Abstract:
A system for printing comprises a rotatable charge-retentive member; imaging means for creating an electrostatic latent image on the imaging surface; and development means for applying a development material to the electrostatic latent image on the imaging surface. The developed image has a raised portion, suitable for transferring a liquid-ink image related to the developed image to a receiving surface. The system can be fitted into a flexographic printing apparatus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The following U.S. patent applications are hereby cross-referenced: U.S. patent application Ser. No. 11/239,072 filed Sep. 30, 2005 by Gabriel Iftime et al, “Reimageable Printing Member” (Attorney File No. 20041820); U.S. patent application Ser. No. 11/239,212 filed Sep. 30, 2005 by Gabriel Iftime et al, “Reimageable Printing Member” (Attorney File No. 20041671); U.S. patent application Ser. No. 11/268,303, filed Nov. 7, 2005 by Mark B. Rene, “Printing System Using Shape-changing Materials” (Attorney File No. 20050523); U.S. patent application Ser. No. 11/613,152 filed Dec. 19, 2006 by Jurgen H. Daniel et al, “Printing Plate And System Using Heat-Decomposable Polymers” (Attorney File No. 20051847); and U.S. patent application Ser. No. 11/644,067 filed Dec. 22, 2006 by Ashish Pattekar et al, “An Improved Method Of Forming A Reconfigurable Relief Surface Using Microvalves” (Attorney File No. 20060604). 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to adapting printing technologies that are not traditionally compatible with accepting digital image data, such as flexography, for digital printing. 
       BACKGROUND 
       [0003]    Since the invention of printing, numerous basic techniques for applying ink in an imagewise fashion to a print sheet have been proposed and implemented. In one strategy a printing “plate” (which could also be a belt or other member) defines a surface having raised portions corresponding to an image desired to be printed. Liquid ink is applied to the raised portions, and then the plate is pressed against a sheet to receive the inked image, much in the manner of a rubber stamp. One technology that currently uses this concept is called “flexography,” so called because the plate is typically in the form of a flexible plastic sheet with imagewise-raised portions. Although one plate can place the same image on an essentially unlimited number of prints, every new image to be printed requires a dedicated plate to be made. 
         [0004]    An alternate type of printing is called “gravure” printing. Gravure printing is similar to flexographic printing, except that, instead of the raised portions of the plate accepting and transferring liquid ink, liquid ink applied to the plate is retained in shallow cavities in the plate, the cavities corresponding to the print-black portions of the image. Once again, however, every new image to be printed requires a dedicated plate to be made. 
         [0005]    As is well known, in the last few years digital printing technologies, such as xerographic “laser” printing and ink-jet printing, have become prevalent. The basic advantages of the digital printing technologies are that the dedicated plates used in older printing techniques do not have to used (or discarded after use), and every printed image can be different, as the images depend solely on the digital image data supplied to the apparatus. 
         [0006]    The present disclosure relates to, inter alia, a system by which a pre-existing design for a flexographic or gravure printing system can be adapted to act like a digital printing apparatus, thus obtaining the practical advantages of a digital-based system in a high-volume, high-speed context. 
         [0007]    U.S. Pat. Nos. 5,436,706; 5,826,147; and 6,125,750; as well as the pending US patent applications cross-referenced above, each teach a variation of a traditional xerographic, flexographic, or gravure printing method. 
       SUMMARY 
       [0008]    According to one embodiment, there is provided an apparatus useful in printing, comprising: a rotatable charge-retentive member, defining an imaging surface; imaging means for creating an electrostatic latent image on the imaging surface; and development means for applying a development material to the electrostatic latent image on the imaging surface, forming a developed image. The developed image has a portion of a first type and a portion of a second type, the portion of the first type including development material and being raised relative to the portion of the second type, the developed image being thereby suitable for transferring a liquid-ink image related to the developed image to a receiving surface. 
         [0009]    According to another embodiment, there is provided a method of printing, comprising: providing a rotatable charge-retentive member, defining an imaging surface; creating an electrostatic latent image on the imaging surface; and applying a development material to the electrostatic latent image on the imaging surface, forming a developed image. The developed image has a portion of a first type and a portion of a second type, the portion of the first type including development material and being raised relative to the portion of the second type, to be thereby suitable for transferring a liquid-ink image related to the developed image. Liquid ink is applied to the developed image, and the liquid ink is transferred from the developed image to a sheet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a simplified elevational view of a flexographic printing station adapted according to the present disclosure. 
           [0011]      FIGS. 2 and 3  are partial views of a portion of a charge receptor surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  is a simplified elevational view of a flexographic printing station, generally indicated as  10 , adapted according to the present disclosure. The objective in  FIG. 1  is to apply a liquid-ink image to a sheet S moving in a process direction P. Although the illustrated station  10  is intended to apply ink of one color to the sheet S, a number of such stations can be arranged along a sheet path to provide successive primary-color separations forming a full-color image on the sheet S. 
         [0013]    Liquid ink is supplied to station  10  at a fountain pan  12 , of a type familiar in the art. Partially submerged in the ink in pan  12  is a rubber ink-fountain roll  14 , again of a type familiar in the art. Roll  14  in turn supplies ink to what can generally be called an “applicator,” such as including an anilox roll  16 . As is familiar in the art, an anilox roll typically defines a set of small cavities in its surface, to convey liquid ink thereon. Ink obtained by anilox roll  16  is doctored by doctor blade  18  soon after being picked up from roll  14 . 
         [0014]    The anilox roll  16  applies the liquid ink to the surface of a charge-receptor  20 . In brief, charge receptor  20  acts in a way largely similar to that of a photoreceptor in the well-known process of xerography: an electrostatic latent image is created in the charge-retentive surface of the charge receptor  20 , and the image is developed with a dry toner that adheres electrostatically to the suitably-charged portions of the latent image. As shown, there is provided at locations around the circumference of charge receptor  20  a charge device  22  for placing an initial even charge on the surface of charge receptor  20 , followed along the direction of rotation by an imaging device  24 , which selectably discharges pixel-sized areas according to digital data applied thereto. Familiar types of imaging device in this context include a rotating-mirror raster output scanner (ROS) or an LED bar. The functions of charge device  22  and imaging device  24  could alternatively be provided by an ionographic printhead. 
         [0015]    Following imaging device  24  along the direction of rotation of charge receptor  20  is a development unit  26 , which may be of any type known in the art of xerography, such as single-component, magnetic-brush, etc. The development unit  26  applies dry toner to the charge receptor  20  so that the toner electrostatically adheres to suitably-charged areas on the electrostatic latent image. 
         [0016]    The system of the present disclosure differs from traditional xerography as follows. In traditional xerography, the toner itself is ultimately transferred from the charge receptor to the print sheet to act as a colorant in the printed image. With the system of the present disclosure, the dry toner forming the developed image on the charge receptor is never transferred to a sheet or to any other member; rather, the toner layer forming the developed image is used to accept liquid ink received on the charge receptor from the applicator, in this case anilox roll  16 . 
         [0017]      FIGS. 2 and 3  are partial views of a portion of a charge receptor surface, showing how, after development, the surface defines portions of a first type and a second type. In one embodiment, such as shown in  FIG. 2 , the toner layer is raised relative to the bare surface of charge receptor  20 , and, when anilox roll  16  applies liquid ink to the developed image, the raised toner layer retains the liquid ink for transfer to sheet S, in the manner of a flexographic plate or rubber stamp. In an alternative embodiment, such as shown in  FIG. 3 , a “gravure” model is used, in which the non-raised portion of the developed image, i.e., the bare charge receptor surface, is intended to retain ink for transfer to sheet S. The relative liquid-ink retention properties of the toner layer and the bare charge receptor surface influence which type of ink retention is used. Depending on the implementation, the surface of charge receptor  20  can be designed to resist the ink sticking to it. 
         [0018]    Returning to  FIG. 1 , once the developed image receives liquid ink from anilox roll  16 , the liquid ink carried by the developed image is transferred to sheet S, for printing in a flexographic or gravure fashion. In the embodiment, electrostatic forces are largely irrelevant to the transfer of the liquid ink to the sheet S. On the opposite side of sheets S is provided an impression cylinder  30  as shown. In one possible embodiment, the impression cylinder  30  can be charged in such a way as to help maintain the toner on the charge receptor roll  20 . Soon after transfer, a cleaning blade  28  (or equivalent device) removes both the toner layer and the residual liquid ink from the surface of charge receptor  20 . After the surface is cleaned, the surface can be charged at charge device  22 , and re-imaged with imaging device  24 . In this way, with every rotation of charge receptor  20 , a new image, based on digital data, can be printed on moving sheet S. 
         [0019]    In one possible variant, cleaning blade  28  (or an equivalent device) can be selectably disengaged from charge receptor  20 , so that the developed toner layer is not disturbed for the following rotation of the charge receptor  20 . In such a case, the toner layer (and, thus, the image it represents) remains on the charge receptor for another rotation of charge receptor  20  and, thus, repeated printing of the image on sheet S. In other words, the cleaning and re-creation of new toner layer images on the charge receptor  20  can be made to occur only when the image is desired to be changed; a toner layer can be used for multiple rotations of charge receptor  20 , and thus can make multiple images on moving sheet S. 
         [0020]    In one possible implementation, the creation of the developed toner-layer image on the charge receptor  20  can be performed in an operational mode separate from the use of the toner layer to print images on the sheet S. For example, in an “image creation” mode, the sheet S and the anilox roll  16  are effectively disengaged from the charge receptor  20 , while the developed image is created; then, once the developed image is in place on the charge receptor  20 , the “xerographic” elements are switched off, and the anilox roll  16  starts supplying ink to the developed image for printing on sheet S, in a “printing” mode. During a mode wherein a toner layer image is created electrostatically on charge receptor  20 , it may be desirable to rotate the charge receptor  20  at a relatively slow rotational speed, in order to obtain a toner layer of desirable properties, such as thickness. When the developed image is used to print on sheet S with liquid ink, however, the requirements of the printing mode may allow charge receptor  20  to be rotated at a significantly higher speed. 
         [0021]    In the embodiment of  FIG. 1 , it can be seen that charge receptor  20 , charge device  22 , imaging device  24 , development unit  26 , and cleaning blade  28  are encased in a cartridge  32  (although the development unit  26  itself could be formed of a separate cartridge). The cartridge  32  could be configured to fit in a pre-existing flexographic apparatus: it is familiar in flexographic printing to have to replace the flexographic plate (which corresponds to charge receptor  20 ) on a regular basis. 
         [0022]    In another implementation, the separate “image creation” and “printing” operational modes, as described above, can be carried out in separate apparatus. In a pre-existing print-shop arrangement, where there is already a flexographic printer, an offline apparatus can be provided, the offline apparatus including all of the elements shown in cartridge  32 . The offline apparatus creates a charge receptor  20  developed with an image desired to be printed; after the charge receptor is developed with a desired image to be printed, the developed charge receptor is removed from the offline apparatus and placed in the existing flexographic printer, as though it were just another cylindrical flexographic printing plate. When the particular print job is complete, the developed charge receptor  20  is removed from the flexographic printer, effectively erased, and re-imaged for another job. 
         [0023]    It will be noted that the toner or other development material applied by development unit  26  to the charge receptor  20  will have properties different from those typically required by toner used in traditional xerography. For instance, because the toner in the embodiment never contacts the print sheet S, the color of the toner is irrelevant. Because a reasonably thick toner layer is desired on the charge receptor  20  to obtain the desired properties, considerations of particle size are different from those of traditional toners. Because the toner is not fused onto a print sheet, considerations of melting points are different from those of traditional toners. 
         [0024]    The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.