Electrophotography – Image formation – Development
Reexamination Certificate
2000-04-10
2002-04-23
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
C399S266000, C399S272000, C399S290000
Reexamination Certificate
active
06377768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to an apparatus and a method for inking a charge image via a toner sprayer for electrographic printer or copier or other like devices with high image carrier speed.
2. Description of the Prior Art
For developing electrostatic charge images or patterns printer devices having high image carrier speed, i.e. with an image carrier speed of 1 m per second and higher, developer systems are known that work with the assistance of two-component magnetic brush systems, with conductive single-component magnetic toner systems, with insulating non-magnetic single-component toner from a toner-air fluid, and with liquid developing systems.
The known two-component magnetic brush systems work with a mixture of toner particles and ferromagnetic carrier particles that triboelectrically charge one another. The soft-magnetic carrier particles form a brush in a magnetic field that is brought into direct contact with the charge image, for example on a photoconductor. The charged toner particles are deposited from the brush on the surface of the charge image-carrying element according to the distribution of the electrical field and of the toner charge. In order to achieve a high-quality image development, the toner particles must be very uniformly charged and the partially conductive brush must not discharge the photoconductor in contact. These conditions can only be met with great difficulty, particularly given a high developing speed and high toner throughput. Due to partial discharge of the photoconductor or inadequately uniform charging of all toner particles, undesired toner deposits, what is referred to as the background, therefore often occur. Due to the direct mechanical contact of the magnetic brush with the charge image-carrying element, moreover, a structuring of the toner image (what is referred to as brush marks) that has already been deposited or a fraying of image edges or a cavitation of large areas to be uniformly developed can arise.
Conductive one-component magnetic brush systems work without a carrier material. The toner particles themselves contain a ferromagnetic component. The toner particles form a brush structure in the magnetic field, charged toner particles being respectively located at the ends thereof. The charging of the toner particles ensues by charge transport from one toner particle to another proceeding from the carrier drum. A disadvantage of this developing method is that the ferromagnetic material component noticeably limits the color reproducibility of these toners. Moreover, the inking power (optical density) is often limited in that, due to the conductivity of the particle brush, only the respectively last particles are deposited and too weakly charged particles are picked up again. Further, the conductivity of the toner particles leads to limitations in the transfer from the photo conductor onto the ultimate image carrier onto a further intermediate carrier, particularly given electrostatic toner transfer.
When developing with insulating, non-magnetic one-component toner from a toner-air fluid, as known from E European Patent Document No P 04 94 454 B 1, toner is fluidized in a uniform air stream and charged in this fluid by a corona discharge, The charged toner is deposited on a conductive drum to which it adheres by electrostatic forces. The toner can leap from the drum surface onto a surface with a charge image corresponding to the topical electrical field distribution and can thus develop an image-by-image toner image. One or more additional drums can be inserted between the aforementioned drum and the surface carrying the charge image in order to separate the toner particles having the correct charge polarity and the adequate charge amount from toner particles that are less charged or are charged with the wrong polarity. Given this development process, the obtainable image quality is physically limited both in view of the uniformity of the inking distribution as well as in view of the detail sharpness.
Added outlays also arise for stabilization of the fluid, the stability thereof decreasing with the function duration as a consequence of the electrical interactions.
In liquid developing systems, fine toner particles are dispersed in a carrier fluid in which they electrostatically charge compared to the particle environment in the liquid. The developer liquid is usually brought into contact with the surface of the element carrying the charge image (for example, photoconductor). The charged toner particles migrate in the direction that is prescribed by the electrical field and the toner charge. The “damp” toner image is then transferred onto the ultimate image carrier (usually paper). The remaining liquid then escapes from the toner image (ultimate image carrier) into the ambient air. This is a considerable disadvantage when the liquid is an organic solvent like the other isopars employed as carrier liquid. Liquid toner systems are also known wherein a highly concentrated solution of highly charged particles leaps—under the influence of an electrical field—from an application drum surface onto those surface regions of the element carrying the charge image to which the electrostatic field vector points, this being formed of the field vector and the toner charge in the liquid. These systems have likewise the disadvantage that organic solvents are employed as carrier liquids.
U.S. Pat. No. 4,481,903 discloses an apparatus for developing a latent electrostatic on a recording medium. The apparatus contains two brushes serving as charging device for the toner, these brushes having deflectable bristles that mechanically hurl the charged toner particles against a developer drum such that a toner layer is formed on the circumferential surface thereof. The toner adhering to the developer drum is then transported into the region of a developing gap where, after overcoming the developing gap, it inks the latent charge image on the recording medium.
SUMMARY OF THE INVENTION
An object of the invention is therefore to offer an apparatus and a method for low-disturbance development of a charge image given high image carrier speed in a printer or copier or other like device.
In the inventive developing apparatus, a uniform, homogeneous toner layer is first generated by powder coating on an application element, such as a drum. Subsequently, this toner layer is transferred in charge-image dependent fashion onto a carrier medium conducted past in close proximity. In particular, the individual toner particles leap over the developing gap and thus ink the charge image located on the carrier medium.
A low-disturbance inking of the charge image is possible on the basis of this principle even given a high image carrier speed (speed of the carrier medium of 1 m/sec. or higher). Both one-component toner as well as multi-component toner can be utilized as toner. The employment of one-component toner has the advantage that the toner can be chromatically mixed in the developer device given employment of the inventive developer device in color printer devices.
Toner sprayer device as known from powder coating systems can be employed in the invention. Such powder coating guns are disclosed, for example, by U.S. Pat. Nos. 5,482,214 and 4,802,625 that are incorporated herein by reference.
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Hulin Jean-Philippe
Muenz Manfred
Schleusener Martin
Wiedemer Manfred
Grainger Quana M.
Oce Printing Systems GmbH
Schiff & Hardin & Waite
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