JP3924272B2 - Mn-Zn ferrite, transformer core and transformer - Google Patents

Description

  The present invention relates to an Mn—Zn ferrite, a transformer core and a transformer, and more specifically, used for a magnetic core of a power transformer such as a switching power supply, and has a low power loss (core loss), particularly in a wide temperature range. The present invention relates to a highly reliable Mn—Zn ferrite, a magnetic core for a transformer, and a transformer that are less deteriorated in core loss and excellent in magnetic stability even under temperature (high temperature storage test).

  In recent years, various electronic devices have been increasingly demanded for reduction in size, thickness, and performance. In switching power supplies and the like, there is a demand for miniaturization and thinning of power transformers and the like, and in order to miniaturize and thin the transformer, it is essential to reduce core loss of the magnetic core. Furthermore, considering the operating environment such as the power supply, the core loss is small in a wide temperature range, and the core loss is less deteriorated even at high temperatures (high temperature storage test) to prevent thermal runaway of electronic circuits. Therefore, a highly reliable magnetic core is required.

Under such demands, several proposals have been made to reduce core loss in a wide temperature range by dissolving an appropriate amount of Co in Mn—Zn-based ferrite (see Patent Documents 1 to 13). .
JP-A-6-290925 JP-A-6-310320 JP-A-8-191011 JP-A-9-2866 JP-A-9-134815 Japanese Patent Laid-Open No. 13-80952 Japanese Patent Laid-Open No. 13-220146 JP 2002-231520 A Japanese Patent Publication No. 61-11892 Japanese Examined Patent Publication No. 61-43291 Japanese Patent Publication No. 4-33755 Japanese Patent Publication No. 5-21859 Here, the reason why the core loss can be reduced in a wide temperature range by dissolving Co in solid solution will be described. Although there is a magnetocrystalline anisotropy constant K1 as a factor governing the core loss, the temperature characteristic of the core loss changes with a temperature change of K1, and the core loss becomes a minimum value at a temperature at which K1 = 0. In order to reduce the core loss in the wide temperature band, K1 must be close to 0 in the wide temperature band. This constant K1 varies depending on the constituent elements of the spinel compound, which is the main phase of ferrite. However, in the case of Mn—Zn ferrite, the temperature dependence of K1 is reduced by dissolving Co ions, and the absolute temperature coefficient of magnetic loss is absolute. It is thought that the value can be reduced.

  Several proposals have been made to reduce core loss in a wide temperature range by dissolving an appropriate amount of Co in Mn—Zn-based ferrite as in the above publication.

  However, in order to prevent thermal runaway of electronic circuits when considering the operating environment such as the power supply, etc., measures to increase the stability and reliability of core loss characteristics under high temperature (high temperature storage test) Is not mentioned.

  In order to solve such a problem, the present invention provides a core for use in a power transformer such as a switching power supply, and the core loss is small in a wide temperature range, and the core loss is deteriorated even at a high temperature (high temperature storage test). An object of the present invention is to provide a highly reliable Mn—Zn-based ferrite, a magnetic core for transformer, and a transformer, which are less in magnetic stability.

  The present inventors pay attention to cations in the Mn-Zn ferrite containing Co, and at a high temperature (high temperature storage test) by setting the value α of the following formula (1) in the ferrite to a predetermined value. The present inventors have found that the stability and reliability of the core loss characteristics can be improved and the present invention has been completed.

That is, the Mn—Zn ferrite according to the first aspect of the present invention is
Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included), in the basic component consisting essentially of MnO in the balance, in terms of Co ₃ O ₄ A Mn—Zn-based ferrite containing 0 to 5000 ppm (excluding 0) of Co oxide,
The value α of the following formula (1) in the ferrite is α ≧ 0.93,
For example, using a BH analyzer, a 100 kHz, 200 mT sinusoidal AC magnetic field is applied to the ferrite, and the core loss values measured at 75 ° C. and 120 ° C. are defined as Pcv 1. When the core loss value measured under the same conditions as the measurement of Pcv1 after storage at high temperature (stored in an atmosphere of 175 ° C. for 96 hours) is Pcv2, the core loss deterioration rate represented by the following formula (2) is: 3% or less at 75 ° C. or 5% or less at 120 ° C.
α = ((Fe ²⁺ −Mn ³⁺ −Co ³⁺ ) × (4.29 × A + 1.91 × B + 2.19 × C + 2.01 × D)) / ((A−B−C−D) × 100) (1)
Core loss deterioration rate (%) = ((Pcv1−Pcv2) / Pcv1) × 100 (2)
In the formula ^{(1), (Fe 2+ -Mn} 3+ -Co 3+): [wt%], A: Fe 2 O 3 [mol%], B: MnO [mol%], C: ZnO [mol%] , D: CoO [mol%].

The Mn—Zn based ferrite according to the second aspect of the present invention is
Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included), in the basic component consisting essentially of MnO in the balance, in terms of Co ₃ O ₄ A Mn—Zn-based ferrite containing 0 to 5000 ppm (excluding 0) of Co oxide,
The value α of the following formula (1) in the ferrite is α ≧ 0.93,
For example, using a BH analyzer, a 100 kHz, 200 mT sinusoidal AC magnetic field is applied to the ferrite, and the core loss values measured at 75 ° C. and 120 ° C. are defined as Pcv 1. When the core loss value measured under the same conditions as the measurement of Pcv1 after storage at high temperature (stored in an atmosphere of 200 ° C. for 96 hours) is Pcv3, the core loss deterioration rate represented by the following formula (3) is: 27% or less at 75 ° C. or 30% or less at 120 ° C.
α = ((Fe ²⁺ −Mn ³⁺ −Co ³⁺ ) × (4.29 × A + 1.91 × B + 2.19 × C + 2.01 × D)) / ((A−B−C−D) × 100) (1)
Core loss deterioration rate (%) = ((Pcv1−Pcv3) / Pcv1) × 100 (3)
In the formula ^{(1), (Fe 2+ -Mn} 3+ -Co 3+): [wt%], A: Fe 2 O 3 [mol%], B: MnO [mol%], C: ZnO [mol%] , D: CoO [mol%].

When the value α of the formula (1) in the ferrite is 0.93 or more, the deterioration of the core loss after the high temperature test (96 hours at 175 ° C.) can be considerably suppressed.

  Specifically, using a BH analyzer, a 100 kHz, 200 mT sinusoidal AC magnetic field was applied to the ferrite, and the core loss values measured at 75 ° C. and 120 ° C. were set to Pcv 1. When the value of the core loss measured under the same conditions as the measurement of Pcv1 is Pcv2 after high-temperature storage (96 hours storage in an atmosphere at 175 ° C.), the core loss represented by the following formula (2) The deterioration rate can be 3% or less at 75 ° C. or 5% or less at 120 ° C.

Core loss deterioration rate (%) = ((Pcv1−Pcv2) / Pcv1) × 100 (2)
Also, using a BH analyzer, a 100 kHz, 200 mT sinusoidal AC magnetic field was applied to the ferrite, and the core loss values measured at 75 ° C. and 120 ° C. were defined as Pcv 1, and the ferrite after measurement of the Pcv 1 Is stored at a high temperature (96 ° C. in an atmosphere of 200 ° C. for 96 hours), and when the core loss value measured under the same conditions as the measurement of Pcv1 is Pcv3, the core loss deterioration rate represented by the following formula (3) is obtained. 27% or less at 75 ° C. or 30% or less at 120 ° C.

Core loss deterioration rate (%) = ((Pcv1−Pcv3) / Pcv1) × 100 (3)
The reason why the deterioration of the core loss can be reduced as described above is not necessarily clear, but is supported by the experiments by the present inventors and is presumed as follows.

The cause of core loss deterioration under high temperature storage may be an increase in magnetic anisotropy due to the movement of Co ions via cation defects. However, in the case of Mn—Zn ferrite in which Co is dissolved, it is difficult to accurately separate and quantify the respective amounts of Fe ²⁺ , Fe ³⁺ , Co ²⁺ , and Co ³⁺ . Therefore, it is difficult to directly determine the amount of cation defects (non-stoichiometric oxygen amount). Therefore, in the present invention, it is possible to suppress the deterioration of the core loss after the high temperature test by devising a parameter called the value α in the equation (1) that can be measured even with the current measuring instrument and controlling the value. The headline and the present invention have been completed.

  According to the present invention, the ferrite according to the present invention is used as a transformer magnetic core used in a power transformer such as a switching power supply, or a transformer (a coil wound around a magnetic core). The core loss becomes small in the wide temperature range. Moreover, the deterioration rate of core loss after a high-temperature storage test (96 hours at 175 ° C.) is also reduced, and a highly reliable magnetic core and transformer excellent in magnetic stability can be obtained. Therefore, in the switching power supply and the power transformer, loss can be reduced, downsizing, thermal runaway can be prevented, and reliability can be improved.

  Next, the reason for limiting the numerical range of the present invention will be described.

When the composition of Fe ₂ O ₃ is smaller than 51.5 mol% or the composition of ZnO is larger than 15 mol%, the initial core loss before the high-temperature storage test is large, and the desired low temperature in the wide temperature range of 25 to 120 ° C. Core loss becomes difficult. When the composition of Fe ₂ O ₃ exceeds 57.0 mol%, the initial core loss before the high-temperature storage test is large, and it is difficult to reduce the core loss in the desired wide temperature range of 25 to 120 ° C. Further, when the composition of ZnO is 0 mol%, the relative density of the sintered body is lowered, the core loss in the initial stage before the high-temperature storage test is large, and it is difficult to reduce the core loss in the desired wide temperature range of 25 to 120 ° C. Become.

When the content of Co oxide in terms of Co ₃ O ₄ is 0 ppm, the initial core loss before the high-temperature storage test is large, and it is difficult to reduce the core loss in a desired wide temperature range of 25 to 120 ° C. Moreover, when the content of Co oxide in terms of Co ₃ O ₄ is larger than 5000 ppm, the core loss in the initial stage before the high-temperature storage test on the high temperature side is particularly large, and the core loss is reduced in the desired wide temperature range of 25 to 120 ° C. It becomes difficult.

The ferrite according to the present invention preferably contains SiO ₂ : 50 to 220 ppm, CaO: 120 to 1400 ppm as other subcomponents. This is to improve the sinterability and to form a high resistance layer at the crystal grain boundary.

Or the content of SiO ₂ is less than 50 ppm, or when the content of CaO becomes smaller than 120 ppm, with the sintering is less likely to be promoted, since a sufficient high resistance layer at the crystal grain boundary is less likely to be formed, SiO ₂ Alternatively, the core loss before the high-temperature storage test and the core loss after the high-temperature storage test tend to be larger than those having the same composition except for the CaO content.

Further, when the content of SiO ₂ is greater than 220 ppm or the content of CaO is greater than 1400 ppm, abnormal grain growth of crystals tends to occur and the grain boundary layer is likely to be excessively formed, and SiO ₂ or CaO The core loss before the high temperature storage test and the core loss after the high temperature storage test tend to be larger than those having the same composition except for the content of.

In the ferrite according to the present invention, preferably, as other subcomponents, Nb ₂ O ₅ : 0 to 500 ppm (excluding 0), ZrO ₂ : 0 to 500 pm (excluding 0), Ta ₂ O ₅ : 0 to 1000 ppm (excluding 0), V ₂ O ₅ : 0 to 500 ppm (excluding 0), HfO ₂ : 0 to 500 ppm (excluding 0) Contains one or more.

  By containing these subcomponents, a high resistance layer can be formed at the crystal grain boundary of ferrite, and particularly eddy current loss in core loss (mainly hysteresis loss and eddy current loss) can be reduced. Therefore, by including these subcomponents, it is possible to reduce the initial core loss before the high temperature storage test as compared with the same composition except that these subcomponents are not included, and the desired 25-120 ° C. The core loss can be easily reduced in a wide temperature range, and the deterioration of the core loss after the high-temperature storage test can be further reduced.

When the content of Nb ₂ O ₅ , ZrO ₂ , V ₂ O ₅ and HfO ₂ is larger than 500 ppm, or the content of Ta ₂ O ₅ is larger than 1000 ppm, the grain boundary layer is easily formed excessively. Thus, the effect of the present invention tends to be reduced.

  The ferrite according to the present invention may contain phosphorus (P) and boron (B), but preferably the content of P and B in the ferrite is P ≦ 35 ppm or B ≦ 35 ppm. The smaller the contents of P and B in the ferrite, the better.

  If the P content is higher than 35 ppm or the B content is higher than 35 ppm, abnormal grain growth of crystals tends to occur, and the effect of the present invention tends to be reduced.

  In the present invention, the value α of the formula (1) in the ferrite is preferably α ≧ 0.94, more preferably α ≧ 0.95, and the upper limit is not particularly limited, but is preferably 1.50 or less. More preferably, it is 1.40 or less, and particularly preferably 1.20 or less. If the value exceeds this value, the production tends to be extremely difficult.

  By setting the value α of the formula (1) in ferrite to α ≧ 0.94, the deterioration rate of the core loss after the high temperature storage test can be further reduced. In addition, by setting α ≧ 0.95, the deterioration rate of the core loss after the high-temperature storage test can be further reduced.

In the present invention, the value α of the equation (1) is obtained as follows. The calculation of the value α in the formula (1) can be performed from composition analysis and quantification of the (Fe ²⁺ -Co ³⁺ ) amount and the Mn ³⁺ amount. That is, for the compositional analysis, after the Mn—Zn ferrite sintered body was pulverized and powdered, Fe ₂ O ₃ , MnO, ZnO using a fluorescent X-ray analyzer (for example, Simultic 3530 manufactured by Rigaku Corporation). And the amount of CoO can be measured.

The amount of (Fe ²⁺ -Co ³⁺ ) and the amount of Mn ^{3+ are} quantified by pulverizing the Mn—Zn-based ferrite sintered body to form a powder, dissolving in acid, and performing potentiometric titration with a K ₂ Cr ₂ O ₇ solution. Regarding the amount of (Fe ²⁺ -Co ³⁺ ), Fe ²⁺ reacts with Co ³⁺ , so in the case of Mn—Zn based ferrite in which Co is dissolved, Fe ²⁺ , Fe ³⁺ , Co ²⁺ , Co ³⁺ It is difficult to accurately separate and quantify each of these, and it is quantified as the (Fe ²⁺ -Co ³⁺ ) amount.

  The Mn—Zn ferrite according to the present invention is preferably produced, for example, as follows.

That is, the manufacturing method of the Mn-Zn ferrite according to the present invention is as follows:
The composition range of the Mn—Zn ferrite according to the present invention (Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included) is included, and the balance is substantially A raw material preparation step of preparing a raw material so as to be 0 to 5000 ppm (but not including 0) Co oxide in terms of Co ₃ O ₄ in a basic component composed of MnO;
A molding step of forming a preform by adding a binder to the raw material and molding it into a predetermined shape;
A firing step of firing the preform,
The firing step includes a high temperature holding step;
When the holding temperature in the high temperature holding step is 1250 ° C. to 1400 ° C., the oxygen partial pressure of the firing atmosphere is PO ₂ (%), and the holding temperature is T (K), the following expression (4) is satisfied. It is characterized by firing with PO ₂ .

_{Log (PO 2) = a-} 13000 / T ... formula (4)
However, a in the formula (4) is 6.95 ≦ a ≦ 8.85.

  For example, when the holding temperature is 1300 ° C., the oxygen partial pressure in the firing atmosphere is 0.05% to 3.80%.

  The firing step preferably includes a temperature raising step, a high temperature holding step, and a temperature lowering step. In the temperature raising step, the oxygen partial pressure in the firing atmosphere is preferably 3.0% or less. In the high temperature holding step, the holding temperature is 1250 ° C to 1400 ° C. For example, at 1300 ° C, the oxygen partial pressure is preferably 0.05% to 3.80%. It is preferable to set the oxygen partial pressure to be lower than in the prior art. However, if the oxygen partial pressure is less than 0.05%, the initial core loss before the high-temperature storage test tends to deteriorate. It is preferable to set the oxygen partial pressure higher as the holding temperature during firing is higher. Further, as the oxygen partial pressure is lower, the value α of the formula (1) is larger, and the deterioration of the core loss after the high-temperature storage test tends to be smaller.

  Moreover, it is preferable to switch to a nitrogen atmosphere in 900 to 1200 degreeC in a temperature fall process. The cooling rate after switching to the nitrogen atmosphere is preferably 2 to 10 times the cooling rate before switching.

  By selecting such manufacturing conditions, the Mn—Zn ferrite according to the present invention can be easily manufactured.

  According to the present invention, as a magnetic core used in a power supply transformer such as a switching power supply, the core loss is small in a wide temperature range, and the core loss is less deteriorated even at a high temperature (high temperature storage test) and excellent in magnetic stability. A highly reliable Mn—Zn ferrite, a transformer core and a transformer can be provided.

Hereinafter, the present invention will be described based on embodiments.
The Mn—Zn based ferrite according to one embodiment of the present invention is
Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included), in the basic component consisting essentially of MnO in the balance, in terms of Co ₃ O ₄ 0 to 5000 ppm (however, 0 is not included) Co oxide,
As other optional subcomponents, SiO ₂ : 50 to 220 ppm, CaO: 120 to 1400 ppm,
Furthermore, as other optional subcomponents, Nb ₂ O ₅ : 0 to 500 ppm (excluding 0), ZrO ₂ : 0 to 500 ppm (excluding 0), Ta ₂ O ₅ : 0 to 1000 ppm ( However, Mn- containing one or more of V ₂ O ₅ : 0 to 500 ppm (however, 0 is not included), HfO ₂ : 0 to 500 ppm (however, 0 is not included) Zn-based ferrite,
A value α of the following formula (1) in the ferrite is α ≧ 0.93.

α = ((Fe ²⁺ −Mn ³⁺ −Co ³⁺ ) × (4.29 × A + 1.91 × B + 2.19 × C + 2.01 × D)) / ((A−B−C−D) × 100) (1)
In the formula ^{(1), (Fe 2+ -Mn} 3+ -Co 3+): [wt%], A: Fe 2 O 3 [mol%], B: MnO [mol%], C: ZnO [mol%] , D: CoO [mol%].

  The ferrite of the present invention may contain phosphorus (P) and boron (B), but preferably the content of P and B in the ferrite is P ≦ 35 ppm or B ≦ 35 ppm.

In order to manufacture the Mn—Zn ferrite according to one embodiment of the present invention, first, starting materials for a main component and subcomponents are prepared. As the starting material for the main component, Fe ₂ O ₃ , Mn ₃ O ₄ , ZnO, or a material that becomes an oxide of these after firing is used. As the starting materials for the _components, a _{Co 3 O 4, SiO 2,} CaO, Nb 2 O 5, ZrO 2, Ta 2 O 5, V 2 O 5, HfO 2 or these oxides after firing, Raw materials are used. These starting materials are weighed so that the composition range after firing is in the above range. These starting materials may contain P and B, but the final composition after firing is adjusted to be in the above range.

  First, the starting material of the main component is weighed so as to be in the above composition range, wet-mixed, then dried, and calcined at about 900 ° C. for about 2 hours in the air. The starting raw material of the auxiliary component is weighed and added to the calcined powder thus obtained, and pulverized after mixing. The average particle size of the powder after pulverization is not particularly limited, but is preferably about 1 to 10 μm. An appropriate binder such as polyvinyl alcohol is added to the powder and granulated with a spray dryer or the like to obtain a preform with a predetermined shape.

  Although it does not specifically limit as a shape of a preforming body, For example, a toroidal shape etc. are illustrated.

  Next, this preform is fired under conditions such that the value α of the formula (1) in the sintered ferrite body after firing satisfies α ≧ 0.93. The firing conditions are preferably the following conditions.

  The firing step preferably includes a temperature raising step, a high temperature holding step, and a temperature lowering step.

  In the temperature raising step, the oxygen partial pressure in the firing atmosphere is preferably 3.0% or less.

In the high temperature holding step, the holding temperature is 1250 ° C to 1400 ° C, more preferably 1260 to 1370 ° C. Further, when the oxygen partial pressure in the atmosphere in the high temperature holding step is PO ₂ (%) and the holding temperature is T (K), the firing is performed with PO ₂ satisfying the following expression (4).

_{Log (PO 2) = a-} 13000 / T ... formula (4)
However, a in the formula (4) is 6.95 ≦ a ≦ 8.85, more preferably 7.96 ≦ a ≦ 8.78. When a is less than 6.95, the core loss increases, and when a exceeds 8.85, the core loss deterioration rate in the high-temperature storage test increases.

  For example, at a high temperature holding temperature of 1300 ° C., the oxygen partial pressure is preferably 0.05% to 3.80%. It is preferable to set the oxygen partial pressure to be lower than in the prior art. However, if the oxygen partial pressure is less than 0.05%, the initial core loss before the high-temperature storage test tends to deteriorate. It is preferable to set the oxygen partial pressure higher as the holding temperature during firing is higher. Further, as the oxygen partial pressure is lower, the value α of the formula (1) is larger, and the deterioration of the core loss after the high-temperature storage test tends to be smaller.

  In the temperature lowering process, it is preferable to switch to a nitrogen atmosphere at 900 ° C. to 1200 ° C. The cooling rate after switching to the nitrogen atmosphere is preferably 2 to 10 times the cooling rate before switching.

  By selecting such manufacturing conditions, the Mn—Zn ferrite according to the present embodiment can be easily manufactured.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

Examples 1-14
The starting material of the main component and the subcomponent was prepared. Fe ₂ O ₃ , Mn ₃ O ₄ , and ZnO were used as starting materials for the main components. Further, Co ₃ O ₄ , SiO ₂ , and CaO were used as the starting materials for the subcomponents. These starting materials were weighed so that the composition range after firing would be the following range.

_{That, Fe 2 O 3: 51.5~57.0mol%} , ZnO: 0~15mol% ( note that 0 contained not in) a, balance being substantially _MnO, Co ₃ O 4: 0~5000ppm (However, 0 was not included), SiO ₂ : 50 to 220 ppm, CaO: 120 to 1400 ppm.

  First, the starting material of the main component was weighed so as to be in the above composition range, wet-mixed, then dried, and calcined at 900 ° C. for 2 hours in the air. To the calcined powder obtained in this manner, the starting materials of the auxiliary components were weighed and added, and pulverized after mixing. The average particle size of the pulverized powder was about 2 μm. To this powder, polyvinyl alcohol was added as a binder and granulated with a spray dryer or the like to obtain a toroidal preform.

  Next, this preform was fired within the range of the firing conditions shown below, and a large number of ferrite sintered body samples having various α values were obtained as shown in Table 1 below. This firing step has a temperature raising step, a high temperature holding step, and a temperature lowering step. In the temperature raising step, the oxygen partial pressure in the firing atmosphere was 3.0% or less. In the high temperature holding step, the holding temperature was 1250 ° C. to 1400 ° C. For example, at 1300 ° C., the oxygen partial pressure was 0.05% to 3.80%. In the temperature lowering step, the atmosphere was switched to a nitrogen atmosphere at 900 ° C to 1200 ° C. The cooling rate after switching to the nitrogen atmosphere was set to 2 to 10 times the cooling rate before switching.

  As shown in Table 1, it was confirmed that the value α of the formula (1) in the sintered ferrite body after firing was α ≧ 0.93.

In addition, calculation of value (alpha) of Formula (1) was computed from the composition analysis and fixed_quantity | quantitative_assay of (Fe2 ⁺ -Co3 ⁺ ) amount and Mn3 ⁺ amount. That is, for composition analysis, the ferrite sintered body was pulverized and powdered, and then using a fluorescent X-ray analyzer (Simultic 3530, manufactured by Rigaku Corporation), Fe ₂ O ₃ , MnO, ZnO and CoO. The amount (mol%) was measured. The amount of (Fe ²⁺ -Co ³⁺ ) and the amount of Mn ³⁺ (% by weight) were quantified by pulverizing the ferrite sintered body to form a powder, dissolving it in an acid, and performing potentiometric titration with a K ₂ Cr ₂ O ₇ solution. Regarding the amount of (Fe ²⁺ -Co ³⁺ ), Fe ²⁺ reacts with Co ³⁺ , so in the case of Mn—Zn based ferrite in which Co is dissolved, Fe ²⁺ , Fe ³⁺ , Co ²⁺ , Co ³⁺ Since it was difficult to accurately separate and quantify each amount, the amount was (Fe ²⁺ -Co ³⁺ ) quantified. In the same ferrite sintered body, the formulas Fe = Fe ²⁺ + Fe ³⁺ and Co = Co ²⁺ + Co ³⁺ hold.

  Moreover, the core loss (Pcv) was measured about the sample of these Mn-Zn type ferrite sintered compacts. Pcv was measured in the range of 25-120 ° C. (25, 75, 120 ° C.) using a BH analyzer and applying a 100 kHz, 200 mT sinusoidal AC magnetic field (Pcv 1). After the Pcv measurement, the sample was further stored in an atmosphere at 175 ° C. or 200 ° C. for 96 hours, and the Pcv value after the storage was measured in the range of 25 to 120 ° C. (25, 75, 120 ° C.) (Pcv 0 , Pcv2, Pcv3), and the deterioration rate of Pcv after storage was calculated from these values at each temperature.

  Pcv degradation rate (%) is Pcv degradation rate (%) = ((core loss Pcv1 before high-temperature storage test 1-core loss Pcv0 or Pcv2 or Pcv3 after high-temperature storage test) / core loss Pcv1 before high-temperature storage test) × 100 It can be calculated by the relational expression.

比較例１〜４
焼成条件を変化させ、組成範囲は実施例１または２と同じであるが、式（１）の値αが実施例１〜１４の範囲から外れる以外は、前記の実施例１〜１４と同様にして、複数のフェライト焼結体のサンプルを作製した。比較例１〜４では、実施例１〜１４に比べて、特に焼成時の高温保持工程における酸素分圧が、例えば１３００℃では、３．８０％よりも大きかった。 Table 1 shown below shows the composition (mol%) of the main component, the content (ppm) of the subcomponent, the value α of the formula (1), the core loss (Pcv) before the high temperature storage test, and the high temperature storage test. The subsequent core loss (Pcv) and the deterioration rate (%) of the core loss are shown. The unit of Pcv is kW / m ³ .

Comparative Examples 1-4
Although the firing conditions were changed and the composition range was the same as in Example 1 or 2, the same as in Examples 1 to 14 except that the value α in formula (1) deviated from the range of Examples 1 to 14. A plurality of ferrite sintered body samples were prepared. In Comparative Examples 1 to 4, compared with Examples 1 to 14, the oxygen partial pressure particularly in the high temperature holding step during firing was larger than 3.80% at 1300 ° C., for example.

  About the sample of the several ferrite sintered compact which concerns on these comparative examples, the measurement and test similar to Examples 1-14 were performed. The composition (mol%) of the main component according to these comparative examples, the content (ppm) of subcomponents, the value α of the formula (1), the core loss (Pcv) before the high temperature storage test, and the high temperature storage test Table 1 shows the core loss (Pcv) and the deterioration rate (%) of the core loss.

Comparative Examples 5 and 6
Samples of a plurality of ferrite sintered bodies were prepared in the same manner as in Examples 1 to 14, except that the range was not within the range of Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol%.

  About the sample of the ferrite sintered compact which concerns on these comparative examples, the same measurement and test as Examples 1-14 were performed. The composition (mol%) of the main component according to these comparative examples, the content (ppm) of subcomponents, the value α of the formula (1), the core loss (Pcv) before the high temperature storage test, and the high temperature storage test Table 1 shows the core loss (Pcv) and the deterioration rate (%) of the core loss.

Comparative Examples 7 and 8
Samples of a plurality of ferrite sintered bodies were produced in the same manner as in Examples 1 to 14 except that it was out of the range of Co ₃ O ₄ : 0 to 5000 ppm (excluding 0).

  About the sample of the ferrite sintered compact which concerns on these comparative examples, the same measurement and test as Examples 1-14 were performed. The composition (mol%) of the main component according to these comparative examples, the content (ppm) of subcomponents, the value α of the formula (1), the core loss (Pcv) before the high temperature storage test, and the high temperature storage test Table 1 shows the core loss (Pcv) and the deterioration rate (%) of the core loss.

Examples 15-18
SiO _2: 50~220ppm, CaO: except outside the scope of 120~1400ppm, the same procedure as in Examples 1-14, were prepared a plurality of samples of ferrite sintered bodies.

  About the sample of the ferrite sintered compact which concerns on these comparative examples, the same measurement and test as Examples 1-14 were performed. The composition (mol%) of the main component according to these comparative examples, the content (ppm) of subcomponents, the value α of the formula (1), the core loss (Pcv) before the high temperature storage test, and the high temperature storage test Table 1 shows the core loss (Pcv) and the deterioration rate (%) of the core loss.

Evaluation 1
As shown in Table 1,
(A) The following could be confirmed by comparing Examples 1-14 with Comparative Examples 1-4. That is, Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included), with the balance being substantially composed of MnO, Co ₃ O ₄ In a Mn—Zn-based ferrite containing Co oxide of 0 to 5000 ppm (excluding 0) in terms of conversion, the value α of the formula (1) in the ferrite is α ≧ 0.93, so that it can be stored at high temperature. The core loss deterioration (Pcv deterioration rate at 75 ° C.) after the test (96 hours at 175 ° C.) can be suppressed to, for example, about 3% or less, and the Pcv deterioration rate at 120 ° C. is, for example, 5% or less ( It was confirmed that it can be suppressed to preferably about 4.5% or less. On the other hand, in Comparative Examples 1 to 4, α ≧ 0.93 was not satisfied, the Pcv deterioration rate at 75 ° C. exceeded 3%, and the Pcv deterioration rate at 120 ° C. also exceeded 5%.

  In addition, deterioration of core loss (Pcv deterioration rate at 75 ° C.) after a high-temperature storage test (96 hours at 200 ° C.) under more severe conditions can be suppressed to, for example, about 27% or less, and further at 120 ° C. It was also confirmed that the Pcv deterioration rate can be suppressed to about 30% or less, for example. On the other hand, in Comparative Examples 1 to 4, α ≧ 0.93 was not satisfied, the Pcv deterioration rate at 75 ° C. exceeded 27%, and the Pcv deterioration rate at 120 ° C. also exceeded 30%.

(B) By comparing Examples 1 to 14 and Comparative Examples 5 to 8, the following could be confirmed. That is, in a basic component containing Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included) and the balance being substantially made of MnO, Co ₃ O ₄ By including 0 to 5000 ppm (but not including 0) Co oxide in terms of conversion, the core loss (Pcv) before the high-temperature storage test is, for example, 500 kW / m ³ in a wide temperature range (25 to 120 ° C.). It was confirmed that it can be suppressed as low as below. In Comparative Examples 5 to 8, the Pcv deterioration rate can be close to that of the example, but the initial core loss before the high-temperature storage test is increased to 500 kW / m ³ or more at a predetermined temperature, and a wide temperature of 25 to 120 ° C. It becomes difficult to reduce the core loss in the band.

(C) By comparing Examples 1 to 14 and Examples 15 to 18, the following could be confirmed. That is, when the SiO ₂ content is less than 50 ppm or the CaO content is less than 120 ppm, the core loss before the high-temperature storage test is higher than that of the same composition except for the SiO ₂ or CaO content. In addition, it was confirmed that the core loss after the high-temperature storage test tends to increase.

  (D) By comparing Examples 1 to 14 with each other, the following could be confirmed. That is, by setting the value α in the formula (1) to α ≧ 0.94, the deterioration rate of the core loss (120 ° C.) after the high-temperature storage test (175 ° C./96 hours) is further reduced to 4.0% or less. We were able to. In addition, the deterioration rate of core loss (75 ° C.) after a more severe high-temperature storage test (200 ° C./96 hours) can be further reduced to within 25%, and the deterioration rate of core loss (120 ° C.) is 27%. And could be made even smaller.

  Further, by setting the value α of the formula (1) in the ferrite to α ≧ 0.95, the deterioration rate of the core loss (120 ° C.) after the high temperature storage test (175 ° C./96 hours) is within 3.5%, It could be made even smaller. Moreover, the deterioration rate of core loss (75 ° C.) after a more severe high-temperature storage test (200 ° C./96 hours) can be further reduced to 23% or less, and the deterioration rate of core loss (120 ° C.) is 25%. And could be made even smaller.

Examples 19-33
Based on the composition of Example 5 (Fe ₂ O ₃ : 53.8 mol%, MnO: 35.9 mol%, ZnO: 10.3 mol%, Co ₃ O ₄ : 3000 ppm, SiO ₂ : 100 ppm, CaO: 500 ppm) As in Examples 1 to 14, except that any of Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , V ₂ O ₅ , and HfO ₂ is contained in the composition range shown below. A sample of the ferrite sintered body was prepared.

That is, in the composition of Example 5, Nb ₂ O ₅ : 0 to 500 ppm (however, 0 is not included), ZrO ₂ : 0 to 500 ppm (however, 0 is not included), Ta ₂ O ₅ : 0 to 1000 ppm ( However, 0 or less), V ₂ O ₅ : 0 to 500 ppm (however, 0 is not included), HfO ₂ : 0 to 500 ppm (however, 0 is not included) were included.

実施例３４〜３８
前記の実施例５の組成（Ｆｅ_２ Ｏ_３ ：５３．８ｍｏｌ％，ＭｎＯ：３５．９ ｍｏｌ％，ＺｎＯ：１０．３ｍｏｌ％，Ｃｏ_３ Ｏ_４ ：３０００ｐｐｍ，ＳｉＯ_２ ：１００ｐｐｍ，ＣａＯ：５００ｐｐｍ）をベースとして、下記に示す組成範囲で、Ｎｂ_２ Ｏ_５ 、ＺｒＯ_２ 、Ｔａ_２ Ｏ_５ 、Ｖ_２ Ｏ_５ 、ＨｆＯ_２ のいずれかを含有させた以外は、実施例１〜１４と同様にして、複数のフェライト焼結体のサンプルを作製した。 About the sample of the ferrite sintered compact which concerns on these Examples, the same measurement and test as Examples 1-14 were performed. The content (ppm) of Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , V ₂ O ₅ , HfO _{2 according to} these examples, the value α of the formula (1), the core loss before the high-temperature storage test ( Table 2 shows Pcv), the core loss after the high-temperature storage test (Pcv), and the deterioration rate (%) of the core loss.

Examples 34-38
The composition of Example 5 (Fe ₂ O ₃ : 53.8 mol%, MnO: 35.9 mol%, ZnO: 10.3 mol%, Co ₃ O ₄ : 3000 ppm, SiO ₂ : 100 ppm, CaO: 500 ppm) As a base, in the composition range shown below, except that any of Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , V ₂ O ₅ , HfO ₂ was contained, the same as in Examples 1 to 14, Samples of a plurality of ferrite sintered bodies were produced.

That is, the composition of Example 5 contained at least one of Nb ₂ O ₅ : 600 ppm, ZrO ₂ : 600 ppm, Ta ₂ O ₅ : 1100 ppm, V ₂ O ₅ : 600 ppm, and HfO ₂ : 600 ppm.

About the sample of the ferrite sintered compact which concerns on these Examples, the same measurement and test as Examples 1-14 were performed. The content (ppm) of Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , V ₂ O ₅ , HfO _{2 according to} these examples, the value α of the formula (1), the core loss before the high-temperature storage test ( Table 2 shows Pcv), the core loss after the high-temperature storage test (Pcv), and the deterioration rate (%) of the core loss.

Evaluation 2
By comparing Example 5 and Examples 19 to 33, any of Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , V ₂ O ₅ , and HfO ₂ can be contained, so that these subcomponents can be added. Compared to the same composition except that it does not contain, the Pcv deterioration rate can be reduced, the core loss after the high-temperature storage test can be easily reduced in the desired wide temperature range of 25 to 120 ° C. It was confirmed that the deterioration can be further reduced.

Further possible, by comparing Examples 34-38 to Example _{19~33, Nb 2 O 5, ZrO} 2, Ta 2 O 5, V 2 O 5, HfO 2 preferred ranges are as follows Was confirmed.

That is, Nb ₂ O ₅ : 0 to 500 ppm (excluding 0), ZrO ₂ : 0 to 500 ppm (excluding 0), Ta ₂ O ₅ : 0 to 1000 ppm (excluding 0) , V ₂ O ₅ : 0 to 500 ppm (excluding 0), HfO ₂ : 0 to 500 ppm (excluding 0) was confirmed to be preferable.

Examples 39-44
Composition of Example 20 (Fe ₂ O ₃ : 53.8 mol%, MnO: 35.9 mol%, ZnO: 10.3 mol%, Co ₃ O ₄ : 3000 ppm, SiO ₂ : 100 ppm, CaO: 500 ppm, Nb ₂ A sample of a plurality of ferrite sintered bodies was prepared in the same manner as in Examples 1 to 14 except that both P and B were contained in the composition range shown below on the basis of O ₅ : 200 ppm).

  That is, phosphorus (P) and boron (B) were contained in the composition of Example 20 in the range of P ≦ 35 ppm or B ≦ 35 ppm.

実施例４５および４６
前記の実施例２０の組成（Ｆｅ_２ Ｏ_３ ：５３．８ｍｏｌ％，ＭｎＯ：３５．９ｍｏｌ％，ＺｎＯ：１０．３ｍｏｌ％，Ｃｏ_３ Ｏ_４ ：３０００ｐｐｍ，ＳｉＯ_２ ：１００ｐｐｍ，ＣａＯ：５００ｐｐｍ，Ｎｂ_２ Ｏ_５ ：２００ｐｐｍ）をベースとして、下記に示す組成範囲で、Ｐ，Ｂの双方を含有させた以外は、実施例１〜１４と同様にして、複数のフェライト焼結体のサンプルを作製した。 About the sample of the ferrite sintered compact which concerns on these Examples, the same measurement and test as Examples 1-14 were performed. The contents (ppm) of P and B according to these examples, the value α of the formula (1), the core loss (Pcv) before the high temperature storage test, the core loss (Pcv) after the high temperature storage test, and the core loss Table 3 shows the deterioration rate (%).

Examples 45 and 46
Composition of Example 20 (Fe ₂ O ₃ : 53.8 mol%, MnO: 35.9 mol%, ZnO: 10.3 mol%, Co ₃ O ₄ : 3000 ppm, SiO ₂ : 100 ppm, CaO: 500 ppm, Nb ₂ A sample of a plurality of ferrite sintered bodies was prepared in the same manner as in Examples 1 to 14 except that both P and B were contained in the composition range shown below on the basis of O ₅ : 200 ppm).

  That is, phosphorus (P) and boron (B) were contained in the composition of Example 20 in the range of P = 45 or 7 ppm and B = 8 or 45 ppm.

  About the sample of the ferrite sintered compact which concerns on these Examples, the same measurement and test as Examples 1-14 were performed. The contents (ppm) of P and B according to these examples, the value α of the formula (1), the core loss (Pcv) before the high temperature storage test, the core loss (Pcv) after the high temperature storage test, and the core loss Table 3 shows the deterioration rate (%).

Evaluation 3
By comparing Examples 39 to 44 with Examples 45 and 46, phosphorus (P) and boron (B) may be contained. Preferably, the content of P and B in the ferrite is P ≦ 35 ppm or It was confirmed that B ≦ 35 ppm. When the P content is greater than 35 ppm or the B content is greater than 35 ppm, the value of Pcv before the test increases and the Pcv reduction action over a wide temperature range of 25 to 120 ° C. is inferior. It was confirmed.

Claims (8)

Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included), in the basic component consisting essentially of MnO in the balance, in terms of Co ₃ O ₄ A Mn—Zn-based ferrite containing 0 to 5000 ppm (excluding 0) of Co oxide,
The value α of the following formula (1) in the ferrite is α ≧ 0.93,
A 100 kHz, 200 mT sinusoidal AC magnetic field was applied to the ferrite, and the core loss values measured at 75 ° C. and 120 ° C. were Pcv 1, and the ferrite after the measurement of Pcv 1 was stored at high temperature (175 ° C. The core loss deterioration rate represented by the following formula (2) is 3% or less at 75 ° C. when the core loss value measured under the same conditions as the measurement of Pcv1 is Pcv2 after being stored in the atmosphere for 96 hours) Or Mn-Zn type ferrite characterized by being 5% or less at 120 ° C.
α = ((Fe ²⁺ −Mn ³⁺ −Co ³⁺ ) × (4.29 × A + 1.91 × B + 2.19 × C + 2.01 × D)) / ((A−B−C−D) × 100) (1)
Core loss deterioration rate (%) = ((Pcv1−Pcv2) / Pcv1) × 100 (2)
In the formula ^{(1), (Fe 2+ -Mn} 3+ -Co 3+): [wt%], A: Fe 2 O 3 [mol%], B: MnO [mol%], C: ZnO [mol%] , D: CoO [mol%]. Fe ₂ O ₃ : 51.5 to 57.0 mol% and ZnO: 0 to 15 mol% (however, 0 is not included), in the basic component consisting essentially of MnO in the balance, in terms of Co ₃ O ₄ A Mn—Zn-based ferrite containing 0 to 5000 ppm (excluding 0) of Co oxide,
The value α of the following formula (1) in the ferrite is α ≧ 0.93,
A 100 kHz, 200 mT sinusoidal AC magnetic field was applied to the ferrite, and the core loss value measured at 75 ° C. and 120 ° C. was defined as Pcv1, and the ferrite after the measurement of Pcv1 was stored at high temperature (200 ° C. The core loss deterioration rate represented by the following formula (3) is 27% or less at 75 ° C. when the value of the core loss measured under the same conditions as the measurement of Pcv1 is Pcv3. Or Mn-Zn type ferrite characterized by being 30% or less at 120 ° C.
α = ((Fe ²⁺ −Mn ³⁺ −Co ³⁺ ) × (4.29 × A + 1.91 × B + 2.19 × C + 2.01 × D)) / ((A−B−C−D) × 100) (1)
Core loss deterioration rate (%) = ((Pcv1−Pcv3) / Pcv1) × 100 (3)
In the formula ^{(1), (Fe 2+ -Mn} 3+ -Co 3+): [wt%], A: Fe 2 O 3 [mol%], B: MnO [mol%], C: ZnO [mol%] , D: CoO [mol%]. Other as an auxiliary _{component, SiO 2: 50~220ppm, CaO:} Mn-Zn ferrite according to claim 1 or 2, characterized in that it contains a 120～1400Ppm. Still other _{subcomponents,} Nb ₂ O 5: _0~500ppm (note that 0 is not _included), ZrO 2: _0~500ppm (note that 0 is not _{included), Ta 2 O 5: 0~1000ppm} ( provided that 0 or less), V ₂ O ₅ : 0 to 500 ppm (however, 0 is not included), HfO ₂ : 0 to 500 ppm (however, 0 is not included) The Mn-Zn ferrite according to any one of claims 1 to 3 . The content of P and B in the ferrite is, P ≦ 35 ppm or Mn-Zn ferrite according to any one of claims 1 to 4, characterized in that a B ≦ 35 ppm. Transformer core that is composed of Mn-Zn ferrite according to any one of claims 1-5. A transformer in which a coil is wound around the transformer magnetic core according to claim 6 . A method for producing the Mn-Zn ferrite according to any one of claims 1 to 5 ,
A raw material preparation step of preparing the raw material so as to be in the composition range;
A molding step of forming a preform by adding a binder to the raw material and molding it into a predetermined shape;
A firing step of firing the preform,
The firing step includes a high temperature holding step;
When the holding temperature in the high temperature holding step is 1250 ° C. to 1400 ° C., the oxygen partial pressure of the firing atmosphere is PO ₂ (%), and the holding temperature is T (K), the following expression (4) is satisfied. A method for producing Mn—Zn ferrite, characterized by firing with PO ₂ .
_{Log (PO 2) = a-} 13000 / T ... formula (4)
However, a in the formula (4) is 6.95 ≦ a ≦ 8.85.