JP2003257753A - Magnetic core and inductance component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic core having excellent DC superimposition characteristics, core-loss characteristics, and heat resistance. <P>SOLUTION: The magnetic core has a gap at one or more points of a magnetic path. A bond magnet, whose specific resistance is 1 Ωcm or higher, comprises powder of 5 kOe or higher specific coercive force, 300°C or higher Tc, 2.0-50 μm powder particle size, and 2.0 or lower average aspect ratio, and contains resin by 15% or more in volume ratio. The magnet is inserted into the gap. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic core suitable for use mainly in a switching power supply and an inductance component using the magnetic core.

[0002]

2. Description of the Related Art Conventionally, good direct current superposition characteristics have been required for choke coil and transformer cores, and ferrite and dust cores have been used for high frequency cores. The ferrite core has a characteristic derived from the physical properties of the material, that is, the initial magnetic permeability is high and the saturation magnetic flux density is small, and the powder magnetic core has the low initial magnetic permeability and the saturated magnetic flux density is high. Therefore, the dust core is often used in a toroidal shape, and the ferrite is often used in the EE core, for example, with a gap inserted in the middle leg of the E-shaped core.

However, due to the demand for miniaturization of electronic parts in response to the demand for miniaturization of electronic equipment in recent years, 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 having high saturation magnetization, that is, a magnetic core that is not magnetically saturated in a high magnetic field. However, the saturation magnetization is necessarily 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 in spite of the large amount of labor spent for improving the saturation magnetization. there were.

As a solution to this problem, it has been conventionally considered to insert a gap in one or more places of the magnetic path and insert a permanent magnet into the gap. This method is an excellent method for improving the DC superposition characteristics, but on the other hand, the use of sintered metal magnets significantly increases the core loss of the magnetic core, and the use of ferrite magnets makes the superposition characteristics unstable. I couldn't stand it.

As a means for solving these problems, for example, Japanese Patent Laid-Open No. 50-133453 discloses that a permanent magnet is used to insert a bond magnet obtained by mixing rare earth magnet powder having a high coercive force and a binder and compression-molding the mixture. , The DC superposition characteristics and core temperature rise have been improved.

[0006]

However, in recent years, demands for improving power conversion efficiency of power supplies have become more and more strict, and the cores for choke coils and transformers are not superior or inferior simply by measuring the core temperature. The level is undecidable. Therefore, it is indispensable to judge the measurement result by the core loss measuring device, and in fact, as a result of the examination by the present inventors, the core loss characteristic may be deteriorated at the resistivity value shown in JP-A-50-133453. It was revealed.
Further, in recent years, a surface mount type coil is desired, and an oxidation resistant rare earth powder is indispensable for such a core.

An object of the present invention is to provide a magnetic core and an inductance component having excellent DC superposition characteristics, core loss characteristics and heat resistance.

[0008]

A magnetic core of the present invention is a magnetic core having a gap in at least one location of a magnetic path of the magnetic core, and a permanent magnet is arranged in the gap,
The magnetic core supplies a magnetic bias from both ends of the gap.

As a result of investigating the permanent magnet to be inserted, when a permanent magnet having a specific resistance of 1 Ω · cm or more and an intrinsic coercive force of 5 kOe or more is used, excellent DC superposition characteristics are obtained and the core loss is reduced. It has been discovered that it is possible to form a magnetic core without deterioration of characteristics. Also, the magnet characteristics required to obtain excellent DC superposition characteristics are
Rather, it is the intrinsic coercive force. Therefore, even if a permanent magnet having a high specific resistance is used, if the intrinsic coercive force is high, a sufficiently high DC superposition characteristic can be obtained.

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, but if the magnet powder has a high coercive force. , Any composition is possible. The types of rare earth magnet powder are SmCo type,
There are NdFeB type and SmFeN type, but when reflow conditions and oxidation resistance are required, a magnet with Tc of 500 ° C. or higher and coercive force of 10 kOe or higher is required. Currently, it is limited to Sm ₂ Co ₁₇ type magnet. To be done.

That is, the present invention is a magnetic core having a gap at least at one or more locations in a magnetic path, wherein the gap has an intrinsic coercive force of 5 kOe or more, Tc of 300 ° C. or more, and a powder particle size of 2. 0 to 50 μm and powder with an average aspect ratio of 2.0 or less, at least 15% by volume
It is a magnetic core in which a bond magnet made of the above resin and having a specific resistance of 1 Ω · cm or more is inserted.

In the bonded magnet according to the present invention, the Z content is 0.1 to 10 wt% with respect to the weight of the magnet powder.
n, Al, Bi, Ga, In, Mg, Pb, Sb, Sn
Of the above, or a magnetic core coated with a magnetic powder of one of these alloys.

The present invention is also the above-mentioned bonded magnet, which is a magnetic core in which magnet powder is previously coated with resin in an amount of 1.0 to 10% by volume.

The present invention is also an inductance component in which the above magnetic core is wound with at least one turn of winding.

(Operation) Here, as the magnetic core for the choke coil and the transformer, any material having a soft magnetic property is effective, but generally, a MnZn-based or NiZn-based ferrite, a powder magnetic core. , Silicon steel plate, amorphous, etc. are used. Also, the shape of the magnetic core is not particularly limited, and the toroidal core, E
The present invention can be applied to magnetic cores of any shape such as E cores and EI cores. A gap is provided in at least one location 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 superimposition characteristics deteriorate, and if the gap length is too wide, the magnetic permeability decreases too much, so the gap length to be inserted is naturally determined.

Next, regarding the required characteristics for the permanent magnet inserted in the gap, with respect to the intrinsic coercive force, the coercive force disappears by the DC magnetic field applied to the magnetic core at 5 kOe or less, so that a coercive force higher than that is required. In addition, the larger the specific resistance, the better, but if it is 1 Ω · cm or more, it does not become a major factor of core loss deterioration. Further, when the average maximum particle size of the powder is 50 μm or more, the core loss characteristics are deteriorated. Therefore, it is desirable that the maximum particle size of the powder is 50 μm or less, and when the minimum particle size is 2.0 μm or less, the powder is heat-treated during the powder heat treatment. The decrease in magnetization due to the oxidation of 2 becomes significant, so 2.
A particle size of 0 μm or more is required. Further, by setting the average aspect ratio of this magnet powder to be 2.0 or less, the specific resistance of the bonded magnet can be improved and a magnetic core with high characteristics can be obtained.

[0017]

EXAMPLES A magnetic core according to an example of the present invention and an inductance component using the magnetic core will be described below.

Example 1 A magnetic core according to Example 1 of the present invention will be described below. 1 is an explanatory diagram of a magnetic core according to a first embodiment of the present invention. In FIG. 1, the magnetic core has a configuration in which E-type ferrite cores 2a and 2b and a bond magnet 1 are arranged in the gap portion.

Here, the raw material of the bonded magnet 1 of the magnetic core of this embodiment has an average aspect ratio of 1.2, 1.5 and 2.0 produced by a jet mill and an average particle diameter of powder. In each case, 4.0 μm Sm ₂ Co ₁₇ system magnet powder was used, and after mixing with this powder an amount of epoxy resin equivalent to 25 vol% of the total volume, pressing was performed in a non-magnetic field.
Each of the specifications of bonded magnets was produced. 10mm x 7.
Each bond magnet processed into a shape of 0 mm × 1.5 mm was magnetized in the magnetic path direction with a pulse magnetic field of about 10 T, and the specific resistance of this bond magnet was measured. The results are shown in Table 1.

[0020]

[Table 1]

Next, a gap of 1.5 mm was formed on the core of an EE core made of MnZn ferrite and having a magnetic path length of 7.5 cm and an effective area of 0.74 cm ² , and the gap was formed and magnetized as described above. The magnet thus prepared was inserted to produce the magnetic core shown in FIG.

Next, a winding was applied to this core and the core loss was measured. The results are shown in Table 1 side by side.

As a comparative example, a bond magnet was prepared in the same manner as in the example, using the same composition as the material for the bond magnet, and magnet powder having a mean particle size of 4.0 μm and a mean aspect ratio of 2.2 prepared by a ball mill. The specific resistance and core loss were measured, and the results are also shown in Table 1.

It can be seen from Table 1 that the powder of the present invention having an average aspect ratio of 2.0 or less has a high specific resistance and excellent core loss characteristics. This is because the eddy current loss, which is a component of core loss, was reduced due to the improved specific resistance.

Further, from the above, when an attempt is made to form a bond magnet having the same specific resistance as that of the comparative example with the powder of the present invention having an aspect ratio of 2.0 or less, the amount of resin can be reduced and the size can be reduced. It can be easily inferred that this can be achieved.

(Example 2) Magnetism according to Example 2 of the present invention
The core will be described below. Where the bond magnet
The raw material has an average aspect ratio of 1.5 and the average particle size of the powder.
Is 4.0 μm Sm _TwoCo₁₇Using magnet powder
Manufactured a magnet, magnetized at about 10T, and bonded magnet
It was made. The amount of binder in the bond magnet is shown in Table 2.
is there. Flux and ratio of these produced bonded magnets
The resistance was measured. The results of these measurements are shown in Table 2. ratio
For comparison, the average aspect ratio is 2.2 and the average particle size is 1.5.
Similarly, a bonded magnet is made of powder, and the flux and specific resistance are
Since the resistance was measured, the results are also shown in Table 2 side by side.

[0027]

[Table 2]

From Table 2, it can be seen that the flux has an aspect ratio of 1.5 and 2.2 and shows almost the same value. Comparing the specific resistances, it can be seen that the one having an aspect ratio of 1.5 according to the present invention exhibits a high specific resistance with less binder than the comparative examples. Aspect ratio is 2.2
For a bonded magnet with a binder content of 10 Vol% and 15 Vol%, a gap of 1.5 mm was formed on the core of an EE core made of the same MnZn ferrite and having a magnetic path length of 7.5 cm and an effective area of 0.74 cm ^2. Then, a bond magnet was inserted into the gap portion to manufacture as shown in FIG.

FIG. 2 shows the results of measuring the DC superposition characteristics of this magnetic core before and after reflowing for 1 hour at 270 ° C. in the atmosphere.

From FIG. 2, the amount of the binder of the present invention is 15V.
It can be confirmed that those having an ol% show good characteristics with little deterioration in the DC superposition characteristics even after reflow. here,
Although the measurement results are shown for the binder amount of 15 vol%, it was confirmed that the 20 vol% and 30 vol% binders also show good characteristics with little deterioration of the characteristics after reflow.

(Embodiment 3) A magnetic core according to Embodiment 3 of the present invention will be described below. Here, the raw material of the bonded magnet has an average particle diameter of 3.5 μm and an average aspect ratio of 1.
The _Sm 2 _{Co 1 7} based magnet powder 8, by mixing 3 wt% of Zn, followed by heat treatment of 2 hours at 500 ° C. in Ar, was taken out into the atmosphere and cooled to room temperature. Epoxy resin was previously added to this powder in a volume ratio of 0.5, 1.0, 5.0, 1
1% at 150 ° C, so that each of them becomes 0,12%.
It was dried for a period of time and coated with magnet powder. The dried product was crushed in an automatic mortar for 30 minutes to be pulverized.

The resin coated with 12 vol% had a high resin strength and could not be crushed. Resins were mixed with these powders other than those coated with 12 vol% so that the total resin amount was 20 wt%, and press molding was performed. These molded bodies were processed into a shape of 10 mm × 7.0 mm × 1.5 mm, magnetized in the magnetic path direction with a pulse magnetic field of about 10 T, and the specific resistance of this bonded magnet was measured. The results are shown in Table 3. Further, since the flux of the bonded magnet before and after the reflow was also measured, Table 3 shows the result of calculating the change rate (demagnetization rate) with 100% before the reflow. As a comparative example, the same magnet powder as that of the example was used, but 50 in Ar was used without adding Zn.
Heat treatment was performed at 0 ° C. for 2 hours, the temperature was cooled to room temperature, the sample was taken out into the atmosphere, a sample was prepared in the same manner as in Example 3, and the specific resistance and the flux were measured.

[0033]

[Table 3]

It can be seen from Table 3 that when the magnetic powder coating is not applied and the flux measurement results are compared in the presence or absence of Zn, the Zn treated one can suppress the deterioration of the flux. However, when the specific resistances are compared, it can be seen that the Zn-treated one has a small specific resistance. This is Zn
This is because the specific resistance of the simple substance is small.

Next, comparing the measurement results of the bonded magnets which have been Zn-treated and powder-coated in advance with resin, the magnet powder of the present invention which was pre-coated with 1.0 to 10% by volume of resin was compared. It can be confirmed that excellent characteristics are exhibited in terms of specific resistance and flux change rate. Further, although not shown here, it was confirmed that the demagnetization rate was suppressed by coating the magnet powder with the metal or alloy shown in claim 2 in the same manner as in Example 3.

Among the bonded magnets shown in Table 3, the magnetic powder made of MnZn-based ferrite having a magnetic path length of 7.5 cm and an effective cross-sectional area of 0.74 cm ² was used for the magnet powder coated with resin in advance.
A gap of 1.5 mm was formed in the core of the E core, and the magnet magnetized as described above was inserted into the gap to prepare the magnetic core shown in FIG. This manufactured magnetic core is 270
After performing reflow at 1 ° C. for 1 hour, the frequency characteristic of μ was measured for this core. The result is shown in FIG. For comparison, the frequency characteristics of μ were also measured in the air gap without sandwiching the bond magnet in the gap of the ferrite core.
Are shown side by side.

Comparing the frequency characteristics of μ in FIG. 3, the resin coated with 1 to 10 vol% of the present invention is 0.5 vol% and shows a higher μ value up to high frequencies than the coated one. I understand. this is,
As can be seen from Table 3, the product of the present invention is 1 to 10 vol.
This is because the resin coated with% has a higher specific resistance than the resin coated with 0.5% by volume.

Here, among the samples for which the frequency characteristics of μ were measured, the DC superposition characteristics were measured with an LCR meter for the core previously coated with 10 Vol% resin, and the results are shown in FIG. As a comparative example, Z in Table 3
Since the direct current superposition characteristics were measured even for the sample which was subjected to the n treatment and not subjected to the resin coating, it is shown side by side in FIG.

As shown in FIG. 4, the core of the present invention, in which the magnet powder was coated with Zn and the resin-coated bond magnet was inserted, showed better DC superposition characteristics than those without resin coating. Can be confirmed.
This can be confirmed from Table 3, but since the Zn treatment and the coating of the magnet powder with the resin suppressed the oxidation of the magnet powder and reduced the demagnetization rate after reflow.

Example 4 A magnetic core according to Example 4 of the present invention will be described below. Here, as in Example 3, the raw material of the bonded magnet was Sm ₂ Co ₁₇ system magnet powder having an average particle size of about 3.5 μm and an average aspect ratio of 1.8, and the addition amount of Zn ₈₉ Al ₁₁ was 0 to 0. The content was changed to 12 wt%, kept at 530 ° C. in Ar for 2 hours, cooled to room temperature, and then taken out into the atmosphere. In the same manner as in Example 3, 1
A bond magnet processed into a shape of 0 mm × 7.0 mm × 1.5 mm is magnetized in the magnetic path direction with a pulse magnetic field of about 10 T,
The flux of this bonded magnet before and after reflow at 270 ° C. for 1 hour was measured. Flux characteristics are for each magnet TO
It was measured by TDF-5 Digital Fluxmeter manufactured by EI.

After the heat treatment at 270 ° C. was completed, re-pulse magnetization was performed, and the amount of the recovered flux was determined as thermal demagnetization due to thermal fluctuation, and the amount that could not be recovered was determined as demagnetization due to oxidation. The results of these measurements are shown in Table 4 with the unheated flux amount as 100%. As a comparative example, a bonded magnet was prepared and measured in the same manner as in Example 4 using the same powder as in this example, but the powder surface was not coated. Therefore, the measurement results are also shown in Table 4.

[0042]

[Table 4]

The uncoated magnet is at 270 ° C. for 24 hours.
Insert the magnet with the oxidation treatment of the coating compared to the% oxidized
What was done was about 1 to 3% of oxidation by heat treatment at 270 ° C.
It was found to show stable characteristics with very little deterioration.
It was This is because the surface of the magnet is Zn₈₉Al₁₁Covered with
As a result, the oxidation of the magnet powder is suppressed and the flux
It is considered that the decrease was suppressed. Also, regarding thermal demagnetization
Even if the magnet powder is Zn ₈₉Al₁₁The magnet coated with
The value was lower than that without coating. this
Is Zn₈₉Al₁₁By coating Sm_TwoCo
₁₇It is thought that the decrease in the coercive force of the magnet was suppressed.
It

Next, the core in which these magnets were inserted was used for 200 with an SY-8232 AC BH tracer manufactured by Iwasaki Tsushinki.
The core loss characteristic at 0.1 T at kHz was measured at room temperature. At the time of measurement, as shown in FIG. 1, the magnetic path length made of Mn-Zn ferrite material was 7.5 cm, and the effective area was 0.74 cm.
The EE core of ² has a gap of 1.5 mm,
Table 5 shows the result of the measurement performed by inserting the bond magnet into this gap.

[0045]

[Table 5]

The core loss without heat treatment increased by 200 kW / m ³ or more in the heat treatment, but the increase in core loss was 0.1 after the metal treatment.
wt% coated 38 kW / m ³ , 1.0 wt%
The coated one has 3 kW / m ³ and the coated one is 0 or less, and the amount of Zn ₈₉ Al ₁₁ is 3.0 wt%.
On the contrary, the above tended to decrease.

Further, in the case where 12 wt% of Zn ₈₉ Al ₁₁ was mixed, the core loss did not increase, but the core loss itself was close to 700 kW / m ³ , showing a very large value. It is considered that this is because although the resistivity of Zn ₈₉ Al ₁₁ was mixed at 12 wt%, the specific resistance was 0.92 Ω · cm, which was very small compared to other compositions, and the eddy current loss increased.
Further, the reduction of the core loss in the reflow can be achieved by changing the temperature of the reflow to 270 ° C. in the atmosphere by using Zn ₈₉ Al ₁₁
It is considered that the oxidization of Al increases the insulation between powders and reduces the eddy current loss.

For the above reason, Zn ₈₉ used for coating
The amount of Al ₁₁ is 0.1 to 10w of the total weight of the bonded magnet.
It has been found that it exhibits very excellent properties in the range of t%, and these are not only Zn ₈₉ Al ₁₁ but also the metals recited in claim 2, or alloys thereof, Zn ₈₉ Al 11.
_Since there is no large difference in specific resistance from No. _11, it can be easily inferred that similar results are obtained.

As described above, the intrinsic coercive force is 10 k.
Oe or more and Tc of 500 ° C or more, the powder particle size is 2.5 to 5
This is a rare earth magnet powder of 0 μm, and the surface of the rare earth magnet powder is 0.1 to 10% by weight of Zn, Al, Bi, Ga, I.
n, Mg, Pb, Sb, Sn magnet powder characterized by being coated with one or an alloy thereof, and at least 15% by volume of resin has a specific resistance of 1 Ω · cm
By inserting the above bond magnet, excellent DC superposition characteristics with little thermal demagnetization even after reflow can be obtained.

(Embodiment 5) FIG. 5 is an explanatory diagram of an inductance component according to an embodiment of the present invention. In FIG.
This inductance component includes E-type ferrite cores 2a, 2
b and the magnetic core in which the bond magnet 1 is arranged in the gap portion thereof, the winding 1 is provided around the bond magnet 1.

[0051]

As described above, according to the present invention, it is possible to provide a magnetic core and an inductance component having excellent DC superposition characteristics, core loss characteristics, and heat resistance.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a magnetic core according to a first embodiment of the present invention.

FIG. 2 is a diagram showing DC superposition characteristics before and after reflow for a magnetic core according to a second embodiment of the present invention.

FIG. 3 is a diagram showing μ frequency characteristics of a magnetic core according to a third embodiment of the present invention.

FIG. 4 is a diagram showing DC superimposition characteristics of a magnetic core according to Example 4 of the present invention.

FIG. 5 is an explanatory diagram of an inductance component according to an embodiment of the present invention.

[Explanation of symbols]

1 Bond magnet 2a, 2b E type ferrite core 3 windings

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Teruhiko Fujiwara             6-7-1 Koriyama, Taihaku-ku, Sendai City, Miyagi Prefecture             Tokin Co., Ltd.

Claims (4)

[Claims] 1. A magnetic core having a gap at least at one or more locations in a magnetic path, wherein the gap has an intrinsic coercive force of 5 kOe or more, a Tc of 300 ° C. or more, and a powder particle size of 2.0 to 50 μm. A magnetic core comprising a powder having an average aspect ratio of 2.0 or less and a bond magnet made of a resin having a volume ratio of at least 15% and having a specific resistance of 1 Ω · cm or more. 2. In the bonded magnet, 0.1 to 10 wt% of Zn, Al, Bi, G based on the weight of the magnet powder is used.
The magnetic core according to claim 1, wherein the magnet powder is coated with one of a, In, Mg, Pb, Sb and Sn or an alloy thereof. 3. The bonded magnet in the bonded magnet,
The magnetic core according to claim 1 or 2, which is previously coated with 1.0 to 10% by volume of resin. 4. An inductance component, wherein the magnetic core according to claim 1 is wound with at least one turn.