Compositions – Magnetic – With wax – bitumen – resin – or gum
Reexamination Certificate
2000-12-11
2003-03-25
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
With wax, bitumen, resin, or gum
C252S062570, C252S062590, C252S062630, C252S062550, C148S301000
Reexamination Certificate
active
06537463
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a resin-bonded magnet useful for wide ranges of magnet applications such as various rotors, magnet rolls for electromagnetic developing-type printers and photocopiers, audio speakers, buzzers, attracting or magnetic field-generating magnets, which has a maximum energy product (BH)
max
at least equal to those of anisotropic, sintered ferrite magnets, improved magnetizability and/or heat resistance as compared with conventional resin-bonded rare earth magnets, as well as small unevenness in a surface magnetic flux density. The present invention also relates to a ferrite magnet powder and a compound both for such a resin-bonded magnet. The present invention further relates to a rotor and a magnet roll each constituted by such a resin-bonded magnet.
PRIOR ART
Recently R-Fe-N-H magnetic alloys including Sm
2
Fe
17
N
x
(x=2-6) magnet materials (U.S. Pat. No. 5,186,766) have come to be used as magnet materials replacing resin-bonded rare earth magnets comprising an isotropic or anisotropic magnet powder containing an Nd
2
Fe
14
B intermetallic compound as a main phase which have poorer magnetizability and high irreversible loss of flux, a measure of heat resistance, which is evaluated by a permeance coefficient. Resin-bonded rare earth magnets comprising Sm
2
Fe
17
N
x
, however are insufficient in heat resistance and magnetizability to satisfy the recent needs of smaller size and higher performance for magnet applications. Therefore, their improvements are desired.
WO 98/38654 (PCT/JP98/00764) discloses an anisotropic, resin-bonded magnet composed of a ferrite magnet powder containing a hexagonal ferrite as a main phase and having a composition comprising 1-13 atomic % of A (at least one element selected from the group consisting of Sr, Ba, Ca and Pb, Sr being indispensable), 0.05-10 atomic % of R (at least one element selected from the group consisting of rare earth elements including Y and Bi, La being indispensable), 80-95 atomic % of Fe, and 0.1-5 atomic % of M (Co or Co and Zn). An example of this anisotropic, resin-bonded magnet is a ferrite magnet powder having coercivity iHc of 4.31 kOe for anisotropic, resin-bonded magnet, which is produced by dry-pulverizing a calcined body having such a composition as to provide a final composition of Sr
0.7
La
0.3
Fe
12−7
Co
0.3
O
19
(0.2% by weight of SiO
2
and 0.15% by weight of CaCO
3
were added before calcining) by a vibration mill, and then annealing the pulverized material at 1,000° C. for 5 minutes in the air. This anisotropic, resin-bonded magnet having (BH)
max
less than those of anisotropic, sintered ferrite magnets is not satisfactory for use as a substitute for anisotropic, sintered ferrite magnets.
Japanese Patent Laid-Open No. 60-223095 discloses a field magnet constituted by a resin-bonded magnet comprising predetermined proportions of a hard ferrite magnet powder and a rare earth element-cobalt magnet powder bonded by a binder resin, assembled into a magnetic field apparatus for bubble memory device having a temperature coefficient of magnetic flux density of −0.03%/°C. to −0.20%/° C. Though this field magnet has a temperature coefficient of a magnetic flux density in the above range, it fails to have improved heat resistance, magnetizability and the like.
“Rare Metal News No. 1936” issued on Feb. 8, 1999 describes that magnetic properties can be improved, for instance, to (BH)
max
of 4-5 MGOe corresponding to the level of anisotropic, sintered ferrite magnets, by mixing an anisotropic Sm-Fe-N magnet powder and a ferrite magnet powder at predetermined proportions. However, the above reference makes no specific mention of the composition of the ferrite magnet powder. Investigation by the inventors has revealed that when a conventional Sm—Fe—N magnet powder for resin-bonded magnets and usual ferrite magnet powder (e.g. Sr-ferrite magnet powder) are compounded at predetermined proportions and bonded with a binder resin, the resultant resin-bonded magnet has (BH)
max
of 3.3 MGOe or more, equal to or more than those of anisotropic, sintered ferrite magnets and improved magnetizability and/or heat resistance, which are important in practical applications of magnets, as well as improved uniformity in a surface magnetic flux density.
OBJECTS OF THE INVENTION
Accordingly, an object of the present invention is to provide a resin-bonded magnet having improved magnetizability and/or heat resistance as compared with those of conventional resin-bonded rare earth magnets and further small unevenness in a surface magnetic flux density.
Another object of the present invention is to provide a ferrite magnet powder and a compound both for such a resin-bonded magnet.
A further object of the present invention is to provide a rotor and a magnet roll each constituted by such a resin-bonded magnet.
SUMMARY OF THE INVENTION
The ferrite magnet powder for resin-bonded magnets according to the present invention comprises powder obtained by disintegrating a sintered ferrite magnetic material, the sintered ferrite magnet powder having a substantially magnetoplumbite-type crystal structure and a basic composition represented by the following general formula:
(A
1−x
R′
x
)O.n[(Fe
1−y
M
y
)
2
O
3
] by atomic ratio,
wherein A is Sr and/or Ba; R′ is at least one selected from the group consisting of rare earth elements including Y, La being indispensable; M is Co or Co and Zn; and x, y and n are numbers meeting the following conditions:
0.01≦x≦0.4,
0.005≦y≦0.04, and
5.0≦n≦6.4.
The sintered ferrite magnet powder preferably contains SiO
2
and CaO in amounts of 0.05-0.55% by weight and 0.35-1% by weight, respectively, per 100% by weight of the sintered ferrite magnet powder, because such a ferrite magnet powder can provide a sintered body having a dense structure, which shows good magnetizability and/or heat resistance.
The sintered ferrite magnet powder preferably has an average particle size of 2-300 &mgr;m, because such a ferrite magnet powder is suitable for molding in a magnetic field.
The compound for resin-bonded magnets according to the present invention is composed substantially of:
(a) an R—T—N-based magnet powder having a basic composition of R
&agr;
T
100−&agr;−&bgr;
N
&bgr;
, wherein R is at least one selected from the group consisting of rare earth elements including Y; T is Fe or Fe and Co; and &agr; and &bgr; satisfy 5≦&agr;≦20 and 5≦&bgr;≦30 by atomic %,
(b) a ferrite magnetic powder for resin-bonded magnets comprising powder obtained by disintegrating a sintered ferrite magnetic material, said sintered ferrite magnetic powder having a substantially magnetoplumbite-type crystal structure and a basic composition represented by the following general formula:
(A
1−x
R′
x
)O.n[(Fe
1−y
M
y
)
2
O
3
] by atomic ratio,
wherein A is Sr and/or Ba; R′ is at least one selected from the group consisting of rare earth elements including Y, La being indispensable; M is Co or Co and Zn; and x, y and n are numbers meeting the following conditions:
0.01≦x≦0.4,
0.005≦y≦0.04, and
5.0≦n≦6.4.
(c) a binder.
By mixing and kneading the R—T—N-based magnet powder having an average particle size of 1-10 &mgr;m, the ferrite magnet powder having an average particle size of 0.9-2 &mgr;m (first ferrite magnet powder) and a binder at appropriate proportions, it is possible to obtain a compound capable of providing a resin-bonded magnet with good magnetizability and/or heat resistance.
By compounding and kneading, at appropriate proportions, the R—T—N-based magnet powder having an average particle size of 110 &mgr;m, the ferrite magnetic anisotropic, granulated powder (second ferrite magnet powder) and a binder, it is possible to obtain a compound capable of providing a resin-bonded magnet with good magnetizability and/or heat resistance and small unevenness in a surface magnetic flux density.
By mixing and kneading the R—T—N-based magnet powder having an
Iwasaki Katsunori
Ogata Yasunobu
Okajima Hiroshi
Shindo Mikio
Tobise Masahiro
Hitachi Metals Ltd.
Koslow C. Melissa
Sughrue & Mion, PLLC
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