The present application is a National Phase of PCT Patent Application No. PCT/IB2013/051717 having International filing date of Mar. 5, 2013.
The present invention relates to a digital printing system.
Digital printing techniques have been developed that allow a printing system to receive instructions directly from a computer without the need to prepare printing plates. Amongst these are color laser printers that use the xerographic process. Color laser printers using dry toners are suitable for certain applications, but they do not produce images of a photographic quality acceptable for publications such as magazines.
A process that is better suited for short run high quality digital printing is used in the HP-Indigo printer. In this process, an electrostatic image is produced on an electrically charged image bearing cylinder by exposure to laser light. The electrostatic charge attracts oil-based inks to form a color ink image on the image bearing cylinder. The ink image is then transferred by way of a blanket cylinder onto paper or any other printing medium, the substrate.
Inkjet and bubble jet processes are commonly used in home and office printers. In these processes droplets of ink are sprayed onto a final substrate in an image pattern. In general, the resolution of such processes is limited due to wicking by the inks into paper substrates, unless coated paper is used. However, using substrates with special coatings engineered to absorb the liquid ink in a controlled fashion or to prevent its penetration below its surface is a costly option that is unsuitable for certain printing applications, especially for commercial printing. Furthermore, the use of coated substrates creates its own problems in that the surface of the substrate remains wet and additional costly and time consuming steps are needed to dry the ink, so that it is not later smeared as the substrate is being handled, for example stacked or wound into a roll. Excessive wetting of the substrate causes cockling and makes printing on both sides of the substrate (also termed perfecting or duplex printing) difficult, if not impossible. Inkjet printing directly onto a substrate results in poor image quality also because of variation of the distance between the print head and the surface of the substrate.
Indirect or offset digital printing systems have been disclosed in the patent literature that comprise an intermediate transfer member, an image forming system operative to form an ink image on the surface of the intermediate transfer member, apparatus serving to dry the ink image as it is transported by the transfer member, and an impression station at which the dried ink image is transferred from the intermediate transfer member onto a substrate supported by an impression cylinder that is rotatable about a fixed axis and driven independently of the intermediate transfer member.
Using an offset printing system overcomes many problems associated with inkjet printing directly onto the substrate. For example, it allows the distance between the surface of the intermediate transfer member and the inkjet print head to be maintained constant and it reduces wetting of the substrate as the ink can be dried on the image transfer surface before being applied to the substrate. Consequently, the final image quality on the substrate is less affected by the physical properties of the substrate.
A digital printing system that is capable of both duplex printing onto substrate sheets and simplex printing at a higher speed is now disclosed.
Some embodiments of the present invention relate to a digital printing system having two independently operable printing towers arranged in series to print on sheets of substrate, each substrate sheet passing sequentially through both printing towers, and a perfecting mechanism provided between the two towers to reverse substrate sheets during their transfer from the first printing tower to the second printing tower, the perfecting mechanism being selectively operable to enable the second tower to print either on the same side of a substrate sheet as the first tower or on the opposite side of the substrate sheet, wherein, when the perfecting system is operative to reverse the substrate sheets during transfer between the two towers, each tower is operative to impress a complete image onto a respective side of the substrate, and when the perfecting system is inoperative, the first printing tower serves to impress at least one selected separation of an image onto each substrate sheet to form a partial image and the second printing tower is operative to impress the remaining separations of the same image onto the same side of the substrate sheet in register with the partial image formed by the first printing tower.
Embodiments of the invention will be described herein that rely on the process taught by co-pending PCT application No. PCT/IB2013/051716 (Agent's reference LIP 5/001 PCT), which claims priority from U.S. Provisional Patent Application No. 61/606,913, (both of which applications are herein incorporated by reference in their entirety). Relevant parts of the disclosure of these applications are included herein for the convenience of the reader.
In accordance with an aspect of the invention, there is provided a digital printing system having two independently operable printing towers each having an endless intermediate transfer member, an image forming system serving under digital control to direct droplets of a water-based ink onto the intermediate transfer member to form an ink image, a drier for drying the ink image while it is being transported by the intermediate transfer member to form a residue film, and an impression station at which the residue film is impressed onto a sheet substrate, wherein the two printing towers are arranged in series such that each substrate sheet passes sequentially through both printing towers, and wherein a selectively operable perfecting mechanism is provided between the two towers to reverse each substrate sheet during transfer from the first printing tower to the second printing tower, the perfecting mechanism selectively enabling the second tower to print either on the same side of each substrate sheet as the first tower or on the opposite side of each substrate sheet, wherein, when the perfecting system acts to reverse the substrate sheets during transfer between the two towers, each tower is operative to impress a complete image onto a respective side of the substrate, and when the perfecting system is inoperative, the first printing tower serves to impress at least one selected separation of an image onto each substrate sheet to form a partial image and the second printing tower is operative to impress the remaining separations of the same image onto the same side of the substrate sheet in register with the partial image formed by the first printing tower.
When operating in this manner, any tower serving to print only selected separations of an image, for instance separate portions or colors of an image, may include a plurality of print bars of the same color circumferentially spaced from one another along the image transfer surface. The image forming system is positioned in the printing system at a location also referred to as the image forming station, and these two terms may be hereinafter interchanged.
In an embodiment of the invention, each printing tower comprises four sequentially disposed print bars and the colors of the print bars are arranged in different sequences in the two printing towers, the colors of the two inner print bars in each printing tower being matched to the colors of the two outer print bars in the other printing tower.
Such a print bar configuration simplifies the changeover from simplex to duplex operation in that it is only then necessary to swap over the two inner or intermediate print bars of the sets in the two printing towers with each other. If such a changeover is performed using an automated print bar positioning system, the time taken for the changeover is significantly reduced in that the transport system may move each pair in one operation.
The print bar positioning system may take the form of a movable carriage guided on rails and having lifting arms for engaging the print bars. For a changeover, the carriage may be aligned with the first tower and its lifting arms used to raise the two intermediate print bars as a pair. The removed pair of print bars may then be parked in a rest position to free the arms of the carriage, which may then be used to raise the two intermediate print bars of the second tower and transfer them to the first tower. As a last step, the temporarily parked pair of print bars may be transferred from the rest position to the second tower.
It is possible for a printing system of the invention to operate in a mode in which after a complete image has been formed on one side of the substrate by the first printing tower, the second tower is use to apply a varnish to the printed side of the substrate instead of forming an image on the opposite side. In this case, the perfecting mechanism would not be used to invert the substrate between the two towers.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which the dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and not necessarily to scale. In the drawings:
General Overview
Essentially the printing system illustrated in
The blanket system 100 comprises an endless belt or blanket 102 that acts as an intermediate transfer member and is guided over two rollers 104, 106. As will be described with reference to
In operation, ink images, each of which is a mirror image of an image to be impressed on a final substrate, are printed by the image forming system 300 onto the upper run of blanket 102. In this context, the term “run” refers to a length or segment of the blanket between any two given rollers over which the blanket is guided. While being transported by the blanket 102, the ink is heated to dry it by evaporation of most, if not all, of its liquid carrier. The ink image is furthermore heated to render tacky the film of ink solids remaining after evaporation of the liquid carrier, this film being referred to as a residue film, to distinguish it from the thicker liquid film formed by flattening of each ink droplet upon impact with the transfer member. At the impression cylinders 502, 504 the image is impressed onto individual sheets 501 of a substrate which are conveyed by substrate transport system 500 from an input stack 506 to an output stack 508 via the impression cylinders 502, 504. The residue film is rendered tacky typically when a polymeric resin of a suitable ink composition is softened so as to increase the subsequent ability of the film to adhere to the substrate as compared to its ability to adhere to the transfer member.
Image Forming System
In an embodiment of the invention, the image forming system 300 comprises print bars 302 each slideably mounted on a frame 304 positioned at a fixed height above the surface of the blanket 102. Each print bar 302 may comprise a strip of print heads as wide as the printing area on the blanket 102 and comprises individually controllable print nozzles. The image forming system can have any number of bars 302, each of which may contain an ink of a different color.
As some print bars may not be required during a particular printing job, the heads can be moved between an operative position, in which they overlie the blanket 102 and an inoperative position. A mechanism is provided for moving print bars 302 between their operative and inoperative positions, but the mechanism is not illustrated and need not be described herein as it is not relevant to the printing process. It should be noted that the bars preferably remain stationary during printing.
When moved to their inoperative position, the print bars can be covered for protection and to prevent the nozzles of the print bar from drying or clogging. In an embodiment of the invention, the print bars are parked above a liquid bath (not shown) that assists in this task. Print bars that are in the inoperative position can be changed and accessed readily for maintenance, even while a printing job is in progress using other print bars.
Within each print bar, the ink may be constantly recirculated, filtered, degassed and maintained at a desired temperature and pressure. As the design of the print bars may be conventional, or at least similar to print bars used in other inkjet printing applications, their construction and operation will be clear to the person skilled in the art without the need for more detailed description.
As different print bars 302 are spaced from one another along the length of the blanket, it is of course essential for their operation to be correctly synchronized with the movement of blanket 102. Further details of suitable control systems for such printing systems are disclosed in co-pending PCT Application No. PCT/IB2013/051727 (Agent's reference LIP 14/001 PCT).
If desired, it is possible to provide a blower 306 following each print bar 302 to blow a slow stream of a hot gas, preferably air, over the intermediate transfer member to commence the drying of the ink droplets deposited by the print bar 302. This assists in fixing the droplets deposited by each print bar 302, that is to say resisting their contraction and preventing their movement on the intermediate transfer member, and also in preventing them from merging into droplets deposited subsequently by other print bars 302.
In one embodiment of the invention, the inks used in the print heads comprise nano-particles of organic polymeric resin and coloring agent (e.g. pigment or dye) suspended or dissolved in an aqueous carrier. The nano-pigments can have an average particle size D50 of at least 10 nm and of at most 300 nm, however such range may vary for each ink color and in some embodiments the pigments may have a D50 of at most 200 nm or of at most 100 nm. Acrylic polymers and acrylic-styrene co-polymers with an average molecular weight around 60,000 g/mole have been found to be suitable resins. Further details of non-limiting examples of ink compositions suitable for the printing processes and systems of the present invention are disclosed in co-pending PCT Application No. PCT/182013/051755 (Agent's reference LIP 11/001 PCT).
Blanket and Blanket Support System
The blanket 102, in one embodiment of the invention, is seamed. In particular, the blanket is formed of an initially elongate flat strip of which the ends are releasably or permanently fastened to one another to form a continuous loop. The releasable fastening may be a zip fastener or a hook and loop fastener that lies substantially parallel to the axes of rollers 104 and 106 over which the blanket is guided. Permanent fastening may be achieved, for example following installation of the blanket over its rollers, by adhering its opposite ends one to another to form a continuous belt loop by soldering, gluing, taping (e.g. using Kapton® tape, RTV liquid adhesives or PTFE thermoplastic adhesives with a connective strip overlapping both ends of the strip), or any other method commonly known. Any method of joining the ends of the blanket may cause a discontinuity, referred to herein as a seam, and it is desirable to avoid an increase in the thickness or discontinuity of chemical and/or mechanical properties of the belt at the seam. In order to avoid a sudden change in the tension of the blanket as the seam passes over these rollers, it is desirable to incline the fastener relative to the axis of the roller but this enlarges the non-printable image area. In an alternative embodiment, the blanket forms a continuous and seamless loop, the belt having the same properties along its circumference.
The primary purpose of the blanket is to receive an ink image from the image forming system and to transfer that image dried but undisturbed to the impression stations. To allow easy transfer of the ink image at each impression station, the blanket has a thin upper release layer that is hydrophobic. The outer surface of the transfer member upon which an aqueous ink can be applied may comprise a silicone material. A silanol-terminated polydialkylsiloxane material, as well as other silanol-, sylyl- or silane-modified or terminated polydialkylsiloxane curable silicone polymers, and amino silicones have been found to work well, but it is believed that the exact formulation of the silicone is not critical and any material that allows for release of the image from the transfer member to a final substrate is believed to be suitable. Further details of non-limiting examples of release layers and intermediate transfer members are disclosed in co-pending PCT Applications No. PCT/IB2013/051743 (Agent's reference LIP 10/002 PCT) and No. PCT/IB2013/051751 (Agent's reference LIP 10/005 PCT). Suitably, the materials forming the release layer allow it to be not absorbent. Preferably, the material is selected so that the transfer member does not swell (or is not solvated) by the carrier liquid of the ink or of any other fluid that may be applied to the release layer.
The strength of the blanket can be derived from a reinforcement layer. In one embodiment, the reinforcement layer is formed of a fabric. If the fabric is woven, the warp and weft threads of the fabric may have a different composition or physical structure so that the blanket should have, for reasons to be discussed below, greater elasticity in its width ways direction (parallel to the axes of the rollers 104 and 106) than in its lengthways direction, in which it is preferably substantially non-extendible. In one embodiment, the fibers of the reinforcement layer in the longitudinal direction are substantially aligned with the printing direction and are made of high performance fibers (e.g. aramid, carbon, ceramic, glass fibers etc.)
The blanket may comprise additional layers between the reinforcement layer and the release layer, for example to provide conformability and compressibility of the release layer to the surface of the substrate, to act as a thermal reservoir or a thermal partial barrier and/or to allow an electrostatic charge to the applied to the release layer. An inner layer may further be provided to control the frictional drag on the blanket as it is rotated over its support structure. Other layers may be included to adhere or connect the afore-mentioned layers one with another or to prevent migration of molecules therebetween.
The structure supporting the blanket is shown in
The roller 106 is journaled in bearings that are directly mounted on outriggers 120. At the opposite end, however, the roller 104 is journaled in pillow blocks 124 that are guided for sliding movement relative to outriggers 120. Motors 126, for example electric motors, which may be stepper motors, act through suitable gearboxes to move pillow blocks 124, so as to alter the distance between the axes of rollers 104 and 106, while maintaining them parallel to one another.
Thermally conductive support plates 130 are mounted on cross beams 122 to form a continuous flat support surface both on the top side bottom sides of the support frame. The junctions between the individual support plates 130 are intentionally offset from each other (e.g. zigzagged) in order not to create a line running parallel to the length of the blanket 102. Electrical heating elements 132 are inserted into transverse holes in the plates 130 to apply heat to the plates 130 and through the plates 130 to the blanket 102. Other means for heating the blanket will occur to the person of skill in the art and may include heating from below, above of within the blanket itself.
Also mounted on the blanket support frame are two pressure or nip rollers 140, 142. The pressure rollers are located on the underside of the support frame in gaps between the support plates 130 covering the underside of the frame. Pressure rollers 140, 142 are aligned respectively with impression cylinders 502, 504 of the substrate transport system. Each impression cylinder and corresponding pressure roller, when engaged as described below, form an impression station.
Each of the pressure rollers 140, 142 is mounted so that it can be raised and lowered from the lower run of the blanket. In one embodiment each pressure roller is mounted on an eccentric that is rotatable by a respective actuator 150, 152. When it is raised by its actuator to an upper position within the support frame, each pressure roller is spaced from the opposing impression cylinder, allowing the blanket to pass by the impression cylinder without making contact with neither the impression cylinder itself nor with a substrate carried by the impression cylinder. On the other hand, when moved downwards by its actuator, each pressure roller 140, 142 projects downwards beyond the plane of the adjacent support plates 130 and deflects the blanket 102, forcing it against the opposing impression cylinder 502, 504. In this lower position, it presses the lower run of the blanket against a final substrate being carried on the impression roller.
In embodiments of the present invention, it is optional for a pressure or nip roller to be disengageable from its impression cylinder. In embodiments using a seamed blanket, it is either possible to use a disengageable nip roller to assist in allowing the seam to pass between the nip roller and the impression cylinder, or one may rely solely on the passage of the seam being timed to coincide with an optional recess in the surface of the impression cylinder that can for instance be used to accommodate grippers for holding the substrate sheets in position on the impression cylinder. In an alternative embodiment, the blanket may be seamless and the impression cylinder continuous, for instance when printing on a web substrate. The rollers 104 and 106 are connected to respective electric motors 160, 162. The motor 160 is the more powerful and serves to drive the blanket clockwise as viewed in
Alternatively, the motors 160 and 162 may be operated in such a manner as to maintain a higher tension in the upper run of the blanket where the ink image is formed and a lower tension in the lower run of the blanket. The lower tension in the lower run may assist in absorbing sudden perturbations caused by the abrupt engagement and disengagement of blanket 102 with impression cylinders 502 and 504.
In an embodiment of the invention, a fan or air blower (not shown) is mounted on the frame to maintain a sub-atmospheric pressure in the volume 166 bounded by the blanket and its support frame. The negative pressure serves to maintain the blanket flat against the support plates 130 on both the upper and the lower side of the frame, in order to achieve good thermal contact. If the lower run of the blanket is set to be relatively slack, the negative pressure would also assist in maintaining the blanket out of contact with the impression cylinders when the pressure rollers 140, 142 are not actuated.
In an embodiment of the invention, each of the outriggers 120 also supports a continuous track 180, which engages formations on the side edges of the blanket to maintain the blanket taut in its width ways direction. The formations may be spaced projections, such as the teeth of one half of a zip fastener sewn or otherwise attached to the side edge of the blanket. Alternatively, the formations may be a continuous flexible bead of greater thickness than the blanket. The lateral track guide channel may have any cross-section suitable to receive and retain the blanket lateral formations and maintain it taut. To reduce friction, the guide channel may have rolling bearing elements to retain the projections or the beads within the channel.
To mount a blanket on its support frame, according to one embodiment of the invention, entry points are provided along tracks 180. One end of the blanket is stretched laterally and the formations on its edges are inserted into tracks 180 through the entry points. Using a suitable implement that engages the formations on the edges of the blanket, the blanket is advanced along tracks 180 until it encircles the support frame. The ends of the blanket are then fastened to one another to form an endless loop. The rollers 104 and 106 can then be moved apart to tension the blanket and stretch it to the desired length. Sections of tracks 180 are telescopically collapsible to permit the length of the track to vary as the distance between rollers 104 and 106 is varied. Further details on non limiting exemplary formations, corresponding tracks and methods of mounting a blanket are disclosed in co-pending PCT Application No. PCT/IB2013/051719 (Agent's reference LIP 7/005 PCT).
In order for the image to be properly formed on the blanket and transferred to the final substrate, a number of different elements of the system must be properly synchronized. In order to position the images properly on the blanket, the position and speed of the blanket must be both known and controlled. In an embodiment of the invention, the blanket is marked at or near its edge with one or more markings spaced in the direction of motion of the blanket. The marking(s) may for example be applied to the surface of the blanket that may be sensed magnetically or optically by a suitable detector. Alternatively, a marking may take the form of an irregularity in the lateral projections that are used to tension the blanket, for example a missing tooth, hence serving as a mechanical position indicator. One or more sensors (not shown) senses the timing of these markings as they pass the sensor. The speed of the blanket and the speed of the surface of the impression rollers should be the same, for proper transfer of the images to the substrate from the transfer blanket. Signals from the sensor 107 are sent to a controller 109 which also receives an indication of the speed of rotation and angular position of the impression rollers, for example from encoders on the axis of one or both of the impression rollers (not shown). The sensor 107, or another sensor (not shown), also determines the time at which the seam of the blanket passes the sensor. For maximum utility of the usable length of the blanket, it is desirable that the images on the blanket start as close to the seam as feasible.
The controller controls the electric motors 160 and 162 to ensure that linear speed of the blanket is the same as the speed of the surface of the impression rollers.
Because the blanket contains an unusable area resulting from the seam, it is important to ensure that this area always remain in the same position relative to the printed images in consecutive cycles of the blanket. Also, it is preferable to ensure that whenever the seam passes the impression cylinder, it should always coincides with a time when the recess in the surface of the impression cylinder that accommodates the substrate grippers faces the blanket.
Preferably, the length of the blanket is set to be a whole number multiple of the circumference of the impression cylinders 502, 504. In embodiments wherein the impression cylinder may accommodate two sheets of substrate, the length of the blanket may be a whole multiple of half the circumference of an impression cylinder. Since the length of the blanket may change with time and/or temperature, the position of the seam relative to the impression rollers is preferably changed, by momentarily changing the speed of the blanket. When synchronism is again achieved, the speed of the blanket is again adjusted to match that of the impression rollers, when it is not engaged with the impression cylinders 502, 504. The length of the blanket can be determined from a shaft encoder measuring the rotation of one of rollers 104, 106 during one sensed complete revolution of the blanket.
The controller also controls the timing of the flow of data to the print bars and may control proper timing of any optional sub-system of the printing system, as known to persons skilled in the art of printing.
This control of speed, position and data flow ensures synchronization between image forming system 300, substrate transport system 500 and blanket system 100 and ensures that the images are formed at the correct position on the blanket for proper positioning on the final substrate.
As its length is a factor in synchronization, the blanket is required to resist stretching and creep. In the transverse direction, on the other hand, it is only required to maintain the blanket flat taut without creating excessive drag due to friction with the support plates 130. It is for this reason that, in an embodiment of the invention, the elasticity of the blanket is intentionally made anisotropic.
Blanket Pre-Treatment
While a roller can be used to apply an even film, in an alternative embodiment the elective pre-treatment material is sprayed onto the surface of the blanket and spread more evenly, for example by the application of a jet from an air knife, a drizzle from sprinkles or undulations from a fountain. The pre-treatment solution may be removed from the transfer member shortly following its exposure therewith (e.g. using air flow).
The average thickness of the elective pre-treatment solution may vary between initial application, optional removal and dried stage and is typically below 1000 nanometers, below 800 nm, below 600 nm, below 400 nm, below 200 nm, below 100 nm, below 50 nm, below 20 nanometers, below 10 nanometers, below 5 nanometers, or below 2 nanometers.
The purpose of the optionally applied chemical agent is to counteract the effect of the surface tension of the aqueous ink upon contact with the hydrophobic release layer of the blanket. It is believed that such pre-treatment chemical agents, for instance some charged or chargeable polymers comprising amine nitrogen atoms in a plurality of functional groups each independently selected from linear, branched and cyclic, primary amines, secondary amines, tertiary amines, and quaternized ammonium groups and having a relatively high charge density and molecular weight (e.g. at least 10,000 g/mole), will bond (temporarily at least), with the silicone surface of the transfer member to form a positively charged layer. Suitable conditioning agents include linear and branched polyethylene imine (PEI), modified polyethylene imine, guar hydroxylpropyltrimonium chloride, hydroxypropyl guar hydroxyl-propyl-trimonium chloride, vinyl pyrrolidone dimethylaminopropyl methacrylamide copolymer, vinyl caprolactam dimethylaminopropyl methacrylamide hydroxyethyl methacrylate, quaternized vinyl pyrrolidone dimethylaminoethyl methacrylate copolymer, poly(diallyldimethyl-ammonium chloride), poly(4-vinylpyridine) and polyallylamine.
However, the amount of charge that is present in such layer is believed to be much smaller than that in the droplet itself. The present inventors have found that a very thin layer, perhaps even a layer of molecular thickness will be adequate. This layer of pre-treatment of the transfer member, if required, may be applied in very dilute form of the suitable chemical agents. Ultimately this thin layer may be transferred onto the substrate, along with the image being impressed. Further details on exemplary pretreatment solutions are disclosed in co-pending PCT Application No. PCT/IB2013/000757 (Agent's reference LIP 12/001 PCT).
When the droplet impinges on the transfer member, the momentum in the droplet causes it to spread into a relatively flat volume. In the prior art, this flattening of the droplet is almost immediately counteracted by the combination of surface tension of the aqueous droplet and the hydrophobic nature of the surface of the transfer member.
The shape of the ink droplet is preferably “frozen” such that at least some and preferably a major part of the flattening and horizontal extension of the droplet present on impact is preserved. It should be understood that since the recovery of the droplet shape after impact is very fast, the methods of the prior art would not effect phase change by agglomeration and/or coagulation and/or migration.
Without wishing to be bound by theory, it is believed that, on impact, van der Waals forces acting between the molecules of the polymer and/or pigment particles in the ink and molecules residing on the surface of the hydrophobic release layer (stemming either from the composition of the release layer and/or from the composition of the pretreatment solution) act to resist the beading up of the droplets under the action of surface tension.
The amount of charge on the surface of the intermediate transfer member is too small to adhere more than a small number of particles, so that, it is believed, the concentration and distribution of particles in the drop is not substantially changed. Furthermore, since the ink is aqueous, the effects of the positive charge are very local, especially in the very short time span needed for freezing the shape of the droplets (at most few seconds and generally less than one).
However, it has been surprisingly found that this attraction has a profound effect on the shape of the droplets after they stabilize. It is believed that the attractive force acts to counteract the repelling of the water in the ink by the silicone. The result is that a relatively flat droplet film of ink of greater extent than would be present in the absence of the charge on the silicone surface is formed on the transfer member. Furthermore, since in areas that are not reached by the droplet the effective hydrophobic nature of the transfer member is maintained, there is little or no spreading of the droplet above that achieved in the initial impact and the boundaries of the droplet are distinct.
While applicants have found that coating or spraying the transfer member with a chargeable polymer is an effective method for fixing the droplets, it is believed that otherwise transferring positive charge to the transfer member is also possible, although this is a much more complex process. Other effects that may contribute to the shape of the droplet remaining as a flattened film are quick heating of the droplet that increases its viscosity, a barrier (the polymer coating) that reduces the hydrophobic effect of the silicone coating and a surfactant that reduces the surface tension of the ink.
The residue film may have an average thickness below 1500 nanometers, below 1200 nm, below 1000 nm, below 800 nanometers, below 600 nm, below 500 nm, below 400 nm, below 300 nm, below 200 nm, and of at least 50 nm, at least 100 nm, or at least 150 nm.
Ink Image Heating
The heaters 132 inserted into the support plates 130 are used to heat the blanket to a temperature that is appropriate for the rapid evaporation of the ink carrier and compatible with the composition of the blanket. For blankets comprising for instance silanol-, sylyl- or silane-modified or terminated polydialkylsiloxane silicones in the release layer, heating is typically of the order of 150° C., though this temperature may vary within a range from 120° C. to 180° C., depending on various factors such as the composition of the inks and/or of the pre-treatment solutions if needed. Blankets comprising amino silicones may generally be heated to temperatures between 70° C. and 130° C. When using the illustrated beneath heating of the transfer member, it is desirable for the blanket to have relatively high thermal capacity and low thermal conductivity, so that the temperature of the body of the blanket 102 will not change significantly as it moves between the optional pre-treatment station, the image forming system and the impression station(s). To apply heat at different rates to the ink image carried by the transfer surface, external heaters or energy sources (not shown) may be used to apply additional energy locally, for example prior to reaching the impression stations to render the ink residue tacky, prior to the image forming system to dry the optional pre-treatment agent and at the image forming system to start evaporating the carrier from the ink droplets as soon as possible after they impact the surface of the blanket.
The external heaters may be, for example, hot gas or air blowers or radiant heaters focusing, for example, infra red radiation onto the surface of the blanket, which may attain temperatures in excess of 175° C., 190° C., 200° C., 210° C., or even 220° C.
If the ink contains components sensitive to ultraviolet light then an ultraviolet source may be used to help cure the ink as it is being transported by the blanket.
Substrate Transport System
In
Though not shown in the drawings, but known per se, the various transport rollers and impression cylinders may incorporate grippers that are cam operated to open and close at appropriate times in synchronism with their rotation so as to clamp the leading edge of each sheet of substrate. In an embodiment of the invention, the tips of the grippers at least of impression cylinders 502 and 504 are designed not to project beyond the outer surface of the cylinders to avoid damaging blanket 102.
After an image has been impressed onto one side of a substrate sheet during passage between impression cylinder 502 and blanket 102 applied thereupon by pressure roller 140, the sheet is fed by a transport roller 522 to a perfecting cylinder 524 that has a circumference that is twice as large as the impression cylinders 502, 504. The leading edge of the sheet is transported by the perfecting cylinder past a transport roller 526, of which the grippers are timed to catch the trailing edge of the sheet carried by the perfecting cylinder and to feed the sheet to second impression cylinder 504 to have a second image impressed onto its reverse side. The sheet, which has now had images printed onto both its sides, is advanced by a belt conveyor 530 from second impression cylinder 504 to output stack 508.
Referring now to the embodiment of the invention shown in
The ensuing description of the embodiment of
The printing system comprises two printing towers 702 and 704. The tower 702 comprises an image transfer drum 706, an image forming system 708 including four print bars (it can have more), a heating station 710 following the image forming system 708 in the direction of rotation of the drum 706 and a pre-treatment station 712 preceding the image forming system 708, the pre-treatment being optional. In addition to external heating station 710, the drum 706 may be internally heated. The drum, which may be internally heated, carries a blanket of which the water impervious outer surface is optionally pre-treated in the pre-treatment station 712 before it arrives at the image forming system 708. The image forming system 708 forms an image made up of ink droplets on the surface of the blanket. The image is dried and rendered tacky as it travels around the axis of the drum 706 to form a thin residue film that is impressed onto a sheet substrate passing between the drum 706 and the impression cylinder 502.
Other than the blanket being wrapped around a drum 706, instead of being guided over rollers, and interacting with only one impression cylinder 502 instead of two, the printing system operates in the same way as already described with reference to
The use of a drum in place of guide rollers to support the blanket simplifies the control system as the blanket is not prone to stretching and the large moment of inertia of the drum reduces fluctuations in speed. The exact determination of the position of the blanket therefore requires fewer sensors and these may take the form of shaft encoders and/or sensors detecting one or more markings on the surface of the blanket.
In the illustrated configuration of the print bars in
In the configuration shown in
When operating in this manner, any tower serving to print only selected separations of an image, may include a plurality of print bars of the same color circumferentially spaced from one another along the image transfer surface. As each printing bar is limited as to the frequency with which it can direct ink droplets onto the intermediate transfer member, increasing the number of print bars of the same color permits a printing tower to operate at a higher speed while maintaining the same dot density in the image.
It would in principle be possible when operating in high speed simplex mode, for each tower to continue to print a full color partial image. However, achieving registration of dots of the same color printed by different towers is more difficult than registration of dots of different colors. It is therefore preferred when operating in simplex mode, to print each color separation using only one tower, so that for four color printing two colors are printed by the first tower and the other two by the second tower.
It will be noted that in
The embodiment of
The contents of all of the above mentioned applications of the Applicant are incorporated by reference as if fully set forth herein.
The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons skilled in the art to which the invention pertains.
In the description and claims of the present disclosure, each of the verbs, “comprise”, “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/IB2013/051717 | 3/5/2013 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2013/132419 | 9/12/2013 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
3898670 | Erikson et al. | Aug 1975 | A |
4009958 | Kurita et al. | Mar 1977 | A |
4093764 | Duckett et al. | Jun 1978 | A |
4535694 | Fukuda | Aug 1985 | A |
4538156 | Durkee et al. | Aug 1985 | A |
4976197 | Yamanari et al. | Dec 1990 | A |
5012072 | Martin et al. | Apr 1991 | A |
5099256 | Anderson | Mar 1992 | A |
5305099 | Morcos | Apr 1994 | A |
5352507 | Bresson et al. | Oct 1994 | A |
5406884 | Okuda et al. | Apr 1995 | A |
5471233 | Okamoto et al. | Nov 1995 | A |
5552875 | Sagiv et al. | Sep 1996 | A |
5587779 | Heeren et al. | Dec 1996 | A |
5613669 | Grueninger | Mar 1997 | A |
5614933 | Hindman et al. | Mar 1997 | A |
5623296 | Fujino et al. | Apr 1997 | A |
5660108 | Pensavecchia | Aug 1997 | A |
5677719 | Granzow | Oct 1997 | A |
5698018 | Bishop et al. | Dec 1997 | A |
5841456 | Takei et al. | Nov 1998 | A |
5884559 | Okubo et al. | Mar 1999 | A |
5978631 | Lee | Nov 1999 | A |
6009284 | Weinberger et al. | Dec 1999 | A |
6024018 | Darel et al. | Feb 2000 | A |
6033049 | Fukuda | Mar 2000 | A |
6055396 | Pang | Apr 2000 | A |
6059407 | Komatsu et al. | May 2000 | A |
6102538 | Ochi et al. | Aug 2000 | A |
6108513 | Landa et al. | Aug 2000 | A |
6195112 | Fassler et al. | Feb 2001 | B1 |
6196674 | Takemoto | Mar 2001 | B1 |
6213580 | Segerstrom et al. | Apr 2001 | B1 |
6234625 | Wen | May 2001 | B1 |
6303215 | Sonobe et al. | Oct 2001 | B1 |
6354700 | Roth | Mar 2002 | B1 |
6363234 | Landa et al. | Mar 2002 | B2 |
6364451 | Silverbrook | Apr 2002 | B1 |
6386697 | Yamamoto et al. | May 2002 | B1 |
6390617 | Iwao | May 2002 | B1 |
6402317 | Yanagawa et al. | Jun 2002 | B2 |
6409331 | Gelbart | Jun 2002 | B1 |
6438352 | Landa | Aug 2002 | B1 |
6454378 | Silverbrook et al. | Sep 2002 | B1 |
6530657 | Polierer | Mar 2003 | B2 |
6559969 | Lapstun | May 2003 | B1 |
6575547 | Sakuma | Jun 2003 | B2 |
6608979 | Landa et al. | Aug 2003 | B1 |
6639527 | Johnson | Oct 2003 | B2 |
6648468 | Shinkoda et al. | Nov 2003 | B2 |
6678068 | Richter et al. | Jan 2004 | B1 |
6682189 | May et al. | Jan 2004 | B2 |
6704535 | Kobayashi et al. | Mar 2004 | B2 |
6719423 | Chowdry et al. | Apr 2004 | B2 |
6755519 | Gelbart et al. | Jun 2004 | B2 |
6761446 | Chowdry et al. | Jul 2004 | B2 |
6789887 | Yang et al. | Sep 2004 | B2 |
6827018 | Hartmann et al. | Dec 2004 | B1 |
6898403 | Baker et al. | May 2005 | B2 |
6912952 | Landa et al. | Jul 2005 | B1 |
6917437 | Myers et al. | Jul 2005 | B1 |
6970674 | Sato et al. | Nov 2005 | B2 |
6974022 | Saeki | Dec 2005 | B2 |
6982799 | Lapstun | Jan 2006 | B2 |
7057760 | Lapstun et al. | Jun 2006 | B2 |
7204584 | Lean et al. | Apr 2007 | B2 |
7224478 | Lapstun et al. | May 2007 | B1 |
7296882 | Buehler et al. | Nov 2007 | B2 |
7300133 | Folkins et al. | Nov 2007 | B1 |
7300147 | Johnson | Nov 2007 | B2 |
7304753 | Richter et al. | Dec 2007 | B1 |
7322689 | Kohne et al. | Jan 2008 | B2 |
7360887 | Konno | Apr 2008 | B2 |
7362464 | Kitazawa et al. | Apr 2008 | B2 |
7459491 | Tyvoll et al. | Dec 2008 | B2 |
7527359 | Stevenson et al. | May 2009 | B2 |
7708371 | Yamanobe | May 2010 | B2 |
7712890 | Yahiro | May 2010 | B2 |
7808670 | Lapstun et al. | Oct 2010 | B2 |
7810922 | Gervasi et al. | Oct 2010 | B2 |
7845788 | Oku | Dec 2010 | B2 |
8025389 | Yamanobe et al. | Sep 2011 | B2 |
8038284 | Hori | Oct 2011 | B2 |
8042906 | Chiwata et al. | Oct 2011 | B2 |
8059309 | Lapstun | Nov 2011 | B2 |
8109595 | Tanaka et al. | Feb 2012 | B2 |
8147055 | Cellura et al. | Apr 2012 | B2 |
8256857 | Folkins et al. | Sep 2012 | B2 |
8264135 | Ozolins et al. | Sep 2012 | B2 |
8295733 | Imoto | Oct 2012 | B2 |
8303072 | Shibata et al. | Nov 2012 | B2 |
8693032 | Goddard et al. | Apr 2014 | B2 |
8711304 | Mathew et al. | Apr 2014 | B2 |
8746873 | Tsukamoto et al. | Jun 2014 | B2 |
8894198 | Hook et al. | Nov 2014 | B2 |
8919946 | Suzuki et al. | Dec 2014 | B2 |
20010022607 | Takahashi et al. | Sep 2001 | A1 |
20030067529 | May et al. | Apr 2003 | A1 |
20030118381 | Law et al. | Jun 2003 | A1 |
20030214568 | Nishikawa et al. | Nov 2003 | A1 |
20030234849 | Pan et al. | Dec 2003 | A1 |
20040228642 | Iida et al. | Nov 2004 | A1 |
20050082146 | Axmann | Apr 2005 | A1 |
20050110855 | Taniuchi et al. | May 2005 | A1 |
20050134874 | Overall et al. | Jun 2005 | A1 |
20050150408 | Hesterman | Jul 2005 | A1 |
20060164488 | Taniuchi et al. | Jul 2006 | A1 |
20070014595 | Kawagoe | Jan 2007 | A1 |
20070054981 | Yanagi | Mar 2007 | A1 |
20070134030 | Lior et al. | Jun 2007 | A1 |
20070146462 | Taniuchi et al. | Jun 2007 | A1 |
20070176995 | Kadomatsu et al. | Aug 2007 | A1 |
20070229639 | Yahiro | Oct 2007 | A1 |
20070285486 | Harris et al. | Dec 2007 | A1 |
20080006176 | Houjou | Jan 2008 | A1 |
20080030536 | Furukawa et al. | Feb 2008 | A1 |
20080032072 | Taniuchi et al. | Feb 2008 | A1 |
20080043082 | Yahiro | Feb 2008 | A1 |
20080055381 | Doi et al. | Mar 2008 | A1 |
20080055385 | Houjou | Mar 2008 | A1 |
20080074462 | Hirakawa | Mar 2008 | A1 |
20080166495 | Maeno et al. | Jul 2008 | A1 |
20080196612 | Rancourt et al. | Aug 2008 | A1 |
20080196621 | Ikuno et al. | Aug 2008 | A1 |
20090022504 | Kuwabara et al. | Jan 2009 | A1 |
20090080949 | Yamanobe et al. | Mar 2009 | A1 |
20090165937 | Inoue et al. | Jul 2009 | A1 |
20090190951 | Torimaru et al. | Jul 2009 | A1 |
20090202275 | Nishida et al. | Aug 2009 | A1 |
20090211490 | Ikuno et al. | Aug 2009 | A1 |
20090317555 | Hori | Dec 2009 | A1 |
20100066796 | Yanagi et al. | Mar 2010 | A1 |
20100075843 | Ikuno et al. | Mar 2010 | A1 |
20100091064 | Araki et al. | Apr 2010 | A1 |
20100303504 | Funamoto et al. | Dec 2010 | A1 |
20100310281 | Miura et al. | Dec 2010 | A1 |
20110058001 | Gila et al. | Mar 2011 | A1 |
20110085828 | Kosako et al. | Apr 2011 | A1 |
20110141188 | Morita | Jun 2011 | A1 |
20110234683 | Komatsu | Sep 2011 | A1 |
20110234689 | Saito | Sep 2011 | A1 |
20110269885 | Imai | Nov 2011 | A1 |
20120013693 | Tasaka | Jan 2012 | A1 |
20120013928 | Yoshida et al. | Jan 2012 | A1 |
20120026224 | Anthony et al. | Feb 2012 | A1 |
20120039647 | Brewington et al. | Feb 2012 | A1 |
20120105525 | Leung et al. | May 2012 | A1 |
20120105561 | Taniuchi et al. | May 2012 | A1 |
20120113203 | Kushida et al. | May 2012 | A1 |
20120127250 | Kanasugi et al. | May 2012 | A1 |
20120140009 | Kanasugi et al. | Jun 2012 | A1 |
20120156624 | Rondon | Jun 2012 | A1 |
20120194830 | Gaertner et al. | Aug 2012 | A1 |
20120237260 | Sengoku et al. | Sep 2012 | A1 |
20150022602 | Landa et al. | Jan 2015 | A1 |
20150024648 | Landa et al. | Jan 2015 | A1 |
20150042736 | Landa et al. | Feb 2015 | A1 |
20150049134 | Shmaiser et al. | Feb 2015 | A1 |
20150054865 | Landa et al. | Feb 2015 | A1 |
Number | Date | Country |
---|---|---|
102010060999 | Jun 2012 | DE |
2002169383 | Jun 2002 | JP |
2002326733 | Nov 2002 | JP |
2003114558 | Apr 2003 | JP |
2003211770 | Jul 2003 | JP |
2004114377 | Apr 2004 | JP |
2004114675 | Apr 2004 | JP |
2005014255 | Jan 2005 | JP |
2006102975 | Apr 2006 | JP |
2006137127 | Jun 2006 | JP |
2006347081 | Dec 2006 | JP |
2007069584 | Mar 2007 | JP |
2007216673 | Aug 2007 | JP |
2008142962 | Jun 2008 | JP |
2008255135 | Oct 2008 | JP |
2009045794 | Mar 2009 | JP |
2009083317 | Apr 2009 | JP |
2009083325 | Apr 2009 | JP |
2009154330 | Jul 2009 | JP |
2009190375 | Aug 2009 | JP |
2009202355 | Sep 2009 | JP |
2009214318 | Sep 2009 | JP |
2009226852 | Oct 2009 | JP |
2009233977 | Oct 2009 | JP |
2009234219 | Oct 2009 | JP |
2010105365 | May 2010 | JP |
2010173201 | Aug 2010 | JP |
2010241073 | Oct 2010 | JP |
2011025431 | Feb 2011 | JP |
2011173325 | Sep 2011 | JP |
2011173326 | Sep 2011 | JP |
2012086499 | Jun 2012 | JP |
2012111194 | Jun 2012 | JP |
WO9307000 | Apr 1993 | WO |
WO2013087249 | Jun 2013 | WO |
WO2013136220 | Sep 2013 | WO |
Entry |
---|
DE 102010060999 Machine Translation (by EPO and Google)—published Jun. 6, 2012; Wolf, Roland, Dr.-Ing. |
JP 2002-169383 Machine Translation (by EPO and Google)—published Jun. 14, 2002 Richo KK. |
JP 2002-326733 Machine Translation (by EPO and Google)—published Dec. 11, 2002 Kyocera Mita Corp. |
JP 2003-114558 Machine Translation (by EPO and Google)—published Apr. 18, 2003 Mitsubishi Chem Corp. |
JP 2003-211770 Machine Translation (by EPO and Google)—published Jul. 29, 2003 Hitachi Printing Solutions. |
JP 2004-114377 Machine Translation (by EPO and Google)—published Apr. 15, 2004; Konica Minolta Holdings Inc, et al. |
JP 2004-114675 Machine Translation (by EPO and Google)—published Apr. 15, 2004; Canon Inc. |
JP 2005-014255 Machine Translation (by EPO and Google)—published Jan. 20, 2005; Canon Inc. |
JP 2006-102975 Machine Translation (by EPO and Google)—published Apr. 20, 2006; Fuji Photo Film Co Ltd. |
JP 2006-137127 Machine Translation (by EPO and Google)—published Jun. 1, 2006; Konica Minolta Med & Graphic. |
JP 2006-347081 Machine Translation (by EPO and Google)—published Dec. 28, 2006; Fuji Xerox. |
JP 2007-069584 Machine Translation (by EPO and Google)—published Mar. 22, 2007 Fuji Film. |
JP 2007-216673 Machine Translation (by EPO and Google)—published Aug. 30, 2007 Brother Ind. |
JP 2008-142962 Machine Translation (by EPO and Google)—published Jun. 26, 2008; Fuji Xerox Co Ltd. |
JP 2008-255135 Machine Translation (by EPO and Google)—published Oct. 23, 2008; Fujifilm Corp. |
JP 2009-045794 Machine Translation (by EPO and Google)—published Mar. 5, 2009; Fujifilm Corp. |
JP 2009-083317 Abstract; Machine Translation (by EPO and Google)—published Apr. 23, 2009; Fujifilm Corp. |
JP 2009-083325 Abstract; Machine Translation (by EPO and Google)—published Apr. 23, 2009 Fujifilm. |
JP 2009-154330 Machine Translation (by EPO and Google)—published Jul. 16, 2009; Seiko Epson Corp. |
JP 2009-190375 Machine Translation (by EPO and Google)—published Aug. 27, 2009; Fuji Xerox Co Ltd. |
JP 2009-202355 Machine Translation (by EPO and Google)—published Sep. 10, 2009; Fuji Xerox Co Ltd. |
JP 2009-214318 Machine Translation (by EPO and Google)—published Sep. 24, 2009 Fuji Xerox Co Ltd. |
JP 2009-226852 Machine Translation (by EPO and Google)—published Oct. 8, 2009; Fujifilm Corp. |
JP 2009-233977 Machine Translation (by EPO and Google)—published Oct. 15, 2009; Fuji Xerox Co Ltd. |
JP 2009-234219 Machine Translation (by EPO and Google)—published Oct. 15, 2009; Fujifilm Corp. |
JP 2010-105365 Machine Translation (by EPO and Google)—published May 13, 2010; Fuji Xerox Co Ltd. |
JP 2010-173201 Abstract; Machine Translation (by EPO and Google)—published Aug. 12, 2010; Richo Co Ltd. |
JP 2010-241073 Machine Translation (by EPO and Google)—published Oct. 28, 2010; Canon Inc. |
JP 2011-025431 Machine Translation (by EPO and Google)—published Feb. 10, 2011; Fuji Xerox Co Ltd. |
JP 2011-173325 Abstract; Machine Translation (by EPO and Google)—published Sep. 8, 2011; Canon Inc. |
JP 2011-173326 Machine Translation (by EPO and Google)—published Sep. 8, 2011; Canon Inc. |
JP 2012-086499 Machine Translation (by EPO and Google)—published May 10, 2012; Canon Inc. |
JP 2012-111194 Machine Translation (by EPO and Google)—published Jun. 14, 2012; Konica Minolta. |
International Search Report for PCT/NL1991/00190 published as WO 1993/007000. |
WO 2013/087249 Machine Translation (by EPO and Google)—published Jun. 20, 2013; Koenig & Bauer AG. |
International Search Report for PCT/IB2013/051719 published as WO 2013/136220. |
Office Action for U.S. Appl. No. 14/382,758 dated Feb. 27, 2015. |
Office Action for U.S. Appl. No. 14/340,122 dated Feb. 27, 2015. |
International Search Report for PCT/IB2013/051717 published as WO/2013/132419. |
Written Opinion for PCT/IB2013/051717 published as WO/2013/132419. |
Number | Date | Country | |
---|---|---|---|
20150049134 A1 | Feb 2015 | US |
Number | Date | Country | |
---|---|---|---|
61606913 | Mar 2012 | US | |
61611286 | Mar 2012 | US | |
61619016 | Apr 2012 | US | |
61619546 | Apr 2012 | US | |
61635156 | Apr 2012 | US | |
61640493 | Apr 2012 | US |