JP6742440B2 - MnCoZn ferrite and method for producing the same - Google Patents

Description

The present invention relates to a MnCoZn-based ferrite having a high specific resistance, a small coercive force, and a defect, and a method for producing the same.
In addition, in this specification, a coercive force says the value in 23 degreeC.

A typical example of the soft magnetic oxide magnetic material is MnZn ferrite. Conventional MnZn ferrite includes ^{Fe 2+} about 2mass% or more with positive anisotropy, ^Fe 3+ having a negative anisotropy, by offsetting the ^{Mn 2+,} high HatsuToru磁rates in kHz region Has achieved low losses.
Since this MnZn ferrite is cheaper than amorphous metal or the like, it is widely used as a noise filter for switching power supplies, magnetic cores for transformers and antennas.

However, since MnZn ferrite has a large amount of Fe ²⁺ , it has a drawback that electrons are easily exchanged between Fe ^{3+ and} Fe ²⁺ , and the specific resistance is as low as 0.1 Ω·m. Therefore, when the frequency range used becomes high, the loss due to the eddy current flowing in the ferrite rapidly increases, the initial permeability greatly decreases, and the loss also increases. Therefore, the useful frequency of MnZn ferrite is limited to about several hundred kHz, and NiZn ferrite is mainly used in the MHz order. The specific resistance of this NiZn ferrite is 10 ⁵ (Ω·m) or more, which is about 10,000 times that of MnZn ferrite, and since the eddy current loss is small, the characteristics of high initial permeability and low loss are not easily lost even in the high frequency region.

However, NiZn ferrite has a big problem. Since the soft magnetic material is required to react sensitively to changes in the external magnetic field, it is preferable that the coercive force Hc is small, but NiZn ferrite is composed only of ions having negative magnetic anisotropy. That is, the value of this coercive force is large. The coercive force is specified in JIS C2560-2.

As a method of obtaining a ferrite having a large specific resistance other than NiZn ferrite, there is a method of increasing the specific resistance by reducing the amount of Fe ²⁺ contained in the MnZn ferrite.
For example, Patent Document 1, Patent Document 2, Patent Document 3, and the like report MnZn ferrite in which the Fe ₂ O ₃ component is less than 50 mol% and the Fe ²⁺ content is reduced to increase the specific resistance. However, since these also consist of only ions having negative magnetic anisotropy like NiZn ferrite, the problem of reduction of coercive force has not been solved at all.

Therefore, techniques for adding Co ²⁺ having a positive magnetic anisotropy other than Fe ²⁺ have been disclosed in Patent Document 4, Patent Document 5 and Patent Document 6, but these aimed at reducing the coercive force. It wasn't something. Further, since the countermeasure against abnormal grains described later is insufficient, it is inferior in terms of cost and manufacturing efficiency.

On the other hand, Patent Document 7 reports a high-resistance MnCoZn ferrite that suppresses the appearance of abnormal grains by controlling the impurity composition, enables stable production, and has a low coercive force.
Note that abnormal grain growth occurs when the grain growth balance is locally disrupted for some reason, and is a phenomenon often observed during manufacturing using powder metallurgy. Substances that greatly impede the movement of the domain wall, such as impurities and lattice defects, are mixed in the abnormally grown grains, so that the soft magnetic properties are lost and the coercive force is increased. At the same time, the formation of crystal grain boundaries becomes insufficient, so that the specific resistance decreases.

JP-A-7-230909 JP 2000-277316 A JP, 2001-220222, A Japanese Patent No. 3418827 JP, 2001-220221, A JP 2001-68325 A Japanese Patent No. 4554959 JP, 2006-44971, A

The development of the above-mentioned Patent Document 7 has made it possible to obtain MnCoZn ferrite having satisfactory magnetic characteristics.
On the other hand, in recent years, the movement of electrification of automobiles has been remarkable, and the number of cases in which MnCoZn ferrite is also mounted in automobiles is increasing. However, the important property for the same purpose is mechanical strength. Compared with electrical products and industrial equipment, which had been the main application until then, vibration occurs during driving in automobiles. Therefore, MnCoZn ferrite, which is a ceramic, is required to be one that will not be damaged by shock due to vibration in in-vehicle applications. Is becoming available.

However, MnCoZn ferrite containing less than 50 mol% of Fe ₂ O ₃ component has few oxygen vacancies, so that sintering is likely to proceed during firing, and therefore vacancies are likely to remain in the crystal grains and crystal grain boundaries are generated. Tends to be uneven. As a result, there is a problem that, when an impact is applied from the outside, it is more likely to be damaged than the conventional MnCoZn ferrite.
That is, the technique disclosed in Patent Document 7 has a problem that the obtained magnetic characteristics are sufficient, but the mechanical strength against this defect is not necessarily sufficient.

As a technique for improving the chipping strength, Patent Document 8 discloses a technique for adding TiO ₂ in the range of 0.01 to 0.5 mass %.
However, on the other hand, addition of TiO ₂ causes a solid solution in the crystal grains to generate Ti ^4+, and a part of Fe ³⁺ is reduced to Fe ²⁺ from the valence balance, resulting in a large decrease in specific resistance. There was a disadvantage.

The present invention, while maintaining good magnetic properties such as high resistance and low coercive force of the related art, suppresses abnormal grain growth while generating uniform crystal grain boundaries, thereby providing a defect resistance represented by a ratler value. The purpose of the present invention is to propose MnCoZn ferrite which also has mechanical strength called property, together with its advantageous manufacturing method.

The inventors first examined the appropriate amounts of Fe ₂ O ₃ , ZnO, and CoO of MnCoZn ferrite required to obtain the desired magnetic properties, and as a result, the results show that the specific resistance is high, the coercive force is small, and the Curie temperature is high. We have found an appropriate range in which all of the high characteristics can be realized at the same time.
In this specification, as described above, the coercive force has a value at 23° C. as a problem. This is because many MnZn ferrite cores used for antennas and noise filters are used at a position away from a power source transformer or a semiconductor, which is a heat source, and these operate at room temperature (5 to 35°C). To do. Therefore, it is important that the magnetic properties are good at 23° C., which is a typical value in the normal temperature range (5 to 35° C.), that is, the coercive force is small.

Next, focusing on the microstructure, it was found that voids in the crystal grains can be reduced, the grain size can be adjusted, and grain boundaries of appropriate thickness can be realized, thereby suppressing defects in the sintered core that can be expressed by the Ratler value. .. Here, in order to realize a desired crystal structure, the addition amounts of SiO ₂ and CaO, which are the components segregated at the crystal grain boundaries, have a great influence, and therefore, we have succeeded in determining the appropriate amount ranges of these components. Within this range, a low Ratler value can be maintained.

Further, as for suppression of the appearance of abnormal grains, which is indispensable for having suitable magnetic properties and mechanical strength against defects, as a result of studying the production conditions when the abnormal grains appear, the above-mentioned SiO ₂ And when CaO is in excess, and when it is contained in natural ores or when impurities such as Cd, Pb, Sb, As, and Se that are mixed in during smelting are contained above a certain value, abnormal grains Was found to appear.
The present invention is based on the above findings.

As described above, in Patent Document 1, Patent Document 2, and Patent Document 3, etc., high specific resistance is mentioned, and in Patent Document 4, Patent Document 5 and Patent Document 6, positive magnetic anomalies are mentioned. Although the description has been made regarding the addition of Co ²⁺ having a directionality, there is no description regarding the coercive force, and Patent Document 5 rather conversely stipulates that Pb is intentionally added. Moreover, since none of these Patent Documents 1 to 6 describes any countermeasure against abnormal grains, it is presumed that the mechanical strength is also insufficient. In addition, also in Patent Document 7 which mentions low coercive force, since the definition of the additive is insufficient, sufficient mechanical strength capable of suppressing defects cannot be expected. Further, even in Patent Document 8 which mentions improvement of the chip strength, a large decrease in specific resistance cannot be avoided.

The gist of the present invention is as follows.
1. A MnCoZn-based ferrite comprising a basic component, a subcomponent, and unavoidable impurities,
As the above basic ingredients,
Iron: 45.0 mol% or more and less than 50.0 mol% in terms of Fe ₂ O ₃ ,
Zinc: 15.5 to 24.0 mol% in terms of ZnO,
Cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese: including the balance,
With respect to the basic components, as the secondary components,
SiO ₂ : 50 to 300 massppm and CaO: 700 to 1300 massppm
Including ,
Cd in the upper Symbol unavoidable impurities, Pb, Sb, As and Se amounts respectively suppressed to less than 20Massppm,
Furthermore ,
La Tolar value is less than 0.85%,
Coercive force at 23°C is 15 A/m or less,
Resistivity 30 [Omega · m or more, and the Curie temperature Ri der 100 ° C. or higher,
Particle size distribution value of d90 is 230μm~300μm and crushing strength is more than 1.18 MPa, the molding of the granulated powder is less than 1.50MPa - MnCoZn ferrite ing a sintered body.

2. 2. The MnCoZn-based ferrite according to 1, wherein the MnCoZn-based ferrite has a sintered density of 4.85 g/cm ³ or more.

3. A calcination step of calcination of a mixture of basic components weighed so as to have a predetermined component ratio;
In the calcined powder obtained in the calcination step, a sub-component adjusted to a predetermined ratio is added, and the mixture is mixed and crushed;
After the binder is added to and mixed with the pulverized powder obtained in the mixing-pulverization step, the granulated powder is produced so that the value of the particle size distribution d90 is 230 μm to 300 μm and the crush strength is 1.18 MPa or more and less than 1.50 MPa. After the granulation, the obtained granulated powder is molded, and then fired under the conditions of the maximum holding temperature: 1290 or more and the holding time: 1 hour or more to obtain a MnCoZn-based ferrite.
A method for producing a MnCoZn-based ferrite comprising a basic component, an auxiliary component, and unavoidable impurities having
As the above basic ingredients,
Iron: 45.0 mol% or more and less than 50.0 mol% in terms of Fe ₂ O ₃ ,
Zinc: 15.5 to 24.0 mol% in terms of ZnO,
Cobalt: 0.5 to 4.0 mol% in terms of CoO and
Manganese: balance
Including,
With respect to the basic component, as the auxiliary component,
SiO ₂ : 50 to 300 massppm and
CaO: 700-1300 massppm
Including,
The amount of Cd, Pb, Sb, As and Se in the inevitable impurities is suppressed to less than 20 massppm,
further,
Ratler value is less than 0.85%,
Coercive force at 23°C is 15 A/m or less,
Specific resistance of 30 Ω・m or more
Curie temperature is over 100℃
A method for producing MnCoZn-based ferrite, which is

4. 4. The method for producing an MnCoZn-based ferrite according to the above 3, wherein the sintered density of the MnCoZn-based ferrite is 4.85 g/cm ³ or more.

5 . 5. The method for producing MnCoZn ferrite according to 3 or 4 above, wherein the granulation is a spray drying method.

According to the present invention, not only has good magnetic properties such as high resistance and low coercive force, but it also suppresses abnormal grain growth at the same time as generating uniform grain boundaries. It is possible to obtain MnCoZn ferrite that also has strength.
The MnCoZn ferrite of the present invention has excellent magnetic properties such that the initial magnetic permeability at 23° C. and 1 kHz is 3000 or more, the initial magnetic permeability at 23° C. and 1 MHz is 2000 or more, and the initial magnetic permeability at 23° C. and 10 MHz is 150 or more. ..

Hereinafter, the present invention will be specifically described.
First, the reason why the composition of MnCoZn ferrite is limited to the above range in the present invention will be described. It should be noted that iron, zinc, cobalt, and manganese contained in the present invention as basic components are all represented by values converted to Fe ₂ O ₃ , ZnO, CoO, and MnO. Further, the contents of these Fe ₂ O ₃ , ZnO, CoO, and MnO are expressed in mol %, while the contents of subcomponents and impurity components are expressed in mass ppm with respect to the whole ferrite.

Fe ₂ O _3: 45.0mol% or more, if less than 50.0mol% Fe ₂ O ₃ is excessively contained, ^{Fe 2+} content is increased, whereby the specific resistance of MnCoZn ferrite is reduced. In order to avoid this, the amount of Fe ₂ O ₃ needs to be suppressed to less than 50 mol %. However, when the amount is too small, the coercive force is increased and the Curie temperature is decreased. Therefore, at least 45.0 mol% of iron is calculated in terms of Fe ₂ O ₃ . The preferable range of Fe ₂ O ₃ is 47.1 mol% or more and less than 50.0 mol%, and more preferably 47.1 to 49.5 mol%.

ZnO: 15.5 mol% to 24.0 mol%
ZnO has a function of increasing the saturation magnetization of ferrite and also of increasing the sintering density and saturation magnetic flux density because of its relatively low saturation vapor pressure, and is an effective component for lowering the coercive force. Therefore, at least zinc should be contained in an amount of 15.5 mol% in terms of ZnO. On the other hand, when the zinc content is more than the proper value, the Curie temperature is lowered, which is a practical problem. Therefore, the upper limit of zinc is 24.0 mol% in terms of ZnO. The preferable range of ZnO is 15.5 to 23.0 mol%, more preferably 17.0 to 23.0 mol%.

CoO: 0.5 mol% to 4.0 mol%
Co ²⁺ in CoO is an ion having a positive magnetic anisotropy energy. With the addition of an appropriate amount of CoO, the absolute value of the total magnetic anisotropy energy decreases, resulting in a decrease in coercive force. It For that purpose, it is essential to add CoO by 0.5 mol% or more. On the other hand, a large amount of addition causes a decrease in resistivity, induces abnormal grain growth, and causes the total magnetic anisotropy energy to be excessively positive, which in turn increases coercive force. In order to prevent this, the maximum addition of CoO is 4.0 mol%. The preferable range of CoO is 1.0 to 3.5 mol%, and more preferably 1.0 to 3.0 mol%.

MnO: Balance The present invention is MnCoZn ferrite, and the balance of the basic component composition needs to be MnO. The reason is that good magnetic characteristics such as high saturation magnetic flux density, low loss and high magnetic permeability cannot be obtained unless MnO is used. The preferable range of MnO is 26.5 to 32.0 mol %.

The basic components have been described above, but the secondary components are as follows.
SiO ₂ : 50 to 300 massppm
It is known that SiO ₂ contributes to the homogenization of the crystal structure of ferrite, and when an appropriate amount of SiO ₂ is added, the number of pores remaining in the crystal grains is reduced, and the residual magnetic flux density is reduced, thereby lowering the coercive force. Let Further, SiO ₂ segregates at the grain boundaries to increase the specific resistance, and at the same time, to reduce crystals having a coarse grain size, so that the ratler value, which is an index of the defect of the sintered body, can be reduced. Therefore, at least 50 massppm of SiO ₂ is included. On the other hand, when the added amount is too large, abnormal grains appear on the contrary, which becomes the starting point of the defect, and the Ratler value increases, and at the same time, the coercive force also increases. Therefore, the content of SiO ₂ is limited to 300 mass ppm or less. There is a need. A more preferable SiO ₂ content is in the range of 60 to 250 mass ppm.

CaO: 700 ~1300massppm
CaO segregates at the crystal grain boundaries of MnCoZn ferrite, has the function of suppressing the growth of crystal grains, and also has the role of reducing the voids remaining in the crystal grains. Therefore, with the addition of an appropriate amount, the specific resistance increases, the coercive force also decreases, and coarse crystals are reduced, so that the Ratler value can be reduced. Therefore, at least 700 mass ppm of CaO is included. On the other hand, if the amount of addition is excessive, abnormal grains will appear, and the Ratler value and coercive force will also rise, so the content of CaO must be limited to 1300 mass ppm or less. The more preferable CaO content is in the range of 700 to 1000 mass ppm.

Next, the impurity components to be suppressed will be described.
Each of Cd, Pb, Sb, As, and Se is less than 20 mass ppm. These are components inevitably contained in the raw material because they are contained in the natural ore or are mixed during smelting. There is no problem if the content of these elements is very small, but if they are contained in a certain amount or more, abnormal grain growth of ferrite is induced and seriously adversely affects various characteristics of the obtained ferrite. As in the present invention, ferrite having a composition containing less than 50 mol% of Fe ₂ O ₃ is more likely to undergo crystal grain growth than one containing 50 mol% or more, and therefore the amount of Cd, Pb, Sb, As and Se is increased. If the amount is large, abnormal grain growth is likely to occur. In that case, not only the coercive force increases, but also the generation of the crystal grain boundaries becomes insufficient, so that the specific resistance decreases, and it becomes the starting point of the defect, so that the Ratler value also increases.
Therefore, in the present invention, the contents of Cd, Pb, Sb, As and Se are each controlled to be less than 20 massppm.
In addition, the allowable amount of inevitable impurities including Cd, Pb, Sb, As, and Se described above needs to be 50 mass ppm or less in total. Preferably, the allowable amount of the unavoidable impurities is 40 mass ppm or less.

Therefore, it is preferable to suppress the mixing of impurities in the basic component and the subsidiary component used as raw materials as much as possible. The total amount of impurities in the basic components and subcomponents used as raw materials is preferably 50 massppm or less, and more preferably 40 massppm or less, including the above-mentioned Cd, Pb, Sb, As and Se .

Further, not only the composition but also various parameters have a great influence on various characteristics of the MnCoZn ferrite. Therefore, in the present invention, it is preferable to satisfy the following conditions in order to have desired magnetic characteristics and strength characteristics.

-Sintering density: 4.85 g/cm ³ or more In MnCoZn ferrite, sintering and grain growth proceed by firing treatment, and crystal grains and crystal grain boundaries are formed. A crystal structure that can realize a low coercive force, that is, a non-magnetic component that should exist in a crystal grain boundary is properly segregated in the crystal grain boundary, and the crystal grain is composed of a component that maintains an appropriate grain size and has uniform magnetism. In order to achieve the desired morphology, the sintering reaction needs to proceed sufficiently. Also, from the viewpoint of preventing chipping, insufficient sintering is not preferable because the strength decreases.
From the above viewpoints, the MnCoZn ferrite of the present invention preferably has a sintered density of 4.85 g/cm ³ or more. By satisfying this, the coercive force can be reduced and the Ratler value can be suppressed low. In order to achieve this sintered density, it is necessary to set the maximum holding temperature during firing to 1290° C. or higher, and to hold at this temperature for 1 hour or longer. Preferably, the maximum holding temperature is 1290 to 1400°C and the holding time is 1 to 8 hours. In addition, since the sintered density does not increase when abnormal grain growth occurs, it is necessary to keep the amount of additives and the amount of impurities described above within an appropriate range so that abnormal grains do not appear.

-Prepared using granulated powder having a particle size distribution d90 of 300 μm or less.
-Granulated powder The crushing strength is less than 1.50 MPa.
In general, MnCoZn ferrite is obtained by filling a mold with granulated powder, and then subjecting the obtained compact to firing and sintering through a powder compacting step of compressing at a pressure of about 100 MPa. Minute irregularities due to the gaps between the granulated powders remain on the surface of the ferrite even after sintering, and this serves as the starting point of damage upon impact, so that the ratler value increases as the number of remaining minute irregularities increases. Therefore, in order to reduce the gap between the granulated powders, it is preferable to remove the granulated powders having a coarse particle size and suppress the crushing strength of the granulated powders to a certain value or less.
As an effective means for satisfying this condition, it is effective to adjust the particle size by passing the obtained granulated powder through a sieve. On the other hand, in order to reduce the crushing strength of the granulated powder, it is effective to prevent the temperature from becoming excessively high during granulation by applying heat as in the spray granulation method. The particle size distribution is measured by particle size analysis by the laser diffraction/scattering method described in JIS Z8825. "D90" represents a particle size of 90% in volume cumulative from the small particle size side in the particle size distribution curve. The crushing strength of the granulated powder is measured by the method specified in JIS Z 8841.
If the value of the particle size distribution d90 is too small, the fluidity will decrease due to the increase in the number of contact points between the granulated powders. since an increase in the problems, the lower limit of d90 are you with 230 [mu] m. In addition, if the crushing strength of the granulated powder is greatly reduced, the granulated powder will be crushed during transportation and when the powder is filled in the mold, and the fluidity will be reduced. since the problem of forming a pressure increase in time occurs, the lower limit of the crush strength shall be the 1.18 MPa.

Next, a method of manufacturing the MnCoZn ferrite of the present invention will be described.
In the production of MnCoZn ferrite, first, Fe ₂ O ₃ , ZnO, CoO, and MnO powders are weighed so as to have a predetermined ratio, sufficiently mixed, and then calcined. Next, the obtained calcined powder is crushed to obtain crushed powder. At this time, the subcomponents specified in the present invention are added in a predetermined ratio and pulverized together with the calcined powder. In this step, the powder is sufficiently homogenized so that there is no bias in the concentration of the added components, and at the same time the calcined powder is refined to a target average particle size. Here, the target average particle diameter of the pulverized powder is 1.4 to 1.0 μm.
Then, an organic binder such as polyvinyl alcohol is added to the powder having the target composition, and granulated by a spray drying method or the like under appropriate conditions so as to obtain a sample having a desired particle size and crush strength. In the case of the spray dry method, it is desirable that the exhaust air temperature be lower than 270°C. Here, the particle size of the granulated powder is 230 ～300Myuemu a value of the particle size distribution d90. Also, pressure壊強of the granulated powder is less than 1.18 MPa or more 1.50MPa.
Next, if necessary, after passing through a step such as sieving for particle size adjustment, pressure is applied by a molding machine to perform molding, and then firing is performed under suitable firing conditions. It is desirable to remove coarse powder on the sieve through a sieve having a mesh of 350 μm.
As described above, appropriate firing conditions are the maximum holding temperature: 1290° C. or higher and the holding time: 1 h or longer.
Further, the obtained ferrite sintered body may be subjected to processing such as surface polishing.

Thus, it was impossible before,
・Rutler value is less than 0.85% ・Coercive force at 23°C is 15 A/m or less ・Specific resistance is 30 Ω・m or more ・Curie temperature is 100°C or more. it can.

Example 1
Iron contained, zinc, all cobalt and manganese _Fe 2 _O 3, ZnO, when calculated as CoO and _MnO, Fe ₂ O 3, ZnO, CoO, and MnO content was weighed so that the ratio shown in Table 1 The raw material powders were mixed for 16 hours using a ball mill, and then calcined in air at 925° C. for 3 hours. Next, to this calcined powder, SiO ₂ and CaO were weighed in amounts corresponding to 150 and 700 mass ppm, respectively, added, and pulverized with a ball mill for 12 hours. Then, polyvinyl alcohol was added to the obtained pulverized slurry, spray-dried granulation was performed at an exhaust air temperature of 250° C., coarse particles were removed through a sieve having an opening of 350 μm, and a pressure of 118 MPa was applied to the toroidal core and the rectangular parallelepiped core. Molded into. The granulated powder used for molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.
After that, the molded body is charged into a firing furnace and fired at a maximum temperature of 1350° C. for 2 hours in a gas flow in which nitrogen gas and air are appropriately mixed, and an outer diameter: 25 mm, an inner diameter: 15 mm, a height: 5 mm. The sintered toroidal core of 5 and 5 sintered cylindrical columnar cores having a diameter of 10 mm and a height of 10 mm were obtained.
Since the high-purity raw material was used, the impurities Cd, Pb, Sb, As, and Se of the sintered body core were all 3 mass ppm.

The contents of Cd, Pb, Sb, As and Se were quantified according to JIS K 0102 (IPC mass spectrometry).

The obtained sample was measured based on JIS C2560-2 at a sintering density of 23° C. by measuring the toroidal core by the Archimedes method and by measuring the specific resistance by the four-terminal method. The initial magnetic permeability of the toroidal core was calculated based on the inductance measured with an LCR meter (4980A manufactured by Keysight Co., Ltd.) after winding the toroidal core for 10 turns. The Curie temperature was calculated from the measurement result of the temperature characteristic of the inductance. The ratler value was measured according to the method specified in JPMA P11-1992. The coercive force Hc was measured at 23° C. according to JIS C2560-2.
The obtained results are also shown in Table 1.

As shown in the table, in Examples 1-1 to 1-7 as the invention examples, the rattle value is high strength of less than 0.85%, the specific resistance at 23° C. is 30 Ω·m or more, and the coercive force is 15 A. It was possible to obtain an MnCoZn ferrite having excellent magnetic properties of not more than /m and a Curie temperature of 100° C. or more.
On the other hand, in Comparative Examples 1-1 and 1-2 containing Fe ₂ O ₃ in an amount of 50.0 mol% or more, the specific resistance is significantly reduced as Fe ²⁺ is generated. On the other hand, in Comparative Example 1-3 in which the amount of Fe ₂ O ₃ is less than 45.0 mol % , an increase in coercive force and a decrease in Curie temperature are observed.
Further, in Comparative Example 1-4 in which the amount of ZnO exceeds the proper range, the Curie temperature is lowered. On the other hand, in Comparative Example 1-5 in which the amount of ZnO is less than the proper range, the coercive force is increased, and the preferable magnetic characteristics cannot be realized.
Furthermore, in Comparative Example 1-6 in which the CoO amount is less than the proper range, the coercive force is high due to lack of positive magnetic anisotropy, while in Comparative Example 1-7 in which the CoO amount exceeds the proper range, excessive positive The coercive force is increased due to the increase in magnetic anisotropy, both of which deviate from the preferable range.

Example 2
When all the contained iron, zinc, cobalt and manganese are converted into Fe ₂ O ₃ , ZnO, CoO and MnO, the Fe ₂ O ₃ amount is 49.0 mol%, the ZnO amount is 21.0 mol% and the CoO amount is 2 The raw materials were weighed so that the composition was 0.0 mol% and the balance MnO was mixed for 16 hours using a ball mill, and then calcined in air at 925° C. for 3 hours. Next, the amounts of SiO ₂ and CaO shown in Table 2 were added to the calcined powder, and the mixture was pulverized with a ball mill for 12 hours. Then, polyvinyl alcohol was added to the obtained pulverized slurry, spray-dried granulation was performed at an exhaust air temperature of 250° C., coarse particles were removed through a sieve having an opening of 350 μm, and then a pressure of 118 MPa was applied to the toroidal core and the cylindrical core. Molded into. The granulated powder used for molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.
After that, the molded body is charged into a firing furnace and fired at a maximum temperature of 1350° C. for 2 hours in a gas flow in which nitrogen gas and air are appropriately mixed, and an outer diameter: 25 mm, an inner diameter: 15 mm, a height: 5 mm. And a cylindrical toroidal core having five diameters of 10 mm and a height of 10 mm were obtained.
Since the high-purity raw material was used as the raw material, the impurities Cd, Pb, Sb, As, and Se of the sintered body core were all 3 mass ppm.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1.
The obtained results are also shown in Table 2.

As shown in the table, in Examples 2-1 to 2-4 in which the amount of SiO _{2 and the} amount of CaO were within the proper ranges, the ratler value was high strength of less than 0.85%, and the specific resistance at 23° C. was 30Ω. It was possible to obtain MnCoZn ferrite having excellent magnetic properties of m or more, coercive force of 15 A/m or less and Curie temperature of 100° C. or more.
On the other hand, in Comparative Examples 2-1 and 2-3 in which even one of SiO ₂ and CaO is less than the proper range, the generation of crystal grain boundaries is insufficient, and thus the size of crystal grains is uniform. Since the Rattler value is higher than 0.85% and the grain boundary thickness is insufficient, the specific resistance remains below 30 Ω·m.
In addition, at the level of Comparative Examples 2-2, 2-4, and 2-5 in which even one of the components is excessive, abnormal grains appear and the sintering density is low because the sintering is inhibited, The ratler value is also high. In addition, the resistivity is low and the coercive force is high due to insufficient formation of crystal grain boundaries.

Example 3
By the method shown in Examples 1 and 2, the ratios of the basic component and the subcomponents are the same as those of Example 1-2, while using raw materials having various amounts of impurities contained, the outer diameter: 25 mm. , A sintered toroidal core having an inner diameter of 15 mm and a height of 5 mm and five cylindrical cores having a diameter of 10 mm and a height of 10 mm were prepared, and the characteristics were evaluated using the same method and apparatus as in Example 1. The results obtained are shown in Table 3. The granulated powder used for molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.

As shown in the table, in Example 3-1 in which the contents of Cd, Pb, Sb, As, and Se are not more than the specified values, the strength represented by the Ratler value, the coercive force, the specific resistance, and the Curie temperature are Good values are obtained for all of the magnetic properties represented by
On the other hand, in any of Comparative Examples 3-1 to 3-7 in which one or more of the five levels exceeds the specified value, abnormal grains appear and sintering is hindered. Since the sintering density is low, the ratler value is high, and the generation of crystal grain boundaries is insufficient, so that the specific resistance is low and the coercive force is also high.

Example 4
A molded body produced by the method shown in Examples 1 and 2 in such a ratio that the basic component, the subcomponent, and the impurity component had the same composition as in Example 1-2 was subjected to various temperature conditions shown in Table 4. It was fired.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1. The results obtained are also shown in Table 4. The granulated powder used for molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.

As shown in the table, Examples 3-1 to 3-3 in which the maximum holding temperature during firing was 1290° C. or higher, the holding time was 1 hour or longer, and the sintering density was 4.85 g/cm ³ or higher. In No. 5, the strength represented by the Ratler value and the magnetic properties represented by the specific resistance, the coercive force, and the Curie temperature were good.
On the other hand, in Comparative Examples 3-1 to 3-6 in which the firing temperature is less than 1290° C. or the holding time is less than 1 hour and the sintered density is less than 4.85 g/cm ³ , the sintered density is low. Therefore, the ratler value is high and the crystal grain growth is insufficient, so that the hysteresis loss is increased. As a result, the coercive force is high, which is not preferable from the viewpoint of both strength and magnetic properties.

Example 5
For the granulated powder obtained by the method shown in Examples 1 and 2 under the same composition and the same spray drying conditions as in Example 1-2, the sieving conditions were changed to obtain the particle size distribution d90 shown in Table 5. The value (crush strength: 1.29 MPa) was applied with a pressure of 118 MPa to form a toroidal core and a cylindrical core. After that, the molded body is charged into a firing furnace and fired at a maximum temperature of 1350° C. for 2 hours in a gas flow in which nitrogen gas and air are appropriately mixed, and an outer diameter: 25 mm, an inner diameter: 15 mm, a height: 5 mm. And a cylindrical toroidal core having five diameters of 10 mm and a height of 10 mm were obtained.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1. The results obtained are also shown in Table 5.

As shown in the table, in Example 5-1 in which the value of the granulated powder particle size distribution d90 is 300 μm or less, the voids between the granulated powders are few remaining, and the starting points of the defects are few, so that the Ratler value is 0.85. It has been suppressed to below %.
On the other hand, in Comparative Examples 5-1 to 5-3 in which the value of d90 is larger than 300 μm, there are many voids between the granulated powders and many origins of defects, so that the ratler value is high and the strength is low.

Example 6
Example 1-2 produced by the method shown in Examples 1 and 2 Slurries produced with the same composition were spray-dried under the exhaust temperature conditions shown in Table 6 to obtain granulated powders having different crushing strengths. After removing coarse powder through a sieve having an opening of 350 μm, a pressure of 118 MPa was applied to form a toroidal core and a cylindrical core. The particle size distribution d90 of the granulated powder at this time was 230 μm.
After that, the molded body is charged into a firing furnace and fired at a maximum temperature of 1350° C. for 2 hours in a gas flow in which nitrogen gas and air are appropriately mixed, and an outer diameter: 25 mm, an inner diameter: 15 mm, a height: 5 mm. And a cylindrical toroidal core having five diameters of 10 mm and a height of 10 mm were obtained.
Table 6 also shows the results of evaluating the characteristics of each of these samples using the same method and apparatus as in Example 1.

As shown in the table, in Examples 1-2 and 6-1 in which the exhaust air temperature of the spray dry granulation was not excessively high, the crushing strength of the granulated powder was less than 1.5 MPa, and the granulated powder was Since it is sufficiently crushed, there are no gaps between the granulated powders, and therefore there are few starting points of defects, so the Ratler value can be suppressed to less than 0.85%.
On the other hand, when focusing on Comparative Examples 6-1 to 6-3 in which the exhaust air temperature is excessively high and the granulated powder crushing strength is 1.5 MPa or more, there are many starting points of defects due to defective granulated powder crushing. Therefore, the ratler value is high and the strength is low.

Claims (5)

A MnCoZn-based ferrite comprising a basic component, a subcomponent, and unavoidable impurities,
As the above basic ingredients,
Iron: 45.0 mol% or more and less than 50.0 mol% in terms of Fe ₂ O ₃ ,
Zinc: 15.5 to 24.0 mol% in terms of ZnO,
Cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese: including the balance,
With respect to the basic component, as the auxiliary component,
SiO ₂ : 50 to 300 massppm and CaO: 700 to 1300 massppm
Including,
The amount of Cd, Pb, Sb, As and Se in the inevitable impurities is suppressed to less than 20 massppm,
further,
Ratler value is less than 0.85%,
Coercive force at 23°C is 15 A/m or less,
The specific resistance is 30Ω·m or more and the Curie temperature is 100°C or more,
A MnCoZn-based ferrite formed of a compacted-sintered body of granulated powder having a particle size distribution d90 of 230 μm to 300 μm and a crush strength of 1.18 MPa or more and less than 1.50 MPa. The MnCoZn ferrite according to claim 1, wherein the MnCoZn ferrite has a sintered density of 4.85 g/cm ³ or more. To the calcining step of calcining the mixture of basic components weighed so as to have a predetermined component ratio and the calcined powder obtained in the above-mentioned calcination process, the subcomponents adjusted to have a predetermined component ratio are added. A mixing-grinding step of mixing and crushing,
After the binder is added to and mixed with the pulverized powder obtained in the mixing-pulverization step, the granulated powder is produced so that the value of the particle size distribution d90 is 230 μm to 300 μm and the crush strength is 1.18 MPa or more and less than 1.50 MPa. After granulating the obtained granulated powder, a basic component, a subcomponent, and a sintering process for obtaining a MnCoZn ferrite by firing under conditions of a maximum holding temperature of 1290° C. or more and a holding time of 1 hour or more A method for producing an MnCoZn-based ferrite containing inevitable impurities, comprising:
As the above basic ingredients,
Iron: 45.0 mol% or more and less than 50.0 mol% in terms of Fe ₂ O ₃ ,
Zinc: 15.5 to 24.0 mol% in terms of ZnO,
Cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese: including the balance,
With respect to the basic component, as the auxiliary component,
SiO ₂ : 50 to 300 massppm and CaO: 700 to 1300 massppm
Including,
The amount of Cd, Pb, Sb, As and Se in the inevitable impurities is suppressed to less than 20 massppm,
further,
Ratler value is less than 0.85%,
Coercive force at 23°C is 15 A/m or less,
A method for producing a MnCoZn-based ferrite having a specific resistance of 30 Ω·m or more and a Curie temperature of 100° C. or more. The method for producing the MnCoZn ferrite according to claim 3, wherein the sintered density of the MnCoZn ferrite is 4.85 g/cm ³ or more. The method for producing an MnCoZn-based ferrite according to claim 3, wherein the granulation is a spray drying method.