JP2012054569A - Soft magnetic powder, method for producing soft magnetic powder, dust core, and magnetic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft magnetic powder of which a low-loss dust core having a smaller loss (iron loss) in a high-frequency region can be produced, a method for producing the soft magnetic powder capable of easily producing the soft magnetic powder, the low-loss dust core produced by using the soft magnetic powder, and a magnetic element equipped with the dust core.SOLUTION: A choke coil 10 has a dust core 11 of a toroidal shape and a lead wire 12 wound to the dust core 11. The dust core 11 is obtained by mixing, pressurizing, and molding the soft magnetic powder and a binder. The soft magnetic powder used for the dust core 11 is a metal powder of which the main component is Fe, an average particle diameter is 5-25 μm, and a maximum particle diameter is smaller than 63 μm. Further, the soft magnetic powder preferably contains at least one of Si and Cr. Because each particle of the soft magnetic powder is insulated by the binder, an eddy current loss especially in a high-frequency region of the choke coil 10 can be reduced.

Description

  The present invention relates to soft magnetic powder, a method for producing soft magnetic powder, a dust core, and a magnetic element.

In recent years, downsizing and weight reduction of mobile devices such as notebook personal computers have been remarkable. In addition, the performance of notebook-type personal computers is being improved to a level comparable to that of desktop personal computers.
Thus, in order to reduce the size and performance of mobile devices, it is necessary to increase the frequency of switching power supplies. For this reason, the driving frequency of the switching power supply is increasing to about several hundred kHz. Along with this, it is necessary to cope with the increase in the drive frequency of magnetic elements such as choke coils and inductors incorporated in mobile devices.

However, when the drive frequency of these magnetic elements is increased, there arises a problem that Joule loss (eddy current loss) due to eddy currents is remarkably increased in the magnetic core provided in each magnetic element.
In order to solve such a problem, a powder magnetic core obtained by pressurizing and molding a mixture of soft magnetic powder and a binder (binder) is used as a magnetic core included in the magnetic element as described above. For example, Patent Document 1 proposes a dust core in which a mixture of an alloy powder mainly composed of Fe, Al, and Si and a binder is compression-molded and then heat-treated in an oxidizing atmosphere. ing.

However, the magnetic element provided with such a powder magnetic core can suppress eddy current loss at a relatively low drive frequency, but as the drive frequency increases from several tens of kHz to several hundred kHz, the eddy current in the powder magnetic core. Loss increases rapidly. For this reason, the eddy current loss of the magnetic element and the amount of heat generated therewith tend to increase remarkably. For mobile devices, reducing the amount of heat generated while increasing the amount of current of the power supply is an important issue, and there is a strong demand to develop a magnetic element with low eddy current loss.
Therefore, by reducing the average particle size of the soft magnetic powder, eddy current loss in the dust core is also reduced, but there is a problem that a high effect as expected is not obtained. .

JP 2001-11563 A

  An object of the present invention is to provide a soft magnetic powder capable of producing a low-loss powder magnetic core with a small loss (iron loss) in a high frequency range, and a method for producing a soft magnetic powder capable of easily producing the soft magnetic powder. Another object of the present invention is to provide a low-loss powder magnetic core manufactured using soft magnetic powder and a magnetic element including the powder magnetic core.

The above object is achieved by the present invention described below.
The soft magnetic powder of the present invention contains Fe as a main component, has an average particle diameter of 5 to 25 μm, and a maximum particle diameter of less than 63 μm.
Thereby, a soft magnetic powder capable of producing a low-loss powder magnetic core with a small loss (iron loss) in a high frequency range is obtained.

The soft magnetic powder of the present invention is preferably produced by an atomizing method.
Thereby, since the shape of each particle | grain of the obtained soft magnetic powder becomes close to a spherical shape, the filling rate of the soft magnetic powder can be increased when the dust core is manufactured. As a result, a dust core having a higher density can be manufactured, and a dust core having a high magnetic permeability and a high magnetic flux density can be obtained.
The soft magnetic powder of the present invention preferably further contains Si at a content of 1 to 8 wt%.
Thereby, the magnetic permeability of the soft magnetic powder can be increased. In addition, since the specific resistance of the soft magnetic powder can be increased, the induced current generated in the dust core can be reduced and eddy current loss can be reduced.
The soft magnetic powder of the present invention preferably further contains Cr at a content of 1 to 13 wt%.
Thereby, the soft magnetic powder excellent in corrosion resistance can be obtained. Moreover, since the specific resistance of soft magnetic powder becomes high, the eddy current loss of a powder magnetic core can be reduced.

The method for producing a soft magnetic powder according to the present invention comprises producing a metal powder containing Fe as a main component by an atomizing method, and then classifying the metal powder so that the maximum particle size is less than 63 μm. The average particle size is controlled to 5 to 25 μm, and the maximum particle size is controlled to be less than 63 μm.
Thereby, the soft magnetic powder which can manufacture the low-loss powder magnetic core with a small loss in a high frequency region can be easily manufactured.

The dust core of the present invention is characterized by being formed by pressing and molding the mixture of the soft magnetic powder of the present invention and a binder.
Thereby, a low-loss powder magnetic core is obtained.
In the dust core of the present invention, the ratio of the binder to the soft magnetic powder is preferably 0.5 to 5 wt%.
Thereby, while reliably insulating each particle of the soft magnetic powder, the density of the dust core can be secured to some extent, and the magnetic permeability and magnetic flux density of the dust core can be prevented from significantly decreasing. As a result, a dust core having higher magnetic permeability and lower loss can be obtained.

The dust core of the present invention is preferably used at a frequency of 300 kHz or higher.
In such a dust core used in a particularly high frequency range, there is a concern that eddy current loss will increase particularly. However, even in such a high frequency range, a dust core capable of reliably preventing an increase in eddy current loss. Is obtained.

In the dust core of the present invention, when the frequency applied to the dust core is f [kHz] and the maximum particle size of the soft magnetic powder is d [μm], f × d may be 15000 or less. preferable.
If the maximum particle diameter d of the soft magnetic powder is set so as to satisfy such conditions, the eddy current loss of the dust core used in a particularly high frequency range of 300 kHz or higher is relatively reduced in each frequency range. In particular, it can be reduced. That is, a low-loss high frequency powder magnetic core can be obtained.
The magnetic element of the present invention is provided with the dust core of the present invention.
Thereby, a small magnetic element with a small calorific value can be obtained.

It is a schematic diagram (plan view) showing a first embodiment of a choke coil. It is a schematic diagram (perspective view) showing a second embodiment of the choke coil. It is a graph which shows the relationship between the largest particle size of the soft-magnetic powder in the powder magnetic core obtained by each Example and each comparative example, and the loss of a powder magnetic core.

Hereinafter, the soft magnetic powder, the method for producing the soft magnetic powder, the dust core and the magnetic element of the present invention will be described in detail with reference to the accompanying drawings.
[Soft magnetic powder]
First, the soft magnetic powder of the present invention will be described.
The soft magnetic powder of the present invention is composed of a metal powder whose main component is Fe (iron). And the soft magnetic powder of this invention has the characteristics that an average particle diameter is 5-25 micrometers and a maximum particle diameter is less than 63 micrometers. Such soft magnetic powder is pressed and molded together with a binder (binder), for example, and becomes a material for obtaining a dust core.

Hereinafter, the features of the soft magnetic powder of the present invention will be described in detail.
Fe is a main element constituting the soft magnetic powder of the present invention, and is an element that greatly affects the basic magnetic characteristics and mechanical characteristics of the soft magnetic powder. And the metal powder which has Fe as a main component can manufacture a high magnetic flux density and high intensity | strength powder magnetic core. In the present invention, the “main component” means a component having the highest content ratio among the components constituting the soft magnetic powder.
The content of Fe in the soft magnetic powder is preferably about 50 to 99.5 wt%, and more preferably about 60 to 95 wt%. As a result, a soft magnetic powder capable of reliably producing a dust core having a higher magnetic flux density and higher strength can be obtained. For this reason, the miniaturization can be achieved while maintaining various characteristics of the powder magnetic core.

  By the way, conventionally, for the purpose of reducing the eddy current loss of the dust core, the average particle diameter of the soft magnetic powder constituting the dust core has been reduced. The eddy current loss is particularly a loss in a high frequency range, and is a loss due to Joule loss of an induced current accompanying an electromotive force generated by electromagnetic induction with respect to a magnetic field change. And this eddy current loss becomes so low that the average particle diameter of the soft-magnetic powder which comprises a dust core is small.

However, in a particularly high frequency range of about several tens of kHz to several hundreds of kHz, there has been a problem that eddy current loss cannot be sufficiently reduced even if the average particle size is reduced. For this reason, even when used in a high frequency range of about several tens of kHz to several hundreds of kHz, the development of a dust core having a sufficiently small loss (iron loss, core loss) and soft magnetic powder capable of producing such a dust core. Was strongly sought after.
In response to such a problem, the present inventor has intensively studied conditions for providing a soft magnetic powder capable of producing a dust core having a small loss even in a high frequency range. It has been found that the eddy current loss of the dust core changes significantly by controlling not only the average particle size but also the maximum particle size.

A soft magnetic powder composed mainly of Fe, having an average particle size of 5 to 25 μm and a maximum particle size of less than 63 μm is effective for significantly reducing the eddy current loss of the dust core. As a result, the present invention has been completed.
That is, the soft magnetic powder of the present invention is a soft magnetic powder containing Fe as a main component, and is characterized by not only reducing the average particle size to 5 to 25 μm but also defining the maximum particle size to be less than 63 μm. To do. Thereby, even if it uses in a high frequency range, the soft magnetic powder which can manufacture a powder magnetic core with a sufficiently small eddy current loss is obtained.

In addition, by reducing the average particle size and the maximum particle size within the above ranges, the contact area between the soft magnetic powder and the binder increases when the soft magnetic powder of the present invention is pressed and molded together with the binder. In addition, the adhesion force at these interfaces increases. For this reason, according to the soft magnetic powder whose particle size is controlled within the above range, it is possible to produce a dust core having high mechanical strength.
Furthermore, by controlling the average particle size and the maximum particle size as described above, the particle filling rate can be increased, so that a powder magnetic core having a higher density can be obtained. Thereby, it is possible to obtain a dust core having particularly high magnetic permeability and magnetic flux density. As a result, it is possible to reduce the size of the dust core while maintaining the magnetic properties, or to increase the magnetic properties of the dust core while maintaining the size.
The “maximum particle size” in the present invention means a particle size at which the cumulative weight becomes 99.9%.

Moreover, although the average particle diameter of soft-magnetic powder shall be 5-25 micrometers as mentioned above, it is preferable that it is about 7-20 micrometers, and it is more preferable that it is about 9-15 micrometers. When the dust core is manufactured using the soft magnetic powder having a small average particle diameter in this way, the path through which the eddy current flows is particularly short, so that the eddy current loss of the dust core can be further reduced.
In addition, when the average particle diameter of the soft magnetic powder is below the lower limit, the soft magnetic powder and the binder are mixed, and when pressing and molding, the moldability of the mixture is reduced. There is a possibility that the magnetic permeability of the magnetic core is lowered. On the other hand, when the average particle diameter of the soft magnetic powder exceeds the upper limit, the path through which the eddy current flows in the dust core becomes extremely long, and there is a risk that the eddy current loss increases rapidly.

Here, it is preferable that the soft magnetic powder of the present invention further contains Si (silicon).
Si is a component that can increase the magnetic permeability of the soft magnetic powder. Moreover, since the specific resistance of the soft magnetic powder is increased by adding Si, it is also a component that can reduce the induced current generated in the dust core and reduce eddy current loss.
Such Si content is preferably about 1 to 8 wt%, and more preferably about 2 to 6 wt%. If the Si content is set within the above range, it is possible to produce a soft magnetic core having a higher magnetic permeability and a smaller eddy current loss while preventing the density of the soft magnetic powder from significantly lowering. Magnetic powder can be obtained.

The soft magnetic powder of the present invention preferably further contains Cr (chromium).
Cr combines with oxygen in the atmosphere to easily generate a chemically stable oxide (for example, Cr ₂ O ₃ or the like). For this reason, the soft magnetic powder containing Cr is excellent in corrosion resistance. Moreover, since the specific resistance of the soft magnetic powder is increased by adding Cr, Cr is also a component that can reduce the eddy current loss of the dust core.
The Cr content is preferably about 1 to 13 wt%, more preferably about 2 to 10 wt%. If the Cr content is set within the above range, it is possible to obtain a soft magnetic powder capable of producing a dust core having excellent corrosion resistance and smaller eddy current loss while preventing a significant decrease in density.

  As described above, the soft magnetic powder of the present invention is preferably used for manufacturing a dust core used in a relatively high frequency range of several tens of kHz to several hundreds of kHz. The frequency is preferably 300 kHz or more, and more preferably 500 kHz or more. In such a dust core used in a particularly high frequency range, there is a concern that the eddy current loss is particularly increased. However, by using the soft magnetic powder of the present invention, the eddy current loss can be achieved even in such a high frequency range. Thus, a dust core capable of reliably preventing an increase in the thickness is obtained.

Here, the present inventor establishes a predetermined correlation between the frequency at which the dust core is used and the maximum particle size of the soft magnetic powder constituting the dust core in a high frequency range of 300 kHz or higher. When found, the eddy current loss of the dust core can be significantly reduced.
On the other hand, in order to obtain a low-loss powder magnetic core, it is preferable that the maximum particle size is as small as possible together with the average particle size. However, in consideration of manufacturability, production efficiency, and manufacturing cost, the average particle size and maximum It is preferable that the particle size is as large as possible.

Therefore, the present inventor has found a correlation between the frequency at which the dust core is used and the maximum particle size of the soft magnetic powder constituting the dust core, thereby reducing the loss according to the frequency. Can be manufactured efficiently and inexpensively.
Specifically, when the frequency at which the dust core is used is f [kHz] and the maximum particle diameter of the soft magnetic powder constituting the dust core is d [μm], f × d is 15000 or less. Is more preferable, and it is more preferable that it is 13500 or less, and it is still more preferable that it is 12000 or less. If the maximum particle diameter d of the soft magnetic powder is set so as to satisfy such conditions, the eddy current loss of the dust core used in a particularly high frequency range of 300 kHz or higher is relatively reduced in each frequency range. In particular, it can be reduced. That is, a low-loss high frequency powder magnetic core can be obtained.

More specifically, when the frequency f at which the dust core is used is 300 kHz, the maximum particle diameter d of the soft magnetic powder is preferably 50 μm or less, more preferably 45 μm or less, and 40 μm or less. More preferably.
Similarly, when f = 400 kHz, d is preferably 37 μm or less, more preferably 33 μm or less, and even more preferably 30 μm or less.
Similarly, when f = 500 kHz, d is preferably 30 μm or less, more preferably 27 μm or less, and even more preferably 24 μm or less.
Similarly, when f = 600 kHz, d is preferably 25 μm or less, more preferably 22 μm or less, and even more preferably 20 μm or less.

  The reason why the high frequency loss can be reduced by defining the maximum particle size in this way is considered as follows. The magnetic flux density distribution in the dust core is not uniform. For example, the surface that is in contact with the molding punch has the highest molding density, so the magnetic flux density is high, and it can be said that the eddy current loss is generated more. Similarly, coarse particles may be mentioned as the places where magnetic flux concentrates. The two reasons of eddy current increase due to magnetic flux concentration in addition to increase in eddy current due to large particle size overlap, so if coarse particles of 63 μm or more are mixed, the core loss is considered to increase extremely.

In addition, since pressure is applied to the coarse particles during molding, the density around the coarse particles tends to increase, which also causes the magnetic flux to concentrate. In addition, it is considered that the insulation is easily broken by a high pressure, and as a result, an intergranular eddy current is generated and the loss is increased.
Such a soft magnetic powder contains other components such as C (carbon), P (phosphorus), S (sulfur), and Mn (manganese) that are inevitably mixed in the manufacturing process. Also good. In that case, the total content of other components is preferably 1 wt% or less.

The soft magnetic powder as described above is produced by various powdering methods such as an atomizing method (for example, a water atomizing method, a gas atomizing method, a high-speed rotating water atomizing method, etc.), a reduction method, a carbonyl method, and a pulverizing method.
Among these, the soft magnetic powder of the present invention is preferably produced by an atomizing method. According to the atomizing method, extremely fine powder can be produced efficiently. In addition, since the shape of each particle of the powder is close to a spherical shape, the filling rate of the soft magnetic powder can be increased when the powder magnetic core is manufactured. Thereby, a powder magnetic core with higher density can be manufactured, and a powder magnetic core with high magnetic permeability and high magnetic flux density can be obtained.

In addition, when the water atomization method is used as the atomization method, the pressure of atomized water to be injected is not particularly limited, but is preferably about 75 to 120 MPa (750 to 1200 kgf / cm ² ). The temperature of the atomized water is not particularly limited, but is preferably about 1 to 20 ° C.
Moreover, you may classify with respect to the soft magnetic powder obtained in this way as needed. Examples of classification methods include sieving classification, inertia classification, dry classification such as centrifugal classification, and wet classification such as sedimentation classification.

Among these, when obtaining the soft magnetic powder of the present invention, it is preferable to use sieving classification. By using sieving classification, particles having a particle size larger than the opening of the sieve are surely removed, so that the maximum particle size can be reliably controlled to a predetermined value. Thereby, the soft magnetic powder of this invention can be manufactured easily.
Moreover, you may granulate the obtained soft magnetic powder as needed.

[Dust core and magnetic element]
The magnetic element of the present invention can be applied to various magnetic elements (electromagnetic components) having a magnetic core such as a choke coil, an inductor, a noise filter, a reactor, a motor, and a generator. That is, the dust core of the present invention can be applied to the dust core provided in these magnetic elements.
Hereinafter, two types of choke coils will be described as representative examples of magnetic elements.

<First Embodiment>
First, a first embodiment of a choke coil (magnetic element of the present invention) will be described.
FIG. 1 is a schematic view (plan view) showing a first embodiment of a choke coil.
A choke coil 10 shown in FIG. 1 has a ring-shaped (toroidal-shaped) dust core 11 and a conductor 12 wound around the dust core 11. Such a choke coil 10 is generally called a toroidal coil.

The dust core 11 is obtained by mixing the soft magnetic powder of the present invention, a binder (binder), and an organic solvent, supplying the resulting mixture to a mold, and pressing and molding. .
Examples of the constituent material of the binder used for producing the dust core 11 include organic binders such as silicone resins, epoxy resins, phenol resins, polyamide resins, polyimide resins, polyphenylene sulfide resins, and phosphoric acid. Inorganic binders such as magnesium, calcium phosphate, zinc phosphate, manganese phosphate, phosphate such as cadmium phosphate, silicate (water glass) such as sodium silicate, etc. are mentioned, especially thermosetting Polyimide or epoxy resin is preferable. These resin materials are easily cured by being heated and have excellent heat resistance. Therefore, the manufacturability and heat resistance of the dust core 11 can be improved.

  Further, the ratio of the binder to the soft magnetic powder is slightly different depending on the intended magnetic permeability and magnetic flux density of the dust core 11 to be produced, allowable eddy current loss, etc., but is about 0.5 to 5 wt%. It is preferable that it is about 1-3 wt%. Thereby, while reliably insulating each particle | grain of soft-magnetic powder, the density of the powder magnetic core 11 can be ensured to some extent, and it can prevent that the magnetic permeability and magnetic flux density of the powder magnetic core 11 fall remarkably. . As a result, a dust core 11 having higher magnetic permeability and lower loss can be obtained.

The organic solvent is not particularly limited as long as it can dissolve the binder, and examples thereof include various solvents such as toluene, isopropyl alcohol, acetone, methyl ethyl ketone, chloroform, and ethyl acetate.
In addition, you may make it add various additives for the arbitrary objectives in the said mixture as needed.

Such a binding material covers the surface of the soft magnetic powder. As a result, each particle of the soft magnetic powder is insulated by an insulative binder, so even if a magnetic field that changes at a high frequency is applied to the dust core 11, it is generated by electromagnetic induction with respect to this magnetic field change. The induced current associated with the electromotive force only reaches a relatively narrow area of each particle. For this reason, the Joule loss by this induced current can be suppressed small.
Further, since this Joule loss causes heat generation of the dust core 11, the amount of heat generated by the choke coil 10 can be reduced by suppressing the Joule loss.

On the other hand, examples of the constituent material of the conductive wire 12 include materials having high conductivity, such as metal materials such as Cu, Al, Ag, Au, and Ni, or alloys containing such metal materials.
In addition, it is preferable to provide the surface of the conducting wire 12 with an insulating surface layer. Thereby, the short circuit with the powder magnetic core 11 and the conducting wire 12 can be prevented reliably.
Examples of the constituent material of the surface layer include various resin materials.

Next, a method for manufacturing the choke coil 10 will be described.
First, the soft magnetic powder of the present invention, a binder, various additives, and an organic solvent are mixed to obtain a mixture.
Subsequently, after drying a mixture and obtaining a blocky dried body, this dried body is grind | pulverized and granulated powder is formed.

Next, this mixture or granulated powder is molded into the shape of a powder magnetic core to be produced to obtain a molded body.
The molding method in this case is not particularly limited, and examples thereof include press molding, extrusion molding, and injection molding.
Note that the shape and size of the molded body is determined in consideration of the shrinkage when the molded body is heated thereafter.

Next, by heating the obtained molded body, the binder is cured and the dust core 11 is obtained.
At this time, although the heating temperature is slightly different depending on the composition of the binder, etc., when the binder is composed of an organic binder, it is preferably about 100 to 250 ° C., more preferably about 120 to 200 ° C. Is done.
Moreover, although heating time changes with heating temperature, it is set as about 0.5 to 5 hours.

  As described above, the powder magnetic core (powder magnetic core of the present invention) 11 formed by pressurizing and molding the soft magnetic powder of the present invention and the conductive wire 12 are wound along the outer peripheral surface of the powder magnetic core 11. The choke coil (magnetic element of the present invention) 10 has a small loss in the high frequency range. Further, as described above, since the soft magnetic powder of the present invention has a small average particle size and maximum particle size, it is possible to easily obtain a dust core 11 having a large density. Thus, it is possible to easily improve the magnetic permeability and the magnetic flux density, reduce the size of the choke coil 10, increase the rated current, and decrease the heat generation.

Second Embodiment
Next, a second embodiment of the choke coil (magnetic element of the present invention) will be described.
FIG. 2 is a schematic view (perspective view) showing a second embodiment of the choke coil.
Hereinafter, although the choke coil according to the second embodiment will be described, the description will be focused on the differences from the choke coil according to the first embodiment, and the description of the same matters will be omitted.

As shown in FIG. 2, the choke coil 20 according to the present embodiment is formed by embedding a conductive wire 22 formed in a coil shape inside a dust core 21. That is, the choke coil 20 is formed by molding the conductive wire 22 with the dust core 21.
The choke coil 20 having such a configuration can be easily obtained in a relatively small size. When such a small choke coil 20 is manufactured, the dust core 21 having a large magnetic permeability and magnetic flux density and a small loss exerts its effects and effects more effectively. That is, the choke coil 20 having a low loss and a low heat generation capable of handling a large current in spite of being smaller is obtained.

Moreover, since the conducting wire 22 is embedded in the dust core 21, a gap is hardly generated between the conducting wire 22 and the dust core 21. For this reason, the vibration by the high frequency switching of the conducting wire 22 can be suppressed and generation | occurrence | production of the noise accompanying this vibration can also be suppressed.
When manufacturing the choke coil 20 according to the present embodiment as described above, first, the conductive wire 22 is disposed in the cavity of the mold, and the cavity is filled with the soft magnetic powder of the present invention. That is, the soft magnetic powder is filled so as to include the conductive wire 22.

Next, a soft magnetic powder is pressed together with the conductive wire 22 to obtain a molded body.
Next, as in the first embodiment, this molded body is subjected to heat treatment. Thereby, the choke coil 20 is obtained.
The soft magnetic powder, the soft magnetic powder manufacturing method, the dust core, and the magnetic element of the present invention have been described based on the preferred embodiments, but the present invention is not limited thereto.
For example, in the above embodiment, the choke coil has been described as an example of the magnetic element of the present invention. However, the same operation and effect as described above can be obtained in other magnetic elements including a dust core.

Next, specific examples of the present invention will be described.
1. Production of dust core and magnetic element (Example 1)
[1] First, raw materials were prepared with the compositions shown in Table 1. The obtained raw material was melted in a high frequency induction furnace and pulverized by a water atomization method to obtain a soft magnetic powder.
[2] Next, the obtained soft magnetic powder was sieved through a sieve having an opening of 20 μm. Thereby, the particle | grains with a particle size more than an opening were removed.

Moreover, the particle size distribution measurement was performed about the soft-magnetic powder after sieving. This measurement was performed with a laser diffraction particle size distribution measuring apparatus (Microtrack, HRA9320-X100, manufactured by Nikkiso Co., Ltd.). And the average particle diameter shown in Table 1 was calculated | required by this measurement.
Moreover, since particles having a particle size larger than the sieve aperture are removed by sieving, the sieve aperture used for sieving is regarded as the maximum particle size of the soft magnetic powder.

[3] Next, the obtained soft magnetic powder was mixed with an epoxy resin (binding material) and toluene (organic solvent) to obtain a mixture. The addition amount of the epoxy resin was 2 wt% with respect to the soft magnetic powder.
[4] Next, after stirring the obtained mixture, it was dried by heating at a temperature of 60 ° C. for 1 hour to obtain a lump-like dried product. Next, this dried body was passed through a sieve having an opening of 500 μm, and the dried body was pulverized to obtain a granulated powder.

[5] Next, the obtained granulated powder was filled in a mold, and a molded body was obtained based on the following molding conditions.
<Molding conditions>
-Molding method: Press molding-Shape of molded body: ring shape-Dimensions of molded body: 28 mm outer diameter, 14 mm inner diameter, 5 mm thickness
Molding pressure: 6 t / cm ² (588 MPa)

[6] Next, the formed body was heated in an air atmosphere at a temperature of 150 ° C. for 1 hour to cure the binder. As a result, a dust core was obtained.
[7] Next, using the obtained dust core, a choke coil (magnetic element) shown in FIG. 1 was manufactured based on the following manufacturing conditions.
<Coil manufacturing conditions>
・ Constituent material of conducting wire: Cu
・ Wire diameter: 0.8mm
・ Number of windings: 30 turns on the primary side, 30 turns on the secondary side

(Examples 2 to 8)
As the soft magnetic powder, a powder magnetic core was obtained in the same manner as in Example 1 except that the powders having the average particle diameter and the maximum particle diameter shown in Table 1 were used, and a choke coil was manufactured using this powder magnetic core. Obtained.
(Comparative Examples 1-4)
As the soft magnetic powder, a powder magnetic core was obtained in the same manner as in Example 1 except that the powders having the average particle diameter and the maximum particle diameter shown in Table 1 were used, and a choke coil was manufactured using this powder magnetic core. Obtained.

2. Evaluation The magnetic permeability and loss (core loss) of the choke coils obtained in the examples and the comparative examples were measured based on the following measurement conditions.
<Measurement conditions>
・ Measurement frequency: 300 kHz or 500 kHz
・ Maximum magnetic flux density: 20mT
Measurement device: AC magnetic property measurement device (Iwatsu Keiki Co., Ltd., BH analyzer SY8232)
The measurement results are shown in Table 1. Moreover, the graph which shows the relationship between the largest particle size of soft-magnetic powder and the loss of a dust core among Table 1 is shown in FIG.

First, as can be seen from Table 1, in each of the examples, a dust core having a small loss could be obtained. This is also apparent in FIG. 3, and it is recognized that when the maximum particle size of the soft magnetic powder is less than 63 μm, the loss of the dust core is remarkably reduced as compared with the case of 63 μm or more.
On the other hand, the dust cores obtained in the respective comparative examples, that is, the dust cores containing soft magnetic powder having a maximum particle size of 63 μm or more, all had large losses.
Further, among the dust cores obtained in the respective examples, those satisfying the condition that the product f × d of the frequency f and the maximum particle size d is 15000 or less (enclosed by an elliptical broken line in FIG. 3) In each frequency, the loss is relatively small. In addition, this tendency was recognized more notably as the frequency is higher (500 kHz).

  10, 20 ... Choke coil 11, 21 ... Dust core 12, 22 ... Conductor

The above object is achieved by the present invention described below.
The soft magnetic powder of the present invention is a soft magnetic powder containing Si with a content of 2 to 6 wt% and Cr with a content of 2 to 10 wt%, with the balance being substantially made of Fe,
The average particle size is 9-15 μm , the maximum particle size is less than 63 μm, and the ratio of average particle size / maximum particle size is 0.23 or more and 0.49 or less,
It is a powder produced by an atomizing method .
Thereby, a soft magnetic powder capable of producing a low-loss powder magnetic core with a small loss (iron loss) in a high frequency range is obtained.

The method for producing a soft magnetic powder of the present invention produced a metal powder containing Si with a content of 2 to 6 wt% and Cr with a content of 2 to 10 wt%, with the balance being substantially Fe, by an atomization method. Then, by classifying with a sieve having an opening of less than 63 μm, the average particle size of the metal powder is controlled to 9 to 15 μm, the maximum particle size is controlled to less than 63 μm, and the average particle size / maximum The particle size ratio is controlled to be 0.23 or more and 0.49 or less .
Thereby, the soft magnetic powder which can manufacture the low-loss powder magnetic core with a small loss in a high frequency region can be easily manufactured.

The powder magnetic core of the present invention is a powder magnetic core formed by pressing and molding the mixture of the soft magnetic powder of the present invention and a binder ,
When the frequency applied to the dust core is f [kHz] (where f is 300 kHz or more) and the maximum particle size of the soft magnetic powder is d [μm], f × d is 15000 or less. Features.
Thereby, a low-loss powder magnetic core is obtained.
In the dust core of the present invention, the ratio of the binder to the soft magnetic powder is preferably 0.5 to 5 wt%.
Thereby, while reliably insulating each particle of the soft magnetic powder, the density of the dust core can be secured to some extent, and the magnetic permeability and magnetic flux density of the dust core can be prevented from significantly decreasing. As a result, a dust core having higher magnetic permeability and lower loss can be obtained.

The magnetic element of the present invention is provided with the dust core of the present invention.
Thereby, a small magnetic element with a small calorific value can be obtained.
In the magnetic element of the present invention, it is preferable that a conductive wire formed in a coil shape is embedded in the dust core.

Claims (10)

  A soft magnetic powder comprising Fe as a main component, having an average particle size of 5 to 25 μm and a maximum particle size of less than 63 μm.   The soft magnetic powder according to claim 1, which is produced by an atomizing method.   The soft magnetic powder according to claim 1 or 2, further comprising Si at a content of 1 to 8 wt%.   The soft magnetic powder according to any one of claims 1 to 3, further comprising Cr at a content of 1 to 13 wt%.   After producing a metal powder containing Fe as a main component by the atomization method, by classifying the metal powder to have a maximum particle size of less than 63 μm, the average particle size of the metal powder is controlled to 5 to 25 μm, And the manufacturing method of the soft-magnetic powder characterized by controlling a maximum particle size to less than 63 micrometers.   A powder magnetic core obtained by pressing and molding the mixture of the soft magnetic powder according to any one of claims 1 to 4 and a binder.   The powder magnetic core according to claim 6, wherein a ratio of the binder to the soft magnetic powder is 0.5 to 5 wt%.   The dust core according to claim 6 or 7, which is used at a frequency of 300 kHz or more.   9. The f × d is 15000 or less, where f [kHz] is the frequency applied to the dust core and d [μm] is the maximum particle size of the soft magnetic powder. Powder magnetic core.   A magnetic element comprising the dust core according to claim 6.

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