JP2024085534A - Soft-magnetic flat powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft-magnetic flat powder allowing for obtaining a magnetic sheet 2 excellent in noise-suppressing performance.

SOLUTION: A magnetic sheet 2 comprises a matrix 4 and powder dispersed in the matrix 4. The matrix 4 is of a polymer composition, and the polymer composition has a base material of rubber or resin. The powder is an aggregate of a multiplicity of flat particles 6, and the flat particles 6 have a material of Fe-Si-Al alloy. The alloy contains C in the amount of 0.01 mass% or more and 0.05 mass% or less. The powder has a preferable median size D50 (volumetric basis) of 20.0 μm or greater and 90.0 μm or smaller. The powder has a preferable tap density TD of 1.25 g/cm³ or lower.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

This specification relates to a powder whose particles are flat and have soft magnetic properties.

Electronic devices such as personal computers and mobile phones have circuits. Radio noise emitted from electronic components attached to these circuits causes radio interference between the electronic components and other electronic components, and between electronic circuits and other electronic circuits. Radio interference can cause electronic devices to malfunction. To prevent malfunctions, magnetic sheets (electromagnetic wave absorbing sheets) are inserted into electronic devices. Magnetic sheets convert electromagnetic waves into magnetic force. Noise can be suppressed by these magnetic sheets.

JP 2017-118114 A discloses a magnetic sheet containing soft magnetic flat powder. The material of this powder is an Fe-Si-Al alloy. The average aspect ratio of this powder is large. This powder can contribute to the high electromagnetic wave absorption performance of the magnetic sheet.

JP2017-118114A

Electronic devices are becoming smaller and more powerful. There is also a growing demand for smaller and more powerful circuit components within electronic devices. In smaller, more powerful devices, the density of electronic components mounted on the circuits is high. As a result, radio noise emitted from these electronic components is likely to cause radio interference between electronic components and between electronic circuits. There is a demand for magnetic components that can better suppress noise.

The applicant's intention is to provide a soft magnetic flat powder that can produce magnetic components with excellent noise suppression performance.

The soft magnetic flat powder disclosed in this specification contains a large number of flat particles. The material of these flat particles is an Fe-Si-Al alloy containing 0.010% by mass or more and 0.050% by mass or less of C.

Preferably, the volume-based median diameter D50 of this soft magnetic flat powder is 20.0 μm or more and 90.0 μm or less.

Preferably, the soft magnetic flat powder has a tap density TD of 1.25 g/ ^cm3 or less.

Preferably, the coercive force of this soft magnetic flat powder is 400 A/m or less when a magnetic field is applied in the longitudinal direction of the particles.

The magnetic member disclosed in this specification has a matrix in which a polymer is used as the base material, and soft magnetic flat powder dispersed in the matrix. This soft magnetic flat powder contains a large number of flat particles. The material of these flat particles is an Fe-Si-Al alloy containing 0.01% by mass or more and 0.05% by mass or less of C.

The coercive force of this soft magnetic flat powder is small. The magnetic permeability of a magnetic member containing this powder is high. This magnetic member has excellent noise suppression performance.

FIG. 1 is a schematic cross-sectional view showing a portion of a magnetic member according to an embodiment. FIG. 2 is an enlarged view showing flat particles contained in the magnetic member of FIG.

A preferred embodiment will be described in detail below, with reference to the drawings as appropriate.

[Magnetic sheet]
1 shows a magnetic sheet 2 (magnetic member). This magnetic sheet 2 has a matrix 4 and a powder dispersed in this matrix 4. The matrix 4 is a polymer composition. A typical base material for this polymer composition is rubber or resin. The powder is a collection of many particles 6.

In the manufacture of the magnetic sheet 2, the powder is kneaded with various chemicals into the base polymer to obtain a polymer composition. A known method can be used for kneading. For example, kneading can be performed using an internal mixer, an open roll, or the like. Examples of chemicals include processing aids such as lubricants and binders.

Next, the magnetic sheet 2 is molded from this polymer composition. Known methods can be used for molding. Molding can be performed by compression molding, injection molding, extrusion molding, rolling, etc.

The shape of the magnetic member is not limited to a sheet shape. Ring, cube, rectangular parallelepiped, cylindrical, and other shapes can be used. This powder is also suitable for magnetic members with more complex shapes.

[Particle shape]
Fig. 2 shows a cross section of one particle 6. In Fig. 1, the reference symbol L1 indicates the length of the major axis of the particle 6, and the reference symbol T1 indicates the thickness of the particle 6. The length L1 is greater than the thickness T1. In other words, the shape of this particle 6 is flat.

The flat particles 6 have shape anisotropy. This anisotropy can contribute to the high real permeability μ' of the magnetic sheet 2. Furthermore, in a magnetic sheet 2 containing flat particles 6 with a small thickness T1, eddy current loss is suppressed, so relaxation of the real permeability μ' is unlikely to occur. The magnetic sheet 2 containing these flat particles 6 can adequately shield noise.

[Particle material]
The material of the flat particles 6 is an Fe-Si-Al alloy containing C. The Fe-Si-Al alloy can have a regular lattice of the D03 structure. Therefore, the Fe-Si-Al alloy can have both a low magnetostriction constant and a low magnetocrystalline anisotropy constant. The powder made of the Fe-Si-Al alloy can achieve a high real permeability μ'. The role of each element will be described in detail below.

[C (carbon)]
C is the most important additive element in the powder according to this embodiment. A small amount of C is added to the Fe-Si-Al alloy. C contributes to a large median diameter D50 of the powder, and therefore a large aspect ratio of the flat particles 6 can be achieved. The magnetic sheet 2 containing particles 6 with a large aspect ratio has a large magnetic permeability. It is presumed that the reason why C contributes to a large median diameter D50 is that part of the D03 structure of the Fe-Si-Al alloy is changed to another structure by C.

In powder made of Fe-Si-Al alloy, a large median diameter D50 can be achieved by changing the Si content or Al content. However, changing the Si content and changing the Al content can lead to an increase in the magnetostriction constant and the magnetocrystalline anisotropy constant. In this embodiment, a large median diameter D50 is achieved by adding a small amount of C. The addition of a small amount of C does not significantly increase the magnetostriction constant of the Fe-Si-Al alloy. The addition of a small amount of C does not significantly increase the magnetocrystalline anisotropy constant of the Fe-Si-Al alloy. In other words, the addition of a small amount of C can achieve a large median diameter D50 without substantially impairing the electromagnetic properties of the Fe-Si-Al alloy.

Furthermore, C preferentially adsorbs oxygen in the alloy. In an alloy containing C, the generation of Fe oxides, Si oxides, and Al oxides is suppressed. In this alloy, the pinning effect of these oxides is suppressed. In other words, C suppresses the coercive force of the powder and can contribute to the high magnetic permeability of the magnetic sheet 2.

From the viewpoint of high magnetic permeability, the C content is preferably 0.010 mass% or more, more preferably 0.015 mass% or more, and particularly preferably 0.020 mass% or more. From the viewpoint of high magnetic permeability, the C content is preferably 0.050 mass% or less, more preferably 0.045 mass% or less, and particularly preferably 0.040 mass% or less.

[Silicon (Si)]
Si contributes to a large resistivity and can reduce eddy current loss. Si also contributes to a high magnetic permeability. Si contributes to noise suppression. From this viewpoint, the Si content is preferably 3.0 mass% or more, more preferably 4.0 mass% or more, and particularly preferably 5.0 mass% or more. Excessive Si leads to a decrease in magnetic permeability due to a decrease in saturation magnetic flux density. From the viewpoint of high magnetic permeability, the Si content is preferably 12.0 mass% or less, more preferably 11.0 mass% or less, and particularly preferably 10.0 mass% or more.

[Aluminum (Al)]
Al contributes to a large resistivity and can reduce eddy current loss. Al also contributes to a high magnetic permeability. From this viewpoint, the content of Al is preferably 2.0 mass% or more, more preferably 2.5 mass% or more, and particularly preferably 3.0 mass% or more. Excessive Al leads to a decrease in magnetic permeability due to a decrease in saturation magnetic flux density. From the viewpoint of high magnetic permeability, the content of Al is preferably 10.0 mass% or less, more preferably 9.0 mass% or less, and particularly preferably 8.0 mass% or more.

[Iron (Fe)]
Fe is the base material of the alloy. Fe has ferromagnetic properties. Fe contributes to the magnetic properties of the powder.

[Preferred Composition]
The Fe-Si-Al alloy particularly suitable for the magnetic sheet 2 is
The alloy contains: Si: 3.0% by mass or more and 12.0% by mass or less; Al: 2.0% by mass or more and 10.0% by mass or less; and C: 0.01% by mass or more and 0.05% by mass or less. The balance is Fe and unavoidable impurities. Regardless of the respective contents of Si, Al, and C, it is preferable that the balance is Fe and unavoidable impurities.

[Median diameter D50]
The length L1 (see FIG. 2) of a particle with a large median diameter D50 is greater than the length L1 of a particle with a thickness T1 equal to that of the particle and a small median diameter D50. In other words, in a flattening process that obtains a predetermined thickness T1, a particle with a large median diameter D50 contributes to a large aspect ratio. From the viewpoint of achieving a large aspect ratio, the median diameter D50 of the powder is preferably 20.0 μm or more, more preferably 30.0 μm or more, and particularly preferably 40.0 μm or more. From the viewpoint of the smoothness of the surface of the magnetic sheet 2, the median diameter D50 is preferably 90.0 μm or less, more preferably 80.0 μm or less, and particularly preferably 70.0 μm or less.

The median diameter D50 is calculated on a volume basis. When the total volume of the powder is taken as 100% and a cumulative curve is drawn, the median diameter D50 is the diameter of the particle 6 at the point on the curve where the cumulative amount is 50%. The median diameter D50 can be measured, for example, by Nikkiso's laser diffraction/scattering particle size distribution measuring device "Microtrac MT3000". The powder is poured into the cell of this device together with pure water, and the median diameter D50 is detected based on the light scattering information of each particle 6 that constitutes the powder.

[aspect ratio]
As described above, the shape of the particles 6 is flat. The particles 6 have shape anisotropy. This anisotropy increases the real permeability μ′ of the magnetic member. From the viewpoint of high permeability, the average aspect ratio of the powder is preferably 1.5 or more, more preferably 5.0 or more, and particularly preferably 8.0 or more. Preferably, the average aspect ratio is 100 or less.

To measure the aspect ratio, a sample is used in which the thickness of the particles 6 can be observed. In this sample, multiple particles 6 are embedded in resin. The sample is polished, and the polished surface is observed with a scanning electron microscope (SEM). The magnification of the image during observation is 1000 times. In analyzing this image, the image data of the particles 6 is binarized. When this binarized image is approximated to an ellipse, the ratio of the length of the major axis to the length of the minor axis of this ellipse is the aspect ratio of the particle 6. The aspect ratios of all particles 6 obtained in the four fields of view are arithmetically averaged to calculate the average aspect ratio of the powder.

[Tap density TD]
The tap density TD of the powder is preferably 1.25 g/ ^cm3 or less. A magnetic sheet 2 having a smooth surface can be obtained from a powder having a tap density TD in this range. For this reason, the tap density TD is more preferably 1.00 g/ ^cm3 or less, and particularly preferably 0.90 g/ ^cm3 or less. The lower limit of the tap density TD is preferably 0.3 g/ ^cm3 or more.

In measuring the tap density TD, about 20 g of powder is filled into a cylinder with a volume of ¹⁰⁰ cm3. The measurement conditions are as follows:
Drop height: 10mm
Number of taps: 200

[Coercive force Hc]
Coercive force Hc is the strength of an external magnetic field required to return a magnetized magnetic material to an unmagnetized state. When a magnetic field is applied in the longitudinal direction of the particles 6, the coercive force Hc of the powder is preferably 400 A/m or less. A powder having a coercive force Hc in this range can achieve a high real permeability μ'. From this viewpoint, the coercive force Hc is more preferably 300 A/m or less, and particularly preferably 200 A/m or less.

To measure the coercive force Hc, for example, a coercive force meter "HC-1031" made by Denshijikiki Kogyo can be used. In the measurement, the flat powder is filled into a resin container and magnetized in the diametric direction of the container. The maximum applied magnetic field is 239 kA/m.

[Method of producing powder]
The powder according to the present embodiment is obtained by subjecting a raw material powder to a flattening process. The raw material powder can be obtained by a gas atomizing method, a water atomizing method, a disk atomizing method, a pulverizing method, or the like. The gas atomizing method and the disk atomizing method are preferred.

In the gas atomization method, the raw metal is heated and melted to obtain molten metal. This molten metal flows out of a nozzle. Gas (argon gas, nitrogen gas, etc.) is sprayed onto the molten metal. The energy of this gas breaks the molten metal into droplets, which cool as they fall. The droplets solidify to form particles. In the gas atomization method, the molten metal instantly turns into droplets and is cooled at the same time, resulting in a uniform, fine structure. Moreover, because the droplets are formed continuously, the compositional difference between particles is extremely small.

In disk atomization, the raw metal is heated and melted to obtain a molten metal. This molten metal flows out of a nozzle. This molten metal is then dropped onto a disk that rotates at high speed. The molten metal is then rapidly cooled and solidifies to obtain a powder.

A typical flattening process is performed by an attritor. Flattening can be performed in a dry or wet manner. In wet flattening, an appropriate amount of organic solvent is used. Various organic solvents can be used in this wet process. Organic solvents that can suppress oxidation of the particles are preferred.

The powder after the flattening process is heat-treated as necessary. From the viewpoint of high magnetic permeability, the preferred heat treatment temperature is 500°C or higher and 900°C or lower. The heat treatment time is adjusted appropriately depending on the amount of powder to be processed, productivity, etc. Heat treatment in a vacuum or in an inert gas is preferred. The raw powder before the flattening process may be heat-treated as necessary.

The powder may be classified. Classification may be performed on the powder before flattening, on the powder after flattening, or on the powder after heat treatment.

The effects of the soft magnetic flat powder according to the examples will be explained below, but the scope of the present specification should not be interpreted as being limited based on the description of these examples.

[Example 1]
A raw powder was obtained by gas atomization and classification. The material of the raw powder analyzed by an ICP (Inductive Coupled Plasma) emission spectrometer was an Fe-9Si-6Al alloy containing 0.011 mass% C. 500 g of the raw powder was put into an attritor together with a naphthenic solvent. The material of the media was high carbon chromium bearing steel (SUJ2). The diameter of the media was 4.8 mm. The raw powder was flattened by the attritor. The powder was heat-treated to obtain the soft magnetic flat powder of Example 1. The heat treatment conditions were as follows.
Temperature: 800°C
Holding time: 1 hour Cooling method: slow cooling This soft magnetic flat powder had a median diameter D50 of 52.6 μm, a tap density TD of 0.77 g/cm ³ , and a coercive force Hc of 133 A/m.

[Examples 2 to 4 and Comparative Examples 1 and 2]
Powders of Examples 2-4 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the C content of the raw material powder was set as shown in Tables 1 and 2 below.

[Comparative Examples 3 and 4]
Powders of Comparative Examples 3 and 4 were obtained in the same manner as in Example 1, except that the composition of the raw material powder was as shown in Table 2 below.

[Measurement of magnetic permeability]
The flat powder and the acrylic resin were kneaded to obtain a slurry. The slurry was subjected to a doctor blade method to obtain a sheet. The sheet was pressed under conditions of a temperature of 60° C. and a pressure of 50 MPa to obtain a magnetic sheet. The volume filling rate of the flat powder in the magnetic sheet was about 35%. The complex permeability of the magnetic sheet was measured using an impedance analyzer (Keysight Technology's product name "E4991B"). The measurement was performed in the range of 1 MHz to 1 GHz, and the average value of the real permeability μ' in the range of 2 MHz to 5 MHz was obtained. The results are shown in Tables 1 and 2 below.

As is clear from Tables 1 and 2, the soft magnetic flat powder of each embodiment can contribute to a large real permeability μ' of the magnetic component. The superiority of this powder is clear from these evaluation results.

The flat powder described above is suitable for a variety of magnetic components.

2: Magnetic sheet 4: Matrix 6: Particles

Claims (5)

It has many flat particles,
The material of these flat particles is an Fe-Si-Al alloy containing 0.010 mass % or more and 0.050 mass % or less of C. The soft magnetic flat powder according to claim 1, having a volume-based median diameter D50 of 20.0 μm or more and 90.0 μm or less. The soft magnetic flat powder according to claim 1 or 2, having a tap density TD of 1.25 g/ ^cm3 or less. The soft magnetic flat powder according to claim 1 or 2, wherein the coercive force of the powder is 400 A/m or less when a magnetic field is applied in the longitudinal direction of the flat particles. The magnetic material has a matrix made of a polymer as a base material and soft magnetic flat powder dispersed in the matrix.
The soft magnetic flat powder contains a large number of flat particles,
The material of the flat particles is an Fe-Si-Al alloy containing 0.01% by mass or more and 0.05% by mass or less of C.

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