Compositions – Magnetic – With wax – bitumen – resin – or gum
Patent
1995-02-13
1999-03-30
Diamond, Alan
Compositions
Magnetic
With wax, bitumen, resin, or gum
252 6257, 29607, 335296, 335302, 148100, 148101, 264DIG61, H01F 108, H01F 4102
Patent
active
058884165
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP93/00611 filed May 11, 1993.
TECHNICAL FIELD
The present invention relates to a rare-earth bonded magnet comprising a rare-earth magnetic powder and a resin component, and more particularly to a rare-earth bonded magnet having a high volume fraction of magnetic powder and thus having high performance, a rare-earth bonded magnet composition for use in the production of the rare-earth bonded magnet and a process for producing the rare-earth bonded magnet.
BACKGROUND ART
Rare-earth bonded magnets hitherto been produced by the following methods.
1. Compression molding
2. Injection molding
3. Extrusion molding
Compression molding is generally a method wherein a magnet composition comprising a magnetic powder and a thermosetting resin is filled into a mold in a press at room temperature, compressed the composition and heated to cure the resin, thereby molding a magnet. In the case of the compression molding method, since the resin content of the magnet composition is lower than that for the other molding methods, the freedom of shape in molding a magnet is smaller although the magnetic properties of the resultant magnet are superior.
Injection molding is a method wherein a magnet composition comprising a magnet power and a resin component is heat-melted to prepare a melt having sufficient fluidity which is then injected into a mold where the melt is molded into a desired shape. In the case of the injection molding, in order to impart sufficient fluidity to the magnet composition, the resin content of the magnet composition is higher than that for the compression molding, resulting in lowered magnetic properties. The freedom in molding, however, is higher than that for the compression molding.
Extrusion molding is a method wherein a magnet composition comprising a magnet powder and a resin component is heat-melted to prepare a melt having sufficient fluidity which is then formed into a shape in a die and set by cooling, thereby providing a product having a desired shape. In the extrusion, like the injection molding, the resin content needs to be high enough to impart the magnet composition to fluidity. This method has an advantage that a thin-walled and long magnet can be easily produced.
Among the above methods, injection molding and extrusion generally use a thermoplastic resin as the resin. These are disclosed in Japanese Patent Laid-Open Nos. 123702/1987, 152107/1987, 194503/1985 and 211908/1985.
However, the conventional rare-earth bonded magnet composition comprising a-rare-earth magnet powder and a thermoplastic resin, used in the prior art methods, particularly in injection molding and extrusion, has the following problems. Specifically, since the rare-earth magnet powder comprises a transition metal element, such as Fe or Co, when it is mixed and kneaded with a thermoplastic resin to prepare a composition which is then molded, the transition metal element catalytically acts on the resin component and causes an increase in molecular weight of the resin component, which results in a change in properties of the composition, such as an increase in melt viscosity. This suggests a lowering in heat stability of the rare-earth bonded magnet composition. The above phenomenon is partly described in "Journal of The Magnetics Society of Japan, vol. 16, No. 2, 135-138 (1992)," indicating that a composition comprising an Nd-Fe-B-based magnet powder and a polyamide resin, due to the influence of temperature and shearstress, undergoes changes in properties, particularly viscosity. The higher the content of the rare-earth magnet powder in the composition and the larger the specific surface area of the rare-earth magnetic powder, the higher the above tendency. The above phenomenon raises problems including that the phenomenon makes it impossible to produce a rare-earth bonded magnet composition; even though a rare-earth bonded magnet composition could be successfully produced, it cannot be stably molded due to the deterioration during molding; and it is difficult to improve the mag
REFERENCES:
patent: 3600748 (1971-08-01), Faehndrich
patent: 5376291 (1994-12-01), Wantanabe
patent: 5409624 (1995-04-01), Watanabe
Patent Abstracts of Japan, vol. 16, No. 403 (E 1254) 26, Aug. 1992 (Seiko Epson KK.).
Patent Abstracts of Japan, vol. 11, No. 4, E-468) 7 Jan. 1987 (Daiseru Hiyurusu KK).
Vieweg et al. Kunststoff-Hanbuch "Polyamide" C.H. Verlag, Munchen De p. 216, paragraph 2, p. 222, paragraph 1. (Date Unknown).
Reference Paper issued by the Magnetics Society of Japan (Issue Date: Oct. 29, 1991).
Journal of the Magnetics Society of Japan (vol. 16, No. 2--1992) (Month Unknown).
Akioka Koji
Ikuma Ken
Ishibashi Toshiyuki
Diamond Alan
Seiko Epson Corporation
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