Abstract:
A printing plate suitable for retaining ink in an imagewise fashion on a main surface thereof defines an array of pixel-sized cavities. Each cavity has associated therewith a quantity of a light-induced shape-memory polymer. When a cavity is exposed with energy, such as from an imaging laser, the quantity of polymer changes shape and/or position, thereby allowing a relatively greater quantity of ink to be retained in the cavity. The printing plate is then inked, to from a transferable image. The apparatus as a whole enables a gravure-like printing plate to be repeatedly imaged using digital image data.

Description:
TECHNICAL FIELD  
       [0001]     The present disclosure relates to a method of printing images, the method having aspects in common with gravure-type printing, and also having aspects in common with digital printing systems.  
       BACKGROUND  
       [0002]     There are currently two popular basic technologies for the mass production of printed images: offset printing and xerography. Offset printing is currently favored for large volumes of identical prints, such as the pages of magazines and books. One downside of offset printing is that a plate must be prepared for every image desired to be printed, and such plates typically cannot be modified for subsequent use after the particular print job is concluded. In recent years xerography has become cost-effective for somewhat smaller print jobs than are typical with offset printing; and, with laser-based imaging, xerography enables images generated at a computer to be readily printed in large volumes without the hands-on work required in offset.  
         [0003]     There have been efforts to make basic offset printing technology adapt to certain imaging techniques that are common in xerography, with some attendant practical advantages. One line of research concerns the making of “flexographic” printing plates, such as described in U.S. Pat. No. 5,279,697, and U.S. Published Patent Application 2005/0150407-A1. Another type of printing technology, within the general realm of offset, includes the use of what are called “Anilox” rolls to retain liquid ink and transfer the ink to a print sheet or blanket roll, such as described in materials published by Harper® Corporation.  
         [0004]     Japanese Kokai 11-258785 proposes another method for using digital imaging techniques in a largely offset-based environment.  
         [0005]      Nature , Vol. 434, pp. 879-882 (14 Apr. 2005) describes what is called a “light-induced shape-memory polymer”.  
         [0006]     U.S. Published Patent Applications 2004/0081911; 2004/0103801; 2004/0241583; and 2005/0221230 disclose various recent approaches to providing digital imaging, such as through a modulating laser, in a largely offset-based environment.  
       SUMMARY  
       [0007]     According to one aspect, there is provided an apparatus for printing an image, comprising a printing plate. The printing plate defines in a main surface thereof an arrangement of imageable areas, each imageable area being capable of selectably increasing or decreasing an amount of marking material retainable thereat, in response to energy applied thereto.  
         [0008]     According to another aspect, there is provided an apparatus for printing an image, comprising a first printing plate and a second printing plate. Each printing plate defines in a main surface thereof an arrangement of imageable areas, each imageable area being capable of selectably increasing or decreasing an amount of marking material retainable thereat, in response to energy applied thereto.  
         [0009]     According to another aspect, there is provided a printing plate useful in printing an image, the printing plate defining in a main surface thereof an arrangement of imageable areas, each imageable area being capable of selectably increasing or decreasing an amount of marking material retainable thereat, in response to energy applied thereto. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a simplified elevational view of a portion of a printing machine.  
         [0011]      FIG. 2  is a detailed view of a portion of a main surface of a plate on which images are to be formed.  
         [0012]      FIG. 3  is a sectional view through line  3 - 3  in  FIG. 2 .  
         [0013]      FIG. 4  is a simplified view of an architecture for a full-color version of a printer. 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  is a simplified elevational view of a portion of a printing machine. In this machine, images are formed on a main surface of what can be called a “plate” indicated as  10 . Although plate  10  is illustrated as a rigid cylinder, in other embodiments the plate could be in the form of a rotatable belt, or a flat platen.  
         [0015]      FIG. 2  is a detailed view of a portion of a main surface of plate  10 , on which images are to be formed. There is defined the main surface of plate  10  a regular array, in this embodiment a hexagonal array, of cavities, here indicated as  20 , which open out to the main surface of plate  10 . Each cavity  20  forms an imageable area of a size comparable to a desired spatial resolution of images created with the plate  10 , as will be described in detail below.  
         [0016]      FIG. 3  is a sectional view through line  3 - 3  in  FIG. 2 , showing some cavities in the main surface of the plate  10 . In the illustrated embodiment, each cavity  20  includes therein a quantity  22  of a material capable of changing at least one of shape or volume in response to energy applied thereto. In one embodiment, the material  22  in each cavity  20  decreases in volume when exposed to an ultraviolet ray of predetermined wavelength, such as a laser, directed at the cavity. When the material  22  decreases in volume, more effectively empty space is left in the cavity.  FIG. 3  shows some cavities  20   a  in which the material  22  is at its full size, substantially filling the cavity  20   a , and other cavities  20   b , wherein the material  22 , having been exposed to ultraviolet radiation, is at least temporarily shrunken, leaving effectively empty space within the cavity  20   b . Types of materials having this property will be described in detail below.  
         [0017]     In overview, the plate  10 , defining a large number of pixel-size cavities  20  in the main surface thereof, is able to retain marking material (typically, but not necessarily, liquid ink) in an imagewise fashion thereon. The cavities such as  20   b  in  FIG. 3 , having a shrunken material  22  therein, are capable of retaining ink in the balance of the available volume thereof. Cavities  20   a , where the material  22  substantially fills the entire cavity, are effectively incapable of retaining ink. Therefore, by controlling which cavities are in a configuration such as  20   b  (capable of retaining ink) or  20   a  (largely incapable of retaining ink), one can form an ink-based image on a portion of the main surface of plate  10 .  
         [0018]     Returning to  FIG. 1 , the plate  10  is in the form of a rotatable cylinder. Image data, relating to an image desired to be printed, originates in a controller  30  and is used to modulate a laser  32 , which in turn is reflected from a rotating mirror  34  to create a raster image, in a manner largely similar to that used in discharging a photoreceptor in a xerographic “laser” printer. The laser  32 , in this embodiment, is of a predetermined ultraviolet wavelength that, when applied to material  22  in cavities  20  in the main surface of plate  10 , causes the material  22  to shrink, and become of a configuration such as  20   b  in  FIG. 3 , and capable of retaining ink therein. Those cavities  20  which are not affected by laser  32  (i.e., the modulating laser is “off” when the beam is positioned near the particular cavity  20 ) remain in the configuration such as  20   a  in  FIG. 3 , and are not capable of retaining ink therein. The laser  32  is thus controlled to be “on” in positions corresponding to dark or inked areas of the image desired to be printed.  
         [0019]     Downstream of laser  32  along the illustrated process direction of plate  10 , the main surface of plate  10  is inked by an inking station generally indicated as  40 . Inking station  40 , which can be of any of variety of configurations as is generally known in, for example, offset printing, applies ink to the main surface of plate  10 , so that ink is retained in the cavities of configuration  20   b  in  FIG. 3 . The surface of plate  10  is then metered, such as by a metering blade  42 , downstream of inking station  40  along the process direction. The imagewise-disposed ink in cavities  20   b  can then be transferred to a print sheet or other ink-receiving member.  
         [0020]     At transfer station  50 , in the illustrated embodiment, a print sheet S is brought into contact with the inked main surface of plate  10 , to receive the ink in imagewise fashion therefrom. A pressure roller  52  is shown, but other mechanisms having the desired transfer effect are known generally in the printing art. Alternatively, instead of transferring the ink directly to a print sheet, there may be provided a “blanket roll” (not shown), as is generally familiar in offset printing, which would receive the ink and in turn transfer it to a print sheet.  
         [0021]     Following transfer, excess ink is removed from the main surface of plate  10  so that the plate  10  can pick up a new image in a following cycle. In the present embodiment, with the energy-sensitive material that will be described below, application of light of a predetermined wavelength, such as from lamp  56 , will cause the material  22  to return to its full size, thus pushing ink out of each cavity  20 . Ink remaining generally on the surface of plate  10  can then be removed by brush  58 , or equivalent. The fact the material  22  can selectably expand and contract, or selectably change its position, enables a particular cavity  20  to selectably retain more or less marking material therein following the application of energy of a particular type, whether from laser  32  or lamp  56 . In this way, the surface of plate  10  can be made erasable via lamp  56  and re-imageable via laser  32 . This erasing and re-imaging can occur with every rotation of the cylindrical or otherwise rotatable plate  10 .  
         [0022]     In alternate embodiments, a control system can operate the illustrated apparatus to enable multiple inking and printing cycles of the rotatable plate  10 , to make multiple identical images, before the image manifest in the cavities  20  is erased by lamp  56 . The properties of the material  22  can be selected depending on whether it will be desired to provide multiple inking and printing cycles, and whether such multiple cycles will be very long term, such as hundreds or thousands of prints made before re-imaging.  
         [0023]     Material  22  comprises, in one embodiment, a “light-induced shape-memory polymer.” Examples of such materials are described in a letter appearing in  Nature , Vol. 434, pp. 879-882 (14 Apr. 2005). Materials such as those described in the article have the property of changing shape, or in some arrangements position, when exposed to light of different frequencies, typically ultraviolet.  
         [0024]     The bulk of plate  10 , in which the cavities  20  are defined, can comprise ceramic, aluminum, copper, carbon, or any other suitable material. A relevant consideration of the material for plate  10  is that it is suitable for permanent attachment of material  22 , such as with an adhesive.  
         [0025]     Although the present embodiment includes a material that changes its shape or volume depending on the application of radiant energy of a predetermined wavelength, other approaches to obtaining the desired effect of each imageable area being capable of changing an amount of marking material disposable thereat, in response to energy applied thereto, can be envisioned. It is conceivable to provide a material that becomes more or less absorbent of an applied liquid depending on the application of different types of energy, radiant or otherwise, applied thereto. The pixel-sized cavities shown in the illustrated embodiment may not be required. Micromechanical structures providing the effect could be provided.  
         [0026]      FIG. 4  is a simplified view of an architecture for a full-color version of a printer using the above-described technology. Here, four cylindrical plates,  10   a - d , with corresponding inking stations  40   a - d  and other ancillary hardware (not shown) transfer imagewise-disposed inks onto an intermediate belt  60 . If each inking station is provided with a different primary color ink (such as CMYK), color separations of a desired image can be accumulated on the intermediate belt and then transferred together to a print sheet.  
         [0027]     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.