JP2023014477A - Ferrite powder for bond magnet and method for manufacturing the same - Google Patents

Abstract

To provide a ferrite powder for a bond magnet capable of obtaining a bond magnet having high remanent magnetization Br and a high coercive force iHc by magnetic field orientation.SOLUTION: A method for manufacturing ferrite powder for a bond magnet includes steps of: mixing powder of composite oxides of iron, strontium, lanthanum and cobalt with iron oxide (preferably hematite (α-Fe2O3)) and granulating the mixture, and then firing (preferably at 1100 to 1275°C) and pulverizing the granulated mixture to obtain ferrite coarse powder (preferably coarse powder having a specific surface area of 0.5 to 1.0 m2/g); mixing coarse ferrite powder and fine ferrite powder having a larger specific surface area than that of the coarse ferrite powder (fine powder whose specific surface area is preferably 5 to 10 m2/g, and more preferably 7 to 9 m2/g); and pulverizing a mixture of the coarse ferrite powder and the fine ferrite powder and then annealing the mixture (preferably at a temperature of 1000°C or less).SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a ferrite powder for bonded magnets and a method for producing the same, and more particularly to a ferrite powder for bonded magnets containing coarse and fine ferrite particles and a method for producing the same.

Conventionally, sintered ferrite magnets have been used as magnets with high magnetic force, such as those used in small motors used in AV equipment, OA equipment, and automotive electronic components, and magnet rolls in copiers. . However, sintered ferrite magnets have problems such as chipping and cracking, and poor productivity due to the need for polishing.

Therefore, in recent years, bond magnets made of rare earth magnets have been used as high-magnetic-force magnets for small motors used in AV equipment, OA equipment, automotive electrical components, and the like. However, since rare earth magnets are about 20 times more expensive than sintered ferrite magnets and are prone to rust, it is desired to use bonded ferrite magnets instead of sintered ferrite magnets. there is
Such a ferrite powder for a bonded magnet has a composition of (Sr _1-x A _x )O·n[(Fe _1-yz Co _y Zn _z ) ₂ O ₃ ] (where A is La, La—Nd , La-Pr or La-Nd-Pr, n = 5.80-6.10, x = 0.1-0.5, y = 0.0083-0.042, 0 ≤ z < 0.0168) Magnetoplumbite-type strontium ferrite particles having a saturation magnetization value σs of 73 Am ² /kg (73 emu/g) or more and an average particle diameter of 1.0 to 3.0 μm, and magnetoplumbite-type strontium ferrite. A strontium ferrite particle powder for bonded magnets has been proposed that contains plate-like particles in a number ratio of 60% or more in the particle powder (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2002-175907 (paragraph number 0025)

However, since the strontium ferrite particle powder for bond magnets of Patent Document 1 contains many plate-like particles, when the particle powder is aligned in the magnetic field direction by magnetic field orientation, the plate-like particles interfere with each other's orientation. Therefore, it was difficult to produce a bonded magnet with high orientation.

Therefore, in view of such conventional problems, the present invention provides a ferrite powder for a bonded magnet and a method for producing the same, which can obtain a bonded magnet having a high remanent magnetization Br and a high coercive force iHc by magnetic field orientation. intended to provide

As a result of intensive research to solve the above problems, the present inventors mixed and granulated a powder of a composite oxide of iron, strontium, lanthanum, and cobalt with iron oxide, and then granulated it at 1100 to 1275 ° C. A step of firing and pulverizing to obtain coarse ferrite powder, a step of mixing coarse ferrite powder and fine ferrite powder having a larger specific surface area than the coarse ferrite powder, and a mixture of coarse ferrite powder and fine ferrite powder. A bonded magnet having high remanent magnetization Br and high coercive force iHc can be obtained by magnetic orientation by a method for producing a ferrite powder for a bonded magnet comprising the step of pulverizing and annealing the ferrite powder for a bonded magnet. The inventors have found that ferrite powder can be produced, and have completed the present invention.

That is, in the method for producing a ferrite powder for a bonded magnet according to the present invention, a powder of a composite oxide of iron, strontium, lanthanum, and cobalt and iron oxide are mixed and granulated, followed by sintering at 1100 to 1275°C. A step of pulverizing to obtain coarse ferrite powder, a step of mixing the coarse ferrite powder and fine ferrite powder having a larger specific surface area than the coarse ferrite powder, and pulverizing the mixture of the coarse ferrite powder and the fine ferrite powder. and a step of annealing afterward.

In this method for producing a ferrite powder for a bonded magnet, the composite oxide powder was obtained by mixing strontium carbonate, lanthanum oxide, iron oxide, and cobalt oxide, granulating them, and then firing them at 1000 to 1250°C. It is preferably obtained by pulverizing the fired product. Further, when mixing the powder of the composite oxide and the iron oxide, the composite oxide is mixed so that the molar ratio of Fe in the iron oxide to the sum of Sr and La is 4.5 to 11.7. powder and iron oxide. The ferrite coarse powder preferably has a specific surface area of 0.5 to 1.0 m ² /g.

Further, the ferrite powder for a bonded magnet according to the present invention has (Sr _1-x La _x )·(Fe _1-y Co _y ) _n O _19-z (where 0<x≦0.5, 0<y≦0 .04, 10.0 ≤ n ≤ 12.5, -1.0 ≤ z ≤ 3.5), and the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer has a particle size of 1 μm 25 to 40% by volume of particles less than 1 μm, 40 to 70% by volume of particles of 1 to 5 μm, and 5 to 22% by volume of particles larger than 5 μm, wherein A mixer was charged with 92.0 parts by mass of ferrite powder for bond magnet, 0.6 parts by mass of silane coupling agent, 0.8 parts by mass of lubricant, and 6.6 parts by mass of powdered polyamide resin, and mixed. The mixture thus obtained was kneaded at 230°C to prepare kneaded pellets having an average diameter of 2 mm, and the kneaded pellets were injection molded in a magnetic field of 9.7 kOe at a temperature of 300°C and a molding pressure of 8.5 N/mm ² . A cylindrical bonded magnet A having a diameter of 15 mm and a height of 8 mm (the orientation direction of the magnetic field is along the central axis of the cylinder) is produced by cutting the bonded magnet A parallel to the direction of the applied magnetic field, By observing the shape of the particles with an electron microscope at a magnification of 2000 and binarizing the obtained electron micrograph, the long axis length (when one particle is sandwiched between two parallel straight lines) is calculated as the particle shape index. The distance between the straight lines (the maximum value of the length of the line segment drawn perpendicular to the two parallel straight lines) is 1.0 μm or more. Find the ratio of the long axis length (long axis length / short axis length) (aspect ratio) to the minimum distance between straight lines when sandwiched (assume each particle is a plate-like particle, and the volume is long axis length × A volume-average aspect ratio weighted by volume is calculated as long axis length×short axis length), and the aspect ratio is 1.5 or less.

10 g of this ferrite powder for bond magnet is filled in a cylindrical mold with an inner diameter of 2.54 cmφ and then compressed at a pressure of 1 ton/cm ² . The compressed density of the ferrite powder for bonded magnets is preferably 3.60 g/cm ³ or more when measured as .

Further, 8 g of the above ferrite powder for bond magnet and 0.4 cc of polyester resin were kneaded in a mortar, and 7 g of the resulting kneaded product was filled in a mold having an inner diameter of 15 mmφ and compressed at a pressure of 2 tons/cm ² for 60 seconds. The coercive force iHc of the compact obtained by removing the molded product obtained by the above from the mold and drying it at 150 ° C. for 30 minutes is measured at a magnetic field of 10 kOe. is preferred. When the residual magnetization Br of the bond magnet A is measured at a magnetic field of 10 kOe, the residual magnetization Br is preferably 3200 G or more. Moreover, when the maximum energy product BH _max of the bond magnet A is measured at a magnetic field of 10 kOe, the maximum energy product BH _max is preferably 2.50 MGOe or more. In addition, a mixer was filled with 93.5 parts by mass of ferrite powder for bond magnet, 0.6 parts by mass of silane coupling agent, 0.8 parts by mass of lubricant, and 5.1 parts by mass of powdered polyamide resin. The mixture obtained by mixing is kneaded at 230 ° C. to prepare kneaded pellets with an average diameter of 2 mm, and the kneaded pellets are placed in a magnetic field of 9.7 kOe at a temperature of 300 ° C. and a molding pressure of 8.5 N / mm ² to produce a cylindrical bond magnet B (the orientation direction of the magnetic field is along the central axis of the cylinder) with a diameter of 15 mm and a height of 8 mm. The residual magnetization Br is preferably 3300 G or more when measured at . When the maximum energy product BH _max of the bond magnet B is measured at a magnetic field of 10 kOe, the maximum energy product BH _max is preferably 2.65 MGOe or more.

A bonded magnet according to the present invention is characterized by comprising the ferrite powder for a bonded magnet and a binder.

According to the present invention, it is possible to produce a ferrite powder for a bonded magnet, which enables obtaining a bonded magnet having a high remanent magnetization Br and a high coercive force iHc by magnetic field orientation.

An embodiment of the method for producing a ferrite powder for a bonded magnet according to the present invention mixes a composite oxide powder of iron, strontium, lanthanum and cobalt with iron oxide (preferably hematite (α-Fe ₂ O ₃ )). After granulating, it is fired at 1100 to 1275° C. (preferably 1150 to 1275° C.) and pulverized to coarse ferrite powder (preferably coarse powder having a specific surface area of 0.5 to 1.0 m ² /g). and coarse ferrite powder and fine ferrite powder having a larger specific surface area than the coarse ferrite powder (fine powder having a specific surface area of preferably 5 to 15 m ² /g, more preferably 7 to 9 m ² /g). and a step of annealing (preferably at 1000° C. or less, more preferably at 880 to 990° C.) after pulverizing a mixture of coarse ferrite powder and fine ferrite powder. Use as a ferrite powder for bonded magnets with high coercive force by using powders of composite oxides of iron, strontium, lanthanum and cobalt and firing at a temperature of 1100 to 1275°C when obtaining coarse ferrite powder. Coarse powder of ferrite can be obtained.

The powder of the composite oxide of iron, strontium, lanthanum and cobalt is obtained by mixing strontium carbonate, lanthanum oxide, iron oxide and cobalt oxide, granulating the powder, and then heating the powder at 1000 to 1250°C (preferably 1050 to 1200°C, more preferably can be obtained by pulverizing the fired product obtained by firing at 1050 to 1150 ° C.).

When mixing the powder of the composite oxide and the iron oxide, the molar ratio Fe/(Sr+La) of Fe in the iron oxide to the sum of Sr and La is preferably 4.5 to 11.7 (more preferably 9.5. 0 to 11.0), the composite oxide powder and iron oxide are mixed.

Fine ferrite powder is obtained by mixing strontium carbonate and iron oxide so that the molar ratio Fe/Sr of Fe in iron oxide to Sr in strontium carbonate is 10.0 to 12.5, and then granulating the powder. It is preferably obtained by pulverizing the fired material obtained by firing at a temperature (preferably 900 to 1100° C.) lower than the firing temperature for obtaining the above.

When the coarse ferrite powder and the fine ferrite powder are mixed, the ratio of the coarse ferrite powder is preferably 60 to 90% by mass. By mixing 60 to 90% by mass of ferrite coarse powder and 10 to 40% by mass of ferrite fine powder, the volume-based particle size distribution measured by a laser diffraction particle size distribution measuring device has a particle size of less than 1 μm. It is possible to obtain a ferrite powder for a bonded magnet in which the ratio is 25% by volume or more and the ratio of particles larger than 5 μm is 5% by volume or more.

A mixture of ferrite coarse powder and ferrite fine powder is pulverized (preferably for 10 to 40 minutes, more preferably for 15 to 30 minutes) using a wet attritor or the like (wet pulverization), and the resulting slurry is filtered. The resulting solid is dried (preferably at 120 to 180° C. for 5 to 20 hours in air), and the resulting dry cake is milled by a vibrating ball mill as a medium of relatively large size (preferably 10 to 15 mm in diameter). After performing pulverization using balls (preferably for 20 to 40 minutes, more preferably for 25 to 35 minutes), a relatively small ball (preferably 5 to 10 mm in diameter) is used as a medium in a vibrating ball mill. (Preferably 20 to 40 minutes, more preferably 25 to 35 minutes) can be pulverized by performing pulverization treatment.

In this way, (Sr _1-x La _x )·(Fe _1-y Co _y ) _n O _19-z (where 0<x≤0.5, 0<y≤0.04, 10.0≤ n≦12.5, −1.0≦z≦3.5).

Further, an embodiment of the ferrite powder for a bonded magnet according to the present invention is (Sr _1-x La _x )·(Fe _1-y Co _y ) _n O _19-z (where 0<x≦0.5 (preferably is 0.01 ≤ x ≤ 0.5, more preferably 0.1 ≤ x ≤ 0.5), 0 < y ≤ 0.04 (preferably 0.01 ≤ y ≤ 0.04), 10.0 ≤ n ≤ 12.5 (preferably 10.0 ≤ n ≤ 12.0), -1.0 ≤ z ≤ 3.5 (preferably -0.5 ≤ z ≤ 3.5)), In the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer, the proportion of particles with a diameter of less than 1 μm is 25 to 40% by volume (preferably 25 to 35% by volume), and the proportion of particles with a diameter of 1 to 5 μm is 40%. -70% by volume (preferably 40 to 65% by volume), and the proportion of particles larger than 5 μm is 5 to 22% by volume (preferably 5 to 20% by volume) for a bonded magnet, for the bonded magnet 92.0 parts by mass of ferrite powder, 0.6 parts by mass of a silane coupling agent, 0.8 parts by mass of a lubricant, and 6.6 parts by mass of a powdery polyamide resin are filled in a mixer and mixed. The resulting mixture is kneaded at 230 ° C. to produce kneaded pellets with an average diameter of 2 mm, and the kneaded pellets are injection molded at a temperature of 300 ° C. and a molding pressure of 8.5 N / mm ² in a magnetic field of 9.7 kOe. A cylindrical bonded magnet A having a size of 15 mm×8 mm in height (the orientation direction of the magnetic field is the direction along the central axis of the cylinder) was prepared, and this bonded magnet A was cut parallel to the direction of the applied magnetic field and examined by an electron microscope. The shape of the particles was observed at a magnification of 2000, and the obtained electron micrographs were binarized. The short axis length of particles with a distance (maximum value of the length of a line segment drawn perpendicular to two parallel straight lines) of 1.0 μm or more (when one particle is sandwiched between two parallel straight lines) (minimum distance between straight lines) to find the ratio of long axis length (major axis length/minor axis length) (aspect ratio) (assuming each particle is a plate-like particle, and the volume is The volume-average aspect ratio weighted by the volume is calculated as x minor axis length), and the aspect ratio is 1.5 or less. If the aspect ratio is 1.5 or less, the particles of the ferrite powder for a bonded magnet are easily aligned in the direction of the magnetic field due to magnetic field orientation, and a bonded magnet with high particle orientation and high remanent magnetization Br and maximum energy product BH _max is produced. Easier to manufacture.

The density of the ferrite powder for bond magnet when 10 g of the above ferrite powder for bond magnet is filled in a cylindrical mold with an inner diameter of 2.54 cmφ and then compressed at a pressure of 1 ton/cm ² is determined by compression of the ferrite powder for bond magnet. When measured as density, the compressed density (CD) of the ferrite powder for bonded magnets is preferably 3.60 g/cm ³ or more, more preferably 3.60 to 4.00 g/cm ³ .

The ferrite powder for bonded magnets preferably has an average particle size of 1.0 to 2.0 μm, more preferably 1.1 to 1.8 μm, and a specific surface area of preferably 1.0 to 2.7 μm. ² /g, more preferably 1.5 to 2.5 m ² /g.

Further, 8 g of the above ferrite powder for bond magnet and 0.4 cc of polyester resin were kneaded in a mortar, and 7 g of the resulting kneaded product was filled in a mold having an inner diameter of 15 mmφ and compressed at a pressure of 2 tons/cm ² for 60 seconds. The molded product obtained was extracted from the mold and dried at 150 ° C. for 30 minutes to prepare a green compact. When the coercive force iHc and remanent magnetization Br of the body are measured, the coercive force iHc is preferably 2700 Oe or more, more preferably 2700 to 4000 Oe, more preferably 2700 to 3500 Oe, and the remanent magnetization Br is preferably 1700 to 2200 G, More preferably 1800-2050G.

When the coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of the bond magnet A are measured at a magnetic field of 10 kOe, the coercive force iHc is 2500 Oe or more, more preferably 2500 to 3500 Oe, and the remanent magnetization Br is , preferably 3200 G or more, more preferably 3200 to 3500 G, and the maximum energy product BH _max is preferably 2.50 MGOe or more, more preferably 2.52 to 2.85 MGOe, most preferably 2.55 to 2 .75 MGOe.

In addition, a mixer was filled with 93.5 parts by mass of ferrite powder for bond magnet, 0.6 parts by mass of silane coupling agent, 0.8 parts by mass of lubricant, and 5.1 parts by mass of powdered polyamide resin. The mixture obtained by mixing is kneaded at 230 ° C. to prepare kneaded pellets with an average diameter of 2 mm, and the kneaded pellets are placed in a magnetic field of 9.7 kOe at a temperature of 300 ° C. and a molding pressure of 8.5 N / mm ² to produce a cylindrical bonded magnet B with a diameter of 15 mm and a height of 8 mm (the orientation direction of the magnetic field is along the central axis of the cylinder). and the maximum energy product BH _max is measured at a measurement magnetic field of 10 kOe, the coercive force iHc is 2300 Oe or more, more preferably 2300 to 3000 Oe, and the remanent magnetization Br is preferably 3300 G or more, more preferably 3300 to 3500 G, The maximum energy product BH _max is preferably 2.65 MGOe or more, more preferably 2.67-3.00 MGOe, and most preferably 2.69-2.90 MGOe.

Further, an embodiment of a bonded magnet according to the present invention includes the above ferrite powder for bonded magnets and a binder (preferably made of resin such as polyamide resin). The fluidity MFR when the ferrite powder for bonded magnets is mixed with a resin or the like to produce this bonded magnet is preferably 30 g/10 minutes or more, more preferably 35 g/10 minutes or more.

Examples of the ferrite powder for bonded magnets and the method for producing the same according to the present invention will now be described in detail.

[Example 1]
(Manufacturing coarse powder of ferrite)
Strontium carbonate (SrCO ₃ , specific surface area 5.8 m ² /g), lanthanum oxide (La ₂ O ₃ , specific surface area 3.8 m ² /g) and hematite (as iron oxide) (α-Fe ₂ O ₃ , specific surface area 5.3 m ² /g) and cobalt oxide (Co ₃ O ₄ , specific surface area 3.3 m ² /g) at a molar ratio Sr:La:Fe:Co=0.70:0.30:0.70:0 This mixture is granulated while adding water in a pan pelletizer, and the obtained spherical granules with a diameter of 3 to 10 mm are put into an internal combustion rotary kiln and placed in the atmosphere. A fired product was obtained by firing (primary firing) at 1100° C. for 20 minutes in an atmosphere. The fired product was pulverized by a roller mill to obtain a composite oxide powder of iron, strontium, lanthanum and cobalt.

The powder of this composite oxide and hematite (as iron oxide) (α-Fe ₂ O ₃ , specific surface area 5.3 m ² /g) were combined with the molar ratio of Fe in iron oxide to the total of Sr and La (Fe/ (Sr + La)) = 10.0 and mixed, and 0.17% by mass of boric acid and 2.3% by mass of potassium chloride (as additives) were added to the mixture and mixed. After that, water is added to granulate, and the resulting spherical granules with a diameter of 3 to 10 mm are put into an internal combustion rotary kiln and fired at 12500 ° C. (firing temperature) for 20 minutes in the atmosphere (secondary firing). The baked product thus obtained was pulverized with a roller mill to obtain a coarse powder. When the specific surface area of this coarse powder was measured by the BET single-point method using a specific surface area measuring device (Monosorb manufactured by Quantachrome), the specific surface area was 0.74 m ² /g.

(Production of ferrite fine powder)
Strontium carbonate (SrCO ₃ , specific surface area 5.8 m ² /g) and hematite (as iron oxide) (α-Fe ₂ O ₃ , specific surface area 5.3 m ² /g) were mixed at a molar ratio Sr:Fe=1.0. : Weighed and mixed to 11.0, granulated while adding water to this mixture in a pan pelletizer, and the resulting spherical granules with a diameter of 3 to 10 mm were charged into an internal combustion rotary kiln. , and sintered at 970° C. for 20 minutes in an air atmosphere to obtain a sintered product. This fired product was pulverized with a roller mill to obtain a fine powder. When the specific surface area of this fine powder was measured by the BET single-point method using a specific surface area measuring device (Monosorb manufactured by Quantachrome Co.), the specific surface area was 7.96 m ² /g.

(Manufacture of ferrite powder for bonded magnets)
75 parts by mass of the coarse powder, 25 parts by mass of the fine powder, and 150 parts by mass of water were put into a wet attritor and pulverized for 20 minutes to obtain a slurry. The solid matter obtained by filtering this slurry was dried in air at 150° C. for 10 hours to obtain a dry cake. The pulverized material obtained by pulverizing the dry cake with a mixer is processed by a vibrating ball mill (Uras Vibrator KEC-8-YH manufactured by Murakami Seiki Co., Ltd.) using steel balls with a diameter of 12 mm as a medium. , After grinding for 28 minutes at a rotation speed of 1800 rpm and an amplitude of 8 mm, the above vibration ball mill was used to grind steel balls with a diameter of 8 mm as a medium at a rotation speed of 1800 rpm and an amplitude of 8 mm for 28 minutes. . The pulverized material thus obtained was annealed in the atmosphere at 925° C. for 30 minutes in an electric furnace to obtain a ferrite powder for bond magnets.

For this ferrite powder for bonded magnets, a composition analysis was performed by calculating the component amount of each element by the fundamental parameter method (FP method) using a fluorescent X-ray analyzer (ZSX100e manufactured by Rigaku Corporation). went. In this composition analysis, the ferrite powder for bonded magnets was packed in a measurement cell, molded by applying a pressure of 10 tons/cm ² for 20 seconds, the measurement mode was EZ scan mode, the measurement diameter was 30 mm, and the sample form was oxide. A standard measurement time was used, and a qualitative analysis was performed in a vacuum atmosphere, and then a quantitative analysis was performed on the detected constituent elements. As a result, the ferrite powder for bonded magnet contained 0.4 mass % MnO, 85.5 mass % Fe ₂ O ₃ , 2.0 mass % Co ₂ O ₃ and 7.9 mass % of SrO, 0.1% by mass of BaO, and 3.8% by mass of La ₂ O ₃ , and Sr, La, Fe, and Co, which are the main components of ferrite powder for bonded magnets, were detected. . Elements such as Cr, Mn, and Ba, which are considered to be derived from impurities in the raw material, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n, and z are calculated, x=0.24, y=0.022, n=11. 00, z=1.50. In addition, z is the valence of Sr +2, the valence of La +3, the valence of Fe +3, the valence of Co +2, and the valence of O -2, and the total valence in the chemical formula is 0. (zero).

In addition, this ferrite powder for bonded magnets was measured using a dry laser diffraction particle size distribution analyzer (manufactured by Nippon Laser Co., Ltd. (HELOS & RODOS)) at a focal length of 20 mm, a dispersion pressure of 5.0 bar, and a suction pressure of 130 mbar. Particle size distribution was measured. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 30.3% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 58.2% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 11.5% by volume. %Met.

Further, this ferrite powder for bonded magnets was measured using a powder X-ray diffractometer (Miniflex 600 manufactured by Rigaku Co., Ltd.) at a tube voltage of 40 kV, a tube current of 15 mA, a measurement range of 15° to 60°, and a scan speed of Measurement was performed by powder X-ray diffractometry (XRD) at 1°/min and a scan width of 0.02°. As a result, all peaks were observed at the same positions as those of SrFe ₁₂ O ₁₉ , confirming that the ferrite powder for bonded magnets of this example had an M-type ferrite structure. This result was the same in Examples 2 to 5 and Comparative Examples 1 to 6 described below.

Further, when the average particle diameter (APD) of the ferrite powder for bonded magnets was measured by an air permeation method using a specific surface area measuring device (SS-100 manufactured by Shimadzu Corporation), the average particle diameter was 1.27 μm. rice field. Further, when the specific surface area of this ferrite powder for bonded magnets was measured by the same method as above, the specific surface area was 2.26 m ² /g.

Also, the density of the ferrite powder for bond magnets when 10 g of the ferrite powder for bond magnets was filled in a cylindrical mold with an inner diameter of 2.54 cmφ and then compressed at a pressure of 1 ton/cm ² was determined as follows. The density (CD) was measured to be 3.63 g/cm ³ .

In addition, 8 g of ferrite powder for bond magnets and 0.4 cc of polyester resin (P-resin manufactured by Nihon Chikagaku Co., Ltd.) were kneaded in a mortar, and 7 g of the resulting kneaded product was filled in a mold with an inner diameter of 15 mmφ, and 2 tons was produced. /cm ² for 60 seconds, the molded product was removed from the mold and dried at 150°C for 30 minutes to obtain a green compact. As the magnetic properties of this compact, a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.) was used to measure the coercive force iHc and remanent magnetization Br of the compact at a measurement magnetic field of 10 kOe. The iHc was 3160 Oe and the remanent magnetization Br was 1970G.

(Manufacture of bonded magnet A)
92.0 parts by mass of the obtained ferrite powder for bonded magnets, 0.6 parts by mass of a silane coupling agent (Z-6094N manufactured by Dow Corning Toray Co., Ltd.), and 0.6 parts by mass of a lubricant (VPN-212P manufactured by Henkel). 8 parts by mass and 6.6 parts by mass of a powdery polyamide resin (P-1011F manufactured by Ube Industries, Ltd.) as a binder are weighed, filled in a mixer and mixed. The resulting mixture is kneaded at 230 ° C. Thus, kneaded pellets having an average diameter of 2 mm were obtained. In addition, using a melt flow indexer (melt flow indexer C-5059D2 manufactured by Toyo Seiki Seisakusho Co., Ltd.), the weight of the above mixture extruded at 270 ° C. and a load of 10 kg was measured, and this weight was measured for 10 minutes. The fluidity MFR at the time of mixing the ferrite powder for bonded magnets was calculated by converting to the amount extruded per hit, and was 125.6 g/10 minutes. The kneaded pellets are loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and injection molded at a temperature of 300 ° C. and a molding pressure of 8.5 N / mm ² in a magnetic field of 9.7 kOe. A cylindrical bonded magnet A (FC 92.0% by mass, 9.7 kOe) having a thickness of 8 mm (the orientation direction of the magnetic field is along the central axis of the cylinder) was obtained.
As the magnetic properties of this bonded magnet A, a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.) was used to measure the coercive force iHc, residual magnetization Br, and maximum energy product BH _max of the bonded magnet A at a magnetic field of 10 kOe. As a result of measurement, the coercive force iHc was 3358 Oe, the residual magnetization Br was 3221 G, and the maximum energy product BH _max was 2.58 MGOe.

Further, this bonded magnet A was cut parallel to the direction of the applied magnetic field, the shape of the particles was observed with a scanning electron microscope (SEM) at a magnification of 2000, and the resulting SEM photograph was binarized to obtain particles. The shape index of 200 or more particles in the SEM photograph (the long axis length at which the entire outer edge is observed in one or more fields of view of the SEM photograph (a straight line when one particle is sandwiched between two parallel straight lines 200 or more particles with a maximum distance between them) of 1.0 μm or more), the ratio of the long axis length to the short axis length (minimum distance between straight lines when one particle is sandwiched between two parallel straight lines) The average value (aspect ratio) of the ratio (major axis length/minor axis length) was found to be 1.41. As this aspect ratio, each particle was assumed to be a plate-like particle, and a volume-average aspect ratio weighted by volume was calculated with a volume of major axis length×major axis length×minor axis length.

(Manufacture of bonded magnet B)
93.5 parts by mass of the obtained ferrite powder for a bonded magnet, 0.6 parts by mass of a silane coupling agent (Z-6094N manufactured by Dow Corning Toray Co., Ltd.), and 0.6 parts by mass of a lubricant (VPN-212P manufactured by Henkel). 8 parts by mass and 5.1 parts by mass of a powdery polyamide resin (P-1011F manufactured by Ube Industries, Ltd.) as a binder are weighed, filled in a mixer and mixed. The resulting mixture is kneaded at 230 ° C. Thus, kneaded pellets having an average diameter of 2 mm were obtained. In addition, using a melt flow indexer (melt flow indexer C-5059D2 manufactured by Toyo Seiki Seisakusho Co., Ltd.), the weight of the above mixture extruded at 270 ° C. and a load of 10 kg was measured, and this weight was measured for 10 minutes. The fluidity MFR at the time of mixing the ferrite powder for bond magnet was calculated by converting to the amount extruded per hit, and it was 47.6 g/10 minutes. The kneaded pellets are loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and injection molded at a temperature of 300 ° C. and a molding pressure of 8.5 N / mm ² in a magnetic field of 9.7 kOe. A cylindrical bonded magnet B (FC 93.5% by mass, 9.7 kOe) having a thickness of 8 mm (the orientation direction of the magnetic field is along the central axis of the cylinder) was obtained.

As the magnetic properties of this bonded magnet B, a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.) was used to measure the coercive force iHc, residual magnetization Br, and maximum energy product BH _max of the bonded magnet B at a magnetic field of 10 kOe. As a result of measurement, the coercive force iHc was 2641 Oe, the residual magnetization Br was 3360 G, and the maximum energy product BH _max was 2.77 MGOe.

[Example 2]
Ferrite powder for bond magnets was produced in the same manner as in Example 1, except that 70 parts by mass of coarse powder, 30 parts by mass of fine powder, and 150 parts by mass of water were added to a wet attritor when manufacturing the ferrite powder for bond magnets. got

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.4% by mass of MnO, 85.9% by mass of Fe ₂ O ₃ and 1.9% by mass of of Co ₂ O ₃ , 7.8% by mass of SrO, 0.1% by mass of BaO, and 3.6% by mass of La ₂ O ₃ . Some Sr, La, Fe, Co were detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z Calculation of x, y, n, and z gives x=0.23, y=0.020, n=11. 26, z=1.11.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 29.9% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 58.9% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 11.2% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle diameter was 1.30 μm, the specific surface area was 2.14 m ² /g, the compression density (CD) was 3.65 g/cm ³ , the coercive force iHc of the green compact was 3200 Oe, and the residual magnetization Br was 1970 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.55 MGOe and the aspect ratio was 1.45. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 155.0 g/10 minutes.

Also, a bonded magnet B was obtained in the same manner as in Example 1 using the above ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bond magnet B were measured in the same manner as in Example 1, and the coercive force iHc was 2828 Oe, the remanent magnetization Br was 3321 G, and the maximum energy product BH _max . was 2.70 MGOe. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was found to be 81.1 g/10 minutes.

[Example 3]
Strontium carbonate (SrCO ₃ , specific surface area 5.8 m ² /g), lanthanum oxide (La ₂ O ₃ , specific surface area 3.8 m ² /g) and hematite (as iron oxide) (α-Fe ₂ O ₃ , specific surface area of 5.3 m ² /g) and cobalt oxide (Co ₃ O ₄ , specific surface area of 3.3 m ² /g) at a molar ratio of Sr:La:Fe:Co=0.70:0.30:0.85:0. Coarse ferrite powder was produced in the same manner as in Example 1, except that the powder was weighed and mixed so as to obtain .15, and the firing temperature in the secondary firing was set to 1225°C. A ferrite powder for bonded magnets was obtained by the method. When the specific surface area of the ferrite coarse powder of this example was measured by the same method as in Example 1, it was 0.76 m ² /g.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.4% by mass of MnO, 86.5% by mass of Fe ₂ O ₃ and 1.0% by mass of of Co ₂ O ₃ , 7.8% by mass of SrO, 0.1% by mass of BaO, and 3.9% by mass of La ₂ O ₃ , and is the main component of the ferrite powder for bonded magnets. Some Sr, La, Fe, Co were detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n, and z are calculated, x=0.24, y=0.011, n=11. 04, z=1.37.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 28.8% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 62.9% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 8.3% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle diameter was 1.32 μm, the specific surface area was 2.07 m ² /g, the compaction density (CD) was 3.69 g/cm ³ , the coercive force iHc of the green compact was 2900 Oe, and the residual magnetization Br was 2000 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.68 MGOe and the aspect ratio was 1.49. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 145.1 g/10 minutes.

Also, a bonded magnet B was obtained in the same manner as in Example 1 using the above ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet B were measured in the same manner as in Example 1, and the coercive force iHc was 2532 Oe, the remanent magnetization Br was 3389 G, and the maximum energy product BH _max . was 2.83 MGOe. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 25.7 g/10 minutes.

[Example 4]
A ferrite powder for a bond magnet was obtained in the same manner as in Example 3, except that the firing temperature in the secondary firing when producing coarse ferrite powder was 1200°C. When the specific surface area of the ferrite coarse powder of this example was measured by the same method as in Example 1, it was 0.83 m ² /g.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.4% by mass of MnO, 86.5% by mass of Fe ₂ O ₃ and 0.9% by mass of of _{Co2O3 ,} 0.1 wt% ZnO, 8.0 wt% SrO, 0.1 wt% BaO, and _3.7 wt% _La2O3 , Sr, La, Fe, and Co, which are the main components of the ferrite powder for bonded magnets, were detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z Calculation of x, y, n, and z gives x=0.23, y=0.010, n=10. 96, z=1.50.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 31.5% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 61.7% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 6.8% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle size was 1.18 μm, the specific surface area was 2.47 m ² /g, the compression density (CD) was 3.62 g/cm ³ , the coercive force iHc of the green compact was 3310 Oe, and the residual magnetization Br was 1950 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.60 MGOe and the aspect ratio was 1.40. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 165.0 g/10 minutes.

Also, a bonded magnet B was obtained in the same manner as in Example 1 using the above ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bond magnet B were measured in the same manner as in Example 1, and the coercive force iHc was 2988 Oe, the remanent magnetization Br was 3348 G, and the maximum energy product BH _max . was 2.75 MGOe. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 34.6 g/10 minutes.

[Example 5]
A ferrite powder for a bond magnet was obtained in the same manner as in Example 3, except that the firing temperature in the secondary firing when producing coarse ferrite powder was 1250°C. When the specific surface area of the ferrite coarse powder of this example was measured by the same method as in Example 1, it was 0.62 m ² /g.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.3% by mass of MnO, 86.6% by mass of Fe ₂ O ₃ and 0.9% by mass of of Co ₂ O ₃ , 8.0% by mass of SrO, 0.1% by mass of BaO, and 3.6% by mass of La ₂ O ₃ . Some Sr, La, Fe, Co were detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n, and z are calculated, x=0.22, y=0.010, n=10. 97, z=1.49.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 34.4% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 49.4% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 16.2% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle size was 1.20 μm, the specific surface area was 2.46 m ² /g, the compaction density (CD) was 3.67 g/cm ³ , the coercive force iHc of the green compact was 2720 Oe, and the residual magnetization Br was 1980 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.61 MGOe and the aspect ratio was 1.47. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 169.5 g/10 minutes.

Also, a bonded magnet B was obtained in the same manner as in Example 1 using the above ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet B were measured in the same manner as in Example 1, and the coercive force iHc was 2357 Oe, the remanent magnetization Br was 3369 G, and the maximum energy product BH _max . was 2.75 MGOe. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was found to be 47.8 g/10 minutes.

[Comparative Example 1]
100 parts by mass of coarse powder obtained by the same method as in Example 1 and 150 parts by mass of water were put into a wet attritor and pulverized for 20 minutes to obtain a slurry. The solid matter obtained by filtering this slurry was dried in air at 150° C. for 10 hours to obtain a dry cake. The pulverized material obtained by pulverizing the dry cake with a mixer is processed by a vibrating ball mill (Uras Vibrator KEC-8-YH manufactured by Murakami Seiki Co., Ltd.) using steel balls with a diameter of 12 mm as a medium. , at a rotation speed of 1800 rpm and an amplitude of 8 mm for 28 minutes. The pulverized material thus obtained was annealed in the atmosphere at 975° C. for 30 minutes in an electric furnace to obtain a ferrite powder for bond magnets.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.3% by mass of MnO, 85.3% by mass of Fe ₂ O ₃ and 2.4% by mass of of Co ₂ O ₃ , 6.8% by mass of SrO, 0.1% by mass of BaO, and 4.9% by mass of La ₂ O ₃ . Some Sr, La, Fe, Co were detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n, and z are calculated, x=0.32, y=0.026, n=11. 47, z=0.79.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 21.3% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 71.9% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 6.8% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle diameter was 1.72 μm, the specific surface area was 1.47 m ² /g, the compression density (CD) was 3.45 g/cm ³ , the coercive force iHc of the green compact was 3060 Oe, and the residual magnetization Br was 1870 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.52 MGOe and the aspect ratio was 1.43. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 69.8 g/10 minutes.

Also, using the above ferrite powder for bond magnets, an attempt was made to produce bond magnet B in the same manner as in Example 1. B could not be produced.

[Comparative Example 2]
After obtaining a powder of a composite oxide of iron, strontium, lanthanum and cobalt by the same method as in Example 1, coarse powder was obtained by the same method as in Example 1 except that the firing temperature was 1300 ° C. rice field. When the specific surface area of this coarse powder was measured by the same method as in Example 1, the specific surface area was 0.68 m ² /g. A ferrite powder for a bonded magnet was obtained in the same manner as in Comparative Example 1 using this coarse powder.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.4% by mass of MnO, 85.1% by mass of Fe ₂ O ₃ and 2.5% by mass of of _{Co2O3 ,} 0.1 wt% ZnO, 6.7 wt% SrO, 0.1 wt% BaO _, and 4.9 wt% _La2O3 , Sr, La, Fe, and Co, which are the main components of the ferrite powder for bonded magnets, were detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n, and z are calculated, x=0.32, y=0.028, n=11. 58, z=0.64.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 17.0% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 62.4% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 20.6% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle size was 1.84 μm, the specific surface area was 1.38 m ² /g, the compaction density (CD) was 3.47 g/cm ³ , the coercive force iHc of the green compact was 2590 Oe, and the residual magnetization Br was 1920 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.56 MGOe and the aspect ratio was 1.49. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was found to be 89.5 g/10 minutes.

Also, using the above ferrite powder for bond magnets, an attempt was made to produce bond magnet B in the same manner as in Example 1. B could not be produced.

[Comparative Example 3]
Strontium carbonate (SrCO ₃ , specific surface area 5.8 m ² /g), lanthanum oxide (La ₂ O ₃ , specific surface area 3.8 m ² /g) and hematite (α-Fe ₂ O ₃ , specific surface area 5.3 m ² /g) g) and cobalt oxide (Co ₃ O ₄ , specific surface area 3.3 m ² /g) so that the molar ratio Sr:La:Fe:Co=0.70:0.30:11.70:0.30 Coarse powder was obtained in the same manner as in Example 1, except that the materials were weighed and mixed, the primary firing temperature was changed from 1100° C. to 1200° C., and the secondary firing was not performed. When the specific surface area of this coarse powder was measured by the same method as in Example 1, the specific surface area was 0.51 m ² /g.

A ferrite powder for a bond magnet was obtained in the same manner as in Comparative Example 1 except that the obtained coarse powder was used and the annealing was performed at 985°C.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.3% by mass of MnO, 85.3% by mass of Fe ₂ O ₃ and 2.4% by mass of of Co ₂ O ₃ , 7.0% by mass of SrO, and 4.9% by mass of La ₂ O ₃ . was detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n, and z are calculated, x=0.31, y=0.026, n=11. 25, z=1.12.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 26.2% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 72.6% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 1.3% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle diameter was 1.25 μm, the specific surface area was 2.21 m ² /g, the compression density (CD) was 3.26 g/cm ³ , the coercive force iHc of the green compact was 3950 Oe, and the residual magnetization Br was 1790 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.21 MGOe and the aspect ratio was 1.62. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was found to be 42.8 g/10 minutes.

Also, using the above ferrite powder for bond magnets, an attempt was made to produce bond magnet B in the same manner as in Example 1. B could not be produced.

[Comparative Example 4]
Coarse powder was obtained in the same manner as in Comparative Example 3, except that the primary firing temperature was 1250°C. When the specific surface area of this coarse powder was measured by the same method as in Example 1, the specific surface area was 0.71 m ² /g.

A ferrite powder for a bonded magnet was obtained in the same manner as in Comparative Example 3 using the obtained coarse powder.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.3% by mass of MnO, 85.3% by mass of Fe ₂ O ₃ and 2.4% by mass of of Co ₂ O ₃ , 7.1% by mass of SrO, and 4.7% by mass of La ₂ O ₃ . was detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n and z are calculated, x=0.30, y=0.026, n=11. 27, z=1.09.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 25.2% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 70.0% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 4.8% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle size was 1.26 μm, the specific surface area was 2.19 m ² /g, the compaction density (CD) was 3.34 g/cm ³ , the coercive force iHc of the green compact was 3590 Oe, and the residual magnetization Br was 1830 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.33 MGOe and the aspect ratio was 1.56. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 61.2 g/10 minutes.

Also, using the above ferrite powder for bond magnets, an attempt was made to produce bond magnet B in the same manner as in Example 1. B could not be produced.

[Comparative Example 5]
Coarse powder was obtained in the same manner as in Comparative Example 3, except that the primary firing temperature was 1300°C. When the specific surface area of this coarse powder was measured by the same method as in Example 1, the specific surface area was 0.98 m ² /g.

A ferrite powder for a bonded magnet was obtained in the same manner as in Comparative Example 3 using the obtained coarse powder.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.3% by mass of MnO, 85.4% by mass of Fe ₂ O ₃ and 2.4% by mass of of Co ₂ O ₃ , 7.0% by mass of SrO, and 4.7% by mass of La ₂ O ₃ . was detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z When x, y, n and z are calculated, x=0.30, y=0.026, n=11. 37, z=0.95.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm is 27.5% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm is 64.3% by volume, and the frequency distribution of particles with a particle size of more than 5 μm is 8.2% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle diameter was 1.22 μm, the specific surface area was 2.41 m ² /g, the compression density (CD) was 3.42 g/cm ³ , the coercive force iHc of the green compact was 3140 Oe, and the residual magnetization Br was 1800 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.36 MGOe and the aspect ratio was 1.58. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 58.6 g/10 minutes.

Also, using the above ferrite powder for bond magnets, an attempt was made to produce bond magnet B in the same manner as in Example 1. B could not be produced.

[Comparative Example 6]
A ferrite powder for a bond magnet was obtained in the same manner as in Example 1, except that the firing temperature in the secondary firing when producing coarse ferrite powder was set to 1300°C. When the specific surface area of the ferrite coarse powder of this example was measured by the same method as in Example 1, it was 0.64 m ² /g.

The composition analysis of this ferrite powder for bonded magnets was performed in the same manner as in Example 1. As a result, the ferrite powder for bonded magnet contained 0.1% by mass of Cr ₂ O ₃ , 0.4% by mass of MnO, 85.5% by mass of Fe ₂ O ₃ and 2.0% by mass of of Co ₂ O ₃ , 7.7% by mass of SrO, 0.1% by mass of BaO, and 4.0% by mass of La ₂ O ₃ . Some Sr, La, Fe, Co were detected. Elements such as Cr, Mn, Zn, and Ba, which are considered to be derived from impurities in the raw materials, were also detected, but they were all trace amounts of 0.4% by mass or less in terms of oxides. These trace elements (1.0% by mass or less in terms of oxides) are regarded as _impurities . _x La _x )·(Fe _1-y Co _y ) _n O _19-z Calculation of x, y, n, and z gives x=0.22, y=0.020, n=11. 26, z=1.11.

In addition, the volume-based particle size distribution of this ferrite powder for bonded magnets was measured in the same manner as in Example 1. As a result, the frequency distribution of particles with a particle size of less than 1 μm was 27.5% by volume, the frequency distribution of particles with a particle size of 1 to 5 μm was 48.1% by volume, and the frequency distribution of particles with a particle size exceeding 5 μm was 24.5% by volume. %Met.

In addition, the average particle size, specific surface area, compaction density (CD), coercive force iHc of the green compact, and residual magnetization Br of this ferrite powder for bonded magnets were measured in the same manner as in Example 1. As a result, the average particle diameter was 1.47 μm, the specific surface area was 1.86 m ² /g, the compaction density (CD) was 3.73 g/cm ³ , the coercive force iHc of the green compact was 2520 Oe, and the residual magnetization Br was 2010 G. there were.

A bonded magnet A was obtained in the same manner as in Example 1 using this ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet A were measured in the same manner as in Example 1, and the aspect ratio was calculated. , the maximum energy product BH _max was 2.68 MGOe and the aspect ratio was 1.48. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 145.1 g/10 minutes.

Also, a bonded magnet B was obtained in the same manner as in Example 1 using the above ferrite powder for bonded magnets. The coercive force iHc, remanent magnetization Br, and maximum energy product BH _max of this bonded magnet B were measured in the same manner as in Example 1, and the coercive force iHc was 2050 Oe, the remanent magnetization Br was 3443 G, and the maximum energy product BH _max . was 2.88 MGOe. The fluidity MFR when the ferrite powder for bonded magnets was mixed was determined by the same method as in Example 1, and was 69.7 g/10 minutes.

Tables 1 to 7 show the results of these Examples and Comparative Examples.

From the results of Examples 1 to 5 and Comparative Examples 1 to 6, in Examples 1 to 5, a bonded magnet having a high remanent magnetization Br and a high coercive force iHc can be obtained by magnetic field orientation. It can be seen that ferrite powder can be produced.

Claims (12)

A step of mixing a powder of a composite oxide of iron, strontium, lanthanum, and cobalt with iron oxide and granulating, firing at 1100 to 1275 ° C. and pulverizing to obtain coarse ferrite powder; A step of mixing the powder with a ferrite fine powder having a larger specific surface area than the ferrite coarse powder, and a step of pulverizing the mixture of the ferrite coarse powder and the ferrite fine powder, followed by annealing. A method for producing ferrite powder for bonded magnets. The powder of the composite oxide is obtained by mixing strontium carbonate, lanthanum oxide, iron oxide and cobalt oxide, granulating the powder, and then firing the powder at 1000 to 1250° C. to pulverize the resulting fired product. The method for producing a ferrite powder for a bonded magnet according to claim 1, characterized by: When the powder of the composite oxide and the iron oxide are mixed, the composite oxide is mixed so that the molar ratio of Fe in the iron oxide to the total of Sr and La is 4.5 to 11.7. 3. A method for producing a ferrite powder for a bonded magnet according to claim 1, wherein said oxide powder and said iron oxide are mixed. 4. The method for producing ferrite powder for a bonded magnet according to claim 1, wherein the ferrite coarse powder has a specific surface area of 0.5 to 1.0 m ² /g. (Sr _1-x La _x )·(Fe _1-y Co _y ) _n O _19-z (where 0<x≦0.5, 0<y≦0.04, 10.0≦n≦12.5 , -1.0 ≤ z ≤ 3.5), and in the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer, the proportion of particles with a particle size of less than 1 μm is 25 to 40% by volume, 92.0 parts by mass of ferrite powder for bonded magnets, wherein the proportion of particles of 1 to 5 μm is 40 to 70% by volume and the proportion of particles larger than 5 μm is 5 to 22% by volume; A mixture obtained by filling a mixer with 0.6 parts by mass of a silane coupling agent, 0.8 parts by mass of a lubricant, and 6.6 parts by mass of a powdery polyamide resin and mixing them is kneaded at 230°C. , Kneaded pellets with an average diameter of 2 mm were prepared, and the kneaded pellets were injection molded in a magnetic field of 9.7 kOe at a temperature of 300 ° C. and a molding pressure of 8.5 N / mm ² to form a cylindrical shape (diameter 15 mm × height 8 mm) ( A bonded magnet A was prepared in which the orientation direction of the magnetic field was along the central axis of the cylinder. , By binarizing the obtained electron micrograph, the long axis length (the distance between two parallel straight lines when one particle is sandwiched between two parallel straight lines) is obtained as the particle shape index. The maximum value of the length of the line segment drawn perpendicular to the surface) is 1.0 μm or more. Calculate the ratio of major axis length (major axis length / minor axis length) (aspect ratio) A ferrite powder for a bonded magnet, characterized by having an aspect ratio of 1.5 or less. 10 g of the ferrite powder for bond magnet is filled in a cylindrical mold having an inner diameter of 2.54 cmφ and then compressed at a pressure of 1 ton/cm ² . 6. The ferrite powder for bonded magnet according to claim 5, wherein the compacted density of the ferrite powder for bonded magnet is 3.60 g/cm ³ or more when measured as . 8 g of the ferrite powder for bond magnet and 0.4 cc of polyester resin were kneaded in a mortar, and 7 g of the resulting kneaded product was filled in a mold with an inner diameter of 15 mmφ and compressed for 60 seconds at a pressure of 2 tons/cm ² to obtain a mold. The molded product is extracted from the mold, dried at 150 ° C. for 30 minutes, and the coercive force iHc of the compact obtained is measured at a magnetic field of 10 kOe, and the coercive force iHc is 2700 Oe or more. 7. The ferrite powder for bonded magnet according to claim 5 or 6, wherein 8. The ferrite powder for a bonded magnet according to claim 5, wherein said bonded magnet A has a residual magnetization Br of 3200 G or more when measured in a magnetic field of 10 kOe. 9. The bond according to any one of claims 5 to 8, wherein the maximum energy product BHmax of the bond magnet A is 2.50 MGOe or more when the _maximum energy product _BHmax is measured at a measurement magnetic field of 10 kOe. Ferrite powder for magnets. 93.5 parts by mass of the ferrite powder for bond magnets, 0.6 parts by mass of a silane coupling agent, 0.8 parts by mass of a lubricant, and 5.1 parts by mass of a powdery polyamide resin are charged into a mixer and mixed. The mixture thus obtained is kneaded at 230°C to prepare kneaded pellets having an average diameter of 2 mm, and the kneaded pellets are injection molded in a magnetic field of 9.7 kOe at a temperature of 300°C and a molding pressure of 8.5 N/mm ² . As a result, a cylindrical bonded magnet B having a diameter of 15 mm and a height of 8 mm (the orientation direction of the magnetic field is along the central axis of the cylinder) was produced, and the residual magnetization Br of this bonded magnet B was measured at a magnetic field of 10 kOe. 10. The ferrite powder for a bonded magnet according to any one of claims 5 to 9, characterized in that the residual magnetization Br is sometimes 3300G or more. 11. The ferrite powder for a bonded magnet according to claim 10, wherein the _maximum energy product _BHmax of the bonded magnet B is 2.65 MGOe or more when measured at a magnetic field of 10 kOe. A bonded magnet comprising the ferrite powder for a bonded magnet according to any one of claims 5 to 11 and a binder.