JP7087539B2 - Soft magnetic material and dust core - Google Patents

Description

The present invention relates to soft magnetic materials and dust cores.

Obtaining a soft magnetic material and a dust core with higher magnetic permeability is still an important issue. In recent years, it has been known that by using a soft magnetic material made of flat powder, higher magnetic permeability can be obtained than in the case of using a soft magnetic material made of spherical powder.

Patent Document 1 describes a soft magnetic material for a dust core that simultaneously uses both a soft magnetic powder having a small particle size and a large aspect ratio and a soft magnetic powder having a large particle size and a small aspect ratio.

However, at present, there is a demand for a dust core having a higher initial permeability μr and a lower core loss tan δ. Further, there is a demand for a dust core having both withstand voltage and moisture resistance.

Patent No. 4909312

An object of the present invention is to provide a powder magnetic core having a high initial magnetic permeability μr, a small core loss tan δ, a high withstand voltage, and a large moisture resistance, and a soft magnetic material contained in the powder magnetic core.

In order to achieve the above object, the soft magnetic material of the present invention is used.
A soft magnetic material having a soft magnetic powder whose surface is insulated and a foil piece whose surface is insulated.
The soft magnetic powder has an average particle size of 10 μm or more and 100 μm or less.
The foil pieces have an average length of 3.0 μm or less and have an average length of 3.0 μm or less.
(Average length of the foil piece / average thickness of the foil piece) is 2.0 or more.
(The average length of the foil pieces / the average particle size of the soft magnetic powder) is 0.300 or less.

Since the soft magnetic material of the present invention has the above-mentioned characteristics, it can be used as a dust core having a high initial magnetic permeability μr, a small core loss tan δ, a high withstand voltage, and a high moisture resistance when used for a dust core. can.

In the soft magnetic material of the present invention, the addition ratio of the foil pieces to the entire soft magnetic material may be 10 vol% or more and 40 vol% or less.

The dust core of the present invention is made of the above-mentioned soft magnetic material.

The dust core of the present invention has the above-mentioned characteristics, so that the dust core has a high initial magnetic permeability μr, a small core loss tan δ, a high withstand voltage, and a high moisture resistance.

In the dust core of the present invention, the angle between the length direction of each of the foil pieces and the reference direction may be 10 ° or less on average.

It is a schematic diagram of the soft magnetic material which concerns on this embodiment. It is a schematic diagram of the sectional view of the dust core and the foil piece which concerns on this embodiment.

Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

As shown in FIG. 1, the soft magnetic material according to the present embodiment includes the soft magnetic powder 11 and the foil piece 13.

The material of the soft magnetic powder 11 and the material of the foil piece 13 are not particularly limited. For example, it may be Fe alone or Fe alloy. The Fe alloy refers to an alloy having an Fe content of 15 at% or more. Examples of Fe alloys include Fe—Si alloys, Fe—Ni alloys, Fe—Si—B alloys, Fe—Cu—Nb—Si—B alloys, Fe—Si—B—Cr alloys, and the like. Will be. The Fe-Si based alloy refers to an alloy in which the Fe content is 97 at% or more, the Si content is 2 at% or more, and the total content of other elements is 1 at% or less. The Fe—Ni-based alloy refers to an alloy in which the Fe content is 15 at% or more, the Ni content is 40 at% or more, and the total content of other elements is 45 at% or less. The above-mentioned Fe—Si—B alloy has a Fe content of 79 at% or more, a Si content of 9 at% or more, a B content of 9 at% or more, and a total of 3 at of other elements. Refers to alloys that are less than or equal to%. The above-mentioned Fe-Cu-Nb-Si-B alloy has a Fe content of 75.6 at% or more, a Cu content of 0.6 at% or more, an Nb content of 0.1 at% or more, and Si. Refers to an alloy in which the content of B is 13.1 at% or more, the content of B is 8.6 at% or more, and the total content of other elements is 2.0 at% or less. The above-mentioned Fe—Si—B—Cr alloy has a Fe content of 75.5 at% or more, a Si content of 10.5 at% or more, a B content of 10.5 at% or more, and a Cr content. An alloy having a ratio of 1.5 at% or more and a total content of other elements of 2.0 at% or less. Further, the material of the soft magnetic powder 11 and the material of the foil piece 13 may be the same or different.

Further, the surface of the soft magnetic powder 11 according to the present embodiment is subjected to an insulating treatment. The type of insulation treatment is arbitrary. For example, an insulating treatment for forming an oxide film on the surface of the soft magnetic powder 11 and an insulating treatment for covering an oxide layer of a non-magnetic metal can be mentioned. The surface of the foil piece 13 is similarly insulated. By performing the insulation treatment, the eddy current of the dust core produced from the soft magnetic material according to the present embodiment is reduced, and the core loss tan δ is reduced.

Here, the soft magnetic powder 11 in the soft magnetic material according to the present embodiment has a shape having a minimum particle size of 5 μm or more and an aspect ratio of 2 or less. The particle size and aspect ratio here refer to the circle-equivalent diameter of the projected area when the soft magnetic material is observed by SEM or TEM. Further, the foil piece 13 has a rectangular parallelepiped shape or a substantially rectangular parallelepiped shape in which the length of the long side is 4 μm or less at the maximum and the value obtained by dividing the length of the long side by the length of the short side is 1.8 or more at the minimum. Have. The length of the long side and the length of the short side here are the length of the long side and the length of the short side when the soft magnetic material is observed by SEM or TEM. Hereinafter, the length of the long side of the foil piece 13 is simply referred to as the length, and the length of the short side of the foil piece 13 is referred to as the thickness.

In the soft magnetic material according to the present embodiment, the soft magnetic powder 11 has an average particle size of 10 μm or more and 100 μm or less, and the foil piece 13 has an average length of 3.0 μm or less (average length of the foil piece 13 / The average thickness of the foil pieces 13) is 2.0 or more, and (the average length of the foil pieces 13 / the average diameter of the soft magnetic powder 11) is 0.300 or less. The amount of the foil piece 13 added to the entire soft magnetic material is arbitrary, but is preferably 10 vol% or more and 40 vol% or less.

In the measurement of the average particle size of the soft magnetic powder 11, the particle size of at least 1000 or more soft magnetic powders 11 is measured and averaged. Further, in the measurement of the average length and the average thickness of the foil pieces 13, the average length and the average thickness of at least 500 or more foil pieces 13 are measured.

The average particle size of the soft magnetic powder 11 can also be measured using XRD, and a value substantially the same as the circle-equivalent diameter of the projected area can be obtained.

In the soft magnetic material according to the present embodiment, the sizes of the soft magnetic powder 11 and the foil piece 13 are different. Therefore, when the dust core 1 is manufactured by applying pressure in the direction of the molding direction 23 shown in FIG. 2, the soft magnetic powder 11 is crushed in the direction of the molding direction 23, and the gap between the soft magnetic powders 11 is crushed. The structure is such that the foil piece 13 fills the space. Then, the length direction 13a of the foil piece 13 is a direction substantially perpendicular to the molding direction 23. Specifically, when the dust core 1 is cut in a cross section parallel to the molding direction 23 and observed by SEM or TEM, the length direction 13a of the foil piece 13 and the reference direction which is the direction perpendicular to the molding direction 23. It is preferable that the average angle θ between 21 and 21 is 10 ° or less. The measurement range in which at least 10 or more soft magnetic powders 11 are observed is set. Further, the thickness direction 13b of the foil piece 13 is a direction substantially parallel to the molding direction 23.

When the soft magnetic powder 11 is crushed in the molding direction 23, the aspect ratio of the soft magnetic powder 11 becomes large. However, the equivalent circle diameter of the soft magnetic powder 11 does not substantially change.

Further, the dust core 1 is cut in a cross section parallel to the molding direction 23, and the average particle size of the soft magnetic powder 11, the average length of the foil piece 13, and the average thickness of the foil piece 13 are obtained by observing with SEM or TEM. It is possible to identify.

The foil piece 13 has the effect of inducing a magnetic flux in the length direction 13a, and the foil piece 13 generally induces the magnetic flux in the direction of the reference direction 21 when viewed as the dust core 1 as a whole. As a result, the relative permeability μr is significantly improved.

The reference direction 21 here can be specified from the direction in which the soft magnetic powder 11 is crushed by observing the cross-sectional view of the powder magnetic core by SEM. More specifically, the reference direction 21 can be specified by averaging the directions in which each soft magnetic powder 11 is crushed and has a long side.

If the average particle size of the soft magnetic powder 11 is too large, the eddy current becomes large and the core loss tan δ increases. Further, it becomes difficult for the foil pieces 13 to line up in the direction of the reference direction 21, and the average of the angles θ becomes large. As a result, the relative permeability μr decreases. Further, the expansion of the gap between the soft magnetic powders 11 lowers the sealing effect, lowers the withstand voltage, and lowers the moisture resistance.

If the average particle size of the soft magnetic powder 11 is too small, the relative magnetic permeability μr decreases.

If the average length of the foil pieces 13 is too long, it becomes difficult for the foil pieces 13 to line up in the reference direction 21, and the average of the angles θ becomes large. As a result, the relative permeability μr decreases.

If (the average length of the foil piece 13 / the average thickness of the foil piece 13) is too small, the orientation of the foil piece 13 is unlikely to change during pressurization, and the foil piece 13 exerts a magnetic flux when viewed from the entire dust core 1. The effect of inducing is reduced. As a result, the relative permeability μr decreases.

When the amount of the foil piece 13 added to the entire soft magnetic material is 10 vol% or more, the relative magnetic permeability μr is likely to be sufficiently improved. Further, when the amount of the foil piece 13 added is 40 vol% or less, the soft magnetic powder 11 is sufficiently easily deformed by the pressure during molding. Further, the foil pieces 13 can be easily arranged in the reference direction 21.

When the soft magnetic powder 11 and the foil piece 13 have different compositions, they can be distinguished by the difference in composition. When the composition is the same, it is possible to distinguish from the difference in shape and / or the difference in size.

When producing the dust core, other compounds may be added to the soft magnetic material as needed. For example, a resin may be added as a binder. However, if too much resin is added, it becomes difficult for the foil pieces 13 to line up in the reference direction 21, and the average angle θ becomes large. As a result, the relative permeability μr decreases.

Here, the total filling rate of the soft magnetic powder 11 and the foil piece 13 in the dust core 1 is not particularly limited. It is preferably 75 vol% or more. Further, there is no particular limitation on the method of calculating the filling rate. For example, the method shown below can be mentioned.

First, the magnetic core is cut in parallel with the molding direction, and the cross section obtained is polished to prepare an observation surface. Next, the observation surface is observed using an electron microscope (SEM). The total area ratio of the soft magnetic powder 11 and the foil piece 13 to the total area of the observation surface is calculated. Then, in the present embodiment, it is considered that the area ratio and the filling rate are equal to each other, and the area ratio is defined as the filling rate.

Further, for the filling rate, the density (ideal density) when the filling rate is assumed to be 100% is calculated from the true density and the compounding ratio of the soft magnetic powder 11 and the foil piece 13 as raw materials, and the actual dust core is actually used. The filling factor may be calculated by dividing the measured density calculated from the dimensions and weight of the above by the ideal density. The filling rate calculated from the SEM and the filling rate calculated from the measured density and the ideal density are substantially the same.

Further, in calculating the filling rate, the observation surface has a size including 100 or more in total of the soft magnetic powder 11 and the foil piece 13. It should be noted that the number of observation surfaces may be multiple, and may be large enough to include 1000 or more in total.

Hereinafter, the method for producing the soft magnetic material and the dust core according to the present embodiment will be described, but the method for producing the soft magnetic material and the dust core according to the present embodiment is not limited to the following methods.

First, a soft magnetic powder having a desired composition is produced. The method for producing the soft magnetic powder is arbitrary, and for example, a usual method in the present technical field such as a gas atomizing method and a water atomizing method can be used. After producing the soft magnetic powder, it is preferable to remove fine powder having a particle size of 10 μm or less by classification. By removing the fine powder, the area of the surface of the heat-insulated surface with respect to the entire soft magnetic powder becomes smaller after the insulation treatment described later, and the covering property is easily improved.

Next, the surface of the soft magnetic powder is insulated. The method of insulation treatment is arbitrary. For example, a method of forming an oxide film by oxidizing the surface of a soft magnetic powder, a method of covering an oxide layer of a non-magnetic metal by heating and reducing after adding a non-magnetic metal, a glass powder (glass frit). A method of coating the above can be mentioned. Further, when the soft magnetic powder is substantially composed of iron only, there is also a method of forming an iron phosphate film on the surface of the soft magnetic powder by phosphoric acid treatment. By performing the insulation treatment, the eddy current of the dust core created from the soft magnetic material according to the present embodiment is reduced, and the core loss is reduced. Normally, the average particle size of the soft magnetic powder does not substantially change before and after the insulation treatment.

In addition, a foil piece having a desired composition is produced. The method for producing the foil piece is arbitrary, and examples thereof include a strip casting method. Hereinafter, a manufacturing method by the strip casting method will be described.

First, a mother alloy having a desired composition is produced. The method for producing the mother alloy is arbitrary, and a method usually used in the present art can be used. Next, the mother alloy is heated and melted, and then sprayed onto a cooling roll to form a thin band. Then, by crushing the thin strip and then classifying it, a foil piece having an arbitrary shape can be obtained.

Next, the surface of the foil piece is insulated. The method of insulation treatment is arbitrary. For example, a method of forming an oxide film by oxidizing the surface of a foil piece, a method of covering an oxide layer of a non-magnetic metal by heating and reducing after adding a non-magnetic metal, and the like can be mentioned. By performing the insulation treatment, the eddy current of the dust core created from the soft magnetic material according to the present embodiment is reduced, and the core loss is reduced. Normally, the average particle size of the foil pieces does not substantially change before and after the insulation treatment. Further, the type of insulation treatment may be changed between the soft magnetic powder and the foil piece.

Then, the soft magnetic powder and the foil piece are mixed to produce the soft magnetic material according to the present embodiment. In the above manufacturing method, the soft magnetic powder and the foil piece are separately insulated, but the soft magnetic powder and the foil piece may be mixed and then collectively insulated.

Then, a dust core is produced from the soft magnetic material according to the present embodiment.

When the powder magnetic core is produced from the soft magnetic material according to the present embodiment, a small amount of the soft magnetic material is put into the mold, the mold is shaken to apply vibration, and pressure is applied in the molding direction. It is preferable to repeat the cycle consisting of the molding steps several to several tens of times. By molding while increasing the filling amount little by little in this way, it becomes easier for the foil pieces to fill the gaps between the soft magnetic powders. Then, the magnetic permeability μr can be improved. Further, the sealing effect is increased, and the withstand voltage and moisture resistance are easily improved.

Specifically, it is preferable to put the soft magnetic material into the mold in increments of approximately 0.1 mm in height. Further, it is preferable to shake the mold to apply vibration, and the foil pieces move downward to fill the gaps between the soft magnetic powders. The molding pressure is arbitrary.

There is no particular limitation on the use of the dust core according to the present embodiment. For example, inductors, reactors, transformers and the like can be mentioned.

Next, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

(Experimental Example 1)
First, a soft magnetic powder was prepared. The composition of the finally obtained soft magnetic powder was set to Fe: Cu: Nb: Si: B = 76: 1: 0.5: 13.5: 9 in terms of atomic number ratio. Further, the soft magnetic powder was prepared by the gas atomizing method so that the average particle size of the soft magnetic powder was as shown in Table 1 below. Then, the soft magnetic powder was classified, and fine powder having a particle size of 10 μm or less was removed. It was confirmed by using a dry particle size distribution measuring instrument that the average particle size after classification was the value shown in Table 1 below.

Next, the surface of the soft magnetic powder was subjected to an insulating treatment. Specifically, a glass frit coating was applied to the soft magnetic powder.

Next, a foil piece was produced. The foil pieces were prepared by the strip casting method shown below.

First, the mother alloy, which is a metal Fe, was heated and melted, and then sprayed onto a cooling roll to create a thin band.

Next, the strips were crushed and then classified to obtain foil pieces. The finally obtained foil pieces were classified so as to have the average length and the average length / average thickness shown in Table 1 below.

Next, the surface of the foil piece was insulated. Specifically, the foil pieces were subjected to (oxidation treatment).

Then, a foil piece was added to the soft magnetic powder and mixed to obtain a soft magnetic material. The amount of the foil piece added to the entire soft magnetic material was set to the amount shown in Table 1 below.

Next, the soft magnetic material was filled in the mold. The shape of the mold is such that the shape of the powder magnetic core finally obtained is a toroidal shape having an outer diameter of 12 mm, an inner diameter of 7 mm, and a height of 2 mm.

When filling a soft magnetic material into a mold, a cycle consisting of a step of charging a small amount of the soft magnetic material into the mold, a step of shaking the mold to apply vibration, and a step of molding at a molding pressure of 8 ton / cm ² . Was repeated 20 times. The amount of soft magnetic material charged into the mold was gradually increased. Finally, a toroidal-shaped dust core was obtained. The molding direction was set to be the height direction of the toroidal shape.

For each Example and Comparative Example, the cross section cut in parallel with the molding direction (height direction) was observed. Specifically, SEM was used to observe at least 1000 soft magnetic particles in the measurement range. It was confirmed that the average equivalent circle diameter obtained by measuring the equivalent circle diameter of each soft magnetic particle was substantially the same as the average particle size of the soft magnetic powder. Furthermore, it was confirmed that the reference direction specified from the degree of crushing of the soft magnetic particles substantially coincided with the direction perpendicular to the molding direction. Then, the average length and the average length / average thickness were calculated for all the foil pieces existing in the measurement range, and it was confirmed that they were in agreement with the average length and the average length / average thickness in the soft magnetic material. Further, the angle θ between the length direction and the reference direction was measured and averaged for all the foil pieces existing in the measurement range. The results are shown in Table 1.

For the dust cores of each Example and Comparative Example, the total filling rate of the soft magnetic particles and the foil pieces was measured using SEM. The results are shown in Table 1 below.

For each Example and Comparative Example, the relative permeability μr and the core loss tan δ were measured at a frequency of 100 kHz. The relative permeability μr was measured using impedance / GAIN-PHASE ANALYZER (4194A, manufactured by Hewlett-Packard Co., Ltd., Yokokawa). Core loss tan δ was measured by a perturbation method using B-HANALYZER (SY-8218 manufactured by Iwatsu Electric Co., Ltd.). In this example, the relative magnetic permeability μr was set to 50 or more. The core loss tan δ was good at 1000 kW / m3 or less. The results are shown in Table 1 below.

Withstand voltage was measured for each Example and Comparative Example. For each Example and Comparative Example, a cylindrical dust core having an outer diameter of φ8 mm and a height of 5 mm was produced by the same method as the toroidal dust core. Then, InGa paste was applied to two circular surfaces having an outer diameter of φ8 mm facing each other in a cylindrical dust core. A voltage was applied to the InGa paste coated with the terminal of the source meter, and the value obtained by dividing the voltage value when a current of 1 mA flowed by the distance (5 mm) between the two facing surfaces was taken as the withstand voltage. The case where the withstand voltage was 200 V / mm or more was regarded as good. The results are shown in Table 1 below.

Moisture resistance tests were performed on each Example and Comparative Example. Specifically, each Example and Comparative Example were left at a temperature of 85 ° C. and a humidity of 85% for 1000 hours. Then, the appearance after being left for 1000 hours was evaluated. Observing the appearance after 1000 hours, ○ if there is no rust on the surface, △ if there is spot rust but the area ratio of rust to the entire surface is less than 10%, and the area ratio of rust to the entire surface is 10. The case where it is% or more was set as x. The order of ◯, Δ, × was preferable, and the case of ◯ or Δ was considered to be good. The results are shown in Table 1.

From Table 1, the powder magnetic cores of Examples 1 to 6 produced by using the soft magnetic material within the range of the present invention had good results of the relative permeability μr, core loss tan δ, withstand voltage and moisture resistance test. ..

On the other hand, in Comparative Example 1 in which the average particle size of the soft magnetic powder was too large, it became difficult for the foil pieces to line up in the reference direction, the relative permeability μr decreased, and the core loss tan δ increased. Further, as the filling rate decreased, the gap expanded and the sealing effect decreased. As a result, the withstand voltage decreased.

In Comparative Example 2 in which the average particle size of the soft magnetic powder was too small, it became difficult for the foil pieces to line up in the reference direction, and the relative magnetic permeability μr decreased.

In Comparative Example 3 and Comparative Example 5 in which the average length of the foil pieces was too long, it became difficult for the foil pieces to line up in the reference direction, and the relative magnetic permeability μr decreased. Further, in Comparative Example 5 in which the average length of the foil pieces / the average particle size of the soft magnetic powder was too large, the gap was widened due to the decrease in the filling rate, and the sealing effect was deteriorated. As a result, the withstand voltage decreased.

In Comparative Example 4 in which the average length / average thickness of the foil pieces was too small, the foil pieces became difficult to line up in the reference direction, and the effect of inducing the magnetic flux of the foil pieces decreased, resulting in a decrease in the relative permeability μr.

(Experimental Example 2)
In Experimental Example 2, the conditions were the same as those in Example 1 except that the type of the soft magnetic powder and / or the type of the foil piece was changed. The results are shown in Table 2 below.

The composition of the Fe—Si—B—Cr alloy in Table 2 below is Fe: Si: B: Cr = 76: 11: 11: 2 in terms of atomic number ratio, and the composition of Fe—Si alloy is Fe: Si in terms of atomic number ratio. = 98: 2, the composition of the Fe—Ni alloy is Fe: Ni = 20: 80 in weight ratio, and the composition of Fe—Si—B alloy is Fe: Si: B = 80: 10: 10 in atomic number ratio.

From Table 2, even if the types of the soft magnetic powder and / or the foil piece were changed, good powder magnetic cores were obtained as the results of the specific magnetic permeability μr, core loss tan δ, withstand voltage and moisture resistance test.

1 ... Powder magnetic core 11 ... Soft magnetic powder 13 ... Foil piece 13a ... Foil piece length direction 13b ... Foil piece thickness direction 21 ... Reference direction 23 ... Molding direction

Claims (2)

A dust core made of a soft magnetic material having a soft magnetic powder whose surface is insulated and a foil piece whose surface is insulated.
The soft magnetic powder has an average particle size of 10 μm or more and 100 μm or less.
The foil pieces have an average length of 3.0 μm or less and have an average length of 3.0 μm or less.
(Average length of the foil piece / average thickness of the foil piece) is 2.0 or more.
(Average length of the foil piece / average particle size of the soft magnetic powder) is 0.300 or less .
A dust core characterized in that the angle between the length direction of each of the foil pieces and the reference direction is 10 ° or less on average . The dust core according to claim 1, wherein the addition ratio of the foil pieces to the entire soft magnetic material is 10 vol% or more and 40 vol% or less.

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