MnZnNiCo ferrite

Abstract

To provide a MnZnNiCo-based ferrite that has a high saturation magnetic flux density while maintaining small magnetic loss over a wide temperature and frequency ranges, and that can also prevent temperature rise of the core under continuous excitation.SOLUTION: A MnZnNiCo-based ferrite comprises: as basic components 53.90 to 55.40 mol% of Fe in Fe2O3 conversion, 9.60 to 10.60 mol% of Zn in ZnO conversion, 1.00 to 3.00 mol% of Ni in NiO conversion, 0.10 to 0.50 mol% of Co in CoO conversion, 32.55 to 35.60 mol% of Mn in MnO conversion; and as accessory components, 50 to 500 mass ppm of Si in SiO2 conversion, 200 to 2000 mass ppm of Ca in CaO conversion, and 50 to 500 mass ppm of Nb in Nb2O5 conversion, based on the basic components.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an MnZnNiCo-based ferrite, and more particularly to an MnZnNiCo-based ferrite with improved magnetic loss that is suitable for the main transformer of an on-vehicle DC-DC converter. [Background technology]

[0002] MnZnNiCo ferrite is one of the most common soft magnetic materials and is used in main transformers and noise filters in automotive DC-DC converters. In particular, MnZnNiCo ferrite, which is used for the power supply of main transformers, has recently been required to have low loss at high frequencies and over a wide temperature range.

[0003] One of the factors that must be controlled to keep magnetic loss low over a wide temperature range is the magnetic anisotropy constant K1. Magnetic loss reaches its minimum value at the temperature where K1 is 0, and the closer the absolute value of K1 is to zero, the smaller the magnetic loss value. Furthermore, K1 is determined by adding up the K1 values ​​of each of the main elements of ferrite. Here, Fe has a positive K1. 2+ and Co 2+ and Fe has a negative K1. 3+ , Ni 2+ , Mn 2+ Co 2+ can reduce the temperature dependency of K1, thereby reducing the temperature change rate of K1. 2+ When Co is present, 2+ Since K1 takes a value close to 0 over a wider temperature range than when is not present, magnetic loss can be reduced over a wider temperature range.

[0004] For example, Patent Document 1 discloses a technology in which the temperature characteristic of magnetic loss becomes flat by introducing 0.01 to 0.5 mol% of Co ions into ferrite whose main components are Fe2O3, MnO, and ZnO, thereby widening the temperature range in which K1 = 0.

[0005] Magnetic loss can be divided into hysteresis loss, eddy current loss, and residual loss. It is known that the eddy current loss can be reduced by improving the resistivity of the ferrite core. To improve the resistivity of the ferrite core, it is effective to add a substance other than the basic components that forms a high-resistivity phase at the grain boundaries.

[0006] For example, Patent Document 2 discloses a technology in which minute amounts of oxides such as calcium oxide and silicon oxide are added as secondary components to MnZn ferrite to cause segregation at grain boundaries and increase the grain boundary resistance, thereby increasing the overall resistivity from approximately 0.01 to 0.05 Ω·m to several Ω·m or more, thereby reducing eddy current loss and overall magnetic loss.

[0007] Furthermore, in recent years, the miniaturization of in-vehicle components has progressed, and as a result, there is a demand for smaller MnZn ferrite cores as well. In order to miniaturize ferrite cores, it is necessary to increase the saturation magnetic flux density.

[0008] It is known that a high saturation magnetic flux density can be achieved even at high temperatures by increasing the content of Fe2O3 in the MnZn ferrite component (see, for example, Patent Document 3).

[0009] Patent Document 4 mentions ferrite that has low loss and high magnetic flux density in the temperature range from room temperature to around 100°C. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Special Publication No. 04-033755 [Patent Document 2] Special Publication No. 36-002283 [Patent Document 3] Japanese Patent Application Publication No. 11-329822 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-31210 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-116700 [Patent Document 6] Japanese Patent Application Laid-Open No. 2013-107811 Summary of the Invention [Problem to be solved by the invention]

[0011] However, as shown in Figure 1 of Patent Document 1, the ferrite described in Patent Document 1 has a minimum loss temperature on the low side, and in the high-temperature operating range of recent years, there is a risk of the temperature rise accelerating and causing thermal runaway. Furthermore, there is no mention of saturation magnetic flux density, a property necessary for the recent miniaturization of ferrite cores.

[0012] In the technology described in Patent Document 2, since Co is not contained, it is thought that the temperature characteristic of magnetic loss is not flat, and it is predicted that the magnetic loss will become higher the further the temperature is from the temperature at which the magnetic loss is at its minimum value, but no mention is made of such magnetic loss.

[0013] In the technology described in Patent Document 3, the content of Fe2O3 is increased, which causes the temperature at which the magnetic loss takes its minimum value to shift to the lower temperature side, resulting in an increase in magnetic loss at higher temperatures. However, no mention is made of such magnetic loss.

[0014] The loss frequency mentioned in Patent Document 4 is 100 kHz, and there is no mention of losses at frequencies higher than this. Furthermore, the loss value at a frequency of 100 kHz and a magnetic flux density of 200 mT is also high, and problems remain with its use as a low-loss material in recent years.

[0015] That is, with conventional techniques, it has been difficult to provide an MnZnNiCo-based ferrite that simultaneously satisfies the magnetic loss and saturation magnetic flux density values ​​described below.

[0016] Furthermore, when MnZnNiCo ferrite is continuously excited under conditions of a certain frequency and magnetic flux density, if the ambient temperature is high, a rise in core temperature is observed. This is thought to be because magnetic loss occurs when the ferrite is excited, which in turn causes a corresponding rise in core temperature. In automotive applications where such MnZnNiCo ferrite is used, cooling technology is used to suppress temperature rises in components, but if the temperature rise of the ferrite core, which is one of those components, can be suppressed, the energy required for cooling can be further reduced. Techniques for preventing heat generation during continuous excitation are disclosed in Patent Documents 5 and 6. However, even the techniques described in these documents are not sufficient to prevent the temperature rise of the core.

[0017] The primary objective of the present invention is to provide an MnZnNiCo-based ferrite that maintains low magnetic loss over a wide temperature and frequency range, has a saturation magnetic flux density of 425 mT or more at a magnetizing force of 1200 A / m at a temperature of 100°C, and is capable of preventing core temperature rise under continuous excitation. In the present invention, a wide temperature range refers to a range of approximately 40 to 120°C, and a wide frequency range refers to a range of approximately 100 to 500 kHz. Furthermore, in the present invention, unless otherwise specified, the term "temperature" refers to a value measured with a thermocouple on the surface of an object such as a ferrite sintered body, core, or component. More specifically, the ambient temperature of the object was set to a predetermined temperature, and the magnetic properties were measured after confirming that the surface temperature of the object was the same as the ambient temperature. [Means for solving the problem]

[0018] The present invention has succeeded in solving the above-mentioned problems by increasing the amount of Fe2O3 to increase the saturation magnetic flux density from conventional MnZnNiCo-based ferrites, while at the same time correcting the deviation in temperature characteristics caused by the increase in Fe2O3 by incorporating NiO into the main component composition.

[0019] That is, the gist and configuration of the present invention are as follows. 1. A MnZnNiCo-based ferrite consisting of basic components, accessory components, and unavoidable impurities, wherein the basic components include 53.90 to 55.40 mol% of Fe calculated as Fe2O3, 9.60 to 10.60 mol% of Zn calculated as ZnO, 1.00 to 3.00 mol% of Ni calculated as NiO, 0.10 to 0.50 mol% of Co calculated as CoO, and 32.55 to 35.60 mol% of Mn calculated as MnO, and the accessory components include 50 to 500 ppm by mass of Si calculated as SiO2, 200 to 2000 ppm by mass of Ca calculated as CaO, and 50 to 500 ppm by mass of Nb calculated as Nb2O5, relative to the basic components.

[0020] 2. Maximum magnetic flux density: 200mT, frequency: 100kHz, magnetic loss in the range of 40 to 120℃: 420kW / m 3 or less, and the magnetic loss in the range of 40 to 120°C at a maximum magnetic flux density of 50 mT and a frequency of 500 kHz is 220 kW / m 3 1. The MnZnNiCo-based ferrite according to 1 above, which is:

[0021] 3. The MnZnNiCo ferrite according to 1 or 2 above, which has a saturation magnetic flux density of 425 mT or more at a temperature of 100° C. and a magnetizing force of 1200 A / m.

[0022] 4. The MnZnNiCo-based ferrite according to any one of 1 to 3 above, wherein the rate of temperature increase of the MnZnNiCo-based ferrite is 20% or less when continuously excited under conditions of a temperature of 120°C, a maximum magnetic flux density of 200 mT, and a frequency of 100 kHz. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an MnZnNiCo-based ferrite that has low magnetic loss and high saturation magnetic flux density at high temperatures even over a wide frequency band and a wide temperature range, and further that effectively reduces the temperature rise of the core during continuous excitation. Furthermore, the present invention can be used as a ferrite for the power supply of a small, energy-efficient main transformer. DETAILED DESCRIPTION OF THE INVENTION

[0024] The MnZnNiCo-based ferrite of the present invention has a basic composition containing FeO, ZnO, NiO, CoO, and MnO in appropriate amounts, as described below, from the viewpoint of having low magnetic loss, high saturation magnetic flux density, and optimizing the temperature characteristics of magnetic loss. The temperature at which magnetic loss is minimized is determined by the composition ratio of Fe2O3, ZnO, NiO, CoO, and MnO. If the temperature at which magnetic loss is minimized is too low or if the overall magnetic loss is large, the rate of temperature rise in the ferrite core will be large. Therefore, from the perspective of the core's rate of temperature rise, the following basic composition is required. Note that the mol% below is the composition ratio within the basic components. Therefore, the total amount of the basic components is 100.00 mol%.

[0025] First, the basic components of the MnZnNiCo ferrite of the present invention will be specifically described. Fe is 53.90-55.40 mol% of the base component in terms of Fe2O3 If the Fe content is less than 53.90 mol% in terms of Fe2O3, the saturation magnetic flux density will fall below 425 mT, so the Fe content must be 53.90 mol% or more in terms of Fe2O3 in the basic components. Preferably, it is 54.00 mol% or more. On the other hand, if the Fe content exceeds 55.40 mol% in terms of Fe2O3 in the basic components, the magnetic loss will become too large. Therefore, the upper limit is set to 55.40 mol%, and preferably 55.38 mol% or less.

[0026] Zn is 9.60 to 10.60 mol% of the base component in terms of ZnO ZnO has a magnetic loss of 420 kW / m over a wide temperature range of 40 to 120°C under conditions of a maximum magnetic flux density of 200 mT and a frequency of 100 kHz. 3 To keep it below this level, the Zn content must be in the range of 9.60 to 10.60 mol % in terms of ZnO, preferably 9.65 mol % or more, and more preferably 10.20 mol % or less.

[0027] Ni is 1.00 to 3.00 mol% of the base component in terms of NiO When Fe is within the above range in terms of Fe2O3, if Ni is less than 1.00 mol% in terms of NiO in the basic composition, the temperature at which the magnetic loss reaches its minimum value will be too low, resulting in a significant deterioration in magnetic loss at a temperature of 120°C. Therefore, Ni must be 1.00 mol% or more in terms of NiO in the basic composition, preferably 1.03 mol% or more. On the other hand, when Fe is within the above range in terms of Fe2O3, if Ni is more than 3.00 mol% in terms of NiO in the basic composition, the saturation magnetic flux density at a magnetizing force of 1200 A / m at a temperature of 100°C will fall below 425 mT. Therefore, the upper limit of Ni, in terms of NiO, in the basic composition is set to 3.00 mol%. Preferably, it is 2.50 mol% or less, and more preferably 2.20 mol% or less.

[0028] Co is 0.10 to 0.50 mol% of the base component as calculated as CoO As mentioned above, CoO functions to adjust the temperature characteristics. However, if CoO is contained in excess, the temperature at which the magnetic loss reaches its minimum value will decrease. Therefore, the upper limit of Co, calculated as CoO, based on the basic composition is 0.50 mol %, and preferably 0.45 mol % or less. On the other hand, if the CoO content is too low, the effect of improving the temperature coefficient will be small, and improvement in the magnetic loss value will not be expected. Therefore, the lower limit of Co, calculated as CoO, based on the basic composition is 0.10 mol %, and preferably 0.20 mol % or more, and more preferably 0.30 mol % or more.

[0029] The present invention relates to an MnZnNiCo-based ferrite, and the remainder of the basic components other than the above-mentioned Fe2O3, ZnO, NiO, and CoO is manganese oxide. When all manganese oxide is converted into MnO, the MnO content ranges from 32.55 to 35.60 mol%. Here, the MnO content range is preferably 32.56 mol% or more. On the other hand, the MnO content range is preferably 35.00 mol% or less, and more preferably 34.80 mol% or less.

[0030] The MnZnNiCo ferrite of the present invention is characterized in that it contains, in addition to the above basic components, SiO2, CaO, Nb2O5, and the like as accessory components.

[0031] SiO2: 50 to 500 mass ppm relative to the basic components SiO2 segregates at grain boundaries with CaO, forming a high-resistivity phase that reduces eddy current loss and has the effect of reducing overall magnetic loss. If the content is less than 50 ppm by mass, the effect is not fully achieved. On the other hand, if the content exceeds 500 ppm by mass, abnormal growth of crystal grains occurs during sintering, which significantly increases magnetic loss. Therefore, SiO2 must be contained in the range of 50 to 500 ppm by mass relative to the basic components. Furthermore, in order to more reliably suppress abnormal grain growth, the content is preferably 50 ppm by mass or more, and preferably 400 ppm by mass or less. SiO2 is more preferably 75 ppm by mass or more. Furthermore, SiO2 is more preferably 300 ppm by mass or less.

[0032] CaO: 200 to 2000 mass ppm relative to the basic components When coexisting with SiO2, CaO segregates at grain boundaries to improve resistance, thereby contributing to the reduction of magnetic loss. However, if the content is less than 200 ppm by mass, the effect of adding CaO is not fully obtained. On the other hand, if the content is more than 2000 ppm by mass, magnetic loss increases. Therefore, CaO must be contained in the range of 200 to 2000 ppm by mass relative to the basic components. The CaO content is preferably 500 ppm by mass or more. Furthermore, the CaO content is preferably 1500 ppm by mass or less.

[0033] Nb2O5: 50 to 500 mass ppm relative to the basic components Nb2O5 effectively contributes to increasing the resistivity in the presence of SiO2 and CaO. If the content is less than 50 ppm by mass, a sufficient effect cannot be obtained. On the other hand, if the content exceeds 500 ppm by mass, magnetic loss increases. Therefore, Nb2O5 must be contained in the range of 50 to 500 ppm by mass relative to the basic components. The content is preferably 75 ppm by mass or more, more preferably 90 ppm by mass or more. The content is also preferably 400 ppm by mass or less, more preferably 350 ppm by mass or less.

[0034] The MnZnNiCo ferrite of the present invention comprises the above-mentioned basic components, accessory components and unavoidable impurities. Here, the unavoidable impurities in the present invention include Cl, Sr, Ba, etc. contained in the raw materials of the basic components, and are permissible if they are about 0.01 mass % or less based on the entire MnZnNiCo ferrite.

[0035] Next, a method for producing the MnZnNiCo ferrite of the present invention will be described. The raw material powders are weighed so that the composition ratios of the basic components Fe2O3, MnO, ZnO, NiO, and CoO fall within the ranges specified in this invention, and then thoroughly mixed and calcined. The calcined powder is then supplemented with the secondary components SiO2, CaO, and Nb2O5, weighed so that the ratios fall within the ranges specified in this invention, and thoroughly mixed and pulverized. A binder is added to the mixed and pulverized powder, which is then granulated and compression-molded using a mold. The molded body is then fired to produce a ferrite sintered body (product).

[0036] Thus, the ferrite sintered body has a saturation magnetic flux density of 425 mT or more at a magnetizing force of 1200 A / m at 100°C, a maximum magnetic flux density of 200 mT, and a magnetic loss of 420 kW / m at a frequency of 100 kHz at 40 to 120°C, all of which have been extremely difficult to achieve with conventional MnZnNiCo ferrites. 3 The magnetic loss measured at 40 to 120°C with a maximum magnetic flux density of 50 mT and a frequency of 500 kHz was 220 kW / m3 When continuously excited at a frequency of 100 kHz and a magnetic flux density of 200 mT at 120°C or less, the temperature rise rate of the core is 20% or less. In other words, when driven at 100 kHz or more while maintaining a high saturation magnetic flux density up to 100°C, the MnZnNiCo-based ferrite of the present invention has small magnetic loss over a wide temperature range and a small temperature rise under continuous excitation.

[0037] Here, if the saturation magnetic flux density at a magnetizing force of 1200 A / m at 100°C is 425 mT or more, the ferrite core can be made smaller, and therefore, for example, the space occupied by the ferrite core in the DC-DC converter in which it is installed can be reduced.

[0038] The magnetic loss measured at 40 to 120°C with a maximum magnetic flux density of 200 mT and a frequency of 100 kHz was 420 kW / m 3 The magnetic loss measured at 40 to 120°C with a maximum magnetic flux density of 50 mT and a frequency of 500 kHz was 220 kW / m 3 When the temperature is below this range, the magnetic loss is low over a wide temperature range, which makes it possible to suppress heat generation in the ferrite core. In addition, the loss is low over a wide frequency range, which makes it possible to support a variety of frequencies.

[0039] If the core temperature rise rate is 20% or less when measured at 120°C with a frequency of 100 kHz and a magnetic flux density of 200 mT, thermal runaway due to continuous use can be prevented.

[0040] Other methods for producing sintered bodies (MnZnNiCo ferrites) not described above are not particularly limited in terms of conditions or equipment used, and may be performed in accordance with so-called conventional methods. [Example]

[0041] Examples confirming the present invention will be described below. First, the basic components Fe2O3, ZnO, MnO, NiO, and CoO were weighed out to obtain the composition ratios (mol%) shown in Table 1. The weighed raw material powders were mixed for 16 hours using a wet ball mill and then calcined in air at 925°C for 3 hours. The calcined powder having the basic components after the calcination was mixed with SiO2, CaO, and Nb2O5 as accessory components in amounts (ppm by mass) shown in Table 1, and pulverized for 16 hours using a wet ball mill. PVA was added as a binder to the pulverized powder obtained by drying after pulverization, and the mixture was granulated by passing it through a sieve. The granulated powder after the granulation was formed into a ring shape with an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm, and fired for 2 hours at a maximum temperature of 1350°C in a mixed gas of nitrogen and air with an oxygen partial pressure controlled within the range of 1 to 5 vol%, to obtain a ring-shaped sample (ferrite sintered body).

[0042] The ring-shaped sample was wound with 40 turns on the primary side and 20 turns on the secondary side, and the magnetic flux density was measured using a DC magnetization characteristic tester when a magnetic field of 1200 A / m was applied at 23 to 120°C. In a magnetic field of this magnitude, the magnetic flux is nearly saturated, so this value of the magnetic flux density is considered to be the saturation magnetic flux density.

[0043] In addition, the primary winding was fitted with 5 turns and the secondary winding with 5 turns. Using an AC BH loop tracer, the magnetic loss was measured when excited to a magnetic flux density of 200 mT at a frequency of 100 kHz, and when excited to a magnetic flux density of 50 mT at a frequency of 500 kHz, in the temperature range of 23 to 130°C. In addition, the core was wound with 5 turns on the primary side and 5 turns on the secondary side, and after maintaining the core at a temperature of 120°C, it was continuously excited for 20 minutes using an AC BH loop tracer at a frequency of 100kHz and a magnetic flux density of 200mT.The difference between the core temperature at the start of excitation (120°C) and the core temperature 20 minutes after the start of excitation, measured with a thermocouple attached to the core, was calculated and divided by the core temperature at the start of excitation to determine the core temperature rise rate during continuous excitation. Furthermore, after the above 20-minute excitation time, the temperature rise in the core subsided and the core temperature became constant, and it was confirmed that the core temperature was sufficiently stable.

[0044] Based on the above measurement results, Table 1 shows the saturation magnetic flux density at 100°C, the minimum magnetic loss temperature, the magnetic loss values ​​at temperatures of 40°C and 120°C, and the core temperature rise rate during continuous excitation. Here, Nos. 1 to 17 in Table 1 are inventive examples that conform to the present invention, while Nos. 18 to 40 in Table 1 are comparative examples that fall outside the scope of the present invention. In the examples in Table 1, it has been confirmed that the amount of unavoidable impurities is 0.01 mass % or less in all cases.

[0045] As can be seen from Table 1, the MnZnNiCo-based ferrites of the invention, which were obtained by appropriately selecting the compositions of the basic components Fe2O3, ZnO, MnO, NiO, and CoO and the accessory components SiO2, CaO, and Nb2O5, all had a magnetizing force of 1200 A / m and a saturation magnetic flux density of 425 mT or more at a temperature of 100°C. In addition, the magnetic loss measured at a maximum magnetic flux density of 200 mT and a frequency of 100 kHz at temperatures between 40 and 120°C was 420 kW / m 3 The magnetic loss measured at temperatures between 40 and 120°C is 220kW / m below the maximum magnetic flux density of 50mT and frequency of 500kHz. 3 It can be seen that all of the inventive examples have low loss over a wide frequency range and a wide temperature range. Furthermore, when the MnZnNiCo ferrite was continuously excited at a temperature of 120° C. under conditions of a maximum magnetic flux density of 200 mT and a frequency of 100 kHz, the temperature rise rate was 20% or less. From these findings, it can be seen that according to the present invention, a MnZnNiCo ferrite material can be obtained that has low magnetic loss in the temperature range of 40 to 120°C and in the wide frequency range of 100 to 500 kHz while maintaining a high saturation magnetic flux density.

[0046] In contrast, when any one of the compositions of the basic components Fe2O3, ZnO, MnO, NiO, and CoO and the accessory components SiO2, CaO, and Nb2O5 deviated from the range of the present invention, at least one of the saturation magnetic flux density at 100°C, the magnetic loss value at temperatures of 40°C or 120°C, or the rate of temperature rise of the core during continuous excitation was inferior.

[0047] [Table 1] [Industrial Applicability]

[0048] The present invention can provide an MnZnNiCo-based ferrite that has a high saturation magnetic flux density, small magnetic loss over a wide frequency range from a low frequency of 100 kHz to a high frequency of 500 kHz, and a low rate of temperature rise during continuous excitation, and therefore can be widely applied to various power transformer cores, choke coils, etc.

Claims

[Claim 1] In a MnZnNiCo-based ferrite consisting of basic components, accessory components, and unavoidable impurities, Among the basic components, Fe is Fe ２ O ３ Converted to 53.90 to 55.40 mol%, Zn is 9.60 to 10.60 mol% in terms of ZnO, Ni is 1.00 to 3.00 mol% in terms of NiO, Co is 0.10 to 0.50 mol% in terms of CoO, and Mn is 32.55 to 35.60 mol% in terms of MnO And, The subcomponent is, relative to the base component, Si is SiO ２ Converted to 50 to 500 mass ppm, Ca is 200 to 2000 mass ppm in terms of CaO, and Nb is Nb ２ O ５ Converted to 50 to 500 mass ppm And, Furthermore, when the maximum magnetic flux density is 200 mT and the frequency is 100 kHz, the magnetic loss in the range of 40 to 120°C is 420 kW / m 3 or less; And, when the maximum magnetic flux density is 50 mT and the frequency is 500 kHz, the magnetic loss in the range of 40 to 120°C is 220 kW / m 3 or less; The saturation magnetic flux density is 425 mT or more at a magnetizing force of 1200 A / m at a temperature of 100°C, The MnZnNiCo-based ferrite has a temperature rise rate of 20% or less when continuously excited at a temperature of 120°C, a maximum magnetic flux density of 200 mT, and a frequency of 100 kHz.

Images