Patent Grant
11020956
The present disclosure is related to marking and printing systems, and more specifically to variable data lithography system using fog development of an electrographic image for creating a fountain solution image.
Offset lithography is a common method of printing today. For the purpose 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, belt, and the like, 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 a 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 the marking material.
The Variable Data Lithography (also referred to as Digital Lithography or Digital Offset) printing process usually begins with a fountain solution used to dampen a silicone imaging plate on an imaging drum. The fountain solution forms a film on the silicone plate that is on the order of about one (1) micron thick. The drum rotates to an ‘exposure’ station where a high power laser imager is used to remove the fountain solution at the locations where the image pixels are to be formed. This forms a fountain solution based ‘latent image’. The drum then further rotates to a ‘development’ station where lithographic-like ink is brought into contact with the fountain solution based ‘latent image’ and ink ‘develops’ onto the places where the laser has removed the fountain solution. The ink is usually hydrophobic for better adhesion on the plate and substrate. An ultra violet (UV) light may be applied so that photo-initiators in the ink may partially cure the ink to prepare it for high efficiency transfer to a print media such as paper. The drum then rotates to a transfer station where the ink is transferred to a printing medium such as paper. The silicone plate is compliant, so an offset blanket is not used to aid transfer. UV light may be applied to the paper with ink to fully cure the ink on the paper. The ink is on the order of one (1) micron pile height on the paper.
The formation of the image on the printing plate is usually done with imaging modules each using a linear output high power infrared (IR) laser to illuminate a digital light projector (DLP) multi-mirror array, also referred to as the “DMD” (Digital Micromirror Device). The mirror array is similar to what is commonly used in computer projectors and some televisions. The laser provides constant illumination to the mirror array. The mirror array deflects individual mirrors to form the pixels on the image plane to pixel-wise evaporate the fountain solution on the silicone plate to create a fountain solution image. If a pixel is not to be turned on, the mirrors for that pixel deflect such that the laser illumination for that pixel does not hit the silicone surface, but goes into a chilled light dump heat sink. A single laser and mirror array form an imaging module that provides imaging capability for approximately one (1) inch in the cross-process direction. Thus a single imaging module simultaneously images a one (1) inch by one (1) pixel line of the image for a given scan line. At the next scan line, the imaging module images the next one (1) inch by one (1) pixel line segment. By using several imaging modules, comprising several lasers and several mirror-arrays, butted together, imaging function for a very wide cross-process width is achieved.
Due to the need to evaporate the fountain solution, in the imaging module, power consumption of the laser accounts for the majority of total power consumption of the whole system. Such being the case, a variety of power and cost saving technologies for the imaging modules have been proposed. For example, the schemes to reduce the size of the image formed on the printing plate, changing the depth of the pixel, and substituting less powerful image creating source such as a conventional Raster Output Scanner (ROS). To evaporate a one (1) micron thick film of water, at process speed requirements of up to five meters per second (5 m/s), requires on the order of 100,000 times more power than a conventional xerographic ROS imager. In addition, cross-process width requirements are on the order of 36 inches, which makes the use of a scanning beam imager problematic. Thus a special imager design is required that reduces power consumption in a printing system. An overlooked area of power conservation is the use of non-laser imagers or alternative ways of creating the fountain solution image.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for increasing speed and lowering power consumption in variable data lithography system.
According to aspects of the embodiments, systems, methods, and fountain solution in accordance with embodiments are provided for producing a fountain solution image without the requirement for a high power laser. Aspects of the embodiments invoke creating a fountain solution image by fog development of a charge image created electrographically that can be inked and transferred to a print substrate or in the alternative transferring the fountain solution image to a silicone surface such as the surface of a drum or belt for inking and transfer to a final substrate.
Exemplary embodiments are intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the composition, apparatus and systems as described herein.
A more complete understanding of the processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations based on convenience and the ease of demonstrating the existing art and/or the present development, and are, therefore, not intended to indicate relative size and dimensions of the assemblies or components thereof In the drawing, like reference numerals are used throughout to designate similar or identical elements.
In one aspect, an ink-based digital printing system useful for ink printing comprising: an imaging member configured for carrying a fountain solution image on the imaging member; an image forming unit that forms an electrostatic charge image of a first polarity on the imaging member; a developer unit proximate the imaging member and adapted to form a fog of charged droplets that are attracted to the electrostatic charge image to form the fountain solution image on the imaging member; and, an inking system, the inking system being configured to apply ink as controlled spatially by the fountain solution image for developing the ink image.
In further aspect, the system further comprising an ink image transfer station positioned downstream of the inking system in a process direction that transfers the inked image from the imaging member to an image receiving media substrate; and ,wherein the inking system applies ink to the fountain solution image on the imaging member to produce the inked image.
In still further aspects the system, further comprising a transfer member, forming a transfer nip with the imaging member, for splitting a controlled fraction of the fountain solution image onto the transfer member; wherein the inking system applies ink to the fraction of the fountain solution image on the transfer member to produce the inked image; and, wherein the inked image is applied to a target image receiving media substrate.
In another aspect, the system wherein the developer unit further comprises an inlet for receiving a fountain solution and a discharge forming the fog of charged droplets, wherein the fog of charged droplets comprises multiple substantially uniformly sized electrically charged droplets of the fountain solution.
In yet another aspect, the system wherein the developer unit further comprising an outlet for clearing fountain solution from the developer unit.
In another further aspect, the system wherein the developer unit further comprising a charged surface disposed proximate the discharge and along the fog of charged droplets to guide the charged droplets to the imaging member.
In another aspect, the system wherein the fog of charged droplets is attracted to the electrostatic charge until the fog of charged droplets neutralizes the electrostatic charge image on the imaging member.
In still another aspect, the system further comprises a controller to create the formed fountain solution image with a desired thickness by controlling the image forming unit and the developer unit.
In yet another aspect, the system wherein the image forming unit is at least one of electrographic imaging system and ionographic imaging system.
In further aspect, the system wherein the liquid immersion fluid comprising a dampening fluid selected from the group consisting essentially of silicone fluids (including D4, D5, OS20, OS30), Isopar fluids.
In another aspect, the system wherein the imaging member comprising a surface selected from the group consisting essentially of silicone elastomers, fluorosilicone elastomers, and Viton.
In another aspect, the system wherein further comprising a transfer member the imaging member and the transfer member forming a fluid image loading nip, the transfer member being adapted to receive the formed fountain solution image at the image fluid loading nip.
In another aspect, the system wherein the fog of charged droplets consisting of frozen particles.
In another aspect, the system wherein the developer unit creates droplets from the fountain solution and suspends said droplets in a carrier gas to form the fog of charged droplets.
In further aspect a method of ink-based digital printing using fountain solution comprising forming a fountain solution image on an imaging member using an image forming unit and a developer unit, the developer unit being positioned proximate the imaging member and adapted to form a fog of charged droplets that are attracted to an electrostatic charge image to form the fountain solution image on the imaging member; applying ink with an inking system to produce an inked image according to the formed fountain solution image; and, transferring the inked image to a print substrate at an ink transfer nip.
Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.
The terms “dampening fluid”, “dampening solution”, and “fountain solution” generally refer to a material which adheres to a substrate and splits in an inking nip to reject ink from adhering to the substrate. In some situations the fountain solution can adhere to a substrate and bind ink which does not otherwise adhere to the substrate. Below we will speak of the former use, however it should be read as applying in either modality. The solution or fluid can be a water or aqueous-based fountain solution which is generally applied in an airborne state such as by vapor or by direct contact with a wetted imaging member through a series of rollers for uniformly wetting the member with the dampening fluid. The solution or fluid can be non-aqueous consisting of, for example, silicone fluids (such as D3, D4, D5, OS10, OS20, OS30 and the like), Isopar fluids, and polyfluorinated ether or fluorinated silicone fluid.
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. For example, the term “about 2” also discloses the value “2” and the range “from about 2 to about 4” also discloses the range “from 2 to 4.”
Although embodiments of the invention are not limited in this regard, the terms “plurality” and “a plurality” as used herein may include, for example, “multiple” or “two or more”. The terms “plurality” or “a plurality” may be used throughout the specification to describe two or more components, devices, elements, units, parameters, or the like. For example, “a plurality of stations” may include two or more stations. The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
The term “printing device”, “printing system”, or “digital printing system” as used herein refers to a digital copier or printer, scanner, image printing machine, digital production press, document processing system, image reproduction machine, bookmaking machine, facsimile machine, multi-function machine, or the like and can include several marking engines, feed mechanism, scanning assembly as well as other print media processing units, such as paper feeders, finishers, and the like. The digital printing system can handle sheets, webs, marking materials, and the like. A digital printing system can place marks on any surface, and the like and is any machine that reads marks on input sheets; or any combination of such machines.
The term “receiving medium” generally refers to a usually flexible, sometimes curled, physical sheet of paper, print substrate, plastic, or other suitable physical print media substrate for images, whether precut or web fed.
Having thus outlined a digital printing system for variable data lithography, and described various sequences of operation, reference is now made to
Systems may include a developer unit 260 or fluid metering system for presenting a uniform layer of fountain solution (not shown) onto a surface of the imaging member 12. The fountain solution is configured to adhere to portions of the imaging member surface according to the electrostatic latent image defined thereon by the ROS imager 250. The fountain solution comprises dampening fluid as charged droplets created by electrospray or other means of atomization. Preferably, the fountain solution is transported by a gas such as nitrogen to carry the charged droplets (charged fog) to the oppositely charged regions on the imaging member 12.
After the fountain solution image is formed, ink from an inker 18 is applied to a transfer member surface 231 to form an ink pattern or inked image. The ink pattern or inked image may be a negative of or may correspond to the dampening fluid pattern. The ink image may be transferred to media 24 at an ink image transfer nip 160 formed by the imaging member 12 and a substrate transport roll 22. The substrate transport roll 240 may urge a paper transport 24, for example, against the image member surface 12 to facilitate contact transfer of an inked image to the print medium carried by the paper transport 22.
Systems may include a rheological conditioning system like 20 in
After transfer of the dampening fluid pattern from the imaging member surface, the imaging member 12 may be further cleaned in preparation for a new cycle by removing dampening fluid and solid particles using the blanket conditioning system 220. Various methods for cleaning the imaging member surface may be used. Due to heat generated by the imager 250 and heat generated by frictional contact between the rollers and the imaging member 12 there may be a need to lower the temperature of the imaging member in between printing operations. In embodiments, the blanket may cool on its own by contact with the colder print substrate (24) and after the removal of heat. Optionally, a blanket chiller 210 such as an air jet producing device may be used to accelerate cooling. This is particularly suitable for printing at very high speeds.
The imager 250, developer unit 260, and other operations of the system for variable lithography may be controlled by controller 300. The controller 300 may be embodied within devices such as a desktop computer, a laptop computer, a handheld computer, an embedded processor, a handheld communication device, or another type of computing device, or the like. The controller 300 may include a memory, a processor, input/output devices, a display and a bus. The bus may permit communication and transfer of signals among the components of the controller 300 or computing device.
System 200 also includes a developer unit 260 for presenting a uniform layer of fountain solution (not shown) onto a surface of the imaging member 12. The fountain solution is configured to adhere to portions of the imaging member surface according to the electrostatic latent image developed thereon by imager 250. The developer unit 260 comprises a means of atomizing and charging a fountain solution 265 that enter an inlet port (P1). A pump, loaded with the fountain solution from a container, supplies the fountain solution to, for example, an electrospray nebulizer at a steady, controlled rate. The fountain solution of the sample can be silicone fluids (D4, D5, OS20, OS30) or Isopar fluids. The fluid may contain charge control agents to assist droplet charging. A gas such as nitrogen, added in a predetermined amount, is introduced to carry the atomized solution to the surface of imaging member 12. The developer unit 260 has an outlet port (P2) to move the unused fountain solution 268 back to the container. The developer unit 260 further includes chambers and a radially enlarged region 272 near plate 275 where a fog of charged droplets 270 from discharge chamber 410 can carry the atomized fountain solution to the charge region on the surface of imaging member 12.
A transfer member 340 may be configured to form a fountain solution image loading nip 310 with the imaging member 12. A fountain solution image produced by the developer unit 260 and imager unit 250 on the surface of the imaging member 12 is transferred to a transfer member 340 surface under pressure at the loading nip. In particular, a light pressure may be applied between the transfer member surface 340 and the imaging member surface 12. At the fountain solution loading nip, the fountain solution image splits as it leaves the nip, and transfers an amount of dampening fluid to the transfer member 340, forming the fountain solution fluid image 330. The amount of dampening fluid or fountain solution transferred may be adjusted by contact pressure adjustments of nip 310. For example, a dampening fluid layer of about 1 micrometer or less may be transferred to the transfer member surface 340. After transfer of the fountain solution pattern from the imaging member surface, the imaging member 12 may be cleaned in preparation for a new cycle by removing dampening fluid and solid particles using the removal system 320. Various methods for cleaning the imaging member surface may be used. After the fountain solution image 330 is transferred to the transfer member 340, ink from an inker 13 is applied to a transfer member surface 340 to form an ink pattern or image. The ink pattern or image may be a negative of or may correspond to the fountain solution pattern. The ink image may be transferred to print media 24 at an ink image transfer nip formed by the transfer member 340 and a substrate transport roll 22. The substrate transport roll 22 may urge a paper transport 24, for example, against the transfer member surface 340 to facilitate contact transfer of an ink image from the transfer member 340 to media carried by the paper transport 22. Like the imaging member 12, the transfer member 340 may be electrically biased to enhance loading of the dampening fluid image at the loading nip 310.
Having thus outlined several embodiments of printing apparatus and processes, and described various sequences of operation, reference is now made to
As shown in
By controlling, such as with controller 300, the charge to mass ratio and the droplet volume parameters and the electrographic surface charge density a desired thickness of fountain solution can controllably coat the latent image regions on the imaging member 12. Voltages on walls of the developer housing can be set so that charged droplets are repelled from uncharged regions of the image. Where no latent image charge resides droplets do not contact the surface of imaging member 12 and stick thereon or can be electrostatically repelled. Unused free droplets can be recycled through a second port (P2). In addition an alternating current (AC) field like voltage 420 applied at plate 275 creates a charged surface 440 to cause a charged wall potential that can reduce the number of droplets near the discharged regions; and, since the discharge surface 440 is disposed proximate the discharge port 410 and the fog of charged droplets the electrostatic force can help in guiding the charged droplets to the surface of imaging member 12.
It should be noted that the fog once generated can be frozen. For example fountain solution like D4 freezes at 17.5 C. So if the carrier gas like nitrogen and the housing of developer unit 260 are maintained below 17 C the fog 270 will consist of frozen particles. Such frozen particles can be useful in controlling the capillary spreading forces of a liquid on a surface like outer surface of imaging member 12. If such particles remain frozen all the way to the nip 310 between the electrographic surface and the transfer member 340 the nip pressure can act to melt the fountain solution and wet the transfer member 340. Alternatively a heat source can be used to melt the fountain particles just before transfer to the transfer member. In yet another alternative a compliant silicone transfer member 340 can preferentially adhere to solid fountain particles and effectively transfer them to the silicone plate where they can subsequently melt before inking.
After creation of the electrostatic latent image, control is then passed to action 530 for development of the image using a developer unit 260 that uses a charged fog of fountain solution that is electrically biased or charged to cause the droplets/particles to adhere to portions of the imaging member 12 having complementary charge. As a result of action 530, a fountain solution image is created without the need of high power lasers, currently used for patterning dampening fluid on an imaging plate, and which account for most of the power usage and reduction in print speed. Control is then passed to action 540 for further processing.
Methods may include inking the imaging member surface having the fountain solution image at action 540. The ink may adhere to portions of the transfer member according to the fountain solution image. For example, the ink may form a positive or negative image or pattern with respect to the fountain solution image. Methods may include transferring the ink image to a recording medium at an ink image transfer nip at action 550. The transfer nip may be formed by a transfer roll 22 and the imaging member 12 or drum 340 like shown in
In particular,
After creation of the electrostatic latent image, control is then passed to action 630 for development of the image using a developer like developer unit 260 that uses a fog of fountain solution that is electrically biased or charged to cause the droplets/particles to adhere to portions of the imaging member 12 having complementary charge. Developing the electrostatic image with a fog of fountain solution overcomes the sensitivity to humidity associated with liquid ink printing. As a result of action 630, a fountain solution image is created without the need of high power lasers, currently used for patterning dampening fluid on an imaging plate, and which account for most of the power usage and reduction in print speed. Control is then passed to action 635 for further processing.
Methods may include transferring fountain solution of the solution image to a transfer member 340 at loading nip 310 formed by the imaging member 12 and a transfer member 340 at S509. A fountain solution image thereby is formed that corresponds to the fountain solution image of the imaging member as developed by developer unit 260. Methods may include biasing the imaging member 12 and the transfer member 340 to retain the fountain solution image on the surface of the imaging member as the solution image is transferred from the imaging member to transfer member 340.
Methods may include inking the imaging member surface having the fountain solution image at action 640. The ink may adhere to portions of the transfer member according to the fountain solution image. For example, the ink may form a positive or negative image or pattern with respect to the fountain solution image. Methods may include transferring the ink image to a recording medium at an ink image transfer nip at action 650. The transfer nip may be formed by a transfer roll 22 and the imaging member 12 or drum 340 like shown in
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
This application is a Continuation of U.S. patent application Ser. No. 16/032,591, filed Jul. 11, 2018, and entitled “Fog Development for Digital Offset Printing Applications”.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2551582 | Carlson | May 1951 | A |
| 8958723 | Liu | Feb 2015 | B2 |
| 9316993 | Veres et al. | Apr 2016 | B2 |
| 20130033686 | Stowe et al. | Feb 2013 | A1 |
| 20140013980 | Veres et al. | Jan 2014 | A1 |
| 20170217150 | Moore et al. | Aug 2017 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20200353743 A1 | Nov 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16032591 | Jul 2018 | US |
| Child | 16941574 | US |
