JP2005194134A - Ferrite core and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite core which has a small standard deviation σ of magnetic characteristics such as initial magnetic permeability or DC superimposing characteristic and a small R expressing the difference between the best point and worst point of each characteristic as an index of dispersion and which has excellent magnetic characteristics, and to provide a method for producing the same. <P>SOLUTION: The method for producing the ferrite core includes a process for firing a formed body which consists of a ferrite raw material containing a Zn compound by using a firing jig made of ferrite containing an oxide of Zn. The difference (M2-M1) between the second molar ratio (M2; mol%) being the molar ratio of the content of the oxide of Zn in the firing tool to the total amount of the ferrite and the first molar ratio (M1; mol%) being the molar ratio of the content of the Zn compound in the formed body to the total amount of the ferrite raw material is set to be -5 mol%≤M2-M1≤5 mol% expressed in terms of ZnO. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ferrite core and a method for manufacturing the same, and more particularly, to a ferrite core having high magnetic properties and a small variation in magnetic properties, such as initial permeability and direct current superimposition, in a mass production process, and a method for manufacturing the same. .

  Generally, a core made of ferrite is used as a core for a transformer such as a communication transmission transformer or a switching power transformer. This is because ferrite can be manufactured at a low cost with less decrease in initial permeability and increase in power loss in a higher frequency band than other soft magnetic metal materials.

  In recent years, in various electronic equipment fields, there have been increasing demands for further downsizing, thinning and high performance of electronic equipment, and in order to meet these demands, the performance improvement of ferrite cores used in various electronic equipment, for example, Attempts have been made to improve magnetic properties. In particular, as a method for improving the performance of the ferrite core, a method for improving the performance of the ferrite core itself by improving the composition ratio of the main component and the added subcomponent constituting the ferrite core has been conventionally performed.

  However, in the actual mass production process, not only the product characteristics but also the product quality is important.In particular, the process capability is improved as an index representing the product quality, and the optimum value of the characteristic is improved, resulting in variations. As an index, it is important to reduce R representing the difference between the best point and the worst point of characteristics.

The process capability is the ability to produce a product within a defined standard limit, and the process capability is evaluated by a process capability index. For example, the process capability index (Cpl) for the lower limit standard is expressed by the following formula (1), and the larger the process capability index (Cpl) calculated from the following formula (1) is better in terms of quality assurance. .
Process capability index (Cpl) = (average value of characteristic−lower limit standard value) / (3 × standard deviation σ) (1)

  Here, from the above equation (1), as a method of increasing the process capability index (Cpl), a method of increasing the average value of the characteristics, decreasing the lower limit standard value, or decreasing the standard deviation σ can be considered. Here, the method of lowering the lower limit standard value is not an effective method because it means lowering the standard value of the product itself. In addition, the method for improving the optimum value of the characteristics has been actively performed by a method such as improving the composition ratio of the main component and the added subcomponent constituting the ferrite, but it is not easy.

  Therefore, as a method of increasing the process capability index (Cpl), a method of improving the manufacturing process at the time of mass production of the ferrite core and reducing the standard deviation σ and R, that is, the variation between products becomes important.

  Various attempts have been made for the purpose of improving the manufacturing process of the ferrite core, particularly the firing process. For example, Patent Document 1 discloses a manufacturing method characterized by firing Mn—Zn-based ferrite using fired granules having the same main component composition and the same additive composition as the Mn—Zn-based ferrite to be fired as an underlay. It is disclosed. According to this document, it is described that an Mn—Zn ferrite having a high magnetic permeability can be obtained because the above-mentioned firing method can prevent impurities from being mixed into the Mn—Zn ferrite.

  Patent Document 2 discloses a method of firing a Mn—Zn-based ferrite core molded body on a ferrite furnace material of the same material as the ferrite core, and the periphery of the Mn—Zn-based ferrite core molded body. A method of firing by surrounding with a furnace material made of ferrite of the same material as the core is disclosed. According to this document, the furnace material that is in direct contact with the ferrite core molded body at the time of firing is the same type of material as the ferrite core by the above firing method, so there is no reaction between them, and no foreign matter or foreign phase is generated. It is described.

  However, in the firing method described in Patent Document 1, since the ferrite granule is fired as an underlay, the ferrite core molded body and the ferrite granule are welded in the firing step, and once separated, it is very difficult to separate. It becomes a problem.

  Patent Document 2 describes that the material of the furnace material may be a material similar to that of the ferrite core molded body, and it is not necessary to strictly match the composition. It is unclear how much the composition should be matched to obtain.

JP-A 62-65970 JP-A-4-360503

  It is an object of the present invention to provide a ferrite core having excellent magnetic properties and a standard deviation σ and R of magnetic properties such as initial magnetic permeability and direct current superimposition characteristics, that is, small variations, and a method for manufacturing the same. Another object of the present invention is to increase the process capability index (Cpl) for the lower limit standard in mass production of ferrite cores by keeping the standard deviation σ and R of magnetic properties low.

  The present inventors use a firing jig composed of ferrite containing Zn when firing a compact composed of a ferrite raw material containing Zn, and in the ferrite raw material constituting the compact In order to complete the present invention, it is found that the object of the present invention can be achieved by setting the difference between the Zn content in the ferrite and the Zn content in the ferrite constituting the firing jig within a predetermined range. It came.

That is, the method for manufacturing a ferrite core according to the present invention is as follows.
Using a firing jig composed of a ferrite material containing a Zn oxide and / or a ferrite raw material containing a compound that becomes a Zn oxide after firing using a ferrite containing Zn oxide Having a firing step of firing,
A first molar ratio (M1; mol%) which is a molar ratio of a content of the oxide of the molded body and / or a compound which becomes an oxide of Zn after firing to the entire ferrite raw material, and the firing jig The difference (M2−M1) from the second molar ratio (M2; mol%), which is the molar ratio of the content of Zn oxide to the entire ferrite, is −5 mol% ≦ M2−M1 ≦ 5 mol in terms of ZnO. %.

  In the method for producing a ferrite core according to the present invention, preferably, a difference (M2-M1) between the first molar ratio and the second molar ratio is −3 mol% ≦ M2-M1 ≦ 3 mol in terms of ZnO. %.

  If the absolute value of the difference (M2−M1) between the Zn content (M1) of the compact and the Zn content (M2) of the firing jig is too large, the present inventors have found that the standard deviation of the magnetic properties It has been found that σ and R, that is, variation increases, the process capability index (Cpl) deteriorates, and as a result, the quality of the ferrite core decreases.

  That is, if the Zn content (M2) of the firing jig is too much or too little with respect to the Zn content (M1) of the molded body, the quality of the ferrite core will be degraded. I found out.

In the method for producing a ferrite core according to the present invention, preferably,
The firing jig has a structure surrounding the molded body;
The firing step is a step of firing in a state where the molded body is surrounded by the firing jig.

  In the method for producing a ferrite core according to the present invention, preferably, the compact is further composed of a Mn—Zn-based ferrite raw material containing a Mn oxide and / or a compound that becomes a Mn oxide after firing. Has been.

  In the method for manufacturing a ferrite core according to the present invention, preferably, the firing jig is made of Mn—Zn-based ferrite containing an oxide of Mn.

  In the method for producing a ferrite core according to the present invention, preferably, the firing step is a step of firing a plurality of the molded bodies simultaneously.

The ferrite core according to the present invention is manufactured by any one of the methods described above.
The ferrite core of the present invention can be used as a magnetic core for inductors, transformers, coils and the like used in various electronic devices.

  In the present invention, by setting the difference between the Zn content in the ferrite raw material constituting the compact and the Zn content in the ferrite constituting the firing jig within a predetermined range, the initial permeability And standard deviation σ and R of magnetic characteristics such as DC superimposition characteristics, that is, variations can be reduced. Therefore, it is possible to increase the process capability index (Cpl) for the lower limit specification of the initial magnetic permeability and DC superposition characteristics, and it is possible to manufacture a high quality ferrite core during mass production.

Similarly, according to the present invention, since the standard deviation σ and R of magnetic characteristics, that is, the variation can be reduced, the process capability index (Cpl) is increased even when the lower limit standard value is set to a high value. It becomes possible. In addition, the process capability index | exponent (Cpl) about a minimum specification is represented by following formula (1).
Process capability index (Cpl) = (average value of characteristic−lower limit standard value) / (3 × standard deviation σ) (1)

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a diagram showing an example of a ferrite core according to an embodiment of the present invention.
FIG. 2 is a sectional view of a firing jig in a state where a plurality of molded bodies are contained,
FIG. 3 is a diagram showing a method for firing a ferrite core according to an embodiment of the present invention,
4A to 4D are views showing a ferrite core firing jig according to an embodiment of the present invention,
FIG. 5 is a graph showing the relationship between the measured temperature and initial permeability in the examples of the present invention,
FIG. 6 is a graph showing the relationship between M2-M1 and the rate of change of the DC superposition characteristic (Δμ _Δ ) in the example of the present invention.

  Examples of the ferrite core of the present embodiment include the EE type, the FT type, the ET type and the like in addition to the toroidal type ferrite core 1 shown in FIG. The shape of the ferrite core is not limited to those listed here, and can be selected as appropriate.

Ferrite Core The ferrite core 1 of this embodiment is composed of a ferrite composition containing an oxide of Zn.
The ferrite composition containing a Zn oxide is not particularly limited, but a Mn—Zn ferrite containing a Mn oxide, a Ni—Zn ferrite containing a Ni oxide, and a Cu oxide. Cu-Zn based ferrite containing In the present embodiment, Fe oxide, Mn oxide, and Mn oxide are reduced because the initial permeability in a high frequency band is reduced and the increase in power loss when a power transformer is made is small and can be manufactured relatively inexpensively. It is preferably a Mn—Zn-based ferrite containing a Zn oxide.

Range of the content of Fe oxide is preferably 51.0～55.0Mol% in terms _{of Fe} 2 _{O 3,} more preferably from 52.0~54.0mol%.

  If the content of Fe oxide is too small, the magnetic permeability tends to decrease or the core loss tends to increase. If the content is too large, the magnetic permeability tends to decrease or the core loss tends to increase.

  The content range of the Mn oxide is preferably 18 to 42 mol%, more preferably 20 to 40 mol% in terms of MnO.

  If the content of the Mn oxide is too small, the Curie point tends to decrease to the actual use temperature range, and the characteristics as a ferrite tend to be lost. If too much, the permeability tends to decrease or the core loss tends to increase. .

  The range of the content of Zn oxide is preferably 4 to 27 mol%, more preferably 6 to 25 mol% in terms of ZnO.

  If the content of the Zn oxide is too small, the magnetic permeability tends to decrease or the core loss tends to increase. If the content is too large, the Curie point decreases to the actual use temperature range, and the properties as a ferrite are lost.

  In addition to the above-described oxide of Fe, oxide of Mn, and oxide of Zn, various additives can be contained within a range in which the object of the present invention can be achieved.

Ferrite core manufacturing method The ferrite core 1 of the present embodiment is prepared by weighing and mixing the raw material powders, calcining them, and crushing the calcined product to have a predetermined average particle size and particle size distribution, and then crushing It is manufactured by granulating the material, forming the granulated product into a predetermined shape, and then firing it.
Hereinafter, the manufacturing method will be specifically described.

  First, as starting materials, the above-described oxides or materials that become these oxides after firing are prepared. Examples of the compound that becomes an oxide after firing include carbonates, halogen compounds, oxalates, nitrates, hydroxides, organometallic compounds, and the like. If necessary, various compounds can be added as subcomponents in addition to the above-described oxides or raw materials that become these oxides after firing. The timing for adding such subcomponents is not particularly limited, and examples include the time of calcination and the time of pulverization after calcination.

  The prepared starting materials are weighed so as to be within the above composition range, and adjusted so as to be within the above range in the final composition after firing.

  The raw material mixture may contain inevitable impurity elements in the raw material. Examples of such elements include B, Al, Si, P, Ca, Cr, Co, Na, K, S, and Cl. In order to suppress the influence on power loss and magnetic characteristics, the weight ratio of these elements to the entire composition is preferably 500 ppm or less, and in particular, B and P are preferably 100 ppm or less.

  The weighed starting materials are mixed and calcined. Calcining causes thermal decomposition of raw materials, homogenization of ingredients, formation of ferrite, disappearance of ultrafine powder due to sintering and grain growth to an appropriate particle size, and converts the raw material mixture into a form suitable for the subsequent process. Done for. Calcination is performed in an oxidizing atmosphere, usually in air. The calcination temperature is preferably 800 to 1000 ° C., and the calcination time is preferably 1 to 3 hours.

  Next, the calcined material obtained above is pulverized to obtain a pulverized material. The pulverization is performed in order to produce a powder having appropriate sinterability by destroying the aggregation of the calcined material. When the calcined material forms a large lump, wet pulverization is performed using a ball mill or an attritor after coarse pulverization.

  Next, the pulverized material is granulated (granular) to obtain a granulated product. The granulation is performed in order to convert the pulverized material into aggregated particles having an appropriate size and convert it into a form suitable for molding. Examples of such a granulation method include a pressure granulation method and a spray drying method. The spray drying method is a method in which a commonly used binder such as polyvinyl alcohol is added to the pulverized material, and then atomized in a spray dryer and dried.

  Next, the granulated product is molded into a predetermined shape to obtain a molded body. Examples of the molding of the granulated product include dry molding, wet molding, and extrusion molding. The dry molding method is a molding method in which a granulated product is filled in a mold and compressed and pressed (pressed). The shape of the molded body is not particularly limited, and may be appropriately determined according to the application.

  Next, the molded body is fired to obtain a sintered body (the ferrite composition of the present embodiment). Firing is performed in order to obtain a dense sintered body by causing sintering in which the powder adheres at a temperature lower than the melting point between the powder particles of the compact including many voids. Firing is preferably performed at 1100 to 1450 ° C. for about 2 to 8 hours in a firing furnace heated at 50 to 300 ° C./hour.

  In the present embodiment, when firing, a firing jig composed of ferrite containing an oxide of Zn is used, and Zn oxide of the ferrite raw material constituting the molded body or oxidation of Zn after firing The difference between the content of the compound to be a product and the content of the Zn oxide of ferrite constituting the firing jig is set within a predetermined range.

  First molar ratio (M1; mol%), which is the molar ratio of the oxide of Zn in the compact or the compound that becomes Zn oxide after firing to the entire ferrite raw material, and the oxide of Zn in the firing jig The difference (M2−M1) from the second molar ratio (M2; mol%), which is the molar ratio of the content of Fe to the entire ferrite, is −5 mol% ≦ M2−M1 ≦ 5 mol% in terms of ZnO, preferably −3 mol% ≦ M2-M1 ≦ 3 mol%, and more preferably −2 mol% ≦ M2-M1 ≦ 2 mol%.

  By setting the difference between the Zn content (M1) in the ferrite raw material constituting the molded body and the Zn content (M2) in the ferrite constituting the firing jig within the above range, Standard deviations σ and R of magnetic characteristics such as magnetic susceptibility and DC superposition characteristics, that is, variations can be reduced. Further, by suppressing the standard deviations σ and R of the magnetic characteristics to be low, the process capability index (Cpl) for the lower limit standard of the initial magnetic permeability and the DC superimposition characteristics can be increased, and a high quality ferrite core at the time of mass production. Can be manufactured.

The present inventors have found that the difference (M2−) between the Zn content (M1) of the ferrite raw material composing the ferrite compact and the ferrite Zn content (M2) composing the firing jig. If the absolute value of M1) is too large, the standard deviations σ and R of the magnetic characteristics, that is, the variation increases, the process capability index (Cpl) deteriorates, and as a result, the quality of the ferrite core decreases. I found it.
That is, if the Zn content (M2) of the firing jig is too much or too little with respect to the Zn content (M1) of the molded body, the quality of the ferrite core will be degraded. I found out.

The reason for this is not necessarily clear, but is thought to be due to the following reason.
Usually, when baking a some molded object, it bakes, for example in the state which put the some molded object in the jig | tool 3 for baking shown in FIG. FIG. 2 is a cross-sectional view of a firing jig 3 composed of a box-shaped mortar and a top plate, and a plurality of molded bodies are in the firing jig 3. ing. At this time, in addition to the molded body 21 that is entirely surrounded by other molded bodies, the molded body 22 that is in direct contact with the firing jig 3 and the molded body 23 located on the outermost surface are unavoidable. It will exist.

  At this time, when the difference between the Zn content of the compact and the Zn content of the firing jig becomes large (for example, 5 mol% or more), the compact 22 that comes into contact with the firing jig 3, and It is considered that the magnetic properties of the molded body 23 located on the outermost surface deteriorate.

  That is, the compact 22 that is in contact with the firing jig 3 and the compact 23 that is located on the outermost surface are different from each other, and the Zn content near the surface changes before and after firing. As a result, a composition in which the Zn content in the vicinity of the surface of the sintered body after firing and the Zn content in the sintered body are different, that is, a deteriorated layer having a modified main component composition in the vicinity of the surface is formed. Therefore, it is considered that the magnetic characteristics are deteriorated.

  The reason why the Zn content in the vicinity of the surface of the molded body 22 in contact with the firing jig 3 is changed is that the surface of the molded body 22 and the firing jig 3 are contacted between the molded body 22 and the firing jig during firing. It is considered that this is because Zn moves to the tool 3 or from the firing jig 3 to the compact 22.

  The reason why the Zn content in the vicinity of the surface of the molded body 23 located on the outermost surface is changed is that Zn in the molded body 23 and the firing jig 3 is vaporized by firing, and is changed from the firing jig 3 to the molded body 23. Alternatively, it is considered that Zn moves from the molded body 23 to the firing jig 3.

  Due to the above-described causes, the magnetic properties of the molded body 22 in contact with the firing jig 3 and the molded body 23 located on the outermost surface are the same as the magnetic characteristics of the molded body 21 surrounded by other molded bodies. As a result, it is considered that the standard deviation σ and R of the magnetic characteristics in the mass production process, that is, the variation becomes large.

  The feature of the present invention is that the difference (M2) between the Zn content (M1) of the ferrite raw material composing the compact and the ferrite Zn content (M2) composing the firing jig. −M1) is within a predetermined range, that is, −5 mol% ≦ M 2 −M 1 ≦ 5 mol%, preferably −3 mol% ≦ M 2 −M 1 ≦ 3 mol%. By doing so, the above-mentioned problems can be solved, and in the mass production process, magnetic characteristics such as initial permeability and process capability index (Cpl) of DC superposition characteristics can be increased, and a high quality ferrite core is manufactured. can do.

  In particular, ferrite cores used for applications such as communication transformers such as LAN cards and high-frequency power transformers have a strong demand for miniaturization. However, when the ferrite core is reduced in size, the surface area of the ferrite core increases with respect to the volume of the ferrite core, so that the proportion of the altered layer formed on the ferrite core surface due to the movement of Zn increases in the ferrite core volume. Therefore, the influence becomes relatively large. According to the present invention, the problem of Zn migration can be effectively solved, so that the effect can be exhibited particularly when the ferrite core is downsized as well as the ferrite core that is not downsized.

  The composition other than the Zn content of the ferrite constituting the firing jig is not particularly limited as long as the Zn content is within the above range. For example, Mn—Zn ferrite, Ni-Zn based ferrite, Cu-Zn based ferrite and the like can be mentioned. In the present embodiment, it is preferable that the composition is the same as that of the molded body to be fired, and particularly preferable is a Mn—Zn-based ferrite containing an oxide of Fe, an oxide of Mn, and an oxide of Zn. It is.

  Although it does not specifically limit as said jig | tool for baking, For example, the setter 31 for baking shown in FIG. 3 can be used. FIG. 3 shows a method of firing by placing one or two or more molded bodies 2 on a setter 31 for firing. In the case of firing two or more molded bodies as shown in FIG. Further, the molded body may be fired in a state of being stacked on the firing setter 31.

  In addition, the firing jig preferably has a structure surrounding the molded body. As a firing jig having a structure surrounding the periphery of the molded body, for example, firing jigs shown in FIGS. 4A to 4D can be used. By making the firing jig used during firing surround the periphery of the compact, it is possible to effectively prevent the movement of Zn in the vicinity of the surface of the compact due to the vaporization of Zn during firing. Therefore, the firing setter 31 can sufficiently obtain the effects of the present invention, but from the viewpoint of further improving the magnetic properties, a firing jig having a structure surrounding the periphery of the molded body can be preferably used. .

  Fig.4 (a) is the baking jig comprised from a box-shaped mortar and a top plate. In the case of using this firing jig, one or two or more shaped bodies are put in a box-shaped bowl, and a top plate is placed on the bowl and the lid is covered and fired.

  FIG. 4B shows a firing jig composed of a disk-shaped bottom plate, a cylindrical side plate having a hollow in the center, and a disk-shaped top plate. In the case of using this firing jig, first, a cylindrical side plate having a hollow in the center is placed on a disc-shaped bottom plate to form a bowl, and a molded body is placed in this bowl. Put one or more. Next, a lid is placed by placing a disk-shaped top plate on the mortar and firing.

  FIG. 4 (c) is a firing jig composed of a disk-shaped bottom plate, a cylindrical side plate having a hollow in the center, and a disk-shaped top plate, as in FIG. 4 (b). There is a configuration in which a plurality of cylindrical side plates having a hollow in the center are stacked. Thus, by stacking a plurality of cylindrical side plates having a hollow in the center, the volume in the firing jig can be adjusted in accordance with the number of molded bodies to be fired.

FIG. 4D shows a firing jig including a bottom plate, four side plates, and a top plate. In the case of using this firing jig, first, four side plates are placed on the bottom plate to form a mortar, and one or more shaped bodies are put into the mortar. Next, the top plate is placed on the lid and fired.
Through such a process, the ferrite core according to the present embodiment is manufactured.

The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.
For example, the specific shape of the ferrite magnetic core manufactured by the manufacturing method of the present invention is not limited to that shown in FIG. 1, and various shapes can be adopted.

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

Example 1
The starting material of the main component and the subcomponent was prepared. Fe ₂ O ₃ , Mn ₃ O ₄ , and ZnO were used as starting materials for the main components. Further, SiO ₂ and CaO were used as starting materials for the subcomponents. These starting materials were weighed so that the composition after firing was as follows.
Fe ₂ O ₃ : 52 mol%
MnO: 30 mol%
ZnO: 18 mol%
SiO ₂ : 0.012% by weight
CaO: 0.030% by weight
The amounts of the main components Fe ₂ O ₃ , MnO, and ZnO are mol% with respect to the entire main components, and the addition amounts of the SiO ₂ and CaO as subcomponents are expressed in weight% with respect to the entire ferrite composition.

Next, these materials were blended, pre-fired, and pulverized under the following conditions to prepare a ferrite material.
-Pot for blending and grinding: Stainless steel ball mill pot used-Media for blending and grinding: Steel ball used-Blending time: 16 hours-Temporary firing conditions: 850 ° C, 3 hours-Grinding time after calcining: 8 hours 1.0 part by weight of polyvinyl alcohol as a binder was added to 100 parts by weight of the ferrite material and granulated to give a granulated product, which was pressure-molded to obtain a molded body. The molded body had a toroidal shape with an outer diameter of 10 mm, an inner diameter of 5 mm, and a height of 3 mm.

  Next, the obtained molded body was fired. The compact was fired using the firing setter shown in FIG. 3 with three compacts placed on the firing setter. The composition of the firing setter used was the composition shown in Table 1, and toroidal ferrite core samples 1 to 5 having different compositions of the firing setter used were prepared.

  The other firing conditions were a heating rate: 300 ° C./hour, a firing temperature: 1200 to 1400 ° C., a firing time: 3 hours, and a cooling rate: 200 ° C./hour. The atmosphere from the stable temperature to room temperature was set according to the equilibrium oxygen partial pressure of Mn—Zn ferrite.

The ferrite core samples 1 to 5 obtained above were wound with a copper wire (wire diameter 0.35 mm) 20 times, and the initial permeability μi was measured.
The initial permeability μi was measured under the conditions of 10 kHz, 10 mV, DC = 0 mA, and a temperature range of −50 to 120 ° C. by measuring an inductance value with a Precision LCR meter 4284A manufactured by Hewlett-Packard. The results are shown in FIG.

  The initial permeability μi was measured using a ferrite core sample fired in a state of direct contact with the firing setter among the ferrite core samples. That is, in this example, the ferrite core sample after sintering the compact 24 in FIG. 3 was used, and the influence of Zn movement on the contact surface between the compact and the firing setter was confirmed.

Evaluation 1
Table 1 shows the composition of the setter for firing used when firing the ferrite core samples 1 to 5, the first molar ratio (M1; mol%) which is the molar ratio of the ZnO content of the molded body, and the setter for firing. The difference (M2-M1) from the second molar ratio (M2; mol%), which is the molar ratio of the ZnO content, is shown. Moreover, the graph which shows the relationship between the measurement temperature in -50-120 degreeC of each sample and initial magnetic permeability in FIG. 5 is shown.

  From FIG. 5, it was confirmed that the sample 2 in which M2−M1 = 0 mol% had higher initial permeability than the other samples 1 and 3 to 5 at any measurement temperature. That is, Sample 1 in which the ZnO content (M2) of the setter for firing is larger than the ZnO content (M1) of the compact, and the ZnO content (M2) of the setter for firing is the ZnO content of the compact. Samples 3 to 5 less than the amount (M1) all resulted in lower initial permeability compared to sample 2 where M2−M1 = 0 mol%.

  Also, samples (for example, Sample 1 and Sample 5) having a large absolute value (M2−M1) of the difference (M2−M1) between the ZnO content (M1) of the compact and the ZnO content (M2) of the setter for firing are high temperatures. As a result, the initial permeability on the side became particularly low. In addition, in the sample 1 in which the ZnO content (M2) of the used setter for firing was larger than the ZnO content (M1) of the molded body, the width of the decrease in the initial permeability on the low temperature side was relatively small. However, it was a result inferior to the sample 2 which is M2-M1 = 0 mol%.

  From this result, the initial permeability decreases if the ZnO content (M2) of the firing setter used is greater or less than the ZnO content (M1) of the molded body, and the firing setter It was confirmed that when the absolute value of the difference (M2−M1) between the ZnO content (M2) and the ZnO content (M1) of the molded body increases, the decrease in the initial magnetic permeability also increases. Therefore, in order to prevent a decrease in the initial permeability after sintering of the compact that is fired in direct contact with the firing setter, the ZnO content (M2) of the firing setter used during firing and the compact It is preferable that the difference from the ZnO content (M1) is smaller.

Example 2
A toroidal shaped molded body was prepared in the same manner as in Example 1 except that the starting materials were prepared so that the final composition of the main components was Fe ₂ O ₃ : 53 mol%, MnO: 30 mol%, ZnO: 17 mol%. It produced and baked.
Firing was performed in a state where 300 molded body samples were placed in the firing jig shown in FIG. 4A and the molded body samples were surrounded by the firing jig. In this example, the ferrite core samples 6 to 15 shown in Table 2 were produced by changing the ZnO content (M2) of the firing jig. That is, the ferrite core samples 6 to 15 are samples having the same composition of the fired molded bodies and different ZnO contents (M2) in the firing jig used during firing. In Table 2, the second molar ratio (M2; mol%) which is the molar ratio of the ZnO content of the used firing jig and the first molar ratio (M1; which is the molar ratio of the ZnO content of the compact). mol%) (M2−M1). The other firing conditions were the same as in Example 1.

The ferrite core samples 6 to 15 obtained by firing were measured for initial permeability μi and DC superposition characteristics (incremental permeability: μ _Δ ). In this example, the initial permeability μi was measured for 100 samples of each of the ferrite core samples 6 to 15 arbitrarily from 300 samples under the same measurement conditions as in Example 1. The average and standard deviation σ were calculated and evaluated. Table 2 shows the results.

The DC bias characteristics mu _delta, in the same manner as in the measurement of the initial permeability .mu.i, each ferrite core samples 6-15, the copper wire (diameter 0.35 mm) for 20 times wrapping sample were measured.

The direct current superimposition characteristic μ _Δ is measured for each of the ferrite core samples 6 to 15 by using a precision LCR meter 4284A, with the frequency and amplitude of the alternating current component kept constant, under a predetermined direct current bias magnetic field (H = 33.2 A / m) Measurements were performed at -40 ° C, 0 ° C, 25 ° C and 85 ° C.

The direct current superimposition characteristic _μΔ was measured for a ferrite core sample obtained by firing in a state of direct contact with the firing jig, and the direct current superposition characteristic of the ferrite core sample 6 in which M2−M1 = 0 mol% was obtained. It was evaluated in; (% Δμ _Δ) the rate of change on the properties mu _delta. The results are shown in Table 3.

Evaluation 2
Table 2 shows the average initial permeability and standard deviation σ of each ferrite core sample at −40 ° C., 25 ° C. and 85 ° C., the process capability index (Cpl) of the lower limit standard for the initial permeability, and the process capability index ( Cpl) is the minimum value. In addition, the process capability index | exponent (Cpl) of the minimum specification about initial permeability was computed by following formula (1). A larger process capability index (Cpl) is preferred. Moreover, the minimum value of the process capability index (Cpl) was defined as the minimum value of the process capability index (Cpl) among the process capability indexes (Cpl) at −40 ° C., 25 ° C., and 85 ° C.
Process capability index (Cpl) = (average value of characteristic−lower limit standard value) / (3 × standard deviation σ) (1)

  From Table 2, the sample 6 of the example in which M2−M1 = 0 mol% is first compared with other samples 7 to 15 in which M2−M1 ≠ 0 mol% at −40 ° C., 25 ° C. and 85 ° C. The average value of the magnetic permeability was a good value. In addition, the standard deviation σ of the initial permeability of the sample 6 of the example in which M2−M1 = 0 mol% is M2−M1 ≠ 0 mol% at any temperature of −40 ° C., 25 ° C., and 85 ° C. Compared to Samples 7 to 15, the value was low, and good results were obtained with little variation in the samples produced under the same conditions.

  On the other hand, M2−M1 <0 mol%, that is, samples 7 to 10 in which the ZnO content (M2) of the used firing jig is smaller than the ZnO content (M1) of the molded body are absolute values of M2−M1. With the increase in the temperature, the average value of the initial permeability and the standard deviation σ tend to deteriorate at temperatures of −40 ° C., 25 ° C., and 85 ° C. This tendency was particularly remarkable at 25 ° C. and 85 ° C. In particular, the samples 9 and 10 of the comparative example in which M2−M1 = −6.8 and −9.0 mol% have a standard deviation σ exceeding 400 at each temperature of 25 ° C. and 85 ° C. As a result, the variation in the prepared sample was particularly large.

  In addition, in the sample where M2-M1 <0 mol%, the process capability index (Cpl) of the lower limit standard for the initial permeability is −40 ° C., 25 ° C., and 85 ° C. as the absolute value of M2-M1 increases. At each temperature, it tends to be a small value, and the samples 9 and 10 of the comparative examples in which M2−M1 = −6.8 and −9.0 mol% have a minimum value of the process capability index (Cpl) of 1. The result was less than 0.

  Similarly, samples 11 to 15 in which M2-M1> 0 mol%, that is, the ZnO content (M2) of the used firing jig is larger than the ZnO content (M1) of the molded body are increased in M2-M1. As a result, at each temperature of −40 ° C., 25 ° C., and 85 ° C., the average value of the initial permeability and the standard deviation σ tended to deteriorate. This tendency was particularly remarkable at 25 ° C. and 85 ° C. Among them, the samples 14 and 15 of the comparative example in which M2−M1 = 5.1 and 8.5 mol% have a standard deviation σ exceeding 350 at 85 ° C., and the variation in the sample manufactured under the same conditions is The result was particularly large.

  In addition, in the sample where M2-M1> 0 mol%, the process capability index (Cpl) of the lower limit standard for the initial magnetic permeability is at −40 ° C., 25 ° C. and 85 ° C. as M2-M1 increases. As a result, the samples 14 and 15 of the comparative example in which M2−M1 = 5.1 and 8.5 mol% tend to be a small value, and the minimum value of the process capability index (Cpl) is less than 1.0. It became.

  From this result, in order to reduce the standard deviation σ of the magnetic properties of the ferrite core, particularly the standard deviation σ of the initial permeability, and improve the process capability index (Cpl), M2−M1 is −5 mol% ≦ M2−. It was desirable that M1 ≦ 5 mol%, and it was confirmed that preferably −3 mol% ≦ M2-M1 ≦ 3 mol%.

Evaluation 3
Table 3 shows the value of M2-M1 of each ferrite core sample and the change rate (Δμ _Δ ) of the DC superposition characteristics at −40 ° C., 0 ° C., 25 ° C., and 85 ° C. FIG. 6 is a graph showing the relationship between M2-M1 and the rate of change (Δμ _Δ ) in the DC superimposition characteristics.
In this example, the direct current superposition characteristics of the sample having the same composition are measured, and among the measured samples, the sample having the best characteristic (μ _Δ is high), that is, the sample having the best characteristic and the most characteristic When a low ( _μΔ is low) sample, that is, a sample with the worst point of the characteristics was examined, the sample with the best characteristics had the same characteristics as the sample 6 with M2−M1 = 0 mol%, and the characteristics It was confirmed that the worst sample was a sample fired in direct contact with the firing jig. Therefore, the direct current of the sample fired in a state of direct contact with the firing jig, that is, the worst point sample of the characteristic, and the sample 6 with M2−M1 = 0 mol% is set as the direct current superposition characteristic change rate (Δμ _Δ ). Based on the measurement result of the superimposition characteristic, it calculated by the following formula (2).
Δμ _Δ = ((μ _Δ (sample of worst point of characteristic) −μ _Δ (sample 6)) / μ _Δ (sample 6)) × 100 (2)
Note that when the value of change rate (Δμ _Δ ) of the DC superimposition characteristic is small, it is considered that the value of R representing the difference between the best point and the worst point of the characteristic is also small as a variation index.

From Table 3, Samples 7, 8, and 11 to 13 of the examples satisfying −5 mol% ≦ M2−M1 ≦ 5 mol% have DC superposition characteristics at temperatures of −40 ° C., 0 ° C., 25 ° C., and 85 ° C. The rate of change (Δμ _Δ ) was low and good results were obtained. In particular, Samples 7, 11 and 12 satisfying −3 mol% ≦ M 2 −M 1 ≦ 3 mol% have a DC superposition characteristic change rate (Δμ) at any temperature of −40 ° C., 0 ° C., 25 ° C. and 85 ° C. The absolute value of _Δ ) was 10% or less, and particularly good results were obtained.

On the other hand, the samples 9 and 10 of the comparative examples with M2−M1 = −6.8 and −9.0 mol% have the DC superposition characteristics at any temperature of −40 ° C., 0 ° C., 25 ° C. and 85 ° C. The rate of change (Δμ _Δ ) was less than −10%. Similarly, in the samples 14 and 15 of the comparative example in which M2−M1 = 5.1 and 8.5 mol%, the change rate (Δμ _Δ ) of the DC superposition characteristics exceeds −10% at 0 ° C. and 25 ° C. It became.

From this result, in order to reduce the rate of change of the DC superposition characteristics (Δμ _Δ ), that is, to reduce the deterioration of the DC superposition characteristics of the ferrite core sample obtained by firing in direct contact with the firing jig. In addition, M2-M1 is desirably −5 mol% ≦ M2-M1 ≦ 5 mol%, and it was confirmed that preferably −3 mol% ≦ M2-M1 ≦ 3 mol%. In this embodiment, as the absolute value of M2-M1 increases, the rate of change of the DC superimposition characteristic (Δμ _Δ ) deteriorates, and the tendency of the deterioration of the DC superimposition characteristic to be remarkable is confirmed. 6 is clear.

Note that in the sample 9,10,14,15 comparative example, in particular sample degradation was greater initial permeability μi and DC bias characteristics mu _delta were samples in direct contact with the firing jig. When the surface of the ferrite core was analyzed for these samples, an increase or decrease in ZnO on the ferrite core surface was confirmed.

The final composition of Reference Experiment main component _{Fe 2 O 3: 52mol%,} MnO: 26mol%, ZnO: and 22 mol%, in the firing step, except that the firing setter used was alumina setters, Example 1 In the same manner, toroidal ferrite core samples 16 to 18 were produced. With respect to the manufactured ferrite core samples 16 to 18, the initial permeability μi was measured under the same conditions as in Example 1. The setter made of alumina is a setter generally used conventionally. In this reference experimental example, the influence of Zn movement when a jig not made of ferrite was used as a firing jig was examined. In addition, the alumina setter used in this reference experimental example contained almost no Zn.

  In this reference experimental example, an alumina setter was used as the firing setter 31 shown in FIG. 3, and the sintered samples of the compacts 24, 25, and 26 were used as ferrite core samples 16, 17, and 18, respectively.

  Table 4 shows the initial permeability μi of the ferrite core samples 16, 17, and 18 in this reference experimental example and the initial permeability value of the ferrite core sample 17 having the best initial permeability as 100%. The percentage of initial permeability of each ferrite core sample is shown as a percentage.

  As is apparent from Table 4, the initial permeability of the ferrite sample 16 which is a sintered body of the molded body 24 fired in direct contact with the alumina setter is 66% lower than that of the ferrite core sample 17. became. From this result, it was confirmed that the initial magnetic permeability was deteriorated by firing in the state of being in direct contact with the alumina setter.

  Similarly, the initial permeability of the ferrite core sample 18, which is a sintered body of the molded body 26 fired in the state positioned in the uppermost stage, was a low value of 74% with respect to the ferrite core sample 17. From this result, it was confirmed that the initial magnetic permeability was deteriorated not only in the molded body fired in the state of being in direct contact with the alumina setter but also in the molded body fired in the state positioned at the uppermost stage.

  Further, when the surface of the ferrite core was analyzed for Samples 16 and 18 in which the initial permeability μi was greatly deteriorated, a decrease in ZnO and an increase in impurities on the ferrite core surface were confirmed. That is, at the time of firing, not only the movement of Zn on the contact surface with the firing jig but also the movement of Zn by vaporization of Zn occurs, and this movement of Zn has a great influence on the magnetic properties of the ferrite core. I was able to confirm.

FIG. 1 is a diagram showing an example of a ferrite core according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the firing jig in a state where a plurality of molded bodies are contained. FIG. 3 is a diagram showing a method for firing a ferrite core according to an embodiment of the present invention. 4A to 4D are views showing a ferrite core firing jig according to an embodiment of the present invention. FIG. 5 is a graph showing the relationship between the measured temperature and the initial permeability in the example of the present invention. FIG. 6 is a graph showing the relationship between M2-M1 and the rate of change of the DC superposition characteristic (Δμ _Δ ) in the example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ferrite core 2 ... Molded body 21 ... Molded body surrounded by other molded bodies 22 ... Molded body in contact with firing jig 23 ... Molded body positioned on outermost surface 24-26 ... Toroidal shape Molded body 3 ... Firing jig 31 ... Firing setter

Claims (7)

Using a firing jig composed of a ferrite material containing a Zn oxide and / or a ferrite raw material containing a compound that becomes a Zn oxide after firing using a ferrite containing Zn oxide Having a firing step of firing,
A first molar ratio (M1; mol%) which is a molar ratio of a content of the oxide of the molded body and / or a compound which becomes an oxide of Zn after firing to the entire ferrite raw material, and the firing jig The difference (M2−M1) from the second molar ratio (M2; mol%), which is the molar ratio of the content of Zn oxide to the entire ferrite, is −5 mol% ≦ M2−M1 ≦ 5 mol in terms of ZnO. %. A method for producing a ferrite core, wherein   2. The method for producing a ferrite core according to claim 1, wherein a difference (M2−M1) between the first molar ratio and the second molar ratio is −3 mol% ≦ M2−M1 ≦ 3 mol% in terms of ZnO. The firing jig has a structure surrounding the molded body;
3. The method for manufacturing a ferrite core according to claim 1, wherein the firing step is a step of firing in a state where the compact is surrounded by the firing jig.   The ferrite according to any one of claims 1 to 3, wherein the compact is further composed of a Mn-Zn ferrite raw material containing a Mn oxide and / or a compound that becomes a Mn oxide after firing. Core manufacturing method.   The method for manufacturing a ferrite core according to any one of claims 1 to 4, wherein the firing jig is further composed of a Mn-Zn ferrite containing an Mn oxide.   The method for producing a ferrite core according to any one of claims 1 to 5, wherein the firing step is a step of firing a plurality of the molded bodies simultaneously.   A ferrite core manufactured by the method according to claim 1.

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