MnZn ferrite and its manufacturing method

Abstract

Provided are an MnZn ferrite and a method for manufacturing the same, which can suppress both a decrease in loss at high frequencies and a change in magnetic properties in a high magnetic field. The MnZn ferrite contains Fe2O3, ZnO, and MnO as main components. Among them, in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol% and ZnO is 3.0 to 12.0 mol%, and the balance is MnO. Relative to 100% by mass of the main components, the MnZn ferrite contains 0.005 to 0.060% by mass of SiO2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co2O3, and 0.05 to 0.30% by mass of TiO2 as sub-components, the average crystal grain size is 4 μm or less, and the sintered density is 4.8 g / cm 3 or more.

Description

Technical Field

[0001] The present invention relates to an MnZn ferrite and a method for manufacturing the same. Background Art

[0002] MnZn ferrites have characteristics such as high magnetic permeability, high magnetic flux density, and easy magnetization even in a small magnetic field, and are widely used in communication device applications, power supply applications, etc. Various studies have been conducted on MnZn ferrites in order to obtain properties according to desired applications (for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses an MnZn ferrite sintered body including a main component composed of a specific amount of Fe2O3, ZnO, and MnO and a sub-component composed of a specific amount of SiO2, CaCO3, Co3O4, ZrO2, and Ta2O5. The MnZn ferrite sintered body has an average crystal grain size of 3 μm or more and less than 8 μm, and has a sintered body density of 4.65 g / cm 3 or more, as an MnZn ferrite sintered body having low core loss in a wide temperature range at a high frequency of 300 kHz to 500 kHz and having a small change over time in core loss in a high-temperature environment.

[0004] In addition, Patent Document 2 discloses a low-loss Mn-Zn ferrite containing Fe, Mn, and Zn as main components, Co, Ca, and Si as first sub-components, and a specific amount of Group Va elements as second sub-components, and having an average crystal grain size of less than 3.2 μm and a low volume resistivity of 1 Ω·m or more, as an Mn-Zn ferrite having low power loss even at a high frequency of 1 MHz or more, in a wide temperature range, and at a wide operating magnetic flux density.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Patent Publication No. WO2018 / 181242

[0008] Patent Document 2: International Patent Publication No. WO2006 / 054749 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] There is a need for an MnZn ferrite to have further reduced loss at high frequencies. On the other hand, the present inventors have found that depending on the method for reducing loss, the magnetic properties can be changed when a high magnetic field is applied.

[0011] The present invention solves the above problems and provides a MnZn ferrite and a method for manufacturing the same, which can suppress both the decrease in loss at high frequencies and the change in magnetic properties in a high magnetic field.

[0012] Means for Solving the Problems

[0013] The MnZn ferrite according to the present invention

[0014] contains Fe2O3, ZnO, and MnO as main components, wherein

[0015] in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol% and ZnO is 3.0 to 12.0 mol%, and the balance is MnO,

[0016] relative to 100% by mass of the main components, the MnZn ferrite contains 0.005 to 0.060% by mass of SiO2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co2O3, and 0.05 to 0.30% by mass of TiO2 as sub-components,

[0017] the average crystal grain size is 4 μm or less, and

[0018] the sintered density is 4.8 g / cm 3 or more.

[0019] In one embodiment of the above MnZn ferrite, the MnZn ferrite further contains 0.010 to 0.100% by mass of ZrO as a sub-component.

[0020] In one embodiment of the above MnZn ferrite, the core loss per unit volume (Pcv) of the MnZn ferrite at 25 °C, 2 MHz, and 50 mT is 1500 mW / cm 3 or less.

[0021] In one embodiment of the above MnZn ferrite, the rate of change of the core loss per unit volume (Pcv) at 25 °C, 2 MHz, and 50 mT, represented by the following formula (1), compared to the core loss per unit volume before the application of the magnetic field, is 100% or less:

[0022] Formula (1): (Pcv - Pcv0) / Pcv0 × 100

[0023] wherein, Pcv0 is the core loss per unit volume before the application of the magnetic field.

[0024] The method for manufacturing a MnZn ferrite according to the present invention is

[0025] A method for manufacturing the MnZn ferrite of the present invention, the method comprising:

[0026] Mixing raw materials containing each main component such that after sintering, in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol%, ZnO is 3.0 to 12.0 mol%, and the balance is MnO;

[0027] Adding raw materials containing each sub-component such that after sintering, the MnZn ferrite contains 0.005 to 0.060% by mass of SiO2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co2O 3、 and 0.05 to 0.30% by mass of TiO2 relative to 100% by mass of the main components; and

[0028] Crushing the obtained mixed powder until the mixed powder becomes a crushed powder having a D90 particle diameter of 1.2 or less.

[0029] An embodiment of the above production method further includes the steps of molding the crushed powder and heat-treating the obtained molded article at a temperature of 1050 °C to 1150 °C.

[0030] Advantages of the Invention

[0031] According to the present invention, there is provided an MnZn ferrite and a method for manufacturing the same, which can suppress both the reduction of loss at high frequencies and the change of magnetic properties in a high magnetic field. Detailed Embodiments

[0032] Hereinafter, the MnZn ferrite and the method for manufacturing the same according to the present invention will be described.

[0033] Unless otherwise specified, a numerical range indicated by using "to" includes its lower limit value and upper limit value.

[0034] [MnZn Ferrite]

[0035] The MnZn ferrite according to the present invention (hereinafter also referred to as the present MnZn ferrite)

[0036] contains Fe2O3, ZnO, and MnO as main components, wherein

[0037] in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol% and ZnO is 3.0 to 12.0 mol%, and the balance is MnO,

[0038] The MnZn ferrite contains, relative to 100% by mass of the main component, 0.005 to 0.060% by mass of SiO2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co2O3, and 0.05 to 0.30% by mass of TiO2 as sub-components,

[0039] The average crystal grain size is 4 μm or less, and

[0040] The sintered density is 4.8 g / cm 3 or more.

[0041] The present inventors have made the following discovery: By adjusting the MnZn ferrite such that each metal oxide is contained in the above-specified ratio, the average crystal grain size is 4 μm or less, and the sintered density is 4.8 g / cm 3 or more, it is possible to reduce the loss at high frequencies (particularly from 1 MHz to 3 MHz), and it is also possible to suppress the change in magnetic properties after the application of a high magnetic field, and the present inventors have completed the present invention.

[0042] The present inventors have made the following discovery: By using an MnZn ferrite having a hysteresis loop with a perminvar property, it is possible to reduce the loss at high frequencies. For an MnZn ferrite having a perminvar property, the residual loss associated with domain wall displacement is reduced by suppressing the displacement (pinning) of domain walls. However, when a high magnetic field is applied, the pinning of domain walls becomes insufficient, and the mobility of domain walls increases, so that the reduction in loss may become insufficient. On the other hand, the MnZn ferrite contains the respective components in the above-specified ratio, and the crystal grain size is reduced to 4 μm or less, thereby reducing the number of domain walls in the crystal grains and reducing the residual loss associated with domain wall displacement. Specifically, the present MnZn ferrite can suppress the core loss per unit volume (Pcv) under the conditions of 25°C, 2 MHz, and 50 mT to 1500 mW / cm 3 or less. Further, the present MnZn ferrite can, for example, set the rate of change of the core loss per unit volume (Pcv) under the conditions of 25°C, 2 MHz, and 50 mT, as represented by the following formula (1), compared to the core loss per unit volume before the application of the magnetic field, to 100% or less:

[0043] Formula (1): (Pcv - Pcv0) / Pcv0 × 100

[0044] As described above, the present MnZn ferrite has the following characteristics: Even when a high magnetic field is applied, it is possible to reduce the loss at high frequencies as in the state without the application of a high magnetic field.

[0045] This MnZn ferrite contains Fe2O3, ZnO, and MnO as the main components. In this MnZn ferrite, among the main components of 100 mol%, Fe2O3 is 53.2 to 56.0 mol% and ZnO is 3.0 to 12.0 mol%, and the balance is MnO (33.0 to 43.8 mol%).

[0046] By setting Fe2O3 to 53.2 mol% or more, preferably 53.5 mol% or more, a MnZn ferrite with a high magnetic flux density can be obtained. On the other hand, by setting Fe2O3 to 56.0 mol% or less, preferably 55.0 mol% or less, more preferably 54.8 mol% or less, its combination with other components inhibits the formation of the MnZn ferrite into a nickel-iron-cobalt alloy, so that the loss can be reduced when a high magnetic field is applied.

[0047] By setting ZnO to 3 mol% or more, preferably 6 mol% or more, its combination with other components can inhibit the formation of the MnZn ferrite into a nickel-iron-cobalt alloy, and the sinterability is excellent, and it is easy to adjust the crystal density to 4.8 g / cm 3 above. On the other hand, by setting ZnO to 12.0 mol% or less, preferably 11.0 mol% or less, a MnZn ferrite with a high magnetic flux density can be obtained.

[0048] In addition, this MnZn ferrite contains at least SiO2, CaO, Co2O3, and TiO2 as the secondary components.

[0049] By setting SiO2 to 0.005 mass% or more, preferably 0.010 mass% or more, a grain boundary phase with a high specific resistance can be sufficiently formed to suppress the generation of eddy currents at high frequencies. In addition, by containing SiO2, the mechanical strength of the MnZn ferrite is improved. On the other hand, by setting SiO2 to 0.060 mass% or less, preferably 0.050 mass% or less, the generation of SiO2 can be suppressed and the deterioration of the loss can be suppressed.

[0050] By setting CaO to 0.010 mass% or more, preferably 0.030 mass% or more, a grain boundary phase with a high specific resistance can be sufficiently formed to suppress the generation of eddy currents at high frequencies. On the other hand, by setting CaO to 0.050 mass% or less, preferably 0.045 mass% or less, the CaO remaining as an impurity can be suppressed and the deterioration of the loss can be suppressed.

[0051] By setting Co2O3 to 0.10 mass % or more, preferably 0.20 mass % or more, the loss in a high-temperature environment can be suppressed. On the other hand, by setting Co2O3 to 0.40 mass % or less, preferably 0.30 mass % or less, the formation of a nickel-iron-cobalt alloy is suppressed, and thus the loss can be reduced when a high magnetic field is applied.

[0052] On the other hand, by setting TiO2 to 0.05 mass % or more, preferably 0.10 mass % or more, the formation of a nickel-iron-cobalt alloy is suppressed, and thus the loss can be reduced when a high magnetic field is applied. On the other hand, by setting TiO2 to 0.30 mass % or less, preferably 0.25 mass % or less, the formation of a nickel-iron-cobalt alloy is suppressed, and thus the loss can be reduced when a high magnetic field is applied.

[0053] This MnZn-based ferrite may also contain other components as long as the effects of the present invention are exhibited. Examples of other components also include other metal oxides added as necessary, and elements inevitably contained.

[0054] Examples of other metal oxides include ZrO2, Ta2O5, Nb2O5, Bi2O3, and MoO3, and among these, ZrO2 is preferred. In addition, examples of elements inevitably contained include C (carbon atoms), P (phosphorus atoms), and B (boron atoms).

[0055] By setting ZrO2 to 0.01 mass % or more, preferably 0.04 mass % or more, a grain boundary phase having a high specific resistance can be sufficiently formed to suppress the generation of eddy currents at high frequencies. On the other hand, by setting ZrO2 to 0.1 mass % or less, preferably 0.08 mass % or less, ZrO2 remaining as an impurity can be suppressed, and the deterioration of the loss can be suppressed.

[0056] With respect to 100 mass % of the main component, the total content of other metal oxides and elements other than ZrO2 is preferably 0.1 mass % or less, more preferably 0.01 mass % or less.

[0057] This MnZn-based ferrite can be suitably used, for example, as a core material for an inductor used in a switching power supply circuit having a high-frequency (e.g., 1 to 3 MHz) switching frequency. In addition, this MnZn-based ferrite can suppress changes in magnetic properties even when a high magnetic field is applied, and thus can be applied to, for example, a transformer or a choke coil that may carry a large current.

[0058] [Method for manufacturing MnZn-based ferrite]

[0059] Next, an embodiment of a method for manufacturing MnZn-based ferrite (hereinafter also referred to as the present manufacturing method) will be described.

[0060] The present manufacturing method may be a manufacturing method capable of appropriately manufacturing the present MnZn ferrite. The method at least includes: a step of mixing raw materials containing each main component such that, after sintering, in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol% and ZnO is 3.0 to 12.0 mol%, and the balance is MnO (mixing step); a step of adding raw materials containing each sub-component such that, after sintering, the present MnZn ferrite contains 0.005 to 0.060 mass% of SiO2, 0.010 to 0.060 mass% of CaO, 0.10 to 0.40 mass% of Co2O3, and 0.05 to 0.30 mass% of TiO2 with respect to 100 mass% of the main components (adding step); and a step of crushing the obtained mixed powder until the mixed powder becomes a crushed powder having a D90 particle diameter of 1.2 μm or less (crushing step). The present manufacturing method may further include the following steps: a drying / granulating step such as adding a binder to the mixed powder of the main components after the mixing step to obtain granules; a calcining step of calcining the obtained granulated body; a drying / granulating step of the crushed powder; a molding step of molding the crushed powder or its granules; or a heat treatment step (sintering step) of heat-treating the obtained molded product.

[0061] In the above mixing step, the main components are mixed such that the main components after sintering have the composition of the present MnZn ferrite. The form of the main components before mixing is not particularly limited, and a powder form is preferred because powders are easy to handle and can be uniformly mixed. The raw material powders of the respective main components are mixed and crushed (if necessary) to obtain a mixed powder. The methods of mixing and crushing can be appropriately selected from known methods. Specific examples thereof include a grinder and a bead mill. The particle diameter of the mixed powder is not particularly limited, and considering aspects such as uniformity, it is preferable to adjust the median diameter D50 to 0.5 μm to 1.5 μm. The particle diameters D50 and D90 described later are the particle diameters (D50) at which the cumulative particle diameter frequency is 50% and the cumulative particle diameter frequency is 90% respectively when measuring the particle size distribution of the target particles. The particle size distribution of the mixed powder can be measured by using a particle size distribution measuring device.

[0062] The drying / granulating step can be applied to the mixed powder of the above main components. In the drying / granulating step, for example, when the total mass of the mixed powder is 100 mass parts, granules can be obtained by adding 0.5 to 1 mass part of a binder (such as polyvinyl alcohol) to the mixed powder obtained in the mixing step and spraying the obtained mixture by using a spray dryer or the like.

[0063] Next, the obtained pellets can be calcined in an air atmosphere at 750 °C for about 1 hour to obtain a calcined product (calcination step).

[0064] Next, a sub-component is added to the calcined product so that the sub-component after sintering has the composition of this MnZn ferrite. Before the addition, the form of the sub-component is not particularly limited, and it is preferably in the form of particles because particles are easy to handle and can be uniformly mixed.

[0065] After adding the sub-component, the obtained mixed powder is crushed to obtain a crushed powder. The crushing can be appropriately adjusted so that the average crystal grain diameter of the obtained MnZn ferrite is 4 μm or less. Examples of the method include a method involving crushing the calcined product until the particle diameter D90 after crushing becomes 1.2 μm or less.

[0066] In the drying / granulation step, when the total mass of the crushed powder is 100 parts by mass, 0.5 to 1.0 part by mass of a binder (such as polyvinyl alcohol) is added to the crushed powder obtained in the crushing step, and the obtained mixture is sprayed using a spray dryer or the like to obtain pellets. At this time, the median diameter D50 of the pellets is desirably 40 μm or more and 200 μm or less.

[0067] In the molding step, the pellets obtained in the drying / granulation step are molded into a predetermined shape. The predetermined shape can be designed according to the application, etc. For example, the pellets are molded into an annular core having an outer diameter of 19 mm, an inner diameter of 13 mm, and a height of 11 mm.

[0068] The molded pellets are heat-treated to obtain a sintered body (this MnZn ferrite). The heat treatment (sintering) conditions are preferably heating at a temperature of 1050 °C to 1150 °C for several hours. By performing the heat treatment at 1050 °C or higher, it is easy to achieve a sintered density of 4.8 g / cm 3 or more. On the other hand, by performing the heat treatment at 1150 °C or lower, it is easy to achieve an average crystal grain diameter of 4 μm or less.

[0069] According to the above manufacturing method, an MnZn ferrite having an average crystal grain diameter of 4 μm or less and a sintered density of 4.8 g / cm 3 or more is preferably manufactured.

[0070] Examples

[0071] Hereinafter, the present invention will be specifically described with reference to examples and comparative examples. The present invention is not limited by the description of the examples.

[0072] [Example 1]

[0073] Weigh and mix each raw material powder such that after sintering, the Fe2O3 content is 54.0 mol%, the ZnO content is 10.0 mol%, and the MnO content is 36.0 mol% to make the total 100 mol%. Relative to 100 parts by mass of the total mixture, add 0.5 part by mass of polyvinyl alcohol to the above mixture, and spray the resulting mixture using a spray dryer to obtain pellets. Next, calcine the pellets in an air atmosphere at 750 °C for 1 hour to obtain a calcined product. Next, add the raw material powders of each sub-component such that relative to 100% by mass of the main component, SiO2 is 0.03% by mass, CaO is 0.04% by mass, Co2O3 is 0.2% by mass, TiO2 is 0.2% by mass, and ZrO2 is 0.08% by mass.

[0074] Next, as a crushing step, crush the mixture of the calcined product and the additive using a crusher such that the particle diameter D90 after crushing is 1.2 μm or less to obtain crushed powder. Next, as a drying / granulation step, when the total mass of the crushed powder is 100 parts by mass, add 1 part by mass of polyvinyl alcohol to the crushed powder, and spray the resulting mixture using a spray dryer to obtain pellets. Next, as a molding step and a sintering step, mold the pellets into a ring core having an outer diameter of 16 mm, an inner diameter of 10 mm, and a height of 5 mm, and sinter at 1100 °C to obtain a sintered body (MnZn ferrite).

[0075] [Examples 2 to 16]

[0076] Obtain the MnZn ferrites of Examples 2 to 16 in the same manner as in Example 1, except that in Example 1, the raw materials are mixed and added such that the content ratios of the main component and the sub-components after sintering are as shown in Table 1.

[0077] [Comparative Example 1]

[0078] Obtain the MnZn ferrite of Comparative Example 1 in the same manner as in Example 1, except that in Example 1, the crushing time is shortened and the particle diameter D90 of the powder after crushing is 4.82 μm.

[0079] [Comparative Examples 2 to 12]

[0080] Obtain the MnZn ferrites of Comparative Examples 2 to 12 in the same manner as in Example 1, except that in Example 1, the raw materials are mixed and added such that the content ratios of the main component and the sub-components after sintering are as shown in Table 1.

[0081] <Evaluation>

[0082] The diameter D90 of the disintegration particles was determined by measuring the slurry of the disintegrated powder obtained during the manufacturing processes of the above-described respective Examples and Comparative Examples using a wet particle size distribution measuring apparatus.

[0083] The average crystal grain size was calculated by performing image analysis on an image obtained by mirror-polishing the MnZn ferrites obtained in the respective Examples and Comparative Examples, dissolving the grain boundary phase by etching, and then observing with a microscope. For each, the measurement was performed on 100 crystal grains.

[0084] The sintered density was measured by the Archimedes method.

[0085] Furthermore, Pcv and Pcv0 of the MnZn ferrites were measured using a BH analyzer, and the Pcv change rate was calculated by the above formula (1). The results are shown in Table 1.

[0086] [Table 1]

[0087]

[0088] [Summary of Results]

[0089] It is shown that the core loss per unit volume (Pcv) of the MnZn ferrites of Examples 1 to 16 at 25°C, 2 MHz, and 50 mT is 1500 mW / cm 3 or less, and the change rate of Pcv with respect to Pcv before applying a magnetic field is 100% or less, where in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol%, ZnO is 3.0 to 12.0 mol%, and the balance is MnO; with respect to 100% by mass of the main components, the MnZn ferrites contain 0.005 to 0.060 mass% of SiO2, 0.010 to 0.060 mass% of CaO, 0.10 to 0.40 mass% of Co2O3, and 0.05 to 0.30 mass% of TiO2 as sub-components; the average crystal grain size is 4 μm or less; and the sintered density is 4.8 g / cm 3 or more. From the above, it has become clear that the present MnZn ferrites can suppress the reduction of loss at high frequencies and the change of magnetic properties in a high magnetic field.

[0090] This application claims priority based on Japanese Patent Application No. 2010-167723 filed on October 2, 2020, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A MnZn ferrite, the MnZn ferrite comprising Fe2O3, ZnO, and MnO as main components, wherein, in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol%, ZnO is 3.0 to 12.0 mol%, and the balance is MnO, relative to 100% by mass of the main components, the MnZn ferrite comprises, as secondary components, 0.005 to 0.060% by mass of SiO2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co2O3, and 0.05 to 0.30% by mass of TiO2, the average crystal grain size is 4 µm or less, The sintered density is 4.8 g / cm 3 or more; and Among them, the core loss per unit volume (Pcv) under the conditions of 25 °C, 2 MHz, and 50 mT is 1500 mW / cm 3 or less.

2. The MnZn ferrite according to claim 1, wherein, the MnZn ferrite further comprises 0.010 to 0.100% by mass of ZrO2 as a secondary component.

3. The MnZn ferrite according to claim 1 or 2, wherein, The rate of change of the core loss per unit volume (Pcv) at 25 °C, 2 MHz, and 50 mT, represented by the following formula (1), compared to the core loss per unit volume before the application of the magnetic field, is 100% or less Formula (1): (Pcv - Pcv0) / Pcv0 × 100 wherein, Pcv0 is the core loss per unit volume before the application of the magnetic field.

4. A method for manufacturing the MnZn ferrite according to any one of claims 1 to 3, the method comprising: mixing raw materials containing the respective main components such that after sintering, in 100 mol% of the main components, Fe2O3 is 53.2 to 56.0 mol%, ZnO is 3.0 to 12.0 mol%, and the balance is MnO; adding raw materials containing the respective secondary components such that after sintering, the MnZn ferrite comprises 0.005 to 0.060% by mass of SiO2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co2O3, and 0.05 to 0.30% by mass of TiO2 relative to 100% by mass of the main components; and crushing the obtained mixed powder until the mixed powder becomes a crushed powder having a D90 particle size of 1.2 µm or less.

5. The method for manufacturing MnZn ferrite according to claim 4, wherein, The method further comprises the steps of shaping the crushed powder and heat-treating the obtained shaped article at a temperature of 1050 °C to 1150 °C.

Images