Compositions – Magnetic – With wax – bitumen – resin – or gum
Reexamination Certificate
2001-02-01
2003-03-04
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
With wax, bitumen, resin, or gum
C252S062550
Reexamination Certificate
active
06527971
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a rare-earth bonded magnet, a rare-earth bonded magnet composition, and a method of manufacturing the rare-earth bonded magnet.
BACKGROUND ART
A rare-earth bonded magnet is manufactured by molding under pressure a mixture (compound) of rare-earth magnetic powder and a binding resin (organic binder) into a desired magnet shape. For molding rare-earth bonded magnets, a compaction molding method, an injection molding method, and an extrusion molding method are utilized.
According to the compaction molding method, a magnet is manufactured by filling the compound in a pressing mold, compressing it to form a molding, and then heating the molding for hardening when the binding resin is a thermosetting resin. This method is advantageous in increasing the amount of the magnetic powder in the manufactured magnet and improving magnetic characteristics thereof because the magnet can be molded with a smaller amount of the binding resin than required in the other methods.
According to the extrusion molding method, a magnet is manufactured by extruding the compound, which has been heated into a molten state, through a die of an extruder, hardening an extrusion under cooling, and then cutting it into a desired length. This method is advantageous in being flexibly adapted for various shapes of magnets and enabling even thin or long magnets to be easily manufactured. To ensure the fluidity of the molten compound in the molding step, however, the amount of the added binding resin must be increased in comparison with that required in the compaction molding method. Therefore, the amount of the magnetic powder in the manufactured magnet is reduced and magnetic characteristics thereof are apt to deteriorate.
According to the injection molding method, the compound is heated into a molten state having sufficient fluidity, and the molten compound is poured into a mold for molding into a predetermined magnet shape. This method is advantageous in being more flexibly adapted for various shapes of magnets than the extrusion molding method and, in particular, enabling even magnets having different shapes to be easily manufactured. However, because the molten compound is required to have a higher level of fluidity in the molding step than the extrusion molding method, the amount of the added binding resin must be further increased in comparison with that required in the extrusion molding method. Therefore, the amount of the magnetic powder in the manufactured magnet is further reduced and magnetic characteristics thereof are apt to further deteriorate.
The binding resin for use in rare-earth bonded magnets is mainly divided into a thermoplastic resin and a thermosetting resin. Of these resins, the thermoplastic resin is superior because it is more advantageous in suppressing an increase of porosity and ensuring a high mechanical strength. Typical examples of the thermoplastic resin, which have hitherto been employed as the binding resin, are polyphenylene sulfides (PPS) and polyamides.
However, polyphenylene sulfides cannot be said as having good wettability with the rare-earth magnetic powder, and are inferior in moldability. Accordingly, if the polyphenylene sulfides are employed as the binding resin, the content of the binding resin in the compound must be increased. This leads to a difficulty in increasing the content of the rare-earth magnetic powder, i.e., in obtaining higher magnetic characteristics.
Furthermore, polyphenylene sulfides have the higher melting points and, in addition, have lower crystallizing rates than polyamides. This results in the necessity of raising the molding temperature and the necessity of prolonging the cooling time after the molding. In other words, the compound is necessarily subjected to a high-temperature environment for a longer time. During the manufacture of rare-earth bonded magnets, therefore, the rare-earth magnetic powder in the compound is likely to deteriorate due to oxidation, etc.
For those reasons, there is a limitation in obtaining rare-earth bonded magnets having superior magnetic characteristics when polyphenylene sulfides are employed as the binding resin.
Moreover, because polyphenylene sulfides have lower crystallizing rates than polyamides, a longer time is required until the rare-earth bonded magnets are hardened after the molding. Consequently, the cycle time is long and the production efficiency of the rare-earth bonded magnets is poor.
On the other hand, as the polyamides, polyamide 6 and polyamide 66 have been employed for the reason of easier availability.
However, polyamide 6 and polyamide 66 are inferior in stability of dimensions and shape. Stated otherwise, rare-earth bonded magnets using the polyamide 6 and the polyamide 66 as the binding resin are susceptible to changes in dimensions, shape, etc. during use for a long period. Accordingly, there is a limitation in using polyamides for magnets having applications in precision devices.
To overcome the above drawback, a rare-earth bonded magnet using polyamide 12 as the binding resin has been developed.
Because of having the lower melting point and softening temperature, however, such a rare-earth bonded magnet is inferior in heat resistance and hence has a difficulty in being employed under a high-temperature environment. Also, when such a rare-earth bonded magnet is used in a device generating heat such as a motor, there is a risk that the rare-earth bonded magnet may deform during a long period of use due to the heat generated from the device.
An object of the present invention is to provide a rare-earth bonded magnet which is superior in magnetic characteristics, shape stability and heat resistance, a rare-earth bonded magnet composition from which the rare-earth bonded magnet can be obtained, and a method of manufacturing the rare-earth bonded magnet.
DISCLOSURE OF THE INVENTION
The above object is achieved with the present invention set forth in the following (1) to (16)
(1) A rare-earth bonded magnet in which magnetic powder containing a rare-earth element is bonded together by a binding resin,
wherein the binding resin contains a high molecular compound comprising the following structure unit;
&Parenopenst;X—R—X—Y—Ar—Y&Parenclosest;
(where X is a functional group containing a nitrogen atom, Y is a functional group containing a carbonyl group, R is a normal-chain or branched alkylene group having a carbon number of 6-16, and Ar is an aromatic ring residue).
(2) A rare-earth bonded magnet in which magnetic powder containing a rare-earth element is bonded together by a binding resin,
wherein the binding resin contains a high molecular compound comprising the following structure unit;
&Parenopenst;X—R—X—Y—Ar—Y&Parenclosest;
(where X is a functional group containing a nitrogen atom, Y is a functional group containing a carbonyl group, R is a normal-chain or branched alkylene group having a carbon number of 9-16, and Ar is an aromatic ring residue).
(3) Preferably, the high molecular compound includes two or more kinds of the structure unit.
(4) Preferably, the melting point of the binding resin is 260-370° C.
(5) Preferably, the content of the magnetic powder is 77-99.5 wt %.
(6) In any one of the above (1) to (5), preferably, porosity is not more than 5 vol %.
(7) In any one of the above (1) to (6), preferably, the magnetic energy product (BH)
max
resulted when the bonded magnet is molded under no magnetic field is not less than 2 MGOe.
(8) In any one of the above (1) to (6), preferably, the magnetic energy product (BH)
max
resulted when the bonded magnet is molded under a magnetic field is not less than 10 MGOe.
(9) A rare-earth bonded magnet composition comprising magnetic powder containing a rare-earth element, and a binding resin,
wherein the binding resin contains a high molecular compound comprising the following structure unit;
&Parenopenst;X—R—X—Y—Ar—Y&Parenclosest;
(where X is a functional group containing a nitrogen atom, Y is a functional group containing a carbonyl group, R is a normal-chain or branched alkylene group having a
Akioka Koji
Nakamura Yoshiki
Harness & Dickey & Pierce P.L.C.
Koslow C. Melissa
Seiko Epson Corporation
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