Patent Publication Number: US-10331073-B2

Title: Cleaning a silicon photoconductor

Description:
PRIORITY 
     This application is a Continuation of commonly assigned and co-pending U.S. patent application Ser. No. 15/511,711, filed Mar. 16, 2017, which is a national stage filing under 35 U.S.C. § 371 of PCT Application Number PCT/EP2014/069898, having an international filing date of Sep. 18, 2014, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     Electro-photographic (EP) printing devices form images on print media by placing a uniform electrostatic charge on a photoconductor and then selectively discharging the photoconductor in correspondence with the images. The selective discharging forms a latent electrostatic image on the photoconductor. Colorant is then developed onto the latent image of the photoconductor, and the colorant is ultimately transferred to the media to form the image on the media. In dry EP (DEP) printing devices, toner is used as the colorant, and it is received by the media as the media passes below the photoconductor. The toner is then fixed in place as it passes through heated pressure rollers. In liquid EP (LEP) printing devices, ink is used as the colorant instead of toner. In LEP devices, an ink image developed on the photoconductor is offset to an image transfer element, where it is heated until the solvent evaporates and the resinous colorants melt. This image layer is then transferred to the surface of the print media being supported on a rotating impression drum. 
     Achieving high print quality (PQ) with an electrophotographic printing device depends in part on keeping the photoconductor clean, so that it has a high surface resistivity that can maintain the electrostatic latent image. However, during the normal printing process, the photoconductive surface accumulates contamination and becomes oxidized. The photoconductive surface can also absorb moisture. The contaminants, oxidation, and moisture, can create lateral conductivity across the surface, resulting in poor PQ, blurriness of edges, and elimination of small elements such as dots and lines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  shows an example of a system for cleaning an amorphous silicon photoconductor; 
         FIG. 2  shows an example of a printing device suitable for use in a system for cleaning an amorphous silicon photoconductor; 
         FIG. 3  shows a box diagram of an example controller suitable for implementing within an LEP printing press to control a heat cycling process to evaporate remaining rinsing solution from a silicon photoconductor; 
         FIGS. 4 and 5  show flow diagrams that illustrate example methods related to cleaning an amorphous silicon photoconductor in a cleaning station using a base-peroxide solution and heat cycling the photoconductor to evaporate liquid following the cleaning. 
     
    
    
     Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. 
     DETAILED DESCRIPTION 
     Photoconductors in electrophotographic printing devices generally comprise a photo imaging component such as an amorphous silicon photoreceptor mounted on or wrapped around an imaging drum or cylinder. The photoreceptor defines an outer surface of the imaging drum on which images can be formed. Over time, as an electrophotographic printing device produces more and more printed output, the surface of the amorphous silicon photoconductor becomes contaminated and develops an outer oxidized layer. The photoconductive surface can also absorb moisture, and contaminants including dirt and other matter can accumulate on the photoconductive surface, for example, by attaching to water vapor. This layer of contamination and oxidation reduces the photoconductor&#39;s ability to print clearly, especially with regard to smaller printed elements such as lines and dots. The contaminated surface of the amorphous silicon photoconductor causes lateral conductivity across the surface that interferes with the formation and strength of latent images on the photoconductor. The lateral conductivity enables ink to move around on the photoconductor surface instead of staying in place. This can cause print quality issues such as printed lines that collide with one another so they appear as branches of a tree instead of as straight lines. 
     Removing contamination from the surface of an amorphous silicon photoconductor has been shown to substantially improve or restore the print quality of electrophotographic printing devices. Prior methods of cleaning the surface of such photoconductors include the use of abrasion techniques that grind off the contamination layer. Unfortunately, such techniques also typically involve contacting the silicon surface of the photoconductor with abrasive material during cleaning, which can grind down and/or deplete the surface of the photoconductor, leading to a significant reduction in photoconductive depth. Such depth reductions can shorten the lifespan of the photoconductor and thereby increase the overall cost of operating the electrophotographic printing device. 
     Accordingly, example methods and systems described herein provide for the cleaning of a silicon photoconductor in a manner that restores high print quality without depleting the photoconductor or otherwise reducing its lifespan. A cleaning process includes contacting the photoconductor with a base-peroxide solution, and then rinsing it with a rinsing solution. In some examples, application of the base-peroxide solution and rinsing solution can take place inside a cleaning station after removing the photoconductor from a printing device. Following the cleaning and rinsing in the cleaning station, the photoconductor surface is wiped substantially dry and then exposed to heat treatment cycles to evaporate the remaining rinsing solution from the photoconductor. The cleaning and heat cycling of the silicon photoconductor significantly improves the quality of printed pages produced with the photoconductor by reducing or eliminating lateral conductivity and the resulting blurriness of print features caused by the contaminants, oxide layer, and moisture. 
     In one example, a method of cleaning a silicon photoconductor on an imaging drum includes contacting the silicon photoconductor with a base-peroxide solution, and rinsing the silicon photoconductor with a liquid. The photoconductor is then heated to evaporate the liquid from the photoconductor. In some examples, excess liquid is wiped off the silicon photoconductor prior to heating the photoconductor. 
     In another example, a system for cleaning a silicon photoconductor includes an electrophotographic printing device and a silicon photoconductor that is removable from the printing device. The system also includes a cleaning station comprising a base-peroxide solution and a rinsing solution. The cleaning station is to receive the photoconductor, and within the cleaning station the photoconductor is to be brought into contact with the base-oxide solution and then rinsed with the rinsing solution. The system also includes a photoconductor heating mechanism to heat the photoconductor to evaporate remaining rinsing solution from the photoconductor. 
     In another example, a non-transitory machine-readable storage medium stores instructions that when executed by a processor of a printing device, cause the printing device to receive from a cleaning station, a silicon photoconductor that has been cleaned and rinsed within the cleaning station using, respectively, a base-peroxide solution and rinsing solution. In response to receiving the silicon photoconductor, the printing device is to perform heat cycling in order to evaporate any remaining rinsing solution from the silicon photoconductor. 
       FIG. 1  conceptually illustrates an example system  100  for cleaning a silicon photoconductor in a manner that restores high print quality without depleting the photoconductor or otherwise reducing the lifespan of the photoconductor. System  100  includes a print-on-demand electrophotographic printing device  102 , such as a liquid electrophotographic printing press. The printing device  102  includes a removable photoconductor  104  for forming images to be printed. In some examples, the removable photoconductor  104  comprises an amorphous silicon photoconductive layer (i.e., a photoreceptor) mounted on, or wrapped around, an imaging drum or cylinder as further discussed herein below. Thus, as discussed herein, the removable photoconductor  104  is generally considered to comprise an amorphous silicon photoconductor  104 . However, there is no intent to limit photoconductor  104  in this regard, and in other examples a photoconductor may incorporate a photoconductive layer comprising another appropriate photoconductive material such as a crystalline silicon photoconductive material. 
     The printing device  102 , discussed in greater detail below, also includes a heating mechanism such as photoconductor heater  106 , and a heat cycling module  108 . In different examples, a heat cycling module  108  can comprise hardware, programming instructions, or a combination of hardware and programming instructions designed to perform a particular function or combination of functions. Hardware incorporated into module  108  can include, for example, a processor and a memory, while the programming instructions comprise code stored on the memory and executable by the processor to perform the designated function. One such function can include, for example, performing cyclical heating of the removable amorphous silicon photoconductor  104  by controlling the photoconductor heater  106 , the removable photoconductor  104 , and other components of printing device  102 . 
     Along with printing device  102 , system  100  includes a cleaning station  110 . Cleaning station  110  comprises a base-peroxide solution  112  and a rinsing solution  114 . In different examples, components of the base-peroxide solution  112  (i.e., base  112   a  and oxidizing agent  112   b ) may be retained in the cleaning station  110  separately or together. Thus, the cleaning station  110  may be adapted for the separate contact of a base  112   a  and an oxidizing agent  112   b  with the photoconductor  104 . In some examples, the cleaning station  110  may comprise separate receptacles, each containing one of the base  112   a  and the oxidizing agent  112   b , so that the photoconductor  104  can be contacted separately with the base  112   a  and the oxidizing agent  112   b . The cleaning station  110  may be adapted to rinse the photoconductor  104  after contact with the base  112   a  and before the oxidizing agent  112   b  or, in another example, after contact with the oxidizing agent  112   b  and before the base  112   a . In some examples, the cleaning station  110  is adapted to contact the base  112   a  and the oxidizing agent  112   b  at the same time with the photoconductor  104 . The cleaning station  110  may comprise a receptacle containing the base  112   a  and the oxidizing agent  112   b  in a carrier liquid (e.g., water, which may be deionized water) as a single base-peroxide solution  112 , so that the photoconductor  104  can be contacted with the base-peroxide solution  112 . The cleaning station  110  may retain the base  112   a  and the photoconductor  104  in any suitable receptacle, which may have walls of a material that is resistant to corrosion from the base  112   a  and the oxidizing agent  112   b . The receptacle may, for example, have walls comprising a material selected from a glass, a metal, such as stainless steel, or a plastic, such as polyethylene. 
     In some examples, contacting the photoconductor  104  with the base-peroxide solution  112  can include immersing some or all of the photoconductor  104  in the solution  112 . In other examples, contacting the photoconductor  104  with the base-peroxide solution  112  can include spraying or running a base-peroxide solution  112  comprising the base  112   a  and the oxidizing agent  112   b  over some or all of the surface of the photoconductor  104 . 
     In some examples, system  100  can be adapted to automatically transfer the amorphous silicon photoconductor  104  from the printing device  102  to the cleaning station  110 , carry out a method of cleaning the photoconductor  104  involving contacting the photoconductor  104  with a base  112   a  and an oxidizing agent  112   b , rinse the photoconductor  104  with a liquid, and transfer the photoconductor  104  from the cleaning station  110  back to the printing device  102 . The system  100  may be adapted to transfer the photoconductor  104  from the printing device  102  to the cleaning station  110  at a point that is initiated by a user or at a point that is predetermined, such as when a certain level of background is measured on print media during printing, or when a certain number of print cycles has been reached (e.g., on the order of 200,000 print cycles to 1,000,000 print cycles. The system  100  may be adapted to carry out a method as described herein, either manually or automatically, and may be controlled by a computer. 
     The method may involve rinsing the photoconductor  104  with a rinsing solution  114 , which may lack or substantially lack an oxidizing agent and a base. The rinsing solution  114  used for rinsing may be the same as or different from any liquid used in the base-peroxide solution  112  for the oxidizing agent  112   b  and the base  112   a  during the contacting step. The method may involve rinsing the photoconductor  104  with a rinsing solution  114  immediately after contacting the photoconductor  104  with the base  112   a  and the oxidizing agent  112   b . There may be no intervening steps between contacting the photoconductor  104  with the base  112   a  and the oxidizing agent  112   b , and rinsing the photoconductor  104  with a rinsing solution  114 . Rinsing may include, for example, immersing the photoconductor  104  in the rinsing solution  114 , or spraying or running the rinsing solution  114  over the surface of the photoconductor  104 . The rinsing solution  114  may be a rinsing solution  114  in which the base and/or the oxidizing agent are soluble. The rinsing solution  114  may be a protic solvent (e.g., selected from water and an alkanol). The rinse may remove all or substantially all of the base  112   a  and the oxidizing agent  112   b  from the photoconductor  104 , and any other matter that may have been removed from the surface of the photoconductor  104  during the contact with the base  112   a  and the oxidizing agent  112   b.    
     The base  112   a  can be selected from a metal hydroxide, ammonia, an alkyl amine, a metal carbonate, and a metal hydrogen carbonate, and/or the base may be dissolved in a liquid carrier medium, which may be a protic solvent, including, but not limited to, a protic solvent selected from water and an alkanol (e.g., a C1 to C5 alkanol, methanol and ethanol). In some examples, the base can be ammonium hydroxide, which can be considered to be ammonia in water. The metal hydroxide can be selected from an alkali metal hydroxide, including, but not limited to, lithium hydroxide, sodium hydroxide, potassium hydroxide, and caesium hydroxide, and an alkali earth metal hydroxide, including, but not limited to, magnesium hydroxide, calcium hydroxide and barium hydroxide. The alkyl amine may be selected from a primary alkyl amine, a secondary alkyl amine and a tertiary alkyl amine. The alkyl amine may be of the formula NRaRbRc, wherein Ra, Rb and Rc are each selected from H and an optionally substituted alkyl, and at least one of Ra, Rb and Rc is an optionally substituted alkyl, which may be straight chain or branched and which may be an optionally substituted C1 to C10 alkyl (C1 to C10 not including any substituents that may be present), in some examples an optionally substituted C1 to C5 alkyl, in some examples an optionally substituted C1 to C3 alkyl. If the alkyl is substituted, the substituents on the alkyl may be selected, for example, from hydroxyl, alkyloxy, aryl, and halogen. The alkyl amine may be selected from methylamine, ethylamine, ethanol amine, dimethylamine, methylethanolamine and trimethylamine. The metal of the aqueous metal hydroxides can be selected from alkali metal hydroxides, including, but not limited to, lithium hydroxide, sodium hydroxide, potassium hydroxide, and caesium hydroxide. The metal of the metal carbonates or metal hydrogen carbonates may be an alkali metal (e.g., lithium, sodium or potassium). 
     The oxidizing agent  112   b  may be selected from a peroxide, ozone, a peroxyacid, and an oxyacid, which may be a metal oxyacid. The peroxide may be selected from hydrogen peroxide, barium peroxide, benzoyl peroxide, 2-butanone peroxide, tert-butyl hydroperoxide, calcium peroxide, cumene hydroperoxide, dicumyl peroxide, lithium peroxide, benzoyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, di-tert-amyl peroxide, lauroyl peroxide, tert-butyl hydroperoxide, magnesium peroxide, nickel peroxide, sodium peroxide, strontium peroxide and zinc peroxide. The peroxy acid may be selected from perbenzoic acid, 3-chloroperbenzoic acid, peracetic acid. The oxidizing agent may be selected from a chromate, a permanganate and osmium tetroxide. The chromate may be selected from ammonium dichromate, 2,2_-Bipyridinium chlorochromate, bis(tetrabutylammonium) dichromate, chromium(VI) oxide, imidazolium dichromate, potassium dichromate, pyridinium dichromate, sodium dichromate dehydrate, and tetrabutylammonium chlorochromate. 
     In some examples, the base-peroxide solution  112  containing the base  112   a  and the oxidizing agent  112   b  is formed by combining 1 part by volume of ammonium hydroxide (e.g. containing about 20-30 wt % ammonia, the balance being water), 1 part by volume of aqueous hydrogen peroxide (e.g., containing about 20 to 35 wt % hydrogen peroxide, with the balance water) and 5 parts by volume water, which may be deionized water. 
     In some examples, the base-peroxide solution  112 , or the base  112   a  and the oxidizing agent  112   b  separately, are at a temperature of approximately 75° C. to 80° C. during the contacting with the amorphous silicon photoconductor  104 . However, in other examples, the base-peroxide solution  112 , or the base  112   a  and the oxidizing agent  112   b  separately, can be at a temperature within the range of about 40° C. to 100° C. during the contacting with the photoconductor  104 . In some examples, the base-peroxide solution  112 , or the base  112   a  and the oxidizing agent  112   b  separately, may contact the photoconductor  104  for a period of time on the order of 10 minutes. However, in other examples, the contact period may be a period within the range of about 1 minute to 20 minutes. 
       FIG. 2  illustrates an example of a printing device  102  suitable for use in a system  100  for cleaning an amorphous silicon photoconductor  104 . As noted above, printing device  102  comprises a print-on-demand device, implemented as a liquid electrophotographic (LEP) printing press  102 . An LEP printing press  102  generally includes a user interface  200  that enables the press operator to manage various aspects of printing, such as loading and reviewing print jobs, proofing and color matching print jobs, reviewing the order of the print jobs, and so on. The user interface  200  typically includes a touch-sensitive display screen that allows the operator to interact with information on the screen, make entries on the screen, and generally control the press  102 . In one example, the user interface  200  enables the press operator to manually initiate a pause phase that temporarily suspends printing, and then to end the pause phase in order to resume printing. A user interface  200  may also include other devices such as a key pad, a keyboard, a mouse, and a joystick, for example. 
     A LEP printing press  102  includes a print engine  202  that receives a print substrate, illustrated as print media  204  (e.g., cut-sheet paper or a paper web) from a media input mechanism  206 . After the printing process is complete, the print engine  202  outputs the printed media  208  to a media output mechanism, such as a media stacker tray  210 . The printing process is generally controlled by a print controller  220  to generate the printed media  208  using digital image data that represents words, pages, text, and images that can be created, for example, using electronic layout and/or desktop publishing programs. Digital image data is generally formatted as one or more print jobs stored and executed on print controller  220 , as further discussed below with reference to  FIG. 3 . 
     The print engine  202  includes a photo imaging component, such as an amorphous silicon photoconductor  104  that is removable from the print engine  202 . Photoconductor  104  comprises an amorphous silicon photoreceptor layer  212  mounted on (e.g., wrapped around) an imaging drum  214  or imaging cylinder  214 . The amorphous silicon photoreceptor layer  212  defines an outer surface of the imaging drum  214  and/or photoconductor  104  on which images can be formed. A charging component such as charge roller  216  generates electrical charge that flows toward the photoreceptor surface and covers it with a uniform electrostatic charge. The print controller  220  uses digital image data to control a laser imaging unit  218  to selectively expose the photoconductor  104 . The laser imaging unit  218  exposes image areas on the photoconductor  104  by dissipating (neutralizing) the charge in those areas. Exposure of the photoconductor  104  creates a ‘latent image’ in the form of an invisible electrostatic charge pattern that replicates the image to be printed. 
     After the latent/electrostatic image is formed on the photoconductor  104 , the image is developed by a binary ink development (BID) roller  222  to form an ink image on the outer surface of the photoconductor  104 . Each BID roller  222  develops one ink color in the image, and each developed color corresponds with one image impression. While four BID rollers  222  are shown, indicating a four color process (i.e., a CMYK process), other press implementations may include additional BID rollers  222  corresponding to additional colors. In addition, although not illustrated, print engine  202  includes an erase mechanism and an internal cleaning mechanism which are generally incorporated as part of any electrophotographic process. In a first image transfer, the single color separation impression of the ink image developed on the photoconductor  104  is transferred electrically and by pressure from the photoconductor  104  to an image transfer blanket  224 . The image transfer blanket  224  is primarily referred to herein as the print blanket  224  or blanket  224 . The ink layer is transferred electrically and by pressure to the blanket  224  as the photoconductor  104  rotates into contact with the electrically charged blanket  224  rotating on the ITM drum  226 , or transfer drum  226 . The print blanket  224  is electrically charged through the transfer drum  226 . The print blanket  224  overlies, and is securely attached to, the outer surface of the transfer drum  226 . 
     The print blanket  224  can be heated both by an internal heating source within the ITM/transfer drum  226 , and from an external heating source such as an infrared heating lamp  228 . The heating source within the drum  226  can also be infrared heating lamps (not illustrated). While the external heating lamp  228  is illustrated as a single lamp, this is not to be construed as a limitation regarding the number, type, or configuration of such a heating lamp. Rather, heating lamp  228  is intended to represent a range of suitable configurations of heating lamps. For example, heating lamp  228  can comprise one or multiple heating lamps in various configurations, such as multiple heating lamps configured in parallel that are controlled together or individually, such as where power can be changed to all of the heating lamps at once or to just one specific heating lamp. 
     In different examples, the heated blanket  224  can perform different functions, such as an image transfer function during normal printing, or a heat cycling function to heat the photoconductor  104 . For example, in a normal printing function, the heat from the heated blanket  224  causes most of the carrier liquid in the ink to evaporate, and it also causes the particles in the ink to partially melt and blend together. This results in a finished ink image in the form of a hot, nearly dry, tacky plastic ink film. In a second image transfer, this hot ink film image impression is then transferred to a substrate such as a sheet of print media  204 , which is held by an impression drum/cylinder  230 . The temperature of the print media substrate  204  is below the melting temperature of the ink particles, and as the ink film comes into contact with the print media substrate  204 , the ink film solidifies, sticks to the substrate, and completely peels off from the blanket  224 . 
     This imaging process is repeated for each color separation in the image, and the print media  204  remains on the impression drum  230  until all the color separation impressions (e.g., C, M, Y, and K) in the image are transferred to the print media  204 . After all the color impressions have been transferred to the sheet of print media  204 , the printed media  208  sheet is transported by various rollers  232  from the impression drum  230  to the output mechanism  210 . 
       FIG. 3  shows a box diagram of an example controller  220  suitable for implementing within an LEP printing press  102  to control a heat cycling process to evaporate remaining rinsing solution  114  from the photoconductor  104  after cleaning the photoconductor  104  in a cleaning station  110 . Referring to  FIGS. 2 and 3 , print controller  220  generally comprises a processor (CPU)  300  and a memory  302 , and may additionally include firmware and other electronics for communicating with and controlling the other components of print engine  202 , the user interface  200 , and media input ( 206 ) and output ( 210 ) mechanisms. Memory  302  can include both volatile (i.e., RAM) and nonvolatile (e.g., ROM, hard disk, optical disc, CD-ROM, magnetic tape, flash memory, etc.) memory components. The components of memory  302  comprise non-transitory, machine-readable (e.g., computer/processor-readable) media that provide for the storage of machine-readable coded program instructions, data structures, program instruction modules, JDF (job definition format), and other data for the printing press  102 , such as heat cycling module  108 . The program instructions, data structures, and modules stored in memory  302  may be part of an installation package that can be executed by processor  300  to implement various examples, such as examples discussed herein. Thus, memory  302  may be a portable medium such as a CD, DVD, or flash drive, or a memory maintained by a server from which the installation package can be downloaded and installed. In another example, the program instructions, data structures, and modules stored in memory  302  may be part of an application or applications already installed, in which case memory  302  may include integrated memory such as a hard drive. 
     As noted above, controller  220  uses digital image data to control the laser imaging unit  218  in the print engine  202  to selectively expose the photoconductor  104 . More specifically, controller  220  receives print data  304  from a host system, such as a computer, and stores the data  304  in memory  302 . Data  304  represents, for example, documents or image files to be printed. As such, data  304  forms one or more print jobs for printing press  102  that each include print job commands and/or command parameters. Using a print job from data  204 , print controller  220  controls components of print engine  202  (e.g., laser imaging unit  218 ) to form characters, symbols, and/or other graphics or images on print media  204  through a printing process as has been generally described above with reference to  FIG. 2 . 
     Referring to  FIGS. 2 and 3 , as previously mentioned, in addition to an image transfer function, the heated blanket  224  enables a photoconductor heat cycling function to heat the amorphous silicon photoconductor  104  and evaporate rinsing solution  114  that may remain on the surface of the photoconductor  104  after the photoconductor  104  undergoes a cleaning process in cleaning station  110 . This heat cycling function can be controlled, for example, by controller  220  executing instructions from heat cycling module  108 . Thus, heat cycling module  108  comprises machine-readable instructions that are executable on processor  300  to control the heat cycling of photoconductor  104 . Controlling the heat cycling can include controlling a photoconductor heater  106  (e.g., heating lamp  228  and blanket  224 ) to cycle the temperature of the photoconductor  104 . In one example, cycling the photoconductor  104  temperature includes heating the blanket  224  with heating lamp  228 , and engaging the blanket  224  with the photoconductor  104  as imaging drum  214  and ITM drum  226  rotate against one another. Thus, upon receiving the photoconductor  104  in the printing press  102  from a cleaning station  110 , the controller  220  can heat the blanket  224  with heating lamp  228 , and cause the heated blanket  224  to be rotated against the photoconductor  104  to heat the photoconductor  104 . The heated blanket  224  can be engaged and disengaged with the photoconductor  104  in this manner a number of times in order to cycle the temperature of the photoconductor  104  up and down. Heating the photoconductor  104  in this manner for time durations and at temperatures described herein, evaporates rinsing solution  114  that may remain on the surface of the photoconductor  104  after the photoconductor  104  has been cleaned and rinsed in the cleaning station  110 . 
     Thus, in some examples, the heating lamps  228  and blanket  224  generally comprise a photoconductor heating mechanism  106  as discussed above with regard to  FIG. 1 . However, in other examples, heat may also be applied directly to photoconductor  104  using other appropriate photoconductor heating mechanisms  106 , rather than applying heat from the blanket  224 . For example, photoconductor  104  may be heated more directly from both internal heating sources positioned within the imaging drum  214 , and from external heating sources positioned outside the drum  214 . Such heating mechanisms can include infrared heating lamps, for example. 
       FIGS. 4 and 5  show flow diagrams that illustrate example methods  400  and  500 , related to cleaning an amorphous silicon photoconductor in a cleaning station using a base-peroxide solution and heat cycling the photoconductor to evaporate liquid following the cleaning. Methods  400  and  500  are associated with the examples discussed above with regard to  FIGS. 1-3 , and details of the operations shown in methods  400  and  500  can be found in the related discussion of such examples. The operations of methods  400  and  500  may be embodied as programming instructions stored on a non-transitory, machine-readable (e.g., computer/processor-readable) medium, such as memory  302  as shown in  FIG. 3 . In some examples, implementing the operations of methods  400  and  500  can be achieved by a processor, such as a processor  300  of  FIG. 3 , reading and executing the programming instructions stored in a memory  302 . In some examples, implementing the operations of methods  400  and  500  can be achieved using an ASIC (application specific integrated circuit) and/or other hardware components alone or in combination with programming instructions executable by processor  300 . 
     Methods  400  and  500  may include more than one implementation, and different implementations of methods  400  and  500  may not employ every operation presented in the respective flow diagrams. Therefore, while the operations of methods  400  and  500  are presented in a particular order within the flow diagrams, the order of their presentation is not intended to be a limitation as to the order in which the operations may actually be implemented, or as to whether all of the operations may be implemented. For example, one implementation of method  400  might be achieved through the performance of a number of initial operations, without performing one or more subsequent operations, while another implementation of method  400  might be achieved through the performance of all of the operations. 
     Referring now to the flow diagram of  FIG. 4 , an example method  400  of cleaning a silicon photoconductor begins at block  402 , with contacting the silicon photoconductor with a base-peroxide solution. In some examples, the contacting occurs in a cleaning station after the photoconductor is removed and transferred manually or automatically from an electrophotographic printing device. In some examples, the base-peroxide solution comprises ammonia and hydrogen peroxide in a carrier liquid. In some examples, the base-peroxide solution is at a temperature of at least 70° C. during the contacting with the silicon photoconductor. As shown at block  404 , the method continues with rinsing the silicon photoconductor with a liquid, which can include water, for example. As shown at block  406 , excess rinsing liquid can then be wiped off of the silicon photoconductor, for example, using a lint-free wipe. 
     The method  400  can continue as shown at block  408 , with heating the silicon photoconductor to evaporate liquid that might be remaining on the surface of the photoconductor. In some examples, the heating comprises transferring the silicon photoconductor back from the cleaning station to the electrophotographic printing device, and then heat cycling the silicon photoconductor in the electrophotographic printing device. The heat cycling can include a single cycle that increases the photoconductor temperature once, or multiple cycles that increase the photoconductor temperature multiple times. A single heat cycle can keep the photoconductor at a higher temperature for a longer time period than multiple heat cycles. In some examples, the time period of a heat cycle can depend on the number of heat cycles being performed and/or the temperature of the heat cycle, and may range from 15 minutes to 90 minutes. In some examples, heating the silicon photoconductor comprises engaging the silicon photoconductor with a heated print blanket to bring the silicon photoconductor to an operating temperature of the print blanket. In some examples, heating the silicon photoconductor comprises heat cycling the silicon photoconductor up to an evaporation temperature within the range of 90° C. to 250° C. 
     Referring now to the flow diagram of  FIG. 5 , an example method  500  related to cleaning an amorphous silicon photoconductor is shown. The method  500  begins at block  502  with receiving a silicon photoconductor that has been cleaned and rinsed by a cleaning station, where the cleaning uses a base-peroxide solution and rinsing uses a rinsing solution such as water. The photoconductor can be received at a printing press from the cleaning station. As shown at block  504 , heat cycling is then performed in response to receiving the silicon photoconductor. The heat cycling is to evaporate remaining rinsing solution from the silicon photoconductor. The heat cycling can take place in the printing press. As shown at block  506 , heat cycling can include heating a print blanket with a heating mechanism. The heat cycling can include engaging the heated print blanket with the silicon photoconductor in a first heat cycle by rotating the heated print blanket and silicon photoconductor together on drums, as shown at block  508 . The heat cycling can further include disengaging the heated print blanket from the silicon photoconductor, and then reengaging the heated print blanket with the silicon photoconductor in a second heat cycle, as shown at blocks  510  and  512 , respectively.