JP6411848B2 - Ferrite core and manufacturing method thereof - Google Patents

Description

  The present invention relates to a MnZn-based ferrite core mainly used for inductors for noise filters and the like and a method for manufacturing the same.

In the fields of large power transformers and coils, a large ferrite core that can be driven at a high frequency of several tens of kHz or more and has a cross-sectional area of 100 mm ² or more is required.

  However, with the increase in the size of the ferrite core, various problems for application to noise filters occur.

  In Patent Document 1, during the cooling step after firing, the temperature range of 1050 to 500 ° C. is cooled at a rate of 5 to 100 ° C./h in a non-oxidizing atmosphere, so that the average value of specific resistance is 1Ω.・ Proposals have been made to improve the core loss when the size is increased to m or more.

  Moreover, in patent document 2, by baking in a pressure-reduced atmosphere in the state where there are enough open pores, the deoxygenation reaction is sufficiently advanced, and even when a large molded body is fired, the magnetic properties are homogenized. Proposals have been made.

  Patent Document 3 discloses a Mn—Zn ferrite core containing Si oxide, Ca oxide, Bi oxide and Mo oxide as subcomponents, and the ZnO content throughout the ferrite core. A ferrite core that exhibits a high initial permeability in a wide band has been proposed by setting the distribution of A within a predetermined range.

JP 2002-134331 A JP-A-53-97012 JP 2006-165479 A

  However, since the invention described in Patent Document 1 aims to reduce the core loss by setting the average value of the specific resistance to 1 Ω · m or more, it is not suitable for noise filter applications utilizing the core loss for noise removal.

  In addition, the invention described in Patent Document 2 is not a viable invention because there is no explanation of what the open pores are and the means for providing the open pores is not disclosed. Therefore, there is a problem that mass production is low due to the restriction of batch processing.

The invention described in Patent Document 3 does not assume application to a so-called large ferrite core. That is, the size of the ferrite core that is the subject of the invention of Patent Document 3 is about 10 to 45 mm in outer diameter, about 5 to 30 mm in inner diameter, and about 5 to 14 mm in height when disclosed in the examples. The toroidal core has a cross-sectional area perpendicular to the magnetic path of about 50 mm ² , and there is no mention of a large ferrite core having a cross-sectional area of 100 mm ² or more.

  Accordingly, an object of the present invention is to provide a large-sized ferrite core having a suitable specific resistance and high magnetic permeability and suitable for noise filter applications and having high mass productivity, and a method for manufacturing the same.

In the present invention, the present invention includes iron oxide, manganese oxide, and zinc oxide as main components, and includes silicon oxide, calcium oxide, bismuth oxide, and molybdenum oxide as subcomponents, and an area of a cross section perpendicular to the magnetic path is 100 mm ² or more. 200 mm ² or less, a distance from the center of the cross section to the nearest cross-sectional edge is 5 mm or more, and an average crystal grain size within a range of 150 μm from the center is 25 μm or more and 60 μm or less. Solve.

  Here, the center of the cross section is the farthest from the ferrite core surface in the cross section, and coincides with the geometric center of gravity.

  The ferrite core of the present invention preferably has a specific resistance of 0.10 Ω · m or more and 0.50 Ω · m or less.

  The ferrite core of the present invention desirably has a real part relative permeability of 10,000 or more at a frequency of 100 kHz.

The composition of the main component, the iron oxide in terms _{of Fe} 2 _{O 3} in 52.0Mol% or more, 53.5Mol% or less, wherein the manganese oxide is 24.0Mol% or more in terms of MnO, less 26.5Mol%, The balance is the zinc oxide, and the composition of the subcomponent is such that the silicon oxide is 0.010 mass% or less (excluding 0) in terms of SiO ₂ and the calcium oxide is in terms of CaO as a mass ratio to the main component. 0.010 mass% or more and 0.050 mass% or less, the bismuth oxide is 0.010 mass% or more and 0.050 mass% or less in terms of Bi ₂ O ₃ , and the molybdenum oxide is 0.150 mass% or less in terms of MoO ₃ (0 Is not included).

  In addition, it is desirable that the noise filter includes the ferrite core and a coil wound around at least a part of the ferrite core, and a maximum value of a current passed through the coil is 20 A or more.

  A step of mixing iron oxide, manganese oxide, zinc oxide, and bismuth oxide powder and pre-baking in the atmosphere at 700 ° C. to 900 ° C. for 1 to 5 hours to prepare the first powder; and the first powder Adding a silicon oxide, calcium oxide, and molybdenum oxide powder to pulverize, adjusting the second powder, adding 1-2 mass% of an organic binder to the second powder, and pressure-molding, 400 ° C. It is desirable to be a method for producing a ferrite core in which binder removal is performed at ˜600 ° C. for 4 to 10 hours and firing is performed at 1300 ° C. to 1350 ° C. for 4 to 10 hours in an inert atmosphere.

  According to the present invention, an appropriate specific resistance obtained by blending the main component and the subcomponent and a high magnetic permeability with a uniform average crystal grain size can be obtained, which is suitable for noise filter applications and does not require heat treatment under reduced pressure. In addition, it is possible to provide a large-sized ferrite core excellent in mass productivity and a manufacturing method thereof because it is not subject to batch processing restrictions.

It is a figure which shows the real part relative magnetic permeability of the ferrite core in this invention, and the frequency characteristic of an inductor. It is a figure which shows the relationship between the average crystal grain diameter of the ferrite core in this invention, and a ferrite core cross-sectional area. It is a figure which shows the relationship between the average crystal grain diameter of the ferrite core in this invention, and binder addition amount.

The present invention includes iron oxide, manganese oxide, and zinc oxide as main components, and includes silicon oxide, calcium oxide, bismuth oxide, and molybdenum oxide as auxiliary components, and has an area of a cross section perpendicular to the magnetic path of 100 mm ² or more and 200 mm ^2. Embodiments of the ferrite core in which the distance from the center of the cross section to the nearest ferrite core surface is 5 mm or more and the average crystal grain size in the range of 150 μm radius from the center is 25 μm or more and 60 μm or less can be taken. .

  Here, the average crystal grain size is more desirably 30 μm or more and 50 μm or less, and further desirably 40 μm or less.

Further, the magnetic path in the area of the cross section perpendicular 124 mm ² or more, as long as 150 mm ² or less, the effect of the present invention can be more preferably receive.

  The ferrite core is, for example, mixed with iron oxide, manganese oxide, zinc oxide, bismuth oxide powder, and silicon oxide, calcium oxide, molybdenum oxide powder is added to the pre-fired powder, compared with the case of manufacturing a conventional ferrite material. It can be manufactured by adding a binder such as polyvinyl alcohol having a mass of 1 to 2 mass% with respect to the mass of the pre-baked powder, followed by pressure molding and firing.

  That is, by adding bismuth oxide to the MnZn-based ferrite material before pre-baking, the crystal grain growth is promoted, the binder is added excessively, and other subcomponents are added after pre-baking and fired. An appropriate specific resistance can be obtained without inhibiting the growth.

  Further, while increasing the relative permeability of the real part and the imaginary part by setting the average crystal grain size to 25 μm or more, by setting the average crystal grain size to 60 μm or less, it is possible to pass the ferrite material into the ferrite material. It is possible to prevent the pores from being blocked.

  By appropriately selecting the subcomponents added before and after pre-baking as described above, it is possible to obtain a crystal grain size of 25 μm or more and 60 μm or less that is homogeneous up to the center of the cross section.

Thereby, even in a ferrite core having a cross section perpendicular to the magnetic path of 100 mm ² or more and 200 mm ² or less, both the real part and the imaginary part have a high relative permeability in a frequency band of 100 kHz or more and at least 300 kHz. Therefore, it is possible to obtain a high-impedance noise filter by winding a coil, particularly in such a frequency band.

  The specific resistance of the ferrite core of the present invention is preferably 0.10 Ω · m or more and 0.50 Ω · m or less, more preferably 0.15 Ω · m or more and 0.30 Ω · m or less. 0.20Ω · m or more and 0.25Ω · m or less is more desirable.

  In order to suppress the generation of eddy current inside the ferrite core and increase the real part relative permeability in a frequency band lower than 100 kHz, it is desirable that the specific resistance is high, but in order to sufficiently secure the imaginary part relative permeability. It is desirable to limit the upper limit of the specific resistance as described above.

In common mode noise filter applications, it is particularly preferable to achieve both high impedance in the range of 100 kHz to 300 kHz and high real permeability μ ′ in the frequency band up to 100 kHz. The relative magnetic permeability μ ′ is desirably 10,000 or more. Here, the specific resistance of the ferrite core having a large cross-sectional area, especially the cross-sectional area perpendicular to the magnetic path, of 100 mm ² or more and 200 mm ² or less is 0.10 Ω · m or more and 0.50 Ω · m or less. This contributes to securing the high impedance in the range of 100 kHz or more and 300 kHz or less and the real relative permeability μ ′ at 100 kHz.

The composition of the main component of the ferrite core is that iron oxide is 52.0 mol% or more and 53.5 mol% or less in terms of Fe ₂ O ₃ , and manganese oxide is 24.0 mol% or more and 26.5 mol% or less in terms of MnO, The remainder is the zinc oxide, and the composition of the subcomponents is 0.010 mass% or less (not including 0) of silicon oxide in terms of SiO _{2 and} calcium oxide in terms of CaO in terms of mass ratio with respect to the main component. 010 mass% or more and 0.050 mass% or less, bismuth oxide is 0.010 mass% or more and 0.050 mass% or less in terms of Bi ₂ O ₃ , and molybdenum oxide is 0.150 mass% or less (excluding 0) in terms of MoO _3. It is desirable to be.

The composition of the main component of the ferrite core is that iron oxide is 52.5 mol% or more and 53.0 mol% or less in terms of Fe ₂ O ₃ , and manganese oxide is 25.5 mol% or more and 26.0 mol% or less in terms of MnO, The balance is the zinc oxide, and the composition of the subcomponents is 0.002 mass% or more and 0.008 mass% or less in terms of SiO _{2 in} terms of mass ratio to the main component, and calcium oxide is 0.002 in terms of CaO. 015 mass% or more and 0.025 mass% or less, bismuth oxide is 0.010 mass% or more and 0.040 mass% or less in terms of Bi ₂ O ₃ , and molybdenum oxide is 0.010 mass% or more and 0.100 mass% or less in terms of MoO ₃ It is more desirable to be.

Moreover, as a mass ratio with respect to the said main component among compositions of a subcomponent, bismuth oxide is 0.010 mass% or more and 0.030 mass% or less in terms of Bi ₂ O ₃ , and molybdenum oxide is 0.010 mass% or more in terms of MoO _3. , 0.080 mass% or less is more desirable.

  The addition amount of silicon and calcium is preferably within the above composition range in order to obtain a ferrite core having a specific resistance necessary for obtaining the above-described real part and imaginary part relative permeability characteristics. That is, if the addition amount of silicon or calcium is decreased, the specific resistance is decreased, and if it is increased, the initial permeability is decreased.

  Similarly, the amount of bismuth and molybdenum added is preferably in the above composition range in order to obtain the crystal grain size necessary for the present invention. That is, if the amount of bismuth or molybdenum added is reduced, crystal growth is suppressed, and if it is increased, growth is promoted.

  In the ferrite core for noise filter use in the present invention, it is possible to obtain a high relative permeability and high impedance necessary for attenuating noise particularly in a frequency band of 100 kHz or more and at least 300 kHz. The object is different from the invention described in 1.

  In addition, the technique described in Patent Document 2 does not disclose a specific method for sufficiently providing open pores, and is not disclosed as a feasible invention. The specific method which was not disclosed in (1) is disclosed.

Furthermore, the technique described in Patent Document 3 does not assume a large ferrite core having a cross-sectional area perpendicular to the magnetic path of 100 mm ² or more, and of course, there is no mention in the present invention. It pays attention and discloses the means to realize it.

First, Fe ₂ O ₃ is weighed so that it is 52.0 mol% or more and 52.4 mol% or less, MnO is 24.0 mol% or more and 26.0 mol% or less, and the balance is ZnO. 0.02 mass% or more and 0.050 mass% or less of Bi ₂ O ₃ was added and mixed with an organic solvent with an Attritor (registered trademark) manufactured by Nippon Coke Industries, Ltd. for 1 hour.

  The slurry of the mixed powder was dried with a spray dryer and then pre-fired in the air at 800 ° C. for 4 hours to obtain a pre-fired powder.

0.005 mass% of SiO ₂ , 0.025 mass% or less of CaO, and 0.013 mass% of MoO ₃ were added to the pre-fired powder, and pulverized with an Attritor (registered trademark) for 1 hour together with an organic solvent.

  0.6 to 1.6 mass% of polyvinyl alcohol was added as a binder to the mass of the pulverized slurry excluding the organic solvent, and granulated with a spray dryer.

The granulated powder was uniformly filled in a mold and pressure-molded with a load of 1.1 t / cm ² .

  The molded body was debindered in the atmosphere at 500 ° C. for 5 hours and then fired in a nitrogen atmosphere at 1320 ° C. for 9 hours to prepare a ferrite core.

Here, for the ferrite core having a toroidal shape, samples of Examples 1 and 2 in Table 1 and Comparative Examples 1 to 4 in which the amount and shape of the binder added and the cross-sectional area perpendicular to the circumferential direction were changed were prepared. did.

  An inductor in which a winding of 10 turns is applied to the obtained ferrite core is manufactured, and the relative relative permeability μ ′ of the ferrite core and the impedance of the inductor are 1 kHz to 10 MHz using an impedance analyzer 4194A manufactured by Agilent Technologies, Inc. The frequency characteristics of were measured.

  FIG. 1 is a diagram showing the real part relative permeability and frequency characteristics of impedance of the ferrite core in the present invention.

  FIG. 1 shows the results of Example 1 and Comparative Example 1. Example 1 and Comparative Example 1 have the same core shape, but differ in the amount of binder added.

  Example 1 in which the amount of binder added to the mass of the pulverized slurry excluding the organic solvent is 1.0 mass% or more has higher real part relative permeability μ ′ and impedance than Comparative Example 1.

  Furthermore, the toroidal ferrite core is cut with a dicing saw so as to be perpendicular to the toroidal circumferential direction which is a magnetic path, the cross section is mirror-polished, etched with hydrofluoric acid, and crystal grains are observed with a metal microscope. Was observed.

  Furthermore, the average value of the crystal grain size within a radius of 150 μm from the center of the cross section was measured.

  Here, the crystal grain size is a circle-equivalent diameter obtained from the area of the crystal grain obtained by image analysis of a photograph taken with a metal microscope.

  Further, since the cross section of each of the example and the comparative example is a square, the intersection of the diagonal lines becomes the center of the cross section.

  FIG. 2 is a diagram showing the relationship between the average crystal grain size of the ferrite core and the ferrite core cross-sectional area in the present invention.

As in Comparative Examples 1 to 3, when the binder addition amount relative to the mass excluding the organic solvent of the pulverized slurry is 0.8 mass%, the average crystal grain size becomes smaller when the ferrite core cross-sectional area is 100 mm ² or more. FIG. 2 shows this.

  Comparative Example 1 and Examples 1 and 2 have the same cross-sectional area. Average crystal grains of Example 2 in which the binder addition amount is 1.0 mass% or more than that of Comparative Example 1 in which the binder addition amount is less than 1.0 mass%, and further, the binder addition amount is 1.5 mass% or more. FIG. 2 shows that the diameter is large.

  If the added amount of the binder exceeds 2.0 mass%, there is a possibility that a problem may be caused in maintaining the shape after the binder removal. Therefore, the added amount of the binder is set to 2.0 mass% or less in both the first and second embodiments.

  From the results of FIG. 1 and FIG. 2, when the binder addition amount is 1.0 mass% or more and 2.0 mass% or less, the average crystal grain size is increased, and the real part relative permeability μ ′, particularly 100 kHz or more. It can be seen that the impedance is improved.

  FIG. 3 is a diagram showing the relationship between the average grain size of the ferrite core and the amount of binder added in the present invention.

  FIG. 3 shows that the average crystal grain size does not change much when the binder addition amount is less than 1.0 mass%, and the average crystal grain size tends to increase when the binder addition amount is 1.0 mass% or more.

  As described above, a ferrite core having magnetic properties suitable for noise filter applications, excellent in mass productivity, and capable of being molded in a larger size than before can be obtained, and a method for manufacturing the same.

  As mentioned above, although the Example of this invention was described, this invention is not limited above, The change and correction of a structure are possible in the range which does not deviate from the summary of this invention.

Claims (3)

Contains iron oxide, manganese oxide, zinc oxide as main components,
Contains silicon oxide, calcium oxide, bismuth oxide, molybdenum oxide as subcomponents,
The composition of the main component is:
The iron oxide is 52.0 mol% or more and 53.5 mol% or less in terms of Fe ₂ O ₃ ,
The manganese oxide is 24.0 mol% or more and 26.5 mol% or less in terms of MnO,
The balance is the zinc oxide,
The composition of the subcomponent is, as a mass ratio with respect to the main component,
The silicon oxide is 0.010 mass% or less (excluding 0) in terms of SiO ₂ ;
The calcium oxide is 0.010 mass% or more and 0.050 mass% or less in terms of CaO,
The bismuth oxide is 0.010 mass% or more and 0.050 mass% or less in terms of Bi ₂ O ₃ ,
The molybdenum oxide is 0.150 mass% or less (excluding 0) in terms of MoO ₃ ,
And
The area of the cross section perpendicular to the magnetic path is 100 mm ² or more and 200 mm ² or less,
The distance from the center of the cross section to the nearest cross section edge is 5 mm or more,
A method for producing a ferrite core, wherein an average crystal grain size within a radius of 150 μm from the center is 25 μm or more and 60 μm or less ,
Mixing the iron oxide, the manganese oxide, the zinc oxide, and the bismuth oxide powder, and pre-baking in the air at 700 ° C. to 900 ° C. for 1 to 5 hours to prepare the first powder; Adding the powder of silicon oxide, calcium oxide and molybdenum oxide to the powder of No. 1 and crushing to prepare a second powder; and adding 1 to 2 mass% of an organic binder to the second powder; A method for producing a ferrite core , comprising: a step of pressure forming, removing a binder at 400 ° C. to 600 ° C. for 4 to 10 hours, and firing at 1300 ° C. to 1350 ° C. for 4 to 10 hours . 2. The method for producing a ferrite core according to claim 1, wherein the specific resistance is 0.10 Ω · m or more and 0.50 Ω · m or less . The method for manufacturing a ferrite core according to claim 1 or 2, wherein the real part relative permeability at a frequency of 100 kHz is 10,000 or more .

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