Soft-magnetic flat powder

Abstract

Provided is a soft-magnetic flat powder that can contribute to the noise suppression performance of a magnetic sheet 2. The magnetic sheet (2) comprises a matrix (4) and a powder dispersed in the matrix (4). The matrix 4 is a polymer composition. The base material of the polymer composition is a rubber or a resin. The powder is an aggregate of a plurality of flat particles 6. These flat particles 6 are composed of an Fe-Si-Al-based alloy. This alloy contains B in the amount of 0.001-0.020 mass%, inclusive, C in the amount of 0.005-0.050 mass%, inclusive, and no more than 1.00 mass% of O.

Description

Soft magnetic flat powder

[0001] The present disclosure relates to a powder having flat particles and soft magnetism.

[0002] Electronic devices such as personal computers and mobile phones have circuits. Due to radio wave noise radiated from electronic components mounted on this circuit, radio wave interference occurs between electronic components and between electronic circuits. Radio wave interference causes malfunction of electronic devices. For the purpose of suppressing malfunction, a magnetic sheet (electromagnetic wave absorption sheet) is inserted into the electronic device. The magnetic sheet converts electromagnetic waves into magnetic force and prevents radio wave emission outside the electronic circuit. By this magnetic sheet, noise can be suppressed. A high magnetic permeability is required for the noise suppression sheet.

[0003] Patent Document 1 (Japanese Patent No. 3401650) discloses an electromagnetic wave interference suppressor having an insulating soft magnetic layer. This insulating soft magnetic layer contains an organic binder and a metal magnetic filler. This metal magnetic filler is composed of an Fe—Si—Al alloy.

[0004] Patent Document 2 (Japanese Patent Application Laid-Open No. 2009-266960) discloses soft magnetic flat powder. In this powder, the porosity is low. Therefore, in this powder, a large median diameter D50 can be achieved. The real part magnetic permeability μ′ of the magnetic sheet containing this powder is large.

[0005] Patent Document 3 (Japanese Patent Application Laid-Open No. 2017-118114) discloses soft magnetic flat powder. This powder is composed of an alloy containing 84.0% or more and 96.0% or less of Fe, 3.0% or more and 8.5% or less of Si, and 1.0% or more and 13.0% or less of Al. The aspect ratio of this powder is 15 or more.

[0006] Japanese Patent No. 3401650 Japanese Patent Application Laid-Open No. 2009-266960 Japanese Patent Application Laid-Open No. 2017-118114

[0007] Electronic devices are becoming smaller and more high-performance. There is a growing demand for smaller and more high-performance circuit components within these devices. In smaller, higher-performance devices, the density of electronic components mounted in the circuit is high. Therefore, radio wave noise emitted from these components makes them susceptible to radio wave interference between components and between electronic circuits. Magnetic materials that can more effectively suppress this noise are needed.

[0008] The objective of the present invention is to provide a soft magnetic flat powder that can contribute to the noise suppression performance of magnetic members.

[0009] The soft magnetic flattened powder of this disclosure has a plurality (numerous) of flattened particles. These flattened particles are composed of an Fe-Si-Al alloy containing 0.001% to 0.020% by mass of B, 0.005% to 0.050% by mass of C, and 1.00% by mass or less of O.

[0010] Preferably, the volume-based median diameter D50 of this soft magnetic flat powder is 50.0 μm or more and 150.0 μm or less.

[0011] Preferably, the tap density TD of this soft magnetic flat powder is 1.25 Mg / m³ ３ The following applies:

[0012] Preferably, when a magnetic field is applied in the longitudinal direction of the flattened particles, the coercivity of the soft magnetic flattened powder is 400 A / m or less.

[0013] The magnetic member of this disclosure comprises a matrix with a polymer as the base material and a soft magnetic flattened powder dispersed in this matrix. This soft magnetic flattened powder contains a plurality (numerous) of flattened particles. These flattened particles are composed of an Fe-Si-Al alloy containing 0.001% to 0.020% by mass of B, 0.005% to 0.050% by mass of C, and 1.00% by mass or less of O.

[0014] The soft magnetic flattened powder according to the present invention has low coercivity. The magnetic permeability of the magnetic member containing this powder is high. This magnetic member has excellent noise suppression performance.

[0015] Figure 1 is a schematic cross-sectional view showing a part of a magnetic member according to one embodiment. Figure 2 is an enlarged view showing the flattened particles contained in the magnetic member of Figure 1.

[0016] Preferred embodiments will be described in detail below, with reference to drawings as appropriate.

[0017] [Magnetic Sheet] Figure 1 shows a magnetic sheet 2 (magnetic member). This magnetic sheet 2 has a matrix 4 and soft magnetic flat powder dispersed in the matrix 4. The matrix 4 is a polymer composition. A typical substrate for this polymer composition is rubber or resin. This flat powder is an aggregate of multiple (many) particles 6.

[0018] In the manufacture of this magnetic sheet 2, a powder is kneaded with a base polymer together with various chemicals to obtain a polymer composition. Known methods can be used for kneading. For example, kneading can be performed using a closed-type kneader, an open-roll kneader, etc. Examples of chemicals include processing aids such as lubricants and binders.

[0019] Next, a magnetic sheet 2 is formed from this polymer composition. Known methods can be used for molding. Molding can be performed by compression molding, injection molding, extrusion molding, rolling, etc.

[0020] The shape of the magnetic material is not limited to a sheet. Ring-shaped, cubic, rectangular, cylindrical, and other shapes can be used. Furthermore, this powder is also suitable for magnetic materials with more complex shapes.

[0021] [Particle Shape] Figure 2 shows a cross-section of a single particle 6. In Figure 1, the symbol L1 indicates the length of the major axis of particle 6, and the symbol T1 indicates the thickness of particle 6. The length L1 is greater than the thickness T1. In other words, the shape of this particle 6 is flattened.

[0022] The flattened particles 6 have shape anisotropy. This anisotropy can contribute to the high real permeability μ' of the magnetic sheet 2. Moreover, in a magnetic sheet 2 containing flattened particles 6 with a small thickness T1, eddy current losses are suppressed, so relaxation of the real permeability μ' is less likely to occur. This magnetic sheet 2 containing flattened particles 6 can sufficiently shield against noise.

[0023] [Particle Material] The flattened particles 6 are composed of an Fe-Si-Al alloy containing B and C. The Fe-Si-Al alloy may have an ordered lattice with a D03 structure. Therefore, in the Fe-Si-Al alloy, a low magnetostriction constant and a low crystal magnetic anisotropy constant can be achieved simultaneously. Powder made of the Fe-Si-Al alloy can achieve a high real permeability μ' of the magnetic sheet 2. The flattened particles 6 are particularly preferably composed of an Fe-9Si-6Al alloy containing B and C. The role of each element will be explained in detail below.

[0024] [B (Boron)] B is the most important additive element in the powder according to this embodiment. B is added in trace amounts to the Fe-Si-Al alloy. B contributes to the large median diameter D50 of the powder after flattening, and therefore a large aspect ratio of the flattened particles 6 can be achieved. The magnetic permeability of the magnetic sheet 2 containing particles with a large aspect ratio is high. The reason why B contributes to the large median diameter D50 is presumed to be that a part of the D03 structure of the Fe-Si-Al alloy is changed to another structure by B.

[0025] In powders composed of Fe-Si-Al alloys, a large median diameter D50 can be achieved by changing the Si content or the Al content. However, changing the Si content and the Al content can lead to an increase in the magnetostrictive constant and the crystalline magnetic anisotropy constant. In this embodiment, a large median diameter D50 is achieved by adding a small amount of B. The addition of a small amount of B does not significantly increase the magnetostrictive constant of the Fe-Si-Al alloy. The addition of a small amount of B does not significantly increase the crystalline magnetic anisotropy constant of the Fe-Si-Al alloy. In other words, a large median diameter D50 can be achieved by adding a small amount of B without significantly impairing the electromagnetic properties of the Fe-Si-Al alloy. As will be described later, C has a similar effect, but the contribution of B to the median diameter D50 is greater than that of C.

[0026] From the viewpoint of high magnetic permeability, the B content in this alloy is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and particularly preferably 0.005% by mass or more. From the viewpoint of high magnetic permeability, the B content is preferably 0.020% by mass or less, more preferably 0.018% by mass or less, and particularly preferably 0.015% by mass or less.

[0027] [C (Carbon)] C is an important additive element in the powder according to this embodiment. C is added in trace amounts to the Fe-Si-Al alloy. C contributes to the large median diameter D50 of the powder, and therefore a large aspect ratio of the flattened particles 6 can be achieved. The magnetic permeability of the magnetic sheet 2 containing particles with a large aspect ratio is high. The reason why C contributes to the large median diameter D50 is presumed to be that a part of the D03 structure of the Fe-Si-Al alloy is changed to another structure by C.

[0028] In powders composed of Fe-Si-Al alloys, a large median diameter D50 can be achieved by changing the Si content or the Al content. However, changing the Si content and the Al content can lead to an increase in the magnetostrictive constant and the crystalline magnetic 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 magnetostrictive constant of the Fe-Si-Al alloy. The addition of a small amount of C does not significantly increase the crystalline magnetic anisotropy constant of the Fe-Si-Al alloy. In other words, a large median diameter D50 can be achieved by adding a small amount of C without significantly impairing the electromagnetic properties of the Fe-Si-Al alloy.

[0029] Furthermore, carbon (C) preferentially adsorbs oxygen in the alloy. In alloys containing carbon, the formation of Fe oxide, Si oxide, and Al oxide is suppressed. In this alloy, the pinning effect caused by these oxides is suppressed. In other words, carbon suppresses the coercivity of the powder and can contribute to the high permeability of the magnetic sheet 2.

[0030] From the viewpoint of high magnetic permeability, the carbon content is preferably 0.005% by mass or more, more preferably 0.010% by mass or more, and particularly preferably 0.015% by mass or more. From the viewpoint of high magnetic permeability, the carbon content is preferably 0.050% by mass or less, more preferably 0.040% by mass or less, and particularly preferably 0.030% by mass or less.

[0031] [Oxygen (O)] O leads to Fe oxide, Si oxide, and Al oxide. These oxides result in high coercivity of the powder and low permeability of the magnetic sheet 2. From the viewpoint of high permeability, the O content is preferably 1.00 mass% or less, more preferably 0.90 mass% or less, and particularly preferably 0.85 mass% or less. O is not an essential element for Fe-Si-Al alloys. Therefore, the O content may be less than the detection limit. One reason for the inclusion of O in the alloy is the oxidation of particles in the manufacturing process, which will be explained in detail later.

[0032] [Silicon (Si)] Si contributes to high magnetic permeability. 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. Excess 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.

[0033] [Aluminum (Al)] Al contributes to high magnetic permeability. From this viewpoint, the Al content is preferably 2.0 mass% or more, more preferably 2.5 mass% or more, and particularly preferably 3.0 mass% or more. Excess 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 Al content is preferably 10.0 mass% or less, more preferably 8.0 mass% or less, and particularly preferably 7.0 mass% or more.

[0034] [Iron (Fe)] Fe is the base material for alloys. Fe is ferromagnetic. Fe contributes to the magnetic properties of powders.

[0035] [Preferred Composition] The Fe-Si-Al alloy most suitable for magnetic sheet 2 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; B: 0.001% by mass or more and 0.020% by mass or less; C: 0.005% by mass or more and 0.050% by mass or less; and O: 1.00% by mass or less. Preferably, the remainder is Fe and unavoidable impurities.

[0036] A Fe-Si-Al alloy particularly suitable for magnetic sheet 2 contains: Si: 3.2% to 11.8% by mass; Al: 2.3% to 9.8% by mass; B: 0.001% to 0.020% by mass; C: 0.005% to 0.050% by mass; and O: 1.00% by mass or less. Preferably, the remainder is Fe and unavoidable impurities.

[0037] [Median Diameter D50] The length L1 (see Figure 2) of a particle 6 with a large median diameter D50 of the powder is greater than the length L1 of a particle 6 having a thickness T1 equivalent to the thickness T1 of the particle 6 and a small median diameter D50 of the powder. In other words, in flattening to obtain a predetermined thickness T1, particles 6 with a large median diameter D50 of the powder contribute to a large aspect ratio. From the viewpoint of achieving a large aspect ratio, the median diameter D50 of the powder is preferably 50.0 μm or more, more preferably 70.0 μm or more, and particularly preferably 85.0 μm or more. From the viewpoint of homogeneity of the magnetic sheet 2 and smoothness of the surface of the magnetic sheet 2, the median diameter D50 is preferably 150.0 μm or less, more preferably 140.0 μm or less, and particularly preferably 130.0 μm or less.

[0038] The median diameter D50 is calculated based on volume. The median diameter D50 is the diameter of particle 6 at the point on the cumulative curve where the cumulative volume reaches 50%, when the total volume of the powder is assumed to be 100%. A suitable device for measuring the median diameter D50 is Nikkiso's laser diffraction / scattering particle size distribution analyzer, "Microtrac MT3000". In this device, powder is poured into the cell along with pure water, and the median diameter D50 is detected based on the light scattering information of each particle 6 that makes up the powder.

[0039] [Aspect Ratio] As mentioned above, the particle 6 has a flattened shape. This particle 6 has 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 higher, more preferably 5.0 or higher, and particularly preferably 8.0 or higher. The upper limit of the average aspect ratio of the powder that can be put into practical use is about 500.

[0040] For the measurement of the aspect ratio, a sample in which the thickness of the particles 6 can be observed is used. In this sample, a plurality of particles 6 are embedded in the resin. This 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 the analysis of this image, the image data of the particles 6 are binarized. When the shape of the particles 6 in this binarized image approximates 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 the particle 6. The aspect ratios of all the particles 6 obtained in four fields of view are averaged additively to calculate the average aspect ratio of the powder.

[0041] [Tap density TD] The tap density TD of the powder is 1.25 Mg / m ３ The following is preferable. From the powder with the tap density TD within this range, a homogeneous and smooth-surface magnetic sheet 2 can be obtained. For simplicity, the tap density TD is 1.00 Mg / m ３ The following is more preferable, and 0.90 Mg / m ３ The following is particularly preferable. The lower limit value of the tap density TD of the powder that can be put into practical use is about 0.3 Mg / m ３ degree.

[0042] The tap density TD is measured in accordance with the provisions of JIS Z 2512:2012. In the measurement of the tap density TD, about 20 g of powder is filled into a cylinder with a volume of 100 cm ３ The measurement conditions are as follows. Drop height: 10 mm Tap number: 200

[0043] [Coercive force Hc] The coercive force Hc is the strength of the external magnetic field required to return the magnetized magnetic body to the non-magnetized 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. The powder with the coercive force Hc within this range can achieve a high real part magnetic permeability μ' of the magnetic sheet 2. From this viewpoint, the coercive force Hc is more preferably 350 A / m or less, and particularly preferably 300 A / m or less.

[0044] As a device suitable for measuring the coercive force Hc, the coercive force meter "HC-1031" of Denshi Jiki Kogyo Co., Ltd. can be cited. In the measurement, the flat powder is filled in a resin container and magnetized in the diameter direction of this container. The maximum applied magnetic field is 239 kA / m.

[0045] [Method for manufacturing powder] The powder according to this embodiment is obtained by subjecting the raw material powder to flat processing. The raw material powder can be obtained by a gas atomization method, a water atomization method, a disk atomization method, a pulverization method, or the like. The gas atomization method and the disk atomization method are preferred.

[0046] In the gas atomization method, the raw material metal is heated and melted to obtain a molten metal. This molten metal flows out from the nozzle. A gas (argon gas, nitrogen gas, etc.) is sprayed onto this molten metal. Due to the energy of this gas, the molten metal is pulverized into droplets and cooled while falling. These droplets solidify to form particles. In this gas atomization method, since the molten metal is instantaneously atomized into droplets and cooled at the same time, a uniform fine structure can be obtained. Moreover, since droplets are continuously formed, the compositional difference between particles is extremely small.

[0047] In the disk atomization method, the raw material metal is heated and melted to obtain a 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 to obtain powder.

[0048] Typical flat processing is performed by an attritor. The flat processing may be performed dry or wet. In wet flat processing, an appropriate amount of organic solvent is used. Various organic solvents can be used for this wet processing. An organic solvent capable of suppressing particle oxidation is preferred.

[0049] The powder after flat processing 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 appropriately adjusted according to the processing amount of the powder, productivity, etc. Heat treatment in a vacuum or an inert gas is preferred. The raw material powder before flat processing may be heat-treated as necessary.

[0050] The powder may be subjected to classification. Classification may be performed on the powder before flattening, on the powder after flattening, or on the powder after heat treatment.

[0051] The effects of the soft magnetic flat powder according to the examples will be clarified below, but the scope disclosed herein should not be interpreted as limiting based on the description of these examples.

[0052] [Example 9] Raw material powder was obtained by gas atomization and classification. The material of the raw material powder, analyzed by an ICP (Inductive Coupled Plasma) emission spectrometer, was an Fe-9Si-6Al alloy containing 0.014 mass% B, 0.024 mass% C, and 0.81 mass% O. 250 g of raw material powder was placed in an attritor together with a naphthenic solvent. The media material was high-carbon chromium bearing steel (SUJ2). The diameter of this media was 4.8 mm. The raw material powder was flattened using this attritor. This powder was heat-treated to obtain the soft magnetic flattened powder of Example 9. The heat treatment conditions were as follows. Atmosphere: Argon gas Temperature: 800°C Holding time: 1 hour Cooling method: Slow cooling The median diameter D50 of this soft magnetic flat powder is 125.7 μm, and the tap density TD is 0.96 Mg / m³ ３ The coercivity Hc was 75.3 A / m, and the average aspect ratio was 112.6.

[0053] [Examples 1-8 and 10-18 and Comparative Examples 1-6] Powders for Examples 1-8 and 10-18 and Comparative Examples 1-6 were obtained in the same manner as in Example 9, except that the composition of the raw material powder was as shown in Tables 1 and 2 below.

[0054] [Measurement of Magnetic Permeability] Flattened powder and acrylic resin were kneaded to obtain a slurry. This slurry was subjected to the doctor blade method to obtain a sheet. This sheet was pressed at a temperature of 60°C and a pressure of 50 MPa to obtain a magnetic sheet. The volume packing rate of the flattened powder in this magnetic sheet was approximately 35%. The complex magnetic permeability of this magnetic sheet was measured using an impedance analyzer (Keysight Technology product name "E4991B"). Measurements were performed in the range of 1 MHz to 1 GHz, and the average value of the real magnetic permeability μ' in the range of 2 MHz to 5 MHz was calculated. The results are shown in Tables 1 and 2 below. The remainder of the composition of each powder is Fe and unavoidable impurities.

[0055]

[0056]

[0057] As is clear from Tables 1 and 2, the soft magnetic flattened powders of each example can contribute to the high real permeability μ' of the magnetic sheet. The superiority of this powder is evident from these evaluation results.

[0058] The flattened powder described above is suitable for various magnetic materials.

[0059] 2... Magnetic sheet 4... Matrix 6... Particles

Claims

1. A soft magnetic flat powder comprising multiple flattened particles, wherein the flattened particles are composed of an Fe-Si-Al alloy containing 0.001% to 0.020% by mass of B, 0.005% to 0.050% by mass of C, and 1.00% or less by mass of O.

2. The soft magnetic flat powder according to claim 1, wherein the volume-based median diameter D50 is 50.0 μm or more and 150.0 μm or less.

3. Tap density TD is 1.25 Mg / m³ ３ The soft magnetic flat powder according to claim 1 or 2, which is as follows:

4. The soft magnetic flat powder according to claim 1 or 2, wherein the coercivity of the soft magnetic flat powder when a magnetic field is applied in the longitudinal direction of the flat particles is 400 A / m or less.

5. A magnetic member comprising a matrix with a polymer as the base material and soft magnetic flat powder dispersed in the matrix, wherein the soft magnetic flat powder contains a plurality of flat particles, and the soft magnetic flat particles are composed of an Fe-Si-Al alloy containing 0.001% by mass or more and 0.020% by mass or less of B, 0.005% by mass or more and 0.050% by mass or less of C, and 1.00% by mass or less of O.

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