JP2001126911A - Oxide magnetic material of low loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce loss of Ni-Zn-Cu based ferrite, in order to provide magnetic material for a small-sized power transformer of high efficiency. SOLUTION: This low-loss oxide magnetic material is Ni-Zn-Cu based ferrite whose main component is Fe2O3, NiO, ZnO and CuO, and has crystal grain size distribution where D50 of crystal grain size distribution, i.e., crystal grain diameter at cumulative frequency 50% is 13-50 μm, and D10, i.e., crystal grain diameter at cumulative frequency 10% is greater than 5 μm, and D90, i.e., the crystal grain diameter at cumulative frequency 90% is smaller than 80 μm. In a manufacturing method of the low-loss oxide magnetic material, an oxygen partial pressure in a sinterning atmosphere is set as at least 25% of atmospheric pressure, in order to control a crystal grain diameter after sinterning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a power transformer or an inductor.
The present invention relates to a magnetic material suitable for a small and highly efficient power supply transformer and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, electronic devices such as portable devices have been rapidly reduced in size. In the power supplies used in them, transformers occupy an important place both in volume and in power loss. Therefore, downsizing of the transformer,
Higher efficiency is required. If the loss of the transformer material is large, not only the efficiency as a power source is poor, but also the risk of thermal runaway due to self-heating occurs. Therefore, as a material for a transformer, generally, the loss is low and the saturation magnetic flux density is high (about 500
mT), a low-cost Mn-Zn ferrite is used.

[0003]

However, Mn-
Zn-based ferrite has a low specific resistance and must be wound through bobbin winding parts to ensure insulation. Therefore, as a transformer material, Mn-Zn
There is a certain limit to miniaturization using the system ferrite. On the other hand, Ni—Zn—Cu-based ferrite has a high specific resistance, and can be wound directly. In addition to the high specific resistance, the addition of Cu enables low-temperature sintering, so that the conductor and the magnetic material can be integrally sintered, and a high degree of miniaturization can be realized. However, conventional Ni-Zn
-Cu-based ferrite has high loss and is inefficient, and has poor safety such as thermal runaway, so that it has been difficult to commercialize it as a transformer material.

Accordingly, the present invention has been made to provide a magnetic material for a power transformer which is small and highly efficient.
It is an object to reduce the loss of u-based ferrite.

[0005]

Means for Solving the Problems] We, the results of various experiments _{investigated, Fe 2 O 3, NiO,} ZnO, in the Ni-Zn-Cu-based ferrite mainly composed of CuO,
A grain size characterized by being sintered at an oxygen partial pressure of 25% or more of atmospheric pressure in a sintering atmosphere, having a grain size distribution D50 of 13 to 50 µm, D10 greater than 5 µm, and D90 less than 80 µm. It has been found that low loss can be realized in the distribution. Here, D10, D50 and D90 mean that the cumulative frequency is 10% and 50%, respectively.
% And 90% are shown.

In general, ferrite loss can be roughly classified into hysteresis loss, eddy current loss, and residual loss. Comparing the loss of the Ni-Zn-Cu ferrite of the present invention with that of the conventional Ni-Zn-Cu ferrite, it was found that the loss was reduced mainly by reducing the hysteresis loss. The hysteresis loss mainly depends on the crystal grain size and the magnetocrystalline anisotropic energy (K1). Since the crystal grain boundary acts as a frictional force against the domain wall movement, under normal firing conditions for uniform grain growth,
The hysteresis loss decreases as the crystal grain size increases. However, when coarse grains locally occur due to abnormal grain growth, the hysteresis loss increases. Usually, Ni-
Zn-Cu ferrite is used in the atmosphere (oxygen partial pressure ２０20
%). The grain size distribution of the product of the present invention is more uniform as compared with the conventional product, and according to the method of the present invention,
Even if the firing temperature is increased, the grains can be uniformly grown without generating local coarse grains. Also, 125
When firing at a temperature of 0 ° C. or higher, the specific resistance of the conventional product decreases, but the product of the present invention can maintain a high specific resistance even when firing at a high temperature.

That is, the low-loss oxide magnetic material of the present invention comprises:
N mainly containing Fe ₂ O ₃ , NiO, ZnO, and CuO
An i-Zn-Cu ferrite having a grain size distribution D50, that is, a grain size at a cumulative frequency of 50% of 13 to 50.
μm and D10, that is, the crystal grain size at a cumulative frequency of 10% is larger than 5 μm, and D90, ie, a cumulative frequency of 9
It is characterized in that it has a crystal grain size distribution in which the crystal grain size at 0% is smaller than 80 μm.

[0008] The production method of the present invention is characterized in that Fe ₂ O ₃ ,
Ni-Zn-C containing NiO, ZnO, and CuO as main components
In the method for producing a u-based ferrite, the oxygen partial pressure of the sintering atmosphere is adjusted to 2 atmospheres in order to control the crystal grain size after sintering.
It is characterized by being at least 5%.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, the main components Fe ₂ O ₃ ,
A predetermined amount of NiO, ZnO, CuO powder is weighed. Next, mixing, granulation, and calcination are performed, and the obtained powder is pulverized, granulated again, and pressed into a predetermined shape.
Bake at 300 ° C. At that time, the oxygen partial pressure during firing is
It is changed within a range of 25% or more of the atmospheric pressure. Ni produced
Regarding -Zn-Cu-based ferrite, the crystal grain size distribution is examined. In addition, frequency 50kHz, magnetic flux density 150mT
The loss is measured in a temperature range of 25 to 140 ° C. under the following magnetic conditions.

The loss decreases as the oxygen partial pressure of the atmosphere during firing increases, but the firing temperature that causes the minimum loss moves to the higher temperature side as the oxygen partial pressure increases. It is good to decide. As an example, 49 mol%
Of _Fe 2 _O 3, _19mol% of NiO, 25 mol% of ZnO, the Ni-Zn-Cu ferrite to CuO and the balance being, the firing temperature 1250 ° C., oxygen partial pressure 95%
Under the firing conditions described above, an excellent loss value can be obtained.

On the other hand, the higher the oxygen partial pressure of the firing atmosphere,
D50 (the crystal grain size at a cumulative frequency of 50%) at which the loss becomes minimum moves to the side where the grain size is large, and the grain size is made uniform. And D50 is 13 to 50 μm and D1
0 (crystal grain size at a cumulative frequency of 10%) is larger than 5 μm, and D90 (crystal grain size at a cumulative frequency of 90%) is 80.
Excellent loss values are obtained when smaller than μm.

As described above, Fe ₂ O ₃ , NiO, ZnO, Cu
Although the Ni-Zn-Cu ferrite containing O as a main component has been described, also in the Ni-Zn ferrite containing Fe ₂ O ₃ , NiO, and ZnO as a main component, control of crystal grain size distribution by oxygen partial pressure and temperature. Has a similar effect on loss reduction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. As a main component composition, 49 mol% of Fe
₂ O ₃ , 19 mol% NiO, 25 mol% Zn
O and the remaining CuO were weighed by a predetermined amount, and mixed for 2 hours using an attritor. After mixing, the mixture was granulated with a spray dryer. The granulated powder was calcined in a rotary kiln. The obtained powder was disintegrated using an attrater.
Thereafter, the mixture was granulated by a spray dryer, pressed into a toroidal shape, and fired at 950 to 1300 ° C.

Table 1 shows the oxygen partial pressure PO during firing.₂The atmospheric pressure
Invention when compared from 20% to 95%
Grain size distribution of 50kHz-
Loss Pcv at 150 mT-80 ° C (ie, frequency 50 kHz)
z, loss at 80 ° C. at a magnetic flux density of 150 mT), and
And specific resistance. Here, the conventional product is the oxygen partial pressure PO
₂= Sample sintered in an atmosphere of 20%, sintering temperature
Are assigned numbers from 1 to 8. On the other hand, the oxygen partial pressure Po₂
Loss Pcv is practical among samples made with 25% or more
Products that are good in terms of quality are referred to as inventions.
8 and the loss Pcv is not practically good.
No. 1-16.

[0015]

[Table 1]

From Table 1, it can be seen that the invention product has a more uniform grain size distribution and a specific resistance equal to or less than that of the conventional product.
It turns out that it is more than that. In addition, the crystal grain size distribution of the invention product shows that D50 is 13 to 50 µm, D10 is larger than 5 µm, and D90 is smaller than 80 µm.

FIG. 1 shows a graph of 50 when the oxygen partial pressure is changed.
The relationship between the loss at kHz-150 mT-80 ° C. and the firing temperature is shown. It can be seen that the firing temperature at which the loss is minimized shifts to higher temperatures as the oxygen partial pressure is higher, and the loss at that time is lower as the oxygen partial pressure is higher.

FIG. 2 shows the relationship between the loss Pcv at 50 kHz-150 mT-80 ° C. and the crystal grain size distribution D50 when the oxygen partial pressure during firing is changed. It can be seen that D50, at which the loss is minimized as the oxygen partial pressure is higher, shifts to a larger particle size side, and the minimum loss at that time is lower as the oxygen partial pressure is higher. In addition, 300mW which is the best value of the conventional product
It can also be seen that the D50 of the sample having a lower loss than / cc is 13 to 50 μm.

FIG. 3 shows 50 kHz of invention product 8 and conventional product 3.
The temperature characteristic of the loss Pcv at -150 mT is shown. Invention 8
Shows that the loss is smaller in the entire temperature range than that of the conventional product 3. Here, the conventional product 3 is 50 kHz among the conventional products.
This is a sample showing the smallest value of the loss at z-150 mT-80 ° C.

[0020]

As described above, the oxide magnetic material according to the present invention has a low loss and is suitable for a high-efficiency power supply transformer.

The product of the present invention has remarkably high specific resistance as compared with the conventional Mn-Zn ferrite. For this reason, the winding can be wound directly around the core, and no winding component such as a bobbin is required, so that the cost can be reduced. In addition, since the specific resistance is high, it is possible to integrally sinter with the conductor, and a high degree of miniaturization is possible.

[Brief description of the drawings]

FIG. 1: 50 kHz-15 when oxygen partial pressure is changed
The figure which shows the relationship between loss Pcv at 0 mT-80 degreeC, and baking temperature.

FIG. 2: 50 kHz-15 when oxygen partial pressure is changed
The figure which shows the relationship between loss Pcv at 0 mT-80 degreeC, and D50 of a crystal grain size distribution.

FIG. 3 shows 50 kHz-15 of invention product 8 and conventional product 3.
The figure which shows the temperature characteristic of loss Pcv at 0 mT.

Claims (2)

[Claims] 1. A Ni—Zn—Cu ferrite mainly composed of Fe ₂ O ₃ , NiO, ZnO, and CuO,
D50 of the crystal grain size distribution, that is, the crystal grain size at a cumulative frequency of 50% is 13 to 50 μm, and D10, that is, the crystal grain size at a cumulative frequency of 10% is larger than 5 μm, and D90,
That is, a low-loss oxide magnetic material having a crystal grain size distribution in which the crystal grain size at a cumulative frequency of 90% is smaller than 80 μm. 2. The method for producing a low-loss oxide magnetic material according to claim 1, wherein the oxygen partial pressure of the sintering atmosphere is reduced to 25 at atmospheric pressure.
% Or less, a method for producing a low-loss oxide magnetic material.