JPH04224116A - Ferrite magnetic powder for magnetic-field-oriented bond magnet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to magnetic powder for anisotropic ferrite-based magnetically oriented bonded magnets suitable for use in rotors of small precision motors, developing magnetic rolls (commonly known as magnet rolls) of copying machines, etc. The aim is to obtain a bonded magnet with better magnetic properties than conventional products.

0002

[Prior Art] Compared to sintered ferrite magnets, ferrite bonded magnets are lighter, easier to form into complex shapes, or can be integrally molded by injection molding, so they can be supplied cheaply as parts and have good dimensional accuracy. Because it has features such as good assembly accuracy with precision parts, it has come to be widely used as magnetic parts for office equipment, etc. However, since the constituent components include synthetic resin binder in addition to magnetic powder, it has inferior magnetic properties compared to sintered products, so it is used in applications such as motors that require high torque and applications that require high magnetic properties. could not be applied, and the scope of use had to be restricted.

[0003] Several proposals have heretofore been made in order to solve the above-mentioned drawbacks and improve the magnetic properties. For example, Japanese Patent Publication No. 55-49030 discloses a so-called flux method in which a low melting point compound is added to a ferrite raw material, fired, and then washed with water and dried. Since the hard ferrite powder obtained by this method has a scaly particle shape, it is used to mechanically orient it by extrusion molding, roll rolling, etc. to obtain a composite magnet. Further, JP-A-56-64407 discloses a method of improving magnetic properties by pulverizing magnetic powder using a dry ball mill to increase the compaction density and increasing the degree of filling of the magnetic powder. Furthermore, JP-A-63-
Japanese Patent No. 162532 proposes a ferrite particle powder for bonded magnets in which the degree of orientation is improved by appropriately selecting the ratio of strontium and barium in strontium and barium-based magnet plumbite-type ferrite.

[0004] The idea common to the above-mentioned conventional methods is to improve the magnetic properties by increasing the filling rate and degree of orientation of the magnetic particles, but the obtained magnetic properties are (BH)max = 2 .2 MGOe is the limit,
I couldn't get anything better than this.

[0005]

[Problems to be Solved by the Invention] This invention attempts to achieve a dramatic improvement in the magnetic properties of ferrite-based bonded magnets, which could not be expected with the prior art, by improving the magnetic particle surface. The purpose is to propose ferrite magnetic powder for magnetically oriented bonded magnets that can provide bonded magnets up to 2.6 MGOe.

[0006]

[Means for solving the problem] As mentioned above, in the past, magnetic properties have been improved by devising the grinding method, adding low-melting-point substances during firing, or adjusting the ratio of barium and strontium. has been attempted, but the improvement was only small because it was not an essential improvement measure.

As a result of intensive research on ferrite magnetic powder for bonding, the inventors found that by appropriately selecting the particle size, particle size distribution, and particle shape of the magnetic powder, the magnetic particle content and degree of orientation of the magnetic powder in the bonded magnet can be improved. can improve,
Furthermore, we obtained knowledge that it is possible to dramatically improve magnetic properties. This invention is based on the above knowledge.

That is, the present invention consists of magnetic powder in which the average major axis/breadth axis ratio of all particles is 3 or less, the primary particle major axis is 2 to 4 μm, and the primary particle major axis and 2
The ratio of the major axis of the secondary particle and the tertiary particle is 10: (3.6 to
4.6): (2.0 to 2.4), and the weight ratio of primary particles to secondary, tertiary, and quartic and lower particles is 74: (3 to 2.4).
5):(1.5-1.9):(0-0.3) Ferrite magnetic powder for magnetically oriented bonded magnets.

As the magnetic powder in the present invention, any of those conventionally used as magnetic powder for bonded magnets is suitable, but magnetoplumbite type ferrite powder having a saturation magnetic flux density of 4,500 Gauss or more is particularly advantageously suitable. The composition of suitable magnetoplumbite-type ferrite powder is shown here: Chemical formula: MO・n(Fe2O3), where M is at least one selected from barium, strontium, or lead, and n is 5.2 to 6. .1.

0010

[Operation] In the present invention, first, it is necessary that the average length/breadth axis ratio of all the magnetic particles is 3 or less. This is because if the average length/breadth ratio of the magnetic powder exceeds 3, the viscosity at the molding temperature of the plastic mag whose basic component is a magnetic powder binder increases significantly, making it difficult to increase the magnetic powder content to the desired level. This is because it causes a decrease in the degree of orientation and an accompanying decrease in magnetic properties. In extreme cases, the viscosity may increase to such an extent that kneading or molding becomes impossible.

[0011] Furthermore, the major diameter of the primary particles must be 2 to 4 μm. This is because if the major axis of the primary particles is less than 2 μm, the surface property per unit volume of magnetic powder increases, resulting in an increase in viscosity, which leads to a significant decrease in the magnetic powder content in the moldable plastic mag composition. , while 4 μm
This is because, if it exceeds this, the intrinsic coercive force of the plastic mag will decrease, causing demagnetization problems such as low-temperature demagnetization.

[0012] Furthermore, the length ratio of the primary particles to the secondary particles and the tertiary particles is 10:(3.6 to 4.6):(2.0 to 2
．． 4) It is necessary to do so. This is because if the major axis ratio deviates from the above range, the viscosity of the plastic mag melt will increase due to a decrease in the space factor of the particles, resulting in a significant decrease in the magnetic powder content in the moldable plastic mag composition. Because it invites you. Here are primary particles, secondary particles, tertiary particles...
means particles obtained by sequential sieving, and the particle size of the primary particles is 2 to 4 μm as described above, and in the case of secondary particles and tertiary particles, the diameter is 2 to 4 μm, depending on the diameter of the primary particles. 0
．． They are 72-1.84 μm and 0.4-0.96 μm.

Furthermore, primary particles, secondary, tertiary and quaternary particles
The weight ratio of each particle below is 74:(3-5):(1.5
~1.9): It is necessary to set it as (0-0.3). This is because if the weight ratio is outside the above range, the space factor of the particles constituting the plastic mag will decrease, causing an increase in the viscosity of the plastic mag melt, and the magnetic powder content in the moldable plastic mag composition will significantly decrease. This is because, at the same time, the degree of orientation during molding in a magnetic field also decreases significantly.

[0014]

[Example] After blending magnetic powders A to C in the proportions shown in Table 1 with banders and other raw materials in the proportions shown in Table 2,
The mixture was mixed in a Henschel mixer for 10 minutes, then baked in a pusher type continuous furnace at 1240°C for 4 hours, and then pulverized in a wet attritor. Next, the particles were classified using a high-shear dispersion type wind classifier, and then appropriately blended to obtain magnetic powder having the particle size ratio, weight ratio, and length/breadth ratio shown in Table 3. At this time, the shape of the magnetic powder (particle diameter, major axis/minor axis ratio) was confirmed using an electron microscope. Thereafter, the pellets were kneaded using a two-axis continuous kneading machine at a kneading temperature of 230°C and a discharge rate of 100 kg/h to create pellets with a diameter of 3 mm and a thickness of 3 mm. Strength:
1200 Oe, cylinder temperature: 290 ℃, mold temperature: 100 ℃, molded product shape: 30 mmφ, 5 m
The molding was performed in a magnetic field under the conditions of a disk shape of m (orientation direction is the thickness direction), and the results shown in Table 4 were obtained.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

As is clear from Table 4, when the magnetic powder according to the present invention is used, the (BH)max can be increased to 2.6 MGOe, which exceeds 2.2 MGOe, which was the limit of ferrite plastic magnets. I was able to improve it to. On the other hand, if magnetic powder outside the appropriate range of this invention is used, it will not be possible to exceed 2.2 MGOe, and in particular, E9 will have a lower intrinsic coercive force, falling below the 2300 Oe required for the product. All I could get was that.

[0020]

According to the present invention, it is possible to obtain a ferrite-based bonded magnet with excellent magnetic properties such as (BH)max≧2.2 MGOe, which exceeds the conventional limit.

Claims (1)

[Claims] [Claim 1] The average length/breadth ratio of all particles is 3.
Consists of magnetic powder with the following primary particle length diameter of 2 to 4 μm
The ratio of the major axis of the primary particle to the major axis of the secondary and tertiary particles is 10:(3.6 to 4.6):(2.
0 to 2.4), and the weight ratio of the primary particles to the secondary, tertiary, and fourth or lower particles is 74:(3 to 5):(1.5 to
1.9): (0 to 0.3) ferrite magnetic powder for magnetically oriented bonded magnets.