JP7808236B2 - Powder magnetic cores for motor cores and stator cores - Google Patents

Description

The present disclosure relates to a powder magnetic core for a motor core and a stator core.
This application claims priority based on Japanese Patent Application No. 2023-129249 filed on August 8, 2023, and incorporates by reference all of the contents of the aforementioned Japanese application.

Patent Document 1 discloses a powder magnetic core used in an axial gap motor. The powder magnetic core includes a yoke portion and teeth portion. A coil is arranged around the outer periphery of the teeth portion. The powder magnetic core includes a compact containing iron-based soft magnetic powder and an insulating resin coating that covers part of the surface of the compact. The insulating resin coating is formed by applying a resin to the surface of the compact. The resin coating is applied by spray coating, electro-deposition coating, or powder coating.

International Publication No. 2019/031209

The powder magnetic core for a motor core disclosed herein comprises a powder compact having a plurality of coated particles and a first insulating coating covering the surface of the powder compact. Each of the plurality of coated particles has an iron-based particle and a second insulating coating covering the surface of the iron-based particle. The thickness of the second insulating coating is 10 nm or more and 1000 nm or less. The first insulating coating contains resin and Fe.

FIG. 1 is a schematic perspective view showing an example of a powder magnetic core for a motor core according to a first embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3 is a schematic cross-sectional view showing a region A in FIG. FIG. 4 is a perspective view showing an outline of a stator core according to the second embodiment. FIG. 5 is a schematic perspective view showing an example of a stator. FIG. 6 is a schematic cross-sectional view showing an example of an axial gap motor.

[Problem to be solved by the present disclosure]
When an axial gap motor is constructed using the above-described powder magnetic core, the distance between the powder magnetic core and the coil can be easily reduced. This is because the above-described powder magnetic core easily improves electrical insulation between the powder compact and the coil due to the insulating resin coating that covers the surface of the powder compact. This small distance allows heat from the coil to be easily transferred to the powder compact. Therefore, the above-described powder magnetic core is less likely to increase the temperature of the coil.

It is desirable to make it even more difficult for the coil temperature to rise. In other words, it is desirable to further improve the electrical insulation of powder magnetic cores.

One of the objectives of this disclosure is to provide a powder magnetic core for a motor core and a stator core that have excellent electrical insulation properties.

[Effects of the present disclosure]
The dust core for a motor core according to the present disclosure has excellent electrical insulation properties.

<<Description of Embodiments of the Present Disclosure>>
First, embodiments of the present disclosure will be listed and described.

(1) A powder magnetic core for a motor core according to one embodiment of the present disclosure comprises a powder compact having a plurality of coated particles and a first insulating coating covering the surface of the powder compact. Each of the plurality of coated particles comprises an iron-based particle and a second insulating coating covering the surface of the iron-based particle. The thickness of the second insulating coating is 10 nm or more and 1000 nm or less. The first insulating coating contains a resin and Fe.

The powder magnetic core for motor core disclosed herein has excellent electrical insulation properties due to the first insulating coating containing resin and Fe, as shown in the test examples described below.

A second insulating coating with a thickness of 10 nm or more easily insulates adjacent iron-based particles. A second insulating coating with a thickness of 1,000 nm or less tends to increase the relative density of the compact.

(2) In the powder magnetic core for a motor core described in (1) above, the thickness of the first insulating coating may be 5 μm or more and 100 μm or less.

A first insulating coating with a thickness of 5 μm or more is likely to improve the electrical insulation of the powder magnetic core for the motor core. A first insulating coating with a thickness of 100 μm or less prevents the powder magnetic core for the motor core from becoming too large.

(3) In the powder magnetic core for a motor core described in (1) or (2) above, the Fe content in the first insulating coating may be 0.5 mass% or more and 10 mass% or less.

The powder magnetic core for motor cores described above in (3) has excellent electrical insulation properties due to the first insulating coating containing a specific content of Fe.

(4) In any of the powder magnetic cores for motor cores described in (1) to (3) above, the hardness of the first insulating coating measured by nanoindentation may be 200 MPa or more.

A first insulating coating with a hardness of 200 MPa or more is likely to mechanically protect the powder compact. A first insulating coating with a hardness of 200 MPa or more has a relatively high cross-link density. A first insulating coating with a high cross-link density has excellent electrical insulation properties. In other words, a first insulating coating with a hardness of 200 MPa or more is likely to improve the electrical insulation properties of powder magnetic cores for motor cores.

(5) In the powder magnetic core for a motor core described above in (4), the hardness of the first insulating coating measured by nanoindentation may be 400 MPa or less.

A first insulating coating with a hardness of 400 MPa or less is less likely to suffer damage such as cracks or breakage due to vibrations when the axial gap motor is in operation, making it easier to improve the electrical insulation of powder magnetic cores for motor cores.

(6) In any of the powder magnetic cores for motor cores described above in (1) to (5), the resin may contain at least one resin selected from the group consisting of epoxy-based, acrylic-based, fluorine-based, and polyimide-based resins.

The above resins are likely to improve the electrical insulation properties of powder magnetic cores used in motor cores.

(7) In any of the powder magnetic cores for motor cores described in (1) to (6) above, the material of the second insulating coating may be at least one selected from the group consisting of phosphate, silica, magnesium oxide, and aluminum oxide.

The above-mentioned second insulating coating can reduce iron losses such as eddy current losses.

(8) In any of the powder magnetic cores for motor cores described above in (1) to (7), the relative density of the powder compact may be 90% or more.

The magnetic properties of the above-mentioned compact, such as saturation magnetic flux density, tend to be high. The mechanical properties of the above-mentioned compact, such as strength, tend to be high.

(9) In any of the powder magnetic cores for motor cores described above in (1) to (8), the powder compact may have a plurality of surface portions and corner portions between adjacent surface portions, and the radius of curvature of the corner portions may be 0.5 mm or more.

By having a corner radius of curvature of 0.5 mm or more, the thickness of the first insulating coating covering the surface and the thickness of the first insulating coating covering the corner are more likely to be uniform. Corners with a curvature radius of 0.5 mm or more are less likely to be damaged.

(10) In the powder magnetic core for a motor core described in (9) above, the radius of curvature of the corner portion may be 3.0 mm or less.

By having a corner curvature radius of 3.0 mm or less, it is easy to increase the cross-sectional area of the compact.

(11) In any of the powder magnetic cores for motor cores described above in (1) to (10), the average particle size of the iron-based particles may be 30 μm or more and 350 μm or less.

Iron-based particles with an average particle size of 30 μm or more tend to have a high relative permeability. Iron-based particles with an average particle size of 300 μm or less tend to have a low eddy current loss.

(12) In any of the powder magnetic cores for motor cores described above in (1) to (11), the iron-based particles are pure iron or an iron alloy, and the iron alloy may be an Fe-Si alloy or an Fe-Al alloy.

The saturation magnetic flux density of iron-based particles made of pure iron is higher than that of iron alloys. Therefore, the saturation magnetic flux density of compacts containing iron-based particles made of pure iron is likely to be high. In addition, iron-based particles made of pure iron have better formability than iron alloys. Therefore, the relative density of compacts containing iron-based particles made of pure iron is likely to be high.

The electrical resistance of iron alloys is higher than that of pure iron. Therefore, iron loss, such as eddy current loss, of iron-based particles made of iron alloys tends to be small. Therefore, losses in powder magnetic cores for motor cores that contain iron-based particles made of iron alloys tend to be small.

(13) A stator core according to one embodiment of the present disclosure is a stator core for an axial gap motor, and includes a powder magnetic core for a motor core according to any one of (1) to (12) above.

The stator core has excellent electrical insulation properties because it is equipped with a powder magnetic core for the motor core.

Details of the embodiments of the present disclosure
The details of the embodiments of the present disclosure are described below. In the drawings, the same reference numerals indicate the same objects.

First Embodiment
[Dust core for motor core]
A motor core powder core 1 according to a first embodiment will be described with reference to FIGS. 1 to 3. As shown in FIG. 2, the motor core powder core 1 according to the first embodiment includes a powder compact 10 and a first insulating coating 50. As shown in FIG. 3, the powder compact 10 is composed of an aggregate of a plurality of coated particles 15. FIG. 3 shows an enlarged view of region A in FIG. 2. FIG. 2 is a cross-sectional view of the motor core powder core 1 according to the first embodiment, taken along line II-II of FIG. 1. As shown in FIG. 3, each coated particle 15 includes an iron-based particle 151 and a second insulating coating 152. The second insulating coating 152 covers the surface of the iron-based particle 151. As shown in FIG. 2, the first insulating coating 50 covers the surface of the powder compact 10. One of the features of the motor core powder core 1 according to the first embodiment is that the first insulating coating 50 shown in FIG. 2 is made of a specific material.

The powder magnetic core 1 for a motor core of embodiment 1 shown in Figure 1 is used to construct, for example, a stator core 7 of embodiment 2 described below with reference to Figure 4. The compact 10 of the powder magnetic core 1 for a motor core that constructs the stator core 7 includes a yoke 30 and teeth 20 described below, as shown in Figure 2. The stator core 7 shown in Figure 4 is used, for example, in a stator 8 described below with reference to Figure 5, and an axial gap motor 9 described below with reference to Figure 6.

[Powder compact]
The green compact 10 shown in FIG. 2 is composed of an aggregate of multiple coated particles 15, as shown in FIG. 3 . The shape of the green compact 10 can be selected as appropriate. As shown in FIG. 2 , the green compact 10 has multiple surface portions 11 and corner portions 12. When the green compact 10 includes a yoke 30 and teeth 20 as described above, the surface portions 11 are the outer peripheral surface 31, inner peripheral surface 32, upper surface 33, lower surface 34, first side surface, and second side surface of the yoke 30, as well as the side surface 21 and end surface 22 of the teeth 20, as described below. The surface portions 11 are flat or curved. The corner portions 12 are provided between adjacent surface portions 11. The corner portions 12 refer to the region between a first inflection point and a second inflection point in a cross section perpendicular to the ridge line constituting the corner portions 12. The first inflection point is the point at which the curvature of a first surface portion 11 changes among adjacent surface portions 11 in the cross section. The second inflection point is a point at which the curvature of the second surface portion 11 of the adjacent surface portions 11 changes in the cross section.

(Corner)
The multiple corners 12 include corners 12 that are curved. Of the corners 12 that are curved, the radius of curvature of the corners 12 that are covered with the first insulating coating 50 is, for example, 0.5 mm or more. When the radius of curvature of the corners 12 is 0.5 mm or more, the thickness of the first insulating coating 50 that covers the surface portion 11 and the thickness of the first insulating coating 50 that covers the corners 12 are likely to be uniform. Of the corners 12 that are curved, the radius of curvature of the corners 12 that are not covered with the first insulating coating 50 may be 0.5 mm or more, or may be less than 0.5 mm. Corners 12 with a radius of curvature of 0.5 mm or more are less likely to be damaged. The radius of curvature of the corners 12 that are not covered with the first insulating coating 50 is also, for example, 0.5 mm or more. The radius of curvature of the corners 12 covered with the first insulating coating 50 and the radius of curvature of the corners 12 not covered with the first insulating coating 50 may be 0.8 mm or more, particularly 1.0 mm or more. The upper limit of the radius of curvature of the corners 12 covered with the first insulating coating 50 and the radius of curvature of the corners 12 not covered with the first insulating coating 50 is practically 3.0 mm. Having a radius of curvature of the corners 12 of 3.0 mm or less facilitates increasing the cross-sectional area of the powder compact 10. The radius of curvature of the corners 12 covered with the first insulating coating 50 and the radius of curvature of the corners 12 not covered with the first insulating coating 50 may be 0.5 mm or more and 3.0 mm or less, particularly 0.8 mm or more and 3.0 mm or less, particularly 1.0 mm or more and 3.0 mm or less. When the corners 12 are composed of multiple curved surfaces with different radii of curvature, the smallest radius of curvature is used as the radius of curvature of the corners 12.

(Constituent materials)
As shown in FIG. 3 , the coated particle 15 has an iron-based particle 151 and a second insulating coating 152 .

<Iron-based particles>
The iron-based particles 151 are made of a soft magnetic material. The soft magnetic material is pure iron or an iron alloy. Pure iron refers to iron (Fe) with a purity of 99% or more. That is, pure iron refers to iron with an Fe content of 99% by mass or more. This content is expressed as a percentage relative to the mass of the soft magnetic material being 100% by mass. The iron-based particles 151 made of pure iron have a higher saturation magnetic flux density than iron alloys. Therefore, the saturation magnetic flux density of the powder compact 10 containing the iron-based particles 151 made of pure iron is likely to be high. Furthermore, the iron-based particles 151 made of pure iron have better moldability than iron alloys. Therefore, the relative density of the powder compact 10 containing the iron-based particles 151 made of pure iron is likely to be high.

An iron alloy contains additive elements, with the remainder consisting of Fe and unavoidable impurities. Iron alloys contain the most Fe. For example, the iron alloy is at least one selected from the group consisting of Fe-Si (silicon)-based alloys, Fe-Al (aluminum)-based alloys, Fe-Si-Al-based alloys, and Fe-Ni (nickel)-based alloys. An example of an Fe-Si-based alloy is silicon steel. An example of an Fe-Si-Al-based alloy is sendust. An example of an Fe-Ni-based alloy is permalloy. The electrical resistance of iron alloys is higher than that of pure iron. Therefore, iron loss, such as eddy current loss, of iron-based particles 151 made of iron alloys tends to be small. Therefore, loss in a powder magnetic core 1 for a motor core having iron-based particles 151 made of iron alloys tends to be small. The powder magnetic core 1 for a motor core may include both iron-based particles 151 made of pure iron and iron-based particles 151 made of an iron alloy.

The average particle size of the iron-based particles 151 is, for example, 30 μm or more and 350 μm or less. Iron-based particles 151 with an average particle size of 30 μm or more tend to have a high relative permeability. Iron-based particles 151 with an average particle size of 350 μm or less tend to have a low eddy current loss. The average particle size of the iron-based particles 151 is further preferably 50 μm or more and 280 μm or less, and particularly preferably 70 μm or more and 260 μm or less.

The average particle size of the iron-based particles 151 is determined as follows: The cross section of the powder compact 10 is observed using a scanning electron microscope (SEM). An observation image of the cross section is acquired. The SEM magnification is 50x or more and 300x or less. The size of the observation image is 2400 μm × 1800 μm. At least 50 observation images are acquired. One observation image may be acquired per cross section, or multiple observation images may be acquired per cross section. Each acquired observation image is subjected to image processing to extract the outline of the iron-based particles 151. Image processing may be, for example, binarization processing. The area of each of all iron-based particles 151 present in each observation image is determined. The diameter of a circle having the same area as each area is determined. The average of all the diameters determined is calculated. This average is used as the average particle size of the iron-based particles 151. At least 500 measurements are required to determine the average particle size.

<Second insulating coating>
The second insulating coating 152 covers the iron-based particles 151. The second insulating coating 152 can reduce iron loss such as eddy current loss. A powder magnetic core 1 for a motor core including the second insulating coating 152 is likely to reduce loss. The material of the second insulating coating 152 is, for example, at least one selected from the group consisting of phosphate, silica, magnesium oxide, and aluminum oxide. Phosphate has excellent adhesion to the iron-based particles 151 and also excellent deformability. Therefore, the second insulating coating 152 is likely to deform in response to the deformation of the iron-based particles 151 and is unlikely to be damaged in step A of producing the compact 10 in the manufacturing method of a powder magnetic core for a motor core described below. Therefore, such a powder magnetic core 1 for a motor core is likely to reduce loss. Materials other than those exemplified above may be used for the second insulating coating 152 as long as they are effective in reducing iron loss such as eddy current loss.

The thickness of the second insulating coating 152 is, for example, 10 nm or more and 1000 nm or less. A second insulating coating 152 with a thickness of 10 nm or more easily insulates adjacent iron-based particles 151 from each other. A second insulating coating 152 with a thickness of 1000 nm or less easily increases the relative density of the powder compact 10. The thickness of the second insulating coating 152 is further preferably 30 nm or more and 700 nm or less, and particularly preferably 50 nm or more and 500 nm or less.

The thickness of the second insulating coating 152 is determined as follows: The cross section of the powder compact 10 is observed using a TEM (Transmission Electron Microscope). An observation image of the cross section is obtained. The TEM magnification is 100,000 times or more and 300,000 times or less. The size of the observation image is 2 μm x 2 μm. Ten or more observation images are obtained. One observation image may be obtained per cross section, or multiple observation images may be obtained per cross section. The thickness of the second insulating coating 152 is measured for each of all coated particles 15 present in each observation image. For each coated particle 15, the length of the second insulating coating 152 along the normal to the outline of the iron-based particle 151 is measured at ten or more locations. The average of all these lengths is defined as the thickness of the second insulating coating 152. The number of measurements required to determine this thickness is 100 or more.

(relative density)
The relative density of the powder compact 10 is, for example, 90% or more. A powder compact 10 with a relative density of 90% or more is likely to have a high saturation magnetic flux density. A powder compact 10 with a relative density of 90% or more is likely to have high mechanical properties, such as strength. Furthermore, a powder compact 10 with a relative density of 90% or more has few voids communicating from the interior to the exterior of the powder compact 10. In some cases, these voids are almost nonexistent. Therefore, even if the first insulating coating 50 (described below) is formed to cover the entire surface of the powder compact 10, air inside the powder compact 10 is unlikely to break through the first insulating coating 50 and escape to the outside during the formation of the first insulating coating 50. Therefore, pinholes are unlikely to form in the first insulating coating 50. In other words, a powder compact 10 with a high relative density is likely to form a first insulating coating 50 with excellent electrical insulation properties. The relative density is preferably 93% or more, and particularly 95% or more. The relative density is 99% or less. That is, the relative density is 90% or more and 99% or less, more preferably 93% or more and 99% or less, and particularly preferably 95% or more and 99% or less.

The relative density of the powder compact 10 refers to the ratio (%) of the actual density of the powder compact 10 to the true density of the powder compact 10. In other words, the relative density of the powder compact 10 is calculated by [(actual density of the powder compact 10 / true density of the powder compact 10) x 100]. The actual density of the powder compact 10 can be calculated using the Archimedes method. The true density of the powder compact 10 is the theoretical density when no voids are present inside.

(yoke)
When the powder magnetic core 1 for a motor core is used to construct the annular stator core 7 shown in Fig. 4, the yoke 30 magnetically couples adjacent teeth 20 among the teeth 20 arranged in the direction around the axis of the stator core 7. In the first embodiment, the shape of the yoke 30 is a fan plate. Unlike the first embodiment, the shape of the yoke 30 may be an annular plate.

The yoke 30 of embodiment 1 has an outer peripheral surface 31, an inner peripheral surface 32, an upper surface 33, a lower surface 34, a first side surface, and a second side surface. The upper surface 33 and the lower surface 34 each connect the outer peripheral surface 31, the inner peripheral surface 32, the first side surface, and the second side surface. The "upper" and "lower" refer to the two opposing surfaces of the yoke 30, with the surface having the teeth 20 referred to as the "upper surface," and the surface without the teeth 20 referred to as the "lower surface." As will be described later with reference to FIG. 6 , this "upper" and "lower" do not necessarily coincide with the upper and lower surfaces of the axial gap motor 9 when the axial gap motor 9 is constructed using the motor core powder magnetic core 1. In the axial gap motor 9 shown in FIG. 6 , the lower surface 34 of the yoke 30 faces the inner surface of the case 92 shown in FIG. 6 . The upper surface 33, the lower surface 34, the first side surface, and the second side surface are planar. Corners 12 are provided between the upper surface 33 and the outer peripheral surface 31, between the upper surface 33 and the inner peripheral surface 32, between the upper surface 33 and the first side surface, between the upper surface 33 and the second side surface, between the lower surface 34 and the outer peripheral surface 31, between the lower surface 34 and the inner peripheral surface 32, between the lower surface 34 and the first side surface, and between the lower surface 34 and the second side surface.

(Teeth)
When the powder magnetic core 1 for a motor core is used to construct the stator core 7 of the stator 8 shown in FIG. 5 , the teeth 20 are provided with coils 80. When the yoke 30 has a fan-shaped configuration as in the first embodiment, the number of teeth 20 for one yoke 30 may be one as in the first embodiment, or may be two or more, unlike the first embodiment. When the yoke 30 has an annular plate shape, unlike the first embodiment, the number of teeth 20 for one yoke 30 is multiple. The teeth 20 are connected to the upper surface 33 of the yoke 30. In this example, the teeth 20 and yoke 30 are integrally configured. No gap that would become a magnetic gap is created between the integrally configured yoke 30 and teeth 20. Therefore, magnetic flux passes smoothly from the teeth 20 to the yoke 30.

The teeth 20 are shaped like a prism or a cylinder. Prismatic or cylindrical refers to a polygonal or circular cross-section taken along a plane perpendicular to the axial direction of the teeth 20. The axial direction of the teeth 20 refers to a direction perpendicular to the lower surface 34 of the yoke 30. A polygonal shape is a triangle or a square. A triangle is an equilateral triangle or an isosceles triangle. A square is a trapezoid or a rectangle. A circle is a perfect circle or an ellipse. Polygonal and circular shapes include not only geometric polygons and circles, but also shapes that are essentially considered polygonal and circular. A polygonal shape includes, for example, shapes with rounded corners. The cross-sectional shape is uniform in the axial direction of the teeth 20. The teeth 20 may be tapered toward their tips.

The shape of the teeth 20 in this example is a trapezoidal column. The cross-sectional shape of the teeth 20 in this example is trapezoidal. The cross-sectional shape of the teeth 20 in this example is uniform in the direction along the axis of the teeth 20. Teeth 20 with a trapezoidal column shape can easily have a large cross-sectional area. Teeth 20 with a trapezoidal column shape can easily reduce dead space in the powder magnetic core 1 for the motor core, making it easy to construct a stator 8 with a high space factor.

The teeth 20 have a side surface 21 and an end surface 22. The side surface 21 is a surface that connects to the top surface 33 of the yoke 30. The end surface 22 is a surface that connects to the end of the side surface 21. The end of the side surface 21 is located on the opposite side from the side that connects to the top surface 33. The corner portion 12 described above is provided between the side surface 21 and the end surface 22.

[First insulating coating]
The first insulating coating 50 improves the electrical insulation of the powder core 1 for a motor core. The first insulating coating 50 covers the surface of the powder compact 10. The area covered by the first insulating coating 50 may be a partial area of the surface of the powder compact 10, or the entire surface of the powder compact 10. For convenience of explanation, FIG. 2 shows a state in which the first insulating coating 50 covers the entire surface of the powder compact 10. For example, if the powder core 1 for a motor core is used to form the stator core 7 of the stator 8 shown in FIG. 5 , the area covered by the first insulating coating 50 is at least the yoke 30 of the powder compact 10 and the area between the teeth 20 and the coil 80. Specifically, the area covered by the first insulating coating 50 is at least the top surface 33 of the yoke 30 and the side surfaces 21 of the teeth 20.

(Constituent materials)
The first insulating coating 50 contains a resin and Fe. The resin contains, for example, at least one resin selected from the group consisting of epoxy-based, acrylic-based, fluorine-based, and polyimide-based resins. These resins tend to improve the electrical insulation of the powder magnetic core 1. It is believed that Fe is typically present in the form of a compound.

The Fe content of the first insulating coating 50 is 0.5% by mass or more and 10% by mass or less. This content is the ratio when the mass of the first insulating coating 50 is 100% by mass. A first insulating coating 50 whose Fe content falls within the above range is likely to improve the electrical insulation of the powder magnetic core 1 for a motor core. The Fe content is further preferably 0.5% by mass or more and 8% by mass or less, and particularly preferably 1% by mass or more and 6% by mass or less.

The Fe content is determined by area analysis of the surface of the first insulating coating 50 using SEM-EDX (Energy Dispersive X-ray Spectroscopy). The magnification of the SEM-EDX is 100x. The size of the observation field is 1000 μm x 1000 μm. The number of measurements is 10 or more. The average value is the Fe content.

(Thickness)
The thickness of the first insulating coating 50 is, for example, 5 μm or more and 100 μm or less. A first insulating coating 50 having a thickness of 5 μm or more is likely to improve the electrical insulation of the motor core powder core 1. When the thickness of the first insulating coating 50 is 100 μm or less, the motor core powder core 1 is less likely to become large. The thickness of the first insulating coating 50 is further preferably 7 μm or more and 80 μm or less, and particularly preferably 10 μm or more and 60 μm or less.

The thickness of the first insulating coating 50 is determined using an electromagnetic induction type film thickness meter. The thickness of the first insulating coating 50 is measured by contacting the probe of the film thickness meter with the surface of the first insulating coating 50. The measurement point is the first insulating coating 50 provided on the flat surface of the powder compact 10. The number of measurements is 100 or more. The average value is the thickness of the first insulating coating 50.

(Hardness)
The hardness of the first insulating coating 50 is, for example, 200 MPa or more. A first insulating coating 50 with a hardness of 200 MPa or more easily mechanically protects the powder compact 10. A first insulating coating 50 with a hardness of 200 MPa or more has a relatively high crosslink density. A first insulating coating 50 with a high crosslink density has excellent electrical insulation properties. That is, a first insulating coating 50 with a hardness of 200 MPa or more easily improves the electrical insulation of the powder core 1 for a motor core. The hardness of the first insulating coating 50 may further be 210 MPa or more, particularly 220 MPa or more. The upper limit of the hardness of the first insulating coating 50 is, for example, 400 MPa. A first insulating coating 50 with a hardness of 400 MPa or less is less likely to suffer damage such as cracks or breakage due to vibrations during operation of the axial gap motor 9, and therefore easily improves the electrical insulation of the powder core 1 for a motor core. The hardness of the first insulating coating 50 may be 200 MPa or more and 400 MPa or less, further 210 MPa or more and 380 MPa or less, particularly 220 MPa or more and 360 MPa or less.

The hardness of the first insulating coating 50 is determined by nanoindentation. The hardness of the first insulating coating 50 is measured by pressing the surface of the first insulating coating 50 with the indenter of a nanoindenter. The number of measurements is 30 or more. The average value is the hardness of the first insulating coating 50.

[Method for manufacturing powder magnetic core for motor core]
The powder magnetic core 1 for a motor core of the first embodiment can be manufactured by a manufacturing method for a powder magnetic core for a motor core including the following steps A and B.
In step A, a powder compact 10 is produced.
In step B, a first insulating coating 50 is formed on the surface of the powder compact 10 .
Each step will be described in detail below.

[Process A]
The green compact 10 can be produced by compressing raw material powder.

The raw material powder includes a plurality of coated particles. Each coated particle has an iron-based particle and a second insulating coating. The material and average particle size of the iron-based particles are as described above. Iron-based particles whose average particle size falls within the above range are easy to handle and to compact. Iron-based particles whose average particle size falls within the above range facilitate the production of a green compact 10 with a high relative density. The material and thickness of the second insulating coating are as described above. The second insulating coating can be formed on the surface of the iron-based particle by a known phosphate coating process. In the raw material stage, the coated particles are covered almost entirely with the second insulating coating. The raw material powder may contain a binder and a lubricant in addition to the coated particles. A lubricant may be applied to the inner surface of the die, which will be described later.

A press molding machine can be used to press-mold the raw material powder. A press molding machine is equipped with a die, an upper punch, and a lower punch. The die and lower punch form a cavity, which is filled with the raw material powder. The upper punch and lower punch press-mold the raw material powder filled in the cavity.

The pressure during compaction is, for example, 500 MPa or more and 2000 MPa or less. If the pressure during compaction is 500 MPa or more, a green compact 10 with a high relative density can be produced. If the pressure during compaction is 2000 MPa or less, the second insulating coating is less likely to be damaged. The pressure during compaction is further preferably 700 MPa or more and 1800 MPa or less, and particularly preferably 800 MPa or more and 1500 MPa or less.

[Process B]
The first insulating coating 50 can be formed by causing a chemical reaction between the powder compact 10 and a chemical solution.

The chemical solution contains a component that dissolves the iron-based particles 151 in the powder compact 10 and ionizes the Fe in the iron-based particles 151, and a resin that precipitates in response to the ionized Fe. The precipitated resin and Fe adhere to the surface of the powder compact, forming a first insulating coating 50 that covers the surface of the powder compact. Such a chemical solution is a resin emulsion that contains an etching component that ionizes the Fe in the iron-based particles 151 that make up the powder compact 10, a surfactant, and a resin component. Such a chemical solution may further contain, for example, at least one of an etching-accelerating component and an additive.

The chemical reaction occurs when the powder compact 10 comes into contact with the chemical solution, specifically, when the powder compact 10 is immersed in the chemical solution. The thickness of the first insulating coating 50 can be adjusted by appropriately selecting the contact time between the powder compact 10 and the chemical solution. The longer the contact time, the thicker the first insulating coating 50 tends to be. Furthermore, the longer the contact time, the higher the Fe content of the first insulating coating 50 tends to be. The contact time is, for example, 5 seconds or more and 2000 seconds or less. A contact time of 5 seconds or more results in a first insulating coating 50 having an Fe content of 0.5% by mass or more. A contact time of 2000 seconds or less results in a first insulating coating 50 having an Fe content of 10% by mass or less. The contact time is preferably 10 seconds or more and 1800 seconds or less, and more preferably 30 seconds or more and 1600 seconds or less.

By masking the surface of the powder compact 10, the area covered by the first insulating coating 50 can be adjusted. The unmasked areas come into contact with the chemical solution, resulting in the formation of the first insulating coating 50. The masked areas do not come into contact with the chemical solution, resulting in the formation of the first insulating coating 50. Masking can be performed, for example, by applying masking tape to the surface of the powder compact 10. Masking tape is, for example, Kapton tape. Kapton is a registered trademark.

After the powder compact 10 is brought into contact with the chemical solution, the powder magnetic core 1 for the motor core is heat-treated. This heat treatment hardens the resin. The heating temperature is, for example, 100°C or higher and 300°C or lower, preferably 130°C or higher and 240°C or lower, and particularly 150°C or higher and 220°C or lower. The heating time is, for example, 5 minutes or higher and 180 minutes or lower, preferably 15 minutes or higher and 150 minutes or lower, and particularly 30 minutes or higher and 120 minutes or lower.

In step B, the powder compact 10 may be subjected to a pretreatment before being brought into contact with the chemical solution. For example, the pretreatment may involve pickling and then rinsing with water. After the powder compact 10 has been brought into contact with the chemical solution, the powder compact 10 may be subjected to a posttreatment before being heat-treated. For example, the posttreatment may involve rinsing with water.

The powder magnetic core 1 for a motor core in embodiment 1 has excellent electrical insulation properties due to the presence of a first insulating coating 50 containing resin and a specific content of Fe.

Second Embodiment
[Stator core]
A stator core 7 of embodiment 2 will be described with reference to FIG. 4 . The stator core 7 of embodiment 2 has a plurality of motor core powder cores 1 arranged in an annular shape. Each of the plurality of motor core powder cores 1 in embodiment 2 is the motor core powder core 1 of embodiment 1. The plurality of motor core powder cores 1 in embodiment 2 are combined in an annular shape such that, among the motor core powder cores 1 adjacent in the direction around the axis of the stator core 7, a first side surface of the yoke 30 of a first motor core powder core 1 and a second side surface of the yoke 30 of a second motor core powder core 1 are in contact with each other. This stator core 7 is used in a stator 8 shown in FIG. 5 and an axial gap motor 9 shown in FIG. 6 . FIG. 6 is a cross-sectional view taken along a plane parallel to the shaft 91 of the axial gap motor 9.

[Stator]
The stator 8 shown in Fig. 5 includes the stator core 7 of the second embodiment and a plurality of coils 80. The coils 80 are arranged on each tooth 20 of the stator core 7. Each coil 80 includes a cylindrical portion formed by spirally winding a wire. The coil 80 in this example is a trapezoidal cylindrical edgewise wound coil using a coated rectangular wire as the winding. Note that Fig. 5 shows only the cylindrical portion, and both ends of the winding are not shown.

[Axial gap motor]
The axial gap motor 9 shown in Fig. 6 is a double stator/single rotor type. The double stator/single rotor type axial gap motor 9 has two stators 8, a first stator 8f and a second stator 8s, and one rotor 90. In the double stator/single rotor type axial gap motor 9, the end faces 22 of the teeth 20 of the first stator 8f and the second stator 8s face the rotor 90 with a gap between them.

The rotor 90 comprises a rotor body 90a and a magnet 90b. The rotor body 90a is rotatably supported relative to a case 92 by a shaft 91. The rotor body 90a is an annular member. A through hole is provided in the center of the rotor body 90a. The shaft 91 is fixed in this through hole.

The magnets 90b are fixed to the rotor body 90a. For example, there may be multiple magnets 90b. Specifically, the number of magnets 90b is the same as the number of teeth 20. The multiple magnets 90b are arranged at equal intervals around the axis of the rotor body 90a. For example, each magnet 90b is flat. The planar shape of each magnet 90b is the same as the planar shape of the end face 22 of the tooth 20. Each magnet 90b is magnetized in a direction along the axis of the shaft 91. The magnetization directions of adjacent magnets 90b around the axis of the rotor body 90a are opposite to each other. The rotating magnetic field generated by the first stator 8f and the second stator 8s causes the magnets 90b to repeatedly attract and repel each tooth 20, causing the rotor 90 to rotate. The rotating magnetic field is generated by exciting the coil 80.

The first stator 8f, the second stator 8s, and the rotor 90 are housed in a case 92. The case 92 has a peripheral wall portion 920, a first plate portion 921, and a second plate portion 922.

The peripheral wall portion 920 surrounds the outer periphery of the first stator 8f, the second stator 8s, and the rotor 90. A first plate portion 921 and a second plate portion 922 are arranged at each end of the peripheral wall portion 920. The first stator 8f is fixed to the first plate portion 921. The second stator 8s is fixed to the second plate portion 922. A through hole is provided in the center of the first plate portion 921 and the second plate portion 922. A bearing 93 is provided in the through hole. The bearing 93 supports the shaft 91 so that it can rotate freely.

Although not shown, the axial gap motor may be a single stator/single rotor type or a single stator/double rotor type. A single stator/single rotor type axial gap motor has one stator and one rotor. In a single stator/single rotor type axial gap motor, the end faces of the stator teeth and the rotor face each other with a gap between them. A single stator/double rotor type axial gap motor has one stator and two rotors. In a single stator/double rotor type axial gap motor, the end faces of the stator face each rotor with a gap between them.

The stator core 7 of embodiment 2 is made of the motor core powder core 1 of embodiment 1, which has excellent electrical insulation properties, and therefore has excellent electrical insulation properties. Therefore, when the stator 8 and axial gap motor 9 are constructed, the stator core 7 can reduce the distance between the motor core powder core 1 and the coil 80. This small distance makes it easier for heat from the coil 80 to be effectively transferred to the powder compact 10. Therefore, the stator core 7 is less likely to increase the temperature of the coil 80.

<Test Example>
The difference in electrical insulation properties of the powder magnetic cores due to differences in the first insulating coating provided on the powder magnetic cores was evaluated.

[Sample No. 1]
The powder magnetic core of Sample No. 1 was produced by sequentially performing steps A and B in the same manner as in the method for producing the powder magnetic core described above.

[Process A]
A powder compact was produced by compressing raw material powder containing a plurality of coated particles.

Each coated particle has an iron-based particle and a second insulating coating. The iron-based particles were composed of pure iron. The average particle size of the iron-based particles was 200 μm. This average particle size is the particle size at which the cumulative volume in the volume particle size distribution measured using a laser diffraction particle size distribution analyzer is 50%. The second insulating coating was composed of phosphate. The thickness of the second insulating coating was 100 nm.

The pressure during press molding was 800 MPa.

The relative density of the green compact was 95%. As described above, the relative density of the green compact was calculated by [(actual green compact density/true green compact density) x 100].

For heat treatment, the compact was heated to 500°C for 300 seconds.

[Process B]
A first insulating coating was formed on the surface of the powder compact by sequentially performing a pretreatment, a main treatment, a post-treatment, and a heat treatment.

As pretreatment, the compact was sequentially pickled and washed with water.

For this treatment, the compact was immersed in a chemical solution to cause a chemical reaction between the compact and the chemical solution. This immersion was performed while the compact was held in a jig. The chemical solution used was a resin emulsion containing a resin component, an etching component, a surfactant, an etching accelerator component, an additive, and a solvent. The resin component was 1 g (solids). This epoxy resin was EP-4901E (product name) manufactured by ADEKA Corporation. The etching component was 0.05 g of sulfuric acid. The surfactant was 0.2 g of ELEMINOL JS-20 (manufactured by Sanyo Chemical Industries). The main component of ELEMINOL JS-20 is sodium alkylaryl sulfosuccinate. The etching accelerator component was 0.06 g of hydrogen peroxide. The additive was 0.002 g of iron(III) fluoride. The solvent was 15.7 g of pure water. The immersion time, i.e., the contact time, was set to 1000 seconds. The chemical solution did not come into contact with the portion where the powder compact was held.

As a post-treatment, the powder core was washed with water. Then, as a heat treatment, the powder core was heated at 190°C for 45 minutes. Specifically, the powder core was placed in an oven at 190°C, held there for 45 minutes, and then allowed to cool at room temperature.

The surface of the powder magnetic core of Sample No. 1 has a first surface made up of a first insulating coating and a second surface not provided with the first insulating coating. The second surface is made up of the surface of the powder compact.

[Average particle size of iron-based particles]
The average particle size of the iron-based particles in the powder magnetic core was determined as follows. An observation image of the cross section of the powder compact was obtained using an SEM. The SEM magnification was 50 times. The size of the observation image was 2400 μm × 1800 μm. 50 observation images were obtained. Each of the obtained observation images was binarized to extract the outlines of the iron-based particles. The area of each of the iron-based particles present in each observation image was determined. The diameter of a circle having the same area as each area was determined. The average of all the determined diameters was calculated. This average was used as the average particle size of the iron-based particles. The number of measurements required to determine the average particle size was 5000. As a result, the average particle size of the iron-based particles in the powder magnetic core was 200 μm.

[Thickness of second insulating coating]
The thickness of the second insulating coating in the powder core was determined as follows. An observation image of the cross section of the powder compact was obtained using a TEM. The TEM magnification was 100,000 times. The size of the observation image was 2 μm × 2 μm. Ten observation images were obtained. The thickness of the second insulating coating was measured for each of all coated particles present in each observation image. The length of the second insulating coating along the normal to the outline of the iron-based particle was measured at 10 locations per coated particle. The average value of all these lengths was taken as the thickness of the second insulating coating. The number of measurements required to determine this thickness was 100. As a result, the thickness of the second insulating coating in the powder core was 100 nm, as described above.

[First insulating coating]
The constituent material, thickness, and hardness of the first insulating coating in the powder magnetic core were determined as follows.

(Constituent materials)
The constituent materials of the first insulating coating were determined by area analysis of the surface of the first insulating coating using SEM-EDX (SUPRA35VP manufactured by ZEISS and OCTANE SUPER manufactured by EDAX). The magnification of the SEM-EDX was 100x. The observation field size was 1000 μm × 1000 μm. The acceleration voltage was 15 kV. Ten measurements were taken, and the average value was calculated. As a result, the first insulating coating was composed of epoxy resin and Fe. The Fe content in the first insulating coating was 1.5 mass%.

(Thickness)
The thickness of the first insulating coating was determined using an electromagnetic induction type film thickness meter. The film thickness meter used was an SWT-9200 manufactured by Sanko Electronics Laboratory Co., Ltd. An L-type probe Fe-0.6EX was used as the film thickness meter probe. The probe contacted the surface of the first insulating coating provided on the flat surface of the powder compact. 100 measurements were taken, and the average value was taken as the thickness of the first insulating coating. As a result, the thickness of the first insulating coating was 30 μm.

(Hardness)
The hardness of the first insulating coating was determined by nanoindentation. The surface of the first insulating coating was pressed with the indenter of a nanoindenter. Thirty measurements were taken. The average value was taken as the hardness of the first insulating coating. As a result, the hardness of the first insulating coating of Sample No. 1 was 230 MPa.

(Pinhole)
The density of pinholes present on the surface of the first insulating coating was measured by SEM observation. The SEM magnification was 50x. The size of the observation field was 1000 µm x 750 µm. The number of observation fields measured was 100. The number of pinholes present per area of the observation field was calculated. As a result, the pinhole density of the first insulating coating of Sample No. 1 was 8 pinholes/ ^cm² .

[Sample No. 101, Sample No. 102]
The powder magnetic cores of Sample No. 101 and Sample No. 102 were produced in the same manner as Sample No. 1, except that the constituent material and formation method of the first insulating coating were different.

For sample No. 101, the first insulating coating was formed by spray painting. For sample No. 101, EB-18M2 manufactured by Kawamura Laboratory Co., Ltd. was used as the paint. For sample No. 102, the first insulating coating was formed by electrodeposition painting. For sample No. 102, INSULEED 3000 manufactured by Nippon Paint Industrial Coatings Co., Ltd. was used as the paint. INSULEED is a registered trademark. These coatings were applied by applying masking tape to part of the surface of the powder compact.

The surfaces of the powder magnetic cores of Samples 101 and 102, like Sample 1, have a first surface made up of a first insulating coating and a second surface not provided with the first insulating coating. The second surface is made up of the surface of the powder compact.

[First insulating coating]
The constituent material, thickness, and hardness of the first insulating coating were determined in the same manner as for Sample No. 1.

The first insulating coating of Samples No. 101 and 102 was composed of the same resin as the resin of the first insulating coating. Unlike the first insulating coating of Sample No. 1, the first insulating coating of Samples No. 101 and 102 did not contain Fe.

The thickness of the first insulating coating for Sample No. 101 and Sample No. 102 was approximately the same as that for Sample No. 1.

The hardness of the first insulating coating of Sample No. 101 was 32 MPa.
The hardness of the first insulating coating of Sample No. 102 was 46 MPa.

The pinhole density in the first insulating coating of Sample No. 101 was 23/cm ^2. The pinhole density in the first insulating coating of Sample No. 102 was 45/cm ² .

[Electrical insulation]
The electrical insulation of each sample powder magnetic core was evaluated. This evaluation was performed by measuring the dielectric breakdown voltage. The dielectric breakdown voltage was measured as follows: Electrodes were attached to the first surface and the uncoated second surface of the powder magnetic core. A constant voltage was applied between the two electrodes for 1 minute. The voltage applied between the two electrodes was increased in steps of 100 V each. The voltage value was measured when the detected current flowing between the two electrodes reached 1 mA or more.

The voltage value of the first insulating coating in the powder core of Sample No. 1 was more than three times the voltage value of the first insulating coating in the powder core of Sample No. 101. The voltage value of the first insulating coating in the powder core of Sample No. 1 was more than five times the voltage value of the first insulating coating in the powder core of Sample No. 102. Thus, Sample No. 1 was found to have superior electrical insulation properties compared to Sample No. 101 and Sample No. 102.

The present invention is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims.

DESCRIPTION OF SYMBOLS 1 Powder core for motor core 10 Powder compact, 11 Surface portion, 12 Corner portion 15 Coated particle, 151 Iron-based particle, 152 Second insulating coating 20 Teeth, 21 Side surface, 22 End surface 30 Yoke, 31 Outer peripheral surface, 32 Inner peripheral surface, 33 Upper surface, 34 Lower surface 50 First insulating coating 7 Stator core 8 Stator, 8f First stator, 8s Second stator 80 Coil 9 Axial gap motor 90 Rotor, 90a Rotor body, 90b Magnet 91 Shaft, 92 Case 920 Peripheral wall portion, 921 First plate portion, 922 Second plate portion 93 Bearing

Claims (15)

a powder compact having a plurality of coated particles;
a first insulating coating covering a surface of the powder compact;
Each of the plurality of coated particles is
iron-based particles;
a second insulating coating covering the surface of the iron-based particles;
the thickness of the second insulating coating is 10 nm or more and 1000 nm or less;
The first insulating coating includes a resin film bonded with Fe ions .
Powder magnetic core for motor cores. The powder magnetic core for a motor core described in claim 1, wherein the thickness of the first insulating coating is 5 μm or more and 100 μm or less. A powder magnetic core for a motor core according to claim 1 or 2, wherein the Fe content in the first insulating coating is 0.5% by mass or more and 10% by mass or less. A powder magnetic core for a motor core according to claim 1 or 2, wherein the hardness of the first insulating coating measured by nanoindentation is 200 MPa or more. The powder magnetic core for a motor core described in claim 3, wherein the hardness of the first insulating coating measured by nanoindentation is 200 MPa or more. The powder magnetic core for a motor core described in claim 4, wherein the hardness of the first insulating coating measured by nanoindentation is 400 MPa or less. The powder magnetic core for a motor core described in claim 5, wherein the hardness of the first insulating coating measured by nanoindentation is 400 MPa or less. The powder magnetic core for a motor core according to claim 3, wherein the resin includes at least one resin selected from the group consisting of epoxy-based, acrylic-based, fluorine-based, and polyimide-based resins. The powder magnetic core for a motor core described in claim 3, wherein the material of the second insulating coating is at least one selected from the group consisting of phosphate, silica, magnesium oxide, and aluminum oxide. The powder magnetic core for a motor core described in claim 3, wherein the relative density of the compact is 90% or more. The powder compact is
A plurality of surfaces;
a corner portion between adjacent surface portions,
The powder magnetic core for a motor core according to claim 10 , wherein the corners have a radius of curvature of 0.5 mm or more. A powder magnetic core for a motor core as described in claim 11, wherein the radius of curvature of the corner is 3.0 mm or less. The powder magnetic core for a motor core according to claim 10, wherein the average particle size of the iron-based particles is 30 μm or more and 350 μm or less. the iron-based particles are pure iron or an iron alloy;
11. The dust core for a motor core according to claim 10, wherein the iron alloy is an Fe-Si alloy or an Fe-Al alloy. A stator core of an axial gap motor,
A motor core comprising the powder magnetic core according to claim 1 or 2.
Stator core.