Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-07-16
2003-11-04
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S323000, C428S328000, C428S329000, C428S480000, C428S482000, C428S900000, C428S407000, C252S06251C, C252S062530, C252S062540, C252S062560, C252S062550
Reexamination Certificate
active
06641919
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a resin-bonded magnet which is excellent in magnetic properties.
THE PRIOR ART
The recent years, ferrite magnets, alnico magnets, rare earth metal magnets and the like have been used in various applications, including motors. However, since such magnets are prepared mainly by a sintering method, they are generally fragile, and magnets of reduced thickness or complicated shapes can not be obtained easily. Further, since shrinkage during sintering is as large as 15 to 20%, they have drawbacks in that high dimensional accuracy can not be obtained and a post treatment such as polishing is necessary for improving shape accuracy.
Resin-bonded type magnets overcome such drawbacks and develop new application uses, and comprise thermoplastic resins such as polyamide resin or polyphenylene sulfide resin as a binder in which magnetic powder is filled.
However, since the resin magnets using the thermoplastic resin as the binder are exposed to a high temperature of 200° C. or higher during molding, they involve problems, particularly, inevitable degradation of the coersive force or shape deterioration of the squareness. Resin bonded magnets with less reduction in magnetic properties after molding have not yet been obtained.
Further, although magnets obtained using a thermosetting resin such as an epoxy resin or bis maleimide triazine resin as a binder in which a magnetic powder is filled have also been proposed, this can provide the resin-bonded type magnet only of a simple molding product by a compression molding process because of the small amount of the binder.
In recent years, the resin-bonded type magnets used for example, in small-sized motors, acoustic equipment and office automation equipment have been required to be excellent in magnetic properties and to have complicated shapes in view of the demand for reducing the size of the equipment.
The relation between the magnetic properties and the shape of the resin-bonded type magnets obtained by the existent methods was insufficient for use in the applications described above and sooner improvement for the resin-bonded type magnets has been demanded.
SUMMARY OF THE INVENTION
In view of the above, it is an object of this invention to overcome the drawbacks in (1) the existent resin-bonded type magnets obtained by the injection molding process using the thermoplastic resin that have low magnetic properties but can be molded into complicated shapes and (2) the resin-bonded type magnets obtained by the compression molding process using the existent thermosetting resin that have high magnetic properties but have only simple shapes, respectively, and to provide a resin-bonded type magnet, particularly, excellent in the magnetic properties, as well as excellent in the degree of freedom for the shape, moldability and mechanical strength, and further, providing excellent anti-rusting effect and improved yield of products, by preventing the lowering of the magnetic properties caused by oxidative degradation during existent high temperature molding and enabling a high degree of orientation in the anisotropic magnet material for which the orientation is important.
That is, the present inventors have made various studies for attaining the foregoing object and, as a result, have accomplished this invention based on the finding that a resin-bonded type magnet having magnetic properties, particularly, excellent coersive force and degree of orientation, degree of freedom for the shape, moldability and mechanical strength, can be obtained from a composition of a magnetic powder and an unsaturated polyester resin and molding in an injection molding process or a transfer molding process.
That is, the resin-bonded type magnet according to this invention is a resin-bonded type magnet formed by molding a composition comprising a magnetic powder and a resin binder in which the resin binder comprises at least one unsaturated polyester resin curing product as a main ingredient.
It is preferred that the resin binder comprising the unsaturated polyester resin curing product as the main ingredient contains a peroxide or a reaction product thereof capable of curing at a temperature of 150° C. or lower, the anisotropic magnetic field (HA) of the magnetic powder is 50 kOe or more, and 50% by weight or more of the particles of the magnetic powder have a grain size of 100 &mgr;M or less.
The resin-bonded type magnet according to this invention can be obtained by an injection molding process, an injection compression molding process, an injection press molding process or a transfer molding process.
The resin-bonded type magnet according to this invention may be coated at the surface thereof with a thermosetting resin.
Any of the resin-bonded type magnets described above may be pulverized again and mixed with a thermosetting resin or a thermoplastic resin again to form a resin-bonded type magnet.
BEST MODE FOR PRACTICING THE INVENTION
This invention will now be described in greater detail with respect to preferred embodiments.
For the magnetic powder used in this invention, those magnetic powders used so far in resin-bonded type magnets can be used and they can include, for example, rare earth metal-cobalt series, rare earth metal- iron-boron series and rare earth metal-iron-nitrogen series magnetic powders, which are magnetic powders having anisotropic magnetic field (HA) of 50 kOe or more.
The present inventors have confirmed that a resin-bonded type magnet particularly having excellent magnetic properties can be obtained by using Sm—Fe—N series fine alloy powder obtained by nitriding and finely pulverizing a coarse Sm—Fe series alloy powder obtained by a reductive diffusion method, a fine alloy powder obtained by finely pulverizing a coarse Sm—Co
5
series alloy powder also obtained by the same reductive diffusion method, an alloy powder obtained by a liquid quenching method of Nd—Fe—B series powder or an anisotropic Nd—Fe—B series alloy powder by an HDDR (Hydrogenation—Disproportionation—Desorption—Recombination) method, as the magnetic powder in the resin-bonded type magnet.
Further, since the Nd—Fe—B series magnetic powder obtained by the liquid quenching method or the anisotropic Nd—Fe—B series magnetic powder obtained by the HDDR method contains a great amount of relatively large particles having a unique shape, it is preferably used after being pulverized by a jet mill or a ball mill. This invention can provide a remarkable effect in a composition containing a magnetic powder, 50% by weight or more of which has a grain size of 100 &mgr;m or less, and the effect is more remarkable in the anisotropic magnetic powder which is essentially molded in the magnetic field than in the isotropic magnetic power in view of the orientation characteristics.
Then, the unsaturated polyester resin as the essential ingredient in this invention cures in a molding die during molding and serves as a binder for the magnetic powder, and generally marketed unsaturated polyester resins can be used with no particular restrictions on their types and two or more of unsaturated polyester resins may also be used as a mixture.
The unsaturated polyester resin comprises a main ingredient, for example, prepared by preliminarily polymerizing an unsaturated polybasic acid and/or saturated polybasic acid and glycols to a molecular weight of about 5000 or less as an oligomer or prepolymer, and monomers also serving as a cross-linker, a curing agent for initiating the reaction, a polymerization inhibitor for ensuring a long time storability and other additives.
Polybasic acid can include, for example, maleic acid anhydride, fumaric acid and itaconic acid and the saturated polybasic acid can include, for example, phthalic acid anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid anhydride, methyltetrahydro phthalic acid anhydride, endomethylene tetrahydrophthalic acid hydride, adipic acid, sebasic acid, HET acid, and tetrabromophthalic acid anhydride. Further, the glycols can include, for example, ethylene glycol, propylene glycol, die
Hayashi Shin'ichi
Yoshizawa Shoichi
Chen Vivian
Dykema Gossett PLLC
Sumitomo Metal & Mining Co., Ltd.
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