JPH05226137A - Oxide magnetic body material and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a material with improved magnetic loss and temperature characteristics by adding at least a specific amount of CaO and SiO2 to MnZn ferrite whose main composition is within a specific range as a low magnetic loss material and further adding a specific amount of MgO to these. CONSTITUTION:The title material contains 52mol.%-57mol.% Fe2O3, 3 mol.%-15 mol.% ZnO, and MnO for the remaining part as main compositions and then at least 0.05wt.%-1.0wt.% MgO, 0.05wt.%-0.3wt.% CaO, 0.005wt.%-0.05wt.% SiO2 as sub-components. The material has less magnetic loss at a high-frequency band (approximately 1MHz) and a high temperature where the loss reaches the minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency low-loss magnetic core material used in electronic parts and electronic equipment, and a switching power supply using the same and having a small loss.

[0002]

2. Description of the Related Art With the recent advances in electronics technology, the miniaturization and higher density of equipment have led to higher frequency usage. Magnetic materials used for switching power supplies and the like are also required to cope with higher frequencies, and in particular, in order to prevent heat generation when miniaturized, low loss at high frequencies is required.

Magnetic core materials are roughly classified into metallic materials and oxide ferrite materials. Metal-based materials have the advantage of high saturation magnetic flux density and high magnetic permeability, but have a low electrical resistivity of about 10 ⁻⁶ to 10 ⁻⁴ Ω · cm, which increases eddy current loss at high frequencies. There was a point. In order to make up for this problem, some foils are processed and rolled in a roll with an insulator sandwiched between them, but there is a limit to thinning them (about 10 microns). Has the drawback of being difficult to make and expensive, 1
It could only be used up to a frequency band of about 00 KHz.

On the other hand, a ferrite material has a saturation magnetic flux density as low as about 1/2 of that of a metal material. However, the electrical resistivity is 1Ω · c for the MnZn type that is usually used.
m, which is much higher than that of metallic materials, and C
By using additives such as aO and SiO _{2, the} electrical resistivity can be further increased to about 10 to several KΩ · cm, and the eddy current loss is relatively small up to high frequencies, and it can be used without special measures. Is. In addition, it has the advantage that it can be easily made into a complicated shape and it is low cost. For this reason, this ferrite-based material has been generally used as a power supply transformer core material at a switching frequency of 100 KHz or more.

[0005]

However, even in such a ferrite-based material, if the temperature coefficient of magnetic loss is positive, the transformer generates heat due to loss during actual use, which causes a rise in temperature and further loss. There is a risk that thermal runaway will occur due to repeated increases in heat generation and increased heat generation. Therefore, the loss is due to the temperature (60 ~
It is required to have a temperature characteristic that is minimum around 80 ° C. However, low loss materials have a minimum loss temperature near room temperature and are prone to thermal runaway. On the other hand, materials with a minimum loss temperature of 60 ° C or higher have a large loss. At the same time, no satisfactory material has been obtained as a material having good temperature characteristics.

In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to provide a MnZn ferrite material having a small magnetic loss and a high temperature at which the loss is minimum in a high frequency band, and a method for producing the same. To do.

[0007]

In order to achieve the above object, the oxide magnetic material of the present invention is a MnZn ferrite-based low loss oxide magnetic material having a main composition of Fe.
52 mol% or more and 57 mol% or less of ₂ O ₃ , ZnO of 3 mol% or more and 15 mol% or less, MnO as a residue, and at least MgO of 0.05
% To 1.0% by weight, 0.05% by weight CaO
The content of SiO ₂ is 0.003% by weight or less and the content of SiO ₂ is 0.005% by weight or more and 0.05% by weight or less.

In the above structure, the average crystal grain size of the sintered body is preferably 4 μm or less. Moreover, in the said structure, it is preferable that the MnZn ferrite low loss oxide magnetic material is a magnetic core of a switching power supply with a switching frequency of 100 KHz-2 MHz.

Next, in the method for producing an oxide magnetic material of the present invention, raw material powders containing at least Fe, Zn, Mn and Mg are mixed and calcined at a temperature of 900 ° C. or higher, and then Ca and Ca are added to the powders. When Si is not added, additives containing Ca and Si are mixed, molded and fired, and Fe ₂ O ₃ as main composition is 52 mol% or more and 57 mol% or less, ZnO is 3 mol% or more and 15 mol% or less. , MnO as a residue, and at least Mg as a secondary component
O is 0.05 wt% or more and 1.0 wt% or less, CaO is 0.05 wt% or more and 0.3 wt% or less, and SiO ₂ is 0.
It is characterized in that a sintered body containing 005% by weight or more and 0.05% by weight or less is produced.

[0010]

According to the structure of the present invention, at least a specific amount of CaO is added to MnZn ferrite having a main composition within the specific range.
By adding SiO ₂ and SiO ₂ to obtain a low magnetic loss material, and further adding a specific amount of MgO thereto, a material having excellent temperature characteristics of magnetic loss can be obtained. The temperature characteristic of magnetic loss varies depending on the main composition, but Mg
By adding O, the temperature at which the loss is minimal can be shifted to a high temperature side by about 20 to 60 ° C. as compared with the case of no addition. Therefore, by changing the combination of the main composition and the added amount of MgO according to the temperature range to be used, it is possible to obtain the optimum ferrite core material having the minimum magnetic loss near that temperature. A switching power supply using this ferrite magnetic core material has high efficiency due to low loss, and has a low risk of runaway.

[0011]

The present invention will be described below with reference to examples. Example 1 As a starting material, α-Fe ₂ O ₃ and MnCO having a purity of 99.5% were used.
₃ and ZnO powders were used. The composition ratio of these powders was Fe ₂ O ₃ = 53 mol% and MnO = 35 mol
%, ZnO = 12 mol%, total weight 300 g
So that each of the
Was added in an amount of 0 to 2% by weight, wet-mixed and ground in a ball mill for 10 hours, and dried. 2 these mixed powders at 900 ℃
After calcination in air for 2 hours, CaCO ₃ of 0.2 wt% as CaO content and 0.05 wt% of SiO ₂ were added, and the mixture was again wet mixed and pulverized for 10 hours in a ball mill and dried,
It was a calcined powder.

10% by weight of a 5% by weight aqueous solution of polyvinyl alcohol was added to these calcined powders, and the mixture was passed through a 30 mesh (#) sieve to granulate. These granulated powders were uniaxially die-molded, the molded body was binder-out in air at 500 ° C. for 1 hour, and then at 1200 ° C. for 2 hours at the time of temperature rising and maximum temperature holding N ₂ -1% O _{In two} atmospheres, when cooled, firing was performed in an atmosphere of nitrogen to obtain a sintered body. The firing time was changed from 2 to 10 hours for some of the added amounts of the samples. The pressure at the time of molding is such that the density of the sintered body is approximately 4.3 to 4.
It was changed to fall within the range of 6 g / cm ³ . From the obtained sintered body, outer diameter 20 mm, inner diameter 14 mm, thickness 2 m
A ring-shaped sample of m was cut out, and the magnetic loss at 1 MHz · 50 mT was measured between 20 ° C and 100 ° C. The average crystal grain size of the sintered body was measured by observing the fracture surface of the sintered body with an electron microscope. The results are shown in Table 1.

[0013]

[Table 1]

As is clear from Table 1, in Sample Nos. 1 and 2 with or without addition of MgO, the loss at room temperature is small, but the loss increases as the temperature rises, and thermal runaway occurs in actual use. Will occur. On the other hand, when the amount of MgO added is 0.05 to 1.0 weight percent, sample number 3 to
In 6 and 9-10, the room temperature loss itself slightly increases, but the temperature at which the loss becomes minimum rises to 40 ° C to 80 ° C, and thermal runaway hardly occurs in actual use. However, when comparing sample numbers 5 to 8 with the same MgO addition amount, in sample numbers 7 and 8 in which the crystal grain size exceeds 4 μm, the overall loss increased and the efficiency decreased.

In the sample numbers 8 and 9 in which the addition amount exceeds 1.0 weight percent, the temperature at which the loss is minimum is as high as 80 ° C., but in the entire temperature range of 20 to 100 ° C. The overall loss was higher and the efficiency was lower than.

As is clear from the above results, the reason why the addition amount of MgO is limited to 0.05 weight percent or more is that the effect of the addition is not clear when the addition amount is less than 1.0 weight percent. The reason for limiting the content to less than or equal to the percentage is that the total loss is increased by the addition at the addition amount exceeding this. The reason why the average crystal grain size is preferably 4 μm or less is that the total loss tends to increase if the average grain size exceeds this.

Example 2 As in Example 1, the composition ratio was Fe ₂ O ₃ = 53 mol.
%, MnO = 37.5 mol%, ZnO = 9.5 mol
%, The raw material powders were weighed so that the total weight became 300 g, 0.5% by weight of MgO was further added thereto, and the mixture was ground and pulverized by a ball mill for 10 hours and dried. After calcining these mixed powders in air at 800 to 1000 ° C. for 2 hours, 0.1% by weight of CaCO ₃ , 0.12% by weight of SiO ₂ and 0.02% by weight of SiO ₂ are added, and the resulting mixture is again ball milled for 10 hours. , Wet mix pulverize and dry,
It was a calcined powder.

In a similar manner, a powder obtained by adding MgO at the time of crushing after calcination, a powder only mixed without calcination,
Then, MgO-free powder was prepared by calcination at 900 ° C.
5% by weight of polyvinyl alcohol was added to these calcined powders.
The aqueous solution was added at 10% by weight, and passed through a 30 # sieve to granulate. These granulated powders were uniaxially die-molded, and the molded body was binder-out in air at 500 ° C. for 1 hour, and then at 1200 ° C. for 2 hours at the time of temperature rising and maximum temperature holding N
_A sintered body was obtained by firing in a 2-1% O ₂ atmosphere and an atmosphere of nitrogen during cooling. The pressure at the time of molding was changed so that the sintered body density was about 4.5 g / cm ³ . From the obtained sintered body, outer diameter 20 mm, inner diameter 14 mm, thickness 3 mm
The ring-shaped sample was cut out and the magnetic loss at 1 MHz and 50 mT was measured in steps of 20 ° C. between 20 ° C. and 100 ° C., and the temperature at which the loss was minimized and the loss value at that time were measured. The average crystal grain size of the sintered body was measured by observing the fracture surface of the sintered body with an electron microscope. The results are shown in Table 2.

[0019]

[Table 2]

As is clear from Table 2, in any addition method, the minimum loss temperature is higher than in the case of no addition, but MgO is added before calcination and the calcination temperature is 900 ° C. or higher. Other than that, the width of temperature rise was small, or the loss at the minimum was considerably large.

Example 3 In the same manner as in Example 1, the composition ratio was Fe ₂ O ₃ = 53 m.
ol%, MnO = 35 mol%, ZnO = 12 mol%
Therefore, a calcined powder containing 0.1% by weight of CaO, 0.02% by weight of SiO ₂ , and MgO not added or at a ratio of 0.2% by weight was prepared, and calcined in the same manner as in Example 2. Conjugates A (without MgO added) and B (MgO = 0.2 wt%)
Addition) was prepared.

The sintered body A has a loss value of 1 M at room temperature.
Although it is as low as 370 kW / m ³ at Hz and 50 mT, it is a sample in which the loss increases as the temperature rises. On the other hand, the sintered body B is
This product has a minimum loss temperature at 60 ° C and a loss value of 490. E-type cores were cut out from each of these sintered bodies, a forward-type switching power supply circuit was prototyped using the cores, operated at 1 MHz at 80 mT on one side, and the temperature rise corresponding to loss was evaluated. As a result, in the power source using the sintered body A of the comparative example, the heat generation at the start of operation is small and the temperature rise is slow, but the temperature rise speed increases with the passage of time, and the temperature rise does not stop,
Caused a thermal runaway. On the other hand, in the power source using the sintered body B of the example, the heat generation at the start of operation was larger than that of the comparative example, but when the temperature rises to some extent, the heat generation becomes small, and the temperature is stabilized at about 60 ° C. And did not cause thermal runaway. This is because the temperature characteristics were improved by adding MgO to the magnetic core material. Therefore, the switching frequency using the developed ferrite material A is 100 KHz-
The 2 MHz power supply has low heat generation, high efficiency, and low risk of thermal runaway.

[0023]

As described above, according to the present invention, at least a specified amount of CaO and SiO ₂ is added to MnZn ferrite whose main composition is within a specified range to obtain a low magnetic loss material, and further a specified amount thereof is added. It is possible to obtain a material having excellent temperature characteristics of magnetic loss by adding MgO.

Further, the switching power supply using this ferrite magnetic core material has high efficiency due to low loss, and the risk of runaway can be reduced. Furthermore, the production method of the present invention can efficiently and rationally produce the oxide magnetic material having low magnetic loss.

Claims (4)

[Claims] 1. A MnZn ferrite-based low loss oxide magnetic material having a main composition of 52 mol of Fe ₂ O ₃ .
% To 57 mol% and ZnO to 3 mol% to 15
mol% or less, containing MnO as the balance, and at least 0.05% by weight to 1.0% by weight of MgO, 0.05% by weight to 0.3% by weight of CaO and SiO ₂ as secondary components An oxide magnetic material containing 0.005% by weight or more and 0.05% by weight or less. 2. The oxide magnetic material according to claim 1, wherein the average crystal grain size of the sintered body is 4 μm or less. 3. A MnZn ferrite-based low-loss oxide magnetic material has a switching frequency of 100 KHz to 2 MHz.
The oxide magnetic material according to claim 1 or 2, which is a magnetic core of the switching power supply. 4. At least Fe, Zn, Mn and Mg
In the case where Ca and Si are not added to this powder after mixing the raw material powders containing
Additives containing Ca and Si are mixed, molded and fired, and Fe ₂ O ₃ as main composition is 52 mol% or more 57 m
ol% or less, ZnO is 3 mol% or more and 15 mol% or less, MnO is contained as a residue, and at least MgO is 0.05 wt% or more and 1.0 wt% or less as a sub-component.
CaO 0.05 wt% to 0.3 wt%, SiO
_A method for producing an oxide magnetic material, comprising producing a sintered body containing 0.005% by weight or more and 0.05% by weight or less.