JP2003109809A - Magnetic core and inductance component using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic core, which has a superior direct current overlapping characteristic, a good frequency characteristic, superior oxidation resistance and rust prevention. SOLUTION: In the magnetic core 1 having gaps 13 at least at one or more places of a magnetic path, a bonded magnet 15 composed of rare earth magnet powder, which has an intrinsic coercive force of 10 KOe or more, a Tc of 500 deg.C or higher, and a powder average particle diameter of 2.5-50 μm, and resin, where resistivity is 1 Ωcm or more, flux variation at 300 deg.C is equal to or less than 5%, and a flux variation after a salt water spray test for 96 hrs is equal to or less than 1%, are inserted in the gaps 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic core used for a switching power supply or the like, and more particularly to a magnetic core used as a choke coil or a transformer.

[0002]

2. Description of the Related Art Good direct current superimposition characteristics are required for magnetic cores for choke coils and transformers.
Ferrite cores and dust cores are used for high-frequency cores. The ferrite magnetic core has a high initial permeability and a small saturation magnetic flux density. Further, the dust core has a characteristic derived from the physical properties of the material that the initial magnetic permeability is low and the saturation magnetic flux density is high.

Therefore, the dust core is often used in a toroidal shape. Ferrite is, for example, two E
Often used as an EE core with a gap between the middle legs of the mold core.

However, with the recent demand for miniaturization of electronic parts in response to the demand for miniaturization of electronic equipment, there is a strong demand for higher magnetic permeability in a larger superimposed magnetic field. In general, in order to improve the DC superposition characteristics, it is essential to select a magnetic core with high saturation magnetization, that is, to select a magnetic core that is not 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.
Therefore, the conventional means for improving the DC superimposition characteristic is that the DC superimposition characteristic does not extend as much as expected, although much effort is spent on improving the saturation magnetization. It was

As a means for solving the problem, it has been conventionally studied to insert the permanent magnet into the gap formed in one or more places of the magnetic path. The method of inserting a permanent magnet into such a gap is an excellent method for improving the DC superposition characteristics. However, on the other hand, when a sintered metal magnet is used, the core loss of the magnetic core is significantly increased. In addition, the use of ferrite magnets was not practical enough because the superposition characteristics were not stable.

Further, as means for solving these problems, for example, in Japanese Patent Laid-Open No. 50-133453 (Prior Art 1),
It has been disclosed that a rare-earth magnet powder having a high coercive force and a binder are mixed and compression-molded is inserted as a permanent magnet, and it is shown that the DC superposition characteristics and the temperature rise of the core are improved.

[0008]

However, in recent years, the demands for improving the power conversion efficiency of the power source have become more and more strict, and the magnetic core for choke coils and the magnetic core for transformers are superior or inferior simply by measuring the core temperature. Is an undecidable level. Therefore, it is indispensable to judge the measurement result by the core loss measuring device, and as a result of actually examining it, it became clear that the core loss characteristic is deteriorated at the resistivity value disclosed in the above-mentioned Prior Art 1. .

Recently, a surface mount type coil has been desired, and an oxidation resistant rare earth powder is essential for such a core. However, it is known that rare earth powders and metal powders rust under a harsh environment containing salt.

In view of the above problems, an object of the present invention is to easily and inexpensively provide a magnetic core having excellent DC superposition characteristics, core loss characteristics, oxidation resistance and rust resistance.

[0011]

According to the present invention, there is provided a magnetic core having a gap at least at one or more points in a magnetic path, the bond magnet being inserted in the gap, the bond magnet having an intrinsic coercive force. Is 10 KOe or more, Curie point temperature is 500 ° C. or more, and the powder has an average particle diameter of 2.5 to 50 μm and is composed of a rare earth magnet powder and a resin, and has a specific resistance of 1 Ω.
cm or more, the amount of flux change at 300 ° C is 5% or less,
A magnetic core is obtained which has a flux variation of 1% or less after 96 hours of the salt spray test.

Further, according to the present invention, there is obtained an inductance component characterized in that the magnetic core is provided with at least one winding having one or more turns.

[0013]

[Function] As a result of studying a permanent magnet to be inserted into a gap, the magnet has a specific resistance of 1 Ω · cm or more and an intrinsic coercive force of 1
It has been found that when a permanent magnet of 0 KOe or more is used, excellent DC superposition characteristics can be obtained, and a magnetic core can be formed without deterioration of core loss characteristics. This is because the magnet characteristics required to obtain excellent DC superposition characteristics are
Rather, it is the intrinsic coercive force. Therefore, it was found that even if a permanent magnet having a high specific resistance is used, a sufficiently high DC superposition characteristic can be obtained if the intrinsic coercive force is high.

A magnet having a high specific resistance and a high intrinsic coercive force is generally obtained by a rare earth bonded magnet formed by mixing rare earth magnet powder with a binder. What kind of magnet powder has a high coercive force? It is also possible to have a different composition.

The types of rare earth magnet powder are SmCo type and N type.
Although there are dFeB type and SmFeN type, the Curie temperature Tc is 500 ° C. in consideration of reflow conditions and oxidation resistance.
As described above, a magnet having a coercive force of 10 KOe or more is required, and at present, the magnet is limited to the Sm2Co17 system magnet. Furthermore, as a result of various studies on the improvement of the oxidation resistance of the bonded magnet, it was found that Zn, Al, Bi, G was formed on the surface of the rare earth magnet powder.
By coating with one of a, In, Mg, Pb, Sb, and Sn or an alloy that is a combination of these selected,
It was revealed that the oxidation resistance was improved. Further, as a result of various studies on the rust preventive property, it was found that the rust preventive property is improved by oxidizing the surface of the coated layer. Further, it was revealed that the rust prevention property is improved by further coating with a resin.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a magnetic core of the present invention and an inductance component using the magnetic core will be described below. FIG. 1 shows a magnetic core according to an embodiment. FIG. 2 shows an inductance component according to one embodiment.

With reference to FIGS. 1 and 2, a magnetic core 1 according to one embodiment has a gap 13 at least at one or more locations on a magnetic path 11. A bond magnet 15 is inserted in the gap 13 of the magnetic core 1. Bond magnet 15
Is a permanent magnet for DC magnetic bias.

The bond magnet 15 has an intrinsic coercive force of 10
It is composed of a rare earth magnet powder having a KOe or more, a Curie point temperature Tc of 500 ° C. or more, and a powder average particle diameter of 2.5 to 50 μm, and a resin. Furthermore, the specific resistance of the bond magnet 15 is 1 Ωcm or more, and the amount of flux change at 300 ° C. is 5
% And the amount of flux change after 96 hours of the salt spray test is 1% or less.

The surface of the rare earth magnet powder is Zn, Al, B.
It has a coating layer coated with one of i, Ga, In, Mg, Pb, Sb and Sn or an alloy thereof. The surface of the coating layer is an oxide layer.

Further, the rare earth magnet powder is previously coated with 1.0 to 15% by volume of coating resin.
The type of coating resin used is one selected from polyamide-imide resin, polyimide resin, and epoxy resin, and the total amount of resin is 20% by volume.
That is all.

The magnetic core 1 is, as shown in FIG.
An inductance component can be obtained by providing at least one winding 17 of one turn or more.

As a magnetic core for a choke coil or a magnetic core for a transformer, any material having a soft magnetic property is effective, but in general, a MnZn-based or NiZn-based ferrite, a powder magnetic core, a silicon steel plate, an amorphous material. Etc. are used. The shape of the magnetic core 1 is not particularly limited, and the present invention can be applied to magnetic cores of any shape such as a toroidal core, EE core, and EI core. The bond magnet 15 in this embodiment is an SmCo bond magnet inserted in the center of the EE type ferrite core.

The length of the gap 13 between the middle legs of the bond magnet 15 (the middle leg of the EE core) is not particularly limited, but if the gap length is too narrow, the DC superimposition characteristics deteriorate and the gap length also increases. If it is too wide, the magnetic permeability will drop too much, so the gap length to be naturally inserted will be determined.

Next, in the required characteristics of the bond magnet 15 inserted in the gap 13, if the intrinsic coercive force is set to 10 KOe or less, the coercive force disappears due to the DC magnetic field applied to the magnetic core 1, so that the coercive force higher than that. is necessary.

The average maximum particle size of the rare earth magnet powder is 5
Since core loss characteristics deteriorate when the particle size is 0 μm or more, the maximum particle size of the rare earth magnet powder is preferably 50 μm or less, and when the minimum particle size is 2.5 μm or less, the magnetization due to the oxidation of the powder during the powder heat treatment and reflow decreases. Since it becomes remarkable, a particle size of 2.5 μm or more is required.

Here, in order to improve the oxidation resistance of the powder, Zn, Al, Bi, Ga,
It is preferably covered with a coating layer of one of In, Mg, Pb, Sb and Sn or an alloy thereof.

However, it is easily inferred that the rare earth magnet powder and the metal powder rust under a harsh environment containing salt,
Rust causes flux deterioration and dimensional change. Therefore, in order to improve rust prevention, the surface of the coating layer is oxidized to obtain a magnetic core having rust prevention, oxidation resistance, high characteristics, and high specific resistance. It is considered that this is because the formation of the oxide makes it more difficult to form chloride than the metal.

Further, by coating the above rare earth magnet powder with a coating resin of 1.0 to 15% in volume ratio in advance, a magnetic core having a balance of rust resistance, oxidation resistance, high characteristics and high specific resistance can be obtained. can get. At this time, the reason for defining the amount of the coating resin is that if it is 1.0 vol% or less, the coating is insufficient and the specific resistance is almost the same as that without coating. If it is 15 vol% or more, it becomes difficult to disintegrate after coating the coating resin. This is because.

Therefore, if the volume ratio of the coating resin is 1.0 to 15%, rust resistance, oxidation resistance, high characteristics,
A magnetic core having both high specific resistance can be obtained. Any coating resin may be used as long as it has heat resistance of 270 ° C. or higher. The coating method of the coating resin is a pressure kneader,
Anything can be used as long as it can be kneaded, such as a liquor machine, and these kneaded materials are hardened and crushed into powder. Further, it is easily inferred that the coating resin can be more uniformly coated by lowering the viscosity of the coating resin with a solvent or the like. Further, uniform coating can be achieved by increasing the number of times the coating resin is coated.

Example 1 For the rare earth magnet powder of the bond magnet 15, 3 wt% of Zn metal powder (powder average particle diameter of about 5 μm) was mixed with Sm—Co magnet powder (powder average particle diameter of about 5 μm) in an Ar atmosphere. In 5
The magnet powder used was heat treated at 00 ° C. for 2 hours. This powder was subjected to oxidation treatment for 1 hr in Air (air) at 200 ° C. in a constant temperature bath.

The produced powder was mixed with an epoxy resin in an amount equivalent to 45 vol% of the total volume, and then pressed in a non-magnetic field to form a bond magnet 15 processed into a shape of 10 mm × 7.0 mm × 1.5 mm to about 10 T. The magnetic field was magnetized in the direction of the magnetic path with the pulsed magnetic field, and the specific resistance and the flux of this bond magnet 15 were measured before and after the reflow. Further, in order to investigate rust, a 96 hr salt water spray test was performed in a 100% atmosphere in which a 5% salt water solution was sprayed at 35 ° C., and changes in the flux before and after the salt water spray test and visual changes were examined.

Here, each bonded magnet 1 in Example 1
The specific resistance of No. 5 is shown in Table 1.

[0033]

[Table 1]

Table 2 shows the results of the flux of each bonded magnet 15.

[0035]

[Table 2]

Table 3 shows the test results of the flux and appearance change of each bonded magnet 15 before and after salt spray.

[0037]

[Table 3]

Next, an EE having a magnetic path length of 7.5 cm and an effective area of 0.74 cm made of a Mn-Zn ferrite material.
1.5 mm at the center of the core (see magnetic core 1 shown in FIG. 1)
The bonded magnet 15 processed into the shape of the gap 13 was magnetized in the direction of the magnetic path 11 with a pulse magnetic field of about 10 T, and then inserted into the gap 13. Bond magnet 15
Winding 17 was applied to the inserted magnetic core 1, and the DC superposition characteristics were measured with an LCR meter, and it was confirmed that there was no deterioration in the DC superposition characteristics due to the powder oxidation treatment. This was similar to the change in flux.

Further, the frequency characteristic of μ was measured with HP4194A, and it was confirmed that μ was extended to a high frequency in the sample subjected to the powder oxidation treatment. This was similar to the change in resistivity.

Further, in Tables 1 to 3, as comparative examples, bonded magnets in which the powder was not subjected to oxidation treatment were also prepared in the same manner as above and shown in the respective tables. As is clear from Table 3, it was revealed that by oxidizing the powder, the specific resistance was improved without changing the flux, and the change in appearance also improved the rust preventive property in Example 1.

From the above, it was found that in Example 1, the magnetic core 1 having excellent characteristics of high corrosion resistance and high specific resistance was obtained by the powder oxidation treatment.

Example 2 As for the rare earth magnet powder of the bonded magnet 15, Sm-Co magnet powder (powder average particle diameter of about 5 μm) was added to Zn as in Example 1.
3 wt% of metal powder (powder average particle size of about 5 μm) was mixed,
The magnet powder used was heat-treated at 500 ° C. for 2 hours in an Ar atmosphere. This powder was placed in a constant temperature bath 20 as in Example 1.
Oxidation treatment was performed for 1 hr at 0 ° C. Air. Polyamide-imide resin (solid content ratio 15%) was added to this powder by NMP.
The solution diluted 0 times is 10 vol% in terms of solid content ratio of resin.
Kneading was performed using a pressure kneader.

Thereafter, the kneaded product was subjected to preliminary drying by volatilizing the solvent at 80 ° C., and the lump was crushed by a liquor machine to be powdered, and the main curing was carried out at 220 ° C. for 30 minutes. A binder (PAI resin) was mixed with these resin-coated powders so that the total volume would be 50 vol%, to prepare a slurry having a viscosity of about 300P.

This slurry was used for 1 with a doctor blade device.
A magnet sheet of 00 μm was prepared and processed into the same shape as in Example 1 above. The specific resistance of this magnet sheet was measured, and the results of the specific resistance are shown in Table 4.

[0045]

[Table 4]

A salt spray test was conducted in the same manner as in Example 1.
Table 5 shows the results of investigating changes in the flux before and after the salt spray test and visual changes for 6 hours.

[0047]

[Table 5]

Further, as a comparative example, a magnet sheet which was not subjected to oxidation treatment or resin coating treatment was prepared in the same manner as above and is shown in Table 5.

From Table 4, it was found that the specific resistance was improved by the oxidation treatment and further improved by the resin coating.
Further, from Table 5, it was found that rust can be prevented by the oxidation treatment, but rust can be almost prevented by further applying a resin coating thereon.

Although only the specific resistance is described in the second embodiment, the demagnetization rate is almost the same level, and the frequency characteristic of μ is measured with the ferrite core inserted as in the first embodiment. It has been confirmed that the coated magnet sheet extends the f characteristic up to high frequencies.

As described above, in the embodiment, the oxidation treatment is performed, and the resin coating is further applied thereon to obtain a magnet sheet having a higher specific resistance, which is more excellent in rust prevention.
It was found that a magnetic core with good characteristics can be obtained.

Although Zn was selected as the metal powder in Example 2, any other low melting point metal may be used, for example, A
It is easily inferred that similar effects can be obtained even with 1, Bi, Ga, In, Mg, Pb, Sb, Sn and alloys thereof.

Further, in Example 2, the oxidation treatment was carried out in a 200 ° C. constant temperature bath, but it can be easily inferred that the oxidation treatment can be carried out even at a high temperature by adjusting the oxygen partial pressure as long as the powder does not ignite. .

Further, as the resin to be coated, the epoxy resin and the PAI resin were selected in this embodiment, but it is easily inferred that the same effect can be obtained if it has heat resistance.

[0055]

As described above, according to the present invention,
Powder surface is oxidized, resin coated with intrinsic coercive force of 10 KOe or more and specific resistance of 1 Ωcm or more, 300
5% or less flux change at ℃, salt spray test 96
Excellent direct current superposition characteristics can be obtained by inserting a bonded magnet having a flux change amount of 1% or less after hr and having no noticeable change in appearance into the gap of the magnetic core.

Further, according to the present invention, it is possible to obtain a magnetic core having excellent frequency characteristics of μ and excellent in oxidation resistance and rust resistance.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a magnetic core according to the present invention.

FIG. 2 is a front view showing an inductance component obtained by winding a winding on the magnetic core shown in FIG. 1, and showing the winding in cross section.

[Explanation of symbols] 1 magnetic core 13 gap 15 Bond magnet 17 windings

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22F 1/02 B22F 1/02 G C08K 9/02 C08K 9/02 9/04 9/04 C08L 101/00 C08L 101/00 H01F 27/24 H01F 27/24 W 38/02 37/02 27/24 J (72) Inventor Haruki Haruki 6-7 Koriyama, Taichiro-ku, Sendai-shi, Miyagi Tokinai Co., Ltd. (72) Inventor Keita Isoya 6-7-1, Koriyama, Taihaku-ku, Sendai-shi, Miyagi Tokin Co., Ltd. F-term (reference) 4J002 AA001 CD001 CM041 DC006 FB076 FB266 FD206 GQ00 4K018 AA11 AA27 BC21 BC28 BC29 BC33 BC35 BD01 CA09 CA11 A03 BC01 5E040 NN01 NN13

Claims (5)

[Claims] 1. A magnetic core having a gap at least at one or more locations in a magnetic path, comprising a bond magnet inserted in the gap, the bond magnet having an intrinsic coercive force of 10 KOe.
As described above, a rare earth magnet powder having a Curie point temperature of 500 ° C. or more and an average particle diameter of powder of 2.5 to 50 μm and a resin,
Further, the magnetic core has a specific resistance of 1 Ωcm or more, a flux change amount at 300 ° C. of 5% or less, and a flux change amount after the salt spray test 96 hours of 1% or less. 2. The magnetic core according to claim 1, wherein Zn, Al, Bi, Ga, In, M is formed on the surface of the rare earth magnet powder.
A magnetic core comprising a coating layer coated with one of g, Pb, Sb and Sn or an alloy thereof, and the surface of the coating layer is an oxide layer. 3. The magnetic core according to claim 1 or 2, wherein the rare earth magnet powder is previously coated with a coating resin in a volume ratio of 1.0 to 15%. 4. The magnetic core according to claim 3, wherein the type of the coating resin used is one selected from a polyamideimide resin, a polyimide resin, and an epoxy resin, and the total coating resin amount is a volume ratio. A magnetic core characterized by being 20% or more. 5. An inductance component, wherein the magnetic core according to any one of claims 1 to 4 is provided with at least one winding having one or more turns.