Patent Publication Number: US-2002011167-A1

Title: Plateless printing system

Description:
RELATED APPLICATIONS  
     [0001] This application is a Continuation-in Part Application of U.S. application Ser. No. 09/396,036, filed Sep. 15, 1999, which is Continuation-in Part Application of a PCT Application PCT/IL99/00026 filed Jan. 14, 1999 which is based on Israeli Application 122953 filed Jan. 15, 1998, which are incorporated herein by reference. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] This present invention relates to offset printing and in particular is directed to a method for plateless printing and to the composition of materials used for this method.  
       BACKGROUND OF THE INVENTION  
       [0003] There are numerous methods known in the art for producing a master printing plate, on which an image is written and which is then used as a printing plate for the reproduction of multiple copies. Examples of such methods are described in “ Chemistry and Technology of Printing and Imaging Systems ”, edited by P. Gregory and published by Blackie Academic &amp; Professional in 1996. Typically, the plate contains one or more coating layers applied to a metal or plastic substrate layer,  
       [0004] The cost of producing a plate is relatively expensive and is generally only economical when utilized for printing large numbers of copies. For short printing runs, the cost of the printing plate adds substantially to the cost per printed copy. The plate cost is contributed from two sources:  
       [0005] a. The price of the plate itself  
       [0006] b. The price of preparing the plate for printing, i.e. film making, exposure, processing.  
       [0007] Recent developments in offset lithography have led to the use of digitally imaged printing plates whereby information is transferred directly from a computer to the printing plate. Though these printing plates are relatively easily prepared and quickly imaged and processed, their cost is even higher than that of conventional plates, so that they still contribute a significant cost to the printing price.  
       [0008] Another significant contributing cost factor in printing is due to what is commonly termed “make-ready” Make-ready refers to the operational stage involved between producing the last copy of one printing job and the first copy of the next job. Reducing the make-ready time improves the efficiency and allows for better utilization of machine time and increases the capacity of the machine.  
       [0009] Color printing generally involves the separating of the color information into four or more color components each on a separate printing plate and then superimposing the images printed from each plate on top of one another on each piece of substrate. In complex color printing, there are additional problems of lining up images on plates and ensuring that the color balance on the printed copies is correct, which can require more time and thus results in a further increase in the cost per copy.  
       [0010] Another time-consuming stage in conventional (“wet”) offset printing is the fine adjustment of the balance of the fountain solution with the ink. This procedure not only is time consuming, but also requires a printer skilled in the art. In addition, the use of fountain solution also causes other problems, such as longer drying times and lower optical density. A waterless printing process for offset printing, which eliminates the use of fountain solution, is described in U.S. Pat. No: 3,511,178 to Curtin. A layer of silicone is used to repel the printing ink instead of the fountain solution.  
       [0011] Printing machines have been developed to minimize the make-ready by imaging directly on-press. Infra red imaging has been used for this purpose because it lends itself to digital imaging and can be done under daylight conditions. For instance, the 74 Karat offset printer, manufactured by Karat LP, 3, Hamada Street, Herzelia, Israel, carries such a digitally imaged infra red system of plate production.  
       [0012] Besides the plate cost issue for short runs as mentioned above, the use of a printing plate has other disadvantages It requires mechanical clamping devices at each end, which produces an unusable area on the plate cylinder as well as requiring the necessity of alignment mechanisms.  
       [0013] Various processes, known in the art, have been introduced for printing which do not require the use of a printing plate. For example, as described in “ Chemistry and Technology of Printing and Imaging Systems ”, edited by P. Gregory and published by Blackie Academic &amp; Professional in 1996, a printing process which may be termed “image one-print one” regenerates an image for each print. Ink jet printing whereby a jet of ink directly sprays the image onto the plate where the information is digitally applied from a computer is an example of an “image one-print one” process. This process is not competitive with high quality, color process printing using a printing plate such as offset lithography, because it is relatively slow and has severe substrate limitations.  
       [0014] Xerographic copying is another example of an “image one-print one” process. Disadvantages of this process, which may be considered as an imaging on-press process, includes its complexity and the relatively high cost per copy that remains almost constant, irrespective of the number of copies made. Furthermore, this process has a generally inferior quality compared to lithography.  
       [0015] Numerous attempts have been made to produce a re-usable imaging surface for a printing process, examples of which are described in U.S. Pat. Nos. 5,206,102; 5,129,321; 5,188,033; 3,741,118; 4,718,340; 5,333,548 and 5,213,041. Generally, the above-mentioned systems generate a “master” which is then used for conventional wet offset printing.  
       [0016] Reference is now made to FIG. 1, which is a cross-sectional view of a printing member, referenced  300 , used in existing conventional digital offset lithographic printing systems. The printing member  300  is formed of at least three layers. A first or substrate layer  310 , forms a base or substrate for the printing member  300 . A second radiation absorbing layer  312 , that carries the image to be printed (once the printing member is imaged by ablation, for example), is over the first layer  310 . A third surface coating layer  314  is over the second layer  312 . Generally, the imaging layer  312  comprises an infrared radiation absorbing material, for absorbing infra red radiation to cause ablation. The substrate  310  has an oleophillic surface. The surface coating layer  314  is of a material with an affinity for the ink(s) substantially different to the affinity for the ink(s) of the surface of the substrate  310 . Ablation results in de-bonding between the surface coating layer  314  and the substrate  310 . On cleaning-either dry or with a liquid—the materials of layers  312  and  314  are removed in the image areas, revealing the surface of  310 .  
       [0017] It would be advantageous to have an offset printing process, which does not require a printing plate. Specifically, it would be of further advantage if such a process could be used in a waterless application. Imaging would be on the printing press and preferably, any processing after imaging would be relatively simple. U.S. Pat. Nos: 5,440,987; 5,634,403; and 5,636,572, all to Williams et. al, describe a seamless offset lithographic printing members. The printing members include a hollow cylinder which is attached to the cylinder jacket of an offset printing press. A polymeric coating layer is coated on to the cylinder and a second polymeric surface layer is coated on top of the first layer. Whilst these patents address the problem of the void area needed for clamping plates on a cylinder, their inventions require a cylinder or cylinders to be removed from the printing press and then to receive two or more coatings before returning to press.  
       [0018] U.S. Pat. No: 5,713,287 to D. Gelbart, describes a plateless process at which a solvent-based, polymeric coating layer is deposited on-press on the cylinder. After drying, the imaging converts at least part of the coated layer to have an opposite chemical property to that of the layer.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0019] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:  
     [0020]FIG. 1 is a cross-sectional view of a prior art printing member;  
     [0021]FIG. 2 is a schematic illustration of a plateless printing system, constructed and operative in accordance with some embodiments of the present invention;  
     [0022]FIG. 3 is a flow chart illustration of the operation of the plateless printing system of FIG. 2 in accordance with some embodiments of the present invention;  
     [0023]FIGS. 4 a -   4   g illustrate an image-carrying cylinder during the various stages of plateless printing in accordance with some embodiments of the present invention; and  
     [0024]FIG. 5 illustrates the web offset application of the plateless process in accordance with some embodiments of the present invention. 
    
    
     [0025] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.  
     DETAILED DESCRIPTION OF THE PRESENT INVENTION  
     [0026] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.  
     [0027] Reference is now made to FIGS. 2 and 3. FIG. 2 is a schematic illustration of a plateless printing system, constructed and operative in accordance with some embodiments of the present invention. FIG. 3 is a flow chart illustration of the operation of the plateless printing system in accordance with some embodiments of the present invention.  
     [0028] A ‘plateless’printing system  10  may comprise an image bearing cylinder  12 , a blanket cylinder  14 , a printing (or inking) system  15  and an imaging system  16 .  
     [0029] In contrast to existing printing systems which carry printing plates, such as waterless IR ablatable printing members, image bearing cylinder  12  does not carry a printing plate. Instead, image bearing cylinder  12  has an imaging layer, generally designated  100 , directly coated onto the cylinder  12 , thereby creating a ‘plateless’printing member, as described in detail hereinbelow.  
     [0030] In alternative embodiments according to the present invention, the cylinder may carry a replaceable substrate, either as a sleeve or as a sheet that may be replaced after a large number of jobs. This has the advantage of protecting the cylinder from wear.  
     [0031] The ‘plateless’printing system  10  may also comprise a mixing system  18  for preparing the imaging layer  100 , a coating head  20  for applying the imaging layer  100 , a plate cleaning system  25  for post-imaging cleaning, an erasing system  22  and a drier/cross linker  24 . In addition, the ‘plateless’printing system  10  may also comprise a cooling system  26  for use after the heating stage and during printing.  
     [0032] Mixing system  18  may comprise apparatus to mix at least two components, generally referenced A and B, which are discharged via a pipe system  27 , or similar, into a mixing container  28  where components A and B are mixed together to form the coating mixture which is then coated onto cylinder  12  to form an imaging layer  100 , An automatic washing system may be added to clean the mixing and coating system on-press in case of a short pot-life of the mixture. Including the mixing (and washing if necessary) stages into the process, makes it possible to use mixtures that have short-pot life or shelf-life (such as a polymer and its cross-linker).  
     [0033] Image bearing cylinder  12  may have an oleophillic surface and may comprise any material, which is suitable, for receiving and adhesion of the oleophobic coating layer  100 . Non-limiting examples of suitable surfaces include plastics, reinforced plastics, metals such as aluminum (or anodized aluminum) and copper, ceramics and stones, such as granite. Thus, in contrast to conventional plate processes, the surface of cylinder  12  which acts as a substrate, may be of a non-pliable material that may or may not be formable into a sheet.  
     [0034] For a wet offset application, the cylinder may be hydrophilic, where the coating layer is oleophillic, or vice versa.  
     [0035] The cylinder  12  may be entirely composed of an infrared absorbent material or, alternatively, only the external surface of the cylinder is composed of a solid infrared absorbent material. Since, in both these two alternative embodiments, the surface of cylinder  12  (that is, the underside of the oleophobic layer  100 ) is infrared absorbent, the coating layer  100 , which is coated on the cylinder  12 , need not itself be infrared absorbent, but may be transparent.  
     [0036] Alternatively, the outer surface of the cylinder or the cylinder itself may be composed of an IR reflecting material, to enhance the sensitivity of the imaging layer; in this case, the coated layer should be IR absorbent.  
     [0037] By coating an imaging layer  100  on to a base with opposite ink or water accepting properties (cylinder  12 ), a single layer printing member is created. This is in contrast to existing printing members, described hereinabove with respect to FIG. 1, which generally comprise a substrate base layer on which at least two layers are coated.  
     [0038] The A and B components of the coating layer  100  for waterless offset application may comprise a film former such as polysiloxane, or other oleophobic polymeric material (compound A) and a separated component, such as a compound of platinum or tin, for example, as a catalyst and/or cross linker (compound B).  
     [0039] The coating layer  100  may be either solventless or may have been deposited from solvents. Water may be utilized as the solvent because of environmental and health and safety considerations. In this case, the resin may be held in the form of an emulsion or as a dissolved substance.  
     [0040] Components A and/or B may incorporate an infrared (IR) absorbing component, such as carbon black or nigrosine. The mixture  100  may also contain wetting agents, adhesion promoters and polymers to enhance the coating and bonding properties of the mixtures.  
     [0041] It has been found that when using water based silicone emulsions, in order to obtain good wetting for a variety of substrates together with good adhesion to said substrates and good release properties of the film formed and good scratch resistance, the following components must be present in the following parts by weight;  
                                          a)   Polysiloxane emulsion (percentage solids   40% to 80%           includes surfactants used during manufacture)       b)   Silicone catalyst (solids content)   0.01 to 3%       c)   Silicone crosslinking agent (percentage solids)   5-15%       d)   Water soluble crosslinkable amine resin   4%-25%       e)   Catalyst for amine resin   0.5% to 5%       f)   Added surfactant   0.5%-10%       g)   Infrared absorber   3%-40%       h)   The remaining material is water                  
 
     [0042] Examples of suitable polysiloxane water-based emulsions are as follows, (each material is supplied with suitable catalysts and crosslinking agent):  
                                       Catalysts/Crosslinking       Polysiloxane Water-Based Emulsions   Agents                  Dehesive 410E (50% solids including a   Crosslinker V72 (35% solids)       platinum catalyst)       Dehesive 38197 VP (50% aqueous   Crosslinker V72 (35% solids)       emulsion addition cross-linkable)       SYL-OFF 7920 silicone emulsion   SYL-OFF 7922 catalyst           emulsion       Silcolease E70888, 70840   Catalyst 70889S or 71823       Silcolease 71841   Catalyst 71842 or 71823       Silcolease 71822   Catalyst 71823       Silcolease E 70840   Catalyst 70827A                  
 
     [0043] Dehesive and Crosslinker products are manufactured by Wacker Chemie GmbH, Munich, Germany). Silcolease products are manufactured by Rhone-Poulenc Silicones UK, Surrey, England. SYL-OFF emulsion products are manufactured by Dow Coming Europe, La Hulpe, Brussels, Belgium.  
     [0044] Examples of suitable crosslinkable water-soluble amine resins are as follows:  
     [0045] a) Cymels 350, 323, 327, 328, 373, 385, 1171, 1172 (manufactured by Dyno-Cytec);  
     [0046] b) Dynomins UM-15 (manufactured by Dyno-Cytec); and  
     [0047] c) BE 312 Beetle Resin (manufactured by BIP Limited, Oldbury, West Midlands, UK,  
     [0048] It has been found that although catalysts for the cross-linking resins may be sulphonic and carboxylic acids, amine blocked acids are most suitable.  
     [0049] An example of a mixture for a waterless offset application is a mixture based on water emulsions of silicones such as the commercially available SYL-OFF 7920 emulsion coating and SYL-OFF 7922 catalyst manufactured by Dow Corning Europe, La Halpe, Brussels, Belgium.  
     [0050] Sufficient material to be formed into the equivalent of a plate is mixed together in mixing container  28  and coated onto the surface of the ‘plateless’cylinder  12 . Depending on the pot life of the mixture, a washing stage of the mixing and coating system may be applied after each mixing. Even though cylinder  12  does not carry a plate, as would be the case in conventional plate cylinder systems, the coating layer  100  (or “plateless” plate) carries out the functions of the conventional digital plate.  
     [0051] The imaging layer  100  is coated on to the cylinder  12  using the coating head  20  with a dye slot, for example. After solvent evaporation or cross-linking, the dry coating thickness may be expressed as a weight of from  1  to  5  grams per square meter. Alternatively, a metered rod or any other application system known in the art may be used as the coating head  20 .  
     [0052] The drier/cross linking station  24  may function in varying ways. In the embodiments where the coating  100  is polymerized or cross-linked before imaging, it would be used to evaporate off any solvent present after initial coating and then possibly to cure the polymerized image areas after non-polymerized material is removed by washing. In the embodiments where the image area is to be destroyed during imaging, the drier/cross linker will evaporate any solvent present after coating and would then cross-link or polymerize either before imaging or after imaging/cleaning to harden and insolubilize the background areas. Alternatively station  24  may comprise a heating unit such as a radiant heater or an ultra-violet (UV) drier. The heating/curing stage may also be obtained by a heated electrical blanket below the upper surface of the cylinder, or by hot air, by combination of means or by any other suitable heating/curing means. With high power imaging unit, it may be used to cure the IR absorbing coating layer as well.  
     [0053] Imaging system  16  may comprise one or more infra red lasers which have been modulated to radiate energy corresponding to a digital image Such a suitable system is described in PCT Patent Application PCT/IL97/005258 (Publication No. WO 97/27065) to the present Applicant, incorporated herein by reference.  
     [0054] Infrared imaging of the system may occur in various ways, as follows: Imaging may occur due to ablation where destruction of material occurs. In contrast to systems where the underlayer contains the infra red absorbing material, in some embodiments of present invention, the infra red absorbing material may be contained in the overlayer, or alternatively in both the overlayer and the underlying cylinder. Waterless plates imaged by debonding ablative mechanisms have been found to be difficult to automatically clean in the post image stage. The debonded oleophobic rubber, such as polysiloxanes commonly used, maintains its elastomeric form and gathers into large solid deposits that clog the cleaning system as well as the press when imaging on-press. It has been found that where the infrared material is in the oleophobic layer itself, the layer is thermally degraded where ablation occurs and the oleophobic resin loses its elastomeric properties and this facilitates automatic cleaning. Where ablation occurs, the decomposed areas of oleophobic coating layer  100  must be removed by dry or wet cleaning so that the exposed areas of the cylinder  12  provide the oleophillic areas during printing.  
     [0055] It is possible that layer  100 , whilst free of solvent before imaging, may remain in an unpolymerized state to facilitate ablation. This may be in a liquid or a semi-solid form in contrast to conventional plates, which have to be packed and handled before use, and thus, conventional plates cannot have a wet surface.  
     [0056] Another possibility is that the heat generated by the thermal imaging process may break the chemical bonds of the polymer. The resulting smaller molecules may then become less chemically or mechanically resistant than the original layer and then may be cleaned away as part of a post imaging treatment.  
     [0057] A further possibility is that the heat generated during imaging may be used to polymerize the coating layer  100  and the unpolymerized coating may be subsequently removed by washing it away.  
     [0058] The cleaning system  25  may comprise any suitable dry or solvent cleaning process. The cleaning element can consist of a brush, rubber roller or other similar element. A vacuum suction may be applied together with the cleaning element in order to remove the debris from the press. A liquid may be used together with the rubbing action of the cleaning element to assist in removing any loose particles (if the ablation process is involved) or pre-polymeric material from the background or image areas with decomposed material. If a liquid or solvent is used, a further rotation of the cylinder  12  without contact with any liquid may be made so as to ensure that the surface is dry.  
     [0059] The solvent erasing system  22  may be used to remove the inked up image after the printing impressions have been made. Cleaning may be any suitable process such as abrasion or by means of a solvent to aid loosening of the resin layer (layer  100 ) or by a combination of both methods. A suitable solvent may be a regular blanket wash.  
     [0060] A corona treatment to decompose the layer and/or a vacuum suction to remove the loosened material may be used as well.  
     [0061] The printing (or inking) system  15  is any suitable inking system known in the art, for applying ink to “plate” cylinders.  
     [0062] Cooling system  26 , which is placed within the image bearing cylinder  12 , may control the temperature of the cylinder to cool it after the heating stage and during printing. Cooling is performed to avoid toning that may occur with waterless inks and to support printing stability.  
     [0063] Offset printing is carried out by means of blanket cylinder  14  on to a printing substrate conveyed by an impression cylinder (not shown). Impressions are taken, usually onto paper, but any required substrate may be printed.  
     [0064] Reference is now made to the flow chart of FIG. 3 to illustrate the plateless printing system.  
     [0065] The imaging layer mixture may prepared in mixing system  18  (step  202 ) by mixing at least two components comprising a film former and a separated component together.  
     [0066] The mixture may then be coated onto the surface of the ‘plateless’cylinder  12  (step  204 ), using a suitable coating head  20 , Such a coating head may be easy to wash and not sensitive to the distance of the coating head to the cylinder, for instance a dye slot coater.  
     [0067] Depending on the pot life of the mixture, a washing stage of the mixing and coating system may be applied as necessary.  
     [0068] After the application of the mixture  100  (step  204 ), the drier/cross linker  24  is used either for drying (i.e. to evaporate any solvent on printing cylinder  12 , which may be collected and condensed (step  208 )), and/or for partial curing and/or for full curing (step  206 )  
     [0069] After stage  206  during which the cylinder is heated and prior to imaging, the image-bearing cylinder may be cooled (step  209 ), in order to avoid dimensional changes of the substrate between the imaging step and the printing step. The imaging layer  100  is then selectively exposed by the imaging system  16  during multiple rotation of the cylinder (step  210 ).  
     [0070] During further rotation of the cylinder, post-imaging cleaning system is operated (step  212 ). Depending on the embodiment, cleaning either removes ablated debris, or removes unpolymerized resin from the background or washes out decomposed material from the image areas. If a liquid cleaner is used, surplus solvent is removed.  
     [0071] After the cleaning process (step  212 ) is completed, the dryer/cross linker may be (optionally) re-operated to further harden background or image areas to give optimum robustness and adhesion to the cylinder needed for the printing part of the cycle (Step  214 ). This second stage of heating may be followed by a second cooling of the cylinder (Step  216 ).  
     [0072] The operational parameters of the dryer/cross linker may in principle be regulated separately for each job in order to optimize the make ready time (as curing time may influence sensitivity and hence imaging time, as well as erasing time) versus required run length (as curing will influence the coating resistance).  
     [0073] The image bearing cylinder surface is now ready to print (step  218 ) and the appropriate offset ink (either waterless or “wet”) is applied by the printing (or inking) system  15  to the cylinder. The image bearing cylinder may be cooled (if necessary) to control the temperature of the ink during printing.  
     [0074] The offset printing process takes place via blanket cylinder  14  by taking a plurality of impressions, usually onto paper, but any required substrate may be used for printing.  
     [0075] The substrate to be printed may be in the form of sheets, or in the form of a web. Reference is now made to FIG. 5, which illustrates a web-offset printing system according to some embodiments of the present invention. FIG. 5 is similar to FIG. 1 with the addition of a substrate unwind  110  and a substrate rewind  112 .  
     [0076] The roll of substrate  115  is fed via an impression roller  114  to receive the print from blanket cylinder  14  and then re-wound onto roll  112 . Alternatively, sheets may be printed.  
     [0077] The application of this technology for a web offset printing has the following advantage: as the plate cylinder may be made seamless, it may carry a continuous image, uninterrupted by the need for clamps which are generally required in order to hold the plates.  
     [0078] After the required number of impressions have been printed, the remaining resin layer (mixture  100 ) plus the inked up image is removed (step  220 ) by the solvent plate erasing system  22 . Cleaning may be any suitable process such as abrasion or by solvent aided loosening or a combination of both.  
     [0079] In special conditions, a corona treatment may be used as a facilitator. If required, cylinder  12  is then dried (stop  222 ). Cylinder  12  is then ready for the application of the mixture, as previously described and the process (steps  202 -  222 ) may be repeated.  
     [0080] It will be appreciated by persons knowledgeable in the art that the present invention is also applicable to existing computer-to-press printing machines, which may be adapted to be used with a ‘plateless’printing member. A typical computer-to-press printing machine is described in PCT Patent Application PCT/US 96/06207 (Publication No. WO 96/34748) to the present Applicant.  
     [0081] It will also be appreciated that such coating material as herein described may be used in the manufacture of a one layer infra red imageable offset printing plate. This may be useful for existing presses, which may not be modified for the plateless process. A single layer plate will still be cheaper than existing plates as coating multiple layers increase dramatically the cost of the plate.  
     [0082] Another possible application of this invention may be to make a plate-setter, which will be used, for implementing the whole plateless process for recycling the plates. Such a plate-setter may be fed with the used plates, erase them, coat, dry, image and clean; the ready plates may be fed into the press. Once done their job, the plates may be re-fed into the platesetter and used again. This may have advantages of reducing plate costs as well as elimination of used aluminum aggregation.  
     [0083] Reference is now made to FIGS. 4 a - 4   g , which illustrates the image carrying cylinder during the plateless printing sequence according to some embodiments of the present invention.  
     [0084]FIGS. 4 a - 4   g  are partial sectional elevations of image bearing cylinder  12  (FIG. 2). FIG. 4 a  shows the cylinder before any coating is applied. The cylinder may be comprised of a single material. Alternatively, it may consist of any or all the following components,  
     [0085] 1. An internal cooling system (  41 )  
     [0086] 2. A hollow cylinder (  45 )  
     [0087] 3. Under-surface electrical heating elements (  42 )  
     [0088] 4. A sleeve or a sheet top surface, which may be replaceable (  43 )  
     [0089] The entire cylinder or only the top (  43 ) may be either IR absorbing or IR reflecting.  
     [0090]FIG. 4 b  shows the cylinder after the coating (  100 ) is applied, dried and (possibly) cured (  101 ). The coating, after drying (and optionally curing) is shown in the right hand side (reference  101 ).  
     [0091]FIG. 4 c  illustrates the coating layer after imaging has taken place. In this case, the imaging ablates or decomposes the imaging area (  102 ).  
     [0092]FIG. 4 d  illustrates the case where imaging cures the background area (reference  103 ).  
     [0093]FIG. 4 e  shows the cylinder after post-imaging cleaning has taken place. After cleaning (whether the imaged area or non-imaged area has been removed), the cured layer is left on the cylinder on the background area (  103 ). The cylinder surface area functions as the ink accepting layer (  43 ).  
     [0094]FIG. 4 f  shows the cylinder after ink (  106 ) is applied during the printing cycle.  
     [0095] Fig,  4   g  shows the cylinder after the erasing stage, fully cleaned, ready for the next job (that is as FIG. 4 a ).  
     Example I—Waterless  
     [0096] The following formulation was prepared as a mixture (all numbers designating parts in the formulation are in parts by weight of the entire formulation),  
                                                          Distilled Water   10 parts               2-Butoxy Ethanol   0.86 parts           Water Soluble Nigrosine   1.3 parts           Cymel 373   1.24 parts           BYK 345   0.6 parts           SYL-OFF 7920   10 parts           SYL-OFF 7922   2 parts                      
 
     [0097] The mixture was applied to a 175 microns polyester film to a wet thickness of 12 grams per square meter and then dried for four minutes at 140° C. The layer was then imaged with the infra red imaging system described in PCT Patent Application PCT/IL97/00528 (Publication No. WO 97/27065) to the present Applicant, using an imaging intensity necessary for material with a sensitivity of 800 milli-joules per square centimeter. The image was gently cleaned with water and mounted on a GTO printing press running with a waterless printing ink. After 5000 impressions, the plate surface was rubbed vigorously with a damp abrasive cloth, damped with aqueous alcohol, removing both the inked image and the silicone based background so that only the polyester surface was left. The polyester was removed from the printing machine and re-coated as previously described and the entire cycle repeated.  
     Example II—Waterless  
     [0098] The following formulation was prepared as a mixture (all numbers designating parts in the formulation are in parts by weight of the entire formulation)  
                                          Dehesive 410E (Wacker Chemie GmbH, Munich,   135   parts       Germany)       CAB-O-JET 200 (Cabot Corporation, Billerca,   58       Massachusetts, US)       Q2-5211 Super wetting agent (Dow Corporation,   6       Midland, MI, USA)       Cymel 373 (Dyno-Cytec)   21       Cycat 4045 (amine blocked p-toluene sulphonic acid,   5.7       Dyno-Cytec)       Crosslinker V72 (Wacker)   25                  
 
     [0099] The complete mixture was then bar coated onto a grained anodized aluminum plate surface and dried at 140° C for four minutes to a dry coating weight of 2.7 grams per square cm.  
     [0100] The layer was then imaged as in Example I. After imaging, the surface was wiped with a dry cloth to remove ablated material and mounted on a GTO printing press. 5000 impressions were made and then the plate was rubbed vigorously with an abrasive cloth to erase all of the coating so that the cleaned aluminum surface could be re-coated. Imaging and printing was repeated and again 5000 impressions were obtained.  
     [0101] It will be appreciated that this experiment signifies that the mixture may be the coating layer  100 , coated onto an anodized aluminum plateless cylinder  12  and dried, cured, imaged, printed, erased, re-coated etc., on the apparatus as shown in FIG. 2 as previously described.  
     [0102] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.