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

Abstract

To provide a magnetic powder capable of suppressing an increase in iron loss of a powder magnetic core due to recycling. [Solution] A magnetic powder containing soft magnetic particles having an insulating coating on the surface, wherein when soft magnetic particles having a diameter equal to or greater than 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 used to measure the average circularity and average envelopment degree, the soft magnetic particles to be measured have an average circularity of 0.20 or more and an average envelopment degree of 0.45 or more.

Description

[Technical Field]

[0001] The present disclosure relates to magnetic powder, dust cores, and methods for recycling dust cores. [Background technology]

[0002] Powder magnetic cores formed by compression molding of magnetic powder are sometimes used as magnetic cores for electromagnetic components. Examples of particles constituting the magnetic powder include soft magnetic metal particles whose surfaces are covered with an insulating coating. For example, Patent Document 1 describes a soft magnetic metal powder containing a plurality of soft magnetic metal particles containing Fe, the surfaces of which are covered with an insulating coating, and the coating containing soft magnetic metal fine particles, thereby providing a powder magnetic core that can achieve both excellent voltage resistance and magnetic properties. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-160942 Summary of the Invention [Problem to be solved by the invention]

[0004] Toward the realization of carbon neutrality and a circular economy, efforts are being made to recycle used powder magnetic cores. However, recycled powder magnetic cores have a problem in that they have higher iron loss (energy loss) than powder magnetic cores before recycling.

[0005] An object of one aspect of the present disclosure is to provide a magnetic powder that can suppress an increase in iron loss in a powder magnetic core due to recycling. [Means for solving the problem]

[0006] The inventors investigated the relationship between the average circularity and average degree of envelopment of soft magnetic particles contained in a magnetic powder and the increase in iron loss of a recycled powder core. They found that a high average circularity (nearly spherical shape) and a high average degree of envelopment (low particle surface irregularity (surface roughness)) of soft magnetic particles can suppress the increase in iron loss of a recycled powder core. The inventors speculate that a powder core using soft magnetic particles with high average circularity and average degree of envelopment can reduce damage to the insulating coating of particles due to collisions between particles when the powder core is pulverized and the resulting powder is re-molded under pressure. As a result, eddy current loss due to damage to the insulating coating can be reduced, thereby suppressing the increase in iron loss of a recycled powder core. However, when measuring the average circularity and average degree of envelopment of the soft magnetic particles, it is necessary to measure soft magnetic particles having a diameter equal to or greater than the 10% cumulative particle diameter (D10) in the number-based particle size distribution of the magnetic powder.

[0007] The present disclosure includes the following aspects. [1] A magnetic powder containing soft magnetic particles having an insulating coating on the surface, wherein when soft magnetic particles having a diameter equal to or greater than 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 used to measure the average circularity and average envelopment degree, the soft magnetic particles to be measured have an average circularity of 0.20 or more and an average envelopment degree of 0.45 or more. [2] The magnetic powder according to [1], wherein the standard deviation of the average circularity of the soft magnetic particles to be measured is 0.20 or less. [3] The magnetic powder according to [1] or [2], wherein the standard deviation of the average envelopment degree of the soft magnetic particles to be measured is 0.20 or less. [4] A dust core comprising the magnetic powder according to any one of [1] to [3]. [5] A method for recycling powder magnetic cores, comprising: a first step of pulverizing a powder magnetic core containing the magnetic powder according to any one of [1] to [3] to obtain a recycled powder; a second step of compression-molding the recycled powder to obtain a molded body; and a third step of heating the molded body to obtain a powder magnetic core. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, it is possible to provide a magnetic powder that can suppress an increase in iron loss of a powder magnetic core due to recycling. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram for explaining the envelopment degree of a particle cross section. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0011] The magnetic powder according to this embodiment contains soft magnetic particles having an insulating coating on their surface. The soft magnetic particles may contain metal particles as core particles, and the metal particles (core particles) may have an insulating coating on their surfaces. The metal constituting the metal particles may be pure iron or an iron-containing alloy. Examples of iron-containing alloys include Fe-Cr alloys (stainless steel), Fe-Ni-Cr alloys (stainless steel), Fe-Si alloys (e.g., Fe-3Si alloys), Fe-Si-Al alloys (sendust), Fe-Ni alloys (permalloy), Fe-Cu-Ni alloys (permalloy), Fe-Co alloys, Fe-Co-V alloys (permendur), Fe-Cr-Si alloys (electromagnetic stainless steel), and Fe-Ni-Mn-C alloys (invar). 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 alloys. The metal particles constituting the soft magnetic particles may be amorphous, or 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 that covers a portion of their surface, or may have an insulating coating that covers their entire surface. From the viewpoint of exhibiting high insulation properties and further reducing eddy current loss in the powder magnetic core, the soft magnetic particles preferably have an insulating coating that covers their entire surface.

[0013] The insulating coating may contain an insulating material (an insulating inorganic material and an insulating organic material). Examples of insulating materials include phosphates, silicate glass, silicone resins, metal oxides, metal nitrides, and metal carbides. The metal element contained in the metal oxides, metal nitrides, and metal carbides may be at least one element 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 be composed of a single insulating coating or multiple insulating coatings. When the insulating coating is composed of multiple insulating coatings, the insulating coating may be composed 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 particle).

[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 providing good insulation between the soft magnetic particles and further reducing the eddy current loss of the powder magnetic core. The thickness of the insulating coating may be 300 nm or less, from the viewpoint of making it easier for the powder magnetic core to have an appropriate density and to maintain a good magnetic flux density. When the insulating coating is composed of multiple insulating coatings, the thickness of each of the insulating coatings constituting the insulating coating may be in the above range, and the total thickness of the multiple insulating coatings may be in the above range. When the insulating coating is formed non-uniformly on the surface of the core particle, the minimum thickness of the insulating coating may be in the above range.

[0017] 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 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 using a laser diffraction particle size distribution analyzer.

[0018] The 50% cumulative particle diameter (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.

[0019] The 90% cumulative particle diameter (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.

[0020] The D10 in the number-based particle size distribution of the magnetic powder 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.

[0021] The D50 in the number-based particle size distribution of the magnetic powder 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.

[0022] The D90 in the number-based particle size distribution of the magnetic powder 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.

[0023] In the magnetic powder according to this embodiment, when soft magnetic particles having a diameter equal to or greater than 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 used as the soft magnetic particles to be measured for average circularity and average envelopment, the soft magnetic particles to be measured have an average circularity of 0.20 or greater and an average envelopment of 0.45 or greater. 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 below. Furthermore, when the particle cross section is not a perfect circle, the "diameter" of the particle cross section refers to the maximum diameter of the particle cross section.

[0024] A method for calculating the average circularity and average envelopment degree of soft magnetic particles to be measured is described below. The method for calculating the average circularity and average envelopment degree of soft magnetic particles to be measured includes 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 envelopment degree of the soft magnetic particles to be measured within the observation surface.

[0025] In the preparation step, a sample containing magnetic powder and an embedding resin is prepared. The embedding resin may contain a thermoplastic resin or a cured thermosetting resin. Examples of the thermoplastic resin include, but are not limited to, polyolefin resin, polyester resin, etc. Examples of the thermosetting resin include, but are not limited to, epoxy resin, phenolic resin, etc. When the sample contains a cured thermosetting resin, the sample may be obtained by mixing the magnetic powder, the thermosetting resin, and a curing agent and curing the thermosetting resin. Examples of the curing agent include, but are not limited to, imidazole-based curing agents, etc.

[0026] The method for polishing the surface of the sample is not particularly limited, and for example, the surface may be polished using a rotary polisher.

[0027] In the observation step, the polished surface (surface exposed by polishing) of the sample obtained in the preparation step is observed using a microscope. The observed surface may be obtained as image data. The microscope used for measurement is, for example, a VHX-8000 (manufactured by Keyence Corporation). The observation magnification of the microscope may be appropriately adjusted within a range in which the cross sections of multiple soft magnetic particles can be observed, and may be, for example, 80 times or more and 500 times or less.

[0028] In the calculation step, the average circularity and average envelopment ratio are calculated for the cross sections of the soft magnetic particles observed in the observation step. The analysis software used for the calculation may be, for example, the analysis software included with the microscope (product names: (1) 3D shape measurement software VHX-H5M, (2) XY measurement software VHX-H3M3, manufactured by Keyence Corporation). The average circularity and average envelopment ratio are calculated for particle cross sections 10 having a diameter equal to or greater than the 10% cumulative particle diameter (D10) in the number-based particle size distribution of the magnetic powder, as measured by a laser diffraction particle size distribution method.

[0029] For cross sections with diameters less than D10 in the number-based particle size distribution of magnetic powder, it is difficult to properly grasp the shape and degree of surface irregularity due to the resolution limit of a microscope. Therefore, even if the cross section is not circular and has a lot of peripheral irregularity, it may be determined to be circular and have little irregularity in analysis. As a result, when all particle cross sections within the observation surface are examined, the average circularity and average envelopment ratio are close to 1 regardless of the cross-sectional characteristics, making it difficult to properly calculate the average circularity and average envelopment ratio. Therefore, the shape and surface irregularity of soft magnetic particles can be more appropriately evaluated by calculating the average circularity and average envelopment ratio for particle cross sections 10 whose diameters are equal to or greater than D10 in the number-based particle size distribution of magnetic powder.

[0030] When calculating the average circularity and average envelopment degree of soft magnetic particles, in order to perform the calculation more appropriately, the average circularity and average envelopment degree may be calculated by excluding from the particle cross section 10 the particle cross section that is partially missing at the edge of the observation surface.

[0031] The average circularity of soft magnetic particles is an index for evaluating whether the shape of the soft magnetic particles is generally close to a sphere, and the closer the average circularity of the soft magnetic particles is to 1, the more the soft magnetic particles are generally close to a sphere. In this specification, the average circularity of the soft magnetic particles to be measured is the average value of the circularities calculated for each particle cross section 10 using the following formula (1). Here, S represents the area of ​​the particle cross section 10 observed under a microscope, and L represents the perimeter of the particle cross section 10 observed under a microscope. Circularity = 4πS / L 2 (1)

[0032] The average circularity of the soft magnetic particles to be measured may be 0.22 or more, 0.23 or more, 0.24 or more, or 0.27 or more, and preferably 0.30 or more, 0.36 or more, 0.38 or more, or 0.44 or more, from the viewpoint of further suppressing an increase in iron loss of the powder magnetic core due to recycling. The average circularity of the soft magnetic particles to be measured may be 0.99 or less, 0.90 or less, or 0.80 or less, from the viewpoint of improving the mechanical strength of the powder magnetic core.

[0033] The standard deviation of the average circularity of the soft magnetic particles to be measured may be 0.01 or more or 0.02 or more.From the viewpoint of further suppressing an increase in iron loss of the powder magnetic core due to recycling, the standard deviation of the average circularity of the soft magnetic particles to be measured may be 0.20 or less or 0.18 or less.

[0034] The average degree of envelopment of soft magnetic particles is an index for evaluating the overall degree of roughness of the surface of a soft magnetic particle, and the closer the average degree of envelopment of a soft magnetic particle is to 1, the less overall roughness the surface of the soft magnetic particle has. FIG. 1 is a schematic diagram for explaining the degree of envelopment of a particle cross section. In this specification, the degree of envelopment of a particle cross section 10 in FIG. 1 is defined as the area of ​​the particle cross section 10 observed under a microscope, A P The envelope area enclosed by the envelope imaginary line M that contacts the convex portion of the particle cross section 10 is A E When this is done, A P / A EIn this specification, the average degree of envelopment of the soft magnetic particles to be measured is the average value of the degree of envelopment of each particle cross section 10. By using the above analysis software, the A P / A E As is clear from the above, the average circularity is an index of the degree of sphericity of the particle shape, whereas the average envelopment is an index of the degree of roughness of the particle surface, and the average circularity and the average envelopment are different evaluation indexes.

[0035] The average degree of envelopment 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, preferably 0.60 or more, 0.70 or more, 0.80 or more, or 0.83 or more, from the viewpoint of further suppressing an increase in iron loss of the powder magnetic core due to recycling. The average degree of envelopment of the soft magnetic particles to be measured may be 0.99 or less or 0.95 or less, from the viewpoint of improving the mechanical strength of the powder magnetic core.

[0036] The standard deviation of the average degree of envelopment 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 powder magnetic core due to recycling, the standard deviation of the average degree of envelopment of the soft magnetic particles to be measured may be 0.20 or less, 0.15 or less, or 0.12 or less.

[0037] The magnetic powder may be obtained by a manufacturing method including the steps of: mixing a metal powder containing metal particles with an insulating material to obtain a mixed powder; and drying the mixed powder. The metal particles and the insulating material may be the same as those described above. The temperature (drying temperature) for drying the mixed powder may be 50°C or higher or 100°C or higher, and may be 300°C or lower. The time (drying time) for drying the mixed powder may be 10 minutes or longer and 1 hour or shorter. The manufacturing method for the magnetic powder may further include the step of crushing the mixed powder after the step of drying the mixed powder.

[0038] When the insulating coating is composed of multiple insulating coatings, the magnetic powder may be obtained by a manufacturing method including the steps of: mixing a metal powder containing metal particles with a first insulating material to obtain a first mixed powder, drying the first mixed powder, mixing the first mixed powder with a second insulating material to obtain a second mixed powder, and drying the second mixed powder. In this case, the inner insulating coating (closer to the core particles) is made of the first insulating material, and the outer insulating coating (farther from the core particles) is made of the second insulating material.

[0039] The powder magnetic core according to this embodiment may be obtained by a manufacturing method including a molding step of compressing and molding magnetic powder to obtain a molded body, and a heating step of heating the molded body.

[0040] 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.

[0041] In the molding step, a lubricant may be added to the magnetic powder before compression molding. The lubricant may be one that is commonly used in compression molding, such as a stearic acid compound (lithium stearate, ethylene bisstearamide, etc.). The amount of lubricant added may be 0.1 parts by mass or more and 1 part by mass or less per 100 parts by mass of the magnetic powder.

[0042] The bulk density of the compact obtained in the molding process is 3 g / cm 3 More than 5g / cm 3 or more than 7g / cm 3 may be 20 g / cm or more, 3 Below, 10g / cm 3 Less than or equal to 8g / cm 3 It may be the following:

[0043] In the heating step, the heating temperature of the compact may be 300° C. or higher and 1000° C. or lower. The heating time of the compact may be 10 minutes or longer and 1 hour or shorter.

[0044] One embodiment of the present disclosure is a powder magnetic core including the magnetic powder.

[0045] The powder magnetic core can have any shape suitable for its application, etc. The powder magnetic core can be used as a component of various devices selected from, for example, inductors, transformers, reactors, thyristor valves, noise filters (EMI filters), choke coils, iron cores for motors, rotors or yokes, solenoid cores (fixed iron cores) for electromagnetic valves incorporated into electronically controlled fuel injection devices, position sensors, and magnetostrictive sensors.

[0046] The powder magnetic core may contain other powders in addition to the magnetic powder. Examples of other powders include non-magnetic powders. The content of other powders may be 0.1 mass % or less based on the total amount of the powder magnetic core.

[0047] One embodiment of the present disclosure is a method for recycling powder magnetic cores, comprising: a first step of pulverizing a powder magnetic core containing the magnetic powder to obtain a recycled powder; a second step of compression-molding the recycled powder to obtain a molded body; and a third step of heating the molded body to obtain a powder magnetic core.

[0048] In the first step, examples of the apparatus used to pulverize the powder magnetic core include a wonder crusher, a screw mill, a stamp mill, a disk mill, a pin mill, a screen mill, a cutter mill, a ball mill, etc. The pulverization time may be 1 minute or more and 15 minutes or less.

[0049] The recycled powder obtained in the first step includes the magnetic powder. The D10, D50, and D90 in the volume-based particle size distribution of the recycled powder, and the D10, D50, and D90 in the number-based particle size distribution of the recycled powder may be the same as those of the magnetic powder.

[0050] The details of the second step may be the same as the details of the compacting step in the method for producing a powder magnetic core, and the details of the third step may be the same as the details of the heating step in the method for producing a powder magnetic core.

[0051] The number of times of recycling (the number of times the recycling method is carried out) may be one or more times, for example, two or more times. [Example]

[0052] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the examples.

[0053] <Preparing 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 containing 20 g of water glass (product name "No. 1 C2", manufactured by Toso Sangyo Co., Ltd., solids content 51% by mass) per liter of water was prepared. Next, 100 g of pure iron powder, which had been pre-screened using a 235 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. The dried mixed powder was crushed to obtain magnetic powder (iron-based soft magnetic powder) 1, which consisted of soft magnetic particles (iron-based soft magnetic particles) comprising 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 D10, D50, and D90 values ​​in the volume-based particle size distribution of Magnetic Powder 1 obtained by the method described below were 76.6 μm, 133.5 μm, and 209.5 μm, respectively, and the D10, D50, and D90 values ​​in the number-based particle size distribution of Magnetic Powder 1 were 52.7 μm, 80.9 μm, and 141.3 μm, respectively.

[0054] (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 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 was prepared. 100 g of the pure iron powder was mixed with 15 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 magnetic powder (iron-based soft magnetic powder) 2, which consisted of soft magnetic particles (iron-based soft magnetic particles) comprising 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 minimum thickness of the phosphate coating (insulating coating) was approximately 40 nm. In addition, the D10, D50 and D90 in the volume-based particle size distribution of magnetic powder 2 obtained by the method described below were 139.7 μm, 258.4 μm and 434.6 μm, respectively, and the D10, D50 and D90 in the number-based particle size distribution of magnetic powder 2 were 95.4 μm, 143.4 μm and 249.6 μm, respectively.

[0055] (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 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 was prepared. Next, 100 g of pure iron powder, which had been pre-screened using a 40-mesh (405 μm mesh) 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 containing 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, Inc., solids content 50% by mass) per liter of ethanol. A mixed powder was obtained by mixing 100 g of the particles having the phosphate coating with 15 mL of the treatment liquid containing the silicone resin. This mixed powder was dried by heating at 70°C for 30 minutes and then pulverized by a crushing process. The powder was then dried by heating at 180°C for 120 minutes in a nitrogen atmosphere. The dried mixed powder was crushed to obtain magnetic powder (iron-based soft magnetic powder) 3 consisting of soft magnetic particles (iron-based soft magnetic particles) having pure iron particles and phosphate coatings and silicone resin coatings as insulating coatings covering the surfaces of the pure iron particles. The phosphate coatings and silicone resin coatings (insulating coatings) were formed non-uniformly on the surfaces of the pure iron particles, and the total thickness of the insulating coatings was approximately 45 nm at a minimum. Furthermore, the D10, D50 and D90 in the volume-based particle size distribution of magnetic powder 3 obtained by the method described below were 89.3 μm, 195.1 μm and 394.3 μm, respectively, and the D10, D50 and D90 in the number-based particle size distribution of magnetic powder 3 were 40.6 μm, 70.3 μm and 148.2 μm, respectively.

[0056] (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 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 was prepared. Next, 100 g of pure iron powder, which had been pre-screened using a 149 mesh (100 μm mesh size) 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 containing 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, Inc., solids content 50% by mass) per liter of ethanol. A mixed powder was obtained by mixing 100 g of the particles having the phosphate coating with 15 mL of the treatment liquid containing the silicone resin. This mixed powder was dried by heating at 70°C for 30 minutes and then pulverized by a crushing process. The powder was then dried by heating at 180°C for 120 minutes in a nitrogen atmosphere. The dried mixed powder was crushed to obtain magnetic powder (iron-based soft magnetic powder) 4, which consisted of soft magnetic particles (iron-based soft magnetic particles) having pure iron particles and phosphate and silicone resin coatings as insulating coatings covering the surfaces of the pure iron particles. The phosphate and silicone resin coatings (insulating coatings) were formed non-uniformly on the surfaces of the pure iron particles, and the total thickness of the insulating coatings was approximately 45 nm at a minimum. Furthermore, the D10, D50 and D90 in the volume-based particle size distribution of magnetic powder 4 obtained by the method described below were 37.3 μm, 59.3 μm and 93.0 μm, respectively, and the D10, D50 and D90 in the number-based particle size distribution of magnetic powder 4 were 28.3 μm, 41.8 μm and 64.8 μm, respectively.

[0057] (Magnetic powder 5) Magnetic powder (iron-based soft magnetic powder) 5 was produced using the same procedure as in the manufacturing method of magnetic powder 4, except that pure iron powder was previously treated with an 83 mesh (opening: 180 μm) sieve to remove particles larger than 180 μm (iron-based soft magnetic powder) composed 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 D10, D50, and D90 values ​​in the volume-based particle size distribution of magnetic powder 5, obtained by the method described below, were 53.1 μm, 103.7 μm, and 175.3 μm, respectively, and the D10, D50, and D90 values ​​in the number-based particle size distribution of magnetic powder 5 were 30.6 μm, 49.8 μm, and 96.0 μm, respectively.

[0058] (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 the core particles. Furthermore, the D10, D50, and D90 in the volume-based particle size distribution of Magnetic Powder 6 obtained by the method described below were 59.3 μm, 112.1 μm, and 200.0 μm, respectively, and the D10, D50, and D90 in the number-based particle size distribution of Magnetic Powder 6 were 34.8 μm, 87.4 μm, and 136.9 μm, respectively.

[0059] (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 powder weight)) was prepared as core particles. A treatment solution containing 40 g of silicone resin (product name "SR2400 Resin", manufactured by Dow-Toray Industries, Inc.; solid content: 50% by mass) per liter of ethanol was prepared. 100 g of the Fe-3Si alloy powder was mixed with 25 mL of the treatment solution 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 by heating at 180°C for 120 minutes in a nitrogen atmosphere. The dried mixed powder was crushed to obtain magnetic powder (iron-based soft magnetic alloy powder) 7, which consisted of soft magnetic particles (iron-based soft magnetic particles) comprising Fe-3Si alloy particles and a silicone resin coating as an insulating coating covering the surfaces 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 minimum thickness of the insulating coating was approximately 50 nm. Furthermore, the D10, D50, and D90 values ​​in the volume-based particle size distribution of Magnetic Powder 7, obtained by the method described below, were 91.2 μm, 131.2 μm, and 187.7 μm, respectively, and the D10, D50, and D90 values ​​in the number-based particle size distribution of Magnetic Powder 7 were 74.5 μm, 103.1 μm, and 151.2 μm, respectively.

[0060] (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 the core particles. Silicone resin coatings (insulating coatings) were formed unevenly on the surfaces of the Fe-3Si alloy particles, and the minimum thickness of the insulating coating was approximately 45 nm. Furthermore, the D10, D50, and D90 values ​​in the volume-based particle size distribution of magnetic powder 8, obtained using the method described below, were 54.7 μm, 95.3 μm, and 157.8 μm, respectively, and the D10, D50, and D90 values ​​in the number-based particle size distribution of magnetic powder 8 were 35.4 μm, 56.2 μm, and 97.2 μm, respectively.

[0061] (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 (specially atomized powder, product name "DAPMS3-B", manufactured by Daido Steel Co., Ltd., Si content: 3 mass% (based on the total amount of powder)) was prepared as the core particles. Silicone resin coatings (insulating coatings) were formed unevenly on the surfaces of the Fe-3Si alloy particles, and the minimum thickness of the insulating coating was approximately 45 nm. Furthermore, the D10, D50, and D90 values ​​in the volume-based particle size distribution of magnetic powder 9, obtained using the method described below, were 52.6 μm, 90.1 μm, and 139.2 μm, respectively, and the D10, D50, and D90 values ​​in the number-based particle size distribution of magnetic powder 9 were 30.8 μm, 51.9 μm, and 90.1 μm, respectively.

[0062] <Measurement of particle size distribution> 100 parts by mass of each of the magnetic powders 1 to 9 was dispersed in purified water with 0.2 parts by mass of a surfactant (trade name "Ribonol T / 15" manufactured by Lion Corporation). The resulting dispersion was placed in the sample water tank of a laser diffraction particle size analyzer (product name "SALD-2300" manufactured by Shimadzu Corporation). The solution was then circulated with a pump while applying ultrasound (pump flow rate was 65% from the maximum), and the amount of water was adjusted to achieve an absorbance of 0.10 to 0.15. The volumetric and number-based particle size distributions were then measured. From the resulting volumetric and number-based particle size distributions, particle sizes corresponding to the D10, D50, and D90 values ​​of the sample were obtained.

[0063] <Measurement of average circularity and average envelopment> Each of the magnetic powders 1 to 9 was embedded in resin, cured, and then surface-polished using a rotary polisher to prepare cross-sectional samples. Next, a digital microscope (product name "VHX-8000" manufactured by Keyence Corporation) was used to observe the particles at an arbitrary magnification that allowed for a full image of the particles, and image data of the particle cross sections was obtained. The acquired image data was then analyzed using particle analysis software (product names "(1) 3D shape measurement software VHX-H5M, (2) XY measurement software VHX-H3M3" manufactured by Keyence Corporation) included with the microscope, and the average circularity and average envelopment ratio were obtained. The particle analysis procedure was as follows: First, the contrast in the analysis software was adjusted to clarify the particle outline. In addition, voids may have occurred inside the particles to be analyzed due to surface polishing, etc., so an embedding process was performed using the analysis software. In addition, particle cross sections with portions missing at the edge of the image data extraction area were removed from the particles to be analyzed, as this may prevent a full image of the particle cross section from being obtained. The average circularity and average envelopment ratio were then automatically calculated for particle cross sections (particle cross sections 10) having a diameter of D10 or more in the number-based 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. The average circularity and average envelopment ratio were also calculated for all particle cross sections observed within the observation plane. The results are shown in Table 2.

[0064] <Production of powder magnetic core> Example 1 Lithium stearate was added as a lubricant to magnetic powder 1 in 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. A ring-shaped green compact (density: 7.50 g / cm) with an outer diameter of 30 mm, an inner diameter of 20 mm, and a height of 5 mm was obtained by compression molding at a molding pressure of 1500 MPa. 3 The resulting green compact was heated at 600°C for 30 minutes to obtain a powder magnetic core from which the lubricant had been removed.

[0065] Example 2 A powder 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 compression molding was performed at a molding pressure of 1100 MPa. The density of the powder compact obtained by compression molding was 7.50 g / cm. 3 It was.

[0066] Example 3 A powder 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 powder compact obtained by compression molding was 7.50 g / cm 3 It was.

[0067] Example 4 A powder 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 green compact obtained by compression molding was 7.50 g / cm 3 It was.

[0068] Example 5 A powder 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 compression molding was performed at a molding pressure of 1400 MPa. The density of the powder compact obtained by compression molding was 7.50 g / cm 3 It was.

[0069] (Comparative Example 1) A powder 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 green compact obtained by compression molding was 7.50 g / cm 3 It was.

[0070] Example 6 A powder 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 powder compact obtained by compression molding was 7.35 g / cm 3 It was.

[0071] (Comparative Example 2) A powder 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 powder compact obtained by compression molding was 7.35 g / cm 3 It was.

[0072] (Comparative Example 3) A powder 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 powder compact obtained by compression molding was 7.35 g / cm 3 It was.

[0073] <AC magnetic properties (iron loss evaluation)> Each ring-shaped powder magnetic core was wrapped in an insulating polyethylene terephthalate film. A 0.5 mm diameter polyester copper wire was wound 100 times around the powder magnetic core on top of the polyethylene terephthalate film using an automatic winding machine. A 0.26 mm diameter polyester copper wire was then wound 20 times around the powder magnetic core as a secondary winding using an automatic winding machine. Iron loss was measured at a frequency of 400 Hz or 1000 Hz at a magnetic flux density of 1 T using an AC magnetic property evaluation device (product name "SY-947" manufactured by Iwasaki Electric Co., Ltd.). The results are shown in Table 1.

[0074] <AC magnetic properties of recycled powder magnetic cores> For each of the ring-shaped powder magnetic cores produced in Examples 1 to 6 and Comparative Examples 1 to 3, the pre-recycling AC magnetic properties were measured, and then the copper wire and insulating polyethylene terephthalate film were removed. The powder magnetic cores were then pulverized using a Wonder Crusher (product name "WC-3," manufactured by Osaka Chemical Co., Ltd.) and sieved through a 30-mesh (opening: 500 μm) sieve to remove coarse particles, yielding magnetic powders 1 to 9. Using these powders, lubricant mixing, compression molding, and heat treatment were carried out in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 3, yielding recycled powder magnetic cores from which the lubricant had been removed. The iron loss of the recycled powder magnetic cores was measured in the same manner as above. The ratio of the iron loss of the recycled powder magnetic cores (iron loss 2) to the iron loss of the pre-recycled powder magnetic cores (iron loss 1) was also calculated. The results are shown in Table 1.

[0075] [Table 1]

[0076] [Table 2]

[0077] As can be seen from Table 2, when all particle cross sections within the observation plane were examined, the average circularity and average degree of envelopment were close to 1, and no differences were observed between magnetic powders. Therefore, when all particle cross sections were examined, the average circularity and average degree of envelopment were close to 1 for all magnetic powders, and the sphericity and surface roughness of the soft magnetic particles could not be properly evaluated. On the other hand, when particle cross sections 10 were examined, clear differences were observed between magnetic powders in the average circularity and average degree of envelopment. Therefore, by calculating the average circularity and average degree of envelopment using particle cross sections 10, the influence of particle cross sections with diameters less than D10 could be eliminated, and the sphericity and surface roughness of the soft magnetic particles could be properly evaluated. Furthermore, by using magnetic powders with appropriately evaluated average circularity and average degree of envelopment within a specific range, the increase in iron loss of the powder magnetic core due to recycling could be suppressed. [Explanation of symbols]

[0078] 10...Particle cross section, A P …area of ​​particle cross section 10, A E ...envelope area, M...envelope imaginary line.

Claims

1. A magnetic powder containing soft magnetic particles having an insulating coating on the surface thereof, When soft magnetic particles having a diameter equal to or greater than 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 used as the objects of measurement for average circularity and average envelopment degree, the soft magnetic particles to be measured have an average circularity of 0.23 or more and an average envelopment degree of 0.50 or more.

2. 2. The magnetic powder according to claim 1, wherein the standard deviation of the average circularity of the soft magnetic particles to be measured is 0.20 or less.

3. 2. The magnetic powder according to claim 1, wherein the standard deviation of the average envelopment degree of the soft magnetic particles to be measured is 0.20 or less.

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