Magnetic core and magnetic component

Abstract

To provide a magnetic core and a magnetic component that combine low core loss with excellent DC superposition characteristics.SOLUTION: A magnetic core has metallic magnetic particles occupying an area of more than or equal to 75% and less than or equal to 90% of its cross-sectional area. The metallic magnetic particles include first large particles 11a having a Haywood diameter of greater than or equal to 3 μm and having a nanocrystalline structure in the cross-section of the magnetic core and second large particles 11b having a Haywood diameter of greater than or equal to 3 μm and having an amorphous structure. An insulating film 4a of each of the first large particles is thicker than an insulating film 4b of each of the second large particles.SELECTED DRAWING: Figure 3A

Description

[Technical field]

[0001] The present disclosure relates to a magnetic core containing a metallic magnetic powder, and a magnetic component having the magnetic core. [Background technology]

[0002] There are known magnetic components such as inductors, transformers, and choke coils that have a magnetic core (dust core) containing a magnetic metal powder and a resin. Various attempts have been made to improve the properties of such magnetic components, such as the magnetic permeability.

[0003] For example, Patent Documents 1 and 2 disclose that by using a metal magnetic powder that is a mixture of crystalline alloy powder and amorphous alloy powder, the filling rate of the metal magnetic powder in the magnetic core can be improved, thereby improving magnetic permeability and core loss (magnetic loss).

[0004] Furthermore, Patent Document 3 discloses that by using two types of metal magnetic powder with different particle sizes and adjusting the particle size ratio of the two types of metal magnetic powder within a predetermined range, a magnetic core in which the metal magnetic powder is densely packed can be obtained, thereby improving magnetic permeability.

[0005] In recent years, there has been an increasing demand for smaller, more efficient, and more energy-efficient magnetic components, and there is a demand for improving both core loss and DC bias characteristics. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2004-197218 A [Patent Document 2] JP 2004-363466 A [Patent Document 3] JP 2011-192729 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure has been made in consideration of the above-described situation, and an object of an exemplary embodiment of the present disclosure is to provide a magnetic core that combines low core loss with good DC bias characteristics, and a magnetic component having the magnetic core. [Means for solving the problem]

[0008] In order to achieve the above object, the magnetic core according to the present disclosure comprises: Contains metallic magnetic particles, The total area ratio of the metal magnetic particles in the cross section of the magnetic core is 75% or more and 90% or less, The metal magnetic particles are a first large particle having a Heywood diameter of 3 μm or more in a cross section of the magnetic core and a nanocrystalline structure; and second large particles having an amorphous structure and a Heywood diameter of 3 μm or more in a cross section of the magnetic core, The insulating coating of the first large particles is thicker than the insulating coating of the second large particles.

[0009] When the magnetic core has the above characteristics, it is possible to achieve both low core loss and good DC bias characteristics.

[0010] The average thickness of the insulating coating of the first large particles is T1, the average thickness of the insulating coating of the second large particles is T2, Preferably, T1 / T2 is 1.3 or more and 20 or less.

[0011] Preferably, the average thickness T2 of the insulating coating of the second large particles is 5 nm or more and 50 nm or less.

[0012] Preferably, the metal magnetic particles include a group of particles having a Heywood diameter in a cross section of the magnetic core of less than 3 μm; The group of particles having a Heywood diameter of less than 3 μm includes two or more types of small particles having different coating compositions.

[0013] The magnetic core of the present disclosure can be applied to various magnetic components such as inductors, transformers, and choke coils. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing a cross section of a magnetic core according to one embodiment. [Figure 2A] FIG. 2A is a graph showing an example of the particle size distribution of a metal magnetic powder. [Figure 2B] FIG. 2B is a graph showing an example of the particle size distribution of the metal magnetic powder. [Figure 2C] FIG. 2C is a graph showing an example of the particle size distribution of the metal magnetic powder. [Figure 3A] FIG. 3A is an enlarged schematic diagram of a cross section of the magnetic core shown in FIG. [Figure 3B] FIG. 3B is an enlarged schematic view of a cross section of the magnetic core according to the second embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an example of a powder processing apparatus used for forming an insulating coating on small particles. [Diagram 5] FIG. 5 is a cross-sectional view illustrating an example of a magnetic component according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the present disclosure will be described in detail based on the embodiments shown in the drawings.

[0016] First embodiment The magnetic core 2 according to this embodiment is not particularly limited in its external dimensions or shape, as long as it maintains a predetermined shape. As shown in the cross-sectional view of Fig. 1, the magnetic core 2 includes at least metal magnetic particles 10 and resin 20, and the metal magnetic particles 10 are dispersed in the resin 20. That is, the metal magnetic particles 10 are bound via the resin 20, so that the magnetic core 2 forms a predetermined shape.

[0017] The total area percentage A0 occupied by the metal magnetic particles 10 in the cross section of the magnetic core 2 is 75% or more and 90% or less. This total area percentage A0 of the metal magnetic particles 10 corresponds to the filling rate of the metal magnetic particles 10 in the magnetic core 2, and may be calculated by analyzing the cross section of the magnetic core 2 using an electron microscope such as a SEM (scanning electron microscope) or a STEM (scanning transmission electron microscope).

[0018] For example, an arbitrary cross section of the magnetic core 2 is divided into multiple consecutive visual fields and observed, and the area of ​​each metal magnetic particle 10 included in each visual field is measured. The total area of ​​the metal magnetic particles 10 is then divided by the total area of ​​the observed visual fields to calculate the total area ratio A0 (%) of the metal magnetic particles 10. In this cross-sectional analysis, the total area of ​​the visual fields must be at least 1,000,000 μm 2 In the cross-sectional analysis, if the cut surface of the observation sample (the surface obtained by cutting and polishing the magnetic core 2) does not satisfy the total area of ​​the visual field, after analyzing a predetermined cut surface, the cut surface is polished again by 100 μm or more, and the cross-sectional analysis is performed again, so that the total area of ​​the visual field is increased to 1,000,000 μm. 2 It may be more than that.

[0019] The metal magnetic particles 10 contained in the magnetic core 2 preferably include a first particle group 10a having a Heywood diameter of 3 μm or more, and further include a second particle group 10b having a Heywood diameter of less than 3 μm. Here, the "Heywood diameter" in this embodiment means the circle-equivalent diameter of each metal magnetic particle 10 observed on the cross section of the magnetic core 2. Specifically, when the area of ​​each metal magnetic particle 10 on the cross section of the magnetic core 2 is S, the Heywood diameter of each metal magnetic particle 10 is expressed as (4S / π) 1 / 2 It is expressed as:

[0020] When the metal magnetic particles 10 include the first particle group 10a and the second particle group 10b, it is preferable that the content of the first particle group 10a is greater than the content of the second particle group 10b in the magnetic core 2. In other words, when the total area ratio occupied by the first particles 10a in the cross section of the magnetic core 2 is A1 and the total area ratio occupied by the second particles 10b is A2, it is preferable that the area ratio of the metal magnetic particles 10 satisfies A1>A2. By increasing the content of the first particles 10a compared to the second particles 10b, the magnetic permeability of the magnetic core 2 can be improved. The sum of A1 and A2 is the total area ratio A0 of the metal magnetic particles 10 (A1+A2=A0), and A1 and A2 may be measured in the same manner as A0.

[0021] In addition, the metal magnetic particles 10 preferably include two or more particle groups with different average particle sizes. For example, the metal magnetic particles 10 may include at least large particles 11 corresponding to the first particle group 10a, but preferably include large particles 11 and small particles 12, and may also include medium particles 13. The large particles 11, small particles 12, and medium particles 13 can be distinguished based on the particle size distribution of the metal magnetic particles 10. The particle size distribution of the metal magnetic particles 10 may be determined by measuring the Heywood diameter of at least 1,000 metal magnetic particles 10 in any cross section of the magnetic core 2.

[0022] For example, the graphs shown in Figures 2A to 2C show the particle size distribution of metal magnetic particles 10. In each of the graphs in Figures 2A to 2C, the vertical axis represents the area-based frequency (%), and the horizontal axis is a logarithmic axis showing the particle diameter (μm) calculated as the Heywood diameter. Note that the particle size distributions shown in Figures 2A to 2C are merely examples, and the particle size distribution of metal magnetic particles 10 is not limited to Figures 2A to 2C.

[0023] When metal magnetic particles 10 are composed of two particle groups (large particles and small particles) with different average particle sizes, the particle size distribution of metal magnetic particles 10 has two peaks as shown in Figure 2A. When metal magnetic particles 10 are composed of three particle groups (large particles, medium particles, and small particles) with different average particle sizes, the particle size distribution of metal magnetic particles 10 has three peaks as shown in Figure 2B.

[0024] 2A and 2B, when the particle size distribution of metal magnetic particles 10 is represented by a series of distribution curves, a particle group belonging to the peak located on the largest diameter side (the peak located on the rightmost side of the horizontal axis) and having a D20 of 3 μm or more is referred to as large particles 11, and a particle group belonging to the peak located on the smallest diameter side (the peak located on the leftmost side of the horizontal axis) and having a D80 of less than 3 μm is referred to as small particles 12. Particles other than large particles 11 and small particles 12 are referred to as medium particles 13.

[0025] Here, "particle group belonging to the peak located on the largest diameter side" means a particle group included in the range from the bottom (rightmost end) of the distribution curve to the local minimum point via the peak top when tracing the distribution curve from the large diameter side (right side of the graph). That is, in the case of the particle size distribution shown in FIG. 2A, the particle group included in the range from EP1 to LP via Peak1 corresponds to "particle group belonging to the peak located on the largest diameter side". In the case of the particle size distribution shown in FIG. 2B, the particle group included in the range from EP1 to LP1 via Peak1 corresponds to "particle group belonging to the peak located on the largest diameter side".

[0026] 2A and 2B, the particle group belonging to Peak 1 has a D20 of 3 μm or more, and the particle group belonging to Peak 1 is large particles 11.

[0027] "Particle group belonging to the peak located on the smallest diameter side" means a particle group included in the range from the tail (leftmost end) of the distribution curve to the local minimum point via the peak top when tracing the distribution curve from the small diameter side (left side of the graph). That is, in the case of the particle size distribution shown in FIG. 2A, the particle group included in the range from EP2 to LP via Peak2 corresponds to "particle group belonging to the peak located on the smallest diameter side". In addition, in the case of the particle size distribution shown in FIG. 2B, the particle group included in the range from EP2 to LP2 via Peak2 corresponds to "particle group belonging to the peak located on the smallest diameter side".

[0028] In addition, D80 means the Heywood diameter at which the cumulative frequency based on area is 80%. In the particle size distribution in FIG. 2A and FIG. 2B, the particle group belonging to Peak 2 has D80 of less than 3 μm, and this particle group belonging to Peak 2 is small particles 12.

[0029] In the particle size distribution shown in FIG. 2B, the particle group from LP1 through Peak 3 to LP2 is the particle group belonging to Peak 3. In this particle group belonging to Peak 3, D20 is less than 3 μm and D80 is 3 μm or more. In other words, the particle group belonging to Peak 3 is medium particles 13 that do not fall into either large particles 11 or small particles 12.

[0030] When the metal magnetic particle 10 includes two or more particle groups with different average particle sizes, the small particles 12 and / or the medium particles 13 may have the same particle composition as the large particles 11, or may have a different particle composition from the large particles 11. Note that "different particle compositions" refers to cases where the types of constituent elements contained in the particle body are different, or cases where the types of constituent elements are the same but the content ratios of each constituent element are different. A constituent element refers to an element that is contained in the particle body at 1 at% or more. In other words, the elements contained in the particle body other than impurity elements are referred to as constituent elements.

[0031] When small particles 12 and / or medium particles 13 have a particle composition different from that of large particles 11, metal magnetic particles 10 may be classified using a combination of composition analysis and particle size analysis. Specifically, when observing the cross section of magnetic core 2 with an electron microscope, an EDX device (energy dispersive X-ray analyzer) or an EPMA (electron probe microanalyzer) is used to analyze the composition of each metal magnetic particle 10 contained in the observation field, and metal magnetic particles 10 are classified based on the composition. Then, by measuring the Heywood diameter of metal magnetic particles 10 belonging to each composition, multiple distribution curves are obtained.

[0032] For example, when metal magnetic particles 10 are composed of four particle groups with different particle compositions, four distribution curves are obtained, as shown in Fig. 2C. In the particle size distribution in Fig. 2C, the distribution curve of the particle group having composition A is shown by a solid line, the distribution curve of the particle group having composition B is shown by a dotted line, the distribution curve of the particle group having composition C is shown by a dashed line, and the distribution curve of the particle group having composition D is shown by a dashed line.

[0033] 2C, when the particle size distribution of metal magnetic particles 10 is represented by multiple distribution curves according to the composition, particle groups having D20 of 3 μm or more are large particles 11, particle groups having D80 of less than 3 μm are small particles 12, and particle groups other than large particles 11 and small particles 12 are medium particles 13. That is, in FIG. 2C, particle groups having composition A and particle groups having composition B are large particles 11, particle groups having composition C are small particles 12, and particle groups having composition D are medium particles 13.

[0034] As described above, the D20 of the large particles 11 is 3 μm or more, and the Heywood diameters of the large particles 11 are preferably 3 μm or more. The average value (arithmetic mean diameter) of the Heywood diameters of the large particles 11 is not particularly limited, and is preferably, for example, 5 μm or more and 40 μm or less, and preferably 10 μm or more and 35 μm or less. The D80 of the small particles 12 is less than 3 μm, and the Heywood diameters of the small particles 12 are preferably, for example, less than 3 μm. The average value (arithmetic mean diameter) of the Heywood diameters of the small particles 12 is not particularly limited, and is preferably, for example, 2 μm or less, and more preferably 0.2 μm or more and less than 2 μm.

[0035] If the total area ratio of the large particles 11 in the cross section of the magnetic core 2 is AL, and the total area ratio of the small particles 12 in the cross section of the magnetic core 2 is AS, then AL is preferably larger than AS (AL>AS). Specifically, the ratio of the total area of ​​the large particles 11 to the total area of ​​the metal magnetic particles 10 (AL / A0) is preferably more than 50% and not more than 90%, and more preferably 60% or more and 82% or less. In addition, the ratio of the total area of ​​the small particles 12 to the total area of ​​the metal magnetic particles 10 (AS / A0) is preferably 8% or more and less than 50%, and more preferably 10% or more and 40% or less. The magnetic core 2 contains the small particles 12 in the above ratio together with the large particles 11, thereby improving the magnetic permeability. The above AL and AS may be measured in the same manner as A0.

[0036] When metal magnetic particles 10 include medium particles 13, the average Heywood diameter (arithmetic mean diameter) of medium particles 13 is not particularly limited and is preferably, for example, 3 μm or more and 5 μm or less. In addition, the ratio of the total area of ​​medium particles 13 to the total area of ​​metal magnetic particles 10 (AM / A0) is preferably 5% or more and 30% or less.

[0037] The average circularity of the large particles 11 in the cross section of the magnetic core 2 is preferably 0.90 or more, and more preferably 0.95 or more. The higher the average circularity of the large particles 11, the more the withstand voltage and DC bias characteristics can be improved. The circularity of each large particle 11 is calculated by S L , where L is the perimeter of each large particle 11, and 2(πS L ) 1 / 2 The circularity of a perfect circle is 1, and the closer the circularity is to 1, the higher the sphericity of the particle. The average circularity of the large particles 11 is preferably calculated by measuring the circularity of at least 100 large particles 11.

[0038] The average circularity of the small particles 12 and the average circularity of the medium particles 13 are not particularly limited, but preferably have a high average circularity, similar to that of the large particles 11. Specifically, the average circularity of the small particles 12 and the average circularity of the medium particles 13 are both preferably 0.80 or more.

[0039] In this embodiment, the method shown in Figures 2A to 2C is presented as a method for classifying metal magnetic particles 10 into large particles 11, small particles 12, etc., but when small particles 12 have the same particle composition as large particles 11, it is preferable to adopt the classification method shown in Figure 2A or Figure 2B, and when small particles 12 have a particle composition different from large particles 11, it is preferable to adopt the classification method shown in Figure 2C.

[0040] In the magnetic core 2 of this embodiment, the large particles 11 can be divided into two types of particle groups having different material states within the particles. Specifically, the large particles 11 include first large particles 11a having a nanocrystalline structure and second large particles 11b having an amorphous structure.

[0041] Here, the term "nanocrystalline structure" refers to a material state in which the degree of amorphization X is less than 85% and the average crystallite diameter is 0.5 nm or more and 30 nm or less. The maximum diameter of the crystallites in the nanocrystalline structure is preferably 100 nm or less. On the other hand, the term "amorphous structure" refers to a material state in which the degree of amorphization X is 85% or more, and the amorphous structure includes a structure having only amorphous and a structure consisting of heteroamorphous. The structure consisting of heteroamorphous refers to a structure in which the initial microcrystals exist in the amorphous, and the average diameter of the initial microcrystals in the heteroamorphous structure is preferably 0.1 nm or more and 10 nm or less. In this embodiment, the term "crystalline structure" refers to a material state in which the degree of amorphization X is less than 85% and the average crystallite diameter is 100 nm or more.

[0042] The material state within the grains (i.e., degree of amorphism X and crystallite size) can be identified by structural analysis using various electron microscopes such as SEM, TEM, and STEM, electron diffraction, XRD (X-ray diffraction), or EBSD (electron backscatter diffraction). For example, EBSD orientation mapping images and bright-field images of electron microscopes allow visual identification of crystalline and amorphous parts, and by analyzing such images, the degree of amorphism X and average crystallite size can be measured. In addition, if no crystal-attributed spots are identified by electron diffraction, the particles to be measured can be identified as having an amorphous structure.

[0043] The degree of amorphousness X (unit: %) is the proportion of crystals P C , the amorphous fraction P A Then, X=(P A / (P C +P A When calculating the degree of amorphousness X using XRD, the crystalline fraction P C is measured as the crystalline scattering integral intensity Ic, and the amorphous fraction P A can be measured as the amorphous scattering integral intensity Ia. When calculating the degree of amorphousness X using EBSD or an electron microscope, P Cis the area ratio of the crystalline part in the grain, P A can be measured as the area ratio of the amorphous portion.

[0044] When classifying large particles 11 using an electron microscope, as described above, structural analysis is performed on the large particles 11 contained within the observation field of view to identify the material state, but this structural analysis may be performed on arbitrarily selected large particles 11 from within the observation field of view. In this case, the large particles 11 whose material state has been identified are regarded as analysis particles, and other large particles 11 having the same composition as the analysis particle can be regarded as having the same material state as the analysis particle.

[0045] For example, when the large particles 11 include a first large particle 11a of Fe-Si-B-Nb-Cu and a second large particle 11b of Fe-Co-BP-Si-Cr, the Fe-Si-B-Nb-Cu particle group and the Fe-Co-BP-Si-Cr particle group can be distinguished by surface analysis using EDX. Then, if any analysis target particle is selected from the Fe-Si-B-Nb-Cu particle group and structural analysis is performed, and it is determined that the analysis target particle has a nanocrystalline structure, all of the Fe-Si-B-Nb-Cu particle group can be considered to have a nanocrystalline structure. Similarly, if any analysis target particle is selected from the Fe-Co-BP-Si-Cr particle group and structural analysis is performed, and it is determined that the analysis target particle has an amorphous structure, all of the Fe-Co-BP-Si-Cr particle group can be considered to have an amorphous structure.

[0046] The first large particles 11a of the nanocrystalline system and the second large particles 11b of the amorphous system are both made of a soft magnetic alloy, and the alloy composition is not particularly limited. The first large particles 11a and the second large particles 11b may have the same alloy composition, although they have different material states, or may have different alloy compositions. Examples of soft magnetic alloys having a nanocrystalline structure or an amorphous structure include Fe-Si-B alloys, Fe-Si-BC alloys, Fe-Si-BC-Cr alloys, Fe-Nb-B alloys, Fe-Nb-BP alloys, Fe-Nb-B-Si alloys, Fe-Co-PC alloys, Fe-Co-B alloys, Fe-Co-B-Si alloys, Fe-Si-B-Nb-Cu alloys, Fe-Si-B-Nb-P alloys, Fe-Co-BP-Si alloys, and Fe-Co-BP-Si-Cr alloys.

[0047] The total area ratio of the nanocrystalline first large particles 11a in the cross section of the magnetic core 2 is designated as AL1, and the ratio of the total area of ​​the first large particles 11a to the total area of ​​the metal magnetic particles 10 is designated as AL1 / A0. Similarly, the total area ratio of the amorphous second large particles 11b in the cross section of the magnetic core 2 is designated as AL2, and the ratio of the total area of ​​the second large particles 11b to the total area of ​​the metal magnetic particles 10 is designated as AL2 / A0. Both AL1 / A0 and AL2 / A0 are preferably 3% or more, and more preferably 7% to 42%.

[0048] In addition, AL1 / (AL1+AL2) and AL2 / (AL1+AL2) are preferably within the range of 4% to 96%, and from the viewpoint of reducing core loss, AL1 / (AL1+AL2) is more preferably 50% to 90%, and from the viewpoint of obtaining better DC bias characteristics, AL2 / (AL1+AL2) is more preferably 50% to 90%. In order to improve the core loss and DC bias characteristics in a well-balanced manner, AL1 / (AL1+AL2) and AL2 / (AL1+AL2) are preferably 20% to 80%, and more preferably 40% to 60%. Note that AL1 and AL2 may be measured in the same manner as the total area ratio A0 of the metal magnetic particles 10.

[0049] When the metal magnetic particle 10 includes the small particles 12, the composition of the small particles 12 is not particularly limited. The small particles 12 may have an amorphous structure or a nanocrystalline structure, but from the viewpoint of saturation magnetic flux, it is preferable that the small particles 12 have a crystalline structure. Examples of soft magnetic metals having a crystalline structure include pure iron such as carbonyl iron, Co, Fe-Ni alloys, Fe-Si alloys, Fe-Si-Cr alloys, Fe-Si-Al alloys, Fe-Si-Al-Ni alloys, Fe-Ni-Si-Co alloys, Fe-Co alloys, Fe-Co-V alloys, Fe-Co-Si alloys, Fe-Co-Si-Al alloys, and Co alloys. The small particles 12 are preferably pure iron particles, Fe-Ni alloy particles, Fe-Co alloy particles, Fe-Si alloy particles, and Co particles.

[0050] Furthermore, when metal magnetic particle 10 includes medium particles 13, there are no particular limitations on the composition of medium particles 13. For example, medium particles 13 may have a crystalline structure, but from the viewpoint of reducing the coercive force, it is preferable for medium particles 13 to have a nanocrystalline structure or an amorphous structure.

[0051] The composition of the metal magnetic particles 10 can be analyzed, for example, using an EDX device or EPMA attached to an electron microscope. When the first large particles 11a and the second large particles 11b have different particle compositions, the first large particles 11a and the second large particles 11b may be distinguished from each other by surface analysis using an EDX device or EPMA. The composition of the metal magnetic particles 10 may also be analyzed using 3DAP (three-dimensional atom probe). When using 3DAP, a small region (e.g., a region of Φ20 nm×100 nm) can be set inside the metal magnetic particle to be measured to measure the average composition, and the composition of the particle body can be identified while excluding the effects of the resin components contained in the magnetic core 2 and the oxidation of the particle surface.

[0052] As shown in Fig. 3A, each of the first large particles 11a has an insulating coating 4a covering the particle surface, and each of the second large particles 11b has an insulating coating 4b covering the particle surface. The insulating coating 4a and the insulating coating 4b may cover the entire particle surface or only a part of the particle surface. Each of the insulating coatings 4a and 4b preferably covers 80% or more of the particle surface observed in the cross section of the magnetic core 2.

[0053] Furthermore, each of the insulating coatings 4a and 4b may have thickness deviations within a single particle, but it is preferable that each have a thickness as uniform as possible. For example, the arithmetic mean height Ra of the profile curve of the coating surface is preferably 0.5 nm or more and 100 nm or less. The above Ra is a type of line roughness parameter, and it is sufficient to specify the outermost surface portion of the insulating coatings (4a, 4b) observed on the cross section of the magnetic core 2 as the profile curve and calculate Ra in accordance with the method specified in JIS standard B601.

[0054] The material of the insulating coating 4a and the material of the insulating coating 4b are not particularly limited, and the insulating coating 4a and the insulating coating 4b may have the same composition or different compositions. For example, the insulating coating 4a and the insulating coating 4b may include a coating formed by oxidation of the particle surface and / or a coating containing an inorganic material such as BN, SiO2, MgO, Al2O3, phosphate, silicate, borosilicate, bismuthate, various glasses, etc.

[0055] From the viewpoint of suppressing a decrease in the resistivity of the magnetic core 2, it is preferable that both the insulating coating 4a and the insulating coating 4b have an oxide glass coating containing one or more elements selected from P, Si, Bi, and Zn. In the oxide glass coating, when the total amount of elements contained in the coating excluding oxygen is taken as 100 wt%, the total amount of one or more elements selected from P, Si, Bi, and Zn is preferably the largest, more preferably 50 wt% or more, and even more preferably 60 wt% or more.

[0056] Examples of the oxide glass coating include phosphate (P2O5)-based glass coating, bismuthate (Bi2O3)-based glass coating, and borosilicate (B2O3-SiO2)-based glass coating. Examples of the phosphate-based glass include P-Zn-Al-O-based glass and P-Zn-Al-RO-based glass (where "R" is one or more elements selected from alkali metals), and the phosphate-based glass coating preferably contains 50 wt% or more of P2O5. Examples of the bismuthate-based glass include Bi-Zn-B-Si-O-based glass and Bi-Zn-B-Si-Al-O-based glass, and the bismuthate-based glass coating preferably contains 50 wt% or more of Bi2O3. Examples of the borosilicate glass include Ba-Zn-B-Si-Al-O-based glass, and the borosilicate glass coating preferably contains 10 wt% or more of B2O3.

[0057] The insulating coating 4a and the insulating coating 4b may each have a single-layer structure or a multi-layer structure. An example of a multi-layer structure is a laminated structure including an oxide layer on the particle surface and an oxide glass layer covering the oxide layer. When the insulating coating (4a and / or 4b) has a multi-layer structure, the total thickness of each layer is defined as the thickness of the insulating coating. The composition of the insulating coating 4a and the insulating coating 4b can be analyzed by, for example, EDX, EPMA, or EELS (electron energy loss spectroscopy).

[0058] In the magnetic core 2 of this embodiment, the insulating coating 4a of the first large particles 11a is thicker than the insulating coating 4b of the second large particles 11b. The first large particles 11a having a nanocrystalline structure have a thicker insulating coating than the second large particles 11b having an amorphous structure (in other words, the second large particles 11b having an amorphous structure have a thinner insulating coating than the first large particles 11a having a nanocrystalline structure), thereby making it possible to improve the DC bias characteristics while reducing core loss.

[0059] If the average thickness of the insulating coating 4a of the first large particles 11a is T1 and the average thickness of the insulating coating 4b of the second large particles 11b is T2, T1 / T2 exceeds 1.0 and is preferably 1.3 or more, and more preferably 1.3 or more and 20 or less. Furthermore, T1 is preferably 200 nm or less, and T2 is preferably 5 nm or more and 50 nm or less.

[0060] T1 may be calculated by observing the cross section of the magnetic core 2 with various electron microscopes, and is preferably calculated by measuring the thickness of the insulating coating 4a for at least ten first large particles 11a. T2 may also be calculated in the same manner as T1.

[0061] The magnetic core 2 may contain large particles 11 that do not have an insulating coating 4 .

[0062] When the metal magnetic particle 10 includes small particles 12, the small particles 12 do not necessarily have an insulating coating, but each small particle 12 preferably has an insulating coating 6 covering the particle surface. The material of the insulating coating 6 is not particularly limited, and for example, the insulating coating 6 can be a coating (oxide coating) formed by oxidation of the surface of the small particles 12, or a coating containing an inorganic material such as BN, SiO2, MgO, Al2O3, phosphate, silicate, borosilicate, bismuthate, or various glasses, and preferably includes a coating of oxide glass. In addition, the insulating coating 6 may have a single layer structure, or may have a structure in which two or more types of coatings are laminated. The average thickness of the insulating coating 6 is not particularly limited, and for example, it is preferably 5 nm or more and 100 nm or less, and more preferably 5 nm or more and 50 nm or less.

[0063] When metal magnetic particles 10 include medium particles 13, medium particles 13, like other particle groups, preferably have an insulating coating covering the particle surface. The composition of the insulating coating of medium particles 13 is not particularly limited, and may have the same composition as the insulating coating (4a or 4b) of large particles 11, or may have a different composition from the insulating coating (4a or 4b) of large particles 11. The average thickness of the insulating coating of medium particles 13 is not particularly limited, and is, for example, preferably 5 nm or more and 200 nm or less, and more preferably 10 nm or more and 50 nm or less.

[0064] As with the insulating coating 4, the insulating coating 6 of the small particles 12 and the insulating coating of the medium particles 13 may cover the entire particle surface or only a portion of the particle surface, and preferably covers 80% or more of the particle surface observed in the cross section of the magnetic core 2. The magnetic core 2 may include small particles 12 and medium particles 13 that do not have an insulating coating.

[0065] Resin 20 functions as an insulating binder that fixes metal magnetic particles 10 in a predetermined dispersed state. The material of resin 20 is not particularly limited, and resin 20 preferably contains a thermosetting resin such as an epoxy resin.

[0066] The magnetic core 2 may contain a modifier for suppressing contact between the soft magnetic metal particles. As the modifier, a polymeric material such as polyethylene glycol (PEG), polypropylene glycol (PPG), polycaprolactone (PCL) or the like may be used, and it is preferable to use a polymeric material having a polycaprolactone structure. Examples of polymers having a polycaprolactone structure include raw materials for urethane such as polycaprolactone diol and polycaprolactone tetraol, or parts of polyester. The content of the modifier is preferably 0.025 wt% or more and 0.500 wt% or less with respect to the total amount of the magnetic core 2. It is considered that the above-mentioned modifier is present by being adsorbed so as to coat the surface of the metal magnetic particle 10.

[0067] An example of a method for manufacturing the magnetic core 2 according to this embodiment will now be described.

[0068] First, as the raw material powder of the metal magnetic particles 10, a raw material powder including the first large particles 11a and a raw material powder including the second large particles 11b are manufactured. In addition, when small particles 12 and medium particles 13 are added to the magnetic core 2, raw material powder including the small particles 12 and raw material powder including the medium particles 13 are prepared. The manufacturing method of each raw material powder is not particularly limited, and a suitable manufacturing method may be adopted according to the desired particle composition. For example, the raw material powder may be manufactured by an atomization method such as a water atomization method or a gas atomization method. Alternatively, the raw material powder may be manufactured by a synthesis method such as a CVD method using at least one of evaporation, reduction, and thermal decomposition of a metal salt. In addition, the raw material powder may be manufactured by an electrolysis method or a carbonyl method, or the raw material powder may be manufactured by pulverizing a starting alloy in a thin ribbon or thin plate shape. In particular, the raw material powder including the first large particles 11a and the raw material powder including the second large particles 11b are preferably manufactured by a quenching gas atomization method.

[0069] The particle size of each raw material powder can be adjusted by the powder production conditions and various classification methods. In addition, it is preferable to perform a heat treatment on the raw material powder containing the first large particles 11a in order to control the crystal structure of the first large particles 11a.

[0070] In addition, when the composition of the small particles 12 is to be the same as that of the large particles 11 (first large particles 11a and / or second large particles 11b), a raw material powder having a wide particle size distribution may be produced and then classified to obtain a raw material powder containing large particles 11 and a raw material powder containing small particles 12.

[0071] Next, a coating process is performed on each raw material powder. When manufacturing a magnetic core using a metal magnetic powder containing multiple particle groups, in order to simplify the manufacturing process, it is common to mix multiple raw material powders and then perform a coating process on the mixed powder at once. However, when the coating process is performed on the mixed powder, the insulating coatings of each particle group will have approximately the same thickness (i.e., T1 ≒ T2). In this embodiment, in order to make the insulating coating 4a of the first large particle 11a thicker than the insulating coating 4b of the second large particle 11b (i.e., to achieve T1 > T2), the first large particle 11a and the second large particle 11b are individually subjected to the coating process.

[0072] Examples of the coating formation method include heat treatment, phosphate treatment, mechanical alloying, silane coupling treatment, and hydrothermal synthesis. An appropriate coating formation method can be selected depending on the type of insulating coating to be formed.

[0073] For example, when the insulating coating 4a and / or the insulating coating 4b includes a coating of oxide glass, the coating of oxide glass is preferably formed by a mechanochemical method using a mechanofusion device. Specifically, in the coating formation process by the mechanochemical method, raw material powder including large particles and a powdered coating material including the constituent elements of the insulating coating are introduced into a rotating rotor of a mechanofusion device, and the rotating rotor is rotated. A press head is installed inside the rotating rotor, and when the rotating rotor is rotated, the mixture of the raw material powder and the coating material is compressed in the gap between the inner wall surface of the rotating rotor and the press head, generating frictional heat. This frictional heat softens the coating material, which is then fixed to the surface of the large particles by the compression action, forming a coating of oxide glass.

[0074] The thickness of insulating film 4a and the thickness of insulating film 4b may be controlled based on the mixture ratio of the coating materials, the rotation speed, the processing time, and the like.

[0075] When forming the insulating coating 6 on the small particles 12, the insulating coating 6 is preferably formed by mixing the raw material powder containing the small particles 12 with a powdered coating material containing the constituent elements of the insulating coating 6 while applying mechanical impact energy, and more preferably by mixing while applying impact, compression, and shear energy. In such a coating formation process, a powder processing device such as a planetary ball mill or Nobilta manufactured by Hosokawa Micron Corporation can be used as a device capable of applying mechanical energy to the powder. For example, in the coating formation process on the small particles 12, a powder processing device 60 as shown in FIG. 4, which can mix at a high rotation speed, can be used.

[0076] The powder processing device 60 has a cylindrical cross section and includes a chamber 61, in which a rotatable blade 62 is installed. The raw material powder containing the small particles 12 and the coating material are fed into the chamber 61, and the blade 62 is rotated at a rotation speed of 2000 to 6000 rpm, whereby mechanical impact, compression, and shear energy can be applied to the mixture 63 of the raw material powder and the coating material. By using such a powder processing device 60, the insulating coating 6 can be formed on the particle surface even for small particles 12 having a small particle size.

[0077] When medium particles 13 having an insulating coating are used, the medium particles 13 may be mixed with the first large particles 11a or the second large particles 11b and subjected to a coating formation treatment together with the first large particles 11a or the second large particles 11b to form an insulating coating on the surface of the medium particles 13. Alternatively, only the raw material powder of the medium particles 13 may be subjected to the coating formation treatment individually.

[0078] A method for manufacturing the magnetic core 2 using each raw material powder of the metal magnetic particles 10 will be described below. First, each raw material powder with an insulating coating formed thereon and a resin raw material (such as a thermosetting resin) are kneaded to obtain a resin compound. In this kneading step, various kneading machines such as a kneader, a planetary mixer, a rotation-revolution mixer, or a twin-screw extruder may be used, and modifiers, preservatives, dispersants, non-magnetic powders, etc. may be added to the resin compound.

[0079] Next, the resin compound is filled into a mold and compression molded to obtain a molded body. The molding pressure at this time is not particularly limited, and is preferably, for example, 50 MPa or more and 1200 MPa or less. The total area ratio of the metal magnetic particles 10 in the magnetic core 2 can be controlled by the amount of resin 20 added, but can also be controlled by the molding pressure. When a thermosetting resin is used as the resin 20, the above molded body is held at 100°C to 200°C for 1 hour to 5 hours to cure the thermosetting resin. Through the above steps, a magnetic core 2 as shown in FIG. 1 is obtained.

[0080] The magnetic core 2 according to this embodiment can be applied to various magnetic components such as inductors, transformers, choke coils, etc. For example, a magnetic component 100 shown in FIG.

[0081] In the magnetic component 100 shown in Fig. 5, the element body is composed of a magnetic core 2 as shown in Fig. 1. A coil 5 is embedded inside the magnetic core 2, which is the element body, and ends 5a, 5b of the coil 5 are each drawn out to an end face of the magnetic core 2. A pair of external electrodes 7, 9 are formed on the end face of the magnetic core 2, and the pair of external electrodes 7, 9 are electrically connected to ends 5a, 5b of the coil 5, respectively. When the coil 5 is embedded inside the magnetic core 2 as in the magnetic component 100, the area ratio of the metal magnetic particles 10 such as A0, A1, A2, AL, and AS is analyzed in a field of view in which the coil 5 is not visible.

[0082] The use of the magnetic component 100 shown in Fig. 5 is not particularly limited, but it is suitable, for example, for a power inductor used in a power supply circuit. Note that the magnetic component including the magnetic core 2 is not limited to the form shown in Fig. 5, and may be a magnetic component in which a wire is wound a predetermined number of times around the surface of the magnetic core 2 having a predetermined shape.

[0083] (Summary of the first embodiment) The magnetic core 2 of this embodiment contains metal magnetic particles 10 and resin 20, and the total area ratio A0 of the metal magnetic particles 10 shown in the cross section of the magnetic core 2 is 75% or more and 90% or less. The metal magnetic particles 10 contain first large particles 11a having a nanocrystalline structure and second large particles 11b having an amorphous structure, and the insulating coatings 4a of the first large particles 11a are thicker than the insulating coatings 4b of the second large particles 11b.

[0084] The magnetic core 2 has the above-mentioned characteristics, so that it is possible to improve both the core loss characteristics and the DC bias characteristics. Specifically, the following facts have become clear through experiments conducted by the inventors of the present disclosure.

[0085] Comparing a magnetic core containing nanocrystalline particles as the main powder (hereinafter referred to as a nanocrystalline magnetic core) with a magnetic core containing amorphous particles as the main powder (hereinafter referred to as an amorphous magnetic core), the core loss of the nanocrystalline magnetic core is lower than that of the amorphous magnetic core, and the DC bias characteristics of the amorphous magnetic core are better than those of the nanocrystalline magnetic core. Therefore, by using a mixed powder of nanocrystalline particles and amorphous particles as the main powder, the core loss can be reduced more than that of the amorphous magnetic core. However, simply mixing nanocrystalline particles and amorphous particles reduces the DC bias characteristics due to the characteristics of the nanocrystalline particles (the change rate (%) of magnetic permeability with application of a DC magnetic field becomes large).

[0086] In the magnetic core 2 of this embodiment, the first large particles 11a of nanocrystalline structure having a relatively thick insulating coating 4a and the second large particles 11b of amorphous structure having a relatively thin insulating coating 4b are mixed, so that the degradation of the DC bias characteristics caused by the particles of nanocrystalline structure can be suppressed. As a result, the magnetic core 2 of this embodiment can obtain excellent DC bias characteristics while reducing the core loss more than that of an amorphous magnetic core.

[0087] The ratio (T1 / T2) of the average thickness T2 of the insulating coating 4a of the first large particles 11a to the average thickness T2 of the insulating coating 4b of the second large particles 11b is preferably 1.3 or more and 20 or less. By setting T1 / T2 in the above range, it is possible to more suitably achieve both low core loss and excellent DC bias characteristics.

[0088] The average thickness T2 of the insulating coating 4b of the second large particles 11b is preferably 5 nm or more and 50 nm or less. Normally, when the insulating coating is made thicker, the molding pressure needs to be increased to ensure the filling rate of the metal magnetic particles. However, when the molding pressure is increased, the core loss may increase due to the influence of magnetostriction. In the magnetic core 2 of this embodiment, by setting T2 in the above range, it is possible to further reduce the core loss while ensuring high magnetic permeability.

[0089] Second embodiment In the second embodiment, a magnetic core 2a shown in Fig. 3B will be described. Note that in the second embodiment, the description of the configuration common to the first embodiment will be omitted and the same reference numerals as in the first embodiment will be used.

[0090] 3B, in the magnetic core 2a of the second embodiment, first large particles 11a having a nanocrystalline structure and second large particles 11b having an amorphous structure are mixed, and the insulating coating 4a of the first large particles 11a is thicker than the insulating coating 4b of the second large particles 11b. Therefore, the magnetic core 2a of the second embodiment can achieve the same effects as the magnetic core 2 of the first embodiment.

[0091] The magnetic core 2a includes two or more types of small particles 12 with different compositions of the insulating coating 6. In other words, the small particles 12 included in the metal magnetic particle 10 can be divided into two or more types of small particle groups based on the coating composition. Specifically, the small particles 12 include at least a first small particle 12a having a first insulating coating 6a and a second small particle 12b having a second insulating coating 6b with a composition different from that of the first insulating coating 6a, and may further include a third small particle 12c to an n-th small particle 12x with coating compositions different from those of the other small particle groups. n means the number of small particle groups when the small particles 12 are divided based on the coating composition, and there is no particular upper limit for n. From the viewpoint of simplifying the manufacturing process, it is preferable that n is 4 or less.

[0092] Here, "different coating compositions" means that the types of constituent elements contained in the insulating coating 6 are different, and the constituent elements of the insulating coating 6 mean elements that are contained in the insulating coating 6 at 1 at % or more, where the total content of elements other than oxygen and carbon is taken as 100 at %. The composition of the insulating coating 6 may be analyzed by area analysis or point analysis using an EDX device or EPMA.

[0093] The material of each insulating coating 6 (first insulating coating 6a, second insulating coating 6b, and third insulating coating 6c to n-th insulating coating 6x) of the small particle 12 is not particularly limited. For example, each insulating coating 6 can be a coating (oxide coating) formed by oxidation of the surface of the small particle 12, or a coating containing an inorganic material such as BN, SiO2, MgO, Al2O3, phosphate, silicate, borosilicate, bismuthate, or various glasses, and preferably includes a coating of oxide glass. Examples of oxide glass include silicate (SiO2)-based glass, phosphate (P2O5)-based glass, bismuthate (Bi2O3)-based glass, and borosilicate (B2O3-SiO2)-based glass.

[0094] The first insulating coating 6a and the second insulating coating 6b may have different compositions, and the combination of the coating compositions is not particularly limited. For example, the combination of the first insulating coating 6a and the second insulating coating 6b is preferably a combination of a PO-based glass coating and a P-Zn-Al-O-based glass coating, a combination of a Bi-Zn-B-Si-O-based glass coating and a Si-O-based glass coating, or a combination of a Ba-Zn-B-Si-Al-O-based glass coating and a Si-O-based glass coating, and more preferably a combination of a Ba-Zn-B-Si-Al-O-based glass coating and a Si-O-based glass coating. Even when the small particles 12 include the third small particles 12c to the n-th small particles 12x in addition to the first small particles 12a and the second small particles 12b, the combination of the coating compositions is not particularly limited, and it is preferable that the third small particles 12c to the n-th small particles 12x also have a coating of oxide glass having a composition different from that of the other small particle groups.

[0095] The average thickness of the insulating coating 6 is not particularly limited, and is, for example, preferably from 5 nm to 100 nm, and more preferably from 5 nm to 50 nm. The first insulating coating 6a to the nth insulating coating 6x may have approximately the same average thickness, or may have different average thicknesses.

[0096] The insulating coating 6 such as the first insulating coating 6a and the second insulating coating 6b may have a layered structure in which a plurality of coating layers are stacked. For example, the insulating coating 6 may have a layered structure including an oxide layer on the particle surface and an oxide glass layer covering the oxide layer. When one or more of the insulating coatings 6 of the first small particles 12a to the n-th insulating coating 6x have a layered structure, it is sufficient that the composition of the outermost layer (the coating layer located on the outermost side) is different among the first insulating coating 6a to the n-th insulating coating 6x, and the composition of the other coating layers located between the outermost layer and the particle surface may be the same or different among the first insulating coating 6a to the n-th insulating coating 6x.

[0097] The first small particles 12a to the nth small particles 12x may all have the same particle composition, or may each have a different particle composition. The material state of the first small particles 12a to the nth small particles 12x is not particularly limited, and any one or more types of small particle groups among the first small particles 12a to the nth small particles 12x may be amorphous or nanocrystalline, but as described above, it is preferable that the first small particles 12a to the nth small particles 12x are all crystalline.

[0098] The total area ratios of the first small particle 12a to the n-th small particle 12x in the cross section of the magnetic core 2a are denoted by AS1 to AS n In this case, the total area ratio AS of the small particles 12 in the cross section of the magnetic core 2a is expressed as AS1 to AS n The ratio of the total area ratio AS of the small particles 12 to the total area ratio AS of each small particle group is expressed as AS1 / AS to AS n It can be expressed as AS1 / AS~AS n In each case, / AS is preferably 1% or more, more preferably 6% or more, and further preferably 10% or more.

[0099] When manufacturing the magnetic core 2a, each small particle group (first small particle 12a to nth small particle 12x) is individually subjected to a coating formation process, and for the coating formation process for each small particle group, it is preferable to use a powder processing apparatus 60 as shown in FIG. 4, as described in the first embodiment. Furthermore, the composition of each insulating coating 6 (first insulating coating 6a, second insulating coating 6b, and third insulating coating 6c to nth insulating coating 6x) may be controlled by the type and composition of the coating material mixed with the raw material powder. The manufacturing conditions other than those mentioned above may be the same as those in the first embodiment.

[0100] (Summary of the second embodiment) In the magnetic core 2a of the second embodiment, the second particle group 10b having a Heywood diameter of less than 3 μm includes two or more types of small particles 12 (such as first small particles 12a and second small particles 12b) having coating compositions different from each other.

[0101] As described above, it is believed that the metal magnetic particles 10 contain two or more types of small particles 12 with different coating compositions, which improves the electrical repulsive force between the metal magnetic particles when kneaded with the resin, and suppresses magnetic aggregation of the metal magnetic particles 10. As a result, the DC superposition characteristics of the magnetic core 2a can be further improved.

[0102] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present disclosure.

[0103] For example, the structure of the magnetic component is not limited to the embodiment shown in Fig. 5, and the magnetic component may be manufactured by combining multiple magnetic cores 2. Furthermore, the manufacturing method of the magnetic core is not limited to the manufacturing method shown in the above embodiment, and the magnetic core 2 and magnetic core 2a may be manufactured by a sheet method or injection molding, or may be manufactured by two-stage compression. In the manufacturing method by two-stage compression, for example, a resin compound is temporarily compressed to produce multiple pre-molded bodies, and then these pre-molded bodies are combined and finally compressed to obtain the magnetic core. EXAMPLES

[0104] The present disclosure will be described in more detail below based on specific examples, although the present disclosure is not limited to the following examples.

[0105] (Experiment 1) In experiment 1, nanocrystalline magnetic core samples (samples A1 to A6) and amorphous magnetic core samples (samples A7 to A12) were manufactured using a metal magnetic powder in which one type of large particles and one type of small particles were mixed. The magnetic cores of samples A1 to A12 shown in experiment 1 correspond to comparative examples of the present disclosure.

[0106] First, as raw powders of the metal magnetic particles, large-diameter powders having a nanocrystalline structure, large-diameter powders having an amorphous structure, and small-diameter powders consisting of small particles of pure iron were prepared. The large-diameter powders having a nanocrystalline structure were Fe-Si-B-Nb-Cu alloy powders, which were produced by subjecting powders obtained by a quenching gas atomization method to heat treatment. The Fe-Si-B-Nb-Cu alloy powders had an average particle size of 20 μm, an amorphous degree of less than 85%, and an average crystallite size within the range of 0.5 nm to 30 nm. The large-diameter powders having an amorphous structure were Fe-Co-BP-Si-Cr alloy powders, which were produced by a quenching gas atomization method. The Fe-Co-BP-Si-Cr alloy powders had an average particle size of 20 μm, and an amorphous degree of 85% or more. The small-diameter powders, which were pure iron powders, had an average particle size of 1 μm.

[0107] In the case of samples A1 to A6 in experiment 1, a coating process was performed on the large-diameter powder with a nanocrystalline structure using a mechanofusion device (AMS-Lab, manufactured by Hosokawa Micron Corporation) to form an insulating coating of P-Zn-Al-O oxide glass on the surface of the large particles. On the other hand, in the case of samples A7 to A12 in experiment 1, a coating process was performed on the large-diameter powder with an amorphous structure using a mechanofusion device to form an insulating coating of P-Zn-Al-O oxide glass on the surface of the large particles. In the above coating process, the amount of coating material added was controlled so that the average thickness of the insulating coating would be the value shown in Table 1.

[0108] The small-diameter powder used in Experiment 1 was subjected to a coating process using a powder processing device (Nobilta, manufactured by Hosokawa Micron Corporation) as shown in Figure 4, and an insulating coating of Ba-Zn-B-Si-Al-O oxide glass was formed on the surface of the small particles. The average thickness of the insulating coating formed on the small particles was within the range of 15±10 nm for all samples.

[0109] Next, the raw powder (large and small diameter powder) of the metal magnetic particles was kneaded with epoxy resin to obtain a resin compound. More specifically, in Samples A1 to A6, the resin compound was obtained by mixing large and small particles with a nanocrystalline structure. On the other hand, in Samples A7 to A12, the resin compound was obtained by mixing large and small particles with an amorphous structure. Note that the amount of epoxy resin added (resin amount) in the resin compound was 2.5 parts by mass per 100 parts by mass of the metal magnetic particles in all samples in Experiment 1. Also, the large and small diameter powders were mixed so that the area ratio of "large particles:small particles = 8:2" in all samples in Experiment 1.

[0110] Next, the resin compound was filled into a mold and pressed to obtain a toroidal shaped compact. The molding pressure was controlled so that the magnetic core had a magnetic permeability (μi) of 30. The above compact was then heat-treated at 180°C for 60 minutes to harden the epoxy resin in the compact, obtaining a toroidal shaped magnetic core (outer diameter 11 mm, inner diameter 6.5 mm, thickness 2.5 mm).

[0111] For each sample in Experiment 1, the fabricated magnetic core was evaluated as follows.

[0112] Cross-sectional observation of magnetic core The cross section of the magnetic core was observed by SEM, and the total area of ​​the observation field (1,000,000 μm 2 ) was calculated (total area ratio A0 of metal magnetic particles). For each sample in Experiment 1, the total area ratio A0 of metal magnetic particles was within the range of 80±2%.

[0113] In addition, during SEM observation, the Heywood diameter of each metal magnetic particle was measured, and surface analysis was performed by EDX to identify the composition of each metal magnetic particle, and each metal magnetic particle observed in the cross section of the magnetic core was classified into large particles and small particles. In each sample of Experiment 1, the D20 of the large particles was 3 μm or more, the average particle size (arithmetic mean value of the Heywood diameter) of the large particles was in the range of 10 μm to 30 μm, the D80 of the small particles was less than 3 μm, and the average particle size of the small particles was in the range of 0.5 μm to 1.5 μm. In addition, the total area of ​​the large particles and the total area of ​​the small particles included in the observation field were measured, and the ratio of the total area of ​​the large particles to the total area of ​​the metal magnetic particles (AL / A0) and the ratio of the total area of ​​the small particles to the total area of ​​the metal magnetic particles (AS / A0) were calculated.

[0114] In addition, in the above SEM observation, the thickness of the insulating coating of each large particle present within the observation field was measured, and the average thickness was calculated.

[0115] Evaluation of magnetic permeability and DC superposition characteristics To evaluate the magnetic permeability and DC bias characteristics, first, polyurethane copper wire (UEW wire) was wound around a toroidal magnetic core. Then, the inductance of the magnetic core at a frequency of 1 MHz was measured using an LCR meter (Agilent Technologies 4284A) and a DC bias power supply (Agilent Technologies 42841A). More specifically, the inductance was measured when no DC magnetic field was applied (0 kA / m) and when a DC magnetic field of 8 kA / m was applied, and μi (magnetic permeability at 0 A / m) and μHdc (magnetic permeability at 8 kA / m) were calculated from these inductances.

[0116] The DC bias characteristics were evaluated based on the rate of change in magnetic permeability when a DC magnetic field was applied. In other words, the rate of change in magnetic permeability (unit: %) is expressed as (μi-μHdc) / μi, and it can be determined that the smaller the rate of change in magnetic permeability, the better the DC bias characteristics.

[0117] Core loss evaluation Core loss of each magnetic core (unit: kW / m 3) was measured using a BH analyzer (SY-8218 manufactured by Iwatsu Measurement Co., Ltd.) The magnetic flux density when measuring the core loss was set to 10 mT, and the frequency was set to 3 MHz.

[0118] The evaluation results of Experiment 1 are shown in Table 1. [Table 1]

[0119] As shown in Table 1, the magnetic cores of Samples A1 to A6 (hereinafter referred to as nanocrystalline magnetic cores) which use large particles with a nanocrystalline structure as the main powder tend to have lower core loss but inferior DC bias characteristics compared to the magnetic cores of Samples A7 to A12 (hereinafter referred to as amorphous magnetic cores) which use large particles with an amorphous structure as the main powder. On the other hand, the amorphous magnetic cores of Samples A7 to A12 tend to have higher core loss but superior DC bias characteristics compared to the nanocrystalline magnetic cores. In other words, it was found that the DC bias characteristics and the core loss show a contradictory relationship depending on the material state of the main powder.

[0120] In both the nanocrystalline magnetic core and the amorphous magnetic core, the core loss was reduced by thinning the insulating coating on the large particles, but the DC bias characteristics were hardly improved by thinning the insulating coating. These results show that when the main powder of the magnetic core consists of only one type of large particles, it is not easy to achieve both low core loss and good DC bias characteristics.

[0121] (Experiment 2) In experiment 2, 36 types of magnetic cores shown in Table 2 were manufactured using a metal magnetic powder that was a mixture of first large particles with a nanocrystalline structure and second large particles with an amorphous structure.

[0122] In experiment 2, the raw powders for the metal magnetic particles were prepared as follows: Fe-Si-B-Nb-Cu alloy powder (first largest particles with nanocrystalline structure), Fe-Co-BP-Si-Cr alloy powder (second largest particles with amorphous structure), and pure iron powder (small particles) with the same specifications as in experiment 1.

[0123] Next, a mechanofusion device was used to form an insulating coating of P-Zn-Al-O oxide glass on the particle surface of the Fe-Si-B-Nb-Cu alloy powder. At this time, the thickness of the insulating coating was adjusted by controlling the amount of coating material added and the processing time, and six types of first large particles with different average thicknesses T1 were obtained. Similarly, a coating formation process was performed on Fe-Co-BP-Si-Cr alloy powder using a mechanofusion device (forming an insulating coating of P-Zn-Al-O oxide glass) to obtain six types of second large particles with different average thicknesses T2. In addition, a coating formation process was performed on pure iron powder using a powder processing device as shown in Figure 4, and an insulating coating of Ba-Zn-B-Si-Al-O oxide glass was formed on the surface of the small particles. The average thickness of the insulating coating of the small particles was within the range of 15±10 nm.

[0124] Next, the first large particles with a nanocrystalline structure, the second large particles with an amorphous structure, the small particles, and the epoxy resin were kneaded together to obtain a resin compound. At this time, the large particles and the small particles were mixed so that the area ratio of the first large particles: the second large particles: the small particles was 4:4:2 in all samples in Experiment 2. In addition, the amount of epoxy resin added (amount of resin) in the resin compound was 2.5 parts by mass per 100 parts by mass of the metal magnetic particles in all samples in Experiment 2.

[0125] Next, the resin compound was filled into a mold and pressed to obtain a toroidal shaped compact. The molding pressure was controlled so that the magnetic core had a magnetic permeability (μi) of 30. The above compact was then heat-treated at 180°C for 60 minutes to harden the epoxy resin in the compact, obtaining a toroidal shaped magnetic core (outer diameter 11 mm, inner diameter 6.5 mm, thickness 2.5 mm).

[0126] In Experiment 2, the same evaluations as in Experiment 1 (cross-sectional observation of the magnetic core, measurement of magnetic permeability, DC superposition characteristics, and core loss) were performed. In the cross-sectional observation of the magnetic core, it was confirmed that in all samples, the D20 of the first large particles and the second large particles was 3 μm or more, the average particle size of the first large particles and the second large particles was in the range of 10 μm to 30 μm, the D80 of the small particles was less than 3 μm, and the average particle size of the small particles was in the range of 0.5 μm to 1.5 μm. In addition, the average thickness T1 of the insulating coating of the first large particles with a nanocrystalline structure, the average thickness T2 of the insulating coating of the second large particles with an amorphous structure, and the ratio of the total area of ​​each particle group to the total area of ​​the metal magnetic particles (AL1 / A0, AL2 / A0, and AS / A0) were shown in Table 2. In addition, in each sample of Experiment 2, the total area ratio A0 of the metal magnetic particles was in the range of 80±2%.

[0127] In experiment 2, the expected value of the DC bias characteristic (the calculated value of the DC bias characteristic calculated from the blending ratio) was calculated based on the blending ratio of the first large particle and the second large particle, and the quality of the DC bias characteristic of each sample was judged based on the expected value. For example, the expected value of the DC bias characteristic of sample B1 was calculated by the following formula. Expected value = [(β1 / α1) × C1] + [(β2 / α7) × C7] α1: Ratio of large nanocrystalline particles in sample A1 (AL / A0) C1: DC superposition characteristics of sample A1 (rate of change in magnetic permeability) α7: Proportion of amorphous large particles in sample A7 (AL / A0) C7: DC superposition characteristics of sample A7 (rate of change in magnetic permeability) β1: Ratio of large nanocrystalline particles in sample B1 (AL1 / A0) β2: Proportion of amorphous large particles in sample B1 (AL2 / A0) As described above, when calculating the expected values, Table 1 was referenced and the characteristic values ​​of magnetic cores (samples A1 to A12) containing large particles with the same specifications (same particle composition, coating composition, and average coating thickness) as the large particles used in each sample (samples B1 to B36) were used.

[0128] After calculating the expected value of the DC bias characteristic using the above method, the difference between the expected value and the measured DC bias characteristic (expected value - measured value) was calculated. The larger this "difference from the expected value" is from 0%, the smaller the rate of change in magnetic permeability ((μi - μHdc) / μi) is, meaning that the DC bias characteristic is improved. In this experiment, the DC bias characteristic of a sample whose difference from the expected value was less than 1% was judged to be "fail (F)," and the DC bias characteristic of a sample whose difference from the expected value was 1% or more was judged to be "pass (G)."

[0129] Regarding core loss, samples that had a lower core loss than the amorphous magnetic cores (samples A7 to A12) shown in Table 1 were judged to be “pass (G).” The evaluation results of Experiment 2 are shown in Table 2.

[0130] [Table 2]

[0131] As shown in Table 2, in each sample of Experiment 2, the core loss could be made lower than that of the amorphous magnetic cores (samples A7 to A12 in Experiment 1). In other words, by mixing the first large particles with a nanocrystalline structure and the second large particles with an amorphous structure, the core loss could be reduced more than that of the amorphous magnetic cores.

[0132] In the comparative examples where T1 / T2 was 1.0 or less, the DC bias characteristics were equal to or worse than the expected value calculated from the compounding ratio. In contrast, in the examples where T1 / T2 was greater than 1.0, DC bias characteristics better than the expected value were obtained. It is believed that in the examples where T1>T2 was satisfied, the increase in the rate of change of magnetic permeability due to the first large particle of the nanocrystalline structure was suppressed.

[0133] As described above, by mixing the first large particles of nanocrystalline structure having a relatively thick insulating coating with the second large particles of amorphous structure having a relatively thin insulating coating, it was possible to achieve both low core loss and good DC bias characteristics. In particular, in the magnetic core (embodiment) satisfying T1>T2, it is preferable to set the average thickness T2 of the insulating coating of the second large particles to 5 nm or more and 50 nm or less, and it was found that this can further reduce the core loss. In addition, it is preferable to set T1 / T2 to 1.3 or more and 20 or less, and it was found that this tends to make the actual measured value of the DC bias characteristics smaller than the expected value, and the effect of improving the DC bias characteristics is further enhanced.

[0134] (Experiment 3) In experiment 3, the composition of the insulating coating on the first large particles and the second large particles was changed to manufacture eight types of magnetic cores (samples C1 to C8) shown in Table 3. In all samples in experiment 3, the average thickness T1 of the insulating coating on the first large particles was 100 nm, and the average thickness T2 of the insulating coating on the second large particles was 15 nm. The manufacturing conditions other than the composition of the insulating coating were the same as those of sample B20 in experiment 2 (i.e., the specifications of the first large particles, second large particles, and small particles (particle composition, average particle size, etc.) were the same as those of sample B20), and each sample in experiment 3 was evaluated in the same way as in experiment 1.

[0135] Table 3 shows the cross-sectional observation results in Experiment 3, and the measurement results of the magnetic permeability, the DC bias characteristics ((μi-μHdc) / μi), and the core loss. [Table 3]

[0136] In each sample in Experiment 3, the DC bias characteristics and core loss were comparable to those of sample B20 in Experiment 2, and it was possible to achieve both good DC bias characteristics and low core loss. This result demonstrated that the composition of the insulating coating formed on each large particle can be set as desired.

[0137] (Experiment 4) In experiment 4, the ratio of the first large particles with a nanocrystalline structure (AL1 / A0) and the ratio of the second large particles with an amorphous structure (AL2 / A0) were changed to manufacture the magnetic core samples (samples D1 to D18) shown in Table 4. In each sample in experiment 4, the total area ratio A0 of the metal magnetic particles in the cross section of the magnetic core was in the range of 80±2%, and the ratio of small particles (AS / A0) was in the range of 20±1%.

[0138] In samples D1 to D6, which are comparative examples, T1 was 15 nm and T2 was 100 nm, and the manufacturing conditions other than the ratio of large particles in samples D1 to D6 were the same as those in sample B10 of experiment 2. In samples D7 to D12, which are comparative examples, T1 and T2 were 15 nm, and the manufacturing conditions other than the ratio of large particles in samples D7 to D12 were the same as those in sample B8 of experiment 2. Meanwhile, in samples D13 to D18, which are examples, T1 was 100 nm and T2 was 15 nm, and the manufacturing conditions other than the ratio of large particles in samples D13 to D18 were the same as those in sample B20 of experiment 2.

[0139] In experiment 4, the same evaluation as in experiment 2 was carried out. The evaluation results are shown in Table 4. [Table 4]

[0140] As shown in Table 4, in the examples where T1>T2 is satisfied, even if the mixing ratio of the first large particles and the second large particles is changed, the core loss can be reduced more than that of an amorphous magnetic core, and better DC bias characteristics than expected are obtained. From this result, it was found that AL1 / A0 and AL2 / A0 are not particularly limited and can be set arbitrarily.

[0141] It was also confirmed that increasing the ratio of the first large particles with a nanocrystalline structure tends to lower the core loss, and increasing the ratio of the second large particles with an amorphous structure tends to improve the DC bias characteristics. It was found that in order to more appropriately achieve both low core loss and good DC bias characteristics, it is preferable for AL1 / (AL1+AL2) to be 20% or more and 80% or less.

[0142] (Experiment 5) In experiment 5, the ratio of small particles (AS / A0) was changed to produce the magnetic core samples shown in Table 5 (samples E1 to E15). In each sample in experiment 5, the first large particles with a nanocrystalline structure and the second large particles with an amorphous structure were blended in a ratio of "1:1". The manufacturing conditions other than the ratio of small particles were the same as in experiment 2, and the magnetic permeability, DC bias characteristics ((μi-μHdc) / μi), and core loss were measured. The evaluation results are shown in Table 5.

[0143] [Table 5]

[0144] As shown in Table 5, even when the ratio of small particles was changed, the examples in which T1 / T2 was greater than 1.0 had better DC bias characteristics than the comparative examples in which T1≦T2. Note that samples E1 to E15 in experiment 5 had lower core loss than the amorphous magnetic cores.

[0145] It was confirmed that increasing the ratio of small particles in the magnetic core improves core loss and DC bias characteristics, while the magnetic permeability tends to decrease. From the viewpoint of improving core loss and DC bias characteristics while maintaining high magnetic permeability, it was found that the ratio of small particles (AS / A0) is preferably between 10% and 40%.

[0146] (Experiment 6) In experiment 6, the filling rate of the metal magnetic particles (i.e., A0) was changed to produce magnetic core samples shown in Tables 6 and 7. The filling rate of the metal magnetic particles was controlled based on the amount of epoxy resin added. The amount of resin (epoxy resin content relative to the metal magnetic particles) and the total area ratio A0 of the metal magnetic particles in each sample in experiment 6 are shown in Tables 6 and 7. Samples F1 to F12 shown in Table 6 are comparative examples that use only either the first large particles with a nanocrystalline structure or the second large particles with an amorphous structure, while samples G1 to G9 shown in Table 7 contain a mixture of the first large particles and the second large particles.

[0147] The other experimental conditions were the same as those in Experiments 1 and 2, and the magnetic permeability, DC bias characteristics, and core loss of each sample were evaluated.

[0148] [Table 6] [Table 7]

[0149] As shown in Table 7, sample G3, sample B20, and sample G6 are examples of experiment 6, and A0 was in the range of 75% to 90% and T1 / T2 was 1.0 or more. These samples G3, B20, and G6 had lower core loss than the amorphous magnetic core and better DC bias characteristics than the comparative example with T1≦T2. Sample G9, in which A0 is less than 75%, had T1 / T2 of 1.0 or more, but the rate of change in magnetic permeability was similar to that of the comparative example, and the DC bias characteristics could not be improved. From this result, it was found that the total area ratio A0 of metal magnetic particles should be set to 75% to 90%.

[0150] As shown in Table 6, it was confirmed that increasing the filling rate of the metal magnetic particles increases the magnetic permeability μi while deteriorating the core loss characteristics and DC bias characteristics. A similar tendency to that in Table 6 was confirmed in the sample (Table 7) in which the first large particles with a nanocrystalline structure and the second large particles with an amorphous structure were mixed, and it was found that from the viewpoint of ensuring high magnetic permeability, it is preferable for A0 to be 78% or more.

[0151] (Experiment 7) In experiment 7, the specifications of the small particles were changed to manufacture the magnetic core samples shown in Tables 8 and 9. Specifically, in sample H1 in Table 8, Fe-Ni alloy particles with an average particle size of 1 μm were used as the small particles, in sample H2, Fe-Co alloy particles with an average particle size of 1 μm were used as the small particles, in sample H3, Fe-Si alloy particles with an average particle size of 1 μm were used as the small particles, and in sample H4, Co particles with an average particle size of 1 μm were used as the small particles. An insulating coating of Ba-Zn-B-Si-Al-O oxide glass with an average thickness of 15±10 nm was formed on the small particles of each sample shown in Table 8. The manufacturing conditions of samples H1 to H4, other than the composition of the small particles, were the same as those of sample B20 in experiment 2.

[0152] In addition, in samples I1 and I2 in Table 9, two types of small particles with different coating compositions were added. Specifically, in sample I1, Fe particles (first small particles) formed with a Ba-Zn-B-Si-Al-O oxide glass coating were mixed with Fe particles (second small particles) formed with a Si-O insulating coating. In sample I2, Fe particles (first small particles) formed with a Si-Ba-Mn-O oxide glass coating were mixed with Fe particles (second small particles) formed with a Si-O insulating coating. In samples I1 and I2, the average thickness of the insulating coating of the small particles was within the range of 15±10 nm. The manufacturing conditions for samples I1 and I2 other than those mentioned above were the same as those for sample B20 in experiment 2.

[0153] The evaluation results of Experiment 7 are shown in Tables 8 and 9. [Table 8] [Table 9]

[0154] As shown in Table 8, samples H1 to H4, in which the composition of the small particles was changed, were able to achieve both low core loss and good DC bias characteristics, similar to B20 in experiment 2. From this result, it was found that when small particles are added to the magnetic core, the composition of the small particles is not particularly limited and can be set arbitrarily.

[0155] As shown in Table 9, in Sample I1 and Sample I2, the DC bias characteristics were improved more than in B20 in Experiment 2. This result shows that the DC bias characteristics can be further improved by dispersing two types of small particles with different coating compositions in the magnetic core.

[0156] (Experiment 8) In experiment 8, medium particles were added in addition to the first large particles, the second large particles, and the small particles to produce three types of magnetic core samples (samples J1 to J3) shown in Table 10. Specifically, nanocrystalline Fe-Si-B-Nb-Cu alloy particles with an average particle size of 5 μm were added as medium particles to the magnetic core of sample J1, crystalline Fe-Si alloy particles with an average particle size of 5 μm were added as medium particles to the magnetic core of sample J2, and amorphous Fe-Si-B alloy particles with an average particle size of 5 μm were added as medium particles to the magnetic core of sample J3. Note that all of the medium particles used in experiment 8 had a D20 of less than 3 μm and a D80 of 3 μm or more.

[0157] The manufacturing conditions other than those mentioned above were the same as those for sample B20 in experiment 2, and the magnetic permeability, DC bias characteristics, and core loss of samples J1 and J2 were measured. The evaluation results are shown in Table 10.

[0158] [Table 10]

[0159] As shown in Table 10, samples J1 to J3, to which medium particles were added, were able to achieve both low core loss and good DC bias characteristics, similar to B20 in experiment 2. The evaluation results of experiment 8 showed that medium particles may be added to the magnetic core, and that when medium particles are added, it is preferable to use nanocrystalline or amorphous medium particles from the viewpoint of further reducing core loss.

[0160] (Experiment 9) In experiment 9, the composition of the first large particles having a nanocrystalline structure and the composition of the second large particles having an amorphous structure were changed to manufacture magnetic core samples shown in Tables 11 and 12. The average particle size of the first large particles used in experiment 9 was all 20 μm, and the average crystallite size of the first large particles was within a range of 0.5 nm to 30 nm. The average particle size of the second large particles used in experiment 9 was all 20 μm, and the degree of amorphization of the second large particles was 85% or more.

[0161] Samples K1 to K9 shown in Table 11 are comparative examples using either the first large particles with a nanocrystalline structure or the second large particles with an amorphous structure, and the ratio of small particles AS / A0 in samples K1 to K9 was 20±1%. The manufacturing conditions for samples K1 to K9 were the same as those for A4 and A8 in Experiment 1. Samples L1 to L27 shown in Table 12 are examples in which the first large particles and the second large particles are mixed, and the AL1 / A0 and AL2 / A0 in samples L1 to L27 were all 40±1%, and the AS / A0 was 20±1%. The manufacturing conditions for samples L1 to L27 were the same as those for sample B20 in Experiment 2.

[0162] The evaluation results of Experiment 9 are shown in Tables 11 and 12. [Table 11] [Table 12]

[0163] In each of the examples shown in Table 12, a lower core loss was obtained than that of an amorphous magnetic core, and the DC bias characteristics were improved by 1% or more compared to the expected value. From the results of Experiment 9, it was found that the compositions of the first large particles and the second large particles are not particularly limited and can be selected arbitrarily. [Explanation of symbols]

[0164] 2 … Magnetic core 10 … Metal magnetic particles 10a … First particle group 11 ... Large particles 11a … First large particle 11b … Second large particle 4 … Large particle insulating coating 4a … Insulating coating of the first large particle 4b … Insulating coating of the second largest particle 10b … Second particle group 12 … small particles 12a … 1st small particle 12b…Second small particle 6 … Small particle insulating coating 6a … First insulating coating 6b … Second insulating coating 13 … medium particles 20 ... Resin 100 ... Magnetic parts 5. Coil 5a... End 5b... End 7,9 … External electrode

Claims

1. a magnetic core including metal magnetic particles; The total area ratio of the metal magnetic particles in the cross section of the magnetic core is 75% or more and 90% or less, The metal magnetic particles are a first large particle having a Heywood diameter of 3 μm or more in a cross section of the magnetic core and a nanocrystalline structure; a second large particle having an amorphous structure and a Heywood diameter of 3 μm or more in a cross section of the magnetic core; A magnetic core in which the insulating coating of the first large particles is thicker than the insulating coating of the second large particles.

2. the average thickness of the insulating coating of the first large particles is T1; The average thickness of the insulating coating of the second large particles is T2, 2. The magnetic core according to claim 1, wherein T1 / T2 is 1.3 or more and 20 or less.

3. 3. The magnetic core according to claim 1, wherein the average thickness T2 of the insulating coating of the second large particles is 5 nm or more and 50 nm or less.

4. the metal magnetic particles include a group of particles having a Heywood diameter of less than 3 μm in a cross section of the magnetic core; 3. The magnetic core according to claim 1, wherein the group of particles having a Heywood diameter of less than 3 [mu]m includes two or more types of small particles having different coating compositions.

5. A magnetic component having the magnetic core according to claim 1 or 2.

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