Electrophotography – Internal machine environment – Forced air circulation
Reexamination Certificate
2001-11-13
2004-08-03
Tran, Hoan (Department: 2852)
Electrophotography
Internal machine environment
Forced air circulation
C399S093000, C399S097000, C399S098000
Reexamination Certificate
active
06771916
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to electrophotographic printing, and more particularly to apparatus and method for managing air quality within an electrophotographic printing machine.
BACKGROUND OF THE INVENTION
The aerial environment within modern high quality output electrostatographic color printing machines must be managed to provide efficient operation. Such color printing machines include a number of tandemly arranged electrostatographic imaging-forming modules. In each module of such a printing machine, a respective single-color toner image may be electrostatically transferred directly from a respective moving primary image-forming member to a moving receiver member, thereby successively building up a full-color toned image on the receiver. More typically, in each module of such an electrostatographic color printing machine, a respective single-color toner image is electrostatically transferred from a respective moving primary image-forming member, e.g., a photoconductive member, to a moving intermediate transfer member, and then subsequently electrostatically transferred from intermediate transfer member to a moving receiver member. In certain printing machines, the receiver member is moved progressively through the imaging-forming modules, wherein in each module the respective single-color toner image is transferred from the respective primary image-forming member to a respective intermediate transfer member and from thence to the moving receiver member, the respective single-color toner images being successively laid down one upon the other on the receiver member so as to complete, in the last of the modules, a full-color toner image, e.g., a four-color toner image, which receiver is then moved to a fusing station wherein the full-color toner image is fused to the receiver. Alternatively, the respective single-color toner images formed in respective modules are transferred atop one another to form a composite full-color toner image on the intermediate transfer member, and the composite image is then transferred to the moving receiver member, which receiver is subsequently moved to a fusing station where the composite image is fused to the receiver. In order to achieve a superior image quality in a modular electrostatographic color printer, important essential parameters include keeping levels of aerial contamination low, as well as providing a stable relative humidity and temperature for all the modules.
In a prior art color electrostatographic printing or color copying machine in which the internal relative humidity (RH) is unregulated, the RH inside such a machine depends upon the relative humidity in the ambient air surrounding the machine, i.e., the internal RH varies from day to day and from season to season. Moreover, even when the ambient relative humidity is stable, the RH inside a modular electrostatographic printer in which the interior environment is unregulated can vary substantially from module to module, and this can have serious consequences for image quality.
It is well known that relative humidity can have a strong influence on the charge-to-mass ratio of toner particles included in a developer for use in a toning station. Thus, if the RH varies within a given module of a modular printer in response to a change of ambient RH or ambient temperature, an image density produced by the corresponding toner on a receiver will also vary, unless well known countermeasures are taken, such as for example adjusting the imaging exposure of the corresponding photoconductive primary imaging member, or adjusting the charging voltage for corona sensitization of the corresponding photoconductive primary imaging member. More seriously, if in response to a change of ambient RH the relative humidity varies within all the toning stations included in the modules of a modular printer, the resulting variations of charge-to-mass ratio from module to module will generally be quite different, because a different developer composition is generally used for each color toning station, and the charge-to-mass ratio of each such developer composition has its own characteristic dependence upon RH. Therefore, unless the above-mentioned countermeasures are taken separately for each of the toning stations (which can be costly and cumbersome) a change of ambient RH in a printer in which the interior environment is unregulated will generally produce different amounts of resulting density change for the different colored toners in a full-color toner image, which is clearly undesirable.
Moreover, changes of RH can produce unwanted changes of photoconductive sensitivity, which changes may require compensation, e.g., by raising or lowering the charging voltage prior to an imaging exposure.
Similarly, changes of RH in a modular machine in which the interior environment is unregulated can produce unwanted changes of resistivity of intermediate transfer members, thereby affecting efficiency of dependent, and therefore changes of RH in a machine in which the interior environment is unregulated electrostatic toner transfer from primary imaging members to intermediate transfer members, and from intermediate transfer members to receiver members. For maintaining a constant transferred density of toner to a receiver, such changes of resistivity may require adjustments of applied voltages, which applied voltages are for example typically applied to intermediate members and to transfer rollers included in the modules.
Moreover, moisture absorption by paper receiver sheets typically causes swelling of the paper, and different sheets within an imaging run may be swelled to different degrees, e.g., depending on how receiver sheets are stacked in the machine prior to use. Swelling due to moisture may also be variable from place on a given sheet, e.g., depending on how uniformly receiver sheets are manufactured. Typically, moisture contained in receiver sheets produces image defects when the sheets pass through the heated rollers of a fusing station. Such image defects include disruption of toner images by steam generated during fusing, as well as non-uniform deformation or buckling of receiver sheets in a fusing station. Also, the moisture content within a paper receiver affects efficiency of electrostatic transfer of toner to the receiver, and consequently an applied transfer bias voltage will generally require adjustments to compensate for changes in moisture content caused by changes of RH. Such adjustments disadvantageously require specialized extra equipment in the machine. Moreover, if moisture content is nonuniformly distributed in such a receiver, efficiency of electrostatic transfer may be different from place to place on the receiver, thereby causing further image defects, e.g., transfer mottle. In order to mitigate these problems in electrostatographic printers, paper receiver members may be conditioned in a pre-conditioning station at a specified RH and temperature in order to keep moisture content within predetermined limits prior to use, thereby improving the reproducibility of image quality from sheet to sheet and reducing moisture-induced defects. Nevertheless, when paper pre-conditioning is carried out and the interior environment of the printer is otherwise unregulated for relative humidity, ambient-induced variations of RH inside the printer can still be harmful, as described above.
Inasmuch as relative humidity is determined by the absolute humidity as well as by the temperature, variations of temperature within an electrostatographic printer will therefore cause corresponding local changes in relative humidity. Thus, in a machine in which the interior temperature is unregulated, local fluctuations of ambient temperature will generally affect the local RH, and in a modular machine, module-to-module variations of temperature will generally give rise to corresponding changes of RH, even when ambient air is flowed through the machine, e.g., for purpose of ventilating the machine.
Furthermore, fluctuations of temperature within an electrostatographic modular printer are undesira
Blank Phillip Henry
Hoffman Gary P.
Luft Carl Allen
May John Walter
Quester John Franklin
Kessler Lawrence P.
Nexpress Solutions LLC
Tran Hoan
LandOfFree
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