WO2019123681A1

WO2019123681A1 - Mncozn ferrite and production method therefor

Info

Publication number: WO2019123681A1
Application number: PCT/JP2018/019533
Authority: WO
Inventors: 裕史吉田; 由紀子中村
Original assignee: Ｊｆｅケミカル株式会社
Priority date: 2017-12-20
Filing date: 2018-05-21
Publication date: 2019-06-27
Also published as: JP6742440B2; CN110178191B; TW201927701A; CN110178191A; JPWO2019123681A1; TWI667200B

Abstract

This invention provides an MnCoZn ferrite containing, as basic constituents, 45.0% by mole or more but less than 50.0% by mole of iron calculated as Fe₂O₃, 15.5 to 24.0% by mole of zinc calculated as ZnO, and 0.5 to 4.0% by mole of cobalt calculated as CoO with the balance being manganese, and containing, as sub-constituents to the basic constituents, 50 to 300 ppm by mass of SiO₂ and 300 to 1300 ppm by mass of CaO, with the balance being unavoidable impurities, wherein the amounts of Cd, Pb, Sb, As and Se in the unavoidable impurities are suppressed to less than 20 ppm by mass each, and furthermore, the Rattler value is brought to less than 0.85%, the coercive force at 23°C to 15 A/m or lower, the specific resistance to 30 Ω•m or higher, and the Curie temperature to 100°C or higher. In this manner, the MnCoZn ferrite not only has excellent magnetic properties of high resistance and low coercive force, but also has excellent mechanical strength.

Description

MnCoZn ferrite and method for producing the same

The present invention relates to a MnCoZn ferrite having a high specific resistance, a small coercive force, and a resistance to breakage, and a method for producing the same.
In the present specification, the coercivity refers to the value at 23 ° C.

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

However, since MnZn ferrite has a large amount of Fe ²⁺ , exchange of electrons between Fe ³⁺ -Fe ²⁺ easily occurs, and there is a disadvantage that the specific resistance is as low as 0.1 Ω · m. Therefore, when the frequency range to be used becomes high, the loss due to the eddy current flowing in the ferrite increases rapidly, the initial permeability significantly decreases, and the loss also increases. For this reason, the service frequency of MnZn ferrite is limited to about several hundred kHz, and NiZn ferrite is mainly used in MHz order. The specific resistance of this NiZn ferrite is 10 ⁵ (Ω · m) or more, about 10,000 times that of MnZn ferrite, and the eddy current loss is small, so the characteristics of high initial permeability and low loss are unlikely to be lost even in a high frequency region.

However, NiZn ferrite has a major 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 be small, but the NiZn ferrite is composed only of ions having negative magnetic anisotropy. The value of this coercivity is large. The coercivity is defined in JIS C 2560-2.

As a method of obtaining a ferrite having a large specific resistance other than the 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, in Patent Document 1, Patent Document 2 and Patent Document 3 etc., there are reported MnZn ferrites whose specific resistance is enhanced by reducing the Fe ²⁺ content by setting the Fe ₂ O ₃ component to less than 50 mol%. However, since these also consist of only ions having negative magnetic anisotropy as in the case of NiZn ferrite, the problem of reducing the coercivity has not been solved at all.

Thus, techniques of adding Co ²⁺ having positive magnetic anisotropy other than Fe ²⁺ have been disclosed in Patent Document 4, Patent Document 5 and Patent Document 6, but these were aimed at lowering the coercive force. It was not a thing. Moreover, since the countermeasure to the abnormal grain mentioned later was inadequate, it was inferior also in terms of cost and manufacturing efficiency.

On the other hand, Patent Document 7 reports high resistivity MnCoZn ferrite having low coercivity, which can suppress the appearance of abnormal grains by providing a specified impurity composition, and can be stably manufactured.
In addition, abnormal grain growth is what occurs when the balance of grain growth is broken locally due to some cause, and is a phenomenon often seen in manufacturing using powder metallurgy. In this abnormally grown grain, a substance that greatly impedes the movement of the domain wall, such as impurities and lattice defects, is mixed, so that the soft magnetic property is lost and the coercivity is increased. At the same time, the resistivity decreases due to the insufficient formation of grain boundaries.

Japanese Patent Application Laid-Open No. 7-230909 JP 2000-277316 A JP 2001-220222 A Patent No. 3418827 gazette Japanese Patent Application Publication No. 2001-220221 Unexamined-Japanese-Patent No. 2001-68325 Patent No. 4554959 JP, 2006-44971, A

With the development of Patent Document 7 mentioned above, MnCoZn ferrite having satisfactory magnetic characteristics has been obtained.
On the other hand, there is a remarkable movement of electrification of automobiles in recent years, and although MnCoZn ferrite is also increasingly mounted in automobiles, the mechanical strength is a property regarded as important in the same application. In comparison with electric products and industrial equipment that were the main applications until that time, vibrations occur during traveling in automobiles, so in vehicles applications it is also required that MnCoZn ferrites, which are ceramics, not be damaged by shock due to vibration It has become possible to

However, MnCoZn ferrite having less than 50 mol% of Fe ₂ O ₃ component tends to sinter easily at the time of firing due to the small number of oxygen vacancies, so that the vacancies easily remain in the crystal grains and the formation of grain boundaries Is likely to be uneven. As a result, when an external impact is received, there is a problem that the chip is easily broken compared to the conventional MnCoZn ferrite.
That is, the technique disclosed in Patent Document 7 has a problem in that the obtained magnetic properties are sufficient but the mechanical strength for the defect is not necessarily sufficient.

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

The present invention maintains the magnetic properties of the conventional high resistance and low coercivity, and at the same time, suppresses abnormal grain growth while generating uniform grain boundaries, so that the defect resistance represented by the rattler value is achieved. An object of the present invention is to propose an MnCoZn ferrite having mechanical strength as well as its properties together with its advantageous manufacturing method.

The inventors first examined the appropriate amounts of Fe ₂ O ₃ , ZnO, and CoO of MnCoZn ferrite necessary to obtain desirable magnetic properties, and as a result, they have high resistivity, low coercivity, and Curie temperature. We found a proper range that can realize all of the characteristics of high simultaneously.
In the present specification, as described above, regarding the coercive force, the value at 23 ° C. is a problem. The reason is that there are many MnZn ferrite cores used for antenna and noise filter applications, which are used at positions away from power source transformers and semiconductors serving as heat sources, and they operate at normal temperature (5 to 35 ° C) Do. Therefore, it is important that the magnetic properties at 23 ° C., which is a typical value in the normal temperature (5 to 35 ° C.) range, be good, that is, the coercivity be small.

Next, focusing on the microstructure, it was found that defects in the sintered core that can be represented by the Latler value can be suppressed by reducing the pores in the crystal grains, adjusting the grain size, and realizing grain boundaries of an appropriate thickness. . Here, in order to realize a desirable crystal structure, the addition amount of SiO ₂ and CaO, which are components segregated in the crystal grain boundaries, greatly influences, and therefore, it was succeeded to set an appropriate range of these components. If it is in this range, a low Latler value can be held.

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 / or CaO is excessive, and abnormal grains are present in natural ore or when impurities such as Cd, Pb, Sb, As and Se, which are impurities mixed during smelting, are contained at a certain value or more. Was found to appear.
The present invention is based on the above findings.

As described above, Patent Document 1, Patent Document 2 and Patent Document 3 refer to high specific resistance, and Patent Document 4, Patent Document 5 and Patent Document 6 show positive magnetic difference. Although the addition of Co ²⁺ having the directionality is described, there is no description on the coercivity, and Patent Document 5 rather conversely restricts the intentional addition of Pb. Moreover, none of these Patent Documents 1 to 6 has any description on measures against abnormal particles, so it is presumed that the mechanical strength is also insufficient. Also, with regard to Patent Document 7 mentioned with respect to low coercivity, since the definition of the additive is insufficient, sufficient mechanical strength which can suppress defects can not be desired. Furthermore, even in Patent Document 8 that mentions improvement in chipping strength, a significant reduction in resistivity can not be avoided.

The essential features of the present invention are as follows.
1. As a basic ingredient,
Iron: 45.0 mol% or more, 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: containing the balance,
As a subcomponent to the above basic component,
SiO ₂ 50 to 300 mass ppm and CaO 300 to 1300 mass ppm
And the remainder is MnCoZn ferrite consisting of unavoidable impurities,
The amounts of Cd, Pb, Sb, As and Se in the above-mentioned unavoidable impurities are each suppressed to less than 20 mass ppm,
Furthermore, in the above-mentioned MnCoZn ferrite,
Latler value less than 0.85%,
Coercivity at 23 ° C is 15A / m or less,
MnCoZn ferrite having a resistivity of 30 Ω · m or more and a Curie temperature of 100 ° C. or more.

2. 5. The MnCoZn ferrite according to 1, wherein a sintering density of the MnCoZn ferrite is 4.85 g / cm ³ or more.

3. 5. The MnCoZn ferrite according to 1 or 2, wherein the MnCoZn ferrite is a MnCoZn ferrite comprising a shaped-sintered body of granulated powder having a particle size distribution d90 of 300 μm or less.

4. The MnCoZn ferrite according to any one of 1 to 3, wherein the MnCoZn ferrite is a MnCoZn ferrite made of a molded-sintered body of granulated powder having a crushing strength of less than 1.50 MPa.

5. Sub-components adjusted to a predetermined ratio are added to the calcined powder obtained in the calcination step of calcining the mixture of the basic components weighed to a predetermined component ratio and the above-mentioned calcination step, and mixed, Grinding-mixing-grinding process,
A binder is added to and mixed with the pulverized powder obtained in the above mixing-pulverization step, and then granulated so 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. The formed granulated powder is sintered and fired under the conditions of maximum holding temperature: 1290 or more and holding time: 1 hour or more to obtain the MnCoZn-based ferrite described in 1 or 2 above. Production method.

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

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

Hereinafter, the present invention will be specifically described.
First, the reason why the composition of the MnCoZn ferrite is limited to the above range in the present invention will be described. Incidentally, showing the iron and zinc are included in the present invention as a basic component, cobalt, all the manganese _{_{Fe 2 O 3, ZnO, CoO}} , a value in terms of MnO. The contents of Fe ₂ O ₃ , ZnO, CoO, and MnO are expressed in mol%, and the contents of one subcomponent and the impurity component are expressed in mass ppm with respect to the entire ferrite.

Fe ₂ O ₃ : 45.0 mol% or more, less than 50.0 mol% When Fe ₂ O ₃ is contained in excess, the amount of Fe ²⁺ increases, whereby the specific resistance of the MnCoZn ferrite decreases. 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 coercivity is increased and the Curie temperature is decreased, so that iron is contained at least 45.0 mol% in terms of Fe ₂ O ₃ . The preferred range of Fe ₂ O ₃ is 47.1 mol% or more and less than 50.0 mol%, more preferably 47.1 to 49.5 mol%.

ZnO: 15.5 mol% to 24.0 mol%
ZnO works to increase the saturation magnetization of ferrite and to increase the sintered density due to its relatively low saturation vapor pressure, thereby increasing the saturation magnetic flux density, and is an effective component for reducing the coercive force. Therefore, at least 15.5 mol% of zinc is contained in terms of ZnO as a minimum. On the other hand, when the zinc content is larger than the appropriate value, the Curie temperature is lowered and there is a problem in practical use. Therefore, the upper limit of zinc is 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 positive magnetic anisotropy energy, and as a result of the addition of an appropriate amount of this CoO, the absolute value of the sum of magnetic anisotropy energy decreases, and as a result, a decrease in coercivity is realized. Ru. For that purpose, it is essential to add 0.5 mol% or more of CoO. On the other hand, a large amount of addition causes a decrease in specific resistance, induction of abnormal grain growth, and an increase in coercivity because the total of magnetic anisotropy energy is positively inclined. In order to prevent this, CoO is limited to the addition of up to 4.0 mol%. The preferred range of CoO is 1.0 to 3.5 mol%, more preferably 1.0 to 3.0 mol%.

MnO: Remainder The present invention is MnCoZn ferrite, and the remainder of the basic component composition needs to be MnO. The reason is that unless MnO is used, good magnetic characteristics of high saturation magnetic flux density, low loss and high permeability can not be obtained. The preferred range of MnO is 26.5 to 32.0 mol%.

The basic components have been described above, but the subcomponents 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, and the coercivity is lowered by reducing the residual magnetic flux density by reducing the pores remaining in the crystal grains with the addition of an appropriate amount. Let In addition, SiO ₂ segregates in grain boundaries to increase the specific resistance and simultaneously reduce coarse crystals, thereby reducing the Latler value, which is an index of defects in a sintered body. Therefore, at least 50 mass ppm of SiO ₂ is included. On the other hand, when the addition amount is excessive, abnormal particles appear on the contrary, which becomes the starting point of the defect, and the rattler value rises at the same time, and the coercivity also rises, so the content of SiO ₂ is limited to 300 mass ppm or less There is a need. The more preferred content of SiO ₂ is in the range of 60 to 250 mass ppm.

CaO: 300 to 1300 mass ppm
CaO is segregated at grain boundaries of MnCoZn ferrite, has a function of suppressing the growth of crystal grains, and also has a role of reducing the pores remaining in the crystal grains. Therefore, with the addition of an appropriate amount, the specific resistance is increased, the coercivity is also reduced, and the coarser crystals are reduced, so that the rattler value can also be reduced. Therefore, at least 300 mass ppm of CaO is included. On the other hand, when the addition amount is excessive, abnormal grains appear, and the Latler value and the coercivity also increase, so it is necessary to limit the content of CaO to 1300 mass ppm or less. A more preferable content of CaO is in the range of 350 to 1000 mass ppm.

Next, the impurity components to be suppressed will be described.
Each less than 20 mass ppm of Cd, Pb, Sb, As and Se These are components inevitably contained in the raw materials because they are contained in natural ore or mixed in smelting or the like. There is no problem if these contents are very small, but if it is contained in a certain amount or more, abnormal grain growth of ferrite is induced, and the various properties of the obtained ferrite are seriously adversely affected. As in the present invention, ferrite having a composition containing less than 50 mol% of Fe ₂ O ₃ is more susceptible to crystal grain growth than those containing 50 mol% or more, and hence the amounts of Cd, Pb, Sb, As and Se If there are many particles, abnormal grain growth is likely to occur. In such a case, not only the coercivity increases, but also the generation of grain boundaries is insufficient, so that the specific resistance is lowered, and furthermore, since it becomes the starting point of defects, the rattler value is also increased.
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, it is necessary to make the allowable amount of unavoidable impurities into 50 mass ppm or less in total including Cd, Pb, Sb, As and Se mentioned above. Preferably, the allowable amount of the unavoidable impurities is 40 mass ppm or less.

Therefore, it is preferable to minimize the mixing of impurities in the basic component and the auxiliary component used as the raw material. The total amount of impurities in the basic component and the subcomponents used as the raw material is preferably 50 mass ppm or less including P, B, S and Cl described above, and more preferably 40 mass ppm or less.

In addition, various properties of the MnCoZn ferrite are greatly affected by various parameters as well as the composition. Therefore, in the present invention, it is preferable to satisfy the following conditions in order to have desired magnetic properties and strength properties.

Sintered density: 4.85 g / cm ³ or more In the MnCoZn ferrite, sintering and grain growth proceed by firing treatment to form crystal grains and grain boundaries. Crystal structure capable of realizing low coercivity, that is, nonmagnetic components to be present at grain boundaries are appropriately segregated at grain boundaries, and grains are composed of components having a suitable grain size and uniform magnetism In order to achieve the desired form, the sintering reaction needs to proceed sufficiently. In addition, from the viewpoint of preventing defects, when the sintering is insufficient, the strength is unfavorably reduced.
From the above viewpoint, the MnCoZn ferrite of the present invention preferably has a sintered density of 4.85 g / cm ³ or more. By satisfying this, the coercivity can be reduced, and the Latler value can be suppressed to be low. In addition, in order to realize this sintering density, it is necessary to make the maximum holding temperature at the time of baking 1290 ° C. or more, and to hold the holding time at this temperature for 1 h or more. 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 manufacture the additive amount and the impurity amount described above within an appropriate range so that abnormal grains do not appear.

-It manufactures using granulated powder whose value of the particle size distribution d90 is 300 micrometers or less.
-It produces using granulated powder whose granulated powder crushing strength is less than 1.50 MPa.
In general, MnCoZn ferrite is obtained by firing and sintering the obtained molded body through a powder forming process in which granulated powder is filled in a mold and then compressed at a pressure of about 100 MPa. On the surface of the ferrite, minute irregularities resulting from the gaps between the granulated powders remain even after sintering, and this becomes the starting point of fracture due to impact, so the Latler value becomes higher as the minute irregularities remain. Therefore, in order to reduce the gaps 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 in terms of particle size. 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 as in the spray granulation method. The particle size distribution is measured by particle size analysis by laser diffraction / scattering method described in JIS Z 8825. "D90" represents a particle size of 90% of the total volume from the small particle size side in the particle size distribution curve. Further, the crushing strength of the granulated powder is measured by the method defined in JIS Z 8841.
If the value of the particle size distribution d90 is too small, the flowability is reduced due to an increase in the contact point between the granulated powder, so that the mold filling failure of the powder during powder molding and the molding pressure during molding It is preferable to set the lower limit of d90 to 75 μm because an increase problem arises. In addition, when the crushing strength of the granulated powder is largely reduced, the granulated powder is crushed during transportation and at the time of filling the powder mold, and the flowability is lowered, so that the defect at the filling of the powder mold and molding The lower limit of the crush strength is preferably set to 0.50 MPa, since the problem of an increase in molding pressure at the time occurs.

Next, the 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 attain a predetermined ratio, and these are sufficiently mixed and then calcined. Next, the obtained calcined powder is pulverized to obtain a pulverized powder. Under the present circumstances, the subcomponent prescribed | regulated by this invention is added by a predetermined | prescribed ratio, and it grinds together with calcined powder. In this step, the powder is sufficiently homogenized so that the concentration of the added component is not uneven, and at the same time, the calcined powder is refined to the target average particle size. Here, the average particle diameter of the target pulverized powder is 1.4 to 1.0 μm.
Next, an organic substance binder such as polyvinyl alcohol is added to the powder having the target composition, and granulated by spray drying 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 to make the exhaust air temperature lower than 270.degree. Here, the preferred particle size of the granulated powder is 75 to 300 μm in terms of the particle size distribution d90. Moreover, the suitable crushing strength of granulated powder is 0.50 Mpa or more and less than 1.50 Mpa.
Next, after passing through processes such as sifting for adjusting the particle size as required, pressure is applied by a forming machine to perform forming, and then firing is performed under suitable firing conditions. It is desirable to remove the coarse powder on the sieve by passing through a 350 μm sieve with a 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.
The obtained ferrite sintered body may be subjected to processing such as surface polishing.

Thus, conventionally it was impossible,
• Latler value less than 0.85% • Coercivity 15 ° A / m or less at 23 ° C. • Specific resistance 30 Ω · m or more • MnCoZn ferrite satisfying all the excellent characteristics such as Curie temperature 100 ° C. or more at the same time 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 using a ball mill for 16 hours, and then calcined at 925 ° C. for 3 hours in air. Next, to this calcined powder, SiO ₂ and CaO were weighed after being respectively equivalent to 150 and 700 mass ppm, and then added, and ground in a ball mill for 12 hours. Next, polyvinyl alcohol is added to the obtained crushed slurry, spray-dried and granulated at an exhaust air temperature of 250 ° C., coarse particles are removed through a sieve with 350 μm openings, and a pressure of 118 MPa is applied to the toroidal core and rectangular solid core Molded into The particle size distribution d90 of the granulated powder used for molding was 230 μm, and the crushing strength was 1.29 MPa.
Thereafter, this molded body is charged into a firing furnace, and fired in a gas flow appropriately mixed with nitrogen gas and air at a maximum temperature of 1350 ° C. for 2 hours, outer diameter: 25 mm, inner diameter: 15 mm, height: 5 mm The sintered toroidal core of the above was obtained, and a five-piece sintered cylindrical core having a diameter of 10 mm and a height of 10 mm was obtained.
Since high purity raw materials were used, all impurities Cd, Pb, Sb, As and Se of the sintered core were 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 C 2560-2, the sintered density was 23 ° C., and the toroidal core was measured by the Archimedes method, and the resistivity was measured by the four-terminal method. The initial permeability of the toroidal core was calculated based on the inductance measured by using a winding of 10 turns on the toroidal core and using an LCR meter (4980A manufactured by Keysight Co., Ltd.). In addition, the Curie temperature was calculated from the temperature characteristic measurement result of the inductance. The Latler value was measured according to the method defined in JPMA P11-1992. The coercive force Hc was measured at 23 ° C. based on JIS C 2560-2.
The results obtained are shown in Table 1.

As shown in the table, in Examples 1-1 to 1-7, which are invention examples, the high strength that the Latler value is less than 0.85%, the specific resistance at 23 ° C. is 30 Ω · m or more, and the coercivity is 15 A An MnCoZn ferrite having excellent magnetic properties such as not more than / m and a Curie temperature of not less than 100 ° C. could be obtained.
On the other hand, in Comparative Examples 1-1 and 1-2 containing 50.0 mol% or more of Fe ₂ O ₃ , the resistivity decreases significantly with the formation 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 coercivity and a decrease in Curie temperature are observed.
In addition, in Comparative Example 1-4 in which the amount of ZnO exceeds the appropriate range, a decrease in Curie temperature is observed. On the other hand, in Comparative Example 1-5 in which the amount of ZnO is less than the appropriate range, the coercivity is increased, and favorable magnetic characteristics can not be realized.
Furthermore, in Comparative Example 1-6 where the amount of CoO does not reach the appropriate range, the coercivity is high due to the lack of positive magnetic anisotropy, while in Comparative Example 1-7 where the amount of CoO exceeds the appropriate range, excessive positive The coercivity is increased due to the increase of the magnetic anisotropy, and both deviate from the preferable range.

Example 2
When iron, zinc, cobalt and manganese contained are all converted as 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%, the amount of CoO is 2 The raw materials were weighed so as to have a composition of 0 mol% and the balance MnO, mixed for 16 hours using a ball mill, and then calcined in air at 925 ° C. for 3 hours. Next, SiO ₂ and CaO in amounts shown in Table 2 were added to the calcined powder, and grinding was performed for 12 hours with a ball mill. Next, polyvinyl alcohol is added to the obtained pulverized slurry, spray-dried and granulated at an exhaust air temperature of 250 ° C., and coarse particles are removed through a sieve with 350 μm openings, and then a pressure of 118 MPa is applied to the toroidal core and cylindrical core. Molded into In addition, the particle size distribution d90 of the granulated powder used for shaping | molding was 230 micrometers, and crushing strength was 1.29 MPa.
Thereafter, this molded body is charged into a firing furnace, and fired in a gas flow appropriately mixed with nitrogen gas and air at a maximum temperature of 1350 ° C. for 2 hours, outer diameter: 25 mm, inner diameter: 15 mm, height: 5 mm The sintered body toroidal core of the above and the cylindrical-shaped core of five diameter: 10 mm and height: 10 mm were obtained.
In addition, since high purity raw materials were used as the raw materials, all impurities Cd, Pb, Sb, As and Se of the sintered core were 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 shown in Table 2.

As shown in the table, in Examples 2-1 to 2-4 in which the SiO ₂ and the amount are within the appropriate range, the high strength that the Latler value is less than 0.85%, and the specific resistance at 23 ° C. is 30 Ω · m. As mentioned above, the MnCoZn ferrite which has the outstanding magnetic characteristic of a coercive force of 15 A / m or less and Curie temperature of 100 degreeC or more was able to be obtained.
On the other hand, in Comparative Examples 2-1 and 2-3 in which even one of SiO ₂ and CaO does not reach the appropriate range, the size of the crystal grains is uniform because the generation of the grain boundaries is insufficient. Because the Latler value is higher than 0.85% and the grain boundary thickness is insufficient, the resistivity is less than 30 Ω · m.
In addition, at the levels of Comparative Examples 2-2, 2-4 and 2-5 where one or more of the same components are excessive, abnormal particles appear and sintering is inhibited, so the sintering density is low, Latler is also high. In addition, since the formation of grain boundaries is insufficient, the resistivity is low and the coercivity is also high.

Example 3
According to the method shown in Examples 1 and 2, the basic components and the auxiliary components have the same composition as in Example 1-2, but the amount of impurities contained is variously different, and the outer diameter is 25 mm. Using a sintered toroidal core with an inner diameter of 15 mm and a height of 5 mm and a cylindrical core with five diameters of 10 mm and a height of 10 mm, the characteristics were evaluated using the same method and apparatus as in Example 1. The results are shown in Table 3. In addition, the particle size distribution d90 of the granulated powder used for shaping | molding was 230 micrometers, and 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 are below specified values, the strength represented by the Latler value, and the coercivity, specific resistance and Curie temperature Good values are obtained for all of the magnetic properties represented by
On the other hand, abnormal particles appear in all of Comparative Examples 3-1 to 3-7 in which one or more of these five levels exceed the specified value, and sintering is inhibited. Since the sintered density is low, the Latler value is high, and the generation of grain boundaries is insufficient, so the specific resistance is low and the coercivity is also high.

Example 4
A molded product produced at a ratio such that the basic component, the accessory component, and the impurity component have the same composition as in Example 1-2 according to the method shown in Examples 1 and 2 was subjected to various temperature conditions shown in Table 4. Baked.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1. The obtained results are shown in Table 4. In addition, the particle size distribution d90 of the granulated powder used for shaping | molding was 230 micrometers, and crushing strength was 1.29 MPa.

As shown in the table, Examples 3-1 to 3-3 having a maximum holding temperature of 1290 ° C. or more and a holding time of 1 hour or more and a sintering density of 4.85 g / cm ³ or more. In No. 5, both the strength represented by the Latler value and the magnetic properties represented by the specific resistance, the coercivity and the Curie temperature were good.
On the other hand, 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 Latler value is high, and the crystal growth is insufficient. As a result, the hysteresis loss is increased. As a result, the coercivity is high, which is not preferable in terms of both strength and magnetic characteristics.

Example 5
With respect to the granulated powder obtained under the same composition and the same spray dry conditions as Example 1-2 by the method shown in Examples 1 and 2, the particle size distribution d90 shown in Table 5 is obtained by changing the screening conditions. The toroidal core and the cylindrical core were formed by applying a pressure of 118 MPa to a value (crush strength: 1.29 MPa). Thereafter, this molded body is charged into a firing furnace, and fired in a gas flow appropriately mixed with nitrogen gas and air at a maximum temperature of 1350 ° C. for 2 hours, outer diameter: 25 mm, inner diameter: 15 mm, height: 5 mm The sintered body toroidal core of the above and the cylindrical-shaped core of five diameter: 10 mm and height: 10 mm were obtained.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1. The obtained results are 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 residual porosity of the granulated powder is small and the origin of defects is small. It can be suppressed to less than%.
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 among the granulated powder and there are many origins of defects, so the rattler value is high and the strength is lowered.

Example 6
Granules having different crush strengths are obtained by spray-drying a slurry prepared with the same composition of Example 1-2 prepared by the method shown in Examples 1 and 2 under the exhaust air temperature conditions shown in Table 6. After removing the coarse powder through a sieve of 350 μm mesh, 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.
Thereafter, this molded body is charged into a firing furnace, and fired in a gas flow appropriately mixed with nitrogen gas and air at a maximum temperature of 1350 ° C. for 2 hours, outer diameter: 25 mm, inner diameter: 15 mm, height: 5 mm The sintered body toroidal core of the above and the cylindrical-shaped core of five diameter: 10 mm and height: 10 mm were obtained.
The results of evaluating the properties of each of these samples using the same method and apparatus as in Example 1 are also shown in Table 6.

As shown in the table, in Examples 6-1 to 6-2 in which the discharge air temperature of spray drying granulation is not excessively high, the crushing strength of the granulated powder is less than 1.5 MPa, and the granulated powder Since it crushes sufficiently, there is no gap between the granulated powder, and hence there are few origins of defects, so the rattler value can be suppressed to less than 0.85%.
On the other hand, 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 caused by the granulated powder crushing failure. Since the Latler value is high, the strength is decreasing.

Claims

As a basic ingredient,
Iron: 45.0 mol% or more, 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: containing the balance,
As a subcomponent to the above basic component,
SiO 2 50 to 300 mass ppm and CaO 300 to 1300 mass ppm
And the remainder is MnCoZn ferrite consisting of unavoidable impurities,
The amounts of Cd, Pb, Sb, As and Se in the above-mentioned unavoidable impurities are each suppressed to less than 20 mass ppm,
Furthermore, in the above-mentioned MnCoZn ferrite,
Latler value less than 0.85%,
Coercivity at 23 ° C is 15A / m or less,
MnCoZn ferrite having a resistivity of 30 Ω · m or more and a Curie temperature of 100 ° C. or more.
The MnCoZn ferrite according to claim 1, wherein a sintered density of the MnCoZn ferrite is 4.85 g / cm 3 or more.
The MnCoZn-based ferrite according to claim 1 or 2, wherein the MnCoZn-based ferrite is a MnCoZn-based ferrite formed of a shaped-sintered body of granulated powder having a particle size distribution d90 of 300 μm or less.
The MnCoZn-based ferrite according to any one of claims 1 to 3, wherein the MnCoZn-based ferrite is a MnCoZn-based ferrite formed of a shaped-sintered body of granulated powder having a crushing strength of less than 1.50 MPa.
A secondary component adjusted to have a predetermined component ratio is added to the calcined powder obtained in the calcination step of calcining the mixture of basic components weighed to a predetermined component ratio and the above-mentioned calcination step. Mixing, grinding, mixing-grinding process,
A binder is added to and mixed with the pulverized powder obtained in the above mixing-pulverization step, and then granulated so 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. MnCoZn ferrite having a firing step of obtaining the MnCoZn ferrite according to claim 1 or 2 by molding the granulated powder and firing under the conditions of maximum holding temperature: 1290 or more and holding time: 1 hour or more Manufacturing method.
The method for producing MnCoZn ferrite according to claim 5, wherein the granulation is a spray drying method.