Soft magnetic flat powder

Abstract

To provide a soft magnetic flat powder that can contribute to the noise suppression performance of magnetic sheet 2. [Solution] The magnetic sheet 2 has a matrix 4 and powder dispersed in the matrix 4. The matrix 4 is a polymer composition. The base material of this polymer composition is rubber or resin. The powder is an aggregate of numerous flattened particles 6. The material of these flattened particles 6 is an Fe-Si-Al alloy. This alloy contains 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.

Description

【Technical Field】 【0001】 This specification relates to a powder in which the particles are flat and have soft magnetism. 【Background Art】 【0002】 Electronic devices such as personal computers and mobile phones have circuits. Due to the 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 the electronic device. 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. With this magnetic sheet, noise can be suppressed. A high magnetic permeability is required for the noise suppression sheet. 【0003】 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. The material of this metal magnetic filler is an Fe-Si-Al alloy. 【0004】 Japanese Unexamined Patent Application Publication 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】 Japanese Unexamined Patent Application Publication No. 2017-118114 discloses soft magnetic flat powder. The material of this powder is 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. 【Prior Art Documents】 【Patent Documents】 【0006】 【Patent Document 1】 Patent No. 3401650 [Patent Document 2] Japanese Patent Publication No. 2009-266960 [Patent Document 3] Japanese Patent Publication No. 2017-118114 [Overview of the Initiative] [Problems that the invention aims to solve] 【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 applicant's intention is to provide a soft magnetic flat powder that can contribute to the noise suppression performance of magnetic materials. [Means for solving the problem] 【0009】 The soft magnetic flattened powder disclosed herein has a large number of flattened particles. The material of these flattened particles is 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. 【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 disclosed in this specification has a matrix with a polymer as a base material and soft magnetic flat powder dispersed in this 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 0.001% 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. 【Advantages of the Invention】 【0014】 The coercive force of this soft magnetic flat powder is small. The magnetic permeability of the magnetic member containing this powder is large. This magnetic member has excellent noise suppression performance. 【Brief Description of the Drawings】 【0015】 [Figure 1] FIG. 1 is a schematic cross-sectional view showing a part of a magnetic member according to an embodiment. [Figure 2] FIG. 2 is an enlarged view showing the flat particles contained in the magnetic member of FIG. 1. 【Modes for Carrying Out the Invention】 【0016】 Hereinafter, preferred embodiments will be described in detail while appropriately referring to the drawings. 【0017】 [Magnetic Sheet] In FIG. 1, a magnetic sheet 2 (magnetic member) is shown. This magnetic sheet 2 has a matrix 4 and soft magnetic flat powder dispersed in this matrix 4. The matrix 4 is a polymer composition. A typical base material of this polymer composition is rubber or resin. This flat powder is an aggregate of a large number of particles 6. 【0018】 In the production of this magnetic sheet 2, the powder is kneaded with various chemicals into the base polymer to obtain a polymer composition. Known methods can be adopted for kneading. For example, kneading can be performed using a closed kneader, an open roll, etc. Examples of the chemicals include processing aids such as lubricants and binders. 【0019】 Next, the magnetic sheet 2 is formed from this polymer composition. Known methods can be adopted for the forming. The forming can be carried out by compression molding, injection molding, extrusion molding, rolling, etc. 【0020】 The shape of the magnetic member is not limited to sheet shape. Shapes such as ring shape, cubic shape, rectangular parallelepiped shape, cylindrical shape, etc. can be adopted. Further, this powder is also suitable for magnetic members having more complicated shapes. 【0021】 [Particle shape] In FIG. 2, a cross-section of one particle 6 is shown. In FIG. 1, what is indicated by reference sign L1 is the length of the long axis of the particle 6, and what is indicated by reference sign T1 is the thickness of the particle 6. The length L1 is larger than the thickness T1. In other words, the shape of this particle 6 is flat. 【0022】 The flat particle 6 has shape anisotropy. This anisotropy can contribute to the high real part magnetic permeability μ' of the magnetic sheet 2. Moreover, in the magnetic sheet 2 containing flat particles 6 with a small thickness T1, eddy current loss is suppressed, so relaxation of the real part magnetic permeability μ' is unlikely to occur. The magnetic sheet 2 containing this flat particle 6 can sufficiently shield noise. 【0023】 [Material of particle] The material of the flat particle 6 is an Fe-Si-Al alloy containing B and C. The Fe-Si-Al alloy can have a regular lattice of D03 structure. Therefore, in the Fe-Si-Al alloy, a low magnetostriction constant and a low crystalline magnetic anisotropy constant can coexist. The powder made of the Fe-Si-Al alloy can achieve the high real part magnetic permeability μ' of the magnetic sheet 2. A particularly preferable material of the flat particle 6 is an Fe-9Si-6Al alloy containing B and C. Hereinafter, the roles of each element will be described in detail. 【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 can be achieved for the flattened particles 6. The magnetic sheet 2 containing particles with a large aspect ratio has a high magnetic permeability. 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 made from 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 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 mass% or more, more preferably 0.002 mass% or more, and particularly preferably 0.005 mass% or more. From the viewpoint of high magnetic permeability, the B content is preferably 0.020 mass% or less, more preferably 0.018 mass% or less, and particularly preferably 0.015 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 can be achieved for the flattened particles 6. 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 made from Fe-Si-Al alloys, a large median diameter D50 can be achieved by changing the Si content or Al content. However, changing the Si content and 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 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 the formation of 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 lower than the detection limit. One reason for the presence of O in the alloy is the oxidation of particles during 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. 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 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 a 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 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 B: 0.001 mass% or more and 0.020 mass% or less C: 0.005 mass% or more and 0.050 mass% or less and O: 1.00% by mass or less It contains [the specified components]. Preferably, the remainder is Fe and unavoidable impurities. 【0036】 Fe-Si-Al alloys particularly suitable for magnetic sheet 2 are: Si: 3.2% by mass or more and 11.8% by mass or less A: 2.3% by mass or more and 9.8% by mass or less B: 0.001 mass% or more and 0.020 mass% or less C: 0.005 mass% or more and 0.050 mass% or less and O: 1.00% by mass or less It contains [the specified components]. 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 is greater than the length L1 of a particle 6 with a thickness T1 equivalent to that of the particle 6 and a small median diameter D50. In other words, in flattening to obtain a predetermined thickness T1, particles 6 with a large median diameter D50 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 the 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. When the total volume of the powder is assumed to be 100% and a cumulative curve is drawn, the median diameter D50 is the diameter of particle 6 at the point on the curve where the cumulative volume reaches 50%. 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 exhibits shape anisotropy. This anisotropy increases the real permeability μ' of the magnetic material. 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】 To measure the aspect ratio, a sample is used in which the thickness of the particle 6 can be observed. In this sample, multiple particles 6 are embedded in the resin. This sample is polished, and the polished surface is observed using a scanning electron microscope (SEM). The magnification of the image during observation is 1000x. In the analysis of this image, the image data of particle 6 is binarized. When the shape of particle 6 is approximated as an ellipse in this binarized image, 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 from four fields of view are given an arithmetic mean to calculate the average aspect ratio of the powder. 【0041】 [Tap Density TD] The tap density (TD) of the powder is 1.25 Mg / m³ 3 The following is preferable. A homogeneous magnetic sheet 2 with a smooth surface can be obtained from a powder having a tap density TD in this range. From this simplicity, the tap density TD is 1.00 Mg / m 3 The following is more preferable: 0.90 Mg / m³ 3 The following is particularly preferable: The lower limit of the tap density TD of the powder that can be put into practical use is 0.3 Mg / m³. 3It is to that extent. 【0042】 In the tap density TD measurement, approximately 20g of powder was found in a volume of 100cm³. 3 It is filled into the cylinder. The measurement conditions are as follows: Drop height: 10mm Number of taps: 200 【0043】 [Coercive force Hc] Coercivity Hc is the strength of the 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 coercivity Hc of the powder is preferably 400 A / m or less. Powders with a coercivity Hc in this range can achieve a high real permeability μ' of the magnetic sheet 2. From this viewpoint, a coercivity Hc of 350 A / m or less is more preferable, and 300 A / m or less is particularly preferable. 【0044】 A suitable device for measuring coercivity (Hc) is the "HC-1031" coercivity meter from Denshi Jiki Kogyo Co., Ltd. In the measurement, flattened powder is filled into a resin container and magnetized in the diametrical direction of the container. The maximum applied magnetic field is 239 kA / m. 【0045】 [Method for producing powder] The powder according to this embodiment is obtained by flattening the raw material powder. The raw material powder can be obtained by gas atomization, water atomization, disc atomization, pulverization, etc. Gas atomization and disc atomization are preferred. 【0046】 In the gas atomization method, the raw metal is heated and melted to obtain molten metal. This molten metal flows out of a nozzle. A gas (argon gas, nitrogen gas, etc.) is blown onto this molten metal. The energy of this gas causes the molten metal to pulverize into droplets, which are cooled as they fall. These droplets solidify, forming particles. In this gas atomization method, the molten metal instantly condenses into droplets and cools simultaneously, resulting in a uniform microstructure. Moreover, because droplets are formed continuously, the compositional difference between particles is extremely small. 【0047】 In the disc atomization method, the raw metal is heated and melted to obtain molten metal. This molten metal flows out of a nozzle and is dropped onto a rapidly rotating disc. The molten metal is rapidly cooled and solidified to obtain powder. 【0048】 Typical flattening is performed by an attritor. Flattening may be performed dry or wet. 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 the oxidation of particles are preferred. 【0049】 The flattened powder is subjected to heat treatment as needed. From the viewpoint of high magnetic permeability, the preferred heat treatment temperature is 500°C to 900°C. The heat treatment time is adjusted as appropriate depending on the amount of powder processed, productivity, etc. Heat treatment in a vacuum or in an inert gas is preferred. The raw material powder before flattening may also be subjected to heat treatment as needed. 【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. [Examples] 【0051】 The effects of the soft magnetic flat powder according to the examples will be revealed below, but the scope disclosed herein should not be interpreted as limiting based on the description of these examples. 【0052】 [Example 9] The raw material powder was obtained by gas atomization and classification. 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 the 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℃ Holding time: 1 hour Cooling method: slow cooling The median diameter D50 of this soft magnetic flattened 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 Example 1-6] Powders for Examples 1-8 and 10-18 and Comparative Example 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 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 permeability μ' in the range of 2 MHz to 5 MHz was calculated. These results are shown in Tables 1 and 2 below. The remainder of the composition of each powder is unavoidable impurities. 【0055】 [Table 1] 【0056】 [Table 2] 【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 these powders is evident from these evaluation results. [Industrial applicability] 【0058】 The flattened powder described above is suitable for various magnetic materials. [Explanation of Symbols] 【0059】 2. Magnetic sheet 4. The Matrix 6...particles

Claims

[Claim 1] It has many flattened particles, A soft magnetic flat powder in which the material of these flat particles is an Fe-Si-Al alloy containing 0.001% to 0.020% by mass of B, 0.012% to 0.048% by mass of C, and 1.00% or less by mass of O. [Claim 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. [Claim 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: [Claim 4] The soft magnetic flat powder according to claim 1 or 2, wherein the coercivity of the powder when a magnetic field is applied in the longitudinal direction of the flat particles is 400 A / m or less. [Claim 5] It comprises a matrix with a polymer as the base material and soft magnetic flattened powder dispersed in this matrix. The above soft magnetic flattened powder contains a large number of flattened particles. A magnetic member in which these flattened particles are made of an Fe-Si-Al alloy containing 0.001% to 0.020% by mass of B, 0.012% to 0.048% by mass of C, and 1.00% or less by mass of O.

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