JP2010232225A - Insulator coating soft magnetic powder, dust core and magnetic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide insulator coating soft magnetic powder, where the surface is coated with an insulator and a dust core having small eddy current loss over a long time can be manufactured, to provide a low-loss magnetic core manufactured by the powder, and to provide a low-loss magnetic element which has the dust core. <P>SOLUTION: A compound particle 1 includes a granular core section 2 constituted of a soft magnetic material, and a coating layer 3 constituted of an insulating material so provided as to cover the core section 2. The coating layer 3 is formed, by mechanically sticking a particle of an insulating material having a diameter smaller than that of the core section 2 to the core section 2. The average grain size of the particles of the insulating material is 1-60% of the average grain size of the core section 2. Tap density of the core section 2 is, preferably, not less than 45% of true density of the core section 2. Also, the average grain size of the core section 2 is, preferably, in the range of 3 to 50 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an insulator-coated 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, driving frequencies of various magnetic elements such as choke coils and inductors built in mobile devices must be adapted to higher frequencies.
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 is used as a magnetic core included in the above-described magnetic element. In such a powder magnetic core, the particles of the soft magnetic powder are insulated by an insulating binder, so that the eddy current generated in the magnetic core is divided between the particles. For this reason, even if it is used at a high frequency, Joule loss due to eddy current, that is, eddy current loss can be reduced.
However, in such a powder magnetic core, when the mixture is pressed and molded at a high pressure, the binder existing between the particles of the soft magnetic powder is cut off, and the insulation between the particles is reduced. The problem is known. When such a problem occurs, it becomes difficult to reduce eddy current loss.

In order to solve the above problems, a method of forming a surface layer of an inorganic material on the surface of soft magnetic powder particles has been proposed.
For example, in Patent Document 1, a magnetic powder having a particle size of 20 to 100 μm and an inorganic binder mainly composed of a silica-based sol are mixed and then heated, and the surface of the magnetic powder is coated with the silica-based sol film. A method of manufacturing a powder magnetic core is proposed in which the obtained magnetic powder is molded after being coated, and then the obtained molded body is sintered.

However, in the powder magnetic core manufactured by such a method, the adhesion strength between the silica-based sol film and the magnetic powder is small, so that these adhesion interfaces are easy to peel off. For this reason, in severe environments, such as high temperature and high humidity, the insulation of magnetic powder particles cannot be maintained over a long period of time, and eddy current loss gradually increases.
In particular, when the magnetic powder contains chromium or aluminum as a constituent component, a chemically stable passive film is formed on the surface of the magnetic powder. Adhesion is further reduced.

JP 2001-196217 A

  An object of the present invention is to provide an insulator-coated soft magnetic powder having a surface coated with an insulator and capable of producing a dust core having a small eddy current loss over a long period of time, and a low-loss powder powder produced using this powder. An object of the present invention is to provide a magnetic core and a low-loss magnetic element including the dust core.

The above object is achieved by the present invention described below.
The insulator-coated soft magnetic powder of the present invention has a particulate core portion made of a soft magnetic material, and a coating layer made of an insulating material provided so as to cover the core portion,
The coating layer is formed by mechanically fixing particles of the insulating material having a smaller diameter than the core portion to the core portion,
The average particle diameter of the insulating material particles is 1 to 60% of the average particle diameter of the core portion.
As a result, it is possible to obtain an insulator-coated soft magnetic powder having a surface coated with an insulator and capable of producing a dust core having a small eddy current loss over a long period of time.

In the insulator-coated soft magnetic powder of the present invention, the tap density of the core part is preferably 45% or more with respect to the true density of the core part.
Thereby, the fluidity | liquidity of a core part becomes high and the rolling ease of a core part becomes high. As a result, the insulating material particles can be uniformly fixed over the entire surface of the core portion, and a uniform coating layer can be formed.

In the insulator-coated soft magnetic powder of the present invention, the average particle size of the core part is preferably 3 to 50 μm.
Thereby, when a powder magnetic core is manufactured using the said insulator covering soft magnetic powder, the path | route through which an eddy current flows can be shortened especially, preventing the powder filling property falling. Therefore, it is possible to manufacture a dust core having low eddy current loss and excellent permeability and mechanical properties.

In the insulator-coated soft magnetic powder of the present invention, the soft magnetic material is preferably an Fe-based alloy.
Thereby, an insulator-coated soft magnetic powder excellent in magnetic properties such as magnetic permeability and magnetic flux density and productivity such as cost can be obtained.
In the insulator-coated soft magnetic powder of the present invention, the insulating material is preferably an inorganic material.
Thereby, compared with organic type material, it is excellent in chemical stability and insulation, and the coating layer which can maintain high insulation over a long term is obtained.

In the insulator-coated soft magnetic powder of the present invention, the softening point of the glass material is preferably 100 to 500 ° C.
Accordingly, when the particles of the insulating material are mechanically fixed to the core portion, the surface of the particles of the insulating material is softened, and the particles can be fixed to the surface of the core portion without any gap. As a result, there is no gap between the coating layer and the core portion, and an insulator-coated soft magnetic powder excellent in long-term durability and magnetic characteristics can be obtained.

In the insulator-coated soft magnetic powder of the present invention, the core part is preferably manufactured by a water atomization method.
Thereby, extremely fine powder can be efficiently produced. In addition, since the shape of each particle of the obtained powder is close to a true sphere, the rollability of the core portion is improved, and the particles of the insulating material are uniformly fixed over the entire surface of the core portion, and the uniform coating layer Can be formed.

In the insulator-coated soft magnetic powder of the present invention, the mechanical fixation is performed by stirring the mixture of the core portion and the particles of the insulating material while pressing them in the same container. It is preferable that
Thereby, mechanical fixation of the particle | grains of the insulating material with respect to a core part can be produced efficiently.
In the insulator-coated soft magnetic powder of the present invention, the coating layer is formed by fusing the surface of the particles to the surface of the core part while maintaining the original shape of the particles of the insulating material. Is preferred.
Thereby, a coating layer tends to become uniform thickness, without becoming thin partially.

The dust core of the present invention is obtained by pressing and molding the mixture of the insulator-coated soft magnetic powder of the present invention and a binder to obtain a molded body, and then curing the binder in the molded body. It is characterized by.
Thereby, a low-loss powder magnetic core is obtained over a long period of time.
The magnetic element of the present invention is provided with the dust core of the present invention.
Thereby, a low-loss magnetic element can be obtained over a long period of time.

It is a longitudinal cross-sectional view which shows embodiment of one particle | grains of the insulator covering soft magnetic powder of this invention. It is a longitudinal cross-sectional view which shows the structure of a powder coating apparatus. It is a schematic diagram (plan view) showing the configuration of the choke coil. It is a schematic diagram (transmission perspective view) showing a configuration of a choke coil.

Hereinafter, the insulator-coated soft magnetic powder, dust core and magnetic element of the present invention will be described based on preferred embodiments shown in the accompanying drawings.
[Insulator-coated soft magnetic powder]
First, the insulator-coated soft magnetic powder of the present invention will be described.
FIG. 1 is a longitudinal sectional view showing an embodiment of one particle of the insulator-coated soft magnetic powder of the present invention.

A composite particle 1, which is one particle of the insulator-coated soft magnetic powder shown in FIG. 1, includes a particulate core portion 2 made of a soft magnetic material, and an insulating coating layer 3 that covers the surface of the core portion 2. I have it.
In such an insulator-coated soft magnetic powder, the surface is covered with the coating layer 3, thereby ensuring insulation between particles. For this reason, by pressing and molding such composite particles 1 together with a binder into a predetermined shape, for example, a dust core having a small eddy current loss can be produced over a long period of time.
Hereinafter, a method for producing the composite particle 1 shown in FIG. 1 will be described in detail.
In this manufacturing method, particles of an insulating material having a smaller particle diameter (hereinafter referred to as “insulating particles”) are mechanically fixed to the core portion 2 to form the coating layer 3. This is a method for producing the composite particle 1.

Hereinafter, this method will be described sequentially.
[1] First, the core part 2 and the insulating particles 30 are prepared.
The core part 2 is one particle of a metal powder made of a soft magnetic material.
Examples of such soft magnetic materials include pure iron, silicon steel (Fe—Si based alloy), permalloy (Fe—Ni based alloy), permendur (Fe—Co based alloy), and Fe—Si— such as Sendust. In addition to various Fe-based alloys such as Al-based alloys and Fe-Cr-Si-based alloys, various Ni-based alloys, various Co-based alloys, various amorphous alloys, and the like can be given. Of these, various Fe-based alloys are preferably used from the viewpoint of magnetic properties such as magnetic permeability and magnetic flux density, and productivity such as cost.

Among Fe-based alloys, silicon steel is an Fe-based soft magnetic material containing Si at a ratio of about 3 to 6% by mass. Silicon steel is suitable for use as a soft magnetic material because it has a high magnetic permeability and is inexpensive.
Permalloy is an Fe-based soft magnetic material containing Ni in a proportion of about 35 to 82% by mass. Permalloy can provide various soft magnetic properties by setting the composition ratio of Fe and Ni within the above-mentioned range or adding additives, but as a whole, the magnetic permeability and magnetic flux density are high. . For this reason, the magnetic permeability and magnetic flux density of the core part 2 can be raised.

Permendur is an Fe-based soft magnetic material containing Co at a ratio of about 40 to 50% by mass. In addition, you may add about 1-3 mass% of V (vanadium) as needed. Since the permendur has a high magnetic flux density, the magnetic flux density of the core part 2 can be improved.
Further, as the Fe—Si—Al-based alloy, Sendust containing Si at a rate of about 5 to 11% by mass and Al at a rate of about 3 to 8% by mass is particularly preferably used. Since Sendust has high magnetic permeability and high hardness, the magnetic permeability and hardness of the core part 2 can be improved.

Such a core part 2 may be manufactured by any method. For example, 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, a pulverizing method, etc. These are produced by various powdering methods.
Among these, what was manufactured by the atomizing method is preferably used for the core part 2. According to the atomizing method, extremely fine powder can be produced efficiently. Moreover, since the shape of each particle | grain of the obtained powder becomes a perfect sphere, the rolling ease of the core part 2 improves and the effect which is mentioned later arises.

On the other hand, the insulating particles 30 are one particle of powder made of an insulating material.
Examples of the insulating material include inorganic insulating materials such as soda lime glass, borosilicate glass, lead glass, aluminosilicate glass, borate glass, phosphate glass, sulfate glass, and vanadic acid. Examples thereof include materials mainly composed of various glass materials such as salt glass. Since such a glass material is excellent in chemical stability and insulation as compared with an organic material, the coating layer 3 capable of maintaining high insulation over a long period of time can be formed. Among these, the glass material that is preferably used has a softening point of 650 ° C. or less, and the glass material that is more preferably used has a softening point of about 100 to 500 ° C.
Examples of the glass material having a softening point of about 100 to 500 ° C. include borate glass containing lead oxide (PbO · B ₂ O ₃ ) and ternary glass in which zinc oxide or silicon oxide is mixed. Examples thereof include phosphate glass (SnO · P ₂ O ₅ ) containing materials and tin oxide.

[2] Next, the insulating particles 30 are mechanically fixed to the core portion 2. Thereby, the coating layer 3 is formed on the surface of the core portion 2.
This mechanical fixation is caused by pressing the insulating particles 30 against the surface of the core portion 2 with a high pressure. Specifically, the composite particles 1 are manufactured by causing the above-described mechanical fixation using a powder coating apparatus 100 as shown in FIG.
FIG. 2 is a longitudinal sectional view showing the configuration of the powder coating apparatus. In the following description, the upper side in FIG. 2 is referred to as “upper” and the lower side is referred to as “lower”.

  Various devices such as a hammer mill, a disk mill, a roller mill, a ball mill, a planetary mill, a jet mill, etc., and an ong mill (registered) are devices that cause mechanical compression and frictional action on the core 2 and the insulating particles 30. Trademark), high-speed elliptical mixer, MixMuller (registered trademark), Jacobson mill, Mechano-Fusion (registered trademark), various friction mixers such as hybridization (registered trademark), etc., but here, as an example, A powder coating apparatus 100 (friction mixer) shown in FIG. 2 having a container 110 and a tip 140 that rotates along the inner wall of the container inside will be described. Such a powder coating apparatus 100 can efficiently cause the mechanical adhesion of the insulating particles 30 to the core portion 2.

The powder coating apparatus 100 includes a cylindrical container 110 and a rod-shaped arm 120 provided in the radial direction inside the container 110.
The container 110 is made of a metal material such as stainless steel, and applies mechanical compression and friction to the mixture of the core portion 2 and the insulating particles 30 charged therein.
A rotation shaft 130 is inserted through the center of the arm 120 in the longitudinal direction, and the arm 120 is rotatably provided with the rotation shaft 130 as a rotation center. The rotating shaft 130 is provided so as to coincide with the central axis of the container 110.

  A tip 140 is provided at one end of the arm 120. The chip 140 has a bowl shape having a convex curved surface and a plane opposite to the convex curved surface, the curved surface faces the inner wall of the container 110, and a distance between the curved surface and the container 110 is a predetermined distance. It is set to be length. As a result, the tip 140 can rotate along the inner wall while maintaining a certain distance from the inner wall of the container 110 as the arm 120 rotates.

  A scraper 150 is provided at the other end of the arm 120. The scraper 150 is a plate-like member, and, like the chip 140, the distance between the scraper 150 and the container 110 is set to a predetermined length. Accordingly, the scraper 150 can scrape the vicinity of the inner wall of the container 110 as the arm 120 rotates.

The rotation shaft 130 is connected to a rotation drive device (not shown) provided outside the container 110, and the arm 120 can thereby be rotated.
In addition, the container 110 can maintain a sealed state while the powder coating apparatus 100 is driven, and can maintain a reduced pressure (vacuum) state or a state in which the inside is replaced with various gases. Preferably, the container 110 is replaced with an inert gas such as nitrogen or argon.

Next, a method for producing the composite particles 1 using the powder coating apparatus 100 will be described.
First, the core part 2 and the insulating particles 30 are put into the container 110. Next, the container 110 is sealed, and the arm 120 is rotated.
Here, FIG. 2A shows the state of the powder coating apparatus 100 when the chip 140 is located above and the scraper 150 is located below, while FIG. The state of the powder coating apparatus 100 when it is located below and the scraper 150 is located above is shown.

The core portion 2 and the insulating particles 30 are scraped off by the scraper 150 as shown in FIG. Thereby, the core part 2 and the insulating particle 30 are lifted upward with the rotation of the arm 120, and are then stirred by dropping.
On the other hand, as shown in FIG. 2B, when the chip 140 is lowered, the core portion 2 and the insulating particles 30 enter the gap between the chip 140 and the container 110, and these are compressed from the chip 140 as the arm 120 rotates. It receives action and friction action.

  By repeating these agitation and compression friction action at high speed, the insulating particles 30 adhere to the surface of the core portion 2. This sticking is considered to occur by various mechanisms, and one of them is fusion of particle surfaces by mechanical compression. Then, a plurality of insulating particles 30 having a small particle diameter are gathered and fixed so as to cover the surface of the core part 2, and finally the fixed insulating particles 30 are connected to cover the surface of the core part 2. The covering layer 3 is formed. In this way, the composite particle 1 is manufactured. In the formed coating layer 3, the original shape of the insulating particles 30 as the particles is substantially maintained. For this reason, the coating layer 3 is likely to have a uniform thickness without being partially thinned.

The number of rotations of the arm 120 is slightly different depending on the amount of powder charged into the container 110, but is preferably about 300 to 1200 times per minute.
Moreover, although the pressing force at the time of the chip | tip 140 compressing powder changes with the magnitude | sizes of the chip | tip 140, it is preferable that it is about 30-500N as an example.
Here, a method of obtaining composite particles by repeating such compression friction action is generally known as a particle surface coating technique. However, it has been difficult to control the state of the coating layer covering the surface of the core part. For this reason, problems such as breakage of the coating layer and opening of holes have occurred, leading to a decrease in the insulating function. In particular, when a passive film is formed on the surface of the core portion, the adhesion between the core portion and the coating layer is remarkably lowered, and problems such as peeling occur.

Therefore, the present inventor finally obtains the mutual relationship between the core part 2 and the insulating particles 30 that are subjected to the compressive friction action because the composite particles 1 are manufactured by repeating the compressive friction action as described above. It was noted that the state of the composite particle 1 is highly likely to greatly influence. In order to reliably form a uniform coating layer 3 on the surface of the core part 2, the mutual relationship between the average particle diameter of the core part 2 and the average particle diameter of the insulating particles 30 is particularly strongly involved. And the present invention was completed by finding this optimal correlation.
Specifically, the average particle diameter of the insulating particles 30 used for the production of the composite particles 1 is 1 to 60% of the average particle diameter of the core portion 2.

It can be said that such insulating particles 30 have an appropriate particle size when subjected to compressive friction. For this reason, the insulating particles 30 can be efficiently fixed to the surface of the core portion 2, and the uniform coating layer 3 can be formed.
More specifically, the above range is a particle size suitable for reliably transmitting a compressive force to the insulating particles 30 by the compression friction action described above, and under the compression wear action, the core This is a range based on the fact that the composite particles 1 having a remarkably large particle size compared to the part 2 cannot be produced.

  That is, when the average particle size of the insulating particles 30 is less than the lower limit value, the compressive friction effect is not sufficiently transmitted to the insulating particles 30, and the insulating particles 30 cannot be fixed to the surface of the core portion 2. On the other hand, when the average particle size of the insulating particles 30 exceeds the upper limit, even if the insulating particles 30 are once fixed to the surface of the core portion 2, the insulating particles 30 and the core portion 2 A large compressive force is applied between the two and the two are separated. As a result, it becomes difficult to manufacture the composite particle 1.

The ratio of the average particle diameter of the insulating particles 30 to the average particle diameter of the core portion 2 is 1 to 60% as described above, but preferably 10 to 50%.
In the present invention, the “average particle diameter” refers to the particle diameter of the powder distributed in a 50% cumulative volume in the particle size distribution of the target powder.
Moreover, the average particle diameter of the core part 2 is not specifically limited, However, It is preferable that it is about 3-50 micrometers, It is more preferable that it is about 5-30 micrometers, It is further more preferable that it is about 8-20 micrometers. Thus, when a dust core is manufactured using the core part 2 with a small average particle diameter, the path | route through which an eddy current flows can be shortened especially. For this reason, the eddy current loss of the dust core can be further reduced.

In addition, when the average particle diameter of the core part 2 is less than the said lower limit, since the filling property of the core part 2 is lowered, the density of the obtained dust core is lowered, and thereby the permeability of the dust core and There is a risk that the mechanical properties will deteriorate. On the other hand, when the average particle diameter of the core part 2 exceeds the upper limit, the path through which the eddy current flows in the powder magnetic core becomes long, so that the eddy current loss may increase rapidly.
Further, from the viewpoint of uniformly forming the coating layer 3 on the surface of the core part 2, it is preferable that the tap density of the core part 2 is high.
Specifically, the ratio of the tap density to the true density of the core portion 2 is preferably 45% or more, and more preferably 55% or more.

The core part 2 that satisfies the above conditions has high fluidity, and it is presumed that each shape is relatively close to a true sphere. For this reason, the fluidity of the core part 2 becomes high, and in the compression friction action mentioned above, it can roll easily with rotation of the chip | tip 140. FIG. That is, the core part 2 that has entered the gap between the chip 140 and the container 110 can easily rotate as the chip 140 moves.
Along with this rotation, a uniform compressive frictional action occurs over the entire surface of the core portion 2, and as a result, a uniform coating layer 3 can be formed on the entire surface of the core portion 2.

  Moreover, if the shape of the core part 2 is close to a true sphere, durability against destruction and wear of the core part 2 can be enhanced. That is, when the shape of the core part 2 is irregular, when compressive friction is applied to the core part 2, stress is likely to concentrate on a part, and there is a possibility that the part may be damaged or worn. If the shape of the part 2 is close to a true sphere, the stress concentration described above is relaxed, and chipping and wear are prevented. As a result, it is possible to prevent the shape and particle size of the core portion 2 from changing in the process of manufacturing the composite particles 1 and to prevent the target powder characteristics from being lost.

  Furthermore, when the core part 2 has a spherical shape relatively close to a true sphere as described above, when the aggregate of the composite particles 1 including such a core part 2 is pressed and molded together with a binder, It is possible to minimize the phenomenon that the binder existing between the composite particles 1 is cut off due to the close proximity of the composite particles 1 due to pressurization. This is because the surface of the composite particle 1 is composed of a smooth curved surface, and there are hardly any remarkable convex portions or the like. As a result, in the powder magnetic core obtained by molding, the binder spreads between the composite particles 1 and the composite particles 1 can be reliably insulated.

Further, since the covering layer 3 is obtained by mechanically fixing the insulating particles 30 to the surface of the core portion 2, the coating layer 3 has extremely high adhesion regardless of the surface state of the core portion 2. For this reason, peeling of the coating layer 3 can be prevented over a long period of time.
Further, unlike the coating method using an aqueous solution, the film formation of the coating layer 3 as described above can be performed under drying, and can also be performed in an inert gas atmosphere. For this reason, there is no possibility that moisture or the like is interposed between the core portion 2 and the coating layer 3 during the film forming process, and the long-term durability of the composite particles 1 can be further enhanced.
Furthermore, even when foreign matter or a passive film adheres to the surface of the core 2 and the film formation of the coating layer 3 is inhibited, the foreign matter is removed by the compressive friction action or the passive film is destroyed. can do. Thereby, the coating layer 3 can be reliably formed into a film.

  In addition, by using a glass material that constitutes the insulating particles 30 with a softening point of 100 to 500 ° C., the surface of the insulating particles 30 is softened in accordance with the above-described compression friction action, and the insulating particles 30 are formed into the core portion 2 can be fixed to the surface of 2 without a gap. Thereby, a gap is not generated between the coating layer 3 and the core part 2, and the composite particle 1 excellent in long-term durability and magnetic characteristics is obtained.

  The coating layer 3 formed in this way preferably has an average film thickness of about 0.1 to 20% of the average particle diameter of the core part 2 and about 0.3 to 10%. More preferred. If the average film thickness of the coating layer 3 is within the above range, the composite particles 1 (insulator-coated soft magnetic powder) have sufficient insulation properties, and the aggregate of the composite particles 1 is pressed and molded. When the dust core is manufactured, a significant decrease in the density of the dust core can be prevented, and as a result, the permeability and magnetic flux density of the dust core can be prevented from significantly decreasing. That is, it is possible to obtain the composite particle 1 that can produce a dust core having low eddy current loss and excellent permeability and magnetic flux density.

In addition, you may classify with respect to the composite particle 1 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.
Further, the core part 2 and the insulating particles 30 may be stirred (mixed) by a stirrer or a mixer before being put into the powder coating apparatus 100.

[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 a magnetic core included in these magnetic elements.

Hereinafter, two types of choke coils will be described as representative examples of magnetic elements.
<First Embodiment>
First, a choke coil to which the first embodiment of the magnetic element of the present invention is applied will be described.
FIG. 3 is a schematic diagram (plan view) showing the configuration of the choke coil.
A choke coil 10 shown in FIG. 3 has a ring-shaped (toroidal-shaped) dust core 11 and a conductive wire 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 composite particles 1 (insulator-coated soft magnetic powder of the present invention), a binder, and an organic solvent, supplying the resulting mixture to a mold, and pressing and molding. It is a thing.
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 magnesium phosphate. Inorganic binders such as calcium phosphate, zinc phosphate, manganese phosphate, phosphate such as cadmium phosphate, and silicate (water glass) such as sodium silicate. Or an 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 be mixed with the composite particle 1 is slightly different depending on the intended magnetic flux density of the powder magnetic core 11 to be produced, allowable eddy current loss, etc. Is preferably about 1 to 3% by mass. Thereby, it is possible to prevent the magnetic permeability and magnetic flux density of the dust core 11 from being significantly reduced by securing the density of the dust core 11 to some extent while more reliably insulating the particles of the composite particle 1. it can. As a result, a dust core 11 having high permeability and magnetic flux density and low 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, chloroform, and ethyl acetate.
In addition, you may make it add various additives for the arbitrary objectives in the said mixture as needed.
By the binder as described above, the aggregate of the composite particles 1 maintains the shape at the time of molding and functions as the dust core 11.

In the dust core 11 thus manufactured, the core portions 2 are reliably insulated from each other by the coating layer 3 covering the surface of the core portion 2 and the binder that has spread over the gaps between the composite particles 1. . As a result, even if a magnetic field that changes at a high frequency is applied to the dust core 11, the induced current that accompanies the electromotive force that is generated by electromagnetic induction in response to this magnetic field change only reaches a relatively narrow region of particles. 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 more reliably.
Examples of the constituent material of the surface layer include various resin materials such as enamel.

Next, a method for manufacturing the dust core 11 and the choke coil 10 will be described.
First, the composite particle 1, a binder, various additives, and an organic solvent are mixed to obtain a mixture.
Next, the obtained mixture is dried to obtain a lump-like dried body, and then the dried body is pulverized to form granulated powder.

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

Next, the choke coil 10 is obtained by winding the conducting wire 12 around the outer peripheral surface of the dust core 11.
In the choke coil 10 described above, the powder magnetic core 11 is obtained by binding the particles of the composite particles 1 with a binder, but each particle of the composite particles 1 includes the coating layer 3 having high insulation. Therefore, the particles 3 of the composite particles 1 may be sintered to fix the coating layers 3 of the composite particles 1 to each other to obtain the dust core 11.

Hereinafter, a method of obtaining the dust core 11 by sintering the particles of the composite particle 1 will be described.
First, the composite particle 1, a binder, various additives, and an organic solvent are mixed to obtain a mixture.
Any binder can be used as long as it is thermally decomposed. For example, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), zinc stearate, lithium stearate, calcium stearate, ethylene bisstearamide, ethylene vinyl copolymer. Examples thereof include polymers, paraffin, wax, sodium alginate, agar, gum arabic, resin, sucrose, and the like, and one or more of these can be used in combination.

Next, the obtained mixture is dried to obtain a lump-like dried body, and then the dried body is pulverized to form granulated powder.
Next, this 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 in the molded body is decomposed and removed (degreasing) to obtain a degreased body.
The heating temperature at this time is slightly different depending on the composition of the binder, but is preferably about 300 to 900 ° C, more preferably about 400 to 700 ° C.
Further, the heating time is not particularly limited, and is, for example, about 0.5 to 10 hours.

Next, by heating the obtained degreased body, the coating layers 3 included in each particle of the composite particle 1 in the molded body are sintered and fixed. As a result, a particularly high-density powder magnetic core 11 containing almost no binder is obtained. Such a dust core 11 has particularly high magnetic permeability and magnetic flux density.
Further, since no binder is interposed between the particles of the composite particle 1, it is difficult for a gap to be generated inside the dust core 11. For this reason, the mechanical properties of the powder magnetic core 11 are improved, and there is no possibility of taking moisture in the atmosphere into the gaps in the powder magnetic core 11, so that the durability of the powder magnetic core 11 is further improved.

The heating temperature at this time should just be more than the sintering temperature of the insulator which comprises the coating layer 3, for example, it is preferable that it is about 800-1200 degreeC, and it is more preferable that it is about 900-1100 degreeC.
Further, the heating time is not particularly limited, and is, for example, about 0.5 to 10 hours.
The dust core 11 can also be manufactured by the above method.

  The powder magnetic core 11 (the powder magnetic core of the present invention) thus obtained has low loss and high durability. For this reason, the choke coil (magnetic element of the present invention) 10 formed by winding the conducting wire 12 along the outer peripheral surface of the dust core 11 can maintain excellent high frequency characteristics over a long period of time. Further, the choke coil 10 can be downsized and the rated current can be increased, and the amount of heat generation can be easily reduced.

<Second Embodiment>
First, a choke coil to which a second embodiment of the magnetic element of the present invention is applied will be described.
FIG. 4 is a schematic diagram (transparent perspective view) showing the configuration of the choke coil.
Hereinafter, the choke coil according to the second embodiment will be described. The choke coil according to the first embodiment will be described mainly with respect to differences from the choke coil according to the first embodiment, and description of similar matters will be omitted.
As shown in FIG. 4, 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.

A relatively small and thin choke coil 20 having such a configuration can be easily obtained. When such a small choke coil 20 is manufactured, the dust core 21 having high magnetic permeability and magnetic flux density and low loss exhibits its function and effect 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 magnetostriction of the powder magnetic core 21 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 composite particles 1. That is, the composite particle 1 is filled so as to include the conductive wire 22.
Next, the composite particle 1 and the binder are 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.

As described above, the insulator-coated soft magnetic powder, 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 to this.
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, a soft magnetic powder (core part) of an Fe—Cr—Si alloy produced by a water atomization method was prepared. This soft magnetic powder is an Fe-based alloy powder containing 4.5 mass% Cr and 3.5 mass% Si. The soft magnetic powder has the following powder characteristics.

<Powder characteristics of soft magnetic powder>
・ Average particle size: 12μm
Tap density: 4.3 g / cm ³
-True density: 7.6 g / cm ³
-Ratio of tap density to true density: 57%
Coercive force: 14.2 Oe (1130 A / m)
Mass susceptibility: 190 emu / g (3 × 10 ⁻⁶ Hm ² / kg)
Further, a phosphate glass powder (insulating particles) containing tin oxide was prepared. This _{powder, SnO-P} 2 O 5 -MgO based glass (SnO: 62 _{mol%, P 2} O 5: 33 mol%, MgO: 5 mol%) is a powder.
<Powder characteristics of glass powder>
・ Average particle size: 3μm
・ Softening point of glass material: 404 ° C
The average particle size of the phosphate glass powder was 25% of the average particle size of the soft magnetic powder.

[2] Next, soft magnetic powder and phosphate glass powder were put into the container 110 of the powder coating apparatus 100 shown in FIG. Then, the powder coating apparatus 100 was operated to obtain composite particles (insulator-coated soft magnetic powder) in which phosphate glass powder was fixed around the soft magnetic powder.
The average thickness of the coating layer of the obtained composite particles was 2 μm, and the ratio of the average thickness of the insulating layer to the average particle diameter of the soft magnetic powder was 17%. The average thickness of this insulating layer was almost the same in the other examples and the comparative examples.

[3] Next, the obtained composite particles, an epoxy resin (organic binder), and toluene (organic solvent) were mixed to obtain a mixture. The addition amount of the epoxy resin was 2% by mass 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 product was passed through a sieve having an opening of 500 μm, and the dried product was pulverized to obtain a granulated powder.

[5] Next, the obtained granulated powder was filled into 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 molded body was heated in an air atmosphere at a temperature of 150 ° C. for 1 hour to cure the epoxy resin. As a result, a dust core was obtained.

[7] Next, using the obtained dust core, a choke coil (magnetic element) shown in FIG. 3 was manufactured based on the following manufacturing conditions.
<Coil manufacturing conditions>
・ Constituent material of conducting wire: Cu
・ Wire diameter: 0.5mm
・ Number of turns (when measuring permeability): 7 turns ・ Number of turns (when measuring iron loss): 30 turns on the primary side, 30 turns on the secondary side

(Example 2)
A dust core and a choke coil were produced in the same manner as in Example 1 except that glass powder having the following powder characteristics was used. The powder characteristics shown below are different from those in Example 1.
<Powder characteristics of glass powder>
・ Average particle size: 5μm
-Ratio of average particle diameter of glass powder to average particle diameter of soft magnetic powder: 42%

Example 3
A dust core and a choke coil were produced in the same manner as in Example 1 except that glass powder having the following powder characteristics was used. The powder characteristics shown below are different from those in Example 1.
<Powder characteristics of glass powder>
・ Average particle size: 7μm
-Ratio of average particle diameter of glass powder to average particle diameter of soft magnetic powder: 58%

Example 4
A dust core and a choke coil were produced in the same manner as in Example 3 except that soft magnetic powder having the following powder characteristics obtained by changing the conditions in the water atomization method was used. The powder characteristics shown below are different from those in Example 3.
<Powder characteristics of soft magnetic powder>
Tap density: 4.2 g / cm ³
-Ratio of tap density to true density: 55%

(Example 5)
A dust core and a choke coil were produced in the same manner as in Example 4 except that glass powder having the following powder characteristics was used. The powder characteristics shown below are different from those in Example 4.
<Powder characteristics of glass powder>
・ Composition: borate glass ・ Softening point of glass material: 600 ° C.
・ Average particle size: 5μm
-Ratio of average particle diameter of glass powder to average particle diameter of soft magnetic powder: 42%

(Comparative Example 1)
A dust core and a choke coil were produced in the same manner as in Example 1 except that glass powder having the following powder characteristics was used. The powder characteristics shown below are different from those in Example 1.
<Powder characteristics of glass powder>
・ Average particle size: 9μm
-Ratio of average particle diameter of glass powder to average particle diameter of soft magnetic powder: 75%

(Comparative Example 2)
A dust core and a choke coil were produced in the same manner as in Example 1 except that glass powder having the following powder characteristics was used. The powder characteristics shown below are different from those in Example 1.
<Powder characteristics of glass powder>
・ Average particle diameter: 11 μm
-Ratio of average particle diameter of glass powder to average particle diameter of soft magnetic powder: 92%

(Comparative Example 3)
First, soft magnetic powder was dispersed in water to obtain a suspension. Next, water glass (sodium silicate) was added to the suspension and stirred. In addition, the addition amount of water glass was 1 mass% with respect to the soft magnetic powder.
Thereafter, the obtained suspension was filtered, washed with water, and dried to obtain composite particles in which soft magnetic powder was coated with a water glass coating (coating method). The average thickness of the water glass film in the obtained composite particles was about 2 μm.
Subsequently, using this composite particle, a dust core and a choke coil were produced in the same manner as in Example 1.
(Comparative Example 4)
A dust core and a choke coil were produced in the same manner as in Example 1 except that the coating of the composite particle coating layer was omitted.

2. 2.1 Measurement / Evaluation of Insulation Resistance Values For the powder magnetic cores obtained in each of the examples and comparative examples, the insulation resistance value when each DC voltage of 100V to 800V was applied was measured with an insulation withstand voltage measuring machine (manufactured by KIKUSUI ELECTRONICS , TOS9000). And the measured insulation resistance value was relatively evaluated according to the following evaluation criteria. The distance between the terminals of the measuring machine was 5 mm.

<Evaluation criteria for insulation resistance (when 500V is applied)>
A: Insulation resistance value is particularly high (1GΩ or more)
○: Slightly high insulation resistance (500 MΩ or more and less than 1 GΩ)
Δ: Slightly low insulation resistance (100MΩ or more and less than 500MΩ)
X: Especially low insulation resistance (less than 100 MΩ)

2.2 Measurement / Evaluation of Loss (Core Loss) and Magnetic Permeability With respect to the choke coils obtained in the examples and comparative examples, the loss (core loss) and magnetic permeability were measured based on the following measurement conditions.
<Measurement conditions>
Measurement frequency: 10 to 200 kHz
・ Maximum magnetic flux density: 50mT
Measurement device: AC magnetic property measurement device (Iwatsu Keiki Co., Ltd., BH analyzer SY8258)
And the obtained loss and magnetic permeability were relatively evaluated according to the following evaluation criteria, respectively.

<Evaluation criteria for loss and permeability>
×: Low magnetic permeability and large loss Δ: High magnetic permeability but large loss, or low magnetic permeability but small loss ○: High magnetic permeability and small loss ◎ : Of the above ○, the permeability is particularly high or the loss is particularly small

2.3 Measurement and evaluation of corrosion resistance For the choke coils obtained in each of the examples and comparative examples, the change in the insulation resistance value in each high-temperature and high-humidity environment was measured (accelerated test). Corrosion resistance and stability were evaluated.
The acceleration test was performed with a constant temperature and humidity machine (manufactured by Daiken Riken Kikai Co., Ltd.), and the test environment was set to a temperature of 85 ° C. and a humidity of 90% as shown in the following drive environment. The insulation resistance value was measured using an insulation withstand voltage measuring device (manufactured by KIKUSUI ELECTRONICS, TOS9000), and the insulation resistance value when 100 V was applied was measured. Then, the initial insulation resistance _{R 0} before the acceleration test (after the start of driving), 100 days (2400 hours) after the lapse insulation resistance value _{R 100} and were measured.
<Choke coil drive environment>
・ Temperature: 80 ℃
Humidity: 90% R.D. H.
・ Pressure: 2 atm (203 kPa)

Then, in each of the choke coil, when the initial insulation resistance R ₀ and 100, to determine the relative value of the insulation resistance value R ₁₀₀ after a lapse of 100 days. And this relative value was evaluated in accordance with the following evaluation criteria.
<Evaluation criteria for insulation resistance>
◎: R ₁₀₀ is 90 or more and 100 or less ○: R ₁₀₀ is 70 or more and less than 90 Δ: R ₁₀₀ is 50 or more and less than 70 ×: R ₁₀₀ is less than 50

Moreover, the external appearance of the powder magnetic core after 100 days passed was visually observed and evaluated according to the following evaluation criteria.
<Evaluation criteria for appearance>
◎: No rust is observed. ○: 1 to 10 point-like rusts are observed. Δ: 11 to 50 point-like rusts are recognized. ×: 50 or more point-like rusts or 1 More than one surface rust is observed

Next, the corrosion resistance was comprehensively evaluated by evaluating the insulation resistance value and appearance according to the following evaluation criteria.
<Comprehensive evaluation standard for corrosion resistance>
◎: Both insulation resistance value and appearance are ◎
○: Both insulation resistance and appearance are ○, or one is ○ and the other is ◎
Δ: Both insulation resistance and appearance are △, or one is △ and the other is ◎ or ○
×: At least one of insulation resistance value and appearance is ×
The measurement results of 2.1 to 2.3 are shown in Table 1 above.

As is apparent from Table 1, in each of the examples, it was possible to obtain a dust core and a choke coil having excellent magnetic properties (high permeability and low loss) and excellent long-term corrosion resistance. .
On the other hand, the choke coil obtained in each comparative example was inferior in either or both of the magnetic characteristics and the corrosion resistance.

  DESCRIPTION OF SYMBOLS 1 ... Composite particle 2 ... Core part 3 ... Covering layer 30 ... Insulating particle 100 ... Powder coating apparatus 110 ... Container 120 ... Arm 130 ... Rotating shaft 140 ... Tip 150 ... Scraper 10, 20 …… Choke coil 11, 21 …… Dust core 12, 22 …… Conductor wire

Claims (11)

It has a particulate core part made of a soft magnetic material, and a coating layer made of an insulating material provided so as to cover the core part,
The coating layer is formed by mechanically fixing particles of the insulating material having a smaller diameter than the core portion to the core portion,
The insulating-coated soft magnetic powder characterized in that the average particle diameter of the insulating material particles is 1 to 60% of the average particle diameter of the core portion.   The insulator-coated soft magnetic powder according to claim 1, wherein a tap density of the core portion is 45% or more with respect to a true density of the core portion.   The insulator-coated soft magnetic powder according to claim 1 or 2, wherein an average particle size of the core portion is 3 to 50 µm.   The insulator-coated soft magnetic powder according to claim 1, wherein the soft magnetic material is an Fe-based alloy.   The insulator-coated soft magnetic powder according to claim 1, wherein the insulating material is an inorganic material.   The insulator-coated soft magnetic powder according to claim 5, wherein a softening point of the glass material is 100 to 500 ° C.   The insulator-coated soft magnetic powder according to any one of claims 1 to 6, wherein the core portion is manufactured by a water atomization method.   8. The mechanical fixing is performed by stirring the mixture of the core portion and the particles of the insulating material while applying pressure in the same container. The insulator-coated soft magnetic powder described.   The insulation according to any one of claims 1 to 8, wherein the covering layer is formed by fusing the surface of the core portion to the surface of the core portion while maintaining the original shape of the particles of the insulating material. Material-coated soft magnetic powder.   A mixture of the insulator-coated soft magnetic powder according to any one of claims 1 to 9 and a binder is pressed and molded to obtain a molded body, and then the binder in the molded body is cured. Powder magnetic core characterized by   A magnetic element comprising the dust core according to claim 10.

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