Compositions – Magnetic – With wax – bitumen – resin – or gum
Reexamination Certificate
2000-03-16
2002-05-14
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
With wax, bitumen, resin, or gum
C252S062550, C264S612000
Reexamination Certificate
active
06387293
ABSTRACT:
TECHNICAL FILED
This invention relates to a composition for a rare earth bonded magnet, the rare earth bonded magnet and a method for manufacturing the rare earth bonded magnet.
BACKGROUND ART
A rare earth bonded magnet is manufactured by using a compound of rare earth bonded magnetic powder and binding resin (organic binder), and by molding it with pressure into a preferable magnet shape. For the molding method, a compaction molding method, an injection molding method and an extrusion molding method are used.
The compaction molding method is a method where a molding is provided by filling a press metallic mold with the compound and by compacting it with pressure, and a magnet is then manufactured by curing thermosetting resin—a binding resin—with heat. Since this method can mold even with less binding resin than other methods, the quantity of resin in a magnet is reduced and the method can improve magnetic properties.
The extrusion molding method is a method where the heated and melted compound is pushed out of a metallic mold of an extrusion-molding machine and is, at the same time, cooled and solidified and then cut into a preferable length to provide a magnet. This method has advantages in that the shapes of magnets are flexible and a light and long magnet can easily be manufactured. However, in order to maintain the fluidity of the melted compound during the molding process, this method needs more binding resin than the compaction molding method, so that there are disadvantages in that the quantity of resin in a magnet will be large and magnetic properties will decline.
The injection molding method is a method where the compound is heated and melted, and the melted material is injected into a metallic mold with sufficient fluidity and is molded into a predetermined magnet shape. This method has more flexibility in shaping magnets than the extrusion molding method, and particularly has an advantage in that magnets of different shapes can also be easily manufactured. However, the method requires higher fluidity for the melted material during the molding process than the extrusion molding method, so that the method needs more binding resin than the extrusion molding method; thus, there are disadvantages in that the quantity of resin in a magnet is large and magnetic properties decline.
When a rare earth bonded magnet is molded in each above-noted molding method, silicone oil and various waxes, metallic soap such as fatty acid zinc and zinc stearate, calcium stearate, etc., or the like are usually added as a lubricant so as to improve molding properties. However, the addition of such a lubricant generates the following inconveniences, depending on the composition and the added quantity.
For instance, when a metallic soap is added, there is a problem in that the mechanical strength of a molding will be less than that of one with no added soap. Also, as a liquid lubricant such as silicone oil is added in a large quantity, particles or the like stick to the surface of a molded magnet in secondary processing such as grinding and trimming, and it is difficult to remove them. Moreover, these deposits result in the deterioration of corrosion resistance of a magnet. Furthermore, due to the generation of “discharge”, coating the surface of a magnet will be difficult.
In order to avoid the above-noted problems, the quantity of a lubricant is kept at a minimum level, but in this case, the improvement of molding properties is sometimes not achieved by such a level. The object of the present invention is to provide a rare earth bonded magnet, a composition for the rare earth bonded magnet, and a method for manufacturing the rare earth bonded magnet that solves the conventional problems such as reduction of mechanical strength by adding fluorine-based resin powder and has excellent molding properties due to lubrication.
DISCLOSURE OF THE INVENTION
(1) A first invention is a composition for a rare earth bonded magnet comprising rare earth magnetic powder and binding resin containing thermoplastic resin; wherein the composition comprises fluorine-based resin powder.
(2) A second invention is a composition for a rare earth bonded magnet provided by kneading the mixture of rare earth magnetic powder, binding resin containing thermoplastic resin and a lubricant; wherein fluorine-based resin powder is contained as the lubricant.
(3) It is preferable that the content of the fluorine-based resin powder is less than 20 vol % relative to the thermoplastic resin.
(4) It is also preferable that the average particle diameter of the fluorine-based resin powder is 2-30 &mgr;m(micro-meter).
(5) It is further preferable that the composition for the rare earth bonded magnet contains an antioxidant.
(6) It is preferable that the content of the antioxidant in the composition for the rare earth bonded magnet is 2-12 vol %.
(7) A third invention is a bonded magnet provided by bonding rare earth magnetic powder with binding resin containing thermoplastic resin; wherein the magnet contains fluorine-based resin powder.
(8) It is preferable that the content of the fluorine-based resin powder is less than 20 vol % relative to the thermoplastic resin.
(9) It is also preferable that the fluorine-based resin powder comprises at least one resin selected from the group consisting of tetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene-propylene hexafluoride copolymer (FEP), tetrafluoroethylene-propylene hexafluoride-perfluoroalkoxyethylene copolymer (EPE), tetrafluoroethylene-ethylene copolymer (ETFE), ethylene chloride trifluoride copolymer (PCTFE), ethylene chloride trifluoride-ethylene copolymer (ECTFE), vinylidene fluoride (PVDF), and polyvinyl fluoride (PVE).
(10) It is preferable that the rare earth bonded magnet is molded by an injection molding method, and that the content of the rare earth magnetic powder is 68-76 vol %.
(11) It is also preferable that the rare earth bonded magnet is molded by an extrusion molding method, and that the content of the rare earth magnetic powder is 78.1-83 vol %.
(12) It is further preferable that the rare earth bonded magnet is molded by a compaction molding method, and that the content of the rare earth magnetic powder is 78-86 vol %.
(13) It is preferable that the compaction molding method is a warm molding method whereby pressing and molding are carried out above the thermal deformation temperature of the thermoplastic resin.
(14) It is also preferable that the rare earth magnetic powder essentially comprises rare earth elements mainly containing Sm and transition metals mainly containing Co.
(15) It is further preferable that the rare earth magnetic powder essentially comprises R (wherein R is at least one rare earth element among rare earth elements containing Y), transition metals mainly containing Fe, and B.
(16) It is preferable that the rare earth magnetic powder essentially comprises rare earth elements mainly containing Sm, transition metals mainly containing Fe, and interstitial elements mainly containing N.
(17) It is also preferable that the rare earth magnetic powder is the mixture of at least two types of the rare earth magnetic powder mentioned in either (14) or (16) above.
(18) It is preferable that the product of isotropic magnetic energy ((BH)
max
) is more than 4.5 MGOe in the rare earth bonded magnet.
(19) It is also preferable that the product of anisotropic magnetic energy ((BH)
max
) is more than 10 MGOe in the rare earth bonded magnet.
(20) It is preferable that a void ratio is below 2 vol % in the rare earth bonded magnet.
(21) A fourth invention comprises the steps of preparing a composition for a rare earth bonded magnet containing rare earth magnetic powder, binding resin including thermoplastic resin, and fluorine-based resin powder; and of molding the composition for a rare earth bonded magnet into a preferable shape.
(22) It is preferable that the step of preparing a composition for a rare earth bonded magnet includes the kneading process above the softening temperature of the binding resin.
Akioka Koji
Ikuma Ken
Nakamura Yoshiki
Harness & Dickey & Pierce P.L.C.
Koslow C. Melissa
Seiko Epson Corporation
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