JP2023134239A - Hexagonal crystal ferrite magnetic powder for bonded magnet and method for manufacturing the same, and bonded magnet and method for manufacturing the same - Google Patents

Abstract

To provide hexagonal crystal ferrite magnetic powder for bonded magnets which can achieve a high residual magnetic flux density Br when used for bonded magnetics and the method for manufacturing the same, as well as a bonded magnetic having a high residual magnetic flux density Br and the method for manufacturing the same.SOLUTION: Hexagonal crystal ferrite magnetic powder for bonded magnets has a composition represented by the composition formula (Sr1-xLax)*(Fe1-y-zCoyZnz)nO19-a (wherein 0<x≤0.500, 0.003≤y≤0.045, 0.001≤z≤0.020, 10.00≤n≤12.50, -1.000≤a≤3.500), and the coercive force iHc of the compact object of the hexagonal crystal ferrite magnetic powder for bonded magnets measured at a measured magnetic field of 10kOe is 2000 Oe or larger.SELECTED DRAWING: None

Description

The present invention relates to a hexagonal ferrite magnetic powder for bonded magnets, a method for manufacturing the same, and a bonded magnet and a method for manufacturing the same.

Conventionally, ferrite-based sintered magnets have been used as high-magnetic-force magnets, such as small motors used in AV equipment, OA equipment, and automobile electrical components, and magnets used in copying machine magnet rolls. . However, ferrite-based sintered magnets have problems in that they suffer from chipping and cracking, and are inferior in productivity because they require polishing, and in addition, they are difficult to process into complex shapes. Therefore, in recent years, bonded rare earth magnets have been used as high magnetic force magnets for small motors used in AV equipment, OA equipment, automobile electrical components, and the like. However, rare earth magnets cost about 20 times as much as sintered ferrite magnets and are susceptible to rust, so it is desired to use bonded ferrite magnets instead of sintered ferrite magnets.

Patent Document 1 describes such ferrite magnetic powder for bonded magnets as (Sr _1-x La _x )・(Fe _1-y Co _y ) _n O _19-z (where 0<x≦0.5, 0 Ferrite magnetic powder for bonded magnets having a composition of <y≦0.04, 10.0≦n≦12.5, −1.0≦z≦3.5) is disclosed.

JP 2021-141151 Publication

The hexagonal ferrite magnetic powder for bonded magnets described in Patent Document 1 was developed as a ferrite bonded magnet with excellent magnetic field orientation and high Br, but it still has a higher residual magnetic flux density Br as a bonded magnet. There is a need for hexagonal ferrite magnetic powder for bonded magnets that can achieve the following.

The present invention provides a hexagonal ferrite magnetic powder for bonded magnets that can obtain a high residual magnetic flux density Br when used in a bonded magnet, a method for producing the same, and a bonded magnet with a high residual magnetic flux density Br and a method for producing the same. The purpose is to

That is, the gist of the present invention is as follows.

The present invention has a compositional formula (Sr _1-x La _x ) (Fe _1-y-z Co _y Zn _z ) _n O _19-a (wherein, 0<x≦0.500, 0.003≦y≦ 0.045, 0.001≦z≦0.020, 10.00≦n≦12.50, -1.000≦a≦3.500) Hexagonal ferrite magnetic powder for bonded magnets 8 g of hexagonal ferrite magnetic powder for bonded magnets and 0.4 cm ³ of polyester resin were kneaded, 7 g of the obtained kneaded material was filled into a mold with an inner diameter of 15 mmφ, and compressed for 60 seconds at a pressure of 196 MPa. The obtained molded product is removed from the mold, dried at 150° C. for 30 minutes, and the resulting green compact has a coercive force iHc of 2000 Oe or more when measured in a measuring magnetic field of 10 kOe. Here, 0.4 cm ³ of polyester resin is a value measured at 25° C. under atmospheric pressure.

A mixer was filled with 93.5 parts by mass of hexagonal ferrite magnetic powder for bonded magnets, 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 resulting mixture was kneaded at 230°C to produce kneaded pellets with an average diameter of 2 mm, and the kneaded pellets were kneaded in a magnetic field of 4.3 kOe at a temperature of 300°C and a molding pressure of 8.5 N/ ^mm2. A cylindrical bonded magnet A with a diameter of 15 mm and a height of 8 mm (the direction of magnetic field orientation is along the central axis of the cylinder) was produced by injection molding, and when this bonded magnet A was measured with a measuring magnetic field of 10 kOe. It is preferable that the residual magnetic flux density Br _A is 3200G or more.

It is preferable that the maximum energy product BHmax _A of the bonded magnet A produced by the above method is 2.45 MGOe or more when measured in a measurement magnetic field of 10 kOe.

Residual magnetic flux density Br _A when bonded magnet A produced by the above method is measured in a measurement magnetic field of 10 kOe, 93.5 parts by mass of hexagonal ferrite magnetic powder for bonded magnets, and 0.6 parts by mass of silane coupling agent. A mixer was filled with 0.8 parts by mass of lubricant and 5.1 parts by mass of powdered polyamide resin, and the resulting mixture was kneaded at 230°C to produce kneaded pellets with an average diameter of 2 mm. 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/ ^mm2 to form a cylinder with a diameter of 15 mm and a height of 8 mm (the orientation direction of the magnetic field was aligned with the central axis of the cylinder). It is preferable that the ratio Br _A /Br _B to the residual magnetic flux density Br _B is 0.95 or more when a bonded magnet B is prepared in a direction along the magnetic field and the bonded magnet B is measured at a measurement magnetic field of 10 kOe.

In an image obtained by observing the cross section of the bonded magnet A produced by the above method at a magnification of 1000 times using an electron microscope, 500 or more pieces observed within a viewing area of 85 μm x 120 μm have an area of 0.5 μm or more and are hexagonal for bonded magnets of ² or more. The ratio a/b of the average long axis length of the crystalline ferrite magnetic powder particles to the average particle diameter b measured by the air permeation method of the hexagonal crystalline ferrite magnetic powder for bonded magnets is 1.5 or more, 3.0 It is preferable that it is less than

It is preferable that the average particle diameter b of the hexagonal ferrite magnetic powder for bonded magnets measured by an air permeation method is 1.00 μm or more and 1.50 μm or less.

In the compositional formula, z is preferably less than 0.010.

In an image of the cross section of the bonded magnet A produced by the above method observed with an electron microscope at a magnification of 1000 times, 500 or more pieces observed within a viewing area of 85 μm x 120 μm have an area of 0.5 μm ² or more. When observing the particles of hexagonal ferrite magnetic powder, less than 60% of the particles have a ratio of major axis length to minor axis length (major axis length/minor axis length) of 1.5 or more. is preferred.

The volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer has peaks in the particle size range of 0.5 μm or more and 2.0 μm or less and 3.0 μm or more and 6.0 μm or less, and is bimodal or more. Preferably, it is a distribution.

In addition, the present invention from a different perspective is a method for producing hexagonal ferrite magnetic powder for bonded magnets, which has the compositional formula (Sr _1-x1 La _x1 ) (Fe _1-y1 Co _y1 ) _n1 O _19-a1 (Formula Hexagonal ferrite magnetic powder represented by: 0<x1≦0.500, 0.005≦y1≦0.050, 10.00≦n1≦12.50, -1.000≦a1≦3.500) A step of mixing powders serving as raw materials and then firing at a first temperature to obtain a coarse powder of hexagonal ferrite, and a step of obtaining a coarse powder of hexagonal ferrite, and a step of obtaining a coarse powder of hexagonal ferrite with a composition formula (Sr _1-x2 La _x2 ) (Fe _1-z2 Zn _z2 ) _n2 O _19- Hexagonal crystal represented by _a2 (wherein, 0<x2≦0.500, 0.005≦z2≦0.050, 10.00≦n2≦12.50, -1.000≦a2≦3.500) A step of mixing powders serving as raw materials for ferrite magnetic powder and then firing at a second temperature to obtain fine hexagonal ferrite powder having a smaller particle size calculated from the BET specific surface area than the coarse powder; The present invention is characterized in that it includes a step of mixing and pulverizing the powder and hexagonal ferrite fine powder to obtain a mixed pulverized powder, and a step of annealing the mixed pulverized mixed powder.

In this method for producing hexagonal ferrite magnetic powder for bonded magnets, the particle size calculated from the BET specific surface area of the hexagonal ferrite coarse powder is 1.00 μm or more and 8.00 μm or less, and the BET specific surface area of the hexagonal ferrite fine powder is It is preferable that the particle size calculated from the above is 0.05 μm or more and 0.50 μm or less.

In the step of obtaining the mixed pulverized powder, the mass ratio of the hexagonal ferrite coarse powder to the total mass of the hexagonal ferrite coarse powder and the hexagonal ferrite fine powder is preferably 60% by mass or more and 90% by mass or less. .

In this method for producing hexagonal ferrite magnetic powder for bonded magnets, it is preferable that the saturation magnetization of the hexagonal ferrite fine powder is 57.0 emu/g or more.

Moreover, the present invention in another aspect is a bonded magnet containing the hexagonal ferrite magnetic powder for bonded magnets of the present invention and a resin.

Furthermore, the present invention from another aspect is a method for producing a bonded magnet using hexagonal ferrite magnetic powder for bonded magnets obtained by the method for producing hexagonal ferrite magnetic powder for bonded magnets of the present invention.

According to the present invention, there is provided hexagonal ferrite magnetic powder for bonded magnets that can obtain a high residual magnetic flux density Br when used in bonded magnets. Further, a method for producing hexagonal ferrite magnetic powder for a bonded magnet that can obtain a high residual magnetic flux density Br when used in a bonded magnet, and a bonded magnet having a high residual magnetic flux density Br are provided together with a method for producing the same.

1 is a graph showing the particle size distribution of hexagonal ferrite magnetic powder for bonded magnets of Example 1. This is a SEM observation image of a cross section of a bonded magnet A using the hexagonal ferrite magnetic powder for bonded magnets of Example 1, magnified 1000 times. This is a SEM observation image of a cross section of bonded magnet A using the hexagonal ferrite magnetic powder for bonded magnets of Example 2, magnified 1000 times. This is a SEM observation image of a cross section of a bonded magnet A using hexagonal ferrite magnetic powder for bonded magnets of Comparative Example 1, magnified 1000 times. It is a 1000 times SEM observation image of the cross section of bonded magnet A using hexagonal ferrite magnetic powder for bonded magnets of Comparative Example 2.

(Hexagonal ferrite magnetic powder for bonded magnets)
The hexagonal ferrite magnetic powder for bonded magnets of the present invention has a composition formula (Sr _1-x La _x ) (Fe _1-y-z Co _y Zn _z ) _n O _19-a (wherein, 0<x≦0 .500, 0.003≦y≦0.045, 0.001≦z≦0.020, 10.00≦n≦12.50, -1.000≦a≦3.500) A hexagonal ferrite magnetic powder for bonded magnets having 8 g of hexagonal ferrite magnetic powder for bonded magnets and 0.4 cm ³ of polyester resin are kneaded, and 7 g of the obtained kneaded material is filled into a mold with an inner diameter of 15 mmφ, The molded product obtained by compressing at a pressure of 196 MPa for 60 seconds is extracted from the mold, and the compact obtained by drying at 150 ° C. for 30 minutes has a coercive force iHc of 2000 Oe or more when measured in a measuring magnetic field of 10 kOe. characterized by something. Below, aspects such as the composition, magnetic properties, powder properties, etc. of the hexagonal ferrite magnetic powder for bonded magnets of the present invention will be explained.

[composition]
The hexagonal ferrite magnetic powder for bonded magnets of the present invention has a composition formula (Sr _1-x La _x ) (Fe _1-y-z Co _y Zn _z ) _n O _19-a (wherein, 0<x≦0 Sr, It is a hexagonal ferrite magnetic powder having a magnetoplumbite crystal structure containing La, Co and Zn as essential elements.
By replacing the Sr sites with La and the Fe sites with Co or Zn in the crystal structure of the Sr-based hexagonal ferrite magnetic powder, we have created a hexagonal ferrite magnetic powder with a higher magnetic force than the Sr-based hexagonal ferrite magnetic powder. You can get the powder. In order to obtain the effect of improving magnetic force, the value of x in the above composition formula is set to be a positive real number, the value of y is set to 0.003 or more, and the value of z is set to 0.001 or more. On the other hand, if each of La, Co, and Zn is added in excess, it becomes difficult to maintain the crystal structure. The value of is 0.020 or less. The numerical range of x is preferably 0.100 or more and 0.400 or less, more preferably 0.150 or more and 0.350 or less. The numerical range of y is preferably 0.005 or more and 0.040 or less, more preferably 0.008 or more and 0.020 or less. The numerical range of z is preferably 0.001 or more and 0.015 or less, more preferably 0.001 or more and less than 0.010. In order to obtain hexagonal ferrite magnetic powder having a magnetoplumbite crystal structure, the value of n in the above compositional formula is set to 10.00 or more and 12.50 or less. From the viewpoint of suppressing the amount of unreacted substances remaining after firing, the value of n is preferably 10.50 or more and 12.00 or less.
The hexagonal ferrite magnetic powder for bonded magnets of the present invention 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. It is preferable to suppress the total content of these to 0.4% by mass or less. The above compositional formula is a compositional formula excluding unavoidable components.

[Particle size distribution]
In order to obtain high filling properties, the hexagonal ferrite magnetic powder for bonded magnets of the present invention has a particle size of 0.5 μm or more and 2.0 μm or less in the volume-based particle size distribution measured with a laser diffraction particle size distribution analyzer. It is preferable that the distribution is bimodal or more, having peaks (upwardly convex mountain-shaped peaks) in the range and in the range of 3.0 μm or more and 6.0 μm or less. By using a mixed powder with such a particle size distribution, high filling properties of hexagonal ferrite magnetic powder for bonded magnets can be obtained for the first time, and in combination with the above composition, a higher residual magnetic flux density Br can be obtained when used as a bonded magnet. be able to. The present inventors found that in the measured particle size distribution, the ferrite particles with the SrLaCo composition have a larger particle size and mainly contribute to the large particle size peak (range of 3.0 μm to 6.0 μm), and the SrLaZn composition has a larger particle size. It is considered preferable to use a hexagonal mixed powder for bonded magnets in which the ferrite particles have a smaller particle size and mainly contribute to the small particle size peak (peak in the range of 0.5 μm or more and 2.0 μm or less). Although the mechanism is not necessarily clear, by using ferrite particles with SrLaCo composition as coarse particles, it is possible to increase the coercive force Hc of hexagonal ferrite magnetic powder for bonded magnets. We believe that by using the ferrite particles of the same composition as microparticles, we were able to improve the magnetic field orientation of the hexagonal ferrite magnetic powder for bonded magnets.
The particle size distribution can be a bimodal distribution having one peak each in the particle size range of 0.5 μm or more and 2.0 μm and 3.0 μm or more and 6.0 μm or less.

[Magnetic properties of compacted powder]
The hexagonal ferrite magnetic powder for bonded magnets of the present invention achieves high Br when used as a bonded magnet. The magnetic properties when used as a bonded magnet can be estimated from the compact magnetic properties. The magnetic properties of the green compact are determined by kneading 8 g of the above-mentioned hexagonal ferrite magnetic powder for bonded magnets and 0.4 cm ³ of polyester resin (measured value at 25°C under atmospheric pressure), and 7 g of the resulting kneaded material. The molded product was filled into a mold of 15 mmφ and compressed for 60 seconds at a pressure of 196 MPa, and the molded product obtained was extracted from the mold and dried at 150° C. for 30 minutes. The green compact obtained could be used for evaluation. . The coercive force iHc of the powder compact when measured under a measurement magnetic field of 10 kOe is 2000 Oe or more, preferably 2100 Oe or more, and more preferably 2300 Oe or more. The higher the coercive force iHc of the powder compact, the easier it is to obtain a high residual magnetic flux density Br when a bonded magnet is manufactured using the hexagonal ferrite magnetic powder for bonded magnets.

[Magnetic properties of bonded magnet]
Using the hexagonal ferrite magnetic powder for bonded magnets of the present invention, 93.5 parts by mass of ferrite magnetic powder for bonded magnets, 0.6 parts by mass of silane coupling agent, 0.8 parts by mass of lubricant, and powdered A mixer was filled with 5.1 parts by mass of polyamide resin 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 produced from the obtained kneaded product, The kneaded pellets were injection molded in a magnetic field of 4.3 kOe at a temperature of 300°C and a molding pressure of 8.5 N/ ^mm2 to form a cylinder with a diameter of 15 mm and a height of 8 mm (the orientation direction of the magnetic field was along the central axis of the cylinder). A bonded magnet A can be produced in a direction (direction).

The residual magnetic flux density Br _A of the bonded magnet A measured under a measurement magnetic field of 10 kOe is preferably 3200G or more, more preferably 3250G or more. The maximum energy product BHmax _A is preferably 2.45 MGOe or more, and more preferably 2.50 MGOe or more.

The bonded magnet, which differs from bonded magnet A only in the magnitude of the magnetic field during injection molding, contains 93.5 parts by mass of hexagonal ferrite magnetic powder for bonded magnets, 0.6 parts by mass of a silane coupling agent, and 0.6 parts by mass of a lubricant. A mixer was filled with 8 parts by mass and 5.1 parts by mass of powdered polyamide resin, and the resulting mixture was kneaded at 230°C to prepare a kneaded product. A 2 mm kneaded pellet was prepared, and the kneaded pellet was injection molded in a 9.7 kOe magnetic field at a temperature of 300°C and a molding pressure of 8.5 N/mm ² to form a cylindrical bonded magnet with a diameter of 15 mm and a height of 8 mm. B can be produced.

At this time, when bonded magnet A and bonded magnet B are measured in a measurement magnetic field of 10 kOe, the ratio Br _A /Br _B of the residual magnetic flux density Br _A of bonded magnet A and the residual magnetic flux density Br _B of bonded magnet B is 0. It is preferably 950 or more, and more preferably 0.955 or more. When the ferrite magnetic powder in the bonded magnet is sufficiently oriented in a magnetic field, it is possible to obtain a large residual magnetic flux density Br as a bonded magnet. When producing a bonded magnet, the ferrite magnetic powder in the bonded magnet, which has excellent orientation, can be sufficiently oriented even in a low magnetic field. Therefore, the closer the value of Br _A /Br _B to 1, the better the orientation of the hexagonal ferrite magnetic powder for bonded magnets. A high residual magnetic flux density Br is easily obtained.

[Particle shape evaluation by cross-sectional observation of bonded magnet A]
In measuring the shape of the hexagonal ferrite magnetic powder for bonded magnets according to the present invention, the cross section of the bonded magnet A can be observed with an electron microscope. Specifically, in an image obtained by observing a cross section of the bonded magnet A parallel to the magnetization direction with an electron microscope at a magnification of 1000 times, the entire outer edge is observed within a viewing area of 85 μm x 120 μm, with an area of 0.5 μm. ^Two or more particles of hexagonal ferrite magnetic powder for bonded magnets can be evaluated. At this time, the length of the line segment where the distance between two points on the outline of the target particle is the maximum is defined as the major axis length, and the target particle is divided into two lines parallel to the line segment whose major axis length was measured. The short axis length is the distance between the straight lines when they are sandwiched. The number of particles used for measurement is 500 or more. This evaluation method is applied to the values based on cross-sectional observation for the following indicators. The above measurement can be performed by binarizing an image obtained by observing a cross section and performing image analysis, and any image analysis software can be used.

<Ratio a/b of average value a of particle long axis length to average particle diameter b>
The above evaluation method targets particles of hexagonal ferrite magnetic powder for bonded magnets with an area of 0.5 μm ² or more whose entire outer edge is observed within the viewing area, so the bond is based on cross-sectional observation using the above evaluation method. When calculating the average value a of the long axis length of particles of hexagonal ferrite magnetic powder for magnets, microparticles with an area of less than 0.5 μm ² in hexagonal ferrite magnetic powder for bonded magnets in cross-sectional observation of bonded magnet A are Not included.

On the other hand, the average particle size b measured by the air permeation method is obtained by passing air through a packed bed of hexagonal ferrite magnetic powder for bonded magnets and measuring the average particle size of the powder from the permeability. This value also includes the contribution of microparticles. Therefore, when observing the cross section of bonded magnet A in the hexagonal ferrite magnetic powder for bonded magnets, the larger the proportion of microparticles with an area of less than 0.5 μm ² in the hexagonal ferrite magnetic powder for bonded magnets, the greater the ratio of a/b. The value increases. That is, the ratio a/b of the average long axis length of the particles to the average particle diameter b is an index indicating the degree of inclusion of microparticles in the hexagonal ferrite magnetic powder for bonded magnets, and the ratio a/b It is preferable that b is 1.5 or more and less than 3.0. Further, it is more preferable that the average particle diameter b measured by an air permeation method is 1.00 μm or more and 1.50 μm or less.

<Ratio of long axis length to short axis length of particles>
According to the above evaluation method, the number of particles having a ratio of major axis length to minor axis length (major axis length/minor axis length) based on cross-sectional observation of 1.5 or more is preferably less than 60%. It is assumed that particles with a large value of this ratio (major axis length/minor axis length) are difficult to orient in response to an external magnetic field. By manufacturing a bonded magnet using the bonded magnet, a high residual magnetic flux density Br can be easily obtained.

(Production method of hexagonal ferrite magnetic powder for bonded magnet)
The method for producing hexagonal ferrite magnetic powder for bonded magnets of the present invention is based on the composition formula (Sr _1-x1 La _x1 ) (Fe _1-y1 Co _y1 ) _n1 O _19-a1 (wherein, 0<x1≦0.500 , 0.005≦y1≦0.050, 10.00≦n1≦12.50, -1.000≦a1≦3.500) After mixing the raw material powder of hexagonal ferrite magnetic powder, _{a step of} firing at a first _temperature to _obtain a coarse powder of hexagonal ferrite _; 0.500, 0.005≦z2≦0.050, 10.00≦n2≦12.50, -1.000≦a2≦3.500). A step of mixing and firing at a second temperature to obtain a fine powder of hexagonal ferrite; a step of mixing and pulverizing the coarse powder of hexagonal ferrite and the fine powder of hexagonal ferrite to obtain a mixed powder subjected to a mixed pulverization process; and a step of annealing the mixed powder that has been mixed and pulverized. By using fine powder with a smaller particle size calculated from the BET specific surface area than coarse powder, it is possible to improve the filling properties of the obtained hexagonal ferrite magnetic powder for bonded magnets, and as a result, it is possible to improve the filling properties of the obtained hexagonal ferrite magnetic powder for bonded magnets. When manufacturing a magnet, a bonded magnet with a high residual magnetic flux density Br can be obtained. Here, the specific surface area of coarse powder is usually smaller than that of fine powder. Each step will be explained in detail below.

[Coarse powder manufacturing process]
Composition formula (Sr _1-x1 La _x1 ) (Fe _1-y1 Co _y1 ) _n1 O _19-a1 (wherein, 0<x1≦0.500, 0.005≦y1≦0.050, 10.00≦n1 ≦12.50, -1.000≦a1≦3.500), which is a raw material for hexagonal ferrite magnetic powder, is mixed and fired at a first temperature to obtain coarse hexagonal ferrite powder. It is a process. Note that in this specification, ferrite substituted with La and Co may be referred to as "SrLaCo ferrite" or simply "SrLaCo."

As the powder serving as the raw material for the coarse powder of hexagonal ferrite, compounds of the constituent elements Sr, La, Fe, and Co can be used. For example, examples of the Sr compound include strontium carbonate, strontium chloride, and strontium sulfate. La compounds include lanthanum oxide, lanthanum hydroxide, and lanthanum sulfate, Fe compounds include iron oxide (hematite, magnetite), iron chloride, iron sulfate, preferably hematite, and Co compounds include cobalt oxide. , cobalt chloride, and cobalt sulfate.

A composite oxide containing two or more of the constituent elements Sr, La, Fe, and Co can also be used as a powder serving as a raw material for the coarse powder of hexagonal ferrite. Such a composite oxide (hereinafter also referred to as precursor powder) and the remaining compounds of Sr, La, Fe, and Co, which become the composition of coarse powder when mixed with the precursor powder, are used as raw materials for coarse powder. be able to.

The precursor powder is equivalent to Sr, La, Co, and a part of the composition of the coarse powder, since it can easily obtain a high compressed density as the final hexagonal ferrite magnetic powder for bonded magnets. It is preferable to use a composite oxide containing Fe. Such a precursor powder can be obtained by a manufacturing method in which powders of an Sr compound, a La compound, an Fe compound, and a Co compound are mixed, fired at a temperature of 1000° C. or more and 1250° C. or less, and then crushed. Such a precursor powder and hematite corresponding to the remainder of Fe to form the composition of the coarse powder can be used as raw materials for the coarse powder of hexagonal ferrite.

In order to obtain the effect of improving the magnetic force of the coarse powder, the value of x1 in the above composition formula is set to a positive real number, and the value of y1 is set to 0.005 or more. Moreover, since it becomes difficult to maintain the hexagonal ferrite crystal structure when each of La and Co is added in excess, the value of x1 is set to 0.500 or less, and the value of y1 is set to 0.050 or less. The numerical range of x1 is preferably 0.100 or more and 0.400 or less, more preferably 0.150 or more and 0.350 or less. The numerical range of y1 is preferably 0.005 or more and 0.040 or less, more preferably 0.008 or more and 0.020 or less.

Further, in order to obtain a hexagonal ferrite magnetic powder having a magnetoplumbite crystal structure, the value of n1 in the above compositional formula is set to 10.00 or more and 12.50 or less. From the viewpoint of suppressing the residual of unreacted substances after firing, the value of n1 is preferably 10.50 or more and 12.00 or less.

The coarse powder 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. It is preferable to suppress the total content of these to 0.4% by mass or less. The above compositional formula is a compositional formula excluding unavoidable components.

The first temperature, which is the firing temperature in the coarse powder manufacturing process, is preferably 1220°C or more and 1400°C or less, more preferably 1220°C or more and 1300°C or less.

In the coarse powder manufacturing process, a mixture of raw material powders may be granulated and fired. The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an air atmosphere. Further, it is preferable to perform a pulverization treatment after firing. The method of the pulverization treatment is not particularly limited, and examples thereof include known methods using a roller mill and the like.

The particle size of the coarse powder determined from the specific surface area measured by the BET single point method is preferably 1.00 μm or more and 8.00 μm or less, more preferably 2.00 μm or more and 5.00 μm.

[Fine powder manufacturing process]
Composition formula (Sr _1-x2 La _x2 ) (Fe _1-z2 Zn _z2 ) _n2 O _19-a2 (wherein, 0<x2≦0.500, 0.005≦z2≦0.050, 10.00≦n2 ≦12.50, -1.000≦a2≦3.500) After mixing the raw material powder of hexagonal ferrite fine powder expressed by This is a process of obtaining hexagonal ferrite fine powder with a small calculated particle size. Note that in this specification, ferrite substituted with La and Zn may be referred to as "SrLaZn ferrite" or simply "SrLaZn."

Compounds of the constituent elements Sr, La, Fe, and Zn can be used as the powder serving as the raw material for the fine powder of hexagonal ferrite. For example, examples of the Sr compound include strontium carbonate, strontium chloride, and strontium sulfate. , La compounds include lanthanum oxide, lanthanum hydroxide, and lanthanum sulfate, Fe compounds include iron oxide (hematite, magnetite), iron chloride, iron sulfate, preferably hematite, and Zn compounds include zinc oxide, Examples include zinc chloride and zinc sulfate.

In order to obtain the effect of improving the magnetic force of the fine powder, the value of x2 in the above composition formula is set to a positive real number, and the value of z2 is set to 0.005 or more. Further, if each of La and Zn is added in excess, it becomes difficult to maintain the hexagonal ferrite crystal structure, so the value of x2 is set to 0.500 or less, and the value of z2 is set to 0.050 or less. The numerical range of x2 is preferably 0.100 or more and 0.400 or less, more preferably 0.150 or more and 0.350 or less. The numerical range of z2 is preferably 0.005 or more and 0.040 or less, more preferably 0.008 or more and 0.020 or less.

Further, in order to obtain a hexagonal ferrite magnetic powder having a magnetoplumbite crystal structure, the value of n2 in the above compositional formula is set to 10.00 or more and 12.50 or less. From the viewpoint of suppressing the residual of unreacted substances after firing, the value of n2 is preferably 10.50 or more and 12.00 or less.

The fine powder may contain impurities contained in raw materials and unavoidable components derived from manufacturing equipment. Examples of such components include oxides of Mn and Ba. It is preferable to suppress the total content of these to 0.4% by mass or less. The above compositional formula is a compositional formula excluding unavoidable components.

The second temperature, which is the firing temperature in the fine powder production process, is preferably 1000°C or more and 1350°C or less, more preferably 1100°C or more and 13000°C or less. By setting the second temperature to 1000° C. or higher, fine powder having a hexagonal ferrite crystal structure can be easily obtained.

In the process of producing fine powder, a mixture of raw material powders may be granulated and fired. The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an air atmosphere. Further, it is preferable to perform a pulverization treatment after firing. The pulverization process can be carried out by a known method using a roller mill or the like, but it is preferable to perform a wet pulverization process. Dry pulverization such as a roller mill and wet pulverization may be combined.

The particle size of the fine powder determined from the specific surface area measured by the BET single point method is preferably 0.05 μm or more and 0.50 μm or less, more preferably 0.10 μm or more and 0.20 μm.

The saturation magnetization of the fine powder is preferably 57.0 emu/g or more, more preferably 58.0 emu/g or more. By setting the saturation magnetization to 57.0 emu/g or more, the saturation magnetization of the obtained hexagonal ferrite magnetic powder for a bonded magnet becomes high, and the residual magnetic flux density Br of the obtained bonded magnet becomes easy to increase.

[Mixing and grinding process]
A mixed powder obtained by mixing and pulverizing separately obtained coarse powder and fine powder at a ratio such that the mass ratio of the coarse powder to the total mass of the coarse powder and fine powder is 60% by mass or more and 90% by mass or less. This is the process of obtaining
It is preferable to use a wet grinding device for the mixing and grinding process, and it is more preferable to use an attritor.

A vibrating ball mill can be used for the mixing and grinding process. From the point of view of promoting pulverization by a vibrating ball mill, it is preferable to use balls with a media diameter of 5 mm or more and 20 mm or less, and after performing the pulverization process using balls with a media diameter of 10 mm or more and 20 mm or less in the first stage, the second stage It is preferable to carry out the crushing process using balls having a diameter of 5 mm or more and 10 mm or less. For example, by using a vibrating ball mill after treatment with an attritor, coarse particles that cannot be crushed with an attritor can be crushed.

As described above, it has been found that by using SrLaCo ferrite as the coarse powder and SrLaZn ferrite as the fine powder, the resulting bonded magnet exhibits extremely excellent magnetic properties. With coarse powder, it is difficult to obtain a high coercive force due to its large particle size, but by using SrLaCo ferrite, it is possible to have high magnetization and ensure a high coercive force. On the other hand, since fine powder has a larger coercive force than coarse powder, by using SrLaZn ferrite, which has better magnetization, in the fine powder, the combination of coarse powder and fine powder can be used for bonded magnets with excellent balance of magnetic properties. It is estimated that hexagonal ferrite magnetic powder was obtained.

[Annealing process]
This is a step of annealing the mixed and pulverized mixed powder obtained in the mixing and pulverizing step to obtain hexagonal ferrite magnetic powder for bonded magnets. Annealing conditions are not particularly limited, and the annealing can be carried out under conditions known as a method for producing hexagonal ferrite magnetic powder for bonded magnets. The annealing temperature is preferably 900°C or more and 1000°C or less, more preferably 930°C or more and 980°C or less. Furthermore, the atmosphere during annealing is preferably an oxidizing atmosphere, more preferably an air atmosphere.

(Bonded magnet and its manufacturing method)
A bonded magnet can be manufactured by molding a kneaded product containing a hexagonal ferrite magnetic powder for bonded magnets obtained by the method for manufacturing hexagonal ferrite magnetic powder for bonded magnets of the present invention and a resin in a magnetic field. The method for manufacturing a bonded magnet is not particularly limited, and any known method can be used. For example, hexagonal ferrite magnetic powder for bonded magnets, resin, and additives such as lubricants are mixed and kneaded to produce kneaded pellets, and then the kneaded pellets are molded in a magnetic field to form bonded magnets.

EXAMPLES Hereinafter, the hexagonal ferrite magnetic powder for bonded magnets and the manufacturing method thereof, and the bonded magnet and the manufacturing method thereof according to the present invention will be explained in detail using Examples.

Evaluations in Examples were performed as follows.

[Composition analysis]
To analyze the composition of hexagonal ferrite magnetic powder for bonded magnets, use a fluorescent X-ray analyzer (ZSX100e manufactured by Rigaku Co., Ltd.) to calculate the amount of each element by the fundamental parameter method (FP method). This was done by In this composition analysis, hexagonal ferrite magnetic powder for bonded magnets was packed into a measurement cell, molded by applying a pressure of 980 MPa for 20 seconds, the measurement mode was EZ scan mode, the measurement diameter was 30 mm, and the sample form was oxide. After qualitative analysis was performed in a vacuum atmosphere using standard time, quantitative analysis was performed on the detected constituent elements.

[XRD measurement]
Regarding hexagonal ferrite magnetic powder for bonded magnets, a powder X-ray diffractometer (Miniflex 600 manufactured by Rigaku Corporation) was used to measure the tube voltage at 40 kV, the tube current at 15 mA, the measurement range from 15° to 60°, and the scanning speed at Measurement was performed by powder X-ray diffraction (XRD) at 1°/min and a scan width of 0.02°.

[BET specific surface area measurement]
The BET specific surface area of the composite oxide obtained during the manufacturing process of hexagonal ferrite magnetic powder for bonded magnets, hexagonal ferrite coarse powder, hexagonal ferrite fine powder, and hexagonal ferrite coarse powder is measured using a specific surface area measuring device (Kantar). It was measured by the BET single point method using Monosorb (manufactured by Chrome).

[Compressed density measurement]
The compressed density of the hexagonal ferrite magnetic powder for bonded magnets and the hexagonal ferrite fine powder is 98 MPa after filling 10.0 g of the magnetic powder into a cylindrical mold with an inner diameter of 2.54 cmφ using a cylindrical piston with a diameter of 2.44 cmφ. The density of the hexagonal ferrite magnetic powder for bonded magnets obtained by compressing the powder at a pressure of 100 ml was measured as the compressed density CD (g/cm ³ ). In addition, the calculation formula (1) for the compressed density CD (g/cm ³ ) is based on the height from the bottom surface inside the cylindrical mold to the tip of the piston after compression as L (cm), and the circumference as π. Then, it is as follows.
Compressed density CD (g/cm ³ ) = 10.00/(2.54 ² x π/4 x L)
...Calculation formula (1)

[Average particle size measurement]
The average particle diameter b (APD) of the hexagonal ferrite magnetic powder for bonded magnets was measured by an air permeation method using a specific surface area measuring device (SS-100 manufactured by Shimadzu Corporation).

[Laser diffraction particle size distribution measurement]
Laser diffraction particle size distribution measurement uses a dry laser diffraction particle size distribution measuring device (manufactured by Nippon Laser Co., Ltd.: HELOS & RODOS) to measure volume-based particle size distribution at a focal length of 20 mm, dispersion pressure of 5.0 bar, and suction pressure of 130 mbar. It was measured.

[Measurement of magnetic properties of compacted powder]
A kneaded product obtained by kneading 8 g of hexagonal ferrite magnetic powder for bonded magnets and 0.4 cm ³ of polyester resin (P-resin (main ingredient) manufactured by Nichika Co., Ltd.) (measured value at 25°C under atmospheric pressure) 7 g was filled into a mold with an inner diameter of 15 mm and compressed for 60 seconds at a pressure of 196 MPa. The resulting molded product was extracted from the mold and dried at 150° C. for 30 minutes to obtain a green compact. The magnetic properties of the green compact of hexagonal ferrite magnetic powder for bonded magnets were determined using a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.) with a coercive force p-iHc of the green compact under a measuring magnetic field of 10 kOe. and residual magnetic flux density p-Br were measured.

<Measurement of major axis length, minor axis length, and area ratio>
(1) Bonded magnet A was cut along a plane parallel to the magnetization direction, and the surface was polished by ion milling to obtain a sample for grain size evaluation. By performing electron microscopic observation from a direction perpendicular to the polished surface, it is possible to measure the major axis length and minor axis length of the crystal of the ferrite particle when viewed from a direction horizontal to the a-b plane.
(2) The particle cross section of the sample for particle size evaluation was observed using a scanning electron microscope (manufactured by JEOL Ltd.: JSM-T220A), and a backscattered electron image was obtained at 1000 times magnification.
(3) Binarize the obtained backscattered electron image using an image analysis program (Azo-kun, manufactured by Asahi Kasei Engineering Co., Ltd.) with automatic settings in crystal grain size analysis mode, and bright areas are divided into particles and dark areas are After separating the background, measure the long axis length of all particles in a field of view (85 μm x 120 μm) with an area of 0.5 μm ^or more, and calculate the number average value a The ratio of the total area of particles of 0.5 μm ² or more to the total area of the bright region was calculated as the area ratio. Here, the length of the line segment where the distance between two points on the particle outline is the maximum is defined as the major axis length, and the distance between the straight lines when the major axis length is sandwiched between two straight lines parallel to the measured line segment. The distance was taken as the short axis length.

[Measurement of flow rate (MFR)]
93.5 parts by mass of the obtained hexagonal ferrite magnetic powder for bonded magnets, 0.6 parts by mass of a silane coupling agent (Z-6094N manufactured by Dow Corning Toray Co., Ltd.), and a lubricant (VPN-212P manufactured by Henkel Corporation). ) and 5.1 parts by mass of powdered polyamide resin (P-1011F manufactured by Ube Industries, Ltd.) as a binder were weighed, and the mixture was filled into a mixer and mixed, resulting in a kneaded pellet. The kneaded pellets were placed in a melt indexer (Melt Indexer C-5059D2 manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the weight of the extruded pellets at 270°C and a load of 10 kg was measured in accordance with JISK7210-1:2014. The fluidity rate (MFR) during injection molding of the kneaded pellets was determined by converting the weight to the amount extruded per 10 minutes.

[Measurement of magnetic properties of bonded magnets]
Using a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd.), the coercive force iHc, residual magnetic flux density Br, and maximum energy product BHmax of bonded magnet A and bonded magnet B were measured at a measurement magnetic field of 10 kOe.

(Example 1)
1-1. Production of hexagonal ferrite magnetic powder for bonded magnet according to Example 1 (1) Production process of hexagonal ferrite coarse powder Strontium carbonate powder (SrCO ₃ , specific surface area 5.8 m ² /g), lanthanum hydroxide powder (La (OH) ₃ , specific surface area: 5.0 m ² /g), hematite powder (α-Fe ₂ O ₃ , specific surface area: 5.3 m ² /g) and cobalt oxide powder (Co ₃ O ₄ , specific surface area: 3. 3 m ² /g) were weighed and mixed so that the molar ratio was Sr:La:Fe:Co=0.70:0.30:0.85:0.15, and this mixture was added to the mixture in a pan pelletizer. Granulation was carried out while adding water to obtain spherical first granules with a diameter of 3 mm to 10 mm. The obtained first granulated product was fired at 1100° C. for 20 minutes in an internal combustion type rotary kiln under a circulating atmosphere to obtain a first fired product. This first fired product was pulverized with a roller mill to obtain a SrLaFeCo composite oxide powder. The BET specific surface area of the obtained SrLaFeCo composite oxide powder was measured and found to be 3.5 m ² /g.

This SrLaFeCo composite oxide powder and hematite (α-Fe ₂ O ₃ : specific surface area 5.3 m ² /g) were mixed so that the mass ratio of SrLaFeCo composite oxide powder: hematite = 1.0:4.0. Weighed and mixed to obtain a mixture, added and mixed 0.17% by mass of boric acid and 2.3% by mass of potassium chloride, and then granulated it in a pan pelletizer while adding water. A second spherical granule with a diameter of 3 mm to 10 mm was obtained. The obtained second granules were put into an internal combustion rotary kiln and fired in the atmosphere at 1300°C (second firing temperature) for 20 minutes.The fired product was crushed with a roller mill to form hexagonal crystals. A coarse ferrite powder was obtained.

The BET specific surface area of the obtained hexagonal ferrite coarse powder was measured and was 0.37 m ² /g, and the particle diameter (DBET) was calculated from the BET specific surface area assuming the true specific gravity of the coarse powder was 5.1 g / cm ³ As a result, it was 3.18 μm. Here, the particle diameter DBET (m ² /g) can be determined by the following calculation formula (2), where the BET specific surface area of the coarse powder is SBET. In this specification, the particle diameter calculated from the BET specific surface area was calculated using this calculation formula (2).
DBET (μm) = 6/(true specific gravity (g/cm ³ ) x SBET (m ² /g))
...Calculation formula (2)

In addition, a compositional analysis of the obtained hexagonal ferrite coarse powder was performed, and from the analytical values of Sr, La, Fe, and Co, the composition formula of the coarse powder was (Sr _1-x1 La _x1 ) (Fe _1-y1 Co _y1 ) When we calculated x1, y1, n1, a1 when expressed as _n1 O _19-a1 , the results were x1=0.298, y1=0.014, n1=11.00, a1=1.428. Ta. The evaluation results of the above coarse powder are shown in Table 1 (the same applies to Examples and Comparative Examples below). In Table 1, the BET specific surface area of the coarse powder is expressed as SBET1, and the particle diameter calculated from the BET specific surface area is expressed as DBET1.

(2) Firing process and crushing process (manufacturing process of hexagonal ferrite fine powder)
Strontium carbonate powder (SrCO ₃ , specific surface area: 5.8 m ² /g) and lanthanum hydroxide powder (La(OH) ₃ , specific surface area: 5.0 m ² /g) are used as the raw material for hexagonal ferrite fine powder. , hematite powder (α-Fe ₂ O ₃ , specific surface area: 5.3 m ² /g) and zinc oxide powder (ZnO, specific surface area: 4.5 m ² /g) in a molar ratio of Sr:La:Fe:Zn= The powder was weighed so that the ratio was 0.70:0.30:11.50:0.30, and 2.45% by mass of potassium chloride powder was weighed based on the total mass of the weighed powder. After mixing these weighed powders, they were granulated in a pan pelletizer while adding water to obtain third spherical granules with a diameter of 3 mm to 10 mm.

The obtained third granulated product was fired for 20 minutes at 1250° C. (third firing temperature) in a rotary kiln under a circulating atmosphere to obtain a third fired product. The obtained third fired product was processed with a roller mill to obtain crushed powder. The resulting crushed powder was dry-pulverized using a vibrating ball mill (Uras Vibrator KEC-8-YH, manufactured by Murakami Seiki Seisakusho) to obtain finely pulverized powder. The pulverization process was carried out for 300 minutes using a steel ball with a medium diameter of 12 mm at a rotation speed of 1800 rpm and an amplitude of 8 mm. Water was added to the resulting finely pulverized powder to form a slurry so that the concentration of the pulverized powder was 20% by mass, and then transferred to an attritor, which is a pulverizer equipped with a stirring blade and a steel ball with a diameter of 5.56 mm. A slurry containing hexagonal ferrite fine powder was obtained by stirring and pulverizing the mixture for 10 minutes (pulverizing time) at a peripheral speed of 1.6 m/s using a stirring blade. A sample of the resulting slurry containing hexagonal ferrite fine powder was sampled, filtered and dried to obtain a fine powder sample for evaluation. The BET specific surface area of the obtained fine powder sample was measured to be 8.09 m ² /g, and the compressed density CD was measured to be 3.25 g/cm ³ , and the particle size was calculated from the BET specific surface area using formula (2). When DBET2 was measured, it was 0.15 μm. Further, the saturation magnetization σs of the obtained fine powder sample was measured using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.: VSM-P7) with an applied magnetic field of 1 T, and found to be 58.4 emu/g. The composition of the obtained fine powder sample was analyzed, and from the analytical values of Sr, La, Fe, and Co, the composition formula of the coarse powder was determined as (Sr _1-x2 La _x2 ) (Fe _1-z2 Zn _z2 ) _n2 O _19-a2 When x2, z2, n2, and a2 were calculated in the case of The evaluation results are shown in Table 2 (the same applies to Examples and Comparative Examples below).

(3) Mixing and grinding process The slurry containing the obtained hexagonal ferrite fine powder contained in the grinding container of the attritor has a mass ratio of coarse powder to fine powder (mass of coarse powder: mass of fine powder) of 70: The coarse powder obtained in (1) was added to the powder to give a powder of 30%, and mixed and pulverized using an attritor for another 20 minutes. After filtering the slurry obtained by mixing and pulverizing, it was dried in the air at 150° C. for 10 hours to obtain a dry cake. A mixed powder was obtained by crushing the dried cake. The obtained mixed powder was pulverized using a vibrating ball mill (Uras Vibrator KEC-8-YH, manufactured by Murakami Seiki Seisakusho). The pulverization process was carried out for 28 minutes using a steel ball with a media diameter of 12 mm at a rotation speed of 1800 rpm and an amplitude of 8 mm, and the resulting pulverized powder was further processed using a steel ball with a media diameter of 8 mm. The pulverization process was carried out for 28 minutes at a rotation speed of 1800 rpm and an amplitude of 8 mm. As a result, a mixed powder that had been mixed and pulverized was obtained.

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

(5) Evaluation of hexagonal ferrite magnetic powder for bonded magnets When the hexagonal ferrite magnetic powder for bonded magnets according to Example 1 was measured by powder X-ray diffraction (XRD), all peaks were SrFe ₁₂ O It was observed at the same position as _{No. 19} , and it was confirmed that the hexagonal ferrite magnetic powder for bonded magnets of this example had an M-type ferrite structure. This result was the same in the Examples and Comparative Examples described below.

The composition of the hexagonal ferrite magnetic powder for bonded magnets according to Example 1 was analyzed, and from the analyzed values of Sr, La, Fe, Co, and Zn, the compositional formula of the hexagonal ferrite magnetic powder for bonded magnets was determined as (Sr _1-x La _x )・(Fe _1-y-z Co _y Zn _z ) _n O _19-a When calculating x, y, z, n, and a, x=0.316, y=0.009 , z=0.006, n=10.89, a=1.586. In addition, in the composition analysis, in addition to Sr, La, Fe, Co, and Zn, metal elements such as Mn and Ba, which are assumed to be derived from raw materials, were also detected, but the total amount of all of them was 0.4% by mass or less in terms of oxides. Since it was a trace amount, it was not included in the composition formula.

Regarding the hexagonal ferrite magnetic powder for bonded magnets according to Example 1, the compressed density was measured to be 3.76 g/cm ³ and the BET specific surface area was measured to be 1.90 m ² /g, which was determined by the air permeation method. The average particle diameter b was measured and found to be 1.48 μm. In addition, when laser diffraction particle size distribution measurement was performed, one peak was confirmed in the range of 0.5 μm or more and 2.0 μm or less, and the peak diameter was 1.3 μm, and 3.0 μm or more and 6.0 μm or less. One peak was confirmed within the range, and the peak diameter was 5.5 μm. A graph of the particle size distribution of Example 1 is shown in FIG.

When the magnetic properties of the compact of hexagonal ferrite magnetic powder for bonded magnets according to Example 1 were measured, the coercive force p-iHc of the compact was 2150 Oe, and the residual magnetic flux density p-Br of the compact was 2010 G. The above evaluation results are shown in Tables 3 and 4 (the same applies to Examples and Comparative Examples below).

1-2. Production of bonded magnet A according to Example 1 93.5 parts by mass of the obtained hexagonal ferrite magnetic powder for bonded magnets, 0.6 parts by mass of a silane coupling agent (Z-6094N manufactured by Dow Corning Toray Co., Ltd.) , 0.8 parts by mass of a lubricant (VPN-212P manufactured by Henkel) and 5.1 parts by mass of powdered polyamide resin (P-1011F manufactured by Ube Industries, Ltd.) as a binder were weighed and filled into a mixer. The resulting mixture was kneaded at 230°C to obtain kneaded pellets with an average diameter of 2 mm. Using a melt indexer (Melt Indexer C-5059D2 manufactured by Toyo Seiki Seisakusho Co., Ltd.), the weight of the above kneaded pellets extruded at 270°C and a load of 10 kg was measured, and this weight was extruded per 10 minutes. The flow rate (MFR) during injection molding of the kneaded pellets was determined by converting the amount into the amount, and found to be 69.2 g/10 minutes. The kneaded pellets were loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) and injection molded in a 4.3 kOe magnetic field at a temperature of 300°C and a molding pressure of 8.5 N/mm ² to form a 15 mm diameter x high A bonded magnet A (ferrite concentration: 93.5% by mass, 4.3 kOe orientation) having a cylindrical shape (the orientation direction of the magnetic field is along the central axis of the cylinder) with a length of 8 mm was obtained.

When the average value a of the major axis length and the area ratio of the hexagonal ferrite magnetic powder for bonded magnets according to Example 1 were measured using a cross-sectional observation image of bonded magnet A by SEM, the average value a of the major axis length was 2. .4 μm, the area ratio was 57.0%, and the ratio a/b of the average long axis length a to the average particle diameter b measured by the air permeation method was calculated to be 1.62. Here, in a cross-sectional observation image observed at a magnification of 1000 times, the number of particles with an area of 0.5 μm or ^more and measured major axis length and short axis length observed within a viewing area of 85 μm x 120 μm is 1695. there were. The proportion of particles having a ratio of major axis length to minor axis length (major axis length/minor axis length) of 1.5 or more among these particles was 36.58%.
The above evaluation results are shown in Table 4 (the same applies to Examples and Comparative Examples below).

When the magnetic properties of this bonded magnet A were measured, the coercive force iHc _A was 1748 Oe, and the residual magnetic flux density Br _A was 3304 G. The above results are shown in Table 5 together with the flow rate (MFR) (the same applies to Examples and Comparative Examples below). Further, a cross-sectional image of the bonded magnet A of Example 1 observed by SEM is shown in FIG.

1-3. Production of bonded magnet B according to Example 1 The kneaded pellets obtained in the production of bonded magnet A according to Example 1 were loaded into an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.), and A 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) is made by injection molding in a magnetic field at a temperature of 300°C and a molding pressure of 8.5 N/ ^mm2 . A ferrite concentration of 93.5% by mass and 9.7 kOe) was obtained.

When the magnetic properties of this bonded magnet B were measured, the coercive force iHc _B was 1691 Oe, and the residual magnetic flux density Br _B was 3450 G. Further, the ratio Br _A /Br _B between the residual magnetic flux density Br _A of bonded magnet A and the residual magnetic flux density Br _B of bonded magnet B was 0.958. The above results are shown in Table 5 (the same applies to Examples and Comparative Examples below).

(Example 2)
Example except that in the manufacturing process of hexagonal ferrite coarse powder, the second firing temperature was 1230°C, and in the manufacturing process of hexagonal ferrite fine powder, the third firing temperature was 1150°C. Hexagonal ferrite magnetic powder for bonded magnets was obtained by the same procedure as in Example 1. The obtained coarse powder, fine powder sample for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets. A bonded magnet A and a bonded magnet B were manufactured using the same, and their magnetic properties and fluidity (MFR) were measured. FIG. 3 shows an SEM cross-sectional image of the bonded magnet A of Example 2. The number of particles whose long axis length and short axis length were measured was 1493.

(Example 3)
In the manufacturing process of hexagonal ferrite fine powder, the powder serving as the raw material for hexagonal ferrite fine powder has a molar ratio of Sr:La:Fe:Zn=0.85:0.15:11.65:0.15. Hexagonal ferrite magnetic powder for bonded magnets was obtained in the same manner as in Example 1, except that the powder was weighed as follows and the third firing temperature was 1150°C. The obtained coarse powder, fine powder sample for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets. A bonded magnet A and a bonded magnet B were manufactured using the same, and their magnetic properties and fluidity (MFR) were measured. The number of particles whose long axis length and short axis length were measured was 842.

(Example 4)
In the manufacturing process of hexagonal ferrite coarse powder, the second firing temperature was 1230°C, and in the manufacturing process of hexagonal ferrite fine powder, the third firing temperature was 1150°C; Hexagonal ferrite magnetic powder for bonded magnets was obtained in the same manner as in Example 1, except that the coarse powder obtained in (1) was added so that the powder:fine powder mass ratio was 60:40. The obtained coarse powder, fine powder sample for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets. A bonded magnet A and a bonded magnet B were manufactured using the same, and their magnetic properties and fluidity (MFR) were measured. The number of particles whose long axis length and short axis length were measured was 622.

(Comparative example 1)
(2) In the firing process and the crushing process, strontium carbonate powder (SrCO ₃ , specific surface area 5.8 m ² /g) and hematite powder (α-Fe ₂ O ₃ , The molar ratio was Sr:Fe=1.00:11.00 using a surface area of 5.3 m ² /g), the third firing temperature was 970°C, and a vibrating ball mill was used. Hexagonal ferrite magnetic powder for bonded magnets was obtained by the same procedure as in Example 1 except that the pulverization time was 56 minutes. The obtained coarse powder, fine powder sample for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets. A bonded magnet A and a bonded magnet B were manufactured using the same, and their magnetic properties and fluidity (MFR) were measured. FIG. 4 shows an SEM cross-sectional image of bonded magnet A of Comparative Example 1. The number of particles whose long axis length and short axis length were measured was 1272.

(Comparative example 2)
(2) In the firing process and the crushing process, cobalt oxide powder (Co ₃ O ₄ , specific surface area: 3.3 m ² /g) was used instead of zinc oxide powder as the raw material for the hexagonal ferrite fine powder. Except for weighing so that the molar ratio was Sr:La:Fe:Co=0.70:0.30:11.20:0.30, and that the third firing temperature was 1150 ° C. A hexagonal ferrite magnetic powder for bonded magnets was obtained by the same procedure as in Example 1. The obtained coarse powder, fine powder sample for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets. A bonded magnet A and a bonded magnet B were manufactured using the same, and their magnetic properties and fluidity (MFR) were measured. FIG. 5 shows an SEM cross-sectional image of bonded magnet A of Comparative Example 2. The number of particles whose long axis length and short axis length were measured was 1734.

(Comparative example 3)
Strontium carbonate powder (SrCO ₃ , specific surface area 5.8 m ² /g) and hematite powder (α-Fe ₂ O ₃ , specific surface area 5.3 m ² /g) were used as raw materials for hexagonal ferrite coarse powder. Weighed and mixed so that the molar ratio was Sr:Fe = 1.00:11.80, and added 0.17% by mass of boric acid and 2.3% by mass of potassium chloride based on the mass of this mixture. After adding and mixing, the mixture was granulated in a pan pelletizer while adding water to obtain spherical granules with a diameter of 3 mm to 10 mm. The obtained granules were put into an internal combustion type rotary kiln and fired at 1250° C. for 20 minutes in the atmosphere, and the resulting fired product was pulverized with a roller mill to obtain coarse powder of hexagonal ferrite.

A bonded magnet was prepared in the same manner as in Example 1, except that in the (3) mixing step of Example 1, the hexagonal ferrite coarse powder obtained above was used in place of the coarse powder obtained in (1). A hexagonal ferrite magnetic powder was obtained. The obtained coarse powder, fine powder sample for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets. A bonded magnet A and a bonded magnet B were manufactured using the same, and their magnetic properties and fluidity (MFR) were measured. The number of particles whose long axis length and short axis length were measured was 605.

(Comparative example 4)
Strontium carbonate powder (SrCO ₃ , specific surface area: 5.8 m ² /g) and lanthanum hydroxide powder (La(OH) ₃ , specific surface area: 5.0 m ² /g) are used as the raw material for hexagonal ferrite coarse powder. ), hematite powder (α-Fe ₂ O ₃ , specific surface area: 5.3 m ² /g) and zinc oxide powder (ZnO, specific surface area: 4.5 m ² /g) in a molar ratio of Sr:La:Fe:Zn = 0.70:0.30:11.60:0.30 and mixed, and to this mixture, 0.17% by mass of boric acid and 2.3% by mass of potassium chloride were added. After mixing, the mixture was granulated in a pan pelletizer while adding water to obtain spherical granules with a diameter of 3 mm to 10 mm. The obtained granules were put into an internal combustion type rotary kiln and fired at 1300° C. for 20 minutes in the atmosphere, and the resulting fired product was ground with a roller mill to obtain coarse powder of hexagonal ferrite.

In addition, strontium carbonate powder (SrCO ₃ , specific surface area: 5.8 m ² /g) and lanthanum hydroxide powder (La(OH) ₃ , specific surface area: 5.0 m ² /g) are used as raw materials for hexagonal ferrite fine powder. ), hematite powder (α-Fe ₂ O ₃ , specific surface area: 5.3 m ² /g) and cobalt oxide powder (Co ₃ O ₄ , specific surface area: 3.3 m ² /g) in a molar ratio of Sr:La: After weighing and mixing so that Fe:Co=0.70:0.30:11.20:0.30, granulate it in a pan pelletizer while adding water to form spherical particles with a diameter of 3 mm to 10 mm. A granulated product was obtained. The obtained granules were put into an internal combustion type rotary kiln and fired in the atmosphere at 1150° C. for 20 minutes to obtain a fired product. The obtained fired product was subjected to the operations after the roller mill treatment in the firing step and the crushing step (2) of Example 1 to obtain a slurry containing fine powder of hexagonal ferrite.

Example 1 (3) except that in the mixing step (3) of Example 1, the slurry containing the hexagonal ferrite fine powder obtained above and the hexagonal ferrite coarse powder obtained above were used. Hexagonal ferrite magnetic powder for bonded magnets was obtained by the same procedure as after the mixing step. The obtained coarse powder, fine powder sample for evaluation, and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and the obtained hexagonal ferrite magnetic powder for bonded magnets. A bonded magnet A and a bonded magnet B were manufactured using the same, and their magnetic properties and fluidity (MFR) were measured. The number of particles whose long axis length and short axis length were measured was 599.

(Comparative example 5)
Strontium carbonate powder (SrCO ₃ , specific surface area: 5.8 m ² /g), lanthanum hydroxide powder (La(OH) ₃ , specific surface area: 5.0 m ² /g), hematite powder (α-Fe ₂ O ₃ , specific surface area: 5.8 m 2 /g) cobalt oxide powder (Co ₃ O ₄ , specific surface area: 3.3 m ² /g) and zinc oxide powder (ZnO ^, specific surface area: 4.5 m ² /g) in a molar ratio of Weighed and mixed so that Sr:La:Fe:Co:Zn=0.70:0.30:11.50:0.20:0.10, 0.17% by mass of this mixture After adding and mixing boric acid and 2.3% by mass of potassium chloride, the mixture was granulated in a pan pelletizer while adding water to obtain spherical granules with a diameter of 3 mm to 10 mm. The obtained granules were put into an internal combustion type rotary kiln and fired at 1300° C. for 20 minutes in the atmosphere, and the resulting fired product was ground with a roller mill to obtain coarse powder of hexagonal ferrite. This coarse powder was pulverized with a vibrating ball mill (Uras Vibrator KEC-8-YH, manufactured by Murakami Seiki Seisakusho) to obtain a pulverized powder. The pulverization process was carried out for 28 minutes using a steel ball with a media diameter of 12 mm at a rotation speed of 1800 rpm and an amplitude of 8 mm, and the resulting pulverized powder was further processed using a steel ball with a media diameter of 8 mm. The pulverization process was carried out for 28 minutes at a rotation speed of 1800 rpm and an amplitude of 8 mm. The obtained pulverized powder was annealed in the atmosphere at 965° C. for 30 minutes to obtain hexagonal ferrite magnetic powder for bonded magnets according to Comparative Example 5.

The obtained coarse powder and hexagonal ferrite magnetic powder for bonded magnets were analyzed and measured in the same manner as in Example 1, and bonded magnet A was prepared using the obtained hexagonal ferrite magnetic powder for bonded magnets. An attempt was made to manufacture bonded magnet B and measure its fluidity (MFR). However, the kneaded material obtained by kneading did not flow, and it was not possible to measure the flow rate (MFR) or mold it. Therefore, ferrite particles were observed using an electron microscope using a bonded magnet obtained by the same procedure as the manufacturing method of bonded magnet A, except that the magnetic powder was 90 parts by mass and the polyamide resin was 8.6 parts by mass. . The number of particles whose long axis length and short axis length were measured was 1109.

The above results are shown in Tables 1 to 5.

Claims (15)

Composition formula (Sr _1-x La _x ) (Fe _1-y-z Co _y Zn _z ) _n O _19-a (wherein, 0<x≦0.500, 0.003≦y≦0.045, 0.001≦z≦0.020, 10.00≦n≦12.50, -1.000≦a≦3.500) Hexagonal ferrite magnetic powder for bonded magnets,
8 g of the hexagonal ferrite magnetic powder for bonded magnets and 0.4 cm ³ of polyester resin were kneaded, 7 g of the resulting kneaded product was filled into a mold with an inner diameter of 15 mmφ, and compressed for 60 seconds at a pressure of 196 MPa. A hexagonal ferrite magnetic powder for bonded magnets, which has a coercive force iHc of 2000 Oe or more when the compact obtained by extracting the molded product from the mold and drying it at 150° C. for 30 minutes is measured in a measuring magnetic field of 10 kOe. Fill a mixer with 93.5 parts by mass of the hexagonal ferrite magnetic powder for bonded magnets, 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 resulting mixture was kneaded at 230°C to produce kneaded pellets with an average diameter of 2 mm, and the kneaded pellets were injection molded at a temperature of 300°C and a molding pressure of 8.5 MPa in a magnetic field of 4.3 kOe. Then, a cylindrical bonded magnet A with a diameter of 15 mm and a height of 8 mm (the direction of magnetic field orientation is along the central axis of the cylinder) was manufactured, and the residual magnetic flux when this bonded magnet A was measured with a measurement magnetic field of 10 kOe. The hexagonal ferrite magnetic powder for bonded magnets according to claim 1, having a density _BrA of 3200G or more. The hexagonal ferrite magnetic powder for a bonded magnet according to claim 1 or 2, wherein the bonded magnet A produced by the method according to claim 2 has a maximum energy product BHmax _A of 2.45 MGOe or more when measured in a measurement magnetic field of 10 kOe. . The residual magnetic flux density Br _A when the bonded magnet A produced by the method according to claim 2 is measured in a measurement magnetic field of 10 kOe,
Fill a mixer with 93.5 parts by mass of the hexagonal ferrite magnetic powder for bonded magnets, 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 resulting mixture was kneaded at 230°C to produce kneaded pellets with an average diameter of 2 mm, and the kneaded pellets were injection molded in a 9.7 kOe magnetic field at a temperature of 300°C and a molding pressure of 8.5 MPa. Then, a cylindrical bonded magnet B with a diameter of 15 mm and a height of 8 mm (the magnetic field orientation direction is along the central axis of the cylinder) was manufactured, and the residual magnetic flux when this bonded magnet B was measured with a measurement magnetic field of 10 kOe. The hexagonal ferrite magnetic powder for bonded magnets according to any one of claims 1 to 3, wherein the ratio Br _A /Br _B with density Br _B is 0.950 or more. In an image obtained by observing a cross section of the bonded magnet A produced by the method according to claim 2 with an electron microscope at a magnification of 1000 times, an area of 500 or more pieces observed within a viewing area of 85 μm x 120 μm has an area of 0.5 μm ^or more. The ratio a/b of the average long axis length a of the particles of the hexagonal ferrite magnetic powder for bonded magnets to the average particle diameter b measured by the air permeation method of the hexagonal ferrite magnetic powder for bonded magnets is 1.5. The hexagonal ferrite magnetic powder for bonded magnets according to any one of claims 1 to 4, wherein the hexagonal ferrite magnetic powder is less than 3.0. The hexagonal ferrite magnetic powder for bonded magnets according to claim 5, wherein the average particle diameter b of the hexagonal ferrite magnetic powder for bonded magnets as measured by an air permeation method is 1.00 μm or more and 1.50 μm or less. The hexagonal ferrite magnetic powder for bonded magnets according to any one of claims 1 to 6, wherein z in the composition formula is less than 0.010. In an image obtained by observing a cross section of the bonded magnet A produced by the method according to claim 2 with an electron microscope at a magnification of 1000 times, an area of 500 or more pieces observed within a viewing area of 85 μm x 120 μm has an area of 0.5 μm ^or more. When observing particles of hexagonal ferrite magnetic powder for bonded magnets, less than 60% of the particles have a ratio of major axis length to minor axis length (major axis length/minor axis length) of 1.5 or more. The hexagonal ferrite magnetic powder for bonded magnets according to any one of claims 1 to 7. The volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer has peaks in the particle size range of 0.5 μm or more and 2.0 μm or less and 3.0 μm or more and 6.0 μm or less, and is bimodal or more. The hexagonal ferrite magnetic powder for bonded magnets according to any one of claims 1 to 8, which has a distribution. Composition formula (Sr _1-x1 La _x1 ) (Fe _1-y1 Co _y1 ) _n1 O _19-a1 (wherein, 0<x1≦0.500, 0.005≦y1≦0.050, 10.00≦n1 ≦12.50, -1.000≦a1≦3.500), which is a raw material for hexagonal ferrite magnetic powder, is mixed and fired at a first temperature to obtain coarse hexagonal ferrite powder. process and
Composition formula (Sr _1-x2 La _x2 ) (Fe _1-z2 Zn _z2 ) _n2 O _19-a2 (wherein, 0<x2≦0.500, 0.005≦z2≦0.050, 10.00≦n2 ≦12.50, -1.000≦a2≦3.500), which is a raw material for hexagonal ferrite magnetic powder, is mixed and then fired at a second temperature to have a BET specific surface area higher than that of the coarse powder. A step of obtaining fine powder of hexagonal ferrite having a small particle size calculated from
a step of mixing and pulverizing the coarse hexagonal ferrite powder and the fine hexagonal ferrite powder to obtain a mixed powder that has been mixed and pulverized;
a step of annealing the mixed powder subjected to the mixing and pulverization treatment;
A method for producing hexagonal ferrite magnetic powder for bonded magnets, including: The particle size calculated from the BET specific surface area of the hexagonal ferrite coarse powder is 1.00 μm or more and 8.00 μm or less,
The method for producing hexagonal ferrite magnetic powder for a bonded magnet according to claim 10, wherein the particle size calculated from the BET specific surface area of the hexagonal ferrite fine powder is 0.05 μm or more and 0.50 μm or less. In the step of obtaining the mixed powder subjected to the mixing and pulverization treatment,
The mass ratio of the hexagonal ferrite coarse powder to the total mass of the hexagonal ferrite coarse powder and the hexagonal ferrite fine powder is 60% by mass or more and 90% by mass or less,
The method for producing hexagonal ferrite magnetic powder for bonded magnets according to claim 10 or 11. The method for producing hexagonal ferrite magnetic powder for bonded magnets according to any one of claims 10 to 12, wherein the hexagonal ferrite fine powder has a saturation magnetization of 57.0 emu/g or more. A bonded magnet comprising the hexagonal ferrite magnetic powder for bonded magnets according to any one of claims 1 to 9 and a resin. A method for producing a bonded magnet, using hexagonal ferrite magnetic powder for bonded magnets obtained by the production method according to any one of claims 10 to 13.

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