EP0549867A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Method and apparatus for directly transferring developed images from a photoconductive drum to a print medium
Assignee: HP Inc
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Filing: 1992-11-02
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Granted: —
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Expires: 2012-11-02
Abstract
Abstract Method and apparatus for electrophotographically transferring a developed color image on the surface of a photoconductive drum (10) directly to an adjacent print media (30). The print media (30) is operative to pass between the one abutting surface location on the photoconductive drum (10) and an adjacent surface location on a transfer roller (28) which is connected to receive a DC bias voltage (42). Once a composite color image has been developed on the surface of the photoconductive drum (10), this surface is illuminated with light (76) within a chosen wavelength range and intensity to thereby cause hole-electron pairs within a layer of the photoconductive drum (10) to recombine and thereby reduce the net voltage across the photoconductive surface layer or layers to a level on the order of about thirty (30) volts. In this manner, the DC bias voltage (42) applied to the direct transfer roller (28) can be made larger than otherwise possible,thereby increasing the maximum achievable electrostatic field strength between the surface of the transfer roller (28) and the photoconductive drum (10). This feature of increasing the electrostatic field strength across the print medium (30) provides image transfer fidelity and print quality during the electrophotographic printing process.
Inventors
- 👤 Thomas Camis
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 15:01
CPC Classifications
G; G03; G03G; G03G15/00; G03G15/14; G03G15/16; G03G15/169; G03G15/01; G03G15/0105; G03G15/0131; G03G15/1665; G03G15/167
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
215 words
A method for electrophotographically color printing which includes the steps of: a. developing a composite color image on the surface of a photoconductive drum (10), b. illuminating the surface of the photoconductive drum (10) with light (76) within a chosen wavelength range corresponding to the wavelength characteristic of the photoconductive drum to thereby cause hole-electron pairs (88) within a layer (90) of the photoconductive drum (10) to recombine and reduce the net voltage (V) across the photoconductive drum layers, and thereafter c. bringing a direct transfer roller (28) into intimate contact with a print medium (30) passing between the transfer roller (28) and the surface of the photoconductive drum (10) while simultaneously, d. applying a predetermined DC bias voltage (42) to the direct transfer roller (28), whereby the reduction of voltage across the surface layer of the photoconductive drum (10) permits a corresponding increase in DC bias voltage (42) to be applied to the direct transfer roller (28) to thereby increase the strength of the electrostatic field established between the surface of the photoconductive drum (10) and the surface of tile transfer roller (20) to thereby, in turn, increase the achievable electrostatic forces for pulling the charged toner and developed color image from the surface of the photoconductive drum (10) onto the print medium (30).
Claim 2
Dependent Claim
219 words
Apparatus for electrophotographic coloring printing including: a. means (12) for developing a composite color image on the surface of a photoconductive drum (10), b. means (76) for illuminating the surface of the photoconductive drum (10) with light within a chosen wavelength range corresponding to the wavelength characteristic of the photoconductive drum to thereby cause hole-electron pairs (88) within a layer (90) of the photoconductive drum (10) to recombine and reduce the net voltage (V) across the photoconductive drum layers (78, 86, 90), c. means for bringing a direct transfer roller (28) into intimate contact with a print medium (30) passing between the transfer roller (28) and the surface of the photoconductive drum (10), and d. means for applying a predetermined DC bias voltage (42) to the direct transfer member (28), whereby the reduction of voltage (V) across the surface layer of the photoconductive drum (10) permits a corresponding increase in DC bias voltage (42) to be applied to the direct transfer roller (28) to thereby increase the strength of the electrostatic field between the surface of the photoconductive drum (10) and the surface of the transfer roller (28) to thereby, in turn, increase the achievable electrostatic forces for pulling the charged toner and develop color image from the surface of the photoconductive drum (10) onto the print medium (30).
Claim 3
Independent Claim
107 words
A method for increasing the electrostatic field strength that may be applied between the surface of a photoconductive drum (10) and an adjacent direct transfer member (28) between which print media (30) passes during the transfer of images from the drum (10) to the media (30) characterized by: illuminating the surface of a photoconductive drum (10) with light (76) within a chosen wavelength range corresponding to the wavelength versus-transmittance characteristic of the photoconductive drum (10) to thereby cause hole-electron pairs (88) within a layer (90) or layers of the photoconductive drum (10) to recombine and reduce the net voltage across the photoconductive drum layers (78, 86, 90).
Claim 4
Dependent Claim
113 words
The method defined in claim 3 which further includes applying a predetermined DC bias voltage (42) to said adjacent direct transfer member (28), whereby the reduction of net charge at the surface layer (90) of said photoconductive drum (10) permits a corresponding increase in DC bias voltage (42) to be applied to said direct transfer member (28) to thereby increase the strength of the electrostatic field between the surface of the photoconductive drum (10) and the surface of said transfer member (28) to thereby, in turn, increase the achievable electrostatic forces for pulling the charged toner and develop color image from the surface of the photoconductive drum (10) onto the print medium (30).
Claim 5
Dependent Claim
20 words
The method defined in claim 4 which further includes applying liquid color toners in series to said photoconductive drum (10).
Claim 6
Dependent Claim
47 words
The method defined in claim 5 which further includes contacting the surface of said photoconductive drum (10) with a deformable conditioning roller (46) for reducing isopar fluid in said liquid toners to thereby further improve the print quality of color images transferred to said print media (30).
Claim 7
Independent Claim
44 words
The method defined in any one of claims 3 through 6 wherein organic photoconductor potentials are lowered in non-imaged areas due to the overall illumination (76) of said photoconductive drum (10), whereby air ionization is presented and undesirable paper (30) charging problems are minimized.
Claim 8
Dependent Claim
38 words
The method defined in claim 6 wherein organic photoconductor potentials are lowered in non-imaged areas due to the overall illumination (76) of said photoconductive drum (10), whereby air ionization is presented and undesirable paper charging problems are minimized.
References Cited (Backward Citations)
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