Soft magnetic powder, magnetic core, and electronic component

Abstract

The technical problem to be solved by the present invention is to provide a soft magnetic powder and a pressed powder core that can maintain high insulation resistance even after exposure to high temperature environments, as well as an electronic component having the pressed powder core. The technical solution to the problem is that the soft magnetic powder comprises soft magnetic metal particles whose surfaces are covered by an inorganic insulating film. The inorganic insulating film has a first coating portion in contact with the surface of the soft magnetic metal particles and a second coating portion formed outside the first coating portion. The first coating portion contains phosphorus and oxygen, and the second coating portion contains silicon and oxygen.

Description

Technical Field

[0001] This invention relates to soft magnetic powders, magnetic cores, and electronic components. Background Technology

[0002] In electronic components such as transformers, choke coils, and inductors, coils (windings) that act as electrical conductors are arranged around or inside a magnetic core that exhibits specified magnetic properties.

[0003] Examples of magnetic materials used for magnetic cores include soft magnetic metals such as Fe-based alloys. Regarding the magnetic core, for example, a pressed powder core can be obtained by compressing soft magnetic powder containing particles of a soft magnetic metal together with resin. In such a pressed powder core, an improvement in magnetic properties can be expected when the proportion of magnetic components (fill rate) is increased. However, the resistivity of soft magnetic metals is lower than that of ferrite materials; therefore, when the fill rate of magnetic components in the pressed powder core is increased, the soft magnetic metal particles tend to come into contact with each other, resulting in a decrease in resistivity.

[0004] Therefore, a technique for forming an insulating film on the surface of soft magnetic metal particles has been proposed. For example, Patent Document 1 describes an example of forming an insulating film composed of a phosphorus oxide compound on the surface of Fe-containing metal particles. Patent Document 2 describes an example of forming a silicon dioxide film on the surface of Fe-containing metal particles instead of a phosphorus oxide compound.

[0005] However, the technologies described in Patent Documents 1 and 2 tend to cause a sharp decrease in the insulation resistance of the powder when the soft magnetic powder is exposed to a high-temperature environment. That is, when using the soft magnetic powder described in Patent Documents 1 and 2 to construct a pressed powder magnetic core, there are problems such as low heat resistance under high-temperature environments.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2009-120915

[0009] Patent Document 2: Japanese Patent Application Publication No. 2009-231481 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] The present invention was made in view of the above circumstances, and its object is to provide a soft magnetic powder and a magnetic core that can maintain a high insulation resistance even after exposure to a high temperature environment, as well as an electronic component having the magnetic core.

[0012] Technical solutions for solving technical problems

[0013] To achieve the above objectives, the present invention provides a soft magnetic powder comprising soft magnetic metal particles whose surfaces are covered by an inorganic insulating film. The inorganic insulating film has a first coating portion in contact with the surface of the soft magnetic metal particles and a second coating portion formed outside the first coating portion. The first coating portion contains phosphorus and oxygen, and the second coating portion contains silicon and oxygen.

[0014] The inventors of this invention conducted meticulous research and discovered that by forming an inorganic insulating film with a multilayer structure consisting of a P-based first film and a Si-based second film on the surface of soft magnetic metal particles, the insulation properties of the soft magnetic powder under high-temperature conditions become excellent. That is, even when exposed to high temperatures for extended periods, the insulation resistance of the soft magnetic powder of this invention does not easily decrease, thus maintaining high insulation performance.

[0015] Preferably, the sum of the thickness (T1) of the first coating portion and the thickness (T2) of the second coating portion is 10nm ≤ T1 + T2 ≤ 150nm.

[0016] The ratio of the thickness (T2) of the second covering portion to the sum of the thicknesses of the first covering portion and the second covering portion (T1+T2) is 20%≤T2 / (T1+T2)≤90%, more preferably 50%≤T2 / (T1+T2)≤80%.

[0017] By controlling the film thickness of the first coating portion and the second coating portion under specified conditions as described above, both high insulation and high magnetic permeability can be obtained simultaneously. That is, even after prolonged exposure to high-temperature environments, the decrease in the insulation resistance of the soft magnetic powder can be further suppressed, and high magnetic permeability can be obtained.

[0018] Preferably, in the aforementioned inorganic insulating film, an intermediate layer containing phosphorus and silicon is formed between the first covering portion and the second covering portion. By forming an intermediate layer containing phosphorus and silicon, the adhesion between the first covering portion and the second covering portion is improved, and the insulation performance under high-temperature environments is enhanced.

[0019] Furthermore, it is preferable that the total thickness (S1) of the aforementioned inorganic insulating film is 200 nm or less, and the ratio of the thickness (M1) of the aforementioned intermediate layer to the total thickness (S1) of the aforementioned inorganic insulating film is 0.05 < M1 / S1 ≤ 0.2. In this way, by controlling the total thickness of the inorganic insulating film and the thickness (M1) of the intermediate layer within a specified range, both high insulation and high magnetic permeability can be obtained simultaneously. That is, even after prolonged exposure to high-temperature environments, the decrease in the insulation resistance of the soft magnetic powder can be further suppressed, and high magnetic permeability can be obtained.

[0020] Preferably, the first coating portion contains one or more elements (α) selected from alkali metals (Li, Na, K, Rb, Cs) and alkaline earth metals (Mg, Ca, Sr, Ba). More preferably, the element (α) contained in the first coating portion is Na. Furthermore, the mole fraction ratio α / P of the element (α) in the first coating portion is preferably 0.05 ≤ α / P ≤ 0.5, more preferably 0.1 ≤ α / P ≤ 0.3.

[0021] Furthermore, it is preferable that the first coating portion contains one or more elements (β) selected from Zn and Al. More preferably, the element (β) contained in the first coating portion is Zn. The content ratio β / P of the element (β) in the first coating portion to phosphorus (P) is preferably 0.5 ≤ β / P ≤ 0.8 in mole fraction, and more preferably 0.5 ≤ β / P ≤ 0.7.

[0022] By including element (α) or element (β) in the first coating portion at a specified ratio as described above, the decrease in insulation resistance after the heat resistance test can be further suppressed, and the insulation performance of the soft magnetic powder under high temperature conditions can be further improved.

[0023] The soft magnetic powder of the present invention is used as a magnetic material for magnetic cores, thereby improving the heat resistance of the magnetic cores under high-temperature environments. Furthermore, magnetic cores containing the soft magnetic powder of the present invention are suitable for electronic components such as transformers, choke coils, inductors, and reactors, and are particularly suitable for use as inductors. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of an inductor element according to one embodiment of the present invention.

[0025] Figure 2 This is a cross-sectional schematic diagram of a soft magnetic powder according to one embodiment of the present invention.

[0026] Figure 3 It is Figure 2 The diagram shows an enlarged cross-sectional view of region III.

[0027] Figure 4 It means along Figure 3 The diagram shown is a schematic representation of the results obtained by membrane analysis of measurement line IV using TEM-EDS.

[0028] Figure 5 This is a schematic diagram showing an enlarged cross-section of the main part of the soft magnetic powder in the second embodiment.

[0029] Figure 6 It means along Figure 5 The diagram shown is a schematic representation of the results obtained by membrane analysis of measurement line VI using TEM-EDS.

[0030] Figure 7 This is a partially enlarged cross-sectional schematic diagram showing the microstructure of the pressed powder magnetic core according to the third embodiment of the present invention. Detailed Implementation

[0031] The present invention will now be described based on the embodiments shown in the accompanying drawings, but the present invention is not limited to the embodiments described below.

[0032] First Implementation Method

[0033] like Figure 1 As shown, an inductor element 100 according to one embodiment of the present invention is composed of a coil 120 and a pressed powder core 110, and has a configuration in which the coil 120 is embedded inside the pressed powder core 110.

[0034] Figure 1 The shape of the pressed powder magnetic core 110 shown is arbitrary and not particularly limited; for example, it can be cylindrical, elliptical cylindrical, prismatic, etc. Furthermore, the pressed powder magnetic core 110 comprises soft magnetic powder 1 and resin as a binding material, constituting... Figure 2 The soft magnetic powder 1 shown is formed by bonding multiple soft magnetic metal particles 4 with resin, thereby shaping them into a predetermined shape. The features of the soft magnetic powder 1 of this embodiment will be described below.

[0035] (Soft magnetic powder)

[0036] like Figure 2 As shown, the soft magnetic powder 1 of this embodiment includes a plurality of coated particles 2 on which an inorganic insulating film 10 is formed on the surface of the soft magnetic metal particles 4. Particles other than the coated particles 2 may also be mixed in the soft magnetic powder 1. When the mass ratio of all particles contained in the soft magnetic powder 1 is set to 100%, the mass ratio of the coated particles 2 is preferably 5% or more. Furthermore, the shape of the soft magnetic metal particles 2 is not particularly limited, and they are typically spherical.

[0037] In this embodiment, the particle size distribution of the soft magnetic powder 1 is preferably in the range of 200 μm or less. The particle size distribution of the coated particles 2, which do not contain uncoated particles, can also be set to the above range, and it is particularly preferred that the particle size distribution of the coated particles 2 is in the range of 0.1 to 10 μm. Furthermore, in this embodiment, the method for measuring the particle size d is not particularly limited. When measuring in powder form, laser diffraction scattering is preferred; when measuring in the form of pressed magnetic cores and magnetic components, cross-sectional observation using a SEM or similar image analysis is preferred.

[0038] In the case of determining particle size through image analysis, specifically, the area of ​​each metal particle is calculated in a region squared at a viewing angle of 400 μm. Furthermore, the circumequivalence diameter of each metal particle is calculated based on the obtained area value. Preferably, the above determination is performed in a region of at least 30 locations to obtain the particle size distribution of the soft magnetic powder 1.

[0039] In this embodiment, the material of the soft magnetic metal particles 4 is not particularly limited as long as it is a material that exhibits soft magnetism. Examples of materials that exhibit soft magnetism include: pure iron, Fe-Si alloys (iron-silicon), Fe-Al alloys (iron-aluminum), permalloy alloys (Fe-Ni), iron-silicon-aluminum magnetic alloys (Fe-Si-Al), Fe-Si-Cr alloys (iron-silicon-chromium), Fe-Si-Al-Ni alloys, Fe-Ni-Si-Co alloys, Fe amorphous alloys, and Fe nanocrystalline alloys.

[0040] Furthermore, in this embodiment, the coated particles 2 of the soft magnetic powder 1 can be made of all the same material, or they can be composed of multiple particle groups with different materials.

[0041] For example, some of the soft magnetic metal particles 4 in the soft magnetic powder 1 can be composed of pure iron particles, while others can be composed of Fe-Si alloys, etc. Examples of different materials include: cases where the metals or constituent elements of the alloy are different; cases where the constituent elements are the same but their compositions are different; and cases where the crystal systems are different. Furthermore, if the soft magnetic powder 1 contains uncoated particles other than coated particles 2, the materials of the coated particles 2 and the uncoated particles can be the same or different.

[0042] (Inorganic insulating film)

[0043] Next, the inorganic insulating film 10 covering the surface of the soft magnetic metal particles 4 will be described. This inorganic insulating film 10 may cover at least a portion of the surface of the soft magnetic metal particles 4, or it may cover the entire surface. That is, the coverage rate of the inorganic insulating film 10 relative to the surface of the soft magnetic metal particles 4 is preferably 60% or more, more preferably 80% or more. Furthermore, the inorganic insulating film 10 may continuously cover the surface of the soft magnetic metal particles 4, or it may intermittently cover the surface of the soft magnetic metal particles 4.

[0044] Figure 3 It is Figure 2 The diagram shows an enlarged cross-sectional view of region III. (See diagram below.) Figure 3As shown, the inorganic insulating film 10 has a first covering portion 12 and a second covering portion 14, and is divided into at least two layers. The first covering portion 12 is in contact with the outermost surface of the soft magnetic metal particle 4, covering the particle surface. When viewed from the soft magnetic metal particle 4, the second covering portion 14 is formed on the outside of the first covering portion 12.

[0045] Figure 4 Roughly representing along Figure 3 The measurement line IV shown is the result obtained by membrane analysis using energy dispersive X-ray spectroscopy (EDS) with a transmission electron microscope (TEM).

[0046] Figure 4 In the diagram, the horizontal axis corresponds to the length of measurement line IV, and the vertical axis represents the atomic fraction (atom%) of each detected element. That is, in... Figure 4 In the graph, the right side represents the composition ratio near the surface of the soft magnetic metal particles 4, the center represents the composition ratio of the inorganic insulating film 10, and the outer side (i.e., the left side of the graph) represents the composition ratio of the resin used for TEM observation. Figure 4 In this study, information on other elements such as carbon (C) is removed from the raw data of membrane analysis using TEM-EDS, and only the atomic fraction of the main elements (i.e., the elements required for the interpretation of this invention) is shown.

[0047] like Figure 4 As shown, the first coating portion 12, which is in contact with the outermost surface of the soft magnetic metal particle 4, contains phosphorus (P) and oxygen (O) as main components. That is, the first coating portion 12 is a phosphorus oxide compound film. More specifically, in this embodiment, the first coating portion 12 refers to a range in which, when the total amount of the main elements (O, P, Si) contained in the film is set to 100 atom%, the atomic fraction of phosphorus (P) is 5% or more, and the atomic fraction of phosphorus (P) is more than 5 times the atomic fraction of silicon (Si).

[0048] In addition, Figure 4In the first coating portion 12 shown, in addition to phosphorus and oxygen, Na is also present as an example. Thus, in this embodiment, it is preferable that the first coating portion 12 contains one or more elements selected from alkali metals (Li, Na, K, Rb, Cs), alkaline earth metals (Mg, Ca, Sr, Ba), Zn, and Al, and more preferably Na or Zn. Furthermore, in this embodiment, one or more elements selected from alkali metals (Li, Na, K, Rb, Cs) and alkaline earth metals (Mg, Ca, Sr, Ba) are designated as additive element α, and one or more elements selected from Zn and Al are designated as additive element β.

[0049] When the first coating portion 12 contains the added element α, and the total amount of the elements contained in the first coating portion 12 is set to 100 mol%, the content ratio of the added element α and phosphorus (P) α / P is preferably 0.05 ≤ α / P ≤ 0.5 in terms of mole fraction, and more preferably 0.1 ≤ α / P ≤ 0.3.

[0050] On the other hand, when the first coating portion 12 contains the added element β, and the total amount of the elements contained in the first coating portion 12 is set to 100 mol%, the content ratio of the added element β and phosphorus (P) β / P is preferably 0.5 ≤ β / P ≤ 0.8 in terms of mole fraction, and more preferably 0.5 ≤ β / P ≤ 0.7.

[0051] In addition, such as Figure 4 As shown, the Na element, which is present as an additive element α, tends to be more concentrated on the soft magnetic metal particle 4 side than on the second coating portion 14 side. The presence of other additive elements α (Li, K, Rb, Cs, Mg, Ca, Sr, Ba) or β (Zn, Al) also exhibits the same atomic fraction as Na.

[0052] like Figure 4 As shown, the second coating portion 14 contains silicon (Si) and oxygen as main components. That is, the second coating portion 14 is an oxide film of Si. More specifically, in this embodiment, the second coating portion 14 refers to a range in which, when the total amount of the main elements (O, P, Si) contained in the film is set to 100 atom%, the atomic fraction of silicon (Si) is 10% or more, and the atomic fraction of silicon (Si) is more than 5 times the atomic fraction of phosphorus (P).

[0053] In addition, although Figure 3 The diagram is omitted, but an intermediate layer 16 may exist between the first covering portion 12 and the second covering portion 14. For example, the intermediate layer 16 may be a diffusion layer containing both phosphorus and silicon. In this embodiment, the intermediate layer 16 refers to a layer in which the atomic fractions of both phosphorus and silicon are 5% or more, and the atomic fraction of phosphorus is in the range of 0.7 to 1.5 times that of silicon.

[0054] like Figure 4 As shown, in this embodiment, the thickness of the intermediate layer 16 is as thin as 0.4 nm or less. Thus, when the layer between the first covering portion 12 and the second covering portion 14 is 0.4 μm or less, as... Figure 3 As shown, it can be assumed that the intermediate layer 16 does not exist. Furthermore, when the intermediate layer 16 is present, the thickness of the intermediate layer 16 is not included in the thickness (T1) of the first covering portion 12 and the thickness (T2) of the second covering portion 14, which will be described later. The case where the intermediate layer 16 is present will be described in detail in the second embodiment.

[0055] The composition of the inorganic insulating film 10 has been described above. However, in addition to the elements mentioned above, the first covering portion 12 and the second covering portion 14 may also contain other elements (γ). For example, the first covering portion 12 may contain iron (Fe), boron (B), etc., and the second covering portion 14 may contain iron, boron, magnesium (Mg), etc. The content ratio of these other elements (γ), calculated in atomic fraction, is preferably 0.01 or less relative to phosphorus (γ / P≤0.01) or 0.1 or less relative to Si (γ / Si≤0.1).

[0056] In this embodiment, it is preferable to control within a specified range. Figure 3 The thickness (T1) of the first covering portion 12 and the thickness (T2) of the second covering portion are shown. Specifically, the sum of the thicknesses of the first covering portion 12 and the second covering portion 14 (T1+T2) is preferably set to 10nm≤T1+T2≤150nm, and more preferably set to 30nm≤T1+T2≤80nm.

[0057] Furthermore, the ratio of the thickness (T2) of the second covering portion 14 to the sum of the thickness of the first covering portion 12 and the thickness of the second covering portion 14 (T1+T2) is preferably set to 20%≤T2 / (T1+T2)≤90%, and more preferably 50%≤T2 / (T1+T2)≤80%.

[0058] The film thickness of the first coating portion 12 and the second coating portion 14 can be measured by the film resolution of the TEM-EDS described above. When measuring the film thickness, 10 arbitrary resolution regions are extracted near the particle surface, and the thickness of each layer is measured in each resolution region. Then, the average value of the obtained data is calculated, and this average value is set as the film thickness T1 and T2 of each layer.

[0059] Furthermore, in this embodiment, as described above, the composition contained in the inorganic insulating film 10 can be analyzed by TEM-EDS. Alternatively, when determining the composition and thickness of each layer of the inorganic insulating film 10 in the state of the pressed powder core 110, a sample for TEM observation can be prepared using a microsampling method employing a focused ion beam (FIB), and film analysis can be performed using the same method as described above.

[0060] Next, the manufacturing method of the soft magnetic powder 1, the pressed magnetic core 110, and the inductor element 100 of this embodiment will be described. Furthermore, the manufacturing method is not limited to the method described below.

[0061] (Method for manufacturing soft magnetic powder)

[0062] First, a plurality of soft magnetic metal particles 4 constituting the soft magnetic powder 1 are prepared. The soft magnetic metal particles 4 can be prepared using known powder manufacturing methods, such as gas atomization, water atomization, rotating disk method, carbonyl method, etc. Alternatively, they can be prepared by mechanically pulverizing a thin strip obtained by a single-roller method. Among these methods, the carbonyl method is preferred from the viewpoint of easily obtaining soft magnetic metal particles with the desired magnetic properties. Furthermore, the particle size of the obtained soft magnetic metal particles 4 can be adjusted by sieving, air classification, etc.

[0063] Next, an inorganic insulating film 10, including a first coating portion 12 and a second coating portion 14, is formed on the obtained soft magnetic metal particles 4 to obtain coated particles 2. The first coating portion 12, containing phosphorus and oxygen, can be formed by phosphate treatment. Specifically, firstly, phosphoric acid or a phosphate containing a specified element (α, β) is dissolved in a solvent such as water or alcohol to prepare a phosphate solution. Then, the soft magnetic metal particles 4 are impregnated in this solution, or the solution is sprayed onto the soft magnetic metal particles 4 and dried, thereby forming the first coating portion 12 on the surface of the soft magnetic metal particles 4. Furthermore, the thickness of the first coating portion 12 can be controlled by the concentration of the precursor (phosphoric acid or phosphate) contained in the phosphate solution, the impregnation treatment time, the spray volume, etc.

[0064] After the first coating portion 12 is formed, a second coating portion 14 containing silicon and oxygen is formed on its surface. The second coating portion is formed by spraying a solution containing a silane coupling agent that serves as a Si source onto the soft magnetic metal particles 4, or by impregnating the soft magnetic metal particles 4 in the solution, followed by drying and / or heat treatment.

[0065] Examples of silane coupling agents used at this time include tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and hexyltrimethylsilane, with TEOS being preferred. Additionally, examples of solvents for dissolving the silane coupling agent include water, ethanol, acetone, and isopropanol, with no particular limitation. Furthermore, the thickness of the second coating portion 14 can be controlled by the concentration of the silane coupling agent contained in the treatment solution, the spray volume, and the immersion treatment time.

[0066] Furthermore, if the soft magnetic powder 1 contains particles other than coated particles 2, after producing coated particles 2 through the above-described process, the other particles can be mixed and the soft magnetic powder 1 can be produced. If a phosphorus oxide-based film or a Si-based oxide film is formed on the surface of the particles other than coated particles 2, phosphate treatment or sol-gel coating can be performed together with the coated particles 2.

[0067] (Manufacturing methods for pressed powder magnetic cores and inductor components)

[0068] Next, the soft magnetic powder 1 described above is used to manufacture the pressed powder core. There are no particular limitations on the specific manufacturing method; known methods can be used. For example, Figure 1 The powder-pressed magnetic core 110 shown can be manufactured by the method shown below.

[0069] First, particles are prepared as the raw material for the pressed powder magnetic core 110. These particles can be obtained by mixing soft magnetic powder 1 containing coated particles 2 with an inorganic insulating film 10 and a binder material diluted with a solvent, followed by drying to obtain particles. The obtained particles can be sized through a sieve with a mesh size of 100–400 μm.

[0070] As a solvent for diluting the binder material during particle production, ketones such as acetone and ethanol can be used. Furthermore, there are no particular limitations on the binder material; examples include: epoxy resin, phenolic resin, melamine resin, urea-formaldehyde resin, furan resin, alkyd resin, unsaturated polyester resin, diallyl phthalate resin, polyamide, polyphenylene sulfide (PPS), polypropylene (PP), liquid crystal polymer (LCP), water glass (sodium silicate), silicone resin, etc. When using a resin as the binder material, it can be any of the above-mentioned thermosetting or thermoplastic resins, with thermosetting resins being preferred.

[0071] Furthermore, there are no particular limitations on the content of the binder material; for example, if the soft magnetic powder 1 is set to 100 parts by weight, it is preferably set to 2 to 5 parts by weight. By mixing the binder material at this ratio, the volume filling rate of the soft magnetic powder 1 in the obtained pressed powder core is about 70 to 90 vol%.

[0072] The aforementioned particles, along with a hollow coil serving as an embedded component, are filled into a mold and compressed. This yields a molded body with the desired shape of the pressed powder magnetic core. By appropriately heat-treating this molded body, the pressed powder magnetic core 110 can be obtained. Furthermore, the heat treatment conditions can be appropriately determined based on the type of bonding material used. The resulting pressed powder magnetic core 110 has a coil 120 embedded within it; therefore, by applying a voltage to the coil 120, it functions as an inductor element 100.

[0073] (Summary of the first implementation method)

[0074] In this embodiment, by covering the surface of the soft magnetic metal particles 4 contained in the soft magnetic powder 1 with a multilayer inorganic insulating film 10 comprising a first coating portion 12 based on phosphorus oxides and a second coating portion 14 based on Si oxides, the heat resistance of the soft magnetic powder 1 can be improved. In this embodiment, improved heat resistance means that even after the soft magnetic powder 1 has been exposed to a high-temperature environment (above 150°C) for a long time (more than 2000 hours), the insulation resistance of the soft magnetic powder 1 does not easily decrease, and it can maintain high insulation performance.

[0075] Furthermore, by controlling the film thickness of the first coating portion 12 and the film thickness of the second coating portion 14 within a specified ratio range, the heat resistance of the soft magnetic powder 1 is further improved. Specifically, as described above, the ratio of the thickness (T2) of the second coating portion 14 to the sum of the thicknesses of the first coating portion 12 and the second coating portion 14 (T1+T2) is preferably 20% ≤ T2 / (T1+T2) ≤ 90%, more preferably 50% ≤ T2 / (T1+T2) ≤ 80%.

[0076] Furthermore, by setting the thickness of the first covering portion 12 and the sum of the thicknesses of the second covering portion 14 (T1+T2) within a specified range, it helps to improve the magnetic properties. Specifically, as described above, it is preferably set to 10nm≤T1+T2≤150nm, and more preferably to 30nm≤T1+T2≤80nm.

[0077] Generally, when the thickness of the insulating film covering the particle surface is increased (e.g., 200 nm or more), the electrical resistance of the soft magnetic powder tends to increase, and the heat resistance also tends to improve. However, when the insulating film becomes thicker, it has an adverse effect on the magnetic properties of the pressed powder core, particularly tending to reduce the permeability. In contrast, when the pressed powder core is formed from the soft magnetic powder 1 of this embodiment, by controlling the film thickness of the first coating portion 12 and the second coating portion 14 within a specified ratio range, even if the thickness of the inorganic insulating film 10 is reduced, the insulation resistance after the heat resistance test can be maintained at a high value, and high permeability can be obtained simultaneously.

[0078] Furthermore, in this embodiment, it is preferable that the first coating portion 12 contains a predetermined amount of additive element α (alkali metal or alkaline earth metal) or additive element β (Zn, Al). By containing these additive elements, the heat resistance of the soft magnetic powder 1 tends to be further improved.

[0079] The reason why adding element α or element β further improves heat resistance is unclear, but it is thought to be for reasons such as the following. Figure 4 As shown, the aforementioned additive element α or additive element β is present in the first coating portion 12, biased towards the surface side of the soft magnetic metal particles 4. Therefore, these elements are considered to have the effect of hindering the diffusion of Fe elements located on the outermost surface of the soft magnetic metal particles 4 into the inorganic insulating film 10 and their combination with oxygen under high-temperature atmosphere. Therefore, when the first coating portion contains additive element α or additive element β, excessive iron oxide formation can be suppressed at the interface between the soft magnetic metal particles 4 and the inorganic insulating film 10, preventing a decrease in insulation resistance.

[0080] Furthermore, the soft magnetic powder 1 of the present invention is used as a magnetic material for the pressed powder core 110, thereby improving the heat resistance of the pressed powder core 110 under high temperature conditions.

[0081] Second Implementation Method

[0082] In the second embodiment, based on Figure 5 and Figure 6 The case where the intermediate layer 16 exists in the inorganic insulating film 10 will be described. Furthermore, descriptions of configurations identical to those in the first embodiment in the second embodiment will be omitted, and the same reference numerals will be used.

[0083] The soft magnetic powder 1 of the second embodiment is the same as that of the first embodiment, and includes coated particles 2 on the surface of the soft magnetic metal particles 4 on which an inorganic insulating film 10 is formed. Figure 5 This is an enlarged cross-sectional view of the area near the surface of the coated particle 2 in the second embodiment. For example... Figure 5 As shown, the inorganic insulating film 10 has a first covering portion 12 and a second covering portion 14 as described in the first embodiment, and is divided into at least two layers. Moreover, in the second embodiment, an intermediate layer 16 is formed between the first covering portion 12 and the second covering portion 14. That is, the first covering portion 12 is in contact with and covers the outermost surface of the soft magnetic metal particle 4, and the second covering portion 14 is formed on the outside of the first covering portion 12 through the intermediate layer 16.

[0084] Figure 6 Briefly indicating along Figure 5 The measurement line VI shown is the result obtained by membrane analysis using TEM-EDS. This is consistent with the first embodiment. Figure 4 Similarly, in Figure 6 In the diagram, the horizontal axis corresponds to the length of the measurement line VI, and the vertical axis represents the atomic fraction (atom%) of each detected element. That is, in... Figure 6 In the graph, the right side represents the composition ratio near the surface of the soft magnetic metal particles 4, the center represents the composition ratio of the inorganic insulating film 10, and the outer side (i.e., the left side of the graph) represents the composition ratio of the resin used for TEM observation. Figure 6 In this study, information on other elements such as carbon (C) is removed from the raw data of membrane analysis using TEM-EDS, and only the atomic fraction of the main elements (i.e., the elements required for the interpretation of this invention) is shown.

[0085] like Figure 6 As shown, the intermediate layer 16 is a diffusion layer containing phosphorus (P), silicon (Si), and oxygen, composed of the components of the first coating portion 12 and the second coating portion 14. In the second embodiment, the diffusion layer 16 also refers to a layer in which the atomic fractions of P and Si are 5% or more, and the atomic fraction of P is 0.7 to 1.5 times that of Si.

[0086] In the second embodiment, the intermediate layer 16 is formed between the first covering portion 12 and the second covering portion 14. This increases the affinity between the first covering portion 12 and the second covering portion 14, making it less likely to damage the inorganic insulating film 10. Therefore, the soft magnetic powder 1 and the pressed powder core 110 containing the soft magnetic powder 1 in the second embodiment exhibit superior heat resistance compared to the case without the intermediate layer 16.

[0087] Next, the film thickness of the inorganic insulating film 10 in the second embodiment will be explained. In the second embodiment, as... Figure 5 As shown, the total thickness (S1) of the inorganic insulating film 10 is expressed as the sum of the thickness (T1) of the first covering portion 12, the thickness (T2) of the second covering portion 14, and the thickness (M1) of the intermediate layer 16. Furthermore, although... Figure 5 and Figure 6 While not explicitly stated, a fourth layer may be formed in the inorganic insulating film 10 in addition to the aforementioned layers 12 to 16. In this embodiment, the total thickness (S1) of the inorganic insulating film 10 is 200 nm or less, preferably 10 nm ≤ S1 ≤ 170 nm, and more preferably 25 nm ≤ S1 ≤ 150 nm.

[0088] The thickness (M1) of the intermediate layer 16 is at least greater than 0.4 nm. As described in the first embodiment, if the thickness M1 is less than or equal to 0.4 nm, the intermediate layer 16 is considered to be absent. Furthermore, the ratio of the thickness (M1) of the intermediate layer 16 to the total thickness (S1) of the inorganic insulating film 10 is preferably 0.05 < M1 / S1 ≤ 0.2, and more preferably 0.07 ≤ M1 / S1 ≤ 0.12.

[0089] Generally, when the thickness of the insulating film covering the particle surface is increased (e.g., S1 is 200 nm or more), the resistance of the soft magnetic powder tends to increase while its permeability decreases. Conversely, when the thickness of the insulating film covering the particle surface is reduced, although the permeability increases, the resistance decreases. That is, the resistance and permeability exhibit opposite tendencies relative to the thickness of the insulating film. In the second embodiment, by forming the intermediate layer 16 with the specified thickness as described above, even if the total thickness S1 of the inorganic insulating film 10 is reduced, both high insulation and high permeability can be obtained simultaneously. That is, the soft magnetic powder 1 of the second embodiment and the pressed powder core 110 containing the soft magnetic powder 1 do not easily experience a decrease in insulation resistance and exhibit high permeability even when exposed to high temperature environments for a long time.

[0090] Furthermore, in the second embodiment, the thickness T1 of the first covering portion 12 and the thickness T2 of the second covering portion 14 are preferably the same as in the first embodiment. That is, the ratio of the thickness (T2) of the second covering portion 14 to the sum of the thicknesses of the first covering portion 12 and the second covering portion 14 (T1+T2) is preferably set to 20%≤T2 / (T1+T2)≤90%, more preferably 50%≤T2 / (T1+T2)≤80%. By having this configuration, the soft magnetic powder 1 and the pressed powder magnetic core 110 of the second embodiment further improve heat resistance and also further improve magnetic permeability.

[0091] Furthermore, in the second embodiment, it is preferable that the first coating portion 12 contains a predetermined amount of additive element α or additive element β. By including additive element α or β in the first coating portion 12, there is a tendency to further improve the heat resistance of the soft magnetic powder 1 and the pressed powder core 110.

[0092] Furthermore, the thickness and composition of each layer 12, 14, and 16 in the second embodiment are the same as those in the first embodiment, and can be analyzed by TEM-EDS membrane analysis.

[0093] Next, the manufacturing method of the soft magnetic powder 1 according to the second embodiment will be described. In the second embodiment, similar to the first embodiment, the first coating portion 12 is formed by phosphate treatment, and the second coating portion 14 is formed by sol-gel coating using a silane coupling agent. Specifically, in order to form an intermediate layer 16 between the first coating portion 12 and the second coating portion 14, after forming the second coating portion 14 by sol-gel coating, the soft magnetic powder 1 is heat-treated under predetermined conditions.

[0094] Specifically, when the intermediate layer 16 is formed by heat treatment, the soft magnetic powder 1 with the second coating 14 is heated in a nitrogen (N2) atmosphere or a vacuum atmosphere at a temperature range of 400°C to 600°C for about 10 to 30 minutes. At this time, it is preferable to set the heating rate to 5 to 10°C / minute. Alternatively, the cooling rate can be controlled at 5 to 10°C / minute. Alternatively, heat treatment can be performed in two stages, in which case the temperature is first held at 400 to 500°C for 3 to 5 minutes, and then the temperature is further increased and held at 500 to 600°C for 7 to 25 minutes.

[0095] To increase the thickness M1 of the intermediate layer 16, in the heat treatment described above, the holding temperature can be set to approximately 550°C to 600°C, or the holding time can be extended to approximately 25 to 30 minutes. Alternatively, the heating rate can be slowed down to approximately 5 to 7°C / minute, or the cooling rate can be slowed down to approximately 5 to 7°C / minute. When the thickness M1 of the intermediate layer 16 needs to be reduced, the factors can be controlled in the opposite direction to the above.

[0096] Furthermore, the manufacturing conditions other than the heat treatment process described above are the same as in the first embodiment, and the soft magnetic powder 1 can be manufactured. Additionally, the pressed magnetic core and inductor element can also be manufactured using the same method as in the first embodiment, and descriptions are omitted here.

[0097] Third Implementation Method

[0098] The following is based on Figure 7 The third embodiment of the present invention will be described. Furthermore, descriptions of configurations in the third embodiment that are the same as those in the first and second embodiments will be omitted, and the same reference numerals will be used.

[0099] Figure 7 This is a partially enlarged cross-sectional schematic diagram showing the fine structure of the pressed powder magnetic core 111 in the third embodiment. For example... Figure 7As shown, in the third embodiment, the soft magnetic powder 8 is also fixed using resin 20 as a binding material. In this third embodiment, the soft magnetic powder 8 is composed of multiple powders with different particle size distributions. Specifically, the soft magnetic powder 8 includes large-diameter powder 6 with relatively large particle size and small-diameter powder 1a with relatively small particle size.

[0100] The particle size distribution of the large-diameter powder 6 is preferably in the range of 200 μm or less, and the median diameter (D50) is preferably 20 to 30 μm. On the other hand, the particle size distribution of the small-diameter powder 1a is preferably in the range of 15 μm or less, and the median diameter (D50) of the small-diameter powder 1a is reduced to about 0.1 to 0.25 times that of the median diameter of the large-diameter powder 6, more specifically, preferably 3 to 5 μm. In addition, the particle size (D90) of the small-diameter powder 1a, which accounts for 90% of the cumulative frequency, is preferably 10 μm or less.

[0101] In the third embodiment, the particle size d and particle size distribution of the large-diameter powder 6 and the small-diameter powder 1a are measured by image analysis using cross-sectional observation, and are performed in the following order. First, as in the first embodiment, the area of ​​each metal particle is calculated in a region squared at a viewing angle of 400 μm. Then, the circumscaping equivalent diameter of each metal particle is calculated based on the obtained area value. In the third embodiment, it is also preferable to perform the above measurement at 30 locations. Then, in the third embodiment, based on the circumscaping equivalent diameter obtained from all measured locations, each metal particle is classified into a group with a diameter less than 15 μm and a group with a diameter greater than 15 μm. The group with a diameter less than 15 μm is referred to as small-diameter powder 1a, and its particle size distribution and particle size at each cumulative frequency are calculated. On the other hand, the group with a diameter greater than 15 μm is referred to as large-diameter powder 6, and its particle size distribution and particle size at each cumulative frequency are calculated.

[0102] Furthermore, in the third embodiment, the proportion of small-diameter powder 1a to the total soft magnetic powder 8 is preferably 5 to 40% by weight, and more preferably 10 to 30%. The proportion of small-diameter powder 1a is not only controlled during the manufacturing process, but can also be controlled by observing the cross-section of the pressed powder core 111 after it is manufactured, such as by SEM observation.

[0103] In this way, by combining powders with different particle sizes, the volume filling rate of the soft magnetic powder 8 in the pressed powder core 111 can be improved, and it tends to further improve the magnetic properties.

[0104] Furthermore, the core particles 2a constituting the small-diameter powder 1a have an insulating film formed on their surface. In the third embodiment, the core particles 2a of the small-diameter powder 1a correspond to the coated particles 2 in the first embodiment or the coated particles 2 in the second embodiment. That is, the surface of the core particles 2a constituting the small-diameter powder 1a is covered by an inorganic insulating film 10, which is a multilayer structure film containing a first coating portion 12 containing phosphorus and oxygen and a second coating portion 14 containing silicon and oxygen.

[0105] like Figure 7 As shown, in the pressed powder core 111, small-diameter powder 1a enters and exists in the gaps between the large-diameter powder 6 particles. When combining powders of different particle sizes, the contribution of the small-diameter powder 1a existing between the large-diameter powder 6 particles to the insulation of the pressed powder core is significant. Therefore, by having a first coating portion 12 and a second coating portion 14 on the surface of the core particles 2a of the small-diameter powder 1a, the insulation of the pressed powder core 111 can be improved more effectively.

[0106] The surface of the core particles 6a of the large-diameter powder 6 may not form an insulating film, or it may only form either a phosphorus oxide-based film or a Si-based oxide film, or it may form a multilayer structure film like the small-diameter powder 1a.

[0107] Since the large-diameter powder 6 contributes significantly to the magnetic properties, it is preferable to minimize the presence of non-magnetic materials such as the coating component. Therefore, it is more preferable to form only a Si-based oxide coating derived from TEOS on the surface of the core particles 6a of the large-diameter powder 6 (i.e., more preferably, only a coating corresponding to the second coating portion 14). With this configuration, the influence of the insulating coating on the magnetic properties (e.g., permeability) can be minimized, and the magnetic properties of the pressed powder core 111 are further improved.

[0108] Furthermore, the core particles constituting both the large-diameter powder 6 and the small-diameter powder 1a are made of the same material as in the first embodiment, and various soft magnetic metal particles containing Fe can be used. The core particles of the large-diameter powder 6 and the small-diameter powder 1a can be made of the same material or different materials.

[0109] In the third embodiment, the small-diameter powder 1a is composed of the coated particles 2 of the first embodiment or the coated particles 2 of the second embodiment. Therefore, the soft magnetic powder and the pressed magnetic core of the third embodiment have the same effect as those of the first embodiment or the second embodiment.

[0110] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. For example, in the above embodiments, an inductor element 100 with a coil 120 is shown embedded inside the pressed powder core 110, but the manner of the inductor element is not particularly limited, and it can also be a structure in which a wire is wound around the surface of a pressed powder core of a predetermined shape with a predetermined number of turns. In this case, the shape of the pressed powder core can be, for example, FT type, ET type, EI type, UU type, EE type, EER type, UI type, drum type, toroidal type, pot type, cup type, etc.

[0111] Furthermore, regarding the manufacturing method of the pressed powder magnetic core, in the above embodiment, the soft magnetic powder 1 is mixed with a resin that serves as a binding material, but a lubricant such as a metal soap can also be used instead of the resin. In this case, a metal soap such as zinc oleate or zinc stearate is mixed with the soft magnetic powder 1. Then, heat and pressure are applied to the mixture to obtain a molded body of arbitrary shape, and the molded body is heat-treated at approximately 450–600°C to obtain the pressed powder magnetic core.

[0112] Furthermore, in the third embodiment, the soft magnetic powder 8 is composed of two powders with different particle sizes, but it is also possible to use three powders to form the soft magnetic powder. For example, in addition to the large-diameter powder 6 and the small-diameter powder 1a, a medium-diameter powder having the median diameter between them can also be included to form the soft magnetic powder. In this case, similar to the third embodiment, it is preferable that the small-diameter powder is composed of... Figure 2 The coated particles 2 shown are used to form the medium-diameter powder, which can be either coated particles 2 or uncoated particles.

[0113] Furthermore, while the above embodiments illustrate an example of an inductor element as an electronic component, from the viewpoint of heat resistance, the present invention can also be applied to electronic components such as transformers, choke coils, and reactors.

[0114] Example

[0115] The present invention will be further described below based on detailed embodiments, but the present invention is not limited to these embodiments.

[0116] Experiment A

[0117] In Experiment A, metal particles having an inorganic insulating film 10 formed of a first coating portion 12 and a second coating portion 14 were used to prepare soft magnetic powder samples and pressed powder core samples of Example A1, and their performance was evaluated. Additionally, in Experiment A, during phosphate treatment, multiple phosphate solutions with different types or contents of added elements were used to prepare soft magnetic powder samples and pressed powder core samples of Examples A2 to A28. The manufacturing methods of each example in Experiment A will be described below.

[0118] (Example A1)

[0119] First, two types of powders were prepared as raw materials for the soft magnetic powder: small-diameter powder and large-diameter powder. Specifically, the small-diameter powder was made of pure iron with a median diameter (D50) of 5 μm, and the large-diameter powder was made of 93.5Fe-6.5Si with a median diameter (D50) of 25 μm.

[0120] Then, for the prepared small-diameter powder, an inorganic insulating film is coated in the following sequence. First, the small-diameter powder is subjected to phosphate treatment to form a first coating on the surface of the core particles of the small-diameter powder. Then, the small-diameter powder is impregnated and stirred in an ethanol solution with added TEOS, and then dried under specified conditions, thereby further forming a second coating outside the first coating.

[0121] On the other hand, for large-diameter powders, only TEOS sol-gel coating is used to form a Si-based oxide film on the surface of the core particles of the large-diameter powder.

[0122] The soft magnetic powder sample of Example A1 is obtained by mixing the small-diameter powder and the large-diameter powder in a prescribed ratio. Furthermore, in this example, the proportion of the small-diameter powder relative to the total soft magnetic powder is set to 30% by weight.

[0123] Next, using the soft magnetic powder sample from Example A1, pressed powder core samples were prepared in the following sequence. First, soft magnetic powder containing both small-diameter and large-diameter powders was mixed with epoxy resin diluted with acetone, dried at 50°C for 120 hours, and then granulated using a 400 μm mesh sieve to obtain raw material particles. At this time, the amount of epoxy resin added was set to 4 parts by weight relative to 100 parts by weight of the soft magnetic powder. Then, the above particles were filled into a ring-shaped mold and pressed at a molding pressure of 6 t / cm² (approximately 6 × 10² MPa) to obtain a molded body. This molded body was then heat-treated at 200°C in an atmospheric atmosphere for 180 minutes to obtain the pressed powder core sample.

[0124] Furthermore, the dimensions of the powder-pressed magnetic core sample of Example A1 obtained through the above process are an outer diameter of 17.5 mm, an inner diameter of 10.5 mm, and a height of 5.0 mm.

[0125] (Examples A2 to A10)

[0126] In Examples A2 to A10, during phosphate treatment, a phosphate solution containing Na as an additive element α was used to form the first coating portion, resulting in small-diameter powder. Furthermore, in Examples A2 to A10, experiments were conducted by varying the concentration of Na-containing phosphate in the phosphate solution to adjust the Na content ratio in the first coating portion. In addition, the experimental conditions other than those described above in Examples A2 to A10 were operated in the same manner as in Example A1 to prepare soft magnetic powder samples and pressed magnetic core samples of Examples A2 to A10.

[0127] (Examples A11-A18)

[0128] In Examples A11 to A18, the type of added element α was changed to an element other than Na, forming a first coating on the surface of the core particles of the small-diameter powder. Furthermore, in Examples A11 to A18, the content ratio (α / P) of added element α was fixed at 0.1. The experimental conditions other than those described above in Examples A11 to A18 were operated in the same manner as in Example A1, and the soft magnetic powder samples and pressed magnetic core samples of Examples A11 to A18 were prepared.

[0129] (Examples A19-A25)

[0130] In Examples A19-A25, during phosphate treatment, a phosphate solution containing Zn as an additive element β was used to form the first coating portion, resulting in small-diameter powder. Furthermore, in Examples A19-A25, experiments were conducted by varying the concentration of Zn-containing phosphate in the phosphate solution to adjust the Zn content ratio in the first coating portion. The experimental conditions other than those described above in Examples A19-A25 were operated in the same manner as in Example A1, and soft magnetic powder samples and pressed magnetic core samples of Examples A19-A25 were prepared.

[0131] (Examples A26-A28)

[0132] In Examples A26-A28, Al was added instead of Zn as the additive element β to form a first coating on the surface of the core particles of the small-diameter powder. The experimental conditions other than those described above in Examples A26-A28 were operated in the same manner as in Example A1 to prepare the soft magnetic powder samples and pressed magnetic core samples of Examples A26-A28.

[0133] (Comparative Example A1)

[0134] In Comparative Example A1, only a phosphorus oxide-based film was formed on the surface of the small-diameter powder core particles; sol-gel coating using TEOS was not performed. All other experimental conditions were the same as in Example A1, and soft magnetic powder samples and pressed magnetic core samples of Comparative Example A1 were prepared.

[0135] (Comparative Example A2)

[0136] In Comparative Example A2, no phosphate treatment was performed on the small-diameter powder; instead, a sol-gel coating using TEOS was applied, forming only a Si-based oxide film on the surface of the core particles of the small-diameter powder. All other experimental conditions were the same as in Example A1, and soft magnetic powder samples and pressed magnetic core samples of Comparative Example A2 were prepared.

[0137] (Comparative Example A3)

[0138] In Comparative Example A3, the same procedure as in Comparative Example A1 was followed, and only a phosphorus oxide-based coating was formed on the surface of the small-diameter powder core particles. In Comparative Example A3, a phosphate solution containing Na as the additive element α was used during the phosphate treatment. All other experimental conditions were the same as in Example A1, and the soft magnetic powder sample and pressed magnetic core sample of Comparative Example A3 were prepared.

[0139] (Comparative Example A4)

[0140] In Comparative Example A4, the same procedure as in Comparative Example A1 was followed, and only a phosphorus oxide-based coating was formed on the surface of the small-diameter powder core particles. In Comparative Example A4, a phosphate solution containing Zn as an additive element β was used during the phosphate treatment. All other experimental conditions were the same as in Example A1, and the soft magnetic powder sample and pressed magnetic core sample of Comparative Example A4 were prepared.

[0141] The powder cores of the above embodiments and comparative examples were evaluated as follows.

[0142] (Analysis of inorganic insulating films using TEM-EDS)

[0143] The inorganic insulating film contained in the pressed powder core samples was confirmed by TEM observation. During TEM observation, for the inorganic insulating film formed on the surface of the small-diameter powder core particles, line analysis was performed at at least 10 sites using EDS to determine the composition of the inorganic insulating film and the thickness of each layer. Furthermore, the samples used for TEM observation were prepared using the FIB microsampling method.

[0144] (Heat resistance test)

[0145] In addition, a heat resistance test was conducted on the powder-pressed magnetic core samples. In the heat resistance test, the powder-pressed magnetic core samples were exposed to a high temperature of 155°C for 2000 hours, and then the insulation resistance was measured. After In-Ga paste was applied to both sides of the ring to form terminal electrodes, the insulation resistance was measured using an HP 4339B high-resistivity meter.

[0146] Furthermore, in all embodiments and comparative examples, the insulation resistance before the heat resistance test was 1×10⁻⁶. 14The resistance is approximately Ω / mm, indicating a similar level of performance. Therefore, in this experiment, it was determined that the higher the insulation resistance after the test, the better the heat resistance.

[0147] The evaluation results of Comparative Examples A1 to A3 and Examples A1 to A18 are shown in Table 1. The evaluation results of Comparative Example A4 and Examples A19 to A28 are shown in Table 2.

[0148] [Table 1]

[0149]

[0150] [Table 2]

[0151]

[0152] Based on the TEM-EDS measurements, it was confirmed that in all Examples A1 to A28 of Experiment A, a first coating portion mainly composed of P and O and a second coating portion mainly composed of Si and O were formed on the surface of the small-diameter powder core particles. In each Example A1 to A28, the thickness T1 of the first coating portion and the thickness T2 of the second coating portion were both in the range of 19 nm to 31 nm. On the other hand, it was confirmed that in Comparative Examples A1, A3, and A4, a phosphorus oxide film was formed on the surface of the small-diameter powder core particles with a thickness of only about 50 nm. In addition, it was confirmed that in Comparative Example A2, a Si oxide film was formed on the surface of the small-diameter powder core particles with a thickness of only about 50 nm. Furthermore, it was confirmed that in all Examples and all Comparative Examples of Experiment A, the total thickness of the inorganic insulating film formed on the small-diameter powder core particles was the same.

[0153] Furthermore, although the results are not shown in Tables 1 and 2, the large-diameter powder contained in each pressed powder core sample was subjected to TEM-EDS film analysis in the same manner as the small-diameter powder. The average thickness of the Si-based oxide film formed on the surface of the large-diameter powder was 50 nm in all examples and comparative examples.

[0154] Furthermore, as shown in Tables 1 and 2, the results of TEM-EDS measurements confirm that, as in Examples A2 to A28 and Comparative Examples A3 to A4, the first coating portion contains an added element (α or β) at a specified content ratio, as intended.

[0155] Next, the results of the heat resistance test were examined. As shown in Table 1, it was confirmed that in Comparative Examples A1 and A2, the insulation resistance after the heat resistance test decreased to the fourth power order, indicating insufficient heat resistance. On the other hand, in Examples A1 to A18 of the present invention, although the total thickness of the film was the same as that of Comparative Examples A1 and A2, the insulation resistance after the test was higher than that of Comparative Examples A1 and A2. Therefore, it can be confirmed that heat resistance is improved by forming a first coating portion and a second coating portion on the surface of the metal particles.

[0156] Furthermore, when comparing Example A1, which does not contain the added element α, and Examples A1 to A10, which contain Na as the added element α, Examples A3 to A7, in which the Na content ratio (α / P) is in the range of 0.05 to 0.5, have higher insulation resistance values ​​after the heat resistance test (on the order of 10th power or higher) and higher heat resistance than Example A1.

[0157] On the other hand, in Comparative Example A3, which only forms the first coating portion, although Na is contained at a content ratio (α / P) of 0.2, the insulation resistance value after the heat resistance test is not significantly improved compared to Comparative Example A1, which does not contain Na, and no improvement in heat resistance can be confirmed compared to Comparative Example A1.

[0158] The results confirm that forming a multilayer film with a first coating portion and a second coating portion, and having the first coating portion contain element α at a specified ratio (i.e., 0.05 ≤ α / P ≤ 0.5), further improves heat resistance. Furthermore, it can be confirmed that in Examples A11 to A18, which contain elements other than Na, the same operation as in Examples A3 to A7 was performed, and by containing element α at a specified ratio, the insulation resistance after the heat resistance test was higher than in Example A1, further improving heat resistance.

[0159] Furthermore, as shown in Table 2, in Comparative Example A4, which only forms the first covering portion, although it contains Zn at a ratio (α / P) of 0.5, the insulation resistance value after the heat resistance test was not significantly improved compared to Comparative Example A1, which does not contain Zn, and no improvement in heat resistance could be confirmed compared to Comparative Example A1.

[0160] In contrast, it can be confirmed that in embodiments A19 to A25 of the present invention having a first covering portion and a second covering portion, and in embodiments A21 to A23 where the Zn content ratio (β / P) is in the range of 0.5 to 0.8, the insulation resistance value after the heat resistance test is high, and the heat resistance is higher than that of embodiment A1. Furthermore, it can be confirmed that in embodiments A26 to A28 containing Al instead of Zn, the same tendency as in embodiments A19 to A25 is observed; by containing Al in the range of 0.5 to 0.8, the insulation resistance after the heat resistance test is higher than that of embodiment A1, and the heat resistance is further improved.

[0161] Therefore, the results shown in Table 2 confirm that the heat resistance is further improved by forming a multilayer structure film with a first coating portion and a second coating portion, and by having the first coating portion contain the additive element β at a specified ratio (i.e., 0.5≤α / P≤0.8).

[0162] Experiment B1

[0163] In Experiment B1, various metal particles with different thicknesses T1 of the first coating portion 12 and T2 of the second coating portion 14 were manufactured. Using these metal particles, soft magnetic powder samples and pressed powder magnetic core samples of Examples B1 to B28 were prepared. The manufacturing methods of each embodiment of Experiment B1 will be described below.

[0164] (Examples B1-B11)

[0165] First, two types of powders were prepared as raw materials for the soft magnetic powder: small-diameter powder and large-diameter powder. Specifically, the small-diameter powder was made of pure iron with a median diameter (D50) of 5 μm, and the large-diameter powder was made of 93.5Fe-6.5Si with a median diameter (D50) of 25 μm.

[0166] Then, an inorganic insulating film is coated onto the prepared small-diameter powder in the following sequence. First, the small-diameter powder is subjected to phosphate treatment to form a first coating on the surface of the core particles of the small-diameter powder. Next, the small-diameter powder is impregnated and stirred in an ethanol solution containing TEOS, and then dried under specified conditions, thereby further forming a second coating outside the first coating.

[0167] Furthermore, in the coating process of this inorganic insulating film, experiments were conducted by varying the concentrations of the phosphate solution and TEOS to produce 11 small-diameter powders with different ratios of the thickness of the first coating layer (T1) and the thickness of the second coating layer (T2). Among these 11 small-diameter powders, the thickness of each layer was controlled such that the sum of the thicknesses of the first and second coating layers (T1+T2) was always within the range of 50±2μm.

[0168] For large-diameter powders, only TEOS sol-gel coating is applied to form a Si-based oxide film on the surface of the core particles of the large-diameter powder.

[0169] The soft magnetic powder samples of Examples B1 to B11 were prepared by mixing the small-diameter powder and the large-diameter powder obtained in this way at a specified mixing ratio. The mixing ratio of the small-diameter powder was the same in all examples of Experiment B1, and was set to 30% by weight relative to the total soft magnetic powder.

[0170] Next, using the soft magnetic powder samples of each Example B1 to B11, under the same manufacturing conditions as Experiment A, pressed powder magnetic cores of the same size as Experiment A were fabricated to obtain pressed powder magnetic core samples of Examples B1 to B11.

[0171] (Examples B21-B28)

[0172] In addition, in Experiment B1, T2 / (T1+T2) was fixed at 60%, and eight small-diameter powders with different sums (T1+T2) of the thickness of the first and second coating portions were prepared. The other experimental conditions were the same as in Examples B1 to B11, and the soft magnetic powder samples and pressed magnetic core samples of Examples 21 to 28 were prepared.

[0173] (Comparative Example B1)

[0174] In Comparative Example B1, only a phosphorus oxide-based film was formed on the surface of the small-diameter powder core particles; sol-gel coating using TEOS was not performed. Other than that, the experimental conditions were the same as in Examples B1 to B11, and the soft magnetic powder sample and pressed powder core sample of Comparative Example B1 were prepared.

[0175] (Comparative Example B2)

[0176] In Comparative Example B2, no phosphate treatment was performed on the small-diameter powder; instead, a sol-gel coating using TEOS was applied, forming only a Si-based oxide film on the surface of the core particles of the small-diameter powder. All other experimental conditions were the same as in Examples B1 to B11, and the soft magnetic powder sample and pressed magnetic core sample of Comparative Example B2 were prepared.

[0177] (Evaluation of Experiment B1)

[0178] Furthermore, in Experiment B1, the same procedures as in Experiment A were followed, including analysis of the inorganic insulating film using TEM-EDS and a heat resistance test. Analysis of the inorganic insulating film confirmed that in all embodiments of Experiment B1, a first coating portion primarily composed of P and O and a second coating portion primarily composed of Si and O were formed on the surface of the small-diameter powder core particles. On the other hand, in Comparative Example B1, it was confirmed that only a phosphorus oxide film was formed on the surface of the small-diameter powder core particles, and in Comparative Example B2, it was confirmed that only a Si oxide film was formed on the surface of the small-diameter powder core particles. Furthermore, in each embodiment and comparative example of Experiment B1, no intermediate layer was formed between the first and second coating portions. Additionally, it was confirmed that in each embodiment and comparative example of Experiment B1, a Si oxide film with an average diameter of 50 nm was formed on the surface of the large-diameter powder contained in each pressed powder core sample.

[0179] Furthermore, in Experiment B1, the insulation resistance before the heat resistance test was 1 × 10⁻⁶ in all the embodiments and comparative examples.14 The resistance is approximately Ω / mm, which is at the same level. Therefore, in Experiment B1, the same procedure as in Experiment A was followed, and it was determined that the higher the insulation resistance after the test, the better the heat resistance.

[0180] In addition, in Experiment B1, the initial permeability μi (unitless) of each powder-pressed magnetic core sample was measured. After winding 50 turns of wire into the powder-pressed magnetic core, the initial permeability μi was measured using an LCR meter (HP LCR428A). In Experiment B1, an initial permeability μi of 20 or higher was considered good.

[0181] The evaluation results of comparative examples B1-B2 and examples B1-B11 are shown in Table 3, and the evaluation results of examples B21-B28 are shown in Table 4.

[0182] [Table 3]

[0183]

[0184] [Table 4]

[0185]

[0186] As shown in Table 3, it can be confirmed that in Comparative Examples B1 and B2, the insulation resistance after the heat resistance test decreased to the fourth power order, indicating insufficient heat resistance. On the other hand, in Examples B1 to B11, although the total thickness of the film was the same as in Comparative Examples B1 and B2, the insulation resistance after the test was higher than that in Comparative Examples B1 and B2. Therefore, it can be confirmed that heat resistance is improved by forming a first coating portion and a second coating portion on the surface of the metal particles.

[0187] Furthermore, when examining the thickness of the first and second covering portions, when T2 / (T1+T2) is 20% to 90% (i.e., Examples B3 to B10), the insulation resistance after testing is on the order of the 7th power or higher, which is higher than in other cases (i.e., Examples B1, B2, and B11). Moreover, when T2 / (T1+T2) is 30% to 80% (Examples B5 to B9), the insulation resistance becomes even higher, on the order of the 8th power or higher, and when T2 / (T1+T2) is 50% to 80% (Examples B7 to B9), the insulation resistance further becomes higher, on the order of the 9th power or higher.

[0188] The results confirm that by setting the ratio of the thickness of the first covering part and the second covering part within a specified range, the heat resistance can be further improved.

[0189] As shown in Table 4, it can be confirmed that by increasing the sum of the thicknesses of the first and second covering portions (T1+T2), the insulation resistance tends to increase after the heat resistance test. On the other hand, the initial permeability μi tends to decrease with increasing film thickness. In particular, in Example B28 where T1+T2 is 150 nm or more, the initial permeability μi decreases to below 20.

[0190] On the other hand, in Examples B22 to B27, where T1+T2 is 10 nm to 150 nm, the insulation resistance after testing is on the order of the 8th power, and the permeability is 20 or higher, satisfying both insulation and magnetic properties. Particularly in Examples B23 to B25, where T1+T2 is 30 nm to 80 nm, the insulation resistance after testing is even higher, on the order of the 9th power, and the permeability is further increased to 24 or higher. Based on these results, it can be confirmed that by controlling the film thickness of the first and second covering portions within a specified ratio range, even with a reduction in the total thickness of the inorganic insulating film, a high insulation resistance can be maintained after the heat resistance test, and a high permeability can be obtained simultaneously.

[0191] Experiment B2

[0192] In Experiment B2, when forming the inorganic insulating film, T1 and T2 were controlled within the most appropriate range, and additive element α or additive element β was added to the first coating part to produce soft magnetic powder samples and pressed powder magnetic core samples of Examples B31 to B61.

[0193] (Examples B31-B46, B51-B61)

[0194] In Examples B31 to B61, during phosphate treatment, a phosphate solution containing additive element α or additive element β was used to form a first coating portion, resulting in small-diameter powder. Specifically, in Examples B31 to B46, the first coating portion of the small-diameter powder contained additive element α selected from alkali metals or alkaline earth metals. The additive element α and its content ratio (α / P) for each Example B31 to B46 are shown in Table 5. Furthermore, in Examples B51 to B61, the first coating portion of the small-diameter powder contained additive element β selected from Zn or Al. The additive element β and its content ratio for each Example B51 to B61 are shown in Table 6.

[0195] Furthermore, in Experiment B2, in all embodiments, the thickness (T1) of the first coating portion was set to 20±1 nm, and the thickness (T2) of the second coating portion was set to 30±1 nm. That is, in all embodiments of Experiment B2, T1+T2 was 50±2 nm, and T2 / (T1+T2) was 60±2%. The experimental conditions other than those described above were operated in the same manner as in Experiment B1, and powder-pressed magnetic core samples of Examples B31–B46 and B51–B61 were prepared, and their performance was evaluated in the same manner as in Experiment B1. The evaluation results of each embodiment are shown in Tables 5 and 6.

[0196] [Table 5]

[0197]

[0198] [Table 6]

[0199]

[0200] As shown in Table 5, in Example B31, the first coating portion did not contain the additive element α. In contrast, in Examples B32 to B38, Na was included as the additive element α. When comparing the insulation resistance after the heat resistance test, Examples B33 to B36, where the Na content (α / P) was in the range of 0.05 to 0.5, had higher insulation resistance values ​​(on the order of the 11th power or higher) and higher heat resistance than Example B31. On the other hand, in Example B32, which had a low Na content, and Examples B37 and B38, which had a high Na content, the insulation resistance after the test was at the same level as that of Example B31, which did not contain Na.

[0201] The results confirm that by controlling T1 and T2 within the optimal range and including element α in the first coating portion at a specified content rate, heat resistance is further improved. Furthermore, in Examples B39 to B46, the type of element α was changed. It was confirmed that, in any element, heat resistance is further improved if the content is within the specified range.

[0202] Furthermore, Table 6 shows the results for cases where the first coating portion contains the added element β. As shown in Table 6, in Example B51, the first coating portion does not contain the added element β. In contrast, in Examples B52 to B58, Zn is contained as the added element β. When comparing the insulation resistance after the heat resistance test, Examples B54 to B56, where the Zn content (β / P) is in the range of 0.5 to 0.8, have high insulation resistance values ​​(on the order of the 11th power or higher) and higher heat resistance than Example B51. On the other hand, in Examples B52 and B53, which have a low Zn content, and Examples B57 and B58, which have a high Zn content, the insulation resistance is at the same level as that of Example B51, which does not contain Zn.

[0203] The results confirm that by controlling T1 and T2 within the optimal range and including the additive element β at a specified content in the first coating portion, the heat resistance is further improved. Furthermore, in Examples B59 to B61, Al is added instead of Zn as the additive element β. In Examples B59 to B61, it is also confirmed that, since the content is in the range of 0.5 to 0.8, the insulation resistance after the heat resistance test is higher than that in Example B51.

[0204] Experiment C1

[0205] In Experiment C1, metal particles with an intermediate layer 16 formed between the first coating portion 12 and the second coating portion 14 were manufactured. Using these metal particles, soft magnetic powder samples and pressed powder magnetic core samples of Examples C1 to C18 were prepared. The manufacturing methods of each embodiment of Experiment C1 will be described below.

[0206] (Examples C1 to C9)

[0207] First, two types of powders, small-diameter powder and large-diameter powder, were prepared as raw materials for the soft magnetic powder. Specifically, for the small-diameter powder, a powder made of pure iron with a median diameter (D50) of 5 μm was prepared, and for the large-diameter powder, a powder made of 93.5Fe-6.5Si with a median diameter (D50) of 25 μm was prepared.

[0208] Then, for the prepared small-diameter powder, an inorganic insulating film is coated in the following sequence. First, the small-diameter powder is subjected to phosphate treatment to form a first coating on the surface of the core particles of the small-diameter powder. Then, the small-diameter powder is impregnated and stirred in an ethanol solution with added TEOS, and then dried under specified conditions, thereby further forming a second coating on the outside of the first coating.

[0209] Furthermore, in the coating process of this inorganic insulating film, before the heat treatment described later (i.e., before the formation of the intermediate layer), the concentration of the phosphate solution is adjusted so that the thickness (T1) of the first coating portion is about 18 to 25 nm. On the other hand, for sol-gel coating, before the heat treatment described later (i.e., before the formation of the intermediate layer), the concentration of the TEOS solution is adjusted so that the thickness (T2) of the second coating portion is 25 to 35 nm.

[0210] For small-diameter powder with a second coating, heat treatment is performed under specified conditions to form an intermediate layer between the first and second coatings. Specifically, the small-diameter powder is heat-treated in a nitrogen atmosphere at a temperature range of 500–600°C for 10–30 minutes. Experiments were conducted by varying the holding time to produce nine different types of small-diameter powder with varying intermediate layer thicknesses.

[0211] In addition, for large-diameter powders, only TEOS sol-gel coating is used to form a Si-based oxide film on the surface of the core particles of the large-diameter powder.

[0212] The soft magnetic powder samples of Examples C1 to C9 were prepared by mixing the small-diameter powder and the large-diameter powder obtained in this way at a specified mixing ratio. The mixing ratio of the small-diameter powder was the same in all examples of this experiment, and was set to 30% by weight relative to the total soft magnetic powder.

[0213] Next, using the soft magnetic powder samples of each embodiment C1 to C9, pressed powder magnetic cores of the same size as those in Experiment A were fabricated under the same manufacturing conditions as in Experiment A, thus obtaining pressed powder magnetic core samples of embodiments C1 to C9.

[0214] (Examples C11-C18)

[0215] In addition, in experiment C1, after controlling the film formation conditions to a ratio of M1 / S1 of approximately 0.08, eight small-diameter powders with different total thicknesses S1 of the inorganic insulating film were prepared. Furthermore, the total thickness S1 of the inorganic insulating film was controlled by adjusting the solution concentration during phosphate treatment and during sol-gel coating using TEOS. Other than that, the experimental conditions were the same as in Examples C1 to C9, and the powder-pressed magnetic core samples of Examples C11 to C18 were prepared.

[0216] (Comparative Example C1)

[0217] In Comparative Example C1, only a phosphorus oxide-based film was formed on the surface of the small-diameter powder core particles; sol-gel coating using TEOS was not performed. Other than that, the experimental conditions were the same as in Examples C1 to C9, and the soft magnetic powder sample and pressed powder core sample of Comparative Example C1 were prepared.

[0218] (Comparative Example C2)

[0219] In Comparative Example C2, the small-diameter powder was not subjected to phosphate treatment; instead, a sol-gel coating using TEOS was applied, forming only a Si-based oxide film on the surface of the core particles of the small-diameter powder. Other than this, the experimental conditions were the same as in Examples C1 to C9, and the soft magnetic powder sample and pressed magnetic core sample of Comparative Example C2 were prepared.

[0220] (Evaluation of Experiment C1)

[0221] Furthermore, in Experiment C1, the same procedures as in Experiment B1 were followed, including analysis of the inorganic insulating film of the TEM-EDS, determination of initial permeability, and heat resistance testing. Analysis of the inorganic insulating film confirmed that in all embodiments of Experiment C1, a first coating portion mainly composed of P and O and a second coating portion mainly composed of Si and O were formed on the surface of the small-diameter powder core particles. Particularly in Examples C2-C9 and C11-C18, it was confirmed that an intermediate layer containing P and Si was formed between the first and second coating portions. On the other hand, in Comparative Example C1, it was confirmed that only a phosphorus oxide film was formed on the surface of the small-diameter powder core particles, and in Comparative Example C2, it was confirmed that only a Si oxide film was formed on the surface of the small-diameter powder core particles. Furthermore, in each embodiment and comparative example of Experiment C1, it was confirmed that an average 50 nm Si oxide film was formed on the surface of the large-diameter powder contained in each pressed powder core sample.

[0222] Furthermore, in Experiment C1, in all the embodiments and comparative examples, the insulation resistance before the heat resistance test was 1 × 10⁻⁶. 14 The resistance is approximately Ω / mm, which is at the same level. Therefore, in this experiment C1, the same procedure as in experiment A was followed, and it was determined that the higher the insulation resistance after the test, the better the heat resistance.

[0223] The evaluation results of comparative examples B1-B2 and examples C1-C9 are shown in Table 7, and the evaluation results of examples C11-C18 are shown in Table 8.

[0224] [Table 7]

[0225]

[0226] [Table 8]

[0227]

[0228] As shown in Table 7, it can be confirmed that in Comparative Examples C1 and C2, the insulation resistance after the heat resistance test decreased to the fourth power order, indicating insufficient heat resistance. On the other hand, in Examples C1 to C9, although the total thickness of the film was the same as in Comparative Examples C1 and C2, the insulation resistance after the test was higher than that in Comparative Examples C1 and C2. Therefore, it can be confirmed that heat resistance is improved by forming a first coating portion and a second coating portion on the surface of the metal particles.

[0229] Furthermore, when examining the thickness of the intermediate layer, it was found that the insulation resistance of Examples C2 to C9, which had an intermediate layer, was higher after the heat resistance test compared to Example C1, which did not have an intermediate layer (i.e., M1 = 0.4 nm or less). This result confirms that heat resistance is further improved by forming an intermediate layer between the first and second covering portions.

[0230] Upon closer examination, examples C4 to C8 exhibited particularly high insulation resistance after the heat resistance test, reaching the order of the 11th power. In examples C4 to C8, the ratio of the intermediate layer thickness M1 to the total thickness S1 of the inorganic insulating film was within the range of 0.05 < M1 / S1 ≤ 0.2. Based on this result, it can be confirmed that by maintaining a specified ratio of the intermediate layer thickness M1 to the total thickness S1 of the inorganic insulating film, the heat resistance becomes exceptionally good. Furthermore, in this experiment C1, examples C5 and C6, with an intermediate layer thickness within the range of 0.07 ≤ M1 / S1 ≤ 0.12, exhibited the best heat resistance, at 5 × 10⁻⁶. 11 Ω / mm or higher.

[0231] Furthermore, as shown in Table 8, it can be confirmed that increasing the total thickness S1 of the inorganic insulating film tends to increase the insulation resistance after the heat resistance test. On the other hand, there is a tendency for the initial permeability μi to decrease with increasing film thickness. In particular, in Example C18 where the total thickness S1 of the inorganic insulating film is 200 nm or more, the initial permeability μi decreases to below 20.

[0232] In embodiments C11 to C17 where the intermediate layer is formed and S1 is less than 200 nm, the insulation resistance after the heat resistance test is as high as the 11th power order, and the initial permeability μi is 20 or higher, satisfying both insulation and magnetic properties. The results demonstrate that by controlling the thickness of the intermediate layer within a specified ratio range, even with a reduction in the total thickness of the inorganic insulating film, a high insulation resistance can be maintained after the heat resistance test, and high permeability can be obtained simultaneously.

[0233] Experiment C2

[0234] In experiment C2, when forming the inorganic insulating film, the film thickness (T1, T2, M1 and S1) of each layer was controlled within the most appropriate range, and additive element α or additive element β was added to the first coating part to produce soft magnetic powder samples and pressed powder magnetic core samples of Examples C21 to C51.

[0235] (Examples C21-C36, C41-C51)

[0236] In Examples C21 to C51, during phosphate treatment, a phosphate solution containing additive element α or additive element β was used to form a first coating portion, resulting in small-diameter powder. Specifically, in Examples C21 to C36, the first coating portion of the small-diameter powder contained additive element α selected from alkali metals or alkaline earth metals. The additive element α and its content ratio (α / P) in each Example C21 to C36 are shown in Table 9. Furthermore, in Examples C41 to C51, the first coating portion of the small-diameter powder contained additive element β selected from Zn or Al. The additive element β and its content ratio in each Example C41 to C51 are shown in Table 10.

[0237] Furthermore, in Experiment C2, in all embodiments, the film formation conditions were controlled such that the thickness T1 of the first coating portion was 18±1 nm, the thickness T2 of the second coating portion was 28±1 nm, and the thickness M1 of the intermediate layer was 4.0±0.5 nm. That is, in all embodiments of Experiment C2, the total thickness S1 of the inorganic insulating film was 50±2 nm, and M1 / S1 was approximately 0.08. Other than the above-mentioned experimental conditions, the same procedures as in Experiment C1 were followed to prepare soft magnetic powder samples and pressed powder core samples of Examples C21–C36 and C41–C51, and their performance was evaluated in the same manner as in Experiment C1. The evaluation results of each embodiment are shown in Tables 9 and 10.

[0238] [Table 9]

[0239]

[0240] [Table 10]

[0241]

[0242] As shown in Table 9, in Example C21, the first coating portion does not contain the additive element α. In contrast, in Examples C22 to C28, Na is contained as the additive element α. When comparing the insulation resistance after the heat resistance test, Examples C23 to C26, where the Na content (α / P) is in the range of 0.05 to 0.5, have higher insulation resistance values ​​(on the order of the 11th power or higher) and higher heat resistance than Example C21. On the other hand, in Example C22, which has a low Na content, and Examples C27 and C28, which have a high Na content, the insulation resistance is at the same level as that of Example C21, which does not contain Na.

[0243] The results confirm that forming an intermediate layer and containing element α at a specified content rate in the first coating portion further improves heat resistance. Furthermore, in Examples C29 to C36, the type of element α was changed. It was confirmed that, for any element type, if the content is within a specified range, the heat resistance is further improved.

[0244] Furthermore, Table 10 shows the results for cases where the first coating portion contains the added element β. As shown in Table 10, in Example C41, the first coating portion does not contain the added element β. In contrast, in Examples C42 to C48, Zn is contained as the added element β. When comparing the insulation resistance after the heat resistance test, Examples C44 to C46, ​​where the Zn content (β / P) is in the range of 0.5 to 0.8, have high insulation resistance values ​​(on the order of the 11th power or higher) and higher heat resistance than Example C41. On the other hand, in Examples C42 and C43, where the Zn content is low, and Examples C47 and C48, where the Zn content is high, the insulation resistance is at the same level as that of Example C41, which does not contain Zn.

[0245] The results confirm that forming an intermediate layer and containing element β at a specified content rate in the first coating portion further improves heat resistance. Furthermore, in Examples C49 to C51, Al was added instead of Zn as element β. It was confirmed that in Examples C49 to C51, since the content rate was in the range of 0.5 to 0.8, the insulation resistance after the heat resistance test was also higher than that in Example C41.

[0246] Furthermore, in experiments A through C above, heat resistance tests and permeability measurements were performed using powder-pressed magnetic core samples for ease of evaluation. However, the same evaluation was conducted on soft magnetic powder samples as on powder-pressed magnetic cores, and the same trends in heat resistance and magnetic properties were observed as with powder-pressed magnetic cores.

[0247] Furthermore, in the above-described embodiment, the mixing ratio of large-diameter powder and small-diameter powder was set to be the same in any sample, but experiments were also conducted in which the mixing ratio of small-diameter powder was changed to 5% to 40%. With the mixing ratio of small-diameter powder changed, the same tendency as in the above-described embodiment was confirmed regarding heat resistance and magnetic properties. Therefore, it can be confirmed that even with a changed mixing ratio, as long as the soft magnetic powder of the present invention is contained in the pressed magnetic core (…),… Figure 2 The effects of the present invention can be obtained by using the coated particles 2 shown.

[0248] Symbol Explanation

[0249] 1, 8… Soft magnetic powder; 1a… Small diameter powder; 2… Coated particles; 4… Soft magnetic metal particles; 6… Large diameter powder; 10… Inorganic insulating film; 12… First coating part; 14… Second coating part; 16… Intermediate layer; 20… Resin; 100… Inductor element; 110, 111… Pressed powder magnetic core; 120… Coil.

Claims

1. A soft magnetic powder, characterized in that: The soft magnetic powder comprises large-diameter powder with a relatively large particle size and small-diameter powder with a relatively small particle size. The large-diameter powder has a particle size of 15 μm or more, and the small-diameter powder has a particle size of less than 15 μm. The small-diameter powder comprises soft magnetic metal particles whose surfaces are covered by an inorganic insulating film. The inorganic insulating film has a first covering portion in contact with the surface of the soft magnetic metal particles and a second covering portion formed on the outside of the first covering portion. The first coating portion contains phosphorus oxides. The second coating contains Si oxide.

2. The soft magnetic powder as described in claim 1, characterized in that: The sum of the thickness T1 of the first coating portion and the thickness T2 of the second coating portion is 10nm ≤ T1 + T2 ≤ 150nm. The ratio of the thickness T2 of the second covering portion to the sum of the thicknesses T1 and T2 of the first covering portion and the second covering portion is 20% ≤ T2 / (T1 + T2) ≤ 90%.

3. The soft magnetic powder as described in claim 2, characterized in that: The ratio of the thickness T2 of the second covering portion to the sum of the thicknesses T1 and T2 of the first covering portion and the second covering portion is 50% ≤ T2 / (T1 + T2) ≤ 80%.

4. The soft magnetic powder as described in claim 1, characterized in that: In the inorganic insulating film, an intermediate layer containing phosphorus and silicon is formed between the first covering portion and the second covering portion.

5. A soft magnetic powder, characterized in that: It contains soft magnetic metal particles whose surfaces are covered by an inorganic insulating film. The inorganic insulating film has a first covering portion in contact with the surface of the soft magnetic metal particles and a second covering portion formed on the outside of the first covering portion. The first coating portion contains phosphorus oxides. The second coating contains Si oxide. In the inorganic insulating film, an intermediate layer containing phosphorus and silicon is formed between the first coating portion and the second coating portion. The total thickness S1 of the inorganic insulating film is less than 200 nm. The ratio of the thickness M1 of the intermediate layer to the total thickness S1 of the inorganic insulating film is 0.06 ≤ M1 / S1 ≤ 0.

19.

6. A soft magnetic powder, characterized in that: It contains soft magnetic metal particles whose surfaces are covered by an inorganic insulating film. The inorganic insulating film has a first covering portion in contact with the surface of the soft magnetic metal particles and a second covering portion formed on the outside of the first covering portion. The first coating portion contains phosphorus oxides. The second coating contains Si oxide. The first coating portion contains one or more α elements selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. The mole fraction of element α to phosphorus P in the first coating portion is 0.05 ≤ α / P ≤ 0.

5.

7. The soft magnetic powder as described in claim 6, characterized in that: The element α contained in the first coating portion is Na.

8. A soft magnetic powder, characterized in that: It contains soft magnetic metal particles whose surfaces are covered by an inorganic insulating film. The inorganic insulating film has a first covering portion in contact with the surface of the soft magnetic metal particles and a second covering portion formed on the outside of the first covering portion. The first coating portion contains phosphorus oxides. The second coating contains Si oxide. The first coating portion contains one or more element β selected from Zn and Al. The mole fraction of element β in the first coating portion is 0.5 ≤ β / P ≤ 0.

8.

9. The soft magnetic powder as described in claim 8, characterized in that: The element β contained in the first coating portion is Zn.

10. A magnetic core, characterized in that: It comprises the soft magnetic powder according to any one of claims 1 to 9.

11. An electronic component, characterized in that: It has the magnetic core as described in claim 10.

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