Electrophotography – Image formation – Development
Reexamination Certificate
2002-07-05
2003-12-02
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Development
C399S274000, C399S282000, C399S284000
Reexamination Certificate
active
06658227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a development method and apparatus for use in image formation apparatus such as printers, facsimiles and copiers, and also relates to an image formation apparatus and a process cartridge. More particularly, it relates to a development method of developing an electrostatic latent image formed on an image carrier using a developer held on a developer carrier to form a toner image on the image carrier at a development region (development nip region) between the developer carrier and the image carrier opposing thereto. The present invention further relates to a development apparatus for executing the development method, an image formation apparatus using the development apparatus and a process cartridge including the development apparatus mounted thereon.
BACKGROUND OF THE INVENTION
Conventionally known development systems for developing the electrostatic latent image on the image carrier in the development nip region are classified into a two-component development type and a one-component development type. The former employs a two-component developer that contains toner and magnetic particles to develop the electrostatic latent image. The latter employs a one-component developer consisting only of toner to develop the electrostatic latent image.
The two-component development system holds the two-component developer consisting of toner and magnetic particles in the form of a brush to form a magnetic brush on the surface of a developer carrier that contains magnets inside. When only toner from the magnetic brush is attached to the electrostatic latent image formed on the image carrier at the development region (development nip region) between the developer carrier and the image carrier opposed thereto, a toner image is formed on the image carrier. This two-component development system is known as an excellent development system because it has a stable and nice transfer property of toner images and development property against temperature and humidity.
In the one-component development system, on the other hand, the one-component developer consisting only of toner is held in the form of a uniform thin film on the surface of the developer carrier. The toner held on the surface of the developer carrier is opposed to an electrostatic latent image formed on the image carrier in a contact or non-contact state. When the toner attaches to the electrostatic latent image at the development region (development nip region) between the developer carrier and the image carrier opposing thereto, a toner image is formed an the image carrier. This one-component development system is known as an advantageous development system because it can provide an image with a high image quality and high resolution. The one-component development system does not employ the magnetic particles like the developer in the two-component development system and accordingly has no disadvantage to cause a development variation due to the magnetic brush that contacts with the surface of the image carrier. Therefore, it is possible to perform development that is highly faithful to the electrostatic latent image.
A development system that has advantages of the one- and two-component development types in combination has been proposed as a development apparatus that employs a developer carrier serving as a toner supplier member having a magnetic brush composed of a two-component developer formed on the surface. In the development apparatus, the magnetic brush on the toner supplier member is employed to supply a one-component developer composed only of toner to the developer carrier serving as a toner carrier (see Japanese Patent Application Laid-Open Nos. 56-40862 and 59-172662, for example).
In these development apparatus, the two-component developer is agitated in the development apparatus to hold the two-component developer on the toner supplier member (such as a magnetic roller and a magnetic brush forming member) to form a magnetic brush. The toner in the magnetic brush is charged to have a certain polarity through friction with magnetic particles. From the magnetic brush on the toner supplier member, only the toner charged to have a certain polarity is displaced to and held on the toner carrier (such as a development roller and a toner layer holding member).
This development apparatus can reduce the stress that is imparted on the toner carrier and the toner more effectively compared with the one-component development system. In addition, as it performs development in the one-component development system, a high image-quality same as that in the one-component development system can be achieved.
In any development systems, however, the above development apparatus have the following subject matters.
After the electrostatic latent image on the image carrier is developed (visualized), the developer layer on the developer carrier is divided into a toner-consumed layer and a toner-resided layer. In the toner-consumed layer, toner corresponding to the image section in the electrostatic latent image is consumed by the development. In the toner-resided layer, toner corresponding to the non-image section in the electrostatic latent image is resided, not consumed.
In such the development apparatus, a difference between the toner-consumed layer and the toner-resided layer occurs in an amount of toner held on the surface of the developer carrier. To resolve the difference in the amount of toner held on the developer carrier, it is required to supply a new toner to the toner-consumed layer through rotations of the developer carrier by an amount corresponding to the consumed amount. It is difficult in practice, however, to supply the new toner only to the toner-consumed layer on the surface of the rotating developer carrier. Accordingly, it is not possible to resolve the difference in the amount of toner held on the developer carrier using the method of simply supplying the new toner. As a result, such the development apparatus causes a hysteresis. For example, due to the difference in the amount of toner held on the developer carrier, an afterimage (ghost) appears as a density difference in an image at the time of a subsequent development.
In order to resolve such the hysteresis, it is effective to once remove the developer from a location in the surface of the developer carrier after developing (visualizing) the electrostatic latent image on the image carrier. A new developer is then supplied to the location in the surface of the developer to resolve the above-described difference in the amount of toner held on the surface of the developer carrier.
To execute such the method of removing and supplying the developer, the development apparatus requires a developer replacement unit which replaces the developer held on the developer carrier. The developer replacement unit may include a blade, scraper or brush roller as a unit which contacts with the surface of the developer carrier to mechanically remove the whole developer from the developer carrier. If such the unit is employed, however, the abrasion over time of the surface of the developer carrier changes the properties of carrying and holding the developer and invites a malfunction because toner spent is caused from the stress during removal. Also in this case, it is required to ensure a space for installing the blade, scraper or brush roller around the developer carrier, resulting in a larger body of the development apparatus.
An approach for resolving such the malfunction due to the use of the mechanical developer replacement unit employs an arrangement of magnetic poles of magnets arranged inside the developer carrier to remove the developer on the developer carrier magnetically. This approach can not be applied to the one-component development apparatus that employs non-magnetic toner, however, although it is effective in the two-component development apparatus and the one-component development apparatus that employs magnetic toner.
Japanese Patent Application Laid-Open No. 6-67546 proposes a development apparatus that can rem
Aoki Katsuhiro
Hodoshima Takashi
Kadota Ichiro
Kai Tsukuru
Miyoshi Yasuo
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pendegrass Joan
Ricoh Company Limited
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