Patent Application
20120274914
The present disclosure is related to marking and printing methods and systems, and more specifically to methods and systems for variably marking or printing multi-component (e.g., multi-color) data using marking or printing materials such as UV lithographic and offset inks.
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 fountain solution (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 fountain solution and accept ink, whereas the fountain solution 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.
In one variation, referred to as dry or waterless lithography or driography, the plate cylinder is coated with a silicone rubber that is oleophobic and patterned to form the negative of the printed image. A printing material is applied directly to the plate cylinder, without first applying any fountain solution as in the case of the conventional or “wet” lithography process described earlier. The printing material includes ink that may or may not have some volatile solvent additives. The ink is preferentially deposited on the imaging regions to form a latent image. If solvent additives are used in the ink formulation, they preferentially diffuse towards the surface of the silicone rubber, thus forming a release layer that rejects the printing material. The low surface energy of the silicone rubber adds to the rejection of the printing material. The latent image may again be transferred to a substrate, or to an offset cylinder and thereafter to a substrate, as described above.
The above-described 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.
Lithography and the so-called waterless process provide very high quality printing, in part due to the quality and color gamut of the inks used. Furthermore, these inks—which typically have a very high color pigment content (typically in the range of 20-70% by weight)—are very low cost compared to toners and many other types of marking materials. Thus, while there is a desire to use the lithographic and offset inks for printing in order to take advantage of the high quality and low cost, there is also a desire to print variable data from page to page. Heretofore, there have been a number of hurdles to providing variable data printing using these inks. Furthermore, there is a desire to reduce the cost per copy for shorter print runs of the same image. Ideally, the desire is to incur the same low cost per copy of a long offset or lithographic print run (e.g., more than 100,000 copies), for medium print run (e.g., on the order of 10,000 copies), and short print runs (e.g., on the order of 1,000 copies), ultimately down to a print run length of 1 copy (i.e., true variable data printing).
One problem encountered is that offset inks have too high a viscosity (often well above 50,000 cps) to be useful in nozzle-based inkjet systems. In addition, because of their tacky nature, offset inks have very high surface adhesion forces relative to electrostatic forces and are therefore almost impossible to manipulate onto or off of a surface using electrostatics. (This is in contrast to dry or liquid toner particles used in xerographic/electrographic systems, which have low surface adhesion forces due to their particle shape and the use of tailored surface chemistry and special surface additives.)
Efforts have been made to create lithographic and offset printing systems for variable data in the past. One example is disclosed in U.S. Pat. No. 3,800,699, incorporated herein by reference, in which an intense energy source such as a laser to pattern-wise evaporate a fountain solution.
In another example disclosed in U.S. Pat. No. 7,191,705, incorporated herein by reference, a hydrophilic coating is applied to an imaging belt. A laser selectively heats and evaporates or decomposes regions of the hydrophilic coating. Next a water based fountain solution is applied to these hydrophilic regions rendering them oleophobic. Ink is then applied and selectively transfers onto the plate only in the areas not covered by fountain solution, creating an inked pattern that can be transferred to a substrate. Once transferred, the belt is cleaned, a new hydrophilic coating and fountain solution are deposited, and the patterning, inking, and printing steps are repeated, for example for printing the next batch of images.
In yet another example, a rewritable surface is utilized that can switch from hydrophilic to hydrophobic states with the application of thermal, electrical, or optical energy. Examples of these surfaces include so called switchable polymers and metal oxides such as ZnO2 and TiO2. After changing the surface state, fountain solution selectively wets the hydrophilic areas of the programmable surface and therefore rejects the application of ink to these areas.
There remain a number of problems associated with these techniques. A number of these problems are addressed by the aforementioned U.S. patent application Ser. No. 13/095,714. However, one limitation not otherwise adequately addressed in known systems for variable data lithography is that most such systems are able to produce only monochrome images. To the extent that any such system provides multicolor printing, it does so with multiple complete printing engines, one for each color, in a multiple impression process. Multiple color printing is highly desired, and for a number reasons including cost, complexity, servicing, size, energy consumption, and so on, a multiple print engine system is less than optimal.
Accordingly, the present disclosure is directed to systems and methods for providing variable data lithographic and offset lithographic printing, which address the shortcomings identified above—as well as others as will become apparent from this disclosure. The present disclosure concerns various embodiments of a multiple color variable imaging lithographic marking system based upon variable patterning of dampening solutions and related methods.
In such a system, an imaging member, such as a drum, plate, belt, web, etc. is provided with a reimageable layer. This layer has specific properties such as composition, surface profile, and so on so as to be well suited for receipt and carrying a layer of a dampening fluid from a dampening fluid subsystem. An optical patterning subsystem such as a scanned, modulated laser patterns the dampening fluid layer, again with the characteristics of the reimageable layer chosen to facilitate this patterning. Ink is then applied at an inking subsystem such that it selectively resides in voids formed by the patterning subsystem in the dampening fluid layer to thereby form an inked latent image. The inked latent image is then transferred to a substrate, and the reimageable surface cleaned so that the process may be repeated. High speed, variable marking is thereby provided.
According to an aspect of the present disclosure, multiple inking subsystems are provided, each with different color ink. Each inking subsystem moves independently into and out of engagement with (i.e., proximate) the reimageable surface layer of the imaging member. The patterning subsystem creates a first pattern in dampening fluid, and the first inking subsystem engages with the reimageable surface to create a first color inked latent image, as described. This first color inked latent image is transferred to a substrate, for example at a transfer nip, and the reimageable surface layer of the imaging member cleaned. A second pattern is created in dampening fluid, the first inking subsystem disengages with the reimageable surface, and the second inking subsystem engages with the reimageable surface to create a second color inked latent image, as described. The substrate then makes another pass through the transfer nip so as to receive the second color inked latent image over the first. In a typical 4-color process, this pattern-engage-ink-print sequence may be repeated 4 times, once for each color. Indeed, it may be repeated more often if different color systems are used or different printing effects are desired.
According to another aspect of the disclosure, after transferring the first color inked latent image to the substrate, the image may be partially cured on the substrate to reduce smear, color transfer from the substrate back to the imagining member, and as subsequent color layers are added thereto. The partial cure may be from the back or front (or both) of the substrate, and be by way of UV exposure, heat, or other method appropriate to the particular ink and substrate being used. In one embodiment, the substrate is in the form of a sheet, such as paper, which is carried on a single drum from first to last pass. In other embodiments, other substrate handling mechanisms are employed.
According to still another aspect of the disclosure, a reimageable portion of one or more imaging members is provided. In one embodiment, the reimageable portion comprises a reimageable surface, for example composed of the class of materials commonly referred to as silicone (e.g., polydimethylsiloxane). The reimageable portion may contain or be formed over a structural material such as a cotton-weave core or other suitable material of sufficient tensile strength, or may be formed over a mounting layer composed of a suitable material such as a thin sheet of metal or cotton-weave backing or other suitable material of sufficient tensile strength. While it may be desirable for the reimageable surface layer to be relatively thin, from the point of view of material costs, etc., it is understood that thickness may be selected to improve other aspects of consideration such as performance, lifetime, and manufacturability. The reimageable portion may further comprise additional layers below the reimageable surface layer and either above or below structural mounting layer. Silicone is a preferred outer layer material because of its low surface energy (i.e., low “stickiness”) which enhances release of the marking material, as will be described in further detail later on in this document. It is noted that the outer reimageable surface material may also be made from materials other than those primarily composed of silicone, which provide suitable low adhesion energy. Other examples of such materials include some types of hydrofluorocarbon compounds (e.g., Teflon, Viton, etc.) with long polymer chains of (—CF3) groups and fluorinated silicone hybrid compounds. It is known that surface materials that display a much larger receding to advancing wetting contact angle generally also display low adhesion energies to viscoelastic marking ink materials, and are therefore suitable materials for an outer layer. It is understood that the above-mentioned specific materials are representative examples only, and these examples should not be interpreted as limiting the scope of this invention to a specific class of materials.
According to another embodiment of this aspect of the disclosure, the reimageable surface layer or any of the underlying layers of the reimageable plate/belt/drum, etc. may incorporate a radiation sensitive filler material that can absorb laser energy or other highly directed energy in an efficient manner. Examples of suitable radiation sensitive materials are, for example, microscopic (e.g., average particle size less than 10 micrometers) to nanometer sized (e.g., average particle size less than 1000 nanometers) carbon black particles, carbon black in the form of nano particles of, single or multi-wall nanotubes, graphene, iron oxide nano particles, nickel plated nano particles, etc., added to the polymer in at least the near-surface region. It is also possible that no filler material is needed if the wavelength of a laser is chosen so to match an absorption peak of the molecules contained within the fountain solution or the molecular chemistry of the outer surface layer. As an example, a 2.94 μm wavelength laser would be readily absorbed due to the intrinsic absorption peak of water molecules at this wavelength.
Further according to this aspect, multiple print stages are provided, each printing a separate color. Each print stage may comprise its own imaging member with reimageable surface, dampening fluid subsystem, patterning subsystem, inking subsystem, partial curing subsystem, transfer nip, and cleaning subsystem. Alternatively, two or more of the multiple stages may share one or more of these subsystems. In a direct marking tandem embodiment, each imaging member sequentially transfers an inked color latent image to a substrate. In a central impression embodiment, each imaging member sequentially transfers an inked color latent image to a central impression drum, which then transfers the color composite image to a substrate.
It is understood that for the purposes of this invention, the terms “optical wavelengths” or “radiation” or “light” may refer to wavelengths of electromagnetic radiation appropriate for use in the system to accomplish patterning of the dampening solution, whether or not these electromagnetic wavelengths are normally visible to the unaided human eye, including, but not limited to, visible light, ultraviolet (UV), and infrared (IR) wavelengths, micro-wave radiation, and the like.
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.
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:
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
With reference to
Reimageable surface layer 20 consists of a polymer such as polydimethylsiloxane (PDMS, or more commonly called silicone) for example with a wear resistant filler material such as silica to help strengthen the silicone and optimize its durometer, and may contain catalyst particles that help to cure and cross link the silicone material. Alternatively, silicone moisture cure (aka tin cure) silicone as opposed to catalyst cure (aka platinum cure) silicone may be used. Returning to
Alternatively, reimageable surface layer 20 may be tinted or otherwise treated to be uniformly radiation sensitive, as shown in
Reimageable surface layer 20 should have a weak adhesion force to the ink at the interface yet good oleophilic wetting properties with the ink, to promote uniform (free of pinholes, beads or other defects) inking of the reimageable surface and to promote the subsequent forward transfer lift off of the ink onto the substrate. Silicone is one material having this property. Other materials providing this property may alternatively be employed, such as certain blends of polyurethanes, fluorocarbons, etc. In terms of providing adequate wetting of dampening solutions (such as water-based fountain fluid), the silicone surface need not be hydrophilic but in fact may be hydrophobic because wetting surfactants, such as silicone glycol copolymers, may be added to the dampening solution to allow the dampening solution to wet the silicone surface.
It will therefore be understood that while a water-based solution is one embodiment of a dampening solution that may be employed in the embodiments of the present disclosure, other non-aqueous dampening solutions with low surface tension, that are oleophobic, are vaporizable, decomposable, or otherwise selectively removable, etc. may be employed. One such class of fluids is the class of HydroFluoroEthers (HFE), such as the Novec brand Engineered Fluids manufactured by 3M of St. Paul, Minn. These fluids have the following beneficial properties in light of the current disclosure: (1) much lower heat of vaporization than water, which translates into lower laser power required for a given print speed, or higher print speed for a given laser power, when an optical laser is used to selectively vaporize the dampening solution to form the latent image; (2) lower heat capacity, which translates into the same benefits; (3) they leave substantially no solid residue after evaporation, which can translate into relaxed cleaning requirements and/or improved long-term stability; (4) vapor pressure and boiling point can be engineered, which can translate into an improved robustness of a spatially selective forced evaporation process; (5) they have a low surface energy, as required for proper wetting of the imaging member; and, (6) they are benign in terms of the environment and toxicity. Additional additives may be provide to control the electrical conductivity of the dampening solution. Other suitable alternatives include fluorinerts and other fluids known in the art, that have all or a majority of the above properties. It is also understood that these types of fluids may not only be used in their undiluted form, but as a constituent in an aqueous non-aqueous solution or emulsion as well.
In addition, the surface energy of silicone may be optimized to provide good wetting properties by controlling and specifying precise amounts of filler nano particles in the silicone as well as the exact chemistry of the silicone material, which can be composed of different distributions of polymer chain lengths and end group capping chemistries. For example, it has been found that single component moisture cure silicones that are tin catalyzed with low concentrations of silica filler have dispersive surface energies between 24-26 dynes/cm. Certain additives may also be added to the marking material in order to dramatically reduce the surface tension of the marking material and improve its surface wetting properties to the silicone. These additives could include, for example, leveling agents based on known copolymer fluoro or silicone chemistries that also incorporate other polymer groups for easy dispersion and curing. For example, leveling agents that can reduce ink surface tension to 21 dynes/cm.
If silicone is used as the reimageable surface layer 20, other particles 27 may also be embedded within layer 20 to help catalyze the curing and cross linking of the silicone.
According to one embodiment, reimageable surface layer 20 has roughness on the order of the desired dampening solution layer thickness to better trap the dampening solution and prevents its spreading beyond the desired non-imaging region boundaries. For example, reimageable surface layer 20 may have measured surface roughness characteristics RSm and Ra defined as:
with reference to
It is desirable that the peaks and valleys are somewhat randomly distributed to reduce the possibility of Moiré interference with a linescreen pattern. In addition, it is desirable that the spatial distance between the peaks is somewhat less than the smallest line screen dot size, for example less than 10 μm. This roughness helps the surface to easily retain dampening solution while eliminating Moiré effects and acts to improve inking uniformity and transfer, as described further below. In one embodiment RSm is less than about 20 μm and the Ra is less than about 4.0 μm, and in a more specific embodiment, RSm is less than 10 μm and the Ra is between 0.1 μm and 4.0 μm.
In addition, the reimageable surface layer 20 must be wear resistant and capable of some flexibility (even under tension) in order to transfer ink off of its surface onto porous or rough paper media uniformly. The reimageable surface layer 20 may be made thick enough to achieve an appropriate elasticity and durometer and sufficient flexibility necessary for coating ink over different media types with different levels of roughness. Of course, systems may be designed for printing to a specific media type, obviating the need to accommodate a variety of media types. In one embodiment the thickness of the silicone layer forming reimageable surface layer 20 is in the range of 0.5 μm to 4 mm.
Finally, reimageable surface layer 20 must facilitate the flow of ink onto its surface with uniformity and without beading or dewetting. Various materials such as silicone can be manufactured or textured to have a range of surface energies, and such energies can be tailored with additives. Reimageable surface layer 20, while nominally having a low value of dynamic chemical adhesion, may have a sufficient surface energy in order to promote efficient ink wetting/affinity without ink dewetting or beading.
Returning to
In addition to or in substitution for chemical methods, physical/electrical methods may be used to facilitate the wetting of dampening solution 32 over the reimageable surface layer 20. In one example, electrostatic assist operates by way of the application of a high electric field between the dampening roller and reimageable surface layer 20 to attract a uniform film of dampening solution 32 onto reimageable surface layer 20. The field can be created by applying a voltage between the dampening roller and the reimageable surface layer 20 or by depositing a transient but sufficiently persisting charge on the reimageable surface layer 20 itself. The dampening solution 32 may be electronically conductive. Therefore, in this embodiment an insulating layer (not shown) may be added to the dampening roller and/or under reimageable surface layer 20. Using electrostatic assist, it may be possible to reduce or eliminate the surfactant from the dampening solution.
Following metering of dampening solution 32 onto reimageable surface layer 20 by dampening solution subsystem 30, the thickness of the metered dampening solution may be measured using a sensor 34 such as an in-situ non-contact laser gloss sensor or laser contrast sensor, such as those sold by Wenglor Sensors (Beavercreek, Ohio). Such a sensor can be used to automate the controls of dampening solution subsystem 30.
After applying a precise and uniform amount of dampening solution, in one embodiment an optical patterning subsystem 36 is used to selectively form a latent image in the dampening solution by image-wise evaporating the dampening solution layer using laser energy, for example. It should be noted here that the reimageable surface layer 20 should ideally absorb most of the energy as close to an upper surface 28 (
It will be understood that a variety of different systems and methods for delivering energy to pattern the dampening solution over the reimageable surface may be employed with the various system components disclosed and claimed herein. However, the particular patterning system and method do not limit the present disclosure.
With reference to
Returning to
Optionally, an air knife 44 may be directed towards reimageable surface layer 20. Air knife 44 may control airflow over the surface layer before the inking subsystems for the purpose of maintaining clean dry air supply, a controlled air temperature and reducing dust contamination.
Each inker subsystem 46a, 46b, 46c, 46d may consist of a “keyless” system using an anilox roller to meter an offset ink onto one or more forming rollers. Alternatively, each inker subsystem 46a, 46b, 46c, 46d may consist of more traditional elements with a series of form rollers that use electromechanical keys to determine the precise feed rate of the ink. The general aspects of inker subsystem architecture will depend on the application of the present disclosure, and will be well understood by one skilled in the art.
Each inker subsystem 46a, 46b, 46c, 46d may be actuated to engage with or disengage from reimageable surface 20. By engage, it is meant that the inker subsystem, or a component thereof, is positioned proximate the reimageable surface such that material carried thereby is permitted to be transferred onto the reimageable surface. This may or may not mean physical contact between the two, depending on many factors. Similarly, disengagement is meant the positioning of the inker subsystem, or a component thereof, such that material carried thereby cannot readily transfer therefrom to the reimageable surface. In the embodiment illustrated in
Returning to
In addition to this rheological consideration, it is also important that the ink composition maintain a hydrophobic character so that it is rejected by dampening solution regions 38. This can be maintained by choosing offset ink resins and solvents that are hydrophobic and have non-polar chemical groups (molecules). When dampening solution covers layer 20, the ink will then not be able to diffuse or emulsify into the dampening solution quickly and because the dampening solution is much lower viscosity than the ink, film splitting occurs entirely within the dampening solution layer, thereby rejecting ink any ink from adhering to areas on layer 20 covered with an adequate amount of dampening solution. In general, the dampening solution thickness covering layer 20 may be between 0.1 μm-4.0 μm, and in one embodiment 0.2 μm-2.0 μm depending upon the exact nature of the surface texture.
In certain embodiments, a metering roller 62 may be employed with a form roller 60, such as illustrated in
Ideally, an optimized ink system splits onto the reimageable surface at a ratio of approximately 50:50 (i.e., 50% remains on the ink forming rollers and 50% is transferred to the reimageable surface at each pass). However, other splitting ratios may be acceptable as long as the splitting ratio is well controlled. For example, for 70:30 splitting, the ink layer over reimageable surface layer 20 is 30% of its nominal thickness when it is present on the outer surface of the forming rollers. It is well known that reducing an ink layer thickness reduces its ability to further split. This reduction in thickness helps the ink to come off from the reimageable surface very cleanly with residual background ink left behind. However, the cohesive strength or internal tack of the ink also plays an important role.
Returning to
Substrate 14 may be maintained within the system in a position such that it may readily be reintroduced to nip 16 for successive passes, each layering a color latent ink image thereon. More specifically, any residual ink and residual dampening solution remaining on reimageable surface 20 after nip 16 must be removed, preferably without scraping or wearing that surface. Much of the dampening solution can be easily and quickly removed using an air knife 70 with sufficient airflow. Removal of remaining ink is accomplished at cleaning subsystem 72. The application of dampening fluid and patterning of the dampening fluid, as previously described is repeated. A new pattern is thereby formed in the dampening fluid layer. Inker subsystem 46a is disengaged from reimageable surface 20, and inker subsystem 46b moved to engage reimageable surface 20. A second color ink may thereby be applied to the patterned dampening fluid layer over reimageable surface 20 to form a latent ink image of the second color. This latent ink image of the second color is transferred to substrate 14 such as by passing substrate 14 through nip 16 between imaging member 12 and impression roller 18. One of a variety of methods for registration of substrate 14 for receipt of the latent ink image of the second color, description of which being beyond the scope of the present disclosure, is employed to ensure the registration of the two latent images. This process is similarly repeated for inker subsystems 46c and 46d.
To assist in preventing smearing, color contamination, color transfer from the substrate back to the imagining member, and so on, following transfer of one inked color latent image to the substrate, the image may be partially cured. The partial cure may be from the back or front (or both) of the substrate, and be by way of UV exposure, heat, or other source 74 appropriate to the particular ink and substrate being used. In addition, the ink may be partially cured on reimageable surface 20 prior to transfer to substrate 14, such as by a UV, heat, or other source 76.
In an exemplary embodiment, substrate 14 is retained on the surface of impression roller 18 for each of the passes through nip 16. The rotation of imaging member 12 and impression roller 18 are synchronized to ensure the aforementioned registration. Substrate 14 makes up to n revolutions (n being, for example, the number of inker subsystems) and is then removed from the impression roller 18. According to another embodiment 80 illustrated in
Other modes of indirect transferring of the ink pattern from an imaging member to a substrate are also contemplated by this disclosure. For example, with reference to
The inked color latent image is transferred to substrate 92 such as by passing substrate 92 through nip 94 between imaging member 82 and impression roller 96. Partial curing other aspects of image optimization and maintaining substrate 92 in position for successive passes for image application may be performed.
Any residual ink and residual dampening solution remaining on the reimageable surface of imaging member 82 after nip 94 is removed using an air knife 98 in combination with a cleaning subsystem 100 (or other suitable cleaning methods and subsystems). The application of dampening fluid and patterning of the dampening fluid, as previously described, is repeated. A new pattern is thereby formed in the dampening fluid layer. Engagement member 91a is retracted, and engagement 91b activated so as to deflect the reimageable surface of imaging member 82 into engagement with inker subsystem 90b. A second color ink may thereby be applied by inker subsystem 90b to the patterned dampening fluid layer over the reimageable surface of imaging member 82 to form a latent ink image of the second color. This latent ink image of the second color is transferred to substrate 92. This process is similarly repeated for inker subsystems 90c and 90d.
While the aforementioned embodiments have primarily involved multi-pass printing according to which colors are successively applied to a patterned intermediate transfer member and transferring that color pattern to the substrate, cleaning the intermediate transfer member, in certain embodiments it may be desirable to successively transfer individual color images directly to a substrate. Such may be the case, for example, where the substrate is continuous or longer than the circumference of the impression roller, where it is not practical to retain a substrate and reintroduce it through a nip successive times, etc.
With reference next to
While in such embodiments it has been assumed that each imaging member comprises a reimageable substrate that is provided with its own dampening fluid layer that is patterned and inked, in certain embodiments one or more of the imaging members may carry a permanent image pattern that is inked and added to the intermediate or final substrate together with an image(s) from a reimageable surface of an imaging member. In this way, variable and non-variable print elements may be combined prior to or onto a substrate.
A system having a single imaging cylinder, without an offset or blanket cylinder, is shown and described herein. The reimageable surface layer is made from material that is conformal to the roughness of print media via a high-pressure impression cylinder, while it maintains good tensile strength necessary for high volume printing. Traditionally, this is the role of the offset or blanket cylinder in an offset printing system. However, requiring an offset roller implies a larger system with more component maintenance and repair/replacement issues, and increased production cost, added energy consumption to maintain rotational motion of the drum (or alternatively a belt, plate or the like). Therefore, while it is contemplated by the present disclosure that an offset cylinder may be employed in a complete printing system, such need not be the case. Rather, the reimageable surface layer may instead be brought directly into contact with the substrate to affect a transfer of an ink image from the reimageable surface layer to the substrate. Component cost, repair/replacement cost, and operational energy requirements are all thereby reduced.
It should be understood that when a first layer is referred to as being “on” or “over” a second layer or substrate, it can be directly on the second layer or substrate, or on an intervening layer or layers may be between the first layer and second layer or substrate. Further, when a first layer is referred to as being “on” or “over” a second layer or substrate, the first layer may cover the entire second layer or substrate or a portion of the second layer or substrate.
The invention described herein, when operated according to the method described herein meets the standard of high ink transfer efficiency, for example greater than 95% and in some cases greater than 99% efficiency of transferring ink off of the imaging member and onto the substrate. In addition, the disclosure teaches combining the functions of the print cylinder with the offset cylinder wherein the rewritable imaging surface is made from material that can be made conformal to the roughness of print media via a high pressure impression cylinder while it maintains good tensile strength necessary for high volume printing. Therefore, we disclose a system and method having the added advantage of reducing the number of high inertia drum components as compared to a typical offset printing system. The disclosed system and method may work with any number of offset ink types but has particular utility with UV lithographic inks.
The physics of modern devices and the methods of their production are not absolutes, but rather statistical efforts to produce a desired device and/or result. Even with the utmost of attention being paid to repeatability of processes, the cleanliness of manufacturing facilities, the purity of starting and processing materials, and so forth, variations and imperfections result. Accordingly, 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.
The present disclosure is a Continuation-In-Part of U.S. patent application titled “Variable Data Lithography System”, Ser. No. 13/095,714, filed on Apr. 27, 2011, which is incorporated herein by reference and to which priority is claimed.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13095714 | Apr 2011 | US |
| Child | 13204567 | US |
