JP2000269680A - Electromagnetic wave absorbing board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance absorbing property for electromagnetic waves in a frequency band within a specific range by causing an electromagnetic wave absorbing board to have an electromagnetic wave absorbing layer, which contains a hydraulic setting inorganic binder within a specific range and an amount within a specific range of magnetic substance powder containing within a specific range magnetic substance particles of diameters not smaller than a specific value. SOLUTION: An electromagnetic wave absorbing board is made by providing an electromagnetic wave absorbing layer, which uses metallic fibrous material and carbon fiber material and contains 30-90 pts.wt. of hydraulic setting inorganic binder which sets, when lime, plaster, calcium silicate, magnesia cement, etc., are mixed with water, and 70-10 pts.wt. of magnetic substance powder containing 20-100 wt.% of magnetic substance particles which are a surface- treated magnetic metal alloy such as silicon steel, sendust, supermalloy, permally, amorphous metal, etc., of particle diameters of 100 μm or larger. Consequently, superior absorbing property for electromagnetic waves in a frequency band of 10-1,000 MHz is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave absorbing board, and more particularly to an electromagnetic wave absorbing board having excellent absorption performance for electromagnetic waves in a frequency band of 10 to 1000 MHz.

[0002]

2. Description of the Related Art Electromagnetic waves emitted from electronic devices using electromagnetic waves may cause various electronic devices to malfunction.
It can cause various problems. However,
In particular, when the space is filled with electromagnetic waves in the frequency range of 10 to 1000 MHz, it is difficult to remove this.

Conventionally, a sintered ferrite has been used as an absorber for absorbing electromagnetic waves in this frequency band. However, at present, a ferrite sintered body can only be used inside an electronic device or as an electronic component. There is also a ferrite sintered body absorber for an anechoic chamber,
And it is heavy and cannot be used for building materials.

[0004] In recent years, devices and equipment for inspecting and measuring magnetism have become widespread. For example, in a magnetically shielded room such as an MRI measurement room or an NMR measurement room, there is a demand for an electromagnetic wave absorber that efficiently absorbs electromagnetic waves in this frequency band leaking from these electronic devices. However, since there is a superconducting magnetic coil or the like for generating magnetism, if a soft ferrite sintered body or the like is used, it may be pulled by the magnetic coil and cannot be used.

[0005] Accordingly, there is a need for a thin, nonflammable electromagnetic wave absorber which can efficiently absorb electromagnetic waves in the 10 to 1000 MHz band and which is not affected by superconducting magnetic coils and the like. .

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been developed in consideration of the above-mentioned situation.
It is an object of the present invention to provide an electromagnetic wave absorbing board having excellent absorption performance for electromagnetic waves in a frequency band of Hz.

[0007]

According to the present invention, a water-curable inorganic binder (a) is used in an amount of 30 to 90 parts by weight and a particle diameter of 100.
An electromagnetic wave absorbing board having an electromagnetic wave absorbing layer containing 70 to 10 parts by weight of a magnetic powder (b) containing 20 to 100% by weight of magnetic particles having a particle size of not less than 20 μm. Hereinafter, the present invention will be described in detail. Note that the following description exemplifies an embodiment of the present invention, but those skilled in the art can make obvious changes in accordance with the purpose of the present invention.
It does not limit the invention in any way.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The water-curable inorganic binder (a) is not particularly limited as long as it is an inorganic binder which cures when mixed with water. For example, gypsum (calcium sulfate), lime, calcium silicate, Magnesia cement, Portland cement, alumina cement, Roman cement, acid-resistant cement, refractory cement, water glass cement and the like can be mentioned. When strength and water resistance are required, Portland cement or alumina cement may be used. Gypsum is preferred when emphasis is placed on weight reduction, workability during installation, and electromagnetic wave absorbing ability.

The magnetic powder (b) has a particle diameter of 100.
It contains 20 to 100% by weight of magnetic particles having a particle size of not less than μm. There is no particular upper limit on the particle diameter of the magnetic particles. It can be used as long as it is within the thickness of the electromagnetic wave absorbing layer. Preferably it is 100-2000 micrometers.

The magnetic powder is not particularly limited as long as it exhibits magnetic loss, and examples thereof include a metal oxide magnetic substance and a metal magnetic substance.

[0011] is not particularly restricted but includes 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. Among these, in the present invention, Li, Mg, Mn, Co, Ni, Cu, Sn, S
It is preferable to use an Fe oxide containing r, Ba, and the like. These may be used alone or in combination of two or more.

The metal magnetic material is not particularly limited.
For example, a magnetic metal simple substance such as Fe, Co, Ni, or the like, or a surface-treated metal magnetic material obtained by subjecting these to a surface treatment such as an oxidation treatment to obtain a stable mode; silicon steel, sendust, supermalloy, permalloy, Magnetic metal alloys such as amorphous metals; Si, B, Al, Co, Ni, Cr, V, S
Examples thereof include an Fe magnetic alloy containing at least one selected from the group consisting of n, Zn, Pb, Mn, Mo, and Ag. Of these, in the present invention, S
i, B, Al, Co, Ni, Cr, V, Sn, Zn, P
Fe magnetic alloy containing at least one selected from the group consisting of b, Mn, Mo and Ag; Fe, Co or N
Preferred is a magnetic metal simple substance i or a surface-treated metal magnetic material which has been subjected to a surface treatment such as an oxidation treatment to make it stable. These may be used alone or in combination of two or more.

In the present invention, among these, it is preferable to use a metal oxide magnetic material in order to reduce the weight of the obtained electromagnetic wave absorbing material and enhance the radio wave absorbing ability. More preferably, MnO to _{Fe 2 O 3, ZnO, NiO} ,
It is a spinel-type ferrite magnetic powder combining MgO, CuO, Li ₂ O and the like. More preferably, Mn-
They are Mg-Zn ferrite magnetic powder and Mn-Zn ferrite magnetic powder.

For the magnetic powder, for example, a block of a magnetic material such as the above-mentioned metal oxide magnetic material or the above-mentioned metal magnetic material is pulverized using a stamp mill or the like, and is subjected to dry sieving, air classification, and wet sieving. It can be obtained by classification by a separation method, mechanical wet classification or the like. The powder obtained as described above usually has a particle size distribution. Particle size 100
In order to confirm that magnetic particles having a particle size of 20 μm or more are contained in the range of 20 to 100% by weight, for example, the particles may be sieved using a sieve having a mesh size of 100 μm or more. Further, magnetic particles having a particle diameter of 100 μm or more may be mixed with fine particles having a particle diameter of 100 μm or less at a predetermined ratio.

In the present invention, the ratio of the magnetic particles having a particle diameter of 100 μm or more to the magnetic particles present in the magnetic powder to be added is 20 to 100% by weight. If this ratio is less than 20% by weight, the absorption performance for electromagnetic waves in the 10 to 1000 MHz band decreases. That is, in order to exhibit the effect of preventing unnecessary leakage of low-frequency electromagnetic waves, the amount of large-diameter magnetic particles that contribute to this performance is important. Thus, in the present invention, the particle diameter is 100 μm
Since attention is paid only to the ratio of the magnetic particles described above, the object of the present invention can be achieved with a magnetic powder containing a predetermined amount of such large-diameter magnetic particles. Accordingly, the magnetic particles having a particle diameter of less than 100 μm are not limited at all. The magnetic powder in which the amount of magnetic particles having a large particle diameter is defined in this manner is different from the conventional notation, for example, the one in which the average particle diameter is defined to be 100 μm or more.

The shape of the magnetic particles is not particularly limited, and may be, for example, irregular particles, flat particles, flaky particles, or the like.

The magnetic powder (b) may be used, if necessary,
Silane coupling agents, titanate coupling agents,
Coupling agents such as aluminate-based coupling agents; surfactants, wetting agents, viscosity reducing agents, and stabilizers for improving the wettability of magnetic powder; even if surface-treated with resins and the like Good. By the surface treatment, it is possible to introduce a functional group that imparts reactivity to the magnetic substance powder or a functional group that governs wettability, so that the wettability with the water-curable inorganic binder (a) and the electromagnetic wave absorbing layer And the dispersion stability can be improved.

The mixing amount of the water-curable inorganic binder (a) and the magnetic powder (b) is 10 times in total of the water-curable inorganic binder (a) and the magnetic powder (b).
Water-curable inorganic binder (a) 30 per 0 parts by weight
To 90 parts by weight, and 70 to 10 parts by weight of the magnetic powder (b). When the amount of the water-curable inorganic binder (a) is less than 30 parts by weight and the amount of the magnetic powder (b) exceeds 70 parts by weight, the productivity of the electromagnetic wave absorbing layer is poor, and the bending strength of the obtained electromagnetic wave absorbing layer is reduced. In addition to exhibiting sufficient physical properties, the content of the magnetic powder increases, and the weight of the electromagnetic wave absorbing layer increases. When the amount of the magnetic powder (b) is less than 10 parts by weight, the electromagnetic wave absorbing layer has insufficient electromagnetic wave absorbing ability and is not suitable for practical use.

When gypsum or calcium silicate is used as the water-curable inorganic binder (a), 55 to 90 parts by weight of the water-curable inorganic binder (a) and 45 to 10 parts by weight of the magnetic powder (b) are used. The amount of the magnetic powder (b) can be reduced, and the weight of the obtained electromagnetic wave absorbing layer can be reduced. In particular, when the water-curable inorganic binder (a) is gypsum, even if the amount of the magnetic powder (b) is small, if it is within the above range, a sufficient electromagnetic wave absorbing ability can be obtained. .

The amount of the water-curable inorganic binder (a) is calculated based on the weight of the inorganic binder in a state of being cured with water. In general, a water-curable inorganic binder is cured by mixing it with an appropriate amount of water, and then at room temperature or by heating, and further applying pressure as needed. For example, calcined gypsum undergoes a hydration reaction with about 17% of its weight in water to form dihydrate gypsum and solidify. In the curing process, water that is unnecessary for the curing evaporates and is discharged to the outside of the system. Therefore, the content of water after curing is generally extremely small. Accordingly, the weight of the inorganic binder after curing is substantially equal to the weight of the inorganic binder containing water in an amount necessary for curing.

In the present invention, the electromagnetic wave absorbing layer may further contain a fibrous conductor (c). The fibrous conductor (c) 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 restricted but includes, for example, simple metals such as stainless steel, brass, copper, aluminum, nickel and lead; metal fibers produced from alloys; Metal-coated fibers obtained by subjecting a surface of an inorganic fiber or the like to metal deposition, plating, coating, or the like can be given.

The carbon-based fiber material is not particularly limited, and examples thereof include polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, and carbon whiskers.

Of these, metal-coated fibers and carbon-based fiber materials are preferable because of good dispersibility and electromagnetic wave absorbing ability during the production of the electromagnetic wave absorbing layer. The fibrous conductor (c) is
Since it is used by being mixed with the above-mentioned water-curable inorganic binder (a), those having excellent wettability to water and dispersion stability are preferred. Even if the fibrous conductor (c) has good wettability to water, if the fiber is curled or the fiber is inferior in rigidity or toughness, the fiber is easily entangled. When it is mixed with the conductive inorganic binder (a) and the magnetic substance powder (b), it tends to form a lump, making uniform dispersion difficult, and therefore, those having both excellent wettability to water and dispersion stability are preferred. .

In the present invention, the above fibrous conductor (c)
Is used in a water-hardening system, and if it is a metal-based fibrous material, a corrosion problem occurs. Therefore, it is more preferable to use a carbon-based fiber material having better corrosion resistance than a metal-based fibrous material.

The specific gravity of the fibrous conductor (c) is 2.5
The following is preferable, the diameter of the fiber is preferably 5 to 50 μm, and the length of the fiber is preferably 2 to 40 mm.

The mixing amount of the fibrous conductor (c) is determined by the above-mentioned water-curable inorganic binder (a) and the above-mentioned magnetic powder (b).
Is preferably 0.005 to 1.0 part by weight with respect to 100 parts by weight in total. When gypsum is used as the water-curable inorganic binder (a), the amount is preferably 0.01 to 0.8 parts by weight. If it is less than 0.01 part by weight, it is not enough to improve the electromagnetic wave absorbing ability, and if it exceeds 0.8 part by weight, electromagnetic wave reflection occurs on the surface of the electromagnetic wave absorbing layer, and the electromagnetic wave absorbing ability decreases. Not preferred.

In the present invention, other fibrous substances may be used in addition to the fibrous conductor (c). The other fibrous substances are not particularly limited, and include, 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 the like. Needle-like reinforcing fibers. The above-mentioned other fibrous substances may be used for reinforcing the electromagnetic wave absorbing layer.

In the present invention, in order to further reduce the weight of the electromagnetic wave absorbing layer, in forming the electromagnetic wave absorbing layer, the water-curable inorganic binder (a), the magnetic powder (b), and the like. In this case, the fibrous conductor (c) may further contain a foamable filler (d). When the foamable filler (d) is contained in the electromagnetic wave absorbing layer, the magnetic powder (b) and the fibrous conductor (c) can be sufficiently dispersed and compounded. Since the specific gravity can be reduced,
The weight can be reduced without lowering the electromagnetic wave absorbing ability.

The foamable filler (d) is not particularly restricted but includes, for example, natural lightweight aggregates such as volcanic rubble, expanded shale, expanded clay, expanded vermiculite, expanded perlite, expanded obsidian, coal gala, molten fly Inorganic foamable fillers such as artificial lightweight aggregates such as ash, silica balloon, perlite, shirasu balloon, and glass balloon; styrene foam particles, urethane foam particles, acrylic resin hollow balloon, acrylic modified resin hollow balloon, melamine resin balloon ,
Organic foamable fillers such as urethane-modified resin hollow balloons can be used.
These may be used alone or in combination of two or more.

As the foamable filler (d), any of the above-mentioned inorganic foamable filler and the above-mentioned organic foamable filler may be used. Having a smooth surface, having a small particle size distribution width, having a low water absorption, not containing a water-soluble component, preferably satisfying conditions such as having no water swelling property are preferable. To satisfy
Expanded vermiculite, perlite, shirasu balloon, styrofoam particles, urethane foam particles, and acrylic resin-based hollow balloons are preferred.

Although the specific gravity of the foamable filler (d) is not particularly limited, it is usually 0.05 to 0.05.
1.70 is preferred, and the unit volume weight is 0.01
~ 0.50 kg / L is preferred.

The average particle size of the expandable filler (d) is not particularly limited, but is generally preferably 0.05 μm to 5 mm. The average particle diameter of the inorganic foamable filler among the foamable fillers (d) is larger than the average particle diameter of the organic foamable filler, and is usually 0.1 to 5 m.
m. The average particle size of the organic foamable filler,
The particle size can be adjusted relatively freely by the synthesis conditions and synthesis method.

The content of the foamable filler (d) is preferably 0.01 to 20 parts by weight based on 100 parts by weight of the total of the water-curable inorganic binder (a) and the magnetic powder (b). . If the amount is less than 0.01 part by weight, the effect of the addition of the expandable filler (d) is small and the effect on weight reduction cannot be obtained. The physical strength of the layer is undesirably reduced.

The thickness of the electromagnetic wave absorbing layer is 5 to 50 mm
Is preferred. If it is less than 5 mm, the physical strength of the electromagnetic wave absorbing layer is weak, and if it exceeds 50 mm, the weight becomes heavy.
Further, when the electromagnetic wave absorbing material is used as a building material, if it is outside the above range, the mounting workability and the fitability are poor. Preferably, it is 7 to 25 mm.

The specific gravity of the electromagnetic wave absorbing layer is 0.50 to 0.50.
1.65 is preferred. 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 absorbing layer increases, which is not preferable. In the present invention, from the viewpoint of mounting workability, the specific gravity is preferably 0.60 to 0.60.
The specific gravity is preferably from 0.60 to 1.00 in order to make it about the same as that of a conventionally used gypsum board.

The electromagnetic wave absorbing material of the present invention may have an electromagnetic wave reflecting layer in addition to the above electromagnetic wave absorbing layer. The electromagnetic wave reflection layer is not particularly limited, but is preferably made of a conductive material, a metal deposition film, a metal foil, or a metal powder. These may be used alone or in combination of two or more. The electromagnetic wave reflecting layer can also serve as a support.

The electromagnetic wave reflection layer has a shielding ability of 20
It is preferably at least dB. More preferably, 30
dB or more.

The conductive material is not particularly limited as long as it provides a shielding performance of at least 20 dB, preferably at least 30 dB, for example, copper, aluminum, steel, iron, nickel, stainless steel, stainless steel, and the like. Metal plates such as brass; metal plates plated with these metals;
Metal cloth; a plated steel plate obtained by plating aluminum, zinc, copper, or the like on a steel plate by heat or electricity can be used. Such a conductive material may have been subjected to a surface treatment or a primer treatment for improving interlayer adhesion, such as a precoated steel sheet.

The metal deposited film is not particularly limited.
For example, a plastic material; paper; and a non-conductive material such as a synthetic paper such as a PET film formed with a vapor-deposited layer of aluminum or the like can be used. The metal foil is not particularly limited, and examples thereof include a metal foil used as the conductive material. The metal powder is not particularly limited, and examples thereof include metal powder used as the conductive material. In the present invention, from the viewpoint of weight reduction as a building material, paper, P
It is preferable to deposit aluminum or the like on a non-conductive material such as an ET film.

In addition to the above, a conductive coating film containing a metal used as the conductive material and a binder is provided on a non-conductive material such as a plastic material, paper, or synthetic paper. Or a metallized material having an electroless plating layer such as copper or nickel formed thereon.

The thickness of the electromagnetic wave reflecting layer is 30 μm to 3 μm.
mm is preferred. When the thickness is less than 30 μm, the mechanical strength of the electromagnetic wave reflection layer decreases, and when it exceeds 3 mm, the weight of the electromagnetic wave reflection layer increases, which is not practical.

The method for providing the electromagnetic wave reflecting layer is not particularly limited. For example, a method in which the electromagnetic wave reflecting layer is adhered to one surface of the electromagnetic wave absorbing layer can be suitably employed. The bonding is performed, for example, by bonding a paper on which aluminum serving as the electromagnetic wave reflection layer is deposited, a paper to which an aluminum foil is bonded, an aluminum foil, or the like to one surface of the electromagnetic wave absorption layer using an adhesive or the like. Can be.

Hereinafter, the method for producing an electromagnetic wave absorbing board of the present invention will be described in detail by taking as an example the case where the electromagnetic wave absorbing layer is a gypsum board, an ALC board, a mortar or a cement board.

[0045]1. Gypsum board  Gypsum, magnetic powder (b), water, if necessary, fibrous
Conductor (c), foamable filler (d), organic binder
-, Foaming agents, stabilizers, dispersants, water reducing agents, aggregates, etc.
Then, after sufficiently mixing with a mixer to make a slurry,
Spread the above slurry on gypsum board base paper,
After adjusting the temperature, further sandwich it with gypsum board base paper and heat it.
Then, the slurry is hardened, coagulated and dried,
Obtain a magnetic wave absorbing layer. One side of the obtained electromagnetic wave absorption layer
If necessary, aluminum for the electromagnetic wave reflection layer is deposited.
Paper, aluminum foil, etc.
Adhering to one side of the magnetic wave absorption layer using an adhesive etc.
Thus, an electromagnetic wave absorbing board is obtained.

In this case, the electromagnetic wave absorbing layer may be reinforced by using another fibrous substance in addition to the fibrous conductor (c).

When the foamable filler (d) is used, the amount of each of the above components is 55 to 55 parts by weight based on 100 parts by weight of the total of the calcined gypsum and the magnetic powder (b).
90 parts by weight, the magnetic powder (b) is 45 to 10 parts by weight, the fibrous conductor (c) is 0.01 to 0.8 parts by weight, and the foamable filler (d) is 0.1-15
It is preferably in parts by weight.

In this case, if the amount of the foamable filler (d) is less than 0.1 part by weight, the effect on weight reduction is not sufficient. If the amount exceeds 15 parts by weight, the effect on the weight reduction is obtained, but the gypsum board is used. It is not preferable because the adhesiveness between the base paper and the material forming the electromagnetic wave absorbing layer is reduced, and the physical strength of the obtained electromagnetic wave absorbing layer is reduced.

[0049]2. ALC board  Portland land as a water-curable inorganic binder (a)
Using calcium carbonate and aluminum powder,
Water-curable inorganic binder (a), magnetic powder
(B), water, if necessary, fibrous conductor (c), foaming
Filler (d), foaming agent, inorganic filler, water-soluble
And mix well with a mixer.
After pouring, pour into mold, cure at about 60 ° C, and cure
After drying at 105 ° C, the electromagnetic wave absorbing layer
Get. If necessary, on one side of the obtained electromagnetic wave absorption layer
To attach the electromagnetic wave reflection layer using an adhesive etc.
Thus, an electromagnetic wave absorbing board is obtained.

In this case, the compounding amount of the fibrous conductor (c) is 0.0 with respect to 100 parts by weight of the total of the water-curable inorganic binder (a) and the magnetic substance powder (b).
It is preferably from 0.5 to 0.2 parts by weight. When the weight is further reduced, the water-curable inorganic binder (a) is 65 to 85 parts by weight with respect to a total of 100 parts by weight of the water-curable inorganic binder (a) and the magnetic substance powder (b). as well as,
The magnetic material powder (b) is preferably 35 to 15 parts by weight, and the fibrous conductor (c) is preferably 0.01 to 0.1 parts by weight. Also, a large amount of a foaming agent may be added to increase the amount of air bubbles to reduce the weight.

When the weight is further reduced by using the foamable filler (d), the water-curable inorganic binder (a) and the magnetic powder (b) are added to the total of 100 parts by weight. 55 to 90 parts by weight of the water-curable inorganic binder (a), 45 to 10 parts by weight of the magnetic powder (b), and 0.01 to 0.8 of the fibrous conductor (c).
Parts by weight, and the foamable filler (d) is 0.01% by weight.
It is preferably from 20 to 20 parts by weight.

[0052]3. mortar  Cement, gypsum as water-curable inorganic binder (a)
And water-hardening inorganic binder using alumina cement
(A), magnetic powder (b), water,
Fiber conductor (c), other fibrous substances, foamable filler
(D), polymer admixture, foaming agent, inorganic filler, water-soluble
Water-soluble polymer, water reducing agent, curing accelerator, curing retarder, etc.
Then, after sufficiently mixing with a mixer to make a slurry,
By pouring into a mold and drying at room temperature of about 20 ° C
Obtain an electromagnetic wave absorbing layer. The obtained electromagnetic wave absorbing layer was obtained.
If necessary, an electromagnetic wave reflection layer may be provided on one side of the electromagnetic wave absorption layer.
By sticking with an adhesive, etc.,
Get the code.

In this case, when the fibrous conductor (c) is blended, the blending amount is a total of 100% of the water-curable inorganic binder (a) and the magnetic powder (b).
It is preferably 0.005 to 0.2 parts by weight based on parts by weight. In order to further reduce the weight, the compounding amount of each of the above components is determined based on the total amount of the water-curable inorganic binder (a) and the magnetic substance powder (b) being 100 parts by weight. ) Is 65 to 85 parts by weight, the magnetic powder (b) is 35 to 15 parts by weight, and the fibrous conductor (c) is preferably 0.01 to 0.1 parts by weight. .

When the foaming filler (d) is used to further reduce the weight, the above-mentioned water-curable inorganic binder (a) and the magnetic powder (b) are used in an amount of 100 parts by weight in total. The water-curable inorganic binder (a) is 55 to 90 parts by weight, the magnetic powder (b) is 45 to 10 parts by weight, and the fibrous conductor (c) is 0.01 to 0.2 parts by weight.
Parts by weight, and the foamable filler (d) is 0.01% by weight.
It is preferably from 20 to 20 parts by weight.

[0055]4. Cement board  Portland cement, magnetic powder (b), water, if necessary
Accordingly, fibrous conductor (c), foamable filler (d),
Polymer admixture, foaming agent, inorganic filler, water soluble
Water, a water reducing agent, a curing accelerator, a curing retarder, etc.
After thoroughly mixing with a mixer to form a slurry,
After pouring, dehydrating under pressure, curing and curing
Obtain an electromagnetic wave absorbing layer. On one side of the obtained electromagnetic wave absorbing layer,
If necessary, attach the electromagnetic wave reflection layer using an adhesive etc.
Thus, an electromagnetic wave absorbing board is obtained.

In this case, the compounding amount of each component is 5 parts of Portland cement with respect to 100 parts by weight of the total of Portland cement and magnetic substance powder (b).
5 to 90 parts by weight, and 45 to 45 parts by weight of the magnetic powder (b)
It is preferably 10 parts by weight.

When the foamable filler (d) is used, the amount of each component is 55 to 55 parts per 100 parts by weight of the total of Portland cement and magnetic powder (b). 90 parts by weight, the magnetic powder (b) is 45 to 10 parts by weight, the fibrous conductor (c) is 0.01 to 0.4 parts by weight, and the foamable filler (d ) Is preferably 0.01 to 20 parts by weight.

The electromagnetic wave absorbing board of the present invention has
Since it has excellent electromagnetic wave absorption at 00 MHz, it can be used as a radio wave control partition in an indoor space such as an intelligent office where there is concern about interference and malfunction due to mutual interference of electromagnetic waves and delay dispersion. As an electromagnetic wave permeable wall material, it is possible to use the electromagnetic wave absorption effect as a transmission absorption loss when an electromagnetic wave is transmitted by being installed in a single sheet or in a sandwich structure by combining two sheets. In addition, it is possible to prevent interference, malfunction and the like due to mutual interference of electromagnetic waves and delay dispersion. In addition, it can be suitably used particularly in a magnetically shielded room such as an MRI measurement room and an NMR measurement room, a room in which a server computer is installed, and particularly, a room in which a plurality of server computers are installed. In these cases, as a mode of use, for example, as illustrated in FIG. 4, around a general personal computer, an AV device, an audio device, an electronic device such as a measuring device, so as to surround them, or A rack, a shelf, a box, or the like for accommodating these may be installed on the inner surface or the like.

Further, when the electromagnetic wave absorbing material of the present invention is installed on a metal surface such as a wall or ceiling of an intelligent office, or installed furniture or the like, the metal surface becomes a reflection surface of the electromagnetic wave, and when the electromagnetic wave is low-reflected. Since the electromagnetic wave absorption effect as the reflection absorption loss of the room can be used, unnecessary electromagnetic waves are gradually absorbed while the indoor electromagnetic waves are repeatedly reflected, and the radio wave environment is improved as a whole. As a mode of its use, for example, on a top plate, a horizontal plate, and a sprinkling board of an office desk or a conference desk; on a side, an upper surface, and a front door of a storage;
Partition board, on the vertical surface of the screen; on the back of the chair,
May be installed. These can be combined into a low reflection system furniture.

Further, since the electromagnetic wave absorbing material of the present invention has an electromagnetic wave absorbing layer made of an inorganic binder such as gypsum, it is lightweight and flame-retardant, and has excellent handling properties and workability as a building material. ing. Therefore, it is also suitable as a building material for walls, ceilings and the like.

[0061]

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 64 parts by weight of calcined gypsum, 60 parts by weight of water, particle size 240 to 100
A slurry was prepared by mixing 25 parts by weight of a magnetic powder containing 78% by weight of 0 μm Ni—Zn ferrite granules with a mixer, and the slurry was poured onto a gypsum board base paper. The base paper for gypsum board is layered on this, and a predetermined thickness (9.5 mm)
Was adjusted. This was heated and dried at about 100 ° C. to obtain a plate-like electromagnetic wave absorber. The specific gravity of this electromagnetic wave absorber was 0.97, and the hydration ratio of calcined gypsum was 17% (about 11 parts by weight of water was hydrated).

The obtained electromagnetic wave absorber was placed inside a box where resonance was observed, and a change in the intensity of resonance was observed.
In measurement, first, a vector network analyzer (MS467, manufactured by Anritsu Corporation) is connected to one end of the waveguide.
0C, MN8602A), and the other was terminated at 50 ohms. As a result of observing the reflected wave from the waveguide in the S11 mode, no remarkable reflected wave was observed at a specific frequency. Therefore, in order to obtain a resonance phenomenon, a metal coil is provided in the waveguide at a distance of 50 from the center of the waveguide.
Installed from the end of the ohm. As a result, a reflected wave due to resonance was observed around 700 MHz. This spectrum is shown in FIGS. The obtained electromagnetic wave absorber was placed in this waveguide at 9.5 cm × 12.0 cm × 5.0.
The sample cut into a size of cm was installed on the bottom of the center of the waveguide, and the reflected wave when installed was measured. The spectrum of the reflected wave at this time is shown by a broken line 3 in FIG. For comparison, the dotted line 2 also shows the spectrum of the reflected wave when a normal gypsum board (GB-R) containing no magnetic substance powder was installed.

Example 2 64 parts by weight of calcined gypsum, 60 parts by weight of water (about 11 parts required for curing)
Parts by weight), Mn-Z having a particle size of 300 to 2000 μm
Magnetic powder 2 containing 80% by weight of n-type ferrite granules
Five parts by weight were mixed with a mixer to obtain a plate-like electromagnetic wave absorber in the same manner as in Example 1. In the obtained electromagnetic wave absorber, a change in resonance intensity was observed in the same manner as in Example 1.
The results are shown in FIG.

Example 3 56 parts by weight of calcined gypsum, 50 parts by weight of water (including about 9 parts by weight required for curing), and 50% by weight of Ni-Zn ferrite granules having a particle diameter of 100 μm or more and having a particle diameter of 1000 μm or more.
35 parts by weight of the magnetic powder contained was mixed with a mixer to obtain a plate-shaped electromagnetic wave absorber in the same manner as in Example 1.
The specific gravity of the obtained electromagnetic wave absorber was 1.2.

Using the obtained electromagnetic wave absorber, the effect of reducing leaked radio waves was examined. The experiment was performed using a device that emits a radio wave near 300 MHz. Measure the reception intensity of the radiated radio wave of this device with a spectrum analyzer and it will be 60dB
μV / m. When the periphery of the device was covered with a zinc iron plate, the reception intensity was reduced to 45 dBμV / m. The electromagnetic wave absorber obtained as described above was installed inside the zinc iron plate, that is, on the device side, and the maximum electric field intensity (dBμV / m) near 300 MHz of the leaked radio wave was measured. The results are shown in Table 1.

Example 4 30 parts by weight of calcined gypsum, 40 parts by weight of water (including about 5 parts by weight required for curing), Ni-Zn having a particle size of 240 to 1000 μm
Powder 65 containing 78% by weight of ferrite-based granules
The parts by weight were mixed with a mixer to obtain a plate-like electromagnetic wave absorber in the same manner as in Example 1. The specific gravity of the obtained electromagnetic wave absorber was 1.5. Using the obtained electromagnetic wave absorber, the effect of reducing leaked radio waves was examined in the same manner as in Example 3. The results are shown in Table 1.

Example 5 64 parts by weight of calcined gypsum and 60 parts by weight of water (about 11 parts required for curing)
Parts by weight), Ni-Co-F having an average particle size of 100 µm.
e-Cr stainless steel granules with a mesh size of 125 μm
And 25 parts by weight of the magnetic substance powder remaining on the sieve were mixed with a mixer to obtain a plate-like electromagnetic wave absorber in the same manner as in Example 1.

The electromagnetic wave shielding effect was examined using the obtained electromagnetic wave absorber. Using the device of Example 3, the device was covered around the device, and the reception intensity was measured. The results are shown in Table 2.

Example 6 When a personal computer was set up across a room partition wall next to a room where several network servers were installed, noise appeared on the display screen. Instead of this room partition wall, a wall plate of 200 cm in length and 360 cm in width in which an aluminum vapor-deposited paper is adhered to one surface of the electromagnetic wave absorber produced in Example 1,
When the aluminum deposition surface was set to face the display, the noise lines that appeared on the display screen disappeared. For comparison, when an aluminum sheet of the same size was installed, the noise on the display screen did not disappear. When the electromagnetic wave absorber produced in Comparative Example 1 shown below was used, although noise was reduced, noise was not lost.

Comparative Example 1 64 parts by weight of calcined gypsum, 60 parts by weight of water (about 11 parts required for curing)
And a slurry was prepared by mixing 25 parts by weight of a Ni—Zn ferrite powder having an average particle diameter of 80 μm with a mixer, and a plate-like electromagnetic wave absorber was obtained in the same manner as in Example 1. In the obtained electromagnetic wave absorber, a change in resonance intensity was observed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 2 64 parts by weight of calcined gypsum, 60 parts by weight of water (about 11 parts required for curing)
25 parts by weight of a magnetic powder containing 90% by weight of Mn-Zn ferrite granules having a particle size of 80 μm or less were mixed with a mixer to form a slurry. Was obtained. In the obtained electromagnetic wave absorber, a change in resonance intensity was observed in the same manner as in Example 1. The results are shown in FIG.

Comparative Example 3 79 parts by weight of calcined gypsum, 50 parts by weight of water (about 13 parts required for curing)
8 parts by weight of magnetic powder containing 50% by weight of Ni-Zn ferrite granules having a particle size of 100 µm or more and a particle size of 1000 µm or more were mixed with a mixer to prepare a slurry. In the same manner as in Example 1, a plate-like electromagnetic wave absorber was obtained. The obtained electromagnetic wave absorber had a specific gravity of 1.0. Using the obtained electromagnetic wave absorber, the effect of reducing leaked radio waves was examined in the same manner as in Example 3. The results are shown in Table 1.

Comparative Example 4 64 parts by weight of calcined gypsum, 60 parts by weight of water (about 11 parts required for curing)
Parts by weight), Ni-Co-F having an average particle size of 100 µm.
e-Cr stainless steel granules with a mesh size of 125 μm
The magnetic material powder remaining on the sieve is further sieved through a sieve having a mesh size of 106 μm, separated, and 25 parts by weight of the magnetic material powder having passed through the sieve are mixed with a mixer to form a slurry. A plate-like electromagnetic wave absorber was obtained in the same manner as in Example 1. Using the obtained electromagnetic wave absorber, the radio wave shielding effect was examined in the same manner as in Example 5. The results are shown in Table 2.

[0075]

[Table 1]

[0076]

[Table 2]

From the results shown in FIG. 1, the peak intensity hardly changed when a normal gypsum board of the same size was used, whereas when the gypsum board of Example 1 was used, the peak intensity was clearly changed. It can be seen that the peak intensity has been reduced. That is, it indicates that the resonating electromagnetic wave has been absorbed.

From the results shown in FIG. 2, it was found that when the board of Comparative Example 1 was used, the decrease in peak intensity was smaller than when the board of Example 1 was used. The difference between Example 1 and Comparative Example 1 is the particle size of the magnetic particles. Therefore, it is shown that if the particle diameter of the magnetic material particles is small, and if it is out of the range of the present invention, a sufficient electromagnetic wave absorbing effect cannot be obtained.

From the results shown in FIG. 3, it was found that when the board of Comparative Example 2 was used, the decrease in peak intensity was smaller than when the board of Example 2 was used. The difference between Example 1 and Comparative Example 1 is the particle size of the magnetic particles. Therefore, the particle diameter of the magnetic material particles becomes small, and if it is out of the range of the present invention, a sufficient electromagnetic wave absorbing effect cannot be obtained.

From the results shown in Table 1, when the board of Example 3 was used, the intensity of the leaked radio wave was sufficiently reduced as compared with the case of using only the zinc steel sheet, and the board of Example 4 was used. In this case, since the content of the magnetic powder is large, it can be seen that the intensity of the leaked radio wave is further reduced. However, Comparative Example 3
It was found that when the board was used, the content of the magnetic powder was less than the range of the present invention, so that the intensity of the leaked radio wave could not be sufficiently reduced.

From the results in Table 2, it can be seen that Comparative Example 4 containing almost no magnetic powder having a particle diameter of 100 μm or more, and Example 5 containing virtually only a magnetic powder having a particle diameter of 100 μm or more.
Are compared. As a result, it was shown that the particle diameter of the magnetic particles is required to be 100 μm or more in order to shield electromagnetic waves in the frequency band targeted by the present invention.

[0082]

Since the electromagnetic wave absorbing board of the present invention has the above-described structure, it can effectively absorb electromagnetic waves in the band of 10 to 1000 MHz, is a low specific gravity, flame-retardant material, It can be suitably used for applications as building materials. Therefore, 10-1000M
It is possible to reduce electromagnetic waves in the Hz band, and it is possible to provide an advantageous material for preparing an electromagnetic wave environment.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of Example 1. In the figure, the solid line 1 indicates the case of no treatment, the dotted line 2 indicates the case of a gypsum board containing no magnetic powder, and the broken line 3 indicates the case of the first embodiment.

FIG. 2 is a graph comparing the results of Example 1 and Comparative Example 1. In the figure, the solid line 1 indicates the case of no treatment, and the broken line 4 indicates the comparative example 1.
The case of is shown.

FIG. 3 is a graph comparing the results of Example 2 and Comparative Example 2. In the figure, the solid line 1 indicates the case of no treatment, and the broken line 5 indicates the second embodiment.
The dotted line 6 indicates the case of Comparative Example 1.

FIG. 4 shows a case where the board of the present invention is placed on the inside (4-
1), the case where the present invention is applied to the inside of a personal computer rack (4-2), and both sides of a desk on a desk (4-3).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Komori 19-17 Ikedanakacho, Neyagawa-shi, Osaka Inside Nippon Paint Co., Ltd. (72) Inventor Kazunori Kanda 19-17 Ikedananakacho, Neyagawa-shi, Osaka Nippon Paint Inside (72) Inventor Takumi Fujita 928 Takamatsu, Kawagoe-cho, Mie-gun, Mie Prefecture Inside Chiyoda Ute Co., Ltd. (72) Inventor Junichi Haneda 928, Takamatsu, Kawagoe-cho, Mie-gun, Mie Prefecture Chiyoda Ute Co., Ltd. F term (reference) 2E001 DH01 GA03 GA06 GA23 GA86 HA01 HA03 HA07 HA20 HA21 HB01 HB02 HB03 HB04 HB05 JA12 JA14 JA21 JA22 JA29 JB00 JB07 JC03 JC06 JC07 JD04 5E321 AA11 BB31 BB53 GG11

Claims (11)

[Claims] 1. A water-curable inorganic binder (a) 30 to 9
0 parts by weight and magnetic particles having a particle diameter of 100 μm or more
Magnetic powder (b) containing 0 to 100% by weight
An electromagnetic wave absorbing board comprising an electromagnetic wave absorbing layer containing parts by weight. 2. The electromagnetic wave absorbing board according to claim 1, wherein the water-curable inorganic binder (a) is at least one selected from the group consisting of cement, mortar, calcium silicate, and gypsum. 3. The electromagnetic wave absorbing board according to claim 1, wherein the magnetic powder (b) is a metal oxide magnetic powder. 4. The metal oxide magnetic powder comprises Li, Mg,
The electromagnetic wave absorbing board according to claim 3, wherein the board is an Fe oxide powder containing at least one selected from the group consisting of Mn, Co, Ni, Cu, Sn, Sr, and Ba. 5. The electromagnetic wave absorbing board according to claim 1, wherein the magnetic powder (b) is a metal magnetic powder. 6. The metal magnetic material powder is composed of Si, B, Al, C
Fe magnetic alloy powder containing at least one selected from the group consisting of o, Ni, Cr, V, Sn, Zn, Pb, Mn, Mo and Ag, or a magnetic metal simple powder of Fe, Co or Ni. The electromagnetic wave absorbing board according to claim 5. 7. The electromagnetic wave absorbing board according to claim 1, wherein the electromagnetic wave absorbing layer has a thickness of 5 to 50 mm. 8. The electromagnetic wave absorbing layer according to claim 1, further comprising a fibrous dielectric (c).
An electromagnetic wave absorption board according to the item. 9. The electromagnetic wave absorbing layer according to claim 1, further comprising a foamable filler (d).
An electromagnetic wave absorption board according to the item. 10. The electromagnetic wave absorbing board according to claim 1, further comprising an electromagnetic wave reflecting layer. 11. The electromagnetic wave reflection layer according to claim 10, wherein the electromagnetic wave reflection layer is made of at least one selected from the group consisting of a conductive material, a metal deposition film, a metal foil and a metal powder, and has a shielding ability of 20 dB or more. Electromagnetic wave absorption board.