JP7637914B2 - Manufacturing method of powder magnetic core - Google Patents

Description

This disclosure relates to powder magnetic cores used in inductors such as choke coils and transformers.

In recent years, autonomous driving systems and advanced driver assistance systems have been developed for vehicles. Behind this lies the increase in sensors installed in vehicles and the development of highly integrated circuits such as SoCs (System on Chip) for high-speed processing of the large amounts of information obtained from these sensors. Inductors used in such applications are required to be compact, capable of handling large currents, and have a low DCR.

As an example of the above-mentioned inductor, a metal composite is known, which is a coil-embedded magnetic element that uses a dust core produced by compressing and molding a metal magnetic powder. Because metal composites use metal magnetic powder, they have a high saturation magnetic flux density and excellent DC bias characteristics, and because they have a dead-space-less structure, they can be made smaller. As a dust core used in such metal composites, Patent Document 1 discloses a composite magnetic material in which metal magnetic powder is bound with a thermosetting resin.

US Patent Application Publication No. 2002-0097124

However, the conventional composite magnetic materials described above may not have sufficient performance as a powder magnetic core. In view of the above, the present disclosure aims to provide a powder magnetic core with higher performance.

A powder magnetic core according to one aspect of the present disclosure comprises a metal magnetic powder, a first resin and a second resin having thermosetting properties, the second resin having a higher degree of shrinkage upon thermosetting than the first resin, a lower degree of elasticity upon thermosetting than the first resin, and a content equal to or less than the first resin.

This disclosure provides a powder magnetic core with higher performance.

FIG. 1 is a schematic perspective view showing the configuration of an electrical component including a powder magnetic core according to an embodiment. FIG. 2 is an SEM image of a powder magnetic core according to an embodiment. FIG. 3 is a flowchart showing a method for manufacturing a powder magnetic core according to an embodiment. FIG. 4 is a diagram for explaining the effect of adding an epoxy resin according to the embodiment. FIG. 5A is a diagram illustrating the effect of the addition of epoxy resin on magnetic permeability according to the embodiment. FIG. 5B is a diagram illustrating the effect of adding an epoxy resin on strength according to the embodiment.

(Knowledge that led to disclosure)
In order to obtain insulation and adhesion between the metal magnetic powder particles, the powdered powder is manufactured by adding an insulating and adhesive resin material to the metal magnetic powder, drying the powder, and then compressing the powdered powder. In order to improve the magnetic properties of the powdered powder core, it is important to reduce the distance between the particles of the metal magnetic powder particles. In other words, it is important to pack the metal magnetic powder densely.

One of the measures to achieve this is to increase the pressure applied during pressure molding. The particles of the metal magnetic powder are pressed against each other in response to the pressure, reducing the distance between them. Another measure is to reduce the amount of resin material added. Since the total amount of resin material is reduced, on average there is less resin material placed between the particles of the metal magnetic powder, improving the filling rate of the metal magnetic powder.

However, although all of these methods are effective in packing the metal magnetic powder at a high density and obtaining a dust core with high magnetic permeability, the bonds between the particles of the metal magnetic powder are broken, making it easier for cracks to occur (reducing mechanical strength or simply strength). If the pressure during pressure molding is lowered or the amount of resin material added is reduced in order to suppress the occurrence of cracks, the density of the metal magnetic powder will decrease and it will not be possible to obtain a dust core with high magnetic properties. In other words, there is a trade-off between the strength and magnetic properties of a dust core.

According to the present disclosure, by combining two types of resin materials to bond the particles of the metal magnetic powder together, it is possible to improve the strength of the powder core while maintaining the magnetic properties, or improve the magnetic properties of the powder core while maintaining the strength, without relying on such a trade-off relationship.

The following describes the embodiment in detail with reference to the drawings.

The embodiments described below each show a specific example of the present disclosure. The numerical values, shapes, materials, components, component placement positions, connection forms, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not described in an independent claim are described as optional components.

(Embodiment)
[composition]
First, an electrical component as an example of the use of a powder magnetic core according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic perspective view showing the configuration of an electrical component including a powder magnetic core according to an embodiment. Fig. 1 shows the general shape of a powder magnetic core 10, which will be described later, and further shows the inside of the powder magnetic core 10 in a see-through manner. For example, components such as a coil member 40 that are hidden by being embedded in the powder magnetic core 10 are shown with dashed lines, indicating that they can be seen through the powder magnetic core 10.

As shown in FIG. 1, the electrical component 100 includes a powder magnetic core 10, a coil member 40, a first terminal member 25, and a second terminal member 35.

As an example, the electrical component 100 is a rectangular metal composite, and the approximate outer shape is determined by the shape of the powder core 10. The powder core 10 can be formed into any shape by pressure molding. In other words, the shape of the powder core 10 during pressure molding can be used to realize an electrical component 100 of any shape.

More specifically, the electrical component 100 is an inductor, a passive element that stores the electrical energy flowing between the first terminal member 25 and the second terminal member 35 as magnetic energy by the coil member 40. In this embodiment, the electrical component 100 is described as one example of the use of the powder magnetic core 10, but the powder magnetic core 10 can simply be used as a magnetic material, and the use example is not limited to the electrical component 100 of this embodiment. The powder magnetic core 10 may be used for any desired application that can utilize the properties of a magnetic material that has both high magnetic properties (specifically, high magnetic permeability) and high strength.

Here, FIG. 2 is an SEM observation image of a powder magnetic core according to an embodiment. FIG. 2 shows an image of a cross section of a powder magnetic core 10 observed using a SEM (Scanning Electron Microscope).

As shown in FIG. 2, the powder magnetic core 10 in this embodiment is composed of metal magnetic powder 11, which is identified as a gray granular object in the figure, a first resin arranged to cover the metal magnetic powder 11, and a second resin present in a scattered manner in the first resin.

Metal magnetic powder 11 is made of Fe-Si-Al, Fe-Si, Fe-Si-Cr, or Fe-Si-Cr-B metal magnetic powder. Metal magnetic powder 11 has a higher saturation magnetic flux density than magnetic powders such as ferrite, making it useful for use under high currents.

For example, when Fe-Si-Al-based metal magnetic powder is used, the composition elements are Si at 8% by weight or more and 12% by weight or less, Al at 4% by weight or more and 6% by weight or less, and the remaining composition elements are Fe and unavoidable impurities. Here, examples of unavoidable impurities include Mn, Ni, P, S, C, etc. By setting the content of the composition elements that make up the metal magnetic powder 11 within the above composition range, high magnetic permeability and low coercive force can be obtained.

For example, when using Fe-Si-based metal magnetic powder, the composition elements include Si with a content of 1% by weight or more and 8% by weight or less, and the remaining composition elements include Fe and unavoidable impurities. Note that the unavoidable impurities are the same as those described above.

For example, when using Fe-Si-Cr-based metal magnetic powder, the composition elements are Si at 1% by weight or more and 8% by weight or less, Cr at 2% by weight or more and 8% by weight or less, and the remaining composition elements are Fe and unavoidable impurities. Note that the unavoidable impurities are the same as those described above.

For example, when Fe-S-Cr-B based magnetic metal powder is used, the composition elements are Si at 1% by weight or more and 8% by weight or less, Cr at 2% by weight or more and 8% by weight or less, and the remaining composition elements are Fe and unavoidable impurities. The unavoidable impurities are the same as those described above.

The role of Si in the composition elements of the above-mentioned metal magnetic powder is to reduce the magnetic anisotropy and magnetostriction constant, increase the electrical resistance, and reduce eddy current loss. By making the Si content in the composition elements 1% by weight or more, it is possible to obtain an improvement effect on the soft magnetic properties, and by making it 8% by weight or less, it is possible to suppress the decrease in saturation magnetization and suppress the decrease in the DC superposition properties.

In addition, by including Cr in the metal magnetic powder, it is possible to impart the effect of improving weather resistance. By making the Cr content in the composition elements 2% by weight or more, it is possible to obtain an improved weather resistance effect, and by making it 8% by weight or less, it is possible to suppress the deterioration of the soft magnetic properties.

The average particle diameter of these metal magnetic powders is, for example, 5.0 μm or more and 35 μm or less. From the viewpoint of ensuring voltage resistance, it is preferable to configure the average particle diameter of the metal magnetic powder to be small in order to reduce electric field concentration between particles, and by setting the average particle diameter as described above, a high filling rate can be ensured. In addition, by setting the average particle diameter of the metal magnetic powder to 35 μm or less, it is possible to reduce core loss in the high frequency range, and in particular eddy current loss. The average particle diameter of the metal magnetic powder is measured using a laser diffraction scattering method or the like.

In this embodiment, the first resin is a silicone resin, and is present, for example, in the locations indicated by the upward white arrows in the figure. The silicone resin is present so as to cover mainly the metal magnetic powder 11, and electrically insulates the particles of the metal magnetic powder 11.

On the other hand, the second resin is scattered throughout the first resin that covers the metal magnetic powder 11. In this embodiment, the second resin is an epoxy resin, and is present, for example, in the locations indicated by the downward white arrows in the figure. Since epoxy resin has high strength, its inclusion in the powder core 10 contributes to improving the strength of the powder core 10.

In this way, the powder magnetic core 10 in this embodiment is composed of two types of thermosetting resin materials. Note that these two types of thermosetting resins are not limited to a combination of silicone resin and epoxy resin, as long as the relationship is satisfied in which the second resin has a higher degree of shrinkage when heat-cured than the first resin, and the second resin has a lower degree of elasticity when heat-cured than the first resin. The thermosetting resin used to form the powder magnetic core 10 can be composed using any combination of the first resin and the second resin that satisfies the above relationship. In addition, it is preferable to select a thermosetting resin whose main agent is liquid at room temperature as the thermosetting resin used in the present invention.

In addition to the first and second resins, the powder core 10 may also contain a third resin different from the first and second resins, as well as other substances such as electrical insulating materials that further strengthen the insulation between the particles of the metal magnetic powder.

Referring again to FIG. 1, the powder magnetic core 10 has rectangular opposing surfaces on which the first terminal member 25 and the second terminal member 35 are respectively formed, and has a shape of a substantially square prism in which the four sides of each opposing surface are connected by a top surface, a bottom surface, and two side surfaces. In this embodiment, the bottom surface and the top surface are rectangular with dimensions of 14.0 mm x 12.5 mm, and the distance from the bottom surface to the top surface is 8.0 mm.

The coil member 40 is wound with a long conductor wire covered with an insulating film (winding portion), and both ends of the wire are connected to the first terminal member 25 and the second terminal member 35, respectively (lead portions 20 and 30). In this embodiment, a round wire with a cross-sectional diameter of 0.65 mm is used as the conductor wire. There is no particular limitation on the thickness and shape of the conductor wire, and as long as the thickness allows winding processing, etc., a round wire or a flat wire with a rectangular cross section can be appropriately selected and used. The winding portion is embedded near the center of the powder core 10. In the lead portions 20 and 30, each of the two ends of the conductor wire extends continuously from the winding portion to the opposing surfaces, and protrudes to the outside of the powder core 10. Here, a part of the lead portion is stretched to have a flat shape and is bent so as to follow the opposing surfaces and the bottom surface. The insulating film coating is peeled off from the stretched portion, making it possible to electrically connect to the outside.

The first terminal member 25 and the second terminal member 35 are made of a conductive plate such as phosphorus bronze or copper. Each of the first terminal member 25 and the second terminal member 35 has a recess near the center along the opposing surface and is configured to recess into the powder core 10. The lead portions 20 and 30 are arranged outside the recess, and the lead portions 20 and 30 are electrically connected to the first terminal member 25 and the second terminal member 35. The lead portions 20 and 30 are connected to the first terminal member 25 and the second terminal member 35 by resistance welding or the like. The first terminal member 25 and the second terminal member 35 are bent so as to be inserted toward the inside of the powder core 10, and the first terminal member 25 and the second terminal member 35 are fixed to the powder core 10 with the bent portion inserted into the powder core 10.

The first terminal member 25 and the second terminal member 35 are also bent together with the lead portions 20 and 30 so as to fit along the bottom surface of the powder core 10. This allows the lead portions 20 and 30 to be held by the first terminal member 25 and the second terminal member 35 while being routed around the bottom underside of the electrical component 100. In other words, the lead portions 20 and 30 can be directly connected to lands (not shown) of a mounting board or the like on which the electrical component 100 is mounted.

Note that the first terminal member 25 and the second terminal member 35 are not essential components. If the lead portions 20 and 30 have the strength to maintain their shape independently, the first terminal member 25 and the second terminal member 35 do not have to be provided.

[Production method]
Next, the manufacturing method of the above-mentioned powder magnetic core 10 will be described with reference to FIG. 3. FIG. 3 is a flowchart showing the manufacturing method of the powder magnetic core according to the embodiment. In the manufacturing of the powder magnetic core 10 in this embodiment, first, a metal magnetic powder 11 containing a predetermined composition element is prepared (preparation step S101). Next, the metal magnetic powder 11 and an electrical insulating material are mixed (not shown). In cases where the electrical insulating material is replaced by a resin material to be added later, mixing of the electrical insulating material is not an essential requirement of the embodiment, and this process may be skipped. The thermosetting resin is mixed in a state in which the metal magnetic powder 11 and the electrical insulating material are substantially uniformly dispersed by mixing.

Specifically, first, the silicone resin, which is the first resin, is dissolved in a solvent in advance and added to a mixture of the metal magnetic powder 11 and the electrical insulating material, and then further mixed (kneaded) (first mixing step S102). The metal magnetic powder 11 is coated with the electrical insulating material and the silicone resin to electrically insulate each particle from each other.

Then, the second resin, epoxy resin, is added to the mixture of the metal magnetic powder 11, the electrical insulating material, and the silicone resin in a state where it has been dissolved in advance in a solvent such as IPA, and then further mixed (kneaded) (second mixing step S103). The kneading of the thermosetting resin described above is performed by mixing the uncured resin material in a mortar, mixer, or the like. In this embodiment, the ratio of the amount of silicone resin and the amount of epoxy resin added is configured to be 0.08 or more and 1.00 or less in terms of the epoxy resin/silicone resin ratio.

This mixture is heated at a temperature of 65°C or higher and 150°C or lower to evaporate the solvent, and then pulverized to obtain a composite magnetic material with good moldability. Furthermore, by classifying this composite magnetic material to obtain a mixed powder with particle sizes aligned within a specified range, moldability can be further improved.

The mixed powder obtained as described above is put into a die and pressure-molded into a desired shape to obtain the powder core 10 (molding step S104). In the molding step S104, pressure molding is performed within a range of a pressure of 3 to 7 ton/ ^cm2 .

As described above, the manufacturing method of the powder magnetic core 10 in this embodiment includes a first mixing step S102 in which a metal magnetic powder is mixed with a first resin having thermosetting properties before curing, a second mixing step S103 in which a second resin having thermosetting properties before curing is mixed after the first mixing step S102, and a molding step S104 in which pressure molding is performed, and the second resin has a higher degree of shrinkage when heat cured than the first resin, a lower degree of elasticity when heat cured than the first resin, and a content equal to or less than that of the first resin.

The first resin of the thermosetting resins used in the powder magnetic core 10 is a silicone resin that is both insulating and elastic. After the metal magnetic powder 11 is coated with the first resin, a second resin, an epoxy resin, which is stronger than the first resin, is added in a smaller amount than the first resin. The second resin hardens after it expands in volume. During the process of the second resin's expansion, the second resin softens once and is dispersed and scattered inside the first resin.

Then, the shrinkage rate of the second resin during the curing process is greater than that of the first resin, and the distance between each particle of the metal magnetic powder 11 can be reduced during the curing process. In this way, the distance between the particles is small and they are densely packed. Therefore, in this embodiment, a dust core 10 with high magnetic permeability and strength can be obtained. In addition, the formed dust core 10 is endowed with heat resistance, which is a characteristic of silicone resin.

Below, we will further explain in detail an example of the powder magnetic core 10 based on the above embodiment.

(Example)
In the following examples, a dust core 10 will be described in which the metal magnetic powder 11 is made of Fe--Si--Cr-based metal magnetic powder having an average particle size of 10 μm.

A mixed powder was prepared by mixing 100 g of metal magnetic powder with silicone resin and epoxy resin at the addition ratio shown in Fig. 4. Fig. 4 is a diagram for explaining the effect of adding epoxy resin according to the embodiment.

The mixed powder was dried at a temperature of 80° C., and then classified to adjust the particle size to a predetermined range. The adjusted mixed powder thus obtained was pressurized at room temperature with a pressure of 4 ton/cm ² to produce a ring core having an outer diameter of 14.0 mm, an inner diameter of 10.0 mm, and a thickness of 2.00 mm. Further, the powder core 10 in this example was produced by drying for 2 hours at a temperature of 150° C. and curing the thermosetting resin.

[Initial permeability]
The initial permeability was calculated by measuring the inductance L at 0 A using an LCR meter, and calculating the initial permeability μi from the following formula 1 (measurement frequency 100 kHz).

μi=(L×le)/(μ0×Ae×n ² )...(1)

Note that le is the effective magnetic path length, μ0 is the vacuum permeability, Ae is the cross-sectional area, and n is the number of turns of the measurement coil.

[Strength]
For strength measurements, pressure molding was performed at a pressure of 4 ton/ ^cm2 to prepare pre-cured test pieces with a length of 12.0 mm, a width W of 12.0 mm, and a thickness T of 0.70 mm. The pre-cured test pieces were then cured by drying at a temperature of 150°C for 2 hours to prepare test pieces.

The prepared test piece was subjected to a three-point bending test in which a load was applied at a rate of 0.5 mm/min, and the load applied when the test piece broke was used as the measured value. From the measured values, the strength σ (N/mm ² ) was calculated using the following formula 2.

σ=3×Pb×Ls/1WT ² ...(2)

Note that Pb is the load (measured value) applied when the test piece broke, and Ls is the distance between the supports in mm.

[result]
The test results of each sample prepared in this example will be described with reference to FIG. 5A and FIG. 5B in addition to FIG.

FIG. 5A is a diagram for explaining the effect of the addition of epoxy resin on the magnetic permeability according to the embodiment. FIG. 5B is a diagram for explaining the effect of the addition of epoxy resin on the strength according to the embodiment. The fifth column of FIG. 4 shows the initial magnetic permeability obtained as a result of the above test as magnetic permeability, and the sixth column of FIG. 4 shows the strength [N/mm ² ] obtained as a result of the above test. FIG. 5A shows a graph in which the magnetic permeability of the specimen is plotted against the additive rate of the epoxy resin, corresponding to the fifth column of FIG. 4. FIG. 5B shows a graph in which the strength of the specimen is plotted against the additive rate of the epoxy resin, corresponding to the sixth column of FIG. 4. In addition, in the first column of FIG. 4, in addition to the specimen number as No., "*" is added to distinguish the comparative example, and for example, the specimen with specimen number 1 indicates that it is a specimen related to the comparative example with "*" added.

As shown in specimens numbered 1 to 3 in Figure 4, in specimens that contain only silicone resin as the thermosetting resin, the magnetic permeability decreases as the amount of thermosetting resin added increases.

On the other hand, as shown in specimens Nos. 4 to 10 in Figure 4, and in Figures 5A and 5B, specimens in which epoxy resin was added in addition to silicone resin as a thermosetting resin showed increased strength according to the amount of epoxy resin added compared to specimen No. 2, and furthermore, the magnetic permeability increased temporarily, peaking at specimen No. 8. Also, specimen No. 10 was found to be a specimen with significantly higher strength while maintaining the same magnetic permeability, compared to specimen No. 3, which had a lower total amount of thermosetting resin added (i.e. silicone resin + epoxy resin).

This result is due to the fact that by adding epoxy resin after coating the metal magnetic powder 11 with silicone resin, the epoxy resin softens as it cures and shrinks, resulting in the epoxy resin being present in a scattered form within the silicone resin. Since the cure shrinkage rate of the scattered epoxy resin is greater than that of the silicone resin, the distance between each particle of the metal magnetic powder 11 can be reduced during the curing process, resulting in a greater magnetic permeability. At the same time, it is possible to obtain a dust core 10 that combines the high strength properties of epoxy resin and the high heat resistance properties of silicone resin.

If the ratio of the silicone resin to the epoxy resin is 1 or more in the epoxy resin/silicone resin ratio, the effect of the epoxy resin becomes dominant in forming gaps between the metal magnetic powder, and the magnetic permeability becomes small. Therefore, it is preferable that the content of the second resin is equal to or less than that of the first resin. In this way, simply constructing a powder core containing a large amount of epoxy resin will only result in a powder core with low magnetic permeability, and there is an appropriate range for the amount of epoxy resin added.

For example, specimen number 4 is prepared by adding 3.00% by weight of silicone resin and 0.25% by weight of epoxy resin and processing it. In the SEM observation image of the cross section of the specimen obtained as a result, the area occupancy of the epoxy resin is 2.28%, the area occupancy of the metal magnetic powder is 65.95%, and the area occupancy of the silicone resin is 31.77%. Therefore, the area ratio of the epoxy resin to the silicone resin in the specimen after preparation is 2.28/31.77=0.07.

Similarly, the specimen with specimen number 10 is prepared by adding 3.00% by weight of silicone resin and 3.00% by weight of epoxy resin and processing them. In the SEM observation image of the cross section of the specimen obtained as a result, the area occupancy of the epoxy resin is 19.62%, the area occupancy of the metal magnetic powder is 58.36%, and the area occupancy of the silicone resin is 22.02%. Therefore, the area ratio of the epoxy resin to the silicone resin in the specimen after preparation is 19.62/22.02=0.89. That is, the area occupancy of the second resin in the cross section is effective when it is contained in at least a small amount, and exists in the range of 19.62% (i.e., 20%) or less. In other words, the area occupancy of the second resin in the cross section may be greater than 0.0% and less than 20%. In addition, the area ratio of the second resin to the first resin in the cross section is greater than 0.07, greater than 0.0, and less than 0.9, less than 0.89. In other words, the area ratio of the second resin to the first resin in the cross section may be in the range of more than 0.0 and less than 0.9.

[Effects, etc.]
As described above, the powder magnetic core 10 according to this embodiment comprises metal magnetic powder 11, and first and second resins having thermosetting properties, the second resin having a higher degree of shrinkage upon thermosetting than the first resin, a lower degree of elasticity upon thermosetting than the first resin, and a content equal to or less than that of the first resin.

In such a powder core 10, the second resin, which is dispersed in the first resin, brings the particles of the metal magnetic powder 11 closer together when it hardens and shrinks, improving the magnetic permeability of the entire powder core 10. In other words, the magnetic properties of the powder core 10 can be improved. This makes it possible to realize a powder core 10 with higher performance.

Also, for example, the first resin may be a silicone resin and the second resin may be an epoxy resin.

This allows the above-mentioned powder magnetic core 10 to be realized by using silicone resin as the first resin and epoxy resin as the second resin. In addition, the high strength properties of epoxy resin can improve the strength of the powder magnetic core 10. Therefore, a powder magnetic core 10 with higher performance can be realized.

Also, for example, the area occupancy rate of the second resin in the cross section of the powder magnetic core may be greater than 0.0% and less than or equal to 20%.

This allows the formation of a powder magnetic core 10 containing an appropriate content of the second resin. Therefore, a powder magnetic core 10 with higher performance can be realized within an appropriate range of the content of the second resin.

Also, for example, the area ratio of the second resin to the first resin in the cross section of the powder magnetic core may be greater than 0.0 and less than 0.9.

This allows the formation of a powder magnetic core 10 containing the second resin at an appropriate area ratio. Therefore, a powder magnetic core 10 with higher performance can be realized within an appropriate range of the area ratio of the second resin.

(Other embodiments, etc.)
Although the powder magnetic cores according to the embodiments and the like of the present disclosure have been described above, the present disclosure is not limited to these embodiments.

For example, coil components using the above-mentioned magnetic materials are also included in the present invention. Examples of coil components include inductance components such as high-frequency reactors, inductors, and transformers. In addition, power supply devices equipped with the above-mentioned coil components are also included in the present invention.

Furthermore, the present disclosure is not limited to this embodiment. As long as it does not deviate from the spirit of the present disclosure, various modifications conceivable by a person skilled in the art to this embodiment and forms constructed by combining components of different embodiments may also be included within the scope of one or more aspects.

The magnetic material disclosed herein can be used as a material for the magnetic cores of high-frequency inductors and transformers.

REFERENCE SIGNS LIST 10 dust core 11 metal magnetic powder 20, 30 lead portion 25 first terminal member 35 second terminal member 40 coil member 100 electrical component

Claims (3)

A metal magnetic powder is prepared.
A first resin, which is a silicone resin that is liquid at room temperature, is added to the metal magnetic powder in a state where the first resin is dissolved in a solvent in advance, and mixed to cover the metal magnetic powder with the first resin. Then,
A second resin, which is an epoxy resin in a liquid state at room temperature, is added to the mixture of the metal magnetic powder and the dissolved first resin in a state of being dissolved in a solvent in advance, and mixed;
a mixture of the metal magnetic powder, the first resin, and the second resin is heated to evaporate the solvent, thereby forming a composite magnetic material;
The composite magnetic material is put into a mold and pressure-molded,
The obtained molded body is heat-treated to cause the second resin to be interspersed in the first resin and to be thermally cured;
The method for producing a powder magnetic core, wherein the second resin has a content, expressed by weight percentage, equal to or less than the first resin. The method for producing a powder magnetic core according to claim 1 , wherein an area occupancy of the second resin in a cross section of the powder magnetic core is greater than 0.0% and not more than 20%. The method for producing a powder magnetic core according to claim 1 , wherein an area ratio of the second resin to the first resin in a cross section of the powder magnetic core is greater than 0.0 and smaller than 0.9.

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