts with respect to 100 parts of epsilon magnetic iron oxide powder. it can. If the resin binder is less than 2 parts, the magnetic iron oxide cannot be dispersed well. In addition, the sheet-like shape cannot be maintained as the magnetic layer. When the amount is more than 50 parts, the volume content of magnetic iron oxide is reduced in the electromagnetic wave absorbing layer, and the magnetic permeability is lowered, so that the effect of electromagnetic wave absorption is reduced.

When the content of the phosphoric acid compound is less than 0.1 part, the magnetic iron oxide cannot be well dispersed using the resin binder. When the amount is more than 15 parts, the effect of satisfactorily dispersing magnetic iron oxide is saturated. In the electromagnetic wave absorbing layer, the volume content of magnetic iron oxide is reduced and the magnetic permeability is lowered, so that the effect of electromagnetic wave absorption is reduced.

[Method of manufacturing electromagnetic wave absorbing sheet]
Here, the manufacturing method of the electromagnetic wave absorption sheet concerning this embodiment is demonstrated.

The electromagnetic wave absorbing sheet of the present embodiment is formed, for example, by producing a magnetic paint containing at least magnetic iron oxide powder and a resinous binder, applying it at a predetermined thickness, drying it, and calendering it. can do.

In addition, as a magnetic coating component, at least magnetic iron oxide powder, a phosphoric acid compound as a dispersant, and a binder resin are mixed at high speed with a high-speed stirrer to prepare a mixture, and then the resulting mixture is dispersed in a sand mill. By doing so, a magnetic paint can be obtained.

An electromagnetic wave absorbing sheet is produced using the magnetic paint thus produced.

When producing an electromagnetic wave absorbing sheet, as shown in FIG. 1, the produced magnetic paint is applied on a resin sheet 2. As an example of the resin sheet 2, a sheet of polyethylene terephthalate (PET) having a thickness of 38 μm, the surface of which has been peeled off by silicon coating, can be used. A magnetic paint is applied onto the resin sheet 2 using an application method such as a table coater method or a bar coater method.

Thereafter, the wet-state magnetic paint is dried and further calendered to form an electromagnetic wave absorbing sheet on the support. The thickness of the electromagnetic wave absorbing sheet can be controlled by the coating thickness, the calendering conditions, and the like. The electromagnetic wave absorbing sheet 1 after the calendar process is peeled from the resin sheet 2 to obtain the electromagnetic wave absorbing sheet 1 having a desired thickness.

The calendar process may be performed as necessary. If the volume content of the magnetic iron oxide powder is within a predetermined range with the magnetic paint dried, the calendar process may not be performed. Absent.

Also, an electromagnetic wave absorbing layer of the electromagnetic wave absorbing sheet is formed by preparing a magnetic compound containing at least a magnetic iron oxide powder and a resin binder such as rubber, molding the resultant to a predetermined thickness, and crosslinking the resultant. Can do.

Specifically, first, a magnetic compound is prepared. The magnetic compound can be obtained by kneading magnetic iron oxide powder, a dispersant, and a resin binder. As an example, the kneaded product can be obtained by kneading with a pressure batch kneader. In addition, a crosslinking agent can be mix | blended as needed at this time.

The obtained magnetic compound is cross-linked and molded into a sheet at a temperature of 150 ° C. using a hydraulic press machine as an example. Thereafter, an electromagnetic wave absorbing layer can be formed by performing a secondary cross-linking treatment in a thermostatic chamber.

In addition, the molding can be performed by extrusion molding or injection molding in addition to the press molding described above. Specifically, magnetic iron oxide powder, a binder, and a dispersant as necessary are pre-blended with a pressure kneader, an extruder, a roll mill, etc., and these blended materials are fed from the resin supply port of the extruder. Supply into plastic cylinder. As an extrusion molding machine, a normal extrusion machine including a plastic cylinder, a die provided at the tip of the plastic cylinder, a screw rotatably disposed in the plastic cylinder, and a drive mechanism for driving the screw. A molding machine can be used. The molten material plasticized by the band heater of the extrusion molding machine is fed forward by the rotation of the screw and extruded from the tip into a sheet shape, whereby an electromagnetic wave absorbing layer having a predetermined thickness can be obtained.

Also, magnetic iron oxide powder, dispersant, and binder are pre-blended as necessary, and these blended materials are fed into the plastic cylinder from the resin supply port of the injection molding machine, and melt kneaded with a screw in the plasticizing cylinder. Thereafter, the molded body can be formed by injecting the molten resin into a mold connected to the tip of the injection molding machine.

[Base film, adhesive layer]
Although illustration is abbreviate | omitted, the electromagnetic wave absorption sheet concerning this embodiment can form the electromagnetic wave absorption layer 1 on a base film.

When the formed electromagnetic wave absorption layer 1 is thin and a predetermined strength as the electromagnetic wave absorption sheet 1 cannot be obtained, it is preferable to laminate a base film which is a resin base material on the back side of the electromagnetic wave absorption layer 1.

In addition, as a base film, it can comprise using paper members, such as various resin films, such as PET film, rubber | gum, and Japanese paper. The material and thickness of the base film do not affect the electromagnetic wave absorption characteristics in the electromagnetic wave absorbing sheet according to the present embodiment, so from a practical viewpoint such as the strength of the electromagnetic wave absorbing sheet and ease of handling, an appropriate material is used. And the base film which has suitable thickness can be selected.

Furthermore, in the electromagnetic wave absorbing sheet according to the present embodiment, an adhesive layer (not shown) is formed on the back side of the electromagnetic wave absorbing layer 1 or on the surface opposite to the side on which the electromagnetic wave absorbing layer 1 of the base film is formed. be able to.

By providing the adhesive layer, the electromagnetic wave absorbing sheet composed of the electromagnetic wave absorbing layer 1 can be easily placed at a desired position on the inner surface of the housing housing the electric circuit, or on the inner surface or outer surface of the electric device, regardless of the presence or absence of the base film. Can be attached. In particular, since the electromagnetic wave absorbing sheet 1 of the present embodiment is one in which the electromagnetic wave absorbing layer 1 has flexibility, it can be easily attached on a curved surface, and the handling ease of the electromagnetic wave absorbing sheet is improved. .

As the adhesive layer, a known material used as an adhesive layer such as an adhesive tape, an acrylic adhesive, a rubber adhesive, a silicone adhesive, or the like can be used. Moreover, a tackifier and a crosslinking agent can also be used in order to adjust the adhesive force to the adherend and reduce adhesive residue. The adhesive strength with respect to the adherend is preferably 5 N / 10 mm to 12 N / 10 mm. When the adhesive strength is less than 5 N / 10 mm, the electromagnetic wave absorbing sheet may be easily peeled off from the adherend or may be displaced. Moreover, when adhesive force is larger than 12 N / 10mm, it will become difficult to peel an electromagnetic wave absorption sheet from a to-be-adhered body.

The thickness of the adhesive layer is preferably 20 μm to 100 μm. When the thickness of the adhesive layer is less than 20 μm, the adhesive force is reduced, and the electromagnetic wave absorbing sheet may be easily peeled off or displaced from the adherend. When the thickness of the adhesive layer 4 is larger than 100 μm, it is difficult to peel the electromagnetic wave absorbing sheet from the adherend. In addition, when the cohesive force of the adhesive layer is small, adhesive residue may be generated on the adherend when the electromagnetic wave absorbing sheet is peeled off.

In the specification of the present application, the adhesive layer may be an adhesive layer that cannot be peeled off or may be an adhesive layer that can be peeled off.

In addition, when adhering the electromagnetic wave absorbing sheet to a predetermined surface, it is needless to say that the electromagnetic wave absorbing sheet has an adhesive layer on the surface on the side of the member on which the electromagnetic wave absorbing sheet is disposed. An electromagnetic wave absorbing sheet can be attached to a predetermined site using adhesiveness or using a double-sided tape or an adhesive. In this respect, the adhesive layer is not an essential component in the electromagnetic wave absorbing sheet shown in the present embodiment.

[Hysteresis loop and differential curve differentiated]
FIG. 5 is a diagram illustrating a hysteresis loop of magnetic characteristics and a differential curve obtained by differentiating the hysteresis loop in the first configuration example of the electromagnetic wave absorbing layer of the electromagnetic wave absorbing sheet according to the present embodiment.

The hysteresis curves shown in the following figures are obtained by preparing a sample containing a predetermined magnetic iron oxide having a diameter of 8 mmφ and a thickness of 2 mm. The vibration sample magnetometer VSM-P7 (product of Toei Kogyo Co., Ltd.) The applied magnetic field was measured in the range of 16 kOe to -16 kOe. The measurement time constant Tc is set to 0.03 sec.

As shown in FIG. 5, a magnetization curve 51 indicating the strength of magnetization remaining in magnetic iron oxide when a magnetic field whose strength changes from the outside is applied draws a so-called hysteresis curve. Magnetic iron oxide that causes magnetic resonance at a high frequency of several tens to several hundreds of gigahertz in the millimeter wave band and further up to 3 terahertz is a gyromagnetic resonance type magnetic material and has a high coercive force. When the magnetic characteristics between 1 and -16 kOe are measured, the hysteresis curve of magnetic iron oxide has a slanting shape. At this time, the value of the applied magnetic field that reaches the saturation magnetic field in the magnetization curve in the hard axis direction is the value of the anisotropic magnetic field _HA of magnetic iron oxide, and this value is the strength of the applied magnetic field in which spins are aligned in one direction. Is shown.

The relationship represented by the following formula (1) is established between the value of the anisotropic magnetic field _HA and the natural magnetic resonance frequency fr of the magnetic material.

fr = ν / 2π * _HA (1)
Here, ν is a gyro magnetic constant, which is a value determined by the type of magnetic material.

As described above, in the gyro magnetic resonance type magnetic body, since the proportional relationship is established between the value of the anisotropic magnetic field _HA and the natural magnetic resonance frequency fr, the electromagnetic wave absorption layer 1 of the present embodiment has different anisotropic properties. By including a plurality of magnetic iron oxides having different coercive forces having values of the sexual magnetic field _{HA in} the electromagnetic wave absorbing sheet, magnetic resonance is caused at different frequencies, and electromagnetic waves of the frequencies are converted into heat and attenuated. As a result, in the electromagnetic wave absorbing sheet according to the present embodiment, each magnetic iron oxide can absorb an electromagnetic wave having a predetermined frequency, and the electromagnetic wave absorbing layer has different coercive forces having different values of the anisotropic magnetic field _HA. By including a plurality of magnetic iron oxides having the above, electromagnetic waves of a plurality of frequencies can be absorbed.

In the electromagnetic wave absorbing sheet according to the present embodiment, the electromagnetic wave absorbing layer 1 includes two or more magnetic iron oxides having different anisotropic magnetic field _HA values, and the electromagnetic wave absorbing sheet is applied from the outside. A differential curve 52 obtained by differentiating the hysteresis curve 51 of the magnetic characteristics between 16 kOe and -16 kOe of the magnetic field intensity has one extreme value, that is, a mountain shape having one peak as shown in FIG. .

In the example shown in FIG. 5, epsilon magnetic iron oxide having an electromagnetic wave shielding frequency (natural resonance frequency) of 76 GHz and 79 GHz was mixed at a ratio of 1: 1, and a magnetic paint was prepared with the following composition.

Magnetic iron oxide powder Epsilon magnetic iron oxide 100 parts (peak absorption wavelength 76 GHz: 79 GHz = 1: 1)
Dispersant DISPERBYK-142 (trade name) 15 parts Solvent Methyl ethyl ketone / toluene (= 1/1 mixed solvent)
95 parts The coercive force of epsilon magnetic iron oxide was 7544 Oe having a peak absorption wavelength of 76 GHz and 7944 Oe having a peak absorption wavelength of 79 GHz.

This magnetic paint component was dispersed with a zirconia bead having a diameter of 0.5 mm in a disc-type sand mill having an internal volume of 2 L. While stirring the dispersed paint thus obtained with a stirrer, the following materials were blended and dispersed under the conditions described as the method for producing the electromagnetic wave absorbing sheet to obtain a magnetic paint.

Magnetic paint component 100 parts Polyurethane binder (Byron UR8700 (trade name)) 46 parts Solvent (dilution) Methyl ethyl ketone / toluene (= 1/1 mixed solvent)
120 copies.

Subsequently, the obtained magnetic coating material was applied onto a 38 μm-thick polyethylene terephthalate (PET) sheet peel-treated with a silicon coat using a bar coater, dried in a wet state at 80 ° C. for 1440 minutes, A 400 μm thick sheet was obtained. The sheet thus obtained was calendered at a temperature of 80 ° C. and a pressure of 150 kg / cm to obtain an electromagnetic wave absorbing sheet having a thickness of 300 μm.

In this electromagnetic wave absorbing sheet, as shown in FIG. 5, the differential curve 52 of the hysteresis curve 51 is expressed as a mountain shape that draws one peak, and the sample to be measured has two anisotropic magnetic fields _HA . While the magnetic oxide having a value is included, the value of the anisotropic magnetic field _HA , that is, the difference in coercive force that determines the frequency of the electromagnetic wave to be absorbed is as small as 400 Oe. It turns out that the electromagnetic wave absorption characteristic which has this is shown.

In the case of the first configuration example of the electromagnetic wave absorbing sheet shown in FIG. 5, the values of the anisotropic magnetic fields _HA of the two epsilon magnetic iron oxides are 7544 Oe and 7944 Oe, and the electromagnetic wave shielding (absorption) frequency (76 GHz). , 79 GHz) was 3 GHz. According to the study by the inventors, if the difference in the shielding frequency of the magnetic iron oxide contained in the electromagnetic wave absorbing layer is 5 GHz or less, the differential curve of the hysteresis curve has one extreme value as the curve 52 shown in FIG. It was confirmed that the shape had a shape, that is, a single mountain shape. On the other hand, when the difference in absorption wavelength is 5 GHz or more, it turns out that the differential curve obtained by differentiating the hysteresis loop becomes a bimodal shape having two peaks, and the electromagnetic wave absorption characteristics at the center of the two peaks are deteriorated. It was.

Next, the magnetic properties of the electromagnetic wave absorbing sheet using strontium ferrite magnetic iron oxide as the electromagnetic wave absorbing material were confirmed.

6 to 10 all show hysteresis curves of magnetic characteristics in which the magnetic field strength applied from the outside of the electromagnetic wave absorbing sheet using strontium ferrite magnetic iron oxide is between 16 kOe and −16 kOe, and differential curves obtained by differentiating the hysteresis curves. Is shown.

FIG. 6 shows the case of the second configuration example of the electromagnetic wave absorbing sheet containing strontium ferrite magnetic iron oxide having electromagnetic wave shielding frequencies of 75 GHz and 76 GHz. Moreover, FIG. 7 shows the case of the 3rd structural example of the electromagnetic wave absorption sheet containing strontium ferrite magnetic iron oxide whose electromagnetic wave shielding frequency is 75 GHz and 77 GHz. FIG. 8 shows the case of the fourth configuration example of the electromagnetic wave absorbing sheet containing strontium ferrite magnetic iron oxide having electromagnetic wave shielding frequencies of 76 GHz and 77 GHz. FIG. 9 shows the case of the fifth configuration example of the electromagnetic wave absorbing sheet containing three types of strontium ferrite magnetic iron oxides having electromagnetic wave shielding frequencies of 75 GHz, 76 GHz, and 77 GHz. Furthermore, FIG. 10 shows the case of the sixth configuration example of the electromagnetic wave absorbing sheet containing five types of strontium ferrite magnetic iron oxides having an electromagnetic wave shielding frequency of 76 GHz, 81 GHz, 86 GHz, 91 GHz, and 96 GHz.

Each electromagnetic wave absorbing sheet was prepared using the following materials using a silicone rubber binder KE-510-U (trade name: manufactured by Shin-Etsu Chemical Co., Ltd.) as a binder.

Magnetic Iron Oxide Powder Strontium Ferrite Magnetic Iron Oxide 100 parts Materials with different shielding frequencies in the same ratio (1: 1, 1: 1: 1,
Mixing with 1: 1: 1: 1: 1) Dispersant DISPERBYK-142 (trade name) 15 parts Solvent Methyl ethyl ketone / toluene (= 1/1 mixed solvent)
95 parts.

This magnetic paint component was dispersed in a disk-type sand mill having an internal volume of 2 L using zirconia beads having a diameter of 0.5 mm as a dispersion medium. While stirring the dispersion paint thus obtained with a stirrer, the following materials were blended and dispersed under the conditions described as the method for producing the electromagnetic wave absorbing sheet to obtain a magnetic paint. Magnetic paint component 100 parts Polyurethane binder ( Byron UR8700 (trade name)) 46 parts Solvent (dilution) Methyl ethyl ketone / toluene (= 1/1 mixed solvent)
120 copies.

Subsequently, the obtained magnetic coating material was applied onto a 38 μm-thick polyethylene terephthalate (PET) sheet peel-treated with a silicon coat using a bar coater, dried in a wet state at 80 ° C. for 1440 minutes, A 400 μm thick sheet was obtained.

Note that the strontium ferrite magnetic iron oxide having different shielding frequencies was produced by changing the substitution amount when the strontium element of the strontium ferrite magnetic iron oxide was substituted with gallium.

As shown in FIGS. 6 to 10, when strontium ferrite magnetic iron oxide is used as the electromagnetic wave absorbing material, hysteresis loops (61, 71, 81) are compared with the case where epsilon magnetic iron oxide shown in FIG. 5 is used. , 91, 101), and the coercivity of strontium ferrite magnetic iron oxide is smaller than that of epsilon magnetic iron oxide. On the other hand, in any of the second configuration to the fifth configuration of the electromagnetic wave absorbing sheet, the differential curve (62, 72, 82, 92, 102) obtained by differentiating the hysteresis loop (61, 71, 81, 91, 101). Each shows a single mountain shape, and it can be seen that the differential curve has one extreme value.

As described above, when strontium ferrite magnetic iron oxide is used as the electromagnetic wave absorbing material, it includes two or more magnetic iron oxides having different anisotropic magnetic field values _HA , while the entire electromagnetic wave absorbing layer has a hysteresis loop. Since the differential curve has one extreme value, it can be seen that both high electromagnetic wave absorption characteristics and a wide absorption wavelength band can be achieved.

Especially in order to improve electromagnetic wave absorption characteristics in a wide absorption band, it can be realized by combining many materials having different shielding frequencies. In this case, in order for the differential curve of the hysteresis curve to have one extreme value and to have a single mountain shape, it is preferable that the difference between the shielding frequencies of the materials at the shielding frequencies is 5 GHz or less.

As an example, the relationship between the frequency and transmission attenuation was measured for an electromagnetic wave absorbing sheet using strontium ferrite magnetic iron oxide having five different shielding frequencies with a shielding frequency difference of 5 GHz shown in FIG.

FIG. 11 is a diagram showing the relationship between the frequency of electromagnetic waves and the amount of transmission attenuation in the electromagnetic wave absorbing sheet of the sixth configuration example.

As shown by reference numeral 111 in FIG. 11, when strontium ferrite magnetic iron oxide having five different shielding frequencies with a difference in shielding frequency of 5 GHz is used, a good transmission attenuation of 10 dB or more in a very wide absorption band It was found that Although illustration of data is omitted, even in an electromagnetic wave absorbing sheet using strontium ferrite magnetic iron oxide having six or more different shielding frequencies, if the difference in shielding frequency of each strontium ferrite magnetic iron oxide is within 5 GHz, It was confirmed that the transmission attenuation was good in a wide absorption band.

5 to 10 described above, the ratio of the magnetic iron oxide contained in the electromagnetic wave absorbing layer is the same in all of the first to sixth structures of the electromagnetic wave absorbing sheet showing the hysteresis loop and its differential curve. That is, the case of 1: 1, 1: 1: 1, or 1: 1: 1: 1: 1 is shown. However, in the electromagnetic wave absorbing sheet according to the embodiment of the present application, the content of the magnetic iron oxide contained in the electromagnetic wave absorbing layer is not limited to the same, and may be contained in different proportions. The inventors have confirmed that the hysteresis loop differential curve is 1 when the content of the magnetic iron oxide contained is the same (1: 1, 1: 1: 1, 1: 1: 1: 1: 1). In the case of having two extreme values, it was confirmed that even when the content of magnetic iron oxide having different anisotropic magnetic field ( _HA ) values was different, the hysteresis loop differential curve had one extreme value. . Furthermore, as shown in FIG. 11, when the ratio of five types of magnetic iron oxides having different shielding frequencies is the same content (1: 1: 1: 1: 1), 10 dB or more in a very wide absorption band It was found that the transmission attenuation was good.

In addition, about content of the magnetic iron oxide contained in an electromagnetic wave absorption layer, it is content of the magnetic iron oxide which has a value of a different anisotropic magnetic field ( _HA ) from a viewpoint of expanding the frequency band of the electromagnetic wave to absorb favorably. The amount is preferably as uniform as possible.

Thus, in the electromagnetic wave absorbing sheet as the electromagnetic wave absorber according to the present embodiment, the value of the anisotropic magnetic field (H _A ) of the magnetic iron oxide contained in the electromagnetic wave absorbing layer is different, while the hysteresis loop derivative of the magnetic characteristics is differentiated. Since the curve has one extreme value, it can have higher absorption characteristics with respect to electromagnetic waves in a wider frequency band than when only one magnetic iron oxide is included. In addition, the electromagnetic wave absorber disclosed in the present application has a predetermined thickness by forming the electromagnetic wave absorption layer as a molded body in addition to a sheet shape having a small thickness with respect to the size when viewed in plan. It can be a block shape.

In the above-described embodiment, an example in which two or more magnetic iron oxides having different anisotropic magnetic field (H _A ) values are included in one electromagnetic wave absorbing layer is shown. However, the anisotropic magnetic field (H _A ) Even if magnetic iron oxides with different values are dispersed and contained in two or more electromagnetic wave absorption layers, the differential curve of the hysteresis loop of magnetic characteristics has one extreme value, It can be set as the electromagnetic wave absorber which can absorb electromagnetic waves favorably.

(Second Embodiment)
Next, the electromagnetic wave absorber composition disclosed in the present application will be described.

The composition for an electromagnetic wave absorber shown as the second embodiment means a magnetic paint used when producing an electromagnetic wave absorbing sheet which is the electromagnetic wave absorber described in the first embodiment.

This magnetic paint contains a plurality of magnetic oxides having different coercive forces by having a predetermined anisotropic magnetic field ( _HA ) value in a resin binder. As a solid electromagnetic wave absorber solidified in a bulk shape, it has the same electromagnetic wave absorption characteristics as the above-mentioned electromagnetic wave absorbing sheet. In addition, as for the magnetic characteristics of the entire electromagnetic wave absorber, the differential curve of the hysteresis loop has one extreme value, as in the electromagnetic wave absorbing sheet described in the first embodiment.

Using magnetic paint as a composition for electromagnetic wave absorber containing magnetic iron oxide particles and resin binder, magnetic paint can be applied to a wide range of building materials such as members with complicated surface shapes, walls, ceilings, etc. A coating film can be formed to impart electromagnetic wave absorption characteristics. It is also possible to apply a magnetic paint to an electronic device such as an IC chip or a transmitter that generates electromagnetic waves, and directly mold a coating layer having electromagnetic absorption characteristics on these electronic devices. As a result, the entire device having a complicated shape that generates electromagnetic waves can be shielded. Further, the entire room can be shielded from electromagnetic waves having a plurality of frequencies.

As a method of applying the electromagnetic wave absorber composition disclosed in the present application to a wide surface portion such as a member having a complicated surface shape, a wall surface, or a ceiling, a method of applying to the surface using a brush or the like, a method of spraying with a spray and so on.

In this case as well, the frequency of the electromagnetic wave absorbed by the composition for electromagnetic wave absorbers depends on the value of the anisotropic magnetic field (H _A ) of the magnetic oxide contained, and contains only one magnetic iron oxide. Compared to the case, electromagnetic waves in a wider frequency band can be favorably absorbed.

In addition, the composition for electromagnetic wave absorbers can function as a member that selectively transmits electromagnetic waves having frequencies other than the extreme value portion of the differential curve, in addition to functioning as a member that absorbs electromagnetic waves having a predetermined frequency.

As described above, the electromagnetic wave absorber disclosed in the present application can be realized in a sheet shape, a block shape, and various shapes. Moreover, the composition for electromagnetic wave absorbers disclosed in the present application is supplied to other members and components including the above-exemplified building members and electronic devices by coating, pouring, sticking, and other methods. Thus, good electromagnetic wave absorption characteristics can be imparted to the other members and components.

As described above, the electromagnetic wave absorber and the electromagnetic wave absorber composition disclosed in the present application include two or more kinds of magnetic iron oxides having different anisotropic magnetic fields _{HA in} the electromagnetic wave absorbing layer, and an external magnetic field. A differential curve obtained by differentiating the hysteresis loop of the magnetic characteristics obtained by application has one extreme value. For this reason, the electromagnetic wave absorber and the electromagnetic wave absorber composition disclosed in the present application have a wider frequency band of absorbed electromagnetic waves than those having an electromagnetic wave absorbing layer containing one type of magnetic iron oxide. And high absorption characteristics can be realized.

Note that the strength of the external magnetic field for measuring the hysteresis loop is set to 16 kOe to −16 kOe means that a good hysteresis loop can be obtained by applying an external magnetic field in this range at least. . For this reason, there is no problem even if the magnitude of the applied external magnetic field is greater than 16 kOe, the hysteresis loop is measured in the range of 16 kOe to −16 kOe, and the derivative is obtained. Find a curve.

The electromagnetic wave absorber and the electromagnetic wave absorber composition disclosed in the present application are useful as an electromagnetic wave absorbing member that satisfactorily absorbs an electromagnetic wave in a wider frequency band in a high frequency band of the millimeter wave band or higher.

1 the electromagnetic wave absorbing layer 1a (1a _1, 1a ₂₎ magnetic iron oxide particles 1b resinous binder

Claims

An electromagnetic wave absorber formed by an electromagnetic wave absorbing layer containing a magnetic iron oxide magnetically resonating at a high frequency of the millimeter wave band or higher and a resin binder,
Including two or more magnetic iron oxides having different values of the anisotropic magnetic field HA ,
An electromagnetic wave absorber characterized in that a differential curve obtained by differentiating a hysteresis loop of a magnetic characteristic having an applied magnetic field strength between 16 kOe and -16 kOe has one extreme value.
2. The electromagnetic wave absorber according to claim 1, wherein two or more kinds of the magnetic iron oxides contained in the electromagnetic wave absorbing layer have the same main element configuration and different substitute elements.
The electromagnetic wave absorber according to claim 1 or 2, wherein the magnetic iron oxide is one of strontium ferrite magnetic iron oxide and epsilon magnetic iron oxide.
The electromagnetic wave absorber according to any one of claims 1 to 3, wherein the electromagnetic wave absorbing layer is formed to be thin with respect to a size when viewed in plan, and has a sheet shape as a whole.
A composition for an electromagnetic wave absorber formed by magnetic iron oxide magnetically resonating at a high frequency of the millimeter wave band or higher, and a resin binder,
Including two or more magnetic iron oxides having different values of the anisotropic magnetic field HA ,
A composition for an electromagnetic wave absorber, wherein a differential curve obtained by differentiating a hysteresis loop having a magnetic characteristic with an applied magnetic field strength between 16 kOe and -16 kOe has one extreme value.
The composition for an electromagnetic wave absorber according to claim 5, wherein two or more kinds of the magnetic iron oxides contained in the electromagnetic wave absorbing layer have the same main element constitution and different substitute elements.
The composition for an electromagnetic wave absorber according to claim 5 or 6, wherein the magnetic iron oxide is one of strontium ferrite magnetic iron oxide and epsilon magnetic iron oxide.
A building member formed using the electromagnetic wave absorber composition according to any one of claims 5 to 7.
An electronic device, wherein at least part of the coating layer is covered with the electromagnetic wave absorber composition according to any one of claims 5 to 7.