JP2002164223A - Magnetic core having magnet for magnetic bias, and inductance component using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic core of an inductance component, with which a core loss in the magnetic core including a permanent magnet for magnetic bias can be reduced and surface mounting can be performed by reflow, without the risk of deteriorating the characteristics due to heat. SOLUTION: As a permanent magnet for providing magnetic bias for a magnetic core of an inductance component, a bonded magnet composed of a rare earth magnetic powder having an intrinsic coercive force of 10 kOe or higher, a Tc of 500 deg.C or higher and an average powder grain size of 2.0-50 μm and a binder resin is used. An oxidation preventing layer, such as a nitride layer, carbide layer, oxide layer or the like, is formed only on the surface of the rare earth magnetic powder. Consequently, an oxidation-resistant magnetic core can be obtained, in which a proper DC-superimposing characteristics can be obtained and moreover deterioration in core loss characteristics does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic core (hereinafter simply referred to as "core") for an inductance component such as a choke coil or a transformer used in a switching power supply or the like.
Also called. In particular, the present invention relates to a magnetic core having a permanent magnet for magnetic bias.

[0002]

2. Description of the Related Art Conventionally, in a choke coil and a transformer used for a switching power supply or the like, for example,
Usually, a voltage is applied in a state where an AC component is superimposed on a DC component. Therefore, the magnetic cores used in these choke coils and transformers do not have magnetic saturation with respect to the DC superposition (this characteristic is called “DC superposition characteristic”).
Is required to be good.

[0003] Ferrite magnetic cores and powder magnetic cores are used as high-frequency magnetic cores. Ferrite magnetic cores have a high initial permeability and a small saturation magnetic flux density, and powder magnetic cores have a low initial magnetic permeability. There is a characteristic derived from the material properties such as high saturation magnetic flux density. Therefore, the dust magnetic core is often used in a toroidal shape. On the other hand, in the case of a ferrite magnetic core, for example, a magnetic gap (magnetic gap) is formed in the middle foot of the E-shaped core to avoid magnetic saturation due to DC superposition.

However, with the demand for miniaturization of electronic components in accordance with the recent demand for miniaturization of electronic equipment, the magnetic gap of the magnetic core has to be reduced, and a magnetic core having a higher magnetic permeability for DC superposition is required. Strongly required.

In order to meet this requirement, it is generally necessary to select a magnetic core having a high saturation magnetization, that is, a magnetic core which does not become magnetically saturated in a high magnetic field. However, the saturation magnetization is inevitably determined by the composition of the material, and cannot be increased infinitely.

As a solution, it has long been proposed to dispose a permanent magnet in a magnetic gap provided in a magnetic path of a magnetic core to cancel a DC magnetic field due to DC superposition, that is, to apply a magnetic bias to the magnetic core. I have.

[0007] The magnetic bias method using a permanent magnet is an excellent method for improving the direct current superposition characteristics. On the other hand, when a sintered metal magnet is used, the core loss of the magnetic core is remarkably increased. However, the use of the compound did not endure the practical use, for example, the superposition characteristics were unstable.

As means for solving these problems, for example, Japanese Patent Application Laid-Open No. 50-133453 discloses a method of using a bonded magnet obtained by mixing a rare earth magnet powder having a high coercive force and a binder and compressing and molding the same as a permanent magnet for magnetic bias. Discloses that the DC bias characteristics and the temperature rise of the core are improved.

However, in recent years, the demand for improving the power conversion efficiency of a power supply has become more and more severe, and the magnetic cores for choke coils and transformers are at a level where it is impossible to determine the superiority or inferiority simply by measuring the core temperature. I have. Therefore, it is indispensable to judge the measurement result by the core loss measurement device, and as a result of the actual examination by the present inventors,
It has been clarified that the core loss characteristics are degraded at the resistivity values disclosed in JP-A-50-133453.

In recent years, a surface mount type coil has been desired. For the surface mount, the coil is subjected to reflow soldering. It is desired that the characteristics of the magnetic core of the coil do not deteriorate under the reflow conditions. In addition, an oxidation-resistant rare earth magnet is essential.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic core having a gap at at least one position in a magnetic path, in which a permanent magnet is arranged near the gap in order to supply a magnetic bias from both ends of the gap. In consideration of the above, in a magnetic core having a magnetic bias magnet
An object of the present invention is to provide a magnetic core having excellent oxidation resistance and excellent resistance to oxidation even under reflow conditions, which is excellent in direct current superposition characteristics, core loss characteristics, and oxidation resistance.

[0012]

SUMMARY OF THE INVENTION According to the present invention, a permanent magnet is arranged near a magnetic core having a gap in at least one position of a magnetic path in order to supply a magnetic bias from both ends of the gap. In order to solve the above-mentioned problem in the magnetic core having the magnetic bias magnet, the permanent magnet has a specific coercive force of 10 kOe or more and 500 ° C.
The powder having the above Curie temperature has an average particle size of 2.5 to 50.
A bond magnet comprising a rare-earth magnet powder having a thickness of μm and a resin for a binder, wherein the bond magnet has an oxidation suppression layer formed on only the surface of the rare-earth magnet powder to suppress oxidation during reflow. Things.

It is preferable that the oxidation suppressing layer is at least one selected from, for example, a nitride layer, a carbide layer, and an oxide layer.

According to an embodiment of the present invention, the bond magnet contains the binder resin in a volume ratio of 20% or more, and has a specific resistance of 1 Ωcm or more.

The required inductance component can be obtained by applying at least one winding of one or more turns to the magnetic core having the magnetic bias magnet of the present invention.

The inductance component is a coil,
The components include a choke coil, a transformer, and other components that generally require a magnetic core and a winding.

[0017]

The present inventors have studied a permanent magnet to be inserted in order to achieve the above object, and found that the specific resistance of the magnet is 1Ω.
It has been discovered that when a permanent magnet having a specific coercive force Hc of 10 kOe or more is used at a height of 10 cm or more, an excellent DC superposition characteristic can be obtained, and a magnetic core without deterioration of the core loss characteristic can be formed. This is because the magnet characteristics necessary for obtaining excellent DC superimposition characteristics are not the product of energy but the intrinsic coercive force, and therefore, even if a permanent magnet with a high specific resistance is used, if the intrinsic coercive force is high, the DC characteristics are sufficiently high. This is because they have found that superimposition characteristics can be obtained.

A magnet having a high specific resistance and a high intrinsic coercive force can be generally obtained by a rare earth bonded magnet formed by mixing a rare earth magnet powder with a binder, and any magnet powder having a high coercive force can be obtained. It is possible to use a composition having a suitable composition.

The type of rare earth magnet powder is SmCo type, Nd
There are FeB type and SmFeN type. Considering reflow conditions and oxidation resistance, a magnet having a Curie temperature of 500 ° C. or more and a coercive force of 10 kOe or more is required.
It is limited to m ₂ Co _17- based magnet. Furthermore, as a result of various studies on the improvement of the oxidation resistance of the bonded magnet, the oxidation resistance is improved by forming an oxidation suppression layer such as a nitride layer, a carbide layer, and an oxide layer only on the surface of the magnet powder, It has been found that excellent DC bias characteristics can be obtained even after reflow.

As the magnetic core for the choke coil and the transformer, any material having soft magnetic properties is effective, but in general, MnZn or NiZn ferrite, dust magnetic core, silicon steel sheet, amorphous, etc. Is used. There is no particular limitation on the shape of the magnetic core, and the present invention can be applied to magnetic cores of any shape such as a toroidal core, an EE core, and an EI core. A gap is provided in at least one portion of the magnetic path of these cores, and a permanent magnet is inserted into the gap.

The gap length is not particularly limited, but if the gap length is too narrow, the DC superposition characteristics deteriorate, and if the gap length is too wide, the magnetic permeability is too low, so the gap length to be inserted naturally is determined.

Next, the required characteristics of the permanent magnet inserted into the gap are as follows. When the intrinsic coercive force is 10 KOe or less, the coercive force disappears due to the DC magnetic field applied to the magnetic core, so that a higher coercive force is required. The larger the specific resistance is, the better. However, if it is 1 Ω · cm or more, it does not become a major factor of core loss deterioration. Also, if the average maximum particle diameter of the powder is 50 μm or more, the core loss characteristics are deteriorated.
The maximum particle size of the powder is desirably 50 μm or less, and if the minimum particle size is 2.5 μm or less, the reduction in magnetization due to oxidation of the powder during powder heat treatment and reflow becomes remarkable, so that a particle size of 2.5 μm or more is required. It is. Here, by forming a nitride layer, a carbide layer, and an oxide layer only on the powder surface, the oxidation resistance of the bonded magnet after reflow can be improved, and the magnetic core having both oxidation resistance and high characteristics can be obtained. Is obtained.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, as an embodiment of the present invention, referring to the drawings, tables and the like, a specific production of a magnetic core will be described, and measurement data thereof will be shown.

(First embodiment) First embodiment of the present invention
The magnetic core according to the above form is a permanent magnet for magnetic bias.
And Sm₂Co₁₇A system bond magnet was used. Elaborate
And a material having an average particle size of about 5 μm
Sm₂Co₁₇A system magnet powder was used. This Sm₂Co
₁₇To form a thin oxide layer on the very surface of the base magnet powder
Therefore, heat treatment was performed in a low oxygen atmosphere. At this time rare earth
In the case of system powder, oxygen during heat treatment may cause characteristic deterioration.
Therefore, the condition of heat treatment is
Vacuum only pump, 1 × 10^-1~ 1 × 10^-3Torr
The degree is desirable, and after evacuation, an inert gas (for example,
Ar, N, H, etc.). Under these conditions, the magnetic characteristics
Deterioration of properties is minimized, and a thin acid
Oxide layer can be formed.

From the above conditions, in the first embodiment, the following conditions were selected to produce a bonded magnet. That is, about 5 μm of Sm ₂ Co
_{The 17-} series magnet powder was put into a predetermined heat treatment board, and 500
Heat treatment was performed at 2 ° C. for 2 hours. The atmosphere was evacuated to 1 × 10 ⁻² Torr using only a rotary pump, and then Ar was sealed as an inert gas. Thereafter, the powder was cooled in Ar and the powder was taken out. Each of the bonded magnets was produced by mixing the resulting powder with 40 vol% of an epoxy resin as a binder, and then performing mold molding without a magnetic field.
At this time, the specific resistance of the bonded magnet was about 10 to 30 Ω · cm.

Next, each of these Sm ₂ Co ₁₇ bonded magnets was processed into a shape having the same cross-sectional shape as the center magnetic leg of the EE core 2 which is a ferrite core shown in FIG. Magnetization was performed with a magnetic field of 4T using a machine.

Next, a magnetic path length of 7.5 cm and an effective area of 0.74 cm made of a general MnZn ferrite material.
^A 1.5 mm magnetic gap was formed in the center leg of the EE core 2 (FIG. 1). In the gap, the Sm prepared above was used.
_{A 2} Co ₁₇ bonded magnet 1 was inserted and arranged to produce a magnetic core as shown in FIG. In the figure, 1 is a bond magnet, and 2 is a ferrite core (EE core).

Next, the magnetic core manufactured as described above includes:
As shown in FIG. 1B, the coil 3 was wound to obtain an inductance component. An alternating current (100 k
Hz) and DC are superimposed and applied, and the DC superimposition characteristic is measured by an LCR meter, and the core constant (core dimension) and the coil 3 are measured.
Was calculated from the number of windings. Changes in the applied DC magnetic field Hm and changes in the effective magnetic permeability μ due to the superimposed DC are shown by black circles in FIG. After the measurement, the sample was held in a constant temperature bath at 270 ° C., which is the condition of a reflow furnace, for 1 hour, cooled to room temperature, and left for 2 hours. 2 is indicated by a white circle.

As a comparative example, the above Sm ₂ Co ₁₇
A bonded magnet in which the surface magnetizing powder was not subjected to a surface oxidation treatment was also prepared and measured in the same manner as above, and the measurement results were also shown in FIG.
Shown in In FIG. 2, black triangles indicate DC superimposition characteristics when the powder is not processed, and white triangles indicate
9 shows a DC superimposition characteristic after reflowing without treating a powder.

FIG. 2 shows that the sample subjected to the surface oxidation treatment has less deterioration of the DC superposition characteristics even after reflowing than the sample not subjected to the surface oxidation treatment. Also, regarding the demagnetization rate of the magnet, the sample subjected to the surface oxidation treatment was less deteriorated than the sample not subjected to the surface oxidation treatment. This is considered to be because the oxide layer formed on the surface suppressed oxidation during reflow.

Further, in the above embodiment, the surface oxidation treatment by heat treatment was described, but the surface oxidation treatment method is not limited to this, and those skilled in the art can easily presume that acid treatment or the like can be performed. I can do it.

(Second Embodiment) In the magnetic core according to the second embodiment of the present invention, as in the first embodiment, Sm ₂ Co _{17 is used} as a permanent magnet for magnetic bias.
A system bond magnet was used. More specifically, as a raw material for the bonded magnet, an average particle size of about 5 as in the first embodiment is used.
Sm ₂ Co _17- based magnet powder of about μm was used. Book second
In the first embodiment, a heat treatment was performed for 1 hour in 1 atm of ammonia in order to form a thin nitride layer on the very surface of the Sm ₂ Co _17- based magnet powder. Then, it was cooled to room temperature. Each of the bonded magnets was manufactured by mixing the powder thus obtained and an epoxy resin as a binder in an amount of 40 vol%, and then performing mold molding without a magnetic field.
At this time, the specific resistance of the bonded magnet was about 10 to 30 Ω · cm.

Next, magnetization is performed in the same manner as in the first embodiment, and the EE core 2 is formed in the same manner as in the first embodiment.
The above-prepared Sm ₂ Co ₁₇ bonded magnet 1 was inserted and arranged in the gap formed in the central leg of FIG. 1 (FIG. 1), and FIG.
As shown in (1), a magnetic core was produced.

Next, the magnetic core thus manufactured is
As shown in FIG. 1B, the coil 3 was wound to obtain an inductance component. An alternating current (100 k
Hz) and DC were superimposed and applied, the DC superposition characteristics were measured with an LCR meter, and the effective magnetic permeability μ was calculated from the core constant and the number of turns of the coil 3. Changes in the applied DC magnetic field Hm and changes in the effective magnetic permeability μ due to the superimposed DC are shown by black circles in FIG. The sample after measurement is kept in a constant temperature bath at 270 ° C., which is the condition of a reflow furnace, for 1 hour, cooled to room temperature,
After standing for 2 hours, the DC superposition characteristics measured by the LCR meter in the same manner as above are similarly shown by white circles in FIG.

As a comparative example, the Sm ₂ Co ₁₇
A bonded magnet in which surface nitriding was not performed on the base magnet powder was also prepared and measured in the same manner as above, and the measurement results were also shown in FIG.
Shown in In FIG. 3, black triangles indicate DC superimposition characteristics when the powder is not treated, and white triangles indicate
9 shows a DC superimposition characteristic after reflowing without treating a powder.

Further, the flux demagnetization ratios of the magnets of the second embodiment and the comparative example before and after reflow were measured. The results are shown in Table 1 below.

[0037]

[Table 1]

FIG. 3 shows that the sample subjected to the surface nitriding treatment has less deterioration of the DC bias characteristics even after reflowing than the sample not subjected to the surface nitriding treatment. Also, from Table 1, with respect to the demagnetization rate of the magnet, the sample subjected to the surface nitriding treatment showed less deterioration than the sample not subjected to the surface nitriding treatment. This is considered to be because the nitrided layer formed on the surface suppressed oxidation during reflow, similarly to the first embodiment.

In the second embodiment, surface nitriding by heat treatment in ammonia has been described. However, the method of surface nitriding is not limited to this, and heat treatment in nitrogen, nitrate bath treatment, or the like can be used. This can be easily inferred by those skilled in the art.

(Third Embodiment) In a third embodiment of the present invention, the surface oxidized powder used in the first embodiment and the surface-untreated powder used in the comparative example are used. 10 vol%, 20 vol%, 30 vol%, 4
0 vol% of an epoxy resin was mixed, and a bonded magnet was produced by molding.

Next, it was processed into the same shape as in the first embodiment, pulse-magnetized, the flux before and after reflow was measured, and the demagnetization rate after reflow was calculated. Table 2 shows the results.

[0042]

[Table 2]

From Table 2, it can be seen that in the powder subjected to the surface oxidation treatment, the binder was 20 vol% and the demagnetization rate was small. The direct current superposition characteristics were also measured by the same method as in the first embodiment, but the powder subjected to the surface oxidation treatment showed good results even after reflow. From the above, it was found that when the powder subjected to the surface oxidation treatment was used, good results were obtained with a binder amount of 20 vol% or more.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications and changes can be made without departing from the spirit of the present invention.
Deformation is possible. For example, in the above-described embodiment,
Although the surface oxidation treatment and the surface nitridation treatment have been exemplified, the same effect can be obtained for the surface carbonization treatment by heat treatment in carbon monoxide, carbon dioxide, or a mixture with a carbide. Further, as a matter of course, a material other than the nitride layer, the carbide layer and the oxide layer may be used as the oxidation suppressing layer for suppressing the oxidation during the reflow.

[0045]

As described above, according to the present invention, a magnetic core having a gap at at least one position in a magnetic path, and a magnet for a magnetic bias in the gap for supplying a magnetic bias from both ends of the gap. In the magnetic core, the magnet for the magnetic bias has an intrinsic coercive force of 10 kOe.
As described above, a rare earth magnet powder having a Curie temperature Tc of 500 ° C. or more and a powder average particle size of 2.5 to 50 μm, and an oxidation suppression layer such as a nitride layer, a carbide layer, and an oxide layer is formed only on the surface of the powder. By using a bonded magnet made of the rare earth magnet powder and the binder resin, it is possible to obtain a magnetic core having excellent DC superposition characteristics with little thermal demagnetization even after reflow.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a magnetic core according to an embodiment of the present invention and a sectional view showing a choke coil using the same.

FIG. 2 shows a bonded magnet using a magnetic powder subjected to a surface oxidation treatment according to the first embodiment of the present invention and a bonded magnet using a magnetic powder not subjected to a surface treatment, each of which is a ferrite core as a magnetic bias magnet. 6 is measurement data showing a change in DC superimposition characteristics before and after reflow of a magnetic core inserted in FIG.

FIG. 3 shows a bond magnet using a magnetic powder subjected to surface nitridation according to the second embodiment of the present invention and a bond magnet using a magnetic powder not subjected to surface treatment applied to a ferrite core as a magnet for magnetic bias. It is measurement data showing a change in DC superimposition characteristics before and after reflow of an inserted magnetic core.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet for magnetic bias 2 Ferrite core (EE core) 3 Coil

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Haruki Hashi 6-7-1, Koriyama, Taishiro-ku, Sendai, Miyagi Prefecture Tokinnai Co., Ltd. (72) Keita Isoya 7-7-1, Koriyama, Tashiro-ku, Sendai, Miyagi Prefecture No. Tokinnai Co., Ltd. (72) Inventor Toru Ito 6-7-1, Koriyama, Taishiro-ku, Sendai-shi, Miyagi F-term (reference) 5E040 AA03 AA06 BB03 CA01 HB11 HB14 HB17 NN12 NN18

Claims (7)

[Claims] 1. A magnetic core having a gap at at least one position in a magnetic path, the magnetic core having a magnetic bias magnet in the gap for supplying a magnetic bias from both ends of the gap. The magnet is a bonded magnet comprising a rare earth magnet powder having a specific coercive force of 10 kOe or more and a Curie temperature of 500 ° C. or more and a resin having an average particle diameter of 2.5 to 50 μm and a binder resin, and the bonded magnet is formed of A magnetic core having a magnet for magnetic bias, wherein an oxidation suppressing layer for suppressing oxidation during reflow is formed only on the surface of a rare earth magnet powder. 2. The magnetic core having the magnet for magnetic bias according to claim 1, wherein the oxidation suppressing layer is at least one selected from a nitride layer, a carbide layer, and an oxide layer. A magnetic core having a magnetic bias magnet. 3. The magnetic core having the magnet for magnetic bias according to claim 1, wherein the bond magnet contains the binder resin in a volume ratio of 20% or more, and has a specific resistance of 1 Ωcm or more. A magnetic core having a magnetic bias magnet. 4. An inductance component, wherein at least one winding of one or more turns is applied to a magnetic core having the magnet for magnetic bias according to claim 1. 5. A magnet for magnetic bias having a gap at at least one position of a magnetic path and inserted into the gap to supply a magnetic bias from both ends of the gap, wherein a specific protection of 10 kOe or more is provided. A bonded magnet comprising a rare earth magnet powder having a magnetic force and a Curie temperature of 500 ° C. or more and a powder average particle diameter of 2.5 to 50 μm and a binder resin, wherein the bonded magnet is provided only on the surface of the rare earth magnet powder. A magnet for magnetic bias, wherein an oxidation suppression layer for suppressing oxidation during reflow is formed. 6. The magnetic biasing magnet according to claim 5, wherein the oxidation suppressing layer is at least one layer selected from a nitride layer, a carbide layer, and an oxide layer. Bias magnet. 7. The magnet for magnetic bias according to claim 5, wherein the bond magnet contains the binder resin in a volume ratio of 20% or more, and has a specific resistance of 1Ωc.
m or more.