Ink supply device and inkjet printing system including the same

Abstract

To provide an ink supply device which may effectively circulate an ink for inkjet printing to stably maintain a state of the ink, and to provide an inkjet printing system including the ink supply device.SOLUTION: An ink supply device includes: an ink storage unit configured to store an ink at least temporarily; a first passage tube configured to supply the ink stored in the ink storage unit to an inkjet head unit; a second passage tube configured to collect the ink from the inkjet head unit; an ink circulation unit configured to move the ink flowing thereinto through the second passage tube along one direction; and a third passage tube configured to supply the ink flowing out from the ink circulation unit to the ink storage unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink supply device and an inkjet printing system including the same, and more particularly to an ink supply device that can effectively circulate ink for inkjet printing and stably maintain the state of the ink, and an inkjet printing system including the same. [Background technology]

[0002] Inkjet printing, which involves spraying liquid ink in the form of droplets onto the surface of a target, is used not only for printing documents and flyers, but also for solution processes in the semiconductor and display fields.

[0003] Small inkjet printers for creating documents have a structure in which the ink is stored in an inkjet head that ejects ink droplets, but large inkjet printers for creating documents and inkjet printers manufactured for industrial use in the manufacture of electronic components and displays use large amounts of ink, so they have a structure in which the ink storage section and the inkjet head are separated.

[0004] For inkjet printing devices to be practically used in industrial applications, they must be highly precise and capable of forming high-resolution patterns and printing ultra-thin films by ejecting ink from multiple nozzle heads. Maintaining the ink condition is essential to achieve these results. Maintaining the ink condition requires removing air bubbles and other foreign matter that may be generated during ink clumping, hardening, gelation, and other processes. By removing air bubbles and foreign matter from the ink path and circulating the ink, large amounts of ink can be ejected stably without problems such as ink blockages and unstable ink flow.

[0005] In order to remove air bubbles from the ink and remove foreign matter generated by ink clumping, etc., various attempts have been made, such as inserting a filter unit above the ink flow path or increasing the flow rate. However, new problems have arisen, such as congestion caused by the filter unit and the inflow of external air due to the pressure change required to increase the flow rate, and there is still a need for an effective technology that can stably maintain the state of the ink without ink congestion or the inflow of external air. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Republic of Korea Publication Patent No. 10-2008-0098266 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides an ink supply device that can remove air bubbles present in ink and circulate the ink to maintain a stable ink condition, and an inkjet printing system equipped with the ink supply device. [Means for solving the problem]

[0008] An ink supply device according to an embodiment of the present invention may include an ink reservoir that stores ink at least temporarily, a first flow path pipe that supplies the ink stored in the ink reservoir to an inkjet head, a second flow path pipe that recovers ink from the inkjet head, an ink circulation section that moves the ink flowing in through the second flow path pipe in one direction, and a third flow path pipe that supplies the ink flowing out from the ink circulation section to the ink reservoir.

[0009] The ink circulation unit may include a cylinder unit that provides a hollow internal space extending in the one direction, a screw unit that extends in the one direction and is inserted into the internal space and arranged to be freely rotatable, and a motor unit that selectively rotates the screw unit.

[0010] The internal space may be cylindrical and have a uniform inner diameter along the one direction, and the screw portion may have a uniform outer diameter along the one direction.

[0011] The outer diameter of the screw portion may be smaller than the inner diameter of the internal space and may be 80% or more of the inner diameter of the internal space.

[0012] The screw portion comprises a shaft portion extending in the one direction and a blade portion arranged to form a spiral along the outer wall of the shaft portion, and the outer diameter and pitch of the blade portion may be the same along the one direction.

[0013] A separation space may be provided between one end of the screw portion and one end inside the internal space, and the third flow path pipe may be connected to the separation space.

[0014] The ink supply device may further include a flow meter unit that measures the flow rate of ink flowing inside the third flow path pipe, and a control unit that controls at least one of the rotation speed, rotation amount, or rotational force of the motor unit according to the flow rate of ink measured by the flow meter unit.

[0015] The ink supply device may further include a capacity detection unit that detects the volume of ink stored in the ink storage unit, and an ink refill unit that is connected to the ink storage unit and refills the missing ink if the volume of ink detected by the capacity detection unit is less than a reference volume.

[0016] The ink supply device may further include a negative pressure setting unit connected to the ink reservoir unit and configured to set the pressure in the internal space of the ink reservoir unit to a pressure lower than atmospheric pressure.

[0017] The ink supply device may further include a buffer section that communicates with the first flow path pipe, is disposed between the ink reservoir section and the inkjet head section, and provides a buffer space having a cross-section larger than that of the first flow path pipe.

[0018] The first flow path pipe may be provided in a plurality of pipes, and the inner diameter of the third flow path pipe may be larger than the inner diameter of the first flow path pipe.

[0019] The ink may contain solids.

[0020] An inkjet printing system according to another embodiment of the present invention may include an inkjet head unit having a plurality of nozzle units that eject ink onto a substrate, and an ink supply device according to an embodiment of the present invention that supplies ink to the inkjet head unit.

[0021] The inkjet head unit may be arranged in plural numbers.

[0022] The first flow path pipe, the second flow path pipe, and the like may be arranged in a plurality of pipes corresponding to the plurality of inkjet head units, and each of the first flow path pipes may be connected to one side of the corresponding inkjet head unit, and each of the second flow path pipes may be connected to the other side of the corresponding inkjet head unit. [Effects of the Invention]

[0023] The ink supply device and inkjet printing system equipped with the ink supply device according to the present invention can remove air bubbles present in the ink or on the ink flow path, making it possible to stably supply ink to the inkjet head without interrupting the ink flow.

[0024] In order to impart various functionalities to the applied coating layer, in the case of inks that contain various solids mixed in or that tend to clump, harden, or gel when the flow is interrupted or stagnated, the ink can be uniformly agitated by continuously circulating the ink between the inkjet head and the ink reservoir, thereby maintaining the ink state. Furthermore, by suppressing the precipitation of solids contained in the ink, the phenomenon of ink clumping, and localized hardening or gelation of the ink, damage to the inkjet head due to nozzle clogging caused by these factors can be prevented.

[0025] Furthermore, air bubbles are removed from the ink and the ink flow path, and sudden pressure changes or pulsation phenomena in the ink reservoir and ink flow path are suppressed, allowing for the formation and maintenance of an accurate meniscus, thereby effectively improving the stability of ink ejection and the accuracy of the ink landing position. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a configuration diagram showing an ink supply device and an inkjet printing system according to the present invention; [Figure 2] FIG. 2 is a diagram showing an ink circulation section of the ink supply device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, the embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various different forms. These embodiments are provided merely to complete the disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art. In describing the present invention, the same reference numerals will be used to refer to the same components, and the drawings may be exaggerated in size to accurately illustrate the embodiments of the present invention. In the drawings, the same numerals will refer to the same components.

[0028] FIG. 1 is a configuration diagram showing an ink supply device and an inkjet printing system according to the present invention, and FIG. 2 is a diagram showing an ink circulation section of the ink supply device according to the present invention.

[0029] 1 and 2, an ink supply device 100 according to an embodiment of the present invention may include an ink reservoir 110 for at least temporarily storing ink, a first flow path 120 for supplying the ink stored in the ink reservoir 110 to an inkjet head 200, a second flow path 130 for recovering ink from the inkjet head 200, an ink circulation section 140 for moving the ink flowing in through the second flow path 130 in one direction, and a third flow path 150 for supplying the ink flowing out from the ink circulation section 140 to the ink reservoir 110.

[0030] The ink reservoir 110 may have an internal space for at least temporarily storing ink, and may be connected to a plurality of flow pipes through which ink flows into and out of the internal space. A partition may be disposed in the internal space so that the ink can mix naturally as it flows in and out. In general, the internal space may not be completely filled with ink, and a portion of the internal space may remain empty.

[0031] The first flow path pipe 120 may be connected to the ink reservoir 110 to provide a flow path for supplying ink stored in the ink reservoir 110 to the inkjet head unit 200 .

[0032] The second flow path 130 may provide a flow path for recovering at least a portion of the ink that has been supplied to the inkjet head 200. When the inkjet head 200 ejects ink for a printing operation, the second flow path 130 may recover the remaining ink that has been supplied to the inkjet head 200, or when the inkjet head 200 is waiting without performing a printing operation, the second flow path 130 may recover all of the ink that has been supplied to the inkjet head 200.

[0033] The ink circulation unit 140 may have one side connected to the second flow path 130 and may function to move the ink flowing in through the second flow path 130 in one direction. By moving the ink flowing in through the second flow path 130 in one direction, a space into which the ink remaining in the inkjet head 200 can flow is formed, allowing the ink to continue flowing in one direction.

[0034] The third flow path pipe 150 may be connected to the other side of the ink circulation section 140 to provide a flow path for supplying ink that moves in one direction by the ink circulation section 140 and flows out of the ink circulation section 140 to the ink reservoir section 110.

[0035] As the ink continuously circulates along the circulation flow path that runs from the ink reservoir 110 through the first flow pipe 120, the inkjet head unit 200, the second flow pipe 130, the ink circulation unit 140, and the third flow pipe 150 back to the ink reservoir 110, the ink flows continuously, improving the ink's dispersibility and maintaining the ink's uniformity. As the ink continuously circulates along the circulation flow path, not only the ink but also the air present in the circulation flow path moves as the ink circulates, allowing it to be discharged into the open space inside the ink reservoir 110.

[0036] The ink supply device 100 may further include a negative pressure setting unit 173 connected to the ink reservoir 110 to set the pressure of the internal space of the ink reservoir 110 to a pressure lower than atmospheric pressure. The negative pressure setting unit 173 includes an exhaust means for exhausting the internal space of the ink reservoir 110 to adjust the pressure in the internal space, and the ink or air present in the circulation flow path also moves as the ink circulates and is discharged into the empty space inside the ink reservoir 110, and can then be exhausted to the outside by the exhaust means of the negative pressure setting unit 173.

[0037] In order to eject a fixed amount of ink from the inkjet head 200 to a fixed position and form accurate dots, it is necessary to apply a negative pressure to the internal space of the ink reservoir 110 so that the ink can maintain a meniscus state, which is a curved surface that is recessed inward by capillary action, at the entrance of the nozzle of the inkjet head 200. The negative pressure setting unit 173 may adjust the pressure in the internal space of the ink reservoir 110 to a pressure lower than atmospheric pressure. When the negative pressure setting unit 173 sets the internal space of the ink reservoir 110 to a negative pressure, the entire ink flow path remains airtight except when the first flow path 120, the inkjet head unit 200, the second flow path 130, the ink circulation unit 140, and the third flow path 150 connected to the ink reservoir 110 are filled with ink or the ink is moving, thereby allowing the ink to maintain a meniscus state at the entrance of the nozzle.

[0038] If the ink itself or solids present inside the ink partially aggregate and block the ink flow path, or if air is present in the ink flow path, the negative pressure set by the negative pressure setting unit 173 cannot be transmitted to the entrance of the nozzle in the internal space of the ink reservoir 110, and as a result, it may become impossible to maintain a meniscus state. However, according to the present invention, the ink continues to circulate through the circulation path without any additional equipment, maintaining a homogeneous ink state and effectively suppressing partial aggregation, and allowing air to be discharged to the outside, thereby effectively maintaining and controlling the meniscus state at the entrance of the nozzle in accordance with the negative pressure set by the negative pressure setting unit 173.

[0039] To circulate the ink along the circulation path, a driving force is required to move the ink. A variety of pumps are available that apply pressure (such as applying positive pressure from the rear or negative pressure from the front) to the ink in the direction of ink movement. For example, an impeller pump may be used, or a pump module may be configured using multiple piezoelectric pumps. Such conventional circulation pumps generate a pressure differential in the ink circulation path to move the ink. However, due to pressure changes in the ink circulation path, the negative pressure established in the internal space of the ink reservoir 110 may not be uniformly transmitted to the ink at the nozzle inlet, which may result in the inability to maintain a meniscus at the nozzle inlet. Furthermore, circulation pumps experience a pulsation phenomenon in which the pressure periodically fluctuates during pump operation. This pulsation phenomenon may make it even more difficult to control the meniscus at the nozzle inlet. In other words, if a normal circulation pump is arranged in the ink circulation path that includes the inkjet head unit 200, it may become difficult to accurately maintain and control the meniscus at the entrance of the nozzle unit of the inkjet head unit.

[0040] To solve this problem, ink may be circulated only between the ink reservoir and the inkjet head by blocking the nozzle of the inkjet head or by bypassing the nozzle of the inkjet head. However, this requires the addition of an additional shutoff valve or bypass flow path, which makes the equipment configuration complicated, and during actual inkjet printing, there is a risk that ink will not circulate and will stagnate in the nozzle of the inkjet head, which is the section from which ink is directly ejected.

[0041] The ink circulation unit 140 may include a cylinder unit 141 that provides a hollow internal space extending in the one direction, a screw unit 142 that extends in the one direction and is inserted into the internal space and arranged to be freely rotatable, and a motor unit 143 that selectively rotates the screw unit 142.

[0042] In the present invention, the ink circulation unit 140 is fitted into the ink flow path through which ink is supplied, discharged, and recovered during inkjet printing operations, so that the ink circulated by the ink circulation unit 140 can circulate including the nozzle portion of the inkjet head unit 200 without blocking or bypassing the nozzle portion of the inkjet head unit 200.

[0043] The cylinder portion 141 may provide a hollow internal space extending in one direction, and may provide a space in which the ink can flow in one direction between the second flow path pipe 130 and the third flow path pipe 150. While the ink circulates, the internal space of the cylinder portion 141 may be completely filled with ink.

[0044] The screw portion 142 may have a shape that extends in one direction and be fitted into an internal space that also extends in one direction so as to be rotatable. The motor portion 143 may apply a rotational force to the screw portion 142 to selectively rotate the screw portion 142.

[0045] When the screw portion 142, which has a shape extending in one direction, is fitted into the hollow internal space of the cylinder portion 141, which provides the ink flow space, and is continuously rotated, the ink flowing into the internal space of the cylinder portion 141 can move along the blade portion formed in a spiral along the screw axis of the screw portion 142. In other words, unlike a conventional circulation pump, there is no need to generate a sudden change in pressure (differential pressure) in the flow path, and the screw portion 142 rotating at a constant speed can stably and continuously move ink at a consistent volumetric flow rate. In addition, because the ink is pushed and moves naturally by the screw portion 142 rotating continuously and constantly in one direction, the pulsation phenomenon that occurs in conventional circulation pumps can be completely eliminated or significantly reduced.

[0046] Therefore, according to the present invention, by effectively suppressing sudden pressure changes and pulsation phenomena, a weak negative pressure can be applied to the ink reservoir 110, thereby accurately maintaining and controlling the ink meniscus state in the nozzle portion of the inkjet head 200, thereby enabling stable ink ejection and inkjet printing.

[0047] In order to accurately control the ink meniscus state using a weak negative pressure applied to the ink reservoir 110, the ink flowing through the ink circulation unit 140 must be able to move naturally as the screw unit 142 rotates without experiencing a sudden change in pressure or a pulsation phenomenon (periodic pressure change). For this purpose, the internal space of the cylinder unit 141 may be cylindrical with a uniform inner diameter along the one direction, and the screw unit 142 may have a uniform outer diameter along the one direction.

[0048] In the present invention, the fact that the sizes of components are the same does not only mean that they are completely the same physically, but also means that they are the same including processing tolerances.

[0049] If the inner diameter of the internal space of the cylinder portion 141 and the outer diameter of the screw portion 142 are the same along one direction, which is the direction in which the ink moves, the moving ink will move naturally, being constantly pushed only by the blade portion of the rotating screw portion 142, without experiencing any pressure changes along that direction.

[0050] The screw portion 142 comprises a shaft portion 142a extending in the one direction and a blade portion 142b arranged in a spiral shape along the outer wall of the shaft portion 142a, and the outer diameter and pitch of the blade portion 142b may be the same along the one direction.

[0051] One end of the shaft portion 142a may be connected to a motor portion 143 that provides a rotational force and may rotate by receiving the rotational force. The blade portion 142b may be arranged in a spiral shape along the outer wall of the rotating shaft portion 142a. The shaft portion 142a and the blade portion 142b may be formed integrally or may be manufactured separately and then combined. In this case, the outer diameter and pitch of the blade portion 142b may be the same along the one direction. The outer diameter of the blade portion 142b may be the height from the outer wall of the shaft portion 142a, and the pitch may be the distance between the blade portions 142b when positioned at the same positions. Since the driving force required to move the ink along one direction is the pushing force of the rotating blade portion 142b, the outer diameter and pitch of the blade portion 142b must be the same along the one direction in order for the ink to move uniformly along the one direction. In particular, as will be described later, in an inkjet printing system having a plurality of inkjet head units 200, ink flows into the ink circulation unit 140 through a plurality of second flow pipes 130 connected to the plurality of inkjet head units 200, respectively. In order for the ink flowing through different paths to move naturally without experiencing large pressure changes, a constant driving force must be transmitted to the ink regardless of the path through which it flows. In other words, even if a plurality of second flow pipes 130 are connected to the internal space of the cylinder unit 141 at regular intervals along one direction, the ink flowing through each second flow pipe 130 is pushed in one direction by a constant force by the blade units 142b, which have the same outer diameter and pitch along that direction, and therefore can move in a uniform manner.

[0052] The outer diameter D1 of the screw portion 142 may be smaller than the inner diameter D2 of the internal space of the cylinder portion 141 and may be 80% or more of the inner diameter D2 of the internal space. In this case, the ink present in the space surrounded by the inner wall of the cylinder portion 141 and the blade portion 142b of the screw portion 142b is pushed as the blade portion 142b rotates, and can move effectively in one direction.

[0053] From the perspective of transmitting force, it may be most effective if the outer diameter D1 of the screw portion 142 and the inner diameter D2 of the internal space are the same, but if the outer diameter D1 of the screw portion 142 and the inner diameter D2 of the internal space are the same, there is a risk that the rotating screw portion 142 will be pinched by the inner wall of the cylinder portion 141, which may prevent the screw portion 142 from continuing to rotate or may damage the cylinder portion 141 or the screw portion 142. On the other hand, if the outer diameter D1 of the screw portion 142 is smaller than 80% of the inner diameter D2 of the internal space, the ink pushed as the screw portion 142 rotates will no longer be supported by the inner wall of the cylinder portion 141, and some of the ink may stagnate along the inner wall of the cylinder portion 141 instead of moving in one direction, which may result in a problem of reduced circulation efficiency.

[0054] A separation space 145 may be provided between one end of the screw portion 142 and one end inside the internal space of the cylinder portion 141, and the third flow path pipe 150 may be connected to the separation space 145.

[0055] If the third flow pipe 150 is disposed at one end of the screw portion 142, and ink moving along the blade portion 142b of the rotating screw portion 142 flows out through the third flow pipe 150 as soon as it reaches one end of the screw portion 142, the position of the blade portion 142b changes as the screw portion 142 rotates, which may result in the ink not flowing out uniformly into the third flow pipe 150. To solve this problem, one end of the screw portion 142 does not abut or come close to one end inside the internal space of the cylinder portion 141, and one end of the screw portion 142 and one end inside the internal space of the cylinder portion 141 are separated from each other to provide a separation space 145, so that the ink that reaches one end of the screw portion 142 is stabilized through the separation space 145 and then flows out into the third flow pipe 150 by being pushed by the constant volumetric flow rate. The separation distance between one end of the screw portion 142 and one end inside the internal space of the cylinder portion 141 may be larger than the inner diameter of the third flow path pipe 150 so as to ensure sufficient space for the ink to be separated from one end of the rotating screw portion 142 and stabilized in the separation space 145 to which the third flow path pipe 150 is connected.

[0056] The ink supply device 100 may further include a flow meter unit 160 that measures the flow rate of ink flowing inside the third flow path pipe 150, and a control unit 144 that controls at least one of the rotation speed, rotation amount, or rotation force of the motor unit 143 in accordance with the ink flow rate measured by the flow meter unit 160.

[0057] The flow meter unit 160 may measure the flow rate of ink flowing from the ink circulation unit 140 and flowing inside the third flow pipe 150, thereby monitoring the ink circulation state within the ink supply device using the ink circulation unit 140. If the flow rate of the circulating ink is too high, there is a risk of wear on the components constituting the circulation flow path, causing a sudden change in pressure and making it difficult to control the meniscus state at the entrance of the nozzle unit. On the other hand, if the flow rate of the circulating ink is too low, the circulating ink will not be sufficiently effective in removing air or stirring and homogenizing the ink. Therefore, it is necessary to monitor whether the ink is circulating within the ink supply device at a preset flow rate.

[0058] The flow meter unit 160 may also be arranged in other paths through which the ink circulates (for example, the first flow path pipe 120, etc.), but by measuring the flow rate of the ink circulating downstream of the ink circulation unit 140, not only can the ink circulation state be confirmed by the flow meter unit 160 itself, but also, as described below, the flow path of the first flow path pipe 120, etc., can be changed to accommodate multiple inkjet head units, and the flow meter unit 160 can be maintained as is.

[0059] The flow meter unit 160 may be a non-contact flow meter that is attached to the outer wall of the third flow pipe 150 by a clamp-on method so as not to interfere with the flow of ink flowing inside the third flow pipe 150. For example, the flow meter unit 160 may be a non-contact ultrasonic flow meter that measures the flow rate by measuring the difference in arrival time of ultrasonic waves using ultrasonic sensors arranged at different positions along the flow direction of the fluid (ink), or may be a non-contact temperature flow meter that measures the flow rate by measuring the temperature difference between two points using temperature sensors arranged at different positions along the flow direction of the fluid.

[0060] The control unit 144 may be connected to the flow meter unit 160 and the motor unit 143, monitor the ink flow rate measured by the flow meter unit 160, and control at least one of the rotation speed, rotation amount, or rotation force of the motor unit 143 according to the ink flow rate measured by the flow meter unit 160.

[0061] The control unit 144 may include a flow rate determination unit 144a that compares a preset flow rate with the ink flow rate measured by the flow meter unit 160 to determine whether the flow rate of the circulating ink is within a normal range, and a drive control unit 144b that, if the flow rate determination unit 144a determines that the measured ink flow rate is outside the normal range, controls at least one of the rotation speed, rotation amount, or rotation force of the motor unit 143. On the other hand, if the flow rate determination unit 144a determines that the measured ink flow rate is within the normal range, the drive control unit may maintain the current operating state of the motor unit 143.

[0062] The ink flowing out of the ink circulation unit 140 is supplied to the ink reservoir 110 via the third flow pipe 150, allowing the ink to continue circulating along the circulation path. The ink flowing in and collected via the third flow pipe 150 connected to one position of the ink reservoir 110 may be mixed with the ink as it flows from one position to another in the ink reservoir 110. To further enhance the mixing effect, a partition (e.g., vertical) may be disposed between the one position and the other position across the flow path to allow the ink to continue mixing as it flows. In this case, the partition may be positioned at least partially away from the inner wall of the ink reservoir 110 so that the ink can flow through the space between the partition and the inner wall of the ink reservoir 110. Furthermore, the air contained in the ink collected through the third flow pipe 150 may be separated from the ink as the ink flows inside the ink reservoir 110 and removed by the negative pressure setting unit 173 connected to the ink reservoir 110. If a partition wall is provided inside the ink reservoir, the ink collides with the partition wall and bypasses the ink, allowing the air contained in the ink to be separated more effectively and to be exhausted very easily.

[0063] The ink supply device 100 may further include a capacity detection unit 171 that detects the volume of ink stored in the ink storage unit 110, and an ink refill unit 172 that is connected to the ink storage unit 110 and refills the missing ink if the volume of ink detected by the capacity detection unit 171 is less than the reference volume.

[0064] The volume sensing unit 171 may sense the volume of ink stored in the ink reservoir 110 to determine whether a certain level of ink is stored in the ink reservoir 110 so that ink can be stably ejected from the inkjet head unit 200. The volume of ink may be measured using a level sensor that measures the height of the surface of the ink stored in the ink reservoir 110, but the present invention is not limited thereto, and the volume of ink may be sensed using a variety of methods.

[0065] If the ink volume detected by the volume detection unit 171 is less than the reference volume, the ink refill unit 172 may supply ink to replenish the ink insufficiency in the ink reservoir 110. The ink refill unit 172 replenishes the ink that is gradually decreasing as it is discharged from the inkjet head unit 200 during inkjet printing, thereby maintaining a constant volume of ink stored in the ink reservoir 110. The ink refill unit 172 may be connected to an external storage tank that stores ink outside the device, and supply the ink stored in the external storage tank to the ink reservoir 110.

[0066] The ink supply device 100 may further include a buffer section 180 that is connected to the first flow path pipe 120, is disposed between the ink reservoir section 110 and the inkjet head section 200, and provides a buffer space having a cross-section larger than that of the first flow path pipe 120.

[0067] Generally, an inkjet printing system includes a plurality of inkjet heads 200 and requires a plurality of first flow tubes 120 for supplying ink to the inkjet heads 200, respectively. If the plurality of first flow tubes 120 are connected to ink reservoirs 110, respectively, and ink circulates along a circulation path, the flow rate of ink moving through the plurality of first flow tubes 120 may vary depending on the connection positions of the ink reservoirs 110. Furthermore, if negative pressure is applied to the ink reservoirs 110 to control the meniscus state at the entrances of the nozzles of the inkjet heads 200, the negative pressure is transmitted through the plurality of first flow tubes 120, but the magnitude of the negative pressure transmitted through each of the plurality of first flow tubes 120 may vary. If the flow rate of ink moving through the plurality of first flow tubes 120 or the magnitude of the negative pressure vary, the state of ink ejected from the plurality of inkjet heads 200 may also vary depending on the position, which may make it difficult to ensure uniform print quality.

[0068] The buffer unit 180, which is connected to the first flow path pipe 120 and provides a buffer space having a larger cross section than the first flow path pipe 120, is disposed between the ink reservoir 110 and the inkjet head unit 200. When the ink flowing through the first flow path pipe 120 flows into the buffer space, which is a larger space than the first flow path pipe 120, the ink is mixed and homogenized, and the negative pressure applied to the first flow path pipe 120 is also made constant. That is, the buffer unit 180 may be connected to a plurality of first flow path pipes 120 to provide a common buffer space to homogenize the ink, and then supply the ink to a plurality of inkjet head units 200 via a plurality of downstream first flow path pipes 120. The first flow path pipe 120 is divided into an upstream first flow path pipe 120A and a downstream first flow path pipe 120B centered on the buffer section 180, and homogenized ink flows through the downstream first flow path pipe 120B, allowing uniform negative pressure to be transmitted to each inkjet head section 200.

[0069] On the other hand, a plurality of first flow path pipes 120 may be provided, and the inner diameter of the third flow path pipe 150 may be larger than the inner diameter of the first flow path pipe 120. Even if ink is collected from a plurality of inkjet head units 200, it accumulates in the ink circulation unit 140 and then flows out and is supplied to the ink reservoir unit 110 via the third flow path pipe 150. Therefore, unless the ink is consumed by being discharged from the inkjet head units 200, it is possible to supply ink to the inkjet head units 200 via the first flow path pipe 120 at the same flow rate as the collected ink. Since the ink moving through the third flow path pipe 150 forming a single flow path circulates through each of the plurality of first flow path pipes 120, the inner diameter of the third flow path pipe 150 may be larger than the inner diameter of each of the plurality of first flow path pipes 120 so that the first flow path pipe 120 and the third flow path pipe 150 constituting the circulation path do not interfere with the circulation of the ink. For accurate comparison, the inner diameter of the third flow path pipe 150 and the inner diameters of the plurality of first flow path pipes 120 that correspond to the same height may be used.

[0070] In the present invention, the ink may contain solids.

[0071] In industrial inkjet printing systems used in the manufacture of electronic products such as display devices, inks containing materials necessary for component manufacturing may be used in addition to or instead of pigments. Various solids may be added to inks to impart desired functionality to parts of electrical and electronic components such as display panels. For example, inks containing quantum dot materials or nanorods exhibiting various optical properties, polymer resins as insulating materials, or metallic copper for conductivity may be used. As described above, inks for inkjet printing systems used in industrial fields contain various components, including solids with different specific gravities from the liquid components. Therefore, simply adding a dispersant may make it difficult to maintain the dispersibility of the various materials contained in the ink for a long period of time. Therefore, the ink supply device according to the present invention continuously circulates ink through an ink circulation path comprising an inkjet head unit 200 for printing in an inkjet printing system, thereby not only removing air present in the ink but also ensuring that various components, including solids, present in the ink are uniformly mixed and maintained.

[0072] The ink supply device 100 may include a flow path pipe including a first flow path pipe 120 to a third flow path pipe 150 through which ink flows, and a plurality of valves 190; 191, 192, 193, 194 disposed in an exhaust pipe connected between the ink reservoir unit 110 and a negative pressure setting unit 173 and capable of controlling the flow rate or exhaust amount of ink as needed. The control unit 144 may be connected to the capacitance sensing unit 171, the flow meter unit 160, the plurality of valves 191 to 194, etc., and may turn the plurality of valves 191 to 194 on / off or adjust the flow rate by generating and transmitting control signals for controlling the plurality of valves 191 to 194 using measurement signals measured by the capacitance sensing unit 171, etc.

[0073] For example, in the process of filling the ink reservoir 110 with an appropriate volume of ink, the valve 193 disposed between the ink refill unit 172 and the ink reservoir 110 may be opened, and the valves 191, 192 disposed in the first to third flow pipes 120 to 150 may be closed. When the ink stored in the ink reservoir 110 reaches an appropriate volume, the valve 193 may be closed, and then the valve 194 disposed between the ink reservoir 110 and the negative pressure setting unit 173 and the valves 191, 192 disposed in the first to third flow pipes 120 to 150 may be opened.

[0074] Referring to Figures 1 and 2, an inkjet printing system according to another embodiment of the present invention may include an inkjet head unit 200 having a plurality of nozzle units that eject ink onto a substrate, and an ink supply device 100 according to an embodiment of the present invention that supplies ink to the inkjet head unit 200.

[0075] In describing the inkjet printing system according to another embodiment of the present invention, the description of the same matters as those described above in relation to the ink supply device 100 according to the embodiment of the present invention will be omitted.

[0076] The inkjet printing system may form and print a coating layer by spraying ink in a solution state containing various functional materials onto a substrate through multiple nozzle units arranged in the inkjet head unit 200.

[0077] In the case of a large substrate, it is difficult to fabricate a head unit equipped with multiple nozzle units corresponding to the area of ​​the substrate, and forming a work space for inkjet printing by spraying ink through multiple nozzle units requires the provision of a large chamber, which may be cumbersome from various perspectives.

[0078] The multiple nozzle units arranged in the inkjet head unit 200 may be aligned along a first direction, but by moving the inkjet head unit 200 or the substrate in a second direction that intersects the first direction, it is possible to form a uniform coating layer over a large area even on a large-area substrate or using a small-scale inkjet printing system.

[0079] Inkjet printing systems manufactured for industrial use to manufacture electronic components and displays use large amounts of ink to accommodate large-area substrates, so they can have a structure in which the ink supply device 100 that stores and stably supplies ink and the inkjet head unit 200 are separated.

[0080] The inkjet head unit 200 may include a plurality of nozzles that eject ink onto a substrate for printing. The inkjet head unit 200 can be operated in a thermal mode, which uses fine heat rays to heat the ink, increasing its volume and ejecting an amount of ink commensurate with the increased volume, or a piezo mode, which uses a piezoelectric element that deforms when a voltage is applied to apply pressure to the inside of the head to eject ink, but the present invention is not limited to these modes.

[0081] The ink supply device 100 may include an ink storage section 110 that stores ink at least temporarily, a first flow path pipe 120 that supplies the ink stored in the ink storage section 110 to an inkjet head section 200, a second flow path pipe 130 that recovers ink from the inkjet head 200, an ink circulation section 140 that moves the ink flowing in through the second flow path pipe 130 in one direction, and a third flow path pipe 150 that supplies the ink flowing out from the ink circulation section 140 to the ink storage section 110.

[0082] According to the ink supply device 100, there is no need to distinguish between an ink circulation path for printing and an ink circulation path for stirring during standby; the ink is circulated using the same circulation path, removing any air bubbles present in the ink, and ink can be supplied to the inkjet head unit 200 while maintaining a homogeneous and stable ink state.This means that ink can be ejected from the inkjet head unit 200 very stably and accurately, thereby improving print quality.

[0083] The inkjet printing system of the present invention may include multiple inkjet head units 200. The multiple inkjet head units 200 may be arranged in various arrangements depending on various purposes. When printing on a large-area substrate, since a single inkjet head unit 200 cannot cover such a large area, multiple inkjet head units 200 may be aligned in a first direction, and the inkjet head units 200 or the substrate may be moved relative to one another. Alternatively, since the spacing between the multiple nozzle units of the inkjet head unit 200 is fixed, if it is necessary to eject ink at closer spacings (i.e., to perform printing with higher resolution), the multiple inkjet head units 200 may be spaced apart in a second direction intersecting the first direction, and the multiple nozzle units may be arranged so that they do not overlap each other, and the inkjet head units 200 or the substrate may be moved relative to one another to perform printing.

[0084] A plurality of first flow conduits 120 for supplying ink to the inkjet head units 200 and a plurality of second flow conduits 130 for recovering ink from the inkjet head units 200 may be provided corresponding to the plurality of inkjet head units 200. Each of the first flow conduits 120 may be connected to one side of the corresponding inkjet head unit 200, and each of the second flow conduits 130 may be connected to the other side of the corresponding inkjet head unit 200. In order to make the flow of ink uniform within the inkjet head unit 200, the one side and the other side to which the first flow conduit 120 and the second flow conduit 130 are connected may be disposed at the same position on the inkjet head unit 200.

[0085] The ink supply device and inkjet printing system equipped with the ink supply device according to the present invention can remove air bubbles present in the ink or on the ink flow path, making it possible to stably supply ink to the inkjet head without interrupting the ink flow.

[0086] In order to impart various functionalities to the applied coating layer, in the case of inks that contain various solids mixed in or that tend to clump, harden, or gel when the flow is interrupted or stagnated, the ink can be uniformly agitated by continuously circulating the ink between the inkjet head and the ink reservoir, thereby maintaining the ink state. Furthermore, by suppressing the precipitation of solids contained in the ink, the phenomenon of ink clumping, and localized hardening or gelation of the ink, damage to the inkjet head due to nozzle clogging caused by these factors can be prevented.

[0087] Furthermore, air bubbles are removed from the ink and the ink flow path, and sudden pressure changes or pulsation phenomena in the ink reservoir and ink flow path are suppressed, allowing for the formation and maintenance of an accurate meniscus, thereby effectively improving the stability of ink ejection and the accuracy of the ink landing position.

[0088] Furthermore, in an inkjet printing system, ink is continuously circulated using an ink circulation path that includes an inkjet head, which is the object to which ink is supplied for printing. This makes it possible to remove air bubbles that may be present in the inkjet head and also effectively prevent the solid matter from clumping together, thereby achieving smooth ink circulation and improved print quality.

[0089] The phrase "on" used in the above description encompasses both direct contact and being positioned opposite the upper or lower surface without direct contact, and means being positioned opposite the entire upper or lower surface, being positioned opposite only a portion of the upper or lower surface, being positioned opposite at a distance from the upper or lower surface, or being in direct contact with the upper or lower surface. Furthermore, the terms "upper," "lower," "front end," "rear end," "upper," "lower," "upper end," "lower," "top end," "bottom end," etc. used in the above description are defined based on the drawings for ease of explanation, and do not in any way limit the shape or position of each component.

[0090] Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the above-described embodiments, and it should be understood by those skilled in the art that various modifications can be made thereto and that equivalent embodiments can be adopted without departing from the spirit of the present invention as claimed in the claims. Therefore, the technical scope of protection of the present invention should be determined by the following claims. [Explanation of symbols]

[0091] 100 Ink supply device 110 Ink storage section 120 First flow pipe 130 Second flow pipe 140 Ink circulation section 141 Cylinder section 142 Screw section 143 Motor section 144 Control Unit 145 Separate space 150 Third Flow Pipe 160 Flow meter section 171 Capacitance sensing section 172 Ink refill section 173 Negative pressure setting section 200 Inkjet head unit

Claims

1. an ink reservoir that at least temporarily stores ink; a first flow path pipe for supplying the ink stored in the ink storage section to an inkjet head section; a second flow path pipe for recovering ink from the inkjet head unit; an ink circulation unit that moves the ink flowing in through the second flow path pipe in one direction; a third flow pipe that supplies the ink flowing out from the ink circulation section to the ink reservoir section; Equipped with The ink circulation unit includes: a cylinder portion providing a hollow internal space extending in one direction; a screw portion extending in the one direction and fitted into the internal space so as to be rotatable; a motor unit that selectively rotates the screw unit; Equipped with the internal space is cylindrical and has a uniform inner diameter along the one direction; the screw portion has a uniform outer diameter along the one direction, An ink supply device in which the ink filling the internal space is pushed by the rotating screw portion and moves in the one direction.

2. 2. The ink supply device according to claim 1, wherein the outer diameter of the screw portion is smaller than the inner diameter of the internal space and is 80% or more of the inner diameter of the internal space.

3. The screw portion a shaft portion extending in the one direction; a blade portion arranged in a spiral shape along an outer wall of the shaft portion; Equipped with The ink supply device according to claim 1 , wherein the outer diameter and pitch of the blade portion are constant along the one direction.

4. a separation space is provided between one end of the screw portion and one end inside the internal space; The ink supply device according to claim 1 , wherein the third flow pipe is connected to the isolated space.

5. a flow meter unit that measures a flow rate of ink flowing inside the third flow tube; a control unit that controls at least one of a rotation speed, a rotation amount, and a rotation force of the motor unit in accordance with the flow rate of the ink measured by the flow meter unit; The ink supply apparatus of claim 1 further comprising:

6. a volume sensing unit that senses the volume of ink stored in the ink storage unit; an ink refill unit connected to the ink reservoir unit to refill the ink when the ink volume sensed by the volume sensing unit is less than a reference volume; The ink supply apparatus of claim 1 further comprising:

7. 2. The ink supply device according to claim 1, further comprising a negative pressure setting unit connected to the ink reservoir unit and setting the pressure in the internal space of the ink reservoir unit to a pressure lower than atmospheric pressure.

8. 2. The ink supply device according to claim 1, further comprising a buffer section communicating with the first flow pipe, disposed between the ink reservoir section and the inkjet head section, and providing a buffer space having a cross section larger than that of the first flow pipe.

9. The first flow path pipe is arranged in a plurality of pieces, 2. The ink supply device according to claim 1, wherein the third flow pipe has an inner diameter greater than the inner diameter of the first flow pipe.

10. The ink supply device of claim 1 , wherein the ink includes solids.

11. an inkjet head unit having a plurality of nozzle units that eject ink onto the substrate; the ink supply device according to claim 1 or any one of claims 4 to 10, which supplies ink to the inkjet head unit; An inkjet printing system comprising:

12. The inkjet printing system according to claim 11 , wherein the inkjet head unit is arranged in a plurality.

13. a plurality of the first flow path pipes and a plurality of the second flow path pipes are arranged corresponding to the plurality of inkjet head units, Each of the first flow passages is connected to one side of the corresponding inkjet head unit, The inkjet printing system of claim 12 , wherein each of the second flow tubes is connected to the other side of a corresponding one of the inkjet head units.

Images