Patent Publication Number: US-8985757-B2

Title: Systems and methods for ink-based digital printing using image offset configuration

Description:
FIELD OF DISCLOSURE 
     The disclosure relates to ink-based digital printing systems and methods. In particular, the disclosure relates to printing variable data using an ink-based digital printing system that includes an offset marking material transfer configuration. 
     BACKGROUND 
     Conventional lithographic printing techniques cannot accommodate true high-speed variable data printing processes in which images to be printed change from impression to impression, for example, as enabled by digital printing systems. The lithography process is often relied upon, however, because it provides very high quality printing due to the quality and color gamut of the inks used. Lithographic inks are also less expensive than other inks, toners, and many other types of printing or marking materials. 
     Ink-based digital printing uses a variable data lithography printing system, or digital offset printing system. A “variable data lithography system” is a system that is configured for lithographic printing using lithographic inks and based on digital image data, which may be variable from one image to the next. “Variable data lithography printing,” or “digital ink-based printing,” or “digital offset printing” is lithographic printing of variable image data for producing images on a substrate that are changeable with each subsequent rendering of an image on the substrate in an image forming process. 
     For example, a digital offset printing process may include transferring radiation-curable ink onto a portion of a fluorosilicone-containing imaging member surface that has been selectively coated with a dampening fluid layer according to variable image data. The ink is then cured and transferred from the printing plate to a substrate such as paper, plastic, or metal on which an image is being printed. The same portion of the imaging plate may be cleaned and used to make a succeeding image that is different than the preceding image, based on the variable image data. Ink-based digital printing systems are variable data lithography systems configured for digital lithographic printing that may include an imaging member having a reimageable surface layer, such as a silicone-containing surface layer. 
     Systems may include a dampening fluid metering system for applying dampening fluid to the reimageable surface layer, and an imaging system for laser-patterning the layer of dampening fluid according to image data. The dampening fluid layer is patterned by the imaging system to form a dampening fluid pattern on a surface of the imaging member based on variable data. The imaging member is then inked to form an ink image based on the dampening fluid pattern. The ink image may be partially cured, and is transferred to a printable medium, and the imaged surface of the imaging member from which the ink image is transferred is cleaned for forming a further image that may be different than the initial image, or based on different image data than the image data used to form the first image. Such systems are disclosed in U.S. patent application Ser. No. 13/095,714 (“714 Application”), titled “Variable Data Lithography System,” filed on Apr. 27, 2011, by Stowe et al., which is commonly assigned, and the disclosure of which is hereby incorporated by reference herein in its entirety. 
     In related art offset printing, a combination of a permanently etched imaging plate and a blanket are used to reproduce static images. As discussed above, a digital or variable image print process includes patterning a printing with a fountain solution, developing with a lithographic-like ink, and almost completely transferred to printable media directly from the imaging member or printing plate. After the image is transferred, any small amount of ink on the printing plate gets cleaned and the plate is prepared for the next printing cycle as described before. The ink-based digital printing plate serves the functions of both an etched imaging plate and a blanket combination as in a related art lithographic print process. These combined functions place demanding and conflicting requirements on the ink-based digital printing plate. 
     SUMMARY 
     It has been found that related art offset approaches are not feasible because of reliance on the ink image splitting, resulting in the need for cleaning left over ink, less than optimal ink waste, and poor run cost for ink-based digital printing. Systems and methods are provided that include using a high-transfer-efficiency-offset architecture for use with lithographic inks in ink-based digital printing processes. In particular, rheological conditioning of the ink and careful tuning of ink-to-plate and ink-to-blanket adhesion enable multiple transfers at near 100% efficiency in system and methods of embodiments. In another embodiment, an offset color printing system configuration enables ink-based digital color printing at desirable run costs by using a plurality of ink-based digital printing modules having a high-transfer-efficiency-offset architecture to form a composite image on a substrate. 
     Exemplary embodiments are described herein. It is envisioned, however, that any system that incorporates features of systems described herein are encompassed by the scope and spirit of the exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side diagrammatical view of a related art ink-based digital printing system; 
         FIG. 2  shows a diagrammatical side view of an ink-based digital printing system including an offset transfer configuration in accordance with an exemplary embodiment; 
         FIG. 3  shows a diagrammatical cross-sectional view of an ink-based digital printing system including an offset transfer color printing configuration in accordance with exemplary embodiments; 
         FIG. 4  shows methods for offset ink-based digital printing in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments are intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the apparatus and systems as described herein. 
     The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). When used with a specific value, it should also be considered as disclosing that value. 
     Reference is made to the drawings to accommodate understanding of systems and methods for ink-based digital printing using an offset transfer configuration in accordance with embodiments. In the drawings, like reference numerals are used throughout to designate similar or identical elements. The drawings depict various embodiments of illustrative systems for ink-based digital printing using an offset printing configuration. 
     The 714 Application describes an exemplary related art variable data lithography system  100  for ink-based digital printing, such as that shown, for example, in  FIG. 1 . A general description of the exemplary system  100  shown in  FIG. 1  is provided here. Additional details regarding individual components and/or subsystems shown in the exemplary system  100  of  FIG. 1  may be found in the 714 Application. 
     As shown in  FIG. 1 , the exemplary system  100  may include an imaging member  110 . The imaging member  110  in the embodiment shown in  FIG. 1  is a drum, but this exemplary depiction should not be interpreted so as to exclude embodiments wherein the imaging member  110  includes a drum, plate or a belt, or another now known or later developed configuration. The reimageable surface may be formed of materials including, for example, a class of materials commonly referred to as silicones, including polydimethylsiloxane (PDMS), among others. The reimageable surface may be formed of a relatively thin layer over a mounting layer, a thickness of the relatively thin layer being selected to balance printing or marking performance, durability and manufacturability. 
     The imaging member  110  is used to apply an ink image to an image receiving media substrate  114  at a transfer nip  112 . The transfer nip  112  is formed by an impression roller  118 , as part of an image transfer mechanism  160 , exerting pressure in the direction of the imaging member  110 . Image receiving medium substrate  114  should not be considered to be limited to any particular composition such as, for example, paper, plastic, or composite sheet film. The exemplary system  100  may be used for producing images on a wide variety of image receiving media substrates. The 714 Application also explains the wide latitude of marking (printing) materials that may be used, including marking materials with pigment densities greater than 10% by weight. As does the 714 Application, this disclosure will use the term ink to refer to a broad range of printing or marking materials to include those which are commonly understood to be inks, pigments, and other materials which may be applied by the exemplary system  100  to produce an output image on the image receiving media substrate  114 . 
     The 714 Application depicts and describes details of the imaging member  110  including the imaging member  110  being comprised of a reimageable surface layer formed over a structural mounting layer that may be, for example, a cylindrical core, or one or more structural layers over a cylindrical core. 
     The exemplary system  100  includes a dampening fluid system  120  generally comprising a series of rollers, which may be considered as dampening rollers or a dampening unit, for uniformly wetting the reimageable surface of the imaging member  110  with dampening fluid. A purpose of the dampening fluid system  120  is to deliver a layer of dampening fluid, generally having a uniform and controlled thickness, to the reimageable surface of the imaging member  110 . As indicated above, it is known that a dampening fluid such as fountain solution may comprise mainly water optionally with small amounts of isopropyl alcohol or ethanol added to reduce surface tension as well as to lower evaporation energy necessary to support subsequent laser patterning, as will be described in greater detail below. Small amounts of certain surfactants may be added to the fountain solution as well. Alternatively, other suitable dampening fluids may be used to enhance the performance of ink based digital lithography systems. Exemplary dampening fluids include water, NOVEC 7600 (1,1,1,2,3,3-Hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxyl)pentane and has CAS#870778-34-0.), and D4 (octamethylcyclotetrasiloxane). Other suitable dampening fluids are disclosed, by way of example, in co-pending U.S. patent application Ser. No. 13/284,114, titled “Dampening Fluid For Digital Lithographic Printing,” filed on Oct. 28, 2011, by Stowe, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     Once the dampening fluid is metered onto the reimageable surface of the imaging member  110 , a thickness of the dampening fluid may be measured using a sensor  125  that may provide feedback to control the metering of the dampening fluid onto the reimageable surface of the imaging member  110  by the dampening fluid system  120 . 
     After a precise and uniform amount of dampening fluid is provided by the dampening fluid system  120  on the reimageable surface of the imaging member  110 , and optical patterning subsystem  130  may be used to selectively form a latent image in the uniform dampening fluid layer by image-wise patterning the dampening fluid layer using, for example, laser energy. Typically, the dampening fluid will not absorb the optical energy (IR or visible) efficiently. The reimageable surface of the imaging member  110  should ideally absorb most of the laser energy (visible or invisible such as IR) emitted from the optical patterning subsystem  130  close to the surface to minimize energy wasted in heating the dampening fluid and to minimize lateral spreading of heat in order to maintain a high spatial resolution capability. Alternatively, an appropriate radiation sensitive component may be added to the dampening fluid to aid in the absorption of the incident radiant laser energy. While the optical patterning subsystem  130  is described above as being a laser emitter, it should be understood that a variety of different systems may be used to deliver the optical energy to pattern the dampening fluid. 
     The mechanics at work in the patterning process undertaken by the optical patterning subsystem  130  of the exemplary system  100  are described in detail with reference to FIG. 5 in the 714 Application. Briefly, the application of optical patterning energy from the optical patterning subsystem  130  results in selective removal of portions of the layer of dampening fluid. 
     Following patterning of the dampening fluid layer by the optical patterning subsystem  130 , the patterned layer over the reimageable surface of the imaging member  110  is presented to an inker subsystem  140 . The inker subsystem  140  is used to apply a uniform layer of ink over the layer of dampening fluid and the reimageable surface layer of the imaging member  110 . The inker subsystem  140  may use an anilox roller to meter an offset lithographic ink onto one or more ink forming rollers that are in contact with the reimageable surface layer of the imaging member  110 . Separately, the inker subsystem  140  may include other traditional elements such as a series of metering rollers to provide a precise feed rate of ink to the reimageable surface. The inker subsystem  140  may deposit the ink to the pockets representing the imaged portions of the reimageable surface, while ink on the unformatted portions of the dampening fluid will not adhere to those portions. 
     The cohesiveness and viscosity of the ink residing in the reimageable layer of the imaging member  110  may be modified by a number of mechanisms. One such mechanism may involve the use of a rheology (complex viscoelastic modulus) control subsystem  150 . The rheology control system  150  may form a partial crosslinking core of the ink on the reimageable surface to, for example, increase ink cohesive strength relative to the reimageable surface layer. Curing mechanisms may include optical or photo curing, heat curing, drying, or various forms of chemical curing. Cooling may be used to modify rheology as well via multiple physical cooling mechanisms, as well as via chemical cooling. 
     The ink is then transferred from the reimageable surface of the imaging member  110  to a substrate of image receiving medium  114  using a transfer subsystem  160 . The transfer occurs as the substrate  114  is passed through a nip  112  between the imaging member  110  and an impression roller  118  such that the ink within the voids of the reimageable surface of the imaging member  110  is brought into physical contact with the substrate  114 . With the adhesion of the ink having been modified by the rheology control system  150 , modified adhesion of the ink causes the ink to adhere to the substrate  114  and to separate from the reimageable surface of the imaging member  110 . Careful control of the temperature and pressure conditions at the transfer nip  112  may allow transfer efficiencies for the ink from the reimageable surface of the imaging member  110  to the substrate  114  to exceed 95%. While it is possible that some dampening fluid may also wet substrate  114 , the volume of such a dampening fluid will be minimal, and will rapidly evaporate or be absorbed by the substrate  114 . 
     Following the transfer of the majority of the ink to the substrate  114 , any residual ink and/or residual dampening fluid must be removed from the reimageable surface of the imaging member  110 , preferably without scraping or wearing that surface. An air knife may be employed to remove residual dampening fluid. It is anticipated, however, that some amount of ink residue may remain. Removal of such remaining ink residue may be accomplished through use of some form of cleaning subsystem  170 . The 714 Application describes details of such a cleaning subsystem  170  including at least a first cleaning member such as a sticky or tacky member in physical contact with the reimageable surface of the imaging member  110 , the sticky or tacky member removing residual ink and any remaining small amounts of surfactant compounds from the dampening fluid of the reimageable surface of the imaging member  110 . The sticky or tacky member may then be brought into contact with a smooth roller to which residual ink may be transferred from the sticky or tacky member, the ink being subsequently stripped from the smooth roller by, for example, a doctor blade. 
     The 714 Application details other mechanisms by which cleaning of the reimageable surface of the imaging member  110  may be facilitated. Regardless of the cleaning mechanism, however, cleaning of the residual ink and dampening fluid from the reimageable surface of the imaging member  110  is essential to preventing ghosting in the proposed system. Once cleaned, the reimageable surface of the imaging member  110  is again presented to the dampening fluid system  120  by which a fresh layer of dampening fluid is supplied to the reimageable surface of the imaging member  110 , and the process is repeated. 
     In related art systems such as those shown in  FIG. 1 , the surface of the imaging member must enable all functions related to imaging, inking, and transfer to substrate. Because ink-based digital printing imaging member surface serves the functions of an offset transfer blanket, the related art imaging surface must be fairly conformable; able to withstand substantial pressure at a transfer nip; able to withstand mechanical wear from repetitive contact with the printable substrate; and able to withstand constant contact with various substrates that can cause chemical contaminations and surface energy change. 
     Systems in accordance with embodiments address these requirements while permitting wider design latitude by partitioning plate functionalities across two distinct physical members: the imaging member and the offset member, instead using a single imaging member or printing plate. In related art lithographic printing, the ink image splits at a transfer efficiency of about 50% at both the plate-to-offset blanket interface, and the blanket-to-substrate interface. This transfer efficiency is undesirable for ink-based digital printing at least because cleaning and reconditioning systems will be affected, waste production will be less than optimal, and run performance will be more costly than desired. Therefore, a high transfer efficiency is required at both transfer interface points, or both ink transfer nips. In particular, systems in accordance with embodiments a are configured to enable an offset blanket to receive an offset ink image from one surface, and release the image onto another surface with high transfer efficiency. 
     Image transfer in the digital lithographic ink printing process relies on a balance of adhesion and cohesion. In systems in accordance with embodiments, materials must be selected to satisfy conditions wherein adhesion of ink to an ink releasing surface is less than cohesion of the ink. Also, the adhesion to the ink releasing surface must be less than adhesion to an ink receiving surface. Cohesion of the ink layer increases with the viscosity of the ink, and decreases rapidly with the ink layer thickness. Ideally, 100% transfer efficiency is achieved when the ink completely adheres to the offset blank after being developed on the imaging member and subsequent completely adheres to the printable substrate. 
     A material that forms the surface of the offset member or offset blanket, for example, must be carefully chosen. In particular, the material must be configured for enabling full release of the ink at final transfer. The materials may be selected from the group of materials comprising silicones, fluoro-silicones, and fluorelastomers such as suitable VITON rubber(s). Moreover, the ink-offset member adhesion should be carefully adjusted to satisfy the following two conditions: 1) adhesion of ink to an ink releasing surface must be less than cohesion of the ink; and 2) the adhesion to the ink releasing surface must be less than adhesion to an ink receiving surface. 
     To achieve the first requirement based on available material sets, a surface roughness of the imaging member and/or offset member may be modified. For example, similar surface materials may be used for both the imaging member and the offset member. The surface of the imaging member may have a smooth finish, while the offset member may have a rougher finish. Desired image quality may be achieved using a smooth imaging member plate with vaporized dampening fluid, for example. Excellent ink release has been achieved using systems wherein the offset blanket has a rougher surface than the imaging plate surface. 
     The second requirement may be achieved by using a rheological conditioning system configured to expose ink on the offset member to radiation such as UV radiation. The conditioning may include any exposure that improves ink layer cohesion of the ink layer disposed on the offset member. For example, rheological conditioning may include UV pre-curing, evaporation, heating, etc. 
     An ink-based digital printing system including an offset transfer configuration in accordance with an embodiment is shown in  FIG. 2 . In particular,  FIG. 2  an ink-based digital printing system  200  having an imaging member  210 . The printing system  200  may include a dampening fluid metering system  220  that is configured to apply a thin, uniform layer of dampening fluid onto a surface of the imaging member  210 . The system  200  may include a dampening fluid patterning system  230 , which may comprise a laser imaging system configured to selectively expose portions of the dampening fluid layer to laser irradiation. The laser imaging system may comprise a UV laser or laser array, for example. The selective exposure according to digital image data may produce a dampening fluid pattern on the imaging member surface. 
     The system  200  may include an inking system  240  for applying ink to the surface of the imaging member  210  after the dampening fluid pattern is formed on the surface thereof. For example, the inking system  240  may comprise an anilox roll ink transfer system. As the ink is transferred to the surface of the imaging member  210 , the ink adheres to select portions of the imaging member surface based on the dampening fluid pattern formed thereon to form an ink image. The ink image may be contact-transferred at a first transfer nip to a second roll before being transferred and fixed onto a printable substrate such as paper.  FIG. 2  shows the system  200  having a cleaning system  270  disposed adjacent to the imaging member  210  for removing excess material from the imaging member surface after an ink image has been transferred therefrom during an ink-based digital printing process. 
     In particular,  FIG. 2  shows an offset member  285  having an offset blanket disposed thereon. The offset member  285  may be configured to be exposed to treatment from an offset member rheological conditioning system  287 . The rheological conditioning system  287  may be a laser configured for curing or partial curing of ink transferred to the offset member  285  from the imaging member  210 . The rheological conditioning system  287  may be configured to expose an ink image carried on the surface of the offset member  285  to UV light for partially curing or curing the ink image. For example, the conditioning system  287  may comprise one or more lamps configured to emit UV light suitable for curing the ink transferred to the offset member  285 . 
     The imaging member  210  and the offset member  285  form the first ink transfer nip  291  at which ink is contact-transferred to the offset member  285  after ink image formation on the imaging member  210 . After the ink image is transferred to the surface of the offset member  285 , and optionally cured or partially cured using the conditioning system  287 , the ink may be transferred at a second ink transfer nip  293  to a printable substrate, such as paper or other printable media. 
     The system  200  must be configured so that the ink-offset member adhesion satisfies the following two conditions: 1) adhesion of ink to an ink releasing surface must be less than cohesion of the ink; and 2) the adhesion to the ink releasing surface must be less than adhesion to an ink receiving surface. 
     To achieve the first requirement based on available material sets, a surface roughness of the imaging member  210  and/or offset member  285  may be modified. For example, similar surface materials may be used for both the imaging member and the offset member. Exemplary surface materials may include silicone, fluorosilicone, and fluoroelastomers such as VITON rubber materials. The surface of the imaging member may have a smooth finish, while the offset member may have a rougher finish than the imaging member surface. Desirable image quality may be achieved using a smooth imaging member plate and vaporized dampening fluid, for example. Excellent ink release has been achieved using systems wherein the offset blanket has a rougher surface than the imaging plate surface. 
     The second requirement may be achieved by using a rheological conditioning system configured to expose ink on the offset member to radiation such as UV radiation. The conditioning may include any exposure that improves ink layer cohesion of the ink layer disposed on the offset member. For example, rheological conditioning may include UV pre-curing, evaporation, heating, etc. 
       FIG. 3  shows a diagrammatical cross-sectional view of an ink-based digital printing system including a plurality of offset transfer architecture printing modules  300  in accordance with exemplary embodiments. In particular,  FIG. 3  shows a ink-based digital printing system having a plurality of ink-based digital printing modules  300 . Each of the modules  300  may be configured for printing a different color ink, for example, Yellow, Magenta, Cyan, and Black. 
     Each module  300  includes an imaging member  310  on which dampening fluid from a dampening fluid metering system  320  may deposited to form a thin, uniform layer of dampening fluid. The dampening fluid may be patterned by exposure to laser treatment according to digital image data to form a patterned dampening fluid layer on the surface of the imaging member  310 . In particular, each module  300  may include a laser imaging system or dampening fluid patterning system  330  that is configured to expose an applied dampening fluid layer on the surface of the imaging member  310  to laser radiation for selectively removing portions of the dampening fluid layer according to digital image data. 
     The patterned dampening fluid layer may inked by an inking system  340  to form an ink image. In an embodiment, the inking system  340  may comprise an anilox roll ink delivery system. After the ink image ink image is transferred from the imaging member  310 , the surface of the imaging member  310  may be cleaned using a cleaning system  370 . The ink image is transferred from the imaging member  310  to an offset member, and subsequently to printable substrate carried through substrate supply path  360 . 
     In particular, the imaging member  310  forms a first transfer nip  391  with the offset member  385 . The developed ink image may be contact-transferred from the imaging member  310  to the offset member  385  at the first transfer nip  391 . The transferred ink image may be subsequently transferred from the offset member  385  to a printable substrate at the second transfer nip  393 . The transfer efficiency at both the first transfer nip  391  and the second transfer nip  393  may preferably be at or near 100%. Systems may include a plurality of modules  300 . 
     Each of the modules  300  may be optionally configured to print using a different color ink. For example, the modules may be configured to produce a print according to digital image data wherein a composite color image is formed using the different color inks of at least two of the plurality of modules. 
     Each of the modules  300  must be configured so that the ink-offset member adhesion satisfies the following two conditions: 1) adhesion of ink to an ink releasing surface must be less than cohesion of the ink; and 2) the adhesion to the ink releasing surface must be less than adhesion to an ink receiving surface. 
     To achieve the first requirement based on available material sets, a surface roughness of the imaging member  310  and/or offset member  385  may be modified. For example, similar surface materials may be used for both the imaging member and the offset member. Exemplary surface materials may include silicone, fluorosilicone, and fluoroelastomers such as VITON rubber materials. The surface of the imaging member may have a smooth finish, while the offset member may have a rougher finish than the imaging member surface. Desirable image quality may be achieved using a smooth imaging member plate and vaporized dampening fluid, for example. Excellent ink release has been achieved using systems wherein the offset blanket has a rougher surface than the imaging plate surface. 
     The second requirement may be achieved by using a rheological conditioning system configured to expose ink on the offset member to radiation such as UV radiation. The conditioning may include any exposure that improves ink layer cohesion of the ink layer disposed on the offset member. For example, rheological conditioning may include UV pre-curing, evaporation, heating, etc. 
     EXAMPLE 
     An ink-based digital printing system in accordance with embodiments was reduced to practice. In particular, the system includes an imaging member having a surface comprising a smooth fluorosilicone material, flow-coated NUSIL. The offset member surface is a textured fluorsilicone surface comprising NUSIL and a surface roughness texture similar to that of a traditional lithographic plate. An ink suitable for ink-based digital printing was applied to the plate with an ink delivery that includes an anilox roll. It was found that the ink was contact-transferred from the imaging member to the offset member with about 100% efficiency. A second ink transfer, from the offset member to a printable substrate, LUSTROGLOSS paper, was also accomplished with a transfer efficiency of greater than 90%. Other suitable materials for use as an imaging member or offset member surface include fluoroelastomers such as VITON, fluorosilicone and silicone. 
     Methods in accordance with embodiments may include printing a single ink image with an ink-based digital printing system or module having an offset configuration as shown in  FIG. 2 . Methods in accordance with embodiments may include printing a composite ink image using a plurality of ink-based digital printing modules that are arranged for sequentially fixing ink images onto a printable substrate such as paper, such as the system shown in  FIG. 3 . 
     In particular,  FIG. 4  shows methods  400  for ink-based digital printing using a system having an offset configuration. For example, methods may include applying a uniform layer of dampening fluid onto an imaging member to form a layer of about 1 micron or less in thickness at S 4001 . The imaging member surface may be formed of, for example, silicone, fluorosilicone, and/or fluoroelastomer components. The imaging member surface may have a smooth texture. 
     Methods may include laser patterning the dampening fluid at S 4005 . The laser patterning includes selectively exposing portions of the dampening fluid layer to radiation to remove the exposed portions, resulting in a pattern. The laser patterning is operated in accordance with digital image data that informs the pattern to be formed by selective evaporation or removal of dampening fluid. 
     The laser-patterned dampening fluid layer may be inked by an inking member at S 4007 . For example, an anilox-roll based ink delivery system may be used to meter ink onto the laser-patterned imaging member surface to form an ink image thereon. The ink image may be transferred to an offset member or offset blanket at S 4009 . The offset member may preferably have a surface texture that is rougher than a surface texture of the imaging member. Further, the offset member may be formed of material selected from silicone, fluorosilicone, and/or fluoroelastomer. The offset member and the imaging member are configured to form a first transfer nip at which the ink is transferred with at or near 100% efficiency. 
     A rheological conditioning system may be disposed adjacent to the offset member. At S 4015 , the ink image transferred to the offset member surface may be conditioned to cure or partially cure the ink of the ink image thereby adjusting cohesion characteristics of the ink. Conditioning may be carried out by curing, drying, and/or heating. Accordingly, the ink may be transferred at a second transferred nip at a transfer efficiency at or near 100%, which may be ensured by optionally conditioning the ink as shown at S 4015 . 
     The ink image may then be transferred at a second ink transfer nip at S 4017 . The second ink transfer nip may be formed by the offset member and a printable substrate such as a paper. The ink may be substantially completely transferred from the surface of the offset member onto a surface of the substrate. In an embodiment, the printing process may end after S 4017 . In another embodiment, the printing process may continue for forming a composite ink image. For example, an offset configuration ink-based digital printing system may be used wherein an ink image is printed on a substrate using a first printing module of a plurality of printing modules. The modules may be arranged for printing a composite image on a printable substrate that is transported from module to module as in the system shown by way of example in  FIG. 3 . 
     For example, methods may include performing S 4001 , S 4005 , S 4007 , S 4009 , optionally S 4015 , and S 4017  to form an ink image on a printable substrate using a first ink-based digital printing module having an offset configuration. Methods may further include transporting the substrate having the printed image to a second ink-based digital printing module for printing a ink image on the substrate at S 4021 . The process may be repeated at subsequent modules as necessary to form a desired composite image. By way of example, each module may be configured for printing with particular color ink. 
     It will be appreciated that the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art.