KR20230144518A - Soft magnetic flat powder - Google Patents

Abstract

The present invention provides soft magnetic flat powder suitable for manufacturing high-performance magnetic sheets. This soft magnetic flat powder is composed of an Fe-Si-Al alloy containing B as an additive element. The content of B in this alloy is 0.002 mass% or more and 0.015 mass% or less. Preferably, this flat powder has a median diameter (D50) of 30 ㎛ or more and 80 ㎛ or less on a volume basis, a tap density (TD) of 1.25 g/cm 3 or less, and a coercive force (Hc) of 400 A/m or less.

Description

Soft magnetic flat powder

The present invention relates to soft magnetic flat powder. In detail, the present invention relates to a soft magnetic flat powder used in a magnetic sheet for noise suppression.

Portable electronic devices such as mobile phones, laptop-type personal computers, and tablet-type personal computers have become popular in recent years. Recently, miniaturization and higher performance of such devices are progressing. As devices become smaller, demands for miniaturization and higher performance are increasing for circuit components within the device. In devices with smaller size and higher performance, the density of electronic components mounted on circuits is high. Therefore, radio wave interference between electronic components and between electronic circuits is likely to occur due to radio wave noise radiated from these electronic components. Radio interference causes malfunction of electronic devices.

For the purpose of suppressing radio interference, noise suppression sheets are sometimes inserted into electronic devices. This noise suppression sheet converts emitted radiated radio waves (noise) into magnetic force and prevents radio waves from being emitted outside the electronic circuit. Noise suppression sheets require high magnetic permeability.

Patent Document 1 (Japanese Patent Publication No. 3401650) discloses an electromagnetic interference suppressor having an insulating soft magnetic layer. This insulating soft magnetic material layer contains an organic binder such as resin and soft magnetic material powder as a metallic magnetic filler. As such a soft magnetic powder, a flat fine powder made of Fe-Si-Al alloy is used. Such metal magnetic fillers are required to realize real (μ') and imaginary parts (μ'') with high complex magnetic permeability in magnetic sheets such as noise suppression sheets. As can be seen from the so-called Ollendorff equation, in order to achieve high real part (μ') and imaginary part (μ'') in the magnetic sheet, it is necessary to highly fill the magnetic sheet with soft magnetic powder and to increase the magnetic permeability. It is important to use high soft magnetic powder and to use flat powder with a high aspect ratio in the magnetization direction to lower the demagnetization field.

Patent Document 2 (Japanese Patent Application Publication No. 2009-266960) describes a flat soft magnetic material whose 50% particle diameter (D50) (median diameter), coercive force (Hc), and bulk density (BD) satisfy a predetermined relationship. It is starting. In Patent Document 2, the median diameter is increased by reducing the porosity of the soft magnetic powder produced by the atomizing method, and a high aspect ratio is obtained accordingly, thereby achieving a high μ'.

Patent Document 3 (Japanese Patent Application Publication No. 2017-118114) states that the composition, in terms of mass%, includes 84.0% to 96.0% of Fe, 3.0% to 8.5% of Si, and 1.0% to 13.0% of Al, A soft magnetic flat powder with an aspect ratio of 15 or more has been proposed. Patent Document 3 discloses a technique for increasing the median diameter (D50) of powder after flattening by adjusting the composition of the Fe-Si-Al alloy.

Patent Document 1: Japanese Patent Publication No. 3401650 Patent Document 2: Japanese Patent Publication No. 2009-266960 Patent Document 3: Japanese Patent Publication No. 2017-118114

Recently, there have been additional requests for improved performance of magnetic sheets such as noise suppression sheets used in electronic devices. In response to these requests, soft magnetic powders that can achieve higher magnetic permeability of magnetic sheets are required.

Conventionally, in soft magnetic powders made of Fe-Si-Al alloy, major changes in alloy composition were required to achieve a large median diameter. However, as described in Patent Document 3, magnetic performance changes significantly with very slight changes in alloy composition. Therefore, even if a large median diameter (D50) is obtained by changing the alloy composition, there are cases where improvement in permeability cannot be expected due to an increase in the magnetostriction constant or a change in the crystalmagnetic anisotropy.

In addition, when soft magnetic powder produced by an atomizing method is used as a raw material, it cannot be expected that the porosity according to the technology disclosed in Patent Document 2 will be further reduced.

The purpose of the present invention is to provide a soft magnetic flat powder suitable for manufacturing high-performance magnetic sheets with high magnetic permeability.

The soft magnetic flat powder according to the present invention is composed of an Fe-Si-Al alloy containing B as an additive element. The content of B in this alloy is 0.002 mass% or more and 0.015 mass% or less.

Preferably, the median diameter (D50) based on volume of this soft magnetic flat powder is 30 ㎛ or more and 80 ㎛ or less.

Preferably, the tap density (TD) of this soft magnetic flat powder is 1.25 g/cm3 or less.

Preferably, the coercive force (Hc) measured by applying a magnetic field in the longitudinal direction of this soft magnetic flat powder is 400 A/m or less.

The soft magnetic flat powder according to the present invention is formed of a Fe-Si-Al alloy containing a trace amount of B as an additive element, and thus has a high magnetic permeability without an increase in the magnetostrictive constant and an excessive change in crystalmagnetic anisotropy. obtained. By mixing such soft magnetic powder as a filler, a magnetic sheet with excellent noise suppression effect is obtained.

Figure 1 is a graph showing the change according to the B content in the real part (μ') of magnetic sheets containing soft magnetic flat powder of Examples and Comparative Examples.
Figure 2 is a graph showing changes in the median diameter (D50) of soft magnetic flat powders of Examples and Comparative Examples depending on the B content.
Figure 3 is a graph showing the change in coercive force (Hc) of the soft magnetic flat powders of Examples and Comparative Examples depending on the B content.

Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings. The present invention is not limited to the embodiments below, and various changes are possible within the scope indicated in the claims. Other embodiments obtained by appropriately combining the technical means disclosed for a plurality of embodiments are also included in the technical scope of the present invention.

Meanwhile, in the present specification, 'X ~ Y' indicating a range means 'X or more and Y or less', and 'mass%' and 'mass%' are treated as the same. Additionally, unless otherwise noted, all test temperatures are room temperature.

The soft magnetic flat powder according to one embodiment of the present invention is composed of a Fe-Si-Al alloy containing B (boron) as an additive element. Usually, in Fe-Si-Al alloy, a regular lattice called D03 structure is formed by adding Si (silicon) and Al (aluminum) to Fe (iron). By having such a regular lattice, in the soft magnetic flat powder made of Fe-Si-Al alloy, low magnetostriction constant and crystalmagnetic anisotropy constant are achieved simultaneously, and magnetic permeability is improved.

[B(boron)]

B is the most important additive element in the present invention. Just by adding a small amount of this B to the Fe-Si-Al alloy, the median diameter (D50) of the powder after flattening can be greatly increased. Moreover, since the increase in the magnetostrictive constant and magnetic crystalline anisotropy constant due to the addition of a small amount of B is very small, it was found that the magnetic permeability is improved by increasing the aspect ratio of the powder according to the increase in the median diameter (D50). This is thought to be an effect that occurs when the D03 structure of the Fe-Si-Al alloy is very slightly reduced by the addition of B.

From the viewpoint of obtaining the permeability improvement effect by adding B, the content of B in the Fe-Si-Al alloy is preferably 0.002 mass% or more and 0.015 mass% or less, and preferably 0.002 mass% or more and 0.01 mass% or less.

[Fe (iron), Si (silicon), and Al (aluminum)]

Fe is a base material for alloys. Fe improves the magnetic properties of soft magnetic flat powder. In the present invention, there is no particular limitation on the content of Si and Al as long as the above-described B is included.

From the viewpoint of improving magnetic permeability, the Si content is preferably 3.0 mass% or more, and more preferably 4.0 mass% or more. From the viewpoint of avoiding a decrease in saturation magnetic flux density and securing high magnetic permeability, the Si content is preferably 12.0 mass% or less, and particularly preferably 10.0 mass% or less.

From the viewpoint of improving magnetic permeability, the Al content is preferably 2.0 mass% or more, and particularly preferably 3.0 mass% or more. From the viewpoint of avoiding a decrease in saturation magnetic flux density and ensuring high magnetic permeability, the Al content is preferably 10.0 mass% or less, and particularly preferably 7.0 mass% or less.

According to a preferred embodiment, the Fe-Si-Al alloy is,

Si: 3.0 mass% or more and 12.0 mass% or less

Al: 2.0 mass% or more and 10.0 mass% or less and

B: Contains 0.002% by mass or more and 0.015% by mass, the balance being Fe and inevitable impurities.

[Median diameter (D50)]

From the viewpoint of obtaining a magnetic sheet with a homogeneous and smooth surface, the median diameter (D50) of the soft magnetic flat powder is preferably 80 μm or less, and more preferably 70 μm or less. From the viewpoint of aspect ratio, the median diameter (D50) is preferably 30 μm or more, and more preferably 40 μm or more.

The median diameter (D50) is the diameter of the particle at the point where the cumulative curve is 50% when the cumulative curve is obtained by taking the total volume of the powder as 100%. That is, the median diameter in this specification is the median diameter (D50) based on volume. The median diameter (D50) is measured, for example, by Nikkiso's laser diffraction/scattering particle diameter distribution measuring device 'Microtrack MT3000'. Into the cell of this device, powder is introduced along with pure water, and the median diameter (D50) is detected based on the light scattering information of each particle constituting the powder.

[Aspect ratio]

Soft magnetic flat powder consists of many flat particles. Flat particles have shape anisotropy. This anisotropy increases the actual permeability (μ') of the magnetic member. From the viewpoint of improving magnetic permeability, the aspect ratio of the soft magnetic flat powder is preferably 1.5 or more, more preferably 5 or more, and especially preferably 8.0 or more. Preferably, the aspect ratio of this flat powder is 100 or less.

To measure the aspect ratio, a resin-embedded sample from which the thickness direction of the flat particles can be observed is used. This sample is polished, and the polished surface is observed by a scanning electron microscope (SEM). The magnification of the image during observation is 1000 times. In this image analysis, image data is binarized. When a binary image is approximated to an ellipse, the ratio of the length of the long axis to the length of the short axis of this ellipse is the aspect ratio of this particle. The aspect ratios of a large number of binarized particles obtained from four fields of view are averaged, and the aspect ratio of the soft magnetic powder is calculated.

[Tap density (TD)]

From the viewpoint of obtaining a magnetic sheet with a homogeneous and smooth surface, the tap density (TD) of the soft magnetic flat powder is preferably 1.25 g/cm3 or less, more preferably 1.00 g/cm3 or less, and 0.90 g/cm3. The following is particularly preferable. The lower limit of tap density (TD) is not particularly limited, but is preferably 0.3 g/cm3 or more.

In the tap density measurement, approximately 20 g of powder is charged into a cylinder with a volume of 100 cm3. The measurement conditions are as follows.

Drop height: 10mm

Number of taps: 200

[Coercivity (Hc)]

When the coercive force (Hc) is high, the real part (μ') is low, and when the coercive force (Hc) is low, the real part (μ') is high. From the viewpoint of achieving high permeability, the coercive force (Hc) is preferably 400 A/m or less, more preferably 300 A/m or less, and especially preferably 200 A/m or less.

Coercive force (Hc) is the strength of the external magnetic field required to return a magnetized magnetic material to its non-magnetized state. To measure coercive force (Hc), for example, Denshi Jiki Kogyo's coercivity meter 'HC-1031' can be used. Specifically, a resin container was filled with flat powder, and the value when the container was magnetized in the radial direction was measured as the coercive force (Hc) in the longitudinal direction of the flat powder. The maximum applied magnetic field during measurement is 239 kA/m.

[Method for manufacturing soft magnetic flat powder]

The soft magnetic flat powder according to the present invention is obtained by subjecting the raw material powder to a flattening process. Raw material powder can be obtained by gas atomization method, water atomization method, disk atomization method, grinding method, etc. Gas atomization method and disk atomization method are preferred.

For example, in the gas atomization method, the raw metal is heated and melted to obtain molten metal. This molten metal flows out from the nozzle. Gas (argon gas, nitrogen gas, etc.) is injected into this molten metal. Due to the energy of this gas, the molten metal differentiates into droplets and cools as it falls. These droplets coagulate to form particles. In this gas atomization method, the molten metal is instantly converted into droplets and cooled at the same time, so that a uniform microstructure is obtained. Moreover, because droplets are formed continuously, the difference in composition between particles is extremely small.

In the disk atomization method, the raw metal is heated and melted to obtain molten metal. This molten metal flows out from the nozzle. This molten metal is dropped onto a disk rotating at high speed. The molten metal is rapidly cooled and solidified, and powder is obtained.

A flattening process is performed on this raw material powder. A typical flattening process is performed by an attritor. Dry processing may be used, or wet processing may be used. In the case of wet processing, it is desirable to use an organic solvent that can suppress oxidation during processing, but the type of organic solvent is not particularly limited. There is no particular limitation on the amount of organic solvent added, and it is appropriately adjusted depending on the type of raw material powder, etc.

The powder after the flattening process is subjected to heat treatment, classification, etc., as needed. Classification and/or heat treatment may be performed on the raw material powder before the flattening process, as needed.

There are no particular restrictions on the heat treatment conditions, but from the viewpoint of improving magnetic permeability, the preferable heat treatment temperature is 500°C to 900°C. The heat treatment time is appropriately adjusted depending on the amount of powder processed, productivity, etc. Heat treatment in vacuum or in inert gas is preferred.

Example

Hereinafter, the effects of the present invention will be clarified through examples, but the present invention is not to be construed as limited based on the description of these examples.

[Example 1]

By gas atomization and classification, raw material powder (composition: Fe-9Si-6Al, amount B 0.0024% by mass) was obtained. 250 g of this raw material powder (processing conditions A) was put into the atliter. A naphthenic solvent was also added to this attritor. As powder media, SUJ2 of 4.8 mm was used. By flattening the powder using this attritor, flat powder was obtained. The soft magnetic flat powder of Example 1 was obtained as the final evaluation powder by holding this flat powder in an argon gas atmosphere at 800°C for 1 hour and slowly cooling it.

[Examples 2 to 4, 17 and 18 and Comparative Examples 12, 13, 19 and 20]

In the same manner as in Example 1 except that the composition was as shown in Table 1, soft magnetic flat powders of Examples 2 to 4, 17, and 18 and Comparative Examples 12, 13, 19, and 20 were obtained.

[Examples 5 to 8 and Comparative Examples 14 and 15]

The composition was as shown in Table 2, and the amount of raw material powder charged into the attritor was 500 g (processing conditions B) in the same manner as in Example 1, and the soft magnetic flat sheets of Examples 5 to 8 and Comparative Examples 14 and 15 were prepared. obtained powder. In accordance with the increase in input amount, processing conditions were appropriately adjusted.

[Examples 9 to 11 and Comparative Examples 16 and 21]

The composition was as shown in Table 3, and the amount of raw material powder charged into the attritor was 1000 g (processing condition C) in the same manner as in Example 1, and the soft magnetic flat sheets of Examples 9 to 11 and Comparative Examples 16 and 21 were prepared. obtained powder. In accordance with the increase in input amount, processing conditions were appropriately adjusted.

[Composition and physical properties of evaluation powder]

The composition, median diameter (D50), tap density (TD), and coercive force (Hc) of each soft magnetic flat powder in Examples and Comparative Examples were measured. For composition analysis, an ICP (Inductive Coupled Plasma) emission spectroscopic analyzer was used. Median diameter (D50), tap density (TD), and coercive force (Hc) were measured by the method described above. The results obtained are shown in Tables 1 to 3. Changes in median diameter (D50) (μm) and coercive force (Hc) (A/m) depending on B content (mass%) are shown in Figures 2 and 3, respectively. Meanwhile, in Figures 2 and 3, the data of Comparative Example 21 is omitted.

[Production and evaluation of magnetic sheets]

A slurry was prepared by kneading each soft magnetic flat powder of Examples and Comparative Examples with an acrylic resin, and molded into a sheet shape by the doctor blade method. After that, press processing was performed at 60°C and 50 MPa to obtain a magnetic sheet. The volumetric filling ratio of the flat powder in the obtained magnetic sheet was all about 35%. The complex magnetic permeability of each magnetic sheet was measured using an impedance analyzer (product name 'E4991B' from Keysight Technology). Measurements are performed at 1 MHz to 1 GHz, and the average values of the actual part (μ') in the range of 2 to 5 MHz are shown in Tables 1 to 3. The change in the real part (μ') of complex permeability according to the B content (mass%) is shown in Figure 1. Meanwhile, in Figure 1, the data of Comparative Example 21 is omitted.

[Table 1]

[Table 2]

[Table 3]

As shown in Tables 1 to 3, it was confirmed that under any processing conditions, a magnetic sheet with a high magnetic permeability could be produced using the soft magnetic flat powder of the Example, compared to the powder of the Comparative Example.

From Figure 2, it can be seen that the median diameter (D50) of the flat powder increases in the region where the B content is 0.002 mass% or more under any processing conditions. From Figure 3, it can be seen that when the B content exceeds 0.015%, the coercive force (Hc) increases excessively. As a result of these results, it is believed that the magnetic permeability was improved in the flat powders of the examples in which the B content was in the range of 0.002 mass% or more and 0.015 mass% or less, compared to the comparative examples in which the B content was less than 0.002 mass% or more than 0.025 mass%. .

From the above evaluation results, the superiority of the present invention is clear.

The soft magnetic flat powder described above can also be applied to the production of various magnetic members.

Claims (4)

As a soft magnetic flat powder,
The flat powder is composed of a Fe-Si-Al alloy containing B as an additive element,
Soft magnetic flat powder wherein the content of B in the alloy is 0.002% by mass or more and 0.015% by mass or less. According to claim 1,
Soft magnetic flat powder with a median diameter (D50) based on volume of 30㎛ or more and 80㎛ or less. The method of claim 1 or 2,
Soft magnetic flat powder with a tap density (TD) of 1.25 g/cm3 or less. The method according to any one of claims 1 to 3,
A soft magnetic flat powder having a coercive force (Hc) of 400 A/m or less, measured by applying a magnetic field in the longitudinal direction of the flat powder.