Degassing device, inkjet recording device

Abstract

A deaeration device (40) removes air dissolved in a liquid in a reduced-pressure atmosphere. The deaeration device comprises a liquid tank (32) that stores a liquid, a vacuum device (62) that reduces the pressure within the liquid tank, a circulation passage (47) that communicates different positions of the liquid tank, a circulation device (67) that causes the liquid to circulate through the circulation passage, and a control device (38) that controls the circulation operation of the circulation device. The control device adjusts the circulation time of the liquid in accordance with the amount of dissolved air in the liquid.

Description

Technical Field

[0001] The present invention relates to a degassing device and an inkjet recording device.

Background Art

[0002] In an inkjet recording device, ink droplets are ejected from the nozzles of a recording head. However, if air bubbles are contained in the ink, the nozzles of the recording head may be clogged. Therefore, it is desirable to suppress the amount of dissolved air in the ink, and a degassing device for removing the air dissolved in the ink has been studied. For example, as a degassing device, there is known one that stirs the ink in a state where the inside of an ink tank is depressurized (see, for example, Patent Documents 1 and 2). In the degassing devices described in Patent Documents 1 and 2, a magnetic force is applied from the outside to a stirrer in the ink tank, and the stirrer is rotated by the magnetic force to stir the ink in the ink tank.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the degassing devices described in Patent Documents 1 and 2, the ink in the ink tank is stirred and the ink is degassed near the liquid surface. However, since the stirrer is located at the bottom of the ink tank, when the ink capacity increases, it becomes difficult to exchange the ink near the liquid surface with less dissolved air and the ink near the bottom surface with more dissolved air. In addition, since the amount of dissolved air in the ink changes according to the surrounding environment, there is a possibility that the degassing of the ink may be insufficient or excessive in a certain degassing time. Further, the same problem occurs when the above degassing device is used for degassing a liquid other than ink.

[0005] Therefore, the present invention aims to improve the degassing efficiency of a degassing device with a simple configuration, even when the liquid volume is large, and to enable degassing without excess or deficiency. [Means for solving the problem]

[0006] The degassing apparatus of the present invention is a degassing apparatus for removing dissolved air from a liquid under a reduced pressure atmosphere, and comprises a liquid tank in which liquid is stored, a pressure reducing device for reducing the pressure inside the liquid tank, a circulation channel connecting different locations in the liquid tank, a circulation device for circulating the liquid through the circulation channel, and a control device for controlling the circulation operation by the circulation device. The control device adjusts the liquid circulation time according to the amount of dissolved air in the liquid.

[0007] The inkjet recording apparatus of the present invention comprises the above-mentioned degassing device and a recording head that ejects the degassed ink as a liquid onto a sheet. [Effects of the Invention]

[0008] According to the configuration of the present invention, dissolved air in the liquid near the liquid surface exposed to a reduced-pressure atmosphere is removed. The liquid in the liquid tank is circulated through the circulation channel, and the liquid near the liquid surface with a low amount of dissolved air is exchanged with the liquid near the bottom with a high amount of dissolved air, resulting in efficient degassing. Furthermore, even if the amount of dissolved air in the liquid changes, the circulation time of the liquid is adjusted according to the amount of dissolved air, allowing for degassing without excess or deficiency. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the inkjet recording device according to the first embodiment. [Figure 2] This is a schematic diagram of the ink supply structure of the first embodiment. [Figure 3] This graph shows the relationship between ink pressure reduction conditions and oxygen saturation. [Figure 4] This figure shows an example of the degassing operation of the circulating degassing method of the first embodiment. [Figure 5] This figure shows an example of the degassing operation of the stirring degassing method in the comparative example. [Figure 6] This graph shows the oxygen saturation levels for circulating degassing and agitated degassing methods. [Figure 7] This is a flowchart showing the adjustment process for the cycle time in the first embodiment. [Figure 8] This figure shows the relationship between oxygen saturation and circulation time in the first embodiment. [Figure 9] This is a schematic diagram of the ink supply structure of the second embodiment. [Modes for carrying out the invention]

[0010] <First Embodiment> The inkjet recording apparatus of the first embodiment will be described below with reference to the drawings. Figure 1 is a schematic diagram of the inkjet recording apparatus of the first embodiment. For the sake of explanation, the front of the paper in Figure 1 will be considered the front side of the inkjet recording apparatus, and the left and right directions will be explained based on the direction in which the inkjet recording apparatus is viewed from the front. The arrows L, R, U, and Lo attached to each figure as appropriate indicate the left, right, top, and bottom sides of the inkjet recording apparatus, respectively.

[0011] As shown in Figure 1, the inkjet recording device 1 is configured to print by ejecting ink from each inkjet recording head 21 toward a sheet S, which serves as a recording medium. The inkjet recording device 1 includes a box-shaped housing 10 that houses various components. A paper feed cassette 11 into which the sheets S are set is housed in the lower part of the housing 10, and a manual feed tray 12 into which the sheets S are manually inserted is installed on the right side of the housing 10. An output tray 13 into which recorded sheets S are stacked is installed on the upper left side of the housing 10.

[0012] A first transport path 14 is formed on the right side of the housing 10 for transporting sheets 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 is a first paper feeding unit 15 for taking sheets S from the sheet bundle in the paper feed cassette 11, and downstream of the first transport path 14 is a pair of registration rollers 18 for adjusting the timing of the sheet S being fed out. Further downstream of the first transport path 14 is a paper feeding path 16 for the manual feed tray 12, and the paper feeding path 16 is equipped with a second paper feeding unit 17 for taking sheets S from the sheet bundle in the manual feed tray 12.

[0013] Downstream of the pair of registration rollers 18 are a transport device 22 and recording heads 21 for each color (e.g., black, cyan, magenta, yellow). The pair of registration rollers 18 correct the skew of the sheet S and feed the sheet S to the transport device 22 in accordance with the ink ejection operation of each recording head 21. The housing 10 is provided with an ink container 31 and an ink tank 32 for each recording head 21. The ink from each ink container 31 is temporarily stored in the ink tank 32, and the ink is degassed as needed before being supplied from the ink tank 32 to the recording head 21.

[0014] The transport device 22 is configured by stretching a transport belt 24 over a plurality of tension rollers 23 installed below each recording head 21. Downstream of the transport device 22, a drying device 25 is provided for drying the ink on the sheet S. Downstream of the drying device 25, a decaling device 26 is provided for correcting the curl that occurs on the sheet S due to the drying of the ink. Downstream of the decaling device 26, a second transport path 27 is formed for transporting the sheet S toward the output tray 13. Downstream of the second transport path 27, a paper discharge section 28 is provided for discharging the recorded sheet S into the output tray 13.

[0015] Below the drying device 25, there are provided a maintenance unit 35 for cleaning the recording head 21 and a cap unit 36 for capping the recording head 21. The maintenance unit 35 is provided with a squeegee-shaped wiping blade, and the ink remaining on the nozzle surface of the recording head 21 is scraped off by the wiping blade. The cap unit 36 is provided with a head cap, and the head cap is placed on the nozzle surface of the recording head 21. The drying of the ink in the nozzles is suppressed by the head cap. The drying of the ink in the nozzles may be further suppressed by storing a liquid such as a cleaning liquid in the head cap.

[0016] Also, the inkjet recording apparatus 1 is provided with a control device 38 for overall control of the entire apparatus. The control device 38 may be constituted by a processor or may be constituted by a logic circuit (hardware) formed in an integrated circuit or the like. When constituted by a processor, various processes are implemented by the processor reading and executing a program stored in a memory. As the processor, for example, a CPU (Central Processing Unit) is used. The memory is constituted by one or a plurality of storage devices such as a ROM (Read Only Memory) and a RAM (Random Access Memory) according to the application.

[0017] At the time of image recording, the sheet S is taken out from the paper feed cassette 11 or the manual feed tray 12 by the first and second paper feed units 15 and 17 and sent to a pair of registration rollers 18. In accordance with the ink ejection timing, the sheet S is sent from the pair of registration rollers 18 to the conveyance belt 24, and the degassed ink is ejected from each recording head 21 and a color image is recorded on the surface of the sheet S. The sheet S is dried by the drying device 25, and the curl of the sheet S is corrected by the decal device 26. The sheet S is conveyed to the paper discharge unit 28 through the second conveyance path 27, and the recorded sheet S is discharged to the paper discharge tray 13 by the paper discharge unit 28.

[0018] By the way, in a machine with a small ink usage amount such as an on-demand machine, the liquid level of the ink in the ink tank touches the air, and air dissolution progresses, and the nozzles of the recording head may be clogged by air bubbles in the ink. Therefore, it is desired to appropriately suppress the amount of dissolved air in the ink. For example, a method has been proposed in which ink is passed through a hollow fiber filter in a state where the periphery of the hollow fiber filter is decompressed, and air moves from the wall surface of the hollow fiber to the decompression side and is degassed. In this method, an expensive hollow fiber filter is required, and regular replacement work is required, increasing the cost.

[0019] Also, in order to prevent nozzle clogging, a method of degassing by stirring the ink with a stirrer in a state where the inside of the ink tank is decompressed below atmospheric pressure (hereinafter referred to as the stirring degassing method) has been proposed. In the stirring degassing method, a magnetic force is externally applied to the stirrer in the ink tank, and the stirrer is rotated by the magnetic force to stir the ink in the ink tank. When the depth of the ink or the diameter of the tank is large, it becomes difficult to stir the ink and the degassing efficiency decreases. If the rotation speed of the stirrer is increased, it becomes easier to stir, but if the rotation speed of the stirrer becomes too high, a runaway phenomenon occurs and the rotation noise of the stirrer also increases.

[0020] Therefore, in the first embodiment, a method of degassing by circulating the ink in the ink tank 32 through the circulation flow path 47 in a state where the inside of the ink tank 32 is decompressed below atmospheric pressure (hereinafter referred to as the circulation degassing method) is adopted (see FIG. 2). In the circulation degassing method, the ink circulates through the circulation flow path 47 and the inside of the ink tank 32, so that the ink near the liquid surface with a small amount of dissolved air and the ink near the bottom surface with a large amount of dissolved air are exchanged, improving the degassing efficiency. Different from the stirring degassing method, it is not affected by the depth of the ink or the diameter of the tank, and the driving noise of the circulation pump is suppressed more than the rotation noise of the stirrer, enhancing the quietness.

[0021] Generally, the recording head 21 may be included in the circulation channel of the circulating degassing system, but in this embodiment, the recording head 21 is not included in the circulation channel 47. In other words, the circulation channel 47 is a dedicated channel for degassing, provided separately from the path that supplies ink to the recording head 21. By not including the recording head 21 in the circulation channel 47, the possibility of external air entering the recording head 21 is reduced because the meniscus formed inside the nozzle of the recording head 21 is destroyed by the reduced pressure during degassing.

[0022] Furthermore, the amount of dissolved air in the ink changes depending on the surrounding environment. For example, the amount of dissolved air in the ink depends on the ambient temperature and atmospheric pressure. Since the ink tank 32 is filled with degassed ink, the amount of dissolved air is low immediately after the ink tank 32 is filled. Also, as the print density increases and the frequency of ink replacement in the ink tank 32 increases, the amount of dissolved air decreases. In these cases, if the ink circulation time is too long relative to the amount of dissolved air in the ink, there is a problem in that the waiting time until printing becomes long. Therefore, in the first embodiment, the ink circulation time is adjusted according to the amount of dissolved air in the ink.

[0023] Referring to Figure 2, the degassing device of the first embodiment will be described. Figure 2 is a schematic diagram of the ink supply structure of the first embodiment. The inkjet recording device of this embodiment is provided with an ink supply structure for each color, but here only one ink supply structure will be described.

[0024] As shown in Figure 2, the ink tank 32 stores ink supplied from the ink container 31 through the supply channel 41. A supply pump 61 and a supply valve 51 are interposed in the supply channel 41, and the supply of ink to the ink tank 32 is controlled by the supply pump 61 and the supply valve 51. The upper space 34 of the ink tank 32 is connected to a depressurization channel 42 and an atmospheric release channel 43. A depressurization pump (depressurization device) 62 and a depressurization valve 52 are interposed in the depressurization channel 42, and the inside of the ink tank 32 is depressurized by the depressurization pump 62 and the depressurization valve 52. An atmospheric release valve 53 is interposed in the atmospheric release channel 43, and the upper space 34 is opened to the atmosphere by the atmospheric release valve 53.

[0025] Ink is supplied from the ink tank 32 to the recording head 21 via the supply channel 44, and ink is recovered from the recording head 21 to the ink tank 32 via the recovery channel 45. A supply pump 64 and a supply valve 54 are interposed in the supply channel 44, and a recovery valve 55 is interposed in the recovery channel 45. The supply pump 64, supply valve 54, and recovery valve 55 control the ink exchange operation and air bubble removal operation within the recording head 21. A bypass channel 46 that bypasses the supply pump 64 is connected to the supply channel 44, and a bypass valve 56 is interposed in the bypass channel 46. During printing, ink is passed through the bypass channel 46 by the bypass valve 56.

[0026] The ink level and bottom of the ink tank 32 are connected by a circulation channel 47. A circulation pump (circulation device) 67 is interposed in the circulation channel 47, and the ink is circulated through the circulation channel 47 by the circulation pump 67. The inlet 72 from the circulation channel 47 to the ink tank 32 is higher than the outlet 71 from the ink tank 32 to the circulation channel 47. Specifically, the outlet 71 is opened on the bottom of the ink tank 32, and the inlet 72 is opened on the side of the ink tank 32 near the liquid level. Various pumps 61, 62, 64, 67 and various valves 51-56 are controlled by a control device 38.

[0027] The control device 38 controls the circulation operation by the circulation pump 67 and adjusts the ink circulation time according to the amount of dissolved air in the ink. In the first embodiment, the amount of dissolved air in the liquid is predicted from the operating environment, and the liquid circulation time is adjusted according to the predicted value of the amount of dissolved air in the liquid. Details of the ink circulation time adjustment process by the control device 38 will be described later. In this ink supply structure of the inkjet recording device 1, a degassing device 40 is formed by the ink tank 32, a pressure reducing channel 42, a pressure reducing pump 62, a pressure reducing valve 52, a circulation channel 47, a circulation pump 67, the control device 38, etc.

[0028] In the standby state of the inkjet recording device 1, the replenishment valve 51, pressure reducing valve 52, and supply valve 54 are closed, while the atmospheric release valve 53, bypass valve 56, and recovery valve 55 are open. Ink is stored in the ink tank 32, and as time passes, air dissolves into the ink as the liquid surface comes into contact with the air in the upper space 34 which is open to the atmosphere. During the pressure reduction operation, only the pressure reducing valve 52 is opened, and the other valves 51, 53-56 are closed. The pressure reducing pump 62 is driven to remove air from the upper space 34 inside the ink tank 32. When the inside of the ink tank 32 reaches the target pressure (for example, -50 [kPa]), the pressure reducing pump 62 is stopped.

[0029] During the degassing operation, all valves 51-56 are closed, and the circulation pump 67 is driven while the reduced pressure state inside the ink tank 32 is maintained, circulating the ink inside the ink tank 32 through the circulation channel 47. Ink near the bottom of the ink tank 32, where there is a large amount of dissolved air, flows out into the circulation channel 47 through the outlet 71, and ink in the circulation channel 47 flows towards the liquid surface inside the ink tank 32 through the inlet 72. The liquid surface of the ink is exposed to a reduced pressure atmosphere, and the air dissolved in the ink near the liquid surface is removed. The ink near the liquid surface, where there is a small amount of dissolved air, and the ink near the bottom, where there is a large amount of dissolved air, are smoothly exchanged, improving the degassing efficiency.

[0030] During the ink replacement operation in the recording head 21, the replenishment valve 51, pressure reducing valve 52, and bypass valve 56 are closed, while the atmospheric release valve 53, supply valve 54, and recovery valve 55 are opened. The supply pump 64 is driven to supply ink from the ink tank 32 to the recording head 21 through the supply channel 44, and the ink is recovered from the recording head 21 to the ink tank 32 through the recovery channel 45. As the ink circulates between the recording head 21 and the ink tank 32, the ink whose viscosity has increased in the recording head 21 is replaced, and air bubbles are removed from the recording head 21.

[0031] Furthermore, during printing operations by the recording head 21, the replenishment valve 51, pressure reducing valve 52, and supply valve 54 are closed, while the atmospheric release valve 53, bypass valve 56, and recovery valve 55 are open. In other words, during printing operations, the ink tank 32 is released to the atmosphere and is at atmospheric pressure. During printing operations, the ink tank 32 is not subjected to a pressure reduction that would cause substantial degassing. Each time ink is ejected from the recording head 21, ink is supplied from the ink tank 32 to the recording head 21 through the bypass channel 46 and the recovery channel 45. Ink may be replenished during operations such as ink replacement or printing. During these ink replenishment operations, the replenishment valve 51 is opened and the replenishment pump 61 is driven. The replenishment pump 61 drives ink from the ink container 31 to the ink tank 32 through the replenishment channel 41.

[0032] Note that Figure 1 and other diagrams are schematic representations; in reality, the recording head 21 is positioned above the ink tank 32. A negative pressure is applied to the ink in the recording head 21 due to the difference in water head between it and the ink in the ink tank 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 the lost ink back from the ink tank 32 to the recording head 21. Alternatively, the recovery valve 55 may be closed, and ink may be supplied to the recording head 21 only through the bypass channel 46.

[0033] Furthermore, if the ink tank 32 is depressurized to the point of substantial degassing while the recording head 21 and the ink tank 32 are connected, there is a risk that the nozzle meniscus may be destroyed. Even if the meniscus is not destroyed, the shape of the meniscus inside the nozzle may change from when the ink tank 32 is open to the atmosphere, which may change the ink ejection characteristics. In this embodiment, during printing, the ink tank 32 is not depressurized to the point of substantial degassing, so the meniscus inside the nozzle of the recording head 21 is not destroyed, nor does its shape change, and therefore the ejection characteristics do not change.

[0034] The degassing performance of the circulating degassing method and the agitation degassing method will be explained with reference to Figures 3-6. Figure 3 is a graph showing the relationship between the reduced pressure conditions of the ink and the oxygen saturation. Figure 4 is a diagram showing an example of the degassing operation of the circulating degassing method. Figure 5 is a diagram showing an example of the degassing operation of the agitation degassing method. Figure 6 is a graph showing the oxygen saturation of the circulating degassing method and the agitation degassing method.

[0035] The degassing device 40 described above utilizes a vacuum degassing method, which removes air by reducing the pressure inside the ink tank 32. In the vacuum degassing method, the amount of dissolved air in the liquid converges to the saturated dissolved amount according to environmental conditions such as atmospheric pressure and liquid temperature, and the amount of dissolved air decreases when the atmospheric pressure decreases or the temperature increases. Often, the amount of dissolved oxygen is used instead of the amount of dissolved air, and in the following explanation, the degassing performance will be explained using the oxygen saturation obtained from the following equation (1). As shown in Figure 3, the oxygen saturation decreases with reduced pressure, but it is necessary to transport the ink to the liquid surface exposed to the reduced pressure atmosphere. (1) Oxygen saturation = Dissolved oxygen amount / Saturated dissolved oxygen amount at atmospheric pressure × 100

[0036] As shown in Figure 4, in the circulating degassing degasser 40, air dissolved in the ink is removed near the liquid surface of the depressurized ink tank 32, resulting in a low oxygen saturation level in the ink near the liquid surface and a high oxygen saturation level in the ink near the bottom. The circulation pump 67 drives the ink near the bottom to the liquid surface via the circulation channel 47, creating an ink flow across both the liquid surface and the bottom. In the circulating degassing method, the ink near the bottom is reliably sent to the liquid surface, exposing the highly oxygen-saturated ink to the reduced-pressure atmosphere and improving degassing efficiency.

[0037] In contrast, as shown in Figure 5, in the agitation-type degassing device 81, an agitator 83 is placed on the bottom surface of the depressurized ink tank 82. A magnet 84 is provided below the ink tank 82, and the magnetic force of the magnet 84 rotates the agitator 83, agitating the ink. The agitation of the ink carries the ink near the bottom surface to the surface. However, in the agitation-type degassing device, the agitator 83 is placed in the center of the bottom surface of the ink tank 82, and the effect of agitation is strong in the center of the bottom surface but weaker near the surface and outer edge, making it difficult for the ink near the bottom surface to reach the surface, thus reducing the degassing efficiency.

[0038] Figure 6 shows the change in oxygen saturation over time from the start of degassing for both the circulating degassing method and the agitation degassing method. In Figure 6, a circulating degassing device is used, in which the bottom and the side near the liquid surface of the ink tank are connected by a circulation channel. In the circulating degassing method, the oxygen saturation drops to below the target value in a short time from the start of degassing. On the other hand, in the agitation degassing method, the oxygen saturation does not drop below the target value in a short time from the start of degassing, and it takes a considerable amount of time for the oxygen saturation to drop below the target value. Thus, the circulating degassing method, which promotes the exchange of ink near the liquid surface and near the bottom, reduces oxygen saturation in a shorter time than the agitation degassing method.

[0039] In the circulating degassing method, if the oxygen saturation (amount of dissolved air) in the ink is low, the amount of dissolved oxygen that needs to be removed from the ink decreases. Therefore, depending on the oxygen saturation in the ink, it is possible to shorten the ink circulation time during the degassing operation or even omit the ink degassing operation. As described above, the control device 38 predicts the oxygen saturation in the ink from the operating environment, and the ink circulation time by the circulation pump 67 is appropriately adjusted according to the operating environment without actually measuring the oxygen saturation in the ink. When the predicted value of the oxygen saturation in the ink is low, the ink circulation time is shortened, and excessive degassing of the ink is suppressed, allowing the ink degassing to be completed in a short time.

[0040] The oxygen saturation in the ink is predicted based on at least one of the operating environment factors: ambient temperature, ambient pressure, time elapsed since filling the ink tank 32 with ink, and print density. The oxygen saturation can be predicted using the characteristics of oxygen saturation, the ink's storage time, and the frequency of ink replacement. For example, the oxygen saturation in the ink has characteristics that depend on ambient temperature or ambient pressure. Therefore, it can be predicted that the oxygen saturation in the ink will decrease as the ambient temperature or ambient pressure decreases. Ambient temperature and ambient pressure refer to the temperature and pressure around the installation location of the degassing device 40.

[0041] Furthermore, the ink tank 32 is filled with degassed ink from the ink container 31. If the time elapsed since the ink was filled is short, the amount of air dissolved in the ink will be small. For this reason, it can be predicted that the oxygen saturation will decrease as the time elapsed since the ink was filled into the ink tank 32 decreases. In addition, if the print density increases, the ink in the ink tank 32 will be replaced more frequently. Since the ink in the ink tank 32 is replaced with degassed ink, it can be predicted that the oxygen saturation will decrease as the print density increases.

[0042] In this case, the inkjet recording device 1 is equipped with various sensors to detect ambient temperature and ambient pressure, and the control device 38 manages the elapsed time since ink filling and the print density during printing. The control device 38 also stores conversion information showing the correspondence between various parameters such as ambient temperature and oxygen saturation. Map data, lookup tables, and conversion formulas are used for the conversion information showing the correspondence between each parameter and oxygen saturation. These map data, lookup tables, and conversion formulas are those that have been determined in advance through experimentation, empiricism, and theory.

[0043] The control device 38 predicts the oxygen saturation level from each parameter, and the ink circulation time is adjusted based on the predicted oxygen saturation level. Here, a first threshold and a second threshold that is greater than the first threshold are used to compare the predicted oxygen saturation level with the first and second thresholds, and the ink circulation time by the circulation pump 67 is adjusted in three stages. Note that the ink circulation time is 0 seconds or longer, and when the ink circulation time is adjusted to 0 seconds, the ink is no longer circulated by the circulation pump 67. Here, the first threshold is set to a target value for oxygen saturation (see Figure 6), and the second threshold is set to a value higher than the target value.

[0044] If the predicted oxygen saturation level in the ink is above the second threshold, it is determined that the oxygen saturation level in the ink is sufficiently higher than the target value, and the ink is degassed over a long period of time until the oxygen saturation level falls below the target value. This prevents clogging of the nozzles of the recording head 21 and improves image quality. If the predicted oxygen saturation level in the ink is above the first threshold but below the second threshold, it is determined that the oxygen saturation level in the ink is slightly higher than the target value, and the ink is degassed over a short period of time until the oxygen saturation level falls below the target value. The shorter time required for the degassing operation reduces the waiting time before printing.

[0045] If the predicted oxygen saturation level in the ink is below the first threshold, it is determined that the oxygen saturation level in the ink is below the target value, and the degassing operation is not performed. The degassing operation is omitted, further shortening the waiting time until printing. Similarly, if the predicted oxygen saturation level is sufficiently high, the ink circulation time is set to be longer and the degassing operation is performed more thoroughly. If the predicted oxygen saturation level is only slightly high, the ink circulation time is set to be shorter and the degassing operation is performed more simply. If the predicted oxygen saturation level is sufficiently low, the ink circulation time is set to 0 seconds and the degassing operation is not performed.

[0046] The process for adjusting the circulation time will be explained with reference to Figures 7 and 8. Figure 7 is a flowchart of the circulation time adjustment process in the first embodiment. Figure 8 is a diagram showing the relationship between oxygen saturation and circulation time in the first embodiment. Note that the reference numerals from Figure 2 will be used as appropriate in this explanation. Also, the following flowchart is merely an example and can be modified as needed.

[0047] As shown in Figure 7, when the inkjet recording device 1 is powered on or wakes up from sleep mode (step S01), the control device 38 predicts the oxygen saturation level in the ink based on the operating environment (step S02). As described above, the oxygen saturation level in the ink is predicted based on at least one of the following: ambient temperature, ambient atmospheric pressure, elapsed time since ink was filled into the ink tank 32, and print density. Note that each parameter such as ambient temperature used for oxygen saturation may be appropriately selected according to the condition of the inkjet recording device 1.

[0048] Next, the control device 38 determines whether the predicted value of the oxygen saturation in the ink is equal to or greater than the second threshold m2 (step S03). If the predicted value of the oxygen saturation in the ink is equal to or greater than the second threshold m2 (Yes in step S03), the ink circulation time by the circulation pump 67 is set to be longer and the degassing operation is performed (step S04, see Figure 8). The ink is degassed thoroughly over a long period of time until the predicted value of the oxygen saturation in the ink falls below the target value. Once the ink circulation time has elapsed and the degassing operation is complete, the inkjet recording device 1 is put into standby mode until a print command is received (step S07).

[0049] If the predicted value of the oxygen saturation in the ink is less than the second threshold m2 (No in step S03), the control device 38 determines whether the predicted value of the oxygen saturation in the ink is equal to or greater than the first threshold m1 (step S05). If the predicted value of the oxygen saturation in the ink is equal to or greater than the first threshold m1 (Yes in step S05), the ink circulation time by the circulation pump 67 is set to a shorter time and a degassing operation is performed (step S06, see Figure 8). The ink is degassed in a short time until the predicted value of the oxygen saturation in the ink falls below the target value. Once the ink circulation time has elapsed and the degassing operation is complete, the inkjet recording device 1 is put into standby mode until a print command is received (step S07).

[0050] If the predicted value of the oxygen saturation in the ink is less than the first threshold m1 (No in step S05), the ink circulation time by the circulation pump 67 is set to 0 seconds and the degassing operation is not performed (see Figure 8). Without performing the degassing operation, the inkjet recording device 1 remains in standby until a print command is received (step S07). In this embodiment, the ink circulation time is set to increase in stages as the saturated oxygen concentration increases using the first and second thresholds m1 and m2, but the ink circulation time may also be set to increase continuously as the saturated oxygen concentration increases.

[0051] As described above, according to the degassing device 40 of the first embodiment, air dissolved in the ink near the liquid surface exposed to a reduced-pressure atmosphere is removed. The ink in the ink tank 32 is circulated through the circulation channel 47, and the ink near the liquid surface with low oxygen saturation and the ink near the bottom with high oxygen saturation are exchanged, resulting in efficient degassing. Furthermore, even if the oxygen saturation in the ink changes, the ink circulation time is adjusted according to the oxygen saturation, allowing for degassing without excess or deficiency.

[0052] Furthermore, by using this degassing device 40 in the inkjet recording device 1, clogging of the recording head 21 due to air bubbles in the ink can be effectively suppressed, thereby improving image quality. By adjusting the ink circulation time, the waiting time before printing can be shortened.

[0053] <Second Embodiment> Next, with reference to Figure 9, the degassing device of the second embodiment will be described. Figure 9 is a schematic diagram of the ink supply structure of the second embodiment. The second embodiment differs from the first embodiment in that the ink circulation time is adjusted according to the measured value of the oxygen saturation in the ink. Therefore, for the second embodiment, the same configuration as in the first embodiment will not be described. Also, for the sake of convenience, the same names as in the first embodiment will be given the same reference numerals.

[0054] As shown in Figure 9, in the second embodiment of the degassing device 40, a bubble sensor (sensor) 69 is installed in the circulation channel 47 in addition to the circulation pump 67, and the bubble sensor 69 measures the number of bubbles in the ink. The measured value from the bubble sensor 69 is output to the control device 38, and the control device 38 determines the oxygen saturation level in the ink from the measured value from the bubble sensor 69. In this way, the bubble sensor 69 is used as a sensor to measure the oxygen saturation level in the ink in the degassing device 40. An oxygen saturation sensor may be used in place of the bubble sensor 69 in the degassing device 40.

[0055] The ink in the circulation channel 47 has less variation in oxygen saturation compared to the ink in the ink tank 32. Therefore, the measurement accuracy of oxygen saturation is improved by actually measuring the oxygen saturation in the ink in the circulation channel 47. Then, as in the first embodiment, the control device 38 compares the measured value of oxygen saturation with the first and second thresholds and adjusts the ink circulation time in three stages. Note that the measurement of oxygen saturation in the ink may be performed when the inkjet recording device 1 is powered on or when it wakes up from sleep mode, or it may be performed after the inkjet recording device 1 has been left idle for a long period of time.

[0056] Furthermore, the bubble sensor 69 can be a photoelectric bubble sensor, a capacitive bubble sensor, an ultrasonic bubble sensor, or the like. In a photoelectric bubble sensor, a light-emitting element and a light-receiving element are installed on either side of the circulation channel 47, and the state of the bubble is detected from the change in the amount of light received by the beam transmitted through the ink. In a capacitive bubble sensor, a detection electrode and a placement electrode are installed on either side of the circulation channel 47, and the state of the bubble is detected from the change in capacitance between these two electrodes. In an ultrasonic bubble sensor, a pair of transducers are installed on either side of the circulation channel 47, and the state of the bubble is detected from the change in ultrasonic waves transmitted through the ink.

[0057] As described above, in the degassing device 40 of the second embodiment, the ink near the liquid surface with low oxygen saturation and the ink near the bottom with high oxygen saturation are exchanged, and degassing is performed efficiently. Furthermore, even if the oxygen saturation in the ink changes, the ink circulation time is adjusted according to the oxygen saturation, allowing for degassing without excess or deficiency.

[0058] In each of the embodiments described above, the ink circulation time was adjusted according to the predicted or measured value of oxygen saturation. However, the ink circulation time may also be adjusted using both the predicted and measured values ​​of oxygen saturation. In this case, the control device predicts the oxygen saturation in the ink based on a coefficient corresponding to the operating environment, and adjusts the ink circulation time according to the predicted value of oxygen saturation. The degassing device is also equipped with a sensor for measuring the oxygen saturation in the ink. The control device compares the predicted and measured values ​​of oxygen saturation in the ink and corrects the coefficient for predicting the oxygen saturation in the ink.

[0059] For example, when oxygen saturation is predicted from ambient temperature using a conversion formula that shows the correspondence between the operating environment, such as ambient temperature, and oxygen saturation, the coefficients used in the conversion formula are corrected to take into account the difference between the predicted and measured values ​​of oxygen saturation in the ink. This allows the control device to predict a value close to the measured value of oxygen saturation in the ink based on the operating environment.

[0060] In this embodiment, a degassing device provided in an inkjet recording device was given as an example, but degassing devices can also be applied to devices used in other fields such as semiconductor manufacturing and display manufacturing. In other words, they can also be applied to degassing of chemicals other than ink, electrolytes, liquid resins, adhesives, solvents, lubricants, liquid foods, beauty serums, etc.

[0061] Furthermore, although a vacuum pump was exemplified as a vacuum device in this embodiment, any device capable of reducing the pressure inside the ink tank is acceptable as a vacuum device; for example, an ejector may also be used as a vacuum device.

[0062] Furthermore, although a circulation pump was exemplified as a circulation device in this embodiment, any device capable of circulating ink through a circulation channel may be used as a circulation device; for example, an ejector may also be used as a circulation device.

[0063] Furthermore, in this embodiment, ambient temperature, ambient pressure, elapsed time since ink was filled into the liquid tank, and print density are given as examples of the operating environment, but the operating environment is not particularly limited as long as the amount of dissolved air (oxygen saturation) in the ink is a predictable parameter.

[0064] Furthermore, in this embodiment, the sheet may be any sheet-like material on which an image is formed, such as plain paper, coated paper, tracing paper, or an OHP (Over Head Projector) sheet.

[0065] Although this embodiment has been described, other embodiments may include combinations of the above embodiments and modifications, either entirely or partially.

[0066] Furthermore, the technology of the present invention is not limited to the embodiments described above, and may be modified, substituted, or transformed in various ways without departing from the spirit of the technical idea. Moreover, if the technical idea can be realized in a different way by advances in the technology or by other derived technologies, it may be implemented by that method. Accordingly, the claims cover all embodiments that may fall within the scope of the technical idea.

Claims

1. A degassing device that removes dissolved air from a liquid under reduced pressure, A liquid tank in which liquid is stored, A pressure reducing device for reducing the pressure inside the liquid tank, A circulation channel connecting different locations in the aforementioned liquid tank, A circulation device that circulates liquid through the aforementioned circulation channel, The system comprises a control device that controls the circulation operation of the aforementioned circulation device, The control device adjusts the liquid circulation time according to the amount of dissolved air in the liquid.

2. The degassing apparatus according to claim 1, wherein the control device predicts the amount of dissolved air in the liquid from the operating environment and adjusts the liquid circulation time according to the predicted value of the amount of dissolved air in the liquid.

3. The degassing device according to claim 2, wherein the control device adjusts the liquid circulation time to be shorter when the predicted value of the amount of dissolved air in the liquid becomes low.

4. The liquid is the ink used for printing on the sheet. The degassing apparatus according to claim 3, wherein the control device predicts the amount of dissolved air in the ink based on at least one of the operating environment, ambient temperature, ambient pressure, time elapsed since ink was filled into the liquid tank, and print density.

5. The degassing apparatus according to claim 4, wherein the control device predicts a lower amount of dissolved air as the ambient temperature or ambient pressure decreases, predicts a lower amount of dissolved air as the elapsed time since ink filling the liquid tank decreases, and predicts a lower amount of dissolved air in the ink as the print density increases.

6. Equipped with a sensor for measuring the amount of dissolved air in a liquid, The degassing apparatus according to claim 1, wherein the control device adjusts the liquid circulation time according to the measured value of the amount of dissolved air in the liquid.

7. The degassing device according to claim 6, wherein the sensor is installed in the circulation channel.

8. Equipped with a sensor for measuring the amount of dissolved air in a liquid, The control device predicts the amount of dissolved air in the liquid based on a coefficient corresponding to the operating environment, and adjusts the liquid circulation time according to the predicted amount of dissolved air. The degassing apparatus according to claim 1, wherein the control device compares a predicted value with an actual value of the amount of dissolved air in the liquid and corrects the coefficient.

9. A degassing device according to claim 1, An inkjet recording device comprising a recording head that ejects degassed ink as a liquid onto a sheet.

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