Electrophotographic imaging apparatus

Abstract: A compact printer for liquid toning having a second transfer roller (17) located above a larger, first transfer roller (15). Paper is stored in an lower internal tray (23), moved vertically past the transfer roller (15), and then imaged and fixed at the nip of the second transfer roller and a fixing roller (21) as it is delivered to a top tray (39) of the printer.

Description: This invention relates to electrophotographic printing and copying and, more specifically, to office or "personal" size devices in which the final paper is conveniently delivered to the user. Electrophotographic imaging employing liquid toner is an established technology. US-A-5,083,165 is illustrative. In such systems the effects of gravity on the flow of toner must be taken into account. US-A-4,755,849 discloses embodiments of an electrophotographic imaging system having an intermediate image transfer member, operating by transfer and fixing with heat and by contact between the transfer member and an opposing roller. US-A-4,455,079 discloses a preheating member on the print-receiving side of the paper curved around a pressure roller. Similarly, US-A-4,518,976 discloses a preheating member on the print-receiving side of the paper curved around the pressure roller as well at least one other embodiment (Fig. 10) in which the heating is to the opposite side. From WO-A-92/03765, which corresponds to US-A-5,083,165 mentioned above, it is known to provide an electrophotographic imaging apparatus comprising an endless photoconductive surface moveable in one direction, means for charging said photoconductive surface, means for exposing said charged surface to an optical image to at least partially discharge said charged surface in the pattern of said image, a first endless surface forming a first nip with said photoconductive surface and moveable at said nip, means to develop said image on said photoconductive surface by applying liquid toner to said first nip from a side of said nip at which said one direction is the direction of gravity, an endless first transfer surface to receive said toned image from said photoconductive surface by contact with said photoconductive surface, paper feed means to move paper or other image receiving substrate to a position where said paper or other substrate receives said image while said paper is moved to exit the apparatus, and a top tray for receiving said exiting paper, said tray being positioned at a part of the apparatus opposite from said paper feed means and being readily accessible to an operator. The present invention, however, is characterised in that said apparatus further comprises an endless second transfer surface positionable generally above said first transfer surface with respect to gravity to receive said toned image from said first transfer surface by contact with said first transfer surface, and a member positioned to form a second nip with said second transfer surface, said paper or other substrate receiving said image at said second nip, and in that said top tray is located on the top front of said apparatus, the front of the apparatus being in the exiting direction of said paper or other image receiving substrate. Thus a preferred embodiment of the invention is a liquid toner electrophotographic imaging device of compact size achieved by having a first intermediate transfer surface to which the toned image is transferred from the photoconductor by contact and a second intermediate transfer surface to which the image is transferred from the first transfer surface. The second transfer surface is generally above the first transfer surface and is formed on a member which is much smaller than that which forms the first transfer surface. Paper is delivered to a nip location between the second transfer surface and a rotating fixing member with heat. Paper exiting this nip is delivered to the top of the apparatus. This configuration permits a photoconductor member and a developer member which turns oppositely from the photoconductor to be positioned under the liquid toner source. This results in the photoconductor moving in the direction of gravity to that location which is essential to the best function. Paper may be fed towards the operator, which is especially convenient, and paper to be imaged may be stored within the printer. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 depicts the internal configuration of a printer employing this invention; Fig. 2 is a side view of the fixing members; Fig. 3 is a top view of the fixing members; and Fig. 4 is a perspective view from the top partially sectioned to show certain elements significant to this invention. As shown in Fig. 1, a laser printhead 1 operates on a photoconductive drum 3 which is electrically charged by a charge roller 5. (Drum 3 is a roller, the term drum being commonly used because it has an empty interior.) Liquid toner is applied by nozzles between drum 3 and a countermoving roller 9. At the nip location of drum 3 and roller 9, drum 3 moves in the direction of gravity. Toner is applied to this nip location from above, sequentially in three colors and in black to form a full-spectrum, colored image. That toner which is not captured by the drum 3 is moved by roller 9 and directed to a tank having parts 11a, 11b, 11c and 11d corresponding to the color of the toner. Squeegee roller 13 removes excess liquid from drum 3. Each toned image is transferred by contact with accumulator drum 15. (Drum 15 is a roller, the term drum being commonly used because it has an empty interior.) For a colored image, drum 3 separately receives the image from laser printhead 1 of each of the three colors and black, and each image is separately developed and transferred to accumulator drum 15 in registration with the other images. Until the four images are on drum 15, transfer roller 17 is spaced away from drum 15. To apply the images to final paper, transfer roller 17 is moved laterally by solenoid 19 into contact with drum 15. Transfer roller 17 may be much smaller than accumulator drum 15 since it need not hold a full-page image simultaneously. It is electrically biased to attract toner from drum 15 at the location of nip contact between drum 15 and roller 17. Specifically, the diameter of roller 17 is one-third or less than the diameter of drum 15, preferably about one-fifth the diameter of the drum. Roller 17 is positioned above and near the top of drum 15. Fixing roller 21 opposes roller 17 to form a pressure nip for the final transfer and fixing on paper. The imaging operation of the foregoing need not be novel to implement this invention and therefore is described only generally and illustratively. The printer would have a number of elements not specifically mentioned, such as a cleaning mechanism for drum 3, and toner resupply mechanism 22 which is shown in general outline located under laser 1. Paper for the final image is stored in the bottom of the device chamber or in tray 23 and moves through a guide track 25, which may be conventional, prior to preheating for fixing. Guide track 25 includes a generally vertical section located between drum 15 and the back of the apparatus. Fig. 2 shows paper 27 where it contacts a flat surface of preheating plate 29 which faces roller 21 and is heated by an electrical heating element 31. This occurs as the paper is moved steadily toward the nip of rollers 17 and 21. Direct contact of paper 27 with plate 29 is assured by flat spring 33 bent against plate 29. Both rollers 17 and 21 have conventional internal heating lamps 35 and 37 respectively. The plane of plate 29 contains the extended tangent line of the nip of rollers 17 and 21. Accordingly, the fixing path of paper 27 is straight and no curling of paper 27 is experienced even though the fixing temperatures are high enough to fix a mineral oil vehicle liquid toner before the oil separates from the solids. Liquid toner has a low surface energy and low cohesive strength which causes the toner, when molten, to tend to adhere to fusing surfaces, resulting in degraded image and fuser roll contamination. Fusing before the vehicle separates into the paper reverses this tendency. No silicone oil or other outside release agent need be employed in the embodiment shown. Fig. 4 shows a printer from the top with paper 27 being exited from the rear onto a top tray, 39. This is highly convenient to an operator since operators are normally positioned at the front of printers and other imaging apparatus. As suggested in Fig. 4 the imaging system employing rollers and drums 3, 9, 15, 17 and 21 is at least coextensive with the width of paper 27.

Claims: An electrophotographic imaging apparatus comprising an endless photoconductive surface (3) moveable in one direction, means (5) for charging said photoconductive surface, means (1) for exposing said charged photoconductive surface to an optical image to at least partially discharge said charged photoconductive surface in the pattern of said image, a first endless surface (9) forming a first nip with said photoconductive surface and moveable at said nip, means to develop said image on said photoconductive surface by applying liquid toner to said first nip from a side of said nip at which said one direction is the direction of gravity, an endless first transfer surface (15) to receive said toned image from said photoconductive surface by contact with said photoconductive surface, paper feed means (25) to move paper (27) or other image receiving substrate to a position where said paper or other substrate receives said toned image while said paper is moved to exit the apparatus, and a top tray (39) for receiving said exiting paper, said tray being positioned at a part of the apparatus opposite from said paper feed means and being readily accessible to an operator, characterised in that said apparatus further comprises an endless second transfer surface (17) positionable generally above said first transfer surface with respect to gravity to receive said toned image from said first transfer surface by contact with said first transfer surface, and a member (21) positioned to form a second nip with said second transfer surface, said paper or other substrate receiving said toned image at said second nip, and in that said top tray (39) is located on the top front of said apparatus, the front of the apparatus being in the exiting direction of said paper or other image receiving substrate. Apparatus as claimed in claim 1, in which said first transfer surface (15) is the surface of a first roller and said second transfer surface (17) is the surface of a second roller, the diameter of said second roller being one-third or less of the diameter of said first roller. Apparatus as claimed in claim 1 or 2, in which said means (1) for optically exposing said photoconductive surface (3) and said means (9) to apply liquid toner are located between said photoconductive surface (3) and the front of said apparatus and said paper feed means includes a generally vertical paper feed path (25) positioned between said first transfer surface (15) and the back of said apparatus. Apparatus as claimed in any preceding claim, having a paper supply chamber (23) at the bottom of the apparatus. Apparatus as claimed in any preceding claim, wherein said endless photoconductive surface (3) comprises a roller. Apparatus as claimed in any preceding claim, wherein said first endless surface (9) comprises a roller. Apparatus as claimed in any preceding claim, wherein the member (21) forming part of said nip comprises a roller.

Inventors: SHAKIB IRAJ DAVID, SHAKIB, IRAJ DAVID
Applicants: LEXMARK INT INC, LEXMARK INTERNATIONAL, INC.
Application year: 1993
Main classification: G03G15
IPC codes: G03G15