Degassing device and ink jet recording apparatus

Abstract

The invention provides a degassing device and an ink jet recording apparatus. The degassing device removes the air dissolved in the liquid in a reduced pressure atmosphere. The degassing device is provided with a liquid storage tank, a decompression device and a lifting device. The liquid storage tank is provided with a small cross-section part and a large cross-section part, the large cross-section part is arranged below or above the small cross-section part, the horizontal cross-section area of the inner space of the large cross-section part is larger than that of the small cross-section part, and 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. The lifting device lifts the liquid level in the liquid storage tank to the small cross-section part and the large cross-section part. As a result, redissolution of air can be suppressed without lowering degassing efficiency.

Description

Technical Field

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

[0002] In inkjet recording devices, when the amount of dissolved air in the ink increases, air bubbles can form inside the recording head, potentially causing poor evacuation. Therefore, in the prior art, a technique for reducing the amount of dissolved air in the ink has been researched. For example, a structure has been developed that degasses the ink by reducing pressure inside the ink reservoir.

[0003] In the above structure, a scheme is proposed to make a float float on the liquid surface in order to suppress the redissolution of air relative to the ink in the ink tank. However, in this structure, the liquid surface becomes narrower due to the float, which leads to a decrease in degassing efficiency. Summary of the Invention

[0004] In view of the above, the object of the present invention is to suppress the redissolution of air without reducing the degassing efficiency.

[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, and a lifting device. The liquid storage tank has a small cross-sectional area and a large cross-sectional area, the large cross-sectional area being located below or above the small cross-sectional area, and its internal horizontal cross-sectional area is larger than that of the small cross-sectional area. This liquid storage tank is used to store liquid. The pressure reducing device reduces the pressure inside the liquid storage tank. The lifting device raises or lowers the liquid level in the liquid storage tank to the small cross-sectional area and the large cross-sectional area.

[0006] The inkjet recording device of the present invention includes the degassing device and the recording head, wherein the recording head discharges the liquid degassed by the degassing device to 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 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 5This is a schematic cross-sectional view of a degassing apparatus according to an embodiment of the present invention.

[0012] Figure 6 It means Figure 4 Section II sectional view.

[0013] Figure 7 This is a perspective view showing the inclined flow path according to an embodiment of the present invention.

[0014] Figure 8 This is a top view showing the inclined flow path according to an embodiment of the present invention.

[0015] Figure 9 This is a cross-sectional view showing the degassing apparatus 40 according to a first modified embodiment of the present invention.

[0016] Figure 10 This is a cross-sectional view showing a degassing apparatus according to a first modified embodiment of the present invention.

[0017] Figure 11 This is a cross-sectional view showing the degassing apparatus according to a second variation of an embodiment of the present invention.

[0018] Figure 12 This is a cross-sectional view showing the degassing apparatus according to the third variation of an embodiment of the present invention.

[0019] Figure 13 This is a cross-sectional view showing the degassing apparatus according to the third variation of an embodiment of the present invention. Detailed Implementation

[0020] The inkjet recording apparatus 1 of this embodiment will now be described with reference to the accompanying drawings. Figure 1 This is a schematic diagram illustrating the inkjet recording apparatus 1 according to this embodiment. For ease of explanation, [the diagram is shown below]. Figure 1 The front side of the paper in the diagram is considered the front side (front side) 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.

[0021] The inkjet recording device 1 ejects ink from each inkjet recording head 21 onto a sheet S, which serves as the recording medium, and performs printing. The inkjet recording device 1 has a box-shaped housing 10 that houses various devices. A paper feed tray 11 for placing 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.

[0022] On the right side of the housing 10, a first transport path 14 is formed to transport sheet S from the paper feed cassette 11 to the recording head 21 in the center of the housing 10. Upstream of the first transport path 14, a first feed section 15 is provided to remove sheet S from the sheet stack of the paper feed cassette 11, and downstream of the first transport path 14, a alignment roller 18 is provided to adjust the feed time of sheet S. Furthermore, the feed path 16 of the manual paper feed tray 12 merges with the first transport path 14 downstream of the first transport path 14, and a second feed section 17 is provided on the feed path 16 to remove sheet S from the sheet stack of the manual paper feed tray 12.

[0023] 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 conjunction with the ink discharge action of each recording head 21, feeds the sheet S to the conveying device 22. Within the housing 10, an ink cartridge 31 and an ink reservoir 32 are provided for each recording head 21. The ink in each ink cartridge 31 is temporarily stored in the ink reservoir 32, and the ink is degassed as needed before being supplied to the recording head 21 from the ink reservoir 32.

[0024] The conveying device 22 is composed of a conveyor belt 24 wound around a plurality of tension rollers 23 located 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 for correcting curling on the sheet S caused by 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 for discharging the recorded sheet S to the paper discharge tray 13.

[0025] Below the drying device 25 are a maintenance unit 35 and a cover unit 36. The maintenance unit 35 cleans the recording head 21, and the cover unit 36 ​​covers the recording head 21. A scraper-like scraper is provided on the maintenance unit 35 to remove ink residue from the nozzle surface of the recording head 21. A top cover is provided on the cover unit 36, covering the nozzle surface of the recording head 21. The top cover helps to prevent the ink inside the nozzle from drying. The drying of the ink inside the nozzle can be further prevented by pre-storing a cleaning solution or other liquid inside the top cover.

[0026] 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) forming an integrated circuit or the like. When configured as a processor, various processes are performed 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).

[0027] During image recording, the first paper feed unit 15 and the second paper feed unit 17 respectively take the sheet S from the paper feed cassette 11 and the manual paper feed tray 12 and feed it to the alignment roller 18. According to the ink discharge time, the sheet S is fed from the alignment roller 18 to the conveyor belt 24, and the degassed ink is discharged from each recording head 21, recording a color image on the surface of the sheet S. The sheet S is dried by the drying device 25, and the curling of the sheet S is corrected by the straightening device 26. The sheet S is conveyed to the paper discharge unit 28 through the second conveying path 27, and the recorded sheet S is discharged from the paper discharge unit 28 to the paper discharge tray 13.

[0028] Furthermore, the ink surface dissolves air upon contact with air within the ink reservoir 32, sometimes causing the nozzle of the recording head 21 to become clogged due to air bubbles in the ink. Therefore, it is desirable to appropriately suppress the amount of dissolved air in the ink. For example, a method has been proposed to degas the ink by passing it through the hollow fiber filter under reduced pressure, thereby moving air from the wall of the hollow fiber towards the depressurization side. However, this method requires expensive hollow fiber filters and necessitates regular replacement, thus increasing costs.

[0029] In addition, to prevent nozzle clogging, a method for degassing the ink by agitating it with a stirrer is proposed, where 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, and the stirrer rotates by the magnetic force to agitate the ink inside the ink reservoir 32. When the ink depth or the reservoir diameter is large, the ink is not easily agitated, thus reducing the degassing efficiency. Increasing the speed of the stirrer makes agitation easier, but when the speed of the stirrer becomes too high, a loss of synchronization occurs, and the rotation noise of the stirrer also increases. Therefore, in this embodiment, the following circulating degassing method is adopted.

[0030] [Degassing device] The degassing device 40 involved in this embodiment will be described. Figure 2This is a schematic diagram illustrating the ink supply mechanism involved in this embodiment. Figure 3 This is a schematic diagram showing the circulating pump 67 involved in this embodiment. Figure 4 , 5 This is a schematic cross-sectional view of the degassing device 40. In the inkjet recording apparatus 1 according to this embodiment, ink supply mechanisms are provided according to the color of each ink, but these ink supply mechanisms have the same structure, so one ink supply mechanism will be described here.

[0031] [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 and axially oriented in the vertical direction. The bottom portion 32B closes the lower end of the side wall portion 32W. The cover portion 32C closes the upper end of the side wall portion 32W. Preferably, the horizontal cross-section of the inner surface of the side wall portion 32W is circular. Preferably, the side wall portion 32W and the bottom portion 32B are integrally formed.

[0032] [Supply Flow] The replenishment flow path 41 is connected to the ink cartridge 31 and the ink reservoir 32. One end of the replenishment flow path 41 is connected to the portion of the side wall 32W of the ink reservoir 32 that is lower than the liquid level. A replenishment pump 61 and a replenishment valve 51 are provided on the replenishment flow path 41.

[0033] [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 on the atmospheric open flow path 43.

[0034] [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 on the pressure-reducing flow path 42.

[0035] [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 on the supply path 44.

[0036] [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 on the recovery flow path 45.

[0037] [Bypass Flow] A bypass flow path 46 is provided on the supply flow path 44, bypassing the supply valve 54 and the supply pump 64. A bypass valve 56 is provided on the bypass flow path 46.

[0038] [Circular Flow Path] The circulation path 47 communicates with the ink reservoir 32 near the bottom and surface of the ink. The circulation path 47 has an outlet 71 and an inlet 72. The outlet 71 allows ink to flow out of the ink reservoir 32 into the circulation path 47; the inlet 72 allows ink to flow into the ink reservoir 32 from the circulation path 47. The outlet 71 is connected to the bottom 32B of the ink reservoir 32, and the inlet 72 is connected to the portion of the side wall 32W of the ink reservoir 32 near the surface of the ink. That is, the inlet 72 is located higher than the outlet 71. A circulation pump 67 is provided on the circulation path 47. The circulation pump 67 circulates the ink through the circulation path 47.

[0039] [Circulation Pump] Since the ink reservoir 32 is under reduced pressure during the degassing process, reciprocating pumps such as diaphragm pumps are easily affected by this pressure reduction. Therefore, it is preferable to use a pump that delivers ink via a rotating body as the circulation pump 67. 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.

[0040] Furthermore, generally, the circulation path 47 in a circulating degassing mode can include the recording head 21, but in this embodiment, the recording head 21 is not included in the circulation path 47. That is, the circulation path 47 and the path for supplying ink to the recording head 21 are provided separately. 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 caused by the depressurization during degassing is reduced.

[0041] like Figure 3 As shown, the pump shaft 73 and motor shaft 75 of the circulating pump 67 can transmit power non-contactly through the partition wall 77. A pump casing 76 is formed in the middle of the circulating flow path 47, and the pump shaft 73 with an impeller 74 is housed inside the pump casing 76. A motor (not shown) is provided on the outside of the circulating flow 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 arranged circumferentially are respectively provided (not shown).

[0042] The pump shaft 73 and 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 impeller 74 inside the pump housing 76 can rotate while maintaining a liquid-tight seal in the pump housing 76 without the motor shaft 75 penetrating through it. Because the disks 78 and 79 of the pump shaft 73 and motor shaft 75 are separated by the partition wall 77 of the pump housing 76, ink leakage caused by a pressure difference generated inside and outside the pump housing 76 when the ink reservoir 32 is depressurized can be reliably prevented.

[0043] [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 the control device 38. The control device 38 includes a determination unit 39 that determines whether degassing is required based on the ink's storage time. If the determination unit 39 determines that ink degassing is not required, the degassing operation is not performed. Even if the air redissolves due to ink storage, the ink can be used without degassing as long as it is within the permissible time.

[0044] [Barometer] A barometer 33 is installed on 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.

[0045] 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.

[0046] [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 open. Ink is stored in the ink tank 32, and air is exposed to the atmosphere through the liquid surface in the upper open space 34. Over time, air dissolves in the ink.

[0047] In standby mode, the determination unit 39 of the control device 38 determines whether degassing is required. For example, a timer is provided in the control device 38 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 time elapsed 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 is the time during which printing is allowed without degassing even when ink is placed. Furthermore, 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, can use mapping data, lookup tables, conversion formulas, etc. These mapping data, lookup tables, and conversion formulas can be mapping data, lookup tables, and conversion formulas derived in advance from experiments, experience, and theory.

[0048] If the ink has been left to stand for a period of time within the allowable time, the determination unit 39 determines that degassing is not required due to the low oxygen saturation. If the ink has been left to stand for a period of time exceeding the allowable time, the determination unit 39 determines that degassing is required due to the high oxygen saturation. If degassing is required, the control device 38 performs the following decompression and degassing processes.

[0049] [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, reducing the pressure in the upper space 34. Control device 38 stops pressure reducing pump 62 when the pressure in the upper space 34, as indicated by barometer 33, reaches a target value (e.g., -50 kPa).

[0050] [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 high 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 low dissolved air and the ink near the bottom surface with high dissolved air are smoothly replaced, thereby improving degassing efficiency. Furthermore, unlike agitation degassing methods, it is not affected by ink depth or tank diameter; compared to the rotation noise of a stir bar, the driving noise of the circulation pump 67 is suppressed, thus improving quietness.

[0051] [First cycle process] The head circulation process can be performed before or after the degassing process, or it can be performed at a separate time. During the 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 reservoir 32 to the recording head 21 through the supply path 44, and ink is recovered from the recording head 21 to the ink reservoir 32 through the recovery path 45. Through the circulation of ink between the recording head 21 and the ink reservoir 32, ink with increased viscosity within the recording head 21 is replaced, and air bubbles are removed from the recording head 21.

[0052] [Printing Process] During the printing operation of the record 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 released from the atmosphere and becomes atmospheric pressure. During the printing operation, the ink reservoir 32 does not undergo depressurization as a substantial degassing process. Whenever ink is discharged from the record head 21, ink is supplied to the record head 21 from the ink reservoir 32 through the bypass flow path 46 and the recovery flow path 45. Sometimes, ink is replenished midway through the printing operation, such as during ink replacement or printing. 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 cartridge 31 to the ink reservoir 32 through the replenishment flow path 41.

[0053] also, Figure 1While schematically depicted, in reality, the recording head 21 is positioned above the ink reservoir 32. A negative pressure is applied to the ink within the recording head 21 due to the pressure difference between the ink and the ink in the ink reservoir 32, creating a meniscus on the nozzle of the recording head 21. After ink is discharged from the recording head 21, the surface tension of the ink reduces the surface area of ​​the meniscus, thereby drawing a reduced amount of ink from the ink reservoir 32 into the recording head 21 through the resulting negative pressure. Furthermore, the recovery valve 55 can be closed, supplying ink to the recording head 21 only from the bypass flow path 46.

[0054] 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 within the nozzle changes relative to when the ink reservoir 32 is released to the atmosphere, potentially altering the ink ejection characteristics. In this embodiment, since the ink reservoir 32 is not depressurized during printing, the meniscus within the nozzle of the recording head 21 is not damaged, and there is no change in shape or ejection characteristics.

[0055] Next, the features of this embodiment will be described in detail. Figure 6 It means Figure 4 Section II sectional view. Figure 7 This is a three-dimensional diagram representing the inclined flow path 82. Figure 8 This is a top view showing the inclined flow path 82.

[0056] The degassing device 40 of this embodiment removes air dissolved in a liquid (e.g., ink) under reduced pressure. 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), and a lifting device (e.g., circulation pump 67, inclined flow path 82). The liquid storage tank has a small cross-section portion 32S and a large cross-section portion 32L, with the large cross-section portion 32L positioned below or above the small cross-section portion 32S. The horizontal cross-sectional area of ​​the internal space is larger than that of the small cross-section portion 32S. This liquid storage tank is used to store liquid. The pressure reducing device reduces the pressure inside the liquid storage tank. The lifting device raises or lowers the liquid level inside the liquid storage tank to the small cross-section portion 32S and the large cross-section portion 32L. Specific details are described below. Furthermore, the pressure reducing pump 62 is as described above; the ink storage tank 32 and the lifting device will be mainly described below. Additionally, the term "small cross-section portion" indicates that the horizontal cross-sectional area of ​​the internal space is smaller than that of the large cross-section portion 32L, and does not indicate an absolute cross-sectional area.

[0057] [Ink Storage Tank] A small cross-section portion 32S and a large cross-section portion 32L are provided on the side wall portion 32W of the ink reservoir 32. The diameter of the horizontal cross-section of the small cross-section portion 32S is smaller than that of the large cross-section portion 32L (see reference). Figure 6 The large cross-section portion 32L occupies most of the vertical direction of the side wall portion 32W, while the small cross-section portion 32S is located near the center of the vertical direction of the side wall portion 32W (see reference). Figure 4 The small cross-section portion 32S and the upper large cross-section portion 32L are connected by an inclined portion 32A that slopes downwards from the center side. The small cross-section portion 32S and the lower large cross-section portion 32L are connected by an inclined portion 32A that slopes upwards from the center side. Without circulating the ink using the circulation pump 67, the ink level is adjusted so that the ink surface is located at the small cross-section portion 32S.

[0058] [Lifting device] The lifting device may include a circulation pump 67 and an inclined flow path 82. When the circulation pump 67 circulates the ink, a portion of the ink moves along the path from the inlet 72 through the inclined flow path 82 to the liquid surface, causing the liquid level to drop. Alternatively, the lifting device may include a replenishment pump 61. Furthermore, the replenishment pump 61 can return ink from the ink reservoir 32 to the ink cartridge 31, thereby lowering the liquid level. Alternatively, the replenishment pump 61 can supply ink from the ink cartridge 31 to the ink reservoir 32, thereby raising the liquid level. The circulation pump 67 has been described above; the inclined flow path 82 will be mainly described below.

[0059] [Inclined Flow Path] The inclined flow path 82 has a bottom 82B, a guide wall 82G, and a limiting wall 82R. The bottom 82B is rectangular and inclined in one direction. A pair of guide walls 82G are provided facing each other along the inclined direction of the bottom 82B. The guide walls 82G guide the ink flow in a way that prevents the ink flow from deviating from the inclined direction. The limiting wall 82R is provided on the lower side of the bottom 82B to block the ink flow. An opening 82A extends vertically through the bottom 82B at the boundary between the limiting wall 82R and the bottom 82B. Supports 82P are provided at multiple locations on the upper end of the guide walls 82G. The inclined flow path 82 is suspended from the cover portion 32C via the supports 82P.

[0060] When the circulation pump 67 does not circulate ink (see reference) Figure 4 The liquid level is located at the small cross-section 32S, thus suppressing the redissolution of air relative to the ink. On the other hand, when the ink is circulated by the circulation pump 67 (see...). Figure 5 A portion of the ink moves along the path from the inlet 72 through the inclined flow path 82 to the liquid surface, thus lowering the liquid surface to the large cross-section 32L and improving degassing efficiency.

[0061] Furthermore, the inclined flow path 82 can be omitted. Even without the inclined flow path 82, when the ink is circulated, the liquid level can drop because a portion of the ink moves along the path from the inlet 72 to the liquid surface. However, in this case, since the amount of liquid level drop is small, the amount of ink in the ink tank needs to be strictly managed. In contrast, if the inclined flow path 82 is provided, the amount of liquid level drop can be increased, thus making it easier to manage the amount of ink.

[0062] According to the degassing device 40 described above in this embodiment, air dissolved in a liquid (e.g., ink) is removed under reduced pressure. 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), and a lifting device (e.g., circulation pump 67, inclined flow path 82). The liquid storage tank has a small cross-section portion 32S and a large cross-section portion 32L, with the large cross-section portion 32L positioned below or above the small cross-section portion 32S. The horizontal cross-sectional area of ​​the internal space is larger than that of the small cross-section portion 32S. This liquid storage tank is used to store liquid. The pressure reducing device reduces the pressure inside the liquid storage tank. The lifting device raises or lowers the liquid level inside the liquid storage tank to the small cross-section portion 32S and the large cross-section portion 32L. With this structure, the redissolution of air can be suppressed without reducing the degassing efficiency.

[0063] Furthermore, according to the degassing device 40 of this embodiment, the lifting device has a circulation path 47 and a circulation device (e.g., a circulation pump 67), wherein the circulation path 47 connects different positions of the liquid storage tank; and the circulation device circulates the liquid through the circulation path 47. With this structure, it is possible to facilitate the exchange between liquid with a high amount of dissolved air near the bottom surface and liquid with a low amount of dissolved air near the liquid surface, thus improving degassing efficiency even when the liquid volume is large. Additionally, with this structure, when the liquid is circulated by the circulation device, since a portion of the ink moves along the path from the inlet 72 to the liquid surface, the liquid level can be raised or lowered by the circulation device. Furthermore, since the liquid level is raised or lowered using the driving force of the circulation device, a dedicated driving force for raising or lowering the liquid level is not required, thereby simplifying the structure.

[0064] Furthermore, in the degassing device 40 according to this embodiment, the inlet 72 for the liquid to flow from the circulation path 47 into the liquid storage tank is located above the liquid surface in the liquid storage tank, and the large cross-section portion 32L is located below the small cross-section portion 32S. Additionally, in the degassing device 40 according to this embodiment, the lifting device includes a circulation device, and when the circulation device does not circulate the liquid, the liquid surface is located at the small cross-section portion 32S. With this structure, when the circulation device circulates the liquid, the liquid surface drops, allowing the liquid surface to move to the large cross-section portion.

[0065] Furthermore, the degassing device 40 according to this embodiment has an inclined flow path 82, which is provided inside the liquid storage tank for the liquid flowing down from the inlet 72. With this structure, the liquid circulation path is lengthened compared to the case without the inclined flow path 82. As a result, the height difference between the liquid level when liquid circulation is not performed and when liquid circulation is performed can be increased, thus facilitating the control of the liquid level.

[0066] Furthermore, the inkjet recording apparatus 1 according to this embodiment includes a degassing device 40 and a recording head 21, wherein the recording head 21 discharges the degassed liquid from the degassing device 40 to the sheet S. With this structure, the reduction in image quality due to the generation of air bubbles can be suppressed.

[0067] The above implementation method can be modified as follows.

[0068] [First Variation] Figure 9 , 10 This is a cross-sectional view showing the degassing device 40 according to the first modification of the above embodiment. In this modification, the lifting device 92 has an immersion member that is immersed in liquid in a liquid tank (e.g., ink tank 32). The immersion member is raised and lowered to an immersion state in which it is immersed in the liquid in the liquid tank, and a retraction state in which it is retracted above the liquid in the liquid tank. Here, immersion also includes a state in which the lower end of the immersion member is in contact with the liquid surface. The lifting device 92 has a shaft 92S and a propeller 92P. The shaft 92S is arranged in the vertical direction and can slide in the vertical direction. The propeller 92P is arranged on the shaft 92S. The immersion component is arranged on the shaft 92S above the propeller 92P and is a large-diameter part 91 with a larger diameter than the shaft 92S. The large cross-section part 32L is arranged below the small cross-section part 32S. When the propeller 92P is not driven, the immersion component is in an immersion state. When the propeller 92P is driven in the direction that pushes the liquid downward, the immersion component is in a retraction state.

[0069] Specifically, a cylindrical bearing portion 92B supporting the upper end of the bearing shaft 92S is provided on the cover portion 32C. The shaft 92S can slide relative to the bearing portion 92B in the vertical direction. The propeller 92P is formed, for example, using a ferromagnetic material. A permanent magnet 92M and a motor 92D that rotates the permanent magnet 92M are provided on the outer side of the bottom 32B of the ink reservoir 32. The magnetic field generated by the permanent magnet 92M constrains the propeller 92P. Since the magnetic field rotates along with the rotation of the permanent magnet 92M, the propeller 92P also rotates. The propeller 92P generates a thrust that pushes the shaft 92S upward (in the direction that pushes the liquid downward). The large-diameter portion 91 is formed to be smaller than the horizontal cross-section of the inner surface of the small-section portion 32S. In this embodiment, since the horizontal cross-section of the inner surface of the small-section portion 32S is circular, the large-diameter portion 91 is also formed as a circular plate. The outer diameter of the large-diameter portion 91 is smaller than the inner diameter of the small-section portion 32S.

[0070] When the control device 38 does not rotate the propeller 92P (see reference) Figure 9 The shaft 92S descends under gravity, and its lower end contacts the upper surface of the bottom 32B. In this case, the large-diameter portion 91 is in an immersed state, with the liquid surface located at the small-section portion 32S. In the immersed state, the lower part of the large-diameter portion 91 is immersed, forming a gap G between the inner surface of the small-section portion 32S and the large-diameter portion 91. The ink only comes into contact with air at the liquid surface within the gap G. Furthermore, while the entire large-diameter portion 91 can be immersed in the immersed state, immersing only the lower part results in a narrower liquid surface compared to immersing the entire large-diameter portion 91; therefore, it is preferable that only the lower part of the large-diameter portion 91 is immersed.

[0071] On the other hand, when the control device 38 rotates the propeller 92P (see reference) Figure 10 The shaft 92S is pushed upward by the thrust generated by the propeller 92P, and the upper end of the shaft 92S contacts the lower surface of the cover portion 32C. In this case, the large-diameter portion 91 is in a retracted state, thus widening the liquid surface. The propeller 92P is provided to agitate the liquid to promote degassing, but in this modified example, since the driving force of the propeller 92P is used to retract the immersion component, a dedicated driving force for retracting the immersion component is not required.

[0072] [Second Variation] Figure 11This is a cross-sectional view showing the degassing device 40 according to the second modification of the above embodiment. In this modification, a detection device 93 is provided, which detects the height of the liquid level, and the lifting device 92 controls the height of the immersion member based on the height of the liquid level detected by the detection device 93. Specifically, the detection device 93 is provided at two locations corresponding to the upper and lower limits of the small cross-section portion 32S. The detection device 93 detects ink, for example, based on changes in resistance. When ink is detected at the lower limit position and not at the upper limit position, the control device 38 determines that the liquid level is located in the small cross-section portion 32S. On the other hand, when no ink is detected at either the lower or upper limit position, the control device 38 determines that the liquid level is located in the lower large cross-section portion 32L. When ink is detected at both the lower and upper limit positions, the control device 38 determines that the liquid level is located in the upper large cross-section portion 32L.

[0073] When the ink level is at the lower large cross-section 32L without ink agitation, the control device 38 replenishes ink from the ink cartridge 31 due to insufficient ink, causing the ink level to rise to the lower small cross-section 32S. When the ink level is at the lower small cross-section 32S with ink agitation, the control device 38 increases the rotational speed of the motor 92D to further raise the large diameter 91, causing the ink level to drop to the lower large cross-section 32L. According to this modified example, the height of the ink level can be easily controlled.

[0074] [3rd Variation] Figure 12 , 13 This is a cross-sectional view showing the degassing device 40 according to the third modification of the above embodiment. In this modification, the large cross-section portion 32L is disposed above the small cross-section portion 32S, and the lifting device 94 has a stirrer 94A that stirs the liquid. When the stirrer 94A is not driven, the liquid level is at the small cross-section portion 32S (see reference). Figure 12 ).

[0075] Specifically, the stir bar 94A is formed, for example, using a ferromagnetic material. The stir bar 94A is formed as a rod with its length in the horizontal direction and is placed on the upper surface of the bottom 32B of the ink reservoir 32. A permanent magnet 94M and a motor 94D for rotating the permanent magnet 94M are provided on the outside of the bottom 32B of the ink reservoir 32. The magnetic field generated by the permanent magnet 94M confines the stir bar 94A. Since the magnetic field also rotates along with the permanent magnet 94M, the stir bar 94A also rotates.

[0076] Without the stir bar 94A (see reference) Figure 12 The liquid level is located at the small cross-section 32S. On the other hand, in the case of driving the stirrer 94A (refer to...), Figure 13A vortex V is generated in the center of the liquid surface, and the liquid surface outside the vortex V moves to the large cross-section portion 32L, thus widening the liquid surface. The stir bar 94A is provided to stir the liquid to promote degassing, but in this embodiment, since the liquid surface is expanded by the driving force that drives the stir bar 94A, a dedicated driving force for expanding the liquid surface is not required.

[0077] [Other variations] In the first modification, an example is shown where the impregnation component is raised and lowered by a propeller 92P, but the impregnation component can be a float (not shown). Specifically, an electromagnet is provided on the cover portion 32C, and a ferromagnetic material (not shown) is provided on the float. In standby mode, during the decompression process, head circulation process, and printing process, the control device 38 does not energize the electromagnet. In this case, the float floats on the liquid surface, and the liquid surface is located at the small cross-section portion 32S. On the other hand, during the degassing process, the control device 38 energizes the electromagnet. In this case, the float is attracted to the electromagnet, and the liquid surface moves to the downward-facing large cross-section portion 32L. According to this modification, it is also possible to suppress the redissolution of air without reducing the degassing efficiency. Furthermore, this modification can be applied to both circulation degassing and agitation degassing methods.

[0078] In the above embodiment, an example is shown where the degassing device 40 is provided in the inkjet recording device 1. However, the degassing device 40 can also be applied to devices used in other fields such as semiconductor manufacturing and display manufacturing. That is, it can also be applied to degassing liquids other than ink, such as pharmaceuticals, electrolytes, liquid resins, adhesives, solvents, lubricants, liquid foods, and cosmetics.

[0079] In the above embodiment, the pressure reducing pump 62 is shown as a pressure reducing device, but any device that can reduce the pressure inside the ink reservoir 32 is acceptable. For example, the pressure reducing device can be an ejector.

[0080] In the above embodiment, the 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 an ejector.

Claims

1. A degassing device that removes dissolved air from a liquid under reduced pressure, characterized in that, It has a liquid storage tank, a pressure reducing device, and a lifting device, among which, The liquid storage tank has a small cross-section and a large cross-section, the large cross-section being located below or above the small cross-section, and the horizontal cross-sectional area of ​​the internal space being larger than that of the small cross-section. The liquid storage tank is used to store liquid. The pressure reducing device reduces the pressure inside the liquid storage tank; The lifting device raises or lowers the liquid level in the liquid storage tank to the small cross-section and the large cross-section.

2. The degassing device according to claim 1, characterized in that, It has a circulating flow path and a circulating device, wherein, The circulation path connects different locations of the liquid storage tank; The circulation device circulates the liquid through the circulation path.

3. The degassing device according to claim 2, characterized in that, The inlet for the liquid to flow from the circulation path into the liquid storage tank is located above the liquid level inside the liquid storage tank. The large cross-section portion is located below the small cross-section portion.

4. The degassing device according to claim 3, characterized in that, It has an inclined flow path, which is provided inside the liquid storage tank to allow the liquid flowing in from the inlet to flow down.

5. The degassing device according to claim 2, characterized in that, The lifting device includes the circulation device. When the circulation device does not circulate the liquid, the liquid level in the liquid storage tank is located at the small cross-section.

6. The degassing device according to claim 1, characterized in that, The lifting device has an immersion component. The immersion component is immersed in the liquid in the liquid storage tank. The immersion component is raised or lowered to an immersion state in which it is immersed in the liquid in the liquid tank, and to a retraction state in which it is retracted above the liquid in the liquid tank.

7. The degassing device according to claim 6, characterized in that, The lifting device has a shaft and a propeller, wherein... The shaft is arranged in the vertical direction and can slide in the vertical direction; The propeller is mounted on the shaft. The impregnation component is located on the shaft above the propeller, and is a large-diameter portion with a diameter larger than the shaft. The large cross-section portion is located below the small cross-section portion. The immersion component is in the immersion state when the propeller is not driven, and in the retraction state when the propeller is driven in the direction that pushes the liquid downward.

8. The degassing device according to claim 6, characterized in that, It has a detection device that detects the liquid level in the liquid storage tank. The lifting device controls the height of the immersion component based on the height of the liquid level in the liquid storage tank detected by the detection device.

9. The degassing device according to claim 1, characterized in that, The large cross-section portion is positioned above the small cross-section portion. The lifting device includes a stirrer that agitates the liquid. Without the agitator being driven, the liquid level in the liquid storage tank is located at the small cross-section.

10. An inkjet recording device, characterized in that... ， It has the degassing device and recording head as described in claim 1, wherein, The recording head discharges the degassed liquid from the degassing device onto the sheet.

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