JP2003332111A - Magnetic core and inductance component using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic core whose hysteresis loss is reduced in order to cope with the requirement for downsizing an electronic apparatus to contain an excellent core loss characteristic and a DC superimposing characteristic, and moreover which contains an oxidation resistance, and an inductance part using the same. <P>SOLUTION: A sheet-like bonded magnet is composed of the powder of a pulverized magnet having an intrinsic coercive force of 800 kA/m and the Curie temperatures of 300°C or above and a binder material, and has a squareness ratio of 60% or above by a magnetic field distribution. The bonded magnet is inserted into a gap provided in a magnet circuit of the magnetic core. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnetic core and an inductance component using the magnetic core.

[0002]

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

Therefore, the dust core is often used in a toroidal shape, and the ferrite core has a gap in the butted portion of the middle leg when the three magnetic legs of the E-shaped magnetic core are butted. Are often used in the EE type as they are formed. However, due to the recent demand for miniaturization of electronic components accompanying the demand for miniaturization of electronic devices, higher magnetic permeability in a larger superimposed magnetic field is strongly required.

In general, in order to improve the direct current superposition characteristic, it is essential to select a magnetic core having a high saturation magnetization, that is, a magnetic core which 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 made higher than the theoretical value. for that reason,
Conventionally, improvement of the saturation magnetization has been studied as a means for improving the DC superposition characteristic, but the expected DC superposition characteristic has not been obtained despite the large amount of labor. Met.

As a means for solving the problem, a method of inserting a gap at one or more places of a magnetic path and inserting a permanent magnet into the gap has been conventionally studied. This method is an excellent method for improving the DC superimposition characteristics, but on the other hand, the use of a sintered metal magnet significantly increases the core loss of the magnetic core, and the use of a ferrite magnet does not stabilize the superposition characteristics.
It wasn't very practical.

As a means for solving these problems, for example, in Japanese Unexamined Patent Publication (Kokai) No. 50-133453, a bonded magnet obtained by compression molding a mixture of a rare earth magnet powder having a high coercive force and a binder is inserted as a permanent magnet. It is disclosed that the direct current superposition characteristic and the temperature rise of the core are improved.

However, in recent years, the demand for improving the power conversion efficiency of the power source is becoming more and more severe, and it is impossible to judge the superiority or inferiority of the magnetic cores for choke coils and transformers simply by measuring the temperature change of the magnetic cores. It is a level. Therefore, the judgment of the measurement result by the core loss measuring device is indispensable, and as a result of the actual study by the present inventors, the core loss characteristic may be deteriorated at the resistivity value disclosed in Japanese Patent Laid-Open No. 50-133453. It was revealed.

Therefore, the inventors of the present invention have made a study as far as 800 k as a permanent magnet to be inserted into the gap.
By inserting a permanent magnet having an intrinsic coercive force of A / m or more, a Curie temperature of 300 ° C. or more (hereinafter referred to as Tc) and a specific resistance of 1 Ω · cm or more, without reducing core loss,
It has been found that good DC superposition characteristics can be obtained. Further, in recent years, there is a great demand for surface mount type coils, and oxidation resistant rare earth powders are indispensable for such magnetic cores.

[0009]

However, the studies so far have focused on reducing the eddy current loss by improving the specific resistance, and there is still room for studying the reduction of the hysteresis loss. Therefore, in order to solve the above-mentioned problems, the technical problem of the present invention is to provide a magnetic core that reduces hysteresis loss, has excellent core loss characteristics and DC superposition characteristics, and has oxidation resistance as well. Is to provide.

[0010]

In order to solve the above-mentioned problems, the present invention examines a permanent magnet to be inserted, and sets the specific resistance of the permanent magnet to be inserted into the gap of the magnetic path to be 1 Ω · cm or more, and the intrinsic coercive force. Was set to 800 kA / m or more, it was found that an excellent direct current superposition characteristic can be obtained and a magnetic core without deterioration of core loss characteristics can be formed. This is because the magnet characteristic required to obtain excellent DC superposition characteristics is the intrinsic coercive force rather than the energy product. Therefore, even if a permanent magnet with a high specific resistance is used, it is sufficient if the intrinsic coercive force is high. This is due to the finding that extremely high DC superposition characteristics can be obtained.

That is, according to the present invention, the height of the gap provided in at least one position of the magnetic path is 90 times the gap width.
% Or less, the permanent magnet is obtained by crushing a rare earth magnet having an intrinsic coercive force of 800 kA / m or more and a Tc of 300 ° C. or more into an average particle size of 2.5 to 50 μm. Made of powder and binder, and has a squareness ratio of 6
It is a magnetic core characterized by being a bonded magnet of 0% or more.

Further, according to the present invention, in the magnetic core, the bonded magnet has an amount of a binder of 20% or more by volume and a specific resistance of 1 Ω · cm or more. .

Further, the present invention is an inductance component characterized in that the magnetic core is provided with a winding of at least 0.5 turns or more.

As a magnet having a high specific resistance and a high coercive force, a rare earth bonded magnet formed by mixing rare earth magnet powder with a binder is generally mentioned. , Any composition is possible. Of these, the type of rare earth magnet is S
Examples include mCo type, NdFeB type, and SmFeN type. In consideration of reflow conditions and oxidation resistance, Tc is required to be 300 ° C. or higher and coercive force is 800 kA / m or higher.
At present, it is limited to Sm ₂ Co ₁₇ system magnets.

As a result of further studies on the reduction of hysteresis loss, it was found that the hysteresis loss of the magnetic core is reduced by improving the squareness ratio of the magnet inserted in the gap. The reason for this is that the hysteresis loss is generally the area of the hysteresis loop in the case of soft magnetic materials, but it is the area of the minor loop in the case of permanent magnets, and the area of the minor loop is reduced by improving the squareness ratio. It is understood that it will be.

As the magnetic core for the choke coil and the transformer, any material having a soft magnetic property can be used, but in general, MnZn or NiZn ferrite, dust core, silicon steel plate, amorphous alloy. Are used. Further, the shape of the magnetic core is not particularly limited, and the present invention can be applied to magnetic cores of all shapes such as a toroidal magnetic core, an EE magnetic core, and an EI magnetic core.

Further, in the present invention, a gap is provided in at least one position of the magnetic path of these magnetic cores and a permanent magnet is inserted into the gap, but the gap width is not particularly limited. However, if the gap width is too narrow, the DC superimposition characteristics deteriorate, and if the gap width is too wide, the required permeability cannot be obtained, so the gap width is naturally limited.

Next, referring to the required characteristics of the permanent magnet inserted in the gap, with respect to the intrinsic coercive force, if the magnetic coercive force is less than 800 kA / m, the coercive force disappears due to the direct-current magnetic field applied to the magnetic core, so that the intrinsic coercive force higher than that is required. Coercive force is required, and the larger the specific resistance, the better, but 1Ω ・
If it is cm or more, it does not become a major factor of deterioration of eddy current loss.

If the average particle size of the powder exceeds 50 μm, the core loss characteristic deteriorates, so the average particle size of the powder is 5 μm.
It is desirable that the average particle diameter is 2.5 μm or less.
If it is less than m, the decrease in magnetization due to the oxidation of the powder during the powder heat treatment and the reflow becomes remarkable, so that the average particle size of 2.5 μm or more is required.

Further, in the present invention, since the bond magnet is inserted into the gap of the magnetic core, the shape of the bond magnet is a sheet. In order to obtain a sheet-shaped bond magnet, an extrusion molding method, a press molding method, an injection molding method, a coating method or the like can be used. By applying a magnetic field to the bond magnet during molding, the magnet powder can be oriented and the characteristics can be improved.

Here, referring to the magnetic field orientation method, the molding method includes an extrusion molding method, a press molding method, and an injection molding method. In the case of the press molding method, even if a magnetic field is applied at the time of molding, it is very special. There is no problem, but in the case of a sheet-shaped magnet produced by the coating method, the binder is not cured because the slurry in which the magnet powder is dispersed is applied to the liquid binder solution or the solid binder solution. If a magnetic field is applied in this state, the powder will be arranged in the direction of the magnetic field, resulting in a sheet full of holes.

For this purpose, for example, a method of gradually increasing the temperature and gradually curing the binder so as to increase the strength of the applied magnetic field in accordance with the degree of curing of the sheet is suitable.

According to such a method, a magnet having a squareness ratio of 60% or more can be obtained. The reason why the squareness ratio is limited is that the hysteresis loss is hardly reduced when the squareness ratio is less than 60%. In the present invention, the amount of the binder is limited to 20% or more by volume because the amount less than this causes insufficient binding of the magnet powder and makes it difficult to maintain the shape of the bonded magnet. Is. Further, the height of the bond magnet is set to 90% or less of the gap width because the workability of insertion is lowered at a height higher than this.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described.

As described above, the Sm ₂ Co ₁₇ system magnet is mainly used in the present invention due to the restriction of the magnetic characteristics. This is ground to an average particle size of 2.5 to 50 μm, and a jaw crusher or the like can be used for coarse grinding and a ball mill or the like can be used for fine grinding. When dry pulverization is performed, it is desirable to perform pulverization in a non-oxidizing atmosphere in order to prevent characteristic deterioration due to oxidation.

The method of mixing the magnet powder and the binder is as follows.
If the binder is a solid thermoplastic polymer material, a pressure kneader, roll, etc. can be used, and if the binder is a liquid thermosetting polymer material or solution, a three roll mill, homogenizer, sand mill. Etc. can be used. Then, the sheet-shaped bonded magnet obtained by the above method is used by inserting it into the gap provided in the magnetic core.

[0027]

EXAMPLES Next, examples of the present invention will be described with reference to specific examples.

(Example 1) Energy product is about 223 kJ
/ M ³ Sm ₂ Co ₁₇ system sintered magnet was roughly crushed with a jaw crusher and then finely crushed with a ball mill to obtain D ₅₀ = 15μ.
m powder was produced. Next, the volume ratio of the Sm ₂ Co ₁₇ system magnet powder and the polyamide-imide resin was 50% after drying, respectively, so that the Sm ₂ Co ₁₇ system magnet powder and the polyamide-imide resin (manufactured by Toyobo: Bilomax HR11
NN) was weighed, n-methylpyrrolidone was added as a solvent, and the mixture was stirred for 5 minutes with a circular defoamer and then kneaded with three rolls to prepare a slurry. The compounding ratio of the solvent is Sm ₂ Co ₁₇
The ratio of the total weight of the system magnet powder and the polyamide-imide resin to the weight of the solvent was set to 70/10.

Next, the prepared slurry was inserted between the pole pieces of the electromagnet as a green sheet having a thickness of 300 μm by the doctor blade method, and was initially 0.05.
A magnetic field of T was applied and orientation was performed for 5 minutes. Next, warm air having a temperature of 50 ° C. was blown on the green sheet for 5 minutes to cure the vicinity of the surface and increase the applied magnetic field,
It was set to 0.1T, 0.2T, 0.4T and 0.8T.

Although the above mixing ratio is used here, the above magnetic field orientation method can be applied as long as a slurry capable of producing a green sheet can be obtained with other components and mixing ratios. . These pre-cured sheets are placed in a drying oven set to a temperature of 200 ° C.,
It was held for 1 hour to carry out main curing to obtain a sheet-shaped bond magnet having a thickness of 265 μm.

Next, the specific resistances of these sheet-like bonded magnets were measured, and it was confirmed that all were 1 Ω · cm or more. Moreover, the squareness ratio was measured with a BH tracer using a sample obtained by punching these into a shape having a diameter of 10 mm and stacking 20 sheets. Table 1 shows the measurement results of the squareness ratio. For the purpose of comparison, Table 1 also shows the measurement results of samples prepared in the same manner as above without applying a magnetic field.

[0032]

[Table 1]

From Table 1, it is apparent that the squareness ratio is improved as compared with the sample to which no magnetic field is applied, and is 60% or more even when the magnetic field is 100 mT. Next, the sheet-shaped bond magnet was cut into a shape of 7.0 × 10.0 mm, and magnetized by applying a pulse magnetic field of 10 T in the thickness direction. And made of general MnZn ferrite material, magnetic path length 7.8 cm, effective area 1.74
A cm ² EE type magnetic core was prepared and processed so that a gap of 300 μm was formed when the middle legs were butted.

Into the gap, a sheet-shaped bond magnet cut into 7.0 × 10.0 mm was inserted and wound.
The DC superposition characteristics were measured. FIG. 1 is a diagram showing the obtained DC superposition characteristics. For comparison, the results obtained by inserting a non-oriented sheet-shaped bond magnet prepared without applying a magnetic field into the gap and measuring the gap alone are also shown in FIG.

Next, the primary winding is made 15 turns and the secondary winding is made 15 turns, and a BH analyzer (Iwasaki Tsushinki: S
The loss characteristic was measured with Y8232). FIG. 2 shows the core loss measurement result when the excitation condition is 50 mT and 200 kHz, and FIG. 3 shows the core loss measurement result when the excitation condition is 50 mT and 500 kHz. For comparison, the results obtained by inserting a non-oriented sheet-shaped bond magnet prepared without applying a magnetic field into the gap and the results obtained by measuring only the gap are also shown in FIGS. 2 and 3. In addition, in FIG. 2 and FIG. 3, the broken line is the measured value in the case of only the gap.

From FIG. 1, it can be seen that the DC superimposition characteristics are significantly improved as compared with only the gap of the comparative example, and extend to a high magnetic field as compared with the case where a non-oriented sheet-shaped bond magnet is inserted. Further, it can be seen from FIGS. 2 and 3 that the core loss decreases as the squareness ratio increases. In particular, when the squareness ratio is 60% or more, it is almost equivalent to the loss characteristic of only the gap. The reason for this is that considering that the resistivity of the sheet-shaped bonded magnet was almost the same in all the samples,
It is considered that the hysteresis loss is reduced by the magnetic field orientation.

From the above results, by inserting a sheet-like bonded magnet having a squareness ratio of 60% or more by magnetically orienting the magnet powder, good DC superimposition characteristics can be obtained without degrading core loss. It turned out to be obtained.

Example 2 Next, an example using a thermosetting polymer material as a binder will be described. Example 1
Similarly, S has an energy product of about 223 kJ / m ³ .
The m ₂ Co ₁₇ system sintered magnet was roughly pulverized and finely pulverized, and D ₅₀ = 15.
A μm powder was prepared. Next, a liquid epoxy resin as a binder is weighed and mixed with this powder so that the volume ratio of the binder and the magnetic powder after curing is 50/50.
It was a mixture for bonded magnets.

This mixture was charged into a mold, and 0.1T, 0.1.
A magnetic field of 2T, 0.4T, 0.8T, and 1.5T was applied in a direction parallel to the press direction for molding, and the binder was cured to produce a bonded magnet. The specific resistance of these bonded magnets was measured, and it was confirmed that all were 1 Ω · cm or more.

Next, regarding these bonded magnets, BH
Squareness was measured using a tracer. Table 2 shows the measurement results of the squareness ratio. For comparison, a sample formed by press molding without applying a magnetic field was measured in the same manner, and the results are also shown in Table 2.

[0041]

[Table 2]

From the results shown in Table 2, the squareness ratio of the bonded magnet molded by applying the magnetic field was improved as compared with the case where the magnetic field was not applied, and when the magnetic field of 200 mT or more was applied,
It can be seen that the squareness ratio is 60% or more.

Next, these bonded magnets were replaced by 7.0 × 10.
It was cut into a shape of 0 × 0.9 mm, and magnetized with a pulse magnetic field of 10 T in the thickness direction. Next, an EE type magnetic core having a magnetic path length of 7.8 cm and an effective area of 1.74 cm ² made of a general MnZn ferrite material was prepared, and a 1 mm gap was formed when the middle legs were butted. Processed as described.

A cut bond magnet was inserted into this gap to measure the core loss characteristics. FIG. 4 shows the core loss measurement result when the excitation condition is 50 mT and 200 kHz,
FIG. 5 shows core loss measurement results when the excitation condition is 50 mT and 500 kHz. For comparison, the results obtained by inserting a non-oriented sheet-shaped bonded magnet prepared without applying a magnetic field into the gap and the results obtained by measuring only the gap are also shown in FIGS. 4 and 5.

From the results shown in FIGS. 4 and 5, it can be seen that the core loss also decreases as the squareness ratio increases, as in the first embodiment. Especially, when the squareness ratio is 60% or more, it is almost the same as the loss characteristic of only the gap.
The result is similar to that of Example 1, and it can be understood that the hysteresis loss is reduced by the magnetic field orientation as in Example 1.

[0046]

As described above, according to the present invention, by inserting a sheet-shaped bond magnet having a squareness ratio of 60% or more into the gap provided in the magnetic path of the magnetic core, hysteresis loss can be reduced. It is possible to obtain a magnetic core which is reduced, has excellent core loss characteristics and direct current superposition characteristics, and is also resistant to oxidation. Therefore, the magnetic core and the inductance component obtained by the present invention can contribute to miniaturization of various electronic devices.

[Brief description of drawings]

FIG. 1 is a diagram showing a DC superposition characteristic.

FIG. 2 is a diagram showing a core loss measurement result when the excitation condition is 50 mT and 200 kHz.

FIG. 3 is a diagram showing a core loss measurement result when the excitation condition is 50 mT and 500 kHz.

FIG. 4 is a diagram showing a core loss measurement result when the excitation condition is 50 mT and 200 kHz.

FIG. 5 is a diagram showing core loss measurement results when the excitation condition is 50 mT and 500 kHz.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Haruki Hoshi             6-7-1 Koriyama, Taihaku-ku, Sendai City, Miyagi Prefecture             NSE Toekin Co., Ltd. F term (reference) 5E040 AA03 BB05 CA01 NN01 NN04                       NN12

Claims (3)

[Claims] 1. A magnetic core in which a permanent magnet having a height of 90% or less of the gap width is arranged in a gap provided in at least one position of a magnetic path, and the permanent magnet has an intrinsic coercive force of 800 kA / m or more, Curie temperature is 300
A magnetic core comprising a powder obtained by crushing a rare earth magnet having a temperature of ℃ or more to an average particle diameter of 2.5 to 50 μm and a binder, and having a squareness ratio of 60% or more. 2. The magnetic core according to claim 1, wherein the bonded magnet has an amount of binder of 20% or more by volume.
A magnetic core having a specific resistance of 1 Ω · cm or more. 3. An inductance component, characterized in that the magnetic core according to claim 1 or 2 is provided with a winding of at least 0.5 turns or more.