Electrophotography – Image formation – Development
Reexamination Certificate
2002-01-10
2004-03-02
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Development
C399S236000, C399S270000, C399S272000, C399S274000, C399S277000
Reexamination Certificate
active
06701114
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a copier, printer, facsimile apparatus or similar image forming apparatus and an image forming process unit removably mounted thereto. More particularly, the present invention relates to a developing device included in the image forming apparatus or the image forming process unit. The developing device is of the type including a rotatable, nonmagnetic developer carrier and means for forming a magnetic field that causes a developer made up of toner and magnetic grains to rise on the developer carrier in the form of a magnet brush in a developing region where the developer carrier faces an image carrier.
2. Description of the Background Art
Generally, an electrophotographic image forming apparatus includes an image carrier implemented as a photoconductive drum or a photoconductive belt. A developing device develops a latent image electrostatically formed on the image carrier to thereby produce a corresponding toner image. It is a common practice with this type of image forming apparatus to use either one of a one-ingredient type developer or toner and a two-ingredient type developer, i.e., a mixture of toner and magnetic grains. Development using the two-ingredient type developer features desirable image transferability and desirable developing characteristics against temperature and humidity. The two-ingredient type developer forms brush chains on a developer carrier in a developing region where the developer carrier faces an image carrier. The toner is fed from the developer on the developer carrier to a latent image formed on the image carrier.
As for development using the two-ingredient type developer, a decrease in the distance between the image carrier and the developer carrier in the developing region allows high image density to be easily attained and reduces the so-called edge effect. This, however, is apt to cause the trailing edge of a black solid image or that or a halftone solid image to be lost. Let this undesirable phenomenon be referred to as the omission of a trailing edge hereinafter. Further, horizontal thin lines appear smaller in width than vertical thin lines when developed. In addition, solitary dots are unstable in shape when developed.
To solve the above problems, Japanese Patent Laid-Open Publication No. 2000-305360, for example, proposes to limit a flux density distribution on a developing sleeve in a direction normal to the sleeve. The limited flux density distribution reduces the width of a developing region, or nip width, in the direction of rotation of the sleeve or increases the developer density of a magnet brush in the developing region.
On the other hand, assume that use is made of nonmagnetic toner. Then, when a developing sleeve rotates, the resulting centrifugal force is apt to cause the toner deposited on the sleeve to fly about. While the nonmagnetic toner may be replaced with magnetic toner, not only usual, electrostatic attraction but also a magnetic force that urges the magnetic toner away from the photoconductive drum act between the toner and the magnetic grains. This again brings about the defects stated earlier.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 5-40410, 10-48958, 11-72998, and 2000-231258.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a developing device capable of obviating the scattering of toner and the omission of a trailing edge and other defects even when a developer carrier moves at a high linear velocity.
It is another object of the present invention to provide an image forming apparatus including the developing device.
It is still another object of the present invention to provide an image forming process unit including the developing device.
It is a further object of the present invention to provide an image forming apparatus including the image forming process unit.
An image forming apparatus of the present invention includes a developing device including a rotatable, nonmagnetic developer carrier and a magnetic field forming device. In a developing region where the developer carrier faces an image carrier, the magnetic field forming device causes a developer made up of toner and magnetic grains to rise on the developer carrier in the form of a magnet brush. In the developing region, the magnet brush on the developer carrier is caused to move at a higher speed than the surface of the image carrier in the same direction as and in contact with the surface of the image carrier, thereby developing the latent image. The toner of the developer is magnetic toner. Flux density set up in the developing region outside of the surface of the developer carrier in a normal direction has an attenuation ratio of 50% or above.
An image forming process unit having the above configuration is also disclosed.
REFERENCES:
patent: 4766458 (1988-08-01), Oka et al.
patent: 5109254 (1992-04-01), Oka et al.
patent: 5227842 (1993-07-01), Hayashi et al.
patent: 5327199 (1994-07-01), Sekine
patent: 5416568 (1995-05-01), Yoshiki et al.
patent: 5557382 (1996-09-01), Tatsumi et al.
patent: 5598254 (1997-01-01), Ikesue et al.
patent: 5734953 (1998-03-01), Tatsumi
patent: 5758241 (1998-05-01), Oyama et al.
patent: 5765079 (1998-06-01), Yoshiki et al.
patent: 5774772 (1998-06-01), Kai et al.
patent: 5828935 (1998-10-01), Tatsumi et al.
patent: 5887224 (1999-03-01), Mizuishi et al.
patent: 5915143 (1999-06-01), Watanabe et al.
patent: 5915155 (1999-06-01), Shoji et al.
patent: 6006050 (1999-12-01), Watanabe et al.
patent: 6055388 (2000-04-01), Watanabe et al.
patent: 6081684 (2000-06-01), Naganuma et al.
patent: 6125243 (2000-09-01), Shoji et al.
patent: 6208826 (2001-03-01), Yoshinaga et al.
patent: 6266501 (2001-07-01), Mizuishi et al.
patent: 6295437 (2001-09-01), Hodoshima et al.
patent: 6335137 (2002-01-01), Suzuki et al.
patent: 6337957 (2002-01-01), Tamaki et al.
patent: 6366751 (2002-04-01), Shakuto et al.
patent: 6385423 (2002-05-01), Kai
patent: 6403275 (2002-06-01), Kuramoto et al.
patent: 6442364 (2002-08-01), Kai et al.
patent: 6449452 (2002-09-01), Kai
patent: 6456806 (2002-09-01), Shoji et al.
patent: 6468706 (2002-10-01), Matsuda et al.
patent: 6505014 (2003-01-01), Aoki et al.
patent: 6507718 (2003-01-01), Ohjimi et al.
patent: 0 738 937 (1996-10-01), None
patent: 1 030 229 (2000-08-01), None
patent: 5-40410 (1993-02-01), None
patent: 6-194961 (1994-07-01), None
patent: 10-31364 (1998-02-01), None
patent: 10-48958 (1998-02-01), None
patent: 11-72998 (1999-03-01), None
patent: 2000-231258 (2000-08-01), None
patent: 2000-305360 (2000-11-01), None
Ikeguchi Hiroshi
Kai Tsukuru
Sekine Takeyoshi
Oblon, Spivak, McClelland, Maier & Neustadt PC
Pendegrass Joan
Ricoh & Company, Ltd.
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