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, a circulation flow path, a circulation device and a floating body. The liquid storage tank stores liquid. And the pressure reducing device is used for reducing the pressure in the liquid storage tank. The circulation flow path enables different positions of the liquid storage tank to be communicated. The circulation device circulates a liquid through the circulation flow path. And the floating body floats on the liquid level in the liquid storage tank. An inlet through which the liquid flows into the liquid storage tank from the circulation flow path is provided above the liquid level. The liquid flowing into the liquid storage tank from the inflow port falls to a portion of the floating body above the liquid level. Thus, redissolution of air can be suppressed without reducing 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, techniques to reduce the amount of dissolved air in the ink have been researched in the past. For example, structures that degas 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, a circulation path, a circulation device, and a float. The liquid storage tank stores liquid. The pressure reducing device reduces 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 float floats on the liquid surface within the liquid storage tank. An inlet for liquid flowing from the circulation path into the liquid storage tank is located above the liquid surface. Liquid flowing into the liquid storage tank from the inlet falls onto the portion of the float that is above the liquid surface.

[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 one embodiment of the present invention.

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

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

[0011] Figure 5 This is a schematic cross-sectional view illustrating a degassing apparatus according to an embodiment of the present invention.

[0012] Figure 6 This is a diagram showing the result of cyclic degassing as described in one embodiment of the present invention.

[0013] Figure 7 This is a diagram showing the result of placing ink after the completion of the cyclic degassing process according to one embodiment of the present invention.

[0014] Figure 8 This is a cross-sectional view showing a degassing apparatus according to a first modified embodiment of the present invention.

[0015] Figure 9 This is a cross-sectional view showing a degassing apparatus according to a second variation of an embodiment of the present invention.

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

[0017] Figure 11 This is a top view showing the buoy involved in the third variation of an embodiment of the present invention.

[0018] Figure 12 It means Figure 11 Section II sectional view.

[0019] Figure 13 This is a perspective view of a float according to a third variation of an embodiment of the present invention.

[0020] Figure 14 This is a top view showing the buoy involved in the third variation of an embodiment of the present invention.

[0021] Figure 15 It means Figure 14 Sectional view of section II-II.

[0022] Figure 16 This is a perspective view of a float according to a third variation of an embodiment of the present invention.

[0023] Figure 17 This is a cross-sectional view showing a degassing apparatus according to a fourth variation of an embodiment of the present invention.

[0024] Figure 18 This is a cross-sectional view showing a degassing apparatus according to a fourth variation of an embodiment of the present invention.

[0025] Figure 19 It means Figure 17Sectional view of section III-III.

[0026] Figure 20 This is a cross-sectional view showing a degassing apparatus according to a sixth variation of an embodiment of the present invention.

[0027] Figure 21 This is a cross-sectional view showing a degassing apparatus according to a sixth variation of an embodiment of the present invention.

[0028] Figure 22 This is a perspective view showing the inclined flow path involved in the sixth variation of an embodiment of the present invention.

[0029] Figure 23 This is a top view showing the inclined flow path according to the sixth variation of an embodiment of the present invention. Detailed Implementation

[0030] 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.

[0031] The inkjet recording device 1 ejects ink from each inkjet recording head 21 onto the 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 mounting 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 circuits (hardware) forming integrated circuits, etc. 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).

[0037] 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.

[0038] 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.

[0039] 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.

[0040] [Degassing device] This describes the degassing device 40 involved in this embodiment. 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 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.

[0041] [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.

[0042] [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.

[0043] [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.

[0044] [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.

[0045] [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.

[0046] [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.

[0047] [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.

[0048] [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 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 center of the cover portion 32C. 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.

[0049] [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.

[0050] 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.

[0051] 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).

[0052] 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.

[0053] 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.

[0054] [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.

[0055] 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.

[0056] [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.

[0057] 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 refers to the time during which printing is allowed even when the ink is placed without degassing. 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.

[0058] 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.

[0059] [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).

[0060] [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.

[0061] [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.

[0062] [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.

[0063] also, Figure 1The illustration is schematic; 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 in the recording head 21 and the ink in the ink reservoir 32. This negative pressure forms 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, and the resulting negative pressure draws a reduced amount of ink from the ink reservoir 32 into the recording head 21. Furthermore, the recovery valve 55 can be closed, supplying ink to the recording head 21 only from the bypass flow path 46.

[0064] 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.

[0065] Next, the features of this embodiment will be described in detail. The degassing device 40 according to 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), a circulation path 47, a circulation device (e.g., circulation pump 67), and a float 81. The liquid storage tank stores 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; the circulation device circulates the liquid through the circulation path 47; and the float 81 floats on the liquid surface within the liquid storage tank. An inlet 72 for liquid to flow from the circulation path 47 into the liquid storage tank is located above the liquid surface, and liquid flowing into the liquid storage tank from the inlet 72 falls onto the portion of the float 81 above the liquid surface. Specifically, as described below. Furthermore, the ink storage tank 32, pressure reducing pump 62, circulation path 47, and circulation pump 67 are as described above; the float 81 will be mainly described below.

[0066] [Floating body] The float 81 is formed of a material such as polypropylene, whose mass per unit volume is smaller than that of ink. The float 81 is formed as a plate with dimensions smaller than the horizontal cross-section of the inner surface of the sidewall portion 32W. In this embodiment, since the horizontal cross-section of the inner surface of the sidewall portion 32W is circular, the float 81 is also formed as a circular plate. The outer diameter of the float 81 is smaller than the inner diameter of the sidewall portion 32W. Therefore, a gap G is formed between the inner surface of the sidewall portion 32W of the ink reservoir 32 and the outer edge of the float 81, reducing contact between the float 81 and the sidewall portion 32W.

[0067] In standby mode, during the decompression process, head circulation process, and printing process (refer to...). Figure 4 Since only the liquid surface within the gap G is in contact with the air, the redissolution of air can be suppressed.

[0068] On the other hand, in the degassing process, the ink is circulated through circulation path 47 (see reference). Figure 5 Ink falls from inlet 72 onto the upper surface of float 81, forming an ink layer covering the upper surface of float 81, and then falls from the outer edge of float 81 to the liquid surface. Assuming that inlet 72 is located below the liquid surface, only the ink in the liquid surface within gap G comes into contact with air. However, in this embodiment, during the period from inlet 72, through the upper surface of float 81, to the liquid surface within gap G, the ink is continuously in contact with air, thus improving degassing efficiency.

[0069] also, Figure 5 The image shows the float 81 maintaining a horizontal orientation, with the ink spreading evenly across its upper surface. In reality, even considering the tilt of the float 81 and the resulting uneven ink flow on its upper surface, the degassing efficiency is improved compared to the case where the inlet 72 is located below the liquid surface, due to the increased area of ​​contact between the ink and air.

[0070] [experiment] Figure 6 This graph shows the results of the cyclic degassing process. The ink viscosity was set to 7 mPa·s, the ink temperature to 25 °C, the diameter of the ink tank 32 to 60 mm, the ink depth to 28 mm, and the ink circulation flow rate to 770 ml / min. The changes in oxygen saturation over time were compared with and without the float 81. The vertical axis represents oxygen saturation (%), and the horizontal axis represents the degassing time (min). According to the graph, the oxygen saturation changed identically with and without the float 81. This indicates that the reduction in degassing efficiency caused by the float 81 was suppressed.

[0071] Figure 7 This graph shows the results of placing the ink after the degassing cycle is complete. The vertical axis represents oxygen saturation (%), and the horizontal axis represents the placement time (hours) after the degassing cycle. According to the graph, the presence of float 81 inhibits the rise in oxygen saturation compared to the absence of float 81. This indicates that the float 81 suppresses the redissolution of air.

[0072] The degassing device 40 according to the above-described embodiment removes dissolved air from the liquid under reduced pressure. The degassing device 40 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, a circulation device (e.g., a circulation pump 67), and a float 81. The liquid storage tank stores liquid (e.g., ink); the pressure reducing device reduces 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; and the float 81 floats on the liquid surface within the liquid storage tank. An inlet 72, through which liquid flows from the circulation path 47 into the liquid storage tank, is located above the liquid surface. Liquid flowing into the liquid storage tank from the inlet 72 falls onto the portion of the float 81 that is above the liquid surface. With this structure, the redissolution of air can be suppressed without reducing the degassing efficiency.

[0073] 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, image quality degradation caused by bubble generation can be suppressed.

[0074] The above implementation method can be modified as follows.

[0075] [First Variation] Figure 8 This is a cross-sectional view showing the degassing device 40 involved in the first modified example. In this modified example, the upper surface of the float 81 forms a conical surface. The inlet 72 is provided above the apex of the conical surface that forms the upper surface of the cone. In the case of circulating ink, the ink flowing in from the inlet 72 falls onto the upper surface of the float 81 and flows down along the upper surface of the float 81. Figure 8 The image shows the ink falling to the apex of the upper surface of the float 81 and spreading evenly across the entire upper surface. In reality, even considering that the float 81 may tilt, or that the float 81 may move horizontally and cause the ink to fall to a position deviating from the apex of the upper surface, resulting in uneven ink flow, the degassing efficiency is still improved compared to the case where the inlet 72 is located below the liquid surface, due to the increased area of ​​contact between the ink and air.

[0076] Furthermore, in the above embodiment, since the upper surface of the float 81 is not inclined, it takes time for the ink to flow from the upper surface of the float 81 to the liquid surface when ink circulation is stopped, which may promote the redissolution of air. Additionally, since the upper surface of the float 81 is not inclined, ink is more likely to remain on the upper surface, but this residual ink does not help reduce the amount of dissolved air in the ink stored in the ink tank 32, thus reducing degassing efficiency. In contrast, in this modified example, when ink circulation is stopped, the ink flows rapidly from the upper surface of the float 81 to the liquid surface, and it is less likely for ink to remain on the upper surface, thus suppressing the redissolution of air without reducing degassing efficiency.

[0077] Furthermore, even if the upper surface of the float 81 is formed into a pyramidal surface, the same effect as in the first modified example can be obtained. In short, it is sufficient as long as the upper surface of the float 81 is formed into a pyramidal surface.

[0078] Furthermore, it is sufficient that the upper surface of the float 81 is at least inclined. By inclining the upper surface of the float 81, an effect similar to that of the first modified example can be obtained. However, when the upper surface of the float 81 is inclined in one direction, the ink flows down from the lower side of the upper surface to a specific part of the liquid surface, and the circulation of the ink may stagnate outside the specific part. In contrast, in this modified example, uneven ink flow can be suppressed.

[0079] [Second Variation] Figure 9 This is a cross-sectional view showing the degassing device 40 involved in the second modification. In this modification, the distance between the inlet 72 and the float 81 is the distance at which the liquid falling onto the float 81 does not scatter. Specifically, compared to the first modification, the inclination angle of the upper surface of the float 81 is larger, and the position of the inlet 72 is lower. Therefore, the distance from the inlet 72 to the upper surface of the float 81 is shorter than in the first modification.

[0080] In the event of ink scattering, ink droplets adhere to the wall of the ink reservoir 32. Due to their small size, these droplets are easily degassed, but are more likely to remain on the wall instead of falling to the liquid surface. Droplets remaining on the wall do not help reduce the amount of dissolved air in the ink stored in the ink reservoir 32, thus reducing degassing efficiency. In contrast, in this modified example, since the ink falling onto the float 81 is less prone to scattering, the reduction in degassing efficiency can be suppressed. Furthermore, the inclined upper surface of the float 81 also has the effect of suppressing ink scattering.

[0081] [3rd Variation] Figure 10 This is a cross-sectional view of the degassing device 40 involved in the third modified example. Figure 11This is a top view of the float 81 involved in the third variation. Figure 12 It means Figure 11 Section II sectional view. Figure 13 This is a perspective view of the float 81 involved in the third variation. Figure 14 This is a top view of the float 81 involved in the third variation. Figure 15 It means Figure 14 Sectional view of section II-II. Figure 16 This is a perspective view of the float 81 involved in the third variation.

[0082] In this modified example, the float 81 has a wall portion 81W and an opening portion 81A, wherein the wall portion 81W blocks the flow of ink, and the opening portion 81A discharges the ink blocked by the wall portion 81W. Specifically, the float 81 has a main body portion 81M identical to that of the float 81 involved in the first modified example. The wall portion 81W stands upright from the edge of the upper surface of the main body portion 81M. Viewed from above, the wall portion 81W forms a circle along the edge of the upper surface of the main body portion 81M. The height of the upper end of the wall portion 81W is approximately equal to the height of the apex of the upper surface of the main body portion 81M.

[0083] Figures 11 to 13 This is an example where an opening 81A is provided on the wall portion 81W. The opening 81A penetrates the wall portion 81W. It is sufficient for the opening 81A to be provided at least one location, but it is preferable to provide it at equal intervals on multiple locations in the circumferential direction (four locations in this modified example).

[0084] on the other hand, Figures 14 to 16 This example shows an opening 81A provided on the main body 81M. The opening 81A extends through the main body 81M in a vertical direction at the boundary between the upper surface of the main body 81M and the inner surface of the wall 81W. It is sufficient to provide the opening 81A at least one location, but it is preferable to provide it at equal intervals on multiple locations in the circumferential direction (four locations in this modified example).

[0085] According to this modified example, compared to the case without the wall portion 81W, the ink remains on the upper surface of the float 81 for a longer period, thus improving degassing efficiency. When a large amount of flowing ink is present, some ink may be blocked, sometimes resulting in temporary ink accumulation. While this accumulation may reduce the surface area of ​​the ink, ink flows in all directions, including vertically, replacing surface ink and increasing the amount of ink exposed to the reduced pressure atmosphere, thus improving degassing efficiency. Furthermore, when ink circulation stops, the ink blocked by the wall portion 81W is discharged from the opening 81A, thus suppressing air redissolution.

[0086] [4th Variation] Figure 17 , 18 This is a cross-sectional view showing the degassing device 40 involved in the fourth modified example. Figure 19 It means Figure 17 A cross-sectional view of section III-III. In this modified example, the ink reservoir 32 has a limiting portion 32R that restricts the descent of the float 81 when the liquid level drops due to ink circulation. Specifically, the limiting portion 32R protrudes from the inner surface of the side wall portion 32W of the ink reservoir 32. The limiting portion 32R is provided at equal intervals on multiple circumferential locations (four locations in this modified example) of the side wall portion 32W (see reference). Figure 19 ).

[0087] When the circulation pump 67 does not circulate ink (see reference) Figure 17 The liquid level is above the limiting part 32R, and the float 81 floats on the liquid surface. When the circulating pump 67 circulates the ink (see...). Figure 18 A portion of the ink moves along a path from the inlet 72 through the upper surface of the float 81 to the liquid surface, causing the liquid surface to drop below the restrictor 32R, on which the float 81 is mounted. In this case, a space is formed between the liquid surface and the lower surface of the float 81. The ink comes into contact with air as it flows down from the upper surface of the float 81, and the air also comes into contact with the liquid surface located below the float 81. Accordingly, according to this modified example, the degassing efficiency can be improved compared to the case without the restrictor 32R.

[0088] [5th ​​Variation] In the above embodiment, by pushing the ink falling from the inlet 72 onto the float 81, at least a portion of the float 81 may sink below the liquid surface. Whether the float 81 sinks depends on various conditions such as the mass of the float 81, the specific gravity of the float 81 relative to the ink, and the inflow rate of ink flowing into the inlet 72 per unit time. However, when a portion of the float 81 sinks, the liquid surface expands above the float 81, thus improving the degassing efficiency. When the entire float 81 sinks, since the liquid surface expands over the entire float 81, the same degassing efficiency as in the above embodiment can be obtained.

[0089] Furthermore, the portion of the ink falling from the float 81 remains above the liquid surface even as the falling ink continues to contact it, but it can also remain below the liquid surface. Even below the surface, the falling ink is less likely to sink to a greater depth than the float, thus improving degassing efficiency. Additionally, if maintaining a high buoyancy height for the float 81 while withstanding falling ink requires a hollow interior for weight reduction, it might be prone to breakage or increase manufacturing costs. However, allowing the float 81 to sink increases the possibility of using a solid float 81.

[0090] [Sixth Variation] Figure 20 , 21 This is a cross-sectional view of the degassing device 40 involved in the sixth modified example. Figure 22 This is a three-dimensional view showing the inclined flow path 82 involved in the sixth variation. Figure 23 This is a top view showing the inclined flow path 82 involved in the sixth variation.

[0091] The degassing device 40 of this modified example has an inclined flow path 82 supported by a float 81, with a gap between the inclined flow path 82 and the float 81. Ink flowing from the circulation flow path 47 into the ink reservoir 32 flows down the inclined flow path 82 to the upper surface of the float 81. Specifically, the inclined flow path 82 has a bottom 82B, guide walls 82G, and restrictive walls 82R. The bottom 82B is rectangular and inclined in one direction. A pair of guide walls 82G facing each other are provided 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 restrictive walls 82R are 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 restrictive walls 82R and the bottom 82B. A plurality of supports 82P are provided on the upper surface of the float 81. The inclined flow path 82 is supported by the supports 82P.

[0092] When the circulation pump 67 does not circulate ink (see reference) Figure 20 ), the float 81 floats on the liquid surface. In this case, since only the liquid on the liquid surface within the gap G is in contact with the air, the redissolution of air can be suppressed. On the other hand, when the circulating pump 67 circulates the ink (see... Figure 21 After the ink flows from the inlet 72 to the inclined flow path 82, it flows along the inclined flow path 82, falls from the opening 82A to the float 81, and flows down from the upper surface of the float 81 to the liquid surface. Therefore, compared with the case without the inclined flow path 82, the contact area between the ink and the air is increased, and the degassing efficiency is improved.

[0093] [Other variations] In the above embodiment, an example is shown where the inlet 72 is connected to the central part of the cover portion 32C. However, it can also be configured such that the inlet 72 is connected to the part of the side wall portion 32W of the ink reservoir 32 above the liquid level, and the ink flows laterally from the inlet 72 and falls onto the upper surface of the float 81.

[0094] 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.

[0095] 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.

[0096] 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, a circulation path, a circulation device, and a float, among which, The liquid storage tank stores 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 path; The float is suspended on the surface of the liquid in the liquid storage tank. The inlet for the liquid flowing from the circulation path into the liquid storage tank is located above the liquid surface. Liquid flowing into the liquid storage tank from the inlet falls onto the portion of the float that is above the liquid surface.

2. The degassing device according to claim 1, characterized in that, The upper surface of the float is inclined.

3. The degassing device according to claim 2, characterized in that, The upper surface of the float forms a conical surface.

4. The degassing device according to claim 1, characterized in that, The distance between the inlet and the float is the distance at which the liquid falling onto the float does not scatter.

5. The degassing device according to claim 1, characterized in that, The float has a wall that blocks the flow of liquid.

6. The degassing device according to claim 5, characterized in that, The float has an opening that allows liquid blocked by the wall to drain out.

7. The degassing device according to claim 1, characterized in that, The liquid storage tank has a limiting part that restricts the descent of the float when the liquid level drops due to liquid circulation.

8. The degassing device according to claim 1, characterized in that, By pushing the liquid falling from the inlet onto the float, at least a portion of the float sinks below the liquid surface.

9. The degassing device according to claim 1, characterized in that, It has an inclined flow path supported by the float, and a gap is provided between the inclined flow path and the float. Liquid flowing into the liquid storage tank from the circulation path flows down to the upper surface of the float via the inclined flow path.

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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