Electrophotography – Image formation – Development
Reexamination Certificate
2000-04-20
2001-11-27
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06324372
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnet roller, a process for producing the magnet roller and a developing unit using the magnet roller. More particularly, the present invention is concerned with a magnet roller which is lowered in production cost by a curtailment of the amount of a composition for magnets to be used, is suppressed in lowering of magnetic force due to voids, and is well suited for use in a developing mechanism portion and the like in image formation apparatuses; a process for efficiently producing the aforesaid magnet roller; and a developing unit equipped with said magnet roller.
2. Description of the Related Arts
There is known, in the field of electrophographic equipment and electrostatic recording equipment such as copying machinery and printers, a method for visualizing an electrostatic latent image by locating a magnet roller which is formed with a composition for a magnet in a rotating sleeve as a developing roller for the purpose of visualizing an electrostatic latent image on a latent image holding body such as a photosensitive drum and by supplying the surface of the latent image holding body with a magnetic developer (toner) through a so-called jumping phenomenon that allows the toner which is held on the surface of the sleeve to jump over onto the latent image holding body by means of the magnetic characteristics of said magnet roller.
The above-mentioned magnet roller is constituted of a shaft portion and a magnet main body portion composed of a composition for magnets. The types of said magnet rollers include, for instance, (1) integrated shaft type in which the magnet main body portion and the shaft portion are integrally molded with a composition for magnets; (2) one side inserted shaft type in which the magnet main body portion and the shaft portion on one side are integrally molded with a composition for magnets and a shaft is inserted on the other side; (3) both sides inserted shaft type in which the magnet main body portion is molded with a composition for magnets and shafts are respectively inserted on both the sides;and (4) penetrated shaft type in which the magnet main body portion is molded with a composition for magnets and a shaft is penetrated therethrough.
In regard to a process for producing such a magnet roller, there is prevailingly employed a process which comprises molding a magnet main body portion by injection molding or extrusion molding of a composition for magnets in which magnetic powders are mixed with a thermoplastic resin binder composed principally of nylon or polypropylene, by the use of a mold which has generated a magnetic field on the circumference of a cavity thereof to mold the composition into the form of a roller and magnetize to desired magnetic force characteristics.
The process for forming a magnet main body portion by injection molding or extrusion molding by means of a mold in the above-mentioned manner, is involved in such problems that since the magnet main body portion to be obtained is compacted with a composition for magnets, the amount of said composition to be used is unfavorably increased, thus causing inevitably high cost of said main body and besides, the vicinity of the outside periphery thereof is usually liable to contain unfavorable voids, thereby often resulting in deteriorated magnetic force.
SUMMARY OF THE INVENTION
In such circumstances, a general object of the present invention is to provide a magnet roller which is lowered in production cost by a curtailment of the amount of a composition for magnets to be used, is suppressed in lowering of magnetic force due to voids, and is well suited for use in a developing mechanism portion and the like in image formation apparatuses; a process for efficiently producing the aforesaid magnet roller; and a developing unit equipped with said magnet roller.
Other objects of the present invention will be obvious from the text of this specification hereinafter disclosed.
In order to attain the above-mentioned object, intensive extensive research and investigation were accumulated by the present inventors. As a result, it has been found that said objects can be achieved by a magnet roller wherein a magnet main body portion has at least one hollow portion in the inside thereof and in particular, voids are substantially absent in the vicinity of the outside periphery of said magnet main body portion, but are present on the periphery of said hollow portion.
It has also been found that the above-mentioned magnet roller can easily be produced by arranging in advance, at least one member for forming the hollow portion in a cavity of a mold which has generated a magnetic field on the circumference of a cavity thereof, pouring a composition for resin magnets into said mold, and thereafter withdrawing said member for forming said hollow portion. In addition, by paying attention to the fact that voids are more apt to be generated on higher temperature side of the magnet main body portion, it has also been found that voids are caused to be substantially absent in the vicinity of the outside periphery of said magnet main body portion, but to be present on the periphery of said hollow portion by causing the temperature of said member for forming the hollow portion to be higher than the temperature of the wall surface of the mold. The present invention has been accomplished by the foregoing findings and information.
Specifically the present invention provides:
(1) a magnet roller which comprises a magnet main body portion and a shaft portion, wherein said magnet main body portion comprises a composition for magnets and has at least one hollow portion in the inside thereof;
(2) the magnet roller as set forth in item (1), wherein voids are substantially absent in the vicinity of the outside periphery of said magnet main body portion, but are present on the periphery of said hollow portion;
(3) a process for producing a magnetic member comprising a magnet main body portion and a shaft portion, which comprises arranging in advance, at least one member for forming a hollow portion in a cavity of a mold which has generated a magnetic field on the circumference of a cavity thereof, pouring a composition for resin magnets into said mold, and thereafter withdrawing said member for forming said hollow portion so as to form at least one hollow portion in the inside of said magnetic member;
(4) the process for producing a magnetic member as set forth in item (3), wherein a heat conductive material is used as the member for forming a hollow portion, the temperature of said member is kept higher than the temperature of the wall surface of the mold, and the the composition for resin magnets is poured into said mold;
(5) a developing unit which comprises a developing roller constituted of a sleeve installed in a freely rotatable manner and a magnet roller installed inside said sleeve; preserves a magnetic developer on the surface of said sleeve by the magnetic characteristics of said magnet roller; forms a thin layer having a prescribed thickness from said magnetic developer by means of a layer forming blade; allows the magnet roller to contact or approach the surface of an image forming body in the above-mentioned state so as to feed said magnetic developer from the sleeve to the surface of the image forming body by the magnetic characteristics of said magnet roller; and thus forms a visible image on the surface of said image forming body, characterized in that the magnet roller in any of the items (1) and (2) is brought into use.
REFERENCES:
patent: 5570167 (1996-10-01), Kuroda
patent: 5583473 (1996-12-01), Yamashita
patent: 5740509 (1998-04-01), Hibi et al.
patent: 5946535 (1999-08-01), Aoki
patent: 6125255 (2000-09-01), Litman et al.
patent: 6132634 (2000-10-01), Nishimuro et al.
patent: 08-162320 (1996-06-01), None
patent: 08-162319 (1996-06-01), None
Bridgestone Corporation
Grimley Arthur T.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Hoan
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