Method for producing magnetic powder, method for producing powder compact, magnetic powder and powder compact

Abstract

The present invention provides a method for producing magnetic powder, which can suppress agglomeration although the magnetic powder is mixed with tiny magnetic particles. The method for producing magnetic powder of the present invention comprises the steps of spraying and drying a spray liquid containing a first magnetic particle, a second magnetic particle, a thermosetting resin and an organic solvent to obtain the magnetic powder. The magnetic powder (10) comprises a first magnetic particle (11) and a thermosetting resin coating (21) arranged on the surface of the first magnetic particle (11). The first magnetic particle (11) is a soft magnetic metal particle. The second magnetic particle (12) is mixed inside the resin coating (21). The average particle size of the second magnetic particle (12) is smaller than the average particle size of the first magnetic particle (11).

Description

Technical Field

[0001] The present invention relates to a method for producing magnetic powder, a method for producing a powder compact, magnetic powder and a powder compact. Background Art

[0002] As a method for manufacturing a powdered magnetic core, Patent Document 1 has the following description: Soft magnetic powder, epoxy resin (binding material) and toluene (organic solvent) are mixed to obtain a mixture. The obtained mixture is stirred and then dried to obtain a block-shaped dry product. Next, the dry product is sieved and crushed to obtain granulated powder. The obtained granulated powder is filled into a molding die to obtain a molding. The obtained molding is heated to solidify the binding material. Thus, a powdered magnetic core is obtained.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-244023 Summary of the invention

[0006] When manufacturing a powdered magnetic core, the magnetic permeability of the powdered magnetic core can be increased by filling the granulated powder at a high density. However, in the method of making granulated powder from a dry product of a mixture containing soft magnetic powder, the obtained granulated powder is easy to agglomerate, so it is difficult to fill the granulated powder at a high density. Therefore, it can be considered to perform a process of cracking the granulated powder and a process of classifying the granulated powder before the process of filling the granulated powder as described in Patent Document 1. However, the granulated powder in the case of agglomeration will become hard, so it is difficult to reduce its particle size, and unnecessary processes will be added, so the manufacturing process will become complicated. Furthermore, in the case of cracking the granulated powder, sometimes an insulating film of epoxy resin or the like is not formed on the cracked surface, so there is a risk of insufficient formation of the insulating film.

[0007] In addition, as a method for further improving the magnetic permeability of the powder core, it is possible to consider adding magnetic particles having an average particle size smaller than that of the soft magnetic powder, for example, an average particle size of nanometer level. For example, based on the method described in Patent Document 1, it is possible to consider adding soft magnetic powder and making granulated powder from a dried product of a mixture containing tiny magnetic particles. However, in this method, the granulated powder is more likely to agglomerate due to the van der Waals force of the tiny magnetic particles.

[0008] The object of the present invention is to provide a method for producing a magnetic powder, wherein the magnetic powder is mixed with fine magnetic particles and can suppress agglomeration. Furthermore, the object of the present invention is to provide a method for producing a powder compact using the magnetic powder obtained by the above-mentioned production method. In addition, the object of the present invention is to provide a magnetic powder and a powder compact, wherein the magnetic powder is mixed with fine magnetic particles and can suppress agglomeration, and the powder compact contains the above-mentioned magnetic powder.

[0009] The method for manufacturing magnetic powder of the present invention comprises: a step of spraying and drying a spray liquid containing first magnetic particles, second magnetic particles, a thermosetting resin and an organic solvent to obtain magnetic powder; the magnetic powder comprises 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.

[0010] The method for producing a powder compact of the present invention comprises: a step of obtaining magnetic powder by the method for producing magnetic powder of the present invention; and a step of obtaining a powder compact by hot-pressing the magnetic powder to cure the thermosetting resin.

[0011] The magnetic powder of the present invention comprises a first magnetic particle and a thermosetting resin coating arranged on the surface of the first magnetic particle, the first magnetic particle is a soft magnetic metal particle, the interior of the resin coating is mixed with a second magnetic particle, and the average particle size of the second magnetic particle is smaller than the average particle size of the first magnetic particle.

[0012] The powder compact of the present invention contains the above-mentioned magnetic powder.

[0013] According to the present invention, it is possible to obtain magnetic powder in which fine magnetic particles are mixed and in which aggregation is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a scanning electron microscope photograph showing an example of magnetic powder obtained after spray drying of the spray liquid.

[0015] Figure 2 This is a schematic diagram showing an example of the structure of a spray dryer including a two-fluid nozzle or a four-fluid nozzle.

[0016] Figure 3 This is a cross-sectional view schematically showing an example of the magnetic powder of the present invention.

[0017] Figure 4 This is a cross-sectional view schematically showing another example of the magnetic powder of the present invention.

[0018] Figure 5 This is a perspective view schematically showing an example of a coil component including a powder magnetic core.

[0019] Figure 6 This is a perspective view schematically showing another example of a coil component including a powder magnetic core.

[0020] Figure 7 Graph showing the frequency characteristics of the magnetic permeability in Example 1.

[0021] Figure 8 3 is a graph showing the frequency characteristics of the magnetic permeability in Example 2.

[0022] Explanation of symbols

[0023] 10, 10A magnetic powder

[0024] 11. First magnetic particle

[0025] 12. Second magnetic particles

[0026] 21. Resin film

[0027] 50, 60 coil parts

[0028] 51, 61 Powder core

[0029] 52, 62 wire

[0030] 52a First end of the wire

[0031] 52b Second end of the wire

[0032] 53, 63 Coil conductor

[0033] 54a 1st connection end

[0034] 54b Second connection end

[0035] 100 Spray Dryer

[0036] 110 Nozzle

[0037] 120 Drying room

[0038] 121 Opening

[0039] 122 Exhaust

[0040] 130 Recycling Department

[0041] 131 Cyclone separator

[0042] 132 Bag filter

[0043] 133 Piping

[0044] 134 Blower

[0045] X Spray Liquid DETAILED DESCRIPTION

[0046] Hereinafter, embodiments of the present invention will be described.

[0047] However, the present invention is not limited to the following embodiments, and can be appropriately changed and used within the scope of the present invention. Combinations of two or more of the desired configurations of the present invention described in the following embodiments also belong to the present invention.

[0048] [Method for producing magnetic powder]

[0049] The method for producing magnetic powder of the present invention comprises the step of spraying a spray liquid and drying the spray liquid to obtain magnetic powder.

[0050] The spray liquid contains first magnetic particles, second magnetic particles, a thermosetting resin, and an organic solvent.

[0051] For example, in the examples described below, the following first magnetic particles, second magnetic particles, thermosetting resin, and organic solvent may be used.

[0052] First magnetic particle: carbonyl iron powder (average particle size D50: 5 μm)...A

[0053] Second magnetic particle: manganese ferrite powder (composition: (FeO, MnO)·Fe2O3, average particle size: 91nm or 250nm)···B

[0054] Main agent of thermosetting resin: Bisphenol A type epoxy resin···C

[0055] Curing agent for thermosetting resin: phenol curing agent···D

[0056] Organic solvent: Methyl ethyl ketone...

[0057] Mixing ratio: first magnetic particles: second magnetic particles = 75% by weight: 25% by weight, etc.

[0058] The ratio of the total weight of the main agent of the thermosetting resin and the curing agent of the thermosetting resin to the total weight of the first magnetic particles, the second magnetic particles, the main agent of the thermosetting resin and the curing agent of the thermosetting resin (C+D / A+B+C+D) is defined as the "resin amount"; the ratio of the total weight of the first magnetic particles, the second magnetic particles, the main agent of the thermosetting resin and the curing agent of the thermosetting resin to the total weight of the first magnetic particles, the second magnetic particles, the main agent of the thermosetting resin, the curing agent of the thermosetting resin and the organic solvent (A+B+C+D / A+B+C+D+E) is defined as the "spray concentration". At this time, for example, while blending the components so that the resin amount is less than 10 weight % (2.5 weight % in the examples described later), the above-mentioned organic solvent is diluted so that the spray concentration is about 50 weight % to 60 weight % (59.5 weight % in the examples described later) to prepare the spray liquid.

[0059] The first magnetic particle is a soft magnetic metal particle. As the soft magnetic metal particle, a crystalline powder or an amorphous powder can be used. As the crystalline powder, for example, carbonyl iron powder, Sendust magnetic powder, Fe-Si-Cr metal powder, Fe-Si metal powder and other Fe-based magnetic metal powders, Permalloy magnetic powder and other Fe-Ni magnetic metal powders, Permalloy and other Fe-Co magnetic metal powders, Fe-Si-B-Nb-Cu nanocrystalline magnetic metal powders, etc. can be cited. As the amorphous powder, Fe-Si-Cr or Fe-B-Si amorphous magnetic powders can be cited.

[0060] 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 (ElectroMagneticInterference) countermeasure component for high-speed signal systems.

[0061] In particular, when the second magnetic particles are ferrite magnetic particles, the powder molded body can have a higher magnetic permeability and a lower core loss up to a high frequency band.

[0062] When the second magnetic particles are ferrite magnetic particles, the ferrite magnetic particles include, for example, one or more ferrites selected from magnetite (iron ferrite), manganese ferrite, magnesium ferrite, strontium ferrite, nickel zinc ferrite, and nickel ferrite.

[0063] When the second magnetic particle is a ferrite magnetic particle, the ferrite magnetic particle preferably contains one or both of magnetite and manganese ferrite in a total amount of 65 wt % or more. By containing one or both of magnetite and manganese ferrite in a predetermined amount in the ferrite magnetic particle, a higher saturation magnetization can be obtained.

[0064] Alternatively, the second magnetic particles may be metal magnetic particles. When the second magnetic particles are metal magnetic particles, the DC superposition characteristics of the powder compact can be improved. Therefore, it is suitable for use as an EMI countermeasure component such as a power inductor.

[0065] The second magnetic particle is preferably spherical. Spherical not only includes a complete sphere, but also includes a shape close to a sphere. If the second magnetic particle is spherical, the second magnetic particle can be filled into the first magnetic particle at a high density, so the magnetic permeability can be improved.

[0066] 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. The magnetic permeability can be further improved by hot pressing such magnetic powder to produce a powder compact.

[0067] The average particle diameter of the second magnetic particles is, for example, 1 nm to 1 μm, or preferably 40 nm to 250 nm.

[0068] Furthermore, 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.

[0069] By controlling the average particle size of the second magnetic particles such as ferrite magnetic particles within the above range, the aggregation of the second magnetic particles can be suppressed. Therefore, magnetic powder having a resin coating uniformly formed on the surface of the first magnetic particles can be produced. In addition, by hot pressing such magnetic powder, a powder compact can be obtained in which the second magnetic particles are densely filled between the first magnetic particles.

[0070] The average particle size of the second magnetic particles can be obtained by: in observation using a scanning electron microscope (SEM) at a magnification of 50,000 times, the equivalent circle diameter of each particle (except for the case where the outer periphery of the particle is not visible due to the overlap of particles, etc.) is obtained by image analysis, and the equivalent circle diameter is calculated from the average value. On the other hand, the average particle size of the first magnetic particles refers to the particle size D50 at the integral value of 50% in the particle size distribution obtained by the laser diffraction scattering method.

[0071] The average particle size of the first magnetic particles is not particularly limited, and is, for example, 2 μm to 35 μm.

[0072] As the first magnetic particles, the first magnetic coarse particles having a relatively large average particle size and the first magnetic fine particles having a relatively small average particle size can be used together. In this case, the average particle size of the second magnetic particles is smaller than the average particle size of the first magnetic coarse particles and smaller than the average particle size of the first magnetic fine particles. The soft magnetic metal constituting the first magnetic coarse particles may be the same as or different from the soft magnetic metal constituting the first magnetic fine particles.

[0073] Examples of the main agent of the thermosetting resin include bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, polyimide resin, polyphenylene sulfide resin, etc. These main agents may be used alone or in combination.

[0074] Examples of the curing agent for the thermosetting resin include phenolic curing agents, aromatic amine curing agents, imidazole curing agents, imide curing agents, etc. These curing agents may be used alone or in combination.

[0075] Examples of the organic solvent include methyl ethyl ketone, toluene, methyl acetate, ethyl acetate, and acetone.

[0076] By spraying and drying the obtained spray liquid, it is possible to produce magnetic powder in which a thermosetting resin coating is provided on the surface of the first magnetic particles and the second magnetic particles are mixed inside the resin coating.

[0077] In this specification, "thermosetting resin film" refers to a resin film composed of a thermosetting resin in an uncured state. The uncured state refers not only to a prepolymer of a thermosetting resin in an uncured state, but also includes a B stage in a semi-cured state where curing has begun but has not yet been completely cured.

[0078] As a method of spraying and drying the spray liquid, a method using a spray dryer equipped with a two-fluid nozzle or a four-fluid nozzle (also called a Micromist spray dryer) is preferred. The magnetic powder can be obtained by spraying the spray liquid from the two-fluid nozzle or the four-fluid nozzle to volatilize the organic solvent.

[0079] For example, in the examples described below, the spray liquid is sprayed using a four-fluid nozzle of a Micromist spray dryer (evaporation capacity 1.3 kg / h) and heated and dried at a temperature of 70°C to 110°C in a closed system controlled by oxygen partial pressure.

[0080] By spraying and drying the spray liquid, the amount of resin defined above is reduced. By reducing the amount of resin after spray drying of the spray liquid, the aggregation of the first magnetic particles can be suppressed, and a resin film can be easily formed on the surface of each first magnetic particle. As a result, magnetic powder with uniform particle size can be obtained at one go. Therefore, the obtained magnetic powder does not need to be subjected to a cracking process and a classification process and can be used directly.

[0081] For example, the resin amount, which is 2.5% by weight when the spray liquid is prepared, is reduced to 1.5% by weight after the spray liquid is spray-dried, according to the actual value measured by thermogravimetric (TG) analysis after granulation.

[0082] The amount of the resin after spray drying of the spray liquid is preferably 0.15% by weight to 3% by weight as a measured value measured by TG analysis after granulation.

[0083] Figure 1 This is a scanning electron microscope photograph showing an example of magnetic powder obtained after spray drying of the spray liquid.

[0084] like Figure 1 As shown, in the magnetic powder obtained by spraying and drying the spray liquid, the first magnetic particles are not agglomerated with each other, and a resin film that buries the second magnetic particles is formed on the surface of each first magnetic particle. Figure 1 The maximum particle size of magnetic powder is about 30μm.

[0085] As described above, in the method for producing magnetic powder of the present invention, the aggregation of the first magnetic body particles can be suppressed, and magnetic powder with uniform particle size can be obtained at one time. As a result, there is no need to perform processes such as a cracking process and a classification process, so the obtained magnetic powder can be used directly. Alternatively, the processes such as a cracking process and a classification process can be simplified. By hot-pressing such magnetic powder, a powder compact filled with magnetic powder at a high density can be produced, and as a result, the magnetic permeability can be improved.

[0086] Figure 2 This is a schematic diagram showing an example of the structure of a spray dryer including a two-fluid nozzle or a four-fluid nozzle.

[0087] Figure 2 The spray dryer 100 shown includes a nozzle 110, a drying chamber 120 and a recovery unit 130; in the drying chamber 120, the spray liquid X is sprayed using the nozzle 110 to volatilize the organic solvent contained in the spray liquid X, thereby drying the magnetic powder; the recovery unit 130 is used to recover the magnetic powder dried in the drying chamber 120.

[0088] A cover is provided at the upper part in the vertical direction of the drying chamber 120, and a nozzle 110 is provided through the cover. The nozzle 110 is a two-fluid nozzle or a four-fluid nozzle. The spray liquid X can be sprayed vertically downward from the nozzle 110. In addition, an opening 121 is provided on the cover, which supplies flowing hot air (for example, air) along the spraying direction from the upstream side of the spraying direction (vertically downward) of the spray liquid X of the nozzle 110.

[0089] A discharge port 122 for discharging the dried magnetic powder to the outside of the drying chamber 120 is provided on the downstream side in the vertical direction of the drying chamber 120 .

[0090] The recovery section 130 is provided with a cyclone separator 131 and a bag filter 132. The exhaust port 122 of the drying chamber 120 and the cyclone separator 131 are connected by a pipe 133, and the dried magnetic powder is transported to the cyclone separator 131 by the airflow of the hot air, and is recovered by the cyclone separator 131. The dried magnetic powder that cannot be recovered by the cyclone separator 131 will be recovered by the bag filter 132 arranged closer to the downstream side of the hot air flow direction than the cyclone separator 131. As a means of recovering the magnetic powder, it is sufficient to have either the cyclone separator 131 or the bag filter 132. By having both at the same time, the recovery rate of the magnetic powder can be improved. On the downstream side of the hot air flow direction of the bag filter 132, there is a blower 134 for exhausting the gas in the device, and the hot air and the air in the gas flow path flowing through the nozzle 110 are discharged from the blower 134 to the outside of the device.

[0091] [Magnetic powder]

[0092] The magnetic powder obtained by the above process comprises a first magnetic particle and a thermosetting resin coating provided on the surface of the first magnetic particle, wherein the first magnetic particle is a soft magnetic metal particle, and the resin coating is mixed with a second magnetic particle, wherein the average particle size of the second magnetic particle is smaller than the average particle size of the first magnetic particle. Such a magnetic powder is also one of the present invention.

[0093] Figure 3 This is a cross-sectional view schematically showing an example of the magnetic powder of the present invention.

[0094] exist Figure 3 In the magnetic powder 10 shown, a thermosetting resin coating 21 is provided on the surface of a first magnetic particle 11, and second magnetic particles 12 are mixed inside the resin coating 21. Figure 3In the magnetic powder 10 shown, among the plurality of second magnetic particles 12, a portion of the second magnetic particles 12 are buried in the resin film 21, and the remaining second magnetic particles 12 protrude from the resin film 21. Therefore, concavities and convexities are formed on the surface of the magnetic powder 10. The thickness of the resin film 21 may be constant or may vary in different places. The proportion of the second magnetic particles 12 buried in the resin film 21 and the proportion of the second magnetic particles 12 protruding from the resin film 21 can be adjusted, for example, by adjusting the particle sizes of the first magnetic particles and the second magnetic particles, the mixing ratio of the first magnetic particles, the second magnetic particles and the thermosetting resin, etc.

[0095] Figure 4 This is a cross-sectional view schematically showing another example of the magnetic powder of the present invention.

[0096] exist Figure 4 In the magnetic powder 10A shown, 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. Figure 4 In the magnetic powder 10A shown in FIG. 1 , all the second magnetic particles 12 are buried in the resin coating 21. Figure 4 As shown, the thickness of the resin coating 21 may be constant or may vary in different places. If the thickness of the resin coating 21 is not constant, the surface of the magnetic powder 10A may be uneven.

[0097] In the magnetic powder obtained by the method for producing a magnetic powder of the present invention or the magnetic powder of the present invention, it is preferred that at least a portion of the second magnetic particles are buried in the resin film, and it is more preferred that all of the second magnetic particles are buried in the resin film. If the second magnetic particles are buried in the resin film, the magnetic powders are easily bonded to each other when the magnetic powders are hot-pressed to obtain a powder compact described later.

[0098] In the method for producing magnetic powder of the present invention, a magnetic powder comprising Figure 3 As shown in FIG. 1 , a portion of the second magnetic particles protrude from the resin film, and as shown in FIG. Figure 4 As shown in FIG. 1 , all the second magnetic particles are buried in the resin film. Similarly, the magnetic powder of the present invention may also include Figure 3 As shown in FIG. 1 , a portion of the second magnetic particles protrude from the resin film, and as shown in FIG. Figure 4 As shown, all the second magnetic particles are buried in the resin film.

[0099] The first magnetic particle is a soft magnetic metal particle. As soft magnetic metal particles, crystalline powder or amorphous powder can be cited. As crystalline powder, for example, carbonyl iron powder, Sendust magnetic powder, Fe-Si-Cr metal powder, Fe-Si metal powder and other Fe-based magnetic metal powders, Permalloy magnetic powder and other Fe-Ni magnetic metal powders, Permalloy and other Fe-Co magnetic metal powders, Fe-Si-B-Nb-Cu nanocrystalline magnetic metal powders, etc. can be cited. As amorphous powder, Fe-Si-Cr or Fe-B-Si amorphous magnetic powders can be cited.

[0100] The second magnetic particles are, for example, metal oxide magnetic particles, preferably ferrite magnetic particles.

[0101] When the second magnetic particles are ferrite magnetic particles, the ferrite magnetic particles include, for example, one or more ferrites selected from magnetite (iron ferrite), manganese ferrite, magnesium ferrite, strontium ferrite, nickel zinc ferrite, and nickel ferrite.

[0102] When the second magnetic particle is a ferrite magnetic particle, the ferrite magnetic particle preferably contains one or both of magnetite and manganese ferrite in a total amount of 65 wt % or more. By containing one or both of magnetite and manganese ferrite in a predetermined amount in the ferrite magnetic particle, a higher saturation magnetization can be obtained.

[0103] Alternatively, the second magnetic particles may be metal magnetic particles.

[0104] The second magnetic particles are preferably spherical.

[0105] The average particle size of the second magnetic particles is smaller than the average particle size of the first magnetic particles.

[0106] The average particle diameter of the second magnetic particles is, for example, 1 nm to 1 μm, or preferably 40 nm to 250 nm.

[0107] Furthermore, 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.

[0108] The average particle size of the first magnetic particles is not particularly limited, and is, for example, 2 μm to 35 μm.

[0109] Examples of the thermosetting resin include bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, polyimide resin, polyphenylene sulfide resin, etc. These thermosetting resins may be used alone or in combination.

[0110] [Method for producing powder compact]

[0111] The method for producing a powder compact of the present invention comprises: a step of obtaining magnetic powder by the method for producing magnetic powder of the present invention; and a step of obtaining a powder compact by hot-pressing the magnetic powder to cure a thermosetting resin coating.

[0112] In the method for producing a powder compact of the present invention, magnetic powder including first magnetic particles, second magnetic particles and a resin coating may be hot pressed, or a mixture including two or more magnetic powders may be hot pressed as in the following modified example.

[0113] (Variant 1)

[0114] A mixture includes a first magnetic powder and a second magnetic powder. The first magnetic powder includes first magnetic coarse particles, second magnetic particles and a resin coating. The second magnetic powder includes first magnetic fine particles, second magnetic particles and a resin coating.

[0115] (Variant 2)

[0116] A mixture includes a first magnetic powder and a second magnetic powder. The first magnetic powder includes first magnetic coarse particles, second magnetic particles and a resin coating, and the second magnetic powder includes first magnetic fine particles and a resin coating.

[0117] (Variant 3)

[0118] A mixture includes a first magnetic powder and a second magnetic powder. The first magnetic powder includes first magnetic coarse particles and a resin coating, and the second magnetic powder includes first magnetic fine particles, second magnetic particles and a resin coating.

[0119] In the step of obtaining the powder compact, the mixture containing the magnetic powder and the oxide powder may be hot-pressed. In this case, the oxide powder acts as a lubricant and can improve the fluidity of the magnetic powder during hot pressing.

[0120] As the oxide powder, for example, silica particles such as fused quartz can be used.

[0121] The average particle size of the oxide powder is preferably 10 nm to 100 nm.

[0122] The amount of the oxide powder added is preferably 0.1 to 0.25 parts by weight relative to 100 parts by weight of the magnetic powder.

[0123] [Powder compact]

[0124] The powder compact obtained by the above steps can be used as, for example, 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.

[0125] In addition, a powder compact containing the magnetic powder of the present invention is also one of the present invention. The powder compact of the present invention may further contain the above-mentioned oxide powder.

[0126] The powder compact of the present invention can be used as, for example, a powder magnetic core. Therefore, in the powder compact of the present invention, a coil conductor may be disposed inside or on the surface of the powder compact.

[0127] Figure 5 This is a perspective view schematically showing an example of a coil component including a powder magnetic core.

[0128] Figure 5 The coil component 50 shown is an example of a powder compact having a coil conductor arranged therein. The coil component 50 includes: a powder core 51 having a box-shaped shape, and a coil conductor 53 having a conductive wire 52 buried therein. The first end 52a and the second end 52b of the conductive wire 52 are located on the surface of the powder core 51 and are exposed. A portion of the surface of the powder core 51 is covered by a first connecting end 54a and a second connecting end 54b that are electrically independent of each other. The first connecting end 54a is electrically connected to the first end 52a of the conductive wire 52, and the second connecting end 54b is electrically connected to the second end 52b of the conductive wire 52. In the coil component 50, the first end 52a of the conductive wire 52 is covered by the first connecting end 54a, and the second end 52b of the conductive wire 52 is covered by the second connecting end 54b.

[0129] The method of embedding the coil conductor 53 inside the powder core 51 is not particularly limited. For example, a member wound with the wire 52 may be arranged in a mold, and magnetic powder may be further supplied into the mold to perform hot pressing. Alternatively, a plurality of members formed by pre-molding magnetic powder in advance may be prepared, these members may be combined, the wire 52 may be arranged in the gap formed at this time, and an assembly may be obtained, and the assembly may be hot pressed.

[0130] Figure 6 This is a perspective view schematically showing another example of a coil component including a powder magnetic core.

[0131] Figure 6 The coil component 60 shown is an example of a powder compact having a coil conductor disposed on the surface thereof. The coil component 60 is a ring-shaped powder core (ring-shaped core) 61 and a coil conductor 63 having a conductive wire 62 wound on the surface of the powder core 61 .

[0132] Example

[0133] Hereinafter, examples further revealing the present invention will be shown, but it should be noted that the present invention is not limited to these examples.

[0134] [Example 1]

[0135] A spray liquid containing a first magnetic particle, a second magnetic particle, a thermosetting resin, and an organic solvent is sprayed and dried to produce magnetic powder. Carbonyl iron powder with an average particle size of 5 μm is used as the first magnetic particle, manganese ferrite powder with an average particle size of 91 nm is used as the second magnetic particle, bisphenol A type epoxy resin is used as the main agent of the thermosetting resin, and phenol curing agent is used as the curing agent of the thermosetting resin. The combination of the first magnetic particle and the second magnetic particle is as follows: Figure 7 As shown. The resin amount during mixing is 2.4% by weight, and the resin amount after drying is 1.5% by weight as measured by TG analysis after granulation. In Example 1, the aggregation of the first magnetic particles can be suppressed, and a magnetic powder having a resin coating in which the second magnetic particles are buried on the surface of the first magnetic particles can be obtained. The obtained magnetic powder is hot-pressed at 150°C and 690MPa for 30 minutes, and then heat-treated at 150°C for 2 hours to prepare a ring core sample.

[0136] [Example 2]

[0137] Manganese ferrite powder with an average particle size of 250 nm was used as the second magnetic particle, and the mixing ratio of the first magnetic particle to the second magnetic particle was changed to Figure 8 Except for the values ​​shown, magnetic powder and annular core samples were prepared in the same manner as in Example 1. In Example 2, aggregation of the first magnetic particles was suppressed, and magnetic powder having a resin coating in which the second magnetic particles were buried on the surface of the first magnetic particles was obtained.

[0138] The magnetic permeability of the prepared toroidal core samples was measured using a Keysight E4991A RF impedance / material analyzer.

[0139] Figure 7 Graph showing the frequency characteristics of the magnetic permeability in Example 1. Figure 8 3 is a graph showing the frequency characteristics of the magnetic permeability in Example 2. Figure 7 and Figure 8 In the figures, the mixing ratio of the first magnetic particles to the second magnetic particles is expressed as a weight ratio. Figure 7 and Figure 8 In the figure, the real part μ' of the magnetic permeability is represented by a solid line, and the imaginary part μ" which is a loss is represented by a dotted line.

[0140] like Figure 7 and Figure 8 As shown, by mixing the second magnetic particles in the resin film provided on the surface of the first magnetic particles, high magnetic permeability can be obtained. Furthermore, by using ferrite magnetic particles as the second magnetic particles, high magnetic permeability and low core loss can be obtained up to a high frequency band.

Claims

1. A method for producing magnetic powder, comprising: spraying and drying a spray liquid containing first magnetic particles, second magnetic particles, a thermosetting resin and an organic solvent to obtain magnetic powder, 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 film. The second magnetic particle is spherical. The average particle size of the second magnetic particles is smaller than that of the first magnetic particles, and the average particle size of the second magnetic particles is 1 / 10 or less of the average particle size of the first magnetic particles. The second magnetic particles are buried in the resin film.

2. The method for producing magnetic powder according to claim 1, wherein: The second magnetic particles have an average particle size of 1 nm to 1 μm.

3. The method for producing magnetic powder according to claim 1 or 2, wherein: The second magnetic particles are metal oxide magnetic particles.

4. The method for producing magnetic powder according to claim 1 or 2, wherein: The second magnetic particles are ferrite magnetic particles.

5. The method for producing magnetic powder according to claim 4, wherein: The ferrite magnetic particles include one or more ferrites selected from the group consisting of magnetite, manganese ferrite, magnesium ferrite, strontium ferrite, nickel zinc ferrite, and nickel ferrite.

6. The method for producing magnetic powder according to claim 4, wherein: The ferrite magnetic particles contain one or both of magnetite and manganese ferrite in a total amount of 65 wt % or more.

7. A method for producing a powder compact, comprising: a step of obtaining magnetic powder by the method for producing magnetic powder according to any one of claims 1 to 6, and A step of hot-pressing the magnetic powder to cure the thermosetting resin coating to obtain a powder compact.

8. The method for producing a powder compact according to claim 7, wherein: In the step of obtaining the powder compact, a mixture containing the magnetic powder and oxide powder is hot-pressed.

9. The method for producing a powder compact according to claim 7 or 8, wherein: The powder compact is a powder magnetic core.

10. The method for producing a powder compact according to claim 7 or 8, wherein: The method further comprises the step of arranging a coil conductor inside or on the surface of the powder compact.

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