Magnetic powder and powder compacts

Abstract

To provide a magnetic powder that contains fine magnetic particles but causes less aggregation.SOLUTION: A magnetic powder 10 comprises a first magnetic particle 11, and a thermosetting resin coating 21 on the surface of the first magnetic particle 11. The first magnetic particle 11 is a soft magnetic metal particle. The resin coating 21 contains second magnetic particles 12 mixed therein. The second magnetic particles 12 have a smaller average particle size than that of the first magnetic particles 11.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a magnetic powder and a powder compact. [Background technology]

[0002] Patent Document 1 describes the following method for producing a powder magnetic core: A soft magnetic powder, an epoxy resin (binder), and toluene (organic solvent) are mixed to obtain a mixture. The resulting mixture is stirred and then dried to obtain a dried mass. The dried mass is then sieved and pulverized to obtain a granulated powder. The obtained granulated powder is filled into a molding die to obtain a green body. The obtained green body is heated to harden the binder. In this way, a powder magnetic core is obtained. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-244023 A Summary of the Invention [Problem to be solved by the invention]

[0004] When manufacturing a dust core, the magnetic permeability of the dust core can be increased by packing the granulated powder at a high density. However, in the method of producing a granulated powder from a dried mixture containing a soft magnetic powder, the obtained granulated powder is prone to agglomeration, making it difficult to pack the granulated powder at a high density. Therefore, as described in Patent Document 1, it is possible to perform a process of crushing and a process of classifying the granulated powder before the process of packing the granulated powder. However, since the granulated powder becomes hard when it aggregates, it is difficult to reduce the particle size, and the manufacturing process becomes complicated due to the increase in extra steps. Furthermore, when the granulated powder is crushed, an insulating film such as an epoxy resin may not be formed on the crushed surface, so that the insulating film may not be formed sufficiently.

[0005] In addition, as a method for further increasing the magnetic permeability of the powder magnetic core, it is possible to add magnetic particles having a smaller average particle size than the soft magnetic powder, for example, an average particle size of nm. For example, based on the method described in Patent Document 1, a method is conceivable in which a granulated powder is produced from a dried mixture containing fine magnetic particles in addition to the soft magnetic powder. However, with this method, the van der Waals forces of the fine magnetic particles make the granulated powder more likely to aggregate.

[0006] The present invention aims to provide a method for producing a magnetic powder in which aggregation is suppressed even though fine magnetic particles are mixed in. The present invention also aims to provide a method for producing a powder compact using the magnetic powder obtained by the above-mentioned production method. The present invention also aims to provide a magnetic powder in which aggregation is suppressed even though fine magnetic particles are mixed in, and a powder compact containing the above-mentioned magnetic powder. [Means for solving the problem]

[0007] The method for producing magnetic powder of the present invention includes a step of obtaining magnetic powder by spraying and drying a spray liquid containing first magnetic particles, second magnetic particles, a thermosetting resin, and an organic solvent, wherein the magnetic powder includes the first magnetic particles and a thermosetting resin coating provided on the surface of the first magnetic particles, the first magnetic particles are soft magnetic metal particles, the second magnetic particles are mixed inside the resin coating, and the average particle size of the second magnetic particles is smaller than the average particle size of the first magnetic particles.

[0008] The method for producing a powder compact of the present invention includes a step of obtaining a magnetic powder by the method for producing a magnetic powder of the present invention, and a step of hot-press molding the magnetic powder to harden the thermosetting resin and obtain a powder compact.

[0009] The magnetic powder of the present invention comprises first magnetic particles and a thermosetting resin coating provided on the surface of the first magnetic particles, the first magnetic particles being soft magnetic metal particles, second magnetic particles being mixed inside the resin coating, and the average particle size of the second magnetic particles being smaller than the average particle size of the first magnetic particles.

[0010] The powder compact of the present invention contains the magnetic powder. Effect of the Invention

[0011] According to the present invention, it is possible to obtain a magnetic powder in which minute magnetic particles are mixed and aggregation is suppressed. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a scanning electron microscope photograph showing an example of a magnetic powder obtained after spray drying of the spray liquid. [Diagram 2] FIG. 2 is a schematic diagram showing an example of the configuration of a spray dryer equipped with a two-fluid nozzle or a four-fluid nozzle. [Diagram 3] FIG. 3 is a cross-sectional view that illustrates an example of the magnetic powder of the present invention. [Figure 4] FIG. 4 is a cross-sectional view that illustrates a schematic diagram of another example of the magnetic powder of the present invention. [Diagram 5] FIG. 5 is a perspective view that illustrates an example of a coil component including a powder magnetic core. [Figure 6] FIG. 6 is a perspective view that illustrates a schematic diagram of another example of a coil component including a powder magnetic core. [Figure 7] FIG. 7 is a graph showing frequency characteristics of magnetic permeability in Example 1. As shown in FIG. [Figure 8] FIG. 8 is a graph showing frequency characteristics of magnetic permeability in Example 2. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention. The present invention also includes a combination of two or more of the individual preferable configurations of the present invention described in the following embodiments.

[0014] [Magnetic powder manufacturing method] The method for producing a magnetic powder of the present invention includes a step of obtaining a magnetic powder by spraying a spray liquid and drying it.

[0015] The spray liquid contains first magnetic particles, second magnetic particles, a thermosetting resin, and an organic solvent.

[0016] For example, in the examples described later, the following first magnetic particles, second magnetic particles, thermosetting resin, and organic solvent are used. First magnetic particle: Carbonyl iron powder (average particle size D50: 5 μm) A Second magnetic particle: Manganese ferrite powder (composition: (FeO, MnO) Fe2O3, average particle size: 91 nm or 250 nm) B Thermosetting resin base: Bisphenol A type epoxy resin...C Hardener for thermosetting resin: Phenol hardener...D Organic solvent: Methyl ethyl ketone...E Mixture ratio: first magnetic particles: second magnetic particles = 75% by weight: 25% by weight, etc.

[0017] When the ratio of the total weight of the thermosetting resin base agent and the thermosetting resin curing agent to the total weight of the first magnetic particles, the second magnetic particles, the thermosetting resin base agent and the thermosetting resin curing agent (C+D / A+B+C+D) is defined as the "resin amount", and the ratio of the total weight of the first magnetic particles, the second magnetic particles, the thermosetting resin base agent, the thermosetting resin curing agent and the organic solvent to the total weight of the first magnetic particles, the second magnetic particles, the thermosetting resin base agent, the thermosetting resin curing agent and the organic solvent (A+B+C+D / A+B+C+D+E) is defined as the "spray concentration", for example, each component is mixed so that the resin amount is 10% by weight or less (2.5% by weight in the example described below), and the spray liquid is prepared by diluting with the organic solvent so that the spray concentration is approximately 50% by weight or more and 60% by weight or less (59.5% by weight in the example described below).

[0018] The first magnetic particle is a soft magnetic metal particle. As the soft magnetic metal particle, a crystalline powder or an amorphous powder is used. As the crystalline powder, for example, Fe-based magnetic metal powder such as carbonyl iron powder, sendust magnetic powder, Fe-Si-Cr-based metal powder, Fe-Si metal powder, Fe-Ni-based magnetic metal powder such as permalloy magnetic powder, Fe-Co-based magnetic metal powder such as permendur, Fe-Si-B-Nb-Cu-based nanocrystalline magnetic metal powder, etc. can be mentioned. As the amorphous powder, Fe-Si-Cr-based or Fe-B-Si-based amorphous magnetic powder, etc. can be mentioned.

[0019] The second magnetic particles are, for example, metal oxide magnetic particles, preferably ferrite magnetic particles. When the second magnetic particles are metal oxide magnetic particles, the insulation and safety of the powder compact can be improved compared to when the second magnetic particles are metal magnetic particles. Therefore, it is suitable for use as an EMI (Electro Magnetic Interference) countermeasure part for high-speed signal systems.

[0020] In particular, when the second magnetic particles are ferrite magnetic particles, high magnetic permeability and low core loss of the powder compact can be achieved up to high frequencies.

[0021] When the second magnetic particles are ferrite magnetic particles, the ferrite magnetic particles contain, for example, one or more types of ferrite selected from the group consisting of magnetite (iron ferrite), manganese ferrite, magnesium ferrite, strontium ferrite, nickel zinc ferrite, and nickel ferrite.

[0022] When the second magnetic particles are ferrite magnetic particles, the ferrite magnetic particles preferably contain 65% by weight or more of magnetite and / or manganese ferrite in total. By containing a predetermined amount of magnetite and / or manganese ferrite in the ferrite magnetic particles, higher saturation magnetization can be obtained.

[0023] Alternatively, the second magnetic particles may be metal magnetic particles. When the second magnetic particles are metal magnetic particles, the DC bias characteristics of the powder compact can be improved. Therefore, it is suitable for use as an EMI countermeasure component such as a power inductor.

[0024] The second magnetic particles are preferably spherical. The spherical shape includes not only a perfect sphere but also a shape close to a sphere. When the second magnetic particles are spherical, the second magnetic particles can be densely packed between the first magnetic particles, thereby increasing the magnetic permeability.

[0025] The average particle size of the second magnetic particles is smaller than that of the first magnetic particles. By mixing the second magnetic particles having an average particle size smaller than that of the first magnetic particles, the gaps between the first magnetic particles can be filled with the second magnetic particles in the obtained magnetic powder. By hot-pressing such a magnetic powder to produce a powder compact, the magnetic permeability can be further increased.

[0026] The average particle size of the second magnetic particles is, for example, 1 nm or more and 1 μm or less, and preferably 40 nm or more and 250 nm or less.

[0027] The average particle size of the second magnetic particles is preferably 1 / 10 or less of the average particle size of the first magnetic particles.

[0028] By controlling the average particle size of the second magnetic particles, such as ferrite magnetic particles, within the above range, it is possible to suppress the aggregation of the second magnetic particles. Therefore, it is possible to produce a magnetic powder in which a resin coating is uniformly formed on the surface of the first magnetic particles. In addition, by subjecting such a magnetic powder to hot press molding, it is possible to obtain a powder compact in which the second magnetic particles are densely packed between the first magnetic particles.

[0029] The average particle size of the second magnetic particles is calculated from the average of the circle equivalent diameters of each particle (excluding particles whose periphery is partially invisible due to overlapping of particles, etc.) obtained by image analysis in observation at a magnification of 50,000 times using a scanning electron microscope (SEM). On the other hand, the average particle size of the first magnetic particles means the particle size D50 at an integrated value of 50% in the particle size distribution obtained by a laser diffraction / scattering method.

[0030] The average particle size of the first magnetic particles is not particularly limited, but is, for example, from 2 μm to 35 μm.

[0031] As the first magnetic particles, first magnetic coarse particles having a relatively large average particle size and first magnetic fine particles having a relatively small average particle size may be used in combination. In this case, the average particle size of the second magnetic particles is smaller than that of the first magnetic coarse particles and smaller than that of the first magnetic fine particles. The soft magnetic metal constituting the first magnetic coarse particles may be the same as or different from that constituting the first magnetic fine particles.

[0032] Examples of the base resin of the thermosetting resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, polyimide resin, polyphenyl sulfide resin, etc. These base resins may be used alone or in combination.

[0033] Examples of the hardener for the thermosetting resin include phenol-based hardeners, aromatic amine-based hardeners, imidazole-based hardeners, imide-based hardeners, etc. These hardeners may be used alone or in combination.

[0034] Examples of the organic solvent include methyl ethyl ketone, toluene, methyl acetate, ethyl acetate, and acetone.

[0035] By spraying and drying the resulting spray liquid, a thermosetting resin coating is formed on the surface of the first magnetic particles, and a magnetic powder can be produced in which the second magnetic particles are mixed inside the resin coating.

[0036] In this specification, the term "thermosetting resin coating" refers to a resin coating made of a thermosetting resin in an uncured state. The uncured state includes not only a prepolymer of the thermosetting resin in which curing has not progressed, but also a B-stage resin in which curing has started to progress but has not yet completely cured, which is a semi-cured state.

[0037] The method of spraying and drying the spray liquid is preferably a method using a spray dryer (also called a micro-mist spray dryer) equipped with a two-fluid nozzle or a four-fluid nozzle. The spray liquid is sprayed from the two-fluid nozzle or the four-fluid nozzle to volatilize the organic solvent, thereby obtaining magnetic powder.

[0038] For example, in the examples described later, the above spray liquid is sprayed using a four-fluid nozzle of a micro-mist spray dryer (evaporation capacity 1.3 kg / h) and then heated and dried at a temperature of 70°C or higher and 110°C or lower in a closed system where the oxygen partial pressure is controlled.

[0039] By spraying the spray liquid and drying it, the resin amount defined above is reduced. The reduced resin amount after spray drying of the spray liquid suppresses aggregation of the first magnetic particles, making it easier to form a resin coating on the surface of each first magnetic particle. As a result, magnetic powder with a uniform particle size can be obtained in one go. Therefore, the obtained magnetic powder can be used as it is without undergoing a crushing process and a classification process.

[0040] After the spray liquid is spray-dried, the resin amount, which was 2.5% by weight when the spray liquid was prepared, is reduced to 1.5% by weight as measured by thermogravimetry (TG) analysis after granulation. The resin amount after the spray liquid is spray-dried is preferably 0.15% by weight or more and 3% by weight or less as measured by TG analysis after granulation.

[0041] FIG. 1 is a scanning electron microscope photograph showing an example of a magnetic powder obtained after spray drying of the spray liquid. As shown in Fig. 1, the magnetic powder obtained by spraying the spray liquid and drying is such that the first magnetic particles are not aggregated, and a resin coating in which the second magnetic particles are embedded is formed on the surface of each first magnetic particle. In Fig. 1, the maximum particle size of the magnetic powder is about 30 μm.

[0042] As described above, the magnetic powder manufacturing method of the present invention can suppress the aggregation of the first magnetic particles, and can obtain magnetic powder with a uniform particle size in one go. This makes it unnecessary to perform processes such as a crushing process and a classification process, and the obtained magnetic powder can be used as is. Alternatively, the crushing process and the classification process can be simplified. By hot-press molding such magnetic powder, a powder compact in which the magnetic powder is densely packed can be produced, and as a result, the magnetic permeability can be increased.

[0043] FIG. 2 is a schematic diagram showing an example of the configuration of a spray dryer equipped with a two-fluid nozzle or a four-fluid nozzle. The spray dryer 100 shown in FIG. 2 includes a nozzle 110, a drying chamber 120 in which the spray liquid X is sprayed using the nozzle 110 to volatilize the organic solvent contained in the spray liquid X and dry the magnetic powder, and a recovery section 130 for recovering the magnetic powder dried in the drying chamber 120.

[0044] A lid is provided at the vertical upper portion of the drying chamber 120, and a nozzle 110 is provided penetrating the lid. The nozzle 110 is a two-fluid nozzle or a four-fluid nozzle. The nozzle 110 sprays the spray liquid X vertically downward. The lid is also provided with an opening 121 to which hot air (e.g., air) flowing from the upstream side of the spray direction (vertical downward) of the spray liquid X from the nozzle 110 is supplied along the spray direction.

[0045] A discharge port 122 through which the dried magnetic powder is discharged to the outside of the drying chamber 120 is provided on the vertical downstream side of the drying chamber 120 .

[0046] The recovery section 130 includes a cyclone 131 and a bag filter 132. The outlet 122 of the drying chamber 120 and the cyclone 131 are connected by a pipe 133, and the dried magnetic powder is carried by the hot air flow to the cyclone 131 and is recovered by the cyclone 131. The dried magnetic powder that cannot be recovered by the cyclone 131 is recovered by a bag filter 132 provided downstream of the cyclone 131 in the hot air flow direction. As a means for recovering the magnetic powder, either the cyclone 131 or the bag filter 132 may be provided, but by providing both, the recovery rate of the magnetic powder can be improved. A blower 134 for exhausting gas from within the device is provided downstream of the bag filter 132 in the hot air flow direction, and the hot air and the air that has passed through the gas flow path of the nozzle 110 are discharged from the blower 134 to the outside of the device.

[0047] [Magnetic powder] The magnetic powder obtained by the above steps includes first magnetic particles and a thermosetting resin coating on the surface of the first magnetic particles, the first magnetic particles being soft magnetic metal particles, the resin coating containing second magnetic particles, and the second magnetic particles having an average particle size smaller than that of the first magnetic particles. Such a magnetic powder also constitutes one aspect of the present invention.

[0048] FIG. 3 is a cross-sectional view that illustrates an example of the magnetic powder of the present invention. In the magnetic powder 10 shown in FIG. 3, a thermosetting resin coating 21 is provided on the surface of the first magnetic particle 11, and the second magnetic particle 12 is mixed inside the resin coating 21. In the magnetic powder 10 shown in FIG. 3, among the multiple second magnetic particles 12, some of the second magnetic particles 12 are embedded in the resin coating 21, and the remaining second magnetic particles 12 protrude from the resin coating 21. Therefore, unevenness is formed on the surface of the magnetic powder 10. The thickness of the resin coating 21 may be constant or may vary from place to place. The ratio of the second magnetic particles 12 embedded in the resin coating 21 and the ratio of the second magnetic particles 12 protruding from the resin coating 21 can be adjusted, for example, by the particle size of the first magnetic particle and the second magnetic particle, the compounding ratio of the first magnetic particle, the second magnetic particle, and the thermosetting resin, etc.

[0049] FIG. 4 is a cross-sectional view that illustrates a schematic diagram of another example of the magnetic powder of the present invention. In the magnetic powder 10A shown in FIG. 4, a thermosetting resin coating 21 is provided on the surface of the first magnetic particle 11, and the second magnetic particles 12 are mixed inside the resin coating 21. In the magnetic powder 10A shown in FIG. 4, all the second magnetic particles 12 are embedded in the resin coating 21. As shown in FIG. 4, the thickness of the resin coating 21 may be constant or may vary from place to place. If the thickness of the resin coating 21 is not constant, unevenness will be formed on the surface of the magnetic powder 10A.

[0050] In the magnetic powder obtained by the magnetic powder manufacturing method of the present invention or the magnetic powder of the present invention, it is preferable that at least a part of the second magnetic particles are embedded in the resin coating, and it is more preferable that all of the second magnetic particles are embedded in the resin coating. If the second magnetic particles are embedded in the resin coating, the magnetic powder particles are easily bonded to each other when the magnetic powder is hot-press molded to obtain a powder compact as described below.

[0051] In the method for producing a magnetic powder of the present invention, a mixture may be obtained that contains a magnetic powder in which some of the second magnetic particles protrude from the resin coating as shown in Fig. 3, and a magnetic powder in which all of the second magnetic particles are embedded in the resin coating as shown in Fig. 4. Similarly, the magnetic powder of the present invention may be a mixture that contains a magnetic powder in which some of the second magnetic particles protrude from the resin coating as shown in Fig. 3, and a magnetic powder in which all of the second magnetic particles are embedded in the resin coating as shown in Fig. 4.

[0052] The first magnetic particle is a soft magnetic metal particle. The soft magnetic metal particle may be a crystalline powder or an amorphous powder. The crystalline powder may be, for example, carbonyl iron powder, sendust magnetic powder, Fe-Si-Cr metal powder, Fe-Si metal powder, or other Fe-based magnetic metal powder, Fe-Ni magnetic metal powder, such as permalloy magnetic powder, Fe-Co magnetic metal powder, such as permendur, or Fe-Si-B-Nb-Cu nanocrystalline magnetic metal powder. The amorphous powder may be Fe-Si-Cr or Fe-B-Si amorphous magnetic powder.

[0053] The second magnetic particles are, for example, metal oxide magnetic particles, and are preferably ferrite magnetic particles.

[0054] When the second magnetic particles are ferrite magnetic particles, the ferrite magnetic particles contain, for example, one or more types of ferrite selected from the group consisting of magnetite (iron ferrite), manganese ferrite, magnesium ferrite, strontium ferrite, nickel zinc ferrite, and nickel ferrite.

[0055] When the second magnetic particles are ferrite magnetic particles, the ferrite magnetic particles preferably contain 65% by weight or more of magnetite and / or manganese ferrite in total. By containing a predetermined amount of magnetite and / or manganese ferrite in the ferrite magnetic particles, higher saturation magnetization can be obtained.

[0056] Alternatively, the second magnetic particles may be metallic magnetic particles.

[0057] The second magnetic particles are preferably spherical.

[0058] The second magnetic particles have an average particle size smaller than the average particle size of the first magnetic particles.

[0059] The average particle size of the second magnetic particles is, for example, 1 nm or more and 1 μm or less, and preferably 40 nm or more and 250 nm or less.

[0060] The average particle size of the second magnetic particles is preferably 1 / 10 or less of the average particle size of the first magnetic particles.

[0061] The average particle size of the first magnetic particles is not particularly limited, but is, for example, from 2 μm to 35 μm.

[0062] Examples of the thermosetting resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, polyimide resin, polyphenyl sulfide resin, etc. These thermosetting resins may be used alone or in combination.

[0063] [Method of manufacturing powder compact] The method for producing a powder compact of the present invention includes a step of obtaining a magnetic powder by the method for producing a magnetic powder of the present invention, and a step of obtaining a powder compact by hot press molding the magnetic powder to harden a thermosetting resin coating.

[0064] In the method for producing a powder compact of the present invention, a magnetic powder containing first magnetic particles, second magnetic particles and a resin coating may be hot-pressed, or a mixture containing two or more types of magnetic powder may be hot-pressed as in the modified example shown below. (Variation 1) A mixture comprising a first magnetic powder including first coarse magnetic particles, second magnetic particles, and a resin coating, and a second magnetic powder including first fine magnetic particles, second magnetic particles, and a resin coating. (Variation 2) A mixture including a first magnetic powder including first coarse magnetic particles, second magnetic particles, and a resin coating, and a second magnetic powder including first fine magnetic particles and a resin coating. (Variation 3) A mixture including a first magnetic powder including first coarse magnetic particles and a resin coating, and a second magnetic powder including first fine magnetic particles, second magnetic particles, and a resin coating.

[0065] In the step of obtaining the powder compact, the mixture containing the magnetic powder and the oxide powder may be hot-press molded. In this case, the oxide powder acts as a lubricant to improve the fluidity of the magnetic powder during hot pressing.

[0066] As the oxide powder, for example, silica particles such as fumed silica can be used.

[0067] The average particle size of the oxide powder is preferably 10 nm or more and 100 nm or less.

[0068] The amount of oxide powder added is preferably 0.1 part by weight or more and 0.25 part by weight or less per 100 parts by weight of the magnetic powder.

[0069] [Powder compact] The powder compact obtained by the above steps is used, for example, as a powder magnetic core. Therefore, the method for producing a powder compact of the present invention may further include a step of arranging a coil conductor inside or on the surface of the powder compact.

[0070] The present invention also includes a powder compact containing the magnetic powder of the present invention. The powder compact of the present invention may further contain the above-mentioned oxide powder.

[0071] The powder compact of the present invention is used, for example, as a powder magnetic core. Accordingly, in the powder compact of the present invention, a coil conductor may be disposed inside or on the surface of the powder compact.

[0072] FIG. 5 is a perspective view that illustrates an example of a coil component including a powder magnetic core. The coil component 50 shown in FIG. 5 is an example of a powder compact having a coil conductor disposed therein. The coil component 50 includes a dust core 51 having a box-shaped shape and a coil conductor 53 having a conductor 52 embedded inside the dust core 51. A first end 52a and a second end 52b of the conductor 52 are located on the surface of the dust core 51 and are exposed. A portion of the surface of the dust core 51 is covered by a first connection end 54a and a second connection end 54b that are electrically independent from each other. The first connection end 54a is electrically connected to the first end 52a of the conductor 52, and the second connection end 54b is electrically connected to the second end 52b of the conductor 52. In the coil component 50, the first end 52a of the conductor 52 is covered by the first connection end 54a, and the second end 52b of the conductor 52 is covered by the second connection end 54b.

[0073] The method of embedding coil conductor 53 inside powder magnetic core 51 is not particularly limited. For example, a member around which conductive wire 52 is wound may be placed in a die, and magnetic powder may be further supplied into the die to perform hot press molding. Alternatively, a plurality of members made by preforming magnetic powder in advance may be prepared, and these members may be combined, conductive wire 52 may be placed in the gaps formed at that time to obtain an assembly, and this assembly may be hot press molded.

[0074] FIG. 6 is a perspective view that illustrates a schematic diagram of another example of a coil component including a powder magnetic core. 6 is an example of a powder compact having a coil conductor disposed on its surface. The coil component 60 includes a ring-shaped powder core (ring core) 61 and a coil conductor 63 having a conductive wire 62 wound around the surface of the powder core 61. EXAMPLES

[0075] EXAMPLES Hereinafter, examples that more specifically disclose the present invention will be described, however, the present invention is not limited to these examples.

[0076] [Example 1] A magnetic powder was produced by spraying and drying a spray liquid containing first magnetic particles, second magnetic particles, a thermosetting resin, and an organic solvent. Carbonyl iron powder with an average particle size of 5 μm was used as the first magnetic particles, manganese ferrite powder with an average particle size of 91 nm was used as the second magnetic particles, bisphenol A type epoxy resin was used as the main agent of the thermosetting resin, and a phenolic hardener was used as the hardener of the thermosetting resin. The compounding ratio of the first magnetic particles and the second magnetic particles is shown in FIG. 7. The amount of resin at the time of mixing was 2.4% by weight, and the amount of resin after drying was 1.5% by weight as an actual value measured by TG analysis after granulation. In Example 1, the aggregation of the first magnetic particles was suppressed, and a magnetic powder was obtained in which a resin coating in which the second magnetic particles were embedded was formed on the surface of the first magnetic particles. The obtained magnetic powder was hot-press molded at 150° C. and 690 MPa for 30 minutes, and then heat-treated at 150° C. for 2 hours to produce a ring core sample.

[0077] [Example 2] A magnetic powder was prepared in the same manner as in Example 1, and a ring core sample was prepared, except that manganese ferrite powder with an average particle size of 250 nm was used as the second magnetic particles, and the compounding ratio of the first magnetic particles to the second magnetic particles was changed to the value shown in Fig. 8. In Example 2, a magnetic powder was obtained in which the aggregation of the first magnetic particles was suppressed, and a resin coating in which the second magnetic particles were embedded was formed on the surface of the first magnetic particles.

[0078] The magnetic permeability of the fabricated ring-core samples was measured using a Keysight E4991A RF impedance / material analyzer.

[0079] FIG. 7 is a graph showing the frequency characteristics of magnetic permeability in Example 1. FIG. 8 is a graph showing the frequency characteristics of magnetic permeability in Example 2. In FIG. 7 and FIG. 8, the compounding ratio of the first magnetic particles to the second magnetic particles is expressed by weight ratio. In FIG. 7 and FIG. 8, the real part μ' of magnetic permeability is shown by a solid line, and the imaginary part μ'', which becomes a loss, is shown by a dashed line.

[0080] As shown in Figures 7 and 8, high magnetic permeability is obtained by mixing second magnetic particles with the resin coating provided on the surface of the first magnetic particles. Furthermore, by using ferrite magnetic particles as the second magnetic particles, high magnetic permeability and low core loss are achieved up to the high frequency band. [Explanation of symbols]

[0081] 10, 10A magnetic powder 11 First magnetic particle 12 Second magnetic particle 21 Resin coating 50, 60 Coil parts 51, 61 powder magnetic core 52, 62 conductor 52a First end of the conductor 52b Second end of the conductor 53, 63 Coil conductor 54a First connection end 54b Second connection end 100 spray dryer 110 Nozzle 120 Drying room 121 Opening 122 Outlet 130 Collection Department 131 Cyclone 132 Bag Filter 133 Piping 134 Blois X Spray liquid

Claims

1. First magnetic particles; a thermosetting resin coating provided on the surface of the first magnetic particle; the first magnetic particles are carbonyl iron powder; The resin coating contains spherical second magnetic particles, which are manganese ferrite powder. a portion of the second magnetic particle protrudes from a surface of the resin coating; The magnetic powder, wherein the average particle size of the second magnetic particles is smaller than the average particle size of the first magnetic particles and is 1 / 10 or less of the average particle size of the first magnetic particles.

2. First magnetic particles; a thermosetting resin coating provided on the surface of the first magnetic particle; the first magnetic particles are carbonyl iron powder; The resin coating contains spherical second magnetic particles, which are manganese ferrite powder. the second magnetic particles are embedded in the resin coating, The surface of the resin coating has projections and recesses that conform to the shape of the second magnetic particles.

3. The magnetic powder according to claim 1 , wherein the second magnetic particles have an average particle size of 1 nm or more and 1 μm or less.

4. A powder compact comprising the magnetic powder according to any one of claims 1 to 3.

5. The powder compact of claim 4 further comprising an oxide powder.

6. The powder compact according to claim 4 or 5, which is a powder magnetic core.

7. The powder compact according to any one of claims 4 to 6, wherein a coil conductor is disposed inside or on a surface of the powder compact.

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