Electrophotography – Image formation – Development
Reexamination Certificate
1999-11-23
2001-03-20
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Development
C399S279000, C399S285000, C399S288000
Reexamination Certificate
active
06205313
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a development apparatus for printing apparatuses and machines.
2. Description of Related Art
Generally, electrophotographic printing includes charging a photoconductive member to a substantially uniform potential. This sensitizes the surface of the photoconductive member. The charged portion of the photoconductive surface is then exposed to a light image from either a modulated light source or from light reflected from an original document being reproduced. This creates an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is created on the photoconductive surface, the latent image is developed. Two component and single component developer materials are commonly used to develop the electrostatic latent image.
A typical two component developer comprises magnetic carrier granules and toner particles that adhere triboelectrically to the magnetic carrier granules. In contrast, a single component developer material typically comprises only toner particles. The toner particles are attracted to the latent image recorded on the photoconductive surface to form a developed image on the photoconductive surface. The developed image is then transferred to a copy sheet. Subsequently, the toner powder image is heated to permanently fuse the toner powder image to the copy sheet.
One method to transport toner particles in a development system in a manner that ensures a uniform dispersion of the toner particles on the resulting copy page is through the use of traveling waves. For example, U.S. Pat. No. 4,647,179 to Schmidlin, incorporated herein by reference in its entirety, generates a traveling wave by alternating voltages of three or more phases applied to a linear array of conductors placed about the outer perimeter of a toner particle conveyor. In this development apparatus, the force F for moving the toner particles about the conveyor is equal to QE
t
, where Q is the charge on the toner particles and E
t
is the tangential force supplied by multiphase alternating current voltage applied to the array of conductors.
A magnetic brush supplies toner particles to the conveyor. The magnetic brush rotates in the same direction as the traveling wave. This gives an initial velocity to the toner particles that enables toner particles having a much lower charge to be propelled by the wave sufficiently to reach the charged photoconductor surface.
Another apparatus for transporting charged toner particles in a predetermined path is disclosed in U.S. Pat. No. 5,893,015 to Mojarradi et al., incorporated herein by reference in its entirety. The incorporated 015 patent discloses an apparatus that includes a donor member adapted to move charged particles on its surface in a predetermined path. The donor member includes an electrode array on its outer surface. The electrode array includes a plurality of spaced apart electrodes extending substantially across the width of the surface of the donor member. The 015 patent further discloses a multiphase direct current voltage source operatively coupled to the electrode array. The phases are shifted with respect to each other to create an electrodynamic wave pattern capable of moving charged particles on the surface of the donor member in a predetermined path.
SUMMARY OF THE INVENTION
The disadvantages of two component development systems described above include an inability to consistently control toner particle concentration, a failure to provide uniform mixtures of toner particles and carrier particles, carrier aging problems, and the need to triboelectrically adhere the toner particles to the carrier particles. Furthermore, the carrier particles of two component developer materials produce granularity, i.e., noise, in the resulting image on the copy page. The granularity, or noise, is directly proportional to the size of the carrier particles.
Single component developer materials comprising only toner particles tend to reduce these problems. Additionally, the granularity of the resulting image becomes solely a function of the diameter of the toner particles. However, when using a single component developer material, it becomes difficult to ensure that the toner particles are properly metered out, uniformly charged, and effectively transported in a manner that ensures a uniform dispersion of the toner particles on the resulting copy page.
This invention provides apparatuses, systems and methods that deliver charged toner particles to an image development zone without using carrier particles.
This invention separately provides apparatuses, systems and methods that eliminate the need for toner particle concentration controls in a charged toner particle delivery system.
This invention separately provides charged toner particle delivery systems that have a substantially simplified design.
This invention separately provides charged toner particle delivery systems with no carrier add mix problems, no carrier aging problems, and no carrier tribo matching requirements.
This invention separately provides charged toner particle delivery systems that enable greater simplicity and latitude in developing high-quality images.
This invention separately provides charged toner particle delivery systems that provide a simple, economic single component development (SCD) system and process.
In accordance with the apparatuses, systems and methods of this invention, one exemplary embodiment of the charged toner particle delivery systems according to this invention uses a gravure roll member that is adapted to charge toner particles contained in cups or grooves on its surface. The gravure roll member includes an electrically conductive core having a relaxable coating layer, formed, for example, of urethane, polycarbonate, ceramic, or the like.
The relaxable coating layer acts as an insulator during a toner charging period, and has a relaxation time that allows acquired charges to be dissipated as the gravure roll member rotates through a cycle. In various exemplary embodiments, the relaxable coating layer has a thickness of greater than about five times the toner particle diameter. With this thickness, the major factor determining the polarity and charge value of the individual toner particles becomes the relaxation layer, rather than the toner particle diameter.
The gravure roll member also has toner retaining elements, such as, for example, grooves or cups, on its outer surface. In various exemplary embodiments, the toner retaining elements have a depth less than three times the toner particle diameter. This tends to minimize shadowing of the toner particles during the toner charging step. In various exemplary embodiments, the toner retaining elements have a depth of approximately twice the diameter of the toner particles.
Other exemplary embodiments of this invention include an apparatus that develops a latent image recorded on an imaging surface including a chamber storing a supply of developer material comprising uncharged toner particles, and the gravure roll member described above, spaced from the image surface, and adapted to transport toner particles on the surface of the gravure roll member to a region opposed to the imaging surface.
Other exemplary embodiments of this invention include an electrophotographic image forming machine that develops an electrostatic latent image recorded on an imaging surface of a photoconductive member to form a visible image. The electrophotographic image forming machine includes a housing defining a chamber that stores a supply of developer material, and the gravure roll member described above, spaced from an image surface. The developer material includes uncharged toner particles. The gravure roll member is adapted to transport the toner particles on its surface to a region opposed to the imaging surface.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of various exemplary embodiments of the systems and methods of this invention.
REFERENC
Grimley Arthur T.
Oliff & Berridg,e PLC
Tran Hoan
Xerox Corporation
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