JPWO2019123681A1 - MnCoZn ferrite and method for producing the same - Google Patents

Abstract

As basic components, iron: 45.0 mol% or more and less than 50.0 mol% in terms of Fe2O3, zinc: 15.5 to 24.0 mol% in terms of ZnO, and cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese. : MnCoZn-based ferrite containing 50 to 300 mass ppm of SiO2 and 300 to 1300 mass ppm of CaO as subcomponents with respect to the above basic component, and the balance is Cd in the unavoidable impurity. , Pb, Sb, As, and Se are each suppressed to less than 20 mass ppm, the Rutler value is less than 0.85%, the coercive force at 23 ° C. is 15 A / m or less, the specific resistance is 30 Ω · m or more, and the Curie temperature is 100. ℃ or higher, good magnetic properties such as high resistance and low coercive force Not only provides MnCoZn ferrite bring together excellent mechanical strength.

Description

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

A typical example of the soft magnetic oxide magnetic material is MnZn ferrite. The conventional MnZn ferrite contains Fe ²⁺ having a positive magnetic anisotropy of about 2 mass% or more, and cancels out Fe ³⁺ and Mn ²⁺ having a negative magnetic anisotropy, thereby increasing the initial permeability in the kHz region. And have achieved low losses.
This MnZn ferrite is widely used as a noise filter for a switching power supply, a magnetic core of a transformer or an antenna because it is inexpensive as compared with an amorphous metal or the like.

However, MnZn ferrite, since ^{Fe 2+} amount is ^large, easily occurs electron transfer between Fe 3+ ^{-Fe 2+,} specific resistance has the disadvantage of low and 0.1 [Omega · m order. Therefore, when the frequency range to be used is increased, the loss due to the eddy current flowing in the ferrite sharply increases, the initial permeability is greatly reduced, and the loss is also increased. For this reason, the usable frequency of MnZn ferrite is limited to about several hundred kHz, and NiZn ferrite is mainly used in the order of MHz. The specific resistance of the NiZn ferrite is 10 ⁵ (Ω · m) or more, which is about 10,000 times that of the MnZn ferrite, and the eddy current loss is small. Therefore, the characteristics of high initial permeability and low loss are hardly lost even in a high frequency region.

  However, NiZn ferrite has a major problem. This is because the soft magnetic material is required to react sensitively to changes in the external magnetic field, so that the coercive force Hc is preferably small, but NiZn ferrite is composed only of ions having negative magnetic anisotropy. Is that the value of this coercive force is large. The coercive force is defined in JIS C 2560-2.

As a method of obtaining 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 Literature 1, Patent Literature 2, Patent Literature 3, and the like report MnZn ferrite in which the specific resistance is increased by reducing the content of Fe ^{2+ by} setting the Fe ₂ O ₃ component to less than 50 mol%. However, since these also consist only of ions having negative magnetic anisotropy like NiZn ferrite, the problem of reduction of coercive force has not been solved at all.

Therefore, Patent Literature 4, Patent Literature 5, and Patent Literature 6 disclose a technique of adding Co ²⁺ having a positive magnetic anisotropy other than Fe ²⁺ , but these techniques aim at lowering the coercive force. It was not something. In addition, because measures for abnormal grains described later are insufficient, cost and production efficiency are also inferior.

On the other hand, Patent Literature 7 reports a high-resistance MnCoZn ferrite having a low coercive force, in which the occurrence of abnormal grains is suppressed by providing a rule for the impurity composition, and stable production is possible.
It should be noted that abnormal grain growth is caused when the balance of grain growth is locally lost for some reason, and is a phenomenon often observed at the time of manufacturing using powder metallurgy. Since a substance that greatly impedes the movement of the domain wall such as an impurity or a lattice defect is mixed in the abnormally grown grains, the soft magnetic properties are lost and the coercive force is increased. At the same time, the resistivity decreases because the formation of crystal grain boundaries becomes insufficient.

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

With the development of Patent Document 7, the MnCoZn ferrite having satisfactory magnetic properties can be obtained.
On the other hand, the trend of electrification of automobiles in recent years has been remarkable, and MnCoZn ferrite has been increasingly mounted on automobiles. However, mechanical strength is an important property in the same application. Compared to electric and industrial equipment, which was the main application up to that time, vibration occurs during driving in automobiles, so MnCoZn ferrite, which is a ceramic, must be not damaged by vibration due to vibration in automotive applications. It is becoming possible.

However, the MnCoZn ferrite containing less than 50 mol% of Fe ₂ O ₃ component has a small number of oxygen vacancies, so that sintering is easy to proceed at the time of sintering. Therefore, vacancies are apt to remain in crystal grains and a crystal grain boundary is formed. Tends to be uneven. As a result, when subjected to an external impact, there is a problem that the MnCoZn ferrite is liable to be broken as compared with the conventional MnCoZn ferrite.
That is, the technique disclosed in Patent Document 7 has a problem that the obtained magnetic properties are sufficient, but the mechanical strength against this defect is not always sufficient.

As the technique for improving the chipping strength, in Patent Document 8, a technique for adding TiO ₂ in the range of 0.01～0.5Mass% are known.
However, the addition of TiO ₂ , on the other hand, 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, so that the specific resistance is greatly reduced. There was a disadvantage.

  SUMMARY OF THE INVENTION The present invention suppresses abnormal grain growth while generating uniform grain boundaries while maintaining good magnetic properties such as conventional high resistance and low coercive force. It is an object of the present invention to propose a MnCoZn ferrite which also has the mechanical strength of the property together with its advantageous production method.

The inventors first studied the appropriate amounts of Fe ₂ O ₃ , ZnO, and CoO of MnCoZn ferrite necessary to obtain desirable magnetic properties, and found that the specific resistance was high, the coercive force was small, and the Curie temperature was low. An appropriate range in which all of the high characteristics can be simultaneously realized has been found.
In this specification, as described above, the value of the coercive force at 23 ° C. is a problem. This is because many of the MnZn ferrite cores used for antennas and noise filters are used in locations away from power transformers and semiconductors as heat sources, and operate at room temperature (5-35 ° C.). I do. This is because it is important that the magnetic properties at 23 ° C., which is a representative value in the normal temperature (5 to 35 ° C.) range, that is, the coercive force be small.

Next, paying attention to the microstructure, it was found that by reducing vacancies in the crystal grains, adjusting the crystal grain size and realizing the grain boundary having an appropriate thickness, it is possible to suppress the loss of the sintered core expressed by the Rutler value. . Here, in order to realize a desirable crystal structure, the addition amounts of SiO ₂ and CaO, which are components segregated at the crystal grain boundaries, have a great influence, and therefore, an appropriate range of these components has been successfully determined. Within this range, a low Rattler value can be maintained.

Moreover, essential in order to having both the mechanical strength to the preferred magnetic characteristics and defects, the suppression of abnormal grain appearance as a result of abnormal grains was examined by focusing on making conditions for occurrence of the aforementioned SiO ₂ And CaO are excessive, and when there are certain or more components such as Cd, Pb, Sb, As, and Se which are impurities in natural ore or mixed during smelting, abnormal grains Appeared.
The present invention is based on the above findings.

As described above, Patent Literature 1, Patent Literature 2, Patent Literature 3, and the like refer to high specific resistance, and Patent Literature 4, Patent Literature 5, and Patent Literature 6 disclose a positive magnetic difference. Although the addition of Co ²⁺ having anisotropy is described, there is no description about the coercive force, and Patent Literature 5 rather conversely specifies that Pb is intentionally added. Moreover, since none of these Patent Documents 1 to 6 describes any measures against abnormal grains, it is presumed that the mechanical strength is insufficient. Further, also in Patent Document 7 which mentions a low coercive force, since the definition of the additive is insufficient, sufficient mechanical strength that can suppress the loss cannot be expected. Further, even in Patent Document 8 which mentions improvement in chipping strength, a significant decrease in specific resistance cannot be avoided.

The gist configuration of the present invention is as follows.
1. As a basic ingredient,
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,
For the above basic components, as subcomponents,
SiO ₂ : 50 to 300 mass ppm and CaO: 300 to 1300 mass ppm
And the remainder is MnCoZn-based ferrite composed of unavoidable impurities,
The amounts of Cd, Pb, Sb, As, and Se in the inevitable impurities are suppressed to less than 20 mass ppm,
Further, in the MnCoZn ferrite,
Ratler value less than 0.85%,
A coercive force at 23 ° C. of 15 A / m or less;
A MnCoZn ferrite having a specific resistance of 30 Ω · m or more and a Curie temperature of 100 ° C. or more.

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

3. 3. The MnCoZn-based ferrite according to the above 1 or 2, wherein the MnCoZn-based ferrite is a MnCoZn-based ferrite formed by molding and sintering a granulated powder having a particle size distribution d90 of 300 μm or less.

4). 4. The MnCoZn-based ferrite according to any one of the above items 1 to 3, wherein the MnCoZn-based ferrite is a MnCoZn-based ferrite formed by molding and sintering a granulated powder having a crushing strength of less than 1.50 MPa.

5. A calcining step of calcining a mixture of the basic components weighed so as to have a prescribed component ratio, and the calcined powder obtained in the calcining step, adding a sub-component adjusted to a prescribed ratio, mixing, Grinding-mixing-grinding step;
After adding and mixing a binder to the pulverized powder obtained in the mixing-pulverization step, the mixture is granulated such that the value of the particle size distribution d90 of the granulated powder is 300 μm or less and / or the crushing strength is less than 1.50 MPa. Baking the obtained granulated powder, firing at a maximum holding temperature of 1290 or more and a holding time of 1 hour or more to obtain a MnCoZn-based ferrite according to 1 or 2 above. Production method.

6). 6. The method for producing a MnCoZn ferrite according to the item 5, wherein the granulation is a spray drying method.

According to the present invention, not only have good magnetic properties such as high resistance and low coercive force, but also have a mechanical property of excellent fracture resistance by suppressing the abnormal grain growth while generating uniform grain boundaries. MnCoZn ferrite having both strength can be obtained.
The MnCoZn ferrite of the present invention has excellent magnetic properties such that the initial permeability at 23 ° C. and 1 kHz is 3000 or more, the initial permeability at 23 ° C. and 1 MHz is 2000 or more, and the initial permeability at 23 ° C. and 10 MHz is 150 or more. .

Hereinafter, the present invention will be described specifically.
First, the reason why the composition of MnCoZn ferrite is limited to the above range in the present invention will be described. Note that iron, zinc, cobalt, and manganese included in the present invention as basic components are all represented by values converted into Fe ₂ O ₃ , ZnO, CoO, and MnO. The contents of 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 relative to the entire ferrite.

Fe ₂ O ₃ : 45.0 mol% or more and less than 50.0 mol% When Fe ₂ O ₃ is excessively contained, the amount of Fe ²⁺ increases, thereby lowering the specific resistance of the MnCoZn ferrite. In order to avoid this, the amount of Fe ₂ O ₃ needs to be suppressed to less than 50 mol%. However, if the amount is too small, the coercive force increases and the Curie temperature decreases, so that at least 45.0 mol% of iron is contained 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 the function of increasing the saturation magnetization of ferrite and increasing the sintering density due to its relatively low saturated vapor pressure, thereby increasing the saturation magnetic flux density, and is an effective component for lowering the coercive force. Therefore, at least 15.5 mol% of zinc is contained in terms of ZnO. On the other hand, when the zinc content is more than an appropriate value, the Curie temperature is lowered, and there is a practical problem. Therefore, zinc has an upper limit of 24.0 mol% in terms of ZnO. The preferred 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 sum of the magnetic anisotropy energy is reduced, so that the coercive force is reduced. You. For that purpose, it is essential to add 0.5 mol% or more of CoO. On the other hand, a large amount of addition lowers the specific resistance, induces abnormal grain growth, and increases the coercive force because the sum of the magnetic anisotropy energy is excessively inclined. In order to prevent this, CoO is limited to a maximum of 4.0 mol%. The preferred range of CoO is 1.0 to 3.5 mol%, 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 properties such as high saturation magnetic flux density, low loss and high magnetic permeability cannot be obtained unless MnO is used. The preferred range of MnO is 26.5 to 32.0 mol%.

The basic components have been described above, and the sub-components are as follows.
SiO ₂ : 50 to 300 mass ppm
SiO ₂ is known to contribute to the homogenization of the crystal structure of ferrite. The addition of an appropriate amount reduces the vacancies remaining in the crystal grains and lowers the residual magnetic flux density, thereby lowering the coercive force. Let it. In addition, since SiO ₂ segregates at the grain boundary to increase the specific resistance and at the same time reduces the crystal having a coarse grain size, it is possible to reduce the Rattler value, which is an index of the loss of the sintered body. Therefore, at least 50 mass ppm of SiO ₂ is contained. On the other hand, when the amount of addition is excessive, abnormal grains appear on the contrary, which becomes the starting point of the defect, so that the Rattler value increases and 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 preferred content of SiO ₂ is in the range of 60 to 250 mass ppm.

CaO: 300 to 1300 mass ppm
CaO segregates at the crystal grain boundaries of MnCoZn ferrite, has a function of suppressing the growth of crystal grains, and also has a role of reducing vacancies remaining in the crystal grains. Therefore, with the addition of an appropriate amount, the specific resistance increases, the coercive force decreases, and the Rutler value can be reduced because coarse crystals are reduced. Therefore, the content of CaO should be at least 300 mass ppm. On the other hand, if the added amount is excessive, abnormal grains appear and the Rattler value and the coercive force also increase. Therefore, the content of CaO must be limited to 1300 mass ppm or less. A more preferred content of CaO is in the range of 350 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 that are unavoidably contained in the raw material because they are contained in natural ore or mixed during smelting. There is no problem if these contents are very small, but if they are contained in a certain amount or more, it induces abnormal grain growth of ferrite and has a serious adverse effect on various properties of the obtained ferrite. A ferrite having a composition containing less than 50 mol% of Fe ₂ O ₃ as in the present invention facilitates crystal grain growth as compared with a ferrite containing 50 mol% or more, so that the amount of Cd, Pb, Sb, As and Se is increased. When the amount is large, abnormal grain growth is likely to occur. In this case, not only the coercive force increases, but also the generation of crystal grain boundaries becomes insufficient, so that the specific resistance decreases. Further, the Rattler value increases because it becomes a starting point of the defect.
Therefore, in the present invention, the contents of Cd, Pb, Sb, As and Se are each suppressed to less than 20 mass ppm.
In addition, the allowable amount of unavoidable 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 minimize mixing of impurities in the basic component and the subcomponent used as the raw material. The total amount of impurities in the basic component and the subcomponent used as a raw material, including the above-mentioned P, B, S, and Cl, is preferably 50 mass ppm or less, and more preferably 40 mass ppm or less.

  Further, not only the composition but also various characteristics of the MnCoZn ferrite are greatly affected by various parameters. 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 Sintering and grain growth of the MnCoZn ferrite proceeds by firing treatment, and crystal grains and grain boundaries are formed. Crystal structure capable of realizing low coercive force, that is, non-magnetic components that should be present at crystal grain boundaries are appropriately segregated at crystal grain boundaries, and crystal grains are composed of components that maintain an appropriate particle size and uniform magnetism In order to realize the required form, the sintering reaction needs to proceed sufficiently. Also, from the viewpoint of preventing loss, when sintering is insufficient, the strength is reduced, which is not preferable.
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 Rattler value can be suppressed low. In order to achieve this sintering density, it is necessary to set the maximum holding temperature during firing at 1290 ° C. or higher, and to hold the firing at this temperature for 1 hour or longer. Preferably, the maximum holding temperature is 1290-1400 ° C. and the holding time is 1-8 hours. In addition, when abnormal grain growth occurs, the sintering density does not increase. Therefore, in order to prevent the appearance of abnormal grains, it is necessary to make the additive amount and the impurity amount described above within appropriate ranges.

-Prepared using granulated powder having a particle size distribution d90 of 300 μm or less.
-A granulated powder is prepared using a granulated powder having a crushing strength of less than 1.50 MPa.
In general, MnCoZn ferrite is obtained by filling a mold with a 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. Fine irregularities due to the gap between the granulated powders remain on the surface of the ferrite even after sintering, and serve as a starting point of a defect due to an impact. As a result, the Rattler value increases as the minute irregularities increase. Therefore, in order to reduce the gap between the granulated powders, it is preferable to remove the granulated powder having a coarse particle size and to suppress the crushing strength of the granulated powder 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 when granulating by applying heat such as spray granulation. The particle size distribution is measured by a particle size analysis by a laser diffraction / scattering method described in JIS Z 8825. “D90” represents a particle size of 90% in total volume from the small particle size side in the particle size distribution curve. The crushing strength of the granulated powder is measured by a method specified in JIS Z8841.
If the value of the particle size distribution d90 is too small, the fluidity decreases due to an increase in the number of contact points between the granulated powders. Since the problem of increase occurs, the lower limit of d90 is preferably set to 75 μm. Also, if the crushing strength of the granulated powder is significantly reduced, the granulated powder is crushed during transportation and filling of the powder with a mold, and the fluidity is reduced. In this case, the lower limit of the crushing strength is preferably set to 0.50 MPa because of the problem of increasing the molding pressure at the time.

Next, a method for producing the MnCoZn ferrite of the present invention will be described.
For production of MnCoZn ferrite, first, Fe ₂ O ₃ , ZnO, CoO, and MnO powders are weighed so as to have a predetermined ratio, and calcined after sufficiently mixing them. Next, the obtained calcined powder is pulverized to obtain a pulverized powder. At this time, the auxiliary component specified in the present invention is added at a predetermined ratio, and pulverized together with the calcined powder. In this step, the powder is sufficiently homogenized so that the concentration of the added components is not biased, and at the same time, the calcined powder is refined to a target average particle size. Here, the target average particle size of the pulverized powder is 1.4 to 1.0 μm.
Next, 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 crushing strength. In the case of the spray drying method, it is desirable that the exhaust air temperature be lower than 270 ° C. Here, the preferred particle size of the granulated powder is 75 to 300 μm in terms of the particle size distribution d90. Further, the preferable crushing strength of the granulated powder is 0.50 MPa or more and less than 1.50 MPa.
Next, after passing through a process such as sieving for adjusting the particle size as required, pressure is applied by a molding machine, followed by molding, followed by firing under suitable firing conditions. It is desirable to remove coarse powder on the sieve through a sieve having a size of 350 μm.
The appropriate firing conditions are, as described above, the maximum holding temperature: 1290 ° C. or more, and the holding time: 1 h or more.
Further, the obtained ferrite sintered body may be subjected to processing such as surface polishing.

Thus, previously impossible,
-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-MnCoZn ferrite which satisfies all of the excellent properties of Curie temperature of 100 ° C or more at the same time can be obtained. 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 Each raw material powder was 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, and then added, followed by grinding with a ball mill for 12 hours. Then, polyvinyl alcohol was added to the obtained ground slurry, spray-dried and granulated at an exhaust air temperature of 250 ° C., and coarse powder was removed through a sieve having an opening of 350 μm. Then, a pressure of 118 MPa was applied to the toroidal core and the rectangular solid core. Molded. The particle size distribution d90 of the granulated powder used for molding was 230 μm, and the crushing strength was 1.29 MPa.
Thereafter, the formed body is placed in 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 the outer diameter is 25 mm, the inner diameter is 15 mm, and the height is 5 mm. And five sintered cylindrical columnar cores having a diameter of 10 mm and a height of 10 mm.
Since the high-purity raw material was used, impurities Cd, Pb, Sb, As and Se in 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).

Based on JIS C 2560-2, the obtained sample measured the toroidal core at 23 ° C. by the Archimedes method and the specific resistance by the four-terminal method at 23 ° C. The initial permeability of the toroidal core was calculated based on inductance measured by using a LCR meter (4980A manufactured by Keysight) with a 10-turn winding wound on the toroidal core. The Curie temperature was calculated from the result of measuring the temperature characteristics of the inductance. The Rattler value was measured according to the method specified in JPMA P11-1992. The coercive force Hc was measured at 23 ° C. based on JIS C 2560-2.
The results obtained are also shown in Table 1.

As shown in the table, in Examples 1-1 to 1-7, which are examples of the invention, high strength with a Rutler value of less than 0.85%, specific resistance at 23 ° C. of 30 Ω · m or more, and coercive force of 15 A / M and a Curie temperature of 100 ° C. or higher.
On the other hand, in Comparative Examples 1-1 and 1-2 containing 50.0 mol% or more of Fe ₂ O ₃ , the specific resistance is significantly reduced with the generation of Fe ²⁺ . 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.
In Comparative Examples 1-4 in which the amount of ZnO exceeds the appropriate range, a decrease in the Curie temperature is observed. On the other hand, in Comparative Example 1-5 in which the amount of ZnO was less than the appropriate range, the coercive force was increased, and favorable magnetic characteristics could not be realized.
Further, in Comparative Example 1-6 in which the amount of CoO 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 amount of CoO exceeds the proper range, too much positive The coercive force increases due to the increase in magnetic anisotropy, and both deviate from the preferable ranges.

Example 2
When the contained iron, zinc, cobalt and manganese are all converted into Fe ₂ O ₃ , ZnO, CoO and MnO, the amount of Fe ₂ O ₃ is 49.0 mol%, the amount of ZnO is 21.0 mol%, and the amount of CoO is 2 The raw materials were weighed so as to have a composition of 0.0 mol% and the balance of MnO, and mixed for 16 hours using a ball mill, and then calcined at 925 ° C. for 3 hours in the air. Next, the amounts of SiO ₂ and CaO shown in Table 2 were added to the calcined powder, and pulverized by a ball mill for 12 hours. Then, polyvinyl alcohol was added to the obtained crushed slurry, and spray-dry granulation was performed at an exhaust air temperature of 250 ° C., coarse powder was removed through a sieve having an opening of 350 μm, and a pressure of 118 MPa was applied to the toroidal core and the cylindrical core. Molded. In addition, the particle size distribution d90 of the granulated powder used for molding was 230 µm, and the crushing strength was 1.29 MPa.
Thereafter, the formed body is placed in 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 the outer diameter is 25 mm, the inner diameter is 15 mm, and the height is 5 mm. And five cylindrical cores having a diameter of 10 mm and a height of 10 mm were obtained.
In addition, since a high-purity raw material was used as a raw material, impurities Cd, Pb, Sb, As, and Se in 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.
Table 2 also shows the obtained results.

As shown in the table, in Examples 2-1 to 2-4 in which the SiO ₂ and the amount are within the appropriate ranges, the high strength with a Rattler value of less than 0.85% and the specific resistance at 23 ° C. of 30 Ω · m. As described above, MnCoZn ferrite having excellent magnetic properties such as a coercive force of 15 A / m or less and a Curie temperature of 100 ° C. or more was obtained.
On the other hand, in Comparative Examples 2-1 and 2-3 in which any one of SiO ₂ and CaO is less than the appropriate range, the size of the crystal grain is adjusted because the generation of the crystal grain boundary is insufficient. Therefore, the Rattler value is higher than 0.85%, and the specific resistance is less than 30 Ω · m because the grain boundary thickness is insufficient.
In Comparative Examples 2-2, 2-4, and 2-5, in which at least one of the components was excessive, abnormal grains appeared and sintering was inhibited, so that the sintering density was low. Rattler value is also high. In addition, since the generation of crystal grain boundaries is insufficient, the specific resistance is low and the coercive force is high.

Example 3
According to the methods shown in Examples 1 and 2, the ratio of the basic component and the sub-component becomes the same as that of Example 1-2, while using raw materials having various different amounts of impurities, and having an outer diameter of 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 produced, and the characteristics were evaluated using the same method and apparatus as in Example 1. Table 3 shows the results. In addition, the particle size distribution d90 of the granulated powder used for molding was 230 µm, and the crushing strength was 1.29 MPa.

As shown in the table, in Example 3-1 in which the contents of Cd, Pb, Sb, As, and Se were equal to or less than the specified values, the strength represented by the Rattler value, and the coercive force, the specific resistance, and the Curie temperature Good values were obtained for all of the magnetic characteristics represented by.
On the other hand, in each of Comparative Examples 3-1 to 3-7 in which one or more of these five levels exceeds the specified value, abnormal grains appear and sintering is inhibited. Since the sintering density is low, the Rattler value is high, and the generation of crystal grain boundaries is insufficient, so that the specific resistance is low and the coercive force is high.

Example 4
By using the methods shown in Examples 1 and 2, molded articles produced at such a ratio that the basic component, the subcomponent and the impurity component have the same composition as in Example 1-2 were prepared under various temperature conditions shown in Table 4. And fired.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1. Table 4 also shows the obtained results. In addition, the particle size distribution d90 of the granulated powder used for molding was 230 µm, and the crushing strength was 1.29 MPa.

As shown in the same table, Examples 3-1 to 3- in which the maximum holding temperature during firing was 1290 ° C. or more and the holding time was 1 hour or more and firing was performed, and the sintered density was 4.85 g / cm ³ or more. In No. 5, both the strength represented by the Rattler value and the magnetic properties represented by the specific resistance, the coercive force and the Curie temperature were good.
In contrast, in Comparative Examples 3-1 to 3-6 in which the sintering temperature is less than 1290 ° C. or the holding time is less than 1 hour, and the sintering density is less than 4.85 g / cm ³ , the sintering density is low. Therefore, the Rattler value is high, and the crystal grain growth is insufficient, and 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
According to the method shown in Examples 1 and 2, the granulated powder obtained under the same composition and the same spray-drying conditions as those of Example 1-2 was subjected to changing the sieving conditions to obtain the particle size distribution d90 shown in Table 5. The value (crush strength: 1.29 MPa) was applied to a pressure of 118 MPa to form a toroidal core and a cylindrical core. Thereafter, the formed body is placed in 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 the outer diameter is 25 mm, the inner diameter is 15 mm, and the height is 5 mm. And five cylindrical cores having a diameter 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. Table 5 also shows the obtained results.

As shown in the table, in Example 5-1 in which the value of the granulated powder particle size distribution d90 was 300 μm or less, the gap between the granulated powders was small, and the starting point of the defect was small. % Or less.
On the other hand, in Comparative Examples 5-1 to 5-3 in which the value of d90 is larger than 300 μm, since there are many voids between the granulated powders and many starting points of defects, the rattle value is high, and the strength is low.

Example 6
Example 1-2 produced by the method shown in Examples 1 and 2 A slurry produced with the same composition was spray-dried under the exhaust air temperature conditions shown in Table 6 to obtain granulated powders having different crushing strengths. After removing coarse powder through a sieve having openings of 350 μm, a pressure of 118 MPa was applied to form a toroidal core and a cylindrical core. At this time, the particle size distribution d90 of the granulated powder was 230 μm.
Thereafter, the formed body is placed in 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 the outer diameter is 25 mm, the inner diameter is 15 mm, and the height is 5 mm. And five cylindrical cores having a diameter of 10 mm and a height of 10 mm were obtained.
Table 6 also shows the results of evaluating the characteristics of these samples using the same method and apparatus as in Example 1.

As shown in the table, in Examples 6-1 to 6-2 in which the exhaust air temperature of spray dry granulation is not excessively high, the crushing strength of the granulated powder is less than 1.5 MPa, and Since the particles are sufficiently crushed, no gap between the granulated powders remains, and thus the starting point of the defect is small, so that the Rattler value can be suppressed to less than 0.85%.
On the other hand, when attention is paid to 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 poor granulated powder crushing. , The Rattler value is high, and the strength is low.

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 And have achieved low losses.
This MnZn ferrite is widely used as a noise filter for a switching power supply and the like and a magnetic core of a transformer and an antenna because it is inexpensive as compared with an amorphous metal or the like.

5. A calcining step of calcining a mixture of the basic components weighed so as to have a prescribed component ratio, and the calcined powder obtained in the calcining step, adding a sub-component adjusted to a prescribed ratio, mixing, Grinding-mixing-grinding step;
After adding and mixing a binder to the pulverized powder obtained in the mixing-pulverization step, the mixture is granulated such that the value of the particle size distribution d90 of the granulated powder is 300 μm or less and / or the crushing strength is less than 1.50 MPa. Baking the obtained granulated powder, firing at a maximum holding temperature of 1290 ° C. or more and a holding time of 1 hour or more to obtain a MnCoZn-based ferrite as described in 1 or 2 above. Manufacturing method.

Therefore, it is preferable to minimize mixing of impurities in the basic component and the subcomponent used as the raw material. The total amount of impurities in the basic component and the subcomponent used as a raw material is preferably 50 mass ppm or less, and more preferably 40 mass ppm or less, including Cd, Pb, Sb, As and Se described above.

-Prepared using granulated powder having a particle size distribution d90 of 300 μm or less.
-A granulated powder is prepared using a granulated powder having a crushing strength of less than 1.50 MPa.
In general, MnCoZn ferrite is obtained by filling a mold with a 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. Fine irregularities due to the gap between the granulated powders remain on the surface of the ferrite even after sintering, and serve as a starting point of a defect due to an impact. As a result, the Rattler value increases as the minute irregularities increase. Therefore, in order to reduce the gap between the granulated powders, it is preferable to remove the granulated powder having a coarse particle size and to suppress the crushing strength of the granulated powder 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 when granulating by applying heat such as spray granulation. The particle size distribution is measured by a particle size analysis by a laser diffraction / scattering method described in JIS Z 8825. “ D 90” represents a particle size of 90% in total volume from the small particle size side in the particle size distribution curve. The crushing strength of the granulated powder is measured by a method specified in JIS Z8841.
If the value of the particle size distribution d90 is too small, the fluidity decreases due to an increase in the number of contact points between the granulated powders. Since the problem of increase occurs, the lower limit of d90 is preferably set to 75 μm. Also, if the crushing strength of the granulated powder is significantly reduced, the granulated powder is crushed during transportation and filling of the powder with a mold, and the fluidity is reduced. In this case, the lower limit of the crushing strength is preferably set to 0.50 MPa since a problem of an increase in molding pressure at the time occurs.

As shown in the table, in Examples 1-1 to 1-7, which are examples of the invention, high strength with a Rutler value of less than 0.85%, specific resistance at 23 ° C. of 30 Ω · m or more, and coercive force of 15 A / M and a Curie temperature of 100 ° C. or higher.
On the other hand, in Comparative Examples 1-1 and 1-2 containing 50.0 mol% or more of Fe ₂ O ₃ , the specific resistance is significantly reduced with the generation of Fe ²⁺ . 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.
In Comparative Examples 1-4 in which the amount of ZnO exceeds the appropriate range, a decrease in the Curie temperature is observed. On the other hand, in Comparative Example 1-5 in which the amount of ZnO was less than the appropriate range, the coercive force was increased, and favorable magnetic characteristics could not be realized.
Further, in Comparative Example 1-6 in which the amount of CoO 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 amount of CoO exceeds the proper range, too much positive The coercive force increases due to the increase in magnetic anisotropy, and both deviate from the preferable ranges.

As shown in the table, in Examples 2-1 to 2-4 in which the amount of SiO _{2 and the} amount of CaO are within appropriate ranges, the high strength of which the Rattler value is less than 0.85%, and the specific resistance at 23 ° C. of 30Ω. MnCoZn ferrite having excellent magnetic properties of not less than m, coercive force of not more than 15 A / m and Curie temperature of not less than 100 ° C. was obtained.
On the other hand, in Comparative Examples 2-1 and 2-3 in which any one of SiO ₂ and CaO is less than the appropriate range, the size of the crystal grain is adjusted because the generation of the crystal grain boundary is insufficient. Therefore, the Rattler value is higher than 0.85%, and the specific resistance is less than 30 Ω · m because the grain boundary thickness is insufficient.
In Comparative Examples 2-2, 2-4, and 2-5, in which at least one of the components was excessive, abnormal grains appeared and sintering was inhibited, so that the sintering density was low. Rattler value is also high. In addition, due to insufficient generation of grain boundaries, specific resistance is low and coercive force is also high.

As shown in the table, in Examples 1-2 and 6-1 in which the exhaust air temperature of the spray-dry granulation is not excessively high, the crushing strength of the granulated powder is less than 1.5 MPa, and Since the particles are sufficiently crushed, no gap between the granulated powders remains, and thus the starting point of the defect is small, so that the Rattler value can be suppressed to less than 0.85%.
On the other hand, when attention is paid to 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 poor granulated powder crushing. , The Rattler value is high, and the strength is low.

The gist configuration 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 components,
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 mass ppm and CaO: 700 to 1300 mass ppm
It includes,
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%,
A coercive force at 23 ° C. of 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.

3. A calcining step of calcining a mixture of the basic components weighed so as to have a predetermined component ratio;
To the calcined powder obtained in the calcining step, a sub-component adjusted to a predetermined ratio is added, mixed and pulverized.
After adding and mixing a binder to the pulverized powder obtained in the mixing-pulverization step, the mixture was formed so that the value of the particle size distribution d90 of the granulated powder was 230 μm to 300 μm and the crushing strength was 1.18 MPa or more and less than 1.50 MPa. A granulating step of obtaining the MnCoZn-based ferrite by forming the obtained granulated powder, firing the mixture under conditions of a maximum holding temperature of 1290 or more and a holding time of 1 hour or more.
A method for producing a MnCoZn-based ferrite comprising a basic component having, a subcomponent and an unavoidable impurity,
As the above basic components,
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 subcomponent,
SiO ₂ : 50 to 300 mass ppm and
CaO: 700 to 1300 mass ppm
Including
The amounts of Cd, Pb, Sb, As, and Se in the inevitable impurities are suppressed to less than 20 mass ppm,
further,
Ratler value less than 0.85%,
A coercive force at 23 ° C. of 15 A / m or less;
The specific resistance is 30Ω · m or more and
Curie temperature over 100 ℃
A method for producing a MnCoZn-based ferrite.

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

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

CaO: 700 to 1300 mass ppm
CaO segregates at the crystal grain boundaries of MnCoZn ferrite, has a function of suppressing the growth of crystal grains, and also has a role of reducing vacancies remaining in the crystal grains. Therefore, with the addition of an appropriate amount, the specific resistance increases, the coercive force decreases, and the Rutler value can be reduced because coarse crystals are reduced. Therefore, the content of CaO should be at least 700 mass ppm. On the other hand, if the added amount is excessive, abnormal grains appear and the Rattler value and the coercive force also increase. Therefore, the content of CaO must be limited to 1300 mass ppm or less. A more preferred CaO content is in the range of 700 to 1000 mass ppm.

-Prepared using granulated powder having a particle size distribution d90 of 300 μm or less.
-A granulated powder is prepared using a granulated powder having a crushing strength of less than 1.50 MPa.
In general, MnCoZn ferrite is obtained by filling a mold with a 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. Fine irregularities due to the gap between the granulated powders remain on the surface of the ferrite even after sintering, and serve as a starting point of a defect due to an impact. As a result, the Rattler value increases as the minute irregularities increase. Therefore, in order to reduce the gap between the granulated powders, it is preferable to remove the granulated powder having a coarse particle size and to suppress the crushing strength of the granulated powder 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 when granulating by applying heat such as spray granulation. The particle size distribution is measured by a particle size analysis by a laser diffraction / scattering method described in JIS Z 8825. “D90” represents a particle size of 90% in total volume from the small particle size side in the particle size distribution curve. The crushing strength of the granulated powder is measured by a method specified in JIS Z8841.
If the value of the particle size distribution d90 is too small, the fluidity decreases due to an 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. Also, if the crushing strength of the granulated powder is significantly reduced, the granulated powder is crushed during transportation and filling of the powder with a mold, and the fluidity is 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 for producing 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, and after these are sufficiently mixed, calcination is performed. Next, the obtained calcined powder is pulverized to obtain a pulverized powder. At this time, the auxiliary component specified in the present invention is added at a predetermined ratio, and pulverized together with the calcined powder. In this step, the powder is sufficiently homogenized so that the concentration of the added components is not biased, and at the same time, the calcined powder is refined to a target average particle size. Here, the target average particle size of the pulverized powder is 1.4 to 1.0 μm.
Next, 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 crushing strength. In the case of the spray drying 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, after passing through a process such as sieving for adjusting the particle size as required, pressure is applied by a molding machine, followed by molding, followed by firing under suitable firing conditions. It is desirable to pass through a sieve having a size of 350 μm to remove coarse powder on the sieve.
The appropriate firing conditions are, as described above, the maximum holding temperature: 1290 ° C. or more, and the holding time: 1 h or more.
Further, the obtained ferrite sintered body may be subjected to processing such as surface polishing.

Claims (6)

As a basic ingredient,
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,
For the above basic components, as subcomponents,
SiO ₂ : 50 to 300 mass ppm and CaO: 300 to 1300 mass ppm
And the remainder is MnCoZn-based ferrite composed of unavoidable impurities,
The amounts of Cd, Pb, Sb, As, and Se in the inevitable impurities are suppressed to less than 20 mass ppm,
Further, in the MnCoZn ferrite,
Ratler value less than 0.85%,
A coercive force at 23 ° C. of 15 A / m or less;
A MnCoZn ferrite having a specific resistance of 30 Ω · m or more and a Curie temperature of 100 ° C. or more. MnCoZn ferrite according to claim 1 sintered density of the MnCoZn ferrite is 4.85 g / cm ³ or more.   3. The MnCoZn-based ferrite according to claim 1, wherein the MnCoZn-based ferrite is a MnCoZn-based ferrite formed by molding and sintering a granulated powder having a particle size distribution d90 of 300 μm or less. 4.   The MnCoZn-based ferrite according to any one of claims 1 to 3, wherein the MnCoZn-based ferrite is a MnCoZn-based ferrite formed by molding and sintering a granulated powder having a crushing strength of less than 1.50 MPa. A calcining step of calcining a mixture of the basic components weighed so as to have a predetermined component ratio, and a calcined powder obtained in the above-mentioned calcining step, to which an auxiliary component adjusted to have a predetermined component ratio is added. Mixing, pulverizing, mixing and pulverizing steps;
After adding and mixing a binder to the pulverized powder obtained in the mixing-pulverization step, the mixture is granulated such that the value of the particle size distribution d90 of the granulated powder is 300 μm or less and / or the crushing strength is less than 1.50 MPa. A MnCoZn-based ferrite having a firing step of obtaining the MnCoZn-based ferrite according to claim 1 or 2 by firing the obtained granulated powder under conditions of a maximum holding temperature of 1290 or more and a holding time of 1 hour or more. Manufacturing method.   The method for producing a MnCoZn-based ferrite according to claim 5, wherein the granulation is a spray drying method.