Degassing device and ink jet recording apparatus

Abstract

The invention provides a degassing device. And the degassing device is used for removing 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 and a circulation 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. And the circulating device is used for enabling liquid to circulate through the circulating flow path. The circulation flow path has an outflow port from the liquid storage tank to the circulation flow path and an inflow port from the circulation flow path to a position below a liquid level in the liquid storage tank. The diameter of the inflow port is smaller than that of the outflow port. Accordingly, degassing efficiency can be improved through a simple structure.

Description

Technical Field

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

[0002] In inkjet recording devices, an increase in the amount of dissolved air in the ink can lead to the formation of air bubbles inside the recording head, causing poor evacuation. Therefore, techniques for reducing the amount of dissolved air in the ink have been continuously researched in the prior art. For example, there are structures that degas the ink by agitating it under reduced pressure within the ink reservoir.

[0003] In the aforementioned degassing device, the ink near the liquid surface is degassed by stirring the ink in the ink tank. However, since the stirrer is located at the bottom of the ink tank, when the ink volume increases, it becomes difficult for the ink near the liquid surface with less dissolved air to exchange with the ink near the bottom with more dissolved air, thus leading to a decrease in degassing efficiency. Summary of the Invention

[0004] In view of the above, the purpose of this invention is to improve degassing efficiency through a simple structure.

[0005] To solve the aforementioned technical problems, the degassing device of the present invention removes air dissolved in a liquid under a reduced pressure atmosphere. The degassing device includes a liquid storage tank, a pressure reducing device, a circulation path, and a circulation device. The liquid storage tank is used to store liquid. The pressure reducing device is used to reduce the pressure inside the liquid storage tank. The circulation path connects different locations within the liquid storage tank. The circulation device is used to circulate the liquid through the circulation path. The circulation path has an outlet from the liquid storage tank to the circulation path and an inlet from the circulation path to below the liquid surface within the liquid storage tank. The diameter of the inlet is smaller than the diameter of the outlet.

[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 the ink supply structure according to an embodiment of the present invention.

[0009] Figure 3 This is a schematic diagram illustrating a circulating pump according to an embodiment of the present invention.

[0010] Figure 4 This is a schematic cross-sectional view of a degassing apparatus according to an embodiment of the present invention.

[0011] Figure 5 This is a cross-sectional view representing a comparative example.

[0012] Figure 6 This is a cross-sectional view showing a degassing apparatus according to a first modified embodiment of the present invention.

[0013] Figure 7 This is a cross-sectional view showing a degassing apparatus according to a second variation of an embodiment of the present invention. Detailed Implementation

[0014] 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 orientations are explained based on the direction from which the inkjet recording device 1 is viewed 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.

[0015] 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 that houses various devices. A paper tray 11 for placing the sheet S is housed in the lower part of the housing 10, and a manual tray 12 for manually placing the sheet S is provided on the right side of the housing 10. A paper discharge tray 13 for stacking the recorded sheets S is provided on the upper side of the left side of the housing 10.

[0016] 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 picks up 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 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 picks up sheet S from the sheet stack of the manual tray 12.

[0017] Downstream of the alignment roller 18 is a conveying device 22 and recording heads 21 arranged 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.

[0018] 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.

[0019] 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 nozzle from drying. Further measures can be taken to prevent the ink from drying by storing a cleaning solution or other liquid inside the recording head cover.

[0020] 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).

[0021] During image recording, sheet S is taken from paper tray 11 and manual 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.

[0022] 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.

[0023] 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.

[0024] [Degassing device] The degassing device 40 involved in this embodiment will be described. Figure 2 This is a schematic diagram illustrating the ink supply structure involved in this embodiment. Figure 3 This is a schematic diagram showing the circulating pump 67 involved in this embodiment. Figure 4 This is a schematic cross-sectional view of the degassing device 40. In the inkjet recording apparatus 1 according to this embodiment, ink supply structures are provided according to the color of the ink. These ink supply structures have the same structure, so one ink supply structure will be described here.

[0025] [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.

[0026] [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.

[0027] [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.

[0028] [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.

[0029] [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.

[0030] [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.

[0031] [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.

[0032] [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 side of the side wall 32W of the ink reservoir 32, and the inlet 72 is connected to the area near the surface of the ink in 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. Alternatively, the outlet 71 can also be connected to the bottom 32B of the ink reservoir 32.

[0033] [Circulation Pump] During the degassing process, the ink reservoir 32 is under reduced pressure, making reciprocating pumps such as diaphragm pumps susceptible to the effects of this pressure reduction. Therefore, the circulation pump 67 is preferably a pump that delivers ink via a rotating body. For example, non-positive displacement pumps such as centrifugal pumps, mixed-flow pumps, and axial-flow pumps can be used as the circulation pump 67, as well as positive displacement rotary pumps such as vane pumps, gear pumps, and screw pumps. By using these pumps, unlike reciprocating pumps, the effects of pressure reduction within the ink reservoir 32 can be suppressed, thus enabling ink circulation.

[0034] 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.

[0035] like Figure 3 As shown, the pump shaft 73 and motor shaft 75 of the circulating pump 67 can transmit power in a non-contact manner through a partition wall 77. A pump casing 76 is formed along the circulation path 47, and the pump shaft 73 with an impeller 74 is housed within the pump casing 76. A motor (not shown) is provided on the outside of the circulation path 47. Discs 78 and 79 are provided at the ends of the pump shaft 73 and motor shaft 75, and the discs 78 and 79 face each other through the partition wall 77 of the pump casing 76. On the facing surfaces of the discs 78 and 79, magnets with alternating S and N poles are arranged circumferentially (not shown).

[0036] The pump shaft 73 and the motor shaft 75 are magnetically connected (magnetically coupled), and power is transmitted from the motor shaft 75 to the pump shaft 73 using magnetic force. The motor shaft 75 does not penetrate the pump housing 76; instead, the impeller 74 inside the pump housing 76 can rotate while the pump housing 76 is liquid-tightly sealed. The disks 78 and 79 of the pump shaft 73 and the motor shaft 75 are separated by a partition wall 77 in the pump housing 76. Therefore, even if a pressure difference occurs inside and outside the pump housing 76 when the ink reservoir 32 is depressurized, ink leakage due to this pressure difference is reliably prevented.

[0037] [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.

[0038] [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.

[0039] 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.

[0040] [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.

[0041] 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.

[0042] 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.

[0043] [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.

[0044] [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 agitation degassing methods, 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.

[0045] [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 through the supply flow path 44, and ink is recovered from the recording head 21 to the ink tank 32 through 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.

[0046] [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.

[0047] 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.

[0048] 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.

[0049] Next, the features of this embodiment will be described in detail. The degassing device 40 according to this embodiment is a degassing device 40 for removing air dissolved in a liquid under a reduced pressure atmosphere. It includes a liquid storage tank (e.g., an ink storage tank 32), a pressure reducing device (e.g., a pressure reducing pump 62), a circulation path 47, and a circulation device (e.g., a circulation pump 67). The liquid storage tank is used to store liquid; the pressure reducing device is used to reduce the pressure inside the liquid storage tank; the circulation path 47 connects different locations within the liquid storage tank; the circulation device circulates the liquid through the circulation path 47. The circulation path 47 has an outlet 71 from the liquid storage tank out of the circulation path 47 and an inlet 72 from the circulation path 47 into the liquid below the liquid surface in the liquid storage tank. The diameter D2 of the inlet 72 is smaller than the diameter D1 of the outlet 71. Details are as follows. Furthermore, since the ink storage tank 32, pressure reducing pump 62, and circulation pump 67 have been described previously, the circulation path 47 will be mainly described below.

[0050] As previously described, outlet 71 is connected to the portion of the side wall 32W of ink reservoir 32 at the bottom 32B side, and inlet 72 is connected to the portion of the side wall 32W of ink reservoir 32 near the liquid surface. The circulation path 47 has an upstream flow path 47U from outlet 71 to circulation pump 67 and a downstream flow path 47D from circulation pump 67 to inlet 72. The diameter of the upstream flow path 47U is equal to the diameter D1 of outlet 71. The diameter of the downstream flow path 47D is equal to the diameter D2 of inlet 72. In other words, the diameter D2 of downstream flow path 47D is smaller than the diameter D1 of upstream flow path 47U.

[0051] Ink is drawn in from outlet 71 and flows through upstream flow path 47U and downstream flow path 47D into ink reservoir 32 below the liquid surface. Here, the difference in circulation speed caused by the size of inlet 72 is examined. Figure 5 This is a cross-sectional view showing a comparative example. In the comparative example, the diameter D2 of the inlet 72 is equal to the diameter D1 of the outlet 71. In contrast, in this embodiment, the diameter D2 of the inlet 72 is smaller than the diameter D1 of the outlet 71.

[0052] When comparing the liquid flow F0 from inlet 72 to outlet 71 in the comparative example with the liquid flow F1 from inlet 72 to outlet 71 in this embodiment, the inflow velocity of flow F1 from inlet 72 is faster than that of flow F0. Therefore, it draws a larger arc than flow F0 and is drawn into outlet 71. Thus, in this embodiment, ink with a higher dissolved air content drawn from outlet 71 is exposed to air over a larger area on the liquid surface than in the comparative example, resulting in improved degassing efficiency. Furthermore, according to this embodiment, the diameter D2 of inlet 72 is smaller than the diameter D1 of outlet 71, thereby improving degassing efficiency, thus eliminating the need for a high-performance circulation pump 67. Therefore, according to this embodiment, degassing efficiency can be improved with a simple structure.

[0053] The degassing apparatus 40 according to the above-described embodiment is a degassing apparatus 40 for removing air dissolved in a liquid under a reduced pressure atmosphere. It includes a liquid storage tank (e.g., an ink tank 32), a pressure reducing device (e.g., a pressure reducing pump 62), a circulation path 47, and a circulation device (e.g., a circulation pump 67). The liquid storage tank stores liquid; the pressure reducing device reduces pressure within 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 path 47 has an outlet 71 flowing out of the liquid storage tank and an inlet 72 flowing into the liquid storage tank below the liquid surface from the circulation path 47. The diameter D2 of the inlet 72 is smaller than the diameter D1 of the outlet 71. With this structure, degassing efficiency can be improved with a simple design.

[0054] Furthermore, according to the degassing apparatus 40 of this embodiment, the circulation flow path 47 has an upstream flow path 47U from the outlet 71 to the circulation device and a downstream flow path 47D from the circulation device to the inlet 72, wherein the diameter D2 of the downstream flow path 47D is smaller than the diameter D1 of the upstream flow path 47U. With this structure, degassing efficiency can be improved simply by using two pipes with different diameters, thus achieving improved degassing efficiency through a simple structure.

[0055] Furthermore, the inkjet recording apparatus 1 according to this embodiment includes a degassing device 40 and a recording head 21, the recording head 21 discharging the degassed liquid from the degassing device 40 to the sheet S. With this structure, image quality degradation due to bubble formation can be suppressed.

[0056] The above implementation method can also be modified as follows.

[0057] [First Variation] Figure 6 This is a cross-sectional view showing the degassing apparatus 40 according to the first modification of the above embodiment. In this modification, the downstream flow path 47D has a tapered portion 47T, the diameter of which decreases as it approaches the inlet 72. Specifically, the tapered portion 47T is provided to cover a predetermined length including the inlet 72. The diameter D3 of the inlet 72, i.e., the downstream portion of the tapered portion 47T, is smaller than the diameter D2 of the upstream section of the tapered portion 47T.

[0058] By further reducing the inlet 72 by providing the tapered portion 47T, the inflow velocity from the inlet 72 can be further increased. Therefore, in this modified example, the liquid flow F2 from the inlet 72 to the outlet 71 draws a larger arc than the flow F1 in the above embodiment and is drawn into the outlet 71. Thus, in this embodiment, ink with a large amount of dissolved air drawn in from the outlet 71 can be exposed to air over a larger area on the liquid surface than in the above embodiment, resulting in improved degassing efficiency. Furthermore, compared to the case where the diameter of the downstream flow path 47D is D3 without the tapered portion 47T, the fluid resistance is reduced, thus suppressing energy loss.

[0059] [Second Variation] Figure 7 This is a cross-sectional view of the degassing apparatus 40 according to the second modification of the above embodiment. In this modification, the end face of the inlet 72 is inclined relative to the liquid surface. Specifically, in the above embodiment, the end face of the inlet 72 is formed perpendicular to the liquid surface, but in this modification, the end face of the inlet 72 is formed obliquely downward relative to the liquid surface. Therefore, the horizontal component of the flow F1 in the above embodiment is significant, but in this modification, since the obliquely downward flow F3 is added, the liquid can circulate over a larger range compared to the above embodiment.

[0060] [Other variations] In the above embodiment, an example is shown in which a degassing device 40 is provided in the inkjet recording apparatus 1. 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 liquid medicines, electrolytes, liquid resins, adhesives, solvents, lubricants, liquid foods, cosmetics, etc., other than inks.

[0061] In the above embodiment, a pressure reducing pump 62 is exemplified as a pressure reducing device, but any device that can reduce the pressure inside the ink reservoir 32 is acceptable, such as a jet injector.

[0062] In the above embodiment, a circulation pump 67 is exemplified as a circulation device, but any device that can circulate ink through the circulation path 47 is acceptable, such as a jet injector.

Claims

1. A degassing device for removing air dissolved in a liquid under reduced pressure, characterized in that, It has a liquid storage tank, a pressure reducing device, a circulation path, and a circulation device, among which, The liquid storage tank is used to store liquid; The pressure reducing device is used to reduce the pressure inside the liquid storage tank; The circulation path connects different locations of the liquid storage tank; The circulation device is used to circulate the liquid through the circulation flow path. The circulating flow path has: From the liquid storage tank to the outlet of the circulation path; and The inlet from the circulation path to the liquid level below the liquid surface in the liquid storage tank. The diameter of the inlet is smaller than the diameter of the outlet.

2. The degassing device according to claim 1, characterized in that, The circulating flow path has the following characteristics: The upstream flow path from the outlet to the circulation device; and The downstream flow path from the circulation device to the inlet. The diameter of the downstream flow path is smaller than the diameter of the upstream flow path.

3. The degassing device according to claim 1, characterized in that, The downstream flow path has a tapered section, the diameter of which decreases as it approaches the inlet side.

4. The degassing device according to claim 1, characterized in that, The end face of the inlet is inclined relative to the liquid surface.

5. An inkjet recording device, characterized in that, The device includes a recording head and the degassing apparatus of claim 1, wherein the recording head is used to discharge liquid degassed by the degassing apparatus onto the sheet.

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