Magnetic materials and inductors

Abstract

The magnetic material 1 is composed of an aggregate of a plurality of magnetic particles (10). The first center of gravity position (G 10X ) is rotated 360 / n degrees (n is an arbitrary integer greater than or equal to 2), the area of ​​the first magnetic particle (10X) after rotation overlaps with the first magnetic particle (10X) before rotation by more than 90%. In the first planar region (P1), there are 9 to 11 centroid positions of the magnetic particles (10) on the first rectangular band portion (B1). For the magnetic particles (10) existing in the first planar region (P1), when the 50% cumulative frequency distribution D50 based on the number of the maximum length of the first direction d1 passing through each centroid position in the first planar region (P1) is set to α, the 10% cumulative frequency distribution D10 is greater than or equal to 0.9α and the 90% cumulative frequency distribution D90 is less than or equal to 1.1α. The surface of the magnetic particle (10) is covered with an insulating film (20).

Description

Technical Field

[0001] The present invention relates to magnetic materials and inductors. Background Art

[0002] Power inductors employ a structure in which a coil conductor is coated with a resin containing magnetic powder. For example, Patent Document 1 discloses a power inductor characterized in that the unit cell comprises a unit cell in which a coil conductor is embedded and terminal electrodes connected to the coil conductor on the outer surface of the unit cell. The unit cell comprises a first insulator, a coil conductor formed on the upper and lower surfaces of the first insulator, a second insulator formed to coat the coil conductor and the first insulator, and a third insulator formed to coat at least the upper and lower surfaces of the second insulator, wherein at least the third insulator is composed of an organic resin containing flat, metallic soft magnetic powder as a filler.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-67214 Summary of the Invention

[0006] The inductor described in Patent Document 1 is expected to have good DC bias characteristics, that is, a high DC current value at which the inductance drops by a certain amount due to magnetic saturation. The DC bias characteristics are a key factor in determining the rated current of an inductor. To achieve good DC bias characteristics, the magnetic material constituting the inductor must have a high DC current value at which the magnetic permeability drops by a certain amount due to magnetic saturation.

[0007] According to Patent Document 1, inductors using metallic soft magnetic powder as filler have a higher maximum DC current before magnetic saturation than ferrite, demonstrating excellent DC bias characteristics. However, from the perspective of improving the DC bias characteristics of magnetic materials, there is still room for improvement.

[0008] The present invention has been made to solve the above-mentioned problems, and its object is to provide a magnetic material having excellent DC superposition characteristics. Another object of the present invention is to provide an inductor using the magnetic material.

[0009] The inventors of this invention realized that by regularly arranging the magnetic particles constituting a magnetic material, the magnetic flux density passing through the material would be uniform, thereby improving the DC superposition characteristics and the rated current of inductors using these magnetic particles. Based on this, they discovered a magnetic material structure that achieves these goals, leading to the completion of the present invention.

[0010] The magnetic material of the present invention is composed of an aggregate of multiple magnetic particles. When a first planar region containing 50 to 200 magnetic particles within a field of view is observed using a scanning electron microscope or an optical microscope, and the first magnetic particles within the first planar region are rotated 360 / n degrees (n being any integer greater than 2) about the first center of gravity, the rotated first magnetic particles overlap by at least 90% of their area. In the first planar region, the first and second directions, orthogonal to each other, are defined as the maximum length of the first magnetic particles passing through the first center of gravity as the first particle diameter and the second particle diameter, respectively. Within the first planar region, the center of gravity positions of nine to eleven magnetic particles are present in a first rectangular band having a length five times the first particle diameter on either side of the first direction and a width equal to the second particle diameter in the second direction. For the magnetic particles present in the first planar region, when α is defined as the 50% cumulative frequency distribution D50 of the number of particles in the first planar region with the maximum length in the first direction passing through each center of gravity, the 10% cumulative frequency distribution D10 is greater than or equal to 0.9α, and the 90% cumulative frequency distribution D90 is less than or equal to 1.1α. The surface of the magnetic particles is coated with an insulating film containing at least two elements selected from the group consisting of C, N, O, P, and Si.

[0011] The inductor of the present invention includes the above-mentioned magnetic material.

[0012] According to the present invention, a magnetic material having excellent DC superposition characteristics can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a perspective view schematically showing an example of the magnetic material of the present invention.

[0014] Figure 2 This is a cross-sectional view schematically showing an example of magnetic particles constituting the magnetic material of the present invention.

[0015] Figure 3 It is a cross-sectional view schematically showing an example of the first plane region.

[0016] Figure 4 A, B, C, D, E, and F in FIG. 1 are cross-sectional views schematically showing examples of the shapes of magnetic particles.

[0017] Figure 5 yes Figure 3 An enlarged view of the 1st plane area is shown.

[0018] Figure 6 It is a schematic diagram for explaining the first particle diameter and the second particle diameter of the first magnetic particle.

[0019] Figure 7 It is a schematic diagram for explaining the third particle diameter and the fourth particle diameter of the first magnetic particle.

[0020] Figure 8 This is a cross-sectional view schematically showing another example of the magnetic material of the present invention.

[0021] Figure 9 This is a diagram of the model used in the simulation experiment of Example 1.

[0022] Figure 10 This is a diagram of a model used in the simulation experiment of Comparative Example 1.

[0023] Figure 11 This is a plan view schematically showing an example of the inductor of the present invention.

[0024] Figure 12 This is a perspective view schematically showing another example of the inductor of the present invention. DETAILED DESCRIPTION

[0025] Hereinafter, the magnetic material and inductor of the present invention will be described.

[0026] However, the present invention is not limited to the following configurations, and can be appropriately modified and applied without changing the gist of the present invention. It should be noted that a configuration in which two or more of the preferred configurations described below are combined also constitutes the present invention.

[0027] [Magnetic materials]

[0028] Figure 1 This is a perspective view schematically showing an example of the magnetic material of the present invention. Figure 2 This is a cross-sectional view schematically showing an example of magnetic particles constituting the magnetic material of the present invention.

[0029] Figure 1 The magnetic material 1 shown is composed of a plurality of magnetic particles 10. Figure 2 As shown, the surface of the magnetic particles 10 is covered with an insulating film 20. If the surface of the magnetic particles 10 is covered with the insulating film 20, the generation of large eddy currents that conduct the plurality of magnetic particles 10 can be suppressed. The insulating film 20 may cover a portion of the surface of the magnetic particles 10, but preferably covers the entire surface of the magnetic particles 10.

[0030] In this specification, when "magnetic particles" are described, unless otherwise specified, they refer to the portion of the particles excluding the insulating film.

[0031] Figure 1The magnetic material 1 shown has a periodic structure at least in the first planar region P1. It is more preferable that the magnetic material 1 also has a periodic structure in the second planar region P2. Figure 1 In the embodiment, the aggregate of the magnetic particles 10 has a face-centered cubic lattice structure, but the periodic structure is not particularly limited. Figure 1 In FIG, six layers of magnetic grains 10 having a periodic structure are stacked on a surface parallel to the first planar region P1. However, the number of stacked magnetic grains 10 is not particularly limited.

[0032] Figure 3 It is a cross-sectional view schematically showing an example of the first plane region.

[0033] like Figure 3 As shown, 50 to 200 magnetic particles 10 are observed in a first plane region P1 within one field of view using a scanning electron microscope or an optical microscope.

[0034] In principle, a scanning electron microscope is used when the particle diameter of the magnetic particles 10 is less than 50 μm, and an optical microscope is used when the particle diameter of the magnetic particles 10 is 50 μm or more.

[0035] When observing the first planar region P1, it is necessary to find a cross-section where the magnetic particles 10 are regularly arranged. For example, observe cross-sections at approximately 5 to 10 locations in different directions, selecting the cross-sections where the particle size variation of the magnetic particles 10 is minimal. The same procedure applies when observing the second planar region P2.

[0036] In the first planar region P1, the first center of gravity position G is the center of gravity position of a magnetic particle (hereinafter referred to as the first magnetic particle 10X). 10X When the first magnetic particle 10X is rotated 360 / n degrees, 90% or more of the area of ​​the rotated first magnetic particle 10X overlaps with the area of ​​the first magnetic particle 10X before rotation. n can be any integer greater than 2, but is preferably 2, 3, 4, or 6.

[0037] It should be noted that the center of gravity of a magnetic particle is not the precise center of gravity of the magnetic particle. For example, the depth of the magnetic particle or density variations within the particle do not need to be considered. In other words, the center of gravity of the magnetic particle 10 is ultimately the center of gravity of the planar shape of the magnetic particle 10 appearing in the first planar region P1. It does not take into account density variations in the planar shape and refers to the center when the density is assumed to be constant (the so-called geometric center of the planar shape). Such a center of gravity of the magnetic particle 10 can be specifically determined using image processing software, etc.

[0038] In this specification, when a magnetic particle is rotated 360 / n degrees around its center of gravity, and the area of ​​the magnetic particle after rotation overlaps by more than 90% with the area of ​​the magnetic particle before rotation, it is defined as "the magnetic particle has C symmetry at n".

[0039] Note that for the magnetic particles to have C symmetry when n is rotated, it is sufficient that at least 90% of the area of ​​the magnetic particles before rotation overlaps with that of the magnetic particles rotated 360 / n degrees. That is, for integers n ≥ 3, as long as the above condition is met, for example, when rotating 2 × 360 / n degrees, the rotated magnetic particles do not need to overlap at least 90% of the area of ​​the magnetic particles before rotation. However, for all integers k from 1 to n-1, it is preferred that at least 90% of the area of ​​the rotated magnetic particles overlap with the magnetic particles before rotation when rotating k × 360 / n degrees.

[0040] In order for the magnetic particles to have C symmetry when n is a number, only one n that satisfies C symmetry is required. However, it is preferable that C symmetry is satisfied when n is a number (non-prime numbers such as n=4, n=6, etc.).

[0041] Figure 4 A, B, C, D, E, and F in FIG. 1 are cross-sectional views schematically showing examples of the shapes of magnetic particles.

[0042] Figure 4 The magnetic particle 10A indicated by A in has a circular (perfectly circular) shape. Therefore, when n=2, 3, 4, 5, 6, 7, 8, 9, or 10, for example, C symmetry holds.

[0043] Figure 4 The magnetic particle 10B shown by B in FIG has an elliptical shape. Therefore, when n=2, C symmetry holds.

[0044] Figure 4 The magnetic particle 10C indicated by C in FIG has a shape of an equilateral triangle. Therefore, when n=3, C symmetry holds.

[0045] Figure 4 The magnetic particle 10D shown by D in FIG has a square shape. Therefore, when n=2 or 4, C symmetry holds.

[0046] Figure 4 The magnetic particle 10E indicated by E in FIG has a rectangular shape. Therefore, when n=2, C symmetry holds.

[0047] Figure 4 The magnetic particle 10F shown by F in FIG has a regular hexagonal shape. Therefore, when n=2, 3, or 6, C symmetry holds.

[0048] The shape of the magnetic particle 10 having C symmetry at n is not particularly limited, as long as the area of ​​the magnetic particle 10 after rotation overlaps by 90% or more with the area of ​​the magnetic particle 10 before rotation when the magnetic particle 10 is rotated 360 / n degrees about the center of gravity of the magnetic particle 10. The shape of the magnetic particle 10 does not need to be a perfect circle, ellipse, or regular polygon. For example, when the magnetic particle 10 is polygonal, some corners may be curved.

[0049] Among the magnetic particles 10 existing in the first planar region P1, the magnetic particles 10 having C symmetry at n may be at least the first magnetic particles 10X, but are preferably the magnetic particles 10X described below. Figure 5 All the magnetic particles 10 present on the first band portion B1 shown are more preferably all the magnetic particles 10 present on the first band portion B1 and the second band portion B2, further preferably all the magnetic particles 10 within the first circular region C1, further preferably all the magnetic particles 10 within the first circular region C1 and the second circular region C2, and particularly preferably all the magnetic particles 10 within the first planar region P1. In the case where the plurality of magnetic particles 10 present in the first planar region P1 have C symmetry at n, it is not necessary for all the magnetic particles 10 to have C symmetry for the same n. For example, the shapes of the magnetic particles 10 having C symmetry may be different from each other, and may satisfy C symmetry at different n. In addition, the magnetic particles 10 having C symmetry for a certain n1 and the magnetic particles 10 having C symmetry for n2 other than n1 may be arranged alternately.

[0050] Figure 5 yes Figure 3 An enlarged view of the 1st plane area is shown. Figure 6 It is a schematic diagram for explaining the first particle diameter and the second particle diameter of the first magnetic particle. Figure 7 It is a schematic diagram for explaining the third particle diameter and the fourth particle diameter of the first magnetic particle.

[0051] like Figure 5 and Figure 6 As shown, for the first direction d1 and the second direction d2 that are orthogonal to each other in the first plane region P1, the first gravity center position G 10X The maximum lengths of the first magnetic particles 10X are defined as the first particle diameter x1 and the second particle diameter x2. Figure 5 As shown, in the first plane area P1, at the first center of gravity position G 10X The center of gravity of 9 to 11 magnetic particles 10 is located on the first rectangular band portion B1, which has a length of 5 times the first particle diameter x1 on both sides in the first direction d1 and a width equal to the second particle diameter x2 in the second direction d2. Figure 5 In the example shown, the center-of-gravity positions of nine magnetic particles 10 exist on the first band portion B1.

[0052] In this specification, when the relationship of the center of gravity positions of 9 to 11 magnetic particles exists in the first band portion in the first plane region, it is defined as "the magnetic particles have periodicity in the first plane region."

[0053] In addition, if Figure 5 and Figure 7 As shown, in the first plane region P1, the third direction d3 intersecting the first direction d1 and the fourth direction d4 perpendicular to the third direction d3 are respectively passed through the first centroid position G 10X The maximum lengths of the first magnetic particles 10X are defined as the third particle diameter x3 and the fourth particle diameter x4. Figure 5 As shown, in the first plane area P1, at the first center of gravity position G 10X The center of gravity of 9 to 11 magnetic particles 10 is preferably present on the second rectangular band portion B2 having a length of 5 times the third particle diameter x3 on both sides of the third direction d3 and a width equal to the fourth particle diameter x4 in the fourth direction d4. Figure 5 In the example shown, since the magnetic particles 10 are circular in shape, nine centers of gravity of the magnetic particles 10 are also present on the second band portion B2. The number of magnetic particles 10 with centers of gravity on the second band portion B2 may be the same as or different from the number of magnetic particles 10 with centers of gravity on the first band portion B1.

[0054] As described above, the particle size of the magnetic particles 10 referred to in this specification is different from the actual particle size of the three-dimensional magnetic particles 10. For example, for each magnetic particle 10 in the first planar region P1, the maximum length along a certain direction passing through the center of gravity is measured and used as the particle size of the magnetic particle 10 in the first planar region P1.

[0055] In addition, if Figure 5 As shown, the first center of gravity position G 10X The area surrounded by a circle having a radius five times the first particle diameter x1 as its center is defined as the first circular area C1. 10X The area surrounded by a circle having a radius five times the third particle diameter x3 as its center is defined as the second circular area C2. Figure 5 In the example shown, since the shape of the first magnetic particle 10X is circular, the first circular region C1 and the second circular region C2 coincide with each other.

[0056] exist Figure 5In the example shown, since the aggregate of magnetic particles 10 has a face-centered cubic lattice structure, the angle formed by the first direction d1 and the third direction d3 in the first planar region P1 is 60 degrees. The angle formed by the first direction d1 and the third direction d3 is not particularly limited and is, for example, 20 to 160 degrees.

[0057] Figure 8 This is a cross-sectional view schematically showing another example of the magnetic material of the present invention.

[0058] exist Figure 8 In the magnetic material 2 shown, rectangular magnetic particles 10 are arranged in a lattice pattern in a first planar region P1.

[0059] exist Figure 8 In the example shown, in the first plane region P1, at the first center of gravity position G 10X The center of gravity of nine magnetic particles 10 exists on the rectangular first band portion B1 having a length five times the first particle diameter x1 on both sides in the first direction d1 and a width equal to the second particle diameter x2 in the second direction d2.

[0060] Furthermore, in the first plane region P1, at the first center of gravity position G 10X The center of gravity of nine magnetic particles 10 exists on the second rectangular band portion B2 having a length five times the third particle diameter x3 on both sides in the third direction d3 and a width equal to the fourth particle diameter x4 in the fourth direction d4.

[0061] It should be explained that Figure 8 1 and 2 are also shown in FIG. 1 .

[0062] In addition, for the magnetic particles 10 existing in the first planar region P1, when the 50% cumulative frequency distribution D50 based on the number of the maximum length in the first direction d1 passing through each center of gravity position in the first planar region P1 is set to α, the 10% cumulative frequency distribution D10 is greater than 0.9α and the 90% cumulative frequency distribution D90 is less than 1.1α.

[0063] Specifically, for the magnetic particles 10 present in the first planar region P1, the maximum length in the first direction d1 passing through each center of gravity in the first planar region P1 is measured to calculate D10, D50, and D90. The same applies to the particle size of the magnetic particles 10 present in the second planar region P2.

[0064] In this specification, for magnetic particles existing in the first plane region, when the 50% cumulative frequency distribution D50 based on the number of the maximum length in the first direction passing through each center of gravity position in the first plane region is set to α, and the relationship between the 10% cumulative frequency distribution D10 being greater than 0.9α and the 90% cumulative frequency distribution D90 being less than 1.1α holds true, it is defined as "the magnetic particles have narrow dispersion in the first plane region."

[0065] Regarding the magnetic material 1, the second plane region P2 (see Figure 1 ), the second planar region P2 is an area where 50 to 200 magnetic particles are observed in one field of view using a scanning electron microscope or an optical microscope and is not on the same plane as the first planar region P1.

[0066] The angle formed by the first planar region P1 and the second planar region P2 is not particularly limited, and is, for example, 20 degrees to 160 degrees.

[0067] In the second planar region P2, when a magnetic particle (hereinafter referred to as the second magnetic particle) is rotated 360 / m degrees about the second center of gravity, the area of ​​the rotated second magnetic particle preferably overlaps by at least 90% with the area of ​​the second magnetic particle before the rotation. That is, in the second planar region P2, the second magnetic particle preferably has C symmetry at m. In the above description, m can be any integer greater than 2, but is preferably 2, 3, 4, or 6. m = n or m ≠ n is also acceptable.

[0068] Note that for a magnetic particle to have C symmetry at m, it is sufficient that at least 90% of the area of ​​the magnetic particle before rotation overlaps with that of the magnetic particle rotated 360 / m degrees. Specifically, for integers m ≥ 3, the above condition is sufficient. For example, for a rotation of 2 × 360 / m degrees, the area of ​​the rotated magnetic particle does not need to overlap at least 90% with the area of ​​the unrotated magnetic particle. However, for all integers k from 1 to m-1, at a rotation of k × 360 / m degrees, it is preferable that at least 90% of the area of ​​the rotated magnetic particle overlap with the area of ​​the unrotated magnetic particle.

[0069] In order for the magnetic particles to have C symmetry when m is present, only one m that satisfies C symmetry is sufficient. However, it is preferable that C symmetry is satisfied when multiple m are present (non-prime numbers such as m=4, m=6, etc.).

[0070] The shape of the magnetic particle 10 having C symmetry at m is not particularly limited, as long as the area of ​​the magnetic particle 10 after rotation overlaps by 90% or more with the area of ​​the magnetic particle 10 before rotation when the magnetic particle 10 is rotated 360 / m. The shape of the magnetic particle 10 does not need to be a perfect circle, ellipse, or regular polygon. For example, when the magnetic particle 10 is polygonal, some corners may be curved.

[0071] The second magnetic particle is preferably a particle different from the first magnetic particle 10X. The shape of the second magnetic particle may be the same as or different from the shape of the first magnetic particle 10X.

[0072] Among the magnetic particles 10 present in the second planar region P2, the magnetic particles 10 having C symmetry at m only need to be at least the second magnetic particles, but preferably all the magnetic particles 10 present on the third band portion described later, more preferably all the magnetic particles 10 present on the third band portion and the fourth band portion, further preferably all the magnetic particles 10 within the third circular region, further preferably all the magnetic particles 10 within the third circular region and the fourth circular region, and particularly preferably all the magnetic particles 10 within the second planar region P2. In the case where a plurality of magnetic particles 10 present in the second planar region P2 have C symmetry at m, it is not necessary for all the magnetic particles 10 to have C symmetry for the same m. For example, the shapes of the magnetic particles 10 having C symmetry may be different from each other, and may satisfy C symmetry at different m. In addition, magnetic particles 10 having C symmetry for a certain m1 and magnetic particles 10 having C symmetry for m2 other than m1 may be arranged alternately.

[0073] In the second planar region P2, the maximum length of the second magnetic particle passing through the second center of gravity position in the fifth and sixth directions, which are orthogonal to each other, is defined as the fifth particle diameter and the sixth particle diameter, respectively. In the second planar region P2, the center of gravity positions of 9 to 11 magnetic particles 10 are preferably present on a rectangular third band portion centered on the second center of gravity position, having a length five times the fifth particle diameter on either side in the fifth direction and a width equal to the sixth particle diameter in the sixth direction.

[0074] Furthermore, within the second planar region P2, for the seventh direction intersecting the fifth direction and the eighth direction orthogonal to the seventh direction, the maximum length of the second magnetic particle passing through the second center of gravity is defined as the seventh particle diameter and the eighth particle diameter, respectively. In the second planar region P2, the center of gravity of nine to eleven magnetic particles 10 is preferably present on the fourth band portion, which is rectangular and has a length five times the seventh particle diameter on either side in the seventh direction and a width equal to the eighth particle diameter in the eighth direction, centered about the second center of gravity. The number of magnetic particles 10 with center of gravity positions on the fourth band portion may be the same as or different from the number of magnetic particles 10 with center of gravity positions on the third band portion.

[0075] In addition, the area surrounded by a circle having a radius of 5 times the 5th particle size with the second center of gravity as the center is defined as the third circle area. Similarly, the area surrounded by a circle having a radius of 5 times the 7th particle size with the second center of gravity as the center is defined as the fourth circle area. The third circle area and the fourth circle area can be consistent.

[0076] The angle formed by the fifth direction and the seventh direction is not particularly limited, and is, for example, 20 degrees to 160 degrees.

[0077] Furthermore, for the magnetic particles 10 present in the second planar region P2, when the 50% cumulative frequency distribution D50 based on the number of the maximum length in the fifth direction passing through each center of gravity in the second planar region P2 is defined as β, it is preferred that the 10% cumulative frequency distribution D10 be 0.9β or greater and the 90% cumulative frequency distribution D90 be 1.1β or less. β may be equal to α or β≠α.

[0078] In the magnetic material 1, by making the magnetic grains 10 have C symmetry in n, it becomes a driving force for the generation of a periodic structure and can control the deformation of the magnetic flux. The same is true when the magnetic grains 10 have C symmetry in m.

[0079] Furthermore, the magnetic particles 10 having periodicity can minimize the density of magnetic flux and make the magnetic flux density uniform.

[0080] Furthermore, the magnetic particles 10 have narrow dispersion, which serves as a driving force for generating a periodic structure.

[0081] As described above, by regularly arranging the magnetic grains 10 constituting the magnetic material 1 , the magnetic flux density passing through the magnetic material 1 becomes uniform, thereby improving the DC superposition characteristics.

[0082] The material constituting the magnetic particles 10 is not particularly limited, but the magnetic particles 10 preferably contain at least one element selected from the group consisting of Fe, Ni, Co, C, Si, and Cr. Examples of the magnetic particles 10 include Ni-P particles containing Ni and P, Fe particles, Fe-Si particles, Fe-Si-Cr particles, Fe-Si-B particles, Fe-Si-B-Cu-Nb particles, Fe-Si-BP-Cu particles, Fe-Ni particles, and Fe-Co particles.

[0083] The particle size of the magnetic particles 10 is not particularly limited; however, the larger the particle size, the smaller the surface area of ​​the particles. In particular, when the surface of the magnetic particles 10 is charged, by setting the particle size of the magnetic particles 10 to the μm level rather than the nm level, the amount of static charge on the surface can be reduced, thereby significantly achieving the effects of the present invention.

[0084] For example, the first particle size x1 of the first magnetic particle 10X is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm. In this case, the above-mentioned α is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm. Similarly, the second particle size x2 of the first magnetic particle 10X is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm, the third particle size x3 is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm, and the fourth particle size x4 is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm. The first particle size x1, second particle size x2, third particle size x3, and fourth particle size x4 of the first magnetic particle 10X may be the same as or different from each other.

[0085] In addition, the fifth particle size of the second magnetic particle is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm. In this case, the above-mentioned β is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm. Similarly, the sixth particle size of the second magnetic particle is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm, the seventh particle size is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm, and the eighth particle size is preferably 0.6 μm to 50 μm, more preferably 1 μm to 30 μm. The fifth particle size, sixth particle size, seventh particle size, and eighth particle size of the second magnetic particle may be the same as or different from each other.

[0086] The magnetic particles 10 are obtained, for example, by mixing an aqueous metal salt solution with an aqueous reducing agent solution to form a core of the microparticles, followed by electroless reduction of the metal to precipitate it on the core. This method, known as the electroless reduction method, yields metal particles that are nearly perfect spheres. This allows for stable, efficient, and low-cost mass production of particles with a desired particle size, symmetry, and narrow dispersion.

[0087] Furthermore, by using the pulsed orifice ejection method (POEM) or the uniform droplet splay method (UDS), metal particles of the order of μm, which are close to true spheres, can be obtained with narrow dispersion.

[0088] The material constituting the insulating film 20 is not particularly limited, as long as it contains at least two elements selected from the group consisting of C, N, O, P, and Si. The inclusion of these elements imparts polarity to the insulating film 20, thereby charging the surface of the magnetic particles 10 and forming a metastable state between the particles due to electrostatic repulsion and van der Waals attraction. As a result, the periodic structure of the magnetic particles 10 can be spontaneously generated. For example, the insulating film 20 can be formed by calcining Fe-Si-Cr particles in an oxygen atmosphere to oxidize their surfaces.

[0089] The elements contained in the insulating film 20 can be confirmed by elemental analysis using, for example, a scanning transmission electron microscope (STEM) and an energy dispersive X-ray spectrometer (EDX).

[0090] The insulating film 20 preferably contains a hydroxyl group or a carbonyl group, and more preferably contains a hydroxyl group and a carbonyl group. Since the hydroxyl group and the carbonyl group are polar functional groups, the insulating film 20 can charge the surface of the magnetic particle 10.

[0091] The functional groups contained in the insulating film 20 can be confirmed by, for example, Fourier transform infrared spectroscopy (FT-IR).

[0092] Specifically, the insulating film 20 contains an inorganic oxide and a water-soluble polymer.

[0093] Examples of the metal species constituting the inorganic oxide include at least one selected from the group consisting of Li, Na, Mg, Al, Si, K, Ca, Ti, Cu, Sr, Y, Zr, Ba, Ce, Ta, and Bi. Among these, Si, Ti, Al, or Zr is preferred in view of the strength and inherent resistivity of the resulting oxide. The above-mentioned metal species are metals of metal alkoxides used to form the insulating film 20. Specific examples of the inorganic oxide include SiO2, TiO2, Al2O3, and ZrO, with SiO2 being particularly preferred.

[0094] The inorganic oxide is contained in an amount within a range of 0.01 wt % to 5 wt % based on the total weight of the magnetic particles 10 and the insulating film 20 .

[0095] Examples of the water-soluble polymer include at least one selected from the group consisting of polyethyleneimine, polyvinyl pyrrolidone, polyethylene glycol, sodium polyacrylate, carboxymethyl cellulose, polyvinyl alcohol, and gelatin.

[0096] The water-soluble polymer is contained in an amount within a range of 0.01 wt % to 1 wt % based on the total weight of the magnetic particles 10 and the insulating film 20 .

[0097] The thickness of the insulating film 20 is not particularly limited. By thinning the insulating film 20, the spatial filling rate of the magnetic particles 10 increases, thereby achieving a high inductance. Furthermore, variations in the effective magnetic permeability due to variations in the thickness of the insulating film 20 can be suppressed, thereby also suppressing variations in the inductance.

[0098] When a region containing one magnetic particle 10 is defined as a unit cell, the length of the insulating film 20 passing through the center of gravity of the magnetic particle 10 in the first direction d1 in the unit cell is defined as the thickness of the insulating film 20 .

[0099] For example, the thickness of the insulating film 20 covering the surface of the first magnetic particle 10X is preferably 10% or less of the first particle diameter x1 of the first magnetic particle 10X. In particular, the thickness of the insulating film 20 covering the surface of the magnetic particles 10 present in the first planar region P1 is preferably 10% or less of the particle diameter of each magnetic particle 10. In this case, the reduction in the ratio of the magnetic particles to the thickness of the insulating film can be suppressed, resulting in high inductance.

[0100] On the other hand, the thickness of the insulating film 20 covering the surface of the first magnetic particle 10X is preferably at least 0.1% of the first particle diameter x1 of the first magnetic particle 10X. In particular, the thickness of the insulating film 20 covering the surface of the magnetic particles 10 present in the first planar region P1 is preferably at least 0.1% of the particle diameter of each magnetic particle 10. This can suppress the increase in eddy currents caused by a decrease in insulation properties and improve the periodicity of the structure due to polarization of the insulating film.

[0101] Specifically, the thickness of the insulating film 20 covering the surface of the first magnetic particle 10X is preferably 30,000 nm or less, and preferably 10 nm or more. Furthermore, the thickness of the insulating film 20 covering the surface of the magnetic particle 10 present in the first planar region P1 is preferably 30,000 nm or less, and preferably 10 nm or more.

[0102] Furthermore, the thickness of the insulating film 20 covering the surface of the second magnetic particle is preferably no greater than 10% of the fifth particle diameter of the second magnetic particle. In particular, the thickness of the insulating film 20 covering the surface of the magnetic particle 10 present in the second planar region P2 is preferably no greater than 10% of the particle diameter of each magnetic particle 10. On the other hand, the thickness of the insulating film 20 covering the surface of the second magnetic particle is preferably no greater than 0.1% of the fifth particle diameter of the second magnetic particle. In particular, the thickness of the insulating film 20 covering the surface of the magnetic particle 10 present in the second planar region P2 is preferably no greater than 0.1% of the particle diameter of each magnetic particle 10.

[0103] Specifically, the thickness of the insulating film 20 covering the surface of the second magnetic particle is preferably 30,000 nm or less, and preferably 10 nm or more. Furthermore, the thickness of the insulating film 20 covering the surface of the magnetic particle 10 present in the second planar region P2 is preferably 30,000 nm or less, and preferably 10 nm or more.

[0104] The thickness of the insulating film 20 can be measured using, for example, an optical microscope, a scanning electron microscope, or a transmission electron microscope. Alternatively, it can be measured using EDX.

[0105] It should be noted that when the thickness of the insulating film 20 is less than 200 nm, a transmission electron microscope is used in principle; when the thickness of the insulating film 20 is greater than 200 nm and less than 50,000 nm, a scanning electron microscope is used in principle; and when the thickness of the insulating film 20 is greater than 50,000 nm, an optical microscope is used in principle.

[0106] The insulating film 20 is formed by the following method described in International Publication No. 2016 / 056351, for example.

[0107] (1) The magnetic particles 10 are dispersed in a solvent.

[0108] (2) Add metal alkoxide and water-soluble polymer to a solvent and stir.

[0109] At this time, the metal alkoxide is hydrolyzed, and as a result, an insulating film 20 containing a metal oxide and a water-soluble polymer, which are hydrolyzates of the metal alkoxide, is formed on the surface of the magnetic particle 10 .

[0110] As the solvent, alcohols such as methanol and ethanol can be used.

[0111] Examples of the metal species M of the metal alkoxide having the M-OR structure include at least one selected from the group consisting of Li, Na, Mg, Al, Si, K, Ca, Ti, Cu, Sr, Y, Zr, Ba, Ce, Ta, and Bi. Among these, Si, Ti, Al, or Zr is preferred in view of the strength and inherent resistivity of the resulting oxide. Examples of the alkoxy group OR of the metal alkoxide include methoxy, ethoxy, and propoxy. Two or more metal alkoxides may be combined.

[0112] To accelerate the hydrolysis rate of the metal alkoxide, a catalyst may be added as needed. Examples of the catalyst include acidic catalysts such as hydrochloric acid, acetic acid, and phosphoric acid; alkaline catalysts such as ammonia, sodium hydroxide, and piperidine; and salt catalysts such as ammonium carbonate and ammonium acetate.

[0113] The stirred dispersion is dried by an appropriate method (oven, spray, vacuum, etc.) The drying temperature is, for example, 50° C. to 300° C. The drying time can be appropriately set, for example, 10 minutes to 24 hours.

[0114] Alternatively, the insulating film 20 can be formed by coating the surface of the magnetic particle 10 with a phosphate solution.

[0115] The following are examples that more specifically disclose the magnetic material of the present invention, but the present invention is not limited to these examples.

[0116] (Example 1)

[0117] As magnetic particles, Ni-P particles with a particle size of 3 μm (manufactured by Hitachi Metals) were prepared. The Ni-P particles were subjected to an insulating coating (inorganic oxide: SiO2, water-soluble polymer: sodium polyacrylate) using the method described in International Publication No. 2016 / 056351. Thus, a 30 nm thick silica insulating film was formed on the surface of the Ni-P particles. Hydroxyl and carbonyl groups are present in the silica insulating film, and the Zeta potential measurement performed using a Zeta potential meter (DT manufactured by NIHON RUFUTO) showed that the film was charged at -40 mV in pure water.

[0118] 20 wt % of Ni—P particles having a silicon dioxide insulating film formed thereon were mixed and stirred with 30 mL of pure water to obtain a colloidal solution.

[0119] Separately, prepare an alkali-free glass substrate (EAGLE XG manufactured by Corning). Wash with 2% NaOH for 15 minutes, and then heat the glass substrate at 200 degrees for 2 hours after ultrasonic cleaning with pure water for 60 minutes. Arrange and clamp a spacer with a thickness of 1.1 mm between the ends of the two above-mentioned glass substrates to make a wedge-shaped glass test cell with an angle of 1.6 degrees. Inject the above-mentioned colloidal solution into the gap of the wedge-shaped glass test cell using capillary phenomenon and let it stand for 30 minutes. Thereafter, press a non-woven fabric between the two pieces of glass in the wedge-shaped glass test cell to absorb the solvent, and obtain its dried body after 48 hours. The magnetic material of Example 1 is produced by the above steps.

[0120] The dried body (magnetic material) obtained in Example 1 was sputter-coated with platinum and observed using a scanning electron microscope (SEM; JSM6010 manufactured by JEOL Ltd.). The results showed that the Ni-P particles had a periodic structure in two directions in a certain plane area and a periodic structure in one direction in another plane area. Specifically, the aggregate of the Ni-P particles had a face-centered cubic lattice structure. A certain Ni-P particle had C symmetry, and 92% of the area was consistent. In addition, the particle size distribution of the Ni-P particles was derived using JMP manufactured by SAS Institute. The results showed that the Ni-P particles were narrowly dispersed. If D50 was set to α, D10 was 0.9α and D90 was 1.1α. In addition, there were 9 Ni-P particles on the band portion passing through the center of gravity position of the above-mentioned Ni-P particles.

[0121] (Comparative Example 1)

[0122] As magnetic particles, Ni-P particles with a particle size of 3 μm (manufactured by Hitachi Metals, Ltd.) and Ni-P particles with a particle size of 6 μm (manufactured by Hitachi Metals, Ltd.) were prepared. As in Example 1, a 30 nm thick silicon dioxide insulating film was formed on each of the Ni-P particles.

[0123] 10 wt% of each Ni-P particle with a silicon dioxide insulating film was mixed and stirred with 30 mL of pure water to obtain a colloidal solution. The subsequent steps were carried out in the same manner as in Example 1 to obtain a dried product. The magnetic material of Comparative Example 1 was prepared by the above steps.

[0124] In the dried product (magnetic material) obtained in Comparative Example 1, the Ni-P particles did not have a periodic structure. A single Ni-P particle exhibited C-symmetry, with 91% of its area being uniform. However, the particle size distribution was not narrowly dispersed, with D10 being 0.7α and D90 being 1.3α. Furthermore, 13 Ni-P particles were present in a band passing through the center of gravity of the Ni-P particle.

[0125] In order to evaluate the characteristics of the magnetic materials obtained in Example 1 and Comparative Example 1, a two-dimensional analysis of a static magnetic field was performed by a simulation experiment (Femtet 2019 manufactured by Murata Manufacturing Co., Ltd.).

[0126] Figure 9 This is a diagram of the model used in the simulation experiment of Example 1. Figure 10 This is a diagram of a model used in the simulation experiment of Comparative Example 1.

[0127] Sieve conditions: Use G2, first-order elements, the minimum number of cuts for the surface is 16, the sieve size is set to 0.01 mm, the external boundary conditions are magnetic wall and electric wall, and the model thickness is 1 mm.

[0128] The relationship between the magnetic flux density B and the magnetic field H, which are magnetization characteristics of Ni—P particles as magnetic particles, is defined by equation (1).

[0129] B=0.8·tanh(0.011·H) (1)

[0130] When the magnetic field H is 0 [A / m] to 400 [A / m], the magnetic flux density B derived from equation (1) is input.

[0131] The area filling rate of non-magnetic and magnetic particles in the insulating film is 52%, the shape of the magnetic particles is a perfect circle, and the model is two-dimensional.

[0132] If the effective magnetic permeability at 0.87A / m is set to μ i , will become 0.7μ i The magnetic field is set to H 30 ,but Figure 9 The H of the magnetic material with regular arrangement of magnetic particles is shown 30 Relative to Figure 10 The H of the magnetic particles randomly arranged 30 It is 1.4 times the value.

[0133] In addition, Figure 9 The inductor shown, in which a conductor is embedded in a magnetic material, can suppress the decrease in inductance caused by an increase in DC current, thereby increasing the rated current (the current at which the inductance decreases by 30%) by 40%.

[0134] [Inductor]

[0135] An inductor including the magnetic material of the present invention is also one of the present invention.

[0136] Figure 11 This is a plan view schematically showing an example of the inductor of the present invention.

[0137] Figure 11 The inductor 100 shown includes a core 110 and a conductor wire 120 wound around the core 110 .

[0138] The core 110 comprises the magnetic material of the present invention (eg Figure 1 Magnetic material 1 shown, etc.).

[0139] The conductor wire 120 is made of, for example, copper or a copper alloy.

[0140] Figure 12 This is a perspective view schematically showing another example of the inductor of the present invention.

[0141] Figure 12The inductor 200 shown includes a unit cell 210 made of the magnetic material of the present invention, an external electrode 220 provided on the surface of the unit cell 210 , and a coil conductor 230 provided inside the unit cell 210 .

[0142] The inductor of the present invention is not limited to the configuration shown in inductor 100 or 200 , and various applications and modifications can be made to the configuration and manufacturing method of the inductor within the scope of the present invention.

[0143] For example, the winding method of the coil conductor may be any of α-winding, honeycomb winding, flat winding, and straight winding.

[0144] The magnetic material of the present invention is not limited to the structure shown in Magnetic Material 1 or 2. Various applications and modifications can be made to the structure and production method of the magnetic material within the scope of the present invention.

[0145] For example, the magnetic material of the present invention may further contain a resin. When the magnetic material of the present invention contains a resin in addition to magnetic particles, the resin can be solidified to produce a molded article in which the magnetic particles are uniformly dispersed in the resin. In this manner, the magnetic particles uniformly dispersed in the resin are also included in the aggregate of magnetic particles.

[0146] When the magnetic material of the present invention contains a resin, the type of resin is not particularly limited and can be appropriately selected according to desired properties and applications. Examples of the resin include epoxy resins, silicone resins, phenolic resins, polyamide resins, polyimide resins, and polyphenylene sulfide resins.

[0147] In the magnetic material of the present invention, for the C symmetry of the magnetic particles at n, the area of ​​the magnetic particles that overlap after rotation only needs to be 90% or greater. Therefore, the area of ​​the magnetic particles that overlap after rotation does not need to be 100% and can be, for example, 99% or less. The same applies to the C symmetry of the magnetic particles at m.

[0148] In the magnetic material of the present invention, the periodicity of the magnetic grains in the first planar region only requires that the number of magnetic grains whose centers of gravity are aligned on the first band portion be 9 to 11. Therefore, the number of magnetic grains whose centers of gravity are aligned on the first band portion does not need to be 9, and can be 10 or 11. The same applies to the periodicity of the magnetic grains in the second planar region.

[0149] In the magnetic material of the present invention, for the narrow dispersion of the magnetic particles in the first planar region, D10 only needs to be 0.9α or greater, and D90 only needs to be 1.1α or less. Therefore, it is not necessary for D10 = D90 = α; for example, D10 can be 0.99α or less and D90 can be 1.01α or greater. The same applies to the narrow dispersion of the magnetic particles in the second planar region.

[0150] Explanation of symbols

[0151] 1.2 Magnetic materials

[0152] 10, 10A, 10B, 10C, 10D, 10E, 10F magnetic particles

[0153] 10X 1st magnetic particles

[0154] 20 Insulation film

[0155] 100, 200 inductors

[0156] 110 core

[0157] 120 conductor wire

[0158] 210 units

[0159] 220 external electrodes

[0160] 230 Coil conductor

[0161] d1 1st direction

[0162] d2 2nd direction

[0163] d3 3rd direction

[0164] d4 4th direction

[0165] x1 1st particle size

[0166] x2 2nd particle size

[0167] x3 3rd particle size

[0168] x4 4th particle size

[0169] B1 1st band

[0170] B2 Second band

[0171] C1 1st circle area

[0172] C2 2nd circle area

[0173] G 10X 1st center of gravity position

[0174] P1 1st plane area

[0175] P2 Second plane area

Claims

1. A magnetic material consisting of an aggregate of multiple magnetic particles. When 50 to 200 magnetic particles are observed in a first plane region of one field of view using a scanning electron microscope or an optical microscope, When the first magnetic particle in the first planar region is rotated 360 / n degrees with the first center of gravity as the center, the first magnetic particle after rotation overlaps with the first magnetic particle before rotation by more than 90% of its area, wherein: n is any integer greater than 2, For the first and second directions orthogonal to each other in the first planar region, when the maximum lengths of the first magnetic particles passing through the first center of gravity position are defined as the first particle diameter and the second particle diameter, respectively, there are 9 to 11 center of gravity positions of the magnetic particles on a first rectangular band portion having a length of 5 times the first particle diameter on both sides of the first direction and a width equal to the second particle diameter in the second direction centered on the first center of gravity position. For the magnetic particles present in the first planar region, when α is set as the number-based 50% cumulative frequency distribution D50 of the maximum length in the first direction passing through each center of gravity position, the 10% cumulative frequency distribution D10 is greater than or equal to 0.9α and the 90% cumulative frequency distribution D90 is less than or equal to 1.1α. Furthermore, the surface of the magnetic particle is covered with an insulating film containing at least two elements selected from C, N, O, P and Si. The thickness of the insulating film covering the surface of the first magnetic particle is 0.1% to 10% of the first particle diameter of the first magnetic particle. The first particle size of the first magnetic particles is 0.6 μm to 50 μm.

2. The magnetic material according to claim 1, wherein In the first planar area, for the third direction intersecting the first direction and the fourth direction orthogonal to the third direction, when the maximum length of the first magnetic particle passing through the first center of gravity position is defined as the third particle diameter and the fourth particle diameter, respectively, there are 9 to 11 center of gravity positions on the second band portion of the rectangle with the first center of gravity position as the center and having a length of 5 times the third particle diameter on both sides of the third direction and a width equal to the fourth particle diameter in the fourth direction.

3. The magnetic material according to claim 2, wherein 50 to 200 magnetic particles are observed in a second plane region that is not coplanar with the first plane region within one field of view using a scanning electron microscope or an optical microscope. When the second magnetic particle is rotated 360 / m degrees around the second center of gravity position of the second magnetic particle in the second planar region, that is, the second center of gravity position, the area of ​​the second magnetic particle after rotation overlaps with the area of ​​the second magnetic particle before rotation by more than 90%, wherein m is any integer greater than 2, For the fifth and sixth directions orthogonal to each other in the second planar region, when the maximum lengths of the second magnetic particles passing through the second center of gravity position are defined as the fifth particle diameter and the sixth particle diameter, respectively, there are 9 to 11 center of gravity positions of the magnetic particles on a third rectangular band portion having a length five times the fifth particle diameter on both sides of the second center of gravity position in the fifth direction and a width equal to the sixth particle diameter in the sixth direction. For the magnetic particles existing in the second plane area, when the 50% cumulative frequency distribution D50 based on the number of the maximum length in the fifth direction passing through each center of gravity position is set to β, the 10% cumulative frequency distribution D10 is greater than 0.9β and the 90% cumulative frequency distribution D90 is less than 1.1β.

4. The magnetic material according to any one of claims 1 to 3, wherein n is 2, 3, 4 or 6.

5. The magnetic material according to any one of claims 1 to 3, wherein The insulating film contains a hydroxyl group or a carbonyl group.

6. The magnetic material according to any one of claims 1 to 3, wherein The magnetic particles contain at least one element selected from the group consisting of Fe, Ni, Co, C, Si, and Cr. 7 . An inductor comprising the magnetic material according to claim 1 .

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