JP2021183556A - MnZnNiCo-BASED FERRITE AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

To provide a MnZnNiCo-based ferrite material that has a small absolute value of iron loss in a wide temperature range of a room temperature to 100°C when driving at high frequency of 500 kHz while maintaining high saturation magnetic flux density until a transformer operation temperature (approximately 80°C) in a high-density loading state, in order to downsize a power supply of an electronic component and increase the performance thereof.SOLUTION: A MnZnNiCo-based ferrite material comprises: Fe2O3, ZnO, NiO, CoO and manganese oxide as fundamental components; and SiO2, CaO and Nb2O5 of predefined amounts with respect to the fundamental components, as accessory components. In addition, an amount of Cl, Sr and Ba each is suppressed to a predefined amount or less with respect to the fundamental components, and sintering density of the MnZnNiCo-based ferrite material is defined in the range of more than 4.85 Mg/m3 and 5.00 Mg/m3 or less.SELECTED DRAWING: None

Description

The present invention relates to MnZnNiCo-based ferrite particularly suitable for the magnetic core of a transformer for a switching power supply and a method for manufacturing the same.

Magnetic materials are roughly classified into oxide-based magnetic materials and metal-based soft magnetic materials.
Oxide-based magnetic materials are classified into hard magnetic materials such as Ba-based ferrite and Sr-based ferrite, and soft magnetic materials such as MnZn-based ferrite and NiZn-based ferrite.

Here, the metal-based soft magnetic material has a feature that the saturation magnetic flux density is higher than that of the oxide-based material, but the electric resistance is small. Therefore, when used in a high frequency region, there is a problem that iron loss becomes large due to the generated eddy current. Therefore, in recent years, the frequency used has been increasing due to the demand for miniaturization and high density of electronic devices. For example, in a switching power supply used in a high frequency band of about 100 kHz, a metal-based soft magnetic material is used. There are few things.

On the other hand, among the above-mentioned oxide magnetic materials, the soft magnetic material is a material that easily magnetizes even with a slight magnetic field, and therefore is widely used in a wide range of fields such as power supplies, communication equipment, measurement control equipment, magnetic recording, and computers. MnZn-based ferrite, which is a soft magnetic material with a small iron loss, has been mainly used as the magnetic core material of the power transformer used in the high frequency band.

This MnZn-based ferrite has a problem that the eddy current loss is high because the electrical resistivity is as low as about 0.01 to 0.05Ω · m. Therefore, there has been a demand for a magnetic material in which the electric resistance is further increased to reduce the eddy current loss, and the iron loss is further reduced as a whole to suppress the calorific value.
To solve this problem, for example, in Patent Document 1, a small amount of an oxide such as calcium oxide or silicon oxide is added to MnZn-based ferrite as an auxiliary component to segregate it at the grain boundaries to increase the grain boundary resistance as a whole. Disclosed is a technique for solving the problem by increasing the resistivity of calcium oxide to several Ω · m or more.

Further, the MnZn-based ferrite for the power source is required to have a high saturation magnetic flux density Bs, a high Curie temperature Tc, and a low magnetic loss Pcv. It is known that the Curie temperature Tc is almost determined by the composition of the main component. Further, it is known that an oxide ferrite compound containing MnZn-based ferrite exhibits ferrimagnetism, and the saturation magnetic flux density and Curie temperature change depending on the type of metal atom having a magnetic moment and the position occupied by the metal atom.

In addition, the saturation magnetic flux density of oxide-based ferrite decreases with increasing temperature and becomes zero at the Curie temperature, which is the temperature at which magnetism disappears. Therefore, the higher the Curie temperature, the more the saturation magnetic flux density from room temperature to the transformer operating temperature. It is known that the temperature can be kept high. As a technique relating to the saturation magnetic flux density, for example, Patent Document 2 discloses that the saturation magnetic flux density can be increased by increasing the amount of _{Fe 2} O _3.

Special Publication No. 36-002283 Japanese Unexamined Patent Publication No. 11-329822 Special Fair 8-1844 Gazette Special Fair 04-033755 Gazette Japanese Unexamined Patent Publication No. 2019-6668 Japanese Unexamined Patent Publication No. 2019-199378

"The Effect of Cobalt substations on some properties of manganese zinc ferrites", A.I. D. Giles and F. F. Westendorp: J.M. Phys. D: Appl. Phys. 9 (1976) 2117 "Low-loss Power Ferrites for frequencies up to 500 kHz", T.I. G. W. Stijintjes and J. J. Roelofsma; Adv. Cer. 16 (1986) 493

However, in recent years, in order to meet the demand for miniaturization of the power supply portion of electronic devices, various parts tend to be loaded at a higher density. In such a high-density loading state, the temperature at which the ferrite core is used, that is, the operating temperature of the transformer reaches 80 ° C. due to the heat generation of various parts.

Regarding those iron losses, the iron loss at 0 to 100 ° C. measured at a maximum magnetic flux density of 50 mT and a frequency of 500 kHz is to increase the drive frequency to achieve miniaturization and to save energy at various ambient temperatures. There is a demand for a performance of 100 kW / m ³ or less and an iron loss value of 75 kW / m ^{3 or less at the minimum iron loss temperature.}

However, in the technique described in Patent Document 1, there is no particular mention of increasing the drive frequency in order to realize miniaturization.

Further, in the technique described in Patent Document 2, no particular reference is made to the operation under a predetermined high temperature condition of 80 ° C. (magnetization force 1200 A / m).

Further, although Patent Document 3 discloses a technique for reducing iron loss at a high frequency of 500 kHz and in a temperature range of 20 to 120 ° C., the absolute value of such iron loss is large and the saturation magnetic flux density is increased. Is not specifically mentioned.

Here, one of the factors governing the core loss of ferrite, and magnetic anisotropy constant K _1. The iron loss changes with the temperature change of the magnetic anisotropy constant K ₁ , and becomes the minimum at the temperature where _{K 1 = 0.} Therefore, to reduce the temperature change of the ferrite core loss, it is necessary to reduce the temperature dependence of the magnetic anisotropy constant K ₁ (the core loss temperature coefficient).

The magnetic anisotropy constant K ₁ is almost determined by the types of elements constituting the spinel compound of ferrite, which is the main phase. In the case of MnZn-based ferrite, the temperature dependence is reduced by introducing Co ions, and iron is used. The absolute value of the temperature coefficient of loss can be reduced (see, for example, Non-Patent Documents 1 and 2). This makes it possible to obtain a ferrite material having a small iron loss in the vicinity of room temperature to 100 ° C. and a relatively small iron loss even in the temperature range before and after that.

Regarding such a technique, for example, in Patent Document 4, _{MnZnCo-based ferrite containing Fe 2} O ₃ , ZnO, and MnO as main components and containing 0.01 mol% or more and less than 0.5 mol% of CoO has a wider temperature than before. It is disclosed that K ₁ = 0 in the range, and high magnetic permeability and low loss can be realized in a wide temperature range.
Further, in the ferrite described in Patent Document 4, as shown in FIG. 1 of the same document, an example in which the minimum temperature of the core loss shifts to the low temperature side is introduced.

However, when Co is added as described in Patent Document 4, the iron loss temperature coefficient and iron loss are minimized due to slight fluctuations in the firing temperature and the oxygen concentration in the firing atmosphere due to the influence of the contained impurities. Not only does the temperature fluctuate, but another problem may arise in which the absolute value of iron loss deteriorates significantly.

Therefore, in the above-mentioned conventional techniques (Patent Documents 1 to 4), there is almost no problem in a high frequency band of about 100 kHz, but the high density required for miniaturization and high efficiency of the power supply of electronic components. Ferrite materials that exhibit low magnetic loss over a wide temperature range of 0 to 100 ° C when driven at high frequencies at 500 kHz while maintaining a high saturation magnetic flux density up to the transformer operating temperature in a loaded state. Neither has been realized.

On the other hand, the inventions described in Patent Documents 5 and 6 aim to solve these problems.
However, in Patent Document 5, although the iron loss value at a drive frequency of about 100 kHz is improved, the iron loss value at a high frequency of about 500 kHz is large, and the maximum magnetic flux density is 50 mT and the frequency is 500 kHz. There remains a problem that the characteristic value that the iron loss at ~ 100 ° C. is 100 kW / m ³ or less and the iron loss value at the minimum iron loss temperature is 75 kW / m ³ or less cannot be satisfied at the same time.
Further, in Patent Document 6, since the sintering density is relatively small (4.65 to 4.85 Mg / m ³ ), there are unstable factors such as small variation in characteristics depending on the loading position of the obtained ferrite material at the time of firing. ..

The present invention has been developed in view of the above-mentioned current situation, and maintains a high saturation magnetic flux density up to the transformer operating temperature (80 ° C.) in a high-density loaded state in order to reduce the size and efficiency of the power supply of electronic components. MnZnNiCo has a small absolute value of iron loss in a wide temperature range of 0 to 100 ° C., a relatively large sintering density, and a small variation in characteristics depending on the loading position during firing of ferrite materials when driven at a high frequency of 500 kHz. It is an object of the present invention to provide a system ferrite material.

In order to solve the above-mentioned problems of the prior art, the inventors have set the contents of the basic components _{such as Fe 2} O ₃ , ZnO, NiO, CoO and MnO to the saturation magnetic flux density, iron loss, and their. In addition to investigating the effects on temperature characteristics in detail, the grain boundary phase of the sintered body obtained by various metal oxides as additive components and various production conditions is determined by the saturation magnetic flux density, iron loss, and their temperatures. We have conducted extensive research on the characteristics and the effect on the sintering density.

As a result, in order to solve the above problem, the basic component in the MnZnNiCo-based ferrite is controlled within an appropriate range, and then the selection of the sub-component as an additive component and the amount thereof are controlled within an appropriate range according to the range. It was found that it is necessary to raise the firing temperature and further increase the cooling rate to a predetermined temperature to properly control the grain boundary phase, and to reduce the content of specific elements. rice field.

In particular, it is necessary to use iron oxide having a Cl content of 500 mass ppm or less as the iron oxide as a ferrite raw material and to suppress the Cl content in the final sintered body to 80 mass ppm or less in order to realize the effect of the present invention. We have found it extremely effective and have completed the present invention. It was also found that the Sr content should be 10.0 mass ppm or less and the Ba content should be 10.0 mass ppm or less in order to achieve such an effect.

The present invention has been completed with further studies based on the above findings, and the gist structure of the present invention is as follows.
1. 1. Basic components, in MnZnNiCo ferrite consisting subcomponent and unavoidable impurities, the basic _{component, Fe 2 O 3: 53.00~57.00mol%} , ZnO: 4.00~11.00mol%, NiO: 0. 50 to 4.00 mol% and CoO: 0.10 to 0.50 mol% The balance is MnO, and the sub-components are SiO ₂ : 50 to 500 mass ppm, CaO: 200 to 2000 mass ppm and Nb _{2 with respect to the basic component.} O ₅ : 50 to 500 mass ppm, and Cl, Sr and Ba in the unavoidable impurities are Cl: 80 mass ppm or less, Sr: 10.0 mass ppm or less and Ba: 10.0 mass ppm or less, respectively, with respect to the basic component. The sintering density is more ^{than 4.85 Mg / m 3} and 5.00 Mg / m ³ or less, and the saturation magnetic flux density at a magnetization force of 1200 A / m at 80 ° C. is 400 mT or more and the maximum. When the magnetic flux density is 50 mT and the frequency is 500 kHz, the iron loss at 0 to 100 ° C. is 100 kW / m ³ or less, and the iron loss at the minimum iron loss temperature is 75 kW / m ³ or less. MnZnNiCo-based ferrite.

2. 2. The method for producing an MnZnNiCo-based ferrite according to 1 above, wherein Fe, Zn, Ni, Co and Mn raw materials as basic components are mixed, calcined, pulverized, and then Si as a sub-component. , Ca and Nb raw materials are mixed, crushed, then molded, fired, and then cooled. The Fe raw material is iron oxide, and the Cl content in the iron oxide is 500 mass ppm or less. A method for producing a MnZnNiCo-based ferrite, which comprises setting the maximum firing temperature to more than 1250 ° C. and further cooling the temperature between the maximum temperature and 1100 ° C. at a rate of 150 ° C./h or higher.

3. 3. 2. The method for producing MnZnNiCo-based ferrite according to 2 above, which comprises cooling from the maximum temperature to 1100 ° C. at a rate of 150 to 350 ° C./h.

4. The method for producing MnZnNiCo-based ferrite according to 2 or 3 above, wherein the maximum temperature is more than 1250 ° C and 1350 ° C or less.

According to the present invention, when a high frequency drive of 500 kHz is performed while maintaining a high saturation magnetic flux density until the transformer operating temperature (80 ° C.) in a high-density loaded state is reached, the magnetic loss is small in a wide temperature range and the magnetic loss is small. It is possible to provide MnZnNiCo-based ferrite having a high sintering density and a small variation in characteristics depending on the loading position at the time of firing the ferrite material.
Further, since the present invention has excellent magnetic characteristics at high frequencies, it is possible to reduce the size of the power transformer and reduce the iron loss.

Hereinafter, the present invention will be specifically described.
MnZnNiCo ferrite of the present invention, from the viewpoint of optimizing the temperature characteristics of reduced further according iron loss and iron loss during high frequency _driving, Fe ₂ O 3, ZnO, and following proper amount of NiO and CoO, the balance It is important that has a basic component consisting of MnO.

First, the basic components of the MnZnNiCo-based ferrite of the present invention will be specifically described.
Fe ₂ O ₃ : 53.00 to 57.00 mol% in the basic components
Fe ₂ O ₃ needs to have a mol ratio of 53.00 mol% or more in the basic component in order to have a saturation magnetic flux density of 1200 A / m at 80 ° C. of 400 mT or more. On the other hand, when Fe ₂ O ₃ exceeds 57.00 mol% in mol ratio in the basic component, the iron loss becomes too large. Therefore, the upper limit is set to 57.00 mol%. It is preferably in the range of 53.00 mol% or more and less than 57.00 mol%, more preferably 54.50 to 56.95 mol%.

ZnO: 4.00-11.00 mol% of the basic components
ZnO is added in a mol ratio in the basic component in order to reduce iron loss and maintain a small loss in a wide temperature range from 0 to 100 ° C. at a maximum magnetic flux density of 50 mT and a frequency of 500 kHz. It should be in the range of 4.00 to 11.00 mol%. It is preferably in the range of 5.50 to 8.50 mol%, more preferably 6.0 to 8.00 mol%.

NiO: 0.50 to 4.00 mol% of the basic ingredients
NiO has a saturation magnetic flux density of 1200 A / m at 80 ° C. and a saturation magnetic flux density of 400 mT or more, reduces iron loss, and has a maximum magnetic flux density of 50 mT and a frequency of 500 kHz, and has a wide temperature range from 0 to 100 ° C. In order to keep the loss small, it is necessary to add the amount in the range of 0.50 to 4.00 mol% in terms of the mol ratio in the basic component. It is preferably in the range of 1.50 to 3.50 mol%, and more preferably in the range of 1.00 to 3.00 mol%. In addition, it is more preferably in the range of 1.45 to 3.00 mol%, and most preferably in the range of 1.50 to 3.00 mol%.

CoO: 0.10 to 0.50 mol% in the basic ingredients
CoO also has a function of reducing the temperature coefficient of magnetic permeability, as described in Japanese Patent Publication No. 52-4753. However, when CoO is excessively contained, not only the temperature coefficient of iron loss becomes positive at room temperature or higher and thermal runaway occurs, but also the change with time becomes large, which is not desirable. Therefore, the upper limit of CoO is 0.50 mol% in terms of the mol ratio in the basic component. On the other hand, when the amount of CoO added is small, the effect of improving the temperature coefficient becomes small, and improvement of the iron loss value cannot be expected. Therefore, the lower limit of CoO is 0.10 mol% as the mol ratio in the basic component.

Ferrite of the present invention is a MnZnNiCo ferrite, the _Fe 2 _O 3, ZnO, basic components other than the NiO and CoO balance being manganese oxide (MnO). The preferable range of MnO is 31.50 to 40.00 mol% in mol ratio in the basic component, and more preferably 31.80 to 39.80 mol%. In addition, it is most preferably 31.80 to 37.40 mol%.

The basic components of the MnZnNiCo-based ferrite of the present invention have been described above, but the MnZnNiCo-based ferrite of the present invention needs to contain the following additive components as subcomponents in addition to the above basic components. _{That is, Fe 2} O ₃ , ZnO, MnO, NiO and CoO, which are the basic components of the ferrite of the present invention, _{form a spinel structure, but SiO 2} , CaO and Nb ₂ O which do not form a spinel are formed therein. _A high-performance MnZnNiCo-based ferrite having a smaller iron loss can be obtained by compound-adding an auxiliary component such as 5. _{In addition, components such as Ta 2} O ₅ , ZrO ₂ and V ₂ O ₅ that do not form spinel may be further added in a small amount.

SiO ₂ : 50 to 500 mass ppm with respect to the basic component
SiO ₂ forms a high resistance phase at the grain boundaries together with CaO, and contributes to the reduction of iron loss. However, if the addition amount is less than 50 mass ppm, the addition effect is small. On the other hand, if it is contained in excess of 500 mass ppm, abnormal grain growth occurs during sintering and iron loss is significantly increased. Therefore, SiO ₂ needs to be added in the range of 50 to 500 mass ppm with respect to the basic component. The range of 50 to 300 mass ppm is preferable in order to more strictly control the generation of abnormal particles in the sintered body structure. Further, the range of 70 to 300 mass ppm is more preferable.

CaO: 200-2000 mass ppm for the basic component
When CaO _{coexists with SiO 2,} it increases the grain boundary resistance and contributes to lower iron loss, but when the addition amount is less than 200 mass ppm, the effect is small. On the other hand, when it becomes more than 2000 mass ppm, the iron loss increases conversely. Therefore, CaO needs to be added in the range of 200 to 2000 mass ppm with respect to the basic component. In order to obtain a ferrite having a lower iron loss, CaO is preferably in the range of 200 to 1500 mass ppm. Further, the range of 400 to 1500 mass ppm is more preferable.

Nb ₂ O ₅ : 50 to 500 mass ppm for the basic component
Nb ₂ O ₅ effectively contributes to an increase in resistivity in the coexistence of SiO ₂ and CaO, but its addition effect is poor when the content is less than 50 mass ppm. On the other hand, if it exceeds 500 mass ppm, the iron loss will increase. Therefore, Nb ₂ O ₅ needs to be added in the range of 50 to 500 mass ppm with respect to the basic component. In order to obtain a ferrite having a lower iron loss, Nb ₂ O ₅ is preferably in the range of 50 to 350 mass ppm, more preferably in the range of 50 to 300 mass ppm. Further, the range of 60 to 270 mass ppm is most preferable.

The sintered density of the ferrite in the present invention, 4.85Mg / ^{m 3} greater than the 5.00 mg / ^{m 3} or less. If it is 4.85 Mg / m ³ or less, the predetermined strength may not be maintained and the characteristics may vary greatly depending on the loading position at the time of firing. On the other hand, if ^{it exceeds 5.00 Mg / m 3} , the iron loss during high frequency driving becomes large. To obtain a high strength ferrite at lower core loss, the sintered density 4.85Mg / ^{m 3} greater than the 4.95 mg / ^{m 3} or less. It is preferably in the range of 4.86 to 4.95 Mg / m ^3.

The MnZnNiCo-based ferrite in the present invention comprises the basic component, the sub-component, and the following unavoidable impurities.
That is, the components other than the basic component and the sub-component of the MnZnNiCo-based ferrite in the present invention are unavoidable impurities. Examples of this unavoidable impurity include Cl, Sr, Ba, P and B. And, as described below, Cl, Sr and Ba are components that need to be suppressed to a predetermined amount or less in particular. The smaller the content of unavoidable impurities, the better, and it is preferable that the content is 0 mass%, but in the present invention, it is allowed to be about 0.01 mass% or less.

Cl: 80 mass ppm or less To suppress the generation of abnormal grains in the sintered structure and the variation in particle size distribution of crystal grains, and to suppress the decrease in saturation magnetic flux density due to the decrease in the density of the sintered core, iron oxide as a raw material It is necessary to reduce the amount of Cl in the sinter to 500 mass ppm or less, and to suppress the amount of Cl remaining in the final sintered body after firing, that is, the MnZnNiCo-based ferrite to 80 mass ppm or less. It is preferably 75 mass ppm or less.
The Cl contained in the raw material iron oxide can be in the above range by volatilizing it during the firing, but if high-purity iron oxide is selected, the firing time is short because the conditions for volatilization are unnecessary. However, it can be within the above component composition range.

Sr: 10.0mass ppm or less, Ba: 10.0mass ppm or less As described above, the MnZnNiCo-based ferrite of the present invention has the composition of the basic components Fe ₂ O ₃ , ZnO, MnO, NiO and CoO in the above range. In addition to controlling each, _{it is necessary to add SiO 2} , CaO and Nb ₂ O as auxiliary components in appropriate amounts in a complex manner. Further, in order to stably realize low iron loss in the temperature range of 0 to 100 ° C., it is necessary to limit the contents of Sr and Ba contained as trace components in addition to Cl as described above. be.

Here, Sr and Ba are elements that do not have a spinel structure and are used when forming hexagonal ferrite, so-called hard ferrite. The mechanism by which these Sr and Ba affect the magnetic properties of the MnZnNiCo-based ferrite, which is the final sintered body, especially the iron loss and magnetic permeability in the temperature range of 0 to 100 ° C. has not been clarified yet. However, the inventors think as follows.
That is, when Co that has a great influence on magnetic anisotropy is contained like MnZnNiCo-based ferrite of the present invention, these Sr and Ba interact with Co to cause an iron loss value. It is thought that this is because it becomes difficult to reduce.

As in the present invention, in order to realize low iron loss in a wide temperature range of 0 to 100 ° C., the contents of Sr and Ba need to be 10.0 mass ppm or less, respectively. This is because if both Sr and Ba are contained in excess of 10.0 mass ppm, a predetermined low iron loss value cannot be obtained. Therefore, the contents of Sr and Ba are suppressed to the range of 10.0 mass ppm or less, respectively. Further, in order to realize low iron loss, it is preferable to keep the Sr and Ba contents in the range of 7.0 mass ppm or less, respectively.

Note that the Sr and Ba, iron oxide _{(Fe 2 O} 3) as a raw material for the main component, zinc oxide (ZnO), and may be included in the manganese oxide (MnO). Therefore, the contents of Sr and Ba can be adjusted by adjusting the amounts of various iron oxide, zinc oxide and manganese oxide raw materials having different contents of Sr and Ba.

Next, a method for producing MnZnNiCo-based ferrite in the present invention will be described.
MnZnNiCo ferrite of the present invention, _{first, Fe 2 O 3, ZnO,} MnO, a powder raw material of NiO and CoO, were weighed to make a predetermined ratio specified in the present invention, calcining a mixture of these well And crush to obtain ferric powder.
At that time, it is important to suppress the Cl content in _{iron oxide (Fe 2} O ₃ ), which is a Fe raw material, to 500 mass ppm or less. For that purpose, for example, the iron oxide obtained by the iron chloride roasting method is washed. The Cl content in iron oxide for ferrite is 0.15% (= 1500 ppm) or less in JIS K1462 (1981), but in the present invention, as described above, the density of the sintered core is reduced. In order to suppress the decrease in saturation magnetic flux density due to the above, it is necessary to further reduce it.

Next, the above-mentioned sub-ingredients are added to the temporary baking powder so as to have a predetermined ratio specified in the present invention, mixed, and further pulverized. In this pulverization work, it is necessary to sufficiently homogenize so that the concentration of the added component is not biased. After that, an organic binder such as polyvinyl alcohol is added to the crushed calcined powder, granulated, and further pressure is applied to form a predetermined shape, which is then fired to form a sintered body (product). do.

Here, it is important that the firing conditions include a cooling step in which the cooling rate in all temperature ranges from the maximum temperature to 1100 ° C. is 150 ° C./h or more. This is because the conditions including such a cooling step can achieve both the sintering density of the ferrite of the present invention and the formation of a desired grain boundary phase. On the other hand, the upper limit of the cooling rate is not particularly limited, but is preferably about 350 ° C./h from the viewpoint of the cost for increasing the cooling capacity. The cooling rate is more preferably 160 to 350 ° C./h, further preferably 185 to 350 ° C./h, and most preferably 200 to 340 ° C./h. Further, the fluctuation of the cooling rate is permissible as long as MnZnNiCo-based ferrite satisfying the constituent requirements of the present invention can be obtained.
Further, the grain boundary phase is _{formed by uniformly precipitating components such as SiO 2} , Ca, and Nb ₂ O ₅ added as trace components in a thin, high concentration, and uniformly, and the cooling rate at the time of firing. By controlling the above, a desired oxidation state can be obtained and the insulating property can be improved. The grain boundary phase from which the effect of the present invention can be obtained can be effectively obtained by using the composition of the present invention and the firing conditions including the cooling step.

The other conditions of the firing are not particularly limited as long as the above-mentioned ferrite sintering density and grain boundary phase can be obtained, but it is important that the maximum temperature is more than 1250 ° C. This is because the desired sintering density cannot be obtained at 1250 ° C. or lower. On the other hand, the upper limit of the maximum temperature is not particularly limited, but is preferably 1350 ° C. or lower from the viewpoint of cost due to heating and the like. The maximum temperature is more preferably in the range of 1260 to 1350 ° C, most preferably 1260 to 1340 ° C.
Further, it is preferable that the maximum temperature holding time is in the range of 1 to 8 hours and the oxygen concentration at the maximum temperature is in the range of 1 to 10 vol%. This is because the above-mentioned ferrite sintering density and grain boundary phase can be effectively obtained. Other conditions not described in the present specification for the firing may be in accordance with a conventional method.

Since the MnZnNiCo-based ferrite thus obtained has the grain boundary phase, the eddy current loss that greatly affects the iron loss at high frequencies is reduced while maintaining the high sintering density, and the conventional MnZn-based ferrite is used. It was extremely difficult to realize this with ferrite, and the saturation magnetic flux density at a magnetization force of 1200 A / m at 80 ° C. was 400 mT or more, preferably 425 mT or more, and the maximum magnetic flux density was 50 mT and the frequency was measured at 0 to 100 ° C. The iron loss is 100 kW / m ³ or less, and the iron loss at the temperature at which the iron loss is minimized (also referred to as the iron loss minimum temperature in the present invention) measured at a maximum magnetic flux density of 50 mT and a frequency of 500 kHz is 75 kW / m ³ or less. Even when driving at a high frequency of 500 kHz while maintaining a high saturation magnetic flux density up to the transformer operating temperature (80 ° C) in a high-density loaded state, the magnetic loss is small over a wide temperature range. In addition, the MnZnNiCo-based ferrite of the present invention has high strength and small variation in characteristics depending on the loading position during firing.

The other steps of producing the MnZnNiCo-based ferrite powder and the sintered body (MnZnNiCo-based ferrite) are not particularly limited and may follow a so-called conventional method.

Hereinafter, examples confirmed for the present invention will be described.
(Example 1)
The _{raw materials of the basic components of Fe 2} O ₃ , ZnO, MnO, NiO and CoO were mixed so as to have various compositions shown in Table 1-1 and Table 2-1. As these raw materials, those having different impurities contents were used.
After the above mixing, calcination was performed at 930 ° C. for 3 hours and pulverized to obtain a calcination powder. _{SiO 2} , CaO and Nb ₂ O ₅ as subcomponents were added to the obtained calcination powder in the amounts shown in Table 1-1 and Table 2-1 with respect to the basic components, and the ball mill was used. It was crushed for 10 hours to obtain crushed powder. Then, polyvinyl alcohol is added as a binder to the crushed powder, and the granulated powder is granulated to obtain a granulated powder, and then the granulated powder is formed into a ring shape having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm. It was made into a molded body. Then, this molded product was calcined at the maximum temperature shown in Table 1-1 and Table 2-1 in a mixed gas of nitrogen and air in which the oxygen partial pressure was controlled in the range of 1 to 5 vol% for 3 hours. .. Finally, a ring-shaped sample (ferrite sintered body) was obtained by cooling from the maximum temperature to 1100 ° C. at the speeds shown in Table 1-1 and Table 2-1. The amount of Cl in iron oxide, the amount of Cl in the sintered body, the amount of Sr, and the amount of Ba in Tables 1-1 and 2-1 were measured by a fluorescent X-ray analysis according to a conventional method, and the ratios to the basic components were measured. Was calculated and calculated. The sintering densities in Tables 1-2 and 2-2 were measured by measuring the ring-shaped sample according to the Archimedes method.
When the ring-shaped sample obtained as described above is wound with 20 turns on the primary side and 40 turns on the secondary side and a magnetic field of 1200 A / m is applied by a DC BH loop tracer at 20 to 200 ° C. The magnetic flux density was measured. This is because the magnetic flux is almost saturated in a magnetic field of this magnitude, and the value of the magnetic flux density at this time is considered to be the saturated magnetic flux density.
Further, 5 windings on the primary side and 5 windings on the secondary side were applied, and an AC BH loop tracer was used to measure the iron loss when the temperature was changed and the magnetic flux density was excited to 50 mT at a frequency of 500 kHz.

Based on the above measurement results, the density of the ferrite sintered body, the saturation magnetic flux density at 80 ° C., the iron loss minimum temperature, and the iron loss value at 0 ° C., 100 ° C. and the iron loss minimum temperature (hereinafter, simply referred to as physical property values). Refers to the physical property values of these 6 items) are shown in Table 1-2 and Table 2-2, respectively. Here, No. 1 and 1 and 2 in Tables 1 and 2. 1-1 to 1-27 are examples of inventions conforming to the present invention, while Nos. 1-1 and 2 in Tables 21 and 2. 2-1 to 2-28 show comparative examples outside the scope of the present invention. In addition, No. In 1-1 to 1-19, the maximum temperature during firing was set to 1300 ° C. 1-20 to 1-23 showed an example in which the maximum temperature during firing was changed to any of 1260 ° C, 1275 ° C, 1325 ° C and 1340 ° C, respectively. In addition, No. 1 and 1 and 2 in Tables 1 and 2. 1-24 to 1-26 are examples in which the cooling rate was changed, Nos. 1 and 2 in Tables 1 and 2. 1-27 shows an example in which the amount of Cl in iron oxide was reduced.

As can be seen from the descriptions in Tables 1-1 and 2 and Tables 2-1 _{and 2 , the composition of the basic components of Fe 2} O ₃ , ZnO, MnO, NiO and CoO and the sub-components of SiO 2, CaO and Nb ₂ O ₅ As iron oxide as a ferrite raw material, iron oxide having a Cl content of 500 mass ppm or less is used, and the Cl content in the final sintered body is suppressed to 80 mass ppm or less. MnZnNiCo ferrite of the invention examples of controlling the Sr and Ba below 10.0 mass ppm is the firing conditions of the present invention, both the sintered density of 4.85Mg / m ³ greater, 5.00 mg / m ³ or less It is in the range of. Further, the saturation magnetic flux density at a magnetization force of 1200 A / m and a measurement temperature of 80 ° C. is 400 mT or more. Further, the iron loss at 0 and 100 ° C. measured at a maximum magnetic flux density of 50 mT and a frequency of 500 kHz is 100 kW / m ³ or less, and the iron loss at the minimum iron loss temperature is 75 kW / m ³ or less.
From these facts, it can be seen that according to the present invention, a MnZnNiCo-based ferrite material having low iron loss can be obtained in the temperature range of 0 to 100 ° C. while maintaining high sintering density and saturation magnetic flux density.

On the other hand, the MnZnNiCo-based ferrites of the comparative examples, which do not satisfy any of the component compositions of the present invention, have an iron loss value of 100 kW at any temperature of 0 or 100 ° C. measured at a maximum magnetic flux density of 50 mT and a frequency of 500 kHz. / ^{m 3} a is over. Further, the iron loss value at the minimum iron loss temperature is only obtained in excess of ^{75 kW / m 3.}

(Example 2)
Hereinafter, an example in which the variation in the characteristic value depending on the loading position of firing is confirmed will be described.
The basic components of Fe ₂ O ₃ , ZnO, MnO, NiO and CoO were added to the sample No. 1 in Table 1-1. The raw materials were mixed so as to have the composition shown in 1-20. After the above mixing, calcination was performed at 930 ° C. for 3 hours and pulverized to obtain a calcination powder. In the obtained calcined powder, SiO ₂ , CaO and Nb ₂ O ₅ were added as auxiliary components to the sample No. 1 in Table 1-1 with respect to the basic components. It was added in the amount shown in 1-20 and pulverized with a ball mill for 10 hours to obtain pulverized powder.
Then, polyvinyl alcohol was added as a binder to the pulverized powder, and the granulated powder was granulated to obtain granulated powder, and then the granulated powder was formed into a ring shape having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm. 192 molded bodies were produced.
The above 192 molded bodies were loaded on a 300 mm square firing base plate in a plane: 8 rows × 8 columns and a height: 3 layers. Then, in the mixed gas of nitrogen and air in which the oxygen partial pressure was controlled in the range of 1 to 5 vol%, the sample No. in Table 1-1. Baking was performed at the maximum temperature shown in 1-20 for 3 hours. Finally, the sample No. in Table 1-1. A ring-shaped sample (ferrite sintered body) was obtained by cooling from the above maximum temperature to 1100 ° C. at the speed shown in 1-20.

The physical property values were measured by the method described in Example 1, and the variation (maximum value-minimum value) of each physical property value depending on the loading position of firing was determined. Each result is presented in Sample No. It is shown in Table 3 as 1-20.
In addition, the sample No. in Table 1-1. 1-21, sample No. 1-22, Sample No. Sample Nos. 1-23 and Table 2-1. For 2-27, samples were prepared in the same procedure, and the variation (maximum value-minimum value) of each physical property value was determined. Each result is presented in Sample No. 1-21, sample No. 1-22, Sample No. 1-23 and sample No. It is also shown in Table 3 as 2-27.

From the results of Example 1 and the results shown in Table 3, the invention examples (Sample No. 1-20, Sample No. 1-21, Sample No. 1-22 and Sample No. 1-23) are comparative examples (sample No. 1-20, sample No. 1-21, sample No. 1-22 and sample No. 1-23). It can be seen that not only the physical property values are superior to those of Sample No. 2-27), but also the variation of the physical property values is small.

(Example 3)
Hereinafter, an experiment will be conducted to clarify the technical meaning that defines the cooling rate up to 1100 ° C., and the technical meaning clarified as a result of the experiment will be described together with the experimental result.
The _{raw materials of the basic components of Fe 2} O ₃ , ZnO, MnO, NiO and CoO were mixed so as to have the composition shown in Table 4-1.
After the above mixing, calcination was performed at 930 ° C. for 3 hours and pulverized to obtain a calcination powder. _{SiO 2} , CaO and Nb ₂ O ₅ as auxiliary components were added to the obtained calcined powder in the amounts shown in Table 4-1 with respect to the basic components, and the mixture was pulverized by a ball mill for 10 hours. It was made into powder. Then, polyvinyl alcohol is added as a binder to the crushed powder, and the granulated powder is granulated to obtain a granulated powder, and then the granulated powder is formed into a ring shape having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm. It was made into a molded body. Then, this molded product was calcined at the maximum temperature shown in Table 4-1 for 3 hours in a mixed gas of nitrogen and air in which the oxygen partial pressure was controlled in the range of 1 to 5 vol%.
Next, the ring-shaped sample (ferrite sintered body) is cooled from the above maximum temperature to 1200 ° C. at the speed shown in Table 4-1 and further cooled from 1200 ° C. to 1100 ° C. at the speed shown in Table 4-1. ) Was obtained. The amount of Cl in iron oxide, the amount of Cl in the sintered body, the amount of Sr, the amount of Ba, and the sintering density in Table 4-1 were measured by the same method as in Example 1.
Further, the physical property values were measured by the same method as in Example 1. The results of each measurement are shown in Table 4-2.

The MnZnNiCo-based ferrites of Samples 4-1 and 4-2, which are comparative examples, have an iron loss value of 100 kW / m at any temperature of 0 or 100 ° C. measured at a maximum magnetic flux density of 50 mT and a frequency of 500 kHz. ^It is over 3. Further, the iron loss value at the minimum iron loss temperature is only obtained in excess of ^{75 kW / m 3.}

According to the result of the third embodiment, cooling from the maximum temperature to 1100 ° C. at a predetermined rate causes a particularly high saturation magnetic flux density until the transformer operating temperature (80 ° C.) in a high-density loaded state is reached. It can be seen that it is an important requirement for suppressing magnetic loss in a wide temperature range when driving at a high frequency of 500 kHz while maintaining the temperature.

INDUSTRIAL APPLICABILITY The present invention can provide a MnZnNiCo-based ferrite having a high saturation magnetic flux density and a small magnetic loss in a wide temperature range even at a high frequency of 500 kHz, and is therefore increasingly used in in-vehicle equipment, industrial equipment, and the like. It can be widely applied to high-frequency drive power supplies using SiC and GaN semiconductor devices.

Claims (4)

In MnZnNiCo-based ferrite consisting of basic components, sub-components and unavoidable impurities,
The basic ingredients
Fe ₂ O ₃ : 53.00 to 57.00 mol%,
ZnO: 4.00-11.00 mol%,
NiO: 0.50 to 4.00 mol% and CoO: 0.10 to 0.50 mol%
The rest is MnO
year,
The sub-component with respect to the basic component
SiO ₂ : 50-500 mass ppm,
CaO: 200-2000 mass ppm and Nb ₂ O ₅ : 50-500 mass ppm
year,
Further, Cl, Sr and Ba in the unavoidable impurities are each set to Cl: 80 mass ppm or less with respect to the basic component.
Sr: 10.0mass ppm or less and Ba: 10.0mass ppm or less are suppressed and included.
The sintering density is more ^{than 4.85 Mg / m 3} and 5.00 Mg / m ³ or less, the saturation magnetic flux density at a magnetization force of 1200 A / m at 80 ° C. is 400 mT or more, and the maximum magnetic flux density is 50 mT. A MnZnNiCo-based ferrite characterized in that the iron loss at 0 to 100 ° C. is 100 kW / m ³ or less and the iron loss at the minimum iron loss temperature is 75 kW / m ^{3 or less when the frequency is 500 kHz.} The method for producing an MnZnNiCo-based ferrite according to claim 1, wherein Fe, Zn, Ni, Co and Mn raw materials, which are basic components, are mixed, calcined, pulverized, and then further become a sub-component. It has the steps of mixing Si, Ca and Nb raw materials, crushing, then molding, firing and then cooling.
The Fe raw material is iron oxide, and the Cl content in the iron oxide is 500 mass ppm or less.
A method for producing MnZnNiCo-based ferrite, which comprises setting the maximum temperature of calcination to more than 1250 ° C. and further cooling from the maximum temperature to 1100 ° C. at a rate of 150 ° C./h or more. The method for producing MnZnNiCo-based ferrite according to claim 2, wherein the mixture is cooled from the maximum temperature to 1100 ° C. at a rate of 150 to 350 ° C./h. The method for producing an MnZnNiCo-based ferrite according to claim 2 or 3, wherein the maximum temperature is more than 1250 ° C and 1350 ° C or less.