Compositions – Magnetic – Iron-oxygen compound containing
Reexamination Certificate
1999-09-23
2001-09-04
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
Iron-oxygen compound containing
C252S062570, C252S06251C, C252S062590, C252S062580, C264S427000, C492S008000
Reexamination Certificate
active
06284150
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-performance 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 and having a higher residual magnetic flux density Br (or higher residual magnetic flux density Br and coercivity iHc) than those of the conventional Sr and/or Ba ferrite powders, and a ferrite powder used therefor and a method for producing such a bonded magnet and a ferrite powder, more particularly to a magnet roll composed of such a high-performance bonded magnet and a method for producing such a magnet roll.
BACKGROUND OF THE INVENTION
As well known, bonded magnets are lighter in weight and higher in dimensional accuracy than sintered magnets and suitable for mass production of articles having complicated shapes, and therefore they are widely used for various magnet applications. Recently, magnet-applied products have been drastically miniaturized and reduced in weight, requiring high-performance ferrite bonded magnets having a higher Br (or higher Br and iHc) suitable for miniaturization and reduction in weight.
Conventional Sr and/or Ba ferrite bonded magnets are obtained by bonding Sr and/or Ba ferrite powder having a composition represented by AO.nFe
2
O
3
, wherein A is Sr and/or Ba, and n=5-6, with binders such as thermoplastic polyolefin resins or rubbers, advantageous in low cost. However, the ferrite bonded magnets are lower in Br and maximum energy product (BH)
max
than sintered ferrite magnets to the extent of volume increase due to non-magnetic portions occupied by binders. To obviate this disadvantage, various attempts have been made conventionally to improve the orientation of a ferrite powder by a magnetic field or a mechanical stress applied for a ferrite powder orientation, and to improve the filling of a ferrite powder in binders. As a result, it is almost considered that no further improvement in magnetic properties would be able to be achieved in bonded magnets comprising a ferrite powders having conventional compositions.
If the filling ratio of a ferrite powder in rubbers or plastics is increased to improve the magnetic properties of bonded magnets, the resultant blends would have extremely high melt viscosity. Even though high-melt viscosity blends are subjected to practical orientating magnetic field or mechanical stress, it would be difficult to obtain bonded magnets having well-oriented ferrite powder. This difficulty is remarkable in an injection molding method, though it is appreciable in an extrusion method and a compression molding method, too. Though the orientation of a ferrite powder in the ferrite bonded magnets is improved by increasing the filling ratio of a ferrite powder in rubbers or plastics, such improvement inevitably causes the deterioration of magnetic properties, failing to satisfy the demand of miniaturization and reduction in weight.
To obviate such problems of conventional technology, it is effective to improve the saturation magnetization &sgr;s or crystal magnetic anisotropy constant of a ferrite powder for bonded magnets. Improvement in &sgr;s directly leads to improvement in coercivity Hc (or iHc). Incidentally, the conventional a ferrite powder for bonded magnets having a composition of AO.nFe
2
O
3
has a magnetoplumbite-type crystal structure, and W-type ferrite having larger &sgr;s than a ferrite powder having a magnetoplumbite-type crystal structure has also been investigated. However, the mass production of the W-type ferrite cannot be materialized so far due to difficulty in the control of a sintering atmosphere.
Japanese Patent Laid-Open No. 9-115715 discloses a ferrite powder for bonded magnets having a main phase constituted by a hexagonal magnetoplumbite-type ferrite represented by the general formula: A
1-x
R
x
(Fe
12-y
M
y
)
z
O
19
, wherein A is at least one element selected from the group consisting of Sr, Ba, Ca and Rb, R is at least one of rare earth elements including Y, La being indispensable, M is Zn and/or Cd, and x, y and z are molar ratios meeting the conditions of 0.04≦x≦0.45, 0.04≦y≦0.45, and 0.7≦z≦1.2. Investigation by the inventors has revealed, however, that it is difficult to obtain bonded magnets having high Br and iHc (for instance, exceeding 3.5 kOe) from this a ferrite powder for bonded magnets.
Accordingly, an object of the present invention is to provide a high-performance bonded magnet having a magnetoplumbite-type crystal structure suitable for mass production, which has higher Br (or higher Br and iHc) than those of conventional Sr and/or Ba ferrite bonded magnets, a magnet roll composed of such a bonded magnet, a ferrite powder used for such a bonded magnet, and methods for producing them.
DESCRIPTION OF THE INVENTION
The inventors have paid attention to the fact that by adding metal compounds (for instance, a combination of a La oxide and at least one oxide of Co, Mn, Ni and Zn, or a combination of a rare earth oxide mixture based on a La oxide as a main component and containing oxides of Nd, Pr, Ce, etc. and an oxide of Co and/or Zn), which have not been conventionally tried, to ferrite represented by AO.nFe
2
O
3
, wherein A is Sr and/or Ba, and n is 5-6, part of A and Fe elements in the above ferrite can be substituted by the metal elements in the metal compounds added, resulting in a ferrite powder suitable for bonded magnets, which has a magnetoplumbite-type crystal structure with a higher saturation magnetization and coercivity than those of conventional Sr and/or Ba ferrite powder.
The magnetism of this magnetoplumbite-type a ferrite powder is derived from a magnetic moment of Fe ions, with a magnetic structure of a ferri-magnet in which magnetic moment is arranged partially in antiparallel by Fe ion sites. There are two methods to improve the saturation magnetization in this magnetic structure. The first method is to replace the Fe ions at sites corresponding to the antiparallel-oriented magnetic moment with another element, which has a smaller magnetic moment than Fe ions or is non-magnetic. The second method is to replace the Fe ions at sites corresponding to the parallel-oriented magnetic moment with another element having a larger magnetic moment than Fe ions.
Also, increase in a crystal magnetic anisotropy constant in the above magnetic structure can be achieved by replacing Fe ions with another element having a stronger interaction with the crystal lattice. Specifically, Fe ions are replaced with an element in which a magnetic moment derived from an orbital angular momentum remains or is large.
With the above findings in mind, research has been conducted for the purpose of replacing Fe ions with various elements by adding various metal compounds such as metal oxides. As a result, it has been found that Mn, Co and Ni are elements remarkably improving magnetic properties.
However, the mere addition of the above elements would not provide a ferrite powders with filly improved magnetic properties, because the replacement of Fe ions with other elements would destroy the balance of ion valance, resulting in the generation of undesirable phases. To avoid this phenomenon, ion sites of Sr and/or Ba should be replaced with other elements for the purpose of charge compensation. For this purpose, the addition of at least one of La, Nd, Pr, Ce, etc., particularly La, is effective. That is, it has been found that a ferrite powder produced by the addition of an R element compound based on La and an M element compound (at least one of Co, Mn, Ni and Zn) provides bonded magnets having higher Br (or higher Br and iHc) than those of the conventional Sr and/or Ba ferrite bonded magnets. It has also been found that bonded magnets formed by using a ferrite powder produced by the addition of an R element compound based on La and a Co element compound and/or a Zn compound has well-balanced Br and iHc, particularly suitable for magnet rolls.
Further investigation
Kubota Yutaka
Ogata Yasunobu
Shiina Shuichi
Takami Takashi
Hitachi Metals Ltd.
Koslow C. Melissa
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Bonded magnet, magnet roll, a ferrite powder used therefor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bonded magnet, magnet roll, a ferrite powder used therefor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bonded magnet, magnet roll, a ferrite powder used therefor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2475335