JP2008081339A - Low loss ferrite material, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low loss ferrite material for transformer, having low loss while maintaining high saturation magnetic flux density, and to provide its production method. <P>SOLUTION: In the low loss ferrite material essentially consisting of 60 to 67 mol% Fe<SB>2</SB>O<SB>3</SB>, 8 to 18 mol% ZnO and 18 to 28 mol% MnO, and admixed with 20 to 200 ppm SiO<SB>2</SB>and 200 to 2,000 ppm CaO, density is ≥4.90×10<SP>3</SP>kg/m<SP>3</SP>, saturation magnetic flux density is ≥550 mT, and core loss per unit volume in 100 kHz, 200 mT is ≤2,000 kW/m<SP>3</SP>at 25°C, and is ≤1,800 kW/m<SP>3</SP>at 100°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a low-loss MnZn-based ferrite material and a method for manufacturing the same, and more particularly to a ferrite material for transformers used in switching power supplies, choke coils, non-contact transformers, etc. It is possible to improve the performance and expand the use environment temperature by reducing the magnetic loss of the material which is largely related to the above problem.

  Switching power supplies are required to have higher performance as electronic devices become lighter, thinner and smaller, but high efficiency is desired for higher performance. When efficiency is considered here, the problem of heat generation of the transformer becomes large. This is because the magnetic loss of a magnetic material such as ferrite increases to generate a loss in the form of heat in order to make a differential with a high magnetic field as much as possible for the purpose of increasing the conversion efficiency of the transformer. In order to generate a high magnetic field, it is effective to increase the saturation magnetic flux density of the magnetic material, increase the number of turns of the coil, and increase the shape of the material.

  In order to increase the saturation magnetic flux density, it is conceivable to use an iron-based metal magnetic material such as silicon steel plate, sendust, or amorphous. However, the metallic magnetic material has a problem that the electrical resistance of the material itself is low and the characteristics are deteriorated due to eddy current loss in a high frequency band of 10 kHz or more. In addition, the method of increasing the number of turns of the coil has a limit because it depends on the saturation magnetic flux density of the magnetic material at the maximum, and the more the number of turns, the more the loss is generated. Further, the increase in shape has a problem such as an increase in power consumption due to a large current in the power supply space, resulting in an increase in cost. Both had some problems.

  Therefore, since the cost of the material is low and the electric resistance is high, it is desired to increase the saturation magnetic flux density of the most common ferrite material (see, for example, Patent Documents 1 to 7). General ferrite includes many composition systems such as MnZn series, NiZn series, and MgZn series. Of these, MnZn series that has a high saturation magnetic flux density and low magnetic loss is used for a transformer for low loss.

  Incidentally, the MnZn-based high saturation magnetic flux density material that is currently required to be improved has been limited to 500 to 520 mT. This is because conventional low-loss materials for transformers cannot be uniformly fired due to the relationship of equilibrium oxygen pressure and the like when the composition is greatly changed.

JP 2003-2736 A JP 2003-257724 A JP-A-6-215920 Japanese Patent Laid-Open No. 5-243034 JP-A-5-238817 JP-A-5-166620 JP 2004-64057 A

  The present invention has been made in view of the above problems in the prior art, and an object thereof is to provide a low-loss ferrite material for a transformer having a low loss while maintaining a high saturation magnetic flux density, and a method for manufacturing the same. To do.

The present invention provided to solve the above-mentioned problems is mainly composed of Fe ₂ O ₃ 60 to 67 mol%, ZnO 8 to 18 mol%, MnO 18 to 28 mol%, and SiO ₂ 20 to ₂₀₀ ppm and CaO 200 to 2000 ppm. A low-loss ferrite material having a density of 4.90 × 10 ³ kg / m ³ or more, a saturation magnetic flux density of 550 mT or more, and a core loss per unit volume at 100 kHz and 200 mT of 2000 kW / m ³ at 25 ° C. Hereinafter, it is a low-loss ferrite material characterized by being 1800 kW / m ³ or less at 100 ° C.

The present invention provided to solve the above-mentioned problems is mainly composed of Fe ₂ O ₃ 60 to 67 mol%, ZnO 8 to 18 mol%, MnO 18 to 28 mol%, and SiO ₂ 20 to ₂₀₀ ppm and CaO 200 to 2000 ppm. A low-loss ferrite material obtained by sintering the starting material, and after calcining the starting material, adding a binder to form and perform main sintering, from the binder decomposition temperature to the maximum firing temperature. It is a low-loss ferrite material produced by setting the oxygen partial pressure at the time of temperature rise to 0.5% or less.

  Here, it is preferable that the oxygen partial pressure in cooling from 1100 ° C. to 800 ° C. is made 0.5% or less in the cooling process after maintaining the maximum firing temperature.

The present invention is provided in order to solve the above _{problems, Fe 2 O 3 60~67mol%,} ZnO 8~18mol%, mainly composed of MnO 18~28mol%, _SiO 2 20~200ppm as sintering promoting material, A method for producing a low-loss ferrite material using a starting material to which 200 to 2000 ppm of CaO is added, and after calcining the starting material, adding a binder to form and perform main sintering, from the binder decomposition temperature A method for producing a low-loss ferrite material, characterized in that an oxygen partial pressure at the time of temperature rise up to a maximum firing temperature is 0.5% or less.

  Here, it is preferable that the oxygen partial pressure in cooling from 1100 ° C. to 800 ° C. is 0.5% or less in the cooling process after maintaining the maximum firing temperature.

According to the low-loss ferrite material of the present invention, the magnetic field of the electromagnetic transformer can be increased, so that it can be applied to various transformers. Specifically, the distance of the generated magnetic field can be extended by a choke coil used for a power source, a non-contact transformer used for a shaver, a telephone slave unit, a charging transformer for an electric vehicle, or the like. In addition, since the transformer's saturation magnetic field is high, it is possible to design a transformer that is smaller than conventional transformers, to reduce the number of coil windings, and to reduce the current that flows. There are effects such as less heat generation. The range of transformer design is widened, leading to cost reduction. It is also effective in reducing power consumption.
According to the method for producing a low-loss ferrite material of the present invention, it is possible to obtain a low-loss ferrite material for a transformer having a low loss while maintaining a high saturation magnetic flux density.

According to the inventors' previous research and development, the main composition is the most important for reducing the loss of ferrite materials, and MnZn-based ferrite has high performance, that additive elements such as SiO ₂ and CaO are indispensable, and the density is I find it expensive. Further, since the low loss material is used for a switching power supply, the minimum temperature of the core loss is set to 60 ° C. to 100 ° C., and this minimum temperature is the crystal magnetic anisotropy constant K1 and magnetostriction constant λs of the ferrite material. It has been found that it is governed by the composition and temperature dependence.

Here, the magnetocrystalline anisotropy K1 and λs depend on the composition, and it is desirable that both become zero as much as possible. However, since the composition dependency is different, both K1 and λs are from 60 ° C. to 100 ° C. The saturation magnetic flux density is as close to zero as possible, and the saturation magnetic flux density is in a range of 52 mol% ≦ Fe ₂ O ₃ ≦ 54 mol%, 9 mol% ≦ ZnO ≦ 11 mol%, 36 mol% ≦ MnO ≦ 38 mol%. If it is away from this composition, K1 and λs increase, and since the temperature characteristics are different, the core loss temperature characteristics deteriorate.

On the other hand, MnZn-based ferrite has a covalent bond of one M ²⁺ ion, two Fe ³⁺ ions, and four O ²⁻ ions, as expressed by the chemical formula (MO) Fe ₂ O ₃ , It is a substance with a spinel structure. Strictly speaking, MnZn ferrite is expressed as (MnZn) O.Fe ₂ O _3, and therefore, when the amount of Fe ₂ O ₃ is 50 mol%, it is a stchiometry. For this reason, if Fe ₂ O ₃ deviates from 50 mol%, spineling becomes difficult and sintering becomes difficult. Therefore, it was considered that the vicinity of the composition where K1 and λs become zero was the limit for sintering.

  In addition, the single crystal of MnZn ferrite is a substance that has the property of becoming a single crystal even if it deviates from the Staquio composition. Since K1 and magnetostriction λ can be controlled to control the magnetic properties, single crystals can be produced with a wide range of compositions. Single crystal ferrites that meet the requirements of magnetic heads have been grown. Furthermore, since the single crystal is formed at a high temperature exceeding 1600 ° C., the equilibrium oxygen pressure needs to be positive (higher than 1 atm), but it is possible even in oxygen. In other words, it seems to suggest that if the equilibrium oxygen pressure is within a certain range, it will be spineled.

From the above knowledge and consideration, it was considered that a high-density spinel ferrite could be produced by controlling the oxygen concentration even with an Fe ₂ O ₃ rich composition, which is considered to have a high saturation magnetic flux density in the present invention. Furthermore, in the case of MnZn-based ferrite, K1 = 0 and λs become 0 when 52 mol% ≦ Fe ₂ O ₃ ≦ 54 mol%, which is a general composition, but even when the composition is Fe ₂ O ₃ of 60 mol% or more, K1 = 0 line Exists. In this composition line, although λs is large but K1 is small, there is a possibility that a material with low core loss exists if sintering is possible.

Therefore, the inventors considered that it would be possible to find a new low loss material with a high saturation magnetic flux density if research and development on sinterability with a composition of Fe ₂ O ₃ near 60 mol% was advanced. As a result of intensive studies, the present invention has been achieved.

Below, the low-loss ferrite material which concerns on this invention, and its manufacturing method are demonstrated.
The low-loss ferrite material according to the present invention is composed mainly of Fe ₂ O ₃ 60 to 67 mol%, ZnO 8 to 18 mol%, MnO 18 to 28 mol%, and SiO _{2 20 to} 200 ppm and CaO 200 to 2000 ppm. The density is 4.90 × 10 ³ kg / m ³ or more, the saturation magnetic flux density is 550 mT or more, and the core loss per unit volume at 100 kHz and 200 mT is 2000 kW / m ³ or less at 25 ° C., 100 ° C. 1800 kW / m ³ or less. Further, 100kHz, core loss per unit volume in 200 mT (core loss) is, 1600kW / ^{m 3} or less at 25 ° C., at 60 ℃ 1500kW / ^{m 3} or less, is preferably 1500 kW / ^{m 3} or less at 100 ° C..

Here, the composition includes CoO (1.0 mol% or less), ZrO ₂ (0.1 mol% or less), SnO ₂ (1.0 mol% or less), TiO ₂ (1.0 mol% or less), Ta ₂ O _5. (0.1 mol% or less), Nb ₂ O ₅ (0.1 mol% or less), Al ₂ O ₃ (0.1 mol% or less), Ga ₂ O ₃ (0.1 mol% or less), In ₂ O ₃ (0 .1 mol% or less) or NiO (1.0 mol% or less), 1 to 3 types may be further added in combination. In addition, the addition amount in that case is good to set it as the numerical value in the parenthesis of each raw material.

  FIG. 1 shows a procedure for producing a low-loss ferrite material according to the present invention. The processing steps in FIG. 1 are the same as a general ceramic manufacturing procedure, and each processing step may be the same as the manufacturing conditions of a normal sintered ferrite material except for the firing step conditions.

First, Fe ₂ O ₃ 60 to 67 mol%, ZnO 8 to 18 mol%, and MnO 18 to 28 mol% are weighed as main components, and SiO _{2 20 to} 200 ppm and CaO 200 to 2000 ppm are weighed as starting materials, respectively. After mixing, fine pulverization, drying, and pulverization, temporary baking is performed and fine pulverization is performed. Next, after drying, it is granulated to an appropriate size, added with granules and binder, and formed into an arbitrary shape by a technique such as pressing. Next, the formed ferrite is placed in a closed firing furnace and fired with a temperature profile shown in FIG.

  The temperature profile of FIG. 2 is divided into five regions. That is, the area A in the figure is the debuy area, the area B is the temperature raising area, the area C is the main sintering area, the area D is the cooling area, and the area E is the furnace cooling area.

  Here, the region A is a region where the temperature in the baking furnace is raised to a temperature of about 600 ° C. (binder decomposition temperature) at which the binder added for molding is decomposed (debide) and the binder is removed. is there. At this time, when raising the temperature to the binder decomposition temperature, a certain oxygen partial pressure is required, for example, 20% which is equivalent to the oxygen partial pressure in the atmosphere.

  In the region B, after debinding, the temperature in the firing furnace is further increased to the main sintering temperature (maximum firing temperature, for example, 1250 to 1350 ° C.), and ferrite is formed and densified. is there. In this region B, that is, at the time of temperature rise from the binder decomposition temperature to the highest firing temperature, the oxygen partial pressure is preferably 0.5% or less. As a method for reducing the oxygen partial pressure, for example, a method of introducing an inert gas such as nitrogen gas into the firing furnace, a method of consuming the oxygen gas in the firing furnace by combustion, or the like may be adopted as appropriate.

  The region C is a region in which the main sintering is performed by holding at this temperature for a predetermined time after reaching the maximum firing temperature (for example, 1310 ° C.).

  The region D is a region where annealing is performed at a predetermined cooling rate from the highest firing temperature. In the region D, the oxygen partial pressure in cooling from 1100 ° C. to 800 ° C. is preferably 0.5% or less. Finally, furnace cooling is performed in the region E.

By performing the above treatment, the density is 4.90 × 10 ³ kg / m ³ or more, the saturation magnetic flux density is 550 mT or more, and the core loss per unit volume at 100 kHz-200 mT is 2000 kW / m ³ or less at 25 ° C., 100 A low-loss ferrite material having a temperature of 1800 kW / m ³ or less at 0 ° C. is obtained.

Hereinafter, details of the present invention will be described based on experimental results.
(Experimental example 1)
As shown in Table 1, the range of 62～66Mol% of _Fe 2 _{O 3} as starting material, ZnO and 10～18Mol% range, MnO varied between 18～26Mol%, and the SiO ₂ 100 ppm, a CaO A sample of ferrite material was prepared by the procedure shown in FIG. 1 at 800 ppm. As shown in FIG. 3, the temperature profile in firing is an atmospheric atmosphere (oxygen partial pressure of 20%) in region A, an atmosphere of oxygen partial pressure of 1% in region B, and an atmosphere of oxygen partial pressure of 2% in region C. The firing temperature was maintained at 1310 ° C. for 4 hours. Further, in region D, annealing was performed slowly in an atmosphere having an oxygen partial pressure of 0.2%, and in region E, furnace cooling was performed in an atmosphere in which N ₂ purge was performed to achieve an oxygen partial pressure of 0%.

  About the obtained ferrite material sample, a magnetic field of 1194 A / m was applied to measure the saturation magnetic flux density, and then the residual magnetic flux density was measured. Further, the coercivity and the magnetic permeability at 10 kHz were measured. Furthermore, the core loss Pc was measured in the temperature range from room temperature (25 ° C.) to 100 ° C. under the condition of 100 kHz-200 mT. The core loss was measured with a SY-8232 manufactured by BH measuring instrument IWATSU. The density was measured with a density measuring device.

Table 2 shows the results of evaluating the sample of this experimental example. Here, as a comparative example 1, a general low-loss material (Fe ₂ O ₃ 53.5 mol%, ZnO 10 mol%, MnO 36.5 mol%, SiO ₂ 100 ppm, CaO 800 ppm is used as a starting material, and firing conditions are different. ).
In samples 3 to 8, it was found that the saturation magnetic flux density was 550 mT or higher, which was higher than the general low-loss material of Comparative Example 1.

(Experimental example 2)
In Experimental Example 1, Samples 1 to 7 have a lower density and a larger core loss value than Comparative Example 1. Therefore, in order to increase the density, firing was performed by controlling the atmosphere during heating in the region B of the firing step and changing the oxygen concentration in the firing atmosphere after removing the binder in the range of 1% to 0.01%. Specifically, the starting material has a composition close to that of sample 3 having the highest saturation magnetic flux density in Experimental Example 1, and is 65 mol% Fe ₂ O ₃ -15 mol% ZnO-20 mol% MnO-100 ppm SiO ₂ -800 ppm CaO, and the temperature shown in FIG. The sintering conditions were the same as in Experimental Example 1 except for the oxygen concentration in the region B as in the profile. The oxygen concentration of 0.01% or less could not be controlled due to the ability of the firing furnace.

Table 3 shows the results of evaluating the sample of this experimental example.
It can be seen that the lower the oxygen concentration, the higher the density and the lower the core loss. The density is 4.85 × 10 ³ kg / m ³ , which is equal to or higher than that of the general low-loss ferrite material of Comparative Example 1, and a maximum of 4.96 × 10 ³ kg / m ³ is realized.

(Experimental example 3)
In Experimental Example 2, a density equal to or higher than that of a general low-loss material was realized, and a higher saturation magnetic flux density was obtained, but the core loss was inferior. Therefore, in Experimental Example 2, as shown in FIG. 5, the oxygen concentration of the atmosphere in the region B is set to 0.1%, the temperature at the highest firing temperature of the region C and the oxygen concentration of the atmosphere are 1270 to 1350 ° C., respectively, Samples were produced under the same conditions as in Experimental Example 2 except that the amount was changed to 1, 2, and 4%.

Table 4 shows the results of evaluating the samples of this experimental example.
It was found that the core loss was low when the maximum firing temperature was 1310 ° C. and the oxygen concentration was 2%. In addition, the saturation magnetic flux density at room temperature (25 ° C.) is 570 mT, and the density is 4.92 × 10 ³ kg / m ³ , both of which are high-saturation magnetic flux densities and high-density low-loss materials. There was found.

(Experimental example 4)
The low loss ferrite material having a high saturation magnetic flux density obtained in Experimental Examples 2 and 3 has a higher core loss value than a general low loss material. Therefore, in order to improve the core loss value, in Experimental Example 2, the oxygen concentration of the atmosphere in the region B is set to 0.1% as shown in FIG. 6, and the temperature from 1100 ° C. to 800 ° C. in the slow cooling process of the region D Samples were produced under the same conditions as in Experimental Example 2 except that the oxygen concentration of the atmosphere in the region was changed in the range of 1 to 0.001%. In addition, the oxygen concentration of 0.001% or less could not be controlled due to the capability of the firing furnace.

Table 5 shows the results of evaluating the samples of this experimental example.
The value of the core loss decreased as the oxygen concentration during the slow cooling was decreased, and 1000 kW / m ³ was obtained at 100 ° C. as the best core loss (Samples 31 and 32).

(Experimental example 5)
In Experimental Example 4, the main composition was reviewed under the firing conditions of Sample 31 having the best core loss value. That is, as a starting material, Fe ₂ O ₃ is changed in a range of 60 to 67 mol%, ZnO is changed in a range of 6 to 20 mol%, MnO is changed in a range of 16 to 30 mol%, SiO _{2 is set} to 100 ppm, and CaO is set to 800 ppm. A sample of a ferrite material was prepared by the procedure shown in FIG. As shown in FIG. 7, the temperature profile in firing is an atmospheric atmosphere (oxygen partial pressure of 20%) in region A, an atmosphere of oxygen partial pressure of 0.1% in region B, and an oxygen partial pressure of 2% in region C. The firing temperature was kept at 1310 ° C. for 4 hours in the atmosphere. Further, in region D, annealing was performed slowly in an atmosphere having an oxygen partial pressure of 0.01%, and in region E, furnace cooling was performed in an atmosphere in which N ₂ purge was performed and the oxygen partial pressure was 0%.

Table 6 shows the result of evaluating the sample of this experimental example.
A high value of saturation magnetic flux density of 550 mT or more is obtained because Fe ₂ O ₃ , ZnO and MnO, which are the main ternary materials of ferrite, are 60 mol% ≦ Fe ₂ O ₃ ≦ 67 mol% and 8 mol% ≦ ZnO ≦, respectively. It was found that the composition range was 18 mol%, 18 mol% ≦ MnO ≦ 28 mol%. FIG. 8 shows a ternary composition diagram showing their composition range. The range of the main ternary material in the present invention is a region indicated by oblique lines in the figure.

(Experimental example 6)
In Experimental Example 5, the composition of the main three elements is 65 mol% Fe ₂ O ₃ -15 mol% ZnO-20 mol% MnO, SiO ₂ is changed in the range of 0 to 250 ppm, CaO is changed in the range of 0 to 2500 ppm, and the others Prepared a sample under the same conditions as in Experimental Example 5.

Table 7 shows the results of evaluating the samples of this experimental example.
From this result, it is necessary to add SiO ₂ and CaO at the same time. When the addition amount is ₂₀ to 200 ppm and CaO is 200 to 2000 ppm, the saturation magnetic flux density is 550 mT or more, and a low loss is realized. I found out that I could do it. Further, the core loss temperature characteristics of the low-loss ferrite material (composition 65 mol% Fe ₂ O ₃ -15 mol% ZnO-20 mol% MnO-100 ppm SiO ₂ -800 ppm CaO) obtained in this experimental example were measured. The result is shown in FIG.

It is a figure which shows the preparation procedures of the low loss ferrite material which concerns on this invention. It is a temperature profile in the sintering process of the low-loss ferrite material of the present invention. 4 is a temperature profile in a sintering process of Experimental Example 1. 4 is a temperature profile in a sintering process of Experimental Example 2. 10 is a temperature profile in a sintering process of Experimental Example 3. 10 is a temperature profile in a sintering process of Experimental Example 4. 10 is a temperature profile in a sintering process of Experimental Example 5. It is a ternary composition diagram of the low-loss ferrite material of the present invention. It is a figure which shows the example of the temperature characteristic of the core loss of the low loss ferrite material which concerns on this invention.

Claims (5)

Fe ₂ O ₃ 60 to 67 mol%, ZnO 8 to 18 mol%, MnO 18 to 28 mol% as a main component, SiO _{2 20 to} 200 ppm, CaO 200 to 2000 ppm is a low loss ferrite material,
Density 4.90 × ^{10 3} kg / ^m 3 or more, the saturation magnetic flux density than 550MT, 100kHz, with the core loss 25 ° C. per unit volume in 200 mT 2000 kW / ^{m 3} or less, at 100 ℃ 1800kW / ^{m 3} or less A low-loss ferrite material characterized by being. Fe ₂ O ₃ 60-67 mol%, ZnO 8-18 mol%, MnO 18-28 mol% as the main component, SiO ₂ 20-200 ppm, CaO 200-2000 ppm added to the low-loss obtained by sintering A ferrite material,
When the starting material is pre-fired, the binder is added, formed, and finally sintered, the oxygen partial pressure at the time of temperature rise from the binder decomposition temperature to the highest firing temperature is 0.5% or less. A low-loss ferrite material characterized by comprising   3. The low-loss ferrite according to claim 2, wherein the low-loss ferrite according to claim 2, wherein the oxygen partial pressure in cooling from 1100 ° C. to 800 ° C. is 0.5% or less in the cooling process after maintaining the maximum firing temperature. material. _{Fe 2 O 3 60~67mol%, ZnO} 8~18mol%, low loss mainly composed of MnO 18~28mol%, using the starting _{materials SiO} 2 _20~200ppm, CaO _200~2000ppm was added as a sintering promoting material A method of manufacturing a ferrite material,
After pre-baking the starting material, when forming a binder by adding a binder and performing main sintering, the oxygen partial pressure at the time of temperature rise from the binder decomposition temperature to the firing maximum temperature should be 0.5% or less. A method for producing a low-loss ferrite material characterized by:   5. The production of a low-loss ferrite material according to claim 4, wherein an oxygen partial pressure in cooling from 1100 ° C. to 800 ° C. is 0.5% or less in the cooling process after being held at the maximum firing temperature. Method.

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