Method for producing magnetoplumbite-type hexagonal ferrite magnetic powder

Abstract

To provide a method for manufacturing a magnetoplumbite-type hexagonal ferrite magnetic powder capable of making a ferrite-based bond magnet exhibit excellent residual magnetization.SOLUTION: A first embodiment of the invention is a method of producing a magnetoplumbite-type hexagonal ferrite magnetic powder, including a firing step of firing a mixture containing a raw material powder and a metal chloride to obtain a fired product, and a pulverizing step of pulverizing the fired product to obtain a powder, in which a molar ratio of an amount of Cl contained in the metal chloride to an amount of Fe contained in the raw material powder is 0.002 or more and 0.020 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing magnetoplumbite-type hexagonal ferrite magnetic powder. [Background technology]

[0002] Traditionally, sintered ferrite magnets have been used as high-magnetic-force magnets, such as those used in small motors for AV equipment, office automation equipment, and automotive electrical components, and in magnet rolls in copiers. However, sintered ferrite magnets have problems such as poor productivity due to chipping and the need for polishing, as well as difficulty in processing them into complex shapes. Bonded rare-earth magnets, for example, are examples of high-magnetic-force magnets that offer excellent productivity and processability. However, rare-earth magnets cost about 20 times as much as sintered ferrite magnets and are prone to rust. For this reason, in recent years, bonded ferrite magnets containing ferrite powder and a binder such as resin or rubber have been used instead of sintered ferrite magnets and bonded rare-earth magnets.

[0003] However, because ferrite-based bonded magnets contain binders such as resin or rubber, they have a lower density than sintered ferrite magnets, which can result in reduced magnetic properties (residual magnetization). To solve this problem, efforts are underway to develop ferrite powders that can impart the excellent magnetic properties of sintered ferrite magnets.

[0004] For example, Patent Document 1 proposes a method for producing ferrite powder for anisotropic bonded magnets, with the aim of obtaining ferrite powder for anisotropic bonded magnets that can be used to produce bonded magnets with high magnetic force, excellent filling ability and orientation while maintaining coercivity. The method includes the steps of granulating multiple raw materials including iron oxide to obtain a granulated product, firing the granulated product under chloride vapor pressure in an atmosphere of 1050°C to 1300°C to obtain a fired product, and crushing or pulverizing the fired product to obtain a powder. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-263201 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the ferrite powder obtained by the conventional manufacturing method has room for improvement in terms of imparting excellent remanent magnetization to the ferrite-based bonded magnet.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for producing magnetoplumbite-type hexagonal ferrite magnetic powder that can provide excellent remanent magnetization in ferrite-based bonded magnets. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have completed the present invention described below.

[0009] That is, the gist and configuration of the present invention for solving the above-mentioned problems is as follows.

[0010] [1] A method for producing magnetoplumbite-type hexagonal ferrite magnetic powder, a calcination step of calcining a mixture containing the raw material powder and the metal chloride to obtain a calcined product; a grinding step of grinding the fired product to obtain a powder; Including, A method for producing magnetoplumbite-type hexagonal ferrite magnetic powder, wherein the molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the raw material powder is 0.002 or more and 0.020 or less.

[0011] [2] A method for producing magnetoplumbite-type hexagonal ferrite magnetic powder, a firing step of firing a first mixture containing a first raw material powder and a metal chloride to obtain a first fired product; a pulverization step of pulverizing the first fired product to obtain a first hexagonal ferrite powder; a mixing step of mixing the first hexagonal ferrite powder with a second hexagonal ferrite powder different from the first hexagonal ferrite powder to obtain a mixed powder; Including, A method for producing magnetoplumbite-type hexagonal ferrite magnetic powder, wherein the molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the first raw material powder is 0.002 or more and 0.020 or less.

[0012] [3] The method for producing the magnetoplumbite-type hexagonal ferrite magnetic powder according to [2], wherein the second hexagonal ferrite powder is obtained by pulverizing a second sintered product obtained by sintering the second raw material powder at a sintering temperature of 900°C or higher but lower than 1100°C.

[0013] [4] The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to any one of [1] to [3], wherein the firing temperature in the firing step is 1100°C or higher and 1220°C or lower.

[0014] [5] The method for producing the magnetoplumbite-type hexagonal ferrite magnetic powder according to any one of [1] to [4], further comprising an annealing step of annealing the powder or the mixed powder.

[0015] [6] The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to [5], wherein the annealing temperature in the annealing step is 900°C or higher and 1000°C or lower.

[0016] [7] The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to any one of [1] to [6], wherein the metal chloride is at least one selected from the group consisting of potassium chloride, sodium chloride, and lithium chloride.

[0017] [8] The method for producing a magnetoplumbite-type hexagonal ferrite magnetic powder according to any one of [1] to [7], wherein the raw material powder or the first raw material powder contains a strontium compound. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a method for producing magnetoplumbite-type hexagonal ferrite magnetic powder that can provide excellent remanent magnetization in a ferrite-based bonded magnet. DETAILED DESCRIPTION OF THE INVENTION

[0019] (Terminology and Measurement Methods) First, prior to describing the embodiments, the terms and measurement methods used in this specification will be explained.

[0020] <Magnetoplumbite-type hexagonal ferrite magnetic powder> Magnetoplumbite-type hexagonal ferrite magnetic powder (hereinafter, sometimes simply referred to as "hexagonal ferrite magnetic powder") means a powder that has a peak attributable to the crystal structure of magnetoplumbite-type hexagonal ferrite when measured with an X-ray diffraction device.

[0021] <Average value of major axis length / minor axis length> The ratio of the major axis length to the minor axis length (major axis length / minor axis length) of particles constituting the hexagonal ferrite magnetic powder is calculated by the following procedure. 4.5g of hexagonal ferrite magnetic powder, 5.7g of nitrocellulose lacquer (clear lacquer, manufactured by Washin Paint Co., Ltd.), and 30g of 2mm diameter stainless steel beads were placed in a centrifugal ball mill (PULNERISETTE type 702, manufactured by FRITSCH) and ground at 200 rpm for 20 minutes to obtain a dispersed coating material. The resulting coating material was then applied to a 0.1mm thick polyethylene terephthalate (PET) sheet (oil transparency) using an applicator bar, and an aligning magnetic field of 5kOe was applied parallel to the coated surface to align the magnetic powder, followed by drying in this state. The dried sheet was then observed using a scanning electron microscope (SEM) (Hitachi High-Technologies Corporation, S-3400N), and the major and minor axis lengths of 200 or more particles (200 or more particles with a major axis length of 1.0 μm or more whose entire outer edge is observed within one or more fields of view of the SEM photograph) in a 5000x magnification SEM photograph were measured, and the average value of (major axis length / minor axis length) was calculated. Here, the major axis length is the maximum distance between two parallel lines when one particle is sandwiched between them, and the minor axis length is the minimum distance between two parallel lines when one particle is sandwiched between them.

[0022] <Average particle size> The average particle diameter (APD) of the hexagonal ferrite magnetic powder is calculated by the air permeation method using a specific surface area measuring device (Shimadzu Corporation, SS-100) according to the following procedure. A 5.0 g sample was pelletized to a height of 10 mm and placed in the device. The specific surface area Sw calculated by the air permeation method and the specific gravity ρ (5.1 g / cm) of hexagonal ferrite were measured. 3 ) and calculate the average particle size using APD = 6 / (ρ × Sw). The specific surface area Sw is calculated by Sw = 14 / ρ × {(ΔP × A × t) / (η × L × Q) × ε 3 / (1-ε) 2} 1 / 2 The porosity ε of the sample packed bed can be calculated by the formula: ε = 1 - W / (ρ × A × L). The meanings of the various symbols in the formula are as follows: ΔP: Pressure difference (40.0g / cm 2 ) A: cross-sectional area of ​​the sample layer (2.0 cm 2 ) η: Viscosity coefficient of air (180×10 -6 P (poise) L: thickness of the sample layer (thickness of the ring (cm)) W: weight of sample (5.0g) Q: Air permeability (2.0cm 3 ) t: Time required for air to pass through (measured value (sec))

[0023] <Specific surface area> The specific surface area of ​​the hexagonal ferrite magnetic powder is the specific surface area measured by the BET method using a specific surface area measuring device (Monosorb manufactured by Quantachrome Co., Ltd.) by the BET single-point method. Note that the measurement is carried out using 1 g of sample after degassing at 200°C for 10 minutes.

[0024] <Compressed density> The compressed density of the hexagonal ferrite magnetic powder is calculated by the following procedure. 10 g of hexagonal ferrite magnetic powder was filled into a cylindrical mold with an inner diameter of 2.54 cm and subjected to a pressure of 1000 kg / cm 2 The density of the resulting compressed product is measured and this measured value is the compressed density of the hexagonal ferrite magnetic powder.

[0025] <Magnetic properties of hexagonal ferrite magnetic powder> The magnetic properties of the hexagonal ferrite magnetic powder are calculated by the following procedure. 8 g of hexagonal ferrite magnetic powder and 0.4 cc of polyester resin (P-resin, manufactured by Nihon Chikagaku Co., Ltd.) were mixed in a mortar, and 7 g of the resulting mixture was filled into a mold with an inner diameter of 15 mm and subjected to a pressure of 1 ton / cm. 2 The compact is compressed at a pressure of 1000 kJ for 60 seconds to obtain a molded product. The resulting molded product is removed from the mold and dried at 150°C for 30 minutes to obtain a green compact. Using a BH tracer (TRF-5BH, manufactured by Toei Kogyo Co., Ltd.), the remanence Br and coercivity iHc of the resulting green compact are measured in a magnetic field of 10 kOe. These measured values ​​are the remanence Br and coercivity iHc of the hexagonal ferrite magnetic powder.

[0026] <Second hexagonal ferrite powder different from the first hexagonal ferrite powder> The second hexagonal ferrite powder being different from the first hexagonal ferrite powder means that at least one of the composition, preparation conditions, and physical properties of the second hexagonal ferrite powder is different from that of the first hexagonal ferrite powder.

[0027] (Method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to the first embodiment) A manufacturing method of magnetoplumbite-type hexagonal ferrite magnetic powder according to a first embodiment of the present invention (hereinafter sometimes referred to as the "manufacturing method of the first embodiment") includes a sintering step in which a mixture containing a raw material powder and a metal chloride is sintered to obtain a sintered product, and a pulverizing step in which the sintered product is pulverized to obtain a powder, in which the molar ratio (Cl / Fe) of the amount of chlorine (Cl) contained in the metal chloride to the amount of iron (Fe) contained in the raw material powder is 0.002 or more and 0.020 or less. The hexagonal ferrite magnetic powder obtained by this manufacturing method can exhibit excellent remanence in ferrite-based bonded magnets. This is presumably because, by setting the molar ratio of Cl contained in the metal chloride to the amount of Fe contained in the raw material powder within the above range, the chloride is always present in a vapor state during sintering of the mixture, which improves the partial pressure relationship between the chloride vapor and gaseous components that may be generated from the raw material powder. As a result, the resulting hexagonal ferrite magnetic powder has a particle size and shape suitable for ferrite-based bonded magnets. Furthermore, the hexagonal ferrite magnetic powder obtained by the manufacturing method of the first embodiment can provide a ferrite-based bonded magnet with excellent coercive force and maximum energy product.

[0028] The manufacturing method of the first embodiment preferably further includes an annealing step in which the powder obtained in the pulverization step is annealed. If the manufacturing method of the first embodiment includes an annealing step, distortion in the powder's crystal structure caused by pulverization or the like can be effectively removed, and a hexagonal ferrite magnetic powder can be obtained that can provide a ferrite-based bonded magnet with superior remanence, coercivity, and maximum energy product.

[0029] <Firing process> In the manufacturing method of the first embodiment, in the firing step, a mixture containing raw material powder and metal chloride is fired to obtain a fired product. The mixture may contain components other than the raw material powder and the metal chloride (hereinafter, these may be referred to as "other components A").

[0030] In the manufacturing method of the first embodiment, the firing temperature in the firing step is preferably 1100°C or higher, more preferably 1150°C or higher, and is preferably 1220°C or lower, more preferably 1190°C or lower. If the firing temperature in the firing step is within the above range, it is possible to obtain a hexagonal ferrite magnetic powder that can effectively provide a ferrite-based bonded magnet with excellent remanence, coercive force, and maximum energy product. For example, when a box-type firing furnace is used, the firing container can be filled with the raw material powder, metal chloride, and any other component A. The atmosphere during firing is not particularly limited, but an oxidizing atmosphere is preferred, and the oxidizing atmosphere is preferably air, oxygen, a mixed gas of oxygen and nitrogen, a mixed gas of oxygen and a rare gas, or the like.

[0031] The raw material powder contained in the mixture is not particularly limited as long as it can produce hexagonal ferrite magnetic powder, but a mixed powder of an iron compound and a non-ferrous metal compound can be used.

[0032] As the iron compound, for example, iron oxide (hematite, magnetite, wustite, etc.), metallic iron, iron sulfate, etc. can be used, and these may be used alone or in combination of two or more.

[0033] Examples of non-ferrous metal compounds that can be used include carbonates, oxides, hydroxides, nitrates, oxalates, and alkoxides of non-ferrous metals. These may be used alone or in combination of two or more. Of these, carbonates are preferred. Examples of non-ferrous metals include strontium, barium, lanthanum, and cerium. These may be used alone or in combination of two or more. Of these, strontium is preferred. The non-ferrous metal compound is preferably a strontium compound, and more preferably strontium carbonate (SrCO3). That is, the raw material powder preferably contains a strontium compound, and more preferably strontium carbonate. If the raw material powder contains a strontium compound, a magnetoplumbite-type hexagonal strontium ferrite magnetic powder can be obtained, and the magnetoplumbite-type hexagonal strontium ferrite magnetic powder can enable a ferrite-based bonded magnet to exhibit excellent remanence, coercive force, and maximum energy product. It should be noted that non-ferrous metal compounds do not include metal chlorides and fluxes, which will be described later.

[0034] The metal chloride contained in the mixture can function as a flux. Examples of metal chlorides that can be used include alkali metal chlorides such as potassium chloride (KCl), sodium chloride (NaCl), lithium chloride (LiCl), rubidium chloride (RbCl), and cesium chloride (CsCl); alkaline earth metal chlorides such as barium chloride (BaCl), strontium chloride (SrCl), and calcium chloride (CaCl); and magnesium chloride (MgCl). These may be used alone or in combination of two or more. Among these, alkali metal chlorides are preferred because they can produce hexagonal ferrite magnetic powder that can exhibit superior remanence, coercivity, and maximum energy product in a ferrite-based bonded magnet. At least one selected from the group consisting of potassium chloride, sodium chloride, and lithium chloride is more preferred, and potassium chloride is even more preferred.

[0035] Here, in the manufacturing method of the first embodiment, the molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the raw material powder is 0.002 or more, preferably 0.005 or more, and is 0.020 or less, preferably 0.010 or less. The molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the raw material powder is not particularly limited as long as it is within the above range, but the amount of metal chloride added per 100 parts by mass of raw material powder is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, preferably 1.5 parts by mass or less, more preferably less than 1.0 part by mass, and even more preferably 0.8 parts by mass or less.

[0036] Other components A that may be contained in the mixture include, for example, fluxes other than the metal chlorides mentioned above. Examples of fluxes that can be used include bismuth oxide, boric acid, borates, sulfates, phosphates, silicic acid, silicates, etc. These may be used alone or in combination of two or more.

[0037] In the manufacturing method of the first embodiment, in the firing step, the mixture containing the raw material powder, the metal chloride, and any other component A may be fired as is, or the mixture may be granulated and the resulting granules may be fired. The granulation method is not particularly limited, and the granules may be formed into pellets by any method. If the granulated product contains moisture, the granules may be further dried thereafter.

[0038] <Crushing process> In the manufacturing method of the first embodiment, in the pulverization step, the fired product obtained in the firing step is pulverized to obtain powder. The powder obtained in the above-mentioned pulverization step can be used as the magnetoplumbite-type hexagonal ferrite magnetic powder obtained by the manufacturing method of the first embodiment.

[0039] In the manufacturing method of the first embodiment, the pulverization step is not particularly limited, but may include coarse pulverization and fine pulverization.

[0040] Here, coarse pulverization means roughly pulverizing the fired product, and any pulverizing method such as impact pulverization using a hammer mill can be used. The particle size of the coarse powder obtained by coarsely pulverizing the fired product is not particularly limited, but is usually 5 mm or less in consideration of handling in the subsequent pulverization step.

[0041] Fine pulverization refers to further pulverizing the fired product (coarse powder) after coarse pulverization into a finer state, and any method such as wet pulverization using an attritor can be used. Alternatively, the wet-pulverized slurry may be subjected to solid-liquid separation and drying by any method, and the dried solid may be further dry-pulverized using a vibrating ball mill or the like.

[0042] <Annealing process> In the manufacturing method of the first embodiment, the powder obtained in the pulverization step is annealed in the optional annealing step, which effectively removes distortion in the crystal structure of the powder caused by pulverization or the like.

[0043] In the manufacturing method of the first embodiment, the annealing temperature in the annealing step is usually lower than the firing temperature in the firing step, and the annealing temperature in the annealing step is preferably 900°C or higher, more preferably 930°C or higher, and is preferably 1000°C or lower, more preferably 980°C or lower. If the annealing temperature is 900° C. or higher, the atoms in the crystal lattice will diffuse, and the distortion of the crystal structure can be more effectively removed. On the other hand, if the annealing temperature is 1000° C. or less, it is possible to effectively prevent sintering of particles. The atmosphere during annealing is not particularly limited, but is preferably an oxidizing atmosphere, and the oxidizing atmosphere is preferably air, oxygen, a mixed gas of oxygen and nitrogen, a mixed gas of oxygen and a rare gas, or the like.

[0044] <Properties of hexagonal ferrite magnetic powder obtained by the manufacturing method of the first embodiment> The ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the hexagonal ferrite magnetic powder obtained by the manufacturing method of the first embodiment (hereinafter sometimes referred to as "hexagonal ferrite magnetic powder of the first embodiment") is preferably greater than 1.00, more preferably 1.20 or more, preferably 2.00 or less, more preferably 1.70 or less, and even more preferably 1.58 or less. If the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the hexagonal ferrite magnetic powder of the first embodiment is within the above range, the ferrite-based bonded magnet can exhibit excellent residual magnetization, coercive force, and maximum energy product.

[0045] The average particle size of the hexagonal ferrite magnetic powder of the first embodiment is, for example, 0.50 μm or more, or may be 1.00 μm or more, or 1.50 μm or more, or may be, for example, 5.00 μm or less, or 3.00 μm or less, or 2.00 μm or less.

[0046] The specific surface area of ​​the hexagonal ferrite magnetic powder of the first embodiment is, for example, 0.50 m 2 / g or more, and 1.00m 2 / g or more, for example, 2.00m 2 / g or less, 1.50m 2 / g or less may be acceptable.

[0047] The compressed density of the hexagonal ferrite magnetic powder of the first embodiment is, for example, 2.5 g / cm 3 or more, 3.00 g / cm 3 More than 3.30g / cm 3 or more, for example, 4.00 g / cm 3 is less than or equal to 3.80 g / cm 3 Less than 3.60g / cm 3 The following is also acceptable.

[0048] The remanent magnetization Br of the hexagonal ferrite magnetic powder of the first embodiment is, for example, 1300 G or more, or may be 1500 G or more, or 1750 G or more, or may be, for example, 2100 G or less, 2000 G or less, or 1920 G or less.

[0049] The coercive force iHc of the hexagonal ferrite magnetic powder of the first embodiment is, for example, 1700 Oe or more, or may be 2000 Oe or more, 2100 Oe or more, or 2140 Oe or more, or may be, for example, 2800 Oe or less, 2600 Oe or less, or 2400 Oe or less.

[0050] (Method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to the second embodiment) A manufacturing method of magnetoplumbite-type hexagonal ferrite magnetic powder according to a second embodiment of the present invention (hereinafter, sometimes referred to as the "manufacturing method of the second embodiment") includes a sintering step of sintering a first mixture containing a first raw material powder and a metal chloride to obtain a first sintered product, a pulverizing step of pulverizing the first sintered product to obtain a first hexagonal ferrite powder, and a mixing step of mixing the first hexagonal ferrite powder with a second hexagonal ferrite powder different from the first hexagonal ferrite powder to obtain a mixed powder, in which the molar ratio (Cl / Fe) of the amount of chlorine (Cl) contained in the metal chloride to the amount of iron (Fe) contained in the first raw material powder is 0.002 or more and 0.020 or less. The hexagonal ferrite magnetic powder obtained by this manufacturing method can exhibit excellent remanence in ferrite-based bonded magnets. The reason for this is presumably the same as that explained in the manufacturing method of the first embodiment. Furthermore, the hexagonal ferrite magnetic powder obtained by the manufacturing method of the second embodiment can provide a ferrite-based bonded magnet with excellent coercive force and maximum energy product.

[0051] The manufacturing method of the second embodiment preferably further includes an annealing step in which the mixed powder obtained in the mixing step is annealed. If the manufacturing method of the second embodiment includes an annealing step, distortion in the crystal structure of the mixed powder caused by pulverization or the like can be effectively removed, and a hexagonal ferrite magnetic powder can be obtained that can provide a ferrite-based bonded magnet with excellent remanence, coercivity, and maximum energy product.

[0052] <Firing process> In the manufacturing method of the second embodiment, in the firing step, a first mixture containing a first raw material powder and a metal chloride is fired to obtain a first fired product. The first mixture may contain components other than the first raw material powder and the metal chloride (hereinafter, these may be referred to as "other components B").

[0053] The firing temperature in the firing step of the manufacturing method of the second embodiment is preferably 1100°C or higher, more preferably 1150°C or higher, and is preferably 1220°C or lower, more preferably 1190°C or lower. If the firing temperature in the firing step is within the above range, it is possible to obtain a hexagonal ferrite magnetic powder that can effectively provide a ferrite-based bonded magnet with excellent remanence, coercive force, and maximum energy product. For example, when a box-type firing furnace is used, the firing container can be filled with the first raw material powder, metal chloride, and any other component B. The atmosphere during firing is not particularly limited, but is preferably an oxidizing atmosphere, and the oxidizing atmosphere is preferably air, oxygen, a mixed gas of oxygen and nitrogen, a mixed gas of oxygen and a rare gas, or the like.

[0054] The first raw material powder, metal chloride, and optional other component B contained in the first mixture can be the same as the raw material powder, metal chloride, and other component A described in the section on the manufacturing method of the first embodiment, respectively.

[0055] Here, in the manufacturing method of the second embodiment, the molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the first raw material powder is 0.002 or more, preferably 0.005 or more, and is 0.020 or less, preferably 0.010 or less. The molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the first raw material powder is not particularly limited as long as it is within the above range, but the amount of metal chloride added per 100 parts by mass of the first raw material powder is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, preferably 1.5 parts by mass or less, more preferably less than 1.0 part by mass, and even more preferably 0.8 parts by mass or less.

[0056] In the manufacturing method of the second embodiment, in the firing step, the first mixture containing the first raw material powder, the metal chloride, and any other component B may be fired as is, or the granules obtained by granulating the first mixture may be fired. The granulation method is not particularly limited, and the mixture may be formed into pellets by any method. If the granulated product contains moisture, the granules may be further dried thereafter.

[0057] <Crushing process> In the manufacturing method of the second embodiment, in the pulverization step, the first fired product obtained in the firing step is pulverized to obtain a first hexagonal ferrite powder.

[0058] In the manufacturing method of the second embodiment, the pulverization step is not particularly limited, but may involve coarse pulverization and fine pulverization. The coarse pulverization and fine pulverization can be carried out in the same procedure as the coarse pulverization and fine pulverization described in the section on the pulverization step of the manufacturing method of the first embodiment.

[0059] <Mixing process> In the mixing step, the first hexagonal ferrite powder obtained in the above-mentioned pulverization step is mixed with a second hexagonal ferrite powder different from the first hexagonal ferrite powder to obtain a mixed powder. The method for mixing the first hexagonal ferrite powder and the second hexagonal ferrite powder is not particularly limited and can be performed by a conventionally known method, but it is preferable to mix them while performing a pulverization process (wet pulverization) using a wet pulverizer. Furthermore, if wet pulverization is performed, it is preferable to further dry and dry pulverize the obtained powder. The mixed powder obtained in the above mixing step can be used as the magnetoplumbite hexagonal ferrite magnetic powder obtained by the manufacturing method of the second embodiment. The first hexagonal ferrite powder is not particularly limited as long as it is obtained through the above-mentioned firing process and pulverization process, but for example, the hexagonal ferrite magnetic powder of the first embodiment may be used as the first hexagonal ferrite powder.

[0060] Here, the second hexagonal ferrite powder is not particularly limited as long as it is different from the first hexagonal ferrite powder, but is preferably a hexagonal ferrite powder obtained by pulverizing a second sintered product obtained by sintering the second raw material powder at a sintering temperature of 900° C. or higher but lower than 1100° C. If the second hexagonal ferrite powder is the above-mentioned hexagonal ferrite powder, it is possible to obtain a hexagonal ferrite magnetic powder that can effectively provide ferrite-based bonded magnets with excellent remanence, coercive force, and maximum energy product. The second raw material powder that can be used to prepare the second hexagonal ferrite powder may be the same as the first raw material powder.

[0061] The pulverization of the second fired product is not particularly limited, but may involve coarse pulverization and fine pulverization. The coarse pulverization and fine pulverization can be carried out in the same procedure as the coarse pulverization and fine pulverization described in the section on the pulverization step of the manufacturing method of the first embodiment.

[0062] The specific surface area of ​​the second hexagonal ferrite powder is, for example, 5.0 m 2 / g or more, and 8.0m 2 / g or more, for example, 12.0m 2 / g or less, and 9.0m 2 / g or less may be acceptable.

[0063] The mixing ratio of the second hexagonal ferrite powder to the total amount of the first hexagonal ferrite powder and the second hexagonal ferrite powder (second hexagonal ferrite powder / (first hexagonal ferrite powder+second hexagonal ferrite powder)) is, by mass, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 30 / 100 or more, and is preferably 50 / 100 or less, and more preferably 40 / 100 or less.

[0064] <Annealing process> In the manufacturing method of the second embodiment, the mixed powder obtained in the mixing step is annealed in the optional annealing step, which effectively removes distortion in the crystalline structure of the mixed powder caused by pulverization or the like.

[0065] In the manufacturing method of the second embodiment, the annealing temperature in the annealing step is usually lower than the firing temperature in the firing step, and the annealing temperature in the annealing step is preferably 900°C or higher, more preferably 930°C or higher, and is preferably 1000°C or lower, more preferably 980°C or lower. The annealing temperature in the annealing step is preferably 900°C or higher, more preferably 930°C or higher, and is preferably 1000°C or lower, more preferably 980°C or lower. If the annealing temperature is 900° C. or higher, the atoms in the crystal lattice will diffuse, and the distortion of the crystal structure can be more effectively removed. On the other hand, if the annealing temperature is 1000° C. or less, it is possible to effectively prevent sintering of particles. The atmosphere during annealing is not particularly limited, but is preferably an oxidizing atmosphere, and the oxidizing atmosphere is preferably air, oxygen, a mixed gas of oxygen and nitrogen, a mixed gas of oxygen and a rare gas, or the like.

[0066] <Properties of hexagonal ferrite magnetic powder obtained by the manufacturing method of the second embodiment> The average particle size of the hexagonal ferrite magnetic powder obtained by the manufacturing method of the second embodiment (hereinafter, sometimes referred to as "hexagonal ferrite magnetic powder of the second embodiment") is, for example, 0.80 μm or more, or may be 1.00 μm or more, or 1.30 μm or more, or may be, for example, 5.00 μm or less, or 3.50 μm or less, or 2.50 μm or less.

[0067] The specific surface area of ​​the hexagonal ferrite magnetic powder of the second embodiment is, for example, 0.80 m 2 / g or more, and 1.20m 2 / g or more, 1.50m 2 / g or more, for example, 4.00m 2 / g or less, and 3.00m 2 / g or less, 2.00m 2 / g or less is acceptable, and 1.80m 2 / g or less may be acceptable.

[0068] The compressed density of the hexagonal ferrite magnetic powder of the second embodiment is, for example, 3.00 g / cm 3 or more, 3.30 g / cm 3 More than 3.50g / cm 3 or more, for example, 4.00 g / cm 3 is less than or equal to 3.80 g / cm 3 The following is also acceptable.

[0069] The remanent magnetization Br of the hexagonal ferrite magnetic powder of the second embodiment is, for example, 1300 G or more, or may be 1500 G or more, or 1750 G or more, or may be, for example, 2500 G or less, or 2300 G or less, or 2000 G or less, or 1950 G or less.

[0070] The coercive force iHc of the hexagonal ferrite magnetic powder of the second embodiment is, for example, 2000 Oe or more, or may be 2300 Oe or more, or 2500 Oe or more, or may be, for example, 3500 Oe or less, 3300 Oe or less, or 3100 Oe or less. [Example]

[0071] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples in any way.

[0072] (Example 1-1) <Production of hexagonal ferrite magnetic powder according to the first embodiment> [Firing process] Iron oxide (hematite) and strontium carbonate were weighed out to a molar ratio of iron oxide:strontium carbonate = 5.9:1 to obtain a raw powder. To the obtained raw powder, 0.18 wt.% boric acid and an amount of potassium chloride (0.6 parts by mass per 100 parts by mass of raw powder) such that the molar ratio of Cl contained in potassium chloride to Fe contained in iron oxide (Cl / Fe) was 0.0074 were added and mixed to obtain a mixture. The resulting mixture was granulated with water to form spheres with a diameter of 3 to 10 mm, and the granules were dried at 150°C in air. 600 g of the dried granules were placed in a 0.68 L alumina container, covered with an alumina lid, and fired in an electric furnace at 1190°C for 80 minutes to obtain a fired product.

[0073] [Crushing process] The sintered product obtained in the sintering process was coarsely pulverized using a hammer mill (Fuji Paudal Eck Sample Mill KII type) to obtain a coarse powder. An X-ray diffractometer confirmed that the coarse powder had a magnetoplumbite-type hexagonal ferrite crystal structure. Water was added to the resulting coarse powder to form a slurry with a coarse powder concentration of 40% by mass. The resulting slurry was placed in an attritor (a milling device with agitating blades) along with 5.56 mm diameter steel balls and wet-pulverized for 20 minutes (pulverization time) to obtain a wet-pulverized slurry. The rotational speed of the impeller was adjusted so that the moving speed (circumferential speed) at the point farthest from the impeller's rotation axis was 1.6 m / s. The slurry was then filtered to separate the solid and liquid, and the solid matter (filtered material) was dried in air at 150°C for 10 hours to obtain a dry cake. The resulting dry cake was crushed and then dry-pulverized using a vibrating ball mill (Uras Vibrator KEC-8-YH, manufactured by Murakami Seiki Seisakusho) to obtain a finely pulverized powder (hexagonal ferrite magnetic powder). The dry grinding treatment was carried out using steel balls with a media diameter of 12 mm at a rotation speed of 1800 rpm and an amplitude of 8 mm for 28 minutes.

[0074] [Annealing process] The powder obtained by the mixed and crushed process was annealed in air at 965°C for 30 minutes to obtain annealed hexagonal ferrite magnetic powder. Using the obtained hexagonal ferrite magnetic powder, the average major axis length / minor axis length, average particle size, specific surface area, compressed density, and magnetic properties of the hexagonal ferrite magnetic powder were measured or calculated using the methods described above. In addition, the magnetic properties of bonded magnets were measured using the obtained hexagonal ferrite magnetic powder using the following method. The results are shown in Table 1.

[0075] <Magnetic properties of bonded magnets> 90.0 parts by mass of hexagonal ferrite magnetic powder, 0.6 parts by mass of a silane coupling agent (Z-6094N, manufactured by Toray Dow Corning Co., Ltd.), 0.8 parts by mass of a lubricant (VPN-212P, manufactured by Henkel), and 8.6 parts by mass of powdered nylon 6 (P1011F, manufactured by UBE Corporation) as a binder were weighed, loaded into a mixer, and mixed to obtain a mixture. The resulting mixture was kneaded at 230°C to obtain kneaded pellets with an average diameter of 2 mm. The kneaded pellets were loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and molded at a temperature of 300°C and a molding pressure of 8.5 N / mm in a magnetic field of 9.7 kOe.2 A cylindrical bonded magnet (magnetic powder concentration 90.0 mass %) with a diameter of 15 mm and a height of 8 mm (the magnetic field was oriented along the central axis of the cylinder) was obtained by injection molding. The remanence Br, coercivity iHc, and maximum energy product BHmax of the resulting bonded magnets were measured in a magnetic field of 10 kOe using a BH tracer (TRF-5BH, manufactured by Toei Kogyo Co., Ltd.). The results are shown in Table 1.

[0076] (Examples 1-2 to 1-4, Comparative Examples 1-1 and 1-2) Various operations and measurements were carried out in the same manner as in Example 1-1, except that the amount of metal chloride added and the firing temperature were changed as shown in Table 1. The results are shown in Table 1.

[0077] Example 2-1 <Production of hexagonal ferrite magnetic powder according to the second embodiment> [Firing process] Iron oxide and strontium carbonate were weighed and mixed at a molar ratio of iron oxide:strontium carbonate = 5.9:1 to obtain a first raw material powder. To the obtained first raw material powder, 0.18 wt. % boric acid and an amount of potassium chloride (0.6 parts by mass per 100 parts by mass of raw material powder) such that the molar ratio of the amount of Cl contained in potassium chloride to the amount of Fe contained in iron oxide (Cl / Fe) was 0.0074 were added and mixed to obtain a first mixture. The resulting mixture was granulated with water into spheres with a diameter of 3 to 10 mm, and the granules were dried at 150°C in air. 600 g of the dried granules were placed in a 0.68 L alumina container, covered with an alumina lid, and fired in an electric furnace at 1190°C for 80 minutes to obtain a first fired product.

[0078] [Crushing process] The first fired product was coarsely pulverized using a hammer mill (Fuji Paudal ECK Sample Mill KII type) to obtain a first coarse powder (first hexagonal ferrite powder). An X-ray diffractometer confirmed that the first coarse powder had a peak attributable to the crystal structure of magnetoplumbite-type hexagonal ferrite.

[0079] [Preparation of second hexagonal ferrite powder] Iron oxide and strontium carbonate were weighed and mixed at a molar ratio of "iron oxide:strontium carbonate = 5.5:1" to obtain a second raw material powder. The obtained second raw material powder was granulated into spherical particles with a diameter of 3 to 10 mm, and the granules were dried at 150°C in air. 600 g of the dried granules were placed in an alumina container with a volume of 0.68 L and fired in an electric furnace at 1070°C in air for 80 minutes to obtain a second fired product. Separately, the second fired product was coarsely pulverized using a hammer mill (Fuji Paudal ECK Sample Mill KII type) to obtain a second coarse powder (second hexagonal ferrite powder). Using an X-ray diffractometer, it was confirmed that the second coarse powder had a peak due to the crystal structure of magnetoplumbite-type hexagonal ferrite. Water was added to the obtained second hexagonal ferrite powder to form a slurry so that the concentration of the second hexagonal ferrite powder was 40% by mass. The obtained slurry was placed in an attritor (a grinding device with agitating blades) together with steel balls having a diameter of 5.56 mm and wet-ground for 90 minutes (grinding time), thereby obtaining a wet-ground slurry. Here, the rotation speed of the agitating blades was adjusted so that the moving speed (circumferential speed) of the point farthest from the rotation axis of the agitating blades was 1.6 m / s. A small amount of the obtained wet-ground slurry was taken, and the specific surface area of ​​the dried powder (second hexagonal ferrite powder) was measured by the BET method using a surface area measuring device (Monosorb, manufactured by Quantachrome). The result was that the specific surface area of ​​the second hexagonal ferrite powder was 8.5 m 2 / g.

[0080] [Mixing process] Next, the first hexagonal ferrite powder obtained in the above milling process was added to the obtained wet-milled slurry so that the mass ratio of the second hexagonal ferrite powder to the first hexagonal ferrite powder was 35:65, and the mixture was further mixed and milled for 20 minutes using an attritor. The rotation speed of the stirring blade was controlled so that the peripheral speed of the stirring blade was 1.6 m / s. The slurry was then filtered to separate the solid and liquid, and the solid matter (filtered residue) was dried in air at 150°C for 10 hours to obtain a dry cake. The obtained dry cake was crushed and further dry-milled using a vibrating ball mill (Uras Vibrator KEC-8-YH, manufactured by Murakami Seiki Seisakusho) to obtain a finely milled mixed powder (hexagonal ferrite magnetic powder). The dry milling was carried out for 28 minutes using steel balls with a media diameter of 12 mm at a rotation speed of 1800 rpm and an amplitude of 8 mm.

[0081] [Annealing process] The mixed powder obtained by the mixed and pulverized process was annealed in air at 965°C for 30 minutes to obtain annealed hexagonal ferrite magnetic powder. Using the obtained hexagonal ferrite magnetic powder, the average particle size, specific surface area, compressed density, and magnetic properties of the hexagonal ferrite magnetic powder were measured or calculated using the methods described above. In addition, the magnetic properties of bonded magnets were measured using the obtained hexagonal ferrite magnetic powder using the following method. The results are shown in Table 2.

[0082] <Magnetic properties of bonded magnets> 92.0 parts by mass of hexagonal ferrite magnetic powder (mixed powder), 0.6 parts by mass of a silane coupling agent (Z-6094N, manufactured by Toray Dow Corning Co., Ltd.), 0.8 parts by mass of a lubricant (VPN-212P, manufactured by Henkel), and 6.6 parts by mass of powdered nylon 6 (P1011F, manufactured by UBE Corporation) as a binder were weighed, loaded into a mixer, and mixed to obtain a mixture. The resulting mixture was kneaded at 230°C to obtain kneaded pellets with an average diameter of 2 mm. The kneaded pellets were loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and molded at a temperature of 300°C and a molding pressure of 8.5 N / mm in a magnetic field of 9.7 kOe. 2A cylindrical bonded magnet (magnetic powder concentration 92.0 mass %) with a diameter of 15 mm and a height of 8 mm (the magnetic field was oriented along the central axis of the cylinder) was obtained by injection molding. The remanence Br, coercivity iHc, and maximum energy product BHmax of the resulting bonded magnets were measured in a magnetic field of 10 kOe using a BH tracer (TRF-5BH, manufactured by Toei Kogyo Co., Ltd.). The results are shown in Table 2.

[0083] (Examples 2-2 to 2-4, Comparative Examples 2-1 and 2-2) Various operations and measurements were carried out in the same manner as in Example 2-1, except that the amount of metal chloride added and the firing temperature were changed as shown in Table 2. The results are shown in Table 2.

[0084] [Table 1]

[0085] [Table 2]

[0086] As is clear from Tables 1 and 2, the magnetoplumbite hexagonal ferrite magnetic powder obtained by the method of the example was able to provide excellent residual magnetization in a ferrite-based bonded magnet. [Industrial Applicability]

[0087] According to the present invention, it is possible to provide a method for producing magnetoplumbite-type hexagonal ferrite magnetic powder that can provide excellent remanent magnetization in a ferrite-based bonded magnet.

Claims

1. A method for producing magnetoplumbite-type hexagonal ferrite magnetic powder, comprising: a calcination step of calcining a mixture containing the raw material powder and the metal chloride to obtain a calcined product; a grinding step of grinding the fired product to obtain a powder; Including, a molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the raw material powder of 0.002 or more and 0.020 or less;

2. A method for producing magnetoplumbite-type hexagonal ferrite magnetic powder, comprising: a firing step of firing a first mixture containing a first raw material powder and a metal chloride to obtain a first fired product; a pulverization step of pulverizing the first fired product to obtain a first hexagonal ferrite powder; a mixing step of mixing the first hexagonal ferrite powder with a second hexagonal ferrite powder different from the first hexagonal ferrite powder to obtain a mixed powder; Including, a molar ratio of the amount of Cl contained in the metal chloride to the amount of Fe contained in the first raw material powder being 0.002 or more and 0.020 or less.

3. 3. The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to claim 2, wherein the second hexagonal ferrite powder is obtained by pulverizing a second sintered product obtained by sintering the second raw material powder at a sintering temperature of 900°C or higher and lower than 1100°C.

4. 3. The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to claim 1, wherein the firing temperature in the firing step is 1100°C or higher and 1220°C or lower.

5. The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to claim 1 or 2, further comprising an annealing step of annealing the powder or the mixed powder.

6. 6. The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to claim 5, wherein the annealing temperature in the annealing step is 900°C or higher and 1000°C or lower.

7. 3. The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to claim 1, wherein the metal chloride is at least one selected from the group consisting of potassium chloride, sodium chloride, and lithium chloride.

8. 3. The method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to claim 1, wherein the raw material powder or the first raw material powder contains a strontium compound.

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