Imaging apparatus

Abstract: In a liquid toner electrophotographic printer (1), an abrasive blade (5), located between the cleaning station (19) and the charging station (9) disturbs the outer, photoconductive surface of drum (3) to continuously rejuvenate that surface. The abrasion merely disturbs the surface and may be accomplished by alternative abrasive mechanisms.

Description: This invention relates to imaging apparatus employing a photosensitive element with liquid developer station. More specifically, this invention relates to the treatment of the photosensitive element with abrasion in such an imaging apparatus. In some electrophotographic systems having organic photoconductor elements, a loss of resolution in print quality occurs over the desired period of use because of a modification of the outer surface of the photosensitive element. In dry electrophotographic systems the surface of a photoconductor tends to become contaminated with materials that reduce the performance of the photoconductor and limit its useful life. The life of such a photoconductor is extended by providing an abrasive toner mix which causes the surface of the photoconductor to slowly abrade away over the intended period of use. This abrasion process cleans the photoconductor surface and keeps the surface fresh. Japanese patent application JP-A-1 196072 published Aug. 7, 1994, assigned to Canon Corp., is understood to be directed to such intentional abrasion in a dry toning system. A device having a rotary grind-stone which is brought into contact with a photoconductive drum of an electrophotographic apparatus is known from Patent Abstracts of Japan, vol. 8, no. 147 (P-285)[1584] and JP-A-59 046,672. This device uses a dry toning system. In liquid toning electrophotographic systems the carrier fluid is typically an oil which lubricates the surface and provides a protective film which decreases the amount of abrasion that the photoconductor experiences in the imaging process. Also, since the electrophotographic process requires the use of elevated temperatures to assist in transferring the toner from the photoconductor, the photoconductor must have a high glass transition temperature (Tg) in order to function properly. The high Tg results in organic photoconductive materials which are more rigid and inflexible, and therefore have more resistance to abrasion. Similarly, a photoconductor subject to liquid developer must have resistance to the solvent action of the developer. A typical liquid developer system is disclosed in GB-A-1,528,586, over which claim 1 is characterised. US-A-4,420,244 employs a liquid developer in which hard particles are included in the developer as spacers. Abrasion from these particles is recognized and is considered undesirable. It has been found that abrasion in some liquid electrophotographic imaging systems is helpful to extend the useful life of the photoconductor. In order to have a controlled abrasion which does not affect the imaging operation and is not affected by the lubricating action of the liquid developer, in accordance with the present invention a mechanical abrasion element or system is located between a cleaning station and the charging station. Thus according to the present invention there is provided an imaging apparatus comprising an endless member having a photosensitive surface, a charging station positioned at a first location to charge said photosensitive surface as said photosensitive surface is moved, an imaging station positioned at a second location past said first location to discharge said photosensitive surface in an image pattern as said photosensitive surface is moved, a liquid toning station positioned at a third location past said second location to develop said image on said photosensitive surface with liquid developer, a transfer station positioned at a fourth location past said third location to transfer said toned image from said photosensitive surface for ultimate transfer of said toned image to paper or other substrate for delivery out of said imaging apparatus, and a cleaning station positioned at a fifth location past said fourth location, said cleaning station substantially removing liquid and loose particles from said photosensitive surface, characterised in that an abrasive member is positioned between said fifth location and said first location and arranged to press against the said photosensitive surface sufficiently to physically disturb said surface but without noticeably roughening said surface. Two embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 illustrates a first imaging apparatus according to the invention; and Fig. 2 illustrates a second such apparatus. The drawings illustrate an electrophotographic imaging apparatus 1, such as a laser printer, having a photoconductive drum 3 of organic surface, such as a polycarbonate or polyestercarbonate binder with charge transporting additives, as may be generally conventional. Abrasion is accomplished by rubbing the outer surface of photoconductive drum 3 with an abrasive member 5 (Fig. 1) or 7 (Fig. 2). Abrasive members 5 and 7 are separate from the toner or other operative members such as a charge roller, photoconductor squeegee, intermediate transfer member or other member which contacts drum 3, thereby permitting the operation of each to be unaffected by the abrasion step. Positioned at stationary locations around the drum are certain members which may be entirely conventional and are therefore shown illustratively. Drum 3 is moved clockwise in the drawing to bring a location on the surface of the drum to a charging station 9; then to a laser imaging station 11 positioned past the charging station 9 which applies light in an image pattern to the charged surface of the drum, thereby discharging drum 3 in the pattern of that image; then to a liquid developer developing station 13 positioned past imaging station 11; then to a transfer station 15 positioned past developing station 13, in which the toned imaged is transferred to an intermediate transfer member 17; and then to a cleaning station 19, positioned past the transfer station 15. The image is subsequently transferred to paper 21 or other final substrate, fixed by heat at a fixing station 22, and ultimately delivered out of printer 1 to a tray 23 for access by an operator of printer 1. In the Fig. 1 embodiment member 5 is a resilient blade element of urethane 2 mm thick, with a layer of 600 to 800 grit sand paper 25 held by adhesive to the surface facing drum 3. Blade 5 is flexed against drum 3 to provide firm contact. Blade 5 is mounted to a bracket 27 which is supported by a pivot 29. A torque is provided around pivot 29, as by a spring (not shown) to produce a force of 100 grams/cm of longitudinal engagement at the point of engagement with drum 3. (A typical length of drum 3 is 25 cm; therefore the foregoing loading typically is 2500 grams.) The abrasion apparatus of Fig. 1 may be so closely positioned with respect to cleaning station 19 as to be in its housing. However, cleaning at station 19 has been substantially accomplished on a surface of drum 3 before that surface of drum 3 encounters blade 5. The surface of drum 3 at blade 5 is therefore substantially dry and cleaned of loose particles, which permits abrasion to be consistent and predictable over a long period. Fig. 2 is an alternative embodiment which uses an abrasive roller 7 instead of blade 5. Roller 7 may be formed with a metal shaft 31 supporting a 3 mm thickness of rubber 33 of 40 Shore A hardness with embedded grit on the surface. Rubber 33 provides compliance needed to maintain uniform loading along the surface of drum 3. Roller 7 is rotated in a direction opposite to the direction of rotation of the surface of photoconductive 3 which it contacts. Roller 7 tends to carry away debris, which can then be collected as desired by cleaning the surface of roller 7 in any conventional manner. Operation of the abrasive members 5 and 7 is just sufficient to physically disturb the outer boundary surface of the drum 3. Although that surface is gradually removed by the action, each pass of drum 3 from cleaning station 19 to charging station 9 is characterized by a rearrangement of the outer boundary surface of the drum, and consequent rejuvenation of its photoconductive effect but not by noticeable roughness of the outer surface of the drum. Abrasion between the cleaning station 19 and the charging station 9 permits the abrasion action to occur without influencing the imaging mechanisms themselves.

Claims: An imaging apparatus comprising an endless member (3) having a photosensitive surface, a charging station (9) positioned at a first location to charge said photosensitive surface as said photosensitive surface is moved, an imaging station (11) positioned at a second location past said first location to discharge said photosensitive surface in an image pattern as said photosensitive surface is moved, a liquid toning station (13) positioned at a third location past said second location to develop said image on said photosensitive surface with liquid developer, a transfer station (15) positioned at a fourth location past said third location to transfer said toned image from said photosensitive surface for ultimate transfer of said toned image to paper or other substrate (21) for delivery out of said imaging apparatus, and a cleaning station (19) positioned at a fifth location past said fourth location, said cleaning station substantially removing liquid and loose particles from said photosensitive surface, characterised in that an abrasive member (5;7) is positioned between said fifth location and said first location and arranged to press against the said photosensitive surface sufficiently to physically disturb said surface but without noticeably roughening said surface. An imaging apparatus as claimed in claim 1, in which said abrasive member (5) is a resilient blade (25) having a surface comprising or equivalent to 600 to 800 grit sand paper for pressing against said photosensitive surface. An imaging apparatus as claimed in claim 1, in which said abrasive member (7) is a resilient roller (33) having embedded grit and mounted to turn at a velocity relative to the movement of said photosensitive surface so as to rub against said surface.

Inventors: CAMPBELL ALAN STIRLING, ELBERT DONALD LEO, MCCORNACK WILLIAM CRAIG, ZIERCHER ERIC LAWRENCE, CAMPBELL, ALAN STIRLING, ELBERT, DONALD LEO, MCCORNACK, WILLIAM CRAIG, ZIERCHER, ERIC LAWRENCE
Applicants: LEXMARK INT INC, LEXMARK INTERNATIONAL, INC.
Application year: 1995
Main classification: G03G21
IPC codes: G03G21, G03G15