Electrophotography – Image formation – Development
Reexamination Certificate
2000-12-18
2002-05-14
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S284000
Reexamination Certificate
active
06389258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to image-forming devices, and more particularly to a development device for use with the electrophotographic image-forming device. The present invention is suitable, for example, for a development device (including a development roller, a blade, and a reset roller) using a nonmagnetic monocomponent developing agent, and an electrophotographic image-forming device having the development device. 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 a developing agent as a recording material on a recordable medium (e.g., printing paper, and OHP film).
With the recent development of office automation, the use of electrophotographic image-forming devices such as a laser printer for computer's output devices, facsimile units, photocopiers, etc. has spread steadily. Particularly, an electrophotographic printer as an 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 (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 −780V). 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 −60 V or so, forming an electrostatic latent image. The development step electrically deposits a developing agent 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 agent 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 a 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 in diameter. The monocomponent developing agent advantageously results in: (1) simple and miniature equipment of the development device due to eliminating a 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) the low transfer performance due to the high content of low electrically resistant magnetic powder which hinders the increased electric charge amount; (2) the bad colorization due to its low transparent, black-color magnetic powder; (3) the low fixing performance due to the magnetic powder which requires high temperature and/or high pressure, increasing a running cost. Accordingly, the nonmagnetic monocomponent developing agent without these disadvantages is expected to be in increasing demand in future.
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, as basically carries no electric charge, needs to be charged by the triboelectrificity or charge injection in the development device.
The development process employing the nonmagnetic monocomponent developing agent is divided into contact- and noncontact-type development processes: the contact-type development process that deposits a developing agent on the photosensitive drum by bringing the development roller carrying the developing agent into contact with the photosensitive drum; and the noncontact-type development process 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 agent from the development roller to and deposits the same onto the photosensitive drum.
It is significant for the noncontact-type 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.
The noncontact-type development device employing the nonmagnetic monocomponent developing agent comprises a toner tank, an agitation paddle, a development roller, a reset roller, and a blade. The toner tank is configured to store toner required for printing, and to supply toner to the reset roller. The agitation paddle is provided in the toner tank, and serves to prevent the toner from agglomerating and coagulating by agitating the toner. The development roller adsorbs onto a surface thereof charged toner in the form of a thin layer, and conveys the toner to a development area in contact with the photosensitive drum. The development roller is connected with a bias power supply that applies a development bias. The reset roller, which is also called supply roller or application roller, contacts the development roller and supplies toner to the development roller. Further a reset bias is applied to the reset roller. The reset roller also serves to scrape off and remove the toner unused for the development and remaining on the development roller, and to collect the same to the toner tank for recycling.
The blade is brought into contact with the development roller, and serves to regulate the toner layer to a uniform thickness. A blade bias is applied to the blade, making the charge injection into toner possible. A toner layer on the development roller, if too thin, would result in a low and uneven image density, while, if too thick, would increase a proportion of oppositely charged or low charged toner, thereby producing a fog in a no-image area (i.e., undesirably coloring with the toner an area which has no image and is therefore expected to be white clarity). Thus, the blade is required to form a toner lay
Chen Sophia S.
Fujitsu Limited
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