Developer, development method, development device and its...

Electrophotography – Image formation – Development

Reexamination Certificate

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Details

C399S279000, C399S281000, C399S285000

Reexamination Certificate

active

06463246

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to developers, development methods, development devices and their elements, and image-forming devices, and more particularly to a nonmagnetic and single component developer, a development method using the nonmagnetic and single component developer, a development roller, a blade regulating a thickness of a nonmagnetic and single component developer layer on the development roller, a method for forming a nonmagnetic and single component developer layer using the blade, a development device having the development roller and the blade, and an electrophotographic image-forming device having one or more of these elements. The present invention is suitable for a color laser printer, for example.
Hereupon, the “nonmagnetic and single component developer” is a single component developer that is not magnetized and includes no carrier. The “electrophotographic image-forming device”, which is typically a laser printer, is a non-impact printer that provides recording by depositing a developer as a recording material on a recorded 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 machines, copiers, etc. have been spreading steadily. The electrophotographic process generally employs a photoconductive insulator (photosensitive drum), and includes the steps of charging, exposure to light, development, transfer, fixing, and other post processes.
The charging step uniformly electrifies the photosensitive drum (e.g., at −600 V). The exposure step irradiates a laser beam etc. onto 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 the developer onto the photosensitive drum using, for example, a 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 developer 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 recorded medium. The fixing step fuses and fixes the toner image on the recorded medium using the heat, pressure, etc., thereby obtaining a printed matter. The post processes may include a discharge and cleaning of the transferred photosensitive drum, a collection and recycle and/or disposal of residual toner, etc.
The developer for use with the aforementioned development step can be broadly divided into a single component system developer using the toner, and a binary component system developer using the toner and carrier. The toner may use 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 single component system developer advantageously results in (1) simple and miniature development equipment due eliminating a carrier deterioration, toner density control, mixing, and agitation mechanisms, and (2) used toner without any waste such as a carrier.
The single component system developer may be further classified into a magnetic and single component developer that includes toner in a magnetic powder, and nonmagnetic and single component developer that does not include the same. However, the magnetic and single component developer is disadvantageous in (1) the low transfer performance due to the high content of low electrical 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 and single component developer without these disadvantages is expected to be in increasing demand in future.
The nonmagnetic and single component developer commonly uses the toner having a relatively high volume resistivity (e.g., at 300 G&OHgr;·cm, etc.). In addition, the toner, as basically carrying no electric charges, needs to be charged by the triboelectricity or charge injection in the development device.
The development method employing the nonmagnetic and single component developer is divided into contact and noncontact development methods: The contact-type development method deposits a developer on the photosensitive drum by bringing the development roller carrying the developer into contact with the photosensitive drum; and the noncontact type development method 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 developer from the development roller to and deposits the same onto the photosensitive drum. Disadvantageously, the contact-type development method may deteriorate the developer by friction between the development roller and the photosensitive drum, and besides cause crack the photosensitive film, shortening the life of photosensitive body. Accordingly, the noncontact-type development method without these deteriorations has recently been highlighted.
It is significant for the noncontact-type development process employing the nonmagnetic and single component developer to ensure a sufficient image density by controlling the amount of toner flying from the development roller to the photosensitive drum. Thus, it is important to form a toner thin 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 an elastic blade (restriction blade) in contact with the development roller to maintain the layer thickness uniform.
The development equipment applying the noncontact-type development method employing the nonmagnetic and single component developer generally comprises a reset roller, a development roller, and a blade. The development roller is connected with a bias power supply, and provided with the development bias of superposed AC and DC voltages from the bias power supply. The reset roller, which is also called a supply roller or application roller, contacts the development roller: The reset roller serves not only to supply the toner to the development roller, and but also to scrape off and remove the toner unused for the development and remaining on the development roller. The development roller, which is, for example, a roller made of metal such as aluminum, adsorbs the charged toner on its surface in the form of the thin layer, and conveys it to a development area.
The blade contacts the development roller and serves to regulate the toner layer to a uniform thickness. The blade may be made up of one elastic member such as urethane, or of a metal member having a contact portion made of resin with the development roller. For instance, according to Japanese Patent Publications (Kokai) Nos. 8-202130 and 6-102748, when a metal member, namely a rigid member, is used for the development roller, the toner layer may be regulated by bringing a blade made of an elastic body such as rubber into contact with the development roller; on the other hand, when a member made of an elastic body such as rubber is used for a surface of the development roller, the toner layer may be regulated by bringing an end portion or non-end portion (namely midsection) into contact with the development roller. In order to avoid damaging the development roller and the blade by mitigating the accuracy in contact pressu

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