JP2003321273A - Method for producing spinel-type ferrite core and spinel- type ferrite core produced thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite which can be reduced in a manufacturing time and a manufacturing cost because of the unnecessariness for a temporary firing step indispensable in prior art and has magnetic properties equivalent to those in prior art, and to provide a method for producing the same. <P>SOLUTION: A mixed powder consisting of Fe<SB>2</SB>O<SB>3</SB>or a monometallic ferrite and at least one metal oxide as the principal components and 0.075-0.7 wt.%, based on the principal components, WO<SB>3</SB>as a subsidiary component is molded. The mixed powder is formed into a ferrite sinter by single firing at 1,040°C or higher. At least a part of the WO<SB>3</SB>may be replaced with MoO<SB>3</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a spinel type ferrite used in, for example, a power transformer, a power inductor or an electromagnetic wave absorbing material.

[0002]

2. Description of the Related Art In recent years, spinel type ferrite cores used for power transformers, power inductors and electromagnetic wave absorbing materials are required to be cheaper and have higher performance.
As shown in FIG. 7 (A), a general ferrite core manufacturing method is as follows. Raw materials are weighed, mixed (blended) (S1), dried (S2), calcined (S3), and crushed. Shi (S
4) Drying and granulating (S5), molding into a predetermined core shape (S6), and firing (S7) to obtain a product.

Japanese Patent Publication No. 6-267724 discloses Ni-
It is described that, by adding WO ₃ to the Zn-Cu type ferrite, a low loss material can be obtained. Also when obtaining a ferrite core having a composition according to this publication, a calcination step at 800 ° C. is performed and the main firing is performed at 1010.
It is described that it is carried out at ℃.

A conventional example using WO ₃ is described in Japanese Patent Publication No. 6-87441. In this publication, W
Since the melting point of O ₃ is 1473 ° C., which is a high-melting oxide, WO ₃ is used as a sintering inhibitor for suppressing the generation of coarse particles in firing when a ferrite core is obtained by a conventional manufacturing method. Is described.

[0005]

As described above, in the conventional method for manufacturing a spinel-type ferrite core, it is necessary to carry out a total of two firing steps: calcination capable of producing ferrite and main firing. As described above, the reason why calcination is required in the conventional manufacturing method is that a single continuous firing without a calcination step cannot form a uniform continuous solid solution, and the ferrite core satisfies the required magnetic properties. Because it was not obtained.

[0006] Therefore, it was expected that by promoting the diffusion of the elements in the raw material components by firing at a higher temperature, the one satisfying the required magnetic properties could be realized and the calcining step could be omitted. However, if the calcination process is omitted and firing is performed at a temperature higher than the normal firing temperature, it is easily affected by impurities in the ferrite raw material component and the grain size distribution, which causes abnormal grain growth and causes remarkable deterioration of magnetic properties. Sometimes. For this reason, it became difficult to control the firing conditions, and it was not possible to secure stable firing conditions.

Therefore, in the method of manufacturing a ferrite core, it has been conventionally indispensable to introduce a calcination step even if the number of steps increases.

The present invention eliminates the calcination step which has been indispensable in the prior art, reduces the manufacturing time and manufacturing cost, and has a magnetic property comparable to that of the conventional ferrite, and its manufacturing method. The purpose is to provide.

[0009]

(1) A method of manufacturing a spinel type ferrite core according to the present invention comprises Fe ₂ O ₃ and one or more of metal oxides as a main component, and a sub-component. As a result, WO ₃ is added to the main component in an amount of 0.075 to
It is characterized in that a mixed powder added with 0.7 wt% is molded, and a ferrite sintered body is obtained by only one firing at 1040 ° C. or higher.

In the conventional manufacturing method having a calcination step,
In the calcination step, if the material is baked at 800 ° C., for example, F
The reaction of e ₂ O ₃ with another metal oxide produces ferrite. That is, for example, the main component raw material is Fe ₂ O ₃ ,
Assuming that NiO, CuO, and ZnO are used, and WO ₃ as a secondary component is calcined, as shown in FIG.
₂ O ₄ , ZnFe ₂ O ₄ , and CuFe ₂ O ₄ are produced in advance. Then, during the main firing, WO ₃ acts as a sintering inhibitor.

On the other hand, in the present invention, Fe ₂ O ₃ and Ni
When O, ZnO, and CuO are used as the main ingredients, WO ₃ is added and mixed, and firing is performed at 1040 ° C. or higher without calcination,
Fe ₂ O ₃ and WO ₃ react with each other to produce Fe ₂ WO ₆ as shown in FIG. This Fe ₂ WO ₆ is WO
₃ unlike, since the liquid phase in comparison low temperature of 1050 ° C., it become possible to low temperature co Yuika. Fig. 8 shows Fe ₂ O
₃ is a phase diagram of the binary system of _3- WO ₃ , Fe at 1050 ° C.
₂ shows that WO ₆ is in a liquid phase.

According to the present invention, since the steps of calcination and pulverization are eliminated, the chance of impurities being mixed in is reduced, and low temperature firing is possible, so the influence of impurities in the ferrite raw material components and the particle size distribution is suppressed. It is possible to prevent abnormal grain growth from occurring. Therefore, remarkable deterioration of the magnetic characteristics can be suppressed at the same time.

Further, as the firing temperature range for ensuring the necessary magnetic characteristics is expanded, low temperature sintering of the ferrite core can be realized at the same time.

Further, in the manufacturing method of the present invention, steps such as calcination and crushing are omitted, so that the manufacturing time is shortened,
Manufacturing costs are reduced.

In the present invention, Fe is used as a main component raw material.
Other than ₂ O ₃ , NiO, ZnO, CuO, Mg
One of O or two or more of these may be contained. More specifically, besides Ni-Cu-Zn system, Ni-Zn system, Mg-Zn system, Mg-Cu-Zn system, M
The present invention is preferably applied to g-Ni-Zn ferrite. (2) When carrying out the production method of the present invention, preferably,
Unitary ferrite AFe ₂ O ₄ (A = any one metal of Ni, Cu and Zn), Fe ₂ O ₃ and the N
The main component is a powder obtained by mixing oxides of metals other than A among iO, CuO, and ZnO. Thus, F
When a part of the metal oxides other than e ₂ O ₃ is mixed in the form of ferrite from the beginning, Fe ₂ O ₃ and other metal oxides when heated to a temperature of 600 ° C. or higher during firing are mixed. Since the degree of expansion and contraction when ferrite is generated by the reaction is reduced, the deformation of the product can be suppressed. (3) The production method of the present invention can be carried out by using MoO ₃ instead of part or all of WO ₃ . (4) The spinel type ferrite core according to the present invention is obtained by the above-mentioned manufacturing method, and preferably, iron oxide as the main component is 48.0 to 49.7 mol% in terms of Fe ₂ O ₃ , and copper oxide is CuO. 7.0 to 11.0 mol% in terms of conversion,
Crystal particles in a ferrite core containing zinc oxide in an amount of 15.7 to 30.3 mol% in terms of ZnO, nickel oxide in the remaining mol%, and tungsten as an accessory component in an amount of 0.075 to 0.7 wt% in terms of WO _3. The composition difference between the oxides is a maximum of 1 mol% or more with respect to the oxide of at least one element of the nickel, copper, and zinc.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION One Embodiment of the Manufacturing Method of the Present Invention
The Ni-Cu-Zn ferrite will be described. main
As the raw material of the component, for example, Fe_TwoO_Three, NiO, C
A mixed powder of uO and ZnO is used. Other implementation
As a form of unitary ferrite AFe _TwoO_Four(A is N
i, Cu, Zn), and Fe_TwoO_ThreeWhen,
A material to which an oxide of a metal other than A is added is used. these
WO for the main ingredient_ThreeIs shown in FIG. 7 (B).
As described above, a predetermined amount is weighed and wet-mixed (blended) (S1),
Dry (S2) and crush. Add binder to this powder
And granulate to form granules and mold the core (S3).
This is baked in the atmosphere at 1000 to 1250 ° C to obtain a product.
(S4).

[Example 1] ZnFe was used as the main component raw material.
₂ O ₄ , Fe ₂ O ₃ , NiO, CuO is used, and Fe ₂
O ₃ = 49.3 mol%, NiO = 21.0 mol%, Cu
O was 8.0 mol%, ZnO was 21.7 mol%, and WO ₃ was added as an accessory component in an amount of 0.3 wt% to obtain a raw material powder. This raw material powder is wet-mixed with a ball mill, and the obtained mixed powder is dried to obtain a dry powder.
Granulation was carried out by adding 10 wt% of PVA 6% aqueous solution. The granules were prepared by sizing with a 20-mesh sieve.
The granules were molded into a ring-shaped core using a dry compression molding machine and a mold. 2 at 1000-1250 ℃ in the atmosphere
Firing was performed for an hour to obtain a ring-shaped core having an outer diameter of about 18 mm, an inner diameter of about 10 mm, and a height of about 6 mm.

[Comparative Example 1] As a comparative example, a ring-shaped core having a composition shown as Comparative Product 1 in Table 1 was prepared by a conventional method including a calcining step.

[Measurement of Magnetic Properties] The ring-shaped core thus obtained was subjected to a magnetic field of 0.4 by an impedance analyzer (4291A manufactured by Hewlett-Packard Co.).
A / m was applied, and the initial magnetic permeability at 100 kHz was measured at room temperature. The saturation magnetic flux density was measured by applying a magnetic field of 4 kA / m at room temperature using a direct current magnetization characteristic automatic recording device Model MHS40 manufactured by Riken Denshi Co., Ltd.

[Measurement Results] The product 1 of the present invention is a product when the firing temperature in Example 1 is 1090 ° C., and the product 1 has the initial magnetic permeability (μi) and saturation measured by the above method. The magnetic flux density (Bs) is shown in Table 1. The target value of the initial magnetic permeability (μi) is ± 25% compared with the sample with calcination (Comparative product 1), and the saturation magnetic flux density (B
The target value of s) is ± 5% compared with the sample with calcination (Comparative product 1).

As can be seen from Table 1, in comparison with the comparative product 1 which has undergone the calcination process, the actual product 1 satisfies both the target values of the initial magnetic permeability (μi) and the saturation magnetic flux density (Bs), and the cost is 30. %, And the production lead time has been reduced by 50%.

[Relationship between Firing Temperature and Density] In Example 1, the change in density when the firing temperature was changed between 1040 and 1150 ° C. was that WO ₃ was not included and calcination was not performed. In contrast, it is shown in FIG. As apparent from FIG. 1, when the addition of WO ₃ is omitted calcination as in the present invention, and without adding WO ₃ as compared to the case of omitting the calcination, suitable as ferrite 5.0 mg / m ^It can be seen that the temperature range in which the density of the sintered body of ³ or more is obtained is expanded, and the low temperature sintering of the ferrite core can be achieved at the same time. In the present invention, the desirable firing temperature is 1040-12.
The temperature is 50 ° C., more preferably 1050 ° C. or higher at which a sintered body density of 5.0 Mg / m ³ or higher is obtained, and 1160 ° C. or lower at which the sintered body density is almost saturated.

[Relationship between Firing Temperature and Initial Permeability] In FIG. 2, in the case of Example 1, the change in the initial permeability when the firing temperature was changed between 1040 and 1150 ° C., not including WO _3. Moreover, it is shown in comparison with the case where calcination is not performed. As is clear from FIG. 1, when WO ₃ is added and calcination is omitted as in the present invention, the target value of initial permeability is 400 ± 25%.
The temperature range in which (300 to 500) is obtained expands, and the firing temperature at which high initial permeability is obtained is shifted to the low temperature side as compared with the case where WO ₃ is not added and calcination is omitted. I understand.

[0024]

[Table 1]

[Change of Raw Material of Example 1] ZnO was used as the main component material instead of ZnFe ₂ O ₄ of Example 1, and the composition, process, and core shape of each oxide were the same as in Example 1. A sample was prepared as follows. The density and the initial magnetic permeability of the thus-obtained sintered core were measured at various firing temperatures, and the results are shown in FIGS. 3 and 4, respectively. As a result, almost the same results as in Example 1 were obtained.

[Effect of WO ₃ Addition Amount] Using the main raw material shown in Example 1, the process and core shape were the same, the firing temperature was 1000 ° C. or higher, and the WO ₃ addition amount was 0 to 1.0 w.
The maximum core density and the maximum initial magnetic permeability at each addition amount (maximum core density and maximum initial magnetic permeability among samples fired at different firing temperatures at each addition amount) were measured while varying variously within the range of t%. . The result is shown in FIG.

From FIG. 5, the target core density is 5.0M.
Those satisfying g / m ³ and initial permeability of 400 ± 25% are WO
It was found that the addition amount of ₃ was 0.075 to 0.7 wt%.

[Influence of the composition of the main component] As the raw material of the main component, the raw material of Example 1 was used, and the composition was changed variously so as to be those described in Examples 2 to 8 in Table 1. The amount of WO ₃ added as a component was fixed at 0.3 wt%, a sample was prepared in the same process as in Example 1, and the initial magnetic permeability (μ
i) and the saturation magnetic flux density (Bs) were measured. For comparison, comparative products 2 to 8 having similar compositions having no WO ₃ and having a calcination process were prepared, and initial permeability (μi), saturation magnetic flux density (Bs) ) Was measured. Table 1 shows the results of the characteristic measurements for each sample.
Shown in.

As is clear from Table 1, in comparison with any of the results, the ferrite composition of the implemented product was higher than that of the comparative product, the initial permeability and the saturation magnetic flux density also satisfied the target values, and the production lead time was Can be reduced by 50% and the manufacturing cost can be reduced by 30%.

In the case of carrying out the present invention, the preferred range of the main component composition is that iron oxide is 4 in terms of Fe ₂ O _3.
8.0 to 49.7 mol%, copper oxide is 7.0 in terms of CuO
~ 11.0 mol%, zinc oxide is 15.7 by ZnO conversion
30.3 mol%, and nickel oxide is the remaining mol%.

If Fe ₂ O ₃ is less than the above lower limit, the initial magnetic permeability and the saturation magnetic flux density tend to decrease, and the core loss tends to increase. Further, when Fe ₂ O ₃ exceeds the upper limit value, there is a tendency that specific resistance decreases, initial permeability due to deterioration of sinterability, saturation magnetic flux density decreases, core loss increases, and stable mass production becomes difficult. .

When CuO is less than the lower limit value, the sinterability tends to be poor, the initial permeability and the saturation magnetic flux density are lowered, and the core loss tends to be increased. If CuO exceeds the upper limit value, the initial magnetic permeability and the saturation magnetic flux density tend to decrease, and the core loss tends to increase.

If ZnO is less than the lower limit, the initial magnetic permeability tends to decrease and the core loss tends to increase. Also, Z
When nO exceeds the upper limit value, the saturation magnetic flux density decreases,
The decrease in the Curie point tends to decrease the temperature at which the core loss is minimized and increase the core loss.

However, the present invention is based on Fe ₂ O ₃ and WO
_The effect is exhibited by the presence of ₃ , and the desired magnetic properties may be adjusted by the composition of the main component element,
Not only Ni-Cu-Zn type ferrite but also Ni-Zn
System, Mg-Zn system, Mg-Cu-Zn system, Mg-Ni-Zn
It can also be applied to series ferrite.

[Composition Difference between Crystal Particles] FIG. 6 (A) is a schematic diagram of a backscattered electron image of the polished surface of the ferrite core in the embodiment 1 taken by a scanning electron microscope. Further, FIG. 6B shows a schematic diagram of the backscattered electron image of the ferrite core of the comparative product 1 manufactured by the manufacturing method having the conventional calcination step. In such a backscattered electron image, heavy particles having a large atomic weight tend to appear with high brightness (white), and light particles with small atomic weight tend to appear with low brightness (black). As can be seen from the comparison between FIGS. 6 (A) and 6 (B), the one using the production method according to the present invention has a large difference in lightness between the crystal grains and a larger lightness difference between the crystal grains than the one obtained by the conventional method. There is a large variation in composition.

Tables 2 and 3 show the results of measuring the composition between the crystal grains of Example 1 and Comparative Example 1 using TEM-EDS, respectively. As can be seen from Table 2, in the case of the product 1, the composition variation of 1 mol% or more among the crystal grains is present in the oxide of at least one element of nickel, copper and zinc. On the other hand, as shown in Table 3, in the case of Comparative product 1, the composition variation is 1 mol%.
Was found to be less than.

[About MoO ₃ ] In the present invention, W
MoO ₃ having a characteristic approximate to WO ₃ in place of the O ₃
Can also be carried out in the same manner. In this case, M
oO ₃ is used in place of part or all of WO ₃ , and the total amount of addition is the same as when WO ₃ is added. Table 4 is W
Comparative Examples 2 and 6 according to the conventional manufacturing method for Examples 9 to 12 in which 0.3 wt% of MoO ₃ was added instead of O ₃ .
Shown in contrast to Nos. 7 and 8. As is clear from Table 4, in comparison with any of the results, the ferrite composition of the implementation product is higher than the comparison product in initial permeability and saturation magnetic flux density, and the production lead time is 50%. It can be shortened and the manufacturing cost can be reduced by 30%.

[0038]

[Table 2]

[0039]

According to the present invention, it is possible to provide a ferrite having magnetic characteristics comparable to those of the conventional ones, since the calcination step is not required, the manufacturing time and the manufacturing cost can be reduced. Further, by expanding the firing temperature range, it is possible to suppress variations in characteristics due to mass production, and it is possible to stably produce a highly reliable ferrite core.

[0040]

[Table 3]

[0041]

[Table 4]

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the firing temperature and the density in Example 1 of the present invention, in comparison with those containing no WO ₃ .

FIG. 2 is a diagram showing the relationship between the firing temperature and the initial magnetic permeability in Example 1 of the present invention, in comparison with those containing no WO ₃ .

FIG. 3 shows the relationship between the firing temperature and the density when the raw material contains unitary ferrite in Example 1 of the present invention.
It is a figure shown in contrast with what does not contain ₃ .

FIG. 4 shows the relationship between the firing temperature and the initial magnetic permeability when the raw material contains unitary ferrite in Example 1 of the present invention.
Shows in comparison with those not containing WO _3.

FIG. 5 is a diagram showing the relationship between the amount of WO ₃ added and the sintered core density and initial magnetic permeability in the present invention.

FIG. 6 is a schematic diagram of a backscattered electron image of a polished surface of a sintered core cross section of Example 1 of the present invention and Comparative Example 1 taken by a scanning electron microscope.

7 (A) and 7 (B) are process diagrams showing a conventional and a method for manufacturing a ferrite core according to the present invention, respectively, and FIG. 7 (C) is a diagram showing the production of ferrite by calcining in the case of a conventional manufacturing method including a calcining step FIG. 3D is a diagram illustrating a reaction between Fe ₂ O ₃ and WO ₃ when the production method according to the present invention is used.

FIG. 8 is a phase diagram of a binary system of Fe ₂ O ₃ —WO ₃ .

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G018 AA23 AA24 AA25 AA39 AB02                       AC16                 5E041 AB12 AB19 BD01 HB17 NN01                       NN06

Claims (5)

[Claims] 1. Fe ₂ O ₃ and a mixture of Fe ₂ O ₃ and one or more metal oxides as a main component, and WO ₃ as a sub-component in an amount of 0.075 to 0.075 with respect to the main component.
A method for producing a spinel-type ferrite core, which comprises molding a mixed powder to which 0.7 wt% is added, and forming a ferrite sintered body only by firing once at 1040 ° C. or more. 2. Fe ₂ O ₃ and NiO, CuO, Z
The main component is one to which one or more of nO is added, and WO ₃ as a sub-component, 0.075 to the main component.
A method for producing a spinel-type ferrite core, which comprises molding a mixed powder to which 0.7 wt% is added, and forming a ferrite sintered body only by firing once at 1040 ° C. or more. 3. A unit ferrite AFe ₂ O ₄ (A = Ni,
Any one of Cu and Zn) and Fe ₂ O
₃ as a main component, and a powder obtained by mixing oxides of metals other than A among NiO, CuO, and ZnO described above, and WO ₃ as a sub-component from 0.075 to 0.075 with respect to the main component.
A method for producing a spinel-type ferrite core, which comprises molding a mixed powder to which 0.7 wt% is added, and forming a ferrite sintered body only by firing once at 1040 ° C. or more. 4. The spinel ferrite core according to any one of claims 1 to 3, wherein MoO ₃ is used in place of part or all of WO _3. Manufacturing method. 5. A spinel type ferrite core obtained by the manufacturing method according to claim 1, wherein iron oxide as a main component is 48.0-4 in terms of Fe ₂ O _3.
9.7 mol%, copper oxide 7.0 to 11.0 in terms of CuO
Mol%, 15.7 to 30.3 mol% of zinc oxide in terms of ZnO, and remaining mol% of nickel oxide, and tungsten as an accessory component in terms of WO ₃ of 0.075 to.
0.7 wt% is included, and the composition difference between the crystal grains in the ferrite core has a composition variation of 1 mol% or more at maximum with respect to the oxide of at least one element of nickel, copper, and zinc. Spinel type ferrite core.