Magnetic powder, dust core, and method for recycling dust core

Abstract

Provided is a magnetic powder containing soft magnetic particles each having an insulating coating film on the surface thereof. When soft magnetic particles having a diameter greater than or equal to the 10% cumulative particle diameter in the number-based particle size distribution of the magnetic powder measured by a laser diffraction particle size distribution method are selected from among the soft magnetic particles as measurement targets for the average circularity and the average envelope degree, the average circularity of the measurement-target soft magnetic particles is greater than or equal to 0.20 and the average envelope degree of the measurement-target soft magnetic particles is greater than or equal to 0.45.

Description

Method for recycling magnetic powder, compacted magnetic core, and compacted magnetic core.

[0001] This disclosure relates to magnetic powder, compacted magnetic core, and a method for recycling compacted magnetic core.

[0002] As a magnetic core for electromagnetic components, a compacted magnetic core formed by compression molding of magnetic powder is sometimes used. Examples of particles constituting the magnetic powder include soft magnetic metal particles whose surfaces are coated with an insulating coating. For example, Patent Document 1 describes how a compacted magnetic core that can achieve both voltage resistance and magnetic properties can be obtained using a soft magnetic metal powder that contains a plurality of soft magnetic metal particles containing Fe, wherein the surface of the soft magnetic metal particles is covered with an insulating coating, and the coating contains soft magnetic metal fine particles.

[0003] Japanese Patent Publication No. 2019-160942

[0004] Efforts are underway to recycle used powdered magnetic cores in order to achieve carbon neutrality and a circular economy. However, a problem has arisen: recycled powdered magnetic cores have greater iron loss (energy loss) compared to the original powdered magnetic cores.

[0005] One aspect of this disclosure is to provide a magnetic powder that can suppress the increase in iron loss in compacted magnetic cores due to recycling.

[0006] The inventors investigated the relationship between the average circularity and average envelope of soft magnetic particles contained in magnetic powder and the increase in iron loss of compacted magnetic cores due to recycling. They found that when the average circularity of the soft magnetic particles is high (close to a spherical shape) and the average envelope is high (the degree of unevenness (surface roughness) of the particles is small), the increase in iron loss of compacted magnetic cores due to recycling can be suppressed. The inventors surmise that in compacted magnetic cores using soft magnetic particles with high average circularity and average envelope, when the compacted magnetic core is crushed and the resulting powder is pressed and reshaped, damage to the insulating coating of the particles due to collisions between particles can be reduced. As a result, eddy current loss caused by damage to the insulating coating can be reduced, and the increase in iron loss of compacted magnetic cores due to recycling can be suppressed. However, when measuring the average circularity and average envelope of the soft magnetic particles as described above, it is necessary to measure soft magnetic particles having a diameter of 10% cumulative particle diameter (D10) or more in the particle size distribution based on the number of particles of the magnetic powder.

[0007] This disclosure includes the following aspects: [1] A magnetic powder containing soft magnetic particles having an insulating coating on its surface, wherein, when the average circularity and average envelope of the soft magnetic particles are measured using the laser diffraction particle size distribution method and the soft magnetic particles having a diameter of 10% cumulative particle diameter or more in the particle size distribution of the magnetic powder based on the number of particles measured, the average circularity of the measured soft magnetic particles is 0.20 or more, and the average envelope of the measured soft magnetic particles is 0.45 or more. [2] The magnetic powder according to [1], wherein the standard deviation of the average circularity of the measured soft magnetic particles is 0.30 or less. [3] The magnetic powder according to [1] or [2], wherein the standard deviation of the average envelope of the measured soft magnetic particles is 0.20 or less. [4] A compacted magnetic core containing the magnetic powder according to any one of [1] to [3]. A method for recycling a powdered magnetic core, comprising: a first step of crushing a powdered magnetic core containing the magnetic powder described in any one of [5] [1] to [3] to obtain recycled powder; a second step of compressing and molding the recycled powder to obtain a molded body; and a third step of heating the molded body to obtain a powdered magnetic core.

[0008] According to one aspect of this disclosure, it is possible to provide a magnetic powder that can suppress the increase in iron loss in compacted magnetic cores due to recycling.

[0009] This is a schematic diagram illustrating the envelope degree of a particle cross-section.

[0010] The embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the embodiments described below.

[0011] The magnetic powder according to this embodiment contains soft magnetic particles having an insulating coating on its surface. The soft magnetic particles may contain metal particles as core particles, and the surface of the metal particles (core particles) may have an insulating coating. The metal constituting the metal particles may be pure iron or an iron-containing alloy. Examples of iron-containing alloys include Fe-Cr alloy (stainless steel), Fe-Ni-Cr alloy (stainless steel), Fe-Si alloy (e.g., Fe-3Si alloy), Fe-Si-Al alloy (Sendust), Fe-Ni alloy (Permalloy), Fe-Cu-Ni alloy (Permalloy), Fe-Co alloy, Fe-Co-V alloy (Permendur), Fe-Cr-Si alloy (electromagnetic stainless steel), Fe-Ni-Mn-C alloy (Invar), etc. The soft magnetic particles may contain metal particles as core particles, composed of at least one metal selected from the group consisting of pure iron and Fe-Si alloy. The metal particles constituting the soft magnetic particles may be amorphous, or they may be particles containing an Fe amorphous alloy or an alloy with a nanocrystalline structure.

[0012] The soft magnetic particles may have an insulating coating covering a portion of their surface, or they may have an insulating coating covering their entire surface. From the viewpoint of exhibiting high insulation properties and further reducing eddy current losses in the compacted magnetic core, it is preferable that the soft magnetic particles have an insulating coating covering their entire surface.

[0013] The insulating coating may contain insulating materials (insulating inorganic materials and insulating organic materials). Examples of insulating materials include phosphates, silicate glass, silicone resins, metal oxides, metal nitrides, and metal carbides. The metal elements contained in the metal oxides, metal nitrides, and metal carbides may be at least one selected from the group consisting of Fe, Al, Ca, Mn, Zn, Mg, V, Cr, Y, Ba, Sr, Zr, and rare earth elements (excluding Y).

[0014] The insulating coating may consist of a single insulating coating or multiple insulating coatings. If the insulating coating consists of multiple insulating coatings, it may consist of an insulating coating containing phosphate and an insulating coating containing silicone resin. In this case, the insulating coating containing phosphate and the insulating coating containing silicone resin may be arranged in this order from the inside (the side closer to the core particles).

[0015] The phosphate may contain at least one element selected from the group consisting of B, Co, Na, S, Si, and W.

[0016] The thickness of the insulating coating may be 1 nm or more, 2 nm or more, or 3 nm or more, from the viewpoint of being able to insulate between soft magnetic particles well and further reducing eddy current losses in the compacted magnetic core. The thickness of the insulating coating may be 300 nm or less, from the viewpoint of the compacted magnetic core being able to easily have an appropriate density and being able to easily maintain a good magnetic flux density. When the insulating coating is composed of multiple insulating coatings, the thickness of each insulating coating constituting the insulating coating may be within the above range, or the total thickness of the multiple insulating coatings may be within the above range. When the insulating coating is formed non-uniformly on the surface of the core particles, the minimum thickness of the insulating coating may be within the above range. In this specification, the thickness of the insulating coating is determined by observing the particle cross-section with a scanning electron microscope (product name: SU5000 (manufactured by Hitachi High-Tech Corporation)) and measuring the thickness of the insulating coating from the observed image.

[0017] The content of soft magnetic particles may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more by mass, based on the total amount of magnetic powder, from the viewpoint of further suppressing the increase in iron loss of the compacted magnetic core due to recycling. The content of soft magnetic particles may be 99.9% or less by mass, or 99% or less by mass, based on the total amount of magnetic powder. The magnetic powder may consist only of soft magnetic particles.

[0018] The 10% cumulative particle size (D10) in the volume-based particle size distribution of the magnetic powder may be 10 μm or more, 20 μm or more, or 30 μm or more, and may be 300 μm or less, 250 μm or less, 200 μm or less, 170 μm or less, or 150 μm or less. In this specification, the particle size distribution (volume-based and number-based) of the magnetic powder is measured by a laser diffraction particle size distribution analyzer.

[0019] The 50% cumulative particle size (D50) in the volume-based particle size distribution of the magnetic powder may be 10 μm or more, 30 μm or more, or 50 μm or more, and may be 400 μm or less, 300 μm or less, or 280 μm or less.

[0020] The 90% cumulative particle size (D90) in the volume-based particle size distribution of the magnetic powder may be 30 μm or more, 50 μm or more, or 80 μm or more, and may be 700 μm or less, 500 μm or less, or 450 μm or less.

[0021] In the particle size distribution of magnetic powder based on particle count, D10 may be 5 μm or more, 10 μm or more, or 20 μm or more, and may be 200 μm or less, 150 μm or less, or 100 μm or less.

[0022] In the particle size distribution of magnetic powder based on particle count, D50 may be 20 μm or more, 30 μm or more, or 40 μm or more, and may be 300 μm or less, 250 μm or less, or 200 μm or less.

[0023] In the particle size distribution of magnetic powder based on particle count, D90 may be 30 μm or more, 50 μm or more, or 60 μm or more, and may be 400 μm or less, 350 μm or less, or 300 μm or less.

[0024] In this embodiment, the magnetic powder is characterized by the following characteristics: when soft magnetic particles having a diameter of 10% or more in the particle size distribution based on the number of particles measured by the laser diffraction particle size distribution method are used as the target for measuring the average circularity and average envelope of the measured soft magnetic particles, the average circularity of the measured soft magnetic particles is 0.20 or higher, and the average envelope of the measured soft magnetic particles is 0.45 or higher. In this specification, the "diameter" of a soft magnetic particle refers to the diameter of the particle cross-section of the soft magnetic particle, as described later. Furthermore, when the particle cross-section is not perfectly circular, the "diameter" of the particle cross-section refers to the maximum diameter of the particle cross-section.

[0025] The following describes a method for calculating the average circularity and average envelope of soft magnetic particles to be measured. The method for calculating the average circularity and average envelope of soft magnetic particles to be measured comprises a preparation step of polishing the surface of a sample containing magnetic powder and embedding resin, an observation step of observing the polished surface with a microscope, and a calculation step of calculating the average circularity and average envelope for the soft magnetic particles to be measured within the observed surface.

[0026] In the preparation step, a sample containing magnetic powder and embedding resin is prepared. The embedding resin may contain a thermoplastic resin or a cured thermosetting resin. The thermoplastic resin is not particularly limited and includes, for example, polyolefin resins and polyester resins. The thermosetting resin is not particularly limited and includes, for example, epoxy resins and phenolic resins. If a cured thermosetting resin is included, the sample may be obtained by mixing the magnetic powder, thermosetting resin and curing agent, and curing the thermosetting resin. The curing agent is not particularly limited and includes, for example, imidazole-based curing agents.

[0027] The method for polishing the surface of the sample is not particularly limited; for example, it may be polished using a rotary polishing machine.

[0028] In the observation step, the polished surface (the surface exposed by polishing) of the sample obtained in the preparation step is observed with a microscope. The observation surface may be acquired as image data. For example, measurement is performed using a VHX-8000 (manufactured by Keyence Corporation) as the microscope. The observation magnification of the microscope may be appropriately adjusted within a range where cross-sections of a plurality of soft magnetic particles can be observed; for example, it may be 80 times or more, and may be 500 times or less.

[0029] In the calculation step, the average circularity and average envelope degree are calculated for cross-sections of the soft magnetic particles observed in the observation step. As analysis software used for calculation, for example, analysis software attached to the aforementioned microscope (product names: "(1) 3D shape measurement software VHX-H5M, (2) XY measurement software VHX-H3M3", manufactured by Keyence Corporation) may be used. At this time, the average circularity and average envelope degree are calculated for particle cross-sections 10 having a diameter equal to or larger than the 10% cumulative particle diameter (D10) in the number-based particle size distribution of the magnetic powder measured by the laser diffraction particle size distribution method.

[0030] For cross-sections having a diameter smaller than D10 in the number-based particle size distribution of the magnetic powder, it is difficult to appropriately grasp the shape and the degree of irregularities on the outer periphery due to the resolution limit of the microscope. Therefore, even if such a cross-section is not circular and has many irregularities on the outer periphery, the analysis may determine that it is circular and has few irregularities. As a result, when all particle cross-sections in the observation surface are targeted, the average circularity and average envelope degree approximate 1 regardless of the characteristics of the cross-section, making it difficult to appropriately calculate the average circularity and average envelope degree. Based on the above, by calculating the average circularity and average envelope degree targeting particle cross-sections 10 whose diameter is equal to or larger than D10 in the number-based particle size distribution of the magnetic powder, the shape of the soft magnetic particles and the degree of surface irregularities can be evaluated more appropriately.

[0031] When calculating the average circularity and average envelope degree of the soft magnetic particles, from the perspective of more appropriate calculation, particle cross-sections that are partially missing at the edge of the observation area may be excluded from the particle cross-sections 10 when calculating the average circularity and average envelope degree.

[0032] The average circularity of soft magnetic particles is an index used to evaluate how close the overall shape of the soft magnetic particles is to a sphere. The closer the average circularity of the soft magnetic particles is to 1, the closer the overall shape of the soft magnetic particles is to a sphere. In this specification, the average circularity of the soft magnetic particles to be measured is the average value of the circularity calculated for each particle cross-section 10 using the following formula (1). Here, S represents the area of ​​the particle cross-section 10 observed with a microscope, and L represents the perimeter of the particle cross-section 10 observed with a microscope. Circularity = 4πS / L ２ (1)

[0033] The average circularity of the soft magnetic particles to be measured may be 0.21 or higher, 0.22 or higher, 0.23 or higher, 0.24 or higher, or 0.27 or higher, preferably 0.30 or higher, 0.36 or higher, 0.38 or higher, or 0.44 or higher, from the viewpoint of further suppressing the increase in iron loss of the compacted magnetic core due to recycling. The average circularity of the soft magnetic particles to be measured may be 0.99 or lower, 0.90 or lower, or 0.80 or lower, from the viewpoint of improving the mechanical strength of the compacted magnetic core.

[0034] The standard deviation of the average circularity of the soft magnetic particles to be measured may be 0.01 or greater, or 0.02 or greater. From the viewpoint of further suppressing the increase in iron loss in the compacted magnetic core due to recycling, the standard deviation of the average circularity of the soft magnetic particles to be measured may be 0.30 or less, 0.27 or less, 0.25 or less, 0.24 or less, 0.22 or less, 0.21 or less, 0.20 or less, or 0.18 or less.

[0035] The average envelope of soft magnetic particles is an index used to evaluate the overall degree of surface irregularity of soft magnetic particles. The closer the average envelope of soft magnetic particles is to 1, the less overall surface irregularity the soft magnetic particles have. Figure 1 is a schematic diagram illustrating the envelope of a particle cross-section. In this specification, the envelope of the particle cross-section 10 in Figure 1 refers to the area of ​​the particle cross-section 10 observed with a microscope as A Ｐ Let A be the envelope area enclosed by the imaginary envelope line M that is tangent to the convex portion of the particle cross-section 10. Ｅ In that case, A Ｐ / A Ｅmeans the value given by . In the present specification, the average envelope degree of the soft magnetic particles to be measured is the average value of the envelope degrees of each particle cross section 10. By using the above analysis software, A in each particle cross section 10 Ｐ / A Ｅ is calculated, and the average envelope degree of the soft magnetic particles is obtained. As is clear from the above, the average circularity is an indicator of the degree of sphericity of the particle shape, whereas the average envelope degree is an indicator of the degree of unevenness on the particle surface, and the average circularity and the average envelope degree are different evaluation indicators.

[0036] From the viewpoint of further suppressing an increase in iron loss of the dust core due to recycling, the average envelope degree of the soft magnetic particles to be measured may be 0.47 or more, 0.48 or more, 0.50 or more, or 0.52 or more, and preferably 0.60 or more, 0.70 or more, 0.80 or more, or 0.83 or more. From the viewpoint of improving the mechanical strength of the dust core, the average envelope degree of the soft magnetic particles to be measured may be 0.99 or less or 0.95 or less.

[0037] The standard deviation of the average envelope degree of the soft magnetic particles to be measured may be 0.01 or more, 0.02 or more, or 0.03 or more. From the viewpoint of further suppressing an increase in iron loss of the dust core due to recycling, the standard deviation of the average envelope degree of the soft magnetic particles to be measured may be 0.20 or less, 0.15 or less, or 0.12 or less.

[0038] The magnetic powder may be obtained by a production method including a step of mixing metal powder containing metal particles and an insulating material to obtain a mixed powder, and a step of drying the mixed powder. The metal particles and the insulating material may be the same as those described above. The temperature for drying the mixed powder (drying temperature) may be 50°C or higher, 100°C or higher, and may be 300°C or lower. The time for drying the mixed powder (drying time) may be 10 minutes or more, and may be 1 hour or less. The method for producing the magnetic powder may further include a step of crushing the mixed powder after the step of drying the mixed powder.

[0039] When the insulating coating is composed of a plurality of insulating coatings, the magnetic powder may be obtained by a manufacturing method including: a step of mixing metal powder containing metal particles with a first insulating material to obtain a first mixed powder; a step of drying the first mixed powder; a step of mixing the first mixed powder with a second insulating material to obtain a second mixed powder; and a step of drying the second mixed powder. In this case, the inner insulating coating (the side closer to the core particles) is an insulating coating formed of the first insulating material, and the outer insulating coating (the side farther from the core particles) is an insulating coating formed of the second insulating material.

[0040] The dust core according to the present embodiment may be obtained by a manufacturing method including: a molding step of compression-molding magnetic powder to obtain a molded body; and a heating step of heating the molded body.

[0041] In the molding step, the molding pressure may be 500 MPa or more, or 1000 MPa or more, and may be 2000 MPa or less, or 1500 MPa or less.

[0042] In the molding step, a lubricant may be added to the magnetic powder before compression molding. As the lubricant, any lubricant commonly used in compression molding may be used, and for example, it may be a stearic acid compound (lithium stearate, ethylene bisstearamide, etc.). The addition amount of the lubricant may be 0.1 parts by mass or more and 1 part by mass or less based on 100 parts by mass of the magnetic powder.

[0043] The bulk density of the molded body obtained in the molding step is 3 g / cm ３ or more, 5 g / cm ３ or more, or 7 g / cm ３ or more, and may be 20 g / cm ３ or less, 10 g / cm ３ or less, or 8 g / cm ３ or less.

[0044] In the heating step, the heating temperature of the molded body may be 300° C. or higher and 1000° C. or lower. The heating time of the molded body may be 10 minutes or more and 1 hour or less.

[0045] One embodiment of the present disclosure is a dust core including the above magnetic powder.

[0046] Compacted magnetic cores can have any shape suitable for their application. For example, compacted magnetic cores can be used as components in various devices selected from inductors, transformers, reactors, thyristor valves, noise filters (EMI filters), choke coils, motor cores, rotors or yokes, solenoid cores (fixed cores) for electromagnetic valves incorporated into electronically controlled fuel injection systems, position sensors, and magnetostrictive sensors.

[0047] The content of soft magnetic particles may be 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, and 100% by mass, based on the total amount of the compacted magnetic core. The content of soft magnetic particles may be 99.9% by mass or less, 90% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total amount of the compacted magnetic core.

[0048] The magnetic powder content may be 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, or 100% by mass, based on the total amount of the compacted magnetic core. The magnetic powder content may be 99.9% by mass or less, 90% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total amount of the compacted magnetic core.

[0049] The compacted magnetic core may contain other powders besides the magnetic powder mentioned above. Examples of other powders include non-magnetic powders. The content of the other powders may be 10% by mass or less, 1% by mass or less, or 0.1% by mass or less, based on the total amount of the compacted magnetic core.

[0050] One embodiment of the present disclosure is a method for recycling a powdered magnetic core, comprising: a first step of crushing a powdered magnetic core containing the above-mentioned magnetic powder to obtain recycled powder; a second step of compressing and molding the recycled powder to obtain a molded body; and a third step of heating the molded body to obtain a powdered magnetic core (recycled powdered magnetic core).

[0051] In the first step, the equipment used for grinding the compacted magnetic core includes a Wonder Crusher, screw mill, stamp mill, disc mill, pin mill, screen mill, cutter mill, and ball mill. The grinding time may be 1 minute or more and 15 minutes or less.

[0052] The details of the compacted magnetic core used in the first step may be the same as the details of the compacted magnetic core described above.

[0053] The recycled powder obtained in the first step includes the magnetic powder. The volume-based particle size distribution of the recycled powder, and the number-based particle size distribution of D10, D50, and D90, may be the same as those of the magnetic powder.

[0054] The recycled powder content may be 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, and 100% by mass, based on the total amount of recycled compacted magnetic core. The recycled powder content may be 99.9% by mass or less, 90% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total amount of recycled compacted magnetic core.

[0055] The details of the second step may be the same as the details of the molding step in the above-described method for manufacturing a powdered magnetic core. The details of the third step may be the same as the details of the heating step in the above-described method for manufacturing a powdered magnetic core.

[0056] The number of recycling cycles (the number of times the above recycling method is performed) may be one or multiple times, for example, two or more times.

[0057] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

[0058] <Preparation of Magnetic Powder> (Magnetic Powder 1) Commercially available pure iron powder (water atomized powder, product name "ABC100.30", manufactured by Höganäs AB) was prepared as core particles. A treatment solution was prepared containing 20 g of water glass (product name "No. 1C2", manufactured by Toso Sangyo Co., Ltd., solid content 51% by mass) per liter of water. Next, 100 g of pure iron powder, which had been pre-treated with a 235 mesh (mesh opening: 63 μm) sieve to remove particles smaller than 63 μm, was mixed with 30 mL of the treatment solution to obtain a mixed powder. This mixed powder was dried by heating at 200°C for 30 minutes. After drying, the mixed powder was crushed to obtain magnetic powder (iron-based soft magnetic powder) 1, which consists of soft magnetic particles (iron-based soft magnetic particles) having pure iron particles and a silicate glass coating as an insulating coating covering the surface of the pure iron particles. The silicate glass coating (insulating coating) was formed non-uniformly on the surface of the pure iron particles, and the minimum thickness of the silicate glass coating (insulating coating) was approximately 40 nm. Furthermore, the volume-based particle size distribution of magnetic powder 1 obtained by the method described later showed that D10, D50, and D90 were 76.6 μm, 133.5 μm, and 209.5 μm, respectively, and the number-based particle size distribution of magnetic powder 1 showed that D10, D50, and D90 were 52.7 μm, 80.9 μm, and 141.3 μm, respectively.

[0059] (Magnetic Powder 2) Commercially available pure iron powder (water atomized powder, product name "300NH", manufactured by Kobe Steel, Ltd.) was prepared as core particles. A treatment solution was prepared containing 21 g of phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 3 g of boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) per liter of water. 100 g of the pure iron powder and 15 mL of the treatment solution were mixed to obtain a mixed powder. This mixed powder was dried by heating at 150°C for 30 minutes. The dried mixed powder was crushed to obtain magnetic powder (iron-based soft magnetic powder) 2, which consists of soft magnetic particles (iron-based soft magnetic particles) having pure iron particles and a phosphate coating as an insulating coating covering the surface of the pure iron particles. The phosphate coating (insulating coating) was formed non-uniformly on the surface of the pure iron particles, and the thickness of the phosphate coating (insulating coating) was at least about 40 nm. Furthermore, the volume-based particle size distributions of magnetic powder 2 obtained by the method described later, D10, D50, and D90, were 139.7 μm, 258.4 μm, and 434.6 μm, respectively, and the number-based particle size distributions of magnetic powder 2, D10, D50, and D90, were 95.4 μm, 143.4 μm, and 249.6 μm, respectively.

[0060] (Magnetic Powder 3) Commercially available pure iron powder (water atomized powder, product name "300NH", manufactured by Kobe Steel, Ltd.) was prepared as core particles. A treatment solution was prepared containing 21 g of phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 3 g of boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) per liter of water. Next, 100 g of pure iron powder, which had been pre-treated with a 40-mesh (mesh opening: 405 μm) sieve to remove particles larger than 405 μm, was mixed with 7 mL of the treatment solution to obtain a mixed powder. This mixed powder was dried by heating at 150°C for 30 minutes. The dried mixed powder was crushed to obtain particles having pure iron particles and a phosphate coating as an insulating coating covering the surface of the pure iron particles. Next, a treatment solution was prepared containing 40 g of silicone resin (product name "SR2400 Resin", manufactured by Dow Toray Industries, Ltd., solids content 50% by mass) per liter of ethanol. 100 g of particles having the phosphate coating and 15 mL of a processing solution containing the silicone resin were mixed to obtain a mixed powder. This mixed powder was dried by heating at 70°C for 30 minutes, and then pulverized by crushing. The powder was then dried in a nitrogen atmosphere by heating at 180°C for 120 minutes. The dried mixed powder was crushed to obtain a magnetic powder (iron-based soft magnetic powder) 3 consisting of pure iron particles and soft magnetic particles (iron-based soft magnetic particles) having a phosphate coating and a silicone resin coating as insulating coatings covering the surface of the pure iron particles. The phosphate coating and silicone resin coating (insulating coating) were formed non-uniformly on the surface of the pure iron particles, and the total thickness of the insulating coating was at least about 45 nm. Furthermore, the volume-based particle size distributions of magnetic powder 3 obtained by the method described later showed that D10, D50, and D90 were 89.3 μm, 195.1 μm, and 394.3 μm, respectively, and the number-based particle size distributions of magnetic powder 3 showed that D10, D50, and D90 were 40.6 μm, 70.3 μm, and 148.2 μm, respectively.

[0061] (Magnetic Powder 4) Commercially available pure iron powder (water atomized powder, product name "ABC100.30", manufactured by Höganäs AB) was prepared as core particles. A treatment solution was prepared containing 21 g of phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 3 g of boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) per liter of water. Next, 100 g of pure iron powder, which had been pre-treated with a 149 mesh (mesh opening: 100 μm) sieve to remove particles larger than 100 μm, was mixed with 7 mL of the treatment solution to obtain a mixed powder. This mixed powder was dried by heating at 150°C for 30 minutes. The dried mixed powder was crushed to obtain particles having pure iron particles and a phosphate coating as an insulating coating covering the surface of the pure iron particles. Next, a treatment solution was prepared containing 40 g of silicone resin (product name "SR2400 Resin", manufactured by Dow-Toray Industries, Ltd., solid content 50% by mass) per liter of ethanol. 100 g of the phosphate-coated particles and 15 mL of the treatment solution containing the silicone resin were mixed to obtain a mixed powder. This mixed powder was dried by heating at 70°C for 30 minutes, and then pulverized by crushing. The powder was then dried under a nitrogen atmosphere by heating at 180°C for 120 minutes. The dried mixed powder was crushed to obtain a magnetic powder (iron-based soft magnetic powder) 4 consisting of pure iron particles and soft magnetic particles (iron-based soft magnetic particles) having a phosphate coating and a silicone resin coating as insulating coatings covering the surface of the pure iron particles. The phosphate coating and silicone resin coating (insulating coating) were formed non-uniformly on the surface of the pure iron particles, and the total thickness of the insulating coating was at least about 45 nm. Furthermore, the volume-based particle size distributions of magnetic powder 4 obtained by the method described later showed that D10, D50, and D90 were 37.3 μm, 59.3 μm, and 93.0 μm, respectively, while the number-based particle size distributions of magnetic powder 4 showed that D10, D50, and D90 were 28.3 μm, 41.8 μm, and 64.8 μm, respectively.

[0062] (Magnetic Powder 5) In the method for producing the magnetic powder 4, a magnetic powder (iron-based soft magnetic powder) 5 was prepared using the same procedure as above, except that pure iron powder was pre-treated with an 83-mesh (mesh opening: 180 μm) sieve to remove particles larger than 180 μm. This preparation consisted of soft magnetic particles (iron-based soft magnetic particles) having a phosphate coating and a silicone resin coating (the total thickness of the insulating coating was at least about 40 nm). Furthermore, the volume-based particle size distribution of the magnetic powder 5 obtained by the method described later showed D10, D50, and D90 to be 53.1 μm, 103.7 μm, and 175.3 μm, respectively, and the number-based particle size distribution of the magnetic powder 5 showed D10, D50, and D90 to be 30.6 μm, 49.8 μm, and 96.0 μm, respectively.

[0063] (Magnetic Powder 6) Magnetic powder 6 was obtained in the same manner as magnetic powder 2, except that commercially available pure iron powder (water atomized powder, product name "ABC100.30", manufactured by Höganäs AB) was prepared as core particles. Furthermore, the volume-based particle size distribution D10, D50, and D90 of magnetic powder 6, obtained by the method described below, were 59.3 μm, 112.1 μm, and 200.0 μm, respectively, and the number-based particle size distribution D10, D50, and D90 of magnetic powder 6 were 34.8 μm, 87.4 μm, and 136.9 μm, respectively.

[0064] (Magnetic Powder 7) Commercially available Fe-3Si alloy powder (gas atomized powder, product name "DAPMS3 (60)", manufactured by Daido Steel Co., Ltd., Si content: 3% by mass (based on the total amount of powder)) was prepared as core particles. A treatment solution containing 40 g of silicone resin (product name "SR2400 Resin", manufactured by Dow Toray Industries, Ltd., solid content 50% by mass) per liter of ethanol was prepared. 100 g of the Fe-3Si alloy powder and 25 mL of the treatment solution were mixed to obtain a mixed powder. This mixed powder was dried by heating at 70°C for 30 minutes, and then pulverized by crushing. The powder was then dried under a nitrogen atmosphere by heating at 180°C for 120 minutes. The dried mixed powder was crushed to obtain a magnetic powder (iron-based soft magnetic alloy powder) 7 consisting of soft magnetic particles (iron-based soft magnetic particles) having Fe-3Si alloy particles and a silicone resin coating as an insulating coating covering the surface of the Fe-3Si alloy particles. The silicone resin coating (insulating coating) was formed non-uniformly on the surface of the Fe-3Si alloy particles, and the thickness of the insulating coating was at least about 50 nm. Furthermore, the volume-based particle size distribution D10, D50, and D90 of the magnetic powder 7 obtained by the method described later were 91.2 μm, 131.2 μm, and 187.7 μm, respectively, and the number-based particle size distribution D10, D50, and D90 of the magnetic powder 7 were 74.5 μm, 103.1 μm, and 151.2 μm, respectively.

[0065] (Magnetic Powder 8) Magnetic powder (iron-based soft magnetic powder) 8 was obtained in the same manner as magnetic powder 7, except that commercially available Fe-3Si alloy powder (water atomized powder, product name "DAPMS3", manufactured by Daido Steel Co., Ltd., Si content: 3 mass% (based on the total amount of powder)) was prepared as core particles. The silicone resin coating (insulating coating) was formed non-uniformly on the surface of the Fe-3Si alloy particles, and the thickness of the insulating coating was at least about 45 nm. Furthermore, the volume-based particle size distribution of magnetic powder 8 obtained by the method described later, D10, D50, and D90 were 54.7 μm, 95.3 μm, and 157.8 μm, respectively, and the number-based particle size distribution of magnetic powder 8, D10, D50, and D90 were 35.4 μm, 56.2 μm, and 97.2 μm, respectively.

[0066] (Magnetic Powder 9) Magnetic powder (iron-based soft magnetic powder) 9 was obtained in the same manner as magnetic powder 7, except that commercially available Fe-3Si alloy powder (special atomized powder, product name "DAPMS3-B", manufactured by Daido Steel Co., Ltd., Si content: 3% by mass (based on the total amount of powder)) was prepared as core particles. The silicone resin coating (insulating coating) was formed non-uniformly on the surface of the Fe-3Si alloy particles, and the thickness of the insulating coating was at least about 45 nm. Furthermore, the volume-based particle size distribution of magnetic powder 9 obtained by the method described later, D10, D50, and D90 were 52.6 μm, 90.1 μm, and 139.2 μm, respectively, and the number-based particle size distribution of magnetic powder 9, D10, D50, and D90 were 30.8 μm, 51.9 μm, and 90.1 μm, respectively.

[0067] (Magnetic Powder 10) In the method for producing magnetic powder 2 described above, pure iron powder was pre-treated with an 83-mesh (mesh opening: 180 μm) sieve to remove particles smaller than 180 μm. In addition, the same procedure as for magnetic powder 2 was used to obtain magnetic powder (iron-based soft magnetic particles) consisting of pure iron particles and a phosphate coating as an insulating coating covering the surface of the pure iron particles. The phosphate coating (insulating coating) was formed non-uniformly on the surface of the pure iron particles, and the thickness of the phosphate coating (insulating coating) was at least about 45 nm. Furthermore, the volume-based particle size distributions of the magnetic powder 10 obtained by the method described later, D10, D50, and D90, were 191.5 μm, 316.4 μm, and 463.9 μm, respectively, and the number-based particle size distributions of the magnetic powder 10, D10, D50, and D90, were 135.4 μm, 187.5 μm, and 290.1 ​​μm, respectively.

[0068] (Magnetic Powder 11) In the method for producing the magnetic powder 9 described above, Fe-3Si alloy powder was pre-treated with a 140-mesh (mesh opening: 106 μm) sieve to remove particles larger than 106 μm, and the Fe-3Si alloy powder (special atomized powder) obtained was used in the same procedure as for magnetic powder 9. The silicone resin coating (insulating coating) was formed non-uniformly on the surface of the Fe-3Si alloy particles, and the thickness of the insulating coating was at least about 50 nm. Furthermore, the volume-based particle size distribution of magnetic powder 11 obtained by the method described later, D10, D50, and D90 were 29.6 μm, 62.4 μm, and 100.8 μm, respectively, and the number-based particle size distribution of magnetic powder 11, D10, D50, and D90 were 27.9 μm, 48.5 μm, and 67.2 μm, respectively.

[0069] <Measurement of Particle Size Distribution> 100 parts by mass of each magnetic powder 1 to 11 were dispersed in purified water together with 0.2 parts by mass of surfactant (product name "Ribonol T / 15", manufactured by Lion Corporation). The resulting dispersion was placed in the sample water tank of a laser diffraction particle size distribution analyzer (product name "SALD-2300", manufactured by Shimadzu Corporation). Next, the solution was circulated by pump while applying ultrasonic waves (pump flow rate was 65% of the maximum value), and the amount of water was adjusted so that the absorbance was 0.10 to 0.15. The particle size distribution based on volume and number was then measured. From the obtained volume-based and number-based particle size distributions, the particle sizes corresponding to D10, D50, and D90 of the sample were obtained.

[0070] <Measurement of Average Circularity and Average Envelopment> Cross-sectional samples were prepared by embedding each of the magnetic powders 1 to 11 in resin, curing, and then surface polishing using a rotary polishing machine. Next, using a digital microscope (product name "VHX-8000", manufactured by Keyence Corporation), the cross-sectional images of the particles were observed at an arbitrary magnification that allowed for the confirmation of the overall image of multiple particles, and image data of the particle cross-sections was acquired. Next, the acquired image data was analyzed using particle analysis software attached to the microscope device (product names "3D Shape Measurement Software VHX-H5M" and "XY Measurement Software VHX-H3M3", manufactured by Keyence Corporation), and the average circularity and average envelope were obtained. The procedure for particle analysis was as follows. First, the contrast on the analysis software was adjusted to clarify the particle contour. In addition, voids may have been created inside the particles to be analyzed due to surface polishing, etc., so the embedding process attached to the analysis software was performed. Furthermore, particle cross-sections that were partially missing at the edge of the extracted region of the image data may not allow for confirmation of the overall image of the particle cross-section, so these were removed from the particles to be analyzed. Subsequently, the average circularity and average envelope were automatically calculated for particle cross-sections (particle cross-section 10) with a diameter of D10 or greater in the particle size distribution obtained using a laser diffraction particle size distribution analyzer (product name "SALD-2300", manufactured by Shimadzu Corporation). The results are shown in Tables 1 and 2. In addition, the average circularity and average envelope were also calculated for all particle cross-sections observed within the observation surface. The results are shown in Table 2.

[0071] <Preparation of Compacted Magnetic Cores> (Example 1) Lithium stearate was added to magnetic powder 1 as a lubricant at a ratio of 0.3 parts by mass per 100 parts by mass of magnetic powder 1. The resulting mixture was filled into a mold having a ring-shaped cavity as a molding material. By compression molding at a molding pressure of 1500 MPa, a ring-shaped compact with an outer diameter of 30 mm, an inner diameter of 20 mm, and a height of 5 mm was formed (density: 7.50 g / cm³). ３ A compacted powder was formed. The formed compacted powder was heated at 600°C for 30 minutes to obtain a compacted magnetic core from which the lubricant had been removed.

[0072] (Example 2) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 2 was used instead of magnetic powder 1 and it was compression molded at a molding pressure of 1100 MPa. The density of the compacted material obtained by compression molding was 7.50 g / cm³. ３ That was the case.

[0073] (Example 3) A compacted magnetic core was obtained in the same manner as in Example 2, except that magnetic powder 3 was used instead of magnetic powder 2. The density of the compacted body obtained by compression molding was 7.50 g / cm³ ３ That was the case.

[0074] (Example 4) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 4 was used instead of magnetic powder 1. The density of the compacted body obtained by compression molding was 7.50 g / cm³. ３ That was the case.

[0075] (Example 5) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 5 was used instead of magnetic powder 1 and it was compression molded at a molding pressure of 1400 MPa. The density of the compacted material obtained by compression molding was 7.50 g / cm³. ３ That was the case.

[0076] (Comparative Example 1) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 6 was used instead of magnetic powder 1. The density of the compacted body obtained by compression molding was 7.50 g / cm³. ３ That was the case.

[0077] (Example 6) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 7 was used instead of magnetic powder 1. The density of the compacted body obtained by compression molding was 7.35 g / cm³. ３ That was the case.

[0078] (Comparative Example 2) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 8 was used instead of magnetic powder 1. The density of the compacted body obtained by compression molding was 7.35 g / cm³. ３ That was the case.

[0079] (Comparative Example 3) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 9 was used instead of magnetic powder 1. The density of the compacted body obtained by compression molding was 7.35 g / cm³. ３ That was the case.

[0080] (Example 7) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 10 was used instead of magnetic powder 1 and it was compression molded at a molding pressure of 1050 MPa. The density of the compacted material obtained by compression molding was 7.50 g / cm³ ３ That was the case.

[0081] (Example 8) A compacted magnetic core was obtained in the same manner as in Example 1, except that magnetic powder 11 was used instead of magnetic powder 1. The density of the compact obtained by compression molding was 7.35 g / cm³. ３ That was the case.

[0082] <AC Magnetic Characteristics (Evaluation of Iron Loss)> An insulating polyethylene terephthalate film was wound around each ring-shaped powder core. On top of the polyethylene terephthalate film, a 0.5 mm diameter polyester copper wire was wound 100 times around the powder core as a primary winding using an automatic winding machine. Furthermore, a 0.26 mm diameter polyester copper wire was wound 20 times around the powder core as a secondary winding using an automatic winding machine. Iron loss at a magnetic flux density of 1 T and frequencies of 400 Hz or 1000 Hz was measured using an AC magnetic characteristics evaluation device (product name "SY-947", manufactured by Iwasaki Communication Equipment Co., Ltd.). The results are shown in Table 1.

[0083] <AC Magnetic Properties of Recycled Powdered Magnetic Cores> For each ring-shaped powdered magnetic core prepared in Examples 1-8 and Comparative Examples 1-3, the AC magnetic properties before recycling were obtained, and then the copper wire and insulating polyethylene terephthalate film were removed. Subsequently, the powdered magnetic cores were pulverized using a Wonder Crusher (product name "WC-3", manufactured by Osaka Chemical Co., Ltd.), and coarse particles were removed by sieving with a 30-mesh sieve (mesh opening: 500 μm) to obtain magnetic powders 1-11 again. Using these powders, lubricant mixing, compression molding, and heat treatment were performed in the same procedure as described in Examples 1-8 and Comparative Examples 1-3 to obtain recycled powdered magnetic cores from which the lubricant had been removed. The iron loss of the recycled powdered magnetic cores was measured in the same manner as described above. In addition, the ratio of the iron loss of the recycled powdered magnetic core (iron loss 2) to the iron loss of the powdered magnetic core before recycling (iron loss 1) × 100 (%) was calculated. The results are shown in Table 1.

[0084]

[0085]

[0086] Table 1 shows that the compacted magnetic cores containing magnetic powders 1-5, 7, and 10-11 (Examples 1-8) had a lower iron loss-to-iron loss ratio of 2 compared to magnetic powders 6 and 8-9 (Comparative Examples 1-3). In other words, magnetic powders 1-5, 7, and 10-11, in which the average circularity of the measured soft magnetic particles was 0.20 or higher and the average envelope of the measured soft magnetic particles was 0.45 or higher, were able to suppress the increase in iron loss of the compacted magnetic core due to recycling compared to magnetic powders 6 and 8-9, in which the average circularity of the measured soft magnetic particles was less than 0.20 or the average envelope of the measured soft magnetic particles was less than 0.45.

[0087] Table 2 shows that when all particle cross-sections within the observation area were considered, the average circularity and average envelope approximated 1, and no difference was observed among the magnetic powders. Therefore, when calculated for all particle cross-sections, the average circularity and average envelope approximated 1 for all magnetic powders, making it impossible to appropriately evaluate the degree of sphericity and surface irregularity of soft magnetic particles. On the other hand, when particle cross-section 10 was considered, a clear difference was observed among the magnetic powders in the average circularity and average envelope. Therefore, by calculating the average circularity and average envelope for particle cross-section 10, the influence of particle cross-sections with a diameter of less than D10 could be eliminated, and the degree of sphericity and surface irregularity of soft magnetic particles could be appropriately evaluated. Furthermore, by using magnetic powders in which the appropriately evaluated average circularity and average envelope were within a specific range, it was possible to suppress the increase in iron loss of compacted magnetic cores due to recycling.

[0088] 10...Particle cross section, A Ｐ ...Area of ​​particle cross-section 10, A Ｅ ...envelope area, M...virtual envelope line.

Claims

1. A magnetic powder containing soft magnetic particles having an insulating coating on its surface, wherein, when the soft magnetic particles having a diameter of 10% or more in the particle size distribution of the magnetic powder measured by the laser diffraction particle size distribution method are used as the target for measuring the average circularity and average envelope, the average circularity of the measured soft magnetic particles is 0.20 or more, and the average envelope of the measured soft magnetic particles is 0.45 or more.

2. The magnetic powder according to claim 1, wherein the standard deviation of the mean circularity of the soft magnetic particles to be measured is 0.30 or less.

3. The magnetic powder according to claim 1, wherein the standard deviation of the mean envelope of the soft magnetic particles to be measured is 0.20 or less.

4. A compacted magnetic core comprising the magnetic powder described in any one of claims 1 to 3.

5. A method for recycling a powdered magnetic core, comprising: a first step of crushing a powdered magnetic core containing the magnetic powder described in any one of claims 1 to 3 to obtain recycled powder; a second step of compressing and molding the recycled powder to obtain a molded body; and a third step of heating the molded body to obtain a powdered magnetic core.

Images