JP2005145803A - Mn-Zn-BASED FERRITE AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Mn-Zn-based ferrite which has a high relative initial magnetic permeability μ<SB>ir</SB>of ≥2,500 and exhibits a small temperature-attributed change in the relative initial magnetic permeability μ<SB>ir</SB>in the wide temperature range of -40 to 100°C. <P>SOLUTION: The ferrite having a composition comprising, by mol, 52-53% Fe<SB>2</SB>O<SB>3</SB>and 20-22% ZnO, and the balance being mainly MnO, and characteristics that the relative initial magnetic permeability at 25°C, 10 kHz is 2,500-3,500 and the coefficient of variation of the relative initial magnetic permeability within a temperature range of -40 to 100°C is ≤5% is obtained by using, as a raw material, iron oxide fine particles characterized in that the median diameter obtained from the particle size distribution measured by the laser diffraction is ≤0.6 μm, the difference between 10% cumulative diameter in the particle size distribution and the median diameter is not higher than 2.0 times of the median diameter, and the primary particle diameter obtained from the specific surface area is ≤0.1 μm, then forming a mixture of the iron oxide, MnO and ZnO without calcining it, and firing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an Mn-Zn ferrite used in various transformers, noise filters, sensors, etc., having a high relative initial permeability μ _ir and a small temperature change over a wide temperature range. Note that the relative initial permeability mu _{ir is, μ ir = μ i / μ} 0 ( where, mu _i is the initial magnetic permeability of at SI units, mu ₀ is the permeability of vacuum) is defined, hereinafter "mu _{ir "both} abbreviated.

Mn-Zn ferrite is composed mainly of Fe ₂ O ₃ , ZnO and MnO, and exhibits a high relative initial permeability in the main component composition in which the magnetic anisotropy constant and magnetostriction constant are zero. . Therefore, Mn-Zn ferrites are used as magnetic cores for transformers, noise filters, sensors, etc., taking advantage of the high relative initial permeability, contributing to the miniaturization and thinning of these electronic components. .

Above all, the Mn-Zn ferrite used for the pulse transformer of the interface part of digital communication equipment such as ISDN is required to have a particularly high relative initial permeability, and those having a μ _ir of 10,000 or more at room temperature are also used. Yes. Furthermore, when this pulse transformer is used for a public telephone or a line terminator, it may be installed outdoors or under an eaves, so it is required to have a high relative initial permeability from low temperature to high temperature. Recently, high specific initial permeability is required in a wide temperature range from a low temperature of −40 ° C. to a high temperature of 100 ° C.

  However, most conventional Mn-Zn ferrites are designed on the assumption that most of them are used at temperatures above room temperature, and the magnetic anisotropy constant and magnetostriction constant become zero near room temperature. A composition having a magnetic permeability is used. Therefore, the temperature curve of the relative initial permeability of conventional Mn-Zn ferrites shows the peak due to the sudden decrease in the magnetic anisotropy constant immediately above the Curie temperature (primary peak) and the magnetic anisotropy constant near room temperature. Two peaks (secondary peaks) due to a smaller magnetostriction constant are shown.

  Therefore, in order to ensure a high relative initial permeability over a wide temperature range, studies have been made to increase the height of the secondary peak or shift the temperature at which the secondary peak is generated to a lower temperature side than room temperature. However, increasing the relative initial permeability near room temperature, conversely, causes a significant decrease in the relative initial permeability in the low temperature range (about −40 to 0 ° C.). Therefore, it is necessary to increase the number of windings in order to ensure inductance in the low temperature range, or to use a material having a relative initial permeability higher than necessary at room temperature in order to increase the relative initial permeability in the low temperature range. Yes, it was inefficient.

For example, in Patent Document 1, the composition range of Fe ₂ O ₃ , ZnO, and MnO, which are main components of Mn—Zn ferrite, is limited to the above problem, and the secondary peak is in the range of −25 to 10 ° C. In the temperature range of −20 to 100 ° C., μ _i (initial permeability in CGS system unit. Equivalent to relative initial permeability μ _ir in SI unit system. The same applies to Patent Documents 2 to 6). A technique for suppressing the change rate due to the temperature to 8000 or more and within 70% is disclosed. Patent Document 2 discloses that by adding bismuth oxide and molybdenum oxide to Mn-Zn ferrite, μ _i is 8500 or more in the range of −20 to 20 ° C. and μ in the temperature range of 20 to 100 ° C. _A technique for obtaining a ferrite in which _i is 10,000 or more is disclosed. Further, Patent Document 3 obtains a high initial magnetic permeability with μ _i of 8000 or more in a temperature range of −30 to 90 ° C. by limiting the amounts of B and P contained as impurities in the Mn—Zn ferrite. Technology is disclosed. However, these techniques do not obtain a high initial magnetic permeability over a wide temperature range from a low temperature of −40 ° C. to a high temperature of 100 ° C. Moreover, even if the required initial magnetic permeability was secured in the temperature range to be used, the temperature change was extremely large.

  Recently, in addition to ensuring the required initial permeability in the temperature range to be used, it has stable magnetic properties against changes in environmental temperature, that is, it has a stable high initial permeability over a wide temperature range. It has been demanded that the change of the value with temperature be as small as possible. In response to such a requirement, there are disclosed techniques for limiting the composition of the main component and suppressing the change in the initial magnetic permeability due to temperature by adding cobalt oxide (see, for example, Patent Documents 4 and 5). ). Further, Patent Document 6 limits the main component composition of the Mn-Zn ferrite and sets the secondary peak to −20 to 10 ° C. or −10 to 0 ° C. It is disclosed that a ferrite with a small change can be obtained.

In addition, when it is important that the temperature change of the initial permeability is smaller than the high initial permeability, an air gap is provided in the magnetic path of the magnetic core.
Japanese Patent Laid-Open No. 06-263447 Japanese Patent Laid-Open No. 10-256025 JP 2000-277318 A Japanese Patent Publication No. 52-031555 Japanese Examined Patent Publication No. 61-011892 JP 09-148115 A

However, in the techniques of Patent Document 4 and Patent Document 5, since the initial magnetic permeability μ _i decreases as the amount of cobalt oxide added increases, the value is often about 1000, and even higher is about 2500 or less. Moreover, the temperature range in which μ _i can be obtained is limited to about −20 ° C. Also, regarding the composition of the main component, for example, the ZnO content is often set to 20 mol% or less, which raises the Curie temperature, and the temperature characteristics of μ _i also have a large undulation, resulting in a temperature change. There was a problem that would become larger. Further, in the technique of Patent Document 6, the range in which the temperature change of μ _i can be reduced is −20 to 100 ° C., and the temperature change is not yet reduced to a low temperature of −40 ° C. Furthermore, the technology to provide a gap in the magnetic path inevitably leads to a decrease in the initial magnetic permeability, so when μ _i 3000 or more is required, it is difficult to simultaneously realize a high μ _i and a low temperature change. It becomes. Further, the increase in man-hours and costs due to the process of providing a gap in the magnetic core and the countermeasure for stabilizing the butt surface of the gap have also been a problem.

The object of the present invention is to have a relative initial permeability μ _ir (SI unit, the same applies hereinafter) as large as 2500 or more, and in a wide temperature range from a very low temperature range of −40 ° C. to a high temperature of 100 ° C. The object is to provide an Mn-Zn ferrite with a small temperature change of _μir .

In order to solve the above-described problems of the prior art, the inventors focused on iron oxide, which is a raw material for Fe ₂ O ₃ , which is the main component of Mn—Zn-based ferrite, and conducted intensive studies. As a result, by controlling the particle size distribution characteristics of this iron oxide and increasing the reactivity, the relative initial permeability μ _ir is high and the temperature ranges from −40 to 100 ° C. without passing through the calcination step. As a result, it was found that the temperature change of the relative initial permeability μ _ir can be kept low, and the present invention was completed.

The present invention developed based on the above knowledge, the median diameter obtained from the particle size distribution measured by laser diffraction is 0.6 μm or less, and the difference between the 10% cumulative diameter and the median diameter in the particle size distribution is 2.0 of the median diameter. The raw material is iron oxide, which is a fine particle with a primary particle size of 0.1 μm or less determined from the specific surface area, and the mixture of iron oxide, MnO and ZnO is molded and calcined without calcining. And Fe ₂ O ₃ : 52 to 53 mol%, ZnO: 20 to 22 mol%, the balance is mainly composed of MnO, and the relative initial permeability at 25 ° C. and 10 kHz is 2500 to 3500, −40 It is a Mn-Zn ferrite exhibiting a characteristic with a coefficient of variation of relative initial permeability at -100 ° C of 5% or less.

Further, the present invention, as a raw material, the median diameter obtained from the particle size distribution measured by laser diffraction is 0.6 μm or less, and the difference between the 10% cumulative diameter and the median diameter in the particle size distribution is not more than twice the median diameter. in, using the iron oxide primary particle diameter is less fine 0.1μm obtained from the specific surface area, molded without calcining a mixture of iron oxide and MnO, and ZnO, by baking, Fe ₂ O ₃ : 52 to 53 mol%, ZnO: 20 to 22 mol%, the balance is mainly composed of MnO, and the relative initial permeability at 25 ° C. and 10 kHz is 2500 to 3500, and the ratio at −40 to 100 ° C. We propose a method for producing an Mn-Zn ferrite characterized by obtaining a ferrite having a characteristic with a coefficient of variation of initial permeability of 5% or less.

According to the present invention, the Mn-Zn ferrite has a relative initial permeability μ _ir at 25 ° C. and 10 kHz of 2500 or more and a coefficient of variation of the relative initial permeability at −40 to 100 ° C. is suppressed to 5% or less. Can be produced without going through a calcination step, and a material extremely useful for applications requiring stable magnetic properties in a wide temperature range can be provided.

The Mn—Zn ferrite according to the present invention has a relative initial permeability μ _ir of 2500 to 3500 at 25 ° C. and 10 kHz, and a coefficient of variation of the relative initial permeability at −40 to 100 ° C. is 5% or less. It is necessary to be. Here, the coefficient of variation is an index representing the magnitude of the temperature change of the relative initial permeability μ _ir , and the average value and standard of μ _ir when μ _ir is measured between −40 ° C. and 100 ° C. It is a value defined by the ratio of deviation (standard deviation / average value). The reason for limiting the relative initial permeability μ _ir at 10 kHz to 2500-3500 is that if μ _ir is 2500 or more, even if there is no calcination step, it can be manufactured at a low cost without precisely controlling the firing conditions. If it exceeds 3500, it is difficult to suppress the temperature change of μ _ir. If the relative initial permeability is in this range, there is no particular problem when used for various transformers, noise filters, sensors, and the like. The reason for limiting the coefficient of variation of the relative initial permeability at −40 to 100 ° C. to 5% or less is that the operating temperature of electronic parts using the recent Mn-Zn ferrite is wide, and its use This is because the temperature change of the relative initial permeability in the temperature range is required to be small, and if this change rate is 5% or less, there is no practical problem.

The Mn—Zn ferrite of the present invention having the above characteristics is composed of Fe ₂ O ₃ : 52 to 53 mol%, ZnO: 20 to 22 mol%, and the balance mainly composed of the main component of MnO. The reason why the composition of the main components Fe ₂ O ₃ and ZnO is limited to the above range is to set the temperature at which the secondary peak of the relative initial permeability μ _ir appears at around room temperature. This is also because the setting is made so that the eddy current loss is minimized near the reference room temperature. In general, in the Mn—Zn ferrite, when the amount of Fe ₂ O ₃ increases, the Curie temperature increases and the secondary peak temperature decreases. On the other hand, when the amount of ZnO increases, the Curie temperature decreases and the secondary peak temperature decreases. Therefore, in the composition region where Fe ₂ O ₃ is less than 52 mol% or more than 53 mol%, and in the composition region where ZnO is less than 20 mol% or more than 22 mol%, the secondary peak of the temperature change of μ _ir is near room temperature (20-25 ° C). In addition, it is difficult to set the Curie temperature to 100 ° C. or higher and to set the relative initial permeability μ _ir to 2500-3500.

Next, iron oxide that is a raw material of the main component Fe ₂ O ₃ , which is a feature of the present invention, will be described.
The iron oxide used as a raw material for the Mn—Zn ferrite needs to be fine particles having a primary particle diameter of 0.1 μm or less determined from the specific surface area. The reason for limiting the primary particle size to 0.1 μm or less is that in the case of Mn-Zn ferrite, the smaller particle size is more reactive, and spinelization and grain growth proceed faster, especially fine particles of 0.1 μm or less This is because relatively high magnetic properties can be obtained without going through the calcination step. Here, the primary particle diameter is a particle diameter calculated from the specific surface area obtained by the BET method or the like, assuming that the particle shape is spherical.

  Further, the iron oxide needs to have a median diameter of 0.6 μm or less measured with a laser diffraction type particle size distribution measuring apparatus. Compared with iron oxide powder with a median diameter of 0.6 μm or less and iron oxide powder with a median diameter greater than 0.6 μm, the powder with 0.6 μm or less is more reactive and obtains high magnetic properties without going through the calcination process. be able to. Here, the median diameter means a particle diameter that gives a height of 50% in the cumulative distribution chart obtained from the particle size distribution data, and there are a number median diameter, a mass median diameter, a volume median diameter, etc. In the invention, the volume median diameter is used. Further, as the laser diffraction type particle size distribution measuring device, for example, a device suitable for measuring the distribution of particles having good dispersibility, such as a particle size distribution measuring device (Microtrac HRA) manufactured by Nikkiso, is preferable. As measurement conditions, it is preferable to measure in a laser light transmission mode.

  Also, even with iron oxide powder having the same median diameter, the dispersibility of the powder is greatly different, that is, powder having a narrow particle size distribution (powder having a sharp particle size distribution) and powder having a wide particle size distribution (powder having a broad particle size distribution). Exists. The inventors investigated the relationship between the dispersibility and reactivity of the iron oxide powder, and found that the particle size distribution on the side of the particle size larger than the median diameter of the particle size distribution curve has a strong correlation with the iron oxide reactivity. Yes, especially when the particle size at which the cumulative value of the volume accumulated from the large particle size side becomes 10% is defined as “10% cumulative diameter”, the difference between the 10% cumulative diameter and the median diameter is small. It was found that the reactivity was excellent. The reason is considered that coarse powder larger than the median diameter hinders spinelization and grain growth. Therefore, in the present invention, the difference between the 10% cumulative diameter and the median diameter is controlled to 2.0 times or less of the median diameter. Preferably it is 1.6 times or less, More preferably, it is 1.5 times or less.

  In addition, in order to make the iron oxide used in the present invention have the above-mentioned particle size distribution characteristics, a method of classifying iron oxide as a raw material in advance and mixing these appropriately and pulverizing, or a wet method A method of controlling the temperature and pH of the solution and optimizing the particle size and distribution can be mentioned, and any method may be used.

The method for producing iron oxide used in the present invention is not particularly limited, but is preferably a wet method. The reason is that the wet method is more suitable for producing iron oxide having a smaller particle size than dry methods such as spray roasting. As used herein, the wet method means a method using a reaction that generates iron oxide in a solution, such as a coprecipitation method, an air oxidation method, or a hydrothermal method. In addition to the iron oxide produced by the wet method referred to in the present invention, in addition to those produced directly in an aqueous solution, hydrous iron oxide such as magnetite (Fe ₃ O ₄ ) and goethite (α-FeOOH) synthesized by the wet method is used. What is manufactured by heating is also included.

Next, a method for producing the Mn—Zn ferrite according to the present invention will be described.
The iron oxide powder described above is used as a raw material for Fe ₂ O ₃ as a main component, and this iron oxide powder and raw material powders for MnO and ZnO as other main components are Fe ₂ O ₃ : 52 to 53 mol%, ZnO: 20 to 22 mol%, preferably mixed in a wet manner so that the balance is mainly composed of MnO and dried to form granules. Here, ZnO and MnO, which are raw materials other than iron oxide, are not particularly limited and may be those normally used. In addition, in the Mn-Zn ferrite of the present invention, as an auxiliary component during the above mixing, for the purpose of improving the specific permeability, the oxidation power of lucium is 50 to 1000 ppm in terms of CaO, and silicon dioxide in terms of SiO ₂ . It is preferable to add in the range of 50 to 200 ppm. In addition, for the purpose of controlling crystal grain growth properties, for example, bismuth oxide, indium oxide, vanadium oxide, tantalum oxide, molybdenum oxide, niobium oxide, titanium oxide, tin oxide, etc. are selected as subcomponents. One or more of these may be added. These addition amounts are preferably 3000 ppm or less in total in terms of Bi ₂ O ₃ , In ₂ O ₃ , V ₂ O ₅ , Ta ₂ O ₃ , MoO _{3 and the} like.

  Next, the granular mixture is kneaded without adding a binder without passing through a calcination step, and then molded into a core having a product shape such as a ring shape, E shape, or ER shape, and fired. To do. As firing conditions at this time, the temperature is raised from room temperature to 600 ° C. at 120 to 1200 ° C./hr, the temperature is raised from 600 ° C. to the firing temperature at 200 to 600 ° C./hr, and then the holding temperature is 1150 to 1400. It is preferable to perform calcination at a temperature of 0.5 to 10 hours and cool. In addition, it is preferable to perform cooling at 200-400 degreeC / hr between holding temperature-600 degreeC. Moreover, the atmosphere during firing is in the atmosphere in the first half of the temperature rise, in the nitrogen atmosphere in the second half, and in an atmosphere in which the oxygen concentration is controlled to 10 vol% or less from soaking to 600 ° C. during cooling, and 600 ° C. The following cooling is preferably performed in a nitrogen atmosphere.

As described above, in the present invention, by using iron oxide with controlled particle size distribution characteristics as a raw material for Fe ₂ O ₃ , the specific initial permeability μ _ir is as high as 2500 or more without performing calcining, and An Mn-Zn ferrite with a small temperature change of μ _ir can be manufactured in a wide temperature range. Although the details of this reason are not yet clear, the iron oxide of the present invention has extremely high reactivity, so even if the calcining step is omitted, the final sintered body obtained is within individual crystal particles. This is probably because the composition has good uniformity, relatively uniform magnetic properties, and a large μ _ir . On the other hand, since the difference in secondary peak between crystal grains due to the difference in composition between individual crystal grains remains, if seen as a whole, a large change in μ _{ir in} the secondary peak is alleviated, and μ in a wide temperature range. It is considered that _ir becomes constant.

Fe (OH) ₂ obtained by neutralizing iron oxide produced by spray culture using ferrous chloride solution as a raw material and mixed solution of ferrous solution and ferric chloride solution with caustic soda is air-oxidized. Two types of iron oxides, iron oxides produced by a wet synthesis method in which magnetite synthesized by heating was oxidized, were produced, and these iron oxide powders were classified using 1000 μm and 106 μm sieves. The classified iron oxide was blended and mixed at the particle size ratio as shown in Table 1, and then pulverized using a jet mill (manufactured by Seishin Corporation: SPJ-200) at a pulverization pressure of 7 kgf / cm ² (0.7 And the sample was fed at a rate of 10 kg / hr. About the powder after grinding | pulverization, the specific surface area was measured by BET method, and the primary particle diameter was calculated | required. In addition, the particle size distribution was measured by using a laser diffraction particle size distribution measuring device (Nikkiso Co., Ltd .: Microtrac HRA), adding iron oxide to a 0.5% sodium hexametaphosphate solution, applying ultrasonic waves for 3 minutes, and then transmitting. Measurement was performed in the mode, and the median diameter and 10% cumulative diameter were obtained.

After mixing the raw material powder of ZnO and MnO so that Fe ₂ O ₃ , ZnO and MnO have the composition shown in Table 1, and adding water to the iron oxide obtained as described above, wet mixing, Spray drying was performed to form granules. During the mixing, 0.04 wt% of calcium oxide in terms of CaO and 0.02 wt% of bismuth oxide in terms of Bi ₂ O ₃ were added as subcomponents. Subsequently, without calcining the granules, 0.6% polyvinyl alcohol was added as a binder and kneaded to form a ring-shaped core, followed by firing. Firing is performed at a heating rate of 250 ° C./hr in the atmosphere from room temperature to 1100 ° C., and from 1100 ° C. to the firing temperature in a nitrogen atmosphere at a heating rate of 500 ° C./hr. After reaching the above, the temperature was maintained for 2 hours in an atmosphere in which the oxygen concentration was controlled to 10 vol% or less, and then cooled. For each of the obtained sintered bodies, the relative initial permeability μ _ir at 10 kHz was measured at a temperature range of −40 ° C. to 120 ° C. at 10 ° C. intervals. The average value and standard deviation of _ir were calculated, and the ratio of standard deviation to average value (standard deviation / average value) was obtained as a coefficient of variation.

The results of the above measurements are also shown in Table 1. FIG. 1 shows a temperature change curve of the relative initial permeability μ _ir of sintered ferrite Nos. 2, 10, 12 and 17. Each of the Mn-Zn ferrites of the present invention has a relative initial permeability μ _ir of 2500 or more at 25 ° C. and a coefficient of variation of the relative initial permeability μ _ir in the temperature range of −40 to 100 ° C. of 5%. It can be seen that excellent magnetic properties are stably obtained over a wide temperature range. On the other hand, the Mn—Zn ferrite outside the present invention has a relative initial permeability μ _{ir at} 25 ° C. of less than 2500, or a coefficient of variation of the relative initial permeability μ _ir in a temperature range of −40 to 100 ° C. It exceeds 5%, and the target characteristic of the present invention is not obtained.

It is the graph which illustrated the temperature change curve of the relative initial permeability (micro | micron | mu) _ir of the invention example of this invention, and a comparative example.

Claims (2)

The median diameter obtained from the particle size distribution measured by laser diffraction is 0.6 μm or less, and the difference between the 10% cumulative diameter and the median diameter in the particle size distribution is 2.0 times or less of the median diameter, and the primary value obtained from the specific surface area. Fe ₂ O ₃ : 52 to 53 mol, using iron oxide, which is a fine particle having a particle size of 0.1 μm or less, as a raw material, and molding and firing a mixture of this iron oxide, MnO and ZnO without calcining %, ZnO: 20 to 22 mol%, the balance is mainly composed of MnO, and the relative initial permeability at 25 ° C. and 10 kHz is 2500 to 3500, and the coefficient of variation of the relative initial permeability at −40 to 100 ° C. Is an Mn-Zn ferrite exhibiting 5% or less. As a raw material, the median diameter obtained from the particle size distribution measured by laser diffraction is 0.6 μm or less, and the difference between the 10% cumulative diameter and the median diameter in the particle size distribution is 2.0 times or less of the median diameter, and obtained from the specific surface area. Fe ₂ O ₃ : 52 to 53 mol is obtained by using iron oxide, which is fine particles having a primary particle size of 0.1 μm or less, and forming and firing a mixture of this iron oxide, MnO and ZnO without calcining. %, ZnO: 20 to 22 mol%, the balance is mainly composed of MnO, and the relative initial permeability at 25 ° C. and 10 kHz is 2500 to 3500, and the coefficient of variation of the relative initial permeability at −40 to 100 ° C. A method for producing Mn-Zn ferrite, characterized in that a ferrite exhibiting a characteristic of 5% or less is obtained.

Images