Fluid Inkjet Printhead

Abstract

A printhead (10) for dispensing fluid is provided, the printhead comprising at least one chamber (12), an array of piezoelectrically actuated channel distributors (14) enclosed in the at least one chamber, a multi-orifice distribution plate (16), and an air distribution element (18) including a source of compressed air and an airflow controller configured to direct the airflow.

Description

[Technical field]

[0001] The present invention relates to a printhead and system for dispensing fluids, and in particular to a printhead in a fluid dispensing system. The printhead is comprised of an array of digitally controlled piezoelectrically actuated channel distributors and air distribution elements, and the resulting system is capable of high precision dispensing or dosing of industrial fluids required for impregnating or coating materials. Materials that can be coated include textiles, paper, textiles, metal surfaces, and plastic surfaces. [Background technology]

[0002] Precision coating is achieved through digital control of the dispenser orifice, allowing the 2D and 3D distribution of industrial fluids to be controlled to within a few percent of the target value. This principle of precise application of fluids for coating or dosing is general and applicable to many industrial applications. Further exemplary applications include textile coating, applying pretreatments to cardboard for printing, producing multi-layer battery materials, manufacturing elements of display devices, and 3D printing molds for metal casting.

[0003] Currently, textile coating is a process that has a negative impact on the environment, mainly due to the large amounts of wastewater generated, typically many times the weight of the textile. Conventional coating processes are bath immersion coating, spraying, and padding with roller application mechanisms. All of these methods generally overdose the fibrous material to ensure that the material being coated remains present in excess throughout the coating process, avoiding the creation of concentration gradients that would tilt the material being coated away from the fibrous material.

[0004] Traditionally, bath dip coating is done to allow absorption of the coating material into the fiber surface. The weight of water used in this process is often many times the weight of the fiber as it is required to wash off the excess. The coating may be substantially insoluble in water and will adsorb to the fiber surface, taking time to diffuse into and become trapped in the fiber. Alternatively, the coating may be applied via a roller "padding" process.

[0005] It is against this background that a new industrial device based on the present invention has arisen for precisely dispensing only the required coating onto a textile substrate, without the need to apply excess coating. The disclosed approach allows a step change in the sustainability profile of the industry by dispensing only the required amount of coating and eliminating or reducing the cleaning process. Digital dispensing processes known in the art, namely digital inkjet printing, are unable to operate at industrial throughputs and dispense fluids at sufficiently high flow rates and sufficiently high droplet velocities to respectively deliver the coating to the internal structures of a 3D substrate.

[0006] The apparatus of the present invention is an industrial print head suitable for applying fluids such as coatings to 2D or 3D substrates, e.g., textiles and fabrics, via a digitally controlled dosing system, with the advantage that the print head can deliver the coating in areas of the textile substrate's capacity to absorb the coating. Thus, the apparatus of the present disclosure can be used to reduce the need for immersion baths and the need to wash excess coating from textiles.

[0007] Corrugated board is often patterned with coatings to provide barrier properties, printability, and decoration. These coatings are currently applied using analog printing techniques or spray coating.

[0008] The printhead that is the subject of this invention is able to digitally pattern a range of low to medium viscosity coatings that are not available with conventional digital inkjet printheads. This allows the coating function to be applied precisely only when needed. For example, in the case of waterproof carton board, the coating can be applied only to the exterior surface of the box. In the case of pre-treatment for digital printing, the coating can be applied only to the areas that will be printed. Summary of the Invention

[0009] According to a first aspect of the present invention, there is provided a printhead for distributing a fluid comprising at least one chamber, an array of piezoelectric actuated flow channel distributors enclosed in the at least one chamber, a multi-orifice distribution plate, and an air distribution element including a source of compressed air and an air flow controller configured to direct the air flow.

[0010] By providing a printhead with an array of piezoelectrically actuated flow channel distributors, the need for traditional coating methods that have a bath of coating fluid is eliminated. Instead, minute droplets of atomized fluid can be dispensed directly onto the material at a controlled rate.

[0011] Air distribution elements can be used to improve the uniformity of the dispensed microdroplets, for example by deflecting droplets into primed areas or by drying oversized droplets in air. The airflow also serves as an integrated cooling system for the printhead.

[0012] The piezoelectric actuated flow channel distributors can be controlled by a processor, which can be configured to control each piezoelectric actuated flow channel distributor independently. Because the flow channel distributors can be controlled by a processor and independently of each other as needed, the amount of fluid deposition can be precisely controlled to match the absorbance capacity of the material. This allows for instantaneous fluid switching while switching between dispensed fluid types, enabling the production of multi-component materials in a single dye run, and also potentially automatic in-line correction of non-uniform defects detected in the material. For example, the amount of fluid dispensed from the distributor can be increased if primed fluid areas are detected.

[0013] The air distribution element can be configured to direct the air flow against a distributor tip of the flow distributor, which can reduce the risk of known issues with accumulation of fluid droplets in the print head that can block or reduce the uniformity of the distributed fluid.

[0014] In some embodiments, the air distribution element can be configured to direct a single air flow to at least one distributor tip of at least two flow channel distributors. Directing a single air flow to the tips of two flow channel distributors can reduce the number of air distribution elements required by up to half, resulting in less maintenance of the print head, less compressed air required, a cheaper overall solution, and a homogenous print head.

[0015] The air distribution element may be configured to direct an air stream substantially parallel to the flow of the distributed fluid from the channel distributor to deflect the distributed fluid in a controlled manner. Directing the air stream substantially parallel to the flow of the fluid may direct the droplets of the fluid to form a homogenous and more precisely directed distribution of droplets. Furthermore, deflecting the distributed fluid with the air stream may advantageously control the diffusion area of ​​the fluid into the material, allowing real-time and versatile control of the application of the fluid to the fibers.

[0016] The air distribution elements may be configured to periodically apply air flow at a frequency ranging from 1 to 1,000 Hz. Periodic deflection of the spray may be used to increase averaging between adjacent nozzles and improve uniformity of the fluid distributed across the array of flow distributors.

[0017] The dispensed gas may include and / or be compressed air. Alternatively, or in addition, the dispensed gas may include an inert gas, such as helium or nitrogen, or a reactive gas, such as ammonia. The dispensed gas may include multiple gas components.

[0018] The or each chamber may be filled with a fluid of known composition and flow profile such that there is a controlled pressure in the chamber, which may be negative or positive. Filling the chamber, including the internal components of the print head, with a well-characterized fluid may reduce undesired evaporation and fluid dripping from the nozzles of the flow distributor and may help seal the chamber from external contamination. Additionally, the controlled pressure may help maintain a constant flow rate from the flow distributor.

[0019] The printhead may further include a sealing layer configured to resist fluid flow through the orifices of the multi-orifice distribution plate. The tip of the flow channel distributor can be configured to contact and protrude from the opening in the sealing layer, and further configured to move relative to the sealing layer with minimal friction or mechanical resistance upon piezoelectric actuation.

[0020] The sealing layer may provide additional protection to the printhead components enclosed within the chambers and reduce unwanted leakage of the dispensed fluid. The nozzle tip of the channel distributor protrudes in contact with the sealing layer, allowing the sealing layer to function without interfering with the actual process of dispensing fluid.

[0021] The sealing layer can be a viscoelastic membrane including a plurality of openings, the membrane covering each orifice of the multi-orifice distributor plate. Further, the diameter of each opening of the membrane through which the flow distributor is configured to protrude can be smaller than the diameter of the tip of the flow distributor. This allows the printhead to be sealed by intimate contact between the nozzle tip and the membrane while minimizing mechanical interference with the piezoelectric motion.

[0022] In some embodiments, the diameter of each opening in the sealing layer through which the flow distributor is configured to protrude may be larger than the diameter of the tip of the flow distributor. A slightly loose seal between the sealing layer and the distributor may prevent the resonant frequency of the distributor from being altered or tuned.

[0023] Alternatively or additionally, the sealing layer may provide damping to the distributor. In some embodiments, this damping may be undesirable. For example, during use, the distribution element may vibrate to generate a standing wave, which may include at least one node and at least one antinode. Thus, the sealing layer may be located at or substantially near the node, the node being a point in the standing wave system where the amplitude of vibration is zero. By doing so, the damping effect of the seal on the vibration of the node may be reduced or eliminated. This may keep the distribution characteristics of the distribution element optimal.

[0024] In some embodiments, the damping provided by the sealing layer is desirable, and the diameter of the opening through which the flow channel distributor is configured to protrude can be configured to provide the desired amount of damping for the distributor to achieve a pre-specified resonant frequency.

[0025] The sealing layer may be constructed of a non-wetting elastomer or an elastomer with a non-wetting coating. The sealing layer may be constructed of a hydrophobic material and / or may include a hydrophobic coating.

[0026] In some embodiments, the sealing layer may be comprised of a metal or alloy. The metal or alloy may include steel and / or aluminum. In some embodiments, the sealing layer may include a coating layer. The coating layer may include polytetrafluoroethylene.

[0027] The metal or alloy sealing layer may include a small gap between the sealing layer and the distribution element. In such an embodiment, the print head may be pressurized, thus causing a flow of fluid from inside the print head to outside the print head. The fluid flow may be continuous and substantially parallel to the distribution element, and may be configured to prevent contaminants from entering the print head, since contaminants would have to travel against the direction of the fluid flow.

[0028] Alternatively or additionally, the tips of the multi-orifice distribution plate and / or the channel distributor may be provided with a non-wetting coating and / or may be manufactured using a hydrophobic material and / or a hydrophobic coating.

[0029] The hydrophobic material and / or coating may include silicone and / or polytetrafluoroethylene. Non-wettable and / or hydrophobic materials and / or coatings can prevent aqueous fluids from accumulating in or around the seal.

[0030] The flow rate through a given flow distributor can be controlled by the duty cycle of the given flow distributor. The velocity of the fluid dispensed by the print head can be controllable by a voltage determined by the processor.

[0031] The processor may be configured to control the spread of the dispensed fluid based on the digital image. The piezoelectric actuated flow distributor may be controlled based on real-time feedback received by the processor, which may include at least one of coat weight detection, color detection, flow rate detection, nozzle resonant frequency, and electrical drive requirements for each nozzle.

[0032] In some embodiments, the piezoelectric actuated flow distributor can be horizontal with respect to the substrate onto which the fluid is distributed, hi some embodiments, the piezoelectric actuated flow distributor can be tilted with respect to the substrate onto which the fluid is distributed to prevent the fluid from wicking up into the nozzle seal area.

[0033] In some embodiments, the flow distributor may be angled up to 90 degrees, 60 degrees, 45 degrees, 30 degrees, 25 degrees, 20 degrees, 15 degrees, 10 degrees, or 5 degrees from horizontal. In some embodiments, the flow distributor may not be tilted. For example, the flow distributor may be angled between 0 and 60 degrees, more preferably between 5 and 45 degrees, and most preferably between 10 and 30 degrees.

[0034] In some embodiments, the flow path distribution element is disposed substantially below the bottom of the tank, which can help to prevent fluid within the distribution element from flowing out of the distributor and clogging or blocking the fluid path.

[0035] The print head can be moved in a reciprocating motion relative to the substrate to distribute the dispensed fluid over a large area, the motion being controlled at least in part based on real-time feedback received by the processor.

[0036] Real-time feedback may be based on color detection across the substrate. There may be increased air pressure within the printhead, which may cause air flow from inside at least one chamber in a direction toward the tip of the channel distributor.

[0037] The printhead may further include an additional chamber surrounding the tip of the channel distributor. The print head may further include a cooling mechanism, which may include a casing operably connected to the print head. The casing may be configured to contain a fluid, such as water or air, which is configured to absorb heat from the print head, thus cooling the print head. In some embodiments where there are multiple print heads, water cooling may be the preferred cooling mechanism.

[0038] Alternatively, or in addition, each print head may include a fan configured to circulate / move warm air near the print head and replace it with cooler air, thus cooling the print head. In some embodiments where there is a single print head, air cooling may be the preferred cooling mechanism.

[0039] Further in accordance with the present invention, there is provided a system for supplying fluid to a plurality of print heads, the system comprising a plurality of tanks for holding fluid to be dispensed from the plurality of print heads, a fluid supply chamber, a sensor for detecting a fluid level in the fluid supply chamber, and a recirculating feed for controlling supply and drainage rates between the fluid supply chamber and each of the plurality of tanks, the fluid supply rate and the fluid drainage rate being determined by a processor based at least in part on the fluid level detected by the sensor.

[0040] With dynamic, digitally controllable recirculating feeds to the multiple printheads, the system maintains sufficient levels of fluid in each tank at all times and returns unnecessary fluid to the main tank, reducing waste and maintaining a constant fluid flow, thus increasing efficiency.

[0041] In some embodiments, the system may include a single tank for holding fluid dispensed from multiple print heads. The supply and drain rates between the fluid supply chamber and each of the multiple tanks may be the same for each tank. By maintaining uniform supply and drain rates to each of the multiple header tanks, the level of fluid in each tank may be approximately the same and therefore may be determined by a single sensor that controls the supply and drain rates from the single fluid supply chamber. This reduces the cost and complexity of the assembly since one sensor can effectively monitor the fluid levels of the multiple header tanks.

[0042] The sensor may be a capacitance sensor, and the system may be configured to increase a supply rate to each of the multiple tanks and decrease a drainage rate from each of the multiple tanks in response to switching on the sensor, and to decrease a supply rate to each of the multiple tanks and increase a drainage rate from each of the multiple tanks in response to switching off the sensor.

[0043] In some embodiments, the sensor may be configured to measure the hydrostatic head of the fluid in the tank. In embodiments in which multiple tanks are provided, a sensor is provided to measure the hydrostatic head of each tank.

[0044] Alternatively, or in addition, the sensor may be a pressure sensor and the system may be configured to increase the supply rate to each of the multiple tanks and decrease the drain rate from each of the multiple tanks in response to the sensor detecting low pressure, and to decrease the supply rate to each of the multiple tanks and increase the drain rate from each of the multiple tanks in response to the sensor detecting high pressure.

[0045] At least one fluid flow path can connect the inlet and outlet of each of the multiple tanks to the fluid supply chamber, and the fluid flow path of each tank can be of equal resistance. The outlet of each tank may be located at a higher level than the inlet of each tank, creating a maximum fluid level in each tank based on the weir principle.

[0046] Each of the plurality of tanks may further include a vacuum bleed valve disposed adjacent the tank inlet, the vacuum bleed valve configured to provide a low resistance flow path if pressure within the tank exceeds a predetermined limit. The pressure in the header tank may be stabilized using a vacuum bleed valve proximate the fluid supply, thereby minimizing overpressure caused by a sudden increase in tank fluid height and allowing air to escape from the headspace via a low resistance route.

[0047] The system may further include at least one vacuum pump, which may be configured to control the pressure in each of the plurality of tanks. The pressure in the header tank may be set using a vacuum applied to the head space. Accurate dispensing of fluid from the print head is highly sensitive to the fluid pressure in the tanks, so accurate dispensing of fluid is highly dependent on a stable header tank pressure.

[0048] Each tank of the plurality of tanks may further comprise an adjustable divider configured to control the fluid level within the respective tank based on the weir principle. The fluid outlet of each tank of the plurality of tanks may be adjusted and configured to control the fluid level within the respective tank by adjusting the level to which the fluid is discharged.

[0049] The pressure control of the system can be closed loop with a latency of less than one second per adjustment. The system may be further configured to heat and / or agitate the fluid.

[0050] The system may be further configured to degas and / or filter the fluid. The system may include a pump that is used to recirculate the fluid within each tank. The system may further include an infrared heater configured to minimize fluid migration and maximize uniformity of the fluid distributed on the fibers.

[0051] The system may further include a vacuum pump configured to control the penetration of the airflow into the fabric. The vacuum pump may be operatively connected to the channel, the channel being disposed substantially below the print head. More specifically, the channel may be disposed substantially below the fabric configured to receive fluid dispensed from the print head.

[0052] The channels can be negatively pressurized by a vacuum pump and configured to draw air from near the dispensing element and through the fibers into the channels, which can further reduce the spreading of the fluid dispensed from the print head and / or increase control of the penetration of the fluid into the fibers.

[0053] The system may further include a filter disposed between the channel and the fiber, the filter configured to prevent fluid and / or contaminants from entering the channel. The filter may be disposable and / or removable. Once removed, the filter may be cleaned and reused. Adding a filter to prevent fluid and / or contaminants from entering the channel also prevents the filter from entering the vacuum pump, thereby reducing the maintenance requirements of the system.

[0054] According to the present invention, there is further provided a method for filling, refilling and / or draining fluid in at least one tank. The method for filling and / or refilling the tank may include at least one of the following steps: supplying the print head from a supply tank and negatively pressurizing the tank to prevent fluid from dripping from a dispensing element filling the tank to a target level with a desired fluid, such as ink, establishing recirculation in the tank, and reducing the negative pressure in the tank to completely fill the dispensing element and prevent pendant drops from forming at the nozzles.

[0055] A method for draining the tank may include at least one of the following steps: negatively pressurizing the tank to prevent fluid from dripping from the dispensing element, stopping the fluid supply to the tank, and draining the tank into a supply tank using a return pump.

[0056] The method of draining the tank may further include adding a detergent composition to the tank and repeating the aforementioned steps. The detergent composition may be water and sodium dodecyl sulfate. Adding the detergent composition dilutes the fluid remaining in the tank, which is then drained from the tank. This step may be repeated multiple times until the tank is determined to be clean by checking the fluid output from the nozzle.

[0057] In some embodiments, the tank may be negatively pressurized so that the fluid within the distribution element is drawn completely back into the tank. In some embodiments, the interior surface of the tank may be coated with a hydrophobic material, such as polytetrafluoroethylene. The hydrophobic coating allows fluids to drain more easily from the tank. Additionally, such a coating can reduce maintenance costs that arise from the need to clean the tank between draining and refilling.

[0058] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0059] [Figure 1A] FIG. 2 illustrates an example of a print head according to the present invention. [Figure 1B] 2A-2C are isometric and side views of another example of a printhead according to the present invention; [Figure 1C] 2A-2C are isometric and side views of another example of a printhead according to the present invention; [Figure 1D] 2A-2C are isometric and side views of another example of a printhead according to the present invention; [Figure 2A]FIG. 2 illustrates a top view of an exemplary array of piezoelectric actuated flow channel distributors and a multi-orifice distribution plate forming part of any of the printheads of FIG. 1. [Figure 2B] FIG. 1 illustrates a side view of an exemplary piezoelectric actuated flow channel distributor for distributing fluid. [Figure 3A] 1A-1C are side views of an exemplary configuration of an air distribution element directing airflow to a tip of a piezoelectric actuated flow path distributor. [Figure 3B] 13A-13C are diagrams of the effect of air distribution elements on an exemplary droplet spreading. [Figure 4] 1A and 1B are diagrams illustrating an example of an air flow controller of an air distribution element. [Figure 5A] 13A-13C are side views of an exemplary configuration of a sealing layer in contact with a flow distributor. [Figure 5B] FIG. 2 is a top view of an exemplary seal layer component including a plurality of openings. [Figure 6] FIG. 10 illustrates one possible configuration of chambers surrounding a piezoelectrically actuated flow distributor, with additional chambers positioned around the tip of the flow distributor and used to control the airflow and gas composition around the distributor tip. [Figure 7] FIG. 2 illustrates a system for supplying fluid to a print head, such as any of the print heads of FIG. 1. [Figure 8A] FIG. 13 illustrates an embodiment in which the fluid level and meniscus pressure in each header tank are controlled by adjustable weirs. [Figure 8B] FIG. 13 illustrates an embodiment in which the fluid level and meniscus pressure in each header tank are controlled by adjustable weirs. [Figure 9A] FIG. 13 illustrates an embodiment in which the outlet of each header tank is adjustable. [Figure 9B] FIG. 13 illustrates an embodiment in which the outlet of each header tank is adjustable. [Figure 10] FIG. 2 shows a block diagram of the digital components of the system according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] To further explain various aspects of the present disclosure, specific embodiments of the present disclosure will now be described in detail in conjunction with the accompanying drawings. With reference to Figures 1A, 1B, 1C and 1D, two examples of print heads 10 are shown. The example shown in Figure 1A is a compact print head 10 with a modest array of 48 piezoelectrically actuated flow distributors 14 providing a print width of 121 mm. Figures 1B, 1C and 1D show side and isometric views of a 1.8 m wide print head including an elongated chamber 12 and a large array of 720 piezoelectrically actuated flow distributors 14 enclosed in the chamber 12. The piezoelectrically actuated flow distributors 14 are, for example, in the form of hollow needles suitable for directing fluid flow. The two examples shown in Figures 1A to 1D have the same main functionality and the following description applies equally to each example.

[0061] The print head 10 further comprises a multi-orifice distributor plate 16 configured to project a tip of the piezoelectrically actuated flow distributor 14. As shown in Figure 2A, the tip of the flow distributor 14 is in the form of a nozzle suitable for dispensing fluid.

[0062] Advantageously, providing an array of piezoelectrically actuated flow channel distributors 14 eliminates the need for conventional coating methods that require a bath of fluid containing an excessive amount of coating. Instead, the apparatus of the present disclosure is configured to dispense minute droplets of atomized fluid at a controlled rate directly onto a substrate material, such as a fabric or fabric.

[0063] The print head 10 shown in each of Figures 1A and 1B, 1C and 1D further includes an air distribution element 18, which includes a source of compressed air 20 and an air flow controller 22 configured to direct an air flow 21.

[0064] Air distribution element 18 can be used to control the spread of the droplets and improve the uniformity of the microdroplets distributed on the substrate by deflecting the droplets into the primed area or, alternatively, by applying air flow 21 to oversized dried droplets in the air.

[0065] The airflow 21 distributed from the air distribution element 18 may simultaneously function as an integrated cooling system to prevent the print head 10 from overheating. 1A-1D is a tank 34, hereafter referred to as the "header tank." The header tank 34 is configured to hold fluid to be dispensed from the printhead 10. In the example shown in FIG 1A, the tank holds between 100 ml and 2.5 liters of fluid to be dispensed.

[0066] Referring now to FIG. 2A, an example configuration of an array of flow distributors 14 is shown in greater detail. In the illustrated configuration, the length of the flow channel distributor 14, which is in the form of a hollow needle, is substantially perpendicular to the direction of the dispensed fluid with the nozzle tip of the needle protruding through the orifice 28 in the multi-orifice distributor plate 16.

[0067] The flow channel distributor 14 is configured to distribute fluid in response to actuation by a vertical piezoelectric actuator (not shown). In particular, when activated, each of the flow channel distributors 14 distributes very small or atomized droplets of fluid in a direction substantially perpendicular to the length of the flow channel.

[0068] Although piezoelectric actuators are not shown, in one embodiment the flow channels can be actuated by multiple piezoelectric actuators in contact with the needles of the flow channel distributor. For example, there can be two piezoelectric actuators mounted perpendicular to the flow channels, allowing control of the flow channels perpendicular to the direction of the substrate on which the fluid is being deposited.

[0069] The configuration of the flow paths and actuators allows for several elements of resolution control, namely fixed offset of individual nozzles in the array perpendicular to the direction of substrate movement, as well as oscillation perpendicular to the direction of substrate advancement and deposition width of dispensed fluid.

[0070] In some embodiments, including that shown diagrammatically in Figure 8, the array of piezoelectric actuated elements 14 is operated by a processor 50, e.g., a microprocessor. The processor 50 is configured to independently control each piezoelectric actuated flow channel distributor such that individual distributors are operated to dispense less or more fluid, or at different frequencies.

[0071] Having flow channel distributors 14 controlled by processor 50 and which can be controlled independently of one another as needed allows precise control of fluid deposition volume to match the determined absorbance capacity of the material. This also allows for instantaneous fluid switching to switch between types of fluids dispensed to the substrate material, thus enabling the production of multi-component materials in a single coating run.

[0072] Additionally, if imperfections are detected in the uniformity of the fluid dispensed onto the substrate material, the above arrangement allows for automatic in-line correction of such non-uniformity, for example, if a primed fluid region is detected, the amount of fluid dispensed from the dispenser can be increased.

[0073] Although the array of piezoelectrically actuated flow distributors 14 is shown as a single row of straight needle distributors of uniform length, other configurations of the array are contemplated herein. For example, the array may include multiple rows of distributors, or distributors of various lengths. The flow distributors 14 may be curved or curved at different angles relative to one another.

[0074] Figure 2B shows a side view of a single flow distributor 14 in the configuration described above in relation to Figure 2A. Additionally, air flow 21 from air distribution element 18 is shown being applied to a nozzle of the flow distributor 14. In some embodiments, air flow 21 is substantially parallel to the direction of travel of the distributed fluid.

[0075] 3A, the air distribution elements 18 of the printhead 10 are shown configured to direct an air flow 21 to the distributor tips of the array of flow distributors 14. The air flow 21 is in a direction substantially perpendicular to the length of the flow distributor 14 and substantially parallel to the direction of travel of the distributed fluid.

[0076] In doing so, the air distribution element 18 deflects droplets of the fluid dispensed from the channel distributor 14 to control the spreading profile of the droplets of the dispensed fluid on the substrate to which the fluid is being dispensed.

[0077] Examples of droplet spread profiles are shown in FIG. 3B, which shows the shape of droplet profile 50 without an applied flow of air 21 from the air distribution element 18, and the shape of droplet profile 52 with an applied flow of air 21 from the air distribution element 18.

[0078] Beneficially, by controlling the droplet profile and spread, the fluid can be dispensed with greater resolution. The velocity of the airflow 21 can be controlled by an airflow controller 22 to achieve the desired resolution, and the airflow can be used to deflect and thus direct the dispensed fluid.

[0079] Additionally, directing the air flow 21 at the tip of the flow channel distributor reduces the risk of a known problem in printheads for dispensing other types of fluids, such as ink, where the dispensed fluid accumulates at the nozzle tip of the dispensing element, blocking the nozzle or reducing the uniformity of the dispensed fluid.

[0080] The ability to deflect the dispensed fluid with airflow 21 and therefore control the area of ​​spread of the fluid onto the material also allows for real-time and versatile control of the application of the fluid to the fibers. In some embodiments, the air flow controller 22 of the air distribution element 18 is configured to periodically apply the air flow 21 to the distributed droplets. For example, the air flow controller may distribute the air flow at a frequency in the range of 1 to 1,000 Hz.

[0081] Periodic deflection of the spray can be used to improve averaging between adjacent nozzles and increase the uniformity of the fluid distributed across the array of channel distributors. In some embodiments, the air flow is between 0.0283 and 2.83 m per minute at a pressure ranging from 2 to 10 PSI or 14 to 69 kPa. 3 (1-100 cubic feet) or 0.00047-0.047 m 3 s -1 It is driven by a flow rate of

[0082] Referring now to FIG. 4, an example configuration of the air distribution element 18 for directing the air flow 21 is shown in more detail. As shown, the air distribution element is enclosed in a casing designed to funnel and direct the air flow from a source of compressed air 20. The casing is configured to be wider closer to the supply from the source of compressed air 20 and narrower at the point within the casing where the air is distributed. Such a configuration allows the air flow 21 to be distributed with high speed and high resolution.

[0083] The airflow controller 22 may take the form of a valve within the casing to control whether air is dispensed. The airflow controller 22 is digitally controlled by a processor. For example, the airflow controller may be controlled by a processor 50.

[0084] 5, a further aspect of the present disclosure is illustrated in which the printhead 10 further includes a sealing layer 26 configured to resist fluid flow through the orifices 28 of the multi-orifice distribution plate 16.

[0085] The sealing layer 26 is configured with a number of openings 30, each configured to align with an orifice 28 in the multi-orifice distribution plate 16 through which a tip of an array of flow distributors 14 protrudes. The diameter of each opening 30 in the sealing layer 26 through which a flow distributor is configured to protrude is smaller than the diameter of the tip of the flow distributor 14, such that the protruding tip is positioned in intimate contact with the edge of the opening 30 in the sealing layer 26 to effectively seal the chamber 12 of the printhead 10.

[0086] In an exemplary embodiment, the sealing layer 26 is a multi-orifice plate constructed of a viscoelastic material such as silicone or a fluoropolymer. The sealing layer 26 can be, for example, a viscoelastic membrane. The orifices in the sealing layer are typically about 10% smaller in diameter than the orifices at the tip of the channel distributor 14. For example, a channel distributor needle with an outer diameter of 900 microns needs to seal with an opening with a diameter of 800 microns.

[0087] The above configuration effectively seals the fluid within the chamber 12 while allowing movement of the flow channel distributor 14 relative to the sealing layer with minimal friction or mechanical resistance when the flow channel distributor 14 is actuated. Thus, the sealing layer of the present disclosure does not impede fluid distribution.

[0088] In some embodiments, the sealing layer 26 is comprised of a non-wetting elastomer or an elastomer with a non-wetting coating 31. If desired, the tips of the multi-orifice distribution plate 16 and the channel distributor 14 are also provided with a non-wetting coating. The sealing layer and non-wetting coating provide additional protection to the components enclosed within the chamber and reduce unwanted leakage of the dispensed fluid.

[0089] The non-wetting coating is selected from any of the following materials: hydrophobic polymers such as parylene, fluoropolymers, polyolefins, polyimides, etc. In some embodiments, the anti-wetting, low-adhesion surface coating described herein is a reaction product of a reactant mixture. The reaction mixture may be composed of at least one triisocyanate and a perfluoropolyether diol compound containing an ethoxylated spacer. In some embodiments, suitable triisocyanates are available under the names Desmodur® Mondur® or Impranil®, e.g., Desmodur® N 3300, Desmodur® N 3790 available from Bayer Materials Science.

[0090] Referring now to FIG. 6, an exemplary configuration of the chamber 12 enclosing the piezoelectrically actuated flow path distributor 14 is shown, where the chamber 12 includes an additional chamber 24 surrounding the tip of the flow path distributor 14, which is used to provide an additional degree of control of the airflow and gas composition around the distributor tip.

[0091] For example, the additional chamber may be filled with a fluid of known composition and flow profile such that the pressure within the chamber is controlled in the range of -100 to 1000 mmH2O or -980 to 9800 Pascals. In some embodiments, the same or a different controlled pressure is applied to chamber 12.

[0092] Filling the chamber 12 containing the internal components of the printhead 10 with a known fluid helps reduce unwanted evaporation or dripping of the fluid from the nozzles of the flow distributor 14, as well as sealing the chamber 12 from outside contamination. Additionally, the controlled pressure helps maintain a constant flow rate from the flow distributor 14.

[0093] A system 32 for supplying fluid to multiple print heads will now be described with reference to Figure 7. The print heads to which fluid is supplied can, for example, be the same as print head 10 described above.

[0094] The system 32 includes a plurality of header tanks 34 corresponding to each of the plurality of printheads 10 such that each header tank 34 contains fluid to be dispensed by each respective printhead 10. The system 32 further includes a fluid supply chamber 38 for supplying fluid to each of the plurality of tanks 34, and a sensor 36 for detecting the level of fluid in the fluid supply chamber.

[0095] The system 32 further includes a digitally controlled recirculation feed 40 for controlling the supply and drainage rates between the fluid supply chamber 38 and each of the multiple tanks 34, the fluid supply and drainage rates being determined by the processor based at least in part on the fluid levels detected by the sensor 36.

[0096] Each header tank 34 includes an inlet 42 for receiving fluid from the recirculation feed and an outlet 44 through which fluid is discharged by the recirculation feed 40 and returned to the fluid supply chamber 38 .

[0097] The above-described aspects of system 32 provide a dynamic, digitally controllable system that can maintain sufficient levels of fluid in each header tank 34 at all times and return unwanted or unused fluid to the fluid supply chamber 38. This reduces waste and maintains a constant fluid flow, reducing the risk of clogging and improving efficiency.

[0098] Further, in some embodiments, the supply rates and drains between the fluid supply chamber 38 and each of the multiple header tanks 34 are the same for each tank, and the fluid flow paths between the fluid supply chamber 38 and each header tank 34 are of equal resistance to maintain a substantially uniform flow of fluid into and out of each header tank 34.

[0099] By maintaining substantially uniform supply and drain rates to each of the multiple header tanks 34, the level of fluid in each tank will be approximately the same and therefore can be determined by a single sensor controlling the supply and drain rates from the single fluid supply chamber 38. This configuration reduces the cost and complexity of assembly by allowing a single sensor 36 to effectively monitor and maintain the fluid levels in multiple header tanks.

[0100] Thus, in the above configuration, in response to the sensor 36 detecting that the fluid level has reached above a particular point in the fluid supply chamber 38, the system is configured to increase the supply rate to each of the plurality of tanks 34 and decrease the drainage rate from each of the plurality of tanks 34. Similarly, in response to the sensor detecting that the fluid level in the fluid supply chamber 38 has reached below a particular point, the system 32 is configured to decrease the supply rate to each of the plurality of tanks 34 and increase the drainage rate from each of the plurality of tanks.

[0101] In some embodiments, the above configuration allows for periodically varying levels of fluid level in the fluid supply chamber 38 with variations of less than 1 mm, maintaining the tank pressure within + / - 0.5 mm.

[0102] The level of the fluid supply tank is maintained by infeed and outfeed pumps. In some embodiments, the sensor is a capacitance sensor with an on / off level change of + / - 0.25 mm. The infeed pump is programmed to increase the flow rate more than the outfeed pump to raise the tank level when the level sensor is off, and vice versa when the level sensor is on, lowering the tank level.

[0103] In some embodiments, the fluid outlet of each header tank 34 is located at a higher level than the inlet 42 of each tank 34 to create a maximum fluid level in each tank in the event of an accidental oversupply of fluid.

[0104] In some embodiments, each of the plurality of tanks 34 further includes a vacuum bleed valve 46 disposed adjacent the tank inlet 42. The vacuum bleed valve is configured to provide a low resistance flow path in the event that pressure within the tank 34 exceeds a predetermined limit. This aspect of the system 32 ensures that the head tank pressure can be stabilized, minimizing overpressure caused by a sudden increase in tank fluid height, by allowing air to escape the headspace via a low resistance path.

[0105] The dispensing of fluid from the print head is very sensitive to the fluid pressure in the tank, with fluctuations of over 2mm H20 or 20 Pa being observed in the fluid dispensing. Therefore, accurate dispensing of fluid is highly dependent on a stable header tank pressure.

[0106] Thus, in some embodiments, the system further includes at least one vacuum pump 48 configured to control the pressure within the headspace of each of the multiple header tanks 34. The vacuum pump may be a high frequency piezoelectric air pump to minimize cyclical fluctuations in pressure.

[0107] 8A, 8B, 9A and 9B, example configurations of the header tank 34 and recirculation feed 40 will now be described in more detail. 8A and 8B illustrate an embodiment in which the fluid level and meniscus pressure in each of a plurality of header tanks 34 are controlled by an adjustable weir 45. In particular, each header tank 34 is configured such that a fluid inlet 42 supplies fluid to a first portion of the tank from above, a rotatable, retractable, or otherwise adjustable weir divides the first portion from a second portion of the tank, and a fluid outlet 44 is located low in the wall of the second portion of the tank 34.

[0108] In such an arrangement, rotating, retracting, or otherwise adjusting the height of adjustable weir 45 allows for control of the fluid level in the tank by altering the level at which fluid in a first portion of the tank spills over the weir into a second portion of the tank and is discharged through fluid outlet 44. Such an arrangement eliminates the need for a vacuum pump.

[0109] In Figure 8A, the header tank 34 is shown in a closed configuration. In Figure 8B, the header tank 34 is shown in an open configuration. The open configuration of Figure 8B simplifies cleaning and maintenance of the tank.

[0110] Although the illustrated embodiment shows the fluid inlet 42 located vertically above the tank and the fluid outlet 44 located low on the back wall, other configurations are possible and both the fluid inlet and outlet can be located above or on any side wall of the header tank.

[0111] An alternative header tank configuration for controlling fluid level and meniscus pressure is shown in Figures 9A and 9B. 9A and 9B, instead of an adjustable weir, the fluid outlet 44 itself is adjustable. For example, in the embodiment shown, both the fluid inlet 42 and the fluid outlet 44 are positioned vertically above the header tank 34, and the fluid outlet 44 is retractable or otherwise adjustable such that the level that it reaches in the header tank 34 is controllable. Thus, the level that the fluid outlet 44 reaches in the tank can be used to control the fluid level in the tank 34.

[0112] In Figure 9A, the header tank 34 is shown in a closed configuration. In Figure 9B, the header tank 34 is shown in an open configuration. The open configuration of Figure 9B simplifies cleaning and maintenance of the tank.

[0113] Referring now to FIG. 10, the digital control of the elements of the present invention will now be described in more detail. As noted above, the array of piezoelectric actuated flow path distributors 14 are individually and independently controlled by processor 50. Similarly, air flow 21 from air distribution element 18 is regulated by air flow controller 22, which is digitally controlled by a processor, which may be processor 50 or another processor. Additionally, sensor 36 and recirculation feed 40 are both in communication with the processor, which determines the above-mentioned supply and exhaust rates based on readings from sensor 36. The control processor may be processor 50 or another processor.

[0114] In the illustrated embodiment, the same processor 50 communicates with and controls the array of piezoelectric actuated flow distributors 14 , the airflow controller 22 , and the sensors 36 and recirculation feed 40 .

[0115] In an exemplary embodiment, the processor 50 corresponds to a microcontroller, a system on a chip, or a single board computer. The processor 50 includes a volatile memory, a non-volatile memory, and an interface. In certain other embodiments, the processor 50 may include multiple volatile memories, non-volatile memories, and / or interfaces. The volatile memories, non-volatile memories, and interfaces communicate with each other via a bus or other form of interconnection. The processor 50 executes computer readable instructions, such as one or more computer programs for controlling certain aspects of the systems described herein. The computer readable instructions are stored in the non-volatile memory. The processor 50 is powered by a power source, which may include a battery.

Claims

1. A printhead (10) for dispensing a fluid, comprising: At least one chamber (12); an array of piezoelectrically actuated flow channel distributors (14) enclosed within said at least one chamber; A multi-orifice distribution plate (16); an air distribution element (18) including a source of compressed air (20) and an air flow controller (22) configured to direct the air flow; a sealing layer (26) configured to resist fluid flow through the orifices (28) of the multi-orifice distribution plate; Equipped with The tip of the piezoelectrically actuated flow distributor is protruding through said multi-orifice distribution plate; Contacts the opening (30) of the sealing layer and protrudes from the opening (30). It is configured as follows: Print head.

2. The piezoelectric actuated flow distributor is controlled by a processor (50); the processor is configured to independently control each piezoelectrically actuated flow distributor; 2. The print head of claim 1.

3. the air distribution element is configured to direct airflow to a distributor tip of the piezoelectrically actuated flow channel distributor.

3. A print head according to claim 1 or 2.

4. The air distribution element distributes the air flow to the fluid flow distributed from the piezoelectrically actuated flow distributor. and configured to deflect the dispensed fluid in a controlled manner by directing the dispensed fluid generally parallel to the 4. The print head of claim 3.

5. The air distribution element is configured to apply the air flow periodically at a frequency in the range of 1 to 1,000 Hz. A print head according to any one of the preceding claims.

6. each of said chambers is filled with a fluid having a known composition and flow profile such that there is a controlled pressure in said chamber, which may be negative or positive; A print head according to any one of the preceding claims.

7. a tip of the piezoelectric actuated flow distributor configured to move relative to the sealing layer with minimal friction or mechanical resistance upon piezoelectric actuation; A print head according to any one of the preceding claims.

8. the sealing layer is a viscoelastic membrane including a plurality of openings; the viscoelastic membrane covers each orifice of the multi-orifice distribution plate; a diameter of each opening in the viscoelastic membrane through which the piezoelectric actuated flow distributor is configured to protrude is smaller than a diameter of a tip of the piezoelectric actuated flow distributor; A print head according to any one of the preceding claims.

9. The sealing layer is composed of a non-wetting elastomer or an elastomer with a non-wetting coating. A print head according to any one of the preceding claims.

10. a non-wetting coating is provided on the tip of the multi-orifice distribution plate and / or the piezoelectrically actuated flow channel distributor; A print head according to any one of the preceding claims.

11. The velocity of fluid dispensed by the print head is controllable by a voltage determined by the processor. A print head according to claim 2 and any one of claims 3 to 10 which recites claim 2.

12. the processor controls the spread of the dispensed fluid based on the digital image. A print head according to claim 2 and any one of claims 3 to 11 which recites claim 2.

13. the piezoelectric actuated flow distributor is controlled based on real-time feedback received by the processor; The real-time feedback includes: a) detection of coat weight; b) Color detection; c) flow rate detection; d) nozzle resonant frequency; e) the electrical drive requirements for each nozzle; At least one of: A print head according to claim 2 and any one of claims 3 to 12 which recites claim 2.

14. The piezoelectrically actuated flow channel distributor includes flow channels that are inclined relative to the substrate onto which the fluid is distributed. A print head according to any one of the preceding claims.

15. the print head is moved in a reciprocating motion relative to the substrate to dispense the dispensed fluid over a large area.

15. The print head of claim 14.

16. the reciprocating motion is controlled based at least in part on real-time feedback received by the processor. A print head according to claim 15 which relies on claim 14 which relies on claim 2.

17. the real-time feedback being based on color detection of the entire substrate; 17. The print head of claim 16.

18. There is increased air pressure within the print head; the air pressure induces an air flow in a direction from inside the at least one chamber toward a tip of the piezoelectrically actuated flow channel distributor. A print head according to any one of the preceding claims.

19. the printhead further comprising an additional chamber surrounding a tip of the piezoelectrically actuated flow channel distributor; A print head according to any preceding claim.

20. a diameter of the opening (30) in the sealing layer (26) configured to be smaller than a diameter of a corresponding tip of the piezoelectrically actuated flow distributor; A print head according to any one of the preceding claims.

21. The sealing layer (26) is made of a viscoelastic material. A print head according to any preceding claim.

22. A system (32) for supplying fluid to a plurality of print heads, comprising: A plurality of print heads according to any one of claims 1 to 21; a plurality of tanks (34) for holding fluids to be dispensed from said plurality of printheads; A fluid supply chamber (38); a sensor (36) for detecting a fluid level in the fluid supply chamber; a recirculation feed (40) for controlling a fluid supply rate and a fluid discharge rate between the fluid supply chamber and each of the plurality of tanks, the fluid supply rate and the fluid discharge rate being determined by a processor based at least in part on the fluid level detected by the sensor; Equipped with system.

23. the fluid supply rate and the fluid discharge rate between the fluid supply chamber and each of the plurality of tanks are the same for each tank; 23. The system of claim 22.

24. the sensor is a capacitance sensor; The system comprises: responsive to the sensor being switched on, increasing a rate of supply of the fluid to each of the plurality of tanks and decreasing a rate of drainage of the fluid from each of the plurality of tanks; In response to the sensor being switched off, the rate at which the fluid is supplied to each of the plurality of tanks is decreased and the rate at which the fluid is drained from each of the plurality of tanks is increased. It is configured as follows:

24. A system according to claim 22 or 23.

25. the sensor is a pressure sensor; The system comprises: responsive to the sensor detecting low pressure, increasing a rate of supply of fluid to each of the plurality of tanks and decreasing a rate of drainage of fluid from each of the plurality of tanks; In response to the sensor detecting high pressure, the rate at which the fluid is supplied to each of the plurality of tanks is decreased and the rate at which the fluid is drained from each of the plurality of tanks is increased. It is configured as follows:

24. A system according to claim 22 or 23.

26. a fluid flow path connecting a fluid inlet (42) and a fluid outlet (44) of each of the plurality of tanks to the fluid supply chamber; the fluid flow paths of each tank have equal resistance; A system according to any one of claims 22 to 25.

27. the fluid outlet of each tank is located at a higher level than the fluid inlet of each tank to create a maximum fluid level in the corresponding tank based on the weir principle; 27. The system of claim 26.

28. Each of the plurality of tanks further comprises a vacuum bleed valve (46) disposed adjacent the fluid inlet; the vacuum bleed valve is configured to provide a low resistance flow path when pressure within the tank exceeds a predetermined limit; 28. A system according to claim 26 or 27.

29. The system further comprises at least one vacuum pump (48); the vacuum pump is configured to control the pressure in each of the plurality of tanks. A system according to any one of claims 22 to 28.

30. each tank of the plurality of tanks further comprising an adjustable divider configured to control the fluid level within the respective tank based on a weir principle; A system according to any one of claims 22 to 28.

31. the fluid outlet of each tank of the plurality of tanks is adjustable; the fluid outlet of each tank is configured to control the fluid level in the respective tank by adjusting the level to which fluid is discharged. A system according to any one of claims 26 to 28.

32. The pressure control is closed loop with a latency of less than 1 second per adjustment.

30. The system of claim 29.

33. The system is further configured to heat and / or agitate the fluid. A system according to any one of claims 22 to 32.

34. The system is further configured to degas and / or filter the fluid. A system according to any one of claims 22 to 33.

35. A pump is used to recirculate the fluid in each tank. A system according to any one of claims 22 to 34.

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