JP2002134309A - Method for manufacturing electromagnetic wave absorbent powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing electromagnetic wave absorbent powder which has superior electromagnetic wave absorbing effect by using powder which is obtained by flattening the gas-atomized magnetic powder of an aspect ratio 2 or below and grain diameter 200 μm or smaller into powder of average s/t (ratio of sectional area to thickness of powder) 50 mm or larger. SOLUTION: Electromagnetic wave absorbent flattened powder size is of average s/t 50 mm or above. The electromagnetic wave absorbent flattened powder is formed of material powder having an aspect ratio of 2 or smaller. Furthermore, the major axis of flattened powder is 200 μm or smaller in length. The electromagnetic wave absorbent powder comprises of a material powder of Permalloy, Fe-Cr-Al, Fe-Cr-Si, Fe-Cr-Si-Al, or powder of 3 to 10 mass% Cr and remaining mass% Fe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a flat powder used for an electromagnetic wave absorber or the like.

[0002]

2. Description of the Related Art In recent years, electronic devices and information devices such as personal computers have been rapidly developed and spread, and electromagnetic waves generated therefrom cause malfunctions and adversely affect the human body. Is a problem. In order to cut off the effects of electromagnetic waves generated from these electronic devices such as personal computers, the source of the electromagnetic waves is wrapped in an electromagnetic wave absorber, and various electromagnetic waves are used to increase the absorption rate of electromagnetic waves by the electromagnetic wave absorber. Absorbers are being studied. However, the frequency of the generated electromagnetic wave has been increasing, and in reality, it cannot be absorbed by a conventional electromagnetic wave absorber.

As an example of the countermeasure, Japanese Patent Laid-Open No. 11-87
No. 117, a soft magnetic material powder having a thickness of 3 μm
A manufacturing method has been proposed in which a flat magnetic material is kneaded into a rubber sheet and exhibits a loss factor μ〃 of complex permeability of 5 or more at a frequency of 2 GHz or more. The metal flat powder used for such an electromagnetic wave absorber or the like is required to have a high saturation magnetic flux density to cope with a high frequency band and a high powder aspect ratio (thin thickness). ) Increases the absorption characteristics. Further, it is known that when the hardness of the powder is low, the flattening treatment is easily performed and it is necessary that the powder has a certain level of corrosion resistance.
For these reasons, it is known to use a powder having an aspect ratio of 15 or more, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-114767.

[0004]

In the above-mentioned conventional technology, the shape of the raw material and the manufacturing method are not specified.
For example, a powder made by general water atomization has an irregular shape. When this powder is subjected to flattening treatment,
Even powders having the same aspect ratio include various shapes such as needle-like powders and rod-like powders. Therefore, there is a problem that these powders are not preferable because the term of the dielectric loss (ε) becomes lower than that of the disk-shaped powder.

[0005] In the case of Japanese Patent Application Laid-Open No. 11-87117, there is no clear disclosure about the detailed conditions for flattening, especially the atmosphere. In addition, this flattening is performed by means such as a ball mill. However, depending on the conditions, a vicious cycle is likely to occur such that the new surface generated during the flattening process is subjected to impact during processing, such as fragmentation and miniaturization, and coarsening due to re-agglomeration. There is a problem that a fine powder is produced. Particularly when used for electromagnetic wave absorbers, etc., the aspect ratio is large,
In addition, a powder having a size equal to or less than a certain value is required, and there is a problem that a large powder deteriorates absorption characteristics.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively developed and found that Fe-
Ni-based and Fe-Cr-Al-Si-based raw materials were prepared by using magnetic powder having an aspect ratio of 2 or less by gas atomization and a particle diameter of 200 µm or less, average s / t (ratio of cross-sectional area to thickness of powder).
Was found to be excellent in electromagnetic wave absorption characteristics by using a powder flattened to 50 mm or more. The gist of the invention is as follows: (1) In the flat powder for an electromagnetic wave absorber, the average powder s
A powder for an electromagnetic wave absorber, wherein the powder is a flat powder having a / t (ratio of cross-sectional area to thickness of the powder) of 50 mm or more. (2) The powder for an electromagnetic wave absorber according to the above (1), wherein a spherical powder having an aspect ratio of 2 or less is used as a raw material powder.

(3) The length of the major axis of the flat powder is 200 μm
The powder for an electromagnetic wave absorber according to the above (1), wherein: (4) Permalloy, Fe—Cr—Al,
The powder for an electromagnetic wave absorber according to any one of (1) to (3), wherein a powder composed of Fe-Cr-Si, Fe-Cr-Si-Al, or Cr: 3 to 10 mass% and the balance of Fe is used. It is in.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, as shown in FIG. 1, the ratio (s / t) between the cross-sectional area S and the thickness t of the powder is set to 50 mm or more. The reason is that electromagnetic wave absorption characteristics can be expressed by the sum of magnetic loss and dielectric loss, but the dielectric loss increases due to the large area,
It has been found that the magnetic loss increases with an increase in s / t, and a value of 50 mm or more is effective. However, if it is less than 50 mm, the effect cannot be obtained. Therefore, the lower limit was set to 50 mm.

Next, a spherical powder having an aspect ratio of 2 or less is used as a raw material powder. The reason is that by using spherical powder as a raw material, the powder after flattening becomes a disk shape as shown in FIG. It has been found that a disk-shaped powder has a larger dielectric loss than a needle-shaped or rice-shaped flat powder, and moreover, it is preferable that the raw material spherical powder is obtained by a gas atomizing method, and the spherical powder is obtained. At the same time, since the oxygen concentration is low, the saturation magnetic flux density is advantageously increased.

The length h of the long axis of the flat powder is 200 μm.
m or less. The reason is that if the length of the major axis exceeds 200 μm, the filling factor at the time of molding the absorbent decreases, which is disadvantageous to the characteristics. Further, as the composition, permalloy, Fe—Cr—Al, Fe—Cr
-Si-based and Fe-Cr-Al-Si-based powders have high corrosion resistance and low hardness, so that powder having a large s / t can be easily produced. Further, since the saturation magnetic flux density is large, it is possible to cope with high frequencies.

[0011] The reason for using Cr: 3 to 10 mass% and the balance of Fe is that corrosion resistance is also provided to some extent and the saturation magnetic flux density is particularly large. Since the hardness is particularly low, it is possible to easily produce a powder having a large s / t. Also, since the viscosity at the time of dissolution is low, a powder having a fine particle size can be produced at the time of atomization, so that the length of the long axis is long. Powder having a thickness of 200 μm or less can be easily produced. If the Cr content is less than 3%, the corrosion resistance is deteriorated. If the Cr content is more than 10%, the absorption characteristics are deteriorated due to a decrease in the saturation magnetic flux density. Therefore, the range is 3 to 1
0 mass%.

[0012]

The present invention will be specifically described below with reference to examples. After producing powder composition Fe-50Ni by gas atomization, it was classified into -106 µm, and flattened by an attritor (s / t was changed by changing the processing time). Attritor processing conditions at this time were as follows: powder processing amount 2 kg, ball weight 10 kg, and partial pressure of Ar gas during attritor processing were controlled.
Changes the oxygen value of the powder. The molding conditions were as follows: chlorinated polyethylene (CPE) resin was mixed at 10 mass%,
The sheet was roll-formed into a sheet having a thickness of 1.0 mm. Table 1 shows the results. As the electromagnetic wave absorption characteristics, the electromagnetic wave absorption characteristics at 100 MHz were measured with a network analyzer, the saturation magnetic flux density was measured with a BH tracer, and the corrosion resistance was checked at 70 ° C.-95% humidity for 96 hours to check for rust.

[0013]

[Table 1]

As shown in Table 1, as shown in FIG. Nos. 1 to 8 are examples of the present invention. 9 to 13 are comparative examples. No. No. 9 has a high aspect ratio of 2.5, and therefore has a small index of dielectric loss. 10 is the length of the major axis of the flat powder is 2
Since it is as large as 30 μm, the filling factor is low, the index of magnetic loss is small, and the absorption of high-frequency electromagnetic waves is low. No. 11 has a low Cr% of 2% and poor corrosion resistance.
No. Sample No. 12 has high corrosion resistance but low saturation magnetic flux density because Cr% is as high as 11%. In addition, No. No. 13 has a magnitude of magnetic loss μ〃 and a magnitude of dielectric loss ε〃 since the ratio (s / t) between the cross-sectional area and the thickness of the powder is as small as 30 mm.
Both are low, indicating that the absorption of high-frequency electromagnetic waves is low.

[0015]

As described above, the powder according to the present invention has a particle size of 20 with an aspect ratio of 2 or less by gas atomization.
By using a powder obtained by flattening a magnetic powder of 0 μm or less to have an average s / t (ratio of cross-sectional area and thickness of the powder) of 50 mm or more, it is possible to efficiently obtain a powder for an electromagnetic wave absorber having an excellent electromagnetic wave absorbing effect. It has excellent effects.

[Brief description of the drawings]

FIG. 1 is a view showing a cross-sectional shape of a flat powder according to the present invention.

[Explanation of symbols]

 S Cross-sectional area t Thickness h Length of major axis

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E040 AA11 AA19 AA20 CA13 HB00 HB15 NN06 5E041 AA07 AA11 AA19 CA01 HB00 HB15 NN01 NN06 5E321 BB53 GG05 GG07 GG11

Claims (4)

[Claims] 1. The flat powder for an electromagnetic wave absorber, wherein the average powder s / t (the ratio of the cross-sectional area to the thickness of the powder) is 50 mm or more. 2. The powder for an electromagnetic wave absorber according to claim 1, wherein a spherical powder having an aspect ratio of 2 or less is used as a raw material powder. 3. The powder for an electromagnetic wave absorber according to claim 1, wherein the major axis of the flat powder has a length of 200 μm or less. 4. A raw material made of permalloy, Fe—Cr—
Al-based, Fe-Cr-Si-based, Fe-Cr-Si-Al
The powder for an electromagnetic wave absorber according to any one of claims 1 to 3, wherein a powder composed of a system or Cr: 3 to 10% by mass and the balance of Fe is used.