Abstract:
Methods and structures are disclosed to minimize the presence of vapor clouding in the path between an energy (e.g., radiation) source and the dampening fluid layer in a variable data lithography system. Also disclosed are conditions for optimizing vaporization of regions of the dampening fluid layer for a given laser source power. Conditions are also disclosed for minimizing re-condensation of vaporized dampening fluid onto the patterned dampening fluid layer. Accordingly, a reduction in the power required for, and an increase in the reproducibility of, patterning of a dampening fluid layer over a reimageable surface in a variable data lithography system are disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present disclosure is related to U.S. patent application titled “Variable Data Lithographic System”, Ser. No. 13/095,714, filed on Apr. 27, 2011, and assigned to the same assignee as the present application, and further which is incorporated herein by reference. 
     BACKGROUND 
     The present disclosure is related to marking and printing methods and systems, and more specifically to methods and systems providing control of conditions local to the point of writing data to a reimageable surface in variable data lithographic system. 
     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. 
     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. 
     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, where the per-page cost is typically independent of the number of copies that are printed. 
     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 heat source (e.g., using radiation such as 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 regions corresponding to the removal of the dampening fluid. The inked surface is then brought into contact with a substrate (such as paper), and the ink pattern transfers 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. 
     The patterning of dampening fluid on the reimageable surface in variable data lithography essentially involves using a heat source such as a laser to selectively boil off or ablate the dampening fluid in selected locations. This process can be energy intensive due to the large latent heat of vaporization of water. At the same time, high-speed printing necessitates the use of high-speed modulation of the heat source, which can be prohibitively expensive for high power lasers. Therefore, from both an energy and cost perspective, it is beneficial to reduce the total amount of laser energy that is needed to achieve pattern-wise vaporization of the dampening fluid. 
     However, one byproduct of the pattern-wise evaporation of dampening fluid is generation of a vapor cloud. This cloud can partially absorb energy from the laser being used to write onto the dampening fluid layer, thus reducing the laser power available for patterning the dampening fluid layer. 
     With reference to  FIG. 1 , a layer  32  of dampening fluid is shown over a portion of a reimageable surface  34  carried by imaging member  12 . A key requirement of dampening fluid subsystem  14  is to deliver dampening fluid such that layer  32  is of a controlled and uniform thickness. In one embodiment layer  32  is in the range of 200 nanometers (nm) to 1.0 micrometer (μm), and very uniform without defects such as pinholes. 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. In another embodiment, the dampening fluid may be non-aqueous, comprises for example of a fluid having a low heat of vaporization. 
     Typically, the thickness of the dampening fluid layer cannot be lower than about 200 nm (e.g., for an aqueous dampening fluid) to ensure reliable ink selectivity between hyodrophilic and hydrophobic regions over the reimageable surface, and the consequent contrast between the image and non-image zones. This is mainly because the selectivity for ink transfer is a result of the splitting of the sacrificial dampening fluid layer from the dampened regions of the reimageable surface, and a thinner dampening fluid layer may not split reliably. 
     This minimum required dampening fluid layer thickness of approximately 200 nm results in a minimum per-pixel energy requirement based on the heating requirements for boiling-off the dampening fluid (e.g., water), equal to the sensible heating (i.e., heat needed to raise the temperature of the water to its boiling point, typically from a room temperature of about 20° C. to approximately 100° C., which equals the specific heat capacity times the temperature rise of approximately 80° C.) and latent heating (i.e., heat or enthalpy of vaporization of water which is about 540 calories per gram at atmospheric conditions). Based on the above information, we can calculate the power requirements for laser based vaporization of a 200 nm thick layer of water for a print speed of 100 pages per minute and a resolution of 600 dpi (42 micron pixel size and pitch), as shown in Table 1, below. 
     
       
         
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Resolution 
                 600 
                 dpi 
               
               
                   
                 Thickness of dampening fluid 
                 0.2 
                 microns 
               
               
                   
                 layer 
               
               
                   
                 Print speed 
                 100 
                 ppm 
               
               
                   
                 Dot size (diameter) 
                 42.33 
                 microns 
               
               
                   
                 Dampening fluid mass per pixel 
                 2.81E−13 
                 kg 
               
               
                   
                 Dampening fluid latent heat 
                 1.52E−07 
                 cal 
               
               
                   
                 required per pixel 
               
               
                   
                 Dampening fluid sensible heat 
                 2.11E−08 
                 cal 
               
               
                   
                 required per pixel 
               
             
          
           
               
                   
                 Total dampening fluid heat 
                 1.73E−07 cal (or 7.24E−07 J) 
               
             
          
           
               
                   
                 required per pixel 
                   
                   
               
               
                   
                 Required minimum energy 
                 5.14E−02 
                 J/cm2 
               
               
                   
                 density 
               
               
                   
                 Number of pixels in a 8.5 × 11″ 
                 33660000 
                 pixels 
               
               
                   
                 page 
               
               
                   
                 Time per pixel 
                 1.78E−08 
                 sec 
               
               
                   
                 Scanning laser power 
                 40.60 
                 Watt 
               
               
                   
                   
               
             
          
         
       
     
     The above are the theoretical minimum energy and power requirements for vaporization of the dampening fluid assuming that it is comprised only of water, and without accounting for heat loss into the reimageable surface or other regions of the system. It will be appreciated that a relatively high power laser source is required under ideal conditions. However, the cloud of dampening vapor resulting from prior boiling off of regions of the dampening fluid layer can absorb a significant amount of the laser source energy. Considering the presence of this cloud, higher laser power levels are needed to enable boiling-off of the regions of dampening fluid. Providing such a high power laser source may be prohibitive from a number of perspectives such as cost, energy consumption, and so on. 
     Furthermore, the cloud of vaporized dampening fluid can re-condense onto the fluid layer, partially filling and altering the wall profiles of the pockets created by laser writing process. This is especially true for dampening fluids containing large solids, where preferential edge development can be seen due to vapor cloud diffusion. 
     Still further, variations in surrounding air humidity can negatively impact the removal rate of dampening fluid from the dampening fluid layer. For example, if a water based dampening solution is used, a higher concentration of water molecules in the surrounding air results in a higher likelihood of re-condensation on areas that are intended to be free of dampening fluid, and an increase in evaporation resulting in more absorptive material interposed between the laser source and the dampening fluid layer as well as variation in layer thickness. 
     SUMMARY 
     Accordingly, the present disclosure is directed to systems and methods providing a reduction in the power required for, and an increase in the reproducibility of, patterning of a dampening fluid layer over a reimageable surface in a variable data lithography system. More specifically, mechanisms are provided, and steps are taken to minimize the presence of vapor clouding in the path between the radiation (e.g., laser) source and the dampening fluid layer. Conditions may also be controlled such that optimal conditions exist for vaporization of regions of the dampening fluid layer for a given laser source power. Conditions may further be controlled such that re-condensation of vaporized dampening fluid onto the patterned dampening fluid layer is minimized. 
     Systems and methods are disclosed herein for controlling the environmental conditions in a region over a surface of a dampening fluid layer proximate a location at which a radiation-based patterning subsystem selectively vaporizes portions of the dampening fluid layer in a variable data lithographic apparatus, comprising: an enclosure disposed over the surface of a dampening fluid layer and proximate the location at which the radiation-based patterning subsystem selectively vaporizes portions of the dampening fluid layer; a gas-flow control subsystem coupled to the enclosure such that a gas-flow may be controllably generated within the enclosure and proximate the location at which a radiation-based patterning subsystem selectively vaporizes portions of the dampening fluid layer; the enclosure configured to permit an output of the radiation-based patterning subsystem to exit there from and thereby be incident on the dampening fluid layer; and, the enclosure further configured to permit the gas-flow to exit the enclosure at a desired location; whereby the gas-flow may evacuate vaporized dampening fluid from a region proximate the location at which the radiation-based patterning subsystem selectively vaporizes portions of the dampening fluid layer. 
     Various alternate embodiments of such systems are also disclosed. Furthermore, variations and combinations of elements of these embodiments are disclosed. 
     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 
       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: 
         FIG. 1  is a side view of an imaging member having a reimageable surface formed thereover, and a dampening fluid layer formed over the reimageable surface, as known in the art. 
         FIG. 2  is a side view of a system for variable data lithography including an imaging member, a dampening fluid subsystem, a radiation-based patterning subsystem, an inking subsystem, a rheology control subsystem, a transfer subsystem, and a surface cleaning subsystem, according to an embodiment of the present disclosure. 
         FIG. 3  is a side view of a pump-based environmental control subsystem for controlling parameters of the environment local to the point at which laser patterning subsystem writes to a dampening fluid layer, according to an embodiment of the present disclosure. 
         FIG. 4  is a side view of a dry gas source-based environmental control subsystem for controlling parameters of the environment local to the point at which laser patterning subsystem writes to a dampening fluid layer, according to an embodiment of the present disclosure. 
         FIG. 5  is a side view of an air-knife-based environmental control subsystem for controlling parameters of the environment local to the point at which laser patterning subsystem writes to a dampening fluid layer, according to an embodiment of the present disclosure. 
         FIG. 6  is a side view of a local temperature control-based environmental control subsystem for controlling parameters of the environment local to the point at which laser patterning subsystem writes to a dampening fluid layer, according to an embodiment of the present disclosure. 
         FIG. 7  is a side view of a downstream vacuum vapor removal subsystem for controlling parameters of the environment local to the point at which laser patterning subsystem writes to a dampening fluid layer, according to an embodiment of the present disclosure. 
         FIG. 8  is a side view of another embodiment of a downstream vacuum vapor removal subsystem for controlling parameters of the environment local to the point at which laser patterning subsystem writes to a dampening fluid layer, according to the present disclosure. 
         FIG. 9  is a side view of an embodiment of an upstream vacuum vapor removal subsystem with air knife for controlling parameters of the environment local to the point at which laser patterning subsystem writes to a dampening fluid layer, according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     With reference to  FIG. 2 , 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 dampening fluid subsystem  14 , heat-based (e.g., laser) 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 . In general, 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. 
     System  10  further comprises an environmental control subsystem, configured and disposed to address a number of conditions that affect required radiation (e.g., laser) power and the “quality” of spots written in the dampening fluid layer. A first set of such conditions relates to environmental parameters proximate the dampening fluid surface that affect the laser power required for writing to the dampening fluid layer. Appropriate manipulation and control of environmental conditions such as temperature, humidity, and air flow local to the point where the thermal energy (e.g., laser beam) is incident on the dampening fluid layer may result in reduced required energy and more effective laser writing processes. 
     Environmental Control 
     It is well known that the process of boiling a liquid substance can only occur at a temperature where the vapor pressure of the liquid equals the surrounding environmental (atmospheric) pressure. This is in contrast to the process of evaporation, which can occur at other temperatures. A liquid is said to boil when it is under a condition such that bubbles of its vapor phase can spontaneously form within its bulk and be sustained upon further addition of energy. Evaporation occurs when surface molecules in the liquid phase acquire sufficient energy (either from the surrounding medium or other molecules within the liquid itself) to escape into the vapor phase. 
     In one embodiment of the present disclosure illustrated in  FIG. 3 , an environmental control subsystem  30  is provide for controlling parameters of the environment local to the point at which laser patterning subsystem  16  writes to (i.e., vaporizes portions of) dampening fluid layer  32 . Numerous parameters may be controlled by such a system, as illustrated in the following. 
     Humidity Control 
     A drier, less humid environment is desired since such an environment provides fewer airborne water molecules in the path of the laser, provides more effective boiling of the dampening fluid, and reduces the number of water molecules which settle into the just-formed wells  50  from which dampening fluid has been boiled off. Therefore, environmental control subsystem  30  may, in one embodiment, be an enclosure proximate imaging member  12  configured to provide a low humidity environment proximate layer  32 . Laser patterning subsystem  16  may be enclosed therein. Environmental control subsystem  30  provides a dry air region  36  at least proximate the point at which a beam from laser patterning subsystem  16  is incident on dampening fluid layer  32 . Dry air may be provided to region  36  from a dry air source selected from a number of options. According to one option, the dry air source may comprise an air pump (blower)  38  with a desiccator cartridge  40  attached to the pump exhaust, so that the air being pumped out is dried as the air is being provided (see, e.g., http://www.dry-air-systems.com/jetpak.html). This dry air may then be circulated within environmental control subsystem  30 , proximate the surface of dampening fluid layer  32 , to enhance the evaporation rate of the dampening fluid and reduce the energy requirements on laser patterning subsystem  16 . In the event that a non-aqueous dampening solution is used in place of an aqueous dampening solution, dry air will help control the local partial pressure of other solventbased dampening solutions. 
     A valve  42  may be disposed between environmental control subsystem  30  and dry air pump  38  to control flow rate through a parallel path  44  that bypasses desiccator cartridge  40 . Accordingly, the exact humidity content of the air entering the print system may be precisely controlled and tuned to achieve reliable digital printing using the selective laser removal of the dampening fluid. 
     According to another embodiment shown in  FIG. 4 , in place of pump  38  and desiccator  40 , a dry gas source  46  may may be provided, for example comprising a cylinder, removably secured to environmental control subsystem  30 . Cylinder  46  may contain compressed air at a desired humidity, and may provide that humidity controlled air at a constant pressure and flow rate to region  36 . The need for a bypass valve, such as valve  42 , is thereby obviated as the humidity of the air is set by the contents of cylinder  46 . 
     Returning to  FIG. 3 , an extraction pump or similar evacuation mechanism  48  may be provide to obtain a desired gas-flow pattern, flow rate, and so on. The output of evacuation mechanism  48  may be vented to the environment, may be filtered to remove harmful components of the dampening fluid vapor, may be condensed into a storage receptacle  49  for recycling and reuse, and so on. 
     A dampening fluid wiper blade  51  may also be employed in association with environmental control subsystem  30 . Wiper blade  51  may be used to govern the thickness of layer  32 , as well as limit air entry into region  36  from upstream of the point at which layer  32  is patterned. This assists with preventing dust and other contaminants from entering region  36  and interfering with the patterning of layer  32 . 
     Air Flow Velocity Control 
     With reference next to  FIG. 5 , there is shown therein another embodiment of an environmental control subsystem  52  further comprising an air knife  54 . Air knife  54  is directed to the point at which a beam from laser patterning subsystem  16  is incident on and writes to dampening fluid layer  32 . Air knife  54  creates a desired airflow vector at this point. This airflow vector results in evaporating water molecules leaving the dampening fluid layer  32  being immediately carried away from their point of ejection into region  36 . Thus, these water molecules will be carried away from the path of the beam generated by laser patterning subsystem  16 , and further will not have a chance to re-condense on the surface of layer  32 . Precise control of the air flow rate and flow direction can be used to manipulate the dampening fluid layer thickness such that the laser power requirement is optimized. Furthermore, air knife  54  may be employed with or without a combination of the humidity control embodiment described above. 
     Ambient and/or Surface Temperature Control 
     With reference next to  FIG. 6 , there is shown therein another embodiment of an environmental control subsystem  56  further comprising a local temperature control source  58 . Local temperature control source  58  may be a heating coil, heat lamp, heated (or cooled) air source, and so on. In addition, while shown within the enclosure forming environmental control subsystem  56 , local temperature control source  58  may be external to the enclosure or form a portion of another element of the subsystem, such as a portion of pump  38  ( FIG. 3 ), air knife  54  ( FIG. 5 ), etc. 
     Manipulation of the temperature in region  36  may be employed to reduce laser energy required to locally vaporize a region of dampening fluid layer  32 . That temperature manipulation may also enhance the dampening fluid evaporation rate. In this latter case, the water molecules that may escape into the surrounding air will be more energetic due to the temperature increase and therefore have a statistically lower chance of re-condensing onto the liquid dampening fluid layer  32 . Furthermore, in response to designed temperature differentials within the enclosure of environmental control subsystem  56 , such as by use of multiple temperature control sources  58 ,  58   a , etc., airflow control within the enclosure can be tailored to blow the vapor away from the path of the beam from laser patterning subsystem  16 . 
     Precise control of these temperature values may thus be utilized to maintain the dampening fluid layer evaporation rate, and corresponding dampening fluid thickness levels, such that the laser power requirement is minimized while maintaining print ink selectivity and image contrast and resolution. 
     Vacuum Vapor Cloud Removal 
     Yet another condition that may be controlled to reduce laser power requirements in a variable data lithographic system is dissipation or re-location of the cloud of vaporized dampening fluid away from the laser path. It is desired that minimal vapor be disposed between the laser source and the dampening fluid layer, and thereby minimize laser power intended for writing to the dampening fluid layer absorbed by the vapor. 
     With reference to  FIG. 7 , there is shown therein another embodiment of an environmental control subsystem  60  further comprising a downstream vacuum vapor removal subsystem  62 . Downstream vacuum vapor removal subsystem  62  may comprise a vacuum pump or other mechanism designed to draw air, and with it the vapor cloud generated by boiling off of portions of dampening fluid layer  32 , from region  36 . Source air may be from the ambient in and around environmental control subsystem  60  and/or may be a humidity controlled source  38  ( FIG. 3 ), air knife  54  ( FIG. 5 ), etc. 
     With reference to  FIG. 8 , another embodiment of an environmental control subsystem  70  further comprising a downstream vacuum vapor removal subsystem  72  is shown. Vacuum vapor removal system  72  extracts air from downstream of the point at which laser vaporization of layer  32  takes place. With that air is also drawn the vaporized water molecules and other components of the dampening fluid layer  32 . This direction of extraction, from downstream over the patterned surface of layer  32 , has the advantage of removing airborne material both from the path of beam  76  of laser patterning subsystem  16  and entrained vapor over the just-patterned region of layer  32 . Thus, material that might otherwise absorb laser energy is removed as well as material that might otherwise settle back into the wells patterned in layer  32 . 
     A dampening fluid wiper blade  78  may also be employed in association with environmental control subsystem  70 . Wiper blade  78  may be used to govern the thickness of layer  32 , as well as limit air entry into region  36  from upstream of the point at which layer  32  is patterned. This promotes the preferential removal of material from downstream of the point at which layer  32  is patterned as well as in the path of beam  76  of laser patterning subsystem  16 , as discussed above. Wiper blade  78  also assists with preventing dust and other contaminants from entering region  36  and the path of beam  76 , which may improve overall system reliability and robustness. 
     Further according to the embodiment of environmental control subsystem  70  shown in  FIG. 8 , a window structure  74 , such as an anti-reflective (AR) coated laser-transparent material (e.g., glass), may be placed in the path of beam  76  of laser patterning subsystem  16 , above the point of vaporization of the dampening fluid. Window structure  74  is transparent at the wavelength of emission of laser patterning subsystem  16 , permitting beam  76  to pass therethrough without reducing the energy of beam  76  available for vaporizing portions of layer  32 . Window structure  74  serves to prevent contamination of optics associated with producing beam  76 , as well as promoting the preferential removal of material from downstream of the point at which layer  32  is patterned as well as in the path of beam  76  of laser patterning subsystem  16 , as discussed above. 
     The embodiment of environmental control  70 , as illustrated, draws ambient air at input  80  into vacuum vapor removal system  72 . Alternatively, humidity-controlled air or other gas may be provided at input  80 , by a system such as discussed above. 
     With reference to  FIG. 9 , another embodiment of an environmental control subsystem  90  is shown. Environmental control subsystem  90  comprises a housing to which is disposed an upstream vacuum vapor removal subsystem  92 . Environmental control subsystem  90  further comprises an air knife  94  directed to the point at which a beam  96  from laser patterning subsystem  16  is incident on layer  32  to vaporize regions thereof. The air flowing from air knife  94  may be ambient air. Alternatively, the air may be humidity-controlled, as discussed above. 
     While vacuum vapor removal subsystem  92  is located upstream of the point at which a beam  96  from laser patterning subsystem  16  is incident on layer  32  (and thus upstream from the point of generation of the dampening fluid vapor cloud), the direction of airflow from air knife  94  results in downstream vapor being directed towards and into vacuum vapor removal subsystem  92 . With appropriate positioning of air knife  94 , and selection of air flow rate therefrom, any vapor generated by the boiling off of dampening fluid from layer  32  can be carried away from beam  96  and away from the downstream surface of patterned layer  32 . 
     It will be appreciated that environmental controls, as described above, enable consistency and reproducibility in the print process. The environmental controls may be used not only to minimize the required laser power, but also to ensure that the same power is required for each unit of dampening fluid being vaporized. Furthermore, resettling of dampening fluid is reduced or eliminated, providing more uniform wells resulting from laser vaporization and more complete removal of dampening fluid from those wells for optimal ink retention therein at the inking stage. 
     The embodiments described above may also form part of an online feedback control mechanism that ensures that the dampening fluid layer thickness immediately prior to the point of laser exposure as well as immediately prior to the point of inking is maintained at a constant, desired level, optimized for quality printing at minimum laser energy usage. With reference again to  FIG. 2 , a dampening fluid thickness sensor subsystem  28  may be communicatively connected (through appropriate feedback control circuitry) to any of the environmental control subsystems described herein as an additional input for control of dampening fluid subsystem  14 . 
     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. 
     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. 
     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.