JPH08181482A - Electromagnetic wave absorber - Google Patents

Abstract

PURPOSE: To provide an electromagnetic wave absorber that is provided with sound absorbing capability as well, lightweight and excellent in handleability. CONSTITUTION: An electromagnetic wave absorber consists of a composite 3 of mixed powder 4, fiber 1 and binder 2. The powder 4 is a dielectric powder 4a, and is held in the voids 5 within the composite by the fiber 1 and the binder 2. The dielectric loss of the dielectric powder 4a provides electromagnetic wave absorbing capability. This, together with the electromagnetic scattering absorbing effect due to the complicated structure of the voids 5 of the composite 3, formed mainly out of fiber 1, achieves high electromagnetic wave absorbing capability. Since the composite 3 is composed of the mixed fiber 1 and binder 2, it is lightweight and excellent in handleability, and its complicated structure of the voids 5 provides high sound absorbing capability. The complicated structure of the voids 5 resulting from the addition of the powder 4 and the vibrating action of the powder 4 enhance the sound absorbing capability of the composite 3 further.

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 used for absorbing and shielding electromagnetic waves.

[0002]

2. Description of the Related Art In recent years, problems concerning the electromagnetic wave environment have been taken up in earnest, and electromagnetic wave interference has become a major social problem. The following are generally mentioned as the so-called electromagnetic interference. (1) Radar radio waves and TV radio interference caused by buildings Electromagnetic interference caused by unnecessary reflection electromagnetic waves caused by high-rise buildings and large-scale buildings (large bridges, noise barriers on elevated roads, steel towers, etc.), such as wall surfaces The electromagnetic waves reflected by the radio wave generate a ghost image on the TV screen or radar screen. (2) Communication failure in electronic communication During data communication on a wireless LAN in a living space or office, this is a communication failure caused by multipath due to electromagnetic wave reflection or unnecessary electromagnetic wave reflection in the living space or office. However, it is expected that more sophisticated social issues such as housing and offices will become more important social issues. (3) Generation of electromagnetic interference waves from electronic circuits This is a failure that causes electromagnetic interference waves (noise) generated from OA devices, personal computers, etc. to cause a reception failure on televisions and radios, or cause malfunctions on other electronic devices. .

Regarding the above (3), various measures such as suppression of electromagnetic wave radiation from electric and electronic devices, noise reduction action, and enhancement of electromagnetic wave shielding ability of damaged electronic devices are taken. Has been. As one of the effective countermeasures against the electromagnetic wave reception obstacles such as (1) and (2), there is a method of installing an electromagnetic wave absorber using an electromagnetic wave absorbing material on the electromagnetic wave reflecting surface to eliminate unnecessary electromagnetic wave reflection. Has been.

The electromagnetic wave absorbing material is a material which converts electromagnetic wave energy into heat energy, and the electromagnetic wave loss can be broadly classified into three types: conductive loss, dielectric loss and magnetic loss. Materials can be roughly classified into the following three types according to this (Yasutaka Shimizu, "Absorption and shielding of electromagnetic waves", page 107, etc., 1989.
Published Nikkei technical books). (A) Conductive Electromagnetic Wave Absorbing Material This is a material that absorbs electromagnetic waves by a conducting current flowing through a resistor and a resistance wire, such as a woven fabric made of conductive fibers (for example, JP-A-3-226000 and JP-A-2-9199).
No. 7). (B) Dielectric Electromagnetic Wave Absorbing Material There are carbon rubber, carbon foam polyurethane, and the like, in which foamed polystyrene having a small relative permittivity is mixed with carbon or graphite which is a dielectric loss material. (C) Magnetic Electromagnetic Wave Absorption Material A typical magnetic loss material, which is obtained by sintering ferrite, which is magnetic powder having electromagnetic wave absorption,
There are ferrite plates and rubber ferrite obtained by kneading ferrite powder into rubber.

These electromagnetic wave absorbing materials are designed as an electromagnetic wave absorber by designing their thickness, structure, etc., and are used as electromagnetic wave absorbers, including the outer wall of a building to prevent electromagnetic interference from the above (1) and (2). Is used in various fields. However, most of the electromagnetic wave absorbers made from these electromagnetic wave absorbing materials are sheet-shaped, plate-shaped, or block-shaped, and have problems in handling. For example, in a ferrite sintered body, the weight becomes heavy, which causes a problem in handling, and since rubber ferrite or a conductive woven fabric has a sheet shape, it cannot hold the structure independently,
In addition to the handling problems, increasing the thickness also causes problems due to the increased weight.

On the other hand, in recent years, in the fields of soundproof walls of elevated roads, partitions and partitions such as houses and offices that handle OA equipment, demands for electromagnetic wave absorbing performance and soundproofing performance have become severe. There are the following two measures to improve the soundproofing performance.
One is a method of blocking the propagation of the sound wave by installing a material such as a metal plate having a high surface density at a position where the propagation path of the sound wave is blocked, that is, a wall or a partition portion. However, with this method, although it is possible to obtain soundproofness and high electromagnetic wave blocking performance, there is a possibility that ghost interference and communication failure of television propagation due to reflection of electromagnetic waves may occur, and soundproofing performance is Not enough.

Another method is to use a sound absorbing material having a high sound absorbing performance as a soundproof wall, an interior material of a living space, or a filling material inside a partition wall. As this sound absorbing material, inorganic fibers such as glass wool and rock wool,
Organic porous materials such as foamed polyurethane are generally widely used. However, although these inorganic fibers and porous materials can be expected to have the effect of improving the soundproofing performance by the sound absorbing effect, almost no effect of absorbing electromagnetic waves can be obtained. That is, it is not possible to obtain electromagnetic wave absorption performance with a sound absorbing material that is widely used for improving sound insulation.

[0008]

As described above, most of the conventional electromagnetic wave absorbing materials have a sheet-like, plate-like, or block-like appearance, so that it is expected that the sound absorbing performance will be improved by the sound absorbing characteristics. Can't
Since the sound absorbing material cannot obtain electromagnetic wave absorbing performance, the present situation is that an electromagnetic wave absorbing body having both electromagnetic wave absorbing performance and sound absorbing performance, and being lightweight and excellent in handleability has not yet been provided.

Therefore, an object of the present invention is to provide an electromagnetic wave absorber having a sound absorbing property, a light weight and an excellent handleability.

[0010]

It is difficult for an electromagnetic wave absorber using a conventional electromagnetic wave absorbing material to have excellent handleability at the same time. Most of the electromagnetic wave absorbers are sheet-like or plate-like or block-like. This is due to the fact that the electromagnetic wave absorber does not have a void structure inside, so that the weight at a predetermined thickness becomes large, and the structure cannot be retained in a shape such as a rubber sheet or a woven fabric.

Further, it is difficult to provide the electromagnetic wave absorber with sound absorbing characteristics because most of the conventional electromagnetic wave absorbers are non-porous materials. In other words, foamed polyurethane and glausur, which have been conventionally used as sound absorbing materials, take advantage of the porosity of the material and, for example, have a complicated cross-sectional shape when sound waves are injected into continuous bubbles, holes, or voids. The sound pressure is reduced due to viscous friction with the wall surface of the bubble or the like while the sound wave is propagated by the bubble or the like, and as a result, the sound wave energy can be absorbed and absorbed in the material. On the other hand, sheet-like,
Since the plate-shaped and block-shaped materials have no bubbles, holes, or voids, they cannot absorb sound wave energy, and there is a limit in improving sound absorption characteristics.

On the other hand, the present inventors have developed a sound absorbing material composed of powder, fiber and resin binder. That is,
A sound-absorbing material is formed by adhering and holding powder inside the voids of a structure in which fibers and binders are mixed, and a sound-absorbing material with this structure has excellent sound absorption performance in the low frequency range. Have found. Then, the present inventors have paid attention to the structure in which the powder, the fiber and the binder are combined, and have come to provide an electromagnetic wave absorber having excellent handleability and sound absorption performance and high electromagnetic wave absorption performance. .

That is, the electromagnetic wave absorber according to claim 1 of the present invention comprises a composite body 3 in which a powder 4, a fiber 1 and a binder 2 are mixed, and the powder 4 is a dielectric loss powder 4a. The powder 4 is held in the internal voids 5 of the composite by the fibers 1 and the binder 2. The electromagnetic wave absorber according to claim 2 of the present invention is
It is characterized in that a conductive layer 6 is formed on one surface of the composite body 3.

The present invention will be described in detail below. FIG. 1 shows an example of a specific form of an electromagnetic wave absorber according to the invention of claim 1, and a large number of fibers 1 mainly constituting a structural skeleton.
Are bonded to each other at their contact points with a binder 2 to form a composite body 3 in which the fibers 1 and the binder 2 are mixed, and a large number of voids 5 are formed between the fibers 1 as pores. ing. The powder 4 is adhered and held inside the large number of voids 5 between the fibers 1.

Here, as the fiber 1 forming the structural skeleton of the composite 3, synthetic fiber such as polyester fiber, nylon (polyamide) fiber, polyacrylonitrile fiber, polypropylene fiber, polyethylene fiber, polyvinyl chloride fiber, or wood is used. Fiber, cotton, hemp fiber, bamboo,
Natural fibers such as linter (forehead of cotton), silk and wool, organic fibers such as regenerated cellulose fibers such as rayon, rock fibers, glass fibers, alumina fibers, and inorganic fibers such as SiC fibers can be used. It is not limited to these.

As the fiber 1, although individual single fibers are generally used in a non-sheet form in which they are disassembled, it is not always necessary that they are in a non-sheet form in which they are disassembled, and may be in a sheet form. Examples thereof include organic fiber structures such as non-woven fabric, artificial pulp and filter paper, and inorganic fiber structures such as granular cotton. In the present invention, the dielectric loss powder 4a is used as the powder 4.
A typical example of a is graphite powder, but any powder having a dielectric loss effect can be used without particular limitation.

What is generally called graphite is one of allotropes of carbon, which is naturally produced as an elemental mineral of carbon and is also artificially produced. The particle size is about 0.1 to 50 μm, and the bulk density is about 0.1 g / cm ^3.
It is generally in the range from about 0.3 g / cm ³ to about 0.3. Specifically, carbon graphite, natural graphite (average particle size 0.1 to 5.0 μm, bulk density 0.1 to 0.3
g / cm ³ ), natural scaly graphite (average particle size 0.1 to 50.
0 μm, bulk density 0.1 to 0.3 g / cm ³ ), artificial graphite (average particle size 1.0 to 50.0 μm, bulk density 0.1 to 0.
3 g / cm ³ ) and other than these, acetylene black and the like can be mentioned. Here, the average particle size is described as an example, but by changing the manufacturing conditions,
In order to obtain a powder having an arbitrary particle size, it is necessary to appropriately select it according to the required performance.

As the binder 2 used in the present invention, a resin binder such as polyethylene resin, polystyrene resin, methacrylic resin, polyurethane resin, phenol resin and urea resin, or natural starch (rice starch, corn starch, tapioca starch, etc.) is used. It is possible to use starch paste made of modified starch. Of course, it is not limited to these. The method of mixing the binder 2 in the fiber 1 or the powder 4 is not particularly limited, and for example, a method of mixing in the form of fine particles or a method of applying the liquid binder 2 can be adopted.

Here, by using a foaming resin binder as the binder 1, it is possible to improve the adhesiveness between the fiber 1 and the powder 4, and to have a high structure retention and to prevent performance deterioration. The body 3 can be obtained. The method for foaming the resin binder is not particularly limited, but basically there are the following methods (1) utilizing a reaction product gas and (2) using a foaming agent.

The method using the reaction product gas of (1) is
This is a method in which a product released when a liquid raw material is resinified, such as carbon dioxide, formaldehyde, or steam, is used as a foaming agent, and this product is vaporized by reaction heat or heating to obtain a foam. . Further, the method of using the foaming agent (2) is further divided into a method of using a volatile foaming agent and a method of using a decomposable foaming agent. The method using a volatile foaming agent is a method in which a gas such as carbon dioxide gas, propane, butane, ether, acetone, benzene or the like or a volatile liquid is absorbed in a resin or a raw material, and this is vaporized to foam. The method of utilizing a decomposable foaming agent is a method of dispersing or dissolving the foaming agent in the resin raw material and then decomposing the foaming agent by heating to foam the resin. Ammonium carbonate, as the foaming agent used at this time,
There are inorganic compounds such as sodium bicarbonate, azo compounds, sulfonyl hydrazide compounds, nitroso compounds, azide compounds and the like, which can be appropriately selected and used according to use conditions and resin raw materials.

The type of the binder 2 must be selected in consideration of the adhesiveness and wettability between the fiber 1 and the powder 4.
The amount of the binder 2 is 5 to 20% by weight with respect to the fiber 1.
A range of degrees is desirable. If the amount of the binder 2 exceeds this range, the sound absorbing effect due to the vibrating action of the powder 4 which will be described later becomes small, which causes deterioration of low frequency performance, which is not preferable.

When forming the composite body 3 in which the powder 4, the fiber 1 and the binder 2 are mixed as described above, the fiber 1
High sound absorbing performance can be obtained due to the complicated structure of the voids 5 formed therebetween, and high electromagnetic wave absorbing performance can be obtained by the dielectric loss effect of the dielectric loss powder 4a used as the powder 4. Is. here,
The electromagnetic wave absorbing mechanism of the electromagnetic wave absorbing material utilizing the dielectric loss will be briefly described as follows.

The electric field reflection coefficient S on the front surface of the electromagnetic wave absorbing material
Displaying in decibels gives the following formula.

[0024]

[Equation 1]

Here,

[0026]

[Equation 2]

And

[0028]

(Equation 3)

[0029] In the present invention, since the numerical values of the real part and the imaginary part of the complex relative permeability are considered to be μr ′ = 1 and μr ″ = 0, the reflection coefficient is calculated by the following equations (1) to (5) as follows. expressed.

[0030]

[Equation 4]

Considering the numerator of this equation (6),

[0032]

(Equation 5)

It can be seen that the reflection coefficient of equation (6) can be reduced by bringing the numerator term of (7) closer to 1. From these facts, the absorption characteristics of the electromagnetic wave absorber are greatly affected by the real and imaginary parts εr ′ and εr ″ of the complex relative permittivity of the material and the material thickness-frequency ratio d / λ _0. I understand.

Further, when the molecular term (7) of the equation (6) becomes 1, the reflection coefficient of the equation (6) becomes 0, and it becomes completely non-reflective, and a perfect electromagnetic wave absorbing material is obtained. FIG. 3 shows the curves of εr ′ and εr ″, which are the real and imaginary parts of the complex relative permittivity, and the value of d / λ ₀ (the number in the graph) that can obtain a non-reflective state. Absorption and shielding "14
7 pages, etc., 1989, Nikkei technical book).

Therefore, in order to improve the electromagnetic wave absorption performance at the target electromagnetic wave wavelength λ ₀ and frequency f, as shown in FIG. 3, a composite obtained by combining the dielectric loss powder 4a and the fiber 1 is obtained. By controlling the thickness d of the body 3 and the complex relative permittivity εr ′ and εr ″, it is possible to reduce the reflection coefficient. As an example, the high frequency range (300 MHz) of the VHF television frequency will be taken up. And its wavelength λ ₀ becomes 1 m, and d / λ ₀ = 0.0 in the graph of FIG.
Looking at point 5, εr ′ is about 25, εr ″ is about 6, and the thickness d is 0.05 m (50 mm). That is, 300 MHz depending on the material having this dielectric constant and the thickness of 50 mm. It has a high electromagnetic wave absorption property.

Further, in the composite body 3 of the present invention in which the fiber 1 and the dielectric loss powder 4a are composited, εr 'and εr "can be controlled by increasing the mixing ratio of the dielectric loss powder 4a such as graphite. For example, both εr ′ and εr ″ can be increased by increasing the mixing amount of the dielectric loss powder 4a. As is clear from the graph of FIG. 3, larger εr ′ and εr ″ are required to reduce d / λ ₀ , that is, to reduce the thickness of the composite body 3. Therefore, the fiber 1 and the dielectric loss powder are required. When designing the electromagnetic wave absorbability of the composite body 3 in which the composite body 4a is composited, the optimum type, particle size, and mixing ratio of the dielectric loss powder 4a are selected, and the thickness of the composite body 3 is designed. It is necessary to bring the complex relative permittivity εr ′ and εr ″ at which the electromagnetic wave absorption by is most effective.

As described above, the optimum mixing ratio between the fiber 1 of the composite 3 used as the electromagnetic wave absorber and the dielectric loss powder 4a is determined by the type and particle size of the dielectric loss powder 4a such as graphite,
Since it varies depending on the thickness of the composite body 3 and the like, it cannot be said unconditionally, but it is desirable to set the mixing volume ratio of the dielectric loss powder 4a to the fiber 1 to be 20 to 80%.

Further, the composite body 3 in which the fiber 1 and the dielectric loss powder 4a are composited has the powder 4 inside the large number of voids 5 between the fibers 1.
Excellent sound absorption performance can be imparted by holding and adhering. That is, by combining the dielectric loss powder 4a, the structure of the void 5 of the composite 3 can be further complicated by the dielectric loss powder 4a, and at the same time, the vibration action of the dielectric loss powder 4a also works. The sound absorption effect in the low frequency range can be enhanced.

The electromagnetic wave absorber according to the second aspect of the present invention is such that by providing the conductive layer 6 on the back surface of the composite body 3 according to the first aspect of the invention, a higher electromagnetic wave absorbing performance can be obtained. Is. FIG. 2 shows an example of a specific form in which the conductive layer 6 is provided on the composite body 3 according to the invention of claim 2, and inside the void 5 formed between the fibers 1 mainly forming the skeleton structure. Powder 4 is binder 2
The conductive layer 6 is adhered and laminated on the back surface of the composite body 3 formed by being adhered and held by.

The conductive layer 6 is not particularly limited, but the conductive property is imparted by plating a metal plate such as an iron plate, an aluminum plate, a galvanized steel plate, or a non-conductive material. A conductive plate or the like can be used. Generally, when high electromagnetic wave absorption performance is required, not only the reflection coefficient S but also the transmission coefficient T must be reduced. The transmission coefficient cannot be generally stated because it depends on the thickness of the material and the degree of attenuation of electromagnetic waves, but it is difficult to completely eliminate the transmitted wave with the structure in which the dielectric loss powder 4a and the fiber 1 are simply combined. is there. On the other hand, according to the second aspect of the present invention, since the conductive layer 6 is provided on the back surface of the composite body 3, the transmitted wave can be completely eliminated. That is, the electromagnetic wave incident on the composite body 3 is reflected between the conductive layer 6 on the back surface of the composite body 3 and the front surface of the composite body 3, whereby the electromagnetic wave is attenuated and higher electromagnetic wave absorption performance can be obtained. You can do it. At this time,
It is necessary to select the material used for the conductive layer 6 in consideration of the deterioration of the sound absorption characteristics due to the conductive layer 6. For example, if the conductive layer is acoustically transparent, that is, if the conductive sheet has a thickness of 50 μm or less, the sound absorbing performance of the composite body 3 is not impaired while maintaining the electromagnetic wave absorbing performance. A typical example of such an acoustically transparent conductive sheet is an aluminum foil.

The electromagnetic wave absorber according to the present invention manufactured as described above is required to have electromagnetic wave absorbing performance and soundproofing performance at the same time as a soundproof wall of an elevated road or a partition or partition of a house or office that handles OA equipment. It is used for a part used for a part to be opened.

[0042]

As described above, the electromagnetic wave absorber of claim 1 is composed of the composite body 3 in which the powder 4, the fiber 1 and the binder 2 are mixed, and the powder 4 is the dielectric loss powder 4a. Since the powder 4 is held in the internal voids 5 of the composite body 3 by the fiber 1 and the binder 2, the dielectric loss action of the dielectric loss powder 4a held inside the composite body 3 can obtain electromagnetic wave absorption performance. A composite body 3 that can be made and is mainly composed of fiber 1
The electromagnetic wave scattering / absorption action due to the complicated structure of the void 5 has a high electromagnetic wave absorption performance. Further, since the composite body 3 is a mixture of the fibers 1 and the binder 2, it is light in weight and excellent in handleability, and it is possible to obtain high sound absorbing performance due to the complicated structure of the voids 5, and the powder The sound absorption performance of the composite body 3 can be further enhanced by the complication of the structure of the void 5 due to the composite of the body 4 and the vibration action of the powder 4.

In addition to the invention of claim 1, since the conductive layer 6 is formed on one surface of the composite 3 in the invention of claim 2, the electromagnetic wave incident on the composite 3 is converted into the conductive layer 6. The electromagnetic wave can be attenuated by being reflected between the other surface of the composite body 3 and the electromagnetic wave absorption performance can be further enhanced.

[0044]

EXAMPLES The present invention will be further described with reference to examples. Needless to say, the present invention is not limited to the examples. (Example 1) Rock fiber (fiber diameter;
Artificial graphite (average particle diameter; 1.0 to 50 μm, bulk density 0.1 to 0.3 g / c) as dielectric loss powder 4a.
m ³ ), and further using phenol foamed resin fine particles as the binder 2, 45% by weight of the fiber 1, 45% by weight of the dielectric loss powder 4a and 10% by weight of the binder 2 are mixed, and then the mixture 7 is prepared. 6, a heating plate 9 of 130 ° C. arranged via a distance bar 8 having a thickness of 30 mm,
The binder 2 was foamed and cured by filling the space between 9 and heat-molding for several minutes to prepare a composite 3, which was used as an electromagnetic wave absorber.

Example 2 Rock fiber (fiber diameter: 10 μm) was used as the fiber 1, and artificial graphite (average particle size: 1.0 to 50 μm, bulk density 0.1 to 10) was used as the dielectric loss powder 4a.
0.3 g / cm ³ ) and using phenol foamed resin fine particles as the binder 2 and mixing these materials at the same mixing ratio as in Example 1, followed by molding in the same manner as in Example 1 to obtain a binder. 2 was foamed and cured to prepare an electromagnetic wave absorption composite body 3. Next, an aluminum foil having a thickness of 40 μm was adhered and laminated on the back surface of this composite body 3 to form a conductive layer 6, thereby obtaining an electromagnetic wave absorber.

Comparative Example 1 Commercially available JIS A 9505
Glass wool felt with a density of 24 kg / m ³ as specified in (Asahi Glass Fiber Co., Ltd. “Glass Wool 24K”)
Was used as an electromagnetic wave absorber. Table 1 shows the thicknesses and densities of the composites 3 of Examples 1 and 2 and Comparative Example 1. Further, the electromagnetic wave absorbing performance and the sound absorbing performance of the electromagnetic wave absorbers of Examples 1 and 2 and Comparative Example 1 were measured. The electromagnetic wave absorption performance is
Reflection coefficient (d) in the range of television radio frequency (VHF)
B) was measured and evaluated, and the sound absorption performance was evaluated by measuring the sound absorption coefficient and the peak frequency of the sound absorption coefficient. Sound absorption coefficient here is J
It is the vertical incident sound absorption coefficient measured according to IS A 1405 "Method for measuring vertical incident sound absorption coefficient of building material by in-pipe method", and is measured when the thickness of the electromagnetic wave absorber is 30 mm. The sound absorption coefficient was calculated using standing waves.

Graphs showing the frequency dependence of the sound absorption coefficient obtained from the sound absorption coefficient measurement are shown in FIGS. 4 and 5. FIG. 4 is for Example 1 and FIG. 5 is for Comparative Example 1, and the frequency at which the sound absorption coefficient is maximum is the sound absorption peak frequency. As seen from the comparison between FIG. 4 and FIG. 5, it is confirmed that the example 1 has excellent sound absorbing performance in the low frequency range.

Table 1 shows the measurement results of electromagnetic wave absorption performance and sound absorption performance. In Examples 1 and 2, -10 dB to -20 d.
It can be seen that the reflection coefficient of about B is obtained and the electromagnetic wave absorption performance is high, whereas the material of Comparative Example 1 has no electromagnetic wave absorption effect. In addition, although the sound absorbing characteristics of the first and second embodiments are substantially the same, it is understood that the electromagnetic wave absorbing performance of the second embodiment in which the conductive layer 6 is laminated on the back surface is superior.

[0049]

[Table 1]

[0050]

As described above, the invention of claim 1 comprises a composite in which powder, fiber and binder are mixed, wherein the powder is a dielectric loss powder and the powder is composed of the fiber and the binder. Since it is characterized in that it is held in the internal voids of the composite, it is possible to obtain electromagnetic wave absorption performance by the dielectric loss action of the dielectric loss powder held inside the composite,
Moreover, the electromagnetic wave scattering and absorption action due to the complex structure of the voids of the composite mainly composed of fibers can be combined to exert a high electromagnetic wave absorption performance, and the composite is a mixture of fibers and a binder. It is lightweight and easy to handle, and high sound absorption performance can be obtained due to the structure of the voids between the fibers. Moreover, the complex structure of the voids due to the composite of the powders and the vibration of the powders. By the action, it is possible to further enhance the sound absorbing performance of the composite body, and it is possible to provide an electromagnetic wave absorbing body which has both electromagnetic wave absorbing performance and sound absorbing performance, and is lightweight and excellent in handleability.

The invention of claim 2 is characterized in that a conductive layer is formed on one surface of the composite,
The electromagnetic wave incident on the composite can be reflected between the conductive layer and the other surface of the composite to attenuate the electromagnetic wave, and the electromagnetic wave absorption performance can be further enhanced.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an embodiment of the invention of claim 1.

FIG. 2 is a schematic cross-sectional view showing the structure of an embodiment of the invention of claim 2;

FIG. 3 is a graph showing a non-reflection curve of a complex relative permittivity in a non-reflection state.

FIG. 4 is a graph showing frequency dependence of sound absorption coefficient in Example 1.

5 is a graph showing frequency dependence of sound absorption coefficient in Comparative Example 1. FIG.

FIG. 6 is a cross-sectional view showing molding of a composite.

[Explanation of symbols]

 1 Fiber 2 Binder 3 Composite 4 Powder 4a Dielectric loss powder 5 Void 6 Conductive layer

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 13, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

On the other hand, in recent years, in the fields of soundproof walls of elevated roads, partitions and partitions such as houses and offices that handle OA equipment, demands for electromagnetic wave absorbing performance and soundproofing performance have become severe. There are the following two measures to improve the soundproofing performance.
One is a method of blocking the propagation of the sound wave by installing a material such as a metal plate having a high surface density at a position where the propagation path of the sound wave is blocked, that is, a wall or a partition portion. However, with this method, although it is possible to obtain soundproofing and high electromagnetic wave blocking performance, there is a possibility of causing ghost interference or communication failure of TV radio waves due to reflection of electromagnetic waves, and soundproofing performance Not enough.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Ando, 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Inventor, Koji Tsuji, 1048, Kadoma, Kadoma City, Osaka Prefecture 72) Inventor Hajime Sugiyama 1048, Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (2)

[Claims] 1. A composite comprising a mixture of powder, fibers and a binder, wherein the powder is a dielectric loss powder and the powder is held in the internal voids of the composite by the fiber and the binder. An electromagnetic wave absorber characterized by: 2. The electromagnetic wave absorber according to claim 1, wherein a conductive layer is formed on one surface of the composite.