WO2007050064A1

WO2007050064A1 - Printer photoreceptor maintenance

Info

Publication number: WO2007050064A1
Application number: PCT/US2005/038738
Authority: WO
Inventors: Marko Richter; Eli Shaya; Yoram Sorek; Alejandro Scharachansky; Mark Sandler
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2005-10-27
Filing date: 2005-10-27
Publication date: 2007-05-03

Abstract

The disclosure presents methods for cleaning a photoreceptor of an eleotrostatographic printer on which latent images are formed. One method comprising cleaning the photoreceptor with a first cleaning method with a first frequency and removing contaminants from the photoreceptor at a second lower frequency. A second method comprises A method of cleaning a photoreceptor of an electrostatographic printer on which latent images are formed, the method comprising providing a contamination removal fluid comprising a substance that dissolves a material from which the photoreceptor is made; and applying the contamination removal fluid to the photoreceptor to etch away an outer surface layer of the photoreceptor.

Description

PRINTER PHOTORECEPTOR MAINTENANCE FIELD OF THE INVENTION

The invention relates to electrophotographic digital printers and to cleaning a photoreceptor in the printer on which latent images are formed. BACKGROUND OF THE INVENTION

To print an image on a substrate, a typical electrophotographic digital printer first forms an electrostatic copy of the image, conventionally referred to as a "latent image", on a photoconductive surface, generally a surface of a rapidly rotating cylindrical roller, hereinafter referred to as a photoreceptor cylinder or simply as a cylinder. As the photoreceptor rotates, photosensitive surface regions of the surface of the photoreceptor pass by a station at which a charger positioned close to the photoreceptor surface charges the surface regions with a substantially uniform surface charge.

Charged surface regions then pass through a station at which the image is formed by discharging portions of the surface regions to generate a pattern of charged and uncharged pixels on the photosensitive surface that replicates the image. Discharging of portions of the photoreceptor surface is generally accomplished by illuminating the portions with a beam (or beams) of light from a laser that scans the photoreceptor as the photoreceptor rotates. A developer applies ink or toner of desired color to the charged or uncharged regions using an electrostatographic process in which an electric field substantially perpendicular to the photoreceptor surface causes charged toner particles to migrate and adhere to the photoreceptor surface.

The toner on the photoreceptor surface is then optionally transferred from the photoreceptor surface to a suitable transfer surface of another roller, conventionally referred to as an "intermediate transfer member" (ITM). The toner is transferred from the ITM to the substrate to print the image when the substrate passes through a nip between the ITM and an impression roller. In some cases, the toner is transferred directly from the photoreceptor surface to the substrate without an intermediate transfer via the ITM.

After toner is transferred from a region of the photoreceptor surface to the ITM or final substrate, the region passes through a cleaning station at which excess toner remaining on the region is removed. Following cleaning, rotation of the photoreceptor returns the photoreceptor region to the charging station to repeat the cycle of forming the latent image and transferring toner to the final substrate or ITM. Conventional cleaning stations in liquid toner digital printers generally prove satisfactory for removal of excess toner and particulate matter, such as toner particles and dirt, from the photoreceptor.

The photoreceptor can be organic or inorganic, although at present organic photoreceptors are preferred. Furthermore, a common type of photoreceptor is a sheet photoreceptor held on the rotating cylinder. The term photoreceptor is sometimes applied to the cylinder having the sheet photoreceptor mounted on it.

US Patent 5,500,724 to Cambell et al, the disclosure of which is incorporated by reference, describes an electrophotographic printer having an abrasive blade or roller located between the printer's cleaning station and the charging station to provide continuous abrasion of the photoreceptor in liquid toner systems. The inventors assert that the additional abrasion rejuvenates the photoconductive effect of the photoreceptor.

SUMMARY OF THE INVENTION

The inventors have found that when liquid toner is used to develop latent images on a photoreceptor, with time and use, the ability of the photoreceptor to hold a charge is reduced. Without being bound by any theory, the present inventors believe that this is caused by toner components that are not completely removed by conventional cleaning process at the cleaning station and accumulate on and contaminate the photoreceptor. The contaminates are believed to contain carrier liquid molecules, pigment and mainly charge director molecules that under the influence of corona, high voltage and heat used in transferring toner to and from the photoreceptor interact with and contaminate the photoreceptor at a molecular level. It is believed that the contaminants generate conductivity paths on or in the photoreceptor lateral to the photoreceptor surface that degrade quality of images printed by the printer and are a factor in shortening a useful lifetime for the photoreceptor. Often, degradation of print quality resulting from the accumulated contaminants determines when the photoreceptor is replaced. It is also surmised that quantities of components of printing substrates, such as additives often used in paper substrates, are transferred from the substrates to the photoreceptor during printing and form a sticky layer on the photoreceptor surface. These contaminants and the changes that they produce in the photoreceptor degrade quality of images printed by the printer and are a factor in shortening a useful lifetime for the photoreceptor. Often, degradation of print quality resulting from the accumulated contaminants determines when the photoreceptor is replaced. Furthermore, it is believed that the corona (or any charging device) may also affect the surface of the photoreceptor itself. It is believed that the surface tension may increase and/or the surface composition may be altered due to bonding of reactive corona species.

An aspect of some embodiments of the invention relates to providing apparatus and materials for providing improved cleaning of a photoreceptor on which latent images in a liquid toner electrophotographic printer are formed.

In some embodiments of the invention, the apparatus comprises a first toner removal cleaning apparatus that cleans the photoreceptor surface of residual toner particles after every printing and a second contaminant removal apparatus that is only intermittently contacted with the photoreceptor. For these embodiments the second contaminant removal apparatus can act to remove the contamination by mechanical (e.g. abrasive) means or by chemical cleaning means (as in the aspects described below).

Optionally, the contaminants are removed from the photoreceptor "on press" without the photoreceptor having to be removed from the printer. An aspect of some embodiments of the invention relates to chemical cleaning means for contaminant removal from a photoreceptor. This chemical cleaning means optionally dissolves phospholipids. Alternatively or additionally, the chemical cleaning means etches the surface of the photoreceptor to remove (i.e., chemically etch) a thin contaminated surface layer of the photoreceptor. In some embodiments of the invention, the cleaning material, hereinafter a "cleaning fluid", is a solution of propylene carbonate in a suitable solvent such as water, alcohol (such as isopropanol alcohol (IPA)), Glycerol formal a dioxane or a dioxalane.

In some embodiments of the invention, the cleaning fluid comprises a solution that dissolves phospholipids. Optionally, the solution is a solution of phosphoric acid or an acetylenic diol. In some embodiments of the invention, the chemical cleaning fluid comprises a solution of at least one Glycol ether chosen from the group of Glycol ethers consisting of: Dipropylene glycol monomethyl ether (DPM); Butylene glycol monobutyl ether (DBE); and Ethylene glycol n-butyl dimethykl ether (DMM).

According to an embodiment of the invention, the chemical cleaning fluid is applied to the photoreceptor by a contaminant removal apparatus incorporated in the printing press. The contaminant removal apparatus optionally comprises a reservoir that contains the cleaning fluid and an applicator that removes cleaning fluid from the reservoir and applies it to the photoreceptor. Optionally, the applicator comprises a roller which the cleaning fluid wets and which rolls along the surface of the photoreceptor to wash and optionally also to etch the photoreceptor with the cleaning fluid.

In some embodiments of the invention, the contaminant removal apparatus comprises a motor or actuator, hereinafter a "driving mechanism", controllable to selectively move the applicator to contact the photoreceptor or separate the applicator from the photoreceptor. In an embodiment of the invention, the applicator does not contact the photoreceptor continuously during printing of images.

It is estimated that the contaminants begin to impact image quality after 50,000 to 70,000 impressions. Thus in one embodiment of the invention, contaminant removal is performed on start up or shut down (if at least a given number of impressions has been made, for example 40,000 impressions). Alternatively, printing is intermittently interrupted for contaminant removal by the contaminant removal apparatus and the driving mechanism controlled to bring the applicator into contact with the photoreceptor to apply the cleaning fluid to the photoreceptor as required to remove contamination from the photoreceptor. This is in contrast with normal mechanical cleaning (including that taught in US 5,500,724) which operates continuously.

In an embodiment of the invention, concentration of dissolving agent in the cleaning fluid and contact time between the applicator and photoreceptor are controlled to control a depth to which the cleaning etches the photoreceptor. The inventors have found that etching to a depth of 100 nanometers is sufficient. However, depending on a number of factors, including the time between chemical cleaning, the depth may be larger or smaller.

There is thus provided, in accordance with an embodiment of the invention a method of cleaning a photoreceptor of an electrostatographic printer on which latent images are formed, the method comprising: cleaning the photoreceptor with a first cleaning method with a first frequency; removing contaminants from the photoreceptor at a second lower frequency.

Optionally, cleaning the photoreceptor with a first frequency comprises cleaning the photoreceptor during or after each printing cycle of the printer. Optionally, the second frequency comprises removing contaminant at an interval greater than 1,000, 5,000, 10,000 or 40,000 impressions. In an embodiment of the invention, removing contaminants comprises removing contaminants by periodically abrading the surface of the receptor.

In an embodiment of the invention, removing contaminants comprises removing contaminants by chemical action on the contaminants. Optionally, removing the contaminants comprises applying a contamination removal fluid to the photoreceptor to etch away an outer surface layer of the photoreceptor. Optionally, wherein the removing the contaminants comprises applying a contamination removal fluid to the photoreceptor to provide at least one effect from the group consisting of dissolving the contaminants, etching the surface of the photoreceptor or breaking a bond between the contaminants and the photoreceptor.

There is further provided, in accordance with an embodiment of the invention, a method of cleaning a photoreceptor of an electrostatographic printer on which latent images are formed, the method comprising: providing a contamination removal fluid comprising a substance that dissolves a material from which the photoreceptor is made; and applying the contamination removal fluid to the photoreceptor to etch away an outer surface layer of the photoreceptor.

Optionally, the contamination removal fluid comprises a substance that dissolves a material from which the photoreceptor is made. Optionally, the method includes controlling an amount of the dissolving substance in the fluid so that the contamination removal fluid etches the photoreceptor to a desired depth. Optionally, the desired depth is less than about 100 or 200 nanometers.

In an embodiment of the invention, applying the contamination removal fluid comprises controlling a duration during which the contamination removal fluid is applied so that the cleaning fluid etches the photoreceptor to the desired depth.

Optionally, the material from which the photoreceptor is made comprises an organic material.

Optionally, the contamination removal fluid comprises a solution comprising propylene carbonate and a solvent. Optionally, the solvent comprises one or more solvents from the group consisting of: water, alcohol, dioxane and dioxalane. Optionally, the solvent is isopropyl alcohol. Optionally, the solvent comprises Glycerol formal. In an embodiment of the invention, the contamination removal fluid comprises between 2% and 10% by weight of propylene carbonate.

In an embodiment of the invention, the contamination removal fluid comprises at least one substance that dissolves phospholipids. Optionally, the at least one substance comprises phosphoric acid or acetylenic diol.

In an embodiment of the invention the method is performed while the photoreceptor is mounted in the printer.

In an embodiment of the invention, the latent images are developed using a liquid toner. In an embodiment of the invention, the photoreceptor is charged by a corona discharge prior to formation of the latent image.

There is further provided, in accordance with an embodiment of the invention printing apparatus, comprising: a photoreceptor on which a latent image is formed; a developer that develops the latent image by adhering toner particles to portions of the latent image; a transfer mechanism for transferring the developed image from the photoreceptor; a cleaning mechanism that remover toner and other solid matter from the photoreceptor after the transfer of the developed image; and a separate contaminant removal system that removes contaminants from the photoreceptor.

Optionally, the cleaning mechanism cleans the photoreceptor at a higher frequency that the contaminant removal system.

Optionally, the cleaning mechanism cleans the photoreceptor after each image is transferred from the photoreceptor. Optionally, the contaminant removal system removes contaminants at a frequency at least an order of magnitude less frequently than the cleaning mechanism cleans the photoreceptor.

Optionally, the developer develops the latent image using liquid toner. In an embodiment of the invention, the contaminant removal system applies a contaminant removal liquid to the photoreceptor. Optionally, the contaminant removal liquid etches the surface of the photoreceptor. Optionally, the contaminant removal system dissolves materials chemically bonded to the photoreceptor. In an embodiment of the invention the contaminant removal system mechanically abrades the surface of the photoreceptor.

BRIEF DESCRIPTION OF FIGURES

Non-limiting examples of embodiments of the present invention are described below with reference to figures attached hereto and listed below. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale.

Fig. 1 schematically shows a digital printing press comprising a cleaner for printing an image in accordance with an embodiment of the present invention;

Fig. 2A shows a schematic cross sectional view of the printing press shown in Fig. 1 with the cleaner disengaged from the printer's photoreceptor, in accordance with an embodiment of the invention; and

Fig. 2B shows a schematic cross sectional view of the printing press shown in Fig. 1 with the cleaner engaged with the printer's photoreceptor in order to clean the photoreceptor, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Fig. 1 schematically shows a digital printer 20, in accordance with an embodiment of the present invention. Printer 20 shown in Fig. 1 is purely schematic to illustrate that the invention can be performed on any liquid toner printer or copier. It is contemplated that the invention will be applied to the HP Indigo family of digital printers and can be applied to sheet fed or web fed (as shown) printers. It can be applied to systems which transfer toner to a final substrate either one color separation as well as to printers which transfer all the separations to an intermediate transfer member and then transfer the group of separations to the final substrate together. Furthermore, the exact mode of development is not important to the practice of the invention, and development can be by binary (layerwise) transfer of high concentration toner or by electrophoretic development using any of the multitude of methods known for bringing the toner into contact with a latent image. It is also noted that whereas in printing press 20, photoreceptor 28 is a cylindrically shaped photoreceptor on a surface of a rotating drum or cylinder, practice of the present invention is not limited to cylindrically shaped photoreceptors or "rotating" photoreceptors. Apparatus or a cleaning fluid in accordance with an embodiment of the invention may be used for example to wash and clean a flat planar photoreceptor or a web or belt type photoreceptor. Printer 20 optionally comprises conventional components such as a photoreceptor imaging cylinder 26 having a photoreceptor 28 attached or bonded to it and an axis 30 about which the cylinder rotates, an intermediate transfer member (ITM) 32 and an impression roller 34. In the printer shown, the images are printed on a web 36. A charger 42 and a laser unit 44 that provides a scanning laser beam 46 for generating latent images on photoreceptor 28, a developer 52 for developing the latent images and a conventional cleaning station 60 are positioned around the perimeter of photoreceptor surface 28. Cleaning station 60 comprises apparatus and is configured to perform cleaning of the surface of photoreceptor 28 in accordance with devices and methods known in the art. Typically, cleaning station 60 comprises a reservoir containing a quantity of a same carrier liquid that is comprised in a liquid toner used by printer 20 to print images and a wetting roller that takes up carrier fluid from the reservoir and applies it to the photoreceptor surface. The applied carrier fluid washes a surface region of photoreceptor 28 to which it is applied of excess toner and dirt and is thereafter removed from the region by a sponge roller and wiper blade in cleaning station 60. Carrier fluid and contaminants removed by the sponge roller are squeezed from the roller and flow back to the reservoir. The wiper blade dries the photoreceptor surface region of carrier fluid remaining after it passes the sponge roller. Carrier fluid in the reservoir is refreshed as needed when contaminants degrade its cleaning effectiveness.

In accordance with an embodiment of the invention, in addition to conventional components, printer 20 comprises a contaminant removal apparatus 70, comprising an applicator, optionally a roller 72, a contamination removing fluid reservoir 74 containing contamination removing fluid 80 and a driving mechanism (not shown). In some embodiments of the invention an abrasive mechanism is used instead of or in addition to contamination removing fluid.

Fig. 2A shows a cross-sectional view of printer 20 in which a part of roller 72 located inside the reservoir is indicated by a dashed line and the surface of the fluid 80 in reservoir 74 is indicated by a dashed line. Roller 72 contacts and is wetted by fluid 80 in the reservoir.

By way of example, printer 20 is shown printing an image 24 (shown as an outline) on substrates, for example on a web 40 of paper. Unprinted web 24 is fed to printer 20 in a direction indicated by block arrow 38 and the printed web is optionally coEected in a manner known in the art. Arrows 41 indicate directions in which the photoreceptor, ITM and impression roller 34 rotate during printing of image 22.

During printing, as schematically indicated in Fig. 1 and Fig. 2A, roller 72 of contaminant removal apparatus 70 is optionally positioned by the cleaner's driving mechanism so that the applicator does not contact the surface of photoreceptor 28.

In the typical printing process shown, as cylinder 26 rotates, charger 42 charges photoreceptor surface 28 so that it has a substantially uniform surface charge density. Laser unit 44 focuses laser beam 46 (or a plurality of laser beams) onto photoreceptor surface 28 and directs the laser beam to repeatedly scan the charged photoreceptor surface along a scan line (or a plurality of parallel lines) substantially parallel to axis 30 of the photoreceptor. A block arrow 48 indicates the scan direction of laser beam 46. During a scan of photoreceptor surface 28, as laser beam 46 moves along the scan line, laser unit 44 selectively turns on and turns off the laser beam to respectively discharge or leave charged, pixels along the scan line and generate a latent image of an image to be printed by printer 20. A toner of suitable color is applied to the latent image as it passes developer 52. The toner is transferred from the latent image to ITM 32 and from the ITM to a sheet of paper 24 fed to printer 20 by conveyor 36 as the sheet passes through a nip 54 between ITM 24 and impression roller 34. In printers that do not comprise an ITM, toner is transferred directly from the photoreceptor to the substrate. Following transfer of toner from photoreceptor 28 to ITM 32, the region of photoreceptor 28 from which the toner was transferred passes through cleaning station 60 where excess toner, and dirt are removed from the photoreceptor in a conventional cleaning process. Thereafter, the region returns to charger 42 where it is again uniformly charged in preparation for generation of another latent image on the photoreceptor. Whereas conventional cleaning station 60 generally performs satisfactorily for removal of excess toner and particulate dirt, it is relatively ineffective in removing charge director and fluid carrier molecules that tend to bond with the organic material from which photoreceptor surface 28 is formed. The accumulated contaminants tend to generate conductive paths in surface 28 that are parallel to the surface of the photoreceptor. As a result, the contaminants degrade the resolution with which laser unit 46 generates latent images on the photoreceptor and uniformity and magnitude of force which adheres toner to the latent image, thereby degrading quality of images printed by the printer. To some extent, deleterious effects of the contaminants may be compensated for by adjusting operating parameters, such as voltage between developer 52 and surface 28. However, over tune the contaminants accumulate to such an extent that their effects on image quality cannot readily be compensated for by adjusting printer parameters to maintain a desired image quality. To maintain a desired printed image quality, photoreceptor 28 is generally replaced. Replacing photoreceptor 28 results in down time for the printer and increased printing costs.

Contaminant removal apparatus 70 operates, in accordance with an embodiment of the invention, to remove contaminants from photoreceptor surface 28 that conventional cleaning station 60 is relatively ineffective in removing and to thereby increase the useful lifetime of the photoreceptor and maintain quality of images printed by printer 20.

In accordance with an embodiment of the invention, during printing of printer 20 printing of images is intermittently interrupted and generation and development of latent images halted to operate contaminant removal apparatus 70 to clean photoreceptor surface 28. (If abrasive contaminant removal is used, the printing may not need to be interrupted.) Alternatively, the process is performed, in the morning at start up. To perform the contaminant removal, the printing press is operated so that cylinder 26 rotates and the driving mechanism of cleaner 70 positions roller 72 so that it contacts and rolls along photoreceptor surface 28. The driving mechanism that moves and positions roller 72 to engage or disengage photoreceptor 28 may be configured in accordance with any of many different methods and comprise any of many different components known in the art. For example, contaminant removal apparatus 70 and/or roller 72 may be controlled and positioned by pneumatic and/or hydraulic pistons, electric or piezoelectric motors or actuators. During contact with photoreceptor 28, roller 72 absorbs cleaning fluid from reservoir 74 and applies the cleaning fluid to the photoreceptor. In one embodiment of the invention, the applied cleaning fluid removes the contaminants, by dissolving a thin layer (generally less than 100 nanometers thick, sometimes up to 200 nanometers may be necessary) from the photoreceptor surface. In some embodiments of the invention, the cleaning fluid removes the contaminants by dissolving them. In some embodiments, both effects take place. In some embodiments, the contaminant removal liquid is removed, mechanically. In others, the liquid evaporates.

Fig. 2B shows a cross section a view of printer 20 with roller 72 in contact with photoreceptor 28. This entire process is optionally controlled by a controller 100. In an embodiment of the invention, the cleaning fluid comprises a 2% to 10% solution by weight of propylene carbonate (an etchant) in a suitable solvent such as water, alcohol (such as isopropanol alcohol (IPA)), Glycerol formal a dioxane or a dioxalane. During each cleaning roller 72 is pressed to contact photoreceptor 28 for a period of time lasting from about 10 sec to about 20 sec. The inventors have found that concentration of propylene carbonate and contact time of the roller and photoreceptor can be varied to provide different aggressiveness of contaminant removal. The contamination (and the results of the contaminant removal) manifest themselves mainly in the efficiency of development and transfer of very small areas of toner, since these are most sensitive to this type of contamination. The time, concentration and interval between contaminant removal can be adjusted to provide satisfactory small area transfer, while minimizing the damage to the photoreceptor.

Optionally, the cleaning fluid comprises a solution that dissolves phospholipids. Optionally, the solution is a solution of phosphoric acid or an acetylenic diol.

In some embodiments of the invention, the cleaning fluid comprises a solution of at least one Glycol ether chosen from the group of Glycol ethers consisting of: Dipropylene glycol monomethyl ether (DPM); Butylene glycol monobutyl ether (DBE); and Ethylene glycol n-butyl dimethykl ether (DMM).

In some embodiments of the invention, a cleaning cycle by cleaner 70 is initiated by an operator of printing press 20 in response to a determination that images printed by the printer are not of acceptable quality. In some embodiments of the invention, cleaning is initiated automatically by a controller that monitors print quality or at specific intervals (numbers of prints.

It is noted that whereas in printing press 20 photoreceptor surface 28 is a cylindrically shaped photoreceptor on a surface of a rotating drum or cylinder, practice of the present invention is not limited to cylindrically shaped photoreceptors or "rotating" photoreceptors. A cleaning fluid in accordance with an embodiment of the invention may be used for example to wash and clean a flat planar photoreceptor or a web or belt type photoreceptor.

In the description and claims of the present application, each of the verbs, "comprise" "include" and "have", and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons of the art. The scope of the invention is limited only by the following claims.

Claims

1. A method of cleaning a photoreceptor of an electro stato graphic printer on which latent images are formed, the method comprising: cleaning the photoreceptor with a first cleaning method with a first frequency; removing contaminants from the photoreceptor at a second lower frequency.

2. A method according to claim 1 wherein cleaning the photoreceptor with a first frequency comprises cleaning the photoreceptor during or after each printing cycle of the printer.

3. A method according to claim 1 or claim 2 wherein the second frequency comprises removing contaminant at an interval greater than 1000 impressions.

4. A method according to claim 3 wherein the interval is greater than 5,000 impressions.

5. A method according to claim 3 wherein the interval is greater than 10,000 impressions.

6. A method according to claim 3 wherein the interval is greater than 40,000 impressions.

7. A method according to any of the preceding claims wherein removing contaminants comprises removing contaminants by periodically abrading the surface of the receptor.

8. A method according to any of the preceding claims wherein removing contaminants comprises removing contaminants by chemical action on the contaminants.

9. A method according to claim 8 wherein removing the contaminants comprises applying a contamination removal fluid to the photoreceptor to etch away an outer surface layer of the photoreceptor.

10. A method according to claim 8 wherein the removing the contaminants comprises applying a contamination removal fluid to the photoreceptor to provide at least one effect from the group consisting of dissolving the contaminants, etching the surface of the photoreceptor or breaking a bond between the contaminants and the photoreceptor.

11. A method of cleaning a photoreceptor of an electrostatographic printer on which latent images are formed, the method comprising: providing a contamination removal fluid comprising a substance that dissolves a material from which the photoreceptor is made; and applying the contamination removal fluid to the photoreceptor to etch away an outer surface layer of the photoreceptor.

12. A method according to claim 9 or claim 10 wherein the contamination removal fluid comprises a substance that dissolves a material from which the photoreceptor is made.

13. A method according to claim 11 or claim 12 and including controlling an amount of the dissolving substance in the fluid so that the contamination removal fluid etches the photoreceptor to a desired depth.

14. A method according to claim 13 wherein the desired depth is less than about 100 nanometers.

15. A method according to any of claims 9-14 wherein applying the contamination removal fluid comprises controlling a duration during which the contamination removal fluid is applied so that the cleaning fluid etches the photoreceptor to the desired depth.

16. A method according to any of the preceding claims wherein the material from which the photoreceptor is made comprises an organic material.

17. A method according to any of claims 9-16 wherein the contamination removal fluid comprises a solution comprising propylene carbonate and a solvent.

18. A method according to claim 17 wherein the solvent comprises one or more solvents from the group consisting of: water, alcohol, dioxane and dioxalane.

19. A method according to claim 18 wherein the solvent is isopropyl alcohol.

20. A method according to claim 8 or claim 9 wherein the solvent comprises Glycerol formal.

21. A method according any of claims 17-20 wherein the contamination removal fluid comprises between 2% and 10% by weight of propylene carbonate.

22. A method according to any of claims 9-21 wherein the contamination removal fluid comprises at least one substance that dissolves phospholipids.

23. A method according to claim 22 wherein the at least one substance comprises phosphoric acid.

24. A method according to claim 22 or claim 23 wherein the at least one substance comprises acetylenic diol.

25. A method according to any of the preceding claims wherein the method is performed while the photoreceptor is mounted in the printer.

26. A method according to any of the preceding claims wherein the latent images are developed using a liquid toner.

27. A method according to any of the preceding claims wherein the photoreceptor is charged by a corona discharge prior to formation of the latent image.

28. Printing apparatus, comprising: a photoreceptor on which a latent image is formed; a developer that develops the latent image by adhering toner particles to portions of the latent image; a transfer mechanism for transferring the developed image from the photoreceptor; a cleaning mechanism that remover toner and other solid matter from the photoreceptor after the transfer of the developed image; and a separate contaminant removal system that removes contaminants from the photoreceptor.

29. Apparatus according to claim 28 wherein the cleaning mechanism cleans the photoreceptor at a higher frequency that the contaminant removal system.

30. Apparatus according to claim 29 or claim 28 wherein the cleaning mechanism cleans the photoreceptor after each image is transferred from the photoreceptor.

31. Apparatus according to any of claims 28-30 wherein the contaminant removal system removes contaminants at a frequency at least an order of magnitude less frequently than the cleaning mechanism cleans the photoreceptor.

32. Apparatus according to any of claims 29-31 wherein the developer develops the latent image using liquid toner.

33. Apparatus according to any of claims 28-32 wherein the contaminant removal system applies a contaminant removal liquid to the photoreceptor.

34. Apparatus according to claim 33 wherein the contaminant removal liquid etches the surface of the photoreceptor.

35. Apparatus according to claim 33 or claim 34 wherein the contaminant removal system dissolves materials chemically bonded to the photoreceptor.

36. Apparatus according to claims 31 or claim 32 wherein the contaminant removal system mechanically abrades the surface of the photoreceptor.