JP2001274007A - Radio absoptive compound with high permeability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio absorptive compound with high permeability which is superior in radio wave absortion in a sub-microwave band of 300 MHz to 3 GHz. SOLUTION: This compound contains 15-30% (%: atom.%) in total of either or both of Al and Si, 3-15% Cr, and 0.5-5% in total of either or both of Sn and Sb, and a remaining part contains Fe and unavoidable impurities. An average thickness d is 0.5-3 μm, and when a particle size is assumed to be D50 at the time when the weight of particles is summed up to 50% from those having small particle size obtained by a particle distribution meter, D50 is 5-30 μm, and an aspect ratio (D50/d) is adjusted to 2-60. Such a flat metallic magnetic powder is sequestered in a flexible thermoplastic resin, a rubber or a binder which is blended with rubber and transformed, and they are arranged in the lengthwise direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin, rubber or a binder obtained by blending thermoplastic resin and rubber, which is used for absorbing electromagnetic noise radiated from a personal computer or a mobile communication device. The present invention relates to a radio wave absorbing composite material containing a flat metal magnetic powder,
Particularly, the present invention relates to a radio-wave absorbing composite material having excellent radio-wave absorption characteristics in a quasi-microwave band of 300 MHz to 3 GHz and having high magnetic permeability.

[0002]

2. Description of the Related Art Generally, Fe-9%
Soft magnetic powder such as Al-5% Si powder (Sendust powder), and further, Cr: 0.5 to 20%, Si: 0.5 to 9
%, Al: 0.5 to 15%, and the balance: a soft magnetic powder having a component composition of Fe and unavoidable impurities, and the like, and a flat metal magnetic powder having a flat shape having such a composition is known. It is generally known that a resin or rubber is oriented and contained, and this is formed into a sheet and used as a radio wave absorbing composite material. This radio-absorbing composite material shows excellent radio-absorbing characteristics in the microwave band exceeding 3 GHz, and is used as an electromagnetic noise countermeasure member for personal computers and mobile communication devices. The main method is to cut out as appropriate and stick it near the noise source of the device for use. For this reason, the electromagnetic wave absorbing composite material is easy to mold and easy to handle.
mm.

[0003]

The flat metal magnetic powder contained in the above-mentioned conventional electromagnetic wave absorbing composite material is obtained by pulverizing an atomized powder or an alloy ingot into a raw material, and using this as an attritor mill. However, in this manufacturing process, there is a problem that a large strain is accumulated inside the powder particles and the soft magnetism of the powder is significantly reduced.

[0004] In order to remove the strain caused by the pulverization and flattening, it is conceivable to perform strain relief annealing on the flat-shaped metal magnetic powder. In this case, however, annealing is limited to a low temperature in order to prevent sintering of the powder. From where the residual strain cannot be completely removed. Due to the internal strain generated in this manufacturing process, the magnetic permeability of the flat metal magnetic powder itself and the radio wave absorbing composite material formed by orienting and containing the metal magnetic powder in a resin or rubber were kept low.

Further, the relationship between the magnetic permeability and the frequency of a conventional sheet-shaped electromagnetic wave absorbing composite material having a thickness of 0.5 to 3 mm draws a curve shown by a dotted line in FIG. The relationship between the quantities draws a curve shown by a dotted line in FIG. 1 (b). Due to the low magnetic permeability, the conventional radio wave absorbing composite material shows excellent radio wave absorption characteristics in a microwave band exceeding 3 GHz. 30 lower than this
In the quasi-microwave band of 0 MNz to 3 GHz, there is a problem that the radio wave absorbing ability is low and the use range is limited.

[0006]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of conducting research to solve these problems of the conventional wave absorbing composite material, the following matters were found. (A) An alloy containing 15 to 30% in total of one or two of Al or Si and 3 to 15% of Cr and having a balance of Fe and unavoidable impurities, Atomized powder and alloy ingot pulverized powder made of an Fe-based alloy produced by adding one or two of Sb and Sb in a total amount of 0.5 to 5% are Sn and Sb.
And Fe compounds precipitate at the crystal grain boundaries, and this compound precipitates at the crystal grain boundaries, which embrittles the grain boundaries, resulting in the process of grinding and flattening using a grinding machine such as an attritor mill. , The powder particles are more easily broken than the grain boundaries, and the strain accumulated inside the powder particles is reduced. (B) In the radio wave absorbing composite material obtained by orienting and containing the thus obtained flat metal magnetic powder having a small internal strain in resin or rubber, the relationship between the magnetic permeability and the frequency is shown in FIG.
The curve shown by the solid line in (a) is drawn, and the relationship between the radio wave attenuation and the frequency is drawn by the curve shown by the solid line in FIG. 1 (b), showing a higher magnetic permeability. The radio wave absorbing composite material having a practical thickness of 0.5 to 3 mm has a higher radio wave absorbing ability than the conventional radio wave absorbing composite material in the quasi-microwave band of 300 MNz to 3 GHz. (C) The atomized powder or the alloy ingot crushed powder having the component composition described in (a) above is obtained by a grinder such as an attritor mill, and has an average thickness d: 0.5 to 3 μm, and is determined by a particle size distribution analyzer. was when the particle size of the smaller particle size when it is 50% by total weight to D ₅₀ D _50: 5~3
0 μm, and the aspect ratio (D ₅₀ / d): 2 to 6
It is preferable to adjust to a flat shape having 0.

The present invention has been made based on the results of such research, and (1) one of Al and Si.
15 to 30% of the species or two in total (however,% indicates atomic%; the same applies hereinafter), Cr: 3 to 15%, and one or two of Sn and Sb in total of 0.5 to 0.5% 5%, the balance being: a component composition comprising Fe and unavoidable impurities, an average thickness d: 0.5 to 3 μm, and a cumulative weight of 50 from the smaller particle size determined by a particle size distribution analyzer.
% Particle size when it becomes a D ₅₀ When D _50: 5～30Myu
m, and an aspect ratio (D ₅₀ / d): 2~60 flat shape metal magnetic powder is adjusted to the thermoplastic resin having flexibility, rubber or a rubber blend in denatured binder, It is characterized by a radio-wave absorbing composite material having high magnetic permeability, which is separated from each other and included in the longitudinal direction thereof.

The flexible thermoplastic resin is preferably made of any one of vinyl chloride, chlorinated polyethylene, and thermoplastic elastomer, and the rubber is any one of silicone rubber and EM-PM-BD copolymer rubber. Is preferable. In addition, as a binder for making a radio wave absorbing composite material, any of vinyl chloride, chlorinated polyethylene, thermoplastic elastomer, silicone rubber, EM-PM-
A binder modified by blending any of the BD copolymer rubbers may be used.

The composition of the flat metal magnetic powder contained in the radio-wave absorbing composite material having high magnetic permeability of the present invention, the average thickness d,
The reason why D ₅₀ and the aspect ratio (D ₅₀ / d) are limited as described above will be described.

(A) Al or Si These components have the effect of increasing the magnetic permeability.
Alternatively, if the content of one or two of Si is less than 15% in total, a sufficient effect cannot be obtained. On the other hand, if the content exceeds 30 atomic%, the powder becomes brittle, and the powder is crushed and flattened. Sometimes, a high aspect ratio cannot be obtained, and good radio wave absorption characteristics cannot be achieved in any case. Therefore, one or two of Al and Si are set to 15 to 30 atomic% in total. A more preferred range for the content of these components is 20 to 25 atomic%.

(B) Cr Cr has the effect of improving the corrosion resistance, but the effect is not obtained if it is less than 3%, while if it exceeds 15%,
Magnetic permeability is remarkably reduced, and in either case, it is not preferable as a radio wave absorber. Therefore, the content of Cr is 3 to 15%.
Determined. A more preferable range of the content of Cr is 4 to 10.
Atomic%.

(C) Sn and Sb These components have the effect of segregating at the crystal grain boundaries in the powder particles to improve the friability of the powder and thereby increase the magnetic permeability. If the content is less than 5%, a sufficient effect cannot be obtained. On the other hand, if the content exceeds 5%, the amount of solid solution in the powder particle matrix increases, so that the magnetic permeability is reduced, and in any case, the radio wave absorption characteristics are reduced. It is not preferable. Therefore, the total content of one or two of Sn and Sb is determined to be in the range of 0.5 to 5%. One or two of Sn and Sb
A more preferred range of total seed content is 0.8-2%
It is.

(D) Average thickness d If the average thickness d of the flat metal magnetic powder is less than 0.5 μm, the residual strain due to heavy working increases significantly and the magnetic permeability decreases, which is not preferable. If d exceeds 3 μm, the loss due to eddy current increases, and in any case, excellent radio wave absorption characteristics cannot be obtained. Therefore, the average thickness d of the flat metal magnetic powder is set to 0.5 to 3 μm. A more preferred range for the average thickness d is 1-2 μm.

(E) D _{50 If} D ₅₀ is less than 5 μm, the residual strain due to heavy working is significantly increased and the magnetic permeability is lowered, which is not preferable.
_{If 50} exceeds 30 μm, it is not preferable because, when producing the radio wave absorbing composite material, the dispersion cannot be uniformly dispersed in the organic binder, and the electric resistance of the entire radio wave absorbing composite material becomes small, so that eddy current loss and sprouting increase. Therefore, D ₅₀ : 5
３０30 μm. A more preferred range of D ₅₀ is 10
20 μm.

(F) Aspect ratio (D ₅₀ / d) The aspect ratio is 2 to 60 by a combination of the range of the average thickness d described in (d) and the range described in (e). A more preferable range of the aspect ratio is 10 to 40.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An alloy raw material is melted by high frequency to produce a melt having a component composition shown in Table 1, and the melt is atomized with water to produce an atomized powder. : Atomized raw material powder having a size of 40 μm or less was prepared. This atomized raw material powder was further pulverized and flattened by an attritor, then placed in a heat treatment furnace, and heat-treated at a temperature of 400 ° C. for 2 hours in an Ar gas atmosphere. The heat-treated powder was classified by an air classifier to produce a flat metal magnetic powder having D ₅₀ , d and aspect ratio (D ₅₀ / d) shown in Table 1.

These flat metallic magnetic powders: 50% by volume
And chlorinated polyethylene resin: 50% by volume are mixed and kneaded, then calender roll-formed, and a sheet made of the electromagnetic wave absorbing composite material of the present invention having a thickness of 2 mm in which flat metal magnetic powders are arranged in parallel to the sheet surface (hereinafter referred to as “sheet”) , A radio wave absorbing sheet of the present invention) 1 to 13;
A sheet made of a conventional radio wave absorbing composite material (hereinafter, referred to as a conventional radio wave absorbing sheet) was produced.

Samples are cut out from the radio wave absorbing sheets 1 to 13 of the present invention, the comparative powder radio wave absorbing sheets 1 and 2 and the conventional radio wave absorbing sheets to prepare samples, and the samples are set in a coaxial holder, and are subjected to complex transmission using a network analyzer. The frequency dependence of magnetic susceptibility and the frequency dependence of radio wave attenuation were investigated.

The relationship between the complex magnetic permeability and the frequency is shown in FIG.
(A), the imaginary part of the complex magnetic permeability was measured, and 300 MHz to 3 GH
The minimum value and the maximum value in the frequency range of z are shown in Table 1, and the frequency dependence of the complex magnetic permeability imaginary part of the radio wave absorbing sheets 1 to 13 of the present invention, the comparative powder radio wave absorbing sheets 1 and 2 and the conventional radio wave absorbing sheet is shown. Was evaluated. further,
The relationship between the radio wave attenuation and the frequency is shown in a curve shown in FIG. 1B. The radio wave attenuation is measured, and the minimum and maximum values in the frequency range of 300 MHz to 3 GHz are shown in Table 1. The frequency dependence of the radio wave attenuation of the radio wave absorbing sheets 1 to 13 of the present invention, the comparative powder radio wave absorbing sheets 1 and 2 and the conventional radio wave absorbing sheet was evaluated by showing.

[0020]

[Table 1]

From the results shown in Table 1, the radio wave absorbing sheets 1 to 13 of the present invention have higher imaginary parts of the complex magnetic permeability than the comparative radio wave absorbing sheets 1 and 2 and the conventional radio wave absorbing sheet. Sheets 1 to 13 are 300MN
It can be seen that in the quasi-microwave band of z to 3 GHz, the radio wave attenuation is larger than that of the conventional radio wave absorbing sheet.

[0022]

According to the present invention, it is possible to provide a radio-wave absorbing composite material having excellent radio wave absorption characteristics in the quasi-microwave band of 300 MHz to 3 GHz and high magnetic permeability, and has excellent effects in the electric and electronic industries. It is.

[Brief description of the drawings]

FIG. 1 is a graph for explaining the frequency dependence of a complex magnetic permeability and the frequency dependence of a radio wave attenuation.

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Claims (5)

[Claims] 1. A total of 15 to 30% of one or two of Al or Si (where% indicates atomic%; the same applies hereinafter), Cr: 3 to 15%, and Sn and Sb 1
Containing 0.5 to 5% of a total of two or more species, and the balance: F
e and a component composition consisting of unavoidable impurities, average thickness d: 0.5 to 3 μm, particle size when the total weight becomes 50% from the smaller particle size obtained by the particle size distribution meter the When D ₅₀ D _50: a 5 to 30 [mu] m, an aspect ratio (D ₅₀ / d): 2~60 flat shape metal magnetic powder is adjusted to have, are isolated from each other on a flexible thermoplastic resin And a radio wave absorbing composite material having a high magnetic permeability, the longitudinal direction of the radio wave absorbing composite material being included. 2. The radio-wave absorbing composite material having high magnetic permeability according to claim 1, wherein said flexible thermoplastic resin is any one of vinyl chloride, chlorinated polyethylene, and thermoplastic elastomer. 3. A method according to claim 1, wherein one or two of Al and Si are 15 to 30% in total, Cr is 3 to 15%, Sn and S
b, containing 0.5 to 5% in total, the balance being: a component composition consisting of Fe and unavoidable impurities, average thickness d: 0.5 to 3 μm, particle size distribution analyzer when D ₅₀ particle size when it becomes 50% by total weight from the smaller particle size obtained by the D _50: a 5 to 30 [mu] m, an aspect ratio (D ₅₀ / d): 2~60 The radio-wave absorbing composite material having high magnetic permeability, wherein the flat metal magnetic powder is separated from each other in rubber and arranged in a longitudinal direction. 4. The rubber is a silicone rubber, EM-PM
The radio-wave absorbing composite material having high magnetic permeability according to claim 3, wherein the composite material is any one of -BD copolymer rubber. 5. A method according to claim 1, wherein one or two of Al and Si are 15 to 30% in total, Cr is 3 to 15%, Sn and S
b, containing 0.5 to 5% in total, the balance being: a component composition consisting of Fe and unavoidable impurities, average thickness d: 0.5 to 3 μm, particle size distribution analyzer when D ₅₀ particle size when it becomes 50% by total weight from the smaller particle size obtained by the D _50: a 5 to 30 [mu] m, an aspect ratio (D ₅₀ / d): 2~60 Wherein the flat metal magnetic powder is isolated from each other in a modified binder obtained by blending the thermoplastic resin according to claim 2 and the rubber according to claim 4, and the longitudinal direction thereof is aligned. A radio-absorbing composite material with high magnetic permeability.