Compositions – Magnetic – With wax – bitumen – resin – or gum
Patent
1987-02-12
1987-10-27
Demers, Arthur P.
Compositions
Magnetic
With wax, bitumen, resin, or gum
335302, 335303, C04B 3504, H01F 100, H01F 126
Patent
active
047028521
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
TECHNICAL FIELD
The present invention relates to a multipolarly magnetized anisotropic ferrite-based plastics magnet. More particularly, it relates to a multipolarly magnetized anisotropic plastics magnet in which the surface magnetic field produced by magnetization is increased by keeping the coercive force of the raw material ferrite powder below a certain level.
BACKGROUND ART
Anisotropic sintered ferrite magnets are dominant in the area of ferrite-based multipolarly magnetized magnets; but they have a disadvantage of being brittle and poor in dimensional accuracy. To eliminate this disadvantage, there has been proposed the use of ferrite-based plastics magnets. However, they are not satisfactory in magnetic properties, especially the surface magnetic fields resulting from multipolar magnetization, because ferrite in them are diluted by an organic binder. Many attempts are being made to improve the performance of plastics magnets by increasing the residual magnetism and intrinsic coercive force and eventually increasing the maximum energy product which is the typical property of permanent magnets. The increase of maximum energy product, however, does not necessarily leads to the improvement of surface magnetic field resulting from multipolar magnetization. Up to now, there has been no satisfactory solution to this problem.
In order to solve this problem, the present inventors studied the factor that governs the surface magnetic field resulting from multipolar magnetization, and they found that the surface magnetic field greatly increases if a magnet rotor is formed by multipolar magnetization with ferrite having magnetic properties in a specific range. The present invention is based on this finding.
DISCLOSURE OF THE INVENTION
The gist of the present invention resides in a multipolarly magnetized anisotropic plastics magnet formed by molding, followed by solidifying, a composition composed of a magnetic powder and an organic binder in the presence of a magnetic field, and subsequently multipolarly magnetizing the thus obtained anisotropic plastics magnet, said magnetic powder being magnetoplumbite ferrite which is characterized by that the green density is not less than 3.1 g/cm.sup.3 and the intrinsic coercive force of the green compact is not more than 2500 oersteds.
In the case of anisotropic plastics magnet, the surface magnetic field formed by multipolar magnetization can be increased to some extent simply by increasing the content of magnetic powder in the plastics magnet or increasing the degree of orientation and hence increasing the anisotropy, whereby increasing the maximum energy product. However, the performance of the magnetic charger is limited even though the maximum energy product is increased, and hence no satisfactory magnetization is accomplished where the plastics magnet has a high coercive force. This is the case particularly where the magnetic poles are magnetized at a small pitch, say, 2 mm or less. It follows, therefore, that even though the maximum coercive force is low, sufficient multipolar magnetization can be accomplished and a great surface magnetic field can be obtained if the intrinsic coercive force is kept below a certain limit.
The ferrite used in this invention is prepared by crushing, followed by heat treatment, magnetoplumbite ferrite represented by the formula MO.multidot.nFe.sub.2 O.sub.3 (M=Ba or Sr, and n=5.5 to 6.5) in such a manner that the resulting powder is composed mainly of single magnetic domains. The ferrite powder thus obtained is characterized by that the green compact formed under a pressure of 1 t/cm.sup.2 has a density of not less than 3.1 g/cm.sup.3 and the green compact has an intrinsic coercive force of not more than 2500 oersteds. With a green density lower than 3.1 g/cm.sup.3, the ferrite cannot be densely filled in the Plastics magnet and the resulting plastics magnet is poor in magnetic properties. Thus the ferrite should preferably have a green density of not less than 3.2 g/cm.sup.3. On the other hand, the ferrite sho
REFERENCES:
patent: 4120806 (1978-10-01), Watanabe et al.
patent: 4120807 (1978-10-01), Watanabe et al.
patent: 4190548 (1980-02-01), Baermann
patent: 4200547 (1980-04-01), Beck
patent: 4308155 (1981-12-01), Tada et al.
patent: 4327346 (1982-04-01), Tada et al.
patent: 4549157 (1985-10-01), Loubier
Chemical Abstracts, vol. 102 (1985), #104922, (Abstract of JP 59, 161003).
Mohri Fumihiko
Nakatsuka Satoshi
Sakauchi Takashi
Tomoda Naohisa
Demers Arthur P.
Kanegafuchi Kagaku Kogyo & Kabushiki Kaisha
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