Electrophotography – Image formation – Development
Reexamination Certificate
2001-01-22
2002-10-15
Beatty, Robert (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06466760
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to image-forming devices, and more particularly to a development device and development method for use with an electrophotographic image-forming device. The present invention also relates, for example, to a development method using a nonmagnetic monocomponent developing agent, development roller, and a blade that regulates a layer thickness of the nonmagnetic monocomponent developing agents on the development roller, and to a method of forming a layer thickness of the nonmagnetic monocomponent developing agents, on a development device wherein the development device has the development roller and the blade, and an electrophotographic image-forming device including one or more of these elements. However, it is to be understood that the scope of application of the present invention is not limited to devices using the nonmagnetic monocomponent developing agent.
The “nonmagnetic monocomponent developing agent” is a single component developing agent that is not magnetized and includes no carrier. The “electrophotographic image-forming device” is an image-forming device employing the Carlson process described in U.S. Pat. No. 2,297,691, as typified by a laser printer, and denotes a nonimpact printer that provides recording by depositing developing agents as a recording material on a recordable medium (e.g., printing paper, and OHP film).
The nonmagnetic monocomponent developing agent commonly includes the toner having a relatively high volume resistivity (e.g., at 300 G&OHgr;·cm, etc.). In addition, the toner, since it basically carries no electric charge, needs to be charged by the triboelectricity or charge injection in the development device.
With the recent development of office automation, the use of electrophotographic image-forming devices for computer output devices, facsimile units, photocopiers, etc. have spread steadily. Particularly, a laser printer as one example of the electrophotographic image-forming devices features good operability, usability for a wide range of media, high cost efficiency, and high printing quality, whereby a further improvement in high-quality and high-speed printability will be expected in future. The electrophotographic image-forming device generally includes a photoconductive insulator (photoconductor; photosensitive drum), and follows the procedural steps of charging, exposure to light, development, transfer, fixing, and other post-processes.
The charging step uniformly electrifies the photosensitive drum (e.g., at −700 V). The exposure step irradiates a laser beam, or the like, on the photosensitive drum, and changes the electrical potential at the irradiated area down, for example, to −50 V or so, forming an electrostatic latent image. The development step electrically deposits developing agents onto the photosensitive drum using, for example, the reversal process, and visualizes the electrostatic latent image. The reversal process is a development method that forms an electric field by a development bias in areas where electric charge is eliminated by exposure to light, and deposits the developing agents having the same polarity as uniformly charged areas on the photosensitive drum by the electric field. The transfer step forms a toner image corresponding to the electrostatic latent image on a recordable medium. The fixing step fuses and fixes the toner image on the medium using heat, pressure, or the like, thereby obtaining a printed output. The post-processes may include charge neutralization and cleaning on the photosensitive drum from which toner has been transferred out, a collection and recycle and/or disposal of residual toner, etc.
The developing agent for use with the aforementioned development step can be broadly divided into a monocomponent developing agent using toner and a dual-component developing agent using toner and a carrier. The toner may include a particle prepared, for example, in such a manner that a colorant, such as a dye and carbon black, or the like, is dispersed in a binder resin made of synthetic macromolecular compound, and then is ground into a fine powder of approximately 3 through 15 &mgr;m. A usable carrier may include, for example, an iron powder or ferrite bead of approximately 100 &mgr;m diameter. The monocomponent developing agent advantageously results in (1) simple and miniature equipment for the development device due to eliminating carrier deterioration, a toner density control, mixing, and agitation mechanisms, and (2) no residual waste, such as a carrier in used toner.
The monocomponent developing agent may be further classified into a magnetic monocomponent developing agent that includes a magnetic powder in toner, and a nonmagnetic monocomponent developing agent that does not include the same. However, the magnetic monocomponent developing agent is disadvantageous in: (1) low transfer performance due to the high content of low electrical resistant magnetic powder which hinders the increased electric charge amount; (2) bad colorization due to its low transparent, black-color magnetic powder; and (3) low fixing performance due to the magnetic powder which requires high temperature and/or high pressure, thereby increasing a running cost. Accordingly, the nonmagnetic monocomponent developing agent without these disadvantages is expected to be in increasing demand in future.
The development method employing the nonmagnetic monocomponent developing agent is divided into two development methods: one is a contact-type development method that deposits developing agents on the photosensitive drum by bringing the development roller carrying the developing agents into contact with the photosensitive drum; and the other is a jumping development method (noncontact-type development method) that provides a certain gap (e.g., of about 350 &mgr;m) between the development roller and the photosensitive drum to space them from each other, and flies the developing agents from the development roller to, and deposits the same onto, the photosensitive drum.
It is significant for the development process employing the nonmagnetic monocomponent developing agent to ensure a sufficient image density by controlling the amount of toner conveyed from the development roller to the photosensitive drum. Thus, it is very important to form a specified toner layer while controlling its thickness on the development roller. As a typical method for regulating a toner layer thickness, it has conventionally been proposed to provide a blade (restriction blade) in contact with the development roller to maintain the layer thickness uniform.
Referring now to
FIG. 8
, a description will be given of a contact-type development device
10
using a nonmagnetic monocomponent developing agent.
FIG. 8
is a schematic sketch of a principal part of the conventional development device
10
for explaining a bias applied to the development device
10
. As shown in
FIG. 8
, the development device
10
includes a development roller
12
, a reset roller
14
, and a blade
16
. The development roller
12
adsorbs onto a surface thereof charged toner as a thin layer, and conveys the toner to a development area in contact with the photosensitive drum. The development roller
12
is connected with a bias power supply (not shown) that applies a development bias V
b
. The reset roller
14
, which is also called a supply roller or application roller, contacts the development roller
12
and serves to supply toner to the development roller
12
. Further the reset roller
14
also serves to scrape off and remove the toner unused for the development and remaining on the development roller
12
. As shown in
FIG. 8
, a reset bias V
r
is applied to the reset roller
14
.
The blade
16
is brought into contact with the development roller
12
, and serves to regulate the toner layer to a uniform thickness. In order to avoid damaging the blade
16
and the development roller
12
by mitigating the accuracy in contact pressure required at the contact portion therebetween, it is so devised t
Armstrong Westerman & Hattori, LLP
Beatty Robert
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