Abstract:
Methods are disclosed for applying a dampening fluid to a reimageable surface of an imaging member in a variable data lithography system without a form roller. Dampening fluid in liquid form is converted to vapor phase, and directed to the reimageable surface. The dampening fluid reverts to the liquid phase directly on the reimageable surface. Controlling the temperatures of elements of the delivery subsystem prevents unwanted condensation of the dampening fluid vapor on those elements. Generation and delivery of the vapor can be controlled in a feedback arrangement as a function of measured layer thickness formed on the reimageable surface to obtain a desired dampening fluid layer thickness formed on the reimageable surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of copending U.S. application for Letters patent Ser. No. 13/204,526, filed on Aug. 5, 2011, which is incorporated by reference herein and to which priority is claimed. 
         [0002]    The present disclosure is also related to U.S. patent application titled “Variable Data Lithographic System”, Ser. No. 13/095,714, filed on Apr. 27, 2011, which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0003]    The present disclosure is related to marking and printing methods and systems, and more specifically to methods and systems for deposition of a dampening fluid directly onto the imaging member, without an intermediate member such as a form roller. 
         [0004]    Offset lithography is a common method of printing today. (For the purposes hereof, the terms “printing” and “marking” are interchangeable.) In a typical lithographic process a printing plate, which may be a flat plate, the surface of a cylinder, or belt, etc., is formed to have “image regions” formed of hydrophobic and oleophilic material, and “non-image regions” formed of a hydrophilic material. The image regions are regions corresponding to the areas on the final print (i.e., the target substrate) that are occupied by a printing or marking material such as ink, whereas the non-image regions are the regions corresponding to the areas on the final print that are not occupied by said marking material. The hydrophilic regions accept and are readily wetted by a water-based fluid, commonly referred to as a dampening fluid or fountain fluid (typically consisting of water and a small amount of alcohol as well as other additives and/or surfactants to reduce surface tension). The hydrophobic regions repel dampening fluid and accept ink, whereas the dampening fluid formed over the hydrophilic regions forms a fluid “release layer” for rejecting ink. Therefore the hydrophilic regions of the printing plate correspond to unprinted areas, or “non-image areas”, of the final print. 
         [0005]    The ink may be transferred directly to a substrate, such as paper, or may be applied to an intermediate surface, such as an offset (or blanket) cylinder in an offset printing system. The offset cylinder is covered with a conformable coating or sleeve with a surface that can conform to the texture of the substrate, which may have surface peak-to-valley depth somewhat greater than the surface peak-to-valley depth of the imaging plate. Also, the surface roughness of the offset blanket cylinder helps to deliver a more uniform layer of printing material to the substrate free of defects such as mottle. Sufficient pressure is used to transfer the image from the offset cylinder to the substrate. Pinching the substrate between the offset cylinder and an impression cylinder provides this pressure. 
         [0006]    Typical lithographic and offset printing techniques utilize plates which are permanently patterned, and are therefore useful only when printing a large number of copies of the same image (long print runs), such as magazines, newspapers, and the like. However, they do not permit creating and printing a new pattern from one page to the next without removing and replacing the print cylinder and/or the imaging plate (i.e., the technique cannot accommodate true high speed variable data printing wherein the image changes from impression to impression, for example, as in the case of digital printing systems). Furthermore, the cost of the permanently patterned imaging plates or cylinders is amortized over the number of copies. The cost per printed copy is therefore higher for shorter print runs of the same image than for longer print runs of the same image, as opposed to prints from digital printing systems. 
         [0007]    Accordingly, a lithographic technique, referred to as variable data lithography, has been developed which uses a non-patterned reimageable surface coated with dampening fluid. Regions of the dampening fluid are removed by exposure to a focused radiation source (e.g., a laser light source). A temporary pattern in the dampening fluid is thereby formed over the non-patterned reimageable surface. Ink applied thereover is retained in pockets formed by the removal of the dampening fluid. The inked surface is then brought into contact with a substrate, and the ink transfers from the pockets in the dampening fluid layer to the substrate. The dampening fluid may then be removed, a new, uniform layer of dampening fluid applied to the reimageable surface, and the process repeated. 
         [0008]    In the aforementioned system it is very important to have an initial layer of dampening fluid that is of a uniform and desired thickness. To accomplish this, a form roller nip wetting system, which comprises a roller fed by a solution supply, is brought proximate the reimageable surface. Dampening fluid is then transferred from the form roller to the reimageable surface. However, such a system relies on the mechanical integrity of the form roller and the reimageable surface to obtain a uniform layer. Mechanical alignment errors, positional and rotational tolerances, and component wear each contribute to variation in the roller-surface spacing, resulting in deviation of the dampening fluid thickness from ideal. 
         [0009]    Furthermore, an artifact known as ribbing instability in the roll-coating process leads to a non-uniform dampening solution layer thickness. This variable thickness manifests as streaks or continuous lines in a printed image. 
         [0010]    Still further, while great efforts are taken to clean the roller after each printing pass, in some systems it is inevitable that contaminants (such as ink from prior passes) remain on the reimageable surface when a layer of dampening fluid is applied. The remaining contaminants can attach themselves to the form roller that deposits the dampening fluid. The roller may thereafter introduce image artifacts from the contaminants into subsequent prints, resulting in an unacceptable final print. 
         [0011]    In addition, cavitation may occur on the form roller in the transfer nip due to Taylor Instabilities (see, e.g., “An Outline of Rheology in Printing” by W. H. Banks, in the journal Rheologica Acta, pp. 272-275 (1965)). To avoid these instabilities, systems have been designed with multiple rollers that move back and forth in the axial direction while also moving in rolling contact with the form roller, to break up the rib and streak formation. However, this roller mechanism adds delay in the “steadying out” of the dampening system so printing cannot start until the dampening fluid layer thickness has stabilized on all the roller surfaces. Also, on-the-fly dampening fluid flow control is not possible since the dampening fluid layer is at that point already built up on the form roller and the other dampening system rollers acts as a buffering mechanism. 
         [0012]    Accordingly, efforts have been made to develop systems to deposit dampening fluid directly on the offset plate surface as opposed to on intermediate rollers or a form roller. One such system applies the dampening fluid onto the reimageable offset plate surface. See, e.g., U.S. Pat. No. 6,901,853 and U.S. Pat. No. 6,561,090. However, due to the fact that these dampening systems are used with conventional (pre-patterned) offset plates, the mechanism of transfer of the dampening fluid to the offset plate includes a ‘forming roller’ that is in rolling contact with the offset plate cylinder to transfer the FS to the plate surface in a pattern-wise fashion—since it is the nip action of contact rolling between the form roller and the patterned offset plate surface that squeezes out the fountain solution from the hydrophobic regions of the offset plate, allowing the subsequent ink transfer selectivity mechanism to work as desired. 
         [0013]    While the spray dampening system provides the advantage of precisely metering out the desired flow rate of the dampening fluid through control of the spray system, as well as the ability to manipulate the dampening fluid layer thickness on-the-fly as needed, the requirement of using the dampening system form roller as the final means of transferring the dampening fluid to the plate surface reintroduces the disadvantages of thickness variation, roller contamination, roller cavitation, and so on. 
       SUMMARY 
       [0014]    Accordingly, the present disclosure is directed to systems and methods providing a dampening fluid directly to a reimageable surface of a variable data lithographic system that does not employ a dampening form roller. Systems and methods are disclosed for application of dampening fluid directly to a reimageable surface of an imaging member in such a system. 
         [0015]    A system and corresponding methods are disclosed herein for applying a dampening fluid to a reimageable surface of an imaging member in a variable data lithography system, comprising a subsystem for converting a dampening fluid from a liquid phase to a fine droplet or vapor state (herein referred to as a dispersed fluid), a subsystem for directing flow of said dispersed fluid comprising the dampening fluid in droplet or vapor phase to the reimageable surface, whereby the dampening fluid reverts to a continuous liquid layer directly on, and is thereby deposited on, the reimageable surface to form a dampening fluid layer. 
         [0016]    A number of alternative systems and methods may be used for converting the liquid dampening fluid to a dispersed fluid, such as: an ultrasonic-based subsystem, a nozzle-based nebulizer subsystem, an impeller-based subsystem, and a vapor chamber subsystem. A bias or ionic charging subsystem may optionally be provided for applying a charge to droplets of dampening fluid while the dampening fluid is in a dispersed fluid state, to thereby enable the droplets to repel each other and avoid recombination prior to deposition on the reimageable surface and to enhance deposition onto the reimageable surface. 
         [0017]    Various feedback and control systems are provided to measure the thickness of the layer of dampening fluid applied to the reimageable surface, and control, dynamically or otherwise, aspects of the dampening fluid deposition process to obtain and maintain a desired layer thickness. 
         [0018]    In an alternative dampening fluid deposition system and method, a continuous ribbon of dampening fluid may be applied directly to the reimageable surface. According to this alternative, a subsystem for applying a dampening fluid to a reimageable surface comprises: a body structure having formed therein a port, the port extending in a first direction substantially perpendicular to a direction of travel of the reimageable surface when in use, the port having a width at least equal to a width of the reimageable surface in the first direction, the port configured to deliver dampening fluid in a continuous fluid ribbon directly to the reimageable surface to thereby form a dampening fluid layer thereover; a mechanism, associated with the body structure, for disrupting an entrained air layer over the reimageable surface when the reimageable surface is in motion; a dampening fluid reservoir disposed to provide dampening fluid to the port; and a control mechanism for controlling the flow of dampening fluid from the reservoir to the port and from the port to the reimageable surface. The mechanism may be a vortex-generating surface formed in the body structure. The control mechanism may be a valve, and may form a part of a thickness sensor control mechanism. 
         [0019]    The above is a summary of a number of the unique aspects, features, and advantages of the present disclosure. However, this summary is not exhaustive. Thus, these and other aspects, features, and advantages of the present disclosure will become more apparent from the following detailed description and the appended drawings, when considered in light of the claims provided herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    In the drawings appended hereto like reference numerals denote like elements between the various drawings. While illustrative, the drawings are not drawn to scale. In the drawings: 
           [0021]      FIG. 1  is a side view of a system for variable lithography including a non-contact dampening fluid deposition subsystem according to an embodiment of the present disclosure. 
           [0022]      FIG. 2  is a cross-sectional view of a first embodiment of an ultrasonic spray subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0023]      FIG. 3  is a cross-sectional view of a second embodiment of an ultrasonic spray subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0024]      FIG. 4  is a cross-sectional view of a first embodiment of a nebulizer-based spray subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0025]      FIG. 5  is a cross-sectional view of a second embodiment of a nebulizer-based spray subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0026]      FIG. 6  is a cross-sectional view of a first embodiment of an impeller-based spray subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0027]      FIG. 7  is a cross-sectional view of a second embodiment of an impeller-based spray subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0028]      FIG. 8  is a cross-sectional view of a first embodiment of a dampening fluid vapor removal subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0029]      FIG. 9  is a cross-sectional view of a second embodiment of a dampening fluid vapor removal subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0030]      FIG. 10  is a cross-sectional view of a first embodiment of a dampening fluid extrusion subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0031]      FIG. 11  is a cross-sectional view of a first embodiment of a vapor chamber-based subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0032]      FIG. 12  is a cross-sectional view of a first embodiment of a blade metering subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0033]      FIG. 13  is a cross-sectional view of a second embodiment of a blade metering subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0034]      FIG. 14  is a cross-sectional view of a third embodiment of a blade metering subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0035]      FIG. 15  is a top view of the third embodiment of a blade metering subsystem comprising a portion of a non-contact dampening fluid deposition subsystem according to the present disclosure. 
           [0036]      FIG. 16  is a side view of another embodiment of a blade metering subsystem comprising a portion of a non-contact dampening fluid deposition subsystem with dampening fluid roller dispenser according to the present disclosure. 
           [0037]      FIG. 17  is a side view of yet another embodiment of a blade metering subsystem comprising a portion of a non-contact dampening fluid deposition subsystem with dampening fluid spray dispenser according to the present disclosure. 
           [0038]      FIG. 18  is a side view of a portion of an embodiment of a metering blade having a bead tip for a blade metering subsystem according to the present disclosure. 
           [0039]      FIG. 19  is a side view of a portion of another embodiment of a metering blade having a wrapped tip for a blade metering subsystem according to the present disclosure. 
           [0040]      FIG. 20  is a side view of a portion of yet another embodiment of a metering blade having a folded geometry for a blade metering subsystem according to the present disclosure. 
           [0041]      FIG. 21  is a side view of a portion of still another embodiment of a metering blade having a belt tip for a blade metering subsystem according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    We initially point out that description of well-known starting materials, processing techniques, components, equipment, and other well-known details are merely summarized or are omitted so as not to unnecessarily obscure the details of the present invention. Thus, where details are otherwise well known, we leave it to the application of the present invention to suggest or dictate choices relating to those details. 
         [0043]    With reference to  FIG. 1 , there is shown therein a system  10  for variable data lithography according to one embodiment of the present disclosure. System  10  comprises an imaging member  12 , in this embodiment a drum, but may equivalently be a plate, belt, etc., surrounded by a no-roller, direct-application dampening fluid subsystem  14 , an optical patterning subsystem  16 , an inking subsystem  18 , a rheology (complex viscoelastic modulus) control subsystem  20 , transfer subsystem  22  for transferring an inked image from the surface of imaging member  12  to a substrate  24 , and finally a surface cleaning subsystem  26 . Many optional subsystems may also be employed, such as a dampening fluid thickness sensor subsystem  28 . Other such subsystems are beyond the scope of the present disclosure. With the exception of the specifics of dampening fluid subsystem  14 , each of these subsystems, as well as operation of the system as a whole, are described in further detail in the aforementioned U.S. patent application Ser. No. 13/095,714. 
         [0044]    The key requirement of dampening fluid subsystem  14  is to deliver a layer of dampening fluid having a uniform and controllable thickness over a reimageable surface layer over imaging member  12 . In one embodiment this layer is in the range of 0.2 μm to 1.0 μm, and very uniform without pinholes. The dampening fluid must have the property that it wets and thus tends to spread out on contact with the reimageable surface. Depending on the surface free energy of the reimageable surface the dampening fluid itself may be composed mainly of water, optionally with small amounts of isopropyl alcohol or ethanol added to reduce its natural surface tension as well as lower the evaporation energy necessary for subsequent laser patterning. In addition, a suitable surfactant may be added in a small percentage by weight, which promotes a high amount of wetting to the reimageable surface layer. In one embodiment, this surfactant consists of silicone glycol copolymer families such as trisiloxane copolyol or dimethicone copolyol compounds which readily promote even spreading and surface tensions below 22 dynes/cm at a small percentage addition by weight. Other fluorosurfactants are also possible surface tension reducers. Optionally the dampening fluid may contain a radiation sensitive dye to partially absorb laser energy in the process of patterning. Optionally the dampening fluid may be non-aqueous consisting of, for example, polyfluorinated ether or fluorinated silicone fluid. 
         [0045]    In the description of embodiments of a dampening fluid subsystem  14  that follow it will be appreciated that as there is no pre-formed hydrophilic-hydrophobic pattern on a printing plate in system  10 , the need for a form roller to transfer the dampening fluid is obviated. As mentioned, a laser (or other radiation source) is used to form pockets in, and hence pattern, the dampening fluid. The characteristics of the pockets (such as depth and cross-sectional shape), which determine the quality of the ultimate printed image, are in large part a function of the effect that the laser has on the dampening fluid. This effect is to a large degree controlled by the thickness of the dampening fluid at the point of incidence of the laser. Therefore, to obtain a controlled and preferred pocket shape, it is important to control and make uniform the thickness of the dampening fluid layer, and to do so without introducing unwanted artifacts into the printed image. 
         [0046]    Ultrasonic Spray Subsystem 
         [0047]    Accordingly, with reference to  FIG. 2 , there is shown therein a dampening fluid subsystem  30  according to a first embodiment of the present disclosure, which forms and delivers a vapor, or mist, of dampening fluid to the reimageable surface layer of imaging member  12 . Dampening fluid subsystem  30  comprises housing  32  in which a reservoir  34  of dampening fluid is maintained. Reservoir  34  feeds a dispersed fluid generation region  36 . An ultrasonic transducer  38 , under control of controller  40 , ejects fine droplets of dampening fluid to form a dispersed fluid. The dispersed fluid, which may further include a delivery fluid (typically air), is transported by way of a positive internal pressure from pressurization means  42  to and ultimately out of a nozzle  44 . The output of nozzle  44  is directed toward the reimageable surface layer of imaging member  12 , thereby depositing a layer of droplets that spread out to form a continuous layer  46  of dampening fluid thereover. 
         [0048]    Many ultrasonic humidifier devices are known in the art, and such devices may be modified based on the present disclosure to perform the function described herein. A commercially available system on which such a system may be based is the KAZ 5520 ultrasonic humidifier manufactured by Honeywell. Other examples include the BNB and BNU Series Stulz-Ultrasonic™ Humidifier, by Stulz Air Technology Systems, Inc. Therefore, the specific embodiment shown in  FIG. 2  is merely by way of example, and shall not otherwise limit the scope of the present disclosure. 
         [0049]    In an alternative embodiment  31 , shown in  FIG. 3 , essentially the same ultrasonic device generates a dispersed fluid of dampening fluid, but rather than being transported by way of internal positive pressure and a directed nozzle, the vapor of dampening fluid is carried from a nozzle  48  by way of a directed carrier stream (e.g., of air) generated using an air knife  51  to the reimageable surface layer of imaging member  12 . By controlling both the amplitude and frequency of the vibrating ultrasonic transducer  38  and also the flow rate of the air knife, one can manipulate the exact amount of dampening fluid that is deposited onto the reimageable surface layer of imaging member  12 . The pressure of air knife  51  is manipulated to control the airflow rate for depositing the dampening fluid at the desired rate. A control subsystem incorporating thickness sensor subsystem  28  may accomplish this dampening fluid deposition control. 
         [0050]    In certain embodiments steps may be taken to ensure that the generated droplets do not re-combine in mid-air, so that a controlled layer of dampening fluid can be formed on the reimageable surface layer of imaging member  12 . One method of achieving this objective is to electrically charge the droplets, to enable the droplets to repel each other and avoid recombination prior to deposition on the reimageable surface. This may be accomplished, for example, by a bias system  52 , which applies a bias to nozzle  44  ( FIG. 2 ) or nozzle  48  ( FIG. 3 ). Furthermore, by placing opposite charge uniformly on the reimageable surface of imaging member  12 , using for example a scorotron,  50 —, upstream of the dispersed fluid deposition region, the oppositely charged droplets can be attracted to the surface to neutralize the charge and form a uniform layer. 
         [0051]    Nozzle-Based Nebulizer Spray Subsystem 
         [0052]    Referring next to  FIG. 4 , according to another embodiment  60 , a nebulizer assembly  62  is utilized to generate the fine droplets of the dampening fluid. While there are many different arrangements of nebulizers, in one example dampening fluid from reservoir  64  is introduced into one end of a tee-structure  66  in which one or more ports  68 ,  70  introduce a carrier, such as air. In one embodiment, one port  68  may introduce the carrier at an elevated temperature as compared to the carrier temperature in second port  70 . The relative pressure within tee-structure  66 , and if present the temperature differential between the introduced carriers, result in creating a dispersed fluid of the dampening fluid and carrier within tee-structure  66 . A narrow exit port (nozzle)  72  is provided in an end of tee-structure  66  through which the dispersed dampening fluid is ejected onto the reimageable surface layer of imaging member  12 . 
         [0053]    Control over the carrier flow rates, carrier temperatures, and rate of dampening fluid introduction into tee-structure  66  provide control over the thickness of the layer  74  of dampening fluid deposited onto the reimageable surface layer of imaging member  12 . A control subsystem incorporating thickness sensor subsystem  28  may accomplish this dampening fluid deposition control. 
         [0054]    In an alternative embodiment  61 , shown in  FIG. 5 , the dispersed fluid created using nebulizer assembly  62  is directed to the reimageable surface layer of imaging member  12  through the use of a directed carrier stream (e.g., of air) generated using an air knife  76 . By controlling the carrier flow rates, carrier temperatures, rate of dampening fluid introduction into tee-structure  66 , and the flow rate of the air knife, control over the thickness of the layer  74  of dampening fluid deposited onto the reimageable surface layer of imaging member  12  may be provided. A control subsystem incorporating thickness sensor subsystem  28  may accomplish this dampening fluid deposition control. 
         [0055]    In certain embodiments steps may be taken to ensure that the generated droplets do not re-combine in mid-air, so that a controlled layer of dampening fluid can be formed on the reimageable surface layer of imaging member  12 . One method of achieving this objective is to electrically charge the droplets exiting at nozzle  72 , to enable the droplets to repel each other and avoid recombination prior to deposition on to the reimageable surface. This may be accomplished, for example, by a bias system  78 , which applies a bias to nozzle  72 , as shown in each of  FIGS. 4 and 5 . 
         [0056]    Impeller-Based Spray Subsystem 
         [0057]    Referring next to  FIG. 6 , according to another embodiment  80 , an impeller-based subsystem  82  is used. There are many different arrangements of impeller systems, such as impeller ejection systems, impeller-humidifiers, and the like, which may provide the functionality described herein. Therefore, while one specific embodiment is described in order to illustrate the desired functionality, it will be understood that alternate systems may equivalently be used. 
         [0058]    In the exemplary subsystem  82 , dampening fluid from reservoir  84  is introduced onto a disk or impeller  86 , which is caused to rotate by motor  88 . The dampening fluid briefly accumulates on impeller  86 , but due to the centrifugal force induced by the rotation of impeller  86 , droplets of the dampening fluid are accelerated in a direction away from the center of impeller  86  toward a diffuser  90  comprised of a mesh, screen, comb filter, etc. The droplets of the dampening fluid hit diffuser  90  at a relatively high velocity, and are thereby broken up into even finer droplets. Temperature of the fluid, impeller  86 , and/or diffuser  90  may be controlled to enhance vapor production. A commercially available system that may form the basis for such an embodiment is the KAZ V400 impeller humidifier, manufactured by Honeywell. The vapor of dampening fluid is directed onto the reimageable surface layer of imaging member  12 , where it accumulates as a layer  94  of dampening fluid. 
         [0059]    In an alternative embodiment  81 , shown in  FIG. 7 , the dispersed fluid created using impeller subsystem  82  is directed to the reimageable surface layer of imaging member  12  through the use of a directed carrier stream (e.g., of air) generated using an air knife  96 . By controlling the rate of deposit of dampening fluid onto impeller  86 , the rotation velocity of impeller  86 , the geometry of diffuser  90 , and the flow rate of air knife  96 , control over the thickness of the layer  94  of dampening fluid deposited onto the reimageable surface layer of imaging member  12  may be provided. A control subsystem incorporating thickness sensor subsystem  28  may accomplish this dampening fluid deposition control. 
         [0060]    In certain embodiments steps may be taken to ensure that the generated droplets do not re-combine in mid-air, so that a controlled layer of dampening fluid can be formed on the reimageable surface layer of imaging member  12 . One method of achieving this objective is to electrically charge the droplets exiting at diffuser  90 , to enable the droplets to repel each other and avoid recombination prior to deposition on to the reimageable surface. This may be accomplished, for example, by a bias system  98 , which applies a bias to diffuser  90 , as shown in each of  FIGS. 6 and 7 . 
         [0061]    In each of the aforementioned embodiments there may be a desire to remove dampening fluid introduced into the environment but not deposited onto the reimageable surface layer of imaging member  12 , referred to herein as overspray. Motivations to do so include reducing waste, ensuring that unsafe additives to the dampening fluid are not vented into the environment, etc. According to one embodiment  100  for capturing overspray illustrated in  FIG. 8 , dampening fluid subsystem  14  is housed in a containment structure  102 . Containment structure  102  is sized and positioned such that a substantial amount of generated dispersed fluid is introduced proximate the reimageable surface layer of imaging member  12 . A portion  104  of the dispersed fluid is deposited onto the reimageable surface, which is carried clear of containment structure  102  by the rotation of imaging member  12 , while the balance of the vapor forming the overspray  106  is contained within containment structure  102 . A fan  108  or similar apparatus operates to extract overspray  106  from within containments structure  102 . The dampening fluid may thereafter be extracted from the mixture of air and overspray through filtering, attraction of droplets to a charged surface  110 , or by other mechanism known in the art, and collected in a reservoir  112 . 
         [0062]    Another embodiment  101  for preventing introduction of dampening fluid into the external environment is illustrated in  FIG. 9 . This embodiment is similar to that shown in  FIG. 8 , with the difference that in place of a containment structure in which dampening fluid subsystem  14  is housed, a local region of low pressure is formed in housing  120  enclosing the system  10 . A fan  108  or similar apparatus may form this local region of low pressure. The dampening fluid may thereafter be extracted from the mixture of air and overspray through filtering, attraction of droplets to a charged surface  110 , or by other mechanism known in the art, and collected in a reservoir  112 . 
         [0063]    Solution-Extrusion Subsystem 
         [0064]    With reference to  FIG. 10 , there is illustrated therein another embodiment  150  for rollerless, direct application of dampening fluid to a reimageable surface in the context of a variable data digital lithography system. Embodiment  150  comprises a liquid ribbon extruder  152  shaped and disposed to be proximate the reimageable surface layer of rotating imaging member  12 . Extruder  152  supplies dampening fluid from a reservoir  154  through a port  156  that extends in the cross-process direction substantially the full width of the reimageable surface. Dampening fluid is thereby essentially extruded as a continuous fluid ribbon that is directly applied to the reimageable surface. With proper control of extrusion rate, such as by way of valve  158 , back pressure on reservoir  154 , dimension of port  156 , viscosity of the dampening fluid, and so on, the ribbon of dampening fluid may be caused to exit port  156  at substantially the same velocity as the circumferential speed of the reimageable surface layer of rotating imaging member  12 . In one embodiment, the ribbon of dampening fluid forms a layer  160  approximately 1-2 microns thick across the surface of the reimageable member. 
         [0065]    In the present case of depositing a relatively thin fluid layer over a rotating surface, surface effects must be considered in order to ensure uniform application of the dampening fluid over the reimageable surface. For various physical reasons, as imaging member  12  rotates, a layer of entrained air (or other ambient fluid) is formed at its surface. This entrained air layer may underlay a fluid layer deposited over the reimageable surface unless the entrained air layer is interrupted. To this aim, extruder  152  may be shaped or have attached thereto or associated therewith a structure for disrupting or evacuating the entrained air layer. According to one embodiment, a vortex generating wall  162  is formed in extruder  152 . As imaging member  12  rotates, at least a portion of the boundary layer entrained air is directed into vortex generating wall  162 . This produces a vortex, resulting in a slight negative pressure in the space between the nozzle and the plate cylinder. This negative pressure extracts the entrained air boundary layer and draws dampening fluid into surface contact with the reimageable surface of imaging member  12 , resulting in more uniform coverage of the dampening fluid over the reimageable surface. 
         [0066]    Vapor Chamber Deposition Subsystem 
         [0067]    With reference next to  FIG. 11 , there is shown therein yet another embodiment  200  for no-roller application of dampening fluid to a reimageable surface in the context of a variable data digital lithography system. Embodiment  200  comprises a vaporization chamber  202  that creates a vapor  204  of dampening fluid from a reservoir of such solution  206 . A boiler  208  or similar apparatus may heat the solution in reservoir  206  to accomplish vaporization in a pressurized environment (other pressure and/or temperature mechanisms may similarly be employed). Such an embodiment may be used in cases of a single component dampening fluid, such as perfluorinated ethers. If the dampening fluid consists of more than one component, and if the various components have different boiling points, then multiple vaporization chambers and boilers (e.g.,  202   a ) with different temperatures, one for each volatile component, can be used in parallel. 
         [0068]    The dampening fluid vapor  204  is transmitted to a heated condensation chamber  210 , by way of a heated or heat-conductive conduit  212 . The surfaces of condensation chamber  210  may be heated by thermal conduction via conduit  212 , or independently heated such as by a heating coil  214 . By heating the surface of heated condensation chamber  210  a temperature differential is created between the interior of condensation chamber  210  and the relatively cooler reimageable surface of imaging member  12 . If the ambient within condensation chamber  210  is well below the boiling point of the vapor, the vapor condenses in the ambient and forms droplets before coming into contact with the reimageable surface of the imaging member  12 . If the interior surfaces of the vapor chamber are heated to near or above the boiling point then condensation occurs only, and preferably, on the reimageable surface. 
         [0069]    In addition, in the case in which the heat flows between the vaporization chamber  202  and the condensation chamber  210 , the heat flow into the vaporization chamber  202  determines the evaporation rate and thus the vapor flow rate. The flow rate of vapor  204  is set to equal the steady state condensation rate on the reimageable surface of imaging member  12  as that surface passes by the condensation chamber  210 . The condensation rate is set to provide the desired thickness of a thus-formed dampening fluid layer  216 . 
         [0070]    When the vapor condenses on the reimageable surface, latent heat is produced. For low latent heat dampening fluids, the latent heat will typically be negligible. However, heating a portion of the reimageable surface of imaging member  12  proximate condensation chamber  210 , such as by its proximity to heating coil  214  or by other mechanisms, before patterning by optical patterning subsystem  16  can provide a small assist by reducing the optical power needed for patterning. Furthermore, heating the reimageable surface before inking at inking subsystem  18  can assist with obtaining a desired rheology change between inking and transfer. 
         [0071]    Blade Metering Subsystem 
         [0072]    With reference next to  FIG. 12 , there is shown therein yet another embodiment  230  for rollerless, direct application of dampening fluid to a reimageable surface in the context of a variable data digital lithography system. Embodiment  230  comprises blade  232  suspended at a desired distance above the reimageable surface of imaging member  12 . Blade  232  may be a soft deformable material consisting of a variety of materials with a variety of durometers and a variety of thickness values. Potential materials include (but are not limited to) silicone, rubber, vinyl, neoprene, Teflon, etc. Moreover, a stiffer material such as a springy metal foil may back blade  232 . In general, blade  232  may consist of several layers of different materials to adjust the flexibility and the surface properties of blade  232 . Blade  232  may also be coated with material such as Parylene or Teflon to prevent adhesion of materials such as ink, dust particles, etc. Blade  232  may also be electrically conductive to dissipate charge. 
         [0073]    A dampening fluid source  234 , such as a pressurized nozzle ejector, deposits dampening fluid in a region upstream (behind) blade  232  in the direction of rotation of imaging member  12  to form an accumulation  236  of dampening fluid. The rate of application of the dampening fluid is adjusted relative to the rate of rotation of imaging member  12  such that dampening fluid does not over-accumulate. The spacing and angle between blade  232  and the reimageable surface determines the thickness of layer  238  of dampening fluid over the reimageable surface. This spacing and angle may be adjustable by way of an optional mount  233 . 
         [0074]    Shown in  FIG. 13  is another embodiment  240  for rollerless, direct application of dampening fluid to a reimageable surface in the context of a variable data digital lithography system. Embodiment  240  is a variation of embodiment  230  shown in  FIG. 12  in that a relatively flexible contour member  242  is secured to (or formed as a part of) blade  232 . One benefit of embodiment  240  is that a controlled and in certain embodiments adjustable force can be applied at the location at which dampening fluid layer  238  is formed. This results in a uniform dampening fluid layer thickness and reduced streaking and other artifacts present in known dampening fluid systems. In one example of this embodiment, flexible contour member  242  comprises a rubber wiper attached to a rigid blade  232 . In another example, blade  232  and flexible contour member  242  are a monolithic structure, with blade portion  232  having a first thickness rendering it relatively rigid and a contour member portion  242  of a second thickness that is thinner than the first thickness to thereby render the contour member portion  242  relatively more flexible. 
         [0075]    In another embodiment  250  shown in  FIG. 14 , a two-part blade/contour member  252  is positioned over the reimageable surface of rotating imaging member  12  so as to meter dampening fluid from accumulation  236  to form layer  238 . Two-part blade/contour member  252  comprises a plate  254  and set-screw  256  used to apply pressure, via plate  254 , to contour member  242 . Set-screw  256  may manually or by way of a servo motor  258  and belt  260  (or similar mechanism) control both the force and physical position of contour member  242  relative to the reimageable surface, to control the thickness of layer  238 . In place of a set-screw and servo, a piezoelectric device may also be used to control the position of and pressure applied by two-part blade/contour member  252 . 
         [0076]    The adjustment provided by two-part blade/contour member  252  may be locally variable, such as illustrated in  FIG. 15 , to compensate for non-uniformities over the width of the reimageable surface. The adjustments may be varied during use to maintain a desired dampening fluid layer thickness. A control subsystem incorporating thickness sensor subsystem  28  may accomplish this dampening fluid deposition control. 
         [0077]    In another embodiment  300  shown in  FIG. 16 , a dampening fluid dispenser subsystem  302  is positioned immediately behind and proximate blade  304 . Dispenser subsystem  302  comprises a dampening fluid reservoir  306  and an applicator  308 , such as a sponge roller, rubber roller etc. A layer  310  of dampening fluid is applied over the surface of rotating imaging member  12  by applicator  308 , which may present undesirable variations in thickness. Blade  304  is maintained at a relatively uniform height over the surface of rotating imaging member  12  so as to meter dampening fluid to form layer  312  of relatively uniform thickness over rotating imaging member  12 . 
         [0078]    With reference to  FIG. 17 , another embodiment  320  providing application and metering of dampening fluid is shown. According to this embodiment, a spray applicator  322  applies a layer dampening fluid  326  to the surface of rotating imaging member  12 . Again, layer  326  may present undesirable variations in thickness. Blade  324  is maintained at a relatively uniform height over the surface of rotating imaging member  12  so as to meter dampening fluid to form layer  326  of relatively uniform thickness over rotating imaging member  12   
         [0079]    A number of different configurations for the tip of the aforementioned blade embodiments are contemplated herein. (While the term “tip” is used in the following, it will be appreciated that due to the blade extending into the page as illustrated in the following-described figures the tip is actually an edge of the blade.) The tip configuration will have a direct impact on the quality of the resulting metered layer of dampening fluid. For example, reduced “streaking” in the dampening fluid layer (and hence in the final image) may be achieved. In one embodiment, smoothness of the tip is an object. In others, a desired surface texture in the object. 
         [0080]    With reference to  FIG. 18 , blade  350  useful in any of the metering embodiments described herein may be provided with a polymer bead  352  applied to the tip thereof. Bead  352  may be applied by any of a variety of methods, such as dipping the tip  354  of blade  350  into a liquid polymer, such as uncured silicone. After curing the silicone, a smooth blade tip (edge) is formed. 
         [0081]    With reference to  FIG. 19 , blade  350  may alternatively be provided with a foil covering  356  at its tip  354 . Foil  356  may, for example, be a thin polyimide, Mylar foil or tape, etc. Foil  356  may be manually applied, applied by a dedicated or general-purpose machine, and so on. Plating, vapor depositing, or other technique of depositing a relatively smooth, uniformly thick metal or metal composite layer may also obtain a similar result. 
         [0082]    With reference to  FIG. 20 , a blade  358  useful in any of the metering embodiments described herein may be constructed by folding a foil, thin polymer sheet (such as a relatively thin rubber or silicone sheet), or the like. The folding process is such that a uniform, smooth tip  360  is produced. 
         [0083]    With reference to  FIG. 21 , blade  350  is disposed within a belt, loop or the like  362 . Belt  362  may be, for example, a thin (e.g., approx. 1 mil) Mylar foil. A drive wheel  364  rotates, causing a rotation of belt  362  past the tip (edge)  366  of blade  350 . As belt  362  rotates, it passes by a cleaning subsystem  368 , which removes marking material and other particle contamination therefrom. In this embodiment, belt  362  may optionally be a consumable item within a marking system to improve longevity of the system and quality of the images produced thereby. 
         [0084]    In various of the above-described embodiments it may be desirable to supplement the dampening fluid deposition mechanisms with a blading metering system to further control the uniformity of the thin layer of dampening fluid applied over the reimageable surface of imaging member  12 . Therefore, the blade metering system described above may be combined with other dampening fluid application embodiments described herein and operated in tandem. 
         [0085]    No limitation in the description of the present disclosure or its claims can or should be read as absolute. The limitations of the claims are intended to define the boundaries of the present disclosure, up to and including those limitations. To further highlight this, the term “substantially” may occasionally be used herein in association with a claim limitation (although consideration for variations and imperfections is not restricted to only those limitations used with that term). While as difficult to precisely define as the limitations of the present disclosure themselves, we intend that this term be interpreted as “to a large extent”, “as nearly as practicable”, “within technical limitations”, and the like. 
         [0086]    Furthermore, while a plurality of preferred exemplary embodiments have been presented in the foregoing detailed description, it should be understood that a vast number of variations exist, and these preferred exemplary embodiments are merely representative examples, and are not intended to limit the scope, applicability or configuration of the disclosure in any way. Various of the above-disclosed and other features and functions, or alternative thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications variations, or improvements therein or thereon may be subsequently made by those skilled in the art which are also intended to be encompassed by the claims, below. 
         [0087]    Therefore, the foregoing description provides those of ordinary skill in the art with a convenient guide for implementation of the disclosure, and contemplates that various changes in the functions and arrangements of the described embodiments may be made without departing from the spirit and scope of the disclosure defined by the claims thereto.