JP2000335961A - Oxide magnetic material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oxide magnetic material which is small in dielectric loss, improved in efficiency as an electric source, and can effectively avoid dangers such as heat runaway due to self heat generation, when used as the core material of a transformer for an electric source, and to provide a method for producing the same. SOLUTION: This method for producing an oxide magnetic material comprising an Ni-Zn-Cu-based ferrite containing Fe2O3, NiO, ZnO and CuO as main components. Therein, the BET(Brunau-Emmet-Teller) average particle diameter of the pulverized powder of an calcination product is <=0.35 μm, and the average crystal particle diameter of the sintered product is >=5 μm. Thereby, the obtained oxide magnetic oxide material having a high specific resistance, having low dielectric loss, and having the minimum dielectric loss in a high temperature region of >=120 deg.C in the temperature characteristics of the loss is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-loss oxide magnetic material used as a transformer material for a switching power supply and the like, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable progress in miniaturization and weight reduction of electronic devices such as portable devices. For this reason, switching power supplies and the like used in such electronic devices have been further reduced in size and weight. It has been demanded.

[0003] In a power supply, a transformer occupies a large part in both the volume and the power loss, so that a reduction in size and an increase in efficiency are strongly demanded. In general, characteristics required as a power transformer material include 1) low loss at a driving frequency, 2) high saturation magnetic flux density, 3) high Curie temperature, and 4) high specific resistance.

[0004] First, the drive frequency is required to have a low loss because if the loss is large, not only the efficiency as a power source is poor but also the risk of thermal runaway due to self-heating is generated. Therefore, it is desirable for the power supply transformer material to have a low loss and a negative temperature characteristic with respect to the loss. Conventionally, a low-cost Mn-Zn based ferrite having a high saturation magnetic flux density (about 500 mT) has been used as a core material of such a power transformer.

[0005]

However, these conventional Mn-Zn ferrites have low specific resistance. Therefore, when used as a transformer core material, it is necessary to ensure insulation properties. The winding had to be done over. Therefore, such Mn-Z
When n-type ferrite is used as a power supply transformer material, there is a limit to downsizing of the transformer and thus the power supply.

Therefore, it is conceivable to use Ni-Zn ferrite as a core material of a power transformer instead of the Mn-Zn ferrite. Since the Ni—Zn-based ferrite has a higher specific resistance than the Mn—Zn-based ferrite, it is possible to directly wind a winding without using a jig such as a bobbin. In addition to the high specific resistance, the addition of Cu also enables low-temperature sintering, so that the conductor and the magnetic material can be sintered together, so that an unlimited miniaturization of the power transformer can be pursued.

However, Ni-Zn based ferrite has a higher loss than the above-mentioned Mn-Zn based ferrite, and thus is inefficient and inferior in safety against thermal runaway and the like. It was difficult to commercialize.

[0008] An object of the present invention is to provide an oxidation device which, when used as a core material of a power supply transformer, has a small loss, improves the efficiency as a power supply, and can effectively avoid the risk of thermal runaway due to self-heating. An object of the present invention is to provide a magnetic material and a method for manufacturing the same.

[0009]

The present inventor has conducted various studies to achieve the above object, and as a result, has found that Fe ₂ O ₃ , Ni
In a method for producing an oxide magnetic material comprising a Ni—Zn—Cu-based ferrite containing O, ZnO, and CuO as main components, a BET (Brunau-Emm)
et-Teller (hereinafter, simply referred to as BET) It has been found that an oxide magnetic material for a power transformer with low loss can be obtained by setting the average particle size to 0.35 μm or less.
The obtained fired body shows excellent low loss characteristics when the average crystal grain size is at least 5 μm or more. This fired body has a minimum power loss temperature characteristic on the high temperature side of 120 ° C. or higher.

That is, the present invention relates to Fe ₂ O ₃ , NiO, Zn
In the method for producing an oxide magnetic material composed of a Ni-Zn-Cu-based ferrite containing O and CuO as main components, the BET average particle size of the calcined ground powder is set to 0.35 µm or less,
Furthermore, the average grain size of the fired body is 5 μm or more.

Further, according to the present invention, Fe ₂ O ₃ , Ni
In an oxide magnetic material composed of Ni-Zn-Cu-based ferrite containing O, ZnO, and CuO as main components, the calcined powder is manufactured to have a BET average particle size of 0.35 µm or less, and An oxide magnetic material having an average crystal grain size of 5 μm or more is obtained. The average crystal grain size of the fired body may be at least 5 μm or more. When it is 8 μm or more, the low loss characteristics are particularly excellent.

The oxide magnetic material of the present invention comprises a conventional Mn-
Compared with Zn-based ferrite, the specific resistance is remarkably large. Since the specific resistance is large, when used as a core material of a power supply transformer, the above-described winding can be directly wound, so that a winding jig such as a bobbin is not required, and cost can be reduced. Further, since the conductor and the magnetic body can be integrally fired due to the large specific resistance, it is possible to miniaturize.

In general, ferrite loss can be roughly divided into three types: hysteresis loss, eddy current loss, and residual loss. Comparing the loss of the oxide magnetic material of the present invention with that of the conventional Ni—Zn-based ferrite, the oxide magnetic material of the present invention shows that among the above three losses, mainly the hysteresis loss is reduced. It was found that the loss was greatly reduced as compared with the conventional Ni-Zn ferrite. The hysteresis loss is a loss generated by irreversible movement of the domain wall. In order to reduce the hysteresis loss, it is necessary to reduce inclusions that hinder domain wall movement. However, if the number of inclusions is excessively reduced, the domain wall moves over a long distance, and conversely increases the hysteresis loss. Since the number of domain walls depends on the average crystal grain size, the crystal grain size is preferably large. From the above, it can be considered that in order to reduce the hysteresis loss, it is desirable that the average crystal grain size be large, and that the crystal grains have moderate inclusions that hinder domain wall movement.

The reason why the loss of the oxide magnetic material of the present invention is small is that, in addition to the large average crystal grain size of 5 μm or more, the ratio of pores in the crystal grains is large, and the hysteresis loss is caused by the pinning action of the domain wall. It is inferred that it has been reduced. In addition, the oxide magnetic material of the present invention has a minimum loss on the high temperature side of 120 ° C. or higher in the temperature characteristic of loss regardless of the composition.

In the manufacturing process of the oxide magnetic material of the present invention, the calcined ground powder has a BET average particle diameter of 0.35 μm.
The reason for this is that if the BET average particle size is 0.35 μm or more, the proportion of pores in the crystal grains is reduced and the loss characteristics are significantly deteriorated. The reason why the average crystal grain size of the manufactured fired body is 5 μm or more is that if the average crystal grain size of the fired body is 5 μm or less, the loss characteristics are deteriorated due to an increase in hysteresis loss. In the oxide magnetic material of the present invention, the composition of the main component is 43.5 to 5
0.5 mol% of Fe ₂ O ₃ , 10 to 40 mol% of Ni
By using O, 1 to 15 mol% of CuO, and the balance of ZnO, more excellent loss characteristics can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an oxide magnetic material and a method for manufacturing the same according to an embodiment of the present invention will be described. (Example 1) The main component composition was fixed, and the BET average particle size of the pulverized powder after calcination in the production process was 0.10 to 0.4.
Five samples of invention products 1 to 4 and a comparison product (a sample whose BET average particle diameter is out of the range of claims) changed between 0 and 1 were prepared.
The characteristics such as specific resistance and core loss were compared.

That is, F of which main component composition is 49.5 mol%
e ₂ O ₃ , 15.0 mol% NiO, 5.0 mol% CuO, and the balance ZnO so that Fe ₂ O ₃ , NiO,
CuO and ZnO were weighed and mixed for 2 hours using an attritor. After mixing, the mixture was granulated using a spray dryer. The granulated powder is 800
Pre-baked (calcined) at ℃. The obtained powder was pulverized using an attritor. For each of the five samples described above, the BET average particle size of the calcined ground powder was 0.10 to 0.10, respectively.
0.40, pulverized, granulated by spray dryer, pressed to toroidal shape,
It was fired at a firing temperature of 150 ° C. BET average particle size is 5
This was varied by adjusting the grinding time for each sample.
An experiment was performed in which a winding was wound directly around the fired toroidal core and the temperature characteristics of the loss and the like were measured. Specifically, each 5
0 kHz, room temperature at 150 mT (Room Tem)
, R .; T = 25 ° C.), 80 ° C., 120
The core loss (Pcv mW / cc) at ° C was measured. These are shown in Table 1 together with the average crystal grain size and specific resistance of each of the obtained fired bodies.

[0018]

[Table 1] Table 1 shows that the calcined ground powder has a BET average particle size of 0.4
In the comparative product 1 of 0 μm, the core loss (Pcv mW / cc) at 50 kHz and 150 mT was 480 at 25 ° C. room temperature (RT), 320 at 80 ° C., and 250 at 120 ° C.
Thus, it shows a large loss at all temperatures. On the other hand, in the invention products 1 to 4 in which the BET average particle diameter of the calcined ground powder is 0.35 μm or less, the core loss (Pcv mW / cc) is significantly smaller than that of the comparison product 1 at all temperatures. Has become. Among invention products 1 to 4, core loss is particularly small in invention products 2, 3, and 4 having a BET average particle size of 0.25 to 0.10 μm,
Inventive product 3 having 0.20 μm shows the smallest value.

The specific resistance (Ωcm) of the comparative product 1 was 7 ×
In contrast to 10 ⁹ , invention products 1 to 4 each have 1 ×
10 ⁹ , 5 × 10 ⁹ , 8 × 10 ⁹ , 4 × 10 ⁹ ,
All of them show extremely large values as compared with general Mn-Zn based ferrite and the like. The average crystal grain size of the fired body was 13 μm for Comparative Product 1 and 1 μm for Invention Products 1-4.
The sizes were 6 μm, 14 μm, 15 μm, and 15 μm, which were almost the same as Comparative Product 1 and Invention Products 1 to 4.

FIG. 1 shows invention products 1, 2, 3 and comparative product 1.
Core loss of 50 kHz-150 mT (Pcv mW /
cc) shows temperature characteristics. It is apparent from FIG. 1 that the invention products 1, 2, and 3 having a BET average particle size of the calcined powder of 0.35 μm or less have a smaller loss (core loss) over the entire temperature range than the comparative product 1. It is. In addition, invention product 1,
The characteristic curves representing a few losses decrease monotonically with increasing temperature and show the minimum of the measured values at a temperature of 120 ° C. Therefore, the loss decreases as the temperature rises, and the characteristic curve decreases monotonously, indicating that the loss is minimized in a temperature region of 120 ° C. or higher. (Embodiment 2) In this embodiment, BET of the ground powder after calcination
The average grain size was fixed at 0.20 μm, and five samples were prepared with different average grain sizes of the fired bodies, and their characteristics such as specific resistance and core loss were compared.

That is, as in Example 1, the main component composition was 4%.
9.5 mol% Fe_TwoO_Three, 15.0 mol% Ni
O, 5.0 mol% CuO, balance ZnO
And Fe _TwoO_Three, NiO, CuO, ZnO are weighed and
Mix for 2 hours using lighter. After mixing, spray
Granulation was performed using a dryer. Rotate granulated powder
Pre-fired (calcined) at 800 ° C. using a kiln. Obtained
The obtained powder was finely ground using an attritor. 5 mentioned above
For each sample, the BE of the ground powder after this calcination was
Invention product 3 having the highest average T particle size in Example 1
0.20 μm, which is the same as the above. Each finely crushed
After that, granulate with a spray dryer to form a toroidal shape
Pressed, Comparative product 2 was 1050 ° C, Invention products 5 to 8 were 1
100 ° C, 1150 ° C, 1200 ° C, 1250 ° C firing
Each was fired at a temperature. Thus, the comparative product 2 and
Mainly change the firing temperature between each sample of bright products 5-8.
Thus, the average crystal grain size of the fired body was changed. Baked
Winding a coil around a rod core and measuring temperature characteristics of loss
An experiment was performed in the same manner as in Example 1.

Table 2 shows the average grain size, specific resistance, and resistivity of each of the obtained fired bodies for each of the comparative product 2 and the invention products 5 to 8.
0 kHz-150 mT core loss (Pcv mW / c
c) is shown together with the firing temperature described above.

[0023]

[Table 2] From Table 2, it can be seen that Comparative Example 2 in which the sintered body had an average crystal grain size of 4 μm had a (BET average grain size of 0.20 μm, such as 0.1%).
50 kHz, 150 m
Core loss (Pcv mW / cc) at 25 ° C.
660 at room temperature (RT), 510 at 80 ° C, 4 at 120 ° C
A large loss, such as 10, is shown at all temperatures. On the other hand, in the invention products 5 to 8 in which the average crystal grain size of the fired body is at least 5 μm or more, the core loss (Pcv mW / cc) is significantly smaller than the comparative product 2 at all temperatures. Among the inventive products 5 to 8, the core loss of the inventive product 6 in which the average crystal grain size of the fired body was 16 μm or more showed the smallest value.

The specific resistance (Ωcm) of the comparative product 3 was 6 ×
In contrast to 10 ⁹ , inventions 5 to 8 are each 5 ×
10 ⁹ , 4 × 10 ⁹ , 4 × 10 ⁹ , 1 × 10 ⁹ ,
All of them show extremely large values as compared with general Mn-Zn based ferrite and the like. (Embodiment 3) In this embodiment, the BET of the pulverized powder after calcination was performed.
The average particle size was fixed at 0.20 μm, a plurality of samples having different main component compositions were prepared, and their characteristics such as specific resistance and core loss were compared.

That is, in the inventions 9 to 14, the content of the main component was 41.5 to 50.5 mol% of Fe ₂ O _3.
, NiO is constant at 15 mol%, Cu
O is constant at 5 mol%, and the remaining ZnO is F
e ₂ O ₃ , NiO, CuO, and ZnO were weighed and mixed for 2 hours using an attritor. After mixing, the mixture was granulated using a spray dryer. The granulated powder was pre-fired (calcined) at 800 ° C. using a rotary kiln. The obtained powder was finely pulverized using an attritor in the same manner as in Example 2 so that the BET average particle diameter of all samples became 0.20 μm. After each pulverization, the mixture was granulated by a spray dryer, pressed into a toroidal shape, and fired at a firing temperature of 1150 ° C.

Next, in the invention products 15 to 20, regarding the main component composition, Fe ₂ O ₃ is constant at 49.5 mol%, NiO is varied within a range of 8 to 42 mol%, and CuO is 5 mol%.
%, Each was weighed as the balance ZnO, and a toroidal core was produced in the same manner as above. Further, Invention 2
In Nos. 1 to 25, regarding the main component composition, Fe ₂ O ₃ was added to 49.
5 mol% constant, NiO constant at 15 mol%, CuO
Was varied in the range of 0 (no addition) to 16 mol%, and the balance was weighed as ZnO to produce a toroidal core in the same manner as described above. With respect to all the samples of the invention products 9 to 25, an experiment was conducted in the same manner as in Examples 1 and 2 in which a winding was wound directly around a fired toroidal core and temperature characteristics of loss and the like were measured.

Table 3 shows that each sample of the invention products 9 to 25 has
Average crystal grain size, specific resistance, 50 kHz of each obtained fired body
A core loss (Pcv mW / cc) of -150 mT is shown together with the main component composition described above.

[0028]

[Table 3] According to Table 3, 43.5 to 50.5 mol% of Fe ₂ O ₃ , 1
0-40 mol% NiO, 1-15 mol% Cu
The core loss (Pcv mW / cc) of the invention products 10 to 14, the invention products 16 to 19, and the invention products 22 to 24 mainly containing O and the balance ZnO was 25 ° C. room temperature (RT), 80 ° C.
The values were relatively small at all temperatures of 120 ° C and 120 ° C. In addition, the average crystal grain size of the fired body is approximately the same size in the range of 14 to 16 μm in the invention products 9 to 20, and the invention product 2
1 to 25 are different in the range of 6 to 22 μm.

[0029]

As is apparent from the above description, according to the present invention, the production of an oxide magnetic material composed of a Ni—Zn—Cu ferrite containing Fe ₂ O ₃ , NiO, ZnO, and CuO as main components. In the method, the Ni—Zn (−) method can reduce the size and cost by directly winding a winding due to a large specific resistance or integrally firing a conductor and a magnetic material by adding Cu.
By making use of the advantages of Cu) -based ferrite, the BET average particle size of the calcined ground powder is set to 0.35 μm or less, and the average crystal particle size of the fired body is set to 5 μm or more, so that oxides having excellent loss characteristics are obtained. Magnetic materials can be manufactured. Therefore, if this oxide magnetic material is used as a core material of a transformer for a power supply, a power supply with small power loss and high efficiency can be realized while downsizing the transformer and the power supply.

Further, in the oxide magnetic material of the present invention, in the temperature characteristic of the loss, the loss becomes smaller as the temperature becomes higher,
It has the characteristic that its loss is minimized in a high temperature region of 0 ° C. or higher. Therefore, even if it is used as a core material of a power transformer, it is easy to avoid the risk of thermal runaway due to heat generation, and it is excellent in safety, so that it is highly practical as a power transformer material.

[Brief description of the drawings]

FIG. 1 is a diagram showing temperature characteristics of loss in an oxide magnetic material according to Example 1 of the present invention, together with a comparative example (comparative product).

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koichi Kondo 6-7-1, Koriyama, Taihaku-ku, Sendai City F-term in Tokin Co., Ltd. (Reference) 4G002 AA06 AB02 AD04 AE02 AE04 4G018 AA23 AA24 AA25 AC01 AC03 AC08 AC16 5E041 AB01 AB19 BD01 CA03 NN02 NN06

Claims (5)

[Claims] In a method for producing an oxide magnetic material composed of a Ni—Zn—Cu ferrite containing Fe ₂ O ₃ , NiO, ZnO, and CuO as main components, a powder of B
A method for producing an oxide magnetic material, wherein the average particle size of an ET (Brunau-Emmet-Teller) is 0.35 μm or less, and the average crystal grain size of a fired body is 5 μm or more. 2. The method for producing an oxide magnetic material according to claim 1, wherein the sintered body has an average crystal grain size of 8 μm or more. 3. An oxide magnetic material composed of a Ni—Zn—Cu ferrite containing Fe ₂ O ₃ , NiO, ZnO, and CuO as main components.
unau-Emmet-Teller).
An oxide magnetic material which is manufactured to have a size of 35 μm or less and has a sintered body having an average crystal grain size of 5 μm or more. 4. The oxide magnetic material according to claim 3, wherein said sintered body has an average crystal grain size of 8 μm or more. 5. The oxide magnetic material according to claim 3, wherein 43.5 to 50.5 mol% of Fe ₂ O ₃ , 10
４０40 mol% NiO, 1-15 mol% CuO,
An oxide magnetic material comprising a balance of ZnO as the main component.