JP2021163855A - Material for powder-compact magnetic core, powder-compact magnetic core, and inductor - Google Patents

Abstract

To provide a material for a powder-compact magnetic core having good magnetic property even in an RF band.SOLUTION: A powder-compact magnetic core material 5 comprises: soft magnetic powder 6; an insulating coat 7 coating the surface of the soft magnetic powder 6; and a lubricant 8. The soft magnetic powder 6 includes Fe as a primary component and 1.5-2.5 at.% of Cr, and has a volume-based average particle diameter of no less than 10 μm and less than 30 μm. The insulating coat 7 is formed by one of aluminum dihydrogen tripolyphosphate and aluminum hydroxide, or both of them.SELECTED DRAWING: Figure 2

Description

The present invention relates to a dust core material, a dust core, and an inductor.

The dust core is a magnetic core for electromagnetic parts manufactured by compression molding soft magnetic powder whose surface is covered with an insulating film. Since this magnetic core is produced from magnetic powder as a raw material, it has an excellent degree of freedom in shape as compared with the magnetic core made of electromagnetic steel sheet or the magnetic core made of ferrite which are widely used in the past. Furthermore, since the individual particles are insulated and the occurrence of eddy current loss can be suppressed, the electromagnetic conversion efficiency is excellent, and therefore the iron content in the magnetic powder can be increased to increase the saturation magnetic flux density, and the magnetic core can be increased. It has the advantage of being able to reduce its size. Taking advantage of these advantages, its applications are expanding year by year, such as transformers such as DC-DC converters and inverters, transformer cores of power supply devices such as switching power supplies equipped with these transformers, and choke coils for noise cutting. The application is expanding.

In recent years, from the viewpoint of resource saving and energy saving, miniaturization and high efficiency of the dust core are required. High frequency is effective to meet this demand. For example, in the case of a chip inductor, it is necessary to correspond to a frequency range of several hundred kHz to several MHz. In order to cope with high frequency, it is important to provide a dust core having high effective magnetic permeability. Further, when considering the use in the high frequency range of the MHz level, the dust core is required to have not only high effective magnetic permeability but also good frequency characteristics and DC superimposition characteristics in the MHz band.

As a material for a dust core that can handle a high frequency band, a method of forming an insulating film by oxidizing or nitriding an element contained in a soft magnetic powder at the time of magnetic annealing is known (Patent Documents 1 and 2).

Japanese Patent No. 6447937 Japanese Patent No. 6397388

When forming an insulating film during magnetic annealing as in Patent Documents 1 and 2, it is necessary to increase the blending ratio of alloying elements. However, since the soft magnetic powder containing an alloy element in a high concentration is hard and difficult to be plastically deformed, it is necessary to mix a binder for molding, and there is a problem that it is difficult to obtain a green compact having a high magnetic powder filling rate. A decrease in the magnetic powder filling rate is a factor that reduces the magnetic characteristics in the high frequency band. Further, even if a green compact having a high magnetic powder filling rate is obtained, it is difficult to obtain a high saturation magnetic flux density due to the large amount of alloy components, and therefore it is difficult to reduce the size even if a dust core is adopted. It becomes.

In view of the above circumstances, it is an object of the present invention to provide a powder magnetic core material having good magnetic properties even in a high frequency band.

The present invention that solves the above problems is a material for a dust core having a soft magnetic powder and an insulating film that covers the surface of the soft magnetic powder. The soft magnetic powder contains Fe as a main component and is 1.5. ~ 2.5 at. It is characterized in that it contains% Cr, has a volume-based average particle size of 10 μm or more and less than 30 μm, and the insulating coating is formed of either or both of aluminum dihydrogen tripolyphosphate and aluminum hydroxide. It is a thing.

As described above, the amount of Cr contained in the soft magnetic powder is 1.5 to 2.5 at. By reducing the percentage to%, it is possible to increase the magnetic permeability and increase the saturation magnetic flux density to obtain good DC superimposition characteristics. On the other hand, when the amount of Cr is reduced, there is a problem that the formation of an oxide film during magnetic annealing becomes insufficient. However, if a predetermined amount of aluminum dihydrogen tripolyphosphate or aluminum hydroxide is blended, magnetic annealing treatment is performed. Moisture is generated from these by heating at the time and promotes the formation of an oxide film. Therefore, an oxide film is formed on the surface of the magnetic powder regardless of the inside or the surface layer of the green compact. Thereby, the insulating property of the insulating layer can be improved.

Further, in the high frequency band, if the particle size of the soft magnetic powder is large, the eddy current loss increases extremely, which is contrary to the improvement of efficiency. Therefore, in the present invention, the average particle size of the soft magnetic powder is used as a volume basis. The particle size of the soft magnetic powder is generally reduced to 10 μm or more and less than 30 μm. In this case, there is a problem that the magnetic permeability decreases as the particle size of the soft magnetic powder becomes smaller. On the other hand, if the insulating film is formed of aluminum dihydrogen tripolyphosphate or aluminum hydroxide, these generate water when heated by magnetic annealing, so not only the formation of oxides by the supply of oxygen from the outside but also the formation of oxides. The formation of oxides from the inside of the green compact also progresses due to the generation of hydrate. Therefore, when the oxide film is formed up to the inside of the green compact, the oxide film near the surface layer does not become thicker than necessary. As a result, the magnetic permeability can be increased even when a soft magnetic powder having a small particle size is used.

The soft magnetic powder is 3.0 to 6.5 at. If it contains% Si, the frequency characteristics can be enhanced. In particular, the Si content is 3.0 to 4.5 at. It is preferable to set it to%.

The material for the dust core is preferably a material having a lubricant. By blending the lubricant, even when molding is performed at a high pressure, the molded product can be smoothly extracted from the mold, which facilitates molding.

A dust core is formed by magnetically annealing the powder magnetic core material described above. In this dust core, an insulating layer made of an oxide containing Cr and Al is formed between the soft magnetic particles derived from the soft magnetic powder.

The relative magnetic permeability of the dust core can be 60 or more.

By mounting the winding on the dust core described above, it can be used as an inductor.

According to the present invention, it is possible to provide a dust core material having good magnetic properties even in a high frequency band.

It is a top view which shows an example of an inductor. It is an enlarged cross-sectional view which shows the schematic structure of the material for a dust core. It is an enlarged cross-sectional view which shows the schematic structure of the dust core. It is a table which shows the measurement result of the magnetic property about an Example and a comparative example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 conceptually shows an example of an inductor 2 using the dust core 1a of the present invention.
In this embodiment, a semicircular shape is illustrated as the dust core 1a. The core 1 is formed by arranging the two dust cores 1a in a ring shape with an air gap 4 formed between both ends of each dust core 1a. By winding the winding 3 around the dust core 1a, an inductor 2 having an air gap 4 in a closed magnetic path is manufactured. The width dimension α of the air gap 4 is set to, for example, 0.5 mm or more and 2.0 mm or less, although it depends on the size of the powder compact. The dust cores 1a are fixed to each other.

The form of the dust core 1 is not limited to the form shown in FIG. 1, and any form other than the ring shape can be adopted. Although FIG. 1 illustrates a core 1 having two air gaps 4, the number of air gaps 4 is arbitrary, and one or more air gaps may be provided. By providing the air gap 4 in this way, it is possible to improve the DC superimposition characteristic of the dust core 1a. If there is no particular problem, the air gap 4 can be omitted. Although FIG. 1 exemplifies the core 1 formed by two dust cores 1a, the number of the dust cores 1a is also arbitrary, and the core 1 is formed by one or three or more dust cores 1a. be able to. The number of windings 3 is also arbitrary, and one or more windings 3 can be mounted on the core 1. The mounting position of the winding 3 is not limited to the position shown in FIG.

The dust core 1a is composed of (1) a preparation step for preparing the dust core material 5, (2) a molding step for compress-molding the dust core material 5, and (3) magnetic annealing for applying magnetic annealing to the dust compact. It is manufactured by going through the processes in order.

FIG. 2 is a diagram showing a schematic configuration of the dust core material 5. As shown in FIG. 2, the dust core material 5 includes a soft magnetic powder 6 and an insulating coating 7 that covers the surface of the soft magnetic powder 6. In the preparation step, the soft magnetic powder 6 is coated with the insulating film 7, and if necessary, the lubricant 8 is adhered to the surface of the insulating film 7 to prepare the dust core material 5.

As the soft magnetic powder 6, Cr was 1.5 to 2.5 at. Fe-Si based alloy powder containing% is used. As the soft magnetic powder, Fe—Si alloy powder that is easily magnetized (high magnetic permeability), has a small coercive force, and has the property of following changes in a magnetic field can be widely used.

The soft magnetic powder 6 contains Fe as a main component (generally 80 mass% or more), but Fe alone has low insulating properties of the oxide film formed on the particle surface, and oxidation easily proceeds to the inside of the particles. Therefore, a decrease in the saturation magnetic flux density becomes a problem. By using Fe—Si based alloy powder containing Cr as an alloy component as the soft magnetic powder 6, the corrosion resistance of the soft magnetic powder 6 is improved, the decrease in saturation magnetic flux density due to oxidation is avoided, and the oxidation has high insulating properties. It becomes possible to form a material film on the surface of particles. Specifically, by containing Cr, an oxide film containing chromium is formed around the soft magnetic powder 6 after magnetic annealing, so that the insulating property is improved. The Cr content is 1.5 at. If it is less than%, the oxide film containing chromium is not sufficiently formed, so that the insulating property is lowered. The Cr content is 2.5 at. If it exceeds%, the magnetic permeability is lowered, and the saturation magnetic flux density is also lowered because the Fe component is reduced. Therefore, the Cr content in the Fe—Si alloy powder is 1.5 to 2.5 at. % Is preferable.

The soft magnetic powder 6 contains Si as an alloy component. By including Si in the soft magnetic powder 6 in this way, the frequency characteristics can be enhanced. The Si content is 6.5 at. If it exceeds%, the magnetostriction becomes zero and the crystal is not distorted when magnetized, so that the loss is reduced and the frequency characteristics can be improved. However, if the Si content is too large, the Fe-Si system is used. There is a problem that the alloy powder becomes hard and the moldability deteriorates, a high-density dust core cannot be obtained, and as a result, the magnetic permeability and the saturation magnetic flux density become low. In consideration of the above, the Si content in the Fe-based alloy powder is 6.5 at. % Or less, especially 4.0 at. It is preferably% or less. In addition, the Si content is 3 at. If it is less than%, the effect of increasing the frequency becomes poor. Therefore, the Si content is 3 at. % Or more, 6.5 at. % Or less.

The Fe-Si alloy powder described above includes Fe—Si—Cr alloy powder, specifically, Fe-3Si-2Cr powder, Fe-4.5Si-2Cr powder, and Fe-6.5Si-2Cr. Powder or the like can be used. Further, as the Fe—Si based alloy powder, an alloy powder containing Al, for example, Fe—Si—Al—Cr based alloy powder can also be used.

As the Fe—Si alloy powder, those produced by the gas atomizing method are preferable because they have high purity. However, Fe-based alloy powder produced by the water atomization method or other processes can also be used.

In the high frequency range of 1 MHz or more, the smaller the particle size of the soft magnetic powder 6, the more the eddy current loss can be suppressed, which can avoid problems such as deterioration of efficiency and deterioration of frequency characteristics. From this point of view, in the present embodiment, the average particle size of the soft magnetic powder 6 is set to 10 μm or more and less than 30 μm (preferably 25 μm or less, more preferably 20 μm or less) on a volume basis, and the soft magnetic powder 6 having a small average particle size is used. I'm using it.

Assuming that the soft magnetic powder 6 is a sphere having a uniform diameter, even if the powder is densely packed, gaps are formed 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 6 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. If the amount of fine powder is large, the fluidity of the powder is lowered, which causes problems such as segregation and penetration of the powder into the clearance of the mold. Therefore, it is also possible to use granulated powder in which fine powders (soft magnetic powders) are bound to each other with a molding binder such as polyvinyl alcohol. 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-based average particle size MV is an average diameter weighted by volume, and particles of d1, d2, ... di, ... dk in a group of particles in ascending order of particle size. Assuming that there are n1, n2, ... ni, ... nk particles having a diameter, 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 x di) / Σ (Vi)
It is represented by. The volume-based average particle size can be measured by using a laser diffraction / scattering type particle size distribution measuring device.

The insulating coating 7 for coating the soft magnetic powder 6 is formed of a material containing Al. In particular, those formed by using a substance that generates moisture during magnetic annealing are preferable. Examples of those that meet this condition include aluminum dihydrogen tripolyphosphate (aluminum primary phosphate) and aluminum hydroxide. Among these, aluminum dihydrogen tripolyphosphate is particularly preferable because it has excellent heat resistance to a heating temperature (up to about 800 ° C.) during magnetic annealing. Either one of the listed aluminum salts may be used alone, or both may be mixed and used.

The material forming the insulating coating 7 includes various oxides and their composite oxides, various carbonates and their composite carbonates, various silicates and their composite silicates, for the purpose of improving the insulating property. Aluminum-free materials such as various alkoxides and their composite alkoxides, various phosphates and their composite phosphates, various silicone resins, and various silane coupling agents may be added. The outermost surface of the insulating coating 7 is preferably a layer containing aluminum.

By forming the insulating film 7 with aluminum dihydrogen dihydrogen tripolyphosphate or aluminum hydroxide, dehydration condensation and crystal transition due to high temperature heating occur during heating by magnetic annealing, and curing bondability is obtained. As the dehydration condensation occurs in this way, moisture is generated inside the green compact during magnetic annealing, so that the inside of the green compact can also be sufficiently oxidized.

The blending amount of aluminum dihydrogen dihydrogen tripolyphosphate or aluminum hydroxide in the dust core material 5 is 0.5 to 1.5 wt. % Is preferable. The blending amount is 0.5 wt. If it is less than%, sufficient insulation cannot be obtained. It is presumed that this is because the amount of water generated during magnetic annealing is insufficient. The blending amount is 1.5 wt. If it exceeds%, the blending amount of the soft magnetic powder itself becomes small, so that sufficient magnetic characteristics cannot be obtained.

The method for forming the insulating coating 7 is not particularly limited, and for example, a rolling flow coating method, various chemical conversion treatments, and the like can be used. The coating method may be either dry or wet.

The lubricant 8 is blended from the viewpoint of extending the life of the mold used in the subsequent molding step or ensuring the fluidity of the dust core material 5. In addition to blending the lubricant 8 with the dust core material 5 before compression molding, the lubricant 8 may be adhered to the wall surface of the mold without blending the lubricant 8.

The lubricant 8 contains Al such as aluminum stearate (aluminum monostearate, aluminum distearate, aluminum tristearate, aluminum 9-hydroxystearate, tri (12-hydroxystearate) aluminum, etc.). An organic compound having lubricity can be used. As a result, an oxide film containing Al is formed around the soft magnetic powder 6 during magnetic annealing, so that the effect of assisting the insulating property can be obtained. As the lubricant 8, an organic compound containing no Al, for example, zinc stearate, calcium stearate, stearic acid amide, or the like can also be used. The lubricant 8 may be used alone or in combination of several types.

The blending amount (or mold adhesion amount) of the lubricant 8 in the dust core material 5 is 0.3 to 0.7 wt. % Is preferable. The blending amount of the lubricant 8 is 0.3 wt. If it is less than%, the required lubrication effect becomes insufficient and the mold life is shortened. The blending amount of the lubricant 8 is 0.7 wt. If it exceeds%, the density of the green compact is lowered, and the magnetic properties and strength are lowered.

In the molding step, the powder compact is formed by compression molding the dust core material 5 obtained in the adjusting step at a predetermined pressure using a mold having a predetermined shape. If the molding pressure is too low, the desired green compact density cannot be obtained, so that sufficient magnetic properties are not exhibited. If the molding pressure is too high, the load on the mold becomes large and the life of the mold may be shortened.

In the magnetic annealing step, the green compact is magnetically annealed for the purpose of removing the magnetostriction of the green compact obtained in the molding step. This annealing treatment is performed in an oxidizing atmosphere. The oxidized atmosphere here means an atmosphere containing oxygen or an atmosphere containing water vapor. The heating temperature (magnetic annealing temperature) during the magnetic annealing treatment is set in consideration of the material of the target dust core material 5, and is usually 600 ° C. or higher and 800 ° C. or lower. If the temperature is lower than 600 ° C., the magnetostriction cannot be sufficiently removed and the iron loss cannot be suppressed. If the temperature exceeds 800 ° C., the eddy current loss increases due to the deterioration of the insulating coating 7. A degreasing step can be provided in the magnetic annealing step.

By carrying out the magnetic annealing treatment described above, the magnetic strain in the powder compacted body is removed, and the powder magnetic core 1a can be used. As shown in FIG. 3, the dust core 1a after magnetic annealing was formed between the soft magnetic particles 10 derived from the soft magnetic powder 6, the insulating layer 11 derived from the insulating coating 7, and the insulating layer 11. It is formed in a porous shape with a large number of pores 12. The insulating layer 11 is a film made of an oxide formed by dehydration condensation accompanying magnetic annealing of the insulating film 7, and contains Cr precipitated from the soft magnetic powder 6. In addition, the oxide of the insulating layer 11 contains Al derived from the insulating coating 7. When the insulating coating 7 contains stearic acid, the oxide of the insulating layer 11 contains P. The organic component derived from the lubricant 8 does not remain in the insulating layer 11 after magnetic annealing.

The volume resistivity of the powder magnetic core 1a after the magnetic annealing is preferably at 1 × 10 ⁶ cm or more. If the volume resistivity ^{is less than 1 × 10 6} cm, 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).

Further, the relative magnetic permeability of the dust core 1a is preferably 60 or more. Relative permeability here is the real part of the complex relative permeability was determined based on JIS C2560 (μ _'r), it is measured using e.g. Hioki EE and KK impedance analyzer (IM3570). To measure the relative magnetic permeability, a winding 3 is wound around a ring-shaped dust core (without an air gap) of φ12.6 mm × φ20.2 mm × h6.4 mm so as to have an inductance of 10 μH to prepare an inductor 2. This is performed by passing an applied current of 10 mA at 10 kHz at room temperature through the winding 3.

In the present embodiment, in order to increase the magnetic permeability and the saturation magnetic flux density to obtain good DC superimposition characteristics, the basic idea is to bring the Fe—Si alloy powder as close to pure iron as possible, and therefore the soft magnetic powder 6 The amount of Cr contained in is 1.5 to 2.5 at. It is as small as%. On the other hand, by reducing the amount of Cr, the formation of the oxide film in the insulating layer 11 becomes insufficient, so how to secure the insulating property of the dust core 1a becomes an issue.

Further, when used in a high frequency band (about 1 MHz), if the particle size of the soft magnetic powder 6 is large, the eddy current loss is extremely increased, which is contrary to the improvement in efficiency. Therefore, in the present embodiment, the particle size of the soft magnetic powder 6 is reduced (the volume-based average particle size is 10 μm or more and less than 30 μm), but if the particle size of the soft magnetic powder 6 is small, the magnetic permeability decreases. There is a problem.

In the present embodiment, in order to supplement the formation of the insulating layer 11, aluminum dihydrogen tripolyphosphate or aluminum hydroxide, which undergoes a dehydration condensation reaction by heating, is used as a material for forming the insulating film 7 of the dust core material 5. doing. In this case, moisture is generated by heating during the magnetic annealing treatment. Due to this moisture, the aluminum component contained in the insulating film forming material is oxidized, the Cr component and Si component on the surface of the Fe-Si alloy powder are oxidized, and the aluminum component contained in the lubricant (for example, a thermal decomposition product of aluminum stearate). Oxidation is promoted. Since the oxides produced by these reactions and the aluminum phosphate produced by dehydration condensation when aluminum dihydrogen tripolyphosphate is used have high insulating properties, the generation of iron oxides that lower the insulating properties is suppressed. At the same time, the insulating property of the insulating layer 11 can be improved.

When the powder magnetic core 1a is thick (for example, when the thickness is 5 mm or more), it becomes difficult for oxygen to diffuse to the inside of the powder during magnetic annealing, and the heating time is lengthened (10 hours to 40 hours) to compensate for this. However, if it is heated for a long time, iron oxide may be generated on the surface of the green compact, which may lead to a decrease in volume resistance and poor insulation. On the other hand, as in the present embodiment, by using aluminum dihydrogen tripolyphosphate or aluminum hydroxide that causes a dehydration condensation reaction as the material for forming the insulating film 7, the inside of the green compact is used when heated by magnetic annealing. Since water is generated from the powder, oxidation inside the green compact can be promoted. Therefore, even if the product is thick, the heating time can be shortened and the problem of deterioration of the insulating property can be avoided. Further, through the same action, it is possible to increase the magnetic permeability even if the particle size of the soft magnetic powder 6 is reduced.

[Example]
Hereinafter, a test performed for confirming the characteristics of the dust core 1a described in the present embodiment will be described.

Each test piece (Example 1) shown in FIG. 4 in which the composition of the soft magnetic powder 6, the particle size of the soft magnetic powder 6 (average particle size based on the volume), the composition of the insulating coating 7, and the composition of the lubricant 8 are different. The magnetic characteristics of ~ 5 and Comparative Examples 1 to 5) were evaluated. The magnetic characteristics to be evaluated are the relative permeability of the dust core, the Q value (quality coefficient) of the inductor, the DC superimposition characteristic of the inductor, and the volume resistivity of the dust core. The test piece was ring-shaped (no air gap).

In Examples 1 to 5 and Comparative Examples 3 and 5, the insulating coating 6 is formed of aluminum tripolyphosphate or aluminum hydroxide. In Comparative Examples 1 and 2, the insulating film 7 was not formed, and the insulating layer 11 was mainly formed by an oxide formed by oxidizing alloy components (Cr, Si, Al, etc.) on the surface of the soft magnetic powder 6. Has been done. In Comparative Example 4, the insulating film 6 is formed of a silicone resin.

The Q value is a value obtained by Q = 2πfL / R (f is frequency, L is self-inductance, and R is resistance component). In this test, the frequency f is set to 1 MHz. The larger the Q value, the better the frequency characteristics (less loss). The DC superimposition characteristic (μ'decrease rate at 10 kA / m,%) is that the DC magnetic field of 10 kA / m is superposed with the effective magnetic permeability when the AC current is 0.01 A, the frequency is 1 kHz, and the DC magnetic field is 0 as 100%. Evaluate by the rate of decrease (%) of the effective magnetic permeability μ'at the time. As already mentioned, the relative magnetic permeability and the effective magnetic permeability are measured by using an impedance analyzer (IM3570) manufactured by Hioki E.E. , And calculated based on the dimensions of the dust core. The winding 3 of the inductor 2 is formed so that the self-inductance is 10 μH. The volume resistivity is measured by applying DC5V.

As is clear from Comparative Examples 1 and 2 in FIG. 4, the amount of Cr is 1.5 to 2.5 at. It was clarified that the required relative permeability (60 or more) could not be obtained when it was out of the range of% (Cr = 4.5 at.%, 1 at.%). On the other hand, the amount of Cr is 1.5 to 2.5 at. In Examples 1 to 6 which are within the range of%, a relative magnetic permeability of 60 or more is obtained in all cases. Furthermore, Q value, the DC bias characteristics, none of the volume resistivity, the conditions required (Q value is 50 or more, reduction rate of mu 'is less than 20%, a volume resistivity of 10 ⁶ or higher) are satisfied .. Therefore, the Cr content in the soft magnetic powder 6 is 1.5 to 2.5 at. The range of% is preferable.

Further, from the comparison between Example 1 and Comparative Examples 3 and 5, it was clarified that the frequency characteristic (Q value) deteriorates as the average particle size of the soft magnetic powder increases. Therefore, the average particle size (volume basis) of the soft magnetic powder is preferably in the range of 10 μm or more and less than 30 μm.

Further, from the comparison of Examples 1 to 3, Si was 3 to 6.5 at. When it is%, it is clear that as the amount of Si increases, the relative permeability and the DC superimposition characteristic slightly decrease, but the Q value greatly improves.

1 Core 1a Powder magnetic core 2 Inductor 3 Winding 4 Air gap 5 Powder magnetic core material 6 Soft magnetic powder 7 Insulation coating 8 Lubricating agent 10 Soft magnetic particles 11 Insulation layer

Claims (6)

In a material for a dust core having a soft magnetic powder and an insulating film that covers the surface of the soft magnetic powder,
The soft magnetic powder contains Fe as a main component and has 1.5 to 2.5 at. % Cr is contained, and the average particle size on a volume basis is set to 10 μm or more and less than 30 μm.
A material for a dust core, wherein the insulating coating is formed of either one or both of aluminum dihydrogen tripolyphosphate and aluminum hydroxide. The soft magnetic powder is 3.0 to 6.5 at. The material for dust core according to claim 1, which contains% Si. The material for a dust core according to claim 1 or 2, further comprising a lubricant. It is formed by magnetically annealing the dust core material according to claims 1 to 3, and an insulating layer made of an oxide containing Cr and Al is formed between the soft magnetic particles derived from the soft magnetic powder. Powder magnetic core. The dust core according to claim 4, wherein the relative permeability is 60 or more. An inductor in which a winding is mounted on a dust core according to claim 3 or 4.

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