JP2008258234A - Powder magnetic core and magnetic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core that has improved magnetic characteristics and heat radiation properties and can maintain corrosion resistance over a long period, and to provide a reliable magnetic element having the dust core. <P>SOLUTION: In a choke coil 80, a conductor 82 formed in a coil shape is buried into the dust core 81. The dust core 81 has: a body section 811 positioned inside and a coating section 812 provided so that the body section 811 is covered entirely. The body section 811 is composed of a pressurized forming body, where first soft magnetic powder composed of a first Fe-based alloy is bound by a binder. The coating section 812 is composed of a pressurized forming body, where second soft magnetic powder composed of a second Fe-based alloy in which Cr is added to the first Fe-based alloy with a ratio of 4-20 wt.% is bound by a binder. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to 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 is used as a magnetic core included in the above-described magnetic element. In the dust core, the generated eddy current is divided between the particles of the soft magnetic powder, so that eddy current loss can be reduced even when used at a high frequency.

  However, since the soft magnetic powder used for the powder magnetic core is generally composed of an Fe-based alloy, it has a problem of oxidizing and generating rust when exposed to the atmosphere for a long period of time, that is, having a problem of low corrosion resistance. Yes. The rust generated in the soft magnetic powder causes deterioration and deterioration of the surrounding binder, and creates a gap between each particle of the soft magnetic powder and the binder. As a result, there is a concern that the insulating properties due to the binder may be reduced, leading to an increase in eddy current loss of the dust core.

Further, when the eddy current loss increases, the amount of heat generated in each particle increases, and there is a concern that this heat causes a vicious circle in which the binder is further deteriorated and deteriorated.
In response to such a problem, a magnetic core having improved corrosion resistance by using a soft magnetic material containing a predetermined amount of Cr has been disclosed (for example, see Patent Document 1).

However, although the soft magnetic material containing Cr increases corrosion resistance, it causes a decrease in magnetic properties such as a decrease in saturation magnetic flux density and an increase in hysteresis loss. For this reason, there exists a problem that the magnetic characteristic of a dust core falls.
In addition, it has been tried to isolate the soft magnetic material from the atmosphere by painting the surface of the dust core or forming a protective layer, but not only do these processes take much effort, Its durability is also insufficient.
Further, heat generated by eddy current loss and hysteresis loss in the powder magnetic core is prevented from being radiated by the coating and the protective layer. For this reason, the heat accumulated in the dust core promotes the alteration and deterioration of the binder and may adversely affect other electronic components provided around the dust core.

Japanese Patent Laid-Open No. 10-83910

  An object of the present invention is to provide a dust core that is excellent in magnetic properties and heat dissipation and can maintain high corrosion resistance over a long period of time, and a highly reliable magnetic element including the dust core.

The above object is achieved by the present invention described below.
The dust core of the present invention has a main body portion and a covering portion provided so as to cover the main body portion,
The main body is composed of a pressure-molded body formed by binding a first soft magnetic powder composed of a first Fe-based alloy with a binder,
The covering portion is formed by binding a second soft magnetic powder composed of a second Fe alloy in which Cr is added to the first Fe alloy at a ratio of 4 to 20 wt% with a binder. It is characterized by comprising a pressure-formed body.
Thereby, while being excellent in a magnetic characteristic and heat dissipation, the powder magnetic core which can maintain high corrosion resistance over a long term is obtained.

In the dust core of the present invention, it is preferable that the first Fe-based alloy is an alloy containing Fe, a main component, and Al, Si, Ni, or Co as the element having the highest content after Fe.
Such an alloy has a reasonably high specific resistance or high magnetic permeability due to the addition of Al, Si, Ni or Co. For this reason, such an alloy can reduce the eddy current loss of the dust core and improve the magnetic permeability, that is, improve the magnetic characteristics.

In the powder magnetic core of the present invention, the first Fe-based alloy is preferably permalloy, silicon steel, permendur, or an Fe-Si-Al alloy.
As a result, the dust core has a particularly high permeability and magnetic flux density.
In the dust core of the present invention, the covering portion preferably has a layer shape with an average thickness of 50 to 1000 μm.
Thereby, corrosion resistance can fully be improved, preventing the remarkable fall of the magnetic permeability of a dust core.

In the powder magnetic core of the present invention, the first soft magnetic powder preferably has an average particle size of 5 to 30 μm.
Thereby, a coating | coated part is comprised by the 2nd soft magnetic powder arranged at high density. For this reason, the space | interval between each particle | grains of 2nd soft-magnetic powder becomes very small, and the function as a protective layer by a coating | coated part becomes more remarkable.

In the dust core of the present invention, it is preferable that the first soft magnetic powder and the second soft magnetic powder are each manufactured by an atomizing method.
Thereby, extremely fine powder can be efficiently produced. Moreover, since the shape of each particle | grain of the obtained powder becomes a spherical shape, when a powder magnetic core is manufactured, the filling rate of each soft-magnetic powder can be made high. Therefore, a dust core having a high density and excellent magnetic permeability and mechanical properties can be obtained.

In the dust core of the present invention, it is preferable that the main body portion and the covering portion are fixed by the binder.
Thereby, since peeling with a main-body part and a coating | coated part can be prevented, it can prevent that the magnetic permeability of a powder magnetic core falls with this peeling.
In the dust core of the present invention, the binder ratio in the dust core is preferably 0.5 to 5 wt%.
As a result, while reliably insulating each particle of each soft magnetic powder with a binder, the density of the dust core is ensured to some extent, and the permeability and mechanical properties of the dust core are prevented from significantly decreasing. Can do. As a result, a dust core having higher magnetic permeability and lower loss can be obtained.

In the dust core of the present invention, the binder is preferably composed mainly of an epoxy resin or a polyimide resin.
These resin materials are easily cured by being heated and have excellent heat resistance. Therefore, it is possible to improve the manufacturability and heat resistance of the dust core.
The magnetic element of the present invention includes the dust core of the present invention.
Thereby, a highly reliable magnetic element is obtained.

Hereinafter, a dust core and a magnetic element of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
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 the magnetic element.
<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 (perspective view) showing a first embodiment of a choke coil and a cross-sectional view taken along the line AA of this schematic view. FIG. 2 is a mold of a molding apparatus used for manufacturing the choke coil shown in FIG. FIG. 3 is a longitudinal sectional view showing a mold opening state of the molding apparatus shown in FIG. 2, and FIGS. 4 to 6 are diagrams for explaining a method of manufacturing the choke coil shown in FIG. (Longitudinal sectional view). In the following description, the upper side in FIGS. 1 to 6 is referred to as “upper” and the lower side is referred to as “lower”.

A choke coil 80 shown in FIG. 1 has a conductive wire 82 formed in a coil shape embedded in a dust core 81. That is, the choke coil 80 is formed by molding the conductive wire 82 with the dust core 81.
A relatively small choke coil 80 having such a configuration can be easily obtained.
In addition, since the conducting wire 82 is embedded in the dust core 81, a gap is hardly generated between the conducting wire 82 and the dust core 81. For this reason, the vibration by the magnetostriction of the dust core 81 can be suppressed, and the generation of noise accompanying this vibration can also be suppressed.

  The dust core 81 is obtained by mixing soft magnetic powder, a binder (binding material), and a solvent, supplying the obtained mixture to a molding die, forming the rectangular parallelepiped shape, and then solidifying the binder. It is.

As shown in FIG. 1B, the dust core 81 according to the present embodiment includes a main body portion 811 located inside thereof and a covering portion provided so as to cover the entire main body portion 811 (the entire surface). 812.
Among these, the main body portion 811 is formed of a compacted body (pressed body) formed by binding the first soft magnetic powder composed of the first Fe-based alloy with a binder.

On the other hand, the covering portion 812 is composed of a compacted body (pressed body) formed by binding the second soft magnetic powder composed of the second Fe-based alloy with a binder.
Thus, in the powder magnetic core 81 comprised with the compacting body, each particle | grains of soft-magnetic powder are bound and fixed by the binder. For this reason, a binder will interpose between each particle | grains, and the insulation between each particle | grain will be ensured. As a result, in the dust core 81, the generated eddy current is divided between the particles. Therefore, even if the choke coil 80 is used at a high frequency, the Joule loss due to the eddy current, that is, the eddy current loss is reduced. The increase can be surely prevented.

Hereinafter, each part of the dust core 81 will be described in detail.
First, the first Fe-based alloy included in the main body 811 may be any material as long as it is a soft magnetic material including Fe. For example, in addition to various Fe-based alloys, pure iron-based materials and low-carbon steels may be used. Etc.
Of these, the first Fe-based alloy is particularly preferably an alloy containing Fe, the main component, and Al, Si, Ni, or Co as the element having the highest content after Fe. Such an alloy has a reasonably high specific resistance or high magnetic permeability due to the addition of Al, Si, Ni or Co. For this reason, by using such an alloy having excellent magnetic properties, it is possible to reduce the eddy current loss of the dust core 81 and improve the permeability, that is, improve the magnetic properties.

  In particular, the first Fe-based alloy is preferably permalloy, silicon steel, permendur, or an Fe-Si-Al alloy. These alloys have a particularly high magnetic permeability and magnetic flux density among soft magnetic materials containing Fe, and are excellent in magnetic properties. For this reason, the powder magnetic core 81 provided with the main-body part 811 comprised by these alloys becomes a thing with especially high magnetic permeability and magnetic flux density.

  Among these, permalloy is an Fe-based soft magnetic material containing Ni at a ratio of about 35 to 82 wt%. 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 dust core 81 can be increased.

  Silicon steel is an Fe-based soft magnetic material containing Si at a ratio of about 3 to 6 wt%. Since silicon steel has a high magnetic permeability and is inexpensive, it is preferably used as the first Fe-based alloy.

  Permendur is an Fe-based soft magnetic material containing Co at a ratio of about 40 to 50 wt%. In addition, you may add about 1-3 wt% of V (vanadium) as needed. Since the permendur has a high magnetic flux density, the magnetic flux density of the dust core 81 can be improved.

In addition, the Fe—Si—Al alloy has a composition corresponding to an Fe-based soft magnetic material containing Si in a proportion of about 5 to 11 wt% and Al in a proportion of about 3 to 8 wt%, that is, Sendust. Preferably there is. Sendust has high magnetic permeability and high hardness. For this reason, the permeability and hardness of the dust core 81 can be improved.
The first soft magnetic powder composed of the first Fe-based alloy preferably has an average particle size of about 5 to 30 μm, more preferably about 7 to 25 μm, and 8 to 20 μm. More preferably, it is about. By manufacturing the main body portion 811 using the first soft magnetic powder having a small average particle diameter in this way, the path through which the eddy current flows is particularly short in the main body portion 811, and thus the eddy current loss of the dust core 81 Can be further reduced.

On the other hand, the second Fe-based alloy included in the covering portion 812 is an Fe-based alloy obtained by adding 4 to 20 wt% of Cr to the first Fe-based alloy described above.
When such an Fe-based alloy comes into contact with oxygen in the atmosphere, Cr is rapidly oxidized. Therefore, a chemically stable chromium oxide layer is formed on the surface of the covering portion 812. Therefore, the surface of the covering portion 812, that is, the surface of the dust core 81 is chemically stably maintained by this chromium oxide layer. As a result, the chromium oxide layer functions as a protective layer, and the corrosion resistance of the dust core 81 can be improved.

Further, by setting the composition of the second Fe-based alloy as described above, the magnetic flux bias is suppressed in the entire dust core 81. For this reason, the dust core 81 excellent in magnetic characteristics is obtained. Furthermore, by suppressing the deviation of the magnetic flux in the dust core 81, it is possible to reliably prevent the eddy current loss from increasing locally and generating heat to a high temperature, and the binder being altered and deteriorated.
Furthermore, since the composition of the second Fe-based alloy is close to that of the first Fe-based alloy, the second Fe-based alloy also exhibits magnetic properties similar to those of the first Fe-based alloy. That is, it is possible to prevent the excellent magnetic properties of the first Fe-based alloy from being canceled by the second Fe-based alloy. As a result, in the entire dust core 81, excellent magnetic characteristics almost the same as those of the first Fe-based alloy can be obtained.

As described above, the composition of the second Fe-based alloy is a composition in which Cr is added to the first Fe-based alloy at a ratio of 4 to 20 wt%. Preferably, the first Fe-based alloy is used. It is set as the composition which added Cr in the ratio of about 6-15 wt%, and more preferably, it is set as the composition which added Cr in the ratio of about 7-12 wt% to the 1st Fe-type alloy.
Further, in the second Fe-based alloy, the content of each component is decreased from the composition of the first Fe-based alloy by the amount of addition of Cr. Specifically, for example, the content ratio of each component may be decreased without reducing only the Fe content ratio or changing the abundance ratio of each component of the first Fe-based alloy.

Of these, if the latter is used, the magnetic properties of the second Fe-based alloy can be brought closer to the magnetic properties of the first Fe-based alloy.
The second soft magnetic powder composed of such a second Fe-based alloy preferably has an average particle size of about 5 to 30 μm, more preferably about 7 to 25 μm, and more preferably 8 to More preferably, it is about 20 μm. By manufacturing the covering portion 812 using the second soft magnetic powder having a small average particle diameter in this way, the covering portion 812 is configured by the second soft magnetic powder arranged at high density. For this reason, the space | interval of each particle | grains of 2nd soft-magnetic powder becomes very small, and the function as a protective layer by the coating | coated part 812 becomes more remarkable.

Further, since the path through which the eddy current flows is particularly short in the covering portion 812, the eddy current loss of the dust core 81 can be further reduced.
Such a first soft magnetic powder and a second soft magnetic powder are respectively, 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, and a pulverizing method. It is manufactured by various powdering methods such as.

  Among these, it is preferable that the first soft magnetic powder and the second soft magnetic powder are each produced by an atomizing method. The atomizing method can efficiently produce extremely fine powder. Moreover, since the shape of each particle | grain of the obtained powder becomes a spherical shape, when a powder magnetic core is manufactured, the filling rate of each soft-magnetic powder can be made high. Therefore, by using each of such soft magnetic powders, the density of the dust core 81 is increased, and the dust core 81 having excellent permeability and mechanical characteristics can be obtained.

  Here, examples of the binder included in the main body portion 811 and the covering portion 812 include, for example, organic binders such as silicone resins, epoxy resins, phenol resins, polyamide resins, polyimide resins, polyphenylene sulfide resins, and phosphoric acid. Examples thereof include inorganic binders such as magnesium, calcium phosphate, zinc phosphate, manganese phosphate, phosphate such as cadmium phosphate, and silicate (water glass) such as sodium silicate.

Among these, particularly those having an epoxy resin or a polyimide resin as a main component are 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 81 can be improved.
Further, the ratio of the binder in the dust core 81 is slightly different depending on the intended magnetic flux density of the dust core 81 to be produced, allowable eddy current loss, etc., but is about 0.5 to 5 wt%. Is preferable, and about 1 to 3 wt% is more preferable. As a result, each particle of each soft magnetic powder is reliably insulated by a binder, and the density of the dust core 81 is secured to some extent to prevent the magnetic permeability and mechanical properties of the dust core 81 from being significantly reduced. can do. As a result, a dust core 81 having higher magnetic permeability and lower loss can be obtained.

In this embodiment, the covering portion 812 has a layered shape. In this case, the average thickness of the covering portion 812 is preferably about 50 to 1000 μm, and more preferably about 100 to 700 μm. . Thereby, corrosion resistance can fully be improved, preventing the remarkable fall of the magnetic permeability of the dust core 81. FIG.
In addition, when the average thickness of the coating | coated part 812 is less than the said lower limit, there exists a possibility that the corrosion resistance of the powder magnetic core 81 cannot fully be improved. On the other hand, when the average thickness of the covering portion 812 exceeds the upper limit, not only a further improvement in corrosion resistance can be expected, but the magnetic permeability of the dust core 81 may be significantly reduced.
Moreover, it is preferable that the main body portion 811 and the covering portion 812 are fixed by a binder. Thereby, since peeling with the main-body part 811 and the coating | coated part 812 can be prevented, it can prevent that the magnetic permeability of the dust core 81 falls with this peeling.

Next, the conducting wire 82 will be described in detail.
Examples of the constituent material of the conductive wire 82 include highly conductive materials, 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 82 with a surface layer having insulating properties. Thereby, the short circuit with the powder magnetic core 81 and the conducting wire 82 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 80 will be described.
Here, prior to the description of the manufacturing process of the choke coil 80, a forming apparatus used in the manufacturing process will be described.
As described above, the choke coil 80 is obtained by supplying a mixture of soft magnetic powder and a binder to a mold, molding the binder, and solidifying the binder.
Although it does not specifically limit as a shaping | molding apparatus used in the case of this shaping | molding, For example, a press molding apparatus, an injection molding apparatus, an extrusion molding apparatus etc. are mentioned.

Below, a press molding apparatus is demonstrated as an example.
A molding apparatus (press molding apparatus) 1 shown in FIGS. 2 and 3 is fixed to a frame 2, a punch fixing table 3 that is fixed to the lower part of the frame 2, and fixes a lower punch described later, and an upper part of the frame 2. It has the plate 4 and the shaping | molding die 10 which shape | molds powder.
The molding die 10 includes a plate-like die 12 having a through-hole 11 penetrating vertically, a rod-like lower punch 13 provided below the die 12, and a rod-like upper punch 14 provided above the die 12. And have. A space surrounded by the die 12, the lower punch 13 and the upper punch 14 becomes a cavity 15.

The cavity 15 shown in FIG. 2 has a rectangular parallelepiped shape. The side surface of the cavity 15 is constituted by a part of the die 12, the lower surface thereof is constituted by a part of the lower punch 13, and the upper surface thereof is constituted by a part of the upper punch 14.
The die 12 is supported by plate-like die sets 121 and 122 provided on the same surface as the die 12.

The lower surfaces of the die sets 121 and 122 are connected to the upper surface of a die set connecting plate 124 provided below the die 12 via the guide posts 123 and 123, respectively. The lower surface of the die set connecting plate 124 is connected to a lower hydraulic cylinder 126 provided on the lower surface of the frame 2 via a cylinder rod 125.
With this configuration, the die sets 121 and 122 can be moved up and down by the lower hydraulic cylinder 126 via the cylinder rod 125, the die set connecting plate 124 and the guide posts 123 and 123.

Further, guide posts 127 and 127 are provided on the upper surfaces of the die sets 121 and 122, respectively.
The cylinder rod 125 is inserted through the through hole 31 provided in the punch fixing table 3.
The lower punch 13 is provided on the base plate 131.

In addition, the lower surface of the base plate 131 is connected to the upper surface of the punch fixing table 3 provided below the base plate 131 via the two columns 132 and 132. Thereby, the lower punch 13 is fixed to the frame 2.
The base plate 131 has two through holes 133 and 133, and two guide posts 123 and 123 are inserted through these through holes 133 and 133. With such a configuration, the guide posts 123 and 123 can move up and down while being guided by the through holes 133 and 133.

The upper punch 14 is provided on the lower surface of the upper punch plate 141.
Further, the upper surface of the upper punch plate 141 is connected to an upper hydraulic cylinder 143 provided on the upper surface of the plate 4 via a cylinder rod 142.
With such a configuration, the upper punch 14 can be moved up and down by the upper hydraulic cylinder 143 via the upper punch plate 141 and the cylinder rod 142.

The upper punch plate 141 has two through holes 144 and 144. Two guide posts 127 and 127 are inserted through these through holes 144 and 144. With this configuration, the guide posts 127 and 127 can move up and down while being guided by the through holes 144 and 144.
The cylinder rod 142 is inserted through the through hole 41 provided in the plate 4.

  In such a molding apparatus 1, the lower punch 13 and the upper punch 14 can be moved relative to the die 12. Further, the lower punch 13 and the upper punch 14 are provided so as to be inserted into and removed from the through hole 11, respectively. Accordingly, the volume of the cavity 15 defined by the die 12, the lower punch 13 and the upper punch 14 changes according to the movement of the lower punch 13 and the upper punch 14, and the mold closing shown in FIG. A state and a mold open state shown in FIG. 3 in which the cavity 15 is opened can be taken.

A powder supply unit 16 is provided on the die set 122.
The powder supply unit 16 includes a box-like feeder box 161 that stores the powder 5 supplied to the cavity 15, a hydraulic cylinder 162, and a cylinder rod 163 that connects the feeder box 161 and the hydraulic cylinder 162. . With this configuration, the feeder box 161 can be moved left and right on the upper surface of the die set 122 via the cylinder rod 163 by the hydraulic cylinder 162.

Here, the lower surface of the box-shaped feeder box 161 is open. For this reason, when the feeder box 161 is moved to the left side of FIG. 2 while the powder 5 is stored, and the feeder box 161 is moved above the cavity 15 as shown in FIG. 3, the powder is removed from the lower surface of the feeder box 161. 5 falls and is supplied to the cavity 15.
By the way, the shaping | molding apparatus 1 is provided with the some coil around the cavity 15, as shown in FIG.

  Specifically, the coil 61 is embedded in the vicinity of the boundary on the die 12 side of each of the die sets 121 and 122 so as to surround the die 12. Thereby, the cavity 15 is surrounded by the coil 61. The coil 61 is connected to a power supply circuit (not shown), and a voltage is applied to the coil 61 by the power supply circuit. When a voltage is applied to the coil 61, a magnetic field is generated in the die 12 and the cavity 15.

  A coil 62 is provided on the lower punch 13 so as to surround the lower punch 13. A power circuit (not shown) is also connected to the coil 62, and a voltage is applied to the coil 62 by the power circuit. When a voltage is applied to the coil 62, a magnetic field is generated in the lower punch 13 and the cavity 15 located above the lower punch 13, respectively.

  A coil 63 is provided below the upper punch 14 so as to surround the upper punch 14. A power circuit (not shown) is also connected to the coil 63, and a voltage is applied to the coil 63 by the power circuit. When a voltage is applied to the coil 63, a magnetic field is generated in each of the upper punch 14 and the cavity 15 positioned below the upper punch 14.

That is, a plurality of coils 61, 62, 63 provided around the cavity 15 and a power supply circuit connected to each coil constitute magnetic field applying means for applying a magnetic field to the cavity 15.
The die 12, the lower punch 13 and the upper punch 14 are each made of a metal material, but are preferably made of a soft magnetic material. Thereby, when each coil 61, 62, 63 is in an energized state, a magnetic field can be generated in the die 12, the lower punch 13 and the upper punch 14, and when each coil 61, 62, 63 is in a non-energized state. The generation of the magnetic field can be stopped. That is, the generation of the magnetic field can be arbitrarily controlled.
When the die 12, the lower punch 13 and the upper punch 14 are made of a hard magnetic material, the energization of the coils 61, 62 and 63 magnetizes the die 12, the lower punch 13 and the upper punch 14. Therefore, even if the coils 61, 62, and 63 are not energized, the generation of the magnetic field may continue.

Next, a method for manufacturing the choke coil 80 using such a molding apparatus 1 will be described.
The method of manufacturing the choke coil 80 includes the first step of supplying the second granulated powder into the cavity 15 of the mold 10 and the application of the magnetic field to the cavity 15, thereby providing the second granulated powder. Is supplied to the inner wall surface of the cavity 15, and the first granulated powder and the conductor 82 are supplied into the cavity 15 in which the second granulated powder is adsorbed to the inner wall surface and molded. It has the 3rd process of obtaining a temporary molded object, and the 4th process of hardening the binder in the obtained temporary molded object.

Hereinafter, each process will be described sequentially.
[1] First, a binder is dissolved in a solvent to prepare a binder solution.
The solvent is not particularly limited as long as it can dissolve the binder. For example, inorganic solvents such as water, carbon disulfide, and carbon tetrachloride, ketone solvents, alcohol solvents, ether solvents, cellosolve solvents , Aliphatic hydrocarbon solvent, aromatic hydrocarbon solvent, aromatic heterocyclic compound solvent, amide solvent, halogen compound solvent, ester solvent, amine solvent, nitrile solvent, nitro solvent, aldehyde solvent Examples include organic solvents such as solvents, and a mixture of one or more selected from these can be used.

Moreover, you may add various additives in a binder solution as needed.
Examples of the various additives used here include dispersants (lubricants), plasticizers, antioxidants, and the like, and one or more of these can be used in combination.
Next, a granulated powder of the first soft magnetic powder is obtained using the first soft magnetic powder and the binder solution. Hereinafter, the granulated powder of the first soft magnetic powder is referred to as “first granulated powder”.

Also, a granulated powder of the second soft magnetic powder is obtained using the second soft magnetic powder and the binder solution. Hereinafter, the granulated powder of the second soft magnetic powder is referred to as “second granulated powder”.
Such granulation of the first soft magnetic powder and the second soft magnetic powder is, for example, tumbling flow granulation method, tumbling granulation method, spray drying method (spray dryer), stirring and mixing granulation, respectively. It can be performed by various granulation methods such as extrusion granulation, crush granulation, and compression granulation.

  The weight of the binder dissolved in the solvent is preferably about 0.5 to 50 g, and about 10 to 30 g, per 1 kg of the first soft magnetic powder or the second soft magnetic powder. More preferred. By setting the weight of the binder to be within the above range, the surface of the first soft magnetic powder or the second soft magnetic powder is coated with a sufficient amount of binder, and a large amount of binder does not contribute to the coating. Can be prevented. As a result, a granulated powder capable of producing a molded body excellent in shape retention and molding density is obtained in the steps described later.

  Further, the weight of the solvent used for dissolving the binder is preferably about 1 to 100 g, more preferably about 7 to 70 g, per 1 g of the binder. By setting the weight of the solvent within the above range, the binder is surely dissolved, the amount of the solvent is excessively increased, the viscosity of the binder solution is remarkably lowered, and the shape retention of the molded body produced in the process described later It is possible to reliably prevent the performance from deteriorating.

The average particle size of the first granulated powder and the second granulated powder thus obtained is preferably about 40 to 180 μm, more preferably about 45 to 140 μm, and more preferably 50 to More preferably, it is about 100 μm. By setting the average particle size of each granulated powder within the above range, when each granulated powder is filled into a mold and a molded body is formed, each granulated powder is converted into fluidity and mold. It is excellent in filling property.
In addition, when an average particle diameter is less than the said lower limit, the fluidity | liquidity of each granulated powder will not be stabilized and the size variation of a molded object may become large. On the other hand, when the average particle size exceeds the upper limit, when forming a particularly small compact, uneven filling of each granulated powder is likely to occur, and the dimensional variation of the compact may increase.

[2] Next, as shown in FIG. 4A, the mold 10 is brought into the mold open state. Then, the second granulated powder 52 is stored in the feeder box 161.
Next, the feeder box 161 is moved to the left until it reaches above the cavity 15. Thereby, as shown in FIG.4 (b), the 2nd granulated powder 52 in the feeder box 161 is supplied to the cavity 15 (1st process).

At this time, by appropriately setting the amount (volume) of the second granulated powder 52 supplied to the cavity 15, the thickness of the covering portion 812 in the finally obtained dust core 81 can be adjusted. .
The amount of the second granulated powder 52 supplied to the cavity 15 can be appropriately set by moving the die 12 in the vertical direction and changing the volume of the cavity 15.

[3] Next, as shown in FIG. 4C, the feeder box 161 is returned to the original position, and the die 12 is moved upward to enlarge the volume of the cavity 15.
The volume of the cavity 15 at this time is determined in consideration of the compression ratio when the first granulated powder 51 and the second granulated powder 52 are compressed in a process described later.
[4] Next, each power supply circuit 610, 620, 630 applies a voltage to each of the coils 61, 62, 63. Thereby, magnetic fields are generated in the die 12, the lower punch 13 and the upper punch 14, respectively. This magnetic field is applied to the cavity 15.
By the action of this magnetic field, the second granulated powder 52 supplied into the cavity 15 is adsorbed on the side surface and the lower surface of the cavity 15 as shown in FIG.

Thereafter, the upper punch 14 is lowered near the upper surface of the die 12. Thereby, a part of 2nd granulated powder 52 is adsorb | sucked to the lower surface of the upper punch 14 (2nd process).
Here, in the present embodiment, a magnetic field is applied to the cavity 15 by the plurality of coils 61, 62, 63 provided around the cavity 15 and the power supply circuits 610, 620, 630 connected to the coils. Magnetic field applying means is configured. According to the magnetic field application means having such a configuration, the application of the magnetic field can be easily and accurately controlled by operating the power supply circuit.
Further, by changing the voltages applied to the coils 61, 62, 63, the strength of the generated magnetic field can be made different among the side surface, the lower surface, and the upper surface of the inner wall surface of the cavity 15. Thereby, the quantity of the 2nd granulated powder 52 adsorb | sucked to the side surface of the cavity 15, a lower surface, and an upper surface can be varied, respectively.

[5] Next, as shown in FIG. 5 (e), the second granulated powder 52 in the feeder box 161 is taken out and replaced with the first granulated powder 51.
Further, the conductive wire 82 formed in a coil shape is held at a predetermined position in the cavity 15.
[6] Next, as shown in FIG. 5 (f), the feeder box 161 is moved to the left until reaching the upper side of the cavity 15 in a state where a voltage is applied to each of the coils 61, 62, 63. As a result, as shown in FIG. 5 (f), the first granulated powder 51 in the feeder box 161 is supplied to and filled in the cavity 15.

[7] Next, with the voltage applied to the coil 63, the feeder box 161 is returned to its original position as shown in FIG.
Next, as shown in FIG. 6 (h), the upper punch 14 is moved downward and inserted into the cavity 15, and the mold 10 is closed. Thereby, the first granulated powder 51 and the second granulated powder 52 in the cavity 15 are pressed and molded. As a result, a temporary molded body 53 is obtained (third step).

[8] Next, as shown in FIG. 6 (i), the upper punch 14 is moved upward to make the mold open.
Further, the die 12 is moved downward, and the temporary molded body 53 in the cavity 15 is pushed up by the lower punch 13. Thereby, the temporary molded body 53 can be taken out from the cavity 15.
As described above, the provisional molded body 53 can be manufactured.

[9] Next, the temporary molded body 53 is heated to cure the binder in the temporary molded body 53 (fourth step).
Although the heating temperature at the time of heating the temporary molded body 53 is slightly different depending on the composition of the binder, for example, when the binder is composed of an organic binder, it is preferably about 100 to 250 ° C., more preferably 120 ˜200 ° C.
Moreover, although heating time changes with heating temperature, it is set as about 0.5 to 5 hours.
By the manufacturing method as described above, the main body portion 811 constituted by the powder compact including the first soft magnetic powder, and the covering portion 812 constituted by the powder compact including the second soft magnetic powder. A choke coil 80 having a dust core 81 and a conductive wire 82 embedded in the dust core 81 can be manufactured.

Second Embodiment
Next, a second embodiment of the dust core and magnetic element of the present invention will be described.
FIG. 7 is a schematic view (plan view) showing a second embodiment of the choke coil and a cross-sectional view taken along the line BB of the schematic view.
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. 7, the choke coil 90 according to the present embodiment includes a ring-shaped (toroidal-shaped) dust core 91 and a conducting wire 92 wound around the dust core 91. Such a choke coil 90 is generally called a toroidal coil.
Among these, the powder magnetic core 91 is obtained by mixing soft magnetic powder, a binder, and a solvent, supplying the obtained mixture to a molding die, forming the ring, and then curing the binder. is there.

As shown in FIG. 7B, the dust core 91 according to the present embodiment includes a main body portion 911 located inside thereof, and a covering portion 912 provided so as to cover the main body portion 911.
Among these, the main body 911 has the same configuration as the main body 811 according to the first embodiment. On the other hand, the covering portion 912 has the same configuration as the covering portion 812 according to the first embodiment.
Even in such a choke coil 90, the same operation and effect as in the first embodiment can be obtained.

As mentioned above, although the dust core and magnetic element of this invention were demonstrated based on suitable embodiment, this invention is not limited to this.
For example, in each said embodiment, although the powder magnetic core had two layers, the main-body part and a coating | coated part, you may have three or more layers. In this case, the outermost layer corresponds to the covering portion in each of the embodiments.
Moreover, in the said embodiment, although the choke coil was demonstrated to the example as a magnetic element of this invention, the effect | action and effect similar to the above are acquired also in another magnetic element provided with a dust core.

Next, specific examples of the present invention will be described.
1. Production of dust core and choke coil (magnetic element) (Example 1)
<1> First, Fe-3 wt% Si silicon steel powder having an average particle size of 10 μm was prepared by a water atomization method.

<2> Next, the obtained silicon steel powder (first soft magnetic powder), an epoxy resin (binder), and toluene (solvent) were mixed to obtain a mixture. The ratio of silicon steel powder to epoxy resin was 98: 2 by weight.
<3> Next, after stirring the obtained mixture, it was heated at a temperature of 60 ° C. for 1 hour and dried to obtain a lump-like dried body. Next, the dried body was passed through a sieve having an opening of 500 μm, and the dried body was pulverized to obtain a first granulated powder having an average particle diameter of 75 μm.

<4> Next, an Fe-3 wt% Si-4 wt% Cr Fe-based alloy powder having an average particle diameter of 13 μm was prepared by a water atomization method.
<5> Next, the obtained Fe-based alloy powder (second soft magnetic powder), an epoxy resin (binder), and toluene (solvent) were mixed to obtain a mixture. The ratio of the Fe-based alloy powder and the epoxy resin was 98: 2 by weight.

<6> 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 body. Next, the dried body was passed through a sieve having an opening of 500 μm, and the dried body was pulverized to obtain a second granulated powder having an average particle diameter of 75 μm.
<7> Next, the second granulated powder was stored in the feeder box of the molding apparatus. And the 2nd granulated powder was supplied in the cavity.

<8> Next, a DC voltage was applied to the coil provided around the cavity of the mold, and a magnetic field was applied in the cavity. As a result, the second granulated powder was adsorbed on the inner wall surface of the cavity.
<9> Next, the second granulated powder of the feeder box was replaced with the first granulated powder, and this first granulated powder was supplied into the cavity and filled.
<10> Next, with the molding die closed, the first granulated powder and the second granulated powder were pressed and molded at a molding pressure of 5 t / cm ² (490 MPa) to obtain a temporary molded body. . Thereafter, the mold was opened and the temporary molded body was taken out.

<11> Next, the temporary molded body was heated in an air atmosphere at a temperature of 150 ° C. for 1 hour to cure the binder. As a result, a toroidal powder magnetic core was obtained.
The obtained powder magnetic core had an outer diameter of 28 mm, an inner diameter of 14 mm, and a thickness of 5 mm.
Moreover, the average thickness of the coating layer comprised with the compacting body of the 2nd granulated powder among the obtained powder magnetic cores was 0.5 mm.
<12> Next, a lead wire made of Cu was wound around the obtained powder magnetic core to produce a choke coil.

(Example 2)
A dust core and a choke coil were produced in the same manner as in Example 1 except that the Cr content in the second soft magnetic powder was changed to 7 wt%.
(Example 3)
A dust core and a choke coil were produced in the same manner as in Example 1 except that the Cr content in the second soft magnetic powder was changed to 20 wt%.

Example 4
Example 1 except that the first soft magnetic powder was changed to a permalloy powder of Fe-45 wt% Ni and the second soft magnetic powder was changed to an alloy powder of Fe-40 wt% Ni-7 wt% Cr. A dust core and a choke coil were produced in the same manner as described above.
(Example 5)
The above implementation was performed except that the first soft magnetic powder was changed to a permendrite powder of Fe-50 wt% Co and the second soft magnetic powder was changed to an alloy powder of Fe-50 wt% Co-7 wt% Cr. A dust core and a choke coil were produced in the same manner as in Example 1.

(Example 6)
The first soft magnetic powder was changed to Sendust powder of Fe-9.5 wt% Si-5.5 wt% Al, and the second soft magnetic powder was changed to Fe-8.5 wt% Si-5 wt% Al-7 wt%. A dust core and a choke coil were produced in the same manner as in Example 1 except that the alloy powder was changed to Cr alloy powder.

(Comparative Example 1)
A dust core and a choke coil were produced in the same manner as in Example 2 except that the use of the second soft magnetic powder was omitted and only the first soft magnetic powder (silicon steel powder) was used.
(Comparative Example 2)
A dust core and a choke coil were produced in the same manner as in Example 2 except that the Cr content in the second soft magnetic powder was changed to 30 wt%.

(Comparative Example 3)
A dust core and a choke coil were produced in the same manner as in Example 4 except that the use of the second soft magnetic powder was omitted and only the first soft magnetic powder (permalloy powder) was used.
(Comparative Example 4)
A dust core and a choke coil were produced in the same manner as in Example 4 except that the Cr content in the second soft magnetic powder was changed to 30 wt%.

(Comparative Example 5)
A dust core and a choke coil were produced in the same manner as in Example 5 except that the use of the second soft magnetic powder was omitted and only the first soft magnetic powder (permendule powder) was used. .
(Comparative Example 6)
A dust core and a choke coil were produced in the same manner as in Example 5 except that the Cr content in the second soft magnetic powder was changed to 30 wt%.

(Comparative Example 7)
A dust core and a choke coil were produced in the same manner as in Example 6 except that the use of the second soft magnetic powder was omitted and only the first soft magnetic powder (Sendust powder) was used.
(Comparative Example 8)
A dust core and a choke coil were produced in the same manner as in Example 6 except that the Cr content in the second soft magnetic powder was changed to 30 wt%.

2. 2.1 Measurement / Evaluation of Magnetic Permeability and Loss (Core Loss) For the choke coils obtained in the examples and the comparative examples, the magnetic permeability and loss (core loss) were measured based on the following measurement conditions.
<Measurement conditions>
・ Measurement frequency: 300 kHz
・ Maximum magnetic flux density: 50mT
Measurement device: AC magnetic property measurement device (Iwatsu Measurement Co., Ltd., BH analyzer SY8232)
And the obtained magnetic permeability and loss were evaluated according to the following evaluation criteria.

<Evaluation criteria>
×: 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

2.2 Measurement and Evaluation of Corrosion Resistance The dust cores obtained in each Example and each Comparative Example were measured by measuring the change in specific resistance value under each high temperature and high humidity environment (acceleration test). The corrosion resistance and stability of the magnetic core 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 a temperature of 85 ° C. and a humidity of 90% as shown in the following drive environment. The specific resistance was measured by using a withstand voltage measuring machine (manufactured by KIKUSUI ELECTRONICS, TOS9000) and measuring the resistance value when 100 V was applied. Then, an initial specific resistance R ₀ before the acceleration test (immediately after the start of driving) and a specific resistance R ₁₀₀ after 100 days (2400 hours) elapsed were measured.

<Choke coil drive environment>
・ Temperature: 80 ℃
Humidity: 90% R.D. H.
・ Pressure: 2 atm (203 kPa)
Next, in each powder magnetic core, when the initial specific resistance R ₀ was 100, the relative value of the specific resistance R ₁₀₀ after 100 days was determined. And this relative value was evaluated in accordance with the following evaluation criteria.

<Evaluation criteria for specific resistance>
A: R ₁₀₀ is 90 or more and 100 or less. O: R ₁₀₀ is 70 or more and less than 90. Δ: R ₁₀₀ is 50 or more and less than 70. X: R ₁₀₀ is less than 50. The appearance of the magnetic core 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 One or more planar rusts were observed. Then, the corrosion resistance was comprehensively evaluated by evaluating the specific resistance and appearance according to the following evaluation criteria.

<Comprehensive evaluation criteria>
◎: Both resistivity and appearance are ◎
○: Both resistivity and appearance are ○, or one is ○ and the other is ◎
△: Both resistivity and appearance are △, or one is △ and the other is ◎ or ○
×: At least one of specific resistance and appearance is ×
The evaluation results of 2.1 to 2.2 are shown in Table 1 above.

As is apparent from Table 1, in each of the examples, a dust core and a choke coil having excellent magnetic properties (high permeability and low loss) and excellent long-term corrosion resistance could be obtained. .
On the other hand, the powder magnetic cores obtained in the respective comparative examples were inferior in either magnetic properties or corrosion resistance.

It is the schematic diagram (perspective view) which shows 1st Embodiment of a choke coil, and the sectional view on the AA line of this schematic diagram. It is a longitudinal cross-sectional view which shows the mold closing state of the shaping | molding apparatus used for manufacture of the choke coil shown in FIG. It is a longitudinal cross-sectional view which shows the mold open state of the shaping | molding apparatus shown in FIG. It is a figure (longitudinal sectional drawing) for demonstrating the manufacturing method of the choke coil shown in FIG. It is a figure (longitudinal sectional drawing) for demonstrating the manufacturing method of the choke coil shown in FIG. It is a figure (longitudinal sectional drawing) for demonstrating the manufacturing method of the choke coil shown in FIG. It is the schematic diagram (plan view) which shows 2nd Embodiment of a choke coil, and the BB sectional drawing of this schematic diagram.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Molding device 2 ... Frame 3 ... Punch fixing table 31 ... Through hole 4 ... Plate 41 ... Through hole 5 ... Powder 51 ... First granulated powder 52 ... Second granulation Powder 53 ... Temporary molded body 10 ... Mold 11 ... Through hole 12 ... Die 121, 122 ... Die set 123 ... Guide post 124 ... Die set connecting plate 125 ... Cylinder rod 126 ... Lower hydraulic pressure Cylinder 127 …… Guide post 13 …… Lower punch 131 …… Base plate 132 …… Prop 133 …… Through hole 14 …… Upper punch 141 …… Upper punch plate 142 …… Cylinder rod 143 …… Upper hydraulic cylinder 144 …… Through Hole 15 ... Cavity 16 ... Powder supply part 161 ... Feeder box 162 ... Hydraulic cylinder 163 ... Cylinder rod 61, 62, 63 ... Coil 610, 620, 630 ... Power supply circuit 80, 90 ... Choke coil 81, 91 ... Dust core 811, 911 ... Main part 812, 912 ... Covering part 82, 92 …… Conductor

Claims (10)

A main body portion and a covering portion provided to cover the main body portion;
The main body is composed of a pressure-molded body formed by binding a first soft magnetic powder composed of a first Fe-based alloy with a binder,
The covering portion is formed by binding a second soft magnetic powder composed of a second Fe alloy in which Cr is added to the first Fe alloy at a ratio of 4 to 20 wt% with a binder. A dust core comprising a compacted body.   2. The dust core according to claim 1, wherein the first Fe-based alloy is an alloy containing Fe as a main component and containing Al, Si, Ni, or Co as an element having the second highest content after Fe.   The dust core according to claim 2, wherein the first Fe-based alloy is permalloy, silicon steel, permendur, or an Fe-Si-Al alloy.   The dust core according to any one of claims 1 to 3, wherein the covering portion has a layer shape with an average thickness of 50 to 1000 µm.   5. The dust core according to claim 1, wherein an average particle diameter of the first soft magnetic powder is 5 to 30 μm.   The dust core according to any one of claims 1 to 5, wherein each of the first soft magnetic powder and the second soft magnetic powder is manufactured by an atomizing method.   The dust core according to claim 1, wherein the main body portion and the covering portion are fixed by the binder.   The dust core according to any one of claims 1 to 7, wherein a ratio of the binder in the dust core is 0.5 to 5 wt%.   The dust core according to any one of claims 1 to 8, wherein the binder is composed mainly of an epoxy resin or a polyimide resin.   A magnetic element comprising the dust core according to claim 1.

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