Inkjet printing apparatus and ink recovery method

Abstract

To provide an inkjet printing device that can readily and properly recover ink.SOLUTION: An inkjet printing device includes: an ink tank for storing ink; a head unit including a plurality of droplet discharge parts for discharging ink; a circulation pipeline for circulating ink between the ink tank and the head unit; and a recovery pipeline for recovering internal ink from the head unit and the circulation pipeline.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an inkjet printing apparatus and an ink recovery method. [Background Art]

[0002] In recent years, methods for manufacturing devices using inkjet apparatuses have attracted attention. An inkjet apparatus has a plurality of nozzles that eject droplets, and performs printing on a print target by ejecting droplets from the nozzles while controlling the positional relationship between the nozzles and the print target. As one type of such inkjet printing apparatus, a configuration including a line head is known (see, for example, Patent Document 1). The line head includes a plurality of module heads arranged in parallel in the width direction of the print target, in other words, a droplet ejection head having a plurality of ejection ports. By arranging the line heads side by side in the sub-scanning direction, which is a direction orthogonal to the main scanning direction within the same horizontal plane, ink can be collectively applied to a wide print target in a single conveyance step. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2013-28040 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] When replacing old ink filled in a printing apparatus with new ink, after recovering pure old ink present in the circulation pipe, a cleaning liquid is filled into the circulation pipe to dilute the old ink remaining in the circulation pipe. Thereafter, recovery of the liquid in the circulation pipe and filling of the cleaning liquid into the circulation pipe are repeated until the concentration of the old ink in the circulation pipe reaches a target concentration that causes no operational problem. When the concentration of the old ink in the circulation pipe reaches the target concentration, recovery of the liquid in the circulation pipe and filling of new ink into the circulation pipe are repeated until the concentration of the new ink in the circulation pipe reaches the target concentration.

[0005] However, due to constraints on the configuration of the circulation piping in order to properly eject ink, the device described in Patent Document 1 cannot flexibly design the ink recovery method and means. Therefore, it becomes difficult to properly recover the ink.

[0006] This disclosure aims to provide an inkjet printing apparatus and an ink recovery method that can easily achieve proper ink recovery. [Means for solving the problem]

[0007] The inkjet printing apparatus of this disclosure comprises an ink tank for storing ink, a head unit having a plurality of droplet ejection sections for ejecting ink, circulation piping for circulating ink between the ink tank and the head unit, and recovery piping for recovering ink from within the head unit and the circulation piping, wherein the ink tank is positioned above the head unit, and the circulation piping does not have a section for guiding ink in the horizontal direction. 。

[0008] The ink recovery method of this disclosure is an ink recovery method performed by an inkjet printing apparatus comprising an ink tank for storing ink, a head unit having a plurality of droplet ejection parts for ejecting ink, a circulation pipe for circulating ink between the ink tank and the head unit, and a recovery pipe, wherein the inkjet printing apparatus recovers the ink in the head unit and the circulation pipe via the recovery pipe, the ink tank is positioned above the head unit, and the circulation pipe does not have a portion for guiding ink in the horizontal direction. 。 [Effects of the Invention]

[0009] According to the inkjet printing apparatus and ink recovery method of this disclosure, it is possible to easily achieve proper ink recovery. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic diagram showing the general configuration of an inkjet printing apparatus according to an embodiment. [Figure 2A] Cross-sectional view showing the state when the inner diameter of the recovery pipe according to the embodiment is not set appropriately. [Figure 2B] Cross-sectional view showing the state when the inner diameter of the recovery pipe according to the embodiment is appropriately set. [Figure 3A] A vertical cross-sectional view showing a method for setting the inner diameter of a recovery pipe according to an embodiment. [Figure 3B] Cross-sectional view along line BB in Figure 3A [Figure 4] A schematic diagram showing the general configuration of a conventional inkjet printing device. [Figure 5A] Cross-sectional view of circulation piping illustrating conventional problems [Figure 5B] Cross-sectional view of circulation piping illustrating conventional problems [Figure 6] Diagram illustrating a simplified ink recovery method in an inkjet printing apparatus according to an embodiment. [Figure 7] Diagram illustrating the method for recovering ink in an inkjet printing apparatus according to this embodiment. [Figure 8] Flowchart showing the ink replacement process in an inkjet printing apparatus according to an embodiment. [Figure 9] A schematic diagram showing the general configuration of an inkjet printing apparatus according to a modified example. [Modes for carrying out the invention]

[0011] [Embodiment] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of an inkjet printing apparatus. FIG. 2A is a cross-sectional view showing a state where the inner diameter of a recovery pipe is not appropriately set. FIG. 2B is a cross-sectional view showing a state where the inner diameter of the recovery pipe is appropriately set. FIG. 3A is a vertical cross-sectional view showing a method for setting the inner diameter of the recovery pipe. FIG. 3B is a cross-sectional view taken along line B-B of FIG. 3A. In the following description and each drawing, the direction parallel to the ink ejection direction from the inkjet printing apparatus is defined as the Z-axis direction, the scanning direction of the head unit constituting the inkjet printing apparatus is defined as the Y-axis direction, and the direction orthogonal to the Z-axis direction and the Y-axis direction is defined as the X-axis direction. In the present embodiment, a case where the Z-axis direction is the vertical direction and the ink ejection direction is the -Z direction will be described.

[0012] First, a schematic configuration of the inkjet printing apparatus will be described. As shown in FIG. 1, the inkjet printing apparatus 1 includes an ink tank unit 10, a head unit 20, a circulation pipe 30, and a recovery pipe 40. In FIG. 1, for facilitating understanding of the configuration, only one set of the head unit 20, the circulation pipe 30, and the recovery pipe 40 is illustrated, but the inkjet printing apparatus 1 includes a plurality of sets of the head unit 20, the circulation pipe 30, and the recovery pipe 40.

[0013] The ink tank unit 10 is an example of the ink tank of the present disclosure. The ink tank unit 10 includes an in-tank 11, an out-tank 12, a buffer tank 13, a supply tank 14, a recovery tank 15, and an intermediate tank 16. The in-tank 11, the out-tank 12, and the buffer tank 13 are disposed above the head unit 20.

[0014] One end (upper end) of a forward pipe 31 constituting the circulation pipe 30 is connected to the in-tank 11. The in-tank 11 stores liquid to be fed to the head unit 20 via the forward pipe 31.

[0015] One end (upper end) of a return pipe 32 constituting a circulation pipe 30 is connected to the outer tank 12. The outer tank 12 stores liquid returned from the head unit 20 via the return pipe 32.

[0016] A buffer tank 13 is disposed between the inner tank 11 and the outer tank 12. The buffer tank 13 is connected to the inner tank 11 via a pipe 17A in which a first pump P1 is disposed. The buffer tank 13 is connected to the outer tank 12 via a pipe 17B in which a second pump P2 is disposed. The buffer tank 13 supplies ink to the inner tank 11 and collects ink from the outer tank 12.

[0017] A supply tank 14 is connected to the buffer tank 13 via a pipe 17C. The supply tank 14 supplies liquid to the buffer tank 13.

[0018] A recovery tank 15 is connected to the buffer tank 13 via a pipe 17D branched from the pipe 17C. The recovery tank 15 stores ink or cleaning liquid which is liquid fed from the buffer tank 13 and has been used for cleaning the inside of the head unit 20 and the inside of the circulation pipe 30.

[0019] One end (upper end) of a recovery pipe 40 is connected to an intermediate tank 16. The intermediate tank 16 is connected to the buffer tank 13 via a pipe 17E.

[0020] Further, an air pressure circuit is disposed in each of the tanks 11, 12, 13, 14, 15, and 16. A liquid level sensor is disposed in each of the inner tank 11, the outer tank 12, and the buffer tank 13 that are necessary for liquid circulation. The liquid level positions of the inner tank 11, the outer tank 12, and the buffer tank 13 are controlled by the driving states of the first and second pumps P1 and P2.

[0021] In the inkjet printing apparatus 1, it is preferable that a liquid circulation device including a pneumatic circuit and first and second pumps P1 and P2 applies driving pressure to the liquid, thereby constantly circulating the liquid between the ink tank unit 10 and the head unit 20 during operation.

[0022] The head unit 20 comprises an upstream distribution tank 21, a plurality of droplet discharge units 22 (only one droplet discharge unit 22 is shown in Figure 1), and a downstream distribution tank 23.

[0023] The other end (lower end) of the supply pipe 31 is connected to the upstream distribution tank 21. The upstream distribution tank 21 supplies ink supplied from the in-tank 11 via the supply pipe 31 to the droplet discharge unit 22.

[0024] The droplet dispensing unit 22 includes a piezoelectric actuator, a diaphragm, a pressure chamber, and a nozzle. The droplet dispensing unit 22 dispenses ink supplied from the upstream distribution tank 21 from the nozzle by driving the piezoelectric actuator.

[0025] The other end (lower end) of the return piping 32 is connected to the downstream distribution tank 23. The ink supplied to the droplet discharge unit 22 that was not discharged from the droplet discharge unit 22 flows into the downstream distribution tank 23. The ink that flows into the downstream distribution tank 23 returns to the out tank 12 via the return piping 32.

[0026] The circulation piping 30 circulates ink between the ink tank unit 10 and the head unit 20. The circulation piping 30 comprises a forward piping 31 and a return piping 32. The forward piping 31 comprises a first forward vertical section 31A extending vertically downward, a forward inclined section 31B extending diagonally downward from the lower end of the first forward vertical section 31A, and a second forward vertical section 31C extending vertically downward from the lower end of the forward inclined section 31B. The return piping 32 comprises a first return vertical section 32A extending vertically downward, a return inclined section 32B extending diagonally downward from the lower end of the first return vertical section 32A, and a second return vertical section 32C extending vertically downward from the lower end of the return inclined section 32B. The first and second forward vertical sections 31A and 31C, and the first and second return vertical sections 32A and 32C guide the liquid in the vertical direction. The forward inclined section 31B and the return inclined section 32B guide the liquid in a direction inclined with respect to the horizontal plane. In other words, the circulation piping 30 is configured such that the parts that extend horizontally do not have parts that guide the liquid in the horizontal direction.

[0027] A forward flow path switching section 51 is located in the middle of the second forward vertical section 31C. A return flow path switching section 52 is located in the middle of the second return vertical section 32C. The forward flow path switching section 51 and the return flow path switching section 52 are examples of flow path switching sections of this disclosure. The other end (lower end) of the recovery pipe 40 is connected to the forward flow path switching section 51. The forward flow path switching section 51 and the return flow path switching section 52 are connected by a flow path switching section connecting pipe 53. The forward flow path switching section 51 and the return flow path switching section 52 are composed of, for example, valves and are configured to allow liquid flowing in from a predetermined pipe connected to them to flow out into at least one of the remaining pipes.

[0028] The portion of the forward piping 31 including the first forward vertical section 31A and the forward inclined section 31B, and the portion of the return piping 32 including the first return vertical section 32A and the return inclined section 32B, are curved to follow the movement of the head unit 20 in the Y-axis direction. In this embodiment, the inclination angle of the forward inclined section 31B and the return inclined section 32B with respect to the horizontal plane is set to 3°, but it may be an angle greater than 3° or an angle less than 3°. If the inclination angle of the forward inclined section 31B and the return inclined section 32B increases, the difference in water head between the liquid level of the ink tank unit 10 and the nozzle surface of the head unit 20 increases, and as a result it becomes necessary to lower the pressure inside the tanks that make up the ink tank unit 10. In this case, the evaporation of the solvent contained in the ink is accelerated, which increases the viscosity of the ink, and there is a risk that the increased viscosity of the ink will clog the nozzles of the head unit 20. When designing the inclination angles of the outbound inclined section 31B and the return inclined section 32B, the design should be carried out taking into consideration the factors mentioned above, or factors such as height restrictions of the equipment.

[0029] The lengths of the forward and return lines 31 and 32 vary depending on the position of each head unit 20. The length of the forward and return lines 31 to the head unit 20 furthest from the ink tank unit 10 is set to 4720 mm, while the length of the forward and return lines 31 to the head unit 20 closest to it is set to 880 mm.

[0030] The inner diameters of the supply pipe 31 and the return pipe 32 are calculated for each head unit 20 connected to the supply pipe 31 and the return pipe 32, based on Hagenpoiseuil's pressure loss formula shown in equation (1).

[0031]

number

[0032] In equation (1), since the fluid density ρ, viscosity μ, and flow rate Q can be considered as constants, if we set them as constants C1, the pressure loss ΔF for each head unit 20 is 10 -1The inner diameter D and length L of the forward pipe 31 and return pipe 32 were calculated so that they would be equal down to the kPa level.

[0033] The recovery piping 40 is arranged to recover ink from the head unit 20 and the circulation piping 30. The recovery piping 40 includes a first vertical recovery section 40A extending vertically downward, a recovery inclined section 40B extending diagonally downward from the lower end of the first vertical recovery section 40A, a second vertical recovery section 40C extending vertically downward from the lower end of the recovery inclined section 40B, and a recovery connection section 40D connecting the lower end of the second vertical recovery section 40C to the forward flow path switching section 51. The first and second vertical recovery sections 40A and 40C guide the liquid in the vertical direction. The recovery inclined section 40B guides the liquid in a direction inclined with respect to the horizontal plane.

[0034] The portion of the recovery piping 40 including the first vertical recovery section 40A and the inclined recovery section 40B is curved to follow the movement of the head unit 20 in the Y-axis direction. In this embodiment, the inclination angle of the inclined recovery section 40B with respect to the horizontal plane is set to 3°, but it may be an angle greater than 3° or an angle less than 3°.

[0035] A portion of the recovery connection section 40D is connected to the flow path switching section connection pipe 53 via the bypass pipe 54. This configuration allows the liquid flowing out from the return flow path switching section 52 to flow into the recovery pipe 40 without passing through the forward flow path switching section 51.

[0036] Furthermore, the recovery pipe 40 is a narrow pipe whose inner diameter is smaller than the inner diameters of the forward pipe 31 and the return pipe 32. If the inner diameter of the recovery pipe 40 is not set appropriately, as shown in Figure 2A, the meniscus Em of the ink E in the recovery pipe 40 will break, causing gas-liquid separation of the ink E. However, if the inner diameter of the recovery pipe 40 is set appropriately, as shown in Figure 2B, the meniscus Em of the ink E in the recovery pipe 40 will not break, and the ink E can be transported by the meniscus Em being pushed by the air layer K. The inner diameter of the recovery pipe 40 is set to a size that satisfies the requirement that the ink meniscus will not break (be interrupted) even if there is a section of the recovery pipe 40 parallel to the horizontal plane when negative pressure is applied to the intermediate tank 16 and ink is drawn up through the recovery pipe 40.

[0037] The method for setting the inner diameter of the recovery pipe 40 will be explained using Figures 3A and 3B. In Figure 3A, T represents the interfacial tension of ink E with respect to pipe 81, θ represents the contact angle of ink E with respect to pipe 81, and R represents the inner radius of pipe 81. In Figure 3B, Mg represents the gravitational force of ink E per unit length, φ represents the angle with respect to the horizontal plane, and r represents the radial length. As shown in Figure 3B, if the upward component of the interfacial tension Tsinθ is larger than the gravitational force Mg of ink E per unit length, the meniscus of ink E will break down, and gas-liquid separation of ink E in the radial direction of pipe 81 will not occur. The formula used to set the inner diameter of the recovery pipe 40 is shown in the following formula (2).

[0038]

number

[0039] The interfacial tension T, contact angle θ, and fluid density ρ of ink E are 30 [mN / m], 65°, and 950 [kg / m], respectively. 3 ] and substituting these into equation (2), the inner radius R of the pipe 81 becomes less than 1.8 mm. In this embodiment, the inner diameter of the recovery pipe 40 was set to 2 mm, which satisfies the result obtained from equation (2). Note that the inner radius R of the recovery pipe 40 that satisfies the above equation (2) will change depending on the physical properties T, θ, and ρ of the liquid used.

[0040] Next, before describing the operation of the inkjet printing apparatus 1 of this embodiment, we will describe a conventional inkjet printing apparatus 9. Figure 4 is a schematic diagram showing the general configuration of a conventional inkjet printing apparatus. Figures 5A and 5B are cross-sectional views of the circulation piping that show the problems of the conventional apparatus. Note that components in the inkjet printing apparatus 9 that are the same as those in the inkjet printing apparatus 1 are given the same reference numerals and names, and their descriptions are omitted or simplified.

[0041] As shown in Figure 4, the inkjet printing apparatus 9 comprises an ink tank unit 91, a plurality of head units 20, and circulation piping 92. In Figure 4, only one set of head units 20 and circulation piping 92 is shown for the sake of understanding the configuration, but the inkjet printing apparatus 9 comprises multiple sets of head units 20 and circulation piping 92.

[0042] The ink tank unit 91 comprises the components of the ink tank unit 10, excluding the intermediate tank 16 and the piping 17E.

[0043] The circulation piping 92 comprises a forward piping 93 and a return piping 94. The forward piping 93 comprises a first forward vertical section 31A, a forward horizontal section 93B extending horizontally from the lower end of the first forward vertical section 31A, and a second forward vertical section 31C connected to the lower end of the forward horizontal section 93B. The return piping 94 comprises a first return vertical section 32A, a return horizontal section 94B extending horizontally downward from the lower end of the first return vertical section 32A, and a second return vertical section 32C connected to the return horizontal section 94B. The forward horizontal section 93B and the return horizontal section 94B guide the liquid horizontally. In other words, the circulation piping 92 is configured to have a horizontally extending section that guides the liquid horizontally.

[0044] Comparing the conventional inkjet printing apparatus 9 with the inkjet printing apparatus 1 of this embodiment, the conventional inkjet printing apparatus 9 differs in that it does not have a recovery pipe 40, and the circulation pipe 92 has a forward horizontal section 93B and a return horizontal section 94B that guide the liquid horizontally. The conventional inkjet printing apparatus 9, having these differences, for example, applies negative pressure to the out tank 12 while applying positive pressure to the in tank 11, thereby creating an airflow in the direction indicated by arrow D9. The ink in the circulation pipe 92 and the head unit 20 is guided in the same direction as the airflow indicated by arrow D9 and recovered in the out tank 12. In other words, the conventional inkjet printing apparatus 9 uses the circulation pipe 92, which has a larger inner diameter than the recovery pipe 40, to recover the ink in the circulation pipe 92 and the head unit 20.

[0045] In the inkjet printer 9 shown in Figure 4, the ink flow rate increases because there are more nozzles compared to a printer using a single head unit 20. When the flow rate increases, the pressure loss changes rapidly due to temporary changes in flow rate. To suppress this change, the inner diameter of the circulation pipe 92 in the inkjet printer 9 is increased. However, when the inner diameter of the circulation pipe 92 is increased, when recovering ink from the inkjet printer 9, as shown in Figure 5A, the meniscus Em of the ink E breaks down in the circulation pipe 92, causing gas-liquid separation in the radial direction of the circulation pipe 92. As a result, only the gas layer is fluidly drawn up, making it difficult to recover the liquid layer of ink E. Therefore, when recovering ink E from the circulation pipe 92, there is a risk that the ink E will remain in the circulation pipe 92, as shown in Figure 5B. Thus, in the conventional inkjet printer 9, there were constraints on the design of the circulation pipe 92 in order to achieve both appropriate ink ejection and appropriate ink recovery.

[0046] Furthermore, in the forward horizontal section 93B, since the ink is not guided downward by gravity, if the ink meniscus breaks, there is a risk of ink accumulating in the forward horizontal section 93B. As explained above, it was difficult for conventional inkjet printers 9 to completely recover the ink in the circulation piping 92 and the head unit 20.

[0047] Furthermore, the cleaning solution used when changing ink in the inkjet printer 9 is recovered in the same manner as the ink. Therefore, it was sometimes difficult for the inkjet printer 9 to completely recover the cleaning solution in the circulation piping 92 and the head unit 20.

[0048] Next, the operation of the inkjet printing apparatus 1 of this embodiment will be described. First, the method of ink circulation during operation of the inkjet printing apparatus 1 will be explained with reference to Figure 1.

[0049] The inkjet printer 1 controls the forward flow path switching section 51 in the forward piping 31 so that the portion above the forward flow path switching section 51 in the forward piping 31 communicates only with the portion below it, creating a circulating state. The inkjet printer 1 also controls the return flow path switching section 52 in the return piping 32 so that the portion above the return flow path switching section 52 in the return piping 32 communicates only with the portion below it, creating a circulating state. As shown by arrow J in Figure 1, the liquid circulation device always flows the ink in a constant direction. That is, the ink flows from the in-tank 11 through the forward piping 31 to the head unit 20, and then through the return piping 32 to the out-tank 12. The liquid circulation device controls the liquid levels in the out-tank 12, buffer tank 13, and in-tank 11, circulating the ink between the ink tank unit 10 and the head unit 20. The cleaning fluid used when changing ink in the inkjet printer 1 is also circulated in the same manner as the ink.

[0050] Next, the method for recovering ink in the inkjet printer 1 will be explained with reference to Figure 6. Figure 6 is an explanatory diagram of a simplified ink recovery method in the inkjet printer. Figure 7 is an explanatory diagram of the ink recovery method in the inkjet printer. When recovering ink from the inkjet printer 1, the recovery process for ink in the forward piping 31, the recovery process for ink in the return piping 32, and the recovery process for ink in the head unit 20 are performed separately. The cleaning solution used when changing ink in the inkjet printer 1 is also recovered in the same way as the ink.

[0051] First, when recovering ink from the supply pipe 31, the inkjet printer 1 controls the supply channel switching section 51 so that the portion of the supply pipe 31 above the supply channel switching section 51 is in communication only with the recovery pipe 40. The inkjet printer 1 then applies negative pressure to the intermediate tank 16 while applying positive pressure to the in-tank 11. This control creates an airflow in the direction indicated by arrow D1 in Figure 6, and this airflow guides the ink in the supply pipe 31 to the intermediate tank 16 via the supply channel switching section 51 and the recovery pipe 40.

[0052] When recovering ink from the return piping 32, the inkjet printer 1 controls the return piping channel switching section 52 so that the portion of the return piping 32 above the return piping channel switching section 52 communicates only with the channel switching section connecting pipe 53, resulting in a recovery state. The inkjet printer 1 controls the forward piping channel switching section 51 so that it prevents ink from flowing to the recovery pipe 40 or the forward piping 31 via the channel switching section connecting pipe 53, resulting in a recovery state. The inkjet printer 1 then applies negative pressure to the intermediate tank 16 while applying positive pressure to the out tank 12. This control creates an airflow in the direction indicated by arrow D2 in Figure 6, and this airflow guides the ink in the return piping 32 to the intermediate tank 16 via the return piping channel switching section 52, the channel switching section connecting pipe 53, the bypass pipe 54, and the recovery pipe 40. Alternatively, the forward flow path switching unit 51 may be controlled so that the flow path switching unit connecting pipe 53 is in a recovery state where it is in communication only with the recovery pipe 40, thereby guiding the ink in the flow path switching unit connecting pipe 53 to the intermediate tank 16 via the forward flow path switching unit 51 and the recovery pipe 40.

[0053] When recovering ink from the head unit 20, the inkjet printer 1 controls the return path switching section 52 so that the portion of the return piping 32 above the return path switching section 52 communicates only with the portion below it, resulting in a recovery state. The inkjet printer 1 also controls the forward path switching section 51 so that the portion of the forward piping 31 below the forward path switching section 51 communicates only with the recovery piping 40, resulting in a recovery state. The inkjet printer 1 then applies negative pressure to the intermediate tank 16 while applying positive pressure to the out tank 12. This control creates an airflow in the direction indicated by arrow D3 in Figure 6, and this airflow guides the ink in the head unit 20 to the intermediate tank 16 via the portion of the forward piping 31 below the forward path switching section 51, the forward path switching section 51, and the recovery piping 40. Furthermore, the airflow in the direction indicated by arrow D3 in Figure 6 guides the ink in the portion of the forward pipe 31 below the forward flow path switching section 51, and the ink in the portion of the return pipe 32 below the return flow path switching section 52, to the intermediate tank 16.

[0054] Alternatively, the ink recovery process in the head unit 20 may be carried out as follows. The inkjet printer 1 controls the forward flow path switching section 51 so that the portion of the forward flow piping 31 above the forward flow path switching section 51 is in a recovery state where it communicates only with the portion below it. The inkjet printer 1 controls the return flow path switching section 52 so that the portion of the return flow piping 32 below the return flow path switching section 52 is in a recovery state where it communicates only with the flow path switching section connecting pipe 53. The inkjet printer 1 then applies negative pressure to the intermediate tank 16 while applying positive pressure to the in-tank 11. This control creates an airflow that flows in the order of forward flow path switching section 51, head unit 20, return flow path switching section 52, flow path switching section connecting pipe 53, bypass pipe 54, and recovery pipe 40, and this airflow guides the ink in the head unit 20 to the intermediate tank 16. In addition, ink in the section of the forward piping 31 below the forward flow path switching section 51, and in the section of the return piping 32 below the return flow path switching section 52, are also guided to the intermediate tank 16.

[0055] After recovering the ink in the forward piping 31, the return piping 32, and the head unit 20 as described above, the inkjet printing device 1 sends the ink stored in the intermediate tank 16 to the recovery tank 15 via the buffer tank 13, as indicated by arrow D4 in Figure 6.

[0056] Furthermore, by controlling the forward flow path switching unit 51 and the return flow path switching unit 52, the ink inside at least one of the forward piping 31 and the return piping 32, and the ink inside the head unit 20 may be recovered simultaneously. Alternatively, the ink stored in the intermediate tank 16 may be directly sent to a waste liquid tank (not shown). Alternatively, the intermediate tank 16 containing the stored ink may be removed from the inkjet printing device 1, and the ink in the removed intermediate tank 16 may be recovered.

[0057] Although Figure 6 was used in the above explanation, as shown in Figure 7, the inkjet printer 1 is equipped with multiple sets of head units 20, circulation piping 30, and recovery piping 40 (only two sets are shown in Figure 7). When recovering ink from the inkjet printer 1, as described above, the inkjet printer 1 controls the in-tank 11, out-tank 12, intermediate tank 16, and the forward flow path switching section 51 and return flow path switching section 52 of each set to a recovery state, forming an airflow in the directions indicated by arrows D1, D2, and D3 to guide the ink in the head units 20 and circulation piping 30 of each set to the intermediate tank 16. Then, the inkjet printer 1 sends the ink stored in the intermediate tank 16 to the recovery tank 15 via the buffer tank 13, as indicated by arrow D4.

[0058] As described above, the inkjet printing apparatus 1 recovers ink from the head unit 20 and the circulation pipe 30 using a recovery pipe 40 that is different from the circulation pipe 30. Therefore, the circulation pipe 30 can be designed to allow for proper ink ejection without considering the destruction of the ink (liquid) meniscus during ink recovery. Furthermore, by making the inner diameter of the recovery pipe 40 large enough so as not to damage the ink meniscus, ink can be easily recovered. Similarly, by making the inner diameter of the recovery pipe 40 large enough so as not to damage the cleaning fluid (liquid) meniscus, the cleaning fluid can be easily recovered. Thus, an inkjet printing apparatus 1 can be provided that can easily achieve proper ink recovery without imposing any constraints on the configuration of the circulation pipe 30.

[0059] Furthermore, in an inkjet printing apparatus 1 that recovers ink using a recovery pipe 40 different from the circulation pipe 30, a pump can also be placed inside the recovery pipe 40. With this configuration, the ink recovery efficiency can be increased by driving the pump inside the recovery pipe 40 during recovery, while not affecting the discharge of ink using the circulation pipe 30. In addition, if the circulation pipe 30 is flexible, at least one of the first forward vertical section 31A and the forward inclined section 31B can be deformed to be perpendicular to the horizontal plane when recovering ink or cleaning fluid. With this configuration, the ink or cleaning fluid in the forward pipe 31 or return pipe 32 can be moved downward by its own weight, and the retention of ink or cleaning fluid in the forward pipe 31 or return pipe 32 can be suppressed.

[0060] The inner diameter of the recovery pipe 40 is smaller than the inner diameter of the circulation pipe 30. In pipes with a small inner diameter, the value obtained by dividing the liquid volume by the surface area is small, and surface forces become dominant over volume forces. In other words, the effect of interfacial tension becomes significant. Therefore, during the recovery of liquid (at least one of ink and cleaning solution) using the recovery pipe 40, the breakdown of the liquid meniscus within the recovery pipe 40 can be suppressed, and the liquid can be easily recovered. In addition, by making the inner diameter of the circulation pipe 30 sufficiently large, it is possible to suppress abrupt changes in pressure loss during printing.

[0061] The circulation piping 30 is configured so as not to have any parts that guide the liquid horizontally. Therefore, the liquid in the circulation piping 30 can be moved downward by gravity. Consequently, the liquid recovery efficiency can be increased by recovering the liquid that has moved downward using the recovery piping 40.

[0062] The inkjet printing apparatus 1 is configured to circulate ink between the ink tank unit 10 and the head unit 20 by setting the forward flow path switching unit 51 and the return flow path switching unit 52 to a circulation state, while simultaneously recovering ink from within the head unit 20 and the circulation piping 30 by setting it to a recovery state. Therefore, the ink circulation state and the recovery state can be switched simply by controlling the state of the forward flow path switching unit 51 and the return flow path switching unit 52.

[0063] Next, the ink replacement process in the inkjet printer 1 will be explained with reference to Figure 8. Figure 8 is a flowchart of the ink replacement process in the inkjet printer 1.

[0064] When replacing old ink with new ink while the inkjet printer 1 contains old ink, the inkjet printer 1 stops the circulation of the old ink (step S1), as shown in Figure 8. After this, the inkjet printer 1 recovers the old ink from the circulation pipe 30 and the head unit 20 using the ink recovery method described above (step S2).

[0065] Next, the inkjet printer 1 cleans the circulation piping 30 and the head unit 20 (step S3). In step S3, the inkjet printer 1 repeats the process of filling the circulation piping 30 and the head unit 20 with cleaning solution supplied from the supply tank 14, and recovering the liquid in the circulation piping 30 and the head unit 20 using the ink recovery method described above, until the concentration of cleaning solution in the recovered liquid is, for example, 99.9% or more. The concentration of cleaning solution in the recovered liquid can be measured using a refractometer. Since the refractive index of the cleaning solution and the concentration of the cleaning solution in the liquid are proportional, the concentration of cleaning solution in the liquid can be measured by measuring the refractive index of the cleaning solution in advance. Note that the concentration of cleaning solution in the liquid may be measured using a spectrometer or other measuring instrument instead of a refractometer.

[0066] Once the cleaning process of the circulation piping 30 and the head unit 20 is complete, the inkjet printer 1 removes the cleaning solution from the circulation piping 30 and the head unit 20 (step S4). In step S4, the inkjet printer 1 repeats the process of filling the circulation piping 30 and the head unit 20 with new ink supplied from the supply tank 14, and recovering the liquid from the circulation piping 30 and the head unit 20 using the ink recovery method described above, until the concentration of new ink in the recovered liquid is, for example, 99.9% or more. The concentration of new ink in the recovered liquid may be measured using the same method as the concentration measurement of the cleaning solution in step S3. Once the concentration of new ink in the recovered liquid is, for example, 99.9% or more, the inkjet printer 1 fills the circulation piping 30 and the head unit 20 with new ink (step S5). This completes the ink replacement process in the inkjet printer 1. In this embodiment, the ink includes not only a coloring agent, but also solder, and semi-solid and liquid materials for manufacturing liquid crystal displays (e.g., color filters), perovskite solar cells, and battery separators.

[0067] As described above, by using a recovery pipe 40 that is different from the circulation pipe 30, the liquid inside the head unit 20 and the circulation pipe 30 can be easily recovered, thereby reducing the time required for ink replacement.

[0068] [Differentiation] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its intent.

[0069] For example, the inkjet printer 100 shown in Figure 9 comprises an ink tank unit 110, a head unit 20, a circulation pipe 30, and a recovery pipe 40. In Figure 9, for the sake of easier understanding of the configuration, only one set of head unit 20, circulation pipe 30, and recovery pipe 40 is shown, but the inkjet printer 100 comprises multiple sets of head unit 20, circulation pipe 30, and recovery pipe 40. The ink tank unit 110 comprises an ink tank 111 and an intermediate tank 16. The ink tank 111 is connected to one end (upper end) of the supply pipe 31, one end (upper end) of the return pipe 32, and the upper end of pipe 17C. The ink tank 111 is connected to the intermediate tank 16 via pipe 117A. A pump P3 is located in the middle of the first supply vertical section 31A of the supply pipe 31. When recovering ink from the inkjet printer 100, the inkjet printer 100 controls the intermediate tank 16, the forward flow path switching unit 51, and the return flow path switching unit 52 in the same manner as the recovery method of the above embodiment, except that it applies positive pressure to the ink tank 111 instead of the in-tank 11 or out-tank 12, to form an airflow in the direction indicated by arrows D1, D2, and D3, and guide the ink to the intermediate tank 16. The inkjet printer 100 then sends the ink stored in the intermediate tank 16 to the recovery tank 15 via the ink tank 111, as indicated by arrow D4.

[0070] The forward piping 31 may be provided with a forward horizontal section 93B instead of a forward inclined section 31B, and the return piping 32 may be provided with a return horizontal section 94B instead of a return inclined section 32B. [Industrial applicability]

[0071] This disclosure can be applied to inkjet printing apparatus and ink recovery methods. [Explanation of Symbols]

[0072] 19,100 Inkjet Printing Equipment 10,91,110 Ink Tank Unit 11 In-tank 12 Out-tank 13 Buffer Tank 14 Supply Tanks 15 Recovery Tanks 16 Intermediate Tank 17A, 17B, 17C, 17D, 17E, 81, 117A piping 20 Head Units 21 Upstream distribution tank 22 Droplet discharge part 23 Downstream distribution tank 30,92 Circulation piping 31,93 Outbound piping 31A First outbound vertical section 31B Outbound incline 31C Second outbound vertical section 32,94 Return piping 32A First return vertical section 32B Return trip incline 32C Second Return Route Vertical Section 40 Recovery piping 40A First vertical recovery section 40B Recovery Incline Section 40C Second vertical recovery section 40D Recovery connection section 51 Outbound path switching section 52 Return path switching section 53 Connection piping for flow path switching section 54 Bypass piping 93B Outbound horizontal section 94B Return journey horizontal section 111 Ink Tank E Ink Em Meniscus K Air layer P1 Pump No. 1 P2 Second pump P3 Pump

Claims

1. An ink tank for storing ink, A head unit having multiple droplet ejection sections for ejecting ink, A circulation pipe for circulating ink between the ink tank and the head unit, The head unit and the circulation piping are provided to include a recovery pipe for recovering the ink in the head unit and the circulation piping, The ink tank is positioned above the head unit. The aforementioned circulation piping does not have a portion that guides ink in the horizontal direction. Inkjet printing device.

2. The recovery piping is connected to the circulation piping, A flow path switching unit is provided at the connection point between the recovery pipe and the circulation pipe to switch between a circulation state in which ink is circulated within the circulation pipe and a recovery state in which ink is recovered through the recovery pipe. The inkjet printing apparatus according to claim 1.

3. An ink recovery method performed by an inkjet printing apparatus comprising an ink tank for storing ink, a head unit having a plurality of droplet ejection parts for ejecting ink, circulation piping for circulating ink between the ink tank and the head unit, and recovery piping, The aforementioned inkjet printing apparatus, The ink in the head unit and the circulation piping is recovered via the recovery piping. The ink tank is positioned above the head unit. The aforementioned circulation piping does not have a portion that guides ink in the horizontal direction. Ink recovery method.

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