Hexagonal ferrite magnetic powder for bonded magnets and its manufacturing method, and bonded magnets and its manufacturing method

Abstract

To provide a hexagonal crystal ferrite magnetic powder for a bond magnet capable of obtaining a high residual magnetic flux density Br in the case of use for the bond magnet, a manufacturing method thereof, a bond magnet having a high residual magnetic flux density Br and a manufacturing method thereof.SOLUTION: The present invention relates to a manufacturing method of a hexagonal crystal ferrite magnetic powder for a bond magnet including the steps of: obtaining a mixed powder on which pulverization processing is performed by performing mixing pulverization of a coarse powder of hexagonal crystal ferrite and a fine powder of hexagonal crystal ferrite; and annealing the mixed powder on which the mixing pulverization processing is performed. Regarding the fine powder of hexagonal crystal ferrite, after a cylindrical die of which the inner diameter is 2.54 cmφ is filled with 10 g of the fine powder of hexagonal crystal ferrite, the relationship between a compression density X(g / cm3) of a mold compressed with a pressure of 1000 kg / cm2 and a specific surface area Y(m3 / g) of the fine powder of hexagonal crystal ferrite satisfies a relational expression of X>-0.03×Y+3.27.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to hexagonal ferrite magnetic powder for bonded magnets and a manufacturing method thereof, and to bonded magnets and a manufacturing method thereof, and more particularly to hexagonal ferrite magnetic powder for bonded magnets containing coarse and fine hexagonal ferrite powder and a manufacturing method thereof. [Background technology]

[0002] Traditionally, ferrite-based sintered magnets have been used as high-coercive magnets, such as those used in small motors for AV equipment, office automation equipment, and automotive electrical components, as well as in magnet rolls in copiers. However, ferrite-based sintered 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. For this reason, in recent years, rare-earth bonded magnets have been used as high-coercive magnets for small motors for AV equipment, office automation equipment, and automotive electrical components. However, rare-earth magnets are approximately 20 times more expensive than ferrite-based sintered magnets and are prone to rust, making it desirable to use ferrite-based bonded magnets instead of ferrite-based sintered magnets.

[0003] Patent Document 1 discloses a manufacturing process for such ferrite powder for bonded magnets, which includes a step of obtaining a coarse powder, a step of obtaining a fine powder, and a step of mixing the obtained coarse powder and fine powder to obtain a mixed powder, after which a mechanical crushing force is applied to the obtained mixed powder. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-72634 Summary of the Invention [Problem to be solved by the invention]

[0005] The hexagonal ferrite magnetic powder for bonded magnets described in Patent Document 1 has excellent fluidity even when the FC value in the compound is increased, and was developed as a ferrite-based bonded magnet with a high BHmax. However, there is still a demand for hexagonal ferrite magnetic powder for bonded magnets that can achieve a higher residual magnetic flux density Br as a bonded magnet. The present invention aims to provide a hexagonal ferrite magnetic powder for bonded magnets that can achieve a high residual magnetic flux density Br when used in bonded magnets, a method for manufacturing the same, and a bonded magnet with a high residual magnetic flux density Br and a method for manufacturing the same. [Means for solving the problem]

[0006] In order to solve the above problems, the inventors conducted extensive research and found that conventional hexagonal ferrite magnetic powder for bonded magnets contains many extremely small particles and agglomerated particles with irregular shapes. They then improved the milling conditions to break down the agglomerated particles while suppressing the generation of fine particles, and confirmed that by uniforming the particle size and shape of the fine hexagonal ferrite powder for bonded magnets, it is possible to obtain a high residual magnetic flux density Br when used in a bonded magnet. It is believed that uniforming the particle size and shape of the hexagonal ferrite fine powder makes it easier to orient in a magnetic field when compounded and used as a bonded magnet, resulting in a bonded magnet with a high residual magnetic flux density Br. In other words, the gist of the present invention is as follows.

[0007] A method for producing hexagonal ferrite magnetic powder for bonded magnets, comprising the steps of: obtaining coarse powder of hexagonal ferrite; obtaining fine powder of hexagonal ferrite having a larger specific surface area than the coarse powder of hexagonal ferrite; co-pulverizing the coarse powder of hexagonal ferrite and the fine powder of hexagonal ferrite to obtain a mixed and pulverized mixed powder; and annealing the mixed and pulverized mixed powder, wherein the fine powder of hexagonal ferrite is obtained by annealing 10 g of the fine powder of hexagonal ferrite at a pressure of 1000 kg / cm after filling 10 g of the fine powder of hexagonal ferrite into a cylindrical mold having an inner diameter of 2.54 cm. 2 The compressed density of the compact compressed at a pressure of X (g / cm 3 ) and the specific surface area Y(m2 / g) is expressed by the following formula (1): X>-0.03×Y+3.27 (1) The hexagonal ferrite magnetic powder is characterized by satisfying the following relational expression: The hexagonal ferrite magnetic powder is preferably hexagonal Sr ferrite.

[0008] In addition, the specific surface area of ​​this hexagonal ferrite coarse powder is 0.2 m 2 / g or more 1.2m 2 / g or less, and the specific surface area of ​​the coarse powder of hexagonal ferrite is 4.0m 2 / g or more 20.0m 2 / g or less is preferable.

[0009] Another aspect of the present invention is a method for producing a bonded magnet using hexagonal ferrite magnetic powder for a bonded magnet obtained by the method for producing hexagonal ferrite magnetic powder for a bonded magnet of the present invention. [Effects of the Invention]

[0010] According to the present invention, by uniforming the particle size and shape of the hexagonal ferrite fine powder in the hexagonal ferrite magnetic powder for bonded magnets, a hexagonal ferrite magnetic powder for bonded magnets is provided that can achieve a high residual magnetic flux density Br when used in bonded magnets. Also provided are a method for manufacturing the hexagonal ferrite magnetic powder for bonded magnets that can achieve a high residual magnetic flux density Br when used in bonded magnets, and a bonded magnet with a high residual magnetic flux density Br. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph showing the relationship between the compressed density X and the specific surface area Y of the fine powder of hexagonal ferrite in Examples 1 to 5 and Comparative Examples 1 to 3. [Figure 2] 1 is a graph showing the relationship between the peripheral speed of the stirring blade during production of fine powder of hexagonal ferrite and the saturation magnetic flux density of the final bonded magnet in Examples 1 to 5 and Comparative Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Method for manufacturing hexagonal ferrite magnetic powder for bonded magnets) The method for producing hexagonal ferrite magnetic powder for bonded magnets of the present invention includes the steps of obtaining coarse hexagonal ferrite powder, obtaining fine hexagonal ferrite powder having a larger specific surface area than the coarse hexagonal ferrite powder, co-pulverizing the coarse hexagonal ferrite powder and the fine hexagonal ferrite powder to obtain a mixed and pulverized mixed powder, and annealing the mixed and pulverized mixed powder. The hexagonal ferrite is not particularly limited in composition, but it is preferable to use hexagonal Sr ferrite magnetic powder. The fine hexagonal ferrite powder is obtained by filling 10 g of the fine hexagonal ferrite powder into a cylindrical mold with an inner diameter of 2.54 cm and then annealing it at a pressure of 1000 kg / cm. 2 The compressed density of the compact compressed at a pressure of X (g / cm 3 ) and the specific surface area Y (m 2 / g) is expressed by the following formula (1): X>-0.03×Y+3.27 (1) The formula (1) is satisfied. By mixing coarse hexagonal ferrite powder with fine hexagonal ferrite powder that satisfies the formula (1), the packing ability of the resulting hexagonal ferrite magnetic powder for bonded magnets can be improved. As a result, when a bonded magnet is manufactured using this magnetic powder, a bonded magnet with a high residual magnetic flux density Br can be obtained. Here, the specific surface area of ​​the coarse powder is usually smaller than that of the fine powder. Each step is explained in detail below.

[0013] [Hexagonal ferrite magnetic powder for bonded magnets] Hexagonal ferrite magnetic powder for bonded magnets can be obtained by mixing and grinding a coarse powder of hexagonal ferrite and a fine powder of hexagonal ferrite, followed by annealing. The composition of the hexagonal ferrite magnetic powder for bonded magnets is not particularly limited, but hexagonal Sr ferrite magnetic powder is preferred.

[0014] [Manufacturing process for coarse hexagonal ferrite powder] This is a process in which raw material powders for the hexagonal ferrite coarse powder are mixed and then fired to obtain the hexagonal ferrite coarse powder. Prior to firing, the raw material powders may be mixed and granulated, and the resulting granules may be fired. The composition of the hexagonal ferrite coarse powder is not particularly limited, but can be appropriately set to the required composition for the hexagonal ferrite magnetic powder for the bonded magnet to be finally obtained. The composition of the hexagonal ferrite coarse powder may be the same as or different from the composition of the hexagonal ferrite fine powder. The raw material powder for the hexagonal ferrite coarse powder contains an Fe compound as an essential compound, and Ca and Sr compounds can also be used. For example, calcium carbonate and calcium hydroxide can be used as Ca compounds, strontium carbonate, strontium chloride, and strontium sulfate can be used as Sr compounds, and iron oxide (hematite, magnetite), iron chloride, and iron sulfate can be used as Fe compounds, with hematite being preferred. To obtain coarse hexagonal ferrite magnetic powder, a composite oxide precursor may be synthesized first, and the resulting precursor may be used as a raw material. By using a multi-stage synthesis process, a suitable shape can be obtained in the final hexagonal ferrite. Furthermore, in order to obtain a hexagonal ferrite magnetic powder having a magnetoplumbite crystal structure, the molar ratio of Fe:Sr between the elements at the Fe site and the elements at the Sr site when charged can be set to a range of 10.0:1.0 to 12.5:1.0. In order to prevent unreacted materials from remaining after firing, the molar ratio of Fe:Sr is preferably set to a range of 11.0:1.0 to 12.0:1.0. The coarse powder of hexagonal ferrite may contain unavoidable components such as impurities contained in the raw materials and impurities derived from the manufacturing equipment. Examples of such components include oxides of Mn and Ba. The content of these components is preferably controlled to 0.4% by mass or less. The above compositional formula excludes these unavoidable components.

[0015] The firing temperature in the process for producing the coarse powder of hexagonal ferrite is preferably 1220°C or higher and 1400°C or lower, and more preferably 1220°C or higher and 1300°C or lower. In the process for producing coarse powder of hexagonal ferrite, a mixture of raw material powders may be granulated and fired. The firing atmosphere is preferably an oxidizing atmosphere, more preferably an air atmosphere. It is also preferable to perform a pulverization treatment after firing. The pulverization method is not particularly limited, and examples thereof include known methods using a roller mill or the like.

[0016] The coarse powder of hexagonal ferrite has a specific surface area of ​​0.3 m2 measured by the BET single-point method. 2 / g or more 1.0m 2 / g or less, and 0.5m 2 / g or more 0.8m 2 It is more preferable that the saturation coefficient is 1 / g or less.

[0017] [Manufacturing process for hexagonal ferrite fine powder] This is a process of mixing powders that serve as raw materials for the hexagonal ferrite fine powder and then firing the mixture to obtain the hexagonal ferrite fine powder. The method for producing the hexagonal ferrite fine powder according to this embodiment includes the steps of mixing powders that serve as raw materials for the hexagonal ferrite fine powder to obtain a mixture, firing the mixture to obtain a fired product, and pulverizing the fired product by dry grinding and wet grinding. Furthermore, prior to firing, the raw material powders may be mixed and then granulated, and the resulting granulated product may be subjected to firing. The composition of the hexagonal ferrite fine powder is not particularly limited, but can be set to the composition required for the hexagonal ferrite magnetic powder for the bonded magnet to be finally obtained. The powder that is the raw material for the hexagonal ferrite fine powder contains an Fe compound as an essential compound, and compounds of Ca, Sr, La, Co, and Zn can also be used. For example, calcium carbonate and calcium hydroxide can be used as Ca compounds, strontium carbonate, strontium chloride, and strontium sulfate can be used as Sr compounds, and iron oxide (hematite, magnetite), iron chloride, and iron sulfate, preferably hematite, can be used as Fe compounds. In order to obtain a hexagonal ferrite magnetic powder having a magnetoplumbite crystal structure, the molar ratio of Fe:Sr between the elements at the Fe site and the elements at the Sr site when charged is set to a value in the range of 10.0:1.0 to 12.5:1.0. In order to suppress the remaining unreacted material after firing, the molar ratio of Fe:Sr is preferably set to a value in the range of 11.0:1.0 to 12.0:1.0. The fine powder of hexagonal ferrite may contain unavoidable components such as impurities contained in raw materials and impurities derived from manufacturing equipment. Examples of such components include oxides of Mn and Ba. The content of these components is preferably controlled to 0.4% by mass or less. The above compositional formula excludes these unavoidable components.

[0018] The firing temperature in the process for producing the hexagonal ferrite fine powder is preferably 900°C or higher and 1100°C or lower, and more preferably 950°C or higher and 1000°C or lower. In the process for producing the hexagonal ferrite fine powder, a mixture of raw material powders may be granulated and fired. The firing atmosphere is preferably an oxidizing atmosphere, more preferably an air atmosphere. It is also preferable to perform a pulverization treatment after firing. The pulverization treatment can be performed by a known method using a roller mill or the like, but wet pulverization is preferable. A dry pulverization treatment such as a roller mill and wet pulverization treatment may be combined. For wet grinding, a wet grinder having a stirring mechanism using a rotary stirring blade can be used, and the peripheral speed of the stirring blade is preferably 0.5 m / s to 2.5 m / s, more preferably 1.0 m / s to 2.0 m / s. Here, the peripheral speed of the stirring blade refers to the speed at the point farthest from the rotation axis of the stirring blade, and is an index of the intensity of grinding in the wet grinder. As a wet grinder having a stirring mechanism using a stirring blade, an attritor is preferably used, and water is preferably used as the solvent, with a media diameter of preferably 2 mm to 15 mm. The grinding time is preferably 30 minutes to 240 minutes, more preferably 100 minutes to 240 minutes. Since the grinding energy is proportional to the cube of the peripheral speed, applying more grinding energy than necessary will generate extremely small particles smaller than the desired grinding particle size, hindering uniformity. Therefore, during wet grinding, it is preferable to appropriately set the peripheral speed of the stirring blade. This makes it possible to increase the residual magnetic flux density Br of the bonded magnet produced using the obtained hexagonal ferrite magnetic powder for bonded magnets.

[0019] In this way, the hexagonal ferrite fine powder was prepared by filling 10 g of the hexagonal ferrite fine powder into a cylindrical mold having an inner diameter of 2.54 cm and then applying a pressure of 1000 kg / cm 2 The relationship between the compressed density X of the compact compressed under the pressure and the specific surface area Y of the hexagonal ferrite fine powder is expressed by the following formula (1): X>-0.03×Y+3.27 (1) The following relation is satisfied. Hexagonal ferrite fine powder produced so as to satisfy relational expression (1) avoids excessive pulverization, and the agglomerated particles that result from sintering are deagglomerated to a state that is close to monodispersion, which is thought to increase the remanence Br of the final bonded magnet.

[0020] The specific surface area of ​​the hexagonal ferrite powder measured by the BET single point method is 4m 2 / g or more 20m 2 / g or less, and 2 / g or more 15m 2 It is more preferable that the saturation coefficient is 1 / g or less.

[0021] [Mixing and grinding process] The separately obtained coarse hexagonal ferrite powder and fine hexagonal ferrite powder are mixed and pulverized to obtain a mixed and pulverized powder. At this time, the mixed and pulverized powder is preferably mixed and pulverized at a ratio of 60% by mass to 90% by mass of the coarse hexagonal ferrite powder relative to the total mass of the coarse hexagonal ferrite powder and the fine hexagonal ferrite powder. For mixing, a wet grinding device is preferably used, more preferably an attritor, and the peripheral speed of the stirring blade is preferably 1.5 m / s or more and 3.5 m / s or less. Furthermore, a vibration ball mill is preferably used for the milling after the mixed milling, and in the milling process using a vibration ball mill, it is preferable to use balls with a medium diameter of 5 mm to 20 mm, and it is preferable to perform the milling process using balls with a medium diameter of 10 mm to 20 mm in the first stage, and then perform the milling process using balls with a medium diameter of 5 mm to 10 mm in the second stage.By using a vibration ball mill, it is possible to mill agglomerated particles that have formed during dehydration and drying after wet milling.

[0022] [Annealing process] This is a process in which the mixed powder obtained in the mixing and pulverizing process is annealed to obtain hexagonal ferrite magnetic powder for bonded magnets. The annealing conditions are not particularly limited, and can be performed under conditions known for manufacturing hexagonal ferrite magnetic powder for bonded magnets. The annealing temperature is preferably 900°C or higher and 1000°C or lower, and more preferably 930°C or higher and 980°C or lower. The annealing atmosphere is preferably an oxidizing atmosphere, and more preferably air.

[0023] (Bonded magnets and their manufacturing methods) A bonded magnet can be obtained by mixing the hexagonal ferrite magnetic powder for a bonded magnet obtained by the method of manufacturing hexagonal ferrite magnetic powder for a bonded magnet of the present invention with a resin, a lubricant, etc., kneading the mixture, and then molding the mixture in a magnetic field. Here, the method for manufacturing the bonded magnet is not particularly limited, and any known method can be used. [Example]

[0024] The ferrite magnetic powder for bonded magnets and the method for producing the same according to the present invention will be described in detail below with reference to examples.

[0025] The evaluations in the examples were carried out as follows. [Average particle size measurement] The average particle diameter (APD) was measured by the air permeation method using a specific surface area measuring device (SS-100 manufactured by Shimadzu Corporation).

[0026] [Specific surface area measurement] The specific surface areas of the hexagonal ferrite magnetic powder for bonded magnets, the coarse hexagonal ferrite powder, and the fine hexagonal ferrite powder were measured by the BET single-point method using a specific surface area measuring device (Monosorb manufactured by Quantachrome).

[0027] [Composition analysis] The composition of the hexagonal ferrite magnetic powder for bonded magnets was analyzed using a fluorescent X-ray analyzer (ZSX100e manufactured by Rigaku Corporation) by calculating the amount of each element using the fundamental parameter method (FP method). In this composition analysis, the powder to be measured was packed into a measurement cell and subjected to a pressure of 10,000 kg / cm. 2 The specimen was molded by applying a pressure of 0.01 for 20 seconds, and the measurement mode was set to EZ scan mode, the measurement diameter to 30 mm, the sample form to oxide, and the measurement time to standard time. After qualitative analysis was performed in a vacuum atmosphere, quantitative analysis was performed on the detected constituent elements.

[0028] [Compressed density measurement] The compressed density of hexagonal ferrite magnetic powder for bonded magnets, hexagonal ferrite coarse powder, and hexagonal ferrite fine powder was measured by filling 10.00 g of the powder to be measured into a cylindrical mold with an inner diameter of 2.54 cm, and then compressing it to 1000 kg / cm using a cylindrical piston with a diameter of 2.44 cm. 2 The density of the compact compressed at this pressure is called the compacted density CD (g / cm 3 The compressed density CD (g / cm 3 The formula for calculating the mass ratio is as follows, where L (cm) is the height from the bottom of the cylindrical mold interior to the tip of the piston after compression, and π is the ratio of the circumference of a circle to its circumference. Compressed density CD (g / cm 3 )=10.00 / (2.54 2 ×π / 4×L)

[0029] [Magnetic property measurement of powder compacts] The magnetic properties of the compacted hexagonal ferrite magnetic powder for bonded magnets were measured by mixing 8g of hexagonal ferrite magnetic powder for bonded magnets with 0.4cm of polyester resin (P-resin manufactured by Japan Geoscience Co., Ltd.). 3 The mixture was kneaded 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 2000 kg / cm 2 The compact was compressed at a pressure of 0.05 for 60 seconds, and the resulting molded product was removed from the mold and dried at 150°C for 30 minutes to obtain a green compact.The magnetic properties of the green compact were measured using a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.) in a measuring magnetic field of 10 kOe to determine the coercive force iHc and residual magnetic flux density Br of the green compact.

[0030] [Flow Rate (MFR) Measurement] 92.0 parts by mass of hexagonal ferrite magnetic powder for bonded magnets, 0.6 parts by mass of silane coupling agent (Z-6094N manufactured by Toray Dow Corning Co., Ltd.), 0.8 parts by mass of lubricant (VPN-212P manufactured by Henkel), and 6.6 parts by mass of powdered polyamide resin (P-1011F manufactured by Ube Industries, Ltd.) as a binder were weighed out, loaded into a mixer, and mixed. The resulting mixture was kneaded at 230°C to produce a kneaded product, and kneaded pellets with an average diameter of 2 mm were obtained from the resulting kneaded product. The obtained kneaded pellets were placed in a melt indexer (Melt Indexer C-5059D2 manufactured by Toyo Seiki Seisakusho, Ltd.), and the weight of the kneaded material extruded at 270°C under a load of 10 kg was measured. This weight was converted into the amount extruded per 10 minutes to determine the fluidity (MFR) of the hexagonal ferrite magnetic powder for bonded magnets.

[0031] [Magnetic property measurement of bonded magnet A] The kneaded pellets obtained by the method described in the MFR measurement were loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and subjected to molding at a temperature of 300°C and a molding pressure of 8.5 N / mm in a magnetic field of 4.3 kOe. 2The bonded magnet A (FC92.0 mass%, 4.3 kOe) was obtained as a cylindrical magnet (the magnetic field was oriented along the central axis of the cylinder) with a diameter of 15 mm and a height of 8 mm. The magnetic properties of this bonded magnet A were measured in a magnetic field of 10 kOe using a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.).

[0032] [Magnetic property measurement of bonded magnet B] The kneaded pellets obtained by the method described in the MFR measurement were loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and subjected to molding at a temperature of 300°C and a molding pressure of 8.5 N / mm in a magnetic field of 9.7 kOe. 2 The bonded magnet B (FC 92.0 mass%, 9.7 kOe) was obtained as a cylindrical magnet (the magnetic field was oriented along the central axis of the cylinder) with a diameter of 15 mm and a height of 8 mm. The magnetic properties of the coercive force iHc and remanent magnetization Br of this bonded magnet B were measured using a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.) in a measuring magnetic field of 10 kOe.

[0033] Example 1 1-1. Production of hexagonal ferrite magnetic powder according to Example 1 (1) Manufacturing process of coarse hexagonal ferrite powder Hematite (α-Fe2O3, specific surface area 5.3m 2 / g) and strontium carbonate (SrCO3, specific surface area 5.8m 2 / g) was weighed out so that the molar ratio of Fe:Sr was 11.8:1.0. Based on the total mass of the weighed hematite and strontium carbonate, 0.18 mass% of boric acid and 2.45 mass% of potassium chloride were weighed out, and the hematite, strontium carbonate, boric acid, and potassium chloride were mixed together, and then water was added to form spherical granules with a diameter of 3 to 10 mm.

[0034] The resulting granules were fired in a rotary kiln at 1250°C for 20 minutes in an air flow atmosphere, and the resulting fired product was treated in a roller mill to obtain coarse powder of hexagonal ferrite.

[0035] The BET specific surface area of ​​the obtained coarse powder of hexagonal ferrite was measured and found to be 0.69 m 2 / g. In addition, the density of the Sr ferrite powder was set to 5.1 g / cm 3 From the obtained BET specific surface area value, the specific surface area diameter of the coarse powder of hexagonal ferrite was calculated to be 1.7 μm. The evaluation results are shown in Table 1.

[0036] (2) Manufacturing process of hexagonal ferrite fine powder Hematite (α-Fe2O3, specific surface area 5.3m 2 / g) and strontium carbonate (SrCO3, specific surface area 5.8m 2 / g) were weighed and mixed so that the molar ratio of Fe:Sr was 11.0:1.0, and then water was added to form spherical granules with a diameter of 3 to 10 mm.

[0037] The resulting granules were fired in a rotary kiln under an air flow atmosphere at 1050°C for 20 minutes, and the fired material was processed in a roller mill to obtain a fine powder. Water was added to the resulting fine powder to form a slurry with a fine powder concentration of 40% by mass. The slurry was then placed in an attritor, a milling device equipped with a stirring blade, together with 5.56 mm diameter steel balls and stirred and pulverized for 60 minutes (pulverization time), to obtain a slurry containing a fine powder of hexagonal ferrite after wet pulverization. The rotation speed of the stirring blade was adjusted so that the movement speed (circumferential speed) of the point farthest from the rotation axis of the stirring blade was 1.6 m / s. A sample was taken from the resulting slurry containing the fine powder of hexagonal ferrite after wet pulverization, and the slurry was filtered and dried to obtain a fine powder sample of hexagonal ferrite for evaluation. The BET specific surface area of ​​the resulting fine powder sample of hexagonal ferrite was measured and found to be 8.7 m. 2 / g, and the compressed density was measured to be 3.02 g / cm 3 The obtained BET specific surface area and the density of the Sr ferrite powder were 5.1 g / cm 3 From this value, the specific surface area diameter of the fine powder sample of hexagonal ferrite was calculated to be 0.14 μm. The evaluation results are shown in Table 1 (the same applies to the following Examples and Comparative Examples).

[0038] (3) Mixing and grinding process The hexagonal ferrite coarse powder obtained in the hexagonal ferrite coarse powder production process (1) was added to the slurry containing the resulting wet-milled hexagonal ferrite fine powder contained in the attritor's milling vessel so that the mass ratio of hexagonal ferrite fine powder to coarse powder was 35:65. The mixture was then mixed and milled for another 20 minutes using the attritor. The rotation speed of the impeller was controlled to a peripheral speed of 1.6 m / s. The slurry was then filtered to separate the solid and liquid, and then dried in air at 150°C for 10 hours to obtain a dried cake. The dried cake was then crushed to obtain a mixed and milled powder. The resulting mixed powder was then crushed using a vibrating ball mill (Uras Vibrator KEC-8-YH, manufactured by Murakami Seiki Seisakusho Co., Ltd.) to obtain a milled mixed powder. The milling process 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.

[0039] (4) Annealing process The mixed and pulverized mixed powder was annealed in air at 965° C. for 30 minutes to obtain the hexagonal ferrite magnetic powder for bonded magnets according to Example 1.

[0040] (5) Evaluation of hexagonal ferrite magnetic powder for bonded magnets The hexagonal ferrite magnetic powder for bonded magnets according to Example 1 was measured by powder X-ray diffraction (XRD) using a powder X-ray diffractometer (Miniflex 600 manufactured by Rigaku Corporation) with a tube voltage of 40 kV, a tube current of 15 mA, a measurement range of 15° to 60°, a scan speed of 1° / min, and a scan width of 0.02°. As a result, all peaks were SrFe 12 O 19 This confirmed that the hexagonal ferrite magnetic powder for bonded magnets of this example had a magnetoplumbite-type crystal structure. The same results were obtained in Examples 2 to 5 and Comparative Examples 1 and 2 described below. A composition analysis was performed on the hexagonal ferrite magnetic powder for bonded magnets according to Example 1, and the composition formula of the hexagonal ferrite magnetic powder for bonded magnets was determined to be SrFe n O 19-z When we calculated n and z in this case, we found that z = 1.08 and n = 11.28.

[0041] The compressed density of the hexagonal ferrite magnetic powder for bonded magnets according to Example 1 was measured and found to be 3.57 g / cm 3 The specific surface area was measured to be 2.41 m 2 / g, and the average particle size was measured to be 1.26 μm.

[0042] When the magnetic properties of a compact of the hexagonal ferrite magnetic powder for bonded magnets according to Example 1 were measured, the coercive force p-iHc of the compact was 2930 Oe, and the remanent magnetization p-Br of the compact was 2000 G. The evaluation results are shown in Table 2 (the same applies to the following Examples and Comparative Examples).

[0043] 1-2. Production of bonded magnet according to Example 1 (1) Manufacturing of bonded magnet A 92.0 parts by weight of the hexagonal ferrite magnetic powder for bonded magnets obtained in Example 1, 0.6 parts by weight of a silane coupling agent (Z-6094N manufactured by Toray Dow Corning Co., Ltd.), 0.8 parts by weight of a lubricant (VPN-212P manufactured by Henkel), and 6.6 parts by weight of a powdered polyamide resin (P-1011F manufactured by Ube Industries, Ltd.) as a binder were weighed, filled into a mixer, and mixed. The resulting mixture was kneaded at 230 ° C to obtain kneaded pellets with an average diameter of 2 mm. Note that a melt flow indexer (Melt Flow Indexer C-5059D2 manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used to measure the weight of the mixture extruded at 270 ° C under a load of 10 kg, and this weight was converted to the amount extruded per 10 minutes to determine the flow rate (MFR) of the ferrite powder for bonded magnets when mixed. It was 137.2 g / 10 min. The kneaded pellets were loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and subjected to molding at a temperature of 300°C and a molding pressure of 8.5 N / mm in a magnetic field of 4.3 kOe. 2A cylindrical bonded magnet A (ferrite concentration 92.0 mass %, 4.3 kOe) 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.

[0044] When the magnetic properties of bonded magnet A, which uses the hexagonal ferrite magnetic powder for bonded magnets according to Example 1, were measured, the coercive force iHc was 3264 Oe and the remanence Br was 3107 G. The results are shown in Table 3 (the same applies to the following Examples and Comparative Examples).

[0045] (2) Manufacturing of bonded magnet B 92.0 parts by weight of the hexagonal ferrite magnetic powder for bonded magnets obtained in Example 1, 0.6 parts by weight of a silane coupling agent (Z-6094N manufactured by Toray Dow Corning Co., Ltd.), 0.8 parts by weight of a lubricant (VPN-212P manufactured by Henkel), and 6.6 parts by weight of a powdered polyamide resin (P-1011F manufactured by Ube Industries, Ltd.) as a binder were weighed, loaded into a mixer, and mixed. The resulting mixture was kneaded at 230 ° C to obtain kneaded pellets with an average diameter of 2 mm. These kneaded pellets were loaded into an injection molding machine, and bonded magnet B was obtained using the same procedure as bonded magnet A, except that the magnetic field was set to 9.7 kOe. When the magnetic properties of this bonded magnet B were measured, the coercive force iHc was 3170 Oe and the remanence Br was 3209 G. The results are shown in Table 3 (the same applies to the following Examples and Comparative Examples).

[0046] Example 2 Hexagonal ferrite magnetic powder for bonded magnets was obtained using the same procedures as in Example 1, except that in the manufacturing process for the hexagonal ferrite fine powder, water was added to the hexagonal ferrite fine powder obtained after roller milling to form a slurry so that the concentration of the hexagonal ferrite fine powder was 20 mass%, and the grinding processing time for the wet grinding of the hexagonal ferrite fine powder was 120 minutes. The obtained hexagonal ferrite coarse powder, a hexagonal ferrite fine powder sample for evaluation, and the hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured using the same procedures as in Example 1, and bonded magnets A and B were manufactured using the obtained hexagonal ferrite magnetic powder for bonded magnets, and their magnetic properties and MFR were measured.

[0047] Example 3 Hexagonal ferrite magnetic powder for bonded magnets was obtained using the same procedures as in Example 1, except that in the manufacturing process for the hexagonal ferrite fine powder, water was added to the hexagonal ferrite fine powder obtained after roller milling to form a slurry so that the concentration of the hexagonal ferrite fine powder was 20 mass%, and the grinding processing time for the wet grinding of the hexagonal ferrite fine powder was 90 minutes. The obtained hexagonal ferrite coarse powder, a hexagonal ferrite fine powder sample for evaluation, and the hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured using the same procedures as in Example 1, and bonded magnets A and B were manufactured using the obtained hexagonal ferrite magnetic powder for bonded magnets, and their magnetic properties and MFR were measured.

[0048] Example 4 (1) Manufacturing process of coarse hexagonal ferrite powder Hematite (α-Fe2O3, specific surface area 5.3m 2 / g) and strontium carbonate (SrCO3, specific surface area 5.8m 2The two compounds (Fe / Sr) were weighed and mixed in a molar ratio of 0.5:1.0 (the molar ratio of Fe to Sr (Fe / Sr) = 1.0), and the mixture was granulated in a pan pelletizer while adding water. The resulting spherical granules with a diameter of 3 to 10 mm were placed in an internal combustion rotary kiln and fired in an air atmosphere at 1050°C for 20 minutes to obtain a fired product. The fired product was pulverized in a roller mill and then crushed to obtain a powder (specific surface area 1.71 m). 2 The iron-strontium composite oxide powder was obtained by mixing the iron-strontium composite oxide powder with hematite (α-FeO, specific surface area 5.3 m 2 Example 4 was prepared by weighing and mixing 0.17% by mass of boric acid and 2.3% by mass of potassium chloride to give a molar ratio of Fe (total) to Sr (Fe (total) / Sr) of 11.0, adding water to the mixture and granulating the mixture. The resulting spherical granules having a diameter of 3 to 10 mm were placed in an internal combustion rotary kiln and fired in the air at 1250°C (firing temperature) for 20 minutes. The fired product was then pulverized in a roller mill to obtain a coarse powder of hexagonal ferrite according to Example 4.

[0049] (2) After the manufacturing process of hexagonal ferrite fine powder Except for using the coarse powder of hexagonal ferrite according to Example 4 in the mixing and grinding step, the same procedures as those from the production step of the fine powder of hexagonal ferrite in Example 2 onwards were used to obtain the hexagonal ferrite magnetic powder for bonded magnets according to Example 4. The obtained coarse powder of hexagonal ferrite, a fine powder sample of hexagonal ferrite for evaluation, and the hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured according to the same procedures as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets was used to produce bonded magnets A and B, and their magnetic properties and MFR were measured.

[0050] Example 5 Hexagonal ferrite magnetic powder for bonded magnets was obtained using the same procedures as in Example 4, except that the firing temperature in the manufacturing process for the coarse powder of hexagonal ferrite was set to 1300°C. The obtained coarse powder of hexagonal ferrite, a fine powder sample of hexagonal ferrite for evaluation, and the hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured using the same procedures as in Example 1. Bonded magnets A and B were also manufactured using the obtained hexagonal ferrite magnetic powder for bonded magnets, and their magnetic properties and MFR were measured.

[0051] (Comparative Example 1) Hexagonal ferrite magnetic powder for bonded magnets was obtained using the same procedures as in Example 1, except that in the manufacturing process for the hexagonal ferrite fine powder, the rotation speed of the stirring blade was adjusted so that the movement speed (circumferential speed) at the point farthest from the stirring blade's rotation axis was 3.2 m / s. The obtained hexagonal ferrite coarse powder, a hexagonal ferrite fine powder sample for evaluation, and the hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured using the same procedures as in Example 1, and bonded magnets A and B were manufactured using the obtained hexagonal ferrite magnetic powder for bonded magnets, and their magnetic properties and MFR were measured.

[0052] (Comparative Example 2) In the manufacturing process for the hexagonal ferrite fine powder, the rotation speed of the stirring blade was adjusted so that the moving speed (circumferential speed) at the point farthest from the rotation axis of the stirring blade was 3.2 m / s, and the grinding processing time for the wet grinding of the hexagonal ferrite fine powder was set to 30 minutes, except that hexagonal ferrite magnetic powder for bonded magnets was obtained using the same procedures as in Example 1. The obtained hexagonal ferrite coarse powder, hexagonal ferrite fine powder samples for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured using the same procedures as in Example 1, and bonded magnets A and B were manufactured using the obtained hexagonal ferrite magnetic powder for bonded magnets, and their magnetic properties and MFR were measured.

[0053] The results are shown in Tables 1 to 3.

[0054] [Table 1]

[0055] [Table 2]

[0056] [Table 3]

[0057] The residual magnetic flux density Br(G) of the bonded magnets of Examples 1 to 5 was greater than the Br(G) values ​​of any of the comparative examples, demonstrating that excellent Br(G) can be obtained by using hexagonal ferrite fine powder that satisfies relational formula (1). Here, although the specific surface areas of Example 1 and Comparative Example 3, and Example 2 and Comparative Example 1 are equivalent, the Br(G) as a bonded magnet was superior in Examples 1 and 2, which satisfied relational formula (1). Furthermore, while Comparative Examples 2 and 3 were more advantageous than Example 2 in terms of compaction density, the Br(G) as a bonded magnet was greater in Example 2, which satisfied relational formula (1). From these results, it is thought that the peripheral speed of the stirring blades in the wet grinding process during preparation of the fine powder of hexagonal ferrite was controlled to 1.6 m / s in the example, but 3.2 m / s in the comparative example, which hinders uniformity. This is thought to be the reason why the relational expression (1) is no longer satisfied.

Claims

1. a step of obtaining a coarse powder of hexagonal ferrite; and a step of obtaining a fine powder of hexagonal ferrite having a larger specific surface area than the coarse powder of hexagonal ferrite. a step of coarsely grinding the hexagonal ferrite powder and finely grinding the hexagonal ferrite powder to obtain a mixed powder; Annealing the mixed powder obtained by the mixed and pulverized treatment, The hexagonal ferrite fine powder was filled in an amount of 10 g into a cylindrical mold having an inner diameter of 2.54 cm and then subjected to a pressure of 1000 kg / cm ２ The compressed density X (g / cm ) of the compact compressed at a pressure of ３ ) and the specific surface area Y (m ２ / g) is expressed by the following formula (1): X>-0.03×Y+3.27...(1) The following relation is satisfied: the specific surface area of ​​the coarse powder of hexagonal ferrite is 0.3 m 2 / g or more and 1.2 m 2 / g or less, and the specific surface area of ​​the fine powder of hexagonal ferrite is 4.0 m 2 / g or more and 20.0 m 2 / g or less; The mass ratio of the coarse powder of hexagonal ferrite to the total mass of the coarse powder of hexagonal ferrite and the fine powder of hexagonal ferrite is 60 mass% or more and 90 mass% or less. Manufacturing method for hexagonal ferrite magnetic powder for bonded magnets.

2. 2. The method for producing hexagonal ferrite magnetic powder for bonded magnets according to claim 1, wherein the hexagonal ferrite magnetic powder for bonded magnets is hexagonal Sr ferrite.

3. 3. The method for producing hexagonal ferrite magnetic powder for bonded magnets according to claim 1 or 2, wherein the fine powder of hexagonal ferrite is pulverized using a wet bead mill with the peripheral speed of the stirring blade set to 0.5 m / s or more and 2.5 m / s or less.

4. A method for producing a bonded magnet, characterized by using a hexagonal ferrite magnetic powder for a bonded magnet obtained by the production method according to any one of claims 1 to 3.

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