Degassing device and ink jet recording apparatus

Abstract

The invention provides a degassing device and an ink jet recording apparatus. The degassing device removes air dissolved in the liquid in a reduced pressure atmosphere. The degassing device is provided with a liquid storage tank, a decompression device, a circulation flow path, a circulation device and a control device. The liquid storage tank is used for storing liquid. And the pressure reducing device is used for reducing the pressure in the liquid storage tank. And the circulating flow path enables different positions of the liquid storage tank to be communicated. The circulation device circulates the liquid through the circulation flow path. The control device drives the circulation device at least one of the time before the pressure reducing device is driven and the time before the liquid storage tank after pressure reduction is opened to the atmosphere. Therefore, the load of the degasser caused by pressure reduction can be reduced.

Description

Technical Field

[0001] This invention relates to a degassing device and an inkjet recording device. Background Technology

[0002] In inkjet recording devices, if the amount of dissolved air in the ink increases, air bubbles may form inside the recording head, leading to poor air removal. Therefore, existing technologies have been researching methods to reduce the amount of dissolved air in the ink. For example, there are structures that degas the ink by agitating it in a depressurized state within the ink reservoir.

[0003] In the aforementioned degassing device, the ink in the ink tank is agitated to degas it near the liquid surface. However, since the agitator is located at the bottom of the ink tank, if the ink volume increases, the ink near the liquid surface, where the amount of dissolved air is less, becomes difficult to exchange with the ink near the bottom, where the amount of dissolved air is more, resulting in a decrease in degassing efficiency. Furthermore, depressurization places a load on the degassing device, which may reduce its durability. Summary of the Invention

[0004] In view of the above, the purpose of the present invention is to reduce the load on the degassing device caused by pressure reduction.

[0005] The degassing device of this invention removes dissolved air from a liquid under reduced pressure. The degassing device includes a liquid storage tank, a pressure reducing device, a circulation path, a circulation device, and a control device. The liquid storage tank is used to store liquid. The pressure reducing device is used to reduce the pressure within the liquid storage tank. The circulation path connects different locations within the liquid storage tank. The circulation device circulates the liquid through the circulation path. The control device drives the circulation device at least once, either before activating the pressure reducing device or before opening the depressurized liquid storage tank to the atmosphere.

[0006] The inkjet recording apparatus of the present invention includes the degassing device and the recording head, the recording head being used to discharge liquid degassed by the degassing device onto the sheet. Attached Figure Description

[0007] Figure 1 This is a schematic diagram illustrating an inkjet recording apparatus according to an embodiment of the present invention.

[0008] Figure 2 This is a schematic diagram illustrating an ink supply mechanism according to an embodiment of the present invention.

[0009] Figure 3 This is a schematic cross-sectional view of a degassing apparatus according to an embodiment of the present invention.

[0010] Figure 4 This is a flowchart illustrating the overall operation of the degassing device according to an embodiment of the present invention.

[0011] Figure 5 This is a flowchart illustrating the operation of the degassing device according to an embodiment of the present invention, specifically the depressurization process.

[0012] Figure 6 This is a flowchart illustrating the operation of the degassing process of the degassing apparatus according to an embodiment of the present invention. Detailed Implementation

[0013] Below, refer to the appendix. Figure 1 The inkjet recording apparatus 1 of this embodiment will be described. Figure 1 This is a schematic diagram illustrating the inkjet recording apparatus 1 according to this embodiment. For ease of explanation, it is shown below. Figure 1 The front side of the paper in the diagram is the front side (front) of the inkjet recording device 1. The left and right directions are explained based on the direction of viewing the inkjet recording device 1 from the front. The arrows L, R, U, and Lo marked in each figure represent the left, right, top, and bottom sides of the inkjet recording device 1, respectively.

[0014] The inkjet recording device 1 prints by ejecting ink from each inkjet recording head 21 onto a sheet S, which serves as the recording medium. The inkjet recording device 1 has a box-shaped housing 10 housing various components. A paper feed cassette 11 for holding the sheet S is housed in the lower part of the housing 10, and a manual paper feed tray 12 for manually placing the sheet S is provided on the right side of the housing 10. A paper discharge tray 13 for loading the recorded sheet S is provided on the upper side of the left side of the housing 10.

[0015] A first transport path 14 is formed on the right side of the housing 10, transporting sheet S from the paper feed cassette 11 to the recording head 21 in the center of the housing 10. A first paper feed unit 15 is provided upstream of the first transport path 14, which removes sheet S from the sheet stack of the paper feed cassette 11. A alignment roller 18 is provided downstream of the first transport path 14 to adjust the feed time of sheet S. Furthermore, the paper feed path 16 of the manual paper feed tray 12 merges with the first transport path 14 downstream, and a second paper feed unit 17 is provided on the paper feed path 16, which removes sheet S from the sheet stack of the manual paper feed tray 12.

[0016] Downstream of the alignment roller 18 is a conveying device 22 and recording heads 21 sorted by color (e.g., black, cyan, magenta, yellow). The alignment roller 18 corrects the skewness of the sheet S and, in coordination with the ink discharge action of each recording head 21, feeds the sheet S to the conveying device 22. On the housing 10, an ink container 31 and an ink reservoir 32 are provided for each recording head 21. The ink in each ink container 31 is temporarily stored in the ink reservoir 32, and the ink is degassed as needed and supplied from the ink reservoir 32 to the recording head 21.

[0017] The conveying device 22 is configured by winding a conveyor belt 24 around a plurality of mounting rollers 23 disposed below each recording head 21. Downstream of the conveying device 22, a drying device 25 is provided for drying the ink on the sheet S. Downstream of the drying device 25, a straightening device 26 is provided to correct any curling that occurs on the sheet S due to ink drying. Downstream of the straightening device 26, a second conveying path 27 is formed for conveying the sheet S to the paper discharge tray 13. Downstream of the second conveying path 27, a paper discharge section 28 is provided to discharge the recorded sheet S to the paper discharge tray 13.

[0018] Below the drying unit 25 are a maintenance unit 35 for cleaning the recording head 21 and a cover unit 36 ​​for covering the recording head 21. The maintenance unit 35 has a scraper-like wiping blade that scrapes away ink residue on the nozzle surface of the recording head 21. The cover unit 36 ​​has a recording head cover that covers the nozzle surface of the recording head 21. The recording head cover helps to prevent the ink inside the nozzles from drying. Further preventing ink drying can be achieved by storing a cleaning solution or other liquid inside the recording head cover.

[0019] Furthermore, the inkjet recording apparatus 1 includes a control unit 38 that encompasses the entire control unit. The control unit 38 can be configured as a processor or as logic circuitry (hardware) formed in an integrated circuit or similar component. When configured as a processor, the processor performs various processes by reading and executing programs stored in memory. For example, a CPU (Central Processing Unit) can be used as the processor. Depending on its purpose, the memory may consist of one or more storage devices such as ROM (Read Only Memory) or RAM (Random Access Memory).

[0020] During image recording, sheet S is taken from paper tray 11 and manual paper tray 12 via first paper feed unit 15 and second paper feed unit 17 respectively, and conveyed to registration roller 18. In coordination with ink discharge timing, sheet S is conveyed from registration roller 18 to conveyor belt 24, and degassed ink is discharged from each recording head 21, recording a color image on the surface of sheet S. Sheet S is dried by drying device 25, and curling of sheet S is corrected by straightening device 26. Sheet S is conveyed to paper discharge unit 28 via second conveying path 27, and the recorded sheet S is discharged to paper discharge tray 13 via paper discharge unit 28.

[0021] However, the ink surface comes into contact with air within the ink reservoir 32, causing air dissolution. Sometimes, air bubbles within the ink can clog the nozzles of the recording head 21. Therefore, it is desirable to appropriately suppress the amount of dissolved air within the ink. For example, a method has been proposed where, after depressurization around a hollow fiber filter, ink is passed through the hollow fiber filter, causing air to move from the wall of the hollow fiber towards the depressurization side for degassing. However, this method requires expensive hollow fiber filters and necessitates regular replacement, thus increasing costs.

[0022] In addition, to prevent nozzle clogging, a method for degassing the ink by agitating it with a stirrer while the pressure inside the ink reservoir 32 is reduced to below atmospheric pressure (hereinafter referred to as the agitation degassing method). In the agitation degassing method, a magnetic force is applied to the stirrer inside the ink reservoir 32 from the outside, causing the stirrer to rotate and agitate the ink inside the ink reservoir 32. When the ink depth is large or the diameter of the ink reservoir is large, it is difficult to agitate the ink, resulting in a decrease in degassing efficiency. Increasing the speed of the stirrer makes agitation easier, but if the speed of the stirrer becomes too high, a loss of synchronization will occur, and the rotation noise of the stirrer will also increase. Therefore, the circulating degassing method shown below is adopted in this embodiment.

[0023] [Degassing device] The degassing device 40 involved in this embodiment will be described. Figure 2 This is a schematic diagram illustrating the ink supply mechanism involved in this embodiment. Figure 3 This is a schematic diagram showing the degassing device 40 according to this embodiment. In the inkjet recording apparatus 1 according to this embodiment, ink supply mechanisms are provided according to the color of the ink. These ink supply mechanisms have the same structure, so one ink supply mechanism will be described here.

[0024] [Ink Storage Tank] The ink reservoir 32 has a side wall portion 32W, a bottom portion 32B, and a cover portion 32C. The side wall portion 32W is cylindrical, with its axial direction defined by the vertical direction. The bottom portion 32B blocks the lower end of the side wall portion 32W. The cover portion 32C blocks the upper end of the side wall portion 32W. The horizontal cross-section of the inner surface of the side wall portion 32W is preferably circular. Preferably, the side wall portion 32W and the bottom portion 32B are integrally formed.

[0025] [Supply Flow] The replenishment flow path 41 is connected to the ink container 31 and the ink reservoir 32. One end of the replenishment flow path 41 is connected to a portion below the liquid level of the side wall portion 32W of the ink reservoir 32. A replenishment pump 61 and a replenishment valve 51 are provided in the replenishment flow path 41.

[0026] [Open Atmospheric Flow Path] The atmospheric open flow path 43 is connected to the cover portion 32C and communicates with the upper space 34 of the ink storage tank 32. An atmospheric open valve 53 is provided in the atmospheric open flow path 43.

[0027] [Decompression Flow Path] The pressure-reducing flow path 42 is connected to the cover portion 32C and communicates with the upper space 34 of the ink reservoir 32. A pressure-reducing pump 62 and a pressure-reducing valve 52 are provided in the pressure-reducing flow path 42.

[0028] [Supply Flow] The supply path 44 is connected to the ink reservoir 32 and the recording head 21. One end of the supply path 44 is connected to the bottom 32B of the ink reservoir 32. A supply valve 54 and a supply pump 64 are provided in the supply path 44.

[0029] [Recycle Flow] The recovery flow path 45 is connected to the ink reservoir 32 and the recording head 21. One end of the recovery flow path 45 is connected to the side wall 32W of the ink reservoir 32. A recovery valve 55 is provided in the recovery flow path 45.

[0030] [Bypass Flow] A bypass flow path 46 is provided in the supply flow path 44, bypassing the supply valve 54 and the supply pump 64. A bypass valve 56 is provided in the bypass flow path 46.

[0031] [Circular Flow Path] The circulation path 47 communicates with the area near the bottom and surface of the ink in the ink reservoir 32. The circulation path 47 has an outlet 71 for ink to flow out of the ink reservoir 32 and an inlet 72 for ink to flow into the ink reservoir 32. The outlet 71 is connected to the bottom 32B of the ink reservoir 32, and the inlet 72 is connected to the portion near the surface of the ink on the side wall 32W of the ink reservoir 32. That is, the inlet 72 is located higher than the outlet 71. A circulation pump 67 is provided in the circulation path 47. The ink circulates through the circulation path 47 via the circulation pump 67.

[0032] [Circulation Pump] Pumps that can be used as circulation pump 67 include non-positive displacement pumps such as centrifugal pumps, mixed-flow pumps, and axial-flow pumps; positive displacement rotary pumps such as vane pumps, gear pumps, screw pumps, and peristaltic pumps (tube pumps); and positive displacement reciprocating pumps such as piston pumps, plunger pumps, and diaphragm pumps. Among these, non-positive displacement pumps, rotary pumps other than peristaltic pumps, and reciprocating pumps other than diaphragm pumps have the advantage of being less affected by pressure reduction when depressurizing the ink reservoir 32. On the other hand, peristaltic pumps and diaphragm pumps are easily affected by pressure reduction, but they have the advantage of being inexpensive. In this embodiment, a peristaltic pump or a diaphragm pump is used as circulation pump 67. Countermeasures against the effects of pressure reduction will be described later.

[0033] Furthermore, generally speaking, the circulation path 47 in the degassing process can include the recording head 21, but in this embodiment, the circulation path 47 does not include the recording head 21. That is, the circulation path 47 is separate from the path that supplies ink to the recording head 21. Since the recording head 21 is not included in the circulation path 47, the possibility of external air entering the recording head 21 due to the disruption of the meniscus formed in the nozzle of the recording head 21 under depressurization during degassing can be reduced.

[0034] [Control Device] The replenishment pump 61, pressure reducing pump 62, supply pump 64, circulation pump 67, and replenishment valve 51, pressure reducing valve 52, atmospheric vent valve 53, supply valve 54, recovery valve 55, and bypass valve 56 are controlled by control device 38. Control device 38 includes a determination unit 39 that determines whether degassing is required based on the ink's storage time. If determination unit 39 determines that degassing is not necessary, degassing is not performed. Even if air dissolves again due to ink storage, the ink can be used without degassing as long as it is within the permissible time.

[0035] [Barometer] A barometer 33 is installed in the ink reservoir 32 to measure the air pressure in the upper space 34 of the ink reservoir 32. The control device 38 obtains air pressure data from the barometer 33.

[0036] Next, the basic operation of the degassing device 40 will be explained. Here, the standby state will be used as the initial state for explanation.

[0037] [Standby mode] In standby mode, the replenishment valve 51, pressure reducing valve 52, and supply valve 54 are closed, while the atmospheric vent valve 53, recovery valve 55, and bypass valve 56 are opened. Ink is stored in the ink tank 32, and the liquid surface is in contact with the air in the upper space 34 open to the atmosphere, thereby dissolving into the ink over time.

[0038] In standby mode, the determination unit 39 of the control device 38 determines whether degassing is required. For example, the control device 38 is equipped with a timer to time the ink placement time. The amount of dissolved air in the ink can be estimated based on one or more parameters such as air pressure, ink temperature, and the elapsed time since the last printing. Therefore, the determination unit 39 stores conversion information showing the correspondence between each parameter and the amount of dissolved air in the ink, and estimates the amount of dissolved air in the ink based on each parameter. In addition, the determination unit 39 stores conversion information showing the correspondence between the amount of dissolved air in the ink and the allowable time, and sets the allowable time based on the amount of dissolved air in the ink. The allowable time refers to the time during which printing is allowed even if ink is placed without degassing. Furthermore, mapping data, lookup tables, and conversion formulas are used in the conversion information showing the correspondence between each parameter and the amount of dissolved air in the ink, and the conversion information showing the correspondence between the amount of dissolved air in the ink and the allowable time. These mapping data, lookup tables, and conversion formulas use information obtained in advance through experiments, experience, and theory.

[0039] If the ink has been left to stand for a period of time within the allowable time, the oxygen saturation is low, and therefore the determination unit 39 determines that degassing is not required. If the ink has been left to stand for a period of time exceeding the allowable time, the oxygen saturation is high, and therefore the determination unit 39 determines that degassing is required. If degassing is required, the control device 38 performs the following decompression and degassing processes.

[0040] [Decompression Process] During the pressure reduction process, control device 38 closes supply valve 51, atmospheric vent valve 53, supply valve 54, recovery valve 55, and bypass valve 56, opens pressure reducing valve 52, and drives pressure reducing pump 62. Air is then drawn out from the upper space 34 of ink reservoir 32, thus reducing the pressure in the upper space 34. When the pressure in the upper space 34, as indicated by barometer 33, reaches a target value (e.g., -50 kPa), control device 38 stops pressure reducing pump 62.

[0041] [Degassing process] When the depressurization process ends, the control device 38 performs the degassing process. During the degassing process, the control device 38 closes the supply valve 51, pressure reducing valve 52, atmospheric release valve 53, supply valve 54, recovery valve 55, and bypass valve 56, and drives the circulation pump 67 at a predetermined time. When the circulation pump 67 is driven, the ink in the ink tank 32 circulates through the circulation path 47. Ink near the bottom surface of the ink tank 32 with a higher amount of dissolved air flows out through the outlet 71 into the circulation path 47, while ink in the circulation path 47 flows into the ink tank 32 near the liquid surface through the inlet 72. The ink surface is exposed to the depressurized atmosphere, and the air dissolved in the ink near the liquid surface is removed. The ink near the liquid surface with less dissolved air and the ink near the bottom surface with more dissolved air exchange smoothly, improving degassing efficiency. Furthermore, unlike the agitation degassing method, it is not affected by ink depth or tank diameter, and the driving noise of the circulation pump 67 is suppressed compared to the rotation noise of an agitator, improving quietness.

[0042] [Record Head Loop Process] The recording head circulation process can be performed before or after the degassing process, or at a separate time. During the recording head circulation process, control device 38 closes the supply valve 51, pressure reducing valve 52, and bypass valve 56, opens the atmospheric vent valve 53, supply valve 54, and recovery valve 55, and drives the supply pump 64. Ink is then supplied from the ink tank 32 to the recording head 21 via the supply flow path 44, and ink is recovered from the recording head 21 to the ink tank 32 via the recovery flow path 45. By circulating the ink between the recording head 21 and the ink tank 32, ink with increased viscosity is exchanged within the recording head 21, and air bubbles are removed from the recording head 21.

[0043] [Printing Process] During the printing operation by the recording head 21, the replenishment valve 51, pressure reducing valve 52, and supply valve 54 are closed, while the atmospheric vent valve 53, recovery valve 55, and bypass valve 56 are opened. That is, during the printing operation, the ink reservoir 32 is open to the atmosphere and becomes atmospheric pressure. During the printing operation, the ink reservoir 32 does not undergo pressure reduction to produce substantial degassing. Whenever ink is discharged from the recording head 21, ink is supplied from the ink reservoir 32 to the recording head 21 through the bypass flow path 46 and the recovery flow path 45. Sometimes, ink is replenished during ink exchange operations or printing operations. During this ink replenishment operation, the replenishment valve 51 is opened and the replenishment pump 61 is activated. Driven by the replenishment pump 61, ink is replenished from the ink container 31 to the ink reservoir 32 through the replenishment flow path 41.

[0044] also, Figure 1While schematically depicted, in reality, the recording head 21 is positioned above the ink reservoir 32. The ink within the recording head 21 is subjected to negative pressure due to the head difference between it and the ink in the ink reservoir 32, causing a meniscus to form at the nozzle of the recording head 21. After ink is discharged from the recording head 21, the surface tension of the ink acts to reduce the surface area of ​​the meniscus, thereby introducing a reduced amount of ink from the ink reservoir 32 to the recording head 21 through the resulting negative pressure. Alternatively, the recovery valve 55 can be closed, supplying ink to the recording head 21 only from the bypass flow path 46.

[0045] Furthermore, when the recording head 21 is connected to the ink reservoir 32, if the ink reservoir 32 is depressurized to the point of causing substantial degassing, the meniscus of the nozzle may be damaged. Even if the meniscus is not damaged, the shape of the meniscus inside the nozzle is different from when the ink reservoir 32 is open to the atmosphere, and the ink discharge characteristics may change. In this embodiment, the ink reservoir 32 is not depressurized to the point of causing substantial degassing during printing, therefore the meniscus inside the nozzle of the recording head 21 is not damaged, and there is no change in shape that alters the discharge characteristics.

[0046] As mentioned above, when a peristaltic pump or a diaphragm pump is used as the circulation pump 67, there is a problem that it is easily affected by pressure reduction.

[0047] For example, in the case of a peristaltic pump, liquid is delivered by squeezing a soft tube made of silicone rubber or the like by multiple rollers. Here, if air enters the section between two rollers, the tube is flattened due to decompression; conversely, the tube expands due to opening to the atmosphere. Due to repeated expansion and contraction over a long period, the tube may break.

[0048] In the case of a diaphragm pump, liquid is delivered by reciprocating motion of the diaphragm using a ramp or similar device. However, when air enters the diaphragm, it is compressed due to decompression, and simultaneously expands due to opening to the atmosphere. This repeated expansion and contraction over a long period can potentially damage the diaphragm.

[0049] Therefore, the degassing device 40 according to this embodiment suppresses the effects of depressurization by means of the method shown below. The degassing device 40 according to this embodiment removes air dissolved in a liquid (e.g., ink) under a depressurized atmosphere. The degassing device 40 includes a liquid storage tank (e.g., ink storage tank 32), a depressurization device (e.g., depressurization pump 62), a circulation path 47, and a circulation device (e.g., circulation pump 67). The liquid storage tank is used to store liquid; the depressurization device depressurizes the liquid storage tank; the circulation path 47 connects different locations within the liquid storage tank; and the circulation device circulates the liquid through the circulation path 47. The circulation device is activated at least once, either before the depressurization device is activated or before the depressurized liquid storage tank is opened to the atmosphere. Specifically, as described below.

[0050] Figure 4 This is a flowchart illustrating the overall operation of the degassing device 40. Figure 5 This is a flowchart illustrating the operation of the degassing process in the degassing unit 40. Figure 6 This is a flowchart illustrating the operation of the degassing process in the degassing device 40.

[0051] Here, the standby state is described as the initial state. In the standby state, the replenishment valve 51, pressure reducing valve 52, and supply valve 54 are closed, while the atmospheric vent valve 53, bypass valve 56, and recovery valve 55 are opened. Ink is stored in the ink tank 32, and the liquid surface is in contact with the air in the upper space 34 open to the atmosphere, so that the air dissolves into the ink over time. In the standby state, the control device 38 periodically repeats... Figure 4 The actions shown.

[0052] Initially, the control unit 38 determines whether a printing task is in progress. Figure 4 (Step S01). If a printing task is in progress (Step S01: Yes), the control device 38 repeatedly performs the determination in Step S01. On the other hand, if a printing task is not in progress (Step S01: No), the determination unit 39 of the control device 38 determines whether to perform degassing (Step S02). For example, in the control device 38 (refer to...) Figure 2 A timer is provided to time the ink placement time. The ink viscosity can be estimated based on one or more parameters such as air pressure, ink temperature, and the elapsed time since the last printing. Therefore, the determination unit 39 stores conversion information showing the correspondence between each parameter and the ink viscosity, and the ink viscosity is estimated based on each parameter. In addition, the determination unit 39 stores conversion information showing the correspondence between ink viscosity and allowable time, and the allowable time is set based on the ink viscosity. Furthermore, the allowable time refers to the time during which printing is allowed even if ink is placed without degassing.

[0053] If the ink's storage time is within the permissible time, the determination unit 39 determines that degassing is not required due to low oxygen saturation, and therefore does not perform degassing. If the ink's storage time exceeds the permissible time, the determination unit 39 determines that degassing is required due to high oxygen saturation, and therefore performs degassing. Furthermore, mapping data, lookup tables, and conversion formulas are used in the conversion information showing the correspondence between various parameters and ink viscosity, and in the conversion information showing the correspondence between ink viscosity and permissible time. These mapping data, lookup tables, and conversion formulas utilize information obtained in advance through experiments, experience, and theory.

[0054] If it is determined in step S02 that degassing will not be performed (step S02: No), the control device 38 repeatedly performs the determination in step S01. On the other hand, if it is determined that degassing will be performed (step S02: Yes), the control device 38 drives the circulation pump 67 for a predetermined time (step S03). When air enters the circulation pump 67 and the circulation path 47, the air is expelled by driving the circulation pump 67, and the circulation pump 67 and the circulation path 47 are filled with ink.

[0055] Next, the control device 38 performs the pressure reduction process. Figure 4 Step S04, refer to Figure 5 Specifically, control device 38 closes supply valve 51, atmospheric vent valve 53, supply valve 54, recovery valve 55, and bypass valve 56, and opens pressure reducing valve 52 (step S11). Next, control device 38 drives pressure reducing pump 62 (step S12) and determines whether the air pressure in ink reservoir 32, as indicated by barometer 33, reaches the specified negative pressure (step S13). If the air pressure is determined not to have reached the specified negative pressure (step S13: No), control device 38 repeats the determination in step S13 while driving pressure reducing pump 62. On the other hand, if the air pressure is determined to have reached the specified negative pressure (step S13: Yes), control device 38 closes pressure reducing valve 52, stopping pressure reducing pump 62 (step S14). In step S03, air is removed by driving circulation pump 67, thus reducing the load on circulation path 47 and circulation pump 67 caused by pressure reduction. Furthermore, since circulation pump 67 is not driven during the pressure reduction process, air re-dissolution in the ink is suppressed.

[0056] Next, control device 38 performs the degassing process. Figure 4 Step S05, refer to Figure 6Specifically, control device 38 drives circulation pump 67 (step S21). When circulation pump 67 is driven, the ink in ink tank 32 circulates through circulation path 47. Ink near the bottom surface of ink tank 32 with a higher amount of dissolved air flows out through outlet 71 into circulation path 47, while ink in circulation path 47 flows into the vicinity of the liquid surface in ink tank 32 through inlet 72. The ink surface is exposed to a reduced pressure atmosphere, and the air dissolved in the ink near the liquid surface is removed. The ink near the liquid surface with a lower amount of dissolved air and the ink near the bottom surface with a higher amount of dissolved air exchange smoothly, improving degassing efficiency.

[0057] Next, the control device 38 determines whether a predetermined time has elapsed since the circulation pump 67 was started (step S22). If it is determined that the predetermined time has not elapsed (step S22: No), the control device 38 repeatedly performs the determination in step S22 while the circulation pump 67 is running. On the other hand, if it is determined that the predetermined time has elapsed (step S22: Yes), the control device 38 stops the circulation pump 67 (step S23). When the degassing process ends, all valves are closed, thus maintaining the pressure reduction state.

[0058] Next, the control device 38 determines whether to execute the printing task. Figure 4 (Step S06). If it is determined that the printing task will not be performed (Step S06: No), the control device 38 repeatedly performs the determination in Step S06. On the other hand, if it is determined that the printing task will be performed (Step S06: Yes), the control device 38 will drive the circulation pump 67 for a predetermined time (Step S07). If air enters the circulation pump 67 and the circulation path 47, the air is expelled by driving the circulation pump 67, and the circulation pump 67 and the circulation path 47 are filled with ink.

[0059] Next, the control device 38 opens the atmospheric vent valve 53 (step S08). In step S07, air is expelled by driving the circulation pump 67, thus reducing the load on the circulation path 47 and the circulation pump 67 caused by opening to the atmosphere. Furthermore, since the circulation pump 67 is not driven, the re-dissolution of air in the ink is suppressed. Next, the control device 38 executes the printing task (step S09), repeating the processing after step S01.

[0060] The degassing device 40 according to the above-described embodiment removes air dissolved in a liquid (e.g., ink) under a reduced pressure atmosphere. The degassing device 40 includes a liquid storage tank (e.g., ink storage tank 32), a pressure reducing device (e.g., pressure reducing pump 62), a circulation path 47, and a circulation device (e.g., circulation pump 67). The liquid storage tank stores the liquid; the pressure reducing device reduces the pressure inside the liquid storage tank; the circulation path 47 connects different locations within the liquid storage tank; and the circulation device circulates the liquid through the circulation path 47. The circulation device is activated at least once, either before the pressure reducing device is activated or before the depressurized liquid storage tank is opened to the atmosphere. With this structure, when air enters the circulation device and circulation path 47, the air is expelled by activating the circulation device, and the circulation device and circulation path 47 are filled with liquid. Therefore, according to this embodiment, the load on the degassing device 40 caused by pressure reduction can be reduced.

[0061] Furthermore, according to the degassing device 40 of this embodiment, the circulation device is not driven during the operation of the pressure reducing device. With this structure, the redissolution of air into the liquid can be suppressed.

[0062] Furthermore, according to the degassing device 40 of this embodiment, the circulation device is not activated while the depressurized liquid storage tank is opened to the atmosphere. This structure prevents air from redissolving in the liquid.

[0063] Furthermore, in the degassing device 40 according to this embodiment, at least one of the circulation path 47 and the circulation device includes a flexible component. With this structure, deterioration of the flexible component can be suppressed.

[0064] Furthermore, according to the degassing device 40 of this embodiment, the circulation device is a peristaltic pump or a diaphragm pump. With this structure, deterioration of the tubing of the peristaltic pump or the diaphragm of the diaphragm pump can be suppressed.

[0065] Furthermore, the inkjet recording apparatus 1 according to this embodiment includes a degassing device 40 and a recording head 21 that discharges the liquid degassed by the degassing device 40 to the sheet S. With this structure, image quality degradation caused by the generation of air bubbles can be suppressed.

[0066] The above implementation method can also be modified as follows.

[0067] In the above embodiment, an example of providing a degassing device 40 in an inkjet recording apparatus 1 is shown. However, the degassing device 40 can also be applied to apparatuses used in other fields such as semiconductor manufacturing and display manufacturing. That is, it can also be applied to the degassing of liquids other than inks, such as pharmaceuticals, electrolytes, liquid resins, adhesives, solvents, lubricants, liquid foods, and cosmetics.

[0068] In the above embodiment, a pressure reducing pump 62 is exemplified as a pressure reducing device, but any device capable of reducing pressure in the ink reservoir 32 is acceptable, such as an ejector.

Claims

1. A degassing device that removes air dissolved in a liquid under reduced pressure, characterized in that, It has a liquid storage tank, a pressure reducing device, a circulation path, a circulation device, and a control device, among which, The liquid storage tank is used to store liquid; The pressure reducing device reduces the pressure inside the liquid storage tank; The circulation path connects different locations of the liquid storage tank; The circulation device circulates the liquid through the circulation flow path; The control device drives the circulation device at least once, either before activating the pressure-reducing device or before opening the depressurized liquid storage tank to the atmosphere.

2. The degassing device according to claim 1, characterized in that, The circulation device is not driven during the operation of the pressure reducing device.

3. The degassing device according to claim 1, characterized in that, The circulation device is not activated while the depressurized liquid storage tank is opened to the atmosphere.

4. The degassing device according to claim 1, characterized in that, At least one of the circulating flow path and the circulating device includes a flexible component.

5. The degassing device according to claim 4, characterized in that, The circulation device is a peristaltic pump or a diaphragm pump.

6. An inkjet recording device, characterized in that, The degassing device as described in claim 1, and The recording head discharges the liquid degassed by the degassing device onto the sheet.

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