Magnetic powder

Abstract

Provided is a magnetic sheet 2 capable of sufficiently absorbing electromagnetic waves in a high-frequency region. The magnetic sheet 2 includes a matrix 4 and powder dispersed in the matrix. The powder is an aggregate of a large number of flat particles 6. The flat particles 6 are composed of an Fe-based alloy. The Fe-based alloy contains 25.0-40.0 mass% Ni, 3.0-15.0 mass% Al, 0.1-10.0 mass% Ti, 0-10.0 mass% Cu, and inevitable impurities, and has a ratio RA of 0.980-1.020, which is calculated by an equation of RA = Fe% / (Ni%+Al%+Ti%+Cu%) (in the equation, Fe%, Ni%, Al%, Ti%, and Cu% respectively represent the atom content rates of Fe, Ni, Al, Ti, and Cu in the Fe-based alloy).

Description

Magnetic powder

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

[0002] Electronic devices such as personal computers and mobile phones have circuits. Due to the radio wave noise radiated from the electronic components mounted on this circuit, radio wave interference occurs between the electronic components and other electronic components, and radio wave interference occurs between the electronic circuits and other 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. A general magnetic sheet contains magnetic powder.

[0003] Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2018-085438) discloses magnetic powder having a composition of Fe—Co—C—Ni or Fe—Co—C—Mn. Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2018-125480) discloses magnetic powder having a composition of Fe—Cr—C or Fe—C—Cr—Ni.

[0004] Japanese Unexamined Patent Application Publication No. 2018-085438 Japanese Unexamined Patent Application Publication No. 2018-125480

[0005] In recent years, the communication speed of electronic devices has been increased. High-frequency radio waves are used for high-speed communication. Suppressing malfunction caused by electromagnetic wave noise in the high-frequency range is important.

[0006] What the applicant intends is to provide a magnetic member that can sufficiently absorb electromagnetic waves in the high-frequency range.

[0007] The magnetic powder according to this disclosure has a plurality (numerous) of flattened particles. These flattened particles are composed of an Fe-based alloy containing Ni: 25.0% to 40.0% by mass, Al: 3.0% to 15.0% by mass, Ti: 0.1% to 10.0% by mass, Cu: 0% to 10.0% by mass, and unavoidable impurities. The ratio RA of this magnetic powder is 0.980 to 1.020, calculated by the following formula: RA = Fe% / (Ni% + Al% + Ti% + Cu%) (wherein Fe%, Ni%, Al%, Ti%, and Cu% represent the atomic content of Fe, Ni, Al, Ti, and Cu in the Fe-based alloy, respectively).

[0008] Preferably, this Fe-based alloy has a structure obtained by spinodal decomposition. This structure may have a ferromagnetic phase α1 containing Fe and a weakly magnetic phase α2 containing Ni, Al, and Ti.

[0009] Preferably, the average particle thickness Tav of the magnetic powder is 3.0 μm or less. Preferably, the saturation magnetization Ms of the magnetic powder is 0.8 T or more. Preferably, the coercivity iHc of the magnetic powder is 20 kA / m or more.

[0010] The polymer composition according to this disclosure comprises a base polymer and a powder dispersed in the base polymer. The powder has a plurality of flattened particles. These particles are composed of an Fe-based alloy containing Ni: 25.0% to 40.0% by mass, Al: 3.0% to 15.0% by mass, Ti: 0.1% to 10.0% by mass, Cu: 0% to 10.0% by mass, and unavoidable impurities. The ratio RA of this polymer composition, calculated using the following formula: RA = Fe% / (Ni% + Al% + Ti% + Cu%) (wherein Fe%, Ni%, Al%, Ti%, and Cu% represent the atomic content of Fe, Ni, Al, Ti, and Cu in the Fe-based alloy, respectively), is 0.980 to 1.020.

[0011] Magnetic materials containing this powder effectively absorb electromagnetic noise in the high-frequency range. This magnetic material can suppress malfunctions in electronic devices.

[0012] 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.

[0013] Preferred embodiments will be described in detail below, with reference to drawings as appropriate.

[0014] [Magnetic Sheet] Figure 1 shows a magnetic sheet 2 (magnetic member). This magnetic sheet 2 has a matrix 4 and magnetic 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. This powder is an aggregate of multiple (many) particles 6.

[0015] 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. The polymer composition may also contain a flame retardant.

[0016] 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.

[0017] The shape of the magnetic material is not limited to a sheet. Magnetic materials can have shapes such as rings, cubes, rectangular parallelepipeds, and cylinders. Furthermore, this powder is suitable for magnetic materials with more complex shapes.

[0018] In the magnetic sheet 2 (magnetic member), the frequency FR at which tanδ (μ'' / μ'), expressed as the ratio of the real permeability μ' to the imaginary permeability μ'', reaches 0.1 is preferably 800 MHz or higher. A magnetic sheet 2 with this frequency FR of 800 MHz or higher sufficiently absorbs electromagnetic wave noise in the high-frequency range. From this viewpoint, this frequency FR is preferably 900 MHz or higher, and particularly preferably 965 MHz or higher.

[0019] [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.

[0020] The flattened particles 6 exhibit 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, making relaxation of the real permeability μ' less likely. In this magnetic sheet 2, the frequency FR at which tanδ(μ'' / μ'), expressed as the ratio of the real permeability μ' to the imaginary permeability μ'', reaches 0.1 is high. This magnetic sheet 2 can absorb electromagnetic noise in the high-frequency range.

[0021] The average Tav of the thickness T1 is preferably 3.0 μm or less. Eddy current loss is suppressed in a magnetic sheet 2 containing powder with an average thickness Tav of 3.0 μm or less. The frequency FR of this magnetic sheet 2, at which tanδ (μ'' / μ') reaches 0.1, is high. From this viewpoint, an average thickness Tav of 2.5 μm or less is more preferable, and 2.0 μm or less is particularly preferable. From the viewpoint of ease of powder manufacturing, an average thickness Tav of 0.1 μm or more is preferred, 0.5 μm or more is more preferable, and 1.0 μm or more is particularly preferable.

[0022] The aspect ratio of this powder is preferably 1.5 or more and 100 or less. In a magnetic sheet 2 containing powder with an aspect ratio of 1.5 or more, the real permeability μ' and imaginary permeability μ'' in the high-frequency range are sufficiently large. From this viewpoint, an aspect ratio of 5 or more is particularly preferred. In a magnetic sheet 2 containing powder with an aspect ratio of 100 or less, the areas where particles 6 come into contact with each other are suppressed, and losses due to eddy currents are suppressed. From this viewpoint, an aspect ratio of 80 or less is particularly preferred.

[0023] For measuring the length L1, thickness T1, and aspect ratio, a resin-embedded sample is used that allows observation of the thickness direction of the flattened particles 6. This sample is polished, and the polished surface is observed using a scanning electron microscope (SEM). The magnification of the image during observation is 500x. In the analysis of this image, the image data is binarized. When the binarized image is approximated as an ellipse, the length of the major axis is the length L1, the length of the minor axis is the thickness T1, and the ratio of the two (length of the major axis / length of the minor axis) is the aspect ratio of each particle 6. These results are given an arithmetic mean to calculate the average thickness Tav and aspect ratio of the powder.

[0024] [Particle Material] The material of the flattened particles 6 is an Fe-based alloy. This Fe-based alloy contains Ni: 25.0% to 40.0% by mass, Al: 3.0% to 15.0% by mass, Ti: 0.1% to 10.0% by mass, Cu: 0% to 10.0% by mass, and unavoidable impurities.

[0025] This Fe-based alloy preferably contains Ni: 25.0% to 40.0% by mass, Al: 3.0% to 15.0% by mass, Ti: 0.1% to 10.0% by mass, and Cu: 0% to 10.0% by mass, with the remainder being Fe and unavoidable impurities.

[0026] [Method for Manufacturing Powder] In the manufacture of powder, first, the raw material powder is prepared. The raw material powder can be obtained by gas atomization, water atomization, disc atomization, pulverization, etc. Gas atomization and disc atomization are preferred. In gas atomization, the raw material metal is heated and melted to obtain molten metal. This molten metal flows out of a nozzle. Gas (argon gas, nitrogen gas, etc.) is blown onto this molten metal. Due to the energy of this gas, the molten metal is pulverized into droplets and cooled as they fall. These droplets solidify, and particles are formed. In this gas atomization method, the molten metal instantly turns into droplets and cools at the same time, so a uniform microstructure can be obtained. Moreover, since droplets are formed continuously, the difference in composition between particles is extremely small. In disc atomization, the raw material metal is heated and melted to obtain molten metal. This molten metal flows out of a nozzle. This molten metal is dropped onto a disc that rotates at high speed. The molten metal is rapidly cooled and solidified, yielding particles.

[0027] This raw material powder is subjected to classification and heat treatment as needed. Furthermore, this raw material powder is flattened. Typical flattening is performed using an attritor. The flattened powder is then subjected to classification and other treatments as needed.

[0028] This powder is subjected to heat treatment. The preferred heat treatment is aging treatment. In aging treatment, the powder is held at a high temperature. The holding temperature is preferably 500°C to 800°C, and particularly preferably 550°C to 750°C. The holding time is preferably 1 hour to 6 hours, and particularly preferably 1 hour to 5 hours. After holding, the powder is slowly cooled. Aging treatment may be performed prior to flattening.

[0029] [Metallic Structure] The structure of the alloy before aging is martensite. This martensite is a supersaturated solid solution. Through aging, the structure decomposes into a ferromagnetic phase α1 containing a large amount of Fe and a weakly magnetic phase α2 containing Ni, Al, and Ti. This decomposition is called spinodal decomposition. The structure after spinodal decomposition has a periodic modulated structure. The period of this structure is on the nano-order. The period of this structure is smaller than that of the deposition type structure. In powder having this structure, the ferromagnetic phase α1 is separated by the weakly magnetic phase α2, so the reversal of the magnetic moment is prevented. The coercivity of this powder is high. The frequency FR at which the tanδ (μ'' / μ') of the magnetic sheet 2 containing this powder reaches 0.1 is high. This magnetic sheet 2 can absorb electromagnetic noise in the high-frequency range.

[0030] During flattening, stress is applied to the particle structure. When spinodal decomposition occurs in the flattened particles, a large magnetoelastic effect is achieved due to the stress applied to the ferromagnetic phase α1, resulting in a large coercivity. A magnetic component containing this powder can achieve a high frequency FR.

[0031] [Specific RA] The specific RA of magnetic powder is calculated using the following formula: RA = Fe% / (Ni% + Al% + Ti% + Cu%). In this formula, Fe%, Ni%, Al%, Ti%, and Cu% represent the atomic content of Fe, Ni, Al, Ti, and Cu in the Fe-based alloy, respectively.

[0032] The relative RA is preferably 0.980 or more and 1.020 or less. In powders with a relative RA of 0.980 or more, a sufficient ferromagnetic phase α1 is generated by spinodal decomposition. This powder has excellent magnetic properties. From this viewpoint, a relative RA of 0.985 or more is more preferable, and 0.990 or more is particularly preferable. In powders with a relative RA of 1.020 or less, the ferromagnetic phase α1 generated by spinodal decomposition is not excessive. Magnetization reversal is less likely to occur in this powder. From this viewpoint, a relative RA of 1.015 or less is more preferable, and 1.010 or less is particularly preferable.

[0033] [Saturation Magnetization Ms] The saturation magnetization Ms of the magnetic powder is preferably 0.8 T or higher. The frequency FR at which the tanδ (μ'' / μ') of the magnetic sheet 2 containing this powder reaches 0.1 is high. This magnetic sheet 2 can absorb electromagnetic noise in the high-frequency range. From this viewpoint, the saturation magnetization Ms is more preferably 0.9 T or higher, and particularly preferably 1.0 T or higher. The saturation magnetization Ms is measured using a vibrating sample magnetometer (VSM). The measurement conditions are as follows: Maximum applied magnetic field: 1204 kA / m Mass of powder: approximately 70 mg

[0034] [Coercivity iHc] The coercivity iHc of the magnetic powder is preferably 20 kA / m or higher. The frequency FR at which the tanδ (μ'' / μ') of the magnetic sheet 2 containing this powder reaches 0.1 is high. This magnetic sheet 2 can absorb electromagnetic noise in the high-frequency range. From this viewpoint, the coercivity iHc is more preferably 22 kA / m or higher, and particularly preferably 24 kA / m or higher. The coercivity iHc is the strength of the external magnetic field required to return a magnetized magnetic material to an unmagnetized state. The coercivity is measured using a vibrating sample magnetometer (VSM). The measurement conditions are the same as those for measuring saturation magnetization Ms. The direction of the applied magnetic field is the longitudinal direction of the flattened particle 6.

[0035] [Median Diameter D50] From the viewpoint of obtaining a homogeneous magnetic sheet 2 with a smooth surface, the median diameter D50 of the powder is preferably 90 μm or less, more preferably 80 μm or less, and particularly preferably 70 μm or less. A median diameter D50 of 10 μm or more is preferred. The median diameter D50 is the particle diameter at the point where the cumulative curve reaches 50% when the cumulative curve is determined with the total volume of the powder as 100%. The median diameter D50 is measured, for example, by Nikkiso's laser diffraction / scattering particle size distribution analyzer "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 the particles 6.

[0036] [Tap Density TD] From the viewpoint of obtaining a homogeneous magnetic sheet 2 with a smooth surface, the tap density TD of the powder is 2.5 g / cm³. ３ The following is preferable: 2.3 g / cm³ ３The following is more preferable: 2.1 g / cm³ ３ The following is particularly preferred: Tap density TD is 0.3 g / cm³. ３ The above is preferable. The tap density TD is measured in accordance with the provisions of "JIS Z 2512:2012". In the measurement, approximately 40 g of powder is used in a volume of 100 cm³. ３ It is filled into a cylinder. The measurement conditions are as follows: • Drop height: 50 mm • Number of taps: 200

[0037] [Elements] The role of each element is explained in detail below.

[0038] [Ni (Nickel)] Ni forms the Fe-Ni martensite phase. Ni is essential for the formation of the weakly magnetic phase α2. The coercivity iHc of powder containing Ni is high. From this viewpoint, the Ni content is preferably 25.0 mass% or more, more preferably 28.0 mass% or more, and particularly preferably 30.0 mass% or more. Excess Ni leads to retained austenite after aging treatment. Retained austenite reduces the saturation magnetization Ms of the powder and reduces the frequency FR of the magnetic sheet 2. From the viewpoint of achieving a high frequency FR, the Ni content is preferably 40.0 mass% or less, more preferably 38.0 mass% or less, and particularly preferably 36.0 mass% or less.

[0039] [Al (Aluminum)] Al is essential for the formation of the weakly magnetic phase α2. Al increases the resistivity of particle 6 and reduces eddy current loss. From this viewpoint, the Al content is preferably 3.0 mass% or more, more preferably 4.0 mass% or more, and particularly preferably 5.0 mass% or more. Excess Al lowers the saturation magnetization Ms and lowers the frequency FR. From the viewpoint of achieving a high frequency FR, the Al content is preferably 15.0 mass% or less, more preferably 14.0 mass% or less, and particularly preferably 13.0 mass% or less.

[0040] [Ti (Titanium)] Ti is mainly dissolved in the weakly magnetic phase α2. The saturation magnetization of the weakly magnetic phase α2 in which Ti is dissolved is low. In alloys containing Ti, the difference between the saturation magnetization of the ferromagnetic phase α1 and the saturation magnetization of the weakly magnetic phase α2 is large. The coercivity iHc of this powder is large. A magnetic member with a high frequency FR can be obtained with this powder. From this viewpoint, the Ti content is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and particularly preferably 0.5 mass% or more. Excess Ti leads to a rapid decrease in the saturation magnetization Ms of the powder, which lowers the frequency FR of the magnetic sheet 2. From the viewpoint of achieving a high frequency FR, the Ti content is preferably 10.0 mass% or less, more preferably 9.0 mass% or less, and particularly preferably 8.0 mass% or less.

[0041] [Cu (copper)] Like Ti, Cu mainly dissolves in the weakly magnetic phase α2. The saturation magnetization of the weakly magnetic phase α2 in which Cu is dissolved is low. In alloys containing Cu, the difference between the saturation magnetization of the ferromagnetic phase α1 and the saturation magnetization of the weakly magnetic phase α2 is large. The coercivity iHc of this powder is large. A magnetic member with a high frequency FR can be obtained with this powder. From these viewpoints, the Cu content is preferably 0 mass% or more, more preferably 1.0 mass% or more, and particularly preferably 2.0 mass% or more. Excess Cu leads to retained austenite after aging. Retained austenite reduces the saturation magnetization Ms of the powder and reduces the frequency FR of the magnetic sheet 2. From the viewpoint of achieving a high frequency FR, the Cu content is preferably 10.0 mass% or less, more preferably 9.0 mass% or less, and particularly preferably 8.0 mass% or less. Cu is not essential in this alloy. Therefore, the alloy does not need to contain Cu other than unavoidable impurities. In other words, the Cu content may be substantially zero.

[0042] [Fe (Iron)] Fe is the main component of this alloy. Fe is dissolved in the ferromagnetic phase α1. Fe can contribute to the magnetic properties of the powder. From this viewpoint, the Fe content is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 45% by mass or more. From the viewpoint that the alloy can sufficiently contain Ni, Al, Ti, or Cu, the Fe content is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and particularly preferably 60% by mass or less.

[0043] [Another aspect] The present disclosure is also directed to a method for manufacturing magnetic powder. This method includes: (1) a step of preparing a raw material powder which is an Fe-based alloy containing Ni: 25.0 mass% or more and 40.0 mass% or less, Al: 3.0 mass% or more and 15.0 mass% or less, Ti: 0.1 mass% or more and 10.0 mass% or less, Cu: 0 mass% or more and 10.0 mass% or less, and inevitable impurities; (2) a step of performing flattening processing on this powder; and (3) a step of performing aging treatment on this powder to cause spinodal decomposition in the metal structure of the powder.

[0044] The present disclosure is also directed to a magnetic member. This magnetic member has a matrix 4 whose base material is a polymer and magnetic powder dispersed in this matrix 4. This magnetic powder includes a large number of flat particles 6. These particles 6 are composed of an Fe-based alloy containing Ni: 25.0 mass% or more and 40.0 mass% or less, Al: 3.0 mass% or more and 15.0 mass% or less, Ti: 0.1 mass% or more and 10.0 mass% or less, Cu: 0 mass% or more and 10.0 mass% or less, and inevitable impurities. For this magnetic member, the ratio RA calculated by the following formula: RA = Fe% / (Ni% + Al% + Ti% + Cu%) is 0.980 or more and 1.020 or less. In this formula, Fe%, Ni%, Al%, Ti%, and Cu% respectively represent the atomic content rates of Fe, Ni, Al, Ti, and Cu in the Fe-based alloy.

[0045] Hereinafter, the effects of the magnetic powder according to the examples will be clarified, but the scope disclosed in this specification should not be construed restrictively based on the description of these examples.

[0046] [Example 1] A raw material powder was obtained by gas atomization and classification. This raw material powder was subjected to flattening processing using a wet attritor. Further, this powder was subjected to aging treatment to produce the powder of Example 1 having the composition shown in Table 1 below. By the aging treatment, spinodal separation occurred, and a ferromagnetic phase α1 and a paramagnetic phase α2 were generated. The median diameter D50, tap density TD, average thickness Tav, saturation magnetization Ms, and coercive force iHc of this powder are shown in Table 2 below.

[0047] [Examples 2-9 and Comparative Examples 1-9] Powders for Examples 2-9 and Comparative Examples 1-9 were prepared in the same manner as in Example 1, except that the composition was as shown in Table 1 below.

[0048] [Measurement of Frequency FR] A resin composition was obtained by mixing 20 parts by mass of powder with 100 parts by mass of base resin. A sheet for magnetic components was molded from this resin composition. Strip-shaped test pieces with a width of 4 mm and a length of 35 mm were cut from this magnetic sheet. Using these test pieces, the relative permeability at room temperature from 1 MHz to 9 GHz was measured with a PMM-9G1 (manufactured by Ryowa Electronics), and the frequency FR at which tanδ (μ'' / μ') reached 0.1 was calculated. The results are shown in Table 2 below.

[0049]

[0050]

[0051] As shown in Table 2, magnetic members with high frequency FR can be obtained from the powders of each example. The superiority of this magnetic powder is clear from these evaluation results.

[0052] The powders described above are suitable for various magnetic materials.

[0053] 2: Magnetic sheet, 4: Matrix, 6: Particles

Claims

1. A magnetic powder comprising a plurality of flattened particles, wherein the flattened particles are composed of an Fe-based alloy containing Ni: 25.0% by mass or more and 40.0% by mass or less, Al: 3.0% by mass or more and 15.0% by mass or less, Ti: 0.1% by mass or more and 10.0% by mass or less, Cu: 0% by mass or more and 10.0% by mass or less, and unavoidable impurities, and the ratio RA calculated by the following formula: RA = Fe% / (Ni% + Al% + Ti% + Cu%) (wherein Fe%, Ni%, Al%, Ti%, and Cu% represent the atomic content of Fe, Ni, Al, Ti, and Cu in the Fe-based alloy, respectively) is 0.980 or more and 1.020 or less.

2. The magnetic powder according to claim 1, wherein the Fe-based alloy has a structure obtained by spinodal decomposition.

3. The magnetic powder according to claim 2, wherein the structure comprises a ferromagnetic phase α1 containing Fe and a weakly magnetic phase α2 containing Ni, Al, and Ti.

4. The magnetic powder according to claim 1 or 2, wherein the average thickness Tav of the particles is 3.0 μm or less.

5. The magnetic powder according to claim 1 or 2, wherein the saturation magnetization Ms is 0.8 T or higher.

6. The magnetic powder according to claim 1 or 2, wherein the coercivity iHc is 20 kA / m or more.

7. A polymer composition comprising a base polymer and a powder dispersed in the base polymer, wherein the powder has a plurality of flattened particles, and the flattened particles are composed of an Fe-based alloy containing Ni: 25.0% by mass or more and 40.0% by mass or less, Al: 3.0% by mass or more and 15.0% by mass or less, Ti: 0.1% by mass or more and 10.0% by mass or less, Cu: 0% by mass or more and 10.0% by mass or less, and unavoidable impurities, and the ratio RA calculated by the following formula: RA = Fe% / (Ni% + Al% + Ti% + Cu%) (wherein Fe%, Ni%, Al%, Ti%, and Cu% represent the atomic content of Fe, Ni, Al, Ti, and Cu in the Fe-based alloy, respectively) is 0.980 or more and 1.020 or less.

Images