Patent Description:
The present invention relates generally to digital printing processes, and particularly to methods and systems for drying ink applied to a surface during a digital printing process.

Optical radiation, such as infrared (IR) and near-IR radiation, has been used for drying ink in various printing processes.

For example, <CIT> describes a process for printing an image including printing a substrate with an aqueous inkjet ink and drying the printed image with a near-infrared drying system. Various embodiments provide a process for inkjet printing and drying inks with improved absorption in the near-IR region of the spectrum for improved drying performance of aqueous, hypsochromic inks, and an inkjet ink set with improved balanced near-IR drying of black and yellow inkjet inks.

The document <CIT> discloses a system comprising a flexible intermediate transfer member, an illumination assembly and a temperature control assembly.

Embodiments of the present invention that are described hereinbelow provide improved techniques for drying ink applied to a surface of a substrate during a digital printing process.

In some embodiments, a digital printing system comprises a movable flexible intermediate transfer member (ITM), also referred to herein as a blanket, an image forming 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 to the ITM.

In some embodiments, the ITM comprises a multi-layered stack comprising (i) a release layer, which is transparent to the IR radiation and is located at an outer surface of the ITM, facing the illumination assembly. The release layer is configured to receive ink droplets from print bars of the image forming station, such that, when the ITM moves, the print bars form multiple ink images at respective sections of the release layer. Subsequently, the ITM is configured to transfer the ink images to a target substrate, such as sheets or a continuous web.

In some embodiments, the ITM further comprises a layer, also referred to herein as an "IR layer," which is coupled to the release layer and is substantially opaque to the 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.

In some embodiments, the IR layer is configured to receive the IR radiation passing 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, so as to dry the ink droplets applied to the release layer.

In some embodiments, the CB particles are arranged within the bulk of the IR layer at a predefined distance from one another and at a given distance from the outer surface of the release layer. In such embodiments, because of the low thermal conductivity of the silicone matrix, the heat emitted from the CB particles may be distributed uniformly within the IR layer and the release layer, and thereby may dry the ink uniformly across the outer surface of the release layer.

Note that the ITM may be damaged at a certain temperature, e.g., at about <NUM> or <NUM>. In some embodiments, the temperature control assembly, comprises an air blower, which is configured to supply pressurized air, at a temperature of about <NUM>, directed to the ITM so as to prevent overheating of the ITM.

In some embodiments, the digital printing system further comprises a processor and multiple temperature sensors mounted at respective locations relative to the ITM. Each of the temperature sensors is configured to produce a temperature signal indicative of the temperature of the ITM at the respective location.

In some cases, the surface of the release layer comprises, between adjacent ink images, a bare section that does not receive the ink droplets, and therefore, the ITM is more prone to overheat at the bare section. In some embodiments, as the ITM moves, the processor is configured to control the temperature sensors to sense the ITM temperature at the bare sections.

In some embodiments, based on the temperature signals, the processor is configured to control the illumination assembly to adjust the intensity of the IR radiation, and/or to control the temperature control assembly to adjust the flow rate of the pressurized air, so as to retain the temperature of the bare sections below the aforementioned certain temperature. In other embodiments, the illumination and cooling assemblies may operate in an open loop, e.g., without measuring and adjusting the temperature.

The image forming station comprises multiple print bars, each of which configured to print a different color of ink image. Note that some sections of the ink image may comprise a mixture of first and second different colors of ink printed, respectively and sequentially, by first and second print bars mounted on the digital printing system at a predefined distance from one another.

In some embodiments, the digital printing system has multiple units, each of which comprising one or more IR light sources and a pressurized air outlet coupled, via an outlet valve, to the temperature control assembly. In such embodiments, a unit is mounted between the first and second print bars, and is configured to partially dry the ink droplets of the first color applied to the ITM by the first print bar so that, after applying the droplets of the second color, the first and second colors of ink droplets will be mixed with one another on the surface of the release layer.

In some embodiments, the digital printing system comprises an array of multiple (e.g., ten) units arranged along a moving direction of the ITM so as to obtain a complete drying of the ink image printed by the print bars on the ITM.

The disclosed techniques improve the quality of printed images by obtaining a uniform drying process across the printed image. Moreover, the disclosed techniques improve the productivity of digital printing systems by reducing the time of ink drying, and therefore, reducing the cycle time of the printing process.

<FIG> is a schematic side view of a digital printing system <NUM>, in accordance with an embodiment of the present invention. In some embodiments, system <NUM> comprises a rolling flexible blanket <NUM> that cycles through an ink supply subsystem, also referred to herein as an image forming station <NUM>, multiple drying stations, an impression station <NUM> and a blanket treatment station <NUM>. In the context of the present invention and in the claims, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably and refer to a flexible member comprising one or more layers used as an intermediate member configured to receive an ink image and to transfer the ink image to a target substrate, as will be described in detail below.

In an operative mode, image forming station <NUM> is configured to form a mirror ink image, also referred to herein as "an ink image" (not shown) or as an "image" for brevity, of a digital image <NUM> on an upper run of a surface of blanket <NUM>. Subsequently the ink image is transferred to a target substrate, (e.g., a paper, a folding carton, a multilayered polymer, or any suitable flexible package in a form of sheets or continuous web) located under a lower run of blanket <NUM>.

In the context of the present invention, the term "run" refers to a length or segment of blanket <NUM> between any two given rollers over which blanket <NUM> is guided.

In some embodiments, during installation, blanket <NUM> may be adhered edge to edge to form a continuous blanket loop (not shown). An example of a method and a system for the installation of the seam is described in detail in <CIT>.

In some embodiments, image forming station <NUM> typically comprises multiple print bars <NUM>, 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 <NUM>. In some embodiments, each print bar <NUM> comprises a strip of print heads as wide as the printing area on blanket <NUM> and comprises individually controllable print nozzles.

In some embodiments, image forming station <NUM> may comprise any suitable number of bars <NUM>, each bar <NUM> may contain a printing fluid, such as an aqueous ink of a different color. The ink typically has visible colors, such as but not limited to cyan, magenta, red, green, blue, yellow, black and white. In the example of <FIG>, image forming station <NUM> comprises seven print bars <NUM>, but may comprise, for example, four print bars <NUM> having any selected colors such as cyan, magenta, yellow and black.

In some embodiments, the print heads are configured to jet ink droplets of the different colors onto the surface of blanket <NUM> so as to form the ink image (not shown) on the outer surface of blanket <NUM>.

In some embodiments, different print bars <NUM> are spaced from one another along the movement axis, also referred to herein as a moving direction of blanket <NUM>, represented by an arrow <NUM>. In this configuration, accurate spacing between bars <NUM>, and synchronization between directing the droplets of the ink of each bar <NUM> and moving blanket <NUM> are essential for enabling correct placement of the image pattern.

In some embodiments, system <NUM> comprises dryers <NUM>. In the present example, each dryer <NUM> comprises an infrared-based (IR-based) heater, which is configured to dry some of the liquid carrier of the ink applied to the ITM surface, by increasing the temperature of blanket <NUM> and evaporating at least part of the liquid carrier of the ink. In the example of <FIG>, dryers <NUM> are positioned in between print bars <NUM>, and are configured to partially dry the ink droplets deposited on the surface of blanket <NUM>.

Note that some sections of the ink image printed on blanket <NUM> may comprise a mixture of two or more colors of ink, so as to produce a different color. For example, a mixture of cyan and magenta may result in a blue color. In this example, the red print bar may be positioned, along the moving direction of blanket <NUM> (represented by arrow <NUM>), before the yellow print bar.

In some embodiments, after jetting the red ink at a given position on the surface of blanket <NUM>, a processor <NUM> of system <NUM> is configured to control one or more of dryers <NUM> located between the red and yellow print bars to partially dry the red ink. In such embodiments, after jetting the yellow ink at the given location, the partial drying of the red ink enables the mixing of the red and yellow inks, so as to form the orange color at the given position on the surface of blanket <NUM>.

In some embodiments, blanket <NUM> has a specification of operational temperatures, for example, blanket <NUM> is configured to operate at temperatures below about <NUM> or <NUM> in order to prevent damage, such as distortion, to the structure of blanket <NUM>. In some embodiments, system <NUM> further comprises a temperature control assembly <NUM>, (described in detail in <FIG> and <FIG> below), which is configured to supply any suitable gas to the surface of blanket <NUM>, so as reduce the heat applied by the IR-based heaters, and thereby, to maintain the temperature of blanket <NUM> below about <NUM> or <NUM> or any other certain temperature.

In some embodiments, the gas may comprise pressurized air and temperature control assembly <NUM> may comprise a central air blower, configured to supply the pressurized air, via outlet valves, to dryers <NUM>. In some embodiments, dryer <NUM> comprises a combination of the aforementioned IR-based heater, for heating blanket <NUM>, and air-flow channels for cooling blanket <NUM>. In such embodiments, the pressurized air may be used for cooling sections of dryer <NUM> that are heated by the IR-based heater.

In some embodiments, temperature control assembly <NUM> further comprises an exhaust, which is configured to pump the pressurized air used for cooling blanket <NUM> and dryer <NUM>, so as to reduce or prevent condensation of ink by products at the surface of the print heads.

In the context of the present disclosure and in the claims, the term "drying unit" may refer to an apparatus comprising a combination of an IR-based heater for heating blanket <NUM>, and air-flow channels for cooling blanket <NUM>. In the example configuration of system <NUM>, each dryer <NUM> may comprise a single drying unit.

The structure and functionality of temperature control assembly <NUM> and of dryers <NUM> are depicted in detail in <FIG> and <FIG> below.

In some embodiments, this heating between the print bars may assist, for example, in reducing or eliminating condensation at the surface of the print heads and/or in handling satellites (e.g., residues or small droplets distributed around the main ink droplet), and/or in preventing blockage of the inkjet nozzles of the print heads, and/or in preventing the droplets of different color inks on blanket <NUM> from undesirably merging into one another.

In some embodiments, system <NUM> comprises a drying station, referred to herein as a main dryer <NUM>, which is configured to dry the ink image applied to the surface of blanket <NUM> by image forming station <NUM>. Note that at each of dryers <NUM> is configured to dry ink droplets during the formation of the ink image.

In the example configuration of system <NUM>, main dryer <NUM> comprises an array of ten drying units arranged in a row parallel to the moving direction of blanket <NUM>. In this configuration, main dryer <NUM> is configured to receive blanket <NUM> at any suitable temperature, for example, between about <NUM> and about <NUM> and to increase the temperature of blanket <NUM> to any suitable temperature, for example, between about <NUM> and about <NUM> after being heated by main dryer <NUM>.

When passing through main dryer <NUM>, blanket <NUM> (having the ink image thereon) is exposed to the IR radiation and may reach the aforementioned temperature (e.g., about <NUM>). In some embodiments, main dryer <NUM> is configured to dry the ink more thoroughly by evaporating most or all of the liquid carrier, and leaving on the surface of blanket <NUM> only a layer of resin and coloring agent, which is heated to the point of being rendered tacky ink film.

The structure and functionality of main dryer <NUM> will be depicted in detail, for example, in <FIG> below.

In some embodiments, system <NUM> comprises a vertical dryer <NUM> having an assembly for pumping (e.g., using vacuum) gas residues evaporated from the surface of blanket <NUM>. Additionally or alternatively, vertical dryer <NUM> may comprise an air knife, which is configured to blow pressurized air (or any other suitable gas) on the surface of blanket <NUM>, so as to reduce the temperature of blanket <NUM> and/or to remove the aforementioned gas residues from the surface of blanket <NUM>.

In some embodiments, processor <NUM> is configured to control, in vertical dryer <NUM>, the vacuum level and/or the air pressure, so as to obtain the desired cleanliness and/or temperature on the surface of blanket <NUM>. Note that the cleanliness of the surface of blanket <NUM> is particularly important before the ink image printed on blanket <NUM> enters impression station <NUM> as will be described in detail herein.

In some embodiments, system <NUM> comprises a blanket pre-heater <NUM>, which comprises an IR radiation source (not shown) having an exemplary length of about <NUM> or any other suitable length. The IR heat source may comprise any suitable product complying with the specified power density (which is application-dependent) supplied, for example by Heraeus (Hanau, Germany), or by Helios (Novazzano, Switzerland). In such embodiments, blanket pre-heater <NUM> is configured for uniformly heating blanket <NUM> to an exemplary temperature of about <NUM>, so as to prepare blanket <NUM> for the printing process (described above) of the ink image, carried out by image forming station <NUM>.

Note that various elements of blanket module <NUM>, such as rollers <NUM>, typically remain at room temperature (e.g., <NUM>) or any other suitable temperature, typically lower than the temperature required for drying the ink jetted on the surface of blanket <NUM>. As a result, blanket <NUM> is cooling when rolling along these elements of blanket module <NUM>. In some embodiments, processor <NUM> controls vertical dryer <NUM> for completion (if needed) of the ink drying before blanket <NUM> enters impression station <NUM>, and further controls blanket pre-heater <NUM> for maintaining the specified temperature (e.g., about <NUM>) of blanket <NUM> before entering image forming station <NUM>.

In other embodiments, blanket pre-heater <NUM> may comprise an air blower (not shown) configured to supply and direct hot air for heating the surface of blanket <NUM>. The inventors found that using IR radiation reduces the time (compared to hot air) for obtaining the specified temperature of blanket <NUM> before receiving the ink image from image forming station <NUM>. The reduced time is particularly important when starting up system <NUM>, thus, improving the availability and productivity of system <NUM>. For example, the inventors found that blanket <NUM> may be heated to about <NUM> within a few (e.g., five) minutes using IR radiation, or within about half hour using the hot air.

In some embodiments, system <NUM> comprises a blanket module <NUM> comprising blanket <NUM>. In some embodiments, blanket module <NUM> comprises one or more rollers <NUM>, wherein at least one of rollers <NUM> may comprise an encoder (not shown), which is configured to record the position of blanket <NUM>, so as to control the position of a section of blanket <NUM> relative to a respective print bar <NUM>.

In some embodiments, the encoder of roller <NUM> typically comprises a rotary encoder configured to produce rotary-based position signals indicative of an angular displacement of the respective roller. Note that in the context of the present invention and in the claims, the terms "indicative of" and "indication" are used interchangeably.

In other embodiments, blanket module <NUM> may comprise any other suitable apparatus for sensing and/or tracking the position of one or more reference points of blanket <NUM>. For example, blanket <NUM> may comprise markers disposed on the blanket surface and/or engraved within the blanket. In such embodiments, system <NUM> may comprise sensing assemblies, configured to sense the markers and to send, e.g., to processor <NUM>, position signals indicative of the positions of respective markers of blanket <NUM>.

In some embodiments, blanket <NUM> may comprise a fabric made from two or more sets of fibers interleaved with one another. The fabric has an opacity that varies in accordance with a periodic pattern of the interleaved fibers. In some embodiments, system <NUM> may comprise an optical assembly (not shown) having a light source at one side of blanket <NUM>, and a light detector at the other side of blanket <NUM>. The optical assembly is configured to illuminate blanket <NUM> with light, to detect the light passing through the fabric, and to derive from the detected light one or more position signals indicative of one or more respective position reference points (e.g., fibers) in the periodic pattern of the fabric.

In some embodiments, based on the signals, processor <NUM> is configured to control the printing process and to monitor the condition of various elements of system <NUM>, such as blanket <NUM>.

Additionally or alternatively, blanket <NUM> may comprise any suitable type of integrated encoder (not shown) for controlling the operation of various modules of system <NUM>. One implementation of the integrated encoder is described in detail, for example, in <CIT>.

In some embodiments, blanket <NUM> is guided over rollers <NUM> and a powered tensioning roller, also referred to herein as a dancer assembly <NUM>. Dancer assembly <NUM> is configured to control the length of slack in blanket <NUM> and its movement is schematically represented by a double sided arrow. Furthermore, any stretching of blanket <NUM> with aging would not affect the ink image placement performance of system <NUM> and would merely require the taking up of more slack by tensioning dancer assembly <NUM>. In some embodiments, dancer assembly <NUM> may be motorized.

The configuration and operation of rollers <NUM> are described in further detail, for example, in <CIT> and in the above-mentioned <CIT>.

In other embodiments, dancer assembly <NUM> may comprise a pressurized-air based dancer assembly (not shown), comprising an air chamber and a light-weight roller fitted in the air chamber. The air chamber may comprise an inlet and an opening, which is sized and shaped to fit snugly over the roller. The pressurized-air based dancer assembly may comprise a controllable air blower (other than the aforementioned air blower of temperature control assembly <NUM>), which is configured to supply pressurized air, via a given inlet, into the air chamber. The pressurized air applies a uniform pressure to the roller and moves the roller along a longitudinal axis of the air chamber. As a result, the roller may protrude from the air chamber through the opening, and applies a tension to blanket <NUM> while being rotated by blanket <NUM>. The pressurized-air based dancer assembly is further described, for example, in <CIT>.

In some embodiments, system <NUM> may comprise one or more tension sensors (not shown) disposed at one or more positions along blanket <NUM>. The tension sensors may be integrated in blanket <NUM> or may comprise sensors external to blanket <NUM> using any other suitable technique to acquire signals indicative of the mechanical tension applied to blanket <NUM>. In some embodiments, processor <NUM> and additional controllers of system <NUM> are configured to receive the signals produce by the tension sensors, so as to monitor the tension applied to blanket <NUM> and to control the operation of dancer assembly <NUM>.

In impression station <NUM>, blanket <NUM> passes between an impression cylinder <NUM> and a pressure cylinder <NUM>, which is configured to carry a compressible blanket.

In some embodiments, system <NUM> comprises a control console <NUM>, which is configured to control multiple modules of system <NUM>, such as blanket module <NUM>, image forming station <NUM> located above blanket module <NUM>, and a substrate transport module <NUM>, which is located below blanket module <NUM> and comprises one or more impression stations as will be described below.

In some embodiments, console <NUM> comprises processor <NUM>, typically a general-purpose computer, with suitable front end and interface circuits for interfacing with controllers of dancer assembly <NUM> and with a controller <NUM>, via an electrical cable, referred to herein as a cable <NUM>, and for receiving signals therefrom.

In some embodiments, controller <NUM>, which is schematically shown as a single device, may comprise one or more electronic modules mounted on system <NUM> at predefined locations. At least one of the electronic modules of controller <NUM> may comprise an electronic device, such as control circuitry or a processor (not shown), which is configured to control various modules and stations of system <NUM>. In some embodiments, processor <NUM> and the control circuitry may be programmed in software to carry out the functions that are used by the printing system, and store data for the software in a memory <NUM>. The software may be downloaded to processor <NUM> and to the control circuitry in electronic form, over a network, for example, or it may be provided on non-transitory tangible media, such as optical, magnetic or electronic memory media.

In some embodiments, console <NUM> comprises a display <NUM>, which is configured to display data and images received from processor <NUM>, or inputs inserted by a user (not shown) using input devices <NUM>. In some embodiments, console <NUM> may have any other suitable configuration, for example, an alternative configuration of console <NUM> and display <NUM> is described in detail in <CIT>.

In some embodiments, processor <NUM> is configured to display on display <NUM>, a digital image <NUM> comprising one or more segments (not shown) of image <NUM> and/or various types of test patterns that may be stored in memory <NUM>.

In some embodiments, blanket treatment station <NUM>, is configured to treat the blanket by, for example, cooling the blanket and/or applying a treatment fluid to the outer surface of blanket <NUM>, and/or cleaning the outer surface of blanket <NUM>. At blanket treatment station <NUM>, the temperature of blanket <NUM> can be reduced to a desired value of temperature. The treatment may be carried out by passing blanket <NUM> over one or more rollers or blades configured for applying cooling and/or cleaning and/or treatment fluid on the outer surface of the blanket.

In some embodiments, blanket treatment station <NUM> may be positioned adjacent to impression station <NUM>. Additionally or alternatively, the blanket treatment station may comprise one or more bars (not shown), adjacent to print bars <NUM>. In this configuration, the treatment fluid may be applied to blanket <NUM> by jetting.

In some embodiments, system <NUM> comprises one or more temperature sensors <NUM>, in the present example, sensors 92A, 92B, 92C and 92D, disposed at one or more respective given locations relative to blanket <NUM> and configured to produce signals indicative of the surface temperature of blanket <NUM>, also referred to herein as "temperature signals.

In some embodiments, at least one of temperature sensors 92A-92D may comprise an IR-based temperature sensor, which is configured to sense the temperature based IR radiation emitted from the surface of blanket <NUM>. In other embodiments, at least one of temperature sensors 92A-92D may comprise any other suitable type of temperature sensor.

In the example configuration of <FIG>, system <NUM> comprises: (i) a first temperature sensor 92A, disposed in close proximity to a blanket-tension drive roller, referred to herein as a roller 78A, (ii) a second temperature sensor 92B, disposed between a first print bar <NUM> and a first dryer, referred to herein as a pre-heater 66A, (iii) a third temperature sensor 92C, disposed between the right-most print bar <NUM> (in the moving direction) and main dryer <NUM>, and (iv) a fourth temperature sensor 92D, disposed in close proximity to a blanket-control drive roller, referred to herein as a roller 78B.

In some embodiments, temperature sensor 92A, which is disposed between blanket pre-heater <NUM> and image forming station <NUM>, is configured to sense the temperature of blanket <NUM> before entering image forming station <NUM>. In an embodiment, temperature sensor 92B is positioned (in the moving direction shown by arrow <NUM>) after pre-heater 66A, so as to measure the temperature of blanket <NUM> before entering the first print bar.

In some embodiments, controller <NUM> and/or processor <NUM> are configured to receive temperature signals from one or more of the temperature sensors described above, and to control the printing process based on the received temperature signals, as will be described in detail below.

In other embodiments, the temperature signal from temperature sensor 92B may be sufficient for controlling starting a new cycle of a printing process carried out by image forming station <NUM>, so that temperature sensor 92A may be redundant, and therefore may be removed from the configuration of system <NUM>.

Note that the temperature of blanket <NUM> is important for the quality of the printing process carried out by image forming station <NUM>. In some embodiments, the temperature of blanket <NUM> is set to a predefined temperature (e.g., about <NUM>) so as to: (i) dry the ink droplets of a first color applied to the ITM by the first print bar, and (ii) regain the blanket temperature (which is cooled by the ink droplets having a typical temperature of about <NUM> or <NUM>) to the predefined temperature of about <NUM>.

In some embodiments, in response to the blanket heating, a controlled amount of vapors of the first printing fluid (e.g., ink) typically evaporate from the blanket surface without adhering to nozzles of any print bars <NUM>. Moreover, based on the required color scheme of the ink image, the temperature of the first ink is control by the blanket temperature, so that, after applying the droplets of the second color, the first and second colors of ink droplets are mixed with one another so as to form the requested color on the surface of a release layer of blanket <NUM>.

In the example configuration of system <NUM>, temperature sensors 92A-92D are positioned after every event or sub-step of the printing process, which affects or may affect the temperature of blanket <NUM>. In some embodiments, based on the temperature signals received from the temperature sensors, processor <NUM> (and/or controller <NUM>) is configured to control a power source (not shown) to adjust the power density applied to one or more infrared sources (shown for example in <FIG> below) of the respective heater.

In such embodiments, processor <NUM> is configured to adjust the power density applied to the dryers using a closed-loop methodology, both in feed-back and feed-forward modes. The term "feed-back" refers to adjusting the power density in a given dryer based on temperature measured after using the given dryer, so as to obtain the required temperature in a subsequent section of the blanket. The term "feed-forward" refers to adjusting the power density based on temperature measured before using the dryer, so as to compensate for any deviation from the required temperature. In the example configuration of <FIG>, processor <NUM> is configured to control the power density applied to the one or more IR source(s) of pre-heaters <NUM> and 66A, based on the temperature signal received from temperature sensor 92A, using, respectively, feed-back and feed-forward modes of the closed loop. For example, when the signal received from sensor 92A indicates that the temperature of a first section of blanket <NUM> is below the predefined <NUM> temperature, processor <NUM> controls the power source to: (i) increase the power density applied to pre-heater 66A for obtaining the <NUM> in the first section of blanket <NUM> (using the feed-forward mode), and (ii) increase the power density applied to pre-heater <NUM> for obtaining the <NUM> in a second section of blanket <NUM>, which follows the first section (using the feed-back mode).

In some embodiments, after adjusting the power density applied to the power source(s) of pre-heater 66A, processor <NUM> receives the temperature signal from temperature sensor 92B. In case the temperature is about <NUM>, processor <NUM> allows the first print bar of image forming station <NUM>, to apply droplets of the first ink to blanket <NUM>. But in case the temperature measured by temperature sensor 92B is substantially different from about <NUM> (e.g., about <NUM>), processor <NUM> prevents the print bars of image forming station <NUM> from applying ink droplets to blanket <NUM>, and controls the power source for adjusting the blanket temperature to the predefined temperature of about <NUM>. Only after obtaining the <NUM>, processor <NUM> controls image forming station <NUM> to resume the printing process using print bars <NUM>, as described above.

In some embodiments, using the techniques described above processor <NUM> is configured to: (i) control the power density applied to main dryer <NUM>, based on temperature signals received from temperature sensor 92C, and (ii) control the power density applied to vertical dryer <NUM>, based on temperature signals received from temperature sensor 92D. Additionally or alternatively, processor <NUM> may use the signals received from temperature sensor 92D for adjusting the power density supplied to main dryer <NUM>.

In some embodiments, in response to receiving the temperature signals, processor <NUM> is configured to control the blanket temperature by adjusting the flow rate of the pressurized air in the air-flow channels shown and described in detail in <FIG> and <FIG> below. Note that processor <NUM> is configured to use the feed-forward and feed-back methodology to carry out the closed-loop control on relevant air blowers of system <NUM>. For example, when the measured temperature exceeds the required temperature of blanket <NUM>, processor <NUM> is configured to control the air blowers to increase the flow of the pressurized air applied to blanket <NUM>. Similarly, when the measured temperature is below the required temperature of blanket <NUM>, processor <NUM> is configured to control the air blowers to reduce the flow of the pressurized air applied to blanket <NUM>.

In some embodiments, processor <NUM> is configured to control both the intensity of IR radiation (by adjusting the power density supply) and the flow of the pressurized air, at the same time, so as to control the temperature of blanket <NUM>. For example, in response to receiving from temperature sensor 92D, a signal indicating that the temperature of blanket <NUM> is substantially different than about <NUM>, processor <NUM> may control at least one of main dryer <NUM> and vertical dryer <NUM>, to adjust the intensity of IR radiation and/or the flow of the pressurized air so as to obtain the specified temperature of about <NUM> on blanket <NUM>.

In other embodiments, based on the aforementioned temperature signals, processor <NUM> is further configured to control the operation of other assemblies and stations of system <NUM>, such as but not limited to blanket treatment station <NUM>. Examples of such treatment stations are described, for example, in <CIT> and <CIT>.

Additionally or alternatively, treatment fluid may be applied to blanket <NUM>, by jetting, prior to the ink jetting at the image forming station.

In the example of <FIG>, station <NUM> is mounted between impression station <NUM> and image forming station <NUM>, yet, station <NUM> may be mounted adjacent to blanket <NUM> at any other or additional one or more suitable locations between impression station <NUM> and image forming station <NUM>. As described above, station <NUM> may additionally or alternatively comprise on a bar adjacent to image forming station <NUM>.

In the example of <FIG>, impression cylinder <NUM> impresses the ink image onto the target flexible substrate, such as an individual sheet <NUM>, conveyed by substrate transport module <NUM> from an input stack <NUM> to an output stack <NUM> via impression cylinder <NUM>.

In some embodiments, the lower run of blanket <NUM> selectively interacts at impression station <NUM> with impression cylinder <NUM> to impress the image pattern onto the target flexible substrate compressed between blanket <NUM> and impression cylinder <NUM> by the action of pressure of pressure cylinder <NUM>. In the case of a simplex printer (i.e., printing on one side of sheet <NUM>) shown in <FIG>, only one impression station <NUM> is needed.

In other embodiments, module <NUM> may comprise two or more impression cylinders so as to permit one or more duplex printing. The configuration of two impression cylinders also enables conducting single sided prints at twice the speed of printing double sided prints. In addition, mixed lots of single and double sided prints can also be printed. In alternative embodiments, a different configuration of module <NUM> may be used for printing on a continuous web substrate. Detailed descriptions and various configurations of duplex printing systems and of systems for printing on continuous web substrates are provided, for example, in <CIT> and <CIT>, in <CIT>, in <CIT>, and in <CIT>.

As briefly described above, sheets <NUM> or continuous web substrate (not shown) are carried by module <NUM> from input stack <NUM> and pass through the nip (not shown) located between impression cylinder <NUM> and pressure cylinder <NUM>. Within the nip, the surface of blanket <NUM> carrying the ink image is pressed firmly, e.g., by compressible blanket (not shown), of pressure cylinder <NUM> against sheet <NUM> (or other suitable substrate) so that the ink image is impressed onto the surface of sheet <NUM> and separated neatly from the surface of blanket <NUM>. Subsequently, sheet <NUM> is transported to output stack <NUM>.

In the example of <FIG>, rollers <NUM> are positioned at the upper run of blanket <NUM> and are configured to maintain blanket <NUM> taut when passing adjacent to image forming station <NUM>. Furthermore, it is particularly important to control the speed of blanket <NUM> below image forming station <NUM> so as to obtain accurate jetting and deposition of the ink droplets, thereby placement of the ink image, by forming station <NUM>, on the surface of blanket <NUM>.

In some embodiments, impression cylinder <NUM> is periodically engaged to and disengaged from blanket <NUM> to transfer the ink images from moving blanket <NUM> to the target substrate passing between blanket <NUM> and impression cylinder <NUM>. In some embodiments, system <NUM> is configured to apply torque to blanket <NUM> using the aforementioned rollers and dancer assemblies, so as to maintain the upper run taut and to substantially isolate the upper run of blanket <NUM> from being affected by mechanical vibrations occurring in the lower run.

In some embodiments, system <NUM> comprises an image quality control station <NUM>, also referred to herein as an automatic quality management (AQM) system, which serves as a closed loop inspection system integrated in system <NUM>. In some embodiments, station <NUM> may be positioned adjacent to impression cylinder <NUM>, as shown in <FIG>, or at any other suitable location in system <NUM>.

In some embodiments, station <NUM> comprises a camera (not shown), which is configured to acquire one or more digital images of the aforementioned ink image printed on sheet <NUM>. In some embodiments, the camera may comprises any suitable image sensor, such as a Contact Image Sensor (CIS) or a Complementary metal oxide semiconductor (CMOS) image sensor, and a scanner comprising a slit having a width of about one meter or any other suitable width.

In the context of the present disclosure and in the claims, the terms "about" or "approximately" for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. For example, "about" or "approximately" may refer to the range of values ±<NUM>% of the recited value, e.g. "about <NUM>%" may refer to the range of values from <NUM>% to <NUM>%.

In some embodiments, station <NUM> may comprise a spectrophotometer (not shown) configured to monitor the quality of the ink printed on sheet <NUM>.

In some embodiments, the digital images acquired by station <NUM> are transmitted to a processor, such as processor <NUM> or any other processor of station <NUM>, which is configured to assess the quality of the respective printed images. Based on the assessment and signals received from controller <NUM>, processor <NUM> is configured to control the operation of the modules and stations of system <NUM>. In the context of the present invention and in the claims, the term "processor" refers to any processing unit, such as processor <NUM> or any other processor or controller connected to or integrated with station <NUM>, which is configured to process signals received from the camera and/or the spectrophotometer of station <NUM>. Note that the signal processing operations, control-related instructions, and other computational operations described herein may be carried out by a single processor, or shared between multiple processors of one or more respective computers.

In some embodiments, station <NUM> is configured to inspect the quality of the printed images and test pattern so as to monitor various attributes, such as but not limited to full image registration with sheet <NUM>, color-to-color (C2C) registration, printed geometry, image uniformity, profile and linearity of colors, and functionality of the print nozzles. In some embodiments, processor <NUM> is configured to automatically detect geometrical distortions or other errors in one or more of the aforementioned attributes. For example, processor <NUM> is configured to compare between a design version (also referred to herein as a "master" or a "source image" of a given digital image and a digital image of the printed version of the given image, which is acquired by the camera.

In other embodiments, processor <NUM> may apply any suitable type image processing software, e.g., to a test pattern, for detecting distortions indicative of the aforementioned errors. In some embodiments, processor <NUM> is configured to analyze the detected distortion in order to apply a corrective action to the malfunctioning module, and/or to feed instructions to another module or station of system <NUM>, so as to compensate for the detected distortion.

In some embodiments, processor <NUM> is configured to detect, based on signals received from the spectrophotometer of station <NUM>, deviations in the profile and linearity of the printed colors.

In some embodiments, processor <NUM> is configured to detect, based on the signals acquired by station <NUM>, various types of defects: (i) in the substrate (e.g., blanket <NUM> and/or sheet <NUM>), such as a scratch, a pin hole, and a broken edge, and (ii) printing-related defects, such as irregular color spots, satellites, and splashes.

In some embodiments, processor <NUM> is configured to detect these defects by comparing between a section of the printed and a respective reference section of the original design, also referred to herein as a master. Processor <NUM> is further configured to classify the defects, and, based on the classification and predefined criteria, to reject sheets <NUM> having defects that are not within the specified predefined criteria.

In some embodiments, the processor of station <NUM> is configured to decide whether to stop the operation of system <NUM>, for example, in case the defect density is above a specified threshold. The processor of station <NUM> is further configured to initiate a corrective action in one or more of the modules and stations of system <NUM>, as described above. The corrective action may be carried out on-the-fly (while system <NUM> continue the printing process), or offline, by stopping the printing operation and fixing the problem in a respective modules and/or station of system <NUM>. In other embodiments, any other processor or controller of system <NUM> (e.g., processor <NUM> or controller <NUM>) is configured to start a corrective action or to stop the operation of system <NUM> in case the defect density is above a specified threshold.

Additionally or alternatively, processor <NUM> is configured to receive, e.g., from station <NUM>, signals indicative of additional types of defects and problems in the printing process of system <NUM>. Based on these signals processor <NUM> is configured to automatically estimate the level of pattern placement accuracy and additional types of defects not mentioned above. In other embodiments, any other suitable method for examining the pattern printed on sheets <NUM> (or on any other substrate described above), can also be used, for example, using an external (e.g., offline) inspection system, or any type of measurements jig and/or scanner. In these embodiments, based on information received from the external inspection system, processor <NUM> is configured to initiate any suitable corrective action and/or to stop the operation of system <NUM>.

The configuration of system <NUM> is simplified and provided purely by way of example for the sake of clarifying the present invention. The components, modules and stations described in printing system <NUM> hereinabove and additional components and configurations are described in detail, for example, in <CIT> and <CIT>, in <CIT>, <CIT> and <CIT>, in <CIT> and <CIT>.

The particular configurations of system <NUM> is shown by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such systems. Embodiments of the present invention, however, are by no means limited to this specific sort of example system, and the principles described herein may similarly be applied to any other sorts of printing systems.

For example, in other embodiments, dryer <NUM> and/or blanket pre-heater <NUM> may comprise more than one source of IR radiation. Similarly, main dryer <NUM> may comprise any other suitable number of drying units, or any other suitable type of ink-drying apparatus.

In alternative embodiments, at least one of the dryers may comprise a radiation sources configured to emit radiation other than IR. For example, near IR, visible light, ultraviolet (UV), or any other suitable wavelength or ranges of wavelengths.

<FIG> is a schematic side view of a digital printing system <NUM>, in accordance with an embodiment of the present invention. In some embodiments, system <NUM> comprises blanket <NUM> that cycles through an image forming station <NUM>, and through drying station <NUM>, vertical dryer <NUM>, blanket pre-heater <NUM>, and blanket treatment station <NUM> described in <FIG> above.

In some embodiments, system <NUM> is configured to transfer the ink images from moving blanket <NUM> to a continuous flexible web substrate, referred to herein as web <NUM>, which is the target substrate of system <NUM>. In such embodiments, system <NUM> comprises a substrate transfer module <NUM>, which is configured to convey web <NUM> from a pre-print buffer unit <NUM>, via one or more impression stations <NUM> for receiving the ink image from blanket <NUM>, to a post-print buffer unit <NUM>.

Each impression station <NUM> may have any configuration suitable for transferring the ink image from blanket <NUM> to web <NUM>. In some embodiments, the lower run of blanket <NUM> may selectively interact, at impression station <NUM>, with an impression cylinder <NUM> to impress the image pattern onto web <NUM> compressed between blanket <NUM> and impression cylinder <NUM> by the action of pressure of a pressure cylinder <NUM>. In case of a simplex printer (i.e., printing on one side of web <NUM>) shown in <FIG>, only one impression station <NUM> is needed. In case of a duplex printed (i.e., printing on both sides of web <NUM>), which is not shown in <FIG>, system <NUM> may comprise, for example, two impression stations <NUM>.

In some embodiments, substrate transfer module <NUM> may have any suitable configuration for conveying web <NUM>. One example implementation is described in detail in U. Provisional Application <NUM>/<NUM>,<NUM>.

In some embodiments, web <NUM> comprises one or more layers of any suitable material, such as an aluminum foil, a paper, polyester (PE), polyethylene terephthalate (PET), biaxially oriented polypropylene (BOPP), oriented polyamide (OPA), biaxially oriented polyamide (BOPA), other types of oriented polypropylene (OPP), a shrinked film also referred to herein as a polymer plastic film, or any other materials suitable for flexible packaging in a form of continuous web, or any suitable combination thereof, e.g., in a multilayered structure. Web <NUM> may be used in various applications, such as but not limited to food packaging, plastic bags and tubes, labels, decoration and flooring.

In some embodiments, image forming station <NUM> typically comprises multiple print bars <NUM>, 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 <NUM>. In some embodiments, each print bar <NUM> comprises a plurality of print heads arranged so as to cover the width of the printing area on blanket <NUM> and comprises individually controllable print nozzles, as also described in <FIG> above.

In some embodiments, image forming station <NUM> may comprise any suitable number of print bars <NUM>, each print bar <NUM> may contain the aforementioned printing fluid, such as the aqueous ink. The ink typically has visible colors, such as but not limited to cyan, magenta, red, green, blue, yellow, black and white. In the example of <FIG>, image forming station <NUM> comprises a white print bar <NUM> and four print bars <NUM> having any selected colors such as cyan, magenta, yellow and black.

In some printing applications white ink is applied to the surface of web <NUM> before all other colors, and in some cases it is important that in at least some sections of web <NUM> the white color will not be mixed with the other colors of ink.

In some embodiments, system <NUM> comprises a white-ink drying station, referred to herein as a white dryer <NUM>, which is configured to dry the white ink applied to the surface of blanket <NUM> by image forming station <NUM>. In such embodiments, white dryer <NUM> may comprise five drying units, each of which comprising a combination of the aforementioned IR-based heater for heating blanket <NUM>, and one or more air-flow channels for cooling blanket <NUM>.

In other embodiments, white dryer <NUM> may comprise any other configuration suitable for drying the white ink, for example, white dryer <NUM> may comprise any other number of drying units, or may comprise any other suitable dryer apparatus using any other suitable drying technique.

In an embodiment, white dryer <NUM> is controlled by processor <NUM> and/or by controller <NUM>, and is configured to dry the white ink applied to the surface of blanket <NUM> by white print bar <NUM>. In this embodiment, processor <NUM> and/or controller <NUM> are configured to control white dryer <NUM> for partially or fully drying the white ink applied to the surface of blanket <NUM>.

In the configuration of system <NUM>, white dryer <NUM> replaces one dryer <NUM> used for drying any color of ink other than white. Note that in the present configuration, system <NUM> does not have a print bar between white dryer <NUM> and the first dryer <NUM>, but in other embodiments, system <NUM> may have any suitable printing components (e.g., a print bar) or sensing components (e.g., a temperature sensor or any other type of sensor), between white dryer <NUM> and the first dryer <NUM>.

In other embodiments, system <NUM> may comprise any other suitable type of dryer for drying, or partially drying, any particular color of ink other than white.

In other printing applications, the white ink may be applied to the surface of web <NUM> after all other colors. In alternative embodiments, the white ink may be applied to the surface of web <NUM>, using a subsystem external to or integrated with system <NUM>. In such embodiments, the white ink is applied to the surface of web <NUM> before or after applying the other colors to the surface of blanket <NUM>, using image forming station <NUM>, and particularly, before or after applying the other colors to the surface of web <NUM> in impression station <NUM>.

In some embodiments, temperature sensor 92B is disposed between the aforementioned first dryer <NUM> and print bar <NUM>, so as to confirm the surface temperature of blanket <NUM> before applying the ink having a color other than white using print bar <NUM>. Moreover, temperature sensor 92B is disposed between the last print bar of image forming station <NUM>, and main dryer <NUM>. Note that temperature sensors 92A, 92C and 92D are disposed at the same positions in both system <NUM> and system <NUM> of <FIG> above. Temperature sensor 92B, however, is disposed, along the path of blanket <NUM>, after the white-color printing and drying (in the present example, after print bar <NUM> and dryer <NUM>) and before the first print bar <NUM> of the colors other than white (e.g., cyan, magenta, yellow, black or any other color).

In some embodiments, temperature sensors 92B, 92C and 92D are disposed after processing sub-steps that typically affect or may affect the temperature of blanket <NUM>, as also described in <FIG> above.

In some embodiments, system <NUM> may comprise a drying station, referred to herein as a bottom dryer <NUM>, which is configured to emit infrared light or any other suitable frequency, or range of frequencies, of light for drying the ink image formed on blanket <NUM> using the technique described above. In the example of <FIG>, bottom dryer <NUM> may comprise five drying units, each of which comprising a combination of the aforementioned IR-based heater for heating blanket <NUM>, and one or more air-flow channels for cooling blanket <NUM>.

In some embodiments, system <NUM> comprises a temperature sensor 92E, disposed between bottom dryer <NUM> and impression station <NUM>, typically in closer proximity to bottom dryer <NUM>.

In some embodiments, processor <NUM> (and/or controller <NUM>) is configured to control the power source (not shown) described in <FIG> above, to adjust the power density applied to one or more infrared sources (shown in <FIG> and <FIG> below) of the respective heater and/or dryer, so as to retain the predefined temperature of blanket <NUM> along the respective section of system <NUM>.

In some embodiments, using the techniques described in <FIG> above, processor <NUM> (and/or controller <NUM>) is configured to perform a closed-loop control on the temperature profile of blanket <NUM> along the respective sections of system <NUM>. The control is carried out based on the temperature signals received from at least one of temperature sensors 92A-92E, and based on the temperature signals, processor <NUM> controls the power density applied to the IR power sources of the respective IR-based heaters (e.g., one or more of heater <NUM> and dryers <NUM>, <NUM>, <NUM>, <NUM> and <NUM>).

In other embodiments, bottom dryer <NUM> may comprise any other suitable configuration adapted for drying the ink at the lower run of blanket <NUM>, before the blanket enters impression station <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to control each dryer of system <NUM> (shown in <FIG>) and system <NUM> (shown in <FIG>) selectively.

The control may be carried out based on various conditions of the particular digital printing application. For example, based on the type, order and surface coverage level of colors applied to the surface of blanket <NUM>, and based on the type of blanket <NUM> and target substrate (e.g., sheet <NUM> or web <NUM>).

The term "coverage level" refers to the amount of color applied to the surface of blanket <NUM>. For example, a <NUM>% coverage level refers to two and half ink layers applied to a predefined section (or the entire area) of the ink image specified for being printed on blanket <NUM> and subsequently, for being transferred to the target substrate. Note that the two and half ink layers may comprise three or more of the aforementioned colors of ink as described above. It will be understood that larger coverage level typically requires larger flux of IR irradiation, and therefore, higher flow of air for cooling blanket <NUM>.

In other embodiments, the ink drying process may be carried out in an open loop, e.g., without controlling at least one of (a) the intensity of the IR radiation and (b) the pressurized-air flow rate by temperature control assembly <NUM>. For example, as part of a process recipe for printing a particular image, a recipe parameter may comprise the coverage level of the ink image, and processor <NUM> and/or controller <NUM> may preset one or more of (a) the intensity of the IR radiation and (b) the pressurized-air flow rate by temperature control assembly <NUM>, so as to dry the ink and maintain the temperature of blanket <NUM> below the specified temperature (e.g., about <NUM> or about <NUM>).

<FIG> is a schematic side view of dryer <NUM> for drying the ink applied by print bars <NUM>, in accordance with an embodiment of the present invention. In some embodiments, dryer <NUM> comprises a single drying unit, such as the drying unit briefly described in <FIG> above and further described in detail herein.

In some embodiments, dryer <NUM> comprises one or more openings to an air inlet channel (AIC) <NUM>, having an air blower and configured to supply pressurized air <NUM> (or any other type of suitable gas) into dryer <NUM>.

In some embodiments, dryer <NUM> further comprises one or more openings to an air outlet channel (AOC) <NUM>, having an air extraction apparatus (e.g., a suitable type of vacuum or negative pressure pump) configured to draw pressurized air <NUM> after cooling at least blanket <NUM>, as will be described herein.

In the concept of the present disclosure and in the claims, the term "temperature control assembly" refers to at least one of AIC <NUM> and AOC <NUM> or a combination thereof, and is configured to direct pressurized air <NUM> (or any other suitable type of gas) to an outer surface <NUM> of blanket <NUM> so as to reduce the temperature of blanket <NUM> below the specified temperature (e.g., about <NUM> or about <NUM>), as will be described herein.

In some embodiments, dryers <NUM> are typically positioned within image forming station <NUM>, and main dryer <NUM> is positioned between image forming station <NUM> and impression station <NUM> such that the drying process of the ink image applied to blanket <NUM> is carried out before the ink image is transferred to the target substrate (e.g., sheet <NUM>) in impression station <NUM>. Note that temperature control assembly <NUM> is configured to supply pressurized air <NUM>, e.g., via pipes or tubes (not shown), to dryers <NUM> and main dryer <NUM>, so as to control the temperature of blanket <NUM> within the specified temperature range described above. In other embodiments, system <NUM> may comprise multiple AICs <NUM> and/or AOCs <NUM>, e.g., a first set of AIC <NUM> and AOC <NUM> for dryers <NUM> and a second set of AIC <NUM> and AOC <NUM> for main dryer <NUM>. In alternative embodiments, system <NUM> may comprise any other suitable configuration of AICs <NUM> and/or AOCs <NUM> controlled by processor <NUM> and/or by local controllers that are synchronized with and/or controlled by processor <NUM>.

In some embodiments, dryer <NUM> comprises one or more IR-based heaters, in the present example an illumination assembly <NUM> having IR radiation sources, referred to herein as sources <NUM> for brevity. In the example of <FIG>, dryer <NUM> comprises two pairs of sources <NUM> arranged in two respective cavities of dryer <NUM>. Each source <NUM> is configured to direct a beam <NUM> of IR radiation to blanket <NUM>. For example, each source <NUM> is configured to emit a power density between about <NUM> w/cm and about <NUM> w/cm toward surface <NUM> of blanket <NUM>.

In other embodiments, dryer <NUM> may comprise any other suitable number of sources <NUM> (or any other suitable type of one or more light sources configured to emit IR or other suitable one or more wavelengths of light) having any suitable geometry and arranged in any suitable configuration.

In some embodiments, dryer <NUM> may comprise one or more reflectors <NUM>, coupled between sources <NUM> and the cavity of dryer <NUM>. Reflectors <NUM> are configured to reflect beams <NUM> emitted from sources <NUM> toward blanket <NUM> so as to improve the efficiency and speed of the IR-based drying process, and for reducing the amount of IR radiation (and therefore excess heating) applied to dryer <NUM> by beams <NUM>.

For example, each reflector <NUM> may reflect about <NUM>% of beams <NUM> toward blanket <NUM> and may absorb the remaining <NUM>%, which may increase the temperature at the cavities of dryer <NUM>.

In some embodiments, dryer <NUM> comprises a heat transfer assembly (HTA) <NUM>, which comprises heat conducting materials (e.g., copper, aluminum or other metallic or non-metallic materials) arranged around reflectors <NUM> as heat-conducting ribs and traces. HTA <NUM> IS configured to dissipate the excess heat away from the respective cavities of dryer <NUM>.

In the example configuration of dryer <NUM>, pressurized air <NUM> enters dryer <NUM>, via AIC <NUM>, at an exemplary temperature of about <NUM> or at any other suitable temperature between about <NUM> and about <NUM>. Subsequently, pressurized air <NUM> flows through an internal channel of dryer <NUM> for transporting heat (e.g., by heat convection) away from HTA <NUM>, and then directed, via an opening <NUM> of dryer <NUM>, toward a position <NUM> on surface <NUM>. Pressurized air <NUM> flow on surface <NUM> for transferring the heat from blanket <NUM>, and subsequently, AOC <NUM> draws pressurized air <NUM> away from surface <NUM>, via an air outlet passage <NUM> of dryer <NUM>, for maintaining the temperature of blanket <NUM> below the specified temperature described above.

As shown in <FIG>, dryer <NUM> may be located adjacent to a print bar <NUM>, and typically between two adjacent print bars <NUM>. In some embodiments, dryer <NUM> is configured to draw pressurized air <NUM> via air outlet passage <NUM>, so that pressurized air <NUM> will not make physical contact with any of print bars <NUM>. Note that pressurized air <NUM> comprises vapors of the ink ingredients that may interfere with the printing process. For example, such vapors may partially or fully block nozzles of print bars <NUM>, which may reduce the quality of the printed image (e.g., missing ink in case of a fully-blocked nozzle, or defects comprising clusters of dried ink in case of partially-blocked nozzle).

In some embodiments, the structure of dryer <NUM> prevents mixture of pressurized air <NUM> incoming from AIC <NUM> with pressurized air <NUM> flowing through opening <NUM> into surface <NUM>. As described above, after flowing through opening <NUM>, pressurized air <NUM> is forced to flow via air outlet passage <NUM>, into AOC <NUM>. In other words, the outflowing air that may contain residues of ink, and the incoming air for cooling surface <NUM> are never mixed with one another within dryer <NUM>.

In some embodiments, beam <NUM> is directed to position <NUM> based on the position of sources <NUM> within the cavity of dryer <NUM>. Similarly, dryer <NUM> is designed such that pressurized air <NUM> is directed to position <NUM> for cooling blanket <NUM>. Note that each drying unit of dryer <NUM> comprises two sets, of IR-based heating and pressurized-air-based cooling, having air outlet passage <NUM> therebetween. In this configuration pressurized air <NUM> inflows toward blanket <NUM> from the sides of dryer <NUM>, and outflows away from blanket <NUM> through air outlet passage <NUM> located at the center of dryer <NUM>, so as to prevent contact between pressurized air <NUM> and print bars <NUM>.

In some embodiments, a distance <NUM>, which is the distance between dryer <NUM> and surface <NUM> may be used for controlling the amount of the IR-based heating and air-based cooling. In principle, smaller distance <NUM> accelerates the heating rate of blanket <NUM>. In other words, when distance <NUM> is small, in response to IR-based heating, blanket <NUM> will reach the specified temperature (e.g., about <NUM> or about <NUM>) faster, resulting in faster drying of the ink on the surface of blanket <NUM>.

In some embodiments, distance <NUM> may be predetermined, e.g., when mounting dryer <NUM> on the frame of system <NUM> and/or system <NUM>. In other embodiments, distance <NUM> may be controlled, e.g., by using any suitable mount for moving dryer <NUM> relative to blanket <NUM>.

In some embodiments, by controlling distance <NUM>, processor <NUM> may control the intensity and uniformity of the power density applied, by source <NUM>, to predefined sections of blanket <NUM>. For example, larger distance <NUM> may result in smaller power density applied to a given section of blanket <NUM>, but may improve the heating uniformity within the given section and in close proximity thereto. Similarly, the proximity between blanket <NUM> and dryer <NUM> may affect the level of cooling by dryer <NUM>. For example, larger distance <NUM> reduces the cooling effectivity of the blanket surface by pressurized air <NUM>.

As described above, when blanket <NUM> is moved in the direction shown by arrow <NUM>, print bar <NUM> that is located adjacent to dryer <NUM>, jets ink droplets to blanket <NUM>. In some embodiments that will be described in more detail in <FIG> below, dryer <NUM> and the blanket are designed such that beam <NUM> is configured to heat blanket <NUM>, and the increased temperature induces evaporation of the liquid carried of the ink so as to dry or partially dry the ink on surface <NUM>. Note that beam <NUM> is not directed to the ink for the evaporation, but is directed to blanket <NUM> for increasing the temperature of the blanket. Similarly, pressurized air <NUM> is directed to blanket <NUM>, by AIC <NUM>, and extracted from blanket by AOC <NUM>, so as to reduce the temperature thereof.

The particular configuration of the drying unit of dryer <NUM> is provided by way of example, in order to illustrate certain problems, such as partially drying the ink image applied to blanket <NUM> and cooling the blanket, which are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of digital printing systems such as systems <NUM> and <NUM> described above. Embodiments of the present invention, however, are by no means limited to this specific configuration and sort of example drying unit, and the principles described herein may similarly be applied to any other sorts of drying units in digital printing systems or any other type of printing systems.

In other embodiments, pressurized air <NUM> may be used solely for reducing the temperature of blanket <NUM>, whereas a separate (e.g., dedicated) cooling apparatus may be used for cooling HTA <NUM>.

<FIG> is a schematic side view of main dryer <NUM>, in accordance with an embodiment of the present invention. In some embodiments, main dryer <NUM> comprises multiple drying units <NUM>, and an air outlet passage <NUM> between a respective pair of neighboring drying units <NUM>.

Reference is now made to an inset <NUM> showing a pair of drying units <NUM> and air outlet passage <NUM> located therebetween. Each drying unit <NUM> is positioned at a distance <NUM> from surface <NUM> of blanket <NUM>. Note that distance <NUM> may differ from distance <NUM> and may be controllable, e.g., using a mount as described in <FIG> above. Alternatively, distance <NUM> may be predetermined based on the distance between the frame of image forming station and the position of blanket <NUM>.

In some embodiments, each drying unit <NUM> has two cavities, each of which having a pair of sources <NUM> of illumination assembly <NUM>, which are configured for directing beam <NUM> so as to heat blanket <NUM>, using the technique described for dryer <NUM> in <FIG> above. Drying unit <NUM> further comprises a heat transfer assembly (HTA) <NUM> having the same cooling functionality of HTA <NUM>, but a different structure that fits the structure of drying unit <NUM>.

In some embodiments, pressurized air <NUM> enters drying unit <NUM>, via AIC <NUM>, at an exemplary temperature of about <NUM> or any other suitable temperature as described, for example in <FIG> above, and flowing through HTA <NUM> for cooling drying unit <NUM>. Subsequently, pressurized air <NUM> is directed out of drying unit <NUM>, through an opening <NUM>, toward blanket <NUM>, so as to reduce the temperature of blanket <NUM> as described for dryer <NUM> in <FIG> above, and pumped away from blanket <NUM>, via air outlet passage <NUM>, toward AOC <NUM>, using the same technique described in <FIG> above.

Note that in this configuration, pressurized air <NUM> outflows from the center of drying unit <NUM> toward blanket <NUM>, and is pumped away from blanket <NUM> through air outlet passages <NUM> located at the sides of drying unit <NUM>.

In the example of <FIG>, main dryer <NUM> comprises nine drying units <NUM> and two halves of drying unit <NUM> at the ends of main dryer <NUM>. In this configuration, main dryer <NUM> comprises ten air outlet passages <NUM>, which improves the extraction of pressurized air <NUM> compared to a set of ten full-sized drying units <NUM> (not shown) having a total number of nine air outlet passages <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to receive temperature signal from one or more of temperature sensors 92A-92E, and based on the temperature signal to control at least one of (a) the intensity of the optical radiation applied to blanket <NUM> by one or more light sources, such as sources <NUM>, and (b) the flow rate of pressurized air <NUM>, or any other suitable gas, directed to surface <NUM> of blanket <NUM>.

In the present example, processor <NUM> and/or controller <NUM> are configured to control the IR light intensity and the flow rate of pressurized air <NUM> based on multiple temperature signals received from multiple temperature sensors disposed along blanket <NUM>. As described above, blanket <NUM> is typically cooled by the temperature of the surrounding environment. For example, the temperature of the surrounding air and of rollers <NUM> may be substantially smaller than <NUM> (e.g., at any temperature between about <NUM> and <NUM>).

In some embodiments, white dryer <NUM> and bottom dryer <NUM> of system <NUM> may comprise, each, five drying units <NUM>, arranged in a configuration similar to that of main dryer <NUM>, or using any other suitable configuration. In an embodiment, blanket pre-heater <NUM> may comprise a single drying unit <NUM>, or one dryer <NUM>, or one or more sources <NUM> without an apparatus for flowing pressurized air <NUM>.

In some embodiments, the structure of drying units <NUM> prevents mixture of pressurized air <NUM> incoming from AIC <NUM> with pressurized air <NUM> flowing through opening <NUM> into surface <NUM>. As described above, after flowing through opening <NUM>, pressurized air <NUM> is forced to flow, via air outlet passage <NUM> located between adjacent units <NUM>, into AOC <NUM>. In other words, after flowing through opening <NUM>, the pressurized air that may contain residues of ink is not mixing with the incoming air flowing within drying unit <NUM>.

The configurations of main dryer <NUM>, white dryer <NUM>, bottom dryer <NUM>, drying units <NUM>, and air outlet passages <NUM> are provided by way of example. In other embodiments, at least one of these dryers and units may have any other suitable configuration. For example, rather than having central AIC <NUM> and AOC <NUM> and controlling the flow rate of pressurized air <NUM> using valves (not shown), system <NUM> and/or system <NUM> may comprise multiple AICs <NUM> and/or AOCs <NUM> coupled to one or more of the dryers described above.

<FIG> is a schematic pictorial illustration of a blanket <NUM> used in a digital printing system, in accordance with an embodiment of the present invention. Blanket <NUM> may replace, for example, blanket <NUM> of systems <NUM> and <NUM> shown in <FIG> above.

In some embodiments, blanket <NUM> is moved in the moving direction represented by arrow <NUM>, and comprises sections <NUM> having the ink image printed thereon and sections <NUM>, located between adjacent sections <NUM> and not receiving the ink droplets from print bars <NUM> and <NUM> described above.

In some embodiments, blanket <NUM> has a width <NUM> of about <NUM> - <NUM>, section <NUM> has a length <NUM> of about <NUM>, and section <NUM> has a length <NUM> of about <NUM>.

In some embodiments, sources <NUM> are typically laid out along width <NUM> and at least some of sources <NUM> have a width of about <NUM> that allows uniform heating along the entire width of blanket <NUM>. In such embodiments, processor <NUM> and/or controller <NUM> are configured to control the movement of blanket <NUM>, in the direction of arrow <NUM>, at a predefined speed (e.g., about <NUM> meters per second) that maintains the uniform heating of the entire area of blanket <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to control temperature sensors <NUM> (e.g., temperature sensors 92A-92E) to measure the temperature of blanket <NUM> at a predefined frequency, in the present example about every <NUM> milliseconds. In such embodiments, at a moving speed of <NUM> meters per second, each temperature sensor <NUM> measures the temperature of blanket <NUM> at a frequency of about every <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to receive temperature signals <NUM> and <NUM> indicative of the temperature measured (e.g., by temperature sensors <NUM>) at sections <NUM> and <NUM> of blanket <NUM>, respectively. As described in <FIG> above, the blanket temperature depends, inter-alia, on the coverage level, which is the amount of ink applied to the blanket surface.

In the example of blanket <NUM>, the coverage level in section <NUM> may vary in accordance with the pattern of the ink image, whereas section <NUM>, which does not receive ink from print bars <NUM> and <NUM>, is expected to have a uniform temperature. Note that due to the latent heat of the ink disposed on section <NUM>, at least some of the energy of beams <NUM> is absorbed by the ink and is less effective for the direct heating of blanket <NUM>.

In some embodiments, when processor <NUM> and/or controller <NUM> receive temperature signals <NUM> and <NUM> from one or more of temperature sensors <NUM> (e.g., selected from among temperature sensors 92A-92E), the temperature measured at section <NUM> is typically higher than the temperature measured at section <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to determine, based on temperature signals <NUM> and <NUM>, the highest temperature of blanket <NUM>, using any suitable analysis. For example, processor <NUM> and/or controller <NUM> may store a predefined amount (e.g., about <NUM>) of the latest temperature signals <NUM> and <NUM>. Subsequently, processor <NUM> and/or controller <NUM> may select, from among the stored signals, the temperature signals indicative of the top three highest temperatures, and may determine the highest temperature of blanket <NUM> by calculating a median of the top three highest temperatures.

In other embodiments, processor <NUM> and/or controller <NUM> may determine the highest temperature of blanket <NUM> using any suitable analysis of temperature signals <NUM> and <NUM>.

In alternative embodiments, processor <NUM> and/or controller <NUM> are configured to control temperature one or more of temperature sensors 92A-92E, to measure the temperature of blanket <NUM> using any other suitable sampling frequency.

In some embodiments, based on the calculated highest temperature of blanket <NUM>, processor <NUM> and/or controller <NUM> are configured to control the intensity of IR radiation emitted from sources <NUM>, and the flow rate of pressurized air <NUM>.

In such embodiments, in response to calculating a highest temperature of about <NUM>, processor <NUM> and/or controller <NUM> are configured to reduce the intensity of beams <NUM> and/or to increase the flow rate of pressurized air <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to calculate the temperature along different sections of blanket <NUM>, based on any suitable sampling amount of temperature signals <NUM> and <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to hold thresholds indicative of the highest and lowest specified temperatures of the printing process, and to maintain the temperature of blanket <NUM> by controlling at least some of the dryers described above (e.g., main dryer <NUM> and bottom dryer <NUM>).

For example, in response to sensing and calculating after main dryer <NUM>, a temperature level lower than the lowest specified temperature, processor <NUM> and/or controller <NUM> are configured to control bottom dryer <NUM> to increase the intensity of beams <NUM> and/or to reduce the flow rate of pressurized air <NUM>.

As described above, in addition to the flow rate of pressurized air <NUM>, the blanket is typically cooled by the surrounding environment that have physical contact with the blanket. For example, the temperature of the air (or other gas) surrounding the blanket, and the temperature of rollers <NUM>, may be substantially smaller than <NUM> (e.g., at any temperature between about <NUM> and <NUM>).

In some embodiments, processor <NUM> may receive position signals indicative of the positions of respective markers or other reference points of the blanket, as described in <FIG> above. Based on the position signals, processor <NUM> and/or controller <NUM> are configured to adjust the intensity of beams <NUM> and/or the flow rate of pressurized air <NUM>, at one or more of the dryers described above.

For example, when blanket is moved in system <NUM>, processor <NUM> may associate first specific markers of blanket <NUM> with sections <NUM>, and second specific markers of blanket <NUM> with sections <NUM>. In an embodiment, when the first specific markers are passing in close proximity to a given source <NUM> of main dryer <NUM>, processor <NUM> may control main dryer <NUM> to increase the intensity of beams <NUM> directed from given source <NUM> to blanket <NUM>.

Similarly, when the second specific markers are passing in close proximity to given source <NUM> of main dryer <NUM>, processor <NUM> may control main dryer <NUM> to reduce the intensity of beams <NUM> emitted from given source <NUM>.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to set, e.g., in dryers <NUM>, a constant intensity of beams <NUM> and a constant flow rate of pressurized air <NUM>. In such embodiments, a first set of ink droplets disposed at a given position on the blanket surface will partially dry so that a second set of ink droplets applied to the given position later by other print bars will be mixed with the first set of ink droplets so as to produce a specified mixed color at the given location of the blanket.

In some embodiments, processor <NUM> and/or controller <NUM> are configured to control the temperature of pressurized air <NUM> applied to the blanket (e.g., blanket <NUM> or blanket <NUM>). For example, the specified temperature of pressurized air <NUM> may be about <NUM>. Systems <NUM> and <NUM> may operate at various countries and seasons having a broad range of environmental temperatures, For example, the environmental temperature may range between about <NUM> in the summer at warm countries and about -<NUM> in the winter at cold countries.

In some embodiments, at an environmental temperature lower than <NUM>, systems <NUM> and <NUM> are configured to filter ink byproducts from the hot air extracted from surface <NUM> of blanket <NUM> by AOC <NUM>. In such embodiments, processor <NUM> and/or controller <NUM> are configured to control AIC <NUM> to mix between the hot filtered air and the air of the environment so as to have air at about <NUM> pressurized and applied to blanket <NUM>.

In some embodiments, at an environmental temperature higher than <NUM>, processor <NUM> and/or controller <NUM> are configured to control AIC <NUM> to mix between the hot air of the environment and air cooled (e.g., using an air conditioning system or any other technique) by a print shop using system <NUM> or <NUM> so as to have air at about <NUM>, and to pressurize and apply the mixed air to blanket <NUM>.

In some embodiments, systems <NUM> and <NUM> comprise a current sensor (not shown) coupled to an electrical cable (not shown) supplying electrical current to source <NUM>. The current sensor is configured to sense the inductance level on the electrical cable. In such embodiments, processor <NUM> and/or controller <NUM> are configured to receive from the current sensor a signal indicative of the electrical current flowing through the electrical cable and to determine whether or not the respective source <NUM> is functional.

<FIG> is a diagram that schematically illustrates a sectional view of a process sequence for producing a blanket <NUM>, in accordance with an embodiment of the present invention. Blanket <NUM> may replace, for example, blanket <NUM> of any of systems <NUM> and <NUM> and features thereof shown and described in <FIG> above.

The process begins with preparing on a carrier (not shown), an exemplary stack of six layers comprising blanket <NUM>.

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

In some embodiments, the carrier may be formed of an antistatic polymeric film, for example, a polyester film. The properties of the antistatic film may be obtained using various techniques, such as addition of various additives, e.g., an ammonium salt, to the polymeric composition.

In some embodiments, the carrier has a polished flat surface (not shown) having a roughness (Ra) on an order of <NUM> or less, also referred to herein as a carrier contact surface.

In some embodiments, a fluid first curable composition (not shown) is provided and a release layer <NUM> is formed therefrom on the carrier contact surface. In some embodiments, release layer <NUM> comprises an ink reception surface <NUM> configured to receive the ink image, e.g., from image forming station <NUM>, and to transfer the ink image to a target substrate, such as sheet <NUM>, shown and described in <FIG> above. Note that layer <NUM>, and particularly surface <NUM> are configured to have low release force to the ink image, measured by a wetting angle, also referred to herein as a receding contact angle (RCA), between surface <NUM> and the ink image, as will be described below.

The low release force enables complete transfer of the ink image from surface <NUM> to sheet <NUM>. In some embodiments, release layer <NUM> may comprise a transparent silicon elastomer, such as a vinyl-terminated polydimethylsiloxane (PDMS), or from any other suitable type of a silicone polymer, and may have an exemplary thickness of about <NUM> - <NUM>, or any other suitable thickness larger than about <NUM>.

In some embodiments, the fluid first curable material comprises a vinyl-functional silicone polymer, e.g., a vinyl-silicone polymer comprising at least one lateral vinyl group in addition to the terminal vinyl groups, for example, a vinyl-functional polydimethyl siloxane.

In some embodiments, the fluid first curable material may comprise a vinyl-terminated polydimethylsiloxane, a vinyl-functional polydimethylsiloxane comprising at least one lateral vinyl group on the polysiloxane chain in addition to the terminal vinyl groups, a crosslinker, and an addition-cure catalyst, and optionally further comprises a cure retardant.

In the example of <FIG>, release layer <NUM> may be uniformly applied to the PET-based carrier, leveled to a thickness of <NUM>-<NUM>, and cured for approximately <NUM>-<NUM> minutes at <NUM>-<NUM>. Note that the hydrophobicity of ink transfer surface <NUM> may have a RCA of about <NUM>°, with a <NUM>-<NUM> microliter (µl) droplet of distilled water. In some embodiments, a surface of release layer <NUM> (that in contact with a surface <NUM> that will be described below) may have a RCA that is significantly higher, typically around <NUM>°.

In some embodiments, PET carriers used to produce ink-transfer surface <NUM> may have a typical RCA of <NUM>° or less. All contact angle measurements were carried out using a Contact Angle analyzer "Easy Drop" FM40Mk2 produced by Krüss™ Gmbh, Borsteler Chaussee <NUM>, <NUM> Hamburg, Germany and/or using a Dataphysics OCA15 Pro, produced by Particle and Surface Sciences Pty. , Gosford, NSW, Australia.

In some embodiments, blanket <NUM> comprises an IR layer <NUM> having an exemplary thickness range of about <NUM> - <NUM>, and configured to absorb the entire IR radiation of beam <NUM> or a significant portion thereof. In the present example, IR layer <NUM> is adapted to absorb, within the top 5µ thereof, about <NUM>% of the IR radiation of beam <NUM>. In other words, IR layer <NUM> is substantially opaque to beam <NUM>.

Reference is now made to an inset <NUM> showing a sectional view of IR layer <NUM>. In some embodiments, IR layer <NUM> is applied to release layer <NUM> and has surface <NUM> interfacing therewith, and a surface <NUM> interfacing with a compliance layer <NUM> described in detail below.

In some embodiments, IR layer <NUM> comprises a matrix made from silicone (e.g., PDMS) and multiple particles <NUM> disposed at given locations within the bulk of the PDMS matrix of layer <NUM>. In some embodiments, particles <NUM> comprise a suitable type of pigment, such as but not limited to off-the-shelf carbon black (CB) particles, each of which having a typical diameter range between about <NUM> (for IR layer <NUM> thickness of about <NUM>) and <NUM> (for IR layer <NUM> thickness of about <NUM>).

In some embodiments, particles <NUM> are embedded at the bulk of IR layer <NUM>, within a distance <NUM> of about <NUM> or <NUM> from surface <NUM>. Particles <NUM> are also arranged uniformly along layer <NUM> at a distance <NUM> of about <NUM> - <NUM> from one another. In other embodiments, distances <NUM> and <NUM> may be altered between different blankets, for example, at least one particle may be in close proximity or in contact with any of surfaces <NUM> or <NUM>. Similarly, distance <NUM> may vary along IR layer <NUM>.

In some embodiments, having particles <NUM> embedded within the bulk of IR layer <NUM>, rather than at surface <NUM>, may improve the adhesive force between IR layer <NUM> and release layer <NUM>. Similarly, having particles <NUM> embedded within the bulk of IR layer <NUM> may improve the adhesive force between IR layer <NUM> and compliance layer <NUM>.

In some embodiments, after coating and curing the release formulation on the PET, IR layer <NUM>, having the CB particles, is coated on the cured release layer and also cured. Note that the insertion of the CB particles, or any other suitable type of particles into IR layer <NUM>, may be carried out by mixing the particles in the matrix of the IR layer before applying the layer to the release layer, or by disposing the particles after applying the IR layer to the release layer, or using any other suitable technique. Subsequently, PDMS layer is coated on top of the cured IR layer, and fiber glass layer is applied and all structure is cured. Finally, silicone resin is coated on fiber glass fabric and cured.

In other embodiments, the CB particles and the position thereof may affect the drying process of the ink applied to surface <NUM> of release layer <NUM>, as will be described in detail below.

Reference is now made back to the general view of blanket <NUM>. In some embodiments, blanket <NUM> comprises compliance layer <NUM>, also referred to herein as a conformal layer, typically made from PDMS and may comprise a black pigment additive. Compliance layer <NUM> is applied to IR layer <NUM> and may have a typical thickness of about <NUM> or any other suitable thickness equal to or larger than about <NUM>.

In some embodiments, compliance layer <NUM> may have mechanical properties (e.g., greater resistance to tension) that differ, for example, from release layer <NUM> and IR layer <NUM>. Such desired differences in properties may be obtained, e.g., by utilizing a different composition with respect to release layer <NUM> and/or IR layer <NUM>, by varying the proportions between the ingredients used to prepare the formulation of release layer <NUM> and/or IR layer <NUM>, and/or by the addition of further ingredients to such formulation, and/or by the selection of different curing conditions. For example, adding filler particles may increase the mechanical strength of compliance layer <NUM> relative to release layer <NUM> and/or IR layer <NUM>.

In some embodiments, compliance layer <NUM> has elastic properties that allows release layer <NUM> and surface <NUM> to follow closely the surface contour of a substrate onto which an ink image is impressed (e.g., sheet <NUM>). The attachment of compliance layer <NUM> to the side opposite to ink-transfer surface <NUM> may involve the application of an adhesive or bonding composition in addition to the material of compliance layer <NUM>.

In some embodiments, blanket <NUM> comprises reinforcement stacked layers, also referred to herein as a support layer <NUM> or a skeleton of blanket <NUM>, which is applied to compliance layer <NUM> and is described in detail below. In some embodiments, support layer <NUM> is configured to provide blanket <NUM> with an improved mechanical resistance to deformation or tearing that may be caused by the torque applied to blanket <NUM>, e.g., by rollers <NUM> and dancer assembly <NUM>. In some embodiments, the skeleton of blanket <NUM> comprises an adhesion layer <NUM>, made from PDMS or any other suitable material, which is formed together with a woven fiberglass layer <NUM>. In some embodiments, layers <NUM> and <NUM> may have typical thickness of about <NUM> and about <NUM>, respectively, or any other suitable thickness, such that the thickness of support layer <NUM> is typically about <NUM>.

In other embodiments, the skeleton may be produced using any other suitable process, e.g., by disposing layer <NUM> and subsequently coupling layer <NUM> thereto and polymerizing, or by using any other process sequence.

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

In other embodiment, the skeleton of blanket <NUM> may comprise any suitable fiber reinforcement, in the form of a web or a fabric, to provide blanket <NUM> with sufficient structural integrity to withstand stretching when blanket <NUM> is held in tension, e.g., in system <NUM>. The skeleton may be formed by coating the fiber reinforcement with any suitable resin that is subsequently cured and remains flexible after curing.

In an alternative embodiment, support layer <NUM> may be separately formed, such that fibers embedded and/or impregnated within an independently cured resin. In this embodiment, support layer <NUM> may be attached to compliance layer <NUM> via an adhesive layer, optionally eliminating the need to cure support layer <NUM> in situ. In this embodiment, support layer <NUM>, whether formed in situ on compliance layer <NUM> or separately, may have a thickness of between about <NUM> and about <NUM>, part of which is attributed to the thickness of the fibers or the fabric, which thickness generally varies between about <NUM> and <NUM>. Note that thickness of support layer <NUM> is not limited to the above values.

In some embodiments, blanket <NUM> comprises a high-friction layer <NUM>, also referred to herein as a grip layer, made from a typically transparent PDMS and configured to make physical contact between blanket <NUM> and the rollers and dancers of system <NUM> and <NUM> described, respectively, in <FIG> and <FIG> above. Note that although layer <NUM> is made from relatively soft materials, the surface facing the rollers has high friction so that blanket <NUM> will withstand the torque applied by the rollers and dancers without sliding. In an example embodiment, layer <NUM> may have a thickness of about <NUM>, but may alternatively have any other suitable thickness, e.g., between <NUM> and <NUM>.

Additional embodiments that implement the production of layers <NUM>, <NUM>, <NUM>, <NUM> and <NUM> of blanket <NUM> are described in detail, for example, in <CIT>.

Reference is now made back to inset <NUM>. As described, for example, in <FIG>, <FIG> and <FIG> above, print bars <NUM> of image forming station <NUM> apply the ink droplets to surface <NUM> of blanket <NUM>. In the example of blanket <NUM> shown in <FIG>, print bars <NUM> of image forming station <NUM> apply the ink droplets to surface <NUM> of release layer <NUM>.

In some embodiments, the CB content of particles <NUM> is configured to absorb the IR radiation of beams <NUM> passing through release layer <NUM>. In response to the IR radiation of beams <NUM>, particles <NUM> are configured to have a temperature larger than the temperature of the silicone matrix of IR layer <NUM>. In other words, the CB particles absorb the IR radiation and emit heat waves <NUM> and <NUM> across IR layer <NUM>. In such embodiments, heat waves <NUM> and <NUM> are increasing the temperature of layers <NUM> and <NUM>, respectively.

In some embodiments, the silicone matrix of IR layer <NUM> has low thermal conductivity so that heat waves <NUM> are progressing within IR layer <NUM> and are forming a uniform increased temperature across IR layer <NUM> and release layer <NUM>.

Additionally or alternatively, the CB particles may be embedded in release layer <NUM>.

In some embodiments, by having release layer <NUM> (which is transparent to IR radiation) on top of IR layer <NUM> (which is configured to absorb the IR radiation) is capturing heat waves <NUM> and <NUM> within blanket <NUM> and is, thereby, expediting the drying process of the ink droplets applied to surface <NUM>.

In such embodiments, the heat produced by heat waves <NUM> may accumulate between and within layers <NUM> and <NUM> and the low thermal conductivity of these layers allowing the heat to be distributed uniformly across surface <NUM> of blanket <NUM>.

Based on the above-description of blanket <NUM>, the total thickness between particle <NUM> and the outer surface of layer <NUM> is about <NUM>, whereas the distance between particle <NUM> and surface <NUM> is about <NUM> or <NUM>. As shown in <FIG>, heat waves <NUM> appear shorter than heat waves <NUM>, so as to show that most of the heat produced by the CB particles is dissipating toward surface <NUM>. In such embodiments, most of the heat produced by the CB particles is used for drying the ink droplets applied to surface <NUM> of blanket <NUM>.

<FIG> is a flow chart that schematically illustrates a method for producing blanket <NUM>, in accordance with an embodiment of the present invention. The method begins at a first layer production step <NUM> with producing release layer <NUM> formed on the PET-based carrier contact surface as described in <FIG> above. In some embodiments, release layer <NUM> comprises an ink reception surface <NUM> configured to receive the ink image, e.g., from image forming station <NUM>, and to transfer the ink image to a target substrate, such as sheet <NUM>, shown and described in <FIG> above. In some embodiments, release layer <NUM> is at least partially transparent to beam <NUM> of the IR radiation and is located at the outer surface of blanket <NUM>, as shown and described in detail in <FIG> above.

At a second layer applying step <NUM>, IR layer <NUM> is applied to release layer <NUM>. In some embodiments, IR layer <NUM> comprises the matrix made from silicone (e.g., PDMS). The matrix holds multiple particles <NUM> (e.g., carbon black particles) disposed at given locations within the bulk of the PDMS matrix of layer <NUM>, and configured to absorb optical radiation (in the present example IR radiation of beam <NUM>) for heating release layer <NUM> and drying at least part of the ink droplets applied to ink reception surface <NUM>. Step <NUM> concludes the method of <FIG>, however, additional steps for producing blanket <NUM> are described in detail in <FIG> above.

<FIG> is a flow chart that schematically illustrates a method for drying ink and controlling the temperature of a blanket during a digital printing process, in accordance with an embodiment of the present invention.

In the context of the present disclosure and in the claims, the term "blanket" refers to blanket <NUM> of <FIG>, to blanket <NUM> of <FIG>, to blanket <NUM> of <FIG>, and to any other sort of suitable ITM. Embodiments of the method of <FIG> are described using blanket <NUM>, but are applicable for all the types of blankets and ITMs described above, and for other suitable types of ITMs.

The method begins at an optical radiation direction step <NUM>, with directing IR radiation, such as beam <NUM>, to surface <NUM> of release layer <NUM>, which is at least partially transparent to the optical radiation, and is configured to: (i) receive the ink droplets, (ii) form the image thereon, and (iii) transfer the image to target substrate, such as sheet <NUM> or web <NUM>. In some embodiments, at least some of the IR radiation of beam <NUM> is absorbed by particles <NUM> (e.g., carbon black particles) disposed at given locations within the bulk of the PDMS matrix of layer <NUM>.

In some embodiments, when absorbed by particles <NUM>, the IR radiation heats release layer <NUM> and at least partially dries the ink droplets of the ink image formed on the surface of the release layer.

At a blanket temperature controlling step <NUM> that concludes the method, processor <NUM> controls the temperature control assembly to direct gas (in the present example, pressurized air) at a predefined flow rate for controlling the temperature of the blanket, e.g., to about <NUM> or <NUM> as described in <FIG> and <FIG> above.

For example, as described on <FIG> and <FIG> above, dryer <NUM> comprises one or more openings to AIC <NUM>, having the air blower and configured to supply pressurized air <NUM> (or any other type of suitable gas) into dryer <NUM>. In some embodiments, dryer <NUM> further comprises one or more openings to AOC <NUM>, having the air extraction apparatus (e.g., a suitable type of vacuum or negative pressure pump) configured to draw pressurized air <NUM> after cooling the blanket.

Claim 1:
A system (<NUM>), comprising:
a flexible intermediate transfer member (ITM) comprising a stack of at least (i) a first layer (<NUM>), located at an outer surface of the ITM and configured to receive ink droplets from an ink supply subsystem having multiple print bars arranged along an axis for applying, to the first layer, the ink droplets having multiple colors, respectively, to form an ink image on the first layer, and to transfer the ink image to a target substrate, and (ii) a second layer (<NUM>) comprising a matrix that holds particles (<NUM>) at respective given locations, wherein the second layer is configured to receive optical radiation passing through the first layer, and wherein the particles are configured to heat the ITM by absorbing at least part of the optical radiation;
an illumination assembly (<NUM>), which is configured to dry the droplets of ink by directing the optical radiation to impinge on at least some of the particles, wherein the illumination assembly comprises an array of a plurality of light sources arranged along the axis and interleaved with the multiple print bars; and
a temperature control assembly (<NUM>), which is configured to control a temperature of the ITM by directing a gas to the ITM, wherein the illumination assembly and the temperature control assembly are packaged together in a housing having at least a cavity facing the substrate and wherein at least a pair of light sources among the pairs of light sources is arranged within the cavity.