WO2018179812A1

WO2018179812A1 - Dust core

Info

Publication number: WO2018179812A1
Application number: PCT/JP2018/003281
Authority: WO
Inventors: 晶二階堂; 暁太朗阿部; 祐米澤; 丈弘郷原; 和宏吉留
Original assignee: Tdk株式会社
Priority date: 2017-03-27
Filing date: 2018-01-31
Publication date: 2018-10-04
Also published as: JP2020095988A

Abstract

The purpose of the present invention is to obtain a dust core configured from a soft magnetic powder and a resin, wherein high permeability and exceptional DC superposition characteristics are realized. The dust core according to the present invention is characterized in that: a soft magnetic powder and a resin are included; when the cross-section of the dust core is polished and observed, the grain diameter distribution of the soft magnetic powder has a plurality of peaks; and when a particle group belonging to the peak having the largest grain diameter is designated as particle group α and a particle group belonging to the peak having the smallest grain diameter is designated as particle group β, the average circularity of particle group α is 1-0.8 and the average circularity of particle group β is 0.8-0.4.

Description

Dust core

The present invention relates to a dust core, and more particularly to a dust core having good permeability and direct current superposition characteristics.

Electric and electronic devices are becoming more and more compact, and along with that, small and highly efficient magnetic cores are required. As magnetic core materials for reactors and inductors used in applications where high current is applied, laminated magnetic steel sheets, ferrite cores, and powder magnetic cores formed from soft magnetic powder (molded, injection molded, sheet molded, etc.) Etc.) are used. Although the laminated magnetic steel sheet has a high saturation magnetic flux density, there is a problem that when the driving frequency of the power supply circuit exceeds several tens of kHz, the iron loss increases and the efficiency decreases. On the other hand, the ferrite core is a magnetic core material with a small high-frequency loss, but there is a problem that the shape is increased because the saturation magnetic flux density is low.

圧 Powder magnetic cores formed from soft magnetic powder are widely used because the high-frequency iron loss is smaller than that of laminated electrical steel sheets and the saturation magnetic flux density is larger than that of ferrite cores. In order to reduce the size of the magnetic core, it is particularly necessary that the magnetic permeability is excellent in a high magnetic field on which direct current is superimposed, that is, the direct current superposition characteristics are excellent. In order to obtain excellent direct current superposition characteristics, it is effective to form soft magnetic powder having a high saturation magnetic flux density with high filling.

Considering the influence of the powder particle size on the relative density, the idea of increasing the relative density of the powder magnetic core by mixing and pressing a relatively coarse powder and a fine powder, Various proposals have been made. By mixing the coarse powder and the fine powder, the particle size distribution of the powder becomes bimodal or multimodal and has a plurality of peaks. It is considered that the relative density is increased as compared with particles having a single mode distribution by filling the gaps of the coarse powder with the fine powder. On the other hand, in addition to the increase in relative density, it is considered that the magnetic anisotropy derived from the shape of the powder affects the direct current superposition characteristics of the dust core.

Patent Document 1 (Japanese Patent Laid-Open No. 2016-12630) discloses a coarse powder which is an amorphous soft magnetic powder having an average particle size of 50 μm to 120 μm and an aspect ratio of 1 to 6, and an average particle size of 1 μm. A dust core made of a mixed powder obtained by mixing fine powder, which is an amorphous soft magnetic powder having an aspect ratio of 4 or more and 15 or less and having an aspect ratio of 4 to 15 is disclosed.

According to the patent document 1, the relative density of the powder magnetic core is improved by mixing coarse powder and fine powder. However, particles with a high aspect ratio have a limit in improving the filling rate, and because of the magnetic anisotropy derived from the shape, it is difficult to achieve both high magnetic permeability and excellent DC superposition characteristics.

JP2016-12630

The present invention has been made in view of the above prior art, and aims to realize high magnetic permeability and excellent DC superposition characteristics in a dust core composed of soft magnetic powder and resin.

The inventors of the present invention have continually studied to improve the permeability and direct current superimposition characteristics of the powder magnetic core. As a result, the filling rate is improved by configuring the magnetic powder to be filled with coarse particles and fine particles. In addition to the conventional knowledge that the magnetic permeability is improved, it has been found that the direct current superimposition characteristics can be improved by controlling the shape of the fine particles. That is, instead of using rod-like or needle-like fine grains having a high aspect ratio as in Patent Document 1, DC superposition characteristics are improved by using coarse grains and fine grains having a circularity in a predetermined range. As a result, the present invention has been completed.

That is, the present invention includes the following gist.
(1) A dust core containing soft magnetic powder and resin,
When polishing and observing the cross section of the dust core,
When the particle size distribution of the soft magnetic powder has a plurality of peaks, and the particle group belonging to the peak with the largest particle size is defined as the particle group α and the particle group β belonging to the peak with the smallest particle size, the average of the particle group α A dust core having a circularity of 1 to 0.8 and an average circularity of the particle group β of 0.8 to 0.4.
(2) The ratio of the area A occupied by the particle group α to the area B occupied by the particle group β in the cross section of the powder magnetic core, A / B is 9 to 1.5, (1) .
(3) The sum of the area A occupied by the particle group α and the area B occupied by the particle group β in the cross section of the dust core is 100 to 50% of the total area of the soft magnetic powder (1) or (2 ).
(4) Any of (1) to (3), wherein the particle group α has a particle size of 10 μm or more and 50 μm or less and the particle group β has a particle size of 0.5 μm or more and less than 10 μm in the cross section of the dust core. The dust core described in 1.

The dust core of the present invention includes soft magnetic powder and resin. The soft magnetic powder is composed of a plurality of particle groups having different particle sizes and shapes. That is, the soft magnetic powder includes substantially spherical coarse particles and fine particles having low circularity. By setting the average circularity of the coarse particles to 1 to 0.8 and the average circularity of the fine particles to 0.8 to 0.4, the filling rate of the soft magnetic powder is improved and the magnetic permeability is improved. Moreover, the direct current superimposition characteristic is improved by using a magnetic powder having a circularity in a predetermined range as a fine particle.

FIG. 1 schematically shows the particle size distribution of a soft magnetic powder showing two peaks.

Hereinafter, the present invention will be described based on specific embodiments, but various modifications are allowed without departing from the gist of the present invention.

(Dust core)
The soft magnetic powder constituting the dust core according to the present embodiment includes coarse particles and fine particles. An insulating coating may be formed on the soft magnetic powder.

Such a powder magnetic core is preferably used as a magnetic core of a coil-type electronic component. For example, it may be a coil-type electronic component in which an air-core coil around which a wire is wound is embedded in a dust core having a predetermined shape, or a wire may be wound on a surface of a dust core having a predetermined shape. It may be a coil-type electronic component that is wound only. Examples of the shape of the magnetic core around which the wire is wound include FT type, ET type, EI type, UU type, EE type, EER type, UI type, drum type, toroidal type, pot type, and cup type. it can.

(Soft magnetic powder)
The soft magnetic powder in the present embodiment exhibits a particle size distribution having at least two peaks. Specifically, when the cross section of the powder magnetic core is polished and observed, the particle size distribution of the soft magnetic powder has a plurality of peaks. FIG. 1 schematically shows the particle size distribution of soft magnetic powder showing two peaks.

Coarse particles belonging to the peak Pα having the largest soot particle size are defined as a particle group α. “Belonging to the peak Pα” means that the particle size distribution is included in the region from the bottom where the peak rises to the peak top through the peak top, and until the distribution curve returns almost horizontally on the large particle size side. Means group. Depending on the particle size distribution of the coarse particles, particles contained within ± 50% of the particle size of the peak Pα can be defined as the particle group α. In this case, when the peak particle size is 10 μm, it means particles having a particle size of 5 to 15 μm. Similarly, coarse particles belonging to the peak Pβ having the smallest particle size are defined as a particle group β.

Note that the peak means a peak in which the number of frequencies belonging to the peak is 5% or more of the total frequency. Therefore, a minute peak such as noise is not regarded as a peak in the above description. For example, even if a minute peak such as noise is present on the larger particle diameter side than the peak Pα having the largest particle diameter, it is not regarded as a peak in the present invention. Moreover, the peak may have a shoulder. The shoulder is also considered to belong to the peak.

In the present embodiment, the average circularity of the particle group α is 1 to 0.8, and the average circularity of the particle group β is 0.8 to 0.4. The circularity in this embodiment means Wadell's circularity. Wadell's circularity is defined by the ratio of the diameter of a circle (equivalent circle diameter) equal to the projected area of the particle cross section to the diameter of the circle circumscribing the particle cross section (equivalent circle diameter / diameter of circumscribed circle). In the case of a perfect circle, Wadell's circularity is 1, and the closer to 1, the higher the roundness. On the other hand, when the shape becomes distorted, the circularity decreases. An optical microscope or SEM can be used for observation, and image analysis can be used for calculation of circularity. In the present embodiment, the circularity is calculated for 20 or more particles arbitrarily selected from the particles belonging to each particle group, and the average value is set as the average circularity of the particle group.

円形 The high degree of circularity of the coarse particles (particle group α) makes it easy for the fine particles (particle group β) to flow in the vicinity of the coarse particles during compacting, and the fine particles are easily filled in the gaps between the coarse particles. On the other hand, when the circularity of the fine particles (particle group β) is in the above range, the direct current superimposition characteristics are improved. That is, in this embodiment, the soft magnetic powder filled in the dust core is composed of coarse particles and fine particles, so that the filling rate is improved and the magnetic permeability is improved. Moreover, the direct current superimposition characteristic is improved by using a magnetic powder having a circularity in a predetermined range as a fine particle.

In the present embodiment, the ratio (A / B) of the area A occupied by the particle group α and the area B occupied by the particle group β in the cross section of the dust core is preferably 9 to 1.5, more preferably 5. It is in the range of 7 to 2.3. In terms of the ratio of area A to area B (A: B), it is preferably in the range of 9: 1 to 6: 4, more preferably 8.5: 1.5 to 7: 3. That is, a relatively large amount of coarse particles (particle group α) is filled with fine particles (particle group β) in the gaps between the coarse particles, so that the filling rate of the soft magnetic powder is improved, and excellent magnetic permeability and DC superposition characteristics are realized.

The area A occupied by the particle group α and the area B occupied by the particle group β in the cross section of the dust core can be calculated from the total area of the particles belonging to each particle group using, for example, a scanning electron microscope (SEM). .

In the present embodiment, the total of the area A occupied by the particle group α and the area B occupied by the particle group β in the cross section of the dust core is preferably 100% to 50% with respect to the total area of the soft magnetic powder. More preferably, it is in the range of 100% to 65%. That is, the dust core according to the present embodiment is substantially composed of the particle group α and the particle group β, and the area of the other soft magnetic powder (hereinafter sometimes referred to as “intermediate particle group γ”). The rate is preferably less than 50%, more preferably 35% or less. In other words, the magnetic powder whose circularity and particle size are out of the range of the particle group α and the particle group β may be contained in a relatively small amount, and it is preferable that the magnetic powder is not substantially contained. Therefore, in the dust core of the present embodiment, the particle size distribution of the soft magnetic powder in the cross section is preferably bimodal. When the area ratio of the intermediate particle group γ increases, the magnetic permeability may decrease even if the direct current superposition characteristics are relatively good.

By configuring the dust core substantially only with the soft magnetic powder belonging to the particle group α and the particle group β, the fine particles (particle group β) are filled in the gaps between the coarse particles (particle group α), and the soft magnetic powder The filling rate is improved, and excellent magnetic permeability is realized. Moreover, since the particles having a high aspect are not substantially contained, the direct current superposition characteristics are also improved.

In the present embodiment, the particle size (equivalent circle diameter) of the particle group α in the cross section of the dust core is preferably 10 μm or more and 50 μm or less, more preferably 15 to 40 μm, and the particle size of the particle group β. (Equivalent circle diameter) is preferably 0.5 μm or more and less than 10 μm, and more preferably 1 to 5 μm. By making the grain size of the coarse and fine grains within the above range, the filling property of the soft magnetic powder is further improved.

Further, in the present embodiment, regarding the particle size distribution of the soft magnetic powder in the magnetic core cross section, the particle size of the peak Pα is preferably 15 to 40 μm, more preferably 20 to 30 μm, and the particle size of the peak Pβ is preferably 0. It is in the range of 8-8 μm, more preferably 1.2-4 μm. By controlling the grain size of the coarse and fine grains within the above range, the filling property of the soft magnetic powder is further improved, and the magnetic permeability and DC superposition characteristics are also improved.

Furthermore, in the present embodiment, the aspect ratio of the fine particles (particle group β) is preferably less than 4, more preferably 1 to 3. If the aspect ratio of the fine grains is too high, the direct current superimposition characteristics may deteriorate.

In this embodiment, coarse particles (particle group α) and fine particles (particle group β) are soft magnetic powders, and Fe-based soft magnetic particles are preferable. Specifically, Fe-based magnetic particles include pure iron, Fe-based alloys, Fe-Si based alloys, Fe-Al based alloys, Fe-Ni based alloys, Fe-Si-Al based alloys, Fe-Co based alloys, Examples include Fe-Ni-Si-Co alloy, Fe-Si-Cr alloy, Fe amorphous alloy, Fe nanocrystal alloy, etc. Pure iron, Fe-Si alloy, Fe-Si-Cr alloy More preferably.

The Fe—Si—Cr alloy, which is a preferred soft magnetic powder, has a composition represented by (100-mn) Fe—mSi—nCr, where m is 2 to 7 and n is in the range of 3 to 8. If it exists, a magnetic permeability and a saturation magnetic charge will become high, and it is preferable.

In this embodiment, the soft magnetic powder may be composed of magnetic particles made of the same material, or may be composed of a mixture of magnetic particles of different materials. The coarse particles (particle group α) and the fine particles (particle group β) may be the same material or may be different.

There are no particular limitations on the method for producing the soft magnetic powder, but various powdering methods such as an atomizing method (for example, a water atomizing method, a gas atomizing method, a high-speed rotating water atomizing method, etc.), a reduction method, a carbonyl method, a pulverizing method, etc. Manufactured by. By using the gas atomization method, particles with high circularity are easily obtained. Therefore, when producing coarse particles (particle group α), a gas atomizing method is preferably used. Moreover, it is easy to obtain particles with low circularity by using the water atomization method. Therefore, when producing fine particles (particle group β), the water atomization method is preferably used.

The average circularity of the coarse particles used as the koji raw material may be 1 to 0.8. The average particle diameter (equivalent circle diameter) of the coarse particles is preferably 10 μm or more and 50 μm or less. Further, the coarse particles preferably have a narrow particle size distribution.

The average circularity of the fine grains used as the koji raw material may be 0.8 to 0.4. The average particle diameter of the fine particles is preferably 0.5 μm or more and less than 10 μm. Further, the fine particles preferably have a narrow particle size distribution. Moreover, it is preferable that the particle size distributions of the coarse particles and the fine particles do not substantially overlap.

The degree of circularity of the soft magnetic powder used as the raw material can be controlled within a desired range by selecting an appropriate manufacturing method as described above. For example, the atomizing method is a manufacturing method in which an alloy melted at a high temperature is dropped as a trickle, and a low-temperature fluid is sprayed onto the alloy to scatter and rapidly solidify the molten alloy into powder, depending on the spray conditions of the fluid. The degree of circularity can be controlled by changing the degree of rapid solidification. In addition, the particle size can be controlled within a predetermined range by means such as classification after the magnetic powder is produced.

The shape of coarse grains and fine grains used as a raw material for straw is almost maintained during mixing and molding. This means that in the finally obtained dust core, the average circularity of the particle group α and the raw material coarse particles is substantially the same, and the average circularity of the particle group β and the raw material fine particles is substantially the same, and It can also be confirmed from the fact that the area ratio (A / B) is substantially equal to the charging ratio of coarse grains and fine grains.

絶縁 An insulating coating may be formed on the soft magnetic powder. Examples of the constituent material of the insulating coating include magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, phosphate such as cadmium phosphate, silicate (water glass) such as sodium silicate, soda lime Inorganic coatings such as glass, borosilicate glass, lead glass, aluminosilicate glass, borate glass, and sulfate glass are preferably used. Since the inorganic coating is particularly excellent in insulation, the Joule loss due to the induced current can be particularly suppressed. Moreover, the insulation between magnetic powder can be improved especially by providing an insulating film.

The thickness of the insulating coating is preferably in the range of 5 to 160 nm, more preferably 30 to 100 nm, and particularly preferably 50 to 95 nm. If the thickness of the insulating coating is too thin, sufficient corrosion resistance cannot be obtained, and if it is too thick, the interval between the magnetic powders may be widened, and the permeability μ as the dust core may be lowered. Moreover, the insulating film does not need to cover the whole surface of magnetic powder, and may cover only one part.

(resin)
As the resin constituting the dust core, a known resin can be used. Specifically, various organic polymer resins, silicone resins, phenol resins, epoxy resins, water glass and the like are exemplified. There is no restriction | limiting in particular in content of soft-magnetic powder and resin. The content of the soft magnetic powder in the entire dust core is preferably 90% by mass to 98% by mass, and the content of the resin is preferably 2% by mass to 10% by mass.

(Production method of dust core)
A method for producing the dust core is not particularly limited, and a known method can be adopted. First, a soft magnetic powder and a resin binder are mixed to obtain a mixed powder. Moreover, it is good also considering the obtained mixed powder as granulated powder as needed. Then, the mixed powder or granulated powder is filled into a mold and compression molded to obtain a molded body having the shape of a magnetic body (a powder magnetic core) to be produced. By subjecting the obtained molded body to a heat treatment, a powder magnetic core having a predetermined shape to which metal magnetic powder is fixed is obtained. There are no particular limitations on the conditions for the thermosetting treatment, and for example, heat treatment is performed at 150 to 220 ° C. for 1 to 10 hours. Moreover, there is no restriction | limiting in particular in the atmosphere at the time of heat processing, You may heat-process in air | atmosphere.

れば According to the present invention, high filling of soft magnetic powder is possible, and the filling rate of soft magnetic powder in the dust core is preferably 70% or more, and more preferably 80% or more. The higher the filling rate, the better. The upper limit is not particularly limited, but about 95% is a limit in industrial implementation.

A coil-type electronic component such as an inductor is obtained by winding a wire a predetermined number of times around the obtained dust core.

Moreover, the above-mentioned mixed powder or granulated powder and an air-core coil formed by winding a wire a predetermined number of times are filled in a mold and compression molded to obtain a molded body in which the coil is embedded. Also good. By performing heat treatment on the obtained molded body, a powder magnetic core having a predetermined shape in which a coil is embedded is obtained. Since such a dust core has a coil embedded therein, it functions as a coil-type electronic component such as an inductor.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications may be made within the scope of the present invention.

EXAMPLES Hereinafter, although an invention is demonstrated in detail using an Example, this invention is not limited to these Examples.
The particle size distribution, area ratio, average circularity, filling rate, and direct current superposition characteristics were measured as follows.

<Particle size distribution and area ratio>
The dust core was fixed with cold embedding resin, the cross-section was cut out, mirror-polished, and observed with an SEM. The equivalent circle diameter of the soft magnetic powder in the SEM image was calculated, and a particle size distribution diagram was obtained from the particle size and frequency. For the peak Pα having the largest particle size, the particles contained in the region up to the bottom of both peaks were defined as a particle group α (coarse particles). For the peak Pβ having the smallest particle size, the particles contained in the region up to the bottom of both peaks were defined as a particle group β (fine particles). The ratio (A / B) of the area A occupied by the particle group α and the area B occupied by the particle group β was determined.
In Sample Nos. 21 to 24, the area C of the particle group γ belonging to the intermediate particle size range between the particle group α (coarse particles) and the particle group β (fine particles) was also obtained.

<Average circularity>
100 particles were arbitrarily selected from the particles belonging to each particle group α, β, γ, the Wadell circularity of each particle was measured, the circularity was calculated, and the average value of each was obtained.

<Filling rate>
As a method for measuring the filling rate, the theoretical density was calculated from the metal composition formula, the dimensional density measurement of the core or the density measurement by Archimedes method was performed, and the filling rate was calculated by the density of the core with respect to the theoretical density.

<DC superposition characteristics>
Using an LCR meter (Agilent Technology 4284A) and a DC bias power supply (Agilent Technology 42841A), the inductance of the dust core at a frequency of 100 kHz was measured, and the permeability of the dust core was calculated from the inductance. Measurements were made for a case where the DC superimposed magnetic field was 0 A / m and 8000 A / m, and the respective magnetic permeability values are shown in Table 1 as μ (0 A / m) and μ (8 kA / m).

(Production example: Preparation of coarse soft magnetic powder)
After preparing an alloy powder of 90.5Fe-4.5Si-5Cr by gas atomization method, it was classified as appropriate, and Fe-Si-Cr-based magnetic powder having the average circularity and average particle diameter shown in the table was prepared. Moreover, various magnetic powders having the average circularity and the average particle size described in the table were prepared.

(Production example: Preparation of fine soft magnetic powder) §
After preparing an alloy powder of 90.5Fe-4.5Si-5Cr by the water atomization method, it was classified as appropriate, and Fe-Si-Cr magnetic powder having the average circularity and the average particle diameter shown in the table was prepared. Moreover, various magnetic powders having the average circularity and the average particle size described in the table were prepared.

(Sample No.1-19: Manufacture of dust core)
As soft magnetic powder, 70 parts by volume of coarse particles listed in Table 1 and 30 parts by volume of fine particles were prepared, and xylene was added so that the silicone resin would be 3% by mass with respect to 100% by mass of the total soft magnetic powder. Diluted and added, kneaded with a kneader and dried, the aggregate obtained was sized so as to be 355 μm or less to obtain granules. This was filled in a toroidal mold having an outer diameter of 17.5 mm and an inner diameter of 11.0 mm, and pressed with a molding pressure of 2 t / cm ² to obtain a molded body. The core weight was 5 g. The obtained molded body was heat-treated in a belt furnace at 750 ° C. for 30 minutes in a nitrogen atmosphere to obtain a dust core (sample No. 1).

The compacted powder magnetic core was fixed with cold embedding resin, the cross section was cut out, mirror-polished and observed with an SEM. The equivalent circle diameter of the soft magnetic powder in the SEM image was calculated, and a particle size distribution diagram was obtained from the particle size and frequency. The peak Pα with the largest particle size was 33 μm, and the peak Pβ with the smallest particle size was 4 μm. Particles contained in the region up to both skirts of the maximum peak were defined as a particle group α (coarse particles). For the peak Pβ having the smallest particle size, the particles contained in the region up to the bottom of both peaks were defined as a particle group β (fine particles). The ratio (A / B) of the area A occupied by the particle group α and the area B occupied by the particle group β was found to be 70/30 = 2.3, and the charging ratio of the coarse particles and fine particles used as raw materials Matched.

The average circularity of the particle group α and the particle group β was determined. The average circularity of the particle group α was 0.9, which coincided with the average circularity of the raw material coarse particles. Further, the average circularity of the particle group β was 0.8, which coincided with the average circularity of the raw material fine particles.
The obtained magnetic powder core was evaluated for DC superposition characteristics. The results are shown in Table 1.

Further, dust cores were obtained in the same manner as Sample No. 1 except that the coarse particles and fine particles shown in Table 1 were used in an amount corresponding to the area ratio shown in Table 1 (Sample Nos. 2 to 19). ). In addition, the area ratio of the particle | grains in a powder magnetic core is substantially equal to the preparation ratio of each particle | grain. The average circularity and area ratio of the particles in the cross section of the dust core almost coincided with the charged material. The obtained magnetic powder core was evaluated for DC superposition characteristics. The results are shown in Table 1. In the table, samples marked with “*” correspond to comparative examples.

From the above, the magnetic permeability and direct current superposition characteristics of the dust core are improved by using the soft magnetic powder (coarse particles) that is almost spherical and large in diameter, and the soft magnetic powder (fine particles) that is low in circularity and small in diameter. I understand that On the other hand, when the circularity of the fine grains is high, the initial permeability is high, but the DC superposition characteristics are lowered (Sample No. 1, 12-15). Further, when the circularity of the fine particles is less than 0.4, both the magnetic permeability and the direct current superimposition characteristic are lowered (Sample No. 6). Even if the magnetic core is composed only of coarse particles, the magnetic permeability and DC superimposition characteristics were similarly insufficient (Sample No. 7). When the circularity of the coarse grains decreased, both the magnetic permeability and the DC superposition characteristics were insufficient (Sample No. 18).

(Sample No.20-24: Manufacture of dust core)
Next, in sample Nos. 20 to 24, when the particle group γ belonging to the intermediate particle size range between the particle group α (coarse particle) and the particle group β (fine particle) is included, the influence of the intermediate particle group γ It was investigated. A dust core was obtained in the same manner as described above except that the coarse particles, fine particles, and intermediate particles shown in Table 2 were used in an amount corresponding to the area ratio shown in Table 2 (Sample No. 21-24). The results are shown in Table 2.

When the particle group γ belonging to a particle size range between the particle group α (coarse particle) and the particle group β (fine particle) is included, if the area C of the particle group γ is 50% or less, the permeability, direct current It can be seen that the superposition characteristics are good (sample No. 21-23), but the magnetic permeability tends to decrease when it exceeds 50% (sample No. 24). Therefore, when using intermediate grains that do not belong to coarse grains and fine grains, it is preferable to use them in such an amount that the area ratio is 50% or less.

(Sample No.25-53: Manufacture of dust core)
Next, in Sample Nos. 25 to 53, the average particle size of coarse particles and the average particle size of fine particles were variously changed, and the relationship between the particle size and DC superposition characteristics was examined. A powder magnetic core was obtained in the same manner as above except that the coarse particles and fine particles shown in Table 3 were used in an amount corresponding to the area ratio shown in Table 3 (Sample No. 25-53). The results are shown in Table 3.

It can be seen that when the particle size of the soot particle group α is 10 μm or more and 50 μm or less and the particle size of the particle group β is 0.5 μm or more and less than 10 μm, a dust core excellent in both magnetic permeability and DC superposition characteristics can be obtained. On the other hand, it is understood that the magnetic permeability or the direct current superimposition characteristic is slightly lowered when the particle size is out of these ranges. Therefore, it is preferable that the particle sizes of the coarse particles and the fine particles are in the above range.

[Supplement under rule 26 08.03.2018]
(Sample No.54-170: Manufacture of dust core)
Next, in Sample No. 54-170, the composition of the soft magnetic powder was examined. Coarse grains and fine grains described in Table 4-1 and Table 4-2 were used in an amount corresponding to the area ratio described in the table. The amount of soft magnetic powder was adjusted so that the magnetic permeability μ0 was about 30 to 34. In addition, when an amorphous or nanocrystalline raw material powder was used, the final heat treatment was performed at 350 ° C. for 30 minutes. The results are shown in Table 4-1 and Table 4-2.

As described above, it can be seen that the DC superposition characteristics improved by controlling the circularity of the coarse particles and the circularity of the fine particles within a predetermined range can be achieved regardless of the composition of the soft magnetic powder.

Claims

A dust core comprising soft magnetic powder and resin,
When polishing and observing the cross section of the dust core,
When the particle size distribution of the soft magnetic powder has a plurality of peaks, and the particle group belonging to the peak with the largest particle size is defined as the particle group α and the particle group β belonging to the peak with the smallest particle size, the average of the particle group α A dust core having a circularity of 1 to 0.8 and an average circularity of the particle group β of 0.8 to 0.4.
The dust core according to claim 1, wherein the ratio A / B of the area A occupied by the particle group α and the area B occupied by the particle group β in the cross section of the powder magnetic core is 9 to 1.5.
The pressure according to claim 1 or 2, wherein the sum of the area A occupied by the particle group α and the area B occupied by the particle group β in the cross section of the dust core is 100 to 50% of the total area of the soft magnetic powder. Powder magnetic core.
The powder compact according to any one of claims 1 to 3, wherein the particle group α has a particle size of 10 µm or more and 50 µm or less and the particle group β has a particle size of 0.5 µm or more and less than 10 µm in the cross section of the powder magnetic core. core.