Drying ink in digital printing using infrared radiation absorbed by particle embedded inside itm

Abstract

To efficiently dry ink that is applied to an intermediate transfer member.SOLUTION: A system 10 includes: (i) a flexible intermediate transfer member ITM, including: a stack of a first layer, located at an outer surface of the ITM, configured to transfer the ink image to a target substrate 50, and a second layer including a matrix holding particles, configured to receive optical radiation passing through the first layer, and to heat the ITM by absorbing the optical radiation; (ii) an illumination assembly, configured to dry the ink droplets by directing the optical radiation to impinge on the particles; and (iii) a temperature control assembly, configured to control a temperature of the ITM by directing a gas to the ITM, where the illumination assembly and the temperature control assembly are packaged in a housing including at least one cavity facing the substrate and at least one of the pair of light sources is disposed in the cavity for efficient drying.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 939,726, filed November 25, 2019, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates generally to digital printing processes, and more particularly to methods and systems for drying ink applied to a surface during a digital printing process. [Background technology]

[0003] Optical radiation, such as infrared (IR) and near-infrared radiation, is used to dry ink in various printing processes.

[0004] For example, U.S. Patent Application Publication No. 2012 / 0249630 describes a process for printing an image that includes printing a substrate with aqueous inkjet inks and drying the printed image with a near-infrared drying system. Various embodiments provide a process for inkjet printing and drying of inks with improved absorption in the near-infrared region of the spectrum for improved drying performance of aqueous, hypsochromic inks, as well as an inkjet ink set with improved and balanced near-infrared drying of black and yellow inkjet inks. Summary of the Invention [Means for solving the problem]

[0005] The embodiments of the invention described herein provide a system including a flexible intermediate transfer member (ITM), an illumination assembly, and a temperature control assembly. The ITM includes at least (i) a first layer disposed on the outer surface of the ITM and configured to receive ink droplets from an ink supply subsystem to form an ink image thereon and transfer the ink image to a target substrate, and (ii) a second layer including a matrix that holds particles in place. The second layer is configured to receive optical radiation passing through the first layer, and the particles are configured to heat the ITM by absorbing at least a portion of the optical radiation. The illumination assembly is configured to dry the ink droplets by directing optical radiation to affect at least a portion of the particles. The temperature control assembly is configured to control the temperature of the ITM by directing gas toward the ITM.

[0006] In some embodiments, the first and second layers are adjacent to one another and the particles are positioned a predetermined distance from one another to uniformly heat the exterior surface. In other embodiments, the particles are embedded within a bulk of the second layer a predetermined distance from the exterior surface to uniformly heat the exterior surface. In yet other embodiments, the system includes a processor, the processor configured to receive a temperature signal indicative of a temperature of the ITM and to control at least one of (i) an intensity of the optical radiation and (ii) a flow rate of the gas based on the temperature signal.

[0007] In one embodiment, the system includes one or more temperature sensors disposed at one or more respective predetermined locations relative to the ITM and configured to generate a temperature signal. In another embodiment, the illumination assembly includes one or more light sources disposed at one or more respective predetermined locations relative to the ITM. In yet another embodiment, at least one of the light sources is mounted adjacent to a print bar of an ink delivery subsystem configured to direct ink droplets toward an exterior surface.

[0008] In some embodiments, the lighting assembly includes at least an array including a plurality of light sources, hi other embodiments, the array includes a plurality of light sources arranged along the direction of movement of the ITM.

[0009] In one embodiment, the optical radiation comprises infrared (IR) radiation and at least one of the particles comprises carbon black (CB). In another embodiment, the gas comprises compressed air and the temperature control assembly includes a blower configured to supply the compressed air.

[0010] In accordance with one embodiment of the present invention, there is additionally provided a method comprising directing optical radiation to a flexible intermediate transfer member (ITM) comprising a stack of at least (i) a first layer disposed on an outer surface of the ITM for receiving ink droplets to form an ink image thereon and for transferring the ink image to a target substrate, and (ii) a second layer including a matrix holding one or more particles disposed at predetermined locations. The optical radiation passes through the first layer, the particles absorbing at least a portion of the optical radiation to heat the ITM, and the optical radiation impinges on at least a portion of the particles of the second layer to dry the ink droplets on the outer surface. The temperature of the ITM is controlled by directing gas toward the ITM.

[0011] There is also provided, in accordance with one embodiment of the present invention, a method for manufacturing a flexible intermediate transfer member (ITM), the method comprising: producing a first layer disposed on an outer surface of the ITM for receiving ink droplets to form an ink image thereon and for transferring the ink image to a target substrate; and applying a second layer to the first layer, the second layer comprising a matrix holding one or more particles disposed at respective predetermined locations.

[0012] In some embodiments, producing the first layer includes applying the first layer to a carrier, and the method includes removing the carrier from the ITM after applying at least the second layer.

[0013] There is further provided, in accordance with one embodiment of the present invention, a system including a flexible intermediate transfer member (ITM), an illumination assembly, and a temperature control assembly.

[0014] In some embodiments, the illumination assembly includes one or more light sources positioned at one or more respective predetermined locations relative to the ITM and configured to direct optical radiation to impinge on at least a portion of the particles, hi other embodiments, at least one of the light sources is mounted adjacent to a print bar that directs ink droplets toward the ITM.

[0015] In one embodiment, the illumination assembly includes at least an array of light sources disposed along a direction of movement of the ITM and configured to direct optical radiation to impinge on at least a portion of the particles, hi another embodiment, the illumination assembly and the temperature control assembly are packaged within a housing.

[0016] The present invention will be more fully understood from the following detailed description of the embodiments thereof when taken in conjunction with the drawings in which: [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic side view of a digital printing system, according to some embodiments of the present invention. [Figure 2] 1 is a schematic side view of a digital printing system, according to some embodiments of the present invention. [Figure 3] 1 is a schematic side view of a dryer for drying ink in a digital printing system, in accordance with one embodiment of the present invention; [Figure 4] FIG. 2 is a schematic side view of a primary dryer for drying ink in a digital printing system, in accordance with one embodiment of the present invention. [Figure 5] 1 is a schematic, pictorial representation of a blanket used in a digital printing system, in accordance with one embodiment of the present invention; [Figure 6]3A-3C are schematic diagrams illustrating cross-sectional views of a process sequence for manufacturing a blanket for use in a digital printing system, in accordance with one embodiment of the present invention. [Figure 7] 1 is a flow chart that schematically illustrates a method for manufacturing a blanket for a digital printing system, in accordance with an embodiment of the present invention. [Figure 8] 2 is a flow chart that schematically illustrates a method for drying ink and controlling blanket temperature during a digital printing process, in accordance with one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] overview DETAILED DESCRIPTION OF THE INVENTION The embodiments of the present invention described below provide improved techniques for drying ink applied to the surface of a substrate during a digital printing process.

[0019] In some embodiments, a digital printing system includes a movable, flexible intermediate transfer member (ITM), also referred to herein as a blanket, an imaging station for applying ink droplets to the ITM, an illumination assembly, and a temperature control assembly. The illumination assembly is configured to direct infrared (IR) radiation toward the ITM.

[0020] In some embodiments, the ITM includes a multilayer stack including (i) a release layer that is transparent to IR radiation and disposed on an outer surface of the ITM facing the illumination assembly. The release layer is configured to receive ink droplets from a print bar of an imaging station so that the print bar forms multiple ink images on respective sections of the release layer as the ITM moves. The ITM is then configured to transfer the ink images to a target substrate, such as a sheet or continuous web.

[0021] In some embodiments, the ITM further comprises a layer, also referred to herein as an "IR layer," bonded to the release layer and that substantially blocks IR radiation. The IR layer has a matrix comprising a suitable type of silicone and carbon black (CB) particles embedded within the matrix of the IR layer.

[0022] In some embodiments, the IR layer is configured to receive IR radiation that passes through the release layer, and in response to the IR radiation, the CB particles are configured to heat at least the IR layer and the release layer of the ITM to dry ink droplets applied to the release layer.

[0023] In some embodiments, the CB particles are positioned at a predetermined distance from each other within the bulk of the IR layer and at a given distance from the outer surface of the release layer. In such embodiments, due to the low thermal conductivity of the silicone matrix, the heat emitted from the CB particles can be uniformly distributed within the IR layer and the release layer, thereby drying the ink uniformly across the outer surface of the release layer.

[0024] It should be noted that the ITM may be damaged at certain temperatures, for example, at about 140° C. or 150° C. In some embodiments, the temperature control assembly includes a blower configured to supply compressed air directed at the ITM at a temperature of about 30° C. to prevent overheating of the ITM.

[0025] In some embodiments, the digital printing system further includes a processor and a plurality of temperature sensors mounted at respective positions relative to the ITM, each configured to generate a temperature signal indicative of the temperature of the ITM at the respective position.

[0026] In some cases, the surface of the release layer includes bare sections between adjacent ink images that do not receive ink droplets, and therefore the ITM tends to overheat in the bare sections. In some embodiments, the processor is configured to control a temperature sensor to sense the ITM temperature in the bare sections as the ITM moves.

[0027] In some embodiments, based on the temperature signal, the processor is configured to control the lighting assembly to adjust the intensity of the IR radiation and / or the temperature control assembly to adjust the flow rate of compressed air to maintain the temperature of the bare section below said certain temperature. In other embodiments, the lighting and cooling assemblies may operate in an open loop, e.g., without measuring and adjusting the temperature.

[0028] In some embodiments, the imaging station may include multiple print bars, each configured to print a different color of the ink image. Note that some sections of the ink image may include first and second different color mixes of ink printed in separate succession by first and second print bars mounted a predetermined distance from each other on the digital printing system.

[0029] In some embodiments, the digital printing system has multiple units, each including one or more IR light sources and a compressed air outlet coupled to a temperature control assembly via a drain valve. In such embodiments, the units are mounted between the first and second print bars to partially dry the first color ink droplets applied to the ITM by the first print bar, so that after the second color droplets are applied, the first and second color ink droplets intermix on the surface of the release layer.

[0030] In some embodiments, the digital printing system includes an array of multiple (e.g., 10) units arranged along the direction of movement of the ITM to achieve complete drying of the ink image printed on the ITM by the print bar.

[0031] The disclosed techniques improve the quality of printed images by achieving a uniform drying process across the printed image. Additionally, the disclosed techniques improve the productivity of digital printing systems by reducing the drying time of the ink, thus reducing the cycle time of the printing process.

[0032] System Description 1 is a schematic side view of a digital printing system 10 according to one embodiment of the present invention. In some embodiments, system 10 includes an ink supply subsystem, also referred to herein as image-forming station 60, multiple drying stations, an impression station 84, and a rotating flexible blanket 44 that cycles through a blanket treatment station 52. In the context of the present invention and in the claims, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably to refer to a flexible member including one or more layers that is used as an intermediate member configured to receive an ink image and transfer the ink image to a target substrate, as described in more detail below.

[0033] In an operational mode, imaging station 60 is configured to form a mirror ink image, also referred to herein as an “ink image” (not shown) or simply “image,” of digital image 42 on an upper run of the surface of blanket 44. The ink image is then transferred to a target substrate (e.g., paper, folding carton, multilayer polymer, or any suitable flexible packaging in the form of a sheet or continuous web) disposed beneath a lower run of blanket 44.

[0034] In the context of the present invention, the term "run" refers to the length or segment of blanket 44 between any two given rollers over which blanket 44 is guided.

[0035] In some embodiments, during installation, the blanket 44 may be attached edge to edge to form a continuous blanket loop (not shown). An example of a method and system for seam installation is described in detail in U.S. Provisional Application No. 62 / 532,400, the disclosure of which is incorporated herein by reference.

[0036] In some embodiments, imaging station 60 typically includes multiple print bars 62, each mounted (e.g., using a slider) on a frame (not shown) positioned at a fixed height above the surface of the upper run of blanket 44. In some embodiments, each print bar 62 includes a strip of print head the same width as the print area on blanket 44 and includes individually controllable print nozzles.

[0037] In some embodiments, imaging station 60 may include any suitable number of bars 62, and each bar 62 may include a printing fluid, such as a different colored water-based ink. The inks typically have visible colors such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. In the example of FIG. 1, imaging station 60 includes seven print bars 62, but may include four print bars 62 having any selected color, such as, for example, cyan, magenta, yellow, and black.

[0038] In some embodiments, the print heads are configured to eject ink droplets of different colors onto the surface of blanket 44 to form ink images (not shown) on the outer surface of blanket 44 .

[0039] In some embodiments, the different print bars 62 are spaced apart from one another along an axis of movement, also referred to herein as the direction of movement of the blanket 44, represented by arrow 94. In this configuration, precise spacing between the bars 62 and synchronization between the direction of the ink droplets of each bar 62 and the moving blanket 44 is essential to enable accurate placement of the image pattern.

[0040] In some embodiments, system 10 includes dryers 66. In this example, each dryer 66 includes an infrared (IR-based) heater that is configured to dry a portion of the ink liquid carrier applied to the ITM surface by increasing the temperature of blanket 44 and evaporating at least a portion of the ink liquid carrier. In the example of FIG. 1, dryers 66 are positioned between print bars 62 and are configured to partially dry ink droplets deposited on the surface of blanket 44.

[0041] It should be noted that some sections of the ink image printed on the blanket 44 may include a mixture of two or more colors of ink to produce different colors. For example, a mixture of cyan and magenta may result in blue. In this example, the red print bar may be positioned in front of the yellow print bar along the direction of travel of the blanket 44 (represented by arrow 94).

[0042] In some embodiments, after ejecting red ink at a given location on the surface of blanket 44, processor 20 of system 10 is configured to control one or more of dryers 66 located between the red and yellow print bars to partially dry the red ink. In such embodiments, after ejecting yellow ink at a given location, the partial drying of the red ink allows the red and yellow inks to mix to form an orange color at the given location on the surface of blanket 44.

[0043] In some embodiments, blanket 44 has an operating temperature specification, for example, blanket 44 is configured to operate at a temperature below about 140° C. or 150° C. to prevent damage, such as distortion, to the structure of blanket 44. In some embodiments, system 10 further includes a temperature control assembly 121 (described in detail in FIGS. 3 and 4 below), which is configured to supply any suitable gas to the surface of blanket 44 to counteract the heat applied by the IR-based heater, thereby maintaining the temperature of blanket 44 below about 140° C. or 150° C. or any other temperature.

[0044] In some embodiments, the gas may include compressed air, and the temperature control assembly 121 may include a central blower configured to supply the compressed air to the dryer 66 via a discharge valve. In some embodiments, the dryer 66 includes a combination of the aforementioned IR-based heater for heating the blanket 44 and airflow channels for cooling the blanket 44. In such embodiments, the compressed air may be used to cool the section of the dryer 66 that is heated by the IR-based heater.

[0045] In some embodiments, the temperature control assembly 121 further includes an exhaust device configured to pump compressed air used to cool the blanket 44 and dryer 66 to reduce or prevent product ink condensation on the print head surface.

[0046] In the context of this disclosure and in the claims, the term "drying unit" may refer to an apparatus that includes a combination of an IR-based heater for heating blanket 44 and airflow channels for cooling blanket 44. In an example configuration of system 10, each dryer 66 may include a single drying unit.

[0047] The structure and function of the temperature control assembly 121 and dryer 66 are shown in detail in FIGS. 3 and 4 below.

[0048] In some embodiments, this heating between the print bars can help, for example, to reduce or eliminate condensation on the surface of the print head, and / or to deal with satellites (e.g., residue or small droplets dispersed around the main ink droplets), and / or to prevent clogging of the inkjet nozzles of the print head, and / or to prevent droplets of different color inks on the blanket 44 from unnecessarily intermixing with each other.

[0049] In some embodiments, system 10 includes a drying station, also referred to herein as primary dryer 64, that is configured to dry the ink images applied to the surface of blanket 44 by image-forming station 60. Note that each of dryers 66 is configured to dry ink droplets during the formation of the ink images.

[0050] In an example configuration of system 10, primary dryer 64 includes an array of ten drying units arranged in a row parallel to the direction of travel of blanket 44. In this configuration, primary dryer 64 is configured to receive blanket 44 at any suitable temperature, for example, between about 60°C and about 100°C, and to raise the temperature of blanket 44 to any suitable temperature, for example, between about 110°C and about 150°C, after it has been heated by primary dryer 64.

[0051] As it passes through the primary dryer 64, the blanket 44 (with the ink image thereon) is exposed to IR radiation and may reach the aforementioned temperatures (e.g., about 140° C.). In some embodiments, the primary dryer 64 is configured to more completely dry the ink by evaporating most or all of the liquid carrier, leaving only a layer of resin and colorant on the surface of the blanket 44, which is heated to the point where it becomes a tacky ink film.

[0052] The structure and function of the primary dryer 64 is shown in detail, for example, in FIG. 4 below.

[0053] In some embodiments, system 10 includes a vertical dryer 96 having an assembly for pumping (e.g., using a vacuum) evaporated gas residue from the surface of blanket 44. Additionally or alternatively, vertical dryer 96 may include an air knife configured to blow compressed air (or any other suitable gas) onto the surface of blanket 44 to reduce the temperature of blanket 44 and / or remove said gas residue from the surface of blanket 44.

[0054] In some embodiments, processor 20 is configured to control the vacuum and / or air pressure in vertical dryer 96 to achieve a desired cleanliness and / or temperature on the surface of blanket 44. Note that the cleanliness of the surface of blanket 44 is particularly important before the ink image printed on blanket 44 enters printing station 84, as described in detail herein.

[0055] In some embodiments, system 10 includes a blanket preheater 98 that includes an IR radiation source (not shown) having an exemplary length of approximately 1120 mm, or any other suitable length. The IR heat source may include any suitable product meeting a specified power density (depending on the application), such as those supplied by Heraeus (Hanau, Germany) or Helios (Novazzano, Switzerland). In such an embodiment, blanket preheater 98 is configured to uniformly heat blanket 44 to an exemplary temperature of approximately 75° C. to prepare blanket 44 for the ink image printing process (described above) performed by imaging station 60.

[0056] It should be noted that the various elements of the blanket module 70, such as the rollers 78, are typically maintained at room temperature (e.g., 25° C.) or any other suitable temperature, which is typically lower than the temperature required to dry the ink jetted on the surface of the blanket 44. As a result, the blanket 44 is cooled as it rotates along these elements of the blanket module 70. In some embodiments, the processor 20 controls a vertical dryer 96 to complete ink drying (if necessary) before the blanket 44 enters the printing station 84, and further controls a blanket preheater 98 to maintain a specified temperature of the blanket 44 (e.g., about 75° C.) before it enters the imaging station 60.

[0057] In other embodiments, the blanket preheater 98 may include a blower (not shown) configured to supply and direct hot air to heat the surface of the blanket 44. The inventors have found that the use of IR radiation reduces the time (compared to hot air) for the blanket 44 to attain a specified temperature prior to receiving an ink image from the imaging station 60. The reduced time is particularly important during start-up of the system 10, thus improving the availability and productivity of the system 10. For example, the inventors have found that the blanket 44 can be heated to approximately 75° C. within a few (e.g., 5) minutes using IR radiation, or within about one-half hour using hot air.

[0058] In some embodiments, system 10 includes a blanket module 70 that includes blanket 44. In some embodiments, blanket module 70 includes one or more rollers 78, and at least one of rollers 78 may include an encoder (not shown) configured to record the position of blanket 44 in order to control the position of sections of blanket 44 relative to their respective print bars 62.

[0059] In some embodiments, the encoders for the rollers 78 typically include rotary encoders configured to generate rotary-based position signals indicative of the angular displacement of the respective rollers. Note that in the context of the present invention and claims, the terms "indicative of" and "indication" are used interchangeably.

[0060] In other embodiments, blanket module 70 may include any other suitable device for sensing and / or tracking the position of one or more reference points on blanket 44. For example, blanket 44 may include markers disposed on the blanket surface and / or engraved within the blanket. In such embodiments, system 10 may include a sensing assembly configured to sense the markers and transmit, for example, to processor 20, position signals indicative of the position of each marker on blanket 44.

[0061] In some embodiments, blanket 44 may include a woven fabric made of two or more sets of fibers interleaved with one another. The woven fabric has an opacity that varies according to the periodic pattern of the interleaved fibers. In some embodiments, system 10 may include an optical assembly (not shown) having a light source on one side of blanket 44 and a photodetector on the other side of blanket 44. The optical assembly is configured to illuminate blanket 44 with light, detect the light that passes through the woven fabric, and derive one or more position signals from the detected light that indicate one or more respective positional reference points (e.g., fibers) within the periodic pattern of the woven fabric.

[0062] In some embodiments, based on the signals, processor 20 is configured to control the printing process and monitor the status of various elements of system 10 , such as blanket 44 .

[0063] Additionally or alternatively, blanket 44 may include any suitable type of embedded encoder (not shown) for controlling the operation of various modules of system 10. One embodiment of an embedded encoder is described in detail, for example, in U.S. Provisional Application No. 62 / 689,852, the disclosure of which is incorporated herein by reference.

[0064] In some embodiments, blanket 44 is guided over roller 78, as well as a powered tensioning roller, also referred to herein as dancer assembly 74. Dancer assembly 74 is configured to control the amount of slack in blanket 44, its movement being represented diagrammatically by a double-headed arrow. Furthermore, any stretching of blanket 44 due to aging will not affect the ink image placement performance of system 10 and will simply require further slack removal by tensioning dancer assembly 74. In some embodiments, dancer assembly 74 may be motorized.

[0065] The configuration and operation of roller 78 is described in further detail, for example, in U.S. Patent Application Publication No. 2017 / 0008272 and the aforementioned PCT International Publication No. WO2013 / 132424, the disclosures of which are incorporated herein by reference in their entireties.

[0066] In other embodiments, the dancer assembly 74 may include an air-based dancer assembly (not shown) that includes an air chamber and a lightweight roller mounted within the air chamber. The air chamber may include an air inlet and an opening sized and shaped to fit snugly over the roller. The air-based dancer assembly may include a controllable blower (other than the aforementioned blower of the temperature control assembly 121) configured to supply compressed air to the air chamber through a given air inlet. The compressed air applies uniform pressure to the roller, moving it along the longitudinal axis of the air chamber. As a result, the roller may protrude from the air chamber through the opening, tensioning the blanket 44 while being rotated by the blanket 44. Air-based dancer assemblies are further described, for example, in U.S. Provisional Application No. 62 / 889,069, the disclosure of which is incorporated herein by reference.

[0067] In some embodiments, system 10 may include one or more tension sensors (not shown) positioned at one or more locations along blanket 44. The tension sensors may be integrated within blanket 44 or may include sensors external to blanket 44 using any other suitable technique for obtaining signals indicative of the mechanical tension applied to blanket 44. In some embodiments, processor 20 and additional controllers of system 10 are configured to receive signals generated by the tension sensors to monitor the tension applied to blanket 44 and to control the operation of dancer assembly 74.

[0068] At the printing station 84, the blanket 44 passes between an impression cylinder 82 and a pressure cylinder 90, which is configured to transport a compressible blanket.

[0069] In some embodiments, the system 10 includes a control console 12 configured to control multiple modules of the system 10, such as a blanket module 70, an image forming station 60 disposed above the blanket module 70, and a substrate transport module 80 disposed below the blanket module 70 and including one or more printing stations, as described below.

[0070] In some embodiments, the console 12 includes a processor 20, typically a general-purpose computer, with appropriate front-end and interface circuitry for interfacing with and receiving signals from the controllers 54 and the dancer assemblies 74 via an electrical cable, referred to herein as cable 57.

[0071] In some embodiments, controller 54, shown diagrammatically as a single device, may include one or more electronic modules mounted in predetermined locations on system 10. At least one of the electronic modules of controller 54 may include an electronic device, such as a control circuit or processor (not shown), that is configured to control the various modules and stations of system 10. In some embodiments, processor 20 and control circuitry may be programmed with software to perform functions used by the printing system, and data for the software may be stored in memory 22. The software may be downloaded in electronic form to processor 20 and control circuitry, for example, via a network, or it may be provided on a non-transitory, tangible medium, such as an optical, magnetic, or electronic memory medium.

[0072] In some embodiments, console 12 includes a display 34 configured to display data and images received from processor 20 or input inserted by a user (not shown) using input device 40. In some embodiments, console 12 may have any other suitable configuration, for example, alternative configurations of console 12 and display 34 are described in detail in U.S. Pat. No. 9,229,664, the disclosure of which is incorporated herein by reference.

[0073] In some embodiments, the processor 20 is configured to display on the display 34 the digital image 42 including one or more segments (not shown) of the image 42 and / or various types of test patterns that may be stored in the memory 22.

[0074] In some embodiments, the blanket treatment station 52 is configured to treat the blanket, for example, by cooling the blanket and / or applying a treatment fluid to the outer surface of the blanket 44 and / or cleaning the outer surface of the blanket 44. In the blanket treatment station 52, the temperature of the blanket 44 can be reduced to a desired temperature value. Treatment can be performed by passing the blanket 44 over one or more rollers or blades configured to cool and / or clean and / or apply a treatment fluid to the outer surface of the blanket.

[0075] In some embodiments, the blanket treatment station 52 may be located adjacent to the printing station 84. Additionally or alternatively, the blanket treatment station may include one or more bars (not shown) adjacent to the print bar 62. In this configuration, the treatment fluid may be applied to the blanket 44 by jets.

[0076] In some embodiments, system 10 includes one or more temperature sensors 92, in this example sensors 92A, 92B, 92C, and 92D, positioned at one or more respective given positions relative to blanket 44 and configured to generate a signal indicative of the surface temperature of blanket 44, also referred to herein as a "temperature signal."

[0077] In some embodiments, at least one of temperature sensors 92A-92D may include an IR-based temperature sensor configured to sense temperature-based IR radiation emitted from the surface of blanket 44. In other embodiments, at least one of temperature sensors 92A-92D may include any other suitable type of temperature sensor.

[0078] In the example configuration of FIG. 1, system 10 includes: (i) a first temperature sensor 92A positioned in close proximity to a blanket tension drive roller, referred to herein as roller 78A; (ii) a second temperature sensor 92B positioned between the first print bar 62 and the first dryer, referred to herein as preheater 66A; (iii) a third temperature sensor 92C positioned between the right-most print bar 62 (in the direction of travel) and the main dryer 64; and (iv) a fourth temperature sensor 92D positioned in close proximity to a blanket control drive roller, referred to herein as roller 78B.

[0079] In some embodiments, temperature sensor 92A, located between blanket preheater 98 and imaging station 60, is configured to sense the temperature of blanket 44 before it enters imaging station 60. In one embodiment, temperature sensor 92B is positioned after preheater 66A (in the direction of travel indicated by arrow 94) to measure the temperature of blanket 44 before it enters the first print bar.

[0080] In some embodiments, the controller 54 and / or the processor 20 are configured to receive temperature signals from one or more of the aforementioned temperature sensors and control the printing process based on the received temperature signals, as described in more detail below.

[0081] In other embodiments, the temperature signal from temperature sensor 92B may be sufficient to control the initiation of a new cycle of the printing process performed by image forming station 60, and therefore temperature sensor 92A may be redundant and therefore removed from the configuration of system 10.

[0082] It should be noted that the temperature of blanket 44 is important to the quality of the printing process performed by imaging station 60. In some embodiments, the temperature of blanket 44 is set to a predetermined temperature (e.g., about 70°C) to (i) dry the ink droplets of the first color applied to the ITM by the first print bar, and (ii) return the blanket temperature (cooled by the ink droplets, which have a typical temperature of about 30°C or 35°C) to the predetermined temperature of about 70°C.

[0083] In some embodiments, in response to heating the blanket, a controlled amount of vapor of the first printing fluid (e.g., ink) typically evaporates from the blanket surface without adhering to the nozzles of any print bar 62. Furthermore, based on the desired coloration of the ink image, the temperature of the first ink is controlled by the temperature of the blanket, such that after applying ink droplets of a second color, the ink droplets of the first and second colors intermix to form the desired color on the surface of the release layer of blanket 44.

[0084] In an example configuration of system 10, temperature sensors 92A-92D are positioned after every event or substep of the printing process that affects or may affect the temperature of blanket 44. In some embodiments, based on the temperature signals received from the temperature sensors, processor 20 (and / or controller 54) is configured to control a power supply (not shown) to adjust the power density applied to one or more infrared sources (e.g., shown in FIG. 3 below) of each heater.

[0085] In such an embodiment, processor 20 is configured to adjust the power density applied to the dryers using closed-loop techniques in both feedback and feedforward modes. The term "feedback" refers to adjusting the power density in a given dryer based on a temperature measured after using the dryer to achieve a desired temperature in a subsequent section of the blanket. The term "feedforward" refers to adjusting the power density based on a temperature measured before using the dryer to correct for deviations from a desired temperature. In the example configuration of FIG. 1 , processor 20 is configured to control the power density applied to one or more IR source(s) of preheaters 98 and 66A based on the temperature signal received from temperature sensor 92A using closed-loop feedback and feedforward modes, respectively. For example, if the signal received from sensor 92A indicates that the temperature of the first section of blanket 44 is below a predetermined temperature of 70°C, processor 20 controls the power supply to: (i) increase the power density applied to preheater 66A to achieve 70°C in the first section of blanket 44 (using feedforward mode), and (ii) increase the power density applied to preheater 98 to achieve 70°C in the second section of blanket 44 following the first section (using feedback mode).

[0086] In some embodiments, after adjusting the power density applied to the power supply(s) of preheater 66A, processor 20 receives a temperature signal from temperature sensor 92B. In the case where the temperature is approximately 70°C, processor 20 enables the first print bar of imaging station 60 to apply droplets of the first ink to blanket 44. However, in the case where the temperature measured by temperature sensor 92B is significantly different from approximately 70°C (e.g., approximately 50°C), processor 20 prevents the print bar of imaging station 60 from applying ink droplets to blanket 44 and controls the power supply to adjust the blanket temperature to a predefined temperature of approximately 70°C. Only after attaining 70°C, processor 20 controls imaging station 60 to resume the printing process using print bar 62, as described above.

[0087] In some embodiments, using the techniques described above, processor 20 is configured to (i) control the power density applied to main dryer 64 based on the temperature signal received from temperature sensor 92C, and (ii) control the power density applied to vertical dryer 96 based on the temperature signal received from temperature sensor 92D. Additionally or alternatively, processor 20 may use the signal received from temperature sensor 92D to adjust the power density applied to main dryer 64.

[0088] In some embodiments, in response to receiving the temperature signal, processor 20 is configured to control the temperature of the blanket by adjusting the flow rate of compressed air in the airflow channel, as shown and described in more detail in FIGS. 3 and 4 below. Note that processor 20 is configured to perform closed-loop control on the associated blowers of system 10 using feedforward and feedback techniques. For example, if the measured temperature is above the desired temperature of blanket 44, processor 20 is configured to control the blowers to increase the flow of compressed air applied to blanket 44. Similarly, if the measured temperature is below the desired temperature of blanket 44, processor 20 is configured to control the blowers to decrease the flow of compressed air applied to blanket 44.

[0089] In some embodiments, processor 20 is configured to simultaneously control both the intensity of IR radiation (by adjusting the power density supply) and the flow of compressed air to control the temperature of blanket 44. For example, in response to receiving a signal from temperature sensor 92D indicating that the temperature of blanket 44 is significantly different from approximately 140° C., processor 20 may control at least one of main dryer 64 and vertical dryer 96 to adjust the intensity of IR radiation and / or the flow of compressed air to achieve a specified temperature of approximately 140° C. on blanket 44.

[0090] In other embodiments, based on the aforementioned temperature signals, processor 20 is further configured to control the operation of other assemblies and stations of system 10, such as, but not limited to, blanket processing station 52. Examples of such processing stations are described, for example, in PCT International Publication Nos. WO 2013 / 132424 and WO 2017 / 208152, the disclosures of which are incorporated herein by reference in their entireties.

[0091] Additionally or alternatively, treatment fluid may be applied to blanket 44 by jetting prior to ink jetting at the imaging stations.

[0092] 1, station 52 is mounted between impression station 84 and imaging station 60, although station 52 may be mounted adjacent blanket 44 in any other or additional suitable location or locations between impression station 84 and imaging station 60. As previously mentioned, station 52 may additionally or alternatively include a bar adjacent imaging station 60.

[0093] In the example of FIG. 1, impression cylinder 82 presses an ink image onto a target flexible substrate, such as an individual sheet 50 , conveyed by substrate transport module 80 from an input stack 86 to an output stack 88 via impression cylinder 82 .

[0094] In some embodiments, the lower run of blanket 44 selectively interacts with impression cylinder 82 at impression station 84 to impress an image pattern onto a target flexible substrate compressed between blanket 44 and impression cylinder 82 under the pressure of pressure cylinder 90. For the simplex printer shown in FIG. 1 (i.e., printing on one side of sheet 50), only one impression station 84 is required.

[0095] In other embodiments, module 80 may include two or more impression cylinders to enable one or more duplex printing runs. A two-impression cylinder configuration also allows for single-sided printing to be performed at twice the speed of duplex printing. In addition, mixed lots of single-sided and double-sided prints can be printed. In alternative embodiments, a different configuration of module 80 may be used for printing on continuous web substrates. Detailed descriptions and various configurations of duplex printing systems and systems for printing on continuous web substrates are provided, for example, in U.S. Pat. Nos. 9,914,316 and 9,186,884, PCT International Publication No. WO 2013 / 132424, U.S. Patent Application Publication No. 2015 / 0054865, and U.S. Provisional Application No. 62 / 596,926, the disclosures of which are incorporated herein by reference in their entirety.

[0096] As briefly described above, a sheet 50 or continuous web substrate (not shown) is conveyed by module 80 from an input stack 86 and passes through a nip (not shown) located between impression cylinder 82 and pressure cylinder 90. Within the nip, the surface of blanket 44 carrying the ink image is pressed firmly against sheet 50 (or other suitable substrate) by, for example, a compressible blanket (not shown) of pressure cylinder 90, thereby imprinting the ink image onto the surface of sheet 50 and cleanly separating it from the surface of blanket 44. Sheet 50 is then conveyed to output stack 88.

[0097] 1, roller 78 is positioned on the upper run of blanket 44 and is configured to keep blanket 44 taut as it passes adjacent to imaging station 60. Furthermore, it is particularly important to control the speed of blanket 44 under imaging station 60 to obtain accurate jetting and deposition of ink droplets onto the surface of blanket 44, and thereby placement of the ink image, by imaging station 60.

[0098] In some embodiments, the impression cylinder 82 is periodically engaged and disengaged from the blanket 44 to transfer the ink image from the moving blanket 44 to a target substrate passing between the blanket 44 and the impression cylinder 82. In some embodiments, the system 10 is configured to apply torque to the blanket 44 using the roller and dancer assembly described above to maintain the upper run taut and substantially isolate the upper run of the blanket 44 from being affected by mechanical vibrations occurring in the lower run.

[0099] In some embodiments, system 10 includes an image quality control station 55, also referred to herein as an automated quality control (AQM) system, which functions as a closed-loop inspection system integrated within system 10. In some embodiments, station 55 may be located adjacent impression cylinder 82, as shown in FIG. 1, or at any other suitable location within system 10.

[0100] In some embodiments, station 55 includes a camera (not shown) configured to acquire one or more digital images of the aforementioned ink images printed on sheet 50. In some embodiments, the camera may include any suitable image sensor, such as a contact image sensor (CIS) or a complementary metal oxide semiconductor (CMOS) image sensor, and a scanner including a slit having a width of about 1 meter or any other suitable width.

[0101] In the context of this disclosure and in the claims, the term "about" or "approximately" in connection with any numerical value or range indicates an appropriate dimensional tolerance that enables a part or collection of components to function for its intended purpose as described herein. For example, "about" or "approximately" may refer to a range of values of ±20% of the recited value, e.g., "about 90%" may refer to a range of values of 72% to 100%.

[0102] In some embodiments, station 55 may include a spectrophotometer (not shown) configured to monitor the quality of the ink printed on sheet 50 .

[0103] In some embodiments, digital images acquired by station 55 are transmitted to a processor, such as processor 20 or any other processor in station 55, which is configured to evaluate the quality of each printed image. Based on that evaluation and signals received from controller 54, processor 20 is configured to control the operation of the modules and stations of system 10. In the context of the present invention and claims, the term "processor" refers to any processing device, such as processor 20 or any other processor or controller connected to or integrated with station 55, that is configured to process signals received from the camera and / or spectrophotometer in station 55. It should be noted that the signal processing operations, control-related instructions, and other computational operations described herein may be performed by a single processor or distributed among multiple processors in one or more respective computers.

[0104] In some embodiments, station 55 is configured to inspect the quality of printed images and test patterns to monitor various attributes, such as, but not limited to, perfect image registration with sheet 50, color-to-color (C2C) registration, printed geometry, image uniformity, color profile and linearity, and print nozzle functionality. In some embodiments, processor 20 is configured to automatically detect geometric distortions or other errors in one or more of the aforementioned attributes. For example, processor 20 is configured to compare between a design version of a given digital image (also referred to herein as a “master” or “source image”) and a digital image of a printed version of the given image, acquired by a camera.

[0105] In other embodiments, processor 20 may apply any suitable type of image processing software, for example, to a test pattern, to detect distortions indicative of the aforementioned errors. In some embodiments, processor 20 is configured to analyze the detected distortions to apply corrective action to the malfunctioning module and / or provide instructions to another module or station of system 10 to correct the detected distortions.

[0106] In some embodiments, processor 20 is configured to detect deviations in the profile and linearity of the printed colors based on signals received from the spectrophotometer of station 55 .

[0107] In some embodiments, processor 20 is configured to detect various types of defects based on signals acquired by station 55: (i) defects in the substrate (e.g., blanket 44 and / or sheet 50), such as scratches, pinholes, and damaged edges, and (ii) printing-related defects, such as irregular color spots, satellites, and splashes.

[0108] In some embodiments, processor 20 is configured to detect these defects by comparison between sections of the print and respective reference sections of the original design, also referred to herein as the master. Processor 20 is further configured to classify the defects and, based on the classification and predetermined criteria, reject sheets 50 having defects that are not within the specified predetermined criteria.

[0109] In some embodiments, the processor of station 55 is configured to determine whether to stop operation of system 10, for example, if the defect density exceeds a specified threshold. The processor of station 55 is further configured to initiate corrective action in one or more of the modules and stations of system 10, as described above. The corrective action may be performed on the fly (while system 10 continues the printing process) or offline by stopping printing operations and correcting the problem within the respective module and / or station of system 10. In other embodiments, any other processor or controller of system 10 (e.g., processor 20 or controller 54) is configured to initiate corrective action or stop operation of system 10 if the defect density exceeds a specified threshold.

[0110] Additionally or alternatively, processor 20 may be configured to receive signals, e.g., from station 55, indicative of additional types of defects and problems in the printing process of system 10. Based on these signals, processor 20 may be configured to automatically estimate the pattern placement accuracy and the level of additional types of defects not previously described. In other embodiments, any other suitable method for inspecting patterns printed on sheet 50 (or on any other substrate previously described) may also be used, e.g., using an external (e.g., offline) inspection system, or any type of measurement fixture and / or scanner. In these embodiments, based on information received from the external inspection system, processor 20 may be configured to initiate any appropriate corrective action and / or to stop operation of system 10.

[0111] The configuration of system 10 is provided in a simplified manner purely as an example to clarify the present invention. The components, modules, and stations described in the foregoing printing system 10, as well as additional components and configurations, are described in detail in, for example, U.S. Patent Nos. 9,327,496 and 9,186,884, PCT International Publication Nos. WO2013 / 132438, WO2013 / 132424, and WO2017 / 208152, and U.S. Patent Application Publication Nos. 2015 / 0118503 and 2017 / 0008272, the disclosures of which are incorporated herein by reference in their entirety.

[0112] The particular configuration of system 10 is shown as an example to illustrate the particular problem addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such systems, but embodiments of the present invention are in no way limited to this particular type of example system, and the principles described herein may be applied to any other type of printing system as well.

[0113] For example, in other embodiments, dryer 66 and / or blanket preheater 98 may include two or more IR radiation sources. Similarly, primary dryer 64 may include any other suitable number of drying units or any other suitable type of ink drying device.

[0114] In alternative embodiments, at least one of the dryers may include a radiation source configured to emit radiation other than IR, such as near-infrared, visible light, ultraviolet (UV), or any other suitable wavelength or range of wavelengths.

[0115] 2 is a schematic side view of a digital printing system 110 according to some embodiments of the present invention. In some embodiments, the system 110 includes the imaging station 160, and the drying station 64, vertical dryer 96, blanket preheater 98, and blanket 44 circulating through the blanket treatment station 52, as described in FIG. 1 above.

[0116] In some embodiments, system 110 is configured to transfer the ink image from the moving blanket 44 to a continuous flexible web substrate, referred to herein as web 51, which is the target substrate for system 110. In such embodiments, system 110 includes a substrate transport module 100, which is configured to transport web 51 from a pre-print buffer unit 186, through one or more printing stations 85 for receiving the ink image from blanket 44, and to a post-print buffer unit 188.

[0117] Each printing station 85 may have any configuration suitable for transferring an ink image from the blanket 44 to the web 51. In some embodiments, a lower run of the blanket 44 may selectively interact with an impression cylinder 192 at the printing station 85 to press an image pattern onto the web 51 compressed between the blanket 44 and the impression cylinder 192 under the pressure of the pressure cylinder 190. For a simplex printer (i.e., printing on one side of the web 51) as shown in FIG. 2, only one printing station 85 is required. For duplex printing (i.e., printing on both sides of the web 51), not shown in FIG. 2, the system 110 may include, for example, two printing stations 85.

[0118] In some embodiments, the substrate transport module 100 may have any suitable configuration for transporting the web 51. One example implementation is described in detail in U.S. Provisional Application No. 62 / 784,576 (Applicant Docket No. LCP16 / 001, Attorney Docket No. 1373-1009), the disclosure of which is incorporated herein by reference.

[0119] In some embodiments, web 51 comprises one or more layers of any suitable material, such as aluminum foil, paper, polyester (PE), polyethylene terephthalate (PET), biaxially oriented polypropylene (BOPP), oriented polyamide (OPA), biaxially oriented polyamide (BOPA), other types of oriented polypropylene (OPP), shrink film, also referred to herein as polymeric plastic film, or any other material suitable for flexible packaging in the form of a continuous web, or any suitable combination thereof, for example, in a multi-layer structure. Web 51 can be used in a variety of applications, such as, but not limited to, food packaging, plastic bags and tubes, labels, decoration, and flooring.

[0120] In some embodiments, imaging station 160 typically includes multiple print bars 62, each mounted (e.g., using sliders) on a frame (not shown) positioned at a fixed height above the surface of the upper run of blanket 44. In some embodiments, as also described above in FIG. 1 , each print bar 62 includes multiple print heads arranged to cover the width of the print area on blanket 44, each print head including individually controllable print nozzles.

[0121] In some embodiments, the imaging station 160 may include any suitable number of print bars 62, and each print bar 62 may include a printing fluid as described above, such as a water-based ink. The inks typically have visible colors such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. In the example of FIG. 2, the imaging station 160 includes a white print bar 61 and four print bars 62 having any selected color, such as cyan, magenta, yellow, and black.

[0122] In some printing applications, white ink is applied to the surface of web 51 before all other colors, and in some cases it is important that the white color does not mix with the other color inks within at least some sections of web 51.

[0123] In some embodiments, system 110 includes a white ink drying station, referred to herein as white dryer 97, which is configured to dry the white ink applied to the surface of blanket 44 by imaging station 160. In such an embodiment, white dryer 97 may include five drying units, each of which includes a combination of the aforementioned IR-based heater for heating blanket 44 and one or more airflow channels for cooling blanket 44.

[0124] In other embodiments, the white dryer 97 may include any other configuration suitable for drying white ink, for example, the white dryer 97 may include any other number of drying units or may include any other suitable drying device using any other suitable drying technology.

[0125] In one embodiment, the white dryer 97 is controlled by the processor 20 and / or the controller 54 and is configured to dry the white ink applied to the surface of the blanket 44 by the white print bar 61. In this embodiment, the processor 20 and / or the controller 54 is configured to control the white dryer 97 to partially or completely dry the white ink applied to the surface of the blanket 44.

[0126] In the configuration of system 110, the white dryer 97 replaces one dryer 66 used to dry any color ink other than white. It should be noted that in this configuration, system 110 does not have a print bar between the white dryer 97 and the first dryer 66, but in other embodiments, system 110 may have any suitable printing component (e.g., a print bar) or sensing component (e.g., a temperature sensor or any other type of sensor) between the white dryer 97 and the first dryer 66.

[0127] In other embodiments, the system 110 may include any other suitable type of dryer for drying or partially drying ink of any particular color other than white.

[0128] In other printing applications, white ink may be applied to the surface of web 51 after all other colors. In alternative embodiments, white ink may be applied to the surface of web 51 using a subsystem external to or integrated into system 110. In such embodiments, white ink is applied to the surface of web 51 before or after other colors are applied to the surface of blanket 44 using imaging station 160, and particularly before or after other colors are applied to the surface of web 51 in impression station 85.

[0129] In some embodiments, temperature sensor 92B is positioned between the aforementioned first dryer 66 and print bar 62 to check the surface temperature of blanket 44 before print bar 62 is used to apply ink having a color other than white. Additionally, temperature sensor 92B is positioned between the last print bar of imaging station 160 and main dryer 64. Note that temperature sensors 92A, 92C, and 92D are positioned in the same locations in both system 110 and system 10 of FIG. 1 above. However, temperature sensor 92B is positioned along the path of blanket 44 after printing and drying white (in this example, after print bar 61 and dryer 97) and before the first print bar 62 of a color other than white (e.g., cyan, magenta, yellow, black, or any other color).

[0130] In some embodiments, temperature sensors 92B, 92C and 92D are positioned after processing substeps that typically affect or may affect the temperature of blanket 44, as also described in FIG. 1 above.

[0131] In some embodiments, system 110 may include a drying station, referred to herein as bottom dryer 75, that is configured to emit infrared light or light of any other suitable frequency or range of frequencies to dry ink images formed on blanket 44 using the techniques described above. In the example of FIG. 2, bottom dryer 75 may include five drying units, each of which includes a combination of the aforementioned IR-based heaters for heating blanket 44 and one or more airflow channels for cooling blanket 44.

[0132] In some embodiments, the system 110 includes a temperature sensor 92E located between the bottom dryer 75 and the printing station 85, typically in close proximity to the bottom dryer 75.

[0133] In some embodiments, processor 20 (and / or controller 54) is configured to control the power supplies (not shown) described in FIG. 1 above to adjust the power density applied to one or more infrared sources (shown in FIGS. 3 and 4 below) of each heater and / or dryer to maintain a predefined temperature of blanket 44 along each section of system 110.

[0134] 1 above, processor 20 (and / or controller 54) is configured to perform closed-loop control over the temperature profile of blanket 44 along each section of system 110. The control is performed based on temperature signals received from at least one of temperature sensors 92A-92E, and based on the temperature signals, processor 20 controls the power density applied to the IR power sources of each IR-based heater (e.g., heater 98 and one or more of dryers 97, 66, 64, 96, and 75).

[0135] In other embodiments, the bottom dryer 75 may include any other suitable configuration suitable for drying the ink on the bottom run of the blanket 44 before the blanket enters the printing station 85 .

[0136] In some embodiments, processor 20 and / or controller 54 are configured to control each dryer of system 10 (shown in FIG. 1) and system 110 (shown in FIG. 1), respectively.

[0137] Control can be performed based on various conditions of a particular digital printing application, such as based on the type, sequence and surface coverage level of colors applied to the surface of the blanket 44, based on the type of blanket 44 and target substrate (e.g., sheet 50 or web 51).

[0138] The term "coverage level" refers to the amount of color applied to the surface of the blanket 44. For example, a 250% coverage level refers to a two-and-a-half times ink layer applied to a predefined section (or entire area) of the ink image printed on the blanket 44 and then designated for transfer to a target substrate. Note that a two-and-a-half times ink layer may include three or more of the aforementioned color inks described above. It will be understood that greater coverage levels typically require a greater flux of IR irradiation and, therefore, a higher air flow for cooling the blanket 44.

[0139] In other embodiments, the ink drying process may be performed open loop, e.g., without controlling at least one of (a) the intensity of the IR radiation and (b) the flow rate of compressed air by the temperature control assembly 121. For example, as part of a process recipe for printing a particular image, the recipe parameters may include an ink image coverage level, and the processor 20 and / or controller 54 may preset, via the temperature control assembly 121, one or more of (a) the intensity of the IR radiation and (b) the flow rate of compressed air to dry the ink and maintain the temperature of the blanket 44 below a specified temperature (e.g., about 140° C. or about 150° C.).

[0140] The particular configuration of system 110 is shown as an example to illustrate the particular problem addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such systems, but embodiments of the present invention are in no way limited to this particular type of example system, and the principles described herein may be applied to any other type of printing system as well.

[0141] Drying unit installed inside the image fixing unit 3 is a schematic side view of a dryer 66 for drying ink applied by print bar 62, in accordance with one embodiment of the present invention. In some embodiments, dryer 66 includes a single drying unit, such as the drying unit briefly described in FIG. 1 above and further described in detail herein.

[0142] In some embodiments, the dryer 66 has a blower and includes one or more openings to an air inlet channel (AIC) 122 configured to supply compressed air 101 (or any other type of suitable gas) to the dryer 66.

[0143] In some embodiments, the dryer 66 further includes one or more openings to an air outlet channel (AOC) 123 with an air extraction device (e.g., a suitable type of vacuum or negative pressure pump) configured to extract the compressed air 101 after at least cooling of the blanket 44, as described herein.

[0144] In the concepts and claims of the present disclosure, the term "temperature control assembly" refers to at least one or a combination of AIC 122 and AOC 123, configured to direct compressed air 101 (or any other suitable type of gas) toward the outer surface 106 of blanket 44 to reduce the temperature of blanket 44 to below a specified temperature (e.g., about 140°C or about 150°C), as described herein.

[0145] In some embodiments, dryer 66 is typically located within image-forming station 60, and primary dryer 64 is located between image-forming station 60 and impression station 84 to perform a drying process on the ink image applied to blanket 44 before the ink image is transferred to a target substrate (e.g., sheet 50) in impression station 84. Note that temperature control assembly 121 is configured to supply compressed air 101 to dryer 66 and primary dryer 64, for example, via pipes or tubing (not shown), to control the temperature of blanket 44 within the aforementioned specified temperature range. In other embodiments, system 10 may include multiple AICs 122 and / or AOCs 123, for example, a first set of AICs 122 and AOCs 123 for dryer 66 and a second set of AICs 122 and AOCs 123 for primary dryer 64. In alternative embodiments, system 10 may include any other suitable configuration of AICs 122 and / or AOCs 123 controlled by processor 20 and / or by a local controller synchronized with and / or controlled by processor 20.

[0146] In some embodiments, dryer 66 includes one or more IR-based heaters, illumination assemblies 113 having IR radiation sources, in this example simply referred to as sources 111. In the example of FIG. 3, dryer 66 includes two pairs of sources 111 disposed within two respective cavities of dryer 66. Each source 111 is configured to direct rays 99 of IR radiation toward blanket 44. For example, each source 111 is configured to emit a power density of between about 30 watts / cm and about 300 watts / cm toward surface 106 of blanket 44.

[0147] In other embodiments, dryer 66 may include any other suitable number of sources 111 (or one or more light sources of any other suitable type configured to emit IR or other suitable one or more wavelengths of light) having any suitable geometry and arranged in any suitable configuration.

[0148] In some embodiments, dryer 66 may include one or more reflectors 108 coupled between source 111 and the cavity of dryer 66. Reflector 108 is configured to reflect light rays 99 emitted from source 111 toward blanket 44 to improve the efficiency and speed of the IR-based drying process and to reduce the amount of IR radiation (and therefore excess heating) applied to dryer 66 by light rays 99.

[0149] For example, each reflector 108 may reflect approximately 90% of the light rays 99 toward the blanket 44 and absorb the remaining 10%, which may increase the temperature in the cavity of the dryer 66 .

[0150] In some embodiments, dryer 66 includes a heat transfer assembly (HTA) 104, which includes a thermally conductive material (e.g., copper, aluminum, or other metallic or non-metallic material) disposed as thermally conductive ribs and traces around a reflector 108. HTA 104 is configured to dissipate excess heat from each cavity of dryer 66.

[0151] In the example configuration of dryer 66, compressed air 101 enters dryer 66 via AIC 122 at an exemplary temperature of about 30° C., or any other suitable temperature between about 5° C. and about 100° C. The compressed air 101 then flows through internal channels of dryer 66 to transport heat (e.g., by thermal convection) from HTA 104, and is then directed through openings 95 of dryer 66 to locations 102 on surface 106. The compressed air 101 flows over surface 106 to transfer heat from blanket 44, and AOC 123 then withdraws compressed air 101 from surface 106 via air outlet passages 112 of dryer 66 to maintain the temperature of blanket 44 below the aforementioned specified temperature.

[0152] As shown in FIGS. 1-3 , the dryer 66 may be positioned adjacent to a print bar 62, typically between two adjacent print bars 62. In some embodiments, the dryer 66 is configured to extract the compressed air 101 via an air outlet passage 112 so that the compressed air 101 does not physically contact any of the print bars 62. Note that the compressed air 101 contains vapors of ink components that may interact with the printing process. For example, such vapors may partially or completely block the nozzles of the print bars 62, which may degrade the quality of the printed image (e.g., defects including missing ink if the nozzles are completely blocked, or clusters of dried ink if the nozzles are partially blocked).

[0153] In some embodiments, the structure of dryer 66 prevents the incoming compressed air 101 from AIC 122 from mixing with the compressed air 101 flowing through openings 95 onto surface 106. As mentioned above, after flowing through openings 95, compressed air 101 is forced into AOC 123 via air outlet passage 112. In other words, the outgoing air, which may contain ink residue, and the incoming air for cooling surface 106 never mix with each other inside dryer 66.

[0154] In some embodiments, the light beam 99 is directed to the location 102 based on the location of the source 111 within the cavity of the dryer 66. Similarly, the dryer 66 is designed so that compressed air 101 is directed to the location 102 to cool the blanket 44. Each drying unit of the dryer 66 includes two sets of IR-based heating and compressed air-based cooling, with an air outlet passage 112 between them. Note that in this configuration, to prevent contact between the compressed air 101 and the print bar 62, the compressed air 101 flows from the side of the dryer 66 toward the blanket 44 and exits from the blanket 44 through the air outlet passage 112, which is located in the center of the dryer 66.

[0155] In some embodiments, distance 131, which is the distance between dryer 66 and surface 106, can be used to control the amount of IR-based heating and air-based cooling. In principle, a smaller distance 131 accelerates the heating rate of blanket 44. In other words, when distance 131 is small, blanket 44 reaches a specified temperature (e.g., about 140° C. or about 150° C.) more quickly in response to IR-based heating, resulting in faster drying of the ink on the surface of blanket 44.

[0156] In some embodiments, distance 131 may be predetermined, for example, when mounting dryer 66 on the frame of system 10 and / or system 110. In other embodiments, distance 131 may be controlled, for example, using any suitable mount for moving dryer 66 relative to blanket 44.

[0157] In some embodiments, by controlling the distance 131, the processor 20 can control the intensity and uniformity of the power density applied by the source 111 to a given section of the blanket 44. For example, a greater distance 131 may result in a lesser power density being applied to a given section of the blanket 44, but may improve the uniformity of heating within and in the immediate vicinity of that given section. Similarly, the proximity between the blanket 44 and the dryer 66 can affect the level of cooling by the dryer 66. For example, a greater distance 131 reduces the effectiveness of the compressed air 101 in cooling the blanket surface.

[0158] As previously mentioned, print bar 62, positioned adjacent dryer 66, ejects ink droplets onto blanket 44 as blanket 44 is moved in the direction indicated by arrow 94. In some embodiments, described in further detail in FIG. 6 below, dryer 66 and blanket are designed such that light beam 99 is configured to heat blanket 44, the increased temperature inducing evaporation of the ink's liquid carrier to dry or partially dry the ink on surface 106. Note that light beam 99 is not directed at the ink for evaporation, but rather at blanket 44 to increase the temperature of the blanket. Similarly, compressed air 101 is directed at blanket 44 by AIC 122 and extracted from the blanket by AOC 123 to reduce the temperature of blanket 44.

[0159] The particular configuration of the drying unit of dryer 66 is provided as an example to illustrate certain problems addressed by embodiments of the present invention, such as partial drying of ink images applied to blanket 44 and blanket cooling, and to demonstrate the application of these embodiments in enhancing the performance of digital printing systems such as the aforementioned systems 10 and 110. However, embodiments of the present invention are in no way limited to this particular configuration and type of example drying unit, and the principles described herein may likewise be applied to any other type of drying unit in a digital printing system or any other type of printing system.

[0160] In other embodiments, compressed air 101 may be used only to reduce the temperature of blanket 44 , while a separate (eg, dedicated) cooling device may be used to cool HTA 104 .

[0161] Dryers containing multiple drying units 4 is a schematic side view of a primary dryer 64, in accordance with one embodiment of the present invention. In some embodiments, primary dryer 64 includes a plurality of drying units 222 and an air outlet passage 130 between each pair of adjacent drying units 222.

[0162] Referring now to inset 133, there is shown a pair of drying units 222 and the air outlet passage 130 disposed therebetween. Each drying unit 222 is disposed a distance 132 from the surface 106 of the blanket 44. Note that distance 132 may be different from distance 131 and may be controllable, for example, using the mount described in FIG. 3 above. Alternatively, distance 132 may be predetermined based on the distance between the frame of the imaging station and the position of the blanket 44.

[0163] In some embodiments, each drying unit 222 has two cavities, each with a pair of sources 111 of lighting assemblies 113 configured to direct light rays 99 to heat blanket 44 using the techniques described for dryer 66 in FIG. 3 above. Drying unit 222 further includes a heat transfer assembly (HTA) 124 with the same cooling function as HTA 104 but with a different structure that matches the structure of drying unit 222.

[0164] In some embodiments, compressed air 101 enters dryer unit 222 via AIC 122 at an exemplary temperature of about 30° C., or any other suitable temperature, for example, as described in FIG. 3 above, and flows through HTA 124 to cool dryer unit 222. Compressed air 101 then exits dryer unit 222 through opening 195, is directed toward blanket 44, and is pumped from blanket 44 via air outlet passage 130 toward AOC 123 using the same technique as described in FIG. 3 above for dryer 66, to reduce the temperature of blanket 44.

[0165] It should be noted that in this configuration, compressed air 101 flows out from the center of the drying unit 222 towards the blanket 44 and is pumped out of the blanket 44 through an air outlet passage 130 located on the side of the drying unit 222.

[0166] 4, the main dryer 64 includes nine drying units 222 and two halves of drying units 222 at either end of the main dryer 64. In this configuration, the main dryer 64 includes ten air outlet passages 130, which improves the extraction of compressed air 101 compared to a set of ten full-size drying units 222 (not shown) having a total of nine air outlet passages 130.

[0167] In some embodiments, processor 20 and / or controller 54 are configured to receive a temperature signal from one or more of temperature sensors 92A-92E and, based on the temperature signal, control at least one of (a) the intensity of optical radiation applied to blanket 44 by one or more light sources, such as source 111, and (b) the flow rate of compressed air 101, or any other suitable gas, directed toward surface 106 of blanket 44.

[0168] In this example, the processor 20 and / or controller 54 are configured to control the IR light intensity and the flow rate of the compressed air 101 based on temperature signals received from temperature sensors positioned along the blanket 44. As mentioned above, the blanket 44 is typically cooled by the temperature of the surrounding environment. For example, the temperature of the surrounding air and rollers 78 may be substantially below 100° C. (e.g., any temperature between about 25° C. and 100° C.).

[0169] In some embodiments, the white dryer 97 and bottom dryer 75 of the system 110 may each include five drying units 222 arranged in a configuration similar to that of the main dryer 64, or using any other suitable configuration. In one embodiment, the blanket preheater 98 may include a single drying unit 222, or one dryer 66, or one or more sources 111 without an apparatus for flowing compressed air 111.

[0170] In some embodiments, the structure of the dryer units 222 prevents the incoming compressed air 101 from the AICs 122 from mixing with the compressed air 101 flowing through the openings 195 onto the surface 106. As mentioned above, after flowing through the openings 195, the compressed air 101 is forced into the AOCs 123 via air outlet passages 130 located between adjacent units 222. In other words, after flowing through the openings 195, the compressed air, which may contain ink residue, does not mix with the incoming air flowing through the dryer units 222.

[0171] The configuration of main dryer 64, white dryer 97, bottom dryer 75, drying unit 222, and air outlet passage 130 is provided as an example. In other embodiments, at least one of these dryers and units may have any other suitable configuration. For example, rather than having a central AIC 122 and AOC 123 and controlling the flow rate of compressed air 101 using valves (not shown), system 10 and / or system 110 may include multiple AICs 122 and / or AOCs 123 coupled to one or more of the aforementioned dryers.

[0172] Controlling the ink drying process 5 is a schematic, pictorial diagram of a blanket 500 used in a digital printing system in accordance with one embodiment of the present invention. Blanket 500 may replace, for example, blanket 44 in systems 10 and 110 shown in FIGS. 1-4 above.

[0173] In some embodiments, blanket 500 is moved in the direction of movement represented by arrow 94 to include sections 502 on which ink images are printed and sections 506 positioned between adjacent sections 502 and which do not receive ink droplets from the aforementioned print bars 61 and 62.

[0174] In some embodiments, blanket 500 has a width 510 of about 1040 mm to 1050 mm, section 502 has a length 504 of about 750 mm, and section 506 has a length 508 of about 750 mm.

[0175] In some embodiments, sources 111 are typically aligned along width 510, with at least some of sources 111 having a width of about 1120 mm to enable uniform heating along the entire width of blanket 500. In such embodiments, processor 20 and / or controller 54 are configured to control the movement of blanket 500 in the direction of arrow 94 at a predefined speed (e.g., about 1.7 meters per second) that maintains uniform heating of the entire area of blanket 500.

[0176] In some embodiments, the processor 20 and / or controller 54 are configured to control the temperature sensors 92 (e.g., temperature sensors 92A-92E) to measure the temperature of the blanket 500 at a predetermined frequency, in this example, approximately every 20 milliseconds. In such an embodiment, at a travel speed of 1.7 meters per second, each temperature sensor 92 measures the temperature of the blanket 500 at a frequency of approximately every 34 mm.

[0177] In some embodiments, processor 20 and / or controller 54 are configured to receive temperature signals 554 and 555 indicative of temperatures measured (e.g., by temperature sensor 92) at sections 502 and 506, respectively, of blanket 500. As explained above in FIG. 2 , blanket temperature depends, among other things, on the coverage level, which is the amount of ink applied to the blanket surface.

[0178] In the example of blanket 500, the coverage level in section 502 may vary according to the pattern of the ink image, while section 506, which does not receive ink from print bars 61 and 62, is expected to have a uniform temperature. Note that due to the latent heat of the ink deposited on section 502, at least a portion of the energy of light beam 99 is absorbed by the ink, making it less effective for directly heating blanket 500.

[0179] In some embodiments, when processor 20 and / or controller 54 receives temperature signals 554 and 555 from one or more of temperature sensors 92 (e.g., selected from temperature sensors 92A-92E), the temperature measured in section 506 is typically higher than the temperature measured in section 502.

[0180] In some embodiments, processor 20 and / or controller 54 is configured to determine the highest temperature of blanket 500 using any suitable analysis based on temperature signals 554 and 555. For example, processor 20 and / or controller 54 may store a predetermined amount (e.g., about 100) of the most recent temperature signals 554 and 555. Processor 20 and / or controller 54 may then select the temperature signals exhibiting the top three highest temperatures from among the stored signals and determine the highest temperature of blanket 500 by calculating the median of the top three highest temperatures.

[0181] In other embodiments, processor 20 and / or controller 54 may determine the maximum temperature of blanket 500 using any suitable analysis of temperature signals 554 and 555 .

[0182] In alternative embodiments, processor 20 and / or controller 54 are configured to control one or more of temperature sensors 92A-92E to measure the temperature of blanket 500 using any other suitable sampling frequency.

[0183] In some embodiments, based on the calculated maximum temperature of the blanket 500, the processor 20 and / or the controller 54 are configured to control the intensity of the IR radiation emitted from the source 111 and the flow rate of the compressed air 101.

[0184] In such an embodiment, in response to calculating a maximum temperature of about 140° C., the processor 20 and / or the controller 54 is configured to reduce the intensity of the light beam 99 and / or increase the flow rate of the compressed air 101.

[0185] In some embodiments, processor 20 and / or controller 54 are configured to calculate temperatures along different sections of blanket 500 based on any suitable sampling of temperature signals 554 and 555 .

[0186] In some embodiments, the processor 20 and / or controller 54 are configured to maintain thresholds indicating specified maximum and minimum temperatures for the printing process and to maintain the temperature of the blanket 500 by controlling at least some of the aforementioned dryers (e.g., the main dryer 64 and the bottom dryer 75).

[0187] For example, after the main dryer 64, in response to detecting and calculating a temperature level below a specified minimum temperature, the processor 20 and / or controller 54 is configured to control the bottom dryer 75 to increase the intensity of the light beam 99 and / or decrease the flow rate of the compressed air 101.

[0188] As mentioned above, in addition to the flow rate of compressed air 101, the blanket is typically cooled by the surrounding environment in physical contact with the blanket. For example, the temperature of the air (or other gas) surrounding the blanket and the temperature of rollers 78 may be significantly less than 100° C. (e.g., anywhere between about 25° C. and 100° C.).

[0189] In some embodiments, processor 20 may receive position signals indicating the location of each marker or other reference point on the blanket, as described above in Figure 1. Based on the position signals, processor 20 and / or controller 54 are configured to adjust the intensity of light beam 99 and / or the flow rate of compressed air 101 in one or more of the dryers described above.

[0190] For example, as the blanket is moved within system 10, processor 20 may associate a first particular marker on blanket 500 with section 502 and a second particular marker on blanket 500 with section 506. In one embodiment, when the first particular marker passes in close proximity to a given source 111 of main dryer 64, processor 20 may control main dryer 64 to increase the intensity of light beam 99 directed from the given source 111 toward blanket 500.

[0191] Similarly, when a second particular marker passes in close proximity to a given source 111 of the main dryer 64, the processor 20 may control the main dryer 64 to reduce the intensity of the light beam 99 emitted from the given source 111.

[0192] In some embodiments, processor 20 and / or controller 54 are configured to set a constant intensity of light beam 99 and a constant flow rate of compressed air 101, for example, at dryer 62. In such embodiments, a first set of ink droplets placed at a given location on the blanket surface are partially dried so that a second set of ink droplets later applied to that given location by another print bar will mix with the first set of ink droplets to produce a specified mixed color at the given location on the blanket.

[0193] In some embodiments, the processor 20 and / or controller 54 is configured to control the temperature of the compressed air 101 applied to the blanket (e.g., blanket 44 or blanket 500). For example, the specified temperature of the compressed air 101 may be approximately 30°C. The systems 10 and 110 may operate in various countries and seasons having a wide range of environmental temperatures. For example, the environmental temperatures may range from approximately 45°C in the summer in warm countries to -30°C in the winter in cold countries.

[0194] In some embodiments, at ambient temperatures below 30° C., systems 10 and 110 are configured to filter ink by-products from the warm air extracted from surface 106 of blanket 44 by AOC 123. In such embodiments, processor 20 and / or controller 54 are configured to control AOC 122 to mix the filtered warm air with ambient air to have the air compressed and applied to blanket 44 at approximately 30° C.

[0195] In some embodiments, at ambient temperatures above 30°C, processor 20 and / or controller 54 are configured to control AIC 122 to mix ambient warm air with air cooled by the print shop (e.g., using an air conditioning system or any other technique) using system 10 or 110 to have air at approximately 30°C, and compress and apply the mixed air to blanket 44.

[0196] In some embodiments, systems 10 and 110 include a current sensor (not shown) coupled to an electrical cable (not shown) that supplies electrical current to source 111. The current sensor is configured to sense an inductance level on the electrical cable. In such embodiments, processor 20 and / or controller 54 are configured to receive a signal from the current sensor indicative of the current flowing through the electrical cable and determine whether each source 111 is operating.

[0197] Blanket structure and process sequence for manufacturing blankets compatible with IR-based drying of inks 6 is a schematic diagram illustrating a cross-sectional view of a process sequence for manufacturing a blanket 600, in accordance with one embodiment of the present invention. Blanket 600 may replace, for example, blanket 44 and its features of any of systems 10 and 110 shown and described in FIGS. 1-5 above.

[0198] The process begins with the preparation of an exemplary six-layer stack containing blanket 600 on a carrier (not shown).

[0199] In some embodiments, the carrier may be formed from a flexible foil, such as, for example, a flexible foil comprising aluminum, nickel, and / or chromium. In one embodiment, the foil comprises a sheet of aluminized polyethylene terephthalate (PET), also referred to herein as polyester, e.g., PET coated with fumed aluminum metal.

[0200] In some embodiments, the carrier may be formed from an antistatic polymeric film, such as a polyester film. Antistatic film properties may be achieved using various techniques, such as the addition of various additives, such as ammonium salts, to the polymer composition.

[0201] In some embodiments, the carrier has a polished flat surface (not shown), also referred to herein as the carrier contact surface, having a roughness (Ra) on the order of 50 nm or less.

[0202] In some embodiments, a first fluid curable composition (not shown) is provided and a release layer 602 is then formed on the carrier contact surface. In some embodiments, the release layer 602 includes an ink-receptive surface 612 configured to receive an ink image, for example, from the imaging station 60, and transfer the ink image to a target substrate, such as the sheet 50 shown and described in FIG. 1 above. It should be noted that the layer 602, and in particular the surface 612, is configured to have a low release force for the ink image, as measured by the wetting angle, also referred to herein as the receding contact angle (RCA), between the surface 612 and the ink image, as described below.

[0203] The low release force allows for complete transfer of the ink image from surface 612 to sheet 50. In some embodiments, release layer 602 may comprise a clear silicone elastomer, such as vinyl-terminated polydimethylsiloxane (PDMS), or any other suitable type of silicone polymer, and may have an exemplary thickness of about 10 μm to 15 μm, or any other suitable thickness greater than 10 μm.

[0204] In some embodiments, the first fluid curable material comprises a vinyl functional silicone polymer, for example, a vinyl silicone polymer that includes at least one lateral vinyl group in addition to terminal vinyl groups, for example, vinyl functional polydimethylsiloxane.

[0205] In some embodiments, the first fluid curable material may include a vinyl-terminated polydimethylsiloxane, a vinyl-functional polydimethylsiloxane that includes at least one pendant vinyl group on the polysiloxane chain in addition to the terminal vinyl groups, a crosslinker, and an addition-cure catalyst, and optionally further includes a cure retarder.

[0206] 6, release layer 602 may be uniformly applied to a flattened PET-based carrier to a thickness of 5-200 μm and cured at 120-130°C for approximately 2-10 minutes. Note that the hydrophobicity of ink transfer surface 612 may have an RCA of approximately 60° with a 0.5-5 microliter (μl) drop of distilled water. In some embodiments, the surface of release layer 602 (in contact with surface 614, described below) may have a significantly higher RCA, typically approximately 90°.

[0207] In some embodiments, the PET carrier used to generate the ink transfer surface 612 may have a typical RCA of 40° or less. All contact angle measurements were performed using a contact angle analyzer "Easy Drop" FM40Mk2 manufactured by Kruss™ GmbH, Borsteler Chaussee 85, 22453 Hamburg, Germany, and / or a Dataphysics OCA15 Pro manufactured by Particle and Surface Sciences Pty. Ltd., Gosford, NSW, Australia.

[0208] In some embodiments, blanket 600 includes IR layer 603 having an exemplary thickness in the range of approximately 30 μm to 150 μm and configured to absorb all or a substantial portion of the IR radiation of light beam 99. In this example, IR layer 603 is adapted to absorb approximately 50% of the IR radiation of light beam 99 within its top 5 μm. In other words, IR layer 603 is substantially opaque to light beam 99.

[0209] Reference is now made to inset 611, which shows a cross-sectional view of IR layer 603. In some embodiments, IR layer 603 has a surface 612 that is applied to and interfaces with release layer 602, and a surface 618 that interfaces with compliant layer 604, which is described in more detail below.

[0210] In some embodiments, the IR layer 603 includes a matrix made from silicone (e.g., PDMS) and a plurality of particles 622 disposed at predetermined locations within the bulk of the PDMS matrix of layer 603. In some embodiments, the particles 622 include any type of pigment, such as, but not limited to, commercially available carbon black (CB) particles, each of which has a typical diameter ranging between about 10 μm (for an IR layer 603 thickness of about 30 μm) and 30 μm (for an IR layer 603 thickness of about 50 μm).

[0211] In some embodiments, particles 622 are embedded in the bulk of IR layer 603 within a distance 616 of about 10 μm or 20 μm from surface 614. Particles 622 are also uniformly spaced along layer 603 at a distance 617 of about 0.1 μm to 5 μm from each other. In other embodiments, distances 616 and 617 may vary between different blankets; for example, at least one particle may be in close proximity to or in contact with either surface 614 or 618. Similarly, distance 617 may vary along IR layer 603.

[0212] In some embodiments, having particles 622 embedded within the bulk of IR layer 603 rather than at the surface 614 may improve adhesion between IR layer 603 and release layer 602. Similarly, having particles 622 embedded within the bulk of IR layer 603 may improve adhesion between IR layer 603 and compliant layer 604.

[0213] In some embodiments, after the release composition is coated and cured on the PET, an IR layer 603 having CB particles is also coated and cured on the cured release layer. Note that the CB particles, or any other suitable type of particles, can be inserted into the IR layer 603 by mixing the particles into the matrix of the IR layer before applying it to the release layer, by disposing the particles after applying it to the release layer, or by using any other suitable technique. A PDMS layer is then coated on the cured IR layer, a fiberglass layer is applied, and the entire structure is cured. Finally, a silicone resin is coated on the fiberglass layer and cured.

[0214] In other embodiments, the CB particles and their location can affect the drying process of the ink applied to the surface 612 of the release layer 602, as will be explained in more detail below.

[0215] Referring again now to an overview of blanket 600, in some embodiments, blanket 600 includes a compliant layer 604, also referred to herein as a conformal layer, typically made from PDMS and may include a black pigment additive. Compliant layer 604 is applied to IR layer 603 and may have a typical thickness of about 150 μm, or any other suitable thickness of about 100 μm or greater.

[0216] In some embodiments, compliant layer 604 can have different mechanical properties (e.g., greater resistance to tension), for example, than release layer 602 and / or IR layer 603. Such desired differences in properties can be achieved, for example, by utilizing different compositions for release layer 602 and / or IR layer 603, by varying the properties among the components used to prepare the compositions of release layer 602 and / or IR layer 603, and / or by adding additional components to such compositions, and / or by selecting different curing conditions. For example, adding filler particles can increase the mechanical strength of compliant layer 604 compared to release layer 602 and / or IR layer 603.

[0217] In some embodiments, compliant layer 604 has elastic properties that allow release layer 602 and surface 612 to conform closely to the surface contours of the substrate (e.g., sheet 50) onto which the ink image is applied. Attachment of compliant layer 602 to the side opposite ink transfer surface 612 may involve the addition of an adhesive or bonding composition in addition to the material of compliant layer 602.

[0218] In some embodiments, blanket 600 includes a reinforcing stack layer, also referred to herein as support layer 607 or the skeleton of blanket 600, applied to compliant layer 604 and described in detail below. In some embodiments, support layer 607 is configured to provide blanket 600 with improved mechanical resistance to deformation or tearing that may be caused by torque applied to blanket 600, for example, by rollers 78 and dancer assembly 74. In some embodiments, the skeleton of blanket 600 includes adhesive layer 606, made of PDMS or any other suitable material, formed together with fiberglass fabric layer 608. In some embodiments, layers 606 and 608 may have typical thicknesses of about 150 μm and about 112 μm, respectively, such that the thickness of support layer 607 is typically about 200 μm.

[0219] In other embodiments, the skeleton may be produced using any other suitable process, for example, by depositing layer 606 and then bonding and polymerizing layer 608 thereto, or by using any other process sequence.

[0220] In some embodiments, the polymerization process may be based on a hydrosilylation reaction catalyzed by a platinum catalyst, commercially known as "addition cure."

[0221] In other embodiments, the skeleton of blanket 600 may include any suitable fiber reinforcement in the form of a web or fabric to provide blanket 600 with sufficient structural integrity to resist elongation when blanket 600 is maintained in tension, for example, within system 10. The skeleton may be formed by coating the fiber reinforcement with any suitable resin that is subsequently cured and remains flexible after curing.

[0222] In an alternative embodiment, support layer 607 may be formed separately, such that the fibers are embedded and / or impregnated in a separately cured resin. In this embodiment, support layer 607 may be attached to compliant layer 604 via an adhesive layer, optionally eliminating the need to cure support layer 607 in situ. In this embodiment, support layer 607, whether formed in situ on compliant layer 604 or separately, may have a thickness between about 100 μm and about 500 μm, with some of that due to the thickness of the fibers or fabric, which generally varies between about 50 μm and about 300 μm. It should be noted that the thickness of support layer 607 is not limited to the aforementioned values.

[0223] In some embodiments, blanket 600 includes a high-friction layer 610, also referred to herein as a grip layer, typically made from transparent PDMS, configured to provide physical contact between blanket 600 and the rollers and dancers of systems 10 and 110 described above in FIGS. 1 and 2, respectively. Note that while layer 610 is made from a relatively soft material, the surface facing the rollers has high friction so that blanket 600 can withstand torque applied by the rollers and dancers without sliding. In example embodiments, layer 610 may have a thickness of approximately 100 μm, but may alternatively have any other suitable thickness, e.g., between 10 μm and 1 mm.

[0224] Additional embodiments for implementing the generation of layers 602, 604, 606, 608, and 610 of blanket 600 are described in detail, for example, in PCT International Publication No. WO2017 / 208144, the disclosure of which is incorporated herein by reference.

[0225] Referring again to inset 611, for example, as described above in Figures 1, 3, and 4, print bars 62 of imaging station 60 apply ink droplets to surface 106 of blanket 44. In the example blanket 600 shown in Figure 6, print bars 62 of imaging station 60 apply ink droplets to surface 612 of release layer 602.

[0226] In some embodiments, the CB content of particles 622 is configured to absorb the IR radiation of light beam 99 passing through release layer 602. In response to the IR radiation of light beam 99, particles 622 are configured to have a temperature greater than the temperature of the silicone matrix of IR layer 603. In other words, the CB particles absorb the IR radiation and emit heat rays 620 and 621 across IR layer 603. In such embodiments, heat rays 620 and 621 increase the temperature of layers 602 and 604, respectively.

[0227] In some embodiments, the silicone matrix of the IR layer 603 has low thermal conductivity, so that the heat rays 620 travel through the IR layer 603, creating a uniform temperature rise across the IR layer 603 and the release layer 602.

[0228] Additionally or alternatively, CB particles may be embedded within the release layer 602 .

[0229] In some embodiments, having a release layer 602 (which is transparent to IR radiation) on top of an IR layer 603 (which is configured to absorb IR radiation) traps the heat rays 620 and 621 within the blanket 600, thereby accelerating the drying process of ink droplets applied to the surface 612.

[0230] In such an embodiment, heat generated by the hot wire 620 can accumulate between and within layers 602 and 603, and the low thermal conductivity of these layers allows the heat to be distributed evenly across the surface 612 of the blanket 600.

[0231] Based on the above description of blanket 600, the total thickness between particles 622 and the outer surface of layer 610 is about 0.5 mm, while the distance between particles 622 and surface 612 is about 20 μm or 30 μm. As shown in FIG. 6 , hot ray 621 appears shorter than hot ray 620 to indicate that most of the heat generated by the CB particles is dissipated toward surface 612. In such an embodiment, most of the heat generated by the CB particles is used to dry the ink droplets applied to surface 612 of blanket 600.

[0232] FIG. 7 is a flow chart that schematically illustrates a method for manufacturing a blanket 600, in accordance with one embodiment of the present invention. The method begins with a first layer generation step 700 that generates a release layer 602 formed on a PET-based carrier contact surface, as described in FIG. 6 above. In some embodiments, the release layer 602 includes an ink-receptive surface 612 configured to receive an ink image, for example, from an imaging station 60, and transfer the ink image to a target substrate, such as a sheet 50, as shown and described in FIG. 1 above. In some embodiments, the release layer 602 is at least partially transparent to a beam of IR radiation 99 and disposed on the outer surface of the blanket 600, as shown and described in detail in FIG. 6 above.

[0233] In a second layer application step 702, an IR layer 603 is applied to the release layer 602. In some embodiments, the IR layer 603 includes a matrix made from silicone (e.g., PDMS). The matrix holds a plurality of particles 622 (e.g., carbon black particles) disposed at predetermined locations within the bulk of the PDMS matrix of layer 603 and configured to absorb optical radiation (IR radiation in this example, light beam 99) to heat the release layer 602 and dry at least a portion of the ink droplets applied to the ink-receiving surface 612. While step 702 completes the method of FIG. 7, additional steps for manufacturing the blanket 600 are described in detail in FIG. 6 above.

[0234] FIG. 8 is a flow chart that schematically illustrates a method for drying ink and controlling blanket temperature during a digital printing process, in accordance with one embodiment of the present invention.

[0235] In the context of this disclosure and in the claims, the term "blanket" refers to blanket 44 of Figures 1-4, blanket 500 of Figure 5, blanket 600 of Figure 6, and any other type of suitable ITM. The method embodiment of Figure 8 is described using blanket 600, but is applicable to all types of blankets and ITMs described above, as well as other suitable types of ITMs.

[0236] The method begins with an optical radiation directing step 800 in which IR radiation, such as light beam 99, is directed toward surface 612 of release layer 602, which is configured to at least partially transmit the optical radiation and (i) receive ink droplets, (ii) form an image thereon, and (iii) transfer the image to a target substrate, such as sheet 50 or web 51. In some embodiments, at least a portion of the IR radiation of light beam 99 is absorbed by particles 622 (e.g., carbon black particles) disposed at predetermined locations within the bulk of the PDMS matrix of layer 603.

[0237] In some embodiments, when absorbed by particles 622, the IR radiation heats the release layer 602, causing ink droplets of the ink image formed on the surface of the release layer to at least partially dry.

[0238] Completing the method is a blanket temperature control step 802 in which the processor 20 controls the temperature control assembly to direct gas (in this example, compressed air) at a predetermined flow rate to control the temperature of the blanket, for example, to about 70°C or 80°C as described above in Figures 1 and 2.

[0239] For example, as described above in Figures 2 and 3, dryer 66 includes one or more openings to AIC 122 having a blower and configured to supply compressed air 101 (or any other type of suitable gas) to dryer 66. In some embodiments, dryer 66 further includes one or more openings to AOC 123 having an air extraction device (e.g., a suitable type of vacuum or negative pressure pump) configured to extract compressed air 101 after cooling the blanket.

[0240] While the embodiments described herein primarily address drying of intermediate transfer members in digital printing systems, the methods and systems described herein may also be used in other applications, such as drying liquids from any substrate, or heating or annealing or curing any substrate, but are not limited to such applications.

[0241] It will therefore be understood that the foregoing embodiments are cited by way of example, and that the present invention is not limited to what has been particularly shown and described herein above. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described above, as well as variations and modifications thereof not disclosed in the prior art that would occur to one skilled in the art upon reading the foregoing description. Documents incorporated by reference in this patent application are to be considered an integral part of this application, and only the definitions therein shall be considered, except to the extent that any term is defined in these incorporated documents in a manner that is inconsistent with a definition expressly or impliedly made herein.

Claims

1. 1. A system comprising: a flexible intermediate transfer member (ITM) comprising at least (i) a first layer disposed on an outer surface of the ITM and configured to receive ink droplets from an ink delivery subsystem having a plurality of print bars arranged along an axis, the first layer having a plurality of colors, the first layer configured to apply ink droplets of the plurality of colors, respectively, to the first layer to form an ink image on the first layer and transfer the ink image to a target substrate; and (ii) a second layer comprising a matrix that holds particles at respective given positions, the second layer configured to receive optical radiation that passes through the first layer, the particles configured to heat the ITM by absorbing at least a portion of the optical radiation; an illumination assembly configured to dry ink droplets by directing the optical radiation to impinge on at least a portion of the particles, the illumination assembly including an array of light sources disposed along the axis and interleaved with the plurality of print bars; a temperature control assembly configured to control a temperature of the ITM by directing gas at the ITM; Equipped with the lighting assembly and the temperature control assembly are packaged together in a housing having at least one cavity facing a substrate, and at least one light source of the pair of light sources is disposed within the cavity; system.

2. The system of claim 1 , wherein the first layer and the second layer are adjacent to each other and the particles are positioned a predetermined distance from each other to uniformly heat the exterior surface.

3. The system of claim 1 , wherein the particles are embedded within the bulk of the second layer at a given distance from the outer surface to uniformly heat the outer surface.

4. 4. The system of claim 1, further comprising a processor configured to receive a temperature signal indicative of a temperature of the ITM and to control at least one of (i) an intensity of optical radiation and (ii) a flow rate of gas based on the temperature signal.

5. The system of any one of claims 1 to 3, wherein the optical radiation comprises infrared (IR) radiation and at least one of the particles comprises carbon black (CB).

6. 6. The system of claim 5, further comprising a reflector coupled between the cavity and the pair of light sources and configured to receive a first portion of the infrared radiation emitted from the pair of light sources and reflect a second portion of the infrared radiation, smaller than the first portion, toward the substrate.

7. 7. The system of claim 6, wherein at least a portion of a third portion of the infrared radiation, which is a difference between the first and second portions of the infrared radiation, is absorbed in the reflector to generate heat, and further comprising a heat transfer assembly (HTA) disposed around the reflector and configured to dissipate at least a portion of the heat generated in the reflector.

8. The system of claim 7 , wherein the heat transfer assembly includes at least one of ribs and traces configured to conduct heat generated by the reflector.

9. 8. The system of claim 7, wherein the temperature control assembly includes at least one air inlet channel (AIC) configured to supply gas into the dryer to direct the gas at a surface of a substrate to cool the substrate, and at least one air outlet channel (AOC) configured to extract gas from the surface of the substrate and discharge it from the dryer.

10. 10. The system of claim 9, wherein the gas comprises compressed air, and the air inlet channel comprises a blower configured to supply the compressed air into the dryer and to flow the compressed air along a first flow path within the dryer.

11. 11. The system of claim 10, wherein the air outlet channel includes an air extractor configured to (i) extract the compressed air from a substrate in the dryer along a second flow path different from the first flow path, and (ii) discharge the compressed air outside the dryer.

12. The system of claim 11 , wherein the air extraction device comprises a vacuum pump.

13. 12. The system of claim 11, comprising a first opening between the housing and a first side of the heat transfer assembly and a second opening on a second side of the heat transfer assembly opposite the first side, the first flow path passing through the first opening and the second flow path passing through the second opening.

14. 12. The system of claim 11, wherein the arrangement includes an additional pair of light sources, an additional reflector, and an additional heat transfer assembly disposed between (i) the second opening and (ii) a third opening between the housing and the additional heat transfer assembly, the air inlet channel configured to flow the additional compressed air along a third flow path through the third opening toward the substrate to cool the additional heat transfer assembly, and the air outlet channel configured to withdraw the additional compressed air along the second flow path.

15. The system of claim 14 , wherein the pair of light sources and the additional pair of light sources are arranged along an axis and equidistant from the substrate.

Images