Mn-Zn FERRITE AND MANUFACTURING METHOD THEREOF

Abstract

To provide a Mn-Zn ferrite having high electrical resistance, suppressed decrease in magnetic permeability in the high frequency band, and good magnetic permeability in a wide frequency band from low to high frequencies, and a manufacturing method thereof.SOLUTION: A Mn-Zn-based ferrite according to the present disclosure contains main components consisting of 49.30 to 52.00 mol% Fe2O3, 30.00 to 35.00 mol% MnO, and 13.00 to 20.70 mol% ZnO, relative to 100 mol% of the total amount of the main components, and contains 0.100 to 0.800 mass% Li2CO3 and 0.600 to 1.700 mass% CuO as accessory components, relative to 100 mass% of the total amount of the main components.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a Mn-Zn ferrite and a method for producing the same. [Background technology]

[0002] Soft magnetic ferrites are used as materials for electronic components such as noise filters such as EMI (Electro Magnetic Interference) removal filters, transformers, inductors, etc. Examples of soft magnetic ferrites include Ni-Zn ferrites and Mn-Zn ferrites. In recent years, in applications such as portable electronic devices, communication speeds and capacities have increased, and signals have become increasingly high frequency. For this reason, there is a demand for soft magnetic ferrites that can be used in a wide frequency range from low to high frequencies in applications such as noise filters. For such applications, Ni-Zn ferrites are the mainstream due to their excellent high frequency characteristics. However, since Ni-Zn ferrites have relatively high raw material costs, the use of Mn-Zn ferrites is being considered from the perspective of reducing raw material costs. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-325922 Summary of the Invention [Problem to be solved by the invention]

[0004] Ni-Zn ferrite has high electrical resistance and can have good magnetic permeability over a wide frequency band from low to high frequencies (see the data of Comparative Example 11 in FIG. 1). In contrast, conventional Mn-Zn ferrites can have high magnetic permeability in a relatively low frequency band (for example, 1 MHz or less), but because of their low electrical resistance, they tend to have large eddy current losses and a large drop in magnetic permeability in a high frequency band (for example, 10 MHz or more) (see the data of Comparative Example 12 in FIG. 1). Conventional Mn-Zn ferrites also require the use of insulating materials such as resin bobbins due to their low electrical resistance. The use of insulating materials leads to increased costs and is not preferable.

[0005] An example of a technique related to the present disclosure is Patent Document 1. Patent Document 1 discloses an Mn-Zn ferrite magnetic material having a composition consisting mainly of 20-50 mol % MnO, 5-40 mol % ZnO, and the remainder Fe2O3, and having a high electrical resistance surface layer on at least a portion of the surface of the Mn-Zn ferrite magnetic material, in which Li and one or more of Ti, Cr, Co, Ni, Cu, and Zn are concentrated in the ferrite magnetic material (Claim 1).

[0006] Patent Document 1 discloses a method for producing the above-mentioned Mn-Zn ferrite magnetic material, which comprises preparing an Mn-Zn ferrite magnetic material having a composition consisting mainly of 20-50 mol % MnO, 5-40 mol % ZnO, and the remainder Fe2O3, adhering a slurry or mixed powder containing a Li compound and one or more of a Ti compound, a Cr compound, a Co compound, a Ni compound, a Cu compound, and a Zn compound to at least a portion of the surface of the Mn-Zn ferrite magnetic material, and then heat treating the material (Claim 2, [Examples] section).

[0007] In Patent Document 1, a high electrical resistance surface layer is formed on at least a portion of the surface of the Mn-Zn ferrite magnetic material, thereby increasing the electrical resistance of the Mn-Zn ferrite magnetic material. However, in Patent Document 1, no evaluation is made on physical properties other than the resistance value, and physical properties other than the resistance value, such as density, crystal grain size, and magnetic permeability, are unknown. In Patent Document 1, a Mn-Zn ferrite magnetic material is prepared as a core formed into a predetermined shape in advance, and a high electrical resistance surface layer is formed on at least a part of the surface to increase the electrical resistance of the surface layer. In this technology, Li and one or more elements selected from Ti, Cr, Co, Ni, Cu, and Zn are present only in the surface layer, and the electrical resistance of the interior (most part other than the surface layer) remains low. In order to increase the magnetic permeability, it is more important to increase the electrical resistance of the interior than the electrical resistance of the surface layer. Even if only the surface layer is made to have a high electrical resistance composition, the effect of reducing eddy current loss and the resulting effect of improving magnetic permeability cannot be obtained.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide an Mn-Zn ferrite that has high electrical resistance, is suppressed from decreasing in magnetic permeability in the high frequency band, and has good magnetic permeability in a wide frequency band from low to high frequencies, and a method for producing the same. [Means for solving the problem]

[0009] The present disclosure provides the following Mn-Zn-based ferrite and a method for producing the same. [1] The main components are 49.30-52.00 mol% Fe2O3, 30.00-35.00 mol% MnO, and 13.00-20.70 mol% ZnO, based on 100 mol% of the total amount of the main components; A Mn-Zn ferrite containing, as auxiliary components, 0.100 to 0.800 mass % of Li2CO3 and 0.600 to 1.700 mass % of CuO relative to a total amount of 100 mass % of the main components.

[0010] [2] The Mn-Zn-based ferrite of [1] further containing, as an accessory component, one or more oxides selected from the group consisting of 0.005 to 0.050 mass% of SiO2, 0.005 to 0.080 mass% of CaO, and 0.005 to 0.080 mass% of Nb2O5, relative to 100 mass% of the total amount of the main components.

[0011] [3] The Mn-Zn-based ferrite of [2], containing, as accessory components, 0.100 to 0.800 mass% Li2CO3, 0.600 to 1.700 mass% CuO, 0.005 to 0.050 mass% SiO2, 0.005 to 0.080 mass% CaO, and 0.005 to 0.080 mass% Nb2O5, relative to 100 mass% of the total amount of the main components.

[0012] [4] Any of the Mn-Zn ferrites of [1] to [3], in which the real part of the complex relative permeability (μ') at 25°C and 100 kHz is 30 to 500, and the real part of the complex relative permeability (μ') at 25°C and 100 MHz is 30 to 100. [5] Resistivity is 1.0×10 5 ~9.0×10 6 Any of the Mn-Zn ferrites [1] to [4] with a modulus of Ω·m. [6] Any of the Mn-Zn ferrites [1] to [5] that are polycrystalline with an average crystal grain size of 1 to 10 μm.

[0013] [7] Density: 4.50-5.50 kg / m 3 The Mn-Zn ferrite of any one of [1] to [6] above is a sintered body. [8] The Mn-Zn-based ferrite according to any one of [1] to [7], which is a sintered body of a mixed powder containing Fe2O3 powder, MnO powder, ZnO powder, Li2CO3 powder, and CuO powder. [9] The Mn-Zn-based ferrite according to any one of [1] to [8], which is a polycrystalline body in which one or more of the main components and one or more of Li2CO3 and CuO are present in at least some of the crystal grains.

[0014]

[10] preparing a mixed powder including Fe2O3 powder, MnO powder, ZnO powder, Li2CO3 powder, and CuO powder; A step of forming the mixed powder into a molded body; and sintering the green compact. Effect of the Invention

[0015] According to the present disclosure, it is possible to provide an Mn-Zn ferrite having high electrical resistance, suppressed decrease in magnetic permeability in the high frequency band, and favorable magnetic permeability in a wide frequency band from low to high frequencies, and a method for producing the same. [Brief description of the drawings]

[0016] [Figure 1] 1 is a graph showing a measurement example of frequency characteristics of complex relative permeability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] In this specification, unless otherwise specified, electrical resistance is DC resistance. In this specification, unless otherwise specified, permeability is relative complex permeability (μ). In this specification, unless otherwise specified, normal temperature is 20 to 30°C. In this specification, unless otherwise specified, the term "to" indicating a numerical range includes the lower limit and the upper limit.

[0018] [Mn-Zn ferrite] The inventors have realized a Mn-Zn ferrite that has high electrical resistance, suppresses a decrease in magnetic permeability in a high frequency band (e.g., 10 MHz or higher), and has good magnetic permeability in a wide frequency band from low to high frequencies (e.g., 1 kHz to 100 MHz) by using Fe2O3, MnO, and ZnO as the main components and Li2CO3 and CuO as the subcomponents and optimizing the content of each component.

[0019] The Mn-Zn-based ferrite of the present disclosure is a ferrite containing Fe2O3, MnO, and ZnO as main components, and Li2CO3 and CuO as accessory components. The Mn-Zn ferrite of the present disclosure can be a sintered body of a mixed powder containing Fe2O3 powder, MnO powder, ZnO powder, Li2CO3 powder, and CuO powder. The Mn-Zn ferrite of the present disclosure may be a polycrystalline body. The Mn-Zn ferrite of the present disclosure may be a polycrystalline body in which at least one of the above main components and at least one of Li2CO3 and CuO are present in at least some of the crystal grains. The Mn-Zn ferrite of the present disclosure differs from the Mn-Zn ferrite magnetic material described in Patent Document 1 in that it can be a sintered body in which the components Fe2O3, MnO, ZnO, Li2CO3, and CuO are distributed throughout.

[0020] The Mn-Zn ferrite of the present disclosure can have good magnetic permeability in a relatively low frequency band of 100 kHz or less (for example, 1 kHz to 100 kHz). The Mn-Zn ferrite of the present disclosure can have good magnetic permeability with no decrease in magnetic permeability even in a high frequency band of 10 MHz or more (for example, 10 MHz to 100 MHz). The Mn-Zn ferrite of the present disclosure has good magnetic permeability over a wide frequency band including 1 kHz to 100 MHz, and can have high impedance characteristics over the wide frequency band.

[0021] The Mn-Zn ferrite of the present disclosure contains Fe2O3, MnO, and ZnO as main components. In the Mn-Zn ferrite of the present disclosure, the content of Fe2O3 is 49.30 to 52.00 mol% relative to the total amount of the main components (100 mol%). The lower limit is preferably 49.50 mol% and the upper limit is preferably 50.00 mol%. When the content of Fe2O3 is within the above range, the Mn-Zn-based ferrite of the present disclosure has high electrical resistance, is suppressed from decreasing in magnetic permeability in the high frequency band, and has good magnetic permeability over a wide frequency band.

[0022] The content of MnO is 30.00 to 35.00 mol% relative to the total amount of the main components (100 mol%). The lower limit is preferably 31.00 mol% and the upper limit is preferably 34.00 mol%. When the content of MnO is within the above range, the Mn-Zn ferrite of the present disclosure has high electrical resistance, is suppressed from decreasing in magnetic permeability in high frequency bands, and has good magnetic permeability over a wide frequency band.

[0023] The content of ZnO is 13.00 to 20.70 mol% relative to the total amount of the main components (100 mol%). The lower limit is preferably 16.00 mol% and the upper limit is preferably 19.05. When the ZnO content is within the above range, the Mn-Zn ferrite of the present disclosure has high electrical resistance, is inhibited from decreasing in magnetic permeability in high frequency bands, and has good magnetic permeability over a wide frequency band.

[0024] The Mn-Zn ferrite of the present disclosure contains Li2CO3 as a secondary component. According to the research of the present inventors, it has been found that by adding an appropriate amount of Li2CO3, the electrical resistance of Mn-Zn ferrite can be increased, thereby reducing eddy current loss and increasing magnetic permeability in the high frequency band. The content of Li2CO3 is 0.100 to 0.800 mass% relative to 100 mass% of the total amount of the main components. The lower limit is preferably 0.200 mass%, more preferably 0.300 mass%, and the upper limit is preferably 0.700 mass%, more preferably 0.600 mass%. When the content of Li2CO3 is within the above range, the Mn-Zn-based ferrite of the present disclosure has a sufficiently high density of the sintered body, high electrical resistance, suppresses the decrease in magnetic permeability in the high frequency band, and has good magnetic permeability over a wide frequency band.

[0025] The Mn-Zn ferrite of the present disclosure contains CuO as a minor component. According to the research of the present inventors, it has been found that the density of a sintered body made of Mn-Zn ferrite can be increased by adding an appropriate amount of CuO, thereby increasing the saturation magnetic flux density (Bs) and saturation magnetization (Ms), increasing the threshold frequency (fr), and increasing the magnetic permeability in the high frequency band. The CuO content is 0.600 to 1.700 mass% relative to 100 mass% of the total amount of the main components. The lower limit is preferably 0.700 mass%, more preferably 0.800 mass%, and the upper limit is preferably 1.600 mass%, more preferably 1.500 mass%. When the CuO content is within the above range, the Mn-Zn-based ferrite of the present disclosure has a sintered body with a sufficiently high density, high electrical resistance, and suppressed decrease in magnetic permeability in the high frequency band, thereby enabling the Mn-Zn-based ferrite to have good magnetic permeability over a wide frequency band.

[0026] The Mn-Zn ferrite of the present disclosure may be a polycrystalline body in which at least one of the above main components and at least one of Li2CO3 and CuO are present in at least some of the crystal grains. It is presumed that the electrical resistance of the Mn-Zn ferrite can be effectively increased by adding an appropriate amount of Li2CO3, which can be dissolved in the crystal grains.

[0027] The Mn-Zn ferrite of the present disclosure may further contain, as an auxiliary component, one or more metal oxides selected from the group consisting of SiO2, CaO, and Nb2O5. At least a part of these auxiliary components is present in the grain boundaries, and can increase the electrical resistance, reduce eddy current loss, and increase the magnetic permeability in the high frequency band.

[0028] In the Mn-Zn ferrite of the present disclosure, the SiO2 content is not particularly limited, and is preferably 0.005 to 0.050 mass% relative to 100 mass% of the total amount of the main components. The lower limit is more preferably 0.010 mass%, and the upper limit is more preferably 0.040 mass%, and particularly preferably 0.030 mass%. When the SiO2 content is within the above range, the Mn-Zn ferrite of the present disclosure has high electrical resistance, is suppressed from decreasing in magnetic permeability in the high frequency band, and has good magnetic permeability over a wide frequency band.

[0029] The CaO content is not particularly limited, and is preferably 0.005 to 0.080 mass% relative to 100 mass% of the total amount of the main components. The lower limit is more preferably 0.010 mass%, and the upper limit is more preferably 0.070 mass%, and particularly preferably 0.060 mass%. When the CaO content is within the above range, the Mn-Zn ferrite of the present disclosure has high electrical resistance, is suppressed from decreasing in magnetic permeability in the high frequency band, and has good magnetic permeability over a wide frequency band.

[0030] The content of Nb2O5 is not particularly limited, and is preferably 0.005 to 0.080 mass% relative to 100 mass% of the total amount of the main components. The lower limit is more preferably 0.010 mass%, and the upper limit is more preferably 0.070 mass%, and particularly preferably 0.060 mass%. When the content of Nb2O5 is within the above range, the Mn-Zn-based ferrite of the present disclosure has high electrical resistance, is suppressed from decreasing in magnetic permeability in the high frequency band, and has good magnetic permeability over a wide frequency band.

[0031] The Mn-Zn ferrite of the present disclosure preferably contains, as accessory components, 0.100 to 0.800 mass% Li2CO3, 0.600 to 1.700 mass% CuO, 0.005 to 0.050 mass% SiO2, 0.005 to 0.080 mass% CaO, and 0.005 to 0.080 mass% Nb2O5.

[0032] The Mn-Zn ferrite of the present disclosure may contain one or more optional components other than those described above, as necessary. The optional components other than those described above include other metal oxides such as TiO2, NiO, ZrO2, MoO3, Ta2O5, and Bi2O3; other inorganic compounds other than oxides; and inevitable elements such as C (carbon), P (phosphorus), and B (boron). The total content of one or more optional components other than those mentioned above is preferably 0 to 0.1 mass %, more preferably 0 to 0.01 mass %, and particularly preferably 0 to 0.001 mass %, relative to 100 mass % of the total amount of the main components.

[0033] The complex relative permeability (μ) is expressed by the following formula (1). μ = μ'-jμ” (1) Here, μ' is the real part (inductance component) of the complex relative permeability, μ" is the imaginary part (resistance component) of the complex relative permeability, and j is the imaginary unit. Impedance Z (Ω) is expressed by the following equation (2). Z=(R 2 +X 2 ) 1 / 2 (2) Here, R and X are represented by the following formulas (3) and (4), respectively. R = (μ” 2πfn 2 A e μ 0 ) / L e (3) X = (μ' 2πfn 2 A e μ 0 ) / L e (4) where f is the frequency (kHz), n is the number of turns in the coil, and A e is the effective cross-sectional area of ​​ferrite (mm 2 ), L e is the magnetic path length of the ferrite (mm), μ 0 is the vacuum permeability (4π×10 -7 (H / m). The complex relative permeability (μ) can be measured using an impedance analyzer by the method described in the Examples section below.

[0034] The real part (μ') of the complex relative permeability at 100 kHz (low frequency condition) of the Mn-Zn ferrite of the present disclosure is not particularly limited, and is preferably 30 to 500. The lower limit is more preferably 50, still more preferably 80, still more preferably 100, particularly preferably 120, and most preferably 150. The upper limit is more preferably 400, particularly preferably 300, and most preferably 200. If the real part (μ') of the complex relative permeability at 100 kHz (low frequency condition) is too high, the permeability may decrease significantly in the high frequency band. If the real part (μ') of the complex relative permeability at 100 kHz (low frequency condition) is within the above range, the Mn-Zn ferrite of the present disclosure can suppress the decrease in permeability in the high frequency band and have good permeability in a wide frequency band.

[0035] The real part (μ') of the complex relative permeability at 100 MHz (high frequency condition) of the Mn-Zn ferrite of the present disclosure is not particularly limited, and is preferably 30 to 100. The lower limit is more preferably 35, particularly preferably 40, and most preferably 45. The upper limit is more preferably 90, even more preferably 80, particularly preferably 70, and most preferably 60. If the real part (μ') of the complex relative permeability at 100 MHz (high frequency condition) is within the above range, the Mn-Zn-based ferrite of the present disclosure can have sufficiently high permeability in the high frequency band and good permeability over a wide frequency band.

[0036] An example of the electrical resistance parameter is resistivity. The resistivity of the Mn-Zn ferrite of the present disclosure is not particularly limited, and is preferably 1.0×10 5 ~9.0×10 6 The lower limit is preferably 5.0×10 5 Ω·m, particularly preferably 8.0×10 5 Ω m, most preferably 1.0×10 6 The upper limit is preferably 8.0×10 6 Ω·m, and more preferably 7.0×10 6 Ω·m, especially preferably 6.0×10 6 Ω·m, most preferably 5.0×10 6 Ω m. When the resistivity is equal to or higher than the lower limit, the Mn-Zn ferrite of the present disclosure has sufficiently high electrical resistance, is suppressed from decreasing in magnetic permeability in high frequency bands, and has good magnetic permeability over a wide frequency band. The resistivity can be measured by the method described in the Examples section below.

[0037] The average crystal grain size of the Mn-Zn ferrite of the present disclosure is not particularly limited. By reducing the average crystal grain size, the electrical resistance can be increased. The average crystal grain size is preferably 1 to 10 μm. The upper limit is more preferably 9 μm, particularly preferably 8 μm, and most preferably 5 μm. The lower limit is more preferably 2 μm, and particularly preferably 3 μm. When the average crystal grain size is equal to or less than the upper limit, the Mn-Zn ferrite of the present disclosure has high electrical resistance, is suppressed from decreasing in magnetic permeability in the high frequency band, and has good magnetic permeability over a wide frequency band. The "average crystal grain size" can be measured by the method described in the Examples section below. The average crystal grain size can be adjusted by the raw material composition, the grain size of the mixed powder obtained after completion of step (S1) described below, the pressing pressure during press molding, the sintering temperature, the sintering time, and the like.

[0038] The density of the sintered body made of the Mn-Zn ferrite of the present disclosure is not particularly limited. By increasing the density of the sintered body, the saturation magnetic flux density (Bs) and saturation magnetization (Ms) can be increased, the threshold frequency (fr) can be increased, and the magnetic permeability in the high frequency band can be increased. The density of the sintered body is preferably 4.50 to 5.50 kg / m 3 The lower limit is more preferably 4.55 kg / m 3 , and more preferably 4.60 kg / m 3 , particularly preferably 4.65 kg / m 3 , most preferably 4.70 kg / m 3 The upper limit is more preferably 5.00 kg / m 3 , particularly preferably 4.80 kg / m 3 It is. When the density of the sintered body is equal to or higher than the above lower limit, the Mn-Zn ferrite of the present disclosure has high electrical resistance, is inhibited from decreasing in magnetic permeability in the high frequency band, and has good magnetic permeability over a wide frequency band. The density of the sintered body can be adjusted by the raw material composition, the particle size of the mixed powder obtained after completion of step (S1) described below, the pressing pressure during press molding, the sintering temperature, the sintering time, and the like.

[0039] [Manufacturing method of Mn-Zn ferrite] The method for producing the Mn-Zn-based ferrite of the present disclosure is not particularly limited, A step (S1) of preparing a mixed powder containing Fe2O3 powder, MnO powder, ZnO powder, Li2CO3 powder, and CuO powder; A step (S2) of molding the mixed powder to obtain a molded body; The method may further include a step (S3) of sintering the green body.

[0040] (Process (S1)) As the raw material powders, Fe2O3 powder, MnO powder, ZnO powder, Li2CO3 powder, and CuO powder are prepared. As the raw material powders, one or more oxide powders selected from the group consisting of SiO2 powder, CaO powder, and Nb2O5 powder may be prepared as necessary. As the raw material powders, one or more other metal oxides may be further prepared as necessary. The prepared multiple raw material powders are mixed. The prepared multiple raw material powders may be mixed all at once or in portions, and the mixing procedure is not particularly limited. Since a uniform mixed powder with a small average particle size is obtained, it is preferable to carry out one or more operations of dispersion, crushing, and pulverization on the prepared multiple raw material powders after or at the same time as mixing.

[0041] The mixing, dispersion, crushing, and pulverization can be carried out by known methods using devices such as powder mixers, ball mills, bead mills, media-agitation type mills, and combinations thereof, etc. Among these, media-agitation type mills such as wet or dry media-agitation type grinders are preferred. In addition, there is no clear definition of crushing and pulverization, and no clear distinction is made between them. In the following description, the term "crushing" is used as a general term for crushing and pulverization. In step (S1), the raw material powder or mixed powder may be subjected to known treatments such as addition of a liquid medium, drying, calcination, granulation, and combinations thereof, as necessary. Powders can be granulated to form granules. There is no clear definition of powder and granules, and no clear distinction between them. In this specification, the term "powder" is used as a general term for powders and granules.

[0042] The particle size parameter of the mixed powder obtained after the step (S1) is the median diameter (d50). The particle size distribution and the median diameter (d50) of the mixed powder obtained after the step (S1) can be measured by a known method using a particle size distribution measuring device. The median diameter (d50) of the mixed powder obtained after the step (S1) is not particularly limited, and is preferably 0.1 to 1.5 μm. The lower limit is more preferably 0.2 μm, particularly preferably 0.3 μm, and most preferably 0.5 μm. The upper limit is more preferably 1.2 μm, even more preferably 1.0 μm, particularly preferably 0.9 μm, and most preferably 0.8 μm. When the median diameter (d50) is equal to or less than the upper limit described above, the density of the sintered body can be increased, thereby increasing the saturation magnetic flux density (Bs) and saturation magnetization (Ms), increasing the threshold frequency (fr), and increasing the magnetic permeability in the high frequency band.

[0043] (Process (S2)) The mixed powder obtained after the step (S1) is molded by a known method, and compression molding is preferred. The shape and size of the molded body are not particularly limited and can be designed according to the application, etc. Examples of the shape of the molded body include a circular ring (toroidal shape), a rod shape (I-shape), and an E-shape.

[0044] (Process (S3)) The molded body obtained after step (S2) is sintered. The firing for sintering can be carried out in one step or multiple steps. When firing is carried out in multiple steps, the firing can include one or more preliminary firings and main firings. The sintering atmosphere (the main sintering atmosphere when sintering is performed in multiple stages) is not particularly limited. Conventional Mn-Zn ferrites are generally sintered in a relatively low oxygen concentration atmosphere with an oxygen concentration of about 3%. Research by the present inventors has revealed that the electrical resistance of the sintered body can be increased by sintering in an atmosphere with a higher oxygen concentration than the conventional sintering atmosphere. The oxygen concentration in the sintering atmosphere is preferably 5% or more. The lower limit is more preferably 8%, further preferably 10%, and particularly preferably 15%. The most preferred sintering atmosphere is an air atmosphere (oxygen concentration: about 21%).

[0045] The sintering temperature (main sintering temperature when sintering is performed in multiple stages) is not particularly limited. For conventional Mn-Zn ferrite, the temperature is generally around 1300°C. According to the research of the present inventors, it has been found that by sintering at a temperature lower than the conventional sintering temperature, the average crystal grain size of the sintered body can be reduced, thereby reducing eddy current loss and increasing magnetic permeability in the high frequency band. The sintering temperature is preferably 950 to 1250° C. The sintering temperature is preferably about 1200° C., about 1100° C., or about 1000° C. The sintering temperature is more preferably 950 to 1100° C., and particularly preferably 950 to 1050° C. The sintering temperature is most preferably about 1000° C. The time for which the sintering temperature is maintained is referred to as the sintering time. The sintering time is not particularly limited, and is preferably 1 to 24 hours, more preferably 5 to 15 hours, and particularly preferably 8 to 12 hours. Approximately 10 hours is particularly preferable. The average crystal grain size can be adjusted by the sintering temperature and sintering time.

[0046] The firing can be carried out using a known firing furnace. After stopping the holding at the sintering temperature, an inert gas at room temperature can be flowed into the sintering furnace, and the obtained sintered body can be air-cooled in the sintering furnace. The inert gas is preferably a gas with an oxygen concentration of 0.1% or less, and nitrogen gas or the like is preferable. For example, when sintering is performed at about 1000°C, it is preferable that the atmosphere in the sintering furnace is gradually replaced with an inert gas after heating is stopped, and the sintering furnace becomes an inert gas atmosphere by the time the temperature is lowered to about 800°C. The temperature at which the atmosphere in the sintering furnace is replaced with an inert gas (preferably the temperature at which the oxygen concentration becomes 0.1% or less) is preferably 700 to 900°C, more preferably 750 to 850°C. The inert gas at room temperature can be continued to flow as it is, and the obtained sintered body can be air-cooled to room temperature. According to the research of the present inventors, it was found that air-cooling under such conditions can increase the electrical resistance of the sintered body.

[0047] As described above, according to the present disclosure, it is possible to provide an Mn-Zn ferrite having high electrical resistance, suppressed decrease in magnetic permeability in the high frequency band, and favorable magnetic permeability in a wide frequency band from low to high frequencies, and a manufacturing method thereof. The Mn-Zn ferrite of the present disclosure has a lower raw material cost than Ni-Zn ferrite and can have frequency characteristics at the same level as Ni-Zn ferrite. The Mn-Zn ferrite of the present disclosure also has a sufficiently high electrical resistance, and therefore does not require the use of an insulating member such as a resin bobbin, unlike conventional Mn-Zn ferrites. By using the Mn-Zn ferrite of the present disclosure, the manufacturing cost of electronic components such as noise filters can be reduced by reducing raw material costs and not using insulating members.

[0048] [Application] The Mn-Zn-based ferrite of the present disclosure is suitable as a material for electronic components such as noise filters, such as EMI (Electro Magnetic Interference) removal filters, transformers, and inductors. For example, a noise filter including a ferrite core made of the Mn-Zn ferrite of the present disclosure can remove noise in a wide frequency band from low to high frequencies. EXAMPLES

[0049] Examples and comparative examples according to the present invention will be described below. [Evaluation items and evaluation methods] The evaluation items and evaluation methods are as follows. (Crushed particle size) The median diameter (d50) of the mixed powder obtained after the crushing and mixing was measured as the particle size (crushed particle size) of the mixed powder using a particle size distribution measuring device.

[0050] (Electrical Resistance) The resistivity (unit: Ω·m) of the sintered bodies obtained in each example was measured as electrical resistance (DC resistance) using an impedance analyzer. The measurement conditions were a temperature of 25°C, a frequency of 100Hz to 5.5MHz, and a current of 0.1mA.

[0051] (Average grain size) The surface of the sintered body obtained in each example was mirror-polished, the grain boundary phase was dissolved and removed using an etching solution (hydrofluoric acid, hydrochloric acid, etc.), and the sample was thoroughly dried. The surface of this sample was observed using a microscope, and the maximum diameter of each of 100 randomly selected crystal grains was measured by image analysis to determine their average grain size.

[0052] (complex relative permeability) A metal wire (copper wire with an outer diameter of 0.5 mmφ) was wound 10 times around the sintered compact obtained in each example, and the real part (μ') and imaginary part (μ") of the complex relative permeability were measured using an impedance analyzer while changing the frequency. The measurement conditions were a temperature of 25°C, a frequency of 10 kHz to 100 MHz, and a current of 0.1 mA. The real part (μ') of the complex relative permeability was determined at 10 kHz (low frequency condition) and 10 MHz (high frequency condition).

[0053] [Example 1-1] As raw material powders, Fe2O3 powder, MnO powder, ZnO powder, SiO2 powder, CaO powder, Nb2O5 powder, Li2CO3 powder, and CuO powder were prepared. Each raw material powder was weighed so that the main component composition after sintering would be Fe2O3: 49.75 mol%, MnO: 32.52 mol%, ZnO: 17.73 mol%, and the subcomponent composition after sintering would be SiO2: 0.01 mass%, CaO: 0.04 mass%, Nb2O5: 0.04 mass%, Li2CO3: 0.30 mass%, and CuO: 1.00 mass%. The amount of each subcomponent is the amount relative to the total amount of the main components, 100 mass%.

[0054] Fe2O3 powder, MnO powder, ZnO powder, and an appropriate amount of liquid medium were put into a media stirring type ultrafine grinding and dispersing machine (Nippon Coke Engineering Co., Ltd.'s "Attritor (wet)") and crushed and mixed at room temperature for 30 minutes. The crushed particle size (median diameter (d50)) of the mixed powder obtained after crushing and mixing was 1.0 μm. 0.8 parts by mass of polyvinyl alcohol was added to 100 parts by mass of the obtained mixed powder, and the mixture was sprayed with a spray dryer to obtain granules. The obtained granules were calcined at 850°C for 1 hour in an air atmosphere. SiO2 powder, CaO powder, Nb2O5 powder, Li2CO3 powder, CuO powder, and an appropriate amount of liquid medium were added to the obtained calcined product, and the mixture was put into a media stirring type ultrafine grinding and dispersing machine (Nippon Coke & Engineering Co., Ltd.'s "Attritor (wet)") and crushed and mixed at room temperature for 3 hours. The crushed particle size (median diameter (d50)) of the mixed powder obtained after crushing and mixing was 0.8 μm. 0.8 parts by mass of polyvinyl alcohol was added to 100 parts by mass of the obtained mixed powder, mixed, and the resulting mixture was sprayed with a spray dryer to obtain granules.

[0055] The resulting granules were compressed using a press to obtain a toroidal compact. The density of this unsintered compact was 2.95 kg / m 3 The molded body was placed in a sintering furnace and sintered by holding it in an air atmosphere at 1000°C for 10 hours. Note that 1000°C is the set temperature of the sintering furnace. Heating in the sintering furnace was stopped, and room temperature nitrogen gas was flowed into the furnace to air-cool the sintered body obtained in the furnace. Approximately 2 hours after heating was stopped, the atmosphere in the furnace was replaced with nitrogen gas, the oxygen concentration became 0.1% or less, and the temperature dropped to approximately 800°C. Room temperature nitrogen gas was continued to flow, and the sintered body obtained was air-cooled to room temperature. In this way, a toroidal Mn-Zn ferrite polycrystalline sintered body was obtained with an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm. The obtained Mn-Zn ferrite was a sintered body in which the components Fe2O3, MnO, ZnO, Li2CO3, and CuO were distributed throughout, and the density of the sintered body was 4.75 kg / m 3 It was.

[0056] The Fe2O3 powder, MnO powder, ZnO powder, SiO2 powder, CaO powder, Nb2O5 powder, Li2CO3 powder, and CuO powder may be mixed together or mixed separately, and the mixing procedure is not particularly limited. Powder processing such as addition of liquid medium, drying, calcination, and granulation are optional. The same Mn-Zn ferrite polycrystalline sintered body as above can also be obtained by crushing and mixing Fe2O3 powder, MnO powder, ZnO powder, SiO2 powder, CaO powder, Nb2O5 powder, Li2CO3 powder, and CuO powder together, forming, and sintering.

[0057] [Examples 1-2 to 1-5, 2-1 to 2-4, 3-1 to 3-4, 4-1 to 4-4, 5-1 to 5-4, 6-1 to 6-4, 7-1 to 7-4, 8-1 to 8-4, 9-1 to 9-4] In each example, Mn-Zn ferrite sintered bodies were obtained in the same manner as in Example 1-1, except that one or more of the conditions of composition, density of sintered body, and average crystal grain size were changed. The density of the sintered body was adjusted by the raw material composition and the pressing pressure during press molding. The average crystal grain size was adjusted by the raw material composition and sintering temperature (within the range of 1000 to 1300°C).

[0058] [Comparative Examples 1-11 to 1-14, 2-11 to 2-14, 3-11 to 3-14, 4-11 to 4-14] In each example, Mn-Zn ferrite sintered bodies were obtained in the same manner as in Example 1-1, except that one or more of the conditions of composition, density of sintered body, and average crystal grain size were changed. The density of the sintered body was adjusted by the raw material composition and the pressing pressure during press molding. The average crystal grain size was adjusted by the raw material composition and sintering temperature (within the range of 1000 to 1300°C).

[0059] [Evaluation Results] The composition and evaluation results of the Mn-Zn ferrite sintered bodies obtained in each example are shown in Tables 1 to 9. In these tables, Ex indicates an example according to the present invention, and ExC indicates a comparative example. In these tables, "density" indicates the density of the sintered body, and "grain size" indicates the average grain size of the sintered body.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3]

[0063] [Table 4]

[0064] [Table 5]

[0065] [Table 6]

[0066] [Table 7]

[0067] [Table 8]

[0068] [Table 9]

[0069] [Summary of results] In Examples 1-1 to 1-5, 2-1 to 2-4, 3-1 to 3-4, 4-1 to 4-4, 5-1 to 5-4, 6-1 to 6-4, 7-1 to 7-4, 8-1 to 8-4, and 9-1 to 9-4, Mn-Zn ferrite was obtained that contained 49.30 to 52.00 mol% of Fe2O3, 30.00 to 35.00 mol% of MnO, and 13.00 to 20.70 mol% of ZnO as main components relative to 100 mol% of the total amount of the main components, and contained 0.100 to 0.800 mass% of Li2CO3 and 0.600 to 1.700 mass% of CuO as accessory components relative to 100 mass% of the total amount of the main components.

[0070] The Mn-Zn ferrite obtained in these examples all had a resistivity of 1.0×10 5 ~9.0×10 6 The real part of the complex relative permeability (μ') at 100 kHz (low frequency condition) was 30 to 500, and the real part of the complex relative permeability (μ') at 100 MHz (high frequency condition) was 30 to 100. All of the Mn-Zn ferrites obtained in these examples had high electrical resistance, suppressed a decrease in magnetic permeability in the high frequency band, and had good magnetic permeability over a wide frequency band from low to high frequencies. All of the Mn-Zn ferrites obtained in these examples had suitable properties for use as noise filters and the like.

[0071] In Comparative Examples 1-11 to 1-14, 2-11 to 2-14, 3-11 to 3-14, and 4-11 to 4-14, Mn—Zn ferrites whose compositions were outside the scope of the present disclosure were obtained. The Mn-Zn ferrites obtained in these comparative examples all had a resistivity of 1.0×10 5 The magnetic permeability was less than Ω·m, and / or the real part of the complex relative permeability (μ') at 100 MHz (high frequency condition) was less than 30, so the material did not have suitable characteristics for use as a noise filter, etc.

[0072] [Permeability vs. Frequency] The frequency characteristics of the Mn-Zn ferrite of the present disclosure, the Ni-Zn ferrite, and the Mn-Zn ferrite of a conventional composition were compared. As representative samples, the Mn-Zn ferrite (Example 1-1) having the composition shown in Table 10, the Ni-Zn ferrite (Comparative Example 11) having the composition shown in Table 10, and the Mn-Zn ferrite (Comparative Example 12) having the conventional composition shown in Table 10 were prepared (all polycrystalline sintered bodies). The solid curve in FIG. 1 shows an example of the frequency characteristics of the real part (μ') of the complex relative permeability of these ferrites. The dashed curve in FIG. 1 shows an example of the frequency characteristics of the imaginary part (μ'') of the complex relative permeability of these ferrites. In Table 10 and FIG. 1, Ex indicates an example according to the present invention, and ExC indicates a comparative example.

[0073] [Table 10]

[0074] 1, the Mn-Zn ferrite (conventional composition) of Comparative Example 12 had a higher real part (μ') of complex relative magnetic permeability in a relatively low frequency band (for example, 1 MHz or less) than the Ni-Zn ferrite of Comparative Example 11. However, the Mn-Zn ferrite (conventional composition) of Comparative Example 12 showed a large decrease in the real part (μ') of complex relative magnetic permeability as the frequency increased in a high frequency band of 10 MHz or more, and the real part (μ') of complex relative magnetic permeability was large compared to the Ni-Zn ferrite at around 100 MHz.

[0075] In the Mn-Zn ferrite obtained in Example 1-1, the frequency dependency of the real part (μ') of the complex relative magnetic permeability was improved, and the frequency characteristics of the real part (μ') of the complex relative magnetic permeability were equivalent to those of Ni-Zn ferrite. In the Mn-Zn ferrite obtained in Example 1-1, the decrease in the real part (μ') of the complex relative magnetic permeability in the high frequency band of 10 MHz or more was suppressed, and even at 100 MHz, the real part (μ') of the complex relative magnetic permeability at the same level as that of Ni-Zn ferrite was realized. The Mn-Zn ferrites obtained in Examples 1-2 to 1-5, 2-1 to 2-4, 3-1 to 3-4, 4-1 to 4-4, 5-1 to 5-4, 6-1 to 6-4, 7-1 to 7-4, 8-1 to 8-4, and 9-1 to 9-4 also gave results similar to those of the Mn-Zn ferrite obtained in Example 1-1.

[0076] [SEM-EDX analysis] Using a scanning electron microscope (SEM), an energy dispersive X-ray (EDX) analysis was performed on the SEM image of the Mn-Zn ferrite obtained in Example 1-1, and the distribution of main metal elements was displayed in color, with each metal element being shown in a different color. It was confirmed that the Mn-Zn ferrite obtained in Example 1-1 was a polycrystalline body in which at least one of the main components and at least one of Li2CO3 and CuO were present in at least some of the crystal grains. Similar results were obtained in the Mn-Zn ferrites obtained in Examples 1-2 to 1-5, 2-1 to 2-4, 3-1 to 3-4, 4-1 to 4-4, 5-1 to 5-4, 6-1 to 6-4, 7-1 to 7-4, 8-1 to 8-4, and 9-1 to 9-4.

[0077] The present invention is not limited to the above-described embodiment and examples, and appropriate design changes are possible without departing from the spirit of the present invention.

Claims

1. 49.30 to 52.00 mol% Fe relative to 100 mol% of the total amount of the main components ２ O ３ and a main component consisting of 30.00 to 35.00 mol % MnO and 13.00 to 20.70 mol % ZnO; As an auxiliary component, 0.100 to 0.800 mass% of Li ２ CO ３ and 0.600 to 1.700 mass % of CuO.

2. Further, as a subcomponent, 0.005 to 0.050 mass% of SiO based on 100 mass% of the total amount of the main components. ２ , 0.005 to 0.080 mass% CaO, and 0.005 to 0.080 mass% Nb ２ O ５ 2. The Mn-Zn ferrite according to claim 1, comprising one or more oxides selected from the group consisting of:

3. As an auxiliary component, 0.100 to 0.800 mass% of Li ２ CO ３ 0.600 to 1.700 mass% CuO, and 0.005 to 0.050 mass% SiO ２ 0.005 to 0.080 mass% CaO, and 0.005 to 0.080 mass% Nb ２ O ５ The Mn-Zn ferrite according to claim 2, comprising:

4. The real part (μ′) of the complex relative permeability at 25° C. and 100 kHz is 30 to 500; 3. The Mn-Zn ferrite according to claim 1, wherein the real part (μ′) of the complex relative permeability at 25° C. and 100 MHz is 30 to 100.

5. Resistivity is 1.0 x 10 ５ ~9.0 x 10 ６ The Mn-Zn ferrite according to claim 1 or 2, wherein the Mn-Zn ferrite has a strength of Ω·m.

6. 3. The Mn-Zn ferrite according to claim 1, which is a polycrystalline body having an average crystal grain size of 1 to 10 μm.

7. Density: 4.50-5.50 kg / m ３ 3. The Mn-Zn ferrite according to claim 1 or 2, which is a sintered body as described above.

8. Fe ２ O ３ powder, MnO powder, ZnO powder, and Li ２ CO ３ 3. The Mn-Zn ferrite according to claim 1, which is a sintered body of a mixed powder containing a Mn-Zn powder and a CuO powder.

9. At least one of the main components and Li are present in at least some of the crystal grains. ２ CO ３ 3. The Mn-Zn ferrite according to claim 1, which is a polycrystalline body containing at least one of MnO and CuO.

10. Fe ２ O ３ powder, MnO powder, ZnO powder, and Li ２ CO ３ preparing a mixed powder containing a powder and a CuO powder; A step of forming the mixed powder into a molded body; 3. The method for producing Mn-Zn ferrite according to claim 1, further comprising a step of sintering the molded body.

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