MnZn ferrite

Abstract

The present invention provides an MnZn ferrite applicable to electronic components such as pulse transformers. When a DC magnetic field of 25 A / m is applied in the temperature range of -40 to 85 °C, the above MnZn ferrite can obtain a higher incremental permeability. The MnZn ferrite of the present invention is composed of a basic component, an auxiliary component, and inevitable impurities. The basic component is: iron: 52.5 to 53.5 mol% in terms of Fe2O3 conversion; zinc: 16.4 to 18.4 mol% in terms of ZnO conversion; and manganese: the balance in terms of MnO conversion. Relative to the above basic component, the auxiliary component is: Si: 30 to 100 mass ppm in terms of SiO2 conversion; Ca: 50 to 160 mass ppm in terms of CaO conversion; Co: 1500 to 3500 mass ppm in terms of Co3O4 conversion; Nb: 100 to 600 mass ppm in terms of Nb2O5 conversion; and V: 100 to 600 mass ppm in terms of V2O5 conversion. The total content of the above Nb and the above V is 200 to 900 mass ppm in terms of Nb2O5 and V2O5 conversion.

Description

Technical Field

[0001] The present invention relates to an MnZn ferrite suitable for electronic components such as pulse transformers. Even when a DC magnetic field of 25 A / m is applied in the temperature range of -40 to 85 °C, the above MnZn ferrite can obtain a high incremental permeability. Background Art

[0002] In transformers of Ethernet (registered trademark) devices, for the purpose of achieving impedance matching at input and output terminals or maintaining electrical insulation, etc., pulse transformers using soft magnetic materials in the magnetic core are used. It is required that the pulse transformer has a high inductance, that is, a high incremental permeability when a DC magnetic field is applied in a wide temperature range of -40 to 85 °C. This incremental permeability is a value representing the magnetic permeability (ease of magnetization) of the magnetic core in a state where a magnetic field is applied. In addition, according to the literature, the term effective permeability is sometimes used instead of incremental permeability, but the two have the same meaning, so they will be unified as incremental permeability hereafter.

[0003] Among the above soft magnetic materials, toroidal MnZn ferrites are usually used in the magnetic core. Among many soft magnetic materials, MnZn ferrites are particularly likely to obtain high magnetic permeability and high inductance. In addition, compared with metallic magnetic materials such as amorphous metals, MnZn ferrites have the advantages of being inexpensive, etc.

[0004] Here, since MnZn ferrites are oxide magnetic materials, they have the characteristic that their magnetic properties change significantly with temperature. Therefore, compared with metallic magnetic materials, they have the disadvantage of being difficult to obtain stable magnetic properties in a wide temperature range.

[0005] In addition, when a pulse transformer is used in a line terminal device, etc., it is sometimes installed outdoors. Therefore, the MnZn ferrite used for pulse transformers needs to have a high initial permeability in a wide temperature range from low temperature to high temperature, especially in the temperature range of -40 to 85 °C.

[0006] Furthermore, in digital communication devices, sometimes the pulse transformer operates by applying a DC magnetic field in a state where it is magnetized by the change in the positive and negative balance of the pulse voltage being transmitted. Even in a state where such a DC magnetic field is applied, high incremental permeability is required for signal conversion. In addition, in such applications, the magnitude of the applied DC magnetic field varies depending on the required inductance specifications, usage methods, etc., and high incremental permeability is required at room temperature. In addition, in most cases, MnZn ferrite cores of general sizes are used in a state where a DC magnetic field of up to 25 A / m is applied.

[0007] Here, the MnZn ferrite used in such fields is based on Fe 2 O 3, composed mainly of ZnO and MnO, exhibits high magnetic permeability in the main components where the magnetic anisotropy constant and magnetostriction constant are 0. Therefore, this MnZn ferrite can be used as a small or thin magnetic core for transformers, noise filters, etc. That is, although there is a problem that it is difficult to obtain stable magnetic properties in a wide temperature range, a method has been proposed to achieve a high incremental magnetic permeability in the temperature range of -40 to 85 °C (or -40 to 100 °C) under the condition of applying a DC magnetic field.

[0008] For example, in Patent Document 1, a MnZn ferrite is proposed in which the incremental magnetic permeability is 2000 or more when a DC magnetic field of 33 A / m higher than normal is applied in the temperature range of -40 to 85 °C. In addition, in Patent Document 2, a MnZn ferrite is proposed in which the incremental magnetic permeability is 2000 or more when a DC magnetic field of about 25 A / m is applied in the temperature range of -40 to 100 °C.

[0009] In addition, in Patent Document 1, the following method is proposed: in the composition of MnZn ferrite (Fe 2 O 3 : 52.0 to 53.0 mol%, ZnO: 22.0 to 23.0 mol%, MnO: the balance) that can obtain a high initial magnetic permeability, SiO 2 and CaO are added simultaneously, and the content of Cr 2 O 3 as an impurity inevitably mixed due to the raw material of iron oxide is reduced to an extremely small amount, thereby controlling the average crystal grain size of the MnZn ferrite within an appropriate range, and obtaining a MnZn ferrite with an initial magnetic permeability of 10000 or more (at 23 °C) and an incremental magnetic permeability of 2000 or more (-40 to 85 °C, when applying a DC magnetic field of 33 A / m).

[0010] In Patent Document 2, the following method is proposed: in the main component composition of MnZn ferrite (Fe 2 O 3 : 51.0 to 52.0 mol%, ZnO: 18.5 to 22.0 mol%, MnO: the balance), it contains 0.5 to 1.5 wt% of TiO 2 as an auxiliary component and trace amounts of SiO 2 , CaO, V 2 O 5 , Nb 2 O 5 of any several kinds, and under the conditions of a residual magnetic flux density of 50 mT or less and a magnetic bias at room temperature of 135 mT (presumably applying a DC magnetic field of 25 A / m), a MnZn ferrite with a relative magnetic permeability of 2100 or more in the range of -40 to 100 °C and less deterioration of the DC superposition characteristics is obtained.

[0011] In Patent Document 3, the following method was proposed: In the basic composition of MnCoZn ferrite (Fe 2 O 3 : 51.0 to 53.0 mol%, ZnO: 13.0 to 18.0 mol%, CoO: 0.04 to 0.60 mol%, MnO: the balance), an appropriate amount of SiO 2 and CaO are added simultaneously, and TiO 2 is used as an essential component, and the contents of P and B, which are inevitably mixed as impurities due to the raw materials of iron oxide, are reduced to extremely low levels. Thus, an MnCoZn ferrite is obtained in which the incremental permeability shows a value of 2300 or more when a DC magnetic field of 33 A / m is applied in the entire temperature range of -40 to 85°C. In addition, in Patent Document 3, since it contains Co, which exhibits the effect of flattening the temperature characteristics of the incremental permeability, a relatively high Curie temperature of 140 to 210°C can be obtained in a wide composition range. Therefore, a relatively high incremental permeability can be obtained even at low temperature (-40°C) and high temperature (85°C).

[0012] In addition, Patent Documents 4 and 5 disclose MnZn ferrites having a composition containing Ti and Bi.

[0013] Prior Art Documents

[0014] Patent Documents

[0015] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-166663;

[0016] Patent Document 2: Japanese Patent Application Laid-Open No. 2004-319811;

[0017] Patent Document 3: Japanese Patent Application Laid-Open No. 2008-143745;

[0018] Patent Document 4: Japanese Patent Application Laid-Open No. 2022-156991;

[0019] Patent Document 5: Chinese Patent Application Publication No. 1686927. Summary of the Invention

[0020] Problems to be Solved by the Invention

[0021] However, the MnZn ferrite obtained by the method described in Patent Document 1 does not contain an auxiliary component such as Co that flattens the temperature characteristics of the incremental permeability. Therefore, even under the condition of applying a mild DC magnetic field of 25 A / m, there is a problem that the incremental permeability at low temperature (-40 °C) and high temperature (85 °C) is lower than that near room temperature. In addition, in the composition range described in Patent Document 1, the Curie temperature is as low as about 120 to 130 °C, so there is inevitably a problem that the incremental permeability in the high temperature range above 85 °C is low.

[0022] In addition, the MnZn ferrite obtained by the method described in Patent Document 2 also does not contain an auxiliary component such as Co that flattens the temperature characteristics of the incremental permeability. Therefore, there is a problem that the incremental permeability at low temperature (-40 °C) and high temperature (85 °C) is lower than that near room temperature. In addition, in the composition range described in Patent Document 2, since the Curie temperature is as low as 110 to 150 °C or lower, there is also a problem that the incremental permeability in the high temperature range above 85 °C is low.

[0023] Furthermore, in the invention described in Patent Document 3, a large amount of SiO 2 , CaO, ZrO 2 , Ta 2 O 5 , HfO 2 , Nb 2 O 5 and other auxiliary components are included. Therefore, it is considered that even when a DC magnetic field of 25 A / m is applied, the incremental permeability in the range of -40 to 85 °C will decrease as a whole.

[0024] Here, the incremental permeability that can be guaranteed by the MnZn ferrites shown in these documents in the range of -40 to 85 °C is mostly around 2300. Although its characteristics are at a level without problems when used in a general pulse transformer, when manufacturing multiple ferrite cores, if the deviation of characteristics is considered, there is a problem of low pass rate of the cores. In order to meet the requirements such as improving the pass rate of the cores, reducing the number of turns of the copper wire, or further miniaturizing the cores, it is necessary to guarantee a higher incremental permeability, and the ability to cope with such problems is insufficient.

[0025] As in the inventions described in Patent Documents 4 and 5, if Ti is contained, the temperature characteristics of the incremental permeability μ dc under the application of a DC magnetic field shift to the low temperature side, and the incremental permeability at high temperature decreases. In addition, if Bi is contained, the initial permeability without the application of a DC magnetic field increases, but the effective permeability μ decreases under the application of a DC magnetic field.

[0026] The present invention has been developed in view of the above circumstances, and an object of the present invention is to provide an MnZn-based ferrite suitable for electronic components such as pulse transformers. When a DC magnetic field of 25 A / m is applied in the temperature range of -40 to 85 °C, the above MnZn-based ferrite can obtain a higher incremental permeability.

[0027] Means for solving the problem

[0028] The present invention provides an MnZn-based ferrite having an incremental permeability of 2800 or more when a DC magnetic field is applied at 25 A / m in the temperature range of -40 to 85 °C. This incremental permeability needs to be increased over a wide temperature range, and the incremental permeability is particularly likely to decrease near -40 °C and near 85 °C. Therefore, in the present invention, the incremental permeability is 2800 or more near -40 °C and near 85 °C. Further, the temperature at which the incremental permeability takes a maximum value is preferably set in the range of 10 to 50 °C. In addition, the MnZn-based ferrite preferably has an incremental permeability of 3700 or more in the temperature range of about 0 to 60 °C and an incremental permeability of 4100 or more in the temperature range of 23 to 40 °C. In addition, in the present invention, the values of the initial permeability and the incremental permeability are expressed as ratios (relative permeabilities) to the permeability μo of vacuum.

[0029] That is, the main configuration of the present invention is as follows.

[0030] [1] An MnZn-based ferrite composed of a basic component, an auxiliary component, and inevitable impurities. When the total of iron, zinc, and manganese is counted as 100 mol% in terms of Fe 2 O 3 , ZnO, and MnO conversions, the above basic components are: iron: 52.5 to 53.5 mol% in terms of Fe 2 O 3 conversion; zinc: 16.4 to 18.4 mol% in terms of ZnO conversion; and manganese: the balance in terms of MnO conversion. Relative to the above basic components, the above auxiliary components are: Si: 30 to 100 mass ppm in terms of SiO 2 conversion; Ca: 50 to 160 mass ppm in terms of CaO conversion; Co: 1500 to 3500 mass ppm in terms of Co 3 O 4 conversion; Nb: 100 to 600 mass ppm in terms of Nb 2 O 5 conversion; and V: 100 to 600 mass ppm in terms of V 2 O 5 conversion. The total content of the above Nb and the above V is in terms of Nb 2 O 5 and V 2 O5 The conversion is 200 to 900 mass ppm.

[0031] [2] The MnZn ferrite according to [1] above, wherein the incremental permeability of the MnZn ferrite when a DC magnetic field of 25 A / m is applied in the temperature range of -40 to 85 °C is 2800 or more, and the temperature showing the maximum value of the incremental permeability is in the range of 10 to 50 °C.

[0032] [3] The MnZn ferrite according to [2] above, wherein the incremental permeability of the MnZn ferrite when a DC magnetic field of 25 A / m is applied in the temperature range of 0 to 60 °C is 3700 or more, and further, the incremental permeability of the MnZn ferrite when a DC magnetic field of 25 A / m is applied in the temperature range of 23 to 40 °C is 4100 or more.

[0033] Advantages of the Invention

[0034] According to the present invention, an MnZn ferrite having an incremental permeability of 2800 or more near -40 °C and 85 °C in the temperature range of -40 to 85 °C when a DC magnetic field of 25 A / m is applied can be obtained. Description of the Drawings

[0035] Figure 1 It is a graph showing the influence of the Fe 2 O 3 content on the incremental permeability (μ dc ).

[0036] Figure 2 It is a graph showing the influence of the ZnO content on the incremental permeability (μ dc ).

[0037] Figure 3 It is a graph showing the influence of the SiO 2 content on the incremental permeability (μ dc ).

[0038] Figure 4 It is a graph showing the influence of the CaO content on the incremental permeability (μ dc ).

[0039] Figure 5 It is a graph showing the influence of the Co 3 O 4 content on the incremental permeability (μ dc ).

[0040] Figure 6 It is a graph showing the influence of the Nb 2 O5 Content and V 2 O 5 Content on the incremental permeability (μ dc ).

[0041] Figure 7 Is a graph showing the values of the incremental permeability (μ dc ) at each measurement temperature of Comparative Example 13, Comparative Example 14, and Comparative Example 15. Detailed Description of the Invention

[0042] Hereinafter, an embodiment of the present invention will be described in detail. In addition, the embodiment described below is an example of embodying the present invention, and does not limit the configuration of the present invention by this specific example.

[0043] (MnZn ferrite)

[0044] The MnZn ferrite is composed of a basic component, an auxiliary component, and inevitable impurities. The basic component is composed of iron, zinc, and manganese, and the above substances exist in the form of oxides. In addition, the following mol% is the composition ratio of the basic component.

[0045] [Incremental Permeability]

[0046] First, each component will be described from the viewpoint of incremental permeability.

[0047] In the present invention, iron is contained in the range of 52.5 to 53.5 mol% in terms of Fe 2 O 3 . The content of this iron is preferably 52.6 mol% or more, more preferably 52.7 mol% or more in terms of Fe 2 O 3 . On the other hand, the content of iron is preferably 53.3 mol% or less, more preferably 53.1 mol% or less in terms of Fe 2 O 3 . In the present invention, the reason for setting the content of iron to be 52.5 to 53.5 mol% in terms of Fe 2 O 3 is as follows. That is, because: when the content of iron is around 53.0 mol% in terms of Fe 2 O 3 , the magnetostriction constant λ = 0, and the incremental permeability when a DC magnetic field of 25 A / m is applied is the highest. On the other hand, when the content of iron is less than 52.5 mol% or more than 53.5 mol% in terms of Fe 2 O 3 , the incremental permeability decreases significantly. In addition, when the content of iron is less than 52.5 mol% or more than 53.5 mol% in terms of Fe 2 O 3The more the transducer deviates from 53.0 mol%, the more the core expands and contracts due to the applied magnetic field, thus applying more stress to the core itself, hindering the movement of magnetic domain walls more, and significantly reducing the incremental permeability.

[0048] It is known that the Curie temperature and the secondary peak of MnZn ferrites vary according to the ratio of iron to zinc. In the present invention, zinc is contained in an amount of 16.4 to 18.4 mol% in terms of ZnO conversion. In addition, the content of zinc is preferably 16.5 mol% or more, more preferably 16.6 mol% or more in terms of ZnO conversion. On the other hand, the content of zinc is preferably 18.3 mol% or less, more preferably 18.2 mol% or less in terms of ZnO conversion. Setting the content of zinc in the range of 16.4 to 18.4 mol% in terms of ZnO conversion is because: the Curie temperature in this range is about 160 to 190 °C, and good incremental permeability can be obtained even at high temperature (85 °C). In addition, it is also because: if the content of zinc is less than 16.4 mol% in terms of ZnO conversion, even if the Curie temperature becomes higher, the initial permeability itself will decrease, so the incremental permeability when applying a DC magnetic field will also decrease. On the other hand, it is because: if the content of zinc is more than 18.4 mol% in terms of ZnO conversion, the Curie temperature will decrease, so the incremental permeability at high temperature (85 °C) will decrease.

[0049] Manganese is the balance of the basic components. It is preferably contained in the range of 28.0 to 31.0 mol% in terms of MnO conversion. In addition, in terms of MnO conversion, the content of manganese is more preferably 28.5 mol% or more, and more preferably 30.7 mol% or less.

[0050] That is, the basic components of the MnZn ferrite make the total of iron, zinc, and manganese 100 mol% in terms of Fe 2 O 3 , ZnO, and MnO conversion.

[0051] Next, the auxiliary components will be described. The MnZn ferrite of the present invention preferably contains Si, Ca, Co, Nb, and V as auxiliary components in addition to the above basic components and is composed of these. These exist in the form of oxides such as SiO 2 , CaO, Co 3 O 4 , Nb 2 O 5 , and V 2 O 5 . In addition, the content of the auxiliary components is expressed in mass ppm relative to the basic components.

[0052] Both Si and Ca are elements that promote grain boundary formation, inhibit grain growth, and increase resistivity. By containing an appropriate amount of Si and Ca, the decrease in the initial permeability can be suppressed overall in a relatively wide temperature range of -40 to 85°C, and the incremental permeability in the low-temperature range and high-temperature range can be increased when a DC magnetic field is applied. Thus, a high incremental permeability can be obtained in a relatively wide temperature range of -40 to 85°C.

[0053] It is important to contain Si in the range of 30 to 100 mass ppm in terms of SiO 2 conversion. Si is preferably contained in an amount of 40 mass ppm or more and preferably 95 mass ppm or less. In addition, it is important to contain Ca in the range of 50 to 160 mass ppm in terms of CaO conversion. Ca is preferably contained in an amount of 90 mass ppm or more and preferably 150 mass ppm or less. When Si is less than 30 mass ppm in terms of SiO 2 conversion or Ca is less than 50 mass ppm in terms of CaO conversion, the incremental permeability in the low-temperature range and high-temperature range decreases, and an incremental permeability of 2800 or more cannot be obtained in a relatively wide temperature range of -40 to 85°C. On the other hand, when Si is more than 100 mass ppm in terms of SiO 2 conversion or Ca is more than 160 mass ppm in terms of CaO conversion, since the initial permeability decreases significantly, the incremental permeability also decreases significantly, and an incremental permeability of 2800 or more cannot be obtained in a relatively wide temperature range of -40 to 85°C.

[0054] Co is an effective component for improving the temperature dependence of the magnetic properties of MnZn ferrites. By containing an appropriate amount of Co, the change in the incremental permeability with respect to temperature when a DC magnetic field is applied becomes smaller, and the incremental permeability in the low-temperature range and high-temperature range increases. However, Co also has the effect of shifting the temperature dependence of the permeability to the low-temperature side. Therefore, if the Co content is too low or too high, the balance of the permeability in the low-temperature range and high-temperature range is disrupted, the incremental permeability in the low-temperature range or high-temperature range decreases, and furthermore, a high incremental permeability cannot be obtained in a relatively wide temperature range of -40 to 85°C.

[0055] It is important to contain Co in the range of 1500 to 3500 mass ppm in terms of Co 3 O 4 conversion. In addition, in terms of Co 3 O 4 conversion, Co is preferably contained in an amount of 1800 mass ppm or more, more preferably 2000 mass ppm or more. On the other hand, in terms of Co 3 O 4 conversion, Co is preferably contained in an amount of 3000 mass ppm or less, more preferably 2900 mass ppm or less. In terms of Co3 O 4 When the content of Co is less than 1500 mass ppm, the maximum point of the temperature characteristic of the incremental permeability shifts to the high-temperature side, the incremental permeability at high temperatures improves, but the characteristics at low temperatures deteriorate. Furthermore, an incremental permeability of 2800 or more cannot be obtained in a wide temperature range of -40 to 85°C. On the other hand, when Co 3 O 4 When the content of Co is greater than 3500 mass ppm, the maximum point of the temperature characteristic of the incremental permeability shifts to the low-temperature side, the low-temperature characteristics of the incremental permeability improve, but the high-temperature characteristics deteriorate. Furthermore, an incremental permeability of 2800 or more cannot be obtained in a wide temperature range of -40 to 85°C.

[0056] Nb and V are elements that have the effect of suppressing the formation of coarse grains by coexisting, thereby obtaining fine and uniform grains and increasing the resistivity. The incremental permeability when applying a DC magnetic field can be increased by containing an appropriate amount of Nb and V.

[0057] Importantly, Nb 2 O 5 is contained in the range of 100 to 600 mass ppm in terms of conversion. Nb is preferably contained at 200 mass ppm or more and preferably at 575 mass ppm or less. In addition, importantly, V 2 O 5 is contained in the range of 100 to 600 mass ppm in terms of conversion. V is preferably contained at 200 mass ppm or more and preferably at 400 mass ppm or less.

[0058] Furthermore, importantly, the total content of Nb and V in the MnZn-based ferrite is in the range of 200 to 900 mass ppm in terms of Nb 2 O 5 and V 2 O 5 in terms of conversion. In terms of Nb 2 O 5 and V 2 O 5 in terms of conversion, the total content of Nb and V is preferably 250 mass ppm or more and preferably 750 mass ppm or less.

[0059] In the case where the content of Nb is less than 100 mass ppm in terms of Nb 2 O 5 in terms of conversion, and in the case where the content of V 2 O 5In the case where the conversion meter V is less than 100 mass ppm, or in the case where the total content of Nb and V is less than 200 mass ppm, the generation of coarse grains cannot be sufficiently suppressed, and the resistivity is also low. Therefore, the incremental permeability when applying a DC magnetic field also decreases. On the other hand, in the case where the conversion meter Nb is greater than 600 mass ppm, in the case where the conversion meter V is greater than 600 mass ppm, or in any one of the cases where the total content of Nb and V is greater than 900 mass ppm, the grains are refined, the resistivity also becomes high, so it becomes difficult for magnetic domain walls to move, and the initial permeability decreases. The incremental permeability when applying a DC magnetic field also decreases accordingly. 2 O 5 In the case where the conversion meter Nb is greater than 600 mass ppm, in the case where the conversion meter V 2 O 5 is greater than 600 mass ppm, or in any one of the cases where the total content of Nb and V is greater than 900 mass ppm, the grains are refined, the resistivity also becomes high, so it becomes difficult for magnetic domain walls to move, and the initial permeability decreases. The incremental permeability when applying a DC magnetic field also decreases accordingly.

[0060] [Defect rate caused by abnormal grain growth]

[0061] Next, from the perspective of the defect rate caused by abnormal grain growth, each component will be described. Generally, auxiliary components such as Si or Ca added to MnZn ferrites not only have a great influence on the properties, but also have a great influence on the formation of grains. In the case of containing an appropriate amount of auxiliary components, the auxiliary components segregate at the grain boundaries, thereby having the functions of suppressing the coarsening of grains, homogenizing the crystal structure, and increasing the resistivity. However, the auxiliary components also have the effect of promoting sintering. Therefore, in the case of containing an excessive amount of auxiliary components, abnormal grain growth is likely to occur, leading to the coarsening of grains. If large abnormal grains are generated, there are problems such as a decrease in resistivity, especially a decrease in the incremental permeability in the low-temperature range and the high-temperature range. Ferromagnetic cores with abnormal grains of a certain size or more generated in this way have problems in terms of appearance and properties, and are therefore regarded as defective products. In addition, the abnormal grains existing on the surface of the sintered core have a different color from that of a healthy ferromagnetic sintered core, and can therefore be distinguished by visual inspection.

[0062] On the other hand, in the case where the contents of Si and Ca in MnZn ferrites are low, the generation of abnormal grains is suppressed, so there is a tendency for the defect rate caused by abnormal grain growth to decrease. In addition, although the influence is not as great as that of Si or Ca, in the case where MnZn ferrites contain an excessive amount of Nb, V, Ti, or Bi, etc., abnormal grain growth is also likely to occur. Therefore, in order to reduce the defect rate caused by abnormal grain growth on the surface of the ferromagnetic sintered core, it is important to reduce the content of auxiliary components that contribute greatly to the generation of abnormal grains.

[0063] In the present invention, the base components and the contents of auxiliary components such as Si and Ca are appropriately selected so as to increase the initial permeability μi. Therefore, it basically has the advantages of less generation of abnormal grains and a low defect rate caused by abnormal grain growth of the ferrite core. That is, when Si is contained in the range of 30 to 100 mass ppm in terms of SiO 2 conversion and Ca is contained in the range of 50 to 160 mass ppm in terms of CaO conversion, the generation of abnormal grains is suppressed and the defect rate of the ferrite core becomes low. On the contrary, when Si is greater than 100 mass ppm in terms of SiO 2 conversion or Ca is greater than 160 mass ppm in terms of CaO conversion, there is a tendency for the generation of abnormal grains to increase and the defect rate caused by abnormal grain growth of the ferrite core to become high.

[0064] Similarly, when the total content of Nb or V in terms of Nb 2 O 5 conversion value and V 2 O 5 conversion value is greater than 900 mass ppm, the defect rate caused by abnormal grain growth of the ferrite core becomes high. Therefore, the content of Nb or V is preferably set to 900 mass ppm or less in terms of the total of Nb 2 O 5 conversion value and V 2 O 5 conversion value. On the other hand, the content of Nb or V is preferably set to 200 mass ppm or more in terms of the total of Nb 2 O 5 conversion value and V 2 O 5 conversion value.

[0065] [Process capability index Cpk]

[0066] Next, from the viewpoint of the process capability index Cpk, each component will be described. Since the content of auxiliary components such as Si or Ca in the MnZn ferrite of one embodiment of the present invention is small, in the temperature range of -40 to 85 °C, the incremental permeability will become the lowest value at either -40 °C or 85 °C. This MnZn ferrite has the advantage that the deviation of the incremental permeability is smaller than that of ferrites with a large content of Si or Ca at this temperature. Therefore, the margin of this MnZn ferrite with respect to the lower limit specification of the incremental permeability considering the deviation is also good. Therefore, from the viewpoint of the defect generation rate below the lower limit specification of the incremental permeability, it is also preferable that the content of auxiliary components such as Si or Ca is small. That is, a MnZn ferrite with a small content of auxiliary components such as Si or Ca can obtain a high process capability index Cpk. In addition, generally, Cpk is preferably 1.33 or more.

[0067] Therefore, from the viewpoint of obtaining a high process capability index Cpk, the total content of Si and Ca in the MnZn ferrite is preferably set to 260 mass ppm or less in terms of SiO 2 and CaO conversion. On the other hand, the total content of Si and Ca in the MnZn ferrite can be set to 80 mass ppm or more in terms of SiO 2 and CaO conversion.

[0068] The MnZn ferrite of the present invention may also contain inevitable impurities such as P, B, S, and Cl. The content of such inevitable impurities is suppressed to 500 mass ppm or less in total.

[0069] (Manufacturing method of MnZn ferrite)

[0070] Next, the manufacturing method of the MnZn ferrite of the present invention will be described.

[0071] The manufacturing method of the MnZn ferrite of the present invention can use a known general manufacturing method. The general manufacturing method is as follows.

[0072] First, powder raw materials of Fe 2 O 3 , ZnO, and Mn 3 O 4 (The composition ratio is not converted to Mn 3 O 4 but is processed by converting to MnO) are weighed in amounts that satisfy the amounts specified in the present invention, and mixed by an attritor or a ball mill to obtain a mixed powder. The mixing method can be either a dry method or a wet method.

[0073] Next, the mixed powder is heated in the range of 800 to 1000 °C for pre-calcination to obtain a pre-calcined powder. Then, the pre-calcined powder is wet-crushed using an attritor or a ball mill until the crushing particle size becomes about 0.8 to 1.6 μm. At this time, an auxiliary component in an amount that satisfies the amount specified in the present invention is added and crushed. In this crushing operation, a homogenization treatment is required so that there is no deviation in the concentration of the auxiliary component.

[0074] An organic binder such as polyvinyl alcohol is added to the slurry obtained by the above wet crushing, and granulation is performed using a spray dryer or the like to obtain a granulated powder. Further, the granulated powder is filled into a metal mold having a specified shape and molded to obtain a molded body. By sintering the molded body thus obtained, a core of the MnZn ferrite according to the present invention can be obtained.

[0075] The incremental permeability of the MnZn ferrite obtained by the present invention is 2800 or more when a DC magnetic field of 25 A / m is applied in the temperature range of -40 to 85°C. Further, it is preferable that the temperature at which the incremental permeability takes the maximum value is in the range of 10 to 50°C. Further, it is preferable to have the property that the incremental permeability is 3700 or more when a DC magnetic field of 25 A / m is applied in the temperature range of 0 to 60°C, and the incremental permeability is as high as 4100 or more when a DC magnetic field of 25 A / m is applied in the temperature range of 23 to 40°C. In addition, since the incremental permeability of the MnZn ferrite is as high as 2800 or more, the number of products that have been unqualified due to non-compliance with the characteristics is reduced during mass production, and the effect of improving the yield can be obtained.

[0076] In addition, the incremental permeability of the core of the MnZn ferrite of the present invention is an upwardly convex curve showing a maximum value when a DC magnetic field of 25 A / m is applied in the temperature range of -40 to 85°C. Here, the temperature at which the incremental permeability shows the maximum value is different from the temperature at which the initial permeability shows the secondary peak. If an appropriate amount of Co 3 O 4 and other auxiliary components are added and the temperature showing the maximum value is appropriate, the balance of the incremental permeability at low temperature (near -40°C) and high temperature (near 85°C) can be achieved, and the above-mentioned high incremental permeability can be stably obtained. That is, in the present invention, it is important that the temperature at which the incremental permeability shows the maximum value is in an appropriate range (the range of 10 to 50°C) by containing appropriate basic components and auxiliary components. The temperature at which the incremental permeability shows the maximum value is preferably 15°C or more and preferably 45°C or less.

[0077] Examples

[0078] [Incremental Permeability]

[0079] First, the effects of the basic components and auxiliary components on the incremental permeability were investigated. The raw material powders were weighed in such a way that Fe 2 O 3 , ZnO, and Mn 3 O 4 (the mixing ratio was processed as MnO) became the composition ratios shown in Tables 1 to 3. High-purity raw material powders were used in all cases.

[0080] Here, the compositions of Comparative Example 13, Comparative Example 14, and Comparative Example 15 were set to the compositions corresponding to Example 11 of Patent Document 4, Example 1 of Patent Document 5, and Example 2 of Patent Document 5, respectively. That is, the composition ratios of Fe 2 O 3 and ZnO were set to the composition ratios described in each patent document, and the remaining MnO was appropriately adjusted so that the total of the basic components became 100 mol%.

[0081] The raw material powders were mixed and pulverized by a ball mill for 16 hours, and then pre-calcined in the atmosphere under the conditions of 925 °C for 3 hours to obtain pre-calcined powder. Then, SiO was added to the pre-calcined powder in a composition ratio shown in Tables 1 to 3 respectively. 2 , CaCo 3 , Co 3 O 4 , Nb 2 O 5 , V 2 O 5 , TiO 2 and Bi 2 O 5 , and pulverized by a ball mill for 12 hours to obtain pulverized powder. Then, polyvinyl alcohol was added to the pulverized powder for granulation, and a pressure of 118 MPa was applied to form a ring-shaped core to make a formed body. After that, the formed body was placed in a sintering furnace and sintered at a maximum temperature of 1350 °C to obtain a sintered body specimen with an outer diameter of 30.5 mm × inner diameter of 19 mm × height of 6.5 mm. In addition, the contents of P, B, S, Cl and other inevitable impurities were quantified according to JIS K0102 (ICP mass spectrometry method) and confirmed to be 500 mass ppm or less. Each of the specimens thus obtained was wound with 20 turns, and a precision LCR meter E4980A (manufactured by Keysight Technologies) was used to obtain the initial permeability and incremental permeability. The initial permeability was measured at 23 °C, 100 kHz without superimposing a DC magnetic field. In addition, the temperature characteristics of the incremental permeability were measured at a frequency of 100 kHz in a state where a DC magnetic field of 25 A / m was superimposed at each temperature of -40 °C, 0 °C, 23 °C, 40 °C, 60 °C and 85 °C. The results are shown in Tables 1 to 3 and Figures 1 to 7 . In addition, the solid line in the figure is a line showing the case where the incremental permeability (μ dc ) is 2800.

[0082] [Table 1]

[0083]

[0084] [Table 2]

[0085]

[0086] [Table 3]

[0087]

[0088] <Basic components>

[0089] As shown in Table 1 and Figure 1 , 2As shown, from the results of Invention Examples 1 to 8 and Comparative Examples 1 to 4, it can be seen that if Fe as the basic component 2 O 3 is in the range of 52.5 to 53.5 mol% and ZnO is in the range of 16.4 to 18.4 mol%, then when a DC magnetic field of 25 A / m is applied, an incremental permeability of 2800 or more can be obtained in the temperature range of -40 to 85 °C, and the temperature at which the incremental permeability shows a maximum value is in the range of 10 to 50 °C. In addition, from Invention Examples 1 to 8, it can also be seen that the incremental permeability when a DC magnetic field of 25 A / m is applied in the temperature range of 0 to 60 °C is 3700 or more, and the incremental permeability when a DC magnetic field of 25 A / m is applied in the temperature range of 23 to 40 °C is 4100 or more.

[0090] <Auxiliary component SiO 2 >

[0091] As shown in Table 2 and Figure 3 it can be seen from the results of Invention Examples 9 to 11 and Comparative Examples 5 to 6 that if SiO as the auxiliary component 2 is in the range of 30 to 100 mass ppm, then when a DC magnetic field of 25 A / m is applied, an incremental permeability of 2800 or more can be obtained in the temperature range of -40 to 85 °C, and the temperature at which the incremental permeability shows a maximum value is in the range of 10 to 50 °C.

[0092] <Auxiliary component CaO>

[0093] As shown in Table 2 and Figure 4 it can be seen from the results of Invention Examples 12 to 15 and Comparative Examples 7 to 8 that if CaO as the auxiliary component is in the range of 50 to 160 mass ppm, then when a DC magnetic field of 25 A / m is applied, an incremental permeability of 2800 or more can be obtained in the temperature range of -40 to 85 °C, and the temperature at which the incremental permeability shows a maximum value is in the range of 10 to 50 °C.

[0094] <Auxiliary component Co 3 O 4 >

[0095] As shown in Table 2 and Figure 5 it can be seen from the results of Invention Examples 16 to 20 and Comparative Examples 9 to 10 that if Co as the auxiliary component 3 O 4 is in the range of 1500 to 3500 mass ppm, then when a DC magnetic field of 25 A / m is applied, an incremental permeability of 2800 or more can be obtained in the temperature range of -40 to 85 °C. In particular, for Invention Examples 17 to 20, the temperature at which the incremental permeability shows a maximum value is in the range of 10 to 50 °C.

[0096] <Auxiliary component Nb2 O 5 and V 2 O 5 >

[0097] As shown in Table 2 and Figure 6 it can be seen from the results of Invention Examples 21 to 24 and Comparative Examples 11 to 12 that if Nb 2 O 5 and V 2 O 5 are both in the range of 100 to 600 mass ppm, and the total of Nb 2 O 5 and V 2 O 5 is in the range of 200 to 900 mass ppm, then when a DC magnetic field of 25 A / m is applied, an incremental permeability of 2800 or more can be obtained in the temperature range of -40 to 85°C, and the temperature at which the incremental permeability shows a maximum value is in the range of 10 to 50°C.

[0098] <Equivalent to the case of Patent Document 4: Comparative Example 13>

[0099] As shown in Table 3 and Figure 7 it can be seen that in Comparative Example 13 (equivalent to Example 11 of Patent Document 4), the temperature characteristic curve shifts to the low temperature side, and the incremental permeability in the high temperature range is less than 2800, and an incremental permeability of 2800 or more cannot be obtained in the temperature range of -40 to 85°C.

[0100] <Equivalent to the case of Patent Document 5: Comparative Example 14, Comparative Example 15>

[0101] As shown in Table 3 and Figure 7 it can be seen that in Comparative Example 14 (equivalent to Example 1 of Patent Document 5) and Comparative Example 15 (equivalent to Example 2 of Patent Document 5), the temperature characteristic curve shifts to the high temperature side, and the incremental permeability in the low temperature range is less than 2800, and an incremental permeability of 2800 or more cannot be obtained in the temperature range of -40 to 85°C. Furthermore, it can be seen that since Co is not added, the change rate of the incremental permeability is large.

[0102] [Defect rate caused by abnormal grain growth]

[0103] Next, the defect rate caused by abnormal grain growth was investigated. For Invention Examples 3, 11, 15, Comparative Examples 6, 8, and 13 to 18 shown in Table 4, ferrite pulverized powder was produced in the same manner as the above method. Polyvinyl alcohol was added to the pulverized powder for granulation, and a pressure of 118 MPa was applied to form a ring-shaped core to obtain a formed body. Thereafter, the formed body was placed in a sagger and loaded into a sintering furnace, and sintered at a maximum temperature of 1350 °C to obtain a sintered body specimen (core) having an outer diameter of 6.0 mm × inner diameter of 3.0 mm × height of 4.0 mm. For the obtained sintered body specimens, the initial permeability and incremental permeability were determined using the above method. Furthermore, 100 sintered body specimens were produced, and the number of sintered body specimens having abnormal grains of 0.5 mm or more on the specimen surface was determined by visual inspection to obtain the defect rate. The results are shown in Table 4.

[0104] Here, Comparative Example 16 was set to have the same composition as Example 7 of Patent Document 1, Comparative Example 17 was set to have the same composition as Suitable Example 1 of Patent Document 2, and Comparative Example 18 was set to have the same composition as Specimen Nos. 1-5 (Invention Example) of Patent Document 3.

[0105] [Table 4]

[0106]

[0107] As shown in Table 4, in Invention Examples 3, 11, and 15, cores were produced using ferrite powder under the conditions composed of the basic components and auxiliary components of the present invention, and an incremental permeability of 2800 or more was obtained in the temperature range of -40 to 85 °C. Furthermore, it was found that no cores with abnormal grains were produced, and the defect rate caused by abnormal grain growth was low.

[0108] As shown in Table 4, in Comparative Examples 6, 8, and 13 to 17, an incremental permeability of 2800 or more could not be obtained in the temperature range of -40 to 85 °C, and the defect rate caused by abnormal grain growth was higher than that of the present invention examples. In addition, in Comparative Example 18, although an incremental permeability of 2800 or more could be obtained in the temperature range of -40 to 85 °C, due to the occurrence of abnormal grain growth, there were defective cores, and the defect rate caused by abnormal grain growth was higher than that of the present invention examples.

[0109] [Process Capability Index Cpk]

[0110] Next, the process capability index Cpk of the present invention was investigated. In Invention Example 15 and Comparative Example 18 where the incremental permeability at -40°C was almost the same, 100 sintered body specimens (cores) were produced by the above method. The incremental permeability of each core was measured, and the standard deviation σ of the incremental permeability at -40°C showing the lowest value was obtained. Then, the lower specification of the incremental permeability at -40°C was set to 2700 (one-sided specification), and the process capability index Cpk considering the deviation was calculated according to the following formula (1). The results are shown in Table 5.

[0111] CpK = (average value - lower specification) / 3σ ··· (1)

[0112] [Table 5]

[0113]

[0114] As shown in Table 5, in Invention Example 15 with a low content of Si or Ca, etc., Cpk was as high as 1.35. In contrast, in Comparative Example 18 with a high content of Ca, Cpk was as low as 0.82. From this result, it can be seen that compared with Comparative Example 18, Cpk of Invention Example 15 is larger and there is a margin with respect to the lower specification of the incremental permeability. Thus, it can be known that compared with the conditions of the invention example of Patent Document 3, the defective rate of the incremental permeability of the present invention with a low content of Si or Ca, etc. is low, and thus it is more preferable.

[0115] Industrial Applicability

[0116] According to the present invention, an MnZn-based ferrite applicable to electronic components such as pulse transformers in the temperature range of -40 to 85°C can be obtained, and the above MnZn-based ferrite also shows a high incremental permeability when a DC magnetic field of 25 A / m is applied. Thereby, the ferrite core can be miniaturized and the number of turns of the copper wire can be reduced.

Claims

1. A MnZn ferrite, which is composed of a basic component, an auxiliary component and inevitable impurities, When the total amount of iron, zinc and manganese calculated as Fe2O3, ZnO and MnO is taken as 100 mol%, The basic ingredients are: Iron: 52.5-53.5 mol% calculated as Fe2O3; Zinc: 16.4 to 18.4 mol% calculated as ZnO; and Manganese: calculated as the balance in terms of MnO. Relative to the basic ingredients, the auxiliary ingredients are: Si: 30 to 100 mass ppm calculated as SiO2; Ca: 50 to 160 mass ppm calculated as CaO; Co: 1500 to 3500 mass ppm calculated as Co3O4; Nb: 100 to 600 ppm by mass calculated as Nb2O5; and V: 100 to 600 mass ppm in terms of V2O5, The total content of the Nb and the V is 200 to 900 mass ppm in terms of Nb2O5 and V2O5.

2. The MnZn-based ferrite according to claim 1, wherein: The incremental magnetic permeability of the MnZn ferrite is above 2800 when a DC magnetic field of 25A / m is applied in a temperature range of -40 to 85°C. The temperature showing the maximum value of the incremental magnetic permeability is in the range of 10 to 50°C.

3. The MnZn-based ferrite according to claim 2, wherein: The incremental magnetic permeability of the MnZn ferrite is 3700 or more when a DC magnetic field of 25A / m is applied in a temperature range of 0 to 60°C. Furthermore, the MnZn-based ferrite has an incremental permeability of 4100 or more when a DC magnetic field of 25 A / m is applied in a temperature range of 23 to 40°C.

Images