JP2002198683A - Electromagnetic wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorber capable of having electromagnetic loss effects like synergistic effects at the time of using both a magnetic body and a high dielectric. SOLUTION: This electromagnetic wave absorber is constituted of a magnetic body (a) whose aspect ratio is 3 or more, a high dielectric (b) whose aspect ratio is 3 or more, and a binder (c).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave absorber which can be suitably installed in a housing of an electronic device, a communication device and the like, a building, a building and the like.

[0002]

2. Description of the Related Art In general, housings of electronic equipment, communication equipment and the like are made of a synthetic resin excellent in lightweight and moldability, a metal plate of aluminum or the like, or a composite material thereof. 2. Description of the Related Art Some internal circuits and electric components of electronic devices generate unwanted electromagnetic waves that cause radio interference such as noise and image distortion. In particular,
Many communication devices, information devices, electronic devices equipped with integrated circuits, etc., handle high-frequency signals, and there is a high possibility that high-frequency leakage causing radio interference will occur. Standards are set for electromagnetic waves generated from electronic devices so as not to adversely affect the environment, and electronic devices are manufactured to meet the standards. However, these series of actions are performed by EMC measures (electromagnetic code).
mpatibility).

When the housing of an electronic device is made of synthetic resin,
Because synthetic resin has the property of transmitting electromagnetic waves well,
The leakage of the electromagnetic waves as described above becomes severe, and radio interference occurs. In order to prevent the leakage of electromagnetic waves, an attempt was made to use an electromagnetic wave shielding resin in which synthetic resin contains metal powder or the like having the property of shielding electromagnetic waves. However, the material cost is high and the performance of the synthetic resin such as moldability is reduced.

[0004] On the other hand, with the development of a highly information-oriented society, the use of the above electronic devices, communication devices, and the like is rapidly spreading not only in corporations but also in ordinary households.
Accordingly, in an intelligent office or the like in which a large number of communication / information devices are installed, mutual interference of electromagnetic waves, interference due to delay dispersion due to multiple reflection, malfunction, and the like are likely to occur. Furniture such as metal furniture has a large number of metal surfaces that reflect electromagnetic waves, and thus, there is a problem of deterioration of the electromagnetic wave environment. In particular, in a space using indoor wireless communication such as a wireless LAN, interference, interference, and the like due to delay dispersion caused by repeated reflection of communication waves in a room are problematic.

[0005] In order to prevent the leakage of electromagnetic waves generated inside the housing of electronic equipment as described above, and to improve the electromagnetic wave environment in buildings, electromagnetic wave absorbers made of electromagnetic wave absorbing materials have conventionally been used. I have. To prevent the leakage of electromagnetic waves generated inside the housing of an electronic device, Japanese Patent Application Laid-Open No. 6-97691 discloses a method in which a conductive layer is provided inside a housing, and a ferrite powder and a binder resin are provided thereon. An electromagnetic wave concealing structure having a thin film composed of the same is disclosed.

Japanese Patent Application Laid-Open No. Hei 6-209180 discloses an inner wall material for a building that absorbs electromagnetic waves, which is mainly composed of gypsum, asbestos cement or calcium silicate, and is composed of carbon, ferrite, metal powder, One containing these mixtures is disclosed.

In general, for an electromagnetic wave, if the values of the relative permittivity and relative permeability of a propagating substance are known, when the electromagnetic wave of an arbitrary frequency is incident on the substance having an arbitrary thickness, Can be estimated by calculation. That is, parameters necessary for estimating the electromagnetic wave absorption of a substance by calculation are the relative permittivity, relative permeability and thickness of the substance through which the electromagnetic wave propagates, and the frequency of the electromagnetic wave. In each of the above-mentioned technologies, a substance having mainly magnetic loss is contained as an electromagnetic wave loss material.

[0008] Japanese Patent Application Laid-Open No. Hei 5-27060 discloses that a shape having a shortest axis of 3 to 15 μm is provided for the purpose of greater electromagnetic wave loss.
An electromagnetic wave absorbing composite material comprising a high magnetic susceptibility magnetic alloy powder having an m and an aspect ratio of 100 or more and an insulator is disclosed. However, particles having a higher aspect ratio of the magnetic material can exhibit greater magnetic loss. However, as the aspect ratio increases, the amount of particles that can be filled in the binder decreases. Therefore,
There is a limit to the method of designing a high-performance electromagnetic wave absorber by adjusting the aspect ratio.

Japanese Patent Application Laid-Open No. Hei 4-212199 discloses a multilayer radio wave absorber comprising a ferrite-containing layer having radio wave loss capability and a magnetic alloy layer containing a transition metal element formed thereon. ing. This is intended to improve the absorption characteristics by laminating sheets having different characteristics.However, this method is a method of using each of them alone to achieve a combined effect of performance or less. Only performance could be expected.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electromagnetic wave absorber having an electromagnetic wave loss effect not synergistically but synergistically when a magnetic material and a high dielectric material are used in combination. Is what you do.

[0011]

According to the present invention, a magnetic material (a) having an aspect ratio of 3 or more, a high dielectric material (b) having an aspect ratio of 3 or more, and a binder (c) are provided. It is a characteristic electromagnetic wave absorber. Hereinafter, the present invention will be described in detail.

By using a combination of the magnetic material (a) having a specific value of the aspect ratio and the high-dielectric material (b), the present inventors have realized a synergistic effect, not a summation effect, of each. Have been found, and the present invention has been completed. In general, a material having a relative dielectric constant A and a material having a relative dielectric constant B are referred to as α volume% and (100
-Α) The relative dielectric constant X of the material composited to be volume%
Is the following logarithmic mixed equation: logX = α / 100 × logA + (100−α) / 1
The value can be estimated as 00 × logB. this is,
When a material having a relative permittivity A and a material having a relative permittivity B are combined, the relative permittivity X of the obtained composite material becomes a sum of the relative permittivities of the respective materials according to the blending volume%. It represents that. However, when the magnetic material (a) having a specific value of the aspect ratio and the high dielectric material (b) are used in combination, it is found that the magnetic material has a very large electromagnetic characteristic value that does not follow the logarithmic mixing equation. The present invention is based on such findings. The magnitude of the magnetic loss of the electromagnetic wave absorber is proportional to the magnitude of the imaginary term of the relative magnetic permeability, and the magnitude of the dielectric loss is proportional to the magnitude of the imaginary term of the relative permittivity.

The electromagnetic wave absorber of the present invention comprises a magnetic substance (a) having an aspect ratio of 3 or more, a high dielectric substance (b) having an aspect ratio of 3 or more, and a binder (c). In the present invention, the magnetic material (a) has an aspect ratio of 3 or more. If the aspect ratio is less than 3,
The developed magnetic loss is small, and the performance of absorbing electromagnetic waves is poor. Examples of the shape of the magnetic material (a) include a fibrous shape such as a whisker; and a flat shape. Preferably, the aspect ratio is from 3 to 500. 5
If it exceeds 00, the amount of the magnetic substance (a) that can be blended in the binder (c) becomes small, and a sufficient magnetic loss may not be exhibited. More preferably, the aspect ratio is from 5 to 300. The magnetic material (a) has an average major axis of 50 to 500 μm, an average minor axis of 1 to 3
One having a thickness of 00 μm and an average thickness of 0.1 to 30 μm can be used.

Examples of the magnetic material (a) include a metal magnetic material and a metal oxide magnetic material. The metal magnetic material is not particularly limited. For example, pure iron-based metal powder, iron nitride powder, Fe-Si-Al alloy (Sendust), Ni-Fe alloy (Permalloy), Co-Fe alloy, Fe-based or An amorphous alloy having a Co group can be used.

[0015] There are no particular restrictions regarding the metal oxide magnetic material, for example, MnO to _{Fe 2 O 3, ZnO, NiO} ,
MgO, CuO, ferrite combining the Li ₂ O or the like; NiO-MnO-ZnO-Fe 2 O 3, MnO-Z
_{nO-Fe 2 O 3, NiO} -ZnO-Fe 2 spinel ferrite of O ₃ and the like; garnet-type ferrite; spinel (cubic) of gamma-Fe ₂ O _3, be mentioned γ-Fe ₄ O _4, etc. it can. Of these, MnO to Fe ₂ O _3,
Spinel-type ferrite combining ZnO, NiO, and MgO is preferable.

In the present invention, the magnetic material (a) is preferably a metal magnetic material, more preferably a Ni-Fe alloy, Sendust, Co-Fe alloy or the like. They are,
They can be used alone or in combination of two or more. It is also possible to use a combination of a metal magnetic material and a metal oxide magnetic material.

In the present invention, the high dielectric substance (b) is dispersed in a chlorinated polyethylene resin (product name: Daisorak; manufacturer: Daiso Co., Ltd.) so that the content of the substance to be measured is 45% by volume. When measured using an HP8510C (Vector Network Analyzer) manufactured by Hewlett-Packard Co., the relative dielectric constant is 20 or more at an electromagnetic wave frequency of 3 GHz.

The high dielectric (b) has an aspect ratio of 3
That is all. When the aspect ratio is less than 3, only a combined effect is obtained when combined with the magnetic material (a), and the performance of absorbing electromagnetic waves is poor. Such a high dielectric (b)
Examples of the shape include fibrous shapes such as whiskers. Preferably, the aspect ratio is from 3 to 100. If it exceeds 100, it is actually difficult to obtain such a high dielectric (b), and the amount of the high dielectric (b) that can be blended in the binder (c) is reduced. In some cases, sufficient dielectric loss cannot be exhibited. More preferably, the aspect ratio is 3 to
50. The high dielectric (b) has an average fiber length of 0.5
５０50 μm and those having an average fiber diameter of 0.05 to 10 μm can be used.

As the high dielectric (b), for example, an oxide high dielectric can be used. In the present invention, MO.TiO ₂ (where M represents at least one metal element selected from the group consisting of barium, strontium, calcium, and magnesium) because of its excellent dielectric properties. It is preferably a metal titanate crystal having the composition shown.

In the above metal titanate crystals, the one in which the molar ratio between the divalent metal M and Ti is in the range of 1: 1.05 to 1.85 is preferable. As the metal titanate crystal, the surface of the metal titanate crystal is made of amorphous Ti.
It is also possible to use composite metal titanate fiber in which O ₂ is wrapped and composite-integrated. This is excellent in that the fiber strength is high.

The above-mentioned metal titanate crystals are disclosed, for example, in JP-B-62-7160, JP-A-3-19617, JP-A-3-69511, and JP-B-62-552.
No. 43, JP-A-63-260822, JP-A-6-279025 and the like.

In the electromagnetic wave absorber of the present invention, a fibrous conductor can be further used if necessary. The fibrous conductor is not particularly limited, but is preferably a metal-based fibrous material or a carbon-based fibrous material. The metal-based fibrous material is not particularly limited, and includes, for example, a simple substance of a metal such as stainless steel copper, brass, copper, aluminum, nickel, lead; a metal fiber manufactured from an alloy; a vegetable fiber, a synthetic fiber, an inorganic fiber, and the like. And metal-coated fibers on the surface of which a metal is deposited, plated, coated or the like. The carbon-based fiber material is not particularly limited, and examples thereof include polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and carbon whisker.

The specific gravity of the fibrous conductor is preferably 2.5 or less. If it exceeds 2.5, the dispersion stability will be poor.
The fibrous conductor preferably has a fiber diameter of 5 to 50 μm. In addition, the length of the fiber is preferably 2 to 40 mm because if the length is too long, the fiber is likely to be entangled. More preferably, it is 3 to 10 mm.

In the present invention, other fibrous conductors may be used in addition to the above fibrous conductors. The other fibrous conductor is not particularly limited, and includes, for example, natural plant fibers such as cotton and hemp; inorganic fibers such as glass fiber and asbestos; synthetic fibers such as polyester, polyacrylonitrile, polyamide, and polypropylene; wollastonite And other needle-like reinforcing fibers. The other fibrous conductor may be used for reinforcing the electromagnetic wave absorbing layer.

In the present invention, the size relationship between the magnetic material (a) and the high dielectric material (b) is such that the average major axis of the magnetic material (a) is the same as or equal to the average fiber length of the high dielectric material (b). Preferably, it is larger. When the average fiber length of the high dielectric substance (b) is longer, the magnetic loss exerted by the magnetic substance (a) acts negatively, and as a result, only a sympathetic electromagnetic characteristic can be obtained. is there.

In the present invention, the binder (c) is not particularly limited as long as it can fix the magnetic substance (a) and the high dielectric substance (b) in the electromagnetic wave absorber. Although it can be mentioned, it can be appropriately selected in consideration of the use in which the electromagnetic wave absorber is used, the wettability with the magnetic material (a) and the high dielectric material (b), and the like.

The organic material is preferably a thermoplastic resin. The thermoplastic resin is not particularly limited, and examples thereof include the following. Non-polar resins such as polyethylene, polypropylene, polymethylpentene, polybutene, polystyrene, polybutadiene, crystalline polybutadiene, and styrene butadiene.

Polyvinyl chloride, polyvinyl acetate, polymethyl methacrylate, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polytetrachloroethylene, ethylene-vinyl acetate copolymer, modified ethylene
Vinyl acetate copolymer resin, ethylene-vinyl acetate-vinyl chloride graft copolymer resin, ethylene-acrylate copolymer, ethylene-acrylate block copolymer. Chlorinated polyethylene resin, styrene-acrylonitrile copolymer resin (SAN resin), acrylonitrile-butadiene-styrene copolymer resin (ABS resin).

Acrylate-styrene-acrylonitrile copolymer resin (ASA resin), chlorinated polyethylene
Acrylonitrile-styrene copolymer resin (ACS resin), polyacetal resin, polyamide resin, polycarbonate resin, polyphenylene ether resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyacrylate resin, polysulfone resin, polyimide resin, polyamideimide resin, polyphenylene sulfide Resin, polyoxybenzoyl resin, polyetheretherketone resin, polyetherimide resin, acrylic resin, fluorine resin, polyurethane resin, polyester resin, silicone resin, silicone-modified acrylic resin, silicone-modified polyester resin, epoxy resin,
Resins such as phosphazene resins, and modified resins thereof; These may be used alone or in combination of two or more.

Examples of the organic material include wettability with the magnetic substance (a) and the high dielectric substance (b), viscosity during kneading of the resin,
It can be appropriately selected in consideration of the temperature, physical properties of the film, chemical resistance, heat resistance, water resistance, adhesiveness to all metals and plastics, and the like. Among them, ethylene-vinyl acetate copolymer, modified ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-vinyl chloride graft copolymer resin, chlorinated polyethylene resin, polyvinyl chloride, polyester resin,
Acrylic resins, amide resins, silicone resins, epoxy resins, and modified resins thereof are preferred.

The organic material preferably has an oxygen index of 30 or more from the viewpoint of flame retardancy and nonflammability. If it is less than 30, the flame retardancy and the nonflammability decrease. More preferably, 4
0 or more. The oxygen index is determined according to JIS K 7201
Can be measured by the plastic flame resistance test method. Among the above organic materials, resins having a high oxygen index include, for example, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polytetrachloroethylene, ethylene-vinyl acetate-vinyl chloride graft copolymer. Coalescing resin, chlorinated polyethylene resin,
Modified chlorinated polyethylene resin, chlorinated polyethylene-acrylonitrile-styrene copolymer, silicone resin,
Examples thereof include a silicone-modified acrylic resin, a silicone-modified polyester resin, and a phosphazene resin. Among them, polyvinyl chloride, ethylene-vinyl acetate-vinyl chloride graft copolymer resin, chlorinated polyethylene resin, modified chlorinated polyethylene resin, and silicone resin are preferable.

The inorganic ceramic material is not particularly restricted but includes, for example, calcium sulfate, calcium silicate, water glass, portland cement, alumina cement, alumina silicate, calcium oxide, clay and the like. These inorganic ceramic materials are also excellent in flame retardancy and nonflammability. Preferred are calcium sulfate, calcium silicate, Portland cement and alumina cement.

The binder (c) and the magnetic material (a)
When compounding with the high dielectric substance (b), a flame retardant may be added in order to improve flame retardancy and nonflammability. Examples of the flame retardant include (1) amines, phenols, and chlorine compounds that stop a chain reaction of oxidative combustion;
Bromine compounds; (2) Phosphorus compounds and boron compounds that block air and prevent contact between oxygen and flammable gas; (3) Inert water, carbon dioxide, ammonia, etc. that dilute flammable gas and reduce calorific value Gas generating agents; (4) hydroxides, hydrates, silica, alumina, etc., which lower the temperature of combustibles to prevent decomposition ignition. More specifically, examples of the flame retardant include hexabromobenzene, decabromobenzylphenyl ether, decabromobenzylphenyl oxide, tetrabromobisphenol,
Tetrabromophthalic anhydride, tetrabromobisphenol A, tricresyl phosphate, triphenyl phosphate, triallyl phosphate, trichloroethyl phosphate, halogen-containing condensed phosphate, paraffin chloride, perchloropentacyclodecane, aluminum hydroxide, magnesium hydroxide , Antimony trioxide, antimony pentoxide, zinc borate, ammonium bromide, titanium phosphate and the like. The compounding amount of the flame retardant is preferably 0.01 to 15% by weight in the electromagnetic wave absorber. When the amount is less than 0.01% by weight, the flame retardancy of the obtained electromagnetic wave absorber is not sufficient. When the amount exceeds 15% by weight, the amount of the binder (c) decreases, and the physical properties of the electromagnetic wave absorber deteriorate. When the amount of the binder (c) is supplemented, the mixing amount of the magnetic substance (a) and the high dielectric substance (b) is reduced, and the electromagnetic wave absorbing ability is reduced.

The binder (c) and the magnetic material (a)
When blending with the high dielectric substance (b), in addition to the flame retardant, a plasticizer, if necessary, to improve layer formation, coating properties, electromagnetic wave absorbing ability, etc. Viscosity modifiers, surfactants, lubricants, defoamers, heat stabilizers, antioxidants and the like may be added.

In the electromagnetic wave absorber of the present invention, the weight ratio of the magnetic substance (a) to the high dielectric substance (b) [weight of the magnetic substance (a)] / [weight of the high dielectric substance (b)] is: 10 / 90-99
/ 1 is preferred. Outside this range, the effect of using a combination of the magnetic substance (a) and the high dielectric substance (b) cannot be obtained.

In the present invention, the ratio of the total weight of the magnetic substance (a) and the high dielectric substance (b) to the weight of the binder (c) [weight of the magnetic substance (a) + high dielectric substance (b)] Weight)
/ [Binder (c)] is preferably 30/70 to 93/7. If the total weight of the magnetic material (a) and the high dielectric material (b) is more than the above range, physical properties when formed into a sheet, panel, or film are inferior. If the amount of the binder (c) is more than the above range, the amounts of the magnetic substance (a) and the high dielectric substance (b) are small, so that a desired electromagnetic wave absorbing effect cannot be obtained.

The electromagnetic wave absorber of the present invention is used as a sheet-shaped or panel-shaped building material for an electromagnetic wave-absorbing panel for interior use in a building or a building, or a constituent member of a surface constituting a space for using a communication device or the like. can do. The thickness depends on the frequency at which the absorption performance is maximized, but it is preferable to use a thick absorber to obtain a larger absorption over a wide band. Specifically, it can be about 3 to 50 mm,
It can be easily adapted to specifications as interior materials.
If it is less than 3 mm, the physical strength of the electromagnetic wave absorber is weak, and if it exceeds 50 mm, the weight becomes heavy. When an electromagnetic wave absorber is used as a building material, installation workability,
Poor fit. More preferably, it is 5 to 25 mm.

In the above case, it is preferable to further include an electromagnetic wave reflection layer having an absolute shielding value of 20 dB or more. The electromagnetic wave reflection layer is not particularly limited, but is preferably made of a conductive material, a metal deposition film, a metal foil, a metal powder, or the like. These may be used alone or in combination of two or more. The electromagnetic wave reflection layer,
It can also serve as a support.

When the electromagnetic wave absorber of the present invention is used as a sheet-like or panel-like building material, the specific gravity is 0.50 to 1.6.
It is preferably 5. If it is less than 0.50, the electromagnetic wave absorbing ability decreases, and if it exceeds 1.65, the weight of the electromagnetic wave absorber increases, which is not preferable. From the viewpoint of installation workability, the specific gravity is preferably 0.6 to 1.20, and in order to make it approximately the same as a conventionally used gypsum board, it is preferable that the specific gravity be 0.60 to 1.00. .

The electromagnetic wave absorber of the present invention can also be used as an electromagnetic wave control material in the form of a film or an electromagnetic wave interferer inside an electronic device.
Can be used for MC countermeasure parts. In this case, it is preferable that the thickness is set to a thickness that allows absorption performance to be ensured while setting the thickness in consideration of the attachment to the housing. In the case of use in which the effect of imparting high-frequency impedance to the conductive surface is intended by attaching to the conductive surface, even if it is thin, it is effective as an EMC countermeasure material.

When the film-shaped electromagnetic wave absorber is installed inside an electronic device, the thickness is usually from 70 to 70%.
It is 500 μm. If the thickness is less than 70 μm, the effect of reducing unnecessary radiation is small, and if it exceeds 500 μm, there is no problem with the effect on the reduction of unnecessary radiation. The range is limited, and installation according to the shape of the housing becomes difficult, and uniformity during film production is impaired. Preferably, 1
20 to 300 μm.

When the film-shaped electromagnetic wave absorber is provided in a portion in contact with the opening on the inner surface of the electronic device housing or in the vicinity of the opening within 10 mm from the opening, the effect of reducing unnecessary radiation is provided. Is preferred because The portion other than the above is preferably a place where the magnetic field strength is maximum, a vicinity of the electronic circuit board, a vicinity of the electromagnetic wave generation unit, or a whole or a part of a joint or joint of the housing.

The method of bonding the film is not particularly limited, and may be, for example, a method of bonding the film to the inside surface of the housing, which has been subjected to a conductive treatment, with a double-sided tape, an adhesive, a high frequency sewing machine, a hot press. For example, a method of integrating the film with the housing, a method of fixing the film to the housing with a tape, another film, a jig, or the like, and the like can be used.

Further, the electromagnetic wave absorber of the present invention may be in the form of a paint. In this case, when an electronic device housing is manufactured, it can be applied to the inner surface and used for an EMC countermeasure member. When used as a paint, the dry film thickness is usually 2
0 to 200 μm.

The electromagnetic wave absorber in the form of a film or paint is used for communication equipment such as automobile telephones, portable telephones, PHS telephones, terminals for wireless LAN, adapters, POS terminals, etc .; office equipment such as personal computers, word processors, small computers, etc. Players for CDs, CD-ROMs, minidiscs, laser discs (registered trademark), DVDs, etc .; home appliances such as game machines, small radios, televisions, etc .; CCDs; cassette recorders; Can be used.

In the method for producing the electromagnetic wave absorber of the present invention, when an organic material is used as the binder (c), the magnetic material (a) and the high-concentration material are mixed using a three-roll, Banbury mixer, pressure kneader, buscon kneader or the like. Dielectric (b)
And a binder (c) and, if necessary, an additive, and a layer can be formed by a commonly used method such as extrusion molding, rolling molding, and calendar molding. When an inorganic ceramic material is used as the binder (c), the layer can be formed by a papermaking method, a molding method, extrusion molding, or the like.

In the above-mentioned production method, a liquid composition obtained by dissolving a magnetic substance (a), a high dielectric substance (b), a binder (c) and, if necessary, an additive in a solvent is coated on a support. Then, if necessary, the film can be applied again by coating and drying to obtain a film-like electromagnetic wave absorber, which can be carried out by a film casting method. Further, the magnetic substance (a), the high dielectric substance (b), the binder (c) and, if necessary, additives are dissolved in a solvent to form a liquid paint, which is applied to a portion where a coating film is required, and dried. In this way, it is also possible to carry out by a coating method for obtaining a film-like electromagnetic wave absorber.

Since the electromagnetic wave absorber of the present invention has the magnetic material (a) having an aspect ratio of 3 or more, when the magnetic material (a) is dispersed in the binder (c), each of the flat particles or As a result, the fibrous magnetic bodies (a) overlap to form a network of a magnetic circuit, so that a large relative permeability and a large magnetic loss can be exhibited. Furthermore, since the high dielectric substance (b) contained in the electromagnetic wave absorber of the present invention has an aspect ratio of 3 or more, it effectively exhibits dielectric properties without breaking the network of the magnetic circuit formed by the magnetic substance (a). And excellent dielectric properties, so that a large dielectric constant can be exhibited. This is the reason for having a relative permittivity larger than the relative permittivity estimated by the logarithmic mixing equation. Therefore, the electromagnetic wave absorber of the present invention can exhibit dielectric properties more effectively by the high dielectric substance (b) without reducing the relative magnetic permeability and the magnetic loss exhibited by the magnetic substance (a). As a result, the electromagnetic characteristics can be improved synergistically.

When the electromagnetic wave absorber of the present invention is used as a component of a panel or a sheet-like building material, unnecessary electromagnetic waves generated from communication equipment and the like used in a space can be effectively absorbed. There is no problem such as interference, malfunction, interference, etc. due to delay dispersion due to multiple reflection of the signal, and the radio wave environment can be improved as a whole. Further, when used in the form of a film or a paint and installed or painted on an electronic device or the like, it is possible to prevent high-frequency leakage that causes radio interference, and it is also effective as an EMC measure.

[0050]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 A metal magnetic material having an aspect ratio of about 30 and containing Fe element and Ni element (molar ratio of Fe, Ni, Si and B: 50:
15:15:20; flat particles, average major axis 150 μm,
72 parts by weight (average minor axis: 70 μm, average thickness: 5 μm), an oxide high dielectric containing Ba element and Ti element having an aspect ratio of about 10 (manufactured by Otsuka Chemical Co., Ltd .; product name: BTW; 3 μm, average fiber diameter about 0.3 μm; B
a and Ti in a molar ratio of 0.9: 1.0), 17 parts by weight, and 11 parts by weight of a chlorinated polyethylene resin (product name: Daisorac; manufacturer: Daiso Co., Ltd.) were mixed at a ratio of 1
The composite was obtained by heating and kneading at 00 ° C. using a roll kneader. The relative magnetic permeability and relative permittivity of the metal magnetic substance and the oxide high dielectric substance are adjusted so that the content of the substance to be measured becomes 45% by volume. )) Was dispersed and prepared using Hewlett-Packard HP8
When measured using 510C (vector network analyzer), at a frequency of 3 GHz of the electromagnetic wave,
The relative permeability of the metal magnetic material was 2.2, the relative permittivity was 32.2, and the relative permeability of the oxide high dielectric material was 1.0 and the relative permittivity was 26.2.

The saturation magnetization of the composite material was measured using a VSM device (vibration-type scanning magnetic balance) for which a calibration curve had been prepared in advance.
The amount of the metallic magnetic substance contained in the composite material was calculated in consideration of the specific gravity of each composite, and was found to be 45% by volume. The relative permittivity of the composite material was measured by Hewlett-Packard H
When measured using P8510C (vector network analyzer), at a frequency of 3 GHz, the relative magnetic permeability was 2.1 (imaginary number item 1.8) and the relative permittivity was 78.7 (real number item 75 and imaginary number 24). FIG. 1 shows the result of the real term of the relative permittivity measured using HP8510C, and FIG. 2 shows the result of the imaginary term. The relative dielectric constant obtained from the logarithmic mixing equation is 64, and the measured relative dielectric constant of the composite material of Example 1 is 78.
7 can be said to be a synergistic effect due to the use of the fibrous high dielectric.

This composite material was rolled at 250 ° C. into a 250 μm-thick film at a temperature of 100 ° C. to obtain a size of 3 cm × 3 cm. A 30 μm-thick double-sided tape was applied to a circuit board around the element which is a noise source. When the intensity of unwanted radiation was measured by a method based on the 3m method in a simple anechoic chamber, the frequency was 3 GHz.
At z, a noise attenuation effect of about 9 dB was observed.

Example 2 The composite material of Example 1 was 5 mm thick and 200 m on each side.
m was pressed into a sheet and backed with an aluminum plate to produce an absorber. 45 degree TM of this absorber
The amount of electromagnetic wave reflection at the time of incidence was measured. FIG. 3 shows the result. Similarly, an absorber was produced with a composite material having a thickness of 8 mm, and the amount of electromagnetic wave reflection was also shown in FIG. From the results of FIG. 3, it can be seen that both the absorbers having a thickness of 5 mm and a thickness of 8 mm have 1 G
Hz or less can greatly reduce the amount of electromagnetic wave reflection,
It was confirmed that it was a good electromagnetic wave absorber.

Example 3 72 parts by weight of the same metal magnetic material as used in Example 1
A coating material was prepared by dispersing 17 parts by weight of the same oxide high dielectric substance as used in Example 1 and 11 parts by weight of an acrylic resin-based varnish (manufactured by Shoei Chemical Co., Ltd .; product name: IB6500) in a solvent toluene. This paint was applied by air spray to a circuit board inside an electronic device housing that radiated electromagnetic noise in the same manner as in Example 1 so as to have a dry coating film thickness of 100 μm. When the intensity of the unnecessary radiation wave was measured in the same manner as in Example 1, a noise attenuation effect of about 6 dB was observed at a frequency of 3 GHz.

Example 4 49 parts by weight of the same metal magnetic substance as used in Example 1, and the same oxide high dielectric substance B as used in Example 1 were used.
1 part by weight of an oxide dielectric obtained by replacing the element a with Sr, 2 parts by weight of carbon fiber having a diameter of 12 μm and a length of 5 mm, and 48 parts by weight of the chlorinated polyethylene resin used in Example 1 Then, a composite material was obtained in the same manner as in Example 1. The amount of the metal magnetic material of this composite material was calculated in the same manner as in Example 1, and it was 14% by volume.

The relative dielectric constant of this composite material was measured in the same manner as in Example 1. As a result, at a frequency of 3 GHz,
Relative permeability 1.6 (imaginary number term 1.3), relative permittivity 23.3
(Real number term 21, imaginary number term 10). The relative magnetic permeability and relative permittivity of the oxide high dielectric substance were measured in a chlorinated polyethylene resin (product name: Daisorak; manufactured by Daiso Co., Ltd.) so that the content of the substance to be measured was 45% by volume. What was prepared by dispersing is Hewlett-Packard H
When measured using a P8510C (vector network analyzer), the relative permeability of the oxide high dielectric substance was 1.0 and the relative permittivity was 19. at an electromagnetic wave frequency of 3 GHz.
It was 6. The relative dielectric constant obtained from the logarithmic mixing equation is 18, and the measured relative dielectric constant of the composite material of Example 4 is 23.3, which is a synergistic effect due to the use of the fibrous high dielectric substance.

Example 5 The metal magnetic material used in Example 1 was prepared using sendust particles having an aspect ratio of 11 (average major axis: 105 μm, average minor axis: 42).
μm, average thickness 9 μm), except that the composite material was obtained in the same manner as in Example 1. When the amount of the metal magnetic material of this composite material was calculated in the same manner as in Example 1, it was 45% by volume.

The relative permittivity of this composite material was measured in the same manner as in Example 1. At a frequency of 3 GHz,
Relative permeability 1.9 (imaginary term 1.7), relative permittivity 70.3
(Real number term 68, imaginary number term 18). The relative magnetic permeability and relative permittivity of the metal magnetic material are dispersed in a chlorinated polyethylene resin (product name: Daisorak; manufacturer: Daiso Co., Ltd.) so that the content of the substance to be measured becomes 45% by volume. HP8 manufactured by Hewlett-Packard Company
When measured using 510C (vector network analyzer), at a frequency of 3 GHz of the electromagnetic wave,
The relative permeability of the metal magnetic material was 2.5 and the relative permittivity was 23.6. The relative permittivity obtained from the logarithmic mixing formula is 59, and the measured relative permittivity 70.3 of the composite material of Example 5 is a synergistic effect due to the use of the fibrous high dielectric.

Example 6 The magnetic metal used in Example 1 was made of stainless steel particles having an aspect ratio of 19 (15% Cr, 0.6% A1-Fe magnetic stainless steel particles, average major axis 153 μm, average minor axis 4).
5 μm, average thickness 8 μm), 75 parts by weight of this metal magnetic material, 12 parts by weight of the oxide high dielectric used in Example 1, and 2 parts by weight of carbon fiber having a diameter of 12 μm and a length of 5 mm. The chlorinated polyethylene resin used in Example 1 was mixed at a ratio of 11 parts by weight, and a composite material was obtained in the same manner as in Example 1. When the amount of the metal magnetic material of this composite material was calculated in the same manner as in Example 1, it was 45% by volume.

The relative dielectric constant of this composite material was measured in the same manner as in Example 1. At a frequency of 3 GHz,
Relative permeability 2.0 (imaginary number term 1.7), relative permittivity 68.2
(Real number term 66, imaginary number term 17). The relative magnetic permeability and relative permittivity of the metal magnetic material are dispersed in a chlorinated polyethylene resin (product name: Daisorak; manufacturer: Daiso Co., Ltd.) so that the content of the substance to be measured becomes 45% by volume. HP8 manufactured by Hewlett-Packard Company
When measured using 510C (vector network analyzer), at a frequency of 3 GHz of the electromagnetic wave,
The relative permeability of the metal magnetic material was 2.1, and the relative permittivity was 27.8. The relative dielectric constant obtained from the logarithmic mixing formula is 55, and the measured relative dielectric constant 68.2 of the composite material of Example 6 can be said to be a synergistic effect due to the use of the fibrous high dielectric.

Comparative Example 1 A composite material was prepared in the same manner as in Example 1 except that 17 parts by weight of a ball milled material (average particle diameter: about 0.7 μm) of the oxide high dielectric used in Example 1 was used. Obtained. When the amount of the metal magnetic material of this composite material was calculated in the same manner as in Example 1, it was 45% by volume, as in the composite material of Example 1. The relative dielectric constant of this composite material was measured in the same manner as in Example 1. At a frequency of 3 GHz, the relative magnetic permeability was 2.1 (imaginary number item 1.8) and the relative dielectric constant was 59.0 (real number item 5).
8, imaginary term 11). FIG. 1 shows the result of the real term of the relative permittivity measured using HP8510C, and FIG. 2 shows the result of the imaginary term. The relative permittivity obtained from the logarithmic mixing equation is 64
When a granular high dielectric substance was used, the relative dielectric constant obtained from the logarithmic mixing equation and the measured relative dielectric constant were almost similar.

Comparative Example 2 A composite material was obtained in the same manner as in Example 1 except that the oxide high dielectric used in Example 1 was not used. When the amount of the metal magnetic material of this composite material was calculated in the same manner as in Example 1, it was 45% by volume, as in the composite material of Example 1.
The relative permittivity of this composite material was measured in the same manner as in Example 1. At a frequency of 3 GHz, the relative magnetic permeability was 2.
2 (imaginary term 1.8), relative permittivity 32.2 (real number term 32,
The imaginary term was 4). FIG. 1 shows the results of the real term of the relative permittivity measured using HP8510C, and FIG.
It was shown to.

As for the relative dielectric constants of the composite material of Comparative Example 1 and the composite material of Comparative Example 2, the values calculated by the logarithmic mixing equation almost agreed with the measured values. However, the relative dielectric constants of the composite materials of Example 1 and Examples 4 to 6 were much larger in the measured values than in the values estimated by the logarithmic mixing equation. In Example 1, Comparative Example 1 and Comparative Example 2, the relative magnetic permeability and the imaginary term of the relative magnetic permeability are almost the same, but in Example 1, a high dielectric substance having an aspect ratio of 3 or more is added. By,
The relative permittivity and the imaginary term of the relative permittivity could be significantly increased without reducing the relative permeability and the imaginary term of the relative permeability.

[0064]

The electromagnetic wave absorber of the present invention has an electromagnetic wave loss effect synergistically, not a summation effect. Therefore, when installed in a housing of electronic equipment, communication equipment, etc., a building, a building or the like. In addition, unnecessary radiation electromagnetic waves can be efficiently absorbed.

[Brief description of the drawings]

FIG. 1 shows H in Example 1, Comparative Example 1 and Comparative Example 2.
It is a graph of the real number term of the relative dielectric constant measured using P8510C.

FIG. 2 shows H in Example 1, Comparative Example 1 and Comparative Example 2.
It is a graph of the imaginary term of the relative dielectric constant measured using P8510C.

FIG. 3 is a graph showing a measurement result of an electromagnetic wave reflection amount at 45 ° TM incidence for an absorber having a thickness of 5 mm and a thickness of 8 mm in Example 2.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Komori 19-17 Ikedanakacho, Neyagawa-shi, Osaka Inside Nippon Paint Co., Ltd. Co., Ltd. (72) Inventor Minoru Aki 463 Kagasuno, Kawauchi-machi, Tokushima City, Tokushima Prefecture Otsuka Chemical Co., Ltd.F-term (reference) 5E321 AA03 AA44 BB32 BB34 BB53 BB55 GG11

Claims (9)

[Claims] 1. A magnetic material (a) having an aspect ratio of 3 or more, a high dielectric material (b) having an aspect ratio of 3 or more,
And an electromagnetic wave absorber comprising a binder (c). 2. The magnetic material (a) is a metal magnetic material and / or a metal oxide magnetic material, and has an aspect ratio of 3 to 500.
The electromagnetic wave absorber according to claim 1, wherein 3. The magnetic material (a) has an aspect ratio of 5 to 3.
The electromagnetic wave absorber according to claim 2, wherein the number is 00. 4. The electromagnetic wave absorber according to claim 2, wherein the magnetic material (a) is a metal magnetic material. 5. The electromagnetic wave absorber according to claim 1, wherein the high dielectric substance (b) is an oxide high dielectric substance. 6. The high dielectric substance (b) is represented by MO.TiO ₂ (where M represents at least one metal element selected from the group consisting of barium, strontium, calcium and magnesium). The electromagnetic wave absorber according to claim 5, which is a metal titanate crystal having the following composition, and is a fibrous high dielectric substance having an aspect ratio of 3 to 100. 7. The high dielectric substance (b) has an aspect ratio of 3 to 3.
The electromagnetic wave absorber according to claim 6, wherein the number is 50. 8. The binder according to claim 1, wherein the binder (c) is an organic material and / or an inorganic material.
The electromagnetic wave absorber according to the above. 9. A weight ratio of the magnetic substance (a) to the high dielectric substance (b) [weight of the magnetic substance (a)] / [weight of the high dielectric substance (b)].
Is 10/90 to 99/1, and the ratio of the total weight of the magnetic substance (a) and the high dielectric substance (b) to the weight of the binder (c) [weight of the magnetic substance (a) + high dielectric substance ( b) weight] /
9. The electromagnetic wave absorber according to claim 1, wherein [binder (c)] is 30/70 to 93/7.