GB1590872A - Electrostatographic apparatus - Google Patents

Description

(54) ELECTROSTATOGRAPHIC APPARATUS (71) We, XEROX CORPORATION of Xerox Square, Rochester, New York, United States of America, a corporation organised under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an electrostatographic apparatus for simultaneous duplex imaging.

One of the best known forms of electrostatographic imaging is the process of xerography, in which a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the areas of the photoconductive layer in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is then effected, for example with a finely divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image.Thereafter, the developed xerographic image is usually transferred to a support surface to which it may be fixed by any suitable means. As an alternative to the dry powder development technique, liquid development techniques are often used. In one liquid development technique, a polar ink is attracted to the electrostatic latent image, the ink being attracted as a body from an out-ofcontact position to the electrostatic latent image. In another liquid development process, the photoconductive layer carrying the electrostatic latent image is immersed in a bath of liquid developer, development taking place by electrophoretic deposition of toner particles from a liquid carrier.

Furthermore, other ways are available for forming an electrostatic latent image, either on a photoconductive layer or on an insulating layer. In such processes, instead of an optical projection system, electronic means such as styli or selective ion discharge, may be used to deposit electrical charges in image configuration.

Most commercial electrostatographic apparatuses produce copies on only one side of a sheet at a time. In those machines which are equipped with a duplex copying facility, copies are first made on one side of a sheet, the sheet then being stored in readiness for a second copy.to be made on the reverse side of the sheet. In order to increase the speed of duplex copying, an arrangement has been proposed in which electrostatic latent images are formed simultaneously on two sides of an input document, developed simultaneously on separate imaging surfaces, and transferred simultaneously to opposite sides of a copy sheet. Such an arrangement is described in UK Patent Specification No 1413190.

It is an object of the present invention to provide an alternative form of electrostatographic apparatus for simultaneous duplex imaging.

According to the present invention there is provided an electrostatographic apparatus for simultaneous duplex imaging, comprising two imaging arrangements, each including an imaging surface arranged for cyclic movements through an imaging station, a developing station, and a transfer station; the imaging station in each case being arranged to form on its associated imaging surface an electrostatic latent image, the developing station in each case being arranged to develop the latent image, and the imaging surfaces of the two imaging arrangements being disposed so as to form at the transfer station a nip wherein the developed images are simultaneously transferred to two back-to-back support surfaces; the electrostatic latent images formed on the two imaging surfaces being of opposite electrical polarities.

An electrostatographic apparatus in accordance with the invention will now be descri bed, by way of example, with reference to the accompanying drawing, which is a diagrammatic cross-sectional view of a simultaneous imaging apparatus using liquid development.

Referring to the drawing, the apparatus includes two cylindrical drums 1, 2, which have imaging surfaces 3, 4 respectively. The imaging surfaces may be of a photoconductive material, carrier transport material or insulator, or, in a preferred embodiment, may consist of a photoconductor overcoated with an insulator. In all cases, the imaging surface has a conductive backing. The drums 1, 2 are mounted for anticlockwise and clockwise rotation about their cylindrical axes, as shown by arrows 5, 6, and are in rolling engagement at a nip 7. The imaging surfaces are mounted on a conformable material (not shown) so as to ensure good contact in the nip 7.A suitable construction for each of the drums 1, 2 consists of a central cylindrical core of metal, a surrounding sleeve of a resilient plastics material, a flexible metal or conductive plastics shell surrounding the sleeve, and a photoconductor overcoated with an insulator deposited on the metal or conductive plastics shell. In an alternative construction, not shown, the imaging surface may be provided on flexible belts which are arranged around two or more rollers, and which pass through a nip in a similar fashion to that just described.

Spaced around the circumference of drum 1 in an anticlockwise direction are an imaging station 8, a developing station 9, a cleaning station 10, and charge erase means.

Corresponding stations, i.e. an imaging station 11 a developing station 12, and a cleaning station 13, are spaced around the circumference of drum 2 in a clockwise direction.

Imaging stations 8 and 11 are arranged to form electrostatic latent images on the imagin surfaces 3 and 4 respectively, the electrostatic latent images being formed by any means appropriate to the kind of imaging surfaces being used. Thus if the imaging surface is of a photoconductive material, the imaging station may include a charging device and an imagewise optical exposure device. On the other hand, if the imaging surface is of an insulating material, the electrostatic latent image may be formed by means of selectively energised electrically conductive styli. In a further embodiment, the imaging surfaces are of a photoconductor overcoated with an insulator, and the imaging station includes an arrangement for simultaneously charging and exposing the imaging surface.

The electrostatic latent images, however formed, are arranged to be of opposite electrical polarities. Thus if the electrostatic charges forming the latent image on imaging surface 3 are of positive polarity, those on imaging surface 4 are negative, and vice versa.

When the electrostatic latent images have been formed on their respective imaging surfaces, they are developed at developing stations 9 and 12, which preferably, but not necessarily, employ the same development process, although of course they are arranged to develop electrostatic latent images of opposite polarities. The development process used may be a liquid or a powder process, and in the case of a liquid process may employ either polar ink development or electrophoretic development.

At the imaging station 7, the developed images are simultaneously transferred from their respective imaging surfaces 3 and 4 to two back-to-back support surfaces, which are preferably the two surfaces of a sheet (or web) 14 of paper. A certain amount of electrostatic assistance is provided in the transfer of each image to the sheet 14 by the opposite polarity charge of the other image. Further assistance, in the form of pre-transfer corotrons 15, 16 is often needed to improve transfer and hence copy quality.

As shown, the path of the paper sheet or web 14 may be a simple, linear path, which allows short, straight and hence reliable paper feeding arrangements to be used. Stripping of the paper from both imaging surfaces may be assisted by air jet or other devices 17, 18.

After transfer of the images to the paper, the images may need to be fixed in place by the use of radiant or other fusing devices 19, 20. Radiant heater devices are suitable for both dry powder and liquid development and either infrared or ultra-violet curing inks can be used with liquid development. The use of a fixing means ensures that the image is not degraded by contact with the guide nip rolls 21.

In order to clean the imaging surfaces 3 and 4 of any residual toner remaining after transfer, cleaning stations 10 and 13 are provided, and are of a kind suited to the development process employed. It may also be arranged to discharge the imaging surface of any residual electrical charges, before, during or after cleaning, by the use of either or both of a flood illumination source and an electrical charging device.

The simultaneous duplex copying apparatus described in UK Patent Specification No 1413190 employs two imaging arrangements which both utilise electrostatic charges of the same polarity. Thus, in the transfer nip, developer carrying charge of a particular polarity is being transferred to both sides of a sheet at the same time, the tendency being for portions of the two images which coincide in the nip to repel each other, thereby making transfer less certain.

In the apparatus of the present invention, there will be a tendency towards mutual attraction of those portions of the two images which coincide in the transfer nip, so there is no reduction in transfer efficiency at the coinciding portions.

WHAT WE CLAIM IS: 1. An electrostatographic apparatus for simultaneous duplex imaging, comprising two imaging arrangements, each including an imaging surface arranged for cyclic movements through an imaging station, a developing station, and a transfer station; the imaging station in each case being arranged to form on its associated imaging surface an electrostatic latent image, the developing station in each case being arranged to develop the latent image, and the imaging surfaces of the two imaging arrangements being disposed so as to form at the transfer station a nip wherein the developed images are simultaneously transferred to two backto-back support surfaces; the electrostatic latent images formed on the two imaging surfaces being of opposite electrical polarities.

2. The apparatus of claim 1 wherein said imaging surfaces are cylindrical.

3. The apparatus of claim 1 wherein said imaging surfaces are on flexible endless belts each arranged around two or more rollers.

4. The apparatus of any one of claims 1 to 3 wherein said imaging surfaces are supported on conformable backings in said nip.

5. The apparatus of any one of claims 1 to 4 wherein said imaging surfaces are of photoconductive material and said imaging stations include means for electrically charging and imagewise exposing the imaging surfaces.

6. The apparatus of any one of claims 1 to 4 wherein said imaging surfaces are of photoconductive material overcoated with insulating material, and the imaging stations include means for simultaneously electrically charging and imagewise exposing the imaging surfaces.

7. The apparatus of any one of claims 1 to 4 wherein the imaging surfaces are of insulating material and the imaging stations include means for the deposition onto said imaging surfaces of electrical charges in image configuration.

8. The apparatus of any one of claims 1 to 7 wherein said developing stations are arranged to develop the electrostatic latent images with a dry powder.

9. The apparatus of any one of claims 1 to 7 wherein said developing stations are arranged to develop the electrostatic latent images with a polar liquid.

10. The apparatus of any one of claims 1 to 7 wherein said developing stations are arranged to develop the electrostatic latent images with a liquid electrophoretic developer.

11. The apparatus of any one of claims 1 to 10 wherein said two back-to-back support surfaces are the two surfaces of a single sheet or web.

12. An electrostatographic apparatus for simultaneous duplex imaging substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. no reduction in transfer efficiency at the coinciding portions. WHAT WE CLAIM IS:

1. An electrostatographic apparatus for simultaneous duplex imaging, comprising two imaging arrangements, each including an imaging surface arranged for cyclic movements through an imaging station, a developing station, and a transfer station; the imaging station in each case being arranged to form on its associated imaging surface an electrostatic latent image, the developing station in each case being arranged to develop the latent image, and the imaging surfaces of the two imaging arrangements being disposed so as to form at the transfer station a nip wherein the developed images are simultaneously transferred to two backto-back support surfaces; the electrostatic latent images formed on the two imaging surfaces being of opposite electrical polarities.

2. The apparatus of claim 1 wherein said imaging surfaces are cylindrical.

3. The apparatus of claim 1 wherein said imaging surfaces are on flexible endless belts each arranged around two or more rollers.

4. The apparatus of any one of claims 1 to 3 wherein said imaging surfaces are supported on conformable backings in said nip.

5. The apparatus of any one of claims 1 to 4 wherein said imaging surfaces are of photoconductive material and said imaging stations include means for electrically charging and imagewise exposing the imaging surfaces.

6. The apparatus of any one of claims 1 to 4 wherein said imaging surfaces are of photoconductive material overcoated with insulating material, and the imaging stations include means for simultaneously electrically charging and imagewise exposing the imaging surfaces.

7. The apparatus of any one of claims 1 to 4 wherein the imaging surfaces are of insulating material and the imaging stations include means for the deposition onto said imaging surfaces of electrical charges in image configuration.

8. The apparatus of any one of claims 1 to 7 wherein said developing stations are arranged to develop the electrostatic latent images with a dry powder.

9. The apparatus of any one of claims 1 to 7 wherein said developing stations are arranged to develop the electrostatic latent images with a polar liquid.

10. The apparatus of any one of claims 1 to 7 wherein said developing stations are arranged to develop the electrostatic latent images with a liquid electrophoretic developer.

11. The apparatus of any one of claims 1 to 10 wherein said two back-to-back support surfaces are the two surfaces of a single sheet or web.

12. An electrostatographic apparatus for simultaneous duplex imaging substantially as hereinbefore described with reference to the accompanying drawing.