Patent Publication Number: US-9409384-B2

Title: Printers, methods and apparatus to form an image on a print substrate

Description:
BACKGROUND 
     Offset printing is a printing technique that uses an intermediate transfer, or offset, between an image plate and a print substrate on which the image is to be formed. Offset printing may be accomplished in sheet-fed (i.e., one sheet fed at a time) or web-fed (i.e., a continuous sheet of substrate is fed) configurations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram of an example printer to form an image on a print substrate in accordance with teachings disclosed herein. 
         FIG. 1B  is a block diagram of another example printer to form an image on a print substrate in accordance with teachings disclosed herein. 
         FIG. 2  is a schematic illustration of an example printer to form an image on a print substrate using a one-shot mode in accordance with teachings disclosed herein. 
         FIG. 3  is a schematic illustration of an example printer to form an image on a print substrate using a four-shot mode in accordance with teachings disclosed herein. 
         FIG. 4  is a schematic illustration of another example printer to form an image on a print substrate using a four-shot mode in accordance with the teachings herein. 
         FIGS. 5A-5D  illustrate an example transfer member accumulating layers of ink and coating to form an image on a print substrate in a one-shot mode. 
         FIGS. 6A-6D  illustrate an example print substrate accumulating layers of ink and coating to form an image on the print substrate in a four-shot mode. 
         FIG. 7  depicts a flowchart representative of an example method to form an image on a print substrate in a one-shot mode. 
         FIG. 8  depicts a flowchart representative of an example method to form an image on a print substrate in a four-shot mode. 
     
    
    
     Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. 
     DETAILED DESCRIPTION 
     Ink adhesion and image durability are factors that designers and users of printers consider. One of several ways to improve image durability is to provide a coating over the image printed on a print substrate. However, the application of known coatings, such as varnish, over images can reduce the speed of printing (e.g., printer throughput), which can also be an important factor in end user satisfaction. To apply known coatings requires separate coating devices and additional drying systems, which add manufacturing and operating costs to the printer and require additional space within the printer. Known coatings are also relatively thick and may not work with particular substrates. 
     Known blankets (e.g., blanket drums) tend to have dot gain, or the tendency for the dot area in a printed image to increase and/or decrease as more impressions are performed. Additionally, known blankets suffer from contamination as the impressions increase. Both dot gain and ink contamination contribute to decreased image quality as known blankets are used. 
     Example methods and apparatus disclosed herein reduce or eliminate background contamination of images, improve scratch resistance of images, and/or improve the useful life of the blanket. In some tests, the useful life of the blanket improved by a factor of 5× (e.g., from about 80,000 impressions to over 400,000 impressions in an example test). Additionally, in some examples, even after hundreds of thousands of impressions, the blanket avoids developing image memory because, in one-shot mode, the ink does not come into direct contact with the blanket and, in four-shot mode, a coating material cleans ink from the blanket with each image. As used herein, printing in “one-shot” mode refers to applying ink particles from a transfer member to a print substrate in one transfer. Printing in “four-shot” mode, as used herein, refers to applying four layers of ink particles to a print substrate via a transfer member in four transfers. While some examples disclosed herein are described with reference to four-shot mode, the methods and apparatus disclosed herein are equally applicable to different numbers of “shots” or transfers to apply ink particles to a substrate. Example methods and apparatus disclosed herein substantially maintain gloss and dot area, which also maintains high print quality. 
     Example printers and apparatus disclosed herein include an applicator to apply a coating material. They also include an ink developer to apply a plurality of ink particles. Such example printers and apparatus further include a transfer cylinder to transfer the ink particles and the coating material to a print substrate to form an image and a coating over the image. Some example printers and apparatus further include a photo imaging surface to which the coating material and/or the ink particles are applied. The coating material and/or the ink particles may then be applied to the print substrate via the transfer cylinder and/or a transfer member such as a rubber blanket. 
       FIG. 1A  is a block diagram of an example printer  100  to form an image on a print substrate  102 . The example printer  100  illustrated in  FIG. 1A  includes an applicator  104 , an ink developer  106 , and a transfer cylinder  108 . The printer  100  may operate in a one-shot mode, in which ink and a coating material accumulate on a transfer member while disengaged from paper, and the transfer cylinder  108  transfers the accumulated ink to the print substrate  102  after engaging the transfer cylinder  108 . 
     The applicator  104  of the illustrated example applies (e.g., to the transfer cylinder  108  or to a photo imaging surface) a first material  110 . The first material  110  may be, for example, a polymer coating or a transparent ink (e.g., Electro Ink, available from Hewlett-Packard). The ink developer  106  applies an ink  112  (e.g., to the transfer cylinder  108 , to another cylinder, or to the first material  110 . The first material  110  and the ink  112  are transferred to the print substrate  102  to form an image (e.g., via the ink  112 ) on the print substrate  102 , and a coating (e.g., via the first material  110 ) over the image to protect the image from damage. In some examples, the ink developer  106  is implemented using an electrophotographic engine. 
       FIG. 1B  is a block diagram of another example printer  114  to form an image on the print substrate  102 . The example printer  114  illustrated in  FIG. 1B  includes the example applicator  104 , the example ink developer  106 , and the example transfer cylinder  108  described above. The example printer  114  of  FIG. 1B  further includes a photo imaging surface  116 . In the example of  FIG. 1B , the applicator  104  and the ink developer  106  apply the first material  110  and the ink  112 , respectively, to the photo imaging surface  116 . The photo imaging surface  116  then transfers the first material  110  and the ink  112  to the print substrate  102  via the transfer cylinder  108 . More detailed examples of the example printers  100 ,  114  of  FIGS. 1A and 1B  operating in one-shot or four-shot modes are described below. While some examples are described in detail as operating in one-shot or four-shot modes, the example printers  100 ,  114  of  FIGS. 1A and 1B  are not limited to one mode of operation and, instead, may be operated in either or both of one-shot mode or four-shot mode. 
       FIG. 2  is a schematic illustration of an example imaging system or printer  200  configured to form an image upon a print substrate  102 . The example printer  200  may be used to implement an offset color press. The printer  200  of  FIG. 2  includes a photo imaging surface  204  (e.g., a photoconductor), a charger  206 , an imager  208 , developer units  210 , a charge eraser  212 , an intermediate transfer member  214 , an external heating system  216 , a dryer  218 , an impression cylinder  222  and a cleaning station  224 . The photo imaging surface  204  of the illustrated example includes a cylindrical drum  230  supporting a photo imaging plate (PIP) or some other type of electrophotographic surface  232 . The electrophotographic surface  232  is a surface that may be electrostatically charged and selectively discharged upon receiving light from the imager  208 . Although the surface  232  of  FIG. 2  is illustrated as being supported by the drum  230 , the surface  232  may alternatively be implemented as an endless belt supported by a plurality of cylinders. In such an example, the exterior surface of the endless belt may be electrostatically charged and selectively discharged to create a latent image in the form of an electrostatic field. 
     The example charger  206  of  FIG. 2  electrostatically charges the surface  232 . This provides a background electrostatic charge, which may be substantially uniform, across the surface  232 . In the illustrated example, the charger  206  includes six corotrons or scorotrons  236 . A more detailed description of a charger that may be used to implement the charger  206  may be found in U.S. Pat. No. 6,438,352, the full disclosure of which is hereby incorporated by reference. However, other devices for electrostatically charging the surface  232  may additionally or alternatively be employed. 
     The example imager  208  of  FIG. 2  may be implemented using any device configured to direct light upon the surface  232  so as to form an image. In the example shown, the imager  208  comprises a scanning laser which is moved across the surface  232  as the photo imaging surface  204  is rotated about an axis  238 . Those portions of the surface  232  which are impinged by the light or laser  240  discharge the background electrostatic charge to form a latent image upon the surface  232 . The portions of the surface  232  that are not impinged by the laser  240  maintain their respective background electrostatic charge. The imager  208  may additionally or alternatively be implemented using any other device(s) to selectively emit or selectively allow light to impinge upon the surface  232 . For example, the imager  208  may include one or more shutter devices which employ liquid crystal materials and/or devices including individual micro or nano light-blocking shutters to alternate between the light blocking and light transmitting states. 
     In some examples, the surface  232  may include an electrographic surface including an array of individual pixels configured to be selectively charged or selectively discharged using an array of switching mechanisms such as transistors or metal-insulator-metal (MIM) devices forming an active array or a passive array for the array of pixels. In these examples, the charger  206  and the imager  208  may be omitted. 
     The example developer units  210  apply ink(s)  244  (or other printing material) to the surface  232  based on the electrostatic charge on the surface  232  and develop the image on the surface  232 . In other words, those areas of the surface  232  that have been discharged by the laser  240  will receive and retain ink(s)  244  whereas those with the background charge will not. In the illustrated example of  FIG. 2 , the ink  244  is a liquid or fluid ink including a liquid carrier and colorant particles. The colorant particles may have a size of less than 1 micron (micrometers, μm), although in some examples the particle size may be different. In the illustrated example, the ink  244  generally includes approximately 2% by weight, colorant particles or solids prior to being applied to the surface  232 . In some examples, the ink  244  is Hewlett-Packard Electro Ink, which is commercially available from Hewlett-Packard. 
     In the example of  FIG. 2 , each developer unit  210  generally includes a toner chamber  246 , a main electrode  248 , a back electrode  250 , a developer roller  252 , a cleaning roller  253 , a squeegee roller  254 , a developer cleaning system  256 , and a reservoir  258 . The toner chamber  246  includes a cavity having an inlet through which printing material is supplied from the reservoir  258  to the toner chamber  246  and between the main electrode  248  and the developer roller  252 . The main electrode  248  and the back electrode  250  are situated opposite to the developer roller  252  and may be electrically charged. In the illustrated example, the back electrode  250  has a dielectric tip opposite the developer roller  252  and cooperates with the main electrode  248  to form the toner chamber  246 . 
     The example developer roller  252  of the illustrated example is rotatably driven and electrically charged to a voltage distinct from the voltage of electrode  248  so as to attract electrically charged ink particles or colorant particles of the ink  244  as the developer roller  252  is rotated. The developer roller  252  is charged such that the charged ink particles being carried by the developer roller  252  are further attracted and drawn to those portions of the surface  232  that are electrostatically charged. The cleaning roller  253  removes excess ink  244  from the surface of the developer roller  252 . In some examples, the squeegee roller  254  may be selectively charged to control the thickness or concentration of the ink  244  on the surface of the developer roller  252 . In the illustrated example of  FIG. 2 , the developer roller  252  and the squeegee roller  254  are appropriately charged so as to form a substantially uniform 6 micron thick film that is composed of approximately 20% solids on the surface of the developer roller  252  and is substantially transferred to the electrophotographic surface  232 . 
     The developer cleaning system  256  of the illustrated example removes ink  244  from the developer roller  252  that has not been transferred to the electrophotographic surface  232 . The removed ink  244  is mixed and pumped back to a reservoir  258  in which colorant particles or solid content of the liquid or fluid is precisely monitored and controlled. An example developer unit that may be used to implement the developer units  210  is discussed in U.S. Pat. No. 6,438,352, the full disclosure of which is hereby incorporated by reference. 
     The charge eraser  212  of the illustrated example is disposed along the electrophotographic surface  232  and is to remove residual charge from the surface  232 . In some examples, the charge eraser  212  is implemented by a light-emitting diode (LED) erase lamp. The intermediate transfer member  214  of the illustrated example transfers the ink  244  from the surface  232  to the print substrate  102 . The intermediate transfer member  214  of  FIG. 2  includes an exterior transfer surface  260  which is resiliently compressible and may be electrostatically charged. Because the transfer surface  260  is resiliently compressible, the surface  260  conforms and/or adapts to irregularities on the print substrate  102 . Additionally, because the surface  260  is configured to be electrostatically charged, the surface  260  may be charged to a voltage to facilitate the transfer of ink  244  from the electrophotographic surface  232  to the transfer surface  260 . In some examples, the surface  260  has a compressibility that reduces the likelihood of damage caused by permanent deformation of the surface  260 . 
     In the illustrated example of  FIG. 2 , the intermediate transfer member  214  includes a drum  262  and an external blanket  264 . The example drum  262  is a cylinder that supports the blanket  264 , and is constructed using material(s) having a relatively low thermal conductivity and/or heat resistance. The example blanket  264  of the illustrated example wraps about the drum  262  and includes the surface  260 . The example blanket  264  is constructed using a resiliently compressible layer and an electrically conductive layer, which enable the transfer surface  260  to conform and to be electrostatically charged. In some examples, the intermediate transfer member  214  includes an endless belt supported by a plurality of cylinders, including a transfer cylinder, in contact and/or in close proximity to the electrophotographic surface  232  and the impression cylinder  222 . 
     The heating system  216  of the illustrated example is external to the transfer surface  260  of the intermediate transfer member  214  and applies heat to the ink  244  being carried by the transfer surface  260  from the photo imaging surface  204  to the print substrate  102 . The heat provided by the heating system  216  drives off and/or evaporates carriers or solvents of the liquid printing material, such as Isopar. The example heating system  216  of  FIG. 2  also applies sufficient heat energy to the ink  244  to partially melt and blend solids and/or colorant particles of ink  244 , thereby forming a hot adhesive liquid plastic. 
     In the example of  FIG. 2 , an applicator  266 , or coating developer, is positioned adjacent the example intermediate transfer member  214 . The example applicator  266  of  FIG. 2  is positioned prior to the transfer point between the photo imaging surface  204  and the intermediate transfer member  214  to apply a material  268  (e.g., a polymer) directly to the transfer surface  260  prior to the transfer of the ink  244  from the photo imaging surface  204 . The example applicator  266  illustrated in  FIG. 2  is implemented using an additional developer unit similar or identical to the example developer units  210 . The example applicator  266  applies the material  268  as a uniform coating across the width of the transfer surface  260 . The photo imaging surface  204  of the illustrated example then transfers the developed ink  244  onto the coating material  268  covering the surface  260  instead of applying the ink  244  directly to the surface  260 . 
     The dryer  218  of the illustrated example facilitates partial drying of the ink  244  on the transfer surface  260 . The example dryer  218  is positioned adjacent the intermediate transfer member  214  to direct air towards the surface  260  and to withdraw air from the surface  260 . In the illustrated example, the dryer  218  forces air through an exit slit  270 , which forms an air knife, and withdraws or sucks air via an exit port  272 . 
     The example impression cylinder  222  of  FIG. 2  is a cylinder located adjacent to the intermediate transfer member  214  so as to form a nip  274  between the intermediate transfer member  214  and the cylinder  222 . The print substrate  102  is fed between the intermediate transfer member  214  and the impression cylinder  222 . The ink  244  is transferred from the intermediate transfer member  214  to the print substrate  102  at the nip  274 . Although the impression cylinder  222  is illustrated as a cylinder, the impression cylinder  222  may alternatively be implemented using an endless belt and/or a stationary surface against which the intermediate transfer member  214  moves. 
     The example cleaning station  224  of  FIG. 2  is positioned proximate to the electrophotographic surface  232  between the intermediate transfer member  214  and the charger  206 . The cleaning station  224  of the illustrated example removes residual ink and electrical charge from the surface  232 . 
     In operation using one-shot mode, the photo imaging surface  204  accumulates the desired layer(s) and/or color(s) of the ink  244  on the intermediate transfer member  214  (e.g., the coating over the surface  260 ) to form an image. In particular, before any layers of ink  244  are applied to the transfer surface  260 , the applicator  266  applies a substantially even layer of the coating material  268  to the surface  260 . 
     To apply a layer of the ink  244 , the charger  206  of the illustrated example electrostatically charges the electrophotographic surface  232 . The surface  232  is then exposed to the laser  240 , which is controlled by a raster image processor that converts instructions from a digital file into on/off instructions for the laser  240 . This controlled application of laser light to the surface results in a latent image being formed on the electrostatically discharged portions of the surface  232 . The ink developer units  210  develop an image upon the surface  232  by applying ink  244  to those portions of surface  232  that remain electrostatically charged. 
     Once an image upon the electrophotographic surface  232  has been developed, the charge eraser  212  of the illustrated example erases any remaining electrical charge on the surface  232  and the ink image is transferred to the transfer surface  260 . However, rather than transferring the developed ink  244  to the transfer surface  260  directly, in the illustrated example the ink  244  is applied to the coating material  268  that covers the transfer surface  260 . The charging, developing, discharging, and transfer from the electrophotographic surface  232  to the transfer surface  260  is then repeated for additional ink layers in preparation for the final image to be transferred to the print substrate  102 . 
     When the inks have been transferred to the transfer surface  260 , the heating system  216  of the illustrated example applies heat to the ink  244  on the surface  260  to evaporate the carrier liquid of the ink  244  and/or to melt toner binder resin of the colorant particles or solids of the ink  244  to form a hot melted adhesive. The dryer  218  dries the melted liquid colorant particles. The surface  260  is then rotated to transfer the layer of melted colorant particles forming the image to the print substrate  102  passing between the intermediate transfer member  214  and the impression cylinder  222 . The layer of melted colorant particles adheres to the print substrate  102  on contact in the nip  274  and forms the desired image on the print substrate  102 . 
     Due to the layering of the coating material  268  and the ink  244  on the intermediate transfer member  214 , in the example of  FIG. 2  the ink  244  is applied to the print substrate  102  and the coating material  268  is applied in an even layer over the print substrate  102 . By applying the coating material  268  to the print substrate  102 , the coating material  268  is substantially completely removed from the surface  260 . The applicator  266  then applies another coating to the transfer surface  260  for the next image. In this manner, the coating material  268  protects the transfer surface  260  and the blanket  264  from image memory and small dot transfer in one-shot mode. 
       FIG. 3  is a schematic illustration of an example printer  300  to form an image on a print substrate  102  using a four-shot mode. The example printer  300  includes the example photo imaging surface  204  (e.g., a photoconductor), the example charger  206 , the example imager  208 , the example developer units  210 , the example charge eraser  212 , the example intermediate transfer member  214 , the example external heating system  216 , the example dryer  218 , the example impression cylinder  222  and the example cleaning station  224  described above in conjunction with  FIG. 2 . However, the example printer  300  is different from the printer  200  in that the example applicator  266  of  FIG. 3  is implemented using one of the developer units  210  (e.g., by replacing ink in the developer unit  210  with the coating material) instead of including an additional applicator  266  adjacent the intermediate transfer member  214 . As a result, the example printer  300  is able to use one less supplementary ink color for printing. However, for many printing applications the reduced color set will not significantly affect print quality. 
     In the illustrated example printer  300  of  FIG. 3 , the applicator  266  is located in place of the second developer unit  210  of  FIG. 2  (as the photo imaging surface  204  rotates counterclockwise). During each impression cycle (e.g., ink color layer or rotation of the photo imaging surface  204 ), the appropriate developer unit  210  applies to the photo imaging surface  204  one of the colored inks (e.g., black, cyan, magenta, yellow) to be used in creating the image on the print substrate  102 . The printer  300  performs an impression cycle for each of the colored inks that are to be used to create the image on the print substrate  102 . After the appropriate developer unit  210  applies a colored ink to the electrophotographic surface  232 , the electrophotographic surface  232  transfers the colored ink to the intermediate transfer member  214 , which transfers the ink to the print substrate  102 . In the four-shot mode of the illustrated example, the colored inks accumulate on the print substrate  102  instead of the intermediate transfer member  214 . 
     If the applicator  266  were to use an additional impression cycle to apply the coating after the ink(s)  244  had been applied, the throughput of the example printer  300  would be reduced significantly because each print would require one additional impression cycle. This would result in a 25% decrease in throughput for four-color prints, a 20% decrease in throughput for five-color prints, etc. 
     To avoid the reduction in throughput, the example applicator  266  of  FIG. 3  applies the coating material  268  to the photo imaging surface  204  during the same impression cycle as one of the colored inks  244  is applied (e.g., the final impression cycle for a print), thereby saving an extra impression cycle and maintaining the throughput of the printer  300 . 
     As described above, the charger  206  applies a background charge (e.g., −950 Volts (V)) to the electrophotographic surface  232 , which is reduced in certain areas by the laser  240  to form a latent image on the electrophotographic surface  232 . The locations where the laser  240  does not write maintain the background charge. After the developer unit  210  applies the ink to the areas forming the latent image, a charge eraser  302  erases the background charge and the charge adjacent the ink  244  on the photoconductor  204  (e.g., to about −50 V). The charge eraser  302  may be constructed using, for example, a light bar including addressable light-emitting polymers (LEPs), a corona charging unit, and/or any other suitable type of eraser lamp. In the example of  FIG. 3 , the charge eraser  302  is provided in addition to the charge eraser  212 . The ink  244  remains fixed to the photoconductor  204  after the charge eraser  302  erases the background charge on the photoconductor  204 . 
     After the charge eraser  302  erases the charge, the applicator  266  of the illustrated example develops or applies the coating material over the ink  244  on the electrophotographic surface  232  to form an even or substantially even layer of the coating material  268 . The drum  230  then turns to apply the coating material  268  and the ink  244  to the intermediate transfer member  214  (e.g., the transfer surface  260 , the blanket  264 , etc.). Because the coating material  268  is applied to the electrophotographic surface  232  after the ink  244 , the coating material  268  is applied to the surface  260  between the ink  244  and the surface  260  (similar to the layering configuration in the one-shot mode described above) when the coating material  268  and the ink  244  are applied to the surface  260 . The coating material  268  therefore protects the surface  260  from at least one layer of the ink  244 . Additionally, the coating material  268  may clean the surface  260  by removing ink particles or droplets from layers of the ink  244  that contacted the surface  260  directly. In this manner, the coating material  268  extends the useful life of the surface  260  and lengthens the time until adverse imaging effects occur due to the surface  260 . 
     When the intermediate transfer member  214  applies the ink  244  and the coating material to the print substrate, the ink  244  is applied to the print substrate and the coating material is applied over the ink  244  (and any previously-applied ink layers) to coat and protect the image. 
       FIG. 4  is a schematic illustration of another example printer  400  to form an image on a print substrate  102  using a four-shot mode. Like the example printer  300  of  FIG. 3 , the example printer  400  illustrated in  FIG. 4  uses the four-shot mode by accumulating the ink  244  on the print substrate  102  instead of the intermediate transfer member  214 . The example printer  400  includes the example photo imaging surface  204  (e.g., a photoconductor), the example charger  206 , the example imager  208 , the example developer units  210 , the example charge eraser  212 , the example intermediate transfer member  214 , the example external heating system  216 , the example dryer  218 , the example impression cylinder  222  and the example cleaning station  224  described above in conjunction with  FIG. 2 . 
     Unlike the printer  300  of  FIG. 3 , however, the example printer  400  of  FIG. 4  implements the applicator  266  in the place of the last developer unit  210  in the rotational direction of the drum  230  (e.g., counterclockwise) and implements the charge eraser  302  immediately prior to the applicator  266 . Because the applicator  266  of  FIG. 4  is positioned after the developer units  210  and the charge eraser  302  is positioned immediately before the applicator  266 , the example charge eraser  212  of  FIG. 2  may be omitted. 
     As described above, the example applicator  266  applies the coating material to the electrophotographic surface  232  during the same impression cycle as one of the ink colors. Inks are applied to the print substrate  102 , one at a time, via the electrophotographic surface  232  and the intermediate transfer member  214 . During the impression cycle for the final color for the image to be printed on the print substrate  102 , the example applicator  266  applies the coating material  268 . To apply the coating material  268 , after the final color for the image is applied to the electrophotographic surface  232  in a desired pattern, the charge eraser  302  erases the background charge on the electrophotographic surface  232 . The applicator  266  then applies the coating material  268  to the electrophotographic surface  232 . 
       FIGS. 5A-5D  illustrate an example accumulation of ink and coating material on an example transfer member  502  (e.g., the transfer surface  260  of  FIGS. 2-4 ) to form an image on a print substrate (e.g., the print substrate  102  of  FIGS. 1A-4 ) in a one-shot mode. In the one-shot mode, the applicator  266  applies the coating material (e.g., the coating material  110 ,  268  of  FIGS. 1A-4 ) to the transfer member  502  before application of ink(s). The ink(s) (e.g., the ink(s)  112 ,  244  of  FIGS. 1A-4 ) that form the image on a print substrate  102  are then applied to the coating material  110 ,  268 . The transfer member  502  may be a rubber blanket such as the blanket  264  described above in conjunction with  FIG. 2 , and may be used to implement the transfer cylinder  108  of  FIG. 1A . An example method to apply the coating material  110 ,  268  and ink(s)  112 ,  244  to the transfer member  502  and to the print substrate  102  is described below with reference to  FIG. 7 . 
       FIG. 5A  illustrates the transfer member  502  prior to applying the coating material or the inks.  FIG. 5B  illustrates the transfer member  502  after the applicator  266  of  FIG. 2  applies a coating material  504  (e.g., a polymer) to the transfer member  502 . In the illustrated example, the applicator  266  applies an even or substantially even layer of the coating material  504  to the transfer member  502 . The coating material  504  is to be removed completely or substantially completely from the transfer member  502  when the transfer member  502  makes the impression of the ink(s) and the coating material  504  on a print substrate. 
       FIG. 5C  illustrates the transfer member  502  after the photo imaging surface  204  (e.g., the electrophotographic surface  232 ) of  FIG. 2  has applied a first layer of ink  506  to the coating material  504 .  FIG. 5D  illustrates the transfer member  502  after the photo imaging surface  204  has applied another layer of ink  508  to the coating material  504 . As illustrated in  FIG. 5C , the coating material  504  protects the transfer member  502  from the ink  506  and  508 . When the transfer member  502  transfers the ink and the coating material  504  to a print substrate, the ink(s)  506  and  508  will contact the print substrate and the coating material will cover the ink(s)  506  and  508  with a protective layer. 
     When making the impression, the coating material  504  and the ink(s)  506  and  508  will be completely or substantially completely transferred from the transfer member  502  to the print substrate. As a result, the transfer member  502  may again be represented by the illustration in  FIG. 5A . The example applicator  266  then applies another layer of the coating material  504  to prepare the transfer member  502  for another impression. 
       FIGS. 6A-6D  illustrate an example accumulation of ink and coating material on a print substrate  602  to form an image on the print substrate  602  in a four-shot mode. In the illustrated example, ink(s) and coating material are applied to the print substrate  602  by accumulating the layer(s) of ink(s)  112 ,  244  and layer(s) of coating material  110 ,  268  to the print substrate  602  from a photo imaging plate (e.g., the photo imaging surface  204 , the electrophotographic surface  232  of  FIGS. 2-4 , etc.) via a transfer member (e.g., the blanket  264  of  FIGS. 2-4 ).  FIG. 6A  illustrates the example print substrate  602  before the ink(s) or the coating material are applied. An example method to form an image on a print substrate in a four-shot mode is described below with reference to  FIG. 8 . 
       FIG. 6B  illustrates the example print substrate  602  after a first layer of ink  604  is applied to the print substrate  602 . For example, a developer unit  210  of  FIGS. 3 and 4  may apply a color (e.g., cyan, magenta, yellow, etc.) to locations on the photo imaging surface  204  where a latent image is formed. The photo imaging surface  204  transfers the ink to a transfer member (e.g., the intermediate transfer member  214  of  FIGS. 3 and 4 ), which in turn transfers the ink to the print substrate  602 .  FIG. 6C  illustrates the example print substrate  602  after a second layer of ink  606  is applied to the print substrate  602 . The second layer of ink  606  may be applied in a manner similar to the method used to apply the first layer of ink  604 . 
       FIG. 6D  illustrates the example print substrate  602  after a final layer of ink  608  and a coating material  610  have been applied. The example ink  608  and the coating material  610  may be applied at the same time as described above in conjunction with  FIGS. 3 and 4  to increase the printing throughput. 
       FIG. 7  depicts a flowchart representative of an example method  700  to form an image on a print substrate in a one-shot mode. The example method of  FIG. 7  may be used to implement the printers  200 ,  300 ,  400  of  FIGS. 2-4  to form an image on a print substrate. The method  700  may be advantageously used in web-fed presses that use continuous or substantially continuous sheets of print substrate. 
     The example method  700  may begin at the beginning of a printing process and/or after a previous image has been formed to (e.g., printed to) a print substrate (e.g., the print substrate  102  of  FIGS. 1A-4 ).  FIG. 5A  illustrates an example state of a transfer member  502  at the beginning of the method  700 . An applicator (e.g., the applicator  266  of  FIG. 2 ) applies a uniform or substantially uniform coating of a coating material (e.g., a polymer) to a transfer member (e.g., the intermediate transfer member  214 , the blanket  264 , and/or the transfer surface  260  of  FIG. 2 ) (block  702 ).  FIG. 5B  illustrates an example state of the transfer member  502  after block  702 . 
     The printer  200  selects (e.g., based on raster data of a desired image) a color of ink (e.g., cyan, magenta, yellow, black) to be included in the desired image (block  704 ). The selected ink may be developed by one of the developer units  210  of  FIG. 2  for eventual application to a print substrate  102  as a part of an image. During the example method  700 , a photo imaging surface (e.g., the photo imaging surface  204  the drum  230 , and/or the electrophotographic surface  232  of  FIG. 2 ) rotates to facilitate several functions as described herein. A photoconductor cleaning station  224  removes ink from the electrophotographic surface  232  that remains from previous impression cycles (block  706 ). Cleaning the electrophotographic surface  232  in this manner improves the image quality. 
     A charge device (e.g., the laser  240  of  FIG. 2 ) applies a latent image to the photoconductor  204  (block  708 ). For example, the laser  240  forms the latent image by charging (or discharging) the electrophotographic surface  232  to a voltage different than the background voltage. The developer unit  210  associated with the determined ink color develops (e.g., applies) ink  244  onto electrophotographic surface  232  (block  710 ). For example, the developer unit  210  may develop the ink  244  such that the ink  244  is attracted to the electrophotographic surface  232  wherever the latent image has been formed. To facilitate the transfer of the ink  244  from the electrophotographic surface  232  to the transfer surface  260 , a charge eraser (e.g., the charge eraser  212  of  FIG. 2 ) erases a charge on the photoconductor  204  (block  712 ). By erasing the charge, the charge eraser  212  allows the ink to be transferred off of the electrophotographic surface  232  when contacted by the transfer surface  260 . The example ink  244  adheres to the photoconductor  204  on contact (e.g., from the developer unit  210 ) and remains adhered to the photoconductor  204  after the charge eraser  212  removes the charge. 
     The electrophotographic surface  232  then applies the developed ink  244  to the transfer surface  260  (block  714 ). If there are additional colors to be applied to form the image (block  716 ), control returns to block  704  to select another color. If all of the colors(s) (e.g., all of the inks  244 ) that are to form the image have been applied (block  716 ), the transfer surface  260  transfers (e.g., applies) the ink  244  and the coating material  268  to a print substrate  102  to form an image (block  718 ). The example method  700  may then end and/or iterate to form another image on another sheet of print substrate  102  and/or another section of print substrate  102 . 
     While the example method  700  is described above with reference to the printer  200  illustrated in  FIG. 2 , the method  700  may be modified to be performed by either of the example printers  300 ,  400  of  FIGS. 3 and 4 . To operate the example printers  300 ,  400  in one-shot mode, the example applicator  266  applies the coating material  268  to the electrophotographic surface  232  (instead of applying the coating material  268  to the transfer surface  260 ) after a developer unit  210  applies a first colored ink  244  to the electrophotographic surface  232  and the charge eraser  302  erases the background charge on the electrophotographic surface  232 . The electrophotographic surface  232  then applies the coating material  268  and the first layer of ink  244  such that the coating material  268  is between the ink  244  and the transfer surface  260 . The example method  700  may then continue by performing the example blocks  704 - 718  as described above to apply an image and the coating material  268  to a print substrate  102 . 
       FIG. 8  depicts a flowchart representative of an example method  800  to form an image on a print substrate (e.g., the print substrates  102 ,  602  of  FIGS. 1-4 and 6 ) in a four-shot mode. The example method  800  may be used to implement the example systems  300  and  400  of  FIGS. 3 and 4  to form an image on a print substrate. The method  800  may begin, for example, at the start of a printing process and/or between impressions of an image on a print substrate. In general, printing in four-shot mode includes transferring layers of ink, one at a time, to a print substrate (e.g., the print substrate  102 ,  602  of  FIGS. 1-4 and 6 ) via the intermediate transfer member  214 , and is advantageously used with sheet-fed printing processes. 
     To begin the method  800 , a printer controller selects a color of ink  244  (e.g., cyan, magenta, yellow, black) to be included in the desired image (block  802 ). The selected ink  244  may be developed by one of the developer units  210  of  FIGS. 3 and 4  for eventual application to a print substrate  102  as a part of an image. During the example method  800 , a photo imaging surface  204  (e.g., the electrophotographic surface  232  and the drum  230  of  FIGS. 3 and 4 ) rotates to facilitate several functions as described herein. A photoconductor cleaning station  224  removes ink from the electrophotographic surface  232  that may have remained from previous impression cycles (block  804 ). 
     A charge device (e.g., the laser  240  of  FIGS. 3 and 4 ) applies a latent image to the electrophotographic surface  232  (block  806 ). For example, the laser  240  forms the latent image by charging (or discharging) the electrophotographic surface  232  to a voltage different than the background voltage. The developer unit  210  associated with the determined ink color develops ink  244  onto the electrophotographic surface  232  (block  808 ). If the developed ink  244  applied to the electrophotographic surface  232  (block  808 ) is not the final developed color in the image (e.g., other colors in the image have yet to be applied) (block  810 ), a charge eraser (e.g., the charge eraser  212  and/or the charge eraser  302  of  FIGS. 3 and 4 ) erases the electrophotographic surface  232  charge (block  812 ). The electrophotographic surface  232  then applies the developed ink  244  to the intermediate transfer member  214  (e.g., the transfer surface  260  and/or the blanket  264  of  FIGS. 3 and 4 ), which transfers the ink  244  to the print substrate  102  (block  814 ). Control then returns to block  802  to select the next color. 
     On the other hand, if the developed ink  244  applied to the photoconductor  204  is the final developed color in the image (e.g., all other colors in the image have been developed and applied to the transfer surface  260  and/or to the print substrate  102 ) (block  810 ), a secondary charge eraser (e.g., the charge eraser  302  of  FIGS. 3 and 4 ) erases the charge from the photoconductor  204  (block  816 ). The secondary charge eraser  302  may be in addition to or an alternative to the charge eraser  212  illustrated in  FIGS. 3 and 4 , and the secondary charge eraser  302  may be included or omitted based on the location of the applicator  266 . After erasing the charge from the electrophotographic surface  232 , the applicator  266  develops and/or applies a coating to the electrophotographic surface  232  over the developed ink  244  (block  818 ). In some examples, the coating is a thin (e.g., about 1 micron thick) layer of a transparent material  268  such as a polymer and/or a transparent ink. 
     The electrophotographic surface  232  then applies the final layer of ink  244  and the layer of coating material  268  to the transfer surface  260 , which transfers the ink  244  and the coating material  268  to the print substrate  102  (block  820 ). As described above, the ink  244  is transferred to the print substrate  102  and the coating material  268  is transferred to the print substrate  102  over the ink  244 . As a result, the coating material  268  protects the ink  244  from damage. 
     While the example method  800  is described above with reference to the printers  300 ,  400  illustrated in  FIGS. 3 and 4 , the method  800  may be modified to be performed by the example printer  200  of  FIG. 2 . To operate the example printer  200  in four-shot mode, block  818  may be modified so the applicator  266  applies the coating material  268  to the transfer surface  260  prior to the electrophotographic surface  232  applying the final ink  244  (for an image) to the transfer surface  260 , instead of applying the coating material  268  to the electrophotographic surface  232  after applying the final ink (for the image) to the electrophotographic surface  232 . As a result, the coating material  268  is disposed between the final ink  244  and the transfer surface  260 , and is then transferred to the print substrate  102  over the inks  244  to protect the image from damage. 
     The above-disclosed example methods and apparatus offer improved image durability, can substantially increase the useful life of a transfer member, and/or reduce undesirable effects in image quality resulting from transfer surfaces having high numbers of impression cycles. Additionally, example methods and apparatus disclosed above provide higher flexibility in selection of inks, selection of coatings, and/or selection of printing methods. 
     Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent.