JP2003105403A - Soft magnetic flat-shaped powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain soft magnetic flat-shaped powder having high flatness and excellent electromagnetic properties. SOLUTION: This flat-shaped powder can be obtained by applying flattening treatment to soft magnetic powder. Moreover, the ratio of bulk density when filling the flat-shaped powder into a vessel of a prescribed capacity and vibrations are applied prescribed number of times (tap density: TD) to specific gravity (D), (TD/D), ranges from 0.1 to 0.25, and oxygen content is made to <=0.15 mass%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft magnetic flat powder, and more particularly to a soft magnetic flat powder suitable for use as an electromagnetic shield material, a radio wave absorber and the like.

[0002]

2. Description of the Related Art In recent years, with the rapid progress of electronics, the problem of electromagnetic noise generated from various electronic devices has become apparent. Therefore, there is an increasing demand for a radio wave absorber having a function of absorbing electromagnetic waves and converting them into heat. Generally, as a radio wave absorber, a ferrite sintered body or one containing carbon in a binder is known, but in order to remove high frequency components of electromagnetic noise, a soft magnetic metal powder is flattened, It has been proved that the one containing the flat powder in the binder is effective.

And, such a flat powder is usually
Crushed powder obtained by mechanically crushing a cast ingot, or
It is general that the powder obtained by the water atomization method is used as a starting material and the raw material powder is subjected to a flattening treatment.

[0004]

However, when crushed powder is used as the raw material powder, crushing takes time, especially if the starting ingot is not a brittle material, which increases the manufacturing cost. Further, since the powder is exposed to a high temperature due to frictional heat during pulverization, there is a problem that the oxidation of the powder progresses and the electromagnetic characteristics deteriorate. Furthermore, since the surface is uneven due to the influence of the oxide film formed on the surface due to this temperature rise, when flattened by, for example, an attritor treatment, crushing proceeds preferentially over flattening, resulting in a flattened powder. There is also the problem that it is difficult to obtain.

On the other hand, when the powder obtained by the water atomizing method is used as the raw material powder, the crushing step as described above can be omitted, so that the cost can be reduced, but the shape is more irregular than the crushed powder. There is also a problem that the crushing proceeds preferentially in the subsequent flattening step. Further, spraying with water causes the powder to oxidize, so that the electromagnetic characteristics deteriorate as in the case of the pulverized powder.

An object of the present invention is to solve the above-mentioned problems of the soft magnetic flat powder used for the electromagnetic wave absorber and to provide a soft magnetic flat powder having electromagnetic characteristics, particularly high magnetic permeability.

[0007]

To achieve the above object, according to the present invention, a flat powder obtained by flattening a soft magnetic powder, wherein The ratio of bulk density (tap density: TD) to specific gravity (D) (TD /
It is provided that D) is 0.1 to 0.25 and the oxygen content is 0.15% by mass or less (Claim 1).

In the above structure, the ratio (TD / D) of the tap density (TD) to the specific gravity (D) of the soft magnetic powder before the flattening treatment is preferably 0.6 or more. Furthermore, the oxygen content of the soft magnetic powder before the flattening treatment is 0.10% by mass or less (claim 3), and the average particle diameter (D50) of the soft magnetic powder before the flattening treatment is 40 μm or more. It is preferable (claim 4) that the soft magnetic powder before the flattening treatment is manufactured by a gas atomization method (claim 5).

The flatness F of the soft magnetic flat powder represented by the following formula: F = (L + S) / (d _max + d _min ) (where L is the plane direction of the flat powder) The major axis length, S also represents the minor axis length in the surface direction, d _max represents the maximum thickness of the flat powder, and d _{min also} represents the minimum thickness.)
Is preferably 20 or more (claim 6).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The soft magnetic flat powder of the present invention will be described in detail below. First, the soft magnetic flat powder of the present invention is obtained by flattening the soft magnetic powder.
The soft magnetic material is not particularly limited,
For example, F, which has magnetism and high absorption of high frequency electromagnetic waves,
Metals such as e, Ni and Co, or alloy powders containing these metals can be used.

Particularly, from the viewpoint of electromagnetic wave absorption characteristics, cost and workability, Fe--Cr alloys and Fe--Si alloys are
An alloy to which 1 and the like are added in combination is preferable. The soft magnetic flat powder of the present invention obtained by flattening these soft magnetic powders has a ratio of the tap density (TD) to the specific gravity (D) (TD /
It is necessary that D) is 0.1 to 0.25.

That is, the powder having no fluidity has a poor reproducibility of the apparent density in a loosely packed state such as a free fall. However, when vibration is applied by tapping, a relatively uniform bulk density is obtained. This is called tap density. In the present invention, the powder is filled in a graduated cylinder having a volume of 18 mL and the number of taps is 1,000.
The packing density at each round was defined as tap density.

This TD / D is originally a numerical value indicating the filling degree of the powder, but in addition to that, it can also be a parameter for knowing the degree of crushing generated during the flattening treatment and the surface quality. That is, if pulverization progresses during the flattening process, the filling property is hindered, and the TD / D becomes small. Also, if the surface texture is uneven due to the presence of an oxide film, etc., friction will occur between the particles and the filling will not proceed even if vibration is applied.
Becomes smaller.

Therefore, when TD / D is less than 0.1, pulverization proceeds during the flattening process due to the formation of a surface oxide film, and conversely, when TD / D exceeds 0.25, the powder is produced. The shape of is similar to a spherical shape before the flattening process.
A particularly preferable value of TD / D is 0.15 to 0.20.
In addition, in the flat powder of the present invention, in addition to the above numerical limitation of TD / D, the oxygen content of the soft magnetic flat powder needs to be 0.15 mass% or less. In general, the fact that the powder has a high oxygen content means in other words that the alloy component contributing to magnetism exists as an oxide which is a non-magnetic material. Therefore, it is desired that the oxygen content be as low as possible. It is preferably 0.1% by mass or less. The oxygen content of the flat powder can be controlled by the treatment time of the flattening treatment step and the like.

TD / D of the soft magnetic powder before the flattening treatment
Is preferably 0.6 or more. Generally, if the powder shape is simple, such as spherical, TD / D will increase. In order to obtain a high flatness after the flattening treatment, it is necessary to prevent the crushing from progressing preferentially in the flattening treatment step, so the powder should be as spherical as possible before the treatment. Is preferred. Therefore, it is preferable to set TD / D to 0.6 or more.

As the soft magnetic powder as the above-mentioned starting material, for example, those obtained by a water atomizing method, a gas atomizing method, a mechanical crushing method or the like can be used, but the above TD / D is 0.6 or more. It is preferable to use the gas atomization method because the spherical powder can be obtained. By the way, TD / D is about 0.3 in the water atomizing method, and TD / D is about 0.4 in the mechanical grinding method. In addition, by using the gas atomizing method, it is possible to suppress the oxidation of the powder and ensure high electromagnetic characteristics.

Further, the oxygen content of the powder before the flattening treatment is preferably 0.10% by mass. That is, in order to set the oxygen content of the powder after the flattening treatment to 0.15 preferably 0.10 mass% or less as described above, it may be 0.10 mass% or less in consideration of the progress of oxidation in the flattening process. The content is preferably 0.05 mass% or less.
The oxygen content of the powder before the flattening treatment can be controlled by various conditions such as the treatment time in the gas atomizing step.

Then, the average particle diameter D5 of the powder before the flattening treatment
0 is preferably 40 μm or more. Here, the average particle diameter D50 means a particle diameter at which the cumulative mass with respect to the total particle mass is 50%. In order to obtain a powder having a high flatness, it is preferable to make the major axis and minor axis of the plane direction as long as possible. For that purpose, it is desired to make the particle size of the powder before treatment as large as possible.

The flatness F of the soft magnetic flat powder obtained after the flattening treatment is preferably 20 or more,
As a result, it is possible to realize high magnetic permeability of the final product and thus better electromagnetic shield characteristics and electromagnetic wave absorption characteristics than conventional materials. This flatness F is expressed by the following formula: F = (L + S) / (d _max + d _min ), where L is the major axis length of the flat powder in the plane direction, and S is the minor axis length of the plane direction. Where d _max is the maximum thickness of the flat powder and d _min is the minimum thickness as well.)
It is represented by.

FIG. 1 is a perspective view schematically showing a flat powder. That is, in the figure, the plane direction of the flat particles is observed by SEM, and the major axis length L and the minor axis length S are respectively measured,
The average value (L + S) / 2 is calculated. Next, after embedding the powder in the resin, polishing is performed, and the maximum thickness d _max and the minimum thickness d _min of the flat powder when observed by an optical microscope are measured. And let the average value ( _dmax + _dmin ) / 2 be the average thickness of the flat powder.

Then, the ratio of the above average diameter to the average thickness: [(L + S) / 2] / [(d _max + d _min ) / 2] = (L +
S) / (d _max + d _min ) is defined as the flatness F. The manufacturing process of the soft magnetic flat powder of the present invention will be described below. That is, first, the soft magnetic alloy powder having the above-described TD / D, oxygen content, and average particle diameter is manufactured by, for example, a gas atomizing method.
Subsequently, the obtained powder is subjected to a flattening treatment. This flattening process step is not particularly limited,
For example, it is preferable to use an attritor or the like.

Specifically, the powder is mixed with a dispersion medium and a lubricant and flattened under predetermined processing conditions. The dispersion medium used at this time may be a non-water-soluble solvent such as xylene or toluene, or a water-soluble solvent such as ethanol or acetone. It is preferable to use a water-soluble solvent. After the above flattening treatment, for example, in a vacuum at 100 to 150 ° C.,
Dried, and further, for example, in an inert gas atmosphere, 60
At 0 to 800 ° C., heat treatment for the purpose of removing strain for 1 to 3 hours is performed to obtain the soft magnetic flat powder of the present invention.

Then, to the soft magnetic flat powder obtained above, for example, chlorinated polyethylene as a binder,
A stabilizer, a plasticizer and the like are added in predetermined amounts, kneaded by a kneader or the like, and then formed into a sheet for various uses such as an electromagnetic wave absorber and an electromagnetic shield material.

[0024]

EXAMPLES Examples 1 to 4, Comparative Examples 1 to 5 (1) Preparation of soft magnetic flat powder Except for Comparative Example 1 using the mechanical pulverization method, TD / D, oxygen content and D50
Fe-Si-Al alloy powder (raw material powder) having the above was prepared. The TD / D and the flatness of the powders shown below were both measured by the methods described above, and the numerical values were calculated. The average particle size D50 of each powder was measured using a laser diffraction particle size distribution analyzer.

Subsequently, each powder was flattened using an attritor. That is, ball weight 18k
g, powder filling amount 1.8 kg, dispersion medium (non-water-soluble organic solvent or water-soluble organic solvent) 1.8 L, 1% by mass of lubricant (stearic acid) with respect to the mass of the powder was put into an attritor, A flattening treatment was performed for 10 to 20 hours at a rotation speed of 250 rpm, and the TD / D and flatness of the obtained flat powder were controlled by changing the treatment time.

Table 1 shows TD / D, oxygen content and flatness of the obtained flat powder. (2) Characteristic evaluation test Each soft magnetic flat powder obtained as described above was placed in a vacuum for 13
After drying at 0 ° C, in an inert gas atmosphere, 800
It heat-processed at 1 degreeC for 1 hour. Next, 100 parts by mass of chlorinated polyethylene, 40 parts by mass of stabilizer and a total of 40 parts by mass of stabilizer were added to 1250 parts by mass of the flattened powder and kneaded with a kneader to prepare a rubber sheet having a thickness of 1.0 mm. .

Each rubber sheet was punched into an outer diameter of 7 mm and an inner diameter of 3 mm, wound with 12 turns, and measured for inductance and resistance up to 100 MHz with an impedance analyzer. 'And the imaginary number μ''were calculated and the results are shown in Table 1.

[0028]

[Table 1]

In general, in order to realize a high electromagnetic wave shielding effect, it is required that the real number of magnetic permeability μ'is high,
On the other hand, in order to realize a high electromagnetic absorption effect, it is required that both the real part μ ′ and the imaginary part μ ″ of the magnetic permeability are high.
As is clear from the results shown in Table 1, those using the soft magnetic flat powder of the present invention can have high values for both the real number and the imaginary number of the magnetic permeability. Particularly, in Example 3, by keeping the oxygen content of the raw material powder as low as 0.03% by mass, the oxygen content of the flat powder can be maintained at a low value, and the TD / D value should be increased. You can Furthermore, in Example 4, it was confirmed that by setting the D50 of the raw material powder to a high value of 45, flattening preferentially progressed in the flattening treatment step, and the electromagnetic characteristics could be improved.

On the other hand, when the raw material powder obtained by the mechanical pulverization method was used (Comparative Example 1), the initial TD / D was 0.42.
Since the oxygen content is as high as 0.15, the pulverization progresses even in the flattening step, TD / D cannot be increased, and the flatness is as low as 15. The oxygen content is also 0.25
It was confirmed that the electromagnetic characteristics were deteriorated due to the progress of surface oxidation.

Comparative Example 2 was obtained by oxidizing the raw material powder by using the gas atomizing method, and the raw material powder had a large oxygen content, and the pulverization proceeded during the flattening treatment due to the influence of the surface oxide film, and the obtained flattened surface was obtained. TD / D of powdery powder is low. Comparative Example 3 also uses the raw material powder obtained by the gas atomization method, but the TD / D of the flattened powder obtained by shortening the flattening treatment time is increased to 0.35. As a matter of course, the flattening is not sufficiently performed, the flatness is as low as 14, and the electromagnetic characteristics are also low.

In Comparative Example 4, a water-soluble solvent was used as a dispersion medium during the flattening treatment. Therefore, the flattened powder is oxidized during the treatment and the amount of oxygen increases to 0.20% by mass.
As a result, the electromagnetic characteristics became poor. Further, in Comparative Example 5, the processing time was lengthened during the flattening process. As a result, crushing progresses and TD / D is small. It also has a high oxygen content and low electromagnetic properties.

[0033]

As is apparent from the above description, the soft magnetic flat powder of the present invention has a low oxygen content and a high flatness, and therefore has an electromagnetic characteristic when used as an electromagnetic shield material or a radio wave absorber. And its industrial value is extremely high.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a method of calculating a flatness of a flat powder according to the present invention.

[Explanation of symbols]

1 Flat powder S Minor axis length L Major axis length d _max Maximum thickness d _min Minimum thickness

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichiro Yahagi             Daido Special, 10 Ryugucho, Minato-ku, Nagoya City, Aichi Prefecture             Special Steel Co., Ltd., Tsukiji Factory F-term (reference) 4K017 AA03 AA04 BA03 BA06 CA01                       CA03 DA02 EB00 EK01 FA14                 4K018 BA04 BA13 BB01 BC08 BD01                       BD05 KA42                 5E041 AA11 AA14 AA17 HB17 NN01                       NN06

Claims (6)

[Claims] 1. A flattened powder obtained by flattening a soft magnetic powder, wherein the flattened powder is filled in a container of a predetermined volume and subjected to a predetermined number of vibrations to obtain a bulk density ( Tap density: TD) and specific gravity (D) ratio (TD / D) is 0.1
~ 0.25, and oxygen content is 0.15 mass% or less, a soft magnetic flat powder. 2. The soft magnetic flat powder according to claim 1, wherein the ratio (TD / D) between the tap density (TD) and the specific gravity (D) of the soft magnetic powder before the flattening treatment is 0.6 or more. 3. The soft magnetic flat powder according to claim 1, wherein the oxygen content of the soft magnetic powder before the flattening treatment is 0.10 mass% or less. 4. The soft magnetic flat powder according to claim 1, wherein the soft magnetic powder before the flattening treatment has an average particle diameter (D50) of 40 μm or more. 5. The soft magnetic flat powder according to claim 1, wherein the soft magnetic powder before the flattening treatment is produced by a gas atomization method. 6. A flatness F of the soft magnetic flat powder represented by the following formula: F = (L + S) / (d _max + d _min ) (where L is a plane direction of the flat powder) The major axis length, S also represents the minor axis length in the surface direction, d _max represents the maximum thickness of the flat powder, and d _{min also} represents the minimum thickness.)
Is 20 or more, The soft magnetic flat powder according to claim 1.