WO2022070786A1

WO2022070786A1 - Dust core

Info

Publication number: WO2022070786A1
Application number: PCT/JP2021/032619
Authority: WO
Inventors: 哲隆加古; 英一郎島津
Original assignee: Ntn株式会社
Priority date: 2020-09-29
Filing date: 2021-09-06
Publication date: 2022-04-07
Also published as: JP2022055966A

Abstract

This dust core comprises a soft magnetic particle 10 and an insulating layer 11 that is formed on the surface of the soft magnetic particle 10. The soft magnetic particle 10 contains an alloy element that contains one or both of Si and Cr. The total content of the alloy element in the soft magnetic particle 10 is from 2.0 mass% to 7.0 mass%. The insulating layer 11 is mainly composed of SiO₂. In addition, the insulating layer 11 has a thickness of from 0.05 μm to 0.6 μm.

Description

Powder magnetic core

The present invention relates to a dust core.

The dust core is manufactured by covering the surface of the soft magnetic powder with an insulating film and compression-molding the soft magnetic powder with the insulating film. Typical examples of dust core applications include DC-DC converters, inverters, transformers used in switching power supplies, and noise-cutting choke coils.

Of the transformants, the inductor (chip inductor) mounted on the board of the power supply circuit is often used in the high frequency range of several hundred kHz to several MHz. Therefore, the powder magnetic core also needs a material composition suitable for use in a high frequency range. The higher the frequency, the greater the loss (iron loss) that is absorbed by the dust core and becomes heat. Since most of this loss is caused by the eddy current loss, how to reduce the eddy current loss is an important issue in examining the material and composition of the dust core. In addition, the dust core for chip inductors is required to have high volume resistivity and high magnetic permeability.

As a dust core for a chip inductor, as described in Patent Document 1, a molded body of Fe—Cr—Al-based soft magnetic powder is heat-treated in an oxidizing atmosphere.

In the high frequency induction heating device, a magnetic field is generated by applying a high frequency current to the induction heating coil, and the work is heated by generating an induced current. At this time, by arranging the iron core in the central portion or the peripheral portion of the exciting coil, the generated magnetic flux density can be increased and the heating efficiency can be improved. Laminated steel sheets, ferrite, etc. are generally used as the iron core material, but in recent years, in order to suppress iron loss and improve efficiency, it has been considered to use a dust core using soft magnetic powder as the iron core. Has been done. In recent years, high-frequency induction heating devices are often used in the high-frequency range of 100 kHz or higher, so how to avoid eddy current loss in the high-frequency range even with a dust core for high-frequency induction heating devices. , It has become an important issue in examining the material and composition of the dust core. Further, a powder magnetic core for a high-frequency induction heating device is required to have high volume resistivity and high strength.

As a dust core for a high-frequency induction heating device, as described in Patent Document 2, an iron-based soft magnetic material powder integrated with an insulating film made of an epoxy resin is known.

Japanese Patent No. 5626672 Japanese Patent No. 6554221

As in Patent Document 1, when the soft magnetic powder is magnetically annealed in an oxidizing atmosphere, an insulating layer is formed around the soft magnetic powder. However, in order to develop stable characteristics (frequency characteristics, volume resistivity) in the dust core described in Patent Document 1, it is necessary to contain a large amount of alloying elements such as Al and Cr. As the alloy component increases, the soft magnetic powder becomes harder and the compressibility decreases. The decrease in compressibility leads to a decrease in relative magnetic permeability, which is an important characteristic.

In addition, since the formation of the insulating layer progresses due to oxygen entering from the surface of the dust core during sintering in an oxidizing atmosphere, the insulating layer inside the dust core for a relatively thick powder core of 10 mm or more. There is also the problem that it is difficult to form.

Further, since the magnetic core for the induction hardening device described in Patent Document 2 uses a mixture of epoxy resin and iron powder, there is a problem that the powder magnetic core tends to deteriorate during continuous use.

In view of the above circumstances, an object of the present invention is to provide a dust core with improved frequency characteristics while ensuring the necessary insulation.

The dust core according to the present invention has soft magnetic particles and an insulating layer formed on the surface of the soft magnetic particles.

In the powder magnetic core according to the present invention, the soft magnetic particles contain an alloy element containing either or both of Si and Cr, and the total content of the alloy element in the soft magnetic particles is 2.0 mass% or more. , 7.0 mass% or less (preferably 6.5 mass% or less), the insulating layer contains SiO ₂ as a main component, and the thickness of the insulating layer is 0.05 μm to 0.6 μm. ..

As described above, the soft magnetic particles contain an alloy element containing either one or both of Si and Cr, and the total content of the alloy elements in the soft magnetic particles is 2.0 mass% or more and 7.0 mass% or less. In the case of a powder magnetic core, the content of the alloying element is reduced, so that it is possible to avoid a decrease in the relative magnetic permeability due to a decrease in compressibility. Further, by using SiO ₂ as a main component of the insulating layer and setting the thickness of the insulating layer to 0.05 μm to 0.6 μm, it is possible to obtain high insulating properties while suppressing a decrease in the specific magnetic permeability. Since the insulating layer containing SiO ₂ as a main component is obtained by heating a substance containing Si and O (silane coupling agent, silicone oligomer, silicone resin, etc.) with magnetic annealing, it relies on atmospheric gas. It is possible to form an insulating layer without the need for silicon. Therefore, oxygen does not need to enter when forming the insulating layer, and it is possible to form the insulating layer even inside a thick dust core.

The volume resistivity of the dust core is preferably 1 × 10 ⁶ Ωcm or more. As a result, the specific resistance of the dust core becomes large, so that the eddy current loss can be reduced.

The volume average particle size of the soft magnetic powder forming the soft magnetic particles is preferably 10 to 30 μm. If the volume average particle size is smaller than 10 μm, cracks (lamination or the like) are likely to occur in the molded body, and if the volume average particle size exceeds 30 μm, the eddy current loss increases and the frequency characteristics deteriorate.

The density (meaning the relative density) of the dust core described above is preferably 5.4 g / cm ³ or more and 6.5 g / cm ³ or less.

The powder magnetic core described above can be used for a chip inductor or an induction heating device.

As described above, according to the present invention, it is possible to obtain a dust core having improved frequency characteristics while ensuring the necessary insulating properties.

It is an enlarged sectional view schematically showing the microstructure of a dust core. It is a table which shows the basic characteristic of the dust core which concerns on this embodiment. It is a table which shows the influence which the type of soft magnetic powder and the volume average particle diameter have on the characteristic. It is a table which shows the influence which the film thickness of an insulating layer has on the characteristic. It is a table which shows the influence which the density of a dust core has on the characteristic.

Hereinafter, an embodiment of the present invention will be described.

The dust core according to the present embodiment can be used as a core for winding a winding in an inductor (particularly a chip inductor) or as a core in a high frequency coil of an induction heating device.

The powder magnetic core has a preparation step of preparing a powder for a powder magnetic core, a molding process of compressing the prepared material for a powder magnetic core to obtain a green compact, and a magnetic bleaching step of magnetically annealing the powder. It is manufactured by going through the steps in sequence.

The material for the dust core includes a soft magnetic powder and an insulating film covering the surface of the soft magnetic powder. In the preparation step, a material for a dust core is prepared by coating the soft magnetic powder with an insulating film.

As the soft magnetic powder, a soft magnetic alloy powder containing Fe as a main component (generally 80 mass% or more), an alloy element, and the balance as an unavoidable impurity is used. The soft magnetic powder contains either or both of Si and Cr as essential alloying elements. By containing Si, it is possible to obtain a dust core that is easily magnetized (high magnetic permeability), has a small coercive force, and easily follows changes in the magnetic field. Further, by containing Cr, the specific resistance can be increased and the eddy current loss can be reduced. In addition to the essential alloying elements described above, the soft magnetic powder includes any one or more of other alloying elements (for example, Al, Ni, Co, Cu, B, Nb, Zr, etc.) as required. ) May be contained. Fe-based amorphous alloys and Fe-based nanocrystalline alloys can also be used as the soft magnetic powder.

As typical soft magnetic powders that can be used in this embodiment, Fe—Si, Fe—Cr, Fe—Si—Cr, Fe—Si—Al, Fe—Al—Cr, Fe—Si—Cr—Al and the like can be used. Can be mentioned.

The total content of alloying elements in the soft magnetic powder shall be 2.0 mass% or more and 7.0 mass% or less. When the content of the essential alloy element is less than 2.0 mass%, the relative permeability, the Q value, and the volume resistivity decrease as described later because it is close to pure iron. Further, when the content of the essential alloy element exceeds 7.0 mass%, the powder becomes hard and is less likely to be plastically deformed during compression molding, and it is difficult to increase the density of the green compact. Therefore, the relative permeability of the dust core decreases.

As the soft magnetic powder, those produced by the gas atomizing method are preferable because they have high purity. However, soft magnetic powder produced by the water atomization method or other processes can also be used.

The smaller the particle size of the soft magnetic powder, the more the eddy current loss in the high frequency range (for example, 1 MHz or more) can be suppressed, which can avoid problems such as deterioration of efficiency and deterioration of frequency characteristics. From this viewpoint, the volume average particle size of the soft magnetic powder is preferably 10 μm or more and 30 μm or less. If the volume average particle size is smaller than 10 μm, cracks (lamination or the like) are likely to occur in the molded body, and if the volume average particle size exceeds 30 μm, the eddy current loss increases and the frequency characteristics deteriorate.

Assuming that the soft magnetic powder is a sphere with a uniform diameter, even if the powder is densely packed, gaps are created between the particles, and it is not possible to achieve a high density of the dust core. It is preferable to prepare the soft magnetic powder so as to have a particle size distribution in the range of, for example, about 1 μm to 100 μm so that the gap can be filled with the fine powder. At this time, the particle size distribution may have a single peak, or the particle size distribution may include a plurality of peaks. Further, two or more different kinds of soft magnetic powders can be mixed and used.

If the soft magnetic powder contains a large amount of fine powder, the fluidity of the powder will decrease, causing problems such as segregation and intrusion of the powder into the clearance of the mold. In order to prevent this, as the soft magnetic powder, granulated powder in which fine powders are bound to each other with a binder can also be used. Various organic binders and inorganic binders can be used as the binder for granulation. In particular, it is preferable to use a silicone resin having a small amount of thermal decomposition during magnetic annealing. As the granulation method, general methods such as rolling granulation, fluidized bed granulation, stirring granulation, compression granulation, extrusion granulation, crushing granulation, melt granulation, and spray granulation can be used. The granulation method may be wet or dry.

The volume average particle size MV is an average diameter weighted by volume, and the particle size of d1, d2, ... di, ... Dk is set in the group of particles in ascending order of particle size. Assuming that there are n1, n2, ... ni, ... nk particles, respectively, and the volume per particle is Vi,
MV = (V1 x d1 + V2 x d2 + ... Vi x di + ... Vk x dk) / (V1 + V2 + ... Vi + ... Vk)
MV = Σ (Vi × di) / Σ (Vi)
It is represented by. The volume average particle size can be measured by using a laser diffraction / scattering type particle size distribution measuring device.

The insulating film that coats the soft magnetic powder is formed of a material that changes to SiO ₂ regardless of the components of the atmospheric gas, which is transformed during heating due to magnetic annealing. In the present embodiment, since the material for the dust core is heated by magnetic annealing after the insulating film is formed, the insulating film is required to have heat resistance to the heating temperature (700 ° C. in this embodiment) at the time of magnetic annealing. Further, it is preferable to form an insulating film with a material having a small heat shrinkage during magnetic annealing. This is because if the heat shrinkage is too large, the insulation between the soft magnetic particles may be destroyed during magnetic annealing, and the soft magnetic particles may be energized. As a material satisfying the above-mentioned required characteristics, a material containing Si and O, for example, various silane coupling agents, various silicone oligomers, various silicone resins (for example, methyl silicone resin) and the like can be used. These materials may be used alone or in combination of two or more. Further, these materials can also be used in combination with a material containing Si but not O (for example, various silanes).

By adhering the material of the insulating film to the entire surface of the soft magnetic powder, an insulating film covering the surface of the soft magnetic powder can be formed. The method for forming the insulating film is not particularly limited, and for example, mixing using a mixer, kneading using a pressurized kneader, coating using a fluidized bed, various chemical conversion treatments, and the like can be used. The coating method may be either dry or wet.

In the molding process, the soft magnetic powder obtained in the preparation process is compression-molded with a mold having a predetermined shape to form a green compact. From the viewpoint of extending the life of the mold used in compression molding or ensuring the fluidity of the soft magnetic powder, a solid lubricant may be added to the powder magnetic core material.

Examples of solid lubricants include zinc stearate, calcium stearate, magnesium stearate, barium stearate, lithium stearate, iron stearate, aluminum stearate, stearic acid amide, ethylene bisstearate amide, oleic acid amide, and ethylene bisolein. Acid amide, erucic acid amide, ethylene bis-erucate amide, lauric acid amide, partimic acid amide, behenic acid amide, ethylene biscapric acid amide, ethylene bishydroxystearic acid amide, montanic acid amide, polyethylene, polyethylene oxide, starch, di It is possible to use molybdenum sulfide, tungsten disulfide, graphite, boron nitride, polytetrafluoroethylene, lauroyl lysine, melamine cyanurate, and the like. The solid lubricant may be used alone or in combination of several types. Further, the fixed lubricant may be blended with the soft magnetic powder as the raw material powder before the compression molding, or may be adhered to the wall surface of the mold. The blending amount (or adhesion amount) at this time is preferably, for example, about 0.3 to 2.0 mass% with respect to the material for total dust core. Excessive blending of solid lubricants leads to a decrease in the density of the green compact, which leads to a decrease in magnetic properties and strength.

In the magnetic annealing step, the green compact is subjected to magnetic annealing treatment for the purpose of removing the magnetostriction of the green compact obtained in the molding step. The type of atmosphere gas for this annealing treatment is not particularly limited, but it is desirable to use an inert or reducing atmosphere gas so that the soft magnetic powder does not oxidize and the magnetic properties do not deteriorate. Examples of these atmospheric gases include inert gases such as nitrogen and argon, and reducing gases such as hydrogen. As described above, the type of atmospheric gas that can be used is not limited to the oxidizing one, which is different from Patent Document 1 described above.

The heating temperature (magnetic annealing temperature) during the magnetic annealing treatment should be set in consideration of the material of the target soft magnetic powder, for example, Fe-Si type, Fe-Cr type, Fe-Si-Cr type. When used, it is better to set it to 700 ° C. or higher and 850 ° C. or lower. This is because at temperatures below 700 ° C., magnetostriction cannot be sufficiently removed and iron loss cannot be sufficiently suppressed. Further, if the temperature exceeds 850 ° C., the eddy current loss increases due to the deterioration of the insulating film. When the methyl silicone resin is used as the material for the insulating coating, it is preferable to set the magnetic annealing temperature to 800 ° C. or higher and 850 ° C. or lower from the viewpoint of increasing the strength of the dust core.

It is important to set the magnetic annealing processing time (holding time of the magnetic annealing temperature) in consideration of the size, material, etc. of the dust core so that the inside of the dust core can be sufficiently heated.

By performing the magnetic annealing treatment described above, the magnetostriction in the powder compact is removed, and the hysteresis loss can be reduced. As shown in FIG. 1, the dust core after magnetic annealing is composed of the soft magnetic particles 10 derived from the soft magnetic powder, the insulating layer 11 derived from the insulating coating and covering the soft magnetic particles 10, and the insulating layer 11. It is formed in a porous form having a large number of pores 12 formed between them. The insulating layer 11 is formed by the transformation of the insulating film by heating during magnetic annealing, and the main component is SiO ₂ . Na, K, Mg, Al, and Ca may be contained as other elements constituting the insulating film. The thickness of the insulating coating varies depending on the observation field of view, but if the thickness is adjusted to 0.05 to 0.6 μm on average, a dust core having desired characteristics can be obtained.

The type and content of the alloying element contained in the soft magnetic particles 10 are substantially the same as the type and content of the alloying element contained in the soft magnetic powder before magnetic annealing. Therefore, the total content of the alloying elements in the soft magnetic particles 10 is 2.0 mass% or more and 7.0 mass% or less. Since the total content of the alloying elements contained in the soft magnetic particles 10 (soft magnetic powder) is reduced in this way, it is possible to avoid a decrease in compressibility due to the hardening of the powder, and thereby a decrease in relative magnetic permeability. Can be avoided. Further, by using SiO ₂ as a main component of the insulating layer and setting the thickness of the insulating layer to 0.05 μm to 0.6 μm, high insulating properties can be obtained while suppressing a decrease in relative magnetic permeability. Since the insulating layer containing SiO ₂ as a main component is obtained by heating a substance containing Si and O (silane coupling agent, silicone oligomer, silicone resin, etc.) with magnetic annealing, it relies on atmospheric gas. It is possible to form an insulating layer without the need for silicon. Therefore, oxygen does not need to enter when forming the insulating layer, and it is possible to form the insulating layer even inside a thick dust core.

If the thickness (thickness) of the insulating layer 11 is less than 0.05 μm, the insulating property may be insufficient, and if it exceeds 0.6 μm, the relative magnetic permeability of the dust core decreases. From this point of view, the thickness of the insulating layer is set to 0.05 μm to 0.6 μm. The thickness of the insulating layer 11 is measured from a cross-sectional SEM photograph (about 10,000 times) taken by cutting the dust core. Specifically, the thickness of the insulating layer 11 existing between the Fe soft magnetic particles 10 can be measured in different 30 fields of view on the SEM photograph, and the average value thereof can be used as the thickness. The thickness of the insulating layer 11 can be changed by adjusting the amount of the binder mixed with the soft magnetic powder in the preparation step.

The volume resistivity of the dust core manufactured by the above procedure is preferably 1 × 10 ⁶ Ωcm or more. If the volume resistivity is less than 1 × 10 ⁶ Ωcm, the specific resistance becomes small and the eddy current loss becomes large. The "volume resistivity" here means the electrical resistance between both sides when a 1 m ³ cube is considered inside the magnetic core and a voltage is applied between the two sides thereof (JIS C2560-1).

[Example]
Hereinafter, the tests conducted to confirm the usefulness of the present invention will be described.

<Conditions for preparing test pieces>
An insulating film was formed on the surface of the soft magnetic powder using a silane coupling agent, and the soft magnetic powder with the insulating film was granulated using a silicone resin. A ring-shaped test piece without an air gap (solid lubricant) is mixed with the powder after granulation, compression-molded at a predetermined pressure at room temperature, and magnetically annealed at a nitrogen temperature of 750 ° C. Powder magnetic core) was manufactured. In the case of compression molding, a high-density product (Examples 1 to 4 and Comparative Examples 1 to 4) having a density (relative density) of 5.8 to 6.5 g / cm ³ after heat treatment and a density after heat treatment (relative density) Two types of low-density products (Example 5 and Comparative Example 5) having a relative density of 5.1 to 5.4 g / cm ³ were produced.

As shown in FIGS. 2 to 5, Fe-4.5Si-2.0Cr was used in Examples 1, 2 and 4 and Fe-2Si was used in Example 3 as the soft magnetic powder, and Example 5 was used. Fe-2.0Cr is used in. Further, as the soft magnetic powder, Fe-3.5Si-4.5Cr is used in Comparative Example 1, Fe-2Si is used in Comparative Example 2, and Fe-4.5Si-2.0Cr is used in Comparative Example 4. In Comparative Example 5, Fe-6.0Cr is used.

For the above high-density products, the evaluation items were relative permeability, Q value, and volume resistivity, assuming use in chip inductors. When measuring the relative permeability, a winding was wound around each test piece so as to have an inductance of 10 μH. When measuring the Q value, two windings were wound around each test piece.

The relative magnetic permeability was measured using an LCR meter (5 kHz, 10 mA, constant current mode) in accordance with the method for measuring the initial magnetic permeability specified in JIS C2560-2: 2006.

The Q value is a value obtained by Q = 2πfL / R (f is frequency, L is self-inductance, R is resistance component). The larger the Q value, the better the frequency characteristics (less loss). The Q value was measured using a BH analyzer (1 MHz, 20 mA).

The volume resistivity was measured according to the measuring method specified in JIS C2139-3-1: 2018.

The measurement results will be described with reference to FIGS. 2 to 5. In addition, the relative magnetic permeability was 60 or more, the Q value was 45 or more, and the volume resistivity was 1 × 10 ⁶ Ωcm or more.

FIG. 2 shows the measurement results of the above evaluation items when Fe-4.5Si-2.0Cr was used as the soft magnetic powder (Example 1).

Next, for Example 1, each evaluation item was measured for the test piece in which the type of soft magnetic powder and the average particle size were changed. The results are shown in FIG. 3 together with Example 1. In addition, in FIG. 2 and FIG. 3, the density and the relative magnetic permeability of Example 1 are slightly different, but this is due to the variation in quality due to the use of different test pieces.

In Example 2 in FIG. 3, Fe-4.5Si-2.0Cr was used as the soft magnetic powder as in Example 1, while the volume average particle size of the soft magnetic powder was larger than that in Example 1. However, in Example 3, Fe-2.0Si is used as the soft magnetic powder, while the volume average particle size of the soft magnetic powder is smaller than that of Example 1. Comparative Example 1 uses Fe-3.5Si-4.5Cr as the soft magnetic powder, and Comparative Example 2 uses Fe-2.0Si as the soft magnetic powder (the volume average particle size is the same as that of Example 1). (Same as above), Comparative Example 3 uses pure iron powder instead of soft magnetic powder.

Example 1 in which the total content of the alloying elements in the soft magnetic powder was 7.0 mass%, and Comparative Example 1 in which the total content of the alloying elements was 8.0 mass (3.5 mass% + 4.5 mass%). From the comparison, it was clarified that the specific magnetic permeability was lower than the target value in Comparative Example 1 in which the amount of alloying elements contained in the soft magnetic powder was large. Further, from the comparison between Example 3 and Comparative Example 3, if the content of the alloying element of the soft magnetic powder is 2.0 mass% or more, the relative permeability, the Q value, and the volume resistivity all exceed the target values. It can be understood that

Also, from FIG. 3, it can be understood that the particle size of the soft magnetic powder also affects the magnetic properties. Specifically, from the comparison between Example 1 and Example 2, it can be understood that even if the volume average particle size of the soft magnetic powder is coarsened to 30 μm, all the evaluation items exceed the target values. Further, from the comparison between Example 3 and Comparative Example 2, if the volume average particle size is reduced to 10 μm, the Q value and the volume resistivity can be improved even if the content of the alloying element is the lower limit. Therefore, if the volume average particle size of the soft magnetic powder is within the range of 10 μm or more and 30 μm or less, it is possible to secure the target value for all the evaluation items.

Next, the change in the evaluation items when the film thickness of the insulating film was changed was measured. The results are shown in FIG.

As is clear from FIG. 4, it was clarified that the relative magnetic permeability was lower than the target value when the film thickness of the insulating layer was 0.7 μm. Further, as is clear from Example 2 of FIG. 3, even if the film thickness is 0.07 μm, the relative magnetic permeability, the Q value, and the volume resistivity exceed the target values. Therefore, the thickness of the insulating layer is preferably 0.05 μm or more and 0.6 μm or less.

The above measurement results are for high-density dust cores, but the same evaluation items were also measured for low-density powder cores.

Higher density is effective for improving the relative permeability. For example, in a dust core for an induction heating device (for example, an induction hardening core), the quenching depth is adjusted by adjusting the frequency of the applied current and the powder core. In addition to the specific resistance, the magnetic permeability of the dust core is also adjusted, so a powder magnetic core with a low specific magnetic permeability (specific magnetic permeability less than 60), which is not used in chip inductors, may be required. Therefore, as long as it has the minimum relative permeability (specific permeability of 15 or more), even a low-density dust core may be used for an induction heating device. Based on the above, for low-density products, assuming use in induction heating equipment, the evaluation items were Q value, volume resistivity, and annular strength. The pressure ring strength was measured according to JIS Z2507: 2000. Other measurement methods are the same as described above. A Q value of 45 or more, a volume resistivity of 1 × 10 ⁶ Ωcm or more, and a ring strength of 40 MPa or more were accepted.

From the comparison between Example 5 and Comparative Example 5 in FIG. 5, if the density is 5.4 g / cm ³ or more, the magnetic characteristics (Q value, volume resistivity, required as the dust core for the induction heating device, It became clear that the pressure ring strength) was satisfied. Further, it was also found that the relative magnetic permeability is smaller than that of the high-density products (Examples 1 to 4), but the specific magnetic permeability that is not particularly problematic for the induction heating device can be obtained. Therefore, the density of the dust core after magnetic annealing is preferably 5.4 g / cm ³ or more. In addition, in order to prevent the mold life from being shortened due to friction with the mold during dust molding, and to prevent deterioration of the insulating film due to friction between the dust core materials, the density of the powder magnetic core after magnetic quenching. Is preferably 6.5 g / cm ³ or less.

In the powder magnetic core for chip inductors, which requires high relative permeability, the density is 6.0 g / cm ³ or more from the measurement results of Comparative Example 1 in FIG. 3, Example 4 in FIG. 4, and Comparative Example 4. Is preferable.

10 Soft magnetic particles 11 Insulation layer 12 Vents

Claims

In a dust core having a soft magnetic particle and an insulating layer formed on the surface of the soft magnetic particle,
The soft magnetic particles contain an alloy element containing either one or both of Si and Cr, and the total content of the alloy element in the soft magnetic particles is 2.0 mass% or more and 7.0 mass% or less.
The insulating layer contains SiO 2 as a main component, and the thickness of the insulating layer is 0.05 μm to 0.6 μm.
The dust core according to claim 1, wherein the volume resistivity is 1 × 10 6 Ωcm or more.
The dust core according to claim 1 or 2, wherein the soft magnetic powder forming the soft magnetic particles has a volume average particle size of 10 to 30 μm.
The dust core according to any one of claims 1 to 3, which has a density of 5.4 g / cm 3 or more and 6.5 g / cm 3 or less.
The dust core according to any one of claims 1 to 4 used for the chip inductor.
The dust core according to any one of claims 1 to 4 used in the induction heating device.